title: Hypoxia induces accumulation of p53 protein, but activation of a G1-phase checkpoint by low-oxygen conditions is independent of p53 status.
abstract: It has been convincingly demonstrated that genotoxic stresses cause the accumulation of the tumor suppressor gene p53. One important consequence of increased p53 protein levels in response to DNA damage is the activation of a G1-phase cell cycle checkpoint. It has also been shown that G1-phase cell cycle checkpoints are activated in response to other stresses, such as lack of oxygen. Here we show that hypoxia and heat, agents that induce cellular stress primarily by inhibiting oxygen-dependent metabolism and denaturing proteins, respectively, also cause an increase in p53 protein levels. The p53 protein induced by heat is localized in the cytoplasm and forms a complex with the heat shock protein hsc70. The increase in nuclear p53 protein levels and DNA-binding activity and the induction of reporter gene constructs containing p53 binding sites following hypoxia occur in cells that are wild type for p53 but not in cells that possess mutant p53. However, unlike ionizing radiation, the accumulation of cells in G1 phase by hypoxia is not strictly dependent on wild-type p53 function. In addition, cells expressing the human papillomavirus E6 gene, which show increased degradation of p53 by ubiquitination and fail to accumulate p53 in response to DNA-damaging agents, do increase their p53 levels following heat and hypoxia. These results suggest that hypoxia is an example of a "nongenotoxic" stress which induces p53 activity by a different pathway than DNA-damaging agents.
authors.affiliation: Department of Radiation Oncology, Stanford University School of Medicine, California 94305.
authors.forename: T G
authors.initials: TG
authors.lastname: Graeber
authors.forename: J F
authors.initials: JF
authors.lastname: Peterson
authors.forename: M
authors.initials: M
authors.lastname: Tsai
authors.forename: K
authors.initials: K
authors.lastname: Monica
authors.forename: A J
authors.initials: AJ
authors.lastname: Fornace
authors.forename: A J
authors.initials: AJ
authors.lastname: Giaccia
mesh_terms: D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins / Q000378:metabolism; D002453:Cell Cycle; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D050883:HSC70 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins / Q000378:metabolism; D006358:Hot Temperature; D006801:Humans; D000860:Hypoxia / Q000378:metabolism*; D066298:In Vitro Techniques; D051379:Mice; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D009856:Oncogene Proteins, Viral / Q000378:metabolism; D012097:Repressor Proteins; D015533:Transcriptional Activation; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D004268:DNA-Binding Proteins; C068651:E6 protein, Human papillomavirus type 16; D050883:HSC70 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; C494371:HSPA8 protein, human; D006360:Heat-Shock Proteins; C494372:Hspa8 protein, mouse; D009838:Oligodeoxyribonucleotides; D009856:Oncogene Proteins, Viral; D012097:Repressor Proteins; D016159:Tumor Suppressor Protein p53