Xenopus death-domain-containing proteins FADD and RIP1 synergistically activate JNK and NF-kappaB.
BACKGROUND
Death receptors (DRs) induce intracellular signalling upon engagement of their cognate ligands, leading to apoptosis, cell survival or pro-inflammatory responses. In mammals, DR signalling is mediated by the recruitment of several DD (death domain)-containing molecules, such as FADD (Fas-associated DD) and RIP1 (receptor-interacting protein 1).


RESULTS
To elucidate the molecular mechanisms of intracellular DR signalling in Xenopus, we have isolated cDNAs encoding xFADD (Xenopus FADD), and xRIP1 and its short isoform xRIP1beta, which is produced by alternative splicing of the xRIP1 gene. These DD-containing proteins interacted with Xenopus DR members xDR-M1 and xDR-M2 through their DDs in co-transfected HEK-293T cells. Overexpression of xFADD activated not only xCaspase 8, but also AP-1 (activator protein 1), which reflects activation of JNK (c-Jun N-terminal kinase) and NF-kappaB (nuclear factor kappaB). A comparative analysis of xRIP1, a kinase-dead mutant of xRIP1 and xRIP1beta indicated that the kinase activity of xRIP1 was required for the activation of AP-1 and NF-kappaB. Interestingly, xFADD and xRIP1 interacted with each other via their DDs, and the expression of a mutant xRIP1 containing only the DD (xRIP1-DD) repressed the xFADD-induced activation of NF-kappaB and AP-1. xFADD and xRIP1 synergistically induced the activation of AP-1 and NF-kappaB, both of which were partially mediated by TRAF2 (tumour-necrosis-factor-receptor-associated factor 2) and TAK1 (transforming-growth-factor-beta-activated kinase 1). We also found that the activation pathways of NF-kappaB induced by xDR-M2 were inhibited by xRIP1-DD.


CONCLUSIONS
Xenopus FADD, RIP1 and its splice variant RIP1beta have been characterized. Interaction of xFADD and xRIP1 induced synergistic activation of JNK and NF-kappaB. In addition, the NF-kappaB activation induced by xDR-M2 was partially mediated by xRIP1.
Ishizawa
Yo-hei
YH
Department of Bioscience, School of Science, Kitasato University, 1-15-1 Kitasato, Sagamihara 228-8555, Japan.
Tamura
Kei
K
Yamaguchi
Tadayuki
T
Matsumoto
Ken
K
Komiyama
Masaru
M
Takamatsu
Nobuhiko
N
Shiba
Tadayoshi
T
Ito
Michihiko
M
D048868:Adaptor Proteins, Signal Transducing / Q000502:physiology*; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D053181:Caspase 8; D020169:Caspases / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D053200:Fas-Associated Death Domain Protein; D015870:Gene Expression / Q000235:genetics; D006801:Humans; D020930:MAP Kinase Kinase Kinases / Q000235:genetics / Q000378:metabolism; D048055:Mitogen-Activated Protein Kinase 8 / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding / Q000502:physiology; D020033:Protein Isoforms / Q000235:genetics; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D053422:Receptor-Interacting Protein Serine-Threonine Kinases; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D047992:TNF Receptor-Associated Factor 2 / Q000235:genetics / Q000378:metabolism; D018808:Transcription Factor AP-1 / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D047988:Tumor Necrosis Factor Receptor-Associated Peptides and Proteins / Q000502:physiology*; D029867:Xenopus Proteins / Q000235:genetics / Q000378:metabolism; D014982:Xenopus laevis; D000099151:MAP Kinase Kinase Kinase 7
D048868:Adaptor Proteins, Signal Transducing; D053181:Caspase 8; D020169:Caspases; D053200:Fas-Associated Death Domain Protein; D020930:MAP Kinase Kinase Kinases; D048055:Mitogen-Activated Protein Kinase 8; D016328:NF-kappa B; D020033:Protein Isoforms; D017346:Protein Serine-Threonine Kinases; D053422:Receptor-Interacting Protein Serine-Threonine Kinases; D011956:Receptors, Cell Surface; D047992:TNF Receptor-Associated Factor 2; D018808:Transcription Factor AP-1; D047988:Tumor Necrosis Factor Receptor-Associated Peptides and Proteins; D029867:Xenopus Proteins; D000099151:MAP Kinase Kinase Kinase 7; C505533:FADD protein, human; C484516:death receptor M1, Xenopus; C484517:death receptor M2, Xenopus; C506249:RIPK1 protein, human; C505530:CASP8 protein, human