Yin Hong, Liu Junling, Li Zhenyu, Berndt Michael C, Lowell Clifford A, Du Xiaoping
Department of Pharmacology, University of Illinois at Chicago, Chicago, IL 60612, USA.
Blood. 2008 Aug 15;112(4):1139-46. doi: 10.1182/blood-2008-02-140970. Epub 2008 Jun 11.
The platelet receptor for von Willebrand factor (VWF), glycoprotein (GP) Ib-IX, mediates initial platelet adhesion and transmits signals leading to platelet activation. Src family tyrosine kinases (SFKs) play an important role in VWF-induced GPIb-IX signaling. However, the SFK-dependent downstream signaling pathway is unclear but is thought to involve thromboxane A2 (TXA2) synthesis. Here we show that, although platelets deficient in SFK members, Lyn or Fyn, were defective in the TXA2-dependent second wave of platelet aggregation induced by botrocetin/VWF, only Lyn-knockout platelets were also defective in stable platelet adhesion to VWF under shear stress that is independent of the TXA2 pathway. Lyn-knockout platelets also spread poorly on VWF but spread normally on fibrinogen, indicating an important role for Lyn in VWF-mediated GPIb signaling but not in integrin outside-in signaling. Importantly, Lyn knockout abrogated VWF-induced cGMP elevation. Addition of low concentrations of 8-bromo-cGMP, however, corrected the defective stable adhesion of Lyn-knockout platelets or PP2-treated platelets on VWF. These results demonstrate an important role for Lyn in VWF/GPIb-IX-induced integrin activation mediated via the cGMP signaling pathway independently of TXA2 synthesis and also indicate that Lyn is critically important in GPIb-IX-mediated activation of the cGMP pathway.
血管性血友病因子（VWF）的血小板受体糖蛋白（GP）Ib-IX介导血小板的初始黏附并传递导致血小板活化的信号。Src家族酪氨酸激酶（SFKs）在VWF诱导的GPIb-IX信号传导中起重要作用。然而，SFK依赖的下游信号通路尚不清楚，但被认为涉及血栓素A2（TXA2）的合成。在此我们表明，尽管缺乏SFK成员Lyn或Fyn的血小板在由蛇毒凝血酶/VWF诱导的TXA2依赖性血小板聚集的第二波中存在缺陷，但只有Lyn基因敲除的血小板在与TXA2途径无关的剪切应力下对VWF的稳定血小板黏附也存在缺陷。Lyn基因敲除的血小板在VWF上也铺展不良，但在纤维蛋白原上正常铺展，这表明Lyn在VWF介导的GPIb信号传导中起重要作用，但在整合素外向内信号传导中不起作用。重要的是，Lyn基因敲除消除了VWF诱导的cGMP升高。然而，添加低浓度的8-溴-cGMP可纠正Lyn基因敲除血小板或PP2处理的血小板在VWF上的缺陷性稳定黏附。这些结果证明Lyn在通过cGMP信号通路介导的VWF/GPIb-IX诱导的整合素活化中起重要作用，且独立于TXA2合成，同时也表明Lyn在GPIb-IX介导的cGMP途径活化中至关重要。
