title: Role of G protein signaling in the formation of the fibrin(ogen)-integrin αIIbβ3-actin cytoskeleton complex in platelets.
abstract: Effective platelet function requires formation of a physical link between fibrin(ogen), integrin αIIbβ3, and cytoplasmic actin filaments. We investigated the role of the Gαq, Gαi, and Gα12/13 families of heterotrimeric GTP-binding proteins (G proteins) in the assembly of a ligand-αIIbβ3-actin cytoskeleton complex. Selective and combined activation of the G proteins was achieved by using combinations of various platelet agonists and inhibitors. Formation and stability of fibrinogen-αIIbβ3 interaction were evaluated by the extent of platelet aggregation and the rate of eptifibatide-induced platelet disaggregation; association of αIIbβ3 with the cytoskeleton was analyzed by western blot. Formation of the fibrin-αIIbβ3-actin cytoskeleton complex was evaluated by rotational thromboelastometry assay in which clot formation was induced by the mixture of reptilase and factor XIIIa. We demonstrated that involvement of heterotrimeric G proteins in the formation of the ligand-αIIbβ3-cytoskeleton complex depends on whether fibrinogen or fibrin serves as the integrin ligand. Formation of the fibrinogen-αIIbβ3-cytoskeleton complex requires combined activation of at least two G protein pathways while the maximal αIIbβ3-cytoskeleton association and the strongest αIIbβ3-fibrinogen binding supporting irreversible platelet aggregation require combined activation of all three-Gαq, Gαi, and Gα12/13-G protein families. In contrast, formation of the fibrin-αIIbβ3-cytoskeleton complex mediating clot retraction is critically dependent on the activation of the Gαi family, especially on the activation of Gαz.
authors.affiliation: a Goldschleger Eye Research Institute and the Department of Human Molecular Genetics and Biochemistry, Sackler Faculty of Medicine , Tel Aviv University , Tel Aviv , Israel.|b Department of Pathophysiology , Sechenov First Moscow State Medical University , Moscow , Russia.
authors.forename: Ivan
authors.initials: I
authors.lastname: Budnik
authors.affiliation: c National Hemophilia Center, Sheba Medical Center , Tel-Hashomer , Israel.
authors.forename: Boris
authors.initials: B
authors.lastname: Shenkman
authors.affiliation: a Goldschleger Eye Research Institute and the Department of Human Molecular Genetics and Biochemistry, Sackler Faculty of Medicine , Tel Aviv University , Tel Aviv , Israel.
authors.forename: Naphtali
authors.initials: N
authors.lastname: Savion
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism*; D000293:Adolescent; D000328:Adult; D000368:Aged; D001792:Blood Platelets / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D005260:Female; D005337:Fibrin / Q000378:metabolism*; D005340:Fibrinogen / Q000378:metabolism*; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D008297:Male; D008875:Middle Aged; D046912:Multiprotein Complexes / Q000378:metabolism; D015539:Platelet Activation; D010974:Platelet Aggregation; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D053657:Platelet-Rich Plasma; D011485:Protein Binding; D015398:Signal Transduction; D055815:Young Adult
chemical_list: D046912:Multiprotein Complexes; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D005337:Fibrin; D005340:Fibrinogen; D019204:GTP-Binding Proteins; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D043802:GTP-Binding Protein alpha Subunits, Gq-G11
keywords: Clot formation; G proteins; cytoskeleton; platelet aggregation; αIIbβ3–actin complex