Abnormal inside-out signal transduction-dependent activation of glycoprotein IIb-IIIa in a patient with impaired pleckstrin phosphorylation.
Platelet-agonist interaction results in activation of glycoprotein (GP) IIb-IIIa complex and fibrinogen binding, a prerequisite for platelet aggregation. Fibrinogen binding exposes new antibody binding sites on GPIIb-IIIa (ligand-induced binding sites: LIBS). Signal transduction events, including pleckstrin phosphorylation by protein kinase C (PKC), are considered to regulate GPIIb-IIIa activation. We studied a 16-year-old white male with lifelong mucocutaneous bleeding manifestations and abnormal platelet aggregation and secretion in response to multiple agonists. Pleckstrin phosphorylation was diminished in response to platelet-activating factor (PAF; 4 and 400 nmol/L) and thrombin (0.05 U/mL). Binding of monoclonal antibodies (MoAbs) 10E5 and A2A9, which bind to both resting and activated GPIIb-IIIa, was normal. Binding of MoAb PAC1, which binds to only activated GPIIb-IIIa, was diminished upon activation with PAF, adenosine diphosphate (ADP), thrombin receptor agonist peptide (SFLLRN), A23187, and 1,2-dioctonylglycerol (DiC8). Signal transduction-dependent LIBS expression (studied using MoAb 62) induced by ADP, SFLLRN, and DiC8 and signal transduction-independent LIBS expression induced by RGDS peptide or disintegrin albolabrin were normal or minimally decreased, indicating the presence of intact ligand binding sites. We conclude that the patient's platelets have a defect in inside-out signal transduction-dependent GPIIb-IIIa activation due to an upstream defect in the signal transduction mechanisms rather than in the GPIIb-IIIa complex itself. Our findings extend the spectrum of congenital mechanisms leading to impaired aggregation from defects in GPIIb-IIIa per se to aberrations in signaling mechanisms.
Gabbeta
J
J
Sol Sherry Thrombosis Research Center, Philadelphia, PA, USA.
Yang
X
X
Sun
L
L
McLane
M A
MA
Niewiarowski
S
S
Rao
A K
AK
D000227:Adenine Nucleotides / Q000378:metabolism; D000293:Adolescent; D000911:Antibodies, Monoclonal; D001798:Blood Proteins / Q000378:metabolism*; D005340:Fibrinogen / Q000378:metabolism; D005434:Flow Cytometry; D006801:Humans; D008297:Male; D010750:Phosphoproteins; D010766:Phosphorylation; D010972:Platelet Activating Factor / Q000494:pharmacology; D010974:Platelet Aggregation; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D012701:Serotonin / Q000378:metabolism; D015398:Signal Transduction; D013917:Thrombin / Q000494:pharmacology; D013928:Thromboxane A2 / Q000378:metabolism
D000227:Adenine Nucleotides; D000911:Antibodies, Monoclonal; D001798:Blood Proteins; D010750:Phosphoproteins; D010972:Platelet Activating Factor; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; C039077:platelet protein P47; D012701:Serotonin; D013928:Thromboxane A2; D005340:Fibrinogen; D011493:Protein Kinase C; D013917:Thrombin