Comparative study of four interleukin 17 cytokines of tongue sole Cynoglossus semilaevis: Genomic structure, expression pattern, and promoter activity

• CsIL-17C, CsIL-17D, CsIL-17F, and CsIL-17Fl belong to three IL-17 subgroups.
• Expression of CsIL-17 was found in multi-tissues and enhanced by bacterial infection.
• Expression of the four CsIL-17 was regulated differently by viral infection.
• The promoter regions of CsIL-17 possess putative transcription factor-binding sites.
• The promoter activities of CsIL-17 were regulated differently by different stimuli.

The interleukin (IL)-17 cytokine family participates in the regulation of many cellular functions. In the present study, we analyzed the genomic structure, expression, and promoter activity of four IL-17 members from the teleost fish tongue sole (Cynoglossus semilaevis), i.e. CsIL-17C CsIL-17D, CsIL-17F, and IL-17F like (IL-17Fl). We found that CsIL-17C, CsIL-17D, CsIL-17F, and CsIL-17Fl share 21.2%–28.6% overall sequence identities among themselves and 31.5%–71.2% overall sequence identities with their counterparts in other teleost. All four CsIL-17 members possess an IL-17 domain and four conserved cysteine residues. Phylogenetic analysis classified the four CsIL-17 members into three clusters. Under normal physiological conditions, the four CsIL-17 expressed in multiple tissues, especially non-immune tissues. Bacterial infection upregulated the expression of all four CsIL-17, while viral infection upregulated the expression of CsIL-17D and CsIL-17Fl but downregulated the expression of CsIL-17C and CsIL-17F. The 1.2 kb 5′-flanking regions of the four CsIL-17 exhibited apparent promoter activity and contain a number of putative transcription factor-binding sites. Furthermore, the promoter activities of CsIL-17C, CsIL-17D, and CsIL-17F, but not CsIL-17Fl, were modulated to significant extents by lipopolysaccharide, PolyI:C, and PMA. This study provides the first evidence that in teleost, different IL-17 members differ in expression pattern and promoter activity.