title: Transcriptional and posttranslational inhibition of dioxin-mediated induction of CYP1A1 by harmine and harmol.
abstract: Dioxins are widespread environmental contaminants that induce the carcinogen-activating enzyme, cytochrome P450 1A1 (CYP1A1) through an aryl hydrocarbon receptor (AhR)-dependent mechanism. We previously demonstrated that harmine inhibits the dioxin-mediated induction of Cyp1a1 activity in murine hepatoma cells. Therefore, the aim of this study is to determine the effect of harmine and its main metabolite, harmol, on the dioxin-mediated induction of CYP1A1 in human HepG2 and murine Hepa 1c1c7 hepatoma cells. Our results showed that harmine and harmol significantly inhibited the dioxin-mediated induction of CYP1A1 at mRNA, protein, and activity levels in a concentration-dependent manner in human and murine hepatoma cells. Moreover, harmine and harmol inhibited the AhR-dependent luciferase activity and the activation and transformation of AhR using the electrophoretic mobility shift assay. In addition, harmine and harmol displaced [(3)H]TCDD in the competitive ligand binding assay. At posttranslational level, both harmine and harmol decreased the protein stability of CYP1A1, suggesting that posttranslational mechanism is involved. Furthermore, we demonstrated that the underlying mechanisms of the posttranslational modifications of both compounds involve ubiquitin-proteasomal pathway and direct inhibitory effects of CYP1A1 enzyme. We concluded that harmine and its metabolite, harmol, are new inhibitors of dioxin-mediated effects.
authors: Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2N8.
authors: Mohamed A M
authors: MA
authors: El Gendy
authors: Anatoly A
authors: AA
authors: Soshilov
authors: Michael S
authors: MS
authors: Denison
authors: Ayman O S
authors: AO
authors: El-Kadi
mesh_terms: D000818:Animals; D002273:Carcinogens / Q000633:toxicity*; D019363:Cytochrome P-450 CYP1A1 / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D004147:Dioxins / Q000633:toxicity*; D015870:Gene Expression / Q000187:drug effects*; D006168:Guinea Pigs; D006247:Harmine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D056945:Hep G2 Cells; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D008996:Monoamine Oxidase Inhibitors / Q000494:pharmacology*; D014176:Protein Biosynthesis / Q000187:drug effects; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: D002273:Carcinogens; D004147:Dioxins; D008996:Monoamine Oxidase Inhibitors; C001326:harmol; D006247:Harmine; D019363:Cytochrome P-450 CYP1A1