IDENTIFICATION OF A NOVEL TRANSFERABLE CIS-ELEMENT IN THE PROMOTER OFAN ESTROGEN-RESPONSIVE GENE THAT MODULATES SENSITIVITY TO HORMONE ANDANTIHORMONE

The estrogen receptor (ER) is a ligand-regulated transcription factor that acts at the promoters of estrogen-regulated genes to modulate the ir expression. In the present study, we examined three estrogen-regula ted 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 est rogen and repression of estrogen-stimulated transcription by antiestro gen (AE)-occupied ER. ER-containing MCF-7 human breast cancer cells we re transfected with reporter gene constructs containing estrogen respo nse elements upstream of the three gene promoters. In this system, PR( P) and PR(D) showed similar dose-response curves for stimulation by es tradiol whereas pS2 was activated by even lower concentrations of estr adiol. By contrast, PR(D) was much less sensitive to repression of est rogen-stimulated activity by all AEs studied, relative to the PR(P) an d the pS2 promoters. Using deletion and mutational analysis, we have i dentified a transferable cis element at -131 to -94 bp in PR(D) that i s involved in modulating the sensitivity of this promoter to both estr ogens and AEs. The element reduced the magnitude of estrogen-stimulate d activity, enhanced the ability of AEs to repress estrogen-stimulated activity, and elicited similiar effects when transferred to the promo ter of another estrogen-responsive gene. Thus, removal of this region from PR(D) further accentuated the insensitivity of this promoter to A E while enhancing its sensitivity (both EC(50) 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 bindin g of these proteins is inversely correlated with the transcriptional e ffectiveness of the ER. The findings demonstrate that a specific cis e lement 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.