ABSTRACT
<p><b>OBJECTIVE</b>To study the regulatory role of BRCA1 in the expression of progesterone receptors A and B (PRA and PRB) in breast cancer cells.</p><p><b>METHODS</b>Breast cancer MCF-7 cells were transfected with pFlag-CMV2-BRCA1 wt plasmid containing a full-length BRCA1 cDNA or with BRCA1-specific siRNA via lipofectamine 2000 to induce overexpression or suppressed expression of BRCA1, respectively. Twenty-four hours after the transfection, the cells were incubated in fresh culture medium containing 100 nmol/L progesterone for 24 h. The total RNA extract or whole cell lysate was prepared for detecting BRCA1, PRA and PRB expressions using RT-PCR and Western blotting.</p><p><b>RESULTS</b>The protein expressions of PRA and PRB were significantly decreased whereas their mRNA expressions remained unchanged in MCF-7 cells overexpressing BRCA1. In MCF-7 cells with BRCA1 knock-down, in contrast, the PRA and PRB protein expressions were markedly increased.</p><p><b>CONCLUSION</b>In breast cancer cells, exogenous and endogenous BRCA1 can both down-regulate the expressions of PRA and PRB at the protein level.</p>