Human breast carcinoma cDNA encoding a galactoside-binding lectin homologous to mouse Mac-2 antigen

Proteolytic processing of galectin-3 by meprin metalloproteases is crucial for host-microbiome homeostasis

The metalloproteases meprin α and meprin β are highly expressed in the healthy gut but significantly decreased in inflammatory bowel disease, implicating a protective role in mucosal homeostasis. In the colon, meprin α and meprin β form covalently linked heterodimers tethering meprin α to the plasma membrane, therefore presenting dual proteolytic activity in a unique enzyme complex. To unravel its function, we applied N-terminomics and identified galectin-3 as the major intestinal substrate for meprin α/β heterodimers. Galectin-3-deficient and meprin α/β double knockout mice show similar alterations in their microbiome in comparison to wild-type mice. We further demonstrate that meprin α/β heterodimers differentially process galectin-3 upon bacterial infection, in germ-free, conventionally housed (specific pathogen-free), or wildling mice, which in turn regulates the bacterial agglutination properties of galectin-3. Thus, the constitutive cleavage of galectin-3 by meprin α/β heterodimers may play a key role in colon host-microbiome homeostasis.

Galectin-3: a key player in microglia-mediated neuroinflammation and Alzheimer's disease

Alzheimer’s disease (AD) is the most common cause of dementia and is characterized by the deposition of extracellular aggregates of amyloid-β (Aβ), the formation of intraneuronal tau neurofibrillary tangles and microglial activation-mediated neuroinflammation. One of the key molecules involved in microglial activation is galectin-3 (Gal-3). In recent years, extensive studies have dissected the mechanisms by which Gal-3 modulates microglial activation, impacting Aβ deposition, in both animal models and human studies. In this review article, we focus on the emerging role of Gal-3 in biology and pathobiology, including its origin, its functions in regulating microglial activation and neuroinflammation, and its emergence as a biomarker in AD and other neurodegenerative diseases. These aspects are important to elucidate the involvement of Gal-3 in AD pathogenesis and may provide novel insights into the use of Gal-3 for AD diagnosis and therapy.

Binding of Gold(III) Porphyrin by the Pro-metastatic Regulatory Protein Human Galectin-3

Gold(III) porphyrin presents an attractive alternative to the use of, for example, cisplatin in chemotherapy. However, approaches that allow to selectively target cancer cells are highly sought. Many plant and mammalian lectins have been shown to bind oligosaccharide sequences of the aberrant glycosylation pattern found on cancerous tumors. For example human galectin-3, of the galectin family specific for β-galactoside, is overexpressed in the extracellular matrix of tumorigenous and metastatic tissues. We searched for non-carbohydrate ligands for galectin-3 that can guide a cytotoxic drug to the cancer cells by maintaining its affinity for tumor associated carbohydrate antigens. Previous findings showed that zinc tetrasulfonatophenylporphyrin can bind galectin-3 with sub-micromolar affinity without disturbing lactose binding. Gold(III) porphyrin is not only cytotoxic to cancer cells, it knows also a potential application as photosensitiser in photodynamic therapy. We investigated the binding of gold(III) porphyrin to galectin-3 using different biophysical interaction techniques and demonstrated a low micromolar affinity of human galectin-3 for the cytotoxic compound. Co-crystallization attempts in order to understand the binding mode of gold porphyrin to galectin-3 failed, but molecular docking emphasized a highly populated secondary binding site that does not hinder lactose or Thomsen Friendenreich disaccharide binding. This suggests that gold(III) porphyrin might significantly enhance its concentration and delivery to cancer cells by binding to human galectin-3 that keeps its orientation towards tumor associated carbohydrate antigens.

Galectin-3: One Molecule for an Alphabet of Diseases, from A to Z

Galectin-3 (Gal-3) regulates basic cellular functions such as cell-cell and cell-matrix interactions, growth, proliferation, differentiation, and inflammation. It is not surprising, therefore, that this protein is involved in the pathogenesis of many relevant human diseases, including cancer, fibrosis, chronic inflammation and scarring affecting many different tissues. The papers published in the literature have progressively increased in number during the last decades, testifying the great interest given to this protein by numerous researchers involved in many different clinical contexts. Considering the crucial role exerted by Gal-3 in many different clinical conditions, Gal-3 is emerging as a new diagnostic, prognostic biomarker and as a new promising therapeutic target. The current review aims to extensively examine the studies published so far on the role of Gal-3 in all the clinical conditions and diseases, listed in alphabetical order, where it was analyzed.

The Many Roles of Galectin-3, a Multifaceted Molecule, in Innate Immune Responses against Pathogens

Galectins are a group of evolutionarily conserved proteins with the ability to bind β-galactosides through characteristic carbohydrate-recognition domains (CRD). Galectin-3 is structurally unique among all galectins as it contains a C-terminal CRD linked to an N-terminal protein-binding domain, being the only chimeric galectin. Galectin-3 participates in many functions, both intra- and extracellularly. Among them, a prominent role for Galectin-3 in inflammation has been recognized. Galectin-3 has also been shown to directly bind to pathogens and to have various effects on the functions of the cells of the innate immune system. Thanks to these two properties, Galectin-3 participates in several ways in the innate immune response against invading pathogens. Galectin-3 has been proposed to function not only as a pattern-recognition receptor (PRR) but also as a danger-associated molecular pattern (DAMP). In this review, we analyze the various roles that have been assigned to Galectin-3, both as a PRR and as a DAMP, in the context of immune responses against pathogenic microorganisms.

Human galectin-3 interacts with two anticancer drugs

Human galectin-3 (hGal-3) is a mammalian lectin involved in regulation of RNA splicing, apoptosis, cell differentiation, and proliferation. Multimerized extracellular hGal-3 is thought to crosslink cells by binding to glycoproteins and glycosylated cancer antigens on the cell surface or extracellular matrix. Fluorescence spectroscopy and circular dichroism were used to study the interaction of hGal-3 with two anticancer agents: bohemine and Zn porphyrin (ZnTPPS(4)). The dissociation constant (k(D)) for binding of bohemine with hGal-3 was k(D) 0.23+/-0.05 microM. The hyperbolic titration curve indicated the presence of a single bohemine binding site. The binding of ZnTPPS(4) to hGal-3 (with and without lactose) is of high affinity having k(D)=0.18-0.20 microM and is not inhibited by lactose, indicating that ZnTPPS(4) and carbohydrate bind different sites. Circular dichroism spectra of the hGal-3 complexes suggested that the binding of the hydrophobic compounds changed the hGal-3 secondary structure. In summary, we show that two compounds with anticancer activity, bohemine and ZnTPPS(4), have high affinity for hGal-3 at a site that is distinct from its carbohydrate site. Since hGal-3 binds to several carbohydrate cancer antigens, the results suggest that it may have utility in the targeted delivery of drugs for cancer.

The mitogaligin protein is addressed to the nucleus via a non-classical localization signal

Mitogaligin, a protein encoded by galig, an internal cytotoxic gene of the galectin-3 locus, is mostly a mitochondrial protein. Mitochondrial targeting is due to an already identified mitochondrial localization signal. Interaction of mitogaligin with mitochondria leads to cytochrome c cytosolic leakage and ultimately to cell death. We have previously pointed out that mitogaligin can also be directed to the nucleus when the mitochondrial addressing signal is inactivated, indicating a possible dual intracellular localization of the protein. When expressed in the nucleus, mitogaligin exhibits also apoptotic properties leading to cell death. In this report, we show that nuclear addressing of mitogaligin depends on a sequence differing from classical signals containing basic, lysine or proline-tyrosine rich residues. The signal consists of a long sequence of amino acids residues based on a series of a short repetitive degenerated sequence.

Galectin-3 in urine of cancer patients: stage and tissue specificity

PURPOSE

Galectin-3 has been implicated in advanced stage of cancer disease. In the current study we examined the possibility of urinary galectin-3 levels to stage cancer disease and to follow up therapy.

EXPERIMENTAL DESIGN

Urine was collected from all types of cancer patients at different stages including patients undergoing radio/chemotherapy. Galectin-3 level was determined by anti-galectin-3 based ELISA and agglutination assays. Immunoblotting and purification on lactosyl affinity column further confirmed the presence of galectin-3.

RESULTS

Cancer samples exhibited stage dependent expression of galectin-3 approx. ranging from 1.0 to 3.3, 4.4 to 5.4, 5.4 to 24.7, 13.1 to 31.9, 13.9 to 32.9 ng/mg C (creatinine) for stage I-V, respectively, at P approximately <0.05 level. Galectin-3 levels were decreased by approx. threefolds after 5th day of therapy.

CONCLUSIONS

Sample collection being simple and non-invasive, urinary galectin-3 may be used as a potential diagnostic tool for monitoring or follow up of the stage of cancer disease.

Pancreatic stellate cells promote proliferation and invasiveness of human pancreatic cancer cells via galectin-3

AIM: To investigate the role of pancreatic stellate cells (PSCs) and galectin-3 (GAL-3) in the proliferation and infiltration of pancreatic cancer cell line SW1990.

METHODS: Human pancreatic cancer cell line SW1990 and PSCs were cultured in vitro. Supernatant fluid of cultured PSCs and SW1990 cells was collected. Expression of GAL-3 in SW1990 cells and PSCs was detected by ELISA, RT-PCR and Western blotting. Proliferation of cultured PSCs and SW1990 cells was measured by 3-(4, 5-methylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay and flow cytometry. Infiltration of SW1990 cells was detected by a cell infiltration kit.

RESULTS: SW1990 cells expressed GAL-3 and this was up-regulated by the supernatant fluid of cultured PSCs. PSCs did not express GAL-3. SW1990 cells stimulated proliferation of PSCs via GAL-3. GAL-3 antibody inhibited SW1990 cell proliferation, while the supernatant fluid of PSCs stimulated proliferation of SW1990 cells through interaction with GAL-3 protein. The supernatant fluid of PSCs enhanced the invasiveness of SW1990 cells through interaction with GAL-3.

CONCLUSION: GAL-3 and PSCs were involved in the proliferation and infiltration process of pancreatic cancer cells.

High expression of eosinophil chemoattractant ecalectin/galectin-9 in drug-induced liver injury

BACKGROUND

Ecalectin/galectin-9 (ECL/GL9) is an eosinophil chemoattractant isolated from T lymphocytes. Drug-induced liver injury (DILI), often caused by an allergic mechanism, is occasionally accompanied by eosinophilic infiltration. In this study, we intended to determine whether DILI can induce augmentation of ECL/GL9 expression. Further, we investigated whether this augmentation is associated with tissue eosinophilia.

METHODS

We examined the expression of ECL/GL9 in biopsy specimens of DILI using the immunohistochemical technique. A rabbit anti-ECL/GL9 antibody was produced by immunizing rabbits with synthetic peptide corresponding to a molecular epitope of ECL/GL9. Thereafter, immunohistochemical staining with the use of this antibody was performed on 16 DILI needle biopsy specimens, and on biopsy specimens of chronic viral hepatitis, liver cirrhosis, and normal liver tissues as controls.

RESULTS

In all cases of DILI specimens, but not in control liver specimens, a clear positive staining for ECL/GL9 was observed. Such positive staining was noted on Kupffer cells, fibroblasts, and histiocytes, but not on lymphocytes or hepatocytes. However, the intensity of immunolabeling did not correlate with the extent of eosinophile leukocyte infiltration.

CONCLUSION

High expression of ECL/GL9 is suggested to be a specific finding of DILI. However, tissue eosinophilia in DILI cannot be explained by the augmentation of ECL/GL9 expression.

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.

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

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

Potential roles of galectins in myeloid differentiation into three different lineages

Little is known about the roles of galectins, a family of beta-galactoside-binding lectins, in myeloid cell differentiation. In the present experiments, we used HL-60 cells as a model of myeloid cell differentiation. The HL-60 cells were differentiated into eosinophil-, monocyte-, and neutrophil-like cells by coculture with sodium butyrate under a mild alkaline condition, phorbol 12-myristate 13-acetate, and dimethyl sulfoxide, respectively. Thus, the expression of galectins in HL-60 cells during differentiation into three different lineages was assessed. Reverse transcriptase-polymerase chain reaction analyses revealed that undifferentiated HL-60 cells expressed galectin-1, -3, -8, -9, and -10 (identical to Charcot Leyden crystal) mRNAs, and galectin-2, -4, and -7 were negligible before and after the differentiations. We failed to detect evident changes in the mRNA levels of galectin-1 and -8 during the differentiations. However, during the eosinophilic differentiation, galectin-9 mRNA expression was gradually decreased, whereas galectin-10 mRNA expression was increased. During the course of monocytic differentiation, galectin-9 mRNA expression was down-regulated, whereas galectin-3 mRNA expression was up-regulated. Moreover, only galectin-10 mRNA expression was enhanced in the process of neutrophilic differentiation. These changes in galectin expressions were confirmed by Western blot and flow cytometry analyses. It is thus suggested that changes in the expressions of galectin-3, -9, and -10 are potentially important for myeloid cell differentiation into specific lineages.

Oligosaccharide specificity of galectins: a search by frontal affinity chromatography

Galectins are widely distributed sugar-binding proteins whose basic specificity for beta-galactosides is conserved by evolutionarily preserved carbohydrate-recognition domains (CRDs). Although they have long been believed to be involved in diverse biological phenomena critical for multicellular organisms, in only few a cases has it been proved that their in vivo functions are actually based on specific recognition of the complex carbohydrates expressed on cell surfaces. To obtain clues to understand the physiological roles of diverse members of the galectin family, detailed analysis of their sugar-binding specificity is necessary from a comparative viewpoint. For this purpose, we recently reinforced a conventional system for frontal affinity chromatography (FAC) [J. Chromatogr., B, Biomed. Sci. Appl. 771 (2002) 67-87]. By using this system, we quantitatively analyzed the interactions at 20 degrees C between 13 galectins including 16 CRDs originating from mammals, chick, nematode, sponge, and mushroom, with 41 pyridylaminated (PA) oligosaccharides. As a result, it was confirmed that galectins require three OH groups of N-acetyllactosamine, as had previously been denoted, i.e., 4-OH and 6-OH of Gal, and 3-OH of GlcNAc. As a matter of fact, no galectin could bind to glycolipid-type glycans (e.g., GM2, GA2, Gb3), complex-type N-glycans, of which both 6-OH groups are sialylated, nor Le-related antigens (e.g., Le(x), Le(a)). On the other hand, considerable diversity was observed for individual galectins in binding specificity in terms of (1) branching of N-glycans, (2) repeating of N-acetyllactosamine units, or (3) substitutions at 2-OH or 3-OH groups of nonreducing terminal Gal. Although most galectins showed moderately enhanced affinity for branched N-glycans or repeated N-acetyllactosamines, some of them had extremely enhanced affinity for either of these multivalent glycans. Some galectins also showed particular preference for alpha1-2Fuc-, alpha1-3Gal-, alpha1-3GalNAc-, or alpha2-3NeuAc-modified glycans. To summarize, galectins have evolved their sugar-binding specificity by enhancing affinity to either "branched", "repeated", or "substituted" glycans, while conserving their ability to recognize basic disaccharide units, Galbeta1-3/4GlcNAc. On these bases, they are considered to exert specialized functions in diverse biological phenomena, which may include formation of local cell-surface microdomains (raft) by sorting glycoconjugate members for each cell type.

Purification and cDNA cloning of Xenopus liver galectins and their expression

We have characterized galectin family proteins in adult tissues of Xenopus laevis and purified 14-kDa and 36-kDa proteins from the liver. The liver galectins showed comparable hemagglutination activities to those of mammalian galectins. Furthermore, we isolated five galectin cDNAs from a Xenopus liver library. These cDNAs revealed that X. laevis galectins (xgalectins) form a family consisting of at least proto and tandem repeat types based on their domain structures, like the mammalian galectin family. Two proto-type xgalectins, -Ia and -Ib, exhibited a high sequence identity (91%) with each other at the amino acid level and were most similar (49-50% identity) to human galectin-1. From their sequence similarity and ubiquitous tissue distributions, xgalectins-Ia and -Ib both seemed to be Xenopus homologues of mammalian galectin-1. Three tandem repeat-type xgalectins were newly identified. Two of them, xgalectins-IIa and -IIIa, seemed to be homologous to human galectins-4 and -9, respectively, judging from their high sequence similarities (42-50% identity). However, xgalectin-IVa seemed to be a novel type. Distributions of mRNAs of xgalectins were analyzed by northern hybridization. In addition to adult tissues, either of three tandem repeat-type xgalectins were expressed in whole embryos. Moreover, amino acid sequence analysis of liver proteins indicated that xgalectins-Ia, -IIa, and -IIIa are produced as abundant galectins in the adult liver.

Determination of the affinity constants of recombinant human galectin-1 and -3 for simple saccharides by capillary affinophoresis

The affinity constants of recombinant human galectin-1 and galectin-3 for sugars were determined by capillary affinophoresis. The monoliganded affinophore contains p-aminophenyl-beta-lactoside as an affinity ligand in the matrix of succinylglutathione and has three negative charges. An analysis of the mobility change of the lectins caused by the affinophore and its inhibition by neutral sugars allowed, for the first time, a determination of the affinity constants between the binding sites of the lectins and sugars. The relative magnitude of the affinity constants for each of the sugars in terms of dissociation constants found to be consistent with previously reported data on the concentrations of sugars that caused a 50% inhibition (I50) in the binding assay of the lectin to oligosaccharide-immobilized agarose beads but the absolute values of the dissociation constants were considerably smaller than the I50 values. Capillary affinophoresis indicated microheterogeneity of the lectin preparations and enabled the separate analysis of the affinity of each component simultaneously showing the advantage in using a separation method for analysis of bioaffinity.

Regulation of galectin-9 expression and release in Jurkat T cell line cells

Ecalectin/galectin-9 was recently described as a novel eosinophil chemoattractant highly expressed in immune tissues. We investigated the regulation of galectin-9 expression and release in Jurkat (a T cell line) cells. We demonstrated that medium and long-sized galectin-9 isoforms were constitutively expressed, and phorbol 12-myriastate 13-acetate (PMA) upregulated the level of galectin-9 mRNA in Jurkat cells. Western blotting and flow cytometry analyses revealed that PMA stimulation resulted in the upregulation of both intracellular and surface galectin-9 protein. The stimulated Jurkat cells simultaneously released evident eosinophil chemoattractant activity (ECA). Main ECA was adsorbed by both lactose and anti-galectin-9 antibody affinity column, suggesting that the ECA was ascribed to galectin-9. When Jurkat cells were stimulated with PMA in the presence of a BB94, a matrix metalloproteinase (MMP) inhibitor, but not tissue inhibitor of metalloproteinase-1 (TIMP-1), the release of galectin-9 was suppressed in a dose-dependent manner. We further found that calphostin c, a protein kinase c (PKC) inhibitor, weakly but significantly suppressed the release of galectin-9. The present data suggested that galectin-9 production in Jurkat cells is provoked by the stimulation with PMA and that some MMP and PKC is, at least, partly involved in the release of galectin-9 from Jurkat cells.

Expression of endogenous galectin-1 and galectin-3 in intrahepatic cholangiocarcinoma

Galectins, a family of beta-galactoside-binding animal lectins, might be involved in tumor progression. In this study, the expression patterns of galectin-1 and -3 were examined immunohistochemically in intrahepatic cholangiocarcinoma (ICC), with emphasis on its development and progression as well as its histopathologic features, by use of samples of normal intrahepatic bile duct (n = 20), biliary epithelial dysplasia (n = 15), ICC (n = 40), and a cholangiocarcinoma cell line, CCKS1. In normal intrahepatic bile ducts, galectin-3 was constitutively but weakly expressed, whereas galectin-1 was not expressed. In hepatolithiasis, biliary epithelial dysplasia was strongly positive for galectin-3 but negative for galectin-1. Galectin-3 was frequently and strongly expressed in the cytoplasm of well-differentiated ICCs, and its expression was significantly decreased and less intense or even absent in poorly differentiated ICCs. Galectin-1 was expressed in carcinoma cells in ICC, and its incidence and extent were correlated with histologic dedifferentiation of ICC. Proliferative cell nuclear antigen (PCNA) labeling index (LI) was higher in ICC cases positive for galectin-1 than in those that were negative. Galectin-1 was strongly expressed in cancerous stroma of ICC, and this stromal expression was related to histologic dedifferentiation of ICC. In the carcinoma cell line CCKS1, galectin-1 and -3 were expressed in the cytoplasm of carcinoma cells, and galectin-1 was additionally detected in the culture medium. These results suggest that galectin-1 was newly expressed on carcinoma cells of ICC, and its overexpression seems to be associated with neoplastic progression and proliferative activities, and the expression of galectin-1 in cancerous stroma may also be related to the progression of ICC. Galectin-3 expression in epithelial cells is up-regulated in the preneoplastic and early neoplastic stages of ICC, although galectin-3 tends to disappear at later stages of ICC. HUM PATHOL 32:302-310.

Alteration of the cytoplasmic/nuclear expression pattern of galectin-3 correlates with prostate carcinoma progression

Galectin-3, a member of the beta-galactoside-binding lectin family, is involved in a variety of biological events including interactions with galactose-containing glycoconjugates, cell proliferation, differentiation and apoptosis. Galectin-3 appears to intervene during tumor progression and altered expression patterns have been reported in a variety of malignancies. In our study, we have examined the expression of galectin-3 in a population of 145 prostate carcinoma samples using immunohistochemistry. We found that most of the non-tumoral prostatic glands exhibited moderate immunostaining for galectin-3 localized in both nucleus and cytoplasm. In prostatic cancer cells, galectin-3 was usually not expressed or decreased compared with the normal glands. Interestingly, when galectin-3 was detected in the cancer cells, it was consistently excluded from the nucleus and only present in the cytoplasmic compartment. The latter observation was also made for prostatic intraepithelial neoplasia (PIN) cells. Furthermore, we found that the levels of galectin-3 expression in the cancer cells were significantly associated with prostate-specific antigen (PSA) relapse in univariate analysis (p = 0.044). Cytoplasmic expression of galectin-3 in the carcinoma cells was an independent predictor of disease progression in multivariate analysis, after the pathological stage and the Gleason score. Our data demonstrate that galectin-3 is generally down-regulated in human prostate carcinoma cells, and consistently excluded from the nucleus. Interestingly, specific cytoplasmic expression of galectin-3 in a subset of lesions is associated with disease progression. These results suggest that galectin-3 might play anti-tumor activities when present in the nucleus, whereas it could favor tumor progression when expressed in the cytoplasm. Further studies should determine the exact role and mechanisms by which galectin-3 differentially affects cell behavior in the different locations where it is expressed.

Ecalectin/galectin-9, a novel eosinophil chemoattractant: its function and production

We have recently succeeded in purifying and cloning a novel eosinophil chemoattractant, ecalectin/galectin-9, which belong to a rapidly growing galectin family. The eosinophil chemoattractant activity of ecalectin is potent and selective for eosinophils. The cellular source of ecalectin has been thought to be antigen-stimulated T cells. Herein, we will review the significance of its divalent galactoside-binding activity in ecalectin-induced eosinophil chemoattraction and the regulation of ecalectin expression in immune cells.

Galectin-3 stimulates cell proliferation

Galectin-3, a beta-galactoside-binding protein, has been shown to be involved in multiple biological processes through interaction with its complementary glycoconjugates. Here we provide the first evidence of galectin-3 as a mitogen. Incubation of quiescent cultures of normal human lung fibroblast IMR-90 cells with recombinant galectin-3 (rgalectin-3) stimulated DNA synthesis as well as cell proliferation in a dose-dependent manner. This mitogenic activity was dependent on the lectin property of galectin-3, as it could be significantly inhibited by lactose, a disaccharide competitive for carbohydrate-binding by galectin-3. Chemical cross-linking and affinity-purification experiments identified binding of rgalectin-3 to cell surface glycoproteins, which were not recognized by antibodies directed against lysosome-associated membrane proteins (LAMPs), putative cellular ligands for galectin-3. Moreover, pulse-chase analysis revealed no secretion of galectin-3 by IMR-90 cells. These results indicate that galectin-3 is a mitogen capable of stimulating fibroblast cell proliferation in a paracrine fashion through interaction with cell surface glycoconjugates different from LAMPs and suggest a possible involvement of galectin-3 in tissue remodeling.

The human LGALS3 (galectin-3) gene: determination of the gene structure and functional characterization of the promoter

Galectin-3 is a beta-galactoside-specific lectin that is a pre-mRNA splicing factor. Here we report the genomic organization of the human LGALS3 (galectin-3) gene and functional characterization of the promoter. Southern blot analysis of genomic DNA revealed that galectin-3 is coded by a single gene in the human genome. The gene is composed of six exons and five introns, spanning a total of approximately 17 kilobases (kb). Based on primer extension and ribonuclease protection analyses, there are two transcription initiation sites located 52 and 50 nucleotides (nt) upstream of the exon I-intron 1 border, and defined here as +1a and +1b, respectively. The translation start site is in exon II. The ribonucleoprotein-like N-terminal domain, containing the proline-glycine-alanine-tyrosine (PGAY) repeat motif, is found entirely within exon III. The carbohydrate recognition sequence is found entirely within exon V. Genomic fragments encompassing -836 to +141 nt (relative to +1a) have significant promoter activity when linked to the luciferase reporter gene and transiently transfected into HeLa cells or human diploid fibroblasts. Quiescent fibroblasts have low promoter activity but the activity increases 100-fold following serum addition. Serum responsive activation regions in the promoter are located between -513 and -339 nt and between -339 and -229 nt; an additional activation region may be located between -105 and -15 nt. Because galectin-3 is an immediate-early gene whose expression is dependent on the proliferative state of the cell, this study provides the basis for determining the molecular mechanisms of transcriptional regulation in neoplasia or cellular senescence.

Structure of the 32-kDa galectin gene of the nematode Caenorhabditis elegans

Galectins are a family of soluble beta-galactoside-binding lectins distributed in both vertebrates and invertebrates and, more recently, found also in fungus. The 32-kDa galectin isolated from the nematode Caenorhabditis elegans (Hirabayashi, J., Satoh, M., and Kasai, K. (1992) J. Biol. Chem. 267, 15485-15490) was the first "tandem repeat-type" galectin, containing two homologous carbohydrate-binding sites. Here, we report the structure of the nematode 32-kDa galectin gene. Physical mapping by yeast artificial chromosome polytene filter hybridization revealed that the 32-kDa galectin gene is located on chromosome II. Analysis of the transcript (1.4 kilobases) showed the presence at its 5'-end of a 22-nucleotide trans-spliced leader sequence (SL1). The entire genomic structure spanning >5 kilobase pairs (kbp), including the 5'-noncoding region, two intervening sequences (introns 1 and 2), and the 3'-noncoding region, was completely determined by the combination of genomic polymerase chain reaction and conventional colony hybridization. Intron 1 was relatively long (2.4 kbp) and was found to be inserted after the ninth codon (TAC) from the initiation codon. This position proved to be almost homologous to the conserved first intron insertion position in the vertebrate galectin genes (i. e. genes of mammalian galectin-1, -2, and -3 and chick 14-kDa galectin). On the other hand, intron 2 was much shorter (0.6 kbp), and it was inserted into the central region of the second carbohydrate-binding site. Although such an insertion pattern has never been observed in the vertebrate galectin genes, it seems to be common in C. elegans tandem repeat-type galectin genes, as predicted by the C. elegans genome project (Coulson, A., and the C. elegans Genome Consortium (1996) Biochem. Soc. Trans. 24, 289-291). Based on extensive sequence comparison, the origin and molecular evolution of the tandem repeat-type galectins are discussed.

Differential expression of galectin-1 and galectin-3 during first trimester human embryogenesis

Development of complex organisms requires specific temporospatial differentiation and expression of the correct phenotype through activation of a variety of genes. Galectins are mammalian lectins able to interact with various extracellular matrix glycoconjugates and have been implicated in several biological events including cell attachment, differentiation, apoptosis, embryogenesis, and cancer invasion and metastasis. In this study, we have examined the expression of galectin-1 and galectin-3 during human first trimester embryogenesis using immunohistochemistry and Western blotting. Variable amounts of galectin-1 and galectin-3 were detected in all tissue protein extracts. Galectin-1 expression was demonstrated in the connective tissue and derived tissues such as smooth and striated muscle cells, and in some epithelia, such as in the basal layers of the skin after 14 weeks and in the epithelial cells of the gonads. Galectin-3 was detected mainly in epithelia, such as the skin, epithelial lining of the digestive and respiratory tract, and urothelium and excretory tubes of the kidney, but also in the myocardial cells, in the peripheral and preossifying hypertrophic chondrocytes, and in the notochord and in the liver. Our study constitutes the first demonstration of galectin-1 and galectin-3 during human embryogenesis. The differential expression of these two lectins suggests that they could participate in the complex processes of tissue differentiation.

The genomic structure of the human Charcot-Leyden crystal protein gene is analogous to those of the galectin genes

The Charcot-Leyden crystal (CLC) protein, or eosinophil lysophospholipase, is a characteristic protein of human eosinophils and basophils; recent work has demonstrated that the CLC protein is both structurally and functionally related to the galectin family of beta-galactoside binding proteins. The galectins as a group share a number of features in common, including a linear ligand binding site encoded on a single exon. In this work, we demonstrate that the intron-exon structure of the gene encoding CLC is analogous to those encoding the galectins. The coding sequence of the CLC gene is divided into four exons, with the entire beta-galactoside binding site encoded by exon III. We have isolated CLC beta-galactoside binding sites from both orangutan (Pongo pygmaeus) and murine (Mus musculus) genomic DNAs, both encoded on single exons, and noted conservation of the amino acids shown to interact directly with the beta-galactoside ligand. The most likely interpretation of these results suggest the occurrence of one or more exon duplication and insertion events, resulting in the distribution of this lectin domain to CLC as well as to the multiple galectin genes.

Fungal galectins, sequence and specificity of two isolectins from Coprinus cinereus

Galectins are members of a genetically related family of beta-galactoside-binding lectins. At least eight distinct mammalian galectins have been identified. More distantly related, but still conserving amino acid residues critical for carbohydrate-binding, are galectins in chicken, eel, frog, nematode, and sponge. Here we report that galectins are also expressed in a species of fungus, the inky cap mushroom, Coprinus cinereus. Two dimeric galectins are expressed during fruiting body formation which are 83% identical to each other in amino acid sequence and conserve all key residues shared by members of the galectin family. Unlike most galectins, these have no N-terminal post-translational modification and no cysteine residues. We expressed one of these as a recombinant protein and studied its carbohydrate-binding specificity using a novel nonradioactive assay. Binding specificity has been well studied for a number of other galectins, and like many of these, the recombinant C. cinereus galectin shows particular affinity for blood group A structures. These results demonstrate not only that the galectin gene family is evolutionarily much older than previously realized but also that fine specificity for complex saccharide structures has been conserved. Such conservation implies that galectins evolved to perform very basic cellular functions, presumably by interaction with glycoconjugates bearing complex lactoside carbohydrates resembling blood group A.

Effects of the carbohydrate-binding protein galectin-3 on the invasiveness of human breast carcinoma cells

Galectin-3 is a Mr 30,000 protein with carbohydrate-binding specificity for type I and II ABH blood group epitopes and polylactosamine glycans expressed on cell surface and extracellular matrix glycoproteins such as laminin. Cell lines propagated from human normal mammary epithelia and from benign or infiltrating components of primary breast tumours express low levels of galectin-3 in the cytoplasm. However, galectin-3 when added exogenously in solution or when bound within a three-dimensional matrix markedly enhanced the migration of the primary tumour cell lines through a Matrigel barrier. Galectin-3 expression in the cytoplasm and intercellularly on surface membranes was greatly increased in cell lines propagated from malignant ascites and pleural effusions of late stage breast cancer. These cell lines were non-invasive in the Matrigel assay and exogenous galectin-3 had no enhancing effect on invasiveness. These results suggest that galectin-3 could play multiple roles in cell metastasis at an early invasive stage by acting in a paracrine manner to stimulate cell migration through an extracellular matrix, and in later stage cancers in synergy with other mediators of cell-cell aggregation. However, endogenous galectin-3 expression in human breast cancers is not correlated directly with their invasive potential in vitro.

Decreased expression of galectin-3 is associated with progression of human breast cancer

Galectin-3, a member of the beta-galactoside-binding lectin family, is involved in several biological events including binding to the basement membrane glycoprotein laminin. Although the exact role of galectin-3 during the interactions between cells and laminin is not yet known, it has recently been observed that its expression is down-regulated at both the protein and the mRNA level in colon cancer tissues in correlation with progression of the disease. This study investigated the possibility that breast cancer cells might also exhibit decreased galectin-3 expression in association with their aggressiveness. The expression of galectin-3 was examined by immunoperoxidase staining, using a polyclonal antibody raised against recombinant galectin-3, in a collection of 98 human breast lesions including 12 fibroadenomas, 15 fibrocystic disease lesions, 22 in situ carcinomas, and 49 infiltrating ductal carcinomas, 19 of which had positive axillary lymph nodes. Normal breast tissue adjacent to the lesions was present in 59 biopsies. Normal breast tissue expressed high levels (3+) of galectin-3. High expression (2+ to 3+) was also found in most benign lesions examined. The expression of galectin-3 was significantly decreased in in situ carcinoma and this down-regulation was more pronounced in invasive ductal carcinoma, particularly when associated with infiltration of axillary lymph nodes. These data constitute the first observation that galectin-3 is down-regulated in breast cancer and suggest the decreased expression of this galactoside-binding lectin is associated with the acquisition of the invasive and metastatic phenotype.

Identification of different galectins by immunoblotting after two-dimensional polyacrylamide get electrophoresis with immobilized pH gradients

Vertebrate soluble beta-galactoside-binding lectins form a growing protein family that recently have been named galectins. Seven different galectins have been sequenced and characterized in mammals, and there is compelling evidence for the existence of other members of this lectin family. Three among six galectins are homodimers with (i) an identical subunit of a relative molecular mass of about 14500, and (ii) amino acid sequence homologies giving rise to possible immunochemical cross-reactivities. They are indistinguishable from each other by conventional sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), even when followed by immunoblotting. However, their different isoelectric points allow their identification using isoelectric focusing and two-dimensional (2-D) polyacrylamide gel electrophoresis. A strategy was developed to identify these galectins in crude extracts from cells and tissues, based on the two-dimensional electrophoresis with immobilized pH gradient (IPG-Dalt) analysis of the specific spots of purified galectins and of the spots of crude extracts, after silver staining. In addition, 2-D immunoblotting using anti-galectin 1 (Gal-1) and anti carbohydrate-binding protein 15 (CPB15) antibodies were performed on brain and leukemia cells (HL60) allowing an identification of related polypeptides. Our results indicate that the use of IPG-Dalt provides a suitable reproducibility and allows the detection of galectins or other galactoside-binding proteins even at basic pIs.

Rat intestinal galactoside-binding lectin L-36 functions as a structural protein in the superficial squamous cells of the esophageal epithelium

Using an affinity purified antibody raised against the RI-H fragment of rat intestinal lectin L-36, the latter protein has been identified within the esophageal epithelium by means of ultracryotomy followed by immunogold labeling. The epithelium consists of 4 morphologically distinct cell-types, namely, the basal, spiny, granular and squamous cells, and each of these exhibits a different immunolabeling pattern. The basal cells form a layer on the basal lamina, and in these a diffuse cytoplasmic staining is observed. This basal cell layer is overlaid by spiny cells that extend many cell processes into wide intercellular spaces. In these cells, immunogold particles are found only on small granular inclusions consisting of an electron-lucent homogeneous substance. The granular cells form a third layer over the spiny cells, and are characterized by a number of large granular inclusions with an electron-dense core rimmed by a less electron-dense substance. Immunogold labeling is found on these granules, both on the core and peripheral region. Squamous cell-types constitute the most superficial layer of the epithelium. They are without granular inclusions, and immunogold labeling is confined to the cytoplasmic surface of the thickened plasma membrane. These findings suggest that L-36 is produced in the basal cells as free cytosolic protein, then becomes progressively aggregated into the granular inclusions of the spiny and granular cells, and is eventually transferred onto the cytoplasmic surface of the squamous cell plasma membrane where it may interact with complementary glycoconjugate(s) located at this site.(ABSTRACT TRUNCATED AT 250 WORDS)

Galectin-3 is expressed in the notochord, developing bones, and skin of the postimplantation mouse embryo

The galectins are a family of low molecular weight, calcium-independent mammalian carbohydrate binding proteins that exhibit specificity for beta-galactoside derivatives. We have examined the expression pattern of galectin-3 in the developing mouse embryo by in situ hybridisation and immunohistochemistry. In the embryo proper, galectin-3 message and protein are first detected in notochord, starting from 8.5 days post coitum (dpc), and persist until this structure disappears. Galectin-3 is later found in cartilage primordia and in developing skin from 13.5 dpc. This very restricted and dynamic pattern suggests that galectin-3 may participate in the establishment and/or maintenance of notochord as well as the formation of cartilage and differentiation of skin. Finally, we find that galectin-3, which is identical to the macrophage marker Mac-2, is also expressed in embryonic macrophages.

Effects of natural complex carbohydrate (citrus pectin) on murine melanoma cell properties related to galectin-3 functions

Citrus pectin (CP) and pH-modified citrus pectin (MCP) are highly branched and non-branched complex polysaccharides, respectively, rich in galactoside residues, capable of combining with the carbohydrate-binding domain of galectin-3. We reported previously that intravenous injection of B16-F1 murine melanoma cells with CP or MCP into syngeneic mice resulted in a significant increase or decrease of lung colonization, respectively (Platt D, Raz A (1992) J Natl Cancer Inst 84:438-42). Here we studied the effects of these polysaccharides on cell-cell and cell-matrix interactions mediated by carbohydrate-recognition. MCP, but not CP, inhibited B16-F1 melanoma cells adhesion to laminin and asialofetuin-induced homotypic aggregation. Both polysaccharides inhibited anchorage-independent growth of B16-F1 cells in semisolid medium, i.e. agarose. These results indicate that carbohydrate-recognition by cell surface galectin-3 may be involved in cell-extracellular matrix interaction and play a role in anchorage-independent growth as well as the in vivo embolization of tumour cells.

Galectin-3 is a novel substrate for human matrix metalloproteinases-2 and -9

The primary structure of galectin-3, a approximately 30 kDa galactoside-binding protein (aka CBP-35, mL-34, hL-31, L-29, Mac-2, and epsilon BP), reveals two structural domains: an amino-terminal domain consists of a Pro-Gly-rich motif, and a globular carboxyl-terminal domain containing a carbohydrate-binding site. In this study, we report that the amino-terminal domain of galectin-3 contains a cleavage site for two members of the matrix metalloproteinase family of enzymes: the 72 kDa (gelatinase A, MMP-2) and the 92 kDa (gelatinase B, MMP-9) proteinases. The major cleavage site for the gelatinases in galectin-3 is at the Ala62-Tyr63 bond, and its hydrolysis by these enzymes was inhibited by TIMP-2. Cell-surface expression of galectin-3 was reduced following treatment of viable T47D human breast carcinoma cells with gelatinase A. These results suggest that galectin-3 may be a substrate for gelatinases and that its degradation may play a role in modulating the biological activities of galectin-3.

Expression of the galactose binding protein Mac-2 by human melanoma cell-lines

The Mac-2 protein is a lectin specific for galactose-containing glycoconjugates. Present in some normal cells, it was also associated with the metastatic potential of some carcinoma cells. We studied Mac-2 expression in three human melanoma cell lines and in five variants and clones from one of them. By using the M3/38 rat monoclonal antibody, Mac-2 was demonstrated on cell surface by flow cytometry as well as in the cytoplasm and in the nucleus by confocal microscopy. The expression of Mac-2 was not correlated with that of terminal unsialylated Gal beta 1-3 GalNac structures on metastatic melanoma cell lines. However, the presence of extracellular Mac-2 containing vesicles was observed in cell lines with metastatic potency. Western blot analysis of cell lysates, in reducing or non-reducing conditions, revealed two bands of 34-36 and 93-98 kDa apparent M(r), also found in HL60 and P388.D1 cell lines used as positive controls.

The adhesive specificity of the soluble human lectin, IgE-binding protein, toward lipid-linked oligosaccharides. Presence of the blood group A, B, B-like, and H monosaccharides confers a binding activity to tetrasaccharide (lacto-N-tetraose and lacto-N-neotetraose) backbones

The immunoglobulin E-binding protein, epsilon BP (also known as CBP35, Mac-2, L-34, and L-29), is a beta-galactoside-binding protein of approximately 30 kDa and a member of the animal lectin family termed S-type or S-Lac. Multiple biological activities have been attributed to this lectin such as mediation of IgE binding to the surface of Langerhans cells and activation of mast cells through binding to the high affinity IgE receptor. In order to better understand the cell-binding activity and the proposed role for epsilon BP as a biological response modifier, we have studied the specificity of binding of the radioiodinated epsilon BP to a series of lipid-linked, structurally defined oligosaccharide sequences of the lacto/neolacto family. The results show that the minimum lipid-linked oligosaccharides that can support epsilon BP binding are pentasaccharides of the lacto/neolacto series and that the lectin binds more strongly to oligosaccharides of this family that bear the blood group A, B, or B-like determinants than to those bearing blood group H. This preferential binding of epsilon BP is also manifest with whole cells, as erythrocytes of blood groups A and B are more strongly bound by epsilon BP than those of blood group O. Blood group Le(a) and Le(x) sequences are not bound by the lectin.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression and function of an IgE-binding animal lectin (epsilon BP) in mast cells

epsilon BP (IgE-binding protein) is a 31,000 M(r) protein originally identified in rat basophilic leukemia (RBL) cells. The protein is composed of two domains with the amino-terminal domain containing a highly conserved repetitive sequence and the carboxyl-terminal domain containing consensus sequences shared by other beta-galactoside-binding soluble lectins. The protein has wide tissue distribution, is found on cell surfaces and in extracellular milieu. By combined efforts from several research groups including ours a multifunctional nature of this lectin began to emerge. This review emphasizes the following characteristics of epsilon BP: (i) epsilon BP is secreted by cells such as macrophages; (ii) like many other lectins, epsilon BP functions at least bivalently; (iii) epsilon BP has specificity for distinct oligosaccharide structures that have a terminal galactose not masked by sialic acids; and (iv) in addition to binding IgE, epsilon BP binds to surfaces of various cell types via lectin-carbohydrate interaction. Importantly, epsilon BP binds to the IgE receptor on mast cells. We propose that epsilon BP can function as a modulatory protein on various cells by cross-linking critical cell surface glycoproteins. The proposed action of epsilon BP on mast cells is presented as a model.

S-type mammalian lectins in allergic inflammation

Our understanding of the mechanisms of allergic disease is continuously influenced by new developments in the bio-medical sciences. The studies of glycoconjugates and animal lectins have emerged as an exciting new frontier. One family of animal lectins, soluble lactose-binding lectins, has been studied extensively by a number of laboratories. Evidence is mounting that members of this family of lectins exist in the extracellular space and may be capable of affecting functions of various cells. In this article Fu-Tong Liu presents a revised view of allergic inflammation with emphasis on the modulatory effect of soluble lectins on mast-cell function.

Decreased expression of Mac-2 (carbohydrate binding protein 35) and loss of its nuclear localization are associated with the neoplastic progression of colon carcinoma

The Mac-2 lectin (carbohydrate binding protein 35) is a soluble, 32- to 35-kDa phosphoprotein that binds galactose-containing glycoconjugates. We report here that the colonic epithelium is a major site of Mac-2 expression in vivo based on immunohistochemistry of human tissue specimens. In this epithelium, proliferating cells at the base of the crypts do not express Mac-2 but its expression increases with differentiation along the crypt-to-surface axis. Mac-2 expression is concentrated in the nuclei of these differentiated epithelial cells. The progression from normal mucosa to adenoma to carcinoma is associated with significant changes in Mac-2 nuclear localization and expression. In all adenomas (9/9) and carcinomas (13/13) examined, Mac-2 was not present in the nucleus but was localized in the cytoplasm. Sequencing of Mac-2 cDNAs from normal mucosa and carcinoma revealed no specific mutations that could account for this loss of nuclear localization. We also observed a 5- to 10-fold decrease in Mac-2 mRNA levels in cancer compared to normal mucosa as well as a significant reduction in the amount of Mac-2 protein expressed. These observations suggest that Mac-2 exclusion from the nucleus and its decreased expression may be related to the neoplastic progression of colon cancer.