DNA-PK Target Identification Reveals Novel Links between DNA Repair Signaling and Cytoskeletal Regulation

The DNA-dependent protein kinase (DNA-PK) may function as a key signaling kinase in various cellular pathways other than DNA repair. Using a two-dimensional gel electrophoresis approach and stable DNA double-strand break-mimicking molecules (Dbait32Hc) to activate DNA-PK in the nucleus and cytoplasm, we identified 26 proteins that were highly phosphorylated following DNA-PK activation. Most of these proteins are involved in protein stability and degradation, cell signaling and the cytoskeleton. We investigated the relationship between DNA-PK and the cytoskeleton and found that the intermediate filament (IF) vimentin was a target of DNA-PK in vitro and in cells . Vimentin was phosphorylated at Ser459, by DNA-PK, in cells transfected with Dbait32Hc. We produced specific antibodies and showed that Ser459-P-vimentin was mostly located at cell protrusions. In migratory cells, the vimentin phosphorylation induced by Dbait32Hc was associated with a lower cellular adhesion and migration capacity. Thus, this approach led to the identification of downstream cytoplasmic targets of DNA-PK and revealed a connection between DNA damage signaling and the cytoskeleton.