title: Coagulation factor Xa cleaves protease-activated receptor-1 and mediates signaling dependent on binding to the endothelial protein C receptor.
abstract: OBJECTIVE
  Coagulation is intrinsically tied to inflammation, and both proinflammatory and anti-inflammatory responses are modulated by coagulation protease signaling through protease-activated receptor-1 (PAR1). Activated factor X (FXa) can elicit cellular signaling through PAR1, but little is known about the role of cofactors in this pathway. Endothelial protein C receptor (EPCR) supports PAR1 signaling by the protein C pathway, and in the present study we tested whether EPCR mediates surface recruitment and signaling of FXa.
  
  
  RESULTS
  Here, we show that FXa binds to overexpressed as well as native endothelial EPCR. PAR1 cleavage by FXa as analyzed with conformation-sensitive antibodies and a tagged PAR1 reporter construct was strongly enhanced if EPCR was available. Anti-EPCR failed to affect the tissue factor-dependent activation of FX, but high concentrations of FXa decreased EPCR-dependent protein C activation. Most importantly, the FXa-mediated induction of Erk1/2 activation, expression of the transcript for connective tissue growth factor and barrier protection in endothelial cells required binding to EPCR.
  
  
  CONCLUSIONS
  Our results demonstrate that EPCR plays an unexpected role in supporting cell surface recruitment, PAR1 activation, and signaling by FXa.
authors.affiliation: Department of Immunology and Microbial Science, The Scripps Research Institute, La Jolla, CA 92037, USA.
authors.forename: R A
authors.initials: RA
authors.lastname: Schuepbach
authors.forename: M
authors.initials: M
authors.lastname: Riewald
mesh_terms: D015703:Antigens, CD / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D055513:Connective Tissue Growth Factor / Q000235:genetics; D042783:Endothelial Cells / Q000201:enzymology*; D000074283:Endothelial Protein C Receptor; D004789:Enzyme Activation; D015951:Factor Xa / Q000378:metabolism*; D006801:Humans; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D011486:Protein C / Q000378:metabolism; D021381:Protein Transport; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D044463:Receptor, PAR-1 / Q000235:genetics / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D013917:Thrombin / Q000378:metabolism
chemical_list: D015703:Antigens, CD; C526317:CCN2 protein, human; D000074283:Endothelial Protein C Receptor; C478370:PROCR protein, human; D011486:Protein C; D012333:RNA, Messenger; D044463:Receptor, PAR-1; D011956:Receptors, Cell Surface; D055513:Connective Tissue Growth Factor; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D013917:Thrombin; D015951:Factor Xa