Characterization of the Forssman-active oligosaccharides from dog gastric mucus glycoprotein isolated with the use of a monoclonal antibody

Gastroprotective agents in mucosal defense against Helicobacter pylori

1. Convincing evidence now exists that infection with H. pylori plays a major role in the pathogenesis of gastric disease. Having a niche bordering two major perimeters of mucosal defenses, the bacterium apparently exerts its detrimental effect on the mucus layer as well as the gastric epithelium. Therefore, gastroprotective agents capable of counteracting these detrimental effects of H. pylori are gaining importance in the treatment of gastric disease. 2. The colonization of gastric mucosa by H. pylori involves specific glycolipid receptors bearing acidic substituents, a process inhibited by gastric sulfomucins. Two antiulcer agents bearing sulfated sugar groups have been demonstrated to possess the ability to interfere with H. pylori colonization process. These are sucralfate and sulglycotide. The two agents are also potent inhibitors of H. pylori glycosulfatase activity directed against indigenous mucosal defenses. 3. A variety of extracellular enzymes such as proteases, lipases and phospholipases, elaborated by H. pylori cause the weakening of the integrity of gastric mucus coat and render the underlying epithelium vulnerable to noxious luminal contents. Among the most potent agents capable of countering the proteolytic activity of H. pylori are nitecapone, ebrotidine and sulglycotide, while ebrotidine and sulglycotide were found to be most effective inhibitors of H. pylori lipolytic activities. 4. The gastric epithelial integrity is compromized by the H. pylori cell-wall lipopolysaccharide untoward effect on the epithelial surface receptors. The interference of the lipopolysaccharide with the laminin receptor was found to be most efficiently countered by ebrotidine, sulglycotide and sucralfate, whereas sulglycotide is the most potent in the reversal of the inhibitory effect of the lipopolysaccharide on mucin receptor binding.

Most of the lipid in purulent sputum is bound to mucus glycoprotein

Mucus glycoprotein (mucin) is the principal biochemical constituent of sputum. Appreciable quantities of lipid, DNA, and nonmucin proteins are also present, particularly in purulent sputum. Previous studies have shown that purified mucin from respiratory tract secretions contains non-covalently bound lipid. However, it is not known whether lipids in purulent sputum are associated only with mucin or with nonmucin proteins and DNA as well. Purulent sputum was obtained from cystic fibrosis patients. Tracheal aspirates were obtained from noncystic patients with purulent secretions due to Pseudomonas species, as well as from noninfected, noncystic patients who had mucoid airway secretions. The lipid content of unfractionated airway secretions (sputum or tracheal aspirates), gel filtration-purified mucin, and nonmucin components of the airway secretions was analyzed. The purified mucin from all three groups had a significantly higher content of solvent-extractable lipid as compared to unfractionated airway secretions. The nonmucin fractions contained only small amounts of lipid. Density gradient centrifugation verified that the lipid recovered in the purified mucin fraction was complexed with the glycoprotein. The results of this study indicate that most of the lipids in purulent sputum are associated with mucin.

Surface expression of Forssman glycosphingolipid antigen on murine bone marrow-derived macrophages is subject to both temporal and population-specific regulation and is modulated by IL-4 and IL-6

The Forssman glycolipid antigen (Fo) has been shown to be a differentiation marker for mouse macrophages both in vivo and in vitro. In order to determine whether or not there is a relationship between stage of differentiation and Fo expression, we have analyzed the kinetics of Fo expression during the growth of cultured mouse bone marrow-derived macrophages (BMDM). BMDM were grown in serum free medium to avoid the possible influence of undefined serum factors. In this medium they could be maintained over a period of up to 20 days with cell yields comparable to those obtained with serum-supplemented media. Fo antigen was assayed with a specific antibody using both a whole cell ELISA and immunocytochemical staining of cells grown on slides. With increasing age in culture, BMDM showed a gradual quantitative increase in Fo expression and parallel increase in the Fo+ BMDM fraction from about 10% Fo+ cells on the 10th day of culture to a maximum of 50%-60% Fo+ cells between the 17th and 19th days. The temporal control over the development of the Fo+ cell fraction was intrinsic to BMDM maturation but was specific for Fo. During the same time period expression of MHC class II (Ia) remained consistently low, whereas expression of both Mac-1 (C3bR) and the macrophage-specific marker ER-BMDM-1 was always high. The interleukins IL-4 and especially IL-6 induced a premature expression of Fo at earlier stages of BMDM culture, but neither could promote further Fo expression once the intrinsically occurring maximum had been reached. No evidence in support of an autocrine regulation of Fo expression by IL-6 could be obtained, nor could a connection between cell cycle status and Fo expression be established. These data provide further evidence that Fo is a temporally regulated differentiation marker for a mouse macrophage subpopulation and for modulation of its expression by lymphokines.

Forssman antigen expressed on lymph node cells of MRL/MpJ-lpr/lpr mice is of a glycoprotein nature

This paper reports the nature of abnormally expressed Forssman (F) antigen in the lymph node cells of MRL/MpJ-lpr/lpr, autoimmune mice, and also reports its autoantibody in sera. By acetylation study of the F antigen with [14C]acetic anhydride, we concluded that the F antigen was not a glycolipid but a glycoprotein. Several bands of F-active glycoproteins were identified on a nitrocellulose sheet after purification by an anti-F antibody affinity column. Hemolysis of SRBC by some sera from MRL/MpJ/lpr/lpr was inhibited by purified F glycoprotein and also by F glycolipid. The antibody in the serum, however, seemed to be more specific for F glycoproteins than F glycolipid, but the opposite was the case for rabbit anti-F glycolipid antibody. No significant difference of the SRBC hemolysis levels was observed between the sera from MRL/MpJ-lpr/lpr and its congenic MRL/MpJ-+/+ mice.

Polarity of the Forssman glycolipid in MDCK epithelial cells

To determine whether epithelial plasma membrane glycolipids are polarized in a manner analogous to membrane proteins, MDCK cells grown on permeable filters were analyzed for the expression of Forssman ceramide pentasaccharide, the major neutral glycolipid in these cells. In contrast to a recent report which described exclusive apical localization of the Forssman glycolipid (Hansson, G.C., Simons, K. and Van Meer, G. (1986) EMBO J. 5, 483-489), immunofluorescence and immunoelectron microscopic staining revealed the Forssman glycolipid on both the apical and basolateral surfaces of polarized cells. Immunoblots indicated that the Forssman antigen was detectable only on glycolipids and not on proteins. Analysis of metabolically labeled glycolipids released into the apical and basal culture medium, either as shed membrane vesicles or in budding viruses, also demonstrated the presence of the Forssman glycolipid on both apical and basolateral membranes of polarized cells. Quantitation of the released glycolipid indicated that the Forssman glycolipid was concentrated in the apical membrane. These results are consistent with previous reports which described quantitative enrichment of glycolipids in the apical domain of several epithelia.

Role of carbohydrates in the viscosity and permeability of gastric mucin to hydrogen ion

The effect of carbohydrate removal on the viscosity of gastric mucin and its ability to impede the diffusion of hydrogen ion was investigated. The mucin, purified from dog gastric mucus, was subjected to partial or extensive deglycosylation with specific exoglycosidases and then used in the measurements. The obtained results revealed that removal of peripheral fucose or N-acetylglucosamine caused in each case only about 5% reduction of the glyco-protein viscosity. An 18% drop in the viscosity, however, occurred following removal of sialic acid, while extensive deglycosylation (removal of 86% carbohydrate) reduced the glycoprotein viscosity by 40%. The ability of mucin to retard the diffusion of hydrogen ion increased by 7% following removal of fucose or N-acetylgalactosamine, a 28% increase was obtained following removal of sialic acid, while the permeability to hydrogen ion of the extensively deglycosylated glycoprotein decreased by 42%. The results suggest that carbohydrates contribute significantly to the viscoelastic and permselective properties of gastric mucin.

Mucin synthesis. Conversion of R1-beta 1-3Gal-R2 to R1-beta 1-3(GlcNAc beta 1-6)Gal-R2 and of R1-beta 1-3GalNAc-R2 to R1-beta 1-3(GlcNAc beta 1-6)GalNAc-R2 by a beta 6-N-acetylglucosaminyltransferase in pig gastric mucosa

A UDP-GlcNAc:R1-beta 1-3Gal(NAc)-R2 [GlcNAc to Gal(NAc)] beta 6-N-acetylglucosaminyltransferase activity from pig gastric mucosa microsomes catalyzes the formation of GlcNAc beta 1-3(GlcNAc beta 1-6)Gal-R from GlcNAc beta 1-3Gal-R where -R is -beta 1-3GalNAc-alpha-benzyl or -beta 1-3(GlcNAc beta 1-6)GalNAc-alpha-benzyl. This enzyme is therefore involved in the synthesis of the I antigenic determinant in mucin-type oligosaccharides. The enzyme also converts Gal beta 1-3Gal beta 1-4Glc to Gal beta 1-3(GlcNAc beta 1-6)Gal beta 1-4Glc. The enzyme was stimulated by Triton X-100 at concentrations between 0 and 0.2% and was inhibited by Triton X-100 at 0.5%. There is no requirement for Mn2+ and the enzyme activity is reduced to 65% in the presence of 10 mM EDTA. Enzyme products were purified and identified by proton NMR, methylation analysis and beta-galactosidase digestion. Competition studies suggest that this pig gastric mucosal beta 6-GlcNAc-transferase activity is due to the same enzyme that converts Gal beta 1-3GalNAc-R to mucin core 2, Gal beta 1-3(GlcNAc beta 1-6)GalNAc-R, and GlcNAc beta 1-3GalNAc-R to mucin core 4, GlcNAc beta 1-3(GlcNAc beta 1-6)GalNAc-R. Substrate specificity studies indicate that the enzyme attaches GlcNAc to either Gal or GalNAc in beta (1-6) linkage, provided these residues are substituted in beta (1-3) linkage by either GlcNAc or Gal. The insertion of a GlcNAc beta 1-3 residue into Gal beta 1-3GalNAc-R to form GlcNAc beta 1-3Gal beta 1-3GalNAc-R prevents insertion of GlcNAc into GalNAc. These studies establish several novel pathways in mucin-type oligosaccharide biosynthesis.

Comparative study on mucus glycoproteins in rat stomach and duodenum

The density of mucus glycoprotein compared to that of the corpus, antrum and duodenum was; 1.52, 1.49 and 1.57 g/ml respectively. Carbohydrate composition of gastrointestinal mucus glycoprotein consisted of N-acetylgalactosamine, N-acetylglucosamine, galactose, fucose and sialic acid. Ratios of carbohydrate composition among corpus, antral and duodenal mucus glycoproteins differed. The average length of an oligosaccharide was found to be about 12-13, 14 and 10 sugars in the corpus, antrum and duodenum, respectively. In the corpus, the amino acid content was found to have the following quantitative order: Thr greater than Ser greater than Glx = Pro; in the antrum: Thr greater than Ser greater than Glx; and in the duodenum: Thr greater than Ser greater than Pro. Corpus, antral and duodenal mucus glycoproteins have the blood-group A antigen; antral mucus glycoprotein in particular exhibited strong blood-group A activity.

The role of surface and intracellular mucus in gastric mucosal protection against hydrogen ion. Compositional differences

The role of surface and intracellular mucus in gastric mucosal protection against hydrogen ion was investigated. Gastric mucosa, prepared from dog and rat stomachs at various stages of mucus depletion, was mounted in the permeability chamber, and the diffusion of hydrogen ion from the luminal to the serosal side was measured. Removal of the surface mucus caused a 42.9% increase in the permeability of rat gastric mucosa and a 47.4% increase in the permeability of dog gastric mucosa. The permeability to hydrogen ion of gastric mucosa depleted of its surface and intracellular mucus increased 216% in the case of the dog and 280% with the rat. Compositional analysis showed that in both animals the intracellular mucus had a higher content of lipids, covalently bound fatty acids, and carbohydrates, whereas the protein content was higher in the surface mucus. The results suggest that, although both the surface and intracellular mucus participate in the retardation of hydrogen ion diffusion, the contribution of the latter appears to be greater.

Demonstration by monoclonal antibodies that carbohydrate structures of glycoproteins and glycolipids are onco-developmental antigens

The hope that hybridoma antibodies would reveal unique cell surface antigens during embryogenesis, differentiation and oncogenesis has been replaced by the realization that such antigens are mainly carbohydrate structures of glycoproteins and glycolipids occurring in many cell types. These findings either may reflect limitations in the methods of selection of hybridoma antibodies or may point to important roles for the diverse carbohydrate structures as receptors for regulators of cell growth and differentiation.

Carbohydrate structure in tumor immunity

Researchers have endeavored to define surface alterations associated with neoplasia for at least 25 years. In comparisons of normal tissues with animal and human tumors, cultured cells before and after transformation with oncogenic agents, tumorigenic and nontumorigenic transformed cells, metastatic and nonmetastatic tumor cells, high- and low-metastatic variants, and tumor cells before and after induction of differentiation to a less malignant phenotype, a consistent finding has been some form of alteration in surface carbohydrate structures. These changes in glycolipids, glycoproteins and glycosaminoglycans are reviewed, and their structures are illustrated. Both nucleotide sugar biosynthesis and glycosyltransferase changes have been associated with these alterations. In some cases, alterations in transformed cells were related to growth, rather than transformation. In others, the altered glycoconjugates are truly tumor-associated. There is evidence that cell surface glycoconjugates may function in growth control. Altered carbohydrate structures could also serve as receptors for growth promoting factors and be directly responsible for altered growth control. Recent studies with monoclonal antibodies indicate that the vast majority of antibodies recognizing tumor-associated antigens are detecting altered carbohydrate structures. Mechanisms by which the immune system can recognize these carbohydrate structures are considered, and immune recognition of tumor-associated carbohydrate structural alterations is explored. A number of these hypotheses relating to alterations in glycosylation, growth control, and tumor immunity deserve further investigation.

Lewis blood group antigens defined by monoclonal anti-colon carcinoma antibodies

Monoclonal antibodies directed against human cancer cells were prepared by the murine hybridoma technique. These antibodies detect Lewis blood group antigens as determined by indirect solid-phase radioimmunoassay, hapten inhibition studies, and chromatogram binding assay. One monoclonal antibody is specific for the Lea terminal carbohydrate of Gal beta 1----3Glc NAc(4----1 alpha Fuc) beta 1----3LacCer. Five monoclonal antibodies react with the Leb terminal carbohydrate sequence of Fuc alpha 1----2Gal beta 1----3GlcNAc(4----1 alpha Fuc) beta 1----3LacCer, and four of these antibodies are highly specific for this glycolipid and do not react with other similar di- and monofucosylated glycolipids. One of the anti-Leb antibodies cross-reacts with blood group H glycolipid and has binding properties similar to those of the previously described antibody NS-10-17 [M. Brockhaus, J. L. Magnani, M. Blaszczyk, Z. Steplewski, H. Koprowski, K.-A. Karlsson, G. Larson, and V. Ginsburg (1981) J. Biol. Chem. 256, 13223-13225]. Two antibodies react with both the Lea and Leb antigens, though both bind preferentially to Leb.

Chlamydomonas agglutinin conjugated to agarose beads as an in vitro probe of adhesion

Flagellar sexual agglutinins are responsible for the primary recognition and adhesion events of mating in Chlamydomonas reinhardi which culminate in zygotic union of plus and minus gametes. Recent studies in this laboratory have shown the plus agglutinin to be an extremely large (greater than 10(6) D) and asymmetric glycoprotein containing a high proportion of hydroxyproline and serine residues [14, 27, 28]. This paper reports an improved method for in vitro investigations of the adhesive nature of this molecule. Purified agglutinin is covalently attached to an insoluble (Affi-gel 15 agarose bead) support and shown to retain potent agglutination activity when presented to living minus gametes, which rapidly and extensively adhere to the coated bead surface by their flagella. The specificity of the response is documented by the lack of interaction of plus gametes with the immobilized plus agglutinin (IA+). Using this simple yet sensitive bioassay, we have subjected IA+ beads to various enzymatic, chemical and physical treatments and assessed the effects on agglutinin activity. These studies reveal that Chlamydomonas plus agglutinin is sensitive to thermolysin or trypsin digestion, alkaline borohydride reduction, periodate oxidation, thiol reduction and heating at 65 degrees C, but unaffected by treatment with chymotrypsin, endo- or exoglycosidases, or incubation with isolated minus agglutinin. The implications of these results for agglutinin structure and possible functional interactions in initial recognition/adhesion events are discussed.

Hydrogen ion diffusion in dog gastric mucus glycoprotein: effect of associated lipids and covalently bound fatty acids

The effect of neutral lipids, glycolipids and phospholipids associated with dog gastric mucus glycoprotein, and that of covalently bound fatty acids on the ability of glycoprotein to retard the diffusion of hydrogen ion was investigated. Purified mucus glycoprotein in its native form, placed between equimolar (0.155M) solutions of HCl and NaCl in a specially designed two-compartment chamber, caused a 90% reduction in permeability to hydrogen ion when compared with a layer of NaCl. Extraction of associated lipids lead to a 68% increase in permeability of the glycoprotein to hydrogen ion, while removal of the covalently bound fatty acids increased further the diffusion rate by 6%. Reassociation of the delipidated glycoprotein with its neutral lipids reduced the permeability to hydrogen ion by 34%, an 11% reduction was obtained with glycolipids, and 23% with phospholipids. Since neutral lipids account for 47% of the glycoprotein lipids, glycolipids 41.1% and phospholipids 11.9%, the quantitative decrease in permeability of the delipidated glycoprotein following its reassociation with phospholipids is 2.7 times greater than that of neutral lipids and 7.3 times greater than that of glycolipids.

Terminal alpha (1 leads to 4)-linked N-acetylglucosamine: a characteristic constituent of duodenal-gland mucous glycoproteins in rat and pig. A high-resolution 1H-NMR study

The structure of the carbohydrate chains of mucous glycoproteins from the gastro-intestinal tract was examined for species- and tissue-specificity. To this purpose, oligosaccharides were released from purified glycoprotein preparations of rat and pig gastric, duodenal-gland and small-intestinal mucus, by alkaline borohydride reductive cleavage. Based on the results of 500-MHz 1H-NMR spectroscopy and of sugar analysis of the total oligosaccharide fractions, terminal GlcNAc, alpha (1 leads to 4)-linked to galactose, appears to be a characteristic constituent of duodenal-gland oligosaccharides. Similarly, NeuAc in alpha (2 leads to 3)-linkage to galactose turns out to be a typical constituent of small-intestinal mucous glycoproteins. In general, glycoproteins from gastric mucus possess larger and more-branched carbohydrate chains than those from duodenal-gland and small-intestinal mucus. Comparing rat and pig, oligosaccharide structures for corresponding tissues are less complex for the former. After fractionation, the rat duodenal-gland oligosaccharides could be characterized by application of 1H-NMR spectroscopy as being branched tetra- up to hexa-saccharide chains, all sharing the italicized trisaccharide element. The chains exhibit microheterogeneity as to the termination by fucose in alpha (1 leads to 2)- or by GlcNAc in alpha (1 leads to 4)-linkage to galactose. The following structures can be proposed for the most abundant rat duodenal-gland oligosaccharides: (table; see text).

Lipids associated with rat small-intestinal mucus glycoprotein

The lipid content and composition of rat small-intestinal mucus, and the purified mucus glycoprotein before and after Pronase digestion were investigated. The mucus, obtained by the instillation of intestine with 2M NaCl, was fractionated on Bio-Gel A-50 in the presence of 6M urea and the mucus glycoprotein free of noncovalently bound protein was isolated. A portion of the purified glycoprotein was subjected to Pronase digestion to yield glycopeptides. The native mucus, and the purified glycoprotein and glycopeptides were extracted with chloroform-methanol, and the lipids contained in the extracts were analyzed. The lipids accounted for 17.6 of the dry weight of mucus, 26.4 of the mucus glycoprotein, and 25.3% of the glycopeptides. In comparison to mucus, the lipids associated with mucus glycoprotein contained 1.9 times more phospholipids and 2.1 times more glycolipids, showed a 26% increase in neutral lipids, and were virtually free of glycosphingolipids. Treatment of the purified glycoprotein with Pronase led to a moderate (22.3%) loss in neutral lipids, 4.3-fold decrease in phospholipids, and 52.3% increase in glyceroglucolipids. The results indicate that while the interaction of mucus glycoprotein with phospholipids involves its Pronase-susceptible region, the interaction with glyceroglucolipids occurs in the glycosylated region of the glycoprotein that is resistant to proteolysis.