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DNA repair functions that control sensitivity to topoisomerase-targeting drugs
1Department of Molecular Pharmacology, St Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.
Abstract:
DNA topoisomerases play critical roles in a wide range of cellular processes by altering DNA topology to facilitate replication, transcription, and chromosome segregation. Topoisomerases alter DNA topology by introducing transient DNA strand breaks that involve a covalent protein DNA intermediate. Many agents have been found to prevent the religation of DNA strand breaks induced by the enzymes, thereby converting the enzymes into DNA-damaging agents. Repair of the DNA damage induced by topoisomerases is significant in understanding drug resistance arising following treatment with topoisomerase-targeting drugs. We have used the fission yeast Schizosaccharomyces pombe to identify DNA repair pathways that are important for cell survival following drug treatment. S. pombe strains carrying mutations in genes required for homologous recombination such as rad22A or rad32 (homologues of RAD52 and MRE11) are hypersensitive to drugs targeting either topoisomerase I or topoisomerase II. In contrast to results observed with Saccharomyces cerevisiae, S. pombe strains defective in nucleotide excision repair are also hypersensitive to topoisomerase-targeting agents. The loss of DNA replication or DNA damage checkpoints also sensitizes cells to both topoisomerase I and topoisomerase II inhibitors. Finally, repair genes (such as the S. pombe rad8+ gene) with no obvious homologs in other systems also play important roles in causing sensitivity to topoisomerase drugs. Since the pattern of sensitivity is distinct from that seen with other systems (such as the S. cerevisiae system), our results highlight the usefulness of S. pombe in understanding how cells deal with the unique DNA damage induced by topoisomerases.
Insights
Fission yeast reveals key DNA repair pathways crucial for survival against topoisomerase-targeting drugs. Understanding these pathways, including homologous recombination and nucleotide excision repair, is vital for combating drug resistance.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- DNA topoisomerases are essential enzymes that regulate DNA topology.
- Topoisomerase-targeting drugs function by preventing the religation of DNA strand breaks, leading to DNA damage.
- Understanding DNA repair mechanisms is critical for addressing drug resistance in cancer therapy.
Purpose of the Study:
- To identify DNA repair pathways in fission yeast (Schizosaccharomyces pombe) that are crucial for cell survival following treatment with topoisomerase-targeting drugs.
- To investigate the distinct roles of homologous recombination, nucleotide excision repair, and checkpoint pathways in response to topoisomerase inhibition.
Main Methods:
- Utilized fission yeast (Schizosaccharomyces pombe) as a model organism.
- Employing mutant strains deficient in specific DNA repair pathways (e.g., homologous recombination, nucleotide excision repair, replication/damage checkpoints).
- Assessed cell survival following treatment with topoisomerase I and topoisomerase II inhibitors.
Main Results:
- Mutations in homologous recombination genes (rad22Δ, rad32) conferred hypersensitivity to both topoisomerase I and II inhibitors.
- Unlike in Saccharomyces cerevisiae, defects in nucleotide excision repair also led to hypersensitivity to topoisomerase-targeting agents in S. pombe.
- Loss of DNA replication or damage checkpoints sensitized cells to topoisomerase inhibitors.
- Novel repair genes, such as rad8+, were identified as important for sensitivity to topoisomerase drugs.
Conclusions:
- The fission yeast model system provides unique insights into cellular responses to topoisomerase-induced DNA damage.
- Distinct DNA repair pathways, including those not conserved in other model organisms, are critical for surviving topoisomerase-targeting drug treatments.
- Findings highlight the importance of diverse repair mechanisms in overcoming drug resistance and inform therapeutic strategies.
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