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Membrane oligomerization and cleavage activates the caspase-8 (FLICE/MACHalpha1) death signal

D A Martin1, R M Siegel, L Zheng

  • 1Laboratory of Immunology, NIAID, National Institutes of Health, Bethesda, Maryland 20892-1892, USA.

The Journal of Biological Chemistry
|March 21, 1998
PubMed

Insights

Oligomerization at the cell membrane triggers caspase-8 autoactivation and apoptosis. However, apoptosis may involve a death signal from the enzyme

Area of Science:

  • Cellular Biology
  • Molecular Biology
  • Biochemistry

Background:

  • Apoptosis, or programmed cell death, is essential for multicellular organisms.
  • Caspase activation is a key step in many apoptosis pathways, including those initiated by death receptors like CD95/Fas/APO-1.
  • The precise mechanisms regulating caspase activation remain incompletely understood.

Purpose of the Study:

  • To investigate the requirements for activating caspase-8, a crucial protease in apoptosis.
  • To determine if membrane localization and oligomerization are sufficient for caspase-8 autoactivation and subsequent apoptosis.

Main Methods:

  • Utilized molecular chimeras, fusing caspase-8 with CD8 or Tac domains.
  • Employed enzyme inhibitors (z-VAD-fmk, z-IETD-fmk, p35) and site-directed mutagenesis to probe caspase activity.
  • Investigated the role of Bcl-2 and mutations affecting caspase release from the membrane.

Main Results:

  • Membrane-associated oligomerization of caspase-8 potently induced autoactivation and apoptosis.
  • Apoptosis was blocked by caspase inhibitors and active site mutations, but not by Bcl-2.
  • Mutations preventing proteolytic release of caspase-8 from its membrane anchor abolished apoptosis.

Conclusions:

  • Oligomerization at the cell membrane is sufficient to trigger caspase-8 autoactivation.
  • Apoptosis induction may involve a death signal transmitted by the proteolytic release of active caspase-8 into the cytoplasm.

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