title: Nucleolar delocalization of human topoisomerase I in response to topotecan correlates with sumoylation of the protein.
abstract: DNA topoisomerase (topo) I is an essential nuclear protein and a target for anticancer drug camptothecin derivatives. As a nuclear protein, topo I is concentrated in the nucleolus. However, this nucleolar distribution of topo I is dynamic. It has been shown recently that topo I rapidly moves out of the nucleolus (nucleolar delocalization) in response to topo I inhibitors. In the present study, we demonstrated that nucleolar delocalization of topo I is associated with its conjugation by SUMOs (small ubiquitin-like modifiers) in response to the topo I inhibitor topotecan. Time-course experiments revealed that SUMO-topo I conjugation occurred at as early as 5 min after drug treatment, which was earlier than its observed nucleolar delocalization. Furthermore, heat shock blocked sumoylation of topo I; it also blocked the nucleolar delocalization of topo I fusion proteins. UBC9 is an E2 (ubiquitin carrier protein)-conjugating enzyme essential for sumoylation. Although overexpression of wild-type UBC9 enhanced both sumoylation and nuclear delocalization of topo I, overexpression of a UBC9 dominant negative mutant attenuated topo I sumoylation and its nucleolar delocalization. Taken together, our results suggest that sumoylation of topo I might serve as an addressing tag for its nucleolar delocalization in response to topo I inhibitors.
authors.affiliation: Department of Molecular Genetics, University of Illinois, Chicago, Illinois 60607, USA.
authors.forename: Yin-Yuan
authors.initials: YY
authors.lastname: Mo
authors.forename: Yanni
authors.initials: Y
authors.lastname: Yu
authors.forename: Zhiyuan
authors.initials: Z
authors.lastname: Shen
authors.forename: William T
authors.initials: WT
authors.lastname: Beck
mesh_terms: D021581:Active Transport, Cell Nucleus; D000970:Antineoplastic Agents / Q000494:pharmacology; D015153:Blotting, Western; D002466:Cell Nucleolus / Q000201:enzymology*; D004260:DNA Repair; D004264:DNA Topoisomerases, Type I / Q000096:biosynthesis*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005799:Genes, Dominant; D006367:HeLa Cells; D006358:Hot Temperature; D006801:Humans; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D025841:Small Ubiquitin-Related Modifier Proteins / Q000378:metabolism*; D013696:Temperature; D013997:Time Factors; D019772:Topotecan / Q000494:pharmacology*; D014162:Transfection
chemical_list: D000970:Antineoplastic Agents; D004791:Enzyme Inhibitors; D011993:Recombinant Fusion Proteins; D025841:Small Ubiquitin-Related Modifier Proteins; D019772:Topotecan; D004264:DNA Topoisomerases, Type I