title: The Ig-ITIM superfamily member PECAM-1 regulates the "outside-in" signaling properties of integrin alpha(IIb)beta3 in platelets.
abstract: Previous studies have implicated the immunoglobulin (Ig)-immunoreceptor tyrosine-based inhibitory motif (ITIM) superfamily member platelet endothelial cell adhesion molecule-1 (PECAM-1) in the regulation of integrin function. While PECAM-1 has been demonstrated to play a role as an inhibitory coreceptor of immunoreceptor tyrosine-based activation motif (ITAM)-associated Fcgamma receptor IIa (FcgammaRIIa) and glycoprotein VI (GPVI)/FcR gamma-chain signaling pathways in platelets, its physiologic role in integrin alpha(IIb)beta3-mediated platelet function is unclear. In this study, we investigate the functional importance of PECAM-1 in murine platelets. Using PECAM-1-deficient mice, we show that the platelets have impaired "outside-in" integrin alpha(IIb)beta3 signaling with impaired platelet spreading on fibrinogen, failure to retract fibrin clots in vitro, and reduced tyrosine phosphorylation of focal adhesion kinase p125 (125FAK) following integrin alpha(IIb)beta3-mediated platelet aggregation. This functional integrin alpha(IIb)beta3 defect could not be attributed to altered expression of integrin alpha(IIb)beta3. PECAM-1-/- platelets displayed normal platelet alpha granule secretion, normal platelet aggregation to protease-activated receptor-4 (PAR-4), adenosine diphosphate (ADP), and calcium ionophore, and static platelet adhesion. In addition, PECAM-1-/- platelets displayed normal "inside-out" integrin alpha(IIb)beta3 signaling properties as demonstrated by normal agonist-induced binding of soluble fluoroscein isothiocyanate (FITC)-fibrinogen, JON/A antibody binding, and increases in cytosolic-free calcium and inositol (1,4,5)P3 triphosphate (IP3) levels. This study provides direct evidence that PECAM-1 is essential for normal integrin alpha(IIb)beta3-mediated platelet function and that disruption of PECAM-1 induced a moderate "outsidein" integrin alpha(IIb)beta3 signaling defect.
authors.affiliation: Kronheimer Building, Austin Research Institute, Austin Health, Studley Road, Heidelberg, Victoria 3084, Australia.
authors.forename: Janet L
authors.initials: JL
authors.lastname: Wee
authors.forename: Denise E
authors.initials: DE
authors.lastname: Jackson
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000378:metabolism* / Q000473:pathology*; D015153:Blotting, Western; D005434:Flow Cytometry; D047468:Immunoprecipitation; D016023:Integrins / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D010973:Platelet Adhesiveness / Q000502:physiology; D010974:Platelet Aggregation / Q000502:physiology; D019408:Platelet Endothelial Cell Adhesion Molecule-1 / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D016023:Integrins; D019408:Platelet Endothelial Cell Adhesion Molecule-1