NEDD4-binding protein 1 (N4BP1) negatively regulates Toll-like receptor (TLR)-induced activation of NF-kappaB and cytokine production in human and mouse cells (Shi H et al. 2021; Gitlin AD et al. 2020). N4BP1 was found to target IKBKG (NEMO, IKKg), the regulatory subunit of the IkB kinase (IKK) complex, which is essential for NF-kappa-B activation. N4BP1 co-immunoprecipitated with IKBKG (NEMO) upon co-expression of tagged proteins in human embryonic kidney 293T (HEK293T) cells (Shi H et al. 2021). The interaction between endogenous N4BP1 and IKBKG was also detected in mouse peritoneal macrophages (Shi H et al. 2021). Linear and K63-linked polyubiquitin chains promoted the interaction between N4BP1 and IKBKG. Binding of N4BP1 to IKBKG is thought to block homooligomerization of IKBKG thereby leading to destabilization of the IKK complex (Shi H et al. 2021). In addition, N4BP1 deficiency in mice and mouse cells increased the production of select NF-kappa-B-dependent cytokines via TICAM1 (TRIF)-independent TLR2, TLR7 or TLR9 signaling pathways, but not upon engagement of TLR3 or TLR4 which utilize the adaptor protein TICAM1 (Shi H et al. 2021; Gitlin AD et al. 2020). Similar results were observed in human monocytic THP-1 cells (Shi H et al. 2021). Further, TLR3- or TRL4-induced TICAM1-dependent activation of caspase-8 (CASP8) was found to inactivate N4BP1 via the proteolytic cleavage thus promoting NF-kappa-B activation (Gitlin AD et al. 2020; Shi H et al. 2021). Downregulation of N4BP1 was not observed in TICAM-1-deficient mouse macrophages treated with LPS (Shi H et al. 2021). These data suggest that N4BP1 limits TICAM1-independent TLR-induced NF-kappa-B activation by blocking the function of the IKK complex, while TICAM1-dependent TLR signaling leads to CASP8-mediated inactivation of N4BP1(Shi H et al. 2021; Gitlin AD et al. 2020).