title: Oligomerized CARD16 promotes caspase-1 assembly and IL-1β processing.
abstract: Increasing evidence indicates that caspase recruitment domain (CARD)-mediated caspase-1 (CASP1) assembly is an essential process for its activation and subsequent interleukin (IL)-1β release, leading to the initiation of inflammation. Both CARD16 and CARD17 were previously reported as inhibitory homologs of CASP1; however, their molecular function remains unclear. Here, we identified that oligomerization activity allows CARD16 to function as a CASP1 activator. We investigated the molecular characteristics of CARD16 and CARD17 in transiently transfected HeLa cells. Although both CARD16 and CARD17 interacted with CASP1CARD, only CARD16 formed a homo-oligomer. Oligomerized CARD16 formed a filament-like structure with CASP1CARD and a speck with apoptosis-associated speck-like protein containing a CARD. A filament-like structure formed by CARD16 promoted CASP1 filament assembly and IL-1β release. In contrast, CARD17 did not form a homo-oligomer or filaments and inhibited CASP1-dependent IL-1β release. Mutated CARD16D27G, mimicking the CARD17 amino acid sequence, formed a homo-oligomer but failed to form a filament-like structure. Consequently, CARD16D27G weakly promoted CASP1 filament assembly and subsequent IL-1β release. These results suggest that oligomerized CARD16 promotes CARD-mediated molecular assembly and CASP1 activation.
authors.affiliation: Division of Inflammation Research, Center for Molecular Medicine, Jichi Medical University, Tochigi, Japan.
authors.forename: Tadayoshi
authors.initials: T
authors.lastname: Karasawa
authors.affiliation: Division of Inflammation Research, Center for Molecular Medicine, Jichi Medical University, Tochigi, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Kawashima
authors.affiliation: Division of Inflammation Research, Center for Molecular Medicine, Jichi Medical University, Tochigi, Japan.
authors.forename: Fumitake
authors.initials: F
authors.lastname: Usui
authors.affiliation: Division of Inflammation Research, Center for Molecular Medicine, Jichi Medical University, Tochigi, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Kimura
authors.affiliation: Division of Inflammation Research, Center for Molecular Medicine, Jichi Medical University, Tochigi, Japan.
authors.forename: Koumei
authors.initials: K
authors.lastname: Shirasuna
authors.affiliation: Division of Inflammation Research, Center for Molecular Medicine, Jichi Medical University, Tochigi, Japan.
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Inoue
authors.affiliation: Division of Inflammation Research, Center for Molecular Medicine, Jichi Medical University, Tochigi, Japan.
authors.forename: Takanori
authors.initials: T
authors.lastname: Komada
authors.affiliation: Division of Inflammation Research, Center for Molecular Medicine, Jichi Medical University, Tochigi, Japan.
authors.forename: Motoi
authors.initials: M
authors.lastname: Kobayashi
authors.affiliation: Division of Inflammation Research, Center for Molecular Medicine, Jichi Medical University, Tochigi, Japan.
authors.forename: Yoshiko
authors.initials: Y
authors.lastname: Mizushina
authors.affiliation: Department of Molecular Oncology, Shinshu University Graduate School of Medicine, Nagano, Japan.
authors.forename: Junji
authors.initials: J
authors.lastname: Sagara
authors.affiliation: Division of Inflammation Research, Center for Molecular Medicine, Jichi Medical University, Tochigi, Japan.
authors.forename: Masafumi
authors.initials: M
authors.lastname: Takahashi
keywords: ANOVA, analysis of variance; ASC, apoptosis-associated speck-like protein containing a caspase recruitment domain; BS3, bis(sulfosccinimidyl)suberate; Bcl10, B-cell lymphoma/leukemia 10; CARD, caspase recruitment domain; CARMA1, CARD-membrane-associated guanylate kinase 1; CASP1, caspase-1; COPs, CARD-only proteins; Caspase; Cytokine; ELISA, enzyme-linked immunosorbent assay; FCS, fetal calf serum; IL, interleukin; Inflammation; Interleukin; LPS, lipopolysaccharide; LRRs, leucine-rich repeats; NF-κB, nuclear factor kappa beta; NLRs, nucleotide-binding domain leucine-rich repeat containing receptors; PYD, pyrin domain