A unique molecular chaperone Cosmc required for activity of the mammalian core 1 beta 3-galactosyltransferase

Substrate O-glycosylation actively regulates extracellular proteolysis

Extracellular proteolysis critically regulates cellular and tissue responses and is often dysregulated in human diseases. The crosstalk between proteolytic processing and other major post-translational modifications (PTMs) is emerging as an important regulatory mechanism to modulate protease activity and maintain cellular and tissue homeostasis. Here, we focus on matrix metalloproteinase (MMP)-mediated cleavages and N-acetylgalactosamine (GalNAc)-type of O-glycosylation, two major PTMs of proteins in the extracellular space. We investigated the influence of truncated O-glycan trees, also referred to as Tn antigen, following the inactivation of C1GALT1-specific chaperone 1 (COSMC) on the general and MMP9-specific proteolytic processing in MDA-MB-231 breast cancer cells. Quantitative assessment of the proteome and N-terminome using terminal amine isotopic labelling of substrates (TAILS) technology revealed enhanced proteolysis by MMP9 within the extracellular proteomes of MDA-MB-231 cells expressing Tn antigen. In addition, we detected substantial modifications in the proteome and discovered novel ectodomain shedding events regulated by the truncation of O-glycans. These results highlight the critical role of mature O-glycosylation in fine-tuning proteolytic processing and proteome homeostasis by modulating protein susceptibility to proteolytic degradation. These data suggest a complex interplay between proteolysis and O-GalNAc glycosylation, possibly affecting cancer phenotypes.

A Versatile One-Step Enzymatic Strategy for Efficient Imaging and Mapping of Tumor-Associated Tn Antigen

Tn antigen (CD175), recognized as the precursor monosaccharide (α-GalNAc) of mucin O-glycan, is a well-known tumor-associated carbohydrate antigen (TACA). It has emerged as a potential biomarker for cancer diagnosis and prognosis. However, the role it plays in cancer biology remains elusive due to the absence of a sensitive and selective detection method. In this study, we synthesized two new probes based on a unique uridine-5'-diphospho-α-d-galactose (UDP-Gal) derivative, each functionalized with either a fluorescence or a cleavable biotin tag, to develop an innovative one-step enzymatic labeling strategy, enabling the visualization, enrichment, and site-specific mapping of the Tn antigen with unparalleled sensitivity and specificity. Our versatile strategy has been successfully applied to detect and image Tn antigen across various samples, including the complex cell lysates, live cells, serum, and tissue samples. Compared to the traditional lectin method, this one-step enzymatic method is simpler and more efficient (>10/100-fold in sensitivity). Furthermore, it allowed us to map 454 Tn-glycoproteins and 624 Tn-glycosylation sites from HEK293FTn+ and Jurkat cells. Therefore, our strategy provides an exceptionally promising tool for revealing the biological functions of the Tn antigen and advancing cancer diagnostics.

Combined Genetic Association and Differed Expression Analysis of UBE2L3 Uncovers a Genetic Regulatory Role of (Immuno)proteasome in IgA Nephropathy

Introduction

IgA nephropathy (IgAN) is a leading cause of end-stage renal disease. The exact pathogenesis of IgAN is not well defined, but some genetic studies have led to a novel discovery that the (immuno)proteasome probably plays an important role in IgAN.

Methods

We firstly analyzed the association of variants in the UBE2L3 region with susceptibility to IgAN in 3,495 patients and 9,101 controls, and then analyzed the association between lead variant and clinical phenotypes in 1,803 patients with regular follow-up data. The blood mRNA levels of members of the ubiquitin-proteasome system including UBE2L3 were analyzed in peripheral blood mononuclear cells from 53 patients and 28 healthy controls. The associations between UBE2L3 and the expression levels of genes involved in Gd-IgA1 production were also explored.

Results

The rs131654 showed the most significant association signal in UBE2L3 region (OR: 1.10, 95% CI: 1.04-1.16, p = 2.29 × 10-3), whose genotypes were also associated with the levels of Gd-IgA1 (p = 0.04). The rs131654 was observed to exert cis-eQTL effects on UBE2L3 in various tissues and cell types, particularly in immune cell types in multiple databases. The UBE2L3, LUBAC, and proteasome subunits were highly expressed in patients compared with healthy controls. High expression levels of UBE2L3 were not only associated with higher proteinuria (r = 0.34, p = 0.01) and lower eGFR (r = -0.28, p = 0.04), but also positively correlated with the gene expression of LUBAC and other proteasome subunits. Additionally, mRNA expression levels of UBE2L3 were also positively correlated with IL-6 and RELA, but negatively correlated with the expression levels of the key enzyme in the process of glycosylation including C1GALT1 and C1GALT1C1.

Conclusion

In conclusion, by combined genetic association and differed expression analysis of UBE2L3, our data support a role of genetically conferred dysregulation of the (immuno)proteasome in regulating galactose-deficient IgA1 in the development of IgAN.

Tumor-associated carbohydrate antigens of MUC1 - Implication in cancer development

Glycosylation of cancerous epithelial MUC1 protein is specifically altered in comparison to that which is presented by healthy cells. One of such changes is appearing tumor-associated carbohydrate antigens (TACAs) which are rare in normal tissues and are highly correlated with poor clinical outcomes and cancer progression. This review summarizes and describes the role of Tn, T antigens, their sialylated forms as well as fucosylated Lewis epitopes in different aspects of tumor development, progression, and metastasis. Finally, applications of MUC1 glycan epitopes as potential targets for therapeutic strategy of cancers are notified. One of the novelties of this review is presentation of TACAs as inherently connected with MUC1 mucin.

High core 1β1,3-galactosyltransferase 1 expression is associated with poor prognosis and promotes cellular radioresistance in lung adenocarcinoma

PURPOSE

Core 1β1,3-galactosyltransferase 1 (C1GALT1) exhibits elevated expression in multiple cancers. The present study aimed to elucidate the clinical significance of C1GALT1 aberrant expression and its impact on radiosensitivity in lung adenocarcinoma (LUAD).

METHODS

The C1GALT1 expression and its clinical relevance were investigated through public databases and LUAD tissue microarray analyses. A549 and H1299 cells with either C1GALT1 knockdown or overexpression were further assessed through colony formation, gamma-H2A histone family member X immunofluorescence, 5-ethynyl-2'-deoxyuridine incorporation, and flow cytometry assays. Bioinformatics analysis was used to explore single cell sequencing data, revealing the influence of C1GALT1 on cancer-associated cellular states. Vimentin, N-cadherin, and E-cadherin protein levels were measured through western blotting.

RESULTS

The expression of C1GALT1 was significantly higher in LUAD tissues than in adjacent non-tumor tissues both at mRNA and protein level. High expression of C1GALT1 was correlated with lymph node metastasis, advanced T stage, and poor survival, and was an independent risk factor for overall survival. Radiation notably upregulated C1GALT1 expression in A549 and H1299 cells, while radiosensitivity was increased following C1GALT1 knockdown and decreased following overexpression. Experiment results showed that overexpression of C1GALT1 conferred radioresistance, promoting DNA repair, cell proliferation, and G2/M phase arrest, while inhibiting apoptosis and decreasing E-cadherin expression, alongside upregulating vimentin and N-cadherin in A549 and H1299 cells. Conversely, C1GALT1 knockdown had opposing effects.

CONCLUSION

Elevated C1GALT1 expression in LUAD is associated with an unfavorable prognosis and contributes to increased radioresistance potentially by affecting DNA repair, cell proliferation, cell cycle regulation, and epithelial-mesenchymal transition (EMT).

Truncated O-glycosylation in metastatic triple-negative breast cancer reveals a gene expression signature associated with extracellular matrix and proteolysis

Breast cancer (BC) is the leading cause of death by cancer in women worldwide. Triple-negative (TN) BC constitutes aggressive and highly metastatic tumors associated with shorter overall survival of patients compared to other BC subtypes. The Tn antigen, a glycoconjugated structure resulting from an incomplete O-glycosylation process, is highly expressed in different adenocarcinomas, including BC. It also favors cancer growth, immunoregulation, and metastasis in TNBC. This work describes the differentially expressed genes (DEGs) associated with BC aggressiveness and metastasis in an incomplete O-glycosylated TNBC cell model. We studied the transcriptome of a TNBC model constituted by the metastatic murine 4T1 cell line that overexpresses the Tn antigen due to a mutation in one of the steps of the O-glycosylation pathway. We analyzed and compared the results with the parental wild-type cell line and with a Tn-negative cell clone that was poorly metastatic and less aggressive than the 4T1 parental cell line. To gain insight into the generated expression data, we performed a gene set analysis. Biological processes associated with cancer development and metastasis, immune evasion, and leukocyte recruitment were highly enriched among functional terms of DEGs. Furthermore, different highly O-glycosylated protein-coding genes, such as mmp9, ecm1 and ankyrin-2, were upregulated in 4T1/Tn+ tumor cells. The altered biological processes and DEGs that promote tumor growth, invasion and immunomodulation might explain the aggressive properties of 4T1/Tn+ tumor cells. These results support the hypothesis that incomplete O-glycosylation that leads to the expression of the Tn antigen, which might regulate activity or interaction of different molecules, promotes cancer development and immunoregulation.

The role of glycosylation in clinical allergy and immunology

While glycans are among the most abundant macromolecules on the cell with widespread functions, their role in immunity has historically been challenging to study. This is in part due to difficulties assimilating glycan analysis into routine approaches used to interrogate immune cell function. Despite this, recent developments have illuminated fundamental roles for glycans in host immunity. The growing field of glycoimmunology continues to leverage new tools and approaches to uncover the function of glycans and glycan-binding proteins in immunity. Here we utilize clinical vignettes to examine key roles of glycosylation in allergy, inborn errors of immunity, and autoimmunity. We will discuss the diverse functions of glycans as epitopes, as modulators of antibody function, and as regulators of immune cell function. Finally, we will highlight immune modulatory therapies that harness the critical role of glycans in the immune system.

Tn antigen interactions of macrophage galactose-type lectin (MGL) in immune function and disease

Protein-carbohydrate interactions are essential in maintaining immune homeostasis and orchestrating inflammatory and regulatory immune processes. This review elucidates the immune interactions of macrophage galactose-type lectin (MGL, CD301) and Tn carbohydrate antigen. MGL is a C-type lectin receptor (CLR) primarily expressed by myeloid cells such as macrophages and immature dendritic cells. MGL recognizes terminal O-linked N-acetylgalactosamine (GalNAc) residue on the surface proteins, also known as Tn antigen (Tn). Tn is a truncated form of the elongated cell surface O-glycan. The hypoglycosylation leading to Tn may occur when the enzyme responsible for O-glycan elongation-T-synthase-or its associated chaperone-Cosmc-becomes functionally inhibited. As reviewed here, Tn expression is observed in many different neoplastic and non-neoplastic diseases, and the recognition of Tn by MGL plays an important role in regulating effector T cells, immune suppression, and the recognition of pathogens.

CRISPR-screen identifies ZIP9 and dysregulated Zn2+ homeostasis as a cause of cancer-associated changes in glycosylation

INTRODUCTION

In epithelial cancers, truncated O-glycans, such as the Thomson-nouveau antigen (Tn) and its sialylated form (STn), are upregulated on the cell surface and associated with poor prognosis and immunological escape. Recent studies have shown that these carbohydrate epitopes facilitate cancer development and can be targeted therapeutically; however, the mechanism underpinning their expression remains unclear.

METHODS

To identify genes directly influencing the expression of cancer-associated O-glycans, we conducted an unbiased, positive-selection, whole-genome CRISPR knockout-screen using monoclonal antibodies against Tn and STn.

RESULTS AND CONCLUSIONS

We show that knockout of the Zn2+-transporter SLC39A9 (ZIP9), alongside the well-described targets C1GALT1 (C1GalT1) and its molecular chaperone, C1GALT1C1 (COSMC), results in surface-expression of cancer-associated O-glycans. No other gene perturbations were found to reliably induce O-glycan truncation. We furthermore show that ZIP9 knockout affects N-linked glycosylation, resulting in upregulation of oligo-mannose, hybrid-type, and α2,6-sialylated structures as well as downregulation of tri- and tetra-antennary structures. Finally, we demonstrate that accumulation of Zn2+ in the secretory pathway coincides with cell-surface presentation of truncated O-glycans in cancer tissue, and that over-expression of COSMC mitigates such changes. Collectively, the findings show that dysregulation of ZIP9 and Zn2+ induces cancer-like glycosylation on the cell surface by affecting the glycosylation machinery.

Mucin Glycans: A Target for Cancer Therapy

Mucin glycans are an important component of the mucus barrier and a vital defence against physical and chemical damage as well as pathogens. There are 20 mucins in the human body, which can be classified into secreted mucins and transmembrane mucins according to their distributions. The major difference between them is that secreted mucins do not have transmembrane structural domains, and the expression of each mucin is organ and cell-specific. Under physiological conditions, mucin glycans are involved in the composition of the mucus barrier and thus protect the body from infection and injury. However, abnormal expression of mucin glycans can lead to the occurrence of diseases, especially cancer, through various mechanisms. Therefore, targeting mucin glycans for the diagnosis and treatment of cancer has always been a promising research direction. Here, we first summarize the main types of glycosylation (O-GalNAc glycosylation and N-glycosylation) on mucins and the mechanisms by which abnormal mucin glycans occur. Next, how abnormal mucin glycans contribute to cancer development is described. Finally, we summarize MUC1-based antibodies, vaccines, radio-pharmaceuticals, and CAR-T therapies using the best characterized MUC1 as an example. In this section, we specifically elaborate on the recent new cancer therapy CAR-M, which may bring new hope to cancer patients.

The gut microbiome tango in the progression of chronic kidney disease and potential therapeutic strategies

Chronic kidney disease (CKD) affects more than 10% population worldwide and becomes a huge burden to the world. Recent studies have revealed multifold interactions between CKD and gut microbiome and their pathophysiological implications. The gut microbiome disturbed by CKD results in the imbalanced composition and quantity of gut microbiota and subsequent changes in its metabolites and functions. Studies have shown that both the dysbiotic gut microbiota and its metabolites have negative impacts on the immune system and aggravate diseases in different ways. Herein, we give an overview of the currently known mechanisms of CKD progression and the alterations of the immune system. Particularly, we summarize the effects of uremic toxins on the immune system and review the roles of gut microbiota in promoting the development of different kidney diseases. Finally, we discuss the current sequencing technologies and novel therapies targeting the gut microbiome.

Targeting Solid Cancers with a Cancer-Specific Monoclonal Antibody to Surface Expressed Aberrantly O-glycosylated Proteins

The lack of antibodies with sufficient cancer selectivity is currently limiting the treatment of solid tumors by immunotherapies. Most current immunotherapeutic targets are tumor-associated antigens that are also found in healthy tissues and often do not display sufficient cancer selectivity to be used as targets for potent antibody-based immunotherapeutic treatments, such as chimeric antigen receptor (CAR) T cells. Many solid tumors, however, display aberrant glycosylation that results in expression of tumor-associated carbohydrate antigens that are distinct from healthy tissues. Targeting aberrantly glycosylated glycopeptide epitopes within existing or novel glycoprotein targets may provide the cancer selectivity needed for immunotherapy of solid tumors. However, to date only a few such glycopeptide epitopes have been targeted. Here, we used O-glycoproteomics data from multiple cell lines to identify a glycopeptide epitope in CD44v6, a cancer-associated CD44 isoform, and developed a cancer-specific mAb, 4C8, through a glycopeptide immunization strategy. 4C8 selectively binds to Tn-glycosylated CD44v6 in a site-specific manner with low nanomolar affinity. 4C8 was shown to be highly cancer specific by IHC of sections from multiple healthy and cancerous tissues. 4C8 CAR T cells demonstrated target-specific cytotoxicity in vitro and significant tumor regression and increased survival in vivo. Importantly, 4C8 CAR T cells were able to selectively kill target cells in a mixed organotypic skin cancer model having abundant CD44v6 expression without affecting healthy keratinocytes, indicating tolerability and safety.

Fucose as a nutrient ligand for Dikarya and a building block of early diverging lineages

Fucose is a deoxyhexose sugar present and studied in mammals. The process of fucosylation has been the primary focus in studies relating to fucose in animals due to the presence of fucose in Lewis antigens. Very few studies have reported its presence in Fungi, mostly in Mucoromycotina. The constitution of 25% and 12% of this sugar in the carbohydrates of cell wall in the respective Umbelopsis and Mucorales strains boosts the need to bridge the gap of knowledge on fucose metabolism across the fungal tree of life. In the absence of a network map involving fucose proteins, we carried out an in-silico approach to construct the fucose metabolic map in Fungi. We analyzed the taxonomic distribution of 85 protein families in Fungi including diverse early diverging fungal lineages. The expression of fucose-related protein-coding genes proteins was validated with the help of transcriptomic data originating from representatives of early diverging fungi. We found proteins involved in several metabolic activities apart from fucosylation such as synthesis, transport and binding. Most of the identified protein families are shared with Metazoa suggesting an ancestral origin in Opisthokonta. However, the overall complexity of fucose metabolism is greater in Metazoa than in Fungi. Massive gene loss has shaped the evolutionary history of these metabolic pathways, leading to a repeated reduction of these pathways in most yeast-forming lineages. Our results point to a distinctive mode of utilization of fucose among fungi belonging to Dikarya and the early diverging lineages. We speculate that, while Dikarya used fucose as a source of nutrients for metabolism, the early diverging group of fungi depended on fucose as a building block and signaling compound.

The gut mucus network: A dynamic liaison between microbes and the immune system

A complex mucus network made up of large polymers of the mucin-family glycoprotein MUC2 exists between the large intestinal microbial mass and epithelial and immune cells. This has long been understood as an innate immune defense barrier against the microbiota and other luminal threats that reinforces the barrier function of the epithelium and limits microbiota contact with the tissues. However, past and recent studies have provided new evidence of how critical the mucus network is to act as a 'liaison' between host and microbe to mediate anti-inflammatory, mutualistic interactions with the microbiota and protection from pathogens. This review summarizes historical and recent insights into the formation of the gut mucus network, how the microbes and immune system influence mucus, and in turn, how the mucus influences immune responses to the microbiota.

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

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

Proteomic cardiovascular risk assessment in chronic kidney disease

AIMS

Chronic kidney disease (CKD) is widely prevalent and independently increases cardiovascular risk. Cardiovascular risk prediction tools derived in the general population perform poorly in CKD. Through large-scale proteomics discovery, this study aimed to create more accurate cardiovascular risk models.

METHODS AND RESULTS

Elastic net regression was used to derive a proteomic risk model for incident cardiovascular risk in 2182 participants from the Chronic Renal Insufficiency Cohort. The model was then validated in 485 participants from the Atherosclerosis Risk in Communities cohort. All participants had CKD and no history of cardiovascular disease at study baseline when ∼5000 proteins were measured. The proteomic risk model, which consisted of 32 proteins, was superior to both the 2013 ACC/AHA Pooled Cohort Equation and a modified Pooled Cohort Equation that included estimated glomerular filtrate rate. The Chronic Renal Insufficiency Cohort internal validation set demonstrated annualized receiver operating characteristic area under the curve values from 1 to 10 years ranging between 0.84 and 0.89 for the protein and 0.70 and 0.73 for the clinical models. Similar findings were observed in the Atherosclerosis Risk in Communities validation cohort. For nearly half of the individual proteins independently associated with cardiovascular risk, Mendelian randomization suggested a causal link to cardiovascular events or risk factors. Pathway analyses revealed enrichment of proteins involved in immunologic function, vascular and neuronal development, and hepatic fibrosis.

CONCLUSION

In two sizeable populations with CKD, a proteomic risk model for incident cardiovascular disease surpassed clinical risk models recommended in clinical practice, even after including estimated glomerular filtration rate. New biological insights may prioritize the development of therapeutic strategies for cardiovascular risk reduction in the CKD population.

Structural insights into Siglec-15 reveal glycosylation dependency for its interaction with T cells through integrin CD11b

Sialic acid-binding Ig-like lectin 15 (Siglec-15) is an immune modulator and emerging cancer immunotherapy target. However, limited understanding of its structure and mechanism of action restrains the development of drug candidates that unleash its full therapeutic potential. In this study, we elucidate the crystal structure of Siglec-15 and its binding epitope via co-crystallization with an anti-Siglec-15 blocking antibody. Using saturation transfer-difference nuclear magnetic resonance (STD-NMR) spectroscopy and molecular dynamics simulations, we reveal Siglec-15 binding mode to α(2,3)- and α(2,6)-linked sialic acids and the cancer-associated sialyl-Tn (STn) glycoform. We demonstrate that binding of Siglec-15 to T cells, which lack STn expression, depends on the presence of α(2,3)- and α(2,6)-linked sialoglycans. Furthermore, we identify the leukocyte integrin CD11b as a Siglec-15 binding partner on human T cells. Collectively, our findings provide an integrated understanding of the structural features of Siglec-15 and emphasize glycosylation as a crucial factor in controlling T cell responses.

Germline C1GALT1C1 mutation causes a multisystem chaperonopathy

Mutations in genes encoding molecular chaperones can lead to chaperonopathies, but none have so far been identified causing congenital disorders of glycosylation. Here we identified two maternal half-brothers with a novel chaperonopathy, causing impaired protein O-glycosylation. The patients have a decreased activity of T-synthase (C1GALT1), an enzyme that exclusively synthesizes the T-antigen, a ubiquitous O-glycan core structure and precursor for all extended O-glycans. The T-synthase function is dependent on its specific molecular chaperone Cosmc, which is encoded by X-chromosomal C1GALT1C1. Both patients carry the hemizygous variant c.59C>A (p.Ala20Asp; A20D-Cosmc) in C1GALT1C1. They exhibit developmental delay, immunodeficiency, short stature, thrombocytopenia, and acute kidney injury (AKI) resembling atypical hemolytic uremic syndrome. Their heterozygous mother and maternal grandmother show an attenuated phenotype with skewed X-inactivation in blood. AKI in the male patients proved fully responsive to treatment with the complement inhibitor Eculizumab. This germline variant occurs within the transmembrane domain of Cosmc, resulting in dramatically reduced expression of the Cosmc protein. Although A20D-Cosmc is functional, its decreased expression, though in a cell or tissue-specific manner, causes a large reduction of T-synthase protein and activity, which accordingly leads to expression of varied amounts of pathological Tn-antigen (GalNAcα1-O-Ser/Thr/Tyr) on multiple glycoproteins. Transient transfection of patient lymphoblastoid cells with wild-type C1GALT1C1 partially rescued the T-synthase and glycosylation defect. Interestingly, all four affected individuals have high levels of galactose-deficient IgA1 in sera. These results demonstrate that the A20D-Cosmc mutation defines a novel O-glycan chaperonopathy and causes the altered O-glycosylation status in these patients.

Side population cells derived from hUCMSCs and hPMSCs could inhibit the malignant behaviors of Tn+ colorectal cancer cells from modifying their O-glycosylation status

BACKGROUND

Cosmc (C1GalT1C1) mutation could cause aberrant O-glycosylation and result in expression of Tn antigen on the surface of tumor cells (Tn⁺ cells), which is associated with the metastasis and prognosis of cancer progression. Mesenchymal stem cells (MSCs) could participate in immunoregulation, tissue damage repair, and tumor inhibition and be seen as an ideal candidate for tumor therapy due to their inherent capacity to migrate to tumor sites. However, their therapeutic effectiveness in different tumors is inconsistent and still controversial. Of note, emerging data reveal that side population (SP) cells have a stronger multilineage developmental potential than main population cells and can function as stem/progenitor cells. The effect of SP cells derived from MSCs on the biological behaviors and the O-glycosylation status of tumor cells remains unclear.

METHODS

SP cells were isolated from human umbilical cord MSCs (hUCMSCs) and human placenta MSCs (hPMSCs). Tn⁺ cells (LS174T-Tn⁺ and HT-29-Tn⁺ cells) and matching Tn^- cells (LS174T-Tn^- and HT-29-Tn^- cells) were isolated from human colorectal cancer cell (CRC) lines LS174T and HT-29 by immune magnetic beads. The proliferation, migration, apoptosis, Tn antigen expression, and O-glycome in Tn⁺ and Tn^- CRC cells before and after co-cultured with SP-MSCs were detected using real-time cell Analysis (RTCA), flow cytometry (FCM), and cellular O-glycome reporter/amplification (CORA), respectively. Cosmc protein and O-glycosyltransferase (T-synthase and C3GnT) activity in CRC cells were, respectively, assessed using western blotting and fluorescence method.

RESULTS

Both SP cells derived from hUCMSCs and hPMSCs could inhibit proliferation and migration, promote apoptosis of CRC cells, significantly reduce Tn antigen expression on Tn⁺ CRC cells, generate new core 1-, 2-, and 3-derived O-glycans, increase T-synthase and C3GnT activity, and elevate the levels of Cosmc and T-synthase protein.

CONCLUSION

SP-hUCMSCs and SP-hPMSCs could inhibit proliferation and migration and promote apoptosis of Tn⁺ CRC cells via increasing O-glycosyltransferase activity to modify O-glycosylation status, which further adds a new dimension to the treatment of CRC.

The biological role of core 1β1-3galactosyltransferase (T-synthase) in mucin-type O-glycosylation in Silkworm, Bombyx mori

O-glycosylation of secreted and membrane-bound proteins is an important post-translational modification that affects recognition of cell surface receptors, protein folding, and stability. However, despite the importance of O-linked glycans, their biological functions have not yet been fully elucidated and the synthetic pathway of O-glycosylation has not been investigated in detail, especially in the silkworm. In this study, we aimed to investigate O-glycosylation in silkworms by analyzing the overall structural profiles of mucin-type O-glycans using LC-MS. We found GalNAc or GlcNAc monosaccharide and core 1 disaccharide (Galβ1-3-GalNAcα1-Ser/Thr) were major components of the O-glycan attached to secreted proteins produced in silkworms. Furthermore, we characterized the 1 b1,3-galactosyltransferase (T-synthase) required for synthesis of the core 1 structure, common to many animals. Five transcriptional variants and four protein isoforms were identified in silkworms, and the biological functions of these isoforms were investigated. We found that BmT-synthase isoforms 1 and 2 were localized in the Golgi apparatus in cultured BmN4 cells and functioned both in cultured cells and silkworms. Additionally, a specific functional domain of T-synthase, called the stem domain, was found to be essential for activity and is presumed to be needed for dimer formation and galactosyltransferase activity. Altogether, our results elucidated the O-glycan profile and function of T-synthase in the silkworm. Our findings allow the practical comprehension of O-glycosylation required for employing silkworms as a productive expression system.

Association of Sialyl Tn antigen with cervical cancer lymph node status: An NRG oncology/GOG study

OBJECTIVE

Detection of lymph node metastases in cervical cancer patients is important for guiding treatment decisions, however accuracies of current detection methods are limited. We evaluated associations of abnormal glycosylation, represented by Tn and STn antigens on mucin (MUC) proteins, in primary tumor specimens with lymph node metastasis or recurrence of cervical cancer patients.

METHODS

Surgical specimens were prospectively collected from 139 patients with locally-advanced cervical cancer undergoing lymphadenectomy enrolled in a nation-wide clinical trial (NCT00460356). Of these patients, 133 had primary cervix tumor, 67 had pelvic lymph node (PLN) and 28 had para-aortic lymph node (PALN) specimens. Fixed tissue serial sections were immunohistochemically stained for Tn, STn, MUC1 or MUC4. Neuraminidase was used to validate Tn versus STn antibody specificity. Stain scores were compared with clinical characteristics.

RESULTS

Primary tumor STn expression above the median was associated with negative PLN status (p-value: 0.0387; odds ratio 0.439, 95% CI: 0.206 to 0.935). PLN had higher STn compared to primary tumor, while primary tumor had higher MUC1 compared to PALN, and MUC4 compared to PALN or PLN (p = 0.017, p = 0.011, p = 0.016 and p < 0.001, respectively). Tn and STn expression correlated in primary tumor, PALN, and PLN, Tn and MUC1 expression correlated in primary tumors only (Spearman correlation coefficient [r] = 0.301, r = 0.686, r = 0.603 and r = 0.249, respectively).

CONCLUSIONS

STn antigen expression in primary cervical tumors is a candidate biomarker for guiding treatment decisions and for mechanistic involvement in PLN metastases.

COSMC expression as a predictor of remission in IgA nephropathy

PURPOSE

The impact of core 1,3-galactosyltransferase-specific molecular chaperon (COSMC) gene expression and methylation profile on clinical progression of IgA nephropathy (IgAN) is unclear. The aim of this study was to determine the clinical significance and the relation of the COSMC gene expression and methylation pattern with the progression of IgAN.

METHODS

Thirty-nine biopsy-confirmed IgAN patients, 11 healthy relatives and 20 healthy controls were recruited. The COSMC mRNA levels and methylation profile of COSMC gene promoter were measured using the quantitative real-time PCR. The galactose-deficient IgA1 (Gd-IgA1) levels were measured using ELISA in serum and cell culture supernatant. The effect of IL-4 and AZA on COSMC expression and methylation and the correlation of COSMC gene expression and methylation levels with baseline kidney function tests, histology and long-term outcomes were examined.

RESULTS

The mean COSMC mRNA level was significantly lower, and serum Gd-IgA1 level was higher in IgAN patients compared with the control groups (p < 0.001, and p =  < 0.001, respectively). The COSMC mRNA levels were correlated with intensity of hematuria (r = - 0.41, p = 0.009), serum creatinine level (r = - 0.37, p = 0.002) and eGFR (r = 0.36, p = 0.002). The COSMC methylation levels were correlated with age (r = 0.25, p = 0.04) and baseline eGFR (r = - 0.326, p = 0.006). Twenty IgAN patients (51.3%) reached to complete (5, 12.8%) or partial remission (15, 38.5%) after a median of 34.5 months (IQR, 13.75-71). In multivariable Cox regression analysis, COSMC mRNA expression (adjusted HR (aHR) 1.871, 95% CI 1.287-2.722, p = 0.001) and Oxford T score (aHR 0.355, 95% CI 0.146-0.859, p = 0.022) predicted the remission.

CONCLUSION

COSMC mRNA level is a novel biomarker candidate to predict the remission in IgAN patients.

Development of Engineered CAR T Cells Targeting Tumor-Associated Glycoforms of MUC1 for the Treatment of Intrahepatic Cholangiocarcinoma

Intrahepatic cholangiocarcinoma (ICC) is a common malignancy arising from the liver with limited 5-year survival. Thus, there is an urgency to explore new treatment methods. Chimeric antigen receptor T (CAR T) cell therapy is a very promising cancer treatment. Though, several groups have investigated CAR T cells targeting MUC1 in solid cancer models, Tn-MUC1-targeted CAR T cells have not yet to be reported in ICC. In this study, we confirmed Tn-MUC1 as a potential therapeutic target for ICC and demonstrated that its expression level was positively correlated with the poor prognosis of ICC patients. More importantly, we successfully developed effective CAR T cells to target Tn-MUC1-positive ICC tumors and explored their antitumor activities. Our results suggest the CAR T cells could specifically eliminate Tn-MUC1-positive ICC cells, but not Tn-MUC1-negative ICC cells, in vitro and in vivo. Therefore, our study is expected to provide new therapeutic strategies and ideas for the treatment of ICC.

Targeting Tn-positive tumors with an afucosylated recombinant anti-Tn IgG

The aberrant expression of the Tn antigen (CD175) on surface glycoproteins of human carcinomas is associated with tumorigenesis, metastasis, and poor survival. To target this antigen, we developed Remab6, a recombinant, human chimeric anti-Tn-specific monoclonal IgG. However, this antibody lacks antibody-dependent cell cytotoxicity (ADCC) effector activity, due to core fucosylation of its N-glycans. Here we describe the generation of an afucosylated Remab6 (Remab6-AF) in HEK293 cells in which the FX gene is deleted (FXKO). These cells cannot synthesize GDP-fucose through the de novo pathway, and lack fucosylated glycans, although they can incorporate extracellularly-supplied fucose through their intact salvage pathway. Remab6-AF has strong ADCC activity against Tn+ colorectal and breast cancer cell lines in vitro, and is effective in reducing tumor size in an in vivo xenotransplant mouse model. Thus, Remab6-AF should be considered as a potential therapeutic anti-tumor antibody against Tn+ tumors.

SLC35A2 deficiency reduces protein levels of core 1 β-1,3-galactosyltransferase 1 (C1GalT1) and its chaperone Cosmc and affects their subcellular localization

Nucleotide sugar transporters (NSTs) are multitransmembrane proteins, localized in the Golgi apparatus and/or endoplasmic reticulum, which provide glycosylation enzymes with their substrates. It has been demonstrated that NSTs may form complexes with functionally related glycosyltransferases, especially in the N-glycosylation pathway. However, potential interactions of NSTs with enzymes mediating the biosynthesis of mucin-type O-glycans have not been addressed to date. Here we report that UDP-galactose transporter (UGT; SLC35A2) associates with core 1 β-1,3-galactosyltransferase 1 (C1GalT1; T-synthase). This provides the first example of an interaction between an enzyme that acts exclusively in the O-glycosylation pathway and an NST. We also found that SLC35A2 associated with the C1GalT1-specific chaperone Cosmc, and that the endogenous Cosmc was localized in both the endoplasmic reticulum and Golgi apparatus of wild-type HEK293T cells. Furthermore, in SLC35A2-deficient cells protein levels of C1GalT1 and Cosmc were decreased and their Golgi localization was less pronounced. Finally, we identified SLC35A2 as a novel molecular target for the antifungal agent itraconazole. Based on our findings we propose that NSTs may contribute to the stabilization of their interaction partners and help them to achieve target localization in the cell, most likely by facilitating their assembly into larger functional units.

Emerging Roles of the Unique Molecular Chaperone Cosmc in the Regulation of Health and Disease

The core-1 β1-3galactosyltransferase-specific chaperone 1 (Cosmc) is a unique molecular chaperone of core-1 β1-3galactosyltransferase(C1GALT1), which typically functions inside the endoplasmic reticulum (ER). Cosmc helps C1GALT1 to fold correctly and maintain activity. It also participates in the synthesis of the T antigen, O-glycan, together with C1GALT1. Cosmc is a multifaceted molecule with a wide range of roles and functions. It involves platelet production and the regulation of immune cell function. Besides that, the loss of function of Cosmc also facilitates the development of several diseases, such as inflammation diseases, immune-mediated diseases, and cancer. It suggests that Cosmc is a critical control point in diseases and that it should be regarded as a potential target for oncotherapy. It is essential to fully comprehend Cosmc's roles, as they may provide critical information about its involvement in disease development and pathogenesis. In this review, we summarize the recent progress in understanding the role of Cosmc in normal development and diseases.

A Sweet Warning: Mucin-Type O-Glycans in Cancer

Glycosylation is a common post-translational modification process of proteins. Mucin-type O-glycosylation is an O-glycosylation that starts from protein serine/threonine residues. Normally, it is involved in the normal development and differentiation of cells and tissues, abnormal glycosylation can lead to a variety of diseases, especially cancer. This paper reviews the normal biosynthesis of mucin-type O-glycans and their role in the maintenance of body health, followed by the mechanisms of abnormal mucin-type O-glycosylation in the development of diseases, especially tumors, including the effects of Tn, STn, T antigen, and different glycosyltransferases, with special emphasis on their role in the development of gastric cancer. Finally, tumor immunotherapy targeting mucin-type O-glycans was discussed.

Identification and characterization of circulating immune complexes in IgA nephropathy

The underlying pathology of immunoglobulin A (IgA) nephropathy (IgAN), the most common glomerulonephritis worldwide, is driven by the deposition of immune complexes containing galactose-deficient IgA1 [Tn(+)IgA1] in the glomerular mesangium. Here, we report that novel anti-Tn circulating immune complexes (anti-Tn CICs) contain predominantly IgM, representing large macromolecular complexes of ~1.2 megadaltons to several megadalton sizes together with Tn(+)IgA1 and some IgG. These complexes are significantly elevated in sera of patients with IgAN, which contains higher levels of complement C3, compared to healthy individuals. Anti-Tn CICs are bioactive and induce specific proliferation of human renal mesangial cells. We found that these anti-Tn CICs can be dissociated with small glycomimetic compounds, which mimic the Tn antigen of Tn(+)IgA1, releasing IgA1 from anti-Tn CICs. This glycomimetic compound can also significantly inhibit the proliferative activity of anti-Tn CICs of patients with IgAN. These findings could enhance both the diagnosis of IgAN and its treatment, as specific drug treatments are now unavailable.

IgA vasculitis update: Epidemiology, pathogenesis, and biomarkers

Immunoglobulin A vasculitis (IgAV), formerly known as Henoch-Schönlein purpura, is the most common systemic vasculitis in children, characterized by diverse clinical manifestations with a wide spectrum ranging from isolated cutaneous vasculitis to systemic involvement. The incidence of IgAV is geographically and ethnically variable, with a prevalence in autumn and winter, suggesting a driving role that genetic and environmental factors play in the disease. Although IgAV has a certain degree of natural remission, it varies widely among individuals. Some patients can suffer from severe renal involvement and even progress to end-stage renal disease. Its pathogenesis is complex and has not been fully elucidated. The formation of galactose-deficient IgA1 (Gd-IgA1) and related immune complexes plays a vital role in promoting the occurrence and development of IgAV nephritis. In addition, neutrophil activation is stimulated through the binding of IgA to the Fc alpha receptor I expressed on its surface, resulting in systemic vascular inflammation and tissue damage. Starting from the epidemiological characteristics, this article will review the role of immunological factors such as Gd-IgA1, autoantibodies, circulating immune complexes, complement system, cellular immunization, and the contributions of environmental and genetic factors in the pathogenesis of IgAV, and conclude with the major biomarkers for IgAV.

Role of tumor cell sialylation in pancreatic cancer progression

Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest malignancies and is currently the third leading cause of cancer death. The aggressiveness of PDAC stems from late diagnosis, early metastasis, and poor efficacy of current chemotherapies. Thus, there is an urgent need for effective biomarkers for early detection of PDAC and development of new therapeutic strategies. It has long been known that cellular glycosylation is dysregulated in pancreatic cancer cells, however, tumor-associated glycans and their cognate glycosylating enzymes have received insufficient attention as potential clinical targets. Aberrant glycosylation affects a broad range of pathways that underpin tumor initiation, metastatic progression, and resistance to cancer treatment. One of the prevalent alterations in the cancer glycome is an enrichment in a select group of sialylated glycans including sialylated, branched N-glycans, sialyl Lewis antigens, and sialylated forms of truncated O-glycans such as the sialyl Tn antigen. These modifications affect the activity of numerous cell surface receptors, which collectively impart malignant characteristics typified by enhanced cell proliferation, migration, invasion and apoptosis-resistance. Additionally, sialic acids on tumor cells engage inhibitory Siglec receptors on immune cells to dampen anti-tumor immunity, further promoting cancer progression. The goal of this review is to summarize the predominant changes in sialylation occurring in pancreatic cancer, the biological functions of sialylated glycoproteins in cancer pathogenesis, and the emerging strategies for targeting sialoglycans and Siglec receptors in cancer therapeutics.

A Pathophysiological Approach To Current Biomarkers

Biomarkers are necessary for screening and diagnosing numerous diseases, predicting the prognosis of patients, and following-up treatment and the course of the patient. Everyday new biomarkers are being used in clinics for these purposes. This section will discuss the physiological roles of the various current biomarkers in a healthy person and the pathophysiological mechanisms underlying the release of these biomarkers. This chapter aims to gain a new perspective for evaluating and interpreting the most current biomarkers.

A novel glycosyltransferase-related lncRNA signature correlates with lung adenocarcinoma prognosis

Background

Lung adenocarcinoma (LUAD) is one of the most fatal cancers in the world. Previous studies have shown the increase in glycosylation level, and abnormal expressions of related enzymes are closely related to various cancers. Long non-coding RNAs (lncRNAs) play an important role in the proliferation, metabolism, and migration of cancer cells, but the underlying role of glycosyltransferase (GT)-related lncRNAs in LUAD remains to be elucidated.

Methods

We abstracted 14,056 lncRNAs from The Cancer Genome Atlas (TCGA) dataset and 257 GT-related genes from the Gene Set Enrichment Analysis (GSEA) database. Univariate, LASSO-penalized, and multivariate Cox regression analyses were conducted to construct a GT-related lncRNA prognosis model.

Results

A total of 2,726 GT-related lncRNAs were identified through Pearson’s correlation analysis, and eight of them were utilized to construct a GT-related lncRNA model. The overall survival (OS) of the low-risk group continued to be superior to that of the high-risk group according to the subgroups classified by clinical features. The risk model was proved to have independent prognostic characteristics for LUAD by univariate and multivariate Cox regression analyses. The status of the tumor immune microenvironment and the relevant immunotherapy response was significantly different between the two risk groups. The candidate drugs aimed at LUAD subtype differentiation were identified.

Conclusion

We constructed a risk model comprising eight GT-related lncRNAs which was identified as an independent predictor of prognoses to predict patient survival and guide-related treatments for patients with LUAD.

CD44 Glycosylation as a Therapeutic Target in Oncology

The interaction of non-kinase transmembrane glycoprotein CD44 with ligands including hyaluronic acid (HA) is closely related to the occurrence and development of tumors. Changes in CD44 glycosylation can regulate its binding to HA, Siglec-15, fibronectin, TM4SF5, PRG4, FGF2, collagen and podoplanin and activate or inhibit c-Src/STAT3/Twist1/Bmi1, PI3K/AKT/mTOR, ERK/NF-κB/NANOG and other signaling pathways, thereby having a profound impact on the tumor microenvironment and tumor cell fate. However, the glycosylation of CD44 is complex and largely unknown, and the current understanding of how CD44 glycosylation affects tumors is limited. These issues must be addressed before targeted CD44 glycosylation can be applied to treat human cancers.

Differential Effects of D-Galactose Supplementation on Golgi Glycosylation Defects in TMEM165 Deficiency

Glycosylation is a ubiquitous and universal cellular process in all domains of life. In eukaryotes, many glycosylation pathways occur simultaneously onto proteins and lipids for generating a complex diversity of glycan structures. In humans, severe genetic diseases called Congenital Disorders of Glycosylation (CDG), resulting from glycosylation defects, demonstrate the functional relevance of these processes. No real cure exists so far, but oral administration of specific monosaccharides to bypass the metabolic defects has been used in few CDG, then constituting the simplest and safest treatments. Oral D-Galactose (Gal) therapy was seen as a promising tailored treatment for specific CDG and peculiarly for TMEM165-CDG patients. TMEM165 deficiency not only affects the N-glycosylation process but all the other Golgi-related glycosylation types, then contributing to the singularity of this defect. Our previous results established a link between TMEM165 deficiency and altered Golgi manganese (Mn²⁺) homeostasis. Besides the fascinating power of MnCl₂ supplementation to rescue N-glycosylation in TMEM165-deficient cells, D-Gal supplementation has also been shown to be promising in suppressing the observed N-glycosylation defects. Its effect on the other Golgi glycosylation types, most especially O-glycosylation and glycosaminoglycan (GAG) synthesis, was however unknown. In the present study, we demonstrate the differential impact of D-Gal or MnCl₂ supplementation effects on the Golgi glycosylation defects caused by TMEM165 deficiency. Whereas MnCl₂ supplementation unambiguously fully rescues the N- and O-linked as well as GAG glycosylations in TMEM165-deficient cells, D-Gal supplementation only rescues the N-linked glycosylation, without any effects on the other Golgi-related glycosylation types. According to these results, we would recommend the use of MnCl₂ for TMEM165-CDG therapy.

Truncated O-Glycan-Bearing MUC16 Enhances Pancreatic Cancer Cells Aggressiveness via α4β1 Integrin Complexes and FAK Signaling

Elevated levels of Mucin-16 (MUC16) in conjunction with a high expression of truncated O-glycans is implicated in playing crucial roles in the malignancy of pancreatic ductal adenocarcinoma (PDAC). However, the mechanisms by which such aberrant glycoforms present on MUC16 itself promote an increased disease burden in PDAC are yet to be elucidated. This study demonstrates that the CRISPR/Cas9-mediated genetic deletion of MUC16 in PDAC cells decreases tumor cell migration. We found that MUC16 enhances tumor malignancy by activating the integrin-linked kinase and focal adhesion kinase (ILK/FAK)-signaling axis. These findings are especially noteworthy in truncated O-glycan (Tn and STn antigen)-expressing PDAC cells. Activation of these oncogenic-signaling pathways resulted in part from interactions between MUC16 and integrin complexes (α4β1), which showed a stronger association with aberrant glycoforms of MUC16. Using a monoclonal antibody to functionally hinder MUC16 significantly reduced the migratory cascades in our model. Together, these findings suggest that truncated O-glycan containing MUC16 exacerbates malignancy in PDAC by activating FAK signaling through specific interactions with α4 and β1 integrin complexes on cancer cell membranes. Targeting these aberrant glycoforms of MUC16 can aid in the development of a novel platform to study and treat metastatic pancreatic cancer.

Structural basis for the synthesis of the core 1 structure by C1GalT1

C1GalT1 is an essential inverting glycosyltransferase responsible for synthesizing the core 1 structure, a common precursor for mucin-type O-glycans found in many glycoproteins. To date, the structure of C1GalT1 and the details of substrate recognition and catalysis remain unknown. Through biophysical and cellular studies, including X-ray crystallography of C1GalT1 complexed to a glycopeptide, we report that C1GalT1 is an obligate GT-A fold dimer that follows a S_N2 mechanism. The binding of the glycopeptides to the enzyme is mainly driven by the GalNAc moiety while the peptide sequence provides optimal kinetic and binding parameters. Interestingly, to achieve glycosylation, C1GalT1 recognizes a high-energy conformation of the α-GalNAc-Thr linkage, negligibly populated in solution. By imposing this 3D-arrangement on that fragment, characteristic of α-GalNAc-Ser peptides, C1GalT1 ensures broad glycosylation of both acceptor substrates. These findings illustrate a structural and mechanistic blueprint to explain glycosylation of multiple acceptor substrates, extending the repertoire of mechanisms adopted by glycosyltransferases.

The glycosyltransferase C1GalT1 directs a key step in protein O-glycosylation important for the expression of the cancer-associated Tn and T antigens. Here, the authors provide molecular insights into the function of C1GalT1 by solving the crystal structure of the Drosophila enzyme-substrate complex.

In vivo models of mucin biosynthesis and function

The secreted mucus layer that lines and protects epithelial cells is conserved across diverse species. While the exact composition of this protective layer varies between organisms, certain elements are conserved, including proteins that are heavily decorated with N-acetylgalactosamine-based sugars linked to serines or threonines (O-linked glycosylation). These heavily O-glycosylated proteins, known as mucins, exist in many forms and are able to form hydrated gel-like structures that coat epithelial surfaces. In vivo studies in diverse organisms have highlighted the importance of both the mucin proteins as well as their constituent O-glycans in the protection and health of internal epithelia. Here, we summarize in vivo approaches that have shed light on the synthesis and function of these essential components of mucus.

The barrier and beyond: Roles of intestinal mucus and mucin-type O-glycosylation in resistance and tolerance defense strategies guiding host-microbe symbiosis

Over the past two decades, our appreciation of the gut mucus has moved from a static lubricant to a dynamic and essential component of the gut ecosystem that not only mediates the interface between host tissues and vast microbiota, but regulates how this ecosystem functions to promote mutualistic symbioses and protect from microbe-driven diseases. By delving into the complex chemistry and biology of the mucus, combined with innovative in vivo and ex vivo approaches, recent studies have revealed novel insights into the formation and function of the mucus system, the O-glycans that make up this system, and how they mediate two major host-defense strategies - resistance and tolerance - to reduce damage caused by indigenous microbes and opportunistic pathogens. This current review summarizes these findings by highlighting the emerging roles of mucus and mucin-type O-glycans in influencing host and microbial physiology with an emphasis on host defense strategies against bacteria in the gastrointestinal tract.

Proteome-wide Mendelian randomization identifies causal links between blood proteins and severe COVID-19

In November 2021, the COVID-19 pandemic death toll surpassed five million individuals. We applied Mendelian randomization including >3,000 blood proteins as exposures to identify potential biomarkers that may indicate risk for hospitalization or need for respiratory support or death due to COVID-19, respectively. After multiple testing correction, using genetic instruments and under the assumptions of Mendelian Randomization, our results were consistent with higher blood levels of five proteins GCNT4, CD207, RAB14, C1GALT1C1, and ABO being causally associated with an increased risk of hospitalization or respiratory support/death due to COVID-19 (ORs = 1.12-1.35). Higher levels of FAAH2 were solely associated with an increased risk of hospitalization (OR = 1.19). On the contrary, higher levels of SELL, SELE, and PECAM-1 decrease risk of hospitalization or need for respiratory support/death (ORs = 0.80-0.91). Higher levels of LCTL, SFTPD, KEL, and ATP2A3 were solely associated with a decreased risk of hospitalization (ORs = 0.86-0.93), whilst higher levels of ICAM-1 were solely associated with a decreased risk of respiratory support/death of COVID-19 (OR = 0.84). Our findings implicate blood group markers and binding proteins in both hospitalization and need for respiratory support/death. They, additionally, suggest that higher levels of endocannabinoid enzymes may increase the risk of hospitalization. Our research replicates findings of blood markers previously associated with COVID-19 and prioritises additional blood markers for risk prediction of severe forms of COVID-19. Furthermore, we pinpoint druggable targets potentially implicated in disease pathology.

Simultaneously Identifying and Distinguishing Glycoproteins with O-GlcNAc and O-GalNAc (the Tn Antigen) in Human Cancer Cells

Glycoproteins with diverse glycans are essential to human cells, and subtle differences in glycan structures may result in entirely different functions. One typical example is proteins modified with O-linked β-N-acetylglucosamine (O-GlcNAc) and O-linked α-N-acetylgalactosamine (O-GalNAc) (the Tn antigen), in which the two glycans have very similar structures and identical chemical compositions, making them extraordinarily challenging to be distinguished. Here, we developed an effective method benefiting from selective enrichment and the enzymatic specificity to simultaneously identify and distinguish glycoproteins with O-GlcNAc and O-GalNAc. Metabolic labeling was combined with bioorthogonal chemistry for enriching glycoproteins modified with O-GlcNAc and O-GalNAc. Then, the enzymatic reaction with galactose oxidase was utilized to specifically oxidize O-GalNAc, but not O-GlcNAc, generating the different tags between glycopeptides with O-GlcNAc and O-GalNAc that can be easily distinguishable by mass spectrometry (MS). Among O-GlcNAcylated proteins commonly identified in three types of human cells, those related to transcription and RNA binding are highly enriched. Cell-specific features are also revealed. Among glycoproteins exclusively in Jurkat cells, those involved in human T-lymphotropic virus type 1 (HTLV-1) infection are overrepresented, which is consistent with the cell line source and suggests that protein O-GlcNAcylation participated in the response to the virus infection. Furthermore, glycoproteins with the Tn antigen have different subcellular distributions in different cells, which may be attributed to the distinct mechanisms for the formation of protein O-GalNAcylation.

Novel Quinic Acid Glycerates from Tussilago farfara Inhibit Polypeptide GalNAc-Transferase

The discovery of a bioactive inhibitor tool for human polypeptide N-acetylgalactosaminyl transferases (GalNAc-Ts), the initiating enzyme for mucin-type O-glycosylation, remains challenging. In the present study, we identified an array of quinic acid derivatives, including four new glycerates (1-4) from Tussilago farfara, a traditional Chinese medicinal plant, as active inhibitors of GalNAc-T2 using a combined screening approach with a cell-based T2-specific sensor and purified enzyme assay. These inhibitors dose-dependently inhibited human GalNAc-T2 but did not affect O-linked N-acetylglucosamine transferase (OGT), the other type of glycosyltransferase. Importantly, they are not cytotoxic and retain inhibitory activity in cells lacking elongated O-glycans, which are eliminated by the CRISPR/Cas9 gene editing tool. A structure-activity relationship study unveiled a novel quinic acid-caffeic acid conjugate pharmacophore that directs inhibition. Overall, these new natural product inhibitors could serve as a basis for developing an inhibitor tool for GalNAc-T2.

Update on the role of C1GALT1 in cancer (Review)

Cancer remains one of the most difficult diseases to treat. In the quest for early diagnoses to improve patient survival and prognosis, targeted therapies have become a hot research topic in recent years. Glycosylation is the most common posttranslational modification in mammalian cells. Core 1β1,3-galactosyltransferase (C1GALT1) is a key glycosyltransferase in the glycosylation process and is the key enzyme in the formation of the core 1 structure on which most complex and branched O-glycans are formed. A recent study reported that C1GALT1 was aberrantly expressed in tumors. In cancer cells, C1GALT1 is regulated by different factors. In the present review, the expression of C1GALT1 in different tumors and its possible molecular mechanisms of action are described and the role of C1GALT1 in cancer development is discussed.

Global Loss of Core 1-Derived O-Glycans in Mice Leads to High Mortality Due to Acute Kidney Failure and Gastric Ulcers

The core 1 structure is the major constituent of mucin-type O-glycans, which are added via glycosylation—a posttranslational modification present on membrane-bound and secretory proteins. Core 1 β1,3-galactosyltransferase (C1galt1), an enzyme that synthesizes the core 1 structure, requires Cosmc, a C1galt1-specific molecular chaperone, for its enzymatic activity. Since Cosmc-knockout mice exhibit embryonic lethality, the biological role of core 1-derived O-glycans in the adult stage is not fully understood. We generated ubiquitous and inducible CAGCre-ER^TM/Cosmc-knockout (iCAG-Cos) mice to investigate the physiological function of core 1-derived O-glycans. The iCAG-Cos mice exhibited a global loss of core 1-derived O-glycans, high mortality, and showed a drastic reduction in weights of the thymus, adipose tissue, and pancreas 10 days after Cosmc deletion. They also exhibited leukocytopenia, thrombocytopenia, severe acute pancreatitis, and atrophy of white and brown adipose tissue, as well as spontaneous gastric ulcers and severe renal dysfunction, which were considered the causes underlying the high mortality of the iCAG-Cos mice. Serological analysis indicated the iCAG-Cos mice have lower blood glucose and total blood protein levels and higher triglyceride, high-density lipoprotein, and total cholesterol levels than the controls. These data demonstrate the importance of core 1-derived O-glycans for homeostatic maintenance in adult mice.

4-Deoxy-4-fluoro-GalNAz (4FGalNAz) Is a Metabolic Chemical Reporter of O-GlcNAc Modifications, Highlighting the Notable Substrate Flexibility of O-GlcNAc Transferase

Bio-orthogonal chemistries have revolutionized many fields. For example, metabolic chemical reporters (MCRs) of glycosylation are analogues of monosaccharides that contain a bio-orthogonal functionality, such as azides or alkynes. MCRs are metabolically incorporated into glycoproteins by living systems, and bio-orthogonal reactions can be subsequently employed to install visualization and enrichment tags. Unfortunately, most MCRs are not selective for one class of glycosylation (e.g., N-linked vs O-linked), complicating the types of information that can be gleaned. We and others have successfully created MCRs that are selective for intracellular O-GlcNAc modification by altering the structure of the MCR and thus biasing it to certain metabolic pathways and/or O-GlcNAc transferase (OGT). Here, we attempt to do the same for the core GalNAc residue of mucin O-linked glycosylation. The most widely applied MCR for mucin O-linked glycosylation, GalNAz, can be enzymatically epimerized at the 4-hydroxyl to give GlcNAz. This results in a mixture of cell-surface and O-GlcNAc labeling. We reasoned that replacing the 4-hydroxyl of GalNAz with a fluorine would lock the stereochemistry of this position in place, causing the MCR to be more selective. After synthesis, we found that 4FGalNAz labels a variety of proteins in mammalian cells and does not perturb endogenous glycosylation pathways unlike 4FGalNAc. However, through subsequent proteomic and biochemical characterization, we found that 4FGalNAz does not widely label cell-surface glycoproteins but instead is primarily a substrate for OGT. Although these results are somewhat unexpected, they once again highlight the large substrate flexibility of OGT, with interesting and important implications for intracellular protein modification by a potential range of abiotic and native monosaccharides.

Finding the sweet spot: glycosylation mediated regulation of intestinal inflammation

Glycans are essential cellular components that facilitate a range of critical functions important for tissue development and mucosal homeostasis. Furthermore, specific alterations in glycosylation represent important diagnostic hallmarks of cancer that contribute to tumor cell dissociation, invasion, and metastasis. However, much less is known about how glycosylation contributes to the pathobiology of inflammatory mucosal diseases. Here we will review how epithelial and immune cell glycosylation regulates gut homeostasis and how inflammation-driven changes in glycosylation contribute to intestinal pathobiology.

Development of Urinary Diagnostic Biomarker for IgA Nephropathy by Lectin Microarray

INTRODUCTION

The pathogenic roles of aberrantly glycosylated IgA1 have been reported. However, it is unexplored whether the profiling of urinary glycans contributes to the diagnosis of IgAN.

METHODS

We conducted a retrospective study enrolling 493 patients who underwent renal biopsy at Okayama University Hospital between December 2010 and September 2017. We performed lectin microarray in urine samples and investigated whether c-statistics of the reference standard diagnosis model employing hematuria, proteinuria, and serum IgA were improved by adding the urinary glycan intensity.

RESULTS

Among 45 lectins, 3 lectins showed a significant improvement of the models: Amaranthus caudatus lectin (ACA) with the difference of c-statistics 0.038 (95% CI: 0.019-0.058, p < 0.001), Agaricus bisporus lectin (ABA) 0.035 (95% CI: 0.015-0.055, p < 0.001), and Maackia amurensis lectin (MAH) 0.035 (95% CI: 0.015-0.054, p < 0.001). In 3 lectins, each signal plus reference standard showed good reclassification (category-free NRI and relative IDI) and good model fitting associated with the improvement of AIC and BIC. Stratified by eGFR, the discriminatory ability of ACA plus reference standard was maintained, suggesting the robust renal function-independent diagnostic performance of ACA. By decision curve analysis, there was a 3.45% net benefit by adding urinary glycan intensity of ACA to the reference standard at the predefined threshold probability of 40%.

CONCLUSIONS

The reduction of Gal(β1-3)GalNAc (T-antigen), Sia(α2-3)Gal(β1-3)GalNAc (Sialyl T), and Sia(α2-3)Gal(β1-3)Sia(α2-6)GalNAc (disialyl-T) was suggested by binding specificities of 3 lectins. C1GALT1 and COSMC were responsible for the biosynthesis of these glycans, and they were known to be downregulated in IgAN. The urinary glycan analysis by ACA is a useful and robust noninvasive strategy for the diagnosis of IgAN.

Abnormal sialylation and fucosylation of saliva glycoproteins: Characteristics of lung cancer-specific biomarkers

Dysregulated surface glycoproteins play an important role in tumor cell proliferation and progression. Abnormal glycosylation of these glycoproteins may activate tumor signal transduction and lead to tumor development. The tumor microenvironment alters its molecular composition, some of which regulate protein glycosylation biosynthesis. The glycosylation of saliva proteins in lung cancer patients is different from healthy controls, in which the glycans of cancer patients are highly sialylated and hyperfucosylated. Most studies have shown that O-glycans from cancer are truncated O-glycans, while N-glycans contain fucoses and sialic acids. Because glycosylation analysis is challenging, there are few reports on how glycosylation of saliva proteins is related to the occurrence or progression of lung cancer. In this review, we discussed glycoenzymes involved in protein glycosylation, their changes in tumor microenvironment, potential tumor biomarkers present in body fluids, and abnormal glycosylation of saliva or lung glycoproteins. We further explored the effect of glycosylation changes on tumor signal transduction, and emphasized the role of receptor tyrosine kinases in tumorigenesis and metastasis.