NIK is a component of the EGF/heregulin receptor signaling complexes

Nuclear factor κB-inducing kinase (NIK) is a member of the MAP kinase kinase kinase family that was first identified as a component of the TNF-R1-induced NF-κB activation pathway (TNF, tumor necrosis factor; nuclear factor kappaB, NF-KB). Gene knockout study, however, suggests that NIK is dispensable for TNF-R1- but required for lymphotoxin-β receptor-induced NF-KB activation. A NIK kinase inactive mutant is a potent inhibitor of NF-KB activation triggered by various stimuli, suggesting that NIK is involved in a broad range of NF-κB activation pathways. To unambiguously identify signaling pathways that NIK participates in, we screened antibody arrays for proteins that are associated with NIK. This effort identified ErbB4, one of the EGF/heregulin receptors, and Grb7, an adapter protein associated with ErbB4 (ErbB, epidermal growth factor receptor family protein; EGF, epidermal growth factor; Grb, growth factor receptor bound). Coimmunoprecipitation experiments demonstrated that NIK interacted with Grb7, as well as Grb10 and Grb14, but not Grb2. Domain mapping experiments indicated that the central GM domain of Grb7 was sufficient for its interaction with NIK. Coimmunoprecipitation experiments also indicated that Grb7 and NIK could be simultaneously recruited into signaling complexes of all known EGF/heregulin receptors, including EGFR, ErbB2, ErbB3, and ErbB4. In reporter gene assays, NIK could potentiate Grb7, ErbB2/ ErbB4, and EGF-induced NF-KB activation. A NIK kinase inactive mutant could block ErbB2/ErbB4 and EGF-induced NF-KB activation. Moreover, EGF/heregulin receptors activated NF-KB in wild-type, but not NIK-/- embryonic fibroblasts. Our findings suggest that NIK is a component of the EGF/heregulin receptor signaling complexes and involved in NF-KB activation triggered by these receptors.