Topoisomerase II (TOP2) relieves topological stress in
DNA by introducing double-strand breaks (DSBs) via a transient, covalently linked TOP2
DNA-
protein intermediate, termed TOP2 cleavage complex (TOP2cc). TOP2ccs are normally rapidly reversible, but can be stabilized by TOP2
poisons, such as the chemotherapeutic agent
etoposide (ETO). TOP2
poisons have shown significant variability in their therapeutic effectiveness across different
cancers for reasons that remain to be determined. One potential explanation for the differential cellular response to these drugs is in the manner by which cells process TOP2ccs. Cells are thought to remove TOP2ccs primarily by proteolytic degradation followed by
DNA DSB repair. Here, we show that
proteasome-mediated repair of TOP2cc is highly error-prone. Pre-treating primary splenic mouse B-cells with
proteasome inhibitors prevented the proteolytic processing of trapped TOP2ccs, suppressed the DNA damage response (DDR) and completely protected cells from ETO-induced
genome instability, thereby preserving cellular viability. When degradation of TOP2cc was suppressed, the TOP2
enzyme uncoupled itself from the
DNA following ETO washout, in an error-free manner. This suggests a potential mechanism of developing resistance to topoisomerase
poisons by ensuring rapid TOP2cc reversal.