Phase specific association of heterotrimeric GTP-binding proteins with the actin-based cytoskeleton during thrombin...

Subcellular distribution of heterotrimeric GTP-binding proteins during thrombin receptor-mediated platelet activation was examined, revealing two phases of translocation to the cytoskeleton. A part of Gi2 alpha and Gs alpha shows first phase translocation to the low-speed pellet (15000 x g pellet) within 1 min after activation, suggesting involvement in platelet shape change or granule secretion. In the second phase, Gi2 alpha, Gs alpha, Gq alpha, and G beta translocate to the low-speed pellet, depending on platelet aggregation. These translocations correlated with the reorganization of the actin-cytoskeleton and were inhibited by cytochalasin D. Reconstitution experiments also revealed that G proteins are associated with the actin-cytoskeleton during platelet activation.