title: Platelet-derived microparticle formation involves glycoprotein IIb-IIIa. Inhibition by RGDS and a Glanzmann's thrombasthenia defect.
abstract: While the physiologic role of platelet microparticles may include a stable, physical dispersion of concentrated surface procoagulant activity the mechanism(s) of platelet vesiculation remains unknown. We demonstrate using flow cytometric methods a central role for the beta 3 integrin glycoprotein (GP) IIb-IIIa complex and its ligand tetrapeptide Arg-Gly-Asp-Ser (RGDS) binding site in platelet vesiculation. Time- and calcium-dependent vesiculation of platelets in response to ADP, collagen, thrombin, phorbol myristate acetate, and the thrombin peptide SFLLRN were dramatically inhibited, in a concentration-dependent manner, by monoclonal antibodies to GPIIb-IIIa (A2A9, 7E3, PAC1) and RGDS. Complete inhibition with A2A9 and RGDS occurred at 7.5 micrograms/ml and 75 microM, respectively, while control antibodies and a mock peptide had no effect. Platelet vesiculation requires intact GPIIb-IIIa and is fully supported by the intracellular pool of GPIIb-IIIa alone since de-complexing of this heterodimer by calcium chelation completely abolished microparticle formation in response to collagen (no alpha-granule release) but not to thrombin or SFLLRN. A central role for GPIIb-IIIa is supported by the near total inability of Glanzmann's thrombasthenic (type I) platelets to vesiculate in response to thrombin, ADP, collagen, and phorbol 12-myristate 13-acetate. This extends the biologic roles of GPIIb-IIIa to include platelet vesiculation and suggests that one or all of its binding ligands play a role.
authors.affiliation: Department of Medicine, University of Toronto.
authors.forename: C H
authors.initials: CH
authors.lastname: Gemmell
authors.forename: M V
authors.initials: MV
authors.lastname: Sefton
authors.forename: E L
authors.initials: EL
authors.lastname: Yeo
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies / Q000276:immunology; D001792:Blood Platelets / Q000187:drug effects / Q000502:physiology*; D002417:Cattle; D002478:Cells, Cultured; D006801:Humans; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000494:pharmacology*; D015539:Platelet Activation; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology*; D010980:Platelet Membrane Glycoproteins / Q000276:immunology / Q000502:physiology*; D013915:Thrombasthenia / Q000097:blood* / Q000378:metabolism
chemical_list: D000906:Antibodies; D009842:Oligopeptides; D010975:Platelet Aggregation Inhibitors; D010980:Platelet Membrane Glycoproteins; C046617:arginyl-glycyl-aspartyl-serine