NF-κB (nuclear factor kappa light chain enhancer of activated B cells) is a family of highly conserved transcription factors that regulate many important cellular behaviors (e.g. inflammatory responses, cellular growth and apoptosis). NF-κB is also involved in diseases such as cancer, arthritis and asthma. NF-κB activation requires the IκB kinase (IKK) complex, which is composed of two serine-threonine kinases (IKKα and IKKβ) and the regulatory subunit NEMO (IKKγ). The IKK complex is a signal integration hub, which sequesters a wide variety of extra and intracellular signals to catalyze phosphorylation of various IκB and NF-κB proteins as well as of other substrates.