title: PI3K-Akt signaling regulates basal, but MAP-kinase signaling regulates radiation-induced XRCC1 expression in human tumor cells in vitro.
abstract: 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.
authors.affiliation: Division of Radiobiology & Molecular Environmental Research, Department of Radiation Oncology, Eberhard-Karls University Tuebingen, Roentgenweg 11, Tuebingen, Germany.
authors.forename: Mahmoud
authors.initials: M
authors.lastname: Toulany
authors.forename: Klaus
authors.initials: K
authors.lastname: Dittmann
authors.forename: Birgit
authors.initials: B
authors.lastname: Fehrenbacher
authors.forename: Martin
authors.initials: M
authors.lastname: Schaller
authors.forename: Michael
authors.initials: M
authors.lastname: Baumann
authors.forename: H Peter
authors.initials: HP
authors.lastname: Rodemann
mesh_terms: D045744:Cell Line, Tumor; D053903:DNA Breaks, Double-Stranded / Q000187:drug effects / Q000528:radiation effects; D004260:DNA Repair / Q000187:drug effects / Q000528:radiation effects; D051747:DNA-Activated Protein Kinase / Q000172:deficiency / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D066246:ErbB Receptors / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D006801:Humans; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000528:radiation effects; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011485:Protein Binding / Q000187:drug effects / Q000528:radiation effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011839:Radiation, Ionizing; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D011995:Recombination, Genetic / Q000187:drug effects / Q000528:radiation effects; D000076105:X-ray Repair Cross Complementing Protein 1
chemical_list: D051747:DNA-Activated Protein Kinase; D004268:DNA-Binding Proteins; D066246:ErbB Receptors; D048049:Extracellular Signal-Regulated MAP Kinases; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt; D011993:Recombinant Fusion Proteins; D000076105:X-ray Repair Cross Complementing Protein 1; C000619371:XRCC1 protein, human