Inhibition of cell growth and sensitization to oxidative damage by overexpression of manganese superoxide dismutase in rat glioma cells

The effects of overexpression of human manganese superoxide dismutase (MnSOD) on cell proliferation and response to oxidative stress in rat glioma cells were studied. MnSOD-overexpressing cells had a 2- to 14-fold increase in MnSOD activity, but did not have consistent changes in the activities of CuZnSOD, catalase, or glutathione peroxidase. Cells with more than a 5-fold increase in MnSOD activity became more sensitive to radiation, 1,3-bis(2- chloroethyl)-1-nitrosourea, and buthionine sulfoximine and had a lower growth rate than parental and vector control cells. The sensitivity to 1,3-bis(2- chloroethyl)-1-nitrosourea was partially reduced by pyruvate, a H₂O₂ scavenger. Our results suggest that overexpression of MnSOD can cause an imbalance of antioxidant enzymes, which we hypothesize results in an elevation of intracellular H2'O₂. Overexpression of MnSOD can either inhibit cell proliferation or increase cell death by oxidative agents, depending on the levels of peroxide-removing enzymes.