Poly(ADP-ribosyl)ation as a DNA damage-induced post-translational modification regulating poly(ADP-ribose) polymerase-1-topoisomerase I interaction.

Poly(ADP-ribosyl)ation is a post-translational modification that occurs immediately after exposure of cells to DNA damaging agents. In vivo, 90% of ADP-ribose polymers are attached to the automodification domain of poly(ADP-ribose) polymerase-1 (PARP-1), the main enzyme catalyzing this modification reaction. This enzyme forms complexes with transcription initiation, DNA replication, and DNA repair factors. In most known cases, the interactions occur through the automodification domain. However, functional implications of the automodification reaction on these interactions have not yet been elucidated. In the present study, we created fluorescent protein-tagged PARP-1 to study this enzyme in live cells and focused on the interaction between PARP-1 and topoisomerase I (Topo I), one of the enzymes that interacts with PARP-1 in vitro. Here, we demonstrate that PARP-1 co-localizes with Topo I throughout the cell cycle. Results from bioluminescence resonance energy transfer assays suggest that the co-localization is because of a direct protein-protein interaction. In response to DNA damage, PARP-1 de-localization and a reduction in bioluminescence resonance energy transfer signal because of the automodification reaction are observed, suggesting that the automodification reaction results in the disruption of the interaction between PARP-1 and Topo I. Because Topo I activity has been reported to be promoted by PARP-1, we then investigated the effect of the disruption of this interaction on Topo I activity, and we found that this disruption results in the reduction of Topo I activity. These results suggest that a function for the automodification reaction is to regulate the interaction between PARP-1 and Topo I, and consequently, the Topo I activity, in response to DNA damage.