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. Copyright ? 2011, American Society for Microbiology. All Rights Reserved.