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RIP and FADD: two "death domain"-containing proteins can induce apoptosis by convergent, but dissociable, pathways

S Grimm1, B Z Stanger, P Leder

  • 1Department of Genetics, Harvard Medical School, Boston, Massachusetts, USA.

Proceedings of the National Academy of Sciences of the United States of America
|October 1, 1996
PubMed

Insights

Receptor-interacting protein (RIP) and Fas-associated death domain (FADD) induce apoptosis through distinct pathways. RIP self-association triggers cell death, while FADD does not require crosslinking, suggesting convergent but separable mechanisms involving caspase proteases.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Immunology

Background:

  • The Fas receptor initiates apoptosis via its death domain, interacting with proteins like RIP and FADD/MORT1.
  • Both RIP and FADD are known to induce apoptosis in mammalian cells.

Purpose of the Study:

  • To investigate the mechanisms by which RIP and FADD induce apoptosis.
  • To determine if RIP and FADD activate distinct or overlapping apoptotic pathways.

Main Methods:

  • Yeast two-hybrid system to identify protein interactions.
  • Receptor fusion constructs to study RIP and FADD function.
  • Apoptosis assays in mammalian cells, including cell lines resistant to known apoptotic stimuli.
  • Use of a dominant-negative FADD mutant and CrmA (a protease inhibitor).

Main Results:

  • Self-association of RIP's death domain is sufficient to induce apoptosis.
  • Optimal RIP-induced cell killing requires both the death domain and adjacent alpha-helical region.
  • FADD induces cell death independently of crosslinking.
  • RIP induces apoptosis in cells resistant to Fas, TNF, and FADD, indicating a distinct pathway.
  • A dominant-negative FADD mutant inhibits RIP-induced apoptosis but not FADD-induced apoptosis.
  • Both RIP and FADD-mediated apoptosis are blocked by CrmA.

Conclusions:

  • RIP and FADD activate separable apoptotic pathways.
  • These pathways converge on a common downstream target, likely a caspase protease.
  • RIP's apoptotic function involves self-association and specific protein domains, while FADD's mechanism differs.

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