title: The ligand occupancy of endothelial protein C receptor switches the protease-activated receptor 1-dependent signaling specificity of thrombin from a permeability-enhancing to a barrier-protective response in endothelial cells.
abstract: Recent studies have indicated that activated protein C (APC) may exert its cytoprotective and anti-inflammatory activities through the endothelial protein C receptor (EPCR)-dependent cleavage of protease-activated receptor 1 (PAR-1) on vascular endothelial cells. Noting that (1) the activation of protein C on endothelial cells requires thrombin, (2) relative to APC, thrombin cleaves PAR-1 with approximately 3 to 4 orders of magnitude higher catalytic efficiency, and (3) PAR-1 is a target for the proinflammatory activity of thrombin, it is not understood how APC can elicit a protective signaling response through the cleavage of PAR-1 when thrombin is present. In this study, we demonstrate that EPCR is associated with caveolin-1 in lipid rafts of endothelial cells and that its occupancy by the gamma-carboxyglutamic acid (Gla) domain of protein C/APC leads to its dissociation from caveolin-1 and recruitment of PAR-1 to a protective signaling pathway through coupling of PAR-1 to the pertussis toxin-sensitive G(i)-protein. Thus, when EPCR is bound by protein C, the PAR-1 cleavage-dependent protective signaling responses in endothelial cells can be mediated by either thrombin or APC. These results provide a new paradigm for understanding how PAR-1 and EPCR participate in protective signaling events in endothelial cells.
authors.affiliation: Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, MO 63104, USA.
authors.forename: Jong-Sup
authors.initials: JS
authors.lastname: Bae
authors.forename: Likui
authors.initials: L
authors.lastname: Yang
authors.forename: Chandrashekhara
authors.initials: C
authors.lastname: Manithody
authors.forename: Alireza R
authors.initials: AR
authors.lastname: Rezaie
mesh_terms: D015703:Antigens, CD / Q000378:metabolism*; D051242:Caveolin 1 / Q000378:metabolism; D002460:Cell Line; D002463:Cell Membrane Permeability / Q000187:drug effects; D042783:Endothelial Cells / Q000378:metabolism* / Q000473:pathology; D000074283:Endothelial Protein C Receptor; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism; D006490:Hemostatics / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D007249:Inflammation / Q000378:metabolism / Q000473:pathology; D008024:Ligands; D021962:Membrane Microdomains / Q000378:metabolism / Q000473:pathology; D011486:Protein C / Q000378:metabolism / Q000494:pharmacology; D044463:Receptor, PAR-1 / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects; D013917:Thrombin / Q000378:metabolism* / Q000494:pharmacology