Estrogen receptor (ER) β modulates ERα-mediated transcriptional activation by altering the recruitment of c-Fos and c-Jun to estrogen-responsive promoters

In this study, an estrogen receptor ( ER) alpha-expressing T47D cell line containing an inducible tet-off FLAG-ER beta was used to examine the influence of ER beta on ER alpha activity. Real-time PCR analysis of mRNA levels of two well-studied estrogen-responsive genes, pS2 and progesterone receptor ( PR), showed that the expression levels of both genes were reduced in the presence of ER beta. Chromatin immunoprecipitation assays showed that the 17 beta-estradiol (E2)-induced recruitment patterns to the pS2 and PR promoters were similar for both ER alpha and ER beta. ER beta expression did not significantly influence the kinetic recruitment profile of ER alpha to the pS2 promoter, but it was evident that ER alpha occupancy at the PR promoter was reduced. The E2-induced recruitment of c-Fos to a 12-O-tetradecanoylphorbol-13-acetate response element site in the PR promoter was significantly reduced in the presence of ER beta, whereas only a slight reduction in the recruitment of c-Fos to the pS2 promoter was observed. ER beta expression resulted in a significant reduction in the E2-induced expression of c-Fos mRNA. The recruitment pattern of c-Jun was also altered by ER beta, although the expression levels of c-Jun were not. Expression of ER beta caused a further 30-50% decrease of the E2-induced reduction in ER alpha protein after 3 h of E2 treatment, showing that ER beta influences ER alpha protein levels. The altered recruitment of the activating protein-1 complex, combined with the reduction in ER alpha protein levels, may partly explain the antagonistic effect of ER beta on ER alpha-mediated transcription.