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Identification of a Novel Transferable cis Element in the Promoter of an Estrogen-Responsive Gene that Modulates Sensitivity to Hormone and Antihormone

Department of Molecular and Integrative Physiology (M.M.M., W.L.K., B.S.K.) Department of Cell and Structural Biology (B.S.K.) University of Illinois, Urbana, Illinois 61801

The estrogen receptor (ER) is a ligand-regulated transcription factor that acts at the promoters of estrogen-regulated genes to modulate their expression. In the present study, we examined three estrogen-regulated promoters, namely the rat progesterone receptor gene distal (PR_D) and proximal (PR_P) promoters and the human pS2 gene promoter, and observed marked differences in their sensitivity to stimulation by estrogen and repression of estrogen-stimulated transcription by antiestrogen (AE)-occupied ER. ER-containing MCF-7 human breast cancer cells were transfected with reporter gene constructs containing estrogen response elements upstream of the three gene promoters. In this system, PR_P and PR_D showed similar dose-response curves for stimulation by estradiol whereas pS2 was activated by even lower concentrations of estradiol. By contrast, PR_D was much less sensitive to repression of estrogen-stimulated activity by all AEs studied, relative to the PR_P and the pS2 promoters. Using deletion and mutational analysis, we have identified a transferable cis element at -131 to -94 bp in PR_D that is involved in modulating the sensitivity of this promoter to both estrogens and AEs. The element reduced the magnitude of estrogen-stimulated activity, enhanced the ability of AEs to repress estrogen-stimulated activity, and elicited similiar effects when transferred to the promoter of another estrogen-responsive gene. Thus, removal of this region from PR_D further accentuated the insensitivity of this promoter to AE while enhancing its sensitivity (both EC₅₀ and fold induction) to estrogen. Gel mobility shift assays showed that proteins from nuclear extracts of MCF-7 cells interact with this element and that the binding of these proteins is inversely correlated with the transcriptional effectiveness of the ER. The findings demonstrate that a specific cis element from the promoter of an estrogen-responsive gene can alter the transcriptional activity of hormone and antihormone-occupied receptor bound at its response element near the promoter. Such ligand response modulatory elements, and changes in the levels and activity of factors that bind to such elements, may underlie the different sensitivities of steroid hormone-regulated genes to both hormones and antihormones.

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