Helicobacter pylori Infection Induces Genetic Instability of Nuclear and Mitochondrial DNA in Gastric Cells

Abstract

Purpose: Helicobacter pylori is a major cause of gastric carcinoma. To investigate a possible link between bacterial infection and genetic instability of the host genome, we examined the effect of H. pylori infection on known cellular repair pathways in vitro and in vivo. Moreover, various types of genetic instabilities in the nuclear and mitochondrial DNA (mtDNA) were examined. Experimental Design: We observed the effects of H. pylori infection on a gastric cell line (AGS), on C57BL/6 mice, and on individuals with chronic gastritis. In AGS cells, the effect of H. pylori infection on base excision repair and mismatch repair (MMR) was analyzed by reverse transcription-PCR, Western blot, and activity assays. In mice, MMR expression was analyzed by reverse transcription-PCR and the CA repeat instabilities were examined by Mutation Detection Enhancement gel electrophoresis. Mutation spectra in AGS cells and chronic gastritis tissue were determined by PCR, single-stranded conformation polymorphism, and sequencing. H. pylori vacA and cagA genotyping was determined by multiplex PCR and reverse hybridization. Results: Following H. pylori infection, the activity and expression of base excision repair and MMR are down-regulated both in vitro and in vivo. Moreover, H. pylori induces genomic instability in nuclear CA repeats in mice and in mtDNA of AGS cells and chronic gastritis tissue, and this effect in mtDNA is associated with bacterial virulence. Conclusions: Our results suggest that H. pylori impairs central DNA repair mechanisms, inducing a transient mutator phenotype, rendering gastric epithelial cells vulnerable to the accumulation of genetic instability and thus contributing to gastric carcinogenesis in infected individuals.

Infection-induced colitis in mice causes dynamic and tissue-specific changes in stress response and DNA damage leading to colon cancer

“…Our observation of H. hepaticus-induced down-regulation of DNA repair transcripts is consistent with studies of H. pylori infection, which has been shown to suppress DNA repair gene expression in infected cells in culture and in infected mouse and human tissues (57,58). Whereas Machado et al observed that infection caused reduced expression of base excision and mismatch repair genes and concomitant increases in genomic instability (58), Kim et al demonstrated that H. pylori coculture with gastric cancer cells lines caused reduced levels of both mRNA and protein for both MutS and MutL mismatch repair protein, with heat-sensitive bacterial products responsible for the reductions (57).…”

Carcinogenic bacterial pathogen Helicobacter pylori triggers DNA double-strand breaks and a DNA damage response in its host cells

“…H. pylori infection of cultured gastric epithelial cells down-regulates the components of the mismatch repair (MMR) and base excision repair machineries at the RNA and protein levels and impairs the efficiency of DNA repair as judged by MMR activity assay (13,14). The down-regulation of MMR proteins was confirmed in experimentally infected murine gastric mucosa (14) and can be reversed by Helicobacter eradication in patients (15), suggesting that impaired DNA repair also is a hallmark of H. pylori infection in vivo.…”

Circulating Mitochondrial DNA Level, a Noninvasive Biomarker for the Early Detection of Gastric Cancer

“…In H. pylori-infected patients, mtDNA mutations are significantly more frequent in patients with gastric cancer than in cancer-free patients (23). According to our previous studies, mtDNA mutations are induced in vitro in H. pyloriinfected gastric epithelial cells and in the gastric mucosa of chronically infected mice (24,25). A decrease in mtDNA content has also been described in most tumor tissues of advanced gastric cancer, compared with nearby nontumor control tissue (26)(27)(28).…”