Molecular characterization of a novel rabbit interleukin-8 receptor isotype

Interleukin-8 (IL-8) mediates the transendothelial migration and activation of neutrophils to the site of inflammation. Two human IL-8 receptor isotype (A and B) and one rabbit IL-8 receptor isotype (A) cDNAs have been previously cloned and characterized on the basis of their pharmacological profile. Human and rabbit IL-8 receptor subtype A binds IL-8 and structurally related peptide melanoma growth-stimulating activity (MGSA) and neutrophil-activating peptide-2 (NAP-2) according to the following affinity binding profile: IL-8 >>> MGSA > NAP-2, whereas the human IL-8 receptor subtype B profile is IL-8 = MGSA > NAP-2 (LaRosa, G., Thomas, K. M., Kaufmann, M., Mark, R., White, M., Taylor, L., Gray, G., Witt, D., and Navarro, J. (1992) J. Biol. Chem. 267, 25402-25406). In this study, we isolated a cDNA clone (5B1a) from a rabbit neutrophil library encoding a G- protein-coupled receptor of the interleukin-8 receptor family. The 5B1a clone encodes a 358-amino acid protein exhibiting 80% amino acid identity to the human IL-8 receptor B, 74% to the rabbit IL-8 receptor A, and 73% to the human IL-8 receptor A. Tissue distribution by Northern blot analysis reveals that the 5B1a mRNA is expressed preferentially in neutrophils. In contrast to previously described IL-8 receptors, the 5B1a receptor exhibited specific ¹²⁵I-IL-8 binding with a novel affinity binding profile of IL-8 >> NAP-2 > MGSA. The corresponding apparent K(i) values for IL-8, NAP-2, and MGSA were 4, 120, and 320 nM, respectively. IL-8 induced intracellular calcium mobilization and desensitization in Chinese hamster ovary cells stably transfected with 5B1a, indicating that this cDNA encodes a functional IL-8 receptor. Sequence analysis of the 5B1a protein with other IL-8 receptor subtypes within the framework of their pharmacological profile reveals putative structural motifs that may correspond to the ligand binding site of the IL-8 receptor.