CASPASE RECRUITMENT DOMAIN-CONTAINING PROTEIN 6; CARD6

Other entities represented in this entry:

• CARD-CONTAINING INHIBITOR OF NOD1- AND CARDIAK-INDUCED NFKB ACTIVATION 1, INCLUDED; CINCIN1, INCLUDED

HGNC Approved Gene Symbol: CARD6

Cytogenetic location: 5p13.1 Genomic coordinates (GRCh38): 5:40,841,196-40,855,353 (from NCBI)

▼ Description
The caspase recruitment domain (CARD) is a protein interaction motif that usually consists of a bundle of 6 antiparallel alpha helices. CARD-containing proteins, such as CARD6, are involved in assembly of signal complexes leading to activation of caspase family proteases and induction of NFKB (see 164011) family transcription factors (Stehlik et al., 2003).

▼ Cloning and Expression
By searching databases for genes encoding CARD-containing proteins, followed by PCR of a skeletal muscle cDNA library, Stehlik et al. (2003) obtained a cDNA encoding CARD6. The deduced 311-amino acid protein contains an N-terminal CARD covering its first 91 amino acids, followed by several potential phosphorylation sites. Northern blot analysis detected a 4.4-kb transcript in all tissues examined except brain, and a 6.3-kb transcript in heart and skeletal muscle only.

By database analysis and PCR of a spleen cDNA library, Dufner et al. (2006) cloned full-length CARD6. The 1,037-amino acid protein contains an N-terminal CARD, followed by a glutamic acid-rich region (GARR), a URG4 homology region, and a C-terminal proline-rich region (PRR). The splice variant reported by Stehlik et al. (2003), which Dufner et al. (2006) called CINCIN1, encodes a protein that contains the CARD and GARR of full-length CARD6, but lacks the URG4 homology region and PRR. Instead, CINCIN1 has a unique 3-prime terminal exon encoding 30 amino acids not present in full-length CARD6. Northern blot analysis detected a 4.2-kb CARD6 transcript in most tissues examined. Endogenous CARD6 localized to microtubules in a human hepatoma cell line.

▼ Gene Function
Using coimmunoprecipitation assays after transfecting the CINCIN1 isoform of CARD6 with 18 other CARD family members, Stehlik et al. (2003) found that only NOD1 (CARD4; 605980), CARDIAK (RIPK2; 603455), TUCAN (CARD8; 609051), and NAC (NALP1; 606636) preferentially interacted with CINCIN1. CINCIN1 did not homodimerize. Coexpression of CARDIAK with CINCIN1 in human embryonic kidney cells markedly increased CINCIN1 protein levels and indirectly induced CINCIN1 phosphorylation. CINCIN1 inhibited the NFKB-inducing activities of NOD1 and CARDIAK, but it did not modulate NFKB activation by any other CARD-containing protein examined. CINCIN1 did not influence the caspase-1 (CASP1; 147678)-activating functions of NOD1 and CARDIAK.

Dufner et al. (2006) found that the full-length CARD6 protein interacted with RICK (RIPK2) on microtubules. The CARDs of CARD6 and RICK were not required for their interaction. CARD6 also bound RIP1 (RIPK1; 603453), which lacks a CARD but contains a C-terminal death domain. When coexpressed, RICK targeted CARD6 to aggresomes, ubiquitin-rich cytoplasmic inclusions that form around the microtubule-organizing center if proteasomes are compromised or overwhelmed. Targeting of CARD6 to aggresomes required the CARD of RICK. Dufner et al. (2006) also found that CARD6 expression had a synergistic effect on NFKB activation by several independent signal transduction pathways.

▼ Gene Structure
Stehlik et al. (2003) determined that the CARD6 gene contains at least 3 exons and spans at least 18.9 kb. Dufner et al. (2006) determined that the CARD6 gene contains 4 alternatively spliced exons.

▼ Mapping
By genomic sequence analysis, Stehlik et al. (2003) mapped the CARD6 gene to chromosome 5p12. They mapped the mouse Card6 gene to a region of chromosome 15A1 that shares homology of synteny with human chromosome 5p12. By genomic sequence analysis, Dufner et al. (2006) mapped the CARD6 gene to chromosome 5p13.1.