TRANSLOCATION OF CORTACTIN (P80 85) TO THE ACTIN-BASED CYTOSKELETON DURING THROMBIN RECEPTOR-MEDIATED PLATELET ACTIVATION/

Cortactin (p80/85) was discovered as a src kinase substrate and an act in filament binding protein. We investigated translocation of cortacti n to the cytoskeleton during thrombin receptor-mediated platelet activ ation. Only a few percent of total cortactin (minor cortactin pool) tr anslocates to the cytoskeleton as early as 5 s after platelet activati on, while about 40% of total cortactin (major cortactin pool) is there after recovered in the cytoskeleton during platelet aggregation. Pretr eatment of platelets with cytochalasin D suppresses completely this tr anslocation, indicating that the translocation is dependent on actin p olymerization. Inhibition of platelet aggregation by a tetrapeptide wi th the sequence RGDS, chelator of extracellular Ca2+, or a nonstirring condition results in marked suppression of translocation of the major cortactin pool. These results suggest that a minor cortactin pool tra nslocates to the cytoskeleton independent of GPII-bIIIa (alpha(IIb)bet a(3) integrin) engagement, and a major pool requires GPIIbIIIa-mediate d signals into the cell for the translocation. Methyl 2,5-hydroxycinam ate, a tyrosine kinase inhibitor, inhibits tyrosine phosphorylation of cortactin without affecting its translocation, indicating that tyrosi ne phosphorylation is not essential for the translocation. Morphologic al studies reveal that cortactin is colocalized with filamentous actin in aggregated platelets and that it is localized at the cell peripher ies along actin filaments in spread platelets. Taking these together, we have demonstrated in this paper that the translocation of cortactin is associated with the reorganization of the actin-based cytoskeleton during platelet activation, particularly with platelet aggregation. ( C) 1995 Academic Press, Inc.