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

Estrogen receptors α and β (ERα and ERβ) 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 ERβ. To investigate how phytoestrogens such as genistein impact ER-regulated gene expression, we used adenoviral gene delivery of ERβ coupled with ERα depletion with small interfering RNA to generate human breast cancer (MCF-7) cells expressing four complements of ERα and ERβ. 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 ERα and ERβ than in cells expressing ERα alone, whereas at high concentration (300 nM), genistein induced transcriptome changes very similar to that of 17β-estradiol. We demonstrate that ERβ is preferentially activated by genistein and is recruited to estrogen-responsive genomic sites and that differential occupancy of ERα and ERβ by genistein and 17β-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 ERα and ERβ and that the ability of ERα and ERβ 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.