title: Modulation of NAD(P)H:quinone oxidoreductase by vanadium in human hepatoma HepG2 cells.
abstract: Recent studies demonstrated the carcinogenicity and the mutagenicity of vanadium compounds. In addition, vanadium (V(5+)) was found to enhance the effects of other genotoxic agents. However, the mechanism by which V(5+) induce toxicity remain unknown. In the current study we examined the effect of V(5+) (as ammonium metavanadate, NH(4)VO(3)) on the expression of NAD(P)H: quinone oxidoreductase 1 (NQO1) in human hepatoma HepG2 cells. Therefore, HepG2 cells were treated with increasing concentrations of V(5+) in the presence of two NQO1 inducers, the 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and isothiocyanate sulforaphane (SUL). Our results showed that V(5+) inhibited the TCDD- and SUL-mediated induction of NQO1 at mRNA, protein and activity levels. Investigating the effect of V(5+) at transcriptional levels revealed that V(5+) significantly inhibited the TCDD- and SUL-mediated induction of antioxidant responsive element (ARE)-dependent luciferase reporter gene expression. In addition, V(5+) was able to decrease the TCDD- and SUL-induced nuclear accumulation of nuclear factor erythroid 2-related factor-2 (Nrf2) without affecting Nrf2 mRNA or protein levels. Looking at the post-transcriptional level, V(5+) did not affect NQO1 mRNA stability, thus eliminating the possible role of V(5+) in decreasing NQO1 mRNA levels through this mechanism. In contrast, at post-translational level, V(5+) was able to significantly decrease NQO1 protein half-life. The present study demonstrates for the first time that V(5+) down-regulates NQO1 at the transcriptional and post-translational levels in the human hepatoma HepG2 cells via AhR- and Nrf2-dependent mechanisms.
authors.affiliation: Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Ghada
authors.initials: G
authors.lastname: Abdelhamid
authors.forename: Anwar
authors.initials: A
authors.lastname: Anwar-Mohamed
authors.forename: Mohey M
authors.initials: MM
authors.lastname: Elmazar
authors.forename: Ayman O S
authors.initials: AO
authors.lastname: El-Kadi
mesh_terms: D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects*; D004347:Drug Interactions; D004790:Enzyme Induction; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000187:drug effects* / Q000201:enzymology; D006801:Humans; D017879:Isothiocyanates / Q000633:toxicity; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000235:genetics / Q000378:metabolism*; D051267:NF-E2-Related Factor 2 / Q000235:genetics / Q000378:metabolism; D000072317:Polychlorinated Dibenzodioxins / Q000633:toxicity; D012323:RNA Processing, Post-Transcriptional / Q000187:drug effects; D012333:RNA, Messenger / Q000378:metabolism; D018336:Receptors, Aryl Hydrocarbon / Q000235:genetics / Q000378:metabolism; D014638:Vanadates / Q000633:toxicity*
chemical_list: D017879:Isothiocyanates; D051267:NF-E2-Related Factor 2; C495635:NFE2L2 protein, human; D000072317:Polychlorinated Dibenzodioxins; D012333:RNA, Messenger; D018336:Receptors, Aryl Hydrocarbon; C037152:isothiocyanic acid; D014638:Vanadates; D016660:NAD(P)H Dehydrogenase (Quinone); C447479:NQO1 protein, human; C101036:ammonium metavanadate