MicroRNA-221 promotes breast cancer resistance to adriamycin via modulation of PTEN/Akt/mTOR signaling.

As a prevalent tumor among women, breast cancer is still an incurable disease due to drug resistance. In this study, we report microRNA-221 to have a significant effect on breast cancer resistance to adriamycin. The microRNA-221 is elevated in tumor tissue compared with nearby nontumor samples, as well as in breast cancer cell line with adriamycin resistance (MCF-7/ADR) compared to its parental line (MCF-7) and the normal breast epithelial cell line (MCF-10A). Enforced level of microRNA-221 promotes cancer resistance to adriamycin, which in turn sustains cell survival and exacerbates malignant formation. Reciprocally, the silence of microRNA-221 in cancer cells augments the sensitivity to chemotherapy, thereby resulting in enhanced apoptosis of MCF-7/ADR cells. Mechanistically, we identify PTEN as a direct target of microRNA-221, which was conversely associated with a microRNA-221 level in breast tumors. The knock-down of PTEN partially reversed the stimulatory role of microRNA-221 in the modulation of the Akt/mTOR signaling. Taken together, these findings suggest microRNA-221 suppresses PTEN transcription and activates Akt/mTOR pathway, which in turn enhances breast cancer resistance to adriamycin and promotes cancer development. Our data thus illuminate the microRNA-221/PTEN axis may act as a promising strategy for the treatment of chemotherapy-resistant breast tumors.