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Apoptosis of Rat Thymocytes Triggered by Prednisolone, Camptothecin, or Teniposide is Selective to G0 Cells and is Prevented by Inhibitors of Proteases

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Abstract

Rat thymocytes were treated in culture with prednisolone or the DNA topoisomerase I or II inhibitors, camptothecin (CAM) or teniposide (TN), and proportions of cells in different phases of the cell cycle were estimated by flow cytometry using a staining methodology which makes it possible to discriminate between G0 and G1 cells, as well as to recognize the cells which undergo apoptosis. The appearance of apoptotic cells in cultures treated with pharmacological concentrations of these drugs, observed as early as 3–6 hr after treatment, coincided with the selective loss of G0 cells in these cultures, while no significant changes in the proportion of S or G2+M cells were apparent. Agarose gel electrophoresis of DNA isolated from the treated cells indicated degradation of the internucleosomal spacer sections, typical of the endonucleolytic activity which accompanies apoptotic cell death. The data indicate that G0 thymocytes were particularly sensitive to agents that induce apoptosis while cells progressing through the cell cycle were resistant. This suggests that under in vivo conditions (immunological response), the selective death of G0 cells may promote the clonal expansion of stimulated thymocytes which enter the cell cycle. Together with our earlier studies on the effects of CAM and TN on MOLT-4 and HL-60 leukemic cell lines, these data indicate that both, phenotypic- and cell cycle phase specific- factors modify the ability of cells to respond to toxic agents, including chemotherapeutics by apoptosis. The present studies also revealed that irreversible inhibitors of proteases, Ntosyl- L-phenylalanylchloromethyl ketone (TPCK) and N-tosyl-L-lysylchloromethyl ketone (TLCK), or the reversible inhibitor N-benzoyl-L-tyrosine ethyl ester (BTEE), each protected thymocytes against DNA degradation induced by prednisolone, CAM, or TN. The latter findings suggest that the protein degradation which occurs early during apoptosis is essential for the endonucleolytic reaction to progress.
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Document Type: Research Article

Publication date: January 1, 1992

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  • Formerly: Oncology Research Incorporating Anti-Cancer Drug Design
    Oncology Research Featuring Preclinical and Clincal Cancer Therapeutics publishes research of the highest quality that contributes to an understanding of cancer in areas of molecular biology, cell biology, biochemistry, biophysics, genetics, biology, endocrinology, and immunology, as well as studies on the mechanism of action of carcinogens and therapeutic agents, reports dealing with cancer prevention and epidemiology, and clinical trials delineating effective new therapeutic regimens.

    From Volume 23, Oncology Research Featuring Preclinical and Clinical Cancer Therapeutics is Open Access under the terms of the Creative Commons CC BY-NC-ND license.

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