Abstract 1413: BRCA1 loss is synthetic lethal with double stranded RNA: A genome wide CRISPR screen to identify mechanisms of RNASEL independent death
Authors: Trastulli Deborah , Vozza Gianluca , Pinamonti Veronica , Mazzarella Luca 
Published: March 2024

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. RNASEL-KO A549 cells were, as expected, refractory to IFN+pI:C induced cell death; however, inhibiting protein synthesis or RNA transcription with Cycloheximide (CHX) or Actinomycin D (ActD) abolished the need for RNASEL causing RNASEL-KO cells to undergo apoptosis, although CHX/ActD alone had no effect. In addition, HT-29 cells revealed no clear dependence on RNASEL for dsRNA-induced cell death. Transient ablation through siRNA showed that this novel death-inducing pathway is independent of other canonical dsRNA sensors such as RIG-I, MDA5 and PKR. We then 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 validated the synthetic lethality of IFN+pI:C with BRCA1 by CRISPR. 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: Deborah Trastulli, Gianluca Vozza, Veronica Pinamonti, Luca Mazzarella. BRCA1 loss is synthetic lethal with double stranded RNA: A genome wide CRISPR screen to identify mechanisms of RNASEL independent death [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1413.