Apotential role for -actinin in inside-out IIb3 signaling

clearly showed that PAR1-activating peptide stimulation induced only transient IIb3 activation, whereas PAR4activating peptide induced long-lasting IIb3 activation. When IIb3 activation signaling dwindled, -actinin became rephosphorylated and reassociated with IIb3. Compared with control platelets, the dissociation of -actinin from IIb3 was only transient in PAR4-stimulated P2Y12-deficient platelets in which the sustained IIb3 activation was markedly impaired. Overexpression of wild-type -actinin, but not the mutant Y12F actinin, increased its binding to IIb3 and inhibited PAR1-induced initial IIb3 activation in the human megakaryoblastic cell line, CMK. In contrast, knockdown of -actinin augmented PAR-induced IIb3 activation in CMK. These observations suggest that -actinin might play a potential role in setting integrins to a default low-affinity ligand-binding state in resting platelets and regulating IIb3 activation by inside-out signaling. (Blood. 2011;117(1):250-258)