DNA-PK promotes DNA end resection at DNA double strand breaks in G0 cells

DNA double-strand break (DSB) repair by homologous recombination is confined to the S and G(2) phases of the cell cycle partly due to 53BP1 antagonizing DNA end resection in G(1) phase and non-cycling quiescent (G(0)) 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(0) 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(0) 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(0) cells. In contrast, a requirement for DNA-PK in promoting DNA end resection in proliferating cells at the G(1) or G(2) phase of the cell cycle was not observed. Our findings establish that DNA-PK uniquely promotes DNA end resection in G(0), but not in G(1) or G(2) phase cells, which has important implications for DNA DSB repair in quiescent cells.

Automated summary

This study uncovered extensive DNA end resection at double-strand breaks (DSBs) in G(0) murine and human cells dependent on MRE11 and CtIP. A whole genome CRISPR/Cas9 screen identified the DNA-dependent kinase (DNA-PK) complex as a key factor in promoting DNA end resection in G(0) cells. However, the requirement for DNA-PK in promoting DNA end resection was not observed in proliferating cells at the G(1) or G(2) phase.