A critical role for phospholipase Cγ2 in αIIbβ 3-mediated platelet spreading

Abstract

The interaction of fibrinogen with the integrin αIIbβ 3, plays a crucial role in platelet adhesion and platelet activation leading to the generation of intracellular signals that nucleate the reorganization of the cytoskeleton. Presently, we have only a limited understanding of the signaling cascades and effector proteins through which changes in the cytoskeletal architecture are mediated. The present study identifies phospholipase Cγ2 (PLCγ2) as an important target of the Src-dependent signaling cascade regulated by αIIbβ 3. Real time phase-contrast microscopy is used to show that formation of filopodia and lamellapodia in murine platelets on a fibrinogen surface is dramatically inhibited in the absence of PLCγ2. Significantly, the formation of these structures is mediated by Ca2+ elevation and activation of protein kinase C, both directly regulated by PLC activity. With the involvement of Syk, SLP-76, and Btk, αIIbβ 3-induced PLCγ2 activation partly overlaps with the pathway used by the collagen receptor glycoprotein VI. Important differences, however, exist between the two signaling cascades in that activation of PLCγ2 by αIIbβ3 is unaltered in murine platelets, which lack the FcR γ-chain or the adaptor LAT, but is abolished in the presence of cytochalasin D. Therefore, PLC γ2 plays not only a crucial role in activation of αIIbβ3 by collagen receptors but also in αIIbβ3-mediated responses.