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

Abstract

The bacterial pathogen Helicobacter pylori chronically infects the human gastric mucosa and is the leading risk factor for the development of gastric cancer. The molecular mechanisms of H. pyloriassociated gastric carcinogenesis remain ill defined. In this study, we examined the possibility that H. pylori directly compromises the genomic integrity of its host cells. We provide evidence that the infection introduces DNA double-strand breaks (DSBs) in primary and transformed murine and human epithelial and mesenchymal cells. The induction of DSBs depends on the direct contact of live bacteria with mammalian cells. The infection-associated DNA damage is evident upon separation of nuclear DNA by pulse field gel electrophoresis and by high-magnification microscopy of metaphase chromosomes. Bacterial adhesion (e.g., via blood group antigenbinding adhesin) is required to induce DSBs; in contrast, the H. pylori virulence factors vacuolating cytotoxin A, γ-glutamyl transpeptidase, and the cytotoxin-associated gene (Cag) pathogenicity island are dispensable for DSB induction. The DNA discontinuities trigger a damage-signaling and repair response involving the sequential ataxia telangiectasia mutated (ATM)-dependent recruitment of repair factors-p53-binding protein (53BP1) and mediator of DNA damage checkpoint protein 1 (MDC1)-and histone H2A variant X (H2AX) phosphorylation. Although most breaks are repaired efficiently upon termination of the infection, we observe that prolonged active infection leads to saturation of cellular repair capabilities. In summary, we conclude that DNA damage followed by potentially imprecise repair is consistent with the carcinogenic properties of H. pylori and with its mutagenic properties in vitro and in vivo and may contribute to the genetic instability and frequent chromosomal aberrations that are a hallmark of gastric cancer.

Listeria monocytogenesinduces host DNA damage and delays the host cell cycle to promote infection

“…12 Lm signals via another DNA damage sensor and key repair enzyme, DNA-PK. Upon infection, DNA-PK is phosphorylated in an Lm dose-dependent manner, together with H2A.X and CDC25A.…”

“…11 In addition, H. pylori was reported to induce host DNA double-strand breaks, contributing to genetic instability and chromosomal aberrations typical of gastric cancer. 12 Chlamydia trachomatis was epidemiologically linked to increased risk of developing cervical cancer. 13 It affects genome stability by several mechanisms: multipolar spindle formation, 14,15 spindle assembly checkpoint override, 16 cytokinesis failure, 17,18 and induction of DNA damage coupled to impaired repair mechanisms.…”

When our genome is targeted by pathogenic bacteria

“…Nuclear IRIF-like foci (induced by bacteria) containing γH2AX, 53BP1 and MDC1 have been observed in ATM kinase-dependent processes [18]. Large breaks on chromatids are detected at metaphases in infected cells, and these defects are independent of the bacterial virulence factors tested [18]. H. pylori infection generates ROS, but, despite a temporal correlation, ROS production is not required for the generation of DSBs.…”

“…H. pylori infection generates ROS, but, despite a temporal correlation, ROS production is not required for the generation of DSBs. The eradication of H. pylori using antibiotics leads to efficient DSB repair and cell survival [18]. Nevertheless, when the infection persists over an extended period of time, residual unrepaired breaks remain, reflecting the saturation of the repair machinery, resulting in a loss of cell viability.…”

“…Unlike CDT, ExoS does not possess any known nuclease activity, thus the direct mechanisms leading to DSBs remain elusive in P. aeruginosa. DSBs could result from the ROS-related oxidation of DNA, or similar to H. pylori, these lesions could be associated to ROS release, without dependence on these molecules [18].…”