DNA-PK promotes DNA end resection at DNA double strand breaks in G cells.

DNA double-strand break (DSB) repair by homologous recombination is confined to the S and G phases of the cell cycle partly due to 53BP1 antagonizing DNA end resection in G phase and non-cycling quiescent (G) cells where DSBs are predominately repaired by non-homologous end joining (NHEJ). Unexpectedly, we uncovered extensive MRE11- and CtIP-dependent DNA end resection at DSBs in G murine and human cells. A whole genome CRISPR/Cas9 screen revealed the DNA-dependent kinase (DNA-PK) complex as a key factor in promoting DNA end resection in G cells. In agreement, depletion of FBXL12, which promotes ubiquitylation and removal of the KU70/KU80 subunits of DNA-PK from DSBs, promotes even more extensive resection in G cells. In contrast, a requirement for DNA-PK in promoting DNA end resection in proliferating cells at the G or G phase of the cell cycle was not observed. Our findings establish that DNA-PK uniquely promotes DNA end resection in G, but not in G or G phase cells, which has important implications for DNA DSB repair in quiescent cells.