Abstract 2098: A Novel Mechanism Of Focal Adhesion Kinase Activation By Integrins And Its Role In Outside-in Signaling In Platelets

Abstract

Ligand binding to integrin αIIbβ3 mediates platelet adhesion/aggregation and transmits outside-in signaling, leading to platelet spreading, granule secretion, and significant expansion of platelet thrombi resulting in thrombosis. Focal Adhesion Kinase (FAK) has been recognized in many cells to play an important role during integrin outside-in signaling. Whereas FAK activation downstream of integrins is characterized by autophosphorylation of FAK at Y 397 followed by Y 576/7 phosphorylation, it is not clear how FAK phosphorylation and activation is regulated and how FAK play roles in outside-in signaling in platelets. Here we show that reactive oxygen species (ROS) plays a key role in integrin-dependent stimulation of FAK phosphorylation and activation and ROS-stimulated FAK activation is downstream of the Gα13-integrin interaction, NOX2 activation, and the Src signaling pathway. Furthermore, FAK, following ROS-dependent activation, is important for the integrin outside-in signaling-mediated activation of Syk and immunoreceptor tyrosine-based activation motif (ITAM) signaling pathway. We further show that FAK is important in amplification of platelet activation and aggregation as well as in vivo thrombosis. Thus, we have identified a novel mechanism of FAK activation and a key role of FAK in integrin outside-in signaling and integrin-dependent ITAM pathway activation, leading to amplification of platelet activation, aggregation, and thrombosis.