The adaptor molecule FADD from Xenopus laevis demonstrates evolutionary conservation of its pro-apoptotic activity.
FADD is an adaptor protein that transmits apoptotic signals from death receptors such as Fas to downstream initiator caspases in mammals. We have identified and characterized the Xenopus orthologue of mammalian FADD (xFADD). xFADD contains both a death effector domain (DED) and a death domain (DD) that are structurally homologous to those of mammalian FADD. We observed xFADD binding to Xenopus caspase-8 and caspase-10 as well as to human caspase-8 and Fas through interactions with their homophilic DED and DD domains. When over-expressed, xFADD was also able to induce apoptosis in wild-type mouse embryonic fibroblasts (MEF), but not in caspase-8-deficient MEF cells. In contrast, DED-deficient xFADD (xFADDdn) acted as a dominant-negative mutant and prevented Fas-mediated apoptosis in mammalian cell lines. These results indicate that xFADD transmits apoptotic signals from Fas to caspase-8. Furthermore, we found that transgenic animals expressing xFADD in the developing heart or eye under the control of tissue-specific promoters show abnormal phenotypes. Taken together, these results suggest that xFADD can substitute functionally for its mammalian homologue in death receptor-mediated apoptosis, and we suggest that xFADD functions as a pro-apoptotic adaptor molecule in frogs. Thus, the structural and functional similarities between xFADD and mammalian FADD provide evidence that the apoptotic pathways are evolutionally conserved across vertebrate species.
Sakamaki
Kazuhiro
K
Department of Animal Development and Physiology, Graduate School of Biostudies, Kyoto University, Kyoto 606-8507, Japan. ksakamak@virus.kyoto-u.ac.jp
Takagi
Chiyo
C
Kominami
Katsuya
K
Sakata
Shin-ichi
S
Yaoita
Yoshio
Y
Kubota
Hiroshi Y
HY
Nozaki
Masami
M
Yonehara
Shin
S
Ueno
Naoto
N
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics*; D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D053455:Caspase 10; D053181:Caspase 8; D020169:Caspases / Q000378:metabolism; D017124:Conserved Sequence; D019143:Evolution, Molecular; D044943:Fatty Acid Desaturases / Q000235:genetics* / Q000378:metabolism; D015870:Gene Expression; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D012333:RNA, Messenger / Q000378:metabolism; D016415:Sequence Alignment; D017384:Sequence Deletion; D015398:Signal Transduction; D029867:Xenopus Proteins / Q000235:genetics* / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D029681:Arabidopsis Proteins; D012333:RNA, Messenger; D029867:Xenopus Proteins; D044943:Fatty Acid Desaturases; C084083:Fad7 protein, Arabidopsis; C505530:CASP8 protein, human; C505526:Casp8 protein, mouse; D053455:Caspase 10; D053181:Caspase 8; D020169:Caspases; C506438:CASP10 protein, human