TRAF1 is a substrate of caspases activated during tumor necrosis factor receptor-alpha-induced apoptosis.
TRAF family proteins are signal-transducing adapter proteins that interact with the cytosolic domains of tumor necrosis factor (TNF) family receptors. Here we show that TRAF1 (but not TRAF2-6) is cleaved by certain caspases in vitro and during TNF-alpha- and Fas-induced apoptosis in vivo. (160)LEVD(163) was identified as the caspase cleavage site within TRAF1, generating two distinct fragments. Significant enhancement of TNF receptor-1 (CD120a)- and, to a lesser extent, Fas (CD95)-mediated apoptosis was observed when overexpressing the C-terminal TRAF1 fragment in HEK293T and HT1080 cells. The same fragment was capable of potently suppressing TNF receptor-1- and TRAF2-mediated nuclear factor-kappaB activation in reporter gene assays, providing a potential mechanism for the enhancement of TNF-mediated apoptosis. Cell death induced by other death receptor-independent stimuli such as cisplatin, staurosporine, and UV irradiation did not result in cleavage of TRAF1, and overexpression of the C-terminal TRAF1 fragment did not enhance cell death in these cases. TRAF1 cleavage was markedly reduced in cells that contain little procaspase-8 protein, suggesting that this apical protease in the TNF/Fas death receptor pathway is largely responsible. These data identify TRAF1 as a specific target of caspases activated during TNF- and Fas-induced apoptosis and illustrate differences in the repertoire of protease substrates cleaved during activation of different apoptotic pathways.
Leo
E
E
Burnham Institute, La Jolla, California 92037, USA.
Deveraux
Q L
QL
Buchholtz
C
C
Welsh
K
K
Matsuzawa
S
S
Stennicke
H R
HR
Salvesen
G S
GS
Reed
J C
JC
D017209:Apoptosis; D020169:Caspases / Q000378:metabolism*; D005260:Female; D006801:Humans; D008213:Lymphocyte Activation; D008214:Lymphocytes / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D047990:TNF Receptor-Associated Factor 1; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000502:physiology*; D019014:fas Receptor / Q000502:physiology
D016328:NF-kappa B; D011506:Proteins; D047990:TNF Receptor-Associated Factor 1; D014409:Tumor Necrosis Factor-alpha; D019014:fas Receptor; D020169:Caspases