Cloning and bioactivity analysis of a CXC ligand in black seabream Acanthopagrus schlegeli: the evolutionary clues of ELR(+)CXC chemokines

BACKGROUND: The ELR(+)CXC chemokines are multifunctional mediators that are mainly responsible for the recruitment of leucocytes to sites of inflammation and infection. Because of their high sequence identity with mammalian IL-8, fish IL-8-like CXCs have been named as piscine 'IL-8' and included in the ELR(+ )subgroup, even though there is no reliable functional or evolutionary evidence to support this classification. RESULTS: In this investigation, a homologue of piscine 'IL-8' from black seabream (Acanthopagrus schlegeli), called BS CXC, has been cloned and analyzed. The results revealed that BS CXC has a high gene similarity and tertiary structure similarity with piscine and mammalian CXC chemokines, both ELR(-)CXC and ELR(+)CXC, although it has a lower identity with ELR(-)CXC, compared with ELR(+)CXC chemokines. Like other piscine IL-8, BS CXC has only an incomplete ELR motif, which is essential for the mammalian ELR(+)CXC ability to attract granulocytes. Bioactivity assay demonstrated that the BS rCXC produced in E. coli significantly stimulated migration of fish neutrophils and macrophages, but had no effect on rat neutrophils and macrophages, whereas hrIL-8 induced strong chemotaxis of fish neutrophils but did not affect fish macrophages. BS CXC seems show some structural and functional properties of the intermediate between ELR(-)CXC and ELR(+)CXC. CONCLUSION: As an incomplete ELR(+)CXC chemokine from a modern fish, BS CXC provides some clues on the evolution from ancient ELR(-)CXC to ELR(+)CXC by retaining some properties of the intermediate stage in evolution, and it may be more appropriate to call this molecule 'piscine CXC with an incomplete ELR', instead of terming it fish 'IL-8'.