Kovacsovics T J, Bachelot C, Toker A, Vlahos C J, Duckworth B, Cantley L C, Hartwig J H
Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts, USA.
J Biol Chem. 1995 May 12;270(19):11358-66. doi: 10.1074/jbc.270.19.11358.
Platelet stimulation by thrombin leads to the activation of phosphoinositide 3-kinase (PI 3K) and to the production of the D3 phosphoinositides, phosphatidylinositol 3,4-bisphosphate (PdtIns-3,4P2) and 3,4,5-trisphosphate (PdtIns-3,4,5-P3). Because changes in the levels of these phosphoinositides correlate with the kinetics of actin assembly, they have been proposed to mediate actin assembly, causing cell shape changes. Wortmannin and LY294002, two unrelated inhibitors of PI 3-K, were used to investigate the role of PI 3-K in platelet actin assembly and aggregation. Both PI 3-K inhibitors abrogated the production of PdtIns-3,4-P2 and PdtIns-3,4,5-P3 in thrombin receptor-activating peptide (TRAP)-stimulated cells. However, neither wortmannin nor LY294002 altered the kinetics of actin assembly or the exposure of nucleation sites in TRAP-stimulated cells. In contrast, PI 3-K inhibitors showed a specific inhibitory pattern of cell aggregation, characterized by a primary phase of aggregation followed by progressive disaggregation. Flow cytometry analysis with the PAC1 monoclonal antibody or with FITC-labeled fibrinogen indicated that wortmannin inhibited the maintenance of the platelet integrin GPIIb-IIIa in its active state. Wortmannin also inhibited, in a dose-dependent manner, platelet aggregation induced by the binding of the monoclonal antibodies P256 and LIBS-6 to GPIIb-IIIa. LIBS Fab-induced aggregation also led to the production of PdtIns-3,4-P2. Platelet secretion, as evidenced by the release of preloaded 14C-5-hydroxy-tryptamine secretion or P-selectin up-regulation, was not affected by PI 3-K inhibition. These results demonstrate that the generation of D3 phosphoinositides is not required for actin assembly in TRAP-activated platelets. However, PI 3-K stimulation is necessary for prolonged GPIIb-IIIa activation and irreversible platelet aggregation. PI 3-K stimulation downstream of GPIIb-IIIa engagement may provide positive feedback required to sustain active GPIIb-IIIa.
凝血酶刺激血小板会导致磷酸肌醇3激酶（PI 3K）激活，并产生D3磷酸肌醇、磷脂酰肌醇3,4 - 二磷酸（PdtIns - 3,4P2）和3,4,5 - 三磷酸（PdtIns - 3,4,5 - P3）。由于这些磷酸肌醇水平的变化与肌动蛋白组装的动力学相关，因此有人提出它们介导肌动蛋白组装，引起细胞形状改变。渥曼青霉素和LY294002是两种不相关的PI 3 - K抑制剂，用于研究PI 3 - K在血小板肌动蛋白组装和聚集过程中的作用。两种PI 3 - K抑制剂均可消除凝血酶受体激活肽（TRAP）刺激的细胞中PdtIns - 3,4 - P2和PdtIns - 3,4,5 - P3的产生。然而，渥曼青霉素和LY294002均未改变TRAP刺激的细胞中肌动蛋白组装的动力学或成核位点的暴露。相反，PI 3 - K抑制剂表现出一种特定的细胞聚集抑制模式，其特征是先有一个聚集的初始阶段，随后是逐渐解聚。用PAC1单克隆抗体或异硫氰酸荧光素（FITC）标记的纤维蛋白原进行流式细胞术分析表明，渥曼青霉素可抑制血小板整合素GPIIb - IIIa维持其活性状态。渥曼青霉素还以剂量依赖的方式抑制单克隆抗体P256和LIBS - 6与GPIIb - IIIa结合诱导的血小板聚集。LIBS Fab诱导的聚集也会导致PdtIns - 3,4 - P2的产生。如预加载的14C - 5 - 羟色胺分泌的释放或P - 选择素上调所证明的血小板分泌不受PI 3 - K抑制的影响。这些结果表明，在TRAP激活的血小板中，肌动蛋白组装不需要D3磷酸肌醇的生成。然而，PI 3 - K刺激对于延长GPIIb - IIIa激活和不可逆的血小板聚集是必要的。GPIIb - IIIa结合下游的PI 3 - K刺激可能提供维持活性GPIIb - IIIa所需的正反馈。
