Protein C inhibits endocytosis of thrombin-thrombomodulin complexes in A549
lung cancer cells and human umbilical vein endothelial cells
I Maruyama and PW Majerus
We investigated the effect of protein C on the endocytosis of thrombin-
thrombomodulin complexes. We previously showed that exposure of umbilical
vein endothelial cells to thrombin stimulated the internalization and
degradation of thrombin. A similar internalization was stimulated by a
monoclonal antithrombomodulin antibody. We have repeated these studies in
the presence of protein C and found that endocytosis of
125I-thrombin-thrombomodulin complexes, but not 125I-
antithrombomodulin-thrombomodulin complexes, is inhibited. Activated
protein C did not inhibit endocytosis of thrombin-thrombomodulin complexes.
Protein C inhibited both internalization and degradation of 125I-thrombin
and diisopropylphosphoryl (DIP) 125I-thrombin in human lung cancer cells
(A549). These effects were observed at protein C concentrations found in
human plasma. Protein S had no effect on the inhibition of endocytosis of
thrombin-thrombomodulin complexes by protein C. We propose that protein C
may regulate the rate of endocytosis of thrombin-thrombomodulin complexes
in vivo and thereby control the capacity for endothelium to activate
protein C.
Volume 69,
Issue 5,
pp. 1481-1484,
05/01/1987
Copyright © 1987 by The American Society of Hematology
