Restricted tissue distribution of a 37-kD possible adherens junction protein

Galectin network in osteoarthritis: galectin-4 programs a pathogenic signature of gene and effector expression in human chondrocytes in vitro

Galectin-4 (Gal-4) is a member of the galectin family, which have been identified as galactose-binding proteins. Gal-4 possesses two tandem repeat carbohydrate recognition domains and acts as a cross-linking bridge in sulfatide-dependent glycoprotein routing. We herein document its upregulation in osteoarthritis (OA) in correlation with the extent of cartilage degradation in vivo. Primary human OA chondrocytes in vitro respond to carbohydrate-inhibitable Gal-4 binding with the upregulation of pro-degradative/-inflammatory proteins such as interleukin-1β (IL-1β) and matrix metalloproteinase-13 (MMP-13), as documented by RT-qPCR-based mRNA profiling and transcriptome data processing. Activation of p65 by phosphorylation of Ser536 within the NF-κB pathway and the effect of three p65 inhibitors on Gal-4 activity support downstream involvement of such signaling. In 3D (pellet) cultures, Gal-4 presence causes morphological and biochemical signs of degradation. Taken together, our findings strongly support the concept of galectins acting as a network in OA pathogenesis and suggest that blocking their activity in disease progression may become clinically relevant in the future.

Chicken GRIFIN: A homodimeric member of the galectin network with canonical properties and a unique expression profile

Occurrence of the adhesion/growth-regulatory galectins as family sets the challenge to achieve a complete network analysis. Along this route taken for a well-suited model organism (chicken), we fill the remaining gap to characterize its seventh member known from rat as galectin-related inter-fiber protein (GRIFIN) in the lens. Its single-copy gene is common to vertebrates, with one or more deviations from the so-called signature sequence for ligand (lactose) contact. The chicken protein is a homodimeric agglutinin with capacity to bind β-galactosides, especially the histo-blood group B tetrasaccharide, shown by solid-phase/cell assays and a glycan microarray. Mass spectrometric identification of two lactose-binding peptides after tryptic on-bead fragmentation suggests an interaction at the canonical region despite a sequence change from Arg to Val at the site, which impairs reactivity of human galectin-1. RT-PCR and Western blot analyses of specimen from adult chicken organs reveal restriction of expression to the lens, here immunohistochemically throughout its main body. This report sets the stage for detailed structure-activity studies to define factors relevant for affinity beyond the signature sequence and to perform the first complete network analysis of the galectin family in developing and adult organs of a vertebrate.

Epithelial stratification and placode invagination are separable functions in early morphogenesis of the molar tooth

Ectodermal organs, which include teeth, hair follicles, mammary ducts, and glands such as sweat, mucous and sebaceous glands, are initiated in development as placodes, which are epithelial thickenings that invaginate and bud into the underlying mesenchyme. These placodes are stratified into a basal and several suprabasal layers of cells. The mechanisms driving stratification and invagination are poorly understood. Using the mouse molar tooth as a model for ectodermal organ morphogenesis, we show here that vertical, stratifying cell divisions are enriched in the forming placode and that stratification is cell division dependent. Using inhibitor and gain-of-function experiments, we show that FGF signalling is necessary and sufficient for stratification but not invagination as such. We show that, instead, Shh signalling is necessary for, and promotes, invagination once suprabasal tissue is generated. Shh-dependent suprabasal cell shape suggests convergent migration and intercalation, potentially accounting for post-stratification placode invagination to bud stage. We present a model in which FGF generates suprabasal tissue by asymmetric cell division, while Shh triggers cell rearrangement in this tissue to drive invagination all the way to bud formation.

Summary: During tooth development in mice, FGF-dependent vertical cell divisions thicken the tooth placode while Shh drives cell rearrangements that cause invagination.

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

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

Galectin-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.

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.

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.

Expression of vinculin in autoimmune cutaneous diseases

BACKGROUND

Reports have appeared that sera of patients with systemic autoimmune disorders have demonstrated autoantibodies to vinculin.

OBJECTIVE

To determine the presence and distribution of vinculin in the skin of patients with cutaneous autoimmune disorders.

METHODS

Semiquantitative immunohistochemistry investigations for presence of vinculin were conducted on skin biopsy specimens from patients with pemphigus vulgaris (PV), bullous pemphigoid (BP), and various collagen vascular diseases, and from healthy controls.

RESULTS

Results of staining for vinculin were positive in 2 of 7 PV patients, 6 of 9 BP patients, and all 6 cutaneous autoimmune patients. Staining results were negative in all controls. Strong immunostaining to vinculin was found in 3 of 6 vinculin-positive BP patients and 5 of 6 vinculin-positive cutaneous autoimmune patients.

CONCLUSIONS

The expression and distribution of vinculin are accentuated in patients with various skin autoimmune diseases and appear to be stronger in diseases involving the basement membrane, where it is thought to be relatively more important than in other skin disorders.

Recognition Mechanism of Galectin-4 for Cholesterol 3-Sulfate

Galectin-4 binds to glycosphingolipids carrying 3-O-sulfated Gal residues, and it co-localizes on the cell surface of human colonic adenocarcinoma cells with glycosphingolipids carrying SO(-)(3)-->3Galbeta1-->3(GalNAc) residues (Ideo, H., Seko, A., and Yamashita, K. (2005) J. Biol. Chem. 280, 4730-4737). In the present study, it was found that galectin-4 also binds to cholesterol 3-sulfate, which has no beta-galactoside moiety. This characteristic of galectin-4 is unique within the galectin family. The site-directed mutated galectin-4-R45A had diminished binding ability toward cholesterol 3-sulfate, suggesting that Arg(45) of galectin-4 is indispensable for cholesterol 3-sulfate recognition. Gel filtration and chemical cross-linking experiments revealed that some galectin-4 exists as dimers, and this multivalency seemed to enhance its avidity for cholesterol 3-sulfate binding. Cholesterol 3-sulfate and sulfatide co-existed with galectin-4 in detergent-insoluble fractions of porcine esophagus and intestine, respectively. These results suggested that not only sulfated glycosphingolipids but also cholesterol 3-sulfate are endogenous ligands for galectin-4 in vivo.

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.

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.

Homodimeric galectin-7 (p53-induced gene 1) is a negative growth regulator for human neuroblastoma cells

The extracellular functions of galectin-7 (p53-induced gene 1) are largely unknown. On the surface of neuroblastoma cells (SK-N-MC), the increased GM1 density, a result of upregulated ganglioside sialidase activity, is a key factor for the switch from proliferation to differentiation. We show by solid-phase and cell assays that the sugar chain of this ganglioside is a ligand for galectin-7. In serum-supplemented proliferation assays, galectin-7 reduced neuroblastoma cell growth without the appearance of features characteristic for classical apoptosis. The presence of galectin-3 blocked this effect, which mechanistically resembles that of galectin-1. By virtue of carbohydrate binding, galectin-7 thus exerts neuroblastoma growth control similar to galectin-1 despite their structural differences. In addition to p53-linked proapoptotic activity intracellularly, galectin-7, acting as a lectin on the cell surface, appears to be capable of reducing cancer cell proliferation in susceptible systems.

Defining the glycophenotype of squamous epithelia using plant and mammalian lectins. Differentiation-dependent expression of alpha2,6- and alpha2,3-linked N-acetylneuraminic acid in squamous epithelia and carcinomas, and its differential effect on binding of the endogenous lectins galectins-1 and -3

A thorough characterization of the properties of squamous epithelial cells is necessary in order to improve our understanding of the functional aspects of normal development and malignant aberrations. Up to now, studies have focused almost exclusively on monitoring distinct protein markers. With our growing awareness of the coding function of glycan chains of cellular glycoconjugates and their interaction with receptors (lectins) in situ, defining the glycophenotype of these cells has become an important issue. Whereas the commonly applied plant lectins are tools used to map the presence and localization of biochemically defined saccharide epitopes, the introduction of endogenous (mammalian) lectins to this analysis enables us to take the step from monitoring the presence of glycan to understanding the functional implications by revealing ligand properties of the detected epitope for tissue lectin. Thus, in this study we investigated a distinct aspect of glycosylation using plant and mammalian lectins, i.e. the linkage type of sialylation. We first mapped the expression profile of the type of sialylation (alpha2,3- or alpha2,6-linked) by plant lectins. Based on the hypothesis that this factor regulates accessibility of ligands for endogenous lectins we introduced two labeled galectins to this study. Galectin-3 (but not galectin-1) binding was related to cell differentiation in normal adult and developing epithelia, cultured epidermal cells, and carcinomas derived from these epithelia. The presented data suggest that alpha2,6-linked N-acetyl-D-neuraminic acid moieties could serve to mask galectin-3-reactive glycoepitopes. As a consequence, monitoring of the linkage type of sialic acid in glycans by plant lectins therefore has implications for the extent of glycan reactivity with endogenous lectins, pointing to a potential function of changes in sialylation type beyond these cell and lectin systems.

Secretion of the galectin family of mammalian carbohydrate-binding proteins

Galectins are cytosolic proteins that lack any signal sequence for transport into the endoplasmic reticulum and are not glycosylated, although several galectins contain consensus sites for N-glycosylation, indicating that these proteins do not traverse the ER-Golgi network. However, there is abundant evidence for the extracellular localisation of some galectins at cell surfaces, in the extracellular matrix and in cell secretions consistent with other evidence for extracellular roles of galectins as modulators of cell adhesion and signalling. How then are galectins secreted if not through the classical secretory pathway? Do all galectins share the same secretory pathway? Can a particular galectin utilise more than one secretory pathway? If galectins play important extracellular roles how is their secretion regulated in relation to function? These are still largely unanswered questions but recent studies are beginning to give glimpses into some novel aspects of the secretion of these intriguing proteins.

Two domains of rat galectin-4 bind to distinct structures of the intercellular borders of colorectal epithelia

Galectin-4 (G4) is a member of a family of soluble galactoside-binding lectins found in various mammalian tissues. To determine the function of this protein in colorectal tissue, we separately produced the N- and C-terminal carbohydrate binding domains (CBD) of rat G4 as a recombinant glutathione S-transferase (GST) fusion protein (G4-N and G4-C) and examined the tissue binding site(s) of each CBD by light and electron microscopy (LM and EM). At the LM level, both fusion proteins stained the intercellular borders of the surface-lining epithelial cells of colorectal mucosa. At the EM level, two proteins recognized spatially close but distinct subcellular structures. G4-N stained electron-lucent flocculent substances freely located in the intercellular spaces, whereas G4-C bound to the lateral cell membranes demarcating the intercellular spaces. These findings suggest that colorectal G4 may be involved in crosslinking the lateral cell membranes of the surface-lining epithelial cells, thereby reinforcing epithelial integrity against mechanical stress exerted by the bowel lumen. (J Histochem Cytochem 47:75-82, 1999)

Novel galactose-binding proteins in Annelida. Characterization of 29-kDa tandem repeat-type lectins from the earthworm Lumbricus terrestris

Novel type lectins were found in the phylum Annelida, i.e. in the earthworm, tubifex, leech, and lugworm. The lectins (29-31 kDa) were extracted from the worms without the use of detergent and purified by affinity chromatography on asialofetuin-agarose. On the basis of the partial primary structures of the earthworm Lumbricus terrestris 29-kDa lectin (EW29), degenerate primers were synthesized for use in the reverse transcriptase-polymerase chain reaction. An amplified 155-base pair fragment was used to screen a cDNA library. Four types of full-length clones were obtained, all of which encoded 260 amino acids, but which were found to differ at 29 nucleotide positions. Since three of them resulted in non-silent substitutions, EW29 mRNA was considered to be a mixture of at least three distinct polynucleotides encoding the following proteins: Ala44-Gln197-Ile213 (clone 5), Gly44-Gln197-Val213 (clone 7), and Ala44-His197-Ile213 (clones 8 and 9; different at the nucleotide level, but encoding an identical polypeptide). Genomic polymerase chain reaction using DNA from a single worm revealed that the single worm already had four sets of cDNAs. The EW29 protein showed two features. First, the lectin was composed of two homologous domains (14,500 Da) showing 27% identity with each other. When each of the domains was separately expressed in Escherichia coli, the C-terminal domain was found to bind to asialofetuin-agarose as strongly as the whole protein, whereas the N-terminal domain did not bind and only retardation was observed. EW29 was found to exist as a monomer under non-denaturing conditions. It had significant hemagglutinating activity, which was inhibited by a wide range of galactose-containing saccharides. Second, EW29 contained multiple short conserved motifs, "Gly-X-X-X-Gln-X-Trp." Similar motifs have been found in many carbohydrate-recognizing proteins from an extensive variety of organisms, e.g. plant lectin ricin B-chain and Clostridium botulinum 33-kDa hemagglutinin. Therefore, these carbohydrate-recognition proteins appear to form a protein superfamily.

Galectin-4 and galectin-6 are two closely related lectins expressed in mouse gastrointestinal tract

Galectins are a family of carbohydrate-binding proteins that share a conserved sequence and affinity for beta-galactosides. Some, such as galectin-1, are isolated as dimers and have a single carbohydrate recognition domain (CRD) in each monomer, whereas others, such as galectin-4, are isolated as monomers and have two CRDs in a single polypeptide chain. In the course of studying mouse colon mRNA for galectin-4, we detected a related mRNA that encodes a new galectin that also has two CRDs in a single peptide chain. The new galectin, galectin-6, lacks a 24-amino acid stretch in the link region between the two CRDs that is present in galectin-4. Otherwise, these two galectins have 83% amino acid identity. Expression of both galectin-4 and galectin-6 is confined to the epithelial cells of the embryonic and adult gastrointestinal tract. Galectin-4 is expressed at about equal levels in colon and small intestine but much less in stomach, whereas galectin-6 is expressed at about equal levels throughout the gastrointestinal tract.

Galectin-4 and small intestinal brush border enzymes form clusters

Detergent-insoluble complexes prepared from pig small intestine are highly enriched in several transmembrane brush border enzymes including aminopeptidase N and sucrase-isomaltase, indicating that they reside in a glycolipid-rich environment in vivo. In the present work galectin-4, an animal lectin lacking a N-terminal signal peptide for membrane translocation, was discovered in these complexes as well, and in gradient centrifugation brush border enzymes and galectin-4 formed distinct soluble high molecular weight clusters. Immunoperoxidase cytochemistry and immunogold electron microscopy showed that galectin-4 is indeed an intestinal brush border protein; we also localized galectin-4 throughout the cell, mainly associated with membraneous structures, including small vesicles, and to the rootlets of microvillar actin filaments. This was confirmed by subcellular fractionation, showing about half the amount of galectin-4 to be in the microvillar fraction, the rest being associated with insoluble intracellular structures. A direct association between the lectin and aminopeptidase N was evidenced by a colocalization along microvilli in double immunogold labeling and by the ability of an antibody to galectin-4 to coimmunoprecipitate aminopeptidase N and sucrase-isomaltase. Furthermore, galectin-4 was released from microvillar, right-side-out vesicles as well as from mucosal explants by a brief wash with 100 mM lactose, confirming its extracellular localization. Galectin-4 is therefore secreted by a nonclassical pathway, and the brush border enzymes represent a novel class of natural ligands for a member of the galectin family. Newly synthesized galectin-4 is rapidly "trapped" by association with intracellular structures prior to its apical secretion, but once externalized, association with brush border enzymes prevents it from being released from the enterocyte into the intestinal lumen.

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

Two beta-galactoside-binding proteins were found to be prominently expressed in the human colon adenocarcinoma T84 cell line. Cloning and sequencing of one, a 36-kDa protein, identified it as the human homolog of galectin-4, a protein containing two carbohydrate binding domains and previously found only in the epithelial cells of the rat and porcine alimentary tract. The other, a 29-kDa protein, is galectin-3, containing a single carbohydrate binding domain, previously found in a number of different cell types including human intestinal epithelium. Despite the marked similarities in the carbohydrate binding domains of these two galectins, their cellular distribution patterns are strikingly different and vary with cellular conditions. In confluent T84 cells, galectin-4 is mostly cytosolic and concentrated at the basal membrane, whereas galectin-3 tends to be concentrated in large granular inclusions mostly at the apical membrane. In subconfluent T84 cells, each galectin is distributed to specific domains of lamellipodia, with galectin-4 concentrated in the leading edge and galectin-3 more proximally. Such different localization of galectins-4 and -3 within T84 cells implies different targeting mechanisms, ligands, and functions. The localization of galectin-4 suggests a role in cell adhesion which is also supported by the ability of immobilized recombinant galectin-4 to stimulate adhesion of T84 cells.

Recombinant galectin-1 recognizes mucin and epithelial cell surface glycocalyces of gastrointestinal tract

Rat gastrointestinal (GI) tract is rich source of galectins, a family of mammalian galactoside-binding lectins. To determine which tissue component is the relevant glycoconjugate ligand for the galectins, we produced recombinant galectin-1 and surveyed its binding sites on tissue sections of rat GI tract. Mucin and epithelial surface glycocalyces of both gastric and intestinal mucosa were intensely stained. This finding raises the possibility that some GI tract galectins known to be secreted by the epithelia may recognize these glycoconjugates and crosslink them into a macromolecular mass. This galectin-ligand complex may play a role in protecting the epithelial surface against luminal contents such as gastric acid, digestive enzymes, and foreign organisms.