A Chemotherapy-Driven Increase in Mcl-1 Mediates the Effect of miR-375 on Cisplatin Resistance in Osteosarcoma Cells

BACKGROUND: Osteosarcoma (OS) is one of the most difficult cancers to treat due to its resistance to chemotherapy. The essential role played by Mcl-1 in promoting chemoresistance has been observed in a variety of cancers, including OS, while the underlying mechanism remains unclear. METHODS: We investigated the expression of Mcl-1 in 42 paired OS specimens obtained before and after adjuvant chemotherapy, and its correlation with clinicopathological characteristics. Loss and gain of function studies were performed to analyze the effects of Mcl-1 modulations on the chemosensitivity, and the mechanism involved in the deregulation of Mcl-1 in OS cells. RESULTS: In OS specimens, the expression of Mcl-1 was significantly upregulated after chemotherapy, and high Mcl-1 expression was associated with poorer overall survival and an increased recurrence rate. Furthermore, we demonstrated that chemotherapy-driven increased Mcl-1 decreased chemosensitivity by promoting tumour proliferation and inhibiting DNA damage. Moreover, Mcl-1 was found to be a direct target of miR-375 in OS cells. The knockdown of Mcl-1 phenocopied miR-375 downregulation, and the overexpression of miR-375 rescued the effects of cisplatin-induced DNA damage mediated by Mcl-1. CONCLUSION: Our data indicated that chemotherapy-driven increase in the expression of Mcl-1 plays a critical role in chemoresistance, and the intervention of the miR-375/Mcl-1 axis may offer a novel strategy to enhance chemosensitivity in OS treatment.