Schedule‐dependent effects of two consecutive, divided, low doses of actinomycin D on translocation of protein B23, inhibition of cell growth and RNA synthesis in hela cells

Abstract

The effects of 2 consecutive, divided, low doses of actinomycin-D (Act-D) on cellular localization of protein B23, inhibition of cell growth, RNA synthesis and colony formation were studied in HeLa cells. The second dose of Act-D was administered at various times after removal of the first dose. One short exposure of HeLa cells to Act-D had previously been shown to induce "reversible" translocation of protein B23, inhibition of cell growth, and RNA synthesis. Relocalization of protein B23 from the nucleoplasm to nucleoli as well as "reversible" inhibition of cell growth and RNA synthesis were still observed in cells that had been treated with a second dose of Act-D administered as early as 0-2 hr or as late as 30 hr after removal of the first dose of Act-D. In contrast, no relocalization of protein B23 from the nucleoplasm to nucleoli was observed in cells that had been treated with a second dose of Act-D administered 9 hr after removal of the first dose. A second exposure to Act-D, administered 9 hr after removal of the first dose, caused irreversible inhibition of cell growth and RNA synthesis; a significant inhibitory effect on colony formation was also observed. RNA synthesis in HeLa cells after 2 sequential exposures to Act-D was further analyzed by 1% agarose gel electrophoresis. There were higher-molecular-weight bands above 28S RNA, which may be the 45S and 32S RNA, observed in the controls and in the cells that had been exposed to Act-D treatment once or in the cells that underwent Act-D exposure twice, in which the second dose was administered as early as 0-2 hr or as late as 30 hr after removal of the first dose. These high-molecular-weight bands were not observed in the cells that underwent Act-D exposure twice, in which the second dose was administered 9 hr after removal of the first. These results indicated that cells at different stages of inhibition or that have recovered from the first exposure to Act-D respond differently to the second short Act-D exposure.

Colocalization within the Nucleolus of Two Highly Related IFN-Induced Human Nuclear Phosphoproteins with Nucleolin

“…Treatment of cells with actinomycin D is known to inhibit RNA synthesis, with high doses (5 g/ml) blocking the transcription of all RNA species, while low doses (0.05 g/ml) preferentially block rRNA synthesis. Thus actinomycin treatment disrupts the function of the nucleolus but does not lead to its disappearance [21,22]. We first observed that both low (0.05 g/ml) and high (5 g/ml) concentrations of actinomycin D caused a dramatic redistribution of fibrillarin and B23 from the nucleoli to the nucleoplasm (Figs.…”

Decrease in nucleophosmin/B23 mRNA and telomerase activity during indomethacin-induced apoptosis of gastric KATO-III cancer cells

“…Nucleophosmin/B23 is localized in granular regions of the nucleolus (Peculis and Gall 1992;Spector et al 1984), associated with preribosomal particles (Prestayko et al 1974;Yung et al 1985) and forms hexamers (Yung and Chan 1987) which may be essential for the assembly of ribosomes. Our previous studies have shown that nucleophosmin/B23 translocates from nucleoli to nucleoplasm during the stationary phase of growth (Yung et al 1990b) or during treatment with certain antitumor drugs, particularly the DNA intercalators (Wu et al 1995;Yung et al 1985Yung et al , 1986Yung et al , 1990aYung et al , 1992. Recent study by Valdez et al (1994) demonstrates that nucleophosmin/B23 binds to amino acid sequence 24-56 of protein p120, a cell cycle related protein.…”

Down-regulation of nucleophosmin/B23 during retinoic acid-induced differentiation of human promyelocytic leukemia HL-60 cells

“…Nucleophosmin/B23 is localized in granular regions of the nucleolus (Spector et al, 1984;Peculis and Gall, 1992), associated with preribosomal particles (Prestayko et al, 1974;Yung et al, 1985) and forms hexamers (Yung and Chan, 1987) which may be essential for the assembly of ribosomes. Our previous studies have shown that nucleophosmin/B23 translocates from nucleoli to nucleoplasm during the stationary phase of growth (Yung et al, 1990a) or during treatment with certain anti-tumor drugs, particularly the DNA intercalators (Yung et al, 1985;Yung et al, 1986Yung et al, , 1990bYung et al, , 1992Wu et al, 1995). Recent study by Valdez et al (1994) demonstrates that nucleophosmin/B23 binds to amino acid sequence 24 ± 56 of protein p120, a cell cycle related protein.…”