Modulation of the antioxidant defense during dexamethasone-induced apoptosis in WEHI7.2 mouse lymphoid cells

Abstract

The modulation of the antioxidant defense during dexamethasone-induced apoptosis in WEHI7.2 cells mouse lymphoid cells was studied. When treated with dexamethasone, antioxidant defense transcripts including catalase, MnSOD, CuZnSOD, DT-diaphorase, GPX, and thioredoxin exhibited a progressive decrease over 24 hours (h) in apoptosis-sensitive wild-type WEHI7.2 and apoptosis-resistant bcl-2 transfected (W.Hb12) cells. Catalase activity was maintained and total SOD and DT-diaphorase activity showed smaller decreases following dexamethasone treatment of bcl-2 transfected cells. Treatment of wild-type and bcl-2 transfected WEHI7.2 cells with a catalase inhibitor, amino-triazole, was not sufficient to induce apoptosis. Antioxidants, including bovine liver catalase, bovine erythrocyte CuZnSOD, sodium selenite and Trolox, a water soluble vitamin E analogue, as well as hypoxia, inhibited dexamethasone-induced apoptosis. Transfection of the WEHI7.2 cells with catalase and thioredoxin resulted in a significant level of protection against dexamethasone-induced apoptosis. Thioredoxin-transfected cells were also protected from apoptosis induced by staurosporine, N-acetyl-sphingosine, etoposide and thapsigargin. When inoculated into severe combined immunodeficient (scid) mice the trx transfected cells formed tumors that showed increased growth compared to wild-type as well as bcl-2 transfected WEHI7.2 cells. The trx and bcl-2 transfected cell tumors both showed less spontaneous apoptosis than tumors formed by the wild-type cells. Unlike tumors formed by the wild-type and bcl-2 transfected WEHI7.2 cells, trx transfected cell tumors did not show growth inhibition upon treatment with dexamethasone. These results suggest that modulation of the antioxidant defense may play a role in dexamethasone-induced apoptosis and that Bcl-2 may prevent apoptosis by maintaining the level of critical antioxidant defense mechanisms including catalase. In addition, the thioredoxin study suggests that increased thioredoxin expression may result in a increased tumor growth through inhibition of spontaneous apoptosis and a decrease in the sensitivity of the tumor to drug-induced apoptosis.