Molecular characterization and expression analysis of the putative interleukin 6 receptor (IL-6Rα and glycoprotein-130) in rainbow trout (Oncorhynchus mykiss): salmonid IL-6Rα possesses a polymorphic N-terminal Ig-domain with variable numbers of two repeats

16 páginas, 6 figuras, 3 tablas.-- The final publication is available at www.springerlink.comInterleukin (IL)-6, the founding member of IL-6 family cytokines, plays non-redundant roles in hematopoiesis and acute phase responses. IL-6 signals via a specific private IL-6Rα and a common beta chain gp130. In this study, we sequence analysed both IL-6Rα and gp130 in rainbow trout. The trout gp130 cDNA encodes 906 aa and is similar in size, extracellular domain structure (D1-6) and presence of intracellular motifs important for signal transduction to tetrapod gp130. The trout IL-6Rα cDNA encodes for 834 aa and is larger compared to tetrapod IL-6Rαs, as are other fish IL-6Rα molecules due to a large D1 domain. However, the cytokine binding domain is well conserved across vertebrates, with four conserved cysteine residues in the N-terminal FNIII domain and a WSXWS motif in the C-terminal FNIII domain. Furthermore, phylogenetic tree analysis confirmed that the reported fish IL-6Rα and gp130 molecules are orthologues to their tetrapod counterparts. The extra-large D1 domain of the salmonid IL-6Rα molecules results from the insertions of two repetitive sequences of [TS]-[TF]-VSTTT-[ND]-TTSNG and TTVS-[AT]-IKD-[DG]-S-[KD]-N-[GR], respectively. Furthermore the numbers of repetitions of the two motifs were variable in different individuals and cell lines, and even in the same fish allelic polymorphism exists. Trout IL-6Rα was expressed at higher levels than gp130 in a number of tissues examined and the expression of both IL-6Rα and gp130 could be modulated by LPS and Poly I:C in four trout cell lines studied. The expression patterns of the receptors suggest that high level expression of IL-6Rα is critical for IL-6 responsiveness.The work was supported by a European Community project IMAQUANIM (FOOD-CT-2005-007103). M.M.C. thanks the Consejo Superior de Investigaciones Científicas (CSIC, Spain) and the Xunta de Galicia for her “Ángeles Alvariño” postdoctoral contract. M.M.M. thanks the FCT (Foundation for Science and Technology, Portugal) and POPH/FSE for her PhD studentship (Grant no. SFRH/ BD/ 38236/ 2007).Peer reviewe