An endoplasmic reticulum stress-specific caspase cascade in apoptosis. Cytochrome c-independent activation of caspase-9 by caspase-12.
Activation of caspase-12 from procaspase-12 is specifically induced by insult to the endoplasmic reticulum (ER) (Nakagawa, T., Zhu, H., Morishima, N., Li, E., Xu, J., Yankner, B. A., and Yuan, J. (2000) Nature 403, 98-103), yet the functional consequences of caspase-12 activation have been unclear. We have shown that recombinant caspase-12 specifically cleaves and activates procaspase-9 in cytosolic extracts. The activated caspase-9 catalyzes cleavage of procaspase-3, which is inhibitable by a caspase-9-specific inhibitor. Although cytochrome c released from mitochondria has been believed to be required for caspase-9 activation during apoptosis (Zou, H., Henzel, W. J., Liu, X., Lutschg, A., and Wang, X. (1997) Cell 90, 405-413, Li, P., Nijhawan, D., Budihardjo, I., Srinivasula, S. M., Ahmad, M., Alnemri, E. S., and Wang, X. (1997) Cell 91, 479-489), caspase-9 as well as caspase-12 and -3 are activated in cytochrome c-free cytosols in murine myoblast cells under ER stress. These results suggest that caspase-12 can activate caspase-9 without involvement of cytochrome c. To examine the role of caspase-12 in the activation of downstream caspases, we used a caspase-12-binding protein, which we identified in a yeast two-hybrid screen, for regulation of caspase-12 activation. The binding protein protects procaspase-12 from processing in vitro. Stable expression of the binding protein renders procaspase-12 insensitive to ER stress, thereby suppressing apoptosis and the activation of caspase-9 and -3. These data suggest that procaspase-9 is a substrate of caspase-12 and that ER stress triggers a specific cascade involving caspase-12, -9, and -3 in a cytochrome c-independent manner.
Morishima
Nobuhiro
N
Bioarchitect Research Group, RIKEN (The Institute of Physical and Chemical Research), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan. morishim@postman.riken.go.jp
Nakanishi
Keiko
K
Takenouchi
Hiromi
H
Shibata
Takehiko
T
Yasuhiko
Yukuto
Y
D000818:Animals; D000951:Antigens, Neoplasm / Q000378:metabolism; D017209:Apoptosis / Q000502:physiology*; D053454:Caspase 12; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism* / Q000502:physiology*; D002460:Cell Line; D003574:Cytochrome c Group / Q000502:physiology*; D004721:Endoplasmic Reticulum / Q000201:enzymology*; D004789:Enzyme Activation; D051379:Mice; D009363:Neoplasm Proteins / Q000378:metabolism
D000951:Antigens, Neoplasm; D003574:Cytochrome c Group; C489519:Mageb3 protein, mouse; D009363:Neoplasm Proteins; C506440:Casp12 protein, mouse; C506434:Casp9 protein, mouse; D053454:Caspase 12; D053453:Caspase 9; D020169:Caspases