植物铁蛋白与氧化胁迫应激

植物铁蛋白是植物体重要的铁调节蛋白。许多研究表明植物铁蛋白与氧化胁迫抗性之间具有较强关联。植物铁蛋白不仅能抵御高铁产生的氧化毒性,在很多氧化胁迫及环境胁迫抗性中也发挥作用。对植物铁蛋白在氧化及逆境胁迫中的应激加以综述,为铁蛋白在生物工程领域的应用提供理论依据。     

Inositol Pyrophosphates Regulate Cell Growth and the Environmental Stress Response by Activating the HDAC Rpd3L

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Growth Response of Clostridium perfringens to Oxidative Stress

The sensitivity of Clostridium perfringens strain 13 to oxygen and its toxic derivatives was investigated in a new, defined medium (MMP). Exponentially growing cells in MMP medium were very sensitive to exposure to air by vigorous shaking. When exposed to air, the cells survived only 1hour and then rapidly died. Addition of cysteine, ascorbic acid, or yeast extract to the medium significantly increased vegetative cell survival without inducing sporulation. The level of toxicity of peroxyl and hydroperoxyl radicals, generated by H₂O₂, t-butyl hydroperoxide or ethanol, was very similar with and without air exposure. By contrast, plumbagin or menadione, which generate superoxide radicals in the presence of oxygen, caused high levels of cell death only in aerobiosic culture. Growth-arrested cells were more resistant to H₂O₂and to redox-cycling agents than were exponentially growing cells, but the resistance required de novo synthesis of proteins. An adaptive response to oxidative stress was also suggested by the higher level of cell resistance to H₂O₂and to ethanol when cells were pretreated with sublethal doses of these oxidants.     

miR482介导的植物生物胁迫响应

植物在生长发育过程中会遇到各种生物胁迫,根据响应过程的不同,可将之分为基于蛋白质的生物胁迫和基于RNA的生物胁迫。miR482是一种植物特有的、已在23个物种中被证实存在的小RNA。miR482参与指导植物次级phasiRNA的合成,其主要靶标为植物庞大的Ⅳ=日§三R尺类家族抗病基因。本文通过整理近年来ETI（effector-triggeredimmunity）相关的NBS-LRR类抗病基因和抗RNA沉默抑制相关miR482级联调控的研究成果,总结出了miR482介导植物两类生物胁迫响应的调控机制。     

Stathmin Mediates Hepatocyte Resistance to Death from Oxidative Stress by down Regulating JNK

Stathmin 1 performs a critical function in cell proliferation by regulating microtubule polymerization. This proliferative function is thought to explain the frequent overexpression of stathmin in human cancer and its correlation with a bad prognosis. Whether stathmin also functions in cell death pathways is unclear. Stathmin regulates microtubules in part by binding free tubulin, a process inhibited by stathmin phosphorylation from kinases including c-Jun N-terminal kinase (JNK). The involvement of JNK activation both in stathmin phosphorylation, and in hepatocellular resistance to oxidative stress, led to an examination of the role of stathmin/JNK crosstalk in oxidant-induced hepatocyte death. Oxidative stress from menadione-generated superoxide induced JNK-dependent stathmin phosphorylation at Ser-16, Ser-25 and Ser-38 in hepatocytes. A stathmin knockdown sensitized hepatocytes to both apoptotic and necrotic cell death from menadione without altering levels of oxidant generation. The absence of stathmin during oxidative stress led to JNK overactivation that was the mechanism of cell death as a concomitant knockdown of JNK1 or JNK2 blocked death. Hepatocyte death from JNK overactivation was mediated by the effects of JNK on mitochondria. Mitochondrial outer membrane permeabilization occurred in stathmin knockdown cells at low concentrations of menadione that triggered apoptosis, whereas mitochondrial β-oxidation and ATP homeostasis were compromised at higher, necrotic menadione concentrations. Stathmin therefore mediates hepatocyte resistance to death from oxidative stress by down regulating JNK and maintaining mitochondrial integrity. These findings demonstrate a new mechanism by which stathmin promotes cell survival and potentially tumor growth.     

氧化应激下植物线粒体自噬分析

线粒体自噬,是指通过选择性的识别并清除损伤、衰老及功能紊乱的线粒体,对维持细胞内线粒体质量和数量的平衡产生了重要作用。与动物和酵母中线粒体自噬的研究进展相比,植物线粒体自噬的途径及具体调控机制尚不明确。基于GFP标签,本文探究了氧化胁迫下植物线粒体自噬发生情况。研究发现甲基紫精诱导线粒体在液泡中积累,并呈现两种状态:1) GFP小体包含的线粒体; 2)不含GFP的线粒体。本研究发展的GFP标签策略可为植物线粒体自噬关键调控因子的筛选提供借鉴。     

Cth2 Protein Mediates Early Adaptation of Yeast Cells to Oxidative Stress Conditions

Cth2 is an mRNA-binding protein that participates in remodeling yeast cell metabolism in iron starvation conditions by promoting decay of the targeted molecules, in order to avoid excess iron consumption. This study shows that in the absence of Cth2 immediate upregulation of expression of several of the iron regulon genes (involved in high affinity iron uptake and intracellular iron redistribution) upon oxidative stress by hydroperoxide is more intense than in wild type conditions where Cth2 is present. The oxidative stress provokes a temporary increase in the levels of Cth2 (itself a member of the iron regulon). In such conditions Cth2 molecules accumulate at P bodies-like structures when the constitutive mRNA decay machinery is compromised. In addition, a null Δcth2 mutant shows defects, in comparison to CTH2 wild type cells, in exit from α factor-induced arrest at the G1 stage of the cell cycle when hydroperoxide treatment is applied. The cell cycle defects are rescued in conditions that compromise uptake of external iron into the cytosol. The observations support a role of Cth2 in modulating expression of diverse iron regulon genes, excluding those specifically involved in the reductive branch of the high-affinity transport. This would result in immediate adaptation of the yeast cells to an oxidative stress, by controlling uptake of oxidant-promoting iron cations.     

Arabidopsis thaliana Metallothionein, AtMT2a, Mediates ROS Balance during Oxidative Stress

Cold stress has been shown to induce the production of reactive oxygen species (ROS), which can elicit a potentially damaging oxidative burden on cellular metabolism. Here, the expression of a metallothionein gene (AtMT2a) was upregulated under low temperature and hydrogen peroxide (H₂O₂) stresses. The Arabidopsis T-DNA insertion mutant, mt2a, exhibited more sensitivity to cold stress compared to WT plants during the seed germination, and H₂O₂ levels in mt2a mutant were higher than that in WT plants during the cold stress. Synthetic GFP fused to AtMT2a was observed to be localized in cytosol. These results indicated that AtMT2a functions in tolerance against cold stress by mediating the ROS balance in the cytosol. Interestingly, mRNA level of AtMT2a was increased in seedlings of Arabidopsis cat2 mutant after cold treatment compared to WT seedlings, and overexpression of AtMT2a in cat2 could improve CAT activity under chilling stress. Moreover, the enzymatic activity of CAT in mt2a was higher than that in WT plants after cold treatment, suggesting that AtMT2a and CAT might complement each other in antioxidative process potentially in Arabidopsis. Taken together, our results provided a novel insight into the relationship between MTs and antioxidative enzymes in the ROS-scavenging system in plants.     

Selective Up-regulation of Human Selenoproteins in Response to Oxidative Stress

Selenocysteine is inserted into selenoproteins via the translational recoding of a UGA codon, normally used as a stop signal. This process depends on the nature of the selenocysteine insertion sequence element located in the 3′ UTR of selenoprotein mRNAs, selenium bioavailability, and, possibly, exogenous stimuli. To further understand the function and regulation of selenoproteins in antioxidant defense and redox homeostasis, we investigated how oxidative stress influences selenoprotein expression as a function of different selenium concentrations. We found that selenium supplementation of the culture media, which resulted in a hierarchical up-regulation of selenoproteins, protected HEK293 cells from reactive oxygen species formation. Furthermore, in response to oxidative stress, we identified a selective up-regulation of several selenoproteins involved in antioxidant defense (Gpx1, Gpx4, TR1, SelS, SelK, and Sps2). Interestingly, the response was more efficient when selenium was limiting. Although a modest change in mRNA levels was noted, we identified a novel translational control mechanism stimulated by oxidative stress that is characterized by up-regulation of UGA-selenocysteine recoding efficiency and relocalization of SBP2, selenocysteine-specific elongation factor, and L30 recoding factors from the cytoplasm to the nucleus.     

拟南芥神经酰胺酶基因对氧化胁迫的响应

以拟南芥哥伦比亚生态型（Col）和神经酰胺酶突变体为实验材料,通过对突变体的一系列生理生化指标的测定,来研究拟南芥神经酰胺酶基因（AtCER）对H2O2的响应。利用PCR和Northern blot获得了9个AtCER纯合单突变体。不同浓度H2O2处理野生型和突变体后,发现突变体对H2O2的反应比野生型更加敏感。H2O2处理后突变体叶片出现比野生型更严重的黄化现象和坏死斑点,总叶绿素含量也比野生型下降的更快,电导率测定也发现突变体比野生型的电导率增加得更多。抗氧化酶活性的分析结果发现H2O2处理后,突变体的抗氧化酶活性比野生型提高了1．5～3倍。上述研究结果说明AtCER参与了H2O2诱导的氧化胁迫反应。     

Oxidative Stress Impairs the Heat Stress Response and Delays Unfolded Protein Recovery

Background

Environmental changes, air pollution and ozone depletion are increasing oxidative stress, and global warming threatens health by heat stress. We now face a high risk of simultaneous exposure to heat and oxidative stress. However, there have been few studies investigating their combined adverse effects on cell viability.

Principal Findings

Pretreatment of hydrogen peroxide (H₂O₂) specifically and highly sensitized cells to heat stress, and enhanced loss of mitochondrial membrane potential. H₂O₂ exposure impaired the HSP40/HSP70 induction as heat shock response (HSR) and the unfolded protein recovery, and enhanced eIF2α phosphorylation and/or XBP1 splicing, land marks of ER stress. These H₂O₂-mediated effects mimicked enhanced heat sensitivity in HSF1 knockdown or knockout cells. Importantly, thermal preconditioning blocked H₂O₂–mediated inhibitory effects on refolding activity and rescued HSF1 +/+ MEFs, but neither blocked the effects nor rescued HSF1 -/- MEFs. These data strongly suggest that inhibition of HSR and refolding activity is crucial for H₂O₂–mediated enhanced heat sensitivity.

Conclusions

H₂O₂ blocks HSR and refolding activity under heat stress, thereby leading to insufficient quality control and enhancing ER stress. These uncontrolled stress responses may enhance cell death. Our data thus highlight oxidative stress as a crucial factor affecting heat tolerance.     

Macrophage Interaction with Paracoccidioides brasiliensis Yeast Cells Modulates Fungal Metabolism and Generates a Response to Oxidative Stress

Macrophages are key players during Paracoccidioides brasiliensis infection. However, the relative contribution of the fungal response to counteracting macrophage activity remains poorly understood. In this work, we evaluated the P. brasiliensis proteomic response to macrophage internalization. A total of 308 differentially expressed proteins were detected in P. brasiliensis during infection. The positively regulated proteins included those involved in alternative carbon metabolism, such as enzymes involved in gluconeogenesis, beta-oxidation of fatty acids and amino acids catabolism. The down-regulated proteins during P. brasiliensis internalization in macrophages included those related to glycolysis and protein synthesis. Proteins involved in the oxidative stress response in P. brasiliensis yeast cells were also up-regulated during macrophage infection, including superoxide dismutases (SOD), thioredoxins (THX) and cytochrome c peroxidase (CCP). Antisense knockdown mutants evaluated the importance of CCP during macrophage infection. The results suggested that CCP is involved in a complex system of protection against oxidative stress and that gene silencing of this component of the antioxidant system diminished the survival of P. brasiliensis in macrophages and in a murine model of infection.