A Drosophila IκB kinase complex required for relish cleavage and antibacterial immunity

Here we report the identification of a Drosophila IκB kinase complex containing DmIKKβ and DmIKKγ, homologs of the human IKKβ and IKKγ proteins. We show that this complex is required for the signal-dependent cleavage of Relish, a member of the Rel family of transcriptional activator proteins, and for the activation of antibacterial immune response genes. In addition, we find that the activated DmIKK complex, as well as recombinant DmIKKβ, can phosphorylate Relish in vitro. Thus, we propose that the Drosophila IκB kinase complex functions, at least in part, by inducing the proteolytic cleavage of Relish. The N terminus of Relish then translocates to the nucleus and activates the transcription of antibacterial immune response genes. Remarkably, this Drosophila IκB kinase complex is not required for the activation of the Rel proteins Dif and Dorsal through the Toll signaling pathway, which is essential for antifungal immunity and dorsoventral patterning during early development. Thus, a yet to be identified IκB kinase complex must be required for Rel protein activation via the Toll signaling pathway.