Enzymatic sulfation of mucus glycoprotein in gastric mucosa. Effect of ethanol

Keratan Sulphate in the Tumour Environment

Keratan sulphate (KS) is a bioactive glycosaminoglycan (GAG) of some complexity composed of the repeat disaccharide D-galactose β1→4 glycosidically linked to N-acetyl glucosamine. During the biosynthesis of KS, a family of glycosyltransferase and sulphotransferase enzymes act sequentially and in a coordinated fashion to add D-galactose (D-Gal) then N-acetyl glucosamine (GlcNAc) to a GlcNAc acceptor residue at the reducing terminus of a nascent KS chain to effect chain elongation. D-Gal and GlcNAc can both undergo sulphation at C6 but this occurs more frequently on GlcNAc than D-Gal. Sulphation along the developing KS chain is not uniform and contains regions of variable length where no sulphation occurs, regions which are monosulphated mainly on GlcNAc and further regions of high sulphation where both of the repeat disaccharides are sulphated. Each of these respective regions in the KS chain can be of variable length leading to KS complexity in terms of chain length and charge localization along the KS chain. Like other GAGs, it is these variably sulphated regions in KS which define its interactive properties with ligands such as growth factors, morphogens and cytokines and which determine the functional properties of tissues containing KS. Further adding to KS complexity is the identification of three different linkage structures in KS to asparagine (N-linked) or to threonine or serine residues (O-linked) in proteoglycan core proteins which has allowed the categorization of KS into three types, namely KS-I (corneal KS, N-linked), KS-II (skeletal KS, O-linked) or KS-III (brain KS, O-linked). KS-I to -III are also subject to variable addition of L-fucose and sialic acid groups. Furthermore, the GlcNAc residues of some members of the mucin-like glycoprotein family can also act as acceptor molecules for the addition of D-Gal and GlcNAc residues which can also be sulphated leading to small low sulphation glycoforms of KS. These differ from the more heavily sulphated KS chains found on proteoglycans. Like other GAGs, KS has evolved molecular recognition and information transfer properties over hundreds of millions of years of vertebrate and invertebrate evolution which equips them with cell mediatory properties in normal cellular processes and in aberrant pathological situations such as in tumourogenesis. Two KS-proteoglycans in particular, podocalyxin and lumican, are cell membrane, intracellular or stromal tissue-associated components with roles in the promotion or regulation of tumour development, mucin-like KS glycoproteins may also contribute to tumourogenesis. A greater understanding of the biology of KS may allow better methodology to be developed to more effectively combat tumourogenic processes.

Biomarkers of human gastrointestinal tract regions

Dysregulation of intestinal epithelial cell performance is associated with an array of pathologies whose onset mechanisms are incompletely understood. While whole-genomics approaches have been valuable for studying the molecular basis of several intestinal diseases, a thorough analysis of gene expression along the healthy gastrointestinal tract is still lacking. The aim of this study was to map gene expression in gastrointestinal regions of healthy human adults and to implement a procedure for microarray data analysis that would allow its use as a reference when screening for pathological deviations. We analyzed the gene expression signature of antrum, duodenum, jejunum, ileum, and transverse colon biopsies using a biostatistical method based on a multivariate and univariate approach to identify region-selective genes. One hundred sixty-six genes were found responsible for distinguishing the five regions considered. Nineteen had never been described in the GI tract, including a semaphorin probably implicated in pathogen invasion and six novel genes. Moreover, by crossing these genes with those retrieved from an existing data set of gene expression in the intestine of ulcerative colitis and Crohn's disease patients, we identified genes that might be biomarkers of Crohn's and/or ulcerative colitis in ileum and/or colon. These include CLCA4 and SLC26A2, both implicated in ion transport. This study furnishes the first map of gene expression along the healthy human gastrointestinal tract. Furthermore, the approach implemented here, and validated by retrieving known gene profiles, allowed the identification of promising new leads in both healthy and disease states.

Glycodynamics of Mucin Biosynthesis in Gastrointestinal Tumor Cells

Glycoproteins found in the secretions and on the surfaces of cancer cells include mucins and mucin-like glycoproteins. These molecules have been shown to carry antigens that are characteristically expressed on cancer cells, including Tn and T antigens and Lewis epitopes. The structures of O-glycans are often abnormal in gastrointestinal tumors, or else are present in abnormal amounts, and these structures greatly contribute to the phenotype and biology of cancer cells. It has been shown that glycans of cancer cells have functional importance in cell adhesion, invasion and metastasis. The possible mechanisms leading to these cancer-specific changes in carbohydrate structures (termed glycodynamics) involve altered mRNA expression and catalytic activities of glycosyltransferases and sulfotransferases found in tissues and cells of gastrointestinal tumors. In a number of cases it has been possible to correlate enzyme changes with oligosaccharide structures. Different mechanisms have been suggested leading to the synthesis of cancer-specific Lewis, T and Tn antigens, but the regulation of cancer mucin antigens generally appears to be very complex and is poorly understood. The expression levels of specific mucin antigens and enzymes in gastro-intestinal tumors have diagnostic as well as prognostic value. These antigens also have potential for cancer immunotherapy. However, we first need to unravel the complexity of the control of glycosylation in cancer cells. Most importantly, studies of the functional implications of the glycodynamics in cancer cells, as related to cell adhesion and impact on the immune system will provide promising directions for future research.

Up-regulation of gastric mucosal inflammatory responses to Helicobacter pylori lipopolysaccharide by aspirin but not indomethacin

Infection with Helicobacter pylori and the use of non-steroidal anti-inflammatory drugs (NSAIDs) are recognized as the two primary factors in the etiology of gastric disease. In this study, we applied the animal model of H. pylori-induced gastritis to assess the influence of NSAIDs on the course of mucosal inflammatory responses to H. pylori. Two days following intragastric application of H. pylori lipopolysaccharide, rats were divided into groups and administered daily for up to 8 days either indomethacin, aspirin or the vehicle, and their gastric mucosal tissue subjected to histological and biochemical assessment. H. pylori lipopolysaccharide elicited within 2 days a pattern of acute mucosal inflammatory responses accompanied by a massive epithelial cell apoptosis, and a marked increase in the expression of membrane-bound and soluble forms of TNF-alpha. The extent of mucosal inflammatory involvement reached a maximum by the 4th day and showed a decline by the 10th day; this was reflected in a 38.1% reduction in apoptosis, a 53.2% decline in membrane-bound TNF-alpha and a 63.8% decrease in soluble TNF-alpha. Compared to the vehicle controls, aspirin caused a 36.2% increase in the severity of the mucosal inflammatory involvement by the second day of administration and a 25.9% increase in the inflammatory involvement occurred by the 8th day; this effect of aspirin was accompanied by a significant (54.5%) induction in apoptosis, a 58.2% decline in membrane-bound TNF-alpha and a 61% increase in soluble TNF-alpha. In contrast, administration of indomethacin evoked only a marginal increase (5-7%) in apoptosis, and caused no discernible changes in the severity of gastric mucosal involvement and the expression of TNF-alpha forms elicited by H. pylori lipopolysaccharide. The findings indicate that aspirin, but not indomethacin, increases the severity of gastric mucosal inflammatory responses to H. pylori. This detrimental influence of aspirin appears to result from up-regulation in the mucosal expression of soluble form of TNF-alpha, which leads to the amplification of apoptotic events that potentiate gastric mucosal inflammatory reaction to H. pylori.

Increasing the intra-Golgi pH of cultured LS174T goblet-differentiated cells mimics the decreased mucin sulfation and increased Thomsen-Friedenreich antigen (Gal beta1-3GalNac alpha-) expression seen in colon cancer

Mucins in ulcerative colitis and colon cancer share common properties of reduced sulfation and increased oncofetal carbohydrate antigen expression. It has previously been shown that there is no simple correlation between these changes and the activity of the relevant glycosyl-, sialyl-, and sulfo-transferases. We examined mucin sulfation and expression of oncofetal Thomsen-Friedenreich (TF) antigen (galactosyl beta1-3N-acetylgalactosamine alpha-) in the goblet cell-differentiated human colon cancer cell line LS174T following treatment with bafilomycin A(1, )which raises intra-Golgi pH, or monensin, which disrupts medial-trans Golgi transport. Cells were dual-labeled with sodium [(35)S]-sulfate and D-[6-(3)H(N)]-glucosamine hydrochloride, or labeled with L-[U-(14)C]-threonine alone. Mucin was purified using Sepharose CL-4B gel filtration. Mucin sulfo-Lewis(a) and TF antigen expression were assessed using the F2 anti-sulfo-Lewis(a) monoclonal antibody and peanut agglutinin binding respectively. Bafilomycin (0.01 microM; 48 h) reduced total mucin sulfation, expressed relative to incorporation of glucosamine, to 0.50 +/- 0.04 d.p.m. [(35)S]-sulfate per d.p.m. [(3)H]-glucosamine compared to control, 0.84 +/- 0.05 (p < 0.001, n = 16). This was accompanied by 50.3 +/- 8.0% increased expression of TF antigen (p < 0.01) and 50.1 +/- 5.5% decreased expression of sulfo-Lewis(a) (p < 0.01). The reduced sulfate:glucosamine ratio was largely due to increased incorporation of glucosamine into newly synthesized mucin rather than reduction in total sulfate incorporation. In contrast, monensin only reduced total mucin glycosylation at concentrations > 0.1 microM and had no significant effect on mucin sulfation or TF expression. Intra-Golgi alkalinization affects mucin glycosylation, resulting in decreased mucin sulfation and increased expression of TF antigen, changes that mimic those seen in cancerous and premalignant human colonic epithelium.

Biochemical differences between two types of N-acetylglucosamine:-->6sulfotransferases in human colonic adenocarcinomas and the adjacent normal mucosa: specific expression of a GlcNAc:-->6sulfotransferase in mucinous adenocarcinoma

6-O-Sulfation of beta-GlcNAc is an initial step in the biosynthesis of N-linked and O-linked sulfated glycans, which are widely distributed in colonic tissues. However, the biochemical mechanism of this sulfation in human colonic carcinogenesis was still unclear. In this study, we found two types of GlcNAc:-->6sulfotransferases (SulT) in human colonic adenocarcinomas and the adjacent normal mucosa, and we determined their enzymatic characteristics. One SulT, named SulT-a, was present in the adjacent normal mucosa and in non-mucinous adenocarcinomas, whereas the other SulT, named SulT-b, was present only in mucinous adenocarcinomas and adenocarcinomas with a mucinous component. SulT-a preferentially acted on Galbeta1-->3(GlcNAcbeta1-->6)GalNAc(alpha1)-p-nitrophenyl (pNP) and GlcNAcbeta1-->2Man, whereas SulT-b could act not only on these two glycans, but also on GlcNAcbeta1-->3GalNAc(alpha1)-pNP and GlcNAcbeta1-->3Galbeta1-->4Glc. The levels of SulT-a activity were significantly lower in non-mucinous adenocarcinomas than in the adjacent mucosa. In contrast, SulT-b was expressed in mucinous adenocarcinomas and in adenocarcinomas with a mucinous component. These results indicate that there are at least two types of GlcNAc:-->6SulT, SulT-a and -b, in colonic mucosa and adenocarcinomas, and that the occurrence of these enzymes is closely correlated with colonic cancer and the presence of areas of mucin accumulation.

Induction of endothelin-converting enzyme-1 in gastric mucosal injury by idomethacin

Endothelin-1 (ET-1) is a 21-amino acid vasoactive peptide produced from a 39-amino acid biologically inactive peptide, big ET-1, by the action of endothelin-converting enzyme-1 (ECE-1). We investigated gastric mucosal expression of ECE-1 during a 16 h course of inflammatory responses associated with gastric mucosal injury caused by indomethacin. The extent of gastric mucosal damage reached a maximum 4 h following the drug, and was accompanied by a 3.9-fold enhancement in the expression of ECE-1 activity and a significant elevation in ET-1 (4.5-fold), TNF-alpha (11.3-fold), and apoptosis (29.9-fold). A 37.2% decrease in the severity of lesion 16 h following the drug was associated with a 44.5% reduction in the mucosal expression of ECE-1 activity and a decline in TNF-alpha (64%), ET-1 (65.2%), and apoptosis (72.3%). The results demonstrate that gastric mucosal injury by indomethacin is associated with up-regulation of ECE-1 expression, which leads to the enhancement of ET-1 production, induction of TNF-alpha, and triggering apoptotic events that disrupt gastric mucosal homeostasis.

Up-regulation of endothelin-converting enzyme-1 in gastric mucosal inflammatory responses to Helicobacter pylori lipopolysaccharide

Endothelin-1 (ET-1) is a vasoactive peptide produced from a biologically inactive big ET-1 by the action of endothelin-converting enzyme-1 (ECE-1). We investigated gastric mucosal expression of ECE-1 during a 10-day course of inflammatory responses associated with acute gastritis elicited by Helicobacter pylori lipopolysaccharide. The ECE-1 activity was associated with microsomal fraction and the level of its expression reflected the extent of mucosal inflammatory involvement. The histologic pattern of inflammation reached a maximum on the 4th day following the lipopolysaccharide and was accompanied by a 4.1-fold enhancement in the expression of ECE-1 activity and a significant elevation in ET-1 (3.1-fold), TNF-alpha (8.8-fold), and apoptosis (11.6-fold). A 41.5% decrease in the severity of mucosal inflammation by the 10th day following the lipopolysaccharide was reflected in a 62.3% reduction in the mucosal expression of ECE-1 and a decline in TNF-alpha, ET-1, and apoptosis. Thus, H. pylori infection causes up-regulation of gastric mucosal ECE-1 expression, which leads to the enhancement of ET-1 production, induction of TNF-alpha, and triggering the apoptotic events that exacerbate the inflammatory process.

Pathways of O-glycan biosynthesis in cancer cells

Glycoproteins with O-glycosidically linked carbohydrate chains of complex structures and functions are found in secretions and on the cell surfaces of cancer cells. The structures of O-glycans are often unusual or abnormal in cancer, and greatly contribute to the phenotype and biology of cancer cells. Some of the mechanisms of changes in O-glycosylation pathways have been determined in cancer model systems. However, O-glycan biosynthesis is a complex process that is still poorly understood. The glycosyltransferases and sulfotransferases that synthesize O-glycans appear to exist as families of related enzymes of which individual members are expressed in a tissue- and growth-specific fashion. Studies of their regulation in cancer may reveal the connection between cancerous transformation and glycosylation which may help to understand and control the abnormal biology of tumor cells. Cancer diagnosis may be based on the appearance of certain glycosylated epitopes, and therapeutic avenues have been designed to attack cancer cells via their glycans.

Glycohistochemical investigation of canine and feline zonae pellucidae of preantral and antral oocytes

Glycoconjugate modifications were analysed in the zona pellucida during development of oocytes in dog and cat using conventional histochemical staining methods with or without previous carbohydrate digestion. A series of lectins combined with desulphation and sialic acid degradation were applied. No differences were observed between dog and cat follicles using conventional histochemical staining methods. In both species, the zona pellucida and follicular fluid/intercellular matrix strongly reacted with PAS and high iron diamine stain (HID) and reacted moderately with low iron diamine stain (LID). Treatment with testicular hyaluronidase, chondroitinase ABC, chondroitinase AC and chondroitinase B treatment diminished HID and LID positivity of follicular fluid and intercellular matrix. Lectins that gave the most intense staining of the zona pellucida of both species were SBA, PNA, RCA-I, GSA-IB4 and WGA, indicating the presence of beta-D-GalNAc, D-Gal and GlcNAc residues. Sulpho- and asulpho-carbohydrates were identified in terminal and/or subterminal positions linked to sialic acid residues. In conclusion, the results indicate that glycosaminoglycans are not present in the zona pellucida of both species. Differences were observed in carbohydrate residues and in their spatial distribution, depending on species and developmental stage of the follicles. The similarity in lectin affinity between ooplasm and zona pellucida of oocytes present in follicles at different stages of development confirm the involvement of oocytes in zona pellucida production.

Intracellular CFTR: localization and function

Intracellular CFTR: Localization and Function. Physiol. Rev. 79, Suppl.: S175-S191, 1999. - There is considerable evidence that CFTR can function as a chloride-selective anion channel. Moreover, this function has been localized to the apical membrane of chloride secretory epithelial cells. However, because cystic fibrosis transmembrane conductance regulator (CFTR) is an integral membrane protein, it will also be present, to some degree, in a variety of other membrane compartments (including endoplasmic reticulum, Golgi stacks, endosomes, and lysosomes). An incomplete understanding of the molecular mechanisms by which alterations in an apical membrane chloride conductance could give rise to the various clinical manifestations of cystic fibrosis has prompted the suggestion that CFTR may also play a role in the normal function of certain intracellular compartments. A variety of intracellular functions have been attributed to CFTR, including regulation of membrane vesicle trafficking and fusion, acidification of organelles, and transport of small anions. This paper aims to review the evidence for localization of CFTR in intracellular organelles and the potential physiological consequences of that localization.

Stimulation of tyrosylprotein sulfotransferase activity by ethanol: role of increased enzyme level

Tyrosylprotein sulfotransferase (TPST), an enzyme involved in the posttranslational modification of proteins, plays important role in the biological activity and secretion of proteins. Previously we have shown an increased activity of this enzyme in gastric mucosa of alcoholics. In the present study, effect of ethanol on TPST was examined in rat liver and gastric mucosa utilizing enzyme assays and Western blot analyses for TPST levels. Male Sprague-Dawley rats were pair-fed Leiber-DeCarli liquid diets for 10 days and controls received a liquid diet in which dextrose was isocalorically substituted for ethanol. After ethanol feeding, rats were sacrificed and liver and gastric mucosa were processed for Golgi membrane preparation. The TPST activity was measured using poly(Glu6, Ala3, Tyr1) as the sulfate acceptor and PAPS as sulfate donor. There was a threefold increase in TPST activity of gastric mucosa of animals subjected to chronic alcohol feeding. In the liver, the increase in tyrosine sulfating activity was also around threefold. The kinetic studies performed to understand the mechanism involved in ethanol stimulation of TPST activity showed no change in the Km values of the enzyme by ethanol. In control and ethanol-treated animals, the Km for EAY was 0.41-0.53 and 0.43-0.53 microM, and the Km for PAPS was 10-12.5 and 9-17 microM, respectively. The Vmax in ethanol-fed animals was increased by 1.5- to 2-fold. The increase in TPST activity in experimental rats was further tested by analyzing the Western blots by Imaging Densitometer for TPST levels. Analysis of TPST levels also showed over threefold increase in the stomach and liver of ethanol-fed rats. Our results indicate that stimulation of TPST by ethanol involves increased TPST level rather than change in affinity for its substrates.

Sulfomucins in the human body

Mucins are widely distributed in mucous secretion fluids or are associated with plasma membranes. Up to now 9 genes of epithelial mucins have been identified, distributed over five chromosomes. Superposed on the genetic diversity, each type of mucin displays heterogeneity in oligosaccharide composition, including the terminal sugar residues. On top of that there is variation between individuals brought about by blood group antigens. Heterogeneity is further incited by the degree of sulfation. This tremendous structural heterogeneity endows mucin molecules with properties suggestive for a multifunctional role. The major biological function assigned to mucins is still the protection of tissues covered by the mucous gel. Current knowledge on the specific biological functions of the sulfate residues is fragmentary and periphrastic. Glycosylation including sulfation appears to be subject to modification under pathological conditions. There is evidence that sulfation rate-limits bacterial degradation of mucins. Moreover, accumulating data focus towards their involvement in recognition phenomena. Sulfate residues on blood group related structures provoke specific epitopes for selective interaction with microorganisms e.g. Helicobacter pylori. A distinct class of mucins acts as ligands for selectins, crucial in cellular recognition processes like cellular homing of lymphocytes. Whereas in earlier days mucins were only seen as water-binding molecules, protecting the underlying mucosa against harmful agents, the current picture of these molecules is characterized by the selective interaction with their environment, including epithelial-, and endothelial cells and microorganisms, thereby regulating a great number of biological processes. However, the specific role of sulfate remains to be further elucidated.

Characterization of an N-acetylglucosamine-6-O-sulfotransferase from human respiratory mucosa active on mucin carbohydrate chains

A microsomal GlcNAc-6-O-sulfotransferase activity from human bronchial mucosa, able to transfer a sulfate group from adenosine 3'-phosphate 5'-phosphosulfate onto methyl-N-acetylglucosaminides or terminal N-acetylglucosamine residues of carbohydrate chains from human respiratory mucins, has been characterized. The reaction products containing a terminal HO3S-6GlcNAc were identified by high performance anion-exchange chromatography. Using methyl-beta-N-acetylglucosaminide as a substrate, the optimal activity was obtained with 0.1% Triton X-100, 30 mM NaF, 20 mM Mn2+, 5 mM AMP in a 30 mM MOPS (3-(N-morpholino) propanesulfonic acid) buffer at pH 6.7. The apparent Km values for adenosine 3'-phosphate 5'-phosphosulfate and methyl-beta-N-acetylglucosaminide were observed at 9.1 x 10(-6) M and 0.54 x 10(-3) M, respectively. The enzyme had more affinity for carbohydrate chains with a terminal GlcNAc residue than for methyl-beta-N-acetylglucosaminide; it was unable to catalyze the transfer of sulfate to position 6 of the GlcNAc residue contained in a terminal Galbeta1-4GlcNAc sequence. However, oligosaccharides with a nonreducing terminal HO3S-6GlcNAc were substrates for a beta1-4 galactosyltransferase from human bronchial mucosa. These data point out that GlcNAc-6-O-sulfotransferase must act before beta1-4 galactosylation in mucin-type oligosaccharide biosynthesis.

Glycosylation differences between a cystic fibrosis and rescued airway cell line are not CFTR dependent

Altered glycosylation of mucus and membrane glycoconjugates could explain reported differences in binding of bacterial pathogens to cystic fibrosis (CF) versus normal tissue. However, because bacteria can alter cell surface glycoconjugates, it is not possible to assess the role of cystic fibrosis transmembrane conductance regulators (CFTR) in glycosylation in these studies. To address this issue, we have developed quantitative lectin binding assays to compare cell surface glycosylation in well-matched immortalized CF cells and rescued cell lines. The CF airway bronchial epithelial cell line IB3-1 consistently bound more peanut agglutinin (PNA) than its clonal derivative S9, which stably expresses functional wild-type CFTR. Pretreatment with neuraminidase increased PNA binding and abolished the difference between the two cell lines. However, infection of the IB3-1 cells with a replication-deficient recombinant adenovirus encoding CFTR restored CFTR function but did not alter PNA binding to cells. In contrast, treatment with the weak base ammonium chloride increased PNA binding to both cell lines as expected. Our data show that even clonally related CF and rescued cells can exhibit significant differences in carbohydrate processing. Although the differences that we found are consistent with the proposed role for CFTR in modulating intraorganellar pH, our data strongly suggest that they are CFTR independent. These studies add a cautionary note to the interpretation of differences in glycosylation between CF and normal primary tissues and immortalized cells.

Characterization of a sulfotransferase from human airways responsible for the 3-O-sulfation of terminal galactose in N-acetyllactosamine-containing mucin carbohydrate chains

A galactose 3-O-sulfotransferase activity able to transfer a sulfate group from adenosine 3'-phosphate 5'-phosphosulfate to methyl galactosides or terminal N-acetyllactosamine-containing carbohydrate chains from human respiratory mucins was characterized in microsomal fractions prepared from human respiratory mucosa. The reaction products, methyl alpha- or beta-galactose 3-sulfate and three oligosaccharide alditols containing the sequence HSO3-3Gal beta 1-4GlcNAc beta 1-6GalNAc-itol were identified by high performance anion-exchange chromatography. Using methyl beta-galactoside as a substrate, the optimum activity was obtained with 0.1% Triton X-100, 30 mM NaF, 20 mM Mn2+, and 10 mM AMP in a 30 mM 2-(N-morpholino)ethanesulfonic acid buffer at pH 6.1. The apparent Km for methyl beta-galactoside and for adenosine 3'-phosphate 5'-phosphosulfate were observed at 0.69 x 10(-3) M and at 4 x 10(-6) M respectively. This sulfotransferase is different from that responsible for sulfatide synthesis.

Inhibition of gastric mucosal mucin receptor by H. pylori lipopolysaccharide: effect of ebrotidine

1. H. pylori infection causes the loss of mucus coat continuity and its patchy appearance. Here, we present evidence that the bacterium, through its cell wall lipopolysaccharide, disrupts the interaction between mucin and its mucosal receptor, and that ebrotidine is capable of counteracting this process. 2. The receptor for mucin, isolated from the solubilized gastric epithelial cell membrane by affinity chromatography on Sepharose-bound wheat germ agglutinin, displayed a molecular weight of 97 kDa and exhibited specific affinity towards mucin-coated surface. 3. The mucin binding to the receptor was susceptible to the inhibitin by H. pylori lipopolysaccharide and reached a maximum of 91%. This effect of the lipopolysaccharide was counteracted by ebrotidine, which caused a dose-dependent relief of the lipopolysaccharide inhibitory effect with maximum restoration in mucin-receptor binding of 51% at 60 microliters/ml ebrotidine. 4. The results show that H. pylori, through its lipopolysaccharide, is capable of disrupting the integrity of mucus perimeter of gastric mucosal defense and that antiulcer agent, ebrotidine, counteracts this untoward effect.

Enhancement in the protective qualities of gastric mucus by ebrotidine during duodenal ulcer healing

1. Gastric mucus from duodenal ulcer patients before and following therapy with a new antiulcer agent, ebrotidine, at 400, 600 and 800 mg dose was examined for changes in the physicochemical qualities and anti-H. pylori activity. 2. The results of physical measurements revealed that successful therapy with ebrotidine was accompanied by a 25% increase in gastric mucus viscosity, and a 20% increase in H+ retardation capacity, while its hydrophobicity increased by 11%. 3. The enhancement in the physical properties of mucus with ebrotidine therapy were also reflected in a marked (2.6-2.9-fold) increase in the proportion of the high molecular weight form of mucin. Furthermore, following therapy with ebrotidine, the gastric mucins showed a 36% higher content of sulfate as compared to that before the therapy. 4. Assays on the H. pylori aggregating titer of gastric mucin revealed that ebrotidine therapy at all three doses evoked a 4-fold increase in mucin anti-H. pylori activity. 5. The data demonstrate that duodenal ulcer therapy with ebrotidine leads to a marked improvement in the protective qualities of gastric mucus essential for the maintenance of mucosal integrity and enhances the inherent mucosal defense against H. pylori infection.

Inhibition of gastric mucosal mucin receptor by Helicobacter pylori lipopolysaccharide: effect of sulglycotide

1. A receptor for mucin was isolated from the solubilized gastric epithelial cell membrane by affinity chromatography on Sepharose-bound wheat germ agglutinin. 2. The receptor protein displayed a molecular weight of 97 kDa and exhibited specific affinity towards mucin-coated surfaces. The optimum for mucin binding occurred at 60-100 micrograms/ml, while the values for the receptor were 2.0-3.1 micrograms/ml. 3. The mucin binding to the receptor was susceptible to Helicobacter pylori lipopolysaccharide which caused maximum inhibition of 91% at 30 mu/ml. This inhibitory effect of the lipopolysaccharide was abolished by a gastroprotective agent, sulglycotide. 4. The effect of sulglycotide was dose dependent and at 50 micrograms/ml produced a 94% restoration in receptor-mucin binding. Furthermore, sulglycotide was also capable of enhancing (97%) the mucin binding to its receptor in the absence of the lipopolysaccharide. 5. The results demonstrate that H. pylori through its lipopolysaccharide interferes in the interaction of mucin with gastric epithelial surfaces and that a gastroprotective agent, sulglycotide, counteracts this effect, and hence is capable of preventing the loss of mucin coat continuity occurring with H. pylori infection.

Effect of sofalcone on tyrosylprotein sulfotransferase

1. Gastric mucus glycoproteins are actively involved in the maintenance of mucosal integrity and the impairment in their elaboration is often a prominent feature in gastric pathology. In this study, we investigated the effect of an antiulcer drug, sofalcone, on the activity of tyrosylprotein sulfotransferase enzyme involved in the secretion of proteins and glycoproteins in male 8 week old rats. 2. Using poly-Glu6, Ala3, Tyr1 (EAY) as sulfate acceptor, and 3'phosphoadenosine 5'-phosphosulfate (PAPS) as sulfate donor the optimum Golgi TPST activity was obtained at pH 6.8, in presence of 0.5% Triton X-100, 20 mM MnCl2, 50 mM NaF and 2 mM 5'-AMP. 3. Introduction of sofalcone to the reaction mixture led to the enhancement in TPST activity. The rate of stimulation was proportional to the drug concentration up to 30 micrograms, at which concentration, a 55% increase in TPST activity was attained. 4. The results attest further to the value of sofalcone as a potent mucosal strengthening agent, and suggest that the agent may promote mucin secretion via activation of tyrosine sulfation.

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.

Inhibition of Helicobacter pylori glycosulfatase activity towards human gastric sulfomucin by a gastroprotective agent, sulglycotide

1. A glycosulfatase activity towards human gastric sulfomucin was identified in the extracellular material elaborated by Helicobacter pylori, a pathogen implicated in the etiology of gastric disease. 2. The purified enzyme displayed an apparent molecular weight of 30 kDa, and exhibited maximum activity at pH 5.7 in the presence of 0.3% Triton X-100 and 100 mM CaCl2. 3. The H. pylori glycosulfatase activity towards human gastric sulfomucin was inhibited by a gastroprotective agent, sulglycotide. The inhibitory effect was proportional to the concentration of sulglycotide up to 20 micrograms/ml, at which a 98% decrease in mucin desulfation occurred. However, the drug lost the inhibitory effect following its chemical desulfation. 4. The results demonstrate that sulglycotide is a potent inhibitor of H. pylori glycosulfatase and, hence, may be of value in the treatment of gastric disease associated with this bacterial infection.

Regulation of buccal mucosal calcium channel activity by salivary mucins

1. The effect salivary mucins on the activity of calcium channel isolated from buccal mucosal cell membranes was investigated. The uptake of 45Ca2+ while only moderately (15%) affected by the intact low and high molecular weight mucin forms, was significantly inhibited, by the acidic low and high molecular weight salivary mucins which evoked 64 and 60% inhibition, respectively. 2. The inhibitory effect of salivary mucins was associated with the sialic acid and sulfate ester groups of the carbohydrate chains, as the removal of either group caused partial loss in the glycoproteins inhibition, and the complete loss in the inhibitory effect occurred following desialylation and desulfation. 3. The channel in the presence of epidermal growth factor (EGF) and ATP responded by an increase in tyrosine phosphorylation of 55 and 170 kDa proteins, and the phosphorylated channels showed a 46% increase in 45Ca2+ uptake. The phosphorylation and the calcium uptake were susceptible to inhibition by a specific tyrosine kinase inhibitor, genistein. 4. The binding of EGF to calcium channel receptor protein was inhibited by the low and high molecular weight acidic mucins, causing 41.2 and 36.1% reduction, respectively. This reduction in binding was dependent upon the presence of sulfate ester and sialic acid groups, as evidenced by the loss of the glycoproteins' inhibitory capacity following removal of these groups. 5. The results for the first time demonstrate that salivary mucins actively participate in the modulation of the EGF-controlled buccal mucosal calcium channel activity expression, a process of importance to the preservation of oral tissue integrity.

Modulation of gastric mucosal calcium channel activity by mucus glycoprotein

1. The effect of gastric mucus glycoprotein on the activity of calcium channel isolated from gastric epithelial cell membrane was investigated. The 45Ca2+ uptake into the vesicle-reconstituted channels, while only moderately (14%) affected by the intact mucus glycoprotein, was found significantly inhibited (59%) by the acidic glycoprotein fraction. This effect was associated with the sialic acid and sulfate ester groups of the glycoprotein, as their removal caused a loss in the inhibition. 2. The channel complex in the presence of epidermal growth factor (EGF) and ATP responded by an increase in protein tyrosine phosphorylation of 55 and 170 kDa proteins, and the vesicles containing the phosphorylated channels showed a 50% increase in 45Ca2+ uptake. The phosphorylation and the calcium uptake were susceptible to inhibition by a specific tyrosine kinase inhibitor, genistein. 3. The channel protein phosphorylation was inhibited by the acidic mucus glycoprotein, which also interfered with the binding of EGF to the channel protein. The inhibitory effect was dependent upon the presence of sulfate ester and sialic acid groups, as evidenced by the loss of the glycoprotein inhibitory capacity following their removal. 4. The results suggest that the acidic gastric mucus glycoproteins, by modulating the EGF-controlled calcium channel phosphorylation, play a major role in gastric mucosal calcium homeostasis.

Effect of ebrotidine on the synthesis and secretion of gastric sulfomucin

1. The effect of a new antiulcer agent, ebrotidine, on the synthesis and secretion of sulfomucin in gastric mucosa was investigated. Rat gastric mucosal segments were incubated in DMEM containing [3H]proline, [3H]glucosamine and [35S]Na2SO4 as markers for mucin synthesis, glycosylation and sulfation, in the presence of 0-150 microM ebrotidine. 2. The drug, while showing no discernible effect on the apomucin synthesis, evoked a dose-dependent increase in mucin glycosylation and sulfation, which at 100 microM ebrotidine, attained its maximum of 2.4 and 2.7-fold stimulation, respectively. 3. The analysis of mucin secretory responses revealed that ebrotidine caused a concentration-dependent enhancement in sulfomucin secretion which attained its maximum increase of 3.3-fold at 100-120 microM ebrotidine. Furthermore, the sulfomucin elaborated in the presence of ebrotidine exhibited a higher content of a large molecular-weight mucus glycoprotein form, the assembly of which is intimately associated with the sulfation event. 4. The results suggest that the ability of ebrotidine to enhance gastric sulfomucin synthesis and secretion may play an important role in the gastroprotective mechanism of action of this agent.

Control of mucin molecular forms expression by salivary protease: differences with caries

1. A protease activity capable of degradation of the high mol. wt salivary mucus glycoprotein to a low mol. wt glycoprotein form was identified in human submandibular gland secretion. 2. The protease exhibited optimum activity at pH 7.0-7.4, and gave on SDS-PAGE under reducing conditions two major protein bands of 48 and 53 kDa. The enzyme showed susceptibility to PMSF, alpha 1antitrypsin, and egg white and soybean inhibitors, a characteristic typical to serine proteases. 3. The activity of the protease towards the high mol. wt mucus glycoprotein was found to be 3.8-fold higher in submandibular gland secretion of caries-resistant individuals than that of caries-susceptible. Furthermore, the enzyme from both groups displayed greater activity against the mucus glycoprotein of caries-resistant subjects. 4. Since the low mol. wt salivary mucus glycoprotein form is more efficient in bacterial clearance than the high mol. wt mucin, the enhanced expression of this indigenous salivary protease activity towards mucin may be the determining factor in the resistance to caries.

Structural features of carbohydrate chains in human salivary mucins

1. The structure of carbohydrate chains in the low and high molecular weight mucus glycoprotein forms from submandibular-sublingual saliva of individuals with blood group B was investigated. 2. Alkaline borohydride reductive cleavage of the glycoproteins yielded in each case a population of neutral (55%) and acidic (45%) oligosaccharide alditols ranging in size from 3 to 16 sugar units. 3. The predominant neutral oligosaccharides in both glycoprotein forms consisted of 16 and 15 sugar units arranged in triantennary fashion, and carried blood group B and I antigenic determinants. 4. Three of the oligosaccharides in each glycoprotein contained sialic acid and ranged in size from 3 to 12 sugar units. In two oligosaccharides sialic acid was linked to C3 of galactose and in one to C6 of N-acetylgalactosamine. The sulfated oligosaccharide in both glycoproteins was identified as a pentasaccharide with the sulfate ester group at C6 of N-acetylglucosamine. 5. The results demonstrate that contrary to the earlier view the low and high molecular weight mucus glycoprotein forms of human saliva contain identical carbohydrate chains.

Clinical aspects of glycoprotein biosynthesis

Glycoproteins are widely distributed among species in soluble and membrane-bound forms, associated with many different functions. The heterogenous sugar moieties of glycoproteins are assembled in the endoplasmic reticulum and in the Golgi and are implicated in many roles that require further elucidation. Glycoprotein-bound oligosaccharides show significant changes in their structures and relative occurrences during growth, development, and differentiation. Diverse alterations of these carbohydrate chains occur in diseases such as cancer, metastasis, leukemia, inflammatory, and other diseases. Structural alterations may correlate with activities of glycosyltransferases that assemble glycans, but often the biochemical origin of these changes remains unclear. This suggests a multitude of biosynthetic control mechanisms that are functional in vivo but have not yet been unraveled by in vitro studies. The multitude of carbohydrate alterations observed in disease states may not be the primary cause but may reflect the growth and biochemical activity of the affected cell. However, knowledge of the control mechanisms in the biosynthesis of glycoprotein glycans may be helpful in understanding, diagnosing, and treating disease.

Nitecapone effect on the synthesis and secretion of gastric sulfomucin

1. The effect of a new antiulcer agent, nitecapone, on the synthesis and secretion of sulfomucin in gastric mucosa was investigated using mucosal segments incubated in the presence of [3H]proline, [3H]glucosamine and [35S]sulfate. 2. The drug, while showing no discernible effect on the apomucin synthesis, evoked a dose-dependent increase in mucin glycosylation and sulfation, which at 225 microM nitecapone, attained its maximum of 1.8 and 2.2-fold stimulation, respectively. 3. The analysis of mucin secretory responses revealed that nitecapone caused a concentration-dependent enhancement in sulfomucin secretion attaining maximum increase of 1.5-fold at 150 microM nitecapone. 4. The stimulatory effect of nitecapone on sulfomucin secretion was accompanied by 1.4-fold increase in mucosal cAMP level, and showed sensitivity to protein kinase A inhibitors, thus pointing towards the involvement of protein kinase A in mediation of gastric sulfomucin secretory responses to nitecapone. 5. The ability of nitecapone to enhance sulfomucin synthesis and secretion could be of importance to the gastroprotective action of this agent.

Role of sulfation in post-translational processing of gastric mucins

1. Gastric mucosal segments were incubated in MEM supplemented with various sulfate concentrations in the presence of [3H]glucosamine, [3H]proline and [35S]Na2SO4, with and without chlorate, an inhibitor of 3'-phosphoadenosine-5'-phosphosulfate formation. 2. Incorporation of glucosamine and sulfate depended upon the sulfate content of the medium and reached a maximum at 300 microM sulfate. Introduction of chlorate into the medium, while having no effect on protein synthesis as evidenced by proline incorporation, caused, at its optimal concentration of 2 mM, a 90% decrease in mucin sulfation and a 40% drop in glycosylation. 3. At low sulfate content in the medium and in the presence of chlorate, the incorporation of sulfate and glucosamine was mainly into the low molecular-weight form of mucin. An increase in sulfate in the medium caused an increase in the high molecular-weight form of mucin and in the extent of sulfation in its carbohydrate chain. 4. The results suggest that the sulfation process is an early event taking place at the stage of mucin subunit assembly and that sulfate availability is essential for the formation of the high molecular-weight mucin polymer.

Helicobacter pylori lipopolysaccharide effect on the synthesis and secretion of gastric sulfomucin

The effect of H. pylori lipopolysaccharide on the synthesis and secretion of sulfated mucin in gastric mucosa was investigated using mucosal segments incubated in the presence of [3H]proline, [3H]glucosamine and [35S]Na2SO4. The lipopolysaccharide, while showing no discernible effect on the apomucin synthesis was found to inhibit the process of mucin glycosylation and sulfation, which at 100 micrograms/ml lipopolysaccharide reached the optimal inhibition of 65%. The analysis of mucin secretory responses revealed that the lipopolysaccharide by first 15 min caused a 57% stimulation in sulfomucin secretion followed thereafter by inhibition, which reached maximum of 32% by 45 min. The results suggest that colonization of gastric mucosa by H. pylori may be detrimental to the process of gastric sulfomucin synthesis and secretion.

Glycosulfatase activity of helicobacter pylori toward gastric mucin

A glycosulfatase activity toward sulfated gastric mucus glycoprotein was identified in the extracellular material elaborated by H. pylori, a bacteria implicated in the etiology of gastric disease. Upon acetone precipitation, an active enzyme fraction at 64% acetone was obtained which on SDS-PAGE gave a major 30kDa protein band. The H. pylori glycosulfatase exhibited maximum activity (314.8 pmol/mg protein/h) at pH 5.7 in the presence of Triton X-100 and CaCl2, and was capable of removal of the sulfate ester groups situated at C-6 of N-acetylglucosamine, galactose and glucose. However, the enzyme was ineffective toward galactosylceramide and lactosylceramide sulfates which contain the sulfate ester group on C-3 of galactose. The results suggest that H. pylori is capable of overcoming the interference by sulfated mucus glycoprotein with its colonization of gastric mucosa.

Chloride channels, Golgi pH and cystic fibrosis

Cystic fibrosis (CF) is associated with a defect in a cAMP-activated chloride channel in secretory epithelia, which leads to decreased fluid secretion. In addition, many mucus glycoproteins show decreased sialylation but increased sulphation. We have recently shown that the pH of intracellular organelles is elevated in CF cells, due to defective chloride conductance in the vesicle membranes. We postulate that this may affect the activity of sialyl-, fucosyl- and sulphotransferases, and thus explain the abnormal glycosylation. Defects in sialylation of glycolipids might also generate receptors for Pseudomonas, which infects the respiratory tract of CF patients.

Identity of mucin's "118-kDa link protein" with fibronectin fragment

Human and rat intestinal mucin was purified by equilibrium density gradient centrifugation and Sepharose 2B chromatography according to M. Mantle, D. Mantle, and A. Allen (1981, Biochem. J. 195, 277-285) and analyzed using mucin, DNA, and fibronectin-specific antibodies in dot-blot, ELISA, and Western blotting. The 118-kDa component of the mucins and the 118-kDa fragment of fibronectin from the same source displayed affinity for concanavalin A and immunoreacted with fibronectin antibodies. The amino acid and carbohydrate compositions of the 118-kDa peptide electroeluted by gel electrophoresis of mucin and fibronectin preparations were identical within each pair of glycopeptides and closely resembled the "link protein component" of human and rat intestinal mucin preparations of R. E. F. Fahim, R. D. Specian, G. G. Forstner, and J. F. Forstner (1987, Biochem. J. 243, 631-640) and M. Mantle and G. Stewart (1989, Biochem. J. 259, 631-640). We therefore conclude that the "link protein" claimed to be an integral part of mucus glycoproteins in actuality is the 118-kDa fragment of fibronectin.

Effect of reserpine on the histochemical and biochemical properties of rat intestinal mucin

Biochemical and histochemical parameters of intestinal mucins were examined in control and reserpine-treated rats. An assay for intestinal mucin sulfotransferase was developed and the activity shown to increase 3.4 times over control levels in rats given intraperitonal reserpine (0.5 mg/kg body wt) daily for 7 days. Histochemical staining of intestinal sections revealed an increase in sulfomucins in goblet cells of reserpine-treated rats. The effects were prominent as early as 1 day following injection, particularly in the distal third of the small intestine, and during the next 6 days these changes spread progressively to the middle and proximal thirds. After 3 days of treatment mucins were purified from each intestinal segment and compared to control mucins with respect to composition and [35S]NaSO4 incorporation. Although individual amino acid and carbohydrate molar ratios were unchanged, the total carbohydrate and sulfate content of mucins in treated animals was elevated (two to three times above control) in the middle and distal thirds of the intestine. In vivo [35S]SO4 incorporation into these mucins was also proportionaltely elevated, and was targetted to O-linked oligosaccharide side chains. These findings are consistent with an action of reserpine causing an increased production of mucin which is enriched in glycoprotein components bearing sulfated oligosaccharide chains. The relevance of these findings to the production of hypersulfated and hyperglycosylated mucins in cystic fibrosis is discussed.

Role of sulphation in post-translational processing of rat salivary mucins

Segments of rat submandibular salivary gland were incubated in MEM supplemented with 10-800 microM sulphate in the presence of [3H]-glucosamine, [3H]-proline and [35S]-Na2SO4, with 0-8 mM chlorate, an inhibitor of 3'-phosphoadenosine-5'-phosphosulphate formation. Incorporation of glucosamine and sulphate depended upon the sulphate content of the medium and reached a maximum at 400 microM sulphate. The introduction of chlorate into the medium, while having no effect on the protein synthesis as shown by [3H]-proline incorporation, caused, at its optimal concentration of 4 mM, a 90% decrease in mucin sulphation and a 29% drop in mucin glycosylation. At low sulphate content in the medium and in the presence of chlorate the incorporation of sulphate and glucosamine was mainly into the low molecular-weight form of mucin. An increase in sulphate in the medium caused an increase in the high molecular-weight form of mucin and in the extent of sulphation in its carbohydrate chain. This effect of sulphate was, however, inhibited by chlorate. The results suggest that sulphation takes place at an early stage of mucin assembly and that sulphate availability is essential for the formation of the high molecular-weight mucin.

Ethanol stimulates pepsinogen release by opening a Ca2+ channel of guinea pig gastric chief cells

To better understand the mechanism by which ethanol causes gastric mucosal injury, the effects of ethanol on isolated guinea pig gastric chief cells were investigated in vitro. Ethanol at 300-900 mmol/L dose-dependently stimulated an increase in pepsinogen release without affecting chief cells' viability. Ethanol stimulated an increase in initial Ca2+ influx rate and intracellular Ca2+ concentration at the same concentrations as it stimulated pepsinogen release, whereas it did not stimulate cyclic adenosine monophosphate accumulation. Pepsinogen release stimulated by 900 mmol/L ethanol was almost equal to that stimulated by 10(-8) mol/L COOH terminal octapeptide of cholecystokinin. Ethanol did not stimulate an increase in the accumulation of inositol trisphosphates and tetrakisphosphates in [3H]inositol-labeled chief cells, whereas cholecystokinin octapeptide caused a significant increase in inositol trisphosphates and tetrakisphosphates. Ethanol-stimulated pepsinogen release and increases in the initial Ca2+ influx rate and intracellular Ca2+ concentration were inhibited by 0.5 mmol/L La3+ or 1 mmol/L ethylene glycol tetraacetic acid but were not inhibited by nifedipine or verapamil. These results suggest that the effect of ethanol on pepsinogen release from the gastric chief cells may be due to its opening of a Ca2+ channel that is sensitive to La3+ and that the pepsinogen releasing action of ethanol may be one of factors for ethanol-induced gastric mucosal injury.