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Blood, 1 October 2007, Vol. 110, No. 7, pp. 2466-2474.
Prepublished online as a Blood First Edition Paper on June 19, 2007; DOI 10.1182/blood-2007-02-075432.
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HEMOSTASIS, THROMBOSIS, AND VASCULAR BIOLOGY
Roles of the C-terminal tyrosine residues of LAT in GPVI-induced platelet activation: insights into the mechanism of PLC 2 activation
Ashraf Ragab1,2,
Sonia Séverin1,2,
Marie-Pierre Gratacap1,2,
Enrique Aguado3,
Marie Malissen3,
Martine Jandrot-Perrus4,
Bernard Malissen3,
Jeannie Ragab-Thomas1,2,5, and
Bernard Payrastre1,2
1 Institut National de la Santé et de la Recherche Médicale (INSERM), U563, Centre de Physiopathologie de Toulouse Purpan, Département Oncogenèse, Signalisation et Innovation Thérapeutique, Toulouse, France;
2 Université Toulouse III Paul-Sabatier, Toulouse, France;
3 Centre d'Immunologie de Marseille-Luminy, INSERM–Centre National de la Recherche Scientifique (CNRS)–Université de la Méditerrané, Marseille France;
4 INSERM, U698, Hôpital Bichat, Paris, France; and
5 Centre Hospitalier Universitaire (CHU) Toulouse, Hôpital Purpan, Toulouse, France
Linker for activation of T cells (LAT) is an adaptor protein required for organization of the signaling machinery downstream of the platelet collagen receptor, the glycoprotein VI (GPVI). Here, we investigated the effect of LAT mutations on specific signaling 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 positions 175, 195, and 235 in the phosphorylation of LAT and in the whole pattern of protein tyrosine phosphorylation in response to Cvx. These 3 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 3 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 2 complementary events: its interaction with the tyrosine 136 of LAT and its membrane location, which itself requires events mediated by the 3 C-terminal tyrosines of LAT.
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