Apoptosis of mortal human fibroblasts transformed by the bovine papillomavirus E5 oncoprotein.
Mortal human fibroblasts can be partially transformed by the bovine papillomavirus E5 oncoprotein through activation of the platelet-derived growth factor beta receptor. Here, we report that these cells undergo massive apoptosis 2 weeks after confluence. Although activation of caspase 3 was observed in the apoptotic cells, it was not required for apoptosis. The appearance of the mitochondrial proteins cytochrome c and apoptosis-inducing factor in cytosolic and nuclear compartments, respectively, provided a basis for mitochondrial dysfunction and a caspase-independent mechanism of apoptosis in these cells. Although an activating conformational change in Bax also was evident in the apoptotic cells, enforced overexpression of Bcl-2 was insufficient to prevent apoptosis. Finally, a small peptide present in the conditioned medium from dying transformed cells appeared responsible for inducing apoptosis through affecting a conformational change in Bax and eventual relocalization of apoptosis-inducing factor to the nucleus. Thus, an atypical apoptotic pathway is activated in mortal human fibroblasts in response to transformation induced by sustained receptor tyrosine kinase activation.
Zhang
Ying
Y
Center for Immunology and Microbial Disease, Albany Medical College, Albany, NY 12208, USA.
Lehman
John M
JM
Petti
Lisa M
LM
D017209:Apoptosis; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002455:Cell Division; D002461:Cell Line, Transformed; D002467:Cell Nucleus / Q000378:metabolism; D017077:Culture Media, Conditioned / Q000494:pharmacology; D003574:Cytochrome c Group / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004789:Enzyme Activation; D005347:Fibroblasts / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D015151:Immunoblotting; D020287:In Situ Nick-End Labeling; D008856:Microscopy, Fluorescence; D018715:Microscopy, Video; D009856:Oncogene Proteins, Viral / Q000378:metabolism*; D011487:Protein Conformation; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D013347:Subcellular Fractions / Q000378:metabolism; D013997:Time Factors; D051028:bcl-2-Associated X Protein
C494826:BAX protein, human; D017077:Culture Media, Conditioned; D003574:Cytochrome c Group; D009856:Oncogene Proteins, Viral; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; C054304:oncogene protein E5, Bovine papillomavirus type 1; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases