Inhibitory Effect of Isoproterenol on NADPH-dependent H2O2 Generation in Human Adipocyte Plasma Membranes Is Mediated by βγ-Subunits Derived from Gs

Abstract

Previous studies revealed that human fat cell plasma membranes contain a multireceptor-linked H(2)O(2)-generating system that is under antagonistic control by hormones and cytokines and is stimulated by insulin via Galpha(i2). In this report, it is shown that the inhibitory action of the beta-adrenergic agonist isoproterenol is mediated by G protein betagamma-subunits, based on observations that its action was specifically reversed by anti-Gbeta antibodies or a C-terminal beta-adrenergic receptor kinase-1 fragment containing the Gbetagamma-binding site of the enzyme, and was mimicked by exogenously supplied G protein betagamma-subunits. Isoproterenol signals through a prototypical G(s)-coupled receptor. Consistent with these results, direct activation of G(s) by cholera toxin or by an anti-Galpha(s) antibody exhibiting beta-adrenergic receptor-mimetic properties (K-20) resulted in an isoproterenol-like inhibition of NADPH-dependent H(2)O(2) generation. In addition, a peptide corresponding to the target sequence of K-20 blocked the action of the catecholamine, apparently by competition between the peptide and G(s) for activated beta-adrenergic receptors, indicating that the G protein betagamma-subunits mediating the inhibitory effects of the catecholamine were in fact derived from G(s).