The N-Terminal Half of NPM Dissociates from Nucleoli of HeLa Cells after Anticancer Drug Treatments

NPM (nucleophosmin/B23) is a nucleolar phosphoprotein abundant in tumor cells. It dissociates from nucleoli of cells after treatments with various anticancer drugs. To determine the domain of NPM responsible for nucleolar binding, the N- and C-terminal halves of NPM were fused to GFP (green fluorescent protein) and introduced into HeLa cells. The N-terminal half (aa 1–150) of NPM (GFP-NPMN) was found localized in the nucleoli. A stable transformant of GFP-NPMN in HeLa cells was prepared and tested for association to nucleoli after anticancer drug treatments. GFP-NPMN dissociates from nucleoli after treatments with daunomycin, actinomycin D, camptothecin, and toyocamycin. The dissociation is time- and dose-dependent, and correlates with the cytotoxicity induced by the drugs. These results indicate that a stable transformant of GFP-NPMN in HeLa cells may be useful for the screening of anticancer drugs.