title: Disruption of period gene expression alters the inductive effects of dioxin on the AhR signaling pathway in the mouse liver.
abstract: The aryl hydrocarbon receptor (AhR) and AhR nuclear translocator (ARNT) are transcription factors that express Per-Arnt-Sim (PAS) DNA-binding motifs and mediate the metabolism of drugs and environmental toxins in the liver. Because these transcription factors interact with other PAS genes in molecular feedback loops forming the mammalian circadian clockworks, we determined whether targeted disruption or siRNA inhibition of Per1 and Per2 expression alters toxin-mediated regulation of the AhR signaling pathway in the mouse liver and Hepa1c1c7 hepatoma cells in vitro. Treatment with the prototypical Ahr ligand, 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), had inductive effects on the primary targets of AhR signaling, Cyp1A1 and Cyp1B1, in the liver of all animals, but genotype-based differences were evident such that the toxin-mediated induction of Cyp1A1 expression was significantly greater (2-fold) in mice with targeted disruption of Per1 (Per1(ldc) and Per1(ldc)/Per2(ldc)). In vitro experiments yielded similar results demonstrating that siRNA inhibition of Per1 significantly increases the TCDD-induced expression of Cyp1A1 and Cyp1B1 in Hepa1c1c7 cells. Per2 inhibition in siRNA-infected Hepa1c1c7 cells had the opposite effect and significantly decreased both the induction of these p450 genes as well as AhR and Arnt expression in response to TCDD treatment. These findings suggest that Per1 may play a distinctive role in modulating AhR-regulated responses to TCDD in the liver.
authors.affiliation: Department of Biology, College Station, Texas 77843-3258, USA; Center for Research on Biological Clocks, College Station, Texas 77843-3258, USA.
authors.forename: Xiaoyu
authors.initials: X
authors.lastname: Qu
authors.forename: Richard P
authors.initials: RP
authors.lastname: Metz
authors.forename: Weston W
authors.initials: WW
authors.lastname: Porter
authors.forename: Vincent M
authors.initials: VM
authors.lastname: Cassone
authors.forename: David J
authors.initials: DJ
authors.lastname: Earnest
mesh_terms: D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000096:biosynthesis / Q000235:genetics; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator / Q000187:drug effects* / Q000378:metabolism; D051792:Basic Helix-Loop-Helix Proteins; D002273:Carcinogens / Q000633:toxicity*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D019363:Cytochrome P-450 CYP1A1 / Q000096:biosynthesis / Q000235:genetics; D065633:Cytochrome P-450 CYP1B1; D004790:Enzyme Induction; D005260:Female; D008099:Liver / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D056950:Period Circadian Proteins; D000072317:Polychlorinated Dibenzodioxins / Q000633:toxicity*; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D018336:Receptors, Aryl Hydrocarbon / Q000187:drug effects* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D001189:Aryl Hydrocarbon Hydroxylases; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D051792:Basic Helix-Loop-Helix Proteins; D002273:Carcinogens; D018797:Cell Cycle Proteins; D019363:Cytochrome P-450 CYP1A1; D065633:Cytochrome P-450 CYP1B1; D009687:Nuclear Proteins; D056950:Period Circadian Proteins; D000072317:Polychlorinated Dibenzodioxins; D034741:RNA, Small Interfering; D018336:Receptors, Aryl Hydrocarbon; D014157:Transcription Factors; C484722:Ahr protein, mouse; C497397:Arnt protein, mouse; C539023:Per1 protein, mouse; C513312:Per2 protein, mouse; C585498:Cyp1b1 protein, mouse