ldentification and characterization of novel enzymes involved in the DNA damage response in human cells

Abstract

A correct DNA damage response is critical in maintaining genome integrity and the prevention of cancer. Efficient DNA repair requires the correct and timely coordination of a multitude of signaling events, in which post-translational modifications play a critical role. Here we investigate enzymes important in the cellular response to DNA damage and the molecular mechanisms of how these enzymes help preventing genome instability. We identified ubiquitin hydrolase USP29 as novel regulator of SETD8, a methyl transferase important for the recruitment of 53BP1 to sites of DNA damage by controlling histone H4K20 methylation. USP29 interacts with and deubiquitinates SETD8 in vivo. USP29 regulates DNA damage-induced H4K20 methylation and focus formation of 53BP1 and depletion of USP29 increases the cellular sensitivity to irradiation. These results suggest that USP29 is critical for the DNA damage response and cell survival. Upon examining of interactors of lysine demethylase PHF2, described to control homolog-directed repair of double strand breaks, we identified USP36 and TRIP13. These novel interactors might collaborate with PHF2 in the maintenance of genome stability. Finally, we describe a role for RNA helicases DDX18, DDX37 and DDX50 in the prevention of DNA damage, likely by the regulation of transcription-dependent R-loop formation. Together, these findings help our understanding of the maintenance of genome integrity and could be of use for the identification of novel therapeutic targets for cancer treatment.