Bcl-2 controls caspase activation following a p53-dependent cyclin D1-induced death signal.
MCF-7 and ZR-75 breast cancer cells infected with an adenovirus constitutively expressing high levels of cyclin D1 demonstrated widespread mitochondrial translocation of Bax and cytochrome c release that was approximately doubled after the addition of all-trans retinoic acid (RA) or Bcl-2 antisense oligonucleotide. By comparison, the percentage of cells in Lac Z virus-infected cultures containing translocated Bax and cytoplasmic cytochrome c was markedly less even after RA treatment. Despite this, RA-treated Lac Z and untreated cyclin D1 virus-infected cultures contained similarly low proportions of cells with active caspase or cells that were permeable to propidium iodide. Bax activation was p53-dependent and accompanied by arrest in G(2) phase. Although constitutive Bcl-2 expression prevented Bax activation, it did not alter cyclin D1-induced cell cycle arrest, illustrating the independence of these events. Both RA and antisense Bcl-2 oligonucleotide decreased Bcl-2 protein levels and markedly increased caspase activity and apoptosis in cyclin D1-infected cells. Thus amplified cyclin D1 expression initiates an apoptotic signal inhibited by different levels of cellular Bcl-2 at two points. Whereas high cellular levels of Bcl-2 prevent mitochondrial Bax translocation, lower levels can prevent apoptosis by inhibition of caspase activation.
Pratt
M A Christine
MA
Department of Cellular and Molecular Medicine, University of Ottawa, Ontario, K1H 8M5, Canada. cpratt@uottawa.ca
Niu
Min-Ying
MY
D017209:Apoptosis; D001692:Biological Transport; D020169:Caspases / Q000378:metabolism*; D002453:Cell Cycle; D016923:Cell Death; D019938:Cyclin D1 / Q000378:metabolism*; D003574:Cytochrome c Group / Q000378:metabolism; D004789:Enzyme Activation; D000939:Epitopes; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D007763:Lac Operon; D008564:Membrane Potentials; D008856:Microscopy, Fluorescence; D008928:Mitochondria / Q000378:metabolism; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D010957:Plasmids / Q000378:metabolism; D011419:Propidium / Q000494:pharmacology; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D015398:Signal Transduction; D013347:Subcellular Fractions / Q000378:metabolism; D013997:Time Factors; D014212:Tretinoin / Q000378:metabolism; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D051028:bcl-2-Associated X Protein
C494826:BAX protein, human; D003574:Cytochrome c Group; D000939:Epitopes; D016376:Oligonucleotides, Antisense; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D016159:Tumor Suppressor Protein p53; D051028:bcl-2-Associated X Protein; D019938:Cyclin D1; D011419:Propidium; D014212:Tretinoin; D020169:Caspases