Galactosylation of N-linked oligosaccharides by human beta-1,4-galactosyltransferases I, II, III, IV, V, and VI expressed in Sf-9 cells

New Inhibitors of β-1,4-Galactosyltransferase I Discovered by Virtual Screening

Seven different enzymes comprise the galactosyltransferases family, of which β-1,4-galactosyltransferase I (β-1,4-GALT1) is the major contributor to galactosylation activity in cells. Since abnormalities in galactosylation are associated with many pathophysiological conditions, β-1,4-GALT1 is an interesting new target for drug discovery and molecular probe design. There are several known β-1,4-GALT1 inhibitors, but most of them suffer from low cell permeability and thus low in vivo activity. In the present work, we describe an in silico screening performed using commercially available virtual compound libraries that led us to the discovery of novel β-1,4-GALT1 inhibitors. A virtual screening campaign was performed by docking compound libraries to the binding site of β-1,4-GALT1, followed by biological evaluation of selected hits for their β-1,4-GALT1 inhibitory activity. The IC50 values were determined for the best performing inhibitors to obtain new chemotypes of β-1,4-GALT1 inhibitors.

Molecular Mechanisms Underlying the Loop-Closing Dynamics of β-1,4 Galactosyltransferase 1

The β-1,4 galactosylation catalyzed by β-1,4 galactosyltransferases (β4Gal-Ts) is not only closely associated with diverse physiological and pathological processes in humans but also widely applied in the N-glycan modification of protein glycoengineering. The loop-closing process of β4Gal-Ts is an essential intermediate step intervening in the binding events of donor substrate (UDP-Gal/Mn2+) and acceptor substrate during its catalytic cycle, with a significant impact on the galactosylation activities. However, the molecular mechanisms in regulating loop-closing dynamics are not entirely clear. Here, we construct Markov state models (MSMs) based on approximately 20 μs of all-atom molecular dynamics simulations to explore the loop-closing dynamics for β-1,4 galactosyltransferase 1 (β4Gal-T1). Our MSM reveals five key metastable states of β4Gal-T1 upon substrate binding, indicating that the entire conformational transition occurs on a time scale of ∼10 μs. Moreover, a regulatory mechanism involving six conserved residues (R187, H190, F222, W310, I341, and D346) among β4Gal-Ts is validated to account for the loop-closing dynamics of the C-loop and W-loop by site-directed mutagenesis and enzymatic activity assays, exhibiting high consistency with our computational predictions. Overall, our research proposes detailed atomic-level insight into the loop-closing dynamics of the C-loop and W-loop on β4Gal-T1, contributing to a deeper understanding of catalytic mechanisms of β-1,4 galactosylation.

Central Role of β-1,4-GalT-V in Cancer Signaling, Inflammation, and Other Disease-Centric Pathways

UDP-Galactose: Glucosylceramide, β-1,4-Galactose transferase-V (β-1,4-GalT-V), is a member of a large glycosyltransferase family, primarily involved in the transfer of sugar residues from nucleotide sugars, such as galactose, glucose mannose, etc., to sugar constituents of glycosphingolipids and glycoproteins. For example, UDP-Galactose: Glucosylceramide, β-1,4-galactosyltransferase (β-1,4-GalT-V), transfers galactose to glucosylceramide to generate Lactosylceramide (LacCer), a bioactive "lipid second messenger" that can activate nicotinamide adenine dinucleotide phosphate(NADPH) oxidase (NOX-1) to produce superoxide's (O2-) to activate several signaling pathways critical in regulating multiple phenotypes implicated in health and diseases. LacCer can also activate cytosolic phospholipase A-2 to produce eicosanoids and prostaglandins to induce inflammatory pathways. However, the lack of regulation of β-1,4-GalT-V contributes to critical phenotypes central to cancer and cardiovascular diseases, e.g., cell proliferation, migration, angiogenesis, phagocytosis, and apoptosis. Additionally, inflammation that accompanies β-1,4-GalT-V dysregulation accelerates the initiation and progression of cancer, cardiovascular diseases, as well as inflammation-centric diseases, like lupus erythematosus, chronic obstructive pulmonary disease (COPD), and inflammatory bowel diseases. An exciting development in this field of research arrived due to the recognition that the activation of β-1,4-GalT-V is a "pivotal" point of convergence for multiple signaling pathways initiated by physiologically relevant molecules, e.g., growth factors, oxidized-low density lipoprotein(ox- LDL), pro-inflammatory molecules, oxidative and sheer stress, diet, and cigarette smoking. Thus, dysregulation of these pathways may well contribute to cancer, heart disease, skin diseases, and several inflammation-centric diseases in experimental animal models of human diseases and in humans. These observations have been described under post-transcriptional modifications of β-1,4- GalT-V. On the other hand, we also point to the important role of β-1-4 GalT-V-mediated glycosylation in altering the formation of glycosylated precursor forms of proteins and their activation, e.g., β-1 integrin, wingless-related integration site (Wnt)/-β catenin, Frizzled-1, and Notch1. Such alterations in glycosylation may influence cell differentiation, angiogenesis, diminished basement membrane architecture, tissue remodeling, infiltrative growth, and metastasis in human colorectal cancers and breast cancer stem cells. We also discuss Online Mendelian Inheritance in Man (OMIM), which is a comprehensive database of human genes and genetic disorders used to provide information on the genetic basis of inherited diseases and traits and information about the molecular pathways and biological processes that underlie human physiology. We describe cancer genes interacting with the β-1,4-GalT-V gene and homologs generated by OMIM. In sum, we propose that β-1,4-GalT-V gene/protein serves as a "gateway" regulating several signal transduction pathways in oxidative stress and inflammation leading to cancer and other diseases, thus rationalizing further studies to better understand the genetic regulation and interaction of β-1,4-GalT-V with other genes. Novel therapies will hinge on biochemical analysis and characterization of β-1,4-GalT-V in patient-derived materials and animal models. And using β-1,4-GalT-V as a "bonafide drug target" to mitigate these diseases.

miR-27b targets MAIP1 to mediate lipid accumulation in cultured human and mouse hepatic cells

Non-alcoholic liver disease (NAFLD) is a condition caused by excessive fat accumulation in the liver and developed via multiple pathways. miR-27b has been suggested to play crucial roles in the development of NAFLD, assuming via targeting genes involved in lipid catabolism and anabolism. However, other pathways regulated by miR-27b are largely unknown. Here we show that lipid accumulation was induced in miR-27b-transfected human and mouse hepatic cells and that knockdowns of three miR-27b-target genes, β-1,4-galactosyltransferase 3 (B4GALT3), matrix AAA peptidase interacting protein 1 (MAIP1) and PH domain and leucine rich repeat protein phosphatase 2 (PHLPP2), induced lipid accumulation. We also show that B4GALT3 and MAIP1 were direct targets of miR-27b and overexpression of MAIP1 ameliorated miR-27b-induced lipid accumulation. In addition, we show that hepatic Maip1 expression declined in mice fed a high-fat diet, suggesting the involvement of decreased Maip1 expression in the condition of fatty liver. Overall, we identified MAIP1/miR-27b axis as a mediator of hepatic lipid accumulation, a potential therapeutic target for NAFLD.

Construction and validation of a prognostic marker and risk model for HCC ultrasound therapy combined with WGCNA identification

Background: Hepatocellular carcinoma (HCC) is a malignant tumor with a highly aggressive and metastatic nature. Ultrasound remains a routine monitoring tool for screening, treatment and post-treatment recheck of HCC. Therefore, it is of great significance to explore the role of ultrasound therapy and related genes in prognosis prediction and clinical diagnosis and treatment of HCC.

Methods: Gene co-expression networks were developed utilizing the R package WGCNA as per the expression profiles and clinical features of TCGA HCC samples, key modules were identified by the correlation coefficients between clinical features and modules, and hub genes of modules were determined as per the GS and MM values. Ultrasound treatment differential expression genes were identified using R package limma, and univariate Cox analysis was conducted on the intersection genes of ultrasound differential expression genes and hub genes of key HCC modules to screen the signatures linked with HCC prognosis and construct a risk model. The median risk score was used as the threshold point to classify tumor samples into high- and low-risk groups, and the R package IOBR was used to assess the proportion of immune cells in high- and low-risk groups, R package maftools to assess the genomic mutation differences in high- and low-risk groups, R package GSVA’s ssgsea algorithm to assess the HALLMARK pathway enrichment analysis, and R package pRRophetic to analyze drug sensitivity in patients with HCC.

Results: WGCNA analysis based on the expression profiles and clinical data of the TCGA LIHC cohort identified three key modules with two major clinical features associated with HCC. The intersection of ultrasound-related differential genes and module hub genes was selected for univariate Cox analysis to identify prognostic factors significantly associated with HCC, and a risk score model consisting of six signatures was finally developed to analyze the prognosis of individuals with HCC. The risk model showed strength in the training set, overall set, and external validation set. The percentage of immune cell infiltration, genomic mutations, pathway enrichment scores, and chemotherapy drug resistance were significantly different between high- and low-risk groups according to the risk scores. Expression of model genes correlated with tumor immune microenvironment and clinical tumor characteristics while generally differentially expressed in pan-cancer tumor and healthy samples. In the immunotherapy dataset, patients in the high-risk group had a worse prognosis with immunotherapy, indicating that subjects in the low-risk group are more responsive to immunotherapy.

Conclusion: The 6-gene signature constructed by ultrasound treatment of HCC combined with WGCNA analysis can be used for prognosis prediction of HCC patients and may become a marker for immune response.

O-GlcNAcylation regulates β1,4-GlcNAc-branched N-glycan biosynthesis via the OGT/SLC35A3/GnT-IV axis

N-Linked glycosylation and O-linked N-acetylglucosamine (O-GlcNAc) are important protein post-translational modifications that are orchestrated by a diverse set of gene products. Thus far, the relationship between these two types of glycosylation has remained elusive, and it is unclear whether one influences the other via UDP-GlcNAc, which is a common donor substrate. Theoretically, a decrease in O-GlcNAcylation may increase the products of GlcNAc-branched N-glycans. In this study, via examination by lectin blotting, HPLC, and mass spectrometry analysis, however, we found that the amounts of GlcNAc-branched tri-antennary N-glycans catalyzed by N-acetylglucosaminyltransferase IV (GnT-IV) and tetra-antennary N-glycans were significantly decreased in O-GlcNAc transferase knockdown cells (OGT-KD) compared with those in wild type cells. We examined this specific alteration by focusing on SLC35A3, which is the main UDP-GlcNAc transporter in mammals that is believed to modulate GnT-IV activation. It is interesting that a deficiency of SLC35A3 specifically leads to a decrease in the amounts of GlcNAc-branched tri- and tetra-antennary N-glycans. Furthermore, co-immunoprecipitation experiments have shown that SLC35A3 interacts with GnT-IV, but not with N-acetylglucosaminyltransferase V. Western blot and chemoenzymatic labeling assay have confirmed that OGT modifies SLC35A3 and that O-GlcNAcylation contributes to its stability. Furthermore, we found that SLC35A3-KO enhances cell spreading and suppresses both cell migration and cell proliferation, which is similar to the phenomena observed in the OGT-KD cells. Taken together, these data are the first to demonstrate that O-GlcNAcylation specifically governs the biosynthesis of tri- and tetra-antennary N-glycans via the OGT-SLC35A3-GnT-IV axis.

Phosphorylation of Specificity Protein 3 Is Critical for Activation of β4-Galactosyltransferase 3 Gene Promoter in SH-SY5Y Human Neuroblastoma Cell Line

Elevated expression of β4-galactosyltransferase (β4GalT) 3 is correlated with poor clinical outcome of neuroblastoma patients. Our recent study has revealed that the transcription of the β4GalT3 gene is activated by Specificity protein (Sp) 3 in SH-SY5Y human neuroblastoma cell line. Here we report the biological significance of the Sp3 phosphorylation in the transcriptional activation of the β4GalT3 gene. The treatment of SH-SY5Y cells with 10% fetal bovine serum (FBS) increased the mitogen-activated protein kinase (MAPK) signaling and the promoter activity of the β4GalT3 gene. Meanwhile, the treatment with U0126, an inhibitor for MAPK kinase, decreased the MAPK signaling and the promoter activity. These findings indicate that the transcriptional activation of the β4GalT3 gene is mediated by the MAPK signaling. In SH-SY5Y cells cultured in the medium containing 10% FBS, the serine (Ser) residues in Sp3 were phosphorylated. Human Sp3 contains four Ser residues, Ser73, Ser563, Ser566, and Ser646, as the putative phosphorylation sites. Sp3 mutant with the mutation of Ser73 did not decrease the promoter activation of the β4GalT3 gene, indicating that Ser73 is uninvolved in the promoter activation of the β4GalT3 gene by Sp3. In contrast, Sp3 mutants with the mutations of Ser563, Ser566, and Ser646 significantly reduced the promoter activation by Sp3. The results suggest that the phosphorylation of these Ser residues is implicated in the promoter activation by Sp3. This study demonstrates that the phosphorylation of Sp3 plays important roles in the transcriptional activation of the β4GalT3 gene in human neuroblastoma.

Expression of β-1,4-galactosyltransferases during Aging in Caenorhabditis elegans

BACKGROUND

Altered plasma activity of β-1,4-galac-tosyl-transferases (B4GALTs) is a novel candidate biomarker of human aging. B4GALT1 is assumed to be largely responsible for this activity increase, but how it modulates the aging process is unclear at present.

OBJECTIVES

To determine how expression of B4GALT1 and other B4GALT enzymes changes during aging of an experimentally tractable model organism, Caenorhabditis elegans.

METHODS

Targeted analysis of mRNA levels of all 3 C. elegans B4GALT family members was performed by qPCR in wild-type and in long-lived daf-2 (insulin/IGF1-like receptor)-deficient or germline-deficient animals.

RESULTS

bre-4 (B4GALT1/2/3/4) is the only B4GALT whose expression increases during aging in wild-type worms. In addition, bre-4 levels also rise during aging in long-lived daf-2-deficient worms, but not in animals that are long-lived due to the lack of germline stem cells. On the other hand, expression of sqv-3 (B4GALT7) and of W02B12.11 (B4GALT5/6) appears decreased or constant, respectively, in all backgrounds during aging.

CONCLUSIONS

The age-dependent bre-4 mRNA increase in C. elegans parallels the age-dependent B4GALT activity increase in humans and is consistent with C. elegans being a suitable experimental organism to define potentially conserved roles of B4GALT1 during aging.

N-glycosylation of the human β1,4-galactosyltransferase 4 is crucial for its activity and Golgi localization

β1,4-galactosyltransferase 4 (B4GalT4) is one of seven B4GalTs that belong to CAZy glycosyltransferase family 7 and transfer galactose to growing sugar moieties of proteins, glycolipids, glycosaminoglycans as well as single sugar for lactose synthesis. Herein, we identify two asparagine-linked glycosylation sites in B4GalT4. We found that mutation of one site (Asn220) had greater impact on enzymatic activity while another (Asn335) on Golgi localization and presence of N-glycans at both sites is required for production of stable and enzymatically active protein and its secretion. Additionally, we confirm B4GalT4 involvement in synthesis of keratan sulfate (KS) by generating A375 B4GalT4 knock-out cell lines that show drastic decrease in the amount of KS proteoglycans and no significant structural changes in N- and O-glycans. We show that KS decrease in A375 cells deficient in B4GalT4 activity can be rescued by overproduction of either partially or fully glycosylated B4GalT4 but not with N-glycan-depleted B4GalT4 version.

Suppression of Malignant Potentials of A549 Human Lung Cancer Cell Line by Downregulation of the β4-Galactosyltransferase 1 Gene Expression

Our previous study demonstrated that downregulation of transcription factor Specificity protein (Sp) 1 suppresses the malignant potentials of A549 human lung cancer cell line with the reduced β4-galactosylation of highly branched N-glycans on cell surface glycoproteins. The reduced β4-galactosylation was brought about by the decreased expression of the β4-galactosyltransferase 1 (β4GalT1) gene. Herein, we examined whether the reduced β4-galactosylation by decreasing the β4GalT1 gene expression suppresses the malignant potentials of A549 cells. In the β4GalT1-downregulated cells, the β4-galactosylation of highly branched N-glycans was reduced in several glycoproteins such as lysosome-associated membrane protein-1 and E-cadherin. The anchorage-independent growth and migratory ability of the β4GalT1-downregulated cells decreased when compared with the control cells. Furthermore, the phosphorylation of p44/42 mitogen-activated protein kinase (MAPK) decreased in the β4GalT1-downregulated cells. These results indicate that downregulation of the β4GalT1 gene decreases the β4-galactosylation of highly branched N-glycans and the phosphorylation of p44/42 MAPK, and suppresses the malignant potentials of A549 cells.

B4GALT3 promotes cell proliferation and invasion in glioblastoma

Background: β-1, 4-galactosyltransferase III (B4GALT3) plays an important role in development tumourigenesis. But its role in human glioblastoma (GBM) is still unknown.Materials and methods: To perform gain-of-function and loss-of-function experiment, we transfected siRNA or vector into GBM cells. CCK-8, EdU staining, transwell, western blot, immunofluorescence staining were applied to perform phenotype and mechanism experiment. GlioVis platform was used to analyze B4GALT3 expression from TCGA datasets.Results: B4GALT3 is upregulated in glioblastoma and predicts poor prognosis. Upregulation of B4GALT3 promotes GBM cell proliferation and invasion while the downregulation of B4GALT3 reduces GBM cell proliferation and invasion. B4GALT3 regulates cell proliferation and invasion via β-catenin and vimentin. B4GALT3 correlates with cell invasion markers in clinical samples.Conclusion: B4GALT3 might be a potential molecular therapeutic target of glioblastoma.

β4GALT1 controls β1 integrin function to govern thrombopoiesis and hematopoietic stem cell homeostasis

Glycosylation is critical to megakaryocyte (MK) and thrombopoiesis in the context of gene mutations that affect sialylation and galactosylation. Here, we identify the conserved B4galt1 gene as a critical regulator of thrombopoiesis in MKs. β4GalT1 deficiency increases the number of fully differentiated MKs. However, the resulting lack of glycosylation enhances β1 integrin signaling leading to dysplastic MKs with severely impaired demarcation system formation and thrombopoiesis. Platelets lacking β4GalT1 adhere avidly to β1 integrin ligands laminin, fibronectin, and collagen, while other platelet functions are normal. Impaired thrombopoiesis leads to increased plasma thrombopoietin (TPO) levels and perturbed hematopoietic stem cells (HSCs). Remarkably, β1 integrin deletion, specifically in MKs, restores thrombopoiesis. TPO and CXCL12 regulate β4GalT1 in the MK lineage. Thus, our findings establish a non-redundant role for β4GalT1 in the regulation of β1 integrin function and signaling during thrombopoiesis. Defective thrombopoiesis and lack of β4GalT1 further affect HSC homeostasis.

Transcription of human β4-galactosyltransferase 3 is regulated by differential DNA binding of Sp1/Sp3 in SH-SY5Y human neuroblastoma and A549 human lung cancer cell lines

Poor prognosis of neuroblastoma patients has been shown to be associated with increased expression of β4-galactosyltransferase (β4GalT) 3. To address the underlying mechanism of the increased expression of β4GalT3, the transcriptional regulation of the human β4GalT3 gene was investigated in SH-SY5Y human neuroblastoma cell line comparing with A549 human lung cancer cell line, in which the β4GalT3 gene expression was the lowest among four cancer cell lines examined. The core promoter region was identified between nucleotides -69 and -6 relative to the transcriptional start site, and the same region was utilized in both cell lines. The promoter region contained two Specificity protein (Sp)1/3-binding sites at nucleotide positions -39/-30 and -19/-10, and the sites were crucial for the promoter activity. Although the gene expression of Sp family transcription factors Sp1 and Sp3 was comparable in each cell line, Sp3 bound to the promoter region in SH-SY5Y cells whereas Sp1 bound to the region in A549 cells. The promoter activities were enhanced by Sp1 and Sp3 in SH-SY5Y cells. In contrast, the promoter activities were enhanced by Sp1 but reduced by Sp3 in A549 cells. Furthermore, the function of each Sp1/3-binding site differed between SH-SY5Y and A549 cells due to the differential binding of Sp1/Sp3. These findings suggest that the transcription of the β4GalT3 gene is regulated by differential DNA binding of Sp3 and Sp1 in neuroblastoma and lung cancer. The increased expression of β4GalT3 in neuroblastoma may be ascribed to the enhanced expression of Sp3, which is observed for various cancers.

The contributions of individual galactosyltransferases to protein specific N-glycan processing in Chinese Hamster Ovary cells

Galactosylation as part of N-glycan processing is conducted by a set of beta-1,4-galactosyltransferases (B4GALTs), with B4GALT1 as the dominant isoenzyme for this reaction. Nevertheless, the exact contributions of this key-player as well as of the other isoenzymes involved in N-glycosylation, B4GALT2, B4GALT3 and B4GALT4, have not been studied in-depth. To increase the understanding of the protein- and site-specific activities of individual galactosyltransferases in Chinese Hamster Ovary cells, a panel of triple deletion cell lines was generated that expressed only one isoform of B4GALT each. Two model proteins were selected for this study to cover a large spectrum of possible N-glycan structures: erythropoietin and deamine-oxidase. They were expressed as Fc-fusion constructs (EPO-Fc and Fc-DAO) and their N-glycan processing status was analyzed by site-specific mass spectrometry. The sole activity of B4GALT1 resulted in a decrease of 15-21 % of fully galactosylated structures for erythropoietin, emphasizing the involvement of other isoenzymes. Interestingly, the contributions of B4GALT2 and B4GALT3 differed for the two model proteins. Unexpectedly, removal of galactosyltransferases influenced the overall process of N-glycan maturation, with the result of a higher occurrence of poorly processed oligosaccharides. In the context of high productivity cell lines, which can push N-glycan maturation towards incomplete galactosylation, galactosyltransferases are potential targets to ensure stable product quality. In view of our results, specifically engineered "designer" cell lines may be required for different proteins.

CRISPR/Cas9-Multiplexed Editing of Chinese Hamster Ovary B4Gal-T1, 2, 3, and 4 Tailors N-Glycan Profiles of Therapeutics and Secreted Host Cell Proteins

In production of recombinant proteins for biopharmaceuticals, N-glycosylation is often important for protein efficacy and patient safety. IgG with agalactosylated (G0)-N-glycans can improve the activation of the lectin-binding complement system and be advantageous in the therapy of lupus and virus diseases. In this study, the authors aimed to engineer CHO-S cells for the production of proteins with G0-N-glycans by targeting B4Gal-T isoform genes with CRISPR/Cas9. Indel mutations in genes encoding B4Gal-T1, -T2, and -T3 with and without a disrupted B4Gal-T4 sequence resulted in only ≈1% galactosylated N-glycans on total secreted proteins of 3-4 clones per genotype. The authors revealed that B4Gal-T4 is not active in N-glycan galactosylation in CHO-S cells. In the triple-KO clones, transiently expressed erythropoietin (EPO) and rituximab harbored only ≈6% and ≈3% galactosylated N-glycans, respectively. However, simultaneous disruption of B4Gal-T1 and -T3 may decrease cell growth. Altogether, the authors present the advantage of analyzing total secreted protein N-glycans after disrupting galactosyltransferases, followed by expressing recombinant proteins in selected clones with desired N-glycan profiles at a later stage. Furthermore, the authors provide a cell platform that prevalently glycosylates proteins with G0-N-glycans to further study the impact of agalactosylation on different in vitro and in vivo functions of recombinant proteins.

Downregulation of Transcription Factor Sp1 Suppresses Malignant Properties of A549 Human Lung Cancer Cell Line with Decreased β4-Galactosylation of Highly Branched N-Glycans

Dramatic changes in the glycan structures of cell surface proteins have been observed upon malignant transformation of cells as induced by the altered expression levels of glycosyltransferases. Such changes are closely associated with the malignant properties of cancer cells. Transcription factor Sp1 regulates the gene expression of various molecules including glycosyltransferases. Herein, we investigated whether or not Sp1-downregulation affects to N-glycosylation of glycoproteins and malignant properties of A549 human lung cancer cell line. We established a stable clone whose Sp1-expression level was reduced to 50% of a control clone by RNA interference. Lectin blotting revealed that the β4-galactosylation of highly branched N-glycans decreases mainly in cell adhesion molecule, E-cadherin. The analysis of underlying mechanism for decreased β4-galactosylation of N-glycans showed that the gene expression level of β4-galactosyltransferase (β4GalT) 1 decreases dramatically by downregulation of Sp1 without changes in those of β4GalT2 and N-acetylglucosaminyltransferase V. Mutations in the Sp1-binding sites of the β4GalT1 gene promoter showed that the promoter activity decreases significantly, indicating that the gene expression is regulated by Sp1. These results indicate that the β4-galactosylation of highly branched N-glycans decreases by downregulation of Sp1 through the reduced expression of the β4GalT1 gene. Furthermore, the Sp1-downregulated cells showed the suppression of the anchorage-independent growth in soft agar and migratory activity when compared to the control cells. The present study demonstrates that downregulation of Sp1 suppresses the malignant properties of A549 cells through the decreased β4-galactosylation of highly branched N-glycans.

Protein glycosylation in cancers and its potential therapeutic applications in neuroblastoma

Glycosylation is the most complex post-translational modification of proteins. Altered glycans on the tumor- and host-cell surface and in the tumor microenvironment have been identified to mediate critical events in cancer pathogenesis and progression. Tumor-associated glycan changes comprise increased branching of N-glycans, higher density of O-glycans, generation of truncated versions of normal counterparts, and generation of unusual forms of terminal structures arising from sialylation and fucosylation. The functional role of tumor-associated glycans (Tn, sTn, T, and sLe^a/x) is dependent on the interaction with lectins. Lectins are expressed on the surface of immune cells and endothelial cells or exist as extracellular matrix proteins and soluble adhesion molecules. Expression of tumor-associated glycans is involved in the dysregulation of glycogenes, which mainly comprise glycosyltransferases and glycosidases. Furthermore, genetic and epigenetic mechanisms on many glycogenes are associated with malignant transformation. With better understanding of all aspects of cancer-cell glycomics, many tumor-associated glycans have been utilized for diagnostic, prognostic, and therapeutic purposes. Glycan-based therapeutics has been applied to cancers from breast, lung, gastrointestinal system, melanomas, and lymphomas but rarely to neuroblastomas (NBs). The success of anti-disialoganglioside (GD2, a glycolipid antigen) antibodies sheds light on glycan-based therapies for NB and also suggests the possibility of protein glycosylation-based therapies for NB. This review summarizes our understanding of cancer glycobiology with a focus of how protein glycosylation and associated glycosyltransferases affect cellular behaviors and treatment outcome of various cancers, especially NB. Finally, we highlight potential applications of glycosylation in drug and cancer vaccine development for NB.

Gene-based analysis of regulatory variants identifies 4 putative novel asthma risk genes related to nucleotide synthesis and signaling

BACKGROUND

Hundreds of genetic variants are thought to contribute to variation in asthma risk by modulating gene expression. Methods that increase the power of genome-wide association studies (GWASs) to identify risk-associated variants are needed.

OBJECTIVE

We sought to develop a method that aggregates the evidence for association with disease risk across expression quantitative trait loci (eQTLs) of a gene and use this approach to identify asthma risk genes.

METHODS

We developed a gene-based test and software package called EUGENE that (1) is applicable to GWAS summary statistics; (2) considers both cis- and trans-eQTLs; (3) incorporates eQTLs identified in different tissues; and (4) uses simulations to account for multiple testing. We applied this approach to 2 published asthma GWASs (combined n = 46,044) and used mouse studies to provide initial functional insights into 2 genes with novel genetic associations.

RESULTS

We tested the association between asthma and 17,190 genes that were found to have cis- and/or trans-eQTLs across 16 published eQTL studies. At an empirical FDR of 5%, 48 genes were associated with asthma risk. Of these, for 37, the association was driven by eQTLs located in established risk loci for allergic disease, including 6 genes not previously implicated in disease cause (eg, LIMS1, TINF2, and SAFB). The remaining 11 significant genes represent potential novel genetic associations with asthma. The association with 4 of these replicated in an independent GWAS: B4GALT3, USMG5, P2RY13, and P2RY14, which are genes involved in nucleotide synthesis or nucleotide-dependent cell activation. In mouse studies, P2ry13 and P2ry14-purinergic receptors activated by adenosine 5-diphosphate and UDP-sugars, respectively-were upregulated after allergen challenge, notably in airway epithelial cells, eosinophils, and neutrophils. Intranasal exposure with receptor agonists induced the release of IL-33 and subsequent eosinophil infiltration into the lungs.

CONCLUSION

We identified novel associations between asthma and eQTLs for 4 genes related to nucleotide synthesis/signaling and demonstrated the power of gene-based analyses of GWASs.

Sweet complementarity: the functional pairing of glycans with lectins

Carbohydrates establish the third alphabet of life. As part of cellular glycoconjugates, the glycans generate a multitude of signals in a minimum of space. The presence of distinct glycotopes and the glycome diversity are mapped by sugar receptors (antibodies and lectins). Endogenous (tissue) lectins can read the sugar-encoded information and translate it into functional aspects of cell sociology. Illustrated by instructive examples, each glycan has its own ligand properties. Lectins with different folds can converge to target the same epitope, while intrafamily diversification enables functional cooperation and antagonism. The emerging evidence for the concept of a network calls for a detailed fingerprinting. Due to the high degree of plasticity and dynamics of the display of genes for lectins the validity of extrapolations between different organisms of the phylogenetic tree yet is inevitably limited.

B4GALT3 up-regulation by miR-27a contributes to the oncogenic activity in human cervical cancer cells

β-1,4-Galactosyltransferase III (B4GALT3) is an enzyme responsible for the generation of poly-N-acetyllactosamine and is involved in tumorigenesis. However, B4GALT3-dysregulation and its role in cervical cancer cells are unknown. Herein, we found that B4GALT3 was upregulated in cervical cancer tissues compared to adjacent non-tumor tissues. B4GALT3-overexpression promoted, whereas B4GALT3-knockdown suppressed the cellular migration, invasion and EMT of HeLa and C33A cervical cancer cells. To explore the mechanism of dysregulation, B4GALT3 was predicted to be a target of miR-27a. EGFP and pGL3-promoter reporter assay showed miR-27a binds to B4GALT3 3'UTR region but enhanced its expression. RT-qPCR showed miR-27a was also upregulated and presented positive correlation with B4GALT3-expression in cervical cancer tissues. miR-27a-overexpression promoted, but blocking-miR-27a repressed these malignancies in HeLa and C33A cells. Furthermore, shR-B4GALT3 counteracted the promotion of malignancies induced by miR-27a, suggesting miR-27a upregulates B4GALT3 to enhance tumorigenic activities. In addition, we found that B4GALT3 significantly enhances β1-integrin stability, thus mediating promotion of B4GALT3 on malignancy in cervical cancer cells. Altogether, our findings evidenced that B4GALT3 upregulated by miR-27a contributes to the tumorigenic activities by β1-integrin pathway and might provide potential biomarkers for cervical cancer.

SLC39A8 Deficiency: A Disorder of Manganese Transport and Glycosylation

SLC39A8 is a membrane transporter responsible for manganese uptake into the cell. Via whole-exome sequencing, we studied a child that presented with cranial asymmetry, severe infantile spasms with hypsarrhythmia, and dysproportionate dwarfism. Analysis of transferrin glycosylation revealed severe dysglycosylation corresponding to a type II congenital disorder of glycosylation (CDG) and the blood manganese levels were below the detection limit. The variants c.112G>C (p.Gly38Arg) and c.1019T>A (p.Ile340Asn) were identified in SLC39A8. A second individual with the variants c.97G>A (p.Val33Met) and c.1004G>C (p.Ser335Thr) on the paternal allele and c.610G>T (p.Gly204Cys) on the maternal allele was identified among a group of unresolved case subjects with CDG. These data demonstrate that variants in SLC39A8 impair the function of manganese-dependent enzymes, most notably β-1,4-galactosyltransferase, a Golgi enzyme essential for biosynthesis of the carbohydrate part of glycoproteins. Impaired galactosylation leads to a severe disorder with deformed skull, severe seizures, short limbs, profound psychomotor retardation, and hearing loss. Oral galactose supplementation is a treatment option and results in complete normalization of glycosylation. SLC39A8 deficiency links a trace element deficiency with inherited glycosylation disorders.

β-1,4-Galactosyltransferase III suppresses extravillous trophoblast invasion through modifying β1-integrin glycosylation

INTRODUCTION

Glycosylation controls diverse protein functions and regulates various cellular phenotypes. Trophoblast invasion is essential for normal placental development. However, the role of glycosylation in human placenta throughout pregnancy is still unclear. The β-1,4-galactosyltransferase III (B4GALT3) has been found to regulate cancer cell invasion. We therefore investigated the expression of B4GALT3 in placenta and its roles in trophoblast.

METHODS

B4GALT3 protein expression was examined by quantitative Western blotting analysis in human placentas. For identification of B4GALT3-positive cells in normal human placenta, immunohistochemistry and immunofluorescence methods were used. To investigate effects of B4GALT3 on extravillous trophoblast (EVT)-like cell and primary EVT cells, we analyzed cell growth, adhesion, migration, and invasion in mock and B4GALT3-transfected cell.

RESULTS

B4GALT3 expression significantly increased in third trimester human placenta. Immunostaining revealed that B4GALT3 expressed in placental villous cytotrophoblast, syncytiotrophoblast, and a subpopulation of EVT cells throughout pregnancy. Interestingly, we found increases in the expression level and percentage of B4GALT3-positive cells in third trimester EVT, but not in syncytiotrophoblasts and cytotrophoblasts of placental villi. Overexpression of B4GALT3 in HTR8/SVneo cells and primary trophoblast cells significantly suppressed cell migration. In addition, B4GALT3 suppressed cell invasion, and enhanced cell adhesion to laminin in HTR8/SVneo cells. Notably, we found that B4GALT3 modified glycans on β1-integrin, suppressed focal adhesion kinase (FAK) signaling, and enhanced β1-integrin degradation.

DISCUSSION

We propose that B4GALT3-mediated glycosylation change not only enhances β1-integrin binding to laminin, but also attenuates β1-integrin stability. Our findings suggest that B4GALT3 is a critical regulator for suppressing EVT invasion in the late stages of pregnancy.

β-1,4-Galactosyltransferase III suppresses β1 integrin-mediated invasive phenotypes and negatively correlates with metastasis in colorectal cancer

Metastasis often occurs in colorectal cancer (CRC) patients and is the main difficulty in cancer treatment. The upregulation of poly-N-acetyllactosamine-related glycosylation is found in CRC patients and is associated with progression and metastasis in cancer. β-1,4-Galactosyltransferase III (B4GALT3) is an enzyme responsible for poly-N-acetyllactosamine synthesis, and therefore, we investigated its expression in CRC patients. We found that B4GALT3 negatively correlated with poorly differentiated histology (P < 0.001), advanced stages (P = 0.0052), regional lymph node metastasis (P = 0.0018) and distant metastasis (P = 0.0463) in CRC patients. B4GALT3 overexpression in CRC cells suppressed cell migration, invasion and adhesion, whereas B4GALT3 knockdown enhanced malignant cell phenotypes. The β1 integrin-blocking antibody reversed the B4GALT3-mediated increase in cell invasion. B4GALT3 expression altered glycosylation on the N-glycan of β1 integrin probably through changes in poly-N-acetyllactosamine expression. Furthermore, more activated β1 integrin along with the activation of its downstream signaling transduction were found in B4GALT3 knockdown cells, whereas overexpression of B4GALT3 suppressed the expression of active β1 integrin and inhibited its downstream signaling. Our results suggest that B4GALT3 is negatively associated with CRC metastasis and suppresses cell invasiveness through inhibiting activation of β1 integrin.

N-glycomic biomarkers of biological aging and longevity: a link with inflammaging

Glycosylation is a frequent co/post-translational modification of proteins which modulates a variety of biological functions. The analysis of N-glycome, i.e. the sugar chains N-linked to asparagine, identified new candidate biomarkers of aging such as N-glycans devoid of galactose residues on their branches, in a variety of human and experimental model systems, such as healthy old people, centenarians and their offspring and caloric restricted mice. These agalactosylated biantennary structures mainly decorate Asn297 of Fc portion of IgG (IgG-G0), and are present also in patients affected by progeroid syndromes and a variety of autoimmune/inflammatory diseases. IgG-G0 exert a pro-inflammatory effect through different mechanisms, including the lectin pathway of complement, binding to Fcγ receptors and formation of autoantibody aggregates. The age-related accumulation of IgG-G0 can contribute to inflammaging, the low-grade pro-inflammatory status that characterizes elderly, by creating a vicious loop in which inflammation is responsible for the production of aberrantly glycosylated IgG which, in turn, would activate the immune system, exacerbating inflammation. Moreover, recent data suggest that the N-glycomic shift observed in aging could be related not only to inflammation but also to alteration of important metabolic pathways. Thus, altered N-glycans are both powerful markers of aging and possible contributors to its pathogenesis.

β-1,4-Galactosyltransferase III enhances invasive phenotypes via β1-integrin and predicts poor prognosis in neuroblastoma

PURPOSE

Neuroblastoma (NB) is a neural crest-derived tumor that commonly occurs in childhood. β-1,4-Galactosyltransferase III (B4GALT3) is highly expressed in human fetal brain and is responsible for the generation of poly-N-acetyllactosamine, which plays a critical role in tumor progression. We therefore investigated the expression and role of B4GALT3 in NB.

EXPERIMENTAL DESIGN

We examined B4GALT3 expression in tumor specimens from 101 NB patients by immunohistochemistry and analyzed the correlation between B4GALT3 expression and clinicopathologic factors or survival. The functional role of B4GALT3 expression was investigated by overexpression or knockdown of B4GALT3 in NB cells for in vitro and in vivo studies.

RESULTS

We found that B4GALT3 expression correlated with advanced clinical stages (P = 0.040), unfavorable Shimada histology (P < 0.001), and lower survival rate (P < 0.001). Multivariate analysis showed that B4GALT3 expression is an independent prognostic factor for poor survival of NB patients. B4GALT3 overexpression increased migration, invasion, and tumor growth of NB cells, whereas B4GALT3 knockdown suppressed the malignant phenotypes of NB cells. Mechanistic investigation showed that B4GALT3-enhanced migration and invasion were significantly suppressed by β1-integrin blocking antibody. Furthermore, B4GALT3 overexpression increased lactosamine glycans on β1-integrin, increased expression of mature β1-integrin via delayed degradation, and enhanced phosphorylation of focal adhesion kinase. Conversely, these properties were decreased by knockdown of B4GALT3 in NB cells.

CONCLUSIONS

Our findings suggest that B4GALT3 predicts an unfavorable prognosis for NB and may regulate invasive phenotypes through modulating glycosylation, degradation, and signaling of β1-integrin in NB cells.

Regulation of glycan structures in murine embryonic stem cells: combined transcript profiling of glycan-related genes and glycan structural analysis

The abundance and structural diversity of glycans on glycoproteins and glycolipids are highly regulated and play important roles during vertebrate development. Because of the challenges associated with studying glycan regulation in vertebrate embryos, we have chosen to study mouse embryonic stem (ES) cells as they differentiate into embryoid bodies (EBs) or into extraembryonic endodermal (ExE) cells as a model for cellular differentiation. We profiled N- and O-glycan structures isolated from these cell populations and examined transcripts encoding the corresponding enzymatic machinery for glycan biosynthesis in an effort to probe the mechanisms that drive the regulation of glycan diversity. During differentiation from mouse ES cells to either EBs or ExE cells, general trends were detected. The predominance of high mannose N-glycans in ES cells shifted to an equal abundance of complex and high mannose structures, increased sialylation, and increased α-Gal termination in the differentiated cell populations. Whereas core 1 O-glycan structures predominated in all three cell populations, increased sialylation and increased core diversity characterized the O-glycans of both differentiated cell types. Increased polysialylation was also found in both differentiated cell types. Differences between the two differentiated cell types included greater sialylation of N-glycans in EBs, whereas α-Gal-capped structures were more prevalent in ExE cells. Changes in glycan structures generally, but not uniformly, correlated with alterations in transcript abundance for the corresponding biosynthetic enzymes, suggesting that transcriptional regulation contributes significantly to the regulation of glycan expression. Knowledge of glycan structural diversity and transcript regulation should provide greater understanding of the roles of protein glycosylation in vertebrate development.

Estrogen induced β-1,4-galactosyltransferase 1 expression regulates proliferation of human breast cancer MCF-7 cells

Beta 1,4-galactosyltransferase 1 (B4GALT1) synthesizes galactose β-1,4-N-acetylglucosamine (Galβ1-4GlcNAc) groups on N-linked sugar chains of glycoproteins, which play important roles in many biological events, including the proliferation and migration of cancer cells. A previous microarray study reported that this gene is expressed by estrogen treatment in breast cancer. In this study, we examined the regulatory mechanisms and biological functions of estrogen-induced B4GALT1 expression. Our data showed that estrogen-induced expression of B4GALT1 is localized in intracellular compartments and in the plasma membrane. In addition, B4GALT1 has an enzyme activity involved in the production of the Galβ1-4GlcNAc structure. The result from a promoter assay and chromatin immunoprecipitation revealed that 3 different estrogen response elements (EREs) in the B4GALT1 promoter are critical for responsiveness to estrogen. In addition, the estrogen antagonists ICI 182,780 and ER-α-ERE binding blocker TPBM inhibit the expression of estrogen-induced B4GALT1. However, the inhibition of signal molecules relating to the extra-nuclear pathway, including the G-protein coupled receptors, Ras, and mitogen-activated protein kinases, had no inhibitory effects on B4GALT1 expression. The knock-down of the B4GALT1 gene and the inhibition of membrane B4GALT1 function resulted in the significant inhibition of estrogen-induced proliferation of MCF-7 cells. Considering these results, we propose that estrogen regulates the expression of B4GALT1 through the direct binding of ER-α to ERE and that the expressed B4GALT1 plays a crucial role in the proliferation of MCF-7 cells through its activity as a membrane receptor.

On the roles and regulation of chondroitin sulfate and heparan sulfate in zebrafish pharyngeal cartilage morphogenesis

The present study addresses the roles of heparan sulfate (HS) proteoglycans and chondroitin sulfate (CS) proteoglycans in the development of zebrafish pharyngeal cartilage structures. uxs1 and b3gat3 mutants, predicted to have impaired biosynthesis of both HS and CS because of defective formation of the common proteoglycan linkage tetrasaccharide were analyzed along with ext2 and extl3 mutants, predicted to have defective HS polymerization. Notably, the effects on HS and CS biosynthesis in the respective mutant strains were shown to differ from what had been hypothesized. In uxs1 and b3gat3 mutant larvae, biosynthesis of CS was shown to be virtually abolished, whereas these mutants still were capable of synthesizing 50% of the HS produced in control larvae. extl3 and ext2 mutants on the other hand were shown to synthesize reduced amounts of hypersulfated HS. Further, extl3 mutants produced higher levels of CS than control larvae, whereas morpholino-mediated suppression of csgalnact1/csgalnact2 resulted in increased HS biosynthesis. Thus, the balance of the Extl3 and Csgalnact1/Csgalnact2 proteins influences the HS/CS ratio. A characterization of the pharyngeal cartilage element morphologies in the single mutant strains, as well as in ext2;uxs1 double mutants, was conducted. A correlation between HS and CS production and phenotypes was found, such that impaired HS biosynthesis was shown to affect chondrocyte intercalation, whereas impaired CS biosynthesis inhibited formation of the extracellular matrix surrounding chondrocytes.

[Regulation of human β-1,4-galactosyltransferase V gene expression in cancer cells]

β-1,4-Galactosyltransferase (β-1,4-GalT) V - whose human and mouse genes were cloned by us - has been suggested to be involved in the biosyntheses of N-glycans, O-glycans, and lactosylceramide by in vitro studies. Our recent study showed that β-1,4-GalT V-knockout mice are embryonic lethal, suggesting the importance of the glycans synthesized by β-1,4-GalT V for embryonic development. A subsequent study showed that murine β-1,4-GalT V is involved in the biosynthesis of lactosylceramide. It is well known that the glycosylation of cell surface glycoproteins and glycolipids changes dramatically upon the malignant transformation of cells. We found that among six β-1,4-GalTs the gene expression of only β-1,4-GalT V increases upon malignant transformation. The expression of the β-1,4-GalT V gene has been shown to be regulated by transcription factors Sp1 and Ets-1 in cancer cells. Both transcription factors regulate the gene expression levels of not only glycosyltransferases, but also key molecules involved in tumor growth, invasion and metastasis. Therefore, the abnormal glycosylation and malignant phenotypes of cancer cells are considered to be suppressed by regulating the expression levels of the transcription factor genes. This review gives a summary account of the gene discovery, in vivo function, and transcriptional mechanism of β-1,4-GalT V. Also, a perspective on applications of the manipulation of transcription factor genes to cancer therapy will be discussed.

B4GALT1-congenital disorders of glycosylation presents as a non-neurologic glycosylation disorder with hepatointestinal involvement

The clinical phenotype of congenital disorders of glycosylation is heterogeneous, mostly including a severe neurological involvement and multisystem disease. We identified a novel patient with a galactosyltransferase deficiency with mild hepatopathy and coagulation anomalies, but normal psychomotor development. The tissue-specific expression of the defective B4GALT1 gene correlated with the clinical phenotype.

The i blood group antigen as a marker for umbilical cord blood-derived mesenchymal stem cells

Multipotent mesenchymal stem cells (MSCs) offer great promise for future regenerative and anti-inflammatory therapies. However, there is a lack of methods to quickly and efficiently isolate, characterize, and ex vivo expand desired cell populations for therapeutic purposes. Single markers to identify cell populations have not been characterized; instead, all characterizations rely on panels of functional and phenotypical properties. Glycan epitopes can be used for identifying and isolating specific cell types from heterogeneous populations, on the basis of their cell-type specific expression and prominent cell surface localization. We have now studied in detail the cell surface expression of the blood group i epitope (linear poly-N-acetyllactosamine chain) in umbilical cord blood (UCB)-derived MSCs. We used flow cytometry and mass spectrometric glycan analysis and discovered that linear poly-N-acetyllactosamine structures are expressed in UCB-derived MSCs, but not in cells differentiated from them. We further verified the findings by mass spectrometric glycan analysis. Gene expression analysis indicated that the stem-cell specific expression of the i antigen is determined by β3-N-acetylglucosaminyltransferase 5. The i antigen is a ligand for the galectin family of soluble lectins. We found concomitant cell surface expression of galectin-3, which has been reported to mediate the immunosuppressive effects exerted by MSCs. The i antigen may serve as an endogenous ligand for this immunosuppressive agent in the MSC microenvironment. Based on these findings, we suggest that linear poly-N-acetyllactosamine could be used as a novel UCB-MSC marker either alone or within an array of MSC markers.

Specific enzyme complex of beta-1,4-galactosyltransferase-II and glucuronyltransferase-P facilitates biosynthesis of N-linked human natural killer-1 (HNK-1) carbohydrate

Human natural killer-1 (HNK-1) carbohydrate is highly expressed in the nervous system and is involved in synaptic plasticity and dendritic spine maturation. This unique carbohydrate, consisting of a sulfated trisaccharide (HSO(3)-3GlcAβ1-3Galβ1-4GlcNAc-), is biosynthesized by the successive actions of β-1,4-galactosyltransferase (β4GalT), glucuronyltransferase (GlcAT-P and GlcAT-S), and sulfotransferase (HNK-1ST). A previous study showed that mice lacking β4GalT-II, one of seven β4GalTs, exhibited a dramatic loss of HNK-1 expression in the brain, although β4GalT-I-deficient mice did not. Here, we investigated the underlying molecular mechanism of the regulation of HNK-1 expression. First, focusing on a major HNK-1 carrier, neural cell adhesion molecule, we found that reduced expression of an N-linked HNK-1 carbohydrate caused by a deficiency of β4GalT-II is not likely due to a general loss of the β1,4-galactose residue as an acceptor for GlcAT-P. Instead, we demonstrated by co-immunoprecipitation and endoplasmic reticulum-retention analyses using Neuro2a (N2a) cells that β4GalT-II physically and specifically associates with GlcAT-P. In addition, we revealed by pulldown assay that Golgi luminal domains of β4GalT-II and GlcAT-P are sufficient for the complex to form. With an in vitro assay system, we produced the evidence that the kinetic efficiency k(cat)/K(m) of GlcAT-P in the presence of β4GalT-II was increased about 2.5-fold compared with that in the absence of β4GalT-II. Finally, we showed that co-expression of β4GalT-II and GlcAT-P increased HNK-1 expression on various glycoproteins in N2a cells, including neural cell adhesion molecule. These results indicate that the specific enzyme complex of β4GalT-II with GlcAT-P plays an important role in the biosynthesis of HNK-1 carbohydrate.

Involvement of murine β-1,4-galactosyltransferase V in lactosylceramide biosynthesis

Human β-1,4-galactosyltransferase (β-1,4-GalT) V was shown to be involved in the biosynthesis of N-glycans, O-glycans and lactosylceramide (Lac-Cer) by in vitro studies. To determine its substrate specificity, enzymatic activity and its products were analyzed using mouse embryonic fibroblast (MEF) cells from β-1,4-GalT V (B4galt5)-mutant mice. Analysis of expression levels of the β-1,4-GalT I-VI genes revealed that the expression of the β-1,4-GalT V gene in B4galt5 ( +/- ) - and B4galt5 ( -/- ) -derived MEF cells are a half and null when compared to that of B4galt5 ( +/+ )-derived MEF cells without altering the expression levels of other β-1,4-GalT genes. These MEF cells showed no apparent difference in their growth. When β-1,4-GalT activities were determined towards GlcNAcβ-S-pNP, no significant difference in its specific activity was obtained among B4galt5 ( +/+ )-, B4galt5 ( +/- ) - and B4galt5 ( -/- ) -derived MEF cells. No significant differences were obtained in structures and amounts of N-glycans and lectin bindings to membrane glycoproteins among B4galt5 ( +/+ )-, B4galt5 ( +/- ) - and B4galt5 ( -/- ) -derived MEF cells. However, when cell homogenates were incubated with glucosylceramide in the presence of UDP-[(3)H]Gal, Lac-Cer synthase activity in B4galt5 ( +/- ) - and B4galt5 ( -/- ) -derived MEF cells decreased to 41% and 11% of that of B4galt5 ( +/+ )-derived MEF cells. Consistent with this, amounts of Lac-Cer and its derivative GM3 in B4galt5 ( -/- ) -derived MEF cells decreased remarkably when compared with those of B4galt5 ( +/+ )-derived MEF cells. These results indicate that murine β-1,4-GalT V is involved in Lac-Cer biosynthesis.

Beta4-galactosyltransferase-5 is a lactosylceramide synthase essential for mouse extra-embryonic development

Glycosphingolipids (GSLs) are important for various biological functions in the nervous system, the immune system, embryogenesis and in other tissues and processes. Lactosylceramide (LacCer), which is synthesized from glucosylceramide (GlcCer) by LacCer synthase, is a core structure of GSLs, including gangliosides. LacCer synthase was reported to be synthesized by the beta4-galactosyltransferase-6 (beta4GalT-6) gene in the rat brain. However, the existence of another LacCer synthase gene was shown in cultured cells lacking beta4GalT-6. Here, we report that LacCer synthase is mainly synthesized by the beta4GalT-5 gene during early mouse embryogenesis, and its disruption is embryonic lethal. beta4GalT-5-deficient embryos showed developmental retardation from E7.5 and died by E10.5 as reported previously. LacCer synthase activity was significantly reduced in beta4GalT-5-deficient embryos and extra-embryonic endoderm (XEN) cells derived from blastocysts, and it was recovered when beta4GalT-5 cDNA was introduced into beta4GalT-5-deficient XEN cells. The amounts of LacCer and GM3 ganglioside were drastically reduced, while GlcCer accumulated in the beta4GalT-5-deficient XEN cells. Hematoma and ectopically accumulated trophoblast giant cells were observed in the anti-mesometrial pole of the extra-embryonic tissues, although all three embryonic layers formed. beta4GalT-5-deficient embryos developed until E12.5 as chimeras with wild-type tetraploid cells, which formed the extra-embryonic membranes, indicating that extra-embryonic defects caused the early embryonic lethality. Our results suggest that beta4GalT-5 is essential for extra-embryonic development during early mouse embryogenesis.

Intrauterine growth restriction modifies the developmental pattern of intestinal structure, transcriptomic profile, and bacterial colonization in neonatal pigs

Neonates with intrauterine growth restriction (IUGR) are prone to suffer from digestive diseases. Using neonatal pigs with IUGR, we tested the hypothesis that IUGR may induce alterations in the developmental pattern of intestinal barrier and thereby may be responsible for IUGR-associated increased morbidity. Piglets with a birth weight near the mean birth weight (+/-0.5 SD) were identified as normal birth weight (control) and piglets with a mean -2 SD lower birth weight (-30%) were defined as piglets with IUGR. The developmental pattern of intestinal structure, transcriptomic profile, and bacterial colonization was investigated from birth to d 5 postnatal. At birth, intestinal weight and length, ileal and colonic weight per unit of length, and villous sizes were lower (P < 0.05) in piglets with IUGR than in same-age control piglets. These IUGR-induced intestinal alterations further persisted, although they were less marked at d 5. Counts of adherent bacteria to ileal and colonic mucosa were greater (P < 0.05) in 2-d-old piglets with IUGR than in same-age control piglets. Dynamic analyses of the transcriptomic profile of the intestine revealed molecular evidence of IUGR-induced intestinal growth impairment that may result from a change in the cell proliferation-apoptosis balance during the first days of life, while a protective process would occur later on. In addition, changes in the expression of several genes suggest a pivotal role of both glucocorticoids and microbiota in driving IUGR intestinal development during the neonatal period.

Involvement of Galectin-3 with vascular cell adhesion molecule-1 in growth regulation of mouse BALB/3T3 cells

beta-Galactose residues on N-glycans have been implicated to be involved in growth regulation of cells. In the present study we compared the galactosylation of cell surface N-glycans of mouse Balb/3T3 cells between 30 and 100% densities and found the beta-1,4-galactosylation of N-glycans increases predominantly in a 100-kDa protein band on lectin blot analysis in combination with digestions by diplococcal beta-galactosidase and N-glycanase. When cells at 100% density were treated with jack bean beta-galactosidase, the incorporation of 5-bromodeoxyuridine into the cells was stimulated in a dose-dependent manner, suggesting the involvement of the galactose residues in growth regulation of cells. A galactose-binding protein was isolated from the plasma membranes of cells at 100% density by affinity chromatography using an asialo-transferrin-Sepharose column and found to be galectin-3 as revealed by mass spectrometric analysis. The addition of recombinant galectin-3 into cells at 50% density inhibited the incorporation of 5-bromodeoxyuridine in a dose-dependent manner, but the inhibition was prevented with haptenic sugar. An immunocytochemical study showed that galectin-3 is present at the surface of cells at 100% density but not at 30% density where it locates inside the cells. Several glycoproteins bind to a galectin-3-immobilized column, a major of which was identified as vascular cell adhesion molecule (VCAM)-1. Immunocytochemical studies showed that some galectin-3 and VCAM-1 co-localize at the surface of cells at 100% density, indicating that the binding of galectin-3 secreted from cells to VCAM-1 is one of the pathways involved in the growth regulation of Balb/3T3 cells.

Beta1,4-galactosyltransferase V A growth regulator in glioma

One of the most prominent transformation-associated changes in the sugar chains of glycoproteins is an increase in the large N-glycans of cell surface glycoprotein. beta1,4-galactosyltransferase V (beta1,4GalT V) could effectively galactosylate the GlcNAcbeta1-->6 branch which is a marker of glioma. The expression of beta1,4GalT V is increased in the process of glioma development. beta1,4GalT V regulates the invasion, growth in vivo and in vitro of glioma cells. Downregulation of beta1,4GalT V expression increases the sensitivity of malignant glioma cells to DNA damage drugs. Furthermore, beta1,4GalT V regulates Ras and AKT signaling involving in glioma behaviors. Meanwhile, Ras/MAPK and PI3K/AKT signaling pathways are involved in the transcription regulation of beta1,4GalT V gene. E1AF transcription factor, a downstream target of Ras/MAPK and PI3K/AKT signaling pathways, regulates the transcription of beta1,4GalT V in cooperation with Sp1 transcription factor. The contribution of beta1,4GalT V in glioma development is further confirmed in glioma-initiation cells. beta1,4GalT V regulates the self-renewal of glioma-initiation cells. We now present evidence that beta1,4GalT V functions as a positive growth regulator in glioma and might represent a novel target in glioma therapy.

Enzymatic synthesis of lacto-N-difucohexaose I which binds to Helicobacter pylori

Helicobacter pylori is known to bind with sugar chains possessing Lewis b structure. We are trying to combine oligosaccharides containing Lewis b sugar chain to water insoluble polysaccharide through some linker. Lacto-N-difucohexaose I (LNDFH I; Fucalpha1-->2Galbeta1-->3[Fucalpha1-->4]GlcNAcbeta1-->3Galbeta1-->4Glc) fits for that purpose, since it consists of Lewis b tetrasaccharide and lactose whose d-glucose residue can be utilized as a linker. We thus developed a method to synthesize this hexaose enzymatically. First, beta-1,3-N-acetylglucosaminyltransferase (beta-1,3-GnT) was partially purified from bovine blood by an established method. Using this enzyme preparation, d-GlcNAc was attached to the d-galactose residue of lactose with a beta-1,3-linkage to produce lacto-N-triose II at 44% yield. The low yield was thought to be due to contaminating N-acetylglucosaminidase that would have hydrolyzed the product, lacto-N-triose II. Next, d-galactose was attached by transglycosylation using ortho-nitrophenyl beta-d-galactopyranoside as a donor with the aid of recombinant beta-1,3-galactosidase from Bacillus circulans to generate lacto-N-tetraose (LNT) at 22% yield. l-Fucose was then linked to the d-galactose residue of LNT via an alpha-1,2-linkage using recombinant human fucosyltransferase I (FUT1) expressed in a baculovirus system (71% yield). The obtained pentasaccharide was subsequently incubated with GDP-beta-l-fucose and commercial fucosyltransferase III (FUT3) to attach l-fucose to the d-GlcNAc residue of LNT with an alpha-1,4-linkage. After purification with an activated carbon column chromatography, 1.7 mg of LNDFH I was obtained (85% yield). We thus produced LNDFH I over four enzymatic steps with a yield of 6%.

Golgi targeting of Drosophila melanogaster beta4GalNAcTB requires a DHHC protein family-related protein as a pilot

Drosophila melanogaster β4GalNAcTB mutant flies revealed that this particular N-acetylgalactosaminyltransferase is predominant in the formation of lacdiNAc (GalNAcβ1,4GlcNAc)-modified glycolipids, but enzymatic activity could not be confirmed for the cloned enzyme. Using a heterologous expression cloning approach, we isolated β4GalNAcTB together with β4GalNAcTB pilot (GABPI), a multimembrane-spanning protein related to Asp-His-His-Cys (DHHC) proteins but lacking the DHHC consensus sequence. In the absence of GABPI, inactive β4GalNAcTB is trapped in the endoplasmic reticulum (ER). Coexpression of β4GalNAcTB and GABPI generates the active enzyme that is localized together with GABPI in the Golgi. GABPI associates with β4GalNAcTB and, when expressed with an ER retention signal, holds active β4GalNAcTB in the ER. Importantly, treatment of isolated membrane vesicles with Triton X-100 disturbs β4GalNAcTB activity. This phenomenon occurs with multimembrane-spanning glycosyltransferases but is normally not a property of glycosyltransferases with one membrane anchor. In summary, our data provide evidence that GABPI is required for ER export and activity of β4GalNAcTB.

Early lethality of beta-1,4-galactosyltransferase V-mutant mice by growth retardation

The beta-1,4-galactosyltransferase (beta-1,4-GalT) V whose human and mouse genes were cloned by us has been suggested to be involved in the biosynthesis of N-glycans and O-glycans, and lactosylceramide. To determine its biological function, beta-1,4-GalT V (B4galt5) mutant mice obtained by a gene trap method were analyzed. Analysis of pre- and post-implantation embryos revealed that the B4galt5(-/-) mice die by E10.5 while B4galt5(+/-) mice were born and grown normally. Histological study showed that most tissues are formed in B4galt5(-/-) embryos but their appearance at E10.5 is close to that of B4galt5(+/-) embryos at E9.0-9.5. The results indicate that the growth is delayed by one to one and half day in B4galt5(-/-) embryos when compared to B4galt5(+/-) embryos, which results in early death of the embryos by E10.5, probably due to hematopoietic and/or placental defects.

Alteration of N-glycosylation in the kidney in a mouse model of systemic lupus erythematosus: relative quantification of N-glycans using an isotope-tagging method

Changes in the glycan structures of some glycoproteins have been observed in autoimmune diseases such as systemic lupus erythematosus (SLE) and rheumatoid arthritis. A deficiency of alpha-mannosidase II, which is associated with branching in N-glycans, has been found to induce SLE-like glomerular nephritis in a mouse model. These findings suggest that the alteration of the glycosylation has some link with the development of SLE. An analysis of glycan alteration in the disordered tissues in SLE may lead to the development of improved diagnostic methods and may help to clarify the carbohydrate-related pathogenic mechanism of inflammation in SLE. In this study, a comprehensive and differential analysis of N-glycans in kidneys from SLE-model mice and control mice was performed by using the quantitative glycan profiling method that we have developed previously. In this method, a mixture of deuterium-labelled N-glycans from the kidneys of SLE-model mice and non-labelled N-glycans from kidneys of control mice was analysed by liquid chromatography/mass spectrometry. It was revealed that the low-molecular-mass glycans with simple structures, including agalactobiantennary and paucimannose-type oligosaccharides, markedly increased in the SLE-model mouse. On the other hand, fucosylated and galactosylated complex type glycans with high branching were decreased in the SLE-model mouse. These results suggest that the changes occurring in the N-glycan synthesis pathway may cause the aberrant glycosylations on not only specific glycoproteins but also on most of the glycoproteins in the SLE-model mouse. The changes in glycosylation might be involved in autoimmune pathogenesis in the model mouse kidney.

Structure and function of beta -1,4-galactosyltransferase

Beta-1,4-galactosylransferase (beta4Gal-T1) participates in the synthesis of Galbeta1-4-GlcNAc-disaccharide unit of glycoconjugates. It is a trans-Golgi glycosyltransferase (Glyco-T) with a type II membrane protein topology, a short N-terminal cytoplasmic domain, a membrane-spanning region, as well as a stem and a C-terminal catalytic domain facing the trans-Golgi-lumen. Its hydrophobic membrane-spanning region, like that of other Glyco-T, has a shorter length compared to plasma membrane proteins, an important feature for its retention in the trans-Golgi. The catalytic domain has two flexible loops, a long and a small one. The primary metal binding site is located at the N-terminal hinge region of the long flexible loop. Upon binding of metal ion and sugar-nucleotide, the flexible loops undergo a marked conformational change, from an open to a closed conformation. Conformational change simultaneously creates at the C-terminal region of the flexible loop an oligosaccharide acceptor binding site that did not exist before. The loop acts as a lid covering the bound donor substrate. After completion of the transfer of the glycosyl unit to the acceptor, the saccharide product is ejected; the loop reverts to its native conformation to release the remaining nucleotide moiety. The conformational change in beta4Gal-T1 also creates the binding site for a mammary gland-specific protein, alpha-lactalbumin (LA), which changes the acceptor specificity of the enzyme toward glucose to synthesize lactose during lactation. The specificity of the sugar donor is generally determined by a few residues in the sugar-nucleotide binding pocket of Glyco-T, conserved among the family members from different species. Mutation of these residues has allowed us to design new and novel glycosyltransferases, with broader or requisite donor and acceptor specificities, and to synthesize specific complex carbohydrates as well as specific inhibitors for these enzymes.