The Keap1-Nrf2 system and autophagy are both involved in the oxidative-stress response, metabolic pathways, and innate immunity, and dysregulation of these processes is associated with pathogenic processes. However, the interplay between these two pathways remains largely unknown. Here, we show that phosphorylation of the autophagy-adaptor protein p62 markedly increases p62's binding affinity for Keap1, an adaptor of the Cul3-ubiquitin E3 ligase complex responsible for degrading Nrf2. Thus, p62 phosphorylation induces expression of cytoprotective Nrf2 targets. p62 is assembled on selective autophagic cargos such as ubiquitinated organelles and subsequently phosphorylated in an mTORC1-dependent manner, implying coupling of the Keap1-Nrf2 system to autophagy. Furthermore, persistent activation of Nrf2 through accumulation of phosphorylated p62 contributes to the growth of human hepatocellular carcinomas (HCCs). These results demonstrate that selective autophagy and the Keap1-Nrf2 pathway are interdependent, and that inhibitors of the interaction between phosphorylated p62 and Keap1 have potential as therapeutic agents against human HCC.

p62/Sqstm1 is a multifunctional protein involved in cell survival, growth and death, that is degraded by autophagy. Amplification of the p62/Sqstm1 gene, and aberrant accumulation and phosphorylation of p62/Sqstm1, have been implicated in tumour development. Herein, we reveal the molecular mechanism of p62/Sqstm1-dependent malignant progression, and suggest that molecular targeting of p62/Sqstm1 represents a potential chemotherapeutic approach against hepatocellular carcinoma (HCC). Phosphorylation of p62/Sqstm1 at Ser349 directs glucose to the glucuronate pathway, and glutamine towards glutathione synthesis through activation of the transcription factor Nrf2. These changes provide HCC cells with tolerance to anti-cancer drugs and proliferation potency. Phosphorylated p62/Sqstm1 accumulates in tumour regions positive for hepatitis C virus (HCV). An inhibitor of phosphorylated p62-dependent Nrf2 activation suppresses the proliferation and anticancer agent tolerance of HCC. Our data indicate that this Nrf2 inhibitor could be used to make cancer cells less resistant to anticancer drugs, especially in HCV-positive HCC patients.

e Transcription factor Nrf2 (NF-E2-related factor 2) regulates a broad cytoprotective response to environmental stresses. Keap1 (Kelch-like ECH-associated protein 1) is an adaptor protein for cullin3-based ubiquitin E3 ligase and negatively regulates Nrf2. Whereas the Keap1-Nrf2 system plays important roles in oxidative stress response and metabolism, the roles Nrf2 plays in the prevention of diabetes mellitus remain elusive. Here we show that genetic activation of Nrf2 signaling by Keap1 gene hypomorphic knockdown (Keap1 flox/؊ ) markedly suppresses the onset of diabetes. When Keap1 flox/؊ mice were crossed with diabetic db/db mice, blood glucose levels became lower through improvement of both insulin secretion and insulin resistance. Keap1 flox/؊ also prevented high-calorie-diet-induced diabetes. Oral administration of the Nrf2 inducer CDDO-Im {oleanolic acid 1-[2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oyl] imidazole} also attenuated diabetes in db/db mice. Nrf2 induction altered antioxidant-, energy consumption-, and gluconeogenesis-related gene expression in metabolic tissues. Thus, the Keap1-Nrf2 system is a critical target for preventing the onset of diabetes mellitus.

cTranscription factor Nrf2 (NF-E2-related factor 2) coordinately regulates cytoprotective gene expression, but under unstressed conditions, Nrf2 is degraded rapidly through Keap1 (Kelch-like ECH-associated protein 1)-mediated ubiquitination. Nrf2 harbors two Keap1-binding motifs, DLG and ETGE. Interactions between these two motifs and Keap1 constitute a key regulatory nexus for cellular Nrf2 activity through the formation of a two-site binding hinge-and-latch mechanism. In this study, we determined the minimum Keap1-binding sequence of the DLG motif, the low-affinity latch site, and defined a new DLGex motif that covers a sequence much longer than that previously defined. We have successfully clarified the crystal structure of the Keap1-DC-DLGex complex at 1.6 Å. DLGex possesses a complicated helix structure, which interprets well the human-cancer-derived loss-of-function mutations in DLGex. In thermodynamic analyses, Keap1-DLGex binding is characterized as enthalpy and entropy driven, while Keap1-ETGE binding is characterized as purely enthalpy driven. In kinetic analyses, Keap1-DLGex binding follows a fast-association and fast-dissociation model, while Keap1-ETGE binding contains a slow-reaction step that leads to a stable conformation. These results demonstrate that the mode of DLGex binding to Keap1 is distinct from that of ETGE structurally, thermodynamically, and kinetically and support our contention that the DLGex motif serves as a converter transmitting environmental stress to Nrf2 induction as the latch site.

Transcription factor Nrf2 (NF-E2-related factor 2) regulates wide-ranging cytoprotective genes in response to environmental stress. Keap1 (Kelch-like ECH-associated protein 1) is an adaptor protein for Cullin3-based ubiquitin E3 ligase and negatively regulates Nrf2. The Keap1-Nrf2 system plays important roles in the oxidative stress response and metabolism. However, the roles Nrf2 plays in prevention of pancreatic b-cell damage remain elusive. To demonstrate the roles of Nrf2 in pancreatic b-cells, we used four genetically engineered mouse models: 1) b-cell-specific Keap1-conditional knockout mice, 2) b-cell-specific Nos2 transgenic mice, 3) conventional Nrf2-heterozygous knockout mice, and 4) b-cell-specific Nrf2-conditional knockout mice. We found that Nrf2 induction suppressed the oxidative DNA-adduct formation in pancreatic islets of iNOS-Tg mice and strongly restored insulin secretion from pancreatic b-cells in the context of reactive species (RS) damage. Consistently, Nrf2 suppressed accumulation of intracellular RS in isolated islets and pancreatic b-cell lines and also decreased nitrotyrosine levels. Nrf2 induced glutathione-related genes and reduced pancreatic b-cell apoptosis mediated by nitric oxide. In contrast, Nrf2 depletion in Nrf2-heterozygous knockout and b-cell-specific Nrf2-conditional knockout mice strongly aggravated pancreatic b-cell damage. These results demonstrate that Nrf2 induction prevents RS damage in pancreatic b-cells and that the Keap1-Nrf2 system is the crucial defense pathway for the physiological and pathological protection of pancreatic b-cells.