Pharmacological characterization and biological function of the interleukin-8 receptor, CXCR2, in largemouth bass (Micropterus salmoides).

Interleukin-8 (IL-8 or C-X-C motif chemokine ligand 8, CXCL8) is a cytokine secreted by numerous cell types and is best known for its functional roles in inflammatory response by binding to specific receptors (the interleukin-8 receptors, IL-8Rs). From the transcriptomic data of largemouth bass (Micropterus salmoides), we identified an IL-8R that is highly homologous to the functionally validated teleost IL-8Rs. The M. salmoides IL-8 receptor (MsCXCR2) was further compared with the C-X-C motif chemokine receptor 2 subfamily by phylogenetic analysis. Briefly, the full-length CDS sequence of MsCXCR2 was cloned into the pEGFP-N1 plasmid, and the membrane localization of fusion expressing MsCXCR2-EGFP was revealed in HEK293 cells. To determine the functional interaction between IL-8 and MsCXCR2, secretory expressed Larimichthys crocea IL-8 (LcIL-8) was used to stimulate MsCXCR2 expressing cells. MsCXCR2 was demonstrated to be activated by LcIL-8, leading to receptor internalization, which was further revealed by the detection of extracellular regulated protein kinase (ERK) phosphorylation. Quantitative real-time PCR was used to evaluate the expressional distribution and variation of MsCXCR2 in healthy and Nocardia seriolae infected fish. Based on our findings, MsCXCR2 was constitutively expressed in all examined tissues, despite at different levels. Furthermore, gene expression was found to be significantly upregulated in the liver and head kidney of diseased fish. Collectively, our findings reveal the molecular activity of MsCXCR2 and indicate the functional involvement of this IL-8R in the immune response induced by N. seriolae in M. salmoides.