Integrated stress response in hepatitis C promotes Nrf2-related chaperone-mediated autophagy: A novel mechanism for host-microbe survival and HCC development in liver cirrhosis.

The molecular mechanism(s) how liver damage during the chronic hepatitis C virus (HCV) infection evolve into cirrhosis and hepatocellular carcinoma (HCC) is unclear. HCV infects hepatocyte, the major cell types in the liver. During infection, large amounts of viral proteins and RNA replication intermediates accumulate in the endoplasmic reticulum (ER) of the infected hepatocyte, which creates a substantial amount of stress response. Infected hepatocyte activates a different type of stress adaptive mechanisms such as unfolded protein response (UPR), antioxidant response (AR), and the integrated stress response (ISR) to promote virus-host cell survival. The hepatic stress is also amplified by another layer of innate and inflammatory response associated with cellular sensing of virus infection through the production of interferon (IFN) and inflammatory cytokines. The interplay between various types of cellular stress signal leads to different forms of cell death such as apoptosis, necrosis, and autophagy depending on the intensity of the stress and nature of the adaptive cellular response. How do the adaptive cellular responses decode such death programs that promote host-microbe survival leading to the establishment of chronic liver disease? In this review, we discuss how the adaptive cellular response through the Nrf2 pathway that promotes virus and cell survival. Furthermore, we provide a glimpse of novel stress-induced Nrf2 mediated compensatory autophagy mechanisms in virus-cell survival that degrade tumor suppressor gene and activation of oncogenic signaling during HCV infection. Based on these facts, we hypothesize that the balance between hepatic stress, inflammation and different types of cell death determines liver disease progression outcomes. We propose that a more nuanced understanding of virus-host interactions under excessive cellular stress may provide an answer to the fundamental questions why some individuals with chronic HCV infection remain at risk of developing cirrhosis, cancer and some do not.

Irisin ameliorates endoplasmic reticulum stress and liver fibrosis through inhibiting PERK-mediated destabilization of HNRNPA1 in hepatic stellate cells.

Liver fibrosis is a common consequence of chronic liver diseases involved with the activation of hepatic stellate cells (HSCs) and endoplasmic reticulum (ER) stress. Irisin is a small polypeptide hormone that shows beneficial effects on metabolic disorders. The current study aimed to investigate the biological function of irisin on hepatic fibrosis. A mouse model of carbon tetrachloride (CCl4)-induced hepatic fibrosis was established. CCl4-treated mice showed elevated serum levels of AST and ALT, increased collagen accumulation, induced ER stress, and upregulated expressions of pro-fibrotic proteins in the liver compared to the controls. The administration of irisin, however, ameliorated CCl4-induced hepatic fibrosis in both cultured HSCs and mice. PKR-like ER kinase (PERK) is a key component of the ER stress-associated signaling pathway. We found that irisin treatment improved the stability of heterogeneous nuclear ribonucleoprotein A1 (HNRNPA1) via regulating the phosphorylation of PERK in mouse livers and isolated HSCs. Also, the knockdown of HNRNPA1 eliminated the hepatoprotective effects of irisin on hepatic fibrosis and ER stress. In summary, this study showed that irisin alleviated ER stress and hepatic fibrosis by inhibiting PERK-mediated HNRNPA1 destabilization, suggesting that irisin may represent a promising therapeutic strategy for patients with liver fibrosis.

Combined Transcriptomic and Proteomic Analysis of Perk Toxicity Pathways.

In Drosophila, endoplasmic reticulum (ER) stress activates the protein kinase R-like endoplasmic reticulum kinase (dPerk). dPerk can also be activated by defective mitochondria in fly models of Parkinson's disease caused by mutations in pink1 or parkin. The Perk branch of the unfolded protein response (UPR) has emerged as a major toxic process in neurodegenerative disorders causing a chronic reduction in vital proteins and neuronal death. In this study, we combined microarray analysis and quantitative proteomics analysis in adult flies overexpressing dPerk to investigate the relationship between the transcriptional and translational response to dPerk activation. We identified tribbles and Heat shock protein 22 as two novel Drosophila activating transcription factor 4 (dAtf4) regulated transcripts. Using a combined bioinformatics tool kit, we demonstrated that the activation of dPerk leads to translational repression of mitochondrial proteins associated with glutathione and nucleotide metabolism, calcium signalling and iron-sulphur cluster biosynthesis. Further efforts to enhance these translationally repressed dPerk targets might offer protection against Perk toxicity.

Unfolded protein response is involved in geniposide-regulating glucose-stimulated insulin secretion in INS-1 cells.

The growing evidence shows that in the early stage of type 2 diabetes mellitus (T2DM) development, when challenged by hyperglycemia and/or insulin resistance, pancreatic islets would produce more insulin to maintain the balance of blood sugar, but at the same time, endoplasmic reticulum (ER) stress will be initiated for the reason of over-compensation, which might be a crucial caused factor of dysfunction and death of pancreatic beta cell. In this study, we showed that high glucose induced a remarkably unfolded protein response (UPR) with the phosphorylation of PERK/eIF2α and IRE1α in INS-1 cells, but geniposide prevented the role of high glucose on the phosphorylation of PERK/eIF2α and IRE1α, respectively. Although inhibition of Txnip expression by siRNA had no significant effect on geniposide-regulating UPR, PERK and IRE1α were associated with geniposide-regulating Txnip degradation and glucose-stimulated insulin secretion (GSIS) in high glucose-cultured INS-1 cells. All these data suggest that geniposide might be an important regulator of ER stress and GSIS, and a promising compound for the treatment of T2DM. SIGNIFICANCE OF THE STUDY: Mounting evidence indicates that endoplasmic reticulum (ER) stress plays an essential role to maintain the normal cellular functions and dysfunction. In this study, we revealed that geniposide might be an important regulator of ER stress and glucose-stimulated insulin secretion in pancreatic beta cells.

ER stress-induced cell death mechanisms.

The endoplasmic-reticulum (ER) stress response constitutes a cellular process that is triggered by a variety of conditions that disturb folding of proteins in the ER. Eukaryotic cells have developed an evolutionarily conserved adaptive mechanism, the unfolded protein response (UPR), which aims to clear unfolded proteins and restore ER homeostasis. In cases where ER stress cannot be reversed, cellular functions deteriorate, often leading to cell death. Accumulating evidence implicates ER stress-induced cellular dysfunction and cell death as major contributors to many diseases, making modulators of ER stress pathways potentially attractive targets for therapeutics discovery. Here, we summarize recent advances in understanding the diversity of molecular mechanisms that govern ER stress signaling in health and disease. This article is part of a Special Section entitled: Cell Death Pathways.

Sorafenib enhances proteasome inhibitor-mediated cytotoxicity via inhibition of unfolded protein response and keratin phosphorylation.

Hepatocellular carcinoma (HCC) is highly resistant to conventional systemic therapies and prognosis for advanced HCC patients remains poor. Recent studies of the molecular mechanisms responsible for tumor initiation and progression have identified several potential molecular targets in HCC. Sorafenib is a multi-kinase inhibitor shown to have survival benefits in advanced HCC. It acts by inhibiting the serine/threonine kinases and the receptor type tyrosine kinases. In preclinical experiments sorafenib had anti-proliferative activity in hepatoma cells and it reduced tumor angiogenesis and increased apoptosis. Here, we demonstrate for the first time that the cytotoxic mechanisms of sorafenib include its inhibitory effects on protein ubiquitination, unfolded protein response (UPR) and keratin phosphorylation in response to endoplasmic reticulum (ER) stress. Moreover, we show that combined treatment with sorafenib and proteasome inhibitors (PIs) synergistically induced a marked increase in cell death in hepatoma- and hepatocyte-derived cells. These observations may open the way to potentially interesting treatment combinations that may augment the effect of sorafenib, possibly including drugs that promote ER stress. Because sorafenib blocked the cellular defense mechanisms against hepatotoxic injury not only in hepatoma cells but also in hepatocyte-derived cells, we must be careful to avoid severe liver injury.

Pro-apoptotic signaling induced by photo-oxidative ER stress is amplified by Noxa, not Bim.

Pro-apoptotic signaling instigated by endoplasmic reticulum (ER) stress is tightly governed by the BH3-only proteins like Noxa and Bim, which help trigger apoptosis, in part by inactivating mitochondria protecting proteins like Mcl-1. Bim/Noxa-based pro-apoptotic signaling has been implicated for various ER stressors but not yet for those causing "ER-focused" production of severe oxidative stress. In the present study we found that photo-oxidative (phox)-ER stress induced by hypericin-based photodynamic therapy is associated with activation of PERK (an ER sessile, stress sensor), robust induction of CHOP (a pro-apoptotic transcription factor) and induction of Bim and Noxa (accompanied by an eventual drop in Mcl-1 levels). Interestingly Noxa, but not Bim, contributed toward phox-ER stress induced apoptosis, regulated by PERK in a CHOP-independent, temporally-defined manner. These observations shed further light on complex signaling pathways elicited byphox-ER stress and vouch for directing more investigation toward the role of PERK in cell death governance.

Effect of Liraglutide on endoplasmic reticulum stress in diabetes.

Endoplasmic reticulum (ER) stress is associated with the development of diabetes. The present study sought to investigate the effect of Liraglutide, a glucagon like peptide 1 analogue, on ER stress in ß-cells. We found that Liraglutide protected the pancreatic INS-1 cells from thapsigargin-induced ER stress and the ER stress associated cell apoptosis, mainly by suppressing the PERK and IRE1 pathways. We further tested the effects of Liraglutide in the Akita mouse, an ER-stress induced type 1 diabetes model. After administration of Liraglutide for 8weeks, p-eIF2α and p-JNK were significantly decreased in the pancreas of the Akita mouse, while the treatment showed no significant impact on the levels of insulin of INS-cells. Taken together, our findings suggest that Liraglutide may protect pancreatic cells from ER stress and its related cell death.

PKR-like ER kinase (PERK) Haplotypes Are Associated with Depressive Symptoms in People with HIV.

Background: Depression is a debilitating and difficult-to-treat condition in people with HIV (PWH) despite viral suppression on antiretroviral therapy (ART). Depression is associated with activation of the PKR-like ER kinase (PERK) pathway, which regulates protein synthesis in response to metabolic stress. We evaluated common PERK haplotypes that influence PERK expression in relation to depressed mood in PWH. Methods: PWH from 6 research centers were enrolled in the study. Genotyping was conducted using targeted sequencing with TaqMan. The major PERK haplotypes A, B, and D were identified. Depressive symptom severity was assessed using the Beck Depression Inventory-II (BDI-II). Covariates including genetically-defined ancestry, demographics, HIV disease/treatment parameters and antidepressant treatments were assessed. Data were analyzed using multivariable regression models. Results: A total of 287 PWH with a mean (SD) age of 57.1±7.8 years were enrolled. Although the largest ethnic group was non-Hispanic white (n=129, 45.3%), African-American (n=124, 43.5%) and Hispanic (n=30, 10.5%) made up over half the sample. 20.3% were female and 96.5% were virally suppressed. Mean BDI-II was 9.6±9.5, and 28.9% scored above the cutoff for mild depression (BDI-II>13). PERK haplotype frequencies were AA57.8%, AB25.8%, AD 10.1%, and BB4.88%. PERK haplotypes were differentially represented according to genetic ancestry (p=6.84e-6). BDI-II scores were significantly higher in participants with the AB haplotype (F=4.45, p=0.0007).This finding was robust to consideration of potential confounds. Conclusion: PERK haplotypes were associated with depressed mood in PWH.Consequently, pharmacological targeting of PERK-related pathways might amelioratedepression in PWH.

ER Stress Decreases Gene Expression Of Transmembrane Protein 117 Via Activation of PKR-like ER Kinase.

Stress response is an inherent mechanism in the endoplasmic reticulum (ER). The inducers of ER cause a specific cascade of reactions, leading to gene expression. Transmembrane protein 117 (TMEM117) is in the ER and plasma membrane. In our previous study, TMEM117 protein expression was found to be decreased by an ER stress inducer. However, the mechanism underlying this decrease in TMEM117 protein expression remains unclear. This study aimed to elucidate the mechanism underlying the decrease in TMEM117 protein expression during ER stress and identify the unfolded protein response (UPR) pathway related to decreased TMEM117 protein expression. We showed that the gene expression levels of TMEM117 were decreased by ER stress inducers and were regulated by PKR-like ER kinase (PERK), indicating that TMEM117 protein expression was regulated by the signaling pathway. Surprisingly, gene knockdown of activating transcription factor 4 (ATF4) downstream of PERK did not affect the gene expression of TMEM117. These results suggest that TMEM117 protein expression during ER stress is transcriptionally regulated by PERK but not by ATF4. TMEM117 has a potential to be a new therapeutic target against ER stress-related diseases.

Ginsenoside Rg1 regulates autophagy and endoplasmic reticulum stress via the AMPK/mTOR and PERK/ATF4/CHOP pathways to alleviate alcohol­induced myocardial injury.

It has been reported that ginsenoside Rg1 (G­Rg1) can alleviate alcoholic liver injury, cardiac hypertrophy and myocardial ischemia, as well as reperfusion injury. Therefore, the present study aimed to investigate the role of G­Rg1 in alcohol­induced myocardial injury, as well as to elucidate its underlying mechanisms of action. For this purpose, H9c2 cells were stimulated with ethanol. Subsequently, H9c2 cell viability and apoptosis were determined using a Cell Counting Kit­8 assay and flow cytometric analysis, respectively. The levels of lactate dehydrogenase and caspase­3 in the H9c2 cell culture supernatant were detected using corresponding assay kits. In addition, the expression of green fluorescent protein (GFP)­light chain 3 (LC3) and that of C/EBP homologous protein (CHOP) were evaluated using GFP­LC3 assay and immunofluorescence staining, respectively. The expression levels of apoptosis­, autophagy­, endoplasmic reticulum stress (ERS)­ and adenosine 5'­monophosphate­activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) pathway­related proteins were detected using western blot analysis. The results revealed that treatment with G­Rg1 enhanced the viability and suppressed the apoptosis of ethanol­stimulated H9c2 cells. G­Rg1 also attenuated autophagy and ERS in ethanol­stimulated H9c2 cells. In addition, the levels of phosphorylated (p)­protein kinase R (PKR)­like ER kinase (PERK), p­eukaryotic translation initiation factor 2a, activating transcription factor 4 (ATF4), CHOP, caspase­12 and p­AMPK were downregulated, while the p­mTOR level was upregulated in ethanol­stimulated H9c2 cells treated with G­Rg1. Furthermore, the co­treatment of G­Rg1­treated ethanol­stimulated H9c2 cells with AICAR, an AMPK agonist, or CCT020312, a PERK agonist, inhibited cell viability and promoted cell apoptosis, autophagy and ERS. Overall, the results of the present study suggest that G­Rg1 suppresses autophagy and ERS via inhibiting the AMPK/mTOR and PERK/ATF4/CHOP pathways to alleviate ethanol­induced H9c2 cell injury.

ER Stress in COVID-19 and Parkinson's Disease: In Vitro and In Silico Evidences.

The outbreak of COVID-19 caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) signifies a serious worldwide concern to public health. Both transcriptome and proteome of SARS-CoV-2-infected cells synergize the progression of infection in host, which may exacerbate symptoms and/or progression of other chronic diseases such as Parkinson's disease (PD). Oxidative stress is a well-known cause of endoplasmic reticulum (ER) stress observed in both SARS-CoV-2 and PD. In the current study, we aimed to explore the influence of PKR-like ER kinase (PERK) stress pathway under SARS-CoV-2-mediated infection and in human cell model of PD. Furthermore, we investigated whether they are interconnected and if the ER stress inhibitors could inhibit cell death and provide cellular protection. To achieve this aim, we have incorporated in silico analysis obtained from gene set enrichment analysis (GSEA), a literature review and laboratory data. The neurotoxin, 6-hydroxy dopamine (6OHDA), was used to mimic the biochemical and neuropathological characteristics of PD by inducing oxidative stress in dopamine-containing neurons differentiated from ReNVM cell line (dDCNs). Furthermore, we explored if ER stress influences activation of caspases-2, -4 and -8 in SARS-CoV-2 and in stressed dDCNs. Our laboratory data using Western blot, immunocytochemistry and 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (MTT) analyses indicated that 6OHDA-induced toxicity triggered activation of caspases-2, -4 and -8 in dDCNs. Under SARS-CoV-2 infection of different cell types, GSEA revealed cell-specific sensitivities to oxidative and ER stresses. Cardiomyocytes and type II alveolar epithelial-like cells were more vulnerable to oxidative stress than neural cells. On the other side, only cardiomyocytes activated the unfolded protein response, however, the PERK pathway was operative in both cardiomyocytes and neural cells. In addition, caspase-4 activation by a SARS-CoV-2 was observed via in silico analyses. These results demonstrate that the ER stress pathway under oxidative stress in SARS-CoV-2 and PD are interconnected using diverse pathways. Furthermore, our results using the ER stress inhibitor and caspase specific inhibitors provided cellular protection suggesting that the use of specific inhibitors can provide effective therapeutic approaches for the treatment of COVID-19 and PD.

Ca2+ signalling system initiated by endoplasmic reticulum stress stimulates PERK activation.

The accumulation of unfolded proteins within the Endoplasmic Reticulum (ER) activates a signal transduction pathway termed the unfolded protein response (UPR), which attempts to restore ER homoeostasis. If this cannot be done, UPR signalling ultimately induces apoptosis. Ca2+ depletion in the ER is a potent inducer of ER stress. Despite the ubiquity of Ca2+ as an intracellular messenger, the precise mechanism(s) by which Ca2+ release affects the UPR remains unknown. Tethering a genetically encoded Ca2+ indicator (GCamP6) to the ER membrane revealed novel Ca2+ signalling events initiated by Ca2+ microdomains in human astrocytes under ER stress, induced by tunicamycin (Tm), an N-glycosylation inhibitor, as well as in a cell model deficient in all three inositol triphosphate receptor isoforms. Pharmacological and molecular studies indicate that these local events are mediated by translocons and that the Ca2+ microdomains impact (PKR)-like-ER kinase (PERK), an UPR sensor, activation. These findings reveal the existence of a Ca2+ signal mechanism by which stressor-mediated Ca2+ release regulates ER stress.

A cyclodextrin-based nanoformulation achieves co-delivery of ginsenoside Rg3 and quercetin for chemo-immunotherapy in colorectal cancer.

The immune checkpoint blockade therapy has profoundly revolutionized the field of cancer immunotherapy. However, despite great promise for a variety of cancers, the efficacy of immune checkpoint inhibitors is still low in colorectal cancer (CRC). This is mainly due to the immunosuppressive feature of the tumor microenvironment (TME). Emerging evidence reveals that certain chemotherapeutic drugs induce immunogenic cell death (ICD), demonstrating great potential for remodeling the immunosuppressive TME. In this study, the potential of ginsenoside Rg3 (Rg3) as an ICD inducer against CRC cells was confirmed using in vitro and in vivo experimental approaches. The ICD efficacy of Rg3 could be significantly enhanced by quercetin (QTN) that elicited reactive oxygen species (ROS). To ameliorate in vivo delivery barriers associated with chemotherapeutic drugs, a folate (FA)-targeted polyethylene glycol (PEG)-modified amphiphilic cyclodextrin nanoparticle (NP) was developed for co-encapsulation of Rg3 and QTN. The resultant nanoformulation (CD-PEG-FA.Rg3.QTN) significantly prolonged blood circulation and enhanced tumor targeting in an orthotopic CRC mouse model, resulting in the conversion of immunosuppressive TME. Furthermore, the CD-PEG-FA.Rg3.QTN achieved significantly longer survival of animals in combination with Anti-PD-L1. The study provides a promising strategy for the treatment of CRC.

SMYD3-PARP16 axis accelerates unfolded protein response and mediates neointima formation.

Neointimal hyperplasia after vascular injury is a representative complication of restenosis. Endoplasmic reticulum (ER) stress-induced unfolded protein response (UPR) is involved in the pathogenesis of vascular intimal hyperplasia. PARP16, a member of the poly(ADP-ribose) polymerases family, is correlated with the nuclear envelope and the ER. Here, we found that PERK and IRE1α are ADP-ribosylated by PARP16, and this might promote proliferation and migration of smooth muscle cells (SMCs) during the platelet-derived growth factor (PDGF)-BB stimulating. Using chromatin immunoprecipitation coupled with deep sequencing (ChIP-seq) analysis, PARP16 was identified as a novel target gene for histone H3 lysine 4 (H3K4) methyltransferase SMYD3, and SMYD3 could bind to the promoter of Parp16 and increased H3K4me3 level to activate its host gene's transcription, which causes UPR activation and SMC proliferation. Moreover, knockdown either of PARP16 or SMYD3 impeded the ER stress and SMC proliferation. On the contrary, overexpression of PARP16 induced ER stress and SMC proliferation and migration. In vivo depletion of PARP16 attenuated injury-induced neointimal hyperplasia by mediating UPR activation and neointimal SMC proliferation. This study identified SMYD3-PARP16 is a novel signal axis in regulating UPR and neointimal hyperplasia, and targeting this axis has implications in preventing neointimal hyperplasia related diseases.

A small molecule UPR modulator for diabetes identified by high throughput screening.

Unfolded protein response (UPR) is a stress response that is specific to the endoplasmic reticulum (ER). UPR is activated upon accumulation of unfolded (or misfolded) proteins in the ER's lumen to restore protein folding capacity by increasing the synthesis of chaperones. In addition, UPR also enhances degradation of unfolded proteins and reduces global protein synthesis to alleviate additional accumulation of unfolded proteins in the ER. Herein, we describe a cell-based ultra-high throughput screening (uHTS) campaign that identifies a small molecule that can modulate UPR and ER stress in cellular and in vivo disease models. Using asialoglycoprotein receptor 1 (ASGR) fused with Cypridina luciferase (CLuc) as reporter assay for folding capacity, we have screened a million small molecule library and identified APC655 as a potent activator of protein folding, that appears to act by promoting chaperone expression. Furthermore, APC655 improved pancreatic ß cell viability and insulin secretion under ER stress conditions induced by thapsigargin or cytokines. APC655 was also effective in preserving ß cell function and decreasing lipid accumulation in the liver of the leptin-deficient (ob/ob) mouse model. These results demonstrate a successful uHTS campaign that identified a modulator of UPR, which can provide a novel candidate for potential therapeutic development for a host of metabolic diseases.

Neurite atrophy and apoptosis mediated by PERK signaling after accumulation of GM2-ganglioside.

GM2-gangliosidosis, a subgroup of lysosomal storage disorders, is caused by deficiency of hexosaminidase activity, and comprises the closely related Tay-Sachs and Sandhoff diseases. The enzyme deficiency prevents normal metabolization of ganglioside GM2, usually resulting in progressive neurodegenerative disease. The molecular mechanisms whereby GM2 accumulation in neurons triggers neurodegeneration remain unclear. In vitro experiments, using microsomes from Sandhoff mouse model brain, showed that increase of GM2 content negatively modulates sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) (Pelled et al., 2003). Furthermore, Ca2+ depletion in endoplasmic reticulum (ER) triggers Unfolded Protein Response (UPR), which tends to restore homeostasis in the ER; however, if cellular damage persists, an apoptotic response is initiated. We found that ER GM2 accumulation in cultured neurons induces luminal Ca2+ depletion, which in turn activates PERK (protein kinase RNA [PKR]-like ER kinase), one of three UPR sensors. PERK signaling displayed biphasic activation; i.e., early upregulation of cytoprotective calcineurin (CN) and, under prolonged ER stress, enhanced expression of pro-apoptotic transcription factor C/EBP homologous protein (CHOP). Moreover, GM2 accumulation in neuronal cells induced neurite atrophy and apoptosis. Both processes were effectively modulated by treatment with the selective PERK inhibitor GSK2606414, by CN knockdown, and by CHOP knockdown. Overall, our findings demonstrate the essential role of PERK signaling pathway contributing to neurodegeneration in a model of GM2-gangliosidosis.

Integrated Stress Responses to Bacterial Pathogenesis Patterns.

Activation of an appropriate innate immune response to bacterial infection is critical to limit microbial spread and generate cytokines and chemokines to instruct appropriate adaptive immune responses. Recognition of bacteria or bacterial products by pattern recognition molecules is crucial to initiate this response. However, it is increasingly clear that the context in which this recognition occurs can dictate the quality of the response and determine the outcome of an infection. The cross talk established between host and pathogen results in profound alterations on cellular homeostasis triggering specific cellular stress responses. In particular, the highly conserved integrated stress response (ISR) has been shown to shape the host response to bacterial pathogens by sensing cellular insults resulting from infection and modulating transcription of key genes, translation of new proteins and cell autonomous antimicrobial mechanisms such as autophagy. Here, we review the growing body of evidence demonstrating a role for the ISR as an integral part of the innate immune response to bacterial pathogens.

Endoplasmic reticulum stress and eIF2α phosphorylation: The Achilles heel of pancreatic ß cells.

BACKGROUND: Pancreatic ß cell dysfunction and death are central in the pathogenesis of most if not all forms of diabetes. Understanding the molecular mechanisms underlying ß cell failure is important to develop ß cell protective approaches. SCOPE OF REVIEW: Here we review the role of endoplasmic reticulum stress and dysregulated endoplasmic reticulum stress signaling in ß cell failure in monogenic and polygenic forms of diabetes. There is substantial evidence for the presence of endoplasmic reticulum stress in ß cells in type 1 and type 2 diabetes. Direct evidence for the importance of this stress response is provided by an increasing number of monogenic forms of diabetes. In particular, mutations in the PERK branch of the unfolded protein response provide insight into its importance for human ß cell function and survival. The knowledge gained from different rodent models is reviewed. More disease- and patient-relevant models, using human induced pluripotent stem cells differentiated into ß cells, will further advance our understanding of pathogenic mechanisms. Finally, we review the therapeutic modulation of endoplasmic reticulum stress and signaling in ß cells. MAJOR CONCLUSIONS: Pancreatic ß cells are sensitive to excessive endoplasmic reticulum stress and dysregulated eIF2α phosphorylation, as indicated by transcriptome data, monogenic forms of diabetes and pharmacological studies. This should be taken into consideration when devising new therapeutic approaches for diabetes.

The role of DAPK-BimEL pathway in neuronal death induced by oxygen-glucose deprivation.

Death-associated protein kinase (DAPK) has been found promoting cell death under stress conditions, including cell death during brain ischemia. However, little is known about the mechanisms how DAPK is involved in the neuronal death-promoting process during ischemia. The present study was to examine the DAPK signal transduction pathways using an ischemia mimicking model, oxygen glucose deprivation (OGD). OGD was induced by incubating SH-SY5Y neuroblastoma cells in glucose-free culture medium flushed with a mixture of N2 and CO2. DAPK expression was inhibited by transfection of SH-SY5Y cells with DAPK short hairpin RNA (shRNA). Cell death induced by OGD exposure was assessed by Annexin V-FITC and propidium iodide (PI) assay. Protein expressions were examined by Western blot and protein interactions were detected with immunoprecipitation followed by Western blot. OGD treatment resulted in neuronal death and led to DAPK activation as demonstrated by increase of DAPK (active form) and decrease of phospho-DAPK (inactive form). The activation of DAPK in turn led to BimEL up-regulation and endoplasmic reticulum (ER) stress activation. Further analyses showed that DAPK mediated BimEL expression through extracellular signal-regulated protein kinase1/2 (ERK1/2) inactivation and c-Jun-N-terminal kinase1/2 (JNK1/2) activation. These findings revealed novel signal transduction pathways leading to neuronal death in response to OGD.