Thymocytes selected for resistance to hydrogen peroxide show altered antioxidant enzyme profiles and resistance to dexamethasone-induced apoptosis

Treatment of WEHI7.2 cells, a mouse thymoma-derived cell line, with dexamet hasone, a synthetic glucocorticoid, causes the cells to undergo apoptosis. Previous work has shown that treatment of WEHI7.2 cells with dexamethasone results in a downregulation of antioxidant defense enzymes, suggesting that increased oxidative stress may play a role in glucocorticoid-induced apopt osis. To test whether resistance to oxidative stress causes resistance to d examethasone-induced apoptosis, WEHI7.2 cell variants selected for resistan ce to 50, 100 and 200 muM H2O2 were developed. Resistance to H2O2 is accomp anied by increased antioxidant enzyme activity, resistance to other oxidant s and a delayed loss of viable cells after dexamethasone treatment. In the 200 muM H2O2-resistant cell variant the delay in cell loss is correlated wi th delayed release of cytochrome c from the mitochondria into the cytosol. This suggests that reactive oxygen species play a role in a signaling event during steroid-mediated apoptosis in lymphocytes.