Myeloproliferative neoplasms (MPNs) are clonal disorders characterized by excessive production of mature blood cells. In the majority of classic MPN—polycythemia vera, essential thrombocythemia, and primitive myelofibrosis—driver oncogenic mutations affecting Janus kinase 2 (JAK2) or MPL lead to constitutive activation of cytokine-regulated intracellular signaling pathways. LNK, c-CBL, or SOCSs (all negative regulators of signaling pathways), although infrequently targeted, may either drive the disease or synergize with JAK2 and MPL mutations. IZF1 deletions or TP53 mutations are mainly found at transformation phases and are present at greater frequency than in de novo acute myeloid leukemias. Loss-of-function mutations in 3 genes involved in epigenetic regulation, TET2, ASXL1, and EZH2, may be early events preceding JAK2V617F but may also occur late during disease progression. They are more frequently observed in PMF than PV and ET and are also present in other types of malignant myeloid diseases. A likely hypothesis is that they facilitate clonal selection, allowing the dominance of the JAK2V617F subclone during the chronic phase and, together with cooperating mutations, promote blast crisis. Their precise roles in hematopoiesis and in the pathogenesis of MPN, as well as their prognostic impact and potential as a therapeutic target, are currently under investigation.

The term “myeloproliferative disorders” (MPDs) was first introduced by William Dameshek in 1951 to describe 4 different diseases with clinical and biologic similarities: polycythemia vera (PV), essential thrombocythemia (ET), primary myelofibrosis (PMF), and chronic myeloid leukemia (CML).1  Later on, chronic neutrophil leukemia, hypereosinophilic syndromes, systemic mastocytosis, atypical chronic myeloid leukemia, and other rare chronic hemopathies were added. Certain disorders that combine myeloproliferation and myelodysplasia features, such as chronic myelomonocytic leukemia, are closely related to MPDs. In 2008, the World Health Organization recommended changing the term myeloproliferative disorders to myeloproliferative neoplasms (MPNs).2  In this review, we will focus on the current molecular knowledge of the BCR-ABL–negative MPNs PV, ET, and PMF.

All MPNs are clonal disorders with an initial hit in the HSCs resulting in an excessive production of blood cells because of hypersensitivity or independence from normal cytokine regulation.3,4  This myeloproliferation results from the absence of feedback regulation by mature cells, decreasing cytokine levels. MPNs involve the 3 main myeloid lineages but predominate in one of them: the erythroid lineage for PV, the megakaryocyte (MK)/platelet lineage for ET, and the MK/granulocytic lineages for PMF. MPNs are associated with a normal maturation but increased numbers of mature blood cells, except in PMF, in which abnormalities in MK differentiation might be responsible for the marrow fibrosis. A continuum exists between the BCR-ABL–negative MPN and myelodysplastic syndromes (MDS), as exemplified by chronic myelomonocytic leukemia (CMML), classified as MPN/MDS by the World Health Organization.

Several MPNs are the result of a genetic event leading to the constitutive activation of a tyrosine kinase that mimics the intracellular signaling pathways induced by hematopoietic growth factors. In CML, oligomerization of the BCR-ABL fusion protein via the BCR coiled-coil domain induces the constitutive activation of ABL that triggers many signaling pathways and drives the disease. Inhibition of the ABL kinase activity in patients results in disease regression, demonstrating that BCR-ABL is the oncogenic event responsible for the disease. Additional fusion proteins with constitutive tyrosine kinase activity involving PDGFRβ, fibroblast growth factor receptor, and PDGFRα, and more recently Janus kinase 2 (JAK2), have been described in hypereosinophilic syndromes (FIP1L1-PDGFRα) and in atypical MPNs.3  In addition, systemic mastocytosis involves gain-of-function mutations in the tyrosine kinase receptor c-KIT. Hence, it was likely that classic MPNs are also “kinase diseases.”

JAK2V617F mutation

The JAK2 locus was found affected by a 9p loss of heterozygosity in 30% of PV patients (Table 1, Figure 1).5  In 2005 a major advance in the understanding of the pathogenesis of MPN was made by the discovery of the JAK2V617F mutation.6-9  The JAK family comprises 4 kinases (JAK1, 2, and 3 and TYK2) that attach to cytokine receptor cytosolic domains. JAK kinases possess 2 highly homologous domains at the carboxyl terminus: an active kinase domain (JAK homology, JH1) and a catalytically “inactive” pseudokinase domain (JH2). The JH2 domain is a negative regulator of the JH1 kinase activity.10  At the N-terminus, the JH5-JH7 domains contain a FERM (Band-4.1, ezrin, radixin, and moesin)–like motif, which plays a role in the binding to the cytosolic domain of cognate cytokine receptors. JAK2 plays a central role in the signaling from “myeloid” cytokine receptors. It binds to the 3 homodimeric “myeloid” receptors (erythropoietin receptor [EPO-R], myeloproliferative leukemia [MPL; TPO-R], G-CSF receptor [G-CSF-R]), to the prolactin and growth hormone receptors, to heterodimeric receptors (GM-CSF-R, IL-3-R, and IL-5-R, which share the common β chain of IL-3-R and the gp130 family of receptors), and to IFN-γ R2. JAK2 is the only JAK capable of mediating the signaling of EPO-R and MPL. JAK2 also functions as a chaperone for trafficking of these 2 receptors to the cell surface and their stability.43  More recently, JAK2 was also shown to promote G-CSF-R cell-surface localization.44  Therefore, JAK2 and the 3 “myeloid receptors” form functional units and have been shown to be required for the promotion of JAK2V617F signaling.45 

Table 1

Genes involved in the pathogenesis of MPN

GeneLocalizationFunctionCommentDisease (frequency)References
JAK2 9p24 Tyrosine kinase, signaling Gain of function PV (95%-99%), ET (50%-70%), PMF (40%-50%) 6,,9,11,12  
MPL 1p34 Receptor, signaling Gain of function ET (4%), PMF (11%) 13,,16  
LNK 12q24 Adaptor, signal regulation Loss of function ET (< 5%), PMF (< 5%), JAK2 mutation-negative erythrocytosis (25%), post-MPN AML (13%) 17,19  
CBL 11q23 Adaptor, E3 ubiquitin ligase, signal regulation Dominant negative PMF (6%), post-MPN AML 20,21  
SOCS1 16p13.2 E3 ubiquitin ligase, signal regulation Methylation ET (14%-25%), PV (11%-13%), PMF (17%) 22,23  
SOCS2 12q22 E3 ubiquitin ligase, signal regulation Methylation All MPN (28%) 24  
SOCS3 17q25.3 E3 ubiquitin ligase, signal regulation Methylation, mutation ET (10%), PV (22%) 22,25,27  
NRAS 1p13.2 GTPase, signaling Gain of function post-MPN AML (7%-13%) 21  
NF1 17q11.2 RAS signaling regulation Deletion PMF (0%-6%), post ET/PV MF (14%) 28,29  
TET2 4q24 DNA hydroxymethylation Loss of function PV (15%), ET (4%-11%), PMF (19%), post-MPN AML (26%) 30,,33  
ASXL1 20q11.21 Chromatin modifications Loss of function PV and ET (< 7%) PMF (19%-40%), post-MPN AML (19%) 34,35  
EZH2 7q35 Chromatin methylation Loss of function PV (3%), PMF (13%) 36,38  
IKZF1 7p12 Transcription factor, lymphopoiesis Deletion post-MPN AML (21%) 39  
RUNX1 21q22.3 Transcription factor, hematopoiesis Loss of function post-MPN AML (37%) 21,40  
RB 13q14 Cell cycle, apoptosis Deletion PMF (19%) 29  
TP53 17p13.1 Cell cycle, apoptosis Loss of function post-MPN AML (20%) 21,41  
IDH1 2q33.3 Metabolism Neomorphic enzyme PMF (2%), post-MPN AML (8%) 42  
IDH2 15q26.1 Metabolism Neomorphic enzyme PMF (2%), post-MPN AML (18%) 42  
GeneLocalizationFunctionCommentDisease (frequency)References
JAK2 9p24 Tyrosine kinase, signaling Gain of function PV (95%-99%), ET (50%-70%), PMF (40%-50%) 6,,9,11,12  
MPL 1p34 Receptor, signaling Gain of function ET (4%), PMF (11%) 13,,16  
LNK 12q24 Adaptor, signal regulation Loss of function ET (< 5%), PMF (< 5%), JAK2 mutation-negative erythrocytosis (25%), post-MPN AML (13%) 17,19  
CBL 11q23 Adaptor, E3 ubiquitin ligase, signal regulation Dominant negative PMF (6%), post-MPN AML 20,21  
SOCS1 16p13.2 E3 ubiquitin ligase, signal regulation Methylation ET (14%-25%), PV (11%-13%), PMF (17%) 22,23  
SOCS2 12q22 E3 ubiquitin ligase, signal regulation Methylation All MPN (28%) 24  
SOCS3 17q25.3 E3 ubiquitin ligase, signal regulation Methylation, mutation ET (10%), PV (22%) 22,25,27  
NRAS 1p13.2 GTPase, signaling Gain of function post-MPN AML (7%-13%) 21  
NF1 17q11.2 RAS signaling regulation Deletion PMF (0%-6%), post ET/PV MF (14%) 28,29  
TET2 4q24 DNA hydroxymethylation Loss of function PV (15%), ET (4%-11%), PMF (19%), post-MPN AML (26%) 30,,33  
ASXL1 20q11.21 Chromatin modifications Loss of function PV and ET (< 7%) PMF (19%-40%), post-MPN AML (19%) 34,35  
EZH2 7q35 Chromatin methylation Loss of function PV (3%), PMF (13%) 36,38  
IKZF1 7p12 Transcription factor, lymphopoiesis Deletion post-MPN AML (21%) 39  
RUNX1 21q22.3 Transcription factor, hematopoiesis Loss of function post-MPN AML (37%) 21,40  
RB 13q14 Cell cycle, apoptosis Deletion PMF (19%) 29  
TP53 17p13.1 Cell cycle, apoptosis Loss of function post-MPN AML (20%) 21,41  
IDH1 2q33.3 Metabolism Neomorphic enzyme PMF (2%), post-MPN AML (8%) 42  
IDH2 15q26.1 Metabolism Neomorphic enzyme PMF (2%), post-MPN AML (18%) 42  

AML indicates acute myeloid leukemia; ET, essential thrombocythemia; JAK2, Janus kinase 2; MPN, myeloproliferative neoplasms; PMF, primary myelofibrosis; and PV, polycythemia vera.

Figure 1

Signaling pathways involved in the pathogenesis of MPNs. (A) JAK2V617F is attached to the cytosolic juxtamembrane region of dimeric cytokine receptors, such as EpoR or MPL (TpoR) but can also be attached to the cytosolic region of other JAK2-using cytokine receptors, such as the IFN-γ receptor 2 chain. When bound to homodimeric cytokine receptors, JAK2V617F induces constitutive signaling via STAT5, STAT3, RAS-MAPK, and PI-3′K-Akt pathways, which all regulate gene expression and promote survival, proliferation, and differentiation of committed myeloid progenitors. Constitutive STAT5 and STAT3 signaling is frequently described in MPN myeloid cells, and constitutive STAT1 signaling has been found in certain cases such as erythroid colonies of ET patients. Negative regulators such as CIS (cytokine-inducible SH2) and SOCS proteins (such as SOCS3) are transcriptionally induced by the activated JAK2 but in general appear to be overwhelmed and cannot efficiently block constitutive JAK2V617F signaling. LNK exerts a negative effect on JAK2V617F signaling and constrains the MPN phenotype. Only a minority of patients have LNK mutations. Activation of RAS signaling is counteracted by NF1 (neurofibromatosis 1), a protein that stimulates the GTPase activity of RAS and that is deleted in a minority of MPN patients. (B) Domain structure of negative signaling regulators LNK, c-CBL, and NF-1. Pro indicates proline-rich domain; PH, plekstrin homology domain; SH2, src-homology 2; TKB, tyrosine kinase binding domain; RING, really interesting new gene finges domain; GRD, GAP (GTPase-activating domain)–related domain; and CRAL-TRIO, cellular retinaldehyde and TRIO domain.

Figure 1

Signaling pathways involved in the pathogenesis of MPNs. (A) JAK2V617F is attached to the cytosolic juxtamembrane region of dimeric cytokine receptors, such as EpoR or MPL (TpoR) but can also be attached to the cytosolic region of other JAK2-using cytokine receptors, such as the IFN-γ receptor 2 chain. When bound to homodimeric cytokine receptors, JAK2V617F induces constitutive signaling via STAT5, STAT3, RAS-MAPK, and PI-3′K-Akt pathways, which all regulate gene expression and promote survival, proliferation, and differentiation of committed myeloid progenitors. Constitutive STAT5 and STAT3 signaling is frequently described in MPN myeloid cells, and constitutive STAT1 signaling has been found in certain cases such as erythroid colonies of ET patients. Negative regulators such as CIS (cytokine-inducible SH2) and SOCS proteins (such as SOCS3) are transcriptionally induced by the activated JAK2 but in general appear to be overwhelmed and cannot efficiently block constitutive JAK2V617F signaling. LNK exerts a negative effect on JAK2V617F signaling and constrains the MPN phenotype. Only a minority of patients have LNK mutations. Activation of RAS signaling is counteracted by NF1 (neurofibromatosis 1), a protein that stimulates the GTPase activity of RAS and that is deleted in a minority of MPN patients. (B) Domain structure of negative signaling regulators LNK, c-CBL, and NF-1. Pro indicates proline-rich domain; PH, plekstrin homology domain; SH2, src-homology 2; TKB, tyrosine kinase binding domain; RING, really interesting new gene finges domain; GRD, GAP (GTPase-activating domain)–related domain; and CRAL-TRIO, cellular retinaldehyde and TRIO domain.

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The JAK2V617F mutation results from a guanine to thymine change at nucleotide 1849 of the cDNA, in exon 14 of the gene. This valine is located at one of the predicted interfaces between JH1 and JH2 domains,46  and the change to a phenylalanine appears to relieve the inhibition of the JH2 domain on the kinase domain. There is evidence that constitutive signaling by JAK2V61F requires the homodimeric receptor, explaining why the JAK2V617F-induced proliferation affects 3 myeloid lineages.45  Indeed, the JAK2V617F mutation has been found in the majority of BCR-ABL–negative MPNs (∼ 95% of patients with PV, 50%-70% with ET, and 40%-50% with PMF), as well as in some cases of atypical MPN (30%-50% splanchnic vein thrombosis and sideroblastic anemia associated with a thrombocytosis).47 

Beside its role in the cytokine receptor signaling cascade (Figure 1), JAK2 has been shown to influence chromatin structure (Figure 2).48,49  In hematopoietic cells, nuclear JAK2 phosphorylates histone H3Y41, thereby blocking recruitment of the repressor heterochromatin protein 1α and allowing increased expression of several genes, including the LMO2 oncogene.50  In the same line, JAK2V617F has been recently described to interact with and phosphorylate the protein arginine methyltransferase PRMT5 with a much greater affinity than wild-type JAK2.51  This property is specific (or enhanced) for the mutant protein and has been shown to disrupt the interaction between PRMT5 and its cofactor MEP50, leading to a decreased methyltransferase activity. The knockdown of PRMT5 increases colony formation and erythroid differentiation of primary cells.51  This emerging nuclear role of mutated JAK2 may reveal mutant-specific chromatin effects that may open a novel therapeutic window.

Figure 2

New mutations and epigenetic modifications in MPNs. Several genes mutated in MPN (black boxes) are implicated either in histone modifications or in DNA methylation control. (A) JAK2 activation phosphorylates histone H3Y41, leading to the exclusion of heterochromatin protein 1α (HP1α) from chromatin. In addition, mutant JAK2 phosphorylates PRMT5, thus impairing the methylation of histone H4 and H2A arginine residues. Both phosphorylations are expected to facilitate gene transcription or reduce gene repression. (B) EZH2 belongs to the PRC2 complex, which methylates H3K27 and may also recruit DNMTs. ASXL1 may belong to a complex (PR-DUB in Drosophila melanogaster) that deubiquitinates histone H2AK119, a function that antagonizes the effect of the PRC1 complex. Inactivation of both genes is expected to prevent transcriptional repression mediated by the PRC complexes. (C) TET2 converts DNA 5mC to 5hmC, thus playing a role in active DNA demethylation that would be associated with gene expression. Activation mutations of JAK2 and mutations impairing EZH2, ASXL1, and TET2 functions may result in the deregulation of both DNA methylation and chromatin structure, resulting in aberrant gene expression, gene activation, or failure of repression.

Figure 2

New mutations and epigenetic modifications in MPNs. Several genes mutated in MPN (black boxes) are implicated either in histone modifications or in DNA methylation control. (A) JAK2 activation phosphorylates histone H3Y41, leading to the exclusion of heterochromatin protein 1α (HP1α) from chromatin. In addition, mutant JAK2 phosphorylates PRMT5, thus impairing the methylation of histone H4 and H2A arginine residues. Both phosphorylations are expected to facilitate gene transcription or reduce gene repression. (B) EZH2 belongs to the PRC2 complex, which methylates H3K27 and may also recruit DNMTs. ASXL1 may belong to a complex (PR-DUB in Drosophila melanogaster) that deubiquitinates histone H2AK119, a function that antagonizes the effect of the PRC1 complex. Inactivation of both genes is expected to prevent transcriptional repression mediated by the PRC complexes. (C) TET2 converts DNA 5mC to 5hmC, thus playing a role in active DNA demethylation that would be associated with gene expression. Activation mutations of JAK2 and mutations impairing EZH2, ASXL1, and TET2 functions may result in the deregulation of both DNA methylation and chromatin structure, resulting in aberrant gene expression, gene activation, or failure of repression.

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The discovery of JAK2V617F mutation is an important breakthrough in the understanding of BCR-ABL–negative MPN and has demonstrated the role of pathologic signaling by the JAK/STAT pathway in MPN. Two other mutations directly affecting this pathway have subsequently been described.

JAK2 exon 12 mutations

In the rare JAK2V617F-negative PV, different somatic gain-of-function mutations in exon 12 of JAK2 have been found.11,12  These mutations span the linker region between the SH2 and JH2 domains. Although not located in the pseudokinase domain, these mutations may modify the structure of the JH2 domain in a very similar fashion as V617F. Along these lines, residue F595, located in the helix C of the pseudokinase domain, was shown to be required for both V617F and K539L mutants but not for cytokine-induced JAK2 activation.52  However, in contrast to JAK2V617F, exon 12 mutations are not associated with ET and PMF, although JAK2 exon 12 PV may progress to a secondary myelofibrosis.53 

MPL mutations

Several gain-of-function mutations of MPL have been found in exon 10, which result in the substitution of a tryptophan 515 to a leucine, lysine, asparagine, or alanine.13-16  Amino acid 515 is located in a stretch of 5 amino acids (K/RWQFP) found inside the cytoplasm just after the transmembrane domain. These 5 amino acids play a major role in the cytosolic conformation of MPL and prevent spontaneous activation of the receptor.54,55  In addition, the MPLS505N mutation, initially described in familial ET, was also found in sporadic MPN.13,16  These MPL mutations have been found in up to 15% of JAK2 V617F-negative ET or PMF.56 

Subsequent modeling of the disease has shown that JAK2 and MPL mutations were able to drive the disease in mice. In mouse models of JAK2V617F, both retroviral transplantation assays and transgenic models, including constitutive or inducible knockin approaches, demonstrated the development of a MPN, usually a PV progressing to myelofibrosis.57-63  However, in some models, an ET-like disorder, usually transient, was observed.57,61,64  This phenotype corresponds to a weak JAK2V617F expression, supporting the hypothesis that phenotypic heterogeneity of the JAK2V617F-induced diseases might be because of the intensity of JAK2 signaling, especially to the number of JAK2V617F copies.61  This assumption fits with the human situation in which most patients with ET have a single JAK2V617F mutation, whereas in most PV cases, 2 copies of JAK2V617F are present because of uniparental disomy.65,66  In addition, strain-specific variations were observed in the retroviral mouse model, suggesting that host modifier genes were involved in the phenotype of the disease.57,58,67,68 

This finding also fits with recent results in humans in which JAK2V617F-heterozygous erythroid cells from PV and ET patients exhibit different gene expression profiles, with erythroid cells from ET patients displaying an IFN-γ–stimulated gene expression pattern.69  This is due to the fact that ET and not PV erythroid colonies are characterized by constitutive activation of STAT1, possibly via activation of IFN-γ receptor 2 or another STAT1-activating receptor.69  This finding plus other data suggest the existence of a modifier gene in the human disease. In MPL, BM transplantation assays with W515L or W515A mutations led to an ET-like disorder rapidly progressing to myelofibrosis.13,55  Thus, BCR-ABL–negative MPN resembles CML with some significant differences.

LNK

LNK, also called SH2B3, is a member of the SH2B family, which contains 2 other members (Table 1, Figure 1).70  This family of adaptor proteins is characterized by a conserved structure with 3 main domains (a proline-rich amino terminus, a plekstrin homology domain, an SH2 domain) and a conserved tyrosine at the C-terminus. LNK plays an important role in hematopoiesis by negatively regulating JAK2 activation through its SH2 domain, thus inhibiting EPO-R and MPL signaling.71,72  In addition, LNK negatively regulates c-KIT and FMS signaling.73  LNK-deficient mice have an increased HSC pool with enhanced self-renewal properties and increased quiescence.74  This phenotype probably results from increased TPO/MPL signaling75  because TPO is required for maintaining HSC quiescence and the HSC reservoir.76,77  In addition, Lnk−/− mice develop MPN with thrombocytosis, splenomegaly, and fibrosis78  and marked B-cell overproduction.

As expected from its negative role in JAK2 signaling, LNK is also capable of attenuating the signaling induced by MPLW515L or JAK2V617F.79  Loss of LNK accelerates the development of MPN induced by JAK2V617F in murine models.80  In JAK2V617F-positive patients, LNK expression is increased and modulates the myeloproliferative process.81  Recently, Oh et al17  identified 2 mutations in LNK exon 2, one in a patient with PMF and the other with ET; both MPNs were JAK2V617F negative. The first mutation leads to a premature stop codon resulting in the absence of the PH and SH2 domains, whereas the second (E208Q) is a missense mutation in the PH domain (Figure 1B). In the first mutation, the capacity to inhibit TPO signaling is lost, whereas in the second mutation, some inhibitory function is maintained.

The frequency of mutations in LNK is low.17  However, other mutations of LNK have been found in leukemic transformation of MPN at a greater frequency (∼13%).18  All mutations, except one, target a hot spot located between codons 208 and 234. Interestingly, some of these mutations appear to be late events involved in disease progression because they were not found in the chronic phase.18  In addition some LNK mutations were associated with JAK2V617F, although it is not known whether LNK mutants and JAK2V617F were present in the same cell. It has been also reported that LNK exon 2 mutations can be found in pure erythrocytosis.19  One mutation (A215V) had been previously described in PMF blast crisis, and another (E208X) leads to absence of the PH and SH2 domains as the mutant described in PMF.17  This finding may suggest that the phenotype of the MPN induced by LNK mutations may depend on different parameters, including the presence of other mutations.

Casitas B-cell lymphoma

The Casitas B-cell lymphoma (CBL) family includes 3 homologs: c-CBL, CBL-b, and CBL-c.82  c-CBL, the founding member, is the cellular counterpart of a murine viral oncogene involved in B-cell and myeloid malignancies. CBL proteins are multifunctional adapter proteins with ubiquitin ligase activity. They are usually involved in negative regulation of receptor tyrosine kinase (RTK) by competitive blocking of signaling and they induce RTK proteosomal degradation by mediating ubiquitination in endosomes. However, CBL may have numerous targets other than RTK, including JAK2 and cytokine receptors such as MPL.83  c-CBL and CBL-b proteins contain several domains: an N-terminal tyrosine kinase binding domain followed by a Ring domain, which is important for the transfer of ubiquitin moieties (Figure 1B). A linker separates these 2 domains. The C-terminus part contains a proline-rich domain involved in the binding of several SH3 proteins. Finally, a C-terminal UBA/LZ domain is implicated in CBL oligomerization and ubiquitin binding.82  CBL-c is the member of the family devoid of the C terminal domains. c-CBL is located at 11q.23.3 and is mutated in a variety of myeloid malignancies.84,85 

The greatest frequency of mutations is found in CMML and juvenile myelomonocytic leukemia. In acute myeloid leukemia (AML), the transforming activity of c-CBL may be related to an increased FLT3 signaling.86  Usually variants are missense mutations, which are homozygous because of an acquired uniparental disomy87  or, rarely, because of a deletion of the wild-type copy. For these reasons, CBL has been considered a tumor suppressor gene. In fact, most mutated CBL forms behave as loss-of-function molecules having a dominant-negative effect not only on c-CBL but also on CBL-b, leading to an excessive sensitivity to a variety of growth factors.88  Retroviral transplantation assays with mutated c-CBL induce a mastocytosis phenotype and myeloid leukemia, albeit with a long latency. Similarly, c-CBL knockout mice develop a mild MPN with an increase in HSC. Cbl-b–deficient mice lack a hematologic phenotype.89  The double knockout leads to a rapidly lethal MPN with leukocytosis and excess of monocytes, a phenotype close to myelo-monocytic leukemia.89 

In the chronic phase of classic MPN, c-CBL mutations have been found in a low percentage of PMF patients (6%) but were not detected in a small series of PV and ET patients.20  In one case, the c-CBL mutation occured after JAK2V617F. However, during progression of the disease, JAK2V617F was outcompeted by the CBL mutant, suggesting that the 2 mutations had occurred in 2 different cells.20  Similarly a c-CBL mutation has been detected in blasts from a JAK2V617F-positive MPN, which became JAK2V617F negative during transformation.21  Presently, c-CBL seems to be involved more in progression toward myelofibrosis or acute leukemia than in the chronic phase of the disorder, but further studies are required to establish its precise role.

Suppressor of cytokine signaling 1, 2, and 3

Suppressor of cytokine signaling (SOCS) proteins are also important negative regulators of JAK signaling through a classic feedback loop.90  Loss of SOCS activity induces excess signaling by cytokines. SOCS1-inactivating mutations have been described in B-cell lymphoma.91  Some mutations in the different SOCS have been found in MPNs, but they seem rare.25  In contrast, hypermethylation of CpG islands in SOCS1 and SOCS3 associated with a decrease in expression was found in JAK2V617F PV and ET as well as in JAK2V617F and MPLW515-mutation negative ET22,23  Treatment with 2′-deoxyazacytidine restored SOCS1 and SOCS3 expression. SOCS1 not only regulates cytokine signaling90  but may also be implicated in direct activation of p53-dependent senescence.92  It was suggested that the association between SOCS3 promoter methylation and diminution of transcription is found specifically in JAK2V617F-negative patients with PMF.26  However, the role of SOCS3 in regulating JAK2V617F signaling is controversial. On the one hand, it has been reported that SOCS3 inhibits JAK2V617F signaling through proteosomal degradation.93  On the other hand, when JAK2V617F-transformed hematopoietic cell lines were used, it was reported that JAK2V617F mutant kinase escapes SOCS3-negative regulation by inducing hyperphosphorylation of the SOCS box, thereby blocking its interaction with Elongin C and stabilizing JAK2V617F.94  Similar results have been obtained with exon 12 JAK2 mutant kinases.95  SOCS2 may also inhibit JAK2V617F signaling, and its promoter is hypermethylated in some MPN.24  Presently, the role of SOCS proteins in the pathogenesis of MPN remains unclear: Is the epigenetic silencing a cooperating event with JAK2V617F27  or is it at the origin of some MPNs such as ET?

Leukemic transformation, or blast phase, occurs in approxiamtely 15% of PMF patients and in < 10% of PV and ET patients (Table 1).96-98  To identify the main actors of leukemic transformation in MPN, several teams have conducted comprehensive genotypic analyses of post–MPN-AML cells, with particular attention to both MPN- and AML-related genes.97-99  To fit the definition of a blast phase-transforming event, the candidate event had to be detected in all blast cells but not in the majority of cells from the preceding MPN clone.21 

IDH1/2 mutations

IDH1 and IDH2 encode isocitrate dehydrogenase 1 and 2, which are NADP+ enzymes that catalyze the conversion of isocitrate to α-ketoglutarate (αKG).100,101  Heterozygous mutations of IDH1 (R132S, R132G) and IDH2 (codon R140 and R172) have been identified in AML.102,103  Mutated IDH1/2 are neomorphic enzymes that catalyze the reduction of αKG to (R)-2-hydroxyglutarate. A subsequent overproduction of (R)-2-hydroxyglutarate has been proposed to affect the function of αKG-dependent enzymes such as TET2, resulting in a decrease of 5hmc.104  Although the effects of IDH1/2 mutations on HSCs and progenitors remain unknown, these mutations may belong to a set of initiating events of the same nature as the TET2 mutations. The analysis of 1473 patients with MPN revealed a low incidence of IDH1/2 mutations in chronic phase ET, PV, and MF (0.8%, 1.9%, and 4.2%, respectively) contrasting with a 21.6% frequency in blast phase.42  Thus IDH1/IDH2 mutations are associated with MPN transformation, but clonal hierarchy and follow-up studies are needed to better define whether they promote the initiation or the progression of MPN to AML.

IKZF deletion

The IKZF1 gene encodes for the Ikaros transcription factor, which regulates the development of B and T cells.105 IKZF1 deletions are frequent in acute lymphoblastic leukemia, especially in BCR-ABL–positive cases.106  Hemizygous deletions of the IKZF1 gene region on chromosome 7p were observed in 1 of 437 patients with chronic-phase MPN and 6 of 29 patients with post–MPN-AML.39  Clonal hierarchy analysis showed that in some cases IKZF1 deletion was a late event in the progression of the disease and was frequently related to a complex karyotype. Thus, like in post–CML- acute lymphoblastic leukemia, IKZF1 deletions in post–MPN-AML are late events in the progression of MPN to AML.

NRAS/KRAS mutations and NF1 deletion

RAS proteins are membrane-associated GTPases that in their active form trigger a variety of effector signaling pathways, such as the MAPK cascade of serine/threonine kinases. The most frequent mutations in KRAS and NRAS occur at codons 12, 13, and 61, leading to an inhibition of the GTP-ase activity, thus allowing constitutive activation of effector pathways such as MAPK signaling and downstream transcriptional control. It is still unknown whether RAS mutations promote the initiation or the progression of myeloid malignancies to acute leukemia. In MPN, this question remains unresolved because NRAS mutations were found in post–MPN-AML blasts and in cells from the preceding chronic phase, but also, in some patients, exclusively in AML blasts at transformation.21 NF1 deletions were mainly found in myelofibrosis and rarely in PV or ET.28,29  Their frequency in leukemic transformation is unknown.

TP53 mutations

TP53 gene encodes p53, a major tumor suppressor protein involved in various biologic activities, including the control of cell-cycle checkpoints and apoptosis. Germline loss-of-function mutations in TP53 predispose patients to a multiplicity of cancers, and acquired mutations in p53 occur in approximately 10% of AML samples.107 TP53 mutations are not associated with the chronic phase of MPNs. However, mutated TP53 have been found with a 20% frequency in post–MPN-AML patients.21,41,108  In one particular case with both MPL and TET2 mutations during chronic-phase ET, multiple TP53 mutations were identified at the time of post–ET-AML that resulted in an oligoclonal pattern in progenitors, with one selected subclone giving rise to leukemic blasts.109  Thus, the picture of TP53 mutations in post–MPN-AMLs suggests that they play a prominent role in the transformation process.

RUNX1 mutations

The RUNX1/AML1 gene encodes a transcription factor with a major role in hematopoiesis. It was found mutated in MDS and AML.110  In a series of 34 post–MPN-AML patients, RUNX1 mutations were found in leukemic blasts of 11, most of which were localized in the RUNT domain (residues 50-177).18,37  This observation suggests that RUNX1 mutation may represent one of the most frequent genetic events implicated in MPN transformation to AML.

An emerging hypothesis posits that mutations in signaling molecules are not sufficient for disease development in humans and that several cooperating genetic hits might be required to induce disease and allow progression (Table 1, Figure 2). This hypothesis was determined by 4 lines of evidence:

  1. Familial MPN has been described with a dominant-autosomal transmission.111,112  The phenotype of these familial forms correspond either to a classic MPNs (PV, ET) in the absence of germinal transmission of JAK2V617F or MPLW515L, or to a larger spectrum of diseases (CML, systemic mastocytosis and also acute leukemia).111,113 

  2. Certain ET and rare PV were clonal as judged by X inactivation assays, whereas JAK2V617F was present only in a minority of cells, suggesting the existence of a pre-JAK2 clone, in which the JAK2V617F mutation has occurred.114,115  In some JAK2V617F MPNs associated with the 20q deletion, this deletion was present in the majority of cells, whereas the JAK2V617F burden was low116 ; furthermore, JAK2V617F was not found in some erythropoietin-independent colonies.115 

  3. More surprisingly, it was initially reported that approximately 50% of acute leukemia developing on a JAK2V617F MPNs was JAK2 wild type, even in the absence of previous chemotherapy.97,117  This finding suggests the existence of a pre-JAK2 clone, on the background of which 2 independent genetic events have occurred, one being the JAK2V617F mutation leading to a MPN and another one being a genetic alteration leading to leukemia.

  4. Hematopoiesis of JAK2V617F MPN is quite surprising for a clonal disorder involving a HSC. In most PV and ET at diagnosis, the allele burden is extremely low in HSC, and the clonal dominance only occurs during late stages of hematopoiesis, corresponding to the maximum activity of hematopoietic cytokines (Figure 3).66,118  In contrast, JAK2V617F HSCs predominate in advanced MPNs such as PMF or secondary myelofibrosis.119,120  This finding suggests that JAK2V617F confers only a weak advantage to HSC.

Figure 3

Dynamic representation of clonal dominance in the presence of TET2 and/or JAK2 mutations in the HSC, hematopoietic stem progenitor (HPC), and mature fractions. JAK2V617F would mainly expand the mature fraction, whereas TET2 mutation would mainly expand the HPC fraction. TET2 and JAK2 mutations are synergistic by combining an early and late amplification. The order of mutations would not matter if they occur before the development of a full-blown disorder. All numbers and ratios are arbitrary.

Figure 3

Dynamic representation of clonal dominance in the presence of TET2 and/or JAK2 mutations in the HSC, hematopoietic stem progenitor (HPC), and mature fractions. JAK2V617F would mainly expand the mature fraction, whereas TET2 mutation would mainly expand the HPC fraction. TET2 and JAK2 mutations are synergistic by combining an early and late amplification. The order of mutations would not matter if they occur before the development of a full-blown disorder. All numbers and ratios are arbitrary.

Close modal

As a consequence of the development of whole genome assays (first comparative genomic hybridization and single nucleotide polymorphism arrays and more recently whole genome sequencing), an increasing number of mutations have been observed in BCR-ABL–negative compared with BCR-ABL–positive MPNs, and these mutations involve genes modifying epigenetic regulation. Mutations in these genes are also found in a great variety of myeloid malignancies, including MDS and AML, suggesting a common pathogenesis in the 3 disorders but implying that these mutated genes are not directly involved in the phenotype of the myeloid malignancies.

Genes that might be mutated before JAK2 in MPNs normally participate in the epigenetic control of transcription. It is not known whether all pre-JAK2 mutations yet to be identified will fall into this category.

EZH2

EZH1 and EZH2 proteins (enhancer of zeste homolog) belong to the polycomb repressive complex 2 (PRC2).121  PRC2 is involved in various cellular processes, including proliferation, differentiation, cell-identity maintenance, aging, and plasticity.121,122  In addition to EZH1 or EZH2, PRC2 includes EED, RbAp46/48, SUZ12, AEBP2, JARID2, and PCL. It is thought that PRC2 contributes to chromatin structure regulation. PRC2 methylates histone H3 at lysine 27, a mark of inactive chromatin, through the SET domain of EZH1 or EZH2.123  Its interaction with DNA in mammals is still elusive but may involve YY1 and long intergenic noncoding (ie, Linc) RNAs. It also associates to DNA-methyltransferase (DNMT) proteins to direct DNA methylation.

EZH2 codes for 1 of the 2 possible catalytic subunits of PRC2. EZH proteins are methyltransferases involved in the di- and trimethylation of K27.123-125  EZH2 overexpression is observed in numerous solid tumors such as breast and prostate cancers and may induce dedifferentiation.126  EZH2 is mutated in B-cell lymphomas, but the recurrent mutation targeting Y641 results in a gain of function: the mutated enzyme preferentially generates trimethylated K27.127  In contrast, in myeloid disorders EZH2 mutations may be associated with deletion of the other copy or preferentially with loss of heterozygosity.36-38 EZH2 mutations are predicted to be inactivating through either the truncation of the protein or modification of essential amino acids. They are not associated with a specific MPN or MDS subtype but might be more frequent in MPD/MPNs and are associated with poor prognosis. EZH2 mutations are not observed in ET, but are seen in 3% of PV and 13% of MF.36 

ASXL1

ASXL1, together with ASXL2 and ASXL3, are related to the Drosophila melanogaster additional sex combs (Asx), a polycomb gene required for long-term repression of the HOX genes.128  Asx has recently been identified in a new polycomb complex (PR-DUB) able to deubiquitinate histone H2A through the activity of the BAP1 protein.129  This activity is the converse of the monoubiquitination mediated by the PRC1 complex, and the balance between the 2 activities is important in the regulation of target genes, such as the HOX genes.121  It is not known whether ASXL1 has a similar function in mammals.

Mutations in ASXL1 are frameshifts and stop mutations located within the 12th exon of the gene; they usually affect only one copy of the gene and result in the loss of the carboxyterminal PHD domain.34,130  The frequency is low in low-grade disorders but greater in late MDS, AML, and in proliferative CMML. However, the veracity of the most frequently reported ASXL1 mutation has been recently questioned.131  In MPNs, ASXL1 mutations are rare in ET and PV (< 7%) but frequent in PMF (from 19%-40%).34,35 

The function of ASXL1 in hematopoiesis is still poorly understood. Asxl1 knockout mice have a mild defect in hematopoiesis, predominantly in lymphopoiesis.132  A marked decrease in myeloerythroid progenitors was observed but without detectable effect on HSC. Its role in human hematopoiesis is unknown.

TET2

The Ten-Eleven-Translocation2 (TET2) gene codes for a 2-oxoglutarate and Fe(II)-dependent hydroxylase that is able to hydroxylate methylated cytosine (methylcytosine; mC).133-135  This function is shared with the 2 other TET proteins known in mammals, TET1 and TET3.133,135  The function of the resulting modified nucleotide, hydroxymethylcytosine (5hmC), is not clear yet, but it appears to be present in all cell types.136-138  5hmc may have a function by itself and/or represent a step toward cytosine demethylation.136  There is preliminary evidence that the function of TET1 and TET2 is mainly related to the generation of 5hmc.139 

The founding member of the TET family is TET1. It has been isolated as a fusion partner of MLL in acute leukemia with the t(10;11)(q21;q32) chromosomal translocation.140,141 TET2 has 9 coding exons. Exon 2 is included in half of the transcripts starting from exon 1 and contains an ATG; a second ATG is located at the beginning of exon 3. The main TET2 protein is 2002 amino acids long (starting from the ATG in exon 3), but a second product is predicted to be translated from a RNA species that is not spliced at the 3′ side of exon 3 and runs on until a polyA site downstream of exon 4.30 

TET2 is mutated in a wide range of myeloid malignancies.30-33  Observed mutations are mainly small insertions and deletions and nonsense mutations that are expected to result in the loss of function of the protein. Missense mutations affecting conserved amino acids have been shown also to impair the catalytic activity of the protein. Accordingly, patients with TET2 mutations have lower global 5hmC content than wild type.142  Of note, the global level of 5hmC may not directly impact the mC level as evaluated on a gene-specific base because TET2-mutated patients have lower mC in MDS samples and greater mC in AML samples.104,142 

TET2 mutations are found in approximately 14% of MPNs ranging from ET (11%) to PMF (19%).32,143  In roughly 20% of the patients, 2 mutations are observed, suggesting that the inactivation of a single copy of TET2 is sufficient for the transformation process. TET2 mutations are not responsible for the familial MPNs identified to date, although a germline mutation has been described.144  In vitro studies have first shown that TET2 mutations occur before JAK2 mutations during the natural history of sporadic MPNs.32  However, subsequent studies suggest that the converse may happen and also that TET2 mutations may occur when MPNs transform to AML.144-147 

One caveat: every mutational event that inactivates TET2 may not have been identified. For example, small deletions outside of the coding sequence or deletion of a single exon would have been missed by the current analyses.

Mutations have been shown to be present in the HSC/progenitor populations.32  In vivo analyses demonstrated that the TET2-mutated cells from MPN samples are able to engraft into immunodeficient mice.32  Clone-amplification studies have shown that TET2 mutations and JAK2V617F act synergistically to induce a clonal dominance at the level of hematopoietic progenitors in PV patients (Figure 3).32,145  TET1 and 2 proteins appear to play a crucial role in stem cell biology as shown in the control of pluripotency of murine embryonic stem cells. Initially, it was suggested that TET1 was involved in the self-renewal of ES cells by controlling Nanog,133  but recent evidence suggests that both TET1 and TET2 are necessary for pluripotency by controlling cell fate through the regulation of distinct sets of genes.139  Thus, TET2 may have a similar role on HSC. Preliminary results show that in the mouse, in vitro knockdown of TET2 by shRNAs increases monocytic differentiation in the presence of GM-CSF, causing an excess of immature forms.105,142  In human hematopoiesis, knocking down TET2 transiently favors monocytic differentiation at the expense of the granulocytic differentiation and decreases the proliferation of erythroid progenitors (F.D., unpublished data, June 2011).

Mutations in EZH2 and in ASXL1 point at deregulation of polycomb activity in MPN. In addition, L3MBTL1, a polycomb gene, may be one of the important lost genes in chromosome 20q deletion frequently seen in MPN.148  It is known that DNMTs interact with EZH2, allowing the coupling between PRC2 and DNA methylation.125  Because DNMT3A interacts with EZH2 and is mutated in AML and MDS,149  mutational analyses of this gene in MPN may identify a new “epigenetic player” in MPN pathogenesis.

Mutations in TET2, ASXL1, and EZH2 genes are observed in a wide range of myeloid malignancies. Furthermore, virtually all the other genes mutated in MPNs are in fact not specific to these disorders. Mutations in JAK2 and MPL have also been described in other diseases, such as acute leukemia,150-153  but they affect different amino acids and their frequency is lower than in MPNs.

Initially, MPNs were considered as simple, single-hit diseases that lead to an increase in mature blood cells. ET and PV, disorders with a pure excess of mature blood cells, fit with this hypothesis, whereas PMF, which also has abnormal MK differentiation, is likely more complex. Thus, as with BCR-ABL in CML, a single mutation in a signaling protein would be at the origin of classic MPNs. The discovery of JAK2 and MPL gain-of-function mutations in classic MPN and the recapitulation of the human disorder in mouse models support this hypothesis. However, other lines of evidence indicate that JAK2V617F mutation may not be the initial event in certain MPNs and that other genetic events may be required for disease development. These data led to the concept of a pre-JAK2 event. At least 3 different genes involved in epigenetic regulation may precede JAK2 mutation in MPNs. It is likely that mutations in other genes have yet to be discovered. Thus, instead of being a single-hit disorder, MPN would result from the combination of several genetic events as exemplified by the finding of EZH2, TET2, and JAK2 mutations in the same MPN patient.36  Thus, the pathogenesis of the MPN has evolved from a simple to a complex model. At a first glance, this appears to sharply contrast with CML, where BCR-ABL is thought to fully explain the disease, although this is not the case for all CML patients.154 

Why would several genetic events be required for the development of MPN?

The hallmark of these disorders is an increased production of mature blood cells. In some instances, a single germline mutation can induce thrombocytosis, erythrocytosis, or neutrophilia.155-161  In inherited diseases, all HSC carry the mutation, whereas in sporadic MPNs the signaling mutation (JAK2V617F, MPLW515L, or BCR-ABL) is acquired by a HSC that must compete with wild-type HSCs.

Mathematical models predict that at least 1%-2% of the HSC need to carry the JAK2V617F mutation to produce the clinical phenotype.162  Given an estimate of 1 × 106 HSCs in humans the initial JAK2V617F-positive HSC must expand 104 fold more than wild-type HSC before inducing a clinical phenotype.163,164  Evaluation of the JAK2V617F burden at different hematopoietic differentiation steps in humans has shown that the clonal expansion occurs mainly in late differentiation steps in PV and ET.66,118  In addition, CD34+ cells from PV or ET patients at diagnosis generate essentially JAK2 wild-type hematopoiesis in xenograft experiments, showing that JAK2V617F HSC are still in minority in early disease.119,165,166  Furthermore, JAK2V617F HSC did not out-compete JAK2 wild-type HSC in one case of allogenic human BM transplantation.167  This mild effect of JAK2V617F on HSC biology is also observed in mouse models. Transgenic JAK2V617F HSCs displayed only a slight advantage on JAK2 wild-type HSC in transplantation assays.59  Furthermore, in one knockin model, JAK2V617F HSCs were at a disadvantage.64  These results are unexpected because the TPO/MPL axis plays an important role in HSC self-renewal76,77,168-170  and quiescence in the BM niche.77,78  Thus, it is possible that MPL signaling differs between HSC and MKs and/or that JAK2V617F only partially activates normal MPL functions in HSC.

Therefore, a crucial (and presently unknown) factor in MPN pathogenesis is the latency between the mutation of JAK2 and the appearance of the disease. On the basis of the log-log incidence of MPN with age (that increases after 60 years), mathematical models suggested that a single mutation, such as JAK2V617F, although providing a minor advantage to HSC, may cause a MPN with a very long latency (> 45 years).163  Another prediction of the model is that > 95% of the JAK2V617F clones die by exhaustion and disappear.163,164  Therefore, cooperation of JAK2V617F with other genetic events modifying HSC biology will greatly facilitate the development of a clinical phenotype. It cannot be excluded, however, that JAK2V617F may give a significant advantage to HSC in specific conditions such as inflammation, as suggested by preliminary studies.171  It is thus conceivable that JAK2V617F HSC remain harmless during a long period, until genetic or environmental changes such as hematopoietic stress or aging allow clonal dominance and MPN emergence. Of note, clonal dominance occurs at the HSC level in PMF that frequently carry several mutations.119,120 

Does a pre-JAK2 event really exist?

There is clear evidence that TET2 mutations, and also ASXL1 and EZH2 mutations, may precede JAK2V617F140  but that the converse may also occur.144-146  This finding suggests that the important issue is not the order of appearance of the mutations but the fact that they all occur in a HSC with the MPN phenotype being mainly driven by the JAK2V617F mutation.172  There is also evidence that secondary acquisition of TET2 mutations may be associated with disease progression and transformation.147  In support of this notion, it has been shown that TET2, EZH2, or ASXL1 mutations are far less frequent in PV and ET than in PMF, which combine at least 2 mutations.32,34-36 

Two classes of MPNs may thus exist; a simple one, in which a single JAK2 or MPL mutation induces PV or ET, and a complex class, with 2 or more mutations producing PMF. For this reason, as previously suggested,173  PMF might be the accelerated phase of classic MPN. Next-generation sequencing may help establish whether a large fraction of ET and PV at diagnosis is the consequence of a single genetic event.

In several MPN patients, the coexistence of 2 oncogenic events, such as JAK2V617F, MPLW515L, JAK2 exon 12, BCR-ABL, and c-CBL mutants, has been demonstrated.18,20,174-178  In nearly all these cases, the 2 events have occurred in 2 different cells; moreover, independent acquisitions of JAK2V617F in a single patient have been reported.108,179  In one case it has been demonstrated that the MPLW515L and JAK2V617F subclones were derived from the same ancestral TET2-mutated clone.21  Thus, a reasonable hypothesis is that TET2, ASXL1, and EZH2 mutations favor the occurrence of secondary genetic events. From the original clone, a complex combination of mutations that does not follow a linear dynamics may give rise to different subclones. Depending on the type of dominant clone, different hemopathies evolving in time and appearing in different sequences will be induced. Such a model will explain the occurrence of JAK2 wild-type leukemia in JAK2V617F-positive MPNs, whereas, in contrast, the linear accumulation of mutations in the JAK2V617F-dominant clone will favor the progression of MPN to myelofibrosis and leukemia. This hypothesis has been validated only in one case of wild-type JAK2 AML, which had emerged from an original TET2 mutated clone found in the initial MPN.180 

In other examples, TET2 mutations were only found in the leukemic cells.21,147  There are 2 possible scenarios for these patients:

  1. The ancestral clone exhibits a mutation different from a coding sequence mutation on TET2 as exemplified by the EZH2 mutation preceding TET2 mutation36 

  2. AML and MPN are independent disorders. This would mean that a “mutator” phenotype exists in some MPN patients. This phenotype may be acquired, for example, related to changes in the hematopoietic environment181,182  or in the germline. This last possibility is supported by a marked increased risk (∼ 5- to 7-fold) among first-degree relatives of MPN patients.183  Such a risk has been at least partly related to 3 SNPs in the JAK2 gene, including one in the exon 14 defining the haplotype 46/1. The haplotype 46/1 is present with an allelic prevalence of approximately10% in the normal populations and confers a 3- and a 1.4-fold increase in the risk of developing a JAK2V617F or exon 12 or a MPLW515 MPN, respectively.184-187  The mechanism of this low penetrance susceptibility is unknown. This predisposition is different from the familial forms of MPN with a Mendelian transmission.112  However, none of the genetic events at the origin of this familial form is presently known, and this could correspond either to a “mutator” phenotype related to an alteration in gene repair or to a haploinsufficiency in a tumor suppressor gene. The precise understanding of the molecular mechanism of these familial forms will be certainly be critical for understanding the pathogenesis of MPN.

What are the consequences for therapy?

New targeted therapies against JAK2 have been developed.188-191  In contrast to the initial results, which showed a targeted effect of JAK2 inhibitors on JAK2V617F cells, including HSC,192,193  there is increasing evidence that they also affect JAK2 wild-type and JAK2V617F cells although having less effect on JAK2V617F HSC.59  This finding supports the clinical results that have shown good clinical responses in constitutional symptoms like asthenia and splenomegaly in myelofibrosis but a weak effect on the JAK2V617F clone.189  However, in cases in which JAK2V617F is not the initiating event, this approach may revert the MPN hematopoiesis to a pre-JAK2 clonal hematopoiesis (pre-JAK2 disorder) with the risk of developing other malignant blood disorders. The proof of this potential was demonstrated in one PV patient treated by pegylated IFN-α, where, after treatment, the JAK2V617F burden was at the threshold of detection, but the hematopoiesis was clonal because of a preexisting TET2 mutation.194  More recently, studies of “epigenetic” therapies in which the authors use either HDAC inhibitors or “demethylating” agents have been initated.195-198  It is unknown whether these therapies will be able to target the alterations induced by ASXL1, EZH2, or TET2 mutations.

Future studies aimed at identifying mutations present in MPN in which the authors use new-generation sequencing will be crucial not only to characterize the many cases of MPNs with no known molecular cause but also to better understand the evolution of the clone and the synergistic effects of the different mutations. This will be very important for understanding MPN pathogenesis and develop new therapies, and also, more generally, to understand the stepwise mechanisms leading to cancer development in humans.

The authors thank Françoise Wendling for a critical reading of the manuscript and Christian Pecquet for helping with the figures.

This work was supported by Inserm and by grants from la Ligue Nationale Contre le Cancer, l'Institut National du Cancer, la Cancéropole Ile de France, l'Association Laurette Fugain, la Fondation de France, the MPD Foundation, the Belgian PAI Program, Salus Sanguinis Foundation, the ARC Program of Université Catholique de Louvain, the Fondation contre le cancer, and the FRS-FNRS Belgium.

Contribution: W.V. and O.A.B. wrote the manuscript; and F.D. and S.N.C. contributed to the writing of the manuscript and made the figures.

Conflict-of-interest disclosure: The authors declare no competing financial interests.

Correspondence: William Vainchenker, Inserm U1009, Institut Gustave Roussy, PR1, 39 rue Camille Desmoulins, 94805 Villejuif, France; e-mail: [email protected].

1
Dameshek
 
W
Some speculations on the myeloproliferative syndromes.
Blood
1951
, vol. 
6
 
4
(pg. 
372
-
375
)
2
Tefferi
 
A
Thiele
 
J
Vardiman
 
JW
The 2008 World Health Organization classification system for myeloproliferative neoplasms: order out of chaos.
Cancer
2009
, vol. 
115
 
17
(pg. 
3842
-
3847
)
3
Delhommeau
 
F
Pisani
 
DF
James
 
C
Casadevall
 
N
Constantinescu
 
S
Vainchenker
 
W
Oncogenic mechanisms in myeloproliferative disorders.
Cell Mol Life Sci
2006
, vol. 
63
 
24
(pg. 
2939
-
2953
)
4
Campbell
 
PJ
Green
 
AR
The myeloproliferative disorders.
N Engl J Med
2006
7
, vol. 
355
 
23
(pg. 
2452
-
2466
)
5
Kralovics
 
R
Guan
 
Y
Prchal
 
JT
Acquired uniparental disomy of chromosome 9p is a frequent stem cell defect in polycythemia vera.
Exp Hematol
2002
, vol. 
30
 
3
(pg. 
229
-
236
)
6
James
 
C
Ugo
 
V
Le Couedic
 
JP
et al. 
A unique clonal JAK2 mutation leading to constitutive signalling causes polycythaemia vera.
Nature
2005
, vol. 
434
 
7037
(pg. 
1144
-
1148
)
7
Baxter
 
EJ
Scott
 
LM
Campbell
 
PJ
et al. 
Acquired mutation of the tyrosine kinase JAK2 in human myeloproliferative disorders.
Lancet
2005
, vol. 
365
 
9464
(pg. 
1054
-
1061
)
8
Kralovics
 
R
Passamonti
 
F
Buser
 
AS
et al. 
A gain-of-function mutation of JAK2 in myeloproliferative disorders.
N Engl J Med
2005
, vol. 
352
 
17
(pg. 
1779
-
1790
)
9
Levine
 
RL
Wadleigh
 
M
Cools
 
J
et al. 
Activating mutation in the tyrosine kinase JAK2 in polycythemia vera, essential thrombocythemia, and myeloid metaplasia with myelofibrosis.
Cancer Cell
2005
, vol. 
7
 
4
(pg. 
387
-
397
)
10
Saharinen
 
P
Silvennoinen
 
O
The pseudokinase domain is required for suppression of basal activity of Jak2 and Jak3 tyrosine kinases and for cytokine-inducible activation of signal transduction.
J Biol Chem
2002
, vol. 
277
 
49
(pg. 
47954
-
4763
)
11
Scott
 
LM
Tong
 
W
Levine
 
RL
et al. 
JAK2 exon 12 mutations in polycythemia vera and idiopathic erythrocytosis.
N Engl J Med
2007
, vol. 
356
 
5
(pg. 
459
-
468
)
12
Pietra
 
D
Li
 
S
Brisci
 
A
et al. 
Somatic mutations of JAK2 exon 12 in patients with JAK2 (V617F)-negative myeloproliferative disorders.
Blood
2008
, vol. 
111
 
3
(pg. 
1686
-
1689
)
13
Pikman
 
Y
Lee
 
BH
Mercher
 
T
et al. 
MPLW515L is a novel somatic activating mutation in myelofibrosis with myeloid metaplasia.
PLoS Med
2006
, vol. 
3
 
7
pg. 
e270
 
14
Beer
 
PA
Campbell
 
PJ
Scott
 
LM
et al. 
MPL mutations in myeloproliferative disorders: analysis of the PT-1 cohort.
Blood
2008
, vol. 
112
 
1
(pg. 
141
-
149
)
15
Boyd
 
EM
Bench
 
AJ
Goday-Fernandez
 
A
et al. 
Clinical utility of routine MPL exon 10 analysis in the diagnosis of essential thrombocythaemia and primary myelofibrosis.
Br J Haematol
2010
, vol. 
149
 
2
(pg. 
250
-
257
)
16
Chaligné
 
R
Tonetti
 
C
Besancenot
 
R
et al. 
New mutations of MPL in primitive myelofibrosis: only the MPL W515 mutations promote a G1/S-phase transition.
Leukemia
2008
, vol. 
22
 
8
(pg. 
1557
-
1566
)
17
Oh
 
ST
Simonds
 
EF
Jones
 
C
et al. 
Novel mutations in the inhibitory adaptor protein LNK drive JAK-STAT signaling in patients with myeloproliferative neoplasms.
Blood
2010
, vol. 
116
 
6
(pg. 
988
-
992
)
18
Pardanani
 
A
Lasho
 
T
Finke
 
C
Oh
 
ST
Gotlib
 
J
Tefferi
 
A
LNK mutation studies in blast-phase myeloproliferative neoplasms, and in chronic-phase disease with TET2, IDH, JAK2 or MPL mutations.
Leukemia
2010
, vol. 
24
 
10
(pg. 
1713
-
1718
)
19
Lasho
 
TL
Pardanani
 
A
Tefferi
 
A
LNK mutations in JAK2 mutation-negative erythrocytosis.
N Engl J Med
2010
, vol. 
363
 
12
(pg. 
1189
-
1190
)
20
Grand
 
FH
Hidalgo-Curtis
 
CE
Ernst
 
T
et al. 
Frequent CBL mutations associated with 11q acquired uniparental disomy in myeloproliferative neoplasms.
Blood
2009
, vol. 
113
 
24
(pg. 
6182
-
6192
)
21
Beer
 
PA
Delhommeau
 
F
LeCouedic
 
JP
et al. 
Two routes to leukemic transformation after a JAK2 mutation-positive myeloproliferative neoplasm.
Blood
2010
, vol. 
115
 
14
(pg. 
2891
-
2900
)
22
Jost
 
E
do
 
ON
Dahl
 
E
et al. 
Epigenetic alterations complement mutation of JAK2 tyrosine kinase in patients with BCR/ABL-negative myeloproliferative disorders.
Leukemia
2007
, vol. 
21
 
3
(pg. 
505
-
510
)
23
Teofili
 
L
Martini
 
M
Cenci
 
T
et al. 
Epigenetic alteration of SOCS family members is a possible pathogenetic mechanism in JAK2 wild type myeloproliferative diseases.
Int J Cancer
2008
, vol. 
123
 
7
(pg. 
1586
-
1592
)
24
Quentmeier
 
H
Geffers
 
R
Jost
 
E
et al. 
SOCS2: inhibitor of JAK2V617F-mediated signal transduction.
Leukemia
2008
, vol. 
22
 
12
(pg. 
2169
-
2175
)
25
Suessmuth
 
Y
Elliott
 
J
Percy
 
MJ
et al. 
A new polycythaemia vera-associated SOCS3 SH2 mutant (SOCS3F136L) cannot regulate erythropoietin responses.
Br J Haematol
2009
, vol. 
147
 
4
(pg. 
450
-
458
)
26
Fourouclas
 
N
Li
 
J
Gilby
 
DC
et al. 
Methylation of the suppressor of cytokine signaling 3 gene (SOCS3) in myeloproliferative disorders.
Haematologica
2008
, vol. 
93
 
11
(pg. 
1635
-
1644
)
27
Chaligné
 
R
Tonetti
 
C
Besancenot
 
R
et al. 
SOCS3 inhibits TPO-stimulated, but not spontaneous, megakaryocytic growth in primary myelofibrosis.
Leukemia
2009
, vol. 
23
 
6
(pg. 
1186
-
1190
)
28
Kawamata
 
N
Ogawa
 
S
Yamamoto
 
G
et al. 
Genetic profiling of myeloproliferative disorders by single-nucleotide polymorphism oligonucleotide microarray.
Exp Hematol
2008
, vol. 
36
 
11
(pg. 
1471
-
1479
)
29
Stegelmann
 
F
Bullinger
 
L
Griesshammer
 
M
et al. 
High-resolution single-nucleotide polymorphism array-profiling in myeloproliferative neoplasms identifies novel genomic aberrations.
Haematologica
2010
, vol. 
95
 
4
(pg. 
666
-
669
)
30
Langemeijer
 
SM
Kuiper
 
RP
Berends
 
M
et al. 
Acquired mutations in TET2 are common in myelodysplastic syndromes.
Nat Genet
2009
, vol. 
41
 
7
(pg. 
838
-
842
)
31
Tefferi
 
A
Levine
 
RL
Lim
 
KH
et al. 
Frequent TET2 mutations in systemic mastocytosis: clinical, KITD816V and FIP1L1-PDGFRA correlates.
Leukemia
2009
, vol. 
23
 
5
(pg. 
900
-
904
)
32
Delhommeau
 
F
Dupont
 
S
Della Valle
 
V
et al. 
Mutation in TET2 in myeloid cancers.
N Engl J Med
2009
, vol. 
360
 
22
(pg. 
2289
-
2301
)
33
Abdel-Wahab
 
O
Mullally
 
A
Hedvat
 
C
et al. 
Genetic characterization of TET1, TET2, and TET3 alterations in myeloid malignancies.
Blood
2009
, vol. 
114
 
1
(pg. 
144
-
147
)
34
Carbuccia
 
N
Murati
 
A
Trouplin
 
V
et al. 
Mutations of ASXL1 gene in myeloproliferative neoplasms.
Leukemia
2009
, vol. 
23
 
11
(pg. 
2183
-
2186
)
35
Tefferi
 
A
Novel mutations and their functional and clinical relevance in myeloproliferative neoplasms: JAK2, MPL, TET2, ASXL1, CBL, IDH and IKZF1.
Leukemia
2010
, vol. 
24
 
6
(pg. 
1128
-
1138
)
36
Ernst
 
T
Chase
 
AJ
Score
 
J
et al. 
Inactivating mutations of the histone methyltransferase gene EZH2 in myeloid disorders.
Nat Genet
2010
, vol. 
42
 
8
(pg. 
722
-
726
)
37
Nikoloski
 
G
Langemeijer
 
SM
Kuiper
 
RP
et al. 
Somatic mutations of the histone methyltransferase gene EZH2 in myelodysplastic syndromes.
Nat Genet
2010
, vol. 
42
 
8
(pg. 
665
-
667
)
38
Makishima
 
H
Jankowska
 
AM
Tiu
 
RV
et al. 
Novel homo- and hemizygous mutations in EZH2 in myeloid malignancies.
Leukemia
2010
, vol. 
24
 
10
(pg. 
1799
-
1804
)
39
Jäger
 
R
Gisslinger
 
H
Passamonti
 
F
et al. 
Deletions of the transcription factor Ikaros in myeloproliferative neoplasms.
Leukemia
2010
, vol. 
24
 
7
(pg. 
1290
-
1298
)
40
Ding
 
Y
Harada
 
Y
Imagawa
 
J
Kimura
 
A
Harada
 
H
AML1/RUNX1 point mutation possibly promotes leukemic transformation in myeloproliferative neoplasms.
Blood
2009
, vol. 
114
 
25
(pg. 
5201
-
5205
)
41
Harutyunyan
 
A
Klampfl
 
T
Cazzola
 
M
Kralovics
 
R
p53 lesions in leukemic transformation.
N Engl J Med
2011
, vol. 
364
 
5
(pg. 
488
-
490
)
42
Pardanani
 
A
Lasho
 
TL
Finke
 
CM
Mai
 
M
McClure
 
RF
Tefferi
 
A
IDH1 and IDH2 mutation analysis in chronic- and blast-phase myeloproliferative neoplasms.
Leukemia
2010
, vol. 
24
 
6
(pg. 
1146
-
1151
)
43
Royer
 
Y
Staerk
 
J
Costuleanu
 
M
Courtoy
 
PJ
Constantinescu
 
SN
Janus kinases affect thrombopoietin receptor cell surface localization and stability.
J Biol Chem
2005
, vol. 
280
 
29
(pg. 
27251
-
27261
)
44
Meenhuis
 
A
Irandoust
 
M
Wolfler
 
A
Roovers
 
O
Valkhof
 
M
Touw
 
IP
Janus kinases promote cell-surface expression and provoke autonomous signalling from routing-defective G-CSF receptors.
Biochem J
2009
, vol. 
417
 
3
(pg. 
737
-
746
)
45
Lu
 
X
Huang
 
LJ
Lodish
 
HF
Dimerization by a cytokine receptor is necessary for constitutive activation of JAK2V617F.
J Biol Chem
2008
, vol. 
283
 
9
(pg. 
5258
-
5266
)
46
Lindauer
 
K
Loerting
 
T
Liedl
 
KR
Kroemer
 
RT
Prediction of the structure of human Janus kinase 2 (JAK2) comprising the two carboxy-terminal domains reveals a mechanism for autoregulation.
Protein Eng
2001
, vol. 
14
 
1
(pg. 
27
-
37
)
47
Plo
 
I
Vainchenker
 
W
Molecular and genetic bases of myeloproliferative disorders: questions and perspectives.
Clin Lymphoma Myeloma
2009
, vol. 
9
 
Suppl 3
(pg. 
S329
-
S339
)
48
Shi
 
S
Calhoun
 
HC
Xia
 
F
Li
 
J
Le
 
L
Li
 
WX
JAK signaling globally counteracts heterochromatic gene silencing.
Nat Genet
2006
, vol. 
38
 
9
(pg. 
1071
-
1076
)
49
Shi
 
S
Larson
 
K
Guo
 
D
et al. 
Drosophila STAT is required for directly maintaining HP1 localization and heterochromatin stability.
Nat Cell Biol
2008
, vol. 
10
 
4
(pg. 
489
-
496
)
50
Dawson
 
MA
Bannister
 
AJ
Gottgens
 
B
et al. 
JAK2 phosphorylates histone H3Y41 and excludes HP1alpha from chromatin.
Nature
2009
, vol. 
461
 
7265
(pg. 
819
-
822
)
51
Liu
 
F
Zhao
 
X
Perna
 
F
et al. 
JAK2V617F-mediated phosphorylation of PRMT5 downregulates its methyltransferase activity and promotes myeloproliferation.
Cancer Cell
2011
, vol. 
19
 
2
(pg. 
283
-
294
)
52
Dusa
 
A
Mouton
 
C
Pecquet
 
C
Herman
 
M
Constantinescu
 
SN
JAK2 V617F constitutive activation requires JH2 residue F595: a pseudokinase domain target for specific inhibitors.
PLoS One
2010
, vol. 
5
 
6
pg. 
e11157
 
53
Passamonti
 
F
Elena
 
C
Schnittger
 
S
et al. 
Molecular and clinical features of the myeloproliferative neoplasm associated with JAK2 exon 12 mutations [published online ahead of print January 11, 2011].
Blood
 
54
Staerk
 
J
Lacout
 
C
Sato
 
T
Smith
 
SO
Vainchenker
 
W
Constantinescu
 
SN
An amphipathic motif at the transmembrane-cytoplasmic junction prevents autonomous activation of the thrombopoietin receptor.
Blood
2006
, vol. 
107
 
5
(pg. 
1864
-
1871
)
55
Pecquet
 
C
Staerk
 
J
Chaligne
 
R
et al. 
Induction of myeloproliferative disorder and myelofibrosis by thrombopoietin receptor W515 mutants is mediated by cytosolic tyrosine 112 of the receptor.
Blood
2010
, vol. 
115
 
5
(pg. 
1037
-
1048
)
56
Pietra
 
D
Brisci
 
A
Rumi
 
E
et al. 
Deep sequencing reveals double mutations in cis of MPL exon 10 in myeloproliferative neoplasms.
Haematologica
2011
, vol. 
96
 
4
(pg. 
607
-
611
)
57
Lacout
 
C
Pisani
 
DF
Tulliez
 
M
Gachelin
 
FM
Vainchenker
 
W
Villeval
 
JL
JAK2V617F expression in murine hematopoietic cells leads to MPD mimicking human PV with secondary myelofibrosis.
Blood
2006
, vol. 
108
 
5
(pg. 
1652
-
1660
)
58
Wernig
 
G
Mercher
 
T
Okabe
 
R
Levine
 
RL
Lee
 
BH
Gilliland
 
DG
Expression of Jak2V617F causes a polycythemia vera-like disease with associated myelofibrosis in a murine bone marrow transplant model.
Blood
2006
, vol. 
107
 
11
(pg. 
4274
-
4281
)
59
Mullally
 
A
Lane
 
SW
Ball
 
B
et al. 
Physiological Jak2V617F expression causes a lethal myeloproliferative neoplasm with differential effects on hematopoietic stem and progenitor cells.
Cancer Cell
2010
, vol. 
17
 
6
(pg. 
584
-
596
)
60
Marty
 
C
Lacout
 
C
Martin
 
A
et al. 
Myeloproliferative neoplasm induced by constitutive expression of JAK2V617F in knock-in mice.
Blood
2010
, vol. 
116
 
5
(pg. 
783
-
787
)
61
Tiedt
 
R
Hao-Shen
 
H
Sobas
 
MA
et al. 
Ratio of mutant JAK2-V617F to wild-type Jak2 determines the MPD phenotypes in transgenic mice.
Blood
2008
, vol. 
111
 
8
(pg. 
3931
-
3940
)
62
Akada
 
H
Yan
 
D
Zou
 
H
Fiering
 
S
Hutchison
 
RE
Mohi
 
MG
Conditional expression of heterozygous or homozygous Jak2V617F from its endogenous promoter induces a polycythemia vera-like disease.
Blood
2010
, vol. 
115
 
17
(pg. 
3589
-
3597
)
63
Xing
 
S
Wanting
 
TH
Zhao
 
W
et al. 
Transgenic expression of JAK2V617F causes myeloproliferative disorders in mice.
Blood
2008
, vol. 
111
 
10
(pg. 
5109
-
5117
)
64
Li
 
J
Spensberger
 
D
Ahn
 
JS
et al. 
JAK2 V617F impairs hematopoietic stem cell function in a conditional knock-in mouse model of JAK2 V617F-positive essential thrombocythemia.
Blood
2010
, vol. 
116
 
9
(pg. 
1528
-
1538
)
65
Scott
 
LM
Scott
 
MA
Campbell
 
PJ
Green
 
AR
Progenitors homozygous for the V617F mutation occur in most patients with polycythemia vera, but not essential thrombocythemia.
Blood
2006
, vol. 
108
 
7
(pg. 
2435
-
2437
)
66
Dupont
 
S
Masse
 
A
James
 
C
et al. 
The JAK2 617V>F mutation triggers erythropoietin hypersensitivity and terminal erythroid amplification in primary cells from patients with polycythemia vera.
Blood
2007
, vol. 
110
 
3
(pg. 
1013
-
1021
)
67
Bumm
 
TG
Elsea
 
C
Corbin
 
AS
et al. 
Characterization of murine JAK2V617F-positive myeloproliferative disease.
Cancer Res
2006
, vol. 
66
 
23
(pg. 
11156
-
11165
)
68
Zaleskas
 
VM
Krause
 
DS
Lazarides
 
K
et al. 
Molecular pathogenesis and therapy of polycythemia induced in mice by JAK2 V617F.
PLoS One
2006
, vol. 
1
 
1
pg. 
e18
 
69
Chen
 
E
Beer
 
PA
Godfrey
 
AL
et al. 
Distinct clinical phenotypes associated with JAK2V617F reflect differential STAT1 signaling.
Cancer Cell
2010
, vol. 
18
 
5
(pg. 
524
-
535
)
70
Rudd
 
CE
Lnk adaptor: novel negative regulator of B cell lymphopoiesis.
Sci STKE
2001
, vol. 
2001
 
85
pg. 
pe1
 
71
Tong
 
W
Zhang
 
J
Lodish
 
HF
Lnk inhibits erythropoiesis and Epo-dependent JAK2 activation and downstream signaling pathways.
Blood
2005
, vol. 
105
 
12
(pg. 
4604
-
4612
)
72
Tong
 
W
Lodish
 
HF
Lnk inhibits Tpo-mpl signaling and Tpo-mediated megakaryocytopoiesis.
J Exp Med
2004
, vol. 
200
 
5
(pg. 
569
-
580
)
73
Simon
 
C
Dondi
 
E
Chaix
 
A
et al. 
Lnk adaptor protein down-regulates specific Kit-induced signaling pathways in primary mast cells.
Blood
2008
, vol. 
112
 
10
(pg. 
4039
-
4047
)
74
Takaki
 
S
Morita
 
H
Tezuka
 
Y
Takatsu
 
K
Enhanced hematopoiesis by hematopoietic progenitor cells lacking intracellular adaptor protein, Lnk.
J Exp Med
2002
, vol. 
195
 
2
(pg. 
151
-
160
)
75
Seita
 
J
Ema
 
H
Ooehara
 
J
et al. 
Lnk negatively regulates self-renewal of hematopoietic stem cells by modifying thrombopoietin-mediated signal transduction.
Proc Natl Acad Sci U S A
2007
, vol. 
104
 
7
(pg. 
2349
-
54
)
76
Yoshihara
 
H
Arai
 
F
Hosokawa
 
K
et al. 
Thrombopoietin/MPL signaling regulates hematopoietic stem cell quiescence and interaction with the osteoblastic niche.
Cell Stem Cell
2007
, vol. 
1
 
6
(pg. 
685
-
697
)
77
Qian
 
H
Buza-Vidas
 
N
Hyland
 
CD
et al. 
Critical role of thrombopoietin in maintaining adult quiescent hematopoietic stem cells.
Cell Stem Cell
2007
, vol. 
1
 
6
(pg. 
671
-
684
)
78
Velazquez
 
L
Cheng
 
AM
Fleming
 
HE
et al. 
Cytokine signaling and hematopoietic homeostasis are disrupted in Lnk-deficient mice.
J Exp Med
2002
, vol. 
195
 
12
(pg. 
1599
-
1611
)
79
Gery
 
S
Gueller
 
S
Chumakova
 
K
Kawamata
 
N
Liu
 
L
Koeffler
 
HP
Adaptor protein Lnk negatively regulates the mutant MPL, MPLW515L associated with myeloproliferative disorders.
Blood
2007
, vol. 
110
 
9
(pg. 
3360
-
3364
)
80
Bersenev
 
A
Wu
 
C
Balcerek
 
J
et al. 
Lnk constrains myeloproliferative diseases in mice.
J Clin Invest
2010
, vol. 
120
 
6
(pg. 
2058
-
2069
)
81
Baran-Marszak
 
F
Magdoud
 
H
Desterke
 
C
et al. 
Expression level and differential JAK2-V617F-binding of the adaptor protein Lnk regulates JAK2-mediated signals in myeloproliferative neoplasms.
Blood
2010
, vol. 
116
 
26
(pg. 
5961
-
5971
)
82
Schmidt
 
MH
Dikic
 
I
The Cbl interactome and its functions.
Nat Rev Mol Cell Biol
2005
, vol. 
6
 
12
(pg. 
907
-
918
)
83
Saur
 
SJ
Sangkhae
 
V
Geddis
 
AE
Kaushansky
 
K
Hitchcock
 
IS
Ubiquitination and degradation of the thrombopoietin receptor c-Mpl.
Blood
2010
, vol. 
115
 
6
(pg. 
1254
-
1263
)
84
Bacher
 
U
Haferlach
 
C
Schnittger
 
S
Kohlmann
 
A
Kern
 
W
Haferlach
 
T
Mutations of the TET2 and CBL genes: novel molecular markers in myeloid malignancies.
Ann Hematol
2010
, vol. 
89
 
7
(pg. 
643
-
652
)
85
Kales
 
SC
Ryan
 
PE
Nau
 
MM
Lipkowitz
 
S
Cbl and human myeloid neoplasms: the Cbl oncogene comes of age.
Cancer Res
2010
, vol. 
70
 
12
(pg. 
4789
-
4794
)
86
Rathinam
 
C
Thien
 
CB
Flavell
 
RA
Langdon
 
WY
Myeloid leukemia development in c-Cbl RING finger mutant mice is dependent on FLT3 signaling.
Cancer Cell
2010
, vol. 
18
 
4
(pg. 
341
-
352
)
87
Ogawa
 
S
Sanada
 
M
Shih
 
LY
et al. 
Gain-of-function c-CBL mutations associated with uniparental disomy of 11q in myeloid neoplasms.
Cell Cycle
2010
, vol. 
9
 
6
(pg. 
1051
-
1056
)
88
Sanada
 
M
Suzuki
 
T
Shih
 
LY
et al. 
Gain-of-function of mutated C-CBL tumour suppressor in myeloid neoplasms.
Nature
2009
, vol. 
460
 
7257
(pg. 
904
-
908
)
89
Naramura
 
M
Nandwani
 
N
Gu
 
H
Band
 
V
Band
 
H
Rapidly fatal myeloproliferative disorders in mice with deletion of Casitas B-cell lymphoma (Cbl) and Cbl-b in hematopoietic stem cells.
Proc Natl Acad Sci U S A
2010
, vol. 
107
 
37
(pg. 
16274
-
16279
)
90
Krebs
 
DL
Hilton
 
DJ
SOCS: physiological suppressors of cytokine signaling.
J Cell Sci
2000
, vol. 
113
 
Pt 16
(pg. 
2813
-
2819
)
91
Melzner
 
I
Bucur
 
AJ
Bruderlein
 
S
et al. 
Biallelic mutation of SOCS-1 impairs JAK2 degradation and sustains phospho-JAK2 action in the MedB-1 mediastinal lymphoma line.
Blood
2005
, vol. 
105
 
6
(pg. 
2535
-
2542
)
92
Calabrese
 
V
Mallette
 
FA
Deschenes-Simard
 
X
et al. 
SOCS1 links cytokine signaling to p53 and senescence.
Mol Cell
2009
, vol. 
36
 
5
(pg. 
754
-
767
)
93
Haan
 
S
Wuller
 
S
Kaczor
 
J
et al. 
SOCS-mediated downregulation of mutant Jak2 (V617F, T875N and K539L) counteracts cytokine-independent signaling.
Oncogene
2009
, vol. 
28
 
34
(pg. 
3069
-
3080
)
94
Hookham
 
MB
Elliott
 
J
Suessmuth
 
Y
et al. 
The myeloproliferative disorder-associated JAK2 V617F mutant escapes negative regulation by suppressor of cytokine signaling 3.
Blood
2007
, vol. 
109
 
11
(pg. 
4924
-
4929
)
95
Elliott
 
J
Suessmuth
 
Y
Scott
 
LM
et al. 
SOCS3 tyrosine phosphorylation as a potential bio-marker for myeloproliferative neoplasms associated with mutant JAK2 kinases.
Haematologica
2009
, vol. 
94
 
4
(pg. 
576
-
580
)
96
Najean
 
Y
Rain
 
JD
The very long-term evolution of polycythemia vera: an analysis of 318 patients initially treated by phlebotomy or 32P between 1969 and 1981.
Semin Hematol
1997
, vol. 
34
 
1
(pg. 
6
-
16
)
97
Campbell
 
PJ
Baxter
 
EJ
Beer
 
PA
et al. 
Mutation of JAK2 in the myeloproliferative disorders: timing, clonality studies, cytogenetic associations, and role in leukemic transformation.
Blood
2006
, vol. 
108
 
10
(pg. 
3548
-
3555
)
98
Mesa
 
RA
Li
 
CY
Ketterling
 
RP
Schroeder
 
GS
Knudson
 
RA
Tefferi
 
A
Leukemic transformation in myelofibrosis with myeloid metaplasia: a single-institution experience with 91 cases.
Blood
2005
, vol. 
105
 
3
(pg. 
973
-
977
)
99
Thoennissen
 
NH
Krug
 
UO
Lee
 
DH
et al. 
Prevalence and prognostic impact of allelic imbalances associated with leukemic transformation of Philadelphia chromosome-negative myeloproliferative neoplasms.
Blood
2010
, vol. 
115
 
14
(pg. 
2882
-
2890
)
100
Dang
 
L
Jin
 
S
Su
 
SM
IDH mutations in glioma and acute myeloid leukemia.
Trends Mol Med
2010
, vol. 
16
 
9
(pg. 
387
-
397
)
101
Yen
 
KE
Bittinger
 
MA
Su
 
SM
Fantin
 
VR
Cancer-associated IDH mutations: biomarker and therapeutic opportunities.
Oncogene
2010
, vol. 
29
 
49
(pg. 
6409
-
6417
)
102
Abbas
 
S
Lugthart
 
S
Kavelaars
 
FG
et al. 
Acquired mutations in the genes encoding IDH1 and IDH2 both are recurrent aberrations in acute myeloid leukemia: prevalence and prognostic value.
Blood
2010
, vol. 
116
 
12
(pg. 
2122
-
2126
)
103
Schnittger
 
S
Haferlach
 
C
Ulke
 
M
Alpermann
 
T
Kern
 
W
Haferlach
 
T
IDH1 mutations are detected in 6.6% of 1414 AML patients and are associated with intermediate risk karyotype and unfavorable prognosis in adults younger than 60 years and unmutated NPM1 status.
Blood
2010
, vol. 
116
 
25
(pg. 
5486
-
5496
)
104
Figueroa
 
ME
Abdel-Wahab
 
O
Lu
 
C
et al. 
Leukemic IDH1 and IDH2 mutations result in a hypermethylation phenotype, disrupt TET2 function, and impair hematopoietic differentiation.
Cancer Cell
2010
, vol. 
18
 
6
(pg. 
553
-
567
)
105
Georgopoulos
 
K
Haematopoietic cell-fate decisions, chromatin regulation and ikaros.
Nat Rev Immunol
2002
, vol. 
2
 
3
(pg. 
162
-
174
)
106
Mullighan
 
C
Downing
 
J
Ikaros and acute leukemia.
Leuk Lymphoma
2008
, vol. 
49
 
5
(pg. 
847
-
849
)
107
Haferlach
 
C
Dicker
 
F
Herholz
 
H
Schnittger
 
S
Kern
 
W
Haferlach
 
T
Mutations of the TP53 gene in acute myeloid leukemia are strongly associated with a complex aberrant karyotype.
Leukemia
2008
, vol. 
22
 
8
(pg. 
1539
-
1541
)
108
Beer
 
PA
Ortmann
 
CA
Campbell
 
PJ
Green
 
AR
Independently acquired biallelic JAK2 mutations are present in a minority of patients with essential thrombocythemia.
Blood
2010
, vol. 
116
 
6
(pg. 
1013
-
1014
)
109
Beer
 
PA
Ortmann
 
CA
Stegelmann
 
F
et al. 
Molecular mechanisms associated with leukemic transformation of MPL-mutant myeloproliferative neoplasms.
Haematologica
2010
, vol. 
95
 
12
(pg. 
2153
-
2156
)
110
Harada
 
Y
Harada
 
H
Molecular pathways mediating MDS/AML with focus on AML1/RUNX1 point mutations.
J Cell Physiol
2009
, vol. 
220
 
1
(pg. 
16
-
20
)
111
Bellanné-Chantelot
 
C
Chaumarel
 
I
Labopin
 
M
et al. 
Genetic and clinical implications of the Val617Phe JAK2 mutation in 72 families with myeloproliferative disorders.
Blood
2006
, vol. 
108
 
1
(pg. 
346
-
352
)
112
Olcaydu
 
D
Rumi
 
E
Harutyunyan
 
A
et al. 
The role of the JAK2 GGCC haplotype and the TET2 gene in familial myeloproliferative neoplasms.
Haematologica
2011
, vol. 
96
 
3
(pg. 
367
-
374
)
113
Posthuma
 
HL
Skoda
 
RC
Jacob
 
FA
van der Maas
 
AP
Valk
 
PJ
Posthuma
 
EF
Hereditary thrombocytosis not as innocent as thought? Development into acute leukemia and myelofibrosis.
Blood
2010
, vol. 
116
 
17
(pg. 
3375
-
3376
)
114
Levine
 
RL
Belisle
 
C
Wadleigh
 
M
et al. 
X-inactivation-based clonality analysis and quantitative JAK2V617F assessment reveal a strong association between clonality and JAK2V617F in PV but not ET/MMM, and identifies a subset of JAK2V617F-negative ET and MMM patients with clonal hematopoiesis.
Blood
2006
, vol. 
107
 
10
(pg. 
4139
-
4141
)
115
Nussenzveig
 
RH
Swierczek
 
SI
Jelinek
 
J
et al. 
Polycythemia vera is not initiated by JAK2V617F mutation.
Exp Hematol
2007
, vol. 
35
 
1
(pg. 
32
-
38
)
116
Kralovics
 
R
Teo
 
SS
Li
 
S
et al. 
Acquisition of the V617F mutation of JAK2 is a late genetic event in a subset of patients with myeloproliferative disorders.
Blood
2006
, vol. 
108
 
4
(pg. 
1377
-
1380
)
117
Theocharides
 
A
Boissinot
 
M
Girodon
 
F
et al. 
Leukemic blasts in transformed JAK2-V617F-positive myeloproliferative disorders are frequently negative for the JAK2-V617F mutation.
Blood
2007
, vol. 
110
 
1
(pg. 
375
-
379
)
118
Moliterno
 
AR
Williams
 
DM
Rogers
 
O
Isaacs
 
MA
Spivak
 
JL
Phenotypic variability within the JAK2 V617F-positive MPD: roles of progenitor cell and neutrophil allele burdens.
Exp Hematol
2008
, vol. 
36
 
11
(pg. 
1480
-
1486
)
119
James
 
C
Mazurier
 
F
Dupont
 
S
et al. 
The hematopoietic stem cell compartment of JAK2V617F-positive myeloproliferative disorders is a reflection of disease heterogeneity.
Blood
2008
, vol. 
112
 
6
(pg. 
2429
-
2438
)
120
Stein
 
BL
Williams
 
DM
Rogers
 
O
Isaacs
 
MA
Spivak
 
JL
Moliterno
 
AR
Disease burden at the progenitor level is a feature of primary myelofibrosis: a multivariable analysis of 164 JAK2 V617F-positive myeloproliferative neoplasm patients.
Exp Hematol
2011
, vol. 
39
 
1
(pg. 
95
-
101
)
121
Sauvageau
 
M
Sauvageau
 
G
Polycomb group proteins: multi-faceted regulators of somatic stem cells and cancer.
Cell Stem Cell
2010
, vol. 
7
 
3
(pg. 
299
-
313
)
122
De Haan
 
G
Gerrits
 
A
Epigenetic control of hematopoietic stem cell aging the case of Ezh2.
Ann N Y Acad Sci
2007
, vol. 
1106
 (pg. 
233
-
239
)
123
Cao
 
R
Zhang
 
Y
The functions of E(Z)/EZH2-mediated methylation of lysine 27 in histone H3.
Curr Opin Genet Dev
2004
, vol. 
14
 
2
(pg. 
155
-
164
)
124
Martinez-Garcia
 
E
Licht
 
JD
Deregulation of H3K27 methylation in cancer.
Nat Genet
2010
, vol. 
42
 
2
(pg. 
100
-
101
)
125
Viré
 
E
Brenner
 
C
Deplus
 
R
et al. 
The Polycomb group protein EZH2 directly controls DNA methylation.
Nature
2006
, vol. 
439
 
7078
(pg. 
871
-
874
)
126
Simon
 
JA
Lange
 
CA
Roles of the EZH2 histone methyltransferase in cancer epigenetics.
Mutat Res
2008
, vol. 
647
 
1–2
(pg. 
21
-
29
)
127
Morin
 
RD
Johnson
 
NA
Severson
 
TM
et al. 
Somatic mutations altering EZH2 (Tyr641) in follicular and diffuse large B-cell lymphomas of germinal-center origin.
Nat Genet
2010
, vol. 
42
 
2
(pg. 
181
-
185
)
128
Fisher
 
CL
Lee
 
I
Bloyer
 
S
et al. 
Additional sex combs-like 1 belongs to the enhancer of trithorax and polycomb group and genetically interacts with Cbx2 in mice.
Dev Biol
2010
, vol. 
337
 
1
(pg. 
9
-
15
)
129
Scheuermann
 
JC
de Ayala Alonso
 
AG
Oktaba
 
K
et al. 
Histone H2A deubiquitinase activity of the Polycomb repressive complex PR-DUB.
Nature
2010
, vol. 
465
 
7295
(pg. 
243
-
247
)
130
Gelsi-Boyer
 
V
Trouplin
 
V
Adelaide
 
J
et al. 
Mutations of polycomb-associated gene ASXL1 in myelodysplastic syndromes and chronic myelomonocytic leukaemia.
Br J Haematol
2009
, vol. 
145
 
6
(pg. 
788
-
800
)
131
Abdel-Wahab
 
O
Kilpivaara
 
O
Patel
 
J
Busque
 
L
Levine
 
RL
The most commonly reported variant in ASXL1 (c. 1934dupG; p.Gly646TrpfsX12) is not a somatic alteration.
Leukemia
2010
, vol. 
24
 
9
(pg. 
1656
-
1657
)
132
Fisher
 
CL
Pineault
 
N
Brookes
 
C
et al. 
Loss-of-function Additional sex combs like 1 mutations disrupt hematopoiesis but do not cause severe myelodysplasia or leukemia.
Blood
2010
, vol. 
115
 
1
(pg. 
38
-
46
)
133
Ito
 
S
D'Alessio
 
AC
Taranova
 
OV
Hong
 
K
Sowers
 
LC
Zhang
 
Y
Role of Tet proteins in 5mC to 5hmC conversion, ES-cell self-renewal and inner cell mass specification.
Nature
2010
, vol. 
466
 
7310
(pg. 
1129
-
1133
)
134
Loenarz
 
C
Schofield
 
CJ
Oxygenase catalyzed 5-methylcytosine hydroxylation.
Chem Biol
2009
, vol. 
16
 
6
(pg. 
580
-
583
)
135
Tahiliani
 
M
Koh
 
KP
Shen
 
Y
et al. 
Conversion of 5-methylcytosine to 5-hydroxymethylcytosine in mammalian DNA by MLL partner TET1.
Science
2009
, vol. 
324
 
5929
(pg. 
930
-
935
)
136
Globisch
 
D
Munzel
 
M
Muller
 
M
et al. 
Tissue distribution of 5-hydroxymethylcytosine and search for active demethylation intermediates.
PLoS One
2010
, vol. 
5
 
12
pg. 
e15367
 
137
Szwagierczak
 
A
Bultmann
 
S
Schmidt
 
CS
Spada
 
F
Leonhardt
 
H
Sensitive enzymatic quantification of 5-hydroxymethylcytosine in genomic DNA.
Nucleic Acids Res
2010
, vol. 
38
 
19
pg. 
e181
 
138
Song
 
CX
Szulwach
 
KE
Fu
 
Y
et al. 
Selective chemical labeling reveals the genome-wide distribution of 5-hydroxymethylcytosine.
Nat Biotechnol
2011
, vol. 
29
 
1
(pg. 
68
-
72
)
139
Koh
 
KP
Yabuuchi
 
A
Rao
 
S
et al. 
Tet1 and Tet2 regulate 5-Hydroxymethylcytosine production and cell lineage specification in mouse embryonic stem cells.
Cell Stem Cell
2011
, vol. 
8
 (pg. 
200
-
213
)
140
Lorsbach
 
RB
Moore
 
J
Mathew
 
S
Raimondi
 
SC
Mukatira
 
ST
Downing
 
JR
TET1, a member of a novel protein family, is fused to MLL in acute myeloid leukemia containing the t(10;11)(q22;q23).
Leukemia
2003
, vol. 
17
 
3
(pg. 
637
-
641
)
141
Ono
 
R
Taki
 
T
Taketani
 
T
Taniwaki
 
M
Kobayashi
 
H
Hayashi
 
Y
LCX, leukemia-associated protein with a CXXC domain, is fused to MLL in acute myeloid leukemia with trilineage dysplasia having t(10;11)(q22;q23).
Cancer Res
2002
, vol. 
62
 
14
(pg. 
4075
-
4080
)
142
Ko
 
M
Huang
 
Y
Jankowska
 
AM
et al. 
Impaired hydroxylation of 5-methylcytosine in myeloid cancers with mutant TET2.
Nature
2010
, vol. 
468
 
7325
(pg. 
839
-
843
)
143
Tefferi
 
A
Pardanani
 
A
Lim
 
KH
et al. 
TET2 mutations and their clinical correlates in polycythemia vera, essential thrombocythemia and myelofibrosis.
Leukemia
2009
, vol. 
23
 
5
(pg. 
905
-
911
)
144
Schaub
 
FX
Looser
 
R
Li
 
S
et al. 
Clonal analysis of TET2 and JAK2 mutations suggests that TET2 can be a late event in the progression of myeloproliferative neoplasms.
Blood
2010
, vol. 
115
 
10
(pg. 
2003
-
2007
)
145
Swierczek
 
SI
Yoon
 
D
Bellanne'-Chantelot
 
C
et al. 
Extent of hematopoietic involvement by TET2 mutations in JAK2V617F polycythemia vera.
Haematologica
2011
, vol. 
96
 
5
(pg. 
775
-
778
)
146
Saint-Martin
 
C
Leroy
 
G
Delhommeau
 
F
et al. 
Analysis of the ten-eleven translocation 2 (TET2) gene in familial myeloproliferative neoplasms.
Blood
2009
, vol. 
114
 
8
(pg. 
1628
-
1632
)
147
Abdel-Wahab
 
O
Manshouri
 
T
Patel
 
J
et al. 
Genetic analysis of transforming events that convert chronic myeloproliferative neoplasms to leukemias.
Cancer Res
2010
, vol. 
70
 
2
(pg. 
447
-
452
)
148
Perna
 
F
Gurvich
 
N
Hoya-Arias
 
R
et al. 
Depletion of L3MBTL1 promotes the erythroid differentiation of human hematopoietic progenitor cells: possible role in 20q- polycythemia vera.
Blood
2010
, vol. 
116
 
15
(pg. 
2812
-
2821
)
149
Ley
 
TJ
Ding
 
L
Walter
 
MJ
et al. 
DNMT3A mutations in acute myeloid leukemia.
N Engl J Med
2010
, vol. 
363
 
25
(pg. 
2424
-
2433
)
150
Kearney
 
L
Gonzalez De Castro
 
D
Yeung
 
J
et al. 
Specific JAK2 mutation (JAK2R683) and multiple gene deletions in Down syndrome acute lymphoblastic leukemia.
Blood
2009
, vol. 
113
 
3
(pg. 
646
-
648
)
151
Mullighan
 
CG
Zhang
 
J
Harvey
 
RC
et al. 
JAK mutations in high-risk childhood acute lymphoblastic leukemia.
Proc Natl Acad Sci U S A
2009
, vol. 
106
 
23
(pg. 
9414
-
9418
)
152
Malinge
 
S
Ben-Abdelali
 
R
Settegrana
 
C
et al. 
Novel activating JAK2 mutation in a patient with Down syndrome and B-cell precursor acute lymphoblastic leukemia.
Blood
2007
, vol. 
109
 
5
(pg. 
2202
-
2204
)
153
Malinge
 
S
Ragu
 
C
Della-Valle
 
V
et al. 
Activating mutations in human acute megakaryoblastic leukemia.
Blood
2008
, vol. 
112
 
10
(pg. 
4220
-
4226
)
154
Boultwood
 
J
Perry
 
J
Pellagatti
 
A
et al. 
Frequent mutation of the polycomb-associated gene ASXL1 in the myelodysplastic syndromes and in acute myeloid leukemia.
Leukemia
2010
, vol. 
24
 
5
(pg. 
1062
-
1065
)
155
Plo
 
I
Zhang
 
Y
Le Couedic
 
JP
et al. 
An activating mutation in the CSF3R gene induces a hereditary chronic neutrophilia.
J Exp Med
2009
, vol. 
206
 
8
(pg. 
1701
-
1707
)
156
Ding
 
J
Komatsu
 
H
Wakita
 
A
et al. 
Familial essential thrombocythemia associated with a dominant-positive activating mutation of the c-MPL gene, which encodes for the receptor for thrombopoietin.
Blood
2004
, vol. 
103
 
11
(pg. 
4198
-
4200
)
157
Skoda
 
RC
Thrombocytosis.
Hematology Am Soc Hematol Educ Program
2009
(pg. 
159
-
167
)
158
de la Chapelle
 
A
Sistonen
 
P
Lehvaslaiho
 
H
Ikkala
 
E
Juvonen
 
E
Familial erythrocytosis genetically linked to erythropoietin receptor gene.
Lancet
1993
, vol. 
341
 
8837
(pg. 
82
-
84
)
159
de la Chapelle
 
A
Traskelin
 
AL
Juvonen
 
E
Truncated erythropoietin receptor causes dominantly inherited benign human erythrocytosis.
Proc Natl Acad Sci U S A
1993
, vol. 
90
 
10
(pg. 
4495
-
4499
)
160
Prchal
 
JT
Sokol
 
L
“Benign erythrocytosis” and other familial and congenital polycythemias.
Eur J Haematol
1996
, vol. 
57
 
4
(pg. 
263
-
268
)
161
Sokol
 
L
Luhovy
 
M
Guan
 
Y
Prchal
 
JF
Semenza
 
GL
Prchal
 
JT
Primary familial polycythemia: a frameshift mutation in the erythropoietin receptor gene and increased sensitivity of erythroid progenitors to erythropoietin.
Blood
1995
, vol. 
86
 
1
(pg. 
15
-
22
)
162
Haeno
 
H
Levine
 
RL
Gilliland
 
DG
Michor
 
F
A progenitor cell origin of myeloid malignancies.
Proc Natl Acad Sci U S A
2009
, vol. 
106
 
39
(pg. 
16616
-
16621
)
163
Vickers
 
MA
JAK2 617V>F positive polycythemia rubra vera maintained by approximately 18 stochastic stem-cell divisions per year, explaining age of onset by a single rate-limiting mutation.
Blood
2007
, vol. 
110
 
5
(pg. 
1675
-
1680
)
164
Catlin
 
SN
Guttorp
 
P
Abkowitz
 
JL
The kinetics of clonal dominance in myeloproliferative disorders.
Blood
2005
, vol. 
106
 
8
(pg. 
2688
-
2692
)
165
Fung
 
TK
Cheung
 
AM
Kwong
 
YL
Liang
 
R
Leung
 
AY
Differential NOD/SCID mouse engraftment of peripheral blood CD34+ cells and JAK2V617F clones from patients with myeloproliferative neoplasms.
Leuk Res
2010
, vol. 
34
 
10
(pg. 
1390
-
1394
)
166
Ishii
 
T
Zhao
 
Y
Sozer
 
S
et al. 
Behavior of CD34+ cells isolated from patients with polycythemia vera in NOD/SCID mice.
Exp Hematol
2007
, vol. 
35
 
11
(pg. 
1633
-
1640
)
167
Van Pelt
 
K
Nollet
 
F
Selleslag
 
D
et al. 
The JAK2V617F mutation can occur in a hematopoietic stem cell that exhibits no proliferative advantage: a case of human allogeneic transplantation.
Blood
2008
, vol. 
112
 
3
(pg. 
921
-
922
)
168
Rongvaux
 
A
Willinger
 
T
Takizawa
 
H
et al. 
Human thrombopoietin knockin mice efficiently support human hematopoiesis in vivo.
Proc Natl Acad Sci U S A
2011
, vol. 
108
 
6
(pg. 
2378
-
2383
)
169
de Graaf
 
CA
Kauppi
 
M
Baldwin
 
T
et al. 
Regulation of hematopoietic stem cells by their mature progeny.
Proc Natl Acad Sci U S A
2010
, vol. 
107
 
50
(pg. 
21689
-
21694
)
170
Kaushansky
 
K
Thrombopoietin: accumulating evidence for an important biological effect on the hematopoietic stem cell.
Ann N Y Acad Sci
2003
, vol. 
996
 (pg. 
39
-
43
)
171
Bumm
 
TGP
VanDyke
 
J
Loriaux
 
M
et al. 
TNF-alpha plays a crucial role in the JAK2-V617F induced myeloproliferative disorder.
Blood
2007
, vol. 
110
 
11
pg. 
675
 
172
Jäger
 
R
Kralovics
 
R
Molecular pathogenesis of philadelphia chromosome negative chronic myeloproliferative neoplasms.
Curr Cancer Drug Targets
2011
, vol. 
11
 
1
(pg. 
20
-
30
)
173
Beer
 
PA
Erber
 
WN
Campbell
 
PJ
Green
 
AR
How we treat essential thrombocythemia.
Blood
2011
, vol. 
117
 
5
(pg. 
1472
-
1482
)
174
Bocchia
 
M
Vannucchi
 
AM
Gozzetti
 
A
et al. 
Insights into JAK2-V617F mutation in CML.
Lancet Oncol
2007
, vol. 
8
 
10
(pg. 
864
-
865
)
175
Bornhäuser
 
M
Mohr
 
B
Oelschlaegel
 
U
et al. 
Concurrent JAK2(V617F) mutation and BCR-ABL translocation within committed myeloid progenitors in myelofibrosis.
Leukemia
2007
, vol. 
21
 
8
(pg. 
1824
-
1826
)
176
Büsche
 
G
Hussein
 
K
Bock
 
O
Kreipe
 
H
Insights into JAK2-V617F mutation in CML.
Lancet Oncol
2007
, vol. 
8
 
10
(pg. 
863
-
864
)
177
Cambier
 
N
Renneville
 
A
Cazaentre
 
T
et al. 
JAK2V617F-positive polycythemia vera and Philadelphia chromosome-positive chronic myeloid leukemia: one patient with two distinct myeloproliferative disorders.
Leukemia
2008
, vol. 
22
 
7
(pg. 
1454
-
1455
)
178
Hussein
 
K
Bock
 
O
Theophile
 
K
et al. 
Biclonal expansion and heterogeneous lineage involvement in a case of chronic myeloproliferative disease with concurrent MPLW515L/JAK2V617F mutation.
Blood
2009
, vol. 
113
 
6
(pg. 
1391
-
1392
)
179
Lambert
 
JR
Everington
 
T
Linch
 
DC
Gale
 
RE
In essential thrombocythemia, multiple JAK2-V617F clones are present in most mutant-positive patients: a new disease paradigm.
Blood
2009
, vol. 
114
 
14
(pg. 
3018
-
3023
)
180
Couronné
 
L
Lippert
 
E
Andrieux
 
J
et al. 
Analyses of TET2 mutations in post-myeloproliferative neoplasm acute myeloid leukemias.
Leukemia
2010
, vol. 
24
 
1
(pg. 
201
-
203
)
181
Raaijmakers
 
MH
Mukherjee
 
S
Guo
 
S
et al. 
Bone progenitor dysfunction induces myelodysplasia and secondary leukaemia.
Nature
2010
, vol. 
464
 
7290
(pg. 
852
-
857
)
182
Lataillade
 
JJ
Pierre-Louis
 
O
Hasselbalch
 
HC
et al. 
Does primary myelofibrosis involve a defective stem cell niche? From concept to evidence.
Blood
2008
, vol. 
112
 
8
(pg. 
3026
-
3035
)
183
Landgren
 
O
Goldin
 
LR
Kristinsson
 
SY
Helgadottir
 
EA
Samuelsson
 
J
Bjorkholm
 
M
Increased risks of polycythemia vera, essential thrombocythemia, and myelofibrosis among 24,577 first-degree relatives of 11,039 patients with myeloproliferative neoplasms in Sweden.
Blood
2008
, vol. 
112
 
6
(pg. 
2199
-
2204
)
184
Jones
 
AV
Chase
 
A
Silver
 
RT
et al. 
JAK2 haplotype is a major risk factor for the development of myeloproliferative neoplasms.
Nat Genet
2009
, vol. 
41
 
4
(pg. 
446
-
449
)
185
Olcaydu
 
D
Harutyunyan
 
A
Jager
 
R
et al. 
A common JAK2 haplotype confers susceptibility to myeloproliferative neoplasms.
Nat Genet
2009
, vol. 
41
 
4
(pg. 
450
-
454
)
186
Kilpivaara
 
O
Mukherjee
 
S
Schram
 
AM
et al. 
A germline JAK2 SNP is associated with predisposition to the development of JAK2(V617F)-positive myeloproliferative neoplasms.
Nat Genet
2009
, vol. 
41
 
4
(pg. 
455
-
459
)
187
Jones
 
AV
Campbell
 
PJ
Beer
 
PA
et al. 
The JAK2 46/1 haplotype predisposes to MPL-mutated myeloproliferative neoplasms.
Blood
2010
, vol. 
115
 
22
(pg. 
4517
-
4523
)
188
Verstovsek
 
S
Janus-activated kinase 2 inhibitors: a new era of targeted therapies providing significant clinical benefit for Philadelphia chromosome-negative myeloproliferative neoplasms.
J Clin Oncol
2011
, vol. 
29
 
7
(pg. 
781
-
783
)
189
Verstovsek
 
S
Kantarjian
 
H
Mesa
 
RA
et al. 
Safety and efficacy of INCB018424, a JAK1 and JAK2 inhibitor, in myelofibrosis.
N Engl J Med
2010
, vol. 
363
 
12
(pg. 
1117
-
1127
)
190
Tefferi
 
A
How I treat myelofibrosis.
Blood
2011
, vol. 
117
 
13
(pg. 
3494
-
3504
)
191
Tefferi
 
A
Vainchenker
 
W
Myeloproliferative neoplasms: molecular pathophysiology, essential clinical understanding, and treatment strategies.
J Clin Oncol
2011
, vol. 
29
 
5
(pg. 
573
-
582
)
192
Geron
 
I
Abrahamsson
 
AE
Barroga
 
CF
et al. 
Selective inhibition of JAK2-driven erythroid differentiation of polycythemia vera progenitors.
Cancer Cell
2008
, vol. 
13
 
4
(pg. 
321
-
330
)
193
Wernig
 
G
Kharas
 
MG
Okabe
 
R
et al. 
Efficacy of TG101348, a selective JAK2 inhibitor, in treatment of a murine model of JAK2V617F-induced polycythemia vera.
Cancer Cell
2008
, vol. 
13
 
4
(pg. 
311
-
320
)
194
Kiladjian
 
JJ
Masse
 
A
Cassinat
 
B
et al. 
Clonal analysis of erythroid progenitors suggests that pegylated interferon alpha-2a treatment targets JAK2V617F clones without affecting TET2 mutant cells.
Leukemia
2010
, vol. 
24
 
8
(pg. 
1519
-
1523
)
195
Wang
 
Y
Fiskus
 
W
Chong
 
DG
et al. 
Cotreatment with panobinostat and JAK2 inhibitor TG101209 attenuates JAK2V617F levels and signaling and exerts synergistic cytotoxic effects against human myeloproliferative neoplastic cells.
Blood
2009
, vol. 
114
 
24
(pg. 
5024
-
5033
)
196
Rambaldi
 
A
Dellacasa
 
CM
Finazzi
 
G
et al. 
A pilot study of the Histone-Deacetylase inhibitor Givinostat in patients with JAK2V617F positive chronic myeloproliferative neoplasms.
Br J Haematol
2010
, vol. 
150
 
4
(pg. 
446
-
455
)
197
Wang
 
X
Zhang
 
W
Ishii
 
T
et al. 
Correction of the abnormal trafficking of primary myelofibrosis CD34+ cells by treatment with chromatin-modifying agents.
Cancer Res
2009
, vol. 
69
 
19
(pg. 
7612
-
7618
)
198
Wang
 
X
Zhang
 
W
Tripodi
 
J
et al. 
Sequential treatment of CD34+ cells from patients with primary myelofibrosis with chromatin-modifying agents eliminate JAK2V617F-positive NOD/SCID marrow repopulating cells.
Blood
2010
, vol. 
116
 
26
(pg. 
5972
-
5982
)
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