Suppressing proteasome mediated processing of topoisomerase II DNA-protein complexes preserves genome integrity

Area of Science:

• Molecular Biology
• Genetics
• Cancer Research

Background:

• Topoisomerase II (TOP2) manages DNA topology by creating transient double-strand breaks (DSBs) through TOP2 cleavage complexes (TOP2ccs).
• TOP2ccs are reversible but can be stabilized by poisons like etoposide (ETO), leading to variable therapeutic effectiveness in cancer.
• Cellular responses to TOP2 poisons may depend on how TOP2ccs are processed, primarily through proteolytic degradation and DNA repair.

Purpose of the Study:

• To investigate the role of proteasome-mediated repair in processing TOP2 cleavage complexes (TOP2ccs).
• To determine if inhibiting proteasome activity affects cellular response to TOP2 poisons like etoposide (ETO).
• To explore a potential mechanism for resistance to topoisomerase poisons.

Main Methods:

• Primary splenic mouse B-cells were pre-treated with proteasome inhibitors.
• Cells were subsequently exposed to the TOP2 poison etoposide (ETO).
• Analysis of TOP2cc processing, DNA damage response (DDR), genome instability, and cellular viability.

Main Results:

• Proteasome inhibition prevented proteolytic processing of trapped TOP2ccs.
• Suppression of TOP2cc degradation inhibited the DNA damage response (DDR).
• Cells protected from etoposide-induced genome instability and preserved viability; TOP2 uncoupled error-free from DNA upon ETO washout.

Conclusions:

• Proteasome-mediated repair of TOP2ccs is an error-prone process.
• Inhibiting proteasome activity protects cells from TOP2 poison-induced genotoxicity.
• Suppression of TOP2cc degradation offers a potential strategy for developing resistance to topoisomerase poisons.