PROTEIN-TYROSINE KINASE-P72(SYK) IS ACTIVATED BY THROMBOXANE-A(2) MIMETIC U44069 IN PLATELETS

We show that p72syk is rapidly activated following the stimulation of thromboxane A2 mimetics, U44069 and STA2 in porcine platelets. The activity of p72syk reached a maximum at 10 s and decreased to a basal level within 60 s after 1 μM U44069 stimulation. This activation was enhanced in a dose-dependent manner and completely canceled by the pretreatment of platelet suspension with ONO3708, a specific antagonist of thromboxane A2. Pretreatment of platelets with aspirin as well as apyrase did not affect the activation of p72syk. When both extra- and intra-cellular Ca2+ were depleted, the activation of p72syk was still persistent; in contrast, the deactivation process was completely abrogated even at 120 s after U44069 stimulation. These results suggest that p72sykis a responsible enzyme to the protein-tyrosine phosphorylation events, and that p72syk functions mainly before Ca2+ recruitment in thromboxane A2-stimulated platelets. © 1993 Academic Press. All rights reserved.