Fig. P1.

Model of thrombin versus APC activation of PAR1 and endothelial barrier regulation. Thrombin binds to and activates PAR1, which results in preferential coupling to the heterotrimeric Gα_q and Gα_12/13 proteins, stimulation of Ca²⁺ mobilization, and PKC and RhoA activation, resulting in endothelial barrier disruption. In contrast, APC binds to its coreceptor endothelial protein C receptor (EPCR) and activates PAR1, resulting in Rac1 signaling and endothelial barrier protection. We now show that PAR1 and β-arrestins exist in a preassembled complex and cosegregate in caveolar-enriched fractions. APC stimulation results in β-arrestin–dependent recruitment and activation of the Dvl-2 scaffold, which is critical for Rac1 activation and endothelial barrier protection.