title: The double-stranded RNA-activated protein kinase mediates radiation resistance in mouse embryo fibroblasts through nuclear factor kappaB and Akt activation.
abstract: OBJECTIVE
  Activation of the double-stranded RNA-activated protein kinase (PKR) leads to the induction of various pathways including the down-regulation of translation through phosphorylation of the eukaryotic translation initiation factor 2alpha (eIF-2alpha). There have been no reports to date about the role of PKR in radiation sensitivity.
  
  
  METHODS
  A clonogenic survival assay was used to investigate the sensitivity of PKR mouse embryo fibroblasts (MEF) to radiation therapy. 2-Aminopurine (2-AP), a chemical inhibitor of PKR, was used to inhibit PKR activation. Nuclear factor-kappaB (NF-kappaB) activation was assessed by electrophoretic mobility shift assay (EMSA). Expression of PKR and downstream targets was examined by Western blot analysis and immunofluorescence.
  
  
  RESULTS
  Ionizing radiation leads to dose- and time-dependent increases in PKR expression and function that contributes to increased cellular radiation resistance as shown by clonogenic survival and terminal nucleotidyl transferase-mediated nick end labeling (TUNEL) apoptosis assays. Specific inhibition of PKR with the chemical inhibitor 2-AP restores radiation sensitivity. Plasmid transfection of the PKR wild-type (wt) gene into PKR(-/-) MEFs leads to increased radiation resistance. The protective effect of PKR to radiation may be mediated in part through NF-kappaB and Akt because both NF-kappaB and Akt are activated after ionizing radiation in PKR+/+ but not PKR-/- cells.
  
  
  CONCLUSIONS
  We suggest a novel role for PKR as a mediator of radiation resistance modulated in part through the protective effects of NF-kappaB and Akt activation. The modification of PKR activity may be a novel strategy in the future to overcome radiation resistance.
authors.affiliation: Department of Surgical Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030, USA.
authors.forename: Urs
authors.initials: U
authors.lastname: von Holzen
authors.forename: Abujiang
authors.initials: A
authors.lastname: Pataer
authors.forename: Uma
authors.initials: U
authors.lastname: Raju
authors.forename: Dora
authors.initials: D
authors.lastname: Bocangel
authors.forename: Stephan A
authors.initials: SA
authors.lastname: Vorburger
authors.forename: Yanna
authors.initials: Y
authors.lastname: Liu
authors.forename: Xiaolin
authors.initials: X
authors.lastname: Lu
authors.forename: Jack A
authors.initials: JA
authors.lastname: Roth
authors.forename: Bharat B
authors.initials: BB
authors.lastname: Aggarwal
authors.forename: Glen N
authors.initials: GN
authors.lastname: Barber
authors.forename: Khandan
authors.initials: K
authors.lastname: Keyomarsi
authors.forename: Kelly K
authors.initials: KK
authors.lastname: Hunt
authors.forename: Stephen G
authors.initials: SG
authors.lastname: Swisher
mesh_terms: D000818:Animals; D003720:Densitometry; D004307:Dose-Response Relationship, Radiation; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D020287:In Situ Nick-End Labeling; D051379:Mice; D008954:Models, Biological; D016328:NF-kappa B / Q000378:metabolism*; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D011839:Radiation, Ionizing; D014162:Transfection; D019892:eIF-2 Kinase / Q000378:metabolism*
chemical_list: D015852:Eukaryotic Initiation Factor-2; D016328:NF-kappa B; D051057:Proto-Oncogene Proteins c-akt; D019892:eIF-2 Kinase