Abstract 2670: Dedifferentiation-induced oncogenic stemness in the intestinal epithelium: implications in tumorigenesis

In vivo mouse models support stem cells as the cell of origin for cancer in the intestine, while histological evidence from colon cancer patients indicates that dysplasia originates from the mature epithelium. The inherent plasticity of the intestinal epithelium makes both of these scenarios plausible. In the top-down model, tumorigenesis begins at the mucosal surface or villi that consists only of differentiated cells, while in the bottom-up model stem cells in the proliferative crypt compartment initiate the tumor. However, the implications of the differences between the bottom-up and the top-down model on carcinogenesis, if any, are unknown. Consistent with the paradigm of intestinal epithelial plasticity allowing cell fate adaptation, my previous studies have reported dedifferentiation of the villi cells leading to tumorigenic stemness in the Smad4 knockout:β-catenin gain-of-function (Smad4KO:β-cateninGOF) conditional mutant mice. Dedifferentiation in this mutant is marked by the appearance of stem cell markers in the mutant villi, followed by development of structures resembling the proliferative crypts, referred to as ectopic crypts, that eventually develop into tumors; thus mimicking the top-down model of tumorigenesis. Our goal is to understand the implications of tumorigenesis from dedifferentiation as opposed to that from the endogenous crypts. To this end, we analyzed the progressive changes in the mutant intestinal epithelium over time before and after the appearance of ectopic crypts in the villi. We find that dedifferentiation is preceded by an increase in hypoxia - specifically in the villi only. The increase in hypoxia, however, is transient and is not observed in the ectopic crypts or the ensuing tumors, suggesting that certain hypoxia-induced changes that promote tumorigenesis persist even in the absence of hypoxia. Most strikingly, we find that the mutation activates notch signaling in the villi even before the formation ectopic crypts develop. Notch signaling is fundamental to cell fate decision and stem cell function in the intestinal epithelium, but is restricted to the crypts in a normal intestine; thus implicating Notch signaling in the oncogenic stemness in the Smad4KO:β-cateninGOF mutant villi. Since Notch signaling has context-specific functions and is positively regulated by hypoxia, we examined differential effects of the ectopic Notch signaling on tumorigenesis. When compared to the endogenous crypts, we find increased expression of the possible markers of tumor aggressiveness, as well as attenuated negative feed-back regulation of Wnt signaling in the ectopic crypts. We are investigating the underlying mechanism and implications of these findings in tumor progression, employing both in vivo and ex vivo approaches using crypt and villi-derived organoids from the Smad4KO:β-cateninGOF mutant mice. Citation Format: Ansu O. Perekatt, Kylee Wrath, Dahlia Matouba, Christina Li, jeel shah, Connor Mills, Kyle Seabold. Dedifferentiation-induced oncogenic stemness in the intestinal epithelium: implications in tumorigenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2670.