The microRNA miR-181c enhances chemosensitivity and reduces chemoresistance in breast cancer cells via down-regulating osteopontin

Acquired resistance to chemotherapy is a frequent challenge in cancer care and one of the leading causes for failing breast cancer therapies. There is accumulative clinical and experimental evidence indicating that microRNAs (miRNAs) play a crucial role in developing therapeutic resistance in cancer cells. We aimed to explore key miRNAs and associated mechanisms by which breast cancer develops chemoresistance. In this study, we found that a particular miRNA species, miR-181c, was significantly low-expressed in breast cancer cell line MCF-7 which developed chemoresistance towards doxorubicin (Adriamycin, ADR, subclone renamed as MCF-7/ADR) than in the wild-type MCF-7 cells. Induced overexpression of miR-181c significantly inhibited cell proliferation, reversed the chemoresistance towards doxorubicin, and reduced the growth of resistant breast cancer xenograft tumors in vitro and in vivo. Using a bioinformatics approach, we also identified osteopontin (OPN) as a direct target of miR-181c. In contrast to low miR-181c expression in MCF-7/ADR cells, OPN showed a reversely high expression in resistant MCF-7/ADR cells. Our results suggest that miR-181c may regulate chemosensitivity and chemoresistance by downregulating OPN, resulting in enhanced p53-dependent transactivation and apoptosis in resistant breast cancer cells. This study provides new insights to develop effective interventions for cancer patients with acquired resistance to chemotherapy.