Abstract 876: Proximity labeling reveals a role for ADAR and DDX54 in suppressing dsRNA sensing in breast cancer

Abstract

The RNA editing enzyme ADAR has been identified as a therapeutic target for multiple cancers. Through its A-to-I editing activity the p150 isoform of ADAR suppresses activation of dsRNA sensors involved in the innate immune response and translational repression. Recently, our laboratory has shown that p150-ADAR is required for the viability of a subset of triple-negative breast cancer cell lines, thus making p150-ADAR a strong therapeutic target for a disease that lacks targeted therapies. Unlike the p150 isoform, which is interferon inducible, the p110 isoform of ADAR is ubiquitously expressed and has not been shown to suppress dsRNA sensing. To date there is much less known about the role of p110-ADAR in cancer, though it is known to be highly expressed in breast cancer. To begin to explore the role of p110-ADAR in breast cancer, we turned to proximity labeling by APEX2 to identify proteins that may interact with p110-ADAR. Mass-spectrometry of proximity labeled proteins revealed numerous nuclear and nucleolar proteins with roles in multiple aspects of RNA biology, including processing of rRNA and ribosome biogenesis. Among the list of enriched proteins were eight members of the DEAD-box RNA helicase family, including the nucleolar localized DDX54. Co-immunoprecipitation confirmed that p110-ADAR and DDX54 interact, furthermore both localize to nucleoli. Knockdown of DDX54 in non-TNBC cell lines (SK-BR-3 and MCF-7) caused apoptosis and reduced proliferation. Additionally, knockdown of DDX54 caused accumulation of dsRNA within the nucleolus and activation of the dsRNA sensor PKR. Knockdown of ADAR, which alone did not affect proliferation or phosphorylation of PKR in the above cell lines, synergized with DDX54 knockdown to cause increased cell death and further activation of PKR. ADAR knockdown did not synergize with knockdown of another ADAR-interacting DEAD-box helicase, DDX17, suggesting that the observed phenotype is not common to combined knockdown of ADAR and any RNA helicase. These findings suggest that combined inhibition/depletion of ADAR and DDX54 may serve as therapeutic strategy for breast tumors, including those that are refractory to ADAR inhibition/depletion alone. Citation Format: Kyle A. Cottrell, Sua Ryu, Luisangely Soto Torres, Angela Schab, Jason D. Weber. Proximity labeling reveals a role for ADAR and DDX54 in suppressing dsRNA sensing in breast cancer [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 876.