Translocation of p72syk to the cytoskeleton in thrombin-stimulated platelets.

Thrombin stimulation induces a dramatic increase in the activity of p72syk in platelets. We have found that activated p72syk, which is phosphorylated on tyrosine residue(s), translocates from the Triton X-100-soluble fraction to the Triton X-100-insoluble, cytoskeleton-rich fraction after thrombin stimulation. In addition, the redistribution of p72syk from the 100,000 x g Triton X-soluble fraction and the membrane skeleton was found to correlate with an increased level of p72syk in the cytoskeleton. Furthermore, the early phase of p72syk translocation (within 60 s) was significantly inhibited with cytochalasin D, whereas the late phase of p72syk translocation (after 90 s) was completely inhibited with RGDS tetrapeptide treatment. These results suggest that translocation of the activated p72syk to the cytoskeleton correlates with different phases of the platelet activation process through actin polymerization and glycoprotein IIb/IIIa-fibrinogen-mediated aggregation of platelets and, hence, may have a regulatory role in tyrosine phosphorylation of platelets.