title: Apoptosis-associated speck-like protein containing a caspase recruitment domain is a regulator of procaspase-1 activation.
abstract: 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.
authors.affiliation: Burnham Institute, La Jolla, CA 92037, USA.
authors.forename: Christian
authors.initials: C
authors.lastname: Stehlik
authors.forename: Sug Hyung
authors.initials: SH
authors.lastname: Lee
authors.forename: Andrea
authors.initials: A
authors.lastname: Dorfleutner
authors.forename: Angela
authors.initials: A
authors.lastname: Stassinopoulos
authors.forename: Junji
authors.initials: J
authors.lastname: Sagara
authors.forename: John C
authors.initials: JC
authors.lastname: Reed
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D000074018:B-Cell CLL-Lymphoma 10 Protein; D053468:CARD Signaling Adaptor Proteins; D019556:COS Cells; D002352:Carrier Proteins / Q000378:metabolism / Q000502:physiology*; D020170:Caspase 1 / Q000378:metabolism; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D002460:Cell Line; D045744:Cell Line, Tumor; D003598:Cytoskeletal Proteins / Q000096:biosynthesis / Q000378:metabolism / Q000502:physiology*; D004789:Enzyme Activation / Q000502:physiology; D004792:Enzyme Precursors / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004793:Enzyme Reactivators / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007375:Interleukin-1 / Q000378:metabolism; D011485:Protein Binding / Q000502:physiology; D011494:Protein Kinases / Q000378:metabolism; D017434:Protein Structure, Tertiary / Q000502:physiology; D053475:Receptor-Interacting Protein Serine-Threonine Kinase 2
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000074018:B-Cell CLL-Lymphoma 10 Protein; C118591:BCL10 protein, human; D053468:CARD Signaling Adaptor Proteins; D002352:Carrier Proteins; D061945:Caspase Inhibitors; D003598:Cytoskeletal Proteins; D004792:Enzyme Precursors; D004793:Enzyme Reactivators; D007375:Interleukin-1; C402202:PYCARD protein, human; D011494:Protein Kinases; C506253:RIPK2 protein, human; D053475:Receptor-Interacting Protein Serine-Threonine Kinase 2; D020169:Caspases; D020170:Caspase 1