Pathways of O-glycan biosynthesis in cancer cells

Glycans as Biomarkers: Status and Perspectives

Protein glycosylation is a ubiquitous and complex co- and post-translational modification leading to glycan formation, i.e. oligosaccharide chains covalently attached to peptide backbones. The significance of changes in glycosylation for the beginning, progress and outcome of different human diseases is widely recognized. Thus, glycans are considered as unique structures to diagnose, predict susceptibility to and monitor the progression of disease. In the »omics« era, the glycome, a glycan analogue of the proteome and genome, holds considerable promise as a source of new biomarkers. In the design of a strategy for biomarker discovery, new principles and platforms for the analysis of relatively small amounts of numerous glycoproteins are needed. Emerging glycomics technologies comprising different types of mass spectrometry and affinity-based arrays are next in line to deliver new analytical procedures in the field of biomarkers. Screening different types of glycomolecules, selection of differentially expressed components, their enrichment and purification or identification are the most challenging parts of experimental and clinical glycoproteomics. This requires large-scale technologies enabling high sensitivity, proper standardization and validation of the methods to be used. Further progress in the field of applied glycoscience requires an integrated systematic approach in order to explore properly all opportunities for disease diagnosis.

State of the art in tumor antigen and biomarker discovery

Our knowledge of tumor immunology has resulted in multiple approaches for the treatment of cancer. However, a gap between research of new tumors markers and development of immunotherapy has been established and very few markers exist that can be used for treatment. The challenge is now to discover new targets for active and passive immunotherapy. This review aims at describing recent advances in biomarkers and tumor antigen discovery in terms of antigen nature and localization, and is highlighting the most recent approaches used for their discovery including “omics” technology.

Polypeptide N-acetylgalactosaminyltransferase 6 expression in pancreatic cancer is an independent prognostic factor indicating better overall survival

BACKGROUND

The family of polypeptide N-acetylgalactosaminyltransferases (GalNAc-Ts) is responsible for the altered glycosylation in cancer. The purpose of our study was to investigate the clinical significance of two isoforms, GalNAc-T6 and -T3, and their correlation with the prognosis of pancreatic cancer.

METHODS

Immunohistochemistry was used to analyse GalNAc-T6 and -T3 expressions in 70 clinicopathologically characterised pancreatic cancer cases.

RESULTS

Positive expressions of GalNAc-T6 and -T3 were immunohistochemically identified in 51% (36 of 70) and in 77% (54 of 70) of patients, respectively. A close relationship was noted between GalNAc-T6 positive expression and pathological well/moderate differentiated type (P=0.001), small tumour size (P=0.044), absence of vascular invasion (P=0.009), and low stage of the American Joint Committee on Cancer systems (P=0.043). The expression of GalNAc-T3 significantly correlated with good differentiation (P=0.001), but not with other clinicopathologic features. Furthermore, univariate and multivariate analyses revealed that GalNAc-T6 expression was an independent prognosis indicator for the disease, whereas GalNAc-T3 expression had no impact on clinical outcome, even though 33 of 36 GalNAc-T6-positive cases also had a positive expression of GalNAc-T3 (P=0.001, r=0.356).

CONCLUSION

Both GalNAc-T6 and -T3 expressions correlated significantly with tumour differentiation, whereas only GalNAc-T6 expression predicted prognosis in pancreatic cancer.

Lactobacillus adhesion to mucus

Mucus provides protective functions in the gastrointestinal tract and plays an important role in the adhesion of microorganisms to host surfaces. Mucin glycoproteins polymerize, forming a framework to which certain microbial populations can adhere, including probiotic Lactobacillus species. Numerous mechanisms for adhesion to mucus have been discovered in lactobacilli, including partially characterized mucus binding proteins. These mechanisms vary in importance with the in vitro models studied, which could significantly affect the perceived probiotic potential of the organisms. Understanding the nature of mucus-microbe interactions could be the key to elucidating the mechanisms of probiotic adhesion within the host.

Co-translational function of Cosmc, core 1 synthase specific molecular chaperone, revealed by a cell-free translation system

The core 1 structure of the mucin type O-glycan is synthesized by core 1 β1,3-galactosyltransferase (C1GalT). Core 1 synthase specific molecular chaperone (Cosmc), a molecular chaperone specific for C1GalT, is essential for the expression of functional C1GalT in mammalian cells. In this study, we have established a procedure for detecting the chaperone activity of Cosmc by using a wheat germ cell-free translation system. Active C1GalT was expressed following simultaneous translation with Cosmc or translation in the presence of recombinant Cosmc protein. Moreover, we show that recombinant Cosmc must be present during the translation of C1GalT, as it is ineffective when added after translation. These results indicate that Cosmc mediates the co-translational activation of C1GalT and that it may prevent the unfavorable aggregation of C1GalT.

Autoantibodies to aberrantly glycosylated MUC1 in early stage breast cancer are associated with a better prognosis

Introduction

Detection of serum biomarkers for early diagnosis of breast cancer remains an important goal. Changes in the structure of O-linked glycans occur in all breast cancers resulting in the expression of glycoproteins that are antigenically distinct. Indeed, the serum assay widely used for monitoring disease progression in breast cancer (CA15.3), detects a glycoprotein (MUC1), but elevated levels of the antigen cannot be detected in early stage patients. However, since the immune system acts to amplify the antigenic signal, antibodies can be detected in sera long before the antigen. We have exploited the change in O-glycosylation to measure autoantibody responses to cancer-associated glycoforms of MUC1 in sera from early stage breast cancer patients.

Methods

We used a microarray platform of 60mer MUC1 glycopeptides, to confirm the presence of autoantibodies to cancer associated glycoforms of MUC1 in a proportion of early breast cancer patients (54/198). Five positive sera were selected for detailed definition of the reactive epitopes using on chip glycosylation technology and a panel of glycopeptides based on a single MUC1 tandem repeat carrying specific glycans at specific sites. Based on these results, larger amounts of an extended repertoire of defined MUC1 glycopeptides were synthesised, printed on microarrays, and screened with sera from a large cohort of breast cancer patients (n = 395), patients with benign breast disease (n = 108) and healthy controls (n = 99). All sera were collected in the 1970s and 1980s and complete clinical follow-up of breast cancer patients is available.

Results

The presence and level of autoantibodies was significantly higher in the sera from cancer patients compared with the controls, and a highly significant correlation with age was observed. High levels of a subset of autoantibodies to the core3MUC1 (GlcNAcβ1-3GalNAc-MUC1) and STnMUC1 (NeuAcα2,6GalNAc-MUC1) glycoforms were significantly associated with reduced incidence and increased time to metastasis.

Conclusions

Autoantibodies to specific cancer associated glycoforms of MUC1 are found more frequently and at higher levels in early stage breast cancer patients than in women with benign breast disease or healthy women. Association of strong antibody response with reduced rate and delay in metastases suggests that autoantibodies can affect disease progression.

PpGalNacT2 participating in vanadium-induced HL-60 cell differentiation

The current study demonstrates vanadium plays the role of antitumor, and its antitumor effect is dosage-dependent. N-acetyl-galactosamine-transferase 2 (polypeptide: N-acetyl-α-galactosaminyl-transferases 2, ppGalNAc-T2) is a member of ppGalNAcTs (polypeptide: N-acetyl-α-galactosaminyl-transferases) family, which proves to play a vital role in the tumor emergence and development process. In this study, we focused on ppGalNAc-T2 and vanadium and aimed to determine whether ppGalNAc-T2 is correlated with vanadium's antitumor effect. We discovered that ppGalNAc-T2 changed with the variation of HL-60 cell growth induced by vanadium at mRNA level. Peanut agglutinin (PNA) is an exogenous lectin. PpGalNacT2 can be indirectly recognized by PNA. By means of flow cytometry and immunofluorescent staining, we found the deviation of PNA binding increased significantly at high concentration vanadium. Then we docked one of the possible compound substances of vanadium onto the body, VO(3) (molecular formula O(13)V(4), partial vanadate tetramer) and ppGalNAcT2, and simulated them via molecular dynamics, which showed that VO(3) may inhibit the activity of the enzyme by stemming conformational changes of a key loop of ppGalNAcT2. To sum up, our results suggested that ppGalNacT2 participated in vanadium induced HL-60 cell differentiation, which might be able to provide a new mechanism of vanadium's antitumor effect.

A novel tumor-associated pancreatic glycoprotein is internalized by human dendritic cells and induces their maturation

Aberrant glycosylation or overexpression of cell-surface glycosylated tumor-associated Ags (TAA) distinguish neoplastic from normal cells. Interactions of TAA MUC1 and HER2/neu with dendritic cells (DC) preclude efficient processing, which impairs immune responses. It is thus important to define the mechanisms of interactions between DC and glycosylated TAA and their trafficking and processing for further T cell activation. In this work, we study interactions between DC and the oncofetal fucose-rich glycovariants of bile salt-dependent lipase (BSDL), expressed in pancreatic cancer tissues and referred to as pathological BSDL carrying the fucosylated J28 glycotope (pBSDL-J28) because it is characterized by the mAb J28. The expression of pBSDL-J28 was assessed by immunohistochemistry and quantified by confocal microscopy. Nontumoral pancreatic tissues and cells do not express pBSDL-J28. Using multidisciplinary approaches and functional studies, we provide the first evidence, to our knowledge, that this tumoral glycoprotein is rapidly internalized by human DC through macropinocytosis and endocytosis via mannose receptors and then transported to late endosomes for processing. Interestingly, pBSDL-J28 per se induced DC maturation with increased expression of costimulatory and CD83 molecules associated with cytokine secretion (IL-8 and IL-6). Surprisingly, DC retained their full ability to internalize Ags, making this maturation atypical. Finally, the allogeneic pBSDL-J28-treated DC stimulated lymphocyte proliferation. Besides, pulsing DC with pBSDL-J28 C-terminal glycopolypeptide and maturation with CD40L triggered CD4(+) and CD8(+) T cell proliferation. Therefore, interactions of pBSDL-J28, expressed on tumoral pancreatic tissue, with DC may lead to adequate Ag trafficking and processing and result in T cell activation.

Structure determination by MALDI-IRMPD mass spectrometry and exoglycosidase digestions of O-linked oligosaccharides from Xenopus borealis egg jelly

Differences in the fertilization behavior of Xenopus borealis from X. laevis and X. tropicalis suggest differences in the glycosylation of the egg jellies. To test this assumption, O-linked glycans were chemically released from the egg jelly coat glycoproteins of X. borealis. Over 50 major neutral glycans were observed, and no anionic glycans were detected from the released O-glycan pool. Preliminary structures of ∼30 neutral oligosaccharides were determined using matrix-assisted laser desorption/ionization (MALDI) infrared multiphoton dissociation tandem mass spectrometry (MS). The mass fingerprint of a group of peaks for the core-2 structure of O-glycans was conserved in the tandem mass spectra and was instrumental in rapid and efficient structure determination. Among the 29 O-glycans, 22 glycans contain the typical core-2 structure, 3 glycans have the core-1 structure and 2 glycans contained a previously unobserved core structure with hexose at the reducing end. There were seven pairs of structural isomers observed in the major O-linked oligosaccharides. To further elucidate the structures of a dozen O-linked glycans, specific and targeted exoglycosidase digestions were carried out and the products were monitored with MALDI-MS. Reported here are the elucidated structures of O-linked oligosaccharides from glycoproteins of X. borealis egg jelly coats. The structural differences in O-glycans from jelly coats of X. borealis and its close relatives may provide a better understanding of the structure-function relationships and the role of glycans in the fertilization process within Xenopodinae.

Protein glycosylation and its impact on biotechnology

Glycosylation is a post-translational modification that is of paramount importance in the production of recombinant pharmaceuticals as most recombinantly produced therapeutics are N- and/or O-glycosylated. Being a cell-system-dependent process, it also varies with expression systems and growth conditions, which result in glycan microheterogeneity and macroheterogeneity. Glycans have an effect on drug stability, serum half-life, and immunogenicity; it is therefore important to analyze and optimize the glycan decoration of pharmaceuticals. This review summarizes the aspects of protein glycosylation that are of interest to biotechnologists, namely, biosynthesis and biological relevance, as well as the tools to optimize and to analyze protein glycosylation.

Glycosidic intermediates identified in 1H MR spectra of intact tumour cells may contribute to the clarification of aspects of glycosylation pathways

The glycosylation process, through the addition of carbohydrates, is a major post-translational modification of proteins and glycolipids. Proteins may be glycosylated in either the secretory pathway leading to N-linked or O-linked glycoproteins or as nucleocytoplasmic glycosylation that targets only single proteins involving a single β-linked N-acetylglucosamine. In both cases, the key precursors are the uridine diphospho-N-acetylhexosamines synthesised by the hexosamine biosynthetic pathway. Furthermore, uridine diphospho-N-acetylglucosamine participates in the biosynthesis of sialic acid. In this work, we propose MRS for the detection of uridine diphospho-N-acetylhexosamines visible in high-resolution MR spectra of intact cells from different human tumours. Signals from the nucleotide and amino sugar moieties, including amide signals observed for the first time in whole cells, are assigned, also taking advantage of spectral changes that follow cell treatment with ammonium chloride. Finally, parallel changes in uridine diphospho-N-acetylhexosamines and glutamine pools, observed after pH changes induced by ammonium chloride in the different tumour cell lines, may provide more details on the glycosylation processes.

Functional assays for the molecular chaperone cosmc

Mucin type O-glycosylation involves sequential actions of several glycosyltransferases in the Golgi apparatus. Among those enzymes, a single gene product termed core 1 beta3-galactosyltransferase (T-synthase) in vertebrates is the key enzyme that converts the precursor Tn antigen GalNAcalpha1-Ser/Thr to the core 1 structure, Galbeta1-3GalNAcalpha1-Ser/Thr, also known as T antigen. This represents the most common structure within typical O-glycans of membrane and secreted glycoproteins. Formation of the active T-synthase requires that it interacts with Core 1 beta3Gal-T Specific Molecular Chaperone (Cosmc), which is a specific molecular chaperone in the endoplasmic reticulum (ER). T-synthase activity is commonly measured by its ability to transfer [3H]Gal from UDP-[3H]Gal to an artificial acceptor GalNAcalpha-1-O-phenyl to form [3H]Galbeta1-3GalNAcalpha-1-O-phenyl, which can then be isolated and quantified. Because the primary function of Cosmc is to form active T-synthase, the activity of Cosmc is assessed indirectly by its ability to promote formation of active T-synthase when it is coexpressed with T-synthase in cells lacking functional Cosmc. Such cells include insect cells, which constitutively lack Cosmc, and Cosmc-deficient mammalian cell lines. Cosmc is encoded by the X-linked Cosmc gene (Xq24 in human, Xc3 in mice), thus, acquired mutations in Cosmc, which have been observed in several human diseases, such as Tn syndrome and cancers, cause a loss of T-synthase, and expression of the Tn antigen. The methods described here allow the functional activities of such mutated Cosmc (mCosmc) to be measured and compared to wild-type (wtCosmc).

5-Aza-2'-deoxycytidine increases sialyl Lewis X on MUC1 by stimulating β-galactoside:α2,3-sialyltransferase 6 gene

Sialyl Lewis X is a tumor-associated antigen frequently found in the advanced cancers. However, the mechanism for the production of this cancer antigen is not entirely clear. The objective of this study is to examine whether epigenetics is involved in the regulation of the formation of this antigen. We observed an increase of sialyl Lewis X in HCT15 cells, a colon cancer cell line, treated with 5-Aza-2'-deoxycytidine. This treatment enhanced the expression of β-galactoside:α2,3-sialyltransferase 6 gene and sialyl Lewis X on MUC1, and the adherence of these cells to E-selectin under dynamic flow conditions. In addition, 5-Aza-2'-deoxycytidine treatment inhibited methylation of β-galactoside:α2,3-sialyltransferase 6 gene and siRNA knockdown of this gene drastically reduced sialyl Lewis X without affecting MUC1 expression. We conclude that 5-Aza-2'-deoxycytidine treatment increases sialyl Lewis X on MUC1 by stimulating the β-galactoside:α2,3-sialyltransferase 6 gene via inhibition of DNA methylation. Increased sialyl Lewis X by 5-Aza-2'-deoxycytidine raises a concern about the safety of this chemotherapeutic drug. In addition, β-galactoside:α2,3-sialyltransferase 6 gene may be a potential therapeutic target for suppressing tumorigenicity of colon cancer.

Glycan changes: cancer metastasis and anti-cancer vaccines

Complex carbohydrates, which are major components of the cell membrane, perform important functions in cell-cell and cell-extracellular matrix interactions, as well as in signal transduction. They comprise three kinds of biomolecules: glycoproteins, proteoglycans and glycosphingolipids. Recent studies have also shown that glycan changes in malignant cells take a variety of forms and mediate key pathophysiological events during the various stages of tumour progression. Glycosylation changes are universal hallmarks of malignant transformation and tumour progression in human cancer, which take place on the whole cells or some specific molecules. Accordingly, those changes make them prominent candidates for cancer biomarkers in the meantime. This review mainly focuses on the correlation between glycosylation and the metastasis potential of tumour cells from comprehensive aspects to further address the vital roles of glycans in oncogenesising. Moreover, utilizing these glycosylation changes to ward off tumour metastasis by means of anti-adhesion approach or devising anti-cancer vaccine is one of promising targets of future study.

Random glycopeptide bead libraries for seromic biomarker discovery

Identification of disease-specific biomarkers is important to address early diagnosis and management of disease. Aberrant post-translational modifications (PTM) of proteins such as O-glycosylations (O-PTMs) are emerging as triggers of autoantibodies that can serve as sensitive biomarkers. Here we have developed a random glycopeptide bead library screening platform for detection of autoantibodies and other binding proteins. Libraries were build on biocompatible PEGA beads including a safety-catch C-terminal amide linker (SCAL) that allowed mild cleavage conditions (I(2)/NaBH(4) and TFA) for release of glycopeptides and sequence determination by ESI-Orbitrap-MS(n). As proof-of-principle, tumor -specific glycopeptide reporter epitopes were built-in into the libraries and were detected by tumor-specific monoclonal antibodies and autoantibodies from cancer patients. Sequenced and identified glycopeptides were resynthesized at the preparative scale by automated parallel peptide synthesis and printed on microarrays for validation and broader analysis with larger sets of sera. We further showed that chemical synthesis of the monosaccharide O-glycopeptide library (Tn-glycoform) could be diversified to other tumor glycoforms by on-bead enzymatic glycosylation reactions with recombinant glycosyltransferases. Hence, we have developed a high-throughput flexible platform for rapid discovery of O-glycopeptide biomarkers and the method has applicability in other types of assays such as lectin/antibody/enzyme specificity studies as well as investigation of other PTMs.

A high-throughput O-glycopeptide discovery platform for seromic profiling

Biomarker microarrays are becoming valuable tools for serological screening of disease-associated autoantibodies. Post-translational modifications (PTMs) such as glycosylation extend the range of protein function, and a variety of glycosylated proteins are known to be altered in disease progression. Here, we have developed a synthetic screening microarray platform for facile display of O-glycosylated peptides (O-PTMs). By introduction of a capping step during chemical solid-phase glycopeptide synthesis, selective enrichment of N-terminal glycopeptide end products was achieved on an amine-reactive hydrogel-coated microarray glass surface, allowing high-throughput display of large numbers of glycopeptides. Utilizing a repertoire of recombinant glycosyltransferases enabled further diversification of the array libraries in situ and display of a new level of potential biomarker candidates for serological screening. As proof-of-concept, we have demonstrated that MUC1 glycopeptides could be assembled and used to detect autoantibodies in vaccine-induced disease-free breast cancer patients and in patients with confirmed disease at time of diagnosis.

Unexpected tolerance of glycosylation by UDP-GalNAc:polypeptide alpha-N-acetylgalactosaminyltransferase revealed by electron capture dissociation mass spectrometry: carbohydrate as potential protective groups

UDP-GalNAc:polypeptide alpha-N-acetylgalactosaminyltransferases (ppGalNAcTs, EC 2.4.1.41), a family of key enzymes that initiate posttranslational modification with O-glycans in mucin synthesis by introduction of alpha-GalNAc residues, are structurally composed of a catalytic domain and a lectin domain. It has been known that multiple Ser/Thr residues are assigned in common mucin glycoproteins as potential O-glycosylation sites and more than 20 distinct isoforms of this enzyme family contribute to produce densely O-glycosylated mucin glycoproteins. However, it seems that the functional role of the lectin domain of ppGalNAcTs remains unclear. We considered that electron capture dissociation mass spectrometry (ECD-MS), a promising method for highly selective fragmentation at peptide linkages of glycopeptides to generate unique c and z series of ions, should allow for precise structural characterization to uncover the mechanism in O-glycosylation of mucin peptides by ppGalNAcTs. In the present study, it was demonstrated that a system composed of an electrospray source, a linear RFQ ion trap that isolates precursor ions, the ECD device, and a TOF mass spectrometer is a nice tool to identify the preferential O-glycosylation sites without any decomposition of the carbohydrate moiety. It should be noted that electrons used for ECD are accelerated within a range from 1.75 to 9.75 eV depending on the structures of glycopeptides of interest. We revealed for the first time that additional installation of a alpha-GalNAc residue at potential glycosylation sites by ppGalNAcT2 proceeds smoothly in various unnatural glycopeptides having alpha-Man, alpha-Fuc, and beta-Gal residues as well as alpha-GalNAc residues. The results may suggest that ppGalNAcT2 did not differentiate totally presubstituted sugar residues in terms of configuration of functional groups, d-, l-configuration, and even alpha-, beta-stereochemistry at an anomeric carbon atom when relatively short synthetic peptides were employed for the acceptor substrates. Unexpected characteristics of ppGalNAcT2 motivated us to challenge site-directed installation of alpha-GalNAc residues at desired position(s) by protecting some hydroxyl groups of Thr/Ser residues with selectively removable sugars, notably a novel concept as "carbohydrate as protective groups", toward a goal of the systematic chemical and enzymatic synthesis of biologically important mucin glycopeptides.

Synthetic vaccines based on N- and O-glycopeptides–molecular tools for immunotherapy and diagnostics

This chapter summarizes available methods for the preparation of synthetic vaccines based on glycopeptides and recent advances in this field. It further includes results of their immunological evaluation. Syntheses of glycopeptides of defined chemical structure and conjugation of these compounds to a carrier protein or an immunostimulant are of interest for the development of new immunotherapeutics and/or antibody-based diagnostics. Since a number of years, the aberrant glycosylation of the tumorassociated mucin MUC1 forming tumor specific epitopes on the epithelial cell surface has been considered an attractive research target for the preparation of such vaccines. Examples of synthetic vaccines directed against the O-glycosylated MUC1 tandem repeats will here be given including synthetic MUC1 glycopeptides conjugated to a T-cell epitope peptide, to a carrier protein, to a lipid immunostimulant or the multimeric presentation of glycopeptides on dendrimers. Other attractive targets for immunotherapy are the viral envelope proteins HIV gp120 and HIV gp41 , which are highly glycosylated with high-mannose and complex type N-glycans. Examples will be given, which illustrate syntheses of high-mannose HIV gp120 or gp41 glycopeptides with the natural peptide backbone or with a non-natural cyclic backbone to mimic the high-mannose cluster domain of HIV gp120. In addition the synthesis and immunological evaluation of a vaccine will be described, which contains the high-mannose cluster mimotope glycopeptide conjugated to an outer membrane protein complex (OMPC) as the carrier.

Solid-phase synthesis of a pentavalent GalNAc-containing glycopeptide (Tn antigen) representing the nephropathy-associated IgA hinge region

Incomplete or aberrant glycosylation leading to Tn antigen (GalNAcalpha1-Ser/Thr) expression on human glycoproteins is strongly associated with human pathological conditions, including tumors, certain autoimmune diseases, such as the idiopathic IgA nephropathy, and may modulate immune homeostasis. In addition, the Tn antigen is highly expressed by certain pathogens and plays a role in host-pathogen interactions. To enable experimental approaches to study interactions of the Tn antigen with the immune system and analyze anti-Tn antibody responses in infection or disorders, we generated a Tn-expressing resource that can be used for high-throughput screening. In consideration of IgA nephropathy in which the hinge region is incompletely glycosylated, we used this hinge sequence that encodes five potential glycosylation sites as the ideal template for the synthesis of a Tn antigen-expressing glycopeptide. Inclusion of an N-terminal biotin in the peptide enabled binding to streptavidin-coated ELISA plates as monitored using Helix pomatia agglutinin or anti-Tn monoclonal antibody. We also found that the biotinylated IgA-Tn peptide is a functional acceptor for beta1-3-galactosylation using recombinant T-synthase (beta1-3-galactosyltransferase). Besides its immunochemical functionality as a possible diagnostic tool for IgA nephropathy, the peptide is an excellent substrate for glycan elongation and represents a novel template applicable for glycan-antigen-associated diseases.

Wisteria floribunda agglutinin-positive mucin 1 is a sensitive biliary marker for human cholangiocarcinoma

Cholangiocarcinoma (CC) is an aggressive malignant tumor for which useful markers are not presently available for early and precise diagnosis. The aim of this study was therefore to identify a high-performance diagnostic marker with a special focus on glyco-alteration of glycoproteins. In the course of study, we found that Wisteria floribunda agglutinin (WFA) is the best probe to differentiate intrahepatic cholangiocarcinoma (ICC) lesions from normal bile duct epithelia (BDE) (P < 0.0001). The subsequent histochemical study confirmed ICC-specific WFA staining on 165 tissue specimens. On the other hand, the WFA staining was shown to be closely associated with that of MY.1E12 established previously against sialylated mucin 1 (MUC1) by double-staining experiments. Moreover, glyco-alteration of MUC1 could be verified by western blotting of WFA-captured bile samples from patients with CC patients. Thus, we attempted to construct an enzyme-linked immunosorbent assay system for more convenient CC diagnosis, where WFA-coated plates, the specific monoclonal antibody MY.1E12, and the bile specimens from CC including ICC (n = 30) and benign diseases (n = 38) were combined. As a result, CC was clearly distinguished from benign diseases with statistical scores (sensitivity = 90.0%, specificity = 76.3%, and area under the curve = 0.85). As a particular note, the obtained sensitivity is the highest score among those having been so far reported.

CONCLUSION

Our approach focusing significant glyco-alteration of a particular glycoprotein yielded a novel diagnostic system for CC with satisfactory clinical scores.

The glycosylation of human synovial lubricin: implications for its role in inflammation

Acidic proteins were isolated from synovial fluid from two osteoarthritic and two rheumatoid arthritic patients and identified by MS. It was found that the most abundant protein in all of the samples was the mucin-like protein lubricin. Further characterization of lubricin from the different patients by LC (liquid chromatography)–MS of released oligosaccharides showed that the core 1 O-linked oligosaccharides NeuAcα2–3Galβ1–3GalNAc and NeuAcα2–3Galβ1–3(NeuAcα2–6)GalNAc were the dominating structures on lubricin. The latter was found to be more prevalent in the rheumatoid arthritis samples, indicating that sialylation is up-regulated as part of the inflammatory response. In addition to these dominating structures, core 2 structures were also found in low amounts, where the largest was the disialylated hexasaccharide corresponding to the sequence NeuAcα2–3Galβ1–3(NeuAcα2–3Galβ1–3/4GlcNAcβ1–6)GalNAc. It was also found that a small proportion of the core 2 oligosaccharides carried sulfate. The ability of lubricin to present complex glycosylation reflecting the state of the joint tissue makes lubricin a candidate as a carrier of inflammatory oligosaccharide epitopes. In particular, it was shown that lubricin from inflamed arthritic tissue was recognized by the antibody MECA-79 and thus carried the sulfated epitope proposed to be part of the L-selectin ligand that is responsible for recruitment of leucocytes to inflammatory sites.

Role of EBAG9 protein in coat protein complex I-dependent glycoprotein maturation and secretion processes in tumor cells

Many proteins mature within the secretory pathway by the acquisition of glycans. Failure to maintain the proper distribution of the glycosylation machinery might lead to disease. High expression levels of the ubiquitous Golgi protein estrogen receptor-binding fragment-associated gene 9 (EBAG9) in human tumors correlate with poor clinical prognosis, and EBAG9 overexpression in epithelial cell lines induces truncated glycans, typical of many carcinomas. Here, we addressed the pathogenetic link between EBAG9 expression and the alteration of the cellular glycome. We applied confocal microscopy, live imaging, pulse-chase labeling in conjunction with immunoprecipitation, and enzymatic activity assays in a variety of EBAG9-overexpressing or depleted epithelial tumor cell lines. EBAG9 shuttles between the ER-Golgi intermediate compartment and the cis-Golgi, and we demonstrate association of EBAG9 with coat protein complex I (COPI)-coated transport vesicles. EBAG9 overexpression imposes delay of endoplasmic reticulum-to-Golgi transport and mislocalizes components of the ER quality control and glycosylation machinery. Conversely, EBAG9 down-regulation accelerates glycoprotein transport through the Golgi and enhances mannosidase activity. Thus, EBAG9 acts as a negative regulator of a COPI-dependent ER-to-Golgi transport pathway in epithelial cells and represents a novel pathogenetic principle in which interference with intracellular membrane trafficking results in the emergence of a tumor-associated glycome.

Profiles of carbohydrate ligands associated with adsorbed proteins on self-assembled monolayers of defined chemistries

Conserved protein-carbohydrate-lipid pathogen-associated molecular patterns (PAMPs) interact with cells of the innate immune system to mediate antigen recognition and internalization and activation of immune cells. We examined if analogous "biomaterial-associated molecular patterns" composed of proteins, specifically their carbohydrate modifications, existed on biomaterials, which can play a role in mediating the innate immune response to biomaterials. To probe for these carbohydrates in the adsorbed protein layer, as directed by the underlying biomaterial chemistry, self-assembled monolayers (SAMs) presenting -CH(3), -OH, -COOH, or -NH(2) were preincubated with serum/plasma, and the presence of carbohydrate ligands of C-type lectin receptors (CLRs) was investigated using lectin probes in an enzyme-linked lectin assay (ELLA). Presentation of CLR ligands was detected on control tissue culture polystyrene (TCPS). Absorbances of mannose or N-acetylglucosamine increased with decreasing incubating serum concentration, whereas absorbances of sialylated epitopes or fucose remained unchanged. Absorbances of alpha-galactose or N-acetylgalactosamine decreased with decreasing incubating serum concentration; beta-galactose was undetectable. Among SAM endgroups, preincubation with 10% serum resulted in differential presentation of CLR ligands: higher alpha-galactose on COOH SAMs than NH(2) or CH(3) SAMs, highest complex mannose on NH(2) SAMs, and higher complex mannose on OH SAMs than CH(3) SAMs. Least sialylated groups were detected on CH(3) SAMs. In summary, biomaterial chemistry may regulate protein adsorption and hence unique presentation of associated carbohydrates. The ultimate goal is to identify the effects of protein glycosylations associated with biomaterials in stimulating innate immune responses.

Preparation of biomolecule microstructures and microarrays by thiol-ene photoimmobilization

A mild, fast and flexible method for photoimmobilization of biomolecules based on the light-initiated thiol-ene reaction has been developed. After investigation and optimization of various surface materials, surface chemistries and reaction parameters, microstructures and microarrays of biotin, oligonucleotides, peptides, and MUC1 tandem repeat glycopeptides were prepared with this photoimmobilization method. Furthermore, MUC1 tandem repeat glycopeptide microarrays were successfully used to probe antibodies in mouse serum obtained from vaccinated mice. Dimensions of biomolecule microstructures were shown to be freely controllable through photolithographic techniques, and features down to 5 microm in size covering an area of up to 75x25 mm were created. Use of a confocal laser microscope with a UV laser as UV-light source enabled further reduction of biotin feature size opening access to nanostructured biochips.

N-Acetylgalactosaminyltransferase-14 as a potential biomarker for breast cancer by immunohistochemistry

Background

The post-translational modification of proteins, including glycosylation, differs between normal and tumor cells. The UDP-N-acetyl-D-galactosamine polypeptide N-acetylgalactosaminyltransferases (GalNAc-Tases) family of enzymes regulates the initial steps of mucin O-glycosylation and is responsible for the altered glycosylation state observed in cancer cells. Recently it was found that GalNAc-T14 mRNA is heterogeneously expressed in breast carcinomas compared to normal tissue, however the expression profile of GalNAc-T14 protein in breast carcinomas compared to normal tissue is still unknown. In this study, we assessed the expression profile of GalNAc-T14 protein in malignant and non-malignant breast tissues by immunohistochemistry to evaluate whether GalNAc-T14 might be a potential biomarker for breast cancer.

Methods

In formalin-fixed tissues, the expression level of GalNAc-T14 protein was evaluated by immunohistochemistry assay in breast tissues. Expression profiles were assessed in normal tissues, benign fibroadenomas and several types of carcinomas.

Results

Our results showed that GalNAc-T14 was heterogeneously expressed in breast carcinomas compared to non-malignant tissue. GalNAc-T14 expression was observed in 47/56 (83.9%) carcinoma samples, 7/48 (14.6%) non-malignant breast tissue samples. GalNAc-T14 expression level was associated with histological grade. For this enzyme a significant association with invasive ductal type, mucinous adenocarcinoma and ductal carcinoma in situ (DCIS) type was found.

Conclusion

Our results provide evidence that GalNAc-T14 may be a potential biomarker for breast cancer by immunohistochemistry. GalNAc-T14 expression level was associated with histological grade. GalNAc-T14 expression can provide new insights about breast cancer glycobiology.

Carbohydrate-based therapeutics

In recent years there has been a resurgence of interest in the biological roles of carbohydrates and as a result it is now known that carbohydrates are involved in a vast array of disease processes. This review summarises progress in the development of carbohydrate-based therapeutics that involve: inhibition of carbohydrate-lectin interactions; immunisation, using monoclonal antibodies for carbohydrate antigens; inhibition of enzymes that synthesise disease-associated carbohydrates; replacement of carbohydrate-processing enzymes; targeting of drugs to specific disease cells via carbohydrate-lectin interactions; carbohydrate based anti-thrombotic agents.

An essential epitope of anti-MUC1 monoclonal antibody KL-6 revealed by focused glycopeptide library

Human serum Krebs von den Lungen-6 (KL-6) antigen, a high-molecular-weight glycoprotein classified as a polymorphic epithelial mucin (MUC1), is a biomarker of diseases such as interstitial pneumonia, lung adenocarcinoma, breast cancer, colorectal adenocarcinoma, and hepatocellular carcinoma. Anti-KL-6 monoclonal antibody (anti-KL-6 MAb) is therefore a potential diagnostic and therapeutic reagent. Although glycosylation at Thr/Ser residues of the tandem-repeating MUC1 peptides appears to determine the disease-associated antigenic structures of KL-6, an essential epitope structure recognized by anti-KL-6 MAb remains unclear. In the present study, a novel compound library of synthetic MUC1 glycopeptides allowed the first rapid and precise evaluation of the specific epitope structure of anti-KL-6 MAb by combined use of a tailored glycopeptides library and common ELISA protocol. We demonstrated that the minimal antigenic structure, an essential epitope, recognized by anti-KL-6 MAb is a heptapeptide sequence Pro-Asp-Thr-Arg-Pro-Ala-Pro (PDTRPAP), in which the Thr residue is modified by Neu5Ac alpha2,3Gal beta1,3GalNAc alpha (2,3-sialyl T antigen, core 1-type O-glycan). Anti-KL-6 MAb did not bind with other tumor-relevant antigens, such as GalNAc alpha (Tn), Neu5Ac alpha2,6GalNAc alpha (STn), and Gal beta1,3GalNAc alpha (T), except for Neu5Ac alpha2,3Gal beta1,3(Neu5Ac alpha2,6)GalNAc alpha (2,3/2,6-disialyl T). However, anti-KL-6 MAb could not differentiate the above minimal antigenic glycopeptide from some core 2-based glycopeptides involving this crucial epitope structure and showed a similar binding affinity toward these compounds, indicating that branching at the O-6 position of GalNAc residue does not influence the interaction of anti-KL-6 MAb with some MUC1 glycoproteins involving an essential epitope. Actually, anti-KL-6 MAb reacts with 2,3/2,6-disialyl T having a 2,3-sialyl T component. This is why anti-KL-6 MAb often reacts with various kinds of tumor-derived MUC1 glycoproteins as well as a clinically important MUC1 glycoprotein biomarker of interstitial pneumonia, namely KL-6, originally discovered as a circulating pulmonary adenocarcinoma-associated antigen. In other words, combined use of anti-KL-6 MAb and some probes that can differentiate the sugars substituted at the O-6 position of the GalNAc residue in MUC1 glycopeptides including the PDTRPAP sequence might be a promising diagnostic protocol for individual disease-specific biomarkers. It was also revealed that glycosylation at neighboring Thr/Ser residues outside the immunodominant PDTRPAP motif strongly influences the interaction between anti-KL-6 MAb and MUC1 glycopeptides involving the identified epitope. Our novel strategy will greatly facilitate the processes for the identification of the tumor-specific and strong epitopes of various known anti-MUC1 MAbs and allow for their practical application in the generation of improved antibody immunotherapeutics, diagnostics, and MUC1-based cancer vaccines.

A glycomics approach to the discovery of potential cancer biomarkers

Glycosylation is highly sensitive to the biochemical environment and plays a key role in development and disease manifestation. Moreover, glycan biosynthesis depends on several highly competitive processes; thus, variations in the concentration of specific glycosyltransferases produce different products. For this reason, monitoring changes in glycosylation may be a more specific and sensitive approach to biomarker discovery and possibly disease diagnosis. Glycans in serum are of particular interest as approximately half of all proteins are glycosylated. We have developed the methods for profiling the glycans in human serum to identify glycan biomarker. Global release methods were used including chemical and enzymatic to access O-linked and N-linked glycans, respectively. Glycans were released from the culture medium of various cancer cell lines, in control sera, and in cancer patients and isolated using solid phase extraction (SPE) with a porous graphitized carbon. The SPE fractions were analyzed by matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry (MALDI FTICR MS). Glycan compositions were determined based on accurate masses and tandem mass spectrometry. Glycosylation changes between control and patient group were monitored. Several glycans were identified as potential markers for ovarian, breast, and prostate cancer. In short, direct glycan analysis of human serum without any protein identification represents a new and innovative approach to disease marker discovery.

Galectin-1 and HIV-1 Infection

Initial binding of human immunodeficiency virus-1 (HIV-1) to its susceptible CD4(+) cells is the limiting step for the establishment of infection as the avidity of viral envelope gp120 for CD4 is not high and the number of viral envelope spikes on the surface is found to be low compared to highly infectious viruses. Several host factors, such as C-type lectins, are listed as being able to enforce or facilitate the crucial interaction of HIV-1 to the susceptible cell. Recent works suggest that a host soluble beta-galactoside-binding lectin, galectin-1, also facilitates both virion binding and the infection of target cells in a manner dependent on lactose but not mannose, suggesting that this soluble galectin can be considered as a host factor that influences HIV-1 pathogenesis. In this chapter, we describe methods used to investigate the potential role of the galectin family in HIV-1-mediated disease progression.

Glycan gene expression signatures in normal and malignant breast tissue; possible role in diagnosis and progression

Glycosylation is the stepwise procedure of covalent attachment of oligosaccharide chains to proteins or lipids, and alterations in this process have been associated with malignant transformation. Simultaneous analysis of the expression of all glycan-related genes clearly gives the advantage of enabling a comprehensive view of the genetic background of the glycobiological changes in cancer cells. Studies focusing on the expression of the whole glycome have now become possible, which prompted us to review the present knowledge on glycosylation in relation to breast cancer diagnosis and progression, in the light of available expression data from tumors and breast tissue of healthy individuals. We used various data resources to select a set of 419 functionally relevant genes involved in synthesis, degradation and binding of N-linked and O-linked glycans, Lewis antigens, glycosaminoglycans (chondroitin, heparin and keratan sulfate in addition to hyaluronan) and glycosphingolipids. Such glycans are involved in a number of processes relevant to carcinogenesis, including regulation of growth factors/growth factor receptors, cell-cell adhesion and motility as well as immune system modulation. Expression analysis of these glycan-related genes revealed that mRNA levels for many of them differ significantly between normal and malignant breast tissue. An associative analysis of these genes in the context of current knowledge of their function in protein glycosylation and connection(s) to cancer indicated that synthesis, degradation and adhesion mediated by glycans may be altered drastically in mammary carcinomas. Although further analysis is needed to assess how changes in mRNA levels of glycan genes influence a cell's glycome and the precise role that such altered glycan structures play in the pathogenesis of the disease, lessons drawn from this study may help in determining directions for future research in the rapidly-developing field of glycobiology.

Current status of mucins in the diagnosis and therapy of cancer

Mucins are the most abundant high molecular weight glycoproteins in mucus. Their nature and glycosylation content dictates the biochemical and biophysical properties of viscoelastic secretions, pointing out an important role in diverse biological functions, such as differentiation, cell adhesions, immune responses, and cell signaling. Mucins are expressed in tubular organs by specialized epithelial cells in the body. Their aberrant expression is well documented in a variety of inflammatory or malignant diseases. From a prognosis point of view, their expression and alterations in glycosylation are associated with the development and progression of malignant diseases. Therefore, mucins can be used as valuable markers to distinguish between normal and disease conditions. Indeed, this alteration in glycosylation patterns generates several epitopes in the oligosaccharide side chains that can be used as diagnostic and/or prognostic markers. Furthermore, these characteristic tumor-associated epitopes are extensively used as appropriate immunotargets of malignant epithelial cells. Therefore, in an effort to detect and treat cancer at the earliest stage possible, mucins are analyzed as potential markers of disease for diagnosis, progression, and for therapeutic purposes. In this review, we focused on the current status of the distribution of mucins in normal and pathologic conditions and their clinical use both in cancer diagnosis and therapeutics treatments.

ST3Gal.I sialyltransferase relevance in bladder cancer tissues and cell lines

BACKGROUND

The T antigen is a tumor-associated structure whose sialylated form (the sialyl-T antigen) involves the altered expression of sialyltransferases and has been related with worse prognosis. Since little or no information is available on this subject, we investigated the regulation of the sialyltransferases, able to sialylate the T antigen, in bladder cancer progression.

METHODS

Matched samples of urothelium and tumor tissue, and four bladder cancer cell lines were screened for: ST3Gal.I, ST3Gal.II and ST3Gal.IV mRNA level by real-time PCR. Sialyl-T antigen was detected by dot blot and flow cytometry using peanut lectin. Sialyltransferase activity was measured against the T antigen in the cell lines.

RESULTS

In nonmuscle-invasive bladder cancers, ST3Gal.I mRNA levels were significantly higher than corresponding urothelium (p < 0.001) and this increase was twice more pronounced in cancers with tendency for recurrence. In muscle-invasive cancers and matching urothelium, ST3Gal.I mRNA levels were as elevated as nonmuscle-invasive cancers. Both non-malignant bladder tumors and corresponding urothelium showed ST3Gal.I mRNA levels lower than all the other specimen groups. A good correlation was observed in bladder cancer cell lines between the ST3Gal.I mRNA level, the ST activity (r = 0.99; p = 0.001) and sialyl-T antigen expression, demonstrating that sialylation of T antigen is attributable to ST3Gal.I. The expression of sialyl-T antigens was found in patients' bladder tumors and urothelium, although without a marked relationship with mRNA level. The two ST3Gal.I transcript variants were also equally expressed, independently of cell phenotype or malignancy.

CONCLUSION

ST3Gal.I plays the major role in the sialylation of the T antigen in bladder cancer. The overexpression of ST3Gal.I seems to be part of the initial oncogenic transformation of bladder and can be considered when predicting cancer progression and recurrence.

Mucin-type O-glycans in tears of normal subjects and patients with non-Sjögren's dry eye

PURPOSE

O-linked carbohydrates (O-glycans) contribute to the hydrophilic character of mucins in mucosal tissues. This study was conducted to identify the repertoire of O-glycans in the tear film and the glycosyltransferases associated with their biosynthesis, in normal subjects and patients with non-Sjögren's dry eye.

METHODS

Human tear fluid was collected from the inferior conjunctival fornix. O-glycans were released by hydrazinolysis, labeled with 2-aminobenzamide, and analyzed by fluorometric, high-performance liquid chromatography (HPLC) coupled with exoglycosidase digestions. O-glycan structures identified in tears were related to potential biosynthetic pathways in human conjunctival epithelium by using a glycogene microarray database. Lectin-binding analyses were performed with agglutinins from Arachis hypogaea, Maackia amurensis, and Sambucus nigra.

RESULTS

The O-glycan profile of human tears consisted primarily of core 1 (Gal beta 1-3GalNAc alpha 1-Ser/Thr)-based structures. Mono-sialyl O-glycans represented approximately 66% of the glycan pool, with alpha2-6-sialyl core 1 being the predominant O-glycan structure in human tears (48%). Four families of glycosyltransferases potentially related to the biosynthesis of these structures were identified in human conjunctiva. These included 13 polypeptide-GalNAc-transferases (GALNT), the core 1 beta-3-galactosyltransferase (T-synthase), three alpha2-6-sialyltransferases (ST6GalNAc), and two alpha2-3-sialyltransferases (ST3Gal). No significant differences in total amount of O-glycans were detected between tears of normal subjects and patients with dry eye, by HPLC and lectin blot. Likewise, no differences in glycosyltransferase expression were found by glycogene microarray.

CONCLUSIONS

This study identified the most common mucin-type O-glycans in human tears and their expected biosynthetic pathways in ocular surface epithelia. Patients with non-Sjögren's dry eye showed no alterations in composition and amount of O-glycans in the tear fluid.

Glycan gimmickry by parasitic helminths: a strategy for modulating the host immune response?

Parasitic helminths (worms) co-evolved with vertebrate immune systems to enable long-term survival of worms in infected hosts. Among their survival strategies, worms use their glycans within glycoproteins and glycolipids, which are abundant on helminth surfaces and in their excretory/ secretory products, to regulate and suppress host immune responses. Many helminths express unusual and antigenic (nonhost-like) glycans, including those containing polyfucose, tyvelose, terminal GalNAc, phosphorylcholine, methyl groups, and sugars in unusual linkages. In addition, some glycan antigens are expressed that share structural features with those in their intermediate and vertebrate hosts (host-like glycans), including Le(X) (Galbeta1-4[Fucalpha1-3]GlcNAc-), LDNF (GalNAcbeta1-4[Fucalpha1-3]GlcNAc-), LDN (GalNAcbeta1-4GlcNAc-), and Tn (GalNAcalpha1-O-Thr/Ser) antigens. The expression of host-like glycan determinants is remarkable and suggests that helminths may gain advantages by synthesizing such glycans. The expression of host-like glycans by parasites previously led to the concept of "molecular mimicry," in which molecules are either derived from the pathogen or acquired from the host to evade recognition by the host immune system. However, recent discoveries into the potential of host glycan-binding proteins (GBPs), such as C-type lectin receptors and galectins, to functionally interact with various host-like helminth glycans provide new insights. Host GBPs through their interactions with worm-derived glycans participate in shaping innate and adaptive immune responses upon infection. We thus propose an alternative concept termed "glycan gimmickry," which is defined as an active strategy of parasites to use their glycans to target GBPs within the host to promote their survival.

GalNAc-T14 may be involved in regulating the apoptotic action of IGFBP-3

Insulin-like growth factor binding protein-3 (IGFBP-3) is known to induce apoptosis in an insulin-like growth factor (IGF)-dependent and IGF-independent manner, but the mechanism underlying the IGF-independent effects remains unclear. Polypeptide N-acetylgalactosaminyltransferase 14 (GalNAc-T14) is a novel IGFBP-3 binding partner. In this paper, small interference RNA (siRNA) targeting GalNAc-T14 was used to examine whether GalNAc-T14 affects the apoptotic action of IGFBP-3. Using semi-quantitative reverse-transcriptase polymerase chain reaction (RT-PCR) and western blot analysis, we determined that GalNAc-T14 expression was downregulated by the siRNA directed against GalNAc-T14. Apoptosis analysis of IGFBP-3-overexpressing cells treated with siRNA against GalNAc-T14 was performed to determine if GalNAc-T14 was specifically involved in IGFBP-3 signalling. The results, as determined by flow cytometric analysis and caspase-3 assay, showed that the extent of apoptosis induced by IGFBP-increased with RNA interference (RNAi) knockdown of GalNAc-T14. Our data suggest that GalNAc-T14 influences the apoptotic action of IGFBP-3 and might mediate the signalling pathway of IGFBP-3. Experiments to determine the role of GalNAc-T14 in the regulation of apoptosis induced by IGFBP-3 are under way.

Elevated mRNA level of hST6Gal I and hST3Gal V positively correlates with the high risk of pediatric acute leukemia

Altered sialylation occurs in essentially all types of human and experimental cancers. Although, aberrant sialylation is believed to mainly due to altered sialyltransferase (ST) level, so far, expression pattern of different STs in acute lymphoblastic leukemia has never been investigated. Accordingly, the aim of our study was to monitor the changes in mRNA expression of ST6Gal I, ST3Gal V and ST8Sia I in patients by real-time PCR, which may provide prognostic information useful in defining appropriate therapeutic options. Our data demonstrated that ST6Gal I and ST3Gal V mRNA were up-regulated in lymphoblasts whereas its presence was negligible in non-malignant donors. In contrast, ST8SiaI was downregulated in patients. The extents of linkage-specific sialylation of glycoconjugates were found to be associated with disease establishment. Additionally, ST6Gal I and ST3Gal V were positively correlated with the high risk of the disease (P=0.0032 and 0.0016). This differential ST level can be used as biomarker with the molecular method of quantitative PCR and may be useful to discriminate normal and cancer patients.

Determination of Tn antigen released from cultured cancer cells by capillary electrophoresis

An incomplete elongation of O-glycans in mucins has been found in epithelial cancers, leading to the expression of shorter carbohydrate structures such as Tn antigen (GalNAc-O-Ser/Thr), which has been reported to be one of the most specific human cancer-associated structures. However, there have been no appropriate physicochemical methods for the determination of Tn antigen in biological samples. In the present paper, we developed a capillary electrophoresis method for the determination of Tn antigen, and applied the method to the analysis of the expressed Tn antigen on some leukemia and epithelial cancer cells.

Inactivating germ-line and somatic mutations in polypeptide N-acetylgalactosaminyltransferase 12 in human colon cancers

Aberrant glycosylation is a pathological alteration that is widespread in colon cancer, and usually accompanies the onset and progression of the disease. To date, the molecular mechanisms underlying aberrant glycosylation remain largely unknown. In this study, we identify somatic and germ-line mutations in the gene encoding for polypeptide N-acetylgalactosaminyltransferase 12 (GALNT12) in individuals with colon cancer. Biochemical analyses demonstrate that each of the 8 GALNT12 mutations identified inactivates the normal function of the GALNT enzyme in initiating mucin type O-linked protein glycosylation. Two of these inactivating GALNT12 mutations were identified as acquired somatic mutations in a set of 30 microsatellite stable colon tumors. Relative to background gene mutation rates, finding these somatic GALNT12 mutations was statistically significant at P < 0.001. Six additional inactivating GALNT12 mutations were detected as germ-line changes carried by patients with colon cancer; however, no inactivating variants were detected among cancer-free controls (P = 0.005). Notably, in 3 of the 6 individuals harboring inactivating germ-line GALNT12 mutations, both a colon cancer and a second independent epithelial cancer had developed. These findings suggest that genetic defects in the O-glycosylation pathway in part underlie aberrant glycosylation in colon cancers, and they contribute to the development of a subset of these malignancies.

Management of the human mucosal defensive barrier: evidence for glycan legislation

The human gastrointestinal barrier comprises several layers which enable protection against the external environment. The mucosal epithelium, lamina propria, glycocalyx and secreted mucus each make a contribution to barrier protection. Glycocalyx and secreted mucins constitute a glycosylated environment which interacts with the enteric microflora. Turnover of the mucus layer and the creation of binding ligands for bacteria are significant factors in gut homeostasis. The gut microbiota is composed of many bacterial species, but improved technology has allowed detection of populations present at different stages of development and in disease. Interaction of the microflora with the gut occurs from birth onwards and enables maturation of gut angiogenesis and glycosylation as demonstrated in mouse models. Glycan legislation regulates the ongoing interaction between the microflora and the host mucosa. This accounts for host glycosylation mechanisms providing a dynamic response to fluctuations in the gut microflora. Evidence for glycan legislation is based on a surgical model where intact mucosa can be compared with and without contact to the faecal microflora. In addition, mucosal cell glycosylation is assessed using inhibitors of O-glycan synthesis. These inhibitors lead to growth arrest in cultured colorectal cancer cell lines through the induction of apoptosis and downregulation of proliferation.

Expression of a core 3 disialyl-Le(x) hexasaccharide in human colorectal cancers: a potential marker of malignant transformation in colon

Cancer-associated alterations in cell surface and secreted glycoproteins have been catalogued for many years but many of the studies of alterations in mucin carbohydrate have relied on histochemical or immunohistochemical methods, with little direct chemical analysis. In this study, we analyzed the O-glycosylation pattern of MUC2 glycoprotein isolated from colorectal carcinomas, transitional mucosa and resection margins from three patients with blood group A, B and O, respectively. After alkaline borohydride treatment, the released oligosaccharides were structurally characterized by nanoESI Q-TOF tandem mass spectrometry without prior fractionation or derivatization. As expected, we found an increased expression of sialyl-Tn antigen in the colonic cancer mucins. A more interesting feature was the increased expression of a core 3 sialyl-Le(x) hexasaccharide, NeuAcalpha2-3Galbeta1-4(Fucalpha1-3)GlcNAcbeta1-3(NeuAcalpha2-6)GalNAc in tumor, which appeared to compete with its sulfo-Le(x) counterpart in normal tissue, SO3-3Galbeta1-4(Fucalpha1-3)GlcNAcbeta1-3(NeuAcalpha2-6)GalNAc. This antigen, whose structure was confirmed by NMR experiments, is based on a core 3 glycan and may be a potential marker for the malignant transformation of colonic cells. Unexpectedly, most of the glycans recovered in normal and carcinomas extracts were based on a sialylated core 3, GlcNAcbeta1-3(NeuAcalpha2-6)GalNAcol. Moreover, the pattern of glycosylation was very similar between mucins isolated from each sample, the main differences related to the level of expression of the major oligosaccharides. The data obtained in this investigation may have value for future screening studies on colorectal cancer.