title: Active GPIIb-IIIa conformations that link ligand interaction with cytoskeletal reorganization.
abstract: Glycoprotein (GP) IIb-IIIa plays a critical role in platelet aggregation and platelet-mediated clot retraction. This study examined the intramolecular relationship between GPIIb-IIIa activation and fibrinogen binding, platelet aggregation, and platelet-mediated clot retraction. To distinguish between different high-affinity activation states of GPIIb-IIIa, the properties of an antibody (D3) specific for GPIIIa that induces GPIIb-IIIa binding to adhesive protein molecules and yet completely inhibits clot retraction were used. Clot retraction inhibition by D3 was not due to altered platelet-fibrin interaction; however, combination treatments of D3 and adenosine diphosphate (ADP) inhibited full-scale aggregation and decreased the amounts of GPIIb-IIIa and talin incorporated into the core cytoskeletons. Morphologic evaluation of the D3/ADP aggregates showed platelets that were activated but to a lesser extent when compared to ADP only. ADP addition to platelets caused an increase in the number of D3 binding sites indicating that ligand had bound to the GPIIb-IIIa receptor. These data suggest that high-affinity GPIIb-IIIa- mediated ligand binding can be separated mechanistically from GPIIb-IIIa-mediated clot retraction and that clot retraction requires additional signaling through GPIIb-IIIa after ligand binding. The conformation recognized by D3 represents the expression of a GPIIb-IIIa activation state that participates in full-scale platelet aggregation, cytoskeletal reorganization, and clot retraction.
authors.affiliation: Vascular Biology Program, University of Tennessee, Memphis, TN, USA.
authors.forename: T H
authors.initials: TH
authors.lastname: Mondoro
authors.forename: M M
authors.initials: MM
authors.lastname: White
authors.forename: L K
authors.initials: LK
authors.lastname: Jennings
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000906:Antibodies / Q000494:pharmacology; D001665:Binding Sites; D001792:Blood Platelets / Q000502:physiology* / Q000648:ultrastructure*; D003018:Clot Retraction; D003599:Cytoskeleton / Q000378:metabolism / Q000648:ultrastructure*; D005340:Fibrinogen / Q000378:metabolism; D006801:Humans; D007457:Iodine Radioisotopes; D008855:Microscopy, Electron, Scanning; D010974:Platelet Aggregation / Q000187:drug effects; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism*; D011487:Protein Conformation; D016608:Talin / Q000378:metabolism
chemical_list: D000906:Antibodies; D007457:Iodine Radioisotopes; D010975:Platelet Aggregation Inhibitors; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D016608:Talin; D000244:Adenosine Diphosphate; D005340:Fibrinogen