title: Caspase 7 can cleave tumor necrosis factor receptor-I (p60) at a non-consensus motif, in vitro.
abstract: Ligand binding to tumor necrosis factor receptor-I (TNFRI) can promote cell survival or activate the apoptotic caspase cascade. Cytoplasmic interaction of TNFRI with TRAF2 and RIP allows for the activation of JNK and NFkappaB pathways. Alternatively, a carboxy terminal death domain protein interaction motif can recruit TRADD, which then recruits FADD/MORT1, and finally procaspase 8. Aggregation of these components form a death inducing signaling complex, leading to the cleavage and activation of caspase 8. We have found that during apoptosis human TNFRI protein is lost in a caspase-dependent manner. The cytoplasmic tail of human TNFRI was found to be susceptible to caspase cleavage but not by caspase 8. Instead, the downstream executioner caspase 7 was the only caspase capable of cleaving TNFRI, in vitro. Identification and characterization of the cleavage site revealed a derivative of the classic EXD motif that incorporates a glutamate (E) in the P1 position. Using several criteria to establish that caspase activity was responsible for cleavage at this site, we confirmed that caspase 7 can cleave at a GELE motif. Mutation of the cleavage site prevented the apoptosis-associated cleavage of TNFRI. This ability of caspase 7 to cleave at a non-EXD or -DXXD motif suggests that the specificity of caspases may be broader than is currently held.
authors.affiliation: Program in Aging, The Burnham Institute, La Jolla, CA 92037, USA. dethell@liai.org
authors.forename: D W
authors.initials: DW
authors.lastname: Ethell
authors.forename: E
authors.initials: E
authors.lastname: Bossy-Wetzel
authors.forename: D E
authors.initials: DE
authors.lastname: Bredesen
mesh_terms: D000595:Amino Acid Sequence; D015703:Antigens, CD / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017209:Apoptosis; D001665:Binding Sites; D053179:Caspase 7; D020169:Caspases / Q000494:pharmacology*; D004789:Enzyme Activation; D006801:Humans; D019169:Jurkat Cells; D008969:Molecular Sequence Data; D009154:Mutation; D010957:Plasmids; D018124:Receptors, Tumor Necrosis Factor / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D047888:Receptors, Tumor Necrosis Factor, Type I; D016415:Sequence Alignment; D015398:Signal Transduction; D014162:Transfection
chemical_list: D015703:Antigens, CD; D018124:Receptors, Tumor Necrosis Factor; D047888:Receptors, Tumor Necrosis Factor, Type I; C505520:CASP7 protein, human; D053179:Caspase 7; D020169:Caspases