title: Interleukin-1-induced NF-kappaB activation is NEMO-dependent but does not require IKKbeta.
abstract: Activation of NF-kappaB by the pro-inflammatory cytokines tumor necrosis factor (TNF) and interleukin-1 (IL-1) requires the IkappaB kinase (IKK) complex, which contains two kinases named IKKalpha and IKKbeta and a critical regulatory subunit named NEMO. Although we have previously demonstrated that NEMO associates with both IKKs, genetic studies reveal that only its interaction with IKKbeta is required for TNF-induced NF-kappaB activation. To determine whether NEMO and IKKalpha can form a functional IKK complex capable of activating the classical NF-kappaB pathway in the absence of IKKbeta, we utilized a panel of mouse embryonic fibroblasts (MEFs) lacking each of the IKK complex subunits. This confirmed that TNF-induced IkappaBalpha degradation absolutely requires NEMO and IKKbeta. In contrast, we consistently observed intact IkappaBalpha degradation and NF-kappaB activation in response to IL-1 in two separate cell lines lacking IKKbeta. Furthermore, exogenously expressed, catalytically inactive IKKbeta blocked TNF- but not IL-1-induced IkappaBalpha degradation in wild-type MEFs, and reconstitution of IKKalpha/beta double knockout cells with IKKalpha rescued IL-1- but not TNF-induced NF-kappaB activation. Finally, we have shown that incubation of IKKbeta-deficient MEFs with a cell-permeable peptide that blocks the interaction of NEMO with the IKKs inhibits IL-1-induced NF-kappaB activation. Our results therefore demonstrate that NEMO and IKKalpha can form a functional IKK complex that activates the classical NF-kappaB pathway in response to IL-1 but not TNF. These findings further suggest NEMO differentially regulates the fidelity of the IKK subunits activated by distinct upstream signaling pathways.
authors.affiliation: Department of Animal Biology, University of Pennsylvania School of Veterinary Medicine, PA 19104, USA.
authors.forename: Laura A
authors.initials: LA
authors.lastname: Solt
authors.forename: Lisa A
authors.initials: LA
authors.lastname: Madge
authors.forename: Jordan S
authors.initials: JS
authors.lastname: Orange
authors.forename: Michael J
authors.initials: MJ
authors.lastname: May
mesh_terms: D000818:Animals; D002384:Catalysis; D002460:Cell Line; D004789:Enzyme Activation; D005786:Gene Expression Regulation; D006801:Humans; D051550:I-kappa B Kinase / Q000378:metabolism* / Q000502:physiology; D007375:Interleukin-1 / Q000502:physiology*; D047908:Intracellular Signaling Peptides and Proteins / Q000502:physiology*; D051379:Mice; D016328:NF-kappa B / Q000378:metabolism*; D010455:Peptides / Q000737:chemistry; D011485:Protein Binding; D011994:Recombinant Proteins / Q000737:chemistry; D015398:Signal Transduction
chemical_list: C491731:IKBKG protein, human; D007375:Interleukin-1; D047908:Intracellular Signaling Peptides and Proteins; C514981:NEMO protein, mouse; D016328:NF-kappa B; D010455:Peptides; D011994:Recombinant Proteins; D051550:I-kappa B Kinase