Interplay of IMP1 and autophagy in intestinal barrier function and tumorigenesis

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 DESCRIPTION (provided by applicant): The intestinal epithelium has an exquisite equilibrium between proliferation and differentiation. Two stem cell populations reside in the crypts and are involved in homeostasis and adaptive responses to stressors, such as inflammation (as in inflammatory bowel disease) and tumorigenesis (colorectal cancer, CRC). It is clear there is interplay between aberrations in epithelial homeostasis and tumorigenesis. Recent discoveries of genetic mutations that promote or suppress CRC have guided development of therapeutic strategies, yet CRC deaths remain elevated, suggesting that additional pathways or molecular mediators are involved. This proposal will examine a new pathway that may contribute to CRC initiation or progression, as well as provide new insights into intestinal epithelial homeostasis and barrier function. Igf2-mRNA binding protein 1 (IMP1) is expressed highly during embryonic development and cancer. IMP1 stabilizes mRNAs, including Igf2, cMyc, and Kras. Our group recently demonstrated that overexpression of IMP1 enhances tumor growth, cancer stem cell marker expression, and decreased E-cadherin (important for cell-cell contacts), in CRC xenograft models. We also have novel preliminary data suggesting that modulation of IMP1 in CRC cells alters expression of autophagic proteins. Autophagy is a process by which cells breakdown organelles or intracellular components during situations of stress, such as cellular damage, inflammation, or cancer. Autophagy can be tumor suppressive or oncogenic. The role of IMP1 in modulating autophagy in homeostasis and cancer is unknown. It is also unknown whether IMP1-expressing cells directly initiate tumor formation, or promote progression through direct augmentation of autophagy-, EMT- or cell differentiation-associated pathways. We hypothesize that IMP1 mediates intestinal barrier function and tumorigenesis via modulation of autophagy. We will test this hypothesis through two interrelated Specific Aims. In Aim 1 we will use cell lines and genetic mouse models to define the functional roles of IMP1 and autophagy in normal barrier function and precancerous inflammation. Specifically, we will utilize lentiviral systems to generate Caco-2 cell lines with IMP1 overexpression or knockdown, generate intestinal enteroids from WT; Imp1fl/fl or VillinCre; Imp1fl/fl mice, and induce acute intestinal damage in WT; Imp1fl/fl or VC; Imp1fl/fl mice using dextran sodium sulftate (DSS). All systems will be interrogated for effects on autophagy using Cyto-ID, trans-epithelial resistance measures in cultured cells, and in vivo permeability assays. In Aim 2 we will define the functional roles of IMP1 and autophagy in tumor initiation and progression. This will be achieved using the AOM/DSS model of inflammation-associated cancer in WT; Imp1fl/fl or VC;Imp1fl/fl mice and the role of IMP1-positive cells in tumor initiation will be assessed by crossing our IMP1 reporter model (Imp1EGFP;DTR;CreER) with Apcflfl mice to examine tumor initiation. In aggregate, these studies will provide new insights into roles of IMP1 in barrier function and tumor initiation/progression. These results will provide a platform for potential translational applications.