Human platelet signaling defect characterized by impaired production of inositol-1,4,5-triphosphate and phosphatidic acid and diminished Pleckstrin phosphorylation: evidence for defective phospholipase C activation.
Signal transduction on platelet activation involves phosphoinositide-specific phospholipase C (PLC)-mediated hydrolysis of phosphatidylinositides and formation of inositol-1,4,5-triphosphate [I(1,4,5)P3], which mediates Ca2+ mobilization, and diacylglycerol (DG), which activates protein kinase C (PKC) to phosphorylate a 47-kD protein (Pleckstrin). We studied these events in two related patients previously reported (Blood 74:664, 1989) to have abnormal aggregation and 14C-serotonin secretion, and impaired intracellular Ca2+ mobilization in response to several agonists. Thrombin-induced I(1,4,5)P3 and phosphatidic acid formation were diminished. Pleckstrin phosphorylation was impaired on activation with thrombin, platelet-activating factor, and ionophore A23187, but was normal with PKC activator 1,2-dioctonyl-sn-glycerol (DiC8). Ca2+ mobilization induced by guanosine triphosphate (GTP) analog guanosine 5'-0-(3 thiotriphosphate) (GTP gamma S) was diminished. Pretreatment with either A23187 or DiC8 did not correct the impaired adenine diphosphate-induced secretion; however, upon stimulation with A23187 plus DiC8, pleckstrin phosphorylation and secretion were normal, indicating that both PKC activation and Ca2+ mobilization are essential for normal secretion. We conclude that these patients have a unique inherited platelet defect in formation of two key intracellular mediators [I(1,4,5)P3 and DG] and in the responses mediated by them due to a defect in postreceptor mechanisms of PLC activation.
Yang
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Sol Sherry Thrombosis Research Center, Temple University School of Medicine, Philadelphia, PA 19140, USA.
Sun
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Ghosh
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Rao
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AK
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000328:Adult; D001792:Blood Platelets / Q000378:metabolism; D001798:Blood Proteins / Q000378:metabolism*; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D004075:Diglycerides / Q000096:biosynthesis; D004789:Enzyme Activation; D005260:Female; D006474:Hemorrhagic Disorders / Q000097:blood / Q000201:enzymology*; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000096:biosynthesis*; D008297:Male; D008875:Middle Aged; D018994:Myosin Light Chains / Q000378:metabolism; D010712:Phosphatidic Acids / Q000172:deficiency*; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D010750:Phosphoproteins; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism*; D010766:Phosphorylation; D010972:Platelet Activating Factor / Q000494:pharmacology; D010974:Platelet Aggregation / Q000187:drug effects; D011499:Protein Processing, Post-Translational; D012701:Serotonin / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D013917:Thrombin / Q000494:pharmacology
D001798:Blood Proteins; D004075:Diglycerides; D018994:Myosin Light Chains; D010712:Phosphatidic Acids; D010750:Phosphoproteins; D010972:Platelet Activating Factor; C039077:platelet protein P47; D012701:Serotonin; D000001:Calcimycin; D000244:Adenosine Diphosphate; D015544:Inositol 1,4,5-Trisphosphate; D010727:Phosphoric Diester Hydrolases; D013917:Thrombin; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D002118:Calcium