Gα_i and Gα_o are target proteins of reactive oxygen species

摘要

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 βγ-subunit of G protein (Gβγ) attenuates hydrogen peroxide (H_2O_2)-induced ERK activation in rat neonatal cardio- myocytes. The Gβγ-responsive ERK activation induced by H_2O_2 is independent of ligands binding to G_i-coupled receptors, but requires phosphatidylinositol-3-kinase and Src activation. In in vitro studies, however, treatment with H_2O_2 increases [~(35)S]GTP-γS binding to cardiac membranes and directly activates purified heterotrimeric G_i and G_o but not G_s. Analysis using heterotrimeric G_o and its individual sub units indicates that H_2O_2 modifies Gα_o but not Gβγ, which leads to subunit dissociation. We conclude that Gα_i and Gα_o are critical targets of oxidative stress for activation of ERK.