The human sialyltransferase family

Computational analysis of the structure, glycosylation and CMP binding of human ST3GAL sialyltransferases

Sialyltransferases (STs) are the fundamental enzymes which are related to many biological processes such as cell signalling, cellular recognition, cell-cell and host-pathogen interactions and metastasis of cancer. All STs catalyse the terminal sialic acid addition from CMP donor to the glycan units. ST3GAL family is one of the most important STs and divided into the six subfamily in mouse and humans which are ST3Gal I, ST3Gal II, ST3Gal III, ST3Gal IV, ST3Gal V, and ST3Gal VI. The members of the ST3GAL family transfer sialic acid to the terminal galactose residues of glycochains through an α2,3-linkage. There are many reports on the ST3GAL function in mammals but, there is a paucity of information about structure of human ST3GAL family. Herein, we investigated the structure, glycosylation and CMP binding site of human ST3GAL family using computational methods. We found for the first time N-glycosylation positions in ST3Gal IV and VI, mucin type glycosylation in ST3Gal III and O-GlcNAcylation in ST3Gal V and their relation with sialylmotifs. In addition, we predicted CMP binding positions of human ST3GAL enzyme family on three-dimensional structure using molecular docking and first demonstrated the sialylmotifs relation with the CMP binding positions in ST3Gal III-VI subfamilies.

Functional roles of ST8SIA3-mediated sialylation of striatal dopamine D2 and adenosine A2A receptors

Sialic acids are typically added to the end of glycoconjugates by sialyltransferases. Among the six ST8 α-N-acetyl-neuraminide α-2,8-sialyltransferases (ST8SIA) existing in adult brains, ST8SIA2 is a schizophrenia-associated gene. However, the in vivo substrates and physiological functions of most sialyltransferases are currently unknown. The ST8SIA3 is enriched in the striatum. Here, we showed that ablation of St8sia3 in mice (St8sia3-KO) led to fewer disialylated and trisialylated terminal glycotopes in the striatum of St8sia3-KO mice. Moreover, the apparent sizes of several striatum-enriched G-protein-coupled receptors (GPCRs) (including the adenosine A_2A receptor (A_2AR) and dopamine D₁/D₂ receptors (D₁R and D₂R)) were smaller in St8sia3-KO mice than in WT mice. A sialidase treatment removed the differences in the sizes of these molecules between St8sia3-KO and WT mice, confirming the involvement of sialylation. Expression of ST8SIA3 in the striatum of St8sia3-KO mice using adeno-associated viruses normalized the sizes of these proteins, demonstrating a direct role of ST8SIA3. The lack of ST8SIA3-mediated sialylation altered the distribution of these proteins in lipid rafts and the interaction between D₂R and A_2AR. Locomotor activity assays revealed altered pharmacological responses of St8sia3-KO mice to drugs targeting these receptors and verified that a greater population of D₂R formed heteromers with A_2AR in the striatum of St8sia3-KO mice. Since the A_2AR-D₂R heteromer is an important drug target for several basal ganglia diseases (such as schizophrenia and Parkinson's disease), the present study not only reveals a crucial role for ST8SIA3 in striatal functions but also provides a new drug target for basal ganglia-related diseases.

Emerging structural insights into glycosyltransferase-mediated synthesis of glycans

Glycans linked to proteins and lipids play key roles in biology; thus, accurate replication of cellular glycans is crucial for maintaining function following cell division. The fact that glycans are not copied from genomic templates suggests that fidelity is provided by the catalytic templates of glycosyltransferases that accurately add sugars to specific locations on growing oligosaccharides. To form new glycosidic bonds, glycosyltransferases bind acceptor substrates and orient a specific hydroxyl group, frequently one of many, for attack of the donor sugar anomeric carbon. Several recent crystal structures of glycosyltransferases with bound acceptor substrates reveal that these enzymes have common core structures that function as scaffolds upon which variable loops are inserted to confer substrate specificity and correctly orient the nucleophilic hydroxyl group. The varied approaches for acceptor binding site assembly suggest an ongoing evolution of these loop regions provides templates for assembly of the diverse glycan structures observed in biology.

Comparison of α2,6-sialyltransferases for sialylation of therapeutic proteins

The development of therapeutic proteins for the treatment of numerous diseases is one of the fastest growing areas of biotechnology. Therapeutic efficacy and serum half-life are particularly important, and these properties rely heavily on the glycosylation state of the protein. Expression systems to produce authentically fully glycosylated therapeutic proteins with appropriate terminal sialic acids are not yet perfected. The in vitro modification of therapeutic proteins by recombinant sialyltransferases offers a promising and elegant strategy to overcome this problem. Thus, the detailed expression and characterization of sialyltransferases for completion of the glycan chains is of great interest to the community. We identified a novel α2,6-sialyltransferase from Helicobacter cetorum and compared it to the human ST6Gal1 and a Photobacterium sp. sialyltransferase using glycoprotein substrates in a 96-well microtiter-plate-based assay. We demonstrated that the recombinant α2,6-sialyltransferase from H. cetorum is an excellent catalyst for modification of N-linked glycans of different therapeutic proteins.

Transcriptome analysis of regeneration during Xenopus laevis experimental twinning

Animal embryos have the remarkable property of self-organization. Over 125 years ago, Hans Driesch separated the two blastomeres of sea urchin embryos and obtained twins, in what was the foundation of experimental embryology. Since then, embryonic twinning has been obtained experimentally in many animals. In a recent study, we developed bisection methods that generate identical twins reliably from Xenopus blastula embryos. In the present study, we have investigated the transcriptome of regenerating half-embryos after sagittal and dorsal-ventral (D-V) bisections. Individual embryos were operated at midblastula (stage 8) with an eyelash hair and cultured until early gastrula (stage 10.5) or late gastrula (stage 12) and the transcriptome of both halves were analyzed by RNA-seq. Since many genes are activated by wound healing in Xenopus embryos, we resorted to stringent sequence analyses and identified genes up-regulated in identical twins but not in either dorsal or ventral fragments. At early gastrula, cell division-related transcripts such as histones were elevated, whereas at late gastrula, pluripotency genes (such as sox2) and germ layer determination genes (such as eomesodermin, ripply2 and activin receptor ACVRI) were identified. Among the down-regulated transcripts, sizzled, a regulator of Chordin stability, was prominent. These findings are consistent with a model in which cell division is required to heal damage, while maintaining pluripotency to allow formation of the organizer with a displacement of 90 ⁰ from its original site. The extensive transcriptomic data presented here provides a valuable resource for data mining of gene expression during early vertebrate development.

Genetic Variants in the ST6GAL1 Gene Are Associated with Thyroglobulin Plasma Level in Healthy Individuals

Background: Thyroglobulin (Tg) is a 660 kDa iodoglycoprotein that serves as a scaffold for thyroid hormone synthesis. Although a twin study showed that variability of serum Tg levels has a substantial genetic basis, no genome-wide association study (GWAS) of serum/plasma Tg levels has been performed to date. The aim of this study was to identify genetic variants associated with plasma Tg levels among healthy individuals. Methods: A GWAS was conducted on two Croatian cohorts, and a combined analysis was performed. The analyses included 1094 individuals. A total of 7,597,379 variants, imputed using the 1000 Genomes reference panel, were analyzed for association. GWAS was performed under an additive model, controlling for age, sex, and relatedness within each data set. Combined analysis was conducted using the inverse-variance fixed-effects method. Results: Sixteen variants located on chromosome 3, within the ST6GAL1 gene, reached genome-wide significance. The lead SNP was rs4012172 ( \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\usepackage{upgreek}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} $$p = 1.29 \times {10^{ - 10}}$$ \end{document} ), which explained 3.19% of the variance in Tg levels. ST6GAL1 belongs to the sialyltransferase protein family, which has a fundamental role in the synthesis of specific sialylated structures on various glycoproteins, including Tg. It is known that only immature Tg (poorly sialylated or desialylated) can be transferred to the bloodstream. Conclusions: A highly biologically plausible locus was identified that could have a role in the regulation of plasma Tg levels in healthy individuals.

Surface display of sialyltransferase on the outer membrane of Escherichia coli and ClearColi

α2,3-Sialyltransferase from Pasteurella multocida (PmST1) is an enzyme that transfers a sialyl group of donor substrates to an acceptor substrate called N-acetyl-d-lactosamine (LacNAc). In this study PmST1 was expressed on the outer membrane of wildtype Escherichia coli (BL21) with lipopolysaccharide (LPS) and ClearColi with no LPS, and then the enzyme activity and expression level of PmST1 were compared. As the first step, the expression levels of PmST1 on the outer membranes of wildtype E. coli (BL21) and ClearColi were compared according to the IPTG induction time, and the absolute amount of surface-displayed PmST1 was calculated using densitometry of SDS-PAGE. As the next step, the influence of LPS on the PmST1 activity was estimated by analyzing Michaelis-Menten plot. The enzyme activity of PmST1 was analyzed by measuring the concentration of CMP, which was a by-product after the transfer of the sialyl group of donor compounds to the acceptor compounds. From a Michaelis-Menten plot, the enzyme activity of the surface-displayed PmST1 and the maximum rate (V_max) of ClearColi were higher than those of wildtype E. coli (BL21). However, the K_M value, which represented the concentration of substrate to reach half the maximum rate (V_max), was similar for both enzymes. These results represented such a difference in enzyme activity was occurred from the interference of LPS on the mass transport of the donor and acceptor to PmST1 for the sialyl group transfer.

Haemophilus parasuis α-2,3-sialyltransferase-mediated lipooligosaccharide sialylation contributes to bacterial pathogenicity

Bacterial lipooligosaccharide (LOS) is an important virulence-associated factor, and its sialylation largely confers its ability to mediate cell adhesion, invasion, inflammation, and immune evasion. Here, we investigated the function of the Haemophilus parasuis α-2,3-sialyltransferase gene, lsgB, which determines the terminal sialylation of LOS, by generating a lsgB deletion mutant as well as a complementation strain. Our data indicate a direct effect of lsgB on LOS sialylation and reveal important roles of lsgB in promoting the pathogenicity of H. parasuis, including adhesion to and invasion of porcine cells in vitro, bacterial load and survival in vivo, as well as a contribution to serum resistance. These observations highlight the function of lsgB in mediating LOS sialylation and more importantly its role in H. parasuis infection. These findings provide a more profound understanding of the pathogenic mechanism of this disease-causing bacterium.

The effect of pyometra on glycosylation of proteins in the uterine tissues from female dogs

The main aim of this study was to investigate the effect of pyometra on glycosylation of proteins in the uterine tissues from female dogs, using western blotting with selected lectins (Sambucus nigra agglutinin - SNA and Maackia amurensis agglutinin - MAL II). In addition protein pattern of examined tissues was also evaluated. The study was performed on 10 female dogs undergoing ovariohysterectomy because of pyometra and 10 clinically healthy female dogs, undergoing elective spaying (ovariohysterectomy). Uterine tissue samples of 1 cm² were taken from the middle region of each uterine horn in both group of animals immediately after ovariohysterectomy. Tissue samples were homogenized and analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and western blotting with SNA and MAL II. SDS-PAGE analysis showed differences between pyometra samples and controls in the amount of obtained protein fractions and the protein content in the individual fractions. Five protein (with a molecular weight of 193.78 kDa, 103.18 kDa, 77.67 kDa, 70.39 kDa, and 53.00 kDa) were found only in the pyometra samples. The remaining fractions differed in intensity of staining, which indicated differ abundance of a given protein. The results of western blotting with SNA and MAL II demonstrated that the pattern obtained from densitometric analysis differs between adequate healthy and pyometra samples with regard to the amount of protein fraction obtained as well as the intensity of staining of particular fraction. The pyometra tissues contained seven SNA-binding proteins (with a molecular weight 189.94 kDa, 165.51 kDa, 100.94 kDa, 59.42 KDa, 41.32 kDa, 35.16 kDa, and 32.6 kDa) that were not in the healthy tissues. Of the nine remaining fractions, six showed significantly higher (P < 0.05) intensity of staining in the healthy uterine tissues. In turn, the MAL II-binding protein with a molecular weight 75.85 kDa, 51.12 kDa, and 49.98 kDa were found only in the pyometra samples. Of the 28 remaining fractions, ten demonstrated significantly higher (P < 0.05), and five fractions had significantly lower (P < 0.05) intensity of staining in the pyometra tissues. The results obtained indicate that proteins in uterine tissues from female dogs with pyometra are differently glycosylated compared to normal uterine tissues. These findings provide the basis for further studies of the possible role of glycosylation in the pathogenesis of canine pyometra.

Selective Engineering of Linkage-Specific α2,6-N-Linked Sialoproteins Using Sydnone-Modified Sialic Acid Bioorthogonal Reporters

The metabolic oligosaccharide engineering (MOE) strategy using unnatural sialic acids has recently enabled the visualization of the sialome in living systems. However, MOE only reports on global sialylation and dissected information regarding subsets of sialosides is missing. Described here is the synthesis and utilization of sialic acids modified with a sydnone reporter for the metabolic labeling of sialoconjugates. The positioning of the reporter on the sugar significantly altered its metabolic fate. Further in vitro enzymatic assays revealed that the 9-modified neuraminic acid is preferentially accepted by the sialyltransferase ST6Gal-I over ST3Gal-IV, leading to the favored incorporation of the reporter into linkage-specific α2,6-N-linked sialoproteins. This sydnone sugar presents the possibility of investigating the roles of specific sialosides.

α-2,3-Sialyltransferase 1 and neuraminidase-3 from monocytes in patients with rheumatoid arthritis correlate with disease activity measures: A pilot study

BACKGROUND

We decided to study the association of monocyte α-2,3-sialyltransferase 1 (ST3Gal-1), neuraminidase-3 (Neu3), α-2,6-sialyltransferase 1 (ST6Gal-1), and neuraminidase-1 (Neu1) levels with disease activity score 28 (DAS28) in human rheumatoid arthritis (RA), considering that mouse monocytes' sialic acid (SIA) levels relate to their phagocytosis and IgG binding ability.

METHODS

ST3Gal-1, Neu3, ST6Gal-1, Neu1, α-2,3-SIA, and α-2,6-SIA levels on RA peripheral blood monocytes, T cells, and polymorphonuclear cells were determined by using fluorochrome-conjugated anti-cell-specific marker antibodies and fluorochrome-conjugated anti-enzyme antibodies. Simple correlation and linear regression were used to correlate enzyme levels with DAS28.

RESULTS

RA monocyte ST3Gal-1 and Neu3 levels correlated with DAS28 in patients having DAS28 >5.1 (r = 0.469, p = 0.002; r = 0.410, p = 0.006, respectively). When multivariable analysis was performed for erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and SIA-related enzyme levels in different cell types as independent variables with DAS28 as a dependent variable, monocyte ST3Gal-1 levels correlated with DAS28 (p = 0.009) but not ESR and CRP in patients having DAS28 >5.1 (both p ≥ 0.292). RA monocyte ST3Gal-1 levels correlated with DAS28 (p = 0.010) and with ESR (p < 0.001) at month 0 when applied to all RA patients including both remission and nonremission groups in multivariable analysis. The latter findings persisted longitudinally at month 3.

CONCLUSION

Monocyte ST3Gal-1 and Neu3 levels correlated longitudinally with DAS28 by two different methods suggest that monocyte ST3Gal-1 and Neu3 levels may be used as biomarkers to monitor RA disease activity.

Dual-type responsive electrochemical biosensor for the detection of α2,6-sialylated glycans based on AuNRs-SA coupled with c-SWCNHs/S-PtNC nanocomposites signal amplification

In this study, a dual-type responsive electrochemical biosensor was developed for the quantitative detection of α2,6-sialylated glycans (α2,6-sial-Gs), a potential biomarker of tumors. The gold nanorods (AuNRs), which exhibited great specific surface area, as well as good biocompatibility, was synthesized by the way of seed growth method. Furthermore, a biotin-streptavidin (biotin-SA) system was introduced to improve the immunoreaction efficiency. Accordingly, a label-free biosensor was fabricated based on AuNRs-SA for the quick detection of α2,6-sial-Gs by recording the signal of differential pulse voltammetry (DPV). Furthermore, to expand the ultrasensitive detection of α2,6-sial-Gs, a carboxylated single-walled carbon nanohorns/sulfur-doped platinum nanocluster (c-SWCNHs/S-PtNC) was synthesized for the first time as a novel signal label, which showed an excellent catalytic performance. The usage of c-SWCNHs/S-PtNC could significantly amplify the electrochemical signal recorded by the amperometric i-t curve. Herein, a sandwich type biosensor was constructed by combining the AuNRs-SA on the electrode and c-SWCNHs/S-PtNC (signal amplifier). The label-free biosensor possessed a linear range from 5 ng mL^-1 to 5 μg mL^-1 with a detection limit of 0.50 ng mL^-1, and the sandwich-type biosensor possessed a wide linear range from 1 fg mL^-1 to 100 ng mL^-1 with a detection limit of 0.69 fg mL^-1. Furthermore, the biosensor exhibited excellent recovery and stability, indicating its potential for use in actual samples.

Novel Zebrafish Mono-α2,8-sialyltransferase (ST8Sia VIII): An Evolutionary Perspective of α2,8-Sialylation

The mammalian mono-α2,8-sialyltransferase ST8Sia VI has been shown to catalyze the transfer of a unique sialic acid residues onto core 1 O-glycans leading to the formation of di-sialylated O-glycosylproteins and to a lesser extent to diSia motifs onto glycolipids like GD1a. Previous studies also reported the identification of an orthologue of the ST8SIA6 gene in the zebrafish genome. Trying to get insights into the biosynthesis and function of the oligo-sialylated glycoproteins during zebrafish development, we cloned and studied this fish α2,8-sialyltransferase homologue. In situ hybridization experiments demonstrate that expression of this gene is always detectable during zebrafish development both in the central nervous system and in non-neuronal tissues. Intriguingly, using biochemical approaches and the newly developed in vitro MicroPlate Sialyltransferase Assay (MPSA), we found that the zebrafish recombinant enzyme does not synthetize diSia motifs on glycoproteins or glycolipids as the human homologue does. Using comparative genomics and molecular phylogeny approaches, we show in this work that the human ST8Sia VI orthologue has disappeared in the ray-finned fish and that the homologue described in fish correspond to a new subfamily of α2,8-sialyltransferase named ST8Sia VIII that was not maintained in Chondrichtyes and Sarcopterygii.

Sialic acid catabolism by N-acetylneuraminate pyruvate lyase is essential for muscle function

Sialic acids are important components of glycoproteins and glycolipids essential for cellular communication, infection, and metastasis. The importance of sialic acid biosynthesis in human physiology is well illustrated by the severe metabolic disorders in this pathway. However, the biological role of sialic acid catabolism in humans remains unclear. Here, we present evidence that sialic acid catabolism is important for heart and skeletal muscle function and development in humans and zebrafish. In two siblings, presenting with sialuria, exercise intolerance/muscle wasting, and cardiac symptoms in the brother, compound heterozygous mutations [chr1:182775324C>T (c.187C>T; p.Arg63Cys) and chr1:182772897A>G (c.133A>G; p.Asn45Asp)] were found in the N-acetylneuraminate pyruvate lyase gene (NPL). In vitro, NPL activity and sialic acid catabolism were affected, with a cell-type-specific reduction of N-acetyl mannosamine (ManNAc). A knockdown of NPL in zebrafish resulted in severe skeletal myopathy and cardiac edema, mimicking the human phenotype. The phenotype was rescued by expression of wild-type human NPL but not by the p.Arg63Cys or p.Asn45Asp mutants. Importantly, the myopathy phenotype in zebrafish embryos was rescued by treatment with the catabolic products of NPL: N-acetyl glucosamine (GlcNAc) and ManNAc; the latter also rescuing the cardiac phenotype. In conclusion, we provide the first report to our knowledge of a human defect in sialic acid catabolism, which implicates an important role of the sialic acid catabolic pathway in mammalian muscle physiology, and suggests opportunities for monosaccharide replacement therapy in human patients.

Human B Cell Differentiation Is Characterized by Progressive Remodeling of O-Linked Glycans

Germinal centers (GC) are microanatomical niches where B cells proliferate, undergo antibody affinity maturation, and differentiate to long-lived memory B cells and antibody-secreting plasma cells. For decades, GC B cells have been defined by their reactivity to the plant lectin peanut agglutinin (PNA), which binds serine/threonine (O-linked) glycans containing the asialylated disaccharide Gal-β1,3-GalNAc-Ser/Thr (also called T-antigen). In T cells, acquisition of PNA binding by activated T cells and thymocytes has been linked with altered tissue homing patterns, cell signaling, and survival. Yet, in GC B cells, the glycobiological basis and significance of PNA binding remains surprisingly unresolved. Here, we investigated the basis for PNA reactivity of GC B cells. We found that GC B cell binding to PNA is associated with downregulation of the α2,3 sialyltransferase, ST3GAL1 (ST3Gal1), and overexpression of ST3Gal1 was sufficient to reverse PNA binding in B cell lines. Moreover, we found that the primary scaffold for PNA-reactive O-glycans in B cells is the B cell receptor-associated receptor-type tyrosine phosphatase CD45, suggesting a role for altered O-glycosylation in antigen receptor signaling. Consistent with similar reports in T cells, ST3Gal1 overexpression in B cells in vitro induced drastic shortening in O-glycans, which we confirmed by both antibody staining and mass spectrometric O-glycomic analysis. Unexpectedly, ST3Gal1-induced changes in O-glycan length also correlated with altered binding of two glycosylation-sensitive CD45 antibodies, RA3-6B2 (more commonly called B220) and MEM55, which (in humans) have previously been reported to favor binding to naïve/GC subsets and memory/plasmablast subsets, respectively. Analysis of primary B cell binding to B220, MEM55, and several plant lectins suggested that B cell differentiation is accompanied by significant loss of O-glycan complexity, including loss of extended Core 2 O-glycans. To our surprise, decreased O-glycan length from naïve to post-GC fates best correlated not with ST3Gal1, but rather downregulation of the Core 2 branching enzyme GCNT1. Thus, our data suggest that O-glycan remodeling is a feature of B cell differentiation, dually regulated by ST3Gal1 and GCNT1, that ultimately results in expression of distinct O-glycosylation states/CD45 glycoforms at each stage of B cell differentiation.

Modulation of Immune Tolerance via Siglec-Sialic Acid Interactions

One of the key features of the immune system is its extraordinary capacity to discriminate between self and non-self and to respond accordingly. Several molecular interactions allow the induction of acquired immune responses when a foreign antigen is recognized, while others regulate the resolution of inflammation, or the induction of tolerance to self-antigens. Post-translational signatures, such as glycans that are part of proteins (glycoproteins) and lipids (glycolipids) of host cells or pathogens, are increasingly appreciated as key molecules in regulating immunity vs. tolerance. Glycans are sensed by glycan binding receptors expressed on immune cells, such as C-type lectin receptors (CLRs) and Sialic acid binding immunoglobulin type lectins (Siglecs), that respond to specific glycan signatures by triggering tolerogenic or immunogenic signaling pathways. Glycan signatures present on healthy tissue, inflamed and malignant tissue or pathogens provide signals for “self” or “non-self” recognition. In this review we will focus on sialic acids that serve as “self” molecular pattern ligands for Siglecs. We will emphasize on the function of Siglec-expressing mononuclear phagocytes as sensors for sialic acids in tissue homeostasis and describe how the sialic acid-Siglec axis is exploited by tumors and pathogens for the induction of immune tolerance. Furthermore, we highlight how the sialic acid-Siglec axis can be utilized for clinical applications to induce or inhibit immune tolerance.

Systems glycomics of adult zebrafish identifies organ-specific sialylation and glycosylation patterns

The emergence of zebrafish Danio rerio as a versatile model organism provides the unique opportunity to monitor the functions of glycosylation throughout vertebrate embryogenesis, providing insights into human diseases caused by glycosylation defects. Using a combination of chemical modifications, enzymatic digestion and mass spectrometry analyses, we establish here the precise glycomic profiles of eight individual zebrafish organs and demonstrate that the protein glycosylation and glycosphingolipid expression patterns exhibits exquisite specificity. Concomitant expression screening of a wide array of enzymes involved in the synthesis and transfer of sialic acids shows that the presence of organ-specific sialylation motifs correlates with the localized activity of the corresponding glycan biosynthesis pathways. These findings provide a basis for the rational design of zebrafish lines expressing desired glycosylation profiles.

Improving Immunotherapy Through Glycodesign

Immunotherapy is revolutionizing health care, with the majority of high impact "drugs" approved in the past decade falling into this category of therapy. Despite considerable success, glycosylation-a key design parameter that ensures safety, optimizes biological response, and influences the pharmacokinetic properties of an immunotherapeutic-has slowed the development of this class of drugs in the past and remains challenging at present. This article describes how optimizing glycosylation through a variety of glycoengineering strategies provides enticing opportunities to not only avoid past pitfalls, but also to substantially improve immunotherapies including antibodies and recombinant proteins, and cell-based therapies. We cover design principles important for early stage pre-clinical development and also discuss how various glycoengineering strategies can augment the biomanufacturing process to ensure the overall effectiveness of immunotherapeutics.

Sialyltransferase ST3GAL1 promotes cell migration, invasion, and TGF-β1-induced EMT and confers paclitaxel resistance in ovarian cancer

Sialyltransferases transfer sialic acid to nascent oligosaccharides and are upregulated in cancer. The inhibition of sialyltransferases is emerging as a potential strategy to prevent metastasis in several cancers, including ovarian cancer. ST3GAL1 is a sialyltransferase that catalyzes the transfer of sialic acid from cytidine monophosphate-sialic acid to galactose-containing substrates and is associated with cancer progression and chemoresistance. However, the function of ST3GAL1 in ovarian cancer is uncertain. Herein, we use qRT-PCR, western blotting, and immunohistochemistry to assess the expression of ST3GAL1 in ovarian cancer tissue and cell lines and investigate whether it influences resistance to paclitaxel in vitro and in a mouse xenograft model. We found that ST3GAL1 is upregulated in ovarian cancer tissues and in the ovarian cancer cell lines SKOV-3 and OVCAR3 but downregulated in A2780 ovarian cancer cells. Overexpression of ST3GAL1 in A2780 cells increases cell growth, migration, and invasion whereas ST3GAL1 knockdown in SKOV-3 cells decreases cell growth, migration, and invasion. Furthermore, overexpression of ST3GAL1 increases resistance to paclitaxel while downregulation of ST3GAL1 decreases resistance to paclitaxel in vitro, and overexpression of ST3GAL1 increases tumorigenicity and resistance to paclitaxel in vivo. Transforming growth factor-β1 can increase ST3GAL1 expression and induce ovarian cell epithelial-mesenchymal transition (EMT). However, knockdown of ST3GAL1 inhibits EMT expression. Taken together, our findings have identified a regulatory mechanism involving ST3GAL1 in ovarian cancer. ST3GAL1 may be a promising target for overcoming paclitaxel resistance in ovarian carcinoma.

Transient CHO expression platform for robust antibody production and its enhanced N-glycan sialylation on therapeutic glycoproteins

Large-scale transient expression in mammalian cells is a rapid protein production technology often used to shorten overall timelines for biotherapeutics drug discovery. In this study we demonstrate transient expression in a Chinese hamster ovary (CHO) host (ExpiCHO-S™) cell line capable of achieving high recombinant antibody expression titers, comparable to levels obtained using human embryonic kidney (HEK) 293 cells. For some antibodies, ExpiCHO-S™ cells generated protein materials with better titers and improved protein quality characteristics (i.e., less aggregation) than those from HEK293. Green fluorescent protein imaging data indicated that ExpiCHO-S™ displayed a delayed but prolonged transient protein expression process compared to HEK293. When therapeutic glycoproteins containing non-Fc N-linked glycans were expressed in transient ExpiCHO-S™, the glycan pattern was unexpectedly found to have few sialylated N-glycans, in contrast to glycans produced within a stable CHO expression system. To improve N-glycan sialylation in transient ExpiCHO-S™, we co-transfected galactosyltransferase and sialyltransferase genes along with the target genes, as well as supplemented the culture medium with glycan precursors. The authors have demonstrated that co-transfection of glycosyltransferases combined with medium addition of galactose and uridine led to increased sialylation content of N-glycans during transient ExpiCHO-S™ expression. These results have provided a scientific basis for developing a future transient CHO system with N-glycan compositions that are similar to those profiles obtained from stable CHO protein production systems. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2724, 2019.

Reciprocal feedback regulation of ST3GAL1 and GFRA1 signaling in breast cancer cells

GFRA1 and RET are overexpressed in estrogen receptor (ER)-positive breast cancers. Binding of GDNF to GFRA1 triggers RET signaling leading to ER phosphorylation and estrogen-independent transcriptional activation of ER-dependent genes. Both GFRA1 and RET are membrane proteins which are N-glycosylated but no O-linked sialylation site on GFRA1 or RET has been reported. We found GFRA1 to be a substrate of ST3GAL1-mediated O-linked sialylation, which is crucial to GDNF-induced signaling in ER-positive breast cancer cells. Silencing ST3GAL1 in breast cancer cells reduced GDNF-induced phosphorylation of RET, AKT and ERα, as well as GDNF-mediated cell proliferation. Moreover, GDNF induced transcription of ST3GAL1, revealing a positive feedback loop regulating ST3GAL1 and GDNF/GFRA1/RET signaling in breast cancers. Finally, we demonstrated ST3GAL1 knockdown augments anti-cancer efficacy of inhibitors of RET and/or ER. Moreover, high expression of ST3GAL1 was associated with poor clinical outcome in patients with late stage breast cancer and high expression of both ST3GAL1 and GFRA1 adversely impacted outcome in those with high grade tumors.

MiR-193a-3p and miR-224 mediate renal cell carcinoma progression by targeting alpha-2,3-sialyltransferase IV and the phosphatidylinositol 3 kinase/Akt pathway

Tumor metastasis is a major cause of cancer-related death in renal cell carcinoma (RCC). MicroRNAs (miRNAs) have been widely known to modulate proliferation invasion, metastasis, and apoptosis of cancer cells. In this study, we aimed to investigate the function and novel target of miR-193a-3p and miR-224 in RCC. The levels of miR-193a-3p and miR-224 were significantly increased in RCC tissues and RCC cell lines. Alpha-2,3-Sialyltransferase IV (ST3GalIV) was highly expressed in adjacent nontumor tissues and human normal proximal tubular cell line HK-2 compared to RCC tissues and cell lines. ST3GalIV expression was negatively correlated with miR-193a-3p and miR-224. Further analysis indicated that miR-193a-3p and miR-224 directly targeted ST3GalIV. MiR-193a-3p and miR-224 increased cell proliferation and migration by directly inhibiting ST3GalIV, and this effect was reversed by co-transfection with ST3GalIV in vitro. Overexpression of miR-193a-3p and miR-224 increased RCC cell proliferation in vivo. Furthermore, the phosphatidylinositol 3 kinase (PI3K)/Akt pathway was mediated by miR-193a-3p and miR-224 in RCC cell lines. Collectively, these results suggested that miR-193a-3p and miR-224 played an important role in regulation of RCC by targeting ST3GalIV via PI3K/Akt pathway.

Sialyltransferase-Based Chemoenzymatic Histology for the Detection of N- and O-Glycans

Profiling specific glycans in histopathological samples is hampered by the lack of selective and sensitive tools for their detection. Here, we report on the development of chemoenzymatic histology of membrane polysaccharide (CHoMP)-based methods for the detection of O- and N-linked glycans on tissue sections via the use of sialyltransferases ST3Gal1 and ST6Gal1, respectively. Combining these two methods, we developed tandem labeling and double labeling strategies that permit the detection of unsialylated and sialylated glycans or the detection of O- and N-linked glycans on the same tissue section, respectively. We applied these methods to screen murine tissue specimens, human multiple-organ cancer arrays, and lymphoma and prostate cancer arrays. Using tandem labeling with ST6Gal1 to analyze N-glycans in a prostate cancer array, we found striking differences in expression patterns of both sialylated and unsialylated N-glycans between cancerous and healthy samples. Such differences were also observed between normal tissue from healthy donors and healthy tissue adjacent to tumors. Our double labeling technique identified significant differences in unsialylated O-glycans between B-cell and T-cell lymphomas and between B-cell lymphomas and normal adjacent lymph nodes. Remarkable differences were also detected between adjacent lymph nodes and spleen tissue samples. These new chemoenzymatic histology methods therefore provide valuable tools for the analysis of glycans in clinically relevant tissue samples.

α2,3-sialyltransferase type I regulates migration and peritoneal dissemination of ovarian cancer cells

Epithelial ovarian cancer (EOC) has the highest mortality rate among gynecologic cancers due to advanced stage presentation, peritoneal dissemination, and refractory ascites at diagnosis. We investigated the role of α2,3-sialyltransferase type I (ST3GalI) by analyzing human ovarian cancer datasets and human EOC tissue arrays. We found that high expression of ST3GalI was associated with advanced stage EOC. Transwell migration and cell invasion assays showed that high ST3GalI expression enhanced migration of EOC cells. We also observed that there was a linear relation between ST3GalI expression and epidermal growth factor receptor (EGFR) signaling in EOC patients, and that high ST3GalI expression blocked the effect of EGFR inhibitors. Co-Immunoprecipitation experiments demonstrated that ST3GalI and EGFR were present in the same protein complex. Inhibition of ST3GalI using a competitive inhibitor, Soyasaponin I (SsaI), inhibited tumor cell migration and dissemination in the in vivo mouse model with transplanted MOSEC cells. Further, SsaI synergistically enhanced the anti-tumor effects of EGFR inhibitor on EOC cells. Our study demonstrates that ST3GalI regulates ovarian cancer cell migration and peritoneal dissemination via EGFR signaling. This suggests α2,3-linked sialylation inhibitors in combination with EGFR inhibitors could be effective agents for the treatment of EOC.

LncRNA HCP5 promotes follicular thyroid carcinoma progression via miRNAs sponge

Long non-coding RNAs (lncRNAs), which are important functional regulators in cancer, have received increased attention in recent years. In this study, next-generation sequencing technology was used to identify aberrantly expressed lncRNAs in follicular thyroid carcinoma (FTC). The long non-coding RNA–HLA complex P5 (HCP5) was found to be overexpressed in FTC. The results of the qPCR analysis were consistent with the sequencing results. In addition, functional experiments showed that overexpression of HCP5 can promote the proliferation, migration, invasiveness and angiogenic ability of FTC cells. Furthermore, according to the sequencing results, HCP5 and alpha-2, 6-sialyltransferase 2 (ST6GAL2) were co-expressed in FTC. We hypothesised that ST6GAL2 may be regulated by HCP5, which would in turn mediate the activity of FTC cells. Through qPCR, immunostaining analyses and functional experiments, we determined that the expression of HCP5 was elevated and was correlated with the levels of ST6GAL2 in FTC tissues and cells. Mechanistic experiments showed that HCP5 functions as a competing endogenous RNA (ceRNA) and acts as a sponge for miR-22-3p, miR-186-5p and miR-216a-5p, which activates ST6GAL2. In summary, our study revealed that HCP5 is a tumour regulator in the development of FTC and that it may contribute to improvement of FTC diagnosis and therapy.

Reconstruction of the sialylation pathway in the ancestor of eukaryotes

The biosynthesis of sialylated molecules of crucial relevance for eukaryotic cell life is achieved by sialyltransferases (ST) of the CAZy family GT29. These enzymes are widespread in the Deuterostoma lineages and more rarely described in Protostoma, Viridiplantae and various protist lineages raising the question of their presence in the Last eukaryotes Common Ancestor (LECA). If so, it is expected that the main enzymes associated with sialic acids metabolism are also present in protists. We conducted phylogenomic and protein sequence analyses to gain insights into the origin and ancient evolution of ST and sialic acid pathway in eukaryotes, Bacteria and Archaea. Our study uncovered the unreported occurrence of bacterial GT29 ST and evidenced the existence of 2 ST groups in the LECA, likely originating from the endosymbiotic event that generated mitochondria. Furthermore, distribution of the major actors of the sialic acid pathway in the different eukaryotic phyla indicated that these were already present in the LECA, which could also access to this essential monosaccharide either endogenously or via a sialin/sialidase uptake mechanism involving vesicles. This pathway was lost in several basal eukaryotic lineages including Archaeplastida despite the presence of two different ST groups likely assigned to other functions.

Transglutaminase and Sialyltransferase Enzymatic Approaches for Polymer Conjugation to Proteins

Proteins hold a central role in medicine and biology, also confirmed by the several therapeutic applications based on biologic drugs. Such therapies are of great relevance thanks to high potency and safety of proteins. Nevertheless, many proteins as therapeutics might present issues like fast kidney clearance, rapid enzymatic degradation, or immunogenicity. Such defects implicate frequent administrations or administrations at high doses of the therapeutics, thus yielding or exacerbating potential side effects. A successful technology for improving the clinical profiles of proteins is the conjugation of polymers to the protein surface. The design of a protein-polymer conjugate presents critical aspects that determine the efficacy and safety of the final product. The control over stoichiometry and conjugation site is a strict criterion on which researchers have been intensively focused during the years, in order to obtain homogeneous and batch-to-batch reproducible products. An innovative site-specific conjugation strategy relies on the use of enzymes as tools to mediate polymer conjugation. Enzymatic approaches are attractive because they allow site-selective polymer conjugation at specific protein amino acids. In these reactions, the polymer is a substrate analog that replaces the native substrate. Furthermore, enzymes can count other advantages such as high yields of conversion and physiological conditions of reaction. This chapter provides a meaningful description of protein-polymer conjugation through transglutaminase-mediated and sialyltransferase-mediated enzymatic strategies, reporting the mechanism of action and some relevant examples.

Identification of proteins with the CDw75 epitope in human colorectal cancer

The CDw75 epitope is an α(2,6) sialylated antigen overexpressed in colorectal cancer (CRC), where its expression correlates with the progression of the disease. The CDw75 epitope is located mainly in N-glycoproteins, whose identity remains unknown. The aim of the present study was to identify proteins with the CDw75 epitope as a strategy to deepen the understanding of molecular pathogenesis of CRC and to identify novel biomarkers for this disease. For this purpose, a two-dimensional electrophoresis approach was employed. Protein spots in the gels were matched to the corresponding CDw75 positive spots in the immunoblotted polyvinylidene difluoride membranes, and further identification of the protein species was performed by mass spectrometry. Additionally, one-dimensional western blotting experiments were performed to verify the expression of these candidate proteins in the colorectal tissue and their coincidence in molecular mass with the CDw75-positive bands. The findings of the present study indicate that haptoglobin and the keratins 8 (K8) and 18 (K18) are proteins with the CDw75 epitope in the colorectal tissue from CRC patients and also suggest novel functions and cellular locations for these proteins in the colorectal tissue and in relation to CRC.

E-Selectin Ligands in the Human Mononuclear Phagocyte System: Implications for Infection, Inflammation, and Immunotherapy

The mononuclear phagocyte system comprises a network of circulating monocytes and dendritic cells (DCs), and “histiocytes” (tissue-resident macrophages and DCs) that are derived in part from blood-borne monocytes and DCs. The capacity of circulating monocytes and DCs to function as the body’s first-line defense against offending pathogens greatly depends on their ability to egress the bloodstream and infiltrate inflammatory sites. Extravasation involves a sequence of coordinated molecular events and is initiated by E-selectin-mediated deceleration of the circulating leukocytes onto microvascular endothelial cells of the target tissue. E-selectin is inducibly expressed by cytokines (tumor necrosis factor-α and IL-1β) on inflamed endothelium, and binds to sialofucosylated glycan determinants displayed on protein and lipid scaffolds of blood cells. Efficient extravasation of circulating monocytes and DCs to inflamed tissues is crucial in facilitating an effective immune response, but also fuels the immunopathology of several inflammatory disorders. Thus, insights into the structural and functional properties of the E-selectin ligands expressed by different monocyte and DC populations is key to understanding the biology of protective immunity and the pathobiology of several acute and chronic inflammatory diseases. This review will address the role of E-selectin in recruitment of human circulating monocytes and DCs to sites of tissue injury/inflammation, the structural biology of the E-selectin ligands expressed by these cells, and the molecular effectors that shape E-selectin ligand cell-specific display. In addition, therapeutic approaches targeting E-selectin receptor/ligand interactions, which can be used to boost host defense or, conversely, to dampen pathological inflammatory conditions, will also be discussed.

miR-182 and miR-135b Mediate the Tumorigenesis and Invasiveness of Colorectal Cancer Cells via Targeting ST6GALNAC2 and PI3K/AKT Pathway

BACKGROUND

Metastasis is a leading cause of cancer-related death including colorectal cancer (CRC). MicroRNAs are known to regulate cancer pathways and to be expressed aberrantly in cancer. Aberrant sialylation is closely associated with malignant phenotype of tumor cells, including invasiveness and metastasis.

AIM

This study aimed to investigate the association of miR-182 and miR-135b with proliferation and invasion by targeting sialyltransferase ST6GALNAC2 in CRC cells and explore the potential molecular mechanism.

METHODS

We measured the levels of miR-182, miR-135b, and ST6GALNAC2 in a series of CRC cell lines and tissues using real-time PCR. Bioinformatics analysis and luciferase reporter assay were performed to test the direct binding of miR-182 and miR-135b to the target gene ST6GALNAC2. We also analyzed the possible role of miR-182/-135b on colony formation, wound healing, invasion, and tube formation.

RESULTS

The expression of miR-182 and miR-135b was higher in tumor tissues compared to adjacent noncancerous tissues of CRC patients, as well as up-regulated in SW620 cells than in SW480 cells with different metastatic potential. By applying bioinformatics analysis and luciferase reporter assay, we identified ST6GALNAC2 as the direct target of miR-182/-135b. Furthermore, miR-182/-135b inhibited significantly ST6GALNAC2 expression, and consistently, ST6GALNAC2 mediated migration, adhesion, invasion, proliferation, and tumor angiogenesis in CRC cell lines. Additionally, PI3K/AKT signaling pathway was regulated by miR-182/135b, which was partially blocked by altered level of ST6GALNAC2 in CRC.

CONCLUSIONS

The miR-182/-135b/ST6GALNAC2/PI3K/AKT axis may serve as a predictive biomarker and a potential therapeutic target in CRC treatment.

Computer-aided design of human sialyltransferase inhibitors of hST8Sia III

Sialyltransferase (ST) upregulation and the resultant hypersialylation of tumour cell surfaces is an established hallmark of many cancers including lung, breast, ovarian, pancreatic and prostate cancer. The role of ST enzymes in tumour cell growth and metastasis, as well as links to multi-drug resistance, has seen ST inhibition emerge as a target for potential antimetastatic cancer treatments. The most potent of these reported inhibitors are transition-state analogues. Although there are several examples of these in the literature, many have suspected poor pharmacokinetic properties and are not readily synthetically accessible. A proposed solution to these problems is the use of a neutral carbamate or 1,2,3-triazole linker instead of the more commonly used phosphodiester linker, and replacing the traditionally utilised cytidine nucleotide with uridine. Another issue in this area is the paucity of structural information of human ST enzymes. However, in late 2015 the structure of human ST8Sia III was reported (only the second human ST described so far), creating the opportunity for structure-based design of selective ST8 inhibitors for the first time. Herein, molecular docking and molecular dynamics simulations with the newly published crystal structure of hST8Sia III were performed for the first time with selected ST transition state analogues. Simulations showed that these compounds could participate in many of the key interactions common with the natural donor and acceptor substrates, and reveals some key insights into the synthesis of potentially selective ST inhibitors.

Transition state-based ST6Gal I inhibitors: Mimicking the phosphodiester linkage with a triazole or carbamate through an enthalpy-entropy compensation

Human β-galactoside α-2,6-sialyltransferase I (ST6Gal I) catalyses the synthesis of sialylated glycoconjugates. Overexpression of ST6Gal I is observed in many cancers, where it promotes metastasis through altered cell surface sialylation. A wide range of sialyltransferase inhibitors have been developed, with analogues structurally similar to the transition state exhibiting the highest inhibitory activity. To improve synthetic accessibility and pharmacokinetics of previously reported inhibitors, the replacement of the charged phosphodiester linker with a potential neutral isostere such as a carbamate or a 1,2,3-triazole has been investigated. Extensive molecular dynamics simulations have demonstrated that compounds with the alternate linkers could maintain key interactions with the human ST6Gal I active site, demonstrating the potential of a carbamate or a 1,2,3-triazole as a phosphodiester isostere. Free energy perturbation calculations provided energetic evidence suggesting that the carbamate and 1,2,3-triazole were slightly more favourable than the phosphodiester. Further exploration with free energy component, quasi-harmonic and cluster analysis suggested that there is an enthalpy-entropy compensation accounting for the replacement of the flexible charged phosphodiester with a neutral and rigid isostere. Overall, these simulations provide a strong rationale for the use of a carbamate or 1,2,3-triazole as a phosphodiester isostere in the development of novel inhibitors of human ST6Gal I.

Regulating Immunogenicity and Tolerogenicity of Bone Marrow-Derived Dendritic Cells through Modulation of Cell Surface Glycosylation by Dexamethasone Treatment

Dendritic cellular therapies and dendritic cell vaccines show promise for the treatment of autoimmune diseases, the prolongation of graft survival in transplantation, and in educating the immune system to fight cancers. Cell surface glycosylation plays a crucial role in the cell–cell interaction, uptake of antigens, migration, and homing of DCs. Glycosylation is known to change with environment and the functional state of DCs. Tolerogenic DCs (tDCs) are commonly generated using corticosteroids including dexamethasone, however, to date, little is known on how corticosteroid treatment alters glycosylation and what functional consequences this may have. Here, we present a comprehensive profile of rat bone marrow-derived dendritic cells, examining their cell surface glycosylation profile before and after Dexa treatment as resolved by both lectin microarrays and lectin-coupled flow cytometry. We further examine the functional consequences of altering cell surface glycosylation on immunogenicity and tolerogenicity of DCs. Dexa treatment of rat DCs leads to profoundly reduced expression of markers of immunogenicity (MHC I/II, CD80, CD86) and pro-inflammatory molecules (IL-6, IL-12p40, inducible nitric oxide synthase) indicating a tolerogenic phenotype. Moreover, by comprehensive lectin microarray profiling and flow cytometry analysis, we show that sialic acid (Sia) is significantly upregulated on tDCs after Dexa treatment, and that this may play a vital role in the therapeutic attributes of these cells. Interestingly, removal of Sia by neuraminidase treatment increases the immunogenicity of immature DCs and also leads to increased expression of pro-inflammatory cytokines while tDCs are moderately protected from this increase in immunogenicity. These findings may have important implications in strategies aimed at increasing tolerogenicity where it is advantageous to reduce immune activation over prolonged periods. These findings are also relevant in therapeutic strategies aimed at increasing the immunogenicity of cells, for example, in the context of tumor specific immunotherapies.

Analyses of N-linked glycans of PrPSc revealed predominantly 2,6-linked sialic acid residues

Mammalian prions (PrP^Sc ) consist of misfolded, conformationally altered, self-replicating states of the sialoglycoprotein called prion protein or PrP^C . Recent studies revealed that the sialylation status of PrP^Sc plays a major role in evading innate immunity and infecting a host. Establishing the type of linkage by which sialic acid residues are attached to galactose is important, as it helps to identify the sialyltransferases responsible for sialylating PrP^C and outline strategies for manipulating the sialyation status of PrP^Sc . Using enzymatic treatment with sialidases and lectin blots, this study demonstrated that in N-linked glycans of PrP^Sc , the sialic acid residues are predominantly alpha 2,6-linked. High percentages of alpha 2,6-linked sialic acids were observed in PrP^Sc of three prion strains 22L, RML, and ME7, as well as PrP^Sc from brain, spleen, or N2a cells cultured in vitro. Moreover, the variation in the percentage of alpha 2,3- versus 2,6-linked sialic acid was found to be relatively minor between brain-, spleen-, or cell-derived PrP^Sc , suggesting that the type of linkage is independent of tissue type. Based on the current results, we propose that sialyltransferases of St6Gal family, which is responsible for attaching sialic acids via alpha 2,6-linkages to N-linked glycans, controls sialylation of PrP^C and PrP^Sc .

How Fucose of Blood Group Glycotopes Programs Human Gut Microbiota

Formation of appropriate gut microbiota is essential for human health. The first two years of life is the critical period for this process. Selection of mutualistic microorganisms of the intestinal microbiota is controlled by the FUT2 and FUT3 genes that encode fucosyltransferases, enzymes responsible for the synthesis of fucosylated glycan structures of mucins and milk oligosaccharides. In this review, the mechanisms of the selection and maintenance of intestinal microorganisms that involve fucosylated oligosaccharides of breast milk and mucins of the newborn's intestine are described. Possible reasons for the use of fucose, and not sialic acid, as the major biological signal for the selection are also discussed.

Contribution of vascular endothelial growth factor receptor-2 sialylation to the process of angiogenesis

Vascular endothelial growth factor receptor-2 (VEGFR2) is the main pro-angiogenic receptor expressed by endothelial cells (ECs). Using surface plasmon resonance, immunoprecipitation, enzymatic digestion, immunofluorescence and cross-linking experiments with specific sugar-binding lectins, we demonstrated that VEGFR2 bears both α,1-fucose and α(2,6)-linked sialic acid (NeuAc). However, only the latter is required for VEGF binding to VEGFR2 and consequent VEGF-dependent VEGFR2 activation and motogenic response in ECs. Notably, downregulation of β-galactoside α(2,6)-sialyltransferase expression by short hairpin RNA transduction inhibits VEGFR2 α(2,6) sialylation that is paralleled by an increase of β-galactoside α(2,3)-sialyltransferase expression. This results in an ex-novo α(2,3)-NeuAc sialylation of the receptor that functionally replaces the lacking α(2,6)-NeuAc, thus allowing VEGF/VEGFR2 interaction. In keeping with the role of VEGFR2 sialylation in angiogenesis, the α(2,6)-NeuAc-binding lectin Sambucus nigra (SNA) prevents VEGF-dependent VEGFR2 autophosphorylation and EC motility, proliferation and motogenesis. In addition, SNA exerts a VEGF-antagonist activity in tridimensional angiogenesis models in vitro and in the chick-embryo chorioallantoic membrane neovascularization assay and mouse matrigel plug assay in vivo. In conclusion, VEGFR2-associated NeuAc plays an important role in modulating VEGF/VEGFR2 interaction, EC pro-angiogenic activation and neovessel formation. VEGFR2 sialylation may represent a target for the treatment of angiogenesis-dependent diseases.

α2,6-linked sialic acid serves as a high-affinity receptor for cancer oncolytic virotherapy with Newcastle disease virus

PURPOSE

Newcastle disease virus (NDV) has been applied to oncolytic virotherapy for decades due to its naturally oncolytic property. In spite of the substantiation of the sialic acid receptors of NDV on host cells, knowledge of preference of sialic acid linkage in viral attachment and oncolytic effect is lacking and imperative to be elucidated.

METHODS

Surface plasmon resonance analysis and competitive inhibition with sialylated glycan receptor analogues were used to determine the affinity and the preference of sialic acid receptor. Treatments of sialyltransferase inhibitors and linkage-specific sialidases and transfection with sialyltransferase expression vector were performed to regulate sialic acids levels.

RESULTS

We demonstrated that sialic acid was essential for NDV binding and infection of tumor cells. α2,6-linked sialic acid served as a high-affinity receptor for NDV and the ST6Gal I sialyltransferase that synthesizes α2-6 linkage of sialylated N-linked glycans in CHO-K1 cells promoted NDV binding and cytopathic effect. More importantly, an enhanced antitumor effect of NDV on aggressive SW620 colorectal carcinoma cells with high-level of cell surface α2,6-sialylation, but not SW480 cells with relative low-level of α2,6-sialylation, was observed both in vitro and in vivo.

CONCLUSIONS

The study provides evidence of optimized therapeutic strategy in oncolytic virotherapy via partly defining α2,6-sialylated receptor as a "cellular marker" for NDV.

Probing the CMP-Sialic Acid Donor Specificity of Two Human β-d-Galactoside Sialyltransferases (ST3Gal I and ST6Gal I) Selectively Acting on O- and N-Glycosylproteins

Sialylation of glycoproteins and glycolipids is catalyzed by sialyltransferases in the Golgi of mammalian cells, whereby sialic acid residues are added at the nonreducing ends of oligosaccharides. Because sialylated glycans play critical roles in a number of human physio-pathological processes, the past two decades have witnessed the development of modified sialic acid derivatives for a better understanding of sialic acid biology and for the development of new therapeutic targets. However, nothing is known about how individual mammalian sialyltransferases tolerate and behave towards these unnatural CMP-sialic acid donors. In this study, we devised several approaches to investigate the donor specificity of the human β-d-galactoside sialyltransferases ST6Gal I and ST3Gal I by using two CMP-sialic acids: CMP-Neu5Ac, and CMP-Neu5N-(4pentynoyl)neuraminic acid (CMP-SiaNAl), an unnatural CMP-sialic acid donor with an extended and functionalized N-acyl moiety.

Active-Site His85 of Pasteurella dagmatis Sialyltransferase Facilitates Productive Sialyl Transfer and So Prevents Futile Hydrolysis of CMP-Neu5Ac

Sialyltransferases of the GT-80 glycosyltransferase family are considered multifunctional because of the array of activities detected. They exhibit glycosyl transfer, trans-sialylation, and hydrolysis activities. How these enzymes utilize their active-site residues in balancing the different enzymatic activities is not well understood. In this study of Pasteurella dagmatis α2,3sialyltransferase, we show that the conserved His85 controls efficiency and selectivity of the sialyl transfer. A His85→Asn variant was 200 times less efficient than wild-type for sialylation of lactose, and exhibited relaxed site selectivity to form not only the α2,3- but also the α2,6-sialylated product (21 %). The H85N variant was virtually inactive in trans-sialylation but showed almost the same CMP-Neu5Ac hydrolase activity as wild-type. The competition between sialyl transfer and hydrolysis in the conversion of CMP-Neu5Ac was dependent on the lactose concentration; this was characterized by a kinetic partition ratio of 85 m^-1 for the H85N variant, compared to 17 000 m^-1 for the wild-type enzyme. His85 promotes the productive sialyl transfer to lactose and so prevents hydrolysis of CMP-Neu5Ac in the reaction.

Genetic Defects Underlie the Non-syndromic Autosomal Recessive Intellectual Disability (NS-ARID)

Intellectual disability (ID) is a neurodevelopmental disorder which appears frequently as the result of genetic mutations and may be syndromic (S-ID) or non-syndromic (NS-ID). ID causes an important economic burden, for patient's family, health systems, and society. Identifying genes that cause S-ID can easily be evaluated due to the clinical symptoms or physical anomalies. However, in the case of NS-ID due to the absence of co-morbid features, the latest molecular genetic techniques can be used to understand the genetic defects that underlie it. Recent studies have shown that non-syndromic autosomal recessive (NS-ARID) is extremely heterogeneous and contributes much more than X-linked ID. However, very little is known about the genes and loci involved in NS-ARID relative to X-linked ID, and whose complete genetic etiology remains obscure. In this review article, the known genetic etiology of NS-ARID and possible relationships between genes and the associated molecular pathways of their encoded proteins has been reviewed which will enhance our understanding about the underlying genes and mechanisms in NS-ARID.

Epigenetic Bases of Aberrant Glycosylation in Cancer

In this review, the sugar portions of glycoproteins, glycolipids, and glycosaminoglycans constitute the glycome, and the genes involved in their biosynthesis, degradation, transport and recognition are referred to as “glycogenes“. The extreme complexity of the glycome requires the regulatory layer to be provided by the epigenetic mechanisms. Almost all types of cancers present glycosylation aberrations, giving rise to phenotypic changes and to the expression of tumor markers. In this review, we discuss how cancer-associated alterations of promoter methylation, histone methylation/acetylation, and miRNAs determine glycomic changes associated with the malignant phenotype. Usually, increased promoter methylation and miRNA expression induce glycogene silencing. However, treatment with demethylating agents sometimes results in silencing, rather than in a reactivation of glycogenes, suggesting the involvement of distant methylation-dependent regulatory elements. From a therapeutic perspective aimed at the normalization of the malignant glycome, it appears that miRNA targeting of cancer-deranged glycogenes can be a more specific and promising approach than the use of drugs, which broad target methylation/acetylation. A very specific type of glycosylation, the addition of GlcNAc to serine or threonine (O-GlcNAc), is not only regulated by epigenetic mechanisms, but is an epigenetic modifier of histones and transcription factors. Thus, glycosylation is both under the control of epigenetic mechanisms and is an integral part of the epigenetic code.

MiRNA expression profiles reveal the involvement of miR-26a, miR-548l and miR-34a in hepatocellular carcinoma progression through regulation of ST3GAL5

MicroRNAs (miRNAs) have key roles in comprehensive physiological and pathological processes by targeting specific genes through translational repression. Identification of miRNAs related to metastasis enables us to obtain better insight into cancer development. In the current study, we investigated the miRNA expressional profiles in the highly invasive human hepatocellular carcinoma cell line MHCC97-H and MHCC97-L with lower metastatic potential using miRNA microarrays. By quantitative real-time PCR, we confirmed the results of miRNA experiments. Thirteen differentially expressed miRNAs were identified between MHCC97-H and MHCC97-L cells; and the same results were found in clinical samples. Using bioinformatic analysis and luciferase reporter assay, we found that ST3GAL5, a sialyltransferase gene, was the direct target of miR-26a, miR-548l and miR-34a. Engineered expression of miR-26a, miR-548l or miR-34a in MHCC97-H or MHCC97-L cells could significantly change their malignant behaviors and oncogenicity in in vitro and in vivo assays. Manipulated expression of ST3GAL5 also led to the alteration of the metastatic potential of MHCC97-H and MHCC97-L cells, in agreement with the effects of above three miRNAs. Altogether, our data indicate that the levels of these miRNAs may be used as biological markers for evaluating hepatocellular carcinoma progression. miR-26a, miR-548l and miR-34a, acting as tumor suppressors, may exert their effects by regulating ST3GAL5.

Transition State-Based Sialyltransferase Inhibitors: Mimicking Oxocarbenium Ion by Simple Amide

In the new transition-state based sialyltransferase inhibitors, an amide group was placed at the corresponding C-2 position of CMP-sialic acid to mimic the geometry and charge distribution in the transition state, and simple aromatic or aliphatic rings were used instead of the sialic acid moiety. All synthetic compounds exhibited excellent α(2-6)-sialyltransferase inhibition, resulting in up to a 2600-fold higher affinity for the enzyme than CMP-Neu5Ac, suggesting that amide is a key element for simulating transition-state features.

A Glycovariant of Human CD44 is Characteristically Expressed on Human Mesenchymal Stem Cells

The clinical effectiveness of systemically administered human mesenchymal stem cells (hMSCs) depends on their capacity to engage vascular endothelium. hMSCs derived from bone marrow (BM-hMSCs) natively lack endothelial binding capacity, but express a CD44 glycovariant containing N-linked sialyllactosamines that can be α(1,3)-fucosylated using fucosyltransferase-VI (FTVI) to enforce sLe^X decorations, thereby creating hematopoietic cell E-/L-selectin ligand (HCELL). HCELL expression programs potent shear-resistant adhesion of circulating cells to endothelial beds expressing E-selectin. An alternative source of hMSCs is adipose tissue (A-hMSCs), and we assessed whether A-hMSCs bind E-selectin and/or possess sialyllactosamine-decorated CD44 accessible to α(1,3)-fucosylation. Similar to BM-hMSCs, we found that A-hMSCs natively lack E-selectin ligands, but FTVI-mediated cell surface α(1,3)-fucosylation induces sLe^X expression and robust E-selectin binding secondary to conversion of CD44 into HCELL. Moreover, treatment with the α(1,3)-fucosyltransferase-FTVII also generated expression of HCELL on both BM-hMSCs and A-hMSCs, with sLe^X decorations created on N-linked glycans of the "standard" CD44 (CD44s) isoform. The finding that hMSCs from both source tissues each lack native E-selectin ligand expression prompted examination of the expression of glycosyltransferases that direct lactosaminyl glycan synthesis. These studies reveal that both types of hMSCs conspicuously lack transcripts encoding α(1,3)-fucosyltransferases, but equally express glycosyltransferases critical to creation of sialyllactosamines. Collectively, these data indicate that assembly of a sialyllactosaminyl-decorated CD44s glycovariant is a conserved feature of hMSCs derived from adipose tissue and marrow, thus identifying a CD44 glycosignature of these cells and supporting the applicability of cell surface α(1,3)-fucosylation in programming migration of systemically administered A-hMSCs to sites of tissue injury/inflammation. Stem Cells 2017;35:1080-1092.