Enhanced glutathione levels and oxidoresistance mediated by increased glucose-6-phosphate dehydrogenase expression

Glucose-6-phosphate dehydrogenase (G6PD) is the key enzyme of the pentose p hosphate pathway that is responsible for the generation of NADPH, which is required in many detoxifying reactions. We have recently demonstrated that G6PD expression is induced by a variety of chemical agents acting at differ ent steps in the biochemical pathway controlling the intracellular redox st atus. Although we obtained evidence that the oxidative stress-mediated enha ncement of G6PD expression is a general phenomenon, the functional signific ance of such G6PD induction after oxidant insult is still poorly understood . In this report, we used a GSH-depleting drug that determines a marked dec rease in the intracellular pool of reduced glutathione and a gradual but no table increase in G6PD expression. Both effects are seen soon after drug ad dition. Once G6PD activity has reached the maximum, the GSH pool is restore d. We suggest and also provide the first direct evidence that G6PD inductio n serves to maintain and regenerate the intracellular GSH pool. We used HeL a cell clones stably transfected with the human G6PD gene that display high er G6PD activity than the parent HeLa cells. Although the activities of glu tathione peroxidase, glutathione reductase, and catalase were comparable in all strains, the concentrations of GSH were significantly higher in G6PD-o verexpressing clones. A direct consequence of GSH increase in these cells i s a decreased reactive oxygen species production, which makes these cells l ess sensitive to the oxidative burst produced by external stimuli. Indeed, all clones that constitutively overexpress G6PD exhibited strong protection against oxidants-mediated cell killing. We also observe that NF-kappa B ac tivation, in response to tumor necrosis factor-alpha treatment, is strongly reduced in human HeLa cells overexpressing G6PD.