Regulation of p53 Tumor Suppressor by Helicobacter pylori in Gastric Epithelial Cells

doi:10.1053/j.gastro.2010.06.018

Gastroenterology

Volume 139, Issue 4, October 2010, Pages 1333-1343.e4

https://doi.org/10.1053/j.gastro.2010.06.018 Get rights and content

Background & Aims

Infection with the gastric mucosal pathogen Helicobacter 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 polymerase chain reaction, immunoblotting, immunofluorescence, and cell survival assays. Short hairpin RNA and dominant-negative mutants were used to inhibit activities of Human Double Minute 2 (HDM2) and AKT1 proteins.

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 AKT1, 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.

Conclusions

H pylori is able to inhibit the tumor suppressor p53. H pylori activates AKT1, 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.

Section snippets

Cell Culture and H pylori Strains

Human gastric cancer cell lines SNU1, AGS, and Kato III were maintained in F-12 medium. HFE-145,¹⁶ a human gastric epithelial cell line, was cultured in Dulbecco's modified Eagle medium/F-12 medium. The p53-null osteosarcoma cell line, SaOs2, was grown in RPMI-1640 medium. All media were supplied by Invitrogen (Carlsbad, CA) and supplemented with 10% fetal bovine serum. The cagA+ H pylori clinical strain J166 and rodent-adapted strain 7.13 were grown in Brucella broth with 5% fetal bovine serum

Protein Levels of p53 Are Dynamically Changed in H pylori–Infected Cells

Although p53 expression has been assessed in gastric tissues from H pylori–infected patients, the dynamics of p53 alterations have not been defined in detail. In addition, there are no data on p53 alterations during the initial phases of infection. To examine how H pylori affects p53 in vivo, we used Mongolian gerbils because gastric pathology induced by H pylori in this system more closely recapitulates human infection than murine models.¹⁸ As a prelude to our analyses, we characterized gerbil

Discussion

In this study, we investigated the regulation of the p53 protein in H pylori–infected gastric epithelial cells and found that this microorganism actively alters levels of p53. Previously, it has been reported that H pylori infection increases the levels of the p53 protein in the gastric mucosa.7, 8, 9 Consistent with these reports, we observed up-regulation of p53 in Mongolian gerbils after H pylori infection. However, our studies also provided evidence that regulation of p53 is more complex.

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Citation Excerpt :
It binds to SHP2 phosphatase and to several kinases including the Focal Adhesion Kinase FAK regulating actin cytoskeleton remodeling, leading to destabilization of cell/cell junctions and loss of cellular polarity [46]. CagA also alters p53 signaling pathway and impairs DNA-damage response, leading to mitotic instability and accumulation of mutations [49–52]. CagA-induced cell signaling thereby affects several oncogenic signaling pathways such as MAPK, β-catenin, nuclear factor kappaB (NF-κB) and Hippo/YAP/TAZ pathways leading to perturbations in the cell proliferation-differentiation balance [34,53–57].
The Helicobacter genus actually comprises 46 validly published species divided into two main clades: gastric and enterohepatic Helicobacters. These bacteria colonize alternative sites of the digestive system in animals and humans, and contribute to inflammation and cancers. In humans, Helicobacter infection is mainly related to H. pylori, a gastric pathogen infecting more than half of the world's population, leading to chronic inflammation of the gastric mucosa that can evolve into two types of gastric cancers: gastric adenocarcinomas and gastric MALT lymphoma. In addition, H. pylori but also non-H. pylori Helicobacter infection has been associated with many extra-gastric malignancies. This review focuses on H. pylori and its role in gastric cancers and extra-gastric diseases, as well as malignancies induced by non-H. pylori Helicobacters. Their different virulence factors and their involvement in carcinogenesis is discussed. This review highlights the importance of both gastric and enterohepatic Helicobacters in gastrointestinal and liver cancers.

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: Conflicts of interest The authors disclose no conflicts.

: Funding This work was supported by the National Institute of Health grants RO1 CA108956, RO1 CA138833, and R21 CA1296550, the NCRR/NIH Vanderbilt CTSA grant UL1 RR024975, and the Vanderbilt Digestive Research Center grant P30DK058404.

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Basic—Alimentary TractRegulation of p53 Tumor Suppressor by Helicobacter pylori in Gastric Epithelial Cells

Background & Aims

Methods

Results

Conclusions

Section snippets

Cell Culture and H pylori Strains

Protein Levels of p53 Are Dynamically Changed in H pylori–Infected Cells

Discussion

Virology

Microbes Infect

Gastroenterology

J Infect Chemother

Cell Host Microbe

J Biol Chem

Biochem Pharmacol

Coadaptation of Helicobacter pylori and humans: ancient history, modern implications

J Clin Invest

Transformed immortalized gastric epithelial cells by virulence factor CagA of Helicobacter pylori through Erk mitogen-activated protein kinase pathway

Oncogene

Transgenic expression of Helicobacter pylori CagA induces gastrointestinal and hematopoietic neoplasms in mouse

Proc Natl Acad Sci U S A