Apoptosis-associated speck-like protein containing a caspase recruitment domain is a regulator of procaspase-1 activation

J Immunol. 2003 Dec 1;171(11):6154-63. doi: 10.4049/jimmunol.171.11.6154.


Apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC)/target of methylation-induced silencing/PYCARD represents one of only two proteins encoded in the human genome that contains a caspase recruitment domain (CARD) together with a pyrin, AIM, ASC, and death domain-like (PAAD)/PYRIN/DAPIN domain. CARDs regulate caspase family proteases. We show here that ASC binds by its CARD to procaspase-1 and to adapter proteins involved in caspase-1 activation, thereby regulating cytokine pro-IL-1beta activation by this protease in THP-1 monocytes. ASC enhances IL-1beta secretion into the cell culture supernatants, at low concentrations, while suppressing at high concentrations. When expressed in HEK293 cells, ASC interferes with Cardiak/Rip2/Rick-mediated oligomerization of procaspase-1 and suppresses activation this protease, as measured by protease activity assays. Moreover, ASC also recruits procaspase-1 into ASC-formed cytosolic specks, separating it from Cardiak. We also show that expression of the PAAD/PYRIN family proteins pyrin or cryopyrin/PYPAF1/NALP3 individually inhibits IL-1beta secretion but that coexpression of ASC with these proteins results in enhanced IL-1beta secretion. However, expression of ASC uniformly interferes with caspase-1 activation and IL-1beta secretion induced by proinflammatory stimuli such as LPS and TNF, suggesting pathway competition. Moreover, LPS and TNF induce increases in ASC mRNA and protein expression in cells of myeloid/monocytic origin, revealing another level of cross-talk of cytokine-signaling pathways with the ASC-controlled pathway. Thus, our results suggest a complex interplay of the bipartite adapter protein ASC with PAAD/PYRIN family proteins, LPS (Toll family receptors), and TNF in the regulation of procaspase-1 activation, cytokine production, and control of inflammatory responses.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adaptor Proteins, Signal Transducing*
  • Animals
  • Apoptosis / physiology*
  • B-Cell CLL-Lymphoma 10 Protein
  • CARD Signaling Adaptor Proteins
  • COS Cells
  • Carrier Proteins / metabolism
  • Carrier Proteins / physiology*
  • Caspase 1 / metabolism
  • Caspase Inhibitors
  • Caspases / metabolism*
  • Cell Line
  • Cell Line, Tumor
  • Cytoskeletal Proteins / biosynthesis
  • Cytoskeletal Proteins / metabolism
  • Cytoskeletal Proteins / physiology*
  • Enzyme Activation / physiology
  • Enzyme Precursors / antagonists & inhibitors
  • Enzyme Precursors / metabolism*
  • Enzyme Reactivators / metabolism
  • HeLa Cells
  • Humans
  • Interleukin-1 / metabolism
  • Protein Binding / physiology
  • Protein Kinases / metabolism
  • Protein Structure, Tertiary / physiology
  • Receptor-Interacting Protein Serine-Threonine Kinase 2


  • Adaptor Proteins, Signal Transducing
  • B-Cell CLL-Lymphoma 10 Protein
  • BCL10 protein, human
  • CARD Signaling Adaptor Proteins
  • Carrier Proteins
  • Caspase Inhibitors
  • Cytoskeletal Proteins
  • Enzyme Precursors
  • Enzyme Reactivators
  • Interleukin-1
  • PYCARD protein, human
  • Protein Kinases
  • RIPK2 protein, human
  • Receptor-Interacting Protein Serine-Threonine Kinase 2
  • Caspases
  • Caspase 1