Runx2 Suppression by miR-342 and miR-363 Inhibits Multiple Myeloma Progression

In multiple myeloma, abnormal plasma cells accumulate and proliferate in the bone marrow. Recently, we observed that Runx2, a bone-specific transcription factor, is highly expressed in multiple myeloma cells and is a major driver of multiple myeloma progression in bone. The primary goal of the present study was to identify Runx2-targeting miRNAs that can reduce tumor growth. Expression analysis of a panel of miRNAs in multiple myeloma patient specimens, compared with healthy control specimens, revealed that metastatic multiple myeloma cells express low levels of miR-342 and miR-363 but high levels of Runx2. Reconstituting multiple myeloma cells (CAG) with miR-342 and miR-363 reduced the abundance of Runx2 and the expression of metastasis-promoting Runx2 target genes RANKL and DKK1, and suppressed Runx2 downstream signaling pathways Akt/b-catenin/survivin, which are required for multiple myeloma tumor progression. Intravenous injection of multiple myeloma cells (5TGM1), stably overexpressing miR-342 and miR-363 alone or together, into syngeneic C57Bl/KaLwRij mice resulted in a significant suppression of 5TGM1 cell growth, decreased osteoclasts and increased osteoblasts, and increased antitumor immunity in the bone marrow, compared with mice injected with 5TGM1 cells expressing a miR-Scramble control. In summary, these results demonstrate that enhanced expression of miR-342 and miR-363 in multiple myeloma cells inhibits Runx2 expression and multiple myeloma growth, decreases osteolysis, and enhances antitumor immunity. Thus, restoring the function of Runx2-targeting by miR-342 and miR-363 in multiple myeloma cells may afford a therapeutic benefit by preventing multiple myeloma progression. Implications: miR-342 and miR-363-mediated downregulation of Runx2 expression in multiple myeloma cells prevents multiple myeloma progression.