Abstract 5435: Role of the WT1 transcription factor in high-grade serous ovarian cancer
Authors: Rodriguez-Malave Norma I. , Kanska Justyna E. , Vavra Kevin C. , Hazelett Dennis , Corona Rosario I. , Seo Ji-Heui , Freedman Matthew , Knott Simon R. , Orsulic Sandra , Karlan Beth Y. , Lawrenson Kate , Gayther Simon A. 
Published: August 2018

Abstract
The Wilms Tumor protein 1 (WT1) transcription factor (TF) is a ubiquitous biomarker of high-grade serous ovarian carcinoma (HGSOC), which is the most common and aggressive subtype of epithelial ovarian cancer (EOC). This TF interacts with a host of cellular factors including the tumor suppressor P53, which is mutated in virtually all HGSOC cases. Studies have suggested a role for WT1 in HGSOC development, but little is known about the underlying mechanism. We have generated unique catalogues of epigenomic landscapes (specifically H3K27ac) in primary HGSOC using chromatin immunoprecipitation sequencing (ChIP-seq). Using Bayesian analyses of H3K27ac profiling in HGSOCs, we identified significant tissue specific enrichment of active chromatin at the WT1 locus in HGSOC when compared to all other EOC tumor histotypes. Furthermore, this locus contains a superenhancer in HGSOCs and in normal fallopian tube secretory epithelial cells (FTSECs). This locus features a bidirectional promoter that is shared by WT1-AS lncRNA and that contains a WT1 binding site. LncRNAs are essential in many cellular processes, and have been shown to play pivotal roles in tumorigenicity. The WT1-AS lncRNA is implicated in other diseases but little is known of its function in EOC. We have investigated the mechanisms of interaction between WT1 and WT1-AS. We observed that both protein and transcript expression for WT1 and WT1-AS are positively correlated in HGSOC cell lines. Analysis of data for &gt;400 primary HGSOCs from TCGA further supported this correlation. We hypothesized that WT1 is a critical TF in the development of HGSOC, and that WT1-AS plays a key role in its regulatory pathway. We evaluated the regulatory role of WT1 first by analyzing cellular phenotypes and target gene expression changes in HGSOC cell lines after shRNA mediated knockdown (KD) of WT1. HGSOC cells with stable WT1 knockdown had impaired proliferation and concomitant reduction of WT1-AS expression. We also identified a decrease in expression of SHMT1 in WT1 KD cells, which is a known WT1 target gene. Integrated genome-wide analysis of the WT1 transcriptome by RNA-seq and the WT1 cistrome by ChIP-seq, in parallel with ChIP-MS, is being used to establish the architecture of the WT1 regulome, specifically to establish the regulatory mechanisms and relationships between WT1 and WT1-AS. Ultimately, these studies aim to establish the mechanisms of action for the WT1 TF in neoplastic transformation of HGSOC.
Citation Format: Norma I. Rodriguez-Malave, Justyna E. Kanska, Kevin C. Vavra, Dennis Hazelett, Rosario I. Corona, Ji-Heui Seo, Matthew Freedman, Simon R. Knott, Sandra Orsulic, Beth Y. Karlan, Kate Lawrenson, Simon A. Gayther. Role of the WT1 transcription factor in high-grade serous ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5435.