The expression levels of ERalpha and miR-155 in MCF-7 and MDA-MB-231 cells. (A) Expression level of ERalpha was detected by western blot of protein extracts from ERalpha (+) MCF-7 and ERalpha (−) MDA-MB-231 cells. (B) Differential expression of miR-155 between MCF-7 and MDA-MB-231 cells. The expression of miR-155 in MCF-7 cells was 3.05-fold that of MDA-MB-231cells. **P < 0.01. All experiments were repeated at least three times.