Helicobacter pylori (Hp) infection is an important cause of chronic gastritis and peptic ulcer, but their pathogenesis is unclear. The role of gastric mucosal barrier dysfunction induced by impaired structure and function of tight junction in the pathogenesis of Hp-associated gastric diseases has received considerable attention in recent years. Tight junction is composed of a variety of proteins and molecules, including 3 integral membrane proteins (occludin, claudins, and junctional adhesion molecules) and a cytoplasmic protein (zonula occludens). This paper mainly describes the composition and function of various tight junction proteins, changes in tight junction protein function induced by Hp infection and their relationship with the incidence of gastric diseases, and the significance of enhancing the tight junction protein function in the prevention and treatment of Hp-associated gastric diseases.
Helicobacter Infections ; complications ; Helicobacter pylori ; pathogenicity ; Humans ; Oxidative Stress ; Stomach Diseases ; etiology ; Stomach Neoplasms ; etiology ; Tight Junction Proteins ; analysis ; chemistry ; physiology

Helicobacter pylori (H. pylori) induces the activation of nuclear factor-kB (NF-kappaB) and cytokine expression in gastric epithelial cells. The Janus kinase/signal transducers and activators of transcription (Jak/Stat) cascade is the inflammatory signaling in various cells. The purpose of the present study is to determine whether H. pylori-induced activation of NF-kappaB and the expression of interleukin-8 (IL-8) are mediated by the activation of Jak1/Stat3 in gastric epithelial (AGS) cells. Thus, gastric epithelial AGS cells were infected with H. pylori in Korean isolates (HP99) at bacterium/cell ratio of 300:1, and the level of IL-8 in the medium was determined by enzyme-linked immonosorbent assay. Phospho-specific and total forms of Jak1/Stat3 and IkappaBalpha were assessed by Western blot analysis, and NF-kappaB activation was determined by electrophoretic mobility shift assay. The results showed that H. pylori induced the activation of Jak1/Stat3 and IL-8 production, which was inhibited by a Jak/Stat3 specific inhibitor AG490 in AGS cells in a dose-dependent manner. H. pylori-induced activation of NF-kappaB, determined by phosphorylation of IkappaBalpha and NF-kappaB-DNA binding activity, were inhibited by AG490. In conclusion, Jak1/Stat3 activation may mediate the activation of NF-kappaB and the expression of IL-8 in H. pylori-infected AGS cells. Inhibition of Jak1/Stat3 may be beneficial for the treatment of H. pylori-induced gastric inflammation, since the activation of NF-kappaB is inhibited and inflammatory cytokine expression is suppressed.
Blotting, Western ; DNA, Bacterial/analysis/genetics ; Epithelial Cells/metabolism ; Gastric Mucosa/drug effects/*immunology/microbiology ; Gene Expression Regulation/drug effects/*immunology ; Gene Expression Regulation, Bacterial ; Helicobacter Infections/immunology/*metabolism ; Helicobacter pylori/genetics/pathogenicity/*physiology ; Humans ; Interleukin-8/genetics/*metabolism ; Janus Kinase 1 ; NF-kappa B/biosynthesis/*metabolism ; Phosphorylation ; RNA, Messenger/metabolism ; STAT3 Transcription Factor ; Signal Transduction/genetics

Helicobacter pylori (H. pylori) induces the activation of nuclear factor-kB (NF-kappaB) and cytokine expression in gastric epithelial cells. The Janus kinase/signal transducers and activators of transcription (Jak/Stat) cascade is the inflammatory signaling in various cells. The purpose of the present study is to determine whether H. pylori-induced activation of NF-kappaB and the expression of interleukin-8 (IL-8) are mediated by the activation of Jak1/Stat3 in gastric epithelial (AGS) cells. Thus, gastric epithelial AGS cells were infected with H. pylori in Korean isolates (HP99) at bacterium/cell ratio of 300:1, and the level of IL-8 in the medium was determined by enzyme-linked immonosorbent assay. Phospho-specific and total forms of Jak1/Stat3 and IkappaBalpha were assessed by Western blot analysis, and NF-kappaB activation was determined by electrophoretic mobility shift assay. The results showed that H. pylori induced the activation of Jak1/Stat3 and IL-8 production, which was inhibited by a Jak/Stat3 specific inhibitor AG490 in AGS cells in a dose-dependent manner. H. pylori-induced activation of NF-kappaB, determined by phosphorylation of IkappaBalpha and NF-kappaB-DNA binding activity, were inhibited by AG490. In conclusion, Jak1/Stat3 activation may mediate the activation of NF-kappaB and the expression of IL-8 in H. pylori-infected AGS cells. Inhibition of Jak1/Stat3 may be beneficial for the treatment of H. pylori-induced gastric inflammation, since the activation of NF-kappaB is inhibited and inflammatory cytokine expression is suppressed.
Blotting, Western ; DNA, Bacterial/analysis/genetics ; Epithelial Cells/metabolism ; Gastric Mucosa/drug effects/*immunology/microbiology ; Gene Expression Regulation/drug effects/*immunology ; Gene Expression Regulation, Bacterial ; Helicobacter Infections/immunology/*metabolism ; Helicobacter pylori/genetics/pathogenicity/*physiology ; Humans ; Interleukin-8/genetics/*metabolism ; Janus Kinase 1 ; NF-kappa B/biosynthesis/*metabolism ; Phosphorylation ; RNA, Messenger/metabolism ; STAT3 Transcription Factor ; Signal Transduction/genetics

OBJECTIVECytotoxin-associated protein (CagA) of H. pylori has been confirmed to be closely associated with gastric inflammation and tumorigenesis, but the mechanism behind it is little understood. In this study, we try to determine roles of CagA(+) strain in activating PI3K/Akt1 signaling pathway, and affecting expression of p21(WAF1/CIP1) and p27(KIP1), and also in releasing IL-8 in host cells.

METHODSAkt1 phosphorylation and IL-8 levels of CagA(+) and CagA⁻ strain infected AGS cells were detected by ELISAs. Two quantitative RT-PCRs were established to measure p21(WAF1/CIP1) and p27(KIP1) mRNA levels in the CagA(+) and CagA⁻ strain infected cells. LY294002, an inhibitor of PI3K/Akt pathway, was used to define effect of the pathway in IL-8 release.

RESULTSCagA(+) strain could induce an obvious elevation of Akt1 phosphorylation in the infected AGS cells while CagA? strain failed to do so. The CagA(+) H. pylori strain infected AGS cells showed significant drops both in p21(WAF1/CIP1) and p27(KIP1) mRNA levels, whereas the CagA⁻ H. pylori strain caused a remarkable increase in p21(WAF1/CIP1) mRNA without affecting p27(KIP1) gene transcription in the AGS cells. Both the CagA(+) and CagA⁻ H. pylori strains enabled AGS cells to produce close elevated levels of IL-8, and the LY294002 block resulted in unexpected elevations of IL-8 levels.

CONCLUSIONSCagA can activate PI3K/Akt1 pathway that plays an inhibitory role in IL-8 release in H. pylori infected AGS cells. Activation of PI3K/Akt1 pathway and subsequent negative regulation of p21(WAF1/CIP1) and p27(KIP1) expression might be involved in CagA-associated carcinogenesis.

Antigens, Bacterial ; genetics ; physiology ; Bacterial Proteins ; genetics ; physiology ; Cell Line ; Cyclin-Dependent Kinase Inhibitor p21 ; biosynthesis ; Cyclin-Dependent Kinase Inhibitor p27 ; Gastric Mucosa ; cytology ; enzymology ; microbiology ; Helicobacter pylori ; metabolism ; pathogenicity ; physiology ; Humans ; Interleukin-8 ; secretion ; Intracellular Signaling Peptides and Proteins ; metabolism ; Phosphatidylinositol 3-Kinases ; metabolism ; Phosphorylation ; Proto-Oncogene Proteins c-akt ; metabolism ; Reverse Transcriptase Polymerase Chain Reaction ; Signal Transduction ; Transcription, Genetic ; Virulence

PURPOSE: In the gastric mucosa of Helicobacter pylori (H. pylori)-infected patients with gastritis or adenocarcinoma, proliferation of gastric epithelial cells is increased. Hyperproliferation is related to induction of oncogenes, such as β-catenin and c-myc. Even though transcription factors NF-κB and AP-1 are activated in H. pylori-infected cells, whether NF-κB or AP-1 regulates the expression of β-catenein or c-myc in H. pylori-infected cells has not been clarified. The present study was undertaken to investigate whether H. pylori-induced activation of NF-κB and AP-1 mediates the expression of oncogenes and hyperproliferation of gastric epithelial cells. MATERIALS AND METHODS: Gastric epithelial AGS cells were transiently transfected with mutant genes for IκBα (MAD3) and c-Jun (TAM67) or treated with a specific NF-κB inhibitor caffeic acid phenethyl ester (CAPE) or a selective AP-1 inhibitor SR-11302 to suppress activation of NF-κB or AP-1, respecively. As reference cells, the control vector pcDNA was transfected to the cells. Wild-type cells or transfected cells were cultured with or without H. pylori. RESULTS: H. pylori induced activation of NF-κB and AP-1, cell proliferation, and expression of oncogenes (β-catenein, c-myc) in AGS cells, which was inhibited by transfection of MAD3 and TAM67. Wild-type cells and the cells transfected with pcDNA showed similar activities of NF-κB and AP-1, proliferation, and oncogene expression regardless of treatment with H. pylori. Both CAPE and SR-11302 inhibited cell proliferation and expression of oncogenes in H. pylori-infected cells. CONCLUSION: H. pylori-induced activation of NF-κB and AP-1 regulates transcription of oncogenes and mediates hyperproliferation in gastric epithelial cells.
Blotting, Western ; Caffeic Acids ; Cell Line, Tumor ; Cell Proliferation ; DNA, Bacterial/analysis/genetics ; DNA-Binding Proteins/*metabolism ; Epithelial Cells/*metabolism ; Gastric Mucosa/*metabolism/pathology ; Gastritis/pathology ; Gene Expression Regulation, Bacterial ; Helicobacter Infections/metabolism/pathology/physiopathology ; Helicobacter pylori/pathogenicity/physiology ; Humans ; NF-kappa B/antagonists & inhibitors/*biosynthesis/metabolism ; Peptide Fragments ; Phenylethyl Alcohol/analogs & derivatives ; Proto-Oncogene Proteins c-jun ; Repressor Proteins ; Transcription Factor AP-1/*biosynthesis ; Transcription Factors/*metabolism ; beta Catenin/*metabolism