title: Non-homologous end-joining protein expression screen from radiosensitive cancer patients yields a novel DNA double strand break repair phenotype.
abstract: BACKGROUND
  Clinical radiosensitivity is a significant impediment to tumour control and cure, in that it restricts the total doses which can safely be delivered to the whole radiotherapy population, within the tissue tolerance of potentially radiosensitive (RS) individuals. Understanding its causes could lead to personalization of radiotherapy.
  
  
  METHODS
  We screened tissues from a unique bank of RS cancer patients for expression defects in major DNA double-strand break repair proteins, using Western blot analysis and subsequently reverse-transcriptase polymerase chain reaction and pulsed-field gel electrophoresis.
  
  
  RESULTS
  We hypothesized that abnormalities in expression of these proteins may explain the radiosensitivity of some of our cancer patients. The cells from one patient showed a reproducibly consistent expression reduction in two complex-forming DNA double-strand break repair protein components (DNA Ligase IV and XRCC4). We also showed a corresponding reduction in both gene products at the mRNA level. Additionally, the mRNA inducibility by ionizing radiation was increased for one of the proteins in the patient's cells. We confirmed the likely functional significance of the non-homologous end-joining (NHEJ) expression abnormalities with a DNA double strand break (DNA DSB) repair assay.
  
  
  CONCLUSIONS
  We have identified a novel biological phenotype linked to clinical radiosensitivity. This is important in that very few molecular defects are known in human radiotherapy subjects. Such knowledge may contribute to the understanding of radiation response mechanisms in cancer patients and to personalization of radiotherapy.
authors.affiliation: University of Sydney, Department of Medicine, Camperdown, 2050 NSW, Australia.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: McKay
authors.affiliation: Peter MacCallum Cancer Centre, Melbourne, VIC, Australia.
authors.forename: Su Kak
authors.initials: SK
authors.lastname: Goh
authors.affiliation: Monash University, Clayton, 3260 VIC, Australia.
authors.forename: Jeremy N
authors.initials: JN
authors.lastname: McKay
authors.affiliation: Genesis Cancer Care, Melbourne, 3001 VIC, Australia.
authors.forename: Michael
authors.initials: M
authors.lastname: Chao
authors.affiliation: Deakin University, Burwood, 3125 VIC, Australia.
authors.forename: Timothy M
authors.initials: TM
authors.lastname: McKay
keywords: DNA double strand break (DNA DSB); Non-homologous end-joining (NHEJ); radiosensitivity cancer