title: Identification of aryl hydrocarbon receptor binding targets in mouse hepatic tissue treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin.
abstract: Genome-wide, promoter-focused ChIP-chip analysis of hepatic aryl hydrocarbon receptor (AHR) binding sites was conducted in 8-week old female C57BL/6 treated with 30 μg/kg/body weight 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) for 2 h and 24 h. These studies identified 1642 and 508 AHR-bound regions at 2h and 24h, respectively. A total of 430 AHR-bound regions were common between the two time points, corresponding to 403 unique genes. Comparison with previous AHR ChIP-chip studies in mouse hepatoma cells revealed that only 62 of the putative target genes overlapped with the 2 h AHR-bound regions in vivo. Transcription factor binding site analysis revealed an over-representation of aryl hydrocarbon response elements (AHREs) in AHR-bound regions with 53% (2 h) and 68% (24 h) of them containing at least one AHRE. In addition to AHREs, E2f-Myc activator motifs previously implicated in AHR function, as well as a number of other motifs, including Sp1, nuclear receptor subfamily 2 factor, and early growth response factor motifs were also identified. Expression microarray studies identified 133 unique genes differentially regulated after 4 h treatment with TCDD. Of which, 39 were identified as AHR-bound genes at 2 h. Ingenuity Pathway Analysis on the 39 AHR-bound TCDD responsive genes identified potential perturbation in biological processes such as lipid metabolism, drug metabolism, and endocrine system development as a result of TCDD-mediated AHR activation. Our findings identify direct AHR target genes in vivo, highlight in vitro and in vivo differences in AHR signaling and show that AHR recruitment does not necessarily result in changes in target gene expression.
authors: Department of Pharmacology & Toxicology, University of Toronto, Toronto, Ontario, Canada.
authors: Raymond
authors: R
authors: Lo
authors: Trine
authors: T
authors: Celius
authors: Agnes L
authors: AL
authors: Forgacs
authors: Edward
authors: E
authors: Dere
authors: Laura
authors: L
authors: MacPherson
authors: Patricia
authors: P
authors: Harper
authors: Timothy
authors: T
authors: Zacharewski
authors: Jason
authors: J
authors: Matthews
mesh_terms: D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000378:metabolism; D045744:Cell Line, Tumor; D004147:Dioxins / Q000494:pharmacology*; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects; D008099:Liver / Q000187:drug effects* / Q000378:metabolism; D008113:Liver Neoplasms / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D020411:Oligonucleotide Array Sequence Analysis; D054730:Protein Interaction Domains and Motifs; D018336:Receptors, Aryl Hydrocarbon / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D004147:Dioxins; D018336:Receptors, Aryl Hydrocarbon; D014157:Transcription Factors; C066841:2,3,7,8-tetrabromodibenzo-4-dioxin