In Vivo Clearance of Ternary Complexes of Vitronectin-Thrombin-Antithrombin Is Mediated by Hepatic Heparan Sulfate Proteoglycans

Abstract

Thrombin is inhibited by its cognate plasma inhibitor antithrombin, through the formation of covalent thrombin-antithrombin (TAT) complexes that are found as ternary complexes with vitronectin (VN-TAT). To determine whether the metabolism of VN-TAT ternary complexes is different from that previously reported for binary TAT complexes, plasma clearance studies were done in rabbits using human VN-TAT.125 I-VN-TAT was shown to be cleared rapidly from the circulation (t1 ⁄2␣ ‫؍‬ 3.8 min) in a biphasic manner mainly by the liver.

Large-Plaque Mutants of Sindbis Virus Show Reduced Binding to Heparan Sulfate, Heightened Viremia, and Slower Clearance from the Circulation

“…Heparin-binding proteins tend to have very short half-lives in the circulation, being rapidly sequestered by tissue HS, particularly in the liver, which has the most highly sulfated HS of any organ (2,35,53,55 reported in several studies that plaque variants of alphaviruses are cleared at variable rates from the circulation after an intravenous injection, with LP variants typically having longer half-lives (19,20,40). Because it is now apparent that one of the factors contributing to increased plaque size is a decreased ability to bind to sulfated polysaccharides, we reexamined the elimination of virus from the circulation.…”

Vitronectin's Basic Domain is a Syndecan Ligand which Functionsin transto Regulate Vitronectin Turnover

“…Binding of syndecan to vitronectin was dependent on the presence of heparan sulfate side chains, as cells expressing a syndecan-1 core protein which was not substituted with heparan sulfate, could not adhere to vitronectin. A role for proteoglycan side chains in mediating the binding of vitronectin to cells has been proposed in previous studies which have shown that treatment of cells with chlorate to inhibit proteoglycan sulfation (88) or β-D xyloside to block addition of glycosaminoglycans to the core protein (85) results in loss of vitronectin binding. Glypican-1, another species of heparan sulfate proteoglycan could not mediate adhesion to vitronectin, suggesting that differences in heparan sulfate structure might modulate binding to vitronectin.…”

“…Our earlier studies have indicated that binding of soluble vitronectin to adherent cells is sensitive to chlorate and heparitinase treatment (88), consistent with heparan sulfate proteoglycans serving as receptors for soluble vitronectin. Studies from our lab, as well as others have suggested that binding of vitronectin to sulfated proteoglycans is important in modulating phenomena such as changes in vitronectin conformation and biological activity (8,70,73,74), extracellular half-life (23,58,60,61,88) and vitronectin-dependent clearance of thrombin-antithrombin complexes (14,15,85). Treatment of dermal fibroblasts (87,88) and HT-1080 fibrosarcoma cells (Figure 3) with chlorate to block proteoglycan sulfation results in a significant reduction in the ability of cells to bind soluble vitronectin.…”

“…Nevertheless, when taken together, these data provide strong evidence that the basic domain constitutes the major heparin binding site in vitronectin. In previous studies, the binding of vitronectin as well as vitronectin-containing complexes to cell surfaces has been shown to be inhibited by heparin, suggesting that vitronectin's heparin binding domain mediates binding of vitronectin to cells (14,15,85,88). In the present study, we have shown that deletion of the basic domain results in the loss of soluble vitronectin binding to adherent cells, thus providing the first direct evidence that vitronectin's heparin binding domain mediates binding of soluble vitronectin to cells.…”

“…In addition, transcytosis of these complexes across endothelial cells can be blocked by adding exogenous heparin (15). In vivo clearance of vitronectincontaining thrombin-anti-thrombin complexes from the circulation and their subsequent degradation by the liver is also sensitive to heparin and thought to be dependent on hepatic heparan sulfate proteoglycans (85). Although there are numerous examples of vitronectin's association with cells being sensitive to reagents known to affect sulfated proteoglycans, specific proteoglycan receptors for vitronectin have not been identified.…”