INCREASED GAMMA-GLUTAMYLCYSTEINE SYNTHETASE AND GAMMA-GLUTAMYL-TRANSPEPTIDASE ACTIVITIES ENHANCE RESISTANCE OF RAT LUNG EPITHELIAL L2 CELLSTO QUINONE TOXICITY

Tert-butylhydroquinone (TBHQ) is a monofunctional Phase II enzyme indu cer, which produces reactive oxygen species. Incubation with a subleth al concentration of TBHQ increased the activities of both gamma-glutam yl transpeptidase (GGT) and gamma-glutamylcysteine synthetase (GCS), a lthough the mechanisms are different (Liu and colleagues, accompanying manuscript). In this study, we found that TBHQ increased intracellula r glutathione (GSH) content in rat lung epithelial L2 cells. L2 cells pretreated with a nontoxic concentration of TBHQ (50 mu M) acquired re sistance to a subsequent challenge with a normally lethal concentratio n of TBHQ (200 mu M). Pretreatment with L-buthionine S,R-sulfoximine ( BSO), an inhibitor of GCS, prevented the TBHQ-induced increase in GSH and markedly diminished resistance to 200 mu M TBHQ. Similarly, pretre atment with acivicin, an inhibitor of GGT, also prevented the TBHQ-ind uced increase in GSH and markedly diminished resistance to 200 mu M TB HQ. Nevertheless, blockage of GGT by acivicin could be bypassed using 2-oxothiazolidine-4-carboxylate (procysteine) to provide the cell with a source of cysteine. This allowed an increase in GSH and restored re sistance in the TBHQ-pretreated cells. The results suggest that elevat ion of GCS and GGT activities participated in acquired resistance to q uinone toxicity.