G alpha(i) and G alpha(o) are target proteins of reactive oxygen species

Reactive oxygen species (ROS) have been identified as central mediators in certain signalling events(1-4). In the heart, ROS have important functions in ischaemia/reperfusion-induced cardiac injury(5,6) and in cytokine-stimul ated hypertrophy(7). Extracellular signal-regulated kinase (ERK) is one of the ROS-responsive serine/threonine kinases. Previous studies showed that t yrosine kinases and small G proteins are involved in the activation of ERK by ROS4,8; however, the initial target protein of ROS that leads to ERK act ivation remains unknown. Here we show that inhibition of the beta gamma -su bunit of G protein (G beta gamma) attenuates hydrogen peroxide (H2O2)-induc ed ERK activation in rat neonatal cardiomyocytes. The G beta gamma -respons ive ERK activation induced by H2O2 is independent of ligands binding to G(i )-coupled receptors, but requires phosphatidylinositol-3-kinase and Src act ivation. In in vitro studies, however, treatment with H2O2 increases [S-35] GTP-gammaS binding to cardiac membranes and directly activates purified het erotrimeric G(i) and G(o) but not G(s). Analysis using heterotrimeric G(o) and its individual subunits indicates that H2O2 modifies G alpha (o) but no t G beta gamma, which leads to subunit dissociation. We conclude that G alp ha (i) and G alpha (o) are critical targets of oxidative stress for activat ion of ERK.