title: Interaction of p53 and DNA-PK in response to nucleoside analogues: potential role as a sensor complex for DNA damage.
abstract: Therapeutic nucleoside analogues such as ara-C, gemcitabine, and fludarabine exert their cytotoxic activity against cancer cells mainly by incorporation into DNA and disruption of further DNA synthesis, resulting in the triggering of apoptosis. However, the molecules that recognize the incorporated analogues in DNA and subsequently initiate the downstream cellular responses remain to be identified. Here, we report that the DNA-dependent protein kinase (DNA-PK) and p53 are able to form a protein complex that interacts with the gemcitabine-containing DNA and plays a role in signaling to apoptotic pathways. DNA-PK/Ku and p53 were copurified in a protein fraction that binds to gemcitabine-containing DNA in preference to normal DNA. Immunoprecipitation experiments revealed that the two proteins physically associate in a complex. Treatment with gemcitabine resulted in an increase of DNA-PK and p53 protein and an increase in the phosphorylation of p53 at Ser15. Furthermore, confocal microscopy demonstrated a colocalization of DNA-PK and p53 to the nucleus in cells treated with gemcitabine. The nuclear localization of the DNA-PK/p53 complex was coincident with the induction of apoptosis in these cells. Although the wild-type p53 present in the protein complex exhibited 3'-5' exonuclease activity, it was incapable of excising the incorporated gemcitabine from DNA. The binding of the p53/DNA-PK complex to DNA substantially blocked further DNA synthesis by DNA polymerases alpha and epsilon in vitro, indicating a stalling of this complex at the site of drug incorporation. These data suggest that DNA-PK and p53 may form a sensor complex that detects the disruption of DNA replication caused by nucleoside analogue incorporation and may subsequently signal for apoptosis.
authors.affiliation: Department of Molecular Pathology, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, USA.
authors.forename: G
authors.initials: G
authors.lastname: Achanta
authors.forename: H
authors.initials: H
authors.lastname: Pelicano
authors.forename: L
authors.initials: L
authors.lastname: Feng
authors.forename: W
authors.initials: W
authors.lastname: Plunkett
authors.forename: P
authors.initials: P
authors.lastname: Huang
mesh_terms: D034961:Antigens, Nuclear; D000964:Antimetabolites, Antineoplastic / Q000378:metabolism / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D001667:Binding, Competitive; D004249:DNA Damage; D004265:DNA Helicases; D004260:DNA Repair; D004261:DNA Replication / Q000187:drug effects; D004273:DNA, Neoplasm / Q000187:drug effects / Q000378:metabolism; D051747:DNA-Activated Protein Kinase; D004268:DNA-Binding Proteins / Q000378:metabolism; D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D000072200:Ku Autoantigen; D007951:Leukemia, Myeloid / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D000093542:Gemcitabine
chemical_list: D034961:Antigens, Nuclear; D000964:Antimetabolites, Antineoplastic; D004273:DNA, Neoplasm; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D016159:Tumor Suppressor Protein p53; D003841:Deoxycytidine; D051747:DNA-Activated Protein Kinase; C497263:PRKDC protein, human; D017346:Protein Serine-Threonine Kinases; D004265:DNA Helicases; C106893:XRCC5 protein, human; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen; D000093542:Gemcitabine