Biological functions of glycosyltransferase genes involved in O-fucose glycan synthesis

Glycobiology in osteoclast differentiation and function

Glycans, either alone or in complex with glycan-binding proteins, are essential structures that can regulate cell biology by mediating protein stability or receptor dimerization under physiological and pathological conditions. Certain glycans are ligands for lectins, which are carbohydrate-specific receptors. Bone is a complex tissue that provides mechanical support for muscles and joints, and the regulation of bone mass in mammals is governed by complex interplay between bone-forming cells, called osteoblasts, and bone-resorbing cells, called osteoclasts. Bone erosion occurs when bone resorption notably exceeds bone formation. Osteoclasts may be activated during cancer, leading to a range of symptoms, including bone pain, fracture, and spinal cord compression. Our understanding of the role of protein glycosylation in cells and tissues involved in osteoclastogenesis suggests that glycosylation-based treatments can be used in the management of diseases. The aims of this review are to clarify the process of bone resorption and investigate the signaling pathways mediated by glycosylation and their roles in osteoclast biology. Moreover, we aim to outline how the lessons learned about these approaches are paving the way for future glycobiology-focused therapeutics.

Proteome analysis of high affinity mouse saliva proteins to hydroxyapatite

Caries sensitivity varies between the two strains of inbred mice, BALB/cA has high sensitivity and C3H/HeN has low sensitivity. One potential reason seems to be a difference in pellicle-forming saliva protein composition. Here, we performed a proteomic analysis in order to identify differences of hydroxyapatite (HAP) adsorbed saliva proteins between these two mouse strains. HAP column chromatography revealed twice the quantity of high-affinity saliva proteins in C3H/HeN compared to BALB/cA. One- and two-dimensional electrophoresis showed 2 bands/spots with deviating migration. They were identified as murine carbonic anhydrase VI (CAVI) by peptide mass fingerprinting and confirmed with western blotting using a specific polyclonal antibody. Total RNA from the salivary glands of both mouse strains, PCR amplification of cDNA with a CAVI specific primer, and sequence analysis revealed one different base in codon 96, resulting in one different amino acid. Glyco-chains of CAVI deviate in one N-glycan, confirmed by mass analysis. CAVI activity was estimated from distinct circular dichroism spectra of the molecules and found higher in C3H/HeN mice. In summary, the CAVI composition of BALB/cA and C3H/HeN differs in one amino acid and a glyco-chain modification. Further, saliva from caries resistant C3H/HeN mice displayed higher CAVI activity and also overall hydroxyapatite adsorption, suggesting a relationship with caries susceptibility.

•

CAVI was the salivary protein with high affinity for hydroxyapatite in two mice strains with different caries susceptibility.

•

CAVI of the two strains showed differences in molecular weight, amino acids and genes, glyco-chain modification and enzyme activity.

•

Differences in CAVI activity might contribute to caries susceptibility.

N-glycan profiling of bovine follicular fluid at key dominant follicle developmental stages

Follicular fluid (FF), an important microenvironment for the development of oocytes, contains many proteins that are glycosylated withN-linked glycans. This study aimed i) to present an initial analysis of theN-linked glycan profile of bovine FF using hydrophilic interaction liquid chromatography, anion exchange chromatography, high performance liquid chromatography (HPLC)-based separations and subsequent liquid chromatography–mass spectrometry/mass spectrometry analysis; ii) to determine differences in theN-glycan profile between FF from dominant and subordinate follicles from dairy heifers and lactating dairy cows and iii) to identify alterations in theN-glycan profile of FF during preovulatory follicle development using newly selected, differentiated (preovulatory) and luteinised dominant follicles from dairy heifers and lactating cows. We found that the majority of glycans on bovine FF are based on biantennary hypersialylated structures, where the glycans are sialylated on both the galactose andN-acetylglucosamine terminal sugars. A comparison of FFN-glycans from cows and heifers indicated higher levels of nonsialylated glycans with a lower proportion of sialylated glycans in cows than in heifers. Overall, as the follicle develops from Selection, Differentiation and Luteinisation in both cows and heifers, there is an overall decrease in sialylated structures on FFN-glycans.

O-fucosylation of the notch ligand mDLL1 by POFUT1 is dispensable for ligand function

Fucosylation of Epidermal Growth Factor-like (EGF) repeats by protein O-fucosyltransferase 1 (POFUT1 in vertebrates, OFUT1 in Drosophila) is pivotal for NOTCH function. In Drosophila OFUT1 also acts as chaperone for Notch independent from its enzymatic activity. NOTCH ligands are also substrates for POFUT1, but in Drosophila OFUT1 is not essential for ligand function. In vertebrates the significance of POFUT1 for ligand function and subcellular localization is unclear. Here, we analyze the importance of O-fucosylation and POFUT1 for the mouse NOTCH ligand Delta-like 1 (DLL1). We show by mass spectral glycoproteomic analyses that DLL1 is O-fucosylated at the consensus motif C²XXXX(S/T)C³ (where C² and C³ are the second and third conserved cysteines within the EGF repeats) found in EGF repeats 3, 4, 7 and 8. A putative site with only three amino acids between the second cysteine and the hydroxy amino acid within EGF repeat 2 is not modified. DLL1 proteins with mutated O-fucosylation sites reach the cell surface and accumulate intracellularly. Likewise, in presomitic mesoderm cells of POFUT1 deficient embryos DLL1 is present on the cell surface, and in mouse embryonic fibroblasts lacking POFUT1 the same relative amount of overexpressed wild type DLL1 reaches the cell surface as in wild type embryonic fibroblasts. DLL1 expressed in POFUT1 mutant cells can activate NOTCH, indicating that POFUT1 is not required for DLL1 function as a Notch ligand.

Evaluating genetic markers and neurobiochemical analytes for fluoxetine response using a panel of mouse inbred strains

RATIONALE

Identification of biomarkers that establish diagnosis or treatment response is critical to the advancement of research and management of patients with depression.

OBJECTIVE

Our goal was to identify biomarkers that can potentially assess fluoxetine response and risk to poor treatment outcome.

METHODS

We measured behavior, gene expression, and the levels of 36 neurobiochemical analytes across a panel of genetically diverse mouse inbred lines after chronic treatment with water or fluoxetine.

RESULTS

Glyoxylase 1 (GLO1) and guanine nucleotide-binding protein 1 (GNB1) mostly account for baseline anxiety-like and depressive-like behavior, indicating a common biological link between depression and anxiety. Fluoxetine-induced biochemical alterations discriminated positive responders, while baseline neurobiochemical differences differentiated negative responders (p < 0.006). Results show that glial fibrillary acidic protein, S100 beta protein, GLO1, and histone deacetylase 5 contributed most to fluoxetine response. These proteins are linked within a cellular growth/proliferation pathway, suggesting the involvement of cellular genesis in fluoxetine response. Furthermore, a candidate genetic locus that associates with baseline depressive-like behavior contains a gene that encodes for cellular proliferation/adhesion molecule (Cadm1), supporting a genetic basis for the role of neuro/gliogenesis in depression.

CONCLUSION

We provided a comprehensive analysis of behavioral, neurobiochemical, and transcriptome data across 30 mouse inbred strains that has not been accomplished before. We identified biomarkers that influence fluoxetine response, which, altogether, implicate the importance of cellular genesis in fluoxetine treatment. More broadly, this approach can be used to assess a wide range of drug response phenotypes that are challenging to address in human samples.

The carbohydrate ligands on the host embryo mediate intercellular migration of the parasitic wasp embryo

Invasive stage embryos of the parasitic wasp Copidosoma floridanum transmigrate through the epithelium of phylogenetically distant host embryos in a manner that is similar to mammalian leukocyte infiltration. Host embryonic cells appear to recognize the invading wasp embryo by components on the cell surface. We developed an in vitro wasp entry inhibition assay and found that C-type lectins of the wasp embryo bound to N-linked carbohydrate chains with fucose residues on the surface of host embryo. This is the first report showing a receptor-ligand interaction between heterologous multicellular organisms.

The crystal structure of the α-neurexin-1 extracellular region reveals a hinge point for mediating synaptic adhesion and function

α- and β-neurexins (NRXNs) are transmembrane cell adhesion proteins that localize to presynaptic membranes in neurons and interact with the postsynaptic neuroligins (NLGNs). Their gene mutations are associated with the autism spectrum disorders. The extracellular region of α-NRXNs, containing nine independently folded domains, has structural complexity and unique functional characteristics, distinguishing it from the smaller β-NRXNs. We have solved the X-ray crystal structure of seven contiguous domains of the α-NRXN-1 extracellular region at 3.0 Å resolution. The structure reveals an arrangement where the N-terminal five domains adopt a more rigid linear conformation and the two C-terminal domains form a separate arm connected by a flexible hinge. In an extended conformation the molecule is suitably configured to accommodate a bound NLGN molecule, as supported by structural comparison and surface plasmon resonance. These studies provide the structural basis for a multifunctional synaptic adhesion complex mediated by α-NRXN-1.

Notch2 governs the rate of generation of mouse long- and short-term repopulating stem cells

HSCs either self-renew or differentiate to give rise to multipotent cells whose progeny provide blood cell precursors. However, surprisingly little is known about the factors that regulate this choice of self-renewal versus differentiation. One candidate is the Notch signaling pathway, with ex vivo studies suggesting that Notch regulates HSC differentiation, although a functional role for Notch in HSC self-renewal in vivo remains controversial. Here, we have shown that Notch2, and not Notch1, inhibits myeloid differentiation and enhances generation of primitive Sca-1(+)c-kit(+) progenitors following in vitro culture of enriched HSCs with purified Notch ligands. In mice, Notch2 enhanced the rate of formation of short-term repopulating multipotential progenitor cells (MPPs) as well as long-term repopulating HSCs, while delaying myeloid differentiation in BM following injury. However, consistent with previous reports, once homeostasis was achieved, neither Notch1 nor Notch2 affected repopulating cell self-renewal. These data indicate a Notch2-dependent role in assuring orderly repopulation by HSCs, MPPs, myeloid cells, and lymphoid cells during BM regeneration.

Helicobacter hepaticus Hh0072 gene encodes a novel alpha1-3-fucosyltransferase belonging to CAZy GT11 family

Lewis x (Le(x)) and sialyl Lewis x (SLe(x))-containing glycans play important roles in numerous physiological and pathological processes. The key enzyme for the final step formation of these Lewis antigens is alpha1-3-fucosyltransferase. Here we report molecular cloning and functional expression of a novel Helicobacter hepaticus alpha1-3-fucosyltransferase (HhFT1) which shows activity towards both non-sialylated and sialylated Type II oligosaccharide acceptor substrates. It is a promising catalyst for enzymatic and chemoenzymatic synthesis of Le(x), sialyl Le(x) and their derivatives. Unlike all other alpha1-3/4-fucosyltransferases characterized so far which belong to Carbohydrate Active Enzyme (CAZy, http://www.cazy.org/) glycosyltransferase family GT10, the HhFT1 shares protein sequence homology with alpha1-2-fucosyltransferases and belongs to CAZy glycosyltransferase family GT11. The HhFT1 is thus the first alpha1-3-fucosyltransferase identified in the GT11 family.

Role of glycans and glycosyltransferases in the regulation of Notch signaling

The evolutionarily conserved Notch signaling pathway plays broad and important roles during embryonic development and in adult tissue homeostasis. Unlike most other pathways used during animal development, Notch signaling does not rely on second messengers and intracellular signaling cascades. Instead, pathway activation results in the cleavage of the Notch intracellular domain and its translocation into the nucleus, where it functions as a transcriptional co-activator of the Notch target genes. To ensure tight spatial and temporal regulation of a pathway with such an unusually direct signaling transduction, animal cells have devised a variety of specialized modulatory mechanisms. One such mechanism takes advantage of decorating the Notch extracellular domain with rare types of O-linked glycans. In this review, we will discuss the genetic and biochemical data supporting the notion that carbohydrate modification is essential for Notch signaling and attempt to provide a brief historical overview of how we have learned what we know about the glycobiology of Notch. We will also summarize what is known about the contribution of specific nucleotide-sugar transporters to Notch biology and the roles-enzymatic and non-enzymatic-played by specific glycosyltransferases in the regulation of this pathway. Mutations in the Notch pathway components cause a variety of human diseases, and manipulation of Notch signaling is emerging as a powerful tool in regenerative medicine. Therefore, studying how sugar modification modulates Notch signaling provides a framework for better understanding the role of glycosylation in animal development and might offer new tools to manipulate Notch signaling for therapeutic purposes.

A role of receptor Notch in ligand cis-inhibition in Drosophila

Notch and its ligands mediate short-range cell interactions that play a conserved role in inducing cell fate specification. Several regulatory mechanisms have been described to ensure robust polarized signaling from signal-sending to signal-receiving cells. High levels of ligand expression activate Notch in nearby cells and exert a cell-autonomous dominant-negative effect on Notch activity. This regulatory process is called cis-inhibition and helps to restrict Notch activation to signal-receiving cells. By combining genetic mosaics in the Drosophila wing primordium with cell culture assays, we present evidence here that Notch promotes the clearance of Serrate ligand from the cell surface and exerts an inhibitory effect on the activity of Serrate expressed in the same cell. These regulatory mechanisms are independent of Notch-mediated transcription and are executed by the extracellular domain of Notch. We show that this process is required to block Serrate-mediated activation of Notch in the signal-sending cell population and helps to restrict Notch activation to the signal-receiving cells. Altogether, our results, in concert with previous results on ligand-mediated Notch cis-inhibition, indicate that mutual inhibition between ligand and receptor in signal-sending cells helps to block Notch activity in these cells and to restrict receptor activation in signal-receiving cells.

O-GlcNAc modification of the extracellular domain of Notch receptors

Epidermal growth factor (EGF) domains are posttranslationally modified with unique O-linked glycans. The classical types of O-glycans on EGF domains are O-fucose and O-glucose glycans, found on many plasma glycoproteins and signaling molecules, whose biological functions have been demonstrated especially in the context of the Notch signaling pathway. We recently discovered O-GlcNAc modification as a new modification of the EGF domain that occurs on the conserved Ser/Thr residue located between the fifth and sixth cysteine residues within the EGF domain of Notch receptors in Drosophila. Here, we describe the methods employed to detect the O-GlcNAc modification of EGF repeats of Notch receptors. These methods include mass spectrometric analysis, galactosyltransferase labeling, immunoblotting with a specific antibody, and beta-N-acetyl-hexosaminidase digestion experiments. We also describe a method to detect O-GlcNAc transferase activity from crude membrane fraction proteins prepared from cultured S2 cells.

Regulation of notch signaling via O-glucosylation insights from Drosophila studies

Recent work using Drosophila melanogaster has shown that a protein O-glucosyltransferase called Rumi regulates Notch signaling. Studies on several alleles of rumi identified in a forward genetic screen indicated that Rumi is a temperature-sensitive regulator of Notch signaling in flies. Further genetic and rescue experiments demonstrated that Rumi is a general regulator of Drosophila Notch signaling. Biochemical analyses showed that Rumi adds glucose to specific EGF repeats in the extracellular domain of Notch receptor in the Drosophila S2 cell line. Furthermore, RNAi-mediated knockdown of Rumi in this cell line resulted in a severe decrease in the level of O-linked glucose on Notch. In this chapter, we discuss the genetic and biochemical methods used to determine the role of Rumi in the regulation of Notch signaling in flies.

O-linked N-acetylglucosamine is present on the extracellular domain of notch receptors

Rare types of glycosylation often occur in a domain-specific manner and are involved in specific biological processes. In particular, O-fucose glycans are reported to regulate the functions of EGF domain-containing proteins such as Notch receptors. In the course of mass spectrometric analysis of O-glycans displayed on Drosophila Notch receptors expressed in S2 cells, we found an unusual O-linked N-acetylhexosamine (HexNAc) modification which occurs at a site distinct from those of O-fucose and O-glucose glycosylations. Modification site mapping by mass spectrometry and amino acid substitution studies revealed that O-HexNAc modification occurs on a serine or threonine located between the fifth and sixth cysteines within the EGF domain. This modification occurs simultaneously along with other closely positioned O-glycosylations. This modification was determined to be O-beta-GlcNAc by galactosyltransferase labeling and beta-N-acetyl-hexosaminidase digestion experiments and by immunoblotting with a specific antibody. O-GlcNAc modification occurs at multiple sites on Notch epidermal growth factor repeats. O-GlcNAc modification was also found on the extracellular domain of Delta, a ligand for Notch receptors. Although the O-GlcNAc modification is known to regulate a wide range of cellular processes, the list of known modified proteins has previously been limited to intracellular proteins in animals. Thus, the finding of O-GlcNAc modification in extracellular environments predicts a distinct glycosylation process that might be associated with a novel regulatory mechanism for Notch receptor activity.

The many facets of Notch ligands

The Notch signaling pathway regulates a diverse array of cell types and cellular processes and is tightly regulated by ligand binding. Both canonical and noncanonical Notch ligands have been identified that may account for some of the pleiotropic nature associated with Notch signaling. This review focuses on the molecular mechanisms by which Notch ligands function as signaling agonists and antagonists, and discusses different modes of activating ligands as well as findings that support intrinsic ligand signaling activity independent of Notch. Post-translational modification, proteolytic processing, endocytosis and membrane trafficking, as well as interactions with the actin cytoskeleton may contribute to the recently appreciated multifunctionality of Notch ligands. The regulation of Notch ligand expression by other signaling pathways provides a mechanism to coordinate Notch signaling with multiple cellular and developmental cues. The association of Notch ligands with inherited human disorders and cancer highlights the importance of understanding the molecular nature and activities intrinsic to Notch ligands. Oncogene (2008) 27, 5148-5167; doi:10.1038/onc.2008.229.

Glucose: a novel regulator of notch signaling

Notch signaling regulates cell fate during the development of many tissues. A new Drosophila mutant, rumi, is defective in Notch signaling because it cannot add glucose to serine in epidermal growth factor repeats of Notch extracellular domain. This is the first biological role for glucose covalently attached to a cell surface signaling receptor.