A Drosophila I kappa B kinase complex required for Relish cleavage and antibacterial immunity

Here we report the identification of a Drosophila I kappa B kinase complex containing DmIKK beta and DmIKK gamma, homologs of the human IKK beta and I KK gamma proteins. We show that this complex is required for the signal-dep endent cleavage of Relish, a member of the Rel family of transcriptional ac tivator proteins, and for the activation of antibacterial immune response g enes. In addition, we find that the activated DmIKK complex, as well as rec ombinant DmIKK beta, can phosphorylate Relish in vitro. Thus, we propose th at the Drosophila I kappa B 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 antibacteria l immune response genes. Remarkably, this Drosophila I kappa B kinase compl ex is not required for the activation of the Rel proteins Dif and Dorsal th rough the Toll signaling pathway, which is essential for antifungal immunit y and dorsoventral patterning during early development. Thus, a yet to be i dentified I kappa B kinase complex must be required for Rel protein activat ion via the Toll signaling pathway.