Negative regulation of the NF-κB pathway by the ubiquitin ligase Nedd4-1(NE).

The NF-κB pathway plays a critical role in mediating the innate immune response downstream of activated immune receptors such as the TNFαR. Activation of this pathway is induced by several ubiquitin ligases (e.g., cIAP, TRAFs, NEMO, β-TrCP, KPC1), including Nedd4-1. Nedd4-1 comprises a C2-WW(4)-HECT domain architecture. We recently characterized a primate-specific splice isoform of Nedd4-1, Nedd4-1(NE), in which the C2 domain is replaced by a large N-terminally Extended (NE) region. Using miniTurbo BioID, we identified here several components of the NF-κB pathway in complex with Nedd4-1(NE) (but not with the canonical Nedd4-1), including IKKα/β and p105-NF-κB1. We further show that (i) Nedd4-1(NE) ubiquitinates and promotes degradation of IKKβ, therefore inhibiting phosphorylation and promoting stability of its substrate, the inhibitory IκBα; (ii) active Nedd4-1(NE) binds and destabilizes NF-κB1, an interaction that is dependent upon Nedd4-1(NE)-mediated KPC1 ubiquitination. Furthermore, KPC1 promotes translocation of NF-κB1 to late endosomal membranes, where Nedd4-1(NE) resides, to facilitate the Nedd4-1(NE): NF-κB1 interaction. Consequently, Nedd4-1(NE)-mediated regulation of both IKKβ and NF-κB1 suppresses NF-κB1 nuclear translocation and activation of its target genes; and (iii) Nedd4-1(NE) (but not canonical Nedd4-1) mRNA expression is increased upon prolonged TNFα treatment of cells. This work uncovered an E3 ubiquitin ligase that suppresses the NF-κB1 pathway to ensure termination of this pro-inflammatory signaling pathway in primates via a negative feedback mechanism; Such an additional layer of immune regulation has important implications for understanding inflammatory homeostasis and its dysregulation in human disease.