DNA topoisomerases and DNA repair

Downes, C. Stephen; Johnson, Robert T.

doi:10.1002/bies.950080602

Cited by 55 publications

(15 citation statements)

References 56 publications

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“…Earlier reports to the contrary (14) were based on work with less specific topoisomerase inhibitors, novobiocin and nalidixic acid, which have a variety of nontopoisomerase targets; this can produce considerable confusion (20,21). We have shown that the metaphaseanaphase transition is sensitive to specific inhibitors of DNA topoisomerase II, but not of topoisomerase I, both in cells accumulated in mitosis and in unsynchronized PtK2 cells, in a largely reversible manner analogous to the effects of top2 but not top] mutations in yeast (3)(4)(5)(6)(7).…”

Section: Discussionmentioning

confidence: 99%

Inhibitors of DNA topoisomerase II prevent chromatid separation in mammalian cells but do not prevent exit from mitosis.

Downes

Mullinger

Johnson

1991

Proc. Natl. Acad. Sci. U.S.A.

159

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DNA topoisomerase II (EC 5.99.1.3) is necessary for chromosome condensation and disjunction in yeast but not for other functions. In mammalian cells, it has been reported to be necessary for progression toward mitosis but not for transit through mitosis. We have found, on the contrary, that specific inhibition of topoisomerase II (but not of topoisomerase I) interferes with mammalian mitotic progression. Metaphase is prolonged, and anaphase separation of chromatids is completely inhibited, in cells given high concentrations of topoisomerase II inhibitors; nevertheless these cells attempt cleavage, sometimes generating nucleate and anucleate daughters. Lower concentrations of inhibitors interfere with anaphase and produce abnormalities of segregation. DNA topoisomerase II activity is therefore necessary for mammalian chromatid separation, but it is not tightly coupled to the control of other mitotic events.In eukaryotic cells DNA topoisomerase II (EC 5.99.1.3) is a major component of the mitotic chromosome core (1), with sites of action adjacent to the attachment points of supercoiled DNA loops (2). This structural role is conserved in all known cases.In budding and in fission yeast, temperature-sensitive top2 mutants show no defect in normal interphase cell functions, including cell cycle progression, at the restrictive temperature; but they are arrested in mitosis (3, 4). In top2 mutants of the fission yeast Schizosaccharomyces pombe, chromosome condensation is partly achieved at the restrictive temperature, but it produces long entangled prophase-like structures, which become fully condensed when the topoisomerase II activity is restored. If topoisomerase II is inactivated after chromosome condensation, the cells remain blocked at metaphase, unable to achieve chromatid separation (4). After release from such arrest, yeast cells show chromosome nondisjunction (5); meiotic nondisjunction can be similarly produced (6). This requirement for topoisomerase II in mitotic condensation and in separation of sister chromatids may be due to the need to separate sister strands of DNA, which inevitably become concatenated during replication but are not decatenated until later (7). Other cellular DNA topoisomerases appear to be adequate for other necessary manipulations of DNA topology but cannot perform this decatenation activity; in top2 mutants, concatenated plasmids accumulate at the restrictive temperature (3,8).Though the topoisomerase II function is necessary for chromatid segregation in fission yeast, other aspects of yeast mitosis continue without it. Temperature-sensitive top2 cells at the restrictive temperature divide into two portions, joined by chromatid fibers that prevent total cytokinesis; in top2 cdcll double mutants, in which septum formation is also blocked, cells reform single active nuclei after an abortive mitosis and enter a new round of replication (8).In mammalian cells the role of topoisomerase II in cycle progression has been reported to be rather different from its role in yeast. No tempe...

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Section: Discussionmentioning

confidence: 99%

Inhibitors of DNA topoisomerase II prevent chromatid separation in mammalian cells but do not prevent exit from mitosis.

Downes

Mullinger

Johnson

1991

Proc. Natl. Acad. Sci. U.S.A.

159

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“…DNA topoisomerase I (TOP1) releases torsional stress of DNA through a single-strand breakage/rejoining reaction and plays critical roles in replication, transcription, and DNA damage repair in mammalian cells (1)(2)(3). During the catalytic cycle, the active site tyrosine of TOP1 links covalently to a 3Ј phosphate of DNA at the break site (4).…”

Section: Introductionmentioning

confidence: 99%

Cullin 3 Promotes Proteasomal Degradation of the Topoisomerase I-DNA Covalent Complex

et al. 2004

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DNA topoisomerase I (TOP1)-DNA covalent complexes are the initial lesions produced by antitumor camptothecins (CPTs). The TOP1-directed drugs stimulate degradation of TOP1 via the ubiquitin-proteasome pathway. We found that proteasome inhibition prevents degradation of DNAbound TOP1 and sustains high levels of covalent complexes, thus enhancing CPT-induced cell death. Consistent with this, increased degradation of TOP1-DNA covalent complexes was seen in acquired CPT-resistant cells. We found that the resistant cells showed elevated expressions of Cul3, a member of the cullin family of E3 ubiquitin ligases. The reduction in Cul3 expression by small interfering RNA decreased degradation of TOP1-DNA covalent complexes. Conversely, Cul3 overexpression by stable transfection promoted covalent complex degradation and reduced CPTinduced cell death without affecting basal TOP1 expression levels. These results indicate that Cul3, by promoting proteasomal degradation of TOP1-DNA covalent complexes, becomes an important regulator for cellular CPT sensitivity.

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“…However, controversy mostly concerns UV-induced excision repair and the use of novobiocin, an agent incorrectly assumed to be a specific inhibitor of the enzyme (Downes & Johnson, 1988). It is premature to rule out involvement of topoisomerase in all repair processes.…”

Section: Resultsmentioning

confidence: 99%

Aberrant DNA topoisomerase II activity, radioresistance and inherited susceptibility to cancer

Cunningham

Francis²,

Holland³

et al. 1991

Br J Cancer

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Summary Inherited susceptibility to a wide variety of neoplasias (Li-Fraumeni syndrome), has been shown in studies of one cancer-prone family, to have an intriguing association with an aberrant c-raf-J gene and inheritance of a radioresistant phenotype in their non-cancerous skin fibroblasts. This association together with observations that DNA topoisomerases, when defective, can introduce errors into DNA and that these enzymes are perturbed in vitro by serine/threonine kinases similar to raf encoded proteins, prompted investigation of DNA topoisomerase activity of the family's fibroblasts. Since radioresistance was transferred to murine cells (NIH-3T3) when the aberrant c-raf-1 gene from this family was transfected, we also examined transformants containing this and other oncogenes. V-raflc-myc and EJ-ras transformants were examined, the former because the family's skin fibroblasts also have 3-8-fold elevated myc expression (not apparently relevant to radioresistance) and the latter because ras, like raf, conveys radioresistance. The family members' fibroblasts and the three transfected murine lines, showed a similar perturbation of a spermidine and ATP-dependent DNA catenation activity (typical of DNA topoisomerase II). There was a significant positive correlation (r = 0.93; P = 0.0026) between the degree of activation of topoisomerase II and one measure of radioresistance (the Dq value). Relaxation of DNA supercoiling (topoisomerase I activity and other DNA nicking enzymes) was not abnormal. Cytotoxicity assays and evaluation of the influence of topoisomerase II inhibitors on DNA/protein complex formation, corroborated the existence of a qualitative topoisomerase II defect in the family's cells and transfectants. Although the contention that the qualitative topoisomerase II abnormalities observed here may be associated with malfunction is highly speculative, these findings may be relevant to the mechanism of oncogenesis, not only in this family, but with raf and ras type oncogenes.

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DNA topoisomerases and DNA repair

Cited by 55 publications

References 56 publications

Inhibitors of DNA topoisomerase II prevent chromatid separation in mammalian cells but do not prevent exit from mitosis.

Inhibitors of DNA topoisomerase II prevent chromatid separation in mammalian cells but do not prevent exit from mitosis.

Cullin 3 Promotes Proteasomal Degradation of the Topoisomerase I-DNA Covalent Complex

Aberrant DNA topoisomerase II activity, radioresistance and inherited susceptibility to cancer

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