Strikingly different localization of galectin-3 and galectin-4 in human colon adenocarcinoma T84 cells. Galectin-4 is localized at sites of cell adhesion

Multifaceted roles of Galectins: from carbohydrate binding to targeted cancer therapy

Galectins play pivotal roles in cellular recognition and signaling processes by interacting with glycoconjugates. Extensive research has highlighted the significance of Galectins in the context of cancer, aiding in the identification of biomarkers for early detection, personalized therapy, and predicting treatment responses. This review offers a comprehensive overview of the structural characteristics, ligand-binding properties, and interacting proteins of Galectins. We delve into their biological functions and examine their roles across various cancer types. Galectins, characterized by a conserved carbohydrate recognition domain (CRD), are divided into prototype, tandem-repeat, and chimera types based on their structural configurations. Prototype Galectins contain a single CRD, tandem-repeat Galectins contain two distinct CRDs linked by a peptide, and the chimera-type Galectin-3 features a unique structural arrangement. The capacity of Galectins to engage in multivalent interactions allows them to regulate a variety of signaling pathways, thereby affecting cell fate and function. In cancer, Galectins contribute to tumor cell transformation, angiogenesis, immune evasion, and metastasis, making them critical targets for therapeutic intervention. This review discusses the multifaceted roles of Galectins in cancer progression and explores current advancements in the development of Galectin-targeted therapies. We also address the challenges and future directions for integrating Galectin research into clinical practice to enhance cancer treatment outcomes. In brief, understanding the complex functions of Galectins in cancer biology opens new avenues for therapeutic strategies. Continued research on Galectin interactions and their pathological roles is essential for developing effective carbohydrate-based treatments and improving clinical interventions for cancer patients.

A comprehensive study on the multifunctional properties of galectin-4 in red-lip mullet (Planiliza haematocheilus): Insights into molecular interactions, antimicrobial defense, and cell proliferation

Galectin-4 belongs to the galactoside-binding protein family and is a type of tandem repeat galectin. Despite previous studies indicating its importance in fish immunology, a comprehensive investigation is necessary to fully understand its role in immunomodulatory functions and cellular dynamics. Therefore, this study aimed to explore the immunomodulatory functions of galectin-4 with a particular focus on its antimicrobial and cellular proliferative properties. The open reading frame of PhGal4 spans 1092 base pairs and encodes a soluble protein of 363 amino acids with a theoretical isoelectric point (IEP) of 6.39 and a molecular weight of 39.411 kDa. Spatial expression analysis under normal physiological conditions revealed ubiquitous expression of PhGal4 across all examined tissues, with the highest level observed in intestinal tissue. Upon stimulation with poly I:C, LPS, and L. garvieae, a significant increase (p < 0.05) in PhGal4 expression was observed in both blood and spleen tissues. Subsequent subcellular localization assay demonstrated that PhGal4 was predominantly localized in the cytoplasm. The recombinant PhGal4 (rPhGal4) exhibited specific binding capabilities to pathogen-associated molecular patterns (PAMPs), including LPS and peptidoglycan, but not poly I:C. The rPhGal4 negatively affected the bacterial growth kinetics. Additionally, rPhGal4 demonstrated complete hemagglutination of fish erythrocytes, which could be inhibited by the presence of D-galactose and α-lactose. The overexpression of PhGal4 in FHM epithelial cells demonstrated a significant suppression of viral replication during VHSV infection. Furthermore, the in vitro scratch assay and WST-1 assay demonstrated a wound healing effect of PhGal4 overexpression in FHM cells, potentially achieved through the promotion of cell proliferation by activating genes involved in cell cycle regulation. In conclusion, the responsive expression to immune stimuli, antimicrobial properties, and cell proliferation promotion of PhGal4 suggest that it plays a crucial role in immunomodulation and cellular dynamics of red-lip mullet. The findings in this study shed light on the multifunctional nature of galectin-4 in teleost fish.

Galectin-4 Antimicrobial Activity Primarily Occurs Through its C-Terminal Domain

Although immune tolerance evolved to reduce reactivity with self, it creates a gap in the adaptive immune response against microbes that decorate themselves in self-like antigens. This is particularly apparent with carbohydrate-based blood group antigens, wherein microbes can envelope themselves in blood group structures similar to human cells. In this study, we demonstrate that the innate immune lectin, galectin-4 (Gal-4), exhibits strain-specific binding and killing behavior towards microbes that display blood group-like antigens. Examination of binding preferences using a combination of microarrays populated with ABO(H) glycans and a variety of microbial strains, including those that express blood group-like antigens, demonstrated that Gal-4 binds mammalian and microbial antigens that have features of blood group and mammalian-like structures. Although Gal-4 was thought to exist as a monomer that achieves functional bivalency through its two linked carbohydrate recognition domains, our data demonstrate that Gal-4 forms dimers and that differences in the intrinsic ability of each domain to dimerize likely influences binding affinity. While each Gal-4 domain exhibited blood group-binding activity, the C-terminal domain (Gal-4C) exhibited dimeric properties, while the N-terminal domain (Gal-4N) failed to similarly display dimeric activity. Gal-4C not only exhibited the ability to dimerize but also possessed higher affinity toward ABO(H) blood group antigens and microbes expressing glycans with blood group-like features. Furthermore, when compared to Gal-4N, Gal-4C exhibited more potent antimicrobial activity. Even in the context of the full-length protein, where Gal-4N is functionally bivalent by virtue of Gal-4C dimerization, Gal-4C continued to display higher antimicrobial activity. These results demonstrate that Gal-4 exists as a dimer and exhibits its antimicrobial activity primarily through its C-terminal domain. In doing so, these data provide important insight into key features of Gal-4 responsible for its innate immune activity against molecular mimicry.

Oligosaccharide Ligands of Galectin-4 and Its Subunits: Multivalency Scores Highly

Galectins are carbohydrate-binding lectins that modulate the proliferation, apoptosis, adhesion, or migration of cells by cross-linking glycans on cell membranes or extracellular matrix components. Galectin-4 (Gal-4) is a tandem-repeat-type galectin expressed mainly in the epithelial cells of the gastrointestinal tract. It consists of an N- and a C-terminal carbohydrate-binding domain (CRD), each with distinct binding affinities, interconnected with a peptide linker. Compared to other more abundant galectins, the knowledge of the pathophysiology of Gal-4 is sparse. Its altered expression in tumor tissue is associated with, for example, colon, colorectal, and liver cancers, and it increases in tumor progression, and metastasis. There is also very limited information on the preferences of Gal-4 for its carbohydrate ligands, particularly with respect to Gal-4 subunits. Similarly, there is virtually no information on the interaction of Gal-4 with multivalent ligands. This work shows the expression and purification of Gal-4 and its subunits and presents a structure-affinity relationship study with a library of oligosaccharide ligands. Furthermore, the influence of multivalency is demonstrated in the interaction with a model lactosyl-decorated synthetic glycoconjugate. The present data may be used in biomedical research for the design of efficient ligands of Gal-4 with diagnostic or therapeutic potential.

Galectin-4 as a Novel Biomarker of Neonatal Intestinal Injury

BACKGROUND

Neonates are at risk of gastrointestinal emergencies including necrotizing enterocolitis (NEC) and spontaneous intestinal perforation (SIP). Identifying biomarkers to aid in diagnosis is imperative. We hypothesized that circulating intestinal-specific protein concentrations would distinguish infants with intestinal injury from controls.

AIMS

To identify serum concentrations of intestinal-specific protein(s) in infants with intestinal injury and controls.

METHODS

We used an in silico approach to identify intestinal-specific proteins. We collected serum from control infants and infants with NEC or SIP and measured protein concentrations using ELISA. If baseline concentrations were near the detection limit in initial control assays, we proceeded to assess concentrations in a larger cohort of controls and infants with injury. Control infants were frequency matched to infants with injury and compared with nonparametric and mixed-effects models analysis.

RESULTS

We evaluated four proteins with high intestinal expression: Galectin-4 (Gal-4), S100G, Trefoil Factor-3, and alanyl aminopeptidase. Only Gal-4 demonstrated consistent results near the lower limit of quantification in controls and was studied in the larger cohorts. Gal-4 concentration was low in 111 control infants (median 0.012 ng/ml). By contrast, Gal-4 was significantly increased at diagnosis in infants with surgical NEC and SIP (n = 14, p ≤ 0.001 and n = 8, p = 0.031) compared to matched controls, but not in infants with medical NEC (n = 32, p = 0.10).

CONCLUSIONS

Of the intestinal-specific proteins evaluated, circulating Gal-4 concentrations were at the assay detection limit in control infants. Gal-4 concentrations were significantly elevated in infants with surgical NEC or SIP, suggesting that Gal-4 may serve as a biomarker for neonatal intestinal injury.

SepA Enhances Shigella Invasion of Epithelial Cells by Degrading Alpha-1 Antitrypsin and Producing a Neutrophil Chemoattractant

Shigella spp. are highly adapted pathogens that cause bacillary dysentery in human and nonhuman primates. An unusual feature of Shigella pathogenesis is that this organism invades the colonic epithelia from the basolateral pole. Therefore, it has evolved the ability to disrupt the intestinal epithelial barrier to reach the basolateral surface. We have shown previously that the secreted serine protease A (SepA), which belongs to the family of serine protease autotransporters of Enterobacteriaceae, is responsible for the initial destabilization of the intestinal epithelial barrier that facilitates Shigella invasion. However, the mechanisms used by SepA to regulate this process remain unknown. To investigate the protein targets cleaved by SepA in the intestinal epithelium, we incubated a sample of homogenized human colon with purified SepA or with a catalytically inactive mutant of this protease. We discovered that SepA targets an array of 18 different proteins, including alpha-1 antitrypsin (AAT), a major circulating serine proteinase inhibitor in humans. In contrast to other serine proteases, SepA cleaved AAT without forming an inhibiting complex, which resulted in the generation of a neutrophil chemoattractant. We demonstrated that the products of the AAT-SepA reaction induce a mild but significant increase in neutrophil transepithelial migration in vitro. Moreover, the presence of AAT during Shigella infection stimulated neutrophil migration and dramatically enhanced the number of bacteria invading the intestinal epithelium in a SepA-dependent manner. We conclude that by cleaving AAT, SepA releases a chemoattractant that promotes neutrophil migration, which in turn disrupts the intestinal epithelial barrier to enable Shigella invasion. IMPORTANCE Shigella is the second leading cause of diarrheal death globally. In this study, we identified the host protein targets of SepA, Shigella's major protein secreted in culture. We demonstrated that by cleaving AAT, a serine protease inhibitor important to protect surrounding tissue at inflammatory sites, SepA releases a neutrophil chemoattractant that enhances Shigella invasion. Moreover, SepA degraded AAT without becoming inhibited by the cleaved product, and SepA catalytic activity was enhanced at higher concentrations of AAT. Activation of SepA by an excess of AAT may be physiologically relevant at the early stages of Shigella infection, when the amount of synthesized SepA is very low compared to the concentration of AAT in the intestinal lumen. This observation may also help to explain the adeptness of Shigella infectivity at low dose, despite the requirement of reaching the basolateral side to invade and colonize the colonic epithelium.

Getting Your Neutrophil: Neutrophil Transepithelial Migration in the Lung

Neutrophil transepithelial migration is a fundamental process that facilitates the rapid trafficking of neutrophils to inflammatory foci and occurs across a diverse range of tissues. For decades there has been widespread interest in understanding the mechanisms that drive this migratory process in response to different pathogens and organ systems. This has led to the successful integration of key findings on neutrophil transepithelial migration from the intestines, lungs, liver, genitourinary tract, and other tissues into a single, cohesive model. However, recent studies have identified organ specific differences in neutrophil transepithelial migration. These findings support a model where the tissue in concert with the pro-inflammatory stimuli dictate a unique collection of signals that drive neutrophil trafficking. This review focuses on the mechanisms that drive neutrophil transepithelial migration in response to microbial infection of a single organ, the lung. Herein we provide a detailed analysis of the adhesion molecules and chemoattractants that contribute to the recruitment of neutrophil into the airways. We also highlight important advances in experimental models for studying neutrophil transepithelial migration in the lung over the last decade.

Identifying Cell-Type Specific Genes and Expression Rules Based on Single-Cell Transcriptomic Atlas Data

Single-cell sequencing technologies have emerged to address new and longstanding biological and biomedical questions. Previous studies focused on the analysis of bulk tissue samples composed of millions of cells. However, the genomes within the cells of an individual multicellular organism are not always the same. In this study, we aimed to identify the crucial and characteristically expressed genes that may play functional roles in tissue development and organogenesis, by analyzing a single-cell transcriptomic atlas of mice. We identified the most relevant gene features and decision rules classifying 18 cell categories, providing a list of genes that may perform important functions in the process of tissue development because of their tissue-specific expression patterns. These genes may serve as biomarkers to identify the origin of unknown cell subgroups so as to recognize specific cell stages/states during the dynamic process, and also be applied as potential therapy targets for developmental disorders.

Immunological Effects of Human Milk Oligosaccharides

Human milk oligosaccharides (HMOs) comprise a group of structurally complex, unconjugated glycans that are highly abundant in human milk. HMOs are minimally digested in the gastrointestinal tract and reach the colon intact, where they shape the microbiota. A small fraction of HMOs is absorbed, reaches the systemic circulation, and is excreted in urine. HMOs can bind to cell surface receptors expressed on epithelial cells and cells of the immune system and thus modulate neonatal immunity in the infant gut, and possibly also sites throughout the body. In addition, they have been shown to act as soluble decoy receptors to block the attachment of various microbial pathogens to cells. This review summarizes the current knowledge of the effects HMOs can have on infections, allergies, auto-immune diseases and inflammation, and will focus on the role of HMOs in altering immune responses through binding to immune-related receptors.

Pathobiology of neutrophil-epithelial interactions

Polymorphonuclear neutrophils (PMNs) are innate immune system cells that play an essential role in eradicating invading pathogens. PMN migration to sites of infection/inflammation requires exiting the microcirculation and subsequent crossing of epithelial barriers in mucosa-lined organs such as the lungs and intestines. Although these processes usually occur without significant damage to surrounding host tissues, dysregulated/excessive PMN transmigration and resultant bystander-tissue damage are characteristic of numerous mucosal inflammatory disorders. Mechanisms controlling PMN extravasation have been well characterized, but the molecular details regarding regulation of PMN migration across mucosal epithelia are poorly understood. Given that PMN migration across mucosal epithelia is strongly correlated with disease symptoms in many inflammatory mucosal disorders, enhanced understanding of the mechanisms regulating PMN transepithelial migration should provide insights into clinically relevant tissue-targeted therapies aimed at ameliorating PMN-mediated bystander-tissue damage. This review will highlight current understanding of the molecular interactions between PMNs and mucosal epithelia and the associated functional consequences.

Bactericidal activity of fish galectin 4 derived membrane-binding peptide tagged with oligotryptophan

Galectins belong to the family of galactoside-binding proteins which act as pathogen recognition receptors by recognizing and binding to the carbohydrate present in the bacterial membranes. In this study, a Galectin-4 sequence was identified from the constructed cDNA library of Channa striatus and its structural features were reported. Gene expression analysis revealed that CsGal4 was highly expressed in liver and strongly induced by Epizootic Ulcerative Syndrome (EUS) causing pathogens such as Aphanomyces invadans, Aeromonas hydrophila and a viral analogue, poly I:C. To understand the antimicrobial role of putative dimerization site of CsGal4, the region was chemically synthesized and its bactericidal effect was determined. G4 peptide exhibited a weak bactericidal activity against Vibrio harveyi, an important aquaculture pathogen. We have also determined the bactericidal activity of the dimerization site by tagging pentamer oligotryptophan (W5) at the C-terminal of G4 peptide. Flow cytometry analysis revealed that G4W induced drastic reduction in cell counts than G4. Electron microscopic images showed membrane blebbings in V. harveyi which indicated the membrane disrupting activity of G4W. Interestingly, both the peptides did not exhibit any hemolytic activity and cytotoxicity towards peripheral blood cells of Channa striatus and the activity was specific only towards the bacterial membrane. Our results suggested that addition of W5 at the C-terminal of membrane-binding peptide remarkably improved its membrane disrupting activity.

Full-length model of the human galectin-4 and insights into dynamics of inter-domain communication

Galectins are proteins involved in diverse cellular contexts due to their capacity to decipher and respond to the information encoded by β-galactoside sugars. In particular, human galectin-4, normally expressed in the healthy gastrointestinal tract, displays differential expression in cancerous tissues and is considered a potential drug target for liver and lung cancer. Galectin-4 is a tandem-repeat galectin characterized by two carbohydrate recognition domains connected by a linker-peptide. Despite their relevance to cell function and pathogenesis, structural characterization of full-length tandem-repeat galectins has remained elusive. Here, we investigate galectin-4 using X-ray crystallography, small- and wide-angle X-ray scattering, molecular modelling, molecular dynamics simulations, and differential scanning fluorimetry assays and describe for the first time a structural model for human galectin-4. Our results provide insight into the structural role of the linker-peptide and shed light on the dynamic characteristics of the mechanism of carbohydrate recognition among tandem-repeat galectins.

Metastatic Progression of Prostate Cancer Is Mediated by Autonomous Binding of Galectin-4-O-Glycan to Cancer Cells

Metastatic prostate cancer continues to pose a difficult therapeutic challenge. Prostate cancer progression is associated with aberrant O-glycosylation of cancer cell surface receptors, but the functional impact of such events is uncertain. Here we report spontaneous metastasis of human prostate cancer xenografts that express high levels of galectin-4 along with genetic signatures of EGFR-HER2 signaling and O-glycosylation. Galectin-4 expression in clinical specimens of prostate cancer correlated with poor patient survival. Galectin-4 binding to multiple receptor tyrosine kinases stimulated their autophosphorylation, activated expression of pERK, pAkt, fibronectin, and Twist1, and lowered expression of E-cadherin, thereby facilitating epithelial-mesenchymal transition, invasion, and metastasis. In vivo investigations established that galectin-4 expression enabled prostate cancer cells to repopulate tumors in orthotopic and heterotopic tissues. Notably, these effects of galectin-4 relied upon O-glycosylation mediated by C1GALT1, a galactosyltransferase implicated in other cancers. Parallel changes in galectin-4 and O-glycosylation triggered aberrant receptor signaling and more aggressive invasive character in prostate cancer cells, which through better survival in the circulation also contributed to the bulk cell progeny of distal tumors. Our findings establish galectin-4 and C1GALT1-mediated glycosylation in a signaling axis that is activated during prostate cancer progression, with implications for therapeutic targeting of advanced metastatic disease. Cancer Res; 76(19); 5756-67. ©2016 AACR.

The role of galectin-4 in physiology and diseases

Galectin-4, a tandem repeat member of the β-galactoside-binding proteins, possesses two carbohydrate-recognition domains (CRD) in a single peptide chain. This lectin is mostly expressed in epithelial cells of the intestinal tract and secreted to the extracellular. The two domains have 40% similarity in amino acid sequence, but distinctly binding to various ligands. Just because the two domains bind to different ligands simultaneously, galectin-4 can be a crosslinker and crucial regulator in a large number of biological processes. Recent evidence shows that galectin-4 plays an important role in lipid raft stabilization, protein apical trafficking, cell adhesion, wound healing, intestinal inflammation, tumor progression, etc. This article reviews the physiological and pathological features of galectin-4 and its important role in such processes.

Structural characterisation of human galectin-4 N-terminal carbohydrate recognition domain in complex with glycerol, lactose, 3'-sulfo-lactose, and 2'-fucosyllactose

Galectin-4 is a tandem-repeat galectin with two distinct carbohydrate recognition domains (CRD). Galectin-4 is expressed mainly in the alimentary tract and is proposed to function as a lipid raft and adherens junction stabilizer by its glycan cross-linking capacity. Galectin-4 plays divergent roles in cancer and inflammatory conditions, either promoting or inhibiting each disease progression, depending on the specific pathological condition. The study of galectin-4's ligand-binding profile may help decipher its roles under specific conditions. Here we present the X-ray structures of human galectin-4 N-terminal CRD (galectin-4N) bound to different saccharide ligands. Galectin-4's overall fold and its core interactions to lactose are similar to other galectin CRDs. Galectin-4N recognises the sulfate cap of 3'-sulfated glycans by a weak interaction through Arg45 and two water-mediated hydrogen bonds via Trp84 and Asn49. When galectin-4N interacts with the H-antigen mimic, 2'-fucosyllactose, an interaction is formed between the ring oxygen of fucose and Arg45. The extended binding site of galectin-4N may not be well suited to the A/B-antigen determinants, α-GalNAc/α-Gal, specifically due to clashes with residue Phe47. Overall, galectin-4N favours sulfated glycans whilst galectin-4C prefers blood group determinants. However, the two CRDs of galectin-4 can, to a less extent, recognise each other's ligands.

Immunohistochemical Studies on Galectin Expression in Colectomised Patients with Ulcerative Colitis

Introduction. The aetiology and pathogenesis of ulcerative colitis (UC) are essentially unknown. Galectins are carbohydrate-binding lectins involved in a large number of physiological and pathophysiological processes. Little is known about the role of galectins in human UC. In this immunohistochemical exploratory study, both epithelial and inflammatory cell galectin expression were studied in patients with a thoroughly documented clinical history and were correlated with inflammatory activity. Material and Methods. Surgical whole intestinal wall colon specimens from UC patients (n = 22) and controls (n = 10) were studied. Clinical history, pharmacological treatment, and modified Mayo-score were recorded. Tissue inflammation was graded, and sections were stained with antibodies recognizing galectin-1, galectin-2, galectin-3, and galectin-4. Results. Galectin-1 was undetectable in normal and UC colonic epithelium, while galectin-2, galectin-3, and galectin-4 were strongly expressed. A tendency towards diminished epithelial expression with increased inflammatory grade for galectin-2, galectin-3, and galectin-4 was also found. In the inflammatory cells, a strong expression of galectin-2 and a weak expression of galectin-3 were seen. No clear-cut correlation between epithelial galectin expression and severity of the disease was found. Conclusion. Galectin expression in patients with UC seems to be more dependent on disease focality and individual variation than on degree of tissue inflammation.

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

INTRODUCTION

The 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 METHODS

Within 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.

RESULTS

We 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 CONCLUSION

The 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.

The role of Galectin-1 and Galectin-3 in the mucosal immune response to Citrobacter rodentium infection

Despite their abundance at gastrointestinal sites, little is known about the role of galectins in gut immune responses. We have therefore investigated the Citrobacter rodentium model of colonic infection and inflammation in Galectin-1 or Galectin-3 null mice. Gal-3 null mice showed a slight delay in colonisation after inoculation with C. rodentium and a slight delay in resolution of infection, associated with delayed T cell, macrophage and dendritic cell infiltration into the gut mucosa. However, Gal-1 null mice also demonstrated reduced T cell and macrophage responses to infection. Despite the reduced T cell and macrophage response in Gal-1 null mice, there was no effect on C. rodentium infection kinetics and pathology. Overall, Gal-1 and Gal-3 play only a minor role in immunity to a gut bacterial pathogen.

Intracellular galectins in cancer cells: potential new targets for therapy (Review)

Dysregulation of galectin expression is frequently observed in cancer tissues. Such an abnormal expression pattern often correlates with aggressiveness and relapse in many types of cancer. Because galectins have the ability to modulate functions that are important for cell survival, migration and metastasis, they also represent attractive targets for cancer therapy. This has been well-exploited for extracellular galectins, which bind glycoconjugates expressed on the surface of cancer cells. Although the existence of intracellular functions of galectins has been known for many years, an increasing number of studies indicate that these proteins can also alter tumor progression through their interaction with intracellular ligands. In fact, in some instances, the interactions of galectins with their intracellular ligands seem to occur independently of their carbohydrate recognition domain. Such findings call for a change in the basic assumptions, or paradigms, concerning the activity of galectins in cancer and may force us to revisit our strategies to develop galectin antagonists for the treatment of cancer.

Galectin-4 Reduces Migration and Metastasis Formation of Pancreatic Cancer Cells

Galectin-4 (Gal-4) is a member of the galectin family of glycan binding proteins that shows a significantly higher expression in cystic tumors of the human pancreas and in pancreatic adenocarcinomas compared to normal pancreas. However, the putative function of Gal-4 in tumor progression of pancreatic cancer is still incompletely understood. In this study the role of Gal-4 in cancer progression was investigated, using a set of defined pancreatic cancer cell lines, Pa-Tu-8988S (PaTu-S) and Pa-Tu-8988T (PaTu-T), as a model. These two cell lines are derived from the same liver metastasis of a human primary pancreatic adenocarcinoma, but differ in their growth characteristics and metastatic capacity. We demonstrated that Gal-4 expression is high in PaTu-S, which shows poor migratory properties, whereas much lower Gal-4 levels are observed in the highly metastatic cell line PaTu-T. In PaTu-S, Gal-4 is found in the cytoplasm, but it is also secreted and accumulates at the membrane at sites of contact with neighboring cells. Moreover, we show that Gal-4 inhibits metastasis formation by delaying migration of pancreatic cancer cells in vitro using a scratch assay, and in vivo using zebrafish (Danio rerio) as an experimental model. Our data suggest that Gal-4 may act at the cell-surface of PaTu-S as an adhesion molecule to prevent release of the tumor cells, but has in addition a cytosolic function by inhibiting migration via a yet unknown mechanism.

Detection of galectin-3 interaction with commensal bacteria

A panel of commensal bacteria was screened for the ability to interact with galectin-3. Two strains of Bifidobacterium longum subsp. infantis interacted to a greater extent than did the pathogenic positive control, Escherichia coli NCTC 12900. Further validation of the interaction was achieved by using agglutination and solid-phase binding assays.

Expression patterns suggest that despite considerable functional redundancy, galectin-4 and -6 play distinct roles in normal and damaged mouse digestive tract

The galectin-4 protein is mostly expressed in the digestive tract and is associated with lipid raft stabilization, protein apical trafficking, wound healing, and inflammation. While most mammalian species, including humans, have a single Lgals4 gene, some mice have two paralogues: Lgals4 and Lgals6. So far, their significant similarities have hindered the analysis of their respective expression and function. We took advantage of two antibodies that discriminate between the galectin-4 and galectin-6 proteins to document their patterns of expression in the normal and the dextran sodium sulfate (DSS)-damaged digestive tract in the mouse. In the normal digestive tract, their pattern of expression from tongue to colon is quite similar, which suggests functional redundancy. However, the presence of galectin-4, but not galectin-6, in the lamina propria of the DSS-damaged colon, its association with luminal colonic bacteria, and differences in subcellular localization of these proteins suggest that they also have distinct roles in the normal and the damaged mouse digestive tract. Our results provide a rare example of ancestral and derived functions evolving after tandem gene duplication.

Galectin-4, a novel neuronal regulator of myelination

Myelination of axons by oligodendrocytes (OLGs) is essential for proper saltatory nerve conduction, i.e., rapid transmission of nerve impulses. Among others, extracellular matrix (ECM) molecules, neuronal signaling, and axonal adhesion regulate the biogenesis and maintenance of myelin membranes, driven by polarized transport of myelin-specific proteins and lipids. Galectin-4, a tandem-repeat-type lectin with affinity to sulfatide and nonsialylated termini of N-glycans, has the ability to regulate adhesion of cells to ECM components and is also involved in polarized membrane trafficking. We, therefore, anticipated that galectin-4 might play a role in myelination. Here, we show that in developing postnatal rat brains galectin-4 expression is downregulated just before the onset of myelination. Intriguingly, when immature OLGs were treated with galectin-4, OLG maturation was retarded, while a subset of the immature OLGs reverted to a morphologically less complex progenitor stage, displaying concomitantly an increase in proliferation. Similarly, myelination was inhibited when galectin-4 or anti-galectin-4 antibodies were added to co-cultures of dorsal root ganglion neurons and OLGs. Neurons and OLGs were identified as a possible source of galectin-4, both in vitro and in vivo. In culture, neurons but not OLGs released galectin-4. Interestingly, in co-cultures, a reduced release of endogenous galectin-4 correlated with the onset of myelination. Moreover, galectin-4-reactive sites are transiently expressed on processes of premyelinating primary OLGs, but not on neurons. Taken together, these results identify neuronal galectin-4 as a candidate for a soluble regulator of OLG differentiation and, hence, myelination. © 2012 Wiley Periodicals, Inc.

Glycan recognition at the interface of the intestinal immune system: target for immune modulation via dietary components

The intestinal mucosa is constantly exposed to the luminal content, which includes micro-organisms and dietary components. Prebiotic non-digestible oligosaccharides may be supplemented to the diet to exert modulation of immune responses in the intestine. Short chain galacto- and long chain fructo-oligosaccharides (scGOS/lcFOS), functionally mimicking oligosaccharides present in human milk, have been reported to reduce the development of allergy through modulation of the intestinal microbiota and immune system. Nonetheless, the underlying working mechanisms of scGOS/lcFOS are unclear. Intestinal epithelial cells lining the mucosa are known to express carbohydrate (glycan)-binding receptors that may be involved in modulation of the mucosal immune response. This review aims to provide an overview of glycan-binding receptors, in particular galectins, which are expressed by intestinal epithelial cells and immune cells. In addition, their involvement in health and disease will be addressed, especially in food allergy and inflammatory bowel disease, diseases originating from the gastro-intestinal tract. Insight in the recognition of glycans in the intestinal tract may open new avenues for the treatment of intestinal inflammatory diseases by either nutritional concepts or pharmacological intervention.

The role of galectins in colorectal cancer progression

Galectins constitute a family of 15 mammalian galactoside-binding proteins that share a consensus amino acid sequence in their carbohydrate binding sites. They are multi-functional molecules and are expressed widely in human tissues. Four galectins: galectin -1, -3, -4 and -8 are expressed in the human colon and rectum and their expressions show significant changes during colorectal cancer development and metastasis. These changes in galectin expression correlate with alterations in cancer cell growth, apoptosis, cell-cell and cell-matrix interactions and angiogenesis. This review summaries current knowledge of the expression and roles of these galectins in the progression of human colorectal cancer and discusses the relevance of galectins and their ligands as potential therapeutic targets for cancer treatment.

Matrilysin-1 (MMP7) cleaves galectin-3 and inhibits wound healing in intestinal epithelial cells

BACKGROUND

Galectin-3 is an animal lectin that has been implicated in wound healing and is decreased in inflammatory bowel disease (IBD). Matrix metalloproteinase-7 (MMP7), also known as matrilysin-1, a protease shown to cleave extracellular matrix proteins, is highly expressed in IBD tissues, especially at the leading edge of gastrointestinal ulcers. The ability of MMP7 to cleave galectin-3 and influence wound healing has not been reported previously. The aim was to determine whether MMP7 cleaves galectin-3 and modulates wound healing in intestinal epithelial cells.

METHODS

The cleaved fragments of galectin-3 were identified by N-terminal sequencing and mass spectrometry. Western blotting was used to detect the cleaved galectin-3 products in a colonic epithelial cell line (T84 cells). Cell migration was studied by the in vitro scratch method.

RESULTS

We demonstrate for the first time that MMP7 cleaves galectin-3 in vitro, resulting in three cleaved fragments (20.2 kDa, 18.9 kDa, and 15.5 kDa). Exogenous treatment of T84 cells with recombinant MMP7 resulted in the appearance of secreted galectin-3 cleavage fragments in the supernatant. MMP7 inhibited cell migration and resulted in wound retraction and the addition of MMP7 to galectin-3 abrogated the wound healing and cell migration induced by galectin-3.

CONCLUSIONS

We have demonstrated that galectin-3 is a substrate for MMP7. Cleavage of galectin-3 may be one mechanism by which MMP7 inhibits wound healing. This study has significance in understanding delayed wound healing in chronic intestinal diseases like intestinal ulcers and IBD, where MMP7 protein expression is elevated with a decreased galectin-3 protein expression.

Shiga toxin 1 interaction with enterocytes causes apical protein mistargeting through the depletion of intracellular galectin-3

Shiga toxins (Stx) 1 and 2 are responsible for intestinal and systemic sequelae of infection by enterohemorrhagic Escherichia coli (EHEC). However, the mechanisms through which enterocytes are damaged remain unclear. While secondary damage from ischemia and inflammation are postulated mechanisms for all intestinal effects, little evidence excludes roles for more primary toxin effects on intestinal epithelial cells. We now document direct pathologic effects of Stx on intestinal epithelial cells. We study a well-characterized rabbit model of EHEC infection, intestinal tissue and stool samples from EHEC-infected patients, and T84 intestinal epithelial cells treated with Stx1. Toxin uptake by intestinal epithelial cells in vitro and in vivo causes galectin-3 depletion from enterocytes by increasing the apical galectin-3 secretion. This Shiga toxin-mediated galectin-3 depletion impairs trafficking of several brush border structural proteins and transporters, including villin, dipeptidyl peptidase IV, and the sodium-proton exchanger 2, a major colonic sodium absorptive protein. The mistargeting of proteins responsible for the absorptive function might be a key event in Stx1-induced diarrhea. These observations provide new evidence that human enterocytes are directly damaged by Stx1. Conceivably, depletion of galectin-3 from enterocytes and subsequent apical protein mistargeting might even provide a means whereby other pathogens might alter intestinal epithelial absorption and produce diarrhea.

The role of galectins in protein trafficking

The galectins, a family of lectins, modulate distinct cellular processes, such as cancer progression, immune response and cellular development, through their specific binding to extracellular or intracellular ligands. In the past few years, research has unravelled interactions of different galectins with lipids and glycoproteins in the outer milieu or in the secretory pathway of cells. Interestingly, these lectins do not possess a signalling sequence to enter the endoplasmic reticulum as a starting point for the classical secretory pathway. Instead they use a so-called non-classical mechanism for translocation across the plasma membrane and/or into the lumen of transport vesicles. Here, they stabilize transport platforms for apical trafficking or sort apical glycoproteins into specific vesicle populations. Modes of ligand interaction as well as the modulation of binding activities and trafficking pathways are discussed in this review.

Immunohistochemical localization of six galectin subtypes in the mouse digestive tract

Galectin, an animal lectin that recognizes beta-galactoside of glycoconjugates, is abundant in the gut. This IHC study showed the subtype-specific localization of galectin in the mouse digestive tract. Mucosal epithelium showed region/cell-specific localization of each galectin subtype. Gastric mucous cells exhibited intense immunoreactions for galectin-2 and galectin-4/6 with a limited localization of galectin-3 at the surface of the gastric mucosa. Electron microscopically, galectin-3 immunoreactivity coated indigenous bacteria on the gastric surface mucous cells. Epithelial cells in the small intestine showed characteristic localizations of galectin-2 and galectin-4/6 in the cytoplasm of goblet cells and the baso-lateral membrane of enterocytes in association with maturation, respectively. Galectin-3 expressed only at the villus tips was concentrated at the myosin-rich terminal web of fully matured enterocytes. Epithelial cells of the large intestine contained intense immunoreactions for galectin-3 and galectin-4/6 but not for galectin-2. The stratified squamous epithelium of the forestomach was immunoreactive for galectin-3 and galectin-7, but the basal layer lacked galectin-3 immunoreactivity. Outside the epithelium, only galectin-1 was localized in the connective tissue, smooth muscles, and neuronal cell bodies. The subtype-specific localization of galectin suggests its important roles in host-pathogen interaction and epithelial homeostasis such as membrane polarization and trafficking in the gut.

The galectin family and digestive disease

The soluble-type lectins or galectins constitute a family of proteins defined by shared consensus amino acid sequence and affinity for beta-galactose-containing oligosaccharides. These molecules are widely distributed in the animal kingdom; to date, 15 mammalian galectins have been described but more are likely to be discovered. These proteins are involved in many biological processes including cell-cell and cell-matrix adhesion, growth regulation, signaling, and cytokine secretion. Over the last decade, a vast amount of reports has shown the importance of several galectins in the development and progression of malignancies in the digestive tract, mainly colorectal cancers. More recent data indicate that some of these molecules are also involved in inflammatory bowel diseases. This review focuses on the current knowledge of galectin expression and putative functions in the oesophagus, stomach, small intestine, and colon. It also highlights that the rapid accumulation of research data promises future scenarios in which individual members of the galectin family and/or their ligands will be used as diagnostic and therapeutic modalities for neoplastic as well as inflammatory disorders. However, the concretization of these potential modalities requires substantial improvements in terms of standardization of galectin expression evaluation together with prospective validation of the present data.

Crystallization and preliminary X-ray diffraction analysis of mouse galectin-4 N-terminal carbohydrate recognition domain in complex with lactose

Galectin-4 is thought to play a role in the process of tumour conversion of cells of the alimentary tract and the breast tissue; however, its exact function remains unknown. With the aim of elucidating the structural basis of mouse galectin-4 (mGal-4) binding specificity, we have undertaken X-ray analysis of the N-terminal domain, CRD1, of mGal-4 in complex with lactose (the basic building block of known galectin-4 carbohydrate ligands). Crystals of CRD1 in complex with lactose were obtained using vapour-diffusion techniques. The crystals belong to tetragonal space group P42(1)2 with unit-cell parameters a = 91.1, b = 91.16, c = 57.10 A and preliminary X-ray diffraction data were collected to 3.2 A resolution. An optimized crystallization procedure and cryocooling protocol allowed us to extend resolution to 2.1 A. Structure refinement is currently under way; the initial electron-density maps clearly show non-protein electron density in the vicinity of the carbohydrate binding site, indicating the presence of one lactose molecule. The structure will help to improve understanding of the binding specificity and function of the potential colon cancer marker galectin-4.

Galectin-3 gene inactivation reduces atherosclerotic lesions and adventitial inflammation in ApoE-deficient mice

This study has examined the role of galectin-3 (GaL3), a multicompartmented N-acetyllactosamine-binding chimeric lectin, on atherogenesis in the ApoE-deficient mouse model of atherosclerosis. Pathological changes consisting of atheromatous plaques, atherosclerotic microaneurysms extending into periaortic vascular channels, and adventitial and periaortic inflammatory infiltrates were assessed in an equal number (n = 36) of apolipoprotein (Apo)E-deficient mice and ApoE-GaL3 double-knockout mice. These mice were divided into three age groups, 21 to 23 weeks, 25 to 31 weeks, and 36 to 44 weeks of age. Results of this morphological analysis have shown an age-related increase in the incidence of aorta atheromatous plaques and periaortic vascular channels in ApoE-deficient mice. By contrast ApoE/GaL3 double-knockout mice did not show an increase in pathological changes with age. The 36- to 44-week group of ApoE(-/-)/GaL3(-/-) mice had a significantly lower number of atherosclerotic lesions (P < 0.004) and fewer atheromatous plaques (P < 0.008) when compared with ApoE(-/-)/GaL3+/+ mice of the same age. ApoE(-/-)/GaL3(-/-) mice had a lower number of perivascular inflammatory infiltrates and mast cells than those found in ApoE(-/-)/GaL3+/+ mice. The reduced number of perivascular mast cells may have resulted in a low level of interleukin-4 that contributed to the reduction in the morphological parameters of atherogenesis correlated with the lack of GaL3 expression. The effect of GaL3 deficiency on atherogenesis decrease could be related to its function as a multifunctional protein implicated in macrophage chemotaxis, angiogenesis, lipid loading, and inflammation.

Galectin-3 stimulates preadipocyte proliferation and is up-regulated in growing adipose tissue

OBJECTIVE

Some cytokines and mediators of inflammation can alter adiposity through their effects on adipocyte number. To probe the molecular basis of obesity, this study determined whether galectin-3 was present in adipose tissue and investigated its effects on fat cell number.

RESEARCH METHODS AND PROCEDURES

In the first study, obesity-prone C57BL/6J mice were fed with high-fat (58%) diet. Epididymal fat pads were collected at Day 0, Day 60, and Day 120 after the start of high-fat feeding.

RESULTS

Levels of adipocyte galectin-3 protein, determined using Western blot analysis, increased as the mice became obese. Galectin-3 mRNA and protein were then detected in human adipose tissue, primarily in the preadipocyte fraction. It was found that recombinant human galectin-3 stimulated proliferation of primary cultured preadipocytes as well as DNA synthesis through lectin-carbohydrate interaction.

DISCUSSION

Galectin-3, which has been known to play a versatile role especially in immune cells, might play a role also in adipose tissue and be associated with the pathophysiology of obesity.

Tumor-associated antigen 90K/Mac-2-binding protein: possible role in colon cancer

The tumor-associated antigen 90K (TAA90K)/Mac-2-binding protein implicated in cancer progression and metastasis is modified by beta1-6 branched N-linked oligosaccharides in colon cancer cells, glycans shown to contribute to cancer metastasis. To elucidate the role of TAA90K in colon cancer, we examined its expression and function in human colon tumors and colon carcinoma cell lines. Immunohistochemical analyses of colon tumors revealed elevated expression of TAA90K in all samples analyzed compared to normal colon. To examine the function of TAA90K in colon cancer, we carried out protein and cell binding assays using TAA90K-His purified from HT-29 cells colon carcinoma cells infected with recombinant vaccinia virus expressing TAA90K containing a C-terminal poly-histidine tag. TAA90K-His bound to fibronectin, collagen IV, laminins-1, -5, and -10 and galectin-3 (Mac-2) but poorly to collagen I and galectin-1. As expected, binding of TAA90K to galectin-3 was dependent on carbohydrate since it was inhibitable by lactose and asiolofetuin, and a TAA90K-His glycoform purified from HT-29 cells treated with the glycosylation inhibitor 1-deoxymannojirimycin bound poorly to galectin-3. Unlike TAA90K isolated from other cell types, TAA90K-His isolated from colon cancer cells failed to mediate adhesion of colon cancer and normal cell lines, possibly due to cell-type specific glycosylation of TAA90K-His and/or its putative cellular receptor. However, at low concentrations, TAA90K-His enhanced galectin-3-mediated HT-29 cell adhesion while at high concentrations, it inhibited cell adhesion. Thus, a possible mechanism by which TAA90K may contribute to colon cancer progression is by modulating tumor cell adhesion to extracellular proteins, including galectin-3.

Mice deficient in galectin-1 exhibit attenuated physiological responses to chronic hypoxia-induced pulmonary hypertension

Pulmonary hypertension (PH) is characterized by sustained vasoconstriction, with subsequent extracellular matrix (ECM) production and smooth muscle cell (SMC) proliferation. Changes in the ECM can modulate vasoreactivity and SMC contraction. Galectin-1 (Gal-1) is a hypoxia-inducible beta-galactoside-binding lectin produced by vascular, interstitial, epithelial, and immune cells. Gal-1 regulates SMC differentiation, proliferation, and apoptosis via interactions with the ECM, as well as immune system function, and, therefore, likely plays a role in the pathogenesis of PH. We investigated the effects of Gal-1 during hypoxic PH by quantifying 1) Gal-1 expression in response to hypoxia in vitro and in vivo and 2) the effect of Gal-1 gene deletion on the magnitude of the PH response to chronic hypoxia in vivo. By constructing and screening a subtractive library, we found that acute hypoxia increases expression of Gal-1 mRNA in isolated pulmonary mesenchymal cells. In wild-type (WT) mice, Gal-1 immunoreactivity increased after 6 wk of hypoxia. Increased expression of Gal-1 protein was confirmed by quantitative Western analysis. Gal-1 knockout (Gal-1(-/-)) mice showed a decreased PH response, as measured by right ventricular pressure and the ratio of right ventricular to left ventricular + septum wet weight compared with their WT counterparts. However, the number and degree of muscularized vessels increased similarly in WT and Gal-1(-/-) mice. In response to chronic hypoxia, the decrease in factor 8-positive microvessel density was similar in both groups. Vasoreactivity of WT and Gal-1(-/-) mice was tested in vivo and with use of isolated perfused lungs exposed to acute hypoxia. Acute hypoxia caused a significant increase in RV pressure in wild-type and Gal-1(-/-) mice; however, the response of the Gal-1(-/-) mice was greater. These results suggest that Gal-1 influences the contractile response to hypoxia and subsequent remodeling during hypoxia-induced PH, which influences disease progression.

Immunohistochemical and in situ hybridization analysis of galectin-3, a β-galactoside binding lectin, in the urinary system of adult mice

Galectin is an animal lectin that has high affinity to beta-galactoside of glycoconjugates. In the present study, cellular expression of galectin subtypes in the urinary system of adult mice was examined by in situ hybridization and immunohistochemistry. The major subtype expressed in the murine urinary system was galectin-3, which was expressed continuously from the kidney to the distal end of the urethra. The renal cortex expressed galectin-3 more intensely than the medulla. Renal galectin-3 immunoreactivity was strongest in the cortical collecting ducts, where principal cells were the sole cellular source. All cell layers of the transitional epithelium from the renal pelvis to the urethra strongly expressed galectin-3 at the mRNA and protein levels. An electron microscopic study demonstrated diffuse cytoplasmic localization of galectin-3 in principal cells of the collecting ducts and in the bladder epithelial cells. Urethral galectin-3 expression at the pars spongiosa decreased in intensity near the external urethral orifice, where the predominant subtype of galectin was substituted by galectin-7. The muscular layer of the ureter and urinary bladder contained significant signals for galectin-1. Taken together, the observations indicate that the adult urinary system shows intense and selective expression of galectin-3 in epithelia of the uretic bud- and cloaca-derivatives.

Galectin-4 expression in carcinoid tumors

Galectins (Gal) are an evolutionarily conserved family of 15 carbohydrate-binding proteins (lectins) that are widely distributed in normal and neoplastic cells in a wide range of organisms. They have roles in inflammation, cell adhesion, tumor progression, and metastasis. The function and distribution of Gal-3 and Gal-1 are well characterized, but less information is available about Gal-4. Recent studies have localized Gal-4 in the enterochromaffin cells of the porcine and murine small intestine. We examined the expression of Gal-4 in primary and metastatic human ileal carcinoid tumors as well as in carcinoid tumors of the stomach, lung, and rectum. A total of 44 primary and 42 ileal metastatic carcinoid tumors were examined by immunohistochemistry using tissue microarrays (TMA) with monoclonal antibodies to Gal-4, Gal-3, and Gal-1. Pulmonary (n = 7), rectal (n = 6), and gastric (n = 6) carcinoids were examined with larger tissue sections. A total of 18 pancreatic neuroendocrine tumors were also examined with larger tissue sections. Western blots of three ileal carcinoids were also done. Gal-4 was most highly expressed in the ileal carcinoids and the levels of expression tended to be higher in primary ileal carcinoids compared to the metastatic tumors (p = 0.069). All 18 pancreatic neuroendocrine tumors were negative for Gal-1, Gal-3, and Gal-4. Western blot showed a 32 kDa band for Gal-4 in the ileal carcinoids. Gal-3 and Gal-1 were not detected in the metastatic ileal carcinoids by Western blotting. Gastric carcinoids also expressed Gal-4, but very few pulmonary or rectal carcinoids were positive for Gal-4 (p = 0.002). Lower levels of Gal-1 and Gal-3 expression were present in ileal carcinoids compared to primary pulmonary and rectal tumors. These results show a differential distribution of Gal-4 in carcinoid tumors in different locations of the gastrointestinal tract and the lungs.

Differential Cellular Expression of Galectin Family mRNAs in the Epithelial Cells of the Mouse Digestive Tract

Galectin is an animal lectin that recognizes β-galactosides of glycoconjugates and is abundant in the gut. This study revealed the cellular expression of galectin subtypes throughout the mouse digestive tract by in situ hybridization. Signals for five subtypes (galectin-2, -3, -4/6, and -7) were detected exclusively in the epithelia. In the glandular stomach, galectin-2 and -4/6 were predominantly expressed from gastric pits to neck of gastric glands, where mucous cells were the main cellular sources. The small intestine exhibited intense, maturation-associated expressions of galectin-2, -3, and -4/6 mRNAs. Galectin-2 was intensely expressed from crypts to the base of villi, whereas transcripts of galectin-3 gathered at villous tips. Signals for galectin-4/6 were most intense at the lower half of villi. Galectin-2 was also expressed in goblet cells of the small intestine but not in those of the large intestine. In the large intestine, galectin-4/6 predominated, and the upper half of crypts simultaneously contained transcripts of galectin-3. Stratified epithelium from the lip to forestomach and anus intensely expressed galectin-7 with weak expressions of galectin-3. Because galectins in the digestive tract may be multi-functional, information on their cell/stage-specific expression contributes to a better understanding of the functions and pathological involvements of galectins.

Monitoring the Expression Profiles of Integrins and Adhesion/Growth-regulatory Galectins in Adamantinomatous Craniopharyngiomas: Their Ability to Regulate Tumor Adhesiveness to Surrounding Tissue and Their Contribution to Prognosis

OBJECTIVE

The purpose of this study was to identify biological markers that may be involved in the adhesiveness of craniopharyngiomas to optical chiasms and/or pituitary stalks.

METHODS

We determined the complete pattern of integrin expression in three craniopharyngiomas by means of a complementary deoxyribonucleic acid microarray. We quantitatively determined the levels of immunohistochemical expression of the different integrins in a series of 37 cases and the pattern of immunohistochemical expression of 10 extracellular matrix components (acting as integrin ligands) in 7 optical chiasms and 11 pituitary stalks. We also quantitatively (computer-assisted microscopy) determined the levels of immunohistochemical expression of galectin-1, -3, -4, -7, and -8 in 50 adamantinomatous craniopharyngiomas.

RESULTS

The present study shows that at both the ribonucleic acid and protein levels, adamantinomatous craniopharyngiomas express the alpha2, alpha6, alpha(v), beta1, beta5, and beta8 integrin subunits, whereas optical chiasms and pituitary stalks express vitronectin, thrombospondin, and various forms of collagens.

CONCLUSION

Our data suggest that at least part of the adhesiveness of craniopharyngiomas to the surrounding tissue, such as optical chiasms and pituitary stalks, could be explained by the interactions between alpha(2beta1) integrin expressed by craniopharyngiomas and collagens on the one hand, and vitronectin expressed by the surrounding tissue on the other hand. In addition, a Cox regression analysis has revealed that the levels of galectin-4 contribute significant information toward the delay in recurrence independently of surgical status.

Gene expression profiles reveal that DCN, DIO1, and DIO2 are underexpressed in benign and malignant thyroid tumors

To investigate the molecular events involved in the pathogenesis and/or progression of thyroid tumors, we compared the gene expression profiles of three thyroid carcinoma cell lines, which represent major tumor subtypes of thyroid cancer and normal thyroid tissue. Using cDNA array methodology, we investigated the expression of 1807 open reading frame expressed sequence tags (ORESTES), selected from head and neck tumor libraries generated through the Brazilian Human Cancer Project-LICR/FAPESP. We found that 505 transcripts were differentially expressed in the thyroid carcinoma cell lines. Using a more stringent criterion, transcripts underexpressed or overexpressed more than fivefold in 1 of 3 or 3 of 3 carcinoma cell lines, a list of 55 ESTs were detected. Five candidate genes were further validated by quantitative polymerase chain reaction (qPCR) in an independent set of 52 thyroid tumors and 22 matched normal thyroid tissues. DCN was found underexpressed in a high percentage of the follicular thyroid adenomas, follicular thyroid carcinomas, and follicular variant of papillary thyroid carcinomas. DIO1 and DIO2 were underexpressed in nearly all papillary thyroid carcinomas. These genes not only could help to better define a tumor signature for thyroid tumors, but may, in part, also become useful as potential targets for thyroid tumor treatment.

Identification of galectin-4 isoforms in porcine small intestine

Lactose-binding proteins with molecular masses of 14-, 17-, 18-, 28-, and 34-kDa were identified in extracts from porcine small intestinal mucosa. Amino acid sequence analysis of peptides generated by CNBr cleavage of the 34-kDa protein, the most abundant of these proteins, identified this protein as porcine galectin-4. To determine if a porcine homolog of murine galectin-6 is expressed in small intestine, primers for a reverse transcriptase-polymerase chain reaction (RT-PCR) were developed that amplified across the linker region of galectin-4, which is the region that differs between murine galectins-4 and -6. Using these primers, this RT-PCR approach identified two galectin-4 isoforms that differed in the length of their linker region. The larger isoform, galectin-4.1, is nine amino acids longer in its linker region than the smaller isoform, galectin-4.2. Based on nucleotide sequence similarities, the two isoforms are likely splice variants of galectin-4 pre-mRNA and not products of separate genes like murine galectins-4 and -6.

Galectin-4 in normal tissues and cancer

Galectin-4 belongs to a subfamily of galectins composed of two carbohydrate recognition domains within the same peptide chain. The two domains have all the conserved galectin signature amino acids, but their overall sequences are only approximately 40% identical. Both domains bind lactose with a similar affinity as other galectins, but their respective preferences for other disaccharides, and larger saccharides, are distinctly different. Thus galectin-4 has a property of a natural cross-linker, but in a modified sense since each domain prefers a different subset of ligands. Similarly to other galectins, galectin-4 is synthesized as a cytosolic protein, but can be externalized. During development and in adult normal tissues, galectin-4 is expressed only in the alimentary tract, from the tongue to the large intestine. It is often found in relatively insoluble complexes, as a component of either adherens junctions or lipid rafts in the microvillus membrane, and it has been proposed to stabilize these structures. Strong expression of galectin-4 can be induced, however, in cancers from other tissues including breast and liver. Within a collection of human epithelial cancer cell lines, galectin-4 is overexpressed and soluble in those forming highly differentiated polarized monolayers, but absent in less differentiated ones. In cultured cells, intracellular galectin-4 may promote resistance to nutrient starvation, whereas--as an extracellular protein--it can mediate cell adhesion. Because of its distinct induction in breast and other cancers, it may be a valuable diagnostic marker and target for the development of inhibitory carbohydrate-based drugs.

Printed covalent glycan array for ligand profiling of diverse glycan binding proteins

Here we describe a glycan microarray constructed by using standard robotic microarray printing technology to couple amine functionalized glycans to an amino-reactive glass slide. The array comprises 200 synthetic and natural glycan sequences representing major glycan structures of glycoproteins and glycolipids. The array has remarkable utility for profiling the specificity of a diverse range of glycan binding proteins, including C-type lectins, siglecs, galectins, anticarbohydrate antibodies, lectins from plants and microbes, and intact viruses.

Galectin-3 binds lactosaminylated lipooligosaccharides from Neisseria gonorrhoeae and is selectively expressed by mucosal epithelial cells that are infected

Galectins are a family of beta-galactoside binding proteins that have been proposed as host receptors for bacteria because beta-galactoside carbohydrates are common in bacterial membrane glycolipid lipooligosaccharides (LOS) and lipopolysaccharides. We investigated the interaction of galectin-3 with gonococcal LOS that make lactosyl (Lc2 or Lac), paraglobosyl (nLc4; LNnT; lacto-N-neotetraose), gangliosyl (IV3GalNAcnLc4), and neolactohexaosyl (nLc6, lactonorhexaosyl) oligosaccharides. All but gangliosyl LOS terminate in beta-galactoside. Galectin-3 had the highest affinity for the nLc6 LOS, which is made by a strain that is highly infectious for the male urethra, but also bound nLc4 LOS and to a Lac LOS. The lacto-N-neotetraose tetrasaccharide was a more potent inhibitor of galectin-3 binding to LOS than either lactose or N-acetyllactosamine. The relative affinity of galectin-3 for gonococci mirrored its affinity for purified LOS. Western blot analysis revealed expression of galectin-3 by human endometrial adenocarcinoma and prostatic epithelial cells that can be invaded by gonococci. Immunohistochemistry of human fallopian tube epithelium showed localized expression of galectin-3 by non-ciliated cells, the specific cell gonococci invade in this tissue. We conclude that because of its location and affinity for gonococcal LOS galectin-3 could play a role in gonococcal infection.