Journal of Biological Chemistry
Volume 274, Issue 4, 22 January 1999, Pages 1898-1904
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CELL BIOLOGY AND METABOLISM
Fc Receptor-mediated Platelet Activation Is Dependent on Phosphatidylinositol 3-Kinase Activation and Involves p120cbl*

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The platelet receptor for the Fc domain of IgGs (FcγRIIa) triggers intracellular signaling through protein tyrosine phosphorylations leading to platelet aggregation. In this study, we focused on the adaptor protein p120cbl (Cbl), which became tyrosine-phosphorylated after platelet activation induced by antibodies. Cbl phosphorylation was dependent on Fc receptor engagement. An association of Cbl with the p85 subunit of phosphatidylinositol 3-kinase (PI 3-K) occurred in parallel with Cbl tyrosine phosphorylation. We showed by in vitro experiments that Cbl/p85 association was mediated by the Src homology 3 domain of p85/PI 3-K and the proline-rich region of Cbl. Inhibition of PI 3-K activity by wortmannin led to the blockade of both platelet aggregation and serotonin release mediated by FcγRIIa engagement, whereas it only partly inhibited those induced by thrombin. Thus, PI 3-K may play a crucial role in the initiation of platelet responses after FcγRIIa engagement. Our results suggest that Cbl is involved in platelet signal transduction by the recruitment of PI 3-K to the FcγRIIa pathway, possibly by increasing PI 3-K activity.

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The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Supported by Diagnostica-Stago (Asnière, France).

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Supported by Ministère de la Recherche et de la Technologie, France.