Cloning and characterization of a homologue of the alpha inhibitor of NF-κB in Rainbow trout (Oncorhynchus mykiss)

A homologue of IκBα, the alpha member of the IκB family of NF-κB inhibitors, was identified in a Rainbow trout suppression subtractive hybridization library enriched in sequences up-regulated in cultured leukocytes after lipopolysaccharide (LPS) and tumor necrosis factor alpha (TNFα) stimulation. The full-length cDNA was isolated and sequenced. The predicted amino acid sequence is 61.5% similar and 54% identical to human IκBα, while only 42% similar and 35% identical to IκBβ, and 38% similar and 32% identical to IκBɛ. Rainbow trout IκBα contains a central ankyrin repeat domain required for its interaction with NF-κB and a putative PEST-like sequence in the C-terminus. Expression of IκBα is up-regulated by LPS and TNFα treatment, two known activators of NF-κB, suggesting the existence of an autoregulatory loop in fish, as is the case for mammals. These results confirm the existence of the NF-κB signalling pathway in fish and suggest a similar functional interaction between IκBα and NF-κB.