Abstract B004: Investigating loss of ARID1A protein on endometrial cancer progression through the destabilization of adherens junctions

Abstract The purpose of this work is to test the hypothesis that loss of ARID1A promotes endometrial cancer progression by destabilizing tumor cell adherens junctions proteins. ARID1A, an important structural subunit of the SWI/SNF chromatin remodeling complex, is mutated in 26-39% of endometrioid tumors. In endometrial cancer loss of ARID1A has been classically linked to loss of ARID1A expression and has been shown to correlate with increasing tumor grade. However, little is known about the functional impact of ARID1A loss on endometrial cancer progression. A common hallmark of aggressive endometrial cancer is decreased membranous expression of adherens junction proteins, E-Cadherin and β-Catenin. In colorectal and gastric cancer loss of ARID1A expression has been shown to directly downregulate E-Cadherin expression. To determine how loss of ARID1A affects adherens junctions and its impact on endometrial cancer progression we utilized human endometrial cancers and human endometrial cancer cell lines. Using immunohistochemistry, we determined the expression and localization of ARID1A and the adherens junction protein β-Catenin in forty-six human endometrioid type endometrial cancers. Intratumoral heterogeneity of ARID1A expression allowed for quantification of membranous E-Cadherin in relation to presence or absence of ARID1A protein within the same human endometrial tumor. To quantify membranous E-Cadherin we performed immunofluorescence and used line intensity measurements in intratumoral areas of ARID1A presence and ARID1A absence. To assess effects of ARID1A loss on adherens junction in vitro we used short-hairpin RNA to acutely knockdown ARID1A in the endometrial cancer cell lines Ishikawa and ECC-1. Protein expression of ARID1A and E-Cadherin in ARID1A knockdown cells was assessed by Western Blot. Within our cohort of forty-six human endometrial tumors, 75% of tumors with wild-type ARID1A and 45% of tumors with mutated ARID1A had absence of ARID1A protein expression. Due to the discordance between presence of an ARID1A gene mutation and the expression of ARID1A protein, we hypothesize that there are alternative mechanisms of ARID1A protein regulation in endometrial cancer. Additionally, tumors with loss of ARID1A show a trend towards nuclear localization of β-Catenin and have a significant decrease in membranous E-Cadherin expression (P0. 001). However, acute knockdown of ARID1A in Ishikawa and ECC-1 human endometrial cancer cells does not affect total E-Cadherin protein. This suggests that loss of ARID1A may decrease adherens junction stability, as decreased membranous expression of E-Cadherin without total protein change is a common phenotype of destabilized adherens junctions. Thus, we hypothesize that loss of ARID1A destabilizes adherens junctions leading to increased endometrial tumor aggression. Citation Format: Savannah E. Wright, Isurika Weerasinghe, Russell R. Broaddus, Andrew B. Gladden. Investigating loss of ARID1A protein on endometrial cancer progression through the destabilization of adherens junctions abstract. In: Proceedings of the AACR Special Conference on Endometrial Cancer: Transforming Care through Science; 2023 Nov 16-18; Boston, Massachusetts. Philadelphia (PA): AACR; Clin Cancer Res 2024;30 (5Suppl): Abstract nr B004.