Platelet activation and signal transduction by convulxin, a C-type lectin from Crotalus durissus terrificus (tropical rattlesnake) venom via the p62/GPVI collagen receptor.
Convulxin, a powerful platelet activator, was isolated from Crotalus durissus terrificus venom, and 20 amino acid N-terminal sequences of both subunits were determined. These indicated that convulxin belongs to the heterodimeric C-type lectin family. Neither antibodies against GPIb nor echicetin had any effect on convulxin-induced platelet aggregation showing that, in contrast to other venom C-type lectins acting on platelets, GPIb is not involved in convulxin-induced platelet activation. In addition, partially reduced/denatured convulxin only affects collagen-induced platelet aggregation. The mechanism of convulxin-induced platelet activation was examined by platelet aggregation, detection of time-dependent tyrosine phosphorylation of platelet proteins, and binding studies with 125I-convulxin. Convulxin induces signal transduction in part like collagen, involving the time-dependent tyrosine phosphorylation of Fc receptor gamma chain, phospholipase Cgamma2, p72(SYK), c-Cbl, and p36-38. However, unlike collagen, pp125(FAK) and some other bands are not tyrosine-phosphorylated. Convulxin binds to a glycosylated 62-kDa membrane component in platelet lysate and to p62/GPVI immunoprecipitated by human anti-p62/GPVI antibodies. Convulxin subunits inhibit both aggregation and tyrosine phosphorylation in response to collagen. Piceatannol, a tyrosine kinase inhibitor with some specificity for p72(SYK), showed differential effects on collagen and convulxin-stimulated signaling. These results suggest that convulxin uses the p62/GPVI but not the alpha2beta1 part of the collagen signaling pathways to activate platelets. Occupation and clustering of p62/GPVI may activate Src family kinases phosphorylating Fc receptor gamma chain and, by a mechanism previously described in T- and B-cells, activate p72(SYK) that is critical for downstream activation of platelets.
Polgár
J
J
Theodor Kocher Institute, University of Berne, Freiestrasse 1, CH-3012 Berne, Switzerland.
Clemetson
J M
JM
Kehrel
B E
BE
Wiedemann
M
M
Magnenat
E M
EM
Wells
T N
TN
Clemetson
K J
KJ
D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D003094:Collagen / Q000494:pharmacology; D003435:Crotalid Venoms / Q000737:chemistry / Q000494:pharmacology*; D017839:Crotalus; D006801:Humans; D016023:Integrins / Q000378:metabolism; D037181:Lectins, C-Type; D008969:Molecular Sequence Data; D010766:Phosphorylation; D015539:Platelet Activation / Q000187:drug effects*; D010974:Platelet Aggregation / Q000187:drug effects; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000378:metabolism; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism*; D011485:Protein Binding; D011489:Protein Denaturation; D038981:Receptors, Collagen; D015398:Signal Transduction / Q000187:drug effects*; D013267:Stilbenes / Q000494:pharmacology; D014443:Tyrosine / Q000378:metabolism
D002352:Carrier Proteins; D003435:Crotalid Venoms; D016023:Integrins; D037181:Lectins, C-Type; D010975:Platelet Aggregation Inhibitors; D019038:Platelet Glycoprotein GPIb-IX Complex; D010980:Platelet Membrane Glycoproteins; D038981:Receptors, Collagen; D013267:Stilbenes; C098341:platelet membrane glycoprotein VI; C028890:convulxin; D014443:Tyrosine; C041525:3,3',4,5'-tetrahydroxystilbene; D003094:Collagen