Chicken tissue binding sites for a purified chicken lectin

Glycobiology of developing chicken kidney: Profiling the galectin family and selected β-galactosides

The concept of the sugar code interprets the cellular glycophenotype as a rich source of information read by glycan-lectin recognition in situ. This study's aim is the comprehensive characterization of galectin expression by immunohistochemistry during chicken nephrogenesis along with mapping binding sites by (ga)lectin histochemistry. Light and two-color fluorescence microscopy were used. First, six plant/fungal lectins that are specific for galectin-binding parts of N- and O-glycans were applied. The spatiotemporally regulated distributions of these glycans in meso- and metanephros equip cells with potential binding partners for the galectins. Complete galectin profiling from HH Stage 20 (about 70-72 hr) onward revealed cell-, galectin-, and stage-dependent expression patterns. Representatives of all three types of modular architecture of the galectin family are detectable, and overlaps of signal distribution in light and two-color fluorescence microscopy illustrate a possibility for functional cooperation among them. Performing systematic galectin histochemistry facilitated comparisons between staining profiles of plant lectins and galectins. They revealed several cases for differences so that tissue lectins appear to be selective among the β-galactosides. Notably, selectivity is also disclosed in intrafamily comparison. Thus, combining experimental series with plant and tissue lectins is a means to characterize target populations of glycans presented by cellular glycoconjugates for individual galectins. Our results document the presence and sophisticated level of elaboration among β-galactosides and among the members of the family of galectins during organogenesis, using chicken galectins and kidney as model. Thus, they provide a clear guideline for functional assays using supramolecular tools, cells, and organ cultures.

Nucleoplasmic and cytoplasmic glycoproteins

We have described a new form of protein glycosylation in which N-acetylglucosamine is glycosidically linked to the hydroxyl of serine or threonine (O-GlcNAc). Unlike most other forms of protein glycosylation, O-GlcNAc is predominantly localized in the nuclear and cytoplasmic compartments of cells, where it occurs on important nuclear pore glycoproteins, well-characterized cytoskeletal proteins, as well as on many chromatin proteins, including factors that regulate gene transcription. Gas-phase protein sequencing of three O-GlcNAc-modified proteins has identified a common structural feature at sites of O-GlcNAc addition. An assay for UDP-GlcNAc:polypeptide O-GlcNAc transferase has been developed. The enzyme appears to be membrane-associated, its active site is cytoplasmic, and it has an absolute requirement for Mn2+. We are now purifying this glycosyltransferase, characterizing its substrate specificity, and determining the extent of elongation of attached saccharide moieties. The functions of O-GlcNAc remain largely unknown, but it may be important in blocking phosphorylation sites, it may be required for the assembly of specific multiprotein complexes, it might serve as a nuclear transport signal, or it may be directly involved in the active transport of macromolecules across nuclear pores.

A comparative nuclear localization study of galectin-1 with other splicing components

Using both conventional and laser confocal fluorescence microscopy, the intracellular distribution of galectin-1 in HeLa cells was analyzed and compared with the localization of previously documented markers of the nucleus and cytoplasm. The Sm epitopes of the small nuclear ribonucleoprotein complexes (snRNPs) and the non-snRNP splicing factor SC35 yielded only nuclear staining. On the other hand, the enzyme lactate dehydrogenase was cytoplasmic. In contrast to these patterns in which nuclear versus cytoplasmic localizations appeared to be mutually exclusive, galectin-1, as well as galectin-3, yielded simultaneous nuclear and cytoplasmic staining. Confocal microscopy showed galectin-1 fluorescence throughout most of the sections from the top of the cell to the bottom. Through the middle sections, as the plane of focus cuts through the nucleus, there was definite fluorescence staining in the nuclear compartment. This nuclear localization was critically dependent on the type of detergent used to permeabilize the cell: cells treated with saponin or digitonin yielded exclusively cytoplasmic staining while Triton X-100-treated cells showed nuclear as well as cytoplasmic labeling. Finally, double-immunofluorescence analysis showed that, within the nucleoplasm, the following pairs of nuclear antigens could be colocalized in certain speckled structures: (a) SC35 versus Sm; (b) galectin-1 versus Sm; (c) galectin-3 versus Sm; and (d) galectin-1 versus galectin-3. These results establish the presence of galectin-1 in the nuclei of HeLa cells, a conclusion consistent with the identification of the protein in nuclear extracts of the same cells and with its documentation as a factor in pre-mRNA splicing.

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.

Characterization of quail intestinal mucin as a ligand for endogenous quail lectin

The S-type lectins have been shown to be components of mucosal scrapings, and in avian systems these lectins have been localized immunohistochemically to the mucosal surface and goblet cells of the intestine. The interaction of lectin specifically with purified mucin has not, however, been established. Quail intestinal mucin was purified by two subsequent isopycnic density-gradient centrifugations in CsCl and chromatography on Sepharose Cl-2B. Purified mucin, obtained from the void volume of the Sepharose column, was characterized by SDS/PAGE, amino acid and carbohydrate analyses, sensitivity to thiol reduction, and cross-reactivity with antibody preparations to rat and human intestinal mucins on Western blots. Antibody raised against purified quail mucin partially cross-reacts with purified rat, rabbit and human intestinal mucins, and specifically labels the mucosal surface and goblet cells of quail intestine by the immunoperoxidase technique. Protein eluted by lactose from an affinity matrix composed of quail intestinal mucin possessed the same molecular mass on SDS/PAGE as intestinal lectin and reacted on Western blots with a lectin-specific antibody. The data clearly demonstrate the co-localization of lectin and mucin in the quail intestine and also the ability of the lectin to specifically interact with the purified mucin, raising the question of the role of endogenous lectins in secretions.

Lectin localization in human nerve by biochemically defined lectin-binding glycoproteins, neoglycoprotein and lectin-specific antibody

Molecular recognition can be mediated by protein (lectin)-carbohydrate interaction, explaining the interest in this topic. Plant lectins and, more recently, chemically glycosylated neoglycoproteins principally allow to map the occurrence of components of this putative recognition system. Labelled endogenous lectins and the lectin-binding ligands can add to the panel of glycohistochemical tools. They may be helpful to derive physiologically valid conclusions in this field for mammalian tissues. Consequently, experiments were prompted to employ the abundant beta-galactoside-specific lectin of human nerves in affinity chromatography and in histochemistry to purify and to localize its specific glycoprotein ligands. In comparison to the beta-galactoside-specific plant lectins from Ricinus communis and Erythrina cristagalli, notable similarities were especially detectable in the respective profiles of the mammalian and the Erythrina lectin. They appear to account for rather indistinguishable staining patterns in fixed tissue sections. Inhibitory controls within affinity chromatography, within solid-phase assays for each fraction of lectin-binding glycoproteins and within histochemistry as well as the demonstration of crossreactivity of the three fractions of lectin-binding glycoproteins with the biotinylated Erythrina lectin in blotting ascertained the specificity of the lectin-glycoprotein interaction. In addition to monitoring the accessible cellular ligand part by the endogenous lectin as probe, the comparison of immunohistochemical and glycohistochemical detection of the lectin in serial sections proved these methods for receptor analysis to be rather equally effective. The observation that the biotinylated lectin-binding glycoproteins are also appropriate ligands in glycohistochemical analysis warrants emphasis.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence that the 14 kDa soluble beta-galactoside-binding lectin in man is encoded by a single gene

A full-length cDNA clone for the 14 kDa soluble beta-galactoside-binding lectin of man has been isolated from a cDNA library from HepG2 hepatoma cells. The derived amino acid sequence is identical with that of the 14 kDa lectin from human placenta. The results of Northern and Southern blotting of several different human cell lines using a cDNA probe for the 14 kDa lectin suggest the presence of a single gene for this protein. Thus, although there are multiple proteins in the range 14-200 kDa which are antigenically related to this lectin, we would conclude from the present study that there is only one gene for the 14 kDa lectin.

Lectin activity and distribution of chicken lactose lectin I in the extracellular matrix of the chick developing kidney

A lectin activity inhibitable by thiodigalactose, N-acetyllactosamine, lactulose, lactose and by an antibody raised against CLL I (chicken-lactose lectin I) has been investigated in the chick embryo developing kidney. At post-induction stages this activity was found in both mesonephros and metanephros. In immunofluorescence and immunoelectron microscopy, the extracellular distribution of CLL I was similar in the mesonephros and the metanephros. The lectin was never found intracellularly; cultured kidney cells did not express any endogenous lectin but were rich in lectin-receptor sites, which led to the hyphothesis that CLL I is not produced in situ but could be adsorbed on renal cells. Potential physiological roles for embryonic lectins are discussed.

Detection of sugar-binding sites in the fibrillar and the granular components of the nucleolus: an experimental study in cultured mammalian cells

The intranucleolar distribution of sugar-binding sites (i.e., lectin-like molecules) was analyzed in segregated nucleoli of actinomycin D-treated HeLa cells. The detection of sugar-binding sites was performed by incubation either of permeabilized nuclei in the presence of fluorescein-labeled neoglycoproteins or of ultrathin sections cut through in situ-fixed nuclei in the presence of gold-labeled neoglycoproteins. In the former case, the fluorescent nucleolar components were identified by comparison with the nucleolar components of similarly treated cells observed in electron microscopy. For the first time, this study reveals the presence of sugar-binding sites in both the fibrillar and the granular components of the nucleolus. In view of the data already reported on the biochemical composition of the nucleolus, some of our results led us to conclude that the nucleolar sugar-binding sites are lectin-like proteins. These proteins could be associated with preribosomes since the nucleolus is the site of both synthesis and stockage of ribosomal precursors. Some results from this study, however, show that the possibility of a relationship between some lectins and a structural component cannot be excluded.

Endogenous lectins from cultured cells: nuclear localization of carbohydrate-binding protein 35 in proliferating 3T3 fibroblasts

Proliferating 3T3 mouse fibroblasts contain higher levels of the lectin carbohydrate-binding protein 35 (CBP35) than do quiescent cultures of the same cells. An immunofluorescence study was carried out with a rabbit antiserum directed against CBP35 to map the cellular fluorescence distribution in a large population of cells under different growth conditions. This cytometric analysis showed that the lectin is predominantly localized in the nucleus of the proliferating cells. In quiescent 3T3 cultures, the majority of the cells lost their nuclear staining and underwent a general decrease in the overall fluorescence intensity. Stimulation of serum-starved quiescent 3T3 cells by the addition of serum resulted in an increase in the level of CBP35. The percentage of cells showing distinct punctate intranuclear staining reached a maximum at about the same time as the onset of the first S-phase of the cell cycle. All of these results suggest that CBP35 may be a protein whose presence in the nucleus, in discrete punctate distribution, is coordinated with the proliferation state of the cell.

Analysis of sugar-binding sites in mammalian cell nuclei by quantitative flow microfluorometry

Quantitative flow microfluorometry of neoglycoprotein (bovine serum albumin coupled to sugar and to fluorescein) binding demonstrated the existence of sugar-binding sites (i.e., lectin-like molecules) in isolated BHK cell nuclei. The very similar labeling intensities obtained with nuclei isolated by cell lysis and with permeabilized karyoplasts obtained by enucleation strengthened the idea that the binding sites are borne by actual nuclear structures and not by cytoplasmic or membrane-derived contaminants. With both nuclei-isolation procedures, neoglycoproteins (containing similar numbers of sugar residues) used as markers can be similarly classified. Fluorescence microscopy further indicated that in both nuclear preparations, the neoglycoprotein binding sites were associated with the nucleoli as well as with nucleoplasmic ribonucleoprotein elements. Nuclei from exponentially growing cells bound much greater amounts of neoglycoprotein than did nuclei from contact-inhibited cells.

Endogenous lectins from cultured cells: subcellular localization of carbohydrate-binding protein 35 in 3T3 fibroblasts

In previous studies, a lectin designated as carbohydrate-binding protein 35 (CBP35) has been isolated from cultured 3T3 fibroblasts. In the present study, rabbit antibodies directed against CBP35 were used to analyze the subcellular distribution of CBP35 in 3T3 cells. Several lines of evidence indicate that CBP35 is found externally exposed at the cell surface: immunofluorescent staining of live 3T3 cells; agglutination of suspension of 3T3 fibroblasts by specific antibodies; and isolation, by immunoaffinity chromatography, of a Mr 35,000 component from cells surface-labeled with 125I. In addition to the plasma membrane, CBP35 could also be found intracellularly, as revealed by immunofluorescence studies of fixed and permeabilized 3T3 cells. The staining pattern showed the presence of CBP35 on the nucleus and in the cytoplasm. These results are consistent with the finding that among several subcellular fractions, CBP35 can be found by immunoblotting procedures in the nuclear pellet, the soluble fraction, and the plasma membrane fraction of the postnuclear supernatant.

Transformation and growth related changes in levels of nuclear and cytoplasmic proteins antigenically related to mammalian beta-galactoside-binding lectin

Immunofluorescence and immunoblotting experiments, using a monoclonal antibody to the 13 kDa mammalian beta-galactoside-binding lectin have shown that human lymphocytes contain nuclear and cytoplasmic proteins of apparent molecular masses of 130, 80, 65 and 13 kDa that are antigenically related to the lectin and whose levels and patterns of expression change in association with transformation, or after stimulation with mitogens. These observations, together with the finding that the myeloid cell line K562 is also rich in the 130 kDa component, whereas the mature granulocytes of normal donors and of patients with chronic myeloid leukaemia are lacking in all of the immunoreactive forms, raise the possibility that this family of lectin-related proteins may be components of growth regulatory systems that are variously elicited in the transformed and stimulated cells.

Endogenous ligands of rat lung beta-galactoside-binding protein (galaptin) isolated by affinity chromatography on carboxyamidomethylated-galaptin-Sepharose

Rat lung beta-galactoside-binding protein (galaptin) is developmentally regulated during postnatal lung development. In common with other vertebrate galaptins, it is very labile when purified and dependent on the presence of exogenous thiol reagents. Reaction of rat lung galaptin with iodoacetamide resulted in a stable active carboxyamidomethylated galaptin that could be coupled to Sepharose. The resultant affinity matrix bound asialoglycoproteins, and these could be quantitatively eluted with disaccharide haptens. The carboxyamidomethylated-galaptin-Sepharose affinity matrix was used to search for endogenous ligands in 13-day-rat lung. Cytosolic fractions of developing rat lung contained no moieties that could be specifically eluted with disaccharide hapten. Only when membranous fractions were extracted with 1% Triton were glycoproteins solubilized that bound to the affinity matrix and could be specifically eluted with disaccharide hapten. The eluted glycoproteins were potent inhibitors of galaptin binding to asialo-orosomucoid. Sodium dodecyl sulphate/polyacrylamide-gel electrophoresis identified these glycoproteins as being of high Mr, with three components of Mr 160000-200000 and a smaller component of Mr 75000. This is the first evidence for specific membrane-associated glycoproteins being the ligands of rat lung galaptin.

Colocalization of discoidin-binding ligands with discoidin in developing Dictyostelium discoideum

The Dictyostelium discoideum lectins, discoidin I and discoidin II, and the endogenous ligands to which they bind were immunohistochemically localized in sections of this organism at successive stages of development. For these studies, an axenic strain, AX3, was grown in a macromolecule-depleted medium rather than on bacteria, which themselves contain discoidin-binding ligands. Discoidin I-binding sites (endogenous ligands) in sections of D. discoideum were concentrated in the slime coat around aggregates, whereas discoidin II-binding sites were observed in a vesicle-like distribution in prespore cells and also in spore coats. In contrast, discoidin II did not bind to the slime coat and discoidin I bound relatively poorly to prespore cells and spore coats. The distributions of the endogenous lectins themselves were the same in axenically grown cells as previously reported for cells raised on bacteria. Discoidin I was concentrated in the slime coat and around stalk cells, and discoidin II was prominent in and around prespore cells. The congruent localization of each lectin with its endogenous ligand suggests that discoidin I normally functions in association with glycoconjugates in the slime around aggregates, and discoidin II with the galactose-rich spore coat polysaccharide.

Production and characterization of monoclonal antibodies to beta-galactoside-binding lectin of bovine heart muscle. Direct evidence that haemagglutinating activity is associated with a 13kDa protein

With the aim of obtaining monospecific antibodies against the beta-galactoside-binding lectin of bovine heart muscle, spleen cells from Lou rats immunized with lectin were fused with the rat myeloma line Y3.Ag1.2.3. Two immunoglobulin M (IgM)-producing clones, designated NIBy 142-36/8 and NIBy 143-9/5, derived from separate fusions, were used to generate ascites containing high-titre binding activity against the 13kDa component in preparations of lectin. Direct evidence that haemagglutinating activity is associated with the 13kDa protein was obtained by the specific elution of 13kDa polypeptides with haemagglutinating activity from an immobilized antibody adsorbent. Solid-phase radiobinding assays and immunoblotting of isolated lectins and/or muscle homogenates confirmed the earlier indications with conventional antisera that the beta-galactoside-binding lectins of bovine, human and monkey muscle tissue are antigenically related.

Soluble lectins: a new class of extracellular proteins

Soluble lectins of cellular slime molds and vertebrates are present at extracellular sites in the developing or adult tissues that make them. Some lectins are concentrated around cell groups, as in extracellular matrix or elastic fibers. Others are at the interface between cells and the external environment, as in mucin or slime. Specific glycoproteins, proteoglycans, or polysaccharides that bind these endogenous lectins may also be present at these sites. Interactions between the lectins and glycoconjugates appear to play a role in shaping extracellular environments.

Endogenous lectins in chickens and slime molds: transfer from intracellular to extracellular sites

Endogenous lectins in both cellular slime molds and chicken tissues have been localized primarily intracellularly, in contrast with the predominantly extracellular localization of the glycoproteins, glycolipids, and glycosaminoglycans with which they might interact. Here we present evidence that lectins in both of these organisms may be externalized and become associated with the cell surface and/or extracellular materials. In chicken intestine, chicken-lactose-lectin-II is shown to be localized in the secretory granules of the goblet cells, along with mucin, and to be secreted onto the intestinal surface. In embryonic muscle, chicken-lactose-lectin-I is shown to be externalized with differentiation, ultimately becoming localized on the surface of myotubes and in the extracellular spaces. In a cellular slime mold, Dictyostelium purpureum, externalization of lectin is elicited by either polyvalent glycoproteins that bind the small amount of endogenous cell surface lectin, or by slime mold or plant lectins that bind unoccupied complementary cell surface oligosaccharides. These results suggest that externalization of endogenous lectin may be a response to specific external signals. We conclude that lectins are frequently held in intracellular reserves awaiting release for specific external functions.