Expression of LacdiNAc groups on N-glycans among human tumors is complex

Comprehensive Glycomic and Glycoproteomic Analyses of Human Programmed Cell Death Protein 1 Extracellular Domain

Human programmed cell death protein 1 (hPD-1) is an essential receptor in the immune checkpoint pathway. It has played an important role in cancer therapy. However, not all patients respond positively to the PD-1 antibody treatment, and the underlying mechanism remains unknown. PD-1 is a transmembrane glycoprotein, and its extracellular domain (ECD) is reported to be responsible for interactions and signal transduction. This domain contains 4 N-glycosylation sites and 25 potential O-glycosylation sites, which implicates the importance of glycosylation. The structure of hPD-1 has been intensively studied, but the glycosylation of this protein, especially the glycan on each glycosylation site, has not been comprehensively illustrated. In this study, hPD-1 ECD expressed by human embryonic kidney 293 (HEK 293) and Chinese hamster ovary (CHO) cells was analyzed; not only N- and O-glycosylation sites but also the glycans on these sites were comprehensively analyzed using mass spectrometry. In addition, hPD-1 ECD binding to different anti-hPD-1 antibodies was tested, and N-glycans were found functioned differently. All of this glycan information will be beneficial for future PD-1 studies.

Metabolism-driven glycosylation represents therapeutic opportunities in interstitial lung diseases

Metabolic changes are coupled with alteration in protein glycosylation. In this review, we will focus on macrophages that are pivotal in the pathogenesis of pulmonary fibrosis and sarcoidosis and thanks to their adaptable metabolism are an attractive therapeutic target. Examples presented in this review demonstrate that protein glycosylation regulates metabolism-driven immune responses in macrophages, with implications for fibrotic processes and granuloma formation. Targeting proteins that regulate glycosylation, such as fucosyltransferases, neuraminidase 1 and chitinase 1 could effectively block immunometabolic changes driving inflammation and fibrosis, providing novel avenues for therapeutic interventions.

Breast Milk Oligosaccharides Contain Immunomodulatory Glucuronic Acid and LacdiNAc

Breast milk is abundant with functionalized milk oligosaccharides (MOs) to nourish and protect the neonate. Yet we lack a comprehensive understanding of the repertoire and evolution of MOs across Mammalia. We report ∼400 MO-species associations (>100 novel structures) from milk glycomics of nine mostly understudied species: alpaca, beluga whale, black rhinoceros, bottlenose dolphin, impala, L'Hoest's monkey, pygmy hippopotamus, domestic sheep, and striped dolphin. This revealed the hitherto unknown existence of the LacdiNAc motif (GalNAcβ1-4GlcNAc) in MOs of all species except alpaca, sheep, and striped dolphin, indicating the widespread occurrence of this potentially antimicrobial motif in MOs. We also characterize glucuronic acid-containing MOs in the milk of impala, dolphins, sheep, and rhinoceros, previously only reported in cows. We demonstrate that these GlcA-MOs exhibit potent immunomodulatory effects. Our study extends the number of known MOs by >15%. Combined with >1900 curated MO-species associations, we characterize MO motif distributions, presenting an exhaustive overview of MO biodiversity.

Advances in the Immunomodulatory Properties of Glycoantigens in Cancer

Simple Summary

This work reviews the role of aberrant glycosylation in cancer cells during tumour growth and spreading, as well as in immune evasion. The interaction of tumour-associated glycans with the immune system through C-type lectin receptors can favour immune escape but can also provide opportunities to develop novel tumour immunotherapy strategies. This work highlights the main findings in this area and spotlights the challenges that remain to be investigated.

Abstract

Aberrant glycosylation in tumour progression is currently a topic of main interest. Tumour-associated carbohydrate antigens (TACAs) are expressed in a wide variety of epithelial cancers, being both a diagnostic tool and a potential treatment target, as they have impact on patient outcome and disease progression. Glycans affect both tumour-cell biology properties as well as the antitumor immune response. It has been ascertained that TACAs affect cell migration, invasion and metastatic properties both when expressed by cancer cells or by their extracellular vesicles. On the other hand, tumour-associated glycans recognized by C-type lectin receptors in immune cells possess immunomodulatory properties which enable tumour growth and immune response evasion. Yet, much remains unknown, concerning mechanisms involved in deregulation of glycan synthesis and how this affects cell biology on a major level. This review summarises the main findings to date concerning how aberrant glycans influence tumour growth and immunity, their application in cancer treatment and spotlights of unanswered challenges remaining to be solved.

The fungal Clitocybe nebularis lectin binds distinct cell surface glycoprotein receptors to induce cell death selectively in Jurkat cells

Clitocybe nebularis lectin (CNL) is a GalNAcβ1-4GlcNAc-binding lectin that exhibits an antiproliferative effect exclusively on the Jurkat leukemic T cell line by provoking homotypic aggregation and dose-dependent cell death. Cell death of Jurkat cells exhibited typical features of early apoptosis, but lacked the activation of initiating and executing caspases. None of the features of CNL-induced cell death were effectively blocked with the pan-caspase inhibitor or different cysteine peptidase inhibitors. Furthermore, CNL binding induced Jurkat cells to release the endogenous damage-associated molecular pattern molecule high-mobility group box 1 (HMGB1). A plant lectin with similar glycan-binding specificity, Wisteria floribunda agglutinin (WFA) showed less selective toxicity and induced cell death in Jurkat, Tall-104, and Hut-87 cell lines. HMGB1 release was also detected when Jurkat cells were treated with WFA. We identified the CD45 and CD43 cell surface glycoproteins on Jurkat cells as the main targets for CNL binding. However, the blockade of CD45 phosphatase activity failed to block either CNL-induced homotypic agglutination or cell death. Overall, our results indicate that CNL triggers atypical cell death selectively on Jurkat cells, suggesting the potential applicability of CNL in novel strategies for treating and/or detecting acute T cell leukemia.

Biosynthesis and Biological Significances of LacdiNAc Group on N- and O-Glycans in Human Cancer Cells

An increasing number of studies have shown that the disaccharide GalNAcβ1→4GlcNAc (LacdiNAc) group bound to N- and O-glycans in glycoproteins is expressed in a variety of mammalian cells. Biosynthesis of the LacdiNAc group was well studied, and two β4-N-acetylgalactosaminyltransferases, β4GalNAcT3 and β4GalNAcT4, have been shown to transfer N-acetylgalactosamine (GalNAc) to N-acetylglucosamine (GlcNAc) of N- and O-glycans in a β-1,4-linkage. The LacdiNAc group is often sialylated, sulfated, and/or fucosylated, and the LacdiNAc group, with or without these modifications, is recognized by receptors and lectins and is thus involved in the regulation of several biological phenomena, such as cell differentiation. The occurrences of the LacdiNAc group and the β4GalNAcTs appear to be tissue specific and are closely associated with the tumor progression or regression, indicating that they will be potent diagnostic markers of particular cancers, such as prostate cancer. It has been demonstrated that the expression of the LacdiNAc group on N-glycans of cell surface glycoproteins including β1-integrin is involved in the modulation of their protein functions, thus affecting cellular invasion and other malignant properties of cancer cells. The biological roles of the LacdiNAc group in cancer cells have not been fully understood. However, the re-expression of the LacdiNAc group on N-glycans, which is lost in breast cancer cells by transfection of the β4GalNAcT4 gene, brings about the partial restoration of normal properties and subsequent suppression of malignant phenotypes of the cells. Therefore, elucidation of the biological roles of the LacdiNAc group in glycoproteins will lead to the suppression of breast cancers.

Characteristics of α2,3-sialyl N-glycosylated PSA as a biomarker for clinically significant prostate cancer in men with elevated PSA level

BACKGROUND

The presence of glycosylated isoforms of prostate-specific antigen (PSA) in prostate cancer (PC) cells is a potential marker of their aggressiveness. We characterized the origin of α2,3-sialylated prostate-specific antigen (S23PSA) by tissue-based sialylation-related gene expression and studied the performance of S23PSA density (S23PSAD) alone and in combination with multiparametric magnetic resonance imaging (MRI) for the detection of clinically significant prostate cancer in men with elevated PSA.

METHODS

Tissue-based quantification of S23PSA and sialyltransferase and sialidase gene expression was evaluated in 71 radical prostatectomy specimens. The diagnostic performance of S23PSAD was studied in 1099 men retrospectively enrolled in a multicenter systematic biopsy (SBx) cohort. We correlated the S23PSAD with Prostate Imaging Reporting and Data System (PI-RADS) scores in 98 men prospectively enrolled in a single-center MRI-targeted biopsy (MRI-TBx) cohort. The primary outcome was the PC-diagnostic performance of the S23PSAD, the secondary outcome was the avoidable biopsy rate of S23PSAD combined with DRE and total PSA (tPSA), and with or without PI-RADS.

RESULTS

S23PSA was significantly higher in Gleason pattern 4 and 5 compared with benign prostate tissue. In the retrospective cohort, the performance of S23PSAD for detecting PC was superior to tPSA or PSA density (PSAD) (AUC: 0.7758 vs. 0.6360 and 0.7509, respectively). In the prospective cohort, S23PSAD was superior to tPSA, PSAD, and PI-RADS (AUC: 0.7725 vs. 0.5901, 0.7439 and 0.7305, respectively), and S23PSAD + PI-RADS + DRE + tPSA was superior to DRE + tPSA+PI-RADS with avoidance rate of MRI-TBx (13% vs. 1%) at 30% risk threshold.

CONCLUSIONS

The diagnostic performance of S23PSAD was superior to conventional strategies but comparable to mpMRI.

Prospects and Challenges of the Study of Anti-Glycan Antibodies and Microbiota for the Monitoring of Gastrointestinal Cancer

Over the past decades, a large amount of data has been accumulated in various subfields of glycobiology. However, much clinically relevant data and many tools are still not widely used in medicine. Synthetic glycoconjugates with the known structure of glycans are an accurate tool for the study of glycan-binding proteins. We used polyacrylamide glycoconjugates (PGs) including PGs with tumour-associated glycans (TAGs) in immunoassays to assess the prognostic potential of the serum level of anti-glycan antibodies (AG Abs) in gastrointestinal cancer patients and found an association of AG Abs with survival. The specificity of affinity-isolated AG Abs was investigated using synthetic and natural glycoconjugates. AG Abs showed mainly a low specificity to tumour-associated and tumour-derived mucins; therefore, the protective role of the examined circulating AG Abs against cancer remains a challenge. In this review, our findings are analysed and discussed in the context of the contribution of bacteria to the AG Abs stimulus and cancer progression. Examples of the influence of pathogenic bacteria colonising tumours on cancer progression and patient survival through mechanisms of interaction with tumours and dysregulated immune response are considered. The possibilities and problems of the integrative study of AG Abs and the microbiome using high-performance technologies are discussed.

Glycosylation: Rising Potential for Prostate Cancer Evaluation

Simple Summary

Aberrant protein glycosylation is a well-known hallmark of cancer and is associated with differential expression of enzymes such as glycosyltransferases and glycosidases. The altered expression of the enzymes triggers cancer cells to produce glycoproteins with specific cancer-related aberrations in glycan structures. Increasing number of data indicate that glycosylation patterns of PSA and other prostate-originated proteins exert a potential to distinguish between benign prostate disease and cancer as well as among different stages of prostate cancer development and aggressiveness. This review summarizes the alterations in glycan sialylation, fucosylation, truncated O-glycans, and LacdiNAc groups outlining their potential applications in non-invasive diagnostic procedures of prostate diseases. Further research is desired to develop more general algorithms exploiting glycobiology data for the improvement of prostate diseases evaluation.

Abstract

Prostate cancer is the second most commonly diagnosed cancer among men. Alterations in protein glycosylation are confirmed to be a reliable hallmark of cancer. Prostate-specific antigen is the biomarker that is used most frequently for prostate cancer detection, although its lack of sensitivity and specificity results in many unnecessary biopsies. A wide range of glycosylation alterations in prostate cancer cells, including increased sialylation and fucosylation, can modify protein function and play a crucial role in many important biological processes in cancer, including cell signalling, adhesion, migration, and cellular metabolism. In this review, we summarize studies evaluating the prostate cancer associated glycosylation related alterations in sialylation, mainly α2,3-sialylation, core fucosylation, branched N-glycans, LacdiNAc group and presence of truncated O-glycans (sTn, sT antigen). Finally, we discuss the great potential to make use of glycans as diagnostic and prognostic biomarkers for prostate cancer.

Detection of N,N-diacetyllactosamine (LacdiNAc) containing free prostate-specific antigen for early stage prostate cancer diagnostics and for identification of castration-resistant prostate cancer patients

Prostate cancer (PCa) is one of the most common cancer types among men and also acommon cause of death globally. With an increasing incidence, there is aneed for low-cost, reliable biomarkers present in samples, which could be provided non-invasively (without a need to perform prostate biopsy). Glycosylation changes of free-PSA (fPSA) are considered cancer-specific, while the level of different PSA forms can increase under other than cancerous conditions. In the present study, we investigated the role ofN,N-diacetyllactosamine (LacdiNAc) epitope of fPSA (i.e. glycoprofile of fPSA or gPSA) in combination with total-PSA (tPSA), prostate volume, and tPSA density (tPSA level divided by prostate volume i.e. PSAd) as biomarkers for monitoring of PCa development and progression in 105 men. Furthermore, we applied an genetic (evolutionary) algorithm to identify any suspicious individuals in abenign cohort having benign prostatic hyperplasia (BPH). We identified 3 suspicious men originally diagnosed with BPH using gPSA analysis. In thefollow-up we found out that two men should not be considered as BPH patients since multiparametric magnetic resonance imaging (mpMRI) identified one man with clinically significant PCa via Prostate Imaging - Reporting and Data System (PI RADS v2 = 4) and the second man was with High-gradeprostatic intraepithelial neoplasia (HG PIN), commonly described as apre-cancerous stage. Moreover, in the study we described for the first time that changed LacdiNAc on PSA can be applied to identify prostatitis patients and most importantly this is the first study suggesting that changed glycosylation on PSA can be applied to identify castration-resistant prostate cancer (CRPCa) patients.

Structural Insights into the Molecular Recognition Mechanism of the Cancer and Pathogenic Epitope, LacdiNAc by Immune-Related Lectins

Interactions of glycan-specific epitopes to human lectin receptors represent novel immune checkpoints for investigating cancer and infection diseases. By employing a multidisciplinary approach that combines isothermal titration calorimetry, NMR spectroscopy, molecular dynamics simulations, and X-ray crystallography, we investigated the molecular determinants that govern the recognition of the tumour and pathogenic glycobiomarker LacdiNAc (GalNAcβ1-4GlcNAc, LDN), including their comparison with the ubiquitous LacNAc epitope (Galβ1-4GlcNAc, LN), by two human immune-related lectins, galectin-3 (hGal-3) and the macrophage galactose C-type lectin (hMGL). A different mechanism of binding and interactions was observed for the hGal-3/LDN and hMGL/LDN complexes, which explains the remarkable difference in the binding specificity of LDN and LN by these two lectins. The new structural clues reported herein are fundamental for the chemical design of mimetics targeting hGal-3/hMGL recognition process.

Lectin-Mediated Binding of Engineered Lactococcus lactis to Cancer Cells

Lectins have been increasingly utilized as carriers for targeted drug delivery based on their specific binding to glycans located on mammalian cells. This study employed two lectins, B subunit of bacterial Shiga holotoxin (Stx1B) and fungal Clitocybe nebularis lectin (CNL), for surface display on the lactic acid bacterium Lactococcus lactis. The specific adhesion of these engineered, lectin-displaying L. lactis to cancer cells was evaluated. The expression and surface display of both lectins on L. lactis were demonstrated by western blotting and flow cytometry, respectively. MTS assays revealed that recombinant Stx1B had no effect on Caco-2 cell viability at concentrations of ≤25 µg/mL, whereas CNL was non-toxic even at relatively high concentrations of ≤250 µg/mL. Stx1B bound to Caco-2, HT-29 and HeLa cells after 1 h of incubation. CNL bound to Caco-2 cells and recognized several glycoproteins in HT-29 and Caco-2 cell homogenates of which a 70 kDa protein predominated. Confocal microscopy revealed adhesion of Stx1B-displaying L. lactis to HeLa, Caco-2, and, to a lesser extent, HT-29 cells; CNL-displaying L. lactis showed a relatively similar level of adherence to HT-29 and Caco-2 cells. Thus, lectin-displaying L. lactis might serve as a carrier in targeted drug delivery when coupled to a therapeutic moiety.

Characterisation of the main PSA glycoforms in aggressive prostate cancer

Serum levels of prostate specific antigen (PSA) are commonly used for prostate cancer (PCa) detection. However, their lack of specificity to distinguish benign prostate pathologies from PCa, or indolent from aggressive PCa have prompted the study of new non-invasive PCa biomarkers. Aberrant glycosylation is involved in neoplastic progression and specific changes in PSA glycosylation pattern, as the reduction in the percentage of α2,6-sialic acid (SA) are associated with PCa aggressiveness. In this study, we have characterised the main sialylated PSA glycoforms from blood serum of aggressive PCa patients and have compared with those of standard PSA from healthy individuals’ seminal plasma. PSA was immunoprecipitated and α2,6-SA were separated from α2,3-SA glycoforms using SNA affinity chromatography. PSA N-glycans were released, labelled and analysed by hydrophilic interaction liquid chromatography combined with exoglycosidase digestions. The results showed that blood serum PSA sialylated glycoforms containing GalNAc residues were largely increased in aggressive PCa patients, whereas the disialylated core fucosylated biantennary structures with α2,6-SA, which are the major PSA glycoforms in standard PSA from healthy individuals, were markedly reduced in aggressive PCa. The identification of these main PSA glycoforms altered in aggressive PCa opens the way to design specific strategies to target them, which will be useful to improve PCa risk stratification.

Altered linkage pattern of N-glycan sialic acids in pseudomyxoma peritonei

Pseudomyxoma peritonei (PMP) is a highly mucinous adenocarcinoma growing in the peritoneal cavity and most commonly originating from the appendix. Glycans play an important role in carcinogenesis, and glycosylation is altered in malignant diseases, including PMP. We have previously demonstrated that fucosylation of N-glycans is increased in PMP, but we did not observe modulation of overall sialylation. As sialic acids can be attached to the rest of the glycan via α2,3- or α2,6-linkage, we have now analyzed the linkage patterns of sialic acids in tissue specimens of normal appendices, low-grade appendiceal mucinous neoplasms (LAMN), low-grade (LG) PMP and high-grade (HG) PMP. For the linkage analysis, the enzymatically released acidic N-glycans were first treated with ethyl esterification or α2,3-sialidase digestion followed by MALDI-TOF mass spectrometry. Significant increase in the relative abundance of α2,6-sialylated and decrease in α2,3-sialylated N-glycans was observed in PMP tumors as compared to the normal appendices (P < 0.025). More specifically, increased α2,6-sialylation (P < 0.05) and decreased α2,3-sialylation (P < 0.01) were detected in afucosylated and monofucosylated N-glycans of PMPs, whereas the less abundant multifucosylated glycans, containing terminal fucose, demonstrated increased α2,3-sialylation (P < 0.01). Importantly, the increase in α2,6-sialylation was also detected between PMP and the appendiceal precursor lesion LAMN (P < 0.01). The identified glycosylation alterations produce ligands for sialic acid-binding immunoglobulin-like lectins (Siglecs) and sialofucosylated glycans binding selectins, which play a role in the peritoneal dissemination and progression of the disease.

N-Glycoproteins Have a Major Role in MGL Binding to Colorectal Cancer Cell Lines: Associations with Overall Proteome Diversity

Colorectal cancer (CRC) is the second-leading cause of cancer death worldwide due in part to a high proportion of patients diagnosed at advanced stages of the disease. For this reason, many efforts have been made towards new approaches for early detection and prognosis. Cancer-associated aberrant glycosylation, especially the Tn and STn antigens, can be detected using the macrophage galactose-type C-type lectin (MGL/CLEC10A/CD301), which has been shown to be a promising tool for CRC prognosis. We had recently identified the major MGL-binding glycoproteins in two high-MGL-binding CRC cells lines, HCT116 and HT29. However, we failed to detect the presence of O-linked Tn and STn glycans on most CRC glycoproteins recognized by MGL. We therefore investigated here the impact of N-linked and O-linked glycans carried by these proteins for the binding to MGL. In addition, we performed quantitative proteomics to study the major differences in proteins involved in glycosylation in these cells. Our results showed that N-glycans have a significant, previously underestimated, importance in MGL binding to CRC cell lines. Finally, we highlighted both common and cell-specific processes associated with a high-MGL-binding phenotype, such as differential levels of enzymes involved in protein glycosylation, and a transcriptional factor (CDX-2) involved in their regulation.

Expression and Malignant Potential of B4GALNT4 in Esophageal Squamous Cell Carcinoma

BACKGROUND

β-1,4-N-Acetyl-galactosaminyltransferase 4 (B4GALNT4), an enzyme involved in ganglioside synthesis, is upregulated in many cancers. We examine B4GALNT4 expression and its relationship to prognosis in esophageal squamous cell carcinoma (ESCC).

PATIENTS AND METHODS

Expression of B4GALNT4 mRNA and B4GALNT4 protein was analyzed by quantitative reverse-transcription polymerase chain reaction (qRT-PCR) and immunohistochemistry, respectively, in 17 human ESCC cell lines and/or clinical specimens from two independent cohorts of 147 and 159 ESCC patients. The contributions of B4GALNT4 to proliferation, invasion, migration, and adhesion was evaluated in ESCC cells subjected to siRNA-mediated gene knockdown. Correlations between clinicopathological parameters and B4GALNT4 expression in clinical specimens were analyzed in both patient cohorts.

RESULTS

B4GALNT4 mRNA expression levels varied widely in ESCC cell lines, regardless of differentiation status or the originating tissue. Knockdown of B4GALNT4 significantly suppressed the proliferation, invasion, migration, and adhesion of ESCC cell lines compared with control cells. B4GALNT4 mRNA was overexpressed in ESCC tissues compared with adjacent normal esophageal tissues. High mRNA expression was significantly associated with poor disease-free survival and hematogenous recurrence, and high B4GALNT4 protein expression was also significantly related to poor disease-specific survival. On multivariable analysis, high B4GALNT4 expression was an independent predictor of poor prognosis. In both patient cohorts, high B4GALNT4 expression did not correlate with known prognostic factors, such as disease stage, lymphovascular invasion, or squamous cell-carcinoma-related antigen level.

CONCLUSIONS

B4GALNT4 influences the malignant behavior of ESCC cells. B4GALNT4 expression may serve as a novel prognostic marker, independent of established risk factors, for ESCC patients.

Profiling natural serum antibodies of non-human primates with a carbohydrate antigen microarray

BACKGROUND

Engineering of α-Galactosyltransferase gene-knockout pigs circumvented hyperacute rejection of pig organs after xenotransplantation in non-human primates. Overcoming this hurdle revealed the importance of non-α-Gal carbohydrate antigens in the immunobiology of acute humoral xenograft rejection.

METHODS

This study analyzed serum from seven naïve cynomolgus monkeys (blood type O/B/AB = 3/2/2) for the intensity of natural IgM and IgG signals using carbohydrate antigen microarray, which included historically reported α-Gal and non-α-Gal carbohydrate antigens with various modifications.

RESULTS

The median (range) of IgM and IgG signals were 12.71 (7.23-16.38) and 9.05 (7.23-15.90), respectively. The highest IgM and IgG signals with narrowest distribution were from mono- and disaccharides, followed by modified structures. Natural anti-α-Gal antibody signals were medium to high in IgM (11.2-15.9) and medium in IgG (8.5-11.6) spectra, and was highest with Lac core structure (Galα1-3Galβ1-4Glc, iGb3) and lowest with LacNAc core structure (Galα1-3Galβ1-4GlcNAc). Similar signal intensities (up to 15.8 in IgM and up to 11.8 in IgG) were observed for historically detected natural non-α-Gal antigens, which included Tn antigen, T antigen, GM2 glycolipid, and Sd^a antigen. The hierarchical clustering analysis revealed the presence of clusters of anti-A antibodies and was capable of distinguishing between the blood group B and AB non-human primates.

CONCLUSIONS

The results presented here provide the most comprehensive evaluation of natural antibodies present in cynomolgus monkeys.

CNL-Clitocybe nebularis Lectin-The Fungal GalNAcβ1-4GlcNAc-Binding Lectin

Clitocybe nebularis lectin (CNL) is present in fruiting bodies of clouded agaric along with several similar isolectins that are all small and stable proteins. It is a beta-trefoil type lectin forming homodimers that are essential for its functionality. It binds specifically N,N′-diacetyllactosediamine (GalNAcβ1-4GlcNAc, LacDiNac) and human blood group A determinant-containing glycan epitopes. Its most probable function is to defend fruiting bodies against predators and parasites. In addition, an endogenous regulatory function is possible for CNL, as indicated by its interaction with fungal protease inhibitors sharing the beta-trefoil fold. CNL is toxic to insects, nematodes and amoebae, as well as to leukemic T-cell lines. Bivalent carbohydrate binding is essential for the toxicity of CNL, against both invertebrates and cancer-derived cell lines. In addition, CNL exhibits potent immunostimulation of human dendritic cells, resulting in a strong T helper cell type 1 response. Based on its unique characteristics, CNL is a promising candidate for applications in human and veterinary medicine as well as in agriculture, for plant protection.

LacdiNAcylation of N-glycans in MDA-MB-231 human breast cancer cells results in changes in morphological appearance and adhesive properties of the cells

We demonstrated previously that the expression of the disaccharide, GalNAcβ1 → 4GlcNAc (LacdiNAc), on N-glycans of cell surface glycoproteins in MDA-MB-231 human breast cancer cells suppresses their malignant properties such as tumor formation in nude mice. Here, we report changes in the morphological appearance and adhesive properties of two kinds of clonal cells of MDA-MB-231 cells overexpressing β4-N-acetyl-galactosaminyltransferase 4. The clonal cells exhibited a cobble stone-like shape as compared to a spindle-like shape of the mock-transfected cells and the original MDA-MB-231 cells. This was associated with an increased expression of cell surface E-cadherin, a marker of epithelial cells, and a decreased expression of N-cadherin, vimentin, α-smooth muscle actin and ZEB1, markers of mesenchymal cells. In addition, the clonal cells showed a lower migratory activity compared to the mock-transfected cells by wound-healing assay. These results suggest that mesenchymal-epithelial transition may be occurring in these clonal cells. Furthermore, increased adhesion to extracellular matrix proteins such as fibronectin, collagen type I, collagen type IV, and laminin was observed. The clonal cells spread and enlarged, whereas the mock-transfected cells demonstrated poor spreading on laminin-coated plates in the absence of fetal calf serum, indicating that expression of LacdiNAc on cell surface glycoproteins results in changes in cell adhesive and spreading properties particularly to laminin.

Identifying Efficient Clostridium difficile Toxin A Binders with a Multivalent Neo-Glycoprotein Glycan Library

Clostridium difficile infections cause gastrointestinal disorders and can lead to life-threatening conditions. The symptoms can vary from severe diarrhea to the formation of pseudomembranous colitis and therefore trigger a need for new therapies. The initial step of disease is the binding of the bacterial enterotoxins toxin A and B to the cell surface of epithelial intestinal cells. Scavenging of the toxins is crucial to inhibit their fatal effect in the human body and circumvent the administration of antibiotics. Cell surface glycans are common as ligands for TcdA. Although crucial for carbohydrate-protein interactions, a multivalent presentation of glycans for binding has been hardly considered. Here, we establish a neo-glycoprotein-based glycan library to identify an effective multivalent glycan ligand for TcdA. It comprises 40 different glycan epitopes based on N-acetyllactosamine precursors. Nine structures exhibit strong binding of the receptor domain. Among them, the Lewis^y-Lewis^x-epitope shows the best performance for binding both the receptor domain and the holotoxin. Therefore, the glycan was synthesized de novo and coupled to BSA as a scaffold for multivalent presentation. The corresponding neo-glycoprotein facilitates the proper scavenging of TcdA in vitro and effectively protects HT29 cells from TcdA-induced cell damage.

Clinical significance of the LacdiNAc-glycosylated prostate-specific antigen assay for prostate cancer detection

To reduce unnecessary prostate biopsies (Pbx), better discrimination is needed. To identify clinically significant prostate cancer (CSPC) we determined the performance of LacdiNAc‐glycosylated prostate‐specific antigen (LDN‐PSA) and LDN‐PSA normalized by prostate volume (LDN‐PSAD). We retrospectively measured LDN‐PSA, total PSA (tPSA), and free PSA/tPSA (F/T PSA) values in 718 men who underwent a Pbx in 3 academic urology clinics in Japan and Canada (Pbx cohort) and in 174 PC patients who subsequently underwent radical prostatectomy in Australia (preop‐PSA cohort). The assays were evaluated using the area under the receiver operating characteristics curve (AUC) and decision curve analyses to discriminate CSPC. In the Pbx cohort, LDN‐PSAD (AUC 0.860) provided significantly better clinical performance for discriminating CSPC compared with LDN‐PSA (AUC 0.827, P = 0.0024), PSAD (AUC 0.809, P < 0.0001), tPSA (AUC 0.712, P < 0.0001), and F/T PSA (AUC 0.661, P < 0.0001). The decision curve analysis showed that using a risk threshold of 20% and adding LDN‐PSA and LDN‐PSAD to the base model (age, digital rectal examination status, tPSA, and F/T PSA) permitted avoidance of even more biopsies without missing CSPC (9.89% and 18.11%, respectively vs 2.23% [base model]). In the preop‐PSA cohort, LDN‐PSA values positively correlated with tumor volume and tPSA and were significantly higher in pT3, pathological Gleason score ≥ 7. Limitations include limited sample size, retrospective nature, and no family history information prior to biopsy. LacdiNAc‐glycosylated PSA is significantly better than the conventional PSA test in identifying patients with CSPC. This study was approved by the ethics committee of each institution (“The Study about Carbohydrate Structure Change in Urological Disease”; approval no. 2014‐195).

N-Glycomic and Transcriptomic Changes Associated with CDX1 mRNA Expression in Colorectal Cancer Cell Lines

The caudal-related homeobox protein 1 (CDX1) is a transcription factor, which is important in the development, differentiation, and homeostasis of the gut. Although the involvement of CDX genes in the regulation of the expression levels of a few glycosyltransferases has been shown, associations between glycosylation phenotypes and CDX1 mRNA expression have hitherto not been well studied. Triggered by our previous study, we here characterized the N-glycomic phenotype of 16 colon cancer cell lines, selected for their differential CDX1 mRNA expression levels. We found that high CDX1 mRNA expression associated with a higher degree of multi-fucosylation on N-glycans, which is in line with our previous results and was supported by up-regulated gene expression of fucosyltransferases involved in antenna fucosylation. Interestingly, hepatocyte nuclear factors (HNF)4A and HNF1A were, among others, positively associated with high CDX1 mRNA expression and have been previously proven to regulate antenna fucosylation. Besides fucosylation, we found that high CDX1 mRNA expression in cancer cell lines also associated with low levels of sialylation and galactosylation and high levels of bisection on N-glycans. Altogether, our data highlight a possible role of CDX1 in altering the N-glycosylation of colorectal cancer cells, which is a hallmark of tumor development.

The β-N-Acetylhexosaminidase in the Synthesis of Bioactive Glycans: Protein and Reaction Engineering

N-Acetylhexosamine oligosaccharides terminated with GalNAc act as selective ligands of galectin-3, a biomedically important human lectin. Their synthesis can be accomplished by β-N-acetylhexosaminidases (EC 3.2.1.52). Advantageously, these enzymes tolerate the presence of functional groups in the substrate molecule, such as the thiourea linker useful for covalent conjugation of glycans to a multivalent carrier, affording glyconjugates. β-N-Acetylhexosaminidases exhibit activity towards both N-acetylglucosamine (GlcNAc) and N-acetylgalactosamine (GalNAc) moieties. A point mutation of active-site amino acid Tyr into other amino acid residues, especially Phe, His, and Asn, has previously been shown to strongly suppress the hydrolytic activity of β-N-acetylhexosaminidases, creating enzymatic synthetic engines. In the present work, we demonstrate that Tyr470 is an important mutation hotspot for altering the ratio of GlcNAcase/GalNAcase activity, resulting in mutant enzymes with varying affinity to GlcNAc/GalNAc substrates. The enzyme selectivity may additionally be manipulated by altering the reaction medium upon changing pH or adding selected organic co-solvents. As a result, we are able to fine-tune the β-N-acetylhexosaminidase affinity and selectivity, resulting in a high-yield production of the functionalized GalNAcβ4GlcNAc disaccharide, a selective ligand of galectin-3.

Characterisation of N-glycans in the epithelial-like tissue of the rat cochlea

Membrane proteins (such as ion channels, transporters, and receptors) and secreted proteins are essential for cellular activities. N-linked glycosylation is involved in stability and function of these proteins and occurs at Asn residues. In several organs, profiles of N-glycans have been determined by comprehensive analyses. Nevertheless, the cochlea of the mammalian inner ear, a tiny organ mediating hearing, has yet to be examined. Here, we focused on the stria vascularis, an epithelial-like tissue in the cochlea, and characterised N-glycans by liquid chromatography with mass spectrometry. This hypervascular tissue not only expresses several ion transporters and channels to control the electrochemical balance in the cochlea but also harbours different transporters and receptors that maintain structure and activity of the organ. Seventy-nine N-linked glycans were identified in the rat stria vascularis. Among these, in 55 glycans, the complete structures were determined; in the other 24 species, partial glycosidic linkage patterns and full profiles of the monosaccharide composition were identified. In the process of characterisation, several sialylated glycans were subjected sequentially to two different alkylamidation reactions; this derivatisation helped to distinguish α2,3-linkage and α2,6-linkage sialyl isomers with mass spectrometry. These data should accelerate elucidation of the molecular architecture of the cochlea.

Identification of Multisialylated LacdiNAc Structures as Highly Prostate Cancer Specific Glycan Signatures on PSA

Serum prostate-specific antigen (PSA) test is the current gold standard for screening and diagnosis of prostate cancer (PCa), while overdiagnosis and overtreatment are social problems. In order to improve the specificity and exclude a false positive diagnosis in PSA test, PCa-specific glycosylation subtypes of PSA were explored using in-depth quantitative profiling of PSA glycoforms based on mass spectrometric oxonium ion monitoring technology. As a result of analysis using sera from 15 PCa or 15 benign prostate hyperplasia (BPH) patients whose PSA levels were in the "gray zone" (4.0-10.0 ng/mL), 52 glycan structures on PSA were quantitatively observed. We found that abundance of multisialylated LacdiNAc (GalNAcβ1-4GlcNAc) structures were significantly upregulated in the PCa group compared to the BPH group. A couple of those glycoforms were then extracted and subjected to establish a novel PCa-specific diagnosis model (PSA G-index). When the diagnostic power was assessed using an independent validation sample set (15 PCa and 15 BPH patients in the PSA gray zone), an AUC of PSA G-index was 1.00, while that of total PSA or PSA f/T ratio was 0.50 or 0.60, respectively. Moreover, both PSA glycoforms showed significant correlation with Gleason scores. Lectin histochemical staining analysis also showed that PCa cells overexpressed glycoproteins containing LacdiNAc and sialic acids moieties. Thus, PSA G-index could serve as not only an effective secondary screening method to exclude false positive diagnosis in PSA screening, but also a potential grading biomarker for PCa.

IgG Antibodies to GlcNAcβ and Asialo-GM2 (GA2) Glycans as Potential Markers of Liver Damage in Chronic Hepatitis C and the Efficacy of Antiviral Treatment

Total serum IgG level is a surrogate marker of hepatitis C (HC) severity. Antibodies (Abs) to microbial glycans could be markers of HC severity caused by the translocation of microbial products. The level of anti-glycan (AG) Abs was analysed in serum samples of patients (n = 128) with chronic HC in ELISA using fourteen synthetic glycans present in microbes and adhesins to evaluate the association of Abs with clinical parameters and the efficacy of antiviral treatment. The anti-GlcNAcβ IgG level was significantly higher in patients with fibrosis (P = 0.021) and severe portal inflammation (P < 0.001) regardless of other clinical parameters. The ROC curve analysis showed sensitivity of 0.59, specificity of 0.84, and AUC of 0.71 in discriminating F0 from F1–4 (HCV genotype-1b-infected patients). The level of anti-GA2 Abs before Peg-IFN/RBV treatment was significantly higher in nonsustained viral response (non-SVR) to treatment than in SVR (P = 0.033). ROC analysis showed sensitivity of 0.62, specificity of 0.70, and AUC of 64. Correlations of AG Abs to clinical parameters were found. The quantification of anti-GlcNAcβ Abs deserves attention in assessment of the hepatic damage while anti-GA2 Abs may be a sign of immune response related to the antiviral treatment.

Identification of a secondary binding site in human macrophage galactose-type lectin by microarray studies: Implications for the molecular recognition of its ligands

The human macrophage galactose-type lectin (MGL) is a C-type lectin characterized by a unique specificity for terminal GalNAc residues present in the tumor-associated Tn antigen (αGalNAc-Ser/Thr) and its sialylated form, the sialyl-Tn antigen. However, human MGL has multiple splice variants, and whether these variants have distinct ligand-binding properties is unknown. Here, using glycan microarrays, we compared the binding properties of the short MGL 6C (MGL^short) and the long MGL 6B (MGL^long) splice variants, as well as of a histidine-to-threonine mutant (MGL^short H259T). Although the MGL^short and MGL^long variants displayed similar binding properties on the glycan array, the MGL^short H259T mutant failed to interact with the sialyl-Tn epitope. As the MGL^short H259T variant could still bind a single GalNAc monosaccharide on this array, we next investigated its binding characteristics to Tn-containing glycopeptides derived from the MGL ligands mucin 1 (MUC1), MUC2, and CD45. Strikingly, in the glycopeptide microarray, the MGL^short H259T variant lost high-affinity binding toward Tn-containing glycopeptides, especially at low probing concentrations. Moreover, MGL^short H259T was unable to recognize cancer-associated Tn epitopes on tumor cell lines. Molecular dynamics simulations indicated that in WT MGL^short, His²⁵⁹ mediates H bonds directly or engages the Tn-glycopeptide backbone through water molecules. These bonds were lost in MGL^short H259T, thus explaining its lower binding affinity. Together, our results suggest that MGL not only connects to the Tn carbohydrate epitope, but also engages the underlying peptide via a secondary binding pocket within the MGL carbohydrate recognition domain containing the His²⁵⁹ residue.

Systems glycomics of adult zebrafish identifies organ-specific sialylation and glycosylation patterns

The emergence of zebrafish Danio rerio as a versatile model organism provides the unique opportunity to monitor the functions of glycosylation throughout vertebrate embryogenesis, providing insights into human diseases caused by glycosylation defects. Using a combination of chemical modifications, enzymatic digestion and mass spectrometry analyses, we establish here the precise glycomic profiles of eight individual zebrafish organs and demonstrate that the protein glycosylation and glycosphingolipid expression patterns exhibits exquisite specificity. Concomitant expression screening of a wide array of enzymes involved in the synthesis and transfer of sialic acids shows that the presence of organ-specific sialylation motifs correlates with the localized activity of the corresponding glycan biosynthesis pathways. These findings provide a basis for the rational design of zebrafish lines expressing desired glycosylation profiles.

Identification of N- and O-linked glycans recognized by AAL in saliva of patients with atrophic gastritis and gastric cancer

BACKGROUND AND AIM

Gastric cancer (GC) is a common and fatal malignancy with a worldwide occurrence. There still lacks effective biomarkers for precisely evaluating GC. Saliva is a biological fluid with enormous diagnostic potentials which emerged many advantages. We aimed to discover the novel biomarkers for accurately distinguishing early GC based on saliva glycopatterns.

METHODS

We used Aleuria Aurantia Lectin (AAL)-magnetic particle conjugates to isolate fucosylated glycoproteins in the pooled saliva of healthy volunteers (HV, n= 51) and patients with atrophic gastritis (AG, n= 51) or GC (n= 51), following to release the N- and O-linked glycans from the isolated proteins with PNGase F and NaClO, and further identified the released glycans by MALDI-TOF/TOF-MS, respectively.

RESULTS

A total of 9/9, 8/11, and 9/9 fucosylated N-/O-linked glycans were annotated in the isolated salivary proteins from HV, AG, and GC, respectively. Among these, six fucosylated N-linked glycansand four O-linked glycans exhibited significantly increased expression levels in GC, while five fucosylated N-linked glycans and ten fucosylated O-linked glycans exhibited significantly decreased expression levels in GC. The proportion of fucosylated N-linked glycans was decreased in GC (41.66%) compared with AG (43.63%) and HV (52.57%), as well as the fucosylated O-linked glycans was apparently decreased in GC (19.58%) compared with AG (25.43%) and HV (55.54%).

CONCLUSIONS

This study could provide pivotal information to distinguish among HV, AG, and GC, and facilitate the discovery of biomarkers for GC diagnosis based on precise alterations of N- and O-linked glycans in saliva.

Biocompatible glyconanomaterials based on HPMA-copolymer for specific targeting of galectin-3

Background

Galectin-3 (Gal-3) is a promising target in cancer therapy with a high therapeutic potential due to its abundant localization within the tumor tissue and its involvement in tumor development and proliferation. Potential clinical application of Gal-3-targeted inhibitors is often complicated by their insufficient selectivity or low biocompatibility. Nanomaterials based on N-(2-hydroxypropyl)methacrylamide (HPMA) nanocarrier are attractive for in vivo application due to their good water solubility and lack of toxicity and immunogenicity. Their conjugation with tailored carbohydrate ligands can yield specific glyconanomaterials applicable for targeting biomedicinally relevant lectins like Gal-3.

Results

In the present study we describe the synthesis and the structure-affinity relationship study of novel Gal-3-targeted glyconanomaterials, based on hydrophilic HPMA nanocarriers. HPMA nanocarriers decorated with varying amounts of Gal-3 specific epitope GalNAcβ1,4GlcNAc (LacdiNAc) were analyzed in a competitive ELISA-type assay and their binding kinetics was described by surface plasmon resonance. We showed the impact of various linker types and epitope distribution on the binding affinity to Gal-3. The synthesis of specific functionalized LacdiNAc epitopes was accomplished under the catalysis by mutant β-N-acetylhexosaminidases. The glycans were conjugated to statistic HPMA copolymer precursors through diverse linkers in a defined pattern and density using Cu(I)-catalyzed azide–alkyne cycloaddition. The resulting water-soluble and structurally flexible synthetic glyconanomaterials exhibited affinity to Gal-3 in low μM range.

Conclusions

The results of this study reveal the relation between the linker structure, glycan distribution and the affinity of the glycopolymer nanomaterial to Gal-3. They pave the way to specific biomedicinal glyconanomaterials that target Gal-3 as a therapeutic goal in cancerogenesis and other disorders.

Electronic supplementary material

The online version of this article (10.1186/s12951-018-0399-1) contains supplementary material, which is available to authorized users.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2013-2014

This review is the eighth update of the original article published in 1999 on the application of Matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2014. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly- saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2018 Wiley Periodicals, Inc. Mass Spec Rev 37:353-491, 2018.

In-depth comparison of N-glycosylation of human plasma-derived factor VIII and different recombinant products: from structure to clinical implications

Essentials Glycosylation heterogeneity of recombinant proteins affects pharmacokinetics and immunogenicity. N-glycomics/glycoproteomics of plasma-derived Factor VIII and 6 recombinant FVIIIs were compared. Depending on cell line, significant differences to plasma-derived FVIII were observed. Recombinant FVIIIs expressed distinct and immunologically relevant epitopes.

SUMMARY

Background/Objective Human factor VIII (FVIII) is a plasma glycoprotein, defects of which result in hemophilia A. Current substitution therapy uses FVIII products purified from human plasma or from various cell lines (recombinant FVIII) with different levels of B-domain deletion. Glycosylation is a post-translational protein modification in FVIII that has a substantial influence on its physical, functional and antigenic properties. Variation in glycosylation is likely to be the reason that FVIII products differ in their pharmacokinetics, pharmacodynamics and immunogenicity. However, the literature on FVIII glycosylation is inconsistent, preventing assembly into a coherent model. Seeking to better understand the glycosylation mechanisms underlying FVIII biology, we studied the N-glycosylation of human plasma-derived (pd)FVIII and six rFVIII products expressed in CHO, BHK or HEK cell lines. Methods FVIII samples were subjected to head-to-head detailed glycomic and glycoproteomic characterization using a combination of MALDI-MS and MS/MS, GC-MS and UPLC-UV-MSE technologies. Results/Conclusion The results of our study detail the N-glycan repertoire of pdFVIII to an unprecedented level, and for the first time, provide evidence of N-glycolylneuraminic acid (NeuGc) found on pdFVIII. Although site-specific glycosylation of rFVIII proved consistent with pdFVIII regardless of the expression system, the entire N-glycan content of each sample appeared significantly different. Although the proportion of biologically important epitopes common to all samples (i.e. sialylation and high-mannose) varied between samples, some recombinant products expressed distinct and immunologically relevant epitopes, such as LacdiNAc (LDN), fucosylated LacdiNAc (FucLDN), NeuGc, LewisX/Y and Galα1,3 Gal epitopes. rFVIII expressed in HEK cells showed the greatest glycomic differences to human pdFVIII.

Poly-N-Acetyllactosamine Neo-Glycoproteins as Nanomolar Ligands of Human Galectin-3: Binding Kinetics and Modeling

Galectin-3 (Gal-3) is recognized as a prognostic marker in several cancer types. Its involvement in tumor development and proliferation makes this lectin a promising target for early cancer diagnosis and anti-cancer therapies. Gal-3 recognizes poly-N-acetyllactosamine (LacNAc)-based carbohydrate motifs of glycoproteins and glycolipids with a high specificity for internal LacNAc epitopes. This study analyzes the mode and kinetics of binding of Gal-3 to a series of multivalent neo-glycoproteins presenting complex poly-LacNAc-based oligosaccharide ligands on a scaffold of bovine serum albumin. These neo-glycoproteins rank among the strongest Gal-3 ligands reported, with K_d reaching sub-nanomolar values as determined by surface plasmon resonance. Significant differences in the binding kinetics were observed within the ligand series, showing the tetrasaccharide capped with N,N'-diacetyllactosamine (LacdiNAc) as the strongest ligand of Gal-3 in this study. A molecular model of the Gal-3 carbohydrate recognition domain with docked oligosaccharide ligands is presented that shows the relations in the binding site at the molecular level. The neo-glycoproteins presented herein may be applied for selective recognition of Gal-3 both on the cell surface and in blood serum.

Tissue glycomics distinguish tumour sites in women with advanced serous adenocarcinoma

In the era of precision medicine, the tailoring of cancer treatment is increasingly important as we transition from organ‐based diagnosis towards a more comprehensive and patient‐centric molecular diagnosis. This is particularly the case for high‐grade serous adenocarcinomas of the ovary and peritoneum, which are commonly diagnosed at an advanced stage, and collectively treated and managed similarly. We characterized the N‐ and O‐glycome of serous ovarian (OC) and peritoneal cancer (PC) tissues using PGC‐LC‐ESI‐IT‐MS/MS profiling and validated the discriminatory glycans and their corresponding glyco‐gene expression levels using cell lines and transcriptomic data from 232 patients. Overall, the N‐ and O‐glycan repertoires of both cancer types were found to comprise mostly of α2,6‐sialylated glycan structures, with the majority of N‐glycans displaying the biantennary mono‐ and disialylation as well as bisecting‐type biantennary glycans. The MS profiling by PGC‐LC also revealed several glycan structural isomers that corresponded to LacdiNAc‐type (GalNAcβ1‐4GlcNAc) motifs that were unique to the serous ovarian cancers and that correlated with elevated gene expression of B4GALNT3 and B4GALNT4 in patients with serous cancer. Statistical evaluation of the discriminatory glycans also revealed 13 N‐ and 3 O‐glycans (P < 0.05) that significantly discriminated tumour‐sampling sites, with LacdiNAc‐type N‐glycans (m/z 1205.0²⁻ and m/z 1059.4²⁻) being associated with ovarian‐derived cancer tissue and bisecting GlcNAc‐type (m/z 994.9²⁻) and branched N‐glycans (m/z 1294.0²⁻ and m/z 1148.4²⁻) upregulated at the metastatic sites. Hence, we demonstrate for the first time that OC and PC display distinct molecular signatures at both their glycomic and transcriptomic levels. These signatures may have potential utility for the development of accurate diagnosis and personalized treatments.

The directed migration of gonadal distal tip cells in Caenorhabditis elegans requires NGAT-1, a ß1,4-N-acetylgalactosaminyltransferase enzyme

Glycoproteins such as growth factor receptors and extracellular matrix have well-known functions in development and cancer progression, however, the glycans at sites of modification are often heterogeneous molecular populations which makes their functional characterization challenging. Here we provide evidence for a specific, discrete, well-defined glycan modification and regulation of a stage-specific cell migration in Caenorhabditis elegans. We show that a chain-terminating, putative null mutation in the gene encoding a predicted β1,4-N-acetylgalactosaminyltransferase, named ngat-1, causes a maternally rescued temperature sensitive (ts) defect in the second phase of the three phase migration pattern of the posterior, but not the anterior, hermaphrodite Distal Tip Cell (DTC). An amino-terminal partial deletion of ngat-1 causes a similar but lower penetrance ts phenotype. The existence of multiple ts alleles with distinctly different molecular DNA lesions, neither of which is likely to encode a ts protein, indicates that NGAT-1 normally prevents innate temperature sensitivity for phase 2 DTC pathfinding. Temperature shift analyses indicate that the ts period for the ngat-1 mutant defect ends by the beginning of post-embryonic development-nearly 3 full larval stages prior to the defective phase 2 migration affected by ngat-1 mutations. NGAT-1 homologs generate glycan-terminal GalNAc-β1-4GlcNAc, referred to as LacdiNAc modifications, on glycoproteins and glycolipids. We also found that the absence of the GnT1/Mgat1 activity [UDP-N-acetyl-D-glucosamine:α-3-D-mannoside β-1,2-N-acetylglucosaminyltransferase 1 (encoded by C. elegans gly-12, gly-13, and gly-14 and homologous to vertebrate GnT1/Mgat1)], causes a similar spectrum of DTC phenotypes as ngat-1 mutations-primarily affecting posterior DTC phase 2 migration and preventing manifestation of the same innate ts period as ngat-1. GnT1/Mgat1 is a medial Golgi enzyme known to modify mannose residues and initiate N-glycan branching, an essential step in the biosynthesis of hybrid, paucimannose and complex-type N-glycans. Quadruple mutant animals bearing putative null mutations in ngat-1 and the three GnT genes (gly-12, gly-13, gly-14) were not enhanced for DTC migration defects, suggesting NGAT-1 and GnT1 act in the same pathway. These findings suggest that GnTI generates an N-glycan substrate for NGAT-1 modification, which is required at restrictive temperature (25°C) to prevent, stabilize, reverse or compensate a perinatal thermo-labile process (or structure) causing late larval stage DTC phase 2 migration errors.

Cytotoxic protein from the mushroom Coprinus comatus possesses a unique mode for glycan binding and specificity

Glycans possess significant chemical diversity; glycan binding proteins (GBPs) recognize specific glycans to translate their structures to functions in various physiological and pathological processes. Therefore, the discovery and characterization of novel GBPs and characterization of glycan-GBP interactions are significant to provide potential targets for therapeutic intervention of many diseases. Here, we report the biochemical, functional, and structural characterization of a 130-amino-acid protein, Y3, from the mushroom Coprinus comatus Biochemical studies of recombinant Y3 from a yeast expression system demonstrated the protein is a unique GBP. Additionally, we show that Y3 exhibits selective and potent cytotoxicity toward human T-cell leukemia Jurkat cells compared with a panel of cancer cell lines via inducing caspase-dependent apoptosis. Screening of a glycan array demonstrated GalNAcβ1-4(Fucα1-3)GlcNAc (LDNF) as a specific Y3-binding ligand. To provide a structural basis for function, the crystal structure was solved to a resolution of 1.2 Å, revealing a single-domain αβα-sandwich motif. Two monomers were dimerized to form a large 10-stranded, antiparallel β-sheet flanked by α-helices on each side, representing a unique oligomerization mode among GBPs. A large glycan binding pocket extends into the dimeric interface, and docking of LDNF identified key residues for glycan interactions. Disruption of residues predicted to be involved in LDNF/Y3 interactions resulted in the significant loss of binding to Jurkat T-cells and severely impaired their cytotoxicity. Collectively, these results demonstrate Y3 to be a GBP with selective cytotoxicity toward human T-cell leukemia cells and indicate its potential use in cancer diagnosis and treatment.

Harnessing benefit from targeting tumor associated carbohydrate antigens

Integrating additive or synergistic antitumor effects that focus on distinct elements of tumor biology are the most rational strategies for cancer treatment. Treatments for breast cancer have increased overall survival, but remain limited by lack of efficacy in a subset of breast cancer patients. The real challenge is to define what elements of tumor biology make the most sense to be integrated. An emerging strategy is to consider a systems biology approach to impact multiple interactions in networks as compare with hitting a specific protein-protein interaction target. In this review, we consider how targeting tumor associated carbohydrate antigens (TACA) that are fundamental to signal pathways might be tailored to harness benefit from combination therapy of sustained immunity with chemotherapy. An approach we are developing makes use of a carbohydrate mimetic peptide (CMP) to induce polyspecific antibodies, which by their nature have numerous on and off target effects. Linking multi-target TACA recognition with mechanisms affecting tumor growth in the context of network heterogeneity and concepts of immune surveillance to tumor cells and the type of breast cancer patients that would benefit from such an approach provides a novel integrative treatment.

Molecular Basis for Recognition of the Cancer Glycobiomarker, LacdiNAc (GalNAc[β1→4]GlcNAc), by Wisteria floribunda Agglutinin

Aberrant glycosylation and the overexpression of specific carbohydrate epitopes is a hallmark of many cancers, and tumor-associated oligosaccharides are actively investigated as targets for immunotherapy and diagnostics. Wisteria floribunda agglutinin (WFA) is a legume lectin that recognizes terminal N-acetylgalactosaminides with high affinity. WFA preferentially binds the disaccharide LacdiNAc (β-d-GalNAc-[1→4]-d-GlcNAc), which is associated with tumor malignancy in leukemia, prostate, pancreatic, ovarian, and liver cancers and has shown promise in cancer glycobiomarker detection. The mechanism of specificity for WFA recognition of LacdiNAc is not fully understood. To address this problem, we have determined affinities and structure of WFA in complex with GalNAc and LacdiNAc. Affinities toward Gal, GalNAc, and LacdiNAc were measured via surface plasmon resonance, yielding K_D values of 4.67 × 10^-4 m, 9.24 × 10^-5 m, and 5.45 × 10^-6 m, respectively. Structures of WFA in complex with LacdiNAc and GalNAc have been determined to 1.80-2.32 Å resolution. These high resolution structures revealed a hydrophobic groove complementary to the GalNAc and, to a minor extent, to the back-face of the GlcNAc sugar ring. Remarkably, the contribution of this small hydrophobic surface significantly increases the observed affinity for LacdiNAc over GalNAc. Tandem MS sequencing confirmed the presence of two isolectin forms in commercially available WFA differing only in the identities of two amino acids. Finally, the WFA carbohydrate binding site is similar to a homologous lectin isolated from Vatairea macrocarpa in complex with GalNAc, which, unlike WFA, binds not only αGalNAc but also terminal Ser/Thr O-linked αGalNAc (Tn antigen).

Galectin Binding to Neo-Glycoproteins: LacDiNAc Conjugated BSA as Ligand for Human Galectin-3

Carbohydrate-lectin interactions are relatively weak. As they play an important role in biological recognition processes, multivalent glycan ligands are designed to enhance binding affinity and inhibitory potency. We here report on novel neo-glycoproteins based on bovine serum albumin as scaffold for multivalent presentation of ligands for galectins. We prepared two kinds of tetrasaccharides (N-acetyllactosamine and N,N-diacetyllactosamine terminated) by multi-step chemo-enzymatic synthesis utilizing recombinant glycosyltransferases. Subsequent conjugation of these glycans to lysine groups of bovine serum albumin via squaric acid diethyl ester yielded a set of 22 different neo-glycoproteins with tuned ligand density. The neo-glycoproteins were analyzed by biochemical and chromatographic methods proving various modification degrees. The neo-glycoproteins were used for binding and inhibition studies with human galectin-3 showing high affinity. Binding strength and inhibition potency are closely related to modification density and show binding enhancement by multivalent ligand presentation. At galectin-3 concentrations comparable to serum levels of cancer patients, we detect the highest avidities. Selectivity of N,N-diacetyllactosamine terminated structures towards galectin-3 in comparison to galectin-1 is demonstrated. Moreover, we also see strong inhibitory potency of our scaffolds towards galectin-3 binding. These novel neo-glycoproteins may therefore serve as selective and strong galectin-3 ligands in cancer related biomedical research.

Enhanced expression of the β4-N-acetylgalactosaminyltransferase 4 gene impairs tumor growth of human breast cancer cells

Two β4-N-acetylgalactosaminyltransferases (β4GalNAcTs), β4GalNAcT3 and β4GalNAcT4, have been shown to be involved in the synthesis of the GalNAcβ1 → 4GlcNAc (LacdiNAc) group expressed on the outer branches of N- and/or O-glycans, and only β4GalNAcT4 is expressed in human mammary gland. We found that the expression level of the LacdiNAc group decreases as human breast cancers progress. To investigate biological significances of this disaccharide in human breast cancers, we transfected the FLAG-tagged β4GalNAcT4 cDNA into MDA-MB-231 cells, and obtained several clones showing enhanced expression of the gene. Clones 1 and 2 showed 15 and 9 times more transcript than mock-transfected cells. The FLAG-β4GalNAcT4 protein and its product, the LacdiNAc group, were detected in clone 1 and 2 cells. No change was observed in their growth rates while significant decreases in colony forming and invasive abilities were observed for clone 1 and 2 cells. When clone 1 cells were transplanted subcutaneously into nude mice, no tumors were formed while tumors were formed with mock-transfected cells. These results indicate that the expression of the LacdiNAc group is quite important for the suppression of malignancies of the MDA-MB-231 cells.

Functional impact of tumor-specific N-linked glycan changes in breast and ovarian cancers

Changes in glycosylation have been implicated in various human diseases, including cancer. Research over the past few decades has produced significant findings that illustrate the importance of cancer-specific alterations in glycosylation in the regulation of tumor formation and metastasis. The identification of glycan-based biomarkers and strategies targeting specific glycan epitopes on the tumor cell surface has become one of the widely pursued research areas. In this chapter, we will summarize and provide perspective on available knowledge about the functional roles that glycan structures play in the development and progression of the gynecological cancers, breast and ovarian, with a specific focus on N-linked glycans. A better understanding of the functional roles for glycans in cancer will drive future innovations for diagnostics and therapeutics.