Oyster IKK-like protein shares structural and functional properties with its mammalian homologues

In our search for genes involved in oyster immunity we isolated a cDNA enco ding a polypeptide closely related to the mammalian I kappa B kinase (IKK) family. IKK proteins play a central role in cell signaling by regulating nu clear factor-kappa B (NF-kappa B) activation. We report here the cloning of an oyster IKK-like protein (oIKK) which possesses the characteristic organ ization of the mammalian IKK proteins, namely an amino-terminal kinase doma in followed by a leucine zipper region and a carboxyl-terminal helix-loop-h elix motif. When transfected into human cell lines, oIKK activated the expr ession of NF-kappa B-controlled reporter gene, whereas transfections with m utants of oIKK deleted within the kinase domain or within the helix-loop-he lix motif respectively abolished and greatly reduced reporter gene activati on. These results indicate that oIKK can replace the hIKK-alpha in catalyzi ng NF-kappa B nuclear translocation, and in triggering gene expression, Our results sustain the concept of an evolutionarily conserved signaling machi nery in which IKK plays a major role. (C) 1999 Federation of European Bioch emical Societies.