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26 S proteasome-mediated degradation of topoisomerase II cleavable complexes
1Department of Pharmacology, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, Piscataway, New Jersey 08854-5635, USA.
Abstract:
DNA topoisomerase II (TOP2) cleavable complexes represent an unusual type of DNA damage characterized by reversible TOP2-DNA cross-links and DNA double strand breaks. Many antitumor drugs and physiological stresses are known to induce TOP2 cleavable complexes leading to apoptotic cell death and genomic instability. However, the molecular mechanism(s) for repair of TOP2 cleavable complexes remains unclear. In the current studies, we show that TOP2 cleavable complexes induced by the prototypic TOP2 poison VM-26 are proteolytically degraded by the ubiquitin/26 S proteasome pathway. Surprisingly the TOP2beta isozyme is preferentially degraded over TOP2alpha isozyme. In addition, transcription inhibitors such as 5,6-dichlorobenzimidazole riboside and camptothecin can substantially block VM-26-induced TOP2beta degradation. These results are consistent with a model in which the repair of TOP2beta cleavable complexes may involve transcription-dependent proteolysis of TOP2beta to reveal the protein-concealed double strand breaks.
Insights
DNA topoisomerase II (TOP2) cleavable complexes are repaired through proteasome degradation, with TOP2beta preferentially targeted. Transcription inhibition blocks this DNA damage repair pathway.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- DNA topoisomerase II (TOP2) cleavable complexes are a form of DNA damage involving TOP2-DNA cross-links and double-strand breaks.
- Antitumor drugs and stress induce these complexes, leading to cell death and genomic instability.
- The precise repair mechanisms for TOP2 cleavable complexes are not fully understood.
Purpose of the Study:
- To investigate the molecular mechanisms underlying the repair of TOP2 cleavable complexes.
- To identify the cellular pathways involved in resolving TOP2-DNA damage.
Main Methods:
- Induction of TOP2 cleavable complexes using the drug VM-26.
- Analysis of TOP2 isozyme degradation via the ubiquitin/26 S proteasome pathway.
- Assessment of the effect of transcription inhibitors (5,6-dichlorobenzimidazole riboside, camptothecin) on TOP2beta degradation.
Main Results:
- VM-26-induced TOP2 cleavable complexes are degraded by the ubiquitin/26 S proteasome pathway.
- The TOP2beta isozyme is preferentially degraded compared to the TOP2alpha isozyme.
- Transcription inhibitors significantly inhibit the degradation of TOP2beta.
Conclusions:
- TOP2 cleavable complex repair involves transcription-dependent proteolysis of TOP2beta.
- This proteolysis may expose protein-concealed double-strand breaks for further repair.
- The findings shed light on a novel DNA damage response pathway involving TOP2beta.