A20: attractive without showing cleavage

A20 (also known as TNFAIP3) is a deubiquitinating enzyme (DUB) that ensures optimal immune responses in cells stimulated by cytokines, such as TNF and IL‐1, or pathogen components, such as lipopolysaccharide. Deletion of A20 in mice results in multi‐organ inflammation and death within 2 weeks 1 . The anti‐inflammatory functions of A20 have been attributed to its ability to negatively regulate NF‐κB signaling 2 . The picture that has emerged over the last decade is that A20 attenuates NF‐κB signaling by removing polyubiquitin chains from specific NF‐κB signaling proteins. A study published in this issue of EMBO reports by Sankar Ghosh and colleagues 3 now shows that A20 knockin mice expressing a catalytically inactive A20 mutant that can no longer remove ubiquitin are normal and do not have an inflammatory phenotype. These results challenge the notion that A20 exerts its NF‐κB inhibitory and anti‐inflammatory function by acting as a DUB.