151PD - Arid1A Role in Cell Cycle Regulation and Proliferation in Mouse and Human Gynaecological Tissues Reveals Potential Therapeutic Targets

Abstract

ABSTRACT Aim: Ovarian clear cell carcinoma (OCCC) arises from endometriosis and can be considered an ectopic uterine cancer. ARID1A mutations occur as an early event in 50% of OCCC and 30% of high-grade endometrial cancers. We aimed to characterise the function of ARID1A in the normal uterus and ovary using an Arid1a mouse model and immortalised human ovarian surface epithelium cells. Methods: Arid1a expression during the mouse estrus cycle and its relationship to estrogen (ER), progesterone receptor and proliferation were assayed in a cohort of 28 mice. Illumina Beadchip arrays and MetaCore pathway analysis were used to assay ARID1A-driven transcriptional programmes in mouse uterus and, after siRNA-mediated knockdown, in mouse embryonic fibroblasts (MEF), immortalised human ovarian surface epithelium (IOSE) and JHOC-5 OCCC cells. SRB proliferation assays were performed in MEFs, IOSE and OCCC cell lines. Proliferation in the uterus was assessed 28 days after tamoxifen-induced knockout in Arid1afl/fl ROSA26Cre-ERT2 or wild type (WT) mice. Results: Arid1a expression was not hormonally regulated in the mouse uterus at either the mRNA or protein level, but Arid1a expression was correlated with stromal ER expression (r = 0.6, p = 0.0003). ARID1A-regulated genes in mouse uterus, MEFs and IOSE cells overlapped significantly (p = 1.7x10-13). Pathways involved in the G2/M checkpoint were significantly enriched in all 3 systems. The conserved core transcriptional program included AURKA, PLK1, PLK4, CCNB1 and CCND1. Conversely, genes involved in inflammation and cell adhesion pathways were ARID1A-regulated in JHOC-5 cells. ARID1A knockdown increased proliferation in MEFs, IOSE cells in an HNF1B-dependent manner and in 4 of 6 ARID1A-expressing OCCC cell lines. In vivo knockout in the uterine epithelium resulted in a dramatic increase in Ki67 staining in Arid1afl/fl compared to WT mice. Conclusions: A core ARID1A-driven transcriptional programme, conserved accross normal tissues and species appears to exist, centred around regulation of genes involved in the G2/M checkpoint. ARID1A loss promotes proliferation in normal tissues, providing important clues as to the mechanisms of ARID1A-driven carcinogenesis. Mitotic kinases emerge as potential therapeutic targets in ARID1A mutant tumours, an observation that is not evident from studies in cancer cell lines. Disclosure: All authors have declared no conflicts of interest.