Valosin-containing protein mediates DNA-dependent protein kinase activation in response to DNA topoisomerase II-associated DNA double-strand breaks.

DNA topoisomerase II (Top2) induces DNA double-strand breaks (DSBs) to relieve the torsional stress associated with DNA replication and transcription. Etoposide (ETP), a Top2 poison in clinical use as an anticancer drug, traps Top2 reactive intermediates, resulting in the accumulation of DSBs, coupled with the formation of Top2-DNA protein crosslinks (Top2-DPC) at the ends of DSBs. Proteasome-dependent processing of trapped Top2 is necessary for some cellular responses to ETP-induced DSBs; however, the effect of suppressing Top2 removal on DSB repair is not well understood. In this study, we focused on valosin-containing protein (VCP), a proteasome mediator, to analyze the effect of the suppression of Top2-DPC resolution on the repair of ETP-induced DSBs. ETP-induced activation of DNA-dependent protein kinase (DNA-PK), a non-homologous end-joining (NHEJ) factor, was suppressed by VCP inhibitors, similar to the effects observed in proteasome-inhibited cells. Consistent with this finding, VCP inhibition suppressed repair activity in response to ETP-induced DSBs. Additionally, VCP inhibition delayed the resolution of ETP-induced Top2-DPC. These results suggest that the processing of trapped Top2 via the VCP-proteasome pathway is important for efficient DNA-PK activation and subsequent repair in response to ETP-induced DSBs.