Accumulating KRX-0401 mouse evidence indicates that HSPGs act to inhibit cellular invasion by promoting tight cell–cell and cell–ECM interactions, and by maintaining the structural integrity and self-assembly of the ECM.33,34 Notably, one of the characteristics of malignant transformation is down-regulation of GAG biosynthesis, especially of the HS chains.33,34 Low levels of cell surface HS also correlate with high metastatic capacity of many tumors. MAMMALIAN HEPARANASE Enzymatic activity capable of cleaving glucuronidic linkages and releasing polysaccharide chains resistant to further degradation by the enzyme was first identified by Ogren and Lindahl.35 The physiological

function of this activity was initially Inhibitors,research,lifescience,medical implicated in degradation of macromolecular heparin to physiologically active fragments.35,36 Heparanase is an endo-β-glucuronidase that cleaves HS side chains presumably at sites of low sulfation, releasing saccharide products with appreciable size (4–7 kDa) that can still associate with protein ligands and facilitate their Inhibitors,research,lifescience,medical biological potency. Mammalian cells express primarily a single dominant functional heparanase enzyme (heparanase-1).16,17,37,38 A second heparanase Inhibitors,research,lifescience,medical (heparanase-2) has been cloned and sequenced but has not been shown to have HS-degrading activity.39 For simplification, throughout this review we will refer to heparanase-1

as heparanase. Enzymatic degradation of HS leads to disassembly of the ECM and is therefore Inhibitors,research,lifescience,medical involved in fundamental biological phenomena associated with tissue remodeling and cell migration, including cancer angiogenesis and metastasis.16,17,37,38 The heparanase mRNA encodes a 61.2-kDa protein

with 543 amino acids. This proenzyme is post-translationally cleaved into 8 and 50 kDa subunits that non-covalently associate to form the active Inhibitors,research,lifescience,medical heparanase (Figure 2).17,38,40 Heterodimer formation is essential for heparanase enzymatic activity.40,41 Site-directed mutagenesis revealed that, similar to other glycosyl hydrolases, heparanase has a common catalytic mechanism that involves two conserved acidic residues, a putative proton donor at Glu225, and a nucleophile (-)-p-Bromotetramisole Oxalate at Glu343 (Figure 2).42 Cellular processing of the latent 65-kDa proheparanase into its active 8+50-kDa heterodimer is inhibited by a cell-permeable inhibitor of cathepsin L.43 Moreover, multiple site-directed mutagenesis and cathepsin L gene-silencing and knock-out experiments indicate that cathepsin L is the predominant enzyme responsible for processing and activation of proheparanase.44 Figure 2 Predicted model of the active heparanase heterodimer showing the 50 + 8 kDa heparanase subunits, TIM-barrel and C-terminus domains, active site (Glu225 and Glu343, red), and heparin-binding domains (sites A and B). Right: Detailed structure of the C-domain. …