Ubiquitin-mediated regulation of TNFR1 signaling

Ubiquitin ligase enzymes promote substrate protein ubiquitination, a post-translational modification whereby the 76-amino acid protein ubiquitin is covalently bound to substrate proteins. Ubiquitination may target substrates for proteasomal degradation or regulate substrate function in a degradation-independent manner. Ubiquitination is reversible, and this is achieved by de-ubiquitinase enzymes [Jackson PK, Eldridge AG, Freed E, et al. The lore of the RINGs: substrate recognition and catalysis by ubiquitin ligases. Trends Cell Biol 2000; 10(October (10)):429-39]. The first identified target of ubiquitination in the Tumor Necrosis Factor Receptor 1 (TNFR1) signaling cascade was Inhibitor of NF-kappa B (I-kappa B), which sequesters Nuclear Factors at K-chain promoters in B-cells (NF-kappa B) transcription factors in the cytosol. Following TNF-alpha stimulation, I-kappa B is ubiquitinated and subsequently degraded by the proteasome, permitting NF-kappa B transcriptional activity [Glickman MH, Ciechanover A. The ubiquitin-proteasome proteolytic pathway: destruction for the sake of construction. Physiol Rev 2002;82(April (2)):373-428]. Since this seminal finding, it is now evident that nearly every step of TNFR1 signaling is regulated by ubiquitination. In this review, we will summarize the ubiquitin/proteasome system and discuss the ubiquitin-mediated regulation of TNFR1 signaling. (c) 2008 Elsevier Ltd. All rights reserved.