Proteasome inhibition induces cytokeratin accumulation in vivo

Chronic ethanol ingestion leads to inhibition of proteasomal activity. As a consequence, proteins accumulate in liver cells. Cytokeratin accumulation as seen in alcoholic hepatitis could lead to the formation of Mallory bodies. In order to study the phenomenon of cytokeratin accumulation in liver cells, rats were fed ethanol or dextrose for 1 month and some were given the proteasome inhibitor, PS-341, to augment the inhibitory effect of ethanol feeding. This was done to study the involvement of proteasome inhibition in the process of cytokeratin accumulation. There was a marked increase in the accumulation of polyubiquitinated proteins, and heat shock proteins (hsp) 25 and 70 in the liver of rats treated with PS-341. Similarly, cytokeratin-8 (CK-8) levels were markedly increased in the liver homogenates of rats fed ethanol when given PS-341. When normal mouse cultured hepatocytes were transfected with cytokeratin-18 (CK-18) tagged with red fluorescent protein (RFP), CK-18 aggresomes formed because proteasome was overloaded. These data provide new evidence that proteasome inhibition is involved in cytokeratin accumulation, when aggresomes are formed in tissue culture. Accumulation of cytokeratin in this way may ultimately lead to Mallory body formation as seen in alcoholic hepatitis.     

The effect of ethanol-induced CYP2E1 on proteasome activity: the role of 4-hydroxynonenal

Previous studies have shown that the induction of P450 cytochrome 2E1 (CYP2E1) is associated with the loss of proteasomal activities. To correlate the loss of proteasomal activity with CYP2E1 induction, ethanol was fed intragastrically for 1, 3, 7, and 15 days. The maximum induction of CYP2E1 (3.5-fold) occurred after 15 days of ethanol feeding. However, there was no significant decrease in the 26 S chymotrypsin-like and trypsin-like activity over this period of time. When ethanol was given to rats for 1 month, CYP2E1 was significantly induced, and the proteasomal activity was significantly decreased. These results indicate that proteasomal activity was not directly affected by ethanol or CYP2E1 induction. Since 4-hydroxynonenal (4-HNE) concentration was significantly increased at 1 month of ethanol feeding, it was suspected that 4-HNE adduct formation with proteasome subunits could be the mechanism of proteasome inhibition. Using an antibody to 4-HNE adducted proteins in Western blot analysis of the 26 S proteasome fraction isolated from the liver of alcohol fed rats, one extra band appeared around 44 kDa. When the antibody to an ATPase Rpt4 was used to stain the stripped membrane, the same band that was detected with the 4-HNE antibody was detected with the Rpt4 antibody. An adduct of 4-HNE formed with the Rpt4 subunit of 26 S could impede the association of 19 S and 20 S and thus account for the observed decrease of proteasomal activity.     

Increased prooxidant production and enhanced susceptibility to glutathione depletion in HepG2 cells co-expressing HCV core protein and CYP2E1

Hepatitis C virus (HCV) and HCV core protein are hypothesized to induce hepatic oxidative stress and exacerbate injury caused by other toxins such as ethanol that induce the cytochrome P450 enzyme, CYP2E1. In the current study, the effects of HCV core protein [sequence genotype 1b, (nt 342-915)] on parameters indicative of oxidative stress were evaluated in HepG2 cells stably over expressing CYP2E1 (E47), or vector controls (C34). Stable (>10 passages) expression of HCV core protein and CYP2E1 was confirmed in clonal cell lines at the level of mRNA and immunoreactive protein. Prooxidant production, as determined by cellular oxidation of dichlorodihydrofluorescin and dihydroethidium (HE), was increased by expression of HCV core protein in the presence or absence of CYP2E1. Depletion of glutathione (GSH) with buthionine sulfoximine (BSO) enhanced prooxidant production in both C34 and E47 cells. In addition, prooxidant production was greater in BSO-treated cells expressing HCV core protein, and this effect was further enhanced in cells expressing both HCV core and CYP2E1. The CYP2E1 inhibitor, 4-methylpyrazole, could suppress increased prooxidant production in E47 cells. Finally, cells co-expressing both CYP2E1 and HCV core protein showed significantly decreased viability following GSH depletion. These studies show simultaneous expression of HCV core protein and CYP2E1 increases parameters indicative of oxidative stress as well as sensitization to cell injury induced by GSH depletion. These results support the hypothesis that enhanced injury in hepatocytes over expressing both HCV core protein and CYP2E1 is mediated by increases in oxidative stress.     

Mallory bodies formed in proteasome-depleted hepatocytes: an immunohistochemical study

Mallory bodies (MBs) are aggregates of proteins, principally cytokeratin proteins found in liver cells. They are also found in a few other cell types such as type II pneumocytes and trophoblasts. Studies on the liver thus far indicate that MBs are derived from hyperphosphorylated, heavily ubiquitinated proteins which have undergone conformational change. The aggregated protein may accumulate because of the failure of the proteasome to remove the altered proteins from the cytoplasm of liver cells. To investigate this possibility, the proteasomes were assessed immunohistochemically in individual liver cells of mice fed a drug which induced MB formation. To accelerate and enhance MB formation, cytochrome P450 2EI knockout mice were used. Proteasomes in individual cells were visualized by immunofluorescence using an antibody to a subunit of the proteasome (P25). The results showed that the groups of liver cells that had formed MBs were often partially depleted of proteasomes. These findings support the possibility that MBs formed as a result of the loss of the proteasome to remove misfolded cytokeratin proteins. Thus MBs may share their pathogenesis with other types of cellular inclusions seen where proteins aggregate in the cytoplasm due to mutation, misfolding, or loss of proteasomes.     

Protective effect of quercetin, EGCG, catechin and betaine against oxidative stress induced by ethanol in vitro

There is a need for a nontoxic antioxidant agent to be identified which will prevent alcoholic liver disease (ALD) in alcoholic patients. We tested 4 candidate agents: quercetin, EGCG, catechin and betaine, all of which occur naturally in food. HepG2 cells overexpressing CYP2E1 were subjected to arachidonic acid, iron and 100 mM ethanol with or without the antioxidant agent. All the agents prevented oxidative stress and MDA/4HNE formation induced by ethanol, except for EGCG. Catechin prevented CYP2E1 induction by ethanol. All the agents tended to down-regulate the ethanol-induced increased expression of glutathionine peroxidase 4 (GPX4). All the agents, except catechin, tended to reduce the expression of SOD2 induced by ethanol. Heat shock protein 70 was up-regulated by ethanol alone and betaine tended to prevent this. All 4 agents down-regulated the expression of Gadd45b in the presence of ethanol, which could explain the mechanism of DNA demethylation associated with the up-regulation of the gene expression observed in experimental ALD. In conclusion, the in vitro model of oxidative stress induced by ethanol provided evidence that all 4 agents tested prevented some aspect of liver cell injury caused by ethanol.     

The mechanism of cytokeratin aggresome formation: the role of mutant ubiquitin (UBB+1)

Aggresome formation in cells involves the failure of the ubiquitin-proteasome pathway to dispose of proteins destined for degradation by the 26S proteasome. UBB(+1) is present in Mallory bodies in alcoholic liver disease and in aggresomes formed in Alzheimer's desease. The present investigation focuses on the role that UBB(+1) plays in cytokeratin aggresome formation in Mallory bodies (MBs) in vitro. Immunoprecipitation with a monoclonal antibody to cytokeratin-8 (CK-8) was used. The immunoprecipitate was incubated for 24 h in the presence of different constituents involved in aggresome formation including ubiquitin, UBB(+1), the proteasome inhibitor PS341, an ATP generating energy source, a deubiquitinating enzyme inhibitor, a purified proteasome fraction, and an E(1-3) conjugating enzyme fraction. MB-like protein aggregates formed in the presence of ubiquitin, plus UBB(+1) or PS341. These aggregates stained positively for CK-8. UBB(+1), and a proteasome subunit Tbp7, as demonstrated on Western blots. A second approach was used to form MBs in vitro in cultured hepatocytes transfected with UBB(+1) protein using Chariot. The cells were double stained using CK-8 and ubiquitin antibodies. The two proteins colocalized in MB-like aggregates. The results support the possibility that aggresome formation is a complex multifactor process, which is favored by inhibition of the proteasome and by the presence of UBB(+1).     

Induction of DNA strand breaks and oxidative stress in HeLa cells by ethanol is dependent on CYP2E1 expression

Induction of cytochrome P4502E1 (CYP2E1) is considered to be an important mechanism by which ethanol can cause toxicity related to oxidative stress both in vivo and in vitro. In the current study, we used HeLa cells with doxycycline-regulated CYP2E1 expression to test the hypothesis that induction of CYP2E1 could lead to secondary DNA oxidation that could potentially contribute to the carcinogenicity of ethanol in vivo. Overexpression of CYP2E1 protein was not associated with oxidative stress per se as assessed by markers of lipid peroxidation (cis-parinaric acid oxidation), glutathione depletion and elevation of intracellular reactive oxygen species (dichlorofluoroscin oxidation) in the presence or absence of ethanol substrate (10 mM, 24 h). Furthermore, there was no evidence of elevation of frequency of DNA strand breaks as assessed by the comet assay. In contrast, however, after pre-incubation of cells with L-buthionine-(S,R)-sulphoximine (BSO, 10 microM) which caused a 75% reduction in intracellular reduced glutathione (GSH) levels, CYP2E1 expression resulted in oxidative stress as assessed by all of these markers and DNA strand breaks but only in the presence of ethanol (10 mM). No effect was observed under these conditions in control cells not expressing CYP2E1. Furthermore, these effects could be attenuated by co-incubation with 1-aminobenzotriazole (0.5 mM), a suicide inhibitor of P450 activity. In conclusion, in this in vitro model CYP2E1-mediated interaction with ethanol results in the intracellular oxidative stress and the formation of DNA strand breaks which are detectable in cells pre-sensitized by depletion of intracellular levels of GSH.     

乙醇刺激HepG2细胞分泌VASN蛋白的生物学功能研究

目的：探究乙醇对HepG2细胞VASN蛋白表达与分泌水平的影响,及其对HUVEC细胞迁移的影响。方法乙醇刺激HepG2细胞,定量PCR （ qPCR）检测HepG2细胞VASN mRNA水平的变化, Western印迹检测HepG2细胞与细胞上清中VASN蛋白水平的变化。划痕愈合实验检测细胞共培养条件下,乙醇刺激的HepG2细胞培养上清对HUVEC细胞迁移的影响。结果 qPCR结果显示,乙醇可上调HepG2细胞VASN mRNA水平。 Western印迹结果显示,细胞VASN蛋白表达与分泌水平升高。划痕愈合实验结果表明乙醇刺激HepG2细胞VASN蛋白的分泌增加,可以促进HUVEC细胞的迁移。结论乙醇刺激导致HepG2细胞VASN蛋白表达水平和分泌水平升高,并可促进与其共培养的HUVEC细胞迁移。     

A case of lung cancer with Mallory bodies]

This paper is a report of a large cell carcinoma (solid carcinoma with mucus formation-WHO) which developed in the right upper lobe of a 71-year-old woman and in which cytoplasmic Mallory body-like inclusions (MBL) similar to Mallory bodies (MB) often found in alcoholic liver disease and hepatocellular carcinoma were noted in the tumor cells. MBL was an eosinophilic massive or reticular hyalin, and showed staining properties similar to those of MB in general stainings. Electron microscopically, it was made up mainly of a fine granular amorphous substance with high electron density and was not surrounded by a membrane. A part of the margin was in close contact with filaments approximately 10 nm in diameter, with tonofibril-like structures around it, which suggested a relationship with cytokeratin. On immunoperoxidase staining using a couple of cytokeratin antibodies, definitely positive findings were not obtained with MBL themselves. MBL of this case basically has the same character as that of MBL which appears in fibrous lesions in the lung and MB in liver disease. It was concluded that it is necessary to preoperatively distinguish this entity cytologically or histologically from pulmonary metastasis of hepatocellular carcinoma.     

Sasa quelpaertensis leaves ameliorate alcohol-induced liver injury by attenuating oxidative stress in HepG2 cells and mice

Oxidative stress plays a crucial role in the progression of alcoholic liver diseases and substances of antioxidant property are of special interest for therapeutic purposes. We investigated the hepatoprotective effect of leaf extracts of Sasa quelpaertensis, an edible bamboo mainly cultivated in Jeju Island, South Korea. We examined the cytotoxicity of different extracts (distilled water, 20–80% EtOH) of S. quelpaertensis on HepG2 cells and their hepatoprotective effect on HepG2 cells stimulated by ethanol (800?mM, 24?h). Furthermore, we measured reactive oxygen species (ROS) production, ethanol toxicity induced cell death, and the activity of antioxidant enzymes. In in vivo experiments, liver damage was induced by oral administration of 5?g/kg ethanol with or without potent ethanol extract of S. quelpaertensis (10 or 100?mg/kg) 12?h interval for a total of 3 doses. Only 80% ethanol extract of S. quelpaertensis (SQEE80) exhibited cytoprotective effect on HepG2 cells against alcohol-induced toxicity. SQEE80 treatment (250, 500?μg/mL) in ethanol exposed HepG2 cells showed significant attenuation of ROS production and ethanol toxicity induced cell death. Furthermore, SQEE80 markedly increased the activity of antioxidant enzyme glutathione peroxidase 1 in ethanol exposed HepG2 cells compared to ethanol stimulated cells. In in vivo experiments, SQEE80 treatment evidently suppressed the alcohol-induced histopathological changes in liver, serum ethanol content, and expression of cytochrome P450 2E1. Furthermore, SQEE80 significantly reversed the reduction of glutathione level in the ethanol challenged liver. Taken together, we suggest the possibility of developing SQEE80 as a natural hepatoprotective substance in attenuating alcohol-induced oxidative stress.     

4-HNE通过抑制TNF-α介导的NF-κB活化诱导酒精性肝损伤

 目的：通过体外细胞及体内动物实验,研究肿瘤坏死因子α（TNF-α）诱导的4-羟基壬烯酸（4-HNE）致敏肝细胞发生死亡的作用及机制。方法：以人肝细胞株HepG2及小鼠原代肝细胞为细胞模型,通过乳酸脱氢酶（LDH）释放及MTT比色法检测4-HNE对TNF-α诱导的肝细胞死亡的作用,利用Western blotting技术检测细胞内4-HNE与蛋白质形成的加合物水平,通过Western blotting和ELISA技术检测细胞核内NF-κB（p65）的表达及其与DNA结合活性。以C57BL/6小鼠为动物模型,利用HE染色、ELISA、Western blotting及TUNEL等技术,检测长期摄入酒精前后动物肝组织形态、甘油三酯（TG）水平、4-HNE水平、TNF-α水平及血浆丙氨酸氨基转移酶（ALT）活性的变化。结果：（1） 4-HNE可以显著增加HepG2细胞及小鼠原代肝细胞对TNF-α杀伤作用的敏感性,从而使TNF-α诱导4-HNE致敏的肝细胞死亡。（2） 4-HNE可显著提高HepG2细胞内4-HNE-蛋白质加合物的水平。（3） 4-HNE抑制HepG2细胞内TNF-α介导的NF-κB活化。（4） 长期摄入酒精导致小鼠肝细胞内4-HNE和TNF-α水平升高,引起肝细胞内TG水平升高,血浆ALT活性升高,肝细胞死亡增多。结论：长期摄入酒精使肝细胞发生氧化应激,其产物4-HNE可作为一种肝细胞致敏因子,通过抑制肝细胞内TNF-α介导的NF-κB抗细胞凋亡信号通路,诱导酒精性肝损伤。这可能是一种新的酒精性肝病发病机制。     

Occurrence of Mallory body-like inclusions in parathyroid chief cells of ozone-treated dogs

Ultrastructural characteristics of chief cells of the parathyroid glands of ozone-treated dogs were examined 3 days, 10-13 days and 28 days after treatment. Dilated Golgi cisternae and vacuoles contained low electron dense fibrillar material. These changes in the Golgi were accompanied by massive accumulation of filaments in the perinuclear area where most of the cell organelles were disrupted to the peripheral zone of the filamentous inclusions. These inclusions were not enclosed by a membrane and corresponded with PAS-positive and diastase-resistant material in the chief cells at light microscopic level. Therefore these inclusions were arbitrarily designated as Mallory body-like inclusions.     

p62 Is a Common Component of Cytoplasmic Inclusions in Protein Aggregation Diseases

Exposure of cells to stress, particularly oxidative stress, leads to misfolding of proteins and, if they are not refolded or degraded, to cytoplasmic protein aggregates. Protein aggregates are characteristic features of a variety of chronic toxic and degenerative diseases, such as Mallory bodies (MBs) in hepatocytes in alcoholic and non-alcoholic steatohepatitis, neurofibrillary tangles in neurons in Alzheimer's, and Lewy bodies in Parkinson's disease. Using 2D gel electrophoresis and mass spectrometry, we identified p62 as a novel MB component. p62 and cytokeratins (CKs) are major MB constituents; HSP 70, HSP 25, and ubiquitinated CKs are also present. These proteins characterize MBs as a prototype of disease-associated cytoplasmic inclusions generated by stress-induced protein misfolding. As revealed by transfection of tissue culture cells overexpressed p62 did not induce aggregation of regular CK filaments but selectively bound to misfolded and ubiquitinated CKs. The general role of p62 in the cellular response to misfolded proteins was substantiated by detection of p62 in other cytoplasmic inclusions, such as neurofibrillary tangles, Lewy bodies, Rosenthal fibers, intracytoplasmic hyaline bodies in hepatocellular carcinoma, and alpha1-antitrypsin aggregates. The presence of p62 along with other stress proteins and ubiquitin in cytoplasmic inclusions indicates deposition as aggregates as a third line of defense against misfolded proteins in addition to refolding and degradation.     

In vitro antioxidant and protective effects of corn peptides on ethanol-induced damage in HepG2 cells

To assess the effect of corn peptides (CPs) as an antioxidant on ethanol (EtOH)-induced oxidative stress in HepG2 cells, the cells were preincubated with CPs for 4?h before treated with EtOH. Methyl thiazolyl tetrazolium and flow cytometry assay were performed to detect the viability of CP-treated HepG2 cells and control cells. The activities of lactate dehydrogenase (LDH), alanine aminotransferase (ALT), aspartate aminotransferase (AST), malondialdehyde (MDA) and superoxide dismutase (SOD) were determined by corresponding kits, respectively. The results showed that treatment with 300?mmol/L EtOH for 24?h resulted in a death of around 50% of the HepG2 cells. Pretreatments of appropriate concentrations of CPs (more than 5?mg/mL, particularly at 20?mg/mL) significantly prevented EtOH-induced cytotoxicity and reduced the increase of ALT, AST, LDH and MDA contents, as well as inhibited the reduction of SOD contents in the HepG2 cells, indicating that CPs protected the cells from oxidative damage induced by EtOH metabolism, and thus had a great application potential in hepatoprotective nutraceuticals.     

Inhibition of proteasome by bortezomib causes intracellular aggregation of hepatic serpins and increases the latent circulating form of antithrombin

Conformational diseases include heterogeneous disorders sharing a similar pathological mechanism, leading to intracellular aggregation of proteins with toxic effects. Serpins are commonly involved in these diseases. These are structurally sensitive molecules that modify their folding under even minor genetic or environmental variations. Indeed, under normal conditions, the rate of misfolding of serpins is high and unfolded serpins must be degraded by the proteasome system. Our aim was to study the effects of bortezomib, a proteasome inhibitor, on conformationally sensitive serpins. The effects of bortezomib were analysed in patients with multiple myeloma, HepG2 cells, and Swiss mice, as well as in vitro. Levels, anti-FXa activity, heparin affinity, and conformational features of antithrombin, a relevant anticoagulant serpin, were analysed. Histological, ultrastructural features and immunohistological distribution of antithrombin and alpha1-antitrypsin (another hepatic serpin) were evaluated. We also studied the intracellular accumulation of conformationally sensitive (fibrinogen) or non-sensitive (prothrombin) hepatic proteins. The inhibition of the proteasome caused intracellular accumulation and aggregation of serpins within the endoplasmic reticulum that was associated with confronting cisternae and Mallory body formation. These effects were accompanied by a heat stress response. Bortezomib also increased the levels of intracellular fibrinogen, but has no significant effect on prothrombin. Finally, bortezomib had only minor effects on the mature circulating antithrombin, with increased amounts of latent antithrombin in plasma. These results suggest that the impairment of proteasomal activities leads to an intracellular accumulation of conformationally sensitive proteins and might facilitate the release of misfolded serpins into circulation where they adopt more stable conformations.     

The proteasome inhibitor, PS-341, causes cytokeratin aggresome formation

Mallory body (MB) experimental induction takes 10 weeks of drug ingestion. Therefore, it is difficult to study the dynamics and mechanisms involved in vivo. Consequently, an in vitro study was done using primary tissue culture of hepatocytes from drug-primed mice livers in which MBs had already formed. The hypothesis to be tested was that MBs are cytokeratin aggresomes, which form when hepatocytes have a defective ubiquitin-proteasome pathway by which turnover of cytokeratin proteins is prevented. To test this hypothesis, primary tissue cultures of the hepatocytes from normal and MB-forming livers were incubated with the proteasome inhibitor PS-341 and then the cytokeratin filaments and the filament connecting proteins, that is, β-actin, and ZO1, were visualized by immunofluorescence microscopy. PS-341 caused detachment of the cytokeratins from the cell surface plasma membrane. The cytokeratin filaments retracted toward the nucleus and cytokeratin aggresomes formed. In human livers, MBs showed colocalization of cytokeratin-8 (CK-8) with ubiquitin but not with β-actin or ZO1. Mouse hepatoma cell lines were studied using PS-341 to induce cytokeratin aggresome formation. In these cell lines, the cytokeratin filaments first retracted toward the nucleus then formed cytokeratin-ubiquitin aggresomes polarized at one side of the nucleus. At the same time, the cells became dissociated from each other, however. The results simulated MB formation. MBs differ from cytokeratin aggresomes both morphologically and in ultrastructure.     

26S蛋白酶体LMP2亚基参与调节血管内皮细胞对氧化应激的耐受性形成

目的: 观察在氧化应激耐受及氧化应激损伤的血管内皮细胞(VECs) 26S蛋白酶体LMP2亚基的表达变化情况,并评价26S蛋白酶体LMP2亚基在调节VECs对氧化应激耐受性中的可能作用。方法: 建立H₂O₂诱导氧化应激损伤及氧化应激预处理VECs模型;采用细胞免疫荧光标记联合Western blotting法检测26S蛋白酶体LMP2的表达;采用脂质体Lipofectamine^TM 2000转染LMP2反义/正义寡核苷酸;检测培养上清中乳酸脱氢酶(LDH)的活性及丙二醛(MDA)的含量。结果: H₂O₂可剂量及时间依赖性地诱导VECs氧化应激损伤,培养上清中MDA浓度及LDH活性明显增加;H₂O₂(10 μmol/L, 24 h)预处理可诱导26S蛋白酶体LMP2亚基的高表达及细胞对H₂O₂ (500 μmol/L, 3 h)诱导氧化应激的耐受,培养上清中MDA浓度及LDH活性明显减少;与H₂O₂ (500 μmol/L, 3 h)处理组比较,采用干扰素γ(IFN-γ,20 μg/L, 48 h)可诱导VECs 26S蛋白酶体LMP2亚基高表达,也可诱导VECs对H₂O₂的耐受,其培养上清中MDA浓度及LDH活性明显降低,而转染LMP2-反义寡核苷酸可抑制IFN-γ诱导的培养上皮细胞26S蛋白酶体LMP2亚基高表达并阻断细胞对H₂O₂ (500 μmol/L, 3 h)的耐受。结论: 26S蛋白酶体LMP2亚基参与VECs对氧化应激耐受性的形成。