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Mol Cell. 2016 Mar 17;61(6):834-49. doi: 10.1016/j.molcel.2016.02.023.

Co-operative and Hierarchical Binding of c-FLIP and Caspase-8: A Unified Model Defines How c-FLIP Isoforms Differentially Control Cell Fate.

Author information

1
MRC Toxicology Unit, Hodgkin Building, P.O. Box 138, Lancaster Road, Leicester LE1 9HN, UK.
2
Department of Dermatology, Venereology and Allergology, Medical Faculty Mannheim, University of Heidelberg, Theodor-Kutzer-Ufer 1-3, 68167 Mannheim, Germany.
3
Department of Dermatology and Allergology, Medical Faculty of the RWTH Aachen, Pauwelsstraße 30, 52074 Aachen, Germany.
4
Henry Wellcome Laboratories of Structural Biology, Department of Molecular and Cell Biology, University of Leicester, Lancaster Road, Leicester LE1 9HN, UK.
5
MRC Toxicology Unit, Hodgkin Building, P.O. Box 138, Lancaster Road, Leicester LE1 9HN, UK. Electronic address: kc5@le.ac.uk.
6
MRC Toxicology Unit, Hodgkin Building, P.O. Box 138, Lancaster Road, Leicester LE1 9HN, UK. Electronic address: mm21@le.ac.uk.

Abstract

The death-inducing signaling complex (DISC) initiates death receptor-induced apoptosis. DISC assembly and activation are controlled by c-FLIP isoforms, which function as pro-apoptotic (c-FLIPL only) or anti-apoptotic (c-FLIPL/c-FLIPS) regulators of procaspase-8 activation. Current models assume that c-FLIP directly competes with procaspase-8 for recruitment to FADD. Using a functional reconstituted DISC, structure-guided mutagenesis, and quantitative LC-MS/MS, we show that c-FLIPL/S binding to the DISC is instead a co-operative procaspase-8-dependent process. FADD initially recruits procaspase-8, which in turn recruits and heterodimerizes with c-FLIPL/S via a hierarchical binding mechanism. Procaspase-8 activation is regulated by the ratio of unbound c-FLIPL/S to procaspase-8, which determines composition of the procaspase-8:c-FLIPL/S heterodimer. Thus, procaspase-8:c-FLIPL exhibits localized enzymatic activity and is preferentially an activator, promoting DED-mediated procaspase-8 oligomer assembly, whereas procaspase-8:c-FLIPS lacks activity and potently blocks procaspase-8 activation. This co-operative hierarchical binding model explains the dual role of c-FLIPL and crucially defines how c-FLIP isoforms differentially control cell fate.

PMID:
26990987
PMCID:
PMC4819448
DOI:
10.1016/j.molcel.2016.02.023
[Indexed for MEDLINE]
Free PMC Article

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