期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2009
卷号：106
期号：15
页码：6393-6397
DOI：10.1073/pnas.0810687106
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Protease-activated receptor-1 (PAR1) is a G-protein-coupled receptor uniquely activated by proteolysis. Thrombin, a coagulant protease, induces inflammatory responses and endothelial barrier permeability through the activation of PAR1. Activated protein C (APC), an anti-coagulant protease, also activates PAR1. However, unlike thrombin, APC elicits anti-inflammatory responses and protects against endothelial barrier dysfunction induced by thrombin. We found that thrombin and APC signaling were lost in PAR1-deficient endothelial cells, indicating that PAR1 is the major effector of protease signaling. To delineate the mechanism responsible for protease-selective signaling by PAR1, we examined the effect of APC and thrombin on the activation of RhoA and Rac1, small GTPases that differentially regulate endothelial barrier permeability. Thrombin caused robust RhoA signaling but not Rac1 activation, whereas APC stimulated a marked increase in Rac1 activation but not RhoA signaling, consistent with the opposing functions of these proteases on endothelial barrier integrity. Strikingly, APC signaling and endothelial barrier protection effects were abolished in cells lacking caveolin-1, whereas thrombin signaling remained intact. These findings suggest that compartmentalization of PAR1 in caveolae is critical for APC selective signaling to Rac1 activation and endothelial barrier protection. We further report that APC induces PAR1 phosphorylation and desensitizes endothelial cells to thrombin signaling but promotes limited receptor cleavage and negligible internalization and degradation even after prolonged APC exposure. Thus, APC selective signaling and endothelial barrier protective effects are mediated through compartmentalization of PAR1 in caveolae and a novel mechanism of PAR1 signal regulation.
