Several commensal and pathogenic Gram‐negative bacteria produce DNA‐damaging toxins that are considered bona fide carcinogenic agents. The microbiota of colorectal cancer (CRC) patients is enriched in genotoxin‐producing bacteria, but their role in the pathogenesis of CRC is poorly understood. The adenomatous polyposis coli (APC) gene is mutated in familial adenomatous polyposis and in the majority of sporadic CRCs. We investigated whether the loss of APC alters the response of colonic epithelial cells to infection by Salmonella enterica, the only genotoxin‐producing bacterium associated with cancer in humans. Using 2D and organotypic 3D cultures, we found that APC deficiency was associated with sustained activation of the DNA damage response, reduced capacity to repair different types of damage, including DNA breaks and oxidative damage, and failure to induce cell cycle arrest. The reduced DNA repair capacity and inability to activate adequate checkpoint responses was associated with increased genomic instability in APC‐deficient cells exposed to the genotoxic bacterium. Inhibition of the checkpoint response was dependent on activation of the phosphatidylinositol 3‐kinase pathway. These findings highlight the synergistic effect of the loss of APC and infection with genotoxin‐producing bacteria in promoting a microenvironment conducive to malignant transformation.
Highlights d Typhoid toxin causes DNA fragmentation in vivo not associated with inflammation d Infection with a genotoxin-producing bacterium induces senescence in vivo d The presence of senescent cells is associated with an antiinflammatory response d The anti-inflammatory effect is lost in mice with acute colitis
Background/Aim: Nanomedicine is a promising scientific field that exploits the unique properties of innovative nanomaterials, providing alternative solutions in diagnostics, prevention and therapeutics. Titanium dioxide nanoparticles (TiO 2 NPs) have a great spectrum of photocatalytic antibacterial and anticancer applications. The chemical modification of TiO 2 optimizes its bioactive performance. The aim of this study was the development of silver modified NPs (Ag/TiO 2 NPs) with anticancer potential. Materials and Methods: Ag/TiO 2 NPs were prepared through the sol-gel method, were fully characterized and were tested on cultured breast cancer epithelial cells (MCF-7 and MDA-MB-231). The MTT colorimetric assay was used to estimate cellular viability. Western blot analysis of protein expression along with a DNA-laddering assay were employed for apoptosis detection. Results and Conclusion: We show that photo-activated Ag/TiO 2 NPs exhibited significant cytotoxicity on the highly malignant MDA-MB-231 cancer cells, inducing apoptosis, while MCF-7 cells that are characterized by low invasive properties were unaffected under the same conditions.Nanomedicine is an emerging inter-disciplinary scientific field that exploits the unique properties of innovative 425 This article is freely accessible online.
The idea that bacterial toxins are not only killers but also execute more sophisticated roles during bacteria–host interactions by acting as negotiators has been highlighted in the past decades. Depending on the toxin, its cellular target and mode of action, the final regulatory outcome can be different. In this review, we have focused on two families of bacterial toxins: genotoxins and pore-forming toxins, which have different modes of action but share the ability to modulate the host’s immune responses, independently of their capacity to directly kill immune cells. We have addressed their immuno-suppressive effects with the perspective that these may help bacteria to avoid clearance by the host’s immune response and, concomitantly, limit detrimental immunopathology. These are optimal conditions for the establishment of a persistent infection, eventually promoting asymptomatic carriers. This immunomodulatory effect can be achieved with different strategies such as suppression of pro-inflammatory cytokines, re-polarization of the immune response from a pro-inflammatory to a tolerogenic state, and bacterial fitness modulation to favour tissue colonization while preventing bacteraemia. An imbalance in each of those effects can lead to disease due to either uncontrolled bacterial proliferation/invasion, immunopathology, or both.
Summary We recently characterized the association between DNA damage and immunoresponse in vivo in colonic mucosa of mice infected with a Salmonella Typhimurium strain expressing a genotoxin, known as typhoid toxin. In this protocol, we describe how to assess the extent and features of infiltrating macrophages by double immunofluorescence. Total macrophage population was determined using an F4/80 antibody, whereas the specific M2-like population was assessed using a CD206 antibody. For complete details on the use and execution of this protocol, please refer to Martin et al. (2021) .
30Bacterial genotoxins cause DNA damage in eukaryotic cells, resulting in activation of the DNA 31 damage response (DDR) in vitro. These toxins are produced by Gram negative bacteria, en-32 riched in the microbiota of Inflammatory Bowel Disease (IBD) and colorectal cancer (CRC) 33 patients. However, their role in infection remains poorly characterized. We have addressed the 34 role of the typhoid toxin in the modulation of the host-microbial interaction in health and dis-35 ease. 36Infection with a genotoxigenic Salmonella protected mice from intestinal inflammation. The 37 toxin-induced DNA damage caused senescence in vivo, which was uncoupled from the inflam-38 matory response, and associated with the maintenance of an anti-inflammatory environment. 39This effect was lost when infection occurred in mice suffering from inflammatory conditions 40 that mimic Ulcerative Colitis, a form of IBD. 41These data highlight a complex context-dependent crosstalk between bacterial genotoxins-in-42 duced DDR and the host immune response, underlining an unexpected role for bacterial geno-43 toxins. 44 45 cumulates in the cytoplasm of senescent cells (Evangelou et al., 2017). As shown in Figures 2C 130 and S3A, we detected a significant increase in GL13 epithelial positive cells in the colon and 131 small intestine of mice infected with the MC1 TT and MC71 TT strains compared to the levels 132 detected in mice infected with the control Salmonella, with the most prominent effect observed 133 in the C57BL/6 mouse strain (cp Figure 2C and Figure S3A). In our model, induction of senes-134 cence was uncoupled from the activation of a pro-inflammatory response (Figures 1, 3 and S2). 135 136The typhoid toxin maintains an anti-inflammatory microenvironment 137 Supplementary Information
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