Identification and characterization of pancreatic eukaryotic initiation factor 2 alpha-subunit kinase, PEK, involved in translational control

PERK Regulates Working Memory and Protein Synthesis-Dependent Memory Flexibility

PERK (EIF2AK3) is an ER-resident eIF2α kinase required for memory flexibility and metabotropic glutamate receptor-dependent long-term depression, processes known to be dependent on new protein synthesis. Here we investigated PERK’s role in working memory, a cognitive ability that is independent of new protein synthesis, but instead is dependent on cellular Ca²⁺ dynamics. We found that working memory is impaired in forebrain-specific Perk knockout and pharmacologically PERK-inhibited mice. Moreover, inhibition of PERK in wild-type mice mimics the fear extinction impairment observed in forebrain-specific Perk knockout mice. Our findings reveal a novel role of PERK in cognitive functions and suggest that PERK regulates both Ca²⁺ -dependent working memory and protein synthesis-dependent memory flexibility.

The integrated stress response

In response to diverse stress stimuli, eukaryotic cells activate a common adaptive pathway, termed the integrated stress response (ISR), to restore cellular homeostasis. The core event in this pathway is the phosphorylation of eukaryotic translation initiation factor 2 alpha (eIF2α) by one of four members of the eIF2α kinase family, which leads to a decrease in global protein synthesis and the induction of selected genes, including the transcription factor ATF4, that together promote cellular recovery. The gene expression program activated by the ISR optimizes the cellular response to stress and is dependent on the cellular context, as well as on the nature and intensity of the stress stimuli. Although the ISR is primarily a pro-survival, homeostatic program, exposure to severe stress can drive signaling toward cell death. Here, we review current understanding of the ISR signaling and how it regulates cell fate under diverse types of stress.

Endoplasmic reticulum stress-mediated neuronal apoptosis by acrylamide exposure

Acrylamide (AA) is a well-known neurotoxic compound in humans and experimental animals. However, intracellular stress signaling pathways responsible for the neurotoxicity of AA are still not clear. In this study, we explored the involvement of the endoplasmic reticulum (ER) stress response in AA-induced neuronal damage in vitro and in vivo. Exposure of SH-SY5Y human neuroblastoma cells to AA increased the levels of phosphorylated form of eukaryotic translation initiation factor 2α (eIF2α) and its downstream effector, activating transcription factor 4 (ATF4), indicating the induction of the unfolded protein response (UPR) by AA exposure. Furthermore, AA exposure increased the mRNA level of c/EBP homologous protein (CHOP), the ER stress-dependent apoptotic factor, and caused the accumulation of reactive oxygen species (ROS) in SH-SY5Y cells. Treatments of SH-SY5Y cells with the chemical chaperone, 4-phenylbutyric acid and the ROS scavenger, N-acetyl-cysteine reduced the AA-induced expression of ATF4 protein and CHOP mRNA, and resulted in the suppression of apoptosis. In addition, AA-induced eIF2α phosphorylation was also suppressed by NAC treatment. In consistent with in vitro study, exposure of zebrafish larvae at 6-day post fertilization to AA induced the expression of chop mRNA and apoptotic cell death in the brain, and also caused the disruption of brain structure. These findings suggest that AA exposure induces apoptotic neuronal cell death through the ER stress and subsequent eIF2α-ATF4-CHOP signaling cascade. The accumulation of ROS by AA exposure appears to be responsible for this ER stress-mediated apoptotic pathway.

Regulation of Stress Responses and Translational Control by Coronavirus

Similar to other viruses, coronavirus infection triggers cellular stress responses in infected host cells. The close association of coronavirus replication with the endoplasmic reticulum (ER) results in the ER stress responses, which impose a challenge to the viruses. Viruses, in turn, have come up with various mechanisms to block or subvert these responses. One of the ER stress responses is inhibition of the global protein synthesis to reduce the amount of unfolded proteins inside the ER lumen. Viruses have evolved the capacity to overcome the protein translation shutoff to ensure viral protein production. Here, we review the strategies exploited by coronavirus to modulate cellular stress response pathways. The involvement of coronavirus-induced stress responses and translational control in viral pathogenesis will also be briefly discussed.

The essential functions of endoplasmic reticulum chaperones in hepatic lipid metabolism

The endoplasmic reticulum (ER) is an essential organelle for protein and lipid synthesis in hepatocytes. ER homeostasis is vital to maintain normal hepatocyte physiology. Perturbed ER functions causes ER stress associated with accumulation of unfolded protein in the ER that activates a series of adaptive signalling pathways, termed unfolded protein response (UPR). The UPR regulates ER chaperone levels to preserve ER protein-folding environment to protect the cell from ER stress. Recent findings reveal an array of ER chaperones that alter the protein-folding environment in the ER of hepatocytes and contribute to dysregulation of hepatocyte lipid metabolism and liver disease. In this review, we will discuss the specific functions of these chaperones in regulation of lipid metabolism, especially de novo lipogenesis and lipid transport and demonstrate their homeostatic role not only for ER-protein synthesis but also for lipid metabolism in hepatocyte.

General control nonderepressible 2 deletion predisposes to asparaginase-associated pancreatitis in mice

Treatment with the antileukemic agent asparaginase can induce acute pancreatitis, but the pathophysiology remains obscure. In the liver of mice, eukaryotic initiation factor 2 (eIF2) kinase general control nonderepressible 2 (GCN2) is essential for mitigating metabolic stress caused by asparaginase. We determined the consequences of asparaginase treatment on the pancreata of wild-type (WT, GCN2-intact) and GCN2-deleted (ΔGcn2) mice. Mean pancreas weights in ΔGcn2 mice treated with asparaginase for 8 days were increased (P < 0.05) above all other groups. Histological examination revealed acinar cell swelling and altered staining of zymogen granules in ΔGcn2, but not WT, mice. Oil Red O staining and measurement of pancreas triglycerides excluded lipid accumulation as a contributor to acini appearance. Instead, transmission electron microscopy revealed dilatation of the endoplasmic reticulum (ER) and accumulation of autophagic vacuoles in the pancreas of ΔGcn2 mice treated with asparaginase. Consistent with the idea that loss of GCN2 in a pancreas exposed to asparaginase induced ER stress, phosphorylation of protein kinase R-like ER kinase (PERK) and its substrate eIF2 was increased in the pancreas of asparaginase-treated ΔGcn2 mice. In addition, mRNA expression of PERK target genes, activating transcription factors 4, 3, and 6 (Atf4, Atf3, and Atf6), fibroblast growth factor 21 (Fgf21), heat shock 70-kDa protein 5 (Hspa5), and spliced Xbp1 (sXbp1), as well as pancreas mass, was elevated in the pancreas of asparaginase-treated ΔGcn2 mice. Furthermore, genetic markers of oxidative stress [sirtuin (Sirt1)], inflammation [tumor necrosis factor-α (Tnfα)], and pancreatic injury [pancreatitis-associated protein (Pap)] were elevated in asparaginase-treated ΔGcn2, but not WT, mice. These data indicate that loss of GCN2 predisposes the exocrine pancreas to a maladaptive ER stress response and autophagy during asparaginase treatment and represent a genetic basis for development of asparaginase-associated pancreatitis.

A Reevaluation of the Role of the Unfolded Protein Response in Islet Dysfunction: Maladaptation or a Failure to Adapt?

Endoplasmic reticulum (ER) stress caused by perturbations in ER homeostasis activates an adaptive response termed the unfolded protein response (UPR) whose function is to resolve ER stress. If unsuccessful, the UPR initiates a proapoptotic program to eliminate the malfunctioning cells from the organism. It is the activation of this proapoptotic UPR in pancreatic β-cells that has been implicated in the onset of type 2 diabetes and thus, in this context, is considered a maladaptive response. However, there is growing evidence that β-cell death in type 2 diabetes may not be caused by a maladaptive UPR but by the inhibition of the adaptive UPR. In this review, we discuss the evidence for a role of the UPR in β-cell dysfunction and death in the development of type 2 diabetes and ask the following question: Is β-cell dysfunction the result of a maladaptive UPR or a failure of the UPR to adequately adapt? The answer to this question is critically important in defining potential therapeutic strategies for the treatment and prevention of type 2 diabetes. In addition, we discuss the potential role of the adaptive UPR in staving off type 2 diabetes by enhancing β-cell mass and function in response to insulin resistance.

miR-216b regulation of c-Jun mediates GADD153/CHOP-dependent apoptosis

The ability of the unfolded protein response, UPR, to regulate cell homeostasis through both gene expression and protein synthesis has been well documented. One primary pro-apoptotic protein that responds to both PERK and Ire1 signalling is the CHOP/GADD153 transcription factor. Although CHOP deficiency delays onset of cell death, questions remain regarding how CHOP regulates apoptosis. Here, we provide evidence demonstrating that CHOP/GADD153-dependent apoptosis reflects expression of micro-RNA, miR-216b. MiR-216b accumulation requires PERK-dependent induction of CHOP/GADD153, which then directly regulates miR-216b expression. As maximal expression of miR-216b is antagonized by Ire1, miR-216b accumulation reflects the convergence of PERK and Ire1 activities. Functionally, miR-216b directly targets c-Jun, thereby reducing AP-1-dependent transcription and sensitizing cells to ER stress-dependent apoptosis. These results provide direct insight into the molecular mechanisms of CHOP/GADD153-dependent cell death.

The transcription factor CHOP/GADD153 regulates apoptosis in response to the unfolded protein response. Here the authors show that CHOP/GADD153 regulates the expression of miR-216b, which targets c-Jun and sensitizes cells to ER stress-dependent apoptosis.

Nuclear Matrix Protein 4 Is a Novel Regulator of Ribosome Biogenesis and Controls the Unfolded Protein Response via Repression of Gadd34 Expression

The unfolded protein response (UPR) maintains protein homeostasis by governing the processing capacity of the endoplasmic reticulum (ER) to manage ER client loads; however, key regulators within the UPR remain to be identified. Activation of the UPR sensor PERK (EIFAK3/PEK) results in the phosphorylation of the α subunit of eIF2 (eIF2α-P), which represses translation initiation and reduces influx of newly synthesized proteins into the overloaded ER. As part of this adaptive response, eIF2α-P also induces a feedback mechanism through enhanced transcriptional and translational expression of Gadd34 (Ppp1r15A),which targets type 1 protein phosphatase for dephosphorylation of eIF2α-P to restore protein synthesis. Here we describe a novel mechanism by which Gadd34 expression is regulated through the activity of the zinc finger transcription factor NMP4 (ZNF384, CIZ). NMP4 functions to suppress bone anabolism, and we suggest that this occurs due to decreased protein synthesis of factors involved in bone formation through NMP4-mediated dampening of Gadd34 and c-Myc expression. Loss of Nmp4 resulted in an increase in c-Myc and Gadd34 expression that facilitated enhanced ribosome biogenesis and global protein synthesis. Importantly, protein synthesis was sustained during pharmacological induction of the UPR through a mechanism suggested to involve GADD34-mediated dephosphorylation of eIF2α-P. Sustained protein synthesis sensitized cells to pharmacological induction of the UPR, and the observed decrease in cell viability was restored upon inhibition of GADD34 activity. We conclude that NMP4 is a key regulator of ribosome biogenesis and the UPR, which together play a central role in determining cell viability during endoplasmic reticulum stress.

The Unfolded Protein Response in Homeostasis and Modulation of Mammalian Immune Cells

The endoplasmic reticulum (ER) plays important roles in eukaryotic protein folding and lipid biosynthesis. Several exogenous and endogenous cellular sources of stress can perturb ER homeostasis leading to the accumulation of unfolded proteins in the lumen. Unfolded protein accumulation triggers a signal-transduction cascade known as the unfolded protein response (UPR), an adaptive mechanism which aims to protect cells from protein aggregates and to restore ER functions. Further to this protective mechanism, in immune cells, UPR molecular effectors have been shown to participate in a wide range of biological processes such as cell differentiation, survival and immunoglobulin and cytokine production. Recent findings also highlight the involvement of the UPR machinery in the maturational program and antigen presentation capacities of dendritic cells. UPR is therefore a key element in immune system homeostasis with direct implications on both adaptive and innate immune responses. The present review summarizes the knowledge on the emerging roles of UPR signaling cascades in mammalian immune cells as well as the consequences of their dysregulation in relation to the pathogenesis of several diseases.

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.

Sequential changes of endoplasmic reticulum stress and apoptosis in myocardial fibrosis of diabetes mellitus-induced rats

The endoplasmic reticulum (ER) is an organelle in which proteins form their appropriate structures. However, several of these proteins become unfolded or misfolded when exposed to stimuli, including hyperglycemia, oxidative stress, ischemia, disturbance of calcium homeostasis and overexpression of abnormal proteins, which activates ER stress and the unfolded protein response (UPR). To date, investigations have demonstrated that ER stress is important in diabetic myocardial fibrosis by inducing cardiac cell apoptosis. Therefore, in the present study, the polymerase chain reaction, western blotting analysis and tissue staining were performed to identify the changes in UPR signaling proteins and apoptotic proteins in diabetic rats at different time points, and to determine whether the myocardial fibrosis is associated with ER-stress-mediated apoptosis using a diabetes mellitus (DM) rat model. It was found that the upregulation of ER stress markers and apoptotic molecules developed over time. It was also demonstrated that anti-apoptotic markers and proapoptotic markers were activated early following model establishment, and then decreased in months 4 and 5. The changes in myocardial fibrosis were found to accelerate in a time-dependent manner with apoptosis in the DM rats.

Endoplasmic reticulum stress: a novel mechanism and therapeutic target for cardiovascular diseases

Endoplasmic reticulum is a principal organelle responsible for folding, post-translational modifications and transport of secretory, luminal and membrane proteins, thus palys an important rale in maintaining cellular homeostasis. Endoplasmic reticulum stress (ERS) is a condition that is accelerated by accumulation of unfolded/misfolded proteins after endoplasmic reticulum environment disturbance, triggered by a variety of physiological and pathological factors, such as nutrient deprivation, altered glycosylation, calcium depletion, oxidative stress, DNA damage and energy disturbance, etc. ERS may initiate the unfolded protein response (UPR) to restore cellular homeostasis or lead to apoptosis. Numerous studies have clarified the link between ERS and cardiovascular diseases. This review focuses on ERS-associated molecular mechanisms that participate in physiological and pathophysiological processes of heart and blood vessels. In addition, a number of drugs that regulate ERS was introduced, which may be used to treat cardiovascular diseases. This review may open new avenues for studying the pathogenesis of cardiovascular diseases and discovering novel drugs targeting ERS.

Tanshinone IIA induces TRAIL sensitization of human lung cancer cells through selective ER stress induction

Although tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promised anticancer medicine targeting only the tumor, most cancers show resistance to TRAIL-induced apoptosis. For this reason, new therapeutic strategies to overcome the TRAIL resistance are required for more effective tumor treatment. In the present study, potential of tanshinone IIA as a TRAIL sensitizer was evaluated in human non-small cell lung cancer (NSCLC) cells. NSCLC cells showed resistance to TRAIL-mediated cell death, but combination treatment of Tanshinone IIA and TRAIL synergistically decreased cell viability and increased apoptosis in TRAIL-resistant NSCLC cells. Tanshinone IIA greatly induced death receptor 5 (DR5), but not death receptor 4 (DR4). Furthermore, DR5 knockdown attenuated the combination treatment of tanshinone IIA with TRAIL-mediated cell death in human NSCLC cells. Tanshinone IIA also increased CHOP and activated the PERK-ATF4 pathway suggesting that tanshinone IIA increased DR5 and CHOP by activating the PERK-ATF4 pathway. Tanshinone IIA also downregulated phosphorylation of STAT3 and expression of survivin. Taken together, these results indicate that tanshinone IIA increases TRAIL-induced cell death via upregulating DR5 and downregulating survivin mediated by, respectively, selective activation of PERK/ATF4 and inhibition of STAT3, suggesting combinatorial intervention of tanshinone IIA and TRAIL as a new therapeutic strategy for human NSCLC.

Decursin enhances TRAIL-induced apoptosis through oxidative stress mediated- endoplasmic reticulum stress signalling in non-small cell lung cancers

BACKGROUND AND PURPOSE

The TNF-related apoptosis-inducing ligand (TRAIL) is a promising anticancer agent due to its remarkable ability to selectively kill tumour cells. However, because most tumours exhibit resistance to TRAIL-induced apoptosis, the development of combination therapies to overcome resistance to TRAIL is required for effective cancer therapy.

EXPERIMENTAL APPROACH

Cell viability and possible synergy between the plant pyranocoumarin decursin and TRAIL was measured by MTT assay and calcusyn software. Reactive oxygen species (ROS) and apoptosis were measured using dichlorodihydrofluorescein and annexin/propidium iodide in cell flow cytometry. Changes in protein levels were assessed with Western blotting.

KEY RESULTS

Combining decursin and TRAIL markedly decreased cell viability and increased apoptosis in TRAIL-resistant non-small-cell lung cancer (NSCLC) cell lines. Decursin induced expression of the death receptor 5 (DR5). Inhibition of DR5 attenuated apoptotic cell death in decursin + TRAIL treated NSCLC cell lines. Interestingly, induction of DR5 and CCAAT/enhancer-binding protein homologues protein by decursin was mediated through selective induction of the pancreatic endoplasmic reticulum kinase (PERK)/activating transcription factor 4 (ATF4) branch of the endoplasmic reticulum stress response pathway. Furthermore, enhancement of PERK/ATF4 signalling by decursin was mediated by ROS generation in NSCLC cell lines, but not in normal human lung cells. Decursin also markedly down-regulated expression of survivin and Bcl-xL in TRAIL-resistant NSCLC cells.

CONCLUSIONS AND IMPLICATIONS

ROS generation by decursin selectively activated the PERK/ATF4 axis of the endoplasmic reticulum stress signalling pathway, leading to enhanced TRAIL sensitivity in TRAIL-resistant NSCLC cell lines, partly via up-regulation of DR5.

Translation from the 5' untranslated region shapes the integrated stress response

Translated regions distinct from annotated coding sequences have emerged as essential elements of the proteome. This includes upstream open reading frames (uORFs) present in mRNAs controlled by the integrated stress response (ISR) that show "privileged" translation despite inhibited eukaryotic initiation factor 2-guanosine triphosphate-initiator methionyl transfer RNA (eIF2·GTP·Met-tRNA(i )(Met)). We developed tracing translation by T cells to directly measure the translation products of uORFs during the ISR. We identified signature translation events from uORFs in the 5' untranslated region of binding immunoglobulin protein (BiP) mRNA (also called heat shock 70-kilodalton protein 5 mRNA) that were not initiated at the start codon AUG. BiP expression during the ISR required both the alternative initiation factor eIF2A and non-AUG-initiated uORFs. We propose that persistent uORF translation, for a variety of chaperones, shelters select mRNAs from the ISR, while simultaneously generating peptides that could serve as major histocompatibility complex class I ligands, marking cells for recognition by the adaptive immune system.

Os odontoideum in wolcott-rallison syndrome: a case series of 4 patients

Wolcott-Rallison Syndrome is the commonest cause of neonatal diabetes in consanguineous families. It is associated with liver dysfunction, epiphyseal dysplasia, and developmental delay. It is caused by mutations in eukaryotic translation initiation factor 2-α kinase 3 (EIF2AK3).

We report 4 children with WRS and Os Odontoideum resulting in significant neurological compromise. This cervical spine abnormality has not previously been described in this syndrome. This additional evidence broadens the clinical spectrum of this syndrome and confirms the role of EIF2AK3 in skeletal development. Furthermore, Os Odontoideum needs to be actively screened for in WRS patients to prevent neurological and respiratory compromise.

Down-Regulatory Effects of miR-211 on Long Non-Coding RNA SOX2OT and SOX2 Genes in Esophageal Squamous Cell Carcinoma

OBJECTIVE

MicroRNAs (miRNAs) are a class of non-coding RNAs (ncRNAs) that tran- scriptionally or post-transcriptionally regulate gene expression through degradation of their mRNA targets and/or translational suppression. However, there are a few reports on miRNA-mediated expression regulation of long ncRNAs (lncRNAs). We have previ- ously reported a significant upregulation of the lncRNA SOX2OT and its intronic cod- ing gene, SOX2, in esophageal squamous cell carcinoma (ESCC) tissue samples. In this study, we aimed to evaluate the effect of induced overexpression of miR-211 on SOX2OT and SOX2 expression in vitro.

MATERIALS AND METHODS

In this experimental study, we performed both bioinformatic and experimental analyses to examine whether these transcripts are regulated by miRNAs. From the list of potential candidate miRNAs, miR-211 was found to have complementary sequences to SOX2OT and SOX2 transcripts. To validate our finding experimentally, we transfected the NT-2 pluripotent cell line (an embryonal carcinoma stem cell) with an expression vector overexpressing miR-211. The expression chang- es of miR-211, SOX2OT, and SOX2 were then quantified by a real-time polymerase chain reaction (RT-PCR) approach.

RESULTS

Compared with mock-transfected cells, overexpression of miR-211 caused a significant down-regulation of both genes (P<0.05). Furthermore, flow-cytometry analysis revealed a significant elevation in sub-G1 cell population following ectopic expression of miR-211 in NT-2 cells.

CONCLUSION

We report here, for the first time, the down-regulation of SOX2OT and SOX2 genes by an miRNA. Considering the vital role of SOX2OT and SOX2 genes in pluripotency and tumorigenesis, our data suggest an important and inhibitory role for miR-211 in the aforementioned processes.

The dysregulation of endoplasmic reticulum stress response in acute-on-chronic liver failure patients caused by acute exacerbation of chronic hepatitis B

Although endoplasmic reticulum (ER) stress is critical in various liver diseases, its role in acute-on-chronic liver failure (AoCLF) caused by acute exacerbation of chronic hepatitis B (CHB) is still elusive. This study aimed to analyse ER stress responses in the progression of HBV-related AoCLF. Normal liver tissues (n = 10), liver tissues of CHB (n = 12) and HBV-related patients with AoCLF (n = 19) were used. Electron microscopy of the ultrastructure of the ER was carried out on liver specimens. The gene and protein expression levels of ER stress-related genes were measured. We further analysed the correlation between the expression levels of ER stress-related molecules and liver injury. Electron microscopy identified typical features of the ER microstructure in AoCLF subjects. Among the three pathways of unfolded protein responses, the PKR-like ER kinase and inositol-requiring enzyme 1 signalling pathway were activated in CHB subjects and inactivated in AoCLF subjects, while the activating transcription factor 6 signalling pathway was sustained in the activated form during the progression of AoCLF; the expression of glucose-regulated protein (Grp)78 and Grp94 was gradually decreased in AoCLF subjects compared to healthy individuals and CHB subjects, showing a negative correlation with serum ALT, AST and TBIL; moreover, the ER stress-related apoptosis molecules were activated in the progression of acute exacerbation of CHB. The dysregulated ER stress response may play a complicated role in the pathogenesis of AoCLF, and a severe ER stress response may predict the occurrence of AoCLF caused by acute exacerbation of CHB.

Gel-free/label-free proteomic analysis of developing rice grains under heat stress

High temperature markedly reduces the yields and quality of rice grains. To identify the mechanisms underlying heat stress-induced responses in rice grains, proteomic technique was used. Developing Khao Dawk Mali 105 rice grains at the milky, dough, and mature stages were treated at 40 °C for 3 days. Aromatic compounds were decreased in rice grains under heat stress. The protein abundance involved in glycolysis and tricarboxylic acid cycle, including glyceraldehyde 3-phosphate dehydrogenase and citrate synthase, was changed in milky and dough grains after heat treatment; however, none changes in mature grains. The abundance involved in amino acid metabolism was increased in dough grains, but decreased in milky grains. In addition, the abundance involved in starch and sucrose metabolism, such as starch synthase, ADP-glucose pyrophosphorylase, granule-bound starch synthase, and alpha amylase, was decreased in milky grains, but increased in dough grains. A number of redox homeostasis-related proteins, such as ascorbate peroxidase and peroxiredoxin, were increased in developing rice grains treated with heat stress. These results suggest that in response to heat stress, the abundance of numerous proteins involved in redox homeostasis and carbohydrate biosynthetic pathways may play a major role in the development of KDML105 rice grains.

BIOLOGICAL SIGNIFICANCE

Yield of Khao Dawk Mali 105 rice, which is an economical aromatic rice, was disrupted by environmental stress. Rice grains developed under heat stress caused loss of aroma compound. To identify the mechanism of heat response in rice grain, gel-free/label-free proteomic technique was used. The abundance of proteins involved in glycolysis and tricarboxylic acid cycle was disrupted by heat stress. High temperature limited starch biosynthesis; however, it enhanced sugar biosynthesis in developing rice grains. Redox homeostasis related proteins were disrupted by heat stress. These results suggest that proteins involved in redox homeostasis and carbohydrate pathway might play a major role in developing grains in Khao Dawk Mali 105 rice under heat stress.

Microscopic and ultrastructural features in Wolcott-Rallison syndrome, a permanent neonatal diabetes mellitus: about two autopsy cases

BACKGROUND

Wolcott-Rallison syndrome (WRS) is a rare autosomal recessive disorder characterized by the association of permanent neonatal or early-infancy insulin-dependent diabetes, multiple bone dysplasia, hepatic dysfunction, and growth retardation. All clinical manifestations result from gene mutations encoding pancreatic endoplasmic reticulum eIF2 α kinase (PERK), an endoplasmic reticulum transmembrane protein that plays a role in the unfolded protein response. Histological and ultrastructural lesions of bone and pancreas have been described in animal models and WRS patients. However, histological and ultrastructural findings of other organs, especially of the liver, are lacking.

METHODS

Autopsy specimens from two pediatric patients with WRS were analyzed. An immunohistochemical study was performed on the pancreas. An ultrastructural study was realized from samples of liver, pancreas, kidney, and myocardium. Our findings were compared with those of the literature and correlated with the molecular data.

RESULTS

Hepatocytes and pancreatic exocrine cells exhibited very peculiar features of necrosis suggestive of secondary changes because of endoplasmic reticulum overload. Steatosis occurred in renal tubular cells, hepatocytes, and myocardial fibers. Abnormal mitochondria were noted in renal and myocardial fibers. Pancreas islets were characterized by a marked reduction in the number of insulin-secreting β cells.

CONCLUSIONS

The histological and ultrastructural features that occur in WRS are directly or indirectly linked to endoplasmic reticulum (ER) dysfunction and can explain the peculiar phenotype of this syndrome.

Constitutive role of GADD34 and CReP in cancellation of phospho-eIF2α-dependent translational attenuation and insulin biosynthesis in pancreatic β cells

Insulin biosynthesis has been well characterized with respect to transcriptional and post-translational regulation. However, the relationship between translational regulation of insulin and protein quality control in the endoplasmic reticulum (ER) remains to be clarified. Here we carried out forced expression of insulin in non-insulin-producing cells and compared activation level of ER stress-responsive molecules between insulin-producing cells and non-insulin-producing cells under normal culture condition or ER stress condition. Forced expression of insulin in non-insulin-producing cells caused severe ER stress with striking translational attenuation through phosphorylation of eIF2α by activation of protein kinase RNA-like endoplasmic reticulum kinase (PERK), resulting in inhibition of insulin production at the protein level. We also found that GADD34 and CReP are highly expressed in the cells that endogenously produce insulin and that eIF2α shows constitutively low phosphorylation level in these cells although PERK is constitutively activated under both normal culture conditions and physiological conditions in the same cells. Inhibition of eIF2α phosphatase further decreased insulin level in pancreatic β cells. These findings suggest that eIF2α phosphorylation level is kept low by GADD34- and/or CReP-regulated phosphatases in pancreatic β cells and that cancellation of phospho-eIF2α-dependent translational inhibition by the molecular mechanism contributes to mass production of insulin in pancreatic β cells.

Panax quinquefolium saponin attenuates cardiomyocyte apoptosis induced by thapsigargin through inhibition of endoplasmic reticulum stress

BACKGROUND

Endoplasmic reticulum (ER) stress-related apoptosis is involved in the pathophysiology of many cardiovascular diseases, and Panax quinquefolium saponin (PQS) is able to inhibit excessive ER stress-related apoptosis of cardiomyocytes following hypoxia/reoxygenation and myocardial infarction. However, the pathway by which PQS inhibits the ER stress-related apoptosis is not well understood. To further investigate the protective effect of PQS against ER stress-related apoptosis, primary cultured cardiomyocytes were stimulated with thapsigargin (TG), which is widely used to model cellular ER stress, and it could induce apoptotic cell death in sufficient concentration.

METHODS

Primary cultured cardiomyocytes from neonatal rats were exposed to TG (1 µmol/L) treatment for 24 h, following PQS pre-treatment (160 µg/mL) for 24 h or pre-treatment with small interfering RNA directed against protein kinase-like endoplasmic reticulum kinase (Si-PERK) for 6 h. The viability and apoptosis rate of cardiomyocytes were detected by cell counting kit-8 and flow cytometry respectively. ER stress-related protein expression, such as glucose-regulated protein 78 (GRP78), calreticulin, PERK, eukaryotic translation initiation factor 2α (eIF2α), activating transcription factor 4 (ATF4), and C/EBP homologous protein (CHOP) were assayed by western blotting.

RESULTS

Both PQS pre-treatment and PERK knockdown remarkably inhibited the cardiomyocyte apoptosis induced by TG, increased cell viability, decreased phosphorylation of both PERK and eIF2α, and decreased protein levels of both ATF4 and CHOP. There was no statistically significant difference between PQS pre-treatment and PERK knockdown in the cardioprotective effect.

CONCLUSIONS

Our data indicate that the PERK-eIF2α-ATF4-CHOP pathway of ER stress is involved in the apoptosis induced by TG, and PQS might prevent TG-induced cardiomyocyte apoptosis through a mechanism involving the suppression of this pathway. These findings provide novel data regarding the molecular mechanisms by which PQS inhibits cardiomyocyte apoptosis.

The unfolded protein response in neurodegenerative diseases: a neuropathological perspective

The unfolded protein response (UPR) is a stress response of the endoplasmic reticulum (ER) to a disturbance in protein folding. The so-called ER stress sensors PERK, IRE1 and ATF6 play a central role in the initiation and regulation of the UPR. The accumulation of misfolded and aggregated proteins is a common characteristic of neurodegenerative diseases. With the discovery of the basic machinery of the UPR, the idea was born that the UPR or part of its machinery could be involved in neurodegenerative diseases like Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and prion disease. Over the last decade, the UPR has been addressed in an increasing number of studies on neurodegeneration. The involvement of the UPR has been investigated in human neuropathology across different neurological diseases, as well as in cell and mouse models for neurodegeneration. Studies using different disease models display discrepancies on the role and function of the UPR during neurodegeneration, which can often be attributed to differences in methodology. In this review, we will address the importance of investigation of human brain material for the interpretation of the role of the UPR in neurological diseases. We will discuss evidence for UPR activation in neurodegenerative diseases, and the methodology to study UPR activation and its connection to brain pathology will be addressed. More recently, the UPR is recognized as a target for drug therapy for treatment and prevention of neurodegeneration, by inhibiting the function of specific mediators of the UPR. Several preclinical studies have shown a proof-of-concept for this approach targeting the machinery of UPR, in particular the PERK pathway, in different models for neurodegeneration and have yielded paradoxical results. The promises held by these observations will need further support by clarification of the observed differences between disease models, as well as increased insight obtained from human neuropathology.

Interplay between unfolded protein response and autophagy promotes tumor drug resistance

The endoplasmic reticulum (ER) is involved in the quality control of secreted protein via promoting the correct folding of nascent protein and mediating the degradation of unfolded or misfolded protein, namely ER-associated degradation. When the unfolded or misfolded proteins are abundant, the unfolded protein response (UPR) is elicited, an adaptive signaling cascade from the ER to the nucleus, which restores the homeostatic functions of the ER. Autophagy is a conserved catabolic process where cellular long-lived proteins and damaged organelles are engulfed and degraded for recycling to maintain homeostasis. The UPR and autophagy occur simultaneously and are involved in pathological processes, including tumorigenesis, chemoresistance of malignancies and neurodegeneration. Accumulative data has indicated that the UPR may induce autophagy and that autophagy is able to alleviate the UPR. However, the detailed mechanism of interplay between autophagy and UPR remains to be fully understood. The present review aimed to depict the core pathways of the two processes and to elucidate how autophagy and UPR are regulated. Moreover, the review also discusses the molecular mechanism of crosstalk between the UPR and autophagy and their roles in malignant survival and drug resistance.

The Emerging Roles of Viroporins in ER Stress Response and Autophagy Induction during Virus Infection

Viroporins are small hydrophobic viral proteins that oligomerize to form aqueous pores on cellular membranes. Studies in recent years have demonstrated that viroporins serve important functions during virus replication and contribute to viral pathogenicity. A number of viroporins have also been shown to localize to the endoplasmic reticulum (ER) and/or its associated membranous organelles. In fact, replication of most RNA viruses is closely linked to the ER, and has been found to cause ER stress in the infected cells. On the other hand, autophagy is an evolutionarily conserved "self-eating" mechanism that is also observed in cells infected with RNA viruses. Both ER stress and autophagy are also known to modulate a wide variety of signaling pathways including pro-inflammatory and innate immune response, thereby constituting a major aspect of host-virus interactions. In this review, the potential involvement of viroporins in virus-induced ER stress and autophagy will be discussed.

Tumor progression and the different faces of the PERK kinase

The serine/threonine endoplasmic reticulum (ER) kinase, protein kinase R (PKR)-like ER kinase (PERK), is a pro-adaptive protein kinase whose activity is regulated indirectly by protein misfolding within the ER. As the oxidative folding environment in the ER is sensitive to a variety of cellular stresses, many of which occur during neoplastic transformation and in the tumor microenvironment, there has been considerable interest in defining whether PERK positively contributes to tumor progression and whether it represents a significant therapeutic target. Herein, we review the current knowledge of PERK-dependent signaling pathways, the contribution of downstream substrates including recently characterized new PERK substrates transcription factors Forkhead box O protein and diacyglycerol a lipid signaling second messenger, and efforts to develop small molecule PERK inhibitors.

Endoplasmic reticulum stress impairs insulin receptor signaling in the brains of obese rats

The incidence of obesity is increasing worldwide. It was reported that endoplasmic reticulum stress (ERS) could inhibit insulin receptor signaling by activating c-Jun N-terminal kinase (JNK) in the liver. However, the relationship between ERS and insulin receptor signaling in the brain during obesity remains unclear. The aim of the current study was to assess whether ERS alters insulin receptor signaling through the hyper-activation of JNK in the hippocampus and frontal cortex in the brains of obese rats. Obesity was induced using a high fat diet (HFD). The Morris water maze test was then performed to evaluate decreases in cognitive function, and western blot was used to verify whether abnormal insulin receptor signaling was induced by ERS in HFD rats exhibiting cognitive decline. In addition, to determine whether ERS activated JNK and consequently impaired insulin receptor signaling, SH-SY5Y cells were treated with the JNK inhibitor, SP600125, followed by tunicamycin or thapsigargin, and primary rat hippocampal and cortical neurons were transfected with siRNA against IRE1α and JNK. We found that the expression of phosphorylation of PKR-like kinase (PERK), phosphorylation of α subunit of translation initiation factor 2 (eIF2α), and phosphorylation of inositol-requiring kinase-1α (IRE-1α) were increased in the brains of rats with HFD when compared with control rats. The level of serine phosphorylation of insulin receptor substrate-1 (IRS-1) was also increased, while protein kinase B (PKB/Akt) was reduced. ERS was also found to inhibit insulin receptor signaling via the activation of JNK in SH-SY5Y cells, primary rat hippocampal, and cortical neurons. These results indicate that ERS was increased, thereby resulting in impaired insulin receptor signaling in the hippocampus and frontal cortex of obese rats.

XBP1 mitigates aminoglycoside-induced endoplasmic reticulum stress and neuronal cell death

Here we study links between aminoglycoside-induced mistranslation, protein misfolding and neuropathy. We demonstrate that aminoglycosides induce misreading in mammalian cells and assess endoplasmic reticulum (ER) stress and unfolded protein response (UPR) pathways. Genome-wide transcriptome and proteome analyses revealed upregulation of genes related to protein folding and degradation. Quantitative PCR confirmed induction of UPR markers including C/EBP homologous protein, glucose-regulated protein 94, binding immunoglobulin protein and X-box binding protein-1 (XBP1) mRNA splicing, which is crucial for UPR activation. We studied the effect of a compromised UPR on aminoglycoside ototoxicity in haploinsufficient XBP1 (XBP1^+/−) mice. Intra-tympanic aminoglycoside treatment caused high-frequency hearing loss in XBP1^+/− mice but not in wild-type littermates. Densities of spiral ganglion cells and synaptic ribbons were decreased in gentamicin-treated XBP1^+/− mice, while sensory cells were preserved. Co-injection of the chemical chaperone tauroursodeoxycholic acid attenuated hearing loss. These results suggest that aminoglycoside-induced ER stress and cell death in spiral ganglion neurons is mitigated by XBP1, masking aminoglycoside neurotoxicity at the organismal level.

Endoplasmic reticulum stress-activated cell reprogramming in oncogenesis

Stress induced by the accumulation of unfolded proteins in the endoplasmic reticulum (ER) is observed in many human diseases, including cancers. Cellular adaptation to ER stress is mediated by the unfolded protein response (UPR), which aims at restoring ER homeostasis. The UPR has emerged as a major pathway in remodeling cancer gene expression, thereby either preventing cell transformation or providing an advantage to transformed cells. UPR sensors are highly regulated by the formation of dynamic protein scaffolds, leading to integrated reprogramming of the cells. Herein, we describe the regulatory mechanisms underlying UPR signaling upon cell intrinsic or extrinsic challenges, and how they engage cell transformation programs and/or provide advantages to cancer cells, leading to enhanced aggressiveness or chemoresistance. We discuss the emerging cross-talk between the UPR and related metabolic processes to ensure maintenance of protein homeostasis and its impact on cell transformation and tumor growth.

SIGNIFICANCE

ER stress signaling is dysregulated in many forms of cancer and contributes to tumor growth as a survival factor, in addition to modulating other disease-associated processes, including cell migration, cell transformation, and angiogenesis. Evidence for targeting the ER stress signaling pathway as an anticancer strategy is compelling, and novel agents that selectively inhibit the UPR have demonstrated preliminary evidence of preclinical efficacy with an acceptable safety profile.

PERK Limits Drosophila Lifespan by Promoting Intestinal Stem Cell Proliferation in Response to ER Stress

Intestinal homeostasis requires precise control of intestinal stem cell (ISC) proliferation. In Drosophila, this control declines with age largely due to chronic activation of stress signaling and associated chronic inflammatory conditions. An important contributor to this condition is the age-associated increase in endoplasmic reticulum (ER) stress. Here we show that the PKR-like ER kinase (PERK) integrates both cell-autonomous and non-autonomous ER stress stimuli to induce ISC proliferation. In addition to responding to cell-intrinsic ER stress, PERK is also specifically activated in ISCs by JAK/Stat signaling in response to ER stress in neighboring cells. The activation of PERK is required for homeostatic regeneration, as well as for acute regenerative responses, yet the chronic engagement of this response becomes deleterious in aging flies. Accordingly, knocking down PERK in ISCs is sufficient to promote intestinal homeostasis and extend lifespan. Our studies highlight the significance of the PERK branch of the unfolded protein response of the ER (UPR^ER) in intestinal homeostasis and provide a viable strategy to improve organismal health- and lifespan.

The long-term maintenance of tissue homeostasis in barrier epithelia requires precise coordination of cellular stress and inflammatory responses with regenerative processes. This coordination is lost with age, resulting in degenerative and proliferative diseases. The Unfolded Protein Response of the Endoplasmic Reticulum (UPR^ER) is emerging as a central regulator of tissue homeostasis in barrier epithelia. The UPR^ER adjusts the protein folding capacity of the ER in response to protein stress in stem cells and differentiated cells, and thus influences proliferative homeostasis, cell differentiation and epithelial inflammatory responses. How these responses are coordinated to maintain epithelial homeostasis in aging organisms remains unclear. In a previous study, we have found that the UPR^ER controls intestinal stem cell (ISC) proliferation in the Drosophila intestinal epithelium by influencing the intracellular redox state. How signaling through the canonical ER stress sensor PERK (PKR-like ER kinase) is integrated into this signaling network remained unclear. Here we show that PERK serves as a central regulator of ISC proliferation and tissue homeostasis in response ER stress. Strikingly, we find that within the intestinal epithelium, PERK is activated specifically in ISCs in response to both systemic and local ER stress, and is required for ISC proliferation under both homeostatic and stress conditions. We identify JAK/Stat signaling as an activator of PERK in ISCs in response to ER stress in neighboring cells, and find that the wide-spread age-associated increase in PERK activity in ISCs is a cause of age-related dysplasia in this tissue. Accordingly, limiting PERK activity in ISCs promotes homeostasis of the intestinal epithelium in old flies and extends lifespan.

p58IPK is an inhibitor of the eIF2α kinase GCN2 and its localization and expression underpin protein synthesis and ER processing capacity

One of the key cellular responses to stress is the attenuation of mRNA translation and protein synthesis via the phosphorylation of eIF2α (eukaryotic translation initiation factor 2α). This is mediated by four eIF2α kinases and it has been suggested that each kinase is specific to the cellular stress imposed. In the present study, we show that both PERK (PKR-like endoplasmic reticulum kinase/eIF2α kinase 3) and GCN2 (general control non-derepressible 2/eIF2α kinase 4) are required for the stress responses associated with conditions encountered by cells overexpressing secreted recombinant protein. Importantly, whereas GCN2 is the kinase that is activated following cold-shock/hypothermic culturing of mammalian cells, PERK and GCN2 have overlapping functions since knockdown of one of these at the mRNA level is compensated for by the cell by up-regulating levels of the other. The protein p58IPK {also known as DnaJ3C [DnaJ heat-shock protein (hsp) 40 homologue, subfamily C, member 3]} is known to inhibit the eIF2α kinases PKR (dsRNA-dependent protein kinase/eIF2α kinase 2) and PERK and hence prevent or delay eIF2α phosphorylation and consequent inhibition of translation. However, we show that p58IPK is a general inhibitor of the eIF2α kinases in that it also interacts with GCN2. Thus forced overexpression of cytoplasmic p58 delays eIF2α phosphorylation, suppresses GCN2 phosphorylation and prolongs protein synthesis under endoplasmic reticulum (ER), hypothermic and prolonged culture stress conditions. Taken together, our data suggest that there is considerable cross talk between the eIF2α kinases to ensure that protein synthesis is tightly regulated. Their activation is controlled by p58 and the expression levels and localization of this protein are crucial in the capacity the cells to respond to cellular stress via control of protein synthesis rates and subsequent folding in the ER.

Expression of three topologically distinct membrane proteins elicits unique stress response pathways in the yeast Saccharomyces cerevisiae

Misfolded membrane proteins are retained in the endoplasmic reticulum (ER) and are subject to ER-associated degradation, which clears the secretory pathway of potentially toxic species. While the transcriptional response to environmental stressors has been extensively studied, limited data exist describing the cellular response to misfolded membrane proteins. To this end, we expressed and then compared the transcriptional profiles elicited by the synthesis of three ER retained, misfolded ion channels: The α-subunit of the epithelial sodium channel, ENaC, the cystic fibrosis transmembrane conductance regulator, CFTR, and an inwardly rectifying potassium channel, Kir2.1, which vary in their mass, membrane topologies, and quaternary structures. To examine transcriptional profiles in a null background, the proteins were expressed in yeast, which was previously used to examine the degradation requirements for each substrate. Surprisingly, the proteins failed to induce a canonical unfolded protein response or heat shock response, although messages encoding several cytosolic and ER lumenal protein folding factors rose when αENaC or CFTR was expressed. In contrast, the levels of these genes were unaltered by Kir2.1 expression; instead, the yeast iron regulon was activated. Nevertheless, a significant number of genes that respond to various environmental stressors were upregulated by all three substrates, and compared with previous microarray data we deduced the existence of a group of genes that reflect a novel misfolded membrane protein response. These data indicate that aberrant proteins in the ER elicit profound yet unique cellular responses.

Drosophila melanogaster activating transcription factor 4 regulates glycolysis during endoplasmic reticulum stress

Endoplasmic reticulum (ER) stress results from an imbalance between the load of proteins entering the secretory pathway and the ability of the ER to fold and process them. The response to ER stress is mediated by a collection of signaling pathways termed the unfolded protein response, which plays important roles in development and disease. Here we show that in Drosophila melanogaster S2 cells, ER stress induces a coordinated change in the expression of genes involved in carbon metabolism. Genes encoding enzymes that carry out glycolysis were up-regulated, whereas genes encoding proteins in the tricarboxylic acid cycle and respiratory chain complexes were down-regulated. The unfolded protein response transcription factor Atf4 was necessary for the up-regulation of glycolytic enzymes and Lactate dehydrogenase (Ldh). Furthermore, Atf4 binding motifs in promoters for these genes could partially account for their regulation during ER stress. Finally, flies up-regulated Ldh and produced more lactate when subjected to ER stress. Together, these results suggest that Atf4 mediates a shift from a metabolism based on oxidative phosphorylation to one more heavily reliant on glycolysis, reminiscent of aerobic glycolysis or the Warburg effect observed in cancer and other proliferative cells.

Obesity promotes alterations in iron recycling

Hepcidin is a key hormone that induces the degradation of ferroportin (FPN), a protein that exports iron from reticuloendothelial macrophages and enterocytes. The aim of the present study was to experimentally evaluate if the obesity induced by a high-fat diet (HFD) modifies the expression of FPN in macrophages and enterocytes, thus altering the iron bioavailability. In order to directly examine changes associated with iron metabolism in vivo, C57BL/6J mice were fed either a control or a HFD. Serum leptin levels were evaluated. The hepcidin, divalent metal transporter-1 (DMT1), FPN and ferritin genes were analyzed by real-time polymerase chain reaction. The amount of iron present in both the liver and spleen was determined by flame atomic absorption spectrometry. Ferroportin localization within reticuloendothelial macrophages was observed by immunofluorescence microscopy. Obese animals were found to exhibit increased hepcidin gene expression, while iron accumulated in the spleen and liver. They also exhibited changes in the sublocation of splenic cellular FPN and a reduction in the FPN expression in the liver and the spleen, while no changes were observed in enterocytes. Possible explanations for the increased hepcidin expression observed in HFD animals may include: increased leptin levels, the liver iron accumulation or endoplasmic reticulum (ER) stress. Together, the results indicated that obesity promotes changes in iron bioavailability, since it altered the iron recycling function.

Co-chaperones of the mammalian endoplasmic reticulum

In mammalian cells, the rough endoplasmic reticulum or ER plays a central role in the biogenesis of most extracellular plus many organellar proteins and in cellular calcium homeostasis. Therefore, this organelle comprises molecular chaperones that are involved in import, folding/assembly, export, and degradation of polypeptides in millimolar concentrations. In addition, there are calcium channels/pumps and signal transduction components present in the ER membrane that affect and are affected by these processes. The ER lumenal Hsp70, termed immunoglobulin-heavy chain binding protein or BiP, is the central player in all these activities and involves up to seven different co-chaperones, i.e. ER-membrane integrated as well as ER-lumenal Hsp40s, which are termed ERj or ERdj, and two nucleotide exchange factors.

Endoplasmic reticulum stress is involved in the lidocaine-induced apoptosis in SH-SY5Y neuroblastoma cells

Lidocaine has been indicated to promote apoptosis and to promote endoplasmic reticulum (ER) stress. However, the mechanism underlining ER stress-mediated apoptosis is unclear. In the present study, we investigated the promotion to ER stress in the lidocaine-induced apoptosis in human neuroblastoma SH-SY5Y cells. Firstly, we confirmed that lidocaine treatment induced apoptosis in SH-SY5Y cells, time-dependently and dose-dependently, via MTT cell viability assay and annexin V/FITC apoptosis detection with a FACScan flow cytometer. And the anti-apoptosis Bcl-2 and Bcl-xL were downregulated, whereas the apoptosis-executive caspase 3 was promoted through Western blot assay and caspase 3 activity assay. Moreover, the ER stress-associated binding immunoglobulin protein (BiP), PKR-like ER kinase (PERK), activating transcription factor 4 (ATF4) and CCAAT/enhancer-binding protein homologous protein (CHOP) were also upregulated at both mRNA and protein levels by lidocaine treatment. On the other hand, downregulation of the ER stress-associated BiP by RNAi method not only blocked the lidocaine-promoted ER stress but also attenuated the lidocaine-induced SH-SY5Y cell apoptosis. In conclusion, the present study confirmed the involvement of ER stress in the lidocaine-induced apoptosis in human neuroblastoma SH-SY5Y cells. Our study provides a better understanding on the mechanism of lidocaine's neurovirulence.

Coronavirus-induced ER stress response and its involvement in regulation of coronavirus-host interactions

Coronavirus replication is structurally and functionally associated with the endoplasmic reticulum (ER), a major site of protein synthesis, folding, modification and sorting in the eukaryotic cells. Disturbance of ER homeostasis may occur under various physiological or pathological conditions. In response to the ER stress, signaling pathways of the unfolded protein response (UPR) are activated. UPR is mediated by three ER transmembrane sensors, namely the PKR-like ER protein kinase (PERK), the inositol-requiring protein 1 (IRE1) and the activating transcriptional factor 6 (ATF6). UPR facilitates adaptation to ER stress by reversible translation attenuation, enhancement of ER protein folding capacity and activation of ER-associated degradation (ERAD). In cells under prolonged and irremediable ER stress, UPR can also trigger apoptotic cell death. Accumulating evidence has shown that coronavirus infection causes ER stress and induces UPR in the infected cells. UPR is closely associated with a number of major signaling pathways, including autophagy, apoptosis, the mitogen-activated protein (MAP) kinase pathways, innate immunity and pro-inflammatory response. Therefore, studies on the UPR are pivotal in elucidating the complicated issue of coronavirus-host interaction. In this paper, we present the up-to-date knowledge on coronavirus-induced UPR and discuss its potential involvement in regulation of innate immunity and apoptosis.

Emerging functions of the unfolded protein response in immunity

The unfolded protein response (UPR) has traditionally been viewed as an adaptive response triggered by the accumulation of unfolded proteins in the endoplasmic reticulum (ER) and aimed at restoring ER function. The UPR can also be an anticipatory response that is activated well before the disruption of protein homeostasis. UPR signaling intersects at many levels with the innate and adaptive immune responses. In some types of cells of the immune system, such as dendritic cells (DCs) and B cells, particular sensors that detect the UPR seem to be constitutively active in the absence of induction of the traditional UPR gene program and are necessary for antigen presentation and immunoglobulin synthesis. The UPR also influences signaling via Toll-like receptors (TLRs) and activation of the transcription factor NF-κB, and some pathogens subvert the UPR. This Review summarizes these emerging noncanonical functions of the UPR in immunity.

Targeting the hallmarks of cancer with therapy-induced endoplasmic reticulum (ER) stress

The endoplasmic reticulum (ER) is at the center of a number of vital cellular processes such as cell growth, death, and differentiation, crosstalk with immune or stromal cells, and maintenance of proteostasis or homeostasis, and ER functions have implications for various pathologies including cancer. Recently, a number of major hallmarks of cancer have been delineated that are expected to facilitate the development of anticancer therapies. However, therapeutic induction of ER stress as a strategy to broadly target multiple hallmarks of cancer has been seldom discussed despite the fact that several primary or secondary ER stress-inducing therapies have been found to exhibit positive clinical activity in cancer patients. In the present review we provide a brief historical overview of the major discoveries and milestones in the field of ER stress biology with important implications for anticancer therapy. Furthermore, we comprehensively discuss possible strategies enabling the targeting of multiple hallmarks of cancer with therapy-induced ER stress.

Unpacking the unfolded protein response

This year, the Albert Lasker Basic Medical Research Award will be shared by Peter Walter and Kazutoshi Mori for discoveries revealing the molecular mechanism of the unfolded protein response, an intracellular quality control system that detects harmful misfolded proteins in the endoplasmic reticulum and then signals the nucleus to carry out corrective measures.

p53 negatively regulates Pin1 expression under ER stress

Accumulating evidence suggests that endoplasmic reticulum (ER) stress plays a major role in the development of many diseases. A previous study indicated that the apoptotic regulator p53 is significantly increased in response to ER stress and participates in ER stress-induced apoptosis. However, the regulators of p53 expression during ER stress are still not fully understood. Here, we investigated whether p53 contributes to the impairment of Pin1 signaling under ER stress. We found that treatment with thapsigargin, a stimulator of p53 expression and an inducer of ER stress, decreased Pin1 expression in HCT116 cells. Also, we identified functional p53 response elements (p53REs) in the Pin1 promoter. Overexpression of p53 significantly decreased Pin1 expression in HCT116 cells while abolition of p53 gene expression induced Pin1 expression. Pin1 expression was significantly increased by treatment with the p53 inhibitor pifithrin-α or down-regulation of p53 expression. Taken together, ER stress decreased Pin1 expression through p53 activation, and this mechanism may be associated with ER stress-induced cell death. These data reported here support the importance of Pin1 as a potential target molecule mediating tumor development.

Induction of the endoplasmic reticulum stress and autophagy in human lung carcinoma A549 cells by anacardic acid

Anacardic acid (AA, 2-hydroxy-6-pentadecylbenzoic acid), a constituent of the cashew-nut shell, has a variety of beneficial effects on the treatment of cancer and tumors. However, the fact that AA induces ER stress and autophagy in cancer cell is not known. We investigated the effect of AA on ER-stress and autophagy-induced cell death in cancer cells. Because of our interest in lung cancer, we used the non-small cell lung adenocarcinoma A549 cells treated with 3.0 μg/ml of AA for this research. In this research we found that AA induces intracellular Ca(2+) mobilization and ER stress. AA induced the ER stress-inducing factors, especially IRE1α, and the hallmarks of UPR, Grp78/Bip and GADD153/CHOP. AA inhibited the expression of p-PERK and its downstream substrate, p-elF2α. We also demonstrated that AA induces autophagy. Up-regulation of autophagy-related genes and the appearance of autophagosome in transfected cells with green fluorescent protein (GFP)-LC3 and GFP-Beclin1 plasmids showed the induction of autophagy in AA-treated A549 cells. The morphological analysis of intracellular organelles by TEM also showed the evidence that AA induces ER stress and autophagy. For the first time, our research showed that AA induces ER stress and autophagy in cancer cells.

Consensus guidelines for the detection of immunogenic cell death

Apoptotic cells have long been considered as intrinsically tolerogenic or unable to elicit immune responses specific for dead cell-associated antigens. However, multiple stimuli can trigger a functionally peculiar type of apoptotic demise that does not go unnoticed by the adaptive arm of the immune system, which we named "immunogenic cell death" (ICD). ICD is preceded or accompanied by the emission of a series of immunostimulatory damage-associated molecular patterns (DAMPs) in a precise spatiotemporal configuration. Several anticancer agents that have been successfully employed in the clinic for decades, including various chemotherapeutics and radiotherapy, can elicit ICD. Moreover, defects in the components that underlie the capacity of the immune system to perceive cell death as immunogenic negatively influence disease outcome among cancer patients treated with ICD inducers. Thus, ICD has profound clinical and therapeutic implications. Unfortunately, the gold-standard approach to detect ICD relies on vaccination experiments involving immunocompetent murine models and syngeneic cancer cells, an approach that is incompatible with large screening campaigns. Here, we outline strategies conceived to detect surrogate markers of ICD in vitro and to screen large chemical libraries for putative ICD inducers, based on a high-content, high-throughput platform that we recently developed. Such a platform allows for the detection of multiple DAMPs, like cell surface-exposed calreticulin, extracellular ATP and high mobility group box 1 (HMGB1), and/or the processes that underlie their emission, such as endoplasmic reticulum stress, autophagy and necrotic plasma membrane permeabilization. We surmise that this technology will facilitate the development of next-generation anticancer regimens, which kill malignant cells and simultaneously convert them into a cancer-specific therapeutic vaccine.