The ubiquitin-editing enzyme A20 (TNFAIP3): mechanisms of activation, biological function, diseases and therapeutic targets.

A20, encoded by tumor necrosis factor alpha-induced protein 3 (TNFAIP3), is a ubiquitin-editing enzyme that acts as a central regulator of inflammatory signal termination, immune homeostasis and tissue protection. By controlling receptor-proximal ubiquitin signaling, A20 limits the amplitude and duration of inflammatory responses and thereby restrains the transition from acute host defense to chronic tissue-damaging inflammation. Genetic, biochemical and disease-model studies have linked altered A20 expression or function to a broad spectrum of human disorders, including monogenic autoinflammation, autoimmunity, barrier and fibrotic diseases, infection and cancer. However, the literature remains fragmented across organ systems and recurrent signaling pathways, obscuring the conserved biological functions of A20 and the contexts in which these functions become pathogenic. Here, we examine the mechanisms governing A20 activation, recruitment and ubiquitin-editing logic, with emphasis on the distinct contributions of the ovarian tumor (OTU) domain and zinc-finger (ZnF) modules. The major biological functions of A20 are then organized into recurrent output modules, including immune-cell homeostasis, signal termination, coordination of cell-death programmes, and oxidative-stress or immunometabolic adaptation. Disease associations are discussed according to dominant pathological outputs and vulnerable cellular compartments rather than by repetitive pathway listing. Finally, the therapeutic implications of A20 are assessed, including its potential as a biomarker and context-dependent therapeutic node, together with the translational challenges posed by cell-type specificity, disease-stage dependence and immune risk. A20 emerges as a context-dependent regulator of inflammation, tissue remodeling and tumour progression with relevance for biomarker development and precision therapeutic targeting.