Metallothionein blocks oxidative DNA damage in vitro.
The role of metallothionein (MT) in mitigation of oxidative DNA damage (ODD) induced by either cadmium (Cd) or the direct oxidant hydrogen peroxide (H(2)O(2)) was systematically examined using MT-I/II double knockout (MT-null) or MT-competent wild-type (WT) cells. Both toxicants were much more lethal to MT-null cells (Cd LC(50) = 6.6 μM; H(2)O(2) LC(50) = 550 μM) than to WT cells (Cd LC(50) = 16.5 μM; H(2)O(2) LC(50) = 930 μM). Cd induced concentration-related MT increases in WT cells, while the basal levels were undetectable and not increased by Cd in MT-null cells. ODD, measured by the immuno-spin trapping method, was minimally induced by sub-toxic Cd levels (1 or 5 μM; 24 h) in WT cells, but markedly increased in MT-null cells (>430 %). Similarly, ODD was induced to higher levels by lower concentrations of H(2)O(2) in MT-null cells than WT cells. Transfection of MT-I into MT-null cells reduced both Cd- and H(2)O(2)-induced cytolethality and ODD. Cd increased the expression of the oxidant defense genes, HO-1, and GSTa2 to a much greater extent in MT-null cells than in WT. Cd or H(2)O(2) exposure increased the expression of key transport genes, Mrp1 and Mrp2, in WT cells but not in MT-null cells. MT protects against Cd- and H(2)O(2)-induced ODD in MT-competent cells possibly by multiple mechanisms, potentially including direct metal ion sequestration and sequestration of oxidant radicals by MT. MT-deficient cells appear to adapt to Cd primarily by turning on oxidant response systems, while MT-competent cells activate MT and transport systems.
Inorganic Toxicology Group, National Toxicology Program Laboratory, Division of the National Toxicology Program, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, USA.
Wei
W
Qu
Jingbo
J
Pi
Michael P
MP
Waalkes
D000818:Animals; D019256:Cadmium Chloride / Q000633:toxicity; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D004249:DNA Damage; D053595:Embryonic Stem Cells / Q000187:drug effects* / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects; D055785:Gene Knockdown Techniques; D005982:Glutathione Transferase / Q000235:genetics; D051547:Heme Oxygenase-1 / Q000235:genetics / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000633:toxicity; D007527:Isoenzymes / Q000235:genetics; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008668:Metallothionein / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics / Q000378:metabolism; D016877:Oxidants / Q000633:toxicity*; D018384:Oxidative Stress / Q000187:drug effects*; D014162:Transfection
D019256:Cadmium Chloride; D005982:Glutathione Transferase; D051547:Heme Oxygenase-1; D006861:Hydrogen Peroxide; D007527:Isoenzymes; D008565:Membrane Proteins; D008668:Metallothionein; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D016877:Oxidants; C496542:Hmox1 protein, mouse; C119995:glutathione S-transferase alpha; C421109:multidrug resistance-associated protein 1