GAMMA-GLUTAMYL-TRANSPEPTIDASE IS INCREASED BY OXIDATIVE STRESS IN RATALVEOLAR L2 EPITHELIAL-CELLS

The tripeptide glutathione (GSH) is used by cells to detoxify hydroper oxides, produced during oxidative stress, and is consumed in the proce ss. Previous studies have indicated that cells can be protected agains t oxidative stress by extracellular GSH through its degradation cataly zed by the exoenzyme gamma-glutamyl transpeptidase (gamma GT) and its de novo synthesis within the cytosol. We hypothesized that gamma GT wo uld be increased as part of the adaptation of cells to oxidative stres s. We examined whether oxidative stress could increase gamma GT activi ty, protein, and mRNA in a lung epithelial cell line (L2). Cultures we re subjected to H2O2-mediated toxicity by 15 min of exposure to the re dox cycling quinone, menadione. Menadione (50 mu M) caused an initial decrease (27 +/- 9% of baseline after 15 min) in intracellular GSH, fo llowed by resynthesis to levels significantly higher than baseline (33 5 +/- 40% after 24 h, P < 0.001). This elevation was prevented by aciv icin, a gamma GT inhibitor. Menadione also caused a dose-dependent inc rease in gamma GT enzymatic activity (715 +/- 125% of control at 24 h after 15 min of exposure to 100 mu M menadione, P < 0.001) that was pr evented by actinomycin D. Western blot analysis indicated increased le vels of gamma GT protein with increasing menadione. A concentration-de pendent increase in gamma GT-mRNA was also observed. Previous investig ation has demonstrated that an increase in gamma GT activity enhances the capacity of cells to utilize extracellular GSH. The findings prese nted here are consistent with a role for gamma GT in cellular adaptati on to oxidative stress.