title: 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).
abstract: 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.
authors.affiliation: Department of Clinical and Laboratory Medicine, Yamanashi Medical University, Nakakoma, Yamanashi, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Suzuki-Inoue
authors.forename: Y
authors.initials: Y
authors.lastname: Yatomi
authors.forename: N
authors.initials: N
authors.lastname: Asazuma
authors.forename: M
authors.initials: M
authors.lastname: Kainoh
authors.forename: T
authors.initials: T
authors.lastname: Tanaka
authors.forename: K
authors.initials: K
authors.lastname: Satoh
authors.forename: Y
authors.initials: Y
authors.lastname: Ozaki
mesh_terms: D000577:Amides / Q000494:pharmacology; D000730:Androstadienes / Q000494:pharmacology; D000906:Antibodies / Q000494:pharmacology; D015703:Antigens, CD / Q000276:immunology; D001081:Apyrase / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects / Q000502:physiology*; D003094:Collagen / Q000494:pharmacology*; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000494:pharmacology; D039421:Integrin alpha2; D019012:Integrin beta1 / Q000276:immunology; D016023:Integrins / Q000276:immunology / Q000502:physiology*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010973:Platelet Adhesiveness; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000097:blood*; D011720:Pyrazoles / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D038981:Receptors, Collagen; D000077191:Wortmannin; D020764:cdc42 GTP-Binding Protein / Q000097:blood; D054462:p21-Activated Kinases; D020744:rac GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000097:blood*
chemical_list: C108123:4-amino-5-(4-methylphenyl)-7-(tert-butyl)pyrazolo(3,4-d)pyrimidine; D000577:Amides; D000730:Androstadienes; D000906:Antibodies; D015703:Antigens, CD; D004791:Enzyme Inhibitors; D007140:Immunoglobulin Fab Fragments; D039421:Integrin alpha2; D019012:Integrin beta1; D016023:Integrins; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011720:Pyrazoles; D011725:Pyridines; D011743:Pyrimidines; D038981:Receptors, Collagen; C108830:Y 27632; D003094:Collagen; C515903:PAK1 protein, human; D017346:Protein Serine-Threonine Kinases; D054462:p21-Activated Kinases; D001081:Apyrase; D020764:cdc42 GTP-Binding Protein; D020744:rac GTP-Binding Proteins; D000077191:Wortmannin