There is a need to identify underlying molecular mechanisms and gene products (targets for intervention and biomarkers) involved in MM chemo- or immuno-resistance. Recent findings from our laboratory have reported high expression of the transcription factor Yin Yang 1 (YY1) in several tumor types and have demonstrated its fundamental role in tumor cell chemo/immuno-resistance (

Gordon, S., et al.,
). In contrast, low levels of the Raf kinase inhibitor protein (RKIP) has been shown to play a pivotal role in the negative regulation of cell survival signaling pathways, and has been considered a metastasis tumor suppressor. The overall objective of our studies is to examine whether MM cell lines and tissues derived from MM patients present deregulated expression patterns of RKIP and YY1, and to demonstrate the roles of YY1 and RKIP in MM pathogenesis and response to various therapies. In the present study, the myeloma cell lines RPMI-8226 and MM-1S were screened for RKIP and YY1 expression at the protein and m-RNA levels. In addition, fresh tissues from MM patients were also examined for RKIP and YY1 expression by IHC and their patterns compared with those observed in normal bone marrow cells. The findings demonstrate that both MM cell lines express remarkably higher levels of RKIP protein and transcripts compared to other tumor cell lines examined (lymphomas and prostate cancer), as assessed by western, RT-PCR and IHC. There was significantly higher expression of RKIP in MM patient’s samples compared to normal bone marrow cells. YY1 protein and m-RNA levels were detected in the MM cell lines; however, they were lower compared to Ramos and PC-3 cells. YY1 expression in MM tissues was significantly elevated compared to normal bone marrow cells. RKIP was basically present in the cytoplasm while YY1 was mainly accumulated in the nucleus. In contrast, normal bone marrow cells presented primarily cytoplasmic YY1 and RKIP expression. The YY1 expressing population was the CD38+/CD138− cell subset, which has been reported to be more susceptible to apoptosis (Mitsiadis, S.C., et al., Blood 98:795, 2001). Overall, the present findings support the potential involvement of two new gene products, such as YY1 and RKIP, in MM pathogenesis and their implication in regulating MM resistance to conventional therapeutics. Moreover, these gene products suggest their potential use as new therapeutic targets and/or biomarkers in multiple myeloma. Future studies with large cohorts of tissues will elucidate the importance of the above findings and will give new insights in the unexpected RKIP over expression and activity in multiple myeloma.

Supported in part by gifts from JCCC Rosenfield Fund under the directorship of David Leveton and by the Institute for Myeloma and Bone Cancer Research, West Hollywood, CA, USA.

Disclosure: No relevant conflicts of interest to declare.

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