ASC directs NF-kappaB activation by regulating receptor interacting protein-2 (RIP2) caspase-1 interactions.
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.
Sarkar
Anasuya
A
Davis Heart and Lung Research Institute, The Ohio State University, Columbus 43210, USA.
Duncan
Michelle
M
Hart
Judy
J
Hertlein
Erin
E
Guttridge
Denis C
DC
Wewers
Mark D
MD
D000818:Animals; D051017:Apoptosis Regulatory Proteins; D053468:CARD Signaling Adaptor Proteins; D020170:Caspase 1 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D007375:Interleukin-1 / Q000378:metabolism; D008264:Macrophages / Q000276:immunology / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D018448:Models, Immunological; D016328:NF-kappa B / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D053475:Receptor-Interacting Protein Serine-Threonine Kinase 2; D053422:Receptor-Interacting Protein Serine-Threonine Kinases; D047988:Tumor Necrosis Factor Receptor-Associated Peptides and Proteins / Q000378:metabolism*
D051017:Apoptosis Regulatory Proteins; D053468:CARD Signaling Adaptor Proteins; D003598:Cytoskeletal Proteins; D007375:Interleukin-1; D016328:NF-kappa B; C402202:PYCARD protein, human; C498534:Pycard protein, mouse; D047988:Tumor Necrosis Factor Receptor-Associated Peptides and Proteins; D017346:Protein Serine-Threonine Kinases; C506253:RIPK2 protein, human; D053475:Receptor-Interacting Protein Serine-Threonine Kinase 2; D053422:Receptor-Interacting Protein Serine-Threonine Kinases; C506255:Ripk2 protein, mouse; D020170:Caspase 1