title: Hypoxia-regulated p53 and its effect on radiosensitivity in cancer cells.
abstract: OBJECTIVE
  To determine the response of tumor suppressor p53 to hypoxia in different tumor cell lines and the involvement of p53 activity regulation in the effect of hypoxia on tumor cell sensitivity to radiation and hyperthermia.
  
  
  METHODS
  Three tumor cell lines with functional p53 were treated with chronic or cyclic hypoxia followed by radiation or hyperthermia to investigate p53 activity and cell survival. Flow cytometry was used to investigate the effect of hypoxia-induced cell cycle arrest on radiosensitivity in KHT-C (mouse fibrosarcoma) cells. Transient transfection was performed to determine the role of altered p53 activity in KHT-C and SCC VII (mouse squamous-cell carcinoma) radiosensitivity.
  
  
  RESULTS
  Aerobic radiosensitivity was decreased in KHT-C and SCC VII cells after in vitro chronic or cyclic hypoxia pretreatment, but in HT1080 cells, it was slightly increased after chronic hypoxia, and was unchanged after acute hypoxia pretreatment. Decreased radiosensitivity in hypoxia-pretreated KHT-C and SCC VII cells was unlikely due to hypoxia-induced cell cycle arrest, but rather seemed to be associated with increased expression of Mdm2 (mouse double minute-2) and decreased p53. Furthermore, hypoxia pretreatment inhibited the activation of p53 by radiation. Similar results were observed in hyperthermia treated KHT-C cells. Finally, decreased radiosensitivity was observed in both KHT-C and SCC VII cells transiently transfected with Mdm2 or anti-sense p53 cDNA.
  
  
  CONCLUSIONS
  We demonstrated that hypoxia may decrease tumor cell radiosensitivity through the suppression of p53 activity in some tumor cell lines. These results suggested the response of p53 to hypoxia can be cell type specific and contribute to radiosensitivity of hypoxic cells.
authors.affiliation: Research Division, Ontario Cancer Institute/Princess Margaret Hospital, University of Toronto, Ontario, Canada.
authors.forename: Li
authors.initials: L
authors.lastname: Zhang
authors.forename: Patrick
authors.initials: P
authors.lastname: Subarsky
authors.forename: Richard P
authors.initials: RP
authors.lastname: Hill
mesh_terms: D002453:Cell Cycle / Q000528:radiation effects*; D045744:Cell Line, Tumor; D004307:Dose-Response Relationship, Radiation; D018274:Electroporation; D005434:Flow Cytometry; D005786:Gene Expression Regulation / Q000528:radiation effects*; D006801:Humans; D000860:Hypoxia; D010100:Oxygen / Q000378:metabolism; D013696:Temperature; D013997:Time Factors; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism* / Q000502:physiology*
chemical_list: C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; D010100:Oxygen