SCF/β-TrCP Promotes Glycogen Synthase Kinase 3-Dependent Degradation of the Nrf2 Transcription Factor in a Keap1-Independent Manner

Abstract

Regulation of transcription factor Nrf2 (NF-E2-related factor 2) involves redox-sensitive proteasomal degradation via the E3 ubiquitin ligase Keap1/Cul3. However, Nrf2 is controlled by other mechanisms that have not yet been elucidated. We now show that glycogen synthase kinase 3 (GSK-3) phosphorylates a group of Ser residues in the Neh6 domain of mouse Nrf2 that overlap with an SCF/␤-TrCP destruction motif (DSGIS, residues 334 to 338) and promotes its degradation in a Keap1-independent manner. Nrf2 was stabilized by GSK-3 inhibitors in Keap1-null mouse embryo fibroblasts. Similarly, an Nrf2 ⌬ETGE mutant, which cannot be degraded via Keap1, accumulated when GSK-3 activity was blocked. Phosphorylation of a Ser cluster in the Neh6 domain of Nrf2 stimulated its degradation because a mutant Nrf2 ⌬ETGE 6S/6A protein, lacking these Ser residues, exhibited a longer half-life than Nrf2 ⌬ETGE . Moreover, Nrf2 ⌬ETGE 6S/6A was insensitive to ␤-TrCP regulation and exhibited lower levels of ubiquitination than Nrf2⌬ETGE . GSK-3␤ enhanced ubiquitination of Nrf2 ⌬ETGE but not that of Nrf2 ⌬ETGE 6S/6A . The Nrf2 ⌬ETGE protein but not Nrf2 ⌬ETGE 6S/6A coimmunoprecipitated with ␤-TrCP, and this association was enhanced by GSK-3␤. Our results show for the first time that Nrf2 is targeted by GSK-3 for SCF/␤-TrCP-dependent degradation. We propose a "dual degradation" model to describe the regulation of Nrf2 under different pathophysiological conditions.

Nrf2 activation in the treatment of neurodegenerative diseases: a focus on its role in mitochondrial bioenergetics and function

“…But beyond these effects, GSK-3 inhibitors are also able to increase Nrf2 activation, so they can exert additional therapeutic effects through this mechanism. As it was described earlier in this review, GSK-3 phosphorylates Nrf2 in the Neh6 domain, targeting the protein for degradation in the proteasome through SCF/β-TrCP and therefore inhibiting Nrf2 activity (Rada et al, 2011). Consequently, GSK-3 inhibitors are able to prevent β-TrCPdependent degradation of Nrf2, increasing its availability and its translocation to the nucleus.…”

“…Exacerbated GSK-3β activity has been reported not only in AD, but also in other neurodegenerative diseases such as PD, and it has been speculated that consequent Nrf2 deficiency can be partially responsible for oxidative stress and energy-deficits that accompanies these conditions (Rada et al, 2011). Under these pathological conditions GSK-3 inhibitors could also cooperate to increase Nrf2 levels.…”

“…This mechanism, which is independent of Keap1, is regulated by glycogen synthase kinase-3 (GSK-3), which phosphorylates Nrf2 in the Neh6 domain, targeting the protein for degradation by the proteasome through SCF/β-TrCP and therefore inhibiting Nrf2 activity (Rada et al, 2011;Chowdhry et al, 2013) ( Figure 1C). It has been proposed that while Keap1 acts as a major sensor of electrophiles and oxidants, GSK-3/β-TrCP system participates in receptor-mediated signal transduction, modulating the Nrf2 levels in response to transient metabolic demands (Cuadrado, 2015).…”

Nuclear Factor–Erythroid-2–Related Factor 2 in Aging and Lung Fibrosis

“…89 Phosphorylation of serine residues (Ser-334 and Ser-338 of DSGIS motif) in the Neh6 domain of Nrf2 by glycogen synthetase kinase 3b also promotes degradation of Nrf2 by b-TrCP, an adaptor protein of Cull3 ligase system. 90 The role of these E3 ubiquitin ligases in context of aging and fibrosis is not well understood, although a general decline in the function of the ubiquitin-proteosomal system with aging is well appreciated.…”

Nutritive values, flavor amino acids, healthcare fatty acids and flesh quality improved by manganese referring to up-regulating the antioxidant capacity and signaling molecules TOR and Nrf2 in the muscle of fish

“…NF-E2-related factor 2 (Nrf2) is a primary nuclear transcription factor, which plays a critical role in redox homeostasis in human embryonic kidney (HEK) 293T cells (Rada et al, 2011). Under normal conditions, Nrf2 is inactivated in fish due to its repressor protein, Kelch-like ECH associating protein 1 (Keap1) (Li et al, 2008).…”