Smac, a Mitochondrial Protein that Promotes Cytochrome c–Dependent Caspase Activation by Eliminating IAP Inhibition

We report here the identification of a novel protein, Smac, which promotes caspase activation in the cytochrome c/Apaf-1/caspase-9 pathway. Smac promotes caspase-9 activation by binding to inhibitor of apoptosis proteins, IAPs, and removing their inhibitory activity. Smac is normally a mitochondrial protein but is released into the cytosol when cells undergo apoptosis. Mitochondrial import and cleavage of its signal peptide are required for Smac to gain its apoptotic activity. Overexpression of Smac increases cells' sensitivity to apoptotic stimuli. Smac is the second mitochondrial protein, along with cytochrome c, that promotes apoptosis by activating caspases.

[1]  Y. Lazebnik,et al.  Caspases: enemies within. , 1998, Science.

[2]  H. Steller,et al.  The head involution defective gene of Drosophila melanogaster functions in programmed cell death. , 1995, Genes & development.

[3]  Dean P. Jones,et al.  Prevention of Apoptosis by Bcl-2: Release of Cytochrome c from Mitochondria Blocked , 1997, Science.

[4]  John Calvin Reed,et al.  Cytochrome c: Can't Live with It—Can't Live without It , 1997, Cell.

[5]  E. Alnemri,et al.  Processing/Activation of At Least Four Interleukin-1β Converting Enzyme–like Proteases Occurs during the Execution Phase of Apoptosis in Human Monocytic Tumor Cells , 1997, The Journal of cell biology.

[6]  W. Haining,et al.  The proapoptotic function of Drosophila Hid is conserved in mammalian cells. , 1999, Proceedings of the National Academy of Sciences of the United States of America.

[7]  G. Mclendon,et al.  STOICHIOMETRY, FREE ENERGY, AND KINETIC ASPECTS OF CYTOCHROME C : APAF-1 BINDING IN APOPTOSIS , 1999 .

[8]  D. Green,et al.  The Release of Cytochrome c from Mitochondria: A Primary Site for Bcl-2 Regulation of Apoptosis , 1997, Science.

[9]  J C Reed,et al.  IAP family proteins--suppressors of apoptosis. , 1999, Genes & development.

[10]  S. Srinivasula,et al.  Cytochrome c and dATP-Dependent Formation of Apaf-1/Caspase-9 Complex Initiates an Apoptotic Protease Cascade , 1997, Cell.

[11]  J. Abrams,et al.  grim, a novel cell death gene in Drosophila. , 1996, Genes & development.

[12]  S. Korsmeyer,et al.  BCL-2 family members and the mitochondria in apoptosis. , 1999, Genes & development.

[13]  J. Sambrook,et al.  Molecular Cloning: A Laboratory Manual , 2001 .

[14]  S. Cory,et al.  The Bcl-2 protein family: arbiters of cell survival. , 1998, Science.

[15]  J C Reed,et al.  IAPs block apoptotic events induced by caspase‐8 and cytochrome c by direct inhibition of distinct caspases , 1998, The EMBO journal.

[16]  R. Armstrong,et al.  Cell-specific Induction of Apoptosis by Microinjection of Cytochrome c , 1997, The Journal of Biological Chemistry.

[17]  G. Rubin,et al.  Drosophila p53 Binds a Damage Response Element at the reaper Locus , 2000, Cell.

[18]  Mike Rothe,et al.  The TNFR2-TRAF signaling complex contains two novel proteins related to baculoviral inhibitor of apoptosis proteins , 1995, Cell.

[19]  Eugene M. Johnson,et al.  Evidence of a Novel Event during Neuronal Death Development of Competence-to-Die in Response to Cytoplasmic Cytochrome c , 1998, Neuron.

[20]  V. Dixit,et al.  Apoptosis Induced by Drosophila Reaper and Grim in a Human System , 1998, The Journal of Biological Chemistry.

[21]  H. Lipkin.  Where is the ?c? , 1978 .

[22]  Xiaodong Wang,et al.  Apaf-1, a Human Protein Homologous to C. elegans CED-4, Participates in Cytochrome c–Dependent Activation of Caspase-3 , 1997, Cell.

[23]  D. Vaux,et al.  Cloning and expression of apoptosis inhibitory protein homologs that function to inhibit apoptosis and/or bind tumor necrosis factor receptor-associated factors. , 1996, Proceedings of the National Academy of Sciences of the United States of America.

[24]  W. Kaiser,et al.  Inhibitor of Apoptosis Proteins Physically Interact with and Block Apoptosis Induced by Drosophila Proteins HID and GRIM , 1998, Molecular and Cellular Biology.

[25]  S. Srinivasula,et al.  Autoactivation of procaspase-9 by Apaf-1-mediated oligomerization. , 1998, Molecular cell.

[26]  Xiaodong Wang,et al.  Induction of Apoptotic Program in Cell-Free Extracts: Requirement for dATP and Cytochrome c , 1996, Cell.

[27]  H. Horvitz,et al.  The Caenorhabditis elegans cell death gene ced-4 encodes a novel protein and is expressed during the period of extensive programmed cell death. , 1992, Development.

[28]  Robert L Moritz,et al.  Identification of DIABLO, a Mammalian Protein that Promotes Apoptosis by Binding to and Antagonizing IAP Proteins , 2000, Cell.

[29]  H. Steller,et al.  Induction of apoptosis by Drosophila reaper, hid and grim through inhibition of IAP function , 2000, The EMBO journal.

[30]  X. Liu,et al.  An APAF-1·Cytochrome c Multimeric Complex Is a Functional Apoptosome That Activates Procaspase-9* , 1999, The Journal of Biological Chemistry.

[31]  B. Dobberstein,et al.  Common Principles of Protein Translocation Across Membranes , 1996, Science.

[32]  J. Martinou,et al.  The Bcl-2 protein family. , 2000, Experimental cell research.

[33]  J C Reed,et al.  A Single BIR Domain of XIAP Sufficient for Inhibiting Caspases* , 1998, The Journal of Biological Chemistry.

[34]  R. J. Clem,et al.  An apoptosis-inhibiting baculovirus gene with a zinc finger-like motif , 1993, Journal of virology.

[35]  H. Steller,et al.  Genetic control of programmed cell death in Drosophila. , 1994, Science.