title: Metallothionein blocks oxidative DNA damage induced by acute inorganic arsenic exposure.
abstract: We studied how protein metallothionein (MT) impacts arsenic-induced oxidative DNA damage (ODD) using cells that poorly express MT (MT-I/II double knockout embryonic cells; called MT-null cells) and wild-type (WT) MT competent cells. Arsenic (as NaAsO2) was less cytolethal over 24h in WT cells (LC50=11.0±1.3μM; mean±SEM) than in MT-null cells (LC50=5.6±1.2μM). ODD was measured by the immuno-spin trapping method. Arsenic (1 or 5μM; 24h) induced much less ODD in WT cells (121% and 141% of control, respectively) than in MT-null cells (202% and 260%). In WT cells arsenic caused concentration-dependent increases in MT expression (transcript and protein), and in the metal-responsive transcription factor-1 (MTF-1), which is required to induce the MT gene. In contrast, basal MT levels were not detectable in MT-null cells and unaltered by arsenic exposure. Transfection of MT-I gene into the MT-null cells markedly reduced arsenic-induced ODD levels. The transport genes, Abcc1 and Abcc2 were increased by arsenic in WT cells but either showed no or very limited increases in MT-null cells. Arsenic caused increases in oxidant stress defense genes HO-1 and GSTα2 in both WT and MT-null cells, but to much higher levels in WT cells. WT cells appear more adept at activating metal transport systems and oxidant response genes, although the role of MT in these responses is unclear. Overall, MT protects against arsenic-induced ODD in MT competent cells by potential sequestration of scavenging oxidant radicals and/or arsenic.
authors.affiliation: National Toxicology Program Laboratory, Division of the National Toxicology Program, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, USA. Electronic address: qu@niehs.nih.gov.
authors.forename: Wei
authors.initials: W
authors.lastname: Qu
authors.affiliation: National Toxicology Program Laboratory, Division of the National Toxicology Program, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, USA.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Waalkes
mesh_terms: D000818:Animals; D001151:Arsenic / Q000633:toxicity*; D002273:Carcinogens / Q000633:toxicity*; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D004249:DNA Damage / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics; D004785:Environmental Pollutants / Q000633:toxicity*; D005786:Gene Expression Regulation / Q000187:drug effects; D005982:Glutathione Transferase / Q000235:genetics; D051547:Heme Oxygenase-1 / Q000235:genetics; D007527:Isoenzymes / Q000235:genetics; D008565:Membrane Proteins / Q000235:genetics; D008668:Metallothionein / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics; D018384:Oxidative Stress; D014157:Transcription Factors / Q000235:genetics; D000097809:Transcription Factor MTF-1
chemical_list: D001151:Arsenic; D002273:Carcinogens; D004268:DNA-Binding Proteins; D004785:Environmental Pollutants; D005982:Glutathione Transferase; D051547:Heme Oxygenase-1; D007527:Isoenzymes; D008565:Membrane Proteins; D008668:Metallothionein; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D014157:Transcription Factors; D000097809:Transcription Factor MTF-1; C496542:Hmox1 protein, mouse; C119995:glutathione S-transferase alpha; C421109:multidrug resistance-associated protein 1
keywords: Arsenic; Metallothionein; Oxidative DNA damage; Reactive oxygen species