Mechanism of let-7c/HMGA2 signaling regulation mediated by DNA methylation in multiple myeloma

Abstract Background: multiple myeloma(MM) represents the second most common hematological malignancy characterized by the infiltration of the bone marrow by plasma cells. MM remains a hard-to-treat disease, and the search for new molecules as targets is expected to improve the prognosis of MM. Objective: To investigate the effect of let-7c and its target gene (HMGA2) regulation on the proliferation of MM cells. Besides, to definite the role of DNA methylation in abnormal expression of let-7c. Methods: The mRNA expression of let-7c and HMGA2 in newly diagnosed MM patients, healthy donors, and human MM cell lines were measured by RT-qPCR. Dual luciferase assay was used to verify the targeting relationship between let-7c and HMGA2. The let-7c mimic/inhibitor were transfected in MM cell lines to establish upregulated/downregulated models. The proliferation, invasion ability and apoptosis were detected by CCK-8 assay, Transwell, and flow cytometry. Cell line-derived xenografts(CDX) to assess the effect of let-7c agomir on the subcutaneous tumorigenic capacity of MM cells in nude mice, and western blot was used to detect the expression of HMGA2 protein and two EMT related proteins (E-cadherin and N-Cadherin). The transcription level of let-7c and HMGA2 in MM cells and cell proliferation were tested again after decitabine exposure. Results: Let-7c was broadly downregulated in MM cell lines and plasma cells from MM patients compared with normal donors' BMMCs. HMGA2 was identified as one of the target genes of let-7c. overexpression of let-7c can inhibit the proliferation, invasion and migration of MM cells. After injection of let-7c mimic, the growth of transplanted tumors was significantly inhibited, as well as the expression of HMGA2 and EMT-related proteins in the treatment group was significantly changed as compared with that in the control group. Decitabine-exposed MM cells showed a statistically increased expression of let-7c and a decreased expression of HMGA2, thereby obviously suppressed the cell proliferation. Conclusion: let-7c inhibits proliferation, invasion and migration of MM cells by negatively regulating HMGA2, and its mechanism involves the regulation of methylation in the let-7c promoter region, which highlights let-7c as a promising target for therapies.