echistatin and Myeloproliferative-Disorders

Defects in glycoprotein (GP)IIb-IIIa or in its activation may cause abnormal platelet aggregation and a bleeding diathesis. We report studies in a 67-year-old man with a myeloproliferative disease and markedly abnormal platelet responses. By flow cytometry, platelet binding of two complex-specific anti-GPIIb-IIIa monoclonal antibodies (mAbs), A2A9 and 10E5, was approximately 50% of normal. An enzyme-linked immunosorbent assay (ELISA) using immobilized kistrin showed 18% of normal membrane GPIIb-IIIa complex. By immunoblot analysis, GPIIb and GPIIIa levels in platelet lysates and membranes were near normal. Activation of GPIIb-IIIa, monitored with mAb PAC-1, was markedly decreased (< 20% of normal) in response to ADP, thrombin and platelet-activating factor (PAF); expression of ligand-induced binding sites (LIBS) was < or = 30% of normal. Signal transduction-independent LIBS expression, induced by echistatin, was approximately 60% of normal, suggesting that the integrin present had intact ligand-binding capability. Sequence analysis of GPIIb and GPIIIa cDNA, and platelet mRNA levels for both subunits, were normal. These findings document an acquired combined defect in membrane expression (secondary to a defect in post-translational processing of the complex) and inside-out signalling-dependent activation of the GPIIb-IIIa complex.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adenosine Diphosphate; Aged; Antibodies, Monoclonal; Binding Sites; Blood Platelets; Calcimycin; Diglycerides; DNA, Complementary; Enzyme Activators; Flow Cytometry; Humans; Immunoblotting; Intercellular Signaling Peptides and Proteins; Ionophores; Macrophage-1 Antigen; Male; Myeloproliferative Disorders; Neutrophils; Peptides; Platelet Activating Factor; Platelet Aggregation; Platelet Aggregation Inhibitors; Platelet Glycoprotein GPIIb-IIIa Complex; Polymerase Chain Reaction; Protein Binding; Protein Kinase C; Receptors, Thrombin; RNA, Messenger; Sequence Analysis, DNA; Serotonin; Signal Transduction