TRANSLOCATION OF P72(SYK) TO THE CYTOSKELETON IN THROMBIN-STIMULATED PLATELETS

Thrombin stimulation induces a dramatic increase in the activity of p7 2(syk) in platelets. We have found that activated p72(syk), which is p hosphorylated on tyrosine residue(s), translocates from the Triton X-1 00-soluble fraction to the Triton X-100-insoluble, cytoskeleton-rich f raction after thrombin stimulation. In addition, the redistribution of p72(syk) from the 100,000 x g Triton X-soluble fraction and the membr ane skeleton was found to correlate with an increased level of p72(syk ) in the cytoskeleton. Furthermore, the early phase of p72(syk) transl ocation (within 60 s) was significantly inhibited with cytochalasin D, whereas the late phase of p72(syk) translocation (after 90 s) was com pletely inhibited with RGDS tetrapeptide treatment. These results sugg est that translocation of the activated p72(syk) to the cytoskeleton c orrelates with different phases of the platelet activation process thr ough actin polymerization and glyco protein IIb/IIIa-fibrinogen-mediat ed aggregation of platelets and, hence, may have a regulatory role in tyrosine phosphorylation of platelets.