Valency dependent patterns of binding of human L-selectin toward sialyl and sulfated oligosaccharides of Le(a) and Le(x) types: relevance to anti-adhesion therapeutics

Cathartocytosis: How Cells Jettison Unwanted Material as They Reprogram

Injury can cause differentiated cells to undergo massive reprogramming to become proliferative to repair tissue via a cellular program called paligenosis. Gastric digestive-enzyme-secreting chief cells use paligenosis to reprogram into progenitor-like Spasmolytic-Polypeptide Expressing Metaplasia (SPEM) cells. Stage 1 of paligenosis is to downscale mature cell architecture via a process involving lysosomes. Here, we noticed that sulfated glycoproteins (which are metaplasia and cancer markers in mice and humans) were not digested during paligenosis but excreted into the gland lumen. Various genetic and pharmacological approaches showed that endoplasmic reticulum membranes and secretory granule cargo were also excreted and that the process proceeded in parallel with, but was independent lysosomal activity. 3-dimensional light and electron-microscopy demonstrated that excretion occurred via unique, complex, multi-chambered invaginations of the apical plasma membrane. As this lysosome-independent cell cleansing process does not seem to have been priorly described, we termed it "cathartocytosis". Cathartocytosis allows a cell to rapidly eject excess material (likely in times of extreme stress such as are induced by paligenosis) without waiting for autophagic and lysosomal digestion. We speculate the ejection of sulfated glycoproteins (likely mucins) would aid in downscaling and might also help bind and flush pathogens (like H pylori which causes SPEM) away from tissue.

3'-sulfated LewisA/C: An oncofetal epitope associated with metaplastic and oncogenic plasticity of the gastrointestinal foregut

Metaplasia, dysplasia, and cancer arise from normal epithelia via a plastic cellular transformation, typically in the setting of chronic inflammation. Such transformations are the focus of numerous studies that strive to identify the changes in RNA/Protein expression that drive such plasticity along with the contributions from the mesenchyme and immune cells. However, despite being widely utilized clinically as biomarkers for such transitions, the role of glycosylation epitopes is understudied in this context. Here, we explore 3'-Sulfo-Lewis A/C, a clinically validated biomarker for high-risk metaplasia and cancer throughout the gastrointestinal foregut: esophagus, stomach, and pancreas. We discuss the clinical correlation of sulfomucin expression with metaplastic and oncogenic transformation, as well as its synthesis, intracellular and extracellular receptors and suggest potential roles for 3'-Sulfo-Lewis A/C in contributing to and maintaining these malignant cellular transformations.

mAb Das-1 recognizes 3'-Sulfated Lewis A/C, which is aberrantly expressed during metaplastic and oncogenic transformation of several gastrointestinal Epithelia

INTRODUCTION

Multiple previous studies have shown the monoclonal antibody Das-1 (formerly called 7E12H12) is specifically reactive towards metaplastic and carcinomatous lesions in multiple organs of the gastrointestinal system (e.g. Barrett's esophagus, intestinal-type metaplasia of the stomach, gastric adenocarcinoma, high-grade pancreatic intraepithelial neoplasm, and pancreatic ductal adenocarcinoma) as well as in other organs (bladder and lung carcinomas). Beyond being a useful biomarker in tissue, mAb Das-1 has recently proven to be more accurate than current paradigms for identifying cysts harboring advanced neoplasia. Though this antibody has been used extensively for clinical, basic science, and translational applications for decades, its epitope has remained elusive.

METHODS

In this study, we chemically deglycosylated a standard source of antigen, which resulted in near complete loss of the signal as measured by western blot analysis. The epitope recognized by mAb Das-1 was determined by affinity to a comprehensive glycan array and validated by inhibition of a direct ELISA.

RESULTS

The epitope recognized by mAb Das-1 is 3'-Sulfo-Lewis A/C (3'-Sulfo-LeA/C). 3'-Sulfo-LeA/C is broadly reexpressed across numerous GI epithelia and elsewhere during metaplastic and carcinomatous transformation.

DISCUSSION

3'-Sulfo-LeA/C is a clinically important antigen that can be detected both intracellularly in tissue using immunohistochemistry and extracellularly in cyst fluid and serum by ELISA. The results open new avenues for tumorigenic risk stratification of various gastrointestinal lesions.

Nucleic acid aptamers for clinical diagnosis: cell detection and molecular imaging

Nucleic acid aptamers have recently attracted significant attention in the field of clinical diagnosis because they have numerous merits, such as high affinity, high specificity, small size, little immunogenicity, stable structures, and ease of synthesis. This review focuses on discussing the potential applications of aptamers in cell detection and molecular imaging. For the ex vivo cell detection, this review discusses the status of five strategies: endogenous nucleic acid analysis, flow cytometry analysis, nanoparticle-based cell sensing, microfluidic cell separation, and histological examination. This review also discusses in vivo molecular and cell imaging by introducing aptamer-based molecular imaging, cell imaging, and integrated imaging and therapy. On the basis of the status of these promising studies, this review summarizes several challenging issues and unmet needs that may require more effort or attention in the future.

New sialyl Lewis(x) mimic containing an alpha-substituted beta(3)-amino acid spacer

A highly convergent and efficient synthesis of a new sialyl Lewis(x) (sLe(x)) mimic, which was predicted by computational studies to fulfil the spacial requirements for a selectin antagonist, has been developed. With a beta(2,3)-amino acid residue l-galactose (bioisostere of the l-fucose moiety present in the natural sLe(x)) and succinate are linked, leading to a mimic of sLe(x) that contains all the required pharmacophores, namely the 3- and 4-hydroxy group of l-fucose, the 4- and 6-hydroxy group of d-galactose and the carboxylic acid of N-acetylneuraminic acid. The key step of the synthesis involves a tandem reaction consisting of a N-deprotection and a suitable O-->N intramolecular acyl migration reaction which is promoted by cerium ammonium nitrate (CAN). Finally, the new sialyl Lewis(x) mimic was biologically evaluated in a competitive binding assay.

Ligands for the β-Glucan Receptor, Dectin-1, Assigned Using “Designer” Microarrays of Oligosaccharide Probes (Neoglycolipids) Generated from Glucan Polysaccharides

Dectin-1 is a C-type lectin-like receptor on leukocytes that mediates phagocytosis and inflammatory mediator production in innate immunity to fungal pathogens. Dectin-1 lacks residues involved in calcium ligation that mediates carbohydrate-binding by classical C-type lectins; nevertheless, it binds zymosan, a particulate beta-glucan-rich extract of Saccharomyces cerevisiae, and binding is inhibited by polysaccharides rich in beta1,3- or both beta1,3- and beta1,6-linked glucose. The oligosaccharide ligands on glucans recognized by Dectin-1 have not yet been delineated precisely. It is also not known whether Dectin-1 can interact with other types of carbohydrates. We have investigated this, since Dectin-1 shows glucan-independent binding to a subset of T-lymphocytes and is involved in triggering their proliferation. Here we assign oligosaccharide ligands for Dectin-1 using the neoglycolipid-based oligosaccharide microarray technology, a unique approach for constructing microarrays of lipid-linked oligosaccharide probes from desired sources. We generate "designer" microarrays from three glucan polysaccharides, a neutral soluble glucan isolated from S. cerevisiae and two bacterial glucans, curdlan from Alcaligenes faecalis and pustulan from Umbilicaria papullosa, and use these in conjunction with 187 diverse, sequence-defined, predominantly mammalian-type, oligosaccharide probes. Among these, Dectin-1 binding is detected exclusively to 1,3-linked glucose oligomers, the minimum length required for detectable binding being a 10- or 11-mer. Thus, the ligands assigned so far are exogenous rather than endogenous. We further show that Dectin-1 ligands, 11-13 gluco-oligomers, in clustered form (displayed on liposomes), mimic the macromolecular beta-glucans and compete with zymosan binding and triggering of tumor necrosis factor-alpha secretion by a Dectin-1-expressing macrophage cell line.

Effect of fixation protocols on in situ detection of L-selectin ligands

In situ binding of (chimeric) proteins to tissue sections is a widely used method to identify ligands and their localization. Many different protocols for the fixation of frozen tissue sections are used for in situ binding studies. We report the effects of different fixation protocols on the binding pattern observed using in situ binding of an L-selectin-IgM chimeric protein to both rat lymph node and kidney tissue sections. L-selectin is a C-type lectin, expressed on leukocytes and is involved in both lymphocyte homing and migration upon inflammation. We show that different in situ binding patterns in rat kidney are observed using different fixation protocols, including glutaraldehyde, methanol, formaldehyde and acetone fixation. The observed staining is specific, as it can be blocked in the presence of EGTA, an L-selectin blocking antibody or by ligand competition. Enzymatic pre-treatment of the tissue sections using sialidase, heparitinase I or chondroitinase ABC has differential effects on in situ binding depending on tissue type and fixation protocol. These data indicate that special attention should be paid in choosing a fixation protocol for in situ binding studies, especially when using lectins. This could prevent biologically relevant ligands remaining undetected or wrong conclusions being drawn based on the localization of observed binding.

Interactions of the gastrotropic bacterium Helicobacter pylori with the leukocyte-endothelium adhesion molecules, the selectins--a preliminary report

The deleterious effects of Helicobacter pylori infection of the stomach are largely the result of a vigorous chronic inflammatory response, and include chronic gastritis, peptic ulceration and gastric cancer. We are exploring the possibility that carbohydrate components on H. pylori contribute to the persistent inflammation through interactions with leukocyte-endothelial adhesion molecules of the host. Lipopolysaccharides of most H. pylori strains contain sequences related to the Lewis (Le(x) or Le(a)) antigens. Carbohydrate sequences of this family encompass ligands for the leukocyte-endothelium adhesion molecules of the host, namely, the E- and P-selectins, which are expressed on inflamed endothelia, and L-selectin, which is constitutively expressed on leukocytes. Here we investigate H. pylori isolates from patients with chronic gastritis, duodenal ulcer and gastric cancer for their interactions with the selectins. Our results provide unequivocal evidence of interactions of isolates from each of the diagnostic groups with E- and L-selectins.

An investigation of the interactions of E-selectin with fuco-oligosaccharides of the blood group family

This investigation is concerned with assignments of Lewis(a) (Le(a)) and Le(x) analogs on linear and branched di- to hexasaccharide backbones as components of the recognition motifs for E-selectin. The influence of the location of fucose residue(s) was investigated using 14 structurally defined and variously fucosylated oligosaccharides in biotinylated form or as neoglycolipids in static binding assays, in microwells, and on thin-layer chromatograms. Results of the two assay systems were in agreement overall and showed that the recognition motifs for E-selectin include 4-fucosyl-lacto (Le(a)) and 3-fucosyl-neo-lacto (Le(x)) sequences strictly at capping positions and not Le(x) at an internal position as a part of VIM-2 antigen sequence. There is greater potency of the Le(a) over the Le(x) series. Additional fucose residues alpha1-2-linked to neighboring galactoses or alpha1-3-linked to inner N-acetyglucosamines or to reducing-terminal glucose residues of the tetrasaccharide backbone had little or no effect on the selectin binding. E-selectin binding to the Le(a) or Le(x )capping motif on a 3-linked branch was equivalent to the binding on the corresponding linear backbone. A lack of E-selectin binding to the Le(x) motif capping a 6-linked branch and to the Le(x) trisaccharide linked to biotin via a nine-carbon spacer indicates that the -GlcNAcbeta1-3Gal- sequence on the oligosaccharide backbone adjoining the Le(x) is a part of recognition motif for E-selectin. These findings contribute to understanding the molecular basis of E-selectin recognition and could influence future designs of selectin antagonists as possible therapeutic substances.

Oligosaccharide microarrays for high-throughput detection and specificity assignments of carbohydrate-protein interactions

We describe microarrays of oligosaccharides as neoglycolipids and their robust display on nitrocellulose. The arrays are obtained from glycoproteins, glycolipids, proteoglycans, polysaccharides, whole organs, or from chemically synthesized oligosaccharides. We show that carbohydrate-recognizing proteins single out their ligands not only in arrays of homogeneous oligosaccharides but also in arrays of heterogeneous oligosaccharides. Initial applications have revealed new findings, including: (i) among O-glycans in brain, a relative abundance of the Lewis(x) sequence based on N-acetyllactosamine recognized by anti-L5, and a paucity of the Lewis(x) sequence based on poly-N-acetyllactosamine recognized by anti-SSEA-1; (ii) insights into chondroitin sulfate oligosaccharides recognized by an antiserum and an antibody (CS-56) to chondroitin sulfates; and (iii) binding of the cytokine interferon-gamma (IFN-gamma) and the chemokine RANTES to sulfated sequences such as HNK-1, sulfo-Lewis(x), and sulfo-Lewis(a), in addition to glycosaminoglycans. The approach opens the way for discovering new carbohydrate-recognizing proteins in the proteome and for mapping the repertoire of carbohydrate recognition structures in the glycome.

Relationship of sialyl-Lewis(x/a) underexpression and E-cadherin overexpression in the lymphovascular embolus of inflammatory breast carcinoma

Inflammatory breast carcinoma (IBC) is characterized by florid tumor emboli within lymphovascular spaces called lymphovascular invasion. These emboli have a unique microscopic appearance of compact clumps of tumor cells retracted away from the surrounding endothelial cell layer. Using a human SCID model of IBC (MARY-X), we, in previous studies, demonstrated that the tumor cell embolus (IBC spheroid) forms on the basis of an intact and overexpressed E-cadherin/alpha,beta-catenin axis that mediates tumor cell-tumor cell adhesion. In the present study we examine the mechanism behind the apparent lack of binding of the tumor embolus to the surrounding endothelium. We find that this lack of tumor cell binding is because of markedly decreased sialyl-Lewis(x/a) (sLe(x/a)) carbohydrate ligand-binding epitopes on its overexpressed MUC1 and other surface molecules that bind endothelial E-selectin. Decreased sLe(x/a) is because of decreased alpha3/4-fucosyltransferase activity in MARY-X. The decreased sLe(x/a) fail to confer electrostatic repulsions between tumor cells, which further contributes to the compactness of the MARY-X spheroid by allowing the E-cadherin homodimeric interactions to go unopposed. MARY-X spheroids were retrovirally transfected with FucT-III cDNA, significantly raising their levels of fucosyltransferase activity and surface sLe(x/a). In parallel experiments, enzymatic transfers with a milk alpha1,3-fucosyltransferase and an alpha2,3-sialyltransferase (ST3GalIV) were performed on the MARY-X spheroids and increased surface sLe(x/a). The addition of sLe(x/a) by either manipulation caused disadherence of the MARY-X spheroids and the disruption of the E-cadherin homodimers mediating cell adhesion. Our findings support the cooperative relationship of sLe(x/a) underexpression and E-cadherin overexpression in the genesis of the lymphovascular embolus of IBC.

Synthesis and applications of end-labeled neoglycopolymers

[reaction: see text] Neoglycopolymers that vary in length and contain a single fluorescent reporter group were synthesized using ring-opening metathesis polymerization (ROMP). The utility of these materials is demonstrated by the development of a cellular binding assay for L-selectin, a cell surface protein that plays a role in inflammation. The data reveal that these multivalent ligands interact with multiple copies of L-selectin.

Chemically synthesized solid phase oligosaccharide probes for carbohydrate-binding receptors. Interactions of the E-, L- and P-selectins with sialyl-Le(x) and O-sulphated forms linked to biotin or to polyacrylamide

There is a growing interest in chemically defined oligosaccharide reagents for identifying proteins that bind carbohydrates and determining the specificities of carbohydrate-binding proteins. Here, we compare three sets of chemically synthesized commercially available oligosaccharide conjugates as immobilized probes, for the binding signals that they elicit with known carbohydrate-binding receptors of the immune system, the E-, P- and L-selectins. The first set of conjugates is of oligosaccharides linked to biotin via a nine-carbon spacer. The second and third sets are multivalent derivatives in which the oligosaccharides are linked, via a three-carbon spacer to poly[N-(2-hydroxyethyl)acrylamide] (PAA) or to biotinylated PAA with an average of 20% substitution of the hydroxyethyl-amide groups by carbohydrate. The conjugates were immobilized on streptavidin-coated microwells if biotinylated, otherwise by drying in uncoated wells. The most robust binding curves, overall, were with the biotinylated PAA derivatives of the ligands immobilized on streptavidin wells. These reagents have permitted a reevaluation of selectin binding signals elicited by sialyl-Lewis(x) (SLe(x)) analogues having sulphate at position 6 of the galactose (6'SuSLe(x)) or of the N-acetylglucosamine (6SuSLe(x)). The results clarify the role of 6SuSLe(x), rather then 6'SuSLe(x), as a ligand for the selectins.

Synergistic interactions of the two classes of ligand, sialyl-Lewis(a/x) fuco-oligosaccharides and short sulpho-motifs, with the P- and L-selectins: implications for therapeutic inhibitor designs

The E-, L- and P-selectins are carbohydrate-recognizing cell-adhesion molecules mediating selective leucocyte recruitment in inflammation. The 3'-sialyl- and 3'-sulpho-oligosaccharides of Lewis(x) (Le(x)) and Lewis(a) (Le(a)) series are bound by them, but for high-avidity binding of P- and L-selectins to the glycoprotein counter-receptor known as P-selectin glycoprotein ligand, PSGL-1, there is a requirement for sulpho-tyrosines neighbouring a sialyl-Le(x) glycan. The two selectins can also bind 3-O- or 6-O-sulphated galacto-lipids (sulphatides). Here we compare some features of the interactions of P- and L-selectins with a novel lipid-linked sulpho-tyrosine probe, and with the sulphatides and neoglycolipids of sialyl- and sulpho-Le(x)/Le(a) fuco-oligosaccharides. The sulpho-tyrosine probe is bound by both selectins. There are close similarities in the interactions of the two selectins with sulpho-tyrosine and the sulphatides; the binding is relatively resistant to chelation of calcium ions, in contrast to the absolute requirement of calcium ions with the long fuco-oligosaccharides, including 6-sulpho-sialyl-Le(x). With both selectins, there is striking synergy in binding signals elicited by the two ligand types when presented as equimolar mixtures on a matrix. Thus, there are two operationally distinct binding sites on both L- and P-selectin; and the binding sites for sulphate groups in the two ligand types are probably distinct. When sulpho-tyrosine and sialyl-Le(x) are presented on liposomes, a potent inhibitory activity is generated toward the binding of P-selectin to HL60 cells, with 50% inhibitory concentration (IC(50)) values in the nanomolar range. These features of the lipid-linked ligand analogues, and the simple approach for their display on liposomes, may have applications in designs and screening of selectin inhibitors as anti-inflammatory compounds.

Salicylates inhibit T cell adhesion on endothelium under nonstatic conditions: induction of L-selectin shedding by a tyrosine kinase-dependent mechanism

Salicylates inhibit T cell adhesion to and transmigration through endothelium by preventing integrin activation induced by contact with endothelial cells. In the present study the effects of aspirin and sodium salicylate on the first steps of T cell adhesion have been analyzed in a nonstatic in vitro system. Salicylates partially reduced adhesion to activated endothelium and, in parallel, L-selectin expression on resting T cells by inducing shedding of the molecule without affecting its mRNA transcript. The role of L-selectin down-regulation in reducing T cell adhesion in this system was supported by the fact that aspirin inhibited T cell adhesion also on plastic-immobilized L-selectin ligand or when alpha(4) integrin-mediated adhesion to endothelium was blocked by specific mAbs. In addition, preincubation of T cells with inhibitors of L-selectin shedding prevented both functional and phenotypic inhibitory effects of salicylates. The decrease in T cell adhesion and L-selectin expression seems to be dependent on intracellular calcium increase and tyrosine kinase activation, because these effects could be reversed by preincubating salicylate-treated T cells with EGTA, genistein, or tyrphostin. Finally, the infusion of aspirin into healthy volunteers induced down-regulation of L-selectin on circulating T cells. These results suggest that salicylates interfere not only with integrin activation, but also with the L-selectin-mediated first steps of T cell binding to endothelium.

‘Glyco-Epitope’ Assignments for the Selectins: Advances Enabled By the Neoglycolipid (Ngl) Technology in Conjunction with Synthetic Carbohydrate Chemistry’

The neoglycolipid (NGL) technology involving the preparation of lipid-linked oligosaccharide probes for binding experiments with carbohydrate-recognizing proteins, and their analysis by mass spectrometry, is a unique and powerful means of discovering oligosaccharide ligands for carbohydrate-binding proteins, and assigning details of their specificities. The key feature is that it enables the pinpointing and sequence determination of bioactive oligosaccharides within highly heterogeneous mixtures derived from natural glycoconjugates. A new generation of NGLs incorporating a fluorescent label now establishes the principles for a streamlined technology whereby oligosaccharide populations are carried through ligand detection and isolation steps, and sequence determination. Advances in selectin research made through applications of the NGL technology include (i) demonstration of the importance of density of selectin expression, and of oligosaccharide ligands, in the magnitude and the specificity of the binding signals; (ii) demonstration of the efficacy of lipid-linked oligosaccharides in supporting selectin-mediated cell interactions; (iii) the discovery of 3-sulphated Le(a)/Le(x) as selectin ligands; (iv) the isolation and sequencing of carbohydrate ligands for E-selectin on murine myeloid cells and kidney; (v) the finding that sulphation at position 6 of the penultimate N-acetylglucosamine confers superior L-selectin binding signals not only to 3-sialyl-Le(x) but also to 3'-sulpho-Le(x); and (vi) the finding that sialic acid de-N-acetylation, or further modification with formation of an intra-molecular amide bond in the carboxyl group, enhances or virtually abolishes, respectively, the potency of the 6'-sulfo-sialyl-Le(X) ligand. Working with biotinylated forms of the oligosaccharide ligands, we have observed that their presentation on a streptavidin matrix influences differentially the efficacy of interactions of the L- and P-selectins (but not E-selectin) with the sialylated and sulphated ligands.

Cell-free rolling mediated by L-selectin and sialyl Lewis(x) reveals the shear threshold effect

The selectin family of adhesion molecules mediates attachment and rolling of neutrophils to stimulated endothelial cells. This step of the inflammatory response is a prerequisite to firm attachment and extravasation. We have reported that microspheres coated with sialyl Lewis(x) (sLe(x)) interact specifically and roll over E-selectin and P-selectin substrates (Brunk et al., 1996; Rodgers et al 2000). This paper extends the use of the cell-free system to the study of the interactions between L-selectin and sLe(x) under flow. We find that sLe(x) microspheres specifically interact with and roll on L-selectin substrates. Rolling velocity increases with wall shear stress and decreases with increasing L-selectin density. Rolling velocities are fast, between 25 and 225 microm/s, typical of L-selectin interactions. The variability of rolling velocity, quantified by the variance in rolling velocity, scales linearly with rolling velocity. Rolling flux varies with both wall shear stress and L-selectin site density. At a density of L-selectin of 800 sites/microm(2), the rolling flux of sLe(x) coated microspheres goes through a clear maximum with respect to shear stress at 0.7 dyne/cm(2). This behavior, in which the maintenance and promotion of rolling interactions on selectins requires shear stress above a threshold value, is known as the shear threshold effect. We found that the magnitude of the effect is greatest at an L-selectin density of 800 sites/microm(2) and gradually diminishes with increasing L-selectin site density. Our study is the first to reveal the shear threshold effect with a cell free system and the first to show the dependence of the shear threshold effect on L-selectin site density in a reconstituted system. Our ability to recreate the shear threshold effect in a cell-free system strongly suggests the origin of the effect is in the physical chemistry of L-selectin interaction with its ligand, and largely eliminates cellular features such as deformability or topography as its cause.

Expression in Escherichia coli, folding in vitro, and characterization of the carbohydrate recognition domain of the natural killer cell receptor NKR-P1A

NKR-P1A is a homodimeric type II transmembrane protein of the C-type lectin family found on natural killer (NK) cells and NK-like T cells and is an activator of cytotoxicity. Toward structure determination by NMR, the recombinant carbohydrate-recognition domain (CRD) of NKR-P1A has been expressed in high-yield in Escherichia coli and folded in vitro. The purified protein behaves as a monomer in size-exclusion chromatography and is bound by the conformation-sensitive antibody, 3.2.3, indicating a folded structure. A polypeptide tag at the N-terminus is selectively cleaved from the CRD after limited trypsin digestion in further support of a compact folded structure. The disulfide bonds have been identified by peptide mapping and electrospray mass spectrometry. These are characteristic of a long form CRD. The 1D NMR spectrum of the unlabeled CRD and the 2D HSQC spectrum of the (15)N-labeled CRD are those of a folded protein. Chemical shifts of H(alpha) and NH protons indicate a considerable amount of beta-strand structure. Successful folding in the absence of Ca(2+), coupled with the lack of chemical shift changes upon addition of Ca(2+), suggests that the NKR-P1A-CRD may not be a Ca(2+)-binding protein.

Progress in deciphering the information content of the 'glycome'--a crescendo in the closing years of the millennium

The closing years of the second millennium have been uplifting for carbohydrate biology. Optimism that oligosaccharide sequences are bearers of crucial biological information has been borne out by the constellation of efforts of carbohydrate chemists, biochemists, immunochemists, and cell- and molecular biologists. The direct involvement of specific oligosaccharide sequences in protein targeting and folding, and in mechanisms of infection, inflammation and immunity is now unquestioned. With the emergence of families of proteins with carbohydrate-binding activities, assignments of information content for defined oligosaccharide sequences will become more common, but the pinpointing and elucidation of the bioactive domains on oligosaccharides will continue to pose challenges even to the most experienced carbohydrate biologists. The neoglycolipid technology incorporates some of the key requirements for this challenge: namely the resolution of complex glycan mixtures, and ligand binding coupled with sequence determination by mass spectrometry.

The cysteine-rich domain of the macrophage mannose receptor is a multispecific lectin that recognizes chondroitin sulfates A and B and sulfated oligosaccharides of blood group Lewis(a) and Lewis(x) types in addition to the sulfated N-glycans of lutropin

The mannose receptor (MR) is an endocytic protein on macrophages and dendritic cells, as well as on hepatic endothelial, kidney mesangial, tracheal smooth muscle, and retinal pigment epithelial cells. The extracellular portion contains two types of carbohydrate-recognition domain (CRD): eight membrane-proximal C-type CRDs and a membrane-distal cysteine-rich domain (Cys-MR). The former bind mannose-, N-acetylglucosamine-, and fucose-terminating oligosaccharides, and may be important in innate immunity towards microbial pathogens, and in antigen trapping for processing and presentation in adaptive immunity. Cys-MR binds to the sulfated carbohydrate chains of pituitary hormones and may have a role in hormonal clearance. A second feature of Cys-MR is binding to macrophages in marginal zones of the spleen, and to B cell areas in germinal centers which may help direct MR-bearing cells toward germinal centers during the immune response. Here we describe two novel classes of carbohydrate ligand for Cys-MR: chondroitin-4 sulfate chains of the type found on proteoglycans produced by cells of the immune system, and sulfated blood group chains. We further demonstrate that Cys-MR interacts with cells in the spleen via the binding site for sulfated carbohydrates. Our data suggest that the three classes of sulfated carbohydrate ligands may variously regulate the trafficking and function of MR-bearing cells.

Recombinant soluble human CD69 dimer produced in Escherichia coli: reevaluation of saccharide binding

We reevaluate here an earlier report of monosaccharide binding by the C-type lectin-like, leukocyte surface protein CD69 in the form of a recombinant soluble dimer, and we examine polysaccharide binding by the protein. We have expressed in Escherichia coli a new construct of the extracellular part (Q(65)-K(199)) of human CD69. We describe the folding in vitro to produce, in good yield, the protein in a soluble, disulphide-linked, dimeric form, and the results of binding experiments with monosaccharides: glucose, galactose, mannose, fucose, N-acetylglucosamine, and N-acetylgalactosamine, linked to bovine serum albumin. Monosaccharide-binding signals are not detectable. Among the polysaccharides, heparin, chondroitin sulphates A, B, and C, fucoidan, and dextran sulphate, CD69 dimer gives a weak binding signal with fucoidan.

Fucose in N-glycans: from plant to man

Fucosylated oligosaccharides occur throughout nature and many of them play a variety of roles in biology, especially in a number of recognition processes. As reviewed here, much of the recent emphasis in the study of the oligosaccharides in mammals has been on their potential medical importance, particularly in inflammation and cancer. Indeed, changes in fucosylation patterns due to different levels of expression of various fucosyltransferases can be used for diagnoses of some diseases and monitoring the success of therapies. In contrast, there are generally at present only limited data on fucosylation in non-mammalian organisms. Here, the state of current knowledge on the fucosylation abilities of plants, insects, snails, lower eukaryotes and prokaryotes will be summarised.

Influence of oligosaccharide presentation on the interactions of carbohydrate sequence-specific antibodies and the selectins. Observations with biotinylated oligosaccharides

This study was aimed at investigating the efficacy of presentation of biotinylated oligosaccharides on streptavidin-coated microwells for interactions with (a) three monoclonal antibodies directed at sialyl-Lewisa (Le(a)) or sulfo-Le(a)-related sequences, and (b) the endothelium-leukocyte adhesion molecules, the E-, L- and P-selectins which recognize both the sulfo- and sialyl-Le(a) series. With the antibodies it was observed that if the biotinylated oligosaccharide incorporated the entire antigenic determinant, and additional saccharide length was not included, the biotinyl tag spacer length was a critical factor in the strength of the binding signal. If oligosaccharide chain beyond the determinant was included, the biotinyl tag spacer length was less important. The E-selectin binding data with the biotinylated sialyl- and sulfo-oligosaccharides were in overall accord with previous knowledge. With the L- and P-selectins, however, unexpectedly low binding signals were elicited by biotinyl sulfo-Le(a) sequences relative to those with the sialyl-analogs. This suppression was more pronounced with the rodent than the human L-selectin. Such differential availabilities of oligosaccharides displayed on streptavidin may relate to biological situations, such as the differential reactivities of the three selectins with a given oligosaccharide ligand presented on different carrier proteins, or on different O-glycan cores on mucin-type glycoproteins.

L-selectin interactions with novel mono- and multisulfated Lewisx sequences in comparison with the potent ligand 3'-sulfated Lewisa

The cell adhesion molecule L-selectin binds to 3'-sialyl-Lewis (Le)x and -Lea and to 3'-sulfo-Lex and -Lea sequences. The binding to 3'-sialyl-Lex is strongly affected by the presence of 6-O-sulfate as found on oligosaccharides of the counter receptor, GlyCAM-1; 6-O-sulfate on the N-acetylglucosamine (6-sulfation) enhances, whereas 6-O-sulfate on the galactose (6'-sulfation) virtually abolishes binding. To extend knowledge on the specificity of L-selectin, we have investigated interactions with novel sulfo-oligosaccharides based on the Lex pentasaccharide sequence. We observe that, also with 3'-sulfo-Lex, the 6-sulfation enhances and 6'-sulfation suppresses L-selectin binding. The 6'-sulfation without 3'-sialyl or 3'-sulfate gives no binding signal with L-selectin. Where the 6-sulfo,3'-sialyl-Lex is on an extended di-N-acetyllactosamine backbone, additional 6-O-sulfates on the inner galactose and inner N-acetylglucosamine do not influence the binding. Although binding to the 6,3'-sulfo-Lex and 6-sulfo, 3'-sialyl-Lex sequences is comparable, the former is a more effective inhibitor of L-selectin binding. This difference is most apparent when L-selectin is in paucivalent form (predominantly di- and tetramer) rather than multivalent. Indeed, as inhibitors of the paucivalent L-selectin, the 3'-sulfo-Lex series are more potent than the corresponding 3'-sialyl-Lex series. Thus, for synthetic strategies to design therapeutic oligosaccharide analogs as antagonists of L-selectin binding, those based on the simpler 3'-sulfo-Lex (and also the 3'-sulfo-Lea) would seem most appropriate.

Malignant and other properties of human colon carcinoma cells after suppression of sulfomucin production in vitro

Although the loss of sulfomucins was known as an indicator of carcinogenesis and malignant progression of colonic epithelia, it was not known whether the loss was directly related to the malignant behavior of colon carcinoma cells. We have studied the biological properties of LS174T human colon carcinoma cells before and after suppression of sulfomucin production. Incorporation of [35S]-sulfate into high molecular weight mucins decreased after carcinoma cell treatment with 1.5% dimethylsulfoxide (DMSO) for 8 days. The amounts of sulfomucin determined using a sulfomucin-specific monoclonal antibody (mAb 91.9H), in Western blot and flowcytometric analyses, also decreased. In addition, the levels of MUC2 and MUC5B mucin gene expression measured by RT-PCR were reduced after DMSO-treatment, whereas the levels of MUC1, MUC5AC, and MUC6 mucin gene expression were not. The DMSO-treated cells were tested in vitro and in vivo for their properties. Differences were not detected in their anchorage-independent growth, anchorage-dependent growth, E-selectin-dependent cell adhesion or sensitivity to interleukin (IL)-2-activated lymphocyte cytolysis. When untreated or DMSO-treated LS174T cells were injected intrasplenically into nude mice, the treated cells lacking certain cell surface sulfomucins formed fewer metastatic colonies in the liver. These results suggest that the loss of sulfomucins by colonic epithelial cells during progression is not directly related to the enhanced malignant behavior.

Inhibition of L-selectin-mediated leukocyte rolling by synthetic glycoprotein mimics

Synthetic carbohydrate and glycoprotein mimics displaying sulfated saccharide residues have been assayed for their L-selectin inhibitory properties under static and flow conditions. Polymers displaying the L-selectin recognition epitopes 3',6-disulfo Lewis x(Glc) (3-O-SO3-Galbeta1alpha4(Fucalpha1alpha3)-6-O-SO3-Glcbeta+ ++-OR) and 3',6'-disulfo Lewis x(Glc) (3, 6-di-O-SO3-Galbeta1alpha4(Fucalpha1alpha3)Glcbeta-OR) both inhibit L-selectin binding to heparin under static, cell-free binding conditions with similar efficacies. Under conditions of shear flow, however, only the polymer displaying 3',6-disulfo Lewis x(Glc) inhibits the rolling of L-selectin-transfected cells on the glycoprotein ligand GlyCAM-1. Although it has been shown to more effective than sialyl Lewis x at blocking the L-selectin-GlyCAM-1 interaction in static binding studies, the corresponding monomer had no effect in the dynamic assay. These data indicate that multivalent ligands are far more effective inhibitors of L-selectin-mediated rolling than their monovalent counterparts and that the inhibitory activities are dependent on the specific sulfation pattern of the recognition epitope. Importantly, our results indicate the L-selectin specificity for one ligand over another found in static, cell-free binding assays is not necessarily retained under the conditions of shear flow. The results suggest that monovalent or polyvalent carbohydrate or glycoprotein mimetics that inhibit selectin binding in static assays may not block the more physiologically relevant process of selectin-mediated rolling.

Novel carbohydrate specificity of monoclonal antibody 91.9H prepared against human colonic sulfomucin: recognition of sulfo-Lewis(a) structure

Monoclonal antibody (mAb) 91.9H was previously prepared against partially purified human colonic sulfomucins. The epitope was detected in normal colonic mucosa and primary and metastatic colorectal carcinoma in decreasing order of magnitude. In the present study, this antibody was shown to recognize sulfo-Le(a) structure, HSO3-3Gal beta 1-3(Fuc alpha 1-4)GlcNAc. Interactions between mAb 91.9H and synthetic oligosaccharides conjugated with biotinylated polyacrylamide carrier were examined by a biosensor based on surface plasmon resonance and by enzyme-linked immunosorbent assays. This mAb bound to sulfo-Lea but not to sulfo-LeX, Le(a), LeX, sialyl-Le(a), or sialyl-LeX. Sulfo-Le(a) oligosaccharides decreased its binding affinity with mAb 91.9H after periodate oxidation of its fucose residue. Immunohistochemical study showed a strong binding of mAb 91.9H to goblet cells in human colonic epithelia of Lewis-positive individuals but a trace binding in Lewis-negative individuals, confirming the specificity of this antibody toward structures containing a fucosylated type 1 backbone.

Expression of mucin-associated sulfo-Lea carbohydrate epitopes on human colon carcinoma cells

The level of sulfo-Lea (SO3-3Gal beta 1-3(Fuc alpha 1-4)GlcNAc) epitope recognized by monoclonal antibody (mAb) 91.9H in hepatic metastasis of colon carcinoma is known to be lower than at the primary sites. We examined 19 human colon carcinoma cell lines for their production of this epitope. Sixteen cell lines were found to produce high M(r) components that metabolically incorporated [35S]sulfate and were resistant to heparitinase I and chondroitinase ABC, and 8 of them were reactive with mAb 91.9H as shown by western blotting analysis. These were all of the 4 cell lines derived from well differentiated primary tumors (HCCP-2998, LS174T, GEO, and CBS), 2 of 10 cell lines (DLD-1 and HCT116) from moderately to poorly differentiated primary tumors, and 2 of 5 cell lines (SW480 and HCC-M1544) from metastases. Incubation of LS174T cells with benzyl-N-acetyl-alpha-D-galactosaminide abrogated the incorporation of [35S]sulfate and the reactivity of mAb 91.9H with high M(r) components in the cell lysates. Sodium chlorate, which inhibits the formation of 3'-phosphoadenosine 5'-phosphosulfate, also inhibited the [35S]sulfate incorporation and reactivity with mAb 91.9H. These treatments did not change the incorporation of [14C]threonine into high M(r) components. These results indicated that sulfo-Lea epitopes were expressed on O-linked carbohydrate chains in sulfomucins. Immunohistochemical studies of tumor tissues in nude mice indicated that sulfo-Lea was expressed at the site of orthotopic transplantation in the cecum. The expression appeared to be suppressed in liver metastatic foci in nude mice.

Oligosaccharide receptors for bacteria: a view to a kill

Oligosaccharide recognition is a major means of bacterial-host cell attachment. Bacterial-host receptor binding can subvert host signaling pathways to cause pathology. In addition, pathogenic bacteria can utilize more than one recognition system to bind host cells. Recent studies of Helicobacter pylori illustrate both these points. Together with this redundancy in recognition, the importance of multivalent sugar binding has become apparent. Multivalent sugar receptor analogs have been used to both prevent and detach adherent bacteria. Several new chemical technologies for the generation of bioactive glycopolymers have been developed and may be successfully adapted to address both these issues.

Monoclonal antibody 91.9H raised against sulfated mucins is specific for the 3'-sulfated Lewisa tetrasaccharide sequence

The IgG1hybridoma antibody, 91.9H, was originally raised against sulfated mucins isolated from normal human colonic mucosa. Previous studies have shown that the 91.9H antigen is expressed on normal colonic epithelial cells and the sulfomucins that they produce, but not in the normal small intestine and stomach. Tissue-specific changes occur in 91.9H antigen expression in disease: the antigen diminishes in colonic carcinomas, whereas in regions of gastric mucosa showing intestinal metaplasia and in gastric carcinomas, the antigen is expressed as a "neo-antigen." This report is concerned with elucidation, by the neoglycolipid technology, of the determinant recognized by antibody 91.9H using sulfated and sialyl oligosaccharides of Lewisa(Lea) and Lextypes, and analogs that lack sulfate, sialic acid, or fucose. Binding experiments with the lipid-linked oligosaccharides immobilized on chromatograms or on microwells, and inhibition of binding experiments with free oligosaccharides based on di-, tri- and tetrasaccharide backbones, show that the 91.9H antigenic determinant is based on a trisaccharide backbone, and consists of the 3'-sulfated Leatetrasaccharide sequence, which is a potent ligand for the E- and L-selectins. The antibody gives a relatively low signal with the 3'-sulfated non-fucosylated backbone, and has no detectable cross-reaction with the 3'-sulfated Lexisomer, nor with sialyl-Leaand -Lexanalogues. Antibody 91.9H is a valuable addition, therefore, to the repertoire of reagents for mapping details of the distribution, and determining the relative importance of sulfated and sialyl oligosaccharides as ligands for the selectins, in normal and pathological epithelia and endothelia.

The Roles of L-Selectin, β7 Integrins, and P-Selectin in Leukocyte Rolling and Adhesion in High Endothelial Venules of Peyer’s Patches

Lymphocyte trafficking into Peyer’s patches requires β7 integrins and L-selectin. Here, we use intravital microscopy to examine leukocyte rolling and adhesion in Peyer’s patch high endothelial venules (HEV) of wild-type, L-selectin-deficient (L−/−), β7 integrin-deficient (β7−/−), and β7/L−/− mice. Although the leukocyte rolling flux fraction was reduced by 70%, Peyer’s patches in L−/− mice were of normal size and cellularity. In β7−/− mice, the rolling flux fraction was normal, but the number of adherent leukocytes in HEV was greatly reduced. The median leukocyte rolling velocity was reduced in L−/− mice and increased in β7−/− mice, suggesting that β7 integrins and L-selectin mediate rolling in Peyer’s patch HEV at different velocities. β7/L−/− exhibited both a low rolling flux fraction and low adhesion and had severely reduced Peyer’s patch size and cellularity. The residual rolling in these mice was completely blocked by a P-selectin mAb. A significant P-selectin component was also detected in the other genotypes. Twenty-six percent of B and T lymphocytes isolated from Peyer’s patches of wild-type mice expressed functional ligands for P-selectin, and this fraction was increased to 57% in β7/L−/− mice. Peyer’s patch HEV were found to express P-selectin under the conditions of intravital microscopy, but not in situ. Our data suggest a novel P-selectin dependent mechanism of lymphocyte homing to Peyer’s patches. In situ, β7 integrins and L-selectin account for all lymphocyte homing to Peyer’s patches, but P-selectin-dependent rolling, as induced by minimal trauma, may support trafficking of effector T lymphocytes to Peyer’s patches.

Sialyl-Lewis(x) sequence 6-O-sulfated at N-acetylglucosamine rather than at galactose is the preferred ligand for L-selectin and de-N-acetylation of the sialic acid enhances the binding strength

Oligosaccharide sequences based on sialyl-Lewis(x) with 6-O-sulfation at galactose (6'-sulfo) or at N-acetylglucosamine (6-sulfo) and expressed on high endothelial venules are considered likely endogenous ligands for the leukocyte adhesion molecule, L-selectin. In the course of high performance TLC of three hexaglycosylceramides 6'-sulfo sialyl Lewis(x), 6-sulfo sialyl Lewis(x), and 6',6-bis-sulfo sialyl Lewis(x), synthesized chemically for selectin recognition studies, two minor byproducts were detected and isolated from each parent compound. By liquid secondary ion mass spectrometry these were identified as isomers containing a de-N-acetylated sialic acid or having a modified carboxyl group. Binding experiments with the parent compounds and the non-sulfated sialyl Lewis(x) glycolipid show that 6-sulfation potentiates, whereas 6'-sulfation virtually abolishes L-selectin binding. Thus the hierarchy of binding strengths were 6-sulfo sialyl > sialyl = 6',6-bis-sulfo sialyl >> 6'-sulfo sialyl Lewis(x). Whereas modification of the sialic acid carboxyl group markedly impaired L-selectin binding, de-N-acetylation resulted in enhanced binding. The natural occurrence on high endothelial venules of this 'super-active' de-N-acetylated form of 6-sulfo sialyl Lewis(x), and related structures, now deserves investigation.