乙型肝炎病毒X基因对肝细胞凋亡的影响及其作用机制

乙型肝炎病毒X基因（HBx）在HBV慢性感染导致肝硬化，原发性肝癌（HCC）的发生过程中，起着重要的作用。X连锁凋亡抑制因子（XIAP）为凋亡抑制蛋白（IAPs）家族成员，是一种强效的凋亡抑制蛋白，可以抑制半胱氨酸蛋白酶活性，阻断细胞凋亡过程。我们观察了肝癌细胞株以及正常肝细胞株在转染HBx前后凋亡抑制蛋白XIAP表达的差异，了解和分析HBx对不同肝细胞系细胞凋亡的作用及其是否与凋亡抑制蛋白XIAP基因相关。     

乙型肝炎病毒X蛋白在原发性肝癌中的作用

乙型肝炎病毒X蛋白(HBx)是一种由HBV X基因编码的多功能蛋白,参与调节基因转录、细胞信号转导、细胞增殖转化、细胞周期和细胞凋亡。目前HBx蛋白被认为在HBV诱发原发性肝癌的过程中发挥重要作用。介绍了HBx蛋白与癌基因、抑癌基因、细胞增殖、细胞凋亡、肝癌侵袭转移和肝癌干细胞的关系,探讨了HBx蛋白在肝癌发生发展中的作用。     

乙型肝炎病毒Ⅹ基因对肝细胞凋亡的影响及其作用机制

乙型肝炎病毒X基因(HBx)在HBV慢性感染导致肝硬化,原发性肝癌(HCC)的发生过程中,起着重要的作用[1].X连锁凋亡抑制因子(XIAP)为凋亡抑制蛋白(IAPs)家族成员,是一种强效的凋亡抑制蛋白,可以抑制半胱氨酸蛋白酶活性,阻断细胞凋亡过程[2].我们观察了肝癌细胞株以及正常肝细胞株在转染HBx前后凋亡抑制蛋白XIAP表达的差异,了解和分析HBx对不同肝细胞系细胞凋亡的作用及其是否与凋亡抑制蛋白XIAP基因相关.     

乙型肝炎病毒x蛋白致线粒体功能障碍相关机制研究进展

乙型肝炎病毒x(hepatitis B x,HBx)蛋白是由乙型肝炎病毒(hepatitis B virus,HBV)所编码的一种多功能蛋白,在慢性乙型肝炎、肝硬化及肝癌发生过程中发挥着不可忽视的作用。x蛋白可定位于线粒体,并通过多种途径致线粒体结构改变,进而引起肝细胞线粒体功能障碍,最终导致肝细胞炎症及肿瘤的发生。HBx致线粒体功能障碍已成为国内外学者的研究热点,本文就目前已知HBx的结构功能及HBx致线粒体功能障碍的可能机制研究进展作一概述。     

自噬与氧化应激对青光眼视神经损伤的调节作用研究进展

视网膜神经节细胞（RGCs）具有长轴突和高密度线粒体,因而对氧化应激更加敏感。细胞内产生的活性氧（ROS）与青光眼的发病机制密切相关。自噬是细胞内一种质量控制系统,可以去除氧化的细胞成分,维持细胞稳态。在各种青光眼视神经损害模型中,氧化应激被激活,ROS通过雷帕霉素靶蛋白通路启动自噬;接着自噬通过促进RGCs线粒体自噬和抗氧化反应减少ROS的积聚。然而当视神经中仍有过量的ROS则会抑制自噬发生,因为多余的ROS会破坏线粒体功能、氧化自噬相关蛋白和降低自噬溶酶体活性,导致青光眼视神经的变性。ROS与自噬相互影响,二者共同参与青光眼视神经损害过程。     

氧化应激与自噬相互作用的分子机制

<正>氧化应激是指体内氧化超过抗氧化的作用,导致蛋白及脂质的氧化损伤以及细胞损伤等。自噬是一个细胞自身结构通过溶酶体机制被降解的过程,帮助细胞维持生理功能的平衡。在近几年的研究中表明,氧化还原与自噬之间有紧密的联系。1氧化应激损伤氧化应激是由自由基对脱氧核糖核酸(DNA)、脂质和蛋白质等产生氧化损伤、从而导致衰老和神经退行性病变〔1〕。氧化蛋白质,脂质和DNA的氧化均与活性氧(ROS)有关〔2〕。此外,     

乙型肝炎病毒HBx蛋白及其下游因子在肝癌细胞中的表达

乙型肝炎病毒HBx蛋白通过多条信号通路参与DNA修复和基因激活,并可调节细胞增殖、凋亡及诱导细胞迁移等,在HBV相关肝细胞癌(HCC)发生过程中发挥重要作用[1,2].核因子κ B(NF-κB)作为一个重要的转录因子,参与细胞调节的多个阶段和抗凋亡基因表达[3].我们回顾分析了HBx蛋白、NF-κB和凋亡增殖相关因子在HBV相关HCC中的作用.     

乙型肝炎病毒X蛋白增强人血管生成因子b FGF基因启动子转录活性

目的 检测乙型肝炎病毒X蛋白（hepatitis B virus X protein, HBx）对人血管生成因子bFGF基因转录的激活作用并确定其作用于bFGF基因启动子的区域,分析HBx激活bFGF基因转录可能的分子机制,为揭示HBx促进肝癌发生的分子机制及发现新的治疗靶点。方法 运用高保真DNA聚合酶从人肝癌HepG2细胞cDNA文库中扩增出bFGF基因启动子DNA序列;从含完整HBV DNA序列的表达载体中扩增HBx编码序列并克隆入真核表达载体p CDNA3-FLAG中,将HBx表达载体转染人肝癌HepG2细胞中,裂解细胞进行蛋白SDS-PAGE电泳,Western blot检测HBx蛋白的表达;将HBx表达载体和含bFGF基因启动子不同区段的荧光素酶报告载体共转染肝癌HepG2和SMMC-7721细胞,检测HBx对bFGF基因启动子转录活性的影响;运用Western blot检测在肝癌细胞中HBx过表达对ERK磷酸化的影响。结果 成功克隆了HBx并使其在肝癌细胞中得到表达;成功克隆了bFGF基因启动子2.2 kb、1.4 kb、720 bp和360 bp的区段;在肝癌细胞SMM...     

B、C基因型乙型肝炎病毒X蛋白在果蝇细胞中的表达与纯化

目的获得高纯度B、C基因型乙型肝炎病毒X蛋白（HBx蛋白）。方法PCR扩增获得B、C基因型乙型肝炎病毒X基因,以AgeⅠ及BglⅡ位点将其克隆入果蝇表达载体pMT/BiP/V5/HisC。重组载体与筛选质粒pCoBlast以脂质体Cellfectine共转染果蝇S2细胞,25μg/ml Blasticidin筛选多克隆抗性细胞株。扩增细胞以CuSO4诱导HBx蛋白表达,Western blot鉴定表达产物并确定最佳蛋白表达时间和诱导浓度。200 ml大规模培养细胞并诱导表达,一步法及两步法分别纯化B、C基因型HBx蛋白。结果成功构建重组表达载体pMT/BiP-HBxb（含B基因型HBx基因）和pMT/BiP-HBxc（含C基因型HBx基因）。在果蝇S2细胞中,B、C基因型HBx蛋白与6×His融合表达（分别为HBxb-His及HBxc-His）,在CuSO4诱导后72 h以及诱导浓度为500μmol/L~1 mmol/L时蛋白表达量最高。在200 ml培养液中,一步法纯化所得HBxb-His及HBxc-His蛋白总量分别为1.52和1.37 mg,纯度为85.23%和84.59%;二步法所得的HBxb-His及HBxc-His蛋白总量分别为5.38和6.42 mg,纯度分别为95.36%和94.62%。结论在果蝇表达系统中表达并获得高纯度B、C基因型乙型肝炎病毒X蛋白,为进一步探讨结构和功能的关系奠定了基础。     

慢病毒-HBx表达载体的构建及其在人正常肝细胞系Chang liver的稳定表达

目的:构建乙型肝炎病毒X基因(hepatitis B virus x,HBx)慢病毒表达载体,建立稳定表达HBx蛋白的人正常肝细胞系Chang liverHBx.方法:应用聚合酶链式反应(polymerase chain reaction,PCR)方法从质粒中扩增HBx基因,并克隆到慢病毒p EB-3xflag-GP-Puro载体上,经PCR、酶切和测序鉴定正确后经慢病毒包装感染人肝细胞Chang liver,再用嘌呤霉素筛选出稳定表达HBx蛋白的细胞株,最后用免疫荧光和Western blot技术检测HBx蛋白的表达.结果:酶切鉴定和基因测序证实HBx基因成功克隆到慢病毒表达载体上,重组慢病毒经包装纯化后获得滴度为1×108 TU/m L,用包装好的重组慢病毒感染人肝细胞Chang liver,经嘌呤霉素筛选获得单克隆细胞株Chang liver-HBx,利用免疫荧光和Western blot技术检测发现细胞株Chang liver-HBx可稳定表达HBx蛋白.结论:成功构建了HBx的重组慢病毒表达载体,获得了稳定表达HBx的Chang liver细胞系Chang liver-HBx,为进一步研究HBx诱导正常肝细胞恶性转化提供细胞模型.     

Alterations of antioxidant enzymes and oxidative stress markers in aging

In accordance with the present state of scientific knowledge, the excessive production of free radicals in the organism, and the imbalance between the concentrations of these and the antioxidant defenses may be related to processes such as aging and several diseases. The aging process has been described by various theories. In particular, the free radical theory of aging has received widespread attention which proposes that deleterious actions of free radicals are responsible for the functional deterioration associated with aging. Although, the relationship between lipid peroxidation and aging have been investigated extensively, the studies have produced conflicting results. To investigate the correlation between the oxidative stress and aging, we have determined the levels of lipid peroxidation expressed as thiobarbituric acid reactive substances (TBARS; MDA) and conjugated dien; oxidative protein damage as indicated by carbonyl content and activities of antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) in a sample of 100 healthy men and women ranging in age from 20 to 70years. In addition, vitamin E, C levels, reduced glutathione and sulphydryl content were determined. The oxidation end product of nitric oxide (nitrate) was also studied to investigate any role of nitrogen radicals in aging. Our data show that there is an age related increase in lipid peroxidation expressed as MDA and oxidative protein damage as indicated by carbonyl content. Aging is not linked to a decline in antioxidant enzymes except GPx. Our data suggests that the level of oxidative stress increase cannot entirely be attributed to a decrease in the activities of antioxidant defense system and probably various factors may contribute to this process.     

One molecule,many derivatives: A never-ending interaction of melatonin with reactive oxygen and nitrogen species?

Melatonin is a highly conserved molecule. Its presence can be traced back to ancient photosynthetic prokaryotes. A primitive and primary function of melatonin is that it acts as a receptor-independent free radical scavenger and a broad-spectrum antioxidant. The receptor-dependent functions of melatonin were subsequently acquired during evolution. In the current review, we focus on melatonin metabolism which includes the synthetic rate-limiting enzymes, synthetic sites, potential regulatory mechanisms, bioavailability in humans, mechanisms of breakdown and functions of its metabolites. Recent evidence indicates that the original melatonin metabolite may be N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK) rather than its commonly measured urinary excretory product 6-hydroxymelatonin sulfate. Numerous pathways for AFMK formation have been identified both in vitro and in vivo. These include enzymatic and pseudo-enzymatic pathways, interactions with reactive oxygen species (ROS)/reactive nitrogen species (RNS) and with ultraviolet irradiation. AFMK is present in mammals including humans, and is the only detectable melatonin metabolite in unicellular organisms and metazoans. 6-hydroxymelatonin sulfate has not been observed in these low evolutionary-ranked organisms. This implies that AFMK evolved earlier in evolution than 6-hydroxymelatonin sulfate as a melatonin metabolite. Via the AFMK pathway, a single melatonin molecule is reported to scavenge up to 10 ROS/RNS. That the free radical scavenging capacity of melatonin extends to its secondary, tertiary and quaternary metabolites is now documented. It appears that melatonin's interaction with ROS/RNS is a prolonged process that involves many of its derivatives. The process by which melatonin and its metabolites successively scavenge ROS/RNS is referred as the free radical scavenging cascade. This cascade reaction is a novel property of melatonin and explains how it differs from other conventional antioxidants. This cascade reaction makes melatonin highly effective, even at low concentrations, in protecting organisms from oxidative stress. In accordance with its protective function, substantial amounts of melatonin are found in tissues and organs which are frequently exposed to the hostile environmental insults such as the gut and skin or organs which have high oxygen consumption such as the brain. In addition, melatonin production may be upregulated by low intensity stressors such as dietary restriction in rats and exercise in humans. Intensive oxidative stress results in a rapid drop of circulating melatonin levels. This melatonin decline is not related to its reduced synthesis but to its rapid consumption, i.e. circulating melatonin is rapidly metabolized by interaction with ROS/RNS induced by stress. Rapid melatonin consumption during elevated stress may serve as a protective mechanism of organisms in which melatonin is used as a first-line defensive molecule against oxidative damage. The oxidative status of organisms modifies melatonin metabolism. It has been reported that the higher the oxidative state, the more AFMK is produced. The ratio of AFMK and another melatonin metabolite, cyclic 3-hydroxymelatonin, may serve as an indicator of the level of oxidative stress in organisms.     

Melatonin: a well‐documented antioxidant with conditional pro‐oxidant actions

Melatonin (N‐acetyl‐5‐methoxytryptamine), an indoleamine produced in many organs including the pineal gland, was initially characterized as a hormone primarily involved in circadian regulation of physiological and neuroendocrine function. Subsequent studies found that melatonin and its metabolic derivatives possess strong free radical scavenging properties. These metabolites are potent antioxidants against both ROS (reactive oxygen species) and RNS (reactive nitrogen species). The mechanisms by which melatonin and its metabolites protect against free radicals and oxidative stress include direct scavenging of radicals and radical products, induction of the expression of antioxidant enzymes, reduction of the activation of pro‐oxidant enzymes, and maintenance of mitochondrial homeostasis. In both in vitro and in vivo studies, melatonin has been shown to reduce oxidative damage to lipids, proteins and DNA under a very wide set of conditions where toxic derivatives of oxygen are known to be produced. Although the vast majority of studies proved the antioxidant capacity of melatonin and its derivatives, a few studies using cultured cells found that melatonin promoted the generation of ROS at pharmacological concentrations (μm to mm range) in several tumor and nontumor cells; thus, melatonin functioned as a conditional pro‐oxidant. Mechanistically, melatonin may stimulate ROS production through its interaction with calmodulin. Also, melatonin may interact with mitochondrial complex III or mitochondrial transition pore to promote ROS production. Whether melatonin functions as a pro‐oxidant under in vivo conditions is not well documented; thus, whether the reported in vitro pro‐oxidant actions come into play in live organisms remains to be established.     

Hepatoprotective actions of melatonin: possible mediation by melatonin receptors

Melatonin,the hormone of darkness and messenger of the photoperiod,is also well known to exhibit strong direct and indirect antioxidant properties. Melatonin has previously been demonstrated to be a powerful organ protective substance in numerous models of injury; these beneficial effects have been attributed to the hormone’s intense radical scavenging capacity. The present report reviews the hepatoprotective potential of the pineal hormone in various models of oxidative stress in vivo,and summarizes the extensive literature showing that melatonin may be a suitable experimental substance to reduce liver damage after sepsis,hemorrhagic shock,ischemia/reperfusion,and in numerous models of toxic liver injury. Melatonin’s influence on hepatic antioxidant enzymes and other potentially relevant pathways,such as nitric oxide signaling,hepatic cytokine and heat shock protein expression,are evaluated. Based on recent literature demonstrating the functional relevance of melatonin receptor activation for hepatic organ protection,this article finally suggests that melatonin receptors could mediate the hepatoprotective actions of melatonin therapy.     

Melatonin protects SK-N-SH neuroblastoma cells from amphetamine-induced neurotoxicity

Several hypotheses regarding the mechanism underlying amphetamine-induced neurotoxicity have been proposed. One of them is based on the observation of free radical formation and oxidative stress produced by auto-oxidation of dopamine (DA). The formation of DA-related reactive oxygen species (ROS) such as superoxide and hydroxyl radicals appears to play an important role in amphetamine-induced neurotoxicity. Melatonin, the main secretory product of pineal gland, is well known for its protective effects that are currently attributed mainly to its radical scavenging and antioxidant properties. The present study was conducted to investigate the protective effects of melatonin on d-amphetamine (AMPH)-induced neurotoxicity in cultured human dopaminergic neuroblastoma SK-N-SH cells. Our data indicate that AMPH significantly reduces cell viability, induces oxidative stress (enhances ROS production and malondialdehyde levels), up-regulates alpha-synuclein expression and decreases intracellular ATP levels. However, pretreatment of SK-N-SH cells with melatonin prevents AMPH-induced loss of cell viability and induction of oxidative stress, while reducing alpha-synuclein expression and increasing ATP production. These results suggest that the antioxidant properties of melatonin may provide a protective mechanism against AMPH-induced neuronal degeneration.     

Hepatitis B Virus HBx Protein Interactions with the Ubiquitin Proteasome System

The hepatitis B virus (HBV) causes acute and chronic hepatitis, and the latter is a major risk factor for the development of hepatocellular carcinoma (HCC). HBV encodes a 17-kDa regulatory protein, HBx, which is required for virus replication. Although the precise contribution(s) of HBx to virus replication is unknown, many viruses target cellular pathways to create an environment favorable for virus replication. The ubiquitin proteasome system (UPS) is a major conserved cellular pathway that controls several critical processes in the cell by regulating the levels of proteins involved in cell cycle, DNA repair, innate immunity, and other processes. We summarize here the interactions of HBx with components of the UPS, including the CUL4 adaptor DDB1, the cullin regulatory complex CSN, and the 26S proteasome. Understanding how these protein interactions benefit virus replication remains a challenge due to limited models in which to study HBV replication. However, studies from other viral systems that similarly target the UPS provide insight into possible strategies used by HBV.     

Peripheral non-enzymatic antioxidant changes with human aging: A selective status report

Oxidative stress is thought to be involved in the agingprocess in aerobic organisms and to play a role in thepathogenesis of several disease states. Since free radicals areextremely reactive, shortly half-lived and therefore verydifficult to measure directly, oxidative stress has been mainlystudied through the search of indirect biomarkers of freeradical-induced damage. In aerobic organisms, oxidative damage totissues and organs is prevented by a network of defenses whichincludes antioxidant and repairing enzymes as well as smallmolecules with scavenging ability, such as antioxidant vitamins.For these reasons, the assay of antioxidant vitamins and of smallmolecular free radical scavengers in biological milieus may beused, if appropriately performed, to quantify the defense statusagainst oxidative damage and to provide an indirect estimate offree radical production in aging humans. Since severalconflicting data have been reported in this area, this review isaimed to summarize the existing evidence and possible faults ofthe research focusing on the role of plasma concentrations ofsmall-molecular, non-enzymatic antioxidants in the process ofsenescence in healthy humans.     

Melatonin: an ancient molecule that makes oxygen metabolically tolerable

Melatonin is remarkably functionally diverse with actions as a free radical scavenger and antioxidant, circadian rhythm regulator, anti‐inflammatory and immunoregulating molecule, and as an oncostatic agent. We hypothesize that the initial and primary function of melatonin in photosynthetic cyanobacteria, which appeared on Earth 3.5–3.2 billion years ago, was as an antioxidant. The evolution of melatonin as an antioxidant by this organism was necessary as photosynthesis is associated with the generation of toxic‐free radicals. The other secondary functions of melatonin came about much later in evolution. We also surmise that mitochondria and chloroplasts may be primary sites of melatonin synthesis in all eukaryotic cells that possess these organelles. This prediction is made on the basis that mitochondria and chloroplasts of eukaryotes developed from purple nonsulfur bacteria (which also produce melatonin) and cyanobacteria when they were engulfed by early eukaryotes. Thus, we speculate that the melatonin‐synthesizing actions of the engulfed bacteria were retained when these organelles became mitochondria and chloroplasts, respectively. That mitochondria are likely sites of melatonin formation is supported by the observation that this organelle contains high levels of melatonin that are not impacted by blood melatonin concentrations. Melatonin has a remarkable array of means by which it thwarts oxidative damage. It, as well as its metabolites, is differentially effective in scavenging a variety of reactive oxygen and reactive nitrogen species. Moreover, melatonin and its metabolites modulate a large number of antioxidative and pro‐oxidative enzymes, leading to a reduction in oxidative damage. The actions of melatonin on radical metabolizing/producing enzymes may be mediated by the Keap1‐Nrf2‐ARE pathway. Beyond its direct free radical scavenging and indirect antioxidant effects, melatonin has a variety of physiological and metabolic advantages that may enhance its ability to limit oxidative stress.