The double-stranded RNA-activated protein kinase mediates radiation resistance in mouse embryo fibroblasts through nuclear factor kappaB and Akt activation

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...

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Bibliographic Details
Published in:Clinical cancer research 2007-10, Vol.13 (20), p.6032
Main Authors: von Holzen, Urs, Pataer, Abujiang, Raju, Uma, Bocangel, Dora, Vorburger, Stephan A, Liu, Yanna, Lu, Xiaolin, Roth, Jack A, Aggarwal, Bharat B, Barber, Glen N, Keyomarsi, Khandan, Hunt, Kelly K, Swisher, Stephen G
Format: Article
Language:English
Subjects:
Animals
Densitometry
Dose-Response Relationship, Radiation
eIF-2 Kinase - metabolism
Eukaryotic Initiation Factor-2 - metabolism
Fibroblasts - metabolism
Gene Expression Regulation, Enzymologic
In Situ Nick-End Labeling
Mice
Models, Biological
NF-kappa B - metabolism
Phosphorylation
Plasmids - metabolism
Proto-Oncogene Proteins c-akt - metabolism
Radiation, Ionizing
Transfection
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Summary: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. 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. 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. 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.
ISSN:1078-0432
1557-3265