Enhanced Glutathione Levels and Oxidoresistance Mediated by Increased Glucose-6-phosphate Dehydrogenase Expression

Abstract

Glucose-6-phosphate dehydrogenase (G6PD) is the key enzyme of the pentose phosphate 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 different steps in the biochemical pathway controlling the intracellular redox status. Although we obtained evidence that the oxidative stress-mediated enhancement of G6PD expression is a general phenomenon, the functional significance of such G6PD induction after oxidant insult is still poorly understood. In this report, we used a GSHdepleting drug that determines a marked decrease in the intracellular pool of reduced glutathione and a gradual but notable increase in G6PD expression. Both effects are seen soon after drug addition. Once G6PD activity has reached the maximum, the GSH pool is restored. We suggest and also provide the first direct evidence that G6PD induction serves to maintain and regenerate the intracellular GSH pool. We used HeLa cell clones stably transfected with the human G6PD gene that display higher G6PD activity than the parent HeLa cells. Although the activities of glutathione peroxidase, glutathione reductase, and catalase were comparable in all strains, the concentrations of GSH were significantly higher in G6PD-overexpressing clones. A direct consequence of GSH increase in these cells is a decreased reactive oxygen species production, which makes these cells less 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-B activation, in response to tumor necrosis factor-␣ treatment, is strongly reduced in human HeLa cells overexpressing G6PD.

Blood glutathione redox status in gestational hypertension

“…Enhanced GSH levels and resistance to oxidation were demonstrated in different cells after an oxidant insult mediated by an increased G6PD expression [30,31]. An efficient level of GSH is crucial for the maintenance of an adequate metabolism, antioxidant protection of Hb, and the membrane integrity of the RBCs.…”

Dehydroascorbic acid uptake in a human keratinocyte cell line (HaCaT) is glutathione-independent

“…The higher DHA uptake by cells in which glutathione synthesis was inhibited by buthionine sulphoximine may be explained as a response of the cell to oxidative stress induced by buthionine sulphoximine, either directly, through the induction of enzymes with DHA reductase activity, or indirectly, through the induction of glucose-6-phosphate deydrogenase, which is responsible for the generation of NADPH required in many detoxifying reactions [33]. Expression of the thioredoxin\thioredoxin reductase system is significantly induced under oxidative conditions in lymphoid and keratinocyte cells [34] ; a similar induction might also occur in HaCaT cells.…”

Isoenzyme replacement of glucose-6-phosphate dehydrogenase in the cytosol improves stress tolerance in plants

“…Defective yeast mutants were found to be susceptible to oxidative stress (8), and a role for G6PDH in supplying NADPH for free-radical scavenging has also been observed in stressed mammalian cells (9). In higher plants, the OPPP is a major source of reduction power (NADPH) required for anabolic biosyntheses and assimilatory processes in the cytosol, as well as in plastids, providing key intermediates for the shikimate pathway and nucleic acid biosynthesis (10,11).…”