Colibactins are hybrid
polyketide-nonribosomal
peptides produced by Escherichia coli, Klebsiella pneumoniae, and other Enterobacteriaceae harboring the pks genomic island. These genotoxic metabolites are produced by pks-encoded
peptide-
polyketide synthases as inactive
prodrugs called precolibactins, which are then converted to colibactins by deacylation for
DNA-damaging effects. Colibactins are bona fide
virulence factors and are suspected of promoting colorectal
carcinogenesis when produced by intestinal E. coli Natural active colibactins have not been isolated, and how they induce DNA damage in the eukaryotic host cell is poorly characterized. Here, we show that
DNA strands are cross-linked covalently when exposed to enterobacteria producing colibactins.
DNA cross-linking is abrogated in a clbP mutant unable to deacetylate precolibactins or by adding the
colibactin self-resistance
protein ClbS, confirming the involvement of the mature forms of colibactins. A similar
DNA-damaging mechanism is observed in cellulo, where interstrand cross-links are detected in the genomic
DNA of cultured human cells exposed to
colibactin-producing bacteria. The intoxicated cells exhibit replication stress, activation of
ataxia-telangiectasia and Rad3-related
kinase (ATR), and recruitment of the
DNA cross-link repair
Fanconi anemia protein D2 (
FANCD2) protein. In contrast, inhibition of ATR or knockdown of FANCD2 reduces the survival of cells exposed to
colibactin-producing bacteria. These findings demonstrate that
DNA interstrand cross-linking is the critical mechanism of
colibactin-induced DNA damage in infected cells.IMPORTANCE
Colorectal cancer is the third-most-common cause of
cancer death. In addition to known risk factors such as high-fat diets and alcohol consumption, genotoxic intestinal Escherichia coli bacteria producing
colibactin are proposed to play a role in
colon cancer development. Here, by using transient
infections with genotoxic E. coli, we showed that colibactins directly generate
DNA cross-links in cellulo Such lesions are converted into double-strand breaks during the repair response.
DNA cross-links, akin to those induced by metabolites of alcohol and high-fat diets and by widely used anticancer drugs, are both severely mutagenic and profoundly cytotoxic lesions. This finding of a direct induction of
DNA cross-links by a bacterium should facilitate delineating the role of E. coli in
colon cancer and engineering new
anticancer agents.