M. Narita et al., 2 RECEPTOR SYSTEMS ARE INVOLVED IN THE PLASMA-CLEARANCE OF TISSUE FACTOR PATHWAY INHIBITOR IN-VIVO, The Journal of biological chemistry, 270(42), 1995, pp. 24800-24804
Tissue factor pathway inhibitor (TFPI) is a potent inhibitor of the bl
ood coagulation factor VIIa-tissue factor complex, as well as a direct
inhibitor of factor Xa. Intravenously administered TFPI is rapidly cl
eared from circulation predominantly via liver. We previously reported
that the low density lipoprotein receptor related protein (LRP), a mu
ltifunctional endocytic receptor, mediates the uptake and degradation
of TFPI in hepatoma cells. This process is inhibited by a 39-kDa recep
tor-associated protein which binds to LRP and regulates its ligand bin
ding activity. However, a distinct, low affinity binding site (perhaps
heparin sulfate proteoglycans, HSPGs) on the endothelium and liver is
thought to be responsible for the majority of TFPI cell surface bindi
ng. In the current study, we investigated the role of LRP and this sec
ond binding site in the clearance of I-125-TFPI in, vivo using competi
tors and inhibitors of the receptors. Mice overexpressing the 39-kDa p
rotein via adenoviral-mediated gene transfer displayed diminished plas
ma clearance of I-125-TFPI. Blockade of cell surface HSPGs sites by in
cubation with the positively charged molecule, protamine, inhibited I-
125-TFPI binding to the hepatoma cells in vitro. In addition, preadmin
istration of protamine in vivo prolonged the plasma clearance of I-125
-TFPI in a dose-dependent manner. However, a dramatic increase of the
plasma half-life of I-125-TFPI and virtual elimination of I-125-TFPI c
learance was observed in mice overexpressing the 39-kDa protein and ad
ministered protamine. Taken together, our results suggest that two rec
eptor mechanisms are involved in the clearance of TFPI in vivo.