Etude des voies de signalisation cellulaire modulées par les génotoxines bactériennes

Certain bacteria producing Cytolethal Distending Toxin (CDT) and colibactin are linked to cancers, particularly colorectal cancer. These toxins directly damage host cell DNA and impair the DNA damage response, leading to genomic instability and mutation accumulation that can be transmitted to daughter cells, potentially promoting carcinogenesis. These genotoxins are increasingly recognized for their critical roles in manipulating host cellular signaling pathways. The aim of the thesis was to evaluate the modulation of two major signaling pathways in the host cellular response to genotoxin exposure: the Hippo-YAP/TAZ-TEAD pathway and the Wnt/β-catenin pathway.The Hippo signaling pathway, which plays a crucial role in regulating cell proliferation, survival, and genomic stability. Some phenotypes induced by these genotoxins (actin cytoskeleton remodeling, stress fibers accumulation, disturbance of focal adhesion, cell-cell junctions’ disassembly, increased ploidy and genome instability, endoreplication) are known to involve the Hippo signaling pathway. This suggests a link between some of the effects induced by these toxins and Hippo signaling pathway. We investigated the Hippo pathway in normal and cancer-derived epithelial intestinal and hepatic cell lines following exposure to CDT/CdtB and colibactin. We demonstrated that active CdtB subunit of CDT modulates the expression of transcripts and proteins related to the Hippo pathway’s central downstream transcriptional coactivators YAP/TAZ. Exposure to CDT/CdtB led to increased TEAD-mediated transcription , as confirmed by the upregulation of direct TEAD target genes. Inhibition of YAP/TAZ binding to TEADs using verteporfin and K-975 dampened the effects of CdtB, particularly regarding DNA damage and repair, and increased ploidy. These findings suggest that YAP/TAZ-TEAD signaling is involved in increased ploidy in cells that survive DNA damage induced by CDT/CdtB.Furthermore, exposure to colibactin, a genotoxic metabolite produced by Escherichia coli, induced similar effects. Overall, our data indicate that infection with genotoxin-producing bacteria involves the YAP/TAZ-TEAD signaling pathway to regulate ploidy following DNA damage in epithelial cells.The second part of our study focused on how bacterial genotoxins affect the Wnt/β-catenin signaling pathway, another key regulator of cell fate, proliferation, and differentiation. Following CDT/CdtB exposure, we observed increased phosphorylation of β-catenin at serine 552, accompanied by its loss from adherens junctions, leading to destabilization of cell-cell junction. This resulted in the release of β-catenin into the cytoplasm and nucleus translocation. Ultimately, this led to the activation of TCF/LEF-dependent transcription, a crucial downstream event of Wnt/β catenin signaling, as well as the upregulation of some direct β catenin target genes. Importantly, inhibition of AKT signaling, either directly with MK 2206 or indirectly through AMPK activation by metformin, reduced many of these CDT/CdtB-induced effects. These effects include β-catenin Ser552 phosphorylation and its nuclear accumulation, which in turn decreased TCF/LEF transcriptional activity. Additionally, both MK 2206 and metformin protected from CdtB-induced disruption of cell-cell junctions, increased nuclear accumulation of SNAIL, enhanced matrix degradation, and the augmented cellular motility. The use of these inhibitors revealed that phosphorylation of β-catenin at serine 552 following CdtB exposure involves AKT activation. Overall, these data show that infection with genotoxin-producing bacteria regulates some epithelial to mesenchymal transition features through β catenin-dependent signaling.Together, these findings demonstrate that bacterial genotoxins modulate host cell signaling through both the Hippo-YAP/TAZ-TEAD and Wnt/β-catenin pathways.