title: Cell death pathways in directly irradiated cells and cells exposed to medium from irradiated cells.
abstract: OBJECTIVE
  The aim of this study was to compare levels of apoptosis, necrosis, mitotic cell death and senescence after treatment with both direct radiation and irradiated cell conditioned medium.
  
  
  METHODS
  Human keratinocytes (HaCaT cell line) were irradiated (0.005, 0.05 and 0.5 Gy) using a cobalt 60 teletherapy unit. For bystander experiments, the medium was harvested from donor HaCaT cells 1 hour after irradiation and transferred to recipient HaCaT cells. Clonogenic assay, apoptosis, necrosis, mitotic cell death, senescence and cell cycle analysis were measured in both directly irradiated cells and bystander cells
  
  
  RESULTS
  A reduction in cell survival was observed for both directly irradiated cells and irradiated cell conditioned medium (ICCM)-treated cells. Early apoptosis and necrosis was observed predominantly after direct irradiation. An increase in the number of cells in G2/M phase was observed at 6 and 12 h which led to mitotic cell death after 72 h following direct irradiation and ICCM treatment. No senescence was observed in the HaCaT cell line following either direct irradiation or treatment with ICCM.
  
  
  CONCLUSIONS
  This study has shown that directly irradiated cells undergo apoptosis, necrosis and mitotic cell death whereas ICCM-treated cells predominantly undergo mitotic cell death.
authors.affiliation: Radiation and Environmental Science Centre, Focas Research Institute, Dublin Institute of Technology, Dublin.
authors.forename: Kishore Kumar
authors.initials: KK
authors.lastname: Jella
authors.forename: Amaya
authors.initials: A
authors.lastname: Garcia
authors.forename: Brendan
authors.initials: B
authors.lastname: McClean
authors.forename: Hugh J
authors.initials: HJ
authors.lastname: Byrne
authors.forename: Fiona M
authors.initials: FM
authors.lastname: Lyng
mesh_terms: D017209:Apoptosis / Q000528:radiation effects; D024201:Bystander Effect / Q000528:radiation effects; D016923:Cell Death / Q000528:radiation effects*; D002460:Cell Line; D002470:Cell Survival / Q000528:radiation effects; D016922:Cellular Senescence / Q000528:radiation effects; D003114:Colony-Forming Units Assay; D017077:Culture Media, Conditioned; D059565:G2 Phase Cell Cycle Checkpoints / Q000528:radiation effects; D006801:Humans; D015603:Keratinocytes / Q000473:pathology / Q000528:radiation effects; D015162:Micronucleus Tests; D008938:Mitosis / Q000528:radiation effects; D009336:Necrosis
chemical_list: D017077:Culture Media, Conditioned