Abstract B025: A genome-wide CRISPR screen identifies synthetic lethality of double-stranded RNA with BRCA1 loss

Abstract Double-stranded RNAs (dsRNAs) are potent immunostimulatory nucleic acids of viral origin but also physiologically produced by mammalian cells. Recent studies demonstrated that elevating dsRNA levels, either exogenously through dsRNA mimetics like Polyinosinic-polycytidylic acid (pI:C) or endogenously through epigenetic modulation of retroviral elements, can elicit anticancer effects. In response to dsRNA, cells elicit a dual response consisting in Interferon (IFN) production and translational shutdown associated, in some cells, with cell death. These two responses are linked in a feed-forward loop in which induced cytokines themselves enhance dsRNA sensing by the death-inducing pathway, complicating our understanding of the cell-intrinsic mechanisms at play. The 2',5'-oligoadenylate synthetase (OAS)-RNASEL system is widely thought to be the main responsible for dsRNA-induced cell death, but it remains unclear how its activity leads to cell death. To elucidate these mechanisms, we decided to minimize the impact of interferon modulation by studying dsRNA-induced death in interferon-saturated conditions. We performed a genome-wide CRISPR screen for factors involved in dsRNA-induced death in our interferon-saturated conditions in HT29 cells. Pathway enrichment analysis of screen hits revealed that RNA surveillance, RNA Polymerase II Transcription Initiation, Mitochondrial translation and respiratory chain and DNA Repair genes have a protective role against dsRNA increase. In particular, we identifiedBRCA1 but not BRCA2 as a candidate hit. The differential sensitivity of BRCA1-KO cells was subsequently validated in cloncal populations. Ongoing research is aimed at validating this interaction in vivo models. Our work shed light on potential new mechanisms involved in dsRNA dependent cell death, revealing a connection with DNA damage and BRCA1. If confirmed, these findings may pave the way for the use of dsRNA mimetics, possibly in conjunction with immune checkpoint inhibitors, in the treatment of BRCA1-mutated tumors. Citation Format: Luca Mazzarella, Deborah Trastulli, Sara Galavotti, Gianluca Vozza, Veronica Pinamonti, Nunzia Zagaria. A genome-wide CRISPR screen identifies synthetic lethality of double-stranded RNA with BRCA1 loss [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Expanding and Translating Cancer Synthetic Vulnerabilities; 2024 Jun 10-13; Montreal, Quebec, Canada. Philadelphia (PA): AACR; Mol Cancer Ther 2024;23(6 Suppl):Abstract nr B025.