Adenosine-to-inosine (A-to-I) editing of double-stranded RNA (dsRNA) by ADAR proteins is a highly prevalent form of RNA base modification that is essential to distinguish between self and non-self dsRNA. The primary physiological function of ADAR1 is to edit long dsRNA structures in endogenous RNAs, resulting in a change in secondary structure. Non-edited endogenous dsRNA would otherwise be recognised as non-self/viral dsRNA by the innate immune system. In the absence of editing the cytosolic dsRNA sensor MDA5 oligomerises on endogenous dsRNAs leading to the ongoing production of interferon-stimulated genes (ISGs) and a permanent antiviral state that is extremely detrimental. Causative mutations have been identified in both Adar1 and Ifih1 (MDA5) in individuals with the rare auto-inflammatory disease, Aicardi-Goutieres syndrome (AGS).
We have developed a cell culture model for Adar1-editing deficiency which recapitulates the in vivo biology in order to perform a genome-wide CRISPR screen for genes which suppress the immune activation in the absence of editing. We have identified 3 genes that have not previously been implicated in dsRNA sensing pathways which act upstream of MDA5 to modify the requirement for ADAR1-editing. I will present data describing the screening approach and the results including the characterization of the novel pathway. These results have implications for auto-inflammatory conditions such as AGS, as well as cancer where inhibition of ADAR1 is being pursued as a novel therapeutic strategy.