N-acetylglucosaminyltransferase III antagonizes the effect of N-acetylglucosaminyltransferase V on alpha3beta1 integrin-mediated cell migration

N-glycan signatures identified in the serum from biliary tract cancer patients: Association with clinical diagnosis and prognosis

BACKGROUND

Changes in the expression of genes related to glycosyltransferases may lead to alterations in N-glycan structure abundance, potentially acting as markers for diagnosis and prognosis in biliary tract cancer (BTC).

METHODS

This study was divided into cross-sectional and longitudinal approaches. The cross-sectional study included 316 BTC and 301 non-BTC. Propensity score matching was applied to adjust for sex and age differences between BTC and non-BTC. Univariate and multivariate logistic regression identified independent risk factors for BTC and constructed the BTC-G model. The ROC curve was used to validate the diagnostic performance of BTC-G. Longitudinal follow-up studies included postoperative (N = 50) and immunotherapy (N = 43) follow-up cohorts. Cox regression analysis identified N-glycan structures impacting BTC prognosis postoperative and immunotherapy, with further confirmation through Kaplan-Meier curves.

RESULTS

Univariate and multivariate analyses identified Peak3 (OR: 0.790, 95% CI: 0.658-0.949), Peak9 (OR: 1.646, 95% CI: 1.409-1.922), and Peak9p (OR: 2.467, 95% CI: 1.267-4.804) as independent BTC risk factors, leading to the creation of the BTC-G. The ROC curve confirmed that BTC-G performed well in training (AUC: 0.753, 95% CI: 0.703-0.799), validation (AUC: 0.811, 95% CI: 0.740-0.870), and CA19-9 negative cohorts (AUC: 0.717, 95% CI: 0.664-0.767). Cox regression analysis and Kaplan-Meier curves established that Peak12 (HR: 5.578, 95% CI: 1.145-27.170) and Peak11 (HR: 1.104, 95% CI: 0.611-1.994) are independent risk factors for BTC prognosis following surgery and immunotherapy, respectively.

CONCLUSIONS

Our NGFP technology supplements BTC diagnostics, distinguishing survival and recurrence subtypes for postoperative and immunotherapy, thereby supporting the development of treatment strategies.

An emerging role of N-glycosylation in cancer chemoresistance

Chemoresistance poses a significant obstacle in the effective treatment of cancer, limiting the success of chemotherapy regimens. N-glycosylation, the most important post-translational modification (PTM), plays multifaceted roles in the intricate landscape of cancer progression, particularly drug resistance in cancer cells. This review explores the complex relationship between N-glycosylation and chemoresistance in cancer. Altered glycosylation patterns have been proven to impact drug efflux mechanisms in cancer cells, which can further influence the intracellular concentration of chemotherapy drugs. Moreover, N-glycosylation also plays a regulatory role in cell signaling pathways and apoptosis regulators, continuously affecting the stemness and survival of cancer cells under the selective pressure of chemotherapy. Additionally, the impact of the tumor microenvironment on glycosylation patterns adds complexity to this interplay. This review discusses current research findings, challenges, and future directions based on the roles of N-glycosylation in cancer chemoresistance, emphasizing the potential for targeted therapeutic interventions to enhance the effectiveness of chemotherapy and improve patient outcomes.

Relevance of glyco-biomakers and glycan profiles in cancer stem cells

Altered and aberrant glycosylation signatures have been linked to being a hallmark in a variety of human disorders including cancer. Cancer stem cells (CSCs), capable of self-renewal and differentiation, have recently been credited with a unique notion of disease genesis and implicated as the cause for initiation and recurrence of the disease in a new regime of neoplastic transformations hypothesis. Many biomarkers relating to diagnostic and prognostic intents have been discovered using the ubiquitous and abundant surface glycan patterns on CSCs. Various technological advancements have been developed to identify and determine concerns with glycosylation structure. However, the nature and purpose of the glycan moiety on these glycosylation pattern have not yet been thoroughly investigated. This review, thus, summarizes the process of glycosylation in CSCs, variations in glycosylation patterns in various stem cells, aberrant glycosylation patterns in cancer, the role of glycosylation in tumor cell adhesion, cell-matrix interactions, and signaling, as well as cancer detection and treatment. The function of carbohydrates as prospective serum biomarkers, some clinically authorized biomarkers, and potential novel biomarkers relating to cancer disease diagnosis and prognosis are also discussed in the review.

The functional roles of protein glycosylation in human maternal-fetal crosstalk

BACKGROUND

The establishment of maternal-fetal crosstalk is vital to a successful pregnancy. Glycosylation is a post-translational modification in which glycans (monosaccharide chains) are attached to an organic molecule. Glycans are involved in many physiological and pathological processes. Human endometrial epithelium, endometrial gland secretions, decidual immune cells, and trophoblasts are highly enriched with glycoconjugates and glycan-binding molecules important for a healthy pregnancy. Aberrant glycosylation in the placenta and uterus has been linked to repeated implantation failure and various pregnancy complications, but there is no recent review summarizing the functional roles of glycosylation at the maternal-fetal interface and their associations with pathological processes.

OBJECTIVE AND RATIONALE

This review aims to summarize recent findings on glycosylation, glycosyltransferases, and glycan-binding receptors at the maternal-fetal interface, and their involvement in regulating the biology and pathological conditions associated with endometrial receptivity, placentation and maternal-fetal immunotolerance. Current knowledge limitations and future insights into the study of glycobiology in reproduction are discussed.

SEARCH METHODS

A comprehensive PubMed search was conducted using the following keywords: glycosylation, glycosyltransferases, glycan-binding proteins, endometrium, trophoblasts, maternal-fetal immunotolerance, siglec, selectin, galectin, repeated implantation failure, early pregnancy loss, recurrent pregnancy loss, preeclampsia, and fetal growth restriction. Relevant reports published between 1980 and 2023 and studies related to these reports were retrieved and reviewed. Only publications written in English were included.

OUTCOMES

The application of ultrasensitive mass spectrometry tools and lectin-based glycan profiling has enabled characterization of glycans present at the maternal-fetal interface and in maternal serum. The endometrial luminal epithelium is covered with highly glycosylated mucin that regulates blastocyst adhesion during implantation. In the placenta, fucose and sialic acid residues are abundantly presented on the villous membrane and are essential for proper placentation and establishment of maternal-fetal immunotolerance. Glycan-binding receptors, including selectins, sialic-acid-binding immunoglobulin-like lectins (siglecs) and galectins, also modulate implantation, trophoblast functions and maternal-fetal immunotolerance. Aberrant glycosylation is associated with repeated implantation failure, early pregnancy loss and various pregnancy complications. The current limitation in the field is that most glycobiological research relies on association studies, with few studies revealing the specific functions of glycans. Technological advancements in analytic, synthetic and functional glycobiology have laid the groundwork for further exploration of glycans in reproductive biology under both physiological and pathological conditions.

WIDER IMPLICATIONS

A deep understanding of the functions of glycan structures would provide insights into the molecular mechanisms underlying their involvement in the physiological and pathological regulation of early pregnancy. Glycans may also potentially serve as novel early predictive markers and therapeutic targets for repeated implantation failure, pregnancy loss, and other pregnancy complications.

The cancer-associated glycosyltransferase GnT-V (MGAT5) recognizes the N-glycan core via residues outside its catalytic pocket

N-acetylglucosaminyltransferase-V (GnT-V or MGAT5) is a glycosyltransferase involved in cancer metastasis that creates the β1,6-branch on N-glycans of target proteins such as cell adhesion molecules and cell surface receptors. The 3D structure of GnT-V and its catalytic site, which are critical for the interaction with the N-glycan terminal, have already been revealed. However, it remains unclear how GnT-V recognizes the core part of N-glycan or the polypeptide part of the acceptor. Using molecular dynamics simulations and biochemical experiments, we found that several residues outside the catalytic pocket are likely involved in the recognition of the core part of N-glycan. Furthermore, our simulation suggested that UDP binding affects the orientation of the acceptor due to the conformational change at the Manα1,6-Man linkage. These findings provide new insights into how GnT-V recognizes its glycoprotein substrates.

Targeting the ATF6-Mediated ER Stress Response and Autophagy Blocks Integrin-Driven Prostate Cancer Progression

Prostate cancer progression to the lethal metastatic castration-resistant phenotype (mCRPC) is driven by αv integrins and is associated with Golgi disorganization and activation of the ATF6 branch of unfolded protein response (UPR). Overexpression of integrins requires N-acetylglucosaminyltransferase-V (MGAT5)-mediated glycosylation and subsequent cluster formation with Galectin-3 (Gal-3). However, the mechanism underlying this altered glycosylation is missing. For the first time, using HALO analysis of IHC, we found a strong association of integrin αv and Gal-3 at the plasma membrane (PM) in primary prostate cancer and mCRPC samples. We discovered that MGAT5 activation is caused by Golgi fragmentation and mislocalization of its competitor, N-acetylglucosaminyltransferase-III, MGAT3, from Golgi to the endoplasmic reticulum (ER). This was validated in an ethanol-induced model of ER stress, where alcohol treatment in androgen-refractory PC-3 and DU145 cells or alcohol consumption in patient with prostate cancer samples aggravates Golgi scattering, activates MGAT5, and enhances integrin expression at PM. This explains known link between alcohol consumption and prostate cancer mortality. ATF6 depletion significantly blocks UPR and reduces the number of Golgi fragments in both PC-3 and DU145 cells. Inhibition of autophagy by hydroxychloroquine (HCQ) restores compact Golgi, rescues MGAT3 intra-Golgi localization, blocks glycan modification via MGAT5, and abrogates delivery of Gal-3 to the cell surface. Importantly, the loss of Gal-3 leads to reduced integrins at PM and their accelerated internalization. ATF6 depletion and HCQ treatment synergistically decrease integrin αv and Gal-3 expression and temper orthotopic tumor growth and metastasis.

IMPLICATIONS

Combined ablation of ATF6 and autophagy can serve as new mCRPC therapeutic.

Focal-adhesion kinase regulates the sialylation of N-glycans via the PI4KIIα-PI4P pathway

Sialylation is a terminal glycosylated modification of glycoproteins that regulates critical biological events such as cell adhesion and immune response. Our previous study showed that integrin α3β1 plays a crucial role in regulating the sialylation of N-glycans. However, the underlying mechanism for the regulation remains unclear. This study investigated how sialylation is affected by focal adhesion kinase (FAK), which is a critical downstream signal molecule of integrin β1. We established a stable FAK knockout (KO) cell line using the CRISPR/Cas9 system in HeLa cells. The results obtained from lectin blot, flow cytometric analysis, and MS showed that the sialylation levels were significantly decreased in the KO cells compared with that in wild-type (WT) cells. Moreover, phosphatidylinositol 4-phosphate (PI4P) expression levels were also reduced in the KO cells due to a decrease in the stability of phosphatidylinositol 4-kinase-IIα (PI4KIIα). Notably, the decreased levels of sialylation, PI4P, and the complex formation between GOLPH3 and ST3GAL4 or ST6GAL1, which are the main sialyltransferases for modification of N-glycans, were significantly restored by the re-expression of FAK. Furthermore, the decreased sialylation and phosphorylation of Akt and cell migration caused by FAK deficiency all were restored by overexpressing PI4KIIα, which suggests that PI4KIIα is one of the downstream molecules of FAK. These findings indicate that FAK regulates sialylation via the PI4P synthesis pathway and a novel mechanism is suggested for the integrin-FAK-PI4KIIα-GOLPH3-ST axis modulation of sialylation in N-glycans.

Glycoproteomic analysis of regulatory effects of bisecting N-glycans on N-glycan biosynthesis and protein expressions in human HK-2 cells

Bisecting N-glycan is known to be a metastasis suppressor and plays a regulatory role in the biosynthesis of N-glycans. Previous studies have shown that bisecting N-glycans are capable of modulating both the branching and terminal modifications of glycans. However, these effects have been investigated mainly by glycomic approaches and it remains unclear how they alter when glycans are attached to different glycosites of proteins. Here, we systematically investigated the regulatory roles of bisecting N-glycans in human HK-2 cells using StrucGP, a strategy we developed for structural interpretation of site-specific N-glycans on glycoproteins. The glycoproteomics analysis showed that most of bisecting N-glycans are complex type and often occur in company with core fucosylation. With the overexpression and knockdown of MGAT3, the only enzyme responsible for bisecting N-glycan synthesis, we found that bisecting N-glycans can impact the biosynthesis of N-glycans from multiple aspects, including glycan types, branching, sialylation, fucosylation (different effects for core and terminal fucosylation) as well as the presence of terminal N-acetylglucosamine. Furthermore, gene ontology analysis suggested that most proteins with bisecting N-glycans located in the extracellular region or membrane, where they function mostly in cell adhesion, extracellular matrix regulation and cell signaling. Finally, we showed that overexpression of bisecting N-glycans had a broad impact on the protein expressions of HK-2 cells, involving multiple biological processes. Taken together, our work systematically demonstrated the expression profiles of bisecting N-glycans, and their regulatory effects on the biosynthesis of N-glycans and protein expressions, which provide valuable information for the functional elucidation of bisecting N-glycans.

Abnormal glycosylation in glioma: related changes in biology, biomarkers and targeted therapy

Glioma is a rapidly growing and aggressive primary malignant tumor of the central nervous system that can diffusely invade the brain tissue around, and the prognosis of patients is not significantly improved by traditional treatments. One of the most general posttranslational modifications of proteins is glycosylation, and the abnormal distribution of this modification in gliomas may shed light on how it affects biological behaviors of glioma cells, including proliferation, migration, and invasion, which may be produced by regulating protein function, cell-matrix and cell‒cell interactions, and affecting receptor downstream pathways. In this paper, from the perspective of regulating protein glycosylation changes and abnormal expression of glycosylation-related proteins (such as glycosyltransferases in gliomas), we summarize how glycosylation may play a crucial role in the discovery of novel biomarkers and new targeted treatment options for gliomas. Overall, the mechanistic basis of abnormal glycosylation affecting glioma progression remains to be more widely and deeply explored, which not only helps to inspire researchers to further explore related diagnostic and prognostic markers but also provides ideas for discovering effective treatment strategies and improving glioma patient survival and prognosis.

Regulation of neural stem cell differentiation and brain development by MGAT5-mediated N-glycosylation

Undifferentiated neural stem and progenitor cells (NSPCs) encounter extracellular signals that bind plasma membrane proteins and influence differentiation. Membrane proteins are regulated by N-linked glycosylation, making it possible that glycosylation plays a critical role in cell differentiation. We assessed enzymes that control N-glycosylation in NSPCs and found that loss of the enzyme responsible for generating β1,6-branched N-glycans, N-acetylglucosaminyltransferase V (MGAT5), led to specific changes in NSPC differentiation in vitro and in vivo. Mgat5 homozygous null NSPCs in culture formed more neurons and fewer astrocytes compared with wild-type controls. In the brain cerebral cortex, loss of MGAT5 caused accelerated neuronal differentiation. Rapid neuronal differentiation led to depletion of cells in the NSPC niche, resulting in a shift in cortical neuron layers in Mgat5 null mice. Glycosylation enzyme MGAT5 plays a critical and previously unrecognized role in cell differentiation and early brain development.

Roles of N-linked glycosylation and glycan-binding proteins in placentation: trophoblast infiltration, immunomodulation, angiogenesis, and pathophysiology

Protein N-linked glycosylation is a structurally diverse post-translational modification that stores biological information in a larger order of magnitude than other post-translational modifications such as phosphorylation, ubiquitination and acetylation. This gives N-glycosylated proteins a diverse range of properties and allows glyco-codes (glycan-related information) to be deciphered by glycan-binding proteins (GBPs). The intervillous space of the placenta is richly populated with membrane-bound and secreted glycoproteins. Evidence exists to suggest that altering the structural nature of their N-glycans can impact several trophoblast functions, which include those related to interactions with decidual cells. This review summarizes trophoblast-related activities influenced by N-glycan-GBP recognition, exploring how different subtypes of trophoblasts actively adapt to characteristics of the decidualized endometrium through cell-specific expression of N-glycosylated proteins, and how these cells receive decidua-derived signals via N-glycan-GBP interactions. We highlight work on how changes in N-glycosylation relates to the success of trophoblast infiltration, interactions of immunomodulators, and uterine angiogenesis. We also discuss studies that suggest aberrant N-glycosylation of trophoblasts may contribute to the pathogenesis of pregnancy complications (e.g. pre-eclampsia, early spontaneous miscarriages and hydatidiform mole). We propose that a more in-depth understanding of how N-glycosylation shapes trophoblast phenotype during early pregnancy has the potential to improve our approach to predicting, diagnosing and alleviating poor maternal/fetal outcomes associated with placental dysfunction.

Aberrant N-glycosylation in cancer: MGAT5 and β1,6-GlcNAc branched N-glycans as critical regulators of tumor development and progression

BACKGROUND

Changes in protein glycosylation are widely observed in tumor cells. N-glycan branching through adding β1,6-linked N-acetylglucosamine (β1,6-GlcNAc) to an α1,6-linked mannose, which is catalyzed by the N-acetylglucosaminyltransferase V (MGAT5 or GnT-V), is one of the most frequently observed tumor-associated glycan structure formed. Increased levels of this branching structure play a pro-tumoral role in various ways, for example, through the stabilization of growth factor receptors, the destabilization of intercellular adhesion, or the acquisition of a migratory phenotype.

CONCLUSION

In this review, we provide an updated and comprehensive summary of the physiological and pathophysiological roles of MGAT5 and β1,6-GlcNAc branched N-glycans, including their regulatory mechanisms. Specific emphasis is given to the role of MGAT5 and β1,6-GlcNAc branched N-glycans in cellular mechanisms that contribute to the development and progression of solid tumors. We also provide insight into possible future clinical implications, such as the use of MGAT5 as a prognostic biomarker.

An insight into new glycotherapeutics in glial inflammation: Understanding the role of glycosylation in mitochondrial function and acute to the chronic phases of inflammation

INTRODUCTION

Glycosylation plays a critical role during inflammation and glial scar formation upon spinal cord injury (SCI) disease progression. Astrocytes and microglia are involved in this cascade to modulate the inflammation and tissue remodeling from acute to chronic phases. Therefore, understating the glycan changes in these glial cells is paramount.

METHOD AND RESULTS

A lectin microarray was undertaken using a cytokine-driven inflammatory mixed glial culture model, revealing considerable differential glycosylation from the acute to the chronic phase in a cytokine-combination generated inflamed MGC model. It was found that several N- and O-linked glycans associated with glia during SCI were differentially regulated. Pearson's correlation hierarchical clustering showed that groups were separated into several clusters, illustrating the heterogenicity among the control, cytokine combination, and LPS treated groups and the day on which treatment was given. Control and LPS treatments were observed to be in dense clusters. This was further confirmed with lectin immunostaining in which GalNAc, GlcNAc, mannose, fucose and sialic acid-binding residues were detected in astrocytes and microglia. However, the sialyltransferase inhibitor inhibited this modification (upregulation of the sialic acid expression), which indeed modulates the mitochondrial functions.

CONCLUSIONS

The present study is the first functional investigation of glycosylation modulation in a mixed glial culture model, which elucidates the role of the glycome in neuroinflammation in progression and identified potential therapeutic targets for future glyco therapeutics in neuroinflammation.

N-linked glycoproteomic profiling in esophageal squamous cell carcinoma

BACKGROUND

Mass spectrometry-based proteomics and glycomics reveal post-translational modifications providing significant biological insights beyond the scope of genomic sequencing.

AIM

To characterize the N-linked glycoproteomic profile in esophageal squamous cell carcinoma (ESCC) via two complementary approaches.

METHODS

Using tandem multilectin affinity chromatography for enrichment of N-linked glycoproteins, we performed N-linked glycoproteomic profiling in ESCC tissues by two-dimensional gel electrophoresis (2-DE)-based and isobaric tags for relative and absolute quantification (iTRAQ) labeling-based mass spectrometry quantitation in parallel, followed by validation of candidate glycoprotein biomarkers by Western blot.

RESULTS

2-DE-based and iTRAQ labeling-based quantitation identified 24 and 402 differentially expressed N-linked glycoproteins, respectively, with 15 in common, demonstrating the outperformance of iTRAQ labeling-based quantitation over 2-DE and complementarity of these two approaches. Proteomaps showed the distinct compositions of functional categories between proteins and glycoproteins with differential expression associated with ESCC. Western blot analysis validated the up-regulation of total procathepsin D and high-mannose procathepsin D, and the down-regulation of total haptoglobin, high-mannose clusterin, and GlcNAc/sialic acid-containing fraction of 14-3-3ζ in ESCC tissues. The serum levels of glycosylated fractions of clusterin, proline-arginine-rich end leucine-rich repeat protein, and haptoglobin in patients with ESCC were remarkably higher than those in healthy controls.

CONCLUSION

Our study provides insights into the aberrant N-linked glycoproteome associated with ESCC, which will be a valuable resource for future investigations.

Structure-based design of UDP-GlcNAc analogs as candidate GnT-V inhibitors

BACKGROUND

N-Glycan branching regulates various functions of glycoproteins. N-Acetylglucosaminyltransferase V (GnT-V) is a GlcNAc transferase that acts on N-glycans and the GnT-V-producing branch is highly related to cancer progression. This indicates that specific GnT-V inhibitors may be drug candidates for cancer treatment. To design novel GnT-V inhibitors, we focused on the unique and weak recognition of the donor substrate UDP-GlcNAc by GnT-V. On the basis of the catalytic pocket structure, we hypothesized that UDP-GlcNAc analogs with increasing hydrophobicity may be GnT-V inhibitors.

METHODS

We chemically synthesized 10 UDP-GlcNAc analogs in which one or two phosphate groups were replaced with hydrophobic groups. To test these compounds, we set up an HPLC-based enzyme assay system for all N-glycan-branching GlcNAc transferases in which GnT-I-V activity was measured using purified truncated enzymes. Using this system, we assessed the inhibitory effects of the synthesized compounds on GnT-V and their specificity.

RESULTS

Several UDP-GlcNAc analogs inhibited GnT-V activity, although the inhibition potency was modest. Compared with other GnTs, these compounds showed a preference for GnT-V, which suggested that GnT-V was relatively tolerant of hydrophobicity in the donor substrate. Docking models of the inhibitory compounds with GnT-V suggested the mechanisms of how these compounds interacted with GnT-V and inhibited its action.

CONCLUSIONS

Chemical modification of the donor substrate may be a promising strategy to develop selective inhibitors of GnT-V.

GENERAL SIGNIFICANCE

Our findings provide new insights into the design of GnT inhibitors and how GnTs recognize the donor substrate.

N-acetylglucosaminyltransferase-V requires a specific noncatalytic luminal domain for its activity toward glycoprotein substrates

N-acetylglucosaminyltransferase-V (GnT-V or MGAT5) catalyzes the formation of an N-glycan β1,6-GlcNAc branch on selective target proteins in the Golgi apparatus and is involved in cancer malignancy and autoimmune disease etiology. Several three-dimensional structures of GnT-V were recently solved, and the recognition mechanism of the oligosaccharide substrate was clarified. However, it is still unclear how GnT-V selectively acts on glycoprotein substrates. In this study, we focused on an uncharacterized domain at the N-terminal side of the luminal region (N domain) of GnT-V, which was previously identified in a crystal structure, and aimed to reveal its role in GnT-V action. Using lectin blotting and fluorescence assisted cell sorting analysis, we found that a GnT-VΔN mutant lacking the N domain showed impaired biosynthetic activity in cells, indicating that the N domain is required for efficient glycosylation. To clarify this mechanism, we measured the in vitro activity of purified GnT-VΔN toward various kinds of substrates (oligosaccharide, glycohexapeptide, and glycoprotein) using HPLC and a UDP-Glo assay. Surprisingly, GnT-VΔN showed substantially reduced activity toward the glycoprotein substrates, whereas it almost fully maintained its activity toward the oligosaccharides and the glycopeptide substrates. Finally, docking models of GnT-V with substrate glycoproteins suggested that the N domain could interact with the substrate polypeptide directly. Our findings suggest that the N domain of GnT-V plays a critical role in the recognition of glycoprotein substrates, providing new insights into the mechanism of substrate-selective biosynthesis of N-glycans.

Roles of Integrins in Gastrointestinal Cancer Metastasis

Integrins are a large family of heterodimeric transmembrane receptors which mediate cell adhesion and transmit signals to the cell interior. The mechanistic roles of integrins have long been an enigma in cancer, given its complexity in regulating different cellular behaviors. Recently, however, increasing research is providing new insights into its function and the underlying mechanisms, which collectively include the influences of altered integrin expression on the aberrant signaling pathways and cancer progression. Many studies have also demonstrated the potentiality of integrins as therapeutic targets in cancer treatment. In this review, we have summarized these recent reports and put a particular emphasis on the dysregulated expression of integrins and how they regulate related signaling pathways to facilitate the metastatic progression of gastrointestinal cancer, including gastric cancer (GC) and colorectal cancer (CRC), which will address the crucial roles of integrins in gastrointestinal cancer.

Clinical importance of high-mannose, fucosylated and complex N-glycans in breast cancermetastasis

BACKGROUND. Although aberrant glycosylation is recognized as a hallmark of cancer, glycosylation in clinical breast cancer (BC) metastasis has not yet been studied. While preclinical studies show that the glycocalyx coating of cancer cells is involved in adhesion, migration, and metastasis, glycosylation changes from primary tumor (PT) to various metastatic sites remain unknown in patients.

METHODS. We investigated N-glycosylation profiles in 17 metastatic BC patients from our rapid autopsy program. Primary breast tumor, lymph node metastases, multiple systemic metastases, and various normal tissue cores from each patient were arranged on unique single-patient tissue microarrays (TMAs). We performed mass spectrometry imaging (MSI) combined with extensive pathology annotation of these TMAs, and this process enabled spatially differentiated cell-based analysis of N-glycosylation patterns in metastatic BC.

RESULTS. N-glycan abundance increased during metastatic progression independently of BC subtype and treatment regimen, with high-mannose glycans most frequently elevated in BC metastases, followed by fucosylated and complex glycans. Bone metastasis, however, displayed increased core-fucosylation and decreased high-mannose glycans. Consistently, N-glycosylated proteins and N-glycan biosynthesis genes were differentially expressed during metastatic BC progression, with reduced expression of mannose-trimming enzymes and with elevated EpCAM, N-glycan branching, and sialyation enzymes in BC metastases versus PT.

CONCLUSION. We show in patients that N-glycosylation of breast cancer cells undergoing metastasis occurs in a metastatic site–specific manner, supporting the clinical importance of high-mannose, fucosylated, and complex N-glycans as future diagnostic markers and therapeutic targets in metastatic BC.

FUNDING. NIH grants R01CA213428, R01CA213492, R01CA264901, T32CA193145, Dutch Province Limburg “LINK”, European Union ERA-NET TRANSCAN2-643638.

Peptide Sequence Mapping around Bisecting GlcNAc-Bearing N-Glycans in Mouse Brain

N-glycosylation is essential for many biological processes in mammals. A variety of N-glycan structures exist, of which, the formation of bisecting N-acetylglucosamine (GlcNAc) is catalyzed by N-acetylglucosaminyltransferase-III (GnT-III, encoded by the Mgat3 gene). We previously identified various bisecting GlcNAc-modified proteins involved in Alzheimer's disease and cancer. However, the mechanisms by which GnT-III acts on the target proteins are unknown. Here, we performed comparative glycoproteomic analyses using brain membranes of wild type (WT) and Mgat3-deficient mice. Target glycoproteins of GnT-III were enriched with E4-phytohemagglutinin (PHA) lectin, which recognizes bisecting GlcNAc, and analyzed by liquid chromatograph-mass spectrometry. We identified 32 N-glycosylation sites (Asn-Xaa-Ser/Thr, Xaa ≠ Pro) that were modified with bisecting GlcNAc. Sequence alignment of identified N-glycosylation sites that displayed bisecting GlcNAc suggested that GnT-III does not recognize a specific primary amino acid sequence. The molecular modeling of GluA1 as one of the good cell surface substrates for GnT-III in the brain, indicated that GnT-III acts on N-glycosylation sites located in a highly flexible and mobile loop of GluA1. These results suggest that the action of GnT-III is partially affected by the tertiary structure of target proteins, which can accommodate bisecting GlcNAc that generates a bulky flipped-back conformation of the modified glycans.

N-Glycomic Signature of Stage II Colorectal Cancer and Its Association With the Tumor Microenvironment

The choice for adjuvant chemotherapy in stage II colorectal cancer is controversial as many patients are cured by surgery alone and it is difficult to identify patients with high risk of recurrence of the disease. There is a need for better stratification of this group of patients. Mass spectrometry imaging could identify patients at risk. We report here the N-glycosylation signatures of the different cell populations in a group of stage II colorectal cancer tissue samples. The cancer cells, compared with normal epithelial cells, have increased levels of sialylation and high-mannose glycans, as well as decreased levels of fucosylation and highly branched N-glycans. When looking at the interface between cancer and its microenvironment, it seems that the cancer N-glycosylation signature spreads into the surrounding stroma at the invasive front of the tumor. This finding was more outspoken in patients with a worse outcome within this sample group.

Golgi α1,2-mannosidase I induces clustering and compartmentalization of CD147 during epithelial cell migration

CD147 is a widely expressed matrix metalloproteinase inducer involved in the regulation of cell migration. The high glycosylation and ability to undergo oligomerization have been linked to CD147 function, yet there is limited understanding on the molecular mechanisms behind these processes. The current study demonstrates that the expression of Golgi α1,2-mannosidase I is key to maintaining the cell surface organization of CD147 during cell migration. Using an in vitro model of stratified human corneal epithelial wound healing, we show that CD147 is clustered within lateral plasma membranes at the leading edge of adjacent migrating cells. This localization correlates with a surge in matrix metalloproteinase activity and an increase in the expression of α1,2-mannosidase subtype IC (MAN1C1). Global inhibition of α1,2-mannosidase I activity with deoxymannojirimycin markedly attenuates the glycosylation of CD147 and disrupts its surface distribution at the leading edge, concomitantly reducing the expression of matrix metalloproteinase-9. Likewise, treatment with deoxymannojirimycin or siRNA-mediated knockdown of MAN1C1 impairs the ability of the carbohydrate-binding protein galectin-3 to stimulate CD147 clustering in unwounded cells. We conclude that the mannose-trimming activity of α1,2-mannosidase I coordinates the clustering and compartmentalization of CD147 that follows an epithelial injury.

Bisecting GlcNAc modification diminishes the pro-metastatic functions of small extracellular vesicles from breast cancer cells

Small extracellular vesicles (sEVs) are enriched in glycoconjugates and display specific glycosignatures. Aberrant expression of surface glycoconjugates is closely correlated with cancer progression and metastasis. The essential functions of glycoconjugates in sEVs are poorly understood. In this study, we observed significantly reduced levels of bisecting GlcNAc in breast cancer. Introduction of bisecting GlcNAc into breast cancer cells altered the bisecting GlcNAc status on sEVs, and sEVs with diverse bisecting GlcNAc showed differing functions on recipient cells. Carcinogenesis and metastasis of recipient cells were enhanced by sEVs with low bisecting GlcNAc, and the pro‐metastatic functions of sEVs was diminished by high bisecting GlcNAc modification. We further identified vesicular integrin β1 as a target protein bearing bisecting GlcNAc. Metastasis of recipient cells was strongly suppressed by high bisecting GlcNAc levels on vesicular β1. Our findings demonstrate the important roles of glycoconjugates on sEVs. Modification of sEV glycosylation may contribute to development of novel targets in breast cancer therapy.

Recognition of glycan and protein substrates by N-acetylglucosaminyltransferase-V

BACKGROUND

N-Glycosylation is crucial for protein folding, trafficking, and functions. N-Glycans have a different number of N-acetylglucosamine (GlcNAc) branches in a protein-selective manner, and the β1,6-linked GlcNAc branch on specific proteins produced by N-acetylglucosaminyltransferase-V (GnT-V or MGAT5) promotes cancer malignancy. However, little is known about how GnT-V acts on specific target proteins.

METHODS

Based on our structural model, we hypothesized that GnT-V interacts with the N-glycan core or polypeptide moiety as well as the accepter site of N-glycan. To explore this possibility, we selected four candidate residues involved in the interaction with the glycan core or surrounding amino acids, created point mutants of these residues, and examined the in vitro and in vivo activities of the mutants.

RESULTS

Our in vitro enzyme assays using various types of substrates including oligosaccharides and glycoproteins revealed that the V354N mutant had dramatically reduced activity for all tested substrates with an altered substrate preference and that K361A had reduced activity for an oligosaccharide with asparagine (Asn), but not a shorter oligosaccharide without the reducing end of GlcNAc and Asn. These results suggest that V354 and K361 are involved in the recognition of N-glycan core and surrounding amino acids. We further performed rescue experiments using GnT-V knockout HeLa cells and confirmed the importance of these residues for modifications of glycoproteins in cells.

CONCLUSIONS

We identified several residues involved in the action of GnT-V toward N-glycan cores and surrounding amino acids.

GENERAL SIGNIFICANCE

Our data provide new insights into how GnT-V recognizes glycoproteins.

Suppression of G6PD induces the expression and bisecting GlcNAc-branched N-glycosylation of E-Cadherin to block epithelial-mesenchymal transition and lymphatic metastasis

Background

As the rate-limit enzyme of the pentose phosphate pathway, glucose-6-phosphate dehydrogenase (G6PD) plays important roles in tumour progression, but the exact mechanism through which G6PD controls cancer metastasis remains unclear.

Methods

G6PD expression in resected oral squamous cell carcinoma (OSCC) samples was analysed by immunohistochemistry. The effects and mechanism of G6PD suppression on OSCC cell lines were measured by transwell assay, wound healing assay, western and lectin blot, mass spectrometer analysis, ChIP-PCR, and luciferase reporter assay. BALB/c-nude mice were used to establish orthotopic xenograft model.

Results

G6PD expression in the tumours of 105 OSCC patients was associated with lymphatic metastasis and prognosis. In vitro cellular study suggested that G6PD suppression impaired cell migration, invasion, and epithelial-mesenchymal transition. Furtherly, G6PD knockdown activated the JNK pathway, which then blocked the AKT/GSK-3β/Snail axis to induce E-Cadherin expression and transcriptionally regulated MGAT3 expression to promote bisecting GlcNAc-branched N-glycosylation of E-Cadherin. An orthotopic xenograft model further confirmed that dehydroepiandrosterone reduced lymphatic metastatic rate of OSCC, which was partially reversed by JNK inhibition.

Conclusions

Suppression of G6PD promoted the expression and bisecting GlcNAc-branched N-glycosylation of E-Cadherin via activating the JNK pathway, which thus acted on OSCC metastasis.

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.

β4GALT1 controls β1 integrin function to govern thrombopoiesis and hematopoietic stem cell homeostasis

Glycosylation is critical to megakaryocyte (MK) and thrombopoiesis in the context of gene mutations that affect sialylation and galactosylation. Here, we identify the conserved B4galt1 gene as a critical regulator of thrombopoiesis in MKs. β4GalT1 deficiency increases the number of fully differentiated MKs. However, the resulting lack of glycosylation enhances β1 integrin signaling leading to dysplastic MKs with severely impaired demarcation system formation and thrombopoiesis. Platelets lacking β4GalT1 adhere avidly to β1 integrin ligands laminin, fibronectin, and collagen, while other platelet functions are normal. Impaired thrombopoiesis leads to increased plasma thrombopoietin (TPO) levels and perturbed hematopoietic stem cells (HSCs). Remarkably, β1 integrin deletion, specifically in MKs, restores thrombopoiesis. TPO and CXCL12 regulate β4GalT1 in the MK lineage. Thus, our findings establish a non-redundant role for β4GalT1 in the regulation of β1 integrin function and signaling during thrombopoiesis. Defective thrombopoiesis and lack of β4GalT1 further affect HSC homeostasis.

Identification of the minimal N-glycosylation on integrin α5β1 required for its inhibitory effect on EGFR signaling and cell proliferation

The N-glycosylation of integrin α5β1 is involved in multiple cell biological functions. Our group previously reported that the N-glycosylation of the Calf-1,2 domain on α5 subunit (S3-5,10-14) was important for its inhibitory effect on EGFR signaling through regulating α5-EGFR complex formation. In this follow-up study, we provide evidence that the N-glycosylation on integrin β1 subunit suppress cell growth by promoting its association with EGFR under fibronectin (FN)-coated conditions. Expression of wild-type (WT) β1, but not the N-glycosylation mutant S4-6 β1, which contains fewer N-glycans, inhibited EGFR signaling and cell proliferation after cell adhesion to FN. Furthermore, consistent restoration of the N-glycans on sites 1-3 of β1 reinstated the inhibitory effects. Mechanistically, the N-glycosylation mutant of β1 (S4-6+1-3) inhibited the EGFR response upon EGF stimulation via facilitating the α5β1-EGFR complex formation. Moreover, we identified the N-glycosylation of sites 10-14 on α5 and 1-3 on β1 were most important for EGFR signaling. Taken together, these data indicate that α5^S3-5+10-14β1^S4-6+1-3 mutant represents the minimal N-glycosylation required for its regulation on EGFR signaling and cell proliferation, providing a plausible mechanism for the crosstalk between with α5β1 and EGFR.

Exploring serum and immunoglobulin G N-glycome as diagnostic biomarkers for early detection of breast cancer in Ethiopian women

BACKGROUND

Alterations in protein glycosylation patterns have potentially been targeted for biomarker discovery in a wide range of diseases including cancer. Although there have been improvements in patient diagnosis and survival for breast cancer (BC), there is no clinically validated serum biomarker for its early diagnosis. Here, we profiled whole serum and purified Immunoglobulin G (IgG) fraction N-glycome towards identification of non-invasive glycan markers of BC.

METHODS

We employed a comprehensive glycomics approach by integrating glycoblotting-based glycan purification with MALDI-TOF/MS based quantitative analysis. Sera of BC patients belonging to stages I-IV and normal controls (NC) were collected from Ethiopian women during 2015-2016. IgG was purified by affinity chromatography using protein G spin plate and further subjected to glycoblotting for glycan release. Mass spectral data were further processed and evaluated rigorously, using various bioinformatics and statistical tools.

RESULTS

Out of 35 N-glycans that were significantly up-regulated in the sera of all BC patients compared to the NC, 17 complex type N-glycans showed profound expression abundance and diagnostic potential (AUC = 0.8-1) for the early stage (I and II) BC patients. Most of these glycans were core-fucosylated, multiply branched and sialylated structures, whose abundance has been strongly associated with greater invasive and metastatic potential of cancer. N-glycans quantified form IgG confirmed their abundance in BC patients, of which two core-fucosylated and agalactosylated glycans (m/z 1591, 1794) could specifically distinguish (AUC = 0.944 and 0.921, p ≤ 0.001) stage II patients from NC. Abundance of such structural features in IgG is associated with a decrease in its immunosuppressive potential towards tumor cells, which in part may correlate with the aggressive nature of BC commonly noticed in black population.

CONCLUSIONS

Our comprehensive study has addressed for the first time both whole serum and IgG N-glycosylation signatures of native black women suffering from BC and revealed novel glyco-biomarkers with marked overexpression and distinguishing ability at early stage patients. Further studies on direct identification of the intact glycoproteins using a glycoprteomics approach will provide a deeper understanding of specific biomarkers towards their clinical utility.

Genome-Wide DNA Methylome and Transcriptome Analysis of Porcine Intestinal Epithelial Cells upon Deoxynivalenol Exposure

Deoxynivalenol (DON) is a type of mycotoxin that is disruptive to intestinal and immune systems. To better understand the molecular effects of DON exposure, we performed genome-wide comparisons of DNA methylation and gene expression from porcine intestinal epithelial cell IPEC-J2 upon DON exposure using reduced representation bisulfite sequencing and RNA-seq technologies. We characterized the methylation pattern changes and found 3030 differentially methylated regions. Moreover, 3226 genes showing differential expression were enriched in pathways of protein and nucleic acid synthesis and ribosome biogenesis. Integrative analysis identified 29 genes showing inverse correlations between promoter methylation and expression. Altered DNA methylation and expression of various genes suggested their roles and potential functional interactions upon DON exposure. Our data provided new insights into epigenetic and transcriptomic alterations of intestinal epithelial cells upon DON exposure and may advance the identification of biomarkers and drug targets for predicting and controlling the toxic effects of this common mycotoxin.

Recognition of Bisecting N-Glycans on Intact Glycopeptides by Two Characteristic Ions in Tandem Mass Spectra

Bisecting N-glycan represents one of the most important modifications to the N-glycan core, and it is involved in various biological processes. Despite many studies on the biological roles of bisecting N-glycans, current approaches for bisecting N-glycan analysis mainly rely on the use of the lectin PHA-E, which are of low specificity and sensitivity. Here, we describe a straightforward method for the recognition of bisecting N-glycans on intact glycopeptides using two characteristic Y ions [peptide+HexNAc₃Hex₁] and [peptide+HexNAc₃Hex₁Fuc₁] in low energy fragmented MS/MS spectra under higher energy collisional dissociation (HCD) mode. The critical aspect of the method is the combination use of low energy HCD fragmentation and intact glycopeptide analysis. With samples from rat renal tissues, we determined the optimal fragmentation energies and analyzed the influence of core fucosylation on the intensity of the [peptide+HexNAc₃Hex₁] ion. Using the method, we identified 183 intact glycopeptides with bisecting N-glycans and investigated the primary bisecting N-glycan structures and the possible biological roles of these identified proteins.

Aberrant glycosylation and cancer biomarker discovery: a promising and thorny journey

Glycosylation is among the most important post-translational modifications for proteins and is of intrinsic complex character compared with DNAs and naked proteins. Indeed, over 50%-70% of proteins in circulation are glycosylated, and the "sweet attachments" have versatile structural and functional implications. Both the configuration and composition of the attached glycans affect the biological activities of consensus proteins significantly. Glycosylation is generated by complex biosynthetic pathways comprising hundreds of glycosyltransferases, glycosidases, transcriptional factors, transporters and the protein backbone. In addition, lack of direct genetic templates and glyco-specific antibodies such as those commonly used in DNA amplification and protein capture makes research on glycans and glycoproteins even more difficult, thus resulting in sparse knowledge on the pathophysiological implications of glycosylation. Fortunately, cutting-edge technologies have afforded new opportunities and approaches for investigating cancer-related glycosylation. Thus, glycans as well as aberrantly glycosylated protein-based cancer biomarkers have been increasingly recognized. This mini-review highlights the most recent developments in glyco-biomarker studies in an effort to discover clinically relevant cancer biomarkers using advanced analytical methodologies such as mass spectrometry, high-performance liquid chromatographic/ultra-performance liquid chromatography, capillary electrophoresis, and lectin-based technologies. Recent clinical-centered glycobiological studies focused on determining the regulatory mechanisms and the relation with diagnostics, prognostics and even therapeutics are also summarized. These studies indicate that glycomics is a treasure waiting to be mined where the growth of cancer-related glycomics and glycoproteomics is the next great challenge after genomics and proteomics.

Cell Surface N-Glycans Influence Electrophysiological Properties and Fate Potential of Neural Stem Cells

Understanding the cellular properties controlling neural stem and progenitor cell (NSPC) fate choice will improve their therapeutic potential. The electrophysiological measure whole-cell membrane capacitance reflects fate bias in the neural lineage but the cellular properties underlying membrane capacitance are poorly understood. We tested the hypothesis that cell surface carbohydrates contribute to NSPC membrane capacitance and fate. We found NSPCs differing in fate potential express distinct patterns of glycosylation enzymes. Screening several glycosylation pathways revealed that the one forming highly branched N-glycans differs between neurogenic and astrogenic populations of cells in vitro and in vivo. Enhancing highly branched N-glycans on NSPCs significantly increases membrane capacitance and leads to the generation of more astrocytes at the expense of neurons with no effect on cell size, viability, or proliferation. These data identify the N-glycan branching pathway as a significant regulator of membrane capacitance and fate choice in the neural lineage.

Structure and mechanism of cancer-associated N-acetylglucosaminyltransferase-V

N-acetylglucosaminyltransferase-V (GnT-V) alters the structure of specific N-glycans by modifying α1-6-linked mannose with a β1-6-linked N-acetylglucosamine branch. β1-6 branch formation on cell surface receptors accelerates cancer metastasis, making GnT-V a promising target for drug development. However, the molecular basis of GnT-V's catalytic mechanism and substrate specificity are not fully understood. Here, we report crystal structures of human GnT-V luminal domain with a substrate analog. GnT-V luminal domain is composed of a GT-B fold and two accessary domains. Interestingly, two aromatic rings sandwich the α1-6 branch of the acceptor N-glycan and restrain the global conformation, partly explaining the fine branch specificity of GnT-V. In addition, interaction of the substrate N-glycoprotein with GnT-V likely contributes to protein-selective and site-specific glycan modification. In summary, the acceptor-GnT-V complex structure suggests a catalytic mechanism, explains the previously observed inhibition of GnT-V by branching enzyme GnT-III, and provides a basis for the rational design of drugs targeting N-glycan branching.

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.

Expression of N-Acetylglucosaminyltransferase III Promotes Trophoblast Invasion and Migration in Early Human Placenta

INTRODUCTION

Trophoblast migration and invasion at the maternal-fetal interface are crucial events for normal placentation and successful pregnancy. This progress is well controlled by many placenta-specific factors. Inadequate trophoblast invasion results in poor placenta plantation or even complications such as preeclampsia. It has been shown that N-acetylglucosaminyltransferase III (GnT-III) participates in tumor invasion and metastasis as a suppressor; however, the expression of GnT-III and its role in normal pregnancy is unclear. Our objective was to characterize GnT-III expression and function during placental development and identify the underlying mechanisms.

METHODS

The expression of GnT-III in human placental tissue from the first trimester was determined by immunohistochemistry. The HTR8/SVneo cell line was used to investigate the effects of GnT-III on proliferation, apoptosis, migration/invasion, matrix metalloproteinase (MMP) 2/9 activity, and the expression of the tissue inhibitor of metalloproteinase (TIMP) 1/2 using cell 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assays, flow cytometric analysis, transwell migration/invasion assays, gelatin zymography, and Western blot, respectively. Moreover, a placental villous explant model was employed to determine its functions in placentation.

RESULTS

In the first-trimester placental tissue, GnT-III was localized within the cytotrophoblast, the syncytiotrophoblast and the trophoblast columns of human placental villi, decidual cells, and some extravillous cells in the maternal decidua. GnT-III silencing significantly inhibited HTR8/SVneo cell invasion and migration as well as extravillous explant outgrowth. The application of GnT-III siRNA significantly attenuated MMP2/9 activity and increased TIMP1/2 expression.

DISCUSSION AND CONCLUSION

GnT-III is expressed in trophoblasts during normal human pregnancy and is involved in regulating trophoblast function.

Lectin from Sambucus sieboldiana abrogates the anoikis resistance of colon cancer cells conferred by N-acetylglucosaminyltransferase V during hematogenous metastasis

Anoikis is a form of anchorage-dependent apoptosis, and cancer cells adopt anokis-resistance molecular machinery to conduct metastasis. Here, we report that N-acetylglucosaminyltransferase V gene expression confers anoikis resistance during cancer progression. Overexpression of N-acetylglucosaminyltransferase V protected detached cancer cells from apoptotic death, and suppression or knockout of the gene sensitized cancer cells to the apoptotic death. The gene expression also stimulated anchorage-dependent as well as anchorage-independent colony formation of cancer cells following anoikis stress treatments. Importantly, treatment with the lectin from Sambucus sieboldiana significantly sensitized anoikis-induced cancer cell deaths in vitro as well as in vivo. We propose that the lectin alone or an engineered form could offer a new therapeutic treatment option for cancer patients with advanced tumors.

The glycomic effect of N-acetylglucosaminyltransferase III overexpression in metastatic melanoma cells. GnT-III modifies highly branched N-glycans

N-acetylglucosaminyltransferase III (GnT-III) is known to catalyze N-glycan "bisection" and thereby modulate the formation of highly branched complex structures within the Golgi apparatus. While active, it inhibits the action of other GlcNAc transferases such as GnT-IV and GnT-V. Moreover, GnT-III is considered as an inhibitor of the metastatic potential of cancer cells both in vitro and in vivo. However, the effects of GnT-III may be more diverse and depend on the cellular context. We describe the detailed glycomic analysis of the effect of GnT-III overexpression in WM266-4-GnT-III metastatic melanoma cells. We used MALDI-TOF and ESI-ion-trap-MS/MS together with HILIC-HPLC of 2-AA labeled N-glycans to study the N-glycome of membrane-attached and secreted proteins. We found that the overexpression of GnT-III in melanoma leads to the modification of a broad range of N-glycan types by the introduction of the "bisecting" GlcNAc residue with highly branched complex structures among them. The presence of these unusual complex N-glycans resulted in stronger interactions of cellular glycoproteins with the PHA-L. Based on the data presented here we conclude that elevated activity of GnT-III in cancer cells does not necessarily lead to a total abrogation of the formation of highly branched glycans. In addition, the modification of pre-existing N-glycans by the introduction of "bisecting" GlcNAc can modulate their capacity to interact with carbohydrate-binding proteins such as plant lectins. Our results suggest further studies on the biological function of "bisected" oligosaccharides in cancer cell biology and their interactions with carbohydrate-binding proteins.

β4-Integrin/PI3K Signaling Promotes Tumor Progression through the Galectin-3-N-Glycan Complex

Malignant transformation is associated with aberrant N-glycosylation, but the role of protein N-glycosylation in cancer progression remains poorly defined. β4-integrin is a major carrier of N-glycans and is associated with poor prognosis, tumorigenesis, and metastasis. Here, N-glycosylation of β4-integrin contributes to the activation of signaling pathways that promote β4-dependent tumor development and progression. Increased expression of β1,6GlcNAc-branched N-glycans was found to be colocalized with β4-integrin in human cutaneous squamous cell carcinoma tissues, and that the β1,6GlcNAc residue was abundant on β4-integrin in transformed keratinocytes. Interruption of β1,6GlcNAc-branching formation on β4-integrin with the introduction of bisecting GlcNAc by N-acetylglucosaminyltransferase III overexpression was correlated with suppression of cancer cell migration and tumorigenesis. N-Glycan deletion on β4-integrin impaired β4-dependent cancer cell migration, invasion, and growth in vitro and diminished tumorigenesis and proliferation in vivo The reduced abilities of β4-integrin were accompanied with decreased phosphoinositol-3 kinase (PI3K)/Akt signals and were restored by the overexpression of the constitutively active p110 PI3K subunit. Binding of galectin-3 to β4-integrin via β1,6GlcNAc-branched N-glycans promoted β4-integrin-mediated cancer cell adhesion and migration. In contrast, a neutralizing antibody against galectin-3 attenuated β4-integrin N-glycan-mediated PI3K activation and inhibited the ability of β4-integrin to promote cell motility. Furthermore, galectin-3 knockdown by shRNA suppressed β4-integrin N-glycan-mediated tumorigenesis. These findings provide a novel role for N-glycosylation of β4-integrin in tumor development and progression, and the regulatory mechanism for β4-integrin/PI3K signaling via the galectin-3-N-glycan complex.Implications:N-Glycosylation of β4-integrin plays a functional role in promoting tumor development and progression through PI3K activation via the galectin-3-N-glycan complex. Mol Cancer Res; 16(6); 1024-34. ©2018 AACR.

O-mannosylation and N-glycosylation: two coordinated mechanisms regulating the tumour suppressor functions of E-cadherin in cancer

Dysregulation of tumor suppressor protein E-cadherin is an early molecular event in cancer. O-mannosylation profile of E-cadherin is a newly-described post-translational modification crucial for its adhesive functions in homeostasis. However, the role of O-mannosyl glycans in E-cadherin-mediated cell adhesion in cancer and their interplay with N-glycans remains largely unknown. We herein demonstrated that human gastric carcinomas exhibiting a non-functional E-cadherin display a reduced expression of O-mannosyl glycans concomitantly with increased modification with branched complex N-glycans. Accordingly, overexpression of MGAT5-mediated branched N-glycans both in gastric cancer cells and transgenic mice models led to a significant decrease of O-mannosyl glycans attached to E-cadherin that was associated with impairment of its tumour suppressive functions. Importantly, overexpression of protein O-mannosyltransferase 2 (POMT2) induced a reduced expression of branched N-glycans which led to a protective effect of E-cadherin biological functions. Overall, our results reveal a newly identified mechanism of (dys)regulation of E-cadherin that occur through the interplay between O-mannosylation and N-glycosylation pathway.

The role of N-glycans in colorectal cancer progression: potential biomarkers and therapeutic applications

Changes in glycosylation, which is one of the most common protein post-translational modifications, are considered to be a hallmark of cancer. N-glycans can modulate cell migration, cell-cell adhesion, cell signaling, growth and metastasis. The colorectal cancer (CRC) is a leading cause of cancer-related mortality and the correlation between CRC progression and changes in the pattern of expression of N-glycans is being considered in the search for new biomarkers. Here, we review the role of N-glycans in CRC cell biology. The perspectives on emerging N-glycan-related anticancer therapies, along with new insights and challenges, are also discussed.

Over forty years of bladder cancer glycobiology: Where do glycans stand facing precision oncology?

The high molecular heterogeneity of bladder tumours is responsible for significant variations in disease course, as well as elevated recurrence and progression rates, thereby hampering the introduction of more effective targeted therapeutics. The implementation of precision oncology settings supported by robust molecular models for individualization of patient management is warranted. This effort requires a comprehensive integration of large sets of panomics data that is yet to be fully achieved. Contributing to this goal, over 40 years of bladder cancer glycobiology have disclosed a plethora of cancer-specific glycans and glycoconjugates (glycoproteins, glycolipids, proteoglycans) accompanying disease progressions and dissemination. This review comprehensively addresses the main structural findings in the field and consequent biological and clinical implications. Given the cell surface and secreted nature of these molecules, we further discuss their potential for non-invasive detection and therapeutic development. Moreover, we highlight novel mass-spectrometry-based high-throughput analytical and bioinformatics tools to interrogate the glycome in the postgenomic era. Ultimately, we outline a roadmap to guide future developments in glycomics envisaging clinical implementation.

Contribution of galectin-1, a glycan-binding protein, to gastrointestinal tumor progression

Gastrointestinal cancer is a group of tumors that affect multiple sites of the digestive system, including the stomach, liver, colon and pancreas. These cancers are very aggressive and rapidly metastasize, thus identifying effective targets is crucial for treatment. Galectin-1 (Gal-1) belongs to a family of glycan-binding proteins, or lectins, with the ability to cross-link specific glycoconjugates. A variety of biological activities have been attributed to Gal-1 at different steps of tumor progression. Herein, we summarize the current literature regarding the roles of Gal-1 in gastrointestinal malignancies. Accumulating evidence shows that Gal-1 is drastically up-regulated in human gastric cancer, hepatocellular carcinoma, colorectal cancer and pancreatic ductal adenocarcinoma tissues, both in tumor epithelial and tumor-associated stromal cells. Moreover, Gal-1 makes a crucial contribution to the pathogenesis of gastrointestinal malignancies, favoring tumor development, aggressiveness, metastasis, immunosuppression and angiogenesis. We also highlight that alterations in Gal-1-specific glycoepitopes may be relevant for gastrointestinal cancer progression. Despite the findings obtained so far, further functional studies are still required. Elucidating the precise molecular mechanisms modulated by Gal-1 underlying gastrointestinal tumor progression, might lead to the development of novel Gal-1-based diagnostic methods and/or therapies.

Native glycan fragments detected by MALDI-FT-ICR mass spectrometry imaging impact gastric cancer biology and patient outcome

Glycosylation in cancer is a highly dynamic process that has a significant impact on tumor biology. Further, the attachment of aberrant glycan forms is already considered a hallmark of the disease state. Mass spectrometry has become a prominent approach to analyzing glycoconjugates. Specifically, matrix-assisted laser desorption/ionisation -mass spectrometric imaging (MALDI-MSI) is a powerful technique that combines mass spectrometry with histology and enables the spatially resolved and label-free detection of glycans. The most common approach to the analysis of glycans is the use of mass spectrometry adjunct to PNGase F digestion and other chemical reactions. In the current study, we perform the analysis of formalin-fixed, paraffin-embedded (FFPE) tissues for natively occurring bioactive glycan fragments without prior digestion or chemical reactions using MALDI-FT-ICR-MSI. We examined 106 primary resected gastric cancer patient tissues in a tissue microarray and correlated native-occurring fragments with clinical endpoints, therapeutic targets such as epidermal growth factor receptor (EGFR) and HER2/neu expressions and the proliferation marker MIB1. The detection of a glycosaminoglycan fragment in tumor stroma regions was determined to be an independent prognostic factor for gastric cancer patients. Native glycan fragments were significantly linked to the expression of EGFR, HER2/neu and MIB1. In conclusion, we are the first to report the in situ detection of native-occurring bioactive glycan fragments in FFPE tissues that influence patient outcomes. These findings highlight the significance of glycan fragments in gastric cancer tumor biology and patient outcome.

Roles of Integrin α6β4 Glycosylation in Cancer

Malignant transformation is accompanied with aberrant glycosylation of proteins. Such changes in glycan structure also occur in the integrins, which are a large family of cell surface receptors for the extracellular matrix and play key roles in tumor progression. There is now increasing evidence that glycosylation of integrins affects cellular signaling and interaction with the extracellular matrix, receptor tyrosine kinases, and galectins, thereby regulating cell adhesion, motility, growth, and survival. Integrin α6β4 is a receptor for laminin-332 and the increased expression level is correlated with malignant progression and poor survival in various types of cancers. Recent studies have revealed that integrin α6β4 plays central roles in tumorigenesis and the metastatic process. In this review, we summarize our current understanding of the molecular mechanisms of tumor progression driven by integrin α6β4 and also discuss the modification of glycans on integrin β4 subunit to address the important roles of glycan in integrin-mediated tumor progression.

N-acetylglucosaminyltransferase IVa promotes invasion of choriocarcinoma

Gestational trophoblastic neoplasia (GTN) results from the malignant transformation of placental trophoblasts which secrete human chorionic gonadotropin (hCG) as do normal placenta or hydatidiform mole. N-acetylglucosaminyltransferase IV (GnT-IV) is a glycosyltransferase which catalyses the formation of β1,4GlcNAc branches on the mannose core of N-glycans. Previous studies reported that β1,4GlcNAc branches on hCG were detected in GTN but not in normal pregnancy or hydatidiform mole. The aim of the present study was to understand the role of GnT-IVa in choriocarcinoma and find the target proteins for GnT-IVa glycosylation which contribute to the malignancy of choriocarcinoma. Immunohistochemistry showed that Griffonia simplicifolia lectin-II staining and GnT-IVa staining were intense in trophoblastic cells of invasive mole and choriocarcinoma. We established a choriocarcinoma cell line with GnT-IVa overexpression (Jar-GnT4a), and examined its malignant potential and target proteins for GnT-IVa glycosylation. GnT-IVa overexpression increased the cell migration and invasion (2.5- and 1.4-fold) as well as the ability to adhere to the extracellular matrix (ECM) components, including fibronectin and collagen type I and IV. The tumour formation potential of Jar-GnT4a in mice was significantly higher than that of control (P=0.0407), and the cumulative survival rate of mice with Jar-GnT4a was relatively lower than those with control. Immunoprecipitation studies showed that β1,4GlcNAc branches of N-glycans on integrin β1 in choriocarcinoma cells were increased by GnT-IVa overexpression. Nano-LC/MS/MS analysis suggested that lysosome-associated membrane glycoprotein 2 (LAMP-2) was a target protein for glycosylation by GnT-IVa. The increase in β1,4GlcNAc branches on LAMP-2 by GnT-IVa overexpression was confirmed by lectin blot analysis using whole cell lysate and conditioned medium. Our results suggest that highly branched N-glycans generated by the action of GnT-IVa are present in trophoblastic cells of GTN in proportion to GnT-IVa expression level, and that GnT-IVa may contribute to the malignancy of choriocarcinoma by promoting cell adhesion, migration and invasion through glycosylation of integrin β1 and LAMP-2.

Specific N-glycan alterations are coupled in EMT induced by different density cultivation of MCF 10A epithelial cells

Epithelial-mesenchymal transition (EMT) is a process in tumor progression during which cancer cells undergo dramatic changes acquiring highly invasive properties. In a widespread adoption of TGF-β-induced EMT model, we have previously observed that expression of bisecting GlcNAc on N-glycans was dramatically decreased. Herein, we performed in vitro studies with the MCF10A cell line. In response to low cell density, MCF10A cells suffered spontaneously morphologic and phenotypic EMT-like changes, including elongated spindle shape, extended out from edge of the cell sheet, cytoskeleton reorganization, vimentin and fibronectin up-regulation, catenins redistribution, and cadherin switching. Moreover, these phenotypic changes were associated with specific N-glycan alterations. Interestingly, the amounts of bisecting GlcNAc structure were declined, by contrast, the formation of β1-6 GlcNAc branches were obviously up-regulated during the EMT induced by sparse cell conditions. We further investigated N-glycans on the β1-integrin, which is a good target of some glycosyltransferases. The reactivity with E4-PHA lectin decreased, whereas the staining for L4-PHA lectin, which recognizes branched GlcNAc, increased in sparse cell conditions compared with dense cell conditions. Taken together, these results demonstrated that specific N-glycan alterations are coupled in EMT process and promoted cells migration at a low cell density.

Cadherins Glycans in Cancer: Sweet Players in a Bitter Process

Cadherins are key components in tissue morphogenesis and architecture, contributing to the establishment of cohesive cell adhesion. Reduced cellular adhesiveness as a result of cadherin dysfunction is a defining feature of cancer. During tumor development and progression, major changes in the glycan repertoire of cancer cells take place, affecting the stability, trafficking, and cell-adhesion properties of cadherins. Importantly, the different glycoforms of cadherins are promising biomarkers, with potential clinical application to improve the management of patients, and constitute targets for the development of new therapies. This review discusses the most recent insights on the impact of glycan structure on the regulation of cadherin function in cancer, and provides a perspective on how cadherin glycans constitute tumor biomarkers and potential therapeutic targets.