title: Cytotoxicity of nitric oxide is alleviated by zinc-mediated expression of antioxidant genes.
abstract: Metallothioneins (MTs) are small, cysteine-rich zinc binding proteins that are powerful antioxidants. In this study, we investigated the interaction between zinc, MTs, and other components of the antioxidant defense system in HepG2 cells. Cells were preincubated with zinc and then exposed to sodium nitroprusside (SNP), a nitric oxide (NO) donor. Both zinc pretreatment and SNP exposure separately induced transcription of MT genes (MT1A, MT2A, MT1E, MT1X), as measured using real time-polymerase chain reaction (PCR) after reverse transcription (RT). Pretreatment of HepG2 cells with zinc sulfate (ZnSO4) followed by SNP exposure caused MT and glucose-6-phosphate dehydrogenase (G6PD) mRNA levels to increase more than in cells only exposed to SNP. However, when cells were incubated with N,N,N',N'-tetrakis(2-pyridylmethyl)ethyl-enediamine (TPEN), a membrane-permeant Zn2+ chelator, the stimulation of MT transcription by SNP was blocked, suggesting that SNP-induced upregulation of these genes is zinc-dependent. Human glutathione-S-transferase (hGSTA1) and G6PD mRNA levels in the cells treated with 5 microM TPEN decreased. Additionally, the induction of MT by SNP after zinc pretreatment appears to be mediated by metal-activated transcription factor-1 (MTF-1), which is induced by labile zinc in the cytosol. SNP cytotoxicity was inhibited by preincubation with zinc. Taken together, these results suggest that NO plays an important role in regulation of cellular zinc homeostasis and that NO-mediated release of protein-bound Zn2+ may be an important signal in antioxidant defense.
authors.affiliation: Division of Food Science, College of Life and Environmental Sciences, Institute of Biomedical Sciences and Safety, Korea University, Seoul 136-713, Korea.
authors.forename: Mi Ja
authors.initials: MJ
authors.lastname: Chung
authors.forename: Christer
authors.initials: C
authors.lastname: Hogstrand
authors.forename: Sung-Joon
authors.initials: SJ
authors.lastname: Lee
mesh_terms: D001483:Base Sequence; D045744:Cell Line, Tumor; D017931:DNA Primers; D005029:Ethylenediamines / Q000494:pharmacology; D005954:Glucosephosphate Dehydrogenase / Q000235:genetics*; D005982:Glutathione Transferase / Q000235:genetics*; D006801:Humans; D008668:Metallothionein / Q000235:genetics*; D009569:Nitric Oxide / Q000378:metabolism*; D020030:Nitric Oxide Donors / Q000494:pharmacology*; D015538:Nitrosation; D018384:Oxidative Stress; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015032:Zinc / Q000494:pharmacology*
chemical_list: D017931:DNA Primers; D005029:Ethylenediamines; D020030:Nitric Oxide Donors; D009569:Nitric Oxide; D008668:Metallothionein; D005954:Glucosephosphate Dehydrogenase; D005982:Glutathione Transferase; D015032:Zinc; C044387:N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine