title: Differential role of DNA-PKcs phosphorylations and kinase activity in radiosensitivity and chromosomal instability.
abstract: The catalytic subunit of DNA-dependent protein kinase (DNA-PKcs) is the key functional element in the DNA-PK complex that drives nonhomologous end joining (NHEJ), the predominant DNA double-strand break (DSB) repair mechanism operating to rejoin such breaks in mammalian cells after exposure to ionizing radiation. It has been reported that DNA-PKcs phosphorylation and kinase activity are critical determinants of radiosensitivity, based on responses reported after irradiation of asynchronously dividing populations of various mutant cell lines. In the present study, the relative radiosensitivity to cell killing as well as chromosomal instability of 13 DNA-PKcs site-directed mutant cell lines (defective at phosphorylation sites or kinase activity) were examined after exposure of synchronized G(1) cells to (137)Cs γ rays. DNA-PKcs mutant cells defective in phosphorylation at multiple sites within the T2609 cluster or within the PI3K domain displayed extreme radiosensitivity. Cells defective at the S2056 cluster or T2609 single site alone were only mildly radiosensitive, but cells defective at even one site in both the S2056 and T2609 clusters were maximally radiosensitive. Thus a synergism between the capacity for phosphorylation at the S2056 and T2609 clusters was found to be critical for induction of radiosensitivity.
authors.affiliation: Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, Colorado 80523, USA.
authors.forename: Hatsumi
authors.initials: H
authors.lastname: Nagasawa
authors.forename: John B
authors.initials: JB
authors.lastname: Little
authors.forename: Yu-Fen
authors.initials: YF
authors.lastname: Lin
authors.forename: Sairei
authors.initials: S
authors.lastname: So
authors.forename: Akihiro
authors.initials: A
authors.lastname: Kurimasa
authors.forename: Yuanlin
authors.initials: Y
authors.lastname: Peng
authors.forename: John R
authors.initials: JR
authors.lastname: Brogan
authors.forename: David J
authors.initials: DJ
authors.lastname: Chen
authors.forename: Joel S
authors.initials: JS
authors.lastname: Bedford
authors.forename: Benjamin P C
authors.initials: BP
authors.lastname: Chen
mesh_terms: D000818:Animals; D016466:CHO Cells; D043171:Chromosomal Instability; D006224:Cricetinae; D003412:Cricetulus; D004260:DNA Repair; D051747:DNA-Activated Protein Kinase / Q000502:physiology*; D016193:G1 Phase; D006801:Humans; D010766:Phosphorylation; D011836:Radiation Tolerance
chemical_list: D051747:DNA-Activated Protein Kinase