Transcription and its regulation pose challenges related to DNA torsion and supercoiling of the DNA template. RNA polymerase tracking the helical groove of the DNA introduces positive helical torsion ...and supercoiling upstream and negative torsion and supercoiling behind its direction of travel. This can inhibit transcriptional elongation and other processes essential to transcription. In addition, chromatin remodeling associated with gene activation can generate or be hindered by excess DNA torsional stress in gene regulatory regions. These topological challenges are solved by DNA topoisomerases via a strand-passage reaction which involves transiently breaking and re-joining of one (type I topoisomerases) or both (type II topoisomerases) strands of the phosphodiester backbone. This review will focus on one of the two mammalian type II DNA topoisomerase enzymes, DNA topoisomerase II beta (TOP2B), that have been implicated in correct execution of developmental transcriptional programs and in signal-induced transcription, including transcriptional activation by nuclear hormone ligands. Surprisingly, several lines of evidence indicate that TOP2B-mediated protein-free DNA double-strand breaks are involved in signal-induced transcription. We discuss the possible significance and origins of these DSBs along with a network of protein interaction data supporting a variety of roles for TOP2B in transcriptional regulation.
TOP2B: The First Thirty Years Austin, Caroline A; Lee, Ka C; Swan, Rebecca L ...
International journal of molecular sciences,
09/2018, Letnik:
19, Številka:
9
Journal Article
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Type II DNA topoisomerases (EC 5.99.1.3) are enzymes that catalyse topological changes in DNA in an ATP dependent manner. Strand passage reactions involve passing one double stranded DNA duplex ...(transported helix) through a transient enzyme-bridged break in another (gated helix). This activity is required for a range of cellular processes including transcription. Vertebrates have two isoforms: topoisomerase IIα and β. Topoisomerase IIβ was first reported in 1987. Here we review the research on DNA topoisomerase IIβ over the 30 years since its discovery.
Type II topoisomerases are required for the management of DNA superhelicity and chromosome segregation, and serve as frontline targets for a variety of small-molecule therapeutics. To better ...understand how these enzymes act in both contexts, we determined the 2.9‐Å‐resolution structure of the DNA cleavage core of human topoisomerase IIα (TOP2A) bound to a doubly nicked, 30‐bp duplex oligonucleotide. In accord with prior biochemical and structural studies, TOP2A significantly bends its DNA substrate using a bipartite, nucleolytic center formed at an N-terminal dimerization interface of the cleavage core. However, the protein also adopts a global conformation in which the second of its two inter-protomer contact points, one at the C-terminus, has separated. This finding, together with comparative structural analyses, reveals that the principal site of DNA engagement undergoes highly quantized conformational transitions between distinct binding, cleavage, and drug-inhibited states that correlate with the control of subunit–subunit interactions. Additional consideration of our TOP2A model in light of an etoposide-inhibited complex of human topoisomerase IIβ (TOP2B) suggests possible modification points for developing paralog-specific inhibitors to overcome the tendency of topoisomerase II-targeting chemotherapeutics to generate secondary malignancies.
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► We determined the structure of human TOP2A bound to DNA. ► Comparing TOP2A to TOP2B reveals approaches for addressing drug cross-reactivity. ► Type II topoisomerase structures adopt distinct, quantized conformations. ► These conformations identify sub-states in the type II topoisomerase mechanism.
Abstract Objective To compare the complications and charges of robotic vs. laparoscopic vs. open surgeries in morbidly obese patients treated for endometrial cancer. Methods Data were obtained from ...the Nationwide Inpatient Sample from 2011. Chi-squared, Wilcoxon rank sum two-sample tests, and multivariate analyses were used for statistical analyses. Results Of 1087 morbidly obese (BMI ≥ 40 kg/m2 ) endometrial cancer patients (median age: 59 years, range: 22 to 89), 567 (52%) had open surgery (OS), 98 (9%) laparoscopic (LS), and 422 (39%) robotic surgery (RS). 23% of OS, 13% of LS, and 8% of RS patients experienced an intraoperative or postoperative complication including: blood transfusions, mechanical ventilation, urinary tract injury, gastrointestinal injury, wound debridement, infection, venous thromboembolism, and lymphedema (p < 0.0001). RS and LS patients were less likely to receive blood transfusions compared to OS (5% and 6% vs. 14%, respectively; p < 0.0001). The median lengths of hospitalization for OS, LS, and RS patients were 4, 1, and 1 days, respectively (p < 0.0001). Median total charges associated with OS, LS, and RS were $39,281, $40,997, and $45,030 (p = 0.037), respectively. Conclusions In morbidly obese endometrial cancer patients, minimally invasive robotic or laparoscopic surgeries were associated with fewer complications and less days of hospitalization relative to open surgery. Compared to laparoscopic approach, robotic surgeries had comparable rates of complications but higher charges.
Topoisomerase II (TOP2) poisons are effective cytotoxic anticancer agents that stabilize the normally transient TOP2-DNA covalent complexes formed during the enzyme reaction cycle. These drugs ...include etoposide, mitoxantrone, and the anthracyclines doxorubicin and epirubicin. Anthracyclines also exert cell-killing activity via TOP2-independent mechanisms, including DNA adduct formation, redox activity, and lipid peroxidation. Here, we show that anthracyclines and another intercalating TOP2 poison, mitoxantrone, stabilize TOP2-DNA covalent complexes less efficiently than etoposide, and at higher concentrations they suppress the formation of TOP2-DNA covalent complexes, thus behaving as TOP2 poisons at low concentration and inhibitors at high concentration. We used induced pluripotent stem cell (iPSC)-derived human cardiomyocytes as a model to study anthracycline-induced damage in cardiac cells. Using immunofluorescence, our study is the first to demonstrate the presence of topoisomerase II
(TOP2B) as the only TOP2 isoform in iPSC-derived cardiomyocytes. In these cells, etoposide robustly induced TOP2B covalent complexes, but we could not detect doxorubicin-induced TOP2-DNA complexes, and doxorubicin suppressed etoposide-induced TOP2-DNA complexes. In vitro, etoposide-stabilized DNA cleavage was attenuated by doxorubicin, epirubicin, or mitoxantrone. Clinical use of anthracyclines is associated with cardiotoxicity. The observations in this study have potentially important clinical consequences regarding the effectiveness of anticancer treatment regimens when TOP2-targeting drugs are used in combination. These observations suggest that inhibition of TOP2B activity, rather than DNA damage resulting from TOP2 poisoning, may play a role in doxorubicin cardiotoxicity. SIGNIFICANCE STATEMENT: We show that anthracyclines and mitoxantrone act as topoisomerase II (TOP2) poisons at low concentration but attenuate TOP2 activity at higher concentration, both in cells and in in vitro cleavage experiments. Inhibition of type II topoisomerases suppresses the action of other drugs that poison TOP2. Thus, combinations containing anthracyclines or mitoxantrone and etoposide may reduce the activity of etoposide as a TOP2 poison and thus reduce the efficacy of drug combinations.
Topoisomerase poisons such as the epipodophyllotoxin etoposide are widely used effective cytotoxic anticancer agents. However, they are associated with the development of therapy-related acute ...myeloid leukemias (t-AMLs), which display characteristic balanced chromosome translocations, most often involving the mixed lineage leukemia (MLL) locus at 11q23. MLL translocation breakpoints in t-AMLs cluster in a DNase I hypersensitive region, which possesses cryptic promoter activity, implicating transcription as well as topoisomerase II activity in the translocation mechanism. We find that 2-3% of MLL alleles undergoing transcription do so in close proximity to one of its recurrent translocation partner genes, AF9 or AF4, consistent with their sharing transcription factories. We show that most etoposide-induced chromosome breaks in the MLL locus and the overall genotoxicity of etoposide are dependent on topoisomerase IIβ, but that topoisomerase lia and -β occupancy and etoposide-induced DNA cleavage data suggest factors other than local topoisomerase II concentration determine specific clustering of MLL translocation breakpoints in t-AML. We propose a model where DNA double-strand breaks (DSBs) introduced by topoisomerase IIβ into pairs of genes undergoing transcription within a common transcription factory become stabilized by antitopoisomerase II drugs such as etoposide, providing the opportunity for illegitimate end joining and translocation.
Myeloperoxidase (MPO) is found almost exclusively in granulocytes and immature myeloid cells. It plays a key role in the innate immune system, catalysing the formation of reactive oxygen species that ...are important in anti‐microbial action, but MPO also oxidatively transforms the topoisomerase II (TOP2) poison etoposide to chemical forms that have elevated DNA damaging properties. TOP2 poisons such as etoposide are widely used anti‐cancer drugs, but they are linked to cases of secondary acute myeloid leukaemias through a mechanism that involves DNA damage and presumably erroneous repair leading to leukaemogenic chromosome translocations. This leads to the possibility that myeloperoxidase inhibitors could reduce the rate of therapy‐related leukaemia by protecting haematopoietic cells from TOP2 poison‐mediated genotoxic damage while preserving the anti‐cancer efficacy of the treatment. We show here that myeloperoxidase inhibition reduces etoposide‐induced TOP2B‐DNA covalent complexes and resulting DNA double‐strand break formation in primary ex vivo expanded CD34+ progenitor cells and unfractionated bone marrow mononuclear cells. Since MPO inhibitors are currently being developed as anti‐inflammatory agents this raises the possibility that repurposing of these potential new drugs could provide a means of suppressing secondary acute myeloid leukaemias associated with therapies containing TOP2 poisons.
TOP2 poisons such as etoposide are widely employed anti‐cancer drugs, but their use is associated with DNA damage that can lead to therapy‐related acute leukaemia. Etoposide is activated by the myeloid‐specific enzyme myeloperoxidase (MPO) to more DNA damaging forms, and we show that MPO inhibition reduces etoposide‐induced DNA damage in bone marrow mononuclear cells in which leukaemias may arise.
Type II DNA topoisomerases have the ability to generate a transient DNA double-strand break through which a second duplex can be passed; an activity essential for DNA decatenation and unknotting. ...Topoisomerase poisons stabilize the normally transient topoisomerase-induced DSBs and are potent and widely used anticancer drugs. However, their use is associated with therapy-related secondary leukemia, often bearing 11q23 translocations involving the MLL gene. We will explain recent discoveries in the fields of topoisomerase biology and transcription that have consequences for our understanding of the etiology of leukemia, especially therapy-related secondary leukemia and describe how these findings may help minimize the occurrence of these neoplasias.
The
(
) gene is frequently rearranged in childhood and adult acute leukaemia (AL) and in secondary leukaemias occurring after therapy with DNA topoisomerase targeting anti-cancer agents such as ...etoposide (t-AL).
chromosome translocation break sites in AL patients fall within an 8 kb breakpoint cluster region (BCR). Furthermore,
break sites in t-AL frequently occur in a much smaller region, or hotspot, towards the 3' end of the BCR, close to the intron 11/exon 12 boundary. These findings have prompted considerable effort to uncover mechanisms behind the apparent fragility of the BCR and particularly the t-AL hotspot. Recent genome-wide analyses have demonstrated etoposide-induced DNA cleavage within the BCR, and it is tempting to conclude that this cleavage explains the distribution of translocation break sites in t-AL. However, the t-AL hotspot and the centre of the observed preferential DNA cleavage are offset by over 250 nucleotides, suggesting additional factors contribute to the distribution of t-AL break sites. We review these recent genomic datasets along with older experimental results, analysis of TOP2 DNA cleavage site preferences and DNA secondary structure features that may lead to break site selection in t-AL
translocations.
DNA topoisomerases regulate the topological state of DNA, relaxing DNA supercoils and resolving catenanes and knots that result from biologic processes, such as transcription and replication. DNA ...topoisomerase II (TOP2) enzymes achieve this by binding DNA and introducing an enzyme-bridged DNA double-strand break (DSB) where each protomer of the dimeric enzyme is covalently attached to the 5' end of the cleaved DNA via an active site tyrosine phosphodiester linkage. The enzyme then passes a second DNA duplex through the DNA break, before religation and release of the enzyme. However, this activity is potentially hazardous to the cell, as failure to complete religation leads to persistent TOP2 protein-DNA covalent complexes, which are cytotoxic. Indeed, this property of topoisomerase has been exploited in cancer therapy in the form of topoisomerase poisons which block the religation stage of the reaction cycle, leading to an accumulation of topoisomerase-DNA adducts. A number of parallel cellular processes have been identified that lead to removal of these covalent TOP2-DNA complexes, facilitating repair of the resulting protein-free DSB by standard DNA repair pathways. These pathways presumably arose to repair spontaneous stalled or poisoned TOP2-DNA complexes, but understanding their mechanisms also has implications for cancer therapy, particularly resistance to anti-cancer TOP2 poisons and the genotoxic side effects of these drugs. Here, we review recent progress in the understanding of the processing of TOP2 DNA covalent complexes, the basic components and mechanisms, as well as the additional layer of complexity posed by the post-translational modifications that modulate these pathways. SIGNIFICANCE STATEMENT: Multiple pathways have been reported for removal and repair of TOP2-DNA covalent complexes to ensure the timely and efficient repair of TOP2-DNA covalent adducts to protect the genome. Post-translational modifications, such as ubiquitination and SUMOylation, are involved in the regulation of TOP2-DNA complex repair. Small molecule inhibitors of these post-translational modifications may help to improve outcomes of TOP2 poison chemotherapy, for example by increasing TOP2 poison cytotoxicity and reducing genotoxicity, but this remains to be determined.
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