MAPK dependence of DNA damage repair: ionizing radiation and the induction of expression of the DNA repair genes XRCC1 and ERCC1 in DU145 human prostate carcinoma cells in a MEK1/2 dependent fashion.
OBJECTIVE
To examine the role of mitogen-activated protein kinase (MAPK) signalling on the induction by ionizing radiation of the nucleotide excision repair gene (ERCC1), the X-ray cross-complementing group 1 protein (XRCC1) and the repair of radiation-induced DNA damage.


METHODS
The expression of ERCC1 and XRCC1 was examined in DU145 human prostate cancer cells following exposure to ionizing radiation. We characterized the MAPK dependence of this expression through RT-PCR analysis, Western analysis, transcription inhibition and measurement of the activation of each promoter. Pre-exposure with the specific MEK1/2 inhibitor PD980059 (10 microM) was used to blunt radiation induction of MAPK without suppressing basal levels of MAPK activity. In addition, we examined the MAPK dependence of DNA damage repair by measuring radiation-induced micronucleus formation and the removal of and nicking activity associated with AP sites.


RESULTS
Irradiation caused a time-dependent, MAPK-dependent increase in the protein levels of both ERCC1 and XRCC1. For each gene product, the protein level increase followed an increase in mRNA, which also was MAPK-dependent. Radiation also enhanced the activities of the ERCC1 and XRCC1 promoters in an MAPK-dependent fashion. Inhibition of transcription by DRB abolished the radiation-induced increase of ERCC1 and XRCC1 proteins. Inhibition of radiation-induced MAPK also diminished the ability of DU145 cells to remove AP sites and increased the number of cells displaying micronuclei following radiation exposure.


CONCLUSIONS
These findings demonstrate a role for radiation-induced MAPK signalling in the regulation of DNA repair enzyme levels and DNA repair. Radiation-induced protein expression of ERCC1 and XRCC1 appears to require de novo transcription. These data suggest a significant role for MAPK signalling in the early response to DNA damage caused by ionizing radiation.
Yacoub
A
A
Department of Radiation Oncology, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA 23298, USA.
Park
J S
JS
Qiao
L
L
Dent
P
P
Hagan
M P
MP
D004249:DNA Damage; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000235:genetics*; D004720:Endonucleases; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D020935:MAP Kinase Signaling System; D008297:Male; D020928:Mitogen-Activated Protein Kinases / Q000502:physiology*; D011401:Promoter Regions, Genetic; D011471:Prostatic Neoplasms / Q000235:genetics / Q000532:radiotherapy*; D011506:Proteins / Q000235:genetics*; D014407:Tumor Cells, Cultured; D000076105:X-ray Repair Cross Complementing Protein 1
D004268:DNA-Binding Proteins; D011506:Proteins; D000076105:X-ray Repair Cross Complementing Protein 1; C000619371:XRCC1 protein, human; D020928:Mitogen-Activated Protein Kinases; C071447:ERCC1 protein, human; D004720:Endonucleases