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 p 72(syk) and p60(c-src) with similar magnitudes. Both thrombin and TRAP induced translocation of p60(c-src) and p54/58(lyn) to cytoskeleton i n an aggreagation-dependent manner. Thrombin also induced cytoskeletal association of p72(syk), but independent of platelet aggregation. Fur thermore, p72(syk) associated with cytoskeleton underwent marked prote olysis, which was partially dependent upon calpain activation. In cont rast, TRAP, even at concentrations as high as 100 mu M, did not induce p72(syk) translocation to cytoskeleton. Our findings suggest that cyt oskeletal translocation of p72(syk) induced by thrombin is governed by a mechanism distinct from those of p60(c-src) and p54/58(lyn) translo cation. It is also suggested that p72(syk) translocation induced by th rombin requires additional signal(s) other than that mediated by the r ecently-cloned thrombin receptor that couples with GTP-binding protein s and interacts with TRAP. (C) 1996 Academic Press. Inc.