Ginsberg M H, Wencel J D, White J G, Plow E F
J Cell Biol. 1983 Aug;97(2):571-3. doi: 10.1083/jcb.97.2.571.
Most of the proposed functions for fibronectin involve its interaction with cells, yet the molecular nature of cellular fibronectin binding site(s) has remained obscure. Thrombin induces saturable platelet binding sites for plasma fibronectin and concurrently stimulates surface expression of a number of platelet alpha-granule constituents including thrombospondin and fibrin which are known to interact with fibronectin. To test the hypothesis that these (or other alpha-granule proteins) mediate plasma fibronectin binding, we used platelets of patients with the Gray Platelet Syndrome. These cells were deficient in thrombospondin, beta-thromboglobulin, platelet factor 4, fibronectin, and fibrinogen as measured in radioimmunoassay. They also had reduced von Willebrand factor content as judged by immunofluorescence. At plasma fibronectin inputs from 0.03 to 3 times the apparent kilodalton, these Gray platelets bound virtually identical quantities of fibronectin as normal cells. Thus, platelets containing 1,500 molecules of thrombospondin per platelet could bind more than 100,000 molecules of plasma fibronectin per cell following thrombin stimulation. These data preclude any simple model in which newly surface expressed thrombospondin (or other alpha-granule protein) functions as the major thrombin-stimulated plasma fibronectin receptor in this cell type.
纤连蛋白的大多数假定功能都涉及其与细胞的相互作用，然而细胞纤连蛋白结合位点的分子性质仍不清楚。凝血酶可诱导血浆纤连蛋白的血小板结合位点达到饱和，并同时刺激多种血小板α-颗粒成分的表面表达，包括已知与纤连蛋白相互作用的血小板反应蛋白和纤维蛋白。为了验证这些物质（或其他α-颗粒蛋白）介导血浆纤连蛋白结合的假说，我们使用了灰色血小板综合征患者的血小板。通过放射免疫测定法测量，这些细胞缺乏血小板反应蛋白、β-血小板球蛋白、血小板因子4、纤连蛋白和纤维蛋白原。通过免疫荧光判断，它们的血管性血友病因子含量也降低。在血浆纤连蛋白输入量为表观千道尔顿的0.03至3倍时，这些灰色血小板与正常细胞结合的纤连蛋白量几乎相同。因此，在凝血酶刺激后，每个血小板含有1500个血小板反应蛋白分子的血小板，每个细胞可结合超过100,000个血浆纤连蛋白分子。这些数据排除了任何简单的模型，即在这种细胞类型中，新表面表达的血小板反应蛋白（或其他α-颗粒蛋白）作为主要的凝血酶刺激血浆纤连蛋白受体发挥作用。
