The glycoprotein Ibalpha-von Willebrand factor interaction induces platelet apoptosis.
BACKGROUND
The interaction of glycoprotein (GP) Ibalpha 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 GPIbalpha-VWF interaction.


OBJECTIVE
To investigate whether the GPIbalpha-VWF interaction induces platelet apoptosis and the role of 14-3-3zeta 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 GPIbalpha-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-GPIbalpha 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 GPIbalpha truncated at residue 551 or a serine-to-alanine mutation at the 14-3-3zeta-binding site in GPIbalpha.


CONCLUSIONS
This study demonstrates that the GPIbalpha-VWF interaction induces apoptotic events in platelets, and that the association of 14-3-3zeta with the cytoplasmic domain of GPIbalpha is essential for apoptotic signaling. This finding may suggest a novel mechanism for platelet clearance or some thrombocytopenic diseases.
School of Biological Science and Medical Engineering, Beihang University, Beijing, China.
S
S
Li
Z
Z
Wang
Y
Y
Liao
W
W
Zhang
Q
Q
Shi
R
R
Yan
C
C
Ruan
K
K
Dai
D048948:14-3-3 Proteins / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001665:Binding Sites; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism / Q000473:pathology*; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D018260:Gelsolin / Q000378:metabolism; D006801:Humans; D053078:Membrane Potential, Mitochondrial; D009154:Mutation; D010718:Phosphatidylserines / Q000378:metabolism; D015539:Platelet Activation; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012310:Ristocetin / Q000494:pharmacology; D015398:Signal Transduction; D013314:Stress, Mechanical; D014162:Transfection; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000378:metabolism; D051028:bcl-2-Associated X Protein / Q000378:metabolism; D014841:von Willebrand Factor / Q000378:metabolism*
D048948:14-3-3 Proteins; C494772:BAK1 protein, human; C494826:BAX protein, human; D018260:Gelsolin; D010718:Phosphatidylserines; D019038:Platelet Glycoprotein GPIb-IX Complex; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; C023592:glycocalicin; D014841:von Willebrand Factor; D012310:Ristocetin