The interaction with NEMO regulates the function of IKKα

The inducible transcription factor NF-κB plays a critical role in many biological processes, including the regulation of innate and adaptive immune responses, inflammation, and cell survival. One signaling component upstream of NF-κB that is absolutely critical for its activation is the IκB kinase complex (IKK). The IKK complex consists of a core of three proteins; two catalytic subunits, IKKα and IKKβ, and a regulatory subunit named NEMO (NF-κB essential modulator). Initial characterization of the IKK complex suggested that both IKKα and IKKβ were responsible for NF-κB activation. However, genetic evidence has demonstrated otherwise, establishing a model that predicts classical NF-κB activation involving the kinase activity of IKKβ when coupled to NEMO through a conserved hexapeptide sequence, named the NEMO-binding domain (NBD). In the absence of either IKKβ or NEMO, TNF-induced NF-κB activation is absent, leaving no apparent role for IKKα. Paradoxically, IKKα possesses a functional NBD that enables its interaction with NEMO. This thesis explores the conserved interaction between IKKα and NEMO and its role in NF-κB signaling and IKK complex formation. Chapter 1 of this thesis focuses on the role of the NEMO:IKKα interaction in classical NF-κB activation. We established that in the absence of IKKβ, IL-1-induced NF-κB activation is intact and governs a signal through a NEMO:IKKα complex that can be blocked by the administration of a cell-permeable NBD peptide. Following up on our results, we assessed the specific role of the NBD in IKKα and IKKβ and how it influences NF-κB activation and IKK complex formation. Chapter 2 describes the absolute requirement for the NBD in IKKβ and its effects mediating TNF-induced NF-κB activation. We also establish that the NBD is critical for the formation of the tripartite IKK complex. Finally, Chapter 3 concentrates on the specific role of the NBD in NEMO:IKKα interaction mediating IL-1-induced NF-κB activation. Collectively, our results highlight the role of the NBD in IKKα and IKKβ mediating NF-κB activation and IKK complex formation