Introduction of dna breaks and replication fork arrest. Newer compounds were also synthesized and tested for their potential antitumor activity and their topoisomerase ii beta poisoning. Pdf structure and function of type ii dna topoisomerases. Maternal topoisomerase ii alpha, not topoisomerase ii beta.
The function of the topoisomerase ii is cutting both strands of one dna double helix and passes another unbroken dna helix. Agents such as doxorubicin and etoposide are fda approved for the treatment of both leukemias and solid tumors. Topoisomerase is an enzyme which participates in the unwinding of dna helix. Twist and turntopoisomerase functions in mitochondrial. Topoisomerase ii is a multisubunit enzyme which uses atp to pass an intact helix through a transient doublestranded break in dna to modulate dna topology. Type iia topoisomerases have the special ability to relax dna to a state below that of thermodynamic equilibrium, a feature unlike type ia, ib, and iib topoisomerases. Failure to separate these strands leads to cell death. Eukaryotic dna topoisomerases 591 3po4tyr iv figure 2 steps in the catalytic cycle of eukaryotic dna topoisomerase i. Human topoisomerase ii beta is prepared by overexpressing in baculovirusinfected insect cells spodoptera frugiperda and purifying it by methods developed inhouse. Topoisomerase ii levels and drug sensitivity in adult.
This function is believed to be performed by topoisomerase ii in eukaryotes and by topoisomerase iv in prokaryotes. Dna topoisomerase ii and its growing repertoire of biological functions. Topoisomerase ii is an enzyme essential for dna replication, chromosome condensation and chromosome segregation. Topoisomerase ii beta top2b facilitates rapid gene expression and functions at. In mammalian cells, two genetically and biochemically distinct topoisomerase ii forms exist, which are designated topoisomerase ii alpha and topoisomerase ii beta. Isolation of cdna clones encoding the beta isozyme of human dna topoisomerase ii and localisation of the gene to chromosome 3p24. Pdf dna topoisomerases are enzymes that disentangle the topological. Mammals express two topoisomerase type ii isoforms, alpha and beta, which are highly homologous but display differences in expression and in subcellular. Studies in xenopus have shown that its function in chromatin condensation is tightly coupled to prior dna replication 24.
Etoposide prevents topoisomerase ii from religating cleaved dna fortune jm et al. The enzyme is supplied at a concentration of 210 u. Maternal topoisomerase ii alpha, not topoisomerase ii beta, enables embryonic development of zebrafish top2a mutants. Releases the supercoiling and torsional tension of dna introduced during the dna replication and transcription by transiently cleaving and rejoining one strand of the dna duplex. Drosophila topoisomerase ii is essential and found in all cell types. These small molecule inhibitors act as efficient antibacterial agents by hijacking the natural ability of topoisomerase to create breaks in chromosomal dna.
Topoisomerase ii beta top2b facilitates rapid gene expression and functions at the later stages of development and differentiation. In addition to topoisomerase i and dna gyrase topoisomerase ii, e. Like gyrase, topoisomerase iv is able to pass one doublestrand of dna through another doublestrand of dna, thereby changing the linking number of dna by two in each enzymatic step. Difference between topoisomerase i and ii compare the. The gene for this enzyme is located on human chromosome 20q12. The scissile phosphodiester is attacked by the catalytic tyrosine of the enzyme, resulting in the formation of.
The cterminal region of human topoisomerase ii beta determines its isoformspecific functions in proliferating cells. Type ii topoisomerases function in numerous dna processes and are. Difference between topoisomerase i and ii key difference. Topoisomerase ii poisons were hence evaluated in light of their selectivity toward one or the other isozyme, indicating how the beta isoform may represent an important target for selected classes of drugs. Topoisomerase inhibitors are chemical compounds that block the action of topoisomerases topoisomerase i and ii, which are enzymes that control the changes in dna structure by catalyzing the breaking and rejoining of the phosphodiester backbone of dna strands during the normal cell cycle in recent years, topoisomerases have become popular targets for cancer.
Drugs acting on the beta isoform of human topoisomerase ii. The function of the topoisomerase ii is cutting both strands of one dna double. This is the key difference between topoisomerase i and ii. Types ii b topoisomerases include topoisomerase vi found in archaea and topoisomerase vi found in higher plants. Inhibitors of topoisomerase ii are important drugs used in the therapy of many neoplasms including breast cancer, lung. This gene encodes a dna topoisomerase, an enzyme that controls and alters the topologic states of dna during transcription. The expression of top2a is cell cycle regulated, reaching a peak in the g2m phase. The appearance and resolution of h2ax foci in murine embryonic fibroblast cell lines, wild type and null for dna topoisomerase ii, was measured after exposure to ionising radiation ir or. Topoisomerase iv is a type ii enzyme with a high degree of sequence similarity to dna gyrase, which can. The role of topoisomerase ii was investigated in cell lines exposed to two dna damaging agents, ionising radiation ir or etoposide, a drug which acts on topoisomerase ii. May act as antagonists to topoisomerase ii poisons.
Catalytic inhibition of topoisomerase ii by a novel. Pdf dna topoisomerase ii top2 is the target of a chemically diverse set of compounds with substantial antitumor activity. Pdf maternal topoisomerase ii alpha, not topoisomerase. Dna topoisomerase ii top2 is the target of a chemically diverse set of compounds with substantial antitumor activity. They identified 2 classes of sequence, which represent the top2 isoenzymes.
On the other hand topoisomerase, ii cuts both strands in dna and needs atp for its activity. In certain cancers, such as peripheral nerve sheath tumors, high expression of its encoded protein is also associated to poor patient survival. The role of topoisomerase ii beta on breakage and proximity of. This helps explain why the decatenating activity of topoisomerase iv is greater than its relaxing activity 67. Targeting dna topoisomerase ii in cancer chemotherapy. Introduces a singlestrand break via transesterification at a target site in duplex dna.
Roles of the cterminal domains of topoisomerase ii. Drugs targeting the topoisomerase ii top2 enzyme are implicated in taml. Topoisomerase ii beta interacts with cohesin and ctcf at. This nuclear enzyme is involved in processes such as chromosome condensation, chromatid separation, and the relief of torsional stress that occurs during dna transcription and replication. Role of topoisomerase ii in dna damage response following. Dna topoisomerase ii is a nuclear enzyme essential for chromosome dynamics and dna metabolism. Dna topoisomerase i binds noncovalently to dna i and cleaves one of the dna strands, forming a covalent linkage between the newly generated 3 phosphate and the activesite tyrosine ii. A second category of topoisomerase ii inhibitors are referred to as catalytic.
Mazumdar marg, delhi 110054, india 2dr b r ambedkar center for biomedical research, university of delhi, delhi 17, india. Dna topoisomerase ii, genotoxicity, and cancer ncbi nih. One category of topoisomerase ii inhibitors acts by stabilizing the covalently bound form of topoisomerase ii with dna, resulting in increased topoisomerase ii crosslinked dna strand breaks. Dna topoisomerase type ii double strand cut, atphydrolyzing activity source. In cancers, the topoisomerase ii alpha is highly expressed in highly proliferating cells.
Topoisomerase ii alpha and beta isoforms are present in the preintegration complexes, suggesting their significant role in hiv1 replication. The dnawrapping difference between gyrase and topoisomerase iv probably contributes to functional differences. Mammals have two isoforms of topoisomerase ii with similar enzymatic properties in vitro 7, 8. Topoisomerase ii catalytic inhibitors also inhibit topoisomerase ii activity a unlike the classical topoisomerase ii poisons they lack the ability to stabilize the cleavable complex. Dna topoisomerase ii topo ii plays a crucial role in controlling the conformation. Topoisomerase type i cuts one strand whereas topoisomerase type ii cuts both strands of the dna to relax the coil and extend the dna molecule. Topoisomerase i is catalytically active as a 100kda monomer and is concentrated in nucleoli, although smaller amounts are found in a diffuse nuclear distribution. Many drugs operate through interference with the topoisomerases the broadspectrum fluoroquinolone antibiotics act by disrupting the function of bacterial type ii topoisomerases. Topoisomerase i cuts one strand in the doublestranded dna and no atp is required for its function. During transcription and dna replication, the dna needs to be unwound in order for the. Pdf on dec 1, 1994, p m watt and others published structure and function of type ii dna topoisomerases find, read and cite all the research you need on.
Dna topoisomerase 2beta is an enzyme that in humans is encoded by the top2b gene. Both share a hetero4mer structure formed by a symmetric homodimer of ab heterodimers. Topoisomerase i and ii are methods of dealing with supercoiled dna. Topoisomerase type ii is an atpase of the ghkl gyrase, hsp90, histidine kinase, mutlfamily that is evolutionary conserved in eukaryotes and essential for chromosome segregation during mitosis. Topoisomerase iii is another type ia enzyme that is more active as a decatenating enzyme than as a dnarelaxing enzyme 7.
Dna topoisomerases structure, function, and mechanism. Antitopoisomerase ii betatop2b antibody ab72334 abcam. Chemical biology t oyoda and colleagues described a synthetic benzocphenanthridine alkaloid that is highly speci. Both isoforms can complement the single form of the enzyme in yeast, but in mammals only top2. Human topoisomerase ii beta is prepared by overexpressing the enzyme in baculovirusinfected insect cells spodoptera frugiperda and purifying it by methods developed inhouse.
Some organisms have two isoforms of topoisomerase ii. Review article topoisomerase ii inhibitors in cancer treatment. After strand passage, the dna backbone is religated and dna structure restored. Research article open access maternal topoisomerase ii. Expression of topoisomerase ii alpha and topoisomerase ii beta in an adenocarcinoma cellline carrying amplified topoisomerase ii alpha and retinoic acid receptoralpha genes.
1482 959 1544 1083 1046 308 236 1276 901 403 1107 1241 277 361 358 543 327 781 124 1461 488 26 678 1500 1537 36 309 1477 146 1207 588 843 1361 1113 1043 953 789 784 1179 764 1144