Abstract 3280: Loss of the tumor suppressor APC in cells expressing lysozyme M results in murine endometrial hyperplasia

Abstract

Abstract The Adenomatous polyposis coli (APC1) tumor suppressor is a multi-function protein that is involved in both the Wnt signaling cascade and cytoskeletal remodeling. Mutations or loss of APC1 can result in defects in cell migration, proliferation, and differentiation. APC frequently collaborates with the canonical Diaphanous-related formin, mDia1 (DIAPH1), which also functions to regulate cytoskeletal dynamics. APC1 and DIAPH1 are genetically linked on Chromosome 5q in a region frequently disrupted in myeloproliferative neoplasms (MPNs). Mice lacking mDia1 (Drf1) and the Apc min mice develop myelodysplastic phenotypes. The physical and functional linkage of APC and mDia1 as 5q tumor suppressors and in cytoskeletal remodeling led us to explore the role of APC in tumor suppression in myeloid-derived cell lineages. We created a mouse which lacks APC in myeloid lineage cells by breeding Apc-flox mice with mice expressing Cre recombinase under the control of lysozyme M (LyzsM) gene promoter. Lysozyme M is expressed in myeloid lineage cells including monocytes, macrophages and granulocytes. Surprisingly, the female mice develop cystic endometrial hyperplasia and are unable to sustain pregnancy. Lysozyme M expression appears to be limited to tissue resident macrophages within the uterus and was not detected in uterine epithelial cells. However, there is a small subset of uterine epithelial cells with increased β-catenin expression, suggesting that these cells lack APC. This subset of cells has elevated expression of cyclin D1, a regulator of cell cycle progression and a downstream effector of Wnt signaling, resulting in increased proliferation. Interestingly, the uterine epithelial cells with increased β-catenin expression also have increased estrogen receptor ≤ (ERα) expression. Estrogen stimulates uterine growth and unopposed estrogen signaling is a hallmark of Type I endometrial cancer. It is unclear if the endometrial hyperplasia seen in these mice is due to lysozyme M expression early on in uterine epithelial cell development or perhaps in a progenitor cell population. A second alternative is that loss of APC in tissue resident myeloid cells residing in the uterine stroma affects epithelial morphology. Regardless, these data suggest that APC plays a role in uterine tissue homeostasis, perhaps even regulating ERα expression. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3280. doi:1538-7445.AM2012-3280