Primary arrest of circulating platelets on collagen involves phosphorylation of Syk, cortactin and focal adhesion kinase: studies under flow conditions.
After a vessel wall injury, platelets adhere to the subendothelium following a sequence of events: arrest of single platelets on the surface, progression to platelet spreading and final aggregation. Primary arrest of circulating platelets on subendothelial components occurs through platelet glycoprotein (GP) Ib and collagen receptors; then platelets spread and aggregate through a GPIIb-IIIa-dependent mechanism. A series of strategies were applied to analyse the tyrosine-phosphorylation mechanisms occurring at the different stages of platelet adhesion on subendothelial components under flow conditions, with special attention to primary arrest. To evaluate spread platelets, samples were exposed to acetylsalicylic acid, which blocks aggregate formation. To study single platelets in contact, a monoclonal antibody specific for GPIIb-IIIa was used to prevent platelet spreading and further aggregation. This experimental situation was also investigated using blood from two patients with Glanzmann's thrombasthenia (i.e. lacking GPIIb-IIIa). Results demonstrated that blockade of both spreading and aggregation results in significant changes in the tyrosine-phosphorylation patterns. Arrest of single platelets on collagen-rich surfaces resulted in phosphorylation of p125, identified as focal adhesion kinase (FAK), the 80/85 kDa doublet (cortactin), and p72, identified as Syk. Arrest of single platelets on von Willebrand factor as adhesive substrate showed that interaction through GPIb induces Syk phosphorylation, but not that of cortactin and FAK. Our data indicate that the initial arrest of platelets on subendothelial components involves Syk phosphorylation, which seems to be GPIb-dependent, and this is followed by activation and phosphorylation of cortactin and FAK. These processes seem to occur before GPIIb-IIIa becomes activated.
Arderiu
Gemma
G
Servei d'Hemoterapia-Hemostasia, Hospital Clínic, Institut de Investigacions Biomèdiques August Pi i Sunyer, Universitat de Barcelona, Spain.
Díaz-Ricart
Maribel
M
Buckley
Byron
B
Escolar
Ginés
G
Ordinas
Antonio
A
D001792:Blood Platelets / Q000378:metabolism*; D002448:Cell Adhesion; D002478:Cells, Cultured; D003094:Collagen / Q000096:biosynthesis*; D051356:Cortactin; D004730:Endothelium, Vascular / Q000378:metabolism; D004792:Enzyme Precursors / Q000378:metabolism*; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008840:Microfilament Proteins / Q000378:metabolism*; D010477:Perfusion; D010766:Phosphorylation; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000737:chemistry; D011233:Precipitin Tests; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D000072377:Syk Kinase; D013997:Time Factors; D014443:Tyrosine / Q000378:metabolism; D014471:Umbilical Veins / Q000378:metabolism; D014841:von Willebrand Factor / Q000378:metabolism
C495868:CTTN protein, human; D051356:Cortactin; D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D008840:Microfilament Proteins; D019038:Platelet Glycoprotein GPIb-IX Complex; D014841:von Willebrand Factor; D014443:Tyrosine; D003094:Collagen; D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496050:PTK2 protein, human; C000606896:SYK protein, human; D000072377:Syk Kinase