Abstract B010: The NuRD subunit CHD4 is essential for ewing sarcoma cell survival as it regulates global chromatin architecture
Authors: Marques Joana Graca , Pavlovic Blaz , Ngo Quy Ai , Pedot Gloria , Roemmele Michaela , Volken Larissa , Wachtel Marco , Schäfer Beat W. 
Published: September 2022

Abstract
Ewing sarcoma tumorigenesis is tightly linked to epigenetic deregulation. Indeed, the aberrant fusion transcription factor and tumor driver EWS-FLI1 produces extensive rewiring of the cancer cell epigenome. At enhancers containing canonical ETS motifs, the fusion protein represses gene expression but, when binding to GGAA repeats, EWS-FLI1 induces transcription by recruiting activating epigenetic regulators such as the acetyltransferase p300 and the BAF chromatin remodeling complex. The nucleosome remodeling and deacetylase (NuRD) complex is an ATP-dependent multi-subunit complex that modulates chromatin architecture and regulates DNA damage repair, genome stability and gene expression. In Ewing sarcoma, NuRD subunits, such as LSD1, have been suggested to interfere with EWS-FLI1 activity and prevent tumor progression. Hence, we here aimed to comprehensively study the role of NuRD in Ewing sarcoma pathogenesis. First, we performed a NuRD-centered, negative selection, CRISPR/Cas9 screen and identified the chromatin remodeling helicase CHD4 as essential for Ewing sarcoma tumor cell survival. Validation assays using two doxycycline-inducible shRNAs targeting CHD4 demonstrated that silencing of this remodeler in fact drastically reduces tumor cell proliferation and completely prevents colony formation. This cell proliferation impairment was caused by an induction of cell death by apoptosis and not by cell cycle arrest. Surprisingly, this cell death phenotype was not linked to impaired fusion protein activity. CHD4 and NuRD, despite primarily locating to enhancers and super-enhancers in Ewing sarcoma cells, did not preferentially localize to GGAA repeats, unlike EWS-FLI1. Moreover, RNA sequencing assays performed upon CHD4 silencing showed that this ATPase does not regulate the EWS-FLI1 signature. As CHD4 is a chromatin remodeler able to move nucleosomes along the DNA, we performed ATAC sequencing experiments to investigate changes in chromatin status that could explain the dependency of Ewing sarcoma cells on CHD4 for survival. We observed that CHD4 depletion from Ewing sarcoma cells causes a drastic and global chromatin relaxation which renders tumor cells prone to DNA damage and increasingly sensitive to DNA damaging agents. Interestingly, augmented sensitivity to DNA damage was not observed by silencing CHD4 in non-tumorigenic human fibroblasts. Finally, CHD4 depletion also reduced Ewing sarcoma tumor growth in vivo and prolonged mice survival. In conclusion, we demonstrate for the first time that CHD4 is crucial for Ewing sarcoma cell survival and highlight this helicase as a promising therapeutic target for Ewing sarcoma with potential for combination therapy with drugs inducing DNA damage. Importantly, this work has initiated ongoing efforts to develop first-in-class small molecules specifically targeting CHD4 which will be crucial for the future validation of this ATPase as a viable target with clinical application.
Citation Format: Joana Graca Marques, Blaz Pavlovic, Quy Ai Ngo, Gloria Pedot, Michaela Roemmele, Larissa Volken, Marco Wachtel, Beat W. Schäfer. The NuRD subunit CHD4 is essential for ewing sarcoma cell survival as it regulates global chromatin architecture [abstract]. In: Proceedings of the AACR Special Conference: Sarcomas; 2022 May 9-12; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(18_Suppl):Abstract nr B010.