Stable interaction of NONO with DBHS family members upon etoposide-induced DNA damage

The Non-POU domain containing octamer binding (NONO) protein is a member of the multifunctional Drosophila behavior/human splicing (DBHS) protein family and a core component of nuclear paraspeckles. NONO forms dimers with the other two DBHS members splicing factor proline and glutamine rich (SFPQ) protein or the paraspeckle component 1 (PSCP1) to modulate RNA metabolism and gene expression both at the transcriptional and post-transcriptional level. Increasing evidence suggests that NONO participates in genome maintenance by stimulating the DNA damage response (DDR) upon induction of DNA double-strand breaks (DSBs). However, the molecular principles that engage NONO in genome stability are poorly understood. We hypothesized that the induction of DSBs alters NONO protein-protein interactions and applied label-free mass spectrometry to test for changes in the interactome of NONO in human U2OS cells upon treatment with the topoisomerase II inhibitor etoposide. Surprisingly, our mass spectrometry data reveal that etoposide treatment does not induce major changes in NONO protein-protein interactions. We confirmed this finding by orthogonal co-immunoprecipitation assays and co-localization assays. Our data suggest that the bulk of interactions between NONO and SFPQ or PSPC1 are insensitive to etoposide treatment and that DBHS family members promote genome stability as stable dimers.