TNF-Induced Mitochondrial Changes and Activation of Apoptotic Proteases are Inhibited by A20

A20 zinc finger protein is a product of a cytokine-induced primary response gene. It functions as a negative regulator of the tumor necrosis factor (TNF) inhibiting both TNF-mediated apoptosis and activation of transcription factors. We demonstrated that A20 overexpression blocks early TNF-induced signaling events including the generation of free radicals, the fall in mitochondrial transmembrane potential (ΔΨm), and the activation of caspase-3-like apoptotic proteases. General inhibitor of caspases, cow pox virus-derived CrmA, also inhibited TNF-induced mitochondrial changes indicating that early caspase activation occurs upstream from mitochondrial changes. Interestingly, changes in mitochondrial function or induction of caspase-3-like activity induced by anti-Fas or doxorubicin were not inhibited by A20. The data show that A20 is a specific inhibitor of TNF signaling and acts upstream of INF-induced free radical formation, fall in mitochondrial transmembrane potential (ΔΨm), and activation of caspase-3-like proteases.