title: Evidence for DNA-PK-dependent and -independent DNA double-strand break repair pathways in mammalian cells as a function of the cell cycle.
abstract: Mice homozygous for the scid (severe combined immune deficiency) mutation are defective in the repair of DNA double-strand breaks (DSBs) and are consequently very X-ray sensitive and defective in the lymphoid V(D)J recombination process. Recently, a strong candidate for the scid gene has been identified as the catalytic subunit of the DNA-dependent protein kinase (DNA-PK) complex. Here, we show that the activity of the DNA-PK complex is regulated in a cell cycle-dependent manner, with peaks of activity found at the G1/early S phase and again at the G2 phase in wild-type cells. Interestingly, only the deficit of the G1/early S phase DNA-PK activity correlated with an increased hypersensitivity to X-irradiation and a DNA DSB repair deficit in synchronized scid pre-B cells. Finally, we demonstrate that the DNA-PK activity found at the G2 phase may be required for exit from a DNA damage-induced G2 checkpoint arrest. These observations suggest the presence of two pathways (DNA-PK-dependent and -independent) of illegitimate mammalian DNA DSB repair and two distinct roles (DNA DSB repair and G2 checkpoint traversal) for DNA-PK in the cellular response to ionizing radiation.
authors.affiliation: Department of Molecular Biology, Cell Biology, and Biochemistry, Brown University, Providence, Rhode Island 02912, USA.
authors.forename: S E
authors.initials: SE
authors.lastname: Lee
authors.forename: R A
authors.initials: RA
authors.lastname: Mitchell
authors.forename: A
authors.initials: A
authors.lastname: Cheng
authors.forename: E A
authors.initials: EA
authors.lastname: Hendrickson
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000166:cytology* / Q000201:enzymology / Q000528:radiation effects; D002453:Cell Cycle / Q000502:physiology*; D002461:Cell Line, Transformed; D004260:DNA Repair / Q000502:physiology*; D051747:DNA-Activated Protein Kinase; D004268:DNA-Binding Proteins; D006367:HeLa Cells; D006720:Homozygote; D006801:Humans; D006918:Hydroxyurea / Q000494:pharmacology; D051379:Mice; D016513:Mice, SCID; D008870:Microtubules / Q000187:drug effects; D015739:Nocodazole / Q000494:pharmacology; D009687:Nuclear Proteins; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011836:Radiation Tolerance
chemical_list: D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D019384:Nucleic Acid Synthesis Inhibitors; D051747:DNA-Activated Protein Kinase; C497263:PRKDC protein, human; D017346:Protein Serine-Threonine Kinases; D015739:Nocodazole; D006918:Hydroxyurea