The turnover of thrombin-thrombomodulin complex in cultured human umbilical vein endothelial cells and A549 lung cancer cells. Endocytosis and degradation of thrombin.
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.
D000818:Animals; D002478:Cells, Cultured; D004591:Electrophoresis, Polyacrylamide Gel; D004705:Endocytosis; D004727:Endothelium / Q000378:metabolism; D005260:Female; D006023:Glycoproteins / Q000037:antagonists & inhibitors; D006801:Humans; D007074:Immunoglobulin G / Q000378:metabolism; D008175:Lung Neoplasms / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D008970:Molecular Weight; D011247:Pregnancy; D011486:Protein C; D011956:Receptors, Cell Surface / Q000378:metabolism*; D018179:Receptors, Thrombin; D013917:Thrombin / Q000378:metabolism*; D013997:Time Factors; D014471:Umbilical Veins / Q000166:cytology* / Q000378:metabolism
D006023:Glycoproteins; D007074:Immunoglobulin G; D011486:Protein C; D011956:Receptors, Cell Surface; D018179:Receptors, Thrombin; D013917:Thrombin