Extracellular lectin and its glycosaminoglycan inhibitor in chick muscle cultures

Purification of Two Novel Sugar Acid-binding Lectins from Haplomitrium Mnioides (bryophyte, Plantae) and their Preliminary Characterization

Two novel sugar acid-binding lectins were purified from Haplomitrium mnioides (Lindb.) Schust. using a procedure consisting of ammonium sulfate precipitation, G-50 gel filtration, hydroxyapatite chromatography, and HW-50 gel filtration. We reported their partial physicochemical properties: molecular weight, affinity for carbohydrates and organic acids, pH stability, and dependence of their hemagglutination activity on metal ions. We also determined their N-terminal amino acid sequences. H. mnioides lectins (HMLs) were monomers (one with a molecular weight of approximately 27 kDa, and the other with a molecular weight of approximately 105 kDa) under both nonreducing and reducing conditions. They were named HML27 and HML105, respectively. Both HMLs had an affinity for N-acetylneuraminic acid, D-glucuronic acid, D-glucaric acid, bovine submaxillary mucin, heparin, and organic acids, such as citrate, 2-oxoglutaric acid, and D-2-hydroxyglutarate. Furthermore, HML27 had an affinity for α-D-galacturonic acid, D-malate, L-malate, and pyruvate, while HML105 had an affinity for D-gluconic acid. HML27 and HML105 are novel plant lectins: they have an affinity for sugar acids and organic acids and specifically recognize the carboxyl group, and there is no homology between their N-terminal amino acid sequences and those of the previously described lectins and agglutinins.

Structure, secretion, and bacterial specificity of an endogenous lectin from cystic fibrosis lung

Endogenous heparin-binding lectin purified from postmortem lung samples of two cystic fibrosis (CF) patients was compared to lectin derived from normal tissue with respect to structure, carbohydrate specificity, interaction with alginate derived from CF isolates of Pseudomonas aeruginosa, and secretion within the lung. Lectin was purified from extracts of lung tissue by gel filtration on Sepharose CL-2B followed by affinity chromatography on heparin-Sepharose. Lectin purified from either CF lung or control tissue ran as two peptides of approximately 16,000 and 13,000 molecular weight on electrophoresis in sodium dodecyl sulfate. The lectins displayed similar carbohydrate specificity and interacted in much the same way with bacterial alginate. An increase in lectin secretion was seen in CF lungs affecting the bronchial epithelial cells and the mucosal glands. The data suggest that the major changes seen in endogenous heparin-binding lectin in CF are related to the quantity and distribution of lectin secretion.

Localization of endogenous galactoside-binding lectin during morphogenesis of Xenopus laevis

A monoclonal antibody has been produced against Xenopus laevis galactoside-binding neural-crest-stage lectin. This antibody inhibits lectin-mediated hemagglutination. Using this antibody in conjunction with immunohistochemical techniques, lectin deposition has been studied in embryos and tadpoles at different stages of morphogenesis, from initial neural crest migration, up to the formation of a swimming tadpole. Lectin levels change during development in different regions of the embryo and tadpole, decreasing in migratory cells, and increasing in sites where cells become more adhesive to one another. The results suggest that galactoside-binding lectins may be an important class of cellular adhesion molecules during these stages of development.

Endogenous lectins as mediators of tumor cell adhesion

Endogenous carbohydrate-binding proteins have been found in various normal tissues and cells. Although lectins with different sugar-binding specificities have been described, the most prevalent ones are those that bind beta-galactosides. The ability of some normal and malignant cells to bind exogenous carbohydrate-containing ligands suggested that lectinlike activity is associated with the cell surface and that carbohydrate-binding proteins might mediate intercellular recognition and adhesion. We found that extracts of various cultured murine and human tumor cells exhibit a galactoside-inhibitable hemagglutinating activity. This activity was associated with two proteins of molecular weights of 34,000 and 14,500 daltons, which were purified by affinity chromatography by using immobilized asialofetuin. That these lectins are present on the cell surface was indicated by the binding of monoclonal antilectin antibodies to the surface of various tumor cells and by the immunoprecipitation of 125I-labeled lectins from solubilized cell-surface iodinated cells by polyclonal antilectin antibodies. That these cell surface lectins are functional was demonstrated by the ability of the galactose-terminating asialofetuin to enhance cell aggregation and of asialofetuin glycopeptides to block this homotypic aggregation as well as to suppress cell attachment to substratum, and by the inhibition of both asialofetuin-induced cell aggregation and cell attachment to substratum by the binding of monoclonal antilectin antibodies to the cell surface. These findings implicate cell surface lectins as mediators of cell-cell and cell-substratum adhesion. Some of these cellular interactions might be important determinants of tumor cell growth and metastasis.

Studies on cellular adhesion of Xenopus laevis melanophores: modulation of cell-cell and cell-substratum adhesion in vitro by endogenous Xenopus galactoside-binding lectin

We have investigated cell-cell and cell-substratum adhesion of Xenopus laevis neural crest cells at various stages of melanophore differentiation. Single-cell suspensions were obtained by trypsinization and aggregated in a cell-cell adhesion assay. Unpigmented cells did not adhere while the rate of adhesion of melanophores correlated with the degree of melanization. Melanophore cell-cell adhesion decreased significantly in the presence of beta-galactosidase, which suggests that cell-surface galactose is involved. Beta-galactoside-binding lectin has been isolated and purified from embryos at the stage of neural crest migration. When added to aggregating cells smaller, looser clusters formed compared to controls. When lectin was added to cells in stationary culture to test cell-substratum adhesion, melanophores spread more smoothly and formed more regular spacing patterns. These results suggest that this lectin can modulate receptors used in cell-cell and cell-substratum adhesion of melanophores.

Endogenous galactoside-binding lectins: a new class of functional tumor cell surface molecules related to metastasis

The formation of secondary tumors by circulating cancer cells (blood-borne metastasis) correlates with an increased tendency of the cells to form emboli by aggregation with other tumor cells or with host cells. Although it is evident that cell-cell recognition and adhesion are mediated by cell surface components, the identity of these molecules is only now being unraveled. Over the last decade an increasing number of studies have demonstrated the presence of endogenous carbohydrate-binding proteins on the surface of various normal cells, and it has been proposed that such lectin-like molecules might be involved in intercellular adhesion. We have shown that various tumor cell lines contain endogenous galactose-specific lectins. Lectin activity was detected at the cell surface by the binding of asialofetuin. This glycoprotein also enhanced the aggregation of the tumor cells. After purification by affinity chromatography on immobilized asialofetuin the lectin activity was associated with two proteins of Mr 14,500 and 34,000. By using polyclonal and monoclonal antilectin antibodies in conjunction with various immunologic techniques we have demonstrated that the endogenous lectins are present on the surface of different tumor cells. Quantitation of cell surface lectins by flow cytometric analyses of antilectin antibody binding revealed that among related tumor cells those exhibiting a higher metastatic potential expressed more lectin on their surface. The binding of monoclonal antilectin antibodies to metastatic cells decreased asialofetuin-induced homotypic aggregation in vitro and suppressed the ability of the cells to form lung metastases after intravenous injection in the tail vein of syngeneic mice. These results strongly implicate the tumor cell surface lectins in cell adhesion and metastasis. We propose that such lectins can increase the ability of tumor cells that enter the blood stream to form aggregates with other tumor cells, or to adhere to host cells or the extracellular matrix and thereby increase their metastatic potential. Other contributing components to tumor cell-host cell interactions are cell surface carbohydrate-binding proteins that have been detected on lymphocytes, platelets, macrophages, hepatocytes, and endothelial cells. These lectin-like molecules might recognize and bind carbohydrates expressed on the surface of tumor cells and enhance emboli formation and organ colonization.

Mitogenic heparin-binding lectin-like protein from cloned thymic myoid cells

A mitogenic heparin-binding (reactive) lectin-like protein (HBP) was purified from the extract of a cloned rat thymic myoid cell R615B2 by a one-step procedure of affinity chromatography on a heparin--Sepharose CL-6B column. Four distinct peptide bands with molecular weights of 10,000, 13,000, 13,700, and 14,600 were detected on SDS-polyacrylamide gel electrophoresis. This protein is mitogenic at concentrations of as low as 1.1-70.0 ng/ml for peanut lectin-nonagglutinated thymocytes and splenocytes from euthymic mice and rats but not for splenocytes from nude mice. These results indicate that thymic myoid cell-derived HBP is an important signal for one particular step in T-cell differentiation.

Association of alginate from Pseudomonas aeruginosa with two forms of heparin-binding lectin isolated from rat lung

An endogenous heparin-binding lectin activity isolated from rat lung was separated into two distinct isolectin forms which showed subtle changes in carbohydrate specificity. The two lectin forms displayed different specificities toward alginic acid-purified cystic fibrosis isolates of Pseudomonas aeruginosa when assayed by inhibition of both hemagglutination and [3H]heparin binding. This ability of isolectin forms to show higher affinity toward alginic acid from certain P. aeruginosa strains may suggest that there is a selective mechanism in the colonization of patients with cystic fibrosis.

Endogenous lectins in normal and dystrophic muscle development

Two endogenous lectin activities, one specific for beta-D-galactose (beta-D-Gal) residues and purified on asialofetuin-Sepharose and the second specific for iduronic acid containing glycosaminoglycans and purified on heparin-Sepharose, have been studied during myogenesis in both normal and dystrophic chickens. The Storrs strain, homozygous for muscular dystrophy, and the dystrophic strain 413 from the University of California at Davis were both used in this study. Strain 412 and local hatchery chickens were used as controls. The lectins derived from all sources appeared to be identical based on physical properties and carbohydrate specificity. Both normal and dystrophic adult chickens possessed similar lectin levels in lung, spleen, kidney, heart, and muscle tissue. No differences were noted in the temporal appearance of the heparin-binding lectin; however, the beta-D-Gal-binding lectin appeared earlier in the Storrs dystrophic strain than it did in the 413, 412, or hatchery embryos.

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.

Endogenous mammalian lectin localized extracellularly in lung elastic fibers

An affinity-purified antibody preparation raised against a beta-galactoside-binding lectin from bovine lung was used to localize a similar lectin in rat lung by immunofluorescence and by electron microscopy after on-grid staining visualized with colloidal gold conjugated second antibody. The endogenous mammalian lectin was found in smooth muscle cells and squamous alveolar epithelial (type I) cells and was concentrated extracellularly in elastic fibers of pulmonary parenchyma and blood vessels. The extracellular localization of this lectin suggests that it, like others, functions by interaction with extracellular glycoconjugates.

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.

Distribution of polyanionic sites in the developing gonads and the dorsal mesentery of the chick embryo

The distribution of glycoconjugates was investigated in the embryonic trunk mesoderm used as a substrate by migrating primordial germ cells (PGCs) by means of ultrastructural cytochemistry. In both mesentery and developing gonads polyanionic sites were abundant in epithelial and mesenchymal cell coats, basal laminae, and extracellular matrices (ECM). In the latter, polyanions distributed on microfibrils and granules were associated with collagen fibers, forming an entangled network. No preferential association of this fibrillo-granular material with PGCs was observed, suggesting that polyanions present in ECM likely act by promoting inflation of the extracellular spaces rather than by providing mechanical guides for the moving cells.

Binding of epithelial cells to lectin-coated surfaces

Epithelial cells may relate to their basement membrane substrates via lectin-like interactions. In a model system for study of this type of interaction, lectin-coated bacteriological plastic petri dishes were presented as substrates for epithelial cell adhesion. Of 21 lectins tested by mixed agglutination against two epithelial cell types, Madin-Darby canine kidney (MDCK), and human embryonic kidney cells (HEK), nine gave less than 5% rosettes and 12 gave 5 to 50% rosettes. Wheat germ agglutinin (WGA) and Geodia cydonium lectin gave the highest percentage of rosettes. Wheat germ agglutinin was readily adsorbed to plastic surfaces and maintained specificity in binding interactions. Both MDCK and HEK cells attached as well to WGA coated petri dishes as to conventional tissue culture dishes. Furthermore, both spread over the lectin-coated surfaces. The MDCK cells grew to confluence and could be subcultured and maintained indefinitely on such surfaces, although WGA in solution was toxic to the cells in concentrations as low as 0.1 to 1.0 microgram/ml. Cell attachment to WGA coated dishes was blocked by cycloheximide only if the cells had been preincubated with the inhibitor for several hours. Cell attachment was not inhibited by pretreatment of cells with neuraminidase. Precoating cells with WGA blocked binding to both WGA-coated surfaces and untreated tissue culture dishes. Cells attached to WGA-coated dishes could not be readily dislodged by trypsin-EDTA for the first 2 h after subculture. By 4 h, attachment was again trypsin sensitive, suggesting that the cells synthesized a trypsin-sensitive material that was laid down between the cell surface and the WGA-coated dish. Regeneration of trypsin sensitivity was not blocked by cycloheximide.

Externalization of an endogenous chicken muscle lectin with in vivo development

Chicken-lactose-lectin-I (CLL-I), an endogenous lectin that is developmentally regulated in embryonic muscle, was localized by immunohistochemical techniques in tissue samples taken at various stages of in vivo development and in primary muscle cultures. Lectin, which was diffusely distributed in myoblasts, became localized in myotubes in a distribution similar to that of the sarcoplasmic reticulum and T tubules. Later in development, lectin was predominantly extracellular. This sequence suggests that externalization may have occurred by migration in the T tubules, which are continuous with the extracellular space, although alternative explanations are possible. Only traces of lectin were found in the adult. These studies did not reveal the function of CLL-I in muscle development. However, we infer that it acts by organizing complementary glycoconjugates in the intracellular tubular network, on the muscle surface, and/or in extracellular materials.

Purification of a high-affinity discoidin I-binding proteoglycan from axenic Dictyostelium discoideum growth medium

The axenic Dictyostelium discoideum growth medium HL-5, prepared using Difco proteose peptone No. 2, contains an extremely potent inhibitor of the binding of 125I-labeled discoidin I to glutaraldehyde-fixed, cohesive D. discoideum cells. Axenic strain A3 D. discoideum cells bind or internalize the inhibitor during growth in HL-5 medium and subsequently shed or excrete it while differentiating in suspension. The inhibitor has been purified from Difco proteose peptone No. 2 by sequential gel filtration on Sepharose 4B and affinity adsorption using discoidin I-Sepharose. The inhibitor is heterogeneous in molecular weight (4 . 10(5)--2 . 10(6)), but is relatively homogeneous in density on CsCl density gradients. The size and activity of the inhibitor are resistant to periodate, reduction and maleylation, proteases, nucleases and heating in the absence or presence of sodium dodecyl sulfate. Mild alkali causes a partial reduction in activity and converts the higher molecular weight fraction of the inhibitor to a lower molecular weight. The purified inhibitor contains neutral hexose, hexosamine and amino acid in an approximate molar ratio of 4 : 3 : 2. These and other properties suggest that the inhibitor is an unusual proteoglycan. Certain well-characterized glycosaminoglycans are relatively potent inhibitors of discoidin I binding. The proteoglycan reported here is the most potent discoidin I-binding inhibitor ever identified.

Heparin-inhibitable lectins: marked similarities in chicken and rat

Extracts of young rat lung contain a heparin-inhibitable lectin that closely resembles one recently purified from chicken liver. Both lectins interact with heparin and N-acetyl-D-galactosamine, and were purified by gel filtration on Sepharose CL-2B followed by affinity chromatography on heparin-Sepharose. They both behave as high molecular weight aggregates that can be dissociated into two peptides with apparent molecular weights of 13,000 and 16,000 by gel electrophoresis in SDS. Samples of purified lectin contained up to 20% DNA by weight, and the degree of lectin aggregation and hemagglutination activity was greatly reduced by treatment with micrococcal nuclease without inhibiting heparin-binding activity. Association of lectin with DNA is an artifact of homogenization in high salt, since only 2% of the lectin is found associated with a purified nuclear fraction.

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.

The role of bacterial surface structures in pathogenesis

Modern research has revealed that the true surfaces of animal cells consist of polysaccharide chains that are linked to proteins hydrophobically anchored in the membrane and protrude to form a dense glycocalyx. It has become increasingly clear that most pathogenic bacteria must position themselves at the surface of their "target" cell in order to exert their toxic or otherwise deleterious effects. The true surface of most pathogenic bacteria has also been recently shown to consist of a protruding mass of polysaccharide chains--the bacterial glycocalyx--that is composed of teichoic acids in many gram-positive species and of acid polysaccharides in many gram-negative organisms. Through this bacterial glycocalyx certain cell surface proteins and organized protein structures (e.g., pili) are known to project, so that the bacterial surface is a mosaic of polysaccharides and proteins; both of these types of molecules have been implicated in instances of specific pathogenic adhesion. Besides their role in specific adhesion to target cells, these surface components interpose a highly charged, and often very extensive, barrier that can prevent the penetration of antibodies and antibiotics to their target sites in the bacterial cell. They may also frustrate mucociliary clearance, phagocytosis, and other clearance mechanisms of the host. We will discuss the chemical and physical nature of these bacterial surface components that mediate pathogenic adhesion and counteract host defense mechanisms sufficiently to allow infections to become established.

Role of a 16S glycoprotein complex in cellular adhesion

Myogenic cells release into their culture medium a glycoprotein complex that mediates cellular adhesion. In the absence of calcium this complex has a sedimentation value of 16S; it aggregates in the presence of calcium. The 16S material both agglutinates and increases the rate of cell-substratum adhesion of a myoblast variant and inhibits the adhesion of a nerve-like cell line to culture dishes. It is also a hemagglutinin. The 16S particle is composed of glycosaminoglycans and several proteins, including fibronectin and collagen.

Chicken tissue binding sites for a purified chicken lectin

A lactose-binding lectin previously purified from embryonic chicken muscle and adult chicken liver, and here referred to as chicken-lactose-lectin-I (CLL-I), was added to sections of various adult chicken tissues to detect available binding sites. Both the sites of binding of added CLL-I as well as the tissue distribution of endogenous CLL-I were determined by indirect immunofluorescence using a rabbit antibody to CLL-I followed by fluorescent goat anti-rabbit IgG. Some tissues such as intestine and kidney showed abundant extracellular binding sites for the lectin, primarily between cells, in basement membrane, and in material on the luminal surface. In contrast, adult heart showed no significant binding sites for CLL-I. Adult pancreas showed considerable endogenous CLL-I in an extracellular site surrounding exocrine lobules, but added CLL-I did not bind substantially. The distribution of CLL-I binding sites in intestine were mimicked by those of purpurin, another lactose-binding lectin. CLL-I binding sites were also detected on the surface of cultured chick embryo skin fibroblasts. The factors controlling the specific distribution of occupied and unoccupied CLL-I binding sites are not known.