title: Accumulation of manganese superoxide dismutase under metal-depleted conditions: proposed role for zinc ions in cellular redox balance.
abstract: A diet low in copper results in increased levels of MnSOD (manganese superoxide dismutase), a critical antioxidative enzyme conferring protection against oxidative stress, in rat liver mitochondria. The mechanism for this was investigated using cultured HepG2 cells, a human hepatocellular carcinoma-derived line. MnSOD activity increased 5-7-fold during incubation in a medium supplemented with metal-depleted fetal bovine serum, with a corresponding elevation of its mRNA levels. Metal depletion also decreased CuZnSOD and glutathione peroxidase levels to approx. 70-80% of baseline. When zinc ions were added to the medium at micromolar levels, MnSOD accumulation was suppressed; however, copper ions had essentially no effect on MnSOD expression. Since the intracellular redox status was shifted to a more oxidized state by metal depletion, we examined the DNA-binding activity of NF-kappaB (nuclear factor-kappaB), an oxidative stress-sensitive transactivating factor that plays a primary role in MnSOD induction. A gel shift assay indicated that the DNA-binding activity of NF-kappaB was increased in cells maintained in metal-depleted culture, suggesting the involvement of the transactivating function of NF-kappaB in this induction. This was further supported by the observation that curcumin suppressed both the DNA-binding activity of NF-kappaB and the induction of MnSOD mRNA in cells cultivated under metal-depleted conditions. These results suggest that the level of zinc, rather than copper, is a critical regulatory factor in MnSOD expression. It is possible that a deficiency of zinc in the low-copper diet may be primarily involved in MnSOD induction.
authors.affiliation: Department of Biochemistry, Yamagata University School of Medicine, 2-2-2 Iidanishi, Yamagata 990-9585, Japan.
authors.forename: Kaoru
authors.initials: K
authors.lastname: Otsu
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Ikeda
authors.forename: Junichi
authors.initials: J
authors.lastname: Fujii
mesh_terms: D002412:Cations / Q000494:pharmacology; D045744:Cell Line, Tumor; D019610:Cytoprotection; D003576:Electron Transport Complex IV / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D008670:Metals / Q000494:pharmacology; D016328:NF-kappa B / Q000378:metabolism; D010084:Oxidation-Reduction; D013482:Superoxide Dismutase / Q000378:metabolism*; D013481:Superoxides / Q000378:metabolism; D015032:Zinc / Q000494:pharmacology / Q000502:physiology*; D000099156:Superoxide Dismutase 2
chemical_list: D002412:Cations; D003576:Electron Transport Complex IV; D006861:Hydrogen Peroxide; D008670:Metals; D016328:NF-kappa B; D013482:Superoxide Dismutase; D013481:Superoxides; D015032:Zinc; D000099156:Superoxide Dismutase 2