Immunoselection of GRP94/endoplasmin from a KNRK cell-specific lambda gt11 library using antibodies directed against a putative heparanase amino-terminal peptide

Heparanase: Historical Aspects and Future Perspectives

Heparanase is an endo-β-glucuronidase that cleaves at a limited number of internal sites the glycosaminoglycan heparan sulfate (HS). Heparanase enzymatic activity was first reported in 1975 and by 1983 evidence was beginning to emerge that the enzyme was a facilitator of tumor metastasis by cleaving HS chains present in blood vessel basement membranes and, thereby, aiding the passage of tumor cells through blood vessel walls. Due to a range of technical difficulties, it took another 16 years before heparanase was cloned and characterized in 1999 and a further 14 years before the crystal structure of the enzyme was solved. Despite these substantial deficiencies, there was steady progress in our understanding of heparanase long before the enzyme was fully characterized. For example, it was found as early as 1984 that activated T cells upregulate heparanase expression, like metastatic tumor cells, and the enzyme aids the entry of T cells and other leukocytes into inflammatory sites. Furthermore, it was discovered in 1989 that heparanase releases pre-existing growth factors and cytokines associated with HS in the extracellular matrix (ECM), the liberated growth factors/cytokines enhancing angiogenesis and wound healing. There were also the first hints that heparanase may have functions other than enzymatic activity, in 1995 it being reported that under certain conditions the enzyme could act as a cell adhesion molecule. Also, in the same year PI-88 (Muparfostat), the first heparanase inhibitor to reach and successfully complete a Phase III clinical trial was patented.Nevertheless, the cloning of heparanase (also known as heparanase-1) in 1999 gave the field an enormous boost and some surprises. The biggest surprise was that there is only one heparanase encoding gene in the mammalian genome, despite earlier research, based on substrate specificity, suggesting that there are at least three different heparanases. This surprising conclusion has remained unchanged for the last 20 years. It also became evident that heparanase is a family 79 glycoside hydrolase that is initially produced as a pro-enzyme that needs to be processed by proteases to form an enzymatically active heterodimer. A related molecule, heparanase-2, was also discovered that is enzymatically inactive but, remarkably, recently has been shown to inhibit heparanase-1 activity as well as acting as a tumor suppressor that counteracts many of the pro-tumor properties of heparanase-1.The early claim that heparanase plays a key role in tumor metastasis, angiogenesis and inflammation has been confirmed by many studies over the last 20 years. In fact, heparanase expression is enhanced in all major cancer types, namely carcinomas, sarcomas, and hematological malignancies, and correlates with increased metastasis and poor prognosis. Also, there is mounting evidence that heparanase plays a central role in the induction of inflammation-associated cancers. The enzymatic activity of heparanase has also emerged in unexpected situations, such as in the spread of HS-binding viruses and in Type-1 diabetes where the destruction of intracellular HS in pancreatic insulin-producing beta cells precipitates diabetes. But the most extraordinary recent discoveries have been with the realization that heparanase can exert a range of biological activities that are independent of its enzymatic function, most notably activation of several signaling pathways and being a transcription factor that controls methylation of histone tails. Collectively, these data indicate that heparanase is a truly multifunctional protein that has the additional property of cleaving HS chains and releasing from ECM and cell surfaces hundreds of HS-binding proteins with a plethora of functional consequences. Clearly, there are many unique features of this intriguing molecule that still remain to be explored and are highlighted in this Chapter.

The Development of Assays for Heparanase Enzymatic Activity: Towards a Gold Standard

The enzyme heparanase, an endo-β-glucuronidase, degrades heparan sulfate (HS) chains on the cell surface and in the extracellular matrix. Heparanase regulates numerous biological processes that drive tumour growth, metastasis and angiogenesis. In addition to its key role in cancer progression, it has also been implicated in an ever-growing number of other diseases, particularly those associated with inflammation. The importance of heparanase in biology has led to numerous efforts over the years to develop assays to monitor its activity and to screen for new inhibitors as potential drug candidates. Despite these efforts and the commercialization of a few kits, most heparanase assays are still complex, labour intensive, costly or have limited application. Herein we review the various methods for assaying heparanase enzymatic activity, focusing on recent developments towards new assays that hold the promise of accelerating research into this important enzyme.

Oligomannurarate sulfate, a novel heparanase inhibitor simultaneously targeting basic fibroblast growth factor, combats tumor angiogenesis and metastasis

Inhibitors of tumor angiogenesis and metastasis are increasingly emerging as promising agents for cancer therapy. Recently, heparanase inhibitors have offered a new avenue for such work because heparanase is thought to be critically involved in the metastatic and angiogenic potentials of tumor cells. Here, we report that oligomannurarate sulfate (JG3), a novel marine-derived oligosaccharide, acts as a heparanase inhibitor. Our results revealed that JG3 significantly inhibited tumor angiogenesis and metastasis, both in vitro and in vivo, by combating heparanase activity via binding to the KKDC and QPLK domains of the heparanase molecule. The JG3-heparanase interaction was competitively inhibited by low molecular weight heparin (4,000 Da) but not by other glycosaminoglycans. In addition, JG3 abolished heparanase-driven invasion, inhibited the release of heparan sulfate-sequestered basic fibroblast growth factor (bFGF) from the extracellular matrix, and repressed subsequent angiogenesis. Moreover, JG3 inactivated bFGF-induced bFGF receptor and extracellular signal-regulated kinase 1/2 phosphorylation and blocked bFGF-triggered angiogenic events by directly binding to bFGF. Thus, JG3 seems to inhibit both major heparanase activities by simultaneously acting as a substrate mimetic and as a competitive inhibitor of heparan sulfate. These findings suggest that JG3 should be considered as a promising candidate agent for cancer therapy.

Novel heparan sulfate mimetic compounds as antitumor agents

Heparan sulfate glycosaminoglycans (HSGAGs) are involved in tumor cell growth, adhesion, invasion, and migration, due to their interactions with various proteins. In this study, novel HSGAG-mimetic compounds (KI compounds) were designed and synthesized. As a result of cell-based assays, KI-105 was found to exert potent inhibitory activities against migration and invasion of human fibrosarcoma HT1080 cells. The present results indicate that a novel invasion/migration inhibitor, KI-105, can increase the adherence of HT1080 cells. It was conceivable that this cellular effect was caused by an increase in the amount of cell-surface HSGAGs and focal adhesions. Although further investigations are needed to decipher the molecular mechanism of KI-105, it is suggested that heparanase and Cdc42 are involved in its biological effects.

Structure-based design of a selective heparanase inhibitor as an antimetastatic agent

Heparanase is an endo-β-d-glucuronidase that degrades heparan sulfate glycosaminoglycans in the extracellular matrix and the basement membrane and is well known to be involved in tumor cell invasion and angiogenesis. We have focused on heparanase as a target for antitumor agents, especially antimetastatic agents. (R)-3-hexadecanoyl-5-hydroxymethyltetronic acid (RK-682) was found to display an inhibitory activity against heparanase in our screening of natural sources. Because RK-682 has been reported to show inhibitory activities against several enzymes, we have tried to develop selective heparanase inhibitors using the method of rational drug design. Based on the structure of the heparanase/RK-682 complex, we speculated that selective inhibitory activity against heparanase could be acquired by arylalkylation, namely, by benzylation of the 4-position of RK-682. Among the rationally designed 4-alkyl-RK-682 derivatives, 4-benzyl-RK-682 has been found to possess a selective inhibitory activity for heparanase (IC50 for heparanase, 17 μmol/L; IC50 for other enzymes, >100 μmol/L). 4-Benzyl-RK-682 also inhibited the invasion and migration of human fibrosarcoma HT1080 cells (IC50 for invasion, 1.5 μmol/L; IC50 for migration, 3.0 μmol/L). On the other hand, RK-682 had no inhibitory effect on the invasion and migration of HT1080 cells at doses of up to 100 μmol/L.

Secretion of Heparanase Protein Is Regulated by Glycosylation in Human Tumor Cell Lines

The endo-beta-d-glucuronidase, heparanase, is capable of specifically degrading heparan sulfate, and this activity is associated with the metastatic potential of tumor cells. The predicted amino acid sequence of heparanase includes six putative N-glycosylation sites; however, the precise biochemical role of glycosylated heparanase remains unknown. In this study, we examined the link between glycosylation and the function of heparanase in human tumor cell lines. Heparanase protein was glycosylated at six Asn residues in human tumor cell lines. Treatment with a glycosylation inhibitor demonstrated that glycosylation was not required for the activity of heparanase. However, glycosylation affected the kinetics of endoplasmic reticulum-to-Golgi transport and of secretion of the enzyme.

Dietary vitamin E affects neutrophil distribution and genetic instability in murine Mutatect tumors

Vitamin E is best known for its ability to scavenge reactive oxygen and nitrogen species. Solid tumors are frequently infiltrated with leukocytes, a potential source of these reactive species. The Mutatect tumor model is a fibrosarcoma that can be grown subcutaneously in syngeneic C57BL/6 mice. We previously showed that these tumors are infiltrated with neutrophils and that the number of neutrophils correlates with the number of hypoxanthine phosphoribosyl transferase (hprt) mutations and loss of an interleukin-8 (IL-8) transgene. Neutrophils are a source of nitric oxide, and tumors contain nitrotyrosine, a marker of damage by nitric oxide-related species. We also showed previously that dietary vitamin E supplements markedly lower the frequency of hprt mutants and the level of myeloperoxidase (a neutrophil marker) in a tumor fraction containing "loosely bound" cells. In the present report, we examine the effect of dietary vitamin E in greater detail. No effect on inducible nitric oxide synthase expression or nitrotyrosine levels was observed. However, dietary vitamin E induced a major redistribution of neutrophils from the loosely bound cellular fraction to the "stromal" fraction, while the total number of neutrophils in tumors was essentially unchanged. The loss of the IL-8 transgene seen earlier in Mutatect tumors was largely prevented. Vitamin E also prevented the large increase in hprt mutants (in the cellular and stromal fractions). Thus vitamin E appears to be protective against genotoxicity by scavenging reactive species, but also its ability to affect the distribution of neutrophils within tumors may be important.

Constitutive expression of interleukin-8 by Mutatect cells markedly affects their tumor biology

Interleukin-8 (IL-8) is a chemokine for neutrophils and an angiogenic factor. Human tumors that express IL-8 may exhibit intense neutrophil infiltration and increased vascularization. Mutatect cells are a murine fibrosarcoma that can be grown as subcutaneous tumors in syngeneic C57BL/6 mice. Since neutrophils are a source of cytotoxic and genotoxic species, we constructed Mutatect cell lines that constitutively express human IL-8 to explore the involvement of neutrophils in tumor biology and genetic instability. An IL-8/neo expression plasmid was stably transfected into Mutatect MC17-51 cells and clone MIL-4 was isolated. Tumors initiated with 5x10(5) MIL-4 cells grew very slowly compared with tumors from pure MC17-51 cells or from 0.5 to 4x10(5) MIL-4 cells mixed with 5x10(5) MC17-51 cells. Over 95% of cells recovered from slow-growing pure MIL-4 tumors lost the transgene as measured by loss of (i) resistance to G418, (ii) expression of IL-8 protein and (iii) IL-8-specific DNA sequences. When tumors from mixed cell types were examined, loss of the transgene did not occur; rather, IL-8 producing cells appeared to have some growth advantage. The neutrophil content of tumors (as measured by myeloperoxidase) was directly proportional to the level of IL-8 expressed at the time tumors were excised. As reported earlier, the frequency of mutations at the hypoxanthine phosphoribosyltransferase locus was also directly proportional to neutrophil content. To explain some of these biological findings, we postulate that early in development of pure MIL-4 tumors, genotoxic/cytotoxic neutrophils are attracted by IL-8, which in turn leads to loss of the transgene and to localized cytotoxicity of IL-8 producing cells. In mixed tumors, where the initial IL-8 concentration may be lower, tumors might become established more readily because fewer neutrophils may be attracted. This relatively simple experimental paradigm has revealed some of the complex biological changes that can occur as a result of IL-8 in tumors.

Heparan sulfate, heparin, and heparinase activity detection on polyacrylamide gel electrophoresis using the fluorochrome tris(2,2'-bipyridine) ruthenium (II)

The paper shows the ability of the fluorochrome tris(2,2'-bipyridine) ruthenium (II) (Rubipy) to detect heparan sulfate, heparin, and heparinase activity of M3 murine mammary adenocarcinoma cells as well as bacterial heparinases I, II, and III in native polyacrylamide gel electrophoresis (PAGE). The technique is based on the electrophoretic mobility of high molecular weight heparins and subsequent staining with Rubipy (50 micrograms/mL). The minimum content of heparin detected by fluorescence in a UV transilluminator was 25-50 ng. The number of Rubipy molecules bound to heparin, determined in relationship to the number of disaccharide units (DU), showed that two to six heparin disaccharide units are bound by each fluorochrome molecule. Scatchard plot analysis showed one Rubipy-binding site (Kd = (8.56 +/- 2.97) x 10(-5) M). Heparinase activity was determined by densitometric analysis of the fluorescence intensity of the heparin-containing band of the gel. While heparinase I (EC 4.2.2.7.) degraded heparin and, to a lower degree, partially N-desulfated N-acetylated heparin (N-des N-Ac), heparinase II (no EC number) could efficiently degrade heparan sulfate (HS) and partially N-des N-Ac heparin. Finally, heparinase III (EC 4.2.2.8.) degraded HS almost exclusively. Only heparin and N-des N-Ac heparin were substrates for M3 tumor cell heparinases. We describe a qualitative, sensitive and simple method to detect heparinase activity and determine its substrate specificity using Rubipy fluorescence with heparin and heparan sulfate in multiple biological samples tested in parallel.

Expression of interleukin-8 promotes neutrophil infiltration and genetic instability in mutatect tumors

Neutrophils represent a potential source of genotoxic reactive oxygen and nitrogen species in the tumor microenvironment. Using Mutatect cell lines, which can form subcutaneous tumors in syngeneic C57BL/6 mice, we have previously established that the number of spontaneously infiltrating neutrophils correlates with the number of mutations at the hypoxanthine phosphoribosyltransferase (Hprt) locus. We now describe the properties of four lines that express different levels of the neutrophil chemokine, interleukin-8 (IL-8), from a tetracycline (TET)-responsive promoter. In a series involving 45 animals, IL-8-expressing lines produced tumors with a higher neutrophil content than the control line. Analysis of the 45 tumors revealed that the neutrophil level again strongly correlated with hprt mutant frequency (MF) (P<.0001, r=0.88). Administration of TET was effective in lowering the neutrophil content of low IL-8-expressing tumors, but not high IL-8-expressing tumors. Although the IL-8 transgene was stable in all lines in vitro, high IL-8-expressing lines completely lost the transgene in vivo whereas low IL-8-expressing lines showed no evidence of transgene instability. These results provide further evidence, based on the study of an endogenous gene (hprt) and an IL-8 transgene, that neutrophils may contribute to genetic instability in tumors.

Characterization of a polyclonal antibody to human thymidylate synthase suitable for the study of colorectal cancer specimens

Measurement of thymidylate synthase (hTS) using immunohistochemical techniques has been reported in several clinical studies. However, its value as a prognostic indicator is still not clear. To pursue this, we have developed a new rabbit polyclonal antibody, hTS7.4. The antigen was recombinant hTS containing an N-terminal His(6)-tag. Antiserum hTS7.4 detected recombinant hTS by ELISA at a titer of 1:100,000. Western blot analysis of several human cell lines showed a single band of the expected 36-kD molecular size. HeLa cells treated with the TS inhibitor 5-FUdR showed the expected additional band corresponding to the ternary complex of hTS-dFUMP-reduced folate. hTS7.4 detected TS in bacterial, rat, mouse, and monkey cell extracts, and hTS8.3 (a closely related antiserum) immunoprecipitated a 36-kD [(35)S]-methionine-labeled protein from HeLa extracts. TS was detectable by indirect immunofluorescence in HeLa cells. Proliferating normal human fibroblasts in culture showed staining, but nonproliferating cells did not. Lymphocytes in the germinal center of human tonsil tissue, which are known to be proliferating, stained with hTS7.4 and also with monoclonal antibody TS106. TS may therefore be useful as an immunohistochemical marker of cell proliferation. Normal colon mucosa showed weak staining, whereas some colorectal cancer specimens stained very strongly with hTS7.4. A clinical study of colorectal cancer using this antibody is in progress. (J Histochem Cytochem 47:1563-1573, 1999)

A myeloperoxidase-specific assay based upon bromide-dependent chemiluminescence of luminol

Measurement of myeloperoxidase (MPO; EC 1.11.1.7) activity is often used as a marker of neutrophil infiltration into tissues. However, most enzymatic assays for MPO are susceptible to interference from other peroxidases (including eosinophil peroxidase, EPX) and hemoproteins (such as hemoglobin and myoglobin) present in the tissues. In this report, we describe a bromide-dependent chemiluminescence (Br-CL) assay that uses luminol as a chemiluminescence probe. The assay can distinguish between MPO and nonspecific peroxidase reactions. The MPO-specific reaction is believed to proceed in two steps: (i) the enzymatic generation of hypobromous acid (HOBr) from KBr and H(2)O(2) at pH 5 and (ii) the spontaneous reaction of HOBr and H(2)O(2) with luminol to give a Br-CL signal. The assay is sufficiently sensitive to allow detection of MPO in <100 human neutrophils. Other peroxidases and hemoproteins do not interfere with the Br-CL signal. Although EPX can also oxidize bromide to generate HOBr, activities of MPO and EPX can be distinguished at different pHs. As a demonstration of the utility of the Br-CL assay, MPO activity was measured in murine tumors known to be infiltrated with neutrophils. A statistically significant correlation was seen between MPO activity and histological neutrophil counts in the tumors (r = 0.69, P < 0.01, n = 14). The assay should have wide application for measuring the neutrophil content of tissues.

Cloning of mammalian heparanase, an important enzyme in tumor invasion and metastasis

The endoglycosidase heparanase is an important in the degradation of the extracellular matrix by invading cells, notably metastatic tumor cells and migrating leukocytes. Here we report the cDNA sequence of the human platelet enzyme, which encodes a unique protein of 543 amino acids, and the identification of highly homologous sequences in activated mouse T cells and in a highly metastatic rat adenocarcinoma. Furthermore, the expression of heparanase mRNA in rat tumor cells correlates with their metastatic potential. Exhaustive studies have shown only one heparanase sequence, consistent with the idea that this enzyme is the dominant endoglucuronidase in mammalian tissues.

Mammalian heparanase: gene cloning, expression and function in tumor progression and metastasis

Heparan sulfate proteoglycans interact with many extracellular matrix constituents, growth factors and enzymes. Degradation of heparan sulfate by endoglycosidic heparanase cleavage affects a variety of biological processes. We have purified a 50-kDa heparanase from human hepatoma and placenta, and now report cloning of the cDNA and gene encoding this enzyme. Expression of the cloned cDNA in insect and mammalian cells yielded 65-kDa and 50-kDa recombinant heparanase proteins. The 50-kDa enzyme represents an N-terminally processed enzyme, at least 100-fold more active than the 65-kDa form. The heparanase mRNA and protein are preferentially expressed in metastatic cell lines and specimens of human breast, colon and liver carcinomas. Low metastatic murine T-lymphoma and melanoma cells transfected with the heparanase cDNA acquired a highly metastatic phenotype in vivo, reflected by a massive liver and lung colonization. This represents the first cloned mammalian heparanase, to our knowledge, and provides direct evidence for its role in tumor metastasis. Cloning of the heparanase gene enables the development of specific molecular probes for early detection and treatment of cancer metastasis and autoimmune disorders.

The 90-kDa molecular chaperone family: structure, function, and clinical applications. A comprehensive review

The 90-kDa molecular chaperone family (which comprises, among other proteins, the 90-kDa heat-shock protein, hsp90 and the 94-kDa glucose-regulated protein, grp94, major molecular chaperones of the cytosol and of the endoplasmic reticulum, respectively) has become an increasingly active subject of research in the past couple of years. These ubiquitous, well-conserved proteins account for 1-2% of all cellular proteins in most cells. However, their precise function is still far from being elucidated. Their involvement in the aetiology of several autoimmune diseases, in various infections, in recognition of malignant cells, and in antigen-presentation already demonstrates the essential role they likely will play in clinical practice of the next decade. The present review summarizes our current knowledge about the cellular functions, expression, and clinical implications of the 90-kDa molecular chaperone family and some approaches for future research.

Molecular chaperones in the etiology and therapy of cancer

Molecular chaperones are ubiquitous, well-conserved proteins that account for 2-5 % of all cellular proteins in most cells. The present review summarizes our current knowledge about their involvement in the etiology and therapy of cancer with special emphasis on the expression of chaperones in malignant cells, their role in folding of (proto)oncogene products, cell cycle regulation, cell differentiation and apoptosis, development of metastasis, and their participation in the recognition of malignant cells. We also overview the importance of chaperones in hyperthermia, drug resistance, and recent approaches in chaperone-immunotherapy.

CXC chemokines connective tissue activating peptide-III and neutrophil activating peptide-2 are heparin/heparan sulfate-degrading enzymes

Heparan sulfate proteoglycans at cell surfaces or in extracellular matrices bind diverse molecules, including growth factors and cytokines, and it is believed that the activities of these molecules may be regulated by the metabolism of heparan sulfate. In this study, purification of a heparan sulfate-degrading enzyme from human platelets led to the discovery that the enzymatic activity residues in at least two members of the platelet basic protein (PBP) family known as connective tissue activating peptide-III (CTAP-III) and neutrophil activating peptide-2. PBP and its N-truncated derivatives, CTAP-III and neutrophil activating peptide-2, are CXC chemokines, a group of molecules involved in inflammation and wound healing. SDS-polyacrylamide gel electrophoresis analysis of the purified heparanase resulted in a single broad band at 8-10 kDa, the known molecular weight of PBP and its truncated derivatives. Gel filtration chromatography of heparanase resulted in peaks of activity corresponding to monomers, dimers, and tetramers; these higher order aggregates are known to form among the chemokines. N-terminal sequence analysis of the same preparation indicated that only PBP and truncated derivatives were present, and commercial CTAP-III from three suppliers had heparanase activity. Antisera produced in animals immunized with a C-terminal synthetic peptide of PBP inhibited heparanase activity by 95%, compared with activity of the purified enzyme in the presence of the preimmune sera. The synthetic peptide also inhibited heparanase by 95% at 250 microM, compared to the 33% inhibition of heparanase activity by two other peptides. The enzyme was determined to be an endoglucosaminidase, and it degraded both heparin and heparan sulfate with optimal activity at pH 5.8. Chromatofocusing of the purified heparanase resulted in two protein peaks: an inactive peak at pI7.3, and an active peak at pI 4.8-5.1. Sequence analysis showed that the two peaks contained identical protein, suggesting that a post-translational modification activates the enzyme.