Muc1 cell surface mucin attenuates epithelial inflammation in response to a common mucosal pathogen

Expression of mucin-1 and mucin-2 in different types of gastric lesions

AIM: To detect the expression of mucin-1 and mucin-2 in gastritis, intestinal metaplasia and gastric cancer.

METHODS: Thirty patients with gastritis (without intestinal metaplasia), thirty patients with intestinal metaplasia and forty-eight patients with gastric cancer, who were treated at our hospital from November 2011 to April 2012, were enrolled in this study. The expression of mucin-1 and mucin-2 in different types of gastric lesions was determined by immunohistochemistry.

RESULTS: The expression of mucin-1 in intestinal metaplasia was lower than that in gastritis (P > 0.05), but the expression of mucin-2 in intestinal metaplasia was higher than that in gastritis (P < 0.05). The rate of Helicobacter pylori (H. pylori) infection in intestinal metaplasia was higher than that in gastritis (P > 0.05). The expression of mucin-1 in gastric cancer was higher than that in intestinal metaplasia (P > 0.05), but the expression of mucin-2 in gastric cancer was lower than that in intestinal metaplasia (P < 0.05). The rate of H. pylori infection in gastric cancer was lower than that in intestinal metaplasia (P < 0.05). The expression of mucin-1 in gastric cancer was lower than that in gastritis (P > 0.05), but the expression of mucin-2 in gastric cancer was higher than that in gastritis (P < 0.05). The rate of H. pylori infection in gastric cancer was lower than that in gastritis (P > 0.05).

CONCLUSION: The expression of mucin-1 is down-regulated in the evolution of gastric cancer; however, the expression of mucin-2 is positive only in precancerous lesions and gastric cancer. This finding suggests that mucin-2 may be more closely related to the occurrence of gastric cancer. There is a negative correlation between expression of mucin-1 and H. pylori infection, but a positive correlation between mucin-2 expression and H. pylori infection.

Influence of monoclonal anti-Lewis b, anti-H type 1, and anti-sialyl Lewis x antibodies on binding of Helicobacter pylori to MUC1 mucin

To assess the influence of monoclonal anti-Lewis b, anti-H type 1, and anti-sialyl Lewis x addition on interactions of sugar structures of MUC1 mucin with Helicobacter pylori. The investigations were carried out on gastric juices of 11 patients and 12 H. pylori strains. The levels of Lewis b and sialyl Lewis x antigens on MUC1 were assessed by sandwich ELISA tests. Anti-Lewis b, anti-H type 1 or anti-sialyl Lewis x monoclonal antibodies were added to MUC1 to determine whether the adhesion activities of H. pylori isolates to examined mucin would be affected. Binding of bacteria to MUC1 was assessed by ELISA test. Clear inhibitory effect of examined antibodies was revealed in 6 of 12 examined H. pylori isolates independently on babA2 status. In the rest of strains this effect was negligible. We confirmed participation of Lewis b, H type 1 and also sialyl Lewis x of MUC1 mucin in interactions with H. pylori independently on babA genopositivity. Not full inhibition and a lack of this effect in some strains suggest an existence of other mechanisms of H. pylori adherence to mucin.

MUC1 and MUC13 differentially regulate epithelial inflammation in response to inflammatory and infectious stimuli

The MUC1 cell-surface mucin is highly expressed on the gastric mucosal surface, while MUC13 is highly expressed on the intestinal mucosal surface. Polymorphisms in both MUC1 and MUC13 have been linked to inflammatory bowel diseases. MUC1 can act as a decoy molecule on the apical cell surface of epithelial cells and thereby limit bacterial adherence, infection, and inflammation. In this study, we examined whether and how MUC1 and MUC13 modulate infectious and inflammatory signaling. Using gastrointestinal tissue from Muc1- or Muc13-deficient mice in ex vivo culture, MUC1 small interfering RNA (siRNA) silencing in MKN7 gastric epithelial cells, and MUC13 siRNA silencing in LS513 intestinal epithelial cells, we showed that loss of MUC1 increased chemokine secretion, whereas loss of MUC13 decreased chemokine secretion in response to tumor necrosis factor-α. Anti-inflammatory activity of MUC1 and pro-inflammatory activity of MUC13 were also seen after exposure to pathogens, NOD1 (nucleotide-binding oligomerisation domain-containing protein-1), and Toll-like receptor ligands. MUC1 and MUC13 both regulate chemokine secretion in gastrointestinal epithelial cells through a nuclear factor-κB-dependent pathway, although MUC13 modulation could also involve other pathways. Our studies demonstrate that MUC1 and MUC13 are important components of gastrointestinal homeostasis and that disruption or inappropriate expression of these mucins could predispose to infectious and inflammatory disease and inflammation-induced cancer.

Activation of the bile acid receptor GPBAR1 protects against gastrointestinal injury caused by non-steroidal anti-inflammatory drugs and aspirin in mice

BACKGROUND AND PURPOSE

Low doses of aspirin (acetylsalicylic acid; ASA) and non-steroidal anti-inflammatory drugs (NSAIDs) increase the risk of gastrointestinal bleeding. GPBAR1 is a bile acid receptor expressed in the gastrointestinal tract. Here, we have investigated whether GPBAR1 was required for mucosal protection in models of gastrointestinal injury caused by ASA and NSAIDs. EXPERIMENTAL APPROCH: GPBAR1(+/+) and GPBAR1(-/-) mice were given ASA (10-50 mg.kg(-1)) or naproxen. Gastric and intestinal mucosal damage was assessed by measuring lesion scores.

KEY RESULTS

Expression of GPBAR1, mRNA and protein, was detected in mouse stomach. Mice lacking GPBAR1 were more sensitive to gastric and intestinal injury caused by ASA and NSAIDs and exhibited a markedly reduced expression of cystathionine-γ-liase (CSE), cystathionine-β-synthase (CBS) and endothelial NOS enzymes required for generation of H(2)S and NO, in the stomach. Treating GPBAR1(+/+) mice with two GPBAR1 agonists, ciprofloxacin and betulinic acid, rescued mice from gastric injury caused by ASA and NSAIDs. The protective effect of these agents was lost in GPBAR1(-/-) mice. Inhibition of CSE by DL-propargylglycine completely reversed protection afforded by ciprofloxacin in wild type mice, whereas treating mice with an H(2)S donor restored the protective effects of ciprofloxacin in GPBAR1(-/-) mice. Deletion of GPBAR1 altered the morphology of the small intestine and increased sensitivity to injury caused by naproxen.

CONCLUSION AND IMPLICATIONS

GPBAR1 is essential to maintain gastric and intestinal mucosal integrity. GPBAR1 agonists protect against gastrointestinal injury caused by ASA and NSAIDs by a COX-independent mechanism.

Cellular and molecular biology of airway mucins

Airway mucus constitutes a thin layer of airway surface liquid with component macromolecules that covers the luminal surface of the respiratory tract. The major function of mucus is to protect the lungs through mucociliary clearance of inhaled foreign particles and noxious chemicals. Mucus is comprised of water, ions, mucin glycoproteins, and a variety of other macromolecules, some of which possess anti-microbial, anti-protease, and anti-oxidant activities. Mucins comprise the major protein component of mucus and exist as secreted and cell-associated glycoproteins. Secreted, gel-forming mucins are mainly responsible for the viscoelastic property of mucus, which is crucial for effective mucociliary clearance. Cell-associated mucins shield the epithelial surface from pathogens through their extracellular domains and regulate intracellular signaling through their cytoplasmic regions. However, neither the exact structures of mucin glycoproteins, nor the manner through which their expression is regulated, are completely understood. This chapter reviews what is currently known about the cellular and molecular properties of airway mucins.

Helicobacter pylori infection impairs the mucin production rate and turnover in the murine gastric mucosa

To protect the surface of the stomach, the epithelial cells secrete a mucus layer, which is mainly comprised of the MUC5AC mucin. Further protection is provided by a thick glycocalyx on the apical surface of the epithelial cell, with the cell surface mucin MUC1 as a major component. Here, we investigate the production rate and turnover of newly synthesized mucin in mice and analyze the effects of early colonization and chronic infection with H. pylori. Metabolic incorporation of an azido GalNAc analog (GalNAz) was used as a nonradioactive method to perform pulse experiments in the whole animal. First, the subcellular movement of newly synthesized mucin and mucin turnover was determined in uninfected mice. Based on the time line for mucin transport and dissemination, 2, 6, and 12 h after GalNAz injection was selected to collect the stomachs from mice infected with H. pylori strain SS1 during early colonization (7 days) and chronic infection (90 days). The results demonstrated that the speed from the start of glycosylation to the final destination is faster for the membrane-bound mucin to reach the glycocalyx (2 h) than for the secretory mucins to become secreted into the mucus layer (5 h). Furthermore, infection with H. pylori reduces the rate of mucin turnover and decreases the levels of Muc1. Since H. pylori colonizes this mucus niche, the decreased turnover rate indicates that H. pylori creates a more stable and favorable environment for itself by impairing the defense mechanism for clearing the mucosal surface of pathogens by mucus flow.

A new role for mucins in immunity: insights from gastrointestinal nematode infection

The body's mucosal surfaces are protected from pathogens and physical and chemical attack by the gel-like extracellular matrix, mucus. The framework of this barrier is provided by polymeric, gel-forming mucins. These enormous O-linked glycoproteins are synthesised, stored and secreted by goblet cells that are also the source of other protective factors. Immune regulation of goblet cells during the course of infection impacts on mucin production and properties and ultimately upon barrier function. The barrier function of mucins in protection of the host is well accepted as an important aspect of innate defence. However, it is becoming increasingly clear that mucins have a much more direct role in combating pathogens and parasites and are an important part of the coordinated immune response to infection. Of particular relevance to this review is the finding that mucins are essential anti-parasitic effector molecules. The current understanding of the roles of these multifunctional glycoproteins, and other goblet cell products, in mucosal defence against intestinal dwelling nematodes is discussed.

The interaction of Helicobacter pylori with the adherent mucus gel layer secreted by polarized HT29-MTX-E12 cells

Helicobacter pylori colonises the gastric mucosa of humans. The majority of organisms live in mucus. These organisms are an important reservoir for infection of the underlying epithelium. Cell culture models for H. pylori infection do not normally possess a mucus layer. The interaction of H. pylori with TFF1, a member of the trefoil factor family found in gastric mucin, is mediated by lipopolysaccharide. To test the hypothesis that the interaction of H. pylori with TFF1 promotes mucus colonization we characterised the interaction of H. pylori with a mucus secreting cell line, HT29-MTX-E12. An isogenic mutant of H. pylori with truncated core oligosaccharides was produced and binding to TFF1 and ability to colonise HT29-MTX-E12 cells determined. The adherent mucus layer of HT29-MTX-E12 cells contained the gastric mucin MUC5AC and trefoil factors, TFF1 and TFF3. H. pylori was found within the mucus layer in discrete clusters and in close association with TFF1. It also interacted with the membrane bound mucin MUC1 and replicated when co-cultured with the cells. An isogenic mutant of H. pylori with a truncated LPS core did not interact with TFF1, and colonization of HT29-MTX-E12 cells was reduced compared to the wild-type strain (p<0.05). Preincubation of cells with wild type LPS but not with truncated LPS resulted in reduced colonization by H. pylori. These results demonstrate that the interaction of TFF1 with H. pylori is important for colonization of gastric mucus and the core oligosaccharide of H. pylori LPS is critical for this interaction to occur. HT29-MTX-E12 cells are a useful system with which to study the interaction of bacteria with mucosal surfaces and the effect of such interactions on mediating colonization.

Suppression of IL-8 production in gastric epithelial cells by MUC1 mucin and peroxisome proliferator-associated receptor-γ

MUC1 is a membrane-tethered mucin expressed on the apical surface of epithelial cells. Our previous report (Guang W, Ding H, Czinn SJ, Kim KC, Blanchard TG, Lillehoj EP. J Biol Chem 285: 20547-20557, 2010) demonstrated that expression of MUC1 in AGS gastric epithelial cells limits Helicobacter pylori infection and reduces bacterial-driven IL-8 production. In this study, we identified the peroxisome proliferator-associated receptor-γ (PPARγ) upstream of MUC1 in the anti-inflammatory pathway suppressing H. pylori- and phorbol 12-myristate 13-acetate (PMA)-stimulated IL-8 production. Treatment of AGS cells with H. pylori or PMA increased IL-8 levels in cell culture supernatants compared with cells treated with the respective vehicle controls. Prior small interfering (si)RNA-induced MUC1 silencing further increased H. pylori- and PMA-stimulated IL-8 levels compared with a negative control siRNA. MUC1-expressing AGS cells pretreated with the PPARγ agonist troglitazone (TGN) had reduced H. pylori- and PMA-stimulated IL-8 levels compared with cells treated with H. pylori or PMA alone. However, following MUC1 siRNA knockdown, no differences in IL-8 levels were seen between TGN/H. pylori and H. pylori-only cells or between TGN/PMA and PMA-only cells. Finally, TGN-treated AGS cells had increased Muc1 promoter activity, as measured using a Muc1-luciferase reporter gene, and greater MUC1 protein levels by Western blot analysis, compared with vehicle controls. These results support the hypothesis that PPARγ stimulates MUC1 expression by AGS cells, thereby attenuating H. pylori- and PMA-induced IL-8 production.

Molecular Interactions between MUC1 Epithelial Mucin, β-Catenin, and CagA Proteins

Interleukin (IL)-8-driven neutrophil infiltration of the gastric mucosa is pathognomonic of persistent Helicobacter pylori infection. Our prior study showed that ectopic over-expression of MUC1 in human AGS gastric epithelial cells reduced H. pylori-stimulated IL-8 production compared with cells expressing MUC1 endogenously. Conversely, Muc1 knockout (Muc1(-/-)) mice displayed an increased level of transcripts encoding the keratinocyte chemoattractant (KC), the murine equivalent of human IL-8, in gastric mucosa compared with Muc1(+/+) mice during experimental H. pylori infection. The current study tested the hypothesis that a decreased IL-8 level observed following MUC1 over-expression is mediated through the ability of MUC1 to associate with β-catenin, thereby inhibiting H. pylori-induced β-catenin nuclear translocation. Increased neutrophil infiltration of the gastric mucosa of H. pylori-infected Muc1(-/-) mice was observed compared with Muc1(+/+) wild type littermates, thus defining the functional consequences of increased KC expression in the Muc1-null animals. Protein co-immunoprecipitation (co-IP) studies using lysates of untreated or H. pylori-treated AGS cells demonstrated that (a) MUC1 formed a co-IP complex with β-catenin and CagA, (b) MUC1 over-expression reduced CagA/β-catenin co-IP, and (c) in the absence of MUC1 over-expression, H. pylori infection increased the nuclear level of β-catenin, (d) whereas MUC1 over-expression decreased bacteria-driven β-catenin nuclear localization. These results suggest that manipulation of MUC1 expression in gastric epithelia may be an effective therapeutic strategy to inhibit H. pylori-dependent IL-8 production, neutrophil infiltration, and stomach inflammation.

MUC1 contributes to BPDE-induced human bronchial epithelial cell transformation through facilitating EGFR activation

Although it is well known that epidermal growth factor receptor (EGFR) is involved in lung cancer progression, whether EGFR contributes to lung epithelial cell transformation is less clear. Mucin 1 (MUC1 in human and Muc1 in animals), a glycoprotein component of airway mucus, is overexpressed in lung tumors; however, its role and underlying mechanisms in early stage lung carcinogenesis is still elusive. This study provides strong evidence demonstrating that EGFR and MUC1 are involved in bronchial epithelial cell transformation. Knockdown of MUC1 expression significantly reduced transformation of immortalized human bronchial epithelial cells induced by benzo[a]pyrene diol epoxide (BPDE), the active form of the cigarette smoke (CS) carcinogen benzo(a)pyrene (BaP)s. BPDE exposure robustly activated a pathway consisting of EGFR, Akt and ERK, and blocking this pathway significantly increased BPDE-induced cell death and inhibited cell transformation. Suppression of MUC1 expression resulted in EGFR destabilization and inhibition of the BPDE-induced activation of Akt and ERK and increase of cytotoxicity. These results strongly suggest an important role for EGFR in BPDE-induced transformation, and substantiate that MUC1 is involved in lung cancer development, at least partly through mediating carcinogen-induced activation of the EGFR-mediated cell survival pathway that facilitates cell transformation.

PPARγ inhibits airway epithelial cell inflammatory response through a MUC1-dependent mechanism

This study was conducted to examine the relationship between the peroxisome proliferator-associated receptor-γ (PPARγ) and MUC1 mucin, two anti-inflammatory molecules expressed in the airways. Treatment of A549 lung epithelial cells or primary mouse tracheal surface epithelial (MTSE) cells with phorbol 12-myristate 13-acetate (PMA) increased the levels of tumor necrosis factor (TNF)-α in cell culture media compared with cells treated with vehicle alone. Overexpression of MUC1 in A549 cells decreased PMA-stimulated TNF-α levels, whereas deficiency of Muc1 expression in MTSE cells from Muc1 null mice increased PMA-induced TNF-α levels. Treatment of A549 or MTSE cells with the PPARγ agonist troglitazone (TGN) blocked the ability of PMA to stimulate TNF-α levels. However, the effect of TGN required the presence of MUC1/Muc1, since no differences in TNF-α levels were seen between PMA and PMA plus TGN in MUC1/Muc1-deficient cells. Similarly, whereas TGN decreased interleukin-8 (IL-8) levels in culture media of MUC1-expressing A549 cells treated with Pseudomonas aeruginosa strain K (PAK), no differences in IL-8 levels were seen between PAK and PAK plus TGN in MUC1-nonexpressing cells. EMSA confirmed the presence of a PPARγ-binding element in the MUC1 gene promoter. Finally, TGN treatment of A549 cells increased MUC1 promoter activity measured using a MUC1-luciferase reporter gene, augmented MUC1 mRNA levels by quantitative RT-PCR, and enhanced MUC1 protein expression by Western blot analysis. These combined data are consistent with the hypothesis that PPARγ stimulates MUC1/Muc1 expression, thereby blocking PMA/PAK-induced TNF-α/IL-8 production by airway epithelial cells.

Membrane-tethered MUC1 mucin is phosphorylated by epidermal growth factor receptor in airway epithelial cells and associates with TLR5 to inhibit recruitment of MyD88

MUC1 is a membrane-tethered mucin glycoprotein expressed on the apical surface of mucosal epithelial cells. Previous in vivo and in vitro studies established that MUC1 counterregulates airway inflammation by suppressing TLR signaling. In this article, we elucidate the mechanism by which MUC1 inhibits TLR5 signaling. Overexpression of MUC1 in HEK293 cells dramatically reduced Pseudomonas aeruginosa-stimulated IL-8 expression and decreased the activation of NF-κB and MAPK compared with cells not expressing MUC1. However, overexpression of MUC1 in HEK293 cells did not affect NF-κB or MAPK activation in response to TNF-α. Overexpression of MyD88 abrogated the ability of MUC1 to inhibit NF-κB activation, and MUC1 overexpression inhibited flagellin-induced association of TLR5/MyD88 compared with controls. The MUC1 cytoplasmic tail associated with TLR5 in all cells tested, including HEK293T cells, human lung adenocarcinoma cell line A549 cells, and human and mouse primary airway epithelial cells. Activation of epidermal growth factor receptor tyrosine kinase with TGF-α induced phosphorylation of the MUC1 cytoplasmic tail at the Y46EKV sequence and increased association of MUC1/TLR5. Finally, in vivo experiments demonstrated increased immunofluorescence colocalization of Muc1/TLR5 and Muc1/phosphotyrosine staining patterns in mouse airway epithelium and increased Muc1 tyrosine phosphorylation in mouse lung homogenates following P. aeruginosa infection. In conclusion, epidermal growth factor receptor tyrosine phosphorylates MUC1, leading to an increase in its association with TLR5, thereby competitively and reversibly inhibiting recruitment of MyD88 to TLR5 and downstream signaling events. This unique ability of MUC1 to control TLR5 signaling suggests its potential role in the pathogenesis of chronic inflammatory lung diseases.

NEU1 sialidase expressed in human airway epithelia regulates epidermal growth factor receptor (EGFR) and MUC1 protein signaling

Epithelial cells (ECs) lining the airways provide a protective barrier between the external environment and the internal host milieu. These same airway epithelia express receptors that respond to danger signals and initiate repair programs. Because the sialylation state of a receptor can influence its function and is dictated in part by sialidase activity, we asked whether airway epithelia express catalytically active sialidase(s). Human primary small airway and A549 ECs expressed NEU1 sialidase at the mRNA and protein levels, and NEU1 accounted for >70% of EC sialidase activity. Blotting with Maackia amurensis and peanut agglutinin lectins established epidermal growth factor receptor (EGFR) and MUC1 as in vivo substrates for NEU1. NEU1 associated with EGFR and MUC1, and NEU1-EGFR association was regulated by EGF stimulation. NEU1 overexpression diminished EGF-stimulated EGFR Tyr-1068 autophosphorylation by up to 44% but enhanced MUC1-dependent Pseudomonas aeruginosa adhesion by 1.6-1.7-fold and flagellin-stimulated ERK1/2 activation by 1.7-1.9-fold. In contrast, NEU1 depletion increased EGFR activation (1.5-fold) and diminished MUC1-mediated bacterial adhesion (38-56%) and signaling (73%). These data indicate for the first time that human airway epithelia express catalytically active NEU1 sialidase that regulates EGFR- and MUC1-dependent signaling and bacterial adhesion. NEU1 catalytic activity may offer an additional level of regulation over the airway epithelial response to ligands, pathogens, and injurious stimuli.

Mucins in inflammatory bowel diseases and colorectal cancer

The gastrointestinal tract is protected by a mucus barrier with both secreted and cell-surface mucins contributing to the exclusion of luminal microbes and toxins. Alterations in the structure and/or quantity of mucins alter the barrier function of mucus and could play roles in initiating and maintaining mucosal inflammation in inflammatory bowel diseases (IBD), and in driving cancer development in the intestine. The aim of this review is to focus on the roles of the mucins in IBD. The polymorphisms of mucin genes that have been associated with susceptibility to IBD, and alterations in mucin expression as well as factors that regulate production of the mucins in IBD, are summarized. Data from animal models of intestinal inflammation, which support the importance of mucins in IBD and cancer development, are also discussed.

Glycomic work-flow for analysis of mucin O-linked oligosaccharides

The high-throughput analysis of the glycosylation of high molecular weight proteins, such as mucins, has been the aim of glycomics initiatives for the last decade. Here, we present a work-flow for the efficient and reproducible analysis of reduced oligosaccharides from a typical mucin sample. This work-flow can be applied to any similar samples of oligosaccharides. We include recently developed bioinformatic procedures for the statistical analysis of sample sets. These procedures can be applied in any laboratory environment, using free programs that are platform independent. The scripts are explained and can be adjusted to suit the individual experiment. Finally, a number of example results are given to highlight the use of the statistical analysis in a biological context.

Pathogenesis of Helicobacter pylori infection

Helicobacter pylori infections and clinical outcome are dependent on sophisticated interactions between the bacteria and its host. Crucial bacterial factors associated with pathogenicity comprise a type IV secretion system encoded by the cag pathogenicity island, the effector protein CagA, the vacuolating cytotoxin (VacA), peptidoglycan, lipopolysaccharide (LPS), γ-glutamyl transpeptidase (GGT), protease HtrA, and the adhesins BabA, SabA, and others. The high number of these factors and allelic variation of the involved genes generates a highly complex scenario and reveals the difficulties in testing the contribution of each individual factor. Much effort has been put into identifying the molecular mechanisms associated with H. pylori-associated pathogenesis using human primary tissues, Mongolian gerbils, transgenic, knockout, and other mice as well as in vitro cell model systems. Interactions between bacterial factors and host signal transduction pathways seem to be critical for mediating the induction of pathogenic downstream processes and disease development. In this review article, we discuss the most recent progress in this research field.

Innate Immunity in the Small Intestine of the Preterm Infant

The gastrointestinal tract comprises the largest surface area of the human body. This area is constantly exposed to myriad antigens as well as the large number of bacteria that coexist in the intestinal lumen. To protect against this exposure and help distinguish "self " from "foreign," the intestinal tract has evolved a sophisticated barrier defense system that includes both innate and adaptive immune systems. However, infants who are born preterm do not have the benefit of an adequate immune response and, therefore, are more susceptible to bacterial injury, inflammation, and intestinal diseases such as necrotizing enterocolitis. In this review, we discuss the components of innate immunity that help to protect the small intestine as well as current knowledge about the role of these components in the pathophysiology of necrotizing enterocolitis.

MUC1/A and MUC1/B splice variants differentially regulate inflammatory cytokine expression

The frequency of a splice variant of mucin 1 (MUC1), MUC1/A was lower in dry eye disease patients compared to normal controls, suggesting a link between the absence of MUC1/A and the development of dry eye disease which is characterized by chronic inflammation. The objectives of the present study were to clone and characterize the phenotype of cells expressing solely MUC1/A versus MUC1/B or a variant lacking the extracellular domain (ΔEX) and to determine whether MUC1/A and MUC1/B differentially modulate inflammatory responses in transfected cells. The additional 27 bp and SNP present in the N-terminus of MUC1/A were cloned into a FLAG-MUC1/B expression vector. Transient transfection of MUC1/A and MUC1/B plasmids into MUC1-null COS-7 cells resulted in similar protein expression and plasma membrane localization. MUC1/B and MUC1/A differed in their ability to modulate tumor necrosis α (TNFα)-induced transcription of IL-1β and IL-8. MUC1/B and MUC1/A inhibited IL-8 induction by TNFα at 4 h. However with 24 h TNFα, MUC1/A increased IL-1β and IL-8 whereas MUC1/B had no effect on cytokine expression. MUC1/B inhibited TNFα-induced luciferase activity from an NF-κB reporter whereas MUC1/A either inhibited or increased this luciferase activity depending on the time of TNFα treatment. MUC1/A, but not MUC1/B, increased the basal TGFβ expression. Both MUC1/B and MUC1/A blocked TNFα-induced miR-21 expression. These data demonstrate that MUC1/A and MUC1/B have different inflammatory activities and support the hypothesis that MUC1 genotypic differences may affect susceptibility to ocular surface damage in dry eye disease.

Mucin dynamics and enteric pathogens

The extracellular secreted mucus and the cell surface glycocalyx prevent infection by the vast numbers of microorganisms that live in the healthy gut. Mucin glycoproteins are the major component of these barriers. In this Review, we describe the components of the secreted and cell surface mucosal barriers and the evidence that they form an effective barricade against potential pathogens. However, successful enteric pathogens have evolved strategies to circumvent these barriers. We discuss the interactions between enteric pathogens and mucins, and the mechanisms that these pathogens use to disrupt and avoid mucosal barriers. In addition, we describe dynamic alterations in the mucin barrier that are driven by host innate and adaptive immune responses to infection.

Importance and regulation of the colonic mucus barrier in a mouse model of colitis

The colonic mucus layer serves as an important barrier and prevents colonic bacteria from invading the mucosa and cause inflammation. The regulation of colonic mucus secretion is poorly understood. The aim of this study was to investigate the role of the mucus barrier in induction of colitis. Furthermore, regulation of mucus secretion by luminal bacterial products was studied. The colon of anesthetized Muc2(-/-), Muc1(-/-), wild-type (wt), and germ-free mice was exteriorized, the mucosal surface was visualized, and mucus thickness was measured with micropipettes. Colitis was induced by DSS (dextran sodium sulfate, 3%, in drinking water), and disease activity index (DAI) was assessed daily. The colonic mucosa of germ-free and conventionally housed mice was exposed to the bacterial products LPS (lipopolysaccharide) and PGN (peptidoglycan). After DSS induction of colitis, the thickness of the firmly adherent mucus layer was significantly thinner after 5 days and onward, which paralleled the increment of DAI. Muc2(-/-) mice, which lacked firmly adherent mucus, were predisposed to colitis, whereas Muc1(-/-) mice were protected with significantly lower DAI by DSS compared with wt mice. The mucus barrier increased in Muc1(-/-) mice in response to DSS, whereas significantly fewer T cells were recruited to the inflamed colon. Mice housed under germ-free conditions had an extremely thin adherent colonic mucus layer, but when exposed to bacterial products (PGN or LPS) the thickness of the adherent mucus layer was quickly restored to levels observed in conventionally housed mice. This study demonstrates a correlation between decreasing mucus barrier and increasing clinical symptoms during onset of colitis. Mice lacking colonic mucus (Muc2(-/-)) were hypersensitive to DSS-induced colitis, whereas Muc1(-/-) were protected, probably through the ability to increase the mucus barrier but also by decreased T cell recruitment to the afflicted site. Furthermore, the ability of bacteria to regulate the thickness of the colonic mucus was demonstrated.

Life at the margins: modulation of attachment proteins in Helicobacter pylori

Helicobacter pylori is the primary cause of peptic ulcer disease and is estimated to account for about 60% of all cases of gastric cancer, the second most common cause of cancer death worldwide. Among the H. pylori virulence factors associated with disease, in addition to the well-known cag pathogenicity island, is the BabA adhesin, an outer membrane protein that binds with high affinity to fucosylated glycans on the gastric epithelium, such as Lewis B (Le(b)) and related terminal fucose residues found on the blood group O (H antigen), A and B antigens. BabA-mediated attachment to the gastric mucosa promotes chronic inflammation and gastric pathology, which from the bacterial perspective carries both risks and benefits. We recently described modulation in expression of BabA and related outer membrane proteins that occurs during colonization of experimental animals. Here we put these findings into a broader context, and speculate on their implications for the host-pathogen relationship.

MUC1 expression and its association with other aetiological factors and localization to mitochondria in preneoplastic and neoplastic gastric tissues

BACKGROUND

The molecular events that underlie the conversion of normal human gastric epithelium into adenocarcinoma are poorly understood. MUC1 overexpression and localization in mitochondria might confer cancer cells with attenuation of stress induced apoptosis. We studied MUC1 expression pattern, interaction with HSP70 and localization in mitochondria in preneoplastic and neoplastic human gastric tissues.

METHODS

Immunohistochemistry and Western blot were used to study MUC1 expression pattern and localization in mitochondria. Coimmunoprecipitation was used to study MUC1 interaction with HSP70. MUC1 expression was correlated with other causative features including erbB2 expression.

RESULTS

MUC1 was expressed in 75.8% (147/194). MUC1 overexpression was detected in 50.0% (19/38 cases) dysplasia and 58.2% (32/55 cases) adenocarcinoma tissues. MUC1-CT-HSP70 interaction was seen in 71.66% (43/60 cases) and MUC1 localized to mitochondria in 33.33% (5/15) dysplasia samples and in 47.05% (8/17) adenocarcinoma samples. MUC1 expression showed significant association with smoking (χ(2)=5.945; p<0.015), alcohol consumption (χ(2)=4.055; p<0.044) and erbB2 positivity (χ(2)=10.75; p<0.001). MUC1 expression did not show appreciable association with age (χ(2)=0.15; p<0.698), sex (χ(2)=0.22; p<0.640) or Helicobacter pylori infection (χ(2)=3.06; p<0.080).

CONCLUSIONS

Significant correlation was found between MUC1 expression and smoking, alcohol and erbB2 expression. MUC1 showed aberrant expression in dysplasia and adenocarcinoma stages. MUC1 cytosolic tail was bound by HSP70 in all the stages but MUC1-CT was found to localize in mitochondria only in dysplasia and adenocarcinoma. MUC1-CT localization to mitochondria in dysplasia and adenocarcinoma might aid in the attenuation of epithelial stress response induced loss of polarity.