Alteration of Cellular Phenotype and Responses to Oxidative Stress by Manganese Superoxide Dismutase and a Superoxide Dismutase Mimic in RWPE-2 Human Prostate Adenocarcinoma Cells

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Abstract
To study biologic effects of increased manganese superoxide dismutase (MnSOD) on cell behavior, we overexpressed MnSOD in a human prostate cancer cell line RWPE-2 by cDNA transfection. Stable transfectants of MnSOD showed a two- to threefold increase in MnSOD protein and enzymatic activity and a decrease in growth rate with prolonged cell population doubling times. Western blot analysis showed a 1.5- to twofold increase in the cyclin-dependent kinase inhibitor p21Waf1 in MnSOD transfectants. Overexpression of MnSOD resulted in a seven- to eightfold increase in reduced glutathione (GSH), 18- to 26-fold increase in oxidized glutathione (GSSG), and a two- to threefold decrease in the ratio of GSH to GSSG. MnSOD-overexpressing cells showed an increase in sensitivity to the cytotoxicity of buthionine sulfoximine, a glutathione-depleting agent, and vitamin C, but a decrease in sensitivity to sodium selenite. Treatment with a superoxide dismutase (SOD) mimic MnTMPyP resulted in similar effects of MnSOD overexpression on cell responses to vitamin C and selenium. These data demonstrate that overexpression of MnSOD or treatment with SOD mimics can result in antioxidant or prooxidant effects in cells, depending on the presence of other antioxidants and prooxidants. MnSOD also has redox regulatory effects on cell growth and gene expression. These findings suggest that MnSOD and SOD mimics have the potential for cancer prevention or treatment.