title: [Cancer stem cells play an important role in resistance of laryngeal squamous cancer to irradiation mediated by hypoxia].
abstract: OBJECTIVE
  To study whether laryngeal cancer stem cells in hypoxia have the characteristic of resistance to irradiation and underlying mechanism.
  
  
  METHODS
  CD133(+) cells were separated from Hep-2 cells with flow cytometry (FCM) and the purity was 92.8%. The separated CD133(+) cells were cultured in serum-free medium in hypoxia in normoxia environment respectively, and hypoxia-inducible factor 1 alpha (HIF-1α) expression was detected by FCM. The cells were exposed respectively to X-rays emitted by linear accelerator with a dose of 0, 5, 10, 15 or 20 Gy for 24 hours, with additional time points of 12, 36, and 48 hours for the cells exposed to 10 Gy. Then the growth inhibition ratios of cells in hypoxia and normoxia groups were detected with MTT assay at different time points. Soft agar colony formation assay was used to detect colony formation ratios of cells in hypoxia and normoxia groups. DNA dependent protein kinase catalytic subunit (DNA-PKcs), ataxia telangiectasia mutate (ATM), Survivin and P53 were detected by FCM.
  
  
  RESULTS
  Growth inhibition ratio of CD133(+) cells in hypoxia group was lower than that in normoxia group (P < 0.05). Colony formation ratio of CD133(+) cells was higher than that of CD133(-) cells (P < 0.01) and the ratio of CD133(+) cells in hypoxia group was higher than that in normoxia group (P < 0.05). The ratio of hypoxia group was not affected by irradiation, while the ratio of normoxia group decreased significantly after irradiation (P < 0.05). The expressions of DNA-PKcs, ATM, Survivin and P53 in CD133(+) cells were higher than those in CD133(-) cells respectively (P < 0.01). In CD133(+) cells with radiation, the expressions of DNA-PKcs and Survivin of hypoxia group were higher those of normoxia group (P < 0.05), but no difference in the expression of ATM or P53 between the two groups.
  
  
  CONCLUSIONS
  Laryngeal cancer stem cells play an important role in radioresistance mediated by hypoxia.
authors.affiliation: Department of Otorhinolaryngology, Head and Neck Surgery, Chinese People Liberation Army General Hospital, Beijing, China.
authors.forename: Mao-xin
authors.initials: MX
authors.lastname: Wang
authors.forename: Xiao-ming
authors.initials: XM
authors.lastname: Li
authors.forename: Yong
authors.initials: Y
authors.lastname: Zhao
authors.forename: Xiu-ying
authors.initials: XY
authors.lastname: Lu
authors.forename: Yong-tao
authors.initials: YT
authors.lastname: Qu
authors.forename: Ou
authors.initials: O
authors.lastname: Xu
authors.forename: Qing-jia
authors.initials: QJ
authors.lastname: Sun
mesh_terms: D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D005434:Flow Cytometry; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism; D007822:Laryngeal Neoplasms / Q000378:metabolism* / Q000532:radiotherapy*; D014411:Neoplastic Stem Cells / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism*
chemical_list: D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D010100:Oxygen