The kinase activity of DNA-PK is required to protect mammalian telomeres

Susan M. Bailey, Mark A. Brenneman, James Halbrook, Jac A. Nickoloff, Robert L. Ullrich, Edwin H. Goodwin

Research output: Contribution to journalArticlepeer-review

68 Scopus citations


The kinase activity of DNA-dependent protein kinase (DNA-PK) is required for efficient repair of DNA double-strand breaks (DSB) by non-homologous end joining (NHEJ). DNA-PK also participates in protection of mammalian telomeres, the natural ends of chromosomes. Here we investigate whether the kinase activity of DNA-PK is similarly required for effective telomere protection. DNA-PK proficient mouse cells were exposed to a highly specific inhibitor of DNA-PK phosphorylation designated IC86621. Chromosomal end-to-end fusions were induced in a concentration-dependent manner, demonstrating that the telomere end-protection role of DNA-PK requires its kinase activity. These fusions were uniformly chromatid-type, consistent with a role for DNA-PK in capping telomeres after DNA replication. Additionally, fusions involved exclusively telomeres produced via leading-strand DNA synthesis. Unexpectedly, the rate of telomeric fusions induced by IC86621 exceeded that which occurs spontaneously in DNA-dependent protein kinase catalytic subunit (DNA-PKcs) mutant cells by up to 110-fold. One explanation, that IC86621 might inhibit other, as yet unknown proteins, was ruled out when the drug failed to induce fusions in DNA-PKcs knock-out mouse cells. IC86621 did not induce fusions in Ku70 knock-out cells suggesting the drug requires the holoenzyme to be effective. ATM also is required for effective chromosome end protection. IC86621 increased fusions in ATM knock-out cells suggesting DNA-PK and ATM act in different telomere pathways. These results indicate that the kinase activity of DNA-PK is crucial to reestablishing a protective terminal structure, specifically on telomeres replicated by leading-strand DNA synthesis.

Original languageEnglish (US)
Pages (from-to)225-233
Number of pages9
JournalDNA Repair
Issue number3
StatePublished - Mar 4 2004
Externally publishedYes


  • Cancer
  • DNA repair
  • DNA-PKcs
  • Double-strand breaks
  • Mammalian telomeres

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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