Detection of IKKβ-IKKγ Subcomplexes in Monocytic Cells and Characterization of Associated Signaling

Abstract The IκB kinase (IKK) complex is one major step in the regulation of the NF-κB/Rel system that is involved in inflammatory and immune responses as well as in proliferation and apoptosis. At present it is not clear whether besides the “classical” IKKα-IKKβ-IKKγ configuration additional complexes exist in vivo that solely contain IKKβ and IKKγ (without IKKα). In the current study we were able to demonstrate in monocytic cells that endogenous complexes, which only include IKKβ as the kinase-active molecule do indeed exist in vivo and that these complexes contain IKKγ as an additional component. Furthermore, we showed that these IKKβ-IKKγ complexes are involved in mainstream NF-κB activation cascades because they can be activated by tumor necrosis factor. In contrast, these subcomplexes appear not to participate in NIK-dependent pathways. As a next step we showed that exogenous IKKβ-IKKγ complexes can be formed in an intact cell by overexpression and that these artificial complexes fulfill the requirement for participation in regular signaling. Finally, in the absence of IKKα we found a retarded proteolysis of IκBα, but not of IκB∈, which is associated with a reduced IKK activity. Differential pathways represented by various IKK subcomplexes may open attractive possibilities in treatment of inflammation or cancer allowing specific therapeutic intervention.