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Small molecule inhibitors confirm ubiquitin-dependent removal of TOP2-DNA covalent complexes

Lookup NU author(s): Rebecca Swan, Luke Poh, Dr Ian CowellORCiD, Professor Caroline AustinORCiD



This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


The American Society for Pharmacology and Experimental Therapeutics.DNA Topoisomerase II (TOP2) is required for the unwinding and decatenation of DNA through the induction of an enzyme-linked double strand break (DSB) in one DNA molecule, and passage of another intact DNA duplex through the break. Anticancer drugs targeting TOP2 (TOP2 poisons) prevent religation of the DSB and stabilise a normally transient intermediate of the TOP2 reaction mechanism called the TOP2-DNA covalent complex. Subsequently, TOP2 remains covalently bound to each end of the enzyme bridged DSB, which cannot be repaired until TOP2 is removed from the DNA. One removal mechanism involves the proteasomal degradation of the TOP2 protein, leading to the liberation of a protein-free DSB. Proteasomal degradation is often regulated by protein ubiquitination, and here we show that inhibition of ubiquitin activating enzymes reduces the processing of TOP2A- and TOP2B- DNA complexes. Depletion or inhibition of ubiquitin activating enzymes indicated that ubiquitination was required for the liberation of etoposide-induced protein-free DSBs and is therefore an important layer of regulation in the repair of TOP2 poison-induced DNA damage. TOP2-DNA complexes stabilised by etoposide were shown to be conjugated to ubiquitin and this was reduced by inhibition or depletion of ubiquitin activating enzymes. SIGNIFICANCE STATEMENT: There is currently great clinical interest in the ubiquitin-proteasome system and ongoing development of specific inhibitors. The results in this paper show that the therapeutic cytotoxicity of TOP2 poisons can be enhanced through combination therapy with UAE inhibitors, or by specific inhibition of the BMI/RING1A ubiquitin ligase which would lead to increased cellular accumulation or persistence of TOP2-DNA complexes.

Publication metadata

Author(s): Swan R, Poh L, Cowell IG, Austin CA

Publication type: Article

Publication status: Published

Journal: Molecular pharmacology

Year: 2020

Volume: 98

Issue: 2

Online publication date: 25/06/2020

Acceptance date: 02/04/2016

Date deposited: 23/10/2020

ISSN (print): 0026-895X

ISSN (electronic): 1521-0111

Publisher: American Society for Pharmacology and Experimental Therapeutics


DOI: 10.1124/mol.119.118893

PubMed id: 32587095


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