Reverse hierarchical DED assembly in the cFLIP-procaspase-8 and cFLIP-procaspase-8-FADD complexes.

cFLIP, a master anti-apoptotic regulator, targets the FADD-induced DED complexes of procaspase-8 in death receptor and ripoptosome signaling pathways. Several tumor cells maintain relatively high levels of cFLIP in achieving their immortality. However, understanding the three-dimensional regulatory mechanism initiated or mediated by elevated levels of cFLIP has been limited by the absence of the atomic coordinates for cFLIP-induced DED complexes. Here we report the crystal plus cryo-EM structures to uncover an unconventional mechanism where cFLIP and procaspase-8 autonomously form a binary tandem DED complex, independent of FADD. This complex gains the ability to recruit FADD, thereby allosterically modulating cFLIP assembly and partially activating caspase-8 for RIPK1 cleavage. Our structure-guided mutagenesis experiments provide critical insights into these regulatory mechanisms, elucidating the resistance to apoptosis and necroptosis in achieving immortality. Finally, this research offers a unified model for the intricate bidirectional hierarchy-based processes using multiprotein helical assembly to govern cell fate decisions. FADD binds Casp-8 and then cFLIP to form the FADD-Casp8-cFLIP complex. The authors found that the DED complex could assemble in reverse order, where cFLIP oligomerizes to bind Casp-8. The resultant complex could bind FADD, generating the cFLIP-Casp-8-FADD complex by a different mechanism. [ABSTRACT FROM AUTHOR]