Platelet GP Ib/IX/V complex: physiological role.

Platelets play an essential role in primary hemostasis and in thrombotic events, particularly in arterial vessels, as rheological conditions originate closer interactions between platelets and endothelium than lower shear rates. In response to vascular injury, platelets adhere to the subendothelial matrix by membrane receptors potentiating the generation of thrombin, become activated, and a series of biochemical processes induce platelet aggregation and liberation of intracellular metabolic products to the extracelular medium. Among platelet receptors, glycoprotein (GP) Ib/IX/V complex is peculiar, as it binds adhesive proteins, mainly von Willebrand factor (vWF), and thrombin, the main platelet agonist. Platelet adhesion and subsequent aggregation under conditions of high shear flow, essentially relies upon this receptor's capacity of binding to the subendothelial matrix, initiating signal transduction. Two proteins associated to GP Ib/IX/V, actin-binding protein (ABP) 280 and 14-3-3zeta, are potential mediators of signal transduction by the complex, but their specific contribution in this process is not yet fully understood. Additionally, two proteins implicated in signal transduction by immune stimuli, FcgammaRIIA and FcR gamma-chain, associate with GPIb/IX/V complex, and increasing data indicate a potential role in GPIbalpha mediated signal transduction.