Differential mobilization of tyrosine kinases in human platelets stimulated with thrombin or thrombin receptor agonist peptide

Both thrombin and thrombin receptor agonist peptide (TRAP) activated p72(syk) and p60(c-src) with similar magnitudes. Both thrombin and TRAP induced translocation of p60(c-src) and p54/58(lyn) to cytoskeleton in an aggreagation-dependent manner. Thrombin also induced cytoskeletal association of p72(syk), but independent of platelet aggregation. Furthermore, p72(syk) associated with cytoskeleton underwent marked proteolysis, which was partially dependent upon calpain activation. In contrast, TRAP, even at concentrations as high as 100 mu M, did not induce p72(syk) translocation to cytoskeleton. Our findings suggest that cytoskeletal translocation of p72(syk) induced by thrombin is governed by a mechanism distinct from those of p60(c-src) and p54/58(lyn) translocation. It is also suggested that p72(syk) translocation induced by thrombin requires additional signal(s) other than that mediated by the recently-cloned thrombin receptor that couples with GTP-binding proteins and interacts with TRAP. (C) 1996 Academic Press. Inc.