Regulation of apoptosis by BH3 domains in a cell-free system.
BACKGROUND
The Bcl-2 family of proteins plays a key role in the regulation of apoptosis. Some family members prevent apoptosis induced by a variety of stimuli, whereas others promote apoptosis. Competitive dimerisation between family members is thought to regulate their function. Homologous domains within individual proteins are necessary for interactions with other family members and for activity, although the specific mechanisms might differ between the pro-apoptotic and anti-apoptotic proteins.


RESULTS
Using a cell-free system based on extracts of Xenopus eggs, we have investigated the role of the Bcl-2 homology domain 3 (BH3) from different members of the Bcl-2 family. BH3 domains from the pro-apoptotic proteins Bax and Bak, but not the BH3 domain of the anti-apoptotic protein Bcl-2, induced apoptosis in this system, as determined by the rapid activation of specific apoptotic proteases (caspases) and by DNA fragmentation. The apoptosis-inducing activity of the BH3 domains requires both membrane and cytosolic fractions of cytoplasm, involves the release of cytochrome c from mitochondria and is antagonistic to Bcl-2 function. Short peptides, corresponding to the minimal sequence of BH3 domains required to bind anti-apoptotic Bcl-2 family proteins, also trigger apoptosis in this system.


CONCLUSIONS
The BH3 domains of pro-apoptotic proteins are sufficient to trigger cytochrome c release, caspase activation and apoptosis. These results support a model in which pro-apoptotic proteins, such as Bax and Bak, bind to Bcl-2 via their BH3 domains, inactivating the normal ability of Bcl-2 to suppress apoptosis. The ability of synthetic peptides to reproduce the effect of pro-apoptotic BH3 domains suggests that such peptides may provide the basis for engineering reagents to control the initiation of apoptosis.
Cosulich
S C
SC
Zeneca Laboratory of Molecular and Cellular Biology, School of Biological Sciences, G38 Stopford Building, University of Manchester, Oxford Road, Manchester, M13 9PT, UK.
Worrall
V
V
Hedge
P J
PJ
Green
S
S
Clarke
P R
PR
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D001665:Binding Sites; D002474:Cell-Free System; D003374:Coumarins / Q000378:metabolism; D017936:Cytochrome a Group / Q000378:metabolism; D003574:Cytochrome c Group / Q000378:metabolism; D003600:Cytosol; D053938:DNA Fragmentation; D005456:Fluorescent Dyes / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology*; D008928:Mitochondria; D009842:Oligopeptides / Q000378:metabolism / Q000494:pharmacology; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000502:physiology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000235:genetics; D013329:Structure-Activity Relationship; D014981:Xenopus; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein
C494772:BAK1 protein, human; C494826:BAX protein, human; D003374:Coumarins; D017936:Cytochrome a Group; D003574:Cytochrome c Group; D005456:Fluorescent Dyes; D008565:Membrane Proteins; D009842:Oligopeptides; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011993:Recombinant Fusion Proteins; C099158:acetyl-aspartyl-glutamyl-valyl-aspartal; C102580:acetyl-aspartyl-glutamyl-valyl-aspartyl-amino-4-methylcoumarin; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein