Ultraviolet light activates NFkappaB through translational inhibition of IkappaBalpha synthesis

Navigating the landscape of the unfolded protein response in CD8+ T cells

Endoplasmic reticulum stress occurs due to large amounts of misfolded proteins, hypoxia, nutrient deprivation, and more. The unfolded protein is a complex intracellular signaling network designed to operate under this stress. Composed of three individual arms, inositol-requiring enzyme 1, protein kinase RNA-like ER kinase, and activating transcription factor-6, the unfolded protein response looks to resolve stress and return to proteostasis. The CD8+ T cell is a critical cell type for the adaptive immune system. The unfolded protein response has been shown to have a wide-ranging spectrum of effects on CD8+ T cells. CD8+ T cells undergo cellular stress during activation and due to environmental insults. However, the magnitude of the effects this response has on CD8+ T cells is still understudied. Thus, studying these pathways is important to unraveling the inner machinations of these powerful cells. In this review, we will highlight the recent literature in this field, summarize the three pathways of the unfolded protein response, and discuss their roles in CD8+ T cell biology and functionality.

TRAIL receptors promote constitutive and inducible IL-8 secretion in non-small cell lung carcinoma

Interleukin-8 (IL-8/CXCL8) is a pro-angiogenic and pro-inflammatory chemokine that plays a role in cancer development. Non-small cell lung carcinoma (NSCLC) produces high amounts of IL-8, which is associated with poor prognosis and resistance to chemo-radio and immunotherapy. However, the signaling pathways that lead to IL-8 production in NSCLC are unresolved. Here, we show that expression and release of IL-8 are regulated autonomously by TRAIL death receptors in several squamous and adenocarcinoma NSCLC cell lines. NSCLC constitutively secrete IL-8, which could be further enhanced by glucose withdrawal or by treatment with TRAIL or TNFα. In A549 cells, constitutive and inducible IL-8 production was dependent on NF-κB and MEK/ERK MAP Kinases. DR4 and DR5, known regulators of these signaling pathways, participated in constitutive and glucose deprivation-induced IL-8 secretion. These receptors were mainly located intracellularly. While DR4 signaled through the NF-κB pathway, DR4 and DR5 both regulated the ERK-MAPK and Akt pathways. FADD, caspase-8, RIPK1, and TRADD also regulated IL-8. Analysis of mRNA expression data from patients indicated that IL-8 transcripts correlated with TRAIL, DR4, and DR5 expression levels. Furthermore, TRAIL receptor expression levels also correlated with markers of angiogenesis and neutrophil infiltration in lung squamous carcinoma and adenocarcinoma. Collectively, these data suggest that TRAIL receptor signaling contributes to a pro-tumorigenic inflammatory signature associated with NSCLC.

Evolutionarily conserved inhibitory uORFs sensitize Hox mRNA translation to start codon selection stringency

Translation start site selection in eukaryotes is influenced by context nucleotides flanking the AUG codon and by levels of the eukaryotic translation initiation factors eIF1 and eIF5. In a search of mammalian genes, we identified five homeobox (Hox) gene paralogs initiated by AUG codons in conserved suboptimal context as well as 13 Hox genes that contain evolutionarily conserved upstream open reading frames (uORFs) that initiate at AUG codons in poor sequence context. An analysis of published cap analysis of gene expression sequencing (CAGE-seq) data and generated CAGE-seq data for messenger RNAs (mRNAs) from mouse somites revealed that the 5' leaders of Hox mRNAs of interest contain conserved uORFs, are generally much shorter than reported, and lack previously proposed internal ribosome entry site elements. We show that the conserved uORFs inhibit Hox reporter expression and that altering the stringency of start codon selection by overexpressing eIF1 or eIF5 modulates the expression of Hox reporters. We also show that modifying ribosome homeostasis by depleting a large ribosomal subunit protein or treating cells with sublethal concentrations of puromycin leads to lower stringency of start codon selection. Thus, altering global translation can confer gene-specific effects through altered start codon selection stringency.

Pulsed Electric Fields Alter Expression of NF-κB Promoter-Controlled Gene

The possibility to artificially adjust and fine-tune gene expression is one of the key milestones in bioengineering, synthetic biology, and advanced medicine. Since the effects of proteins or other transgene products depend on the dosage, controlled gene expression is required for any applications, where even slight fluctuations of the transgene product impact its function or other critical cell parameters. In this context, physical techniques demonstrate optimistic perspectives, and pulsed electric field technology is a potential candidate for a noninvasive, biophysical gene regulator, exploiting an easily adjustable pulse generating device. We exposed mammalian cells, transfected with a NF-κB pathway-controlled transcription system, to a range of microsecond-duration pulsed electric field parameters. To prevent toxicity, we used protocols that would generate relatively mild physical stimulation. The present study, for the first time, proves the principle that microsecond-duration pulsed electric fields can alter single-gene expression in plasmid context in mammalian cells without significant damage to cell integrity or viability. Gene expression might be upregulated or downregulated depending on the cell line and parameters applied. This noninvasive, ligand-, cofactor-, nanoparticle-free approach enables easily controlled direct electrostimulation of the construct carrying the gene of interest; the discovery may contribute towards the path of simplification of the complexity of physical systems in gene regulation and create further synergies between electronics, synthetic biology, and medicine.

Exploring ER stress response in cellular aging and neuroinflammation in Alzheimer's disease

One evident hallmark of Alzheimer's disease (AD) is the irregular accumulation of proteins due to changes in proteostasis involving endoplasmic reticulum (ER) stress. To alleviate ER stress and reinstate proteostasis, cells undergo an integrated signaling cascade called the unfolded protein response (UPR) that reduces the number of misfolded proteins and inhibits abnormal protein accumulation. Aging is associated with changes in the expression of ER chaperones and folding enzymes, leading to the impairment of proteostasis, and accumulation of misfolded proteins. The disrupted initiation of UPR prevents the elimination of unfolded proteins, leading to ER stress. In AD, the accumulation of misfolded proteins caused by sustained cellular stress leads to neurodegeneration and neuronal death. Current research has revealed that ER stress can trigger an inflammatory response through diverse transducers of UPR. Although the involvement of a neuroinflammatory component in AD has been documented for decades, whether it is a contributing factor or part of the neurodegenerative events is so far unknown. Besides, a feedback loop occurs between neuroinflammation and ER stress, which is strongly associated with neurodegenerative processes in AD. In this review, we focus on the current research on ER stress and UPR in cellular aging and neuroinflammatory processes, leading to memory impairment and synapse dysfunction in AD.

Autophagy, Unfolded Protein Response, and Neuropilin-1 Cross-Talk in SARS-CoV-2 Infection: What Can Be Learned from Other Coronaviruses

The COVID-19 pandemic is caused by the 2019-nCoV/SARS-CoV-2 virus. This severe acute respiratory syndrome is currently a global health emergency and needs much effort to generate an urgent practical treatment to reduce COVID-19 complications and mortality in humans. Viral infection activates various cellular responses in infected cells, including cellular stress responses such as unfolded protein response (UPR) and autophagy, following the inhibition of mTOR. Both UPR and autophagy mechanisms are involved in cellular and tissue homeostasis, apoptosis, innate immunity modulation, and clearance of pathogens such as viral particles. However, during an evolutionary arms race, viruses gain the ability to subvert autophagy and UPR for their benefit. SARS-CoV-2 can enter host cells through binding to cell surface receptors, including angiotensin-converting enzyme 2 (ACE2) and neuropilin-1 (NRP1). ACE2 blockage increases autophagy through mTOR inhibition, leading to gastrointestinal complications during SARS-CoV-2 virus infection. NRP1 is also regulated by the mTOR pathway. An increased NRP1 can enhance the susceptibility of immune system dendritic cells (DCs) to SARS-CoV-2 and induce cytokine storm, which is related to high COVID-19 mortality. Therefore, signaling pathways such as mTOR, UPR, and autophagy may be potential therapeutic targets for COVID-19. Hence, extensive investigations are required to confirm these potentials. Since there is currently no specific treatment for COVID-19 infection, we sought to review and discuss the important roles of autophagy, UPR, and mTOR mechanisms in the regulation of cellular responses to coronavirus infection to help identify new antiviral modalities against SARS-CoV-2 virus.

Redox and Inflammatory Signaling, the Unfolded Protein Response, and the Pathogenesis of Pulmonary Hypertension

Protein folding overload and oxidative stress disrupt endoplasmic reticulum (ER) homeostasis, generating reactive oxygen species (ROS) and activating the unfolded protein response (UPR). The altered ER redox state induces further ROS production through UPR signaling that balances the cell fates of survival and apoptosis, contributing to pulmonary microvascular inflammation and dysfunction and driving the development of pulmonary hypertension (PH). UPR-induced ROS production through ER calcium release along with NADPH oxidase activity results in endothelial injury and smooth muscle cell (SMC) proliferation. ROS and calcium signaling also promote endothelial nitric oxide (NO) synthase (eNOS) uncoupling, decreasing NO production and increasing vascular resistance through persistent vasoconstriction and SMC proliferation. C/EBP-homologous protein further inhibits eNOS, interfering with endothelial function. UPR-induced NF-κB activity regulates inflammatory processes in lung tissue and contributes to pulmonary vascular remodeling. Conversely, UPR-activated nuclear factor erythroid 2-related factor 2-mediated antioxidant signaling through heme oxygenase 1 attenuates inflammatory cytokine levels and protects against vascular SMC proliferation. A mutation in the bone morphogenic protein type 2 receptor (BMPR2) gene causes misfolded BMPR2 protein accumulation in the ER, implicating the UPR in familial pulmonary arterial hypertension pathogenesis. Altogether, there is substantial evidence that redox and inflammatory signaling associated with UPR activation is critical in PH pathogenesis.

General Control Non-derepressible 1 (AtGCN1) Is Important for Flowering Time, Plant Growth, Seed Development, and the Transcription/Translation of Specific Genes in Arabidopsis

We have previously demonstrated that General Control Non-derepressible 1 (AtGCN1) is essential for translation inhibition under cold stress through interacting with GCN2 to phosphorylate eukaryotic translation initiation factor 2 (eIF2). Here, we report that the flower time of the atgcn1 mutant is later than that of the wild type (WT), and some siliques of atgcn1 cannot develop and produce seeds. Total and polysomal RNA of atgcn1-1 and wild type (WT) after cold treatments were sequenced. The sequencing results show that the mutation of atgcn1 selectively alters the expression of genes at both transcriptional and translational levels. The classification of AtGCN1 target genes reveals that AtGCN1 regulated gens are involved in flower development, seed dormancy and seed development, response to osmotic stress, amino acid biosynthesis, photosynthesis, cell wall organization, protein transport and localization, lipid biosynthesis, transcription, macroautophagy, proteolysis and cell death. Further analysis of AtGCN1 regulated genes at translational levels shows that the Kozak sequence and uORFs (upstream open reading frame) of transcripts affect translation selection. These results show that AtGCN1 is required for the expression of selective genes in Arabidopsis.

Inositol and Non-Alcoholic Fatty Liver Disease: A Systematic Review on Deficiencies and Supplementation

Liver lipid accumulation is a hallmark of non-alcoholic fatty liver disease (NAFLD), broadly associated with insulin resistance. Inositols (INS) are ubiquitous polyols implied in many physiological functions. They are produced endogenously, are present in many foods and in dietary supplements. Alterations in INS metabolism seems to play a role in diseases involving insulin resistance such as diabetes and polycystic ovary syndrome. Given its role in other metabolic syndromes, the hypothesis of an INS role as a supplement in NAFLD is intriguing. We performed a systematic review of the literature to find preclinical and clinical evidence of INS supplementation efficacy in NAFLD patients. We retrieved 10 studies on animal models assessing Myoinosiol or Pinitol deficiency or supplementation and one human randomized controlled trial (RCT). Overall, INS deficiency was associated with increased fatty liver in animals. Conversely, INS supplementation in animal models of fatty liver reduced hepatic triglycerides and cholesterol accumulation and maintained a normal ultrastructural liver histopathology. In the one included RCT, Pinitol supplementation obtained similar results. Pinitol significantly reduced liver fat, post-prandial triglycerides, AST levels, lipid peroxidation increasing glutathione peroxidase activity. These results, despite being limited, indicate the need for further evaluation of INS in NAFLD in larger clinical trials.

Interplay between Endoplasmic Reticulum Stress and Large Extracellular Vesicles (Microparticles) in Endothelial Cell Dysfunction

Upon increased demand for protein synthesis, accumulation of misfolded and/or unfolded proteins within the endoplasmic reticulum (ER), a pro-survival response is activated termed unfolded protein response (UPR), aiming at restoring the proper function of the ER. Prolonged activation of the UPR leads, however, to ER stress, a cellular state that contributes to the pathogenesis of various chronic diseases including obesity and diabetes. ER stress response by itself can result in endothelial dysfunction, a hallmark of cardiovascular disease, through various cellular mechanisms including apoptosis, insulin resistance, inflammation and oxidative stress. Extracellular vesicles (EVs), particularly large EVs (lEVs) commonly referred to as microparticles (MPs), are membrane vesicles. They are considered as a fingerprint of their originating cells, carrying a variety of molecular components of their parent cells. lEVs are emerging as major contributors to endothelial cell dysfunction in various metabolic disease conditions. However, the mechanisms underpinning the role of lEVs in endothelial dysfunction are not fully elucidated. Recently, ER stress emerged as a bridging molecular link between lEVs and endothelial cell dysfunction. Therefore, in the current review, we summarized the roles of lEVs and ER stress in endothelial dysfunction and discussed the molecular crosstalk and relationship between ER stress and lEVs in endothelial dysfunction.

Mechanisms, regulation and functions of the unfolded protein response

Cellular stress induced by the abnormal accumulation of unfolded or misfolded proteins at the endoplasmic reticulum (ER) is emerging as a possible driver of human diseases, including cancer, diabetes, obesity and neurodegeneration. ER proteostasis surveillance is mediated by the unfolded protein response (UPR), a signal transduction pathway that senses the fidelity of protein folding in the ER lumen. The UPR transmits information about protein folding status to the nucleus and cytosol to adjust the protein folding capacity of the cell or, in the event of chronic damage, induce apoptotic cell death. Recent advances in the understanding of the regulation of UPR signalling and its implications in the pathophysiology of disease might open new therapeutic avenues.

Prdx6 is required to protect human corneal epithelial cells against ultraviolet B injury

BACKGROUND

The protective role of Prdx6 on rat corneal tissue against ultraviolet B injury in vivo has been confirmed previously. We further investigated the function and molecular mechanism of Prdx6 in human corneal epithelial cells under ultraviolet B radiation.

METHODS

The experimental groups were designed as follows: (1) Prdx6 RNAi, (2) Prdx6 RNAi + ultraviolet B radiation, (3) normal human corneal epithelial cells, (4) normal human corneal epithelial cells + ultraviolet B radiation, (5) wild-type Prdx6 overexpression, (6) wild-type Prdx6 overexpression + ultraviolet B radiation, (7) mutant-type Prdx6 overexpression, and (8) mutant-type Prdx6 overexpression + ultraviolet B radiation. The cell survival rate was detected by a Thiazolyl Blue Tetrazolium Bromide assay. Apoptosis, reactive oxygen species, and malondialdehyde were detected with a commercial kit. Gene expression was detected by real-time polymerase chain reaction.

RESULTS

We found the following results. (1) Compared to normal cells, the survival rates were 32%, 87%, and 58% under ultraviolet B radiation in the Prdx6 interference, wild-type overexpression, and mutant-type overexpression groups, respectively. The survival rates were decreased to 50% at 24 h and 31% at 48 h when the phospholipase A2 activity of Prdx6 was inhibited after ultraviolet B radiation. (2) Apoptosis, reactive oxygen species content, and malondialdehyde levels were increased when Prdx6 was downregulated. This phenomenon became more severe under ultraviolet B radiation. (3) The expression levels of apoptosis-related and antioxidant genes all changed along with the changes in expression of Prdx6.

CONCLUSION

(1) Both peroxidase and phospholipase A2 activities of Prdx6 are crucial for its protective role in corneal tissue. (2) Downregulated expression of Prdx6 resulted in high endoplasmic reticulum stress. (3) Apoptosis in human corneal epithelial cells with downregulated Prdx6 coupled with ultraviolet B radiation was related to the pathways of DNA damage and the death receptor. (4) Low levels of antioxidants are sufficient for maintaining homeostasis in human corneal epithelial cells without external stimuli. Under the condition that Prdx6 was downregulated, human corneal epithelial cells were more sensitive to ultraviolet B radiation.

Jiang-Zhi granules decrease sensitivity to low-dose CCl4 induced liver injury in NAFLD rats through reducing endoplasmic reticulum stress

Background

Non-alcoholic fatty liver disease (NAFLD) may increase the sensitivity to liver injury caused by stimulants such as drugs and poisons. The traditional Chinese medicine (TCM) Jiang-Zhi Granule (JZG) has been proven effective for improving liver function, reducing hepatic fat accumulation and inflammation in NAFLD. The purpose of this study is to evaluate the effect of JZG on the susceptibility of NAFLD rats to liver injury and to identify the relevant mechanism.

Methods

Forty wistar rats were randomly divided into five groups, normal group, normal+CCl₄ group, high-fat diet (HFD) group, HFD + CCl₄ group, and HFD + CCl₄ + JZG group. NAFLD were established with HFD for 8 weeks. Then Low-dose CCl₄ was given intraperitoneally to induce liver injury in NAFLD rats for 48 h. From the 5th week of HFD, intragastric administration of JZG was simultaneously given to the rats in the HFD + CCl₄ + JZG group. At the end of the experiment, liver histological pathology, serum transaminase, lipid in liver and blood, as well as hepatic expression levels of endoplasmic reticulum stress (ERS) related molecules were evaluated.

Results

NAFLD rat model was established by eight-week HFD feeding, exhibiting elevated levels of hepatic lipid, blood lipid, serum transaminase and significantly increased expression of ERS related molecules including glucose regulating protein 78 (GRP78), protein kinase RNA-like endoplasmic reticulum kinase (PERK), eukaryotic translation initiation factor 2α (EIF2α), and nuclear factor-kappa B (NFκB) in liver tissues. After injection of CCl₄ in NAFLD rats, elevated serum transaminases, severe inflammation and focal necrosis were observed in liver tissue, but no obvious change was found in the rats of normal group. JZG reduced hepatic inflammation, hepatic necrosis, hepatic lipid, blood transaminases and blood lipids in HFD + CCl₄ rats. ERS related molecules were significantly elevated by low-dose CCl₄ in NAFLD rats, and were down-regulated by JZG.

Conclusion

The sensitivity to CCl₄-induced liver injury is increased in NAFLD rats, which could be improved by JZG. The pharmacological mechanism may involve the regulation of ERS signaling pathway by JZG.

The potential therapeutic actions of melatonin in colorectal cancer

Colorectal cancer (CRC) is the third most common cancer and lethal disease worldwide. Melatonin, an indoleamine produced in pineal gland, shows anticancer effects on a variety of cancers, especially CRC. After clarifying the pathophysiology of CRC, the association of circadian rhythm with CRC, and the relationship between shift work and the incidence of CRC is reviewed. Next, we review the role of melatonin receptors in CRC and the relationship between inflammation and CRC. Also included is a discussion of the mechanism of gene regulation, control of cell proliferation, apoptosis, autophagy, antiangiogenesis and immunomodulation in CRC by melatonin. A review of the drug synergy of melatonin with other anticancer drugs suggests its usefulness in combination therapy. In summary, the information compiled may serve as comprehensive reference for the various mechanisms of action of melatonin against CRC, and as a guide for the design of future experimental research and for advancing melatonin as a therapeutic agent for CRC.

Upregulation of PD-L1 via HMGB1-Activated IRF3 and NF-κB Contributes to UV Radiation-Induced Immune Suppression

Solar ultraviolet radiation (UVR) suppresses skin immunity, which facilitates initiation of skin lesions and establishment of tumors by promoting immune evasion. It is unclear whether immune checkpoints are involved in the modulation of skin immunity by UVR. Here, we report that UVR exposure significantly increased expression of immune checkpoint molecule PD-L1 in melanoma cells. The damage-associated molecular patterns molecule HMGB1 was secreted by melanocytes and keratinocytes upon UVR, which subsequently activated the receptor for advanced glycation endproducts (RAGE) receptor to promote NF-κB- and IRF3-dependent transcription of PD-L1 in melanocytes. UVR exposure significantly reduced the susceptibility of melanoma cells to CD8⁺ T-cell-dependent cytotoxicity, which was mitigated by inhibiting the HMGB1/TBK1/IRF3/NF-κB cascade or by blocking the PD-1/PD-L1 checkpoint. Taken together, our findings demonstrate that UVR-induced upregulation of PD-L1 contributes to immune suppression in the skin microenvironment, which may promote immune evasion of oncogenic cells and drive melanoma initiation and progression. SIGNIFICANCE: These findings identify PD-L1 as a critical component of UV-induced immune suppression in the skin, which facilitates immunoevasion of oncogenic melanocytes and development of melanoma.See related commentary by Sahu, p. 2805.

Parkin targets NOD2 to regulate astrocyte endoplasmic reticulum stress and inflammation

Loss of substantia nigra dopaminergic neurons results in Parkinson disease (PD). Degenerative PD usually presents in the seventh decade whereas genetic disorders, including mutations in PARK2, predispose to early onset PD. PARK2 encodes the parkin E3 ubiquitin ligase which confers pleotropic effects on mitochondrial and cellular fidelity and as a mediator of endoplasmic reticulum (ER) stress signaling. Although the majority of studies investigating ameliorative effects of parkin focus on dopaminergic neurons we found that astrocytes are enriched with parkin. Furthermore, astrocytes deficient in parkin display stress-induced elevation of nucleotide-oligomerization domain receptor 2 (NOD2), a cytosolic receptor integrating ER stress and inflammation. Given the neurotropic and immunomodulatory role of astrocytes we reasoned that parkin may regulate astrocyte ER stress and inflammation to control neuronal homeostasis. We show that, in response to ER stress, parkin knockdown astrocytes exhibit exaggerated ER stress, JNK activation and cytokine release, and reduced neurotropic factor expression. In coculture studied we demonstrate that dopaminergic SHSY5Y cells and primary neurons with the presence of parkin depleted astrocytes are more susceptible to ER stress and inflammation-induced apoptosis than wildtype astrocytes. Parkin interacted with, ubiquitylated and diminished NOD2 levels. Additionally, the genetic induction of parkin ameliorated inflammation in NOD2 expressing cells and knockdown of NOD2 in astrocytes suppressed inflammatory defects in parkin deficient astrocytes and concurrently blunted neuronal apoptosis. Collectively these data identify a role for parkin in modulating NOD2 as a regulatory node in astrocytic control of neuronal homeostasis.

Role of eIF2α Kinases in Translational Control and Adaptation to Cellular Stress

A central mechanism regulating translation initiation in response to environmental stress involves phosphorylation of the α subunit of eukaryotic initiation factor 2 (eIF2α). Phosphorylation of eIF2α causes inhibition of global translation, which conserves energy and facilitates reprogramming of gene expression and signaling pathways that help to restore protein homeostasis. Coincident with repression of protein synthesis, many gene transcripts involved in the stress response are not affected or are even preferentially translated in response to increased eIF2α phosphorylation by mechanisms involving upstream open reading frames (uORFs). This review highlights the mechanisms regulating eIF2α kinases, the role that uORFs play in translational control, and the impact that alteration of eIF2α phosphorylation by gene mutations or small molecule inhibitors can have on health and disease.

The Crosstalk of Endoplasmic Reticulum (ER) Stress Pathways with NF-κB: Complex Mechanisms Relevant for Cancer, Inflammation and Infection

Stressful conditions occuring during cancer, inflammation or infection activate adaptive responses that are controlled by the unfolded protein response (UPR) and the nuclear factor of kappa light polypeptide gene enhancer in B-cells (NF-κB) signaling pathway. These systems can be triggered by chemical compounds but also by cytokines, toll-like receptor ligands, nucleic acids, lipids, bacteria and viruses. Despite representing unique signaling cascades, new data indicate that the UPR and NF-κB pathways converge within the nucleus through ten major transcription factors (TFs), namely activating transcription factor (ATF)4, ATF3, CCAAT/enhancer-binding protein (CEBP) homologous protein (CHOP), X-box-binding protein (XBP)1, ATF6α and the five NF-κB subunits. The combinatorial occupancy of numerous genomic regions (enhancers and promoters) coordinates the transcriptional activation or repression of hundreds of genes that collectively determine the balance between metabolic and inflammatory phenotypes and the extent of apoptosis and autophagy or repair of cell damage and survival. Here, we also discuss results from genetic experiments and chemical activators of endoplasmic reticulum (ER) stress that suggest a link to the cytosolic inhibitor of NF-κB (IκB)α degradation pathway. These data show that the UPR affects this major control point of NF-κB activation through several mechanisms. Taken together, available evidence indicates that the UPR and NF-κB interact at multiple levels. This crosstalk provides ample opportunities to fine-tune cellular stress responses and could also be exploited therapeutically in the future.

The unfolded protein response mediated by PERK is casually related to the pathogenesis of intervertebral disc degeneration

Although the number of patients with intervertebral disc (IVD) degeneration is increasing in aging societies, its etiology and pathogenesis remain elusive and there is currently no effective treatment to prevent this undesirable condition. The unfolded protein response (UPR) is a cellular machinery that plays critical roles in handling endoplasmic reticulum (ER) stress, a condition caused by the accumulation of unfolded proteins in the ER lumen. This study aimed to elucidate the potential role of the UPR mediated by pancreatic endoplasmic reticulum kinase (PERK), one of the major ER stress sensors in mammalian cells, in the development of IVD degeneration. IVD degeneration was artificially induced in Wister rats by percutaneously puncturing the coccyx IVDs and human IVDs were collected from patients who underwent spinal surgery. Expression of the UPR target genes was elevated in degenerative IVDs in both humans and rats. The induction of ER stress in annulus fibrosus cells significantly increased the transcripts for tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6) in a nuclear factor (NF)-κB pathway-dependent manner. The expression of TNF-α and IL-6 was significantly reduced by treatment with a selective PERK inhibitor, GSK2606414, and by gene silencing against PERK and activating transcription factor 4 (ATF4) transcripts. Our findings indicate that the UPR mediated by the PERK pathway is causally related to the development of IVD degeneration, suggesting that PERK may be a potential molecular target for suppressing the degenerative changes in IVDs. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1334-1345, 2018.

Experimental Nonalcoholic Steatohepatitis and Liver Fibrosis Are Ameliorated by Pharmacologic Activation of Nrf2 (NF-E2 p45-Related Factor 2)

BACKGROUND & AIMS

Nonalcoholic steatohepatitis (NASH) is associated with oxidative stress. We surmised that pharmacologic activation of NF-E2 p45-related factor 2 (Nrf2) using the acetylenic tricyclic bis(cyano enone) TBE-31 would suppress NASH because Nrf2 is a transcriptional master regulator of intracellular redox homeostasis.

METHODS

Nrf2+/+ and Nrf2-/- C57BL/6 mice were fed a high-fat plus fructose (HFFr) or regular chow diet for 16 weeks or 30 weeks, and then treated for the final 6 weeks, while still being fed the same HFFr or regular chow diets, with either TBE-31 or dimethyl sulfoxide vehicle control. Measures of whole-body glucose homeostasis, histologic assessment of liver, and biochemical and molecular measurements of steatosis, endoplasmic reticulum (ER) stress, inflammation, apoptosis, fibrosis, and oxidative stress were performed in livers from these animals.

RESULTS

TBE-31 treatment reversed insulin resistance in HFFr-fed wild-type mice, but not in HFFr-fed Nrf2-null mice. TBE-31 treatment of HFFr-fed wild-type mice substantially decreased liver steatosis and expression of lipid synthesis genes, while increasing hepatic expression of fatty acid oxidation and lipoprotein assembly genes. Also, TBE-31 treatment decreased ER stress, expression of inflammation genes, and markers of apoptosis, fibrosis, and oxidative stress in the livers of HFFr-fed wild-type mice. By comparison, TBE-31 did not decrease steatosis, ER stress, lipogenesis, inflammation, fibrosis, or oxidative stress in livers of HFFr-fed Nrf2-null mice.

CONCLUSIONS

Pharmacologic activation of Nrf2 in mice that had already been rendered obese and insulin resistant reversed insulin resistance, suppressed hepatic steatosis, and mitigated against NASH and liver fibrosis, effects that we principally attribute to inhibition of ER, inflammatory, and oxidative stress.

The Mechanisms of Carnosol in Chemoprevention of Ultraviolet B-Light-Induced Non-Melanoma Skin Cancer Formation

Carnosol is a natural compound extracted from rosemary and sage, which has been demonstrated to have anti-inflammatory, anti-oxidant, and anti-cancer properties. In this report, we evaluated the therapeutic potential and elucidated the potential mechanism of action of carnosol in chemoprevention of ultraviolet B-light (UVB) induced non-melanoma skin cancer formation. Our data indicated that carnosol could partially reduce UVB-induced reactive oxygen species (ROS) elevation and thus reduce DNA damage. It could also reduce UVB-induced formation of cyclobutane pyrimidine dimers (CDP) in keratinocytes possibly through its ability in absorbing UVB radiation. In addition, carnosol could inhibit the UVB-induced activation of NF-κB and also reduce UVB-induced transformation of keratinocytes. Taken together, the results indicate the role of carnosol as a potential chemopreventive agent upon UVB radiation.

Enhancement of Protective Effects of Radix Scutellariae on UVB-induced Photo Damage in Human HaCaT Keratinocytes

Radix Scutellariae (RS) has long been used in the treatment of inflammatory and allergic diseases. Its main flavonoids, baicalin (BG) and wogonoside (WG), can be hydrolyzed into their corresponding aglycones, baicalein (B) and wogonin (W). In this study, we developed a safe and effective method of transforming these glycosides using Peclyve PR. The transformation rate of BG and WG reached 98.5 and 98.1%, respectively, with 10% enzyme at 40 °C for 60 h. Furthermore, we compared the anti-photoaging activity of RS before and after enzyme treatment, as well as their respective main components, in UVB-irradiated HaCaT cells. Results found that enzyme-treated RS (ERS) appeared to be much better at preventing UVB-induced photoaging than RS. ERS significantly inhibited the upregulation of matrix metalloproteinase-1 and IL-6 caused by UVB radiation by inactivating the MAPK/AP-1 and NF-κB/IκB-α signaling pathways. ERS treatment also recovered UVB-induced reduction of procollagen type I by activating the TGF-β/Smad pathway. In addition, ERS exhibited an excellent antioxidant activity, which could increase the expression of cytoprotective antioxidants such as HO-1 and NQ-O1, by facilitating Nrf2 nuclear transfer. These findings demonstrated that the photoprotective effects of RS were significantly improved by enzyme-modified biotransformation.

Subclinical cutaneous inflammation remained after permeability barrier disruption enhances UV sensitivity by altering ER stress responses and topical pseudoceramide prevents them

Stratum corneum forms the UV barrier. The effect of ultraviolet B (UVB) on normal skin was extensively studied; however, its effect on barrier perturbed skin remains undefined. Both barrier perturbation and UVB irradiation induce endoplasmic reticulum (ER) stress and unfolded protein response (UPR) in keratinocytes. Mild ER stress activates homeostatic UPR, while severe ER stress leads to abnormal UPR, promoting apoptosis and inflammation. Here, we investigated UV sensitivity and UVB-induced UPR in barrier-disrupted human skin and the effects of pseudoceramide-dominant emollient on UVB-induced skin responses. Tape-stripped skin of healthy volunteers showed enhanced susceptibility to erythema and augmented proinflammatory cytokines induction following suberythemal UVB irradiation. Suberythemal UVB activated XBP1 in normal skin, while increased CHOP transcription in barrier perturbed skin. After tape stripping, pseudoceramide-dominant emollient was applied for 3 days, and then, the areas were irradiated with suberythemal UVB. Pretreatment with topical pseudoceramide protected against UVB-induced upregulation of IL-1β, IL-6, and TNF-α transcription and reduced susceptibility to erythema following UVB. Topical pseudoceramide also suppressed suberythemal UVB-induced CHOP transcription in barrier-disrupted skin. Taken together, these data indicate that permeability barrier disruption increases UV sensitivity in human skin, partly via switch the UVB-induced UPR, from homeostatic signals to pro-apoptotic and proinflammatory signals. In addition, we conclude that pseudoceramide-dominant emollient suppresses excessive ER stress induction and CHOP activation following UVB in barrier damaged skin, providing evidence that pseudoceramide-dominant emollients can be promising strategies for photoprotection of the barrier damaged skin.

Endoplasmic Reticulum Stress and Oxidative Stress: A Vicious Nexus Implicated in Bowel Disease Pathophysiology

The endoplasmic reticulum (ER) is a complex protein folding and trafficking organelle. Alteration and discrepancy in the endoplasmic reticulum environment can affect the protein folding process and hence, can result in the production of misfolded proteins. The accumulation of misfolded proteins causes cellular damage and elicits endoplasmic reticulum stress. Under such stress conditions, cells exhibit reduced functional synthesis, and will undergo apoptosis if the stress is prolonged. To resolve the ER stress, cells trigger an intrinsic mechanism called an unfolded protein response (UPR). UPR is an adaptive signaling process that triggers multiple pathways through the endoplasmic reticulum transmembrane transducers, to reduce and remove misfolded proteins and improve the protein folding mechanism, in order to improve and maintain endoplasmic reticulum homeostasis. An increasing number of studies support the view that oxidative stress has a strong connection with ER stress. During the protein folding process, reactive oxygen species are produced as by-products, leading to impaired reduction-oxidation (redox) balance conferring oxidative stress. As the protein folding process is dependent on redox homeostasis, the oxidative stress can disrupt the protein folding mechanism and enhance the production of misfolded proteins, causing further ER stress. It is proposed that endoplasmic reticulum stress and oxidative stress together play significant roles in the pathophysiology of bowel diseases.

MCPIP1 contributes to the inflammatory response of UVB-treated keratinocytes

BACKGROUND

Monocyte chemoattractant protein-1-induced protein-1 (MCPIP1), also known as regnase-1, negatively regulates many cellular processes including the cellular response to inflammatory agents, differentiation, viability, and proliferation. It possesses a PilT N-terminus (PIN) domain that is directly involved in regulating the stability of transcripts and miRNAs by recognizing stem loop structures and degrading them by endonucleolytic cleavage.

OBJECTIVE

We investigated the role of MCPIP1 in the response of human primary keratinocytes to UVB stress.

METHODS

Keratinocytes were treated with UVB, siRNA against MCPIP1, pharmacological inhibitors of signaling pathways, or subjected to control treatments. The mRNA and protein levels of MCPIP1 and MCPIP1-dependent changes gene expression were analyzed by quantitative (Q)-RT-PCRs and Western blots. Secretion of TNFα and IL-8 was determined by ELISA.

RESULTS

UVB treatment of keratinocytes induced upregulation of MCPIP1 at the mRNA level after 4-8h and at the protein level after 8-16h. MCPIP1 abundance depended on NF-κB activity. Using an siRNA strategy, we found that diminished MCPIP1 resulted in an up-regulation of transcripts coding for IL-8, TNFα, COX-2, and BCL-2, as well as an enhanced release of IL-8. Moreover, decreased phosphorylation of NF-κB and p38 signaling pathways were observed in addition to a slight up-regulation of ERK1/2 directly after UVB treatment. Twenty-four hours later, decreased phosphorylation was observed only for NF-κB and p38. Furthermore, in MCPIP1-suppressed cells, the levels of pro-apoptotic Puma, the phosphorylated form of p53 and the abundance of its target p21 as well as the activity of caspase 3 decreased, while the level of cyclin D1 increased.

CONCLUSION

MCPIP1 contributes to the UVB response of keratinocytes by altering metabolic and apoptotic processes and the release of inflammatory mediators.

Endoplasmic reticulum stress and the development of endothelial dysfunction

The vascular endothelium plays a critical role in cardiovascular homeostasis, and thus identifying the underlying causes of endothelial dysfunction has important clinical implications. In this regard, the endoplasmic reticulum (ER) has recently emerged as an important regulator of metabolic processes. Dysfunction within the ER, broadly termed ER stress, evokes the unfolded protein response (UPR), an adaptive pathway that aims to restore ER homeostasis. Although the UPR is the first line of defense against ER stress, chronic activation of the UPR leads to cell dysfunction and death and has recently been implicated in the pathogenesis of endothelial dysfunction. Numerous risk factors for endothelial dysfunction can induce ER stress, which may in turn disrupt endothelial function via direct effects on endothelium-derived vasoactive substances or by activating other pathogenic cellular networks such as inflammation and oxidative stress. This review summarizes the available data linking ER stress to endothelial dysfunction.

The inhibition of protein translation mediated by AtGCN1 is essential for cold tolerance in Arabidopsis thaliana

In yeast, the interaction of General Control Non-derepressible 1 (GCN1) with GCN2 enables GCN2 to phosphorylate eIF2α (the alpha subunit of eukaryotic translation initiation factor 2) under a variety of stresses. Here, we cloned AtGCN1, an Arabidopsis homologue of GCN1. We show that AtGCN1 directly interacts with GCN2 and is essential for the phosphorylation of eIF2α under salicylic acid (SA), ultraviolet (UV), cold stress and amino acid deprivation conditions. Two mutant alleles, atgcn1-1 and atgcn1-2, which are defective in the phosphorylation of eIF2α, showed increased sensitivity to cold stress, compared with the wild type. Ribosome-bound RNA profiles showed that the translational state of mRNA was higher in atgcn1-1 than in the wild type. Our result also showed that cold treatment reduced the tendency of the tor mutant seedlings to produce purple hypocotyls. In addition, the kinase activity of TOR was transiently inhibited when plants were exposed to cold stress, suggesting that the inhibition of TOR is another pathway important for plants to respond to cold stress. In conclusion, our results indicate that the AtGCN1-mediated phosphorylation of eIF2α, which is required for inhibiting the initiation of protein translation, is essential for cold tolerance in Arabidopsis.

The role of Prdx6 in the protection of cells of the crystalline lens from oxidative stress induced by UV exposure

PURPOSE

The immediate aim of this study was to investigate alterations in peroxiredoxin (Prdx) 6 at posttranslational levels, and the levels of protein oxidation, lipid peroxidation, and reactive oxygen species (ROS) in lens epithelial cells (LECs) after exposure to severe oxidative stress, such as ultraviolet-B (UV-B). Our ultimate aim was to provide new information on antioxidant defenses in the lens and their regulation, thereby broadening existing knowledge of the role of Prdx6 in lens physiology and pathophysiology.

METHODS

The expression of the hyperoxidized form of Prdx6 and oxidation of protein were analyzed by western blotting and the OxyBlot assay in human LECs (hLECs). ROS levels were quantified using DCFH-DA dye, and cell viability was quantified by the MTS and TUNEL assays. To evaluate the protective effect of Prdx6, we cultured lenses with or without the TAT transduction domain (TAT-HA-Prdx6) and observed (and photographed) the cultures at specified time-points after the exposure to UV-B for the development of opacity.

RESULTS

Prdx6 in hLECs was hyperoxidized after exposure to high amounts of UV-B. UV-B treatment of hLECs increased the levels of cell death, protein oxidation, and ROS. hLECs exposed to UV-B showed higher levels of ROS, which could be reduced by the application of extrinsic TAT-HA-Prdx6, attenuating UV-B-induced lens opacity and apoptotic cell death.

CONCLUSION

Excessive oxidative stress induces the hyperoxidation of Prdx6 and may reduce the ability of Prdx6 to protect LECs against ROS or stresses. Because extrinsic Prdx6 could attenuate UV-B-induced abuse, this molecule may have a potential in preventing cataractogenesis.

Gastric bypass surgery is protective from high-fat diet-induced non-alcoholic fatty liver disease and hepatic endoplasmic reticulum stress

AIM

High-fat diets are known to contribute to the development of obesity and related co-morbidities including non-alcoholic fatty liver disease (NAFLD). The accumulation of hepatic lipid may increase endoplasmic reticulum (ER) stress and contribute to non-alcoholic steatohepatitis and metabolic disease. We hypothesized that bariatric surgery would counter the effects of a high-fat diet (HFD) on obesity-associated NAFLD.

METHODS

Sixteen of 24 male Sprague Dawley rats were randomized to Sham (N = 8) or Roux-en-Y gastric bypass (RYGB) surgery (N = 8) and compared to Lean controls (N = 8). Obese rats were maintained on a HFD throughout the study. Insulin resistance (HOMA-IR), and hepatic steatosis, triglyceride accumulation, ER stress and apoptosis were assessed at 90 days post-surgery.

RESULTS

Despite eating a HFD for 90 days post-surgery, the RYGB group lost weight (-20.7 ± 6%, P < 0.01) and improved insulin sensitivity (P < 0.05) compared to Sham. These results occurred with no change in food intake between groups. Hepatic steatosis and ER stress, specifically glucose-regulated protein-78 (Grp78, P < 0.001), X-box binding protein-1 (XBP-1) and spliced XBP-1 (P < 0.01), and fibroblast growth factor 21 (FGF21) gene expression, were normalized in the RYGB group compared to both Sham and Lean controls. Significant TUNEL staining in liver sections from the Obese Sham group, indicative of accelerated cell death, was absent in the RYGB and Lean control groups. Additionally, fasting plasma glucagon like peptide-1 was increased in RYGB compared to Sham (P < 0.02).

CONCLUSION

These data suggest that in obese rats, RYGB surgery protects the liver against HFD-induced fatty liver disease by attenuating ER stress and excess apoptosis.

An initial phase of JNK activation inhibits cell death early in the endoplasmic reticulum stress response

Accumulation of unfolded proteins in the endoplasmic reticulum (ER) activates the unfolded protein response (UPR). In mammalian cells, UPR signals generated by several ER-membrane-resident proteins, including the bifunctional protein kinase endoribonuclease IRE1α, control cell survival and the decision to execute apoptosis. Processing of XBP1 mRNA by the RNase domain of IRE1α promotes survival of ER stress, whereas activation of the mitogen-activated protein kinase JNK family by IRE1α late in the ER stress response promotes apoptosis. Here, we show that activation of JNK in the ER stress response precedes activation of XBP1. This activation of JNK is dependent on IRE1α and TRAF2 and coincides with JNK-dependent induction of expression of several antiapoptotic genes, including cIap1 (also known as Birc2), cIap2 (also known as Birc3), Xiap and Birc6 ER-stressed Jnk1(-/-) Jnk2(-/-) (Mapk8(-/-) Mapk9(-/-)) mouse embryonic fibroblasts (MEFs) display more pronounced mitochondrial permeability transition and increased caspase 3/7 activity compared to wild-type MEFs. Caspase 3/7 activity is also elevated in ER-stressed cIap1(-/-) cIap2(-/-) and Xiap(-/-) MEFs. These observations suggest that JNK-dependent transcriptional induction of several inhibitors of apoptosis contributes to inhibiting apoptosis early in the ER stress response.

Therapeutic microRNAs targeting the NF-kappa B signaling circuits of cancers

MicroRNAs (miRNAs) not only directly regulate NF-κB expression, but also up- or down-regulate NF-κB activity via upstream and downstream signaling pathways of NF-κB. In many cancer cells, miRNA expressions are altered accompanied with an elevation of NF-κB activity, which often plays a role in promoting cancer development and progression as well as hindering the effectiveness of chemo and radiation therapies. Thus NF-κB-targeting miRNAs have been identified and characterized as potential therapeutics for cancer treatment and sensitizers of chemo and radiotherapies. However, due to cross-targeting and instability of miRNAs, some limitations of using miRNA as cancer therapeutics still exist. In this review, the mechanisms for miRNA-mediated alteration of NF-κB expression and activation in different types of cancers will be discussed. The results of therapeutic use of NF-κB-targeting miRNA for cancer treatment will be examined. Some limitations, challenges and potential strategies in future development of miRNA as cancer therapeutics are also assessed.

AMPK/mTOR-mediated inhibition of survivin partly contributes to metformin-induced apoptosis in human gastric cancer cell

Recent studies demonstrated that metformin exerts anti-neoplastic effect in a spectrum of malignancies. However, the mechanism whereby metformin affects various cancers, including gastric cancer, is poorly elucidated. Considering apoptosis plays critical role in tumorigenesis, we, in the present study, investigated the in vitro apoptotic effect of metformin on human gastric cancer cell and the underlying mechanism. Three differently-differentiated gastric cancer cell lines, MKN-28, SGC-7901 and BGC-823, along with one noncancerous gastric cell line GES-1 were used. We found that metformin treatment selectively induces apoptosis in the 3 cancer cell lines, but not the noncancerous one, as confirmed by flow cytometry, Caspase-Glo assay and western blotting against PARP and cleaved caspase 3. Moreover, the apoptotic effect of metformin seems to correlate negatively with the differentiation degree of gastric cancer. Metformin-induced apoptosis may be partially mediated through inhibition of anti-apoptotic survivin. Additionally, AMPK and mTOR, 2 important regulatory molecules responsible for metformin action, were investigated for their possible involvements in metformin-induced apoptosis of gastric cancer cell. AMPK knockdown by siRNA restores metformin-inhibited survivin expression and partially abolishes metformin-induced apoptosis. Similarly, forced overexpression of mTOR downstream effector p70S6K1 relieves metformin-induced inhibition of survivin and partly attenuates metformin-induced apoptosis. More importantly, survivin overexpression alleviates metformin-induced apoptosis. Xenograft nude mouse experiment also confirmed that AMPK/mTOR-mediated decrease of suvivin is in vivo implicated in metformin-induced apoptosis. Taken together, these evidences suggest that AMPK/mTOR-mediated inhibition of survivin may partly contribute to metformin-induced apoptosis of gastric cancer cell.

The role of constitutive nitric-oxide synthase in ultraviolet B light-induced nuclear factor κB activity

NF-κB is a transcription factor involved in many signaling pathways that also plays an important role in UV-induced skin tumorigenesis. UV radiation can activate NF-κB, but the detailed mechanism remains unclear. In this study, we provided evidence that the activation of constitutive nitric-oxide synthase plays a role in regulation of IκB reduction and NF-κB activation in human keratinocyte HaCaT cells in early phase (within 6 h) post-UVB. Treating the cells with l-NAME, a selective inhibitor of constitutive nitric-oxide synthase (cNOS), can partially reverse the IκB reduction and inhibit the DNA binding activity as well as nuclear translocation of NF-κB after UVB radiation. A luciferase reporter assay indicates that UVB-induced NF-κB activation is totally diminished in cNOS null cells. The cNOS-mediated reduction of IκB is likely due to the imbalance of nitric oxide/peroxynitrite because treating the cells with lower (50 μm), but not higher (100-500 μm), concentration of S-nitroso-N-acetylpenicillamine (SNAP) can reverse the effect of l-NAME in partial restore IκB level post-UVB. Our data also showed that NF-κB activity was required for maintaining a stable IκB kinase α subunit (IKKα) level because treating the cells with NF-κB or cNOS inhibitors could reduce IKKα level upon UVB radiation. In addition, our data demonstrated that although NF-κB protects cells from UVB-induced death, its pro-survival activity was likely neutralized by the pro-death activity of peroxynitrite after UVB radiation.

A molecular web: endoplasmic reticulum stress, inflammation, and oxidative stress

Execution of fundamental cellular functions demands regulated protein folding homeostasis. Endoplasmic reticulum (ER) is an active organelle existing to implement this function by folding and modifying secretory and membrane proteins. Loss of protein folding homeostasis is central to various diseases and budding evidences suggest ER stress as being a major contributor in the development or pathology of a diseased state besides other cellular stresses. The trigger for diseases may be diverse but, inflammation and/or ER stress may be basic mechanisms increasing the severity or complicating the condition of the disease. Chronic ER stress and activation of the unfolded-protein response (UPR) through endogenous or exogenous insults may result in impaired calcium and redox homeostasis, oxidative stress via protein overload thereby also influencing vital mitochondrial functions. Calcium released from the ER augments the production of mitochondrial Reactive Oxygen Species (ROS). Toxic accumulation of ROS within ER and mitochondria disturbs fundamental organelle functions. Sustained ER stress is known to potentially elicit inflammatory responses via UPR pathways. Additionally, ROS generated through inflammation or mitochondrial dysfunction could accelerate ER malfunction. Dysfunctional UPR pathways have been associated with a wide range of diseases including several neurodegenerative diseases, stroke, metabolic disorders, cancer, inflammatory disease, diabetes mellitus, cardiovascular disease, and others. In this review, we have discussed the UPR signaling pathways, and networking between ER stress-induced inflammatory pathways, oxidative stress, and mitochondrial signaling events, which further induce or exacerbate ER stress.

Endoplasmic reticulum stress and oxidative stress in cell fate decision and human disease

SIGNIFICANCE

The endoplasmic reticulum (ER) is a specialized organelle for the folding and trafficking of proteins, which is highly sensitive to changes in intracellular homeostasis and extracellular stimuli. Alterations in the protein-folding environment cause accumulation of misfolded proteins in the ER that profoundly affect a variety of cellular signaling processes, including reduction-oxidation (redox) homeostasis, energy production, inflammation, differentiation, and apoptosis. The unfolded protein response (UPR) is a collection of adaptive signaling pathways that evolved to resolve protein misfolding and restore an efficient protein-folding environment.

RECENT ADVANCES

Production of reactive oxygen species (ROS) has been linked to ER stress and the UPR. ROS play a critical role in many cellular processes and can be produced in the cytosol and several organelles, including the ER and mitochondria. Studies suggest that altered redox homeostasis in the ER is sufficient to cause ER stress, which could, in turn, induce the production of ROS in the ER and mitochondria.

CRITICAL ISSUES

Although ER stress and oxidative stress coexist in many pathologic states, whether and how these stresses interact is unknown. It is also unclear how changes in the protein-folding environment in the ER cause oxidative stress. In addition, how ROS production and protein misfolding commit the cell to an apoptotic death and contribute to various degenerative diseases is unknown.

FUTURE DIRECTIONS

A greater fundamental understanding of the mechanisms that preserve protein folding homeostasis and redox status will provide new information toward the development of novel therapeutics for many human diseases.

Pseudomonas aeruginosa quorum-sensing molecule homoserine lactone modulates inflammatory signaling through PERK and eI-F2α

Pseudomonas aeruginosa secrete N-(3-oxododecanoyl)-homoserine lactone (HSL-C12) as a quorum-sensing molecule to regulate bacterial gene expression. Because HSL-C12 is membrane permeant, multiple cell types in P. aeruginosa-infected airways may be exposed to HSL-C12, especially adjacent to biofilms where local (HSL-C12) may be high. Previous reports showed that HSL-C12 causes both pro- and anti-inflammatory effects. To characterize HSL-C12's pro- and anti-inflammatory effects in host cells, we measured protein synthesis, NF-κB activation, and KC (mouse IL-8) and IL-6 mRNA and protein secretion in wild-type mouse embryonic fibroblasts (MEF). To test the role of the endoplasmic reticulum stress inducer, PERK we compared these responses in PERK(-/-) and PERK-corrected PERK(-/-) MEF. During 4-h treatments of wild-type MEF, HSL-C12 potentially activated NF-κB p65 by preventing the resynthesis of IκB and increased transcription of KC and IL-6 genes (quantitative PCR). HSL-C12 also inhibited secretion of KC and/or IL-6 into the media (ELISA) both in control conditions and also during stimulation by TNF-α. HSL-C12 also activated PERK (as shown by increased phosphorylation of eI-F2α) and inhibited protein synthesis (as measured by incorporation of [(35)S]methionine by MEF). Comparisons of PERK(-/-) and PERK-corrected MEF showed that HSL-C12's effects were explained in part by activation of PERK→phosphorylation of eI-F2α→inhibition of protein synthesis→reduced IκBα production→activation of NF-κB→increased transcription of the KC gene but reduced translation and secretion of KC. HSL-C12 may be an important modulator of early (up to 4 h) inflammatory signaling in P. aeruginosa infections.

Potential For Cell-mediated Immune Responses In Mouse Models Of Pelizaeus-Merzbacher Disease

Although activation of the innate and adaptive arms of the immune system are undoubtedly involved in the pathophysiology of neurodegenerative diseases, it is unclear whether immune system activation is a primary or secondary event. Increasingly, published studies link primary metabolic stress to secondary inflammatory responses inside and outside of the nervous system. In this study, we show that the metabolic stress pathway known as the unfolded protein response (UPR) leads to secondary activation of the immune system. First, we observe innate immune system activation in autopsy specimens from Pelizaeus-Merzbacher disease (PMD) patients and mouse models stemming from PLP1 gene mutations. Second, missense mutations in mildly- and severely-affected Plp1-mutant mice exhibit immune-associated expression profiles with greater disease severity causing an increasingly proinflammatory environment. Third, and unexpectedly, we find little evidence for dysregulated expression of major antioxidant pathways, suggesting that the unfolded protein and oxidative stress responses are separable. Together, these data show that UPR activation can precede innate and/or adaptive immune system activation and that neuroinflammation can be titrated by metabolic stress in oligodendrocytes. Whether or not such activation leads to autoimmune disease in humans is unclear, but the case report of steroid-mitigated symptoms in a PMD patient initially diagnosed with multiple sclerosis lends support.

CD36 deletion improves recovery from spinal cord injury

CD36 is a pleiotropic receptor involved in several pathophysiological conditions, including cerebral ischemia, neurovascular dysfunction and atherosclerosis, and recent reports implicate its involvement in the endoplasmic reticulum stress response (ERSR). We hypothesized that CD36 signaling contributes to the inflammation and microvascular dysfunction following spinal cord injury. Following contusive injury, CD36(-/-) mice demonstrated improved hindlimb functional recovery and greater white matter sparing than CD36(+/+) mice. CD36(-/-) mice exhibited a reduced macrophage, but not neutrophil, infiltration into the injury epicenter. Fewer infiltrating macrophages were either apoptotic or positive for the ERSR marker, phospho-ATF4. CD36(-/-) mice also exhibited significant improvements in injury heterodomain vascularity and function. These microvessels accumulated less of the oxidized lipid product 4-hydroxy-trans-2-nonenal (4HNE) and exhibited a reduced ERSR, as detected by vascular phospho-ATF4, CHOP and CHAC-1 expression. In cultured primary endothelial cells, deletion of CD36 diminished 4HNE-induced phospho-ATF4 and CHOP expression. A reduction in phospho-eIF2α and subsequent increase in KDEL-positive, ER-localized proteins suggest that 4HNE-CD36 signaling facilitates the detection of misfolded proteins upstream of eIF2α phosphorylation, ultimately leading to CHOP-induced apoptosis. We conclude that CD36 deletion modestly, but significantly, improves functional recovery from spinal cord injury by enhancing vascular function and reducing macrophage infiltration. These phenotypes may, in part, stem from reduced ER stress-induced cell death within endothelial and macrophage cells following injury.

Stress-regulated translational attenuation adapts mitochondrial protein import through Tim17A degradation

Stress-regulated signaling pathways protect mitochondrial proteostasis and function from pathologic insults. Despite the importance of stress-regulated signaling pathways in mitochondrial proteome maintenance, the molecular mechanisms by which these pathways maintain mitochondrial proteostasis remain largely unknown. We identify Tim17A as a stress-regulated subunit of the translocase of the inner membrane 23 (TIM23) mitochondrial protein import complex. We show that Tim17A protein levels are decreased downstream of stress-regulated translational attenuation induced by eukaryotic initiation factor 2α (eIF2α) phosphorylation through a mechanism dependent on the mitochondrial protease YME1L. Furthermore, we demonstrate that decreasing Tim17A attenuates TIM23-dependent protein import, promotes the induction of mitochondrial unfolded protein response (UPR)-associated proteostasis genes, and confers stress resistance in C. elegans and mammalian cells. Thus, our results indicate that Tim17A degradation is a stress-responsive mechanism by which cells adapt mitochondrial protein import efficiency and promote mitochondrial proteostasis in response to the numerous pathologic insults that induce stress-regulated translation attenuation.

UVC inhibits collagen biosynthesis through up-regulation of NF-κB p65 signaling in cultured fibroblasts

The effects of UVC on collagen biosynthesis, prolidase activity, expression of α₂β₁ integrin, IGF-I receptor, FAK, MAP-kinases (ERK1 and ERK2) and the transcription factor NF-κB p65 were evaluated in human dermal fibroblasts. Confluent fibroblasts were treated with UVC light at a rates of 30 and 60 J/m(2). It was found that UVC-dependent decrease in collagen biosynthesis was not accompanied by parallel decrease in prolidase activity and expression. Since insulin-like growth factor receptor (IGF-IR) and α₂β₁ integrin signaling are the most potent regulators of collagen biosynthesis, the effect of UVC on IGF-IR and α₂β₁ integrin receptor expressions were evaluated. It was found that the exposure of the cells to UVC contributed to decrease in α₂β₁ integrin receptor and FAK expression and to an increase in IGF-IR and pERK1, pERK2 expressions. It was accompanied by an increase in the expression of NF-κB p65, the known inhibitor of collagen gene expression. The data suggest that UVC-dependent decrease of collagen biosynthesis in cultured human skin fibroblasts results from decrease in α₂β₁ integrin receptor signaling and activation of NF-κB p65, that is responsible for down-regulation of collagen gene expression.

Zidovudine (AZT) and hepatic lipid accumulation: implication of inflammation, oxidative and endoplasmic reticulum stress mediators

The clinical effectiveness of Zidovudine (AZT) is constrained due to its side-effects including hepatic steatosis and toxicity. However, the mechanism(s) of hepatic lipid accumulation in AZT-treated individuals is unknown. We hypothesized that AZT-mediated oxidative and endoplasmic reticulum (ER) stress may play a role in the AZT-induced hepatic lipid accumulation. AZT treatment of C57BL/6J female mice (400 mg/day/kg body weight, i.p.) for 10 consecutive days significantly increased hepatic triglyceride levels and inflammation. Markers of oxidative stress such as protein oxidation, nitration, glycation and lipid peroxidation were significantly higher in the AZT-treated mice compared to vehicle controls. Further, the levels of ER stress marker proteins like GRP78, p-PERK, and p-eIF2α were significantly elevated in AZT-treated mice. The level of nuclear SREBP-1c, a transcription factor involved in fat synthesis, was increased while significantly decreased protein levels of phospho-acetyl-CoA carboxylase, phospho-AMP kinase and PPARα as well as inactivation of 3-keto-acyl-CoA thiolase in the mitochondrial fatty acid β-oxidation pathway were observed in AZT-exposed mice compared to those in control animals. Collectively, these data suggest that elevated oxidative and ER stress plays a key role, at least partially, in lipid accumulation, inflammation and hepatotoxicity in AZT-treated mice.

ER stress transcription factor Xbp1 suppresses intestinal tumorigenesis and directs intestinal stem cells

X-box–binding protein 1 suppresses tumor formation in the gut by regulating Ire1α and Stat3-mediated regenerative responses in the epithelium as a consequence of ER stress.

Unresolved endoplasmic reticulum (ER) stress in the epithelium can provoke intestinal inflammation. Hypomorphic variants of ER stress response mediators, such as X-box–binding protein 1 (XBP1), confer genetic risk for inflammatory bowel disease. We report here that hypomorphic Xbp1 function instructs a multilayered regenerative response in the intestinal epithelium. This is characterized by intestinal stem cell (ISC) expansion as shown by an inositol-requiring enzyme 1α (Ire1α)–mediated increase in Lgr5⁺ and Olfm4⁺ ISCs and a Stat3-dependent increase in the proliferative output of transit-amplifying cells. These consequences of hypomorphic Xbp1 function are associated with an increased propensity to develop colitis-associated and spontaneous adenomatous polyposis coli (APC)–related tumors of the intestinal epithelium, which in the latter case is shown to be dependent on Ire1α. This study reveals an unexpected role for Xbp1 in suppressing tumor formation through restraint of a pathway that involves an Ire1α- and Stat3-mediated regenerative response of the epithelium as a consequence of ER stress. As such, Xbp1 in the intestinal epithelium not only regulates local inflammation but at the same time also determines the propensity of the epithelium to develop tumors.

The bacterial quorum-sensing signal molecule N-3-oxo-dodecanoyl-L-homoserine lactone reciprocally modulates pro- and anti-inflammatory cytokines in activated macrophages

The bacterial molecule N-3-oxo-dodecanoyl-l-homoserine lactone (C12) has critical roles in both interbacterial communication and interkingdom signaling. The ability of C12 to downregulate production of the key proinflammatory cytokine TNF-α in stimulated macrophages was suggested to contribute to the establishment of chronic infections by opportunistic Gram-negative bacteria, such as Pseudomonas aeruginosa. We show that, in contrast to TNF-α suppression, C12 amplifies production of the major anti-inflammatory cytokine IL-10 in LPS-stimulated murine RAW264.7 macrophages, as well as peritoneal macrophages. Furthermore, C12 increased IL-10 mRNA levels and IL-10 promoter reporter activity in LPS-stimulated RAW264.7 macrophages, indicating that C12 modulates IL-10 expression at the transcriptional level. Finally, C12 substantially potentiated LPS-stimulated NF-κB DNA-binding levels and prolonged p38 MAPK phosphorylation in RAW264.7 macrophages, suggesting that increased transcriptional activity of NF-κB and/or p38-activated transcription factors serves to upregulate IL-10 production in macrophages exposed to both LPS and C12. These findings reveal another part of the complex array of host transitions through which opportunistic bacteria downregulate immune responses to flourish and establish a chronic infection.

NF-κB-dependent role for cold-inducible RNA binding protein in regulating interleukin 1β

The cold inducible RNA binding protein (CIRBP) responds to a wide array of cellular stresses, including short wavelength ultraviolet light (UVC), at the transcriptional and post-translational level. CIRBP can bind the 3'untranslated region of specific transcripts to stabilize them and facilitate their transport to ribosomes for translation. Here we used RNA interference and oligonucleotide microarrays to identify potential downstream targets of CIRBP induced in response to UVC. Twenty eight transcripts were statistically increased in response to UVC and these exhibited a typical UVC response. Only 5 of the 28 UVC-induced transcripts exhibited a CIRBP-dependent pattern of expression. Surprisingly, 3 of the 5 transcripts (IL1B, IL8 and TNFAIP6) encoded proteins important in inflammation with IL-1β apparently contributing to IL8 and TNFAIP6 expression in an autocrine fashion. UVC-induced IL1B expression could be inhibited by pharmacological inhibition of NFκB suggesting that CIRBP was affecting NF-κB signaling as opposed to IL1B mRNA stability directly. Bacterial lipopolysaccharide (LPS) was used as an activator of NF-κB to further study the potential link between CIRBP and NFκB. Transfection of siRNAs against CIRBP reduced the extent of the LPS-induced phosphorylation of IκBα, NF-κB DNA binding activity and IL-1β expression. The present work firmly establishes a novel link between CIRBP and NF-κB signaling in response to agents with diverse modes of action. These results have potential implications for disease states associated with inflammation.

Endoplasmic reticulum stress in nonalcoholic fatty liver disease

The underlying causes of nonalcoholic fatty liver disease are unclear, although recent evidence has implicated the endoplasmic reticulum in both the development of steatosis and progression to nonalcoholic steatohepatitis. Disruption of endoplasmic reticulum homeostasis, often termed ER stress, has been observed in liver and adipose tissue of humans with nonalcoholic fatty liver disease and/or obesity. Importantly, the signaling pathway activated by disruption of endoplasmic reticulum homeostasis, the unfolded protein response, has been linked to lipid and membrane biosynthesis, insulin action, inflammation, and apoptosis. Therefore, understanding the mechanisms that disrupt endoplasmic reticulum homeostasis in nonalcoholic fatty liver disease and the role of the unfolded protein response in the broader context of chronic, metabolic diseases have become topics of intense investigation. The present review examines the endoplasmic reticulum and the unfolded protein response in the context of nonalcoholic fatty liver disease.

Cross-talk between the unfolded protein response and nuclear factor-κB signalling pathways regulates cytokine-mediated beta cell death in MIN6 cells and isolated mouse islets

AIMS/HYPOTHESIS

Pancreatic beta cell destruction in type 1 diabetes may be mediated by cytokines such as IL-1β, IFN-γ and TNF-α. Endoplasmic reticulum (ER) stress and nuclear factor-κB (NFκB) signalling are activated by cytokines, but their significance in beta cells remains unclear. Here, we investigated the role of cytokine-induced ER stress and NFκB signalling in beta cell destruction.

METHODS

Isolated mouse islets and MIN6 beta cells were incubated with IL-1β, IFN-γ and TNF-α. The chemical chaperone 4-phenylbutyric acid (PBA) was used to inhibit ER stress. Protein production and gene expression were assessed by western blot and real-time RT-PCR.

RESULTS

We found in beta cells that inhibition of cytokine-induced ER stress with PBA unexpectedly potentiated cell death and NFκB-regulated gene expression. These responses were dependent on NFκB activation and were associated with a prolonged decrease in the inhibitor of κB-α (IκBα) protein, resulting from increased IκBα protein degradation. Cytokine-mediated NFκB-regulated gene expression was also potentiated after pre-induction of ER stress with thapsigargin, but not tunicamycin. Both PBA and thapsigargin treatments led to preferential upregulation of ER degradation genes over ER-resident chaperones as part of the adaptive unfolded protein response (UPR). In contrast, tunicamycin activated a balanced adaptive UPR in association with the maintenance of Xbp1 splicing.

CONCLUSIONS/INTERPRETATION

These data suggest a novel mechanism by which cytokine-mediated ER stress interacts with NFκB signalling in beta cells, by regulating IκBα degradation. The cross-talk between the UPR and NFκB signalling pathways may be important in the regulation of cytokine-mediated beta cell death.