title: Hypoxia perturbs aryl hydrocarbon receptor signaling and CYP1A1 expression induced by PCB 126 in human skin and liver-derived cell lines.
abstract: The aryl hydrocarbon receptor (AhR) is an important mediator of toxic responses after exposure to xenobiotics including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and dioxin-like polychlorinated biphenyls (PCBs). Activation of AhR responsive genes requires AhR dimerization with the aryl hydrocarbon receptor nuclear translocator (ARNT), a heterodimeric partner also shared by the hypoxia-inducible factor-1α (HIF-1α) protein. TCDD-stimulated AhR transcriptional activity can be influenced by hypoxia; however, it less well known whether hypoxia interferes with AhR transcriptional transactivation in the context of PCB-mediated AhR activation in human cells. Elucidation of this interaction is important in liver hepatocytes which extensively metabolize ingested PCBs and experience varying degrees of oxygen tension during normal physiologic function. This study was designed to assess the effect of hypoxia on AhR transcriptional responses after exposure to 3,3',4,4',5-pentachlorobiphenyl (PCB 126). Exposure to 1% O2 prior to PCB 126 treatment significantly inhibited CYP1A1 mRNA and protein expression in human HepG2 and HaCaT cells. CYP1A1 transcriptional activation was significantly decreased upon PCB 126 stimulation under conditions of hypoxia. Additionally, hypoxia pre-treatment reduced PCB 126 induced AhR binding to CYP1 target gene promoters. Importantly, ARNT overexpression rescued cells from the inhibitory effect of hypoxia on XRE-luciferase reporter activity. Therefore, the mechanism of interference of the signaling crosstalk between the AhR and hypoxia pathways appears to be at least in part dependent on ARNT availability. Our results show that AhR activation and CYP1A1 expression induced by PCB 126 were significantly inhibited by hypoxia and hypoxia might therefore play an important role in PCB metabolism and toxicity.
authors.affiliation: Interdisciplinary Graduate Program in Human Toxicology, The University of Iowa, Iowa City, IA, USA; Department of Radiation Oncology, The University of Iowa, Iowa City, IA, USA.
authors.forename: Sabine U
authors.initials: SU
authors.lastname: Vorrink
authors.affiliation: Department of Pharmacology and Toxicology, The University of Arizona, Tucson, AZ, USA.
authors.forename: Paul L
authors.initials: PL
authors.lastname: Severson
authors.affiliation: Department of Surgery, The University of Iowa, Iowa City, IA, USA.
authors.forename: Mikhail V
authors.initials: MV
authors.lastname: Kulak
authors.affiliation: Department of Pharmacology and Toxicology, The University of Arizona, Tucson, AZ, USA.
authors.forename: Bernard W
authors.initials: BW
authors.lastname: Futscher
authors.affiliation: Interdisciplinary Graduate Program in Human Toxicology, The University of Iowa, Iowa City, IA, USA; Department of Radiation Oncology, The University of Iowa, Iowa City, IA, USA; Department of Surgery, The University of Iowa, Iowa City, IA, USA. Electronic address: frederick-domann@uiowa.edu.
authors.forename: Frederick E
authors.initials: FE
authors.lastname: Domann
mesh_terms: D051784:Aryl Hydrocarbon Receptor Nuclear Translocator / Q000235:genetics / Q000378:metabolism; D051792:Basic Helix-Loop-Helix Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D015687:Cell Hypoxia / Q000187:drug effects; D019363:Cytochrome P-450 CYP1A1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D011078:Polychlorinated Biphenyls / Q000633:toxicity*; D000072317:Polychlorinated Dibenzodioxins / Q000633:toxicity; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018336:Receptors, Aryl Hydrocarbon / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D012867:Skin / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D015533:Transcriptional Activation
chemical_list: D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D051792:Basic Helix-Loop-Helix Proteins; D019363:Cytochrome P-450 CYP1A1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D011078:Polychlorinated Biphenyls; D000072317:Polychlorinated Dibenzodioxins; D012333:RNA, Messenger; D018336:Receptors, Aryl Hydrocarbon; C111235:AHR protein, human; C497396:ARNT protein, human; C497442:HIF1A protein, human; C569463:CYP1A1 protein, human; C023035:3,4,5,3',4'-pentachlorobiphenyl
keywords: 2,2′,4,4′,5,5′-hexachlorobiphenyl; 2,3,7,8-tetrachlorodibenzo-p-dioxin; 3,3′,4,4′,5-pentachlorobiphenyl; 6,2′,4′-trimethoxyflavone; ARNT; AhR; CYP1A1; ChIP; DMSO; EMSA; HIF-1α; HRE; Hypoxia; PCB; PCB 126; PCB 153; RPLP0; TCDD; TMF; XRE; aryl hydrocarbon receptor; aryl hydrocarbon receptor nuclear translocator; bHLH/PAS; basic helix-loop-helix/PER-ARNT-SIM; chromatin immunoprecipitation; cytochrome P450 1A1; dimethyl sulfoxide; electrophoretic mobility shift assay; hypoxia response element; hypoxia-inducible factor-1α; polychlorinated biphenyl; qRT-PCR; quantitative real-time reverse transcription polymerase chain reaction; ribosomal protein, large, P0; xenobiotic response element