Maternally acquired genotoxic Escherichia coli alters offspring’s intestinal homeostasis

The neonatal gut is rapidly colonized by a newly dominant group of commensal Escherichia coli strains among which a large proportion produces a genotoxin called colibactin. In order to analyze the short- and long-term effects resulting from such evolution, we developed a rat model mimicking the natural transmission of E. coli from mothers to neonates. Genotoxic and non-genotoxic E. coli strains were equally transmitted to the offspring and stably colonized the gut across generations. DNA damage was only detected in neonates colonized with genotoxic E. coli strains. Signs of genotoxic stress such as anaphase bridges, higher occurrence of crypt fission and accelerated renewal of the mature epithelium were detected at adulthood. In addition, we observed alterations of secretory cell populations and gut epithelial barrier. Our findings illustrate how critical is the genotype of E. coli strains acquired at birth for gut homeostasis at adulthood.     

E. coli and colorectal cancer: a complex relationship that deserves a critical mindset

To the multiple factors that may eventually result in colorectal cancer (CRC), strains of E. coli have now been added, in particular strains producing colibactin from their polyketide synthesis (pks) locus. The evidence and mechanistic explanations for this unfortunate effect of what is in most cases a harmless commensal are discussed in the first part of this review. In the second part, observations are presented and discussed that do not fit with the hypothesis that colibactin-producing E. coli produce CRC. The last part of this review is reserved for an alternative explanation of the function of this enigmatic colibactin, a toxin that has not yet been isolated. It is hypothesized that E. coli preferentially colonizes cancerous lesions as an effect rather than a cause and that colibactin production provides a selective advantage to compete with other bacteria.     

Shining a Light on Colibactin Biology

Colibactin is a secondary metabolite encoded by the pks gene island identified in several Enterobacteriaceae, including some pathogenic Escherichia coli (E. coli) commonly enriched in mucosal tissue collected from patients with inflammatory bowel disease and colorectal cancer. E. coli harboring this biosynthetic gene cluster cause DNA damage and tumorigenesis in cell lines and pre-clinical models, yet fundamental knowledge regarding colibactin function is lacking. To accurately assess the role of pks⁺ E. coli in cancer etiology, the biological mechanisms governing production and delivery of colibactin by these bacteria must be elucidated. In this review, we will focus on recent advances in our understanding of colibactin’s structural mode-of-action and mutagenic potential with consideration for how this activity may be regulated by physiologic conditions within the intestine.     

The bacterial genotoxin colibactin promotes colon tumor growth by modifying the tumor microenvironment

The gut microbiota is suspected to promote colorectal cancer (CRC). Escherichia coli are more frequently found in CCR biopsies than in healthy mucosa; furthermore, the majority of mucosa-associated E. coli isolated from CCR harbors the pks genomic island (pks+ E. coli) that is responsible for the synthesis of colibactin, a genotoxic compound. We have recently reported that transient contact of a few malignant cells with colibactin-producing E. coli increases tumor growth in a xenograft mouse model. Growth is sustained by cellular senescence that is accompanied by the production of growth factors. We demonstrated that cellular senescence is a consequence of the pks+ E. coli-induced alteration of p53 SUMOylation, an essential post-translational modification in eukaryotic cells. The underlying mechanisms for this process involve the induction of miR-20a-5p expression, which targets SENP1, a key protein in the regulation of the SUMOylation process. These results are consistent with the expression of SENP1, miR-20a-5p and growth factors that are observed in a CRC mouse model and in human CCR biopsies colonized by pks+ E. coli. Overall, the data reveal a new paradigm for carcinogenesis in which pks+ E. coli infection induces cellular senescence characterized by the production of growth factors that promote the proliferation of uninfected cells and, subsequently, tumor growth.     

Association of Escherichia coli containing polyketide synthase in the gut microbiota with colorectal neoplasia in Japan

Escherichia coli containing polyketide synthase in the gut microbiota (pks ⁺ E coli) produce a polyketide‐peptide genotoxin, colibactin, and are suspected to play a role in the development of colorectal neoplasia. To clarify the role of pks ⁺ E coli in the early stage of tumorigenesis, we investigated whether the pks status of E coli was associated with the prevalence of colorectal neoplasia. This cross‐sectional analysis of data from a prospective cohort in Izu Oshima, Japan included asymptomatic residents aged 40‐79 years who underwent screening colonoscopy and provided a stool sample. We identified 543 participants with colorectal neoplasia (22 colorectal cancer and 521 adenoma) as cases and 425 participants with normal colon as controls. The pks status of E coli was assayed using stool DNA and specific primers that detected pks ⁺ E coli. The proportion of pks ⁺ E coli was 32.6% among cases and 30.8% among controls. Compared with those with pks ⁻ E coli, the odds ratio (OR) (95% confidence interval) for participants with pks ⁺ E coli was 1.04 (0.77‐1.41) after adjusting for potential confounders. No statistically significant associations were observed regardless of tumor site or number of colorectal adenoma lesions. However, stratified analyses revealed increased ORs among participants who consumed cereals over the median intake or vegetables under the median intake. Overall, we found no statistically significant association between pks ⁺ E coli and the prevalence of colorectal adenoma lesions among this Japanese cohort. However, positive associations were suggested under certain intake levels of cereals or vegetables.     

Colibactin-positive Escherichia coli induce a procarcinogenic immune environment leading to immunotherapy resistance in colorectal cancer

Colibactin-producing E. coli (CoPEC) are frequently detected in colorectal cancer (CRC) and exhibit procarcinogenic properties. Because increasing evidence show the role of immune environment and especially of antitumor T-cells in CRC development, we investigated the impact of CoPEC on these cells in human CRC and in the APC^Min/+ mice colon. T-cell density was evaluated by immunohistochemistry in human tumors known for their CoPEC status. APC^min/+ mice were chronically infected with a CoPEC strain (11G5). Immune cells (neutrophils and T-cell populations) were then quantified by immunofluorescent staining of the colon. The quantification of lymphoid populations was also performed in the mesenteric lymph nodes (MLNs). Here, we show that the colonization of CRC patients by CoPEC is associated with a decrease of tumor-infiltrating T lymphocytes (CD3⁺ T-cells). Similarly, we demonstrated, in mice, that CoPEC chronic infection decreases CD3⁺ and CD8⁺ T-cells and increases colonic inflammation. In addition, we noticed a significant decrease in antitumor T-cells in the MLNs of CoPEC-infected mice compared to that of controls. Moreover, we show that CoPEC infection decreases the antimouse PD-1 immunotherapy efficacy in MC38 tumor model. Our findings suggest that CoPEC could promote a procarcinogenic immune environment through impairment of antitumor T-cell response, leading to tumoral resistance to immunotherapy. CoPEC could thus be a new biomarker predicting the anti-PD-1 response in CRC.     

The bacterial genotoxin colibactin promotes colon tumor growth by modifying the tumor microenvironment

The gut microbiota is suspected to promote colorectal cancer (CRC). Escherichia coli are more frequently found in CCR biopsies than in healthy mucosa; furthermore, the majority of mucosa-associated E. coli isolated from CCR harbors the pks genomic island (pks+ E. coli) that is responsible for the synthesis of colibactin, a genotoxic compound. We have recently reported that transient contact of a few malignant cells with colibactin-producing E. coli increases tumor growth in a xenograft mouse model. Growth is sustained by cellular senescence that is accompanied by the production of growth factors. We demonstrated that cellular senescence is a consequence of the pks+ E. coli-induced alteration of p53 SUMOylation, an essential post-translational modification in eukaryotic cells. The underlying mechanisms for this process involve the induction of miR-20a-5p expression, which targets SENP1, a key protein in the regulation of the SUMOylation process. These results are consistent with the expression of SENP1, miR-20a-5p and growth factors that are observed in a CRC mouse model and in human CCR biopsies colonized by pks+ E. coli. Overall, the data reveal a new paradigm for carcinogenesis in which pks+ E. coli infection induces cellular senescence characterized by the production of growth factors that promote the proliferation of uninfected cells and, subsequently, tumor growth.     

Tackling the Threat of Cancer Due to Pathobionts Producing Colibactin: Is Mesalamine the Magic Bullet?

Colibactin is a genotoxin produced primarily by Escherichia coli harboring the genomic pks island (pks⁺ E. coli). Pks⁺ E. coli cause host cell DNA damage, leading to chromosomal instability and gene mutations. The signature of colibactin-induced mutations has been described and found in human colorectal cancer (CRC) genomes. An inflamed intestinal environment drives the expansion of pks⁺ E. coli and promotes tumorigenesis. Mesalamine (i.e., 5-aminosalycilic acid), an effective anti-inflammatory drug, is an inhibitor of the bacterial polyphosphate kinase (PPK). This drug not only inhibits the production of intestinal inflammatory mediators and the proliferation of CRC cells, but also limits the abundance of E. coli in the gut microbiota and diminishes the production of colibactin. Here, we describe the link between intestinal inflammation and colorectal cancer induced by pks⁺ E. coli. We discuss the potential mechanisms of the pleiotropic role of mesalamine in treating both inflammatory bowel diseases and reducing the risk of CRC due to pks⁺ E. coli.     

The complex interplay between inflammation,the microbiota and colorectal cancer

The microbiome has captured the attention of scientists from multiple research fields including ecology, immunology, microbiology and cancer biology. The microbial community living in the gastrointestinal tract is the most abundant and diverse niche of the human body and it is not surprising that microbiome research has predominantly focused upon this organ system. In this addendum, we summarize the latest developments in microbiome research on inflammatory bowel diseases and colorectal cancer. In addition, we highlight our recent findings that chronic intestinal inflammation modulates microbial community composition and the development of colorectal cancer. Our findings redefine the paradigm of inflammation-associated cancer by illuminating the key role of bacteria in development of colorectal cancer.