Human nuclear Dicer restricts the deleterious accumulation of endogenous double strand RNA

Dicer is a central enzymatic player in RNA interference (RNAi) pathways that acts to regulate gene expression in nearly all eukaryotes. Although the cytoplasmic function of Dicer is well documented in mammals, there is little known about any possible nuclear function. Here we show that Dicer is present in both the nucleus and cytoplasm, but that its nuclear levels are tightly regulated. In its nuclear manifestation Dicer interacts with RNA polymerase II (Pol II) at actively-transcribed gene loci. Loss of Dicer causes the appearance of endogenous dsRNA, leading to induction of the interferon response pathway and consequent cell death. Our results suggest that Pol II-associated Dicer restricts endogenous dsRNA formation from overlapping non-coding RNA transcription units. Failure to do so has catastrophic effects on cell function. Taken together, we present here a micro (mi)RNA independent role for human nuclear Dicer. DICER ChIP-seq profile in wt 293 HEK cells, and dsRNA-seq profile in wt and DICER-depleted 293 HEK cells