RGT, a synthetic peptide corresponding to the integrin ß3 cytoplasmic C-terminal sequence, selectively inhibits outside-in signaling in human platelets by disrupting the interaction of integrin αIIbβ3 with Src kinase

Mutational analysis has established that the cytoplasmic tail of the integrin (53 subunit binds c-Src (termed as Src in this study) and is critical for bidirectional integrin signaling. Here we show in washed human platelets that a cell-permeable, myristoylated RGT peptide (myr-RGT) corresponding to the integrin β3 C-terminal sequence dose-dependently inhibited stable platelet adhesion and spreading on immobilized fibrinogen, and fibrin clot retraction as well. Myr-RGT also inhibited the aggregation-dependent plate-let secretion and secretion-dependent second wave of platelet aggregation induced by adenosine diphosphate, ristocetin, or thrombin. Thus, myr-RGT inhibited integrin outside-in signaling. In contrast, myr-RGT had no inhibitory effect on adenosine diphosphate-induced soluble fibrinogen binding to platelets that is dependent on integrin inside-out signaling. Furthermore, the RGT peptide induced dissociation of Src from integrin (Í3 and dose-dependently inhibited the purified recombinant (53 cytoplasmie domain binding to Src-SH3. In addition, phosphorylation of the (53 cytoplasmic tyrosines, Y⁷⁴⁷ and Y ⁷⁵⁹, was inhibited by myr-RGT. These data indicate an important role for β3-Src interaction in outside-in signaling. Thus, in intact human platelets, disruption of the association of Src with (53 and selective blockade of integrin αllbβ3 out-side-in signaling by myr-RGT suggest a potential new antithrombotic strategy.