An Estrogen Receptor-α/p300 Complex Activates the BRCA-1 Promoter at an AP-1 Site That Binds Jun/Fos Transcription Factors: Repressive Effects of p53 on BRCA-1 Transcription1

One of the puzzles in cancer predisposition is that women carrying BRCA-1 mutations preferentially develop tumors in epithelial tissues of the breast and ovary. Moreover, sporadic breast tumors contain lower levels of BRCA-1 in the absence of mutations in the BRCA-1 gene. The problem of tissue specificity requires analysis of factors that are unique to tissues of the breast. For example, the expression of estrogen receptor-α (ERα) is inversely correlated with breast cancer risk, and 90% of BRCA-1 tumors are negative for ERα. Here, we show that estrogen stimulates BRCA-1 promoter activity in transfected cells and the recruitment of ERα and its cofactor p300 to an AP-1 site that binds Jun/Fos transcription factors. The recruitment of ERα/p300 coincides with accumulation in the S-phase of the cell cycle and is antagonized by the antiestrogen tamoxifen. Conversely, we document that overexpression of wild-type p53 prevents the recruitment of ERα to the AP-1 site and represses BRCA-1 promoter activity. Taken together, our findings support a model in which an ERα/AP-1 complex modulates BRCA-1 transcription under conditions of estrogen stimulation. Conversely, the formation of this transcription complex is abrogated in cells overexpressing p53.