Abstract
Breast cancer stem cells (BCSCs) have been considered responsible for cancer progression, recurrence, metastasis and drug resistance. However, the mechanisms by which cells acquire self-renewal and chemoresistance properties are remaining largely unclear. Herein, we evaluated the role of miR-708 and metformin in BCSCs, and found that the expression of miR-708 is significantly down-regulated in BCSCs and tumour tissues, and correlates with chemotherapy response and prognosis. Moreover, miR-708 markedly inhibits sphere formation, CD44(+) /CD24(-) ratio, and tumour initiation and increases chemosensitivity of BCSCs. Mechanistically, miR-708 directly binds to cluster of differentiation 47 (CD47), and regulates tumour-associated macrophage-mediated phagocytosis. On the other hand, CD47 is essential for self-renewal, tumour initiation and chemoresistance of BCSCs, and correlates with the prognosis of breast cancer patients. In addition, the anti-type II diabetes drug metformin are found to be involved in the miR-708/CD47 signalling pathway. Therefore, our study demonstrated that miR-708 plays an important tumour suppressor role in BCSCs self-renewal and chemoresistance, and the miR-708/CD47 regulatory axis may represent a novel therapeutic mechanism of metformin in BCSCs.