The chicken 9E3/CEF4 CXC chemokine is the avian orthologue of IL8 and maps to chicken Chromosome 4 syntenic with genes flanking the mammalian chemokine cluster

Abstract

 The gene encoding the chicken chemokine 9E3/CEF4 was cloned, sequenced, and mapped; 9E3/CEF4 was the first nonmammalian cytokine cDNA to be cloned and has significant amino acid identity with both human IL8 and human GROα. These results show that this cytokine is chicken IL8 and not GROα. The exon:intron structure of chicken IL8 corresponds almost exactly to that of human IL8 and differs from those of other known mammalian CXC chemokine genes. Analysis of the predicted amino acid sequence suggests that overall protein structure is conserved between human and chicken IL8, but that the receptor binding sites are not. Genetic distance analysis also suggests that this gene encodes chicken IL8. A number of potential regulatory sequences similar to those found in human IL8 have been identified in the promoter. These include (5′-3′) a hepatocyte NF-1 binding site, an NF-κB binding site, and a TATAAA box. The human AP-1 binding site and CCAT box are poorly conserved in the promoter of the chicken gene, but there are other potential AP-1 binding sites and a potential CCAT box. The human IRF-1 and octamer binding sites seem to be absent. However, the chicken gene promoter contains a GATA motif not present in the promoter of human IL8. Sequence comparisons also identify conserved regions in the promoter that may function as transcription factor binding sites as yet undescribed in the human IL8 promoter. Promoter sequence polymorphisms have been identified in chicken lines C and 6₁, but neither lie in any of the regulatory regions mentioned above. Chicken IL8 contains nine repeats of the "instability" motif ATTTA in the 3' untranslated region (UTR) in exon 4. A multiple restriction single-stranded conformational polymorphism was identified which enabled chicken IL8 to be genetically mapped to Chromosome (Chr) 4, linked to SPP1 and ALB1, and thus showing conserved synteny with mouse Chr 5 and human Chr 4. This is the first nonmammalian chemokine gene to be genetically mapped.