Antioxidant defenses in TNF-treated MCF-7 cells: Selective increase in MnSOD

Oxidative stress has been implicated in the mechanism of tumor necrosis fac tor-alpha (TNF)-induced apoptosis, raising a question about the status of a ntioxidant defenses in TNF-sensitive cells. Antioxidant defenses were exami ned in MCF-7 cells after treatment with TNF. Cell morphology and DNA fragme ntation assays were used to confirm increased apoptosis as a result of TNF treatment. The expression and activity of antioxidant defenses were assesse d using Northern blot hybridization analyses and biochemical assays, respec tively. Five- and ten-fold increases in manganese superoxide dismutase (MnS OD) mRNA were measured after one and five days of TNF treatment, respective ly. The expression of copper,zinc superoxide dismutase, catalase or thiored oxin was not altered. An approximate five-fold increase in MnSOD activity f ollowed the change in gene expression, but no difference in the activity of catalase or glutathione peroxidase was seen. Thus, increased MnSOD activit y was not accompanied by an increase in other antioxidant defenses and in p articular, H2O2-scavenging enzymes. MnSOD has previously been shown to affo rd protection against TNF-mediated cytotoxicity. The observed lack of incre ased peroxidase activity is consistent with mitochondrially-generated super oxide anion radical contributing to the mechanism of TNF-induced apoptosis. (C) 1999 Elsevier Science Inc.