Demonstrating a Role for Nuclear APC in Intestinal Cellular Differentiation

Abstract

Colon cancer is the second leading cause of cancer‐related mortality in the United States, resulting in over 50,000 deaths annually. Approximately 80% of colon cancers begin with a mutation in the gene coding for the tumor suppressor, Adenomatous Polyposis Coli, APC. Facilitated by two nuclear localization signals (NLS) and multiple nuclear export signals, APC protein can shuttle between the cytoplasm and the nucleus of cells. To understand the functions of nuclear APC, our lab generated a knock‐in mouse model with mutations introduced that inactivate both Apc NLS, thus dramatically decreasing their amount of nuclear Apc. We have previously shown increased proliferation and Wnt target gene expression in intestinal epithelial cells from ApcmNLS/mNLS mice, suggesting a role for nuclear APC in inhibition of proliferation and Wnt signaling. Here we examine the role of nuclear Apc in intestinal epithelial differentiation and stem cell homeostasis. Paraffin‐embedded tissue from the intestines of Apc+/+ and ApcmNLS/mNLS mice was sectioned and stained for markers of enterocytes (alkaline phosphatase), goblet cells (alcian blue), enteroendocrine cells (chromogranin A) and Paneth cells (lysozyme C). Quantification of positive cells indicated that ApcmNLS/mNLS mice had fewer differentiated enterocytes, goblet cells, and Paneth cells, yet more enteroendocrine cells than their wild‐type littermates. Together, these data support a role for nuclear Apc in promoting enterocyte, goblet cell, and Paneth cell differentiation while inhibiting enteroendocrine cell differentiation. No significant change was observed in quiescent stem cell (DCAMKL‐1) populations. Information gathered from this analysis will contribute to our understanding of the mechanism of intestinal differentiation and tumorigenesis.