bongkrekic-acid and Leukemia

The role of p53 in apoptosis and the contrasting p53 status in tumors prompted us to investigate the bleomycin-induced apoptosis in p53-null human leukemia HL-60 cells (bleomycin at 160 microM for 7.5 h). Cells with apoptotic phenotype increased from 0.87% in controls to 9.40% in bleomycin-treated cells. Both the enzymes, caspase-3 and -8, were activated. Furthermore, the apoptotic phenotypes totally disappeared with zVAD-fmk, a caspase inhibitor. Besides, cytochrome c release from mitochondria happened simultaneously to apoptotic phenotypes, shrinkage of mitochondria but being independent of the mitochondrial permeability transition, since cyclosporine A and bongkrekic acid were inefficient on induced apoptosis. On the other hand, incubations with bleomycin (BLM) did not result in detectable changes in the expression of Bcl-2- and Bax-mRNA neither Bcl-2- or Bax-proteins. In conclusion, we suggest that BLM can produce apoptosis independently of p53 through three mechanisms: i) at the nuclear level by its endonuclease activities; ii) at the cell membrane, by activating caspases; and iii) at the mitochondria by releasing cytochrome c. These results indicate that BLM-induced apoptosis in HL-60 cells results from the activation of a mitochondria-dependent caspase cascade which includes also the activation of the initiator caspase-8.

Topics: Amino Acid Chloromethyl Ketones; Antimetabolites, Antineoplastic; Apoptosis; bcl-2-Associated X Protein; Bleomycin; Blotting, Western; Bongkrekic Acid; Caspase 3; Caspase 8; Caspases; Cell Line; Cyclosporine; Cytochromes c; DNA Fragmentation; Enzyme Activation; Genes, p53; HL-60 Cells; Humans; Leukemia; Microscopy, Electron; Mitochondria; Phenotype; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-bcl-2; Reverse Transcriptase Polymerase Chain Reaction; RNA; RNA, Messenger; Time Factors; Tumor Suppressor Protein p53