title: PAR1 cleavage and signaling in response to activated protein C and thrombin.
abstract: Activated protein C (APC), a natural anticoagulant protease, can trigger cellular responses via protease-activated receptor-1 (PAR1), a G protein-coupled receptor for thrombin. Whether this phenomenon contributes to the physiological effects of APC is unknown. Toward answering this question, we compared the kinetics of PAR1 cleavage on endothelial cells by APC versus thrombin. APC did cleave PAR1 on the endothelial surface, and antibodies to the endothelial protein C receptor inhibited such cleavage. Importantly, however, APC was approximately 10(4)-fold less potent than thrombin in this setting. APC and thrombin both triggered PAR1-mediated responses in endothelial cells including expression of antiapoptotic (tumor necrosis factor-alpha-induced a20 and iap-1) and chemokine (interleukin-8 (il-8) and cxcl3) genes, but again, APC was approximately 10(4)-fold less potent than thrombin. The addition of zymogen protein C to endothelial cultures did not alter the rate of PAR1 cleavage at low or high concentrations of thrombin, and PAR1 cleavage was substantial at thrombin concentrations too low to trigger detectable conversion of protein C to APC. Thus, locally generated APC did not contribute to PAR1 cleavage beyond that effected by thrombin in this system. Although consistent with reports that sufficiently high concentrations of APC can cleave and activate PAR1 in culture, our data suggest that a significant physiological role for PAR1 activation by APC is unlikely.
authors.affiliation: Cardiovascular Research Institute, University of California, San Francisco, California 94143-0130, USA.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Ludeman
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kataoka
authors.forename: Yoga
authors.initials: Y
authors.lastname: Srinivasan
authors.forename: Naomi L
authors.initials: NL
authors.lastname: Esmon
authors.forename: Charles T
authors.initials: CT
authors.lastname: Esmon
authors.forename: Shaun R
authors.initials: SR
authors.lastname: Coughlin
mesh_terms: D017209:Apoptosis; D015152:Blotting, Northern; D002478:Cells, Cultured; D054360:Chemokine CXCL1; D019743:Chemokines, CXC / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism; D016209:Interleukin-8 / Q000378:metabolism; D007700:Kinetics; D010716:Phosphatidylinositols / Q000737:chemistry; D011485:Protein Binding; D011486:Protein C / Q000737:chemistry* / Q000502:physiology; D017434:Protein Structure, Tertiary; D044463:Receptor, PAR-1 / Q000378:metabolism / Q000502:physiology*; D013917:Thrombin / Q000737:chemistry* / Q000502:physiology; D013997:Time Factors; D014471:Umbilical Veins / Q000166:cytology
chemical_list: C475829:CXCL1 protein, human; D054360:Chemokine CXCL1; D019743:Chemokines, CXC; D018076:DNA, Complementary; D036341:Intercellular Signaling Peptides and Proteins; D016209:Interleukin-8; D010716:Phosphatidylinositols; D011486:Protein C; D044463:Receptor, PAR-1; D013917:Thrombin