Abstract 3886: 3D genome conformation analysis in ST-EPN-ZFTA ependymoma identifies RCOR2 as a potential target
Authors: Camgöz Aylin , Okonechnikov Konstantin , Chapman Owen , Maurmann Monika , Buchholz Frank , Pfister Stefan , Chavez Lukas , Kool Marcel 
Published: June 2022

Abstract
Ependymoma (EPN) is a tumor of the central nervous system that occurs in children and adults. Childhood EPNs are one of the most aggressive pediatric brain tumors, arising both in infratentorial and supratentorial (ST) regions of the brain. Molecular profiling has identified distinct subgroups of ependymomas, including ST-EPN-ZFTA and PF-EPN-A as the most common and most aggressive ones in children. To this date, the only curative and indispensable treatment option is surgical resection followed by radiation. Unfortunately, there are no targeted therapies in clinical use. However, EPN cells have been extremely difficult to culture and expand in vitro, which explains why molecular studies on EPN cells have been hampered. This shortcoming has recently been overcome by establishing EPN models including human cell lines and organoids as well as patient derived xenografts (PDX). 3D genome conformation analysis has emerged as a powerful approach to understand tumor development and to identify novel drug targets for the treatment of different tumors. In this project we have used genome-wide chromosome conformation capture (Hi-C), complemented with H3K27ac (active enhancers) as well as gene expression in primary ependymoma tumors and cell lines to identify regulatory mechanisms underlying aberrant expression of genes that are essential for ependymoma tumorigenesis. Results of this study showed that the fusion between ZFTA and RELA leads to the formation of new regulatory environments that are recurrently associated with aberrant overexpression of RCOR2 only in ST-EPN-ZFTA ependymoma cells. Indeed, compared to all other ependymoma subgroups as well as to normal brain, RCOR2 is significantly upregulated only in ST-EPN-ZFTA patient samples. To test oncogenic relevance of RCOR2 for growth and maintenance, we depleted RCOR2 by RNAi and observed a strongly reduced cell survival in several ST-EPN-ZFTA cell lines but not or to a lesser extent in PF-EPN-A cells. Since RCOR2 is an adaptor protein lacking enzymatic activity, we looked at the expression of the proteins known as an interacting partner of RCOR2. Lysine-histone demethylase 1 (LSD1) is one of them and its expression in ST-EPN-ZFTA significantly correlates with RCOR2 expression. We therefore hypothesized that ST-EPN-ZFTA cells may be sensitive to LSD1 depletion, too. Indeed, depletion of LSD1 by RNAi resulted in a strong growth inhibition in ST-EPN-ZFTA cells, but not in PF-EPN-A cells. However, none of the tested LSD1 inhibitors exerted anti-proliferative activity at clinically reachable doses in the ST-EPN-ZFTA cells indicating a potential LSD1 non-enzymatic function in this particular tumor type. In summary, our study nominates RCOR2 as a oncogenic gene specific for ST-EPN-ZFTA ependymomas. Current studies focus on the identification of other interacting partners of the RCOR2-LSD1 complex and how to target these for therapeutic approaches.
Citation Format: Aylin Camgöz, Konstantin Okonechnikov, Owen Chapman, Monika Maurmann, Frank Buchholz, Stefan Pfister, Lukas Chavez, Marcel Kool. 3D genome conformation analysis in ST-EPN-ZFTA ependymoma identifies RCOR2 as a potential target [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3886.