title: FLIP(L) induces caspase 8 activity in the absence of interdomain caspase 8 cleavage and alters substrate specificity.
abstract: Caspase 8 is an initiator caspase that is activated by death receptors to initiate the extrinsic pathway of apoptosis. Caspase 8 activation involves dimerization and subsequent interdomain autoprocessing of caspase 8 zymogens, and recently published work has established that elimination of the autoprocessing site of caspase 8 abrogates its pro-apoptotic function while leaving its proliferative function intact. The observation that the developmental abnormalities of caspase 8-deficient mice are shared by mice lacking the dimerization adapter FADD (Fas-associated death domain) or the caspase paralogue FLIP(L) [FLICE (FADD-like interleukin 1β-converting enzyme)-inhibitory protein, long form] has led to the hypothesis that FADD-dependent formation of heterodimers between caspase 8 and FLIP(L) could mediate the developmental role of caspase 8. In the present study, using an inducible dimerization system we demonstrate that cleavage of the catalytic domain of caspase 8 is crucial for its activity in the context of activation by homodimerization. However, we find that use of FLIP(L) as a partner for caspase 8 in dimerization-induced activation rescues the requirement for intersubunit linker proteolysis in both protomers. Moreover, before processing, caspase 8 in complex with FLIP(L) does not generate a fully active enzyme, but an attenuated species able to process only selected natural substrates. Based on these results we propose a mechanism of caspase 8 activation by dimerization in the presence of FLIP(L), as well as a mechanism of caspase 8 functional divergence in apoptotic and non-apoptotic pathways.
authors.affiliation: Program in Apoptosis and Cell Death Research, Sanford-Burnham Medical Research Institute, La Jolla, CA 92037, USA.
authors.forename: Cristina
authors.initials: C
authors.lastname: Pop
authors.affiliation: Dept. of Immunology, St Jude Children's Research Hospital, 262 Danny Thomas Pl., Memphis, TN 38105 USA.
authors.forename: Andrew
authors.initials: A
authors.lastname: Oberst
authors.affiliation: Program in Apoptosis and Cell Death Research, Sanford-Burnham Medical Research Institute, La Jolla, CA 92037, USA.|Division of Medicinal Chemistry and Microbiology, Faculty of Chemistry, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland.
authors.forename: Marcin
authors.initials: M
authors.lastname: Drag
authors.affiliation: Program in Apoptosis and Cell Death Research, Sanford-Burnham Medical Research Institute, La Jolla, CA 92037, USA.
authors.forename: Bram J
authors.initials: BJ
authors.lastname: Van Raam
authors.affiliation: Program in Apoptosis and Cell Death Research, Sanford-Burnham Medical Research Institute, La Jolla, CA 92037, USA.
authors.forename: Stefan J
authors.initials: SJ
authors.lastname: Riedl
authors.affiliation: Dept. of Immunology, St Jude Children's Research Hospital, 262 Danny Thomas Pl., Memphis, TN 38105 USA.
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Green
authors.affiliation: Program in Apoptosis and Cell Death Research, Sanford-Burnham Medical Research Institute, La Jolla, CA 92037, USA.
authors.forename: Guy S
authors.initials: GS
authors.lastname: Salvesen
mesh_terms: D000818:Animals; D017209:Apoptosis; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000502:physiology*; D053181:Caspase 8 / Q000378:metabolism*; D019281:Dimerization; D004789:Enzyme Activation; D053200:Fas-Associated Death Domain Protein; D006868:Hydrolysis; D051379:Mice; D018345:Mice, Knockout; D013379:Substrate Specificity
chemical_list: D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D053200:Fas-Associated Death Domain Protein; D053181:Caspase 8