title: Live-cell imaging visualizes frequent mitotic skipping during senescence-like growth arrest in mammary carcinoma cells exposed to ionizing radiation.
abstract: OBJECTIVE
  Senescence-like growth arrest in human solid carcinomas is now recognized as the major outcome of radiotherapy. This study was designed to analyze cell cycle during the process of senescence-like growth arrest in mammary carcinoma cells exposed to X-rays.
  
  
  METHODS
  Fluorescent ubiquitination-based cell cycle indicators were introduced into the human mammary carcinoma cell line MCF-7. Cell cycle was sequentially monitored by live-cell imaging for up to 5 days after exposure to 10 Gy of X-rays.
  
  
  RESULTS
  Live-cell imaging revealed that cell cycle transition from G2 to G1 phase without mitosis, so-called mitotic skipping, was observed in 17.1% and 69.8% of G1- and G2-irradiated cells, respectively. Entry to G1 phase was confirmed by the nuclear accumulation of mKO(2)-hCdt1 as well as cyclin E, which was inversely correlated to the accumulation of G2-specific markers such as mAG-hGeminin and CENP-F. More than 90% of cells skipping mitosis were persistently arrested in G1 phase and showed positive staining for the senescent biochemical marker, which is senescence-associated ß-galactosidase, indicating induction of senescence-like growth arrest accompanied by mitotic skipping. While G2 irradiation with higher doses of X-rays induced mitotic skipping in approximately 80% of cells, transduction of short hairpin RNA (shRNA) for p53 significantly suppressed mitotic skipping, suggesting that ionizing radiation-induced mitotic skipping is associated with p53 function.
  
  
  CONCLUSIONS
  The present study found the pathway of senescence-like growth arrest in G1 phase without mitotic entry following G2-irradiation.
authors.affiliation: Department of Radiation Medical Sciences, Atomic Bomb Disease Institute, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki, Japan. msuzuki@nagasaki-u.ac.jp
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Suzuki
authors.forename: Motohiro
authors.initials: M
authors.lastname: Yamauchi
authors.forename: Yasuyoshi
authors.initials: Y
authors.lastname: Oka
authors.forename: Keiji
authors.initials: K
authors.lastname: Suzuki
authors.forename: Shunichi
authors.initials: S
authors.lastname: Yamashita
mesh_terms: D001943:Breast Neoplasms / Q000473:pathology / Q000503:physiopathology / Q000532:radiotherapy*; D018797:Cell Cycle Proteins / Q000378:metabolism; D045744:Cell Line, Tumor; D016922:Cellular Senescence / Q000502:physiology*; D019927:Cyclin E / Q000378:metabolism; D005260:Female; D005455:Fluorescent Antibody Technique / Q000379:methods; D016193:G1 Phase / Q000502:physiology / Q000528:radiation effects*; D016195:G2 Phase / Q000502:physiology / Q000528:radiation effects*; D006801:Humans; D008858:Microscopy, Phase-Contrast / Q000379:methods; D008938:Mitosis / Q000502:physiology / Q000528:radiation effects*; D034741:RNA, Small Interfering / Q000378:metabolism; D011829:Radiation Dosage; D013997:Time Factors; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: C467199:CDT1 protein, human; D018797:Cell Cycle Proteins; D019927:Cyclin E; D034741:RNA, Small Interfering; D016159:Tumor Suppressor Protein p53; D001616:beta-Galactosidase