Glycosylation, galectins and cellular signaling

The galectin LEC-5 is a novel binding partner for RAB-11

RAB-11/Rab11 is an endosomal GTPase with conserved roles in directional trafficking and apical domain formation in polarized epithelial cells. From a yeast two-hybrid screen using full-length C. elegans RAB-11 as bait, we identified LEC-5 as a novel binding protein for RAB-11. LEC-5 is an ortholog of mammalian Galectin-9 which associates with glycosphingolipids and is implicated in apical cargo sorting. We further confirmed the interaction between RAB-11 and LEC-5 via GST-pull down, co-immunoprecipitation and bimolecular fluorescence complementation. In addition, we showed that LEC-5 binds to RAB-11 with its C-terminus. Our results indicate a novel role of RAB-11 in apical sorting via LEC-5. Such a role would extend RAB-11's function as a master regulator of apical trafficking and suggest it could translate apical sorting signals into apical vesicle directionality.

The Golgi architecture and cell sensing

An array of signalling molecules are located at the Golgi apparatus, including phosphoinositides, small GTPases, kinases, and phosphatases, which are linked to multiple signalling pathways. Initially considered to be associated predominantly with membrane trafficking, signalling pathways at the Golgi are now recognised to regulate a diverse range of higher-order functions. Many of these signalling pathways are influenced by the architecture of the Golgi. In vertebrate cells, the Golgi consists of individual stacks fused together into a compact ribbon structure and the function of this ribbon structure has been enigmatic. Notably, recent advances have identified a role for the Golgi ribbon in regulation of cellular processes. Fragmentation of the Golgi ribbon results in modulation of many signalling pathways. Various diseases and disorders, including cancer and neurodegeneration, are associated with the loss of the Golgi ribbon and the appearance of a dispersed fragmented Golgi. Here, we review the emerging theme of the Golgi as a cell sensor and highlight the relationship between the morphological status of the Golgi in vertebrate cells and the modulation of signalling networks.

Structure and mechanism of cancer-associated N-acetylglucosaminyltransferase-V

N-acetylglucosaminyltransferase-V (GnT-V) alters the structure of specific N-glycans by modifying α1-6-linked mannose with a β1-6-linked N-acetylglucosamine branch. β1-6 branch formation on cell surface receptors accelerates cancer metastasis, making GnT-V a promising target for drug development. However, the molecular basis of GnT-V's catalytic mechanism and substrate specificity are not fully understood. Here, we report crystal structures of human GnT-V luminal domain with a substrate analog. GnT-V luminal domain is composed of a GT-B fold and two accessary domains. Interestingly, two aromatic rings sandwich the α1-6 branch of the acceptor N-glycan and restrain the global conformation, partly explaining the fine branch specificity of GnT-V. In addition, interaction of the substrate N-glycoprotein with GnT-V likely contributes to protein-selective and site-specific glycan modification. In summary, the acceptor-GnT-V complex structure suggests a catalytic mechanism, explains the previously observed inhibition of GnT-V by branching enzyme GnT-III, and provides a basis for the rational design of drugs targeting N-glycan branching.

Identification of Galectin-2-Mucin Interaction and Possible Formation of a High Molecular Weight Lattice

Galectins comprise a group of animal lectins characterized by their specificity for β-galactosides. Galectin-2 (Gal-2) is predominantly expressed in the gastrointestinal tract and has been identified as one of the main gastric mucosal proteins that are proposed to have a protective role in the stomach. As Gal-2 is known to form homodimers in solution, this may result in crosslinking of macromolecules with the sugar structures recognized by Gal-2. In this study, we report that Gal-2 could interact with mucin, an important component of gastric mucosa, in a β-galactoside-dependent manner. Furthermore, Gal-2 and mucin could form an insoluble precipitate, potentially through the crosslinking of mucins via Gal-2 and the formation of a lattice, resulting in a large insoluble complex. Therefore, we suggest that Gal-2 plays a role in the gastric mucosa by strengthening the barrier structure through crosslinking the mucins on the mucosal surface.

An approach for N-linked glycan identification from MS/MS spectra by target-decoy strategy

Glycan structure determination serves as an essential step for the thorough investigation of the structure and function of protein. Currently, appropriate sample preparation followed by tandem mass spectrometry has emerged as the dominant technique for the characterization of glycans and glycopeptides. Although extensive efforts have been made to the development of computational approaches for the automated interpretation of glycopeptide spectra, the previously appeared methods lack a reasonable quality control strategy for the statistical validation of reported results. In this manuscript, we introduced a novel method that constructed a decoy glycan database based on the glycan structures in the target database, and searched the experimental spectra against both the target and decoy databases to find the best matched glycans. Specifically, a two-layer scoring scheme for calculating a normalized matching score is applied in the search procedure which enables the unbiased ranking of the matched glycans. Experimental analysis showed that our proposed method can report more structures with high confidence compared with previous approaches.

The Modulatory Roles of N-glycans in T-Cell-Mediated Autoimmune Diseases

Glycosylation is a ubiquitous posttranslational modification of proteins that occurs in the endoplasmic reticulum/Golgi. N-glycans and mucin-type O-glycans are achieved via a series of glycohydrolase- and glycosyltransferase-mediated reactions. Glycosylation modulates immune responses by regulating thymocyte development and T helper cell differentiation. Autoimmune diseases result from an abnormal immune response by self-antigens and subsequently lead to the destruction of the target tissues. The modification of N-glycans has been studied in several animal models of T-cell-mediated autoimmune diseases. This review summarizes and highlights the modulatory effects of N-glycosylation in several autoimmune diseases, including multiple sclerosis, systemic lupus erythematosus, inflammatory bowel disease, and type 1 diabetes mellitus.

Metabolic flux-driven sialylation alters internalization, recycling, and drug sensitivity of the epidermal growth factor receptor (EGFR) in SW1990 pancreatic cancer cells

In prior work we reported that advanced stage, drug-resistant pancreatic cancer cells (the SW1990 line) can be sensitized to the EGFR-targeting tyrosine kinase inhibitors (TKIs) erlotinib and gefitinib by treatment with 1,3,4-O-Bu₃ManNAc (Bioorg. Med. Chem. Lett. (2015) 25(6):1223-7). Here we provide mechanistic insights into how this compound inhibits EGFR activity and provides synergy with TKI drugs. First, we showed that the sialylation of the EGFR receptor was at most only modestly enhanced (by ∼20 to 30%) compared to overall ∼2-fold increase in cell surface levels of this sugar. Second, flux-driven sialylation did not alter EGFR dimerization as has been reported for cancer cell lines that experience increased sialylation due to spontaneous mutations. Instead, we present evidence that 1,3,4-O-Bu₃ManNAc treatment weakens the galectin lattice, increases the internalization of EGFR, and shifts endosomal trafficking towards non-clathrin mediated (NCM) endocytosis. Finally, by evaluating downstream targets of EGFR signaling, we linked synergy between 1,3,4-O-Bu₃ManNAc and existing TKI drugs to a shift from clathrin-coated endocytosis (which allows EGFR signaling to continue after internalization) towards NCM endocytosis, which targets internalized moieties for degradation and thereby rapidly diminishes signaling.

The Golgi ribbon in mammalian cells negatively regulates autophagy by modulating mTOR activity

In vertebrates, individual Golgi stacks are joined into a compact ribbon structure; however, the relevance of a ribbon structure has been elusive. Here, we exploit the finding that the membrane tether of the trans-Golgi network, GCC88 (encoded by GCC1), regulates the balance between Golgi mini-stacks and the Golgi ribbon. Loss of Golgi ribbons in stable cells overexpressing GCC88 resulted in compromised mechanistic target of rapamycin (mTOR) signaling and a dramatic increase in LC3-II-positive autophagosomes, whereas RNAi-mediated depletion of GCC88 restored the Golgi ribbon and reduced autophagy. mTOR was absent from dispersed Golgi mini-stacks whereas recruitment of mTOR to lysosomes was unaffected. We show that the Golgi ribbon is a site for localization and activation of mTOR, a process dependent on the ribbon structure. We demonstrate a strict temporal sequence of fragmentation of Golgi ribbon, loss of Golgi mTOR and subsequent increased autophagy. Golgi ribbon fragmentation has been reported in various neurodegenerative diseases and we demonstrate the potential relevance of our findings in neuronal cells using a model of neurodegeneration. Overall, this study highlights a role for the Golgi ribbon in pathways central to cellular homeostasis.This article has an associated First Person interview with the first author of the paper.

Is galectin-3 a promoter of ventricular dysfunction?

Heart failure is nowadays a common condition associated with high mortality and increased healthcare-related costs. Over the years, the research on heart failure management has been extensive in order to better diagnose and treat the condition. Since the progression of left ventricular dysfunction is a consequence of myocardial inflammation, apopotosis, and fibrosis leading to myocardium remodelling, several molecules that are involved in the inflammation pathways have been explored as possible biomarkers for the condition. The study of biomarkers and their key roles in inflammation could allow early identification of patients with heart failure, improve prognostic assessment, and provide a target for future therapies. Among currently studied biomarkers, extensive research has been conducted on galectin-3, a galactoside-binding lectin, which is synthetised and secreted when cardiomyocytes and fibroblasts are submitted to mechanical stress. Accordingly, it has been hypothesised that galectin-3 could be a promoter of left ventricular dysfunction. Galectin-3 has been shown to mediate inflammation by several different pathways which are further detailed in the current review. Also, we aimed to provide a comprehensive overview of existing evidence on the utility of galectin-3 in clinical settings associated with heart failure.

Hallmarks of glycosylation in cancer

Aberrant glycosylation plays a fundamental role in key pathological steps of tumour development and progression. Glycans have roles in cancer cell signalling, tumour cell dissociation and invasion, cell-matrix interactions, angiogenesis, metastasis and immune modulation. Aberrant glycosylation is often cited as a ‘hallmark of cancer’ but is notably absent from both the original hallmarks of cancer and from the next generation of emerging hallmarks. This review discusses how glycosylation is clearly an enabling characteristic that is causally associated with the acquisition of all the hallmark capabilities. Rather than aberrant glycosylation being itself a hallmark of cancer, another perspective is that glycans play a role in every recognised cancer hallmark.

Systematic Tuning of Fluoro-galectin-3 Interactions Provides Thiodigalactoside Derivatives with Single-Digit nM Affinity and High Selectivity

Symmetrical and asymmetrical fluorinated phenyltriazolyl-thiodigalactoside derivatives have been synthesized and evaluated as inhibitors of galectin-1 and galectin-3. Systematic tuning of the phenyltriazolyl-thiodigalactosides' fluoro-interactions with galectin-3 led to the discovery of inhibitors with exceptional affinities (K_d down to 1-2 nM) in symmetrically substituted thiodigalactosides as well as unsurpassed combination of high affinity (K_d 7.5 nM) and selectivity (46-fold) over galectin-1 for asymmetrical thiodigalactosides by carrying one trifluorphenyltriazole and one coumaryl moiety. Studies of the inhibitor-galectin complexes with isothermal titration calorimetry and X-ray crystallography revealed the importance of fluoro-amide interaction for affinity and for selectivity. Finally, the high affinity of the discovered inhibitors required two competitive titration assay tools to be developed: a new high affinity fluorescent probe for competitive fluorescent polarization and a competitive ligand optimal for analyzing high affinity galectin-3 inhibitors with competitive isothermal titration calorimetry.

Revealing biomedically relevant cell and lectin type-dependent structure–activity profiles for glycoclusters by using tissue sections as an assay platform

The increasing realization of the involvement of lectin-glycan recognition in (patho)physiological processes inspires envisioning therapeutic intervention by high-avidity/specificity blocking reagents. Synthetic glycoclusters are proving to have potential for becoming such inhibitors but the commonly used assays have their drawbacks to predict in vivo efficacy. They do not represent the natural complexity of (i) cell types and (ii) spatial and structural complexity of glycoconjugate representation. Moreover, testing lectins in mixtures, as present in situ, remains a major challenge, giving direction to this work. Using a toolbox with four lectins and six bi- to tetravalent glycoclusters bearing the cognate sugar in a model study, we here document the efficient and versatile application of tissue sections (from murine jejunum as the model) as a platform for routine and systematic glycocluster testing without commonly encountered limitations. The nature of glycocluster structure, especially core and valency, and of protein features, i.e. architecture, fine-specificity and valency, are shown to have an influence, as cell types can differ in response profiles. Proceeding from light microscopy to monitoring by fluorescence microscopy enables grading of glycocluster activity on individual lectins tested in mixtures. This work provides a robust tool for testing glycoclusters prior to considering in vivo experiments.

Introducing tissue sections for testing glycocluster activity as inhibitors of lectin binding close to in vivo conditions.

Glycobiology of Aging

Glycosylation is one of the most frequent post-translational modification of proteins. Many membrane and secreted proteins are decorated by sugar chains mainly linked to asparagine (N-linked) or to serine or threonine (O-linked). The biosynthesis of the sugar chains is mainly controlled by the activity of their biosynthetic enzymes: the glycosyltransferases. Glycosylation plays multiple roles, including the fine regulation of the biological activity of glycoproteins. Inflammaging is a chronic low grade inflammatory status associated with aging, probably caused by the continuous exposure of the immune system to inflammatory stimuli of endogenous and exogenous origin. The aging-associated glycosylation changes often resemble those observed in inflammatory conditions. One of the most reproducible markers of calendar and biological aging is the presence of N-glycans lacking terminal galactose residues linked to Asn₂₉₇ of IgG heavy chains (IgG-G0). Although the mechanism(s) generating IgG-G0 remain unclear, their presence in a variety of inflammatory conditions suggests a link with inflammaging. In addition, these aberrantly glycosylated IgG can exert a pro-inflammatory effect through different mechanisms, triggering a self-fueling inflammatory loop. A strong association with aging has been documented also for the plasmatic forms of glycosyltrasferases B4GALT1 and ST6GAL1, although their role in the extracellular glycosylation of antibodies does not appear likely. Siglecs, are a group of sialic acid binding mammalian lectins which mainly act as inhibitory receptors on the surface of immune cells. In general activity of Siglecs appears to be associated with long life, probably because of their ability to restrain aging-associated inflammation.

Galectin-7 in Epithelial Homeostasis and Carcinomas

Galectins are small unglycosylated soluble lectins distributed both inside and outside the cells. They share a conserved domain for the recognition of carbohydrates (CRD). Although galectins have a common affinity for β-galatosides, they exhibit different binding preferences for complex glycans. First described twenty years ago, galectin-7 is a prototypic galectin, with a single CRD, able to form divalent homodimers. This lectin, which is mainly expressed in stratified epithelia, has been described in epithelial tissues as being involved in apoptotic responses, in proliferation and differentiation but also in cell adhesion and migration. Most members of the galectins family have been associated with cancer biology. One of the main functions of galectins in cancer is their immunomodulating potential and anti-angiogenic activity. Indeed, galectin-1 and -3, are already targeted in clinical trials. Another relevant function of galectins in tumour progression is their ability to regulate cell migration and cell adhesion. Among these galectins, galectin-7 is abnormally expressed in various cancers, most prominently in carcinomas, and is involved in cancer progression and metastasis but its precise functions in tumour biology remain poorly understood. In this issue, we will focus on the physiological functions of galectin-7 in epithelia and present the alterations of galectin-7 expression in carcinomas with the aim to describe its possible functions in tumour progression.

Ablation of the mammalian lectin galectin-8 induces bone defects in mice

Mice overexpressing galectin-8 [gal-8 transgenic (Tg)], a secreted mammalian lectin, exhibit enhanced bone turnover and reduced bone mass, similar to cases of postmenopausal osteoporosis. Here, we show that gal-8 knockout (KO) mice have increased bone mass accrual at a young age but exhibit accelerated bone loss during adulthood. These phenotypes can be attributed to a gal-8-mediated increase in receptor activator of NF-κB ligand (RANKL) expression that promotes osteoclastogenesis, combined with direct inhibition of osteoblast differentiation, evident by reduced bone morphogenetic protein (BMP) signaling, reduced phosphorylation of receptor regulated mothers against decapentaplegic homolog (R-SMAD) and reduced expression of osteoblast differentiation markers osterix, osteocalcin, runt-related transcription factor 2 (RUNX2), dentin matrix acidic phosphoprotein-1 (DMP1), and alkaline phosphatase. At the same time, gal-8 promotes expression of estrogen receptor α (ESR1). Accordingly, the rate of bone loss is accelerated in ovariectomized, estrogen-deficient gal-8 Tg mice, whereas gal-8 KO mice, having low levels of ESR1, are refractory to ovariectomy. Finally, gal-8 mRNA positively correlates with the mRNA levels of osteoclastogenic markers RANKL, tartrate-resistant acid phosphatase, and cathepsin K in human femurs. Collectively, these findings identify gal-8 as a new physiologic player in the regulation of bone mass.-Vinik, Y., Shatz-Azoulay, H., Hiram-Bab, S., Kandel, L., Gabet, Y., Rivkin, G., Zick, Y. Ablation of the mammalian lectin galectin-8 induces bone defects in mice.

Galectin-3 is Persistently Increased in Early Rheumatoid Arthritis (RA) and Associates with Anti-CCP Seropositivity and MRI Bone Lesions, While Early Fibrosis Markers Correlate with Disease Activity

Galectin-3 has been suggested as a pro-inflammatory mediator in animal arthritis and rheumatoid arthritis (RA). We aimed to study the serum level of galectin-3 in patients with newly diagnosed RA and associations with disease profile, Magnetic resonance imaging (MRI) findings and seromarkers of synovial matrix inflammation. One hundred and sixty DMARD naïve patients newly diagnosed with RA were included (CIMESTRA study). Clinical, serological and imaging data were recorded before treatment and at 6 weeks, 3 and 12 months. Galectin-3 and hyaluronan (HYA) were measured by ELISA (R&D and Corgenix, USA), and the N-terminal propeptide of type III collagen (PIIINP) by radioimmunoassay (Orion Diagnostica, Finland). One hundred and nineteen, 87 and 60 blood donors served as controls for galectin-3, HYA and PIIINP, respectively. Baseline galectin-3 was significantly elevated in anti-CCP positive (4.2 μg/l IQR [3.6;6.1]) patients as compared with anti-CCP negatives (4.0 μg/l [2.6;4.9], P = 0.05) and controls (3.8 μg/l [3.0;4.8], P < 0.01). During treatment, galectin-3 remained elevated, but increased transiently with peak values at 6 weeks. Galectin-3 correlated with baseline smoking, anti-CCP, and with MRI erosion score after 1 year of follow-up. HYA and PIIINP were elevated (P < 0.001) irrespective of anti-CCP status and correlated positively with synovitis assessed clinically and by MRI. HYA and PIIINP did not correlate with galectin-3. These observations indicate that HYA and PIIINP mainly reflect expansive synovitis proliferation while galectin-3 is more closely linked to autoimmunity, smoking and joint destructive processes.

Over forty years of bladder cancer glycobiology: Where do glycans stand facing precision oncology?

The high molecular heterogeneity of bladder tumours is responsible for significant variations in disease course, as well as elevated recurrence and progression rates, thereby hampering the introduction of more effective targeted therapeutics. The implementation of precision oncology settings supported by robust molecular models for individualization of patient management is warranted. This effort requires a comprehensive integration of large sets of panomics data that is yet to be fully achieved. Contributing to this goal, over 40 years of bladder cancer glycobiology have disclosed a plethora of cancer-specific glycans and glycoconjugates (glycoproteins, glycolipids, proteoglycans) accompanying disease progressions and dissemination. This review comprehensively addresses the main structural findings in the field and consequent biological and clinical implications. Given the cell surface and secreted nature of these molecules, we further discuss their potential for non-invasive detection and therapeutic development. Moreover, we highlight novel mass-spectrometry-based high-throughput analytical and bioinformatics tools to interrogate the glycome in the postgenomic era. Ultimately, we outline a roadmap to guide future developments in glycomics envisaging clinical implementation.

A Proteomic Analysis Provides Novel Insights into the Stress Responses of Caenorhabditis elegans towards Nematicidal Cry6A Toxin from Bacillus thuringiensis

Cry6A represents a novel family of nematicidal crystal proteins from Bacillus thuringiensis. It has distinctive architecture as well as mechanism of action from Cry5B, a highly focused family of nematicidal crystal proteins, and even from other insecticidal crystal proteins containing the conserved three-domain. However, how nematode defends against Cry6A toxin remains obscure. In this study, the global defense pattern of Caenorhabditis elegans against Cry6Aa2 toxin was investigated by proteomic analysis. In response to Cry6Aa2, 12 proteins with significantly altered abundances were observed from worms, participating in innate immune defense, insulin-like receptor (ILR) signaling pathway, energy metabolism, and muscle assembly. The differentially expressed proteins (DEPs) functioning in diverse biological processes suggest that a variety of defense responses participate in the stress responses of C. elegans to Cry6Aa2. The functional verifications of DEPs suggest that ILR signaling pathway, DIM-1, galectin LEC-6 all are the factors of defense responses to Cry6Aa2. Moreover, Cry6Aa2 also involves in accelerating the metabolic energy production which fulfills the energy demand for the immune responses. In brief, our findings illustrate the global pattern of defense responses of nematode against Cry6A for the first time, and provide a novel insight into the mechanism through which worms respond to Cry6A.

Contributions of Noncanonical Smoothened Signaling During Embryonic Development

The Sonic Hedgehog (Shh) signaling pathway is active during embryonic development in metazoans, and provides instructional cues necessary for proper tissue patterning. The pathway signal transducing component, Smoothened (Smo), is a G protein-coupled receptor (GPCR) that has been demonstrated to signal through at least two effector routes. The first is a G protein–independent canonical route that signals to Gli transcriptional effectors to establish transcriptional programs specifying cell fate during early embryonic development. The second, commonly referred to as the noncanonical Smo signal, induces rapid, transcription-independent responses that are essential for establishing and maintaining distinct cell behaviors during development. Herein, we discuss contributions of this noncanonical route during embryonic development. We also highlight important open questions regarding noncanonical Smo signal route selection during development, and consider implications of noncanonical signal corruption in disease.

The Function of the Golgi Ribbon Structure - An Enduring Mystery Unfolds!

The Golgi apparatus in vertebrate cells consists of individual Golgi stacks fused together in a continuous ribbon structure. The ribbon structure per se is not required to mediate the classical functions of this organelle and the relevance of the "ribbon" structure has been a mystery since first identified ultrastructurally in the 1950s. Recent advances recognize a role for the Golgi apparatus in a range of cellular processes, some mediated by signaling networks which are regulated at the Golgi. Here we review the cellular processes and signaling events regulated by the Golgi apparatus and, in particular, explore an emerging theme that the ribbon structure of the Golgi contributes directly to the regulation of these higher order functions.

Key regulators of galectin-glycan interactions

Protein-ligand interactions serve as fundamental regulators of numerous biological processes. Among protein-ligand pairs, glycan binding proteins (GBPs) and the glycans they recognize represent unique and highly complex interactions implicated in a broad range of regulatory activities. With few exceptions, cell surface receptors and secreted proteins are heavily glycosylated. As these glycans often represent highly regulatable post-translational modifications, alterations in glycosylation can fundamentally impact GBP recognition. Among GBPs, galectins in particular appear to engage a diverse set of glycan determinants to impact a broad range of biological processes. In this review, we will explore factors that impact galectin activity, including the effect of glycan modification on galectin-glycan interactions.

Galectin-3 induced by hypoxia promotes cell migration in thyroid cancer cells

Background

The aim of this study is to investigate the role of Galectin-3 in human thyroid cancer migration.

Methods

The expression of Galectin-3 in surgical specimens was investigated using immunohistochemistry and western blot. A papillary thyroid cancer cell line (B-cpap) and an anaplastic thyroid cancer cell line (8305c) were transfected with short-hairpin RNA against Galectin-3 (Gal-3-shRNA). Low-molecular citrus pectin (LCP) was also used to antagonize Galectin-3. The migration and invasion of the cell lines were examined. The related signaling pathways were investigated to explore the Galectin-3 mechanism of action.

Results

Galectin-3 was highly expressed in metastasized thyroid cancers. Knocking down and antagonizing Galectin-3 significantly suppressed the migration of thyroid cancer cells. Knocking down Galectin-3 inhibited the activity of Wnt, MAPK, Src and Rho signaling pathways. Galectin-3 was up-regulated via HIF-1α in a hypoxic environment. Galectin-3 knockdown could reduce cell motility in hypoxic environments.

Conclusion

This study suggests that Galectin-3 could act as a modulator of thyroid cancer migration, especially in hypoxic microenvironments. This regulation function of Galectin-3 may work through multiple signaling pathways.

Hyaluronic Acid Microgels Modulate Inflammation and Key Matrix Molecules toward a Regenerative Signature in the Injured Annulus Fibrosus

Low back pain results from disc degeneration, which is a chronic inflammatory disease characterized by an imbalance between anabolic and catabolic factors. Today, regenerative medicine is focused on identifying inflammatory markers to target disc disease. Hyaluronan is used as a scaffold for cell delivery in disc degeneration; however, to date high molecular weight hyaluronan (HMW HA) is evaluated for its anti-inflammatory and matrix modulatory properties in an in vivo disc injury model. Ex vivo bovine organ culture studies demonstrate the anti-inflammatory and matrix modulatory effects of HMW HA on the IFNα2β signaling pathway that provides the motivation for evaluating its efficacy in regenerating the annulus fibrosus in an in vivo disc injury model. It is demonstrated that the HMW HA microgel acts as an anti-inflammatory molecule in the annulus fibrosus, by downregulating the expression of the pro-inflammatory interferon gamma (IFNα) and pro-apoptotic insulin-like growth factor-binding protein 3 (IGFBP3) and the apoptosis marker caspase 3. Mass spectrometry studies demonstrate that the HMW HA microgel modulates the matrix modulatory effect by upregulating hyaluronic acid link protein (HAPLN1) and aggrecan, which are further confirmed by immunostaining. The microgel's regenerative capacity is illustrated by the increase in the disc height index.

Old dogs-new tricks: immunoregulatory properties of C3 and C5 cleavage fragments

The activation of the complement system by canonical and non-canonical mechanisms results in the generation of multiple C3 and C5 cleavage fragments including anaphylatoxins C3a and C5a as well as opsonizing C3b/iC3b. It is now well appreciated that anaphylatoxins not only act as pro-inflammatory mediators but as immunoregulatory molecules that control the activation status of cells and tissue at several levels. Likewise, C3b/iC3b is more than the opsonizing fragment that facilitates engulfment and destruction of targets by phagocytes. In the circulation, it also facilitates the transport and delivery of bacteria and immune complexes to phagocytes, through a process known as immune adherence, with consequences for adaptive immunity. Here, we will discuss non-classical immunoregulatory properties of C3 and C5 cleavage fragments. We highlight the influence of anaphylatoxins on Th2 and Th17 cell development during allergic asthma with a particular emphasis on their role in the modulation of CD11b⁺ conventional dendritic cells and monocyte-derived dendritic cells. Furthermore, we discuss the control of anaphylatoxin-mediated activation of dendritic cells and allergic effector cells by adaptive immune mechanisms that involve allergen-specific IgG1 antibodies and plasma or regulatory T cell-derived IL-10 production. Finally, we take a fresh look at immune adherence with a particular focus on the development of antibacterial cytotoxic T-cell responses.

Dimerization of the fungal defense lectin CCL2 is essential for its toxicity against nematodes

Lectins are used as defense effector proteins against predators, parasites and pathogens by animal, plant and fungal innate defense systems. These proteins bind to specific glycoepitopes on the cell surfaces and thereby interfere with the proper cellular functions of the various antagonists. The exact cellular toxicity mechanism is in many cases unclear. Lectin CCL2 of the mushroom Coprinopsis cinerea was previously shown to be toxic for Caenorhabditis elegans and Drosophila melanogaster. This toxicity is dependent on a single, high-affinity binding site for the trisaccharide GlcNAc(Fucα1,3)β1,4GlcNAc, which is a hallmark of nematode and insect N-glycan cores. The carbohydrate-binding site is located at an unusual position on the protein surface when compared to other β-trefoil lectins. Here, we show that CCL2 forms a compact dimer in solution and in crystals. Substitution of two amino acid residues at the dimer interface, R18A and F133A, interfered with dimerization of CCL2 and reduced toxicity but left carbohydrate-binding unaffected. These results, together with the positioning of the two carbohydrate-binding sites on the surface of the protein dimer, suggest that crosslinking of N-glycoproteins on the surface of intestinal cells of invertebrates is a crucial step in the mechanism of CCL2-mediated toxicity. Comparisons of the number and positioning of carbohydrate-binding sites among different dimerizing fungal β-trefoil lectins revealed a considerable variability in the carbohydrate-binding patterns of these proteins, which are likely to correlate with their respective functions.

Two New Tools for Glycopeptide Analysis Researchers: A Glycopeptide Decoy Generator and a Large Data Set of Assigned CID Spectra of Glycopeptides

The glycopeptide analysis field is tightly constrained by a lack of effective tools that translate mass spectrometry data into meaningful chemical information, and perhaps the most challenging aspect of building effective glycopeptide analysis software is designing an accurate scoring algorithm for MS/MS data. We provide the glycoproteomics community with two tools to address this challenge. The first tool, a curated set of 100 expert-assigned CID spectra of glycopeptides, contains a diverse set of spectra from a variety of glycan types; the second tool, Glycopeptide Decoy Generator, is a new software application that generates glycopeptide decoys de novo. We developed these tools so that emerging methods of assigning glycopeptides' CID spectra could be rigorously tested. Software developers or those interested in developing skills in expert (manual) analysis can use these tools to facilitate their work. We demonstrate the tools' utility in assessing the quality of one particular glycopeptide software package, GlycoPep Grader, which assigns glycopeptides to CID spectra. We first acquired the set of 100 expert assigned CID spectra; then, we used the Decoy Generator (described herein) to generate 20 decoys per target glycopeptide. The assigned spectra and decoys were used to test the accuracy of GlycoPep Grader's scoring algorithm; new strengths and weaknesses were identified in the algorithm using this approach. Both newly developed tools are freely available. The software can be downloaded at http://glycopro.chem.ku.edu/GPJ.jar.

Galectin-3 Inhibits Galectin-8/Parkin-Mediated Ubiquitination of Group A Streptococcus

Group A streptococcus (GAS) is an important human pathogen that causes a wide variety of cutaneous and systemic infections. Although originally thought to be an extracellular bacterium, numerous studies have demonstrated that GAS can trigger internalization into nonimmune cells to escape from immune surveillance or antibiotic-mediated killing. Epithelial cells possess a defense mechanism involving autophagy-mediated targeting and killing of GAS within lysosome-fused autophagosomes. In endothelial cells, in contrast, we previously showed that autophagy is not sufficient for GAS killing. In the present study, we showed higher galectin-3 (Gal-3) expression and lower Gal-8 expression in endothelial cells than in epithelial cells. The recruitment of Gal-3 to GAS is higher and the recruitment of Gal-8 to GAS is lower in endothelial cells than in epithelial cells. We further showed that Gal-3 promotes GAS replication and diminishes the recruitment of Gal-8 and ubiquitin, the latter of which is a critical protein for autophagy sequestration. After knockdown of Gal-3 in endothelial cells, the colocalization of Gal-8, parkin, and ubiquitin-decorated GAS is significantly increased, as is the interaction of Gal-8 and parkin, an E3 ligase. Furthermore, inhibition of Gal-8 in epithelial cells attenuates recruitment of parkin; both Gal-8 and parkin contribute to ubiquitin recruitment and GAS elimination. Animal studies confirmed that Gal-3-knockout mice develop less-severe skin damage and that GAS replication can be detected only in the air pouch and not in organs and endothelial cells. These results demonstrate that Gal-3 inhibits ubiquitin recruitment by blocking Gal-8 and parkin recruitment, resulting in GAS replication in endothelial cells.

In epithelial cells, GAS can be efficiently killed within the lysosome-fused autophaosome compartment. However, we previously showed that, in spite of LC-3 recruitment, the autophagic machinery is not sufficient for GAS killing in endothelial cells. In this report, we provide the first evidence that Gal-3, highly expressed in endothelial cells, blocks the tagging of ubiquitin to GAS by inhibiting recruitment of Gal-8 and parkin, leading to an enhancement of GAS replication. We also provide the first demonstration that Gal-8 can interact with parkin, the critical E3 ligase, for resistance to intracellular bacteria by facilitating the decoration of bacteria with ubiquitin chains. Our findings reveal that differential levels of Gal-3 and Gal-8 expression and recruitment to GAS between epithelial cells and endothelial cells may contribute to the different outcomes of GAS elimination or survival and growth of GAS in these two types of cells.

Native glycan fragments detected by MALDI-FT-ICR mass spectrometry imaging impact gastric cancer biology and patient outcome

Glycosylation in cancer is a highly dynamic process that has a significant impact on tumor biology. Further, the attachment of aberrant glycan forms is already considered a hallmark of the disease state. Mass spectrometry has become a prominent approach to analyzing glycoconjugates. Specifically, matrix-assisted laser desorption/ionisation -mass spectrometric imaging (MALDI-MSI) is a powerful technique that combines mass spectrometry with histology and enables the spatially resolved and label-free detection of glycans. The most common approach to the analysis of glycans is the use of mass spectrometry adjunct to PNGase F digestion and other chemical reactions. In the current study, we perform the analysis of formalin-fixed, paraffin-embedded (FFPE) tissues for natively occurring bioactive glycan fragments without prior digestion or chemical reactions using MALDI-FT-ICR-MSI. We examined 106 primary resected gastric cancer patient tissues in a tissue microarray and correlated native-occurring fragments with clinical endpoints, therapeutic targets such as epidermal growth factor receptor (EGFR) and HER2/neu expressions and the proliferation marker MIB1. The detection of a glycosaminoglycan fragment in tumor stroma regions was determined to be an independent prognostic factor for gastric cancer patients. Native glycan fragments were significantly linked to the expression of EGFR, HER2/neu and MIB1. In conclusion, we are the first to report the in situ detection of native-occurring bioactive glycan fragments in FFPE tissues that influence patient outcomes. These findings highlight the significance of glycan fragments in gastric cancer tumor biology and patient outcome.

Proteome-wide Identification of Glycosylation-dependent Interactors of Galectin-1 and Galectin-3 on Mesenchymal Retinal Pigment Epithelial (RPE) Cells

Identification of interactors is a major goal in cell biology. Not only protein-protein but also protein-carbohydrate interactions are of high relevance for signal transduction in biological systems. Here, we aim to identify novel interacting binding partners for the β-galactoside-binding proteins galectin-1 (Gal-1) and galectin-3 (Gal-3) relevant in the context of the eye disease proliferative vitreoretinopathy (PVR). PVR is one of the most common failures after retinal detachment surgeries and is characterized by the migration, adhesion, and epithelial-to-mesenchymal transition of retinal pigment epithelial cells (RPE) and the subsequent formation of sub- and epiretinal fibrocellular membranes. Gal-1 and Gal-3 bind in a dose- and carbohydrate-dependent manner to mesenchymal RPE cells and inhibit cellular processes like attachment and spreading. Yet knowledge about glycan-dependent interactors of Gal-1 and Gal-3 on RPE cells is very limited, although this is a prerequisite for unraveling the influence of galectins on distinct cellular processes in RPE cells. We identify here 131 Gal-3 and 15 Gal-1 interactors by galectin pulldown experiments combined with quantitative proteomics. They mainly play a role in multiple binding processes and are mostly membrane proteins. We focused on two novel identified interactors of Gal-1 and Gal-3 in the context of PVR: the low-density lipoprotein receptor LRP1 and the platelet-derived growth factor receptor β PDGFRB. Addition of exogenous Gal-1 and Gal-3 induced cross-linking with LRP1/PDGFRB and integrin-β1 (ITGB1) on the cell surface of human RPE cells and induced ERK/MAPK and Akt signaling. Treatment with kifunensine, an inhibitor of complex-type N-glycosylation, weakened the binding of Gal-1 and Gal-3 to these interactors and prevented lattice formation. In conclusion, the identified specific glycoprotein ligands shed light into the highly specific binding of galectins to dedifferentiated RPE cells and the resulting prevention of PVR-associated cellular events.

Salivary glycopatterns as potential biomarkers for diagnosis of gastric cancer

Gastric cancer (GC) is still an extremely severe health issue with high mortality due to the lacking of effective biomarkers. In this study, we aimed to investigate the alterations of salivary protein glycosylation related to GC and assess the possibility of salivary glycopatterns as potential biomarkers for the diagnosis of GC. Firstly, 94 patients with GC (n = 64) and atrophic gastritis (AG) (n = 30), as well as 30 age- and sex-matched healthy volunteers (HV) were enrolled in the test group to probe the difference of salivary glycopatterns using lectin microarrays, the results were validated by saliva microarrays and lectin blotting analysis. Then, the diagnostic model of GC (Model GC) and AG (Model AG) were constructed based on 15 candidate lectins which exhibited significant alterations of salivary glycopattern by logistic stepwise regression. Finally, two diagnostic models were assessed in the validation group including HV (n = 30) and patients with GC (n = 23) and AG (n = 24) and achieved high diagnostic power (Model GC (AUC: 0.89, sensitivity: 0.96 and specificity: 0.80), Model AG (AUC: 0.83, sensitivity: 0.92 and specificity: 0.72)). This study provides pivotal information to distinguish HV, AG and GC based on precise alterations in salivary glycopatterns, which have great potential to be biomarkers for diagnosis of GC.

Spindle pole cohesion requires glycosylation-mediated localization of NuMA

Glycosylation is critical for the regulation of several cellular processes. One glycosylation pathway, the unusual O-linked β-N-acetylglucosamine glycosylation (O-GlcNAcylation) has been shown to be required for proper mitosis, likely through a subset of proteins that are O-GlcNAcylated during metaphase. As lectins bind glycosylated proteins, we asked if specific lectins interact with mitotic O-GlcNAcylated proteins during metaphase to ensure correct cell division. Galectin-3, a small soluble lectin of the Galectin family, is an excellent candidate, as it has been previously described as a transient centrosomal component in interphase and mitotic epithelial cells. In addition, it has recently been shown to associate with basal bodies in motile cilia, where it stabilizes the microtubule-organizing center (MTOC). Using an experimental mouse model of chronic kidney disease and human epithelial cell lines, we investigate the role of Galectin-3 in dividing epithelial cells. Here we find that Galectin-3 is essential for metaphase where it associates with NuMA in an O-GlcNAcylation-dependent manner. We provide evidence that the NuMA-Galectin-3 interaction is important for mitotic spindle cohesion and for stable NuMA localization to the spindle pole, thus revealing that Galectin-3 is a novel contributor to epithelial mitotic progress.

Effects of altered sialic acid biosynthesis on N-linked glycan branching and cell surface interactions

GNE (UDP-GlcNAc 2-epimerase/ManNAc kinase) myopathy is a rare muscle disorder associated with aging and is related to sporadic inclusion body myositis, the most common acquired muscle disease of aging. Although the cause of sporadic inclusion body myositis is unknown, GNE myopathy is associated with mutations in GNE. GNE harbors two enzymatic activities required for biosynthesis of sialic acid in mammalian cells. Mutations to both GNE domains are linked to GNE myopathy. However, correlation between mutation-associated reductions in sialic acid production and disease severity is imperfect. To investigate other potential effects of GNE mutations, we compared sialic acid production in cell lines expressing wild type or mutant forms of GNE. Although we did not detect any differences attributable to disease-associated mutations, lectin binding and mass spectrometry analysis revealed that GNE deficiency is associated with unanticipated effects on the structure of cell-surface glycans. In addition to exhibiting low levels of sialylation, GNE-deficient cells produced distinct N-linked glycan structures with increased branching and extended poly-N-acetyllactosamine. GNE deficiency may affect levels of UDP-GlcNAc, a key metabolite in the nutrient-sensing hexosamine biosynthetic pathway, but this modest effect did not fully account for the change in N-linked glycan structure. Furthermore, GNE deficiency and glucose supplementation acted independently and additively to increase N-linked glycan branching. Notably, N-linked glycans produced by GNE-deficient cells displayed enhanced binding to galectin-1, indicating that changes in GNE activity can alter affinity of cell-surface glycoproteins for the galectin lattice. These findings suggest an unanticipated mechanism by which GNE activity might affect signaling through cell-surface receptors.

Genetic deletion of galectin-3 enhances neuroinflammation, affects microglial activation and contributes to sub-chronic injury in experimental neonatal focal stroke

The pathophysiology of neonatal stroke and adult stroke are distinct in many aspects, including the inflammatory response. We previously showed endogenously protective functions of microglial cells in acute neonatal stroke. We asked if galectin-3 (Gal3), a pleotropic molecule that mediates interactions between microglia/macrophages and the extracellular matrix (ECM), plays a role in early injury after transient middle cerebral occlusion (tMCAO) in postnatal day 9-10 mice. Compared to wild type (WT) pups, in Gal3 knockout pups injury was worse and cytokine/chemokine production altered, including further increase of MIP1α and MIP1β levels and reduced IL6 levels 72h after tMCAO. Lack of Gal3 did not affect morphological transformation or proliferation of microglia but markedly attenuated accumulation of CD11b⁺/CD45^med-high cells after injury, as determined by multi-color flow cytometry. tMCAO increased expression of αV and β₃ integrin subunits in CD11b⁺/CD45^low microglial cells and cells of non-monocyte lineage (CD11b^-/CD45^-), but not in CD11b⁺/CD45^med-high cells within injured regions of WT mice or Gal3-/- mice. αV upregulated in areas occupied and not occupied by CD68⁺ cells, most prominently in the ECM, lining blood vessels, with expanded αV coverage in Gal3-/- mice. Cumulatively, these data show that lack of Gal3 worsens subchronic injury after neonatal focal stroke, likely by altering the neuroinflammatory milieu, including an imbalance between pro- and anti-inflammatory molecules, effects on microglial activation, and deregulation of the composition of the ECM.

Biological roles of glycans

Simple and complex carbohydrates (glycans) have long been known to play major metabolic, structural and physical roles in biological systems. Targeted microbial binding to host glycans has also been studied for decades. But such biological roles can only explain some of the remarkable complexity and organismal diversity of glycans in nature. Reviewing the subject about two decades ago, one could find very few clear-cut instances of glycan-recognition-specific biological roles of glycans that were of intrinsic value to the organism expressing them. In striking contrast there is now a profusion of examples, such that this updated review cannot be comprehensive. Instead, a historical overview is presented, broad principles outlined and a few examples cited, representing diverse types of roles, mediated by various glycan classes, in different evolutionary lineages. What remains unchanged is the fact that while all theories regarding biological roles of glycans are supported by compelling evidence, exceptions to each can be found. In retrospect, this is not surprising. Complex and diverse glycans appear to be ubiquitous to all cells in nature, and essential to all life forms. Thus, >3 billion years of evolution consistently generated organisms that use these molecules for many key biological roles, even while sometimes coopting them for minor functions. In this respect, glycans are no different from other major macromolecular building blocks of life (nucleic acids, proteins and lipids), simply more rapidly evolving and complex. It is time for the diverse functional roles of glycans to be fully incorporated into the mainstream of biological sciences.

Glycolipids and Lectins in Endocytic Uptake Processes

A host of endocytic processes has been described at the plasma membrane of eukaryotic cells. Their categorization has most commonly referenced cytosolic machinery, of which the clathrin coat has occupied a preponderant position. In what concerns intra-membrane constituents, the focus of interest has been on phosphatidylinositol lipids and their capacity to orchestrate endocytic events on the cytosolic leaflet of the membrane. The contribution of extracellular determinants to the construction of endocytic pits has received much less attention, depite the fact that (glyco)sphingolipids are exoplasmic leaflet fabric of membrane domains, termed rafts, whose contributions to predominantly clathrin-independent internalization processes is well recognized. Furthermore, sugar modifications on extracellular domains of proteins, and sugar-binding proteins, termed lectins, have also been linked to the uptake of endocytic cargoes at the plasma membrane. In this review, we first summarize these contributions by extracellular determinants to the endocytic process. We thus propose a molecular hypothesis - termed the GL-Lect hypothesis - on how GlycoLipids and Lectins drive the formation of compositional nanoenvrionments from which the endocytic uptake of glycosylated cargo proteins is operated via clathrin-independent carriers. Finally, we position this hypothesis within the global context of endocytic pathway proposals that have emerged in recent years.

Circulating blood and platelets supply glycosyltransferases that enable extrinsic extracellular glycosylation

Glycosyltransferases, usually residing within the intracellular secretory apparatus, also circulate in the blood. Many of these blood-borne glycosyltransferases are associated with pathological states, including malignancies and inflammatory conditions. Despite the potential for dynamic modifications of glycans on distal cell surfaces and in the extracellular milieu, the glycan-modifying activities present in systemic circulation have not been systematically examined. Here, we describe an evaluation of blood-borne sialyl-, galactosyl- and fucosyltransferase activities that act upon the four common terminal glycan precursor motifs, GlcNAc monomer, Gal(β3)GlcNAc, Gal(β4)GlcNAc and Gal(β3)GalNAc, to produce more complex glycan structures. Data from radioisotope assays and detailed product analysis by sequential tandem mass spectrometry show that blood has the capacity to generate many of the well-recognized and important glycan motifs, including the Lewis, sialyl-Lewis, H- and Sialyl-T antigens. While many of these glycosyltransferases are freely circulating in the plasma, human and mouse platelets are important carriers for others, including ST3Gal-1 and β4GalT. Platelets compartmentalize glycosyltransferases and release them upon activation. Human platelets are also carriers for large amounts of ST6Gal-1 and the α3-sialyl to Gal(β4)GlcNAc sialyltransferases, both of which are conspicuously absent in mouse platelets. This study highlights the capability of circulatory glycosyltransferases, which are dynamically controlled by platelet activation, to remodel cell surface glycans and alter cell behavior.

Loss of Mgat5a-mediated N-glycosylation stimulates regeneration in zebrafish

Background

We are using genetics to identify genes specifically involved in hearing regeneration. In a large-scale genetic screening, we identified mgat5a, a gene in the N-glycosylation biosynthesis pathway whose activity negatively impacts hair cell regeneration.

Methods

We used a combination of mutant analysis in zebrafish and a hair cell regeneration assay to phenotype the loss of Mgat5a activity in zebrafish. We used pharmacological inhibition of N-glycosylation by swansonine. We also used over-expression analysis by mRNA injections to demonstrate how changes in N-glycosylation can alter cell signaling.

Results

We found that mgat5a was expressed in multiple tissues during zebrafish embryo development, particularly enriched in neural tissues including the brain, retina, and lateral line neuromasts. An mgat5a insertional mutation and a CRISPR/Cas9-generated truncation mutation both caused an enhancement of hair cell regeneration which could be phenocopied by pharmacological inhibition with swansonine. In addition to hair cell regeneration, inhibition of the N-glycosylation pathway also enhanced the regeneration of lateral line axon and caudal fins. Further analysis showed that N-glycosylation altered the responsiveness of TGF-beta signaling.

Conclusions

The findings from this study provide experimental evidence for the involvement of N-glycosylation in tissue regeneration and cell signaling.

Electronic supplementary material

The online version of this article (doi:10.1186/s13619-016-0031-5) contains supplementary material, which is available to authorized users.

Glycosylation-dependent binding of galectin-8 to activated leukocyte cell adhesion molecule (ALCAM/CD166) promotes its surface segregation on breast cancer cells

BACKGROUND

We previously demonstrated that the activated leukocyte cell adhesion molecule (ALCAM/CD166) can interact with galectin-8 (Gal-8) in endothelial cells. ALCAM is a member of the immunoglobulin superfamily that promotes homophilic and heterophilic cell-cell interactions. Gal-8 is a "tandem-repeat"-type galectin, known as a matricellular protein involved in cell adhesion. Here, we analyzed the physical interaction between both molecules in breast cancer cells and the functional relevance of this phenomenon.

METHODS

We performed binding assays by surface plasmon resonance to study the interaction between Gal-8 and the recombinant glycosylated ALCAM ectodomain or endogenous ALCAM from MDA-MB-231 breast cancer cells. We also analyzed the binding of ALCAM-silenced or control breast cancer cells to immobilized Gal-8 by SPR. In internalization assays, we evaluated the influence of Gal-8 on ALCAM surface localization.

RESULTS

We showed that recombinant glycosylated ALCAM and endogenous ALCAM from breast carcinoma cells physically interacted with Gal-8 in a glycosylation-dependent fashion displaying a differential behavior compared to non-glycosylated ALCAM. Moreover, ALCAM-silenced breast cancer cells exhibited reduced binding to Gal-8 relative to control cells. Importantly, exogenously added Gal-8 provoked ALCAM segregation, probably trapping this adhesion molecule at the surface of breast cancer cells.

CONCLUSIONS

Our data indicate that Gal-8 interacts with ALCAM at the surface of breast cancer cells through glycosylation-dependent mechanisms.

GENERAL SIGNIFICANCE

A novel heterophilic interaction between ALCAM and Gal-8 is demonstrated here, suggesting its physiologic relevance in the biology of breast cancer cells.

Design of a peptidic inhibitor that targets the dimer interface of a prototypic galectin

Galectins are small soluble lectins that bind β-galactosides via their carbohydrate recognition domain (CRD). Their ability to dimerize is critical for the crosslinking of glycoprotein receptors and subsequent cellular signaling. This is particularly important in their immunomodulatory role via the induction of T-cell apoptosis. Because galectins play a central role in many pathologies, including cancer, they represent valuable therapeutic targets. At present, most inhibitors have been directed towards the CRD, a challenging task in terms of specificity given the high structural homology of the CRD among galectins. Such inhibitors are not effective at targeting CRD-independent functions of galectins. Here, we report a new class of galectin inhibitors that specifically binds human galectin-7 (hGal-7), disrupts the formation of homodimers, and inhibits the pro-apoptotic activity of hGal-7 on Jurkat T cells. In addition to representing a new means to achieve specificity when targeting galectins, such inhibitors provide a promising alternative to more conventional galectin inhibitors that target the CRD with soluble glycans or other small molecular weight allosteric inhibitors.

Glycomic profile of the human parotid gland between 18th and 26th week of fetal development

The formation of new and functional structural components of several organs, such as parotid glands, can be influenced by the glycocode. This study analyzed the glycobiology of parotid salivary gland tissue during fetal development using specific biochemical probes (lectins and antibodies). Eleven parotid gland samples from human fetuses were obtained from spontaneous abortions at 14-28 weeks of gestation, and tissue sections were analyzed for lectin histochemistry and immunohistochemistry. From the 18th to 26th week, Canavalia ensiformis agglutinin, wheat germ agglutinin, Ulex europaeus agglutinin-I, peanut agglutinin, Sambucus nigra agglutinin, and Vicia villosa agglutinin lectin staining were predominantly observed in the apical and/or basement membranes of the ducts and tubulo-acinar units. Moreover, the presence of galectin-1 was found in the membrane, cytoplasm, and nucleus of both structures. Conversely, Gal-3 and mucin-1 were restricted to the glandular ducts. The lectin staining pattern changed during the weeks evaluated. Nevertheless, the carbohydrate subcellular localization represented a key factor in the investigation of structural distribution profiles and possible roles of these glycans in initial parotid gland development. These findings are defined by their high biological value and provide an important base for the development of subsequent studies. (J Oral Sci 58, 353-360, 2016).