title: Depletion of securin induces senescence after irradiation and enhances radiosensitivity in human cancer cells regardless of functional p53 expression.
abstract: OBJECTIVE
  Radiotherapy is one of the best choices for cancer treatment. However, various tumor cells exhibit resistance to irradiation-induced apoptosis. The development of new strategies to trigger cancer cell death besides apoptosis is necessary. This study investigated the role of securin in radiation-induced apoptosis and senescence in human cancer cells.
  
  
  METHODS
  Cell survival was determined using clonogenic assays. Western blot analysis was used to analyze levels of securin, caspase-3, PARP, p53, p21, Rb, gamma-H2AX, and phospho-Chk2. Senescent cells were analyzed using a beta-galactosidase staining assay. A securin-expressed vector (pcDNA-securin) was stably transfected into securin-null HCT116 cells. Securin gene knockdown was performed by small interfering RNA and small hairpin RNA in HCT116 and MDA-MB-231 cells, respectively.
  
  
  RESULTS
  Radiation was found to induce apoptosis in securin wild type HCT116 cells but induced senescence in securin-null cells. Restoration of securin reduced senescence and increased cell survival in securin-null HCT116 cells after irradiation. Radiation-induced gamma-H2AX and Chk2 phosphorylation were induced transiently in securin-wild-type cells but exhibited sustained activation in securin-null cells. Securin gene knockdown switches irradiation-induced apoptosis to senescence in both HCT116 p53-null and MDA-MB-231 cells.
  
  
  CONCLUSIONS
  Our results demonstrated that the level of securin expression plays a determining role in the radiosensitivity and fate of cells. Depletion of securin impairs DNA repair after irradiation, increasing DNA damage and promoting senescence in the residual surviving cells regardless of functional p53 expression. The knockdown of securin may contribute to a novel radiotherapy protocol for the treatment of human cancer cells that are resistant to irradiation.
authors.affiliation: Department of Life Science, Tzu Chi University, Hualien, Taiwan.
authors.forename: Wen-Shu
authors.initials: WS
authors.lastname: Chen
authors.forename: Yi-Chu
authors.initials: YC
authors.lastname: Yu
authors.forename: Yi-Jang
authors.initials: YJ
authors.lastname: Lee
authors.forename: Ji-Hshiung
authors.initials: JH
authors.lastname: Chen
authors.forename: Hsue-Yin
authors.initials: HY
authors.lastname: Hsu
authors.forename: Shu-Jun
authors.initials: SJ
authors.lastname: Chiu
mesh_terms: D017209:Apoptosis / Q000502:physiology* / Q000528:radiation effects; D015153:Blotting, Western; D053148:Caspase 3 / Q000378:metabolism; D045744:Cell Line, Tumor / Q000528:radiation effects; D016922:Cellular Senescence / Q000502:physiology* / Q000528:radiation effects; D064447:Checkpoint Kinase 2; D003114:Colony-Forming Units Assay / Q000379:methods; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D004260:DNA Repair; D055785:Gene Knockdown Techniques / Q000379:methods; D045325:HCT116 Cells / Q000528:radiation effects; D006657:Histones / Q000378:metabolism; D006801:Humans; D009363:Neoplasm Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011836:Radiation Tolerance / Q000502:physiology*; D016160:Retinoblastoma Protein / Q000378:metabolism; D064249:Securin; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*
chemical_list: D050759:Cyclin-Dependent Kinase Inhibitor p21; C468783:H2AX protein, human; D006657:Histones; D009363:Neoplasm Proteins; D016160:Retinoblastoma Protein; D064249:Securin; D016159:Tumor Suppressor Protein p53; C578002:pituitary tumor-transforming protein 1, human; C499320:PARP1 protein, human; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases; D064447:Checkpoint Kinase 2; C578634:CHEK2 protein, human; D017346:Protein Serine-Threonine Kinases; D053148:Caspase 3