FcgammaRII mediates platelet aggregation caused by disintegrins and GPIIb/IIIa monoclonal antibody, AP2.
OBJECTIVE
Disintegrins, snake venom-derived Arg-Gly-Asp (RGD)-containing polypeptides, and GPIIb/IIIa antagonist (AP2) block fibrinogen binding to GPIIb/IIIa of activated platelets, however, the combination of these two agents caused platelet aggregation. We hypothesize that disintegrin initially binds to specific epitope of GPIIb/IIIa, causing conformational change, and the recruitment of FcgammaRII, which can be bound by AP2, and finally triggering platelet aggregation.


METHODS
We prepared human platelet suspensions and measured platelet aggregation, Ca2+ mobilization, thromboxane B2 formation, and signal transduction.


RESULTS
Disintegrin (e.g., accutin) and AP2 (a monoclonal antibody [mAb]-raised against GPIIb/IIIa) individually inhibited human platelet aggregation caused by collagen. However, as both accutin and AP2 were sequentially added into platelet suspension, platelet aggregation occurred. Accutin/AP2 caused shape change, cytosolic Ca2+ mobilization, P-selectin expression, and thromboxane A2 formation. Tirofiban, FcgammaRII mAb, or indomethacin completely inhibited platelet aggregation caused by accutin/AP2. Accutin/AP2 also caused tyrosine phosphorylation of signal molecules. Disintegrins enhanced AP2 binding to platelets, and AP2 also promoted disintegrin binding to platelets. FcgammaRII mAb inhibited the enhanced fluorescein isothiocyanate-disintegrin binding to platelet caused by AP2. Immunoprecipitation of the lysates of disintegrin/AP2-treated platelets using FcgammaRII Ab showed complex formation of GPIIb/IIIa and FcgammaRII.


CONCLUSIONS
FcgammaRII mediates platelet aggregation caused by disintegrin and AP2, triggering a phospholipase C, phospholipase A2, Src-, Syk kinases, and Ca2+-dependent activation process. AP2 triggers platelet aggregation via binding to accessible FcgammaRII and the conformation-altered GPIIb/IIIa caused by disintegrin.
Huang
Tur-Fu
TF
Department of Pharmacology, College of Medicine, National Taiwan University, Taipei, Taiwan. turfu@ntu.edu.tw
Chang
Chien-Hsin
CH
Ho
Pei-Ling
PL
Chung
Ching-Hu
CH
D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D001792:Blood Platelets / Q000166:cytology / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects; D019483:Disintegrins / Q000737:chemistry / Q000494:pharmacology*; D000939:Epitopes / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D054467:Phospholipases A2 / Q000378:metabolism; D010974:Platelet Aggregation / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors / Q000737:chemistry / Q000494:pharmacology*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011487:Protein Conformation / Q000187:drug effects; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D017452:Receptors, IgG / Q000378:metabolism*; D012910:Snake Venoms / Q000737:chemistry; D000072377:Syk Kinase; D010738:Type C Phospholipases / Q000378:metabolism; D019061:src-Family Kinases / Q000378:metabolism
D000911:Antibodies, Monoclonal; D019483:Disintegrins; D000939:Epitopes; D047908:Intracellular Signaling Peptides and Proteins; D010975:Platelet Aggregation Inhibitors; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D017452:Receptors, IgG; D012910:Snake Venoms; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; D019061:src-Family Kinases; D054467:Phospholipases A2; D010738:Type C Phospholipases; D002118:Calcium