Histone Deacetylase 7 and FoxA1 in Estrogen-Mediated Repression of RPRM

ABSTRACT Activation of estrogen receptor α (ERα) results in both induction and repression of gene transcription; while mechanistic details of estrogen induction are well described, details of repression remain largely unknown. We characterized several ERα-repressed targets and examined in detail the mechanism for estrogen repression of Reprimo (RPRM), a cell cycle inhibitor. Estrogen repression of RPRM is rapid and robust and requires a tripartite interaction between ERα, histone deacetylase 7 (HDAC7), and FoxA1. HDAC7 is the critical HDAC needed for repression of RPRM; it can bind to ERα and represses ERα's transcriptional activity—this repression does not require HDAC7's deacetylase activity. We further show that the chromatin pioneer factor FoxA1, well known for its role in estrogen induction of genes, is recruited to the RPRM promoter, is necessary for repression of RPRM, and interacts with HDAC7. Like other FoxA1 recruitment sites, the RPRM promoter is characterized by H3K4me1/me2. Estrogen treatment causes decreases in H3K4me1/me2 and release of RNA polymerase II (Pol II) from the RPRM proximal promoter. Overall, these data implicate a novel role for HDAC7 and FoxA1 in estrogen repression of RPRM, a mechanism which could potentially be generalized to many more estrogen-repressed genes and hence be important in both normal physiology and pathological processes.

Estrogen Receptor β Isoform-Specific Induction of Transforming Growth Factor β-Inducible Early Gene-1 in Human Osteoblast Cells: An Essential Role for the Activation Function 1 Domain

The estrogen receptors (ER) α and β are important ligand-mediated transcription factors known to play significant biological roles in numerous tissues including bone. Despite the high homology shared by these receptors, recent studies have suggested that their function is largely unique. Although these receptors have been studied in detail for more than a decade, little data exist concerning the mechanisms by which these two proteins regulate distinct sets of genes. Using the TGFβ-inducible early gene-1 (TIEG) as a model, we demonstrate that TIEG is rapidly induced in response to estrogen in osteoblasts by ERβ, but not ERα. We have identified the regulatory elements utilized by ERβ and have demonstrated that ERβ recruits steroid receptor coactivator (SRC)1 and SRC2 to this regulatory region. Additionally, deletion of the ERβ-activation function 1 (AF1) domain drastically decreases the estrogen induction of TIEG. Through the use of chimeric receptors, we have demonstrated that the AF1 domain of ERβ is responsible for recruiting SRC1 and SRC2 and inducing the expression of TIEG in osteoblasts. Finally, SRC1, but not SRC2, is essential for TIEG induction by ERβ. Overall, these data demonstrate that the estrogen induction of TIEG is ERβ specific and that the AF1 domain of ERβ confers this specificity. Finally, a novel and important role for ERβ’s AF1 is implicated in the recruitment of specific coactivators, suggesting that the AF1 may play a significant role in conferring the differences in regulation of gene expression by these two receptors.