Control of NF-κB subunits by ubiquitination.

NF-κB is an essential regulator of inflammation and is also required for normal immune development and homeostasis. The inducible activation of NF-κB by a wide range of immuno-receptors such as the toll-like receptors (TLR), Tumour Necrosis Factor receptor (TNFR), and antigen T cell and B cell receptors requires the ubiquitin-triggered proteasomal degradation of IκBα to promote the nuclear translocation and transcriptional activity of NF-κB dimers. More recently, an additional role for ubiquitination and proteasomal degradation in the control of NF-κB activity has been uncovered. In this case, it is the ubiquitination and proteasomal degradation of the NF-κB subunits that play a critical role in the termination of the NF-κB-dependent transcriptional response induced by receptor activation. The primary trigger of NF-κB ubiquitination is DNA binding by NF-κB dimers and is further controlled by specific phosphorylation events which regulate the interaction of NF-κB with the E3 ligase complex and the deubiquitinase enzyme USP7. It is the balance between ubiquitination and deubiquitination that shapes the NF-κB-mediated transcriptional response. This chapter describes methods for the analysis of NF-κB ubiquitination.