Project description:BackgroundEndocrine disrupting chemicals (EDCs) are exogenous compounds that interfere with the endocrine system of vertebrates, often through direct or indirect interactions with nuclear receptor proteins. Estrogen receptors (ERs) are particularly important protein targets and many EDCs are ER binders, capable of altering normal homeostatic transcription and signaling pathways. An estrogenic xenobiotic can bind ER as either an agonist or antagonist to increase or inhibit transcription, respectively. The receptor conformations in the complexes of ER bound with agonists and antagonists are different and dependent on interactions with co-regulator proteins that vary across tissue type. Assessment of chemical endocrine disruption potential depends not only on binding affinity to ERs, but also on changes that may alter the receptor conformation and its ability to subsequently bind DNA response elements and initiate transcription. Using both agonist and antagonist conformations of the ERα, we developed an in silico approach that can be used to differentiate agonist versus antagonist status of potential binders.MethodsThe approach combined separate molecular docking models for ER agonist and antagonist conformations. The ability of this approach to differentiate agonists and antagonists was first evaluated using true agonists and antagonists extracted from the crystal structures available in the protein data bank (PDB), and then further validated using a larger set of ligands from the literature. The usefulness of the approach was demonstrated with enrichment analysis in data sets with a large number of decoy ligands.ResultsThe performance of individual agonist and antagonist docking models was found comparable to similar models in the literature. When combined in a competitive docking approach, they provided the ability to discriminate agonists from antagonists with good accuracy, as well as the ability to efficiently select true agonists and antagonists from decoys during enrichment analysis.ConclusionThis approach enables evaluation of potential ER biological function changes caused by chemicals bound to the receptor which, in turn, allows the assessment of a chemical's endocrine disrupting potential. The approach can be used not only by regulatory authorities to perform risk assessments on potential EDCs but also by the industry in drug discovery projects to screen for potential agonists and antagonists.

Project description:Using the estrogen receptor alpha (ERalpha) as a model ligand inducible transcription factor, we sought to explicitly define parameters that determine transcription factor binding site selection on a genomic scale in an inducible system that minimizes confounding chromatin effects by the transcription factor itself. By examining several genetic and epigenetic parameters, we find that an energetically favorable estrogen response element (ERE) motif sequence, evidence of occupancy of a "pioneering" transcription factor FOXA1, the presence of the enhancer mark, H3K4me1, and an open chromatin configuration (FAIRE) at the pre-ligand state provide specificity for ER binding. Genome-wide ChIP-sequencing was done in MCF-7 cancer cell line for the following histone H3 modifications: monomethylation H3K4me1, trimethylation H3K4me3, H3K9me3, H3K27me3, acetylation H3K9ac, H3K14ac. In addition sequencing of RNA Pol II was done at same treatment conditions (E2 and DMSO). In addition, we assessed the chromatin configuration of ERα binding sites by deeply sequencing fragments isolated by Formaldehyde-Assisted Isolation of Regulatory Elements (FAIRE) (Giresi et al, 2007) which enriches for nucleosome free genomic DNA in the aqueous phase of a phenol extraction. The analysis histone modifications in MCF-7 cancer cells was done by ChIP-seq data obtained either with E2 stimulation or without stimulation using vehicle as a control. Using the ERα binding sites defined by ChIP-seq (separate submission), we analyzed the population characteristics of the chromatin configuration of the ERα binding sites. To this end, we performed ChIP-seq analysis for the occupancy configuration of each of the following marks before and after E2 exposure: RNA Pol II, the activation marks H3K4me1, H3K4me3, H3K9ac and H3K14ac, and the repression marks H3K9me3 and H3K27me3. We assessed the chromatin configuration of ERα binding sites by deeply sequencing fragments isolated by Formaldehyde-Assisted Isolation of Regulatory Elements (FAIRE) (Giresi et al, 2007) which enriches for nucleosome free genomic DNA in the aqueous phase of a phenol extraction. The tag count of FAIRE fragments reflects the nucleosome depletion at any given site. RNA Pol II - Cat# ab5408, Abcam; H3K9me3 - Cat# ab8898, Abcam; H3K27me3 - Cat# 07-449, Upstate Biotechnology Inc.; H3K4me1 - Cat# ab8895, Abcam; H3K4me3 - Cat# ab8580, Abcam; H3K9ac - Cat# 07-352, Upstate Biotechnology Inc.; H3K14ac - Cat# 07-353, Upstate Biotechnology Inc.

Dataset Information

Genome-wide dynamics of chromatin binding of estrogen receptors alpha and beta: mutual restriction and competitive site selection.

Publications

Genome-wide dynamics of chromatin binding of estrogen receptors alpha and beta: mutual restriction and competitive site selection.

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