Association of Tissue Factor Pathway Inhibitor With Human Umbilical Vein

Tissue factor pathway inhibitor (TFPI) is a serine protease endocytosis after biotinylation of the cell surface, which indi-inhibitor of the extrinsic coagulation system, synthesized in cated that TFPI was being co-internalized with the surface endothelial cells, which has recently been shown to play biotin. The binding of exogenously added 125I-TFPI increased an important role in the regulation of activated coagulation linearly to HUVEC over the concentration range of 0 to 32 factors at the endothelial cell surface. In the present study nmol/L without saturation, the binding was not affected by we investigated the subcellular localization and metabolism up to a thousand-fold molar excess of unlabeled TFPI, and of TFPI in human umbilical vein endothelial cells (HUVEC). heparin inhibited the binding dose dependently. An intact C-Immunocytochemical labeling of HUVEC with anti-TFPI terminal domain was important for the interaction between showed specific labeling associated with the cell surface and TFPI and the cell surface of HUVEC, because less than 10% with many intracellular organelles including the Golgi com- of a C-terminal truncated form of TFPI (TFPI1-161) was bound plex. Further characterization of these organelles was per- after addition of equimolar concentrations of full-length formed by colocalizing the anti-TFPI with 3-(2,4-dinitroanil- TFPI. Exogenously added 125I-TFPI was not degraded in HU-ino)*-amino-N-methyldipropylamine (DAMP; to demonstrate VEC during 4 hours at 377C. The presence of TFPI in endocytic low pH), mannose phosphate receptor (endosomes), and and recycling compartments support the hypothesis that LAMP 1 (late endocytic compartments). TFPI also colocalize