MiR-208a stimulates the cocktail of SOX2 and β-catenin to inhibit the let-7 induction of self-renewal repression of breast cancer stem cells and formed miR208a/let-7 feedback loop via LIN28 and DICER1

MiR-208a stimulates cardiomyocyte hypertrophy, fibrosis and beta-MHC (beta-myosin heavy chain) expression, being involved in cardiovascular diseases. Although miR-208a is known to play a role in cardiovascular diseases, its role in cancer and cancer stem cells (CSCs) remains uncertain. We identified an inverse relationship between miR-208a and let-7a in breast cancer specimens, and found that SOX2, beta-catenin and LIN28 are highly expressed in patients with advanced breast cancer opposed to lesser grades. Further, we isolated ALDH1+ CSCs from ZR75-1 and MDA-MB-231 (MM-231) breast cancer cell lines to test the role of miR-208a in breast CSCs (BrCSCs). Our studies showed that overexpression of miR-208a in these cells strongly promoted the proportion of ALDH1+ BrCSCs and continuously stimulated the self-renewal ability of BrCSCs. By using siRNAs of SOX2 and/or beta-catenin, we found that miR-208a increased LIN28 through stimulation of both SOX2 and beta-catenin. The knockdown of either SOX2 or beta-catenin only partially attenuated the functions of miR-208a. Let-7a expression was strongly inhibited in miR-208a overexpressed cancer cells, which was achieved by miR-208a induction of LIN28, and the restoration of let-7a significantly inhibited the miR-208a induction of the number of ALDH1+ cells, inhibiting the propagations of BrCSCs. In let-7a overexpressed ZR75-1 and MM-231 cells, DICER1 activity was significantly inhibited with decreased miR-208a. Let-7a failed to decrease miR-208a expression in ZR75-1 and MM-231 cells with DICER1 knockdown. Our research revealed the mechanisms through which miR-208a functioned in breast cancer and BrCSCs, and identified the miR-208a-SOX2/beta-catenin-LIN28-let-7a-DICER1 regulatory feedback loop in regulations of stem cells renewal.