Rac, a small guanosine triphosphate-binding protein, and p21-activated kinase are activated during platelet spreading on collagen-coated surfaces: roles of integrin alpha(2)beta(1)

• Published in: Blood 2001-12, Vol.98 (13), p.3708-3716
• Main Authors: Suzuki-Inoue, K, Yatomi, Y, Asazuma, N, Kainoh, M, Tanaka, T, Satoh, K, Ozaki, Y
• Format: Article
• Language: English
• Subjects: Amides - pharmacology; Androstadienes - pharmacology; Antibodies - pharmacology; Antigens, CD - immunology; Apyrase - pharmacology; Blood Platelets - drug effects; Blood Platelets - physiology; cdc42 GTP-Binding Protein - blood; Collagen - pharmacology; Enzyme Activation; Enzyme Inhibitors - pharmacology; Humans; Immunoglobulin Fab Fragments - pharmacology; Integrin alpha2; Integrin beta1 - immunology; Integrins - immunology; Integrins - physiology; p21-Activated Kinases; Phosphoinositide-3 Kinase Inhibitors; Platelet Adhesiveness; Protein-Serine-Threonine Kinases - antagonists & inhibitors; Protein-Serine-Threonine Kinases - blood; Pyrazoles - pharmacology; Pyridines - pharmacology; Pyrimidines - pharmacology; rac GTP-Binding Proteins - antagonists & inhibitors; rac GTP-Binding Proteins - blood; Receptors, Collagen; Wortmannin
• ISSN: 0006-4971
• DOI: 10.1182/blood.V98.13.3708

In this study, the receptors and signals involved in collagen-induced platelet spreading were examined. It was found that platelet spreading on collagen (presenting a polygon shape with a number of filopodialike projections) was inhibited by the anti-integrin alpha(2) antibody, suggesting the involvement of integrin alpha(2)beta(1) in this process. Studies with a glutathione-S-transferase fusion protein that binds specifically to activated Rac and in vitro p21-activated kinase (PAK) kinase assays revealed that Rac and PAK were activated during this collagen-activated process. Platelet spreading on collagen-coated surfaces was inhibited strongly by PP1 (a Src family kinase inhibitor) or weakly by wortmannin (a phosphatidylinositol 3-kinase [PI3-kinase] inhibitor) but not at all by Y-27632 (a Rho kinase inhibitor). The surfaces coated with anti-integrin alpha(2)beta(1) antibodies also induced platelet spreading (presenting an almost complete round shape) and activation of Rac and PAK, although more slowly than collagen-coated surfaces. The antibody-induced responses were strongly inhibited by PP1 or wortmannin but not by Y-27632. The same concentration of Y-27632 inhibited collagen-induced shape change of platelets in suspension. These findings suggest that Rac and/or PAK activation, but not Rho, may play certain roles in platelet spreading via integrin alpha(2)beta(1) and that Src family kinases and PI3-kinase participate in these processes. Furthermore, the difference between spreading on collagen and the anti-integrin antibody suggests the involvement of other receptor(s) (in addition to the integrin alpha(2)beta(1)) for collagen-induced spreading, the most likely candidate being glycoprotein VI.