Laboratory of Pharmacology and Toxicology
Laboratory of Physiological Chemistry, Graduate School of Pharmaceutical Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Reactive oxygen species (ROS) have been identified as central mediators in certain signalling events. In the heart, ROS have important functions in ischaemia/reperfusion-induced cardiac injury and in cytokine-stimulated hypertrophy. Extracellular signal-regulated kinase (ERK) is one of the ROS-responsive serine/threonine kinases. Previous studies showed that tyrosine kinases and small G proteins are involved in the activation of ERK by ROS; however, the initial target protein of ROS that leads to ERK activation remains unknown. Here we show that inhibition of the [beta] [gamma] -subunit of G protein (G [beta] [gamma] ) attenuates hydrogen peroxide (H2O2)-induced ERK activation in rat neonatal cardiomyocytes. The G [beta] [gamma] -responsive ERK activation induced by H2O2 is independent of ligands binding to Gi-coupled receptors, but requires phosphatidylinositol-3-kinase and Src activation. In in vitro studies, however, treatment with H 2O2 increases [35S]GTP- [gamma] S binding to cardiac membranes and directly activates purified heterotrimeric Gi and Go but not Gs. Analysis using heterotrimeric G o and its individual subunits indicates that H2O2 modifies G [alpha] o but not G [beta] [gamma] , which leads to subunit dissociation. We conclude that G [alpha] i and G [alpha] o are critical targets of oxidative stress for activation of ERK.