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ASC filament formation serves as a signal amplification mechanism for inflammasomes

Mathias S Dick1, Lorenzo Sborgi2, Sebastian Rühl1

  • 1Focal Area Infection Biology, Biozentrum, University of Basel, Klingelbergstrasse 50/70, 4056 Basel, Switzerland.

Nature Communications
|June 23, 2016
PubMed

Insights

The ASC speck, crucial for inflammasome activation, forms via ASC(PYD) filament oligomerization and ASC(CARD) cross-linking. Speck formation drives IL-1β processing but not pyroptosis, amplifying caspase-1 activity.

Area of Science:

  • Immunology
  • Molecular Biology
  • Cell Biology

Background:

  • Inflammasome activation is a key immune response.
  • The ASC speck, formed by ASC protein, is a hallmark of inflammasome activation.
  • ASC protein contains pyrin (PYD) and caspase recruitment (CARD) domains.

Purpose of the Study:

  • To elucidate the molecular mechanism of ASC speck assembly.
  • To determine the role of ASC speck formation in inflammasome signaling pathways.
  • To investigate the functional consequences of ASC speck assembly on cytokine processing and pyroptosis.

Main Methods:

  • Site-directed mutagenesis of ASC protein domains (PYD and CARD).
  • Analysis of ASC speck formation in vitro and in primary macrophages.
  • Assays for IL-1β processing and gasdermin-D cleavage to assess inflammasome activity.

Main Results:

  • ASC speck assembly requires ASC(PYD) oligomerization into filaments and ASC(CARD) cross-linking.
  • Mutants lacking functional CARD assemble filaments but not specks, and disrupt endogenous specks.
  • ASC speck formation is essential for efficient IL-1β processing but not for gasdermin-D cleavage or pyroptosis.
  • Oligomerization of ASC acts as a signal amplification mechanism for caspase-1 activation.

Conclusions:

  • ASC speck assembly is a multi-step process involving filament formation and cross-linking.
  • The ASC speck is critical for inflammasome-mediated IL-1β production.
  • ASC speck formation specifically regulates cytokine processing, distinct from pyroptosis induction.

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