Preventing E-cadherin aberrant N-glycosylation at Asn-554 improves its critical function in gastric cancer

Structure and function of N-acetylglucosaminyltransferase V (GnT-V)

BACKGROUND

The β1,6-GlcNAc branch in N-glycans, produced by a glycosyltransferase N-acetylglucosaminyltransferase V (GnT-V or MGAT5), is associated with cancer and autoimmune diseases.

SCOPE

Here, we summarize the structure and activity regulation of GnT-V. We also describe the roles of the β1,6-GlcNAc branch on glycoproteins in cells and the phenotypes of Mgat5-deficient mice, focusing on cancer and the immune system.

MAJOR CONCLUSIONS

GnT-V has a unique structure for substrate recognition, and its activity and function are regulated by shedding. The glycans produced by GnT-V play pivotal roles in the differentiation of neural cells, cancer malignancy and immunotherapy, and the development of autoimmune diseases by regulating the functions and cell surface residency of glycoproteins.

GENERAL SIGNIFICANCE

Controlling the expression or activity of GnT-V could be a therapeutic option against cancer and autoimmune diseases. Future work should clarify how GnT-V selectively modifies the specific glycoproteins or N-glycosylation sites in vivo.

Insights into the role of glycosyltransferase in the targeted treatment of gastric cancer

Gastric cancer is a remarkably heterogeneous tumor. Despite some advances in the diagnosis and treatment of gastric cancer in recent years, the precise treatment and curative outcomes remain unsatisfactory. Poor prognosis continues to pose a major challenge in gastric cancer. Therefore, it is imperative to identify effective targets to improve the treatment and prognosis of gastric cancer patients. It should be noted that glycosylation, a novel form of posttranslational modification, is a process capable of regulating protein function and influencing cellular activities. Currently, numerous studies have shown that glycosylation plays vital roles in the occurrence and progression of gastric cancer. As crucial enzymes that regulate glycan synthesis in glycosylation processes, glycosyltransferases are potential targets for treating GC. Hence, investigating the regulation of glycosyltransferases and the expression of associated proteins in gastric cancer cells is highly important. In this review, the related glycosyltransferases and their related signaling pathways in gastric cancer, as well as the existing inhibitors of glycosyltransferases, provide more possibilities for targeted therapies for gastric cancer.

Golgi apparatus targeted therapy in cancer: Are we there yet?

Membrane trafficking within the Golgi apparatus plays a pivotal role in the intracellular transportation of lipids and proteins. Dysregulation of this process can give rise to various pathological manifestations, including cancer. Exploiting Golgi defects, cancer cells capitalise on aberrant membrane trafficking to facilitate signal transduction, proliferation, invasion, immune modulation, angiogenesis, and metastasis. Despite the identification of several molecular signalling pathways associated with Golgi abnormalities, there remains a lack of approved drugs specifically targeting cancer cells through the manipulation of the Golgi apparatus. In the initial section of this comprehensive review, the focus is directed towards delineating the abnormal Golgi genes and proteins implicated in carcinogenesis. Subsequently, a thorough examination is conducted on the impact of these variations on Golgi function, encompassing aspects such as vesicular trafficking, glycosylation, autophagy, oxidative mechanisms, and pH alterations. Lastly, the review provides a current update on promising Golgi apparatus-targeted inhibitors undergoing preclinical and/or clinical trials, offering insights into their potential as therapeutic interventions. Significantly more effort is required to advance these potential inhibitors to benefit patients in clinical settings.

Emerging methods and techniques for cancer biomarker discovery

Modern cancer research depends heavily on the identification and validation of biomarkers because they provide important information about the diagnosis, prognosis, and response to treatment of the cancer. This review will provide a comprehensive overview of cancer biomarkers, including their development phases and recent breakthroughs in transcriptomics and computational techniques for detecting these biomarkers. Blood-based biomarkers have great potential for non-invasive tumor dynamics and treatment response monitoring. These include circulating tumor DNA, exosomes, and microRNAs. Comprehensive molecular profiles are provided by multi-omic technologies, which combine proteomics, metabolomics, and genomes to support the identification of biomarkers and the targeting of therapeutic interventions. Genetic changes are detected by next-generation sequencing, and patterns of protein expression are found by protein arrays and mass spectrometry. Tumor heterogeneity and clonal evolution can be understood using metabolic profiling and single-cell studies. It is projected that the use of several biomarkers-genetic, protein, mRNA, microRNA, and DNA profiles, among others-will rise, enabling multi-biomarker analysis and improving individualised treatment plans. Biomarker identification and patient outcome prediction are further improved by developments in AI algorithms and imaging techniques. Robust biomarker validation and reproducibility require cooperation between industry, academia, and doctors. Biomarkers can provide individualized care, meet unmet clinical needs, and enhance patient outcomes despite some obstacles. Precision medicine will continue to take shape as scientific research advances and the integration of biomarkers with cutting-edge technologies continues to offer a more promising future for personalized cancer care.

Regulation of intracellular activity of N-glycan branching enzymes in mammals

Most proteins in the secretory pathway are glycosylated, and N-glycans are estimated to be attached to over 7000 proteins in humans. As structural variation of N-glycans critically regulates the functions of a particular glycoprotein, it is pivotal to understand how structural diversity of N-glycans is generated in cells. One of the major factors conferring structural variation of N-glycans is the variable number of N-acetylglucosamine branches. These branch structures are biosynthesized by dedicated glycosyltransferases, including GnT-III (MGAT3), GnT-IVa (MGAT4A), GnT-IVb (MGAT4B), GnT-V (MGAT5), and GnT-IX (GnT-Vb, MGAT5B). In addition, the presence or absence of core modification of N-glycans, namely, core fucose (included as an N-glycan branch in this manuscript), synthesized by FUT8, also confers large structural variation on N-glycans, thereby crucially regulating many protein-protein interactions. Numerous biochemical and medical studies have revealed that these branch structures are involved in a wide range of physiological and pathological processes. However, the mechanisms regulating the activity of the biosynthetic glycosyltransferases are yet to be fully elucidated. In this review, we summarize the previous findings and recent updates regarding regulation of the activity of these N-glycan branching enzymes. We hope that such information will help readers to develop a comprehensive overview of the complex system regulating mammalian N-glycan maturation.

Decoding the glycoproteome: a new frontier for biomarker discovery in cancer

Cancer early detection and treatment response prediction continue to pose significant challenges. Cancer liquid biopsies focusing on detecting circulating tumor cells (CTCs) and DNA (ctDNA) have shown enormous potential due to their non-invasive nature and the implications in precision cancer management. Recently, liquid biopsy has been further expanded to profile glycoproteins, which are the products of post-translational modifications of proteins and play key roles in both normal and pathological processes, including cancers. The advancements in chemical and mass spectrometry-based technologies and artificial intelligence-based platforms have enabled extensive studies of cancer and organ-specific changes in glycans and glycoproteins through glycomics and glycoproteomics. Glycoproteomic analysis has emerged as a promising tool for biomarker discovery and development in early detection of cancers and prediction of treatment efficacy including response to immunotherapies. These biomarkers could play a crucial role in aiding in early intervention and personalized therapy decisions. In this review, we summarize the significant advance in cancer glycoproteomic biomarker studies and the promise and challenges in integration into clinical practice to improve cancer patient care.

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.

Dynamics and functions of E-cadherin complexes in epithelial cell and tissue morphogenesis

Cell-cell adhesion is at the center of structure and dynamics of epithelial tissue. E-cadherin-catenin complexes mediate Ca2+-dependent trans-homodimerization and constitute the kernel of adherens junctions. Beyond the basic function of cell-cell adhesion, recent progress sheds light the dynamics and interwind interactions of individual E-cadherin-catenin complex with E-cadherin superclusters, contractile actomyosin and mechanics of the cortex and adhesion. The nanoscale architecture of E-cadherin complexes together with cis-interactions and interactions with cortical actomyosin adjust to junctional tension and mechano-transduction by reinforcement or weakening of specific features of the interactions. Although post-translational modifications such as phosphorylation and glycosylation have been implicated, their role for specific aspects of in E-cadherin function has remained unclear. Here, we provide an overview of the E-cadherin complex in epithelial cell and tissue morphogenesis focusing on nanoscale architectures by super-resolution approaches and post-translational modifications from recent, in particular in vivo, studies. Furthermore, we review the computational modelling in E-cadherin complexes and highlight how computational modelling has contributed to a deeper understanding of the E-cadherin complexes.

Decoding TROP2 in breast cancer: significance, clinical implications, and therapeutic advancements

Breast cancer is a heterogeneous disease characterized by distinct molecular subtypes, varied prognoses, and differential treatment responses. Understanding the molecular landscape and identifying therapeutic targets, such as trophoblast cell-surface antigen 2 (TROP2), is vital. TROP2 is notably overexpressed in breast cancer, playing a significant role in tumor growth, invasion, metastasis, and treatment resistance. While significant progress has been made in targeting TROP2 in breast cancer, several challenges and knowledge gaps remain. These challenges include the heterogeneity of TROP2 expression within breast cancer subtypes, resistance to its targeted therapies, potential off-target effects, limited therapeutic agents, and identifying optimal combination treatments. Integrating findings from clinical trials into clinical practice further complicates the landscape. This review article delves deep into TROP2 in breast cancer, highlighting its expression patterns, clinical implications, and therapeutic advancements. By understanding the role of TROP2, we can pave the way for personalized treatments, and transform the landscape of breast cancer care.

Golgi's Role in the Development of Possible New Therapies in Cancer

The Golgi apparatus is an important organelle found in most eukaryotic cells. It plays a vital role in the processing and sorting of proteins, lipids and other cellular components for delivery to their appropriate destinations within the cell or for secretion outside of the cell. The Golgi complex also plays a role in the regulation of protein trafficking, secretion and post-translational modifications, which are significant in the development and progression of cancer. Abnormalities in this organelle have been observed in various types of cancer, although research into chemotherapies that target the Golgi apparatus is still in its early stages. There are a few promising approaches that are being investigated: (1) Targeting the stimulator of interferon genes protein: The STING pathway senses cytosolic DNA and activates several signaling events. It is regulated by numerous post-translational modifications and relies heavily on vesicular trafficking. Based on some observations which state that a decreased STING expression is present in some cancer cells, agonists for the STING pathway have been developed and are currently being tested in clinical trials, showing encouraging results. (2) Targeting glycosylation: Altered glycosylation, which refers to changes in the carbohydrate molecules that are attached to proteins and lipids in cells, is a common feature of cancer cells, and there are several methods that thwart this process. For example, some inhibitors of glycosylation enzymes have been shown to reduce tumor growth and metastasis in preclinical models of cancer. (3) Targeting Golgi trafficking: The Golgi apparatus is responsible for the sorting and trafficking of proteins within the cell, and disrupting this process may be a potential therapeutic approach for cancer. The unconventional protein secretion is a process that occurs in response to stress and does not require the involvement of the Golgi organelles. P53 is the most frequently altered gene in cancer, dysregulating the normal cellular response to DNA damage. The mutant p53 drives indirectly the upregulation of the Golgi reassembly-stacking protein 55kDa (GRASP55). Through the inhibition of this protein in preclinical models, the reduction of the tumoral growth and metastatic capacity have been obtained successfully. This review supports the hypothesis that the Golgi apparatus may be the target of cytostatic treatment, considering its role in the molecular mechanisms of the neoplastic cells.

Aberrant protein glycosylation: Implications on diagnosis and Immunotherapy

Glycosylation-mediated post-translational modification is critical for regulating many fundamental processes like cell division, differentiation, immune response, and cell-to-cell interaction. Alterations in the N-linked or O-linked glycosylation pattern of regulatory proteins like transcription factors or cellular receptors lead to many diseases, including cancer. These alterations give rise to micro- and macro-heterogeneity in tumor cells. Here, we review the role of O- and N-linked glycosylation and its regulatory function in autoimmunity and aberrant glycosylation in cancer. The change in cellular glycome could result from a change in the expression of glycosidases or glycosyltransferases like N-acetyl-glucosaminyl transferase V, FUT8, ST6Gal-I, DPAGT1, etc., impact the glycosylation of target proteins leading to transformation. Moreover, the mutations in glycogenes affect glycosylation patterns on immune cells leading to other related manifestations like pro- or anti-inflammatory effects. In recent years, understanding the glycome to cancer indicates that it can be utilized for both diagnosis/prognosis as well as immunotherapy. Studies involving mass spectrometry of proteome, site- and structure-specific glycoproteomics, or transcriptomics/genomics of patient samples and cancer models revealed the importance of glycosylation homeostasis in cancer biology. The development of emerging technologies, such as the lectin microarray, has facilitated research on the structure and function of glycans and glycosylation. Newly developed devices allow for high-throughput, high-speed, and precise research on aberrant glycosylation. This paper also discusses emerging technologies and clinical applications of glycosylation.

Glucose-mediated N-glycosylation of RPTPα affects its subcellular localization and Src activation

Receptor-type protein tyrosine phosphatase α (RPTPα) is one of the typical PTPs that play indispensable roles in many cellular processes associated with cancers. It has been considered as the most powerful regulatory oncogene for Src activation, however it is unclear how its biological function is regulated by post-translational modifications. Here, we show that the extracellular segment of RPTPα is highly N-glycosylated precisely at N21, N36, N68, N80, N86, N104 and N124 sites. Such N-glycosylation modifications mediated by glucose concentration alter the subcellular localization of RPTPα from Golgi apparatus to plasma membrane, enhance the interaction of RPTPα with Src, which in turn enhances the activation of Src and ultimately promotes tumor development. Our results identified the N-glycosylation modifications of RPTPα, and linked it to glucose starvation and Src activation for promoting tumor development, which provides new evidence for the potential antitumor therapy.

Glycans as shapers of tumour microenvironment: A sweet driver of T-cell-mediated anti-tumour immune response

Essentially all cells are covered with a dense coat of different glycan structures/sugar chains, giving rise to the so-called glycocalyx. Changes in cellular glycosylation are a hallmark of cancer, affecting most of the pathophysiological processes associated with malignant transformation, including tumour immune responses. Glycans are chief macromolecules that define T-cell development, differentiation, fate, activation and signalling. Thus, the diversity of glycans expressed at the surface of T cells constitutes a fundamental molecular interface with the microenvironment by regulating the bilateral interactions between T-cells and cancer cells, fine-tuning the anti-tumour immune response. In this review, we will introduce the power of glycans as orchestrators of T-cell-mediated immune response in physiological conditions and in cancer. We discuss how glycans modulate the glyco-metabolic landscape in the tumour microenvironment, and whether glycans can synergize with immunotherapy as a way of rewiring T-cell effector functions against cancer cells.

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.

Systems-Wide Site-Specific Analysis of Glycoproteins

Glycosylation is one of the most common and complex post-translation modifications that influence the structural and functional properties of proteins. Glycoproteins are highly heterogeneous and exhibit site- and protein-specific expression differences. Mass spectrometry in combination with liquid chromatography has emerged as the most powerful tool for the comprehensive characterization of glycosylation. The analysis of intact glycopeptides has emerged as a promising strategy to analyze glycoproteins for their glycan heterogeneity at both protein- and site-specific levels. Nevertheless, intact glycopeptide characterization is challenging as elucidation of the glycan and peptide moieties requires specific sample preparation workflows that, combined with the tandem mass spectrometry approach, enable the identification of single glycopeptide species. In this chapter, we provide a detailed description of the methods that include procedures for (i) proteolytic digestion using specific proteases, (ii) optional glycopeptide enrichment using hydrophilic interaction liquid chromatography, (iii) nano-LC-MS/MS analysis of glycopeptides, and (iv) data analysis for identification of glycopeptides. Together, our workflow provides a framework for the system-wide site-specific analysis of N- and O-glycopeptides derived from complex biological or clinical samples.

Activation of Laminin γ2 by Helicobacter pylori Promotes Invasion and Survival of Gastric Cancer Cells With E-Cadherin Defects

BACKGROUND

Helicobacter pylori infection induces cellular phenotypes relevant for cancer progression, namely cell motility and invasion. We hypothesized that the extracellular matrix (ECM) could be involved in these deleterious effects.

METHODS

Microarrays were used to uncover ECM interactors in cells infected with H. pylori. LAMC2, encoding laminin γ2, was selected as a candidate gene and its expression was assessed in vitro and in vivo. The role of LAMC2 was investigated by small interference RNA (siRNA) combined with a set of functional assays. Laminin γ2 and E-cadherin expression patterns were evaluated in gastric cancer cases.

RESULTS

Laminin γ2 was found significantly overexpressed in gastric cancer cells infected with H. pylori. This finding was validated in vitro by infection with clinical isolates and in vivo by using gastric biopsies of infected and noninfected individuals. We showed that laminin γ2 overexpression is dependent on the bacterial type IV secretion system and on the CagA. Functionally, laminin γ2 promotes cell invasion and resistance to apoptosis, through modulation of Src, JNK, and AKT activity. These effects were abrogated in cells with functional E-cadherin.

CONCLUSIONS

These data highlight laminin γ2 and its downstream effectors as potential therapeutic targets, and the value of H. pylori eradication to delay gastric cancer onset and progression.

Hereditary Diffuse Gastric Cancer: A 2022 Update

Gastric cancer is ranked fifth among the most commonly diagnosed cancers, and is the fourth leading cause of cancer-related deaths worldwide. The majority of gastric cancers are sporadic, while only a small percentage, less than 1%, are hereditary. Hereditary diffuse gastric cancer (HDGC) is a rare malignancy, characterized by early-onset, highly-penetrant autosomal dominant inheritance mainly of the germline alterations in the E-cadherin gene (CDH1) and β-catenin (CTNNA1). In the present study, we provide an overview on the molecular basis of HDGC and outline the essential elements of genetic counseling and surveillance. We further provide a practical summary of current guidelines on clinical management and treatment of individuals at risk and patients with early disease.

Regulation of multiple dimeric states of E-cadherin by adhesion activating antibodies revealed through Cryo-EM and X-ray crystallography

E-cadherin adhesion is regulated at the cell surface, a process that can be replicated by activating antibodies. We use cryo-electron microscopy (EM) and X-ray crystallography to examine functional states of the cadherin adhesive dimer. This dimer is mediated by N-terminal beta strand-swapping involving Trp2, and forms via a different transient X-dimer intermediate. X-dimers are observed in cryo-EM along with monomers and strand-swap dimers, indicating that X-dimers form stable interactions. A novel EC4-mediated dimer was also observed. Activating Fab binding caused no gross structural changes in E-cadherin monomers, but can facilitate strand swapping. Moreover, activating Fab binding is incompatible with the formation of the X-dimer. Both cryo-EM and X-ray crystallography reveal a distinctive twisted strand-swap dimer conformation caused by an outward shift in the N-terminal beta strand that may represent a strengthened state. Thus, regulation of adhesion involves changes in cadherin dimer configurations.

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.

TMT-Based Multiplexed Quantitation of N-Glycopeptides Reveals Glycoproteome Remodeling Induced by Oncogenic Mutations

Glycoproteomics, or the simultaneous characterization of glycans and their attached peptides, is increasingly being employed to generate catalogs of glycopeptides on a large scale. Nevertheless, quantitative glycoproteomics remains challenging even though isobaric tagging reagents such as tandem mass tags (TMT) are routinely used for quantitative proteomics. Here, we present a workflow that combines the enrichment or fractionation of TMT-labeled glycopeptides with size-exclusion chromatography (SEC) for an in-depth and quantitative analysis of the glycoproteome. We applied this workflow to study the cellular glycoproteome of an isogenic mammary epithelial cell system that recapitulated oncogenic mutations in the PIK3CA gene, which codes for the phosphatidylinositol-3-kinase catalytic subunit. As compared to the parental cells, cells with mutations in exon 9 (E545K) or exon 20 (H1047R) of the PIK3CA gene exhibited site-specific glycosylation alterations in 464 of the 1999 glycopeptides quantified. Our strategy led to the discovery of site-specific glycosylation changes in PIK3CA mutant cells in several important receptors, including cell adhesion proteins such as integrin β-6 and CD166. This study demonstrates that the SEC-based enrichment of glycopeptides is a simple and robust method with minimal sample processing that can easily be coupled with TMT-labeling for the global quantitation of glycopeptides.

Diffuse-type Gastric Cancer

Gastric cancer is the most prevalent malignant tumor in Korea. Histologically, it is often classified into intestinal-type and diffuse-type. Intestinal-type gastric cancer is known to occur mainly from chronic gastritis caused by Helicobacter pylori (H. pylori) through atrophic gastritis and intestinal metaplasia, a precancerous change of the mucosa, whereas diffuse-type gastric cancer is caused by H. pylori infection, wherein active inflammation of the gastric mucosa occurs without precancerous changes in the mucosa. Compared with intestinal-type gastric cancer, it occurs at a young age, there is no difference in male to female ratio, or tends to occur more in women, and is more aggressive than intestinal-type gastric cancer. Intestinal-type gastric cancer is predominant in East Asian populations such as Koreans and Japanese, whereas diffuse-type gastric cancer has more uniform geographic distribution. In the present manuscript, I have reviewed diffuse-type gastric cancer, distinct from intestinal-type gastric cancer.

HER2-CDH1 Interaction via Wnt/B-Catenin Is Associated with Patients' Survival in HER2-Positive Metastatic Gastric Adenocarcinoma

Simple Summary

A deeper understanding of the molecular mechanisms involved in gastric cacner (GC) pathologenesis would help the identification of prognostic biomarkers and the development of new treatments. Human epidermal growth factor receptor 2 (HER2/ErbB2), a membrane-bound receptor of the EGFR family, may be overexpressed in GC. Trastuzumab is a HER2 inhibitor used to treat HER2+ metastatic gastric cancer (mGC). The present study aims to investigate the relationship between CDH1 mRNA expression and HER2-positivity in mGC using a multiplexed gene expression profile in two series of GC patients: 38 HER2+ and HER2- mGC and 36 HER2- GC with and without metastasis. Our results revealed the relationship between CDH1 and HER2 mRNA expression in mGC via the canonical WNT/β-catenin pathway and identified EGF as an independent prognostic biomarker for survival.

Abstract

Trastuzumab is a human epidermal growth factor receptor 2 (HER2) inhibitor used to treat HER2+ metastatic gastric cancer (mGC). The present study aims to investigate the relationship between CDH1 mRNA expression and HER2-positivity in mGC using a multiplexed gene expression profile in two series of gastric cancer (GC): Series 1 (n = 38): HER2+ and HER2- mGC; Series 2 (n = 36) HER2- GC with and without metastasis. To confirm the results, the same expression profiles were analyzed in 354 GC from The Cancer Genome Atlas (TCGA) dataset. The difference in gene expression connected HER2 overexpression with canonical wingless-type (Wnt)/β-catenin pathway and immunohistochemical (IHC) expression loss of E-cadherin (E-CAD). CDH1 mRNA expression was simultaneously associated with the rs16260-A variant and an increase in E-CAD expression. Differences in retinoic acid receptor alfa (RARA), RPL19 (coding for the 60S ribosomal L19 protein), catenin delta 1 (CTNND1), and epidermal growth factor (EGF) mRNA levels—all included in the Wnt/β-catenin pathway—were found associated with overall survival (OS). RARA, CTNND1, and EGF resulted in independent OS prognostic factors. EGF was confirmed as an independent factor along with TNM stage in HER2-overpressed mGC from TCGA collection. Our study highlighted factors involved in the WNT/β-catenin pathway that interconnected E-CAD with HER2 overexpression and patient survival.

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.

Glycomics reveal that ST6GAL1-mediated sialylation regulates uterine lumen closure during implantation

Objectives

Implantation failure is a major cause of prenatal mortality. The uterine lumen closure contributes to embryo adhesion to the uterus, but its underlying mechanisms are largely unknown. Our previous study has reported that endometrial fold extension can lead to uterine lumen closure in pigs. The objective of this study was to reveal molecular mechanisms of the uterine lumen closure by characterizing the molecular basis of the endometrial fold extension during implantation in pigs.

Materials and methods

Uterine and endometrium tissues during implantation were collected in pigs. MALDI‐TOF MS was used to characterize the N‐glycomic profiles. Histochemistry, siRNA transfection, Western blotting, lectin immumoprecipitation, mass spectrometry and assays of wounding healing and cell aggregation were performed to investigate the molecular basis.

Results

We observed that uterine luminal epithelium (LE) migrated collectively during endometrial fold extension. For the first time, we identified a large number of N‐glycan compositions from endometrium during implantation using MALDI‐TOF MS. Notably, the α2,6‐linked sialic acid and ST6GAL1 were highly expressed in uterine LE when the endometrial folds extended greatly. Subsequently, the role of ST6GAL1‐mediated 2,6‐sialylation in collective epithelial migration was demonstrated. Finally, we found that ST6GAL1‐mediated α2,6‐sialylation of E‐cadherin may participate in collective migration of uterine LE.

Conclusions

The study reveals a mechanism of uterine lumen closure by identifying that ST6GAL1‐mediated α2,6‐sialylation of cell adhesion molecules contributes to endometrial fold extension through regulating collective migration of uterine LE.

A novel mechanism for C1GALT1 in the regulation of gastric cancer progression

Background

Gastric cancer (GC) is a highly aggressive and lethal disease around the world. High expression of core 1 β 1, 3-galactosyltransferase 1 (C1GALT1), the primary enzyme responsible for protein O-glycosylation, plays a critical role in gastric carcinogenesis. However, proteins that can be O-glycosylated by C1GALT1 in GC have not been completely elucidated. Also, the mechanism leading to its upregulation in GC is currently unknown.

Results

Using public databases and our patient samples, we confirmed that C1GALT1 expression was upregulated at both the mRNA and protein levels in GC tissues. Elevated expression of C1GALT1 protein was closely associated with advanced TNM stage, lymph node metastasis, tumor recurrence, and poor overall survival. With gain- and loss-of-function approaches, we demonstrated that C1GALT1 promoted GC cell proliferation, migration, and invasion. By employing lectin pull-down assay and mass spectrometry, integrin α5 was identified as a new downstream target of C1GALT1 in GC. C1GALT1 was able to modify O-linked glycosylation on integrin α5 and thereby modulate the activation of the PI3K/AKT pathway. Functional experiments indicated that integrin α5 inhibition could reverse C1GALT1-mediated tumor growth and metastasis both in vitro and in vivo. Moreover, transcription factor SP1 was found to bind to the C1GALT1 promoter region and activated its expression. Further investigation proved that miR-152 negatively regulated C1GALT1 expression by directly binding to its 3′ -UTR.

Conclusions

Our findings uncover a novel mechanism for C1GALT1 in the regulation of GC progression. Thus, C1GALT1 may serve as a promising target for the diagnosis and treatment of GC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-021-00678-2.

VE-cadherin N-glycosylation modified by N-acetylglucosaminyltransferase V regulates VE-cadherin-β-catenin interaction and monocyte adhesion

NEW FINDINGS

What is the central question of this study? Inflammation-induced monocyte adhesion is the initiator of most vascular diseases. The underlying mechanisms that mediate monocyte adhesion remain to be clarified fully. What is the main finding and its importance? N-acetylglucosaminyltransferase V (GnT-V)-mediated N-glycosylation of VE-cadherin regulates the dissociation of the VE-cadherin-β-catenin complex to modulate monocyte adhesion, but GnT-V overexpression cannot rescue monocyte adhesion induced by interleukin-1β. This study clarified the molecular mechanism of VE-cadherin in regulating the monocyte adhesion process.

ABSTRACT

Monocyte adhesion is a crucial step in the initial stage of atherosclerosis, and dysfunction of VE-cadherin has been reported to be involved in this process. Our group previously found that VE-cadherin and its binding protein, β-catenin, were modified by sialylation, and the levels of sialylation were decreased in pro-inflammatory cytokine-treated human umbilical vein EA.hy926 cells. In this study, we confirmed that the sugar chains of VE-cadherin were modified by N-acetylglucosaminyltransferase V (GnT-V). We showed that the levels of GnT-V and β1,6-N-acetylglucosamine on the VE-cadherin were reduced in the presence of interleukin-1β, whereas the level of monocyte transendothelial migration was increased. Moreover, the interaction between VE-cadherin and β-catenin was increased, accompanied by an increased accumulation of degradative VE-cadherin and cytoplasmic β-catenin, indicating impairment of cell-cell junctions after interleukin-1β treatment. Furthermore, GnT-V short hairpin RNA and overexpression analysis confirmed that glycosylation of VE-cadherin was modified by GnT-V in EA.hy926 cells, which contributed to the monocyte-endothelial adhesion process. Taken together, these results suggest that the function of VE-cadherin in facilitating monocyte adhesion might result from the decreasing GnT-V expression and disorder of GnT-V-catalysed N-glycosylation. Our study clarified the molecular mechanism of VE-cadherin in regulation of the monocyte adhesion process and provided new insights into the post-transcriptional modifications of VE-cadherin.

Glycosylation and raft endocytosis in cancer

Changes in glycosylation on proteins or lipids are one of the hallmarks of tumorigenesis. In many cases, it is still not understood how glycan information is translated into biological function. In this review, we discuss at the example of specific cancer-related glycoproteins how their endocytic uptake into eukaryotic cells is tuned by carbohydrate modifications. For this, we not only focus on overall uptake rates, but also illustrate how different uptake processes-dependent or not on the conventional clathrin machinery-are used under given glycosylation conditions. Furthermore, we discuss the role of certain sugar-binding proteins, termed galectins, to tune glycoprotein uptake by inducing their crosslinking into lattices, or by co-clustering them with glycolipids into raft-type membrane nanodomains from which the so-called clathrin-independent carriers (CLICs) are formed for glycoprotein internalization into cells. The latter process has been termed glycolipid-lectin (GL-Lect) hypothesis, which operates in a complementary manner to the clathrin pathway and galectin lattices.

The Repertoire of Glycan Alterations and Glycoproteins in Human Cancers

Cancer as the leading cause of death worldwide has many issues that still need to be addressed. Since the alterations on the glycan compositions or/and structures (i.e., glycosylation, sialylation, and fucosylation) are common features of tumorigenesis, glycomics becomes an emerging field examining the structure and function of glycans. In the past, cancer studies heavily relied on genomics and transcriptomics with relatively little exploration of the glycan alterations and glycoprotein biomarkers among individuals and populations. Since glycosylation of proteins increases their structural complexity by several orders of magnitude, glycome studies resulted in highly dynamic biomarkers that can be evaluated for cancer diagnosis, prognosis, and therapy. Glycome not only integrates our genetic background with past and present environmental factors but also offers a promise of more efficient patient stratification compared with genetic variations. Therefore, studying glycans holds great potential for better diagnostic markers as well as developing more efficient treatment strategies in human cancers. While recent developments in glycomics and associated technologies now offer new possibilities to achieve a high-throughput profiling of glycan diversity, we aim to give an overview of the current status of glycan research and the potential applications of the glycans in the scope of the personalized medicine strategies for cancer.

Changes in Protein Glycosylation in Head and Neck Squamous Cell Carcinoma

Glycosylation is an important posttranslational modification of proteins, and it has a profound influence on diverse life processes. An abnormal polysaccharide structure and mutation of the glycosylation pathway are closely correlated with human cancer progression. Glycoproteins such as EGFR, E-cadherin, CD44, PD-1/PD-L1, B7-H3 and Muc1 play important roles in the progression of head and neck squamous cell carcinoma (HNSCC), and their levels of glycosylation and changes in glycosyl structure are closely linked to HNSCC progression and malignant transformation. The regulation of protein glycosylation in HNSCC provides potential strategies to control cancer stem cell (CSC) subgroup expansion, epithelial-mesenchymal transition (EMT), tumor-related immunity escape and autophagy. Glycoproteins with altered glycosylation can be used as biomarkers for the early diagnosis, monitoring and prognostication of HNSCC. However, the glycobiology of cancer is still a new field that needs to be deeply studied, especially in HNSCC.

N-Glycosylation

N-glycosylation is a highly conserved glycan modification, and more than 7000 proteins are N-glycosylated in humans. N-glycosylation has many biological functions such as protein folding, trafficking, and signal transduction. Thus, glycan modification to proteins is profoundly involved in numerous physiological and pathological processes. The N-glycan precursor is biosynthesized in the endoplasmic reticulum (ER) from dolichol phosphate by sequential enzymatic reactions to generate the dolichol-linked oligosaccharide composed of 14 sugar residues, Glc₃Man₉GlcNAc₂. The oligosaccharide is then en bloc transferred to the consensus sequence N-X-S/T (X represents any amino acid except proline) of nascent proteins. Subsequently, the N-glycosylated nascent proteins enter the folding step, in which N-glycans contribute largely to attaining the correct protein fold by recruiting the lectin-like chaperones, calnexin, and calreticulin. Despite the N-glycan-dependent folding process, some glycoproteins do not fold correctly, and these misfolded glycoproteins are destined to degradation by proteasomes in the cytosol. Properly folded proteins are transported to the Golgi, and N-glycans undergo maturation by the sequential reactions of glycosidases and glycosyltransferases, generating complex-type N-glycans. N-Acetylglucosaminyltransferases (GnT-III, GnT-IV, and GnT-V) produce branched N-glycan structures, affording a higher complexity to N-glycans. In this chapter, we provide an overview of the biosynthetic pathway of N-glycans in the ER and Golgi.

Altered glycosylation in cancer: A promising target for biomarkers and therapeutics

Glycosylation is a well-regulated cell and microenvironment specific post-translational modification. Several glycosyltransferases and glycosidases orchestrate the addition of defined glycan structures on the proteins and lipids. Recent advances and systemic approaches in glycomics have significantly contributed to a better understanding of instrumental roles of glycans in health and diseases. Emerging research evidence recognized aberrantly glycosylated proteins as the modulators of the malignant phenotype of cancer cells. The Cancer Genome Atlas has identified alterations in the expressions of glycosylation-specific genes that are correlated with cancer progression. However, the mechanistic basis remains poorly explored. Recent researches have shown that specific changes in the glycan structures are associated with 'stemness' and epithelial-to-mesenchymal transition of cancer cells. Moreover, epigenetic changes in the glycosylation pattern make the tumor cells capable of escaping immunosurveillance mechanisms. The deciphering roles of glycans in cancer emphasize that glycans can serve as a source for the development of novel clinical biomarkers. The ability of glycans in intervening various stages of tumor progression and the biosynthetic pathways involved in glycan structures constitute a promising target for cancer therapy. Advances in the knowledge of innovative strategies for identifying the mechanisms of glycan-binding proteins are hoped to hold great potential in cancer therapy. This review discusses the fundamental role of glycans in regulating tumorigenesis and tumor progression and provides insights into the influence of glycans in the current tactics of targeted therapies in the clinical setting.

State-of-the-Art Glycomics Technologies in Glycobiotechnology

Glycosylation affects the properties of biologics; thus regulatory bodies classified it as critical quality attribute and force biopharma industry to capture and control it throughout all phases, from R&D till end of product lifetime. The shift from originators to biosimilars further increases importance and extent of glycoanalysis, which thus increases the need for technology platforms enabling reliable high-throughput and in-depth glycan analysis. In this chapter, we will first summarize on established glycoanalytical methods based on liquid chromatography focusing on hydrophilic interaction chromatography, capillary electrophoresis focusing on multiplexed capillary gel electrophoresis, and mass spectrometry focusing on matrix-assisted laser desorption; we will then highlight two emerging technologies based on porous graphitized carbon liquid chromatography and on ion-mobility mass spectrometry as both are highly promising tools to deliver an additional level of information for in-depth glycan analysis; additionally we elaborate on the advantages and challenges of different glycoanalytical technologies and their complementarity; finally, we briefly review applications thereof to biopharmaceutical products. This chapter provides an overview of current state-of-the-art analytical approaches for glycan characterization of biopharmaceuticals that can be employed to capture glycoprotein heterogeneity in a biopharmaceutical context.

True significance of N-acetylglucosaminyltransferases GnT-III, V and α1,6 fucosyltransferase in epithelial-mesenchymal transition and cancer

It is well known that numerous cancer-related changes occur in glycans that are attached to glycoproteins, glycolipids and proteoglycans on the cell surface and these changes in structure and the expression of the glycans are largely regulated by glycosyl-transferases, glycosidases, nucleotide sugars and their related genes. Such structural changes in glycans on cell surface proteins may accelerate the progression, invasion and metastasis of cancer cells. Among the over 200 known glycosyltransferases and related genes, β 1,6 N-acetylglucosaminyltransferase V (GnT-V) (the MGAT5 gene) and α 1,6 fucosyltransferase (FUT8) (the FUT8 gene) are representative enzymes in this respect because changes in glycans caused by these genes appear to be related to cancer metastasis and invasion in vitro as well as in vivo, and a number of reports on these genes in related to epithelial-mesenchymal transition (EMT) have also appeared. Another enzyme, one of the N-glycan branching enzymes, β1,4 N-acetylglucosaminyltransferase III (GnT-III) (the MGAT3 gene) has been reported to suppress EMT. However, there are intermediate states between EMT and mesenchymal-epithelial transition (MET) and some of these genes have been implicated in both EMT and MET and are also probably in an intermediate state. Therefore, it would be difficult to clearly define which specific glycosyltransferase is involved in EMT or MET or an intermediate state. The significance of EMT and N-glycan branching glycosyltransferases needs to be reconsidered and the inhibition of their corresponding genes would also be desirable in therapeutics. This review mainly focuses on GnT-III, GnT-V and FUT8, major players as N-glycan branching enzymes in cancer in relation to EMT programs, and also discusses the catalytic mechanisms of GnT-V and FUT8 whose crystal structures have now been obtained.

Glycans as Immune Checkpoints: Removal of Branched N-glycans Enhances Immune Recognition Preventing Cancer Progression

Tumor growth is accompanied with dramatic changes in the cellular glycome, such as the aberrant expression of complex branched N-glycans. However, the role of this protumoral N-glycan in immune evasion and whether its removal contributes to enhancement of immune recognition and to unleashing an antitumor immune response remain elusive. We demonstrated that branched N-glycans are used by colorectal cancer cells to escape immune recognition, instructing the creation of immunosuppressive networks through inhibition of IFNγ. The removal of this "glycan-mask" exposed immunogenic mannose glycans that potentiated immune recognition by DC-SIGN-expressing immune cells, resulting in an effective antitumor immune response. We revealed a glycoimmune checkpoint in colorectal cancer, highlighting the therapeutic efficacy of its deglycosylation to potentiate immune recognition and, thus, improving cancer immunotherapy.

Essential Functions of Glycans in Human Epithelia Dissected by a CRISPR-Cas9-Engineered Human Organotypic Skin Model

The glycome undergoes characteristic changes during histogenesis and organogenesis, but our understanding of the importance of select glycan structures for tissue formation and homeostasis is incomplete. Here, we present a human organotypic platform that allows genetic dissection of cellular glycosylation capacities and systematic interrogation of the roles of distinct glycan types in tissue formation. We used CRISPR-Cas9 gene targeting to generate a library of 3D organotypic skin tissues that selectively differ in their capacity to produce glycan structures on the main types of N- and O-linked glycoproteins and glycolipids. This tissue library revealed distinct changes in skin formation associated with a loss of features for all tested glycoconjugates. The organotypic skin model provides phenotypic cues for the distinct functions of glycoconjugates and serves as a unique resource for further genetic dissection and identification of the specific structural features involved. The strategy is also applicable to other organotypic tissue models.

Reducing Heart Dose with Protons and Cardiac Substructure Sparing for Mediastinal Lymphoma Treatment

Purpose

Electrocardiogram-gated computed tomography with coronary angiography can be used for cardiac substructure sparing (CSS) optimization, which identifies and improves avoidance of cardiac substructures when treating with intensity modulated radiotherapy (IMRT). We investigated whether intensity modulated proton therapy (IMPT) would further reduce dose to cardiac substructures for patients with mediastinal lymphoma.

Patients and Methods

Twenty-one patients with mediastinal lymphoma were enrolled and underwent electrocardiogram-gated computed tomography angiography during or shortly after simulation for radiotherapy planning. Thirteen patients with delineated cardiac substructures underwent comparative planning with both IMPT and IMRT. Plans were normalized for equivalent (95%) target volume coverage for treatment comparison.

Results

Thirteen patients met criteria for this study. The median size of the mediastinal lymphadenopathy was 7.9 cm at the greatest diameter. Compared with IMRT-CSS, IMPT-CSS significantly reduced mean dose to all cardiac substructures, including 3 coronary arteries and 4 cardiac valves. Use of IMPT significantly reduced average whole-heart dose from 9.6 to 4.9 Gy (P < .0001), and average mean lung dose was 9.7 vs 5.8 Gy (P < .0001). Prospectively defined clinically meaningful improvement was observed in at least 1 coronary artery in 9 patients (69%), at least 1 cardiac valve in 10 patients (77%), and whole heart in all 13 patients.

Conclusions

For patients with mediastinal lymphoma, IMPT-CSS treatment planning significantly reduced radiation dose to cardiac substructures. The significant improvements outlined in this study for proton therapy suggest possible clinical improvement in alignment with previous analyses of CSS optimization.

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.

NEGATIVE ION MASS SPECTROMETRY FOR THE ANALYSIS OF N-LINKED GLYCANS

N-glycans from glycoproteins are complex, branched structures whose structural determination presents many analytical problems. Mass spectrometry, usually conducted in positive ion mode, often requires extensive sample manipulation, usually by derivatization such as permethylation, to provide the necessary structure-revealing fragment ions. The newer but, so far, lesser used negative ion techniques, on the contrary, provide a wealth of structural information not present in positive ion spectra that greatly simplify the analysis of these compounds and can usually be conducted without the need for derivatization. This review describes the use of negative ion mass spectrometry for the structural analysis of N-linked glycans and emphasises the many advantages that can be gained by this mode of operation. Biosynthesis and structures of the compounds are described followed by methods for release of the glycans from the protein. Methods for ionization are discussed with emphasis on matrix-assisted laser desorption/ionization (MALDI) and methods for producing negative ions from neutral compounds. Acidic glycans naturally give deprotonated species under most ionization conditions. Fragmentation of negative ions is discussed next with particular reference to those ions that are diagnostic for specific features such as the branching topology of the glycans and substitution positions of moieties such as fucose and sulfate, features that are often difficult to identify easily by conventional techniques such as positive ion fragmentation and exoglycosidase digestions. The advantages of negative over positive ions for this structural work are emphasised with an example of a series of glycans where all other methods failed to produce a structure. Fragmentation of derivatized glycans is discussed next, both with respect to derivatives at the reducing terminus of the molecules, and to methods for neutralization of the acidic groups on sialic acids to both stabilize them for MALDI analysis and to produce the diagnostic fragments seen with the neutral glycans. The use of ion mobility, combined with conventional mass spectrometry is described with emphasis on its use to extract clean glycan spectra both before and after fragmentation, to separate isomers and its use to extract additional information from separated fragment ions. A section on applications follows with examples of the identification of novel structures from lower organisms and tables listing the use of negative ions for structural identification of specific glycoproteins, glycans from viruses and uses in the biopharmaceutical industry and in medicine. The review concludes with a summary of the advantages and disadvantages of the technique. © 2020 John Wiley & Sons Ltd. Mass Spec Rev.

The Autophagy Machinery Contributes to E-cadherin Turnover in Breast Cancer

Autophagy is an intracellular catabolic process that is increasingly being recognized as a crucial factor in several human diseases including cancers. Mounting evidence suggests that autophagy allows tumor cells to overcome otherwise fatal stresses and to increase dissemination. Nevertheless, how autophagy controls these processes and in particular how it impinges on cell-cell adhesion is still poorly understood. Here, we investigate the role of autophagy in the turnover of the epithelial adhesion molecule E-cadherin in the context of breast cancer. We demonstrated in breast cancer cell lines that autophagy impinges on E-cadherin expression and in the configuration of adherens junctions. Besides, we showed that E-cadherin colocalizes with LC3B and SQSTM1/p62, two components of the autophagosome machinery. Pull down and immunoprecipitation analyses provided evidence that E-cadherin and SQSTM1/p62 physically interact. Moreover, the physical closeness of E-cadherin and SQSTM1/p62 was demonstrated by proximity ligation assays in breast cancer cell lines and primary tumors. Finally, we proved that the silencing of SQSTM1/p62 diminished the E-cadherin/LC3B colocalization, further supporting the role of SQSTM1/p62 in E-cadherin delivery to autophagosomes. These findings suggest that the activation of autophagy, reported in breast cancers with poor prognosis and in dormant breast cancer cells, may contribute to the control of tumor progression via downmodulation of E-cadherin protein levels.

Biological and Technical Challenges in Unraveling the Role of N-Glycans in Immune Receptor Regulation

N-glycosylation of membrane receptors is important for a wide variety of cellular processes. In the immune system, loss or alteration of receptor glycosylation can affect pathogen recognition, cell-cell interaction, and activation as well as migration. This is not only due to aberrant folding of the receptor, but also to altered lateral mobility or aggregation capacity. Despite increasing evidence of their biological relevance, glycosylation-dependent mechanisms of receptor regulation are hard to dissect at the molecular level. This is due to the intrinsic complexity of the glycosylation process and high diversity of glycan structures combined with the technical limitations of the current experimental tools. It is still challenging to precisely determine the localization and site-occupancy of glycosylation sites, glycan micro- and macro-heterogeneity at the individual receptor level as well as the biological function and specific interactome of receptor glycoforms. In addition, the tools available to manipulate N-glycans of a specific receptor are limited. Significant progress has however been made thanks to innovative approaches such as glycoproteomics, metabolic engineering, or chemoenzymatic labeling. By discussing examples of immune receptors involved in pathogen recognition, migration, antigen presentation, and cell signaling, this Mini Review will focus on the biological importance of N-glycosylation for receptor functions and highlight the technical challenges for examination and manipulation of receptor N-glycans.

CD2AP inhibits metastasis in gastric cancer by promoting cellular adhesion and cytoskeleton assembly

Diffuse gastric cancer (DGC) is a lethal malignancy lacking effective systemic therapy. Among the most provocative recent results in DGC has been that the alter of the cellular cytoskeleton and intercellular adhesion. CD2‐associated protein (CD2AP) is one of the critical proteins regulating cytoskeleton assembly and intercellular adhesion. However, no study has investigated the expression and biological significance of CD2AP in gastric cancer (GC) to date. Therefore, the aim of our study was to explore if the expression of CD2AP is associated with any clinical features of GC and to elucidate the underlying mechanism. Immunohistochemistry of 620 patient tissue samples indicated that the expression of CD2AP is downregulated in DGC. Moreover, a low CD2AP level was indicative of poor patient prognosis. In vitro, forced expression of CD2AP caused a significant decrease in the migration and invasion of GC cells, whereas depletion of CD2AP had the opposite effect. Immunofluorescence analysis indicated that CD2AP promoted cellular adhesion and influenced cell cytoskeleton assembly via interaction with the F‐actin capping protein CAPZA1. Overall, the upregulation of CD2AP could attenuate GC metastasis, suggesting CD2AP as a novel biomarker for the prognosis and treatment of patients with GC.

3D Structure and Function of Glycosyltransferases Involved in N-glycan Maturation

Glycosylation is the most ubiquitous post-translational modification in eukaryotes. N-glycan is attached to nascent glycoproteins and is processed and matured by various glycosidases and glycosyltransferases during protein transport. Genetic and biochemical studies have demonstrated that alternations of the N-glycan structure play crucial roles in various physiological and pathological events including progression of cancer, diabetes, and Alzheimer's disease. In particular, the formation of N-glycan branches regulates the functions of target glycoprotein, which are catalyzed by specific N-acetylglucosaminyltransferases (GnTs) such as GnT-III, GnT-IVs, GnT-V, and GnT-IX, and a fucosyltransferase, FUT8s. Although the 3D structures of all enzymes have not been solved to date, recent progress in structural analysis of these glycosyltransferases has provided insights into substrate recognition and catalytic reaction mechanisms. In this review, we discuss the biological significance and structure-function relationships of these enzymes.

Protein Glycosylation as a Diagnostic and Prognostic Marker of Chronic Inflammatory Gastrointestinal and Liver Diseases

Glycans are sequences of carbohydrates that are added to proteins or lipids to modulate their structure and function. Glycans modify proteins required for regulation of immune cells, and alterations have been associated with inflammatory conditions. For example, specific glycans regulate T-cell activation, structures, and functions of immunoglobulins; interactions between microbes and immune and epithelial cells; and malignant transformation in the intestine and liver. We review the effects of protein glycosylation in regulation of gastrointestinal and liver functions, and how alterations in glycosylation serve as diagnostic or prognostic factors, or as targets for therapy.

CDH1 (E-Cadherin) Mutation and Gastric Cancer: Genetics, Molecular Mechanisms and Guidelines for Management

Introduction

Germline mutation in CDH1 (E-cadherin) tumor suppressor gene is associated with hereditary diffuse gastric cancer (HDGC) and lobular breast cancers (LBC). E-Cadherin protein is necessary for physiological signaling pathways, such as cell proliferation, maintenance of cell adhesion, cell polarity and epithelial-mesenchymal transition. Dysregulation leads to tumor proliferation, invasion, migration and metastases. We review current perspectives in CDH1 genetics with molecular mechanisms and also discuss management strategies for this aggressive form of gastric cancer.

Methods

Relevant articles from PubMed/Medline and Embase (1994–2019) were searched and collected using the phrases “Hereditary diffuse gastric cancer, Familial gastric cancer, CDH1 mutation, E-Cadherin, Lobular breast cancer, Prophylactic total gastrectomy”.

Results

Current guidelines suggest maintaining a high degree of suspicion of hereditary etiology and recommend testing for CDH1 mutations in patients with familial clustering of HDGC and LBC, especially onset at an early age (before 40 years). In families lacking CDH1 mutations but with high suspicion for hereditary predisposition, testing of CTNNA1 and other closely related HDGC susceptibility genes could be considered. Prophylactic total gastrectomy is recommended for individuals with identified pathogenic germline variants. Endoscopic surveillance with biopsies is recommended for those choosing to delay prophylactic gastrectomy.

Conclusion

Mutation or transcriptional silencing of the CDH1 gene is associated with familial diffuse gastric cancer. Further studies on the expression and the alteration in the proteins in the E-cadherin pathways may serve as biomarkers for early detection; stratify risk and selection of appropriate therapy in these families. Until then prophylactic total gastrectomy is recommended for individuals with CDH1 mutations and family history of diffuse gastric cancer. Endoscopic surveillance and biopsies by experienced gastroenterologists is recommended for those choosing not to have prophylactic gastrectomy and in individuals with CDH1 variants.

Genome-Wide Analysis of Whole Human Glycoside Hydrolases by Data-Driven Analysis in Silico

Glycans are involved in various metabolic processes via the functions of glycosyltransferases and glycoside hydrolases. Analysing the evolution of these enzymes is essential for improving the understanding of glycan metabolism and function. Based on our previous study of glycosyltransferases, we performed a genome-wide analysis of whole human glycoside hydrolases using the UniProt, BRENDA, CAZy and KEGG databases. Using cluster analysis, 319 human glycoside hydrolases were classified into four clusters based on their similarity to enzymes conserved in chordates or metazoans (Class 1), metazoans (Class 2), metazoans and plants (Class 3) and eukaryotes (Class 4). The eukaryote and metazoan clusters included N- and O-glycoside hydrolases, respectively. The significant abundance of disordered regions within the most conserved cluster indicated a role for disordered regions in the evolution of glycoside hydrolases. These results suggest that the biological diversity of multicellular organisms is related to the acquisition of N- and O-linked glycans.

Molecular Mobility-Mediated Regulation of E-Cadherin Adhesion

Cells in epithelial tissues utilize homotypic E-cadherin interaction-mediated adhesions to both physically adhere to each other and sense the physical properties of their microenvironment, such as the presence of other cells in close vicinity or an alteration in the mechanical tension of the tissue. These position E-cadherin centrally in organogenesis and other processes, and its function is therefore tightly regulated through a variety of means including endocytosis and gene expression. How does membrane molecular mobility of E-cadherin, and thus membrane physical properties and associated actin cytoskeleton, impinges on the assembly of adhesive clusters and signaling is discussed.

Carcinoembryonic antigen carrying SLeX as a new biomarker of more aggressive gastric carcinomas

Malignant transformation of gastric cells is accompanied by the deregulated expression of glycosyltransferases leading to the biosynthesis of tumor-associated glycans such as the sialyl-Lewis X antigen (SLe^x). SLe^x presence on cell surface glycoconjugates increases the invasive capacity of gastric cancer cells and is associated with tumor metastasis. ST3Gal IV enzyme is involved in the synthesis of SLe^x antigen and overexpressed in gastric carcinomas. Herein, we identified the glycoproteins carrying SLe^x in gastric cancer cells overexpressing ST3Gal IV enzyme and evaluated their biomarker potential for gastric carcinoma.

Methods: SLe^x modified glycoproteins were identified applying western blot and mass spectrometry. Immunoprecipitation, proximity ligation assay (PLA), E-selectin binding assay and CRISPR/cas9 knockout experiments were performed to characterize the presence of SLe^x on the identified glycoprotein. Protein N-glycans of the SLe^x protein carrier were in deep analyzed by porous-graphitized-carbon liquid-chromatography and tandem mass spectrometry glycomics. In silico expression analysis of α2-3 sialyltransferase ST3Gal IV and SLe^x protein carrier was performed and the conjoint expression of the SLe^x modified glycoproteins evaluated by immunohistochemistry and PLA in a series of gastric carcinomas.

Results: Carcinoembryonic antigen (CEA; CEACAM5) was identified and validated by different methodologies as a major carrier of SLe^x. N-glycomics of CEA revealed that complex N-glycans are capped with α2-3 linked sialic acid (Neu5Acα2-3Galβ1-4GlcNAc). Data set analysis of ST3Gal IV and CEA showed that ST3Gal IV expression was associated with patient´s poor survival, whereas CEA did not show any prognostic value. The co-expression of both CEA and SLe^X was observed in 86,3% of gastric carcinoma cases and 74,5% of the total cases displayed the conjoint CEA+SLe^xin situ PLA expression. This expression was associated with clinicopathological features of the tumors, including infiltrative pattern of tumor growth, presence of venous invasion and patient's poor survival. CEA immunoprecipitation from gastric carcinoma tissues also confirmed the presence of SLe^x.

Conclusion: CEA is the major glycoprotein carrying SLe^x in gastric carcinoma and the conjoint detection of CEA-SLe^x is associated with aggressive tumor features highlighting its PLA detection as a biomarker of gastric cancer patient prognosis for theranostic applications.

E-Cadherin Protein as a Potential Marker for Gastric Cancer and Its Association with Helicobacter Pylori- Induced Gastritis and Gastric Ulcer

BACKGROUND

Gastric cancer is still the main health threat being the third leading cause of deaths from cancers in the world. The major risk behind the gastric cancer is that it remains asymptomatic in the early stages and in (97%) cases it metastasizes to other organs. Gastric cancer is a multifactorial disease in which Helicobacter pylori (H. pylori) has been known as a risk factor. However, patients with gastritis, especially atrophic gastritis and gastric ulcer have been shown to be at an increased risk for developing gastric cancer.

METHODS

This study included measuring the serum levels of E-Cadherin protein, carbohydrate antigen 19-9 (CA19-9) and carcinoembryonic antigen (CEA) in 30 patients diagnosed with gastritis, 20 gastric ulcer patients, 20 gastric cancer patients and in 20 healthy volunteers serving as the control group.

RESULTS

Infection with H. pylori was diagnosed by serology (IgA and IgG antibodies) as well as by rapid urease test (RUT) and histology. The results showed that 50 (71.4%) of the patients were positive for H. pylori. Levels of E-Cadherin were increased significantly in all patients in comparison to the control group with a large significant increase in the gastric cancer group. The levels of E-Cadherin were also significantly increased in H. pylori infected patients compared to H. pylori negative patients. A non-significant difference in the levels of CA19-9 and CEA was observed in all patients in comparison to healthy controls.

CONCLUSION

This study concluded that serum E-Cadherin could be considered as a potential marker in diagnosis of gastric cancer.

Translational glycobiology: from bench to bedside

The importance of sugars to protein function is real and is of significant clinical relevance. Technology advances enable large population studies to be carried out, shedding light on individual sugar variation and variations with time. Three-dimensional mass spectroscopy on solid pathological specimens is going to open up a whole new world of pathology visualisation. The door is now open to exploit carbohydrate recognition in new therapeutics by identifying novel biomarkers in cancer to aid diagnosis, and also providing therapeutic targets for treatment. Glycan age correlates with biological age. This means we can map the reversal of biological age with exercise and diet.