Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:5.99.1.3 (topoisomerase)
 9,911 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

DNA topoisomerase I and II have been shown to be modified with a ubiquitin-like protein SUMO in response to their specific inhibitors called 'poisons'. These drugs also damage DNA by stabilizing the enzyme-DNA cleavable complex and induce a degradation of the enzymes through the 26S proteasome system. A plausible link between sumoylation and degradation has not yet been elucidated. We demonstrate here that topoisomerase IIbeta, but not its isoform IIalpha, is selectively degraded through proteasome by exposure to the catalytic inhibitor ICRF-193 which does not damage DNA. The beta isoform immunoprecipitated from ICRF-treated cells was modified by multiple modifiers, SUMO-2/3, SUMO-1, and polyubiquitin. When the SUMO conjugating enzyme Ubc9 was conditionally knocked out, the ICRF-induced degradation of topoisomerase IIbeta did not occur, suggesting that the SUMO modification pathway is essential for the degradation.
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PMID:The SUMO pathway is required for selective degradation of DNA topoisomerase IIbeta induced by a catalytic inhibitor ICRF-193(1). 1283 72

We have analyzed the abundance of SUMO-conjugated species during the cell cycle in Xenopus egg extracts. The predominant SUMO conjugation products associated with mitotic chromosomes arose from SUMO conjugation of topoisomerase II. Topoisomerase II was modified exclusively by SUMO-2/3 during mitosis under normal circumstances, although we observed conjugation of topoisomerase II to SUMO-1 in extracts with exogenous SUMO-1 protein. Inhibition of SUMO modification by a dominant-negative mutant of the SUMO-conjugating enzyme Ubc9 (dnUbc9) did not detectably alter topoisomerase II activity, but it did increase the amount of unmodified topoisomerase II retained on mitotic chromosomes after high salt washing. dnUbc9 did not disrupt the assembly of condensed mitotic chromosomes or block progression of extracts through mitosis, but it did block the dissociation of sister chromatids at the metaphase-anaphase transition. Together, our results suggest that SUMO conjugation is important for chromosome segregation in metazoan systems, and that mobilization of topoisomerase II from mitotic chromatin may be a key target of this modification.
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PMID:SUMO-2/3 regulates topoisomerase II in mitosis. 1459 74

Type 2 topoisomerases, in particular the alpha isoform in human cells, play a key role in cohesion and sister chromatid separation during mitosis. These enzymes are thus vital for cycling cells and are obvious targets in cancer chemotherapy. Evidence obtained in yeast and Xenopus model systems indicates that conjugation of topoisomerase 2 with small ubiquitin-like modifier (SUMO) proteins is required for its mitotic functions. Here, we provide biochemical and cytologic evidence that topoisomerase 2 alpha is conjugated to SUMO-2/3 during interphase and mitosis in response to topoisomerase 2 inhibitors and "poisons" (ICRF-187, etoposide, doxorubicin) that stabilize catalytic intermediates (cleavage complexes, closed clamp forms) of the enzyme onto target DNA. During mitosis, SUMO-2/3-modified forms of topoisomerase 2 alpha localize to centromeres and chromosome cores/axes. However, centromeres are unresponsive to inhibitors during interphase. Furthermore, formation of topoisomerase 2 alpha-SUMO-2/3 conjugates within mitotic chromosomes strongly correlates with incomplete chromatid decatenation and decreases progressively as cells approach the metaphase-anaphase transition. We also found that the PIASy protein, an E3 ligase for SUMO proteins, colocalizes with SUMO-2/3 at the mitotic chromosomal cores/axes and is necessary for both formation of SUMO-2/3 conjugates and proper chromatid segregation. We suggest that the efficacy of topoisomerase inhibitors to arrest cells traversing mitosis may relate to their targeting of topoisomerase 2 alpha-SUMO-2/3 conjugates that concentrate at mitotic chromosome axes and are directly involved in chromatid arm separation.
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PMID:Conjugation of human topoisomerase 2 alpha with small ubiquitin-like modifiers 2/3 in response to topoisomerase inhibitors: cell cycle stage and chromosome domain specificity. 1838 49

Posttranslational protein modification by the Small Ubiquitin-like MOdifiers (SUMO) is involved in many cellular functions including organization of nuclear structures and chromatin, transcriptional regulation, and nucleo-cytoplasmic transport. Both genetic and biochemical studies indicate that the SUMO modification pathway plays an important role in proper cell cycle control, especially in the normal progression of mitosis. DNA topoisomerase II has been shown to be modified by SUMO in budding yeast as well as in vertebrates. We have shown by biochemical analysis using the Xenopus egg extract (XEE) cell-free assay system that DNA topoisomerase IIalpha (Topo IIalpha) is modified by SUMO-2/3 on mitotic chromosomes in the early stages of mitosis. Inhibition of mitotic SUMOylation in the XEE assay system causes aberrant sister chromatid separation in anaphase and alters Topo IIalpha association with chromosomes.
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PMID:Analysis of SUMOylation of topoisomerase IIalpha with Xenopus egg extracts. 1976 53

RNF4, a SUMO-targeted ubiquitin ligase (STUbL), localizes to the nucleus and functions in the DNA damage response during interphase of the cell cycle. RNF4 also exists in cells undergoing mitosis, where its regulation and function remain poorly understood. Here we showed that administration of etoposide, an anticancer DNA topoisomerase II poison, to mitotic human cervical cancer HeLa cells induced SUMO-2/3-dependent localization of RNF4 to chromosomes. The FK2 antibody signals, indicative of poly/multi-ubiquitin assembly, were detected on etoposide-exposed mitotic chromosomes, whereas the signals were negligible in cells depleted for RNF4 by RNA interference. This suggests that RNF4 functions as a STUbL in the etoposide-induced damage response during mitosis. Indeed, RNF4-depletion sensitized mitotic HeLa cells to etoposide and increased cells with micronuclei. These results indicate the importance of the RNF4-mediated STUbL pathway during mitosis for the maintenance of chromosome integrity and further implicate RNF4 as a target for topo II poison-based therapy for cancer patients.
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PMID:The SUMO-targeted ubiquitin ligase RNF4 localizes to etoposide-exposed mitotic chromosomes: implication for a novel DNA damage response during mitosis. 2469 17

Topoisomerases form transient covalent DNA cleavage complexes to perform their reactions. Topoisomerase I cleavage complexes (TOP1ccs) are trapped by camptothecin and TOP2ccs by etoposide. Proteolysis of the trapped topoisomerase DNA-protein cross-links (TOP-DPCs) is a key step for some pathways to repair these lesions. We describe a pathway that features a prominent role of the small ubiquitin-like modifier (SUMO) modification for both TOP1- and TOP2-DPC repair. Both undergo rapid and sequential SUMO-2/3 and SUMO-1 modifications in human cells. The SUMO ligase PIAS4 is required for these modifications. RNF4, a SUMO-targeted ubiquitin ligase (STUbL), then ubiquitylates the TOP-DPCs for their subsequent degradation by the proteasome. This pathway is conserved in yeast with Siz1 and Slx5-Slx8, the orthologs of human PIAS4 and RNF4.
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PMID:A conserved SUMO pathway repairs topoisomerase DNA-protein cross-links by engaging ubiquitin-mediated proteasomal degradation. 3318 14