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  • Structural and functional c...
    Cuadrado, Antonio

    Free radical biology & medicine, 11/2015, Letnik: 88, Številka: Pt B
    Journal Article

    Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) is a master regulator of cellular homeostasis that controls the expression of more than 1% of human genes related to biotransformation reactions, redox homeostasis, energetic metabolism, DNA repair, and proteostasis. Its activity has a tremendous impact on physiology and pathology and therefore it is very tightly regulated, mainly at the level of protein stability. In addition to the very well established regulation by the ubiquitin E3 ligase adapter Keap1, recent advances have identified a novel mechanism based on signaling pathways that regulate glycogen synthase kinse-3 (GSK-3). This kinase phosphorylates specific serine residues in the Neh6 domain of Nrf2 to create a degradation domain that is then recognized by the ubiquitin ligase adapter β-TrCP and tagged for proteasome degradation by a Cullin1/Rbx1 complex. Here we review the mechanistic elements and the signaling pathways that participate in this regulation by GSK-3/β-TrCP. These pathways include those activated by ligands of tyrosine kinase, G protein-coupled, metabotropic, and ionotropic receptors that activate phosphatidyl inositol 3-kinase (PI3K)/ATK and by the canonical WNT signaling pathway, where a fraction of Nrf2 interacts with Axin1/GSK-3. Considering that free Nrf2 protein is localized in the nucleus, we propose a model termed “double flux controller” to explain how Keap1 and β-TrCP coordinate the stability of Nrf2 in several scenarios. The GSK-3/β-TrCP axis provides a novel therapeutic strategy to modulate Nrf2 activity. Display omitted •Nrf2 is regulated by cell signaling pathways that inhibit GSK-3.•GSK-3 phosphorylates Nrf2 to create a recognition motif for the E3 ligase adapter β-TrCP.•GSK-3/β-TrCP leads to Keap1-independent ubiquitin-proteasome degradation of Nrf2.•β-TrCP and Keap1 coordinate to control Nrf2 protein levels to specific demands.•GSK-3/β-TrCP and Keap1 provide two pharmacologic strategies for modulating Nrf2 levels.