Integrin-independent tyrosine phosphorylation of p125(fak) in human platelets stimulated by collagen.
Collagen fibers or a glycoprotein VI-specific collagen-related peptide (CRP-XL) stimulated tyrosine phosphorylation of the focal adhesion kinase, p125(fak) (FAK), in human platelets. An integrin alpha(2)beta(1)-specific triple-helical peptide ligand, containing the sequence GFOGER (single-letter nomenclature, O = Hyp) was without effect. Antibodies to the alpha(2) and beta(1) integrin subunits did not inhibit platelet FAK tyrosine phosphorylation caused by either collagen fibers or CRP-XL. Tyrosine phosphorylation of FAK caused by CRP-XL or thrombin, but not that caused by collagen fibers, was partially inhibited by GR144053F, an antagonist of integrin alpha(IIb)beta(3). The intracellular Ca(2+) chelator, BAPTA, and the protein kinase C inhibitor, Ro31-8220, were each highly effective inhibitors of the FAK tyrosine phosphorylation caused by collagen or CRP-XL. These data suggest that, in human platelets, 1) occupation or clustering of the integrin alpha(2)beta(1) is neither sufficient nor necessary for activation of FAK, 2) the fibrinogen receptor alpha(IIb)beta(3) is not required for activation of FAK by collagen fibers, and 3) both intracellular Ca(2+) and protein kinase C activity are essential intermediaries of FAK activation.
Achison
M
M
Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, United Kingdom.
Elton
C M
CM
Hargreaves
P G
PG
Knight
C G
CG
Barnes
M J
MJ
Farndale
R W
RW
D000328:Adult; D000818:Animals; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002417:Cattle; D003094:Collagen / Q000494:pharmacology*; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D016023:Integrins / Q000378:metabolism*; D015759:Ionomycin / Q000494:pharmacology; D008024:Ligands; D010446:Peptide Fragments / Q000494:pharmacology; D010766:Phosphorylation; D010879:Piperazines / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000037:antagonists & inhibitors; D011233:Precipitin Tests; D011493:Protein Kinase C / Q000187:drug effects / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000276:immunology / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism*
C090662:GR 144053; D007211:Indoles; D016023:Integrins; D008024:Ligands; D010446:Peptide Fragments; D010879:Piperazines; D010880:Piperidines; D010975:Platelet Aggregation Inhibitors; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D014443:Tyrosine; D004533:Egtazic Acid; D015759:Ionomycin; D003094:Collagen; D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496050:PTK2 protein, human; D011493:Protein Kinase C; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium; C064758:Ro 31-8220