Structure and expression pattern of teleost caspase recruitment domain (CARD) containing proteins that are potentially involved in NF-κB signalling

Caspase-associated recruitment domain (CARD) proteins play critical roles in regulation of caspase activation, or regulation of NF-κB activation. In the present study, 9 CARD-genes, which may be involved in NF-κB activation, were identified in teleost fish. Phylogenetic analysis showed that the orthologs to mammalian RIPK2, NOD1, PYCARD, CARD9, CARD10, CARD11, CARD14, NOD2 and BCL10 were evident in teleost fish, but clear orthologs to mammalian CARD6 and CARD8 were not found in teleost fish. In zebrafish, most CARD-genes were expressed in embryos and larvae. In adult zebrafish, zfRIPK2, zfNOD1, zfPYCARD, zfCARD9 and zfNOD2 transcripts were constitutively expressed in kidney, gill, intestine, liver, brain and spleen whilst zfCARD11, zfCARD14 and BCL10 exhibited limited tissue distribution. A CARD-related gene (zfCARD-rel), containing a single CARD domain, was identified in the zebrafish genome and the EST databases and its transcripts were detected only in spleen and kidney. Phylogenetic analysis suggested that zfCARD-rel might be the ortholog of mammalian CARD8 or the short isoform of NLRP1. Overexpression of zfCARD-rel had a significantly inhibitory effect on NF-κB activity, demonstrating the zfCARD-rel protein might serve as a negative regulator of cell death and inflammatory response.