Multiple factors influence estrogen receptor ␣ (ER␣) transcriptional activity. Current models suggest that the silencing mediator of retinoic acid and thyroid hormone receptor (SMRT) corepressor functions within a histone deactylase-containing protein complex that binds to antiestrogen-bound ER␣ and contributes to negative regulation of gene expression. In this report, we demonstrate that SMRT is required for full agonistdependent ER␣ activation. Chromatin immunoprecipitation assays demonstrate that SMRT, like ER␣ and the SRC-3 coactivator, is recruited to an estrogen-responsive promoter in estrogen-treated MCF-7 cells. Depletion of SMRT, but not histone deacetylases 1 or 3, negatively impacts estradiol-stimulated ER␣ transcriptional activity, while exogenous expression of SMRT's receptor interaction domains blocks ER␣ activity, indicating a functional interaction between this corepressor and agonist-bound ER␣. Stimulation of estradiol-induced ER␣ activity by SMRT overexpression occurred in HeLa and MCF-7 cells, but not HepG2 cells, indicating that these positive effects are cell type specific. Similarly, the ability of SMRT depletion to promote the agonist activity of tamoxifen was observed for HeLa but not MCF-7 cells. Furthermore, impairment of agoniststimulated activity by SMRT depletion is specific to ER␣ and not observed for receptors for vitamin D, androgen, or thyroid hormone. Nuclear receptor corepressor (N-CoR) depletion increased the transcriptional activity of all four tested receptors. SMRT is required for full expression of the ER␣ target genes cyclin D1, BCL-2, and progesterone receptor but not pS2, and its depletion significantly attenuated estrogen-dependent proliferation of MCF-7 cells. Taken together, these data indicate that SMRT, in conjunction with gene-specific and cell-dependent factors, is required for positively regulating agonist-dependent ER␣ transcriptional activity.Estrogens are potent mitogens in a number of target tissues, including the mammary gland, where they play a pivotal role in the development and progression of breast tumorigenesis. The effects of estrogen are mediated via estrogen receptor ␣ (ER␣) and ER␤, which are nuclear receptors that belong to a superfamily of ligand-regulated transcription factors (61). Subsequent to estradiol (E2) binding to ER␣, the receptor undergoes a conformational change, dimerizes, and either binds directly to DNA via estrogen response elements (EREs) or indirectly binds DNA via interactions with other DNA-bound transcription factors, such as Sp1 or AP-1 (41, 61, 68). Although ER␣ binds within the promoter regions of some estrogen-sensitive target genes, it has been estimated that only ϳ4% of ER␣ binding sites lie within 1 kb of proximal promoter regions, and the good correlation of ER␣ binding sites within 50 kb of the transcriptional start sites of estrogen-induced genes suggests that ER␣ can regulate the expression of these genes from a substantial distance (7-9, 42). The central involvement of estrogens in the genesis and progression of b...

Acting via the estrogen receptor (ER), estradiol exerts pleomorphic effects on the uterus, producing cyclical waves of cellular proliferation and differentiation in preparation for embryo implantation. In the classical pathway, the ER binds directly to an estrogen response element to activate or repress gene expression. However, emerging evidence supports the existence of nonclassical pathways in which the activated ER alters gene expression through protein-protein tethering with transcription factors such as c-Fos/ c-Jun B (AP-1) and Sp1. In this report, we examined the relative roles of classical and nonclassical ER signaling in vivo by comparing the estrogen-dependent uterine response in mice that express wild-type ER␣, a mutant ER␣ (E207A/G208A) that selectively lacks ERE binding, or ER␣ null. In the compound heterozygote (AA/؊) female, the nonclassical allele (AA) was insufficient to mediate an acute uterotrophic response to 17␤-estradiol (E 2 ). The uterine epithelial proliferative response to E 2 and 4-hydroxytamoxifen was retained in the AA/؊ females, and uterine luminal epithelial height increased commensurate with the extent of ER␣ signaling. This proliferative response was confirmed by 5-bromo-2-deoxyuridine incorporation. Microarray experiments identified cyclin-dependent kinase inhibitor 1A as a nonclassical pathwayresponsive gene, and transient expression experiments using the cyclin-dependent kinase inhibitor 1A promoter confirmed transcriptional responses to the ER␣ (E207A/G208A) mutant. These results indicate that nonclassical ER␣ signaling is sufficient to restore luminal epithelial proliferation but not other estrogen-responsive events, such as fluid accumulation and hyperemia. We conclude that nonclassical pathway signaling via ER␣ plays a critical physiologic role in the uterine response to estrogen.The uterus responds to cyclical changes in estrogen and progesterone levels in preparation for embryo implantation. Estrogen mediates the principal proliferative response of the uterus through two related but distinct estrogen receptors (ER␣ 2 and ER␤) (1-3). ER␣ is the predominant form in the murine uterus (4), but ER␤ transcripts are also detected at very low levels (4). After estrogens bind to the ligand domain of the ER, it undergoes conformational changes that allow interactions with coactivator molecules (5-7). In the classical pathway of estrogen action, the ER binds as a dimer to EREs in the promoter regions of target genes (8). However, it is now clear that the ER can regulate genes that lack a canonical ERE, suggesting additional pathways for estrogen action (9 -11). For example, the ER may activate genes via protein-protein tethering with c-Fos/c-Jun B (AP-1) and Sp1 (12, 13) or suppress expression mediated through NF-B (14). This alternate response mechanism has been referred to as the tethered or nonclassical pathway.We previously generated an ER␣ mutant that selectively functions via the nonclassical pathway. Substitution of two amino acids in the DNA recognition sequence of the fir...

We describe the first missense mutation in the aminoterminus of DAX1 and conclude that mutations in this region may be partially compensated by redundant functional domains. Mild DAX1 mutations may be a cause of isolated mineralocorticoid deficiency.