Regulation of platelet function-Pathogentical analysis of platelet signal transduction disorders

我们分析了先天性血小板疾病患者血小板信号转导通路的缺陷部位。6例对血栓素A_2（TXA_2）反应性受损，3例对钙离子载体A23187（Ca ~（2+））反应性受损，1例对胶原反应性受损。（1）血小板对血栓素A_2的反应性受损我们发现，<60>在所有血小板疾病患者中，血栓素A_2受体（TXR）第一胞浆环的Arg → Leu突变。我们还阐明了该突变导致TXR和磷脂酶C激活之间的偶联受损，表明<60>TXR的第一个胞质环中的Arg或周围区域在TXR和磷脂酶C之间的偶联中具有重要作用。（2）对Ca ~（2+）载体A23187的反应性减弱凝血酶、STA_2或A23187诱导的第二信使形成和Ca ~（2+）动员均正常。此外，47 kDa蛋白（pleckstrin）和20 kDa蛋白（myosin licht chain，MLC）对这些激动剂的磷酸化反应是正常的。这些发现表明，患者血小板中的缺陷部位位于蛋白激酶C激活、Ca^2+动员和MLC磷酸化的远端或独立的过程中。（3）对胶原的反应性减弱凝血酶、STA_2或A23187诱导的1，4，5-三磷酸肌醇形成和Ca^2+动员均正常。然而，这些对胶原蛋白的反应在患者的血小板中是选择性缺陷的。此外，47 kDa蛋白（pleckstrin）和20 kDa蛋白（myosin licht chain，MLC）对这些激动剂的磷酸化反应是正常的。这些结果表明，患者血小板的缺陷部位位于胶原受体（GPVI或GPIa/IIa）与磷脂酶C激活之间的过程中。

We analyzed the defective site of platelet signal transduction pathway in patients with congenital platelet disorders. Six cases with impaired response to thromboxane A_2, 3 cases with impaired response to Ca ionophore A23187, and one case with impaired response to collagen were investigated.(1)Impaired platelet response to thromboxane A_2We found that Arg^<60> to Leu mutation in the first cytoplasmic loop of the thromboxane A_2 receptor (TXR) were observed in all cases with this platelet disorders. We also clarified that this mutation causes impaired coupling between TXR and phospholipase C activation, suggesting that Arg^<60> or the surrounding region in the first cytoplasmic loop of the TXR has an important role in coupling between TXR and phospholipase C.(2)Impaired response to Ca ionophore A23187The analysis of second messenger formation showed that inositol 1,4,5-triphosphate formation or Ca^<2+> mobilization induced by thrombin, STA_2 or A23187 was normal. Furthermore, the phosphorylation of 47 kDa protein (pleckstrin) and 20 kDa protein (myosin licht chain, MLC) in response to those agonists was normal. These findings suggest that the defective site in the patients' platelets lies in the process distal to or independent of protein kinase C activation, Ca^<2+> mobilization and MLC phosphorylation.(3)Impaired response to collagenThe analysis of second messenger formation showed that inositol 1,4,5-triphosphate formation or Ca^<2+> mobilization induced by thrombin, STA_2 or A23187 was normal. However, these responses to collagen were selectively defective in the patient's platelets. Furthermore, the phosphorylation of 47 kDa protein (pleckstrin) and 20 kDa protein (myosin licht chain, MLC) in response to those agonists was normal. These findings suggest that the defective site in the patients' platelets lies in the process between collagen receptor (GPVI or GPIa/IIa) and phospolipase C activation.