MULTIPLE MYELOMA (MM) is a clonal B-cell neoplasm that affects terminally differentiated B cells (ie, plasma cells) and may proceed through different phases: an inactive phase in which tumor cells are nonproliferating mature plasma cells, an active phase with a small percentage (<1%) of proliferating plasmablastic cells, and a fulminant phase with the frequent occurrence of extramedullary proliferation and an increase in plasmablastic cells. During the past years, considerable progress has been made in identifying some of the critical components of neoplastic transformation in MM. This review intends to propose a model of a stepwise malignant transformation during MM pathogenesis. Both diagnostic and therapeutic implications of this model will be discussed.

IMMORTALIZATION

Normal Plasma Cell Development

Productive stimulation of mature B cells with antigen results in proliferation and differentiation into memory B cells and plasmablasts. The plasmablasts terminally differentiate into short-lived plasma cells that remain in the local site and die within 3 days; the Ig secreted by short-lived plasma cells is not somatically hypermutated, and is often IgM, although switching to other isotypes (G, A, D, E) can occur. Alternatively, activated B cells enter germinal centers where they are stimulated to actively hypermutate rearranged Ig V sequences but subject to programmed cell death unless rescued by antigen selection. The resultant plasmablasts that undergo IgH switch to another isotype typically migrate to the BM, where they interact with stromal cells and differentiate into long-lived plasma cells that survive for about 30 days (Fig 1).

Fig. 1.

Normal plasma cell development. Functional V(D)J rearrangements of IgH and IgL genes in pre-B cells in the BM generate an immature B cell that expresses a functional Ig on the cell surface, which then exits the BM as a virgin (mature) B cell, and homes to the secondary lymphoid tissues. Early in the immune response productive interaction with antigen stimulates formation of a lymphoblast which differentiates into a short-lived nonswitched (IgM), or switched (IgG, IgA, IgE, or IgD) PC. Later in the primary response or in a secondary response, the lymphoblast generated by productive interaction with antigen enters a germinal center, where it undergoes somatic hypermuation of its IgH and IgL genes, and antigen selection of cells with high affinity Ig receptor. A germinal center plasmablast that undergoes productive IgH switch recombination typically homes to the BM where it differentiates into a long-lived plasma cell (cf. myeloma cell).

Fig. 1.

Normal plasma cell development. Functional V(D)J rearrangements of IgH and IgL genes in pre-B cells in the BM generate an immature B cell that expresses a functional Ig on the cell surface, which then exits the BM as a virgin (mature) B cell, and homes to the secondary lymphoid tissues. Early in the immune response productive interaction with antigen stimulates formation of a lymphoblast which differentiates into a short-lived nonswitched (IgM), or switched (IgG, IgA, IgE, or IgD) PC. Later in the primary response or in a secondary response, the lymphoblast generated by productive interaction with antigen enters a germinal center, where it undergoes somatic hypermuation of its IgH and IgL genes, and antigen selection of cells with high affinity Ig receptor. A germinal center plasmablast that undergoes productive IgH switch recombination typically homes to the BM where it differentiates into a long-lived plasma cell (cf. myeloma cell).

The Malignant Myeloma Cell Corresponds to a Long-lived Plasma Cell

The malignant plasma cells in MM are localized to the bone marrow (BM) in close association with stromal cells, and are rarely found in other locations. They are long-lived cells with a very low labeling index (LI = 1% to 2%). The rearranged Ig genes are extensively somatically hypermutated in a manner compatible with antigen selection,1 with no evidence that the process of hypermutation is continuing. However, myeloma cells have a significantly lower rate of Ig secretion than normal plasma cells. Thus, it appears that the critical oncogenic events in MM cells either occur after or do not interfere with most of the normal differentiation process involved in generating a long-lived plasma cell. In the BM, the myeloma cells and stromal cells secrete cytokines and interact through adhesion molecules, activating the stromal cells (including osteoclasts) that further support the growth and survival of the myeloma cells and lead to the complications associated with MM.2,3 

Karyotypic Abnormalities

By conventional analyses, karyotypic abnormalities are detected at a frequency of 30% to 50% in large studies of myeloma tumors.4-15 The frequency and extent of karyotypic abnormalities correlates with the stage, prognosis, and response to therapy, eg, approximately 20% abnormal in stage I, 60% in stage III, and greater than 80% for extramedullary tumor. This analysis is dependent on obtaining reliable metaphase preparations and greatly underrepresents the extent of DNA alterations in these infrequently dividing cell populations. By interphase fluorescence in situ hybridization (FISH) analysis using probes for 5 or 10 different chromosomes, respectively, two studies report that at least one chromosome is trisomic in 96% or 89% of myeloma.16,17Although conventional karyotypes are not reported for monoclonal gammopathy of undetermined significance (MGUS), it appears that a substantial fraction of MGUS plasma cells are aneuploid as well. By FISH analysis using only 4 chromosome probes, the incidence of trisomy for at least one chromosome was 43% and 53% in two studies of MGUS cells; in the former case 61% of the cells had an aneuploid DNA content by image analysis.16,18 Despite the limited analyses available for MGUS, it appears that processes leading to karyotypic instability begin in MGUS, progress substantially in frankly malignant MM, and continue to progress throughout the entire course of the disease.

The characteristic numerical abnormalities are monosomy 13, and trisomies of chromosome 3, 5, 7, 9, 11, 15, and 19. Nonrandom structural abnormalities most frequently involve chromosome 1 with no apparent locus specificity; 14q32(IgH locus) in 20% to 40%; 11q13(bcl-1 locus) in about 20% but mostly translocated to 14q32; 13q14 interstitial deletion in 15%; and 8q24 in about 10%, with about half of these involved in a translocation.

Low Incidence of Karyotypically Detectable Translocations to Ig Loci in MM

The hallmark genetic lesion in many B-lymphocyte tumors involves dysregulation of an oncogene as a consequence of a translocation involving the IgH locus (14q32.3), or, less frequently, variant translocations involving one of the IgL loci (2p12, κ or 22q11, λ).19-23 From conventional karyotypic analyses, translocations involving 14q32 appear to occur in about 20% to 40% of myeloma tumors with an abnormal karyotype (references as above). The incidence of these translocations is significantly higher at the extramedullary phase of the disease and in cell lines, perhaps due to a higher number of metaphase spreads that can be examined. In about 30% of these translocations, the partner chromosomal locus is 11q13 (bcl-1, cyclin D1) but in most cases the partner is not identified (14q32+). Other recurrent partner loci have been identified infrequently, eg, 8q24(c-myc) in less than 5%, 18q21(bcl-2), 11q23(MLL-1), 6p21.1. Variant translocations involving 8q24(c-myc) have been detected in a few percent of myeloma tumors.6,9,11,13,14 

Translocations Involving the IgH Locus Are Essentially Invariant in Myeloma Cell Lines

Recently, by combining conventional karyotypic analysis with a comprehensive Southern blot assay that detects translocations involving IgH switch regions, it has become apparent that most (19 of 21) myeloma cell lines and the one primary tumor fully examined have IgH translocations that mainly involve IgH switch regions.24-26Notably, seven of nine cell lines with no karyotypically detectable 14q32 translocation have a translocation involving an IgH switch region using this assay. For four of the cell lines it was possible to examine primary tumor material and show the presence of the translocation breakpoint, indicating that the translocations are not an artifact of cell culture. In six cases, there is translocation involving 11q13 and overexpression of cyclin D1. The four cloned translocation breakpoints are into or near an IgH switch region, whereas the same translocation in mantle cell lymphoma invariably involves JH regions.19Five additional lines and the tumor have been determined to have an IgH switch translocation breakpoint involving the telomeric end of chromosome 4 (ie, 4p16.3, near the tip of 4p), despite the fact that no karyotypic translocation was detected in 5 of 6 of these samples.27 The apparent oncogene dysregulated by the 4;14 translocation is the fibroblast growth factor receptor 3 (FGFR3) gene. The cloning of three other translocation breakpoints identified four different chromosome loci (6, 8q24, 16q23, and 21q22).24 

The t(6;14) breakpoint was also independently cloned from the same myeloma cell line (SK-MM1) and found to map to 6p25 near IRF4 (MUM1/ICSAT/LSIRF), a member of the interferon regulatory factor (IRF) family of transcription factors.28 The level of IRF4 mRNA was significantly over-expressed in the SK-MM1 cell line compared to the basal level in 10 other MM cell lines, suggesting that juxtaposition of this gene to IgH regulatory elements may have deregulated its expression.28 IRFs are involved in the transcriptional regulation of interferon (IFN) and the IFN-stimulated genes through recognition of the IFN-stimulated response element. IRF4 is a lymphoid specific gene that is rapidly induced by T- and B-cell receptor cross-linking, and is basally expressed in most B, but not T, tumor cell lines.29 Mice deficient in IRF4 have profound hypogammaglobulinemia and cannot mount detectable antibody responses, indicating a critical role of this gene in normal plasma cell development.30 

IgH Translocations Involving a Promiscuous Array of Partner Chromosomes: Possibly a Universal and Early Event in MM

Based on the results presented above, it appears that translocations to the IgH or one of the IgL loci may be a nearly universal event in MM despite the apparent low incidence by karyotypic analysis. These translocations are usually into IgH switch regions. They involve two nonrandom loci, ie, 11q13 (bcl-1, cyclin D1) in 25% and 4p16.3 (FGFR3) in 25%. The remaining 50% or so of cases involve a promiscuous array of chromosome partners, some of which have been identified in at least two unrelated tumors [8q24(c-myc), 18q21(bcl-2), 6p21.1 (?), 11q23 (MLL-1)], and others of which have been identified in only one tumor thus far [1p13, 1q21, 3p11, 6p25, 7q11, 12q24, 16q23, and 21q22]. Considering the developmental pathway for long-lived plasma cells (Fig1), the timing of normal IgH switching, and the shared productive switch for paired MGUS and myeloma cells, we hypothesize that this translocation affects the nonproductive Ig allele, and may be one of the earliest molecular events in the pathogenesis of MM, although this remains to be confirmed.

Oncogenes Dysregulated by Recurrent IgH Translocations in Myeloma

c-myc.

c-myc, the cellular homologue of the transforming gene v-myc from the oncogenic avian retrovirus, appears to play a central role in controlling proliferation, differentiation, and apoptosis.31-33 In BALB/c plasmacytomas and rat immunocytomas, activation of c-myc by chromosome translocation into a switch region of the IgH locus (or by a variant translocation to one of the IgL loci) is a universal event.22,34,35 In human MM, by contrast, a t(8;14) occurs in less then 5% of cases, and variant translocations involving 8q24 are reported in only a few percent of tumors (references above). Karyotypic abnormalities of 8q24 other than translocation to one of the Ig loci have also been identified in a small fraction of myeloma samples.9 DNA rearrangement of c-myc has been detected by Southern blot in a few patients.3,36-38 Rearrangements have also been seen in the MLVI-4 locus located 20 kb downstream of c-myc.38,39Infrequently, DNA amplification of c-myc has also been reported.3,36 

Adding together Ig translocations and other karyotypic abnormalities involving 8q24, DNA rearrangements involving c-myc or the MLVI-4 locus, and DNA amplification of c-myc, structural genetic abnormalities near c-myc may be present in 10% to 20% of tumors. Both a normal and a polymorphic c-myc allele were found in six myeloma cell lines, but no apparent karyotypic abnormality, DNA rearrangement, or amplification involving c-myc. The c-myc mRNA was expressed from only one of the two alleles, consistent with cis-dysregulation in every informative line.40 However, there is evidence that elevated expression of c-myc and selective expression of one c-myc allele may occur frequently in myeloma,37,40-43 even though structural genetic changes near c-myc have been identified in only 10% to 20% of tumors. Moreover, expression of the c-Myc protein is frequently increased in MM cells44 and cell lines45independently of the c-myc mRNA levels. The elevated c-Myc expression might be caused by mutations in the 5′ untranslated region of the c-myc gene leading to a deregulated translational control of c-myc gene expression.46 

bcl-1/PRAD-1/cyclin D1.

The bcl-1 locus at 11q13 is involved in recurrent translocations to 14q32 in chronic lymphocytic leukemia (CLL), lymphomas, and myeloma. This translocation is almost invariant in mantle cell lymphoma, where the breakpoints on 11q13 are clustered predominantly in one region (called MTC, for major translocation cluster), and the breakpoints in the IgH locus are in the JH regions. Rearrangements involving the MTC are rare in myeloma [0 of 58 unselected; and 0 of 13 with t(11;14)].19,39,47-51 The first t(11;14) breakpoints have recently been cloned from myeloma samples and in contrast to mantle zone lymphoma, the MTC region was not involved, and the breakpoints in the IgH locus are frequently into switch regions.24,26 The cyclin D1 gene is approximately 120 kb telomeric to these breakpoints. Cyclin D1 together with CDK4 phosphorylates (and inactivates) pRB and allows for progression through the G1 phase of the cell cycle.52 Unlike other genes identified in this region of 11q13, there is a close association between t(11;14) and enhanced expression of cyclin D1.53Furthermore, a variant translocation (ie, involving a light chain gene) just telomeric to cyclin D154 and a translocation breakpoint within the 3′ untranslated region of cyclin D1 (resulting in a 3′ truncated mRNA)51 serve to effectively define cyclin D1 as the gene targeted by the t(11;14), although given the distance of the breakpoints from cyclin D1, it is possible that other genes may also be involved.

Cyclin D1 has been studied extensively in lymphoma and found to be expressed almost exclusively, and universally in mantle zone lymphoma.55 The expression of cyclin D1 has not been extensively studied in myeloma. In 21 myeloma cell lines, 6 of which have t(11;14), there is a 1:1 correlation between the presence of the translocation and over-expression of cyclin D1 protein.24,26 Expression has been studied in 19 bone and 3 head and neck plasmacytomas using a monoclonal antibody (MoAb), and 1 of 22 have been found to be reactive.55 It should be noted that the presence of the t(11;14)(q13;q32) translocation in myeloma is associated with a lymphoplasmacytic cell morphology as well as with more aggressive disease and a poorer prognosis.27,56,57 

FGFR3.

Recently the fibroblast growth factor receptor 3 gene at 4p16.3 was identified as dysregulated by t(4;14)(p16;q32) in 5 of 21 myeloma cell lines and 3 of 11 primary tumors.27 This novel, karyotypically silent translocation has not been described before and may be unique to myeloma, although it has not yet been examined in other tumors, nor has it been extensively studied in primary tumor samples. Because it involves the telomere of 4p16 this translocation generally is not identified by conventional karyotypes, and more sensitive techniques (eg, fluorescent in situ hybridization or Southern blot) are required to detect it. FGFR3 is normally expressed in the lung, kidney, and the chondrocytes at the ends of growing bones. Different germline mutations of FGFR3 result in distinct dwarfing conditions of increasing severity: hypochondroplasia, achondroplasia, and thanatophoric dysplasia.58-63 FGFR3 is expressed at a high level only in those myeloma cell lines with t(4;14). Activating mutations of FGFR3 occur frequently in myeloma cell lines and primary tumors with 4;14 translocations (in 3 of 6 cell lines and 1 of 3 primary tumor samples). The same mutations have been described previously in patients with the most severe form of dwarfism, thanatophoric dysplasia, and they are thought (for some mutations proven) to be activating mutations.64,65 In addition, although both alleles are present in the genomic DNA, in each case only the mutant allele is expressed, indicating that the translocation has caused cis-dysregulation, ie, selective expression of this allele.

We postulate that myeloma cells with dysregulated expression of FGFR3 as a result of t(4;14) receive an FGFR3-mediated signal from FGF produced by stromal cells in the BM micro-environment. Presumably the continuous signal in this environment interferes with their terminal differentiation and apoptosis, and may also stimulate growth. In addition, it seems likely that the activating mutations occurred at a later time than the translocation, and resulted in progression of the tumor to survival and/or growth in the absence of an FGF ligand.

ESTABLISHMENT

The Role of Growth Factors and the Bone Marrow (BM) Microenvironment

The proliferation, differentiation, and function of lympho-hematopoietic cells is regulated by a complex network of lympho-hematopoietic growth factors and cell surface molecules which establish a fine-tuned communication between stroma cells and lympho-hematopoietic precursors in the BM.66-68 These growth factors bind to specific cell-surface receptors that belong to different families, the receptor tyrosine kinases and the hematopoietic cytokine receptors.69-72 The nature of the biological response to any growth factor is defined by the tissue or lineage distribution of growth factor receptors and by distinct transmembrane signaling events in which tyrosine kinases play a pivotal role.73,74 

The pathogenesis of MM depends on the presence of some of these growth factors which support the survival, proliferation, and differentiation of MM cells in the BM during the different disease stages.75,76 These cytokines involved in MM pathogenesis are similar to those mediating the proliferation of normal early plasma cells (plasmablastic cells), and their differentiation to mature plasma cells (plasmacytic cells). Interleukin-6 (IL-6) is of particular importance during this process.

IL-6 is a cytokine that has pleiotropic effects on hematopoietic and nonhematopoietic cells.71,77-82 It induces purified B cells to differentiate into Ig-secreting plasma cells.77,78,81,82It acts also as a growth factor for MM (see below).75,83,84Thus, IL-6 mediates the expansion of plasmablastic cells, but also of their malignant counterparts.

The evidence that IL-6 is involved in MM pathogenesis was established by the following experimental and clinical findings: (1) IL-6 could induce in vitro growth of myeloma cells freshly isolated from patients, (2) myeloma cells spontaneously produced IL-6 and expressed IL-6R, (3) anti-IL6 antibodies inhibited the growth of MM cells or cell lines in vitro, and (4) treatment of MM patients with MoAbs to IL-6 showed some antitumor effect.76,83-85 

IL-6 supports the survival and/or expansion of MM cells not only by stimulating cell division, but also by preventing programmed cell death (apoptosis) which can be induced by serum starvation,86 or by treatment with compounds like vitamin D3 or its derivative EB1089,87dexamethasone,86,88,89 anti-Fas antibodies,90or suramin.88 Retinoid acid (RA) induces programmed cell death in MM cell lines by downmodulating the IL-6R expression.91 Similarly IL-6R antagonists, which block the activation of MM cells by IL-6, act as pro-apoptotic factors for MM cells.92 

There is still some controversy about the source of IL-6 provided as a MM growth factor during disease progression. Some investigators have found IL-6 to be produced by the tumor itself in an autocrine manner,84 but stronger evidence supports the notion of a paracrine IL-6 secretion by the tumor microenvironment in the BM.76,83 IL-6 is probably produced in large amounts by BM stroma cells (BMSC), osteoblasts, and osteoclasts.93-95 The IL-6 secretion by BMSCs seems to be regulated by cytokines like IL-1β secreted by the tumor, although the experimental proof for this hypothesis has been hampered by the difficulty to generate pure myeloma cell samples.76 Antibodies to IL-1 or the use of the IL-1 receptor antagonists were able to block the IL-6 production in short-term cultures of BM cells from MM patients.76 Colony-stimulating factor-1 (CSF-1) is also produced by MM cells, but a role in stimulating IL-6 secretion has not been shown so far.96 

Viral IL-6 (vIL-6) produced by BM dendritic cells infected with Kaposi's sarcoma–associated herpesvirus (KSHV) is an alternative source for IL-6 in MM pathogenesis.97 KSHV has been detected consistently in human immunodeficiency (HIV)-related and HIV-unrelated cases of Kaposi's sarcoma (KS), pleural effusion lymphoma, and multicentric Castleman's disease.98 A homolog to human IL-6 has recently been identified in the KSHV genome which has biological properties of human IL-6 in that it supports the growth of IL-6–dependent cell lines. Using a sensitive polymerase chain reactive (PCR) assay, Rettig et al97 detected KSHV DNA in the BM dendritic cells of 15 out of 15 MM patients but not in malignant plasma cells or BM dendritic cells from normal individuals, or patients with other malignancies. In addition, the virus was detected in the BM dendritic cells of 2 of 8 MGUS patients. vIL-6 was found to be transcribed in the myeloma BM dendritic cells.97 These data indicate that KSHV infection of BM dendritic cells and vIL-6 may be involved in transformation from MGUS to myeloma and perpetuate the growth of malignant plasma cells.

Stimulation of cells by IL-6 requires binding to the IL-6 receptor (IL-6R) composed of at least two subunits with apparent molecular weights (m.w.) of 80 and 130 kD, the IL-6R α (IL-6Rα) and β chain (IL-6Rβ or gp130). Binding of IL-6 to IL-6Rα induces the tyrosine phosphorylation and association with gp130, the signal transducing subunit of the IL-6R, and the subsequent formation of gp130 homodimers.99 gp130 is the common β subunit shared by the receptors for ciliary neurotropic factor (CNTF), oncostatin M (OSM), leukemia inhibitory factor (LIF), IL-11, cardiotrophin 1, and IL-6 and is essential for transmitting their respective signals.71Accordingly, these six cytokines share some biological functions with IL-6, and some MM cell lines respond to LIF, OSM, or CNTF if the appropriate receptor α chain is expressed.100 In some MM patients, IL-11 levels may also be elevated in the BM, but the effects of IL-11 and of the other three cytokines on the growth of MM cells in vivo remain uncertain and have not been studied with the same scrutiny as the effects of IL-6.76 

Another potential mechanism contributing to the growth and expansion of MM is the agonistic effect of the soluble IL-6Rα which enhances the sensitivity of myeloma cell lines to the effects of IL-6.101 These soluble IL-6Rα are generated by receptor shedding from the cell membrane or by alternative RNA splicing.102,103 High serum levels of IL-6 were shown to predict a poor prognosis or to reflect an active disease in MM by many studies.101,104-111 Serum IL-6 receptor levels may less reflect the disease activity in MM.101 However, decreases of both parameters have been reported to accompany the response to treatment in MM.112 

Additional Growth Factors for MM

Granulocyte colony-stimulating factor (G-CSF) is a hematopoietic growth factor with structural homology to IL-6.113,114 Moreover, the G-CSF receptor shares also some homology with gp130.115Both G-CSF and IL-6 induce activation of NF-IL-6, a transcription factor involved in the synthesis of IL-6.116 G-CSF is a potent growth factor for freshly explanted myeloma cells, and MM cell lines may respond to G-CSF.76 The mechanism of action by which G-CSF mediates MM growth is unknown. However, the data caution that treatment of MM patients with G-CSF after high-dose chemotherapy or for stem cell harvest might eventually enhance proliferation of the tumor,76 although this has never been shown in clinical practice.

Interferon-α (IFN-α) is another growth factor for MM in vitro, although growth inhibitory effects have been reported as well (see below). IFN-α stimulates the proliferation of fresh myeloma cells from 16% to 50% of patients.117-119 IFN-α also stimulates the growth of IL-6–dependent MM cell lines.120This effect seems to be mediated by an enhancement of the autocrine IL-6 production by MM cell lines.120 These results may explain why adjuvant IFN-α treatment has little, if any beneficial effect in MM: despite encouraging results in an early clinical trial with adjuvant IFN-α treatment after chemotherapy,121 more recent studies have failed to demonstrate a benefit for IFN-α maintenance.122-125 

IL-10 is also a growth factor for MM cells, because it enhances the proliferation of freshly explanted myeloma cells in short-term BM culture.126 Moreover, the growth of myeloma cell lines is also supported by IL-10.76 IL-10 has inhibitory effects on the production of IL-6 by MM cells; therefore, its effects are probably not mediated by IL-6. More likely, IL-10 enhances the responsiveness of MM cells by regulating the expression of other cytokines and cytokine receptors. IL-10 might increase the responsiveness of some myeloma cells to IL-11 by upregulating the expression of IL-11 receptors.127 Moreover, IL-10 induces an autocrine OSM loop in human myeloma cells, probably by increasing the expression of the LIF receptor which forms with gp130 a receptor for OSM.128 

Granulocyte-macrophage-CSF (GM-CSF), IL-3, stem cell factor (SCF), tumor necrosis factor-α (TNF-α), hepatocyte growth factor (HGF), and insulin-like growth factor 1 and 2 (IGF-1 and IGF-2) are also potential MM growth factors, because they were shown to stimulate growth and/or specific intracellular signaling events of MM cells or cell lines in vitro, often in a synergistic manner with IL-6.129-138 

Factors Inhibiting the Growth of MM Cells

Interferon-γ (IFN-γ) was reported to inhibit IL-6–dependent proliferation of fresh MM cells.139 It did not affect the endogenous IL-6 production, but seemed to act directly on MM cells. It is possible that IFN-γ interferes with IL-6 transmembrane signaling, resulting in enhanced apoptosis. Interestingly, IFN-γ also inhibits cytokine-mediated bone resorption, which is a relevant clinical problem in MM.76 TNF-α and transforming growth factor-β (TFG-β) are other potential inhibitors of the proliferative effects of IL-6.140 

IFN-β and IFN-α were both shown to inhibit the proliferation of the MM cell line U266.141-143 These effects are mediated, at least in part, by a downmodulation of the IL-6R.141,143 As a consequence, IFN-β reduces the IL-6–dependent tyrosine phosphorylation and activation of several signaling proteins, including Ras.142 These observations are in contrast to the above described stimulatory effects of IFN-α on MM cell proliferation. It is possible that the effects of type I interferons (IFN-β and IFN-α) vary in different MM cell lines or patients. Although a therapeutic modulation of the BM microenvironment by type I interferons has been well documented in chronic myeloid leukemia,144-146 this has not been demonstrated for MM.

Stimulation of the Fas antigen (alternatively termed APO-1/CD95), a transmembrane molecule of the TNF nerve growth factor (NGF) receptor superfamily, induces programmed cell death in different cell types, including MM cells.147-150 Fas is expressed on almost all MM tumors and cell lines.151 However, activation of Fas induces MM apoptosis only in some patients' samples.151Activation of MM cells by IL-6 was shown to antagonize the cellular effects of Fas, including the activation of a stress activated protein kinase (SAPK), thus preventing Fas-triggered apoptosis.90This antagonism of IL-6 and Fas may serve as a paradigm for the many interactions that regulate MM growth in a fine-tuned network of cytokines and growth factors in the BM microenvironment.

Taken together, a variety of growth factors promote the growth of myeloma cells in vitro and/or in vivo: IL-6, IL-11, OSM, LIF, G-CSF, SCF, IFN-α (?), IL-10, TNF-α (?), IGF-1, and IGF-2. In contrast, stimulation of myeloma cells with anti-Fas antibodies and IFN-γ seems to inhibit cell growth. It is difficult to clarify the functional relevance of these redundant growth factor effects on MM cells. Moreover, it seems important to emphasize that the expression of the various cytokine receptors may vary among individual patients, and also among different tumor cells in a given patient. Nevertheless, IL-6 clearly seems to be the most important stimulatory factor of these cytokines, because the biologically active IL-6 concentrations found in vitro and in vivo are 500- to 5,000-fold higher than the concentrations of other MM growth factors.76 

Adhesion Molecules and Other Cell-Surface Antigens

The differentiation of lymphoid precursor cells into mature B lymphocytes is accompanied by characteristic changes of cell-surface antigens. The application of high resolution, multiparameter flow cytometry has been used to identify and characterize normal plasma cells in the human BM. Plasma cells exist in at least two different subpopulations, early lymphoplasmacytoid plasma cells and late mature plasma cells.152 These two populations appeared phenotypically different, but both strongly express CD38. In distinction to mature plasma cells, early lymphoplasmacytoid cells express CD22, CD35, and surface IgE receptors, and intracytoplasmatic Ig light chain only at low density. Subpopulations of mature, normal plasma cells show a very heterogeneous immunophenotype in that they can express early B-cell antigens (CD19, CD20, CD10), myeloid antigens (CD13, CD33), HLA-DR, common hematopoietic antigens (CD45), and adhesion molecules (CD11b, CD11c).153 

The neoplastic cells of MM probably follow this maturational pattern. Although the MM “stem cell” is unknown, there is evidence for cell clones which show the immunophenotype of early B-cell precursors which express CD38 at high levels, as well as CD10, CD34, CD19, CD20, and CD24.154,155 Immature myeloma cells (CD38++CD45 or CD38++CD49E+) appear to express the same clonal idiotype as mature cells (CD38++CD45 or CD38++CD49E+). Whether CD34 is expressed on MM cells remains controversial. In a recent study, 74% to 94% of individual sorted CD34+19+ B cells from four different MM patients were shown to express clonotypic IgH mRNA, as detected by in situ reverse transcriptase (RT)-PCR with patient-specific primers.156 Other studies failed to detect CD34 on myeloma cells157 or did not find myeloma cells in anti-CD34 MoAb-enriched stem cell harvests.158 Myeloma cells show a similar heterogeneity in their immunophenotype as their normal counterparts, according to their differentiation stage. It is believed that myeloma cells originate outside the BM and give rise to plasma cells upon migration, using expression of unique adhesion molecules to interact with the marrow microenvironment.159Finally, costimulatory molecules such as CD28 and B7-1 or B7-2 seem to be expressed by some immature myeloma cells, but may be lacking in mature MM or in MM cell lines.160,161 This may prevent activation of T cells against the tumor.

Despite the similarity of most antigens expressed on myeloma cells and normal plasma cells, some of the antigens detectable on myeloma cells are rather unique. For example, the adhesion molecule CD56, which is the 140-kD isoform of N-CAM, is highly expressed on some myeloma but not on normal mature plasma cells.129,162 It seems to mediate adhesion of myeloma cells to each other (homotypic adhesion). Some MM cells or cell lines lack expression of the B-lineage–specific antigen CD19 antigen which is a key member of a B-cell surface signal transduction complex which includes TAPA-1, Leu 13, and CD21, and initiates multiple intracellular signaling cascades, either through CD19 directly or through other members of the complex.163,164 

The expression of adhesion molecules and other cell-surface molecules is important for the communication of MM cells with the BM micro-environment. In a murine BM metastasis model, expression of at least three adhesion molecules, CD44, VLA-4, and ICAM-1, was important for mediating adherence of B9/BM myeloma cells to stromal cells.165 Adhesion of MM cells triggers IL-6 secretion by normal and MM BM stroma cells (BMSCs).166 Adhesion of MM cells to BMSCs induces IL-6 gene transcription in BMSCs which is conferred by NF-κB binding to the IL-6 promoter.167 One of the cell-surface molecules triggering IL-6 secretion in MM cells is CD40, a member of the TNF receptor superfamily that is expressed on various lymphoid malignancies.168-171 Activation of CD40 induces the clonogenic growth and enhances the survival of MM cells in vitro.172 Stimulation of CD40 by its ligand, CD40L, stimulates the secretion of IL-6 from MM cells and cell lines, suggesting the possibility for induction of IL-6–mediated autocrine MM cell growth.173,174 However, the source of CD40 stimulation in the BM stroma remains unknown; expression of CD40L seems to be restricted to T lymphocytes, but its expression on BMSCs has not been investigated. Some of the remaining questions on the homing and adhesion of MM cells in the BM may now be addressed using in vivo models, because human MM cell lines seem to engraft in the human bone marrow of severe combined immunodeficient-human (SCID-hu) mice and maintain the characteristics of clonal MM tumors.175 

Mechanisms of Signal Transduction

IL-6 receptor.

Because IL-6 is of central importance in the pathogenesis of MM, the intracellular signaling events elicited by this cytokine are also of potential relevance. Recently, some progress has been made in understanding the biochemical events involved in IL-6 transmembrane signaling at a molecular level (Fig 2).Binding of IL-6 to IL-6Rα induces the formation of a hexameric receptor complex composed of 2 IL-6Rα, 2 gp130, and 2 IL-6 molecules. Subsequently, receptor-associated tyrosine kinases mediate the phosphorylation of gp130, the signal transducing subunit of the IL-6R.99 This receptor complex further activates tyrosine kinases including members of the Janus kinase (JAK) and Src kinase families which mediate the phosphorylation of cytosolic phosphoproteins.176-181 Because both IL-6Rα and gp130 do not possess any apparent kinase domain, their association with nonreceptor tyrosine kinases like JAKs or Src kinases is critical for mediating the effects of IL-6.

Fig. 2.

Transmembrane signaling of IL-6, which is a major growth factor for MM. Binding of IL-6 to the α chain (gp80) of the IL-6 receptor (IL-6R) causes the formation of multimeric complexes composed of 2 IL-6R α chains, 2 β chains (IL-6Rβ or gp130), and 2 IL-6 molecules. Subsequently, tyrosine kinases (JAKs and Src kinases, in particular Hck) which are bound constitutively to the IL-6Rβ, become activated and (trans)phosphorylate the receptor. This creates specific docking sites for several signaling proteins including STAT1, STAT3, and Shc (?) on the IL-6Rβ, allowing further phosphorylation of these proteins by receptor-associated kinases. Activation of Shc recruits Grb2/Sos1 to the cell membrane. Sos1, a Ras-GDP/GTP exchange factor activates Ras; this activates a signaling cascade of several serine/threonine kinases including Raf-1, MKK, MAPK. Finally, MAPK phosphorylates substrates like c-Myc, c-Jun, c-Fos, RSK, and these events eventually enhance MM proliferation or prevent apoptosis. Upon phosphorylation, STAT1 and STAT3 form homodimers and heterodimers that are translocated to the nucleus and act as transcription factors for IL-6–induced promoters. Although the Ras-MAPK signaling cascade is believed to promote MM growth, no such function has yet been reported for the JAK-STAT pathway, believed to trigger rather metabolic events.

Fig. 2.

Transmembrane signaling of IL-6, which is a major growth factor for MM. Binding of IL-6 to the α chain (gp80) of the IL-6 receptor (IL-6R) causes the formation of multimeric complexes composed of 2 IL-6R α chains, 2 β chains (IL-6Rβ or gp130), and 2 IL-6 molecules. Subsequently, tyrosine kinases (JAKs and Src kinases, in particular Hck) which are bound constitutively to the IL-6Rβ, become activated and (trans)phosphorylate the receptor. This creates specific docking sites for several signaling proteins including STAT1, STAT3, and Shc (?) on the IL-6Rβ, allowing further phosphorylation of these proteins by receptor-associated kinases. Activation of Shc recruits Grb2/Sos1 to the cell membrane. Sos1, a Ras-GDP/GTP exchange factor activates Ras; this activates a signaling cascade of several serine/threonine kinases including Raf-1, MKK, MAPK. Finally, MAPK phosphorylates substrates like c-Myc, c-Jun, c-Fos, RSK, and these events eventually enhance MM proliferation or prevent apoptosis. Upon phosphorylation, STAT1 and STAT3 form homodimers and heterodimers that are translocated to the nucleus and act as transcription factors for IL-6–induced promoters. Although the Ras-MAPK signaling cascade is believed to promote MM growth, no such function has yet been reported for the JAK-STAT pathway, believed to trigger rather metabolic events.

JAK-STAT pathway.

As indicated above, IL-6 binding to IL-6Rα results in the formation of a hexameric complex consisting of 2 IL-6, 2 IL-6Rα, and 2 gp130 molecules. Subsequently, Janus kinases JAK-1, JAK-2, and Tyk2, which are constitutively associated with gp130, become phosphorylated and activated.182-185 This results in the activation of a recently described signaling cascade named JAK-STAT pathway.186-188 JAKs are protein tyrosine kinases that associate with various cytokine receptors and induce phosphorylation of the receptor and of cellular substrates called STAT (signaltransducer andactivation oftranscription) proteins.178,184STATs were identified on the search for transcription factors binding to IFN-responsive promoters.189,190 STATs are present in a latent form in the cytoplasm and become phosphorylated on a single tyrosine within minutes after ligand binding. Phosphorylated STATs dimerize and translocate to the nucleus.191,192 Many growth factors activate the JAK-STAT pathway.186 IL-6 activates STAT3 and STAT1 via distinct cytoplasmic domains of the IL-6 signal transducer gp130.183,184,186,193-196 However, the role of the JAK-STAT pathway for the pathogenesis of MM remains uncertain. Both STAT1 and STAT3 seem constitutively active in IL-6 responsive and nonresponsive MM cells, and stimulation of cells by IL-6 does not increase the activity of both STATs.197,198 Therefore, and in contrast to the Ras-MAPK pathway described below, STATs seem less involved in MM pathogenesis.

Ras-MAP kinase signaling pathway.

The three proteins encoded by the human ras genes (H-ras, K-ras, N-ras) are membrane-associated guanosine triphosphatases (GTPases) with a m.w. of 21 kD.199 These three proteins are usually referred to as Ras or p21ras. The essential feature of Ras is its ability to bind the guanine nucleotides GTP and guanosine diphosphate (GDP). Ras is active in the GTP-bound form, and inactive in the GDP-bound form. Ras functions as an important mediator of many biological responses stimulated by tyrosine kinases. Activation of Ras lies downstream of receptor and nonreceptor tyrosine kinases and upstream of a kinase cascade which includes other important signaling intermediates such as Raf-1 and MAPK (see below and Fig 2).200 

More recently, some novel mammalian proteins have been identified that are involved in the regulation and activation of Ras by tyrosine kinases. Shc (Srchomology and collagen), Grb2 (growth factorreceptor bound protein 2), and Sos1 (Son ofsevenless) are members of a group of mammalian proteins involved in the regulation and activation of p21ras by tyrosine kinases. Shc is a SH2 domain containing protein which binds itself to the SH2 domain of Grb2; Grb2 is a small protein with one SH2 domain flanked by two SH3 domains; Sos1 is a guanine nucleotide releasing factor for p21ras.200-210 Activation of p21rasrequires the coordinate interaction of these proteins and is regulated by tyrosine phosphorylation. A model of p21ras activation has been proposed from studies on epidermal growth factor (EGF) and insulin receptors (EGFR, IR).200 After ligand-induced receptor activation and homodimerization, the SH2 domains of Grb2 bound in a complex with Sos1, become attached to specific tyrosine residues of the receptor, thus relocating Sos1 to the plasma membrane. Subsequently, Sos1 induces an exchange of GDP for GTP on membrane-bound p21ras, thereby activating p21ras.200,202 Activated p21ras is later shut off by hydrolysis of GTP to GDP; this reaction is enhanced by GTPase activating proteins such asrasGAP.202,211 In contrast to the EGFR, stimulation of p21ras by the insulin receptor (IR) involves two additional proteins, Shc and insulin receptor substrate-1 (IRS-1). Upon stimulation with insulin, both proteins become activated and bind to Grb2 to recruit Grb2/Sos-1 complexes to the cell membrane.210 

Different events with critical importance for cell growth and/or malignant transformation activate Shc: stimulation with growth factors, activation of the T-cell receptor/CD3 complex and the B-cell antigen receptor, as well as cellular transformation with v-src, v-fps, orbcr/abl-oncogenes.210,212-223 IL-6 and other cytokines known to act through gp130 (CNTF, LIF, OSM) induce the activation and complex formation of Shc and Grb2 in a time- and concentration-dependent manner in human MM cells.185,194,224,225 This may enable Shc to interact with the adaptor protein Grb2 and with Sos1 to activate p21ras.226 Thereafter, the other signaling intermediates of the Ras signaling pathway like Raf-1 and MAPK become activated.185 

The tyrosine kinase(s) that phosphorylate and activate Shc and Grb2 in response to IL-6 are unknown. JAKs may be involved, because OSM was shown to induce activation of JAK2, and its subsequent binding to the SH2 domain of Grb2.224 IL-6–induced activation of the Src-family kinases Hck, Lyn, or Fyn might also stimulate the Ras pathway (M. Hallek, G. de Vos, C. Neumann, M. Schäffer, unpublished results, August 1997).180,181,227 In MM cell lines, IL-6 activates the Src-kinases Hck, Lyn, and Fyn. Hck is associated with gp130.181 The overexpression of a constitutively active Hck kinase induces similar effects as constitutively active v-Ha-Ras, providing further support for the hypothesis that the Ras signaling pathway involves Hck.227 

Vav, a multifunctional signaling protein expressed exclusively in hematopoietic cells and trophoblasts,228-230 also associates with the membrane-distal region of gp130 and becomes phosphorylated on tyrosine residues in response to IL-6 and to IGF-1 in the MM cell line U266.231,232 Vav coimmunoprecipitates with MAPK and Grb2.231 Therefore, Vav might be another protein regulating the Ras-MAPK signaling cascade in MM cells.

The activation of p21ras usually induces the subsequent phosphorylation and activation of downstream signaling proteins like Raf-1 and MAPK; this signaling pathway has therefore been termed Ras or MAPK signaling pathway (Fig 2). MAPKs (alternatively namedextracellular signalregulatedkinases, ERKs) are serine-threonine kinases present at low abundance and in different isoforms of 39 to 45 kD in many cell types that are enzymatically activated by tyrosine and threonine phosphorylation in response to various extracellular stimuli.233,234 The best-characterized MAPKs are the 42-kD and 44-kD isoforms (p42MAPK and p44MAPK; ERK2 and ERK1). They are activated by different growth factors and are involved in cell-cycle progression.233 MAPKs are an important integration point in the signal transduction machinery, because they interact with a variety of substrates, including a 90-kD cell-cycle regulatedS6 protein kinase (RSK or pp90RSK), cytosolic phospholipase A2, c-Jun, c-Myc, c-Fos, NF-IL-6, myelin basic protein (MBP), TAL-1 and Raf-1.74,233-236 MAPKs are activated by at least two MAP kinase kinases, MKK1 and MKK2.237,238 MKKs are activated by the serine-threonine kinase Raf-1, although this is not the only way of activation.237 

Like many lympho-hematopoietic growth factors, IL-6 activates MAPK and its substrates.73,185,233,239 The functional consequence of the IL-6 triggered Ras-MAPK activation for MM pathogenesis is becoming better understood. Studies with IL-6–responsive and IL-6–nonresponsive cell lines suggest that a lack of Sos1 activation is observed only in IL-6–nonresponsive cells, and that Sos1 seems to be constitutively complexed with Grb2 in some of the IL-6–nonresposive cells.197 The activation of the Ras-MAPK signaling cascade by IL-6 but not the JAK-STAT pathway (STAT1, STAT3) correlates with the proliferative response of MM cells to IL-6.240 Treatment with MAPK antisense oligonucleotides inhibits the proliferation of cells induced by IL-6.240 Activation of MAPK by IL-6 causes an increase of the transcriptional activity of NF-IL-6 by phosphorylation on threonine residue 235.241 This effect is similar to oncogenic p21ras, which also increases the transcriptional activity of NF-IL-6 by activation of MAP kinases.241 Taken together, these data support the view that a (constitutive) activation of MAPK by IL-6, oncogenic p21ras, or by other mechanisms is important to sustain MM growth.

ESCAPE: ACTIVATION OF GROWTH FACTOR INDEPENDENT GROWTH, OR PREVENTION OF PROGRAMMED CELL DEATH

Chromosomal aberrations increase with disease progression in MM,242 indicating that the transformation from MGUS to MM or plasma cell leukemia requires additional mutations to enable the malignant cell clone to survive and proliferate in the absence of the marrow microenvironment.

Ras Mutations

The above-described studies on IL-6 signaling strongly suggest a critical role for p21ras in the pathogenesis of MM. This hypothesis is further nourished by the finding that rasmutations occur in about 39% of newly diagnosed MM patients (Table1). Interestingly, the frequency ofras mutations increases with disease progression: Mutations of N- and K-ras are rarely detected in solitary plasmacytoma and monoclonal gammopathies of undetermined significance (MGUS), but more frequently in MM (in 9% to 30%), and in the majority of terminal disease or plasma cell leukemia patients (63.6% to 70%).243-246 N-ras codon 61 mutations seem more frequent than N-ras codon 12 and 13, or K-ras mutations (Table1).243-245 

Table 1.

Ras Point Mutations in MM

First Author  N12  N13  N61  K12  K13  K61 Total  
Neri, patients at diagnosis244  2  9  2  1  0  12/43  
Neri, patients at relapse244  0  1  3  2  0  0  6/13 
Matozaki247  2  3  2     4/13 
Portier246  4  1  4  3  0  14/30  
Tanaka245  1  2  2  0  0  5/10  
Paquette248    2     2/17 
Corradini243  2  1  7  1  0  11/90  
Yasuga249  0      2/45  
Liu250  6/129  5/129 50/346  16/139  7/139   63/160  
Total  17/373 15/328  81/607  24/325  8/325  3/186  
 4.5% 4.6%  13.3%  7.4%  2.5%  1.6%  34% 
First Author  N12  N13  N61  K12  K13  K61 Total  
Neri, patients at diagnosis244  2  9  2  1  0  12/43  
Neri, patients at relapse244  0  1  3  2  0  0  6/13 
Matozaki247  2  3  2     4/13 
Portier246  4  1  4  3  0  14/30  
Tanaka245  1  2  2  0  0  5/10  
Paquette248    2     2/17 
Corradini243  2  1  7  1  0  11/90  
Yasuga249  0      2/45  
Liu250  6/129  5/129 50/346  16/139  7/139   63/160  
Total  17/373 15/328  81/607  24/325  8/325  3/186  
 4.5% 4.6%  13.3%  7.4%  2.5%  1.6%  34% 

The number of mutations of N-ras codon 12 (N12), codon 13 (N13), and codon 61 (N61), and of K-ras codon 12 (K12), codon 13 (K13), and codon 61 (K61) detected in MM patients in various studies is summarized.

Overexpression of H-ras or N-ras oncogenes in Epstein-Barr virus (EBV)-infected human B lymphoblasts induces the malignant transformation and plasmacytoid differentiation of these cells.251 The introduction of a constitutively active N-ras cDNA containing a glutamine to arginine (CAA-CGA) amino acid substitution at codon 61 into the IL-6–dependent myeloma cell line ANBL6 resulted in significant IL-6–independent growth, as well as augmentation of growth at suboptimal concentrations of IL-6.252 Furthermore, mutant N-ras expression decreased the percentage of cells undergoing apoptosis in the absence of IL-6.252 This suggests that activating mutations of the ras oncogenes may result in growth factor independence and suppression of apoptosis in MM. Taken together, these findings support the following scenario: in early disease where myeloma cell growth seems strictly dependent on the presence of IL-6, p21ras is (constitutively) activated by the paracrine secretion of IL-6 in the BM microenvironment. At later disease stages, activating mutations of N- or K-ras replace this function, thus allowing an IL-6–independent tumor expansion and dissemination outside the marrow. This hypothesis awaits its verification by a careful analysis of the p21ras function at different MM stages.

Inhibitors of Programmed Cell Death: p53 and bcl-2

Bcl-2 and related proteins.

Apoptosis or programmed cell death is a process of pivotal importance during normal development, for immunoselection against autoreactive T and B cells, or in the elimination of old or damaged cells. Apoptosis is also induced by a variety of drugs, heat shock, or by growth factor deprivation. The membrane protein Bcl-2 is a highly conserved, ubiquitous membrane protein associated with the outer-membrane of mitochondria and nuclei, and with the endoplasmatic reticulum which regulates apoptosis.253 Overexpression of bcl-2 in cancer cells can result in chemoresistance and blocks apoptosis. Recent work has shown the existence of several Bcl-2–related proteins that can inhibit (Bcl-XL, Mcl-1, NR-13, A1, Bcl-W) or enhance (Bax, Bcl-XS, Bak, Bad) apoptosis.254,255 Bcl-2 forms inactivating or activating heterodimers with other proteins encoded by these genes of the bcl-2 superfamily.

Expression of bcl-2 is thought to play an important role in B-cell malignancies, in particular in follicular lymphoma, where more than 80% of the patients have the translocation t(14;18), which results in overexpression of Bcl-2.256 This translocation occurs at lower frequency (0% to 15%) in MM, but despite this an overexpression of Bcl-2 is seen in the majority of MM and in MM cell lines.257-259 High levels of Bcl-2 protein are likely to mediate the resistance of MM cells to apoptosis induced by dexamethasone, IL-6 deprivation, staurosporine, or other drugs.260-262 In a murine myeloma cell line, Bcl-XL showed a predominant role in preventing apoptosis in response to cycloheximide treatment or IL-6 withdrawal.263Similarly, overexpression of Bcl-2 or Bcl-XL could prevent apoptosis induced by IL-6 withdrawal in the IL-6–dependent cell line B-9.262 

p53.

The tumor suppressor gene p53 has many effects on cell growth and differentiation and is often viewed as a gate-keeper to enter the cell cycle. Recently, is has been found that p53 binds to response elements on bcl-2 and bax genes, resulting in the downregulation of bcl-2 and in an upregulation of bax. Therefore, it was postulated that p53 induces the synthesis of bax and reduces the synthesis of bcl-2, thereby affecting the balance between cell growth and death.264 

In MM cell lines, p53 mutations occur frequently but without apparent correlation with autonomous, IL-6–independent cell growth.265 Overexpression of wildtype p53 can suppress the autocrine IL-6 production and proliferation of U266 cells.266 p53 mutations are infrequent in MM, and a late event in the disease. p53 mutations occur in about 5% of inactive MM, and in 20% to 40% of acute plasma cell leukemia.246,249,267-270 Thus, p53 mutations might cause a block of plasmablastic apoptosis and differentiation at the final stages.

Retinoblastoma (Rb) Gene and Other Cell-Cycle Regulatory Genes

Rb.

The retinoblastoma tumor suppressor gene product (pRb) is involved in cell growth and differentiation. pRb is a nuclear phosphoprotein that suppresses the G1 → S transition in the cell cycle by inhibiting E2F-mediated transactivation of a variety of genes involved in initiating DNA synthesis, such as c-myc, b-myb, cdc2, dihydrofolate reductase, and thymidine kinase.271-276 pRb function is regulated by phosphorylation: hypophosphorylated or dephosphorylated pRb is activated and binds E2F, thereby inducing cell-cycle arrest; in contrast, phosphorylated pRb is inactivated and cannot bind E2F, thereby promoting entry of cells into S phase.271 Mutations of the Rb gene contribute to cellular transformation in many types of malignancies. To date, mutations of the Rb gene or abnormalities in pRb have been described in up to 70% of MM patients and 80% of MM-derived cell lines.267,277,278 MM cells may show a very strong expression of pRb,279 mostly in its phosphorylated form.280 

As noted above, monosomies of chromosome 13 have been identified in approximately 30% of abnormal MM karyotypes. By Southern blot or interphase FISH analysis, monoallelic deletion of Rb (loss of one copy of chromosome 13 or interstitial deletions encompassing the 13q12-14 region) has been reported in about 50% to 60% of MM tumors and cell lines, independent of the disease stage. Bi-allelic deletion of Rb was found in 1 of 22 MM cell lines and in 1 of 10 primary tumors.267,277,278,281 The monoallelic lesions were not associated with any effect on the pRb expression, and no mutations or rearrangements of Rb have been described. These findings suggest that a bi-allelic loss of the Rb gene is infrequent in MM and, like in CLL, there may be a tumor suppressor gene other than Rb (DMB, deleted in B-cell malignancies?; BRCA2?) on 13q12-14 that is activated in MM.282 

Transforming growth factor (TGFβ) does not suppress pRb phosphorylation and proliferation of MM cells, in contrast to normal B cells, consistent with the notion that pRb may contribute to MM cell growth.283 Incubation of MM cells with Rb antisense oligonucleotides triggers IL-6 secretion and cell proliferation.280 Overexpression of wild-type pRb can suppress the autocrine IL-6 production and proliferation of U266 cells.266 In IL-6–responsive MM cells, stimulation with IL-6 further shifts pRb from its dephosphorylated to its phosphorylated form, thereby promoting MM cell growth.280 This suggests that IL-6–induced signaling through pRb may have two effects, the phosphorylation (inactivation) of pRb and the upregulation of IL-6 secretion, which both augment proliferation of MM cells. Taken together, both molecular studies and the occasional observation of pRb inactivation in MM cells indicate that the loss of pRb function may contribute to MM transformation.

Inhibitors of cyclin-dependent kinases.

The p16INK4A (p16) protein is an inhibitor of cyclin-dependent kinases (CDK) 4 and CDK6. It is expressed in some MM cells or cell lines, and a higher expression correlates with IL-6 responsiveness of more mature MM tumors (VLA-5+, MPC+).284,285 In contrast, expression of cyclin D1 is more frequent in immature MM tumors (VLA-5−, MPC−).285 The p16 gene is frequently hypermethylated in MM.286 This hypermethylation occurs more frequently in advanced disease (plasma cell leukemia [PCL]) and in MM cell lines.287 Treatment with the demethylating agent 5-deoxyazacytidine restores the p16 protein expression and induces G1 growth arrest in patient PCL cells and in MM cell lines.287 This suggests that inactivation of the p16 gene by hypermethylation may be associated with decreased growth control and with the development of PCL. Homozygous deletions of genes encoding for the CDK inhibitors p15INK4B, p16INK4A, and p18INK4Cmay also occur in some patients with MM.288 

p21WAF1.

p21WAF1 (p21) inhibits cell proliferation by both p53-dependent and -independent mechanisms. It is believed that p21 protects from (p53 dependent) apoptosis by induction of cell-cycle arrest and subsequent DNA repair.289,290 In the majority of MM cells, p21 seems to be constitutively expressed, while it is not detected in normal B cells.291 IL-6 downregulates and IFN-γ upregulates p21 expression, and this effect correlates with G1 → S transition induced by IL-6 in MM cells.291 Taken together, p21 overexpression in MM may induce resistance to apoptosis (by chemical agents or radiation), and slow clinical progression of disease.

MDM2.

The murine double minute 2 (MDM2) gene product facilitates the G1 → S transition by direct DNA binding and enhancing transcription of genes associated with proliferation, or by activation of E2F-1-DP1; it also abrogates tumor suppressive functions of wild-type p53. Recently, the overexpression of the MDM2 protein has been reported in MM cell lines and PCL cells from patients.292 MDM2 protein was found to be constitutively bound to wild-type or mutant p53 in MM cells.292 Treatment with MDM2 antisense oligonucleotides seemed to induce G1 arrest.292 This suggests that MDM2 enhances cell-cycle progression in MM.

Multiple Drug Resistance (MDR) Gene

The MDR gene encodes a 170-kD p-glycoprotein which is responsible for the resistance of tumor cells to a variety of antineoplastic drugs. The amplification of MDR gene expression can be detected in myeloma cells, and its expression is correlated with a resistance to doxorubicin and vincristine (VAD regimen).293-295 Recently, clinical trials have been activated to overcome this treatment refractoriness with drug-resistance modifiers like cyclosporin A and verapamil.295 

THERAPEUTIC IMPLICATIONS

The central role of IL-6 as a growth factor for MM cells suggests that strategies to block its effects could be exploited therapeutically. This effect may be achieved either by conventional therapeutic agents or by compounds specifically designed to block the action of IL-6. Among the conventional agents is IFN-γ, which may inhibit the growth of IL-6–dependent MM cell lines by a downregulation of the IL-6R expression on MM cells.139,296 All-trans retinoic acid (ATRA) inhibits the IL-6–dependent growth of freshly isolated MM cells and MM cell lines, decreases the IL-6 production by MM cells and BMSCs and downregulates IL-6R and gp130.91,297,298 IFN-α may downregulate IL-6R and gp130, thereby inhibiting MM growth.141 Glucocorticoids (GC), which are very common components of MM therapy, were also reported to repress IL-6 gene transcription and production and to induce apoptosis of MM cells.89,299 IL-4 has inhibitory effects on the in vitro growth of MM cells and suppresses the IL-6 gene transcription in BMSCs.300,301 

More specific antagonists of IL-6–dependent growth are anti–IL-6 MoAbs or anti–IL-6R MoAbs that disrupt autocrine or paracrine IL-6R stimulation. Both strategies have been shown to suppress the growth of MM or PCL cells in vivo and in vitro.302-304 For repeated administration, humanization of these MoAbs seems critical to decrease their immunogenicity in vivo.302,305 Similarly, toxic fusion proteins targeting the IL-6R on MM cells may be used for treatment. Recombinant proteins consisting of IL-6 fused toPseudomonas exotoxin (IL-6-PE4E) or to diphtheria toxin were successfully used to kill MM cells.306,307 These compounds may be particularly helpful for ex vivo purging of autologous BM or peripheral blood stem cells (PBSCs) contaminated with tumor cells.307 Antisense oligonucleotides that inhibit the expression of IL-6 or IL-6R genes may be used to suppress MM growth, and the principal feasibility of this approach has been shown in vitro.308 A very elegant method of blocking the effects of IL-6 on MM growth may be the use of recombinant chimeric human/murine IL-6 proteins which introduce biologically inactive murine residues into the human IL-6 protein, thereby blocking the interaction with gp130.309 The resulting IL-6 molecules were inactive on human myeloma cells and in addition completely inhibited wild-type IL-6 activity on these cells. A similar approach is the molecular modeling of IL-6 superantagonists that contain variant binding motifs with higher affinity to the IL-6Rα chain, but impair efficient gp130 dimerization by antagonistic amino acid substitutions in sites critical for the contact with gp130.310-312 Some of these IL-6 superantagonists are potent inducers of apoptotic cell death in MM cell lines and inhibit intracellular signaling.92 Chemically synthesized peptides may also block the IL-6Rα/gp130 interaction.313 Such antagonists will be tested as specific inhibitors of IL-6 activity in vivo.

Novel strategies may also target the signaling intermediates or oncogene products involved in MM pathogenesis. The above-described experiments with antisense oligonucleotides used to block the Ras-MAPK pathway are another potential way to antagonize some critical components of neoplastic plasma cell growth.240 Of equal importance are efforts to create specific inhibitors of tyrosine kinases and their substrates. Unfortunately, most tyrosine kinase inhibitors available (genistein, staurosporin, erbstatin) are not specific and therefore too toxic. The recently discovered inhibitors of Ras farnesyltransferases, which block the action of Ras, may act more specifically and may be particularly helpful in MM patients.314 Because the cellular mechanisms of (proto-)oncogene activation are inherently linked with signaling pathways of MM growth factors, the ongoing research in this field will certainly contribute to the development of new molecular therapies for MM.

Because growth of MM seems to depend critically on the support by the BM environment and on a defective antitumor immune response, novel therapeutic strategies might also act here. For example, bisphosphonates like pamidronate which reduce skeletal complications and improve survival of MM patients, were shown to suppress the IL-6 production by BMSCs.315 Thus, pamidronate might inhibit MM growth more specifically than originally thought. It has also been shown that the gene transfer of costimulatory molecules B7-1 and B7-2 into B7-negative MM cells is able to induce a cytolytic T-cell response against MM cells in vitro.161 Thus, adjuvant gene transfer modified tumor vaccines might add to the novel, molecular therapeutic arsenal against this disease.

SUMMARY

Based on the information described above, we propose a working multi-step model of the molecular pathogenesis of myeloma (Fig3). The cell that gives rise to myeloma appears to have passed through the pathway that generates the long-lived plasma cell which has a phenotype similar to myeloma cells. Thus, the oncogenic events in myeloma either occur after or do not interfere with the normal maturation process that generates long-lived plasma cells. Like a long-lived plasma cell, a myeloma cell has undergone three developmentally regulated changes in the DNA structure of the IgH and IgL loci, including productive V(D)J recombination of its IgH and IgL genes, somatic hypermutation of the IgH and IgL V regions, and productive IgH switch recombination to another IgH isotype. It is attractive to speculate that errors in one or more of these processes has caused genetic changes that contribute to the malignant process.

Fig. 3.

Progressive genetic events in MM. Although not every stage is discernible in each patient, there appears to be an ordered progression from a normal plasma cell; to MGUS where the cells are immortalized, but not transformed, and do not progressively accumulate or cause bone destruction; to intra-medullary myeloma, where the cells are confined to the BM micro-environment, accumulate and cause bone destruction; to extra-medullary myeloma, where the cells proliferate more rapidly and grow in the blood (plasma cell leukemia) or other extra-medullary sites; to a myeloma cell line, where the cells may be propagated in vitro. This model summarizes the possible timing of genetic events in relation to clinical progression. When the event may occur at a discrete time, we have indicated this with an arrow. When it is clearly associated with a defined clincal stage we have indicated this with a solid line. When the timing is unclear, we have used a dashed line. We suspect that the 14q32 translocation may be an early event, concordant with isotype switch recombination, so that it may precede MGUS. Some translocations [eg, t(11;14)] may lead more rapidly to fulminant disease. There is evidence of karyotypic instability in MGUS that continues throughout all stages of tumour progression. Monosomy 13 is present in intramedullary myeloma, independent of stage, but there is no evidence as to whether or not it is present in MGUS. Dysregulation of c-myc appears to be common, but the timing is unclear. In patients with ectopic FGFR3 expression caused by t(4;14), a mutation of FGFR3 could lead to ligand independence and clinical progression, as is suggested in one analyzed example. Mutations of N- and K-ras are not present in MGUS, but are present in intramedullary myeloma, with an increasing incidence as the disease progresses. Mutations of p53 are a late event associated with aggressive extra-medullary myeloma.

Fig. 3.

Progressive genetic events in MM. Although not every stage is discernible in each patient, there appears to be an ordered progression from a normal plasma cell; to MGUS where the cells are immortalized, but not transformed, and do not progressively accumulate or cause bone destruction; to intra-medullary myeloma, where the cells are confined to the BM micro-environment, accumulate and cause bone destruction; to extra-medullary myeloma, where the cells proliferate more rapidly and grow in the blood (plasma cell leukemia) or other extra-medullary sites; to a myeloma cell line, where the cells may be propagated in vitro. This model summarizes the possible timing of genetic events in relation to clinical progression. When the event may occur at a discrete time, we have indicated this with an arrow. When it is clearly associated with a defined clincal stage we have indicated this with a solid line. When the timing is unclear, we have used a dashed line. We suspect that the 14q32 translocation may be an early event, concordant with isotype switch recombination, so that it may precede MGUS. Some translocations [eg, t(11;14)] may lead more rapidly to fulminant disease. There is evidence of karyotypic instability in MGUS that continues throughout all stages of tumour progression. Monosomy 13 is present in intramedullary myeloma, independent of stage, but there is no evidence as to whether or not it is present in MGUS. Dysregulation of c-myc appears to be common, but the timing is unclear. In patients with ectopic FGFR3 expression caused by t(4;14), a mutation of FGFR3 could lead to ligand independence and clinical progression, as is suggested in one analyzed example. Mutations of N- and K-ras are not present in MGUS, but are present in intramedullary myeloma, with an increasing incidence as the disease progresses. Mutations of p53 are a late event associated with aggressive extra-medullary myeloma.

A chromosome translocation to the IgH locus, most frequently into a switch region, is a nearly universal event in myeloma cell lines, and it appears to be equally frequent in primary tumor samples. We postulate that these translocations occur at the time of isotype switch recombination, on the nonproductive allele. Because MGUS and myeloma share the same legitimate switch recombination on the productive allele, they may also share the same illegitimate switch recombination on the nonproductive allele. The result of these translocations is to dysregulate the expression of an oncogene (eg, c-myc) by juxtaposing it to the strong regulatory sequences of the IgH locus, resulting in immortalization of the malignant clone. The presence of intraclonal heterogeneity in the Ig hypervariable regions in MGUS indicates that these cells are still subject to somatic hypermutation.316After immortalization, the malignant cell establishes a supportive environment in the BM with a network of cytokines, adhesion molecules, and other costimulatory interactions with the stromal cells. Later additional mutations which might be caused by a spillover of the hypermutational process onto ras or a tumor suppressor gene on chromosome 13, result in the selection of a single clone for malignant expansion. Further mutations, like p53, lead to stroma-independent growth, and escape from the BM micro-environment. Further understanding of this transformation process in MM will allow the development of new therapies defined at the molecular level.

ACKNOWLEDGMENT

P.L.B. would like to acknowledge the equal contribution of Michael Kuehl to our shared results and ideas presented here.

M.H. is supported by in part by grants from the Deutsche Forschungsgemeinschaft (Ha 1680/2-2) and the Deutsche Krebshilfe (no. 10-1094-Ha I).

Address reprint requests to Michael Hallek, MD, Medizinische Klinik, Klinikum Innenstadt, Universität München, Ziemssenstrasse 1, D-80336 München, Germany.

REFERENCES

REFERENCES
1
Vescio
RA
Cao
J
Hong
CH
Lee
JC
Wu
CH
Der Danielian
M
Wu
V
Newman
R
Lichtenstein
AK
Berenson
JR
Myeloma Ig heavy chain V region sequences reveal prior antigenic selection and marked somatic mutation but no intraclonal diversity.
J Immunol
155
1995
2487
2
Klein
B
Zhang
XG
Lu
ZY
Bataille
R
Interleukin-6 in human multiple myeloma.
Blood
85
1995
863
3
Bakkus
MH
Heirman
C
Van Riet
I
Van Camp
B
Thielemans
K
Evidence that multiple myeloma Ig heavy chain VDJ genes contain somatic mutations but show no intraclonal variation.
Blood
80
1992
2326
4
Lewis
JP
Mackenzie
MR
Non-random chromosomal aberrations associated with multiple myeloma.
Hematol Oncol
2
1984
307
5
Dewald
GW
Kyle
RA
Hicks
GA
Greipp
PR
The clinical significance of cytogenetic studies in 100 patients with multiple myeloma, plasma cell leukemia, or amyloidosis.
Blood
66
1985
380
6
Gould
J
Alexanian
R
Goodacre
A
Pathak
S
Hecht
B
Barlogie
B
Plasma cell karyotypes in multiple myeloma.
Blood
71
1988
453
7
Weh HJ, Gutensohn K, Selbach J, Kruse R, Wacker-Backhaus G, Seeger D, Fiedler W, Fett W, Hossfeld DK: Karyotype in multiple myeloma and plasma cell leukaemia. Eur J Cancer 29A:1269, 1993
8
Lai
JL
Zandecki
M
Mary
JY
Bernardi
F
Izydorczyk
V
Flactif
M
Morel
P
Jouet
JP
Bauters
F
Facon
T
Improved cytogenetics in multiple-myeloma—A study of 151 patients including 117 patients at diagnosis.
Blood
85
1995
2490
9
Sawyer
JR
Waldron
JA
Jagannath
S
Barlogie
B
Cytogenetic findings in 200 patients with multiple myeloma.
Cancer Genet Cytogenet
82
1995
41
10
Zandecki
M
Bernardi
F
Lai
JL
Facon
T
Izydorczyk
V
Bauters
F
Cosson
A
Image analysis in multiple myeloma at diagnosis.
Cancer Genet Cytogenet
74
1994
115
11
Sole
F
Woessner
S
Acin
P
Perez-Losada
A
Florensa
L
Besses
C
Sans-Sabrafen
J
Cytogenetic abnormalities in 13 patients with multiple myeloma.
Cancer Genet Cytogenet
86
1996
162
12
Tabernero
D
San Miguel
JF
Garcia-Sanz
R
Najera
L
Garcia-Isidoro
M
Perez-Simon
JA
Gonzalez
M
Wiegant
J
Raap
AK
Orfao
A
Incidence of chromosome numerical changes in multiple myeloma.
Am J Pathol
149
1996
153
13
Taniwaki
M
Nishida
K
Ueda
Y
Takashima
T
Non-random chromosomal rearrangements and their implications in clinical features and outcome of multiple myeloma and plasma cell leukemia.
Leuk Lymphoma
21
1995
25
14
Ferti
A
Panani
A
Arapakis
G
Raptis
S
Cytogenetic study in multiple myeloma.
Cancer Genet Cytogenet
12
1984
247
15
Jonveaux
P
Berger
R
Chromosome studies in plasma cell leukemia and multiple myeloma in transformation.
Genes Chromosom Cancer
4
1992
321
16
Drach
J
Angerler
J
Schuster
J
Rothermundt
C
Thalhammer
R
Haas
OA
Jager
U
Fiegl
M
Geissler
K
Ludwig
H
Huber
H
Interphase fluorescence in situ hybridization identifies chromosomal abnormalities in plasma cells from patients with monoclonal gammopathy of undetermined significance.
Blood
86
1995
3915
17
Flactif
M
Zandecki
M
Lai
JL
Bernardi
F
Obein
V
Bauters
F
Facon
T
Interphase fluorescence in situ hybridization (FISH) as a powerful tool for the detection of aneuploidy in multiple myeloma.
Leukemia
9
1995
2109
18
Zandecki
M
Obein
V
Bernardi
F
Soenen
V
Flactif
M
Lai
JL
Francois
M
Facon
T
Monoclonal gammopathy of undetermined significance: Chromosome changes are a common finding within bone marrow plasma cells.
Br J Haematol
90
1995
693
19
Williams
ME
Swerdlow
SH
Rosenberg
CL
Arnold
A
Chromosome 11 translocation breakpoints at the PRAD1/cyclin D1 gene locus in centrocytic lymphoma.
Leukemia
7
1993
241
20
Korsmeyer
SJ
Chromosomal translocations in lymphoid malignancies reveal novel proto-oncogenes.
Annu Rev Immunol
10
1992
785
21
Ye
BH
Changanti
S
Chang
CC
Niu
H
Corradini
P
Chaganti
RS
Dalla-Favera
R
Chromosomal translocations cause deregulated BCL6 expression by promoter substitution in B cell lymphoma.
EMBO J
14
1995
6209
22
Potter
M
Wiener
F
Plasmacytomagenesis in mice: Model of neoplastic development dependent upon chromosomal translocations.
Carcinogenesis
13
1992
1681
23
Dalla-Favera R: Chromosomal translocations involving the c-myc oncogene in lymphoid neoplasia, in Kirsch IR (eds): The Causes and Consequences of Chromosomal Aberrations. New York, NY, CRC, 1993, p 313
24
Bergsagel
PL
Chesi
M
Nardini
E
Brents
LA
Kirby
SL
Kuehl
WM
Promiscuous translocations into immunoglobulin heavy chain switch regions in multiple myeloma.
Proc Natl Acad Sci USA
93
1996
13931
25
Bergsagel
PL
Nardini
E
Brents
L
Chesi
M
Kuehl
WM
IgH translocations in multiple myeloma: A nearly universal event that rarely involves c-myc.
Curr Topics Microbiol Immunol
224
1997
283
26
Chesi
M
Bergsagel
PL
Brents
LA
Smith
CA
Gerhard
DS
Kuehl
WM
Dysregulation of cyclin D1 by translocation into an IgH gamma switch region in two multiple myeloma cell lines.
Blood
88
1996
674
27
Chesi
M
Nardini
E
Brents
LA
Schrock
E
Ried
T
Kuehl
WM
Bergsagel
PL
Frequent translocation t(4;14)(p16.3;q32.3) in multiple myeloma: Association with increased expression and activating mutations of fibroblast growth factor receptor 3.
Nature Genet
16
1997
260
28
(abstr, suppl 1)
Iida
S
Butler
M
Rao
P
Carradini
P
Boccadoro
M
Klein
B
Chaganti
RSK
Dalla-Favera
R
MUM1/ICSAT, a member of the interferon regulatory factor family (IRF) is involved in chromosomal translocations in multiple myeloma.
Blood
88
1996
450a
29
Grossman
A
Mittrucker
HW
Nicholl
J
Suzuki
A
Chung
S
Antonio
L
Suggs
S
Sutherland
GR
Siderovski
DP
Mak
TW
Cloning of human lymphocyte-specific interferon regulatory factor (hLSIRF/hIRF4) and mapping of the gene to 6p23-p25.
Genomics
37
1996
229
30
Mittrucker
HW
Matsuyama
T
Grossman
A
Kundig
TM
Potter
J
Shahinian
A
Wakeham
A
Patterson
B
Ohashi
PS
Mak
TW
Requirement for the transcription factor LSIRF/IRF4 for mature B and T lymphocyte function.
Science
275
1997
540
31
Amati
B
Land
H
Myc-Max-Mad: A transcription factor network controlling cell cycle progression, differentiation and death.
Curr Opin Genet Dev
4
1994
102
32
Henriksson
M
Luscher
B
Proteins of the myc network: Essential regulators of cell growth and differentiation.
Adv Cancer Res
68
1996
109
33
Li
L
Nerlov
C
Prendergast
G
MacGregor
D
Ziff
EB
Myc represses transcription in vivo by a novel mechanism dependent on the initiator element and Myc box II.
EMBO J
13
1994
4070
34
Muller
JR
Janz
S
Potter
M
Differences between Burkitt's lymphomas and mouse plasmacytomas in the immunoglobulin heavy-chain c-myc recombinations that occur in their chromosomal translocations.
Cancer Res
55
1995
5012
35
Bazin
H
Pear
WS
Sumegi
J
Louvain rat immunocytomas.
Adv Cancer Res
50
1988
279
36
Sumegi
J
Hedberg
T
Bjorkholm
M
Godal
T
Mellstedt
H
Nilsson
MG
Perlman
C
Klein
G
Amplification of the c-myc oncogene in human plasma-cell leukemia.
Int J Cancer
36
1985
367
37
Selvanayagam
P
Blick
M
Narni
F
van Tuinen
P
Ledbetter
DH
Alexanian
R
Saunders
GF
Barlogie
B
Alteration and abnormal expression of the c-myc oncogene in human multiple myeloma.
Blood
71
1988
30
38
Palumbo
AP
Boccadoro
M
Battaglio
S
Corradini
P
Tsichlis
PN
Huebner
K
Pileri
A
Croce
CM
Human homologue of Moloney leukemia virus integration-4 locus (MLVI-4), located 20 kilobases 3′ of the myc gene, is rearranged in multiple myelomas.
Cancer Res
50
1990
6478
39
Ladanyi
M
Wang
S
Niesvizky
R
Feiner
H
Michaeli
J
Proto-oncogene analysis in multiple myeloma.
Am J Pathol
141
1992
949
40
Kuehl
WM
Chesi
M
Brents
LA
Huppi
K
Bergsagel
PL
Dysregulation of c-myc in multiple myeloma.
Curr Topics Microbiol Immunol
224
1997
277
41
Nobuyoshi
M
Kawano
M
Tanaka
H
Ishikawaka
H
Tanabe
O
Iwato
K
Asaoku
H
Sakai
A
Kuramoto
A
Increased expression of the c-myc gene may be related to the aggressive transformation of human myeloma cells.
Br J Haematol
77
1991
523
42
Greil
R
Fasching
B
Loidl
P
Huber
H
Expression of the c-myc proto-oncogene in multiple myeloma and chronic lymphocytic leukemia: An in situ analysis.
Blood
78
1991
180
43
Fourney
R
Palmer
M
Ng
A
Dietrich
K
Belch
A
Paterson
M
Brox
L
Elevated c-myc messenger RNA in multiple myeloma cell lines.
Dis Markers
8
1990
117
44
Brown
RD
Pope
B
Luo
XF
Gibson
J
Joshua
D
The oncoprotein phenotype of plasma cells from patients with multiple myeloma.
Leuk Lymphoma
16
1994
147
45
Jernberg-Wiklund
H
Pettersson
M
Larsson
LG
Anton
R
Nilsson
K
Expression of myc-family genes in established human multiple myeloma cell lines: L-myc but not c-myc gene expression in the U-266 myeloma cell line.
Int J Cancer
51
1992
116
46
Paulin
FE
West
MJ
Sullivan
NF
Whitney
RL
Lyne
L
Willis
AE
Aberrant translational control of the c-myc gene in multiple myeloma.
Oncogene
13
1996
505
47
Williams
ME
Meeker
TC
Swerdlow
SH
Rearrangement of the chromosome 11 bcl-1 locus in centrocytic lymphoma: analysis with multiple breakpoint probes.
Blood
78
1991
493
48
Fiedler
W
Weh
HJ
Hossfeld
DK
Comparison of chromosome analysis and BCL-1 rearrangement in a series of patients with multiple myeloma.
Br J Haematol
81
1992
58
49
Meeus
P
Stul
MS
Mecucci
C
Cassiman
JJ
Van den Berghe
H
Molecular breakpoints of t(11;14)(q13;q32) in multiple myeloma.
Cancer Genet Cytogenet
83
1995
25
50
Raynaud
SD
Bekri
S
Leroux
D
Grosgeorge
J
Klein
B
Bastard
C
Gaudray
P
Simon
MP
Expanded range of 11q13 breakpoints with differing patterns of cyclin D1 expression in B-cell malignancies.
Genes Chromosom Cancer
8
1993
80
51
Seto
M
Yamamoto
K
Iida
S
Akao
Y
Utsumi
KR
Kubonishi
I
Miyoshi
I
Ohtsuki
T
Yawata
Y
Namba
M
Motokura
T
Arnold
A
Takahashi
T
Ueda
R
Gene rearrangement and overexpression of PRAD1 in lymphoid malignancy with t(11;14)(q13;q32) translocation.
Oncogene
7
1992
1401
52
Motokura
T
Arnold
A
Cyclin D and oncogenesis.
Curr Opin Genet Dev
3
1993
5
53
Akiyama
N
Tsuruta
H
Sasaki
H
Sakamoto
H
Hamaguchi
M
Ohmura
Y
Seto
M
Ueda
R
Hirai
H
Yazaki
Y
Sugimura
T
Terada
M
Messenger RNA levels of five genes located at chromosome 11q13 in B-cell tumors with chromosome translocation t(11;14)(q13;q32).
Cancer Res
54
1994
377
54
Komatsu
H
Iida
S
Yamamoto
K
Mikuni
C
Nitta
M
Takahashi
T
Ueda
R
Seto
M
A variant chromosome translocation at 11q13 identifying PRAD1/cyclin D1 as the BCL-1 gene.
Blood
84
1994
1226
55
Zukerberg
LR
Yang
WI
Arnold
A
Harris
NL
Cyclin D1 expression in non-Hodgkin's lymphomas. Detection by immunohistochemistry.
Am J Clin Pathol
103
1995
756
56
Weh
HJ
Bartl
R
Seeger
D
Selbach
J
Kuse
R
Hossfeld
DK
Correlations between karyotype and cytologic findings in multiple myeloma.
Leukemia
9
1995
2119
57
Tricot
G
Barlogie
B
Jagannath
S
Bracy
D
Mattox
S
Vesole
DH
Naucke
S
Sawyer
JR
Poor prognosis in multiple myeloma is associated only with partial or complete deletions of chromosome 13 or abnormalities involving 11q and not with other karyotype abnormalities.
Blood
86
1995
4250
58
Shiang
R
Thompson
LM
Zhu
YZ
Church
DM
Fielder
TJ
Bocian
M
Winokur
ST
Wasmuth
JJ
Mutations in the transmembrane domain of FGFR3 cause the most common genetic form of dwarfism, achondroplasia.
Cell
78
1994
335
59
Prinos
P
Costa
T
Sommer
A
Kilpatrick
MW
Tsipouras
P
A common FGFR3 gene mutation in hypochondroplasia.
Hum Mol Genet
4
1995
2097
60
Rousseau
F
Bonaventure
J
Legeai-Mallet
L
Pelet
A
Rozet
JM
Maroteaux
P
Le Merrer
M
Munnich
A
Mutations in the gene encoding fibroblast growth factor receptor-3 in achondroplasia.
Nature
371
1994
252
61
Tavormina
PL
Shiang
R
Thompson
LM
Zhu
YZ
Wilkin
DJ
Lachman
RS
Wilcox
WR
Rimoin
DL
Cohn
DH
Wasmuth
JJ
Thanatophoric dysplasia (types I and II) caused by distinct mutations in fibroblast growth factor receptor 3.
Nat Genet
9
1995
321
62
Stoilov
I
Kilpatrick
MW
Tsipouras
P
A common FGFR3 gene mutation is present in achondroplasia but not in hypochondroplasia.
Am J Med Genet
55
1995
127
63
Meyers
GA
Orlow
SJ
Munro
IR
Przylepa
KA
Jabs
EW
Fibroblast growth factor receptor 3 (FGFR3) transmembrane mutation in Crouzon syndrome with acanthosis nigricans.
Nat Genet
11
1995
462
64
Naski
MC
Wang
Q
Xu
J
Ornitz
DM
Graded activation of fibroblast growth factor receptor 3 by mutations causing achondroplasia and thanatophoric dysplasia.
Nature Genet
13
1996
233
65
Rousseau
F
Ghouzzi
V
Delezoide
AL
Legeai-Mallet
L
Le Merrer
M
Munnich
A
Bonaventure
J
Missense FGFR3 mutations create cysteine residues in thanatophoric dwarfism type I (TD1).
Hum Mol Genet
5
1996
509
66
Clark
SC
Kamen
R
The human hematopoietic colony-stimulating factors.
Science
236
1987
1229
67
Metcalf
D
The molecular control of cell division, differentiation, commitment and maturation in haemopoietic cells.
Nature
339
1989
27
68
Sieff
CA
Biological and clinical aspects of the hematopoietic growth factors.
Annu Rev Med
41
1990
483
69
Nicola
NA
Hemopoietic cell growth factors and their receptors.
Annu Rev Biochem
58
1989
45
70
Ullrich
A
Schlessinger
J
Signal transduction by receptors with tyrosine kinase activity.
Cell
61
1990
203
71
Taga T, Kishimoto T: Cytokine receptors and signal transduction. FASEB J 6:3387, 1992
72
Miyajima
A
Kitamura
T
Harada
N
Yokota
T
Arai
K
Cytokine receptors and signal transduction.
Annu Rev Immunol
10
1992
295
73
Hallek M: Tyrosine kinases and phosphatases in hematopoietic growth factor signaling, in Herrmann F, Mertelsmann R (eds): Advances in Hematopoietic Growth Factors. New York, NY, Dekker, 1994, p 19
74
Kishimoto
T
Taga
T
Akira
S
Cytokine signal transduction.
Cell
76
1994
253
75
Klein
B
Bataille
R
Cytokine network in human multiple myeloma.
Hematol Oncol Clin North Am
6
1992
273
76
Klein
B
Cytokine, cytokine receptors, transduction signals and oncogenes in multiple myeloma.
Semin Hematol
32
1995
4
77
Akira
S
Taga
T
Kishimoto
T
Interleukin-6 in biology and medicine.
Adv Immunol
54
1993
1
78
Kishimoto
T
Akira
S
Taga
T
IL-6 receptor and mechanism of signal transduction.
Int J Immunopharmacol
14
1992
431
79
Bauer
J
Herrmann
F
Interleukin-6 in clinical medicine.
Ann Hematol
62
1991
203
80
Akira S, Hirano T, Taga T, Kishimoto T: Biology of multifunctional cytokines: IL-6 and related molecules. FASEB J 4:2860, 1990
81
Kishimoto
T
The biology of interleukin-6.
Blood
74
1989
1
82
Hirano
T
Akira
S
Taga
T
Kishimoto
T
Biological and clinical aspects of interleukin 6.
Immunol Today
11
1990
443
83
Klein
B
Zhang
X-G
Content
J
Houssiau
F
Aarden
L
Piechaczyk
M
Bataille
R
Paracrine rather than autocrine regulation of myeloma-cell growth and differentiation by interleukin-6.
Blood
73
1989
517
84
Kawano
M
Hirano
T
Matsuda
T
Taga
T
Horii
Y
Iwato
K
Asaoku
H
Tang
B
Tanabe
O
Tanaka
H
Kuramoto
A
Kishimoto
T
Autocrine generation and requirement of BSF-2/IL-6 for human multiple myeloma.
Nature
332
1988
83
85
Zhang
XG
Bataille
R
Widjenes
J
Klein
B
Interleukin-6 dependence of advanced malignant plasma cell dyscrasia.
Cancer
69
1992
1373
86
Lichtenstein
A
Tu
Y
Fady
C
Vescio
R
Berenson
J
Interleukin-6 inhibits apoptosis of malignant plasma cells.
Cell Immunol
162
1995
248
87
Puthier
D
Bataille
R
Barille
S
Mellerin
MP
Harousseau
JL
Ponzio
A
Robillard
N
Wijdenes
J
Amiot
M
Myeloma cell growth arrest, apoptosis, and interleukin-6 receptor modulation induced by EB1089, a vitamin D3 derivative, alone or in association with dexamethasone.
Blood
88
1996
4659
88
Shiao
RT
Miglietta
L
Khera
SY
Wolfson
A
Freter
CE
Dexamethasone and suramin inhibit cell proliferation and interleukin-6-mediated immunoglobulin secretion in human lymphoid and multiple myeloma cell lines.
Leuk Lymphoma
17
1995
485
89
Hardin
J
MacLeod
S
Grigorieva
I
Chang
R
Barlogie
B
Xiao
H
Epstein
J
Interleukin-6 prevents dexamethasone-induced myeloma cell death.
Blood
84
1991
3063
90
Chauhan
D
Kharbanda
S
Ogata
A
Urashima
M
Teoh
G
Robertson
M
Kufe
DW
Anderson
KC
Interleukin-6 inhibits Fas-induced apoptosis and SAP kinase activation in multiple myeloma cells.
Blood
89
1997
227
91
Levy
Y
Labaume
S
Colombel
M
Brouet
JC
Retinoic acid modulates the in vivo and in vitro growth of IL-6 autocrine human myeloma cell lines via induction of apoptosis.
Clin Exp Immunol
104
1996
167
92
Demartis
A
Bernassola
F
Savino
R
Melino
G
Ciliberto
G
Interleukin-6 receptor superantagonists are potent inducers of human multiple myeloma cell death.
Cancer Res
56
1996
4213
93
Caligaris-Cappio
F
Bergui
L
Gregoretti
MG
Gaidano
G
Gaboli
M
Schena
M
Zallone
AZ
Marchisio
PC
Role of bone marrow stromal cells in the growth of human multiple myeloma.
Blood
77
1991
2688
94
Caligaris-Cappio
F
Gregoretti
MG
Ghia
P
Bergui
L
In vitro growth of human multiple myeloma: Implications for biology and therapy.
Hematol Oncol Clin North Am
6
1992
257
95
Bataille
R
Chappard
D
Marcelli
C
Dessauw
P
Baldet
P
Sany
J
Alexandre
C
Recruitment of new osteoblasts and osteoclasts is the earliest critical event in the pathogenesis of human multiple myeloma.
J Clin Invest
88
1991
62
96
Nakamura
M
Merchav
S
Carter
A
Ernst
TJ
Demetri
GD
Furukawa
Y
Anderson
K
Freedman
AS
Griffin
JD
Expression of a novel 3.5-kb macrophage colony-stimulating factor transcript in human myeloma cells.
J Immunol
143
1989
3543
97
Rettig
MB
Ma
HJ
Vescio
RA
Pöld
M
Schiller
G
Belson
D
Savage
A
Nishikubo
C
Wu
C
Fraser
J
Said
JW
Berenson
JR
Kaposi's sarcoma-associated herpesvirus infection of bone marrow dendritic cells from multiple myeloma patients.
Science
276
1997
1851
98
Cesarman
E
Knowles
DM
Kaposi's sarcoma-associated herpesvirus: A lymphotropic human herpesvirus associated with Kaposi's sarcoma, primary effusion lymphoma, and multicentric Castleman's disease.
Semin Diagn Pathol
14
1997
54
99
Murakami
M
Hibi
M
Nakagawa
N
Nakagawa
T
Yasukawa
K
Yamanishi
K
Taga
T
Kishimoto
T
IL-6-induced homodimerization of gp130 and associated activation of a tyrosine kinase.
Science
260
1993
1808
100
Zhang
XG
Gu
JJ
Lu
ZY
Yasukawa
K
Yancopoulos
GD
Turner
K
Shoyab
M
Taga
T
Kishimoto
T
Bataille
R
Klein
B
Ciliary neurotropic factor, interleukin 11, leukemia inhibitory factor, and oncostatin M are growth factors for human myeloma cell lines using the interleukin 6 signal transducer gp130.
J Exp Med
179
1994
1337
101
Gaillard
JP
Bataille
R
Brailly
H
Zuber
C
Yasukawa
K
Attal
M
Maruo
N
Taga
T
Kishimoto
T
Klein
B
Increased and highly stable levels of functional soluble interleukin-6 receptor in sera of patients with monoclonal gammopathy.
Eur J Immunol
23
1993
820
102
Lust
JA
Donovan
KA
Kline
MP
Greipp
PR
Kyle
RA
Maihle
NJ
Isolation of an mRNA encoding a soluble form of the human interleukin-6 receptor.
Cytokine
4
1992
96
103
Mullberg
J
Dittrich
E
Graeve
L
Gerhartz
C
Yasukawa
K
Taga
T
Kishimoto
T
Heinrich
PC
Rose-John
S
Differential shedding of the two subunits of the interleukin-6 receptor.
FEBS Lett
332
1992
174
104
Filella
X
Blade
J
Guillermo
AL
Molina
R
Rozman
C
Ballesta
AM
Cytokines (IL-6, TNF-alpha, IL-1alpha) and soluble interleukin-2 receptor as serum tumor markers in multiple myeloma.
Cancer Detect Prev
20
1996
52
105
Bataille
R
Harousseau
J-L
Multiple myeloma.
N Engl J Med
336
1997
1657
106
Nachbaur
DM
Herold
M
Maneschg
A
Huber
H
Serum levels of interleukin-6 in multiple myeloma and other hematological disorders: Correlation with disease activity and other prognostic parameters.
Ann Hematol
62
1991
54
107
Papadaki
H
Kyriakou
D
Foudoulakis
A
Markidou
F
Alexandrakis
M
Eliopoulos
GD
Serum levels of soluble IL-6 receptor in multiple myeloma as indicator of disease activity.
Acta Haematol
97
1997
191
108
Thaler
J
Fechner
F
Herold
M
Huber
H
Interleukin-6 in multiple myeloma: Correlation with disease activity and Ki-67 proliferation index.
Leuk Lymphoma
12
1994
265
109
Bataille
R
Jourdan
M
Zhang
XG
Klein
B
Serum levels of interleukin 6, a potent myeloma cell growth factor, as a reflect of disease severity in plasma cell dyscrasias.
J Clin Invest
84
1989
2008
110
Pulkki
K
Pelliniemi
TT
Rajamaki
A
Tienhaara
A
Laakso
M
Lahtinen
R
Soluble interleukin-6 receptor as a prognostic factor in multiple myeloma. Finnish Leukaemia Group.
Br J Haematol
92
1996
370
111
Merlini
G
Perfetti
V
Gobbi
PG
Quaglini
S
Franciotta
DM
Marinone
G
Ascari
E
Acute phase proteins and prognosis in multiple myeloma.
Br J Haematol
83
1993
595
112
Kyrtsonis
M-C
Dedoussis
G
Zervas
C
Perifanis
V
Baxevanis
C
Stamatelou
M
Maniatis
A
Soluble interleukin-6 receptor (sIL-6R), a new prognostic factor in multiple myeloma.
Br J Haematol
93
1996
398
113
Nagata
S
Tsuchiya
M
Asano
S
Kaziro
Y
Yamazaki
T
Yamamoto
O
Hirata
Y
Kubota
N
Oheda
M
Nomura
H
Ono
M
Molecular cloning and expression of cDNA for human granulocyte colony stimulating factor.
Nature
319
1986
415
114
Souza
LM
Boone
TC
Gabrilove
J
Lai
PH
Zsebo
KM
Murdock
DC
Chazin
VR
Bruszewski
J
Lu
H
Chen
KK
Barendt
J
Platzer
E
Moore
MAS
Mertelsmann
R
Welte
K
Recombinant human granulocyte colony-stimulating factor.
Science
232
1986
61
115
Cosman
D
Lyman
SD
Idzerda
RL
Beckmann
MP
Park
LS
Goodwin
RG
March
CJ
A new cytokine receptor family.
Trends Biochem Sci
15
1990
265
116
Chen-Kiang
S
Hsu
W
Natkunam
Y
Zhang
X
Nuclear signaling by interleukin-6.
Curr Opin Immunol
5
1993
124
117
Brenning
G
The in vitro effect of leucocyte alpha-interferon on human myeloma cells in a semisolid agar culture system.
Scand J Haematol
35
1985
178
118
Brenning
G
Ahre
A
Nilsson
K
Correlation between in vitro and in vivo sensitivity to human leucocyte interferon in patients with multiple myeloma.
Scand J Haematol
35
1985
543
119
Ludwig
CU
Durie
BG
Salmon
SE
Moon
TE
Tumor growth stimulation in vitro by interferons.
Eur J Cancer Clin Oncol
19
1983
1625
120
Jourdan
M
Zhang
X-G
Portier
M
Boiron
JM
Bataille
R
Klein
B
IFN-alpha induced autocrine production of IL-6 in myeloma cell lines.
J Immunol
147
1991
4402
121
Mandelli
F
Avvisati
G
Amadori
S
Boccadoro
M
Gernone
A
Lauta
VM
Marmont
F
Petrucci
MT
Tribalto
M
Vegna
ML
Dammacco
F
Pileri
A
Maintenance treatment with recombinant interferon alfa-2b in patients with multiple myeloma responding to conventional induction chemotherapy.
N Engl J Med
322
1990
1430
122
Cheson B: Treatment strategies for multiple myeloma. ASCO Education Book Spring: 115, 1997
123
The Nordic Myeloma Study Group
Interferon-α2b added to melphalane-prednisone for initial and maintenance therapy in multiple myeloma.
Ann Intern Med
124
1996
212
124
Westin
J
Rodjer
S
Turesson
I
Cortelezzi
A
Hjorth
M
Zador
G
Interferon alfa-2b versus no maintenance therapy during the plateau phase in multiple myeloma: A randomized study.
Br J Haematol
89
1995
561
125
Avvisati
G
Mandelli
F
The role of interferon-α in the management of myelomatosis.
Hematol Oncol Clin North Am
6
1992
395
126
Lu
ZY
Zhang
XG
Rodriguez
C
Wijdenes
J
Gu
ZJ
Morel
FB
Harousseau
JL
Bataille
R
Rossi
JF
Klein
B
Interleukin-10 is a proliferation factor but not a differentiation factor for human myeloma cells.
Blood
85
1995
2521
127
Lu
ZY
Gu
ZJ
Zhang
XG
Wijdenes
J
Neddermann
P
Rossi
JF
Klein
B
Interleukin-10 induces interleukin-11 responsiveness in human myeloma cell lines.
FEBS Lett
377
1995
515
128
Gu
Z-J
Costes
V
Lu
ZY
Zhang
X-G
Pitard
V
Moreau
J-F
Bataille
R
Wijdenes
J
Rossi
J-F
Klein
B
Interleukin-10 is a growth factor for human myeloma cells by induction of an oncostatin M autocrine loop.
Blood
88
1996
3972
129
Zhang
XG
Gaillard
JP
Robillard
N
Lu
ZY
Gu
ZJ
Jourdan
M
Boiron
JM
Bataille
R
Klein
B
Reproducible obtaining of human myeloma cell lines as a model for tumor stem cell study in human multiple myeloma.
Blood
83
1994
3654
130
Zhang
XG
Bataille
R
Jourdan
M
Saeland
S
Banchereau
J
Mannoni
P
Klein
B
Granulocyte-macrophage colony-stimulating factor synergizes with interleukin-6 in supporting the proliferation of human myeloma cells.
Blood
76
1990
2599
131
Lemoli
RM
Fortuna
A
c-Kit ligand (SCF) in human multiple myeloma cells.
Leuk Lymphoma
20
1996
457
132
Freund
GG
Kulas
DT
Mooney
RA
Insulin and IGF-1 increase mitogenesis and glucose metabolism in the multiple myeloma cell line, RPMI 8226.
J Immunol
151
1993
1811
133
(abstr, suppl 1)
Arendt
K
French
J
Witzig
JE
Jelinek
DF
A role for insulin-like growth factor (IGF) in the regulation of interleukin-6 (IL-6)-responsive myeloma cell growth.
Blood
88
1996
106a
134
Georgii-Hemming
P
Wiklund
HJ
Ljunggren
O
Nilsson
K
Insulin-like growth factor I is a growth and survival factor in human multiple myeloma cell lines.
Blood
88
1996
2250
135
Borset
M
Waage
A
Brekke
OL
Helseth
E
TNF and IL-6 are potent growth factors for OH-2, a novel human myeloma cell line.
Eur J Haematol
53
1994
31
136
Hata
H
Matsuzaki
H
Takatsuki
K
Autocrine growth by two cytokines, interleukin-6 and tumor necrosis factor alpha, in the myeloma cell line KHM-1A.
Acta Haematol
83
1990
133
137
Borset
M
Hjorth-Hansen
H
Seidel
C
Sundan
A
Waage
A
Hepatocyte growth factor and its receptor c-met in multiple myeloma.
Blood
88
1996
3998
138
Borset
M
Lien
E
Espevik
T
Helseth
E
Waage
A
Sundan
A
Concomitant expression of hepatocyte growth factor/scatter factor and the receptor c-MET in human myeloma cell lines.
J Biol Chem
271
1996
24655
139
Portier
M
Zhang
XG
Caron
E
Lu
ZY
Bataille
R
Klein
B
γ-Interferon in multiple myeloma: Inhibition of interleukin-6 (IL-6)-dependent myeloma cell growth and downregulation of IL-6-receptor expression in vitro.
Blood
81
1993
3076
140
Schwabe
M
Cox
GW
Bosco
MC
Prohaska
R
Kung
H-F
Multiple cytokines inhibit interleukin-6-dependent murine hybridoma/plasmacytoma proliferation.
Cell Immunol
168
1996
117
141
Schwab
M
Brini
AT
Bosco
MC
Rubboli
F
Egawa
M
Zhao
J
Princler
GL
Kung
H
Disruption by interferon-α of an autocrine interleukin-6 growth loop in IL-6-dependent U266 myeloma cells by homologous and heterologous down-regulation of IL-6 receptor α- and β-chains.
J Clin Invest
94
1994
2317
142
Berger
LC
Hawley
RG
Interferon-β interrupts interleukin-6-dependent signaling events in myeloma cells.
Blood
89
1997
261
143
Anthes
JC
Zhan
Z
Gilchrest
H
Egan
RW
Siegel
MI
Billah
MM
Interferon-alpha down-regulates the interleukin-6 receptor in a human multiple myeloma cell line, U266.
Biochem J
309
1995
175
144
Verfaillie
CM
Hurley
R
Lundell
BI
Zhao
C
Bhatia
R
Integrin-mediated regulation of hematopoiesis: Do BCR/ABL-induced defects in integrin function underlie the abnormal circulation and proliferation of CML progenitors?
Acta Haematol
97
1997
40
145
Peschel
C
Aulitzky
WE
Huber
C
Influence of interferon-alpha on cytokine expression by the bone marrow microenvironment—Impact on treatment of myeloproliferative disorders.
Leuk Lymphoma
1
1996
129
146
Aman
MJ
Rudolf
G
Goldschmitt
J
Aulitzky
WE
Lam
C
Huber
C
Peschel
C
Type-I interferons are potent inhibitors of interleukin-8 production in hematopoietic and bone marrow stromal cells.
Blood
82
1993
2371
147
Nagata
S
Apoptosis regulated by a death factor and its receptor: Fas ligand and Fas.
Philos Trans R Soc Lond Biol Sci
345
1994
281
148
Nagata
S
Fas and Fas ligand: a death factor and its receptor.
Adv Immunol
57
1994
129
149
Suda
T
Nagata
S
Purification and characterization of the Fas-ligand that induces apoptosis.
J Exp Med
179
1994
873
150
Nagata
S
Golstein
P
The Fas death factor.
Science
267
1995
1449
151
Shima
Y
Nishimoto
N
Ogata
A
Fujii
Y
Yoshizaki
K
Kishimoto
T
Myeloma cells express Fas antigen/APO-1 (CD95) but only some are sensitive to anti-Fas antibody resulting in apoptosis.
Blood
85
1995
757
152
Terstappen
LW
Johnsen
S
Segers-Nolten
I
Loken
MR
Identification and characterization of plasma cells in normal human bone marrow by high-resolution flow cytometry.
Blood
76
1990
1739
153
Moscinski
LC
Ballester
OF
Recent progress in multiple myeloma.
Hematol Oncol
12
1994
111
154
Takishita
M
Kosaka
M
Goto
T
Saito
S
Cellular origin and extent of clonal involvement in multiple myeloma: genetic and phenotypic studies.
Br J Haematol
87
1994
735
155
Pilarski
LM
Jensen
GS
Monoclonal circulating B cells in multiple myeloma: A continuously differentiating, possibly invasive, population as defined by expression of CD45 isoforms and adhesion molecules.
Hematol Oncol Clin North Am
6
1992
297
156
Szczepek
AJ
Bergsagel
PL
Axelsson
L
Brown
CB
Belch
AR
Pilarski
LM
CD34+ cells in the blood of patients with multiple myeloma express CD19 and IgH mRNA and have patient-specific IgH VDJ gene rearrangements.
Blood
89
1997
1824
157
Kimlinger
T
Witzig
TE
Expression of the hematopoietic stem cell antigen CD34 on blood and bone marrow monoclonal plasma cells from patients with multiple myeloma.
Bone Marrow Transplant
19
1997
553
158
Gazitt
Y
Reading
CC
Hoffman
R
Wickrema
A
Vesole
DH
Jagannath
S
Condino
J
Lee
B
Barlogie
B
Tricot
G
Purified CD34+ Lin-Thy+ stem cells do not contain clonal myeloma cells.
Blood
86
1995
381
159
Vidriales
MB
Anderson
KC
Adhesion of multiple myeloma cells to the bone marrow microenvironment: Implications for future therapeutic strategies.
Mol Med Today
1
1996
425
160
Epstein J, Hoover R, Kornbluth J, Barlogie B: Biological aspects of multiple myeloma. Baillère's Clin Haematol 8:721, 1995
161
Wendtner
CM
Nolte
A
Mangold
E
Buhmann
R
Maass
G
Chiorini
JA
Emmerich
B
Kotin
RM
Winnacker
E-L
Hallek
M
Enhancement of cytolytic T cell activity after rAAV mediated transfer of costimulatory molecules into human multiple myeloma cells.
Gene Ther
4
1997
726
162
Harada
H
Kawano
MM
Huang
N
Harada
Y
Iwato
K
Tanabe
O
Tanaka
H
Sakai
A
Asaoku
H
Kuramoto
A
Phenotypic difference of normal plasma cells from mature myeloma cells.
Blood
81
1993
2658
163
Bradbury
LE
Kansas
GS
Levy
S
Evans
RL
Tedder
TF
The CD19/CD21 signal transducing complex of human B lymphocytes includes the target of antiproliferative antibody-1 and Leu-13 molecules.
J Immunol
149
1992
2841
164
Bradbury
LE
Goldmacher
VS
Tedder
TF
The CD19 signal transduction complex of B lymphocytes. Deletion of the CD19 cytoplasmic domain alters signal transduction but not complex formation with TAPA-1 and Leu 13.
J Immunol
151
1993
2915
165
Okada
T
Hawley
RG
Adhesion molecules involved in the binding of murine myeloma cells to bone marrow stromal elements.
Int J Cancer
63
1995
823
166
Uchiyama
H
Barut
BA
Mohrbacher
AF
Chauhan
D
Anderson
KC
Adhesion of human myeloma-derived cell lines to bone marrow stromal cells stimulates interleukin-6 secretion.
Blood
82
1993
3712
167
Chauhan
D
Uchiyama
H
Akbarali
Y
Urashima
M
Yamamoto
K
Libermann
TA
Anderson
KC
Multiple myeloma cell adhesion-induced interleukin-6 expression in bone marrow stromal cells involves activation of NF-kappa B.
Blood
87
1996
1104
168
Kluin-Nelemans
HC
Beverstock
GC
Mollevanger
P
Wessels
HW
Hoogendoorn
E
Willemze
R
Falkenburg
JHF
Proliferation and cytogenetic analysis of hairy cell leukemia upon stimulation via the CD40 antigen.
Blood
84
1994
3134
169
Noelle
RJ
Ledbetter
JA
Aruffo
A
CD40 and its ligand, an essential ligand-receptor pair for thymus-dependent B-cell activation.
Immunol Today
13
1992
431
170
Banchereau
J
Bazan
F
Blanchard
D
Briere
F
Galizzi
JP
van Kooten
C
Liu
YJ
Rousset
F
Saeland
S
The CD40 antigen and its ligand.
Annu Rev Immunol
12
1994
881
171
Durie
FH
Foy
TM
Masters
SR
Laman
JD
Noelle
RJ
The role of CD40 in the regulation of humoral and cell-mediated immunity.
Immunol Today
15
1994
406
172
Tong
AW
Zhang
BQ
Mues
G
Solano
M
Hanson
T
Stone
MJ
Anti-CD40 antibody binding modulates human multiple myeloma clonogenicity in vitro.
Blood
84
1994
3026
173
Urashima
M
Chauhan
D
Uchiyama
H
Freeman
GJ
Anderson
KC
CD40 ligand triggered interleukin-6 secretion in multiple myeloma.
Blood
85
1995
1903
174
Tong
AW
Stone
MJ
CD40 and the effect of anti-CD40-binding on human myeloma clonogenicity.
Leuk Lymphoma
21
1996
1
175
Urashima
M
Chen
BP
Chen
S
Pinkus
GS
Bronson
RT
Dedera
DA
Hoshi
Y
Teoh
G
Ogata
A
Treon
SP
Chauhan
D
Anderson
KC
The development of a model for the homing of multiple myeloma cells to human bone marrow.
Blood
90
1997
754
176
Nakajima
K
Wall
R
Interleukin-6 signals activating junB and tis11 gene transcription in a B-cell hybridoma.
Mol Cell Biol
11
1991
1409
177
Wilks AF, Harpur A: Cytokine signal transduction and the JAK family of protein tyrosine kinases. BioEssays 16:313, 1994
178
Ihle
JN
Witthuhn
BA
Quelle
FW
Yamamoto
K
Thierfelder
WE
Kreider
B
Silvennoinen
O
Signaling by the cytokine receptor superfamily: JAKs and STATs.
Trends Biochem Sci
19
1994
222
179
Schieven
GL
Kallestad
JC
Brown
TJ
Ledbetter
JA
Linsley
PS
Oncostatin M induces tyrosine phosphorylation in endothelial cells and activation of p62yes tyrosine kinase.
J Immunol
149
1992
1676
180
Ernst
M
Gearing
DP
Dunn
AR
Functional and biochemical association of Hck with the LIF/IL-6 receptor signal transducing subunit gp130 in embryonic stem cells.
EMBO J
13
1994
1574
181
Hallek M, Neumann C, Schäffer M, Danhauser-Riedl S, von Bubnoff N, de Vos G, Druker B, Griffin JD, Emmerich B: Interleukin-6 induces tyrosine phosphorylation of multiple cytosolic proteins and activation of the Src family kinases Hck, Lyn and Fyn. Exp Hematol 1997 (in press)
182
Narazaki
M
Witthuhn
B
Yoshida
K
Silvennoinen
O
Yasukawa
K
Ihle
JN
Kishimoto
T
Taga
T
Activation of JAK2 kinase by the interleukin 6 signal transducer gp130.
Proc Natl Acad Sci USA
91
1994
2285
183
Lütticken
C
Wegenka
UM
Yuan
J
Buschmann
J
Schindler
C
Ziemiecki
A
Harpur
AG
Wilks
AF
Yasukawa
K
Taga
T
Kishimoto
T
Barbieri
G
Pellegrini
S
Sendtner
M
Heinrich
PC
Horn
F
Association of transcription factor APRF and protein kinase Jak1 with the interleukin-6 signal transducer gp130.
Science
263
1994
89
184
Stahl
N
Boulton
T
Farruggella
T
Ip
NY
Davis
S
Witthuhn
BA
Quelle
FW
Silvennoinnen
O
Barbieri
G
Pellegrini
S
Ihle
JN
Yancopoulos
GD
Association and activation of Jak-Tyk kinases by CNTF-LIF-OSM-IL-6 β receptor components.
Science
263
1994
92
185
Kumar
G
Gupta
S
Wang
S
Nel
AE
Involvement of Janus kinases, p52Shc, Raf-1, and MEK-1 in the IL-6 induced mitogen-activated protein kinase cascade of a growth-responsive B cell line.
J Immunol
153
1994
4436
186
Heim
MH
The Jak-STAT pathway: Specific signal transduction from the membrane to the nucleus.
Eur J Clin Invest
26
1996
1
187
Ihle
JN
STATs: Signal transducers and activators of transcription.
Cell
84
1996
331
188
Darnell Jr
JE
Kerr
IM
Stark
GR
Jak-STAT pathways and transcriptional activation in response to IFNs and other extracellular signaling proteins.
Science
264
1994
1415
189
Schindler
C
Fu
XY
Improta
T
Aebersold
R
Darnell
JE
Jr
Proteins of transcription factor ISGF-3: One gene encodes the 91- and 84-kDa ISGF-3 proteins that are activated by interferon alpha.
Proc Natl Acad Sci USA
89
1992
7836
190
Fu
XY
Schindler
C
Improta
T
Aebersold
R
Darnell
JE
Jr
The proteins of ISGF-3, the interferon alpha-induced transcriptional activator, define a gene family involved in signal transduction.
Proc Natl Acad Sci USA
89
1992
7840
191
Shuai
K
Schindler
C
Prezioso
VR
Darnell
JE
Jr
Activation of transcription by IFN-gamma: Tyrosine phosphorylation of a 91-kD DNA binding protein.
Science
258
1992
1808
192
Schindler
C
Shuai
K
Prezioso
VR
Darnell
JE
Jr
Interferon-dependent tyrosine phosphorylation of a latent cytoplasmic transcription factor.
Science
257
1992
809
193
Zhong
Z
Wen
Z
Darnell
JJ
Stat3: A STAT family member activated by tyrosine phosphorylation in response to epidermal growth factor and interleukin-6.
Science
264
1994
95
194
Boulton
TG
Stahl
N
Yancopoulos
GD
Ciliary neurotrophic factor/leukemia inhibitory factor/interleukin 6/oncostatin M family of cytokines induces tyrosine phosphorylation of a common set of proteins overlapping those induced by other cytokines and growth factors.
J Biol Chem
269
1994
11648
195
Hemmann
U
Gerhartz
C
Heesel
B
Sasse
J
Kurapka
G
Grötzinger
J
Wollmer
A
Zhong
Z
Darnell
JE
Jr
Graeve
L
Heinrich
PC
Horn
F
Differential activation of acute phase response factor/Stat3 and Stat1 via the cytoplasmic domain of the interleukin 6 signal transducer gp130.
J Biol Chem
271
1996
12999
196
Gerhartz
C
Heesel
B
Sasse
J
Hemmann
U
Landgraf
C
Schneider-Mergener
J
Horn
F
Heinrich
PC
Graeve
L
Differential activation of acute phase response factor/STAT3 and STAT1 via the cytoplasmic domain of the interleukin 6 signal transducer gp130.
J Biol Chem
271
1996
12991
197
Ogata
A
Chauhan
D
Urashima
M
Teoh
G
Treon
S
Anderson
KC
Blockade of MAPK cascade signaling in interleukin-6 independent multiple myeloma cells.
Clin Cancer Res
3
1997
1017
198
(abstr, suppl 1)
Grigorieva
I
Chapman
M
Epstein
J
Constitutively activated STAT3 in myeloma cells.
Blood
88
1996
104a
199
Barbacid
M
ras genes.
Annu Rev Biochem
56
1987
779
200
Schlessinger
J
How receptor tyrosine kinases activate ras.
Trends Biochem Sci
18
1993
273
201
Pelicci
G
Lanfrancone
L
Grignani
F
McGlade
J
Cavallo
F
Forni
G
Nicoletti
I
Grignani
F
Pawson
T
Pelicci
PG
A novel transforming protein (SHC) with an SH2 domain is implicated in mitogenic signal transduction.
Cell
70
1992
93
202
Marshall
MS
The effector interactions of p21ras.
Trends Biochem Sci
18
1993
250
203
Lowenstein
EJ
Daly
RJ
Batzer
AG
Li
W
Margolis
B
Lammers
R
Ullrich
A
Skolnik
EY
Bar-Sagi
D
Schlessinger
J
The SH2 and SH3 domain-containing protein GRB2 links receptor tyrosine kinases to ras signaling.
Cell
70
1992
431
204
Li
N
Batzer
A
Daly
R
Yajnik
V
Skolnik
E
Chardin
P
Bar-Sagi
D
Margolis
B
Schlessinger
J
Guanine-nucleotide-releasing factor hSos1 binds to Grb2 and links receptor tyrosine kinases to Ras signalling [see comments].
Nature
363
1993
85
205
Baltensperger
K
Kozma
LM
Cherniack
AD
Klarlund
JK
Chawla
A
Banerjee
U
Czech
MP
Binding of the Ras activator son of sevenless to insulin receptor substrate-1 signaling complexes.
Science
260
1993
1950
206
Buday
L
Downward
J
Epidermal growth factor regulates p21ras through the formation of a complex of receptor, Grb2 adapter protein, and Sos nucleotide exchange factor.
Cell
73
1993
611
207
Chardin P, Camonis JH, Gale NW, van AL, Schlessinger J, Wigler MH, Bar-Sagi D: Human Sos1: A guanine nucleotide exchange factor for Ras that binds to GRB2. Science 260:1338, 1993
208
Egan
SE
Giddings
BW
Brooks
MW
Buday
L
Sizeland
AM
Weinberg
RA
Association of Sos Ras exchange protein with Grb2 is implicated in tyrosine kinase signal transduction and transformation [see comments].
Nature
363
1993
45
209
Rozakis-Adcock
M
Fernley
R
Wade
J
Pawson
T
Bowtell
D
The SH2 and SH3 domains of mammalian Grb2 couple the EGF receptor to the Ras activator mSos1 [see comments].
Nature
363
1993
83
210
Skolnik
EY
Batzer
A
Li
N
Lee
CH
Lowenstein
E
Mohammadi
M
Margolis
B
Schlessinger
J
The function of GRB2 in linking the insulin receptor to Ras signaling pathways.
Science
260
1993
1953
211
Bollag
G
McCormick
F
Regulators and effectors of ras proteins.
Annu Rev Cell Biol
7
1991
601
212
Matsuguchi
T
Salgia
R
Hallek
M
Eder
M
Druker
B
Ernst
T
Griffin
JD
Shc phosphorylation in myeloid cells is regulated by GM-CSF, IL-3 and Steel factor and is constitutively increased by p210bcr/abl.
J Biol Chem
269
1994
5016
213
Welham
MJ
Duronio
V
Leslie
K
Bowtell
D
Schrader
JW
Multiple hemopoietins, with the exception of interleukin-4, induce modification of Shc and mSos1, but not their translocation.
J Biol Chem
269
1994
21165
214
Tauchi
T
Boswell
HS
Leibowitz
D
Broxmeyer
HE
Coupling between p210bcr-abl and Shc and Grb2 adaptor proteins in hematopoietic cells permits growth factor receptor-independent link to Ras-activation pathway.
J Exp Med
179
1994
167
215
Burns
LA
Karnitz
LM
Sutor
SL
Abraham
RT
Interleukin-2-induced tyrosine phosphorylation of p52Shc in T lymphocytes.
J Biol Chem
268
1993
17659
216
Damen
JE
Liu
L
Cutler
RL
Krystal
G
Erythropoietin stimulates the tyrosine phosphorylation of Shc and its association with Grb2 and a 145-Kd tyrosine phosphorylated protein.
Blood
82
1993
2296
217
Cutler
RL
Liu
L
Damen
JE
Krystal
G
Multiple cytokines induce the tyrosine phosphorylation of Shc and its association with Grb2 in hemopoietic cells.
J Biol Chem
268
1993
21463
218
Lioubin
MN
Myles
GM
Carlberg
K
Bowtell
D
Rohrschneider
LR
Shc, Grb2, Sos1, and a 150-kilodalton tyrosine-phosphorylated protein form complexes with Fms in hematopoietic cells.
Mol Cell Biol
14
1994
5682
219
Buday
L
Egan
SE
Rodriguez
PR
Cantrell
DA
Downward
J
A complex of Grb2 adaptor protein, Sos exchange factor, and a 32-kDa membrane-bound tyrosine phosphoprotein is implicated in Ras activation in T cells.
J Biol Chem
269
1994
9019
220
Smit
L
de Vries-Smits
AMM
Bos
JL
Borst
J
B cell antigen receptor stimulation induces formation of a Shc-Grb2 complex containing multiple tyrosine-phosphorylated proteins.
J Biol Chem
269
1994
20209
221
Rozakis-Adcock
M
McGlade
J
Mbamalu
G
Pelicci
G
Daly
R
Li
W
Batzer
A
Thomas
S
Brugge
J
Pelicci
PG
Schlessinger
J
Pawson
T
Association of the Shc and Grb2/Sem5 SH2-containing proteins is implicated in activation of the Ras pathway by tyrosine kinases.
Nature
360
1992
689
222
McGlade
J
Cheng
A
Pelicci
G
Pelicci
PG
Pawson
T
Shc proteins are phosphorylated and regulated by the v-Src and v-Fps protein-tyrosine kinases.
Proc Natl Acad Sci USA
89
1992
8869
223
Puil
L
Liu
L
Gish
G
Mbamalu
G
Bowtell
D
Pelicci
G
Arlinghaus
R
Pawson
T
Bcr-abl oncoproteins bind directly to activators of the ras signaling pathway.
EMBO J
13
1994
764
224
Chauhan
D
Kharbanda
SM
Ogata
A
Urashima
M
Frank
D
Malik
N
Kufe
DW
Anderson
KC
Oncostatin M induces association of Grb2 with Janus kinase JAK2 in multiple myeloma cells.
J Exp Med
182
1995
1801
225
Neumann
C
Zehentmaier
G
Danhauser-Riedl
S
Emmerich
B
Hallek
M
IL-6 induces tyrosine phosphorylation of the Ras activating protein Shc, and its complex formation with Grb2 in the human multiple myeloma cell line LP-1.
Eur J Immunol
26
1996
379
226
Nakafuku
M
Satoh
T
Kaziro
Y
Differentiation factors, including nerve growth factor, fibroblast growth factor, and interleukin-6, induce an accumulation of an active Ras-GTP complex in rat pheochromocytoma PC12 cells.
J Biol Chem
267
1992
19446
227
Ernst
M
Oates
A
Dunn
AR
gp130-mediated signal transduction in embryonic stem cells involves activation of Jak and Ras/mitogen-activated protein kinase pathways.
J Biol Chem
271
1996
30136
228
Katzav
S
Martin-Zanca
D
Barbacid
M
vav, a novel human oncogene derived from a locus ubiquitously expressed in hematopoietic cells.
EMBO J
8
1989
2283
229
Bustelo
XR
Barbacid
M
Tyrosine phosphorylation of the vav proto-oncogene product in activated B cells.
Science
256
1992
1196
230
Bustelo
XR
Ledbetter
JA
Barbacid
M
Product of vav proto-oncogene defines a new class of tyrosine protein kinase substrates.
Nature
356
1992
68
231
Lee
I-S
Liu
Y
Narazaki
M
Hibi
M
Kishimoto
T
Taga
T
Vav is associated with signal transducing molecules gp130, Grb2 and Erk2, and is tyrosine phosphorylated in response to interleukin-6.
FEBS Lett
401
1997
133
232
Uddin
S
Yetter
A
Katzav
S
Hofmann
C
White
MF
Platanias
LC
Insulin-like growth factor-1 induces rapid tyrosine phosphorylation of the vav proto-oncogene product.
Exp Hematol
24
1996
622
233
Crews
CM
Alessandrini
A
Erikson
RL
Erks: Their fifteen minutes has arrived.
Cell Growth Differ
3
1992
135
234
Blenis
J
Signal transduction via the MAP kinases: Proceed at your own RSK.
Proc Natl Acad Sci USA
90
1993
5889
235
Cheng
J-T
Cobb
MH
Baer
R
Phosphorylation of the TAL1 oncoprotein by the extracellular-signal-regulated protein kinase ERK1.
Mol Cell Biol
13
1993
801
236
Lin
L-L
Wartman
M
Lin
AY
Knopf
JL
Seth
A
Davis
RJ
cPLA2 is phosphorylated and activated by MAP kinase.
Cell
72
1993
269
237
Nishida
E
Gotoh
Y
The MAP kinase cascade is essential for diverse signaling pathways.
Trends Biochem Sci
18
1993
128
238
Wu
J
Harrison
JK
Dent
P
Lynch
KR
Weber
MJ
Sturgill
TW
Identification and characterization of a new mammalian mitogen-activated protein kinase kinase, MKK2.
Mol Cell Biol
13
1993
4539
239
Yin
T
Yang
Y-C
Mitogen-activated protein kinases and ribosomal S6 protein kinases are involved in signaling pathways shared by interleukin-11, interleukin-6, leukemia inhibitory factor, and oncostatin M in mouse 3T3-L1 cells.
J Biol Chem
269
1994
3731
240
Ogata
A
Chauhan
D
Urashima
M
Teoh
G
Hatziyanni
M
Vidriales
MB
Schlossman
RL
Anderson
KC
Interleukin-6 triggers multiple myeloma cell growth via the Ras dependent mitogen activated protein kinase cascade.
J Immunol
159
1997
2212
241
Nakajima
T
Kinoshita
S
Sasagawa
T
Sasaki
K
Naruto
M
Kishimoto
T
Akira
S
Phosphorylation at threonine-235 by a ras-dependent mitogen-activated protein kinase cascade is essential for transcription factor NF-IL6.
Proc Natl Acad Sci USA
90
1993
2207
242
Jonveaux
P
Berger
R
Chromosome studies in plasma cell leukemia and multiple myeloma in transformation.
Genes Chromosom Cancer
4
1992
321
243
Corradini
P
Ladetto
M
Voena
C
Palumbo
A
Inghirami
G
Knowles
DM
Boccadoro
M
Pileri
A
Mutational activation of N- and K-ras oncogenes in plasma cell dyscrasias.
Blood
81
1993
2708
244
Neri
A
Murphy
JP
Cro
L
Ferrero
D
Tarella
C
Baldini
L
Dalla-Favera
R
Ras oncogene mutation in multiple myeloma.
J Exp Med
170
1989
1715
245
Tanaka
K
Takechi
M
Asaoku
H
Dohy
H
Kamada
N
A high frequency of N-RAS oncogene mutations in multiple myeloma.
Int J Hematol
56
1992
119
246
Portier
M
Moles
JP
Mazars
GR
Jeanteur
P
Bataille
R
Klein
B
Theillet
C
P53 and RAS gene mutations in multiple myeloma.
Oncogene
7
1992
2539
247
Matozaki
S
Nakagawa
T
Nakao
Y
Fujita
T
RAS gene mutations in multiple myeloma and related monoclonal gammopathies.
Kobe J Med Sci
37
1991
35
248
Paquette
RL
Berenson
J
Lichtenstein
A
McCormick
F
Koeffler
HP
Oncogenes in multiple myeloma: Point mutation of N-ras.
Oncogene
5
1990
1659
249
Yasuga
Y
Hirosawa
S
Yamamoto
K
Tomiyama
J
Nagata
K
Aoki
N
N-ras and p53 gene mutations are very rare events in multiple myeloma.
Int J Hematol
62
1995
91
250
Liu
PC
Leong
T
Quam
L
Billadeau
D
Kay
NE
Greipp
P
Kyle
RA
Oken
MM
Van Ness
B
Activating mutations of N- and K-ras in multiple myeloma show different clinical associations—Analysis of the Eastern Cooperative Oncology Group phase III trial.
Blood
88
1996
2699
251
Seremetis
S
Inghirami
G
Ferrero
D
Newcomb
EW
Knowles
DM
Dotto
G-P
Dalla-Favera
R
Transformation and plasmacytoid differentiation of EBV-infected human B lymphoblasts by ras oncogenes.
Science
243
1989
660
252
Billadeau
D
Jelinek
DF
Shah
N
LeBien
TW
Van Ness
B
Introduction of an activated N-ras oncogene alters the growth characteristics of the interleukin 6-dependent myeloma cell line ANBL6.
Cancer Res
55
1995
3640
253
Korsmeyer
SJ
Bcl-2 initiates a new category of oncogenes: regulators of cell death.
Blood
80
1992
879
254
Gajewski
TF
Thompson
CB
Apoptosis meets signal transduction: elimination of a BAD influence.
Cell
87
1996
589
255
Yang
E
Korsmeyer
SJ
Molecular thanatopsis: A discourse on the bcl-2 family and cell death.
Blood
88
1996
386
256
Hermine O, Haioun C, Lepage E, d'Agay MF, Lavignac C, Fillet G, Salles G, Marolleau JP, Diebold J, Reyas F, Gaulard P, Groupe d'Etude des Lymphomes de l'Adulte (GELA): Prognostic significance of bcl-2 protein expression in aggressive non-Hodgkin's lymphoma. Blood 87:265, 1996
257
Ong
F
Nieuwkoop
JA
De Groot-Swings
GMJS
Hermans
J
Harvey
MS
Kluin
PHM
Kluin-Nelemans
HC
Bcl-2 protein expression is not related to short survival in multiple myeloma.
Leukemia
9
1995
1282
258
Pettersson
M
Jernberg-Wiklund
H
Larsson
LG
Sundstrom
C
Givol
I
Tsujimoto
Y
Nilsson
K
Expression of the bcl-2 gene in human multiple myeloma cell lines and normal plasma cells.
Blood
79
1992
495
259
Ladanyi
M
Wang
S
Niesvizky
R
Feiner
H
Michaeli
J
Proto-oncogene analysis in multiple myeloma.
Am J Pathol
141
1992
949
260
Tian
E
Gazitt
Y
The role of p53, bcl-2 and bax network in dexamethasone induced apoptosis in multiple myeloma cell lines.
Int J Oncol
8
1996
719
261
Ray
S
Diamond
B
Generation of a fusion partner to sample the repertoire of splenic B cells destined for apoptosis.
Proc Natl Acad Sci USA
91
1994
5548
262
Schwarze
MMK
Hawley
RG
Prevention of myeloma cell apoptosis by ectopic bcl-2 expression or interleukin-6 mediated up-regulation of bcl-XL.
Cancer Res
55
1995
2262
263
Gauthier
ER
Piché
L
Lemieux
G
Lemieux
R
Role of bcl-XL in the control of apoptosis in murine myeloma cells.
Cancer Res
56
1996
1451
264
Korsmeyer
S
Regulators of cell death.
Trends Genet
11
1995
101
265
Mazars
CR
Portier
M
Zhang
XG
Jourdan
M
Bataille
R
Theillet
C
Klein
B
Mutations of the p53 gene in human myeloma cell lines.
Oncogene
7
1993
1015
266
(abstr, suppl 1)
Liu
P
Rowley
M
van Ness
B
Wildtype Rb and p53 can suppress autocrine IL-6 production and proliferation of U266 myeloma cells.
Blood
88
1996
100a
267
Corradini
P
Inghirami
G
Astolfi
M
Ladetto
M
Voena
C
Ballerini
P
Gu
W
Nilsson
K
Knowles
DM
Boccadoro
M
Pileri
A
Dalla-Favera
R
Inactivation of tumor suppressor genes, p53 and Rb1, in plasma cell dyscrasias.
Leukemia
8
1994
758
268
Neri
A
Baldini
L
Trecca
D
Cro
L
Polli
E
Maiolo
AT
p53 gene mutations in multiple myeloma are associated with advanced forms of malignancy.
Blood
81
1993
128
269
Preudhomme
C
Facon
T
Zandecki
M
Vanrumbeke
M
Lai
JL
Nataf
E
Loucheux-Lefebvre
MH
Kerckaert
JP
Fenaux
P
Rare occurrence of P53 gene mutations in multiple myeloma.
Br J Haematol
81
1992
440
270
Willems
PM
Kuypers
AW
Meijerink
JP
Holdrinet
RS
Mensink
EJ
Sporadic mutations of the p53 gene in multiple myeloma and no evidence for germline mutations in three familial multiple myeloma pedigrees.
Leukemia
7
1993
986
271
Weinberg
RA
The retinoblastoma gene and cell cycle control.
Cell
81
1995
381
272
Livingston
DM
DeCaprio
JA
Ludlow
JW
Does the product of the RB-1 locus have a cell cycle regulatory function?
Princess Takamatsu Symp
20
1989
187
273
DeCaprio
JA
Ludlow
JW
Lynch
D
Furukawa
Y
Griffin
J
Piwnica
WH
Huang
CM
Livingston
DM
The product of the retinoblastoma susceptibility gene has properties of a cell cycle regulatory element.
Cell
58
1989
1085
274
Adams
PD
Kaelin
WG
Jr
The cellular effects of E2F overexpression.
Curr Top Microbiol Immunol
208
1996
79
275
Weinberg
RA
Tumor suppressor genes.
Science
254
1991
1138
276
Weinberg
R
Tumor suppressor genes.
Neuron
11
1993
191
277
Dao
DD
Sawyer
JR
Epstein
J
Hoover
RG
Barlogie
B
Tricot
G
Deletion of the retinoblastoma gene in multiple myeloma.
Leukemia
8
1994
1280
278
Juge-Morineau
N
Mellerin
MP
Francois
S
Rapp
MJ
Harousseau
JL
Amiot
M
Bataille
R
High incidence of deletions but infrequent inactivation of the retinoblastoma gene in human myeloma cells.
Br J Haematol
91
1995
664
279
Zukerberg
LR
Benedict
WF
Arnold
A
Dyson
N
Harlow
E
Harris
NL
Expression of the retinoblastoma protein in low-grade B-cell lymphoma: Relationship to cyclin D1.
Blood
88
1996
268
280
Urashima
M
Ogata
A
Chauhan
D
Vidriales
MB
Teoh
G
Hoshi
Y
Schlossman
RL
DeCaprio
JA
Anderson
KC
Interleukin-6 promotes multiple myeloma cell growth via phosphorylation of retinoblastoma protein.
Blood
88
1996
2219
281
Zandecki
M
Facon
T
Preudhomme
C
Vanrumbeke
M
Vachee
A
Quesnel
B
Lai
JL
Cosson
A
Fenaux
P
The retinoblastoma gene (RB-1) status in multiple myeloma: A report on 35 cases.
Leuk Lymphoma
18
1995
497
282
Garcia-Maraco
JA
Caldas
C
Price
CM
Wiedemann
LM
Ashworth
A
Carovsky
D
Frequent somatic deletion of the 13q12.3 locus encompassing BRCA2 in chronic lymphocytic leukemia.
Blood
88
1996
1568
283
Urashima
M
Ogata
A
Chauhan
D
Hatziyanni
M
Vidriales
MB
Dedera
DA
Schlossman
RL
Anderson
KC
Transforming growth factor-β1: Differential effects on multiple myeloma versus normal B cells.
Blood
87
1996
1928
284
Urashima M, Teoh G, Ogata A, Chauhan D, Hoshi Y, DeCaprio J, Anderson K: Role of CDK4 and p16INK4A in interleukin-6 mediated growth of multiple myeloma. Leukemia 1997 (in press)
285
(abstr, suppl 1)
Kawano
MM
Mahmoud
MS
Huang
N
Cyclin D1 and p16INK4A are preferentially expressed in immature and mature myeloma cells.
Blood
88
1996
294a
286
Ng
MHL
Chung
YF
Lo
KW
Wickham
NWR
Lee
JCK
Huang
DP
Frequent hypermethylation of p16 and p15 genes in multiple myeloma.
Blood
87
1997
2500
287
Urashima M, Teoh G, Ogata A, Chauhan D, Treon SP, Sugimoto Y, Kaihara C, Matsuzaki M, Hoshi Y, DeCaprio JA, Anderson KC: Characterization of p16INKA expression in multiple myeloma and plasma cell leukemia. Clin Cancer Res 1997 (in press)
288
Tasaka
T
Berenson
J
Vescio
R
Hirama
T
Miller
CW
Nagai
M
Takahara
J
Koeffler
HP
Analysis of the p16INK4A, p15INK4B and p18INK4C genes in multiple myeloma.
Br J Haematol
96
1997
98
289
Polyak
K
Waldman
T
He
T-C
Kinzler
KW
Vogelstein
B
Genetic determinants of p53-induced apoptosis and growth arrest.
Genes Dev
10
1996
1945
290
Attadi
LD
Lowe
SW
Brugarolas
J
Jacks
T
Transcriptional activation by p53, but not induction of the p21 gene is essential for oncogene-mediated apoptosis.
EMBO J
15
1996
3693
291
Urashima
M
Teoh
G
Chauhan
D
Hoshi
Y
Ogata
A
Treon
SP
Schlossman
RL
Anderson
KC
Interleukin-6 overcomes p21WAF1 upregulation and G1 growth arrest induced by dexamethasone and interferon-γ in multiple myeloma cells.
Blood
90
1997
279
292
Teoh
G
Urashima
M
Ogata
A
Chauhan
D
DeCaprio
J
Treon
S
Schlossman
RL
Anderson
KC
MDM2 protein overexpression promotes proliferation and survival of multiple myeloma cells.
Blood
90
1997
1987
293
Dalton
WS
Grogan
TM
Rybski
JA
Scheper
RJ
Richter
L
Kailey
J
Broxterman
HJ
Pinedo
HM
Salmon
SE
Immunohistochemical detection and quantitation of P-glycoprotein in multiple drug-resistant human myeloma cells: Association with level of drug resistance and drug accumulation.
Blood
73
1989
747
294
Epstein
J
Xiao
H
Oba
BK
P-Glycoprotein expression in plasma-cell myeloma is associated with resistance to VAD.
Blood
74
1989
913
295
Sonneveld
P
Modulation of multidrug resistance in multiple myeloma.
Baillieres Clin Haematol
8
1995
831
296
Jernberg-Wiklund
H
Petterson
M
Nilsson
K
Recombinant interferon-γ inhibits the growth of IL-6-dependent human multiple myeloma cell lines in vitro.
Eur J Hematol
46
1991
231
297
Ogata
A
Nishimoto
N
Shima
Y
Yoshizaki
K
Kishimoto
T
Inhibitory effect of all-trans retinoic acid on the growth of freshly isolated myeloma cells via interference with interleukin-6 signal transduction.
Blood
84
1994
3040
298
Chen
Y-H
Desai
P
Shiao
R-T
Lavelle
D
Haleem
A
Chen
J
Inhibition of myeloma cell growth by dexamethasone and all-trans retinoic acid: Synergy through modulation of interleukin-6 autocrine loop at multiple sites.
Blood
87
1996
314
299
Ishikawa
H
Tanaka
H
Iwato
K
Tanabe
O
Asaoku
H
Nobuyoshi
M
Yamamoto
I
Kawano
M
Kuramoto
A
Effect of glucocorticoids on the biologic activities of plasma cells: inhibition of interleukin-1b osteoclast activating factor-induced bone resorption.
Blood
75
1990
715
300
Herrmann
F
Andreef
M
Gruss
H-J
Brach
MA
Lübbert
M
Mertelsmann
R
Interleukin-4 inhibits growth of multiple myelomas by suppressing interleukin-6 expression.
Blood
78
1991
2070
301
Taylor
C
Grogan
TM
Salmon
SE
Effects of interleukin-4 on the in vitro growth of human lymphoid and plasma cell neoplasms.
Blood
75
1990
1114
302
Klein
B
Wijdenes
J
Zhang
XG
Jourdan
M
Boiron
JM
Brochier
J
Liautard
J
Merlin
M
Clement
C
Morel
FB
Lu
ZY
Mannoni
P
Sany
J
Bataille
R
Murine anti-interleukin-6 monoclonal antibody therapy for a patient with plasma cell leukemia.
Blood
78
1991
1198
303
Suzuki
H
Yasukawa
K
Saito
T
Goitsuka
R
Hasegawa
A
Ohsugi
Y
Taga
T
Kishimoto
T
Anti-human interleukin-6 receptor antibody inhibits human myeloma growth in vivo.
Eur J Immunol
22
1992
1989
304
Sato
K
Tsuciya
M
Saldanha
J
Koshihara
Y
Ohsugi
Y
Kishimoto
T
Bendig
MM
Reshaping a human antibody to inhibit interleukin-6 dependent tumor cell growth.
Cancer Res
53
1993
851
305
Ogata
A
Anderson
KC
Therapeutic strategies for inhibition of interleukin-6 mediated multiple myeloma cell growth.
Leuk Res
20
1996
303
306
Kreitman
RJ
Siegall
CB
Fitzgerald
DJP
Epstein
J
Barlogie
B
Pastan
I
Interleukin-6 fused to mutant form of Pseudomonas exotoxin kills malignant cells from patients with multiple myeloma.
Blood
79
1992
1775
307
Chadwick
DE
Jamal
N
Nessner
HA
Murphy
JR
Minden
MD
Differential sensitivity of human myeloma cells to a recombinant diphtheria toxin-interleukin-6 fusion protein.
Br J Haematol
85
1993
25
308
Keller
ET
Ershler
WB
Effect of IL-6 receptor antisense oligodeoxynucleotide on in vitro proliferation of myeloma cells.
J Immunol
154
1995
4091
309
Ehlers
M
de Hon
FD
Bos
HK
Horsten
U
Kurapkat
G
van de Leur
HS
Grotzinger
J
Wollmer
A
Brakenhoff
JP
Rose
JS
Combining two mutations of human interleukin-6 that affect gp130 activation results in a potent interleukin-6 receptor antagonist on human myeloma cells.
J Biol Chem
270
1995
8158
310
de Hon
FD
Ehlers
M
Rose-John
S
Ebeling
SB
Bos
HK
Aarden
LA
Brakenhoff
JPJ
Development of an interleukin (IL) 6 receptor antagonist that inhibits IL-6-dependent growth of human myeloma cells.
J Exp Med
180
1994
2395
311
Sporeno
E
Savino
R
Ciapponi
L
Paonessa
G
Cabibbo
A
Lahm
A
Pulkki
K
Sun
R-X
Toniatti
C
Klein
B
Ciliberto
G
Human interleukin-6 receptor super-antagonists with high potency and wide spectrum on multiple myeloma cells.
Blood
87
1996
4510
312
Saviano
R
Lahm
A
Salvati
AL
Ciapponi
L
Sporeno
E
Altamura
S
Paonessa
G
Toniatti
C
Ciliberto
G
Generation of interleukin-6 receptor antagonists by molecular-modeling guided mutagenesis of residues important for gp130 activation.
EMBO J
13
1994
1357
313
Halimi
H
Eisenstein
M
Oh
J-W
Revel
M
Chebath
J
Epitope peptides from interleukin-6 receptor which inhibit the growth of human myeloma cells.
Eur Cytokine Netw
6
1995
135
314
Tamanoi
F
Inhibitors of Ras farnesyltransferases.
Trends Biochem Sci
18
1993
349
315
(abstr, suppl 1)
Savage
AD
Belson
DJ
Vescio
RA
Lichtenstein
AK
Berenson
JR
Pamidronate reduces IL-6 production by bone marrow stroma from multiple myeloma patients.
Blood
88
1996
105a
316
Sahota
SS
Leo
R
Hamblin
TJ
Stevenson
FK
Ig VH gene mutational patterns indicate different tumor cell status in human myeloma and monoclonal gammopathy of undetermined significance.
Blood
87
1996
746