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The adaptor protein FADD and the initiator caspase-8 mediate activation of NF-κB by TRAIL

M Grunert1, K Gottschalk, J Kapahnke

  • 1Research Group Apoptosis, Department of Gene Vectors, Helmholtz Center Munich-German Research Center for Environmental Health, Marchioninistrasse 25, 81377 Munich, Germany.

Cell Death & Disease
|October 26, 2012
PubMed

Insights

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) activates NF-κB through a pathway involving Fas-associated protein with death domain (FADD) and caspase-8. This study clarifies the mediators of TRAIL-induced NF-κB signaling, distinct from apoptosis pathways.

Area of Science:

  • Cellular signaling pathways
  • Molecular biology
  • Immunology

Background:

  • Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is known to induce apoptosis and activate NF-κB.
  • The precise molecular mechanism of TRAIL-mediated NF-κB activation is not fully understood.
  • TRAIL signaling involves TRAIL receptors, FADD, and caspase-8 in apoptosis, but NF-κB pathway mediators are debated.

Purpose of the Study:

  • To elucidate the receptor-proximal mediators of NF-κB activation by TRAIL.
  • To differentiate the signaling molecules involved in TRAIL-induced apoptosis versus NF-κB activation.
  • To establish the specific roles of FADD and caspase-8 in TRAIL-induced NF-κB signaling.

Main Methods:

  • Deletion analysis of TRAIL receptor death domains (DD).
  • RNA interference (RNAi)-mediated knockdown of FADD and FLICE-like inhibitory protein (FLIP).
  • Analysis of NF-κB signaling in FADD-deficient JURKAT T-cell leukemia cells.
  • Functional rescue experiments using exogenous FADD and caspase-8 variants (wild-type and catalytically inactive).

Main Results:

  • Deletion of the death domain (DD) of TRAIL receptors 1 and 2 was essential for NF-κB signaling.
  • Knockdown or deficiency of FADD significantly reduced or abolished TRAIL-induced NF-κB activation.
  • TRAIL-induced NF-κB activation was independent of receptor-interacting protein 1 (RIP1) and FLIP.
  • FADD's ability to recruit caspase-8 was crucial for mediating NF-κB activation.
  • Caspase-8 deficiency inhibited TRAIL-induced NF-κB activation, which could be rescued by wild-type caspase-8 but not an inactive mutant.
  • Signaling for TRAIL-induced apoptosis and NF-κB activation diverges downstream of caspase-8.

Conclusions:

  • The study establishes a clear mechanism for TRAIL-induced NF-κB activation.
  • Key mediators identified are the TRAIL receptor DD, FADD, and caspase-8.
  • RIP1 and FLIP are not required for TRAIL-induced NF-κB activation.
  • TRAIL signaling bifurcates downstream of caspase-8, leading to distinct apoptosis and NF-κB pathways.

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