Two opposing roles of O-glycans in tumor metastasis

Role of Truncated O-GalNAc Glycans in Cancer Progression and Metastasis in Endocrine Cancers

Glycans are an essential part of cells, playing a fundamental role in many pathophysiological processes such as cell differentiation, adhesion, motility, signal transduction, host-pathogen interactions, tumour cell invasion, and metastasis development. These glycans are also able to exert control over the changes in tumour immunogenicity, interfering with tumour-editing events and leading to immune-resistant cancer cells. The incomplete synthesis of O-glycans or the formation of truncated glycans such as the Tn-antigen (Thomsen nouveau; GalNAcα- Ser/Thr), its sialylated version the STn-antigen (sialyl-Tn; Neu5Acα2-6GalNAcα-Ser/Thr) and the elongated T-antigen (Thomsen-Friedenreich; Galβ1-3GalNAcα-Ser/Thr) has been shown to be associated with tumour progression and metastatic state in many human cancers. Prognosis in various human cancers is significantly poor when they dedifferentiate or metastasise. Recent studies in glycobiology have shown truncated O-glycans to be a hallmark of cancer cells, and when expressed, increase the oncogenicity by promoting dedifferentiation, risk of metastasis by impaired adhesion (mediated by selectins and integrins), and resistance to immunological killing by NK cells. Insight into these truncated glycans provides a complimentary and attractive route for cancer antigen discovery. The recent emergence of immunotherapies against cancers is predicted to harness the potential of using such agents against cancer-associated truncated glycans. In this review, we explore the role of truncated O-glycans in cancer progression and metastasis along with some recent studies on the role of O-glycans in endocrine cancers affecting the thyroid and adrenal gland.

Deciphering Protein O-GalNAcylation: Method Development and Disease Implication

Mucin-type O-glycosylation is an important protein post-translational modification that is abundantly expressed on cell surface proteins. Protein O-glycosylation plays a variety of roles in cellular biological functions including protein structure and signal transduction to the immune response. Cell surface mucins are highly O-glycosylated and are the main substance of the mucosal barrier that protects the gastrointestinal or respiratory tract from infection by pathogens or microorganisms. Dysregulation of mucin O-glycosylation may impair mucosal protection against pathogens that can invade cells to trigger infection or immune evasion. Truncated O-glycosylation, also known as Tn antigen or O-GalNAcylation, is highly upregulated in diseases such cancer, autoimmune disorders, neurodegenerative diseases, and IgA nephropathy. Characterization of O-GalNAcylation helps decipher the role of Tn antigen in physiopathology and therapy. However, the analysis of O-glycosylation, specifically the Tn antigen, remains challenging due to the lack of reliable enrichment and identification assays compared to N-glycosylation. Here, we summarize recent advances in analytical methods for O-GalNAcylation enrichment and identification and highlight the biological role of the Tn antigen in various diseases and the clinical implications of identifying aberrant O-GalNAcylation.

Dysregulation and prometastatic function of glycosyltransferase C1GALT1 modulated by cHP1BP3/ miR-1-3p axis in bladder cancer

Background

Abnormal glycosylation in a variety of cancer types is involved in tumor progression and chemoresistance. Glycosyltransferase C1GALT1, the key enzyme in conversion of Tn antigen to T antigen, is involved in both physiological and pathological conditions. However, the mechanisms of C1GALT1 in enhancing oncogenic phenotypes and its regulatory effects via non-coding RNA are unclear.

Methods

Abnormal expression of C1GALT1 and its products T antigen in human bladder cancer (BLCA) were evaluated with BLCA tissue, plasma samples and cell lines. Effects of C1GALT1 on migratory ability and proliferation were assessed in YTS-1 cells by transwell, CCK8 and colony formation assay in vitro and by mouse subcutaneous xenograft and trans-splenic metastasis models in vivo. Dysregulated circular RNAs (circRNAs) and microRNAs (miRNAs) were profiled in 3 pairs of bladder cancer tissues by RNA-seq. Effects of miR-1-3p and cHP1BP3 (circRNA derived from HP1BP3) on modulating C1GALT1 expression were investigated by target prediction program, correlation analysis and luciferase reporter assay. Functional roles of miR-1-3p and cHP1BP3 on migratory ability and proliferation in BLCA were also investigated by in vitro and in vivo experiments. Additionally, glycoproteomic analysis was employed to identify the target glycoproteins of C1GALT1.

Results

In this study, we demonstrated upregulation of C1GALT1 and its product T antigen in BLCA. C1GALT1 silencing suppressed migratory ability and proliferation of BLCA YTS-1 cells in vitro and in vivo. Subsets of circRNAs and miRNAs were dysregulated in BLCA tissues. miR-1-3p, which is reduced in BLCA tissues, inhibited transcription of C1GALT1 by binding directly to its 3′-untranslated region (3′-UTR). miR-1-3p overexpression resulted in decreased migratory ability and proliferation of YTS-1 cells. cHP1BP3 was upregulated in BLCA tissues, and served as an miR-1-3p “sponge”. cHP1BP3 was shown to modulate migratory ability, proliferation, and colony formation of YTS-1 cells, and displayed tumor-suppressing activity in BLCA. Target glycoproteins of C1GALT1, including integrins and MUC16, were identified.

Conclusions

This study reveals the pro-metastatic and proliferative function of upregulated glycosyltransferase C1GLAT1, and provides preliminary data on mechanisms underlying dysregulation of C1GALT1 via miR-1-3p / cHP1BP3 axis in BLCA.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-022-02438-7.

Principles of glycocalyx engineering with hydrophobic-anchored synthetic mucins

The cellular glycocalyx is involved in diverse biological phenomena in health and disease. Yet, molecular level studies have been challenged by a lack of tools to precisely manipulate this heterogeneous structure. Engineering of the cell surface using insertion of hydrophobic-terminal materials has emerged as a simple and efficient method with great promise for glycocalyx studies. However, there is a dearth of information about how the structure of the material affects membrane insertion efficiency and resulting density, the residence time of the material, or what types of cells can be utilized. Here, we examine a panel of synthetic mucin structures terminated in highly efficient cholesterylamide membrane anchors for their ability to engineer the glycocalyx of five different cell lines. We examined surface density, residence time and half-life, cytotoxicity, and the ability be passed to daughter cells. We report that this method is robust for a variety of polymeric structures, long-lasting, and well-tolerated by a variety of cell lines.

Exploring Prognosis-Associated Biomarkers of Estrogen-Independent Uterine Corpus Endometrial Carcinoma by Bioinformatics Analysis

Background

Uterine corpus endometrial carcinoma (UCEC) is one of the most common female cancers with high incidence and mortality rates. In particular, the prognosis of type II UCEC is poorer than that of type I. However, the molecular mechanism underlying type II UCEC remains unclear.

Methods

RNA-seq data and corresponding clinical information on UCEC patients were downloaded from The Cancer Genome Atlas database, which were then separated into mRNA, lncRNA, and miRNA gene expression profile matrix to perform differentially expressed gene analysis. Weighted gene co-expression network analysis (WGCNA) was used to identify key modules associated with different UCEC subtypes based on mRNA and lncRNA expression matrix. Following that, a subtype-associated competing endogenous RNA (ceRNA) regulatory network was constructed. In addition, GO functional annotation and KEGG pathway analysis were performed on subtype-related DE mRNAs, and STRING database was utilized to predict the interaction network between proteins and their biological functions. The key mRNAs were validated at the protein and gene expression levels in endometrial cancerous tissues as compared with normal tissues.

Results

In summary, we identified 4611 mRNA, 3568 lncRNAs, and 47 miRNAs as differentially expressed between endometrial cancerous tissues and normal endometrial tissues. WGCNA demonstrated that 72 mRNAs and 55 lncRNAs were correlated with pathological subtypes. In the constructed ceRNA regulatory network, LINC02418, RASGRF1, and GCNT1 were screened for their association with poor prognosis of type II UCEC. These DE mRNAs were linked to Wnt signaling pathway, and lower expression of LEF1 and NKD1 predicted advanced clinical stages and worse prognosis of UCEC patients.

Conclusion

This study revealed five prognosis-associated biomarkers that can be used to predict the worst prognosis of type II UCEC.

The evolving role of MUC16 (CA125) in the transformation of ovarian cells and the progression of neoplasia

MUC16 (the cancer antigen CA125) is the most commonly used serum biomarker in epithelial ovarian cancer, with increasing levels reflecting disease progression. It is a transmembrane glycoprotein with multiple isoforms, undergoing significant changes through the metastatic process. Aberrant glycosylation and cleavage with overexpression of a small membrane-bound fragment consist MUC16-related mechanisms that enhance malignant potential. Even MUC16 knockdown can induce an aggressive phenotype but can also increase susceptibility to chemotherapy. Variable MUC16 functions help ovarian cancer cells avoid immune cytotoxicity, survive inside ascites and form metastases. This review provides a comprehensive insight into MUC16 transformations and interactions, with description of activated oncogenic signalling pathways, and adds new elements on the role of its differential glycosylation. By following the journey of the molecule from pre-malignant states to advanced stages of disease it demonstrates its behaviour, in relation to the phenotypic shifts and progression of ovarian cancer. Additionally, it presents proposed differences of MUC16 structure in normal/benign conditions and epithelial ovarian malignancy.

Core 2 β1,6-N-acetylglucosaminyltransferases accelerate the escape of choriocarcinoma from natural killer cell immunity

Hyperglycosylated human chorionic gonadotropin (H-hCG) is secreted from choriocarcinoma and contains a core2 O-glycan formed by core2 β1,6-N-acetylglucosaminyl transferase (C2GnT). Choriocarcinoma is considered immunogenic as it is gestational and contains paternal chromosomal components. Here we examined the function of C2GnT in the evasion of choriocarcinoma cells from natural killer (NK) cell-mediating killing. We determined that C2GnT is highly expressed in malignant gestational trophoblastic neoplasms. C2GnT KO downregulates core2 O-glycan expression in choriocarcinoma cells, which are more efficiently killed by NK cells than control cells. C2GnT KO cell containing tumor necrosis factor-related apoptosis inducing ligand have lower viability than control cells. Additionally, poly-N-acetyllactosamine in core2 branched oligosaccharides on MHC class I-related chain A (MICA) and mucin1 (MUC1) is significantly reduced in C2GnT KO cells. Meanwhile, the cumulative survival rate of nude mice inoculated with C2GnT KO tumors was higher than that of the control group. These findings suggest that choriocarcinoma cells may escape NK cell-mediated killing via glycosylation of MICA and MUC1.

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C2GnT knockout reduces core2 O-glycan expression in choriocarcinoma cells

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C2GnT KO cells are more readily killed by NK cells

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C2GnT KO cells containing TRAIL have lower viability than controls

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MHC class I-related chain A and MUC1 glycosylation is reduced in C2GnT KO cells

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Survival rate of nude mice inoculated with C2GnT KO tumors is higher than controls

The Roles of Glycans in Bladder Cancer

Bladder cancer is one of the most common malignant tumors of the urogenital system with high morbidity and mortality worldwide. Early diagnosis and personalized treatment are the keys to successful bladder cancer treatment. Due to high postoperative recurrence rates and poor prognosis, it is urgent to find suitable therapeutic targets and biomarkers. Glycans are one of the four biological macromolecules in the cells of an organism, along with proteins, nucleic acids, and lipids. Glycans play important roles in nascent peptide chain folding, protein processing, and translation, cell-to-cell adhesion, receptor-ligand recognition, and binding and cell signaling. Glycans are mainly divided into N-glycans, O-glycans, proteoglycans, and glycosphingolipids. The focus of this review is the discussion of glycans related to bladder cancer. Additionally, this review also addresses the clinical value of glycans in the diagnosis and treatment of bladder cancer. Abnormal glycans are likely to be potential biomarkers for bladder cancer.

GALNT6 promotes breast cancer metastasis by increasing mucin-type O-glycosylation of α2M

Breast cancer is the most lethal malignancy in women. N-acetylgalactosaminyltransferase 6 (GALNT6) is an enzyme which mediates the initial step of mucin-type O-glycosylation, and has been reported to be involved in mammary carcinogenesis. However, the molecular mechanism of GALNT6 in breast cancer metastasis has not been fully explored. In this study, based on online database analyses and tissue microarrays, the overall survival (OS) of breast cancer patients with high expression of GALNT6 was found to be shorter than those with low expression of GALNT6. Also, high GALNT6 expression was positively correlated with advanced pN stage and pTNM stage. GALNT6 was shown to be able to promote the migration and invasion of breast cancer cells, and enhance the level of mucin-type O-glycosylation of substrates in the supernatants of breast cancer cells. Qualitative mucin-type glycosylomics analysis identified α2M as a novel substrate of GALNT6. Further investigation showed that GALNT6 increased O-glycosylation of α2M, and the following activation of the downstream PI3K/Akt signaling pathway was involved in the promotion of migration and invasion of breast cancer cells. This study identified a new substrate of GALNT6 and provides novel understanding of the role of GALNT6 in promoting metastasis and poor prognosis in breast cancer.

Deep Structural Analysis and Quantitation of O-Linked Glycans on Cell Membrane Reveal High Abundances and Distinct Glycomic Profiles Associated with Cell Type and Stages of Differentiation

Proteins on cell membrane are modified by N- and O-glycans. N-Glycans have been extensively characterized using advanced separation and mass spectrometry techniques. However, O-glycans remain a challenge, because of the lack of universal enzymes to release them and the large background abundances of N-glycans. Here, we report a method for in-depth structural analysis and quantitation of O-glycans derived from human cell membrane. O-Glycans were chemically released from isolated cell membrane glycoproteins following N-glycan and lipid/glycolipid removal by PNGase F digestion and Folch extraction, respectively. Released O-glycans were purified by an optimized protocol to eliminate interference from small molecules and degraded proteins. Cell surface O-glycans were then analyzed using a nanoLC-chip-QTOF mass spectrometer with a porous graphitized carbon (PGC) column, while the N-glycans and glycolipids isolated from the same cell membrane fractions were analyzed in parallel using previously reported methods. The monosaccharide compositions and linkages of the detected O-glycans were identified by exoglycosidase digestion facilitated with tandem mass spectrometry (MS/MS). Using this method, we identified 44 cell membrane O-glycan isomers with MS/MS, and, among them, we unambiguously characterized 25 O-glycan structures with exoglycosidase digestion to create a library with their complete structures, accurate masses, and retention times. In this process, we identified and characterized unexpected mannose oligomers that are α(1-2/3) linked. This library enabled the identification and quantification of unique cell surface O-glycans from different cell lines and the study of specific O-glycan changes during cell differentiation.

Serum N-glycan profiling can predict biopsy-proven graft rejection after living kidney transplantation

BACKGROUND

To evaluate whether serum N-glycan profile can be used as a diagnostic marker of graft rejection after living-donor kidney transplants (KT).

METHODS

We retrospectively examined 174 KT recipients at five medical centers. N-Glycan levels were analyzed in postoperative serum samples using glycoblotting combined with mass spectrometry. We developed an integrated score to predict graft rejection based on a combination of age, gender, immunological risk factors, and serum N-glycan levels at post-KT day D1 and D7. Rejection-free survival rates stratified by the sum of integrated scores (D1 + D7) were evaluated using Kaplan-Meier curves.

RESULTS

Of 174, 52 showed graft rejection (Rejection-pos. group) and 122 recipients did not show graft rejection (Rejection-neg. group). The integrated scores were significantly higher in the Rejection-pos. group than those of the Rejection-neg. group. Area-under-curve (AUC) value of integrated scores at post-KT D1, and D7 were 0.84 and 0.84, respectively. The sum of integrated scores (D1 + D7) ≥ 0.50 identified graft rejection with 81% sensitivity and 80% specificity; with an AUC value of 0.87. Recipients with higher sum of integrated scores (D1 + D7 ≥ 0.5) had significantly shorter rejection-free survival than those with lower scores.

CONCLUSION

Evaluation of serum N-glycosylation profiles can identify recipients who are prone to rejection.

Highly Efficient Analysis of Glycoprotein Sialylation in Human Serum by Simultaneous Quantification of Glycosites and Site-Specific Glycoforms

Aberrant sialylation of glycoproteins is closely related to many malignant diseases, and analysis of sialylation has great potential to reveal the status of these diseases. However, in-depth analysis of sialylation is still challenging because of the high microheterogeneity of protein glycosylation, as well as the low abundance of sialylated glycopeptides (SGPs). Herein, an integrated strategy was fabricated for the detailed characterization of glycoprotein sialylation on the levels of glycosites and site-specific glycoforms by employing the SGP enrichment method. This strategy enabled the identification of up to 380 glycosites, as well as 414 intact glycopeptides corresponding to 383 site-specific glycoforms from only initial 6 μL serum samples, indicating the high sensitivity of the method for the detailed analysis of glycoprotein sialylation. This strategy was further employed to the differential analysis of glycoprotein sialylation between hepatocellular carcinoma patients and control samples, leading to the quantification of 344 glycosites and 405 site-specific glycoforms, simultaneously. Among these, 43 glycosites and 55 site-specific glycoforms were found to have significant change on the glycosite and site-specific glycoform levels, respectively. Interestingly, several glycoforms attached onto the same glycosite were found with different change tendencies. This strategy was demonstrated to be a powerful tool to reveal subtle differences of the macro- and microheterogeneity of glycoprotein sialylation.

Integrated Glycome Strategy for Characterization of Aberrant LacNAc Contained N-Glycans Associated With Gastric Carcinoma

Aberrant glycosylation is not only a feature of malignant cell transformation, but also plays an important role in metastasis. In the present study, an integrated strategy combining the lectin microarrays and lectin cytochemistry was employed to investigate and verify the altered glycopatterns in gastric cancer (GC) cell lines as well as resected tumor specimens from matched tissue sets of 46 GC patients. Subsequently, lectin-mediated affinity capture glycoproteins, and MALDI-TOF/TOF-MS were employed to further acquire precise structural information of the altered glycans. According to the results, the glycopatterns recognized by 10 (e.g., ACA, MAL-I, and ConA) and 3 lectins (PNA, MAL-I, and VVA) showed significantly variations in GC cells and tissue compared to their corresponding controls, respectively. Notably, the relative abundance of Galβ-1,4GlcNAc (LacNAc) recognized by MAL-I exhibited a significant increase in GC cells (p < 0.001) and tissue from patients at stage II and III (p < 0.05), and a significant increase in lymph node positive tumor cases, compared with lymph node negative tumor cases (p < 0.05). More LacNAc contained N-glycans were characterized in tumor sample with advanced stage compared to corresponding control. Moreover, there were 10 neo-LacNAc-contained N-glycans (e.g., m/z 1625.605, 1803.652, and 1914.671) only presented in GC tissue with advanced stage. Among these, six N-glycans were modified with sialic acid or fucose based on LacNAc to form sialylated N-glycans or lewis antigens, respectively. Our results revealed that the aberrant expression of LacNAc is a characteristic of GC, and LacNAc may serve as a scaffold to be further modified with sialic acid or fucose. Our findings provided useful information for us to understand the development of GC.

Integrins: Moonlighting Proteins in Invadosome Formation

Invadopodia are actin-rich protrusions developed by transformed cells in 2D/3D environments that are implicated in extracellular matrix (ECM) remodeling and degradation. These structures have an undoubted association with cancer invasion and metastasis because invadopodium formation in vivo is a key step for intra/extravasation of tumor cells. Invadopodia are closely related to other actin-rich structures known as podosomes, which are typical structures of normal cells necessary for different physiological processes during development and organogenesis. Invadopodia and podosomes are included in the general term 'invadosomes,' as they both appear as actin puncta on plasma membranes next to extracellular matrix metalloproteinases, although organization, regulation, and function are slightly different. Integrins are transmembrane proteins implicated in cell-cell and cell-matrix interactions and other important processes such as molecular signaling, mechano-transduction, and cell functions, e.g., adhesion, migration, or invasion. It is noteworthy that integrin expression is altered in many tumors, and other pathologies such as cardiovascular or immune dysfunctions. Over the last few years, growing evidence has suggested a role of integrins in the formation of invadopodia. However, their implication in invadopodia formation and adhesion to the ECM is still not well known. This review focuses on the role of integrins in invadopodium formation and provides a general overview of the involvement of these proteins in the mechanisms of metastasis, taking into account classic research through to the latest and most advanced work in the field.

A New Searching Strategy for the Identification of O-Linked Glycopeptides

For the analysis of homogeneous post-translational modifications such as protein phosphorylation and acetylation, setting a variable modification on the specific residue(s) is applied to identify the modified peptides for database searching. However, this approach is often not applicable to identify intact mucin-type O-glycopeptides due to the high microheterogeneity of the glycosylation. Because there is virtually no carbohydrate-related tag on the peptide fragments after the O-glycopeptides are dissociated in HCD, we find it is unnecessary to set the variable mass tags on the Ser/Thr residues to identify the peptide sequences. In this study, we present a novel approach, termed as O-Search, for the interpretation of O-glycopeptide HCD spectra. Instead of setting the variable mass tags on the Ser/Thr residues, we set variable mass tags on the peptide level. The precursor mass of the MS/MS spectrum was deducted by every possible summed mass of O-glycan combinations on at most three S/T residues. All the spectra with these new precursor masses were searched against the protein sequence database without setting variable glycan modifications. It was found that this method had much decreased search space and had excellent sensitivity in the identification of O-glycopeptides. Compared with the conventional searching approach, O-Search yielded 96%, 86%, and 79% improvement in glycopeptide spectra matching, glycopeptide identification, and peptide sequence identification, respectively. It was demonstrated that O-Search enabled the consideration of more glycan structures and was fitted to analyze microheterogeneity of O-glycosylation.

Highly Efficient Identification of O-GalNAc Glycosylation by an Acid-Assisted Glycoform Simplification Approach

Compared with N-linked glycosylation, the analysis of O-GalNAc glycosylation is extremely challenging due to the high structure diversity of glycans and lack of glycosidases to release O-GalNAc glycans. In this work, a glycoform simplification strategy by combining HILIC enrichment with chemical de-sialylation to characterize O-GalNAc glycosylation of human serum is presented. This method is first validated by using the bovine fetuin as the test sample. It is found that more than 90% of the sialic acid residues can be removed from bovine fetuin by the acid-assisted de-sialylation method, which significantly simplifies the glycan structure and improves identification sensitivity. Indeed, the number of identified peptide backbones increases nearly one fold when this strategy is used. This method is further applied to analyze the human serum sample, where 185 O-GalNAc modified peptide sequences corresponding to 94 proteins with high confidence (FDR (false detection rate) <1%) are identified. This straight forward strategy can significantly reduce the variations of glycan structures, and is applicable to analysis of other biological samples with high complexity.

Behavior of blood plasma glycan features in bladder cancer

Despite systemic therapy and cystectomy, bladder cancer is characterized by a high recurrence rate. Serum glycomics represents a promising source of prognostic markers for monitoring patients. Our approach, which we refer to as "glycan node analysis", constitutes the first example of molecularly "bottom-up" glycomics. It is based on a global glycan methylation analysis procedure that is applied to whole blood plasma/serum. The approach detects and quantifies partially methylated alditol acetates arising from unique glycan features such as α2-6 sialylation, β1-4 branching, and core fucosylation that have been pooled together from across all intact glycans within a sample into a single GC-MS chromatographic peak. We applied this method to 122 plasma samples from former and current bladder cancer patients (n = 72 former cancer patients with currently no evidence of disease (NED); n = 38 non-muscle invasive bladder cancer (NMIBC) patients; and n = 12 muscle invasive bladder cancer (MIBC) patients) along with plasma from 30 certifiably healthy living kidney donors. Markers for α2-6 sialylation, β1-4 branching, β1-6 branching, and outer-arm fucosylation were able to separate current and former (NED) cases from certifiably healthy controls (ROC curve c-statistics ~ 0.80); but NED, NMIBC, and MIBC were not distinguished from one another. Based on the unexpectedly high levels of these glycan nodes in the NED patients, we hypothesized that recurrence of this disease could be predicted by some of the elevated glycan features. Indeed, α2-6 sialylation and β1-6 branching were able to predict recurrence from the NED state using a Cox proportional hazards regression model adjusted for age, gender, and time from cancer. The levels of these two glycan features were correlated to C-reactive protein concentration, an inflammation marker and known prognostic indicator for bladder cancer, further strengthening the link between inflammation and abnormal plasma protein glycosylation.

Glycosylation of Cancer Stem Cells: Function in Stemness, Tumorigenesis, and Metastasis

Aberrant glycosylation plays a critical role in tumor aggressiveness, progression, and metastasis. Emerging evidence associates cancer initiation and metastasis to the enrichment of cancer stem cells (CSCs). Several universal markers have been identified for CSCs characterization; however, a specific marker has not yet been identified for different cancer types. Specific glycosylation variation plays a major role in the progression and metastasis of different cancers. Interestingly, many of the CSC markers are glycoproteins and undergo differential glycosylation. Given the importance of CSCs and altered glycosylation in tumorigenesis, the present review will discuss current knowledge of altered glycosylation of CSCs and its application in cancer research.

Glycosylation and Integrin Regulation in Cancer

Integrins are transmembrane receptors that coordinate extracellular matrix (ECM)-cell and cell-cell interactions, signal transmission, gene expression, and cell function. The aberration of integrin function is one of the well-recognized mechanisms of cancer. The activity of integrins is strongly influenced by glycans through glycosylation events and the establishment of glycan-mediated interactions. Glycans represent a class of ubiquitous biomolecules that display an extraordinary complexity and diversity in both structure and function. Widely expressed both in the ECM and on the cell surface, they play a crucial role in mediating cell proliferation, survival, and metastasis during cancer. The purpose of this review is to provide an overview of how both glycosylation of integrins and integrin interaction with the cancer glyco-microenvironment can regulate cancer progression.

Polypeptide N-acetylgalactosaminyltransferase-6 expression independently predicts poor overall survival in patients with lung adenocarcinoma after curative resection

Background

Polypeptide N-acetylgalactosaminyltransferases (GalNAc-Ts) are important glycosyltransferases in cancer, but the clinical role of its individual isoforms is unclear. We investigated the clinical significance and survival relevance of one isoform, GalNAc-T6 in lung adenocarcinoma after curative resection.

Results

GalNAc-T6 was identified in 27.8% (55/198) of patients, and statistically indicated advanced TNM stage (P = 0.069). Multivariate analysis showed GalNAc-T6 to be an independent predictor for reduced overall survival of patients (P = 0.027), and the result was confirmed with bootstraping techniques, and on line “Kaplan-Meier Plotter” and “SurvExpress” database analysis, respectively. Moreover, ROC curve demonstrated that GalNAc-T6 expression significantly improved the accuracy of survival prediction.

Methods

With 198 paraffin-embedded tumor samples from lung adenocarcinoma patients, GalNAc-T6 expression was immunohistochemically assessed for the association with clinicopathological parameters. The prognostic significance was evaluated by Cox proportional hazards regression analysis with 1000 bootstraping. “Kaplan-Meier Plotter”, “SurvExpress” database analysis, and receiver-operating characteristic (ROC) curve were performed to provide further validation.

Conclusions

GalNAc-T6 expression correlated significantly with advanced TNM stage, and independently predicted worse OS for lung adenocarcinoma.

Stage Dependence, Cell-Origin Independence, and Prognostic Capacity of Serum Glycan Fucosylation, β1-4 Branching, β1-6 Branching, and α2-6 Sialylation in Cancer

Glycans represent a promising but only marginally accessed source of cancer markers. We previously reported the development of a molecularly bottom-up approach to plasma and serum (P/S) glycomics based on glycan linkage analysis that captures features such as α2-6 sialylation, β1-6 branching, and core fucosylation as single analytical signals. Based on the behavior of P/S glycans established to date, we hypothesized that the alteration of P/S glycans observed in cancer would be independent of the tissue in which the tumor originated yet exhibit stage dependence that varied little between cancers classified on the basis of tumor origin. Herein, the diagnostic utility of this bottom-up approach as applied to lung cancer patients (n = 127 stage I; n = 20 stage II; n = 81 stage III; and n = 90 stage IV) as well as prostate (n = 40 stage II), serous ovarian (n = 59 stage III), and pancreatic cancer patients (n = 15 rapid autopsy) compared to certifiably healthy individuals (n = 30), nominally healthy individuals (n = 166), and risk-matched controls (n = 300) is reported. Diagnostic performance in lung cancer was stage-dependent, with markers for terminal (total) fucosylation, α2-6 sialylation, β1-4 branching, β1-6 branching, and outer-arm fucosylation most able to differentiate cases from controls. These markers behaved in a similar stage-dependent manner in other types of cancer as well. Notable differences between certifiably healthy individuals and case-matched controls were observed. These markers were not significantly elevated in liver fibrosis. Using a Cox proportional hazards regression model, the marker for α2-6 sialylation was found to predict both progression and survival in lung cancer patients after adjusting for age, gender, smoking status, and stage. The potential mechanistic role of aberrant P/S glycans in cancer progression is discussed.

Core 3 mucin-type O-glycan restoration in colorectal cancer cells promotes MUC1/p53/miR-200c-dependent epithelial identity

The attachment of cell-surface carbohydrates to proteins mediated by the amino acids serine or threonine (O-glycan) is involved in tumor metastasis; the roles of O-glycans vary depending on their structure, but the detailed mechanisms by which O-glycans trigger signaling to control tumor metastasis are largely unknown. In this study, we found that the reduced expression of core 3 synthase correlated with metastasis to lymph nodes and distant organs, resulting in poor prognosis for colorectal cancer (CRC) patients. Mechanically, we revealed that mucin-type core 3 O-glycan was synthesized at the membrane-tethered MUC1 N terminus because of core 3 synthase expression in colon cancer cells. This further inhibited the translocation of MUC1-C to the nucleus, initiated p53 gene transcription that was dependent on the inhibition of MUC1-C nucleus translocation, activated p53-mediated miR-200c expression and resulted in mesenchymal-epithelial transition (MET). Inhibition of MUC1 via small interfering RNA (siRNA) in re-expressed core 3 synthase colon cancer cells further inhibited MUC1-C nucleus translocation, increased p53 and miR-200c expression, and enhanced MET. However, inhibition of p53 via siRNA or miR-200c via miR-200c inhibitor in re-expressed core 3 synthase colon cancer cells promoted the epithelial-mesenchymal transition (EMT) in a reversible manner. Core 3 synthase mRNA levels and the p53 mRNA levels or miR-200c levels in the colon cancerous samples were positively correlated. Our findings suggest a novel mechanism linking mucin-type core 3 O-glycan to the EMT-MET plasticity of CRC cells via MUC1/p53/miR-200c-dependent signaling cascade and shed light on therapeutic strategies to treat this malignancy.

Proteomics Analysis of O-GalNAc Glycosylation in Human Serum by an Integrated Strategy

The diversity of O-linked glycan structures has drawn increasing attention due to its vital biological roles. However, intact O-glycopeptides with different glycans are typically not well elucidated using the current methods. In this work, an integrated strategy was developed for comprehensive analysis of O-GalNAc glycosylation by combining hydrophilic interaction chromatography (HILIC) tip enrichment, beam-type collision induced decomposition (beam-CID) detection, and in silico deglycosylation method for spectra interpretation. In this strategy, the intact O-GalNAc glycopeptides were selectively enriched and the original spectra obtained by time-of-flight (TOF)-CID were preprocessed using an in silico deglycosylation method, enabling direct searching without setting multiple glycosylation modifications, which could significantly decrease the search space. This strategy was applied to analyze the O-GalNAc glycoproteome of human serum, leading to identification of 407 intact O-GalNAc glycopeptides from 93 glycoproteins. About 81% of the glycopeptides contained at least one sialic acid, which could reveal the microheterogeneity of O-GalNAc glycosylation. Up until now, this is the largest data set of intact O-GalNAc glycoforms from complex biological samples at the proteome level. Furthermore, this method is readily applicable to study O-glycoform heterogeneity in other complex biological systems.

Recent progress and perspectives on prostate cancer biomarkers

The application of prostate-specific antigen (PSA) in prostate cancer (PC) screening, diagnosis, and prognosis has improved the clinical management of PC patients. However, the PSA assay has been faced with criticism due to its potential association with over-diagnosis and subsequent overtreatment of patients with indolent disease. The United States Preventive Services Task Force incited much debate over PSA-based screening in 2012 by recommending against this approach. However, the PSA assay remains the first-line tool for the early detection of PC. This debate highlights the unmet need for non-invasive PC biomarkers with greater sensitivity and specificity that are capable of distinguishing aggressive disease from indolent disease, predicting treatment response, and guiding treatment decisions. Recent investigations into putative PC biomarkers have focused on PSA isoform assays (prostate health index, 4-kallikurein panel), PC-associated genes in the urine (PCA3 and TMPRSS2-ERG), glycan-associated biomarkers (S2, 3PSA, GCNT1, and tri- and tetra-antennary serum N-glycans), and circulating tumor cells. Although substantial efforts to identify novel PC biomarkers that might replace PSA have been put forth, the majority of the putative PC biomarkers reported in the last few years are still under investigation or validation. This review provides an overview of the current state of PC biomarker research and focuses on a few promising PC biomarkers in development.

Metastatic Progression of Prostate Cancer Is Mediated by Autonomous Binding of Galectin-4-O-Glycan to Cancer Cells

Metastatic prostate cancer continues to pose a difficult therapeutic challenge. Prostate cancer progression is associated with aberrant O-glycosylation of cancer cell surface receptors, but the functional impact of such events is uncertain. Here we report spontaneous metastasis of human prostate cancer xenografts that express high levels of galectin-4 along with genetic signatures of EGFR-HER2 signaling and O-glycosylation. Galectin-4 expression in clinical specimens of prostate cancer correlated with poor patient survival. Galectin-4 binding to multiple receptor tyrosine kinases stimulated their autophosphorylation, activated expression of pERK, pAkt, fibronectin, and Twist1, and lowered expression of E-cadherin, thereby facilitating epithelial-mesenchymal transition, invasion, and metastasis. In vivo investigations established that galectin-4 expression enabled prostate cancer cells to repopulate tumors in orthotopic and heterotopic tissues. Notably, these effects of galectin-4 relied upon O-glycosylation mediated by C1GALT1, a galactosyltransferase implicated in other cancers. Parallel changes in galectin-4 and O-glycosylation triggered aberrant receptor signaling and more aggressive invasive character in prostate cancer cells, which through better survival in the circulation also contributed to the bulk cell progeny of distal tumors. Our findings establish galectin-4 and C1GALT1-mediated glycosylation in a signaling axis that is activated during prostate cancer progression, with implications for therapeutic targeting of advanced metastatic disease. Cancer Res; 76(19); 5756-67. ©2016 AACR.

Perspectives on Anti-Glycan Antibodies Gleaned from Development of a Community Resource Database

Antibodies are used extensively for a wide range of basic research and clinical applications. While an abundant and diverse collection of antibodies to protein antigens have been developed, good monoclonal antibodies to carbohydrates are much less common. Moreover, it can be difficult to determine if a particular antibody has the appropriate specificity, which antibody is best suited for a given application, and where to obtain that antibody. Herein, we provide an overview of the current state of the field, discuss challenges for selecting and using antiglycan antibodies, and summarize deficiencies in the existing repertoire of antiglycan antibodies. This perspective was enabled by collecting information from publications, databases, and commercial entities and assembling it into a single database, referred to as the Database of Anti-Glycan Reagents (DAGR). DAGR is a publicly available, comprehensive resource for anticarbohydrate antibodies, their applications, availability, and quality.

DNA hypomethylation upregulates expression of the MGAT3 gene in HepG2 cells and leads to changes in N-glycosylation of secreted glycoproteins

Changes in N-glycosylation of plasma proteins are observed in many types of cancer, nevertheless, few studies suggest the exact mechanism involved in aberrant protein glycosylation. Here we studied the impact of DNA methylation on the N-glycome in the secretome of the HepG2 cell line derived from hepatocellular carcinoma (HCC). Since the majority of plasma glycoproteins originate from the liver, the HepG2 cells represent a good model for glycosylation changes in HCC that are detectable in blood, which is an easily accessible analytic material in a clinical setting. Two different concentrations of 5-aza-2′-deoxycytidine (5-aza-2dC) differentially affected global genome methylation and induced different glycan changes. Around twenty percent of 84 glyco-genes analysed changed expression level after the 5-aza-2dC treatment as a result of global genome hypomethylation. A correlation study between the changes in glyco-gene expression and the HepG2 glycosylation profile suggests that the MGAT3 gene might be responsible for the glycan changes consistently induced by both doses of 5-aza-2dC. Core-fucosylated tetra-antennary structures were decreased in quantity likely as a result of hypomethylated MGAT3 gene promoter followed by increased expression of this gene.

The Sweet Side of Immune Evasion: Role of Glycans in the Mechanisms of Cancer Progression

Glycans are part of the essential components of a cell. These compounds play a fundamental role in several physiopathological processes, including cell differentiation, adhesion, motility, signal transduction, host-pathogen interactions, tumor cell invasion, and metastasis development. Glycans are also able to exert control over the changes in tumor immunogenecity, interfering with tumor editing events and leading to immune-resistant cancer cells. The involvement of glycans in cancer progression is related to glycosylation alterations. Understanding such changes is, therefore, extremely useful to set the stage for their use as biomarkers, improving the diagnostics and therapeutic strategies. Herein, we discuss the basis of how modifications in glycosylation patterns may contribute to cancer genesis and progression as well as their importance in oncology field.

Glyco-genes change expression in cancer through aberrant methylation

BACKGROUND

Most eukaryotic proteins are modified by covalent addition of glycan molecules that considerably influence their function. Aberrant glycosylation is profoundly involved in malignant transformation, tumor progression and metastasis. Some glycan structures are tumor-specific and reflect disturbed glycan biosynthesis pathways.

METHODS

We analyzed DNA methylation and expression of 86 glyco-genes in melanoma, hepatocellular, breast and cervical cancers using data from publicly available databases. We also analyzed methylation datasets without the available matching expression data for glyco-genes in lung cancer, and progression of melanoma into lymph node and brain metastases.

RESULTS

Ten glyco-genes (GALNT3, GALNT6, GALNT7, GALNT14, MGAT3, MAN1A1, MAN1C1, ST3GAL2, ST6GAL1, ST8SIA3) showing changes in both methylation and expression in the same type of cancer belong to GalNAc transferases, GlcNAc transferases, mannosidases and sialyltransferases, which is in line with changes in glycan structures already reported in the same type of tumors. Some of those genes were additionally identified as potentially valuable for disease prognosis. The MGAT5B gene, so far identified as specifically expressed in brain, emerged as a novel candidate gene that is epigenetically dysregulated in different cancers other than brain cancer. We also report for the first time aberrant expression of the GALNT and MAN genes in cancer by aberrant promoter methylation.

CONCLUSIONS

Aberrant expression of glyco-genes due to aberrant promoter methylation could be a way leading to characteristic glycosylation profiles commonly described in cancer.

GENERAL SIGNIFICANCE

Methylation status in promoters of candidate glyco-genes might serve as prognostic markers for specific tumors and point to potential novel targets for epigenetic drugs. This article is part of a Special Issue entitled "Glycans in personalised medicine" Guest Editor: Professor Gordan Lauc.

Liquid chromatography mass spectrometry-based O-glycomics to evaluate glycosylation alterations in gastric cancer

PURPOSE

Gastric cancer is the fourth most common malignant cancer worldwide. Important for tumorigenesis and progression, aberrant glycosylation occurs frequently in cancers. We investigated the differences in O-glycosylation in the serum of 157 gastric cancer patients (GC) and 144 healthy donors.

EXPERIMENTAL DESIGN

We used the method of labeling O-glycans (released from proteins) with 1-phenyl-3-methyl-5-pyrazolone followed by LC-MS analysis. Analyzing the LC-MS data by partial least squares discriminant and unpaired Student t test, combined with the structural information of O-glycans from LC-MS/MS in positive mode.

RESULTS

The expression level of core1, core2, ST antigen, and core2 complex O-glycans (m/z 733.33, m/z 809.42) were increased significantly (p < 0.0001), whereas m/z 529.75 and diST-antigen were decreased in the serum of GC compared with controls (p < 0.001). In addition, there were significant correlations between the abundance of the O-glycans and glycoproteins (MUC1, CEA) in the serum of GC.

CONCLUSION AND CLINICAL RELEVANCE

Glycomics approaches identified multiple candidate antigens for patients with GC. The O-glycan structures are increased in the serum of GC, they may be candidates for carbohydrate tumor markers.

PD-1- and CTLA-4-based inhibitory chimeric antigen receptors (iCARs) divert off-target immunotherapy responses

T cell therapies have demonstrated long-term efficacy and curative potential for the treatment of some cancers. However, their use is limited by damage to bystander tissues, as seen in graft-versus-host disease after donor lymphocyte infusion, or "on-target, off-tumor" toxicities incurred in some engineered T cell therapies. Nonspecific immunosuppression and irreversible T cell elimination are currently the only means to control such deleterious responses, but at the cost of abrogating therapeutic benefits or causing secondary complications. On the basis of the physiological paradigm of immune inhibitory receptors, we designed antigen-specific inhibitory chimeric antigen receptors (iCARs) to preemptively constrain T cell responses. We demonstrate that CTLA-4- or PD-1-based iCARs can selectively limit cytokine secretion, cytotoxicity, and proliferation induced through the endogenous T cell receptor or an activating chimeric receptor. The initial effect of the iCAR is temporary, thus enabling T cells to function upon a subsequent encounter with the antigen recognized by their activating receptor. iCARs thus provide a dynamic, self-regulating safety switch to prevent, rather than treat, the consequences of inadequate T cell specificity.

Mammalian O-mannosylation pathway: glycan structures, enzymes, and protein substrates

The mammalian O-mannosylation pathway for protein post-translational modification is intricately involved in modulating cell–matrix interactions in the musculature and nervous system. Defects in enzymes of this biosynthetic pathway are causative for multiple forms of congenital muscular dystophy. The application of advanced genetic and biochemical technologies has resulted in remarkable progress in this field over the past few years, culminating with the publication of three landmark papers in 2013 alone. In this review, we will highlight recent progress focusing on the dramatic expansion of the set of genes known to be involved in O-mannosylation and disease processes, the concurrent acceleration of the rate of O-mannosylation pathway protein functional assignments, the tremendous increase in the number of proteins now known to be modified by O-mannosylation, and the recent progress in protein O-mannose glycan quantification and site assignment. Also, we attempt to highlight key outstanding questions raised by this abundance of new information.

Hepatoprotective bioactivity of the glycoprotein, antrodan, isolated from Antrodia cinnamomea mycelia

Antrodan, a protein-bound polysaccharide isolated from Antrodia cinnamomea mycelia, was demonstrated to exhibit significant anti-inflammatory bioactivity in vitro. However, its role in hepatic injury in vivo still remains unclear. We hypothesized that antrodan may have beneficial hepatoprotective effects. To verify this, a lipopolysaccharide (LPS)-Sprague-Dawley rat model was used. Antrodan protected against liver damage by suppressing LPS-stimulated serum glutamine-oxaloacetic transaminase (GOT), glutamic-pyruvic transaminase (GPT), interleukin (IL)-6, hepatic thiobarbituric acid reactive substances (TBARS), nitric oxide (NO), inducible NO synthase (iNOS) and nuclear factor (NF)-κB, and by effectively alleviating the downregulated hepatic superoxide dismutase (SOD), catalase, and glutathione peroxidase (GSH-Px). Hematoxylin-eosin staining revealed that antrodan at a dosage of 40 mg/kg was able to alleviate LPS-induced liver damage to a normal status. In addition, we identified the partial main architectural backbone of antrodan to have a 1 → 3 linear β-glycosidic backbone of mannan linked by β-1 → 3 glucosidic branches. Conclusively, antrodan can potentially ameliorate liver damage in vivo by suppressing oxidative stress induced by LPS.

Sweet and sour: the impact of differential glycosylation in cancer cells undergoing epithelial-mesenchymal transition

Glycosylation changes are a feature of disease states. One clear example is cancer cells, which commonly express glycans at atypical levels or with different structural attributes than those found in normal cells. Epithelial–mesenchymal transition (EMT) was initially recognized as an important step for morphogenesis during embryonic development, and is now shown to be one of the key steps promoting tumor metastasis. Cancer cells undergoing EMT are characterized by significant changes in glycosylation of the extracellular matrix (ECM) components and cell-surface glycoconjugates. Current scientific methodology enables all hallmarks of EMT to be monitored in vitro and this experimental model has been extensively used in oncology research during the last 10 years. Several studies have shown that cell-surface carbohydrates attached to proteins through the amino acids, serine, or threonine (O-glycans), are involved in tumor progression and metastasis, however, the impact of O-glycans on EMT is poorly understood. Recent studies have demonstrated that transforming growth factor-beta (TGF-β), a known EMT inducer, has the ability to promote the up-regulation of a site-specific O-glycosylation in the IIICS domain of human oncofetal fibronectin, a major ECM component expressed by cancer cells and embryonic tissues. Armed with the knowledge that cell-surface glycoconjugates play a major role in the maintenance of cell homeostasis and that EMT is closely associated with glycosylation changes, we may benefit from understanding how unusual glycans can govern the molecular pathways associated with cancer progression. This review initially focuses on some well-known changes found in O-glycans expressed by cancer cells, and then discusses how these alterations may modulate the EMT process.

Aberrant glycosylation as biomarker for cancer: focus on CD43

Glycosylation is a posttranslational modification of proteins playing a major role in cell signalling, immune recognition, and cell-cell interaction because of their glycan branches conferring structure variability and binding specificity to lectin ligands. Aberrant expression of glycan structures as well as occurrence of truncated structures, precursors, or novel structures of glycan may affect ligand-receptor interactions and thus interfere with regulation of cell adhesion, migration, and proliferation. Indeed, aberrant glycosylation represents a hallmark of cancer, reflecting cancer-specific changes in glycan biosynthesis pathways such as the altered expression of glycosyltransferases and glycosidases. Most studies have been carried out to identify changes in serum glycan structures. In most cancers, fucosylation and sialylation are significantly modified. Thus, aberrations in glycan structures can be used as targets to improve existing serum cancer biomarkers. The ability to distinguish differences in the glycosylation of proteins between cancer and control patients emphasizes glycobiology as a promising field for potential biomarker identification. In this review, we discuss the aberrant protein glycosylation associated with human cancer and the identification of protein glycoforms as cancer biomarkers. In particular, we will focus on the aberrant CD43 glycosylation as cancer biomarker and the potential to exploit the UN1 monoclonal antibody (UN1 mAb) to identify aberrant CD43 glycoforms.

Dissecting the molecular basis of the role of the O-mannosylation pathway in disease: α-dystroglycan and forms of muscular dystrophy

Dystroglycanopathies form a subgroup of muscular dystrophies that arise from defects in enzymes that are implicated in the recently elucidated O-mannosylation pathway, thereby resulting in underglycosylation of α-dystroglycan. The emerging identification of additional brain proteins modified by O-mannosylation provides a broader context for interpreting the range of neurological consequences associated with dystroglycanopathies. This form of glycosylation is associated with protein mucin-like domains that present numerous serine and threonine residues as possible sites for modification. Furthermore, the O-Man glycans coexist in this region with O-GalNAc glycans (conventionally associated with such protein sequences), thus resulting in a complex glycoconjugate landscape. Sorting out the relationships between the various molecular defects in glycosylation and the modes of disease presentation, as well as the regulatory interplay among the O-Man glycans and the effects on other modes of glycosylation in the same domain, is challenging. Here we provide a perspective on chemical biology approaches employing synthetic and analytical methods to address these questions.

Mucins in pancreatic cancer and its microenvironment

Pancreatic cancer remains a lethal malignancy with poor prognosis owing to therapeutic resistance, frequent recurrence and the absence of treatment strategies that specifically target the tumour and its supporting stroma. Deregulated cell-surface proteins drive neoplastic transformations and are envisioned to mediate crosstalk between the tumour and its microenvironment. Emerging studies have elaborated on the role of mucins in diverse biological functions, including enhanced tumorigenicity, invasiveness, metastasis and drug resistance through their characteristic O-linked and N-linked oligosaccharides (glycans), extended structures and unique domains. Multiple mucin domains differentially interact and regulate different components of the tumour microenvironment. This Review discusses: the expression pattern of various mucins in the pancreas under healthy, inflammatory, and cancerous conditions; the context-dependent attributes of mucins that differ under healthy and pathological conditions; the contribution of the tumour microenvironment in pancreatic cancer development and/or progression; diagnostic and/or prognostic efficacy of mucins; and mucin-based therapeutic strategies. Overall, this information should help to delineate the intricacies of pancreatic cancer by exploring the family of mucins, which, through various mechanisms in both tumour cells and the microenvironment, worsen disease outcome.

Exploring the glycosylation of serum CA125

Ovarian cancer is the most lethal gynaecologic cancer affecting women. The most widely used biomarker for ovarian cancer, CA125, lacks sensitivity and specificity. Here, we explored differences in glycosylation of CA125 between serum from patients with ovarian cancer and healthy controls. We found differences between CA125 N-glycans from patient sera compared to controls. These include increases in core-fucosylated bi-antennary monosialylated glycans, as well as decreases in mostly bisecting bi-antennary and non-fucosylated glycans in patients compared to controls. Measurement of the glycosylated state of CA125 may therefore provide a more specific biomarker for patients with ovarian cancer.

Monoclonal antibodies toward different Tn-amino acid backbones display distinct recognition patterns on human cancer cells. Implications for effective immuno-targeting of cancer

The Tn antigen (GalNAcα-O-Ser/Thr) is a well-established tumor-associated marker which represents a good target for the design of anti-tumor vaccines. Several studies have established that the binding of some anti-Tn antibodies could be affected by the density of Tn determinant or/and by the amino acid residues neighboring O-glycosylation sites. In the present study, using synthetic Tn-based vaccines, we have generated a panel of anti-Tn monoclonal antibodies. Analysis of their binding to various synthetic glycopeptides, modifying the amino acid carrier of the GalNAc(*) (Ser* vs Thr*), showed subtle differences in their fine specificities. We found that the recognition of these glycopeptides by some of these MAbs was strongly affected by the Tn backbone, such as a S*S*S* specific MAb (15G9) which failed to recognize a S*T*T* or a T*T*T* structure. Different binding patterns of these antibodies were also observed in FACS and Western blot analysis using three human cancer cell lines (MCF-7, LS174T and Jurkat). Importantly, an immunohistochemical analysis of human tumors (72 breast cancer and 44 colon cancer) showed the existence of different recognition profiles among the five antibodies evaluated, demonstrating that the aglyconic part of the Tn structure (Ser vs Thr) plays a key role in the anti-Tn specificity for breast and colon cancer detection. This new structural feature of the Tn antigen could be of important clinical value, notably due to the increasing interest of this antigen in anticancer vaccine design as well as for the development of anti-Tn antibodies for in vivo diagnostic and therapeutic strategies.

Tumor defense systems using O-glycans

During the process of hematogenous tumor metastasis, tumor cells that dissociated from the primary site enter the blood vessels and are exposed to innate immune systems in host blood circulation. In the innate immune systems, natural killer (NK) cells play a major role in rejecting tumors and suppressing metastasis. To establish metastasis, tumor cells therefore need to defend themselves against tumor rejection by NK cells. It has been recently discovered that some tumor cells develop defense systems against NK cell attack using certain types of cell-surface carbohydrates. The types of carbohydrates attached to cell-surface glycoproteins through serine or threonine residues contain a branch consisting of β-1,6-linkage of N-acetylglucosamine and N-acetylgalactosamine and are designated as core2 O-glycans. Tumor cells expressing core2 O-glycans evade NK cell-mediated tumor rejection, thereby surviving longer in host circulation and acquiring high-metastatic phenotypes. This review explains two types of tumor defense systems against NK cell immunity using core2 O-glycans.

A lectin-based glycomic approach to identify characteristic features of Xenopus embryogenesis

Cell surface glycans show dynamic changes during cell differentiation. Several glycans are useful biomarkers of tumors, stem cells, and embryogenesis. Glycomic studies have been performed using liquid chromatography and mass spectrometry, which are powerful tools for glycan structural analysis but are difficult to use for small sample sizes. Recently, a lectin microarray system was developed for profiling cell surface glycome changes to terminal carbohydrate chains and branch types, using sample sizes of a few micrograms. In this study, we used the lectin microarray system for the first time to investigate stage-specific glycomes in Xenopus laevis embryos. Unsupervised cluster analysis of lectin microarray data indicated that glycan profiles changed sequentially during development. Nine lectin probes showed significantly different signals between early and the late-stage embryos: 4 showed higher signals in the early stages, and 5 exhibited higher signals in the late stages. The gene expression profiles of relevant glycosyltransferase genes support the lectin microarray data. Therefore, we have shown that lectin microarray is an effective tool for high-throughput glycan analysis in Xenopus embryogenesis, allowing glycan profiling of early embryos and small biopsy specimens.

Context-dependent multifunctionality of galectin-1: a challenge for defining the lectin as therapeutic target

INTRODUCTION

One route of translating the information encoded in the glycan chains of cellular glycoconjugates into physiological effects is via receptor (lectin) binding. A family of endogenous lectins, sharing folding, a distinct sequence signature and affinity for β-galactosides (thus termed galectins), does so effectively in a context-dependent manner.

AREAS COVERED

An overview is given on the multifunctional nature of galectins, with emphasis on galectin-1. The broad range of functions includes vital processes such as adhesion via glycan bridging, glycoconjugate transport or triggering signaling relevant, for example, for growth regulation. Besides distinct glycoconjugates, this lectin can also interact with certain proteins so that it can target counterreceptors at all sites of location, that is, in the cytoplasm and/or nucleus, at both sides of the membrane or extracellularly. Approaches to strategically exploit galectin activities with therapeutic intentions are outlined.

EXPERT OPINION

The wide versatility of sugar coding and the multifunctionality of galectin-1 explain why considering to turn the protein into a therapeutic target is an ambitious aim. Natural pathways shaped by physiologic master regulators (e.g., the tumor suppressor p16(INK4a)) are suggested to teach inspiring lessons as to how the lectin might be recruited to clinical service.

Core2 O-glycan-expressing prostate cancer cells are resistant to NK cell immunity

Core2 β-1,6-N-acetylglucosaminyltransferase (C2GnT) forms an N-acetylglucosamine branch in the O-glycans (core2 O-glycans) of cell surface glycoproteins. We previously revealed that the expression of C2GnT is positively correlated with poor prognosis in prostate cancer patients. However, the detailed mechanisms underlying their poor prognosis remain unclear. In the current study, we report that the core2 O-glycans carried by the surface MUC1 glycoproteins of prostate cancer cells play an important role in the evasion of NK cell immunity. In C2GnT-expressing prostate cancer cells, the MUC1 core2 O-glycans are modified with poly-N-acetyllactosamine. MUC1 glycoproteins carrying poly-N-acetyllactosamine attenuated the interaction of the cancer cells with NK cells, resulting in decreased secretion of granzyme B by the NK cells. Poly-N-acetyllactosamine also interfered with the ability of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) to access the cancer cell surface. These effects of poly-N-acetyllactosamine on NK cells render C2GnT-expressing prostate cancer cells resistant to NK cell cytotoxicity. By contrast, C2GnT-deficient prostate cancer cells carrying a lower amount of poly-N-acetyllactosamine than the C2GnT-expressing prostate cancer cells were significantly more susceptible to NK cell cytotoxicity. Our results strongly suggest that C2GnT-expressing prostate cancer cells evade NK cell immunity and survive longer in the host blood circulation, thereby resulting in the promotion of prostate cancer metastasis.