Sequence determinants of nuclear localization in the alpha and beta isoforms of human topoisomerase II.
The alpha and beta isoforms of DNA topoisomerase II (topo II) are targets for several widely used chemotherapeutic agents, and resistance to some of these drugs may be associated with reduced nuclear localization of the alpha isoform. Human topo IIalpha contains a strong bipartite nuclear localization signal (NLS) sequence between amino acids 1454 and 1497 (alphaNLS(1454-1497)). In the present study, we show that human topo IIalpha tagged with green fluorescence protein is still detectable in the nucleus when alphaNLS(1454-1497) has been disrupted. Seven additional regions in topo IIalpha containing overlapping potential bipartite NLSs were evaluated for their nuclear targeting abilities using a beta-galactosidase reporter system. A moderately functional NLS was identified between amino acids 1259 and 1296. When human topo IIbeta was examined in a similar fashion, it was found to contain two strongly functional sequences betaNLS(1522-1548) and betaNLS(1538-1573) in the region of topo IIbeta comparable to the region in topo IIalpha that contains the strongly functional alphaNLS(1454-1497). The third, betaNLS(1294-1332), although weaker than the other two beta sequences, is significantly stronger than the analogous alphaNLS(1259-1296). Differences in the NLS sequences of human topo II isoforms may contribute to their differences in subnuclear localization.
Mirski
S E
SE
Cancer Research Laboratories, Queen's University, Kingston, Ontario, K7L 3N6, Canada.
Gerlach
J H
JH
Cole
S P
SP
D000595:Amino Acid Sequence; D000818:Animals; D000951:Antigens, Neoplasm; D001692:Biological Transport; D019556:COS Cells; D002451:Cell Compartmentation; D004250:DNA Topoisomerases, Type II / Q000235:genetics* / Q000378:metabolism; D004268:DNA-Binding Proteins; D004351:Drug Resistance; D017930:Genes, Reporter; D049452:Green Fluorescent Proteins; D006801:Humans; D007527:Isoenzymes / Q000235:genetics* / Q000378:metabolism; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D019913:Nuclear Localization Signals; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017421:Sequence Analysis
D000951:Antigens, Neoplasm; D004268:DNA-Binding Proteins; D007527:Isoenzymes; D008164:Luminescent Proteins; D019913:Nuclear Localization Signals; D010446:Peptide Fragments; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D004250:DNA Topoisomerases, Type II