The I-kappa-B-kinase (IKK) complex consists of two catalytic subunits, IKBKA (KKα or CHUK) and IKBKB (IKKβ), associated with a regulatory subunit IKBKG (NEMO). Yeast two-hybrid screening identified inhibitor of nuclear factor kappa-B kinase-interacting protein (IKBIP or IKIP) as an IKBKB-binding protein (Hofer-Warbinek R et al. 2004). IKBIP was found to downregulate NF-kappa-B activation and induction of proinflammatory cytokines in human and mouse myeloid cells in response to Toll-like receptor (TLR) ligands (Wu H et al. 2020). In addition, IKBIP deficiency resulted in prolonged phosphorylation of IKBKB, CHUK and p65, and increased expression of NF-kappaB-responsive genes in myeloid cells after stimulation with LPS, TNF-α, and IL-1β. Moreover, IKBIP co-immunoprecipitated with IKBKA (CHUK) and IKBKB subunits, but not with IKBKG, upon co-expression of tagged proteins in human embryonic kidney HEK293T cells (Wu H et al. 2020). Mutagenesis analysis revealed that the N-terminal region of IKBIP interacts with leucine zipper (LZ) and helix-loop-helix (HLH) domains of IKBKB. Confocal microscopy showed that IKBKB colocalizes with IKBIP in the endoplasmic reticulum (ER) upon co-expression of tagged proteins in Hela cells (Wu H et al. 2020). These data suggest that IKBIP negatively regulates NF-kappa-B activation via targeting IKBKB and CHUK and inhibiting their phosphorylation (Wu H et al. 2020).