Mammalian small stress proteins protect against oxidative stress through their ability to increase glucose-6-phosphate dehydrogenase activity and by maintaining optimal cellular detoxifying machinery

The protective activity of small stress proteins (sHsp) against H2O2-mediat ed cell death in the highly sensitive murine L929 fibroblast has been analy zed. We report here that the human Hsp27- and murine Hsp25-mediated rise in glutathione (GSH) levels as well as the maintenance of this redox modulato r in its reduced form was directly responsible for the protection observed at the level of cell morphology and mitochondrial membrane potential, sHsp expression also buffered the increase in protein oxidation following H2O2 t reatment and protected several key enzymes against inactivation. In this ca se, however, the protection necessitated both an increase in GSH and the pr esence of sHsp per se since the pattern of protection against protein oxida tion mediated by a simple GSH increase was different from that induced by s Hsp expression. Among the enzymes analyzed, we noticed that sHsp significan tly increased glucose-6-phosphate dehydrogenase (G6PD) activity and to a le sser extent glutathione reductase and glutathione transferase activities. M oreover, an increased GSH level was observed in G6PD-overexpressing L929 ce ll clones. Taken together our results suggest that sHsp protect against oxi dative stress through a G6PD-dependent ability to increase and uphold GSH i n its reduced form and by using this redox modulator as an essential parame ter of their in vivo chaperone activity against oxidized proteins. (C) 1999 Academic Press.