title: The nuclear death domain protein p84N5 activates a G2/M cell cycle checkpoint prior to the onset of apoptosis.
abstract: In contrast to extracellular signals, the mechanisms utilized to transduce nuclear apoptotic signals are not well understood. Characterizing these mechanisms is important for predicting how tumors will respond to genotoxic radiation or chemotherapy. The retinoblastoma (Rb) tumor suppressor protein can regulate apoptosis triggered by DNA damage through an unknown mechanism. The nuclear death domain-containing protein p84N5 can induce apoptosis that is inhibited by association with Rb. The pattern of caspase and NF-kappaB activation during p84N5-induced apoptosis is similar to p53-independent cellular responses to DNA damage. One hallmark of this response is the activation of a G(2)/M cell cycle checkpoint. In this report, we characterize the effects of p84N5 on the cell cycle. Expression of p84N5 induces changes in cell cycle distribution and kinetics that are consistent with the activation of a G(2)/M cell cycle checkpoint. Like the radiation-induced checkpoint, caffeine blocks p84N5-induced G(2)/M arrest but not subsequent apoptotic cell death. The p84N5-induced checkpoint is functional in ataxia telangiectasia-mutated kinase-deficient cells. We conclude that p84N5 induces an ataxia telangiectasia-mutated kinase (ATM)-independent, caffeine-sensitive G(2)/M cell cycle arrest prior to the onset of apoptosis. This conclusion is consistent with the hypotheses that p84N5 functions in an Rb-regulated cellular response that is similar to that triggered by DNA damage.
authors.affiliation: Department of Molecular and Cellular Oncology, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, USA.
authors.forename: J
authors.initials: J
authors.lastname: Doostzadeh-Cizeron
authors.forename: N H
authors.initials: NH
authors.lastname: Terry
authors.forename: D W
authors.initials: DW
authors.lastname: Goodrich
mesh_terms: D000256:Adenoviridae; D016590:Aphidicolin / Q000494:pharmacology; D017209:Apoptosis / Q000502:physiology*; D002110:Caffeine / Q000494:pharmacology; D020169:Caspases / Q000378:metabolism; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology*; D018797:Cell Cycle Proteins; D002460:Cell Line; D019926:Cyclin B / Q000378:metabolism; D004261:DNA Replication / Q000187:drug effects; D004268:DNA-Binding Proteins; D016195:G2 Phase; D017930:Genes, Reporter; D005822:Genetic Vectors; D006801:Humans; D007700:Kinetics; D008938:Mitosis; D016328:NF-kappa B / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism*; D016601:RNA-Binding Proteins; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection
chemical_list: D018797:Cell Cycle Proteins; D019926:Cyclin B; D004268:DNA-Binding Proteins; D016328:NF-kappa B; D009687:Nuclear Proteins; D016601:RNA-Binding Proteins; D011994:Recombinant Proteins; C400546:THOC1 protein, human; D016590:Aphidicolin; D002110:Caffeine; D020169:Caspases