• 14-3-3ζ;
  • apoptosis;
  • GPIbα;
  • platelets;
  • von Willebrand factor

Summary. Background: The interaction of glycoprotein (GP) Ibα with von Willebrand factor (VWF) initiates platelet adhesion, and simultaneously triggers intracellular signaling cascades leading to platelet aggregation and thrombus formation. Some of the signaling events are similar to those occurring during apoptosis, however, it is still unclear whether platelet apoptosis is induced by the GPIbα–VWF interaction. Objectives: To investigate whether the GPIbα–VWF interaction induces platelet apoptosis and the role of 14-3-3ζ in apoptotic signaling. Methods: Apoptotic events were assessed in platelets or Chinese hamster ovary (CHO) cells expressing wild-type (1b9) or mutant GPIb–IX interacting with VWF by flow cytometry or western blotting. Results: Ristocetin-induced GPIbα–VWF interaction elicited apoptotic events in platelets, including phosphatidylserine exposure, elevations of Bax and Bak, gelsolin cleavage, and depolarization of mitochondrial inner transmembrane potential. Apoptotic events were also elicited in platelets exposed to pathologic shear stresses in the presence of VWF; however, the shear-induced apoptosis was eliminated by the anti-GPIbα antibody AK2. Furthermore, apoptotic events occurred in 1b9 cells stimulated with VWF and ristocetin, but were significantly diminished in two CHO cell lines expressing mutant GPIb–IX with GPIbα truncated at residue 551 or a serine-to-alanine mutation at the 14-3-3ζ-binding site in GPIbα. Conclusions: This study demonstrates that the GPIbα–VWF interaction induces apoptotic events in platelets, and that the association of 14-3-3ζ with the cytoplasmic domain of GPIbα is essential for apoptotic signaling. This finding may suggest a novel mechanism for platelet clearance or some thrombocytopenic diseases.