Gene expression changes associated with the endoplasmic reticulum stress response induced by microsomal cytochrome p450 overproduction

Production of perillic acid from orange essential oil by Yarrowia lipolytica using a top-aerated bioreactor

R-(+)-Perillic acid, a promising anticancer and immunomodulatory agent, is the major product from the biotransformation of R-(+)-limonene-rich orange essential oil by the yeast Yarrowia lipolytica. Due to the abundance and low cost of orange essential oil, which is a byproduct of the citrus industry, we attempted to improve the biotransformation process by optimizing yeast cell mass production. Then, the whole process was transposed and adapted to a 2-L instrumented bioreactor. Cell mass production was optimized in shaker flasks using a statistical experimental design. The optimized medium (g·L-1: 22.9 glucose, 7.7 peptone, 4.1 yeast extract and 1.0 malt extract) resulted in a 13.0 g·L-1 final cell concentration and 0.18 g cell·L-1·h-1 productivity. A further increase to 18.0 g·L-1 was achieved in a 2-L bioreactor upon fed-batch culture. High-purity limonene bioconversion was performed in the same bioreactor utilizing top aeration to diminish terpene volatilization; as a result, 839.6 mg·L-1 perillic acid accumulated after 48 h. Under the same conditions, industrial orange essential oil afforded 806.4 mg·L-1 perillic acid. The yeast growth medium optimization resulted in a twofold increase in biomass accumulation and a reduction in growth medium nitrogen sources, which lowered the catalytic biomass production cost. Compared with conventional bottom aeration, the bioreactor top aeration strategy resulted in higher bioconversion rates. The conditions developed for high-purity limonene bioconversion were successfully applied to low-cost orange essential oil, showing the robustness of Y. lipolytica yeast.

Pathogenic mechanisms and regulatory factors involved in alcoholic liver disease

Alcoholism is a widespread and damaging behaviour of people throughout the world. Long-term alcohol consumption has resulted in alcoholic liver disease (ALD) being the leading cause of chronic liver disease. Many metabolic enzymes, including alcohol dehydrogenases such as ADH, CYP2E1, and CATacetaldehyde dehydrogenases ALDHsand nonoxidative metabolizing enzymes such as SULT, UGT, and FAEES, are involved in the metabolism of ethanol, the main component in alcoholic beverages. Ethanol consumption changes the functional or expression profiles of various regulatory factors, such as kinases, transcription factors, and microRNAs. Therefore, the underlying mechanisms of ALD are complex, involving inflammation, mitochondrial damage, endoplasmic reticulum stress, nitrification, and oxidative stress. Moreover, recent evidence has demonstrated that the gut-liver axis plays a critical role in ALD pathogenesis. For example, ethanol damages the intestinal barrier, resulting in the release of endotoxins and alterations in intestinal flora content and bile acid metabolism. However, ALD therapies show low effectiveness. Therefore, this review summarizes ethanol metabolism pathways and highly influential pathogenic mechanisms and regulatory factors involved in ALD pathology with the aim of new therapeutic insights.

Involvement of endoplasmic reticulum stress in rifampicin-induced liver injury

Rifampicin is a first-line antituberculosis drug. Hepatocyte toxicity caused by rifampicin is a significant clinical problem. However, the specific mechanism by which rifampicin causes liver injury is still poorly understood. Endoplasmic reticulum (ER) stress can have both protective and proapoptotic effects on an organism, depending on the environmental state of the organism. While causing cholestasis and oxidative stress in the liver, rifampicin also activates ER stress in different ways, including bile acid accumulation and cytochrome p450 (CYP) enzyme-induced toxic drug metabolites via pregnane X receptor (PXR). The short-term stress response helps the organism resist toxicity, but when persisting, the response aggravates liver damage. Therefore, ER stress may be closely related to the “adaptive” mechanism and the apoptotic toxicity of rifampicin. This article reviews the functional characteristics of ER stress and its potentially pathogenic role in liver injury caused by rifampicin.

The toxic effects of titanium dioxide nanoparticles on plasma glucose metabolism are more severe in developing mice than in adult mice

Titanium dioxide nanoparticles (TiO₂ NPs) are authorized food additives, and children have the highest exposure. Therefore, children are likely more susceptible to the adverse effects of TiO₂ NPs than adults. Previous study showed that oral administration of 50 mg/kg body weight (bw) TiO₂ NPs increase plasma glucose in mice. However, few studies have directly compared the adverse effects of exposure to TiO₂ NPs on plasma glucose metabolism of different age groups. In this study, the developing (age 3 weeks) and adult mice (age 10 weeks) were orally administered with 50 mg/kg bw TiO₂ NPs per day. The TiO₂ NPs induced hyperglycemia earlier in the developing mice than in the adult mice. Then mechanisms were analyzed after mice were oral administration of TiO2 NPs for 8 weeks and 26 weeks, respectively. Results showed that the treatment with TiO₂ NPs activated xenobiotic biodegradation in livers of both developing and adult mice at the early stage. However, only in the developing mice, TiO₂ NPs induced endoplasmic reticulum (ER) stress in livers and increased reactive oxygen species in livers and sera in the early stage. The ER stress and ROS activated an inflammation response and mitogen-activated protein kinase pathways, thereby inducing insulin resistance in the livers of developing mice at the early stage. The response of the adult mice was delayed, and these changes were observed in the late stage of the study. The results of this study all suggest that children are more susceptible than adults to the toxicity of orally administered TiO₂ NPs.

Histological, biochemical and transcriptomic analyses reveal liver damage in zebrafish (Danio rerio) exposed to phenanthrene

Phenanthrene (PHE) is a common polycyclic aromatic hydrocarbon (PAH) in aquatic environments, and this contaminant can cause adverse effects on teleostean performance. In this study, we exposed the model freshwater fish (zebrafish; Danio rerio) to 300 μg/L PHE for 15 days. Histological analysis demonstrated that liver morphology deteriorated in PHE-exposed zebrafish, and cellular damage in the liver increased. Biological analysis revealed that exposure to PHE elicited significant changes in glutathione S-transferases (GST) and superoxide dismutase (SOD) activities. 476 differentially expressed genes (DEGs) were identified in liver between control and PHE treated groups through the transcriptomic analysis. Gene Ontology enrichment analysis (GO) suggested that PHE exposure induced changes in the expression of genes associated with "lipid transporter activity", "catalytic activity", "metal ion binding", "lipid transport" and "transmembrane transport". Furthermore, the "vitamin digestion and absorption" and "fat digestion and absorption" pathways enriched in Kyoto Encyclopedia of Genes and Genomes analysis (KEGG). Additionally, five candidate biomarkers associated with the PHE response in zebrafish were identified. In conclusion, our results elucidate the physiological and molecular responses to PHE exposure in the liver of zebrafish, and provide a framework for further studies of the mechanisms underlying the toxic effects of polycyclic aromatic hydrocarbons (PAHs) on aquatic organisms.

Regulation of the ER stress response by a mitochondrial microprotein

Cellular homeostasis relies on having dedicated and coordinated responses to a variety of stresses. The accumulation of unfolded proteins in the endoplasmic reticulum (ER) is a common stress that triggers a conserved pathway called the unfolded protein response (UPR) that mitigates damage, and dysregulation of UPR underlies several debilitating diseases. Here, we discover that a previously uncharacterized 54-amino acid microprotein PIGBOS regulates UPR. PIGBOS localizes to the mitochondrial outer membrane where it interacts with the ER protein CLCC1 at ER–mitochondria contact sites. Functional studies reveal that the loss of PIGBOS leads to heightened UPR and increased cell death. The characterization of PIGBOS reveals an undiscovered role for a mitochondrial protein, in this case a microprotein, in the regulation of UPR originating in the ER. This study demonstrates microproteins to be an unappreciated class of genes that are critical for inter-organelle communication, homeostasis, and cell survival.

Cells trigger an unfolded protein response (UPR) in the endoplasmic reticulum, but its regulation by mitochondria is unclear. Here, the authors report a 54-residue microprotein PIGBOS that participates in inter-organelle contact between the endoplasmic reticulum and the mitochondria and may regulate UPR.

Sec61β facilitates the maintenance of endoplasmic reticulum homeostasis by associating microtubules

Sec61β, a subunit of the Sec61 translocon complex, is not essential in yeast and commonly used as a marker of endoplasmic reticulum (ER). In higher eukaryotes, such as Drosophila, deletion of Sec61β causes lethality, but its physiological role is unclear. Here, we show that Sec61β interacts directly with microtubules. Overexpression of Sec61β containing small epitope tags, but not a RFP tag, induces dramatic bundling of the ER and microtubule. A basic region in the cytosolic domain of Sec61β is critical for microtubule association. Depletion of Sec61β induces ER stress in both mammalian cells and Caenorhabditis elegans, and subsequent restoration of ER homeostasis correlates with the microtubule binding ability of Sec61β. Loss of Sec61β causes increased mobility of translocon complexes and reduced level of membrane-bound ribosomes. These results suggest that Sec61β may stabilize protein translocation by linking translocon complex to microtubule and provide insight into the physiological function of ER-microtubule interaction.

Structural reorganization of the fungal endoplasmic reticulum upon induction of mycotoxin biosynthesis

Compartmentalization of metabolic pathways to particular organelles is a hallmark of eukaryotic cells. Knowledge of the development of organelles and attendant pathways under different metabolic states has been advanced by live cell imaging and organelle specific analysis. Nevertheless, relatively few studies have addressed the cellular localization of pathways for synthesis of fungal secondary metabolites, despite their importance as bioactive compounds with significance to medicine and agriculture. When triggered to produce sesquiterpene (trichothecene) mycotoxins, the endoplasmic reticulum (ER) of the phytopathogenic fungus Fusarium graminearum is reorganized both in vitro and in planta. Trichothecene biosynthetic enzymes accumulate in organized smooth ER with pronounced expansion at perinuclear- and peripheral positions. Fluorescence tagged trichothecene biosynthetic proteins co-localize with the modified ER as confirmed by co-fluorescence and co-purification with known ER proteins. We hypothesize that changes to the fungal ER represent a conserved process in specialized eukaryotic cells such as in mammalian hepatocytes and B-cells.

ENDOPLASMIC RETICULUM STRESS IN SEPSIS

Sepsis is an enormous public health issue and the leading cause of death in critically ill patients in intensive care units. Overwhelming inflammation, characterized by cytokine storm, oxidative threats, and neutrophil sequestration, is an underlying component of sepsis-associated organ failure. Despite recent advances in sepsis research, there is still no effective treatment available beyond the standard of care and supportive therapy. To reduce sepsis-related mortality, a better understanding of the biological mechanism associated with sepsis is essential. Endoplasmic reticulum (ER), a subcellular organelle, is responsible for the facilitation of protein folding and assembly and involved in several other physiological activities. Under stress and inflammatory conditions, ER loses homeostasis in its function, which is termed ER stress. During ER stress, unfolded protein response (UPR) is activated to restore ER function to its normal balance. However, once stress is beyond the compensatory capacity of UPR or protracted, apoptosis would be initiated by triggering cell injuries, even cell death. As such, ER stress and UPR are reported to be implicated in several pathological and inflammatory conditions. Although the detrimental role of ER stress during infections has been demonstrated, there is growing evidence that ER stress participates in the pathogenesis of sepsis. In this review, we summarize current research in the context of ER stress and UPR signaling associated with sepsis and its related clinical conditions, such as trauma-hemorrhage and ischemia/reperfusion injury. We also discuss the potential implications of ER stress as a novel therapeutic target and prognostic marker in patients with sepsis.

Hepatic Overexpression of GRP94 in a Rabbit Model of Parenteral Nutrition-Associated Liver Disease

Objective. To use a rabbit model of parenteral nutrition-associated liver disease (PNALD) to study changes of the endoplasmic reticulum stress (ERS) marker glucose regulatory protein 94 (GRP94) and determine its role in the pathogenesis of PNALD. Methods. A rabbit PNALD model total parenteral nutrition (TPN) group was established. A corresponding control group received breast-feeding for one week. Serum biochemical parameters were measured and liver histological examinations were performed. The level of GRP94 mRNA and protein were measured. Results. The results showed that the serum TBIL, DBIL, and γ-GT levels in the TPN group were significantly higher than those in the control group, while levels of serum ALB in TPN group were significantly lower than those in the control group. The immunohistochemistry results showed that the protein expression level of GRP94 in the liver of TPN group was significantly increased compared with the control group. The RT-PCR results showed that the level of GRP94 mRNA in the liver of the TPN group was significantly higher compared with the control group. Conclusions. The mRNA and protein levels of GRP94 in the TPN group were both significantly increased, indicating that ERS may be directly related to the occurrence and development of PNALD.

ER reorganization is remarkably induced in COS-7 cells accumulating transmembrane protein receptors not competent for export from the endoplasmic reticulum

The newly synthesized mutant L501fsX533 Frizzled-4 form and the alpha3beta4 nicotinic acetylcholine receptor expressed in the absence of nicotine accumulate in the endoplasmic reticulum of COS-7 cells and induce the formation of large areas of smooth and highly convoluted cisternae. This results in a generalized block of the transport to the Golgi complex of newly synthesized proteins. Intriguingly, both effects happen peculiarly in COS-7 cells; HeLa, Huh-7, and HEK293 cells expressing the two receptors at similar level than COS-7 cells show normal ER and normal transport toward the plasma membrane. These results question the conclusion that a dominant-negative mechanism would explain the dominance of the mutant L501fsX533 Fz4 allele in the transmission of a form of Familial exudative vitreoretinopathy. Moreover, they indicate that the coordination of endoplasmic reticulum homeostasis in COS-7 cells is particularly error prone. This finding suggests that COS-7 cells may be extremely useful to study the molecular mechanisms regulating endoplasmic reticulum size and architecture.

Elimination of endoplasmic reticulum stress and cardiovascular, type 2 diabetic, and other metabolic diseases

Multiple factors including unhealthy living habits influence the life-maintaining functions of the endoplasmic reticulum (ER) and induce ER stress and metabolic abnormalities. The ER responds to the disturbances by activating mechanisms that increase the capacity to eliminate ER stress. This article elucidates the effects of ER activation that eliminates both ER stress and associated cardiovascular, type 2 diabetic (DM2), and other metabolic diseases. ER-activating compounds eliminate ER stress by lowering elevated cholesterol, regress atherosclerosis, decrease cardiovascular mortality, reduce blood glucose and insulin, and, together with the normalization of glucose-insulin homeostasis, remove insulin resistance, pancreatic β-cell failure, and DM2. A deficient cytochrome P450 activity in hepatic ER leads to cholesterol accumulation that induces stress and xanthoma formation, whereas P450-activating therapy up-regulates apolipoprotein AI and LDLR genes, down-regulates apolipoprotein B gene, and produces an antiatherogenic plasma lipoprotein profile. The ER activation reduces the stress also by eliminating hepatic fat and converting saturated fatty acids (FAs) to unsaturated FAs. Cognitive processes require gene expression modification, and preclinical studies indicate that ER-activating therapy improves cognition. Promotion of healthy lifestyle choices and indicated therapies are key factors in the prevention and elimination of ER stress and associated global health problems.

Identification of the nanogold particle-induced endoplasmic reticulum stress by omic techniques and systems biology analysis

Growth inhibition and apoptotic/necrotic phenotype was observed in nanogold particle (AuNP)-treated human chronic myelogenous leukemia cells. To elucidate the underlying cellular mechanisms, proteomic techniques including two-dimensional electrophoresis/mass spectrometry and protein microarrays were utilized to study the differentially expressed proteome and phosphoproteome, respectively. Systems biology analysis of the proteomic data revealed that unfolded protein-associated endoplasmic reticulum (ER) stress response was the predominant event. Concomitant with transcriptomic analysis using mRNA expression, microarrays show ER stress response in the AuNP-treated cells. The ER stress protein markers' expression assay unveiled AuNPs as an efficient cellular ER stress elicitor. Upon ER stress, cellular responses, including reactive oxygen species increase, mitochondrial cytochrome c release, and mitochondria damage, chronologically occurred in the AuNP-treated cells. Conclusively, this study demonstrates that AuNPs cause cell death through induction of unmanageable ER stress.

The new murine hepatic 3A cell line responds to stress stimuli by activating an efficient Unfolded Protein Response (UPR)

In the present study we have investigated the properties of a novel cell line (3A cells) obtained from the liver of 14.5 days post coitum (dpc) wild-type mouse embryo. 3A cells morphology was characterized by fluorescent localization of F-actin and β-catenin. The expression of specific genes and proteins essential to liver function in these cells was comparable or even more efficient then in the differentiated hepatocytic cell line MMH-D6. 3A cells also showed the capability to excrete molecules in extracellular spaces resembling functional bile canaliculi, glycogen storage activity and the ability to control retinol-binding protein 4 secretion in response to retinol deprivation. Their response to the exogenous stress stimulus induced by tunicamycin was analysed by PCR Pathway Array containing 84 genes involved in the Unfolded Protein Response (UPR). 3A cells were shown to activate the UPR following a typical stressful event, indicating that this cellular model could be further exploited to investigate hepatic proteins secretion and specific reaction to different injuries.

Selective activation of the transcription factor ATF6 mediates endoplasmic reticulum proliferation triggered by a membrane protein

It is well known that the endoplasmic reticulum (ER) is capable of expanding its surface area in response both to cargo load and to increased expression of resident membrane proteins. Although the response to increased cargo load, known as the unfolded protein response (UPR), is well characterized, the mechanism of the response to membrane protein load has been unclear. As a model system to investigate this phenomenon, we have used a HeLa-TetOff cell line inducibly expressing a tail-anchored construct consisting of an N-terminal cytosolic GFP moiety anchored to the ER membrane by the tail of cytochrome b5 [GFP-b(5)tail]. After removal of doxycycline, GFP-b(5)tail is expressed at moderate levels (1-2% of total ER protein) that, nevertheless, induce ER proliferation, as assessed both by EM and by a three- to fourfold increase in phosphatidylcholine synthesis. We investigated possible participation of each of the three arms of the UPR and found that only the activating transcription factor 6 (ATF6) arm was selectively activated after induction of GFP-b(5)tail expression; peak ATF6α activation preceded the increase in phosphatidylcholine synthesis. Surprisingly, up-regulation of known ATF6 target genes was not observed under these conditions. Silencing of ATF6α abolished the ER proliferation response, whereas knockdown of Ire1 was without effect. Because GFP-b(5)tail lacks a luminal domain, the response we observe is unlikely to originate from the ER lumen. Instead, we propose that a sensing mechanism operates within the lipid bilayer to trigger the selective activation of ATF6.

The role of circadian timing system on drug metabolism and detoxification

INTRODUCTION

It has been known for a long time that the efficiency and toxicity of drugs change during a 24-h period. However, the molecular mechanisms involved in these processes have started to emerge only recently.

AREAS COVERED

This review aims to highlight recent discoveries showing the direct role of the molecular circadian clock in xenobiotic metabolism at the transcriptional and post-transcriptional levels in the liver and intestine, and the different ways of elimination of these metabolized drugs via biliary and urine excretions. Most of the related literature focuses on transcriptional regulation by the circadian clock of xenobiotic metabolism in the liver; however, the role of this timing system in the excretion of metabolized drugs and the importance of the kidney in this phenomenon are generally neglected. The goal of this review is to describe the molecular mechanisms involved in rhythmic drug metabolism and excretion.

EXPERT OPINION

Chronopharmacology is used to analyze the metabolism of drugs in mammals according to the time of day. The circadian timing system plays a key role in the changes of toxicity of drugs by influencing their metabolisms in the liver and intestine in addition to their excretion via bile flow and urine.

Cell-bound exopolysaccharide from probiotic bacteria induces autophagic cell death of tumour cells

AIM

Lactic acid bacteria (LAB) are beneficial micro-organisms that have been associated with several probiotic effects in both humans and animals. Here, using proteome analysis, we investigate the antitumour effects of cell-bound exopolysaccharides (cb-EPS) isolated from Lactobacillus acidophilus 606 on colon cancer cells and explore the proteins critical for their antitumour activity.

METHODS AND RESULTS

cb-EPS inhibited the proliferation of HT-29 colon cancer cells by directly affecting cell morphology and not the cell cycle. Using two-dimensional polyacrylamide gel electrophoresis coupled with matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF/MS) and immunoblot analysis, we found that cb-EPS dramatically induced Beclin-1 and GRP78, and affected Bcl-2 and Bak regulation.

CONCLUSIONS

The results of this study indicate that cb-EPS are antitumourigenic against HT-29 colon cancer cells and that this activity is because of the activation of autophagic cell death promoted directly by the induction of Beclin-1 and GRP78, as well as indirectly through the induction of Bcl-2 and Bak.

SIGNIFICANCE AND IMPACT OF THE STUDY

These results may contribute to understanding the novel mechanisms by which probiotic bacteria induce tumour cell death via autophagy.

Fatty Acid Desaturase 3 (Fads3) is a singular member of the Fads cluster

Since its identification in 2000, no function has been attributed to the Fatty Acid Desaturase 3 (Fads3) gene. This gene is located within the Fads cluster, which also contains Fads1 and Fads2, coding respectively for the Δ5- and Δ6- desaturases. Based on the sequence homology between these three genes, Fads3 may be a new fatty acid desaturase. It is thus essential to understand its involvement in Polyunsaturated Fatty Acid (PUFA) biosynthesis in order to improve our knowledge on lipid metabolism. Gene expression studies provided evidences on the specificity of Fads3 compared to Fads1 and Fads2, concerning the tissue distribution, alternative splicing and regulation. These works also identified possible physiological functions in which Fads3 could be involved. Thus, the Fads3 gene was transcripted in many tissues, and displayed a weak expression in the liver compared to other organs such as the lung or spleen. Fads3 was also showed to be a target gene for NK-κB, MYCN or p63 transcription factors and could consequently be involved in cell survival mechanisms. Polymorphism analysis underlined the possible implication of Fads3 in lipid homeostasis, particularly by modulating cholesterol and triglyceride plasma levels. In terms of proteins, FADS3 has been recently described in rodents. One of the identified isoforms may display the classical structure of a fatty acid desaturase but no enzymatic activity has been observed yet. Therefore, it is essential to consider the desaturase diversity in terms of catalysis and substrates to elucidate the FADS3 function.

The asthma-associated ORMDL3 gene product regulates endoplasmic reticulum-mediated calcium signaling and cellular stress

Alterations of protein folding or Ca(2+) levels within the endoplasmic reticulum (ER) result in the unfolded-protein response (UPR), a process considered as an endogenous inducer of inflammation. Thereby, understanding how genetic factors modify UPR is particularly relevant in chronic inflammatory diseases such as asthma. Here we identified that ORMDL3, the only genetic risk factor recently associated to asthma in a genome wide study, alters ER-mediated Ca(2+) homeostasis and facilitates the UPR. Heterologous expression of human ER-resident transmembrane ORMDL3 protein increased resting cytosolic Ca(2+) levels and reduced ER-mediated Ca(2+) signaling, an effect reverted by co-expression with the sarco-endoplasmic reticulum Ca(2+) pump (SERCA). Increased ORMDL3 expression also promoted stronger activation of UPR transducing molecules and target genes while siRNA-mediated knock-down of endogenous ORMDL3 potentiated ER Ca(2+) release and attenuated the UPR. In conclusion, our findings are consistent with a model in which ORMDL3 binds and inhibits SERCA resulting in a reduced ER Ca(2+) concentration and increased UPR. Thus, we provide a first insight into the molecular mechanism explaining the association of ORMDL3 with proinflammatory diseases.

Circadian clock-coordinated 12 Hr period rhythmic activation of the IRE1alpha pathway controls lipid metabolism in mouse liver

The mammalian circadian clock plays a fundamental role in the liver by regulating fatty acid, glucose, and xenobiotic metabolism. Impairment of this rhythm has been shown to lead to diverse pathologies, including metabolic syndrome. Currently, it is supposed that the circadian clock regulates metabolism mostly by regulating expression of liver enzymes at the transcriptional level. Here, we show that the circadian clock also controls hepatic metabolism by synchronizing a secondary 12 hr period rhythm characterized by rhythmic activation of the IRE1alpha pathway in the endoplasmic reticulum. The absence of circadian clock perturbs this secondary clock and provokes deregulation of endoplasmic reticulum-localized enzymes. This leads to impaired lipid metabolism, resulting in aberrant activation of the sterol-regulated SREBP transcription factors. The resulting aberrant circadian lipid metabolism in mice devoid of the circadian clock could be involved in the appearance of the associated metabolic syndrome.

Genomic consequences of cytochrome P450 2C9 overexpression in human hepatoma cells

Cytochrome P450 2C9 (P450 2C9) is one of the most important P450 isoforms in the human liver, as it metabolizes numerous exogenous and endogenous substrates. Moreover, it is inducible by several compounds, such as rifampicin, phenobarbital, and NSAIDs (nonsteroidal anti-inflammatories). The aim of this study was to investigate the global cellular consequences of P450 2C9 overexpression at the transcriptional level using an untargeted approach: pangenomic microarrays. Recombinant adenovirus was used to express P450 2C9 instead of an inducer to prevent a per se effect of inducer or its metabolites. P450 2C9 overexpression induced endoplasmic reticulum (ER) stress and regulated genes implicated in the unfolded protein response (UPR) as heat shock protein (HSP) (we studied particurlarly HSPA5 and HSPB1) and in the endoplasmic reticulum associated degradation (ERAD) system as Sec61 and ubiquitin and proteasome pathways. UPR and ERAD are two mechanisms of adaptative response to ER stress. Moreover, activation of Akt was observed in HepG2 cells that overexpress P450 2C9 and might participate in the cellular adaptive response to stress, thus leading to the activation of cell survival pathways. UPR and ERAD should be caused by accumulation of native and misfolded P450 2C9 protein. Our results indicated that P450 2C9 overexpression did not lead to toxicity but induced an ER stress due to protein overexpression rather than mono-oxygenase activity. The ER stress triggered activation of the adaptative response and of pathways leading to cell survival.

Toxicogenomic biomarkers for liver toxicity

Toxicogenomics (TGx) is a widely used technique in the preclinical stage of drug development to investigate the molecular mechanisms of toxicity. A number of candidate TGx biomarkers have now been identified and are utilized for both assessing and predicting toxicities. Further accumulation of novel TGx biomarkers will lead to more efficient, appropriate and cost effective drug risk assessment, reinforcing the paradigm of the conventional toxicology system with a more profound understanding of the molecular mechanisms of drug-induced toxicity. In this paper, we overview some practical strategies as well as obstacles for identifying and utilizing TGx biomarkers based on microarray analysis. Since clinical hepatotoxicity is one of the major causes of drug development attrition, the liver has been the best documented target organ for TGx studies to date, and we therefore focused on information from liver TGx studies. In this review, we summarize the current resources in the literature in regard to TGx studies of the liver, from which toxicologists could extract potential TGx biomarker gene sets for better hepatotoxicity risk assessment.

Expression of endoplasmic reticulum molecular chaperone GRP94 in human nonalcoholic fatty liver and its clinical significance

AIM: To detect the expression of GRP94 in human nonalcoholic fatty liver injury, and to explore the mechanism of human nonalcoholic fatty liver disease (NAFLD).

METHODS: Using immunohistochemistry and RT-PCR, GRP94 protein and mRNA expression were detected in fatty liver specimens and normal liver specimens. Hepatic steatosis, inflammation and necrosis were graded by routine H&E staining of liver sections, and their correlations were analyzed.

RESULTS: Steatosis, inflammation and necrosis were markedly increased in nonalcoholic fatty liver group than in the control group (3.89 ± 0.32 vs 0.20 ± 0.4; 3.67 ± 0.49 vs 0; 0.44 ± 0.51 vs 0, P < 0.01 or 0.05). The expression of GRP94 mRNA and its protein expression were enhanced significantly in nonalcoholic fatty liver group than in the normal control group (0.86 ± 0.02vs 0.37 ± 0.03; 0.34 ± 0.01 vs 0.31 ± 0.01, both P < 0.01). The expression of GRP94 mRNA and its protein expression were positively associated with steatosis, inflammation and necrosis scores (P < 0.01).

CONCLUSION: The excessive expression of GRP94 could participate in the development of nonalcoholic fatty liver disease.

The Endoplasmic Reticulum in Xenobiotic Toxicity

The endoplasmic reticulum (ER) is involved in an array of cellular functions that play important roles in xenobiotic toxicity. The ER contains the majority of cytochrome P450 enzymes involved in xenobiotic metabolism, as well as a number of conjugating enzymes. In addition to its role in drug bioactivation and detoxification, the ER can be a target for damage by reactive intermediates leading to cell death or immune-mediated toxicity. The ER contains a set of luminal proteins referred to as ER stress proteins (including GRP78, GRP94, protein disulfide isomerase, and calreticulin). These proteins help regulate protein processing and folding of membrane and secretory proteins in the ER, calcium homeostasis, and ER-associated apoptotic pathways. They are induced in response to ER stress. This review discusses the importance of the ER in molecular events leading to cell death following xenobiotic exposure. Data showing that the ER is important in both renal and hepatic toxicity will be discussed.

Proteasome inhibition compromises direct retention of cytochrome P450 2C2 in the endoplasmic reticulum

To determine whether protein degradation plays a role in the endoplasmic reticulum (ER) retention of cytochromes P450, the effects of proteasomal inhibitors on the expression and distribution of green fluorescent protein chimeras of CYP2C2 and related proteins was examined. In transfected cells, expression levels of chimeras of full-length CYP2C2 and its cytosolic domain, but not its N-terminal transmembrane sequence, were increased by proteasomal inhibition. Redistribution of all three chimeras from the reticular ER into a perinuclear compartment and, in a subset of cells, also to the cell surface was observed after proteasomal inhibition. Redistribution was blocked by the microtubular inhibitor, nocodazole, suggesting that redistribution to the cell surface followed the conventional vesicular transport pathway. Similar redistributions were detected for BAP31, a CYP2C2 binding chaperone; CYP2E1 and CYP3A4, which are also degraded by the proteasomal pathway; and for cytochrome P450 reductase, which does not undergo proteasomal degradation; but not for the ER membrane proteins, sec61 and calnexin. Redistribution does not result from saturation of an ER retention "receptor" since in some cases protein levels were unaffected. Proteasomal inhibition may, therefore, alter ER retention by affecting a protein critical for ER retention, either directly, or indirectly by affecting the composition of the ER membranes.

Ethanol-related increases in degenerating bodies in the Purkinje neuron dendrites of aging rats

Chronic ethanol consumption in aging rats results in regression of Purkinje neuron (PN) dendritic arbors ([Pentney, 1995 Measurements of dendritic pathlengths provide evidence that ethanol-induced lengthening of terminal dendritic segments may result from dendritic regression. Alcohol Alcohol. 30, 87-96]), loss of synapses (Dlugos and Pentney, 1997), dilation of the smooth endoplasmic reticulum (SER), and the formation of degenerating bodies within PN dendrites ([Dlugos, C.A., 2006a. Ethanol-Related Smooth Endoplasmic Reticulum Dilation in Purkinje Dendrites of Aging Rats. Alcohol., Clin. Exp. Res. 30, 883-891,Dlugos, C.A., 2006b. Smooth endoplasmic reticulum dilation and degeneration in Purkinje neuron dendrites of aging ethanol-fed female rats. Cerebellum. 5, 155-162]). Dilation of the SER and the formation of degenerating bodies may be a predictor of dendritic regression. Ethanol-induced effects on mitochondria may be involved as mitochondria cooperate with the SER to maintain calcium homeostasis. The purpose of this study was to determine whether degenerating body number and mitochondrial density and structure are altered by chronic ethanol treatment in PN dendrites. Male, Fischer 344 rats, 12 months of age, were fed an ethanol or pair-fed liquid diet, or rat chow for a period of 10, 20, or 40 weeks (15 rats/treatment; 45 rats/treatment duration). Ethanol-fed rats received 35% of their calories as ethanol. At the end of treatment, all animals were euthanized, perfused, and tissue prepared for electron microscopy. The densities of degenerating bodies and mitochondria, mitochondrial areas, and the distance between the SER and the mitochondria were measured. Results showed that there was an ethanol-related increase in degenerating bodies compared to controls at 40 weeks. Ethanol-induced alterations to mitochondria were absent. Correlation of the present results with those of previous studies suggest that degenerating bodies may be formed from membrane reabsorption during dendritic regression or from degenerating SER whose function has been compromised by dilation.

The nuclear factor-kappa B pathway regulates cytochrome P450 3A4 protein stability

We have previously observed that CYP3A4 protein levels are suppressed by inhibition of the proteasome in primary cultured hepatocytes. Because this result is opposite of what would be expected if CYP3A4 were degraded by the proteasome, it seemed likely that there might be another protein susceptible to proteasomal degradation that regulated CYP3A4 expression. In this study, we evaluated whether the nuclear factor-kappaB (NF-kappaB) pathway was involved in that process. Our model system used an adenovirus system to express CYP3A4 protein in HepG2 cells, which are derived from human cancer cells. Similar to results in primary hepatocytes, the inhibition of the proteasome with N-benzoyloxycarbonyl (Z)-Leu-Leu-leucinal (MG132) suppresses CYP3A4 protein levels. We also found that MG132 treatment had a broad affect on the NF-kappaB pathway, including down-regulation of NF-kappaB DNA binding activity and IkappaB kinase (IKK)alpha levels and up-regulation of IKKbeta and inhibitory kappaB levels. Treatment of the HepG2 cells with several structurally distinct NF-kappaB inhibitors also suppressed CYP3A4 protein levels. When the HepG2 cells were treated with cycloheximide, a general inhibitor of protein synthesis, the loss of CYP3A4 protein was accelerated by cotreatment with either proteasome or NF-kappaB inhibitors. These results indicate that NF-kappaB activity regulated CYP3A4 protein stability, and they suggest that the NF-kappaB pathway was responsible for the decrease in CYP3A4 protein levels that resulted from the proteasomal inhibition.

Expression of cytochrome P450 2A5 in a glucose-6-phosphate dehydrogenase-deficient mouse model of oxidative stress

Murine hepatic cytochrome P450 2A5 (CYP2A5), unlike most CYP enzymes, is upregulated during hepatitis and hepatotoxic conditions, but the common stimulus for its induction remains unknown. We investigated the involvement of oxidative stress in the regulation of CYP2A5 expression using an oxidative stress-sensitive glucose-6-phosphate dehydrogenase (G6PD)-deficient mouse model. Treatment of deficient and wild-type mice with the prototypical CYP2A5-inducer pyrazole for 72h led to a significantly greater degree of induction of CYP2A5 mRNA, protein and activity in deficient mice, with the greatest increase observed in animals homozygous for the deficiency. However, markers of oxidative stress including protein carbonyl, 8-hydroxydeoxyguanosine, malondiadehyde and 4-hydroxyalkenal levels were unaltered with pyrazole treatment. Furthermore, CYP2A5 expression was not altered in G6PD-deficient mice treated with the pro-oxidant menadione whereas DNA, lipid, and protein markers of oxidative stress were significantly increased. The antioxidant polyethylene glycol-conjugated catalase, while decreasing oxidative stress in menadione-treated mice, did not prevent the induction of CYP2A5 by pyrazole. Finally, the ER stress marker protein, GRP78, was increased following pyrazole treatment in G6PD-deficient compared to wild-type mice. These findings do not support a central role for generalized cellular oxidative stress in the regulation of CYP2A5 and suggest that additional factors related to G6PD-deficiency, such as ER stress, may be involved.

Endoplasmic reticulum stress during the embryonic development of the central nervous system in the mouse

In the present study, we have found evidence for ER stress occurring during development of the central nervous system in the mouse. Several ER-resident stress-regulated chaperones, such as calreticulin, glucose regulated protein 78, glucose regulated protein 94, ER protein 57 and protein disulfide isomerase, were expressed at higher levels in embryonic brain and retina, compared with adult tissues. In contrast, calnexin, a chaperone that is not regulated by stress was equally abundant in embryonic and adult tissues. We also detected unfolded protein response during embryonic development. Both eukaryotic translation initiation factor 2 alpha and its phosphorylated form were more abundant in embryonic brain and retina than in adult tissues. Spliced X-box binding protein-1 mRNA was detected in embryonic brain and retina, while it was absent in adult counterparts. Partially glycosylated form of activating transcription factor 6 alpha, another ER stress indicator, was detected predominantly in embryonic brain. Finally, apoptotic pathway components, caspase-7 and -12, were more abundant in embryonic brain than in adult. The pattern of expression of chaperones together with activation of the unfolded protein response factors suggests the presence of ER stress during development of brain and retina. Furthermore, our data suggest that ER stress-like mechanism may induce apoptosis via activation of the caspases during embryonic development of the central nervous system.

Chaperones as Parts of Organelle Networks

The efficiency, divergence, and specificity of virtually all intracellular metabolic and signalling pathways largely depend on their compartmentalized organization. A corollary of the requirement of compartmentalization is the dynamic structural partition of the intracellular space by endomembrane systems. A branch of these membranes communicate with the extracellular space through the endo- and exocytotic processes. Others, like the mitochondrial and endoplasmic reticulum networks accomplish a further role, being fundamental for the maintenance of cellular energy balance and for determination of cell fate under stress conditions. Recent structural and functional studies revealed that the interaction of these networks and the connectivity state of mitochondria controls metabolic flow, protein transport, intracellular Ca2+ signalling, and cell death. Moreover, reflecting the fact that the above processes are accomplished in a microdomain between collaborating organelle membranes, the existence of macromolecular complexes at their contact sites have also been revealed. Being not only assistants of nascent protein folding, chaperones are proposed to participate in assembling and maintaining the function of the above complexes. In this chapter we discuss recently found examples of such an assembly of protein interactions driven by chaperone proteins, and their role in regulating physiological and pathological processes.

Regulation of TNF-alpha-activated PKC-zeta signaling by the human biliverdin reductase: identification of activating and inhibitory domains of the reductase

Human biliverdin reductase (hBVR) is a dual function enzyme: a catalyst for bilirubin formation and a S/T/Y kinase that shares activators with protein kinase C (PKC) -zeta, including cytokines, insulin, and reactive oxygen species (ROS). Presently, we show that hBVR increases PKC-zeta autophosphorylation, stimulation by TNF-alpha, as well as cytokine stimulation of NF-kappaB DNA binding and promoter activity. S149 in hBVR S/T kinase domain and S230 in YLS230F in hBVR's docking site for the SH2 domain of signaling proteins are phosphorylation targets of PKC-zeta. Two hBVR-based peptides, KRNRYLS230F (#1) and KKRILHC281 (#2), but not their S-->A or C-->A derivatives, respectively, blocked PKC-zeta stimulation by TNF-alpha and its membrane translocation. The C-terminal-based peptide KYCCSRK296 (#3), enhanced PKC-zeta stimulation by TNF-alpha; for this, Lys296 was essential. In metabolically 32P-labeled HEK293 cells transfected with hBVR or PKC-zeta, TNF-alpha increased hBVR phosphorylation. TNF-alpha did not stimulate PKC-zeta in cells infected with small interfering RNA for hBVR or transfected with hBVR with a point mutation in the nucleotide-binding loop (G17), S149, or S230; this was similar to the response of "kinase-dead" PKC-zeta(K281R). We suggest peptide #1 blocks PKC-zeta-docking site interaction, peptide #2 disrupts function of the PKC-zeta C1 domain, and peptide #3 alters ATP presentation to the kinase. The findings are of potential significance for development of modulators of PKC-zeta activity and cellular response to cytokines.

Reticulon 3 mediates Bcl-2 accumulation in mitochondria in response to endoplasmic reticulum stress

Reticulon3 (RTN3), firstly isolated from the retina and widely expressed in human tissues with the highest expression in the brain, is presumed to play an important role in the developing axons through the transport of liquids and proteins. We have identified and characterized RTN3 as a RTN4B/ASY interaction protein. Here we demonstrated that ER-stress activated RTN3 expression. CHOP and ATF6 were sufficient to up-regulate the expression of RTN3. The down-regulation of RTN3 would induce apoptosis and attenuate the anti-apoptotic activity of Bcl-2, indicating RTN3 was required for the cellular survival and optimal anti-apoptotic activity of Bcl-2. Our present studies also indicated ER-stress induced RTN3 up-regulation could trigger Bcl-2 translocation from ER to mitochondria. Moreover, the previous studies showed that RTN4B was also a Bcl-2-interacted protein. We found that RTN3 and RTN4B could block the access of Bcl-2 to each other and thereafter determined the Bcl-2 subcellular distribution. Taken together, our findings indicate that RTN3 is directly involved in the ER-constituents trafficking events through dually acting as an essential and important ER-stress sensor, and a trigger for the Bcl-2 translocation.

General and specific host responses to bacterial infection in Peyer's patches: a role for stromelysin-1 (matrix metalloproteinase-3) during Salmonella enterica infection

Salmonella enterica serovar Typhimurium (S. typhimurium) and Yersinia enterocolitica are enteric pathogens capable of colonizing and inducing inflammatory responses in Peyer's patches (PPs) and mesenteric lymph nodes (MLNs). Although the tissue colonization pattern is similar between these two pathogens, their pathogenic lifestyles are quite different. For example, while S. typhimurium is primarily an intracellular pathogen, Y. enterocolitica survives primarily extracellularly. We determined and compared the transcriptional changes occurring in response to S. typhimurium and Y. enterocolitica colonization of PP using Affymetrix GeneChip technology. Both pathogens elicited a general inflammatory response indicated by the upregulation of cytokines and chemokines. However, specific differences were also observed, most notably in the transcriptional regulation of gamma interferon (IFN-gamma) and IFN-gamma-regulated genes in response to S. typhimurium but not Y. enterocolitica. Of particular note, a group of genes encoding matrix metalloproteinases (MMPs) had increased transcript numbers in the PPs following infection with both pathogens. The experiments described here compare oral S. typhimurium or Y. enterocolitica infection in stromelysin-1 (MMP-3)-deficient mice (mmp-3(-/-)) with mice possessing functional MMP-3 (mmp-3(+/+)). There was little difference in the survival of MMP-3-deficient mice infected with Y. enterocolitica when compared with littermate controls. Surprisingly though, mmp-3(-/-) mice were markedly more resistant to S. typhimurium infection than the control mice. S. typhimurium was able to colonize mmp-3(-/-) mice, albeit in a delayed fashion, to equivalent levels as mmp-3(+/+) mice. Nevertheless, significantly lower levels of inflammatory cytokines were detected in tissues and serum in the mmp-3(-/-) mice in comparison with mmp-3(+/+) mice. We hypothesize that MMP-3 is involved in initiating an early and lethal cytokine response to S. typhimurium colonization.

Role of the unfolded protein response in cell death

Unfolded protein response (UPR) is an important genomic response to endoplasmic reticulum (ER) stress. The ER chaperones, GRP78 and Gadd153, play critical roles in cell survival or cell death as part of the UPR, which is regulated by three signaling pathways: PERK/ATF4, IRE1/XBP1 and ATF6. During the UPR, accumulated unfolded protein is either correctly refolded, or unsuccessfully refolded and degraded by the ubiquitin-proteasome pathway. When the unfolded protein exceeds a threshold, damaged cells are committed to cell death, which is mediated by ATF4 and ATF6, as well as activation of the JNK/AP-1/Gadd153-signaling pathway. Gadd153 suppresses activation of Bcl-2 and NF-kappaB. UPR-mediated cell survival or cell death is regulated by the balance of GRP78 and Gadd153 expression, which is coregulated by NF-kappaB in accordance with the magnitude of ER stress. Less susceptibility to cell death upon activation of the UPR may contribute to tumor progression and drug resistance of solid tumors.

Transcriptional profiles in liver from rats treated with tumorigenic and non-tumorigenic triazole conazole fungicides: Propiconazole, triadimefon, and myclobutanil

Conazoles are a class of fungicides used as pharmaceutical and agricultural agents. In chronic bioassays in rats, triadimefon was hepatotoxic and induced follicular cell adenomas in the thyroid gland, whereas, propiconazole and myclobutanil were hepatotoxic but had no effect on the thyroid gland. These conazoles administered in the feed to male Wistar/Han rats were found to induce hepatomegaly, induce high levels of pentoxyresorufin-O-dealkylase, increase cell proliferation in the liver, increase serum cholesterol, decrease serum T3 and T4, and increase hepatic uridine diphosphoglucuronosyl transferase activity. The goal of the present study was to define pathways that explain the biologic outcomes. Male Wistar/Han rats (3 per group), were exposed to the 3 conazoles in the feed for 4, 30, or 90 days of treatment at tumorigenic and nontumorigenic doses. Hepatic gene expression was determined using high-density Affymetrix GeneChips (Rat 230_2). Differential gene expression was assessed at the probe level using Robust Multichip Average analysis. Principal component analysis by treatment and time showed within group sample similarity and that the treatment groups were distinct from each other. The number of altered genes varied by treatment, dose, and time. The greatest number of altered genes was induced by triadimefon and propiconazole after 90 days of treatment, while myclobutanil had minimal effects at that time point. Pathway level analyses revealed that after 90 days of treatment the most significant numbers of altered pathways were related to cell signaling, growth, and metabolism. Pathway level analysis for triadimefon and propiconazole resulted in 71 altered pathways common to both chemicals. These pathways controlled cholesterol metabolism, activation of nuclear receptors, and N-ras and K-ras signaling. There were 37 pathways uniquely changed by propiconazole, and triadimefon uniquely altered 34 pathways. Pathway level analysis of altered gene expression resulted in a more complete description of the associated toxicological effects that can distinguish triadimefon from propiconazole and myclobutanil.

Regulation of drug-metabolizing enzymes and transporters in inflammation

Inflammation and infection have long been known to downregulate the activity and expression of cytochrome P450 (CYP) enzymes involved in hepatic drug clearance. This can result in elevated plasma drug levels and increased adverse effects. Recent information on regulation of human CYP enzymes is presented, as are new developments in our understanding of the mechanisms of regulation. Experiments to study the effects of modulating CYP activities on the inflammatory response have yielded possible insights into the physiological consequences, if not the purpose, of the downregulation. Regulation of hepatic flavin monooxygenases, UDP-glucuronosyltransferases, sulfotransferases, glutathione S-transferases, as well as of hepatic transporters during the inflammatory response, exhibits similarities and differences with regulation of CYPs.

BAP31 Is Involved in the Retention of Cytochrome P450 2C2 in the Endoplasmic Reticulum

Microsomal cytochrome P450 2C2 is an integral endoplasmic reticulum (ER) membrane protein that is directly retained in the ER and excluded from transport vesicles. We have used bimolecular fluorescence complementation and co-immunoprecipitation to show that a ubiquitous ER membrane protein (BAP31) interacts with P450 2C2 in transfected COS-1 cells. A chimera containing only the N-terminal signal anchor of P450 2C1 (P450 2C1-(1-29)) also interacted with BAP31, which is consistent with interaction of the two proteins via their transmembrane domains. Down-regulation of BAP31 expression with small interfering RNA resulted in redistribution of green fluorescent protein-tagged P450 2C2 or P450 2C1-(1-29) from the ER into the nuclear membrane and compact perinuclear compartment structures as well as the cell surface in a small fraction of the cells. In Bap31-null embryonic stem cells, a significant fraction of P450 2C2 or P450 2C1-(1-29) was detected at the cell surface and nuclear envelope, but was redistributed to the ER by expression of BAP31. The expression level of P450 2C2 was significantly increased in COS-1 cells with repressed levels of BAP31. Formation of the pro-apoptotic p20 fragment of BAP31 was detected in transfected COS-1 cells expressing P450 2C2, and annexin V staining was consistent with the activation of an apoptotic pathway in these cells. Down-regulation of BAP31 with small interfering RNA partially reversed the apoptosis. These results suggest that interaction of P450 2C2 with BAP31 is important for its ER retention and expression level and that BAP31 may be involved in the regulation of apoptosis induced by the ER overload response to increased expression of P450.

Molecular mechanism investigation of cycloheximide-induced hepatocyte apoptosis in rat livers by morphological and microarray analysis

Male F344 rats were intravenously treated with 6 mg/kg cycloheximide (CHX), and microarray analysis was conducted on their livers 1, 2 and 6h after the CHX treatment. The histopathological examination and serum chemistry results indicated a mild hepatic cell death 2 and 6h after the CHX treatment, respectively. Multi-focal hepatocellular necrosis with slight neutrophil infiltration was observed 6h after the CHX treatment. The TUNEL staining results showed that the number of apoptotic hepatocytes was the highest 2h after the CHX treatment. Dramatic increases in the mRNA levels of ATF3 and CHOP genes, both of which were reported to play roles in the ER stress-mediated apoptosis pathway, were observed from 1h after the CHX treatment. In addition, increase of GADD45, p21 and p53 mRNA levels also suggested a time course-related stimulation of hepatocellular apoptotic signals. These results suggest that the hepatocyte apoptosis induced by the CHX treatment is triggered by ER stress. The hepatic mRNA levels of proinflammatory genes, such as TNFalpha, IL-1alpha and beta, were also increased 1 and 2h after the CHX treatment, supposedly mediated by the activated Kupffer cells engulfing the apoptotic hepatocytes.

Adaptation and increased susceptibility to infection associated with constitutive expression of misfolded SP-C

Mutations in the gene encoding SP-C (surfactant protein C; SFTPC) have been linked to interstitial lung disease (ILD) in children and adults. Expression of the index mutation, SP-C(Deltaexon4), in transiently transfected cells and type II cells of transgenic mice resulted in misfolding of the proprotein, activation of endoplasmic reticulum (ER) stress pathways, and cytotoxicity. In this study, we show that stably transfected cells adapted to chronic ER stress imposed by the constitutive expression of SP-C(Deltaexon4) via an NF-kappaB-dependent pathway. However, the infection of cells expressing SP-C(Deltaexon4) with respiratory syncytial virus resulted in significantly enhanced cytotoxicity associated with accumulation of the mutant proprotein, pronounced activation of the unfolded protein response, and cell death. Adaptation to chronic ER stress imposed by misfolded SP-C was associated with increased susceptibility to viral-induced cell death. The wide variability in the age of onset of ILD in patients with SFTPC mutations may be related to environmental insults that ultimately overwhelm the homeostatic cytoprotective response.

Thrombopoietin stimulates migration and activates multiple signaling pathways in hepatoblastoma cells

Thrombopoietin (TPO), a cytokine that participates in the differentiation and maturation of megakaryocytes, is produced in the liver, but only limited information is available on the biological response of liver-derived cells to TPO. In this study, we investigated whether HepG2 cells express c-Mpl, the receptor for TPO, and whether TPO elicits biological responses and intracellular signaling in this cell type. Specific transcripts for c-Mpl were detected in HepG2 cells by RT-PCR, and expression of the protein was demonstrated by Western blot analysis and immunofluorescence. Exposure of HepG2 cells to TPO was associated with a dose-dependent increase in cell migration and chemoinvasion through Matrigel-coated filters. A checkerboard analysis showed that the effects of TPO on cell migration were dependent on both chemotaxis and chemokinesis. Exposure of HepG2 cells to TPO resulted in the activation of different members of the MAPK family, including ERK and JNK, as assessed using phosphorylation-specific antibodies and immune complex kinase assays. TPO also activated phosphatidylinositol 3-kinase (PI3K) and the downstream kinase Akt in a time-dependent manner. Finally, activation of c-Mpl was associated with increased activation of nuclear factor-kappaB. With the use of specific inhibitors, tyrosine phosphorylation and activation of PI3K were found to be required for the induction of migration in response to TPO. We conclude that TPO exerts biological actions on cultured hepatoblastoma cells via activation of c-Mpl and its downstream signaling.

The structure and location of SIMP/STT3B account for its prominent imprint on the MHC I immunopeptidome

Proteins show drastic discrepancies in their contribution to the collection of self-peptides that shape the repertoire of CD8 T cells (MHC I self-immunopeptidome). To decipher why selected proteins are the foremost sources of MHC I-associated self-peptides, we chose to study SIMP/STT3B because this protein generates very high amounts of MHC I-associated peptides in mice and humans. We show that the endoplasmic reticulum (ER)-associated degradation pathway and MHC I processing intersect at SIMP/STT3B. Relevant key features of SIMP/STT3B are its lysine-rich region, its propensity to misfold and its location in the ER membrane in close proximity to the immunoproteasome. Moreover, we show that coupling to SIMP/STT3B can be used to foster MHC I presentation of a selected peptide, here the ovalbumin peptide SIINFEKL. These data yield novel insights into relations between the cell proteome and the MHC I immunopeptidome. They suggest that the contribution of a given protein to the MHC I immunopeptidome results from the interplay of at least three factors: the presence of degrons (degradation signals), the tendency of the protein to misfold and its subcellular localization. Furthermore, they indicate that substrates of the ER-associated degradation pathway may have a prominent imprint on the MHC I self-immunopeptidome.

The dynamic ER: experimental approaches and current questions

The endoplasmic reticulum (ER) is an extremely plastic and dynamic organelle. Its size and shape can undergo drastic changes to meet changing demands for ER-related functions, or as a response to drugs or pathogens. Because of the ER's key functions in protein and lipid synthesis, this organelle is a hotbed of detailed molecular analysis.

Hepatic Gene Expression Changes in Mouse Models with Liver-specific Deletion or Global Suppression of the NADPH-Cytochrome P450 Reductase Gene

NADPH-cytochrome P450 reductase (CPR) is an essential component for the function of many enzymes, including microsomal cytochrome P450 (P450) monooxygenases and heme oxygenases. In liver-Cpr-null (with liver-specific Cpr deletion) and Cpr-low (with reduced CPR expression in all organs examined) mouse models, a reduced serum cholesterol level and an induction of hepatic P450s were observed, whereas hepatomegaly and fatty liver were only observed in the liver-Cpr-null model. Our goal was to identify hepatic gene expression changes related to these phenotypes. Cpr-lox mice (with a floxed Cpr gene and normal CPR expression) were used as the control. Through microarray analysis, we identified many genes that were differentially expressed among the three groups of mice. We also recognized the 12 gene ontology terms that contained the most significantly changed gene expression in at least one of the two mouse models. We further uncovered potential mechanisms, such as an increased activation of constitutive androstane receptor and a decreased activation of peroxisomal proliferator-activated receptor-alpha by precursors of cholesterol biosynthesis, that underlie common changes (e.g. induction of multiple P450s and suppression of genes for fatty acid metabolism) in response to CPR loss in the two mouse models. Additionally, we observed model-specific gene expression changes, such as the induction of a fatty-acid translocase (Cd36 antigen) and the suppression of carnitine O-palmitoyltransferase 1 (Cpt1a) and acyl-CoA synthetase long chain family member 1 (Acsl1), that are potentially responsible for the severe hepatic lipidosis and an altered fatty acid profile observed in liver-Cpr-null mice.

ER Ca2+ depletion triggers apoptotic signals for endoplasmic reticulum (ER) overload response induced by overexpressed reticulon 3 (RTN3/HAP)

Perturbance of endoplasmic reticulum (ER) function, either by the mutant proteins not folding correctly, or by an excessive accumulation of proteins in the organelle, will lead to the unfolded protein response (UPR) or ER overload response (EOR). The signal-transducing pathways for UPR have been identified, whereas the pathway for EOR remains to be elucidated. Our previous study demonstrated that the overexpression of reticulon 3 (RTN3, also named HAP, homologue of ASY protein) caused apoptosis with the depletion of ER Ca(2+) stores. In present research, we characterized RTN3 as a novel EOR-induced protein, triggering the apoptotic signals through the release of ER Ca(2+) and the elevation of cytosolic Ca(2+). Our studies showed that overexpressed RTN3 induced EOR, eliciting ER-specific apoptosis with activation of caspase-12 and mitochondrial dysfunction through ER Ca(2+) depletion and the sustained elevation of cytosolic Ca(2+). Furthermore, we demonstrated that overexpressed RTN3 and stimuli that activate both EOR and UPR, not UPR only, were able to induce up-regulation of inducible nitric oxide synthase (iNOS) in HeLa cells through ER Ca(2+) release and reactive oxygen intermediates (ROIs), resulting in endogenous calcium-dependent nitric oxide protecting cells against ER specific apoptosis, which suggested that the nitric oxide and iNOS represented a likely protective response to EOR, not the UPR. These results supported that the release of ER Ca(2+) stores triggered the initial signal-transducing pathways for EOR induced by overexpressed RTN3.