The spacing of S-domains on HS glycosaminoglycans determines whether the chain is a substrate for intracellular heparanases

State-of-the-art glycosaminoglycan characterization

Glycosaminoglycans (GAGs) are heterogeneous acidic polysaccharides involved in a range of biological functions. They have a significant influence on the regulation of cellular processes and the development of various diseases and infections. To fully understand the functional roles that GAGs play in mammalian systems, including disease processes, it is essential to understand their structural features. Despite having a linear structure and a repetitive disaccharide backbone, their structural analysis is challenging and requires elaborate preparative and analytical techniques. In particular, the extent to which GAGs are sulfated, as well as variation in sulfate position across the entire oligosaccharide or on individual monosaccharides, represents a major obstacle. Here, we summarize the current state-of-the-art methodologies used for GAG sample preparation and analysis, discussing in detail liquid chromatograpy and mass spectrometry-based approaches, including advanced ion activation methods, ion mobility separations and infrared action spectroscopy of mass-selected species.

Enrichment of Two Isomeric Heparin Oligosaccharides Exhibiting Different Affinities toward Monocyte Chemoattractant Protein-1

Chemokine-GAG interactions are crucial to facilitate chemokine immobilization, resulting in the formation of chemokine gradients that guide cell migration. Here we demonstrate chromatographic isolation and purification of two heparin hexasaccharide isomers that interact with the oligomeric chemokine Monocyte Chemoattractant Protein-1 (MCP-1)/CCL2 with different binding affinities. The sequences of these two hexasaccharides were deduced from unique MS/MS product ions and HPLC compositional analysis. Ion mobility mass spectrometry (IM-MS) showed that the two isolated oligosaccharides have different conformations and both displayed preferential binding for one of the two distinct conformations known for MCP-1 dimers. A significant shift in arrival time distribution of close to 70 Ų was observed, indicating a more compact protein:hexasaccharide conformation. Clear differences in the MS spectra between bound and unbound protein allowed calculation of K_d values from the resulting data. The structural difference between the two hexasaccharides was defined as the differential location of a single sulfate at either C-6 of glucosamine or C-2 of uronic acid in the reducing disaccharide, resulting in a 200-fold difference in binding affinity for MCP-1. These data indicate sequence specificity for high affinity binding, supporting the view that sulfate position, and not simply the number of sulfates, is important for heparan sulfate protein binding.

Pharmacology of Heparin and Related Drugs

Heparin has been recognized as a valuable anticoagulant and antithrombotic for several decades and is still widely used in clinical practice for a variety of indications. The anticoagulant activity of heparin is mainly attributable to the action of a specific pentasaccharide sequence that acts in concert with antithrombin, a plasma coagulation factor inhibitor. This observation has led to the development of synthetic heparin mimetics for clinical use. However, it is increasingly recognized that heparin has many other pharmacological properties, including but not limited to antiviral, anti-inflammatory, and antimetastatic actions. Many of these activities are independent of its anticoagulant activity, although the mechanisms of these other activities are currently less well defined. Nonetheless, heparin is being exploited for clinical uses beyond anticoagulation and developed for a wide range of clinical disorders. This article provides a "state of the art" review of our current understanding of the pharmacology of heparin and related drugs and an overview of the status of development of such drugs.

Glycosaminoglycans affect heparanase location in CHO cell lines

Glycosaminoglycans (GAG) play a ubiquitous role in tissues and cells. In eukaryotic cells, heparan sulfate (HS) is initially degraded by an endo-β-glucuronidase called heparanase-1 (HPSE). HS oligosaccharides generated by the action of HPSE intensify the activity of signaling molecules, activating inflammatory response, tumor metastasis, and angiogenesis. The aim of the present study was to understand if sulfated GAG could modulate HPSE, since the mechanisms that regulate HPSE have not been completely defined. CHO-K1 cells were treated with 4-methylumbelliferone (4-MU) and sodium chlorate, to promote total inhibition of GAG synthesis, and reduce the sulfation pattern, respectively. The GAG profile of the wild CHO-K1 cells and CHO-745, deficient in xylosyltransferase, was determined after [(35)S]-sulfate labeling. HPSE expression was determined via real-time quantitative polymerase chain reaction. Total ablation of GAG with 4-MU in CHO-K1 inhibited HPSE expression, while the lack of sulfation had no effect. Interestingly, 4-MU had no effect in CHO-745 cells for these assays. In addition, a different enzyme location was observed in CHO-K1 wild-type cells, which presents HPSE mainly in the extracellular matrix, in comparison with the CHO-745 mutant cells, which is found in the cytoplasm. In view of our results, we can conclude that GAG are essential modulators of HPSE expression and location. Therefore, GAG profile could impact cell behavior mediated by the regulation of HPSE.

Composition, sequencing and ion mobility mass spectrometry of heparan sulfate-like octasaccharide isomers differing in glucuronic and iduronic acid content

Here we report ion mobility mass spectrometry (IMMS) separation and tandem mass spectrometry (MS(2)) sequencing methods used to analyze and differentiate six synthetically produced heparin/heparan sulfate (HS)-like octasaccharide (dp8) isomeric structures. These structures are isomeric with regard to either glucuronic acid (GlcA) or iduronic acid (IdoA) residues at various positions. IMMS analysis showed that a fully GlcA structure exhibited a more compact conformation, whereas the fully IdoA structure was more extended. Interestingly, the change from IdoA to GlcA in specific locations resulted in strong conformational distortions. MS(2) of the six isomers showed very different spectra with unique sets of diagnostic product ions. Analysis of MS(2) product ion spectra suggests that the GlcA group correlated with the formation of a glycosidic product ion under lower energy conditions. This resulted in an earlier product ion formation and more intense product ions. Importantly, this knowledge enabled a complete sequencing of the positions of GlcA and IdoA in each of the four positions located in each unique dp8 structure.

The effect of proteoglycans inhibited by RNA interference on metastatic characters of human salivary adenoid cystic carcinoma

BACKGROUND

Salivary adenoid cystic carcinoma (SACC) is one of the most common malignancies of salivary gland. Recurrence or/and early metastasis is its biological properties. In SACC, neoplastic myoepithelial cells secrete proteoglycans unconventionally full of the cribriform or tubular and glandular structures of SACC. Literatures have demonstrated that extracellular matrix provided an essential microenvironment for the biological behavior of SACC. However, there is rare study of the effect of proteoglycans on the potential metastasis of SACC.In this study, human xylosyltransferase-I (XTLY-I) gene, which catalyzes the rate-limited step of proteoglycans biosynthesis, was knocked down by RNA interference (RNAi) to inhibit the proteoglycans biosynthesis in SACC cell line with high tendency of lung metastasis (SACC-M). The impact of down-regulated proteoglycans on the metastasis characters of SACC-M cells was analyzed and discussed. This research could provide a new idea for the clinical treatment of SACC.

METHODS

The eukaryotic expression vector of short hairpin RNA (shRNA) targeting XTLY-I gene was constructed and transfected into SACC-M cells. A stably transfectant cell line named SACC-M-WJ4 was isolated. The XTLY-I expression was measured by real-time PCR and Western blot; the reduction of proteoglycans was measured. The invasion and metastasis of SACC-M-WJ4 cells were detected; the effect of down-regulated proteoglycans on the potential lung metastasis of nude mice was observed, respectively.

RESULTS

The shRNA plasmid targeting XTLY-I gene showed powerful efficiency of RNAi. The mRNA level of target gene decreased by 86.81%, the protein level was decreased by 80.10%, respectively. The silence of XTLY-I gene resulted in the reduction of proteoglycans significantly in SACC-M-WJ4 cells. The inhibitory rate of proteoglycans was 58.17% (24 h), 66.06% (48 h), 57.91% (72 h), 59.36% (96 h), and 55.65% (120 h), respectively. The reduction of proteoglycans suppressed the adhesion, invasion and metastasis properties of SACC-M cells, and decreased the lung metastasis of SACC-M cells markedly either.

CONCLUSION

The data suggested that the silence of XTLY-I gene in SACC-M cells could suppress proteoglycans biosynthesis and secretion significantly. The reduction of proteoglycans inhibited cell adhesion, invasion and metastasis of SACC-M cells. There is a close relationship between proteoglycans and the biological behavior of SACC.

The heparan sulfate proteoglycan (HSPG) glypican-3 mediates commitment of MC3T3-E1 cells toward osteogenesis

Heparan sulfate (HS) sugar chains attached to core proteoglycans (PGs) termed HSPGs mediate an extensive range of cell-extracellular matrix (ECM) and growth factor interactions based upon their sulfation patterns. When compared with non-osteogenic (maintenance media) culture conditions, under established osteogenic culture conditions, MC3T3-E1 cells characteristically increase their osteogenic gene expression profile and switch their dominant fibroblast growth factor receptor (FGFR) from FGFR1 (0.5-fold decrease) to FGFR3 (1.5-fold increase). The change in FGFR expression profile of the osteogenic-committed cultures was reflected by their inability to sustain an FGF-2 stimulus, but respond to BMP-2 at day 14 of culture. The osteogenic cultures decreased their chondroitin and dermatan sulfate PGs (biglycan, decorin, and versican), but increased levels of the HS core protein gene expression, in particular glypican-3. Commitment and progress through osteogenesis is accompanied by changes in FGFR expression, decreased GAG initiation but increased N- and O-sulfation and reduced remodeling of the ECM (decreased heparanase expression) resulting in the production of homogenous (21 kDa) HS chain. With the HSPG glypican-3 expression strongly upregulated in these processes, siRNA was used to knockdown this gene to examine the effect on osteogenic commitment. Reduced glypican-3 abrogated the expression of Runx2, and thus differentiation. The reintroduction of this HSPG into Runx2-null cells allowed osteogenesis to proceed. These results demonstrate the dependence of osteogenesis on specific HS chains, in particular those associated with glypican-3.

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.

Structural recognition by recombinant human heparanase that plays critical roles in tumor metastasis. Hierarchical sulfate groups with different effects and the essential target disulfated trisaccharide sequence

Human heparanase is an endo-beta-d-glucuronidase that degrades heparan sulfate/heparin and has been implicated in a variety of biological processes, such as inflammation, tumor angiogenesis, and metastasis. Although the cloned enzyme has been demonstrated to have a critical role in tumor metastasis, the substrate specificity has been poorly understood. In the present study, the specificity of the purified recombinant human heparanase was investigated for the first time using a series of structurally defined oligosaccharides isolated from heparin/heparan sulfate. The best substrates were deltaHexUA(+/-2S)-GlcN(NS,6S)-GlcUA-GlcN(NS,6S)-GlcUA-GlcN(NS,6S) and deltaHexUA(2S)-GlcN(NS,6S)-GlcUA-GlcN(NS,6S) (where deltaHexUA, GlcN, GlcUA, NS, 2S, and 6S represent unsaturated hexuronic acid, d-glucosamine, d-glucuronic acid, 2-N-sulfate, 2-O-sulfate, and 6-O-disulfate, respectively). Based on the percentage conversion of the substrates to products under identical assay conditions, several aspects of the recognition structures were revealed. 1) The minimum recognition backbone is the trisaccharide GlcN-GlcUA-GlcN. 2) The target GlcUA residues are in the sulfated region. 3) The -GlcN(6S)-GlcUA-GlcN(NS)- sequence is essential but not sufficient as the cleavage site. 4) The IdoUA(2S) residue, located two saccharides away from the target GlcUA residue, claimed previously to be essential, is not indispensable. 5) The 3-O-sulfate group on the GlcN is dispensable and even has an inhibitory effect when located in a highly sulfated region. 6) Based on these and previous results, HexUA(2S)-GlcN(NS,6S)-IdoUA-GlcNAc(6S)-GlcUA-GlcN(NS,+/-6S)-IdoUA(2S)-GlcN(NS,6S) (where HexUA represents hexuronic acid) has been proposed as a probable physiological target octasaccharide sequence. These findings will aid establishing a quantitative assay method using the above tetrasaccharide and designing heparan sulfate-based specific inhibitors of the heparanase for new therapeutic strategies.

Characterization of a novel intracellular heparanase that has a FERM domain

The catabolism of cell-surface heparan sulphate proteoglycans is initiated by endosomal heparanases, which are endoglycosidases that cleave the glycosaminoglycans off core proteins and degrade them to shorter oligosaccharides. We have purified previously four intracellular heparanase activities from Chinese hamster ovary (CHO) cells [Bame, Hassall, Sanderson, Venkatesan and Sun (1998) Biochem. J. 336, 191-200], and in the present study we characterize further the most abundant activity (C1A heparanase). This enzyme purifies as a family of 37-48 kDa proteins from both CHO cells and the rat liver, with the major species being 37 and 40 kDa. Amino acid sequence analysis shows the purified C1A heparanase protein is highly homologous with the N-terminal domain, or FERM domain, of the approximately 80 kDa proteins ezrin, radixin and moesin (ERM proteins, after ezrin-radixin-moesin). This domain, which is also found in erythrocyte protein 4.1, links cytoplasmic proteins to membranes. Antibodies against the FERM domain recognize all the C1A heparanase proteins on Western blots, suggesting that the smaller species are derived from a larger protein. Activity binds to, and is affected by, molecules known to interact with FERM domains, supporting the hypothesis that the intracellular C1A heparanase is the purified FERM domain protein. Since bacterially expressed FERM domains of radixin and moesin lack heparanase activity, and some tryptic peptides generated from the enzyme do not have a match in any ERM protein, it appears that, rather than being derived from ezrin, radixin or moesin, C1A heparanase may be a new member of the FERM domain family.

Heparanases: endoglycosidases that degrade heparan sulfate proteoglycans

Heparanases are endoglycosidases that cleave the heparan sulfate glycosaminoglycans from proteoglycan core proteins and degrade them to small oligosaccharides. Inside cells, these enzymes are important for the normal catabolism of heparan sulfate proteoglycans (HSPGs), generating glycosaminoglycan fragments that are then transported to lysosomes and completely degraded. When secreted, heparanases are thought to degrade basement membrane HSPGs at sites of injury or inflammation, allowing extravasion of immune cells into nonvascular spaces and releasing factors that regulate cell proliferation and angiogenesis. Heparanases have been described in a wide variety of tissues and cells, but because of difficulties in developing simple assays to follow activity, very little has been known about enzyme diversity until recently. Within the last 10 years, heparanases have been purified from platelets, placenta, and Chinese hamster ovary cells. Characterization of the enzymes suggests there may be a family of heparanase proteins with different substrate specificities and potential functions.