The p53 response to DNA damage in vivo is independent of DNA-dependent protein kinase.
Ionizing radiation (IR) exposure causes mammalian cells to undergo p53-dependent cell cycle arrest and/or apoptosis. The in vivo role of DNA-dependent protein kinase (DNA-PK) in the transduction of the DNA damage signal to p53 remains unresolved. To determine the relationship between DNA-PK and p53, we studied the cell cycle and apoptotic responses to IR in mice deficient in DNA-PK. Using the slip mouse, which harbors an inactivating mutation of the DNA-PK catalytic subunit (DNA-PKcs), we demonstrated not only that these DNA-PKcs null mutants were highly radiosensitive but also that upon IR treatment, p53 accumulated in their cultured cells and tissue. Induced p53 was transcriptionally active and mediated the induction of p21 and Bax in slip cells. Examination of the thymic cell cycle response to IR treatment indicated that the slip G(1)/S-phase cell cycle checkpoint function was intact. We further show that slip mice exhibited a higher level of spontaneous thymic apoptosis as well as a more robust apoptotic response to IR than wild-type mice. Together, these data demonstrate that the p53-mediated response to DNA damage is intact in cells devoid of DNA-PK activity and suggest that other kinases, such as the product of the gene (ATM) mutated in ataxia telangiectasia, are better candidates for regulating IR-induced phosphorylation and accumulation of p53.
Jhappan
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Laboratory of Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-4255, USA. cjhappan@helix.nih.gov
Yusufzai
T M
TM
Anderson
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Anver
M R
MR
Merlino
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D000818:Animals; D017209:Apoptosis; D002453:Cell Cycle; D002478:Cells, Cultured; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000096:biosynthesis; D004249:DNA Damage / Q000528:radiation effects*; D051747:DNA-Activated Protein Kinase; D004268:DNA-Binding Proteins; D005260:Female; D016193:G1 Phase; D005720:Gamma Rays; D008297:Male; D051379:Mice; D008817:Mice, Mutant Strains; D017346:Protein Serine-Threonine Kinases / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis; D016196:S Phase; D015398:Signal Transduction; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D051028:bcl-2-Associated X Protein
C494827:Bax protein, mouse; C493957:Cdkn1a protein, mouse; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004268:DNA-Binding Proteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D016159:Tumor Suppressor Protein p53; D051028:bcl-2-Associated X Protein; D051747:DNA-Activated Protein Kinase; D017346:Protein Serine-Threonine Kinases