CASP12

CASP12 Background

The CASP12 encodes caspase-12, which is one of the inflammatory group caspases ^[1]. Caspase-12 is localized on the cytoplasmic side of the ER (endoplasmic-reticulum) membrane and is involved in the ER stress-induced apoptosis ^[2]. Crystal structure analysis found that a caspase-associated recruitment domain (CARD), two catalytic domains, p20, and p10 in caspase-12. In humans, the caspase-12 gene has a single nucleotide polymorphism that facilitates the synthesis of either a truncated or full-length caspase-12 protein ^[3]. When exposed to ER stresses, cytosolic calcium levels are increased, inducing the activation of m-calpain. Activated m-calpain cleaves Bcl-XL and proteolytically activates caspase-12 ^[4]. Takunari Yoneda et al. found that ER stress led to the dissociation of procaspase-12 from TRAF2 of the stable complex formed in unstressed cells and simultaneous dimerization (or oligomerization) of procaspase-12 ^[6]. Active caspase-12 translocates from the ER to the cytosol and activates caspase-9 independent of Apaf-1, followed by activation of caspase-3 ^[5]. The activation of executioner caspase-3 promotes the cleavage and degradation of downstream target molecules that are important for cellular survival, thus leading to apoptosis. Mice deficient in caspase-12 are resistant to ER stress-induced apoptosis, but their cells undergo apoptosis in response to other death stimuli. In addition to the essential role in apoptosis, caspase-12 also exerts roles in the inflammation. In humans, a caspase-12 isozyme functions as a dominant-negative regulator of the pro-inflammatory signaling pathway ^[7]. Because it inhibits the activation of caspase-1 in inflammasome complexes, blocks the production of the pro-inflammatory cytokines IL-1β and IL-18, and disturbs the overall response to sepsis.

[1] Martinon, F. and Tschopp, J. Inflammatory caspases: linking an intracellular innate immune system to autoinflammatory diseases [J]. Cell, 2004, 117, 561-574.
[2]Nakagawa, T., Zhu, H., et al. Caspase-12 mediates endoplasmic-reticulum-specific apoptosis and cytotoxicity by amyloid-beta [J]. Nature, 2000, 403, 98-136-21842.
[3] Saleh, M., Vaillancourt, et al. Differential modulation of endotoxin responsiveness by human caspase-12 polymorphisms [J]. Nature, 2004, 429, 75-79.
[4]Nakagawa, T. and Yuan, J. Cross-talk between two cysteine protease families. Activation of caspase-12 by calpain in apoptosis [J]. J. Cell Biol. 2000, 150, 887-894.7-894.
[5] Rao, R. V., Castro-Obregon, S., et al. Coupling endoplasmic reticulum stress to the cell death program. An Apaf-1-independent intrinsic pathway [J]. J. Biol. Chem. 2002, 277, 21836-21842.
[6] Takunari Yoneda,‖, Kazunori Imaizumi, et al. Activation of Caspase-12, an Endoplasmic Reticulum (ER) Resident Caspase, through Tumor Necrosis Factor Receptor-associated Factor 2-dependent Mechanism in Response to the ER Stress [J]. The Journal of Biological Chemistry, 2001,276, 13935-13940.
[7] Saleh, M., Vaillancourt, J. P., et al. Differential modulation of endotoxin responsiveness by human caspase-12 polymorphisms [J]. Nature, 2002, 429, 75-79.