title: Epidermal growth factor-induced cell death and radiosensitization in epidermal growth factor receptor-overexpressing cancer cell lines.
abstract: OBJECTIVE
  The aim of the present study was to suggest potential mechanisms of epidermal growth factor (EGF)-induced cell death and radiosensitization in EGF receptor (EGFR)-overexpressing cancer cell lines.
  
  
  METHODS
  Two EGFR-overexpressing cancer cell lines (AMC-HN3, and A431), one EGFR-null cancer cell line (H520) and normal fibroblasts were cultured with 0.01-1000 nM of recombinant human EGF (rhEGF), and a clonogenic assay was performed. After culturing serum-starved cells with 10 nM rhEGF, the expression patterns of two apoptosis-associated proteins (cleaved caspase-3 and cleaved poly(ADP-ribose) polymerase (PARP)) and the phosphoinositide 3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR) signaling pathway were measured using immunoblotting. The radiosensitizing effect of EGF was also evaluated with a clonogenic assay and phosphorylated H2AX (γH2AX) immunofluorescence.
  
  
  RESULTS
  In the clonogenic assay, the number of colonies was decreased in a dose-dependent manner in EGFR-overexpressing cancer cell lines. The expression of cleaved caspase-3 and cleaved PARP was significantly induced in EGFR-overexpressing cancer cell lines. As for the PI3K/AKT/mTOR signaling pathway, EGF paradoxically suppressed the expression of PI3K, AKT and mTOR in a time-dependent manner. As for the radiosensitizing effect, EGF enhanced the radiosensitivity of AMC-HN3 and A431 cells.
  
  
  CONCLUSIONS
  rhEGF treatment induced cell death in the two EGFR-overexpressing cancer cell lines, and the mode of cell death was apoptosis. Moreover, cell death might be associated with the paradoxical suppression of PI3K/AKT/mTOR signaling pathway. rhEGF in combination with radiation augmented the radiation effect in EGFR-overexpressing cancer cell lines via inhibition of DNA damage repair.
authors.affiliation: Department of Radiation Oncology, Seoul National University College of Medicine, Seoul, Republic of Korea.
authors.forename: Kyubo
authors.initials: K
authors.lastname: Kim
authors.affiliation: Department of Radiation Oncology, Seoul National University College of Medicine, Seoul, Republic of Korea Cancer Research Institute, Seoul National University College of Medicine, Seoul, Republic of Korea Institute of Radiation Medicine, Medical Research Center, Seoul National University, Seoul, Republic of Korea wuhg@snu.ac.kr.
authors.forename: Hong-Gyun
authors.initials: HG
authors.lastname: Wu
authors.affiliation: Department of Radiation Oncology, Seoul National University College of Medicine, Seoul, Republic of Korea.
authors.forename: Sang-Rok
authors.initials: SR
authors.lastname: Jeon
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004354:Drug Screening Assays, Antitumor; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D066246:ErbB Receptors / Q000378:metabolism*; D006801:Humans; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D011836:Radiation Tolerance; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D015398:Signal Transduction
chemical_list: D000970:Antineoplastic Agents; D051017:Apoptosis Regulatory Proteins; D011838:Radiation-Sensitizing Agents; D004815:Epidermal Growth Factor; C512478:EGFR protein, human; D066246:ErbB Receptors
keywords: EGF; EGFR-overexpressing cancer cell line; PI3K/AKT/mTOR signaling pathway; apoptosis; radiosensitization