Abstract AP23: EARLY LOSS OF MONOUBIQUITYLATION OF HISTONE H2B ALTERS KEY IMMUNE SIGNALING PATHWAYS PROMOTING THE PROGRESSION OF HIGH-GRADE SEROUS OVARIAN CANCER
Authors: Hooda Jagmohan , Novak Marián , Salomon Matthew P. , MacDuffie Emily , Song Melissa , Lester Jenny , Parkash Vinita , Karlan Beth Y. , Oren Moshe , Hoon Dave S. , Drapkin Ronny 
Published: June 2021

Abstract
High-grade serous ovarian carcinoma (HGSOC) is the most common form of ovarian cancer, accounting for over 70% of all cases. HGSOC is frequently complicated by the inevitable development of therapeutic resistance, and thus remains an incurable disease. Recent insights supporting the fallopian tube epithelium (FTE) as the point of origin for HGSOC and the serous tubal intraepithelial carcinoma (STIC) as the precursor lesion for a majority of HGSOCs provide the necessary context to study the mechanisms that drive the development and progression of HGSOC. Understanding these key molecular processes is essential to inform the development of next generation therapies. In this study we investigated the role of the ubiquitin ligase RNF20 and histone H2B monoubiquitylation (H2Bub1) in serous tumorigenesis. H2Bub1, catalyzed largely by RNF20, is an epigenetic mark with tumor suppressor properties. The loss of RNF20/H2Bub1 has been linked with cancer progression. We used immunohistochemistry to characterize the expression of H2Bub1 in HGSOC and FTE precursors. We found that H2Bub1 is lost or downregulated in a large proportion of STICs and HGSOC tumors, implicating RNF20/H2Bub1 loss as an early event in serous tumorigenesis. Consistent with our findings, analysis of TCGA data shows that the majority of HGSOCs exhibit heterozygous loss of RNF20. Functionally, we demonstrate that shRNA-mediated knockdown of RNF20, with concomitant loss of H2Bub1, is sufficient to increase cell migration and clonogenic growth, both in 2D and 3D, of immortalized FTE cells. To understand the mechanisms underlying these effects, we performed ATAC-seq and RNA-seq in RNF20 knockdown cells. Interestingly, major changes were observed in a number of immune signaling pathways, providing early mechanistic insights for the observed oncogenic phenotypes. Using ELISA we confirmed the upregulation of IL6 and other cytokines in RNF20 knockdown cells. Additionally, we confirmed that the oncogenic phenotype, enhanced migration, is in part driven by the increased levels of IL6 in RNF20 and H2Bub1 knockdown cells which can be neutralized by using an anti-IL6 antibody. In summary, our study identifies that loss of H2Bub1 is an early epigenetic event in HGSOC that rewires certain immune signaling pathways and may represent unique therapeutic opportunities.
Citation Format: Jagmohan Hooda, Marián Novak, Matthew P. Salomon, Emily MacDuffie, Melissa Song, Jenny Lester, Vinita Parkash, Beth Y. Karlan, Moshe Oren, Dave S. Hoon, and Ronny Drapkin. EARLY LOSS OF MONOUBIQUITYLATION OF HISTONE H2B ALTERS KEY IMMUNE SIGNALING PATHWAYS PROMOTING THE PROGRESSION OF HIGH-GRADE SEROUS OVARIAN CANCER [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr AP23.