title: Characterization and cellular localization of nucleophosmin/B23 in HeLa cells treated with selected cytotoxic agents (studies of B23-translocation mechanism).
abstract: 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.
authors.affiliation: Department of Pharmacology, Baylor College of Medicine, Houston, Texas 77030.
authors.forename: P K
authors.initials: PK
authors.lastname: Chan
mesh_terms: D001345:Autoradiography; D002166:Camptothecin / Q000494:pharmacology*; D002466:Cell Nucleolus / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D003609:Dactinomycin / Q000494:pharmacology*; D015180:Electrophoresis, Gel, Two-Dimensional; D004591:Electrophoresis, Polyacrylamide Gel; D005455:Fluorescent Antibody Technique; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D008239:Lysine / Q000378:metabolism; D008727:Methotrexate / Q000494:pharmacology*; D009687:Nuclear Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D000090243:Nucleophosmin; D010710:Phosphates / Q000378:metabolism*; D010750:Phosphoproteins / Q000032:analysis / Q000378:metabolism*; D010761:Phosphorus Radioisotopes; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational / Q000187:drug effects*; D014316:Tritium; D014529:Uridine / Q000378:metabolism
chemical_list: C000716967:NPM1 protein, human; D009687:Nuclear Proteins; D010710:Phosphates; D010750:Phosphoproteins; D010761:Phosphorus Radioisotopes; D014316:Tritium; D000090243:Nucleophosmin; D003609:Dactinomycin; D008239:Lysine; D014529:Uridine; D002166:Camptothecin; D008727:Methotrexate