title: Pifithrin-alpha protects against DNA damage-induced apoptosis downstream of mitochondria independent of p53.
abstract: Pifithrin-alpha (PFT-alpha) was shown to specifically block transcriptional activity of the tumor suppressor p53 and was therefore proposed to be useful in preventing the severe side effects often associated with chemo- and radiotherapy. We report here that although PFT-alpha efficiently protected different cell types from DNA damage-induced apoptosis, it mediated this effect regardless of the presence or absence of p53. Interestingly, PFT-alpha blocked the apoptosome-mediated processing and activation of caspase-9 and -3 without interfering with the activation of mitochondria. Neither the DNA damage-induced activation of Bax or Bak nor the loss of the mitochondrial membrane potential or the final release of cytochrome c were inhibited by this compound. Instead, the ability of PFT-alpha to protect p53-deficient cells from DNA damage-induced caspase activation and apoptosis was greatly diminished after siRNA-mediated downregulation of cyclin-D1 expression. In contrast, downregulation of other proteins involved in cell-cycle progression, such as the retinoblastoma protein, cyclin D3, as well as the cyclin-dependent kinases, 2, 4 and 6, could not abolish this protection. Thus, our data show that PFT-alpha protects cells from DNA damage-induced apoptosis also by a p53-independent mechanism that takes place downstream of mitochondria and that might involve cyclin D1.
authors.affiliation: Laboratory of Molecular Radiooncology, Clinic and Policlinic for Radiation Therapy and Radiooncology, University of Düsseldorf, Düsseldorf, Germany.
authors.forename: D
authors.initials: D
authors.lastname: Sohn
authors.forename: V
authors.initials: V
authors.lastname: Graupner
authors.forename: D
authors.initials: D
authors.lastname: Neise
authors.forename: F
authors.initials: F
authors.lastname: Essmann
authors.forename: K
authors.initials: K
authors.lastname: Schulze-Osthoff
authors.forename: R U
authors.initials: RU
authors.lastname: Jänicke
mesh_terms: D017209:Apoptosis; D053478:Apoptosomes / Q000378:metabolism; D052160:Benzothiazoles / Q000494:pharmacology*; D053148:Caspase 3 / Q000378:metabolism; D053453:Caspase 9 / Q000378:metabolism; D002460:Cell Line; D019938:Cyclin D1 / Q000172:deficiency / Q000378:metabolism; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D004249:DNA Damage; D006801:Humans; D008928:Mitochondria / Q000502:physiology*; D034741:RNA, Small Interfering / Q000378:metabolism; D011839:Radiation, Ionizing; D016160:Retinoblastoma Protein / Q000378:metabolism; D014050:Toluene / Q000031:analogs & derivatives* / Q000494:pharmacology; D016159:Tumor Suppressor Protein p53 / Q000172:deficiency / Q000378:metabolism*
chemical_list: D053478:Apoptosomes; D052160:Benzothiazoles; D034741:RNA, Small Interfering; D016160:Retinoblastoma Protein; D016159:Tumor Suppressor Protein p53; D019938:Cyclin D1; D014050:Toluene; C121565:pifithrin; D018844:Cyclin-Dependent Kinases; D053148:Caspase 3; D053453:Caspase 9