title: p21 is Responsible for Ionizing Radiation-induced Bypass of Mitosis.
abstract: OBJECTIVE
  To explore the role of p21 in ionizing radiation-induced changes in protein levels during the G2/M transition and long-term G2 arrest.
  
  
  METHODS
  Protein expression levels were assessed by western blot in the human uveal melanoma 92-1 cells after treatment with ionizing radiation. Depletion of p21 was carried out by employing the siRNA technique. Cell cycle distribution was determined by flow cytometry combined with histone H3 phosphorylation at Ser28, an M-phase marker. Senescence was assessed by senescence- associated-β-galactosidase (SA-β-gal) staining combined with Ki67 staining, a cell proliferation marker.
  
  
  RESULTS
  Accompanying increased p21, the protein levels of G2/M transition genes declined significantly in 92-1 cells irradiated with 5 Gy of X-rays. Furthermore, these irradiated cells were blocked at the G2 phase followed by cellular senescence. Depletion of p21 rescued radiation-induced G2 arrest as demonstrated by the upregulation of G2/M transition kinases, as well as the high expression of histone H3 phosphorylated at Ser28. Knockdown of p21 resulted in entry into mitosis of irradiated 92-1 cells. However, cells with serious DNA damage failed to undergo cytokinesis, leading to the accumulation of multinucleated cells.
  
  
  CONCLUSIONS
  Our results indicated that p21 was responsible for the downregulation of G2/M transition regulatory proteins and the bypass of mitosis induced by irradiation. Downregulation of p21 by siRNA resulted in G2-arrested cells entering into mitosis with serious DNA damage. This is the first report on elucidating the role of p21 in the bypass of mitosis.
authors.affiliation: Gansu Key Laboratory of Space Radiobiology, Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, Gansu, China; University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Xu Rui
authors.initials: XR
authors.lastname: Zhang
authors.affiliation: Gansu Key Laboratory of Space Radiobiology, Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, Gansu, China; University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Yong Ai
authors.initials: YA
authors.lastname: Liu
authors.affiliation: Gansu Key Laboratory of Space Radiobiology, Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, Gansu, China; University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Fang
authors.initials: F
authors.lastname: Sun
authors.affiliation: Gansu Key Laboratory of Space Radiobiology, Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, Gansu, China; University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: He
authors.initials: H
authors.lastname: Li
authors.affiliation: Chinese Center for Disease Control and Prevention, Beijing 100049, China.
authors.forename: Su Wen
authors.initials: SW
authors.lastname: Lei
authors.affiliation: Gansu Key Laboratory of Space Radiobiology, Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, Gansu, China.
authors.forename: Ju Fang
authors.initials: JF
authors.lastname: Wang
mesh_terms: D059447:Cell Cycle Checkpoints / Q000528:radiation effects; D045744:Cell Line, Tumor; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000378:metabolism*; D004249:DNA Damage; D015536:Down-Regulation; D005347:Fibroblasts / Q000378:metabolism* / Q000528:radiation effects*; D005786:Gene Expression Regulation / Q000528:radiation effects; D006801:Humans; D008938:Mitosis / Q000528:radiation effects*; D034622:RNA Interference; D034741:RNA, Small Interfering; D011839:Radiation, Ionizing; D015854:Up-Regulation
chemical_list: C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D034741:RNA, Small Interfering
keywords: DNA damage; G2 arrest; G2/M transition; Ionizing radiation