Nucleolar detention of NONO shields DNA double-strand breaks from aberrant transcripts [mNET]

RNA-binding proteins emerge as effectors of the DNA damage response (DDR). The multifunctional non-POU domain-containing octamer-binding protein NONO/p54nrb marks nuclear paraspeckles in unperturbed cells, but also undergoes re-localisation to the nucleolus upon induction of DNA double-strand breaks (DSBs). However, NONO nucleolar re-localisation is poorly understood. Here we show that the topoisomerase-II inhibitor etoposide stimulates the production of RNA polymerase II-dependent, DNA damage-induced nucleolar antisense RNAs (diNARs) in human cancer cells. diNARs originate from distinct nucleolar intergenic spacer regions and form DNA-RNA hybrids to tether NONO to the nucleolus in ab RRM1 domain-dependent manner. NONO occupancy at protein-coding gene promoters is reduced by etoposide, which attenuates pre-mRNA synthesis, enhances NONO binding to pre-mRNA transcripts and is accompanied by nucleolar detention of a subset of such transcripts. The depletion or mutation of NONO interferes with detention and prolongs DSB signaling. Together, we describe a nucleolar DDR pathway that shields NONO and aberrant transcripts from DSBs to promote DNA repair. Overall design: Profile of newly transcribed RNA associated with PolII of cells, with or without etoposide treatment