DNA-PKcs inhibition sensitizes cancer cells to carbon-ion irradiation via telomere capping disruption

PLoS One. 2013 Aug 27;8(8):e72641. doi: 10.1371/journal.pone.0072641. eCollection 2013.

Abstract

Heavy-ion irradiation induces a higher frequency of DNA double strand breaks (DSBs) which must be properly repaired. Critical shortening of telomeres can trigger DNA damage responses such as DSBs. Telomeres are very sensitive to oxidative stress such as ionizing radiation. The DNA-dependent protein kinase catalytic subunit (DNA-PKcs) is the central component in the non-homologous end joining (NHEJ) repair complex and participates in telomere maintenance. Therefore, it is expected to enhance the cell killing effect of heavy-ion irradiation via DNA-PKcs inhibition. To test this hypothesis, cellular radiosensitivity was measured by the clonal genetic assay. DNA damage repair was relatively quantified by long PCR. Apoptosis was quantified by flow-cytometric analysis of annexin V/PI double staining, and senescence was analyzed by galactosidase activity. Telomere length was semi-quantified by real-time PCR. P53 and p21 expression was determined by western blotting. Our data demonstrated that MCF-7 and HeLa cells with DNA-PKcs inhibition were more susceptible to carbon-ion irradiation than Those without DNA-PKcs inhibition. Even though NHEJ was inhibited by the DNA-PKcs specific inhibitor, NU7026, most DNA damage induced by carbon-ion irradiation was repaired within 24 hours after irradiation in both cell lines. However, potential lethal damage repair (PLDR) could not restore cellular inactivation in DNA-PKcs inhibited cells. MCF-7 cells showed extensive senescence and accelerated telomere length reduction, while HeLa cells underwent significant apoptosis after irradiation with NU7026 incubation. In addition, both cell lines with shorter telomere were more susceptible to carbon-ion radiation. Our current data suggested that DNA-PKcs inhibition could enhance cellular sensitivity to carbon-ion radiation via disturbing its functional role in telomere end protection. The combination of DNA-PKcs inhibition and carbon-ion irradiation may be an efficient method of heavy-ion therapy.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • DNA Damage*
  • DNA End-Joining Repair* / drug effects
  • DNA End-Joining Repair* / radiation effects
  • DNA-Activated Protein Kinase / antagonists & inhibitors
  • DNA-Activated Protein Kinase / genetics
  • DNA-Activated Protein Kinase / metabolism*
  • HeLa Cells
  • Humans
  • Nuclear Proteins / antagonists & inhibitors
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism*
  • Protein Kinase Inhibitors / pharmacology*
  • Radiation, Ionizing*
  • Telomere / genetics
  • Telomere / metabolism*
  • Time Factors
  • Tumor Suppressor Protein p53 / genetics
  • Tumor Suppressor Protein p53 / metabolism

Substances

  • Nuclear Proteins
  • Protein Kinase Inhibitors
  • TP53 protein, human
  • Tumor Suppressor Protein p53
  • DNA-Activated Protein Kinase
  • PRKDC protein, human

Grants and funding

This work was supported by grants from the National Basic Research Program of China (2010CB834202), the National Natural Science Foundation of China (10835011), and the Scientific Technology Research Projects of Gansu Province (0702NKDA045, 0806RJYA020) and HIMAC project 11J364 which is supported by National Institute of Radiological Sciences. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.