GLYCOPROTEIN IIB-IIIA AND THE TRANSLOCATION OF RAP2B TO THE PLATELET CYTOSKELETON

The stimulation of human platelets with physiological agonists results in the incorporation of several proteins into the cytoskeleton, fibri nogen binding, and platelet aggregation. We recently demonstrated that the Ras-related low molecular weight GTP-binding protein Rap2B associ ates with the cytoskeleton in activated platelets and that this intera ction requires platelet aggregation. In the present study we demonstra te that agonist-induced actin polymerization is necessary for the tran slocation of Rap2B to the cytoskeleton, suggesting that Rap2B interact s with the newly formed actin filaments. Moreover, the association of Rap2B with Triton X-100-insoluble material from platelets was totally blocked by treatment of intact platelets with monoclonal antibodies ag ainst the fibrinogen receptor glycoprotein IIh-IIIa. Platelets from: p atients affected by Glanzmann thrombastenia, a genetic disorder in whi ch platelet plasma membranes lack glycoprotein IIb-IIIa but possess no rmal levels of Pas-related proteins, failed to incorporate Rap2B into the cytoskeleton upon acti vation by thrombin. Comparative immunoblott ing revealed that the translocation of Rap2B to the cytoskeleton durin g platelet aggregation was accompanied by the simultaneous translocati on of glycoprotein IIb-IIIa. Moreover, the cytoskeleton from aggregate d platelets contained Rap2B and glycoprotein II-IIIa in comparable amo unts. These results demonstrate the association of Rap2B and glycoprot ein IIb-IIIa and their translocation to the cytoskeleton in aggregated human platelets.