Escherichia coli induces DNA damage in vivo and triggers genomic instability in mammalian cells

Abstract

Escherichia coli is a normal inhabitant of the human gut. However, E. coli strains of phylogenetic group B2 harbor a genomic island called "pks" that codes for the production of a polyketide-peptide genotoxin, Colibactin. Here we report that in vivo infection with E. coli harboring the pks island, but not with a pks isogenic mutant, induced the formation of phosphorylated H2AX foci in mouse enterocytes. We show that a single, short exposure of cultured mammalian epithelial cells to live pks + E. coli at low infectious doses induced a transient DNA damage response followed by cell division with signs of incomplete DNA repair, leading to anaphase bridges and chromosome aberrations. Micronuclei, aneuploidy, ring chromosomes, and anaphase bridges persisted in dividing cells up to 21 d after infection, indicating occurrence of breakage-fusion-bridge cycles and chromosomal instability. Exposed cells exhibited a significant increase in gene mutation frequency and anchorage-independent colony formation, demonstrating the infection mutagenic and transforming potential. Therefore, colon colonization with these E. coli strains harboring the pks island could contribute to the development of sporadic colorectal cancer.T he dense bacterial consortium, called "microbiota," that inhabits the intestinal tract is recognized increasingly as playing a major role in human health and disease. The microbiota generally influences the host in a beneficial fashion by shaping gastrointestinal and immune functions, exerting protection against pathogens, and contributing to metabolic pathways (1). Escherichia coli is a consistent member of the human intestinal microbiota, colonizing the intestine within a few days after birth and persisting throughout the life of the host. The E. coli strain population can be categorized in at least four major phylogenetic groups (A, B1, B2, and D), each group being more specifically associated with certain ecological niches. E. coli strains belonging to group B2 are recovered from the environment less frequently but can persist longer in the colon than other groups and represent 30-50% of strains isolated from the feces of healthy humans living in high-income countries (2, 3). We recently discovered that up to 34% of commensal E. coli strains of the phylogenetic group B2 carry a conserved genomic island named "pks island" (4-6). This gene cluster codes for nonribosomal peptide synthetases (NRPS) and polyketide synthetases (PKS) that allow production of a putative hybrid peptide-polyketide genotoxin, Colibactin. In vitro infection with these strains induces DNA double-strand breaks (DSBs) in cultivated human cells, but the pks island was not proved to cause DNA damage in vivo (4).In this study, we wished to explore whether those bacteria were able to induce genetic damage in vivo on the colonic mucosa and to characterize the consequences of this damage on mammalian cells in relation with the number of infecting bacteria. We report that pks + E. coli induced DSBs in vivo. In addition, infection of various ma...

Enterotoxicity of a nonribosomal peptide causes antibiotic-associated colitis

“…Mucosa-associated pks+ E. coli were found in a significantly high percentage of inflammatory bowel disease and colorectal cancer patients (46). The structure of colibactin is yet to be determined but its biological activity has been characterized (41,47,48). Colibactin damages DNA, inducing chromosome instability and mutations in host cells and may therefore contribute to colon cancer.…”

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

“…Producers of genotoxins, such as cytolethal distending toxins or colibactin, cause direct DNA injury, inducing genomic instability and ultimately cell cycle arrest and cell death. 7,[35][36][37] Other bacteria, such as C. trachomatis, 19 Pseudomonas aeruginosa, 38 H. pylori, 12 N. gonorrhoeae 39 , and Shigella flexneri, 40 induce the production of reactive oxygen species (ROS) that promote oxidative DNA damage, thereby increasing γH2A.X levels and impairing host DNA repair mechanisms. To our knowledge, Lm does not express toxins that can directly injure host DNA.…”

When our genome is targeted by pathogenic bacteria

“…Chk1 and Chk2 subsequently phosphorylate Cdc25 phosphatase, thereby inactivating this enzyme and inducing cell cycle arrest at the G2/M or G1/S transition. DSBs are observed in enterocytes of the colon mucosa of mice infected with E. coli pks+ [20]. At low multiplicity of infection (MOI), cells repair DNA and resume cell division, but massive cell death is observed in cells deficient in the NHEJ repair pathway [20].…”

“…DSBs are observed in enterocytes of the colon mucosa of mice infected with E. coli pks+ [20]. At low multiplicity of infection (MOI), cells repair DNA and resume cell division, but massive cell death is observed in cells deficient in the NHEJ repair pathway [20]. In addition, some cells maintain γH2AX foci, like scars of infection, and chromosomal aberrations.…”

“…Infection can also promote aneuploidy (gain or loss of chromosomes) or tetraploidy (8n cells) as a consequence of division anomalies. Moreover, an increase in mutation frequency is observed and cells acquire an enhanced capacity to grow in semi-liquid medium, as an early sign of cell transformation [20]. Under these conditions, it is likely that the multiple lesions induced by colibactin accumulate with time, perhaps contributing to the cell transformation process, a critical step before cancer onset.…”