Characterization of DNA topoisomerase II alpha/beta heterodimers in HeLa cells.
In mammalian cells, DNA topoisomerase II is the product of two distinct genes encoding the alpha and beta isoforms of the enzyme. Besides homodimeric topoisomerase IIalpha and IIbeta, we have recently shown that alpha/beta heterodimers constitute a third population of topoisomerase II in HeLa cells. We found that topoisomerase II heterodimers are not restricted to HeLa cells but exist in different mammalian cell types, and up to 25% of the total topoisomerase IIbeta population is involved in heterodimer formation. Studies of topoisomerase II phosphorylation in HeLa cells show that heterodimers are phosphorylated in vivo to a significantly lower level compared to homodimeric alpha enzymes, but in contrast to the latter neither heterodimers nor topoisomerase IIbeta homodimers coprecipitate together with a kinase activity that is able to mediate their phosphorylation. However, both enzymes can still be phosphorylated by exogenously added casein kinase II. The differential phosphorylation of topoisomerase II heterodimers suggests an alternative regulation of this topoisomerase II subclass compared to the homodimeric topoisomerase IIalpha counterparts.
Gromova
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I
Department of Molecular and Structural Biology, University of Aarhus, Denmark.
Biersack
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H
Jensen
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S
Nielsen
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Westergaard
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O
Andersen
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AH
D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D000951:Antigens, Neoplasm; D047390:Casein Kinase II; D004250:DNA Topoisomerases, Type II / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins; D019281:Dimerization; D004795:Enzyme Stability; D018922:HL-60 Cells; D006367:HeLa Cells / Q000201:enzymology*; D006801:Humans; D007527:Isoenzymes / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D010766:Phosphorylation / Q000187:drug effects; D011233:Precipitin Tests; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism / Q000494:pharmacology; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism
D000951:Antigens, Neoplasm; D004268:DNA-Binding Proteins; D007527:Isoenzymes; D011994:Recombinant Proteins; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases; D004250:DNA Topoisomerases, Type II