The opportunistic pathogen Pseudomonas aeruginosa activates the DNA double-strand break signaling and repair pathway in infected cells
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Highly hazardous DNA double-strand breaks can be induced in eukaryotic cells by a number of agents including pathogenic bacterial strains. We have investigated the genotoxic potential of Pseudomonas aeruginosa, an opportunistic pathogen causing devastating nosocomial infections in cystic fibrosis or immunocompromised patients. Our data revealed that infection of immune or epithelial cells by P. aeruginosa triggered DNA strand breaks and phosphorylation of histone H2AX (γH2AX), a marker of DNA double-strand breaks. Moreover, it induced formation of discrete nuclear repair foci similar to gamma-irradiation-induced foci, and containing γH2AX and 53BP1, an adaptor protein mediating the DNA-damage response pathway. Gene deletion, mutagenesis, and complementation in P. aeruginosa identified ExoS bacterial toxin as the major factor involved in γH2AX induction. Chemical inhibition of several kinases known to phosphorylate H2AX demonstrated that Ataxia Telangiectasia Mutated (ATM) was the principal kinase in P. aeruginosa-induced H2AX phosphorylation. Finally, infection led to ATM kinase activation by an auto-phosphorylation mechanism. Together, these data show for the first time that infection by P. aeruginosa activates the DNA double-strand break repair machinery of the host cells. This novel information sheds new light on the consequences of P. aeruginosa infection in mammalian cells. As pathogenic Escherichia coli or carcinogenic Helicobacter pylori can alter genome integrity through DNA double-strand breaks, leading to chromosomal instability and eventually cancer, our findings highlight possible new routes for further investigations of P. aeruginosa in cancer biology and they identify ATM as a potential target molecule for drug design.
KeywordsDNA double-strand breaks Infection Pseudomonas aeruginosa ATM H2AX
ADP ribosyl transferase
Ataxia telangiectasia mutated
8-oxoguanine DNA glycosylase
CT-10 regulator of kinase
Multiplicity of infection
Cytolethal distending toxin
Calf intestine phosphatase
Type III secretion system
We thank Drs. F. Boulay for very helpful scientific discussions, I. Attrée for advice and critical reading of the manuscript, J. Gaffé for discussion and corrections, H.P. Schweizer for the gift of mini-CTX1, Prof. B. Toussaint and Prof. B. Polack for the CHAΔTlox and CHAΔSTlox strains, D. Dacheux for the exoS mutagenesis, B. Schaack for annexin labeling reagents, J. Baudier for H1299 cells, P. Obeid for her advice on comet assays and E. Lebel for technical help. Images were obtained at the confocal microscopy facility of the “Institut de Recherches en Technologies et Sciences pour le Vivant” (iRTSV, CEA-Grenoble). Irradiations were performed in the “Anémome/Bio” irradiator in the “ARC -Nucléart” facility at the CEA-Grenoble. Part of the work of S. Elsen, V. Collin-Faure and C. Lemercier was performed in the former laboratory CEA-iRTSV-LBBSI, CNRS UMR5092 directed by Dr. F. Boulay. This work was supported by the Institut National de la Santé et de la Recherche Médicale (INSERM), the Commissariat à l’Energie Atomique et aux Energies Renouvelables (CEA), the Centre National de la Recherche Scientifique (CNRS) and the Université Joseph Fourier (UJF Grenoble).
Conflict of interest
The authors declare that they have no conflicts of interest.