p47 negatively regulates IKK activation by inducing the lysosomal degradation of polyubiquitinated NEMO

Abstract

The persistent or excess activation of nF-κB causes various inflammatory and autoimmune diseases, but the molecular mechanisms that negatively regulate nF-κB activation are not fully understood. Here we show that p47, an essential factor for Golgi membrane fusion, associates with the nEmo subunit of the IκB kinase (IKK) complex upon TnF-α or IL-1 stimulation, and inhibits IKK activation. p47 binds to Lys63-linked and linear polyubiquitin chains, which are conjugated to nEmo upon such stimulation. The binding of p47 to polyubiquitinated nEmo triggers the lysosomal degradation of nEmo, thereby inhibiting IKK activation. The silencing of p47 results in enhanced TnF-α-or IL-1-induced IKK activation, and an increased expression of genes encoding inflammatory mediators. Taken together, our results suggest that p47 is critical for negatively regulating stimulation-induced IKK activation in a manner that is mechanistically distinct from the previously characterized negative regulators, such as A20 and CYLD.

Ubiquitin-associated Domain-containing Ubiquitin Regulatory X (UBX) Protein UBXN1 Is a Negative Regulator of Nuclear Factor κB (NF-κB) Signaling

“…1C). In previous reports, NSFL1C and FAF1 had been found to be related to NF-B signaling in 2012 and 2007 (19,20). Those data show that UBXN1 down-regulates TNF␣-triggered NF-B activa-FIGURE 1.…”

TNF biology, pathogenic mechanisms and emerging therapeutic strategies

“…These ‘signalling brakes’ operate by targeting receptor-proximal signalling events, by inhibiting IKK-complex activity, or by regulating downstream checkpoints. The mech anisms utilized by these negative regulators include cleavage or internalization of TNFRs 10 , destabilization of signalling complexes 28 , displacement of signalling molecules from complexes by antagonists 29–34 , as well as degradation (proteasomal or lysosomal) 31,35–37 , inactivation (for example, dephosphory lation) 38–41 , or seques tration of signalling factors 42–44 . Although the expression and activity of negative regulators can be constitutive, induction by TNF is consistent with a model of ‘applying the brakes’ as part of inducible inhibitory-feedback loops 42 .…”

UBXD Proteins: A Family of Proteins with Diverse Functions in Cancer

“…These findings suggest that p47 plays an anti-cancer function in cancer cells by interfering with the NF-κB pathway. This is accomplished by reversing this tumorigenic pathway in cancer cells via degradation of NEMO independent of the ubiquitin-proteasome pathway (Figure 3) [93]. …”

“…In addition, p47 expression is dramatically reduced at both the mRNA and protein levels in patients with T cell leukemia and human T cell leukemia virus type 1-infected cell lines in which the NF-κB pathway is constitutively active [93]. Therefore, enhanced expression of p47 and its distinct inhibitory mechanism in the NF-κB pathway can be an effective therapy in tumors with a low level of p47 and a dysregulated NF-κB pathway.…”

“…A siRNA screen of UBA domain-containing proteins revealed that silencing three members of the UBXD family, UBXN1, p47, and FAF1, can markedly potentiate TNFα-triggered NF-κB activation [123]. The negative regulatory functions of FAF1 and p47 in the NF-κB pathway were previously covered in an earlier part of this review [93,108]. However, the overexpression experiments showed that UBXN1 has the strongest inhibiting ability on TNFα-triggered NF-κB activity in comparison to p47 and FAF1 [123].…”