翻译后修饰对转录因子NF-E2相关因子2功能的调控

抗氧化反应组件（AREs）普遍存在于编码抗氧化和/或解毒酶基因的启动子区域,为这些基因的转录启动所必需;而这些基因的表达对维持细胞内氧化还原稳态,抵抗活性氧类（ROS）引起的细胞损伤发挥重要作用。转录因子NF E2相关因子2(nuclear factor erythroid 2 related factor 2, NRF2)作为抗氧化反应中的关键转录因子,可以与ARE结合,启动其下游靶基因,在氧化应激及亲电子剂应激中发挥重要的调控作用,广泛参与炎症、增殖、凋亡、细胞分化、组织再生和代谢等过程;因此,激活NRF2有望成为治疗肿瘤及其他与氧化、炎症相关疾病的新策略。蛋白质的翻译后修饰,对蛋白质空间构象、稳定性及其与其他蛋白质间相互作用具有重要作用。因此,探究NRF2的翻译后修饰如磷酸化、乙酰化和泛素化的修饰过程等,对深入了解NRF2的功能及调控机制至关重要,并与某些疾病的发生发展密切相关。本文对近年来翻译后修饰对NRF2的活性及功能的调控进行综述。     

The protective effect of sulforaphane against oxidative stress in granulosa cells of patients with polycystic ovary syndrome (PCOS) through activation of AMPK/AKT/NRF2 signaling pathway

Increased production of reactive oxygen species (ROS) in granulosa cells (GCs) causes oxidative stress (OS) and plays a role in pathogenesis of polycystic ovary syndrome (PCOS). Sulforaphane (SFN) has received a great deal of attention as potent antioxidant because of its ability to induce expression of antioxidant enzymes through nuclear factor (erythroid-derived 2)-like 2 (NRF2) signaling pathway. Therefore, the present study was done to investigate the protective effect of SFN against OS in granulosa-lutein cells (GLCs) of patients with PCOS through activation of AMP-activated protein kinase (AMPK)/AKT/NRF2 signaling pathway. GLCs were isolated from patients with PCOS and healthy fertile women, as control group, during egg retrieval procedure. Level of intracellular ROS and apoptosis was determined in the isolated cells. For investigating the protective effect of SFN against ROS production and apoptosis in GLCs, the cells were cultured for 24 h in the presence or absence of SFN. Finally, expression of AMPK, AKT, and NRF2 proteins and genes was evaluated by western blotting and quantitative real-time polymerase chain reaction (qRT-PCR), respectively. The results indicated the increased ROS and apoptosis levels in GLCs isolated from patients with PCOS compared to the control group. Addition of SFN to culture medium of GLCs of patients with PCOS reduced intracellular ROS and apoptosis levels, and increased expression of AMPK, AKT, and NRF2 proteins and genes. Our findings demonstrated the protective effect of SFN against OS by lowering level of ROS and apoptosis possibly through activation of AMPK, AKT, and NRF2 proteins and genes expression.     

Modulation of NRF2 signaling pathway by nuclear receptors: Implications for cancer

Nuclear factor-erythroid 2 p45-related factor 2 (NRF2, also known as Nfe2l2) plays a critical role in regulating cellular defense against electrophilic and oxidative stress by activating the expression of an array of antioxidant response element-dependent genes. On one hand, NRF2 activators have been used in clinical trials for cancer prevention and the treatment of diseases associated with oxidative stress; on the other hand, constitutive activation of NRF2 in many types of tumors contributes to the survival and growth of cancer cells, as well as resistance to anticancer therapy. In this review, we provide an overview of the NRF2 signaling pathway and discuss its role in carcinogenesis. We also introduce the inhibition of NRF2 by nuclear receptors. Further, we address the biological significance of regulation of the NRF2 signaling pathway by nuclear receptors in health and disease. Finally, we discuss the possible impact of NRF2 inhibition by nuclear receptors on cancer therapy.     

Increased Iron Sequestration in Alveolar Macrophages in Chronic Obtructive Pulmonary Disease

Free iron in lung can cause the generation of reactive oxygen species, an important factor in chronic obstructive pulmonary disease (COPD) pathogenesis. Iron accumulation has been implicated in oxidative stress in other diseases, such as Alzheimer’s and Parkinson’s diseases, but little is known about iron accumulation in COPD. We sought to determine if iron content and the expression of iron transport and/or storage genes in lung differ between controls and COPD subjects, and whether changes in these correlate with airway obstruction. Explanted lung tissue was obtained from transplant donors, GOLD 2–3 COPD subjects, and GOLD 4 lung transplant recipients, and bronchoalveolar lavage (BAL) cells were obtained from non-smokers, healthy smokers, and GOLD 1–3 COPD subjects. Iron-positive cells were quantified histologically, and the expression of iron uptake (transferrin and transferrin receptor), storage (ferritin) and export (ferroportin) genes was examined by real-time RT-PCR assay. Percentage of iron-positive cells and expression levels of iron metabolism genes were examined for correlations with airflow limitation indices (forced expiratory volume in the first second (FEV₁) and the ratio between FEV₁ and forced vital capacity (FEV₁/FVC)). The alveolar macrophage was identified as the predominant iron-positive cell type in lung tissues. Futhermore, the quantity of iron deposit and the percentage of iron positive macrophages were increased with COPD and emphysema severity. The mRNA expression of iron uptake and storage genes transferrin and ferritin were significantly increased in GOLD 4 COPD lungs compared to donors (6.9 and 3.22 fold increase, respectively). In BAL cells, the mRNA expression of transferrin, transferrin receptor and ferritin correlated with airway obstruction. These results support activation of an iron sequestration mechanism by alveolar macrophages in COPD, which we postulate is a protective mechanism against iron induced oxidative stress.     

NRF2 as a determinant of cellular resistance in retinoic acid cytotoxicity

Clinical use of retinoic acids (RA) is hindered by toxicity possibly related to oxidative stress. Recently, RA at relatively low concentrations was shown to inhibit NRF2 and the expression of its target antioxidative genes. This raises the possibility that RA toxicity may result from cellular inability to cope with resultant oxidative stress. Using in vitro cell and in vivo mouse models, we report that RA, specifically all-trans-RA (atRA) at concentrations implicated in toxicity, can activate NRF2 and induce NRF2 target genes, particularly the subunits of the rate-limiting enzyme of glutathione biosynthesis, glutamate cysteine ligase (GCLM/GCLC). RNA interference-mediated silencing of NRF2, but not of retinoid X receptor-alpha and -beta, reduced basal and atRA-induced GCLM/GCLC gene expression. Moreover, RA increased nuclear accumulation of NRF2, antioxidant response element (ARE) reporter activity, and NRF2 occupancy at AREs. 4-Hydroxynonenal, a lipid peroxidation product, was increased by RA. Inhibition of MEK1/ERK mitogen-activated protein kinases significantly suppressed atRA-induced NRF2 activation and ARE-regulated gene expression, reducing cell resistance against toxic concentrations of RA. NRF2-silenced cells were vulnerable to atRA-induced mitochondrial toxicity and apoptosis. In conclusion, toxic RA activates NRF2, thereby triggering an adaptive response against the resultant oxidative stress. NRF2 enhancement as a therapeutic target of retinoid toxicity awaits further investigation.     

Localization of gamma-glutamylcysteine synthetase messenger rna expression in lungs of smokers and patients with chronic obstructive pulmonary disease

Cigarette smoking results in an oxidant/antioxidant imbalance in the lungs and inflammation, which are considered to be key factors in the pathogenesis of chronic obstructive pulmonary disease (COPD). Glutathione (GSH) is an important protective antioxidant in lung epithelial cells and epithelial lining fluid. De novo GSH synthesis in cells occurs by a two-enzyme process. The rate-limiting enzyme is gamma-glutamylcysteine synthetase (gamma-GCS), in which the heavy subunit (HS) constitutes most of its catalytic activity. The localization and expression of gamma-GCS-HS in specific lung cells as well as possible differences in its expression between smokers with and without COPD have not yet been studied. The purpose of this study was to investigate gamma-GCS-HS expression using messenger RNA in situ hybridization in peripheral lung tissue. We studied 23 current or ex-smokers with similar smoking histories with (n = 11; forced expiratory volume in 1 s [FEV(1)] < 75% predicted) or without COPD (n = 12; FEV(1) < 84% predicted). We assessed the relations between pulmonary gamma-GCS-HS expression, FEV(1) and transforming growth factor-beta1 (TGFbeta(1)), because TGFbeta(1) can modulate gamma-GCS-HS expression in lung epithelial cells. Gamma-GCS-HS is predominantly expressed by airway and alveolar epithelial cells, alveolar CD68+ cells (macrophages), and endothelial cells of both arteries and veins. In subjects with COPD, semiquantitative analysis revealed higher levels of gamma-GCS-HS messenger RNA in alveolar epithelium (1.5 times, p <.04) and a trend for a higher expression in bronchiolar epithelium (1.3 times, p =.075) compared with subjects without COPD. We did not observe a significant correlation between airway and alveolar epithelial gamma-GCS-HS expression and TGFbeta(1) expression (r =.20), FEV(1) percentage predicted (r =.18), or FEV(1)/forced vital capacity ratio (r =.14; p.05). Our results show that gamma-GCS-HS is localized, particularly in lung epithelium, and shows higher expression in smokers with COPD. This suggests a specific role for enhanced GSH synthesis as a mechanism to provide an adaptive response against oxidative stress in patients with COPD.     

Systemic poly(ADP-ribose) polymerase-1 activation,chronic inflammation,and oxidative stress in COPD patients

Oxidative stress and systemic inflammation in chronic obstructive pulmonary disease (COPD) strongly suggest a role for the nuclear enzyme poly(ADP-ribose) polymerase-1 (PARP-1, E.C.2.4.2.30) in the disease pathophysiology. PARP-1 is highly activated by reactive oxygen species-induced DNA strand breaks, upon which it forms extensive poly(ADP-ribose) (PAR) polymers from its substrate NAD(+). We hypothesized that in COPD, chronic inflammation and oxidative stress would lead to systemic PARP-1 activation and to a reduced NAD(+) status. In a patient-control study, systemic PARP-1 activation was assessed by immunofluorescent detection of PAR polymers in peripheral blood lymphocytes. The percentage of PAR polymer-positive lymphocytes appeared to be higher in COPD patients (27 +/- 3%) than in healthy age-matched controls (17 +/- 2%, p <.05). Trolox equivalent antioxidant capacity (TEAC) of deproteinized plasma (p <.001), plasma uric acid (p <.05), as well as blood NAD(+) (p <.01) of stable COPD patients were significantly reduced when compared to controls. In addition, levels of proinflammatory cytokines IL-6, IL-8, and sICAM-1 were increased (p <.005) in COPD patients. In this study, evidence was found for the presence of systemic inflammation, chronic oxidative stress, and systemic PARP-1 activation in stable COPD patients. These data support a contribution of oxidative stress-induced PARP-1 activation to the pathophysiology of COPD.     

Cigarette smoke-induced oxidative stress activates NRF2 to mediate fibronectin disorganization in vascular formation

Cigarette smoke significantly induces oxidative stress, resulting in cardiovascular disease. NRF2, a well-known antioxidative stress response factor, is generally considered to play protective roles in cardiovascular dysfunction triggered by oxidative stress. Interestingly, recent studies reported adverse effects of NRF2 on the cardiovascular system. These unfavourable pathogenic effects of NRF2 need to be further investigated. Our work shows that cigarette smoke extract (CSE)-induced oxidative stress disturbs fibronectin (FN) assembly during angiogenesis. Furthermore, this effect largely depends on hyperactive NRF2-STAT3 signalling, which consequently promotes abnormal FN deposition. Consistently, disruption of this pathway by inhibiting NRF2 or STAT3 prevents CSE-induced FN disorganization and vasculature disruption in human umbilical vein endothelial cells or zebrafish. Taken together, these findings demonstrate the cardiovascular dysfunction caused by CSE from a novel perspective that NRF2-dependent signalling engages in FN disorganization.