Sumoylation of topoisomerase I is involved in its partitioning between nucleoli and nucleoplasm and its clearing from nucleoli in response to camptothecin

J Biol Chem. 2002 Oct 18;277(42):40020-6. doi: 10.1074/jbc.M200388200. Epub 2002 Jul 30.


Previous studies identified a small fraction of putatively sumoylated topoisomerase I (TOP1) under basal conditions ( approximately 1%), and anticancer camptothecins that trap the TOP1-DNA covalent intermediate markedly increase the sumoylation of TOP1 (<or=10%). To study the role of the sumoylation of TOP1, we mutated sites on green fluorescent protein (GFP)-TOP1 corresponding to the consensus sequence for protein sumoylation (PsiKXE, where Psi is a hydrophobic residue) and assayed the mutants for basal and camptothecin-induced sumoylation. Only one of the eight mutants, K117R, located in the highly charged NH2-terminal region, showed a substantial reduction ( approximately 5-fold) in basal and camptothecin-induced sumoylation; thus, Lys-117 appears to be the major sumoylation site. A triple mutant having the PsiKXE sequences flanking K117R additionally mutated (K103R/K117R/K153R) showed little if any sumoylation, but was degraded like wild-type GFP-TOP1 during camptothecin treatment. However, K103R/K117R/K153R-GFP-TOP1 was markedly concentrated within nucleoli, depleted from the remainder of nucleus, and failed to be cleared from nucleoli in response to camptothecin treatment. These data are consistent with a model wherein basal transient sumoylation of the NH2-terminal, highly charged, disordered region prevents TOP1 binding to sites in nucleoli, thus driving it to bind in the nucleoplasm; and camptothecin treatment, which increases TOP1 sumoylation, further shifts the binding resulting in delocalization of TOP1 from nucleoli to nucleoplasm.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Antineoplastic Agents, Phytogenic / pharmacology
  • Arginine / chemistry
  • Binding Sites
  • CHO Cells
  • Camptothecin / pharmacology
  • Cell Line
  • Cell Nucleolus / enzymology*
  • Cell Nucleus / enzymology*
  • Cell Nucleus / metabolism
  • Cricetinae
  • Cytoplasm / enzymology
  • DNA Topoisomerases, Type I / chemistry*
  • DNA Topoisomerases, Type I / metabolism
  • Green Fluorescent Proteins
  • HeLa Cells
  • Humans
  • Luminescent Proteins / metabolism
  • Lysine / chemistry
  • Molecular Sequence Data
  • Mutation
  • Plasmids / metabolism
  • Protein Binding
  • Protein Structure, Tertiary
  • Transfection


  • Antineoplastic Agents, Phytogenic
  • Luminescent Proteins
  • Green Fluorescent Proteins
  • Arginine
  • DNA Topoisomerases, Type I
  • Lysine
  • Camptothecin