No abstract

The ubiquitin-editing enzyme A20 is a critical negative regulator of inflammation and cytokine-mediated activation of the transcription factor NF-kappaB; however, little is known about the mechanisms of A20-mediated inactivation of signaling intermediates such as RIP1. Here we demonstrate that the regulatory molecule TAX1BP1 recruited the E3 ligase Itch to A20 via two 'PPXY' motifs. Itch was essential for the termination of tumor necrosis factor receptor signaling by controlling A20-mediated recruitment and inactivation of RIP1. Furthermore, the Tax oncoprotein of human T cell leukemia virus type I targeted this complex for inactivation by disrupting the interaction among TAX1BP1, A20 and Itch. Thus, our studies show a previously unappreciated complexity of A20 substrate recognition and inactivation whereby TAX1BP1 and Itch function as essential subunits of an A20 ubiquitin-editing complex.

The RING domain protein RNF11 is overexpressed in breast cancers and promotes tumour growth factor‐beta (TGF‐β) signalling. RNF11 has been proposed to regulate TGF‐β signalling by interacting with HECT‐ and SCF‐type E3 ligases; however, the role of RNF11 in other signalling pathways is poorly understood. Here, we demonstrate a novel function of RNF11 as a negative regulator of NF‐κB and jun N‐terminal kinase (JNK) signalling pathways. Knockdown of RNF11 with siRNA resulted in persistent tumour necrosis factor (TNF)‐ and lipopolysaccharide (LPS)‐mediated NF‐κB and JNK signalling. RNF11 interacted with the NF‐κB inhibitor A20 and its regulatory protein TAX1BP1 in a stimulus‐dependent manner. RNF11 negatively regulated RIP1 and TRAF6 ubiquitination upon stimulation with TNF and LPS, respectively. Furthermore, RNF11 was required for A20 to interact with and inactivate RIP1 to inhibit TNF‐mediated NF‐κB activation. Our studies reveal that RNF11, together with TAX1BP1 and Itch, is an essential component of an A20 ubiquitin‐editing protein complex that ensures transient activation of inflammatory signalling pathways.