DNA ligase IV and artemis act cooperatively to suppress homologous recombination in human cells: implications for DNA double-strand break repair

PLoS One. 2013 Aug 14;8(8):e72253. doi: 10.1371/journal.pone.0072253. eCollection 2013.


Nonhomologous end-joining (NHEJ) and homologous recombination (HR) are two major pathways for repairing DNA double-strand breaks (DSBs); however, their respective roles in human somatic cells remain to be elucidated. Here we show using a series of human gene-knockout cell lines that NHEJ repairs nearly all of the topoisomerase II- and low-dose radiation-induced DNA damage, while it negatively affects survival of cells harbouring replication-associated DSBs. Intriguingly, we find that loss of DNA ligase IV, a critical NHEJ ligase, and Artemis, an NHEJ factor with endonuclease activity, independently contribute to increased resistance to replication-associated DSBs. We also show that loss of Artemis alleviates hypersensitivity of DNA ligase IV-null cells to low-dose radiation- and topoisomerase II-induced DSBs. Finally, we demonstrate that Artemis-null human cells display increased gene-targeting efficiencies, particularly in the absence of DNA ligase IV. Collectively, these data suggest that DNA ligase IV and Artemis act cooperatively to promote NHEJ, thereby suppressing HR. Our results point to the possibility that HR can only operate on accidental DSBs when NHEJ is missing or abortive, and Artemis may be involved in pathway switching from incomplete NHEJ to HR.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Line
  • DNA Breaks, Double-Stranded* / drug effects
  • DNA Breaks, Double-Stranded* / radiation effects
  • DNA End-Joining Repair* / drug effects
  • DNA End-Joining Repair* / radiation effects
  • DNA Ligase ATP
  • DNA Ligases / deficiency
  • DNA Ligases / metabolism*
  • DNA Replication / drug effects
  • DNA Replication / radiation effects
  • DNA Topoisomerases, Type II / metabolism
  • DNA-Binding Proteins
  • Endonucleases
  • Gene Knockout Techniques
  • Gene Targeting
  • Homologous Recombination* / drug effects
  • Homologous Recombination* / radiation effects
  • Humans
  • Mutation
  • Nuclear Proteins / deficiency
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism*
  • Topoisomerase II Inhibitors / pharmacology


  • DNA-Binding Proteins
  • LIG4 protein, human
  • Nuclear Proteins
  • Topoisomerase II Inhibitors
  • DCLRE1C protein, human
  • Endonucleases
  • DNA Topoisomerases, Type II
  • DNA Ligases
  • DNA Ligase ATP

Grant support

This work was supported by grants from Yokohama City University (Strategic Research Promotion G2201/G2301/G2401) and by Grants-in-Aid from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.