Background & Aims Infection with the gastric mucosal pathogen H. pylori is the strongest identified risk factor for distal gastric cancer. These bacteria colonize a significant part of the world’s population. We investigated the molecular mechanisms of p53 regulation in H. pylori-infected cells. Methods Mongolian gerbils were challenged with H. pylori and their gastric tissues were analyzed by immunohistochemistry and immunoblotting with p53 antibodies. Gastric epithelial cells were co-cultured with H. pylori and the regulation of p53 was assessed by real-time PCR, immunoblotting, immunofluorescence, and cell survival assays. shRNA and dominant-negative mutants were used to inhibit activities of HDM2 and AKT. Results We found that in addition to previously reported up-regulation of p53, H. pylori can also negatively regulate p53 by increasing ubiquitination and proteasomal degradation via activation of the serine/threonine kinase AKT, which phosphorylates and activates the ubiquitin ligase HDM2. These effects were mediated by the bacterial virulence factor, CagA; ectopic expression of CagA in gastric epithelial cells increased phosphorylation of HDM2 along with the ubiquitination and proteasomal degradation of p53. The decrease in p53 levels increased survival of gastric epithelial cells that had sustained DNA damage. Conclusion H. pylori is able to inhibit the tumor suppressor p53. H. pylori activates AKT, resulting in phosphorylation and activation of HDM2 and subsequent degradation of p53 in gastric epithelial cells. H. pylori-induced dysregulation of p53 is a potential mechanism by which the microorganism increases the risk of gastric cancer in infected individuals.

Background & Aims-Helicobacter pylori-induced gastritis predisposes to the development of gastric cancer. Increased epithelial tight junctions permeability and alterations in apical-junctional complexes are also associated with an increased risk of carcinogenesis. Phosphorylation of myosin regulatory light chain (MLC) by MLC kinase (MLCK) regulates tight junction function. We determined whether MLCK was activated by H. pylori and defined the mechanisms through which such activation dysregulates gastric epithelial barrier function.

Helicobacter pylori is the strongest known risk factor for gastric adenocarcinoma, yet only a fraction of infected persons develop cancer. One H. pylori constituent that augments disease risk is the cytotoxin-associated gene (cag) pathogenicity island, which encodes a secretion system that translocates bacterial effector molecules into host cells. Matrix metalloproteinase (MMP)-7, a member of a family of enzymes with tumor-initiating properties, is overexpressed in premalignant and malignant gastric lesions, and H. pylori cag ؉ strains selectively increase MMP-7 protein levels in gastric epithelial cells in vitro and in vivo. We now report that H. pylori-mediated mmp-7 induction is transcriptionally regulated via aberrant activation of p120-catenin (p120), a component of adherens junctions. H. pylori increases mmp-7 mRNA levels in a cagand p120-dependent manner and induces translocation of p120 to the nucleus in vitro and in a novel ex vivo gastric gland culture system. Nuclear translocation of p120 in response to H. pylori relieves Kaiso-mediated transcriptional repression of mmp-7, which is implicated in tumorigenesis. These results indicate that selective and coordinated induction of mmp-7 expression by H. pylori cag ؉ isolates may explain in part the augmentation in gastric cancer risk associated with these strains. INTRODUCTIONHelicobacter pylori induces an inflammatory response in the stomach that persists for decades, and biological costs incurred by this pathogen include an increased risk for gastric adenocarcinoma and non-Hodgkins lymphoma of the stomach (Nomura et al., 1991;Parsonnet et al., 1991;Peterson, 1991;Hansson et al., 1993;Correa, 1996;Uemura et al., 2001;Peek and Blaser, 2002;Moss and Sood, 2003). However, only a fraction of colonized persons ever develop neoplasia, and enhanced cancer risk is related to strain-specific differences, aberrant host responses, and/or specific interactions between microbial and host determinants.H. pylori strains that possess the cytotoxin-associated gene (cag) pathogenicity island increase the risk for cancer compared with strains that lack this genetic locus (Peek and Blaser, 2002). The cag island encodes proteins, such as CagE, that form a type IV secretion system that translocates components of bacterial peptidoglycan and CagA, the product of the terminal gene of the island, into host cells (Asahi et al., 2000;Backert et al., 2000;Odenbreit et al., 2000;Stein et al., 2000;Selbach et al., 2002;Viala et al., 2004). After translocation, peptidoglycan initiates innate immune signaling via activation of the intracellular pattern recognition receptor, Nod-1, and the transcriptional activator nuclear factor-B (NF-B) (Viala et al., 2004). Intracellular CagA undergoes Src-dependent tyrosine phosphorylation and activates a eukaryotic phosphatase, leading to dephosphorylation of host cell proteins and cellular morphological changes (Backert et al., 2000;Higashi et al., 2002;Selbach et al., 2002;Stein et al., 2002). Recently, CagA has been shown to activate ␤-catenin and...

Background & Aims Colonization of gastric mucosa by Helicobacter pylori leads to epithelial hyperproliferation, which increases the risk for gastric adenocarcinoma. One H. pylori virulence locus associated with cancer risk, cag, encodes a secretion system that transports effectors into host cells and leads to aberrant activation of β-catenin and p120-catenin (p120). Peroxisome proliferator-activated receptor (PPAR)δ is a ligand-activated transcription factor that affects oncogenesis in conjunction with β-catenin. We used a carcinogenic H. pylori strain to define the role of microbial virulence constituents and PPARδ in regulating epithelial responses that mediate development of adenocarcinoma. Methods Gastric epithelial cells or colonies were co-cultured with the H. pylori cag+ strain 7.13 or cagE−, cagA−, slt−, or cagA−/slt− mutants. Levels of PPARδ and Cyclin E1 were determined by real-time, reverse transcription PCR, immunoblot analysis, or immunofluorescence microscopy; proliferation was measured in 3-dimensional culture. PPARδ and Ki67 expression were determined by immunohistochemical analysis of human biopsies and rodent gastric mucosa. Results H. pylori induced β-catenin- and p120-dependent expression and activation of PPARδ in gastric epithelial cells, which were mediated by the cag secretion system substrates CagA and peptidoglycan. H. pylori stimulated proliferation in vitro, which required PPARδ-mediated activation of Cyclin E1; H. pylori did not induce expression of Cyclin E1 in a genetic model of PPARδ deficiency. PPARδ expression and proliferation in rodent and human gastric tissue was selectively induced by cag+ strains and PPARδ levels normalized following eradication of H. pylori. Conclusions The H. pylori cag secretion system activates β-catenin, p120, and PPARδ, which promote gastric epithelial cell proliferation via activation of Cyclin E1. PPARδ might contribute to gastric adenocarcinoma development in humans.

Persistent gastritis induced by Helicobacter pylori is the strongest known risk factor for peptic ulcer disease and distal gastric adenocarcinoma, a process for which adherence of H. pylori to gastric epithelial cells is critical. Decay-accelerating factor (DAF), a protein that protects epithelial cells from complement-mediated lysis, also functions as a receptor for several microbial pathogens. In this study, we investigated whether H. pylori utilizes DAF as a receptor and the role of DAF within H. pylori-infected gastric mucosa. In vitro studies showed that H. pylori adhered avidly to Chinese hamster ovary cells expressing human DAF but not to vector controls. In H. pylori, disruption of the virulence factors vacA, cagA, and cagE did not alter adherence, but deletion of DAF complement control protein (CCP) domains 1-4 or the heavily O-glycosylated serinethreonine-rich COOH-terminal domain reduced binding. In cultured gastric epithelial cells, H. pylori induced transcriptional upregulation of DAF, and genetic deficiency of DAF attenuated the development of inflammation among H. pylori-infected mice. These results indicate that DAF may regulate H. pylori-epithelial cell interactions relevant to pathogenesis.