Membrane-associated 41-kDa GTP-binding protein in collagen-induced platelet activation.
Initially we established that the binding of collagen to human blood platelets stimulates both the rapid loss of PIP2 and the generation of inositol-4,5-bisphosphate (IP2) and inositol-1,4,5-triphosphate (IP3). These results indicate that the binding of collagen stimulates inositol phospholipid-specific phospholipase C during platelet activation. The fact that GTP or GTP-gamma-S augments, and pertussis toxin inhibits, collagen-induced IP3 formation suggests that a GTP-binding protein (or (or proteins) may be directly involved in the regulation of phospholipase C-mediated phosphoinositide turnover in human platelets. We have used several complementary techniques to isolate and characterize a platelet 41-kDa polypeptide (or polypeptides) that has a number of structural and functional similarities to the regulatory alpha i subunit of the GTP-binding proteins isolated from bovine brain. This 41-kDa polypeptide (or polypeptides) is found to be closely associated with at least four membrane glycoproteins (e.g., gp180, gp110, gp95, and gp75) in a 330-kDa complex that can be dissociated by treatment with high salt plus urea. Most important, we have demonstrated that antilymphoma 41-kDa (alpha i subunit of GTP-binding proteins) antibody cross-reacts with the platelet 41-kDa protein (or proteins) and the alpha i subunit of bovine brain Gi alpha proteins, and blocks GTP/collagen-induced IP3 formation. These data provide strong evidence that the 41-kDa platelet GTP-binding protein (or proteins) is directly involved in collagen-induced signal transduction during platelet activation.
Walker
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Department of Cell Biology and Anatomy, University of Miami Medical School, Florida 33101.
Bourguignon
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D000246:Adenosine Diphosphate Ribose / Q000097:blood; D000328:Adult; D001345:Autoradiography; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002855:Chromatography, Thin Layer; D003094:Collagen / Q000494:pharmacology*; D019204:GTP-Binding Proteins / Q000097:blood* / Q000302:isolation & purification; D006801:Humans; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000097:blood / Q000302:isolation & purification; D008970:Molecular Weight; D037342:Pertussis Toxin; D010743:Phospholipids / Q000097:blood / Q000302:isolation & purification; D010761:Phosphorus Radioisotopes; D015539:Platelet Activation / Q000187:drug effects*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D007295:Inositol Phosphates; D010743:Phospholipids; D010761:Phosphorus Radioisotopes; D010566:Virulence Factors, Bordetella; D000246:Adenosine Diphosphate Ribose; D003094:Collagen; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins