Activation of Nrf2 by arsenite and monomethylarsonous acid is independent of Keap1-C151: enhanced Keap1-Cul3 interaction

Drinking water contaminated with arsenic, a human carcinogen, is a worldwide health issue. An understanding of cellular signaling events in response to arsenic exposure and rational designing of strategies to reduce arsenic damages by modulating signaling events are important to fight against arsenic-induced diseases. Previously, we reported that activation of the Nrf2-mediated cellular defense pathway confers protection against toxic effects induced by sodium arsenite [As(III)] or monomethylarsonous acid [MMA(III)]. Paradoxically, arsenic has been reported to induce the Nrf2-dependent signaling pathway. Here, we report the unique mechanism of Nrf2 induction by arsenic. Similar to tert-butylhydroquinone (tBHQ) or sulforaphane (SF), arsenic induced the Nrf2-dependent response through enhancing Nrf2 protein levels by inhibiting Nrf2 ubiquitination and degradation. However, the detailed action of arsenic in Nrf2 induction is different from that of tBHQ or SF. Arsenic markedly enhanced the interaction between Keap1 and Cul3, subunits of the E3 ubiquitin ligase for Nrf2, which led to impaired dynamic assembly/disassembly of the E3 ubiquitin ligase and thus decreased its ligase activity. Furthermore, induction of Nrf2 by arsenic is independent of the previously identified C151 residue in Keap1 that is required for Nrf2 activation by tBHQ or SF. Distinct mechanisms of Nrf2 activation by seemingly harmful and beneficial reagents provide a molecular basis to design Nrf2-activating agents for therapeutic intervention.     

Kinetic analyses of Keap1-Nrf2 interaction and determination of the minimal Nrf2 peptide sequence required for Keap1 binding using surface plasmon resonance

The Keap1-Nrf2 interaction plays important roles in regulation of Nrf2 activity and induction of chemopreventive enzymes. To better understand the interaction and to determine the minimal Nrf2 sequence required for Keap1 binding, we synthesized a series of Nrf2 peptides containing ETGE motif and determined their binding affinities to the Kelch domain of Keap1 in solution using a surface plasmon resonance-based competition assay. The equilibrium dissociation constant for the interaction between 16mer Nrf2 peptide and Keap1 Kelch domain in solution (K(solution)(D)) was found to be 23.9 nM, which is 10× lower than the surface binding constant (K(surface)(D)) of 252 nM obtained for the direct binding of Keap1 Kelch domain to the immobilized 16mer Nrf2 peptide on a surface plasmon resonance sensor chip surface. The binding affinity of Nrf2 peptides to Keap1 Kelch domain was not lost until after deletion of eight residues from the N-terminus of the 16mer Nrf2 peptide. The 9mer Nrf2 peptide has a moderate binding affinity with a (K(solution)(D)) of 352 nM and the affinity was increased 15× upon removal of the positive charge at the peptide N-terminus by acetylation. These results suggest that the minimal Nrf2 peptide sequence required for Keap1 binding is the 9mer sequence of LDEETGEFL.     

癌症预防中的Keap1-Nrf2-ARE通路

癌症的治疗至今仍未取得重大进展,因此做好癌症的预防工作就尤为关键。目前有很多自然物质（如从植物中提取的抗氧化剂）或化学合成物质（如添加在食品中的抗氧化剂）被用来预防癌症。最近发现,有些癌症预防物是通过诱导二相抗氧化酶来清除体内的致癌物质或其它毒物,而且这种诱导作用是通过Keap1-Nrf2-ARE信号通路。因此,对这一通路的了解有利于拓展癌症的研究及预防。     

Keap1-Nrf2信号通路相关表观遗传调控的研究进展

Kelch样ECH联合蛋白1-核转录因子E2相关因子2(Keap1-Nrf2)信号通路是细胞抵御氧化损伤和电子损伤的重要调控途径,激活Nrf2的表达被认为可以预防慢性病。机体内除了基因突变对Keap1-Nrf2信号通路有调控作用以外,表观遗传被认为是另一种重要的调控机制。本文综述了表观遗传(包括DNA甲基化、组蛋白修饰和微RNA)对Keap1-Nrf2信号通路的调控作用,为Keap1-Nrf2信号通路相关的表观遗传调控的深入研究提供参考。     

Bisphenol A induces Nrf2-dependent drug-metabolizing enzymes through nitrosylation of Keap1

Bisphenol A (BPA) is an endocrine-disrupting chemical, and activates the aryl hydrocarbon receptor (AhR) and the estrogen receptor, leading to the induction of drug metabolizing enzymes. In this study, we found that BPA increased nitric oxide (NO) levels but not reactive oxygen species (ROS) levels in the human hepatoma cell line, Hep3B, and induced drug-metabolizing enzymes such as UDP-glucuronosyltransferase (UGT). Nuclear factor erythroid 2-related factor 2 (Nrf2) has been reported to be activated by ROS through inactivation of its regulating protein, Kelch-like ECH-associated protein (Keap1), and to be the key mediator of phase I and phase II drug metabolizing enzymes, and phase III drug transporters. Treatment of Hep3B with BPA increased the levels of nitrous oxide, a metabolite of nitric oxide and activated Nrf2 by nitrosylation of Keap1, leading to the induction of heme oxygenase-1 (HO-1) and UGT2B1 mRNAs. A nitric oxide donor, 1-Hydroxy-2-oxo-3-(N-methyl-3-aminopropyl)-3-methyl-1-triazene (NOC7), also activated Nrf2 and a NOS inhibitor, N^G-Monomethyl-l-arginine, monoacetate salt (L-NMMA), inhibited activation of Nrf2 by BPA. Furthermore, calcium efflux by BPA was observed. These results suggested the new idea that BPA increases NO levels and activates Nrf2 via Keap1 inactivation, leading to induction of Nrf2-dependent drug-metabolizing enzymes.     

Cyanobacterial nodularin is a potent inhibitor of type 1 and type 2A protein phosphatases.

The present study characterizes the inhibitory effects of nodularin, a recently isolated hepatotoxic compound from the cyanobacterium Nodularia spumigena, on type 1 (PP1), type 2A, (PP2A), type 2B (PP2B), and type 2C (PP2C) protein phosphatases. Both PP2A and PP1 were potently inhibited (IC50 = 0.026 and 1.8 nM, respectively) by nodularin, whereas PP2B was inhibited to a lesser extent (IC50 = 8.7 microM). Nodularin had no apparent effect on PP2C, alkaline phosphatase, acid phosphatase, insulin receptor tyrosine kinase, protein kinase A, phosphorylase kinase, or protein kinase C. In a whole-cell extract of T51B liver cells, nodularin inhibited PP1 and PP2A activity with a potency similar to that seen with their purified catalytic subunits. Thus, due to the high specificity of nodularin for PP2A and PP1, this hepatotoxin may prove to be useful as a probe for distinguishing the activity of these protein phosphatases in cell extracts.     

Nrf2/Keap1/ARE信号通路与难治性呼吸系统疾病研究进展

Nrf2/Keap1/ARE是重要的抗氧化信号通路,对维持体内抗氧化物与过氧化物平衡有重要作用。氧化应激发生时,Nrf2/Keap1/ARE信号通路被激活,调控下游抗氧化蛋白表达,减轻氧化应激对机体的损伤并减弱氧化应激的程度。近年来的研究发现,Nrf2/Keap1/ARE信号通路与肺纤维化、肺癌、慢性阻塞性肺病等难治性呼吸系统疾病的发生发展有密切联系,该通路可能作为治疗这类疾病的潜在靶点。该文就Nrf2/Keap1/ARE信号通路在难治性呼吸系统疾病中的作用进行综述,进一步了解其在难治性呼吸系统疾病中的作用机制,为这类疾病发病机制和治疗方案的研究提供可靠的参考。     

Keap1-Nrf2-ARE信号通路及其激活剂的研究进展

Keap1-Nrf2-ARE信号通路是细胞防御氧化应激损伤的最重要机制之一。许多具有解毒、抗氧化防御功能的蛋白质,其转录调控都依赖于Nrf2信号通路的激活。研究表明,Nrf2信号通路已成为氧化应激相关疾病(神经退行性疾病、癌症、心血管系统疾病、代谢和炎症等疾病)预防和治疗的靶点。因此,Nrf2信号通路的激活剂在多种氧化应激诱发的疾病方面都表现出良好的预防及治疗作用,发现及研究Nrf2信号通路的激活剂已越来越受到研究者们的重视。该文概述了Keap1-Nrf2-ARE通路的作用机制,并阐述了Keap1-Nrf2-ARE信号通路小分子激活剂的研究进展。     

Anti-inflammatory Effect of a Cell-Penetrating Peptide Targeting the Nrf2/Keap1 Interaction

Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) is increasingly recognized as a central regulator of multiple signaling pathways in inflammation and cancer, and the ability to use chemical biological tools to investigate its biological effects is very attractive. A peptide comprising a TAT-conjugated Nrf2 sequence is shown to activate Nrf2 and its downstream target gene heme-oxygenase-1 (HO-1) in a dose-dependent manner in intact human THP-1 monocytes. Levels of Nrf2 protein peak after 3 h, whereas HO-1 mRNA and protein peak after 6 and 12 h, respectively. The peptide is also shown to inhibit the production of the pro-inflammatory cytokine TNF. The TAT-14mer constitutes a useful chemical biology tool with potential therapeutic applications.     

AMP-activated protein kinase and type 2 diabetes

AMP-activated protein kinase (AMPK) is an enzyme that works as a fuel gauge, being activated in situations of high-energy phosphate depletion. Upon activation, AMPK functions to restore cellular ATP by modifying diverse metabolic pathways. AMPK is activated robustly by skeletal muscle contraction and myocardial ischemia, and may be involved in the stimulation of glucose transport and fatty acid oxidation produced by these stimuli. In liver, activation of AMPK results in enhanced fatty acid oxidation and in decreased production of glucose, cholesterol, and triglycerides. Recent studies have shown that AMPK is the cellular mediator for many of the metabolic effects of drugs such as metformin and thiazolidinediones, as well as the insulin sensitizing adipocytokines leptin and adiponectin. These data, along with evidence from studies showing that chemical activation of AMPK in vivo with 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) improves blood glucose concentrations and lipid profiles, make this enzyme an attractive pharmacological target for the treatment of type 2 diabetes and other metabolic disorders.     

红景天苷对支气管肺炎大鼠Nrf2/Keap1通路及气道炎症的影响

目的 通过构建支气管肺炎SD大鼠实验模型,探究红景天苷对支气管肺炎大鼠核因子红细胞相关因子2（Nrf2）/ Kelch样环氧氯丙烷相关蛋白（Keap1）通路及气道炎症的影响。方法 将SD大鼠随机分为对照组、模型组及红景天苷低、高剂量（30、60 mg/kg）组和鸦胆子苦醇组,红景天苷＋鸦胆子苦醇组,每组10只。红景天苷组大鼠分别ip 30、60 mg/kg红景天苷,鸦胆子苦醇组大鼠ip 100 mg/mL鸦胆子苦醇,红景天苷＋鸦胆子苦醇组ip 60 mg/kg红景天苷和100 mg/mL鸦胆子苦醇。对照组使用同等剂量生理盐水。取各组大鼠肺泡灌洗液,对灌洗液中嗜酸性粒细胞、中性粒细胞和淋巴细胞数量进行分类和计数,ELISA法检测肺泡灌洗液中白细胞介素-1β（IL-1β）、白细胞介素-13（IL-13）、白细胞介素-18（IL-18）水平。苏木精–伊红（HE）染色法观测各组大鼠肺组织形态,Western blotting法检测大鼠肺组织IL-1β、诱导型一氧化氮合酶（iNOS）及Nrf2/Keap1信号通道相关蛋白表达水平。结果 与模型组相比,红景天苷30、60 mg/kg组大鼠肺泡灌洗液中嗜酸性粒细胞、中性粒细胞和淋巴细胞数量,IL-1β、IL-13、IL-18水平及肺组织IL-1β、iNOS、Keap1蛋白表达、炎症评分显著降低,肺组织Nrf2蛋白表达水平显著升高（P＜0.05）;与红景天苷60 mg/kg组相比,红景天苷＋鸦胆子苦醇组大鼠肺泡灌洗液中嗜酸性粒细胞、中性粒细胞和淋巴细胞数量,肺泡灌洗液IL-1β、IL-13、IL-18水平,肺组织IL-1β、iNOS、Keap1蛋白表达水平,炎症评分显著升高,肺组织Nrf2蛋白表达水平显著降低（P＜0.05）。结论 红景天苷可能通过激活Nrf2/Keap1信号通道缓解支气管肺炎炎症。     

PTP-1B及其抑制剂与2型糖尿病的研究现状

蛋白酪氨酸磷酸酶-1B (PTP-1B)是蛋白酪氨酸磷酸酶(PTP)家族中的一员,在胰岛素信号转导途径中发挥重要作用.经研究发现,PTP-1B与2型糖尿病的发生、发展有密切关系. 本文按PTP-1B 小分子抑制剂的结构类别对近年来文献报道的代表性小分子PTP-1B 抑制剂进行综述.表明深入研究PTP-1B及其有效的抑制剂对于2型糖尿病治疗具有良好的发展前景.