Induction of the fibrinogen receptor on human platelets by intracellular mediators.
Induction of the fibrinogen receptor on human platelets by intracellular mediators.
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DOI：
10.1016/s0021-9258(19)75739-1
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发表时间：
1987-01
期刊：
影响因子：
--
通讯作者：
S. Shattil;L. Brass
中科院分区：
文献类型：
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作者：
S. Shattil;L. Brass
我们用皂苷使血小板通透性来研究血小板活化导致纤维蛋白原表面受体暴露的机制。用125I-纤维蛋白原和125I-PAC1检测受体暴露，125I-PAC1是针对纤维蛋白原受体激活形式的单抗。被研究的潜在介质包括鸟苷-5‘-基亚胺二磷酸(GPP(NH)p)和鸟苷5’O-(硫代三磷酸)(GTP-Gamma S)，它们引起血小板G蛋白依赖性磷脂酶C的激活；1，4，5-三磷酸肌醇(IP3)，引起血小板致密管系统的钙释放；以及二酰甘油和佛波酯，激活蛋白激酶C。这些分子中的每一个都引起纤维蛋白原和PAC1结合。IP3通过提高通透性血小板内游离钙离子浓度来模拟IP3的作用。但消炎痛或阿司匹林可阻断IP3和Ca~(2+)诱导的PAC1结合，对GPP(NH)p、佛波酯或甘油二酯引起的PAC1结合无影响。这表明花生四烯酸对IP3和Ca~(2+)的反应是由于花生四烯酸代谢产物的形成所致。一种这样的代谢物TXA2被认为通过刺激G蛋白依赖的磷脂酰肌醇水解来激活血小板。事实上，我们发现G蛋白抑制剂鸟苷-5‘-基硫代磷酸酯(GDPbeta S)抑制了由血栓素A2类似物(U46619)、IP3和钙离子引起的PAC1结合，但对二酰甘油或佛波酯诱导的PAC1结合没有影响。凝血酶诱导的PAC1结合和肌醇磷脂水解酶活性也被S和百日咳毒素所抑制。提高凝血酶浓度可克服国内生产总值βS对PAC1结合的抑制，但不能克服肌醇磷脂对PAC1结合的抑制。这些观察表明，纤维蛋白原受体的暴露至少通过两种途径发生。其中一种对凝血酶和U46619等激动剂的反应是由G蛋白依赖的磷脂酰肌醇水解启动的，涉及IP3和二酰甘油的形成。IP3似乎通过刺激依赖于钙离子的花生四烯酸代谢来发挥作用，而花生四烯酸代谢反过来又触发了磷脂酰肌醇的进一步水解。甘油二酯通过刺激蛋白激酶C起作用。第二种途径是由高浓度的凝血酶激活，不依赖于肌醇磷脂的水解。
We have used platelets permeabilized with saponin to examine the mechanism by which platelet activation causes the exposure of surface receptors for fibrinogen. Receptor exposure was detected using 125I-fibrinogen and 125I-PAC1, a monoclonal antibody specific for the activated form of the fibrinogen receptor. The potential mediators that were studied included guanyl-5'-yl imidodiphosphate (Gpp(NH)p) and guanosine 5'O-(thiotriphosphate) (GTP gamma S), which cause G protein-dependent phospholipase C activation in platelets; inositol 1,4,5-triphosphate (IP3), which causes Ca2+ release from the platelet dense tubular system; and diacylglycerol and phorbol ester, which activate protein kinase C. Each of these molecules caused fibrinogen and PAC1 binding. The effect of IP3 was mimicked by raising the cytosolic free Ca2+ concentration in the permeabilized platelets. However, IP3 and Ca2+-induced PAC1 binding were abolished by indomethacin or aspirin, which had no effect on PAC1 binding caused by Gpp(NH)p, phorbol ester, or diacylglycerol. This suggests that the response to IP3 and Ca2+ is due to the formation of metabolites of arachidonic acid. One such metabolite, TxA2, is believed to activate platelets by stimulating G protein-dependent phosphoinositide hydrolysis. Indeed, we found that the G protein inhibitor guanyl-5'-yl thiophosphate (GDP beta S) inhibited PAC1 binding caused by a thromboxane A2 analog (U46619), IP3, and Ca2+, but had no effect on diacylglycerol or phorbol ester-induced PAC1 binding. Thrombin-induced PAC1 binding and phosphoinositide hydrolysis were also inhibited by GDP beta S and by pertussis toxin. Increasing the thrombin concentration overcame the inhibition of PAC1 binding caused by GDP beta S but did not overcome the inhibition of phosphoinositide hydrolysis. These observations demonstrate that fibrinogen receptor exposure occurs by at least two routes. One of these, in response to agonists such as thrombin and U46619, is initiated by G protein-dependent phosphoinositide hydrolysis and involves the formation of IP3 and diacylglycerol. IP3 appears to act by stimulating Ca2+-dependent arachidonic acid metabolism which, in turn, triggers further phosphoinositide hydrolysis. Diacylglycerol acts by stimulating protein kinase C. A second route is activated by high concentrations of thrombin and is independent of phosphoinositide hydrolysis.