Abstract A45: Delineating roles of Pten and Pik3ca in endometrial carcinoma using mouse models
Authors: Joshi Ayesha , Miller Christopher , Ellenson Lora H. 
Published: May 2015

Uterine endometrioid carcinoma (UEC) are indolent cancers often arising in the setting of unopposed estrogen from complex atypical hyperplasia (CAH) the non-invasive precursor. The light microscopic distinction between UEC and CAH on endometrial biopsy or curettage samples is challenging. Given that approximately 25-40% of cases initially diagnosed with CAH progress to UEC, there is a compelling need to identify molecular diagnostic and/or prognostic markers distinguishing CAH from UEC. Mutational profiling of CAH and UEC has revealed distinct molecular differences between the two types of lesions. While PTEN (the most frequently mutated gene in UEC) mutations were found at an equal frequency in both CAH and UEC, PIK3CA mutations were almost exclusively found in UEC. Furthermore, 48% of UEC with PTEN mutations have PIK3CA mutations. With a Pten+/- mouse model, we demonstrated that CAH and UEC completely lose expression of Pten due to loss of heterozygosity (LOH) or intragenic mutations in the wild type allele with similar frequencies in CAH and UEC, suggesting that biallelic inactivation of Pten, though an early event, may not be sufficient for progression to invasive carcinoma and may require additional events such as mutations in Pik3ca. To test this hypothesis and to unravel the role of Pik3ca in UEC, we have used mice with one Pik3ca allele harboring an activating lox-stop-lox E545K mutation (Pik3caE545K/+ mice) and crossed them with PtenloxP/loxP mice. Driving expression of Cre under two epithelial cell-specific promoters, we show that mutant Pik3ca leads to CAH and/or UEC only in the setting of simultaneous biallelic Pten inactivation. Presence of activated Pik3ca alone does not result in hyperplasia or carcinoma. To dissect out molecular mechanisms underlying these observations, primary uterine epithelial cell cultures were prepared from PtenloxP/loxP;Pik3ca+/+, Pten+/+ ; Pik3caE545K/+ and PtenloxP/loxP;Pik3caE545K/+ mice. Pten deletion and/or activation of Pik3ca was achieved in vitro by treatment with adenovirus expressing Cre (Ad-Cre) for 48 hrs. RNA sequencing was performed on RNA extracted from Ad-Cre treated cells. Cells treated with GFP expressing virus were used as control. PtenloxP/loxP;Pik3ca+/+, Pten+/+ ; Pik3caE545K/+ and PtenloxP/loxP;Pik3caE545K/+ cells exhibited distinct and minimally overlapping gene expression profiles, suggesting that Pten inactivation, Pik3ca activation or both lead to different downstream responses. These results, in conjunction with the human studies, support distinct roles for PTEN and PIK3CA mutations in the development and progression of endometrial hyperplasia/carcinoma.

Citation Format: Ayesha Joshi, Christopher Miller, Lora H. Ellenson. Delineating roles of Pten and Pik3ca in endometrial carcinoma using mouse models. [abstract]. In: Proceedings of the AACR Special Conference: The Translational Impact of Model Organisms in Cancer; Nov 5-8, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(11 Suppl):Abstract nr A45.