title: Dioxin induces localized, graded changes in chromatin structure: implications for Cyp1A1 gene transcription.
abstract: In mouse hepatoma cells, the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, or dioxin) induces Cyp1A1 gene transcription, a process that requires two basic helix-loop-helix regulatory proteins, the aromatic hydrocarbon receptor (AhR) and the aromatic hydrocarbon receptor nuclear translocator (Arnt). We have used a ligation-mediated PCR technique to analyze dioxin-induced changes in protein-DNA interactions and chromatin structure of the Cyp1A1 enhancer-promoter in its native chromosomal setting. Dioxin-induced binding of the AhR/Arnt heteromer to enhancer chromatin is associated with a localized (about 200 bp) alteration in chromatin structure that is manifested by increased accessibility of the DNA; these changes probably reflect direct disruption of a nucleosome by AhR/Arnt. Dioxin induces analogous AhR/Arnt-dependent changes in chromatin structure and accessibility at the Cyp1A1 promoter. However, the changes at the promoter must occur by a different, more indirect mechanism, because they are induced from a distance and do not reflect a local effect of AhR/Arnt binding. Dose-response experiments indicate that the changes in chromatin structure at the enhancer and promoter are graded and mirror the graded induction of Cyp1A1 transcription by dioxin. We discuss these results in terms of a TCDD-induced shift in an equilibrium between nucleosomal and nonnucleosomal chromatin configurations.
authors.affiliation: Department of Molecular Pharmacology, Stanford University School of Medicine, California 94305-5332, USA.
authors.forename: S T
authors.initials: ST
authors.lastname: Okino
authors.forename: J P
authors.initials: JP
authors.lastname: Whitlock
mesh_terms: D000818:Animals; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D001483:Base Sequence; D006528:Carcinoma, Hepatocellular / Q000235:genetics; D002843:Chromatin / Q000187:drug effects* / Q000648:ultrastructure; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics*; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins; D003850:Deoxyribonuclease I / Q000494:pharmacology; D004742:Enhancer Elements, Genetic / Q000235:genetics; D004790:Enzyme Induction; D008113:Liver Neoplasms / Q000235:genetics; D051379:Mice; D008957:Models, Genetic; D008969:Molecular Sequence Data; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology*; D016133:Polymerase Chain Reaction / Q000379:methods; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D018336:Receptors, Aryl Hydrocarbon / Q000378:metabolism; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics*; D013463:Sulfuric Acid Esters / Q000494:pharmacology; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
chemical_list: C497397:Arnt protein, mouse; D002843:Chromatin; D004268:DNA-Binding Proteins; D000072317:Polychlorinated Dibenzodioxins; D018336:Receptors, Aryl Hydrocarbon; D013463:Sulfuric Acid Esters; D014157:Transcription Factors; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D004247:DNA; D003577:Cytochrome P-450 Enzyme System; D003850:Deoxyribonuclease I; C007482:dimethyl sulfate