Analysis of function and regulation mechanism of expression of thrombomodulin, a regulating factor of blood coagulation, on surface of endothelial cells

正常的内皮细胞在产生抗凝血因子的过程中抑制凝血，并抑制血栓的形成。表达于内皮细胞表面的血栓调节蛋白(Tm)与凝血酶形成复合体，抑制凝血酶的促凝活性，如纤维蛋白的形成、血小板的激活以及凝血因子V、VIII的激活。通过复合体的形成，进一步诱导活化蛋白C的活性，抑制凝血酶的产生，从而调节凝血酶的促凝活性和抗凝血活性，发挥抗凝血剂的作用。尽管TM的上述功能是从纯化的TM的体外实验中推测出来的，但TM在内皮细胞表面的作用和功能尚未确定。目前的研究表明：1.表达于内皮细胞表面的TM还与凝血酶和表面的复杂激活蛋白C形成复合体…TM激活细胞表面蛋白C的辅因子活性约为纯化的TM的10倍。我们证明了表达于内皮细胞表面的TM具有有效的抗凝作用。进一步发现，当内皮细胞暴露于肿瘤坏死因子(TNF)或白介素1(IL-1)时，TM的转录水平和蛋白质合成减少，激活细胞表面蛋白C的辅因子活性也降低；4.用维甲酸(维生素A酸)处理内皮细胞后，TM的转录水平、蛋白质合成和辅因子活性增加，5.即使细胞受到肿瘤坏死因子的刺激，TM的转录水平、蛋白质合成和辅因子活性也恢复正常。我们提出，肿瘤或炎症中血栓形成的原因之一可能是细胞因子导致TM表达下降，并提出了维甲酸治疗上述疾病血栓形成的可能性。较少

Normal endothelial cells repress blood coagulation during generation of anticoagulant factors and are inhibiting formation of thrombosis. Thrombomodulin (TM) expressed on the surface of endothelial cells forms complex with thrombin and inhibits procoagulant activity of thrombin such as fibrin formation, platelet activation and activation of coagulation factors V and VIII. By the formation of complex, activity to activate protein C is further induced and production of thrombin is inhibited by activated protein C. Thus, TM modurates procoagulant activity of thrombin to anticoagulant activity and functions as anticoagulant. Although the above mentioned functions of TM were suggested from in vitro expeiments using purified TM, role and function of TM on the surface of endothelial cells had not been identified.In the present studies, it was indicated that 1. TM expressed on the surface of endothelial cells also formed complex with thrombin and the complex activated protein C on the surface, … More 2. the cofactor activity of TM to activate protein C on the cell surface was about 10 times higher than that of purified TM. We demonstrated that TM expressed on surface of endothelial cells effectively functions as anticoagulant. It was further revealed that 3. when endothelial cells were exposed to tumor necrosis factor (TNF) or interleukin-1 (IL-1), transcriptional level and protein synthesis of TM was reduced and the cofactor activity to activate protein C on the cell surface was also decreased, 4. treatment of endothelial cells with retinoic acid (vitamin A acid) increased transcription level, protein synthesis and the cofactor activity of TM, and 5. retinoic acid returned to normal level of TM on the cells surface even when TM level was reduced by exposure of the cells to TNF. We proposed that one of causes of thrombosis generation in tumor or inflammation could be due to decrease in TM expression by exposure to the cytokines, and suggested possibility of therapy by retinoic acid on thrombosis in the case of above deseases. Less