Helicobacter pylori infection induces genetic instability of nuclear and mitochondrial DNA in gastric cells.
OBJECTIVE
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.


METHODS
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.
Machado
Ana Manuel Dantas
AM
Department of Science, Systems and Models, Roskilde University, Roskilde, Denmark.
Figueiredo
Ceu
C
Touati
Eliette
E
Máximo
Valdemar
V
Sousa
Sonia
S
Michel
Valérie
V
Carneiro
Fátima
F
Nielsen
Finn Cilius
FC
Seruca
Raquel
R
Rasmussen
Lene Juel
LJ
D000230:Adenocarcinoma / Q000235:genetics / Q000382:microbiology / Q000473:pathology; D000328:Adult; D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D002467:Cell Nucleus / Q000235:genetics* / Q000378:metabolism; D049109:Cell Proliferation; D002478:Cells, Cultured; D004260:DNA Repair; D004272:DNA, Mitochondrial / Q000235:genetics* / Q000378:metabolism; D018900:Dinucleotide Repeats / Q000235:genetics; D005260:Female; D042822:Genomic Instability; D016481:Helicobacter Infections / Q000235:genetics* / Q000382:microbiology; D016480:Helicobacter pylori / Q000502:physiology*; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008875:Middle Aged; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013274:Stomach Neoplasms / Q000235:genetics* / Q000382:microbiology / Q000473:pathology
D004272:DNA, Mitochondrial; D012333:RNA, Messenger