Molecular Requirements for the Interaction of Thrombospondin With Thrombin-Activated Human Platelets: Modulation of Platelet Aggregation

• Published in: Blood Vol. 79; no. 8; pp. 1995 - 2003
• Main Authors: Legrand, Chantal, Thibert, Valerie, Dubernard, Veronique, Bégault, Beatrice, Lawler, Jack
• Format: Journal Article
• Language: English
• Published: Washington, DC Elsevier Inc 15.04.1992; The Americain Society of Hematology
• Subjects: Antibodies; Antibodies, Monoclonal; Biological and medical sciences; Blood coagulation. Blood cells; Blood Platelets - drug effects; Blood Platelets - physiology; Blotting, Western; Fundamental and applied biological sciences. Psychology; Humans; Kinetics; Macromolecular Substances; Molecular and cellular biology; Platelet; Platelet Activation; Platelet Aggregation; Platelet Membrane Glycoproteins - biosynthesis; Platelet Membrane Glycoproteins - immunology; Platelet Membrane Glycoproteins - metabolism; Recombinant Fusion Proteins - immunology; Thrombin - pharmacology; Thrombospondins; Aggregation; Human; Platelet; Thrombospondin
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V79.8.1995.1995

We have investigated the molecular requirements for throm-bospondin (TSP) to bind to the platelet surface and to support the subsequent secretion-dependent platelet aggregation. For this, we used two distinct murine monoclonal antibodies (MoAbs), designated MAI and MAII, raised against human platelet TSP, and three polyclonal antibodies, designated R3, R6, and R5, directed against fusion proteins containing the type 1 (Gly 385-lle 522), type 2 (Pro 559-lle 669), and type 3 (Asp 784-Val 932) repeating sequences, respectively. Among them, R5 and R6, but not R3, inhibited thrombin-induced aggregation of washed platelets and the concomitant secretion of serotonin. These antibodies, however, did not inhibit the expression of TSP on thrombin-activated platelets, as measured by the binding of a radiolabeled MoAb to TSP, suggesting that they may inhibit platelet aggregation by interfering with a physiologic event subsequent to TSP binding. In contrast, MoAb MAII, which reacts with an epitope located within the heparin-binding domain of TSP, inhibited both TSP surface expression and platelet aggrega-tion/secretion induced by thrombin. In addition, this MoAb inhibited in a dose-dependent manner (IC50 ≈ 0.5 μmol/L) the interaction of 125I-TSP with immobilized fibrinogen and platelet glycoprotein IV, both potential physiologic receptors for TSP on thrombin-activated platelets. These results indicate that the interaction of TSP with the surface of activated platelets can be modulated at the level of a specific epitope located within the amino terminal heparin-binding domain of the molecule. Thus, selective inhibition of the platelet/TSP interaction may represent an alternative approach to the inhibition of platelet aggregation. © 1992 by The American Society of Hematology.