Glycogen Synthase Kinase-3β Inhibits the Xenobiotic and Antioxidant Cell Response by Direct Phosphorylation and Nuclear Exclusion of the Transcription Factor Nrf2

Abstract

The transcription factor Nrf2 (nuclear factor E2-related factor 2) regulates the expression of antioxidant phase II genes and contributes to preserve redox homeostasis and cell viability in response to oxidant insults. Nrf2 should be coordinated with the canonical cell survival pathway represented by phosphatidylinositol 3-kinase (PI3K) and the Ser/Thr kinase Akt but so far the mechanistic connections remain undefined. Here we identify glycogen synthase kinase-3␤ (GSK-3␤), which is inhibited by Akt-mediated phosphorylation, as the link between both processes. Using heme oxygenase-1 (HO-1) as a model phase II gene, we found that both PI3K and Akt increased mRNA and protein levels of this enzyme. Pharmacological inhibitors (LiCl and PDZD-8) and genetic variants of GSK-3␤ (constitutively active and dominant negative mutants) indicated that PI3K/Akt activates and GSK-3␤ inhibits the antioxidant response elements of the ho1 promoter and pointed Nrf2 as directly involved in this process. Indeed, GSK-3␤ phosphorylated Nrf2 in vitro and in vivo. Immunocytochemistry and subcellular fractionation analyses demonstrated that the effect of GSK-3␤-mediated phosphorylation of Nrf2 is to exclude this transcription factor from the nucleus. Nrf2 up-regulated the expression of HO-1, glutathione peroxidase, glutathione S-transferase A1, NAD(P)H: quinone oxidoreductase and glutamate-cysteine ligase and protected against hydrogen peroxide-induced glutathione depletion and cell death, whereas co-expression of active GSK-3␤ attenuated both phase II gene expression and oxidant protection. These results contribute to clarify the cross-talk between the survival signal elicited by PI3K/Akt and the antioxidant phase II cell response, and introduce GSK-3␤ as the key mediator of this regulation mechanism.

Nrf2 target genes are induced under marginal selenium-deficiency

“…In the previous study [28], we found the Wnt pathway activated, indicated by the enhanced expression of b-catenin, Dvl2, Lef1 and c-Myc and the down-regulation of Gsk3b. GSK3b, a multifunctional serine/threonine kinase, is not only involved in glycogen metabolism and canonical Wnt signaling but has also been shown to inactivate the Nrf2 pathway [23,49]. Fyn kinase is phosphorylated and thereby activated by GSK3b.…”

Pyrroloquinoline quinone rescues hippocampal neurons from glutamate-induced cell death through activation of Nrf2 and up-regulation of antioxidant genes

“…Functional interference between GSK3β and Nrf2 protects hippocampal neurons against kainate-induced cell death (Salazar et al, 2006;Rojo et al, 2008). Under basal conditions, Nrf2 binds tightly to the regulatory protein Kelch-like ECH-associated protein 1 (Keap1) and retains it in the cytoplasm.…”

Lithium in the Kidney: Friend and Foe?

“…[107][108][109][110][111] Although the involved mechanisms are poorly studied, they might involve GSK3-mediated degradation of the transcription factor Nrf2, which upregulates the expression of different antioxidant proteins, like Bcl-2, and recently emerged as an important player in protection against AKI. [112][113][114][115][116] …”