miR-137 suppresses the phosphorylation of AKT and improves the dexamethasone sensitivity in multiple myeloma cells via targeting MITF.

Background: Multiple myeloma (MM), a clonal B cell malignancy characterized by the proliferation of plasma cells within the bone marrow, is still an incurable disease, and therefore, finding new therapeutic targets is urgently required. Although microRNA-137 (miR-137), which is involved in a variety of cellular processes, has been reported to be under-expressed in many types of solid tumors, its role in MM is less known. Methods: In this study, the target gene and the potential effect of miR-137 in MM were investigated.  Results: The results showed significantly down regulated expression of miR-137 in MM cell lines and in the CD138+ bone marrow mononuclear cells of MM patients. A dual luciferase reporter gene analysis revealed that MITF is a direct target of miR-137. The overexpression of miR-137 or transfection of MITF-shRNA had no significant effect on the expression of serine/ threonine protein kinase (AKT), but the expression of MITF, c-MET, p-AKT, and its phosphorylated substrate protein decreased significantly, which was accompanied by an increase in p53 expression. In addition, the overexpression of miR-137 or MITF-shRNA significantly improved the 36-hour inhibition rate and apoptosis rate in multiple myeloma cells treated with dexamethasone. The overexpression of MITF could counteract the biological effect of miR-137 in multiple myeloma cells. Conclusion: We conclude that MITF is a direct target of miR-137. The miR-137 can improve the dexamethasone sensitivity in multiple myeloma cells by reducing the c-MET expression and further decreasing the AKT phosphorylation via targeting MITF.