L-14 lectin recognition of laminin and its promotion of in vitro cell adhesion

Insecticidal action of mammalian galectin-1-transfected Arabidopsis thaliana

BACKGROUND

Galectins (GALs) are a family of mammalian sugar-binding proteins specific for β-galactosides. Our previous studies have shown that the larval development of the diamondback moth (Plutella xylostella) is significantly disturbed when fed with recombinant mammalian galectin 1 (GAL1) derived from Escherichia coli. To further explore its applicability, two GAL1-overexpressed Arabidopsis [GAL1-Arabidopsis (whole plant) and GAL1-Arabidopsis-vas (vascular bundle-specific)] lines were established for insecticidal activity and mechanism studies.

RESULTS

The expression level of GAL1 in transgenic Arabidopsis is 1-0.5% (GAL1-Arabidopsis) and 0.08-0.01% (GAL1-Arabidopsis-vas) of total leaf soluble protein. Survival, body weight, and food consumption significantly decreased in a time-dependent manner in P. xylostella larvae (with chewing mouthparts) fed on GAL1-Arabidopsis. The mortality of Kolla paulula (with piercing-sucking mouthparts and xylem feeder) fed on GAL1-Arabidopsis-vas was also significantly higher than that fed on wild-type Arabidopsis (WT-Arabidopsis), but was lower than that fed on GAL1-Arabidopsis. The histochemical structure and results of immunostaining suggested that the binding of GAL1 to the midgut epithelium of P. xylostella fed on GAL1-Arabidopsis was dose- and time-dependent. Ultrastructural studies further showed the disruption of microvilli, abnormalities in epithelial cells, and fragments of the peritrophic membrane (PM) in P. xylostella larvae fed on GAL1-Arabidopsis.

CONCLUSION

The insecticidal mechanism of GAL1 involves interference with PM integrity and suggests that GAL1 is a potential candidate for bioinsecticide development. © 2024 Society of Chemical Industry.

Galectins in Early Pregnancy and Pregnancy-Associated Pathologies

Galectins are a family of conserved soluble proteins defined by an affinity for β-galactoside structures present on various glycoconjugates. Over the past few decades, galectins have been recognized as important factors for successful implantation and maintenance of pregnancy. An increasing number of studies have demonstrated their involvement in trophoblast cell function and placental development. In addition, several lines of evidence suggest their important roles in feto-maternal immune tolerance regulation and angiogenesis. Changed or dysregulated galectin expression is also described in pregnancy-related disorders. Although the data regarding galectins' clinical relevance are still at an early stage, evidence suggests that some galectin family members are promising candidates for better understanding pregnancy-related pathologies, as well as predicting biomarkers. In this review, we aim to summarize current knowledge of galectins in early pregnancy as well as in pregnancy-related pathologies.

The Sweet-Side of Leukocytes: Galectins as Master Regulators of Neutrophil Function

Among responders to microbial invasion, neutrophils represent one of the earliest and perhaps most important factors that contribute to initial host defense. Effective neutrophil immunity requires their rapid mobilization to the site of infection, which requires efficient extravasation, activation, chemotaxis, phagocytosis, and eventual killing of potential microbial pathogens. Following pathogen elimination, neutrophils must be eliminated to prevent additional host injury and subsequent exacerbation of the inflammatory response. Galectins, expressed in nearly every tissue and regulated by unique sensitivity to oxidative and proteolytic inactivation, appear to influence nearly every aspect of neutrophil function. In this review, we will examine the impact of galectins on neutrophils, with a particular focus on the unique biochemical traits that allow galectin family members to spatially and temporally regulate neutrophil function.

Pregnancy Galectinology: Insights Into a Complex Network of Glycan Binding Proteins

Galectins are a phylogenetically conserved family of soluble β-galactoside binding proteins, consisting of 15 different types, each with a specific function. Galectins contribute to placentation by regulating trophoblast development, migration, and invasion during early pregnancy. In addition, galectins are critical players regulating maternal immune tolerance to the embedded embryo. Recently, the role of galectins in angiogenesis during decidualization and in placenta formation has gained attention. Altered expression of galectins is associated with abnormal pregnancies and infertility. This review focuses on the role of galectins in pregnancy-associated processes and discusses the relevance of galectin-glycan interactions as potential therapeutic targets in pregnancy disorders.

Integrin β1 is bound to galectin-1 in human trophoblast

Interaction of sugar binding proteins-galectins, with glycoconjugates is considered relevant for various reproductive processes. Galectin-1 (gal-1) is a molecule involved in trophoblast cell invasion, which is accomplished through interaction with cell surface and/or extracellular matrix glycoproteins. A possibility of interaction of endogenous gal-1 and trophoblast β1 integrins, both previously shown relevant for trophoblast invasion, was investigated. Confocal microscopy showed overlap in gal-1 and β1 integrin localization at the plasma membrane of isolated cytotrophoblast, HTR-8/SVneo extravillous trophoblast cell line and JAr choriocarcinoma cells. Immunoprecipitation confirmed an interaction of gal-1 with integrin β1, but not with α1 or α5 integrin subunits. Nondenaturing electrophoresis and subcellular fractionation suggested association of gal-1 with β1 integrin in intracellular and plasma membrane compartments of HTR-8/SVneo cells. Gal-1/β1 integrin complex was sensitive to chemical and enzyme treatments, indicating carbohydrate dependent interaction. Down-regulation of gal-1 by siRNA, however, had no effect on level or distribution of β1 integrin, as determined by qPCR and flow cytometry. These results suggest complex lectin type interaction of gal-1 with β1 integrin at the trophoblast cell membrane, which could influence trophoblast cell adhesion, migration and invasion.

Biotinylated N-Acetyllactosamine- and N,N-Diacetyllactosamine-Based Oligosaccharides as Novel Ligands for Human Galectin-3

Galectin inhibitor design is an emerging research field due to the involvement of galectins in cancer. Galectin-3, in particular, plays an important role in tumor progression. To generate inhibitors, modifications of the glycan structure can be introduced. Conjugation of hydrophobic compounds to saccharides has proven to be promising as increased binding of galectin-3 can be observed. In the present study, we report on neo-glycans carrying hydrophobic biotin as novel ligands for human galectin-3. We modified N-acetyllactosamine- and N,N-diacetyllactosamine-based tetrasaccharides at the C6-position of the terminal saccharide unit using selective enzymatic oxidation and subsequent chemical conjugation of biotinamidohexanoic acid hydrazide. These neo-glycans were much better bound by galectin-3 than the unmodified counterparts. High selectivity for galectin-3 over galectin-1 was also proven. We generated multivalent neo-glycoproteins by conjugation of neo-glycans to bovine serum albumin showing high affinity for galectin-3. Compared to non-biotinylated neo-glycoproteins, we achieved high binding levels of galectin-3 with a lesser amount of conjugated neo-glycans. Multivalent ligand presentation of neo-glycoproteins significantly increased the inhibitory potency towards galectin-3 binding to asialofetuin when compared to free monovalent glycans. Our findings show the positive impact of 6-biotinylation of tetrasaccharides on galectin-3 binding, which broadens the recent design approaches for producing high-affinity ligands.

Galectin-1 Couples Glycobiology to Inflammation in Osteoarthritis through the Activation of an NF-κB-Regulated Gene Network

Osteoarthritis is a degenerative joint disease that ranks among the leading causes of adult disability. Mechanisms underlying osteoarthritis pathogenesis are not yet fully elucidated, putting limits to current disease management and treatment. Based on the phenomenological evidence for dysregulation within the glycome of chondrocytes and the network of a family of adhesion/growth-regulatory lectins, that is, galectins, we tested the hypothesis that Galectin-1 is relevant for causing degeneration. Immunohistochemical analysis substantiated that Galectin-1 upregulation is associated with osteoarthritic cartilage and subchondral bone histopathology and severity of degeneration (p < 0.0001, n = 29 patients). In vitro, the lectin was secreted and it bound to osteoarthritic chondrocytes inhibitable by cognate sugar. Glycan-dependent Galectin-1 binding induced a set of disease markers, including matrix metalloproteinases and activated NF-κB, hereby switching on an inflammatory gene signature (p < 10(-16)). Inhibition of distinct components of the NF-κB pathway using dedicated inhibitors led to dose-dependent impairment of Galectin-1-mediated transcriptional activation. Enhanced secretion of effectors of degeneration such as three matrix metalloproteinases underscores the data's pathophysiological relevance. This study thus identifies Galectin-1 as a master regulator of clinically relevant inflammatory-response genes, working via NF-κB. Because inflammation is critical to cartilage degeneration in osteoarthritis, this report reveals an intimate relation of glycobiology to osteoarthritic cartilage degeneration.

Functional interplay between ganglioside GM1 and cross-linking galectin-1 induces axon-like neuritogenesis via integrin-based signaling and TRPC5-dependent Ca²⁺ influx

Axon‐like neuritogenesis in neuroblastoma (NG108‐15) cells and primary cerebellar granular neurons is furthered by the presence of ganglioside GM1. We describe here that galectin‐1 (Gal‐1), a homobivalent endogenous lectin, is an effector by cross‐linking the ganglioside and its associated glycoprotein α₅β₁‐integrin. The thereby triggered signaling cascade involves autophosphorylation of focal adhesion kinase and activation of phospholipase Cγ and phosphoinositide‐3 kinase. This leads to a transient increase in the intracellular Ca²⁺ concentration by opening of TRPC5 channels, which belong to the signal transduction‐gated cation channels. Controls with GM1‐defective cells (NG‐CR72 and neurons from ganglio‐series KO mice) were retarded in axonal growth, underscoring the relevance of GM1 as functional counterreceptor for Gal‐1. The lectin's presence was detected in the NG108‐15 cells, suggesting an autocrine mechanism of action, and in astrocytes in situ. Gal‐1, as cross‐linking lectin, can thus translate metabolic conversion of ganglioside GD1a to GM1 by neuraminidase action into axon growth.

Galectin‐1 (Gal‐1) was shown an effector of axonogenesis in cerebellar granule neurons (CGNs) and NG108‐15 cells by cross‐linking GM1 ganglioside and its associated glycoprotein α₅β₁‐integrin. The resulting signaling led to a transient increase in intracellular Ca²⁺ by opening TRPC5 channels. CGNs deficient in GM1 showed retarded axonogenesis, underscoring the relevance of GM1 as functional counterreceptor for Gal‐1 in this process. This Gal‐1/GM1‐induced signaling was manifest only at the earliest, initiating stage of axon development.

Interaction of extravillous trophoblast galectin-1 and mucin(s)-Is there a functional relevance?

In the course of embryo implantation extensive interaction of the trophoblast with uterine tissue is crucial for adequate trophoblast invasion. This interaction is highly controlled, and it has been pointed out that a specific glycocode and changes in glycosylation may be important for successful implantation and maintenance of pregnancy. Both uterine and trophoblast cells have been shown to express cell surface glycoconjugates and sugar binding proteins, such as mucins (MUC) and galectins (gals). An increasing number of studies have investigated potential candidates interacting in this process. However, knowledge about the biochemical nature of the interactions and their importance for trophoblast cell function, and, consequently, for pregnancy outcome are still lacking. This review is aimed at deliberating the possibility that mucins, as heavily glycosylated proteins, might be among the functionally relevant galectin ligands in human trophoblast, based on both published data and our original research.

Galectin-1 regulates tissue exit of specific dendritic cell populations

During inflammation, dendritic cells emigrate from inflamed tissue across the lymphatic endothelium into the lymphatic vasculature and travel to regional lymph nodes to initiate immune responses. However, the processes that regulate dendritic cell tissue egress and migration across the lymphatic endothelium are not well defined. The mammalian lectin galectin-1 is highly expressed by vascular endothelial cells in inflamed tissue and has been shown to regulate immune cell tissue entry into inflamed tissue. Here, we show that galectin-1 is also highly expressed by human lymphatic endothelial cells, and deposition of galectin-1 in extracellular matrix selectively regulates migration of specific human dendritic cell subsets. The presence of galectin-1 inhibits migration of immunogenic dendritic cells through the extracellular matrix and across lymphatic endothelial cells, but it has no effect on migration of tolerogenic dendritic cells. The major galectin-1 counter-receptor on both dendritic cell populations is the cell surface mucin CD43; differential core 2 O-glycosylation of CD43 between immunogenic dendritic cells and tolerogenic dendritic cells appears to contribute to the differential effect of galectin-1 on migration. Binding of galectin-1 to immunogenic dendritic cells reduces phosphorylation and activity of the protein-tyrosine kinase Pyk2, an effect that may also contribute to reduced migration of this subset. In a murine lymphedema model, galectin-1(-/-) animals had increased numbers of migratory dendritic cells in draining lymph nodes, specifically dendritic cells with an immunogenic phenotype. These findings define a novel role for galectin-1 in inhibiting tissue emigration of immunogenic, but not tolerogenic, dendritic cells, providing an additional mechanism by which galectin-1 can dampen immune responses.

Galectin Binding to Neo-Glycoproteins: LacDiNAc Conjugated BSA as Ligand for Human Galectin-3

Carbohydrate-lectin interactions are relatively weak. As they play an important role in biological recognition processes, multivalent glycan ligands are designed to enhance binding affinity and inhibitory potency. We here report on novel neo-glycoproteins based on bovine serum albumin as scaffold for multivalent presentation of ligands for galectins. We prepared two kinds of tetrasaccharides (N-acetyllactosamine and N,N-diacetyllactosamine terminated) by multi-step chemo-enzymatic synthesis utilizing recombinant glycosyltransferases. Subsequent conjugation of these glycans to lysine groups of bovine serum albumin via squaric acid diethyl ester yielded a set of 22 different neo-glycoproteins with tuned ligand density. The neo-glycoproteins were analyzed by biochemical and chromatographic methods proving various modification degrees. The neo-glycoproteins were used for binding and inhibition studies with human galectin-3 showing high affinity. Binding strength and inhibition potency are closely related to modification density and show binding enhancement by multivalent ligand presentation. At galectin-3 concentrations comparable to serum levels of cancer patients, we detect the highest avidities. Selectivity of N,N-diacetyllactosamine terminated structures towards galectin-3 in comparison to galectin-1 is demonstrated. Moreover, we also see strong inhibitory potency of our scaffolds towards galectin-3 binding. These novel neo-glycoproteins may therefore serve as selective and strong galectin-3 ligands in cancer related biomedical research.

Dissecting molecular aspects of cell interactions using glycodendrimersomes with programmable glycan presentation and engineered human lectins

Glycodendrimersomes with programmable surface display of glycan, together with artificially engineered galectins, were used to understand the physiological significance of human lectins with homodimeric and tandem-repeat-type displays. The mode of topological surface presentation and the density of glycan affected vesicle aggregation mediated by multivalent carbohydrate-protein interactions. The cross-linking capacity of homodimeric lectins was enhanced by covalent connection of the two carbohydrate-binding sites. These findings highlight the value of glycodendrimersomes as versatile cell membrane mimetics, and assays provide diagnostic tools for protein functionality. This work also provides guidelines for the design of cell separators, bioactive matrices, bioeffectors, and other biomedical applications.

Analysis of the intracellular role of galectins in cell growth and apoptosis

Galectins are a family of animal lectins with conserved carbohydrate-recognition domains that recognize β-galactosides. Despite structural similarities, these proteins have diverse functions in a variety of cellular processes. While a large number of extracellular functions have been demonstrated for galectins, the existence of intracellular functions has been clearly shown for a number of galectins, including regulation of cell growth and apoptosis; these latter functions may not involve glycan binding. There is considerable interest in intracellular regulation by galectins of cell growth and apoptosis, as these are fundamental cellular processes in normal homeostasis. Their dysregulation can cause pathologies such as autoimmune disorders, cancer, and neural degenerative diseases. Here we describe methods that we routinely perform in the laboratory to investigate the role of galectins in cell growth and apoptosis. These include methods for cell isolation, cell maintenance, and genetic manipulations to perturb galectin gene expression, as well as assays for cell growth and apoptosis.

Differential expression of galectin-1 and its interactions with cells and laminins in the intervertebral disc

Galectin-1 (Gal-1), an endogenous β-galactoside-binding protein, binds to laminins, which are highly expressed in the nucleus pulposus (NP) of the intervertebral disc (IVD). The objective of this study is to evaluate the expression of Gal-1 protein in IVD tissues during aging and the effect of Gal-1 on IVD cell adhesion to laminins. Tissues from rat, porcine, and human (scoliosis or disc degeneration) IVDs were used to evaluate Gal-1 expression via immunostaining, RT-PCR, and Western blot analysis. Attachment of isolated IVD cells (porcine and human) on select laminin isoforms (LM-111 and LM-511) was compared with/without pre-incubation with exogenous Gal-1. A biotinylated Gal-1(B-Gal-1) was used to evaluate for binding to IVD cells and to select for IVD cells by magnetic activated cell sorting (MACS). NP cells expressed high levels of Gal-1 protein as compared to anulus fibrosus (AF) cells in immature tissues, while exogenous Gal-1 increased both NP and AF cell attachment to laminins and exhibited a similar binding to both cell types in vitro. With aging, Gal-1 levels in NP tissue appeared to decrease. In addition, incubation with B-Gal-1 was able to promote the retention of more than 50% of IVD cells via MACS. Our results provide new findings for the presence and functional role of Gal-1 within IVDs. Similar staining patterns for Gal-1 and LM-511 in IVD tissue suggest that Gal-1 may serve as an adhesion molecule to interact with both cells and laminins. This MACS protocol may be useful for selecting pure IVD cells from mixed cells of pathological tissue.

Galectin-1 binds to influenza virus and ameliorates influenza virus pathogenesis

Innate immune response is important for viral clearance during influenza virus infection. Galectin-1, which belongs to S-type lectins, contains a conserved carbohydrate recognition domain that recognizes galactose-containing oligosaccharides. Since the envelope proteins of influenza virus are highly glycosylated, we studied the role of galectin-1 in influenza virus infection in vitro and in mice. We found that galectin-1 was upregulated in the lungs of mice during influenza virus infection. There was a positive correlation between galectin-1 levels and viral loads during the acute phase of viral infection. Cells treated with recombinant human galectin-1 generated lower viral yields after influenza virus infection. Galectin-1 could directly bind to the envelope glycoproteins of influenza A/WSN/33 virus and inhibit its hemagglutination activity and infectivity. It also bound to different subtypes of influenza A virus with micromolar dissociation constant (K(d)) values and protected cells against influenza virus-induced cell death. We used nanoparticle, surface plasmon resonance analysis and transmission electron microscopy to further demonstrate the direct binding of galectin-1 to influenza virus. More importantly, we show for the first time that intranasal treatment of galectin-1 could enhance survival of mice against lethal challenge with influenza virus by reducing viral load, inflammation, and apoptosis in the lung. Furthermore, galectin-1 knockout mice were more susceptible to influenza virus infection than wild-type mice. Collectively, our results indicate that galectin-1 has anti-influenza virus activity by binding to viral surface and inhibiting its infectivity. Thus, galectin-1 may be further explored as a novel therapeutic agent for influenza.

Effect of recombinant galectin-1 on the growth of immortal rat chondrocyte on chitosan-coated PLGA scaffold

The effect of galectin-1 (GAL1) on the growth of immortal rat chondrocyte (IRC) on chitosan-modified PLGA scaffold is investigated. The experimental results showed that water absorption ratio of chitosan-modified PLGA scaffold was 70% higher than that of PLGA alone after immersion in ddH(2)O for 2 weeks, indicating that chitosan-modification significantly enhances the hydrophilicity of PLGA. The experimental results also showed that GALl efficiently and spontaneously coats the chitosan-PLGA scaffold surface to promote adhesion and growth of immortal rat chondrocyte (IRC). To investigate the effect of endogenous GAL1, the full-length GAL1 cDNAs were cloned and constructed into pcDNA3.1 vectors to generate a plasmid expressed in IRC (IRC-GAL1). The results showed that IRC-GAL1 growth was significantly higher than that of IRC on chitosan-PLGA scaffold. The GAL1-potentiated IRC growth on chitosan-PLGA scaffold was dose-dependently inhibited by TDG (specific inhibitor of GAL1 binding). These results strongly suggest that GAL1 is critical for enhancing IRC cell adhesion and growth on chitosan-PLGA scaffold. Moreover, GAL1-coating or expression tends to promote IRC cell-cell aggregation on chitosan-PLGA scaffold and significantly enhances IRC migration. These results suggest that GAL1 probably could induce tissue differentiation and facilitates cartilage reconstruction. In conclusion, the experimental results suggest that both GAL1 and chitosan are important for enhancing IRC cell adhesion and growth on PLGA scaffold, and GAL1 is a potential biomaterial for tissue engineering.

Cell surface N-glycans-mediated isolation of mouse neural stem cells

The isolation of neural stem cells (NSCs) has been hampered by the lack of valid cell-surface antigens on NSCs, and novel valuable markers have been proposed. Glycan (oligosaccharide chain) is a potential candidate as a marker to isolate NSCs, because the species and the combination order of saccharides in glycan generate remarkable structural diversity and specificity. At present, the expression of hundreds of glycoconjugates with glycans have been found in the NSCs; however, just a few glycan-epitopes have been identified as valuable cell-surface markers. This review focused on the isolation of NSC using glycoprotein, especially complex type N-glycans. The cell-surface N-glycan-mediated isolation of NSCs is therefore expected to provide a comprehensive understanding of the biologic characteristics of NSCs in the brain, and thereby help to develop novel strategies in the field of regenerative medicine.

Differential expression of immunomodulatory galectin-1 in peripheral leukocytes and adult tissues and its cytosolic organization in striated muscle

Galectin-1 (Gal-1) is important in immune function and muscle regeneration, but its expression and localization in adult tissues and primary leukocytes remain unclear. To address this, we generated a specific monoclonal antibody against Gal-1, termed alphahGal-1, and defined a sequential peptide epitope that it recognizes, which is preserved in human and porcine Gal-1, but not in murine Gal-1. Using alphahGal-1, we found that Gal-1 is expressed in a wide range of porcine tissues, including striated muscle, liver, lung, brain, kidney, spleen, and intestine. In most types of cells, Gal-1 exhibits diffuse cytosolic expression, but in cells within the splenic red pulp, Gal-1 showed both cytosolic and nuclear localization. Gal-1 was also expressed in arterial walls and exhibited prominent cytosolic and nuclear staining in cultured human endothelial cells. However, human peripheral leukocytes and promyelocytic HL60 cells lack detectable Gal-1 and also showed very low levels of Gal-1 mRNA. In striking contrast, Gal-1 exhibited an organized cytosolic staining pattern within striated muscle tissue of cardiac and skeletal muscle and colocalized with sarcomeric actin on I bands. These results provide insights into previously defined roles for Gal-1 in inflammation, immune regulation and muscle biology.

Insecticidal action of mammalian galectin-1 against diamondback moth (Plutella xylostella)

BACKGROUND

Previous studies showed that mammalian galectin-1 (GAL1) could interact with chitosan or chitin, one component of the peritrophic membrane (PM). This finding suggests that the PM could be a target of GAL1, which prompted the authors to explore the effect of GAL1 on larval growth and its potential mechanism.

RESULTS

The development of Plutella xylostella (L.) larvae was significantly disturbed after they were fed recombinant GAL1. The histochemical structure and immunostaining pattern suggested that GAL1 treatment resulted in dose- and time-dependent disruption of the microvilli and abnormalities in these epithelial cells. Ultrastructural studies showed that the PM was not present in the midgut of GAL1-treated insects; instead, numerous bacteria were found in the lumen area. These results indicate that the protective function of the PM was disrupted by GAL1 treatment. Moreover, in vitro data showed that GAL1 interacts with chitosan/chitin in a dose-dependent manner, and also specifically binds to the PM in vitro.

CONCLUSION

In view of the fact that the carbohydrate recognition domain of GAL1 recognises the structural motif N-acetyl lactosamine (Gal beta 1-4 GlcNAc), which is similar to that of chitin (beta-1,4 N-acetyl-D-glucosamine), it is proposed that the insecticidal mechanism of GAL1 involves direct binding with chitin to interfere with the structure of the PM.

Mammalian galectins: structure, carbohydrate specificity, and functions

Galectins are a family of beta-galactoside binding lectins, homological by a sequence of the carbohydrate-binding site. In this review literature data about structure and carbohydrate specificity of galectins are discussed. The role of galectins in the regulation of cell adhesion in immune response, inflammation, and cancer progression is considered.

Different affinity of galectins for human serum glycoproteins: galectin-3 binds many protease inhibitors and acute phase proteins

Here we report the first survey of galectins binding to glycoproteins of human serum. Serum was subjected to affinity chromatography using immobilized galectins, and the bound glycoproteins were analyzed by electrophoresis, Western blotting, and mass spectrometry. Galectins-3, -8, and -9 bound a much broader range of ligands in serum than previously known, galectin-1 bound less, and galectins-2, -4, and -7 bound only traces or no serum ligands. Galectin-3 bound most major glycoproteins, including alpha-2-macroglobulin and acute phase proteins such as haptoglobin. It bound only a selected minor fraction of transferrin, and bound none or little of IgG. Galectins-8 and -9 bound a similar range of glycoproteins as galectin-3, but in lower amounts, and galectin-8 had a relative preference for IgA. Galectin-1 bound mainly a fraction of alpha-2-macroglobulin and only traces of other glycoproteins. The binding of galectin-3 to serum glycoproteins requires affinity for LacNAc, since a mutant (R186S), which has lost this affinity, did not bind any serum glycoproteins. The average affinity of galectin-3 for serum glycoproteins was estimated to correspond to K(d) approximately 1-5 muM by modeling of the affinity chromatography and a fluorescence anisotropy assay. Since galectins are expressed on endothelial cells and other cells exposed to serum components, this report gives new insight into function of galectins and the role of their different fine specificity giving differential binding to the serum glycoproteins.

Galectin-1, a novel ligand of neuropilin-1, activates VEGFR-2 signaling and modulates the migration of vascular endothelial cells

Galectin-1 (Gal-1), a homodimeric prototype of the galectins with a single carbohydrate-recognition domain, was recently identified as being overexpressed in tumor-associated capillary endothelial cells. The role of Gal-1 in endothelial cellular functions and the mechanism of action of Gal-1 remain unknown. Neuropilin-1 (NRP1) is a neuronal receptor that mediates repulsive growth cone guidance, and NRP1 functions in endothelial cells as a coreceptor (with vascular endothelial growth factor receptors (VEGFRs)) for VEGF(165). In this study, we found that Gal-1 was overexpressed in the tumor-associated endothelial cells of oral squamous cell carcinomas (P<0.001). Gal-1 increased the proliferation and adhesion of endothelial cells, and enhanced cell migration in combination with VEGF(165). Surprisingly, Gal-1 selectively bound NRP1 via the carbohydrate-recognition domain, but did not bind VEGFR-1, VEGFR-2 or VEGFR-3. The Gal-1-NRP1 interaction mediated the migration and adhesion of endothelial cells. The binding of Gal-1 to NRP1 enhanced VEGFR-2 phosphorylation and stimulated the activation of the mitogen activated protein (MAP) kinases SAPK1/JNK (stress activated protein kinase-1/c-Jun NH2-terminal kinase). These findings show, for the first time, that Gal-1 can directly bind to NRP1 on endothelial cells, and can promote the NRP1/VEGFR-2-mediated signaling pathway as well as NRP1-mediated biological activities.

Galectin-1, an endogenous lectin produced by arterial cells, binds lipoprotein(a) [Lp(a)] in situ: Relevance to atherogenesis

Lipoprotein(a) [Lp(a)], a modified LDL molecule, is implicated in atherogenesis. Mechanisms of the accumulation of [Lp(a)] in atherosclerotic vessels is lacking in literature. We sought to investigate the complementarities of the carbohydrate structures on Lp(a) and LDL with galectin-1(a carbohydrate binding protein) and whether endogenous galectin-1 binds Lp(a) in situ. We investigated T-antigen structures on Lp(a) and LDL by enzyme-linked lectin assay using T-antigen specific lectins, galectin-1 and jacalin. Both jacalin and galectin-1 bound strongly to Lp(a) and to a much lesser extent, to LDL. Galectin-1 recognition of the lipoproteins was abolished when the O-linked sugars were selectively removed. Localization of endogenous galectin-1 within histological sections of human internal mammary artery and in vitro binding of Lp(a) to the tissues was analyzed by immunohistochemical staining. The Lp(a)-binding pattern was found to overlap with the localization of galectin-1. The poor Lp(a)-binding on inhibiting tissue galectin-1 with lactose, suggested the binding of Lp(a) to galectin-1. This may be suggestive of a mechanism by which Lp(a) accumulates within arterial walls in atherogenesis.

Galectins: novel anti-inflammatory drug targets

Galectins are a protein family defined by their affinity for beta-galactosides and consensus sequences. They are pleiotropic regulators involved in a multitude of functions, both in and out of the cell. Extracellularly, they have the potential to bind to various surface receptors on a variety of cell types as well as extracellular matrix (ECM) proteins, thus causing cell activation or apoptosis, modulating cell adhesion and inducing cell migration. Intracellularly, they can regulate cell growth, apoptosis and cell cycle progression. Galectins are either pro-inflammatory or anti-inflammatory. Some, such as galectin-1, may be employed as anti-inflammatory agents, while others, such as galectin-3, are evidently suitable targets for anti-inflammatory drugs. The extracellular functions of galectins involve their lectin-carbohydrate interactions and thus their carbohydrate ligands or mimetics would be suitable inhibitors. While the intracellular functions of galectins do not appear to engage lectin-carbohydrate interactions, the carbohydrate-binding sites of these proteins may still be involved. Therefore, the same inhibitors may be used regardless of whether intracellular or extracellular galectins are to be targeted.

Galectin interactions with extracellular matrix and effects on cellular function

In vivo, cells exist within a complex mixture of glycoproteins and proteoglycans termed the extracellular matrix (ECM). The components of the ECM are secreted by the cells in that site, and the ECM provides not only a physical support but also outside-in signals that regulate many cellular functions, including cell proliferation, differentiation, migration, and survival. Altering the composition of the ECM can thus significantly alter cell behavior. Many types of cells, including normal and malignant epithelial and mesenchymal cells, secrete galectin-1, a member of the galectin family of lectins, into the ECM surrounding the cells. Galectin-1 is known to regulate many of these same cellular functions (i.e., proliferation, differentiation, migration, and death), so that the presence of galectin-1 in ECM will modify the effects of ECM on cells. In this chapter, we present three types of assays that allow interrogation of the effects of galectin-1 on cell adhesion to ECM, cell migration through ECM, and cell death in ECM, using T-cell lines as a model cell type.

Galectin-1 receptors in different cell types

Galectins are a family of animal lectins defined by two properties: shared amino acid sequences in their carbohydrate-recognizing domain, and beta-galactoside affinity. A wide variety of biological phenomena are related to galectins, i.e., development, differentiation, morphogenesis, tumor metastasis, apoptosis, RNA splicing, and immunoregulatory function. In this review, we will focus on galectin-1 receptors, and some of the mechanisms by which this lectin affects different cell types. Several galectin-1 receptors are discussed such as CD45, CD7, CD43, CD2, CD3, CD4, CD107, CEA, actin, extracellular matrix proteins such as laminin and fibronectin, glycosaminoglycans, integrins, a beta-lactosamine glycolipid, GM1 ganglioside, polypeptide HBGp82, glycoprotein 90 K/MAC-2BP, CA125 cancer antigen, and pre-B cell receptor.

New roles for galectins in brain tumors--from prognostic markers to therapeutic targets

Despite advances in diagnosis and treatment, brain tumors continue to be the leading cause of cancer-related death in patients under 35 years of age, demonstrating the need for better prognostic and therapeutic targets. Galectins, a family of mammalian carbohydrate binding proteins, are involved in many processes important for tumor survival and dissemination, including proliferation, apoptosis, transcriptional regulation, intracellular signaling, cell adhesion, and cell migration. Several galectins are expressed in human brain, with many galectins demonstrating altered expression during tumor progression. Thus, galectins and the functions regulated by this family of proteins are potential targets for the diagnosis and treatment of brain cancer. This review highlights the roles of galectins in cancer and specifically, the developing field of galectins in brain cancer.

IgA1 is the premier serum glycoprotein recognized by human galectin-1 since T antigen (Galbeta1-->3GalNAc-) is far superior to non-repeating N-acetyl lactosamine as ligand

Human heart galectin-1 (HHL) was separated by high pressure liquid chromatography from endogenous glycoproteins co-purified with it during affinity chromatography. These glycoproteins offered excellent ligands for HHL binding and were rich in T antigen (Galbeta1-->3 GalNAc-) of O-linked oligosaccharides. In enzyme linked lectin assay and hemagglutination inhibition assay, human IgA1, bovine fetuin and other O-glycosylated T antigen-bearing glycoproteins bound to the lectin efficiently in contrast to single N-acetyl lactosamine (LacNAc)-bearing N-linked oligosaccharides released from them and to IgG which is not O-glycosylated. HHL binding to IgA1 and fetuin was unaffected by removal of their N-linked oligosaccharides by alpha-mannosidase. When immobilized, O-glycosylated serum proteins but not IgG could capture HHL from its solutions. Desialylated or polymeric IgA1 was better inhibitor than monomeric IgA1. The findings suggest a possible role for galectin-1 in anchoring of microbial and cancer cells known to be rich in T antigen, in high serum IgA1 turn over and in tissue sequestering of IgA1 immune complexes especially after their microbial desialylation in IgA nephropathy and other immune complex-mediated disorders.

Fluorescence polarization as an analytical tool to evaluate galectin-ligand interactions

Galectins are a family of beta-galactose binding lectins associated with functions such as immunological and malignant events. To study the binding affinity of galectins for natural and artificial saccharides and glycoconjugates we have developed an assay using fluorescence polarization. A collection of fluorescein-conjugated saccharides was synthesized and used as probes with galectins-1 and -3 and the two carbohydrate recognition domains of galectin-4. Direct binding of a fixed probe amount with different amounts of each galectin defined specificity and selectivity and permitted selection of the optimal probe for inhibition studies. Then fixed amounts of galectin and selected probe were used to screen the inhibitory potency of a library of nonfluorescent compounds. As the assay is in solution and does not require separation of free and bound probe, it is simple and rapid and can easily be applied to different unlabeled galectins. As all interaction components are known, K(d) values for galectin-inhibitor interaction can be directly calculated without approximation other than the assumption of a simple one-site competition.

Regulatory Roles of Galectins in the Immune Response

Galectins are a family of animal lectins with affinity for beta-galactosides. They are differentially expressed by various immune cells and their expression levels appear to be dependent on cell differentiation and activation. They can interact with cell-surface and extracellular matrix glycoconjugates (glycoproteins and glycolipids), through lectin-carbohydrate interactions. Through this action, they can promote cell growth, affect cell survival, modulate cell adhesions, and induce cell migration. They appear to do so by binding to different glycoconjugates decorated by suitable saccharides, rather than through specific receptors. Galectins do not have a classical signal peptide and are often localized in intracellular compartments, including the nucleus. Intracellularly, they can regulate cell growth and survival by interacting with cytoplasmic and nuclear proteins, through protein-protein interactions, thereby affecting intracellular signaling pathways. Current research indicates that galectins play important roles in the immune response through regulating the homeostasis and functions of the immune cells.

Dimeric galectin-1 binds with high affinity to alpha2,3-sialylated and non-sialylated terminal N-acetyllactosamine units on surface-bound extended glycans

Galectin-1 is a member of the galectin family of glycan-binding proteins and occurs as an approximately 29.5-kDa noncovalent homodimer (dGal-1) that is widely expressed in many tissues. Here, we report that human recombinant dGal-1 bound preferentially and with high affinity (apparent K(d) approximately 2-4 microM) to immobilized extended glycans containing terminal N-acetyllactosamine (LN; Galbeta1-4GlcNAc) sequences on poly-N-acetyllactosamine (PL; (-3Galbeta1-4GlcNAcbeta1-)(n)) sequences, complex-type biantennary N-glycans, or novel chitin-derived glycans modified to contain terminal LN. Although terminal Gal residues are important for dGal-1 recognition, dGal-1 bound similarly to alpha3-sialylated and alpha2-fucosylated terminal LN, but not to alpha6-sialylated and alpha3-fucosylated terminal LN. The binding specificity of human recombinant dGal-1 was similar to that observed with purified bovine heart-derived dGal-1. Unexpectedly, dGal-1 bound free ligands in solution with relatively low affinity and displayed no preference for extended glycans, indicating that dGal-1 preferentially recognizes extended glycans only when they are surface-bound, such as found on cell surfaces. Human dGal-1 also bound to both native and desialylated human promyelocytic HL-60 cells with similar affinity as observed for immobilized long chain PL. Binding to these cells was reduced upon treatment with endo-beta-galactosidase, which cleaves PL sequences, indicating that cell-surface PLs are ligands. To test the role of dimerization in dGal-1 binding, we examined the binding of a mutated form of dGal-1 that weakly dimerizes (monomeric Gal-1 (mGal-1)) and a covalently dimerized (chemically cross-linked) form of mGal-1 (cd-mGal-1). dGal-1 and cd-mGal-1 had similar affinities that were both approximately 3.5-fold higher for immobilized PL than observed for mGal-1, suggesting that dGal-1 acts as a dimer to cross-link terminal LN units on immobilized PL. These results indicate that dGal-1 functions as a dimer to recognize LN units on extended PLs on cell surfaces.

Introduction to galectins

Good evidence suggest roles of galectins in cancer, immunity and inflammation, and development, but a unifying picture of their biological function is lacking. Instead galectins appear to have a particularly diverse, bewildering but intriguing array of activities both inside and outside cells--"clear truths and mysteries are inextricably twined". Fortunately this has not discouraged but rather enthused a large number of good galectin researchers, some of which have contributed to this special issue of Glycoconjugate Journal to provide a personal, critical status of the field. Here we will give a brief introduction to the galectins as a protein family with some comments on nomenclature.

Molecular dynamics simulations of galectin-1-oligosaccharide complexes reveal the molecular basis for ligand diversity

Galectin-1 is a member of a protein family historically characterized by its ability to bind carbohydrates containing a terminal galactosyl residue. Galectin-1 is found in a variety of mammalian tissues as a homodimer of 14.5-kDa subunits. A number of developmental and regulatory processes have been attributed to the ability of galectin-1 to bind a variety of oligosaccharides containing the Gal-beta-(1,4)-GlcNAc (LacNAc(II)) sequence. To probe the origin of this permissive binding, solvated molecular dynamics (MD) simulations of several representative galectin-1-ligand complexes have been performed. Simulations of structurally defined complexes have validated the computational approach and expanded upon data obtained from X-ray crystallography and surface plasmon resonance measurements. The MD results indicate that a set of anchoring interactions between the galectin-1 carbohydrate recognition domain (CRD) and the LacNAc core are maintained for a diverse set of ligands and that substituents at the nonreducing terminus of the oligosaccharide extend into the remainder of a characteristic surface groove. The anionic nature of ligands exhibiting relatively high affinities for galectin-1 implicates electrostatic interactions in ligand selectivity, which is confirmed by a generalized Born analysis of the complexes. The results suggest that the search for a single endogenous ligand or function for this lectin may be inappropriate and instead support a more general role for galectin-1, in which the lectin is able to crosslink heterogeneous oligosaccharides displayed on a variety of cell surfaces. Such binding promiscuity provides an explanation for the variety of adhesion phenomena mediated by galectin-1.

GnT-V, macrophage and cancer metastasis: a common link

GnT-V generated, beta1,6-branched polylactosamines are a common feature shared by normal granulocytes, monocytes, and a variety of malignant cells. Furthermore, activation of GnT-V in oncogenic transformation induces invasiveness and metastatic potential in mice as well as in humans. In view of the common expression of lymphocytic/monocytic trait, motility, and GnT-V by metastatic cancer cells, macrophage fusion hybrids were generated in vitro with Cloudman S91 mouse melanoma cells to test whether the parental traits are co-expressed in hybrids and how those are related to altered phenotypes in relation to metastasis. In fact, the fusion hybrids are highly metastatic in vivo, motile in vitro, and express macrophage-associated traits of increased GnT-V activity, beta1,6 branching, and polylactosamine content. A Spontaneously formed lung melanoma metastases have been identified and characterized as host x tumor hybrid containing higher DNA content than parental cells and increased GnT-V activity. The results, taken together, could reflect prior fusion of tumor-associated macrophages with cells of the primary tumor, and therefore establish a possible common link between elevated expression of GnT-V and malignant transformation, a well-known report. Moreover, the fusion hybrids with metastatic potential ranging from high to low offer a genetically matched model system, for identification and characterization of differentially expressed genes in association with metastasis, since the fusion partners are derived from the same species of mouse (DBA/2J).

Carbohydrate binding proteins galectin-1 and galectin-3 in human trabecular meshwork

PURPOSE

Galectins are a family of carbohydrate binding proteins involved in a variety of biological processes including cell-cell and cell-matrix interactions. We examined galectin-1 and galectin-3 to determine if galectins are expressed in the human trabecular meshwork and Schlemm's canal.

METHODS

Human trabecular meshworks were dissected from donor eyes within 12 hr of death. Galectin-1 and galectin-3 expression was examined by RT-PCR and Western blot analysis. Immunohistochemistry of galectin-1 and galectin-3 was analyzed in normal and glaucomatous tissue.

RESULTS

Expression of mRNA and protein of Galectin-1 (14 kDa) and galectin-3 (31 kDa) was found in the outflow pathway. Immunostaining revealed galectin-1 and galectin-3 throughout the meshwork, cells lining Schlemm's canal, and extracellular spaces in the inner and outer walls of the canal. Comparison of normal, POAG and PEX samples revealed no difference in location or intensity for either galectin-1 and galectin-3.

CONCLUSION

Galectin-1 and galectin-3 are present in human trabecular meshwork of normal and glaucomatous eyes.

Stimulation of proliferation of rat hepatic stellate cells by galectin-1 and galectin-3 through different intracellular signaling pathways

We found that the expression of galectin-1 and galectin-3 was significantly up-regulated in hepatic stellate cells (HSCs) both in the course of their transdifferentiation into myofibroblasts, a process of "self-activation," and in the fibrosis of liver tissues. Recombinant galectin-1 and galectin-3 stimulated the proliferation of cultured HSCs via the MEK1/2-ERK1/2 signaling pathway. However, galectin-3 utilized protein kinases C and A to induce this process, whereas galectin-1 did not. We also found that thiodigalactoside, a potent inhibitor of beta-galactoside binding, attenuated the effects of both galectins. In addition, galectin-1, but not galectin-3, promoted the migration of HSCs. Thus, it appears that galectin-1 and galectin-3, generated by activated HSCs, could participate in beta-galactoside binding and induce different intracellular signaling pathways leading to the proliferation of HSCs.

Olfactory ensheathing cells: historical perspective and therapeutic potential

Olfactory ensheathing cells (OECs) are the glial cells that ensheath the axons of the first cranial nerve. They are attracting increasing attention from neuroscientists as potential therapeutic agents for use in the repair of spinal cord injury and as a source of myelinating glia for use in remyelinating axons in demyelinating diseases such as multiple sclerosis. This review mainly addresses the cell biological aspects of OECs pertinent to addressing two questions. Namely, where do OECs fit into the groupings of central nervous system (CNS)/peripheral nervous system (PNS) glial cells and should OECs be viewed as a clinically relevant alternative to Schwann cells in the treatment of spinal cord injury? The evidence indicates that OECs are indeed a clinically relevant alternative to Schwann cells. However, much more work needs to be done before we can even come close to answering the first question as to the lineage and functional relationship of OECs to the other types of CNS and PNS glial cells.

Upregulation of galectins-1 and -3 in human colon cancer and their role in regulating cell migration

To probe the potential contribution of beta-galactoside-contributing epitopes and receptor proteins (gal-1 and gal-3) to colon malignancy, we first examined the expression of galectins and binding sites in clinical specimens by lectin and immunohistochemistry. Sixty-seven colonic surgical resections were studied, including 10 normal, 10 mild dysplasias, 10 severe dysplasias and 37 cancers. gal-1 and gal-3 were expressed in variable amounts in the epithelial cells and the connective tissue of normal colon. Their expression significantly increased with the degree of dysplasia, suggesting that gal-1 and gal-3 and their binding sites are related to malignant progression, while gal-8 has been associated with suppressor activity. To study the functional aspects, the influence of these galectins on the migration of 4 human colorectal cancer cell lines (HCT-15, LoVo, DLD-1, CoLo201) was studied. In agreement with histopathologic monitoring, these tumor cells were found to produce gal-3, while only CoLo201 was positive for gal-1. Except for DLD-1 and gal-1, the lines exhibited gal-1 binding sites on the surface, prompting study by computer-assisted videomicroscopy of the effect on cell migration of the presence of galectin on the culture substrate. The level of cell migration for HCT-15, LoVo and CoLo201 cells was significantly reduced by 0.15 microg/cm(2) gal-1, and the presence of a blocking antibody at least reduced this effect. gal-3 significantly reduced cell migration in all 4 of the in vitro cell lines.

Galectins and urological cancer

Galectins are a family of proteins defined by their affinity for beta-galactoside and by their conserved sequence. Each galectins exhibits a specific expression pattern in various tissues and their expression is regulated during development. Their expression is altered in many types of cancers and non-cancerous disorders. They interact with glycoproteins in both extracellular and intracellular milieu and regulate various biological phenomenon including cell growth, cell differentiation, cell adhesion, and apoptosis. A series of experimental and clinical evidences have been reported to support correlation between galectin expressions and neoplastic transformation. The recent findings show that expressions of galectins are elevated with neoplastic progression in certain malignancies, and therefore, galectins are expected to serve as reliable tumor markers. In this review, we describe the expression and role of galectins in urological cancers and their clinical applications for diagnostic and therapeutic use.

Galectin-1 modulates human glioblastoma cell migration into the brain through modifications to the actin cytoskeleton and levels of expression of small GTPases

We show that high-grade astrocytic tumors with high levels of galectin-1 expression are associated with dismal prognoses. The immunohistochemical analysis of galectin-1 expression of human U87 and U373 glioblastoma xenografts from the brains of nude mice revealed a higher level of galectin-1 expression in invasive areas rather than non-invasive areas of the xenografts. Nude mice intracranially grafted with U87 or U373 cells constitutively expressing low levels of galectin-1 (by stable transfection of an expression vector containing the antisense mRNA of galectin-1) had longer survival periods than those grafted with U87 or U373 cells expressing normal levels of galectin-1. Galectin-1 added to the culture media markedly and specifically increased cell motility levels in human neoplastic astrocytes. These effects are related to marked modifications in the organization of the actin cytoskeleton and the increase in small GTPase RhoA expression. All the data obtained indicate that galectin-1 enhances the migratory capabilities of tumor astrocytes and, therefore, their biological aggressiveness.