Tandem-repeat Type Galectin Research Articles

Impact of mutations in carbohydrate binding sites of tandem-repeat type galectin from Takifugu obscurus on its antimicrobial activity

Galectins belong to a family of galactoside-binding proteins and exhibit diverse biological functions. In the present research, a tandem-repeat type galectin (named ToGalectin) was identified from obscure puffer Takifugu obscurus. The 296 amino acids ToGalectin contained two carbohydrate recognition domains (CRDs), one of which possessed two conserved carbohydrate binding motifs. Phylogenetic analysis showed that ToGalectin clustered tightly with other galectin-8 proteins from teleost fish. ToGalectin transcripts were ubiquitously expressed in all tissues examined and its expression was significantly upregulated in the liver, kidney, and intestine after Vibrio harveyi or Staphylococcus aureus infection. To investigate the effect of carbohydrate binding sites on biological activity, ToGalectin and its mutant (MUT-ToGalectin) were expressed and purified. The recombinant ToGalectin and MUT-ToGalectin proteins showed strong agglutinating activity against both V. harveyi and S. aureus. rToGalectin could bind to all tested carbohydrates and bacteria, whereas rMUT-ToGalectin bound to some carbohydrates and bacteria with specific and relatively strong affinity. rToGalectin significantly suppressed the growth of all six bacteria detected and promoted bacterial clearance in vivo, whereas MUT-ToGalectin inhibited the growth of only two bacterial species, which could be attributed to the differences in conserved motifs within the CRDs. Our results suggested that ToGalectin is involved in the immune response against bacterial infection and the clearance of pathogens in T. obscurus.

Different roles of the heterodimer architecture of galectin-4 in selective recognition of oligosaccharides and lipopolysaccharides having ABH antigens

The dimeric architecture of tandem-repeat type galectins, such as galectin-4 (Gal-4), modulates their biological activities, although the underlying molecular mechanisms have remained elusive. Emerging evidence show that tandem-repeat galectins play an important role in innate immunity by recognizing carbohydrate antigens present on the surface of certain pathogens, which very often mimic the structures of the human self-glycan antigens. Herein, we have analyzed the binding preferences of the C-domain of Gal-4 (Gal-4C) toward the ABH-carbohydrate histo-blood antigens with different core presentations and their recognition features have been rationalized by using a combined experimental approach including NMR, solid-phase and hemagglutination assays, and molecular modeling. The data show that Gal-4C prefers A over B antigens (two-fold in affinity), contrary to the N-domain (Gal-4N), although both domains share the same preference for the type-6 presentations. The behavior of the full-length Gal-4 (Gal-4FL) tandem-repeat form has been additionally scrutinized. Isothermal titration calorimetry and NMR data demonstrate that both domains within full-length Gal-4 bind to the histo-blood antigens independently of each other, with no communication between them. In this context, the heterodimeric architecture does not play any major role, apart from the complementary A and B antigen binding preferences. However, upon binding to a bacterial lipopolysaccharide containing a multivalent version of an H-antigen mimetic as O-antigen, the significance of the galectin architecture was revealed. Indeed, our data point to the linker peptide domain and the F-face of the C-domain as key elements that provide Gal-4 with the ability to cross-link multivalent ligands, beyond the glycan binding capacity of the dimer.

Chimera and Tandem-Repeat Type Galectins: The New Targets for Cancer Immunotherapy.

In humans, a total of 12 galectins have been identified. Their intracellular and extracellular biological functions are explored and discussed in this review. These galectins play important roles in controlling immune responses within the tumour microenvironment (TME) and the infiltration of immune cells, including different subsets of T cells, macrophages, and neutrophils, to fight against cancer cells. However, these infiltrating cells also have repair roles and are hijacked by cancer cells for pro-tumorigenic activities. Upon a better understanding of the immunomodulating functions of galectin-3 and -9, their inhibitors, namely, GB1211 and LYT-200, have been selected as candidates for clinical trials. The use of these galectin inhibitors as combined treatments with current immune checkpoint inhibitors (ICIs) is also undergoing clinical trial investigations. Through their network of binding partners, inhibition of galectin have broad downstream effects acting on CD8+ cytotoxic T cells, regulatory T cells (Tregs), Natural Killer (NK) cells, and macrophages as well as playing pro-inflammatory roles, inhibiting T-cell exhaustion to support the fight against cancer cells. Other galectin members are also included in this review to provide insight into potential candidates for future treatment(s). The pitfalls and limitations of using galectins and their inhibitors are also discussed to cognise their clinical application.

Galectin-9: A novel promoter of atherosclerosis progression

Background and aimsAtherosclerosis is widely accepted to be an inflammatory disease driven by lipid accumulation and leukocyte recruitment. More recently, galectins, a family of β-galactoside binding proteins, have been shown to play a role in leukocyte recruitment among other immunomodulatory functions. Galectin (Gal) −9, a tandem repeat type galectin expressed by the endothelium in inflammatory environments, has been proposed to promote leukocyte recruitment. However, the role of Gal-9 in the context of monocyte recruitment remains elusive. Methods and ResultsHere, we characterise the immunomodulatory role of Gal-9 in context of atherosclerosis. We show that ApoE−/−Gal-9−/− mice have a significantly reduced aortic plaque burden compared to their ApoE−/− littermate controls after 12 weeks of high fat diet. RNA sequencing data from two independent studies reveal Lgals9 expression in leukocyte clusters isolated from murine atherosclerotic plaques. Additionally, soluble Gal-9 protein induces monocyte activation and a pro-inflammatory phenotype in macrophages. Furthermore, we show that immobilised recombinant Gal-9 acts as capture and adhesion molecule for CD14+ monocytes in a β2-integrin and glycan dependent manner, while adhesion of monocytes to stimulated endothelium is reduced when Gal-9 is knocked down. Gal-9 also facilitates enhanced recruitment of leukocytes from peripheral arterial disease (PAD) patients compared to healthy young and aged controls. We further characterise the endothelium as source of circulating Gal-9, which is increased in plasma of PAD patients compared to healthy controls. ConclusionsThese results highlight a pathological role for Gal-9 as promoter of monocyte recruitment and atherosclerotic plaque progression, making it a novel target in the prevention of plaque formation and progression.

Galectin-9 inhibits cell proliferation and induces apoptosis in Jurkat and KE-37 acute lymphoblastic leukemia cell lines via caspase-3 activation.

Background and purpose:Acute lymphoblastic leukemia (ALL) is a type of cancer of blood and bone marrow characterized by abnormal proliferation of lymphoid progenitor cells. Galectin-9 is a tandem-repeat type galectin expressed in various tumor cells. It seems that the connection between galectin-9 and T cell immunoglobulin mucin-3 receptor acts as a negative regulator of cancer cells proliferation.Experimental approach:In this research, the effects of galectin-9 were investigated using MTS cell proliferation colorimetric, colony-forming, annexin V-FITC/PI, and caspase-3 assays in the Jurkat and KE-37 cell lines of ALL. Furthermore, the western blotting technique was used to evaluate the levels of apoptotic proteins such as Bax and Bcl-2 in these cell lines.Findings/Results:Our results indicated that galectin-9 can considerably reduce the cell growth and colony formation ability of both Jurkat and KE-37 cell lines in a concentration-dependent manner. Besides, galectin-9 induced apoptosis in a concentration-dependent manner in ALL cells by a mechanism associated with Bax/Bcl-2 expression and activation of the caspase-3 activation.Conclusion and implications:Galectin-9 inhibited the growth and proliferation of cell lines with increased programmed cell death, therefore it can be considered as a potential factor in the progression of ALL therapeutics that needs more research in this context.

Expression and antibacterial analysis of galectin-8 and -9 genes in mandarin fish, Siniperca chuatsi

Galectin-8 and galectin-9 belong to tandem repeat-type galectins, and in the present study, these two genes were cloned in mandarin fish Siniperca chuatsi. The open reading frame (ORF) of the mandarin fish galectin-8 and galectin-9 contains 942, and 1008 bp, encoding 313 and 335 amino acids, respectively. As a conserved feature, an N-terminal carbohydrate recognition domain (CRD), and a C-terminal CRD were observed in each of the two galectins in mandarin fish. In healthy fish, galectin-8 and -9 were constitutively expressed in all organs/tissues examined, and their expression can be induced following the stimulation of LPS and poly(I:C). It is obvious that galectin-8 had a higher increase at mRNA level following the stimulation of poly(I:C). It is further demonstrated that mandarin fish galectin-8 inhibited the growth of Flavobacterium columnare and Streptococcus agalactiae, and in addition to the two species of bacteria, galectin-9 inhibited also the growth of Edwardsiella piscicida, which provides the basis for further understanding their antibacterial role in immune response of mandarin fish.

Full-length galectin-8 and separate carbohydrate recognition domains: the whole is greater than the sum of its parts?

Galectin-8 (Gal-8) is a tandem-repeat type galectin with affinity for β-galactosides, bearing two carbohydrate recognition domains (CRD) connected by a linker peptide. The N- and C-terminal domains (Gal-8N and Gal-8C) share 35% homology, and their glycan ligand specificity is notably dissimilar: while Gal-8N shows strong affinity for α(2-3)-sialylated oligosaccharides, Gal-8C has higher affinity for non-sialylated oligosaccharides, including poly-N-acetyllactosamine and/ or A and B blood group structures. Particularly relevant for understanding the biological role of this lectin, full-length Gal-8 can bind cell surface glycoconjugates with broader affinity than the isolated Gal-8N and Gal-8C domains, a trait also described for other tandem-repeat galectins. Herein, we aim to discuss the potential use of separate CRDs in modelling tandem-repeat galectin-8 and its biological functions. For this purpose, we will cover several aspects of the structure-function relationship of this protein including crystallographic structures, glycan specificity, cell function and biological roles, with the ultimate goal of understanding the potential role of each CRD in predicting full-length Gal-8 involvement in relevant biological processes.

Brugia malayi galectin 2 is a tandem-repeat type galectin capable of binding mammalian polysaccharides

Galectins are among the most abundant excretory/secretory (ES) products of filarial worms, but their role in filarial biology is poorly understood. Galectin-2 (Lec-2), a major component of Brugia malayi extracellular vesicles, is released by filarial worms, and was recently identified in the serum of persons with loiasis. We therefore sought to clone and characterize Lec-2, and to develop reagents to examine its potential as a biomarker and its role in parasite biology. We cloned and expressed recombinant B. malayi Lec-2 (rBmLec-2), generated a Lec-2-specific monoclonal antibody (4B4), and used it to confirm the presence of Lec-2 in B. malayi ES products and whole worm lysate. We show that Lec-2 is absent in B. malayi oocytes, and increases in concentration as embryos mature. Recombinant BmLec-2 hemagglutinates rabbit red blood cells at concentrations less than 1 μg/mL, and this is abrogated by single amino acid substitutions in the predicted carbohydrate recognition domains. rBmLec-2 binds multiple LacNAc oligosaccharides on a mammalian carbohydrate array. Sera from 17/23 (78 %) persons with microfilaremic loiasis and 4/10 (40 %) persons with bancroftian filariasis had detectable antibody to Lec-2 by western blot. Our studies confirm the functionality of BmLec-2 and indicate anti-Lec-2 antibody responses are common in persons with filariasis. These studies set the stage for further examination of the role of Lec-2 in filarial biology and in filarial-host interactions.

Investigating the immunological role of galectin-9 on natural killer (NK) cells in human immunodeficiency virus (HIV)

Abstract NK cells play an integral role in mediating immune responses to viral infections; however, their function is compromised during chronic diseases such as HIV, partly due to an increase expression of inhibitory receptors. Thus, the reduced immune responses elicited by NK cells in HIV can be the result of the engagement of inhibitory immune checkpoint molecules with their respective ligands. Galectin-9 (Gal-9) is a tandem-repeat type galectin that possess a wide range of immunomodulatory properties such as interacting with Tim-3, which is upregulated on T cells during chronic conditions. Previously, our group has shown that interaction of Gal-9 on regulatory T cells with Tim-3 on CD8+T cells, renders these T cells more permissible to immunosuppression and subsequently leads to their exhaustion. We aimed to further study the role of Gal-9 on NK cell function in HIV patients. As a comparison, we also analyzed another inhibitory receptor known as TIGIT. Our preliminary data indicates upregulation of surface Gal-9 on NK cells in HIV infected individuals when compared to healthy controls. We observed two effector NK cell populations with dichotomous functionality. TIGIT+NK cells expressed more cytotoxic molecules (GzmB and perforin) and less IFNγ. Conversely, Gal-9+NK cells expressed less cytotoxic molecules, but more IFNγ. Additionally, Gal-9+NK cells, in contrast to Gal-9−NK cells, co-express negligible amounts of GzmB and perforin, which is detrimental to their cytotoxic abilities. We believe that understanding the underlying biochemical pathway associated with Gal-9+NK cell dysfunction can pave the way for potential therapeutic strategies.

MicroRNA profiles during galectin-9-induced apoptosis of pancreatic cancer cells.

Pancreatic cancer is the eighth-leading cause of cancer-associated mortality in males and the ninth-leading cause in females worldwide. Even when diagnosed early enough to be potentially resectable, the prognosis of invasive pancreatic cancer is poor. Galectin-9 (Gal-9) is a tandem-repeat type galectin that has recently been demonstrated to possess an anti-proliferative effect on cancer cells. Therefore, the present study evaluated the effects of Gal-9 on the proliferation of human pancreatic cancer cells and examined the microRNAs that are associated with the antitumor effects of Gal-9. Gal-9 suppressed the proliferation of multiple pancreatic cancer cell lines. In addition, Gal-9 treatment increased the levels of caspase-cleaved keratin 18 and the expression of cytochrome c in pancreatic cancer cell lines. This data suggests that Gal-9 induces intrinsic apoptosis in pancreatic cancer cell lines through the caspase-dependent and caspase-independent pathways. In addition, Gal-9 reduced the expression levels of phosphorylated epidermal growth factor receptor and numerous receptor tyrosine kinases (RTKs). In conclusion, Gal-9 may suppress the growth of human pancreatic cancer cells in vitro. These findings suggest that Gal-9 may be a new therapeutic agent for the treatment of pancreatic cancer.

A novel beta-galactose-specific lectin of the tubeworm, Ridgeia piscesae, from the hydrothermal vent

Lectins are sugar-specific binding proteins or glycoproteins that play important physiological roles in cellular recognition and regulation. And they are also valuable in medicine and pharmacy. Tubeworm is the representative species around the hydrothermal vent in the deep sea. They have developed unique mechanisms to adapt to the harsh environment. In this study, a 1 092 bp cDNA, designed as rpgal, was first cloned and characterized from the tubeworm Ridgeia piscesae. Sequence analysis showed that RPGAL had low homology with the known galectin. And it had two homologous carbohydrate-recognition domains, which is the characteristic of the tandem-repeat type galectins. The RPGAL was successfully recombinant expressed in Escherichia coli and purified. Analysis of biological activity revealed that RPGAL was metal ion independent and it could agglutinate all the vertebrate erythrocytes tested. It was stable at 10–50°C and pH 5–10. And the hemagglutinating activity of RPGAL was strongly inhibited by D-Lactose and lipopolysaccharide. Although RPGAL had no effect on the microorganisms tested, it showed anti-tumor activity towards HeLa cells and HT1080 cells, which was accomplished by apoptosis. The study demonstrated that RPGAL was a novel galectin and provided a potential candidate for therapy of anti-tumor.

Effects of galectin-9 on apoptosis, cell cycle and autophagy in human esophageal adenocarcinoma cells

The incidence of esophageal adenocarcinoma (EAC) is rapidly increasing in western countries. The overall mortality of this disease remains high with a 5-year survival rate of less than 20%, despite remarkable advances in the care of patients with EAC. Galectin-9(Gal-9) is a tandem-repeat type galectin that exerts anti-proliferative effects on various cancer cell types. The aim of the present study was to evaluate the effects of Gal-9 on human EAC cells and to assess the expression of microRNAs (miRNAs) associated with the antitumor effects of Gal-9 invitro. Gal-9 suppressed the proliferation of the EAC cell lines OE19, OE33, SK-GT4, and OACM 5.1C. Additionally, Gal-9 treatment induced apoptosis and increased the expression levels of caspase-cleaved cytokeratin 18, activated caspase-3 and activated caspase-9. However, it did not promote cell cycle arrest by reducing cell cycle-related protein levels. Furthermore, Gal-9 increased the level of the angiogenesis-related protein interleukin-8(IL-8) and markedly altered miRNA expression. Based on these findings, Gal-9 may be of clinical use for the treatment of EAC.

Heterologous expression of newly identified galectin-8 from sea urchin embryos produces recombinant protein with lactose binding specificity and anti-adhesive activity.

Galectin family members specifically bind beta-galactoside derivatives and are involved in different cellular events, including cell communication, signalling, apoptosis, and immune responses. Here, we report a tandem-repeat type galectin from the Paracentrotus lividus sea urchin embryo, referred to as Pl-GAL-8. The 933nt sequence encodes a protein of 34.73 kDa, containing the conserved HFNPRF and WGxExR motifs in the two highly similar carbohydrate-recognition domains (CRD). The three-dimensional protein structure model of the N-CRD confirms the high evolutionary conservation of carbohydrate binding sites. The temporal gene expression is regulated during development and transcripts localize at the tip of the archenteron at gastrula stage, in a subset of the secondary mesenchyme cells that differentiate into blastocoelar (immune) cells. Functional studies using a recombinant Pl-GAL-8 expressed in bacteria demonstrate its hemo-agglutinating activity on human red blood cells through the binding to lactose, as well as its ability in inhibiting the adhesion of human Hep-G2 cells to the substrate. The recent implications in autoimmune diseases and inflammatory disorders make Gal-8 an attractive candidate for therapeutic purposes. Our results offer a solid basis for addressing the use of the new Pl-GAL-8 in functional and applicative studies, respectively in the developmental and biomedical fields.

Molecular characterization of Galectin-8 from Nile tilapia (Oreochromis niloticus Linn.) and its response to bacterial infection.

Galectins belong to the family of galactoside-binding proteins and play a major role in the immune and inflammatory responses of vertebrates and invertebrates. The galectin family is divided into three subtypes based on molecular structure; prototypes, chimera types, and tandem-repeated types. We isolated and characterized the cDNA of galectin-8 (OnGal-8) in Nile tilapia (Oreochromis niloticus). OnGal-8 consisted of a 966 bp open reading frame (ORF) that encoded a 321 amino acid protein (43.47 kDa). Homology and phylogenetic tree analysis suggested the protein was clustered with galectin-8s from other animal species and shared at least 56.8% identity with salmon galectin-8. Structurally, the amino acid sequence included two distinct N- and C- terminus carbohydrate recognition domains (CRDs) of 135 and 133 amino acids, respectively, that were connected by a 39 amino acid polypeptide linker. The N- and C-CRDs contained two conserved WG-E-I and WG-E-T motifs, suggesting they have an important role in mediating the specific interactions between OnGal-8 and saccharide moieties such as β-galactoside. The structure of OnGal-8 was characterized by a two-fold symmetric pattern of 10-and 12-stranded antiparallel ß-sheets of both N- and C-CRDs, and the peptide linker presumably formed a random coil similar to the characteristic tandem-repeat type galectin. The expression of OnGal-8 in healthy fish was highest in the skin, intestine, and brain. Experimental challenge of Nile tilapia with S. agalactiae resulted in significant up-regulation of OnGal-8in the spleen after 5 d. Our results suggest that OnGal-8 is involved in the immune response to bacterial infection.

Fetal gender specific expression of tandem-repeat galectins in placental tissue from normally progressed human pregnancies and intrauterine growth restriction (IUGR)

IntroductionThe tandem-repeat type galectins, which comprise of gal-4, -6, -8, -9, and -12, form a sub-family of galectins. Gal-6 is expressed only in rodents, whereas the other four galectins, tandem-repeat galectins, are also detectable in human tissue. The placental expression of individual members of the tandem-repeat gal family is increasingly known, however, systematic, comparative analysis especially in the human placenta from normal or pathological pregnancies is still lacking. Material and MethodsWithin this study, third trimester placentas obtained at delivery (n = 14 IUGR, n = 15 controls, equally divided in placentas from male and female fetuses) were analyzed for the expression of gal-4, -8, -9 and -12 by immunohistology and immunofluorescence, data were obtained by using a semiquantitative scoring system. Double immune-fluorescence with trophoblast specific markers was used to identify co-expression in the decidua. ResultsWe identified dysregulation of tandem repeat galectins in IUGR placentas with a strong connection to the fetal gender. We identified a significantly lower expression of gal-4 and gal-9 in villous trophoblast tissue of IUGR placentas with male fetuses and a downregulation of gal-4 and gal-8 in extravillous trophoblast (EVT) from IUGR and male fetuses. Conversely, expression of gal-9 and gal-12 was higher in EVT of IUGR cases in placentas with female fetuses. Double immunofluorescence using cytokeratin-7 confirmed the expression of tandem-repeat galectins in EVT. Discussion and ConclusionThe human placenta expresses tandem-repeat type galectins in villous trophoblasts, EVT, endothelial cells and decidual stromal cells. Summarizing all effects, there is significant down-regulation of gal-4, -8 and gal-9 in the IUGR trophoblast of male fetuses. In contrast, in IUGR pregnancies with female fetus gal-9 and gal-12 are upregulated in the EVT and in endothelial cells in the cases of gal-12. Therefore we propose a fetal-gender specific action of tandem repeat galectins in IUGR placentas.

Recombinant expression, purification and preliminary biophysical and structural studies of C-terminal carbohydrate recognition domain from human galectin-4

Galectin-4 (Gal4), a tandem-repeat type galectin, is expressed in healthy epithelium of the gastrointestinal tract. Altered levels of Gal4 expression are associated with different types of cancer, suggesting its usage as a diagnostic marker as well as target for drug development. The functional data available for this class of proteins suggest that the wide spectrum of cellular activities reported for Gal4 relies on distinct glycan specificity and structural characteristics of its two carbohydrate recognition domains. In the present work, two independent constructs for recombinant expression of the C-terminal domain of human galectin-4 (hGal4-CRD2) were developed. His6-tagged and untagged recombinant proteins were overexpressed in Escherichia coli, and purified by affinity chromatography followed by gel filtration. Correct folding and activity of hGal4-CRD2 were assessed by circular dichroism and fluorescence spectroscopies, respectively. Diffraction quality crystals were obtained by vapor-diffusion sitting drop setup and the crystal structure of CRD2 was solved by molecular replacement techniques at 1.78 Å resolution. Our work describes the development of important experimental tools that will allow further studies in order to correlate structure and binding properties of hGal4-CRD2 and human galectin-4 functional activities.

Galectin-8 promotes regulatory T-cell differentiation by modulating IL-2 and TGFβ signaling.

Galectins have emerged as potent immunoregulatory molecules that control chronic inflammation through distinct mechanisms. Galectin-8 (Gal-8), a tandem-repeat type galectin with unique preference for α2,3-sialylated glycans, is ubiquitously expressed, but little is known about its role in T cell differentiation. Here, we report that Gal-8 promotes the polyclonal differentiation of primary mouse Treg cells in vitro. We further show that Gal-8 also facilitates antigen-specific differentiation of regulatory T (Treg) cells, and that Treg cells polarized in the presence of Gal-8 express cytotoxic T lymphocyte antigen-4 (CTLA-4) and IL-10 at a higher frequency than control Treg cells, and efficiently inhibit proliferation of activated T cells in vitro. Investigation of the mechanism by which Gal-8 promotes Treg conversion revealed that Gal-8 activates TGFβ signaling and promotes sustained IL-2R signaling. Taken together, these data suggest that Gal-8 promotes the differentiation of highly suppressive Treg cells, which has implications for the treatment of inflammatory and autoimmune diseases.

Specificity of human galectins on cell surfaces.

Galectins are β-galactoside-binding proteins sharing homology in amino acid sequence of their carbohydrate-recognition domain. Their carbohydrate specificity outside cells has been studied previously. The main conclusion of these studies was that several levels of glycan ligand recognition exist for galectins: (i) disaccharide Galβ1-4GlcNAc (LN, N-acetyllactosamine) binds stronger than β-galactopyranose; (ii) substitution at O-2 and O-3 of galactose residue as well as core fragments ("right" from GlcNAc) provides significant increase in affinity; (iii) similarly glycosylated proteins can differ significantly in affinity to galectins. Information about the natural cellular receptors of galectins is limited. Until recently, it was impossible to study specificity of cell-bound galectins. A model based on controlled incorporation of a single protein into glycocalyx of cells and subsequent interaction of loaded cells with synthetic glycoprobes measured by flow cytometry made this possible recently. In this review, data about glycan specificity of proto-, chimera-, and tandem-repeat type galectins on the cell surface are systematized, and comparative analysis of the results with data on specificity of galectins in artificial systems was performed. The following conclusions from these studies were made: (i) cellular galectins have practically no ability to bind disaccharide LNn, but display affinity to 3'-substituted oligolactosamines and oligomers LNn; (ii) tandem-repeat type galectins recognize another disaccharide, namely Galβ1-3GlcNAc (Le(c)); (iii) on the cell surface, tandem-repeat type galectins conserve the ability to display high affinity to blood group antigens of ABH system; (iv) in general, when galectins are immersed into glycocalyx, they are more selective regarding glycan interactions. Thus, we conclude that competitive interaction of galectins with cell microenvironment (endogenous cell glycans) is the main factor providing selectivity of galectins in vivo.

Galectin-9 in Cancer Therapy

Galectin-9 is a tandem-repeat type galectin with two carbohydrate-recognition domains, and it was first identified as an eosinophil chemoattractant and activation factor. Subsequent studies revealed that galectin-9, similar to other galectins, modulates a variety of biological functions including cell aggregation and adhesion, as well as apoptosis of tumor cells. Galectin-9 has recently been shown to have an anti-proliferative effect on cancer cells. Recent studies have uncovered additional mechanisms by which T cell immunoglobulin mucin-3 (Tim-3), a receptor for galectin-9, negatively regulates T cell responses by promoting CD8+ T cell exhaustion and inducing expansion of myeloid-derived suppressor cells. These mechanisms are involved in tumor growth and escape from immunity. In many solid cancers, the loss of galectin-9 expression is closely associated with metastatic progression, and treatment with recombinant galectin-9 prevents metastatic spread in various preclinical cancer models. Here, we review the biology and physiological role of galectin-9, and discuss the therapeutic potential of galectin-9 in cancer as well as relevant patents.

Sugar-Binding Properties of the Two Lectin Domains of LEC-1 with Respect to the Gal.BETA.1-4Fuc Disaccharide Unit Present in Protostomia Glycoconjugates

Galβ1-4Fuc disaccharide unit was recently reported to be the endogenous structure recognized by the galectin LEC-6 isolated from the nematode Caenorhabditis elegans. LEC-1, which is another major galectin from this organism, is a tandem repeat-type galectin that contains two carbohydrate recognition domains, the N-terminal lectin domain (LEC-1Nh) and the C-terminal lectin domain (LEC-1Ch), and was also found to have an affinity for the Galβ1-4Fuc disaccharide unit. In the present study, we compared the binding strengths of LEC-1, LEC-1Nh, and LEC-1Ch to Galβ1-4Fuc, Galβ1-3Fuc, and Galβ1-4GlcNAc units as well as to LEC-6-ligand N-glycans by using frontal affinity chromatography (FAC) analysis. The two lectin domains of LEC-1 exhibited the highest affinity for Galβ1-4Fuc, though sugar-binding properties differed somewhat between LEC-1Nh and LEC-1Ch. Furthermore, these two domains had significantly lower affinities for the LEC-6-binding glycans. These results suggest that the endogenous recognition unit of LEC-1 is likely to be Galβ1-4Fuc, and that the endogenous ligands for LEC-1 are different from those for LEC-6.