Abstract: Objective To investigate the effect of miR-424 on the proliferation and apoptosisof multiple myeloma ( MM) cells by targeting the F-box and WD repeat domain containing 7(FBXW7). Methods Real-time fluorescence quantitative PCR ( RT-qPCR) experiment was applied to detect the expression levels of miR-424 and FBXW7 in human normal bone marrow plasma cells and MM cell lines MM. 1S, RPMI 8226, U266. U266 cells were cultured in vitro and randomly separated into 5 groups: control group, miR-424 inhibitor group, FBXW7 overexpression group, negative control group, miR-424 inhibitor + FBXW7 knockdown group. Edu staining and TUNELstaining were applied to detect the cell proliferation and apoptosis, respectively. Western blotting assay was applied to detect the expression levels of proliferation related proteins ( Cyclin D1, PCNA), apoptosis related proteins (Bax, Bcl-2), and FBXW7 protein. A nude mouse model of multiple myeloma transplantation was constructed by subcutaneous inoculation of transfected U266 cells in the right axilla of nude mice, the growth of the transplanted tumors were detected and the transplanted tumor volume was compared on the 21st day. Dual luciferase reporter experiment was applied to verify the targeted regulatory effect of miR-424 on FBXW7 in U266 cells. Results In comparisonwith those in the normal human bone marrow plasma cells, the expression of miR-424 in theMM. 1S, RPMI 8226, and U266 cells were increased ( P < 0. 05 ), while the expression of FBXW7 mRNA were decreased ( P < 0. 05). In addition, when compared with the control group, the miR-424 inhibitor group and the FBXW7 overexpression group showed decreased cell proliferation rate, lower protein expression levels of Cyclin D1, PCNA and Bcl-2, and decreased transplanted tumor volume on the 21st day (P < 0. 05), and increased apoptosis rate, FBXW7 mRNA and protein expression levels, and Bax protein expression level ( P < 0. 05). There was no significant difference in the indicators in cells of the negative control group (P > 0. 05). Moreover, when compared with the miR-424 inhibitor group, the miR-424 inhibitor + FBXW7 knockdown group exhibited increased cell proliferation rate, Cyclin D1, PCNA and Bcl-2 protein expression, and transplanted tumor volume on the 21st day (P < 0. 05), and decreased apoptosis rate, FBXW7 mRNA and protein expression levels, and Bax protein expression level ( P < 0. 05). It was also observed that miR-424 was able to targetly downregulate FBXW7 expression in U266 cells. Conclusion Down-regulation of miR-424 can inhibit MM cell proliferation and growth in nude mice, and promote the apoptosis by up-regulating FBXW7 expression.

Key words: miR-424, FBXW7, multiple myeloma, proliferation, apoptosis