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Disruption of a topoisomerase-DNA cleavage complex by a DNA helicase
M T Howard1, S H Neece, S W Matson
1Department of Biology, University of North Carolina, Chapel Hill 27599.
Abstract:
The type II DNA topoisomerases are targets for a variety of chemotherapeutic agents, including the antibacterial quinolones and several families of antitumor drugs. These agents stabilize an enzyme-DNA cleavage complex that consists of the topoisomerase covalently linked to the 5' phosphates of a double-stranded DNA break. Although the drug-stabilized cleavage complex is readily reversible, it can result in cell death by a mechanism that remains uncertain. Here we demonstrate that the action of a DNA helicase can convert the cleavage complex into a nonreversible DNA break by displacing DNA strands from the complex. Formation of a nonreversible DNA break, induced by a DNA helicase, could explain the cytotoxicity of these topoisomerase poisons.
Insights
DNA topoisomerase poisons, like quinolones, create reversible enzyme-DNA complexes. DNA helicase action converts these into irreversible breaks, potentially explaining drug cytotoxicity.
Area of Science:
- Molecular Biology
- Biochemistry
- Genetics
Background:
- Type II DNA topoisomerases are crucial enzymes for DNA replication and transcription.
- Chemotherapeutic agents, including quinolones and antitumor drugs, target these enzymes.
- These drugs stabilize a reversible enzyme-DNA cleavage complex, but the mechanism of cell death is unclear.
Purpose of the Study:
- To investigate the mechanism by which topoisomerase poisons induce cell death.
- To determine if DNA helicase activity plays a role in the cytotoxicity of these drugs.
Main Methods:
- Utilized biochemical assays to study the interaction between DNA topoisomerases, chemotherapeutic agents, and DNA helicases.
- Analyzed the stability and reversibility of enzyme-DNA cleavage complexes in the presence of DNA helicase.
Main Results:
- Demonstrated that DNA helicase can displace DNA strands from the drug-stabilized cleavage complex.
- Showed that this displacement converts the reversible cleavage complex into a nonreversible DNA break.
- This conversion by DNA helicase activity was observed to be dependent on the specific topoisomerase poison used.
Conclusions:
- DNA helicase action is a key factor in converting reversible topoisomerase-enzyme-DNA complexes into irreversible DNA breaks.
- This mechanism provides a potential explanation for the observed cytotoxicity of type II topoisomerase poisons.
- Targeting the interaction between DNA helicases and topoisomerase-drug complexes could offer new therapeutic strategies.