Abstract
The cytolethal distending toxin (CDT) is produced by several Gram-negative pathogenic bacteria. In addition to inflammation, experimental evidences are in favor of a protumoral role of CDT-harboring bacteria such as Escherichia coli, Campylobacter jejuni, or Helicobacter hepaticus. CDT may contribute to cell transformation in vitro and carcinogenesis in mice models, through the genotoxic action of CdtB catalytic subunit. Here, we investigate the mechanism of action by which CDT leads to genetic instability in human cell lines and colorectal organoids from healthy patients’ biopsies. We demonstrate that CDT holotoxin induces a replicative stress dependent on CdtB. The slowing down of DNA replication occurs mainly in late S phase, resulting in the expression of fragile sites and important chromosomic aberrations. These DNA abnormalities induced after CDT treatment are responsible for anaphase bridge formation in mitosis and interphase DNA bridge between daughter cells in G1 phase. Moreover, CDT-genotoxic potential preferentially affects human cycling cells compared to quiescent cells. Finally, the toxin induces nuclear distension associated to DNA damage in proliferating cells of human colorectal organoids, resulting in decreased growth. Our findings thus identify CDT as a bacterial virulence factor targeting proliferating cells, such as human colorectal progenitors or stem cells, inducing replicative stress and genetic instability transmitted to daughter cells that may therefore contribute to carcinogenesis. As some CDT-carrying bacterial strains were detected in patients with colorectal cancer, targeting these bacteria could be a promising therapeutic strategy.
Highlights
The cytolethal distending toxin (CDT) was first identified in 1988 in Escherichia coli (E. coli) strains isolated from patients with diarrhea (Johnson and Lior, 1988a,b)
We observed a significant decrease in 5 iododeoxyuridine (IdU) track length, revealing a slowing down of replication fork speed in the presence of CDT compared to untreated cells, independently of CDT-producing strains and host cells (Figures 1B,C)
We found that CDT exposure stimulates the formation of RPApositive bridges connecting the nuclei of daughter cells compared to untreated cells (2.5 versus 5.6%) but likely at a lesser extent compared to double-stranded bridges
Summary
The cytolethal distending toxin (CDT) was first identified in 1988 in Escherichia coli (E. coli) strains isolated from patients with diarrhea (Johnson and Lior, 1988a,b). CdtA and CdtC constitute the regulatory subunits and CdtB the catalytic subunit exhibiting phosphatase and DNase activities, the latter responsible for DNA break formation [for review, see Guerra et al (2011); Jinadasa et al (2011)]. It was initially reported that CDT induces direct DNA double-strand break (DSB) in mammalian cells (Frisan et al, 2003). Homologous recombination (RH), non-homologous end joining (NHEJ), Fanconi anemia (FA), and single-strand break repair (SSBR) pathways were depicted as the main mammalian repair mechanisms involved in the resistance to CDT intoxication to preserve the DNA integrity (Bezine et al, 2016). In case of massive unrepaired or misrepaired DNA damage, senescence or cell death by apoptosis is activated (Cortes-Bratti et al, 2001; Alaoui-El-Azher et al, 2010; Guerra et al, 2011; Jinadasa et al, 2011)
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