Effects of camptothecin or TOP1 overexpression on genetic stability in Saccharomyces cerevisiae |
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Institution: | 1. Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, NC 27710, United States;2. Developmental Therapeutics Branch and Laboratory of Molecular Pharmacology, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, MD 20892, United States;1. Institute of Molecular Biology (IMB), Mainz, 55128, Germany;2. Johannes Gutenberg University Mainz, Faculty of Biology, Institute of Developmental Biology and Neurobiology, Mainz, 55128, Germany;1. Département de Microbiologie et Infectiologie, Faculté de Médecine, Université de Sherbrooke, Sherbrooke, QC J1H 5N4, Canada;2. Institut für Biochemie, Genetik und Mikrobiologie, Universität Regensburg, 93053 Regensburg, Germany;3. Biochemistry and Biophysics, School of Molecular Biosciences, Washington State University, Pullman, WA 99164-7520, United States |
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Abstract: | Topoisomerase I (Top1) removes DNA torsional stress by nicking and resealing one strand of DNA, and is essential in higher eukaryotes. The enzyme is frequently overproduced in tumors and is the sole target of the chemotherapeutic drug camptothecin (CPT) and its clinical derivatives. CPT stabilizes the covalent Top1-DNA cleavage intermediate, which leads to toxic double-strand breaks (DSBs) when encountered by a replication fork. In the current study, we examined genetic instability associated with CPT treatment or with Top1 overexpression in the yeast Saccharomyces cerevisiae. Two types of instability were monitored: Top1-dependent deletions in haploid strains, which do not require processing into a DSB, and instability at the repetitive ribosomal DNA (rDNA) locus in diploid strains, which reflects DSB formation. Three 2-bp deletion hotspots were examined and mutations at each were elevated either when a wild-type strain was treated with CPT or when TOP1 was overexpressed, with the mutation frequency correlating with the level of TOP1 overexpression. Under both conditions, deletions at novel positions were enriched. rDNA stability was examined by measuring loss-of-heterozygosity and as was observed previously upon CPT treatment of a wild-type strain, Top1 overexpression destabilized rDNA. We conclude that too much, as well as too little of Top1 is detrimental to eukaryotic genomes, and that CPT has destabilizing effects that extend beyond those associated with DSB formation. |
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Keywords: | Topoisomerase I Campthothecin Mutagenesis Recombination Yeast |
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