Studies of Lewis antigens and H. pylori adhesion in CHO cell lines engineered to express Lewis b determinants

Computational Modeling of O-Linked Glycan Biosynthesis in CHO Cells

Glycan biosynthesis simulation research has progressed remarkably since 1997, when the first mathematical model for N-glycan biosynthesis was proposed. An O-glycan model has also been developed to predict O-glycan biosynthesis pathways in both forward and reverse directions. In this work, we started with a set of O-glycan profiles of CHO cells transiently transfected with various combinations of glycosyltransferases. The aim was to develop a model that encapsulated all the enzymes in the CHO transfected cell lines. Due to computational power restrictions, we were forced to focus on a smaller set of glycan profiles, where we were able to propose an optimized set of kinetics parameters for each enzyme in the model. Using this optimized model we showed that the abundance of more processed glycans could be simulated compared to observed abundance, while predicting the abundance of glycans earlier in the pathway was less accurate. The data generated show that for the accurate prediction of O-linked glycosylation, additional factors need to be incorporated into the model to better reflect the experimental conditions.

Identification by mass spectrometry and immunoblotting of xenogeneic antigens in the N- and O-glycomes of porcine, bovine and equine heart tissues

Animal bioprosthetic heart valves (BHV) are used to replace defective valves in patients with valvular heart disease. Especially young BHV recipients may experience a structural valve deterioration caused by an immune reaction in which α-Gal and Neu5Gc are potential target antigens. The expression of these and other carbohydrate antigens in animal tissues used for production of BHV was explored. Protein lysates of porcine aortic and pulmonary valves, and porcine, bovine and equine pericardia were analyzed by Western blotting using anti-carbohydrate antibodies and lectins. N-glycans were released by PNGase F digestion and O-glycans by β-elimination. Released oligosaccharides were analyzed by liquid chromatography – tandem mass spectrometry. In total, 102 N-glycans and 40 O-glycans were identified in animal heart tissue lysates. The N- and O-glycan patterns were different between species. α-Gal and Neu5Gc were identified on both N- and O-linked glycans, N,N´-diacetyllactosamine (LacdiNAc) on N-glycans only and sulfated O-glycans. The relative amounts of α-Gal-containing N-glycans were higher in bovine compared to equine and porcine pericardia. In contrast to the restricted number of proteins carrying α-Gal and LacdiNAc, the distribution of proteins carrying Neu5Gc-determinants varied between species and between different tissues of the same species. Porcine pericardium carried the highest level of Neu5Gc-sialylated O-glycans, and bovine pericardium the highest level of Neu5Gc-sialylated N-glycans. The identified N- and O-linked glycans, some of which may be immunogenic and remain in BHVs manufactured for clinical use, could direct future genetic engineering to prevent glycan expression rendering the donor tissues less immunogenic in humans.

Recombinant mucin-type proteins carrying LacdiNAc on different O-glycan core chains fail to support H. pylori binding

The β4-N-acetylgalactosaminyltransferase 3 (B4GALNT3) transfers GalNAc in a β1,4-linkage to GlcNAc forming the LacdiNAc (LDN) determinant on oligosaccharides. The LacdiNAc-binding adhesin (LabA) has been suggested to mediate attachment of Helicobacter pylori to the gastric mucosa via binding to the LDN determinant. The O-glycan core chain specificity of B4GALNT3 is poorly defined. We investigated the specificity of B4GALNT3 on GlcNAc residues carried by O-glycan core 2, core 3 and extended core 1 precursors using transient transfection of CHO-K1 cells and a mucin-type immunoglobulin fusion protein as reporter protein. Binding of the LabA-positive H. pylori J99 and 26695 strains to mucin fusion proteins carrying the LDN determinant on different O-glycan core chains and human gastric mucins with and without LDN was assessed in a microtiter well-based binding assay, while the binding of ¹²⁵I-LDN-BSA to various clinical H. pylori isolates was assessed in solution. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) and western blotting confirmed the requirement of a terminal GlcNAc for B4GALNT3 activity. B4GALNT3 added a β1,4-linked GalNAc to GlcNAc irrespective of whether the latter was carried by a core 2, core 3 or extended core 1 chain. No LDN-mediated adhesion of H. pylori strains 26 695 and J99 to LDN determinants on gastric mucins or a mucin-type fusion protein carrying core 2, 3 and extended core 1 O-glycans were detected in a microtiter well-based adhesion assay and no binding of a ¹²⁵I-labelled LDN-BSA neoglycoconjugate to clinical H. pylori isolates was identified.

Recombinant Mucin-Type Fusion Proteins with a Galα1,3Gal Substitution as Clostridium difficile Toxin A Inhibitors

The capability of a recombinant mucin-like fusion protein, P-selectin glycoprotein ligand-1/mouse IgG2b (PSGL-1/mIgG2b), carrying Galα1,3Galβ1,4GlcNAc determinants to bind and inhibit Clostridium difficile toxin A (TcdA) was investigated. The fusion protein, produced by a glyco-engineered stable CHO-K1 cell line and designated C-PGC2, was purified by affinity and gel filtration chromatography from large-scale cultures. Liquid chromatography-mass spectrometry was used to characterize O-glycans released by reductive β-elimination, and new diagnostic ions to distinguish Galα1,3Gal- from Galα1,4Gal-terminated O-glycans were identified. The C-PGC2 cell line, which was 20-fold more sensitive to TcdA than the wild-type CHO-K1, is proposed as a novel cell-based model for TcdA cytotoxicity and neutralization assays. The C-PGC2-produced fusion protein could competitively inhibit TcdA binding to rabbit erythrocytes, making it a high-efficiency inhibitor of the hemagglutination property of TcdA. The fusion protein also exhibited a moderate capability for neutralization of TcdA cytotoxicity in both C-PGC2 and CHO-K1 cells, the former with and the latter without cell surface Galα1,3Galβ1,4GlcNAc sequences. Future studies in animal models of C. difficile infection will reveal its TcdA-inhibitory effect and therapeutic potential in C. difficile-associated diseases.

Carcinoma-associated fucosylated antigens are markers of the epithelial state and can contribute to cell adhesion through CLEC17A (Prolectin)

Terminal fucosylated motifs of glycoproteins and glycolipid chains are often altered in cancer cells. We investigated the link between fucosylation changes and critical steps in cancer progression: epithelial-to-mesenchymal transition (EMT) and lymph node metastasis.Using mammary cell lines, we demonstrate that during EMT, expression of some fucosylated antigens (e.g.: Lewis Y) is decreased as a result of repression of the fucosyltransferase genes FUT1 and FUT3. Moreover, we identify the fucose-binding bacterial lectin BC2L-C-Nt as a specific probe for the epithelial state.Prolectin (CLEC17A), a human lectin found on lymph node B cells, shares ligand specificities with BC2L-C-Nt. It binds preferentially to epithelial rather than to mesenchymal cells, and microfluidic experiments showed that prolectin behaves as a cell adhesion molecule for epithelial cells. Comparison of paired primary tumors/lymph node metastases revealed an increase of prolectin staining in metastasis and high FUT1 and FUT3 mRNA expression was associated with poor prognosis. Our data suggest that tumor cells invading the lymph nodes and expressing fucosylated motifs associated with the epithelial state could use prolectin as a colonization factor.

A Panel of Recombinant Mucins Carrying a Repertoire of Sialylated O-Glycans Based on Different Core Chains for Studies of Glycan Binding Proteins

Sialylated glycans serve as key elements of receptors for many viruses, bacteria, and bacterial toxins. The microbial recognition and their binding specificity can be affected by the linkage of the terminal sugar residue, types of underlying sugar chains, and the nature of the entire glycoconjugate. Owing to the pathobiological significance of sialylated glycans, we have engineered Chinese hamster ovary (CHO) cells to secrete mucin-type immunoglobulin-fused proteins carrying terminal α2,3- or α2,6-linked sialic acid on defined O-glycan core saccharide chains. Besides stably expressing P-selectin glycoprotein ligand-1/mouse immunoglobulin G2b cDNA (PSGL-1/mIgG2b), CHO cells were stably transfected with plasmids encoding glycosyltransferases to synthesize core 2 (GCNT1), core 3 (B3GNT6), core 4 (GCNT1 and B3GNT6), or extended core 1 (B3GNT3) chains with or without the type 1 chain-encoding enzyme B3GALT5 and ST6GAL1. Western blot and liquid chromatography-mass spectrometry analysis confirmed the presence of core 1, 2, 3, 4, and extended core 1 chains carrying either type 1 (Galb3GlcNAc) or type 2 (Galb4GlcNAc) outer chains with or without α2,6-linked sialic acids. This panel of recombinant mucins carrying a repertoire of sialylated O-glycans will be important tools in studies aiming at determining the fine O-glycan binding specificity of sialic acid-specific microbial adhesins and mammalian lectins.

DCIR interacts with ligands from both endogenous and pathogenic origin

C-type lectins on dendritic cells function as antigen uptake and signaling receptors, thereby influencing cellular immune responses. Dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) is one of the best-studied C-type lectin receptors expressed on DCs and its glycan specificity and functional requirements for ligand binding have been intensively investigated. The carbohydrate specificity of dendritic cell immunoreceptor (DCIR), another DC-expressed lectin, was still debated, but we have recently confirmed DCIR as mannose/fucose-binding lectin. Since DC-SIGN and DCIR may potentially share ligands, we set out to elucidate the interaction of DCIR with established DC-SIGN-binding ligands, by comparing the carbohydrate specificity of DCIR and DC-SIGN in more detail. Our results clearly demonstrate that DC-SIGN has a broader glycan specificity compared to DCIR, which interacts only with mannotriose, sulfo-Lewis(a), Lewis(b) and Lewis(a). While most of the tested DC-SIGN ligands bound DCIR as well, Candida albicans and some glycoproteins on some cancer cell lines were identified as DC-SIGN-specific ligands. Interestingly, DCIR strongly bound human immunodeficiency virus type 1 (HIV-1) gp140 glycoproteins, while its interaction with the well-studied DC-SIGN-binding HIV-1 ligand gp120 was much weaker. Furthermore, DCIR-specific ligands were detected on keratinocytes. Furthermore, the interaction of DCIR with its ligands was strongly influenced by the glycosylation of DCIR. In conclusion, we show that sulfo-Lewis(a) is a high affinity ligand for DCIR and that DCIR interacts with ligands from both pathogenic and endogenous origin of which most are shared by DC-SIGN.

Characterization and in vitro properties of oral lactobacilli in breastfed infants

Background

Lactobacillus species can contribute positively to general and oral health and are frequently acquired by breastfeeding in infancy. The present study aimed to identify oral lactobacilli in breast and formula-fed 4 month-old infants and to evaluate potential probiotic properties of the dominant Lactobacillus species detected. Saliva and oral swab samples were collected from 133 infants who were enrolled in a longitudinal study (n=240) examining the effect of a new infant formula on child growth and development. Saliva was cultured and Lactobacillus isolates were identified from 16S rRNA gene sequences. Five L. gasseri isolates that differed in 16S rRNA sequence were tested for their ability to inhibit growth of selected oral bacteria and for adhesion to oral tissues. Oral swab samples were analyzed by qPCR for Lactobacillus gasseri.

Results

43 (32.3%) infants were breastfed and 90 (67.7%) were formula-fed with either a standard formula (43 out of 90) or formula supplemented with a milk fat globule membrane (MFGM) fraction (47 out of 90). Lactobacilli were cultured from saliva of 34.1% breastfed infants, but only in 4.7% of the standard and 9.3% of the MFGM supplemented formula-fed infants. L. gasseri was the most prevalent (88% of Lactobacillus positive infants) of six Lactobacillus species detected. L. gasseri isolates inhibited Streptococcus mutans binding to saliva-coated hydroxyapatite, and inhibited growth of S. mutans, Streptococcus sobrinus, Actinomyces naeslundii, Actinomyces oris, Candida albicans and Fusobacterium nucleatum in a concentration dependent fashion. L. gasseri isolates bound to parotid and submandibular saliva, salivary gp340 and MUC7, and purified MFGM, and adhered to epithelial cells. L. gasseri was detected by qPCR in 29.7% of the oral swabs. Breastfed infants had significantly higher mean DNA levels of L. gasseri (2.14 pg/uL) than infants fed the standard (0.363 pg/uL) or MFGM (0.697 pg/uL) formula.

Conclusions

Lactobacilli colonized the oral cavity of breastfed infants significantly more frequently than formula-fed infants. The dominant Lactobacillus was L. gasseri, which was detected at higher levels in breastfed than formula-fed infants and displayed probiotic traits in vitro.

Engineering of therapeutic and diagnostic O-glycans on recombinant mucin-type immunoglobulin fusion proteins expressed in CHO cells

Metabolic engineering of mammalian cells for optimized glycosylation is usually done to improve activity and the pharmacokinetic features of glycoprotein therapeutics. The field is mainly focused around engineering of N-glycans. We have created a platform in which recombinant mucin-type immunoglobulin fusion proteins are used as scaffolds for multivalent expression of O-glycans with diagnostic or therapeutic potential. The methods used to make stable CHO cell lines secreting a mucin-type fusion protein with blood group A or B determinants following expression of up to five different cDNAs are described.

Human gastric mucins differently regulate Helicobacter pylori proliferation, gene expression and interactions with host cells

Helicobacter pylori colonizes the mucus niche of the gastric mucosa and is a risk factor for gastritis, ulcers and cancer. The main components of the mucus layer are heavily glycosylated mucins, to which H. pylori can adhere. Mucin glycosylation differs between individuals and changes during disease. Here we have examined the H. pylori response to purified mucins from a range of tumor and normal human gastric tissue samples. Our results demonstrate that mucins from different individuals differ in how they modulate both proliferation and gene expression of H. pylori. The mucin effect on proliferation varied significantly between samples, and ranged from stimulatory to inhibitory, depending on the type of mucins and the ability of the mucins to bind to H. pylori. Tumor-derived mucins and mucins from the surface mucosa had potential to stimulate proliferation, while gland-derived mucins tended to inhibit proliferation and mucins from healthy uninfected individuals showed little effect. Artificial glycoconjugates containing H. pylori ligands also modulated H. pylori proliferation, albeit to a lesser degree than human mucins. Expression of genes important for the pathogenicity of H. pylori (babA, sabA, cagA, flaA and ureA) appeared co-regulated in response to mucins. The addition of mucins to co-cultures of H. pylori and gastric epithelial cells protected the viability of the cells and modulated the cytokine production in a manner that differed between individuals, was partially dependent of adhesion of H. pylori to the gastric cells, but also revealed that other mucin factors in addition to adhesion are important for H. pylori-induced host signaling. The combined data reveal host-specific effects on proliferation, gene expression and virulence of H. pylori due to the gastric mucin environment, demonstrating a dynamic interplay between the bacterium and its host.

BabA-mediated adherence is a potentiator of the Helicobacter pylori type IV secretion system activity

Chronic infection of Helicobacter pylori in the stomach mucosa with translocation of the bacterial cytotoxin-associated gene A (CagA) effector protein via the cag-Type IV secretion system (TFSS) into host epithelial cells are major risk factors for gastritis, gastric ulcers, and cancer. The blood group antigen-binding adhesin BabA mediates the adherence of H. pylori to ABO/Lewis b (Le(b)) blood group antigens in the gastric pit region of the human stomach mucosa. Here, we show both in vitro and in vivo that BabA-mediated binding of H. pylori to Le(b) on the epithelial surface augments TFSS-dependent H. pylori pathogenicity by triggering the production of proinflammatory cytokines and precancer-related factors. We successfully generated Le(b)-positive cell lineages by transfecting Le(b)-negative cells with several glycosyltransferase genes. Using these established cell lines, we found increased mRNA levels of proinflammatory cytokines (CCL5 and IL-8) as well as precancer-related factors (CDX2 and MUC2) after the infection of Le(b)-positive cells with WT H. pylori but not with babA or TFSS deletion mutants. This increased mRNA expression was abrogated when Le(b)-negative cells were infected with WT H. pylori. Thus, H. pylori can exploit BabA-Le(b) binding to trigger TFSS-dependent host cell signaling to induce the transcription of genes that enhance inflammation, development of intestinal metaplasia, and associated precancerous transformations.

Cytolethal distending toxin family members are differentially affected by alterations in host glycans and membrane cholesterol

Cytolethal distending toxins (CDTs) are tripartite protein exotoxins produced by a diverse group of pathogenic Gram-negative bacteria. Based on their ability to induce DNA damage, cell cycle arrest, and apoptosis of cultured cells, CDTs are proposed to enhance virulence by blocking cellular division and/or directly killing epithelial and immune cells. Despite the widespread distribution of CDTs among several important human pathogens, our understanding of how these toxins interact with host cells is limited. Here we demonstrate that CDTs from Haemophilus ducreyi, Aggregatibacter actinomycetemcomitans, Escherichia coli, and Campylobacter jejuni differ in their abilities to intoxicate host cells with defined defects in host factors previously implicated in CDT binding, including glycoproteins, and glycosphingolipids. The absence of cell surface sialic acid sensitized cells to intoxication by three of the four CDTs tested. Surprisingly, fucosylated N-linked glycans and glycolipids, previously implicated in CDT-host interactions, were not required for intoxication by any of the CDTs tested. Finally, altering host-cellular cholesterol, also previously implicated in CDT binding, affected intoxication by only a subset of CDTs tested. The findings presented here provide insight into the molecular and cellular basis of CDT-host interactions.