91 results found
Isman O, Porter A, 2021, U5 snRNA interactions with exons ensure splicing precision, Frontiers in Genetics, Vol: 12, ISSN: 1664-8021
Imperfect conservation of human pre-mRNA splice sites is necessary to produce alternative isoforms. This flexibility is combined with the precision of the message reading frame. Apart from intron-termini GU_AG and the branchpoint A, the most conserved are the exon-end guanine and +5G of the intron start. Association between these guanines cannot be explained solely by base-pairing with U1 snRNA in the early spliceosome complex. U6 succeeds U1 and pairs +5G in the pre-catalytic spliceosome, while U5 binds the exon end. Current U5 snRNA reconstructions by CryoEM cannot explain the conservation of the exon-end G. Conversely, human mutation analyses show that guanines of both exon termini can suppress splicing mutations. Our U5 hypothesis explains the mechanism of splicing precision and the role of these conserved guanines in the pre-catalytic spliceosome. We propose: (1) optimal binding register for human exons and U5—the exon junction positioned at U5Loop1 C39|C38; (2) common mechanism for base-pairing of human U5 snRNA with diverse exons and bacterial Ll.LtrB intron with new loci in retrotransposition—guided by base pair geometry; and (3) U5 plays a significant role in specific exon recognition in the pre-catalytic spliceosome. Statistical analyses showed increased U5 Watson–Crick pairs with the 5′exon in the absence of +5G at the intron start. In 5′exon positions −3 and −5, this effect is specific to U5 snRNA rather than U1 snRNA of the early spliceosome. Increased U5 Watson–Crick pairs with 3′exon position +1 coincide with substitutions of the conserved −3C at the intron 3′end. Based on mutation and X-ray evidence, we propose that −3C pairs with U2 G31 juxtaposing the branchpoint and the 3′intron end. The intron-termini pair, formed in the pre-catalytic spliceosome to be ready for transition after branching, and the early involvement of the 3′intron end ensure that the 3′exon
Antoniou-Kourounioti M, Mimmack ML, Porter ACG, et al., 2019, The impact of the C-terminal region on the interaction of topoisomerase II alpha with mitotic chromatin, International Journal of Molecular Sciences, Vol: 20, ISSN: 1422-0067
Type II topoisomerase enzymes are essential for resolving DNA topology problems arising through various aspects of DNA metabolism. In vertebrates two isoforms are present, one of which (TOP2A) accumulates on chromatin during mitosis. Moreover, TOP2A targets the mitotic centromere during prophase, persisting there until anaphase onset. It is the catalytically-dispensable C-terminal domain of TOP2 that is crucial in determining this isoform-specific behaviour. In this study we show that, in addition to the recently identified chromatin tether domain, several other features of the alpha-C-Terminal Domain (CTD). influence the mitotic localisation of TOP2A. Lysine 1240 is a major SUMOylation target in cycling human cells and the efficiency of this modification appears to be influenced by T1244 and S1247 phosphorylation. Replacement of K1240 by arginine results in fewer cells displaying centromeric TOP2A accumulation during prometaphase-metaphase. The same phenotype is displayed by cells expressing TOP2A in which either of the mitotic phosphorylation sites S1213 or S1247 has been substituted by alanine. Conversely, constitutive modification of TOP2A by fusion to SUMO2 exerts the opposite effect. FRAP analysis of protein mobility indicates that post-translational modification of TOP2A can influence the enzyme’s residence time on mitotic chromatin, as well as its subcellular localisation.
Motea EA, Fattah FJ, Xiao L, et al., 2018, Kub5-Hera(RPRD1B) deficiency promotes “BRCAness” and vulnerability to PARP inhibition in BRCA-proficient breast cancers, Clinical Cancer Research, Vol: 24, Pages: 6459-6470, ISSN: 1078-0432
Purpose: Identification of novel strategies to expand the use of PARP inhibitors beyond BRCA deficiency is of great interest in personalized medicine. Here, we investigated the unannotated role of Kub5-Hera(RPRD1B) (K-H) in homologous recombination (HR) repair and its potential clinical significance in targeted cancer therapy. Experimental Design: Functional characterization of K-H alterations on HR repair of double-strand breaks (DSB) were assessed by targeted gene silencing, plasmid reporter assays, immunofluorescence, and Western blots. Cell survival with PARP inhibitors was evaluated through colony-forming assays and statistically analyzed for correlation with K-H expression in various BRCA1/2 nonmutated breast cancers. Gene expression microarray/qPCR analyses, chromatin immunoprecipitation, and rescue experiments were used to investigate molecular mechanisms of action. Results: K-H expression loss correlates with rucaparib LD50 values in a panel of BRCA1/2 nonmutated breast cancers. Mechanistically, K-H depletion promotes BRCAness, where extensive upregulation of PARP1 activity was required for the survival of breast cancer cells. PARP inhibition in these cells led to synthetic lethality that was rescued by wild-type K-H reexpression, but not by a mutant K-H (p.R106A) that weakly binds RNAPII. K-H mediates HR by facilitating recruitment of RNAPII to the promoter region of a critical DNA damage response and repair effector, cyclin-dependent kinase 1 (CDK1). Conclusions: Cancer cells with low K-H expression may have exploitable BRCAness properties that greatly expand the use of PARP inhibitors beyond BRCA mutations. Our results suggest that aberrant K-H alterations may have vital translational implications in cellular responses/survival to DNA damage, carcinogenesis, and personalized medicine. (C) 2018 AACR.
Kozuki T, Chikamori K, Surleac MD, et al., 2017, Roles of the C-terminal domains of topoisomerase II alpha and topoisomerase II beta in regulation of the decatenation checkpoint, NUCLEIC ACIDS RESEARCH, Vol: 45, Pages: 5995-6010, ISSN: 0305-1048
Topoisomerase (topo) IIα and IIβ maintain genome stability and are targets for anti-tumor drugs. In this study, we demonstrate that the decatenation checkpoint is regulated, not only by topo IIα, as previously reported, but also by topo IIβ. The decatenation checkpoint is most efficient when both isoforms are present. Regulation of this checkpoint and sensitivity to topo II-targeted drugs is influenced by the C-terminal domain (CTD) of the topo II isoforms and by a conserved non-catalytic tyrosine, Y640 in topo IIα and Y656 in topo IIβ. Deletion of most of the CTD of topo IIα, while preserving the nuclear localization signal (NLS), enhances the decatenation checkpoint and sensitivity to topo II-targeted drugs. In contrast, deletion of most of the CTD of topo IIβ, while preserving the NLS, and mutation of Y640 in topo IIα and Y656 in topo IIβ inhibits these activities. Structural studies suggest that the differential impact of the CTD on topo IIα and topo IIβ function may be due to differences in CTD charge distribution and differential alignment of the CTD with reference to transport DNA. Together these results suggest that topo IIα and topo IIβ cooperate to maintain genome stability, which may be distinctly modulated by their CTDs.
Ahrabi S, Sarkar S, Pfister SX, et al., 2016, A role for human homologous recombination factors in suppressing microhomology-mediated end joining, Nucleic Acids Research, Vol: 44, Pages: 5743-5757, ISSN: 1362-4962
DNA double-strand breaks (DSBs) are toxic lesions, which if improperly repaired can result in cell death or genomic instability. DSB repair is usually facilitated by the classical non-homologous end joining (C-NHEJ), or homologous recombination (HR) pathways. However, a mutagenic alternative NHEJ pathway, microhomology-mediated end joining (MMEJ), can also be deployed. While MMEJ is suppressed by C-NHEJ, the relationship between HR and MMEJ is less clear. Here, we describe a role for HR genes in suppressing MMEJ in human cells. By monitoring DSB mis-repair using a sensitive HPRT assay, we found that depletion of HR proteins, including BRCA2, BRCA1 or RPA, resulted in a distinct mutational signature associated with significant increases in break-induced mutation frequencies, deletion lengths and the annealing of short regions of microhomology (2-6 bp) across the break-site. This signature was dependent on CtIP, MRE11, POLQ and PARP, and thus indicative of MMEJ. In contrast to CtIP or MRE11, depletion of BRCA1 resulted in increased partial resection and MMEJ, thus revealing a functional distinction between these early acting HR factors. Together these findings indicate that HR factors suppress mutagenic MMEJ following DSB resection.
Beck D, Zobel J, Barber R, et al., 2016, Synthetic lethal screen demonstrates that a JAK2 inhibitor suppresses a BCL6 dependent IL10RA/JAK2/STAT3 pathway in high grade B-cell lymphoma., Journal of Biological Chemistry, Vol: 291, Pages: 16686-16698, ISSN: 1083-351X
We demonstrate the usefulness of synthetic lethal screening of a conditionally BCL6 deficient Burkitt lymphoma cell line, DG75-AB7, with a library of small molecules to determine survival pathways suppressed by BCL6 and suggest mechanism-based treatments for lymphoma. Lestaurtinib, a JAK2 inhibitor and one of the hits from the screen repressed survival of BCL6 deficient cells in vitro and reduced growth and proliferation of xenografts in vivo. BCL6 deficiency in DG75-AB7 induced JAK2 mRNA and protein expression and STAT3 phosphorylation. Surface IL10RA was elevated by BCL6 deficiency and blockade of IL10RA repressed STAT3 phosphorylation. Therefore, we define an IL10RA/JAK2/STAT3 pathway each component of which is repressed by BCL6. We also show, for the first time, that JAK2 is a direct BCL6 target gene: BCL6 bound to the JAK2 promoter in vitro and was enriched by ChIP-seq. The place of JAK2 inhibitors in the treatment of diffuse large B-cell lymphoma has not been defined: we suggest that JAK2 inhibitors might be most effective in poor prognosis ABC-DLBCL, which shows higher levels of IL10RA, JAK2 and STAT3 but lower levels of BCL6 than GC-DLBCL and might be usefully combined with novel approaches such as inhibition of IL10RA.
Porter ACG, Gravells P, Ahrabi S, et al., 2015, Use of the HPRT gene to study nuclease-induced DNA double strand break repair, Human Molecular Genetics, Vol: 24, Pages: 7097-7110, ISSN: 1460-2083
Understanding the mechanisms of chromosomal double strand break repair (DSBR) provides insight into genome instability, oncogenesis, and genome engineering, including disease gene correction. Research into DSBR exploits rare-cutting endonucleases to cleave exogenous reporter constructs integrated into the genome. Multiple reporter constructs have been developed to detect various DSBR pathways. Here, using a single endogenous reporter gene, the X-chromosomal disease gene encoding hypoxanthine phosphoribosyl transferase (HPRT), we monitor the relative utilization of three DSBR pathways following cleavage by I-SceI or CRISPR/Cas9 nucleases. For I-SceI our estimated frequencies of accurate or mutagenic nonhomologous end-joining and gene correction by homologous recombination are 4.1%, 1.5% and 0.16%, respectively. Unexpectedly, I-SceI and Cas9 induced markedly different DSBR profiles. Also, using an I-SceI-sensitive HPRT minigene, we show that gene correction is more efficient when using long double-stranded DNA than single- or double-stranded oligonucleotides. Finally, using both endogenous HPRT and exogenous reporters, we validate novel cell cycle phase-specific I-SceI derivatives for investigating cell cycle variations in DSBR. The results obtained using these novel approaches provide new insights into template design for gene correction and the relationships between multiple DSBR pathways at a single endogenous disease gene.
Motea EA, Fattah F, Xiao L, et al., 2015, Kub5-Hera/RPRD1B controls CDK1 regulation and synthetic lethality to PARP1 inhibition, CANCER RESEARCH, Vol: 75, ISSN: 0008-5472
Xu K, Stewart AF, Porter ACG, 2015, Stimulation of Oligonucleotide-Directed Gene Correction by Red beta Expression and MSH2 Depletion in Human HT1080 Cells, MOLECULES AND CELLS, Vol: 38, Pages: 33-39, ISSN: 1016-8478
Barber R, Zobel J, Beck D, et al., 2014, JAK2 Is a Direct BCL6 Target Gene: Implications for Therapy in Diffuse Large B-Cell Lymphoma, ISSN: 0006-4971
Pfister SX, Ahrabi S, Zalmas L-P, et al., 2014, SETD2-dependent histone H3K36 trimethylation is required for homologous recombination repair and genome stability, Cell Reports, Vol: 7, Pages: 2006-2018, ISSN: 2211-1247
Modulating chromatin through histone methylation orchestrates numerous cellular processes. SETD2-dependent trimethylation of histone H3K36 is associated with active transcription. Here, we define a role for H3K36 trimethylation in homologous recombination (HR) repair in human cells. We find that depleting SETD2 generates a mutation signature resembling RAD51 depletion at I-SceI-induced DNA double-strand break (DSB) sites, with significantly increased deletions arising through microhomology-mediated end-joining. We establish a presynaptic role for SETD2 methyltransferase in HR, where it facilitates the recruitment of C-terminal binding protein interacting protein (CtIP) and promotes DSB resection, allowing Replication Protein A (RPA) and RAD51 binding to DNA damage sites. Furthermore, reducing H3K36me3 levels by overexpressing KDM4A/JMJD2A, an oncogene and H3K36me3/2 demethylase, or an H3.3K36M transgene also reduces HR repair events. We propose that error-free HR repair within H3K36me3-decorated transcriptionally active genomic regions promotes cell homeostasis. Moreover, these findings provide insights as to why oncogenic mutations cluster within the H3K36me3 axis.
Farr CJ, Antoniou-Kourounioti M, Mimmack ML, et al., 2014, The alpha isoform of topoisomerase II is required for hypercompaction of mitotic chromosomes in human cells, NUCLEIC ACIDS RESEARCH, Vol: 42, Pages: 4414-4426, ISSN: 0305-1048
de Poot SAH, Lai KW, van der Wal L, et al., 2014, Granzyme M targets topoisomerase II alpha to trigger cell cycle arrest and caspase-dependent apoptosis, CELL DEATH AND DIFFERENTIATION, Vol: 21, Pages: 416-426, ISSN: 1350-9047
Cytotoxic lymphocyte protease granzyme M (GrM) is a potent inducer of tumor cell death. The apoptotic phenotype and mechanism by which it induces cell death, however, remain poorly understood and controversial. Here, we show that GrM-induced cell death was largely caspase-dependent with various hallmarks of classical apoptosis, coinciding with caspase-independent G2/M cell cycle arrest. Using positional proteomics in human tumor cells, we identified the nuclear enzyme topoisomerase II alpha (topoll alpha) as a physiological substrate of GrM. Cleavage of topoll alpha by GrM at Leu(1280) separated topoll alpha functional domains from the nuclear localization signals, leading to nuclear exit of topoll alpha catalytic activity, thereby rendering it nonfunctional. Similar to the apoptotic phenotype of GrM, topoll alpha depletion in tumor cells led to cell cycle arrest in G2/M, mitochondrial perturbations, caspase activation, and apoptosis. We conclude that cytotoxic lymphocyte protease GrM targets topoll alpha to trigger cell cycle arrest and caspase-dependent apoptosis.
Vannocci T, Kurata H, de la Fuente J, et al., 2014, Nuclease-stimulated homologous recombination at the human beta-globin gene, JOURNAL OF GENE MEDICINE, Vol: 16, Pages: 1-10, ISSN: 1099-498X
Bhosle J, Kiakos K, Porter ACG, et al., 2013, Treatment with Gefitinib or Lapatinib Induces Drug Resistance through Downregulation of Topoisomerase II alpha Expression, MOLECULAR CANCER THERAPEUTICS, Vol: 12, Pages: 2897-2908, ISSN: 1535-7163
Gravells P, Tomita K, Booth A, et al., 2013, Chemical genetic analyses of quantitative changes in Cdk1 activity during the human cell cycle, HUMAN MOLECULAR GENETICS, Vol: 22, Pages: 2842-2851, ISSN: 0964-6906
Ray S, Panova T, Miller G, et al., 2013, Topoisomerase II alpha promotes activation of RNA polymerase I transcription by facilitating pre-initiation complex formation, NATURE COMMUNICATIONS, Vol: 4, ISSN: 2041-1723
Tamaichi H, Sato M, Porter ACG, et al., 2013, Ataxia telangiectasia mutated-dependent regulation of topoisomerase II alpha expression and sensitivity to topoisomerase II inhibitor, CANCER SCIENCE, Vol: 104, Pages: 178-184, ISSN: 1347-9032
Arlanov R, Ishikawa T, Porter A, et al., 2013, Functional characterization of ABCC11 protein variants by a targeted Tet-Off gene expression system in HEK 293 cells, NAUNYN-SCHMIEDEBERGS ARCHIVES OF PHARMACOLOGY, Vol: 386, Pages: S5-S5, ISSN: 0028-1298
Ray S, Panova T, Miller G, et al., 2013, The role of DNA Topoisomerases in transcription of large ribosomal RNAs, INTERNATIONAL JOURNAL OF MOLECULAR MEDICINE, Vol: 32, Pages: S29-S29, ISSN: 1107-3756
Arlanov R, Porter A, Strand D, et al., 2012, Functional characterization of protein variants of the human multidrug transporter ABCC2 by a novel targeted expression system in fibrosarcoma cells, HUMAN MUTATION, Vol: 33, Pages: 750-762, ISSN: 1059-7794
The multidrug resistance-associated protein 2 (MRP2/ABCC2) is involved in the efflux of endogenous and xenobiotic substrates, including several anticancer and antiviral drugs. The functional consequences of ABCC2 protein variants remain inconsistent, which may be due to shortcomings of the in vitro assays used. To study systematically the functional consequences of nonsynonymous ABCC2 variants, we used a novel Screen and Insert (ScIn) technology to achieve stable and highly reproducible expression of 13 ABCC2 variants in HT1080 cells. Western blotting revealed lower (3065%) ABCC2 expression for D333G, R1174H, and R1181L as compared with wild type (WT; 100%), whereas the linked variant V1188E/C1515Y resulted in higher expression (150%). R1174H caused mislocalization of ABCC2 to the cytoplasm with an endoplasmic reticulum-like distribution. Variants N1244K and R1174H decreased transport of glutathionemethylfluorescein (GSMF) and glutathionemonochlorobimane (GSMCB) by 80% and 50%, respectively, whereas R1181L and P1291L reduced only GSMCB transport by 50% as compared with WT. Contrary to protein data, the double variant V1188E/C1515Y decreased specific transport activity for GSMF and GSMCB by 40%. The ScIn approach is a feasible and reliable method to functionally characterize systematically ABCC2 variants. D333G, R1174H, R1181L, N1244K, P1291L, and double variant V1188E/C1515Y have been identified as most promising for further clinical evaluation. Hum Mutat 33:750762, 2012. (c) 2012 Wiley Periodicals, Inc.
Vannocci T, Kurata H, de la Fuente J, et al., 2011, A Zinc Finger Nuclease specific for the human beta-globin gene, European Society of Gene and Cell Therapy British Society for Gene Therapy Collaborative Congress 2011, Publisher: Mary Ann Liebert, Inc., Pages: A60-A61, ISSN: 1043-0342
Beta-thalassaemia and sickle cell disease are, together, the most common monogenic diseases worldwide; both are caused by mutations in the beta-globin gene. Current treatments are blood transfusions or bone marrow transplants, but these are limited, respectively, by iron overload and donor availability. Ggene replacement in autologous haematopoietic stem cells (HSCs) is subject to the dangers of uncontrolled vector integration and inappropriate and/or unstable expression levels. Gene correction, by homologous recombination (HR) with a delivered DNA repair template, would circumvent all these issues and is stimulated to practical frequencies by cleavage of the chromosomal target gene. The development of zinc finger nucleases (ZFNs), and other customised endonuclease technologies, has therefore raised hopes that gene correction will soon become a viable approach for the treatment of many monogenic diseases. At present, however, no β-globin gene-specific ZFN has been described. We have used public and commercial approaches to developing β-globin specific ZFNs and will describe our results. We have detected specific ZFN-mediated cleavage of the β-globin gene in two cell lines. In the absence of a delivered repair template, cleavage is indicated by the formation of small deletions/insertion due to inaccurate repair by non-homologous end-joining. Specificity is indicated by analysis of the closely related delta-globin gene which suffers no such cleavage/repair events under identical conditions. We have also demonstrated ZFN-stimulated HR that depends on the presence of the β-globin target sequence. Development of vectors for delivering the ZFN to human HSCs is in progress.
Arlanov R, Porter A, Strand D, et al., 2011, FUNCTIONAL COMPARISON OF NATURAL VARIANTS OF THE ABC MEMBRANE TRANSPORTER MRP2 USING A TARGETED EXPRESSION SYSTEM IN HUMAN FIBROSARCOMA CELLS, BRITISH JOURNAL OF CLINICAL PHARMACOLOGY, Vol: 72, Pages: 34-34, ISSN: 0306-5251
Arlanov R, Porter A, Brough R, et al., 2010, GENERATING TETRACYCLINE INDUCIBLE MRP2 CELL-LINES, BRITISH JOURNAL OF CLINICAL PHARMACOLOGY, Vol: 70, Pages: 7-7, ISSN: 0306-5251
Buecker C, Chen HH, Polo JM, et al., 2010, A murine ESC-like state facilitates transgenesis and homologous recombination in human pluripotent stem cells, Cell Stem Cell, Vol: 6, Pages: 535-546
Murine pluripotent stem cells can exist in two functionally distinct states, LIF-dependent embryonic stem cells (ESCs) and bFGF-dependent epiblast stem cells (EpiSCs). However, human pluripotent cells so far seemed to assume only an epiblast-like state. Here we demonstrate that human iPSC reprogramming in the presence of LIF yields human stem cells that display morphological, molecular, and functional properties of murine ESCs. We termed these hLR5 iPSCs because they require the expression of five ectopic reprogramming factors, Oct4, Sox2, Klf4, cMyc, and Nanog, to maintain this more naive state. The cells are "metastable" and upon ectopic factor withdrawal they revert to standard human iPSCs. Finally, we demonstrate that the hLR5 state facilitates gene targeting, and as such provides a powerful tool for the generation of recombinant human pluripotent stem cell lines.
Papadopoulou V, Postigo A, Sánchez-Tilló E, et al., 2010, ZEB1 and CtBP form a repressive complex at a distal promoter element of the BCL6 locus., Biochem J, Vol: 427, Pages: 541-550
BCL6 is essential for normal antibody responses and is highly expressed in germinal centre B-cells. Constitutive expression due to chromosomal translocations or mutations of cis-acting regulatory elements contributes to diffuse large B-cell lymphoma. BCL6 expression is therefore tightly regulated in a lineage- and developmental-stage-specific manner, and disruption of normal controls can contribute to lymphomagenesis. In order to discover potential cis-acting control regions we carried out DNase I-hypersensitive site mapping. Gel-shift assays and chromatin immunoprecipitation of the core region of a hypersensitive site 4.4 kb upstream of BCL6 transcription initiation (HSS-4.4) showed an E-box element-binding ZEB1 (zinc finger E-boxbinding homeobox 1) and the co-repressor CtBP (C-terminal binding protein). As compared with peripheral blood B-cells, ZEB1, a two-handed zinc finger transcriptional repressor, is expressed at relatively low levels in germinal centre cells, whereas BCL6 has the opposite pattern of expression. Transfection of ZEB1 cDNA caused a reduction in BCL6 expression and a mutated ZEB1, incapable of binding CtBP, lacked this effect. siRNA (small interfering RNA)-mediated knockdown of ZEB1 or CtBP produced an increase in BCL6 mRNA. We propose that HSS-4.4 is a distal promoter element binding a repressive complex consisting of ZEB1 and CtBP. CtBP is ubiquitously expressed and the results of the present study suggest that regulation of ZEB1 is required for control of BCL6 expression.
Papadopoulou V, Porter ACG, Postigo A, et al., 2009, A DNASE I HYPERSENSITIVE SITE IN THE DISTAL PROMOTER REGION OF THE BCL-6 LOCUS BINDS ZEB1 AND IS RESPONSIBLE FOR TRANSCRIPTIONAL REPRESSION, Publisher: FERRATA STORTI FOUNDATION, Pages: 6-7, ISSN: 0390-6078
Papadopoulou V, Porter ACG, Postigo A, et al., 2009, A DNASE I HYPERSENSITIVE SITE IN THE DISTAL PROMOTER REGION OF THE BCL-6 LOCUS BINDS ZEB1 AND IS RESPONSIBLE FOR TRANSCRIPTIONAL REPRESSION, 14th Annual Meeting of the European-Hematology-Association, Publisher: FERRATA STORTI FOUNDATION, Pages: 6-7, ISSN: 0390-6078
Yan T, Deng S, Metzger A, et al., 2009, Topoisomerase II alpha-dependent and -independent apoptotic effects of dexrazoxane and doxorubicin, MOLECULAR CANCER THERAPEUTICS, Vol: 8, Pages: 1075-1085, ISSN: 1535-7163
Porter ACG, 2009, Depletion and mutation of topoisomerase II in animal cells., Methods Mol Biol, Vol: 582, Pages: 245-263
Eukaryotic type II topoisomerases (Topo II) are implicated in a wide range of cellular processes. Cells in which Topo II protein has been specifically depleted or mutated provide powerful systems for analysing the normal in vivo functions of Topo II proteins and for assessing their roles in various chemotherapy regimens. Summarised here are the ways in which Topo II has been depleted or mutated in animal cells and the type of information gleaned. The cell lines generated are tabulated and represent a useful resource for further in vivo studies of Topo II function, one that we expect to grow in size and utility in the coming years.
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