The RNA helicase DDX1 associates with the nuclear RNA exosome and modulates R-loops [RNA-seq]
The RNA exosome is a ten-subunit complex that mediates both RNA processing and degradation. This complex is evolutionarily conserved, ubiquitously expressed, and required for fundamental cellular functions, including rRNA processing. The RNA exosome plays many roles in regulating gene expression and protecting the genome, including modulating the accumulation of R-loops at sites of transcription. The RNA exosome interacts with specific target RNAs for decay or processing by interacting proteins termed cofactors. Attributing to the essential function of the RNA exosome for processes critical in all cells, such as production of mature rRNA, missense mutations in structural subunit genes of this complex cause neurological diseases. One possibility for why point mutations cause neurological diseases is that the RNA exosome partners with cell- or tissue-specific protein cofactors. Here, we employed a murine neuronal cell line (N2A) and performed immunoprecipitation of the RNA exosome subunit, EXOSC3, followed by mass spectrometry to obtain a snapshot of the RNA exosome interactome. We validated an interaction with DDX1, a putative RNA helicase. DDX1 plays roles in double-strand break repair, rRNA processing, and RNA metabolism. To explore shared functions of EXOSC3 and DDX1, we investigated the interaction after inducing DNA damage, and performed DNA/RNA immunoprecipitation followed by sequencing (DRIP-Seq) and RNA-seq on N2A cells depleted of either EXOSC3 or DDX1. These findings suggest that EXOSC3 and DDX1 function together in the absence of severe DNA damage to modulate spontaneous events such as RNA-DNA hybrid (R-loop) formation. Overall design: RNA profiles of DDX1 or EXOSC3 knockdown N2a cells