title: DNA-dependent protein kinase-independent activation of p53 in response to DNA damage.
abstract: Phosphorylation at serine 15 of the human p53 tumor suppressor protein is induced by DNA damage and correlates with accumulation of p53 and its activation as a transcription factor. The DNA-dependent protein kinase (DNA-PK) can phosphorylate serine 15 of human p53 and the homologous serine 18 of murine p53 in vitro. Contradictory reports exist about the requirement for DNA-PK in vivo for p53 activation and cell cycle arrest in response to ionizing radiation. While primary SCID (severe combined immunodeficiency) cells, that have defective DNA-PK, show normal p53 activation and cell cycle arrest, a transcriptionally inert form of p53 is induced in the SCID cell line SCGR11. In order to unambiguously define the role of the DNA-PK catalytic subunit (DNA-PKcs) in p53 activation, we examined p53 phosphorylation in mouse embryonic fibroblasts (MEFs) from DNA-PKcs-null mice. We found a similar pattern of serine 18 phosphorylation and accumulation of p53 in response to irradiation in both control and DNA-PKcs-null MEFs. The induced p53 was capable of sequence-specific DNA binding even in the absence of DNA-PKcs. Transactivation of the cyclin-dependent-kinase inhibitor p21, a downstream target of p53, and the G1 cell cycle checkpoint were also found to be normal in the DNA-PKcs -/- MEFs. Our results demonstrate that DNA-PKcs, unlike the related ATM protein, is not essential for the activation of p53 and G1 cell cycle arrest in response to ionizing radiation.
authors.affiliation: Life Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
authors.forename: S
authors.initials: S
authors.lastname: Burma
authors.forename: A
authors.initials: A
authors.lastname: Kurimasa
authors.forename: G
authors.initials: G
authors.lastname: Xie
authors.forename: Y
authors.initials: Y
authors.lastname: Taya
authors.forename: R
authors.initials: R
authors.lastname: Araki
authors.forename: M
authors.initials: M
authors.lastname: Abe
authors.forename: H A
authors.initials: HA
authors.lastname: Crissman
authors.forename: H
authors.initials: H
authors.lastname: Ouyang
authors.forename: G C
authors.initials: GC
authors.lastname: Li
authors.forename: D J
authors.initials: DJ
authors.lastname: Chen
mesh_terms: D000818:Animals; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000096:biosynthesis; D004249:DNA Damage; D051747:DNA-Activated Protein Kinase; D004268:DNA-Binding Proteins; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D016193:G1 Phase / Q000528:radiation effects*; D005720:Gamma Rays; D051379:Mice; D008817:Mice, Mutant Strains; D016513:Mice, SCID; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000235:genetics*; D014157:Transcription Factors / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D015854:Up-Regulation
chemical_list: C493957:Cdkn1a protein, mouse; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004268:DNA-Binding Proteins; D014157:Transcription Factors; D016159:Tumor Suppressor Protein p53; D010768:Phosphoserine; D051747:DNA-Activated Protein Kinase; D017346:Protein Serine-Threonine Kinases