Proton Irradiation Increases the Necessity for Homologous Recombination Repair Along with the Indispensability of Non-Homologous End Joining

Cells. 2020 Apr 5;9(4):889. doi: 10.3390/cells9040889.

Abstract

Technical improvements in clinical radiotherapy for maximizing cytotoxicity to the tumor while limiting negative impact on co-irradiated healthy tissues include the increasing use of particle therapy (e.g., proton therapy) worldwide. Yet potential differences in the biology of DNA damage induction and repair between irradiation with X-ray photons and protons remain elusive. We compared the differences in DNA double strand break (DSB) repair and survival of cells compromised in non-homologous end joining (NHEJ), homologous recombination repair (HRR) or both, after irradiation with an equal dose of X-ray photons, entrance plateau (EP) protons, and mid spread-out Bragg peak (SOBP) protons. We used super-resolution microscopy to investigate potential differences in spatial distribution of DNA damage foci upon irradiation. While DNA damage foci were equally distributed throughout the nucleus after X-ray photon irradiation, we observed more clustered DNA damage foci upon proton irradiation. Furthermore, deficiency in essential NHEJ proteins delayed DNA repair kinetics and sensitized cells to both, X-ray photon and proton irradiation, whereas deficiency in HRR proteins sensitized cells only to proton irradiation. We assume that NHEJ is indispensable for processing DNA DSB independent of the irradiation source, whereas the importance of HRR rises with increasing energy of applied irradiation.

Keywords: DNA damage foci; DNA repair; entrance plateau (EP) protons; ionizing radiation; linear energy transfer (LET), DNA double-strand break (DSB), non-homologous end joining (NHEJ), homologous recombination repair (HRR) , relative biological effectiveness (RBE); relative biological effectiveness (RBE); spread-out Bragg peak (SOBP).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Line
  • Cell Survival / radiation effects
  • Clone Cells
  • DNA Damage
  • DNA End-Joining Repair / radiation effects*
  • DNA Ligase ATP / metabolism
  • Fibroblasts / metabolism
  • Fibroblasts / radiation effects
  • Histones / metabolism
  • Humans
  • Mice
  • Photons
  • Protons*
  • Recombinational DNA Repair / radiation effects*
  • Time Factors
  • X-Rays

Substances

  • Histones
  • Protons
  • gamma-H2AX protein, mouse
  • DNA Ligase ATP