Maruyama I, Majerus P W
J Biol Chem. 1985 Dec 15;260(29):15432-8.
We have prepared a monoclonal antibody directed against human thrombomodulin. We used the antibody to measure thrombomodulin molecules in cultured human endothelial cells from umbilical vein and in a human lung cancer cell line (A549). Endothelial cells contain approximately 30,000-55,000 molecules of thrombomodulin/cell while the A549 cell has about 1/4 of this number. About 50-60% of thrombin binding sites on endothelial cells are thrombomodulin, while about 90% of thrombin binding sites on A549 cells are thrombomodulin. Exposure of these cells to thrombin decreased thrombomodulin on the cell surface suggesting that internalization of thrombin-thrombomodulin occurred. The internalized 125I-thrombin was degraded in the cells and thrombomodulin reappeared on the cell surface after 30 min, suggesting the recycling of thrombomodulin. The rate of protein C activation correlated with the presence of the thrombin-thrombomodulin complex on the cell surface. The binding of thrombin to cell-surface thrombomodulin accelerates protein C activation; the subsequent internalization of the thrombin-thrombomodulin complex is associated with cessation of protein C activation. Therefore, endocytosis of thrombin-thrombomodulin may serve to control protein C activation. The uptake and degradation of thrombin bound to thrombomodulin may provide a mechanism for clearance of thrombin from the circulation.
我们制备了一种针对人血栓调节蛋白的单克隆抗体。我们用该抗体来检测来自人脐静脉的培养内皮细胞以及人肺癌细胞系（A549）中的血栓调节蛋白分子。内皮细胞每个细胞含有约30,000 - 55,000个血栓调节蛋白分子，而A549细胞的这一数量约为其1/4。内皮细胞上约50 - 60%的凝血酶结合位点是血栓调节蛋白，而A549细胞上约90%的凝血酶结合位点是血栓调节蛋白。将这些细胞暴露于凝血酶会使细胞表面的血栓调节蛋白减少，这表明发生了凝血酶 - 血栓调节蛋白的内化。内化的125I - 凝血酶在细胞内被降解，30分钟后血栓调节蛋白重新出现在细胞表面，这表明血栓调节蛋白发生了再循环。蛋白C激活的速率与细胞表面凝血酶 - 血栓调节蛋白复合物的存在相关。凝血酶与细胞表面血栓调节蛋白的结合加速了蛋白C的激活；随后凝血酶 - 血栓调节蛋白复合物的内化与蛋白C激活的停止相关。因此，凝血酶 - 血栓调节蛋白的内吞作用可能有助于控制蛋白C的激活。与血栓调节蛋白结合的凝血酶的摄取和降解可能为从循环中清除凝血酶提供一种机制。
