Apoptosis initiated by Bcl-2-regulated caspase activation independently of the cytochrome c/Apaf-1/caspase-9 apoptosome

Apoptosis is an evolutionarily conserved cell suicide process executed by cysteine proteases (caspases) and regulated by the opposing factions of the Bcl-2 protein family. Mammalian caspase-9 and its activator Apaf-1 were thought to be essential, because mice lacking either of them display neuronal hyperplasia and their lymphocytes and fibroblasts seem resistant to certain apoptotic stimuli. Because Apaf-1 requires cytochrome c to activate caspase-9, and Bcl-2 prevents mitochondrial cytochrome c release, Bcl-2 is widely believed to inhibit apoptosis by safeguarding mitochondrial membrane integrity. Our results suggest a different, broader role, because Bcl-2 overexpression increased lymphocyte numbers in mice and inhibited many apoptotic stimuli, but the absence of Apaf-1 or caspase-9 did not. Caspase activity was still discernible in cells lacking Apaf-1 or caspase-9, and a potent caspase antagonist both inhibited apoptosis and retarded cytochrome c release. We conclude that Bcl-2 regulates a caspase activation programme independently of the cytochrome c/Apaf-1/caspase-9 ‘apoptosome’, which seems to amplify rather than initiate the caspase cascade.

[1]  M. Moskowitz,et al.  Defects in regulation of apoptosis in caspase-2-deficient mice. , 1998, Genes & development.

[2]  Ximena Opitz-Araya,et al.  Requirement for Caspase-2 in Stress-Induced Apoptosis Before Mitochondrial Permeabilization , 2002, Science.

[3]  X. Wang The expanding role of mitochondria in apoptosis. , 2001, Genes & development.

[4]  Francesco Cecconi,et al.  Apaf1 (CED-4 Homolog) Regulates Programmed Cell Death in Mammalian Development , 1998, Cell.

[5]  Patrick R. Griffin,et al.  Identification and inhibition of the ICE/CED-3 protease necessary for mammalian apoptosis , 1995, Nature.

[6]  S. Nagata,et al.  A caspase-activated DNase that degrades DNA during apoptosis, and its inhibitor ICAD , 1998, Nature.

[7]  Xiaodong Wang,et al.  DFF, a Heterodimeric Protein That Functions Downstream of Caspase-3 to Trigger DNA Fragmentation during Apoptosis , 1997, Cell.

[8]  K. Valentino,et al.  Characterization of the caspase inhibitor IDN-1965 in a model of apoptosis-associated liver injury. , 2001, The Journal of pharmacology and experimental therapeutics.

[9]  T. Mak,et al.  Apoptotic Protease Activating Factor 1 (Apaf-1)–Independent Cell Death Suppression by Bcl-2 , 2000, The Journal of experimental medicine.

[10]  D. Green,et al.  The role of ARK in stress-induced apoptosis in Drosophila cells , 2002, The Journal of cell biology.

[11]  D. Vaux,et al.  Caspase-2 is not required for thymocyte or neuronal apoptosis even though cleavage of caspase-2 is dependent on both Apaf-1 and caspase-9 , 2002, Cell Death and Differentiation.

[12]  S. Cory,et al.  The Bcl2 family: regulators of the cellular life-or-death switch , 2002, Nature Reviews Cancer.

[13]  S. Cory,et al.  Apoptosomes: engines for caspase activation. , 2002, Current opinion in cell biology.

[14]  R. Hammer,et al.  Adult Apaf-1-deficient mice exhibit male infertility. , 2000, Developmental biology.

[15]  T. Mak,et al.  The Apoptotic Protease-Activating Factor 1-Mediated Pathway of Apoptosis Is Dispensable for Negative Selection of Thymocytes1 , 2002, The Journal of Immunology.

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

[17]  Keisuke Kuida,et al.  Reduced Apoptosis and Cytochrome c–Mediated Caspase Activation in Mice Lacking Caspase 9 , 1998, Cell.

[18]  A. Strasser,et al.  Apoptosis signaling. , 2000, Annual review of biochemistry.

[19]  M. Hengartner The biochemistry of apoptosis , 2000, Nature.

[20]  T. Mak,et al.  Apaf1 Is Required for Mitochondrial Pathways of Apoptosis and Brain Development , 1998, Cell.

[21]  A. Strasser,et al.  BH3-only Bcl-2 family member Bim is required for apoptosis of autoreactive thymocytes , 2002, Nature.

[22]  A. Strasser,et al.  Proapoptotic Bcl-2 relative Bim required for certain apoptotic responses, leukocyte homeostasis, and to preclude autoimmunity. , 1999, Science.

[23]  José Luis de la Pompa,et al.  Differential Requirement for Caspase 9 in Apoptotic Pathways In Vivo , 1998, Cell.

[24]  Tak W. Mak,et al.  Two Distinct Pathways Leading to Nuclear Apoptosis , 2000, The Journal of experimental medicine.

[25]  A. Strasser,et al.  Pro-Apoptotic Apoptosis Protease–Activating Factor 1 (Apaf-1) Has a Cytoplasmic Localization Distinct from Bcl-2 or Bcl-XL , 2000, The Journal of cell biology.

[26]  L. Fritz,et al.  Irreversible caspase inhibitors: tools for studying apoptosis. , 1999, Methods.

[27]  C. Print,et al.  Constitutive Bcl-2 expression throughout the hematopoietic compartment affects multiple lineages and enhances progenitor cell survival. , 1999, Proceedings of the National Academy of Sciences of the United States of America.

[28]  I. Weissman,et al.  Prevention of programmed cell death in Caenorhabditis elegans by human bcl-2. , 1992, Science.

[29]  Sharad Kumar,et al.  The role of cytochrome c in caspase activation in Drosophila melanogaster cells , 2002, The Journal of cell biology.

[30]  B. Mignotte,et al.  Mitochondria and apoptosis. , 1998, European journal of biochemistry.