Caspase recruitment domain-containing protein 9 is an adaptor protein of the CARD-CC protein family, which in humans is encoded by the CARD9 gene. [5] [6] It mediates signals from pattern recognition receptors to activate pro-inflammatory and anti-inflammatory cytokines, regulating inflammation. Homozygous mutations in CARD9 are associated with defective innate immunity against yeasts, like Candida and dermatophytes.
CARD9 is a member of the CARD protein family, which is defined by the presence of a characteristic caspase-associated recruitment domain (CARD). This protein was identified by its selective association with the CARD domain of BCL10, a positive regulator and NF-κB activation. [7] It is thought to function as a molecular scaffold for the assembly of a BCL10 signaling complex that activates NF-κB. Several alternatively spliced transcript variants have been observed, but their full-length nature is not clearly defined. [6]
In 2006, it became clear that Card9 plays important roles within the innate immune response against yeasts. Card9 mediates signals from so called pattern recognition receptors (Dectin-1) to downstream signalling pathways such as NF-κB and by this activates pro-inflammatory cytokines (TNF, IL-23, IL-6, IL-2) and an anti-inflammatory cytokine (IL-10) and subsequently an appropriate innate and adaptive immune response to clear an infection. [8] An autosomal recessive form of susceptibility to chronic mucocutaneous candidiasis was found in 2009 to be associated with homozygous mutations in CARD9. [9] Deep dermatophytosis and Card9 deficiency reported in an Iranian family led to its discovery in 17 people from Tunisian, Algerian, and Moroccan families with deep dermatophytosis. [10]
CARD9 mutations have been associated with inflammatory diseases such as ankylosing spondylitis and inflammatory bowel disease (Crohn's Disease and Ulcerative Colitis). [11] A genetic variant, c.IVS11+1G>C was found to be protective against crohn's disease, ulcerative colitis, and ankylosing spondilitis by Manuel Rivas, Mark Daly and colleagues. [12] CARD9 S12NΔ11, is a rare splice variant in which exon 11 of CARD9 is deleted. This allele, identified by deep sequencing of GWAS loci, results in a protein with a C-terminal truncation. In a functional follow-up study, using re-expressed human CARD9 isoforms in murine Card9−/− bone marrow-derived dendritic cells (BMDCs) were assessed for cytokine production. BMDCs expressing the predisposing variant CARD9 S12N showed increased TNFα and IL-6 production compared to BMDCs expressing wild-type CARD9. In contrast, CARD9 Δ11 and CARD9 S12NΔ11, as well as the C-terminal truncated variant CARD9 V6, showed significant impairment in TNFα and IL-6 production. CARD9 Δ11 was found to have a dominant negative effect on CARD9 function when co-expressed with wild-type CARD9 in human and mouse dendritic cells. [13]
Model organisms have been used in the study of CARD9 function. A conditional knockout mouse line called Card9tm1a(EUCOMM)Hmgu was generated at the Wellcome Trust Sanger Institute. [14] Male and female animals underwent a standardized phenotypic screen [15] to determine the effects of deletion. [16] [17] [18] [19] Additional screens performed: - In-depth immunological phenotyping [20] - in-depth bone and cartilage phenotyping [21]
| Characteristic | Phenotype |
|---|---|
| All data available at. [15] [20] | |
| Insulin | Normal |
| Homozygous viability at P14 | Normal |
| Homozygous Fertility | Normal |
| Body weight | Normal |
| Neurological assessment | Normal |
| Grip strength | Normal |
| Dysmorphology | Normal |
| Indirect calorimetry | Normal |
| Glucose tolerance test | Normal |
| Auditory brainstem response | Normal |
| DEXA | Normal |
| Radiography | Normal |
| Eye morphology | Normal |
| Clinical chemistry | Normal |
| Haematology 16 Weeks | Normal |
| Peripheral blood leukocytes 16 Weeks | Normal |
| Heart weight | Normal |
| Salmonella infection | Normal |
| Cytotoxic T Cell Function | Normal |
| Spleen Immunophenotyping | Normal |
| Mesenteric Lymph Node Immunophenotyping | Normal |
| Bone Marrow Immunophenotyping | Normal |
| Epidermal Immune Composition | Normal |
| Influenza Challenge | Normal |
Caspases are a family of protease enzymes playing essential roles in programmed cell death. They are named caspases due to their specific cysteine protease activity – a cysteine in its active site nucleophilically attacks and cleaves a target protein only after an aspartic acid residue. As of 2009, there are 12 confirmed caspases in humans and 10 in mice, carrying out a variety of cellular functions.
NLR family pyrin domain containing 3 (NLRP3), is a protein that in humans is encoded by the NLRP3 gene located on the long arm of chromosome 1.
Pyroptosis is a highly inflammatory form of lytic programmed cell death that occurs most frequently upon infection with intracellular pathogens and is likely to form part of the antimicrobial response. This process promotes the rapid clearance of various bacterial, viral, fungal and protozoan infections by removing intracellular replication niches and enhancing the host's defensive responses. Pyroptosis can take place in immune cells and is also reported to occur in keratinocytes and some epithelial cells.
Caspase-8 is a caspase protein, encoded by the CASP8 gene. It most likely acts upon caspase-3. CASP8 orthologs have been identified in numerous mammals for which complete genome data are available. These unique orthologs are also present in birds.
Caspase-6 is an enzyme that in humans is encoded by the CASP6 gene. CASP6 orthologs have been identified in numerous mammals for which complete genome data are available. Unique orthologs are also present in birds, lizards, lissamphibians, and teleosts. Caspase-6 has known functions in apoptosis, early immune response and neurodegeneration in Huntington's and Alzheimer's disease.
B-cell lymphoma/leukemia 10 is a protein that in humans is encoded by the BCL10 gene. Like BCL2, BCL3, BCL5, BCL6, BCL7A, and BCL9, it has clinical significance in lymphoma.
Tumor necrosis factor, alpha-induced protein 3 or A20 is a protein that in humans is encoded by the TNFAIP3 gene.
Receptor-interacting serine/threonine-protein kinase 2 is an enzyme that in humans is encoded by the RIPK2 gene.
Caspase recruitment domain-containing protein 11 also known as CARD-containing MAGUK protein 1 is a protein in the CARD-CC protein family that in humans is encoded by the CARD11 gene. CARD 11 is a membrane associated protein that is found in various human tissues, including the thymus, spleen, liver, and peripheral blood leukocytes. Similarly, CARD 11 is also found in abundance in various lines of cancer cells.
Mitochondrial antiviral-signaling protein (MAVS) is a protein that is essential for antiviral innate immunity. MAVS is located in the outer membrane of the mitochondria, peroxisomes, and mitochondrial-associated endoplasmic reticulum membrane (MAM). Upon viral infection, a group of cytosolic proteins will detect the presence of the virus and bind to MAVS, thereby activating MAVS. The activation of MAVS leads the virally infected cell to secrete cytokines. This induces an immune response which kills the host's virally infected cells, resulting in clearance of the virus.
Caspase recruitment domain-containing protein 10 is a protein in the CARD-CC protein family that in humans is encoded by the CARD10 gene.
Mucosa-associated lymphoid tissue lymphoma translocation protein 1 is a protein that in humans is encoded by the MALT1 gene. It's the human paracaspase.
NACHT, LRR and PYD domains-containing protein 4 is a protein that in humans is encoded by the NLRP4 gene.
The nucleotide-binding oligomerization domain-like receptors, or NOD-like receptors (NLRs), are intracellular sensors of pathogen-associated molecular patterns (PAMPs) that enter the cell via phagocytosis or pores, and damage-associated molecular patterns (DAMPs) that are associated with cell stress. They are types of pattern recognition receptors (PRRs), and play key roles in the regulation of innate immune response. NLRs can cooperate with toll-like receptors (TLRs) and regulate inflammatory and apoptotic response.
Inflammasomes are cytosolic multiprotein oligomers of the innate immune system responsible for the activation of inflammatory responses. Activation and assembly of the inflammasome promotes proteolytic cleavage, maturation and secretion of pro-inflammatory cytokines interleukin 1β (IL-1β) and interleukin 18 (IL-18), as well as cleavage of gasdermin D. The N-terminal fragment resulting from this cleavage induces a pro-inflammatory form of programmed cell death distinct from apoptosis, referred to as pyroptosis, and is responsible for secretion of the mature cytokines, presumably through the formation of pores in the plasma membrane. Additionally, inflammasomes can be incorporated into larger cell death-inducing complexes called PANoptosomes, which drive another distinct form of pro-inflammatory cell death called PANoptosis.
Caspase recruitment domain-containing protein 14, also known as D-containing MAGUK protein 2, is a protein in the CARD-CC protein family that in humans is encoded by the CARD14 gene.
Bcl10-interacting CARD protein, also known as BinCARD, is a protein that in humans is encoded by the C9orf89 gene on chromosome 9. BinCARD is a member of the death-domain superfamily and contains a caspase recruitment domain (CARD). This protein regulates apoptosis and the immune response by inhibiting Bcl10, thus implicating it in diseases stemming from Bcl10 dysfunction.
The CARD-CC protein family is defined by an evolutionary conserved "caspase activation and recruitment domain" (CARD) and a coiled-coil (CC) domain. Coiled-coils (CC) act as oligomerization domains for many proteins such as structural and motor proteins, and transcription factors. This means that monomers are converted to macromolecular complexes by polymerization. In humans and other jawed vertebrates, the family consists of CARD9 and the three "CARD-containing MAGUK protein" (CARMA) proteins CARD11 (CARMA1), CARD14 (CARMA2) and CARD10 (CARMA3). Although the MAGUK protein DLG5 contains both a CARD domain and a CC domain, it does not belong to the same family as the CARD-CC proteins since the evolutionary origin of its CARD domain is very likely to be different.
Vishva Mitra Dixit is a physician of Indian origin who is the current Vice President of Discovery Research at Genentech.
Autoinflammatory diseases (AIDs) are a group of rare disorders caused by dysfunction of the innate immune system. They are characterized by periodic or chronic systemic inflammation, usually without the involvement of adaptive immunity.
