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Abstract
Canonical and noncanonical nuclear factor κB (NF-κB) signaling are the two basic pathways responsible for the release of NF-κB dimers from their inhibitors. Enhanced NF-κB signaling leads to inflammatory and proliferative diseases; thus, inhibitory pathways that limit its activity are critical. Whereas multiple negative feedback mechanisms control canonical NF-κB signaling, none has been identified for the noncanonical pathway. Here, we describe a mechanism of negative feedback control of noncanonical NF-κB signaling that attenuated the stabilization of NF-κB–inducing kinase (NIK), the central regulatory kinase of the noncanonical pathway, induced by B cell–activating factor receptor (BAFF-R) and lymphotoxin β receptor (LTβR). Inhibitor of κB (IκB) kinase α (IKKα) was previously thought to lie downstream of NIK in the noncanonical NF-κB pathway; we showed that phosphorylation of NIK by IKKα destabilized NIK. In the absence of IKKα-mediated negative feedback, the abundance of NIK increased after receptor ligation. A form of NIK with mutations in the IKKα-targeted serine residues was more stable than wild-type NIK and resulted in increased noncanonical NF-κB signaling. Thus, in addition to the regulation of the basal abundance of NIK in unstimulated cells by a complex containing tumor necrosis factor receptor–associated factor (TRAF) and cellular inhibitor of apoptosis (cIAP) proteins, IKKα-dependent destabilization of NIK prevents the uncontrolled activity of the noncanonical NF-κB pathway after receptor ligation.
