title: ER alpha-AHR-ARNT protein-protein interactions mediate estradiol-dependent transrepression of dioxin-inducible gene transcription.
abstract: The aryl hydrocarbon receptor (AHR) and the aryl hydrocarbon receptor nuclear translocator (ARNT) form a heterodimeric transcription factor upon binding a wide variety of environmental pollutants, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). AHR target gene activation can be repressed by estrogen and estrogen-like compounds. In this study, we demonstrate that a significant component of TCDD-inducible Cyp1a1 transcription is the result of recruitment of estrogen receptor (ER)-alpha by AHR/ARNT as a transcriptional co-repressor. Both AHR and ARNT were capable of interacting directly with ER alpha, as ascertained by glutathione S-transferase pull-down. 17Beta-estradiol repressed TCDD-activated Cyp1a1 and Cyp1b1 gene transcription in MCF-7 cells in the presence of cycloheximide, as determined by reverse transcription/real-time PCR. Furthermore, chromatin immunoprecipitation (ChIP) assays have shown that ER alpha is present at the Cyp1a1 enhancer only after co-treatment with E2 and TCDD, in MCF-7 cells. Sequential two-step ChIP assays were performed which demonstrate that AHR and ER alpha are present together at the same time on the Cyp1a1 enhancer during transrepression. Taken together these data support a role for ER-mediated transrepression of AHR-dependent gene regulation.
authors.affiliation: Center for Molecular Toxicology and Carcinogenesis and Department of Veterinary Sciences, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: Timothy V
authors.initials: TV
authors.lastname: Beischlag
authors.forename: Gary H
authors.initials: GH
authors.lastname: Perdew
mesh_terms: D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D015153:Blotting, Western; D045744:Cell Line, Tumor; D047369:Chromatin Immunoprecipitation; D003513:Cycloheximide / Q000494:pharmacology; D019363:Cytochrome P-450 CYP1A1 / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry*; D004147:Dioxins / Q000494:pharmacology*; D004742:Enhancer Elements, Genetic; D004787:Environmental Pollution; D047628:Estrogen Receptor alpha / Q000378:metabolism*; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D010957:Plasmids / Q000378:metabolism; D000072317:Polychlorinated Dibenzodioxins; D011485:Protein Binding; D018336:Receptors, Aryl Hydrocarbon / Q000737:chemistry*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014157:Transcription Factors / Q000737:chemistry*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection
chemical_list: C497396:ARNT protein, human; D004268:DNA-Binding Proteins; D004147:Dioxins; D047628:Estrogen Receptor alpha; D000072317:Polychlorinated Dibenzodioxins; D018336:Receptors, Aryl Hydrocarbon; D014157:Transcription Factors; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D003513:Cycloheximide; D019363:Cytochrome P-450 CYP1A1; D005982:Glutathione Transferase