Control of mucin-type O-glycosylation: a classification of the polypeptide GalNAc-transferase gene family

Sugar symphony: glycosylation in cancer metabolism and stemness

Glycosylation is a complex co-translational and post-translational modification (PTM) in eukaryotes that utilizes glycosyltransferases to generate a vast array of glycoconjugate structures. Recent studies have highlighted the role of glycans in regulating essential molecular, cellular, tissue, organ, and systemic biological processes with significant implications for human diseases, particularly cancer. The metabolic reliance of cancer, spanning tumor initiation, disease progression, and resistance to therapy, necessitates a range of uniquely altered cellular metabolic pathways. In addition, the intricate interplay between cell-intrinsic and -extrinsic mechanisms is exemplified by the communication between cancer cells, cancer stem cells (CSCs), cancer-associated fibroblasts (CAFs), and immune cells within the tumor microenvironment (TME). In this review article, we explore how differential glycosylation in cancer influences the metabolism and stemness features alongside new avenues in glycobiology.

Galnt3, an enzyme engaged in protein glycosylation modification, is essential for the maintaining of intestinal health in zebrafish

Intestinal inflammation significantly impairs intestinal function and is closely associated with various health complications. Understanding its molecular mechanisms is crucial for developing effective therapeutic strategies. Galnt3, a member of the polypeptide N-acetylgalactosaminyltransferase family, participates in multiple biological processes, yet its specific role in intestinal inflammation remains poorly understood. In this study, we observed a significant downregulation of zebrafish galnt3 in response to GCRV virus or poly(I:C) infection. Galnt3 knockout (galnt3-/-) zebrafish exhibited reduced survival rates, particularly following GCRV virus inoculation, accompanied by severe ascites and abdominal hemorrhage. Histopathological examination of intestinal tissues revealed thinning of intestinal walls, shortened villi, and increased acidic mucus secretion, all indicative of aggravated intestinal inflammation. Furthermore, galnt3 deficiency was found to trigger the upregulation of numerous pro-inflammatory cytokine genes. Through cell scratch assays and p38 MAPK phosphorylation analysis, we demonstrated that Galnt3 inhibits p38 MAPK phosphorylation and macrophage migration, thereby reducing the production of pro-inflammatory factors. Our findings highlight the pivotal role of Galnt3 in maintaining intestinal homeostasis and regulating inflammatory responses, providing valuable insights into the molecular mechanisms underlying intestinal inflammation and identifying potential therapeutic targets.

Molecular mechanisms and pathophysiological implications of mucin-type O-glycosylation dysregulation in colorectal cancer progression

Colorectal cancer (CRC) is among the most prevalent malignancies globally, with 1.9 million new cases annually. While CRC pathogenesis has been widely attributed to the adenoma-carcinoma and serrated sequences, our study highlights the critical and multifaceted role of O-glycosylation impairment in this malignancy. Mucin-type O-glycosylation, a key post-translational modification, exerts significant effects on tumor cells, impacting their proliferation, migration, and invasiveness. Additionally, its influence on the immune response to CRC presents novel perspectives for potential therapeutic interventions. The authors conducted a systematic literature review following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, using databases such as Google Scholar, PubMed, and Scopus. In this article, we provide a comprehensive analysis of the mechanisms underlying mucin-type O-glycosylation disruption in CRC and examine how these mechanisms could serve as biomarkers for early diagnosis and personalized treatment strategies. Our findings contribute to a more detailed understanding of CRC pathogenesis and offer promising directions for innovative diagnostic and therapeutic approaches, which in the future may lead to improved patient prognosis.

Analysis of O-Glycans by Oxidative Release Combined with 3-Nitrophenylhydrazine Derivatization

Glycosylation profiling is an effective methodology for achieving a comprehensive understanding of glycoproteins and their alterations in a multitude of pathological conditions. However, in comparison to N-glycosylation, O-glycosylation presents significant challenges in terms of both qualitative and quantitative mass spectrometric analyses. A recently developed oxidative release protocol enables the selective formation of O-glycans containing a carboxyl group derived from the amino acid residue. In this study, 3-nitrophenylhydrazine was used to derivatize the common carboxyl group in a mild hydrophilic solution. Derivatization resulted in the generation of a series of report ions for serine, threonine, sialic acid, and O-acetylated sialic acid residues, thereby facilitating the identification of O-glycans and their attached amino acid residues, as well as the determination of the number of O-acetyl groups. A total of 65 O-glycans can be identified from bovine mucin. Furthermore, the analytical strategy revealed that O-acetylated N-acetylneuraminic acid (Neu5Ac)-containing O-glycans from horse serum exhibited distinctive fragmentation patterns in comparison to those from bovine mucin. Additionally, the presence of deaminoneuraminic acid (KDN)-containing O-glycans was successfully confirmed in fish intestinal tissue. These findings suggest that this method provides an economical and potentially valuable tool for large-scale O-glycosylation studies in complex biological samples.

Glycosylation in T2 high and Th17 Asthma: A Narrative Review

Glycosylation, a fundamental biochemical process, entails the covalent attachment of sugar molecules to proteins, DNA, or RNA. Beginning with an overview of the pathophysiological features of asthma, this review proceeds to elucidate various facets of glycosylation in asthma pathology, specifically in T2 high asthma and Th17-mediated responses. We examined glycosylation's involvement in regulating airway inflammation, encompassing the modulation of pro-inflammatory cytokine release such as IL-4, IL-5, and IL-13, key components of T2 inflammation, as well as its significance in modulating immune cell functionality, notably T cells and dendritic cells. Moreover, we explored glycosylation's impact on airway remodeling processes, including its regulation of airway smooth muscle cell proliferation and migration. Addressing molecular mechanisms, this review delved into several glycosylation modifications of proteins and genes implicated in asthma pathogenesis, including IgE, IL-4 receptor, TGF-β, and the regulation of select glycosylation enzymes. Additionally, the review highlights the role of Th17 cells in T2 high asthma and their modulation through glycosylation. We underscored future research imperatives, including biomarker discovery, therapeutic realization, and the potential utility of glycosylation modifications in asthma prevention and management. In short, this review provides an in-depth analysis of the critical role of glycosylation in the pathogenesis of T2 high asthma and Th17 responses.

Exonic CircGUCY1A2 inhibits pulmonary artery smooth muscle cells phenotypic switching via regulating O-glycosylation of COL3A1 in pulmonary hypertension

Pulmonary hypertension (PH) is a fatal disease characterized by pulmonary vascular remodeling, whose regulatory mechanisms remain unclear. Circular RNAs (circRNAs) are a unique class of RNA molecules produced by covalent linkages via back-splicing of linear RNA and play vital roles in regulating physiological and pathological processes. However, the dysregulation of circRNAs and their underlying mechanisms in PH remain unclear. In this study, we identified and investigated the specific functions of circGUCY1A2 in human pulmonary artery smooth muscle cells (PASMCs). We found that circGUYC1A2 expression was markedly downregulated in human PASMCs exposed to hypoxia. Overexpression of circGUCY1A2 impedes the transition of human PASMCs to a synthetic phenotype in vitro and pulmonary vascular remodeling in vivo. Additionally, through mechanistic exploration, we discovered that circGUCY1A2 hindered its glycosylation and attenuated its stability by interacting with the Ser1132 and Ser1145 sites of COL3A1, thereby affecting the expression of osteopontin (OPN) and inhibiting phenotypic switching in human PASMCs. In conclusion, our study revealed that circGUCY1A2 effectively hindered the transition of human PASMCs to a synthetic phenotype by binding to and regulating the O-glycosylation modification of COL3A1. These results identify circGUCY1A2 as a potential therapeutic target and reveal a novel post-transcriptional regulatory mechanism in PH.

Cell-free synthesis system: An accessible platform from biosensing to biomanufacturing

The fundamental aspect of cell-free synthesis systems is the in vitro transcription-translation process. By artificially providing the components required for protein expression, in vitro protein production alleviates various limitations tied to in vivo production, such as oxygen supply and nutrient constraints, thus showcasing substantial potential in engineering applications. This article presents a comprehensive review of cell-free synthesis systems, with a primary focus on biosensing and biomanufacturing. In terms of biosensing, it summarizes the recognition-response mechanisms and key advantages of cell-free biosensors. Moreover, it examines the strategies for the cell-free production of intricate proteins, including membrane proteins and glycoproteins. Additionally, the integration of cell-free metabolic engineering approaches with cell-free synthesis systems in biomanufacturing is thoroughly discussed, with the expectation that biotechnology will embrace greater prosperity.

Glycosylation editing: an innovative therapeutic opportunity in precision oncology

Cancer is still one of the most arduous challenges in the human society, even though humans have found many ways to try to conquer it. With our incremental understandings on the impact of sugar on human health, the clinical relevance of glycosylation has attracted our attention. The fact that altered glycosylation profiles reflect and define different health statuses provide novel opportunities for cancer diagnosis and therapeutics. By reviewing the mechanisms and critical enzymes involved in protein, lipid and glycosylation, as well as current use of glycosylation for cancer diagnosis and therapeutics, we identify the pivotal connection between glycosylation and cellular redox status and, correspondingly, propose the use of redox modulatory tools such as cold atmospheric plasma (CAP) in cancer control via glycosylation editing. This paper interrogates the clinical relevance of glycosylation on cancer and has the promise to provide new ideas for laboratory practice of cold atmospheric plasma (CAP) and precision oncology therapy.

The emerging role of glycans and the importance of sialylation in cardiovascular disease

Glycosylation is the process by which glycans (i.e. 'sugars') are enzymatically attached to proteins or lipids to form glycoconjugates. Growing evidence points to glycosylation playing a central role in atherosclerosis. Glycosylation occurs in all human cells and post-translationally modifies many signalling molecules that regulate cardiovascular disease, affecting their binding and function. Glycoconjugates are present in abundance on the vascular endothelium and on circulating lipoproteins, both of which have well-established roles in atherosclerotic plaque development. Sialic acid is a major regulator of glycan function and therefore the process of sialylation, in which sialic acid is added to glycans, is likely to be entwined in any regulation of atherosclerosis. Glycans and sialylation regulators have the potential to present as new biomarkers that predict atherosclerotic disease or as targets for pharmacological intervention, as well as providing insights into novel cardiovascular mechanisms. Moreover, the asialoglycoprotein receptor 1 (ASGR1), a glycan receptor, is emerging as an exciting new regulator of lipid metabolism and coronary artery disease. This review summarises the latest advances in the growing body of evidence that supports an important role for glycosylation and sialylation in the regulation of atherosclerosis.

Charge matters: how flanking substrate charge modulates O-glycan Core elongation

Mucin type O-glycan core elongation is typically performed by the C1GALT1, B3GNT6, and ST6GalNAc-I/-II O-glycosyltransferases. These enzymes target the Tn antigen (GalNAc-O-Thr/Ser) dictating the fate of O-glycan elongation, playing important roles in health and disease. Changes in transferase expression and glycan structure are commonly associated with diseases such as cancer, Tn-syndrome, and ulcerative colitis. Despite their significance, their substrate specificities and their biological roles remain elusive. Here, we examine the roles of flanking glycopeptide substrate charge using a library of differently charged glycopeptides and a small library of PSGL-1 Thr57 based charged glycopeptides. We found that C1GALT1 was most influenced by flanking charge preferring negatively charged substrates, while B3GNT6 and ST6GalNAc-II were less influenced, showing unique N- and C-terminal charge preferences. Interestingly, ST6GalNAc-I was not influenced by flanking charge. These charge specificities were further maintained against the charged PSGL-1 glycopeptides, although ST6GalNAc-I showed an increased preference towards a remote N-terminal positive charge. The observed charge preferences were to a large part driven by substrate interactions with the electrostatic surface of the transferase. We propose that negative flanking charge may assist C1GALT1 in targeting key glycosites such as in PSGL-1 and podoplanin. Our findings are consistent with a Golgi hierarchy, where the cis-Golgi localized GalNAc-Ts and C1GALT1 determine the site and thus fate of glycosylation, while the trans-Golgi less-specific ST6GalNAc-I provides a final capping function. This characterization of substrate charge preference furthers our understanding of how these enzymes select their substrates and may contribute to our understanding of their biological roles.

High soluble expression and characterization of human GalNAc transferase T2 and T11 in Escherichia coli

The efficient expression of soluble glycosyltransferases from mammalian sources in Escherichia coli (E. coli) remains a significant challenge, often resulting in misfolding and the formation of inclusion bodies. In this study, we investigated strategies to enhance the solubility and catalytic activity of human GalNAc-T2 and GalNAc-T11, two O-glycosyltransferases involved in O-glycosylation of glycoproteins. We found that fusion with maltose-binding protein (MBP) and cellulase catalytic domain (Cel-CD), which led to majority of the fusion proteins being soluble, could increase the solubility of the recombinant proteins. Enzyme activity assays revealed that the fusion glycosyltransferase exhibited significantly higher catalytic efficiency than non-fused enzymes. In addition, the influence of GalNAc-T11 lectin domain on substrate specificity was also determined. The presence of lectin domain had no influence on the recognition of specific substrate and the specific activity of GalNAc-T11. This work offers an efficient approach for the large-scale production of human glycosyltransferases with enhanced bioactivity, highlighting its potential for glycosylation engineering of glycoprotein drugs.

Exploring the combined roles of GALNT1 and GALNT2 in hepatocellular carcinoma malignancy and EGFR modulation

BACKGROUND

Hepatocellular carcinoma (HCC), the most formidable subtype of primary liver cancers, is becoming increasingly concerning due to its rising incidence worldwide. HCC ranks as the sixth most diagnosed cancer globally and is the third leading cause of cancer-related deaths. Glycosylation, a common post-translational modification of proteins, is frequently altered in tumors and is associated with the progression of malignancies. GALNT1 and GALNT2 are GalNAc-transferases that initiate protein O-glycosylation and are closely linked to cancer development. Investigating the relationship between GALNT1 and GALNT2 in HCC could provide new insights into the disease's pathogenesis. Thus, this study aimed to explore the combined effects of GALNT1 and GALNT2 transfection on HCC, compared to the effects of modifying each gene individually.

MATERIALS AND METHODS

GALNT1 and GALNT2 were assessed by bioinformatics, qPCR, and Western blot analyses to detect their expression in HCC tissues and cell lines. The effects of GALNT1/GALNT2 overexpression and knockdown on cell viability, proliferation, migration, invasion, and apoptosis were evaluated in HCC cells using CCK8, colony formation, transwell migration and invasion, wound healing, TUNEL, and flow cytometry assays. EGFR protein levels were also analyzed by Western blotting.

RESULTS

Co-transfection of GALNT1 knockdown with GALNT2 overexpression significantly suppressed proliferation, migration, and invasion, while promoting apoptosis in HCC cells. Conversely, co-transfection of GALNT1 overexpression with GALNT2 knockdown enhanced these malignant characteristics compared to the modified single gene. Notably, we observed that GALNT1 and GALNT2 modulated EGFR protein expression. Overall, our findings suggest that the combined activity of GALNT1 and GALNT2 is critical in regulating HCC malignant behaviors.

ER O-glycosylation in synovial fibroblasts drives cartilage degradation

How arthritic synovial fibroblasts (SFs) activate cartilage ECM degradation remains unclear. GALNT enzymes initiate O-glycosylation in the Golgi; when relocated to the ER, their activity stimulates ECM degradation. Here, we show that in human rheumatoid and osteoarthritic synovial SFs, GALNTs are relocated to the ER. In an RA mouse model, GALNTs relocation occurs shortly before arthritis symptoms and abates as the animal recovers. An ER GALNTs inhibitor prevents cartilage ECM degradation in vitro and expression of this chimeric protein in SFs results in the protection of cartilage. One of the ER targets of GALNTs is the resident protein Calnexin, which is exported to the cell surface of arthritic SFs. Calnexin participates in matrix degradation by reducing ECM disulfide bonds. Anti-Calnexin antibodies block ECM degradation and protect animals from RA. In sum, ER O-glycosylation is a key switch in arthritic SFs and glycosylated surface Calnexin could be a therapeutic target.

ILC3s regulate the gut microbiota via host intestinal galactosylation to limit pathogen infection in mice

Host immunity and commensal bacteria synergistically maintain intestinal homeostasis and mediate colonization resistance against pathogens. However, the molecular and cellular mechanisms remain unclear. Here, with a mouse infection model of Citrobacter rodentium, a natural mouse intestinal pathogen that mimics human enteropathogenic Escherichia coli and enterohaemorrhagic Escherichia coli, we find that group 3 innate lymphoid cells (ILC3s) can protect the host from infection by regulating gut microbiota. Mechanistically, ILC3s can control gut dysbiosis through IL-22-dependent regulation of intestinal galactosylation in mice. ILC3 deficiency led to an increase in intestinal galactosylation and the expansion of commensal Akkermansia muciniphila in colonic mucus. The increased A. muciniphila and A. muciniphila-derived metabolic product succinate further promoted the expression of pathogen virulence factors tir and ler, resulting in increased susceptibility to C. rodentium infection. Together, our data reveal a mechanism for ILC3s in protecting against pathogen infection through the regulation of intestinal glycosylation and gut microbiota metabolism.

GALNT5 promotes migration and invasion of pancreatic ductal adenocarcinoma cells by activating Erk signaling pathway

Aberrant glycosylation has been implicated in promoting the progression and metastasis of pancreatic ductal adenocarcinoma (PDAC). However, the contribution of different glycosylation-related genes in PDAC remains to be clarified. In this study, we performed a differential analysis of RNA-Seq data from TCGA and GTEx and found GALNT5 as the most significant upregulated glycosylation-related gene in PDAC. Using publicly available single-cell sequencing data, we further revealed that GALNT5 is predominantly expressed in malignant ductal epithelial cells of PDAC. Correlation analysis indicated that GALNT5 is the essential member of the GALNT family associated with poor prognosis of PDAC. Overexpression of GALNT5 in PANC-1 or MIAPaCa-2 cells with low endogenous GALNT5 enhances migration and invasion. Conversely, knockdown of GALNT5 in AsPC-1 cells with high endogenous GALNT5 inhibits migration and invasion. Mechanistically, we discovered that GALNT5 activates the Erk signaling pathway in PDAC. Our findings suggest GALNT5 is a potential therapeutic target for PDAC.

GALNT3 in Ischemia-Reperfusion Injury of the Kidney

Key Points

N -acetylgalactosaminyltransferase-3 (GALNT3) was downregulated in both ischemic AKI and cisplatin nephrotoxicity. GALNT3 played a protective role in renal tubular cells, and its downregulation contributed to AKI. Mechanistically, GALNT3 protected kidney tubular cells at least partially through O-glycosylation of EGF receptor.

Background

Damages to subcellular organelles, such as mitochondria and endoplasmic reticulum, are well recognized in tubular cell injury and death in AKI. However, the changes and involvement of Golgi apparatus are much less known. In this study, we report the regulation and role of N -acetylgalactosaminyltransferase-3 (GALNT3), a key enzyme for protein glycosylation in Golgi apparatus, in AKI.

Methods

AKI was induced in mice by renal ischemia–reperfusion injury or cisplatin. In vitro , rat kidney proximal tubular cells were subjected to hypoxia/reoxygenation (H/R) injury. To determine the role of GALNT3, its specific inhibitor T3inh-1 was tested in mice, and the effects of GALNT3 overexpression as well as knockdown were examined in the rat renal proximal tubular cells. EGF receptor (EGFR) activation was induced by recombinant EGF or by overexpressing EGFR.

Results

GALNT3 was significantly decreased in both in vivo and in vitro models of AKI induced by renal ischemia–reperfusion injury and cisplatin. T3Inh-1, a specific GALNT3 inhibitor, exacerbated ischemic AKI and suppressed tubular cell proliferation in mice. Moreover, knockdown of GALNT3 increased apoptosis during H/R treatment in rat renal proximal tubular cells, whereas overexpression of GALNT3 attenuated H/R-induced apoptosis, further supporting a protective role of GALNT3. Mechanistically, GALNT3 contributed to O-glycosylation of EGFR and associated EGFR signaling. Activation or overexpression of EGFR suppressed the proapoptotic effect of GALNT3 knockdown in H/R-treated rat renal proximal tubular cells.

Conclusions

GALNT3 protected kidney tubular cells in AKI at least partially through O-glycosylation of EGFR.

RCL glycosylation of serum corticosteroid-binding globulin: implications in cortisol delivery and septic shock

Corticosteroid-binding globulin (CBG) is a serum glycoprotein that binds and delivers anti-inflammatory cortisol to inflammatory sites through neutrophil elastase-mediated proteolysis of an exposed reactive centre loop (RCL) on CBG. Timely and tissue-specific delivery of cortisol is critical to alleviate inflammation including in life-threatening septic shock conditions. Herein, we firstly summarise our recently published report of functional RCL O- and N-glycosylation events of serum CBG (Chernykh, J Biol Chem, 2023). A key finding of that published work was the LC-MS/MS-based discovery of RCL O-glycans at Thr342 and Thr345 of serum CBG and their inhibitory roles in neutrophil elastase-mediated RCL proteolysis. While these observations are of significance as they implicate RCL O-glycosylation as a potential regulator of cortisol delivery, the link to septic shock remains unexplored. To this end, we used a similar LC-MS/MS approach to profile the RCL O-glycosylation of CBG purified from serum of twelve septic shock patients. Serum CBG from all patients exhibited RCL O-glycosylation comprising (di)sialyl T (NeuAc1-2Gal1GalNAc1) core 1-type O-glycan structures decorating exclusively the Thr342 site. Importantly, relative to less severe cases, individuals presenting with the most severe illness displayed elevated RCL O-glycosylation upon ICU admission, suggesting a previously unknown link to septic shock severity. Overall, we have elucidated the coordinated RCL N- and O-glycosylation events of serum CBG, which improve our understanding of molecular mechanisms governing the timely and tissue-specific delivery of cortisol to inflammatory sites. This work provides clues to molecular aberrations and disease mechanisms underpinning septic shock.

Dual functional POGases from bacteria encompassing broader O-glycanase and adhesin activities

Mucin-type O-glycans on glycoproteins are pivotal for biology and impact the quality of biotherapeutics. Furthermore, glycans on host cells serve as ligands for lectins/adhesins on bacteria for bacterium-host interactions in the colonization or attachment/invasion of bacteria. Defining the structure-function relationship of O-glycans is hindered by a lack of enzyme(s) to release sialylated O-glycans from glycoproteins. Here we show identification of endo-α-N-acetylgalactosaminidases (O-glycanases, GH101) with broad substrate specificities, termed Peptide:O-Glycosidase (POGase). In 5 POGase orthologs identified, we characterize one that releases sialylated O-glycans from glycopeptides, glycoproteins and biotherapeutics. Three peptide motifs differentiate the POGase existing in phylum Actinomycetota from known O-glycanases in other bacteria. While the GH101 domain classifies POGases, other domains confer the efficient enzyme activity and binding to major glycans decorating epithelial cells. The dual functional POGases encompassing broader O-glycanase and adhesin activities will facilitate the study of O-glycomics, quality assessment of biotherapeutics, and development of microbiology and medicine.

Differential expression of CD175 and CA19-9 in pancreatic adenocarcinoma

Alterations in protein glycosylation are observed in many solid tumor types leading to formation of tumor-associated carbohydrate antigens (TACAs). The most common TACA is the Tn antigen (CD175), which is a mucin-type O-GalNAc-Ser/Thr/Tyr glycan in membrane and secreted glycoproteins. In addition, two other TACAs are CA19-9 (sialyl-Lewis a), which is used as a prognostic serum marker for pancreatic cancer, and its isomer sialyl-Lewis x (SLex, CD15s), which is overexpressed in many cancer types and associated with metastasis. While CD175 and other TACAs may be expressed by many human carcinomas, little is known about their differential expression patterns in tumors, thus limiting their use as tissue biomarkers or therapeutic targets. Here we address the clinicopathological relevance of the expression of CA19-9, CD15s, and CD175 in pancreatic ductal adenocarcinoma (PDAC) tissues. Semi-quantitative IHC staining with well-defined monoclonal antibodies demonstrates that CD175 is expressed in all PDAC specimens analyzed. Unexpectedly, however, these TACAs are differentially expressed within PDAC specimens and their glycoproteins, but not significantly expressed in adjacent normal tissues. These data provide avenues for novel therapeutic approaches that could combine CD175- and CA19-9-targeting therapies for PDAC patients.

Androgens suppress the sialyltransferases ST3GAL1 and ST3GAL4 and modulate mucin 10 glycosylation in the submandibular gland, related to sex differences in commensal microbiota composition in mice

Sex differences exist in the commensal microbiota that impact on multiple physiological processes in the host. Here, we examined the mechanism by which the sex differences are formed. In addition to the epithelial ductal cell, the acinar cell mass in the submandibular gland was associated with androgen-androgen receptor (AR) signaling. Sex differences in the formation of submandibular mucin 10 (MUC10) were identified using SDS-PAGE. Neuraminidase treatment, which hydrolyzes terminal sialic acid, influenced the mobility shift of MUC10. Androgen-AR signaling negatively regulated ST3 β-galactoside α-2,3-sialyltransferase 1 (St3gal1) and St3gal4 in the submandibular gland. There was a trend and significant sex differences in α-diversity (Shannon, P = .09) and β-diversity (unweighted UniFrac) in oral microbiota composition, respectively. Some female-preferring bacteria including Akkermansia muciniphila can assimilate mucin by degrading terminal sialic acids. Our results indicate that androgen-AR signaling suppresses ST3GAL1 and ST3GAL4, which can influence sex differences in commensal microbiota composition.

The diversity of glycan chains in jellyfish mucin of three Cubozoan species: the contrast in molecular evolution rates of the peptide chain and Glycans

The O-glycan composition of jellyfish (JF) mucin (qniumucin: Q-mucin) extracted from three Cubozoan species was studied after the optimization of the purification protocol. Application of a stepwise gradient of ionic strength to anion exchange chromatography (AEXC) was effective for isolating Q-mucin from coexisting impurities. In the three species, the amino acid sequence of the tandem repeat (TR) region in Q-mucin in all three Cubozoans seemed to remain the same as that in all Scyphozoans, although their glycan chains seemed to exhibit clear diversity. In particular, the amounts of acidic moieties on the glycan chains of Q-mucin from the Cubozoans markedly varied even in these genetically close species. In two of the three Cubozoan species, the fraction of disaccharides was large, showing a sharp contrast to that of the glycans of Q-mucin in Scyphozoans. This study also indicates that the simple sequence of TR commonly inherited in all Cubozoan and Scyphozoan JF species after the long term of evolution over 500 M years. According to this research, the glycans and the TR of mucin-type glycoproteins (MTGPs), forming a hierarchical structure, appear to complement each other in the evolutionary changes because the time required for their hereditary conversion is considerably different. The cooperation of these mechanisms is a strategy to achieve the contradictory functions of biosystems, namely species conservation and diversity acquisition.

Proximity Labeling-Based Identification of MGAT3 Substrates and Revelation of the Tumor-Suppressive Role of Bisecting GlcNAc in Breast Cancer via GLA Degradation

Glycosylation plays a critical role in various biological processes, yet identifying specific glycosyltransferase substrates remains a challenge due to the complexity of glycosylation. Here, we employ proximity labeling with biotin ligases BASU and TurboID to map the proximitome of MGAT3, a glycosyltransferase responsible for the biosynthesis of the bisecting GlcNAc structure, in HEK293T cells. This approach enriched 116 and 189 proteins, respectively, identifying 17 common substrates shared with bisecting GlcNAc-bearing proteome obtained via intact glycopeptide enrichment methods. Gene ontology analysis revealed that the enriched proteins were predominantly localized in the exosome, endoplasmic reticulum, and Golgi apparatus, consistent with subcellular localization of MGAT3 substrates. Notably, four novel substrates, GOLM2, CCDC134, ASPH, and ERO1A, were confirmed to bear bisecting GlcNAc modification, validating the utility of the proximity labeling method. Furthermore, we observed that bisecting GlcNAc modification inhibits breast cancer progression by promoting the degradation of α-galactosidase A (GLA). These findings demonstrate the efficacy of proximity labeling in identifying glycosyltransferase substrates and provide insights into the functional impact of bisecting GlcNAc modification.

Silver Oxide Promoted Synthesis of Alpha O-GalNAc Containing Glyco-Amino Acids: Synthesis of Core 2 Containing Glyco-Amino Acids for Solid Phase Synthesis of Glycopeptides

O-GalNAc glycans on glycoproteins with eight different core structures sharing a common α-glycosidic linkage (O-GalNAc-α-Ser/Thr) are critical in various physiological and pathological processes. Among the eight O-GalNAc glycan cores, core 2 characterized by a GlcNAcβ1-6(Galβ1-3)GalNAc structural motif plays a significant role in regulating diverse biological processes, such as immune response modulation, adhesive properties of selectins, and gastrointestinal tract protection. However, the large-quantity synthesis of core 2 containing glyco-amino acids for downstream solid-phase peptide synthesis is challenging. In this work, we successfully employed a silver oxide for coupling a 2-azido-galactosyl chloride donor with two acceptors, Fmoc-Ser/Thr-OtBu, respectively, for the large-scale synthesis of the two important intermediates, α-GalN3-Fmoc-Ser/Thr-OtBu, which can be further utilized for the large-scale synthesis of core 2 containing glyco-amino acids. The two intermediates, α-GalN3-Fmoc-Ser/Thr-OtBu, were utilized for synthesizing core 2 containing Fmoc-Ser/Thr-COOH. The synthesis of core 2 containing Fmoc-Ser-COOH was achieved on a 1.95 g scale, while the synthesis of core 2 containing Fmoc-Thr-COOH was achieved on a 0.38 g scale. Additionally, the synthesis of the 2-azido-galactosyl chloride donor was optimized into a three-step process with only one column chromatography purification. Finally, core 2 containing Fmoc-Ser/Thr-COOH were applied for the synthesis of glycosylated CCR1 and CCR5 N-terminal peptides.

Diverse perspectives on proteomic posttranslational modifications to address EGFR-TKI resistance in non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is the main histological subtype of lung cancer. For locally advanced and advanced NSCLC, epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI)-targeted therapy has been the first choice for NSCLC patients with EGFR mutations. TKIs, as targeted drugs, inhibit kinase activity and autophosphorylation by competitively binding to the ATP binding site of the EGFR tyrosine kinase domain, which blocks the signal transduction mediated by EGFR and thus inhibits the proliferation of tumor cells. However, drug resistance to TKIs is inevitable. EGFR is also a highly glycosylated receptor tyrosine kinase, and a wide range of crosstalk occurs between phosphorylation and glycosylation. Therefore, can the phosphorylation state be altered by glycosylation to improve drug resistance? In this review, we summarize phosphorylation, glycosylation and the crosstalk between these processes as well as the current research status and methods. We also summarize the autophosphorylation and glycosylation sites of the EGFR protein and their crosstalk. By exploring the relationship between EGFR glycosylation and autophosphorylation in targeted TKI therapy, we find that research on EGFR glycosylation is crucial for targeted NSCLC treatment and will become a research direction for identifying potential targets related to regulating TKI drug sensitivity.

GALNT6 drives lenvatinib resistance in hepatocellular carcinoma through autophagy and cancer-associated fibroblast activation

BACKGROUND

Hepatocellular carcinoma (HCC) remains a significant global health challenge with limited treatment options. Lenvatinib, a tyrosine kinase inhibitor, has shown promise but is often undermined by the development of drug resistance.

METHODS

Utilizing high-throughput sequencing, we investigated the molecular mechanisms underlying lenvatinib resistance in HCC cells, with a focus on metabolic pathways. Key genes, including GALNT6, were validated through quantitative real-time PCR. The effects of GALNT6 knockdown on lenvatinib sensitivity were examined in vitro and in vivo. O-GalNAc glycosylation was assessed using Vicia Villosa Lectin. Immune cell infiltration and interactions were analyzed in the TCGA-LIHC cohort, with further validation by Western blotting and immunohistochemistry.

RESULTS

Our findings indicate that lenvatinib resistance in HCC is driven by the mucin-type O-glycosylation pathway, with GALNT6 playing a critical role. Knockdown of GALNT6 led to reduced O-GalNAc glycosylation, including the modification of LAPTM5, resulting in decreased LAPTM5 activity and autophagy inhibition. Additionally, GALNT6 silencing disrupted the PDGFA-PDGFRB axis, impairing the activation of cancer-associated fibroblasts (CAFs) and reducing their secretion of SPP1, which collectively diminished lenvatinib resistance.

CONCLUSIONS

GALNT6 is integral to the resistance mechanisms against lenvatinib in HCC by modulating autophagy and CAF activation. Targeting GALNT6 offers a promising strategy to enhance lenvatinib efficacy and improve therapeutic outcomes in HCC.

Altered O-Glycans in stimulated whole saliva from patients with primary Sjögren's syndrome and non-pSS sicca

To investigate if salivary O-linked glycans are altered in primary Sjögren's syndrome (pSS), and thus contributing to explain symptoms of oral dryness, and an impaired oral mucosal barrier function leading to changes in microbial metabolism and colonization by both pathogenic and commensal microorganisms and increased prevalence of oral diseases. O-linked oligosaccharides from stimulated whole saliva (SWS) samples from 24 patients with pSS, 38 patients with non-pSS sicca, and 23 healthy controls were analyzed using liquid chromatography mass spectrometer (LC-MS). Non-fractionated reduced and alkylated saliva was dot-blotted to PVDF-membrane and O-linked oligosaccharides were released using reductive beta-elimination. The 50 most abundant glycans were identified and their intensity compared for each sample, reflecting the relative abundance of individual monosaccharide residues. Comparison of the compositions of O-glycans in SWS samples revealed higher relative levels of sialic acid (NeuAc) and lower levels of neutral amino-monosaccharides (HexNAc) in pSS and non-pSS sicca patients than in the healthy controls. MS2 fragmentation analysis of salivary O-glycans suggests that altered sulfation, fucosylation, sialylation and distribution of core types may all contribute to the observed alteration, directly or indirectly. Additionally, the short disaccharide sialyl-Tn was most abundant in the saliva samples from patients with pSS. Our findings indicate that the salivary mucin-type O-glycan profile is altered in pSS, reflecting a dysfunction of the post-translational modification of salivary mucins leading to rheological changes of saliva, oral dryness symptoms, and impaired oral mucosal barrier function. The pathophysiological significance of the aberrant O-glycosylation needs further elucidation.

Giantin mediates Golgi localization of Gal3-O-sulfotransferases and affects salivary mucin sulfation in patients with Sjögren's disease

Sjögren's disease is a chronic autoimmune disease characterized by symptoms of oral and ocular dryness and extraglandular manifestations. Mouth dryness is not only due to reduced saliva volume, but also to alterations in the quality of salivary mucins in patients with Sjögren's disease. Mucins play a leading role in mucosa hydration and protection, where sulfated and sialylated oligosaccharides retain water molecules at the epithelial surface. The correct localization of glycosyltransferases and sulfotransferases within the Golgi apparatus determines adequate O-glycosylation and sulfation of mucins, which depends on specific golgins that tether enzyme-bearing vesicles. Here, we show that a golgin called Giantin was mislocalized in salivary glands from patients with Sjögren's disease and formed protein complexes with Gal3-O-sulfotransferases (Gal3STs), which changed their localization in Giantin-knockout and -knockdown cells. Our results suggest that Giantin could tether Gal3ST-bearing vesicles and that its altered localization could affect Gal3ST activity, explaining the decreased sulfation of MUC5B observed in salivary glands from patients with Sjögren's disease.

C1GALT1 high expression enhances the progression of glioblastoma through the EGFR-AKT/ERK cascade

Core1 β1,3-galactosyltransferase (C1GALT1) is an essential glycotransferase controlling the elongation of GalNAc-type O-glycosylation and its altered expression contributes tumor progression in various cancers. However, the mechanism how C1GALT1 influences gliomas remains unclear. Here，our results from The Cancer Genome Atlas (TCGA) database, The Chinese Glioma Genome Atlas (CGGA) database and the Clinical Proteomic Tumor Analysis Consortium (CPTAC) database showed that the expression of C1GALT1 was increased in higher grade gliomas namely glioblastoma compared with low grade gliomas or non-tumor tissues and significantly associated with poor survival. Downregulation of C1GALT1 suppressed cell proliferation, invasion, and migration in glioma cell lines. Consistent with the result in vitro, C1GALT1 knockdown distinctly inhibited the weight and tumor growth in nude mice. Mechanistically, C1GALT1 knockdown decreased the level of terminal galactose O-glycosylation and phosphorylation on epidermal growth factor receptor (EGFR). Moreover, The AKT/ERK phosphorylation was attenuated in C1GALT1 knockdown cells. And C1GALT1 knockdown decreased the expression of cyclinD1, matrix metalloproteinase 9 (MMP9) through the AKT/ERK signaling pathway Furthermore, transcription factor SP1 which the expression was found to be associated the C1GALT1 expression could bind to the promoter of C1GALT1 gene and regulated its expression. In conclusion, our data show that C1GALT1 enhances the progression of glioma by regulated the O-glycosylation and phosphorylation of EGFR and the subsequent downstream AKT/ERK signaling pathway. Therefore, C1GALT1 represents a potential target for the diagnosis and treatment of glioma.

Regulation of human GnT-IV family activity by the lectin domain

N-Glycan branching critically regulates glycoprotein functions and is involved in various diseases. Among the glycosyltransferases involved in N-glycan branching is the human N-acetylglucosaminyltransferase-IV (GnT-IV) family, which has four members: GnT-IVa, GnT-IVb, GnT-IVc, and GnT-IVd. GnT-IVa and GnT-IVb have glycosyltransferase activity that generates the type-2 diabetes-related β1,4-GlcNAc branch on the α1,3-Man arm of N-glycans, whereas GnT-IVc and GnT-IVd do not. Recently, this enzyme family was found to have a unique lectin domain in the C-terminal region, which is essential for enzyme activity toward glycoprotein substrates but not toward free N-glycans. Furthermore, interaction between the lectin domain of GnT-IV and N-glycan attached to GnT-IV enables self-regulation of GnT-IV activity, indicating that the lectin domain plays a unique and pivotal role in the regulation of GnT-IV activity. In this review, we summarize the GnT-IV family's biological functions, selectivity for glycoprotein substrates, and regulation of enzymatic activity, with a focus on its unique C-terminal lectin domain.

Resolving and functional analysis of RNA editing sites in sheep ovaries and associations with litter size

Sheep litter size is a critical trait in mutton production. While litter size regulation in relation to DNA transcription have been rigorously investigated, the function of RNA editing remains less explored. To elucidate the mechanisms controlling sheep fecundity at the RNA editing level and identify pivotal RNA editing sites, this study scrutinised RNA editing sites (RESs) in follicular and luteal phases of ovaries from sheep with high and low fecundity, and the functions of population-specific RESs were subsequently analysed. A total of 2 182 475 RESs, 74.61% of which were A-to-I and C-to-U sites, were identified. These RESs were fairly evenly dispersed over the chromosomes, with 46.8% showing close clustering (inter-site distance < 300 bp). Notably, 93% were primarily situated in intronic and intergenic regions. In the follicular phase, pivotal RESs were found in the introns of genes including LPS responsive beige-like anchor, MCC regulator of Wnt signalling, and RWD domain containing 3, among others, and in the exon region of EvC ciliary complex subunit 2. In the luteal phase, RESs were observed in the introns of genes such as H/ACA ribonucleoprotein assembly factor and SDA1 domain-containing 1, and the exon and 3'UTR regions of polypeptide N-acetylgalactosaminyltransferase 15 and ilvB acetolactate synthase-like, respectively. High-fecundity sheep showed RESs in the follicular phase in genes such as fibrillin 1, cyclin-dependent kinase 6, and roundabout 1, and in genes such as autophagy-related 2B and versican in the luteal phase. Thirteen RESs specific to the follicular phase and eight specific to the luteal phase were identified in high-fecundity sheep ovaries. These RESs offer promising molecular targets and enhance understanding of multiple births in sheep from the perspective of posttranscriptional alterations.

Breaking Down the Bottlebrush: Atomically Detailed Structural Dynamics of Mucins

Mucins, the biomolecular components of mucus, are glycoproteins that form a thick physical barrier at all tissue-air interfaces, forming a first line of defense against pathogens. Structural features of mucins and their interactions with other biomolecules remain largely unexplored due to the challenges associated with their high-resolution characterization. Combining limited mass spectrometry glycomics and protein sequencing data, we present all-atom, explicitly solvated molecular dynamics simulations of a major respiratory mucin, MUC5B. We detail key forces and degrees of freedom imposed by the extensive O-glycosylation, which imbue the canonically observed bottlebrush-like structures to these otherwise intrinsically disordered protein backbones. We compare our simulation results to static structures observed in recent scanning tunneling microscopy experiments as well as other published experimental efforts. Our work represents the demonstration of a workflow applied to a mucin example, which we hope will be employed by other groups to investigate the dynamics and interactions of other mucins, which can inform on structural details currently inaccessible to experimental techniques.

MALAT1/miR-582-5p/GALNT1/MUC1 axis modulates progression of AML leukemia stem cells by regulating JAK2/STAT3 pathway

Acute myeloid leukemia (AML) is characterized by uncontrolled clonal expansion and differentiation block of immature myeloid cells. Some studies have shown that leukemia stem cells (LSC) are thought to be responsible for the initiation and development of leukemia. Moreover, abnormal O-glycosylation is a key modification in the process of cancer malignancy. In this study, GALNT1 expression was significantly upregulated in LSCs, while knockdown of GALNT1 inhibited cell viability and promoted apoptosis. Importantly, GALNT1 was the direct target of miR-582-5P, and MALAT1 directly interacted with miR-582-5P. In addition, Our investigation corroborated that MALAT1 functioned as an endogenous sponge of miR-582-5P to regulate mucin1 (MUC1) expression, catalyzed by GALNT1, which modulated the activity of JAK2/STAT3 pathway. MALAT1 and MUC1 were targets of transcription factor STAT3 and were regulated by STAT3. In general, these new findings indicated that MALAT1/miR-582-5P/GALNT1 axis is involved in the progression of LSCs, illuminating the possible mechanism mediated by O-glycosylated MUC1 via JAK2/STAT3 pathway.

Polycystic Ovary Syndrome and Ferroptosis: Following Ariadne's Thread

Background: Recent literature suggests that ferroptosis (FPT) may be a key player in polycystic ovary syndrome (PCOS) pathogenesis, but the underlying mechanism(s) remain(s) unclear. Aim: Therefore, herein, we made an effort to reproduce the molecular signature of the syndrome by including FPT and exploring novel drug targets for PCOS. Methods: (a) Our previously constructed PCOS interactions molecular network was extended with the addition of FPT-associated genes (interaction score above 0.7) and (b) gene set enrichment analysis was performed so as to detect over-represented KEGG pathways. Results: The updated interactome includes 140 molecules, 20 of which are predicted/novel, with an interaction score of 7.3, and 12 major hubs. Moreover, we identified 16 over-represented KEGG pathways, with FPT being the most overexpressed pathway. The FPT subnetwork is connected with the PCOS network through KDM1A. Conclusions: FPT cell death is involved in PCOS development, as its major hub TP53 was shown to be the most important hub in the whole PCOS interactome, hence representing a prioritized drug target.

N-acetylgalactosaminyltransferase GALNT6 is a potential therapeutic target of clear cell renal cell carcinoma progression

High expression of truncated O-glycans Tn antigen predicts adverse clinical outcome in patients with clear cell renal cell carcinoma (ccRCC). To understand the biosynthetic underpinnings of Tn antigen changes in ccRCC, we focused on N-acetylgalactosaminyltransferases (GALNTs, also known as GalNAcTs) known to be involved in Tn antigen synthesis. Data from GSE15641 profile and local cohort showed that GALNT6 was significantly upregulated in ccRCC tissues. The current study aimed to determine the role of GALNT6 in ccRCC, and whether GALNT6-mediated O-glycosylation aggravates malignant behaviors. Gain- and loss-of-function experiments showed that overexpression of GALNT6 accelerated ccRCC cell proliferation, migration, and invasion, as well as promoted ccRCC-derived xenograft tumor growth and lung metastasis. In line with this, silencing of GALNT6 yielded the opposite results. Mechanically, high expression of GALNT6 led to the accumulation of Tn antigen in ccRCC cells. By undertaking immunoprecipitation coupled with liquid chromatography/mass spectrometry, vicia villosa agglutinin blot, and site-directed mutagenesis assays, we found that O-glycosylation of prohibitin 2 (PHB2) at Ser161 was required for the GALNT6-induced ccRCC cell proliferation, migration, and invasion. Additionally, we identified lens epithelium-derived growth factor (LEDGF) as a key regulator of GALNT6 transcriptional induction in ccRCC growth and an upstream contributor to ccRCC aggressive behavior. Collectively, our findings indicate that GALNT6-mediated abnormal O-glycosylation promotes ccRCC progression, which provides a potential therapeutic target in ccRCC development.

O-glycosylation of IgA1 and the pathogenesis of an autoimmune disease IgA nephropathy

IgA nephropathy is a kidney disease characterized by deposition of immune complexes containing abnormally O-glycosylated IgA1 in the glomeruli. Specifically, some O-glycans are missing galactose that is normally β1,3-linked to N-acetylgalactosamine of the core 1 glycans. These galactose-deficient IgA1 glycoforms are produced by IgA1-secreting cells due to a dysregulated expression and activity of several glycosyltransferases. Galactose-deficient IgA1 in the circulation of patients with IgA nephropathy is bound by IgG autoantibodies and the resultant immune complexes can contain additional proteins, such as complement C3. These complexes, if not removed from the circulation, can enter the glomerular mesangium, activate the resident mesangial cells, and induce glomerular injury. In this review, we briefly summarize clinical and pathological features of IgA nephropathy, review normal and aberrant IgA1 O-glycosylation pathways, and discuss the origins and potential significance of natural anti-glycan antibodies, namely those recognizing N-acetylgalactosamine. We also discuss the features of autoantibodies specific for galactose-deficient IgA1 and the characteristics of pathogenic immune complexes containing IgA1 and IgG. In IgA nephropathy, kidneys are injured by IgA1-containing immune complexes as innocent bystanders. Most patients with IgA nephropathy progress to kidney failure and require dialysis or transplantation. Moreover, most patients after transplantation experience a recurrent disease. Thus, a better understanding of the pathogenetic mechanisms is needed to develop new disease-specific treatments.

GALNT6 promotes bladder cancer malignancy and immune escape by epithelial-mesenchymal transition and CD8+ T cells

Bladder cancer (BC) ranks as the sixth cancer in males and the ninth most common cancer worldwide. Conventional treatment modalities, including surgery, radiation, chemotherapy, and immunotherapy, have limited efficacy in certain advanced instances. The involvement of GALNT6-mediated aberrant O-glycosylation modification in several malignancies and immune evasion is a subject of speculation. However, its significance in BC has not been investigated. Through the integration of bioinformatics analysis and laboratory experimentation, we have successfully clarified the role of GALNT6 in BC. Our investigation revealed that GALNT6 has significant expression in BC, and its high expression level correlates with advanced stage and high grade, leading to poor overall survival. Moreover, both in vitro and in vivo experiments demonstrate a strong correlation between elevated levels of GALNT6 and tumor growth, migration, and invasion. Furthermore, there is a negative correlation between elevated GALNT6 levels, the extent of CD8+ T cell infiltration in the tumor microenvironment, and the prognosis of patients. Functional experiments have shown that the increased expression of GALNT6 could enhance the malignant characteristics of cancer cells by activating the epithelial-mesenchymal transition (EMT) pathway. In brief, this study examined the impact of GALNT6-mediated abnormal O-glycosylation on the occurrence and progression of bladder cancer and its influence on immune evasion. It also explored the possible molecular mechanism underlying the interaction between tumor cells and immune cells, as well as the bidirectional signaling involved. These findings offer a novel theoretical foundation rooted in glycobiology for the clinical application of immunotherapy in BC.

Comprehensive Glycomic and Glycoproteomic Analyses of Human Programmed Cell Death Protein 1 Extracellular Domain

Human programmed cell death protein 1 (hPD-1) is an essential receptor in the immune checkpoint pathway. It has played an important role in cancer therapy. However, not all patients respond positively to the PD-1 antibody treatment, and the underlying mechanism remains unknown. PD-1 is a transmembrane glycoprotein, and its extracellular domain (ECD) is reported to be responsible for interactions and signal transduction. This domain contains 4 N-glycosylation sites and 25 potential O-glycosylation sites, which implicates the importance of glycosylation. The structure of hPD-1 has been intensively studied, but the glycosylation of this protein, especially the glycan on each glycosylation site, has not been comprehensively illustrated. In this study, hPD-1 ECD expressed by human embryonic kidney 293 (HEK 293) and Chinese hamster ovary (CHO) cells was analyzed; not only N- and O-glycosylation sites but also the glycans on these sites were comprehensively analyzed using mass spectrometry. In addition, hPD-1 ECD binding to different anti-hPD-1 antibodies was tested, and N-glycans were found functioned differently. All of this glycan information will be beneficial for future PD-1 studies.

GALNT9 enrichment attenuates MPP+-induced cytotoxicity by ameliorating protein aggregations containing α-synuclein and mitochondrial dysfunction

BACKGROUND

GALNTs (UDP-GalNAc; polypeptide N-acetylgalactosaminyltransferases) initiate mucin-type O-GalNAc glycosylation by adding N-GalNAc to protein serine/threonine residues. Abnormalities in O-GalNAc glycosylation are involved in various disorders such as Parkinson's disease (PD), a neurodegenerative disorder. GALNT9 is potentially downregulated in PD patients.

METHODS

To determine whether GALNT9 enrichment ameliorates cytotoxicity related to PD-like variations, a pcDNA3.1-GALNT9 plasmid was constructed and transfected into SH-SY5Y cells to establish a GALNT9-overexpressing cell model.

RESULTS

Downregulation of GALNT9 and O-GalNAc glycosylation was confirmed in our animal and cellular models of PD-like variations. GALNT9 supplementation greatly attenuated cytotoxicity induced by MPP+ (1-Methyl-4-phenylpyridinium iodide) since it led to increased levels of tyrosine hydroxylase and dopamine, reduced rates of apoptosis, and significantly ameliorated MPP+-induced mitochondrial dysfunction by alleviating abnormal levels of mitochondrial membrane potential and reactive oxygen species. A long-lasting mPTP (mitochondrial permeability transition pores) opening and calcium efflux resulted in significantly lower activity in the cytochrome C-associated apoptotic pathway and mitophagy process, signifying that GALNT9 supplementation maintained neuronal cell health under MPP+ exposure. Additionally, it was found that glycans linked to proteins influenced the formation of protein aggregates containing α-synuclein, and GALNT9 supplement dramatically reduced such insoluble protein aggregations under MPP+ treatment. Glial GALNT9 predominantly appears under pathological conditions like PD-like variations.

CONCLUSIONS

GALNT9 enrichment improved cell survival, and glial GALNT9 potentially represents a pathogenic index for PD patients. This study provides insights into the development of therapeutic strategies for the treatment of PD.

Aberrant glycosylation in schizophrenia: insights into pathophysiological mechanisms and therapeutic potentials

Schizophrenia (SCZ) is a severe neuropsychiatric disorder characterized by cognitive, affective, and social dysfunction, resulting in hallucinations, delusions, emotional blunting, and disordered thinking. In recent years, proteomics has been increasingly influential in SCZ research. Glycosylation, a key post-translational modification, can alter neuronal stability and normal signaling in the nervous system by affecting protein folding, stability, and cellular signaling. Recent research evidence suggests that abnormal glycosylation patterns exist in different brain regions in autopsy samples from SCZ patients, and that there are significant differences in various glycosylation modification types and glycosylation modifying enzymes. Therefore, this review explores the mechanisms of aberrant modifications of N-glycosylation, O-glycosylation, glycosyltransferases, and polysialic acid in the brains of SCZ patients, emphasizing their roles in neurotransmitter receptor function, synaptic plasticity, and neural adhesion. Additionally, the effects of antipsychotic drugs on glycosylation processes and the potential for glycosylation-targeted therapies are discussed. By integrating these findings, this review aims to provide a comprehensive perspective to further understand the role of aberrant glycosylation modifications in the pathophysiology of SCZ.

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.

In vivo mapping of the mouse Galnt3-specific O-glycoproteome

The UDP-N-acetylgalactosamine polypeptide:N-acetylgalactosaminyltransferase (GalNAc-T) family of enzymes initiates O-linked glycosylation by catalyzing the addition of the first GalNAc sugar to serine or threonine on proteins destined to be membrane-bound or secreted. Defects in individual isoforms of the GalNAc-T family can lead to certain congenital disorders of glycosylation (CDG). The polypeptide N-acetylgalactosaminyltransferase 3 (GALNT)3-CDG, is caused by mutations in GALNT3, resulting in hyperphosphatemic familial tumoral calcinosis due to impaired glycosylation of the phosphate-regulating hormone fibroblast growth factor 23 (FGF23) within osteocytes of the bone. Patients with hyperphosphatemia present altered bone density, abnormal tooth structure, and calcified masses throughout the body. It is therefore important to identify all potential substrates of GalNAc-T3 throughout the body to understand the complex disease phenotypes. Here, we compared the Galnt3-/- mouse model, which partially phenocopies GALNT3-CDG, with WT mice and used a multicomponent approach using chemoenzymatic conditions, a product-dependent method constructed using EThcD triggered scans in a mass spectrometry workflow, quantitative O-glycoproteomics, and global proteomics to identify 663 Galnt3-specific O-glycosites from 269 glycoproteins across multiple tissues. Consistent with the mouse and human phenotypes, functional networks of glycoproteins that contain GalNAc-T3-specific O-glycosites involved in skeletal morphology, mineral level maintenance, and hemostasis were identified. This library of in vivo GalNAc-T3-specific substrate proteins and O-glycosites will serve as a valuable resource to understand the functional implications of O-glycosylation and to unravel the underlying causes of complex human GALNT3-CDG phenotypes.

O-glycosylation contributes to mammalian glycoRNA biogenesis

There is an increasing appreciation for the role of cell surface glycans in modulating interactions with extracellular ligands and participating in intercellular communication. We recently reported the existence of sialoglycoRNAs, where mammalian small RNAs are covalently linked to N-glycans through the modified base acp3U and trafficked to the cell surface. However, little is currently known about the role for O-glycosylation, another major class of carbohydrate polymer modifications. Here, we use parallel genetic, enzymatic, and mass spectrometry approaches to demonstrate that O-linked glycan biosynthesis is responsible for the majority of sialoglycoRNA levels. By examining the O-glycans associated with RNA from cell lines and colon organoids we find known and previously unreported O-linked glycan structures. Further, we find that O-linked glycans released from small RNA from organoids derived from ulcerative colitis patients exhibit higher levels of sialylation than glycans from healthy organoids. Together, our work provides flexible tools to interrogate O-linked glycoRNAs (O-glycoRNA) and suggests that they may be modulated in human disease.

Polypeptide N-acetylgalactosaminyltransferase-15 regulates adipogenesis in human SGBS cells

Adipogenesis involves intricate molecular mechanisms regulated by various transcription factors and signaling pathways. In this study, we aimed to identify factors specifically induced during adipogenesis in the human preadipocyte cell line, SGBS, but not in the mouse preadipocyte cell line, 3T3-L1. Microarray analysis revealed distinct gene expression profiles, with 1460 genes induced in SGBS cells and 1297 genes induced in 3T3-L1 cells during adipogenesis, with only 297 genes commonly induced. Among the genes uniquely induced in SGBS cells, we focused on GALNT15, which encodes polypeptide N-acetylgalactosaminyltransferase-15. Its expression increased transiently during adipogenesis in SGBS cells but remained low in 3T3-L1 cells. Overexpression of GALNT15 increased mRNA levels of CCAAT-enhancer binding protein (C/EBPα) and leptin but had no significant impact on adipogenesis in SGBS cells. Conversely, knockdown of GALNT15 suppressed mRNA expression of adipocyte marker genes, reduced lipid accumulation, and decreased the percentage of cells with oil droplets. The induction of C/EBPα and peroxisome proliferator-activated receptor γ during adipogenesis was promoted or suppressed in SGBS cells subjected to overexpression or knockdown of GALNT15, respectively. These data suggest that polypeptide N-acetylgalactosaminyltransferase-15 is a novel regulatory molecule that enhances adipogenesis in SGBS cells.

Glycosylation: mechanisms, biological functions and clinical implications

Protein post-translational modification (PTM) is a covalent process that occurs in proteins during or after translation through the addition or removal of one or more functional groups, and has a profound effect on protein function. Glycosylation is one of the most common PTMs, in which polysaccharides are transferred to specific amino acid residues in proteins by glycosyltransferases. A growing body of evidence suggests that glycosylation is essential for the unfolding of various functional activities in organisms, such as playing a key role in the regulation of protein function, cell adhesion and immune escape. Aberrant glycosylation is also closely associated with the development of various diseases. Abnormal glycosylation patterns are closely linked to the emergence of various health conditions, including cancer, inflammation, autoimmune disorders, and several other diseases. However, the underlying composition and structure of the glycosylated residues have not been determined. It is imperative to fully understand the internal structure and differential expression of glycosylation, and to incorporate advanced detection technologies to keep the knowledge advancing. Investigations on the clinical applications of glycosylation focused on sensitive and promising biomarkers, development of more effective small molecule targeted drugs and emerging vaccines. These studies provide a new area for novel therapeutic strategies based on glycosylation.

O-Glycosylation of a male seminal fluid protein influences sperm binding and female postmating behavior

Glycoproteins are abundant within the human reproductive system and alterations in glycosylation lead to reproductive disorders, suggesting that glycans play an important role in reproductive function. In this study, we used the Drosophila reproductive system as a model to investigate the biological functions of O-glycosylation. We found that O-glycosylation in the male accessory glands, an organ responsible for secreting seminal fluid proteins, plays important roles in female postmating behavior. The loss of one O-glycosyltransferase, PGANT9, in the male reproductive system resulted in decreased egg production in mated females. We identified one substrate of PGANT9, lectin-46Ca (CG1656), which is known to affect female postmating responses. We further show that the loss of lectin-46Ca O-glycosylation affects its ability to associate with sperm tails, resulting in reduced transfer within the female reproductive system. Our results provide the first example that O-glycosylation of a seminal fluid protein affects its ability to associate with sperm in vivo. These studies may shed light on the biological function of O-glycans in mammalian reproduction.

O-glycosylation of SARS-CoV-2 spike protein by host O-glycosyltransferase strengthens its trimeric structure

Protein O-glycosylation, also known as mucin-type O-glycosylation, is one of the most abundant glycosylation in mammalian cells. It is initially catalyzed by a family of polypeptide GalNAc transferases (ppGalNAc-Ts). The trimeric spike protein (S) of SARS-CoV-2 is highly glycosylated and facilitates the virus's entry into host cells and membrane fusion of the virus. However, the functions and relationship between host ppGalNAc-Ts and O-glycosylation on the S protein remain unclear. Herein, we identify 15 O-glycosites and 10 distinct O-glycan structures on the S protein using an HCD-product-dependent triggered ETD mass spectrometric analysis. We observe that the isoenzyme T6 of ppGalNAc-Ts (ppGalNAc-T6) exhibits high O-glycosylation activity for the S protein, as demonstrated by an on-chip catalytic assay. Overexpression of ppGalNAc-T6 in HEK293 cells significantly enhances the O-glycosylation level of the S protein, not only by adding new O-glycosites but also by increasing O-glycan heterogeneity. Molecular dynamics simulations reveal that O-glycosylation on the protomer-interface regions, modified by ppGalNAc-T6, potentially stabilizes the trimeric S protein structure by establishing hydrogen bonds and non-polar interactions between adjacent protomers. Furthermore, mutation frequency analysis indicates that most O-glycosites of the S protein are conserved during the evolution of SARS-CoV-2 variants. Taken together, our finding demonstrate that host O-glycosyltransferases dynamically regulate the O-glycosylation of the S protein, which may influence the trimeric structural stability of the protein. This work provides structural insights into the functional role of specific host O-glycosyltransferases in regulating the O-glycosylation of viral envelope proteins.

CCDC88C, an O-GalNAc glycosylation substrate of GALNT6, drives breast cancer metastasis by promoting c-JUN-mediated CEMIP transcription

Coiled-coil domain containing 88C (CCDC88C) is a component of non-canonical Wnt signaling, and its dysregulation causes colorectal cancer metastasis. Dysregulated expression of CCDC88C was observed in lymph node metastatic tumor tissues of breast cancer. However, the role of CCDC88C in breast cancer metastasis remains unclear. To address this, the stable BT549 and SKBR3 cell lines with CCDC88C overexpression or knockdown were developed. Loss/gain-of-function experiments suggested that CCDC88C drove breast cancer cell motility in vitro and lung and liver metastasis in vivo. We found that CCDC88C led to c-JUN-induced transcription activation. Overlapping genes were identified from the genes modulated by CCDC88C and c-JUN. CEMIP, one of these overlapping genes, has been confirmed to confer breast cancer metastasis. We found that CCDC88C regulated CEMIP mRNA levels via c-JUN and it exerted pro-metastatic capabilities in a CEMIP-dependent manner. Moreover, we identified the CCDC88C as a substrate of polypeptide N-acetylgalactosaminyltransferase 6 (GALNT6). GALNT6 was positively correlated with CCDC88C protein abundance in the normal breast and breast cancer tissues, indicating that GALNT6 might be associated with expression patterns of CCDC88C in breast cancer. Our data demonstrated that GALNT6 maintained CCDC88C stability by promoting its O-linked glycosylation, and the modification was critical for the pro-metastatic potential of CCDC88C. CCDC88C also could mediate the pro-metastatic potential of GALNT6 in breast cancer. Collectively, our findings uncover that CCDC88C may increase the risk of breast cancer metastasis and elucidate the underlying molecular mechanisms.

Gastroprotective Effect of Isoferulic Acid Derived from Foxtail Millet Bran against Ethanol-Induced Gastric Mucosal Injury by Enhancing GALNT2 Enzyme Activity

Excessive alcohol consumption has led to the prevalence of gastrointestinal ailments. Alleviating gastric disorders attributed to alcohol-induced thinning of the mucus layer has centered on enhancing mucin secretion as a pivotal approach. In this study, foxtail millet bran polyphenol BPIS was divided into two components with MW < 200 D and MW > 200 D by molecular interception technology. Combined with MTT, cell morphology observation, and trypan blue staining, isoferulic acid (IFA) within the MW < 200 D fraction was determined as the effective constituent to mitigate ethanol-induced damage of gastric epithelial cells. Furthermore, a Wistar rat model with similar clinical features to alcohol-induced gastric mucosal injury was established. Then, gastric morphological observation, H&E staining, and assessments of changes in gastric hexosamine content and gastric wall binding mucus levels were carried out, and the results revealed that IFA (10 mg/Kg) significantly ameliorated alcohol-induced gastric mucosal damage. Finally, we applied techniques including Co-IP, molecular docking, and fluorescence spectroscopy and found that IFA inhibited the alcohol-induced downregulation of N-acetylgalactosamintransferase 2 (GALNT2) activity related to mucus synthesis through direct interaction with GALNT2 in gastric epithelial cells, thus promoting mucin synthesis. Our study lays a foundation for whole grain dietary intervention tailored to individuals suffering from alcoholic gastric mucosal injury.

Production of CA125 with Tn antigens using a glycosylphosphatidylinositol anchoring system

Cancer antigen 125 (CA125) is a serum marker associated with ovarian cancer. Despite its widespread use, CA125 levels can also be elevated in benign conditions. Recent reports suggest that detecting serum CA125 that carries the Tn antigen, a truncated O-glycan containing only N-acetylgalactosamine on serine or threonine residues, can improve the specificity of ovarian cancer diagnosis. In this study, we engineered cells to express CA125 with a Tn antigen. To achieve this, we knocked out C1GALT1 and SLC35A1, genes encoding Core1 synthase and a transporter for cytidine-5'-monophospho-sialic acid respectively, in human embryonic kidney 293 (HEK293) cells. In ClGALT1-SLC35A1-knockout (KO) cells, the expression of the Tn antigen showed a significant increase, whereas the expression of the T antigen (galactose-β1,3-N-acetylgalactosamine on serine or threonine residues) was decreased. Due to the inefficient secretion of soluble CA125, we employed a glycosylphosphatidylinositol (GPI) anchoring system. This allowed for the expression of GPI-anchored CA125 on the cell surface of ClGALT1-SLC35A1-KO cells. Cells expressing high levels of GPI-anchored CA125 were then enriched through cell sorting. By knocking out the PGAP2 gene, the GPI-anchored form of CA125 was converted to a secretory form. Through the engineering of O-glycans and the use of a GPI-anchoring system, we successfully produced CA125 with Tn antigen modification.

Targeting host O-linked glycan biosynthesis affects Ebola virus replication efficiency and reveals differential GalNAc-T acceptor site preferences on the Ebola virus glycoprotein

Ebola virus glycoprotein (EBOV GP) is one of the most heavily O-glycosylated viral glycoproteins, yet we still lack a fundamental understanding of the structure of its large O-glycosylated mucin-like domain and to what degree the host O-glycosylation capacity influences EBOV replication. Using tandem mass spectrometry, we identified 47 O-glycosites on EBOV GP and found similar glycosylation signatures on virus-like particle- and cell lysate-derived GP. Furthermore, we performed quantitative differential O-glycoproteomics on proteins produced in wild-type HEK293 cells and cell lines ablated for the three key initiators of O-linked glycosylation, GalNAc-T1, -T2, and -T3. The data show that 12 out of the 47 O-glycosylated sites were regulated, predominantly by GalNAc-T1. Using the glycoengineered cell lines for authentic EBOV propagation, we demonstrate the importance of O-linked glycan initiation and elongation for the production of viral particles and the titers of progeny virus. The mapped O-glycan positions and structures allowed to generate molecular dynamics simulations probing the largely unknown spatial arrangements of the mucin-like domain. The data highlight targeting GALNT1 or C1GALT1C1 as a possible way to modulate O-glycan density on EBOV GP for novel vaccine designs and tailored intervention approaches.IMPORTANCEEbola virus glycoprotein acquires its extensive glycan shield in the host cell, where it is decorated with N-linked glycans and mucin-type O-linked glycans. The latter is initiated by a family of polypeptide GalNAc-transferases that have different preferences for optimal peptide substrates resulting in a spectrum of both very selective and redundant substrates for each isoform. In this work, we map the exact locations of O-glycans on Ebola virus glycoprotein and identify subsets of sites preferentially initiated by one of the three key isoforms of GalNAc-Ts, demonstrating that each enzyme contributes to the glycan shield integrity. We further show that altering host O-glycosylation capacity has detrimental effects on Ebola virus replication, with both isoform-specific initiation and elongation playing a role. The combined structural and functional data highlight glycoengineered cell lines as useful tools for investigating molecular mechanisms imposed by specific glycans and for steering the immune responses in future vaccine designs.