Estrogens, acting through their
nuclear receptors have a broad impact on target cells, eliciting a transcriptional response program that involves gene repression as well as gene stimulation. While much is known about the mechanisms by which the
estrogen-occupied
estrogen receptor (ER) stimulates gene expression, the molecular events that lead to gene repression by the
hormone-ER complex are largely unknown. Because
estradiol represses expression of the
cyclin G2 gene, which encodes a negative regulator of the cell cycle, our aim was to understand the mechanism by which
cyclin G2 is repressed by
estrogen. We show that
cyclin G2 is a primary ER target gene in MCF-7
breast cancer cells that is rapidly and robustly down-regulated by
estrogen. Promoter analysis reveals a responsive region containing a half-
estrogen response element and GC-rich region that interact with ER and Sp1
proteins. Mutation of the half-ERE abrogates
hormone-mediated repression. Mutational mapping of receptor reveals a requirement for its N-terminal region and
DNA binding domain to support
cyclin G2 repression. Following
estradiol treatment of cells,
chromatin immunoprecipitation analyses reveal recruitment of ER to the
cyclin G2 regulatory region, dismissal of
RNA polymerase II, and recruitment of a complex containing N-CoR and
histone deacetylases, leading to a hypoacetylated
chromatin state. Our study provides evidence for a mechanism by which the
estrogen-occupied ER is able to actively repress gene expression in vivo and indicates a role for
nuclear receptor corepressors and associated
histone deacetylase activity in mediating negative gene regulation by this
hormone-occupied
nuclear receptor.