Radiation-induced survivin nuclear accumulation is linked to DNA damage repair.
OBJECTIVE
Increased expression of survivin has been identified as a negative prognostic marker in a variety of human cancers. We have previously shown that survivin is a radiation-resistance factor and that the therapeutic effect of survivin knock-down might result from an impaired DNA repair capacity. In this study, we aimed to elucidate an interrelationship between survivin's cellular localization and DNA double-strand break repair.


METHODS
Survivin's cellular distribution and nuclear complex formation were assayed by Western blotting of subcellular fractions, by immunofluorescence staining, and co-immunoprecipitation in SW480 colorectal cancer cells. DNA repair capacity was analyzed by kinetics of gamma-H2AX foci formation, and by DNA-dependent protein kinase (DNA-PKcs) assays in the presence of survivin-specific or nonspecific control siRNA.


RESULTS
Following irradiation, we observed a rapid nuclear accumulation of survivin and subsequent phosphorylation of the protein in the nucleus. Co-immunoprecipitation analyses from nuclear extracts revealed an interaction among survivin, Ku70, gamma-H2AX, MDC1, and DNA-PKcs that was confirmed by immunofluorescence co-localization in nuclear foci. Survivin knock down by siRNA resulted in an impaired DNA double strand break repair, as demonstrated by an increased detection of gamma-H2AX foci/nucleus at 60 min and a higher amount of residual gamma-H2AX foci at 24 hr postirradiation. Furthermore, we detected in survivin-depleted cells a hampered S2056 autophosphorylation of DNA-PKcs and a significantly decreased DNA-PKcs kinase activity.


CONCLUSIONS
These data indicate that nuclear survivin is linked to DNA double-strand break repair by interaction with members of the DNA double-strand breaks repair machinery, thus regulating DNA-PKcs activity.
Capalbo
Gianni
G
Departments of Radiation Therapy and Oncology, University of Frankfurt/Main, Frankfurt, Germany.
Dittmann
Klaus
K
Weiss
Christian
C
Reichert
Sebastian
S
Hausmann
Eva
E
Rödel
Claus
C
Rödel
Franz
F
D048868:Adaptor Proteins, Signal Transducing; D018797:Cell Cycle Proteins; D002467:Cell Nucleus / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D053903:DNA Breaks, Double-Stranded; D004249:DNA Damage; D004260:DNA Repair / Q000502:physiology* / Q000528:radiation effects; D051747:DNA-Activated Protein Kinase / Q000378:metabolism; D006657:Histones / Q000378:metabolism; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism; D010766:Phosphorylation; D034741:RNA, Small Interfering; D000077022:Survivin; D015534:Trans-Activators / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000528:radiation effects
D048868:Adaptor Proteins, Signal Transducing; C107489:BIRC5 protein, human; D018797:Cell Cycle Proteins; C468783:H2AX protein, human; D006657:Histones; D051034:Inhibitor of Apoptosis Proteins; C413163:MDC1 protein, human; D008869:Microtubule-Associated Proteins; D009687:Nuclear Proteins; D034741:RNA, Small Interfering; D000077022:Survivin; D015534:Trans-Activators; D051747:DNA-Activated Protein Kinase