J Immunol. 2006 Apr 15;176(8):4979-86.

ASC directs NF-kappaB activation by regulating receptor interacting protein-2 (RIP2) caspase-1 interactions.External

Sarkar, A., Duncan, M., Hart, J., Hertlein, E., Guttridge, D. C., Wewers, M. D.,
--- - Davis Heart and Lung Research Institute, The Ohio State University, Columbus 43210, USA.
Receptor interacting protein-2 (RIP2) is a caspase recruitment domain (CARD)-containing kinase that interacts with caspase-1 and plays an important role in NF-kappaB activation. Apoptosis-associated speck-like protein containing a CARD (ASC) is a PYRIN and CARD-containing molecule, important in the induction of apoptosis and caspase-1 activation. Although RIP2 has also been linked to caspase-1 activation, RIP2 knockout animals fail to show a defect in caspase-1-mediated processing of proIL-1beta to its active form. Therefore, RIP2 function in binding to caspase-1 remains poorly understood. We hypothesized that caspase-1 may serve as a scaffolding molecule that promotes RIP2 interaction with IkappaB kinase-gamma thus inducing NF-kappaB activation. We further hypothesized that ASC, which also interacts with caspase-1 via its CARD, may interfere with the caspase-1 RIP2 interaction. In HEK293 cells, ASC induced prominent activation of caspase-1 and proIL-1beta processing. RIP2 transient transfection induced transcription of an NF-kappaB reporter gene. This RIP2-induced NF-kappaB activity and caspase-1 binding was inhibited in a dose-dependent fashion by ASC. Consistent with a role for caspase-1 as a scaffold for RIP2, caspase-1 knockout macrophages were suppressed in their ability to activate NF-kappaB, and septic caspase-1 knockout animals produced less IL-6, a functional marker of NF-kappaB activity. Lastly, THP-1 cells treated with small interfering RNA for ASC decreased their caspase-1 activity while enhancing their NF-kappaB signal. These data suggest that ASC may direct caspase-1 away from RIP2-mediated NF-kappaB activation, toward caspase-1-mediated processing of proIL-1beta by interfering with the RIP2 caspase-1 interaction.
PMID: 16585594External
Arrow2 In vitro interaction Arrow2 In vivo interaction Arrow2 Characterization Arrow2 Functional role Arrow2 top
In vivo interaction
  Endogenous
expression
Overexpression DD1 DD2 Reference
Family DD1 DD2 Method Species Region Species Region
CARD ASC Link Caspase1 Co-immunoprecipitation HEK293 Not specified Not specified Not specified Not specified 16585594
CARD ASC Link Caspase1 Co-immunoprecipitation THP-1 16585594
CARD Caspase1 Link RIPK2 Co-immunoprecipitation HEK293 Not specified Not specified Not specified Not specified 16585594
CARD Caspase1 Link RIPK2 Co-immunoprecipitation THP-1 16585594
(Link: click this icon to show interactions only between the two corresponding DDs)
Arrow2 In vitro interaction Arrow2 In vivo interaction Arrow2 Characterization Arrow2 Functional role Arrow2 top
Functional Role
Family DD1 DD2 Method Death-related Death-unrelated Reference
CARD ASC Link Caspase1 ELISA IL-1b secretion 16585594
CARD Caspase1 Link RIPK2 Luciferase assay NF-kB activation 16585594
(Link: click this icon to show interactions only between the two corresponding DDs)