title: Irradiation-induced translocation of p53 to mitochondria in the absence of apoptosis.
abstract: The tumor suppressor protein p53 promotes apoptosis in response to death stimuli by transactivation of target genes and by transcription-independent mechanisms. Recently, it was shown that during apoptosis p53 can specifically translocate to mitochondria, where it physically interacts with and inactivates prosurvival Bcl-2 proteins. In the present study, we therefore investigated the role of mitochondrial translocation of p53 for the stress response of tumor cells. In various cell lines, DNA damage induced by either ionizing irradiation or topoisomerase inhibitors triggered a robust translocation of a fraction of p53 to mitochondria to a similar extent. Nevertheless, the cells succumbed to apoptosis only in response to topoisomerase inhibitors, but remained resistant to apoptosis induced by ionizing radiation. Irradiated cells became senescent, although irradiation triggered a functional p53 response and induced expression of p21, Bax, and Puma. Interestingly, even the targeted expression of p53 to mitochondria was insufficient to launch apoptosis, whereas overexpression of wild-type p53 induced Bax activation and apoptotic alterations. Together, these results suggest that, in contrast to previous reports, mitochondrial translocation of p53 does not per se lead to cell death and that this might constitute a mechanism that contributes to the resistance of tumor cells to ionizing radiation-induced apoptosis.
authors.affiliation: Institute of Molecular Medicine, University of Düsseldorf, 40225 Düsseldorf, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Essmann
authors.forename: Stephan
authors.initials: S
authors.lastname: Pohlmann
authors.forename: Bernhard
authors.initials: B
authors.lastname: Gillissen
authors.forename: Peter T
authors.initials: PT
authors.lastname: Daniel
authors.forename: Klaus
authors.initials: K
authors.lastname: Schulze-Osthoff
authors.forename: Reiner U
authors.initials: RU
authors.lastname: Jänicke
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000528:radiation effects*; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology; D003110:Colonic Neoplasms / Q000378:metabolism / Q000473:pathology; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D004249:DNA Damage / Q000187:drug effects / Q000528:radiation effects*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology; D006801:Humans; D051379:Mice; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects*; D021381:Protein Transport; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D034741:RNA, Small Interfering / Q000494:pharmacology; D011839:Radiation, Ionizing; D059004:Topoisomerase I Inhibitors; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D051028:bcl-2-Associated X Protein / Q000378:metabolism
chemical_list: D051017:Apoptosis Regulatory Proteins; C438378:BBC3 protein, human; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004791:Enzyme Inhibitors; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering; D059004:Topoisomerase I Inhibitors; D016159:Tumor Suppressor Protein p53; D051028:bcl-2-Associated X Protein