Organismal life encounters reactive oxidants from internal metabolism and environmental toxicant exposure. Reactive oxygen and nitrogen species cause oxidative stress and are traditionally viewed as being harmful. On the other hand, controlled production of oxidants in normal cells serves useful purposes to regulate signaling pathways. Reactive oxidants are counterbalanced by complex antioxidant defense systems regulated by a web of pathways to ensure that the response to oxidants is adequate for the body's needs. A recurrent theme in oxidant signaling and antioxidant defense is reactive cysteine thiol–based redox signaling. The nuclear factor erythroid 2–related factor 2 (Nrf2) is an emerging regulator of cellular resistance to oxidants. Nrf2 controls the basal and induced expression of an array of antioxidant response element–dependent genes to regulate the physiological and pathophysiological outcomes of oxidant exposure. This review discusses the impact of Nrf2 on oxidative stress and toxicity and how...

/pdf/role-of-nrf2-in-oxidative-stress-and-toxicity-2utmvoa3ko.pdf

Role of nrf2 in oxidative stress and toxicity.

Reactive oxygen species (ROS) have been shown to be toxic but also function as signalling molecules. This biological paradox underlies mechanisms that are important for the integrity and fitness of living organisms and their ageing. The pathways that regulate ROS homeostasis are crucial for mitigating the toxicity of ROS and provide strong evidence about specificity in ROS signalling. By taking advantage of the chemistry of ROS, highly specific mechanisms have evolved that form the basis of oxidant scavenging and ROS signalling systems.

/pdf/ros-as-signalling-molecules-mechanisms-that-generate-uoe9i48umf.pdf

ROS as signalling molecules: mechanisms that generate specificity in ROS homeostasis

http://www.jbc.org/content/284/20/13291.full.pdf

The Nrf2-Antioxidant Response Element Signaling Pathway and Its Activation by Oxidative Stress

Histones are characterized by numerous posttranslational modifications that influence gene transcription. However, because of the lack of global distribution data in higher eukaryotic systems, the extent to which gene-specific combinatorial patterns of histone modifications exist remains to be determined. Here, we report the patterns derived from the analysis of 39 histone modifications in human CD4(+) T cells. Our data indicate that a large number of patterns are associated with promoters and enhancers. In particular, we identify a common modification module consisting of 17 modifications detected at 3,286 promoters. These modifications tend to colocalize in the genome and correlate with each other at an individual nucleosome level. Genes associated with this module tend to have higher expression, and addition of more modifications to this module is associated with further increased expression. Our data suggest that these histone modifications may act cooperatively to prepare chromatin for transcriptional activation.

/pdf/combinatorial-patterns-of-histone-acetylations-and-3tprg69q8k.pdf

Combinatorial patterns of histone acetylations and methylations in the human genome

The heme oxygenases, which consist of constitutive and inducible isozymes (HO-1, HO-2), catalyze the rate-limiting step in the metabolic conversion of heme to the bile pigments (i.e., biliverdin and bilirubin) and thus constitute a major intracellular source of iron and carbon monoxide (CO). In recent years, endogenously produced CO has been shown to possess intriguing signaling properties affecting numerous critical cellular functions including but not limited to inflammation, cellular proliferation, and apoptotic cell death. The era of gaseous molecules in biomedical research and human diseases initiated with the discovery that the endothelial cell-derived relaxing factor was identical to the gaseous molecule nitric oxide (NO). The discovery that endogenously produced gaseous molecules such as NO and now CO can impart potent physiological and biological effector functions truly represented a paradigm shift and unraveled new avenues of intense investigations. This review covers the molecular and biochemical characterization of HOs, with a discussion on the mechanisms of signal transduction and gene regulation that mediate the induction of HO-1 by environmental stress. Furthermore, the current understanding of the functional significance of HO shall be discussed from the perspective of each of the metabolic by-products, with a special emphasis on CO. Finally, this presentation aspires to lay a foundation for potential future clinical applications of these systems.

/pdf/heme-oxygenase-1-carbon-monoxide-from-basic-science-to-2rhjm6458g.pdf

Heme oxygenase-1/carbon monoxide: from basic science to therapeutic applications.

Transcription factor Nrf2 is a major regulator of genes encoding phase 2 detoxifying enzymes and antioxidant stress proteins in response to electrophilic agents and oxidative stress. In the absence of such stimuli, Nrf2 is inactive owing to its cytoplasmic retention by Keap1 and rapid degradation through the proteasome system. We examined the contribution of Keap1 to the rapid turnover of Nrf2 (half-life of less than 20 min) and found that a direct association between Keap1 and Nrf2 is required for Nrf2 degradation. In a series of domain function analyses of Keap1, we found that both the BTB and intervening-region (IVR) domains are crucial for Nrf2 degradation, implying that these two domains act to recruit ubiquitin-proteasome factors. Indeed, Cullin 3 (Cul3), a subunit of the E3 ligase complex, was found to interact specifically with Keap1 in vivo. Keap1 associates with the N-terminal region of Cul3 through the IVR domain and promotes the ubiquitination of Nrf2 in cooperation with the Cul3-Roc1 complex. These results thus provide solid evidence that Keap1 functions as an adaptor of Cul3-based E3 ligase. To our knowledge, Nrf2 and Keap1 are the first reported mammalian substrate and adaptor, respectively, of the Cul3-based E3 ligase system.

Oxidative Stress Sensor Keap1 Functions as an Adaptor for Cul3-Based E3 Ligase To Regulate Proteasomal Degradation of Nrf2

Small Maf proteins serve as dual-function transcription factors through an exchange of their heterodimerization partners. For example, as heterodimers with hematopoietic cell-specific p45 NF-E2 or NF-E2-related factors (Nrf), they activate the β-globin or antioxidative stress enzyme heme oxygenase 1 (HO-1) genes, respectively. In contrast, together with Bach1, they repress these same genes. However, the signals leading to this partner exchange are not known. Using chromatin immunoprecipitation assays in NIH 3T3 cells, we show that heme, an inducer of ho-1, promotes displacement of Bach1 from the MafK-occupied ho-1 enhancers, which is followed by Nrf2 binding to these elements. Whereas histone H3 at the ho-1 enhancers and promoter is hyperacetylated irrespective of gene activity, exposure of cells to heme results in de novo hyperacetylation and hypermethylation of histone H3 in the transcribed region. These data indicate that, under normal conditions, the chromatin structure of ho-1 is in a preactivation state, but transcription is repressed by Bach1. Heme induces switching of Maf dimers, resulting in ho-1 expression. Heme also promotes displacement of Bach1 from the β-globin locus control region without affecting MafK binding in murine erythroleukemia cells. Thus, heme functions as a signaling molecule for gene expression in higher eukaryotes.

/pdf/heme-regulates-the-dynamic-exchange-of-bach1-and-nf-e2-wplup5uuj1.pdf

Heme regulates the dynamic exchange of Bach1 and NF-E2-related factors in the Maf transcription factor network

Bach1 is a transcriptional repressor of heme oxygenase-1 and β-globin genes, both of which are known to be transcriptionally induced by heme. To test the hypothesis that heme regulates the activity of Bach1, we expressed wild type and mutated versions of Bach1 together with or without its heterodimer partner MafK in human 293T and GM02063 cells and examined their subcellular localization. Inhibition of heme synthesis enhanced the nuclear accumulation of Bach1, whereas treating cells with hemin resulted in nuclear exclusion of Bach1. While the cadmium-inducible nuclear export signal (NES) of Bach1 was dispensable for the heme response, a region containing two of the heme-binding motifs was found to be critical for the heme-induced nuclear exclusion. This region functioned as a heme-regulated NES dependent on the exporter Crm1. These results extend the regulatory roles for heme in protein sorting, and suggest that Bach1 transduces metabolic activity into gene expression.

/pdf/heme-regulates-gene-expression-by-triggering-crm1-dependent-3skb8hlpf8.pdf

Heme regulates gene expression by triggering Crm1‐dependent nuclear export of Bach1

A 45-year-old female presented with generalized fatigue, unaccompanied by other symptoms. Investigation revealed severe anemia due to gastric bleeding, and hereditary hemorrhagic telangiectasia accompanied by a large pulmonary arteriovenous malformation (PAVM). Additionally, the presence of hepatic arteriovenous and portovenous shunts indicated hepatic involvement. In addition to hypoxemia due to right-to-left shunting in PAVM, hyperammonemia with normal hepatic function was detected. The large PAVM was successfully managed with surgical resection. Hyperammonemia, persisting despite the hemostasis of gastric bleeding, improved postoperatively in the absence of treatment directed at hepatic involvement. We believe that resection of large PAVM contributed to the improvement of hyperammonemia.

Large pulmonary arteriovenous malformation with hyperammonemia.

われわれは直腸原発GISTの術後7年目の肩甲骨転移に対して,メシル酸イマチニブ(商品名グリベック)を使用した症例を経験した.症例は67歳男性で, 1996年直腸粘膜下腫瘍で腹会陰式直腸切断術を行い,病理診断はleiomyosarcomaであった. 1998年肝転移に対して切除術を実施した. 2002年10月右上肢のしびれを自覚し,胸部写真,胸部CTで右第2肋骨に腫瘍を認めた.直腸腫瘍の骨転移と診断し,前方アプローチで1, 2肋骨を含め腫瘍切除術を施行し,病理診断はc-kit陽性のmalignant GISTであった.術後骨シンチグラフィーなどで右肩甲骨へも転移が疑われたため,現在外来でメシル酸イマチニブを投与している.術後1年経過しているが,転移巣の増大は認めていない.

Yukari Zenke

Papers

Oxidative Stress Sensor Keap1 Functions as an Adaptor for Cul3-Based E3 Ligase To Regulate Proteasomal Degradation of Nrf2

Heme regulates the dynamic exchange of Bach1 and NF-E2-related factors in the Maf transcription factor network

Heme regulates gene expression by triggering Crm1‐dependent nuclear export of Bach1

Large pulmonary arteriovenous malformation with hyperammonemia.

A case report of gastrointestinal tumor (gist) metastasis treated with imatinib mesylate