A spatial and functional interaction of a heterotetramer Survivin-DNA-PKcs complex in DNA damage response

Substantial evidence has shown that overexpression of the inhibitor of apoptosis protein (IAP) Survivin in human tumors correlates significantly with treatment resistance and poor patient prognosis. Survivin serves as a radiation resistance factor that impacts the DNA damage response by interacting with DNA-dependent protein kinase (DNA-PKcs). However, the complexity, molecular determinants and functional consequences of this interrelationship remain largely unknown. By applying co-immunoprecipitation and flow cytometry-based Forster resonance energy transfer assays, we demonstrated a direct involvement of the Survivin baculovirus IAP repeat (BIR) domain in the regulation of radiation survival and DNA repair. This Survivin-mediated activity required an interaction of residues S20 and W67 with the phosphoinositide 3-kinase (PI3K) domain of DNA-PKcs. In silico molecular docking and dynamics simulation analyses, in vitro kinase assays, and large-scale mass spectrometry suggested a heterotetrameric Survivin-DNA-PKcs complex that results in a conformational change within the DNA-PKcs PI3K domain. Overexpression or depletion of Survivin resulted in enhanced PI3K enzymatic activity and detection of differentially abundant phosphopeptides and proteins implicated in the DNA damage response. The Survivin-DNA-PKcs interaction altered the S/T-hydrophobic motif substrate specificity of DNA-PKcs with a predominant usage of S/T-P phosphorylation sites and an increase of DNA-PKcs substrates including Foxo3. These data demonstrate that Survivin differentially regulates DNA-PKcs-dependent radiation survival and DNA double-strand break repair via formation of a Survivin-DNA-PKcs heterotetrameric complex.