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ChIP-Seq of ERalpha and RNA polymerase II defines genes differentially responding to ligands

ABSTRACT: We used ChIP-Seq to map ERalpha binding sites and to profile changes in RNA polymerase II (RNAPII) occupancy in MCF-7 cells in response to estradiol (E2), tamoxifen or fulvestrant. We identified 10,205 high confidence ERalpha binding sites in response to E2 of which 68% contained an estrogen response element (ERE) and only 7% contained a FOXA1 motif. Remarkably, 596 genes already change significantly in RNAPII occupancy (59% up and 41% down) following one hour of E2 exposure. Although pausing of RNA polymerase II occurs frequently in MCF-7 cells (17%) it is only observed on a minority of E2-regulated genes (4%). Tamoxifen and fulvestrant partially reduce ERalpha DNA binding and prevent RNAPII loading on the promoter and coding body on E2-upregulated genes. Both antagonists act differently on E2-downregulated genes. Tamoxifen acts as an agonist, also downregulating these genes while fulvestrant antagonizes E2 induced repression and often increases RNAPII occupancy. Furthermore our data identified genes preferentially regulated by tamoxifen but not by E2 or fulvestrant. Thus, antagonist loaded ERalpha acts mechanistically different on E2-activated and E2-repressed genes.

ORGANISM(S): Homo sapiens

PROVIDER: GSE14664 | GEO | 2009/03/09

SECONDARY ACCESSION(S): PRJNA112357

REPOSITORIES: GEO

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Project description:To explore the global mechanisms of estrogen-regulated transcription, we used chromatin immunoprecipitation coupled with DNA microarrays to determine the localization of RNA polymerase II (Pol II), estrogen receptor alpha (ERalpha), steroid receptor coactivator proteins (SRC), and acetylated histones H3/H4 (AcH) at estrogen-regulated promoters in MCF-7 cells with or without estradiol (E2) treatment. In addition, we correlated factor occupancy with gene expression and the presence of transcription factor binding elements. Using this integrative approach, we defined a set of 58 direct E2 target genes based on E2-regulated Pol II occupancy and classified their promoters based on factor binding, histone modification, and transcriptional output. Many of these direct E2 target genes exhibit interesting modes of regulation and biological activities, some of which may be relevant to the onset and proliferation of breast cancers. Our studies indicate that about one-third of these direct E2 target genes contain promoter-proximal ERalpha-binding sites, which is considerably more than previous estimates. Some of these genes represent possible novel targets for regulation through the ERalpha/AP-1 tethering pathway. Our studies have also revealed several previously uncharacterized global features of E2-regulated gene expression, including strong positive correlations between Pol II occupancy and AcH levels, as well as between the E2-dependent recruitment of ERalpha and SRC at the promoters of E2-stimulated genes. Furthermore, our studies have revealed new mechanistic insights into E2-regulated gene expression, including the absence of SRC binding at E2-repressed genes and the presence of constitutively bound, promoter-proximally paused Pol IIs at some E2-regulated promoters. These mechanistic insights are likely to be relevant for understanding gene regulation by a wide variety of nuclear receptors. Keywords: MCF7 cells, E2, Estrogen, RNA, ER, RNA Polymerase II, SRC, Acetylated histones, ChIP-chip

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ChIP-Seq of ERalpha and RNA polymerase II defines genes differentially responding to ligands

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