Activation of the DNA-dependent protein kinase by drug-induced and radiation-induced DNA strand breaks

Radiat Res. 2003 Sep;160(3):291-301. doi: 10.1667/0033-7587(2003)160[0291:aotdpk];2.


The DNA-dependent protein kinase (DNA-PK) is a DNA-end activated protein kinase that is required for efficient repair of DNA double-strand breaks (DSBs) and for normal resistance to ionizing radiation. DNA-PK is composed of a DNA-binding subunit, Ku, and a catalytic subunit, DNA-PKcs (PRKDC). We have previously shown that PRKDC is activated when the enzyme interacts with the terminal nucleotides of a DSB. These nucleotides are often damaged when DSBs are introduced by anticancer agents and could therefore prevent recognition by DNA-PK. To determine whether DNA-PK could recognize DNA strand breaks generated by agents used in the treatment of cancer, we damaged plasmid DNA with anticancer drugs and ionizing radiation. The DNA breaks were tested for the ability to activate purified DNA-PK. The data indicate that DSBs produced by bleomycin, calicheamicin and two types of ionizing radiation ((137)Cs gamma rays and N(7+) ions: high and low linear energy transfer, respectively) activate DNA-PK to levels matching the kinase activation obtained with simple restriction endonuclease-induced DSBs. In contrast, the protein-linked DSBs produced by etoposide and topoisomerase II failed to bind and activate DNA-PK. Our findings indicate that DNA-PK recognizes DSBs regardless of chemical complexity but cannot recognize the protein-linked DSBs produced by etoposide and topoisomerase II.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Aminoglycosides*
  • Anti-Bacterial Agents / pharmacology
  • Antibiotics, Antineoplastic / pharmacology
  • Antigens, Nuclear / metabolism
  • Antimetabolites, Antineoplastic / pharmacology
  • Bleomycin / pharmacology
  • DNA / drug effects*
  • DNA / metabolism
  • DNA / pharmacology
  • DNA / radiation effects*
  • DNA Damage*
  • DNA Helicases*
  • DNA Repair
  • DNA Topoisomerases, Type II / metabolism
  • DNA-Activated Protein Kinase
  • DNA-Binding Proteins / metabolism
  • Dose-Response Relationship, Drug
  • Enediynes
  • Energy Transfer
  • Enzyme Activation*
  • Etoposide / pharmacology
  • Ferritins / pharmacology
  • Ku Autoantigen
  • Models, Biological
  • Nucleic Acid Synthesis Inhibitors / pharmacology
  • Plasmids / drug effects
  • Plasmids / metabolism
  • Plasmids / radiation effects
  • Protein Binding
  • Protein Serine-Threonine Kinases / metabolism*
  • Radiation, Ionizing


  • Aminoglycosides
  • Anti-Bacterial Agents
  • Antibiotics, Antineoplastic
  • Antigens, Nuclear
  • Antimetabolites, Antineoplastic
  • DNA-Binding Proteins
  • Enediynes
  • Nucleic Acid Synthesis Inhibitors
  • calicheamicin gamma(1)I
  • Bleomycin
  • Etoposide
  • DNA
  • Ferritins
  • DNA-Activated Protein Kinase
  • Protein Serine-Threonine Kinases
  • DNA Helicases
  • XRCC5 protein, human
  • Xrcc6 protein, human
  • Ku Autoantigen
  • DNA Topoisomerases, Type II