title: Dependence of adaptive response and its bystander transmission on the genetic background of tested cells.
abstract: OBJECTIVE
  Radiation-induced adaptive response (AR) is a phenomenon of increased radioresistance mediated by a low priming dose of ionizing radiation (IR) applied prior to a higher challenging dose. We have previously shown that in mouse-embryo fibroblasts (MEF) and human A549 cells, AR is associated with enhanced repair of DNA double-strand breaks (DSB) by the DNA-PK-dependent pathway of non-homologous end-joining (D-NHEJ). Importantly, AR was 'transmitted' to non-irradiated bystander cells through transfer of medium from cells that had received a priming dose of IR. Here, we examine the influence of the genetic background in these responses.
  
  
  METHODS
  Two plasmid-based assays specifically designed to measure the efficiency of NHEJ and HRR (homologous recombination repair) were deployed. MEF and the primary human fibroblast cell lines HF12 and HF19 were exposed to 10 mGy to 5 Gy X-rays. Bystander effects were investigated using the medium-transfer technique.
  
  
  RESULTS
  In contrast to MEF, which induce robust AR to NHEJ, even as a bystander response, human fibroblasts fail to develop such phenomena.
  
  
  CONCLUSIONS
  The development of AR is cell-type-specific. The same holds true for the development of AR as a bystander effect. Better understanding of the underlying mechanisms will help to understand the molecular basis of these differences in response.
authors.affiliation: Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, Essen, Germany.
authors.forename: Holger
authors.initials: H
authors.lastname: Klammer
authors.forename: Li-Hua
authors.initials: LH
authors.lastname: Zhang
authors.forename: Munira
authors.initials: M
authors.lastname: Kadhim
authors.forename: George
authors.initials: G
authors.lastname: Iliakis
mesh_terms: D000818:Animals; D024201:Bystander Effect / Q000235:genetics* / Q000528:radiation effects*; D059447:Cell Cycle Checkpoints / Q000235:genetics / Q000528:radiation effects; D002460:Cell Line; D002470:Cell Survival / Q000235:genetics / Q000528:radiation effects; D059766:DNA End-Joining Repair / Q000235:genetics / Q000528:radiation effects; D005347:Fibroblasts / Q000166:cytology; D017930:Genes, Reporter / Q000235:genetics; D059765:Homologous Recombination / Q000235:genetics / Q000528:radiation effects; D006801:Humans; D008164:Luminescent Proteins / Q000235:genetics; D051379:Mice; D011836:Radiation Tolerance / Q000235:genetics*
chemical_list: D008164:Luminescent Proteins