Expression of the Estrogen-Regulated pS2 Gene in MCF-7 Human Breast Cancer Cells

摘要

To gain a better understanding of how estrogen-responsive genes are regulated we utilized in vivo footprinting and in vitro binding assays to define cis elements and transacting factors involved in conferring estrogen responsiveness to the pS2 and PR genes in MCF-7 breast cancer cells. The consensus pS2 ERE half site was protected in the absence of hormone and both the consensus and imperfect ERE half sites were protected in the presence of estrogen. 4-hydroxytatnoxifen and ICI 182,780 elicited distinct footprinting patterns, which differed from those observed with vehicle- or with estrogen- treated cells. Footprinting patterns in and around the TATA and CAAT sequences were identical in the presence and in the absence of estrogen suggesting that the basal promoter is accessible and poised for transcription even in the absence of hormone. In vitro DNase I footprinting experiments demonstrated that the estrogen receptor bound to the pS2 ERE and that adjacent nucleotides were protected by MCF-7 nuclear proteins. The PR gene is also induced by E2 in MCF-7 cells. Although the PR gene lacks an identifiable ERE, it does contain a complex array of conserved transcription factor binding sites. We have provided evidence that two AP-l sites help to confer estrogen responsiveness to the PR gene. In addition the ER enhances Sp 1 binding to its recognition site and binds directly to an adjacent ERE half site in the PR Promoter A. Taken together, our combined studies of the pS2 and the PR gene suggest that the ER has direct and indirect effects on formation of an active transcription complex.