Up-regulation in endothelin-1 by Helicobacter pylori lipopolysaccharide interferes with gastric mucin synthesis via epidermal growth factor receptor transactivation.
ABSTRACT Endothelin-1 (ET-1), a key mediator of inflammatory processes associated with bacterial infection, is a 21-amino acid peptide produced from a biologically inactive big ET-1 by the action of endothelin-converting enzyme-1 (ECE-1) that acts through G protein-coupled ET(A) and ET(B) receptors. Here we report on the role of ET-1 in the mediation of the detrimental influence of Helicobacter pylori on the synthesis of gastric mucin.
Rat gastric mucosal cells were exposed to H. pylori key virulence factor, lipopolysaccharide (LPS).
The LPS inhibitory effect on gastric mucin synthesis was accompanied by a marked increase in ET-1 generation and enhancement in ECE-1 activity. Inhibition of ECE-1 with phosphoramidon not only led to the impedance of LPS-induced ET-1 generation, but also countered the detrimental effect of LPS on mucin synthesis. Moreover, the LPS inhibitory effect on mucin synthesis was blocked by ET(A) receptor antagonist BQ610, but not by ET(B) receptor antagonist BQ788. Furthermore, the LPS-induced suppression in gastric mucin synthesis was countered in a concentration-dependent fashion by PD153035 (81.7%), a specific inhibitor of epidermal growth factor receptor (EGFR) kinase as well as PP2 (69.8%), a selective inhibitor of tyrosine kinase Src responsible for ligand-independent EGFR transactivation.
Our findings are the first to show that the detrimental effect of H. pylori on gastric mucin synthesis is intimately linked to the events associated with ECE-1 up-regulation, enhancement in ET-1 production, and G protein-coupled ET(A) receptor activation that triggers the EGFR transactivation.
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ABSTRACT: Helicobacter pylori (H. pylori) causes pathological changes of gastric epithelial cells induced by pathogenic factors such as CagA and VacA, namely hummingbird cells (HBC) formation and vacuolization, respectively, in cultured cell lines. Cytopathic effects of other pathogenic factors produced by H. pylori have not been reported. In this study, we examined whether H. pylori induces unique morphological changes other than HBC formation and vacuolization, and we established a new marker of the bacterial infection in vitro. The cytotoxicity of H. pylori was examined in the AGS cell line, and a new morphological change, namely multinuclear giant cells (MNGC) formation, was observed in this cell line. The enhancement of MNGC formation was observed following H. pylori infection but was not associated with CagA, which causes HBC formation. We characterized the factor causing MNGC formation enhancement as heat-stable and water-soluble, and finally considered the factor to be H. pylori lipopolysaccharide (LPS). We considered that H. pylori LPS enhances MNGC formation in vitro. The cytopathic effect may provide an important marker that may clarify the mechanism of H. pylori pathogenesis in human gastric epithelial cells.01/2007;
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ABSTRACT: MUC6 was first discovered by screening a gastric mucosa cDNA library and is expressed in the mucous cells of the neck zone and antral glands of the stomach. The aim of the present study was to clarify whether down-regulation has any clinicopathological or prognostic significance in gastric neoplasia. Expression of MUC6, MUC5AC and MUC2 was examined using tissue microarrays for immunohistochemistry in gastric carcinomas (n = 225), adenomas (n = 40), and normal mucosa (n = 89) and compared with clinicopathological parameters and survival data. MUC6 expression was lower in gastric carcinomas than in adenomas or normal mucosa (P < 0.05) and inversely correlated with tumor size, depth of invasion, lymphatic and venous invasion, lymph node metastasis and UICC staging (P < 0.05). Positive links with expression of MUC2 and MUC5AC were noted (P < 0.05). MUC6 expression was lower in diffuse-type than intestinal-type lesions (P < 0.05). Kaplan-Meier analysis indicated that cumulative survival of patients with no MUC6 expression was significantly lower than with weak, moderate or strong expression in all and even advanced gastric carcinoma (P < 0.05). Multivariate analysis showed three independent prognostic factors, depth of invasion, lymphatic and venous invasion, to concordantly affect the relationship between MUC6 expression and prognosis. Down-regulation of MUC6 may contribute to malignant transformation of gastric epithelial cells and underlie the molecular bases of growth, invasion, metastasis and differentiation of gastric carcinoma. Altered expression might therefore be employed as an indicator of pathobiological behaviors and prognosis of gastric carcinoma.Journal of Cancer Research and Clinical Oncology 01/2007; 132(12):817-23. · 3.01 Impact Factor
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ABSTRACT: Abstract Purpose: Membrane-associated mucins (MAMs) play important roles in barrier function and tear stability, and their expression on the ocular surface is altered in dry eye disease. Rebamipide is a mucin secretagogue that promotes the production of mucin-like glycoproteins in human corneal epithelial (HCE) cells. However, the expression of MAMs on the corneal epithelia (MUC1, MUC4, MUC16), which is induced by rebamipide, is poorly understood. In this study, we investigated the effect of rebamipide on the regulation of MAM expression in HCE cells. Materials and Methods: MUC16, Ki67 and PCNA expression levels in HCE cells isolated at confluence and at 24 hours after confluence were examined by Western blotting to assess cell proliferation. HCE cells isolated at 24 hours after confluence were cultured in medium supplemented with 1-10 µM rebamipide or 0.3-30 nM of epidermal growth factor (EGF). Real-time PCR (RT-PCR) and Western blot analysis of MAMs were performed to evaluate the effect of rebamipide. Western blot analysis of cells treated with an EGF receptor inhibitor (AG1478) or MEK1/2 inhibitor (U0126) was performed to reveal the relationship between EGF receptor activation and rebamipide-induced MAM expression. Results: HCE cells isolated at 24 hours after confluence had lower cell proliferation activity and increased MUC16 expression compared with cells isolated at confluence. RT-PCR and Western blot analysis revealed that rebamipide increased MAM gene expression for 2 hours and protein expression for 24 hours in HCE cells. EGF inhibitor treatment led to reduced levels of all three MAMs that are normally induced by rebamipide, whereas EGF induced the expression of all three MAMs. Conclusions: We suggested that rebamipide increased MUC1, MUC4 and MUC16 expression levels through signals involved in EGF receptor activation in the human corneal epithelia. These data suggest that rebamipide may improve subjective symptoms of dry eye disease by upregulating MAM expression.Current eye research 09/2013; · 1.51 Impact Factor