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A SUMO‐ubiquitin mediated proteasome pathway in repair of DNA damage induced by topoisomerase II inhibitors
Author(s) -
Sun Yilun,
Nitiss John
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.lb57
Subject(s) - sumo protein , topoisomerase , dna damage , proteasome , dna repair , ubiquitin , microbiology and biotechnology , dna ligase , ubiquitin ligase , biology , dna , chemistry , biochemistry , gene
DNA topoisomerases play a critical role in nuclear processes such as replication and transcription by managing the topology of DNA duplexes. Topoisomerase II (Top2) is an established target for anti‐cancer agents such as doxorubicin and etoposide, which act by trapping Top2 on DNA. This leads to accumulation of Top2‐DNA covalent complexes (Top2ccs) and Top2‐induced DNA double‐strand breaks (DSBs). The mechanisms causing tumor‐specific cell killing by Top2 inhibitors may arise from DNA repair defects in cancer cells. Therefore, targeting pathways for repair of Top2‐mediated damage is a potential strategy to enhance the action of Top2 inhibitors. We hypothesize that the primary step in repair of Top2‐mediated DSBs is removal of trapped Top2 from DNA, and that the ubiquitin‐proteasome system is required for this removal. To explore the proteolytic pathway for processing Top2cc, we developed a sensitive method to detect ubiquitylation and other post‐translational modifications (PTMs) on Top2cc by modifying the ICE assay, a biochemical approach for detecting protein‐DNA crosslink. Using a yeast system, we showed that the proteasome plays a key role in repair of Top2 damage by degrading Top2cc. We found that deletion of genes encoding ubiquitin ligase Slx5/Slx8 led to decreased ubiquitylation of Top2cc. Depletion of Siz1, a SUMO ligase, was found to reduce not only SUMOylation of Top2cc but also ubiquitylation of the enzyme. These findings taken together suggest a signaling axis wherein Siz1‐mediated SUMOylation primes Top2cc for Slx5/Slx8‐mediated ubiquitylation and the consequent proteasomal degradation. Finally, we demonstrated that Rnf4, the human ortholog of Slx5/Slx8, plays an important role in repairing Top2cc by modulating its ubiquitylation and proteolysis in human cells. Our work is a key step in elucidating how DNA‐protein adducts are processed in eukaryotic cells, and may lead to the identification of novel anti‐cancer drug targets.