Identification, cloning and characterisation of interleukin-1F5 (IL-36RN) in the chicken.
The human IL-1 family contains eleven genes encoded at three separate loci. Nine, including IL-36 receptor antagonist (IL-36RN), also known as IL-1F5, are present at a single locus on chromosome 2, whereas IL-18 and IL-33 lie on chromosomes 11 and 9 respectively. There are currently only three known orthologues in the chicken - IL-1β, IL-18 and IL-1RN - which are encoded on chromosomes 22, 24 and unplaced, respectively. A novel chicken IL-1 family sequence representing IL-36RN (IL-1F5) was initially identified from an expressed sequence tag (EST) library by its similarity to both chicken IL-1RN and chicken IL-1β. Following isolation of the cDNA from the liver of an uninfected bird, a number of unique sequence features were identified. The predicted protein has a longer NH(2)-terminus than the human protein; however, as in mammals, this region contains neither a prodomain nor a signal peptide. A putative nuclear export sequence is also apparent, yet a similar motif is absent in mammalian IL-36RN. Although chIL-36RN exhibits low homology with its mammalian orthologues, it encodes a predicted β-trefoil structure whose β-strands are conserved with those of the mouse sequence. Unlike in mammals, chIL-36RN expression was constitutive in all tissues and cell subsets examined. In response to viral infection, expression was significantly downregulated in a line of birds which are susceptible to the virus. Chicken IL-36RN, like chIL-1RN, is not encoded at the chIL-1β locus, further emphasising the genomic fragmentation of the large IL-1 gene cluster found in mammals. This suggests differential evolution of this cytokine family since the divergence of birds and mammals from a common ancestor, and underlines the difficulty of determining the full repertoire of chIL-1 family members.
Institute for Animal Health, Compton, Berkshire, UK. mark.gibson@iah.ac.uk
M S
MS
Gibson
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N
Salmon
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S
Bird
P
P
Kaiser
M
M
Fife
D000595:Amino Acid Sequence; D000818:Animals; D030161:Avian Proteins / Q000737:chemistry / Q000235:genetics* / Q000276:immunology*; D002460:Cell Line; D002645:Chickens / Q000276:immunology*; D003001:Cloning, Molecular; D019143:Evolution, Molecular; D006801:Humans; D007378:Interleukins / Q000737:chemistry / Q000235:genetics* / Q000276:immunology*; D008264:Macrophages / Q000276:immunology; D008969:Molecular Sequence Data; D010802:Phylogeny; D060888:Real-Time Polymerase Chain Reaction; D016415:Sequence Alignment; D013047:Specific Pathogen-Free Organisms
D030161:Avian Proteins; D007378:Interleukins