Double-stranded RNA (dsRNA) is a conspicuous molecular signature which innate immune activators use to detect viruses. However, it is also a pervasive feature of the cellular transcriptome. Understanding the pathways that protect cells from auto-inflammatory responses to self dsRNA while maintaining immunity to viruses is critical to a range of health conditions.
Adenosine-to-inosine (A-to-I) editing of double-stranded RNA (dsRNA) by ADAR1 is a highly prevalent form of RNA modification that is essential to distinguish between self and non-self dsRNA. In the absence of A-to-I editing by ADAR1 the cytosolic dsRNA sensor MDA5 oligomerises on endogenous unedited dsRNAs and activates interferon signalling. We have developed a cell culture model to screen for new regulators of dsRNA following loss of ADAR1-mediated editing.
We performed a genome-wide loss of function screen to identify genes that are required for innate immune activation by unedited endogenous dsRNAs. We identified known regulators of interferon pathways but also many hits not previously associated with the dsRNA response. Three candidates, GGNBP2, CNOT10 and CNOT11 were far more enriched than any known regulators and form a protein complex. When these candidates are deleted, the interferon response induced by the loss of ADAR1 is prevented, suggesting they play essential roles in dsRNA regulation. Interestingly, GGNBP2 KO cells can still respond to exogenous dsRNA and interferon indicating it plays a cell intrinsic role in dsRNA regulation. Transcriptome profiling suggests GGNBP2 modifies the expression and nuclear/cytoplasmic distribution of cellular transcripts normally subjected to A-to-I editing. These results have implications for auto-inflammatory conditions such as Aicardi-Goutieres Syndrome caused by mutations in ADAR, as well as cancer where inhibition of ADAR1 is being pursued as a novel therapeutic strategy.