Expression of core 2 beta1,6-N-acetylglucosaminyltransferase facilitates prostate cancer progression

Cancer snap-shots: Biochemistry and glycopathology of O-glycans: A review

Cancer pathogenesis is strongly linked to the qualitative and quantitative alteration of the cell surface glycans, that are glycosidically linked to proteins and lipids. Glycans that are covalently linked to the polypeptide backbone of a protein through nitrogen or oxygen, are known as N-glycans or O-glycans, respectively. Although the role of glycans in the expression, physiology, and communication of cells is well documented, the function of these glycans in tumor biology is not fully elucidated. In this context, current review summarizes biosynthesis, modifications and pathological implications of O-glycans The review also highlights illustrative examples of cancer types modulated by aberrant O-glycosylation. Related O-glycans like Thomsen-nouveau (Tn), Thomsen-Friedenreich (TF), Lewisa/x, Lewisb/y, sialyl Lewisa/x and some other O-glycans are discussed in detail. Since, the overexpression of O-glycans are attributed to the aggressiveness and metastatic behavior of cancer cells, the current review attempts to understand the relation between metastasis and O-glycans.

The role of GCNT1 mediated O-glycosylation in aggressive prostate cancer

Prostate cancer is the most common cancer in men and a major cause of cancer related deaths worldwide. Nearly all affected men develop resistance to current therapies and there is an urgent need to develop new treatments for advanced disease. Aberrant glycosylation is a common feature of cancer cells implicated in all of the hallmarks of cancer. A major driver of aberrant glycosylation in cancer is the altered expression of glycosylation enzymes. Here, we show that GCNT1, an enzyme that plays an essential role in the formation of core 2 branched O-glycans and is crucial to the final definition of O-glycan structure, is upregulated in aggressive prostate cancer. Using in vitro and in vivo models, we show GCNT1 promotes the growth of prostate tumours and can modify the glycome of prostate cancer cells, including upregulation of core 2 O-glycans and modifying the O-glycosylation of secreted glycoproteins. Furthermore, using RNA sequencing, we find upregulation of GCNT1 in prostate cancer cells can alter oncogenic gene expression pathways important in tumour growth and metastasis. Our study highlights the important role of aberrant O-glycosylation in prostate cancer progression and provides novel insights regarding the mechanisms involved.

Glycosylation in Renal Cell Carcinoma: Mechanisms and Clinical Implications

Renal cell carcinoma (RCC) is one of the most prevalent malignant tumors of the urinary system, accounting for around 2% of all cancer diagnoses and deaths worldwide. Clear cell RCC (ccRCC) is the most prevalent and aggressive histology with an unfavorable prognosis and inadequate treatment. Patients' progression-free survival is considerably improved by surgery; however, 30% of patients develop metastases following surgery. Identifying novel targets and molecular markers for RCC prognostic detection is crucial for more accurate clinical diagnosis and therapy. Glycosylation is a critical post-translational modification (PMT) for cancer cell growth, migration, and invasion, involving the transfer of glycosyl moieties to specific amino acid residues in proteins to form glycosidic bonds through the activity of glycosyltransferases. Most cancers, including RCC, undergo glycosylation changes such as branching, sialylation, and fucosylation. In this review, we discuss the latest findings on the significance of aberrant glycans in the initiation, development, and progression of RCC. The potential biomarkers of altered glycans for the diagnosis and their implications in RCC have been further highlighted.

Association between the expression of core 3 synthase and survival outcomes of patients with cholangiocarcinoma

Cholangiocarcinoma (CCA) is a highly aggressive and metastatic type of malignant carcinoma that is associated with high mortality rates and is difficult to detect at early stages. Core 3 structure is a mucin-type O-glycans synthesized by β1,3-N-acetylglucosaminyltransferase 6 (core 3 synthase), which plays an important role in the digestive system, in particular gastrointestinal goblet cells. It has been reported that core 3 synthase-expressing cells show lower migratory and invasive rates, and lower metastatic activity. A immunohistochemical study also showed that this enzyme was expressed in normal epithelial cells of the colon, but completely disappeared in colorectal cancer cells. The present study aimed to identify biomarkers that could be used to predict the prognosis of patients with CCA. Pathological specimens of 185 CCA tissues were immunohistochemically stained with two antibodies, G8-144 and MECA-79, which recognize core 3 synthase and 6-sulfated N-acetyllactosamine on the extended core-1 O-glycans, respectively. The association between G8-144 or MECA-79 positivity and patient prognosis was statistically analyzed. Positive expression of G8-144 was associated with improved prognosis in patients with distal CCA (dCCA). Patients with dCCA positive for G8-144 showed lower mortality rates than those with negative expression. However, the positive expression of MECA-79 was associated with CCA progression and metastasis, indicating that it is a poor prognostic marker for CCA. In conclusion, as both antibodies resulted in mirror-image staining, the involvement of G8-144 and MECA-79 in O-glycan synthesis could be considered as potential favorable and unfavorable biomarkers, respectively, for CCA prognosis.

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.

Narrative review of urinary glycan biomarkers in prostate cancer

Prostate cancer (PC) is the second most common cancer in men worldwide. The application of the prostate-specific antigen (PSA) test has improved the diagnosis and treatment of PC. However, the PSA test has become associated with overdiagnosis and overtreatment. Therefore, there is an unmet need for novel diagnostic, prognostic, and predictive biomarkers of PC. Urinary glycoproteins and exosomes are a potential source of PC glycan biomarkers. Urinary glycan profiling can provide noninvasive monitoring of tumor heterogeneity and aggressiveness throughout a treatment course. However, urinary glycan profiling is not popular due to technical disadvantages, such as complicated structural analysis that requires specialized expertise. The technological development of glycan analysis is a rapidly advancing field. A lectin-based microarray can detect aberrant glycoproteins in urine, including PSA glycoforms and exosomes. Glycan enrichment beads can enrich the concentration of N-linked glycans specifically. Capillary electrophoresis, liquid chromatography-tandem mass spectrometry, and matrix-assisted laser desorption/ionization-time of flight mass spectrometry can detect glycans directory. Many studies suggest potential of urinary glycoproteins, exosomes, and glycosyltransferases as a biomarker of PC. Although further technological challenges remain, urinary glycan analysis is one of the promising approaches for cancer biomarker discovery.

Post-Translational Modifications That Drive Prostate Cancer Progression

While a protein primary structure is determined by genetic code, its specific functional form is mostly achieved in a dynamic interplay that includes actions of many enzymes involved in post-translational modifications. This versatile repertoire is widely used by cells to direct their response to external stimuli, regulate transcription and protein localization and to keep proteostasis. Herein, post-translational modifications with evident potency to drive prostate cancer are explored. A comprehensive list of proteome-wide and single protein post-translational modifications and their involvement in phenotypic outcomes is presented. Specifically, the data on phosphorylation, glycosylation, ubiquitination, SUMOylation, acetylation, and lipidation in prostate cancer and the enzymes involved are collected. This type of knowledge is especially valuable in cases when cancer cells do not differ in the expression or mutational status of a protein, but its differential activity is regulated on the level of post-translational modifications. Since their driving roles in prostate cancer, post-translational modifications are widely studied in attempts to advance prostate cancer treatment. Current strategies that exploit the potential of post-translational modifications in prostate cancer therapy are presented.

The Complexity and Dynamics of the Tissue Glycoproteome Associated With Prostate Cancer Progression

The complexity and dynamics of the immensely heterogeneous glycoproteome of the prostate cancer (PCa) tumor microenvironment remain incompletely mapped, a knowledge gap that impedes our molecular-level understanding of the disease. To this end, we have used sensitive glycomics and glycoproteomics to map the protein-, cell-, and tumor grade-specific N- and O-glycosylation in surgically removed PCa tissues spanning five histological grades (n = 10/grade) and tissues from patients with benign prostatic hyperplasia (n = 5). Quantitative glycomics revealed PCa grade-specific alterations of the oligomannosidic-, paucimannosidic-, and branched sialylated complex-type N-glycans, and dynamic remodeling of the sialylated core 1- and core 2-type O-glycome. Deep quantitative glycoproteomics identified ∼7400 unique N-glycopeptides from 500 N-glycoproteins and ∼500 unique O-glycopeptides from nearly 200 O-glycoproteins. With reference to a recent Tissue and Blood Atlas, our data indicate that paucimannosidic glycans of the PCa tissues arise mainly from immune cell-derived glycoproteins. Furthermore, the grade-specific PCa glycosylation arises primarily from dynamics in the cellular makeup of the PCa tumor microenvironment across grades involving increased oligomannosylation of prostate-derived glycoproteins and decreased bisecting GlcNAcylation of N-glycans carried by the extracellular matrix proteins. Furthermore, elevated expression of several oligosaccharyltransferase subunits and enhanced N-glycoprotein site occupancy were observed associated with PCa progression. Finally, correlations between the protein-specific glycosylation and PCa progression were observed including increased site-specific core 2-type O-glycosylation of collagen VI. In conclusion, integrated glycomics and glycoproteomics have enabled new insight into the complexity and dynamics of the tissue glycoproteome associated with PCa progression generating an important resource to explore the underpinning disease mechanisms.

Mucin-Type O-GalNAc Glycosylation in Health and Disease

Mucin-type GalNAc O-glycosylation is one of the most abundant and unique post-translational modifications. The combination of proteome-wide mapping of GalNAc O-glycosylation sites and genetic studies with knockout animals and genome-wide analyses in humans have been instrumental in our understanding of GalNAc O-glycosylation. Combined, such studies have revealed well-defined functions of O-glycans at single sites in proteins, including the regulation of pro-protein processing and proteolytic cleavage, as well as modulation of receptor functions and ligand binding. In addition to isolated O-glycans, multiple clustered O-glycans have an important function in mammalian biology by providing structural support and stability of mucins essential for protecting our inner epithelial surfaces, especially in the airways and gastrointestinal tract. Here the many O-glycans also provide binding sites for both endogenous and pathogen-derived carbohydrate-binding proteins regulating critical developmental programs and helping maintain epithelial homeostasis with commensal organisms. Finally, O-glycan changes have been identified in several diseases, most notably in cancer and inflammation, where the disease-specific changes can be used for glycan-targeted therapies. This chapter will review the biosynthesis, the biology, and the translational perspectives of GalNAc O-glycans.

Investigation of gene-gene interactions in cardiac traits and serum fatty acid levels in the LURIC Health Study

Epistasis analysis elucidates the effects of gene-gene interactions (G×G) between multiple loci for complex traits. However, the large computational demands and the high multiple testing burden impede their discoveries. Here, we illustrate the utilization of two methods, main effect filtering based on individual GWAS results and biological knowledge-based modeling through Biofilter software, to reduce the number of interactions tested among single nucleotide polymorphisms (SNPs) for 15 cardiac-related traits and 14 fatty acids. We performed interaction analyses using the two filtering methods, adjusting for age, sex, body mass index (BMI), waist-hip ratio, and the first three principal components from genetic data, among 2,824 samples from the Ludwigshafen Risk and Cardiovascular (LURIC) Health Study. Using Biofilter, one interaction nearly met Bonferroni significance: an interaction between rs7735781 in XRCC4 and rs10804247 in XRCC5 was identified for venous thrombosis with a Bonferroni-adjusted likelihood ratio test (LRT) p: 0.0627. A total of 57 interactions were identified from main effect filtering for the cardiac traits G×G (10) and fatty acids G×G (47) at Bonferroni-adjusted LRT p < 0.05. For cardiac traits, the top interaction involved SNPs rs1383819 in SNTG1 and rs1493939 (138kb from 5’ of SAMD12) with Bonferroni-adjusted LRT p: 0.0228 which was significantly associated with history of arterial hypertension. For fatty acids, the top interaction between rs4839193 in KCND3 and rs10829717 in LOC107984002 with Bonferroni-adjusted LRT p: 2.28×10⁻⁵ was associated with 9-trans 12-trans octadecanoic acid, an omega-6 trans fatty acid. The model inflation factor for the interactions under different filtering methods was evaluated from the standard median and the linear regression approach. Here, we applied filtering approaches to identify numerous genetic interactions related to cardiac-related outcomes as potential targets for therapy. The approaches described offer ways to detect epistasis in the complex traits and to improve precision medicine capability.

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.

The expression and functional analysis of the sialyl-T antigen in prostate cancer

Aberrant glycosylation is a featured characteristic of cancer and plays a role in cancer pathology; thus an understanding of the compositions and functions of glycans is critical for discovering diagnostic biomarkers and therapeutic targets for cancer. In this study, we used MALDI-TOF-MS analysis to determine the O-glycan profiles of prostate cancer cells metastasized to bone (PC-3), brain (DU145), lymph node (LNCaP), and vertebra (VCaP) in comparison to immortalized RWPE-1 cells derived from normal prostatic tissue. Prostate cancer (CaP) cells exhibited an elevation of simple/short O-glycans, with a reduction of complex O-glycans, increased O-glycan sialylation and decreased fucosylation. Core 1 sialylation was increased dramatically in all CaP cells, and especially in PC-3 cells. The expression of Neu5Acα2-3Galβ1-3GalNAc- (sialyl-3T antigen) which is the product of α2,3-sialyltransferase-I (ST3Gal-I) was substantially increased. We therefore focused on exploring the possible function of ST3Gal-I in PC-3 cells. ST3Gal-I silencing studies showed that ST3Gal-I was associated with PC-3 cell proliferation, migration and apoptosis. Further in vivo studies demonstrated that down regulation of ST3Gal-I reduced the tumor size in xenograft mouse model, indicating that sialyl-3T can serve as a biomarker for metastatic prostate cancer prognosis, and that ST3Gal-I could be a target for therapeutic intervention in cancer treatment.

Glycans as Biomarkers in Prostate Cancer

Prostate cancer is the most commonly diagnosed malignancy in men, claiming over350,000 lives worldwide annually. Current diagnosis relies on prostate-specific antigen (PSA)testing, but this misses some aggressive tumours, and leads to the overtreatment of non-harmfuldisease. Hence, there is an urgent unmet clinical need to identify new diagnostic and prognosticbiomarkers. As prostate cancer is a heterogeneous and multifocal disease, it is likely that multiplebiomarkers will be needed to guide clinical decisions. Fluid-based biomarkers would be ideal, andattention is now turning to minimally invasive liquid biopsies, which enable the analysis oftumour components in patient blood or urine. Effective diagnostics using liquid biopsies willrequire a multifaceted approach, and a recent high-profile review discussed combining multipleanalytes, including changes to the tumour transcriptome, epigenome, proteome, and metabolome.However, the concentration on genomics-based paramaters for analysing liquid biopsies ispotentially missing a goldmine. Glycans have shown huge promise as disease biomarkers, anddata suggests that integrating biomarkers across multi-omic platforms (including changes to theglycome) can improve the stratification of patients with prostate cancer. A wide range ofalterations to glycans have been observed in prostate cancer, including changes to PSAglycosylation, increased sialylation and core fucosylation, increased O-GlcNacylation, theemergence of cryptic and branched N-glyans, and changes to galectins and proteoglycans. In thisreview, we discuss the huge potential to exploit glycans as diagnostic and prognostic biomarkersfor prostate cancer, and argue that the inclusion of glycans in a multi-analyte liquid biopsy test forprostate cancer will help maximise clinical utility.

Glycosylation is a global target for androgen control in prostate cancer cells

Changes in glycan composition are common in cancer and can play important roles in all of the recognised hallmarks of cancer. We recently identified glycosylation as a global target for androgen control in prostate cancer cells and further defined a set of 8 glycosylation enzymes (GALNT7, ST6GalNAc1, GCNT1, UAP1, PGM3, CSGALNACT1, ST6GAL1 and EDEM3), which are also significantly upregulated in prostate cancer tissue. These 8 enzymes are under direct control of the androgen receptor (AR) and are linked to the synthesis of important cancer-associated glycans such as sialyl-Tn (sTn), sialyl LewisX (SLeX), O-GlcNAc and chondroitin sulfate. Glycosylation has a key role in many important biological processes in cancer including cell adhesion, migration, interactions with the cell matrix, immune surveillance, cell signalling and cellular metabolism. Our results suggest that alterations in patterns of glycosylation via androgen control might modify some or all of these processes in prostate cancer. The prostate is an abundant secretor of glycoproteins of all types, and alterations in glycans are, therefore, attractive as potential biomarkers and therapeutic targets. Emerging data on these often overlooked glycan modifications have the potential to improve risk stratification and therapeutic strategies in patients with prostate cancer.

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.

Glycosylation is an Androgen-Regulated Process Essential for Prostate Cancer Cell Viability

Steroid androgen hormones play a key role in the progression and treatment of prostate cancer, with androgen deprivation therapy being the first-line treatment used to control cancer growth. Here we apply a novel search strategy to identify androgen-regulated cellular pathways that may be clinically important in prostate cancer. Using RNASeq data, we searched for genes that showed reciprocal changes in expression in response to acute androgen stimulation in culture, and androgen deprivation in patients with prostate cancer. Amongst 700 genes displaying reciprocal expression patterns we observed a significant enrichment in the cellular process glycosylation. Of 31 reciprocally-regulated glycosylation enzymes, a set of 8 (GALNT7, ST6GalNAc1, GCNT1, UAP1, PGM3, CSGALNACT1, ST6GAL1 and EDEM3) were significantly up-regulated in clinical prostate carcinoma. Androgen exposure stimulated synthesis of glycan structures downstream of this core set of regulated enzymes including sialyl-Tn (sTn), sialyl Lewis(X) (SLe(X)), O-GlcNAc and chondroitin sulphate, suggesting androgen regulation of the core set of enzymes controls key steps in glycan synthesis. Expression of each of these enzymes also contributed to prostate cancer cell viability. This study identifies glycosylation as a global target for androgen control, and suggests loss of specific glycosylation enzymes might contribute to tumour regression following androgen depletion therapy.

The role of glycans in the development and progression of prostate cancer

Prostate cancer is a unique and heterogeneous disease. Currently, a major unmet clinical need exists to develop biomarkers that enable indolent disease to be distinguished from aggressive disease. The prostate is an abundant secretor of glycoproteins of all types, and alterations in glycans are, therefore, attractive as potential biomarkers and therapeutic targets. Despite progress over the past decade in profiling the genome and proteome, the prostate cancer glycoproteome remains relatively understudied. A wide range of alterations in the glycoproteins on prostate cancer cells can occur, including increased sialylation and fucosylation, increased O-β-N-acetylglucosamine (GlcNAc) conjugation, the emergence of cryptic and high-mannose N-glycans and alterations to proteoglycans. Glycosylation can alter protein function and has a key role in many important biological processes in cancer including cell adhesion, migration, interactions with the cell matrix, immune surveillance, cell signalling and cellular metabolism; altered glycosylation in prostate cancer might modify some, or all of these processes. In the past three years, powerful tools such as glycosylation-specific antibodies and glycosylation gene signatures have been developed, which enable detailed analyses of changes in glycosylation. Thus, emerging data on these often overlooked modifications have the potential to improve risk stratification and therapeutic strategies in patients with prostate cancer.

Short O-GalNAc glycans: regulation and role in tumor development and clinical perspectives

BACKGROUND

While the underlying causes of cancer are genetic modifications, changes in cellular states mediate cancer development. Tumor cells display markedly changed glycosylation states, of which the O-GalNAc glycans called the Tn and TF antigens are particularly common. How these antigens get over-expressed is not clear. The expression levels of glycosylation enzymes fail to explain it.

SCOPE OF REVIEW

We describe the regulation of O-GalNAc glycosylation initiation and extension with emphasis on the initiating enzymes ppGalNAcTs (GALNTs), and introduce the GALA pathway--a change in GALNTs compartmentation within the secretory pathway that regulates Tn levels. We discuss the roles of O-GalNAc glycans and GALNTs in tumorigenic processes and finally consider diagnostic and therapeutic perspectives.

MAJOR CONCLUSIONS

Contrary to a common hypothesis, short O-glycans in tumors are not the result of an incomplete glycosylation process but rather reveal the activation of regulatory pathways. Surprisingly, high Tn levels reveal a major shift in the O-glycoproteome rather than a shortening of O-glycans. These changes are driven by membrane trafficking events.

GENERAL SIGNIFICANCE

Many attempts to use O-glycans for biomarker, antibody and therapeutic vaccine development have been made, but suffer limitations including poor sensitivity and/or specificity that may in part derive from lack of a mechanistic understanding. Deciphering how short O-GalNAc glycans are regulated would open new perspectives to exploit this biology for therapeutic usage. This article is part of a Special Issue entitled "Glycans in personalised medicine" Guest Editor: Professor Gordan Lauc.

I-branching N-acetylglucosaminyltransferase regulates prostate cancer invasiveness by enhancing α5β1 integrin signaling

Cell surface carbohydrates are important for cell migration and invasion of prostate cancer (PCa). Accordingly, the I‐branching N‐acetylglucosaminyltransferase (GCNT2) converts linear i‐antigen to I‐branching glycan, and its expression is associated with breast cancer progression. In the present study, we identified relationships between GCNT2 expression and clinicopathological parameters in patients with PCa. Paraffin‐embedded PCa specimens were immunohistochemically tested for GCNT2 expression, and the roles of GCNT2 in PCa progression were investigated using cell lines with high GCNT2 expression and low GCNT2 expression. GCNT2‐positive cells were significantly lesser in organ‐confined disease than in that with extra‐capsular extensions, and GCNT2‐negative tumors were associated with significantly better prostate‐specific antigen‐free survival compared with GCNT2‐positive tumors. Subsequent functional studies revealed that knockdown of GCNT2 expression in PCa cell lines significantly inhibited cell migration and invasion. GCNT2 regulated the expression of cell surface I‐antigen on the O‐glycan and glycolipid. Moreover, I‐antigen‐bearing glycolipids were subject to α5β1 integrin–fibronectin mediated protein kinase B phosphorylation. In conclusion, GCNT2 expression is closely associated with invasive potential of PCa.

Core 2 β-1, 6-N-acetylglucosaminyltransferase-1 expression in prostate biopsy specimen is an indicator of prostate cancer aggressiveness

INTRODUCTION

To avoid over-treatment of early stage prostate cancer (PCa), predictive biomarkers for PCa aggressiveness which can be obtained during pre-treatment evaluation are essential. Core 2 β-1, 6-N-acetylglucosaminyl-transferase-1 (GCNT1) is a key enzyme that forms core 2 branched O-glycans, the expression of which is associated with aggressive potential of prostate cancer. We examined whether GCNT1 expression in prostate biopsy specimen can predict cancer recurrence after radical prostatectomy for the patients with with PCa. We then investigated molecular background for aggressive malignant potential mediated by GCNT1 expression.

METHODS

Paraffin-embedded PCa biopsy specimens were immunohisto-chemically tested for GCNT1 expression using an anti-GCNT1 monoclonal antibody. We also examined the role of GCNT1 in PCa progression using cell lines which express high or low levels of GCNT1.

RESULTS

GCNT1 expression correlated with D' Amico's recurrence risk classification. The GCNT1-positive rate in organ confined PCa was significantly lower than that in PCa with extra-prostatic extension. GCNT1-negative tumors were associated with significantly better prostate-specific antigen (PSA)-free survival compared with GCNT1-positive tumors. Multivariate analysis revealed that GCNT1 expression status was an independent risk factor for PSA recurrence after radical prostatectomy. Subsequent basic study revealed that GCNT1-over-expressing cells produced a significantly larger amount of growth factors when co-cultured with prostate stromal cells compared with GCNT1-knocked down cells and formed larger tumors.

CONCLUSIONS

GCNT1 expression in prostate biopsy specimen is a significant and independent predictor of recurrence after radical prostatectomy, which can be used in pre-treatment decision making for the patient. Further validation study is necessary to establish clinical implication of GCNT1 in management of PCa.

The androgen receptor controls expression of the cancer-associated sTn antigen and cell adhesion through induction of ST6GalNAc1 in prostate cancer

Patterns of glycosylation are important in cancer, but the molecular mechanisms that drive changes are often poorly understood. The androgen receptor drives prostate cancer (PCa) development and progression to lethal metastatic castration-resistant disease. Here we used RNA-Seq coupled with bioinformatic analyses of androgen-receptor (AR) binding sites and clinical PCa expression array data to identify ST6GalNAc1 as a direct and rapidly activated target gene of the AR in PCa cells. ST6GalNAc1 encodes a sialytransferase that catalyses formation of the cancer-associated sialyl-Tn antigen (sTn), which we find is also induced by androgen exposure. Androgens induce expression of a novel splice variant of the ST6GalNAc1 protein in PCa cells. This splice variant encodes a shorter protein isoform that is still fully functional as a sialyltransferase and able to induce expression of the sTn-antigen. Surprisingly, given its high expression in tumours, stable expression of ST6GalNAc1 in PCa cells reduced formation of stable tumours in mice, reduced cell adhesion and induced a switch towards a more mesenchymal-like cell phenotype in vitro. ST6GalNAc1 has a dynamic expression pattern in clinical datasets, beingsignificantly up-regulated in primary prostate carcinoma but relatively down-regulated in established metastatic tissue. ST6GalNAc1 is frequently upregulated concurrently with another important glycosylation enzyme GCNT1 previously associated with prostate cancer progression and implicated in Sialyl Lewis X antigen synthesis. Together our data establishes an androgen-dependent mechanism for sTn antigen expression in PCa, and are consistent with a general role for the androgen receptor in driving important coordinate changes to the glycoproteome during PCa progression.

Detection of Core2 β-1,6-N-Acetylglucosaminyltransferase in Post-Digital Rectal Examination Urine Is a Reliable Indicator for Extracapsular Extension of Prostate Cancer

To identify appropriate candidates for aggressive treatment such as radical prostatectomy or radiation therapy of localized prostate cancer (PCa), novel predictive biomarkers of PCa aggressiveness are essential. Core2 β-1,6-N-acetylglucosaminyltransferase-1 (GCNT1) is a key enzyme that forms core 2-branched O-glycans. Its expression is associated with the progression of several cancers. We established a mouse IgG monoclonal antibody (mAb) against GCNT1 and examined the relationship of GCNT1 expression to the clinicopathological status of PCa. Paraffin-embedded PCa specimens were analyzed by immunohistochemistry for GCNT1 expression using a newly established mouse anti-GCNT1 mAb by ourselves. GCNT1-positive tumor showed significantly higher Gleason score and larger tumor volume. The number of GCNT1-positive cases was significantly lower in cases of organ-confined disease than in cases of extracapsular extension. GCNT1-negative tumors were associated with significantly better prostate-specific antigen (PSA)-free survival compared with GCNT1-positive tumors. Multivariate analysis revealed that detection of GCNT1 expression was an independent risk factor for PSA recurrence. We established new methods for GCNT1 detection from PCa specimens. Immunoblotting was used to examine post-digital rectal examination (DRE) urine from PCa patients. Over 90% of GCNT1-positive PCa patients with high concentrations of PSA showed extracapsular extension. In conclusion, GCNT1 expression closely associates with the aggressive potential of PCa. Further research aims to develop GCNT1 detection in post-DRE urine as a marker for PCa aggressiveness.

Biosynthetic Machinery Involved in Aberrant Glycosylation: Promising Targets for Developing of Drugs Against Cancer

Cancer cells depend on altered metabolism and nutrient uptake to generate and keep the malignant phenotype. The hexosamine biosynthetic pathway is a branch of glucose metabolism that produces UDP-GlcNAc and its derivatives, UDP-GalNAc and CMP-Neu5Ac and donor substrates used in the production of glycoproteins and glycolipids. Growing evidence demonstrates that alteration of the pool of activated substrates might lead to different glycosylation and cell signaling. It is already well established that aberrant glycosylation can modulate tumor growth and malignant transformation in different cancer types. Therefore, biosynthetic machinery involved in the assembly of aberrant glycans are becoming prominent targets for anti-tumor drugs. This review describes three classes of glycosylation, O-GlcNAcylation, N-linked, and mucin type O-linked glycosylation, involved in tumor progression, their biosynthesis and highlights the available inhibitors as potential anti-tumor drugs.

Meta-analysis of prostate cancer gene expression data identifies a novel discriminatory signature enriched for glycosylating enzymes

BACKGROUND

Tumorigenesis is characterised by changes in transcriptional control. Extensive transcript expression data have been acquired over the last decade and used to classify prostate cancers. Prostate cancer is, however, a heterogeneous multifocal cancer and this poses challenges in identifying robust transcript biomarkers.

METHODS

In this study, we have undertaken a meta-analysis of publicly available transcriptomic data spanning datasets and technologies from the last decade and encompassing laser capture microdissected and macrodissected sample sets.

RESULTS

We identified a 33 gene signature that can discriminate between benign tissue controls and localised prostate cancers irrespective of detection platform or dissection status. These genes were significantly overexpressed in localised prostate cancer versus benign tissue in at least three datasets within the Oncomine Compendium of Expression Array Data. In addition, they were also overexpressed in a recent exon-array dataset as well a prostate cancer RNA-seq dataset generated as part of the The Cancer Genomics Atlas (TCGA) initiative. Biologically, glycosylation was the single enriched process associated with this 33 gene signature, encompassing four glycosylating enzymes. We went on to evaluate the performance of this signature against three individual markers of prostate cancer, v-ets avian erythroblastosis virus E26 oncogene homolog (ERG) expression, prostate specific antigen (PSA) expression and androgen receptor (AR) expression in an additional independent dataset. Our signature had greater discriminatory power than these markers both for localised cancer and metastatic disease relative to benign tissue, or in the case of metastasis, also localised prostate cancer.

CONCLUSION

In conclusion, robust transcript biomarkers are present within datasets assembled over many years and cohorts and our study provides both examples and a strategy for refining and comparing datasets to obtain additional markers as more data are generated.

Serum tri- and tetra-antennary N-glycan is a potential predictive biomarker for castration-resistant prostate cancer

BACKGROUND

The U.S. FDA has approved several novel systemic agents including abiraterone acetate and taxoid cabazitaxel for metastatic castration-resistant prostate cancer (CRPC) result in a complicated decision-making while selecting an appropriate treatment. Therefore, a predictive biomarker for CRPC would provide useful information to physicians. The aim of this study is to evaluate the diagnostic potential of serum N-glycan profiling in CRPC.

METHODS

Serum N-glycomics was performed in 80 healthy volunteers and 286 benign prostatic hyperplasia, 258 early-stage PC, 46 PC with androgen deprivation therapy (ADT), and 68 CRPC patients using the glycoblotting method. A total of 36 types of N-glycan levels in each patient were analyzed using logistic regression analysis and receiver operating characteristic curves. We also examined the expression of N-glycan branching enzyme genes in PC cell lines using quantitative RT-PCR.

RESULTS

We observed that tri- and tetra-antennary N-glycans were significantly higher in CRPC patients than in any other groups. The longitudinal follow-up of tri- and tetra- antennary N-glycan levels revealed that one PC with ADT patient showed an increase that was more than the cut-off level and two consecutive increases in tri- and tetra-antennary N-glycan levels 3 months apart; resulted in biochemical recurrence despite the castrate level of testosterone, and the patient was defined as CRPC. Expression of N-glycan branching enzyme genes were significantly upregulated in CRPC cell lines.

CONCLUSIONS

These results suggest that the overexpression of tri- and tetra-antennary N-glycan may be associated with the castration-resistant status in PC and may be a potential predictive biomarker for CRPC.

UAP1 is overexpressed in prostate cancer and is protective against inhibitors of N-linked glycosylation

Prostate cancer is the second most common cause of cancer-associated deaths in men, and signaling via a transcription factor called androgen receptor (AR) is an important driver of the disease. Consequently, AR target genes are prominent candidates to be specific for prostate cancer and also important for the survival of the cancer cells. Here we assess the levels of all hexosamine biosynthetic pathway (HBP) enzymes in 15 separate clinical gene expression data sets and identify the last enzyme in the pathway, UDP-N-acetylglucosamine pyrophosphorylase 1 (UAP1), to be highly overexpressed in prostate cancer. We analyzed 3261 prostate cancers on a tissue microarray and found that UAP1 staining correlates negatively with Gleason score (P=0.0039) and positively with high AR expression (P<0.0001). Cells with high UAP1 expression have 10-fold increased levels of the HBP end-product, UDP-N-acetylglucosamine (UDP-GlcNAc). UDP-GlcNAc is essential for N-linked glycosylation occurring in the endoplasmic reticulum (ER) and high UAP1 expression associates with resistance against inhibitors of N-linked glycosylation (tunicamycin and 2-deoxyglucose) but not with a general ER stress-inducing agent, the calcium ionophore A23187. Knockdown of UAP1 expression re-sensitized cells towards inhibitors of N-linked glycosylation, as measured by proliferation and activation of ER stress markers. Taken together, we have identified an enzyme, UAP1, which is highly overexpressed in prostate cancer and protects cancer cells from ER stress conferring a growth advantage.

Restoration of compact Golgi morphology in advanced prostate cancer enhances susceptibility to galectin-1-induced apoptosis by modifying mucin O-glycan synthesis

Prostate cancer progression is associated with upregulation of sialyl-T antigen produced by β-galactoside α-2,3-sialyltransferase-1 (ST3Gal1) but not with core 2-associated polylactosamine despite expression of core 2 N-acetylglucosaminyltransferase-L (C2GnT-L/GCNT1). This property allows androgen-refractory prostate cancer cells to evade galectin-1 (LGALS1)-induced apoptosis, but the mechanism is not known. We have recently reported that Golgi targeting of glycosyltransferases is mediated by golgins: giantin (GOLGB1) for C2GnT-M (GCNT3) and GM130 (GOLGA2)-GRASP65 (GORASP1) or GM130-giantin for core 1 synthase. Here, we show that for Golgi targeting, C2GnT-L also uses giantin exclusively whereas ST3Gal1 uses either giantin or GM130-GRASP65. In addition, the compact Golgi morphology is detected in both androgen-sensitive prostate cancer and normal prostate cells, but fragmented Golgi and mislocalization of C2GnT-L are found in androgen-refractory cells as well as primary prostate tumors (Gleason grade 2-4). Furthermore, failure of giantin monomers to be phosphorylated and dimerized prevents Golgi from forming compact morphology and C2GnT-L from targeting the Golgi. On the other hand, ST3Gal1 reaches the Golgi by an alternate site, GM130-GRASP65. Interestingly, inhibition or knockdown of non-muscle myosin IIA (MYH9) motor protein frees up Rab6a GTPase to promote phosphorylation of giantin by polo-like kinase 3 (PLK3), which is followed by dimerization of giantin assisted by protein disulfide isomerase A3 (PDIA3), and restoration of compact Golgi morphology and targeting of C2GnT-L. Finally, the Golgi relocation of C2GnT-L in androgen-refractory cells results in their increased susceptibility to galectin-1-induced apoptosis by replacing sialyl-T antigen with polylactosamine.

IMPLICATIONS

This study demonstrates the importance of Golgi morphology and regulation of glycosylation and provides insight into how the Golgi influences cancer progression and metastasis.

Hill CA, Walcheck B, Brooks JD. Increased expression of GCNT1 is associated with altered O-glycosylation of PSA, PAP, and MUC1 in human prostate cancers

BACKGROUND

Protein glycosylation is a common posttranslational modification and glycan structural changes have been observed in several malignancies including prostate cancer. We hypothesized that altered glycosylation could be related to differences in gene expression levels of glycoprotein synthetic enzymes between normal and malignant prostate tissues.

METHODS

We interrogated prostate cancer gene expression data for reproducible changes in expression of glycoprotein synthetic enzymes. Over-expression of GCNT1 was validated in prostate samples using RT-PCR. ELISA was used to measure core 2 O-linked glycan sialyl Lewis X (sLe(x) ) of prostate specific antigen (PSA), Mucin1 (MUC1), and prostatic acidic phosphatase (PAP) proteins.

RESULTS

A key glycosyltransferase, GCNT1, was consistently over-expressed in several prostate cancer gene expression datasets. RT-PCR confirmed increased transcript levels in cancer samples compared to normal prostate tissue in fresh-frozen prostate tissue samples. ELISA using PSA, PAP, and MUC1 capture antibodies and a specific core 2 O-linked sLe(x) detection antibody demonstrated elevation of this glycan structure in cancer compared to normal tissues for MUC1 (P = 0.01), PSA (P = 0.03) and near significant differences in PAP sLe(x) levels (P = 0.06). MUC1, PSA and PAP protein levels alone were not significantly different between paired normal and malignant prostate samples.

CONCLUSIONS

GCNT1 is over-expressed in prostate cancer and is associated with higher levels of core 2 O-sLe(x) in PSA, PAP and MUC1 proteins. Alterations of O-linked glycosylation could be important in prostate cancer biology and could provide a new avenue for development of prostate cancer specific glycoprotein biomarkers.

Carbohydrate sequence of the prostate cancer-associated antigen F77 assigned by a mucin O-glycome designer array

Monoclonal antibody F77 was previously raised against human prostate cancer cells and has been shown to recognize a carbohydrate antigen, but the carbohydrate sequence of the antigen was elusive. Here, we make multifaceted approaches to characterize F77 antigen, including binding analyses with the glycolipid extract of the prostate cancer cell line PC3, microarrays with sequence-defined glycan probes, and designer arrays from the O-glycome of an antigen-positive mucin, in conjunction with mass spectrometry. Our results reveal F77 antigen to be expressed on blood group H on a 6-linked branch of a poly-N-acetyllactosamine backbone. We show that mAb F77 can also bind to blood group A and B analogs but with lower intensities. We propose that the close association of F77 antigen with prostate cancers is a consequence of increased blood group H expression together with up-regulated branching enzymes. This is in contrast to other epithelial cancers that have up-regulated branching enzymes but diminished expression of H antigen. With knowledge of the structure and prevalence of F77 antigen in prostate cancer, the way is open to explore rationally its application as a biomarker to detect F77-positive circulating prostate cancer-derived glycoproteins and tumor cells.

Serum N-glycan profiling predicts prognosis in patients undergoing hemodialysis

Background. The aim of this study is to evaluate the usefulness of serum N-glycan profiling for prognosis in hemodialysis patients. Methods. Serum N-glycan analysis was performed in 100 hemodialysis patients in June 2008 using the glycoblotting method, which allows high-throughput, comprehensive, and quantitative N-glycan analysis. All patients were longitudinally followed up for 5 years. To evaluate the independent predictors for prognosis, patients' background, blood biochemistry, and N-glycans intensity were analyzed using Cox regression multivariate analysis. Selected N-glycans and independent factors were evaluated using the log-rank test with the Kaplan-Meier method to identify the predictive indicators for prognosis. Each patient was categorized according to the number of risk factors to evaluate the predictive potential of the risk criteria for prognosis. Results. In total, 56 N-glycan types were identified in the hemodialysis patients. Cox regression multivariate analysis showed cardiovascular events, body mass index, maximum intima media thickness, and the serum N-glycan intensity of peak number 49 were predictive indicators for overall survival. Risk classification according to the number of independent risk factors revealed significantly poor survival by increasing the number of risk factors. Conclusions. Serum N-glycan profiling may have a potential to predict prognosis in patients undergoing hemodialysis.

Serum N-glycan alteration associated with renal cell carcinoma detected by high throughput glycan analysis

PURPOSE

Biomarkers for the early detection and prediction of survival in patients with renal cell carcinoma have not been established. We developed what is to our knowledge a novel glycoblotting method that allows high throughput, comprehensive, quantitative analysis of glycans in human serum. In this study we identified alterations in serum N-glycans associated with renal cell carcinoma.

MATERIALS AND METHODS

We performed a comprehensive N-glycan structural analysis of serum from 64 patients with renal cell carcinoma and 34 age matched, healthy volunteers using glycoblotting methods and matrix-assisted laser desorption/ionization-time of flight mass spectrometry. The peak intensity of N-glycan was analyzed using logistic regression analysis and ROCs were used to select candidate N-glycans. Candidate N-glycans with a statistically significant relationship to renal cell carcinoma or overall survival were independently evaluated using a Cox regression model to determine superiority compared to other conventional renal cell carcinoma biomarkers.

RESULTS

We identified 56 types of N-glycans in serum from healthy volunteers and patients with renal cell carcinoma. Peaks 40 and 43 were significantly more intense in patients than in volunteers. Peak 19 intensity was significantly higher and peak 49 intensity was significantly lower in patients with renal cell carcinoma who survived for a longer period. Multivariate analysis revealed that peaks 19 and 49 were independent predictors of overall survival.

CONCLUSIONS

Serum N-glycan analysis is a promising approach to discovering new biomarkers for renal cell carcinoma. Further study is warranted to validate our results.

Expression of core 3 synthase in human pancreatic cancer cells suppresses tumor growth and metastasis

Core 3-derived glycans, a major type of O-glycan expressed by normal epithelial cells of the gastrointestinal tract, are downregulated during malignancy because of loss of expression of functional β3-N-acetylglucosaminyltransferase-6 (core 3 synthase). We investigated the expression of core 3 synthase in normal pancreas and pancreatic cancer and evaluated the biological effects of re-expressing core 3 synthase in pancreatic cancer cells that had lost expression. We determined that pancreatic tumors and tumor cell lines have lost expression of core 3 synthase. Therefore, we re-expressed core 3 synthase in human pancreatic cancer cells (Capan-2 and FG) to investigate the contribution of core 3 glycans to malignant progression. Pancreatic cancer cells expressing core 3 synthase showed reduced in vitro cell proliferation, migration and invasion compared to vector control cells. Expression of core 3 O-glycans induced altered expression of β1 integrin, decreased activation of focal adhesion kinase, led to the downregulation of expression of several genes including REG1α and FGFR3 and altered lamellipodia formation. The addition of a GlcNAc residue by core 3 synthase leads to the extension of the tumor-associated Tn structure on MUC1. Orthotopic injection of FG cells expressing core 3 synthase into the pancreas of nude mice produced significantly smaller tumors and decreased metastasis to the surrounding tissues compared to vector control FG cells. These findings indicate that expression of core 3-derived O-glycans in pancreatic cancer cells suppresses tumor growth and metastasis through modulation of glycosylation of mucins and other cell surface and extracellular matrix proteins.

Tumor-Associated Glycans and Immune Surveillance

Changes in cell surface glycosylation are a hallmark of the transition from normal to inflamed and neoplastic tissue. Tumor-associated carbohydrate antigens (TACAs) challenge our understanding of immune tolerance, while functioning as immune targets that bridge innate immune surveillance and adaptive antitumor immunity in clinical applications. T-cells, being a part of the adaptive immune response, are the most popular component of the immune system considered for targeting tumor cells. However, for TACAs, T-cells take a back seat to antibodies and natural killer cells as first-line innate defense mechanisms. Here, we briefly highlight the rationale associated with the relative importance of the immune surveillance machinery that might be applicable for developing therapeutics.

Immunohistochemical expression of core 2 β1,6-N-acetylglucosaminyl transferase 1 (C2GnT1) in endometrioid-type endometrial carcinoma: a novel potential prognostic factor

AIMS

It has been reported that the expression of core 2 β1,6-N-acetylglucosaminyl transferase 1 (C2GnT1), which synthesizes the core 2 branching structure on O-glycans, may be associated with the biological aggressiveness of tumour cells. Therefore, the aim of this study was to examine the relationship between the expression of C2GnT1 and clinicopathological parameters of patients with endometrial carcinoma.

METHODS AND RESULTS

The immunohistochemical expression of C2GnT1 was examined in 84 cases of endometrioid-type endometrial carcinoma, 15 cases of endometrial hyperplasia, and 30 normal endometria. The staining intensity was reported according to a positivity index (PI, full score 100), calculated from the percentage of positive cells. The expression of C2GnT1 was significantly higher in endometrial carcinoma (PI = 8.31 ± 15.29) than in normal endometrium (PI = 0.52 ± 1.24) (P < 0.0005). In carcinomas, the PI was higher in high-grade or advanced-stage tumours, but not significantly. Topologically, C2GnT1 was strongly expressed at sites of deep myometrial invasion. In addition, patients with C2GnT1 overexpression (PI ≥ 10) had significantly shorter survival (P < 0.0005). Multivariable analysis also indicated that C2GnT1 overexpression was an independent prognostic factor (P = 0.017).

CONCLUSIONS

C2GnT1 appears to be involved in the biological aggressiveness of endometrial carcinoma. C2GnT1 might become a novel prognostic factor for endometrial carcinoma.

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.

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.

Glycosylation potential of human prostate cancer cell lines

Altered glycosylation is a universal feature of cancer cells and altered glycans can help cancer cells escape immune surveillance, facilitate tumor invasion, and increase malignancy. The goal of this study was to identify specific glycoenzymes, which could distinguish prostate cancer cells from normal prostatic cells. We investigated enzymatic activities and gene expression levels of key glycosyl- and sulfotransferases responsible for the assembly of O- and N-glycans in several prostatic cells. These cells included immortalized RWPE-1 cells derived from normal prostatic tissues, and prostate cancer cells derived from metastasis in bone (PC-3), brain (DU145), lymph node (LNCaP), and vertebra (VCaP). We found that all cells were capable of synthesizing complex N-glycans and O-glycans with the core 1 structure, and each cell line had characteristic biosynthetic pathways to modify these structures. The in vitro measured activities corresponded well to the mRNA levels of glycosyltransferases and sulfotransferases. Lectin and antibody binding to whole cells supported these results, which form the basis for the development of tumor cell-specific targeting strategies.

MUC1 carrying core 2 O-glycans functions as a molecular shield against NK cell attack, promoting bladder tumor metastasis

Core 2 β-1,6-N-acetylglucosaminyltransferase (C2GnT) forms an N-acetylglucosamine branch in O-glycans (core 2 O-glycans) of cell surface glycoproteins. C2GnT-expressing bladder tumors acquire highly metastatic phenotypes by surviving longer in host blood circulation. However, the detailed mechanisms underlying this increased survival remain unclear. In this study, we report that the expression of C2GnT in bladder tumors positively correlates with tumor progression and that bladder tumor cell-surface mucin 1 (MUC1) carrying core 2 O-glycans plays an important role in the evasion from natural killer (NK) cell attack. In C2GnT-expressing bladder tumor cells, heavily core 2 O-glycosylated MUC1 carries poly-N-acetyllactosamine in its O-glycans and galectin-3 binds to MUC1 through this poly-N-acetyllactosamine. The binding of galectin-3 to poly-N-acetyllactosamine in MUC1 core 2 O-glycans attenuates the interaction of the tumor cells with NK cells and interferes with the access of tumor necrosis factor-related apoptosis-inducing ligand to the tumor cell surface. These effects of MUC1 carrying core 2 O-glycans on NK cell attack facilitate C2GnT-expressing tumor cells to evade NK cell immunity and survive longer in host blood circulation. We reveal that MUC1 carrying core 2 O-glycans thus functions as a molecular shield against NK cell attack, thereby promoting bladder tumor metastasis.

Two opposing roles of O-glycans in tumor metastasis

Despite the high prevalence of metastatic cancers and the poor outcome for patients, the processes of tumor metastasis still remain poorly understood. It has been shown that cell-surface carbohydrates attached to proteins through the amino acids serine or threonine (O-glycans) are involved in tumor metastasis, with the roles of O-glycans varying depending on their structure. Core2 O-glycans allow tumor cells to evade natural killer (NK) cells of the immune system and survive longer in the circulatory system, thereby promoting tumor metastasis. Core3 O-glycans or O-mannosyl glycans suppress tumor formation and metastasis by modulating integrin-mediated signaling. Here, we highlight recent advances in our understanding of the detailed molecular mechanisms by which O-glycans promote or suppress tumor metastasis.

A novel strategy for evasion of NK cell immunity by tumours expressing core2 O-glycans

The O-glycan branching enzyme, core2 β-1,6-N-acetylglucosaminyltransferase (C2GnT), forms O-glycans containing an N-acetylglucosamine branch connected to N-acetylgalactosamine (core2 O-glycans) on cell-surface glycoproteins. Here, we report that upregulation of C2GnT is closely correlated with progression of bladder tumours and that C2GnT-expressing bladder tumours use a novel strategy to increase their metastatic potential. Our results showed that C2GnT-expressing bladder tumour cells are highly metastatic due to their high ability to evade NK cell immunity and revealed the molecular mechanism of the immune evasion by C2GnT expression. Engagement of an NK-activating receptor, NKG2D, by its tumour-associated ligand, Major histocompatibility complex class I-related chain A (MICA), is critical to tumour rejection by NK cells. In C2GnT-expressing bladder tumour cells, poly-N-acetyllactosamine was present on core2 O-glycans on MICA, and galectin-3 bound the NKG2D-binding site of MICA through this poly-N-acetyllactosamine. Galectin-3 reduced the affinity of MICA for NKG2D, thereby severely impairing NK cell activation and silencing the NK cells. This new mode of NK cell silencing promotes immune evasion of C2GnT-expressing bladder tumour cells, resulting in tumour metastasis.

C2-O-sLeX glycoproteins are E-selectin ligands that regulate invasion of human colon and hepatic carcinoma cells

Similar to mechanisms of recruitment of activated leukocytes to inflamed tissues, selectins mediate adhesion and extravasation of circulating cancer cells. Our objective was to determine whether sialyl Lewis X modified core 2 O-glycans (C2-O-sLe^X) present on colon and hepatic carcinoma cells promote their adhesion and invasion. We examined membrane expression of C2-O-sLe^X, selectin binding, invasion of human colon and hepatic carcinoma cell lines, and mRNA levels of alpha-2,3 fucosyltransferase (FucT-III) and core 2 beta-1,6 N-acetylglucosaminyltransferase (C2GnT1) genes, necessary for C2-O-sLe^X synthesis, by quantitative reverse-transcriptase (RT) PCR. Synthesis of core 2 branched O-glycans decorated by sLe^X is dependent on C2GnT1 function and thus we determined enzyme activity of C2GnT1. The cell lines that expressed C2GnT1 and FucT-III mRNA by quantitative RT-PCR were highly positive for C2-O-sLe^X by flow cytometry, and colon carcinoma cells possessed highly active C2GnT1 enzyme. Cells bound avidly to E-selection but not to P- and L-selectin. Gene knock-down of C2GnT1 in colon and hepatic carcinoma cells using short hairpin RNAs (shRNA) resulted in a 40–90% decrease in C2-O-sLe^X and a 30–50% decrease in E-selectin binding compared to control cells. Invasion of hepatic and colon carcinoma cells containing C2GnT1 shRNA was significantly reduced compared to control cells in Matrigel assays and C2GnT1 activity was down-regulated in the latter cells. The sLe^X epitope was predominantly distributed on core 2 O-glycans on colon and hepatic carcinoma cells. Our findings indicate that C2GnT1 gene expression and the resulting C2-O-sLe^X carbohydrates produced mediate the adhesive and invasive behaviors of human carcinomas which may influence their metastatic potential.

Core 2 N-acetylglucosaminyltransferase-1 expression induces aggressive potential of testicular germ cell tumor

We studied orchiectomy specimens from 130 patients immuhistochemically with testicular germ cell tumor (TGCT) using anti-core 2 N-acetylglucosaminyltransferase-1 (C2GnT-1) antibody. The incidence of C2GnT-1 positivity in stage I disease (29.5%, 21/71) was significantly lower than that in higher stages (84.7%, 50/59) (P < 0.001, chi(2) test). This significant difference was also found when the cases were divided into seminoma and NSGCT according to histopathological classification. Kaplan-Meier plots and the log rank test showed that in the patients with stage I seminoma, C2GnT-1-positive cases had a higher risk for recurrence (P < 0.001). This was also the case with the patients with stage I NSGCT (P < 0.001). To determine whether C2GnT-1 promotes aggressive behavior of cancer cells, a C2GnT-1-negative human TGCT cell line, JKT-1, was stably transfected with a mammalian expression vector containing C2GnT-1 cDNA. In vitro assays revealed that JKT-1-C2 cells are more invasive than mock transfectants, although there are no differences in proliferation activity. When orthotopically inoculated into athymic nude mice, JKT-1-C2 cells produced larger testicular tumors extending to the retroperitoneum with mesenteric metastasis, while mock transfectants produced small tumors without metastasis (P < 0.01, Mann-Whitney's U-test). When injected via the tail vein, JKT-1-C2 cells produced a number of metastatic lung foci. In contrast, mock transfectants produced a small number of nodules (p < 0.01, Mann-Whitney's U-test). These results strongly suggest that C2GnT-1 enhances the metastatic potential of TGCT and may be a reliable biomarker for aggressive potential of TGCT.

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

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

Characterization of mice with targeted deletion of the gene encoding core 2 beta1,6-N-acetylglucosaminyltransferase-2

The three glycosyltransferases of the Core 2 beta1,6-N-acetylglucosaminyltransferase (C2GnT) family, C2GnT1, C2GnT2, and C2GnT3, are able to initiate the Core 2 branch of O-glycans. However, C2GnT2, which is highly expressed in the digestive tract, has a broader acceptor substrate specificity that allows it to also generate Core 4 O-glycans and I branches. We discovered that C2GnT2 KO mice have decreased mucosal barrier function in the digestive tract, reduced levels of circulating IgGs and fecal IgA, and increased susceptibility to experimental colitis. Mass spectrometric analyses also revealed that C2GnT2 KO mice had a reduction in Core 2 O-glycans in the digestive tract with a corresponding increase in elongated Core 1 O-glycans. Unexpectedly, we saw that the loss of C2GnT2 and especially the loss of all three C2GnTs resulted in the expression of elongated O-mannose structures in the stomach, suggesting that the elongation of these structures is controlled by competition for UDP-GlcNAc [Stone, E. L., Ismail, M. N., Lee, S. H., Luu, Y., Ramirez, K., Haslam, S. M., Ho, S. B., Dell, A., Fukuda, M. and Marth, J. D. (2009). Glycosyltransferase function in Core 2-type protein O-glycosylation. Mol. Cell. Biol. 29, 3370-3782].