Thrombin induces activation and translocation of Bid, Bax and Bak to the mitochondria in human platelets

Background: Thrombin is a physiological platelet agonist that activates apoptotic events, including cytochrome c release and phosphatidylserine exposure; however, the mechanisms underlying these events remain unclear. Objectives: The present study is aimed to investigate whether thrombin induces activation and mitochondrial translocation of Bid, Bax and Bak. Methods: Changes in the mitochondrial membrane potential were registered using the dye JC-1; Bid, Bax and Bak translocation to the mitochondria was detected by immunoprecipitation and Western blotting in samples from mitochondrial and cytosolic fractions. Results: Treatment of platelets with thrombin or ADP induces activation and mitochondrial association of active Bid, Bax and Bak. Translocation of Bid and Bax to the mitochondria was reduced by cytochalasin D, latrunculin A or jasplakinolide. Platelet exposure to exogenous H(2)O(2) (10 mu M) results in activation of Bid and Bax, which was found to be similar to the effect of thrombin. Thrombin evokes mitochondrial membrane depolarization, which is attenuated by catalase. Conclusion: Our results indicate that thrombin induces activation and mitochondrial translocation of Bid, Bax and Bak, which is likely to be one of the apoptotic events in human platelets.