PHAPI, CAS, and Hsp70 promote apoptosome formation by preventing Apaf-1 aggregation and enhancing nucleotide exchange on Apaf-1.
During apoptosis, cytochrome c is released from mitochondria to the cytosol, where it binds Apaf-1. The Apaf-1/cytochrome c complex then oligomerizes either into heptameric caspase-9-activating apoptosome, which subsequently activates caspase-3 and caspase-7, or bigger inactive aggregates, depending on the availability of nucleotide dATP/ATP. A tumor suppressor protein, PHAPI, enhances caspase-9 activation by promoting apoptosome formation through an unknown mechanism. We report here the identification of cellular apoptosis susceptibility protein (CAS) and heat shock protein 70 (Hsp70) as mediators of PHAPI activity. PHAPI, CAS, and Hsp70 function together to accelerate nucleotide exchange on Apaf-1 and prevent inactive Apaf-1/cytochrome c aggregation. CAS expression is induced by multiple apoptotic stimuli including UV irradiation. Knockdown of CAS by RNA interference (RNAi) in cells attenuates apoptosis induced by UV light and causes endogenous Apaf-1 to form aggregates. These studies indicated that PHAPI, CAS, and Hsp70 play an important regulatory role during apoptosis.
Kim
Hyun-Eui
HE
Howard Hughes Medical Institute, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA.
Jiang
Xuejun
X
Du
Fenghe
F
Wang
Xiaodong
X
D017209:Apoptosis; D053478:Apoptosomes / Q000378:metabolism*; D053477:Apoptotic Protease-Activating Factor 1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D053453:Caspase 9 / Q000378:metabolism; D061945:Caspase Inhibitors; D029563:Cellular Apoptosis Susceptibility Protein / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D009687:Nuclear Proteins; D009711:Nucleotides / Q000378:metabolism; D034622:RNA Interference; D016601:RNA-Binding Proteins
C087425:ANP32A protein, human; C506592:APAF1 protein, human; D053478:Apoptosomes; D053477:Apoptotic Protease-Activating Factor 1; D061945:Caspase Inhibitors; D029563:Cellular Apoptosis Susceptibility Protein; D018840:HSP70 Heat-Shock Proteins; D047908:Intracellular Signaling Peptides and Proteins; D009687:Nuclear Proteins; D009711:Nucleotides; D016601:RNA-Binding Proteins; D053453:Caspase 9