Characterization of the oligosaccharides associated with the human ovarian tumor marker CA125

Regulation of glycan structures in animal tissues: transcript profiling of glycan-related genes

Glycan structures covalently attached to proteins and lipids play numerous roles in mammalian cells, including protein folding, targeting, recognition, and adhesion at the molecular or cellular level. Regulating the abundance of glycan structures on cellular glycoproteins and glycolipids is a complex process that depends on numerous factors. Most models for glycan regulation hypothesize that transcriptional control of the enzymes involved in glycan synthesis, modification, and catabolism determines glycan abundance and diversity. However, few broad-based studies have examined correlations between glycan structures and transcripts encoding the relevant biosynthetic and catabolic enzymes. Low transcript abundance for many glycan-related genes has hampered broad-based transcript profiling for comparison with glycan structural data. In an effort to facilitate comparison with glycan structural data and to identify the molecular basis of alterations in glycan structures, we have developed a medium-throughput quantitative real time reverse transcriptase-PCR platform for the analysis of transcripts encoding glycan-related enzymes and proteins in mouse tissues and cells. The method employs a comprehensive list of >700 genes, including enzymes involved in sugar-nucleotide biosynthesis, transporters, glycan extension, modification, recognition, catabolism, and numerous glycosylated core proteins. Comparison with parallel microarray analyses indicates a significantly greater sensitivity and dynamic range for our quantitative real time reverse transcriptase-PCR approach, particularly for the numerous low abundance glycan-related enzymes. Mapping of the genes and transcript levels to their respective biosynthetic pathway steps allowed a comparison with glycan structural data and provides support for a model where many, but not all, changes in glycan abundance result from alterations in transcript expression of corresponding biosynthetic enzymes.

Proteomic profiling identifies afamin as a potential biomarker for ovarian cancer

PURPOSE

To discover and validate serum glycoprotein biomarkers in ovarian cancer using proteomic-based approaches.

EXPERIMENTAL DESIGN

Serum samples from a "discovery set" of 20 patients with ovarian cancer or benign ovarian cysts or healthy volunteers were compared by fluorescence two-dimensional differential in-gel electrophoresis and parallel lectin-based two-dimensional profiling. Validation of a candidate biomarker was carried out with Western blotting and immunoassay (n = 424).

RESULTS

Twenty-six proteins that changed significantly were identified by mass spectrometric sequencing. One of these, confirmed by Western blotting, was afamin, a vitamin E binding protein, with two isoforms decreasing in patients with ovarian cancer. Validation using cross-sectional samples from 303 individuals (healthy controls and patients with benign, borderline, or malignant ovarian conditions and other cancers) assayed by ELISA showed significantly decreased total afamin concentrations in patients with ovarian cancer compared with healthy controls (P = 0.002) and patients with benign disease (P = 0.046). However, the receiver operating characteristic areas for total afamin for the comparison of ovarian cancer with healthy controls or benign controls were only 0.67 and 0.60, respectively, with comparable figures for CA-125 being 0.92 and 0.88 although corresponding figures for a subgroup of samples analyzed by isoelectric focusing for afamin isoform 2 were 0.85 and 0.79. Analysis of a further 121 samples collected prospectively from 9 patients pretreatment through to relapse indicated complementarity of afamin with CA-125, including two cases in whom CA-125 was noninformative.

CONCLUSIONS

Afamin shows potential complementarity with CA-125 in longitudinal monitoring of patients with ovarian cancer, justifying prospective larger-scale investigation. Changes in specific isoforms may provide further information.

Mucins in the mucosal barrier to infection

The mucosal tissues of the gastrointestinal, respiratory, reproductive, and urinary tracts, and the surface of the eye present an enormous surface area to the exterior environment. All of these tissues are covered with resident microbial flora, which vary considerably in composition and complexity. Mucosal tissues represent the site of infection or route of access for the majority of viruses, bacteria, yeast, protozoa, and multicellular parasites that cause human disease. Mucin glycoproteins are secreted in large quantities by mucosal epithelia, and cell surface mucins are a prominent feature of the apical glycocalyx of all mucosal epithelia. In this review, we highlight the central role played by mucins in accommodating the resident commensal flora and limiting infectious disease, interplay between underlying innate and adaptive immunity and mucins, and the strategies used by successful mucosal pathogens to subvert or avoid the mucin barrier, with a particular focus on bacteria.

Glycans as a Target in the Detection of Reproductive Tract Cancers

The significance of changes in glycosylation for the beginning, progress and outcome of different human diseases is highly recognized. In this review we summarized literature data on the alteration of glycans in cancer, especially glycoforms of tumor markers of reproductive tract cancers: prostate-specific antigen (PSA) and cancer antigen 125 (CA125). We aimed to highlight the diagnostic potential and relevance of glycan microheterogeneity and to present some novel methods for cancer detection. A computerized search of articles published up to 2007 was performed through the PubMed database. Search terms utilized included prostate/ovarian cancer glycosylation, prostate/ovarian cancer detection, PSA/CA125 glycosylation. Additional sources were identified through cross-referencing and researching in available biomedical books. The comparative studies of sugar chain structures of the PSA and CA125 indicated specific structural alterations associated with malignant transformation, in relation to glycan branching, sialylation and fucosylation. These glycan modifications should be better in distinguishing between benign and malignant conditions than the measurement of marker concentrations alone, which is widely used in practice. Cancer-associated changes in the glycosylation could yield more sensitive and discriminative diagnostic tests for reproductive tract cancer detection, i.e. for improvement of the clinical utility of known tumor markers or the discovery of new ones.

Distinctive characteristics of MALDI-Q/TOF and TOF/TOF tandem mass spectrometry for sequencing of permethylated complex type N-glycans

Concerted MALDI-MS profiling and CID MS/MS sequencing of permethylated glycans is one of the most effective approaches for high throughput glycomics applications. In essence, the identification of larger complex type N-glycans necessitates an unambiguous definition of any modification on the trimannosyl core and the complement of non-reducing terminal sequences which constitute the respective antennary structures. Permethylation not only affords analyses of both neutral and sialylated glycans at comparable ease and sensitivity but also yields more sequence-informative fragmentation pattern. Facile glycosidic cleavages directed mostly at N-acetylglucosamine under low energy CID, as implemented on a quadrupole/time-of-flight (Q/TOF) instrument, often afford multiple losses of the attached antenna resulting in characteristic ions related to the number of antennary branches on the trimannosyl core. Non-reducing terminal epitopes can be easily deduced but information on the linkage specific substituent on the terminal units is often missing. The high energy CID MS/MS afforded by TOF/TOF instrument can fill in the gap by giving an array of additional cross-ring and satellite ions. Glycosidic cleavages occurring specifically in concert with loss of 2-linked or 3-linked substituents provide an effective way to identify the branch-specific antennary extension. These characteristics are shown here to be effective in deriving the sequences of additionally galactosylated, sialylated and fucosylated terminal N-acetyllactosamine units and their antennary location. Together, a highly reproducible fragmentation pattern can be formulated to simplify spectral assignment. This work also provides first real examples of sequencing multiply sialylated complex type N-glycans by high energy CID on a TOF/TOF instrument.

Expression of bisecting type and Lewisx/Lewisy terminated N-glycans on human sperm

Human sperm lack major histocompatibility class I molecules, making them susceptible to lysis by natural killer (NK) cells. Major histocompatibility class I negative tumor cells block NK cell lysis by expressing sufficient amounts of bisecting type N-glycans on their surfaces. Therefore, sperm could employ the same strategy to evade NK cell lysis. The total N-glycans derived from sperm were sequenced using ultrasensitive mass spectrometric and conventional approaches. Three major classes of N-glycans were detected, (i) high mannose, (ii) biantennary bisecting type, and (iii) biantennary, triantennary, and tetraantennary oligosaccharides terminated with Lewisx and Lewisy sequences. Immunostaining of normal sperm showed that glycoproteins bearing Lewisy sequences are localized to the acrosome and not the plasma membrane. In contrast, defective sperm showed distinct surface labeling with anti-Lewisy antibody. The substantial expression of high mannose and complex type N-glycans terminated with Lewisx and Lewisy sequences suggests that sperm glycoproteins are highly decorated with ligands for DC-SIGN. Based on previous studies, the addition of such carbohydrate signals should inhibit antigen-specific responses directed against sperm glycoproteins in both the male and female reproductive systems. Thus, the major N-glycans of human sperm are associated with the inhibition of both innate and adaptive immune responses. These results provide more support for the eutherian fetoembryonic defense system hypothesis that links the expression of carbohydrate functional groups to the protection of gametes and the developing human in utero. This study also highlights the usefulness of glycomic profiling for revealing potential physiological functions of glycans expressed in specific cell types.

Analysis of protein glycosylation by mass spectrometry

We present a detailed protocol for the structural analysis of protein-linked glycans. In this approach, appropriate for glycomics studies, N-linked glycans are released using peptide N-glycosidase F and O-linked glycans are released by reductive alkaline beta-elimination. Using strategies based on mass spectrometry (matrix-assisted laser desorption/ionization-time of flight mass spectrometry and nano-electrospray ionization mass spectrometry/mass spectrometry (nano-ESI-MS-MS)), chemical derivatization, sequential exoglycosidase digestions and linkage analysis, the structures of the N- and/or O-glycans are defined. This approach can be used to study the glycosylation of isolated complex glycoproteins or of numerous glycoproteins encountered in a complex biological medium (cells, tissues and physiological fluids).

The sperm agglutination antigen-1 (SAGA-1) glycoforms of CD52 are O-glycosylated

CD52 is composed of a 12 amino acid peptide with N-linked glycans bound to the single potential glycosylation site at position 3, and a glycosylphosphatidylinositol-anchor attached at the C-terminus. Some glycoforms of this molecule expressed in the male reproductive tract are recognized by complement-dependent sperm-immobilizing antibodies in infertile patients making this antigen an important target for immunocontraception and fertility studies. Although the amount of posttranslational modification is already remarkable for such a small polypeptide, O-glycosylation of CD52 has additionally been implicated by several studies, but never rigorously characterized. In this report, we show clear evidence for the presence of O-glycans in CD52 preparations immunopurified using the murine S19 monoclonal antibody generated against sperm agglutination antigen-1 (SAGA-1), a male reproductive tract specific form of CD52. The O-glycans have been characterized by MALDI-TOF and tandem mass spectrometry after reductive elimination and permethylation. The data indicate that the major SAGA-1 O-glycans are core 1 and 2 mucin-type structures, with and without sialic acid (NeuAc(0-2)Hex(1-3)HexNAc(1-2)HexNAcitol). Minor fucosy- lated O-glycans are also present including some struc- tures with putative Le(y) epitopes (NeuAc(0-1)Fuc(1-3)Hex(1-2) HexNAc(0-1)HexNAcitol). Analysis of O-glycopeptides by tandem mass spectrometry provided an additional level of support for the O-glycosylation of SAGA-1. Elucidation of the O-glycosylation of SAGA-1 adds to the complexity of this molecule and may help to explain its biological activity.

Peritoneal natural killer cells from epithelial ovarian cancer patients show an altered phenotype and bind to the tumour marker MUC16 (CA125)

The ovarian tumour marker MUC16 (CA125) inhibits the cytotoxic responses of human natural killer (NK) cells and down-regulates CD16. Here we show that approximately 10% of the peripheral blood NK cells (PBNK) from the epithelial ovarian cancer (EOC) patients are CD16(-) CD56(br) whereas 40% of the peritoneal fluid NK (PFNK) carry this phenotype, which is usually associated with NK cells from the lymph nodes or human decidua. PBNK from healthy donors exposed to PF show a significant increase in the CD16(-) CD56(br) population. This shift in phenotype is not caused by increased apoptosis of the CD16(+) CD56(dim) cells or selective proliferation of the CD16(-) CD56(br) NK cells. Thus, the terminal differentiation of the CD16(-) CD56(br) NK cells to CD16(+) CD56(dim) subset that occurs during normal NK cell development may actually be a reversible step. A majority of the NK cell receptors (NKp46, NKp44, NKG2D, CD244, CD226, CD158a, CD158b, and CD158e) studied were down-regulated in the PFNK. MUC16 binds selectively to 30-40% of CD16(+) CD56(dim) NK cells in EOC patients indicating that phenotypic alterations in these cells are mediated by tumour-derived soluble factors. Similar to EOC, MUC16 in early pregnancy also binds to NK cells suggesting shared mechanisms of NK cell suppression in feto-maternal tolerance and immune evasion by ovarian cancers.

Analysis of protein-linked glycosylation in a sperm-somatic cell adhesion system

Murine sperm initiate fertilization by binding to the specialized extracellular matrix of their complementary eggs, known as the zona pellucida. On the basis of data reported in this study, mouse sperm also bind to rabbit erythrocytes with higher affinity than they do to murine eggs. This unusual interaction between a germ cell and a somatic cell ("sperm-somatic cell adhesion system") is also carbohydrate dependent based on its sensitivity to mild periodate oxidation. To determine what types of carbohydrate sequences could be involved in this interaction, the protein-linked oligosaccharides of rabbit erythrocytes were sequenced using novel matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry methods that enabled the analysis of individual components up to m/z 9000. The N-glycans are primarily complex biantennary and triantennary types terminated with Galalpha1-3Gal sequences. The majority of these oligosaccharides also possess one antenna consisting of a highly branched polylactosamine-type sequence that is also associated with many glycosphingolipids that coat rabbit erythrocytes. These erythrocytes also express Core 1 and Core 2 O-glycans terminated primarily with Galalpha1-3Gal sequences and to a lesser extent sialic acid. These results confirm that rabbit erythrocytes and mouse eggs present very different types of carbohydrate sequences on their surfaces. However, oligosaccharides terminated with beta1-6-linked N-acetyllactosamine or its alpha1-3 galactosylated analog are expressed on both the mouse zona pellucida and this somatic cell type. The far more abundant presentation of such sequences on rabbit erythrocytes compared with murine eggs could explain why mouse sperm display such exceptional affinity for this somatic cell type.

Analysis of the protein and glycan parts of CA125 antigen from human amniotic fluid

CA125 antigen is a mucin-type molecule with a complex protein backbone and oligosaccharide chain structure. In this study, we characterized CA125 antigen from human amniotic fluid by gel filtration, ion-exchange chromatography, peptide mass fingerprinting and lectin-binding assays. The obtained results indicate CA125 to be structurally heterogeneous, existing in different glycoisoforms with subtle differences in the profile of molecular forms in comparison to placental tissue-derived and cancer-derived CA125 antigen. The complexity of CA125 structure suggests that it can act as a multifunctional molecule. Further investigation is therefore needed in order for the biological meaning of the tissue-specific structural forms to be comprehended fully. .

Respiratory distress and neonatal lethality in mice lacking Golgi alpha1,2-mannosidase IB involved in N-glycan maturation

There are three mammalian Golgi alpha1,2-mannosidases, encoded by different genes, that form Man5GlcNAc2 from Man(8-9)GlcNAc2 for the biosynthesis of hybrid and complex N-glycans. Northern blot analysis and in situ hybridization indicate that the three paralogs display distinct developmental and tissue-specific expression. The physiological role of Golgi alpha1,2-mannosidase IB was investigated by targeted gene ablation. The null mice have normal gross appearance at birth, but they display respiratory distress and die within a few hours. Histology of fetal lungs the day before birth indicate some delay in development, whereas neonatal lungs show extensive pulmonary hemorrhage in the alveolar region. No significant histopathological changes occur in other tissues. No remarkable ultrastructural differences are detected between wild type and null lungs. The membranes of a subset of bronchiolar epithelial cells are stained with lectins from Phaseolus vulgaris (leukoagglutinin and erythroagglutinin) and Datura stramonium in wild type lungs, but this staining disappears in lungs from null mice. Mass spectrometry of N-glycans from different tissues shows no significant changes in global N-glycans of null mice. Therefore, only a few glycoproteins required for normal lung function depend on alpha1,2-mannosidase IB for maturation. There are no apparent differences in the expression of several lung epithelial cell and endothelial cell markers between null and wild type mice. The alpha1,2-mannosidase IB null phenotype differs from phenotypes caused by ablation of other enzymes in N-glycan biosynthesis and from other mouse gene disruptions that affect pulmonary development and function.

Mesothelin-MUC16 binding is a high affinity, N-glycan dependent interaction that facilitates peritoneal metastasis of ovarian tumors

Background

The mucin MUC16 and the glycosylphosphatidylinositol anchored glycoprotein mesothelin likely facilitate the peritoneal metastasis of ovarian tumors. The biochemical basis and the kinetics of the binding between these two glycoproteins are not clearly understood. Here we have addressed this deficit and provide further evidence supporting the role of the MUC16-mesothelin interaction in facilitating cell-cell binding under conditions that mimic the peritoneal environment.

Results

In this study we utilize recombinant-Fc tagged human mesothelin to measure the binding kinetics of this glycoprotein to MUC16 expressed on the ovarian tumor cell line OVCAR-3. OVCAR-3 derived sublines that did not express MUC16 showed no affinity for mesothelin. In a flow cytometry-based assay mesothelin binds with very high affinity to the MUC16 on the OVCAR-3 cells with an apparent K_d of 5–10 nM. Maximum interaction occurs within 5 mins of incubation of the recombinant mesothelin with the OVCAR-3 cells and significant binding is observed even after 10 sec. A five-fold molar excess of soluble MUC16 was unable to completely inhibit the binding of mesothelin to the OVCAR-3 cells. Oxidation of the MUC16 glycans, removal of its N-linked oligosaccharides, and treatment of the mucin with wheat germ agglutinin and erythroagglutinating phytohemagglutinin abrogates its binding to mesothelin. These observations suggest that at least a subset of the MUC16-asscociated N-glycans is required for binding to mesothelin. We also demonstrate that MUC16 positive ovarian tumor cells exhibit increased adherence to A431 cells transfected with mesothelin (A431-Meso⁺). Only minimal adhesion is observed between MUC16 knockdown cells and A431-Meso⁺ cells. The binding between the MUC16 expressing ovarian tumor cells and the A431-Meso⁺ cells occurs even in the presence of ascites from patients with ovarian cancer.

Conclusion

The strong binding kinetics of the mesothelin-MUC16 interaction and the cell adhesion between ovarian tumor cells and A431-Meso+ even in the presence of peritoneal fluid strongly support the importance of these two glycoproteins in the peritoneal metastasis of ovarian tumors. The demonstration that N-linked glycans are essential for mediating mesothlein-MUC16 binding may lead to novel therapeutic targets to control the spread of ovarian carcinoma.

Ascites is the primary cause of cancer antigen-125 (CA-125) elevation in systemic lupus erythematosus (SLE) patients with nephrotic syndrome

Tumor markers or tumor antigens are used for the monitoring of the response to treatment, follow-up, and potentially for diagnosis and screening. However, use of CA-125 serum assay as a single diagnostic tool is restricted by the fact that it is also produced by normal epithelia, not only by the ovarian cancer cells. Systemic lupus eryhtematosus (SLE) and related systemic autoimmune syndromes are associated with elevation of CA-125. In this group of patients antigen elevation had been tried to be linked with SLE disease activity. Although not found to be related with the disease activity, CA-125 serum levels were found to be related with the presence of nephrotic syndrome in the English literature. Although particularly important, the presence of ascites was not taken into consideration during the statistical analysis of the relationship between CA-125 elevation and nephrotic syndrome in SLE patients. However most of the SLE patients with nephrotic syndrome would have had accompanying ascites secondary to protein loss. Ascites itself could induce elevation in CA-125 serum levels. With this in mind we can hypothesize that the development of ascites was the primary cause for the elevation of CA-125 in SLE patients with nephrotic syndrome rather than the nephrotic syndrome itself. Probably the presence of ascites was the cause of observed relationship. Most likely ascites was a confounding variable biasing the results and statistical analysis. Failure to control for the presence of confounding variables such as ascites might lead to bias in all clinical trials. Otherwise a causative role for nephrotic syndrome in the elevation of serum CA-125 level seems somewhat inconsequential.

Screening of glycosylation patterns in serum using natural glycoprotein microarrays and multi-lectin fluorescence detection

Protein glycosylation has been implicated in key biological processes including immunological recognition, cellular adhesion, protein folding, and signaling as well as disease progression. Although several methods are available to assess glycosylation of protein structures, none of them is able to screen complex biological samples at a global as well as an individual scale. A novel strategy presented here uses an all-liquid phase enrichment and prefractionation methodology coupled to glycoprotein microarray technology using a multiple lectin-based, biotin-streptavidin detection scheme. Selective detection of glycan structures was made possible by employing multiple lectins to screen glycoprotein standards as well as serum samples from normal subjects or patients with chronic pancreatitis or pancreatic cancer. Interestingly, in some instances, a greater degree of glycosylation was seen in proteins that were underexpressed based on the reversed-phase chromatogram alone. Studies with standard proteins established the limits of detection to be in the 2.5-5-fmol range. Studies on serum samples showed differences in glycosylation patterns, particularly with respect to sialylation, mannosylation, and fucosylation, in normal, pancreatitis, and cancer sera. By coupling glycoprotein enrichment and fractionation with a microarray platform, we have shown that naturally occurring glycoproteins from human serum can be screened and characterized for different glycan structures, thereby allowing one to do comparative studies that monitor individual glycosylation changes within a glycoproteome representing different biological states. This approach may be useful to identify potential biomarkers in cancer.

Overview on advances in capillary electrophoresis-mass spectrometry of carbohydrates: A tabulated review

The increasing interest for carbohydrates as holder of essential bioinformations has boosted their full characterization through analytical techniques. The intent of this review is to summarize the recent trends regarding on-line and off-line CE-MS coupling for carbohydrate analysis. A statistical survey on the articles that use derivatizing agents as well as on the analyzer and type of instrument coupling (i.e. on- or off-line) is depicted. From a general overview it can be concluded that, whereas derivatization might be useful for the detection of neutral carbohydrates improving separation selectivity with volatile buffers and increasing sensitivity of the MS detection, relatively few works with derivatized carbohydrates were found; this was noticed in particular for glycosides and saccharides carrying ionizable groups, which are normally analyzed without any chemical modification. The most applied coupling is the on-line sheath-liquid interface; for on-line applications, ESI is the sole source used, whilst the most common analyzer is the IT. MS(n) is often exploited, as fragmentation increases the achieved structural information. CE-MS turned out to be mainly used for the analysis of carbohydrates in drug development (i.e. study of oligosaccharides from pathogens, carbohydrate-based drugs and drug metabolites), in nutrition and for characterization of glycans from glycoproteins. The reader will find elucidating tables regarding these recent CE-MS applications, including the main information on the analysis conditions. Comments are meant to help the immediate focus on the usefulness of the analytical technique and predict the difficulties found during analysis and, in case, their overcoming.

N-Glycosylation of the MUC1 mucin in epithelial cells and secretions

The MUC1 mucin is an important tumor-associated antigen that shows extensive glycosylation in vivo. The O-glycosylation of this molecule, which has been well characterized in many cell types and tissues, is important in conferring the unusual biochemical and biophysical properties on a mucin. N-Glycosylation is crucial to the folding, sorting, membrane trafficking, and secretion of many proteins. Here, we evaluated the N-glycosylation of MUC1 derived from two sources: endogenous MUC1 isolated from human milk and a recombinant epitope-tagged MUC1F overexpressed in Caco2 colon carcinoma cells. N-Glycans on purified MUC1F/MUC1 were analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), gas chromatography-mass spectrometry (GC-MS), and CAD-ESI-MS/MS. The spectra indicate that MUC1F N-glycans have compositions consistent with high-mannose structures (Hex(5-9)HexNAc(2)) and complex/hybrid-type glycans (NeuAc(0-3)Fuc(0-3)Hex(3-8)HexNAc(3-7)). Many of the N-glycan structures are identical on MUC1F and native MUC1; however, a marked difference is seen between the N-glycans on membrane-bound and secreted forms of the native molecule.

Probing mucin-type O-linked glycosylation in living animals

Changes in O-linked protein glycosylation are known to correlate with disease states but are difficult to monitor in a physiological setting because of a lack of experimental tools. Here, we report a technique for rapid profiling of O-linked glycoproteins in living animals by metabolic labeling with N-azidoacetylgalactosamine (GalNAz) followed by Staudinger ligation with phosphine probes. After injection of mice with a peracetylated form of GalNAz, azide-labeled glycoproteins were observed in a variety of tissues, including liver, kidney, and heart, in serum, and on isolated splenocytes. B cell glycoproteins were robustly labeled with GalNAz but T cell glycoproteins were not, suggesting fundamental differences in glycosylation machinery or metabolism. Furthermore, GalNAz-labeled B cells could be selectively targeted with a phosphine probe by Staudinger ligation within the living animal. Metabolic labeling with GalNAz followed by Staudinger ligation provides a means for proteomic analysis of this posttranslational modification and for identifying O-linked glycoprotein fingerprints associated with disease.

The pattern of glycosyl- and sulfotransferase activities in cancer cell lines: a predictor of individual cancer-associated distinct carbohydrate structures for the structural identification of signature glycans

Carbohydrate chains of cancer glycoprotein antigens contain major outer changes dictated by tissue-specific regulation of glycosyltransferase genes, the availability of sugar nucleotides, and competition between enzymes for acceptor intermediates during glycan elongation. However, it is evident from recent studies with recombinant mucin probes that the final glycosylation profiles of mucin glycoproteins are mainly determined by the cellular repertoire of glycosyltransferases. Hence, we examined various cancer cell lines for the levels of fucosyl-, beta-galactosyl, beta-N-acetylgalactosaminyl-, sialyl-, and sulfotransferase activities that generate the outer ends of the oligosaccharide chains. We have identified glycosyltransferases activities at the levels that would give rise to O-glycan chains as reported by others in breast cancer cell lines, T47D, ZR75-1, MCF-7, and MDA-MB-231. Most breast cancer cells express Gal-3-O-sulfotransferase specific for T-hapten Gal beta1-->3GalNAc alpha-, whereas the enzyme from colon cancer cells exhibits a vast preference for the Gal beta1,4GlcNAc terminal unit in O-glycans. We also studied ovarian cancer cells SW626 and PA-1 and hepatic cancer cells HepG2. Our studies show that alpha1,2-L-fucosyl-T, alpha(2,3) sialyl-T, and 3-O-Sulfo-T capable of acting on the mucin core 2 tetrasaccharide, Gal beta1,4GlcNAc beta1,6(Gal beta1,3)GalNAc alpha-, can also act on the Globo H antigen backbone, Gal beta1,3GalNAc beta1,3Gal alpha-, suggesting the existence of unique carbohydrate moieties in certain cancer-associated glycolipids. Briefly, our study indicates the following: (i) 3'-Sulfo-T-hapten has an apparent relationship to the tumorigenic potential of breast cancer cells; (ii) the 3'-sulfo Lewis(x), the 3-O-sulfo-Globo unit, and the 3-fucosylchitobiose core could be uniquely associated with colon cancer cells; (iii) synthesis of a polylactosamine chain and T-hapten are favorable in ovarian cancer cells due to negligible sialyltransferase activities; and (iv) a 6'-sialyl LacNAc unit and 3'-sialyl T-hapten appear to be prevalent structures in hepatic cancer cell glycans. Thus, it is apparent that different cancer cells are expressing unique glycan epitopes, which could be novel targets for cancer diagnosis and treatment.

Glycomic profiling of cells and tissues by mass spectrometry: fingerprinting and sequencing methodologies

Over the past decade, rapid, high-sensitivity mass spectrometric strat-egies have been developed and optimized for screening for the types of N- and O-glycans present in a diverse range of biological material, including secretions, cell lines, tissues, and organs. These glycomic strategies are based on matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass fingerprinting of permethylated derivatives, combined with electrospray (ES) or MALDI tandem mass spectrometry (MS/MS) sequencing and gas chromatography (GC)-MS linkage analysis, complemented by chemical and enzymatic degradations. Protocols for these methods are described in the first part of this chapter. Glycomic experiments yield large volumes of MS data, and interpretation of the resulting spectra remains a time-consuming bottleneck in the process. In the second part of this chapter, we describe the use and operation of a mass spectral viewer program capable of displaying and automatically labeling spectra arising from MALDI fingerprinting of N-glycans.

A focused microarray approach to functional glycomics: transcriptional regulation of the glycome

Glycosylation is the most common posttranslational modification of proteins, yet genes relevant to the synthesis of glycan structures and function are incompletely represented and poorly annotated on the commercially available arrays. To fill the need for expression analysis of such genes, we employed the Affymetrix technology to develop a focused and highly annotated glycogene-chip representing human and murine glycogenes, including glycosyltransferases, nucleotide sugar transporters, glycosidases, proteoglycans, and glycan-binding proteins. In this report, the array has been used to generate glycogene-expression profiles of nine murine tissues. Global analysis with a hierarchical clustering algorithm reveals that expression profiles in immune tissues (thymus [THY], spleen [SPL], lymph node, and bone marrow [BM]) are more closely related, relative to those of nonimmune tissues (kidney [KID], liver [LIV], brain [BRN], and testes [TES]). Of the biosynthetic enzymes, those responsible for synthesis of the core regions of N- and O-linked oligosaccharides are ubiquitously expressed, whereas glycosyltransferases that elaborate terminal structures are expressed in a highly tissue-specific manner, accounting for tissue and ultimately cell-type-specific glycosylation. Comparison of gene expression profiles with matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) profiling of N-linked oligosaccharides suggested that the alpha1-3 fucosyltransferase 9, Fut9, is the enzyme responsible for terminal fucosylation in KID and BRN, a finding validated by analysis of Fut9 knockout mice. Two families of glycan-binding proteins, C-type lectins and Siglecs, are predominately expressed in the immune tissues, consistent with their emerging functions in both innate and acquired immunity. The glycogene chip reported in this study is available to the scientific community through the Consortium for Functional Glycomics (CFG) (http://www.functionalglycomics.org).

Glycans in cancer and inflammation--potential for therapeutics and diagnostics

Changes in glycosylation are often a hallmark of disease states. For example, cancer cells frequently display glycans at different levels or with fundamentally different structures than those observed on normal cells. This phenomenon was first described in the early 1970s, but the molecular details underlying such transformations were poorly understood. In the past decade advances in genomics, proteomics and mass spectrometry have enabled the association of specific glycan structures with disease states. In some cases, the functional significance of disease-associated changes in glycosylation has been revealed. This review highlights changes in glycosylation associated with cancer and chronic inflammation and new therapeutic and diagnostic strategies that are based on the underlying glycobiology.

Complement-inhibiting effect of ovarian cancer antigen CA-125

Malignant transformation of ovarian cells of surface epithelial origin is associated with expression of a membrane-spanning glycoprotein, cancer antigen (CA)-125. The bulk of the putative CA-125 molecule is comprised a very large, folded, multivalent, mucin-like exodomain. That the extracellular motif of CA-125 exerts immunosuppressive effects which promote tumor progression has been suggested. We report that CA-125 attenuates complement lysis of antibody-sensitized cells. The secreted form of CA-125 derived from culture medium of the human ovarian adenocarcinoma cell line OVCAR-3 caused a dose-response inhibition of sheep erythrocyte hemolysis. Moreover, OVCAR-3 cells became prone to complement attack (trypan blue uptake) mediated by a gonadotropin-releasing hormone receptor antibody when (membrane-bound) CA-125 was excised/removed by trypsin/washing; this effect was counteracted by replacement with (soluble) CA-125. It is conceivable that CA-125 entraps/sheds effectors of the complement cascade.

Molecular forms and microheterogeneity of the oligosaccharide chains of pregnancy-associated CA125 antigen

BACKGROUND

The cancer antigen CA125 has a very complex molecular architecture in terms of both protein backbone and oligosaccharide chains. In this study, we examined the molecular forms and microheterogeneity of oligosaccharide chains of pregnancy-associated CA125, as a first step towards gaining an insight into its possible involvement as a ligand in carbohydrate-dependent interactions. The glycobiochemical properties of CA125 may be of diagnostic and biomedical importance as specific markers of physiological and pathological conditions of early pregnancy, as well as targets in different therapeutic procedures.

METHODS

Pregnancy-associated CA125 was characterized by gel filtration and ion-exchange chromatography, followed by lectin-affinity chromatography with a panel of plant lectins as ligands.

RESULTS

CA125 antigen isolated from first trimester placental extract was found to be heterogeneous in respect to molecular mass and the existence of different glyco-isoforms. Thus, elution profiles from the lectin-affinity columns demonstrated molecular subpopulations bound with low, intermediate and high affinity. Under the applied experimental conditions, CA125 bound most strongly to Triticum vulgaris agglutinin (WGA) and Ricinus communis agglutinin (RCA), but low affinity interactions occurred with the other lectins tested.

CONCLUSIONS

The assessment of the carbohydrate composition of N- and O-glycans of pregnancy-associated CA125 was in general agreement with available data on CA125 of cancer origin. The main difference was observed in reactivity to Canavalia ensiformis agglutinin (ConA) and Phaseolus vulgaris erythroagglutinin (PHA-E) binding.

Automatic annotation of matrix-assisted laser desorption/ionizationN-glycan spectra

Matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) is the pre-eminent technique for mass mapping of glycans. In order to make this technique practical for high-throughput screening, reliable automatic methods of annotating peaks must be devised. We describe an algorithm called Cartoonist that labels peaks in MALDI spectra of permethylated N-glycans with cartoons which represent the most plausible glycans consistent with the peak masses and the types of glycans being analyzed. There are three main parts to Cartoonist. (i) It selects annotations from a library of biosynthetically plausible cartoons. The library we currently use has about 2800 cartoons, but was constructed using only about 300 archetype cartoons entered by hand. (ii) It determines the precision and calibration of the machine used to generate the spectrum. It does this automatically based on the spectrum itself. (iii) It assigns a confidence score to each annotation. In particular, rather than making a binary yes/no decision when annotating a peak, it makes all plausible annotations and associates them with scores indicating the probability that they are correct.

Characterisation and proposed origin of mass spectrometric ions observed 30 Th above the ionised molecules of per-O-methylated carbohydrates

Derivatisation of carbohydrates by permethylation significantly improves the mass spectrometric intensity of carbohydrate-derived ions and allows more readily interpretable fragmentation; in addition, samples are conveniently separated from salts, and larger oligosaccharides are more readily ionised. It has previously been recognised that, in the mass spectra of permethylated carbohydrates, a series of ions indicating species 30 Da larger than the fully methylated carbohydrate molecules are also observed. These species have not been characterised in the literature despite their apparently ubiquitous occurrence in the mass spectra of permethylated carbohydrates. Tandem mass spectrometry (MS/MS) experiments were performed on permethylated carbohydrates and reduced permethylated carbohydrates that exhibit the artefact, demonstrating that the artefact is not reducing terminal specific, and that the artefact can be introduced at any hydroxyl residue. It was further demonstrated through the use of different alkylation reagents that the origin of this artefact group is the alkylating reagent itself. It is proposed that side reactions that occur between the permethylation reagents allow the production of small amounts of iodomethyl methyl ether. This reagent can then compete with methyl iodide for reaction with the carbohydrate -OH groups. The result is partial incorporation of a methoxymethyl moiety instead of a methyl group, detected as '+30' artefact ions.

Structural determination of neutral O-linked oligosaccharide alditols by negative ion LC-electrospray-MSn

Neutral O-linked oligosaccharides released from the salivary mucin MUC5B were separated and detected by negative ion LC-MS and LC-MS(2). The resolution of the chromatography and the information obtained from collision induced dissociation of detected [M - H](-) ions were usually sufficient to identify the sequence of individual oligosaccharides, illustrated by the fact that 50 different oligosaccharides ranging from disaccharides to nonasaccharides could be assigned from the sample. Fragmentation was shown to yield mostly reducing end sequence fragments (Z(i) and Y(i)), enabling primary sequence assignment. Specific fragmentation pathways or patterns were also detected giving specific linkage information. The reducing end core (Gal/GlcNAcbeta1-3GalNAcol or Gal/GlcNAcbeta1-3(GlcNAcbeta1-6)GalNAcol) could be deduced from the pronounced glycosidic C-3 cleavage and A(i) type cleavages of the reducing end GalNAcol, together with the non reducing end fragment from the loss of a single substituted GalNAcol. Substitution patterns on GlcNAc residues were also found, indicative for C-4 substitution ((0,2)A(i) - H(2)O cleavage) and disubstitution of C-3 and C-4 (Z(i)/Z(i) cleavages). This kind of fragmentation can be used for assigning the mode of chain elongation (Galbeta1-3/4GlcNAcbeta1-) and identification of Lewis type antigens like Lewis a/x and Lewis b/y on O-linked oligosaccharides. In essence, negative ion LC-MS(2) was able to generate extensive data for understanding the overall glycosylation pattern of a sample, especially when only a limited amount of material is available.

Immunological treatment of ovarian cancer

PURPOSE OF REVIEW

Development of immunological treatments for ovarian cancer has not been a conspicuous success story over the past few years. Only a handful of clinical trials have reported immunological responses, and correlation with clinical benefit has been elusive. Several recent studies presented in this review, however, point to a revival of optimism for the development of novel immunotherapeutic strategies.

RECENT FINDINGS

The cloning and sequencing of CA125, coupled with novel structural and functional insights, undoubtedly represent important steps forward. The possibility that CA125 could play a role in evasion of immunity by ovarian tumors may represent a new challenge, but does not detract from its potential as a therapeutic target. Of the recent clinical trial reports, the most intriguing results were seen from immunotherapy with a conventional mouse monoclonal antibody specific for CA125, in which human anti-mouse antibody responses correlated significantly with improved survival of patients with advanced stage ovarian cancer and clinical evidence of recurrent disease at the time of treatment.

SUMMARY

There is little doubt that CA125 will undergo a renaissance as an important target antigen for development of novel immunological treatments, particularly with regard to cellular therapies. Identification of other novel ovarian tumor antigens will also accelerate research focused on stimulation of T-cell immunity. Current research trends suggest a paradigm shift in emphasis from vaccines designed to elicit antibody responses to strategies such as dendritic cell vaccination that are designed to induce broader immunity, including ovarian tumor antigen-specific helper T-lymphocyte and cytotoxic T-lymphocyte responses.

Binding of ovarian cancer antigen CA125/MUC16 to mesothelin mediates cell adhesion

Mesothelin is a glycosylphosphatidylinositol-linked cell surface molecule expressed in the mesothelial lining of the body cavities and in many tumor cells. Based on the finding that a soluble form of mesothelin specifically binds to ovarian carcinoma cell line OVCAR-3, we isolated cDNAs encoding a mesothelin-binding protein by expression cloning. The polypeptides encoded by the two cloned cDNA fragments matched to portions of CA125, an ovarian cancer antigen and a giant mucin-like glycoprotein present at the surface of tumor cells. By flow cytometric analysis and immunoprecipitation, we demonstrate that CA125 binds to mesothelin in a specific manner. Binding of CA125 to membrane-bound mesothelin mediates heterotypic cell adhesion as anti-mesothelin antibody blocks binding of OVCAR-3 cells expressing CA125 to an endothelial-like cell line expressing mesothelin. Finally, we show that CA125 and mesothelin are co-expressed in advanced grade ovarian adenocarcinoma. Taken together, our data indicate that mesothelin is a novel CA125-binding protein and that CA125 might contribute to the metastasis of ovarian cancer to the peritoneum by initiating cell attachment to the mesothelial epithelium via binding to mesothelin.

Murine and human zona pellucida 3 derived from mouse eggs express identical O-glycans

Murine sperm initiate fertilization by binding to the outer covering of the egg known as the murine zona pellucida (mZP). This binding is thought to require the interaction of O-glycans linked to a specific mZP glycoprotein (mZP3) with egg-binding proteins coating the sperm plasma membrane. The precise molecular basis of this interaction remains to be resolved. In this study, we analyzed the O-glycosylation of the individual mZP glycoproteins by using ultrasensitive MS methods. We found that the majority of the O-glycans that are linked to mZP3 are core type 2 sequences terminated with sialic acid, lacNAc (Galbeta1-4GlcNAc), lacdiNAc (Gal-NAcbeta1-4GlcNAc), Galalpha1-3Gal, and NeuAcalpha2-3[GalNAcbeta1-4]Galbeta1-4 (Sda antigen). Many of these terminal sequences have been implicated previously in murine sperm-egg binding. Core type 1 O-glycans are also present and are generally unmodified, although some are terminated with sialic acid, beta-linked N-acetylhexosamine, or NeuAcalpha2-3[GalNAcbeta1-4]Galbeta1-4. Eggs expressing human ZP (huZP) glycoprotein huZP3, derived from transgenic mice, bind murine but not human sperm, implying that huZP3 acquires the same O-glycans as native mZP3. Sequencing of huZP3-associated O-glycans confirms that this implication is correct. The data obtained in this investigation may prove to be very useful for studies to determine the precise molecular basis of initial murine sperm-egg binding.