title: Dynamics of human DNA topoisomerases IIalpha and IIbeta in living cells.
abstract: DNA topoisomerase (topo) II catalyses topological genomic changes essential for many DNA metabolic processes. It is also regarded as a structural component of the nuclear matrix in interphase and the mitotic chromosome scaffold. Mammals have two isoforms (alpha and beta) with similar properties in vitro. Here, we investigated their properties in living and proliferating cells, stably expressing biofluorescent chimera of the human isozymes. Topo IIalpha and IIbeta behaved similarly in interphase but differently in mitosis, where only topo IIalpha was chromosome associated to a major part. During interphase, both isozymes joined in nucleolar reassembly and accumulated in nucleoli, which seemed not to involve catalytic DNA turnover because treatment with teniposide (stabilizing covalent catalytic DNA intermediates of topo II) relocated the bulk of the enzymes from the nucleoli to nucleoplasmic granules. Photobleaching revealed that the entire complement of both isozymes was completely mobile and free to exchange between nuclear subcompartments in interphase. In chromosomes, topo IIalpha was also completely mobile and had a uniform distribution. However, hypotonic cell lysis triggered an axial pattern. These observations suggest that topo II is not an immobile, structural component of the chromosomal scaffold or the interphase karyoskeleton, but rather a dynamic interaction partner of such structures.
authors.affiliation: Department of Clinical Chemistry, Medizinische Poliklinik, University of Würzburg, D-97070 Würzburg, Germany.
authors.forename: Morten O
authors.initials: MO
authors.lastname: Christensen
authors.forename: Morten K
authors.initials: MK
authors.lastname: Larsen
authors.forename: Hans Ullrich
authors.initials: HU
authors.lastname: Barthelmes
authors.forename: Robert
authors.initials: R
authors.lastname: Hock
authors.forename: Claus L
authors.initials: CL
authors.lastname: Andersen
authors.forename: Eigil
authors.initials: E
authors.lastname: Kjeldsen
authors.forename: Birgitta R
authors.initials: BR
authors.lastname: Knudsen
authors.forename: Ole
authors.initials: O
authors.lastname: Westergaard
authors.forename: Fritz
authors.initials: F
authors.lastname: Boege
authors.forename: Christian
authors.initials: C
authors.lastname: Mielke
mesh_terms: D000705:Anaphase / Q000502:physiology; D000951:Antigens, Neoplasm; D002460:Cell Line; D002467:Cell Nucleus / Q000201:enzymology; D002678:Chimera; D002875:Chromosomes / Q000201:enzymology; D004250:DNA Topoisomerases, Type II / Q000235:genetics / Q000378:metabolism*; D018105:DNA, Kinetoplast / Q000032:analysis; D004268:DNA-Binding Proteins; D015971:Gene Expression Regulation, Enzymologic; D049452:Green Fluorescent Proteins; D006801:Humans; D007202:Indicators and Reagents / Q000378:metabolism; D007668:Kidney / Q000166:cytology; D008164:Luminescent Proteins / Q000235:genetics; D008677:Metaphase / Q000502:physiology; D008856:Microscopy, Fluorescence; D010777:Photochemistry
chemical_list: D000951:Antigens, Neoplasm; D018105:DNA, Kinetoplast; D004268:DNA-Binding Proteins; D007202:Indicators and Reagents; D008164:Luminescent Proteins; D049452:Green Fluorescent Proteins; D004250:DNA Topoisomerases, Type II