Estrogen receptors α and β as determinants of gene expression:: Influence of ligand, dose, and chromatin binding

Estrogen receptors alpha and beta ( ER alpha and ER beta) mediate the actions of estrogens in a variety of normal and cancer target cells. Estrogens differ in their preference for these ERs, and many phytoestrogens bind preferentially to ER beta. To investigate how phytoestrogens such as genistein impact ER-regulated gene expression, we used adenoviral gene delivery of ER beta coupled with ER alpha depletion with small interfering RNA to generate human breast cancer ( MCF- 7) cells expressing four complements of ER alpha and ER beta. We examined the dose-dependent effects of genistein on genome-wide gene expression by DNA microarrays and monitored the recruitment of ERs and coregulators to responsive regions of estrogen-regulated genes. At a low ( 6 nM) concentration, genistein regulated gene expression much more effectively in cells coexpressing ER alpha and ER beta than in cells expressing ER alpha alone, whereas at high concentration ( 300 nM), genistein induced transcriptome changes very similar to that of 17 beta-estradiol. We demonstrate that ER beta is preferentially activated by genistein and is recruited to estrogen- responsive genomic sites and that differential occupancy of ER alpha and ER beta by genistein and 17 beta-estradiol in turn influences the recruitment patterns of coregulators such as steroid receptor coactivator 3 ( SRC3) and receptor-interacting protein 140 ( RIP140). Our observations indicate that genistein is a potency-selective ligand for gene expression regulation by ER alpha and ER beta and that the ability of ER alpha and ER beta to serve as determinants of gene expression is greatly influenced by the nature of the ligand, by ligand dose, and by the differential abilities of ligand-ER complexes to recruit different coregulators at ER binding sites of hormone-regulated genes.