Heparanase uptake is mediated by cell membrane heparan sulfate proteoglycans

Chemical Tumor Biology of Heparan Sulfate Proteoglycans

Heparan sulfate proteoglycans (HSPGs) play vital roles in every step of tumor progression allowing cancer cells to proliferate, escape from immune response, invade neighboring tissues, and metastasize to distal sites away from the primary site. Several cancers including breast, lung, brain, pancreatic, skin, and colorectal cancers show aberrant modulation of several key HS biosynthetic enzymes such as 3-O Sulfotransferase and 6-O Sulfotransferase, and also catabolic enzymes such as HSulf-1, HSulf-2 and heparanase. The resulting tumor specific HS fine structures assist cancer cells to breakdown ECM to spread, misregulate signaling pathways to facilitate their proliferation, promote angiogenesis to receive nutrients, and protect themselves against natural killer cells. This review focuses on the changes in the expression of HS biosynthetic and catabolic enzymes in several cancers, the resulting changes in HS fine structures, and the effects of these tumor specific HS signatures on promoting invasion, proliferation, and metastasis. It is possible to retard tumor progression by modulating the deregulated biosynthetic and catabolic pathways of HS chains through novel chemical biology approaches.

A novel human heparanase splice variant, T5, endowed with protumorigenic characteristics

Heparanase is a mammalian endo-beta-d-glucuronidase that can cleave heparan sulfate side chains, an activity strongly implicated in tumor cell dissemination. The current study aimed to identify and characterize heparanase splice variants. LEADS, Compugen's alternative splicing modeling platform (Compugen, Tel Aviv, Israel), was used to search for splice variants in silico; tumor-derived cell lines (i.e., CAG myeloma) and tumor biopsies were utilized to validate T5 expression in vivo; signaling (i.e., Src phosphorylation) was evaluated following T5 gene silencing or overexpression and correlated with cell proliferation, colony formation, and tumor xenograft development. A novel spliced form of human heparanase, termed T5, was identified. In this splice variant, 144 bp of intron 5 are joined with exon 4, which results in a truncated, enzymatically inactive protein. T5 overexpression resulted in increased cell proliferation and larger colonies in soft agar, mediated by Src activation. Furthermore, T5 overexpression markedly enhanced tumor xenograft development. T5 expression is up-regulated in 75% of human renal cell carcinoma biopsies examined, which suggests that this splice variant is clinically relevant. Controls included cells overexpressing wild-type heparanase or an empty plasmid and normal-looking tissue adjacent the carcinoma lesion. T5 is a novel functional splice variant of human heparanase endowed with protumorigenic characteristics.-Barash, U., Cohen-Kaplan, V., Arvatz, G., Gingis-Velitski, S., Levy-Adam, F., Nativ, O., Shemesh, R., Ayalon-Sofer, M., Ilan, N., Vlodavsky, I. A novel human heparanase splice variant, T5, endowed with protumorigenic characteristics.

Syndecan-1 and FGF-2, but not FGF receptor-1, share a common transport route and co-localize with heparanase in the nuclei of mesenchymal tumor cells

Syndecan-1 forms complexes with growth factors and their cognate receptors in the cell membrane. We have previously reported a tubulin-mediated translocation of syndecan-1 to the nucleus. The transport route and functional significance of nuclear syndecan-1 is still incompletely understood. Here we investigate the sub-cellular distribution of syndecan-1, FGF-2, FGFR-1 and heparanase in malignant mesenchymal tumor cells, and explore the possibility of their coordinated translocation to the nucleus. To elucidate a structural requirement for this nuclear transport, we have transfected cells with a syndecan-1/EGFP construct or with a short truncated version containing only the tubulin binding RMKKK sequence. The sub-cellular distribution of the EGFP fusion proteins was monitored by fluorescence microscopy. Our data indicate that syndecan-1, FGF-2 and heparanase co-localize in the nucleus, whereas FGFR-1 is enriched mainly in the perinuclear area. Overexpression of syndecan-1 results in increased nuclear accumulation of FGF-2, demonstrating the functional importance of syndecan-1 for this nuclear transport. Interestingly, exogenously added FGF-2 does not follow the route taken by endogenous FGF-2. Furthermore, we prove that the RMKKK sequence of syndecan-1 is necessary and sufficient for nuclear translocation, acting as a nuclear localization signal, and the Arginine residue is vital for this localization. We conclude that syndecan-1 and FGF-2, but not FGFR-1 share a common transport route and co-localize with heparanase in the nucleus, and this transport is mediated by the RMKKK motif in syndecan-1. Our study opens a new perspective in the proteoglycan field and provides more evidence of nuclear interactions of syndecan-1.

Heparanase: busy at the cell surface

Heparanase activity is strongly implicated in structural remodeling of the extracellular matrix, a process which can lead to invasion by tumor cells. In addition, heparanase augments signaling cascades leading to enhanced phosphorylation of selected protein kinases and increased gene transcription associated with aggressive tumor progression. This function is apparently independent of heparan sulfate and enzyme activity, and is mediated by a novel protein domain localized at the heparanase C-terminus. Moreover, the functional repertoire of heparanase is expanded by its regulation of syndecan clustering, shedding, and mitogen binding. Recent reports indicate that modified glycol-split heparin, which inhibits heparanase activity, can profoundly inhibit the progression of tumor xenografts produced by myeloma and carcinoma cells, thus moving anti-heparanase therapy closer to reality.

Structure-function approach identifies a COOH-terminal domain that mediates heparanase signaling

Heparanase is an endo-beta-d-glucuronidase capable of cleaving heparan sulfate, activity that is strongly implicated in cellular invasion associated with tumor metastasis, angiogenesis, and inflammation. In addition, heparanase was noted to exert biological functions apparently independent of its enzymatic activity, enhancing the phosphorylation of selected protein kinases and inducing gene transcription. A predicted three-dimensional structure of constitutively active heparanase clearly delineates a TIM-barrel fold previously anticipated for the enzyme. Interestingly, the model also revealed the existence of a COOH-terminal domain (C-domain) that apparently is not an integral part of the TIM-barrel fold. We provide evidence that the C-domain is critical for heparanase enzymatic activity and secretion. Moreover, the C-domain was found to mediate nonenzymatic functions of heparanase, facilitating Akt phosphorylation, cell proliferation, and tumor xenograft progression. These findings support the notion that heparanase exerts enzymatic activity-independent functions, and identify, for the first time, a protein domain responsible for heparanase-mediated signaling. Inhibitors directed against the C-domain, combined with inhibitors of heparanase enzymatic activity, are expected to neutralize heparanase functions and to profoundly affect tumor growth, angiogenesis, and metastasis.

Endothelial heparanase secretion after acute hypoinsulinemia is regulated by glucose and fatty acid

Following diabetes, the heart increases its lipoprotein lipase (LPL) at the coronary lumen by transferring LPL from the cardiomyocyte to the endothelial lumen. We examined how hyperglycemia controls secretion of heparanase, the enzyme that cleaves myocyte heparan sulphate proteoglycan to initiate this movement. Diazoxide (DZ) was used to decrease serum insulin and generate hyperglycemia. A modified Langendorff technique was used to separate coronary from interstitial effluent, which were assayed for heparanase and LPL. Within 30 min of DZ, interstitial heparanase increased, an effect that closely mirrored an augmentation in interstitial LPL. Endothelial cells were incubated with palmitic acid (PA) or glucose, and heparanase secretion was determined. PA increased intracellular heparanase, with no effect on secretion of this enzyme. Unlike PA, glucose dose-dependently lowered endothelial intracellular heparanase, which was strongly associated with increased heparanase activity in the incubation medium. Preincubation with cytochalasin D or nocodazole prevented the high glucose-induced depletion of intracellular heparanase. Our data suggest that following hyperglycemia, translocation of LPL from the cardiomyocyte cell surface to the apical side of endothelial cells is dependent on the ability of the fatty acid to increase endothelial intracellular heparanase followed by rapid secretion of this enzyme by glucose, which requires an intact microtubule and actin cytoskeleton.

Heparanase augments epidermal growth factor receptor phosphorylation: correlation with head and neck tumor progression

Heparanase is an endoglycosidase that specifically cleaves heparan sulfate side chains, a class of glycosaminoglycans abundantly present in the extracellular matrix and on the cell surface. Heparanase activity is strongly implicated in tumor metastasis attributed to remodeling of the subepithelial and subendothelial basement membranes, resulting in dissemination of metastatic cancer cells. Moreover, heparanase up-regulation was noted in an increasing number of primary human tumors, correlating with tumors larger in size, increased microvessel density, and reduced postoperative survival rate, implying that heparanase function is not limited to tumor metastasis. This notion is supported by recent findings revealing induction of signaling molecules (i.e., Akt, p38) and gene transcription [i.e., tissue factor, vascular endothelial growth factor (VEGF)] by enzymatically-inactive heparanase. Here, we provide evidence that active and inactive heparanase proteins enhance epidermal growth factor receptor (EGFR) phosphorylation. Enhanced EGFR phosphorylation was associated with increased cell migration, cell proliferation, and colony formation, which were attenuated by Src inhibitors. Similarly, heparanase gene silencing by means of siRNA was associated with reduced Src and EGFR phosphorylation levels and decreased cell proliferation. Moreover, heparanase expression correlated with increased phospho-EGFR levels and progression of head and neck carcinoma, providing a strong clinical support for EGFR modulation by heparanase. Thus, heparanase seems to modulate two critical systems involved in tumor progression, namely VEGF expression and EGFR activation. Neutralizing heparanase enzymatic and nonenzymatic functions is therefore expected to profoundly affect tumor growth, angiogenesis, and metastasis.

Heparanase stimulation of protease expression implicates it as a master regulator of the aggressive tumor phenotype in myeloma

High levels of heparanase are an indicator of poor prognosis in myeloma patients, and up-regulation of the enzyme enhances tumor growth, angiogenesis, and metastasis in animal models. At least part of the impact of heparanase in driving the aggressive tumor phenotype is due to its effect on increasing the expression and shedding of the heparan sulfate proteoglycan syndecan-1, a molecule known to promote myeloma progression. The present work demonstrated that elevation in heparanase expression in myeloma cells stimulates sustained ERK phosphorylation that in turn drives MMP-9 expression. In addition, urokinase-type plasminogen activator (uPA) and uPA receptor expression levels increased, and blocking the proteolytic activation of either MMP-9 or uPA inhibited the heparanase-induced increase in syndecan-1 shedding. Together these data provide a mechanism for heparanase-induced syndecan-1 shedding and, more importantly, demonstrate that heparanase activity in myeloma cells can lead to increased levels of proteases that are known to play important roles in the aggressive behavior of myeloma tumors. This in addition to its other known biological roles, indicates that heparanase acts as a master regulator of the aggressive tumor phenotype by up-regulating protease expression and activity within the tumor microenvironment.

Heparanase is overexpressed in lung cancer and correlates inversely with patient survival

BACKGROUND

Heparanase is an endo-beta-D-glucuronidase that is capable of cleaving heparan sulfate (HS) side chains at a limited number of sites, yielding HS fragments of still appreciable size (approximately 5-7 kDa). Heparanase activity has been detected frequently in several cell types and tissues. Heparanase activity correlates with the metastatic potential of tumor-derived cells, a correlation that has been attributed to enhanced cell dissemination as a consequence of HS cleavage and remodeling of the extracellular matrix barrier.

METHODS

In this study, the authors examined heparanase expression in 114 patients with lung cancer by means of immunohistochemistry and correlated clinical-pathologic data with heparanase immunostaining and cellular localization.

RESULTS

Heparanase was overexpressed in 75% of the study patients. Heparanase expression was correlated with lung cancer lymph node status and metastasis classification (P = .04 and P = .01, respectively) and was correlated inversely with patient survival (P = .007). It is noteworthy that this adverse effect depended largely on the cellular localization of heparanase. Thus, whereas cytoplasmic staining of heparanase is associated with a poor prognosis, nuclear heparanase predicts a favorable outcome for patients with lung cancer.

CONCLUSIONS

The current findings suggest that heparanase expression and cellular localization are decisive for lung cancer patients' prognosis, most likely because of heparanase-mediated tumor cell dissemination by blood and lymph vessels.

Requirement of the conserved, hydrophobic C-terminus region for the activation of heparanase

Heparanase is an endo-beta-D-glucuronidase responsible for the cleavage of heparan sulfate, participating in extracellular matrix degradation and remodeling. Heparanase activity is well correlated with the potential for metastasis and angiogenesis in a large number of tumor-derived cell types, directly implicating the involvement of heparanase in tumor progression. Here, we provide the first evidence that the hydrophobic C-terminus region of heparanase has specific roles in intracellular trafficking, secretion, activation, and heparanase-mediated tumor cell migration. Furthermore, partial deletion of this hydrophobic C-terminus region, substitution within the hydrophobic C-terminus region to hydrophilic amino acids, and experiments of single amino acid mutations further point out the importance of the hydrophobic C-terminus region. Therefore, our findings suggest that the hydrophobic C-terminus region of heparanase is a determinant for its intracellular trafficking to the Golgi apparatus, followed by secretion, activation, and tumor cell migration.

Heparanase facilitates cell adhesion and spreading by clustering of cell surface heparan sulfate proteoglycans

Heparanase is a heparan sulfate (HS) degrading endoglycosidase participating in extracellular matrix degradation and remodeling. Apart of its well characterized enzymatic activity, heparanase was noted to exert also enzymatic-independent functions. Non-enzymatic activities of heparanase include enhanced adhesion of tumor-derived cells and primary T-cells. Attempting to identify functional domains of heparanase that would serve as targets for drug development, we have identified heparin binding domains of heparanase. A corresponding peptide (residues Lys¹⁵⁸-Asp¹⁷¹, termed KKDC) was demonstrated to physically associate with heparin and HS, and to inhibit heparanase enzymatic activity. We hypothesized that the pro-adhesive properties of heparanase are mediated by its interaction with cell surface HS proteoglycans, and utilized the KKDC peptide to examine this possibility. We provide evidence that the KKDC peptide interacts with cell membrane HS, resulting in clustering of syndecan-1 and syndecan-4. We applied classical analysis of cell morphology, fluorescent and time-lapse microscopy and demonstrated that the KKDC peptide efficiently stimulates the adhesion and spreading of various cell types, mediated by PKC, Src, and the small GTPase Rac1. These results support, and further substantiate the notion that heparanase function is not limited to its enzymatic activity.

Cathepsin L is responsible for processing and activation of proheparanase through multiple cleavages of a linker segment

Heparanase is an endo-beta-d-glucuronidase that degrades heparan sulfate in the extracellular matrix and on the cell surface. Human proheparanase is produced as a latent protein of 543 amino acids whose activation involves excision of an internal linker segment (Ser(110)-Gln(157)), yielding the active heterodimer composed of 8- and 50-kDa subunits. Applying cathepsin L knock-out tissues and cultured fibroblasts, as well as cathepsin L gene silencing and overexpression strategies, we demonstrate, for the first time, that removal of the linker peptide and conversion of proheparanase into its active 8 + 50-kDa form is brought about predominantly by cathepsin L. Excision of a 10-amino acid peptide located at the C terminus of the linker segment between two functional cathepsin L cleavage sites (Y156Q and Y146Q) was critical for activation of proheparanase. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry demonstrates that the entire linker segment is susceptible to multiple endocleavages by cathepsin L, generating small peptides. Mass spectrometry demonstrated further that an active 8-kDa subunit can be generated by several alternative adjacent endocleavages, yielding the precise 8-kDa subunit and/or slightly elongated forms. Altogether, the mode of action presented here demonstrates that processing and activation of proheparanase can be brought about solely by cathepsin L. The critical involvement of cathepsin L in proheparanase processing and activation offers new strategies for inhibiting the prometastatic, proangiogenic, and proinflammatory activities of heparanase.

Clinical significance of urine heparanase in bladder cancer progression

Heparanase is an endo-beta-glucuronidase capable of cleaving heparan sulfate (HS), an activity implicated in tumor metastasis. Heparanase expression is upregulated in primary human tumors, correlating with reduced post operative survival and elevated microvessel density. An ELISA method was used to quantify heparanase in urine from 282 individuals. Urine was collected from healthy volunteers (n = 41), patients diagnosed with noncancerous pathologic disorders (n = 90), and bladder cancer patients (n = 92). Fifty-nine bladder carcinoma patients after transurethral resection (TUR) with no evidence of disease (NED) were also included. Heparanase levels were significantly elevated in urine from bladder cancer patients compared with healthy controls (P < .001) and with noncancerous urinary disorders (P < .05). Heparanase elevation strongly correlated with tumor grade (P < .001) and stage (P = .027). An optimal cutoff value of 154 pg/ml was determined. Of 199 individuals enrolled (59 patients after TUR and 24 patients with recurring disease were excluded), 65 had heparanase levels above 154 pg/ml. Only 3 of 65 (4.6%) were healthy individuals. In contrast, 52.3% (34 of 65) of individuals with heparanase levels above 154 pg/ml were bladder cancer patients. The results indicate that urine heparanase levels are elevated during bladder cancer progression, suggesting that the ELISA method may be applied for bladder cancer diagnosis.

Are primed polymorphonuclear leukocytes contributors to the high heparanase levels in hemodialysis patients?

Patients on chronic hemodialysis (HD) are at high risk for developing atherosclerosis and cardiovascular complications. Heparanase, an endoglycosidase that cleaves heparan sulfate (HS) side chains of proteoglycans, is involved in extracellular matrix degradation and, as such, may be involved in the atherosclerotic lesion progression. We hypothesize that heparanase is elevated in HD patients, partly due to its release from primed circulating polymorphonuclear leukocytes (PMNLs), undergoing degranulation. Priming of PMNLs was assessed by levels of CD11b and the rate of superoxide release. Heparanase mRNA expression in PMNLs was determined by RT-PCR. PMNL and plasma levels of heparanase were determined by immunoblotting, immunofluorescence, and flow cytometry analyses. The levels of soluble HS in plasma were measured by a competition ELISA. This study shows that PMNLs isolated from HD patients have higher mRNA and protein levels of heparanase compared with normal control (NC) subjects and that heparanase levels correlate positively with PMNL priming. Plasma levels of heparanase were higher in HD patients than in NC subjects and were further elevated after the dialysis session. In addition, heparanase expression inversely correlates with plasma HS levels. A pronounced expression of heparanase was found in human atherosclerotic lesions. The increased heparanase activity in the blood of HD patients results at least in part from the degranulation of primed PMNLs and may contribute to the acceleration of the atherosclerotic process. Our findings highlight primed PMNLs as a possible source for the increased heparanase in HD patients, posing heparanase as a new risk factor for cardiovascular complications and atherosclerosis.

Heparanase up-regulation in tongue cancer: tissue and saliva analysis

BACKGROUND

Heparanase up-regulation has been correlated with reduced postoperative survival in various cancers.

METHODS

Heparanase expression was analyzed in 60 consenting tongue (mobile) cancer patients by means of immunohistochemistry. Heparanase levels were also analyzed in the saliva of both healthy controls and tongue cancer patients using a novel heparanase enzyme-linked immunosorbent assay method.

RESULTS

Heparanase staining was positive (>0) in 92% and negative (=0) in 8% of the tumors and staining intensity correlated with tumor size and tumor stage. Moreover, the survival probability of patients negative for heparanase (=0) at 60 months was 100%, compared with only 41% for patients positive for heparanase (>0), suggesting that heparanase may serve as a prognostic factor for this malignancy and an attractive target for anticancer drug development. Heparanase was detected in the saliva of healthy controls and the mean concentration was determined as 119 +/- 37 pg/mL. Importantly, a nearly 3-fold increase of heparanase levels was detected in saliva collected from tongue cancer patients (334 +/- 69 pg/mL), a difference that is statistically highly significant (P = .004).

CONCLUSIONS

These findings support heparanase up-regulation in tongue cancer and raise the possibility of using this simple test as a diagnostic tool to monitor tongue cancer progression and response to treatment.

Survivin-driven and fiber-modified oncolytic adenovirus exhibits potent antitumor activity in established intracranial glioma

The poor prognosis of patients with malignant gliomas necessitates the development of novel therapies. Virotherapy, using genetically engineered adenovectors that selectively replicate in and kill neoplastic cells, represents one such strategy. In this study, we examined several oncolytic vectors with modified transcriptional and transductional control of viral replication. First, we incorporated the survivin promoter (S) to drive E1A gene expression. We then modified the adenovirus serotype 5 (Ad5) fiber protein via genetic knob switching or incorporation of peptide ligands to target the following glioma-associated receptors: the Ad3 attachment protein, or CD46, alpha(v) beta(3)/alpha(v)beta(5) integrins, or heparan sulfate proteoglycans. The three conditionally replicative adenoviruses, CRAd-S-5/3, CRAd-S-RGD, and CRAd-S-pk7, were then examined in vitro with respect to transduction efficiency and tissue specificity. The most promising virus was then tested in vivo for evidence of tumor growth inhibition. CRAd-S-pk7 provided the highest level of viral replication and tumor oncolysis in glioma cell lines. At the same time, we observed minimal viral replication and toxicity in normal human brain. Injection of CRAd-S-pk7 inhibited xenograft tumor growth by more than 300% (p < 0.001). Sixty-seven percent of treated mice with intracranial tumors were long-term survivors (>110 days; p < 0.005). Analysis of tumor tissue indicated increased adenoviral infectivity, decreased mitotic activity, and enhanced tumor apoptosis. These findings demonstrate the effectiveness of CRAd-S-pk7 and provide the rationale for further development of this novel oncolytic virus for glioma gene therapy.

Mammalian heparanase: what is the message?

Heparan sulphate proteoglycans are ubiquitous macromolecules of cell surfaces and extracellular matrices. Numerous extracellular matrix proteins, growth factors, morphogens, cytokines, chemokines and coagulation factors are bound and regulated by heparan sulphate. Degradation of heparan sulphate thus potentially profoundly affects cell and tissue function. Although there is evidence that several heparan sulphate-degrading endoglucuronidases (heparanases) might exist, so far only one transcript encoding a functional heparanase has been identified: heparanase-1. In the first part of this review, we discuss the current knowledge about heparan sulphate proteoglycans and the functional importance of their versatile interactions. In the second part, we summarize recent findings that have contributed to the characterization of heparanase-1, focusing on the molecular properties, working mechanism, substrate specificity, expression pattern, cellular activation and localization of this enzyme. Additionally, we review data implicating heparanase-1 in several normal and pathological processes, focusing on tumour metastasis and angiogenesis, and on evidence for a potentially direct signalling function of the molecule. In that context, we also briefly discuss heparanase-2, an intriguing close homologue of heparanase-1, for which, so far, no heparan sulphate-degrading activity could be demonstrated.

Brain heparanase expression is up-regulated during postnatal development and hypoxia-induced neovascularization in adult rats

Heparanase is an endo-beta-d-glucuronidase which specifically cleaves extracellular and cell surface heparan sulphates at intra-chain sites. Its enzymatic activity is strongly implicated in cell dissemination associated with tumor metastasis and inflammation. Indeed, heparanase gene is expressed in various tumors and its over-expression is correlated with increased tumor vascularity and metastatic potential of tumor cells. However, heparanase expression in non-invasive and non-immune tissue, including brain, has received less attention. Using RT-qPCR, western blot and histological analysis, we demonstrate in the adult rat that heparanase transcript is differentially expressed according to brain area, and that heparanase protein is mainly detected in neurons. Furthermore, we provide evidence that heparanase transcript and protein reach their greatest levels at early postnatal stages, in particular within the neocortex characterized by intensive structural plasticity. Using the in vitro model of PC12-induced neuronal differentiation, we suggest that developmental regulation of heparanase may coincide with axonal and dendritic pathfinding. At adulthood, we demonstrate that the increased heparanase transcript level correlates in the hippocampus with enhanced angiogenesis following repeated hypoxia exposures. Taken together, our results emphasize the potential importance of heparanase in brain homeostasis, both during development and adaptative responses to severe environmental challenges.

Heparanase cleavage of perlecan heparan sulfate modulates FGF10 activity during ex vivo submandibular gland branching morphogenesis

Heparan sulfate proteoglycans are essential for biological processes regulated by fibroblast growth factors (FGFs). Heparan sulfate (HS) regulates the activity of FGFs by acting as a coreceptor at the cell surface, enhancing FGF-FGFR affinity, and being a storage reservoir for FGFs in the extracellular matrix (ECM). Here we demonstrate a critical role for heparanase during mouse submandibular gland (SMG) branching morphogenesis. Heparanase, an endoglycosidase, colocalized with perlecan in the basement membrane and in epithelial clefts of SMGs. Inhibition of heparanase activity in organ culture decreased branching morphogenesis, and this inhibition was rescued specifically by FGF10 and not by other FGFs. By contrast, exogenous heparanase increased SMG branching and MAPK signaling and, surprisingly, when isolated epithelia were cultured in a three-dimensional ECM with FGF10, it increased the number of lateral branches and end buds. In a solid-phase binding assay, an FGF10-FGFR2b complex was released from the ECM by heparanase. In addition, surface plasmon resonance (SPR) analysis showed that FGF10 and the FGF10-FGFR2b complex bound to purified perlecan HS and could be released by heparanase. We used the FGF10-FGFR2b complex as a probe for HS in SMGs, and it colocalized with perlecan in the basement membrane and partly colocalized with syndecan 1 in the epithelium, and binding was reduced by treatment with heparanase. In summary, our results show heparanase releases FGF10 from perlecan HS in the basement membrane, increasing MAPK signaling, epithelial clefting, and lateral branch formation, which results in increased branching morphogenesis.

Low and high affinity receptors mediate cellular uptake of heparanase

Heparanase is an endoglycosidase which cleaves heparan sulfate and hence participates in degradation and remodeling of the extracellular matrix. Importantly, heparanase activity correlated with the metastatic potential of tumor-derived cells, attributed to enhanced cell dissemination as a consequence of heparan sulfate cleavage and remodeling of the extracellular matrix barrier. Heparanase has been characterized as a glycoprotein, yet glycan biochemical analysis was not performed to date. Here, we applied the Qproteometrade mark GlycoArray kit to perform glycan analysis of heparanase, and compared the kit results with the more commonly used biochemical analyses. We employed fibroblasts isolated from patients with I-cell disease (mucolipidosis II), fibroblasts deficient of low density lipoprotein receptor-related protein and fibroblasts lacking mannose 6-phosphate receptor, to explore the role of mannose 6-phosphate in heparanase uptake. Iodinated heparanase has been utilized to calculate binding affinity. We provide evidence for hierarchy of binding to cellular receptors as a function of heparanase concentration. We report the existence of a high affinity, low abundant (i.e., low density lipoprotein receptor-related protein, mannose 6-phosphate receptor), as well as a low affinity, high abundant (i.e., heparan sulfate proteoglycan) receptors that mediate heparanase binding, and suggest that these receptors co-operate to establish high affinity binding sites for heparanase, thus maintaining extracellular retention of the enzyme tightly regulated.

Heparanase induces Akt phosphorylation via a lipid raft receptor

The endoglycosidase heparanase is the predominant enzyme that degrades heparan sulfate side chains of heparan sulfate proteoglycans, activity that is strongly implicated in tumor metastasis. Apart of its well characterized enzymatic activity, heparanase was noted to exert also enzymatic-independent functions. Among these is the induction of Akt/PKB phosphorylation noted in endothelial- and tumor-derived cells. Protein domains of heparanase required for signaling were not identified to date, nor were identified heparanase binding proteins/receptors capable of transmitting heparanase signals. Here, we examined the possible function of mannose 6-phosphate receptor (MPR) and low-density lipoprotein-receptor related protein (LRP), recently implicated in cellular uptake of heparanase, as heparanase receptors mediating Akt phosphorylation. We found that heparanase addition to MPR- and LRP-deficient fibroblasts elicited Akt activation indistinguishable from control fibroblasts. In contrast, disruption of lipid rafts abrogated Akt/PKB phosphorylation following heparanase addition. These results suggest that lipid raft-resident receptor mediates heparanase signaling.

Anti-heparanase monoclonal antibody enhances heparanase enzymatic activity and facilitates wound healing

Heparanase is a mammalian endo-beta-D-glucuronidase capable of cleaving HS side chains at a limited number of sites, activity that is strongly implicated in tumor metastasis, neovascularization, inflammation, and autoimmunity. Clinically, up-regulation of heparanase mRNA and protein expression has been documented in a variety of primary human tumors, correlating with reduced postoperative survival and increased lymph node and distant metastasis, thus providing strong clinical support for the prometastatic feature of the enzyme and making it an attractive target for the development of anticancer and anti-inflammatory drugs. Screening a panel of monoclonal antibodies for their ability to inhibit heparanase enzymatic activity, we noted that one hybridoma, 6F8, exhibited the opposite effect and significantly enhanced heparanase activity. Here, we provide evidence that antibody 6F8 enhances the activity of recombinant and cellular heparanase, facilitates invasion of tumor-derived cells in vitro, and improves wound healing in a mouse punch model in vivo. These results support a role of heparanase in the course of wound healing and, moreover, suggest that monoclonal antibodies can be applied clinically for the enhancement, rather than inhibition, of certain enzymes.

Heparanase expression and function during early pregnancy in mice

Embryo implantation is a complex process that involves interactions between cell-surface and extracellular components of the blastocyst and the uterus, including blastocyst adhesion to the uterine luminal epithelium, epithelial basement membrane penetration and stromal extracellular matrix remodeling, angiogenesis, and decidualization. These processes all involve interactions with heparan sulfate (HS) proteoglycans, which harbor various growth factors and cytokines and support cell adhesion. Heparanase (HPSE) is an endo-beta-glucuronidase that cleaves HS at specific sites. HPSE also can act as an adhesion molecule independent of its catalytic activity. Thus, HPSE is a multifunctional molecule contributing to and modulating HS-dependent processes. Exogenously added HPSE improves embryo implantation in mice; however, no information is available regarding the normal pattern of HPSE expression and activity during the implantation process in any system. Using several approaches, including real-time RT-PCR, in situ hybridization, and immunohistochemistry, we determined that uterine HPSE expression increases dramatically during early pregnancy in mice. Heparanase mRNA and protein were primarily expressed in decidua and were rapidly induced at the implantation site. Uterine HPSE activity was characterized and demonstrated to increase >40-fold during early pregnancy. Finally, we demonstrate that the HPSE inhibitor PI-88 severely inhibits embryo implantation in vivo. Collectively, these results indicate that HPSE plays a role in blastocyst implantation and complements previous studies showing a role for HS-dependent interactions in this process.

Heparanase: a target for drug discovery in cancer and inflammation

The remodelling of the extracellular matrix (ECM) has been shown to be highly upregulated in cancer and inflammation and is critically linked to the processes of invasion and metastasis. One of the key enzymes involved in specifically degrading the heparan sulphate (HS) component of the ECM is the endo-beta-glucuronidase enzyme heparanase. Processing of HS by heparanase releases both a host of bioactive growth factors anchored within the mesh of the ECM as well as defined fragments of HS capable of promoting cellular proliferation. The finding that heparanase is elevated in a wide variety of tumor types and is subsequently linked to the development of pathological processes has led to an explosion of therapeutic strategies to inhibit its enzyme activity. So far only one compound, the sulphated oligosaccharide PI88, which both inhibits heparanase activity and has effects on growth factor binding has reached clinical trials where it has shown to have promising efficacy. The scene has clearly been set however for a new generation of compounds, either specific to the enzyme or with dual roles, to emerge from the lab and enter the clinic. The aim of this review is to describe the current drug discovery status of small molecule, sugar and neutralising antibody inhibitors of heparanase enzyme activity. Potential strategies will also be discussed on the selection of suitable biomarker strategies for specific monitoring of in vivo heparanase inhibition which will be crucial for both animal model and clinical trial testing.

Heparanase expression correlates with poor survival in metastatic ovarian carcinoma

OBJECTIVE

To analyze the expression of Heparanase, an enzyme involved in cancer metastasis and angiogenesis, in ovarian and breast carcinoma cells in effusions.

METHODS

Heparanase protein expression was analyzed in malignant effusions from ovarian (=200) and breast (=41) carcinoma patients using immunocytochemistry. The levels of secreted heparanase were analyzed in 45 effusion supernatants using a newly established ELISA test. Heparanase expression levels were analyzed for clinical significance.

RESULTS

Heparanase was expressed at the cell membrane in 106/200 (53%) ovarian and 22/41 (54%) breast carcinomas. Cytoplasmic expression was found in 180/200 (90%) ovarian and 26/41 (63%) breast carcinomas. Reactive mesothelial cells showed frequent cytoplasmic, but not membrane expression. ELISA showed secreted heparanase in all 45 analyzed effusions. Higher levels were detected in peritoneal compared to pleural effusions (p=0.031). In univariate survival analysis of ovarian carcinoma patients with post-chemotherapy effusions, membrane expression in >5% of tumor cells correlated with shorter overall survival (OS, p=0.013). FIGO stage (p=0.03 for all patients, p=0.045 for those with post-chemotherapy specimens) and response to first-line chemotherapy (p<0.0001 for all patients, p=0.049 for those with post-chemotherapy specimens) were the clinical parameters related to OS. In Cox analysis of this subset of patients, heparanase expression (p=0.02) and response to chemotherapy (p=0.049) were independent predictors of poor OS. Heparanase expression did not correlate with survival in breast carcinoma.

CONCLUSIONS

Our data show that heparanase is frequently expressed in metastatic gynecologic adenocarcinomas, and that it is secreted into the effusion fluid in body cavities. The correlation between heparanase expression and poor survival in ovarian carcinoma suggests a role for this molecule in ovarian cancer metastasis and supports its role as a marker of aggressive clinical behavior at disease recurrence.

Salivary gland branching morphogenesis

Salivary gland branching morphogenesis involves coordinated cell growth, proliferation, differentiation, migration, apoptosis, and interaction of epithelial, mesenchymal, endothelial, and neuronal cells. The ex vivo analysis of embryonic mouse submandibular glands, which branch so reproducibly and beautifully in culture, is a powerful tool to investigate the molecular mechanisms regulating epithelium-mesenchyme interactions during development. The more recent analysis of genetically modified mice provides insight into the genetic regulation of branching morphogenesis. The review begins, as did the field historically, focusing on the role of the extracellular matrix (ECM), and its components such as glycosaminoglycans, collagens, and laminins. Following sections describe the modification of the ECM by proteases and the role of cell-matrix and cell-cell receptors. The review then focuses on two major families of growth factors implicated in salivary gland development, the fibroblast growth factors (FGFs) and the epidermal growth factors (EGFs). The salivary gland phenotypes in mice with genetic modification of FGFs and their receptors highlight the central role of FGFs during salivary gland branching morphogenesis. A broader section mentions other molecules implicated from analysis of the phenotypes of genetically modified mice or organ culture experiments. The review concludes with speculation on some future areas of research.

The role of heparan sulphate in inflammation

The polysaccharide heparan sulphate is ubiquitously expressed as a proteoglycan in extracellular matrices and on cell surfaces. Heparan sulphate has marked sequence diversity that allows it to specifically interact with many proteins. This Review focuses on the multiple roles of heparan sulphate in inflammatory responses and, in particular, on its participation in almost every stage of leukocyte transmigration through the blood-vessel wall. Heparan sulphate is involved in the initial adhesion of leukocytes to the inflamed endothelium, the subsequent chemokine-mediated transmigration through the vessel wall and the establishment of both acute and chronic inflammatory reactions.

Translocation of active heparanase to cell surface regulates degradation of extracellular matrix heparan sulfate upon transmigration of mature monocyte-derived dendritic cells

After Ag capture and exposure to danger stimuli, maturing dendritic cells (DCs) migrate to regional lymph nodes, where antigenic peptides are presented to T lymphocytes. To migrate from peripheral tissue such as the epidermis to regional lymph nodes, Ag-bearing epidermal Langerhans cells must move through an extracellular matrix (ECM) of various compositions. The nature of their capacity to transmigrate via ECM is not well understood, although MIP-3beta and CCR7 play critical roles. We were interested in verifying whether heparanase, a heparan sulfate-degrading endo-beta-d-glucuronidase that participates in ECM degradation and remodeling, is expressed and functional in monocyte-derived DCs. Using immunohistochemistry, confocal microscopy, RT-PCR, Western blot analysis, assays for heparanase activity, and Matrigel transmigration, we show that heparanase is expressed in both nuclei and cytoplasm of immature DCs, and that gene expression and synthesis take place mainly in monocytes and early immature DCs. We also found that both nuclear and cytoplasm fractions show heparanase activity, and upon LPS-induced maturation, heparanase translocates to the cell surface and degrades ECM heparan sulfate. Matrigel transmigration assays showed a MIP-3beta-comparable role for heparanase. Because heparan sulfate glycosaminoglycans play a key role in the self-assembly, insolubility, and barrier properties of the ECM, the results of this study suggest that heparanase is a key enzyme in DC transmigration through the ECM.

Regulation, function and clinical significance of heparanase in cancer metastasis and angiogenesis

Heparanase is an endoglycosidase which cleaves heparan sulfate (HS) and hence participates in degradation and remodeling of the extracellular matrix (ECM). Heparanase is preferentially expressed in human tumors and its over-expression in tumor cells confers an invasive phenotype in experimental animals. The enzyme also releases angiogenic factors from the ECM and thereby induces an angiogenic response in vivo. Heparanase upregulation correlates with increased tumor vascularity and poor post-operative survival of cancer patients. Heparanase is synthesized as a 65 kDa inactive precursor that undergoes proteolytic cleavage, yielding 8 and 50 kDa protein subunits that heterodimerize to form an active enzyme. Human heparanase is localized primarily within late endosomes and lysosomes and occasionally on the cell surface and within the cell nucleus. Transcriptional activity of the heparanase promoter is stimulated by demethylation, early growth response 1 (EGR1) transcription factor, estrogen, inflammatory cytokines and inactivation of p53. N-acetylated glycol-split species of heparin as well as siRNA heparanase gene silencing inhibit tumor metastasis and angiogenesis in experimental models. These observations and the unexpected identification of a single functional heparanase, suggest that the enzyme is a promising target for anti-cancer and anti-inflammatory drug development. Heparanase exhibits also non-enzymatic activities, independent of its involvement in ECM degradation and changes in the extracellular microenvironment. For example, cell surface expression of heparanase elicits a firm cell adhesion, reflecting an involvement in cell-ECM interaction. Heparanase enhances Akt signaling and stimulates PI3K- and p38-dependent endothelial cell migration and invasion. It also promotes VEGF expression via the Src pathway. The enzyme may thus activate endothelial cells and elicits angiogenic and survival responses. Studies with heparanase over-expressing transgenic mice revealed that the enzyme functions in normal processes involving cell mobilization, HS turnover, tissue vascularization and remodeling. In this review, we summarize the current status of heparanase research, emphasizing molecular and cellular aspects of the enzyme, including its mode of processing and activation, control of heparanase gene expression, enzymatic and non-enzymatic functions, and causal involvement in cancer metastasis and angiogenesis. We also discuss clinical aspects and strategies for the development of heparanase inhibitors.

Characterization of mechanisms involved in secretion of active heparanase

Heparanase is an endo-beta-D-glucuronidase involved in extracellular matrix remodeling and degradation and implicated in tumor metastasis, angiogenesis, inflammation, and autoimmunity. The enzyme is synthesized as a latent 65-kDa protein and is processed in the lysosomal compartment to an active 58-kDa heterodimer, where it is stored in a stable form. In contrast, its heparan sulfate substrate is localized extracellularly, suggesting the existence of mechanisms that trigger heparanase secretion. Here we show that secretion of the active enzyme is mediated by the protein kinase A and C pathways. Moreover, secretion of active heparanase was observed upon cell stimulation with physiological concentrations of adenosine, ADP, and ATP, as well as by the noncleavable ATP analogue adenosine 5'-O-(thiotriphosphate). Indeed, heparanase secretion was noted upon cell stimulation with a specific P2Y1 receptor agonist and was inhibited by P2Y receptor antagonists. The kinetics of heparanase secretion resembled the secretion of cathepsin D, a lysosomal enzyme, indicating that the secreted heparanase is of lysosomal origin. We suggest that secretion of active heparanase is initiated by extracellular cues activating the protein kinase A and C signaling pathways. The secreted enzyme(s) then facilitate cell invasion associated with cancer metastasis, angiogenesis, and inflammation.

Impaired trafficking of choline transporter-like protein-1 at plasma membrane and inhibition of choline transport in THP-1 monocyte-derived macrophages

The present study investigates choline transport processes and regulation of choline transporter-like protein-1 (CTL1) in human THP-1 monocytic cells and phorbol myristate 13-acetate (PMA)-differentiated macrophages. Choline uptake is saturable and therefore protein-mediated in both cell types, but its transport characteristics change soon after treatments with PMA. The maximal rate of choline uptake intrinsic to monocytic cells is greatly diminished in differentiated macrophages as demonstrated by alterations in Vmax values from 1,973 ± 118 to 380 ± 18 nmol·mg−1·min−1, when the binding affinity did not change significantly ( Km values 56 ± 8 and 53 ± 6 μM, respectively). Treatments with hemicholinim-3 effectively inhibit most of the choline uptake, establishing that a choline-specific transport protein rather than a general transporter is responsible for the observed kinetic parameters. mRNA screening for the expression of various transporters reveals that CTL1 is the most plausible candidate that possesses the described kinetic and inhibitory properties. Fluorescence-activated cell sorting analyses at various times after PMA treatments further demonstrate that the disappearance of CTL1 protein from the cell surface follows the same trend as the reduction in choline uptake. Importantly, the loss of functional CTL1 from the cell surface occurs without significant changes in total CTL1 protein or its mRNA level indicating that an impaired CTL1 trafficking is the key contributing factor to the reduced choline uptake, subsequent to the PMA-induced THP-1 differentiation to macrophages.

An ELISA method for the detection and quantification of human heparanase

Heparanase is a mammalian endo-beta-D-glucuronidase that cleaves heparan sulfate side chains at a limited number of sites. Heparanase enzymatic activity is thought to participate in degradation and remodeling of the extracellular matrix and to facilitate cell invasion associated with tumor metastasis, angiogenesis, and inflammation. Traditionally, heparanase activity was well correlated with the metastatic potential of a large number of tumor-derived cell types. More recently, heparanase upregulation was detected in an increasing number of primary human tumors, correlating, in some cases, with poor postoperative survival and increased tumor vascularity. The present study was undertaken to develop a highly sensitive ELISA suitable for the determination and quantification of human heparanase in tissue extracts and body fluids. The assay preferentially detects the 8+50 kDa active heparanase heterodimer vs. the latent 65 kDa proenzyme and correlates with immunoblot analysis of heparanase containing samples. It detects heparanase at concentrations as low as 200 pg/ml and is suitable for quantification of heparanase in tissue extracts and urine.

Heparanase induces vascular endothelial growth factor expression: correlation with p38 phosphorylation levels and Src activation

Heparanase is an endo-beta-D-glucuronidase involved in cleavage of heparan sulfate moieties and hence participates in extracellular matrix (ECM) degradation and remodeling. Traditionally, heparanase activity was correlated with the metastatic potential of a variety of tumor-derived cell types. Cloning of the heparanase gene indicated that heparanase expression is up-regulated in a variety of primary human tumors. In some cases, heparanase up-regulation correlated with increased tumor vascularity, an angiogenic feature that could be recapitulated in a number of in vitro and in vivo models. The mechanism by which heparanase enhances angiogenic responses is not entirely clear but is thought to be mediated primarily by release of ECM-resident angiogenic growth factors such as basic fibroblast growth factor and vascular endothelial growth factor (VEGF). Here, we examined the possibility that heparanase directly participates in VEGF gene regulation. We provide evidence that heparanase overexpression in human embryonic kidney 293, MDA-MB-435 human breast carcinoma, and rat C6 glioma cells resulted in a 3- to 6-fold increase in VEGF protein and mRNA levels, which correlated with elevation of p38 phosphorylation. Moreover, heparanase down-regulation in B16 mouse melanoma cells by a specific siRNA vector was accompanied by a decrease in VEGF and p38 phosphorylation levels, suggesting that VEGF gene expression is regulated by endogenous heparanase. Interestingly, a specific p38 inhibitor did not attenuate VEGF up-regulation by heparanase whereas Src inhibitors completely abrogated this effect. These results indicate, for the first time, that heparanase is actively involved in the regulation of VEGF gene expression, mediated by activation of Src family members.

Mapping heparanase expression in the spinal cord of adult rats

This work addresses the cellular localization of heparanase and its colocalization with syndecan-3, a transmembrane heparan sulfate proteoglycan in spinal cords of adult rats. Reverse transcriptase/polymerase chain reaction (RT-PCR) and in situ hybridization for the heparanase transcript revealed expression in neurons and white matter glia. This was confirmed by immunohistochemistry showing cytoplasmic localization of the heparanase protein. Double immunofluorescence for heparanase and syndecan-3 revealed colocalization of the proteins in cell bodies of neurons and oligodendrocytes, suggestive of constitutive expression in these cell types. In contrast, only subpopulations of astrocytes and NG2-expressing glia in the white matter expressed heparanase, and these did not show expression of syndecan-3. Cultures of astrocytes further evidenced upregulation of heparanase expression with TGF-beta(1) treatment, but no accompanying upregulation of syndecan-3 was detectable. These first findings of heparanase expression in the adult cord therefore provide the cellular basis for understanding functional interactions of heparanase and syndecan-3 in the normal neural network or otherwise in glial reactions to spinal cord injury.

Glycosaminoglycans and their proteoglycans: host‐associated molecular patterns for initiation and modulation of inflammation

Glycosaminoglycans, linear carbohydrates such as heparan sulfate and hyaluronan, participate in a variety of biological processes including cell-matrix interactions and activation of chemokines, enzymes and growth factors. This review will discuss progress in immunology and the science of wound repair that has revealed the importance of glycosaminoglycans, and their proteoglycans, in the inflammatory process. Heparan sulfate enables growth factor function and modifies enzyme/inhibitor functions, such as antithrombin III and heparin cofactor II. Heparan sulfate also interacts with cytokines/chemokines and participates in leukocyte selectin binding to promote the recruitment of leukocytes. Chondroitin sulfate/dermatan sulfate regulates growth factor activity and is an alternate modulator of heparin cofactor II. In addition, dermatan sulfate induces ICAM-1 expression on endothelial cells and also recruits leukocytes via selectin interactions. Hyaluronan alternatively participates in leukocyte recruitment via interaction with CD44, while activating various inflammatory cells, such as macrophages, through CD44-dependent signaling. Hyaluronan also signals through Toll-like receptor 4 to induce dendritic cell maturation and promote cytokine release by dendritic cells and endothelial cells. Taken together, the field of glycosaminoglycan biology provides new clues and explanations of the process of inflammation and suggests new therapeutic approaches to human disease.

A defect in exodegradative pathways provides insight into endodegradation of heparan and dermatan sulfates

Within cells, dermatan sulfate (DS) and heparan sulfate (HS) are degraded in two steps. The initial endohydrolysis of these polysaccharides is followed by the sequential action of lysosomal exoenzymes to reduce the resulting oligosaccharides to monosaccharides and inorganic sulfate. Mucopolysaccharidosis (MPS) type II is a lysosomal storage disorder caused by a deficiency of the exoenzyme iduronate-2-sulfatase (I2S). Consequently, partially degraded fragments of DS and HS have been shown to accumulate in the lysosomes of affected cells and are excreted in the urine. Di- to hexadecasaccharides, isolated from the urine of a MPS II patient using anion exchange and gel filtration chromatography, were identified using electrospray ionization-tandem mass spectrometry (ESI-MS/MS). These oligosaccharides were shown to have non-reducing terminal iduronate-2-sulfate residues by digestion with recombinant I2S. A pattern of growing oligosaccharide chains composed of alternating uronic acid and N-acetylhexosamine residues was identified and suggested to originate from DS. A series of oligosaccharides consisting of hexosamine/N-acetylhexosamine alternating with uronic acid residues was also identified and on the basis of the presence of unacetylated hexosamine; these oligosaccharides are proposed to derive from HS. The presence of both odd and even-length oligosaccharides suggests both endo-beta-glucuronidase and endo-N-acetylhexosaminidase activities toward both glycosaminoglycans. Furthermore, the putative HS oligosaccharide structures identified indicate that heparanase activities are directed toward regions of both low and high sulfation, while the N-acetylhexosaminidase activity acted only in regions of low sulfation in this polysaccharide.

Cellular uptake of mammalian heparanase precursor involves low density lipoprotein receptor-related proteins, mannose 6-phosphate receptors, and heparan sulfate proteoglycans

Mammalian heparanase, strongly implicated in the regulation of cell growth, migration, and differentiation, plays a crucial role in inflammation, angiogenesis, and metastasis. There is thus a clear need for understanding how heparanase activity is regulated. Cells can generate an active form of the enzyme from a larger inactive precursor protein by a process of secretion-recapture, internalization, and proteolytic processing in late endosomes/lysosomes. Cell surface heparan sulfate proteoglycans are the sole known components with a role in this trafficking of the heparanase precursor. Here, we provide evidence that heparan sulfate proteoglycans are not strictly required for this process. More importantly, by heparanase transfection, binding, and uptake experiments and by using a combination of specific inhibitors and receptor-defective cells, we have identified low density lipoprotein receptor-related proteins and mannose 6-phosphate receptors as key elements of the receptor system that mediates the capture of secreted heparanase precursor and its trafficking to the intracellular site of processing/activation.

Heparanase processing by lysosomal/endosomal protein preparation

Heparanase is an endo-beta-glucuronodase involved in cleavage of heparan sulfate side chains, activity that is strongly implicated in cell dissemination associated with tumor metastasis and inflammation. Heparanase is first synthesized as a latent 65 kDa precursor that is converted into an active enzyme upon proteolytic processing. Previously, we have reported that elevation of the lysosomal pH results in complete inhibition of heparanase processing, suggesting that lysosomal protease(s) and acidic pH conditions are required for heparanase processing. Here, we adopted a cell fractionation approach and provide evidence that incubation of the pro-enzyme with lysosome/endosome, but not with cytoplasmic fractions resulted in processing and activation of the 65 kDa latent heparanase. Moreover, while the water soluble lysosome/endosome fraction exhibited no apparent processing activity, heparanase processing by the water insoluble lysosome/endosome membrane fraction was readily detected and exhibited the expected pH dependency.

Identification and characterization of heparin/heparan sulfate binding domains of the endoglycosidase heparanase

The endo-beta-glucuronidase, heparanase, is an enzyme that cleaves heparan sulfate at specific intra-chain sites, yielding heparan sulfate fragments with appreciable size and biological activities. Heparanase activity has been traditionally correlated with cell invasion associated with cancer metastasis, angiogenesis, and inflammation. In addition, heparanase up-regulation has been documented in a variety of primary human tumors, correlating with increased vascular density and poor postoperative survival, suggesting that heparanase may be considered as a target for anticancer drugs. In an attempt to identify the protein motif that would serve as a target for the development of heparanase inhibitors, we looked for protein domains that mediate the interaction of heparanase with its heparan sulfate substrate. We have identified three potential heparin binding domains and provided evidence that one of these is mapped at the N terminus of the 50-kDa active heparanase subunit. A peptide corresponding to this region (Lys(158)-Asp(171)) physically associates with heparin and heparan sulfate. Moreover, the peptide inhibited heparanase enzymatic activity in a dose-responsive manner, presumably through competition with the heparan sulfate substrate. Furthermore, antibodies directed to this region inhibited heparanase activity, and a deletion construct lacking this domain exhibited no enzymatic activity. NMR titration experiments confirmed residues Lys(158)-Asn(162) as amino acids that firmly bound heparin. Deletion of a second heparin binding domain sequence (Gln(270)-Lys(280)) yielded an inactive enzyme that failed to interact with cell surface heparan sulfate and hence accumulated in the culture medium of transfected HEK 293 cells to exceptionally high levels. The two heparin/heparan sulfate recognition domains are potentially attractive targets for the development of heparanase inhibitors.

Site-directed mutagenesis, proteolytic cleavage, and activation of human proheparanase

Heparanase is an endo-beta-D-glucuronidase that degrades heparan sulfate in the extracellular matrix and cell surfaces. Human proheparanase is produced as a latent 65-kDa polypeptide undergoing processing at two potential proteolytic cleavage sites, located at Glu109-Ser110 (site 1) and Gln157-Lys158 (site 2). Cleavage of proheparanase yields 8- and 50-kDa subunits that heterodimerize to form the active enzyme. The fate of the linker segment (Ser110-Gln157) residing between the two subunits, the mode of processing, and the protease(s) engaged in proheparanase processing are currently unknown. We applied multiple site-directed mutagenesis and deletions to study the nature of the potential cleavage sites and amino acids essential for processing of proheparanase in transfected human choriocarcinoma cells devoid of endogenous heparanase but possessing the enzymatic machinery for proper processing and activation of the proenzyme. Although mutagenesis at site 1 and its flanking sequences failed to identify critical residues for proteolytic cleavage, processing at site 2 required a bulky hydrophobic amino acid at position 156 (i.e. P2 of the cleavage site). Substitution of Tyr156 by Ala or Glu, but not Val, resulted in cleavage at an upstream site in the linker segment, yielding an improperly processed inactive enzyme. Processing of the latent 65-kDa proheparanase in transfected Jar cells was inhibited by a cell-permeable inhibitor of cathepsin L. Moreover, recombinant 65-kDa proheparanase was processed and activated by cathepsin L in a cell-free system. Altogether, these results suggest that proheparanase processing at site 2 is brought about by cathepsin L-like proteases. The involvement of other members of the cathepsin family with specificity to bulky hydrophobic residues cannot be excluded. Our results and a three-dimensional model of the enzyme are expected to accelerate the design of inhibitory molecules capable of suppressing heparanase-mediated enhancement of tumor angiogenesis and metastasis.