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Homotypic FADD interactions through a conserved RXDLL motif are required for death receptor-induced apoptosis

J R Muppidi1, A A Lobito, M Ramaswamy

  • 1Immunoregulation Unit, Autoimmunity Branch, NIAMS, NIH, Bethesda, MD 20892, USA.

Cell Death and Differentiation
|January 18, 2006
PubMed

Insights

Death receptors initiate apoptosis by recruiting FADD and caspase-8. FADD self-association via its DED RXDLL motif is crucial for this process, enabling caspase-8 recruitment and DISC formation for programmed cell death.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Immunology

Background:

  • Death receptors, part of the TNF receptor superfamily, trigger apoptosis.
  • Apoptosis signaling involves recruiting FADD and caspase-8 to form a death-inducing signaling complex (DISC).
  • The precise protein-protein interactions within the DISC remain incompletely understood.

Purpose of the Study:

  • To investigate the role of FADD self-association in death receptor-mediated apoptosis.
  • To elucidate the structural basis of FADD interactions within the DISC.
  • To determine if FADD self-association is essential for initiating apoptosis signaling.

Main Methods:

  • Site-directed mutagenesis of the FADD death effector domain (DED) RXDLL motif.
  • Reconstitution assays using FADD-deficient cells.
  • Analysis of caspase-8 recruitment to the DISC.
  • Assessment of FasL- and TRAIL-induced apoptosis.
  • Microscopic observation of receptor oligomer formation.

Main Results:

  • FADD self-associates through a conserved RXDLL motif in its DED.
  • Mutants lacking the RXDLL motif fail to reconstitute FasL- or TRAIL-induced apoptosis.
  • These FADD mutants cannot recruit caspase-8 into the DISC.
  • Disrupting FADD self-association creates a dominant-negative effect, inhibiting apoptosis and receptor oligomerization.

Conclusions:

  • Lateral interactions among adapter molecules, specifically FADD self-association, are essential for death receptor apoptosis signaling.
  • Self-association into oligomeric assemblies is a critical function of FADD in initiating apoptosis.
  • Understanding FADD self-association provides new insights into the molecular mechanisms of programmed cell death.

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