Mir‐1307 regulates cisplatin resistance by targeting Mdm4 in breast cancer expressing wild type P53

BACKGROUND: Many chemotherapy regimens are used to treat breast cancer; however, breast cancer cells often develop drug resistance that usually leads to relapse and poor prognosis. MicroRNAs (miRNAs) are short non‐coding RNA molecules that post‐transcriptionally regulate gene expression and play crucial roles in diverse biological processes, such as development, differentiation, apoptosis, and proliferation. We investigated the roles of miRNAs in the development of drug resistance in human breast cancer cells. METHODS: MiRNA expression was detected in human breast cancer cell lines MCF‐7 and MDA‐MB‐468 via real time PCR; 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazoliumbromide, cell viability, colony formation, and luciferase reporter gene assays; Western blot; and immunohistochemistry. RESULTS: MiR‐1307 was downregulated while MDM4 was upregulated in MCF‐7/cisplatin (CDDP) and MDA‐MB‐468/CDDP cells compared with parental MCF‐7 and MDA‐MB‐468 cells. in vitro drug sensitivity assay demonstrated that overexpression of miR‐1307 sensitized MCF‐7/CDDP cells to CDDP. Luciferase activity assay with a reporter containing sequences from the 3′ untranslated region of Mdm4 in MCF‐7/CDDP cells suggested that Mdm4 was the direct target gene of miR‐1307. Ectopic miR‐1307 expression reduced the MDM4 protein level and sensitized MCF‐7/CDDP cells to CDDP‐induced apoptosis. CONCLUSION: Our findings suggest, for the first time, that miR‐1307 could play a role in the development of CDDP resistance in breast cancer, at least in part by modulating apoptosis by targeting Mdm4.