NF-κB suppression by the deubiquitinating enzyme Cezanne -: A novel negative feedback loop in pro-inflammatory signaling

Transcription factors belonging to the NF-kappa B family regulate inflammation by inducing pro-inflammatory molecules (e. g. interleukin (IL)-8) in response to cytokines (e. g. tumor necrosis factor (TNF) alpha, IL-1) or other stimuli. Several negative regulators of NF-kappa B, including the ubiquitin-editing enzyme A20, participate in the resolution of inflammatory responses. We report that Cezanne, a member of the A20 family of the deubiquitinating cysteine proteases, can be induced by TNF alpha in cultured cells. Silencing of endogenous Cezanne using small interfering RNA led to elevated NF-kappa B luciferase reporter gene activity and enhanced expression of IL-8 transcripts in TNF alpha-treated cells. Thus we conclude that endogenous Cezanne can attenuate NF-kappa B activation and the induction of pro-inflammatory transcripts in response to TNF receptor (TNFR) signaling. Overexpression studies revealed that Cezanne suppressed NF-kappa B nuclear translocation and transcriptional activity by targeting the TNFR signaling pathway at the level of the I kappa B kinase complex or upstream from it. These effects were not observed in a form of Cezanne that was mutated at the catalytic cysteine residue (Cys(209)), indicating that the deubiquitinating activity of Cezanne is essential for NF-kappa B regulation. Finally, we demonstrate that Cezanne can be recruited to activated TNFRs where it suppresses the build-up of polyubiquitinated RIP1 signal adapter proteins. Thus we conclude that Cezanne forms a novel negative feedback loop in pro-inflammatory signaling and that it suppresses NF-kappa B activation by targeting RIP1 signaling intermediaries for deubiquitination.