Zfp106 binds to G-quadruplex RNAs and inhibits RAN translation and formation of RNA foci caused by G4C2 repeats

Expansion of intronic GGGGCC repeats in the C9orf72 gene causes amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Transcription of the expanded repeats results in the formation of RNA-containing nuclear foci and altered RNA metabolism. In addition, repeat-associated non-AUG (RAN) translation of the expanded GGGGCC-repeat sequence results in the production of highly toxic dipeptide-repeat (DPR) proteins. GGGGCC-repeat-containing transcripts form G-quadruplexes, which are associated with formation of RNA foci and RAN translation. Zfp106, an RNA-binding protein essential for motor neuron survival in mice, suppresses neurotoxicity in a Drosophila model of C9orf72 ALS via a previously unknown mechanism. Here, we show that Zfp106 inhibits formation of RNA foci and significantly reduces RAN translation caused by GGGGCC-repeats in mammalian cells. Further, we show that Zfp106 binds to RNA G-quadruplexes and causes a conformational change in the G-quadruplex structure formed by GGGGCC-repeats. These data suggest that Zfp106 suppresses GGGGCC repeat-mediated cytotoxicity through alteration of the repeats G-quadruplex structure.