Non-catalytic ubiquitin binding by A20 prevents psoriatic arthritis-like disease and inflammation

The deubiquitinase A20 is a potent inhibitor of NF-kappa B signaling pathways. Ma and colleagues identify distinct roles for A20 ubiquitin-binding ZF4 and ZF7 domains, which exhibit different phenotypes upon mutation, but play synergistic roles in regulating inflammatory responses. A20 is an anti-inflammatory protein that is strongly linked to human disease. Here, we find that mice expressing three distinct targeted mutations of A20's zinc finger 7 (ZF7) ubiquitin-binding motif uniformly developed digit arthritis with features common to psoriatic arthritis, while mice expressing point mutations in A20's OTU or ZF4 motifs did not exhibit this phenotype. Arthritis in A20(ZF7) mice required T cells and MyD88, was exquisitely sensitive to tumor necrosis factor and interleukin-17A, and persisted in germ-free conditions. A20(ZF7) cells exhibited prolonged I kappa B kinase activity that drove exaggerated transcription of late-phase nuclear factor-kappa B response genes in vitro and in prediseased mouse paws in vivo. In addition, mice expressing double-mutant A20 proteins in A20's ZF4 and ZF7 motifs died perinatally with multi-organ inflammation. Therefore, A20's ZF4 and ZF7 motifs synergistically prevent inflammatory disease in a non-catalytic manner.