^FADDDED filaments coordinate complex IIa assembly during TNF-induced apoptosis

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Extrinsic apoptosis is triggered by death receptors, assembling RIPK1, FADD, and caspase-8.
• Caspase-8 activation involves filament formation via its tandem death effector domain (tDED).
• The oligomeric structure and function of FADD's DED (^FADDDED) in apoptosis are not well understood.

Purpose of the Study:

• To elucidate the structural basis of ^FADDDED filament formation.
• To investigate the role of ^FADDDED filamentation in extrinsic apoptosis initiation.
• To uncover novel mechanisms of cFLIP in regulating apoptosis.

Main Methods:

• Cryogenic-electron microscopy (cryo-EM) to determine the structure of ^FADDDED filaments.
• Site-directed mutagenesis to assess the functional impact of filament disruption.
• Molecular dynamics simulations to analyze protein-protein interactions and thermodynamic preferences.

Main Results:

• ^FADDDED filaments form three-helical chains stabilized by iterative interactions.
• Disruption of ^FADDDED filaments impairs RIPK1/caspase-8 recruitment and abrogates TNF-induced apoptosis.
• ^FADDDED filamentation is required for RIPK1-FADD interaction and is antagonized by cFLIP.

Conclusions:

• ^FADDDED filament formation is a critical mechanistic step in TNF-induced extrinsic apoptosis.
• This process is essential for the assembly of the death-inducing signaling complex (DISC).
• cFLIP employs an additional anti-apoptotic mechanism by destabilizing ^FADDDED filaments.