Regulation of apoptotic protease activating factor-1 oligomerization and apoptosis by the WD-40 repeat region.
Apoptotic protease activating factor-1 (Apaf-1) has been identified as a proximal activator of caspase-9 in cell death pathways that trigger mitochondrial damage and cytochrome c release. The mechanism of Apaf-1 action is unclear but has been proposed to involve the clustering of caspase-9 molecules, thereby facilitating autoprocessing of adjacent zymogens. Here we show that Apaf-1 can dimerize via the CED-4 homologous and linker domains of the molecule providing a means by which Apaf-1 can promote the clustering of caspase-9 and facilitate its activation. Apaf-1 dimerization was repressed by the C-terminal half of the molecule, which contains multiple WD-40 repeats, but this repression was overcome in the presence of cytochrome c and dATP. Removal of the WD-40 repeat region resulted in a constitutively active Apaf-1 that exhibited greater cytotoxicity in transient transfection assays when compared with full-length Apaf-1. These data suggest a mechanism for Apaf-1 function and reveal an important regulatory role for the WD-40 repeat region.
Molecular Cell Biology Laboratory, Department of Biology, National University of Ireland, Maynooth, County Kildare, Ireland.
C
C
Adrain
E A
EA
Slee
M T
MT
Harte
S J
SJ
Martin
D017209:Apoptosis; D053477:Apoptotic Protease-Activating Factor 1; D001665:Binding Sites; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism*; D002460:Cell Line; D019281:Dimerization; D004789:Enzyme Activation; D006801:Humans; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D012091:Repetitive Sequences, Nucleic Acid; D012441:Saccharomyces cerevisiae
C506592:APAF1 protein, human; D053477:Apoptotic Protease-Activating Factor 1; D011506:Proteins; C506433:CASP9 protein, human; D053453:Caspase 9; D020169:Caspases