Expanding role of ubiquitination in NF-κB signaling

Best known for its role in targeting protein degradation by the proteasome, ubiquitin modification has also emerged as an important mechanism that regulates cell signaling through proteasome-independent mechanisms. The role of ubiquitin as a versatile signaling tag is characteristically illustrated in the NF-kappa B pathways, which regulate a variety of physiological and pathological processes in response to diverse stimuli. Here, we review the role of ubiquitination in different steps of the NF-kappa B signaling cascades, focusing on recent advances in understanding the mechanisms of protein kinase activation by polyubiquitin chains in different pathways that converge on NF-kappa B.