Polycomb-like Protein 3 Induces Proliferation and Drug Resistance in Multiple Myeloma and Is Regulated by miRNA-15a

Multiple myeloma remains incurable due to the persistence of a minor population of multiple myeloma cells that exhibit drug resistance, which leads to relapsed and/or refractory multiple myeloma. Elucidating the mechanism underlying drug resistance and developing an effective treatment are critical for clinical management of multiple myeloma. Here we showed that promoting expression of the gene for polycomb-like protein 3 (PHF19) induced multiple myeloma cell growth and multidrug resistance in vitro and in vivo. PHF19 was overexpressed in high-risk and drug-resistant primary cells from patients. High levels of PHF19 were correlated with inferior survival of patients with multiple myeloma, in the Total Therapy 2 cohort and in the Intergroup Francophone du Myeloma (IFM) cohort. Enhancing PHF19 expression levels increased Bcl-xL, Mcl-1, and HIF-1a expression in multiple myeloma cells. PHF19 also bound directly with EZH2 and promoted the phosphorylation of EZH2 through PDK1/AKT signaling. miR-15a is a small noncoding RNA that targeted the 3'UTR of PHF19. We found that downregulation of miR-15a led to high levels of PHF19 in multiple myeloma cells. These findings revealed that PHF19 served a crucial role in multiple myeloma proliferation and drug resistance and suggested that the miR-15a/PHF19/EZH2 pathway made a pivotal contribution to multiple myeloma pathogenesis, offering a promising approach to multiple myeloma treatment. IMPLICATIONS: Our findings identify that PHF19 mediates EZH2 phosphorylation as a mechanism of myeloma cell drug resistance, providing a rationale to explore therapeutic potential of targeting PHF19 in relapsed or refractory patients with multiple myeloma.