Project description:This SuperSeries is composed of the following subset Series:; GSE9757: Response to estradiol-ERalpha; GSE9758: Response to estradiol-ERalpha ERE Binding defective mutant; GSE9759: Response to estradiol-Erbeta and estradiol-ERbeta ERE binding defective mutant Experiment Overall Design: Refer to individual Series
Project description:ChIP followed by deep sequencing was performed with antibodies to ERalpha in U2OS-ERalpha cells treated with 17beta-estradiol. Examination of Eralpha binding sites in U2OS-Eralpha cells. Sequenced input was used as a control
Project description: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. Examination of ERalpha binding sites upon the binding of different ligands and association with transcription via RNAPII occupancy.
Project description: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.
Project description:Using a chromatin immunoprecipitation-paired end diTag cloning and sequencing strategy, we mapped estrogen receptor alpha (ERalpha) binding sites in MCF-7 breast cancer cells. We identified 1,234 high confidence binding clusters of which 94% are projected to be bona fide ERalpha binding regions. Only 5% of the mapped estrogen receptor binding sites are located within 5 kb upstream of the transcriptional start sites of adjacent genes, regions containing the proximal promoters, whereas vast majority of the sites are mapped to intronic or distal locations (>5 kb from 5' and 3' ends of adjacent transcript), suggesting transcriptional regulatory mechanisms over significant physical distances. Of all the identified sites, 71% harbored putative full estrogen response elements (EREs), 25% bore ERE half sites, and only 4% had no recognizable ERE sequences. Genes in the vicinity of ERalpha binding sites were enriched for regulation by estradiol in MCF-7 cells, and their expression profiles in patient samples segregate ERalpha-positive from ERalpha-negative breast tumors. The expression dynamics of the genes adjacent to ERalpha binding sites suggest a direct induction of gene expression through binding to ERE-like sequences, whereas transcriptional repression by ERalpha appears to be through indirect mechanisms. Our analysis also indicates a number of candidate transcription factor binding sites adjacent to occupied EREs at frequencies much greater than by chance, including the previously reported FOXA1 sites, and demonstrate the potential involvement of one such putative adjacent factor, Sp1, in the global regulation of ERalpha target genes. Unexpectedly, we found that only 22%-24% of the bona fide human ERalpha binding sites were overlapping conserved regions in whole genome vertebrate alignments, which suggest limited conservation of functional binding sites. Taken together, this genome-scale analysis suggests complex but definable rules governing ERalpha binding and gene regulation. Keywords: time course