title: Rapamycin-induced autophagy sensitizes A549 cells to radiation associated with DNA damage repair inhibition.
abstract: BACKGROUND
  Autophagy has been reported to increase in cancer cells after radiation. However, it remains unknown whether increased autophagy as a result of radiation affects DNA damage repair and sensitizes cancer cells. In this study, the radiosensitization effect of rapamycin, a mammalian target of rapamycin inhibitor that induces autophagy, on human lung adenocarcinoma A549 cells was investigated.
  
  
  METHODS
  A549 cells were treated with different concentrations of rapamycin. Cell viability was evaluated by methyl-thiazolyl-tetrazolium assay. Survival fraction values of A549 cells after radiotherapy were detected by colony formation assay. Autophagosome was observed by a transmission electron microscope. Furthermore, Western blot was employed to examine alterations in autophagy protein LC3 and p62, DNA damage protein γ-H2AX, and DNA damage repair proteins Rad51, Ku70, and Ku80. Rad51, Ku70, and Ku80 messenger ribonucleic acid (mRNA) expression levels were examined by real-time polymerase chain reaction.
  
  
  RESULTS
  Rapamycin suppressed A549 cell proliferation in dose and time-dependent manners. An inhibitory concentration (IC) 10 dose of rapamycin could induce autophagy in A549 cells. Rapamycin combined with radiation significantly decreased the colony forming ability of cells, compared with rapamycin or radiation alone. Rapamycin and radiation combined increased γ-H2AX expression levels and decreased Rad51 and Ku80 expression levels, compared with single regimens. However, rapamycin treatment did not induce any change in Rad51, Ku70, and Ku80 mRNA levels, regardless of radiation.
  
  
  CONCLUSIONS
  These findings indicate that increasing autophagy sensitizes lung cancer cells to radiation.
authors.affiliation: Department of Medical Oncology The First Affiliated Hospital of Nanchang University Nanchang Jiangxi China.
authors.forename: Yong
authors.initials: Y
authors.lastname: Li
authors.affiliation: Critical Care Medicine The First Affiliated Hospital of Nanchang University Nanchang Jiangxi China.
authors.forename: Fen
authors.initials: F
authors.lastname: Liu
authors.affiliation: Department of Medical Oncology The First Affiliated Hospital of Nanchang University Nanchang Jiangxi China.
authors.forename: Yong
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Neurosurgery The First Affiliated Hospital of Nanchang University Nanchang Jiangxi China.
authors.forename: Donghai
authors.initials: D
authors.lastname: Li
authors.affiliation: The institute of Burn Research The First Affiliated Hospital of Nanchang University Nanchang Jiangxi China.
authors.forename: Fei
authors.initials: F
authors.lastname: Guo
authors.affiliation: Department of Medical Oncology The First Affiliated Hospital of Nanchang University Nanchang Jiangxi China.
authors.forename: Liyao
authors.initials: L
authors.lastname: Xu
authors.affiliation: Critical Care Medicine The First Affiliated Hospital of Nanchang University Nanchang Jiangxi China.
authors.forename: Zhengguo
authors.initials: Z
authors.lastname: Zeng
authors.affiliation: Department of Medical Oncology The First Affiliated Hospital of Nanchang University Nanchang Jiangxi China.
authors.forename: Xiaojun
authors.initials: X
authors.lastname: Zhong
authors.affiliation: Critical Care Medicine The First Affiliated Hospital of Nanchang University Nanchang Jiangxi China.
authors.forename: Kejian
authors.initials: K
authors.lastname: Qian
keywords: DNA damage; lung cancer; radiotherapy; rapamycin