Cell Surface Heparan Sulfate Proteoglycans Participate in Factor VIII Catabolism Mediated by Low Density Lipoprotein Receptor-related Protein

Abstract

Factor VIII (fVIII) 1 is an essential component of the intrinsic pathway of blood coagulation, since genetic deficiency in fVIII results in a coagulation disorder known as hemophilia A and occurs in 1 per 5000 males. In the intrinsic pathway, activated fVIII (fVIIIa) functions as a cofactor for the serine protease factor IXa, and their membrane-bound complex (Xase complex) activates factor X to factor Xa (1). Factor Xa subsequently participates in activation of prothrombin into thrombin, the key enzyme of the coagulation cascade.FVIII is a glycoprotein (ϳ300 kDa, 2332 amino acid residues) consisting of three homologous A domains, two homologous C domains, and the unique B domain, which are arranged in the order of A1-A2-B-A3-C1-C2 (2). Prior to its secretion to plasma, fVIII is processed intracellularly to a series of Me 2ϩ -linked heterodimers produced by cleavage at the B-A3 junction (3) and by a number of additional cleavages within the B domain (2). These cleavages generate a heavy chain (HCh) consisting of the A1 (residues 1-336), A2 (residues 373-740), and B domains (residues 741-1648), and a light chain (LCh) composed of the domains A3 (residues 1690 -2019), C1 (residues 2020 -2172), and C2 (residues 2173-2332).In circulation, most of fVIII is bound to vWf, which confers from physiological concentrations of the proteins, which are ϳ1 (4) and ϳ50 nM (5), respectively, and a high affinity (0.2-0.5 nM) of their interaction (6, 7). Binding to vWf prevents fVIII from premature interaction with components of Xase complex and is also required for maintenance of the normal fVIII level in plasma (8), since vWf deficiency in both humans (8, 9) and animals (10, 11) leads to a secondary deficiency of fVIII.We have recently shown that fVIII catabolism from its complex with vWf in vitro and in vivo is mediated by low density lipoprotein receptor-related protein (LRP) (12). LRP, a member of the low density lipoprotein receptor family (13), is responsible for plasma clearance of lipoprotein remnants, serine proteinases, and their complexes with inhibitors (serpins) (13,14). LRP is most prominent in liver on hepatocytes, and in vasculature it is presented on the surface of smooth muscle cells, fibroblasts, and macrophages (15). Besides fVIII, LRP mediates the clearance of a number of other proteins involved in blood coagulation and fibrinolysis, such as factors IXa (16) and Xa (17, 18), plasminogen activators, and their complexes with plasminogen activator inhibitor (19 -21). A unique place among LRP ligands belongs to 39-kDa receptor-associated protein (RAP), which binds to LRP with a high affinity (K d ϭ 4 nM) and efficiently inhibits binding and endocytosis of all known LRP ligands (22).The sites of fVIII involved in interaction with LRP were localized within the A2 domain residues 484 -509 (12) and

Differential Regulation of Extracellular Tissue Inhibitor of Metalloproteinases-3 Levels by Cell Membrane-bound and Shed Low Density Lipoprotein Receptor-related Protein 1

“…HSPGs have been demonstrated to mediate endocytosis of ligands including lipoproteins (44). Alternatively, HSPGs might act as co-receptors of LRP-1-mediated endocytosis as proposed for thrombospondin 1 (45), tissue factor pathway inhibitor (46), amyloid-␤ (47), and factor VIII (48). However, we found that TIMP-3 endocytosis was not affected in xylosyltransferase-deficient CHO-745 cells, indicating that sulfated cell surface proteoglycans are not required for TIMP-3 endocytosis.…”

Mapping the Binding Region on the Low Density Lipoprotein Receptor for Blood Coagulation Factor VIII

“…Such affinities are unlikely to provide effective direct interactions of FVIII with both receptors in vivo, considering the concentration of FVIII in plasma (ϳ0.3 nM). For LRP, its in vivo interaction with FVIII is facilitated by cell surface heparan sulfate proteoglycans (34). Whether this type of receptors serves a similar role for LDLR is unknown.…”

Elevated plasma factor VIII in a mouse model of low-density lipoprotein receptor–related protein deficiency

“…Investigation of the molecular basis thereof has recently started. [11][12][13] It has been demonstrated that FVIII clearance is facilitated by cell surface heparan sulfate proteoglycans. 13 These are thought to act by preconcentrating ligands on the cell surface that subsequently transfer their ligands to endocytic receptors.…”

“…[11][12][13] It has been demonstrated that FVIII clearance is facilitated by cell surface heparan sulfate proteoglycans. 13 These are thought to act by preconcentrating ligands on the cell surface that subsequently transfer their ligands to endocytic receptors. 14 Recently, it has been demonstrated that FVIII comprises multiple binding sites that mediate the interaction with the low-density lipoprotein receptorrelated protein (LRP).…”