Requirement of cooperative functions of two repeated death effector domains in caspase-8 and in MC159 for induction and inhibition of apoptosis, respectively.
BACKGROUND
The death effector domain (DED), which functions as a domain for a homophilic protein interaction, plays a role in death receptor-mediated apoptosis. Two tandemly repeated DEDs in the prodomain of caspase-8 (Casp8NC-DED) and those in MC159 (viral FLIP) have been shown to positively and negatively regulate apoptosis, respectively, by binding to caspase-8 and/or Fas-associated death domain (FADD). However, characteristics of each DED in Casp8NC-DED and those in MC159 have not been well examined.


RESULTS
We analysed deletion and chimera mutants of DEDs derived from Casp8NC-DED and MC159, and found that MC159 and Casp8NC-DED require the combined effects of the two repeated DEDs to exert their binding and biological activities. The carboxy-terminal DED of Casp8NC-DED (Casp8C-DED) has the potential to induce apoptosis, and the amino-terminal DED of MC159 showed a dominant inhibitory effect on apoptosis when combined with Casp8C-DED. In addition, the two repeated DEDs in Casp8NC-DED and MC159 were shown to regulate the activities of caspase differently from the caspase recruitment domain (CARD) in the prodomains of caspase-2, -9 and Apaf-1.


CONCLUSIONS
Although each of the DEDs in Casp8NC-DED and MC159 has the potential to stimulate or inhibit apoptosis, the combination of the two-repeated DEDs is necessary for the DED-containing proteins to stimulate or inhibit apoptosis.
Tsukumo
S I
SI
Institute for Virus Research, Kyoto University, Kawahara-cho, Shogoin, Sakyo-ku, Kyoto 606-8507, Japan.
Yonehara
S
S
D000818:Animals; D017209:Apoptosis / Q000235:genetics; D015153:Blotting, Western; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000235:genetics / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D020080:Tandem Repeat Sequences; D020798:Two-Hybrid System Techniques
D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D002352:Carrier Proteins; C506387:Cflar protein, mouse; D047908:Intracellular Signaling Peptides and Proteins; C505526:Casp8 protein, mouse; C506434:Casp9 protein, mouse; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases