PARENT SESSION
MINISYMPOSIUM IV. Coactivators in Steroid Hormone Action and Reproductive Physiology
11:00 AM-12:30 PM
Grand Ballroom VI
Chair: McCarthy, Margaret¹, ¹

(M10) THE ROLE OF COACTIVATORS, CHROMATIN, AND EPIGENETIC MODIFICATIONS IN ESTROGEN-DEPENDENT GENE REGULATION.

Kraus, W. Lee^1,2, Cheung, Edwin¹, Kim, Mi Young¹, Acevedo, Mari Luz¹, Lee, Kathleen¹, Hsiao, Susan¹, Schwabish, Marc¹, Zarifyan, Alla¹, ¹ Department of Molecular Biology and Genetics, Ithaca, NY² Department of Pharmacology, New York, NY

ABSTRACT- The molecular actions of estrogens are mediated by two distinct estrogen receptor (ER) isoforms, ER and ER. The ERs belong to a large conserved superfamily of nuclear hormone receptors that function as ligand-regulated, DNA-binding transcriptional activators. In vivo, ERs bind to estrogen response elements in the promoters or regulatory regions of estrogen-responsive genes assembled into chromatin in the nuclear environment of the cell. The assembly of genes into chromatin has important functional consequences for gene regulation by ERs and other transcriptional activators since chromatin acts as a general repressor of transcription by RNA polymerase II. A variety of cofactors with chromatin- and histone-modifying activities have evolved to assist the ERs and other transcriptional activators in overcoming chromatin-mediated repression to activate gene expression. These cofactors include chromatin remodeling complexes and coactivators. Understanding the biochemistry of the physical and functional interactions between the ERs and their associated cofactors will provide insights into the molecular details of gene regulation by estrogenic hormones, as well as antiestrogenic antagonists. We have been using a variety of biochemical approaches to study ER-dependent transcription in the context of chromatin, including an in vitro chromatin assembly and transcription system that accurately recapitulates the known ligand-dependent activities of the ERs, to examine the broad hypothesis that physical and functional interactions among the ERs, their associated cofactors, and chromatin regulate the transcriptional response to estrogens. Some questions that we have addressed using this approach include the following: (1) What specific role(s) do coactivators, such as p300/CBP and the SRC family members, play in the process of estrogen-dependent transcription with chromatin?; (2) What effect do linker histones, such as histone H1, have on the transcriptional activities of the ERs?; (3) What is the mechanistic basis for the different transcriptional activities of ER and ER in the context of chromatin?; (4) Are there functional interactions between coactivators with histone-modifying enzymatic activities (e.g., the histone acetyltransferase p300/CBP) and the multisubunit Mediator complexes (e.g., TRAP, DRIP, ARC, SMCC) during ER-dependent transcription?; and (5) Can we develop specific inhibitors of interactions between the ERs and their associated cofactors that will allow us to explore the mechanisms of ER-dependent transcription in vitro and in vivo. The biochemical approach that we have used is ideally suited for addressing these and other detailed mechanistic questions. The challenge that we face now is to apply these biochemical techniques on a global scale to understand the gene-specific mechanisms of transcriptional regulation for the numerous estrogen-regulated genes that have been identified using genomic approaches.

KEY WORDS: estrogen receptor, coactivator, transcription, chromatin