IkappaB kinase beta (IKKbeta) 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-kappaB. 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-kappaB 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 TNFalpha-stimulated NF-kappaB activation. The E(T/S)GE motif, which is found only in the IKKbeta 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-kappaB activity, and up-regulated the expression of NF-kappaB target genes. Ectopic expression of KEAP1 decreased the expression of IKKbeta, which was restored by an autophagy inhibitor. IKK phosphorylation stimulated by TNFalpha was blocked by KEAP1. Our data demonstrate that KEAP1 is involved in the negative regulation of NF-kappaB signaling through the inhibition of IKKbeta phosphorylation and the mediation of autophagy-dependent IKKbeta degradation.
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