Functional implications of tyrosine protein phosphorylation in platelets. Simultaneous studies with different agonists and inhibitors

Author:

Bachelot C1,Cano E2,Grelac F1,Saleun S1,Druker B J3,Levy-Toledano S1,Fischer S4,Rendu F1

Affiliation:

1. U150 INSERM, Hôp Lariboisiere, 6 rue Guy Patin, 75010 Paris, France

2. Facultad de Farmacia, Santiago de Compostela, Spain

3. Dana-Farber Cancer Institute, 44 Binney St., Boston, MA 02115, U.S.A.

4. U332 INSERM, ICGM Cochin, 75014 Paris, France

Abstract

During activation of platelets by agonists, a number of proteins become phosphorylated at tyrosine residues. Using immunoblotting with a monoclonal anti-phosphotyrosine antibody, we have compared the different phosphotyrosine-protein (PTP) profiles of platelets stimulated with thrombin, collagen, ADP, arachidonic acid, phorbol myristate acetate and P256, an anti-glycoprotein-IIb-IIIa (GPIIb-IIIa) monoclonal antibody (mAb). Only a few PTPs were observed in resting platelets, of molecular masses 130, 64, 56-60 and 36 kDa. After stimulation by different agonists these proteins were more intensely phosphorylated and additional PTPs appeared with molecular masses of 170, 150, 140, 120, 105/97 (doublet), 85, 80, 75 and 45 kDa. The kinetics of phosphorylation differed from one agonist to another, but no significant differences in the overall patterns were detected, except in presence of ADP and P256-F(ab')2, which induced only the additional tyrosine phosphorylation of the 64 kDa protein and to a lesser extent that of a 75 kDa protein. The use of various agonists and the inhibitors (staurosporine, ajoene and RGDS) permitted a better characterization of the relationship between the different steps of activation and phosphorylation on tyrosine residues. The studies suggest the following conclusions: (i) stimulation of tyrosine phosphorylation occurs after activation of protein kinase C; (ii) there is a relationship between ligand binding to GPIIb-IIIa and the tyrosine phosphorylation of the 64 kDa protein; and (iii) there is a close relationship between PTP formation and the intensity of platelet activation and aggregation.

Publisher

Portland Press Ltd.

Subject

Cell Biology,Molecular Biology,Biochemistry

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