BRCA1 and breast cancer: Based on the pathological findings indicating breast cancer cells express the higher BRCA1and the lower PINK1/Parkin expressions as compared with those in normal tissues (Fig. 4), we next examined the role of BRCA1 in cancer cell proliferation by knocking down BRCA1 in MCF7 cells by expressing either tetracycline-inducible BRCA1 shRNA (MCF7 Tet-shBRCA1) or nontargeting shRNA (MCF7 Tet-shNT).