Interaction of linker for activation of T cells with multiple adapter proteins in platelets activated by the glycoprotein VI-selective ligand, convulxin

J Biol Chem. 2000 Oct 27;275(43):33427-34. doi: 10.1074/jbc.M001439200.

Abstract

The snake venom toxin convulxin activates platelets through the collagen receptor glycoprotein VI (GPVI)/Fc receptor gamma-chain (FcR gamma-chain) complex leading to tyrosine phosphorylation and activation of the tyrosine Syk and phospholipase Cgamma2 (PLCgamma2). In the present study, we demonstrate that convulxin is a considerably more powerful agonist than collagen or the GPVI-selective collagen-related peptide (CRP). Confirmation that the response to convulxin is mediated solely via Syk was provided by studies on Syk-deficient platelets. The increase in phosphorylation of the FcR gamma-chain is associated with marked increases in tyrosine phosphorylation of downstream proteins including Syk, linker for activation of T cells (LAT), SLP-76, and PLCgamma2. The transmembrane adapter LAT coprecipitates with SLP-76 and PLCgamma2, as well as with a number of other adapter proteins, some of which have not been previously described in platelets, including Cbl, Grb2, Gads, and SKAP-HOM. Gads is constitutively associated with SLP-76 and is probably the protein bridging its association with LAT. There was no detectable association between Grb2 and SLP-76 in control or stimulated cells, suggesting that the interaction of LAT with Grb2 is present in a separate complex to that of LAT-Gads-SLP-76. These results show that the trimeric convulxin stimulates a much greater phosphorylation of the FcR gamma-chain and subsequent downstream responses relative to CRP and collagen, presumably because of its ability to cause a greater degree of cross-linking of GPVI. The adapter LAT appears to play a critical role in recruiting a number of other adapter proteins to the surface membrane in response to activation of GPVI, presumably at sites of glycolipid-enriched microdomains, enabling an organized signaling cascade that leads to platelet activation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing*
  • Blood Platelets / drug effects*
  • Blood Platelets / metabolism
  • Carrier Proteins / physiology*
  • Collagen / pharmacology
  • Crotalid Venoms / pharmacology*
  • Cyclic AMP Receptor Protein / pharmacology
  • GRB2 Adaptor Protein
  • Humans
  • Integrins / metabolism*
  • Intracellular Signaling Peptides and Proteins
  • Lectins, C-Type*
  • Membrane Proteins*
  • Phosphoproteins / physiology*
  • Phosphorylation
  • Proteins / physiology
  • Receptors, Collagen
  • Receptors, IgG / physiology
  • Type C Phospholipases / physiology

Substances

  • Adaptor Proteins, Signal Transducing
  • Carrier Proteins
  • Crotalid Venoms
  • Cyclic AMP Receptor Protein
  • FYB1 protein, human
  • GRB2 Adaptor Protein
  • GRB2 protein, human
  • Integrins
  • Intracellular Signaling Peptides and Proteins
  • LAT protein, human
  • Lectins, C-Type
  • Membrane Proteins
  • Phosphoproteins
  • Proteins
  • Receptors, Collagen
  • Receptors, IgG
  • SLP-76 signal Transducing adaptor proteins
  • src kinase associated phosphoprotein 2
  • convulxin
  • Collagen
  • Type C Phospholipases