cDNA cloning, genomic structure, molecular characterization and mRNA expression analysis of the Pekin duck interleukin-10 receptor 1

Summary Interleukin‐10 (IL‐10) mediates its broad anti‐inflammatory and immunoregulatory effects through two cell surface receptors by which binding to the IL‐10 receptor 1 (IL‐10R1) is the initial step that leads to recruitment of IL‐10R2 and initiation of the ternary complex signal transduction cascade. The duck IL‐10R1 (duIL‐10R1) cDNA was obtained by using RT‐PCR and 5′RACE. The deduced 574 amino acid protein has an amino acid identity of 62%, 27% and 28% with chicken, mouse and human IL‐10R1, respectively. Comparison of the duIL‐10R1 cDNA with duck genomic sequences revealed a seven exon–six intron structure of the duck IL‐10R1 gene that shares a similar size with the respective exons 1–7 of the chicken and human IL‐10R1 genes, but the avian genes are more compact. Promoter analysis identified putative binding sites for regulatory elements such as CCAAT enhancer binding protein‐α, specificity protein 1 (Sp1), nuclear factor 1 (NF1), transcriptional regulatory protein Oct‐1, nuclear factor (NF) κB and interferon‐stimulated gene factor‐3 (ISGF‐3). A canonical TATA box was absent in proximity of the transcription initiation site, but a CpG island was present. Sequence analysis of the predicted duIL‐10R1 protein revealed characteristic features of class‐II cytokine receptors (CFR2) family members and a considerable degree of conservation of residues implicated in ligand binding across higher vertebrates. The predicted secondary structure of the duIL‐10R1 extracellular domain is compatible with the two‐subdomain structure of the human IL‐10R1 protein established by its crystal structure. The 3D model structure shows conservation of the positions of conserved contact residues within four of the five ligand‐binding loops. Within the cytoplasmic domain, residues implicated in signal transduction were conserved including two redundant peptide motifs GYXXQ essential for recruitment and activation of STAT3. DuIL‐10R1 mRNA expression was most abundant in spleen, thymus, peripheral blood mononuclear cells (PBMCs) and lung. Mitogen stimulation of PBMCs transiently increased duIL‐10R1 mRNA expression. Our observations suggest significant evolutionary conservation of the IL‐10R1 genomic organization, protein structure and receptor function through the JAK/STAT signalling pathway across higher vertebrates.