Characterization and cellular localization of nucleophosmin/B23 in HeLa cells treated with selected cytotoxic agents (studies of B23-translocation mechanism)

Exp Cell Res. 1992 Nov;203(1):174-81. doi: 10.1016/0014-4827(92)90053-b.


Previous studies indicated that nucleophosmin/B23, an abundant nucleolar phosphoprotein, accumulated in the nucleoplasm (B23-translocation) of cells after exposure to selected cytotoxic drugs. Attempts were made to understand the B23-translocation mechanism. This paper reports that: (1) B23-translocation is a reversible process. Upon removal of camptothecin, which induced B23-translocation in HeLa cells, nucleophosmin/B23 relocalized into nucleoli within 2 h. Relocation occurs in the presence of cycloheximide which inhibits new protein synthesis. There is no reduction or degradation of nucleophosmin/B23 detected during drug treatments. Nucleophosmin/B23 has a half-life of 18-20 h. Taken together, these results indicate that B23-translocation is a reversible process. Drug treatment causes redistribution of nucleophosmin/B23 in nucleoplasm. (2) Inhibition of RNA synthesis does not cause the B23-translocation. Over 80% of RNA synthesis was inhibited in HeLa cells by treatment with actinomycin D, camptothecin, and methotrexate. While actinomycin D and camptothecin cause B23-translocation in all cells, 40% of methotrexate-treated cells remain untranslocated. (3) There is no significant change of phosphorylation in nucleophosmin/B23 during drug treatment. An identical oligomeric cross-linkage pattern was obtained in drug-treated cells. (4) HeLa cells treated with B23-translocation effective drugs have small and round nucleoli while control cells have large and irregular-shaped nucleoli.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Autoradiography
  • Camptothecin / pharmacology*
  • Cell Nucleolus / drug effects
  • Cell Nucleolus / metabolism
  • Cell Nucleolus / ultrastructure
  • Dactinomycin / pharmacology*
  • Electrophoresis, Gel, Two-Dimensional
  • Electrophoresis, Polyacrylamide Gel
  • Fluorescent Antibody Technique
  • HeLa Cells
  • Humans
  • Kinetics
  • Lysine / metabolism
  • Methotrexate / pharmacology*
  • Nuclear Proteins / analysis
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism*
  • Nucleophosmin
  • Phosphates / metabolism*
  • Phosphoproteins / analysis
  • Phosphoproteins / metabolism*
  • Phosphorus Radioisotopes
  • Phosphorylation
  • Protein Processing, Post-Translational / drug effects*
  • Tritium
  • Uridine / metabolism


  • NPM1 protein, human
  • Nuclear Proteins
  • Phosphates
  • Phosphoproteins
  • Phosphorus Radioisotopes
  • Tritium
  • Nucleophosmin
  • Dactinomycin
  • Lysine
  • Uridine
  • Camptothecin
  • Methotrexate