Submitted February 20, 2007
Accepted June 11, 2007
Roles of the C-terminal tyrosine residues of LAT in GPVI-induced platelet activation; insights in the mechanism of PLC
2 activation
Ashraf Ragab, Sonia Severin, Marie-Pierre Gratacap, Enrique Aguado, Marie Malissen, Martine Jandrot-Perrus, Bernard Malissen, Jeannie Ragab-Thomas, and Bernard Payrastre*
Dept Oncogenese, Signalisation et Innovatiion therapeutique, Inserm U564, Centre de Physiopathologie de Toulouse Purpan, Toulouse, France
Centre d'Immunologie de Marseille-Luminy, Inserm-CNRS-Universite de la Mediterrane, Marseille-Luminy, France
Inserm U698, Hopital Bichat, Paris, France
* Corresponding author; email: payrastr{at}toulouse.inserm.fr.
Linker for activation of T cells (LAT) is an adaptor protein required for organisation of the signalling machinery downstream of the platelet collagen receptor, the glycoprotein VI (GPVI). Here, we investigated the effect of LAT mutations on specific signalling pathways and on platelet functions in response to GPVI triggering by convulxin (Cvx). Using mice containing tyrosine to phenylalanine mutations of the adaptor, we show the crucial role played by the tyrosine residues at position 175, 195 and 235 in the phosphorylation of LAT and in the whole pattern of protein tyrosine phosphorylation in response to Cvx. These three C-terminal tyrosine residues are important to recruit the tyrosine kinase Fyn which may be involved in LAT phosphorylation. Efficient phosphoinositide 3-kinase (PI3K) activation requires the three C-terminal tyrosine residues of LAT but not its tyrosine 136. Interestingly, single mutation of the tyrosine 136 results in the loss of phospholipase C
2 (PLC2) activation without affecting its PI3K-dependent membrane association, and is sufficient to impair platelet responses to Cvx. Thus, activation of PLC2 via GPVI is dependent on two complementary events; its interaction with the tyrosine 136 of LAT and its membrane location which itself requires events mediated by the three C-terminal tyrosines of LAT.
