Rhodocytin induces platelet aggregation by interacting with glycoprotein Ia/IIa (GPIa/IIa, Integrin alpha 2beta 1). Involvement of GPIa/IIa-associated src and protein tyrosine phosphorylation.
Although glycoprotein Ia/IIa (GPIa/IIa, integrin alpha(2)beta(1)) has established its role as a collagen receptor, it remains unclear whether GPIa/IIa mediates activation signals. In this study, we show that rhodocytin, purified from the Calloselasma rhodostoma venom, induces platelet aggregation, which can be blocked by anti-GPIa monoclonal antibodies. Studies with rhodocytin-coupled beads ... and liposomes loaded with recombinant GPIa/IIa demonstrated that rhodocytin directly binds to GPIa/IIa independently of divalent cations. In vitro kinase assays and Western blotting of GPIa immunoprecipitates revealed that Src and Lyn constitutively associate with GPIa/IIa and that Src activity increases transiently after rhodocytin stimulation. Src specifically associates with p130 Crk-associated substrate (Cas) in a manner dependent upon Cas phosphorylation, suggesting that Src is responsible for Cas tyrosine phosphorylation. While all these phenomena occur early after rhodocytin stimulation in a cAMP-resistant manner, tyrosine phosphorylation of Syk and phospholipase Cgamma2, intracellular Ca(2+) mobilization, and platelet aggregation occur later in a cAMP-sensitive manner. Cytochalasin D, which interferes with actin polymerization and blocks receptor clustering, inhibits all the rhodocytin-mediated signals we examined in this study. We suggest that rhodocytin, by clustering GPIa/IIa, activates GPIa/IIa-associated Src, which then mediates downstream activation signals.
Mesh Terms:
Animals, Antibodies, Monoclonal, Blood Platelets, Blood Proteins, Dinoprostone, Humans, In Vitro Techniques, Integrins, Kinetics, Lectins, Lectins, C-Type, Mice, Mice, Inbred C57BL, Phosphorylation, Phosphotyrosine, Platelet Adhesiveness, Platelet Aggregation, Receptors, Collagen, Receptors, IgG, Tyrosine, Viper Venoms, Viperidae
Animals, Antibodies, Monoclonal, Blood Platelets, Blood Proteins, Dinoprostone, Humans, In Vitro Techniques, Integrins, Kinetics, Lectins, Lectins, C-Type, Mice, Mice, Inbred C57BL, Phosphorylation, Phosphotyrosine, Platelet Adhesiveness, Platelet Aggregation, Receptors, Collagen, Receptors, IgG, Tyrosine, Viper Venoms, Viperidae
J. Biol. Chem.
Date: Jan. 12, 2001
PubMed ID: 11038351
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