Suppressing Proteasome Mediated Processing of Topoisomerase II DNA-Protein Adducts Preserves Genome Integrity

Here, we utilize high-resolution mapping of ETO-induced TOP2 lesions genome-wide (END-seq) (Canela et al., 2016), to examine the impact of proteasome inhibition on the fate of TOP2ccs. We found that once ETO-stabilized TOP2ccs had been proteolytically processed throughout the genome, and a robust DDR had been initiated, the large number of newly generated protein-free DSBs were repaired in a highly error-prone manner, resulting in toxic chromosomal translocations and rearrangements that lead to cell death. Notably, mis-repair of ETO-induced lesions occurred independently of the classical NHEJ or HR pathways. By inhibiting proteasome-mediated degradation of TOP2ccs either through chemical inhibition or by ablation of the ubiquitination of TOP2ccs by RNF4, an intact and enzymatically competent TOP2 was able to re-seal the protein-linked DSBs without invoking a significantly DDR. As a result, cells were protected from genomic instability, which ultimately led to enhanced cell survival after treatment with topoisomerase poisons. END-seq profiles in B-cells treated with etoposide and proteasome inhibitor