ICRF-193, a catalytic inhibitor of DNA topoisomerase II (TOP2), induces the formation of the TOP2 closed-clamp intermediate. Only the ICRF-193-induced topoisomerase IIβ (TOP2B) closed clamp is known to be selectively and rapidly degraded in vertebrates, but the details are unknown. In this study, we focused on the C-terminal domain (CTD) of TOP2B, which regulates its nuclear dynamics, and sought the region that affects the ICRF-193-induced TOP2B closed-clamp degradation. Using a CTD-swapping mutant between topoisomerase IIα (TOP2A) and TOP2B, we found that the CTD of TOP2B, but not that of TOP2A, is involved in the TOP2B closed-clamp degradation. Furthermore, we identified the C-terminal region (CTR) of TOP2B (amino acids 1570-1621) as a domain that affects TOP2B closed-clamp degradation using a CTR truncation mutant (ΔCTR). A transcription inhibitor inhibited the ICRF-193-induced TOP2B closed-clamp degradation, but the TOP2B ΔCTR closed-clamp degradation was not. In addition, the results of co-immunoprecipitation and immunofluorescence staining showed that the proximity of TOP2B and RNA polymerase II on chromatin in the presence of ICRF-193 tended to be reduced by the lack of TOP2B CTR. Taken together, our data indicate that the TOP2B CTR is involved in the transcription-dependent TOP2B closed-clamp degradation induced by ICRF-193.
