J Biol Chem, Vol. 274, Issue 8, 4962-4969, February 19, 1999
Down-regulation of Monocyte Tissue Factor Mediated by Tissue
Factor Pathway Inhibitor and the Low Density Lipoprotein
Receptor-related Protein
Anne
Hamik
§,
Hendra
Setiadi
¶,
Guojun
Bu
,
Rodger
P.
McEver
¶, and
James H.
Morrissey
§
From the
Cardiovascular Biology Research Program,
Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104, the § Department of Pathology, and ¶ W. K. Warren
Medical Research Institute, Departments of Medicine and Biochemistry & Molecular Biology, University of Oklahoma Health Sciences Center,
Oklahoma City, Oklahoma 73104, and the
Departments of
Pediatrics and Cell Biology & Physiology, Washington University School
of Medicine, St. Louis, Missouri 63110
Inflammatory mediators like bacterial
lipopolysaccharide induce monocytes to express tissue factor (TF), the
cell-surface protein that triggers the blood clotting cascade in
hemostasis and thrombotic disease. The physiologic ligand for TF is the
serine protease, factor VIIa (FVIIa), and the resulting bimolecular
enzyme, TF/FVIIa, can be reversibly inhibited by tissue factor pathway inhibitor (TFPI). Culturing monocytic cells in the presence of both
FVIIa and TFPI caused down-regulation of TF expression via reducing its
half-life. To exert this effect, FVIIa had to be competent to bind both
TF and TFPI, and TFPI had to contain the C-terminal domain required for
binding to other cell-surface receptors, including the low density
lipoprotein receptor-related protein (LRP). TF down-regulation by FVIIa
plus TFPI was abrogated by the 39-kDa receptor-associated protein,
which blocks binding of all known ligands to LRP. Furthermore,
treatment with FVIIa plus TFPI caused monocyte TF to colocalize with
-adaptin, a component of clathrin-coated pits. Thus, in addition to
reversibly inhibiting TF/FVIIa catalytic activity, TFPI also mediates
the permanent down-regulation of cell-surface TF in monocytic cells via
LRP-dependent internalization and degradation. This
represents an unusual mechanism for receptor internalization, requiring
ligand-dependent bridging of one cell-surface receptor (TF)
to a second cell-surface receptor (LRP), the latter being capable of
clathrin-mediated internalization.
Copyright © 1999 by The American Society for Biochemistry and Molecular Biology, Inc.