ASSOCIATION OF THE LOW-MOLECULAR-WEIGHT GTP-BINDING PROTEIN RAP2B WITH THE CYTOSKELETON DURING PLATELET-AGGREGATION

The intracellular distribution of the low-molecular-weight GTP-binding protein rap2B was investigated in resting and agonist-activated human platelets. In both cases, platelets were lysed by Triton X-100, and c ell fractions were obtained by differential centrifugations. Using a s pecific polyclonal antiserum, we found that rap2B in resting platelets was completely detergent-soluble. When platelets were aggregated with thrombin, the thromboxane analogue U46619, or the Ca2+-ATPase inhibit or thapsigargin, a significant amount of rap2B became associated with the cytoskeleton. This association was paralleled by a decrease of rap 2B in the Triton X-100-soluble fraction. Translocation of rap2B to the cytoskeleton strictly depended on platelet aggregation, and maximal i ncorporation was found when almost-equal-to 50% aggregation was measur ed. Inhibition of fibrinogen binding to the glycoprotein IIb-IIIa comp lex completely prevented the interaction of rap2B with the cytoskeleto n. These results clearly demonstrate that changes in the intracellular localization of rap2B occur during platelet activation and represent evidence that this low molecular weight GTP-binding protein may be inv olved in platelet function.