title: Differential S-phase progression after irradiation of p53 functional versus non-functional tumour cells.
abstract: BACKGROUND
  Many pathways seem to be involved in the regulation of the intra-S-phase checkpoint after exposure to ionizing radiation, but the role of p53 has proven to be rather elusive. Here we have a closer look at the progression of irradiated cells through S-phase in dependence of their p53 status.
  
  
  METHODS
  Three pairs of tumour cell lines were used, each consisting of one p53 functional and one p53 non-functional line. Cells were labelled with bromodeoxyuridine(BrdU) immediately after irradiation, they were then incubated in label-free medium, and at different times afterwards their position within the S-phase was determined by means of flow cytometry.
  
  
  RESULTS
  While in the p53 deficient cells progression through S-phase was slowed significantly over at least a few hours, it was halted for just about an hour in the p53 proficient cells and then proceeded without further delay or even at a slightly accelerated pace.
  
  
  CONCLUSIONS
  It is clear from the experiments presented here that p53 does play a role for the progress of cells through the S-phase after X-ray exposure, but the exact mechanisms by which replicon initiation and elongation is controlled in irradiated cells remain to be elucidated.
authors.affiliation: Institute of Medical Radiobiology, Medical Faculty, University Duisburg-Essen, Germany ; Department of Radiology, Toxicology and Civil Protection, Faculty of Health and Social Studies, University of South Bohemia in České Budějovice, Czech Republic.
authors.forename: Friedo
authors.initials: F
authors.lastname: Zölzer
authors.affiliation: Institute of Medical Radiobiology, Medical Faculty, University Duisburg-Essen, Germany.
authors.forename: Tamare
authors.initials: T
authors.lastname: Mußfeldt
authors.affiliation: Institute of Medical Radiobiology, Medical Faculty, University Duisburg-Essen, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Streffer
keywords: flow cytometry, relative movement; intra-S-phase checkpoint; x-rays