CARD9

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 Card9^{tm1a(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]

• Human CARD9 genome location and CARD9 gene details page in the UCSC Genome Browser.