Gene Expression Mechanism and Repertoire of ASC-Mediated

identified 75 genes that were induced by ASC activation. A large proportion of them was related to transcription (23%), inflammation (21%), or cell death (16%), indicating that ASC is a potent inducer of inflammatory and cell death-related genes. This is the first report of ASC-mediated AP-1 activation and the repertoire of genes induced downstream of ASC activation. T he caspase recruitment domain (CARD) 4-containing protein, apoptosis-associated speck-like protein containing a CARD (ASC; also called TMS-1), was originally identified as a protein that forms large aggregates (called specks) in HL-60 human leukemia cells treated with chemo-therapeutic agents (1), and as the product of a gene that is silenced in cancer cells by DNA methylation (2). Thus, ASC has been implicated in apoptosis and tumor suppression. ASC consists of an N-terminal pyrin domain and a C-terminal CARD. Pyrin domain and CARD belong to the death domain-fold domains, which engage in homophilic protein-protein interactions. In this context, ASC resembles Fas-associated death domain protein (FADD), an adaptor protein that recruits caspase-8 to death receptors. In fact, ASC has been found to recruit caspase-1 to several members of the nucleotide-binding domain and leucine-rich repeat (LRR)-containing proteins (NLRs), including cryopyrin (also called NLRP3), and to induce caspase-1-mediated IL-1␤ maturation (3– 6). Because these NLRs function as cytoplasmic sensors for invading bacteria and viruses in cells, and because macrophages from ASC-deficient mice are defective in the production of IL-1␤ upon microbial infection, ASC is considered to be an important molecular component of the innate immune system (7–10). In terms of the proinflammatory activity of ASC, it has been demonstrated that ASC by itself or in combination with NLRs, including cryopyrin and CARD12 (also called NLRC4, IPAF, CLR2.1, and CLAN), induces NF-␬B activation when expressed in HEK293 cells by genetic reconstitution (3, 11, 12). Consistent with this, the knockdown of ASC expression by RNA interference in human monocytic/macrophagic cell lines results in reduced NF-␬B activation as well as diminished IL-8 and TNF-␣ production upon Porphyromonas gingivalis infection (13), indicating that ASC plays an essential role in the transcriptional activation of inflammatory cytokine genes in human macrophages, although studies involving ASC-deficient mice have indicated that ASC is not essential for the expression of cytokine genes and NF-␬B activation induced by microbial infection in murine macrophages (7, 14, 15). To investigate the molecular mechanism of ASC-mediated NF-␬B activation, we previously developed a chimeric protein (C12N2) consisting of the CARD from …