PI3K-Akt signaling regulates basal, but MAP-kinase signaling regulates radiation-induced XRCC1 expression in human tumor cells in vitro.
As demonstrated recently, ionizing radiation (IR) can mediate phosphorylation of DNA-PKcs in human tumor cells through stimulation of the PI3K/Akt pathway. It is also known that DNA-PKcs directly interacts the X-ray repair cross-complementing group 1 protein (XRCC1) involved in base excision repair (BER). Therefore, in the present study we investigated ... the role of PI3K/Akt activity and DNA-PKcs on XRCC1 expression/stabilization. In contrast to the DNA-PKcs-deficient glioblastoma cell line MO59J, the DNA-PKcs-proficient counterpart MO59K as well as human lung adenocarcinoma A549 cells presented a high basal level of XRCC1 expression. Radiation doses of 3-12Gy did not stimulate a further enhanced expression of XRCC1 in DNA-PKcs-proficient cells (MO59K and A549) within 180min post-irradiation. However, a marked induction of XRCC1 expression was apparent in DNA-PKcs-deficient MO59J cells. Targeting of DNA-PKcs as well as PI3K/Akt pathway by specific kinase inhibitors and/or siRNA reduced basal XRCC1 expression in un-irradiated DNA-PKcs-proficient cells to the level observed in DNA-PKcs-deficient cells. Reduction of basal expression of XRCC1 by XRCC1-siRNA, AKT-siRNA as well as DNA-PKcs inhibitor facilitated IR-induced XRCC1 expression. XRCC1 expression induced by irradiation, however, was independent of PI3K/Akt signaling, but dependent of MAPK-ERK1/2. By immuno-precipitation experiments and confocal microscopy a complex formation of XRCC1 and DNA-PKcs was shown. Applying gamma-H2AX foci analysis it was shown that basal expression of XRCC1 is important for the repair of IR-induced DNA-double strand breaks (DNA-DSBs). These data indicate that IR-induced XRCC1 expression is dependent on the expression level of DNA-PKcs and basal activity status of PI3K/Akt signaling. Likewise, potential of IR-induced XRCC1 expression depends on its basal expression level.
Mesh Terms:
Cell Line, Tumor, DNA Breaks, Double-Stranded, DNA Repair, DNA-Activated Protein Kinase, DNA-Binding Proteins, Extracellular Signal-Regulated MAP Kinases, Humans, MAP Kinase Signaling System, Mitogen-Activated Protein Kinases, Phosphatidylinositol 3-Kinases, Protein Binding, Protein Kinase Inhibitors, Proto-Oncogene Proteins c-akt, Radiation, Ionizing, Receptor, Epidermal Growth Factor, Recombinant Fusion Proteins, Recombination, Genetic
Cell Line, Tumor, DNA Breaks, Double-Stranded, DNA Repair, DNA-Activated Protein Kinase, DNA-Binding Proteins, Extracellular Signal-Regulated MAP Kinases, Humans, MAP Kinase Signaling System, Mitogen-Activated Protein Kinases, Phosphatidylinositol 3-Kinases, Protein Binding, Protein Kinase Inhibitors, Proto-Oncogene Proteins c-akt, Radiation, Ionizing, Receptor, Epidermal Growth Factor, Recombinant Fusion Proteins, Recombination, Genetic
DNA Repair (Amst.)
Date: Oct. 01, 2008
PubMed ID: 18678286
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