The cytolethal distending toxin modulates cell differentiation and elicits epithelial to mesenchymal transition

Abstract We are frequently exposed to bacterial genotoxins, such as cytolethal distending toxin (CDT), a prevalent heterotrimeric toxin whose active moiety is its CdtB subunit. CdtB triggers potent DNA damage, predisposing factors in the development of cancers, in host cells. CDT from Helicobacter hepaticus , a mouse pathogen, was shown to be directly involved in the development of murine hepatocarcinoma. Preliminary studies have shown that CDT induces certain phenotypes reminiscent of epithelial to mesenchymal transition (EMT), a process by which cells lose their epithelial characteristics in favor of mesenchymal ones, conducive to cell motility. In the present study, we investigated the different steps of EMT using liver tissues of mice infected with H. hepaticus , as well as human epithelial cell lines and xenograft mouse models following H. hepaticus CdtB expression. Most of the different steps of the EMT process were reproduced throughout the studied models. Indeed, microarray data showed a CdtB- dependent regulation of EMT-related transcripts. The key transcriptional regulators of EMT (SNAIL1 and ZEB1) and EMT markers (Vimentin, Fibronectin and α5β1 integrin) were upregulated both at RNA and protein levels in response to CdtB. It also induced cell-cell junctions’ disassembly, causing individualization of cells and acquisition of a spindle-like morphology. CdtB activated the expression and activity of matrix metalloproteases and increased cell motility. This study demonstrated that CDT/CdtB elicits EMT process activation, supporting the idea that infection with genotoxin-producing bacteria can promote malignant transformation. Author Summary We are frequently exposed to infection with genotoxin--producing bacterial from the gut microbiota, such as cytolethal distending toxin (CDT). CDT, via its active CdtB subunit, causes severe DNA damage in host cells, well-known risk factor of cancer development and progression. Chronic infection with CDT-producing bacteria is thus involved in cancer development. CDT is widespread among many bacteria and its impact in human cancer seems likely underestimated. Despite its major significance, CDT remains little studied. Here, we showed that cells exposed to CdtB are no longer cohesive, become individualized and acquire a spindle-shaped morphology known to be conducive to migration. These cells also express increased level of mesenchymal markers, as well as increased level of SNAIL1 and ZEB1, two key transcription factors orchestrating a crucial mechanism for cancer initiation and progression: epithelial to mesenchymal transition. These effects induced by CdtB were associated with increased matrix metalloproteinases degrading activity and emergence of cellular motility. Collectively, these data showed that CdB activates epithelial to mesenchymal transition, supporting the role of CDT in tumorigenesis.