title: Interactions between the aryl hydrocarbon receptor and P-TEFb. Sequential recruitment of transcription factors and differential phosphorylation of C-terminal domain of RNA polymerase II at cyp1a1 promoter.
abstract: The expression of the cytochrome P450 1A1 gene (cyp1a1) is regulated by the aryl hydrocarbon receptor (AhR), which is a ligand-activated transcription factor that mediates most toxic responses induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In the nucleus, ligand-activated AhR binds to the xenobiotic response elements, initiating chromatin remodeling and recruitment of coregulators, leading to the formation of preinitiation complex followed by elongation. Here, we report that ligand-activated AhR recruits the positive transcription elongation factor (P-TEFb) and RNA polymerase II (RNA PII) to the cyp1a1 promoter with concomitant phosphorylation of the RNA PII carboxyl domain (CTD). Interestingly, the serine 2 and serine 5 of the heptapeptide repeats (YSPTSPS) were sequentially phosphorylated upon TCDD treatment. Inhibition of P-TEFb kinase activity by 5,6-dichloro-1-beta-d-ribofuranosyl-benzimidazole (DRB) suppressed CTD phosphorylation (especially serine 2 phosphorylation) and abolished processive elongation without disrupting the assembly of the preinitiation complex at the cyp1a1 promoter. Remarkably, we found that activation of NF-kappaB by TNF-alpha selectively inhibited TCDD-induced serine 2 phosphorylation in mouse liver cells, suggesting that residue-specific phosphorylation of RNA PII CTD at the cyp1a1 promoter is an important regulatory point upon which signal "cross-talk" converges. Finally, we show that ligand-activated AhR associated with P-TEFb through the C terminus of cyclin T1, suggesting that AhR recruit the P-TEFb to the cyp1a1 promoter whereupon its kinase subunit phosphorylates the RNA PII CTD.
authors.affiliation: Department of Veterinary Physiology and Pharmacology, MS 4466, Texas A&M University, College Station, Texas 77843, USA. ytian@cvm.tamu.edu
authors.forename: Yanan
authors.initials: Y
authors.lastname: Tian
authors.forename: Sui
authors.initials: S
authors.lastname: Ke
authors.forename: Min
authors.initials: M
authors.lastname: Chen
authors.forename: Tao
authors.initials: T
authors.lastname: Sheng
mesh_terms: D000818:Animals; D001665:Binding Sites; D056906:Cyclin T; D042863:Cyclin-Dependent Kinase 9 / Q000378:metabolism; D016213:Cyclins / Q000235:genetics / Q000378:metabolism; D019363:Cytochrome P-450 CYP1A1 / Q000235:genetics*; D004247:DNA / Q000378:metabolism; D015870:Gene Expression; D006801:Humans; D008099:Liver / Q000378:metabolism; D051379:Mice; D016296:Mutagenesis; D016328:NF-kappa B / Q000502:physiology; D010766:Phosphorylation; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology; D042925:Positive Transcriptional Elongation Factor B / Q000502:physiology*; D011401:Promoter Regions, Genetic / Q000235:genetics*; D012319:RNA Polymerase II / Q000378:metabolism*; D020239:Receptor Cross-Talk; D018336:Receptors, Aryl Hydrocarbon / Q000235:genetics / Q000502:physiology*; D012441:Saccharomyces cerevisiae; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction; D014157:Transcription Factors / Q000378:metabolism*; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D020798:Two-Hybrid System Techniques
chemical_list: C503684:CCNT1 protein, human; C503685:Ccnt1 protein, mouse; D056906:Cyclin T; D016213:Cyclins; D016328:NF-kappa B; D000072317:Polychlorinated Dibenzodioxins; D018336:Receptors, Aryl Hydrocarbon; D014157:Transcription Factors; D014409:Tumor Necrosis Factor-alpha; D012694:Serine; D004247:DNA; D019363:Cytochrome P-450 CYP1A1; D042925:Positive Transcriptional Elongation Factor B; D042863:Cyclin-Dependent Kinase 9; D012319:RNA Polymerase II