Factor XI Physiology and Molecular Biology

描述(申请人提供)：血浆蛋白酶因子XI是一个关键 凝血的内在途径的组成部分。最初被认为是 需要启动纤维蛋白凝块的形成，大量的临床和 生化证据现在表明，凝集素XI是巩固所必需的 以及在初始纤维蛋白形成后对血栓的保护。这是最多的 严重出血或纤溶活性高的部位很重要。 此外，最近对人类和小鼠的研究表明，因子XI可能 影响血栓性疾病的进程。凝血因子XI的分子结构 与其他凝固酶有很大的不同。与之形成鲜明对比的是 依赖维生素K的蛋白质(凝血酶原和凝血因子VII、IX和X)， 凝血因子XI缺乏钙结合的GLA结构域。而磷脂几乎没有 对其活动的影响。因此，因子XI的性质并不容易 从对依赖维生素K的蛋白酶的观察中推断出来的。这个 这项建议的目标是了解凝血因子XI 在正常止血过程中附着于血小板，以研究其对 激活因子IX，并确定调节血浆因子的因子 XI水平。我们表达了含有结构域的重组因子XII分子 结构上相关的蛋白前激肽释放酶的取代，以及 具有特定定点突变的因子XI分子。这些已经被使用过了 鉴定凝血因子IX、活化血小板和凝血因子XI的结合部位 肝素。我们建议使用这些和额外的重组蛋白来研究 凝血因子XI与高分子量激肽原相互作用的机制 和凝血酶原与血小板结合，并研究其作用机制 凝血因子IX在血小板表面被激活。我们已经克隆了启动子 因子XI和前激肽释放酶基因的区域，并确定共同的 可能影响功能的多态现象。我们将确定 组织特异性表达所需的启动子，识别转录 参与基因表达的因素，并研究基因多态性对基因表达的影响 血浆凝血因子XII水平。最后，我们已经证明了因子XI 缺乏部分拯救蛋白C缺陷小鼠的早期死亡 播散性血栓形成。我们将测试凝血因子XI缺乏对 载脂蛋白E缺乏和PAL-1过度表达的小鼠的表型。这 工作将大大增加我们对一个相对较差的 部分表征了凝聚机理，并将提供更坚固的 用于评估因子XI和 血栓栓塞症的内在途径。

DESCRIPTION (provided by applicant): The plasma protease factor XI is a key component of the intrinsic pathway of coagulation. Originally thought to be required for initiation of fibrin clot formation, an abundance of clinical and biochemical evidence now suggests that factor XI is required for consolidation and protection of the clot after initial fibrin formation. This is most important with severe bleeding or at sites with high fibrinolytic activity. Furthermore, recent studies in humans and mice suggest that factor XI may influence thrombotic disease processes. The molecular structure of factor XI differs substantially from those of other coagulation proteases. In contrast to the vitamin K-dependent proteins (prothrombin and factors VII, IX, and X), factor XI lacks a calcium binding Gla domain. and phospholipid has little influence on its activity. Properties of factor XI therefore, are not easily extrapolated from observations made on the vitamin K-dependent proteases. The goals of this proposal are to understand the mechanism by which factor XI attaches to platelets during normal hemostasis, to study its contribution to factor IX activation, and to determine the factors that regulate plasma factor XI levels. We have expressed recombinant factor XII molecules containing domain substitutions from the structurally related protein prekallikrein, as well as factor XI molecules with specific site-directed mutations. These have been used to identify binding sites on factor XI for factor IX, activated platelets, and heparin. We propose to use these, and additional recombinant proteins to study the mechanism by which factor XI interacts with high molecular weight kininogen and prothrombin while binding to platelets, and to study the mechanism by which factor IX is activated on the platelet surface. We have cloned the promoter regions for the factor XI and prekallikrein genes, and identified common polymorphisms that may influence function. We will identify areas of the promoters required for tissue specific expression, identify transcription factors involved in expression, and study the influences of polymorphisms on plasma factor XII levels. Finally, we have demonstrated that factor XI deficiency partially rescues protein C deficient mice from early death due to disseminated thrombosis. We will test the effect of factor XI deficiency on the phenotypes of mice with ApoE deficiency, and with PAl-1 over-expression. This work will substantially increase our understanding of a relatively poorly characterized part of the coagulation mechanism, and will provide a firmer knowledge base from which to assess the contribution of factor XI and the intrinsic pathway to thromboembolic disease.