Suzuki-Inoue Katsue, Inoue Osamu, Frampton Jon, Watson Steve P
Department of Pharmacology, University of Oxford, United Kingdom.
Blood. 2003 Aug 15;102(4):1367-73. doi: 10.1182/blood-2003-01-0029. Epub 2003 May 1.
Collagen stimulates platelet activation through a tyrosine kinase-based pathway downstream of the glycoprotein VI (GPVI)-Fc receptor (FcR) gamma-chain complex. Genetic ablation of FcR gamma-chain results in a complete inhibition of aggregation to collagen. In contrast, a steady increase in light transmission is induced by collagen in phospholipase Cgamma2-deficient (PLCgamma2-/-) platelets in a Born aggregometer, indicating a weak level of activation. This increase is inhibited partially in the presence of an alpha2beta1-blocking antibody or an alphaIIbbeta3 antagonist and completely by a combination of the 2 inhibitors. It is also abolished by the Src kinase inhibitor PP1 and reduced in the presence of the phosphatidylinositol (PI) 3-kinase inhibitor wortmannin. The GPVI-specific agonists convulxin and collagen-related peptide (CRP) also stimulate weak aggregation in PLCgamma2-/- platelets, which is inhibited by wortmannin and PP1. Collagen and CRP stimulate tyrosine phosphorylation of PLCgamma1 at its regulatory site, Tyr 783, in murine but not in human platelets through a Src kinase-dependent pathway. Adhesion of PLCgamma2-/- platelets to a collagen monolayer is severely reduced at a shear rate of 800 s-1, relative to controls, whereas it is abolished in FcR gamma-chain-/- platelets. These results provide strong evidence that engagement of GPVI stimulates limited integrin activation in PLCgamma2-/- platelets via PLCgamma1 and PI3-kinase.
胶原蛋白通过糖蛋白VI（GPVI）-Fc受体（FcR）γ链复合物下游基于酪氨酸激酶的途径刺激血小板活化。FcRγ链的基因缺失导致对胶原蛋白聚集的完全抑制。相比之下，在博恩血小板聚集仪中，胶原蛋白可诱导磷脂酶Cγ2缺陷型（PLCγ2-/-）血小板的透光率稳步增加，表明活化水平较弱。在存在α2β1阻断抗体或αIIbβ3拮抗剂的情况下，这种增加受到部分抑制，而两种抑制剂联合使用则可完全抑制。它也被Src激酶抑制剂PP1消除，在磷脂酰肌醇（PI）3激酶抑制剂渥曼青霉素存在的情况下降低。GPVI特异性激动剂convulxin和胶原蛋白相关肽（CRP）也刺激PLCγ2-/-血小板的弱聚集，这被渥曼青霉素和PP1抑制。胶原蛋白和CRP通过Src激酶依赖性途径刺激小鼠而非人血小板中PLCγ1在其调节位点Tyr 783处的酪氨酸磷酸化。相对于对照，在800 s-1的剪切速率下，PLCγ2-/-血小板与胶原蛋白单层的粘附严重减少，而在FcRγ链-/-血小板中则完全消除。这些结果提供了强有力的证据，即GPVI的结合通过PLCγ1和PI3激酶刺激PLCγ2-/-血小板中有限的整合素活化。
