Regulator of G Protein Signaling 2 (RGS2) Inhibits Intracellular Ca2+ Mobilization and RhoA Activation: Role in Regulation of Endothelial Permeability

Abstract

The microvascular endothelial monolayer actively regulates the tissue fluid balance. Edemagenic agonists such as thrombin binds to protease activated receptor-1 (PAR-1) that activates Gq, G12 and G13 proteins, which in turn stimulates small GTPase RhoA and increase intracellular Ca2+ mobilization leading to increased endothelial permeability. Regulators of G protein signaling (RGS) bind to G subunits of G proteins and stimulate their GTPase activity, which ‘switch off’ G-protein-mediated signaling events. However, the role of RGS proteins in regulating endothelial permeability in response to G protein coupled receptor-agonists remains unclear. We investigated the possible role of RGS2, a GTPase activating protein (GAP) for Gq, in the mechanism of thrombin-induced increase in endothelial permeability. We showed, using human endothelial cells, that overexpression of RGS2 attenuated thrombin-induced increase in intracellular Ca2+ transients and RhoA activity, reduced actin stress fiber formation and suppressed endothelial permeability-increase in response to thrombin. Importantly, down regulation of endogenous RGS2 by siRNA potentiated RhoA activity as well as the increase in endothelial permeability after stimulation with thrombin. Thus, RGS2 is a critical regulator of endothelial barrier function because its GAP activity antagonizes Gq-induced increase in intracellular Ca2+ as well as RhoA activity tapering off thrombin-induced increase in endothelial permeability. ααα