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因子的过程中抑制血液凝固，并抑制血栓形成。血栓调节蛋白（Thrombomodulin，TM）表达于内皮细胞表面，与凝血酶形成复合物，抑制凝血酶的促凝血活性，如纤维蛋白形成、血小板活化和凝血因子V和VIII的活化。通过形成复合物，进一步诱导活化蛋白C的活性，并通过活化蛋白C抑制凝血酶的产生。因此，TM将凝血酶的促凝血活性调节为抗凝活性并起到抗凝剂的作用。虽然TM的上述功能已从纯化TM的体外实验中得到证实，但TM在内皮细胞表面的作用和功能尚未得到证实。内皮细胞表面表达的TM还与凝血酶形成复合物，复合物激活了内皮细胞表面的蛋白C， ...更多信息 2. TM激活细胞表面蛋白C的辅因子活性比纯化的TM高约10倍。我们证明了TM在内皮细胞表面的表达有效地发挥抗凝作用。据进一步透露，3.当内皮细胞暴露于肿瘤坏死因子（TNF）或白细胞介素-1（IL-1）时，TM的转录水平和蛋白合成减少，细胞表面激活蛋白C的辅因子活性也降低。用视黄酸（维生素A酸）处理内皮细胞增加TM的转录水平、蛋白质合成和辅因子活性，以及5.视黄酸恢复到细胞表面TM的正常水平，即使当TM水平通过细胞暴露于TNF而降低时。我们认为，肿瘤或炎症中血栓形成的原因之一可能是由于暴露于细胞因子导致TM表达减少，并提出了维甲酸治疗上述疾病血栓形成的可能性。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