A Novel regulatory Role of Protein S in Blood coagulation

描述(申请人提供)：S蛋白在凝血蛋白中的新作用S(PS)是一种重要的抗凝血剂，其缺乏是导致血栓形成的几个已知风险因素之一，并增加了血液凝块的风险，如深静脉血栓形成(DVT)和肺血栓(PE)。在PS缺乏的严重病例中，婴儿出生后不久就会患上一种威胁生命的凝血障碍，称为暴发性紫癜症。然而，尽管对这种重要的抗凝剂进行了30年的研究，但PS的确切功能仍不清楚。S蛋白最初被鉴定为活化蛋白C的辅因子，但PS仅使活化蛋白C的活性略有增加。在缺乏APC的情况下，血浆分析提示PS的其他重要的、不依赖于APC的作用。一些报道认为PS可抑制凝血酶原激活为凝血酶，但由于PS多聚体的伪影，这些报道的有效性受到了质疑。2006年的研究表明，PS在启动凝血过程中是组织因子途径抑制物(TFPI)的辅因子。我们最近的工作表明PS抑制因子IX(FixA)；重要的是，我们使用了一些条件，例如，高浓度的磷脂小泡，避免了PS多聚体的伪影。我们的目标是从机制上定义PS的生理相关功能以及PS抑制FixA的特异性。我们将使用多方面的方法来确定PS的调节作用。我们的建议涉及详细的体外、体外和体内研究，以确定S蛋白对FXA的抑制具有特异性和生理学重要性。该建议包括两个目的：1)确定FIX与PS之间的接触区域；2)建立S蛋白抑制FIX的生理意义和特异性。我们的提案的成功完成将极大地挑战PS独立于APC和TFPI运行的新的监管角色。我们对这一新的调节功能机制的了解将使未来针对FIX和PS之间的接触点的新疗法的开发成为可能。此外，PS活性的抑制剂将形成血友病辅助治疗的基础，通过抑制功能亢进的修复，PS可用于X连锁血栓的治疗。

DESCRIPTION (provided by applicant): A Novel Role of Protein S in Blood Coagulation Protein S (PS) is an important anticoagulant, deficiencies of which are one of several known risk factors for thrombophilia and increased risk of blood clots such as Deep Vein Thrombosis (DVT) and Pulmonary Embolism (PE). In severe cases of PS deficiency, soon after birth infants develop a life-threatening blood clotting disorder called purpura fulminans. However, despite 30 years of study of this important anticoagulant, the exact function of PS is still unknown. Protein S was initially characterized as a cofactor of activated protein C (APC), but PS confers only a modest increase in APC activity. Plasma assays in the absence of APC suggested other important, APC-independent roles of PS. Some reports suggest that PS inhibits prothrombin activation to thrombin, but the validity of those reports has been questioned because of artifacts due to PS multimerization. In 2006, it was shown that PS acts as a cofactor of tissue factor pathway inhibitor (TFPI) in the initiation of coagulation. Our recent work has shown that PS inhibits factor IX (FIXa); importantly, we used conditions, e.g., high concentrations of phospholipid vesicles that avoid artifacts from PS multimers. Our goal is to mechanistically define both the physiologically relevant function of PS and the specificity of PS inhibition of FIXa. We will use a multifaceted approach to identify the regulatory role of PS. Our proposal involves detailed in vitro, ex vivo and in vivo studies to establish that protein S inhibition of FXa is specific and physiologically important. This proposal consists of two aims: 1) Determine the contact regions between FIX and PS and 2) establish the physiological significance and specificity of protein S inhibition of FIX. Successful completion of our proposal will sharply defie a novel regulatory role of PS that operates independently of APC and TFPI. The knowledge we acquire of the mechanism of this novel regulatory function will enable future development of new therapeutics designed to target the contact point between FIX and PS. Also, inhibitors of PS activity will form the basis of an adjunct therapy for hemophilia, and, by inhibiting hyper- functional FIX, PS could be used in the treatment of X-linked thrombophilia.