Fig. 4.
Platelet activation by collagen. Platelets use several different molecular complexes to support platelet activation by collagen. These complexes include (1) VWF-mediated binding of collagen to the GPIb-IX-V complex and integrin αIIbβ3 and (2) a direct interaction between collagen and both the integrin α2β1 and the GPVI/FcRγ-chain complex. Clustering of GPVI results in the phosphorylation of tyrosine residues in the FcRγ cytoplasmic domain, followed by the activation of the tyrosine kinase, Syk. One consequence of Syk activation is the activation of PLCγ2, leading to phosphoinositide hydrolysis, secretion of ADP, and the production of TXA2. COX-1, cyclooxygenase 1; DAG, diacylglycerol; PG, prostaglandin; PI3K, phosphatidylinositol 3-kinase; PKC, protein kinase C; PLA2, phospholipase A2.