Tickling the tails:: cytoplasmic domain proteins that regulate integrin αIIbβ3 activation

Purpose of review Integrin alpha IIb beta 3 activation is essential for platelet aggregation and related hemostatic events. In recent years, intense effort has been put forward to understand the molecular mechanisms regulating platelet integrin alpha IIb beta 3 activation. Here we review the current models of alpha IIb beta 3 activation and highlight the potential regulatory roles of proteins that interact directly with the alpha IIb beta 3 cytoplasmic domains, with emphasis on the alpha IIb cytoplasmic domain binding protein, CIB1. Recent findings Mutational and crystallographic studies reveal the importance of integrin transmembrane and cytoplasmic domains in propagating bidirectional signaling events. Proteins that interact directly with the integrin cytoplasmic domains may play important roles in mediating these signaling events. Of particular interest is the interaction between CIB1 and the alpha IIb tail which may function to negatively regulate alpha IIb beta 3 activation. In addition, a number of CIB1 interacting proteins have been identified, including p21-activated kinase and serum-inducible kinase, which may act in concert with CIB1 to regulate platelet function. Summary Understanding the molecular mechanisms underlying integrin activation will be important in developing novel therapies to regulate platelet function in cardiovascular disease. Discussion of recent developments in elucidating the mechanism of integrin activation, with particular focus on the platelet integrin alpha IIb beta 3, is provided in this review.