title: The epidermal growth factor receptor mediates radioresistance.
abstract: OBJECTIVE
  The epidermal growth factor (EGF) receptor is frequently overexpressed in malignant tumors, and its level is correlated with increased cellular resistance to ionizing radiation. However, no precedent studies have investigated whether expression of EGF receptor would by itself confer on cancer cells resistance to radiation. The current study is aimed to address this question.
  
  
  METHODS
  A full-length human EGF receptor expression vector was transfected into the OCA-I murine ovarian carcinoma cells for stable clones expressing various levels of EGF receptors. Apoptosis and cell clonogenic survival assays were used to evaluate the sensitivity of the resulting cell clones to ionizing radiation.
  
  
  RESULTS
  OCA-I cell clones expressing various levels of EGF receptor (OCA-I EGFR) were obtained. These clones showed an EGF receptor level-dependent increase in resistance to ionizing radiation, measured by apoptosis and cell clonogenic survival assays. Compared with the results for parental OCA-I and control vector-transfected OCA-I cells at the 10% cell survival level, the radioresistance was increased by a factor of 1.60 for EGFR-C5 (high level of EGF receptor expression), 1.37 for EGFR-C3 (intermediate level of EGF receptor expression), and 1.28 for EGFR-C1 (low level of EGF receptor expression). Treatment of the OCA-I EGF receptor transfectants with the anti-EGF receptor monoclonal antibody C225 downregulated the levels of EGF receptor, reduced the phosphorylation levels of EGF receptor downstream substrates (such as Akt and MAPK), and reversed the cellular radioresistance.
  
  
  CONCLUSIONS
  Our results demonstrate that overexpression of the EGF receptor conferred cellular resistance to ionizing radiation. The EGF receptor is thus a valid target for potential radiosensitization.
authors.affiliation: Department of Experimental Therapeutics, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
authors.forename: Ke
authors.initials: K
authors.lastname: Liang
authors.forename: K Kian
authors.initials: KK
authors.lastname: Ang
authors.forename: Luka
authors.initials: L
authors.lastname: Milas
authors.forename: Nancy
authors.initials: N
authors.lastname: Hunter
authors.forename: Zhen
authors.initials: Z
authors.lastname: Fan
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000528:radiation effects; D003001:Cloning, Molecular; D004307:Dose-Response Relationship, Radiation; D004815:Epidermal Growth Factor / Q000235:genetics / Q000378:metabolism*; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D051379:Mice / Q000235:genetics; D010051:Ovarian Neoplasms / Q000378:metabolism*; D011829:Radiation Dosage; D011836:Radiation Tolerance; D013223:Statistics as Topic; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D004815:Epidermal Growth Factor