Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:5.99.1.2 (topoisomerase)
 9,166 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The RecQ helicase superfamily has been implicated in DNA repair and recombination. At least five human RecQ-related genes exist: RecQ1, BLM, WRN, RecQ4 and RecQ5. Mutations in BLM, WRN and RecQ4 are associated with Bloom, Werner and Rothmund-Thomson syndromes, respectively, involving a predisposition to malignancies and a cellular phenotype that includes increased chromosome instability. RecQ5 is small, containing only a core part of the RecQ helicase, but three isomer transcripts code for small RecQ5alpha (corresponding to the original RecQ5 with 410 amino acids), new large RecQ5beta (991 amino acids) and small RecQ5gamma (435 amino acids) proteins that contain the core helicase motifs. By determining the genomic structure, we found that the three isoforms are generated by differential splicing from the RecQ5 gene that contains at least 19 exons. Northern blot analysis using a RecQ5beta-specific probe indicates that RecQ5beta mRNA is expressed strongly in the testis. Immunocytochemical staining of three N-terminally tagged RecQ5 isomers expressed in 293EBNA cells showed that RecQ5beta migrates to the nucleus and exists exclusively in the nucleoplasm, while the small RecQ5alpha and RecQ5gamma proteins stay in the cytoplasm. Immunoprecipitation and an extended cytochemical experiment suggested that the nucleoplasmic RecQ5beta, like yeast Sgs1 DNA helicase, binds to topoisomerases 3alpha and 3beta, but not to topoisomerase 1. These results predict that RecQ5beta may have an important role in DNA metabolism and may also be related to a distinct genetic disease.
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PMID:Human RecQ5beta, a large isomer of RecQ5 DNA helicase, localizes in the nucleoplasm and interacts with topoisomerases 3alpha and 3beta. 1071 Apr 32

Bloom's syndrome is a rare genetic disorder associated with loss of genomic integrity and a large increase in the incidence of many types of cancer at an early age. The Bloom's syndrome gene product, BLM, belongs to the RecQ family of DNA helicases, which also includes the human Werner's and Rothmund-Thomson syndrome gene products and the Sgs1 protein of Saccharomyces cerevisiae. This family shows strong evolutionary conservation of protein structure and function. Previous studies have shown that Sgs1p interacts both physically and genetically with topoisomerase III. Here, we have investigated whether this interaction has been conserved in human cells. We show that BLM and hTOPO IIIalpha, one of two human topoisomerase III homologues, co-localize in the nucleus of human cells and can be co-immunoprecipitated from human cell extracts. Moreover, the purified BLM and hTOPO IIIalpha proteins are able to bind specifically to each other in vitro, indicating that the interaction is direct. We have mapped two independent domains on BLM that are important for mediating the interaction with hTOPO IIIalpha. Furthermore, through characterizing a genetic interaction between BLM and TOP3 in S. cerevisiae, we have identified a functional role for the hTOPO IIIalpha interaction domains in BLM.
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PMID:The Bloom's syndrome gene product interacts with topoisomerase III. 1073 15

Deficiency in a helicase of the RecQ family is found in at least three human genetic disorders associated with cancer predisposition and/or premature ageing. The RecQ helicases encoded by the BLM, WRN and RECQ4 genes are defective in Bloom's, Werner's and Rothmund-Thomson syndromes, respectively. Cells derived from individuals with these disorders in each case show inherent genomic instability. Recent studies have demonstrated direct interactions between these RecQ helicases and human nuclear proteins required for several aspects of chromosome maintenance, including p53, BRCA1, topoisomerase III, replication protein A and DNA polymerase delta. Here, we review this network of protein interactions, and the clues that they present regarding the potential roles of RecQ family members in DNA repair, replication and/or recombination pathways.
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PMID:DNA helicase deficiencies associated with cancer predisposition and premature ageing disorders. 1125 7

Targeted gene disruption in the murine TOP3beta gene-encoding DNA topoisomerase IIIbeta was carried out. In contrast to the embryonic lethality of mutant mice lacking DNA topoisomerase IIIalpha, top3beta(-/-) nulls are viable and grow to maturity with no apparent defects. Mice lacking DNA topoisomerase IIIbeta have a shorter life expectancy than their wild-type littermates, however. The mean lifespan of the top3beta(-/-) mice is about 15 months, whereas that of their wild-type littermates is longer than 2 years. Mortality of the top3beta(-/-) nulls appears to correlate with lesions in multiple organs, including hypertrophy of the spleen and submandibular lymph nodes, glomerulonephritis, and perivascular infiltrates in various organs. Because the DNA topoisomerase III isozymes are likely to interact with helicases of the RecQ family, enzymes that include the determinants of human Bloom, Werner, and Rothmund-Thomson syndromes, the shortened lifespan of top3beta(-/-) mice points to the possibility that the DNA topoisomerase III isozymes might be involved in the pathogenesis of progeroid syndromes caused by defective RecQ helicases.
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PMID:Mice lacking DNA topoisomerase IIIbeta develop to maturity but show a reduced mean lifespan. 1133 80

The Sgs1 protein of the budding yeast Saccharomyces cerevisiae is a member of the RecQ DNA helicase family that includes the human Bloom, Werner, and Rothmund-Thompson syndrome proteins. The N-terminal region outside the central DNA helicase core of Sgs1, particularly the part containing the first 100 amino acid residues of the 1,447-residue protein, is known to be functionally important and has been implicated in Sgs1-DNA topoisomerase III (Top3) interaction. We show in this work that the functionality of a truncated Sgs1 lacking its N-terminal 106 residues can be restored by replacing the truncated region with Top3. Fusion of Top3 to a mutant Sgs1 with a Val-29 to Glu substitution, which interferes with Sgs1-Top3 interaction, similarly restores the functionality of the mutant Sgs1(V29E) protein. The Top3-Sgs1(Delta1-106) and Top3-Sgs1(V29E) fusion proteins behave like wild-type Sgs1 in complementing several aspects of the sgs1 phenotype, including the hypersensitivity of sgs1 cells to methyl methanesulfonate and hydroxyurea. Complementation by the fusion proteins required both the topoisomerase activity of Top3 and the helicase activity of the Sgs1 polypeptide. These results suggest that the sole function of the N-terminal 106 amino acid residues of Sgs1 is for Top3 binding, and that the coordinated actions of Sgs1 and Top3 are important in cellular processes such as the processing of DNA after exposure of cells to DNA-damaging agents.
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PMID:Association of yeast DNA topoisomerase III and Sgs1 DNA helicase: studies of fusion proteins. 1155 89

The RecQ family of DNA helicases is highly conserved in evolution from bacteria to humans. Of the five known human RecQ family members, three (BLM, WRN and RECQ4, which cause Bloom's syndrome, Werner's syndrome and Rothmund-Thomson syndrome respectively) are mutated in distinct clinical disorders associated with cancer predisposition and/or premature aging. BLM forms part of a multienzyme complex including topoisomerase IIIalpha, replication protein A and a newly identified factor called BLAP75. Together, these proteins play a role in the resolution of DNA structures that arise during the process of homologous recombination repair. In the absence of BLM, cells show genomic instability and a high incidence of sister-chromatid exchanges. In addition to a DNA structure-specific helicase activity, BLM also catalyses Holliday-junction branch migration and the annealing of complementary single-stranded DNA molecules.
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PMID:Roles of the Bloom's syndrome helicase in the maintenance of genome stability. 1624 45

Schizosaccharomyces pombe Rqh1 is a member of the RecQ DNA helicase family. Members of this protein family are mutated in cancer predisposition diseases, causing Bloom's, Werner, and Rothmund-Thomson syndromes. Rqh1 forms a complex with topoisomerase III and is proposed to process or disrupt aberrant recombination structures that arise during S phase to allow proper chromosome segregation during mitosis. Intriguingly, in the absence of Rqh1, processing of these structures appears to be dependent on Rad3 (human ATR) in a manner that is distinct from its role in checkpoint control. Here, we show that rad3 rqh1 mutants are normally committed to a lethal pathway of DNA repair requiring homologous recombination, but blocking this pathway by Rhp51 inactivation restores viability. Remarkably, viability is also restored by overexpression of Cut8, a nuclear envelope protein involved in tethering and proper function of the proteasome. In keeping with a recently described function of the proteasome in the repair of DNA double-strand breaks, we found that Cut8 is also required for DNA double-strand break repair and is essential for proper chromosome segregation in the absence of Rqh1, suggesting that these proteins might function in a common pathway in homologous recombination repair to ensure accurate nuclear division in S. pombe.
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PMID:Fission yeast Cut8 is required for the repair of DNA double-strand breaks, ribosomal DNA maintenance, and cell survival in the absence of Rqh1 helicase. 1717 39

Sgs1, the RecQ helicase homolog, and Top3, the type-IA topoisomerase, physically interact and are required for genomic stability in budding yeast. Similarly, topoisomerase III genes physically pair with homologs of SGS1 in humans that are involved in the cancer predisposition and premature aging diseases Bloom, Werner, and Rothmund-Thompson syndromes. In the absence of Top1 activity, sgs1 mutants are severely growth impaired. Here, we investigate the role of Sgs1 helicase activity and its N-terminal Top3 interaction domain by using an allele-replacement technique to integrate mutant alleles at the native SGS1 genomic locus. We compare the phenotype of helicase-defective (sgs1-hd) and N-terminal deletion (sgs1-NDelta) strains to wild-type and sgs1 null strains. Like the sgs1 null, sgs1-hd mutations suppress top3 slow growth, cause a growth defect in the absence of Srs2 helicase, and impair meiosis. However, for recombination and the synthetic interaction with top1Delta mutations, loss of helicase activity exhibits a less severe phenotype than the null. Interestingly, deletion of the Top3 interaction domain of Sgs1 causes a top3-like phenotype, and furthermore, this effect is dependent on helicase activity. These results suggest that the protein-protein interaction between these two DNA-metabolism enzymes, even in the absence of helicase activity, is important for their function in catalyzing specific changes in DNA topology.
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PMID:The genetic consequences of ablating helicase activity and the Top3 interaction domain of Sgs1. 1827 35