Sialylation of N-linked glycans influences the immunomodulatory effects of IgM on T cells
ABSTRACT: Human serum IgM antibodies are composed of heavily glycosylated polymers with five glycosylation sites on the μ (heavy) chain and one glycosylation site on the J chain. In contrast to IgG glycans, which are vital for a number of biological functions, virtually nothing is known about structure-function relationships of IgM glycans. Natural IgM is the earliest immunoglobulin produced and recognizes multiple antigens with low affinity, whilst immune IgM is induced by antigen exposure and is characterized by a higher antigen specificity. Natural anti-lymphocyte IgM is present in the serum of healthy individuals and increases in inflammatory conditions. It is able to inhibit T cell activation, but the underlying molecular mechanism is not understood. Here we show, for the first time, that sialylated N-linked glycans induce the internalization of IgM by T cells, which in turn causes severe inhibition of T cell responses. The absence of sialic acid residues abolishes these inhibitory activities, showing a key role of sialylated N-glycans in inducing the IgM-mediated immune suppression.
Project description:Activation of murine CD4+ and CD8+ T lymphocytes leads to dramatic remodeling of N-linked glycans. Naïve and activated CD4 T cells, CD8 T cells and B cells were compared for their N-linked glycan structures by MALDI-TOF MS profiling and for expression of glycan transferase genes to assess the biosynthetic basis for any change observed. The major change observed in activated CD4 and CD8 T cells was dramatic reduction of sialylated bi-antennary N-glycans carrying the terminal NeuGc?2-6Gal sequence, and corresponding increase in glycans carrying the Gal?1-3Gal sequence. This change was accounted for by a decrease in the expression of the sialyltransferase ST6Gal, and increase in the expression of the galactosyltransferase ?1-3GalT. Conversely, in B cells no change in terminal sialylation of N-linked glycans was evident, and the expression of the same two glycosyltransferases were increased and decreased, respectively. Keywords = N-linked glycosylation, T cell, B cell, activation, glycosyltransferase, carbohydrate, glycomics, glycan, galactosyltransferase, sialyltransferase Keywords: other
Project description:We want to characterize the glycan moieties on the surface of leukocytes treated with fluorinated analogs of glucosamine. Since these metabolic inhibitors compete with natural-occuring glucosamine used in oligosaccharide chain formation, these compounds have been shown to be effective in lowering Type 2 lactosamine and sialylated Lewis antigens, which results in altered selectin ligand functions. Overall design: We need to establish specific structural evidence that glycans are indeed blunted/altered. Current research efforts include investigations on how circulating leukocytes traffic to inflamed tissues, how circulating solid tumor cells interact with endothelial linings to enhance metastatic potential, and how treatment with analogs of glucosamine disrupt leukocyte trafficking mechanisms and/or influence effector/regulatory function of T cells.
Project description:We want to characterize the glycan moieties on the surface of leukocytes treated with fluorinated analogs of glucosamine. Since these metabolic inhibitors compete with natural-occuring glucosamine used in oligosaccharide chain formation, these compounds have been shown to be effective in lowering Type 2 lactosamine and sialylated Lewis antigens, which results in altered selectin ligand functions. We need to establish specific structural evidence that glycans are indeed blunted/altered. Current research efforts include investigations on how circulating leukocytes traffic to inflamed tissues, how circulating solid tumor cells interact with endothelial linings to enhance metastatic potential, and how treatment with analogs of glucosamine disrupt leukocyte trafficking mechanisms and/or influence effector/regulatory function of T cells.
Project description:Our lab has previously used the Glyco v3 gene-chip to analyze RNA from human macrophages and T-cells, as part of a project examining the effect of cellular origin on the viral infectivity of HIV/SIV. Our experiments have led us to hypothesize that the different glycosylation pathways present in macrophages and T-cells result in the production of virions with differently glycosylated viral proteins and different glycans present on the virion surface. Furthermore, studies with glycosidases using the Glyco v3 gene-chip have indicated that these differences in the glycosylation profiles of virions derived from different cell types may influence viral infectivity. Here we used glyco v3 chips for identifying the enzymes active in the glycosylation pathways of 174xCEM and 293 cells, which are cell types commonly used in HIV and SIV research. These analyses will allow us a better understanding of the role of glycans and glycosylation in cell-type specific effects on viral infectivity because there is a much larger amount of data on virus derived from these cell types and we will be able to relate our studies more directly to previous work in our lab and other labs. RNA from 174xCEM and HEK293 cells, cell types commonly used in HIV and SIV research, was isolated and sent to Microarray Core (E). RNA was prepared in duplicate, totaling 4 samples. Samples were labeled and hybridized to the GLYCOv3 array and gene expression patterns were used to identify enzymes active in glycosylation pathways.
Project description:Bladder carcinogenesis and tumour progression is accompanied by profound alterations in protein glycosylation. These include the presence of short chain O-glycans such as Tn and T antigens and their sialylated counterparts sialyl-Tn(STn) and sialyl-T(ST). The presence of such structures is commonly associated with poor prognosis. In search for prognosis biomarkers and novel therapeutic targets we have screened, using immunohistochemistry, a series of bladder tumours with differing clinicopathology for these short-chain O-glycans. Aiming at identifying protein targets, we have studied the O-glycoproteome of a pool of STn positive tumours from muscle invasive bladder cancer (MIBC) patients.
Project description:A comprehensive glycosylation profile of donkey lactoferrin, isolated by ion exchange chromatography from an individual milk sample, was obtained by means of chymotryptic digestion, TiO2 and HILIC enrichment, reversed-phase high performance liquid chromatography, electrospray mass spectrometry, and high collision dissociation fragmentation. The results obtained allowed the identification of 26 different glycan structures, including high mannose, complex and hybrid N-glycans, linked to the protein backbone via an amide bond to asparagine residues located at the positions 137, 281 and 476. Altogether, the N-glycan structures determined revealed that in donkey milk lactoferrin most of the N-glycans identified are neutral complex/hybrid. Actually, 10 neutral non-fucosylated complex/hybrid N-glycans and 4 neutral fucosylated complex/hybrid N-glycans were found. In addition, 2 high mannose N-glycans, 4 sialylated fucosylated complex/hybrid N-glycans and 6 sialylated non-fucosylatedN-glycans, one of which containing N-glycolylneuramin acid (Neu5Gc), were found. A comparison of the glycosylation profile of donkey milk lactoferrin with respect to that of human, bovine and goat milk lactoferrin is reported.
Project description:Our studies provide direct evidence that O-glycosylation pathways play a role in the regulation of cell growth through apoptosis and proliferation pathways. Eight small molecular weight analogues of the GalNAc-alpha-1-O-serine/threonine structure based on 1-benzyl-2-acetamido-2- deoxy-alpha-O-D-galactopyranoside have been synthesised and tested in 5 human colorectal cancer cell lines. Three inhibitors, 1-benzyl-2-acetamido-2-deoxy-alpha-O-D-galactopyranoside and the corresponding 2-azido- and C-glycoside analogues, were screened in two colorectal cancer cell lines at 0.5mM and showed induction of apoptosis. Proliferation was down regulated in the same two cell lines with all three inhibitors, as detected by Ki67 staining and gene array. Treatment both cell lines with inhibitors led to changes in glycosylation detected with peanut lectin. The competitive action of the inhibitors resulted in the intracellular formation of 28 aryl-glycan products which were identified by MALDI and electrospray mass spectroscopy. The structures found map onto known O-glycosylation biosynthetic pathways and showed a differential pattern for each of the inhibitors in both cell lines. Gene array analysis of the glycogenes illustrated a pattern of glycosytransferases that matched the glycan structures found in glycoproteins and aryl-glycans formed in the PC/AA/C1/SB10C cells, however there was no action of the three inhibitors on glycogene transcript levels. The inhibitors act at both intermediary metabolic and genomic levels, resulting in altered protein glycosylation and arylglycan formation. These events may play a part in growth arrest. Keywords: Response to inhibitors, Apoptosis, Aryl-glycans, Benzyl-O-GalNAc, Growth Inhibition, O-Glycans Overall design: The effects of the O-glycan inhibitors Benzyl 2-azido-2-deoxy-alpha-D-galactopyranoside (alpha-OBn GalN3), Benzyl 2-acetamido-2-deoxy-alpha-D-galactopyranoside (alpha-OBn GalNAc), and 2-(2-acetamido-2-deoxy-alpha-D-galactopyranosyl)-1-phenylethane (alpha-CBn GalNAc) on the colorectal cancer cell line PC/AA/C1/SB10C were examined. The PC/AA/C1/SB10C cells were treated with with 0.5 mM of the inhibitors for four days. In control experiments cells were cultivated without inhibitor. All experiments were performed twice. Total RNA was extracted with RNAzol reagent in accordance to the manufacturer instructions (PeQLab, Biotechnology Fareham, UK), treated with RNase-free DNase (DNA-free, Ambion,Warrington, UK) and integrity verified using the Agilent Bioanalyzer (Agilent Technologies, West Lothian, UK), by the presence of the 28S and 18S rRNA on agarose gels and an A260/280 ratio in the range of 1.9–2.1. A sample (5 μg) of total RNA was used for production of biotinylated cRNA as described in the Affymetrix GeneChip analysis instruction manual (Affymetrix UK, High Wycombe, UK). The human genome 133A 2.0 array was then hybridized with the biotin-labeled cRNA fragments for 16 h at 45°C. Washing steps for the chip, staining with streptavidin-phycoerythrin, signal amplification and scanning were performed according to the manufacturer’s instructions (Affymetrix UK, High Wycombe, UK). Signal values were exported with the GeneChip operating software (GCOS, Affymetrix). Further analyses were performed with the software “CorrXpression”, which is described in detail elsewhere (Klein et al. 2005, J Mol Med. 83:362-376; Wessel et al. 2006, In Silico Biol.6:61-70).
Project description:One of the most common genetic backgrounds for mice used as model to investigate human diseases is the BALB/c strain. This work is aimed to characterize the pattern of natural anti-carbohydrate antibodies present in serum of BALB/c mice by printed glycan array technology. Natural antibodies from serum of BALB/c mice interacted with at least 70 glycans from a library of 419 different carbohydrate structures. However, only a restricted number of these (12, ~17%) were highly recognized by natural antibodies, and shared by more than 80% of mice under examination. This conserved pattern differed dramatically from that of humans. This finding together with not identical repertoires of antibodies between individual mice should be specially considered when mouse models are intended to be used for investigation of human natural antibodies in different biomedical research and diagnostic contexts. Overall design: To study the repertoire of natural circulating anti-carbohydrate antibodies, serum from 20 BALB/c mice was evaluated by printed glycan-array technology (PGA). Microarrays were prepared by Semiotik LLC (Moscow, Russia) from 419 different amine-functionalized glycans, using N-hydroxysuccinimide-derivatized glass slides H Schott-Nexterion (Germany). All glycans were printed in 6 replicates. The glycan library included blood group antigens and other most frequent terminal oligosaccharides and their cores of mammalian N- and O-linked glycoproteins and glycolipids, tumour-associated carbohydrate antigens.
Project description:Dr. Schwarting's research is focused on the analysis of developmentally regulated cell surface molecules and their role in axon guidance and neuronal migration, using the olfactory system as a model. The interaction of cell surface glycans with endogenous lectins in the extracellular matrix provides one mechanism by which axons can utilize specific pathways as they grow towards their targets. Overall design: We have a mutant mouse (b3GNT2 KO) that up-regulates the expression of lactosamine containing glycans in a subset of olfactory neurons. Gene expression profiling was performed using control and mutant mice that up-regulate the expression of lactosamine containing glycans in a subset of olfactory neurons. Glycosyltransferase expression that differed between control and mutant mice were identified.