Suppression of NF-κB signaling by KEAP1 regulation of IKKβ activity through autophagic degradation and inhibition of phosphorylation

I kappa B kinase beta (IKK beta) plays a crucial role in biological processes, including immune response, stress response, and tumor development by mediating the activation of various signaling molecules such as NF-kappa B. Extensive studies on the mechanisms underlying IKK activation have led to the identification of new activators and have facilitated an understanding of the cellular responses related to NF-kappa B and other target molecules. However, the molecular processes that modulate IKK activity are still unknown. In this study, we show that KEAP1 is a new IKK binding partner, which is responsible for the down-regulation of TNF alpha-stimulated NF-kappa B activation. The E(T/S)GE motif, which is found only in the IKK beta subunit of the IKK complex, is essential for interaction with the C-terminal Kelch domain of KEAP1. Reduction of KEAP1 expression by small interfering RNA enhanced NF-kappa B activity, and up-regulated the expression of NF-kappa B target genes. Ectopic expression of KEAP1 decreased the expression of IKK beta, which was restored by an autophagy inhibitor. IKK phosphorylation stimulated by TNF alpha was blocked by KEAP1. Our data demonstrate that KEAP1 is involved in the negative regulation of NF-kappa B signaling through the inhibition of IKK beta phosphorylation and the mediation of autophagy-dependent IKK beta degradation. (C) 2010 Elsevier Inc. All rights reserved.