Abstract
G6PD (glucose-6-phosphate dehydrogenase) is the rate-limiting enzyme in the oxidative pentose phosphate pathway that can generate cytosolic NADPH for biosynthesis and oxidative defense. Since cytosolic NADPH can be compensatively produced by other sources, the enzymatic activity deficiency alleles of G6PD are well tolerated in somatic cells but the effect of null mutations is unclear. Herein, we show that G6PD KO sensitizes cells to the stresses induced by hydrogen peroxide, superoxide, hypoxia, and the inhibition of the electron transport chain. This effect can be completely reversed by the expressions of natural mutants associated with G6PD deficiency, even without dehydrogenase activity, exactly like the WT G6PD. Furthermore, we demonstrate that G6PD can physically interact with AMPK (AMPK-activated protein kinase) to facilitate its activity and directly bind to NAMPT (nicotinamide phosphoribosyltransferase) to promote its activity and maintain the NAD(P)H/NAD(P)+ homeostasis. These functions are necessary to the antistress ability of cells but independent of the dehydrogenase activity of G6PD. In addition, the WT G6PD and naturally inactive mutant also can similarly regulate the metabolism of glucose, glutamine, fatty acid synthesis, and GSH and interact with the involved enzymes. Therefore, our findings reveal the previously unidentified functions of G6PD that can act as the important physiological neutralizer of stresses independently of its enzymatic activity.