The NLRC4 protein is highly conserved across mammalian species. It bears homology to the c. elegans Ced4 protein. It contains an n-terminal CARD domain, a central nucleotide binding/NACHT domain, and a c-terminal leucine rich repeat (LRR) domain. It belongs to a family of NLR proteins that includes the transcriptional co-activator CIITA and the canonical inflammasome protein NLRP3. A truncated murine NLRC4 was the first member of this family whose crystal structure was solved.
NLRC4 is best associated with triggering formation of the inflammasome. Unlike NLRP3, certain inflammasome-dependent functions of NLRC4 may be carried out independently of the inflammasome scaffold ASC. Human Ced4 homologs include APAF1, NOD1 (CARD4), and NOD2 (CARD15). These proteins have at least 1 N-terminal CARD domain followed by a centrally located nucleotide-binding domain (NBD or NACHT) and a C-terminal regulatory domain, found only in mammals, that contains either WD40 repeats or leucine-rich repeats (LRRs). CARD12 is a member of the Ced4 family and can induce apoptosis.
NLRC4 has been shown to interact with NAIP (there is one human NAIP but mice express at least 4 distinct NAIP proteins). The NAIP/NLRC4 interaction may determine the ligand specificity. NLRC4-dependent inflammasome activity activates CASP1. Under certain circumstances, NLRC4 and NLRP3 may occupy the same inflammasome complex.
Humans bearing activating mutations in NLRC4 can develop an autoinflammatory syndrome characterized by acute fever, hepatitis, very high serum ferritin, and other features suggestive of Macrophage Activation Syndrome (MAS). Some patients also developed a potentially life-threatening enterocolitis that abated during early childhood. In these patients, chronic and extraordinary elevation of serum IL-18 is found, in distinction from patients with NLRP3 mutations who develop Cryopyrin Associated Periodic Syndromes. A large Japanese family had much milder disease associated with cold-induced urticaria that was caused by a dominantly inherited NLRC4 mutation.
^Geddes BJ, Wang L, Huang WJ, Lavellee M, Manji GA, Brown M, Jurman M, Cao J, Morgenstern J, Merriam S, Glucksmann MA, DiStefano PS, Bertin J (Jun 2001). "Human CARD12 is a novel CED4/Apaf-1 family member that induces apoptosis". Biochemical and Biophysical Research Communications. 284 (1): 77–82. PMID11374873. doi:10.1006/bbrc.2001.4928.
^Hu Z, Yan C, Liu P, Huang Z, Ma R, Zhang C, Wang R, Zhang Y, Martinon F, Miao D, Deng H, Wang J, Chang J, Chai J (Jul 2013). "Crystal structure of NLRC4 reveals its autoinhibition mechanism". Science. 341 (6142): 172–5. PMID23765277. doi:10.1126/science.1236381.
Poyet JL, Srinivasula SM, Tnani M, Razmara M, Fernandes-Alnemri T, Alnemri ES (Jul 2001). "Identification of Ipaf, a human caspase-1-activating protein related to Apaf-1". The Journal of Biological Chemistry. 276 (30): 28309–13. PMID11390368. doi:10.1074/jbc.C100250200.
Fu WN, Bertoni F, Kelsey SM, McElwaine SM, Cotter FE, Newland AC, Jia L (Jan 2003). "Role of DNA methylation in the suppression of Apaf-1 protein in human leukaemia". Oncogene. 22 (3): 451–5. PMID12545166. doi:10.1038/sj.onc.1206147.
Agostini L, Martinon F, Burns K, McDermott MF, Hawkins PN, Tschopp J (Mar 2004). "NALP3 forms an IL-1beta-processing inflammasome with increased activity in Muckle-Wells autoinflammatory disorder". Immunity. 20 (3): 319–25. PMID15030775. doi:10.1016/S1074-7613(04)00046-9.
Damiano JS, Newman RM, Reed JC (Nov 2004). "Multiple roles of CLAN (caspase-associated recruitment domain, leucine-rich repeat, and NAIP CIIA HET-E, and TP1-containing protein) in the mammalian innate immune response". Journal of Immunology. 173 (10): 6338–45. PMID15528373. doi:10.4049/jimmunol.173.10.6338.
Sadasivam S, Gupta S, Radha V, Batta K, Kundu TK, Swarup G (Jan 2005). "Caspase-1 activator Ipaf is a p53-inducible gene involved in apoptosis". Oncogene. 24 (4): 627–36. PMID15580302. doi:10.1038/sj.onc.1208201.
Lu C, Wang A, Wang L, Dorsch M, Ocain TD, Xu Y (Jun 2005). "Nucleotide binding to CARD12 and its role in CARD12-mediated caspase-1 activation". Biochemical and Biophysical Research Communications. 331 (4): 1114–9. PMID15882992. doi:10.1016/j.bbrc.2005.04.027.
Thalappilly S, Sadasivam S, Radha V, Swarup G (Jun 2006). "Involvement of caspase 1 and its activator Ipaf upstream of mitochondrial events in apoptosis". The FEBS Journal. 273 (12): 2766–78. PMID16817903. doi:10.1111/j.1742-4658.2006.05293.x.