Adhesion and activation of human platelets induced by convulxin involve glycoprotein VI and integrin alpha2beta1.
We analyzed the interaction of convulxin (Cvx), a 72-kDa protein isolated from the venom of Crotalus durissus terrificus, with human platelets. Cvx is a potent platelet agonist that induces an increase in the intracellular Ca2+ concentration ([Ca2+]i), granule exocytosis and aggregation. 125I-Labeled Cvx binds specifically and rapidly to platelets at binding sites of high and moderate affinity. Platelets adhere to immobilized Cvx in a time-dependent but cation-independent manner. Platelet exocytosis and aggregation induced by Cvx were inhibited by an anti-integrin alpha2beta1 monoclonal antibody (6F1) and by the Fab fragments of a polyclonal anti-glycoprotein VI (GPVI) antibody. Both the adhesion of platelets to Cvx and the Cvx-induced increase in [Ca2+]i were inhibited by anti-GPVI Fab fragments but not by 6F1. Ligand blotting assay showed that 125I-Cvx binds to a 57-kDa platelet protein with an electrophoretic mobility identical to that of GPVI. In addition, we observed the following: (i) 125I-Cvx binds to GPVI immunoprecipitated by the anti-GPVI antibody from a platelet lysate, and (ii) Cvx inhibits the binding of anti-GPVI IgG to GPVI. Taken together, these results demonstrate that GPVI behaves as a Cvx receptor and that the alpha2beta1 integrin appears to be involved in the later stages of Cvx-induced platelet activation, i.e. exocytosis and aggregation.
Jandrot-Perrus
M
M
Laboratoire de Recherche sur l'Hémostase et la Thrombose, Faculté de Médecine Xavier Bichat, BP 416, 75870 Paris Cedex 18, France.
Lagrue
A H
AH
Okuma
M
M
Bon
C
C
D000911:Antibodies, Monoclonal / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects / Q000502:physiology*; D003094:Collagen / Q000494:pharmacology; D003435:Crotalid Venoms / Q000494:pharmacology*; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000494:pharmacology; D019012:Integrin beta1 / Q000097:blood / Q000187:drug effects; D016023:Integrins / Q000097:blood* / Q000187:drug effects; D007700:Kinetics; D037181:Lectins, C-Type; D015539:Platelet Activation / Q000187:drug effects / Q000502:physiology*; D010973:Platelet Adhesiveness / Q000187:drug effects / Q000502:physiology*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D010980:Platelet Membrane Glycoproteins / Q000187:drug effects / Q000502:physiology*; D038981:Receptors, Collagen
D000911:Antibodies, Monoclonal; D003435:Crotalid Venoms; D007140:Immunoglobulin Fab Fragments; D019012:Integrin beta1; D016023:Integrins; D037181:Lectins, C-Type; D010975:Platelet Aggregation Inhibitors; D010980:Platelet Membrane Glycoproteins; D038981:Receptors, Collagen; C098341:platelet membrane glycoprotein VI; C028890:convulxin; D003094:Collagen