Activation of protein kinase Cepsilon stimulates DNA-repair via epidermal growth factor receptor nuclear accumulation.
OBJECTIVE
To elucidate the interaction between radioprotector O-phospho-l-tyrosine (P-Tyr) with epidermal growth factor receptor (EGFR).


METHODS
Molecular effects of P-Tyr at the level of EGFR responses were investigated in vitro with TP53-wildtype bronchial carcinoma cell line A549, which is radio-protected by P-Tyr treatment. Nuclear EGFR accumulation was followed by confocal microscopy and Western blotting. PKCepsilon protein expression was impaired by specific siRNA. Residual DNA-damage was quantified with gammaH(2)AX foci analysis.


RESULTS
P-Tyr mediated radio-protection was associated with nuclear EGFR accumulation. Radiation-induced nuclear EGFR presented increased phosphorylation at residue No. T654. We identified PKCepsilon as responsible for T654-phosphorylation. Knockdown of PKCepsilon by siRNA blocked both radiation- and P-Tyr-triggered nuclear EGFR accumulation. Furthermore, nuclear accumulation of EGFR was associated with increased phosphorylation of DNA-dependent protein kinase (DNA-PK) at residue No. T2609, essential for DNA-repair. Consequently P-Tyr mediated effects upon DNA-PK resulted in a significant reduction of radiation-induced residual gammaH(2)AX-foci. Knockdown of PKCepsilon increased radiation-induced residual damage and abolished the P-Tyr associated radioprotection. In addition, P-Tyr mediated radioprotection was completely absent in colony formation assay.


CONCLUSIONS
The data presented herein suggest that P-Tyr-treatment mediates activation of PKCepsilon, which triggers nuclear EGFR accumulation. Nuclear EGFR is involved in phosphorylation of DNA-PK at Thr2609, which has a significant impact upon DNA-DSB repair.
Department of Radiation Oncology, University of Tübingen, Germany
Gabriele
G
Wanner
Claus
C
Mayer
Rainer
R
Kehlbach
H Peter
HP
Rodemann
Klaus
K
Dittmann
D015153:Blotting, Western; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair / Q000502:physiology*; D066246:ErbB Receptors / Q000378:metabolism*; D006801:Humans; D018613:Microscopy, Confocal; D019000:Phosphotyrosine / Q000494:pharmacology; D051744:Protein Kinase C-epsilon / Q000378:metabolism*; D011837:Radiation-Protective Agents
D011837:Radiation-Protective Agents; D019000:Phosphotyrosine; D066246:ErbB Receptors; D051744:Protein Kinase C-epsilon