Optimal function of the DNA repair enzyme TDP1 requires its phosphorylation by ATM and/or DNA-PK.

Human tyrosyl-DNA phosphodiesterase (TDP1) hydrolyzes the phosphodiester bond at a DNA 3' end linked to a tyrosyl moiety. This type of linkage is found at stalled topoisomerase I (Top1)-DNA covalent complexes, and TDP1 has been implicated in the repair of such complexes. Here we show that Top1-associated DNA double-stranded breaks (DSBs) induce the phosphorylation of TDP1 at S81. This phosphorylation is mediated by the protein kinases: ataxia-telangiectasia-mutated (ATM) and DNA-dependent protein kinase (DNA-PK). Phosphorylated TDP1 forms nuclear foci that co-localize with those of phosphorylated histone H2AX (gammaH2AX). Both Top1-induced replication- and transcription-mediated DNA damages induce TDP1 phosphorylation. Furthermore, we show that S81 phosphorylation stabilizes TDP1, induces the formation of XRCC1 (X-ray cross-complementing group 1)-TDP1 complexes and enhances the mobilization of TDP1 to DNA damage sites. Finally, we provide evidence that TDP1-S81 phosphorylation promotes cell survival and DNA repair in response to CPT-induced DSBs. Together; our findings provide a new mechanism for TDP1 post-translational regulation by ATM and DNA-PK.