Abstract
Recent studies have suggested that human RNA helicase, DDX3X, is important for DNA repair, but little is known about the nuclear activity of this protein. In vitro analysis of nuclear DDX3X interactions and localization with DNA damage pointed to a direct role for DDX3X in the DNA damage response. We aimed to investigate whether DDX3X plays a direct role in the DNA damage response in live cells. In order to track nuclear DDX3X, we generated a nuclear-export deficient DDX3X mutant construct and performed microirradiation in live cells. We found that DDX3X accumulates at sites of microirradiation shortly after DNA damage induction. We further found DDX3X recruitment to be mediated by its intrinsically disordered domains, similar to other RNA binding proteins that are recruited to sites of DNA damage. Inhibition of liquid-liquid phase separation also reduced DDX3X recruitment. CRISPR/Cas9-mediated knockout of PARP1 ablated DDX3X recruitment, which was restored upon transgenic expression of wild-type PARP1 but not catalytically inactive PARP1, suggesting that DDX3X recruitment is PARP1-dependent.