Hypoxia perturbs aryl hydrocarbon receptor signaling and CYP1A1 expression induced by PCB 126 in human skin and liver-derived cell lines.
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.
['Vorrink|Sabine U|SU|', 'Severson|Paul L|PL|', 'Kulak|Mikhail V|MV|', 'Futscher|Bernard W|BW|', 'Domann|Frederick E|FE|']
D051784:Aryl Hydrocarbon Receptor Nuclear Translocator D051792:Basic Helix-Loop-Helix Transcription Factors D015687:Cell Hypoxia D019363:Cytochrome P-450 CYP1A1 D056945:Hep G2 Cells D022781:Hepatocytes D006801:Humans D051795:Hypoxia-Inducible Factor 1, alpha Subunit D008099:Liver D011078:Polychlorinated Biphenyls D000072317:Polychlorinated Dibenzodioxins D011401:Promoter Regions, Genetic D011485:Protein Binding D012333:RNA, Messenger D018336:Receptors, Aryl Hydrocarbon D015398:Signal Transduction D012867:Skin D015533:Transcriptional Activation
Hypoxia aryl hydrocarbon receptor CYP1A1 PCB PCB 126 AhR 2,3,7,8-tetrachlorodibenzo-p-dioxin TCDD polychlorinated biphenyl aryl hydrocarbon receptor nuclear translocator ARNT hypoxia-inducible factor-1α HIF-1α 2,2′,4,4′,5,5′-hexachlorobiphenyl 3,3′,4,4′,5-pentachlorobiphenyl 6,2′,4′-trimethoxyflavone ChIP DMSO EMSA HRE PCB 153 RPLP0 TMF XRE bHLH/PAS basic helix-loop-helix/PER-ARNT-SIM chromatin immunoprecipitation cytochrome P450 1A1 dimethyl sulfoxide electrophoretic mobility shift assay hypoxia response element qRT-PCR quantitative real-time reverse transcription polymerase chain reaction ribosomal protein, large, P0 xenobiotic response element