Molecular cloning and characterization of an IKK homologue from amphioxus (Branchiostoma belcheri)

The IκB kinase (IKK) plays a crucial role in activation of the transcription factor nuclear factor kappa B (NF-κB) by phosphorylating the Inhibitory of NF-κB (IκB), which triggers the subsequent polyubiquitylation and degradation of IκBα through the 26S proteasome. In this study, we reported the cloning of an IKK homologue cDNA (designated as AmphiIKK) from amphioxus, Branchiostoma belcheri. The full-length cDNA consists of 3,087 bp with an ORF that encoded a predicted protein of 777 amino acid residues. The putative amphioxus IKK protein possesses the characteristic organization of the mammalian IKK proteins, which consists of a serine/threonine kinase domain, a leucine zipper motif and a putative helix-loop-helix motif. And the deduced amino acid of AmphiIKK shared 43.8–64.0 % similarity and 23.6–43.3 % identified with the IKKs from other species. Real-time PCR (RT-PCR) analysis indicated that AmphiIKK was ubiquitously expressed in all tissues and we also discovered that the expression of AmphiIKK was affected after lipopolysaccharides stimulation. Our findings help to highlight a potential important regulatory pathway in the innate immune response in the amphioxus and the evolution of the IKK family.