title: Significance of prolyl hydroxylase 2 in the interference of aryl hydrocarbon receptor and hypoxia-inducible factor-1 alpha signaling.
abstract: Hypoxia-inducible factor-1 alpha (HIF-1 alpha) and the aryl hydrocarbon receptor (AhR) work as environmental sensors in human tissues. These proteins are members of the helix-loop-helix/Per-ARNT-SIM transcription factor family and form heterodimers with the aryl hydrocarbon receptor nuclear translocator. HIF-1 alpha can be activated by low oxygen concentrations and hypoxia-inducing agents. The AhR is activated by xenobiotica such as dioxins. Here, we analyze the interference between the AhR signaling, activated by 10 nM 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD), and the HIF-1 alpha pathway, induced by hypoxia (5% O2), in two human cell lines, the breast carcinoma cell line MCF-7 and the hepatocyte cell line HepG2. In both cell lines, treatment with TCDD and hypoxia clearly reduced the stabilization of HIF-1 alpha and HRE-mediated promoter activity when compared to the induction under hypoxia alone. Because these effects were not observed after alpha-naphthoflavone treatment and HIF-1 alpha mRNA was not down-regulated, HIF-1 alpha stabilization was revealed to be the target by TCDD in an AhR-depended mechanism. Under exposure to TCDD or hypoxia, the main regulator of HIF-1 alpha stability, the prolyl hydroxylase domain containing protein 2 (PHD2) showed an increase in promoter activity, transcript numbers, and protein amount. Therefore, PHD2 expression is regulated in an AhR-dependent manner under normoxia. The AhR-dependent regulation of PHD2 under normoxia, however, is overwritten by the TCDD-mediated destabilization of HIF-1 alpha. The destabilization of HIF-1 alpha is the dominant effect causing the reduced PHD2 expression after simultaneous exposure to TCDD and hypoxia. We conclude that PHD2 does not mediate the TCDD-mediated HIF-1 alpha destabilization and does not control the interference of AhR and HIF-1 alpha pathways.
authors: Department of Anatomy and Cell Biology, Martin Luther University Faculty of Medicine, D-06097 Halle (Saale), Germany. anja.seifert@medizin.uni-halle.de
authors: Anja
authors: A
authors: Seifert
authors: Dörthe M
authors: DM
authors: Katschinski
authors: Sarah
authors: S
authors: Tonack
authors: Bernd
authors: B
authors: Fischer
authors: Anne
authors: A
authors: Navarrete Santos
mesh_terms: D001571:Benzoflavones / Q000494:pharmacology; D001943:Breast Neoplasms; D006528:Carcinoma, Hepatocellular; D015687:Cell Hypoxia / Q000502:physiology; D045744:Cell Line, Tumor; D015536:Down-Regulation; D005786:Gene Expression Regulation / Q000187:drug effects; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D064799:Hypoxia-Inducible Factor-Proline Dioxygenases; D008113:Liver Neoplasms; D000072317:Polychlorinated Dibenzodioxins / Q000633:toxicity; D011393:Procollagen-Proline Dioxygenase / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D018336:Receptors, Aryl Hydrocarbon / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D001571:Benzoflavones; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D000072317:Polychlorinated Dibenzodioxins; D012333:RNA, Messenger; D018336:Receptors, Aryl Hydrocarbon; C011512:alpha-naphthoflavone; C490190:EGLN1 protein, human; D011393:Procollagen-Proline Dioxygenase; D064799:Hypoxia-Inducible Factor-Proline Dioxygenases