Colorectal cancer (CRC) is a leading cause of cancer-related deaths globally. CRC contains a well-defined cancer stem cell population capable of both self-renewal and differentiation into daughter cells that comprise the bulk of the tumor. It has recently been shown that normal intestinal stem cells are the cell of origin in CRC, as oncogenic mutations activating the Wnt pathway (primarily through genetic inactivation of the APC tumor suppressor) result in tumor formation only when they occur in an intestinal stem cell, and not its differentiated progeny. It is therefore a priority to understand how mechanisms underlying stem cell fate determination in normal intestinal stem cells can become deregulated and contribute to the ontogeny of CRC. Adult stem cells often undergo asymmetric cell fate determination to insure that the proper ratio of stem cells to differentiated cells is maintained during homeostasis. In neuroblasts of Drosophila melanogaster this process is governed by the activity of the Musashi RNA binding protein, whose mammalian orthologs, Msi1 and Msi2, are highly expressed in mammalian intestinal stem cells and in human CRC. We propose that deregulation of Msi proteins alters cell fate determination in CRC such that stem cells expand at the expense of their differentiated progeny, thus resulting in the promotion of aggressive, undifferentiated tumors. This hypothesis will be addressed using genetically altered mice in which Msi protein levels can be modulated in the intestinal stem cells. Initially, we will determin whether Msi gain of function is sufficient to induce stem cell-driven tumorigenesis. To this end, drug inducible Msi1 and Msi2 transgenic mice have been generated, enabling efficient induction of Msi activity with precise spatio-temporal control. To determine whether Msi activity is required for the onset and progression tumorigenesis in the APCmin/+ model of stem cell-driven intestinal cancer, conditional deletion alleles of both Msi1 and Msi2 were generated. Deletion of Msi genes at the onset or during the course of tumor progression will unequivocally determine their functional role in disease ontogeny. Finally, using an in vivo CLIP-Seq approach, we have recently identified a number of Msi1 RNA binding targets associated with regulation of the Wnt pathway and have also observed that Msi genes are activated in response to Wnt signaling in vivo. We will therefore address the hypothesis that Msi is an important effector of Wnt-mediated intestinal transformation and that Msi resides in a negative feedback loop with the Wnt signaling pathway to govern the normal balance between stem cells and their differentiated progeny in the intestine. This study will provide novel insight into the fundamental mechanisms by which stem cell-driven cancers are initiated and progress. Moreover, as cancer stem cells are often resistant to conventional therapeutics such as radiation or chemotherapy and their survival can promote tumor recurrence, we predict that our studies will identify novel therapeutic targets for the treatment of CRC and other stem cell- driven tumors. !

Public Health Relevance

Colorectal cancer is the third leading cause of cancer related deaths in the world and is driven by a well-defined cancer stem cell population capable of both self-renewal and differentiation. We have recently identify the Msi family of RNA binding proteins as potent regulators of developmental potency in somatic stem cells and have developed mouse models to address the hypothesis that Msi deregulation alters intestinal stem cell fate determination thereby contributing to the oncogenic transformation that leads to colorectal cancer. Our findings will identify novel points of therapeutic intervention not only in colorectal cancer, but also in a wide range of stem cell-driven epithelial cancers.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA168654-03
Application #
8677823
Study Section
Cancer Molecular Pathobiology Study Section (CAMP)
Program Officer
Watson, Joanna M
Project Start
2012-08-07
Project End
2017-05-31
Budget Start
2014-06-01
Budget End
2015-05-31
Support Year
3
Fiscal Year
2014
Total Cost
Indirect Cost
Name
University of Pennsylvania
Department
Veterinary Sciences
Type
Schools of Veterinary Medicine
DUNS #
City
Philadelphia
State
PA
Country
United States
Zip Code
19104
Yousefi, Maryam; Nakauka-Ddamba, Angela; Berry, Corbett T et al. (2018) Calorie Restriction Governs Intestinal Epithelial Regeneration through Cell-Autonomous Regulation of mTORC1 in Reserve Stem Cells. Stem Cell Reports 10:703-711
Yousefi, Maryam; Li, Linheng; Lengner, Christopher J (2017) Hierarchy and Plasticity in the Intestinal Stem Cell Compartment. Trends Cell Biol 27:753-764
Kharas, Michael G; Lengner, Christopher J (2017) Stem Cells, Cancer, and MUSASHI in Blood and Guts. Trends Cancer 3:347-356
Cedeno, Ryan James; Nakauka-Ddamba, Angela; Yousefi, Maryam et al. (2017) The histone variant macroH2A confers functional robustness to the intestinal stem cell compartment. PLoS One 12:e0185196
Li, Ning; Yousefi, Maryam; Nakauka-Ddamba, Angela et al. (2016) Heterogeneity in readouts of canonical wnt pathway activity within intestinal crypts. Dev Dyn 245:822-33
Yousefi, Maryam; Li, Ning; Nakauka-Ddamba, Angela et al. (2016) Msi RNA-binding proteins control reserve intestinal stem cell quiescence. J Cell Biol 215:401-413
Li, Ning; Nakauka-Ddamba, Angela; Tobias, John et al. (2016) Mouse Label-Retaining Cells Are Molecularly and Functionally Distinct From Reserve Intestinal Stem Cells. Gastroenterology 151:298-310.e7
Li, Ning; Yousefi, Maryam; Nakauka-Ddamba, Angela et al. (2015) The Msi Family of RNA-Binding Proteins Function Redundantly as Intestinal Oncoproteins. Cell Rep 13:2440-2455
Wang, Shan; Li, Ning; Yousefi, Maryam et al. (2015) Transformation of the intestinal epithelium by the MSI2 RNA-binding protein. Nat Commun 6:6517
Li, Ning; Yousefi, Maryam; Nakauka-Ddamba, Angela et al. (2014) Single-cell analysis of proxy reporter allele-marked epithelial cells establishes intestinal stem cell hierarchy. Stem Cell Reports 3:876-91