Bajzar L, Nesheim M, Morser J, Tracy P B
Department of Biochemistry, University of Vermont College of Medicine, Burlington, Vermont 05405, USA.
J Biol Chem. 1998 Jan 30;273(5):2792-8. doi: 10.1074/jbc.273.5.2792.
Thrombin-activable fibrinolysis inhibitor (TAFI) is a recently described plasma zymogen that can be activated by thrombin to an enzyme with carboxypeptidase B-like activity. The enzyme, TAFIa, potently attentuates fibrinolysis. TAFI activation, like protein C activation, is augmented about 1250-fold by thrombomodulin (TM). In this work, the effects of both soluble and cellular forms of TM on TAFI activation-dependent suppression of fibrinolysis were investigated. Soluble TM included in clots formed from purified components, barium citrate-adsorbed plasma, or normal human plasma maximally increased the tissue plasminogen activator-induced lysis time 2-3-fold, with saturation occurring at 5, 10, and 1 nM TM in the three respective systems. Soluble TM did not effect lysis in the system of purified components lacking TAFI or in plasmas immunodepleted of TAFI. In addition, the antifibrinolytic effect of TM was negated by monoclonal antibodies against either TAFI or TM. The inhibition of fibrinolysis by cellular TM was assessed by forming clots in dialyzed, barium citrate-adsorbed, or normal plasma over cultured human umbilical vein endothelial cells (HUVECs). Tissue plasminogen activator-induced lysis time was increased 2-fold, with both plasmas, in the presence of HUVECs. The antifibrinolytic effect of HUVECs was abolished 66% by specific anti-TAFI or anti-TM monoclonal antibodies. A newly developed functional assay demonstrated that HUVECs potentiate the thrombin-catalyzed, TM-dependent formation of activated TAFI. Thus, endothelial cell TM, in vitro at least, appears to participate in the regulation of not only coagulation but also fibrinolysis.
凝血酶激活的纤维蛋白溶解抑制剂（TAFI）是一种最近发现的血浆酶原，可被凝血酶激活为具有羧肽酶B样活性的酶。该酶TAFIa能有效减弱纤维蛋白溶解。与蛋白C激活一样，凝血酶调节蛋白（TM）可使TAFI激活增强约1250倍。在本研究中，研究了可溶性和细胞形式的TM对TAFI激活依赖性纤维蛋白溶解抑制作用的影响。可溶性TM包含在由纯化成分、柠檬酸钡吸附血浆或正常人血浆形成的凝块中，可使组织型纤溶酶原激活物诱导的溶解时间最大增加2至3倍，在三个相应系统中，分别在5、10和1 nM TM时达到饱和。可溶性TM在缺乏TAFI的纯化成分系统或TAFI免疫耗尽的血浆中不影响溶解。此外，针对TAFI或TM的单克隆抗体可消除TM的抗纤维蛋白溶解作用。通过在培养的人脐静脉内皮细胞（HUVEC）上的透析、柠檬酸钡吸附或正常血浆中形成凝块来评估细胞TM对纤维蛋白溶解的抑制作用。在HUVEC存在的情况下，两种血浆的组织型纤溶酶原激活物诱导的溶解时间均增加了2倍。特异性抗TAFI或抗TM单克隆抗体可消除HUVEC 66%的抗纤维蛋白溶解作用。一项新开发的功能测定表明，HUVEC可增强凝血酶催化的、TM依赖性的活化TAFI的形成。因此，至少在体外，内皮细胞TM似乎不仅参与凝血调节，还参与纤维蛋白溶解调节。
