Utility of a bacterial infection model to study epithelial-mesenchymal transition, mesenchymal-epithelial transition or tumorigenesis

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DCLK1 and Lgr5 have recently been identified as markers of quiescent and cycling stem cells in the small intestinal crypts, respectively. Epithelial-mesenchymal transition (EMT) is a key development program that is often activated during cancer invasion and metastasis, and also imparts a self-renewal capability to disseminating cancer cells. Utilizing the Citrobacter rodentium (CR)-induced transmissible murine colonic hyperplasia (TMCH) model, we observed a relative decrease in DCLK1 expression in the colonic crypts, with significant shift towards stromal staining at peak (12 days post infection) hyperplasia, whereas staining for Lgr5 and Msi-1 increased several fold. When hyperplasia was regressing (days 20-34), an expansion of DCLK1+ve cells in the CR-infected crypts compared with that seen in uninfected control was recorded. Purified colonic crypt cells exhibiting epigenetic modulation of the transforming growth factor-β (TGFβ), Wnt and Notch pathways on 12 or 34 days post infection formed monolayers in vitro, and underwent trans-differentiation into fibroblast-like cells that stained positive for vimentin, fibronectin and DCLK1. These cells when trypsinized and regrown in soft agar, formed colonospheres/organoids that developed into crypt-like structures (colonoids) in Matrigel and stained positive for DCLK1. Mice exhibiting 12 or 34 days of TMCH were given azoxymethane once for 8 h (Gp1) or weekly for 3 weeks (Gp2), and subjected to crypt isolation. Crypt cells from Gp1 animals formed monolayers as well as colonospheres in soft agar and nodules/tumors in nude mice. Crypt cells isolated from Gp2 animals failed to form the monolayers, but developed into colonospheres in soft agar and nodules/tumors in nude mice. Thus, both hyperplasia and increased presence of DCLK1+ve cells promote cellular transformation in response to a second hit. The TMCH model, therefore, provides an excellent template to study how alterations in intestinal stem cells promote trans-differentiation, crypt regeneration or colon carcinogenesis following bacterial infection.

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