Identification and further characterization of the specific cell binding fragment from sponge aggregation factor.

Monoclonal antibodies (McAbs) were raised against the aggregation factor (AF) from the marine sponge Geodia cydonium. Two clones were identified that secrete McAbs against the cell binding protein of the AF complex. Fab fragments of McAbs: 5D2-D11 completely abolished the activity of the AF to form secondary aggregates from single cells. The McAbs were determined to react with the AF in vitro; this interaction was prevented by addition of the aggregation receptor, isolated and purified from the same species. After dissociation of the AF by sodium dodecyl sulfate and 2-mercaptoethanol, followed by electrophoretical fractionation, a 47-kD protein was identified by immunoblotting which interacted with the McAbs: 5D2-D11. During this dissociation procedure, the sunburst structure of the AF was destroyed. In a second approach, the 47-kD protein was isolated by immunoprecipitation; 12 molecules of this protein species were calculated to be associated with the intact AF particle. The 47-kD AF fragment bound to dissociated Geodia cells with a high affinity (Ka of 7 X 10(8) M-1) even in the absence of Ca++ ions; the number of binding sites was approximately 4 X 10(6)/cell. This interaction was prevented by addition of the aggregation receptor to the 47-kD protein in the homologous cell system. Moreover, it was established that this binding occurs species-specifically. The 47-kD fragment of the AF was localized only extracellularly by indirect immunofluorescence staining in cryostat slices. These data suggest that the 47-kD protein is the cell binding molecule of the AF from Geodia.

Monoclonal antibody FW6 defines an epitope on alpha 3/4-monofucosylated polylactosaminoglycans expressed by fetal and colon carcinoma-associated mucins.

A mouse IgM monoclonal antibody FW6 was established after immunization of mice with mucins from human amniotic fluid and was characterized with regard to its binding epitope. According to a series of biochemical criteria the epitope is located on O-linked neutral carbohydrates of M(r) 700,000 and M(r) 570,000 mucins in human amniotic fluid. The epitope is presumed to contain alpha 3/4-linked fucose and terminal beta 3/4-linked galactose that are labile to the fucosidase I from almond emulsion or to the galactosidase from bovine testes, respectively. Immunoreactive fractions of glycan alditols from human amniotic fluid mucins were partially characterized by fast atom bombardment-mass spectrometry and methylation analysis to be composed of monofucosylated polylactosamine-type deca- or nonasaccharides. According to antibody competition studies, inhibition assays with defined carbohydrates and binding assays on neoglycolipids monoclonal antibody FW6 are presumed to recognize a novel epitope that is distinct from known carbohydrate markers of the Lex/Ley family associated with colonic carcinomas. The selective reactivity of this monoclonal antibody to the majority of human colonic carcinomas and its nonreactivity to normal colonic mucosa may render this antibody as a valuable tool in cancer diagnosis or cancer treatment.

Characterization of the oligosaccharide side chain of apolipoprotein C-III from human plasma very low density lipoproteins.

Apolipoprotein C-III1 and apolipoprotein C-III2 each contain one oligosaccharide side chain, bound O-glycosidically to threonine in position 74 of the amino acid sequence. The studies reported in this paper characterize these alkali labile oligosaccharides, thereby demonstrating the complete structure of apolipoprotein C-III. Monosaccharide analysis revealed the following sugar composition: D-galactose/N-acetyl-D-galactosamine/sialic acid 1 : 1 : 1 and 1 : 1 : 2 for apolipoprotein C-III1 and apolipoprotein C-III2, respectively. Treatment of desialylated apolipoproteins with alkaline borohydride released the reduced disaccharide beta-D-galactosyl-(1 leads to 3)-N-acetyl-D-galactosaminitol, which was detected by gas-liquid chromatography. Further studies employing periodate oxidation and Smith degradation indicated that the structure of the trisaccharide from apolipoprotein C-III1 was alpha-N-acetylneuraminyl-(2 leads to 3)-beta-D-galactosyl-(1 leads to 3)-N-acetyl-D-galactosaminitol. The tetrasaccharide structure from apolipoprotein C-III2 is made up of this trisaccharide plus one sialic acid residue linked to C6 of N-acetyl-D-galactosaminitol, as was shown by the assessment of chromogens formed upon alkaline degradation.

Comparison of isolated peanut agglutinin receptor glycoproteins from human, bovine and porcine erythrocyte membranes.

Affinity chromtography has been used to isolate and compare the peanut agglutinin receptors from neuraminidase-treated human, bovine and porcine erythrocyte membranes. Passage of Triton X-100-solubilised membrane material through either Sepharose- or acrylamide-based affinity columns resulted in the reversible binding of receptor molecules to the immobilised lectin. Elution with 0.2 M galactose released specifically bound glycoprotein fractions, the composition and molecular weights of which were determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate. Carbohydrate analysis by gas chromatography identified these bound glycoprotein fractions as the major sources of the O-glycosidic-linked disaccharide galactosyl-beta-(1 leads to 3)-N-acetylgalactosamine in these membranes. It is suggested that these isolated fractions represent a discrete population of glycoproteins within the membranes studied, which possess both O-glycosidic- and N-glycosidic-linked carbohydrates.

Alkali-labile oligosaccharides from glycoproteins of different erythrocyte and milk fat globule membranes.

Phenol extraction of horse, sheep, cow, pig and human erythrocyte membranes and human milk fat globule membranes gave glycoprotein fractions, all of which were shown by gas chromatography to contain the reduced disaccharide beta-D-galactosyl (1-3)-N-acetyl-D-galactosaminital after treatment with alkaline borohydride. Cow and pig erythrocyte membrane glycoproteins were found however to contain much lower amounts than the erythrocyte membrane glycoproteins of the other species tested. After gel filtration, a tetrasaccharide was isolated from horse and sheep glycoproteins containing the disaccharide plus two molecules of sialic acid. Periodate oxidation together with paper chromatography of alkaline degraded fragments showed these two molecules of sialic acid to be linked to positions C3 and C6 of the galactosyl and N-acetylgalactosamine residues respectively. Evidence was obtained for a similar structure from pig and cow erythrocyte glycoproteins and human milk fat globule membrane glycoproteins although the complete structure was not elucidated. In all native glycoprotein fractions, the unsubstituted disaccharide beta-D-galactosyl (1-3)-N-acetyl-D-galactosamine was found to be present to different extents. Haemagglutination inhibition tests against human anti-T serum, Arachis hypogoea and Vicia graminea by desialylated glycoproteins showed the presence of the T-antigen, confirming the chemical findings. Inhibition was found to be proportional to the chemically detected amounts of disaccharide in each fraction. Evidence for a second carbohydrate chain in horse, sheep and human erythrocyte glycoproteins with a sialic acid substituted N-acetylgalactosamine residue as the terminal sequence was obtained using the agglutinin from Helix pomatia.

Polyclonal antibodies to mannan from yeast also recognize the carbohydrate structure of gp120 of the AIDS virus: an approach to raise neutralizing antibodies to HIV-1 infection in vitro.

This study initiates a new method of developing an antigen which might be useful in the prevention of HIV-1 infection. Using a mannan preparation from Saccharomyces cerevisiae neutralizing antiserum was raised in rabbits which prevents HIV-1 infection in vitro up to a titre of 1:128. The corresponding antibody preparation neutralized the in vitro infectivity down to a concentration of 5 micrograms/ml. Analytical studies suggest that the antibodies are directed against the mannose residues of the HIV-1 glycoprotein (gp) 120 and its precursor gp 160.

Protein kinase C phosphorylates the sponge aggregation receptor after its binding to the homologous aggregation factor.

The aggregation factor from the sponge Geodia cydonium functions also as a growth factor after binding to the aggregation receptor (= growth factor receptor) on the plasma membrane of homologous cells. We have recently shown that protein kinase C is involved in the pathway transducing the growth factor signal. Here we report that the aggregation receptor (a polypeptide with an Mr of 43,500) is phosphorylated by protein kinase C. Using a plasma membrane fraction only this phosphoprotein (pp) 43.5 became phosphorylated by kinase C. The phosphorylation of pp43.5 in intact cells in response to the binding of the aggregation factor to this polypeptide was a late event and occurred 10 to 15 h after addition of the aggregation factor. Based on studies with phorbol esters it appears to be very likely that protein kinase C also phosphorylates pp43.5 in vitro. The degree of phosphorylation of pp43.5 paralleled with both the extent of DNA synthesis and ras oncogene expression. The latter process resulted in a switch of the responsiveness of the cells to growth factors signals: 10 to 15 h after addition of the aggregation factor to dissociated cells, this factor lost its growth factor function while the homologous lectin gained the ability to stimulate cell proliferation (to be published). These results support the idea that phosphorylation of pp43.5 (= aggregation receptor) results in an inhibition of its function, i.e., the transduction of the growth factor (= aggregation factor) signal.

Cell aggregation of the marine sponge Geodia cydonium. Identification of lectin-producing cells.

A D-galactose-specific lectin, purified from the marine sponge Geodia cydonium, is present on the cell surface of mucoid cells, free choanocytes and choanocyte clusters, as revealed first, by the adhesion assay which is based on the formation of "rosettes" with erythrocytes, and second, by immunofluorescence studies. Using the same techniques no lectin could be identified on the surface of archaeocytes. Rosette formation was inhibited in the presence of 20 mM D-lactose as well as after preincubation of erythrocytes with purified lectin. Titration experiments in a hemagglutination assay showed that the highest level of extractable lectin (5% of the total protein) is found in mucoid cells, lower concentrations are determined in choanocyte clusters (0.07%), free choanocytes (0.05%) and archaeocytes (0.01%). Only the mucoid cells were found to synthesize lectin which is secreted and subsequently transferred to the cell surface of other cell types. As one consequence of the binding of the lectin to the cell surface of aggregation-deficient choanocytes or archaeocytes, the conversion of these cells to aggregation-susceptible ones is observed. These results support previous evidence that the lectin is involved in the reaggregation process of single cells in the homologous biological system.

Primary structure of a major sialyl-saccharide alditol from human amniotic mucins expressing the tumor-associated sialyl-X antigenic determinant.

A major sialyl-saccharide alditol isolated from mucins of human amniotic fluid was purified by high-performance liquid chromatography followed by high-performance thin-layer chromatography of the methylated derivative and subjected to structural analyses which comprised fast atom bombardment and electron impact-mass spectrometry, methylation analysis, exoglycosidase digestion and CrO3 oxidation. The structure of a disialylated pentasaccharide characterized by a sialyl-X antigenic determinant was established: (formula; see text)

Antibodies against defined carbohydrate structures of Candida albicans protect H9 cells against infection with human immunodeficiency virus-1 in vitro.

In this study we raised antibodies against Candida albicans mannans of serotype A and B which comprise mannose alpha(1----2)-and mannose alpha(1----3)-linked residues. These antibodies inhibited human immunodeficiency virus type IIIB (HIV-IIIB) infection of H9 cells in vitro; 5 micrograms/ml of antibodies against mannan from serotype A and 10 micrograms/ml of antibodies against serotype B mannan were sufficient to inhibit infection by almost 100 and 85%, respectively, after an incubation period of 4 days. During a prolonged incubation period (8-12 days), the amount of HIV particles (as measured by reverse transcriptase activity in the culture medium) increased again in assays with antibodies raised against serotype B, but only little in assays containing antibodies against serotype A. Applying the Western blotting technique and a novel enzyme-linked immunosorbent assay system it was established that the antibodies reacted with the gp120 of HIV-1 exclusively. Immunofluorescence inspection using a confocal laser scanning microscope revealed that the gp120 protein is exposed on the outer surface of H9 cells where it is recognized by the anti-mannan antibodies. These results indicate that mannan residues of C. albicans can serve as antigens to raise neutralizing antibodies against HIV infection.

Inhibition of liver tumor cell colonization in two animal tumor models by lectin blocking with D-galactose or arabinogalactan.

Repeated administration of the hepatic lectin blocking agents D-galactose or arabinogalactan completely prevented the settling of metastatic cells of sarcoma L-1 tumor in the liver of Balb/c mice and greatly reduced the colonization process of highly metastatic ESb lymphoma cells of the liver of DBA/2 mice. Therefore, when hepatic lectins were blocked with competitive glycoconjugates, tumor cell colonization of the liver could be prevented in two different model systems.

A novel galactose- and arabinose-specific lectin from the sponge Pellina semitubulosa: isolation, characterization and immunobiological properties.

A new lectin from the sponge Pellina semitubulosa is derived which was extracted and purified to homogeneity. The purified lectin is probably a hexamer of polypeptide chains (each M(r) 34,000) which are covalently linked via disulfide linkages; the isoelectric point is 6.1. The lectin displays the following specificities: D-galactose (50% inhibition of hemagglutination at 0.2 mM) = L-arabinose (0.2 mM) greater than D-fucose (1.5 mM) greater than D-glucose (3.0 mM). It precipitates human erythrocytes (A1, A2, A1B, B, and O) with a titer between 2(8) and 2(11) and erythrocytes from sheep and rabbits with a titer between 2(5) and 2(10). The Pellina lectin displays a strong mitogenic effect on spleen lymphocytes from mice. Immunochemical analyses revealed that both murine T- and B-lymphocytes display a capping of the lectin receptors on their cell surfaces after lectin treatment. Murine macrophages were found to endocytose the lectin. Pellina lectin at concentrations between 0.3 and 10.0 micrograms/ml potently enhances interleukin 1 (IL-1) release from mouse peritoneal macrophages and interleukin 2 (IL-2) production in mixed murine lymphocyte cultures.

Occurrence and distribution of glycoconjugates in human tissues as detected by the Erythrina cristagalli lectin.

We applied a horseradish peroxidase-Erythrina cristagalli agglutinin (HRP-ECA) conjugate for histochemical staining of tissue sections from various formalin-fixed, paraffin-embedded human tissue specimens. The HRP-ECA conjugate showed broad reactivity, but there was a distinct distribution of native (not masked by sialic acid) and sialic acid-masked ECA binding sites in the various organs. Free ECA binding sites could be detected on red blood cells, lymphocytes of thymus, tonsil, lymph node, and in mucous substances of different organs. Independent of blood group type, the vascular endothelium exhibited strong ECA reactivity. Free ECA binding sites occurred in the cytoplasm of Kupffer's cells in liver, in histiocytic cells of thymus, lymph node, tonsil, and in bone marrow. Podocytes of kidney glomerulus, syncytiotrophoblasts of placenta, megakaryocytes in bone marrow, myelin sheath of nerve, medullary thymocytes, and hepatocytes, as well as islet cells of pancreas, contained only sialic acid-capped ECA binding sites. Inhibiting studies with galactose, lactose, and N-acetyl-lactosamine, as well as other sugars, revealed that this lectin is specific for galactosyl residues. In comparison to galactose and lactose, N-acetyl-lactosamine exhibited the highest inhibitory activity on lectin binding, supporting the concept that this lectin is most reactive with N-acetyl-lactosamine-type (type 2 chain) glycoconjugates.

Characterization of glycoconjugates of human gastrointestinal mucosa by lectins. II. Lectin binding to the isolated glycoproteins of normal and malignant gastric mucosa.

Using affinity chromatography on HPA-, PNA-, Con A, and WGA-agarose columns only a part (10-30%) of the high molecular weight mucous glycoproteins could be isolated from the Triton X-100 solubilized components of normal as well as carcinomatous gastric mucosa. The main part of the mucus was not bound by the lectins, which corresponds to our earlier lectin histochemical observations on paraffin-embedded tissue sections. The lectin-bound mucous glycoproteins had a relatively lower molecular weight, ranging from about 250-1,000 kilodaltons, as indicated by polyacrylamide gradient gel electrophoresis and by gel filtration on Biogel A 1.5 m column. In gas chromatographic analysis the molar ratio of aminohexoses to galactose was found to be much higher (3:1) in the lectin-bound mucous substances than in the whole high molecular weight mucus (1:1). This finding indicates that lectins have a higher affinity to the hexosamine rich components of mucus, which may be special forms of mucous glycoprotein molecules or the incompletely glycosylated core and backbone regions of the oligosaccharide chains of mucus. Extremely high hexosamine values (10:1) were found in the PNA isolated mucus of gastric adenocarcinoma. Since it is known that PNA binds to the terminal disaccharide, beta-galactose-(1-3)-N-acetylgalactosamine, which is localized at the reducing end of the oligosaccharide chains of mucus, it is highly probable that the elongation of the oligosaccharide side chains is disturbed in gastric cancer cells.

Histochemical reactivity of the Geodia cydonium agglutinin (GCA) in human tissues.

We applied a peroxidase-antiperoxidase technique to study the distribution pattern and binding characteristics of the lectin from the marine sponge Geodia cydonium (Geodia cydonium agglutinin; GCA) in various human tissues. This lectin has been shown to possess a broad reactivity, but there was a distinct distribution of binding sites within the different organs. In the histochemical system GCA displayed no blood group specificity and labeled red blood cells, the vascular endothelium, and epithelial cells showing blood group antigen expression independent of the ABH blood group status. However, inhibition of GCA reactivity by simple sugars and complex carbohydrates demonstrated tissue-specific differences of lectin binding related to the ABH blood group status of the tissue and revealed information on the structural requirements of the histological lectin binding site. Tissues that totally lacked blood group antigens or that expressed only the H-antigen disclosed a GCA reactivity which was completely inhibited by lactose. In contrast, tissues that expressed blood group A- or blood group B-antigen exhibited a lactose-resistant lectin binding which was inhibited only by water-soluble blood group substance A from peptone A and by bovine glycophorin but not by other complex carbohydrates, including human glycophorin and human asialoglycophorin. Competitive inhibition studies in situ revealed that GCA binding was not inhibited by blood group type I/II carbohydrate sequence-specific lectins or by lectins with other sugar specificities. Inhibition by lactose of GCA binding to some histological sites indicates that the binding site consists of a beta-linked galactose-containing disaccharide. However, periodate oxidation of tissue sections had no effect on lectin binding, pointing to a subterminal location of the relevant sequence. The results obtained from inhibition studies with simple saccharides and complex carbohydrates in relation to the expression of ABH blood group antigens suggest a complex lectin combining site(s) in histological specimens. The lectin may possess either one binding site with a range of affinities for different carbohydrates (besides beta-linked disaccharides the GCA binding site accommodates to carbohydrate determinants carrying the blood group A or blood group B determinant), or may possess two different binding sites. Besides an acceptor site for beta-linked disaccharides, an additional binding site may exist accommodating to extended carbohydrate sequences related to A or B blood group structures. In conclusion, GCA represents a blood group-nonspecific lectin whose binding affinities are determined by the ABH blood group status of the tissue.

Sponge aggregation factor: identification of the specific collagen-binding site by means of a monoclonal antibody.

The aggregation factor (AF) from the sponge Geodia cydonium is known to be a complex proteinaceous particle, composed of a series of different (glyco)proteins (Mr lower than 150,000) around a 90S sunburst-like core structure. One of the low-Mr proteins is the 47-KD cell binding fragment. We describe a new monoclonal antibody (mAb), III1E6, raised against purified AF particles, which recognizes in tissue slices structures present both on the plasma membrane and in a network-like manner in the extracellular space. By applying immunoelectron microscopical, immunoblotting, and immunoaffinity chromatographical techniques, the mAb III1E6 was shown to recognize the core structure of the AF particle. Cell adhesion studies revealed that the mAb does not inhibit AF mediated cell-cell adhesion but abolishes AF-caused attachment of cells to collagen. Electron microscopic data show that III1E6 prevents association of AF particles with collagen fibrils. By applying the techniques of immunoblotting and of protein-protein recognition on the solid phase in vitro, we could formulate the following series of events: the AF particle recognizes, with its 47-KD cell binding fragment, the aggregation receptor protein in the plasma membrane and with its core structure the collagen fibrils. These fibrils interact optionally, either via the same route or via the collagen assembly factor, with an adjacent cell surface. These findings demonstrate that the AF particle is not only the key molecule for cell-cell adhesion but also a component of cell-matrix interactions.

Histochemical distribution of certain biochemical constituents in the albumin glands of snails.

The presence in situ of the biochemical constituents galactans, proteinase-inhibitors, and erythro-agglutinin anti-A in snail's albumin gland tissues has been demonstrated by histochemical techniques using fluorescein isothiocyanate (FITC)-conjugated counterparts; namely, anti-galactan-specific lectins, different proteinases, and blood group A substance. Invariably, these constituents are localized as globular structures, predominantly within the lobules of the gland tissue. There is a good correlation between the histochemical findings and the previously reported biochemical and serological findings for these substances.

Characterization of glycoconjugates of human gastrointestinal mucosa by lectins. I. Histochemical distribution of lectin binding sites in normal alimentary tract as well as in benign and malignant gastric neoplasms.

Labeled lectins with binding specificity to the hexose components of mucus glycoproteins (HPA, RCA I, PNA, Con A, WGA, and UEA I) were used to demonstrate structural differences in the glycoprotein composition of various cell types of the normal, benign and malignant gastrointestinal mucosa. While in the RCA I, UEA I, and WGA binding of normal mucus secreting cell types only quantitative differences were observed, the mucus in the surface epithelial cells of gastric mucosa and in the colonic goblet cells was characterized by the absence of PNA, Con A, and PNA, HPA binding sites, respectively. These lectins, however, showed a strong binding to the supranuclear, Golgi-region in the undifferentiated or activated forms of these cells. Even the staining intensity of the luminal membrane surfaces of the non mucinous parietal and chief cells was often stronger by PNA, HPA, and RCA I lectins than that of the mucus secretions in the highly differentiated mucus cells. These results indicate the existence of either heterogeneous glycoprotein components or mucus molecules with variations in the degree of glycosylation of their oligosaccharide chains in the different cells. The latter seems more likely since in benign and malignant alterations lectin binding sites appear in great density, which were found to be characteristic of the undifferentiated mucus cells or for the non mucinous cells of the normal gastric mucosa. Similarly in some gastric cancers which do not stain with the periodic acid-Schiff reaction at all, large amount of free or neuraminic acid substituted PNA binding sites can be detected.

Immunochemical detection of the Thomsen-Friedenreich antigen (T-antigen) on platelet plasma membranes.

Platelet plasma membranes were found to possess the disaccharide beta-D-galactosyl (1-3)-N-acetyl-D-galactosamine which was measured by gas chromatography after release by alkaline borohyride treatment and desialylation. Immunological evidence using the specific lectins from Arachis hypogoea and Agaricus bisporus and an anti-T serum confirmed the presence of this disaccharide, the immunodominant group of the Thomsen-Friedenreich antigen (T-antigen). This receptor was only found after prior neuraminidase treatment indicating that it is normally a cryptic antigen, i.e. masked by sialic acid in the native membrane. Evidence for a second receptor with terminal N-acetylgalactosamine was obtained using the lectin from Helix pomatia. The binding of myxovirus and the lectins from Phaseolus vulgaris (PHA) and Canavalia ensiformis (Con A) to platelet membrane was also demonstrated. The implication of the T-antigen in elimination of the platelets and its role in the haemolytic-uraemic syndrome is discussed.

Isolation and characterization of a lectin from the hemolymph of the cephalopod Octopus vulgaris (Lam.) inhibited by alpha-D-lactose and N-acetyl-lactosamine.

The hemolymph of Octopus vulgaris is known to contain a lactose-specific agglutinin. This has been isolated by a two-step affinity-chromatographical procedure using, firstly immobilized asialofetuin followed by its binding to and elution from Con A-Sepharose. The lectin is a glycoprotein with a carbohydrate content of about 8%, and has a molecular weight (M.W.) of 260 kDa. Disulfide bridges connect subunits of molecular weights ranging between 30-32 kDa and of differing isoelectric points (pH 6.4, 6.6, 7.0, 7.3). Ca++-ions are required for ligand binding of the lectin; the pH-optimum for binding reactions is between pH 8.2-8.5 as determined by precipitation experiments with asialofetuin. Heating to 60-80 degrees C reduces agglutinating activity which is completely destroyed at 90 degrees C.