Identification of novel stress-induced genes downstream of chop

Deubiquitylase OTUD3 Mediates Endoplasmic Reticulum Stress through Regulating Fortilin Stability to Restrain Dopaminergic Neurons Apoptosis

OTU domain-containing protein 3 (OTUD3) knockout mice exhibited loss of nigral dopaminergic neurons and Parkinsonian symptoms. However, the underlying mechanisms are largely unknown. In this study, we observed that the inositol-requiring enzyme 1α (IRE1α)-induced endoplasmic reticulum (ER) stress was involved in this process. We found that the ER thickness and the expression of protein disulphide isomerase (PDI) were increased, and the apoptosis level was elevated in the dopaminergic neurons of OTUD3 knockout mice. These phenomena were ameliorated by ER stress inhibitor tauroursodeoxycholic acid (TUDCA) treatment. The ratio of p-IRE1α/IRE1α, and the expression of X-box binding protein 1-spliced (XBP1s) were remarkably increased after OTUD3 knockdown, which was inhibited by IRE1α inhibitor STF-083010 treatment. Moreover, OTUD3 regulated the ubiquitination level of Fortilin through binding with the OTU domain. OTUD3 knockdown resulted in a decrease in the interaction ability of IRE1α with Fortilin and finally enhanced the activity of IRE1α. Taken together, we revealed that OTUD3 knockout-induced injury of dopaminergic neurons might be caused by activating IRE1α signaling in ER stress. These findings demonstrated that OTUD3 played a critical role in dopaminergic neuron neurodegeneration, which provided new evidence for the multiple and tissue-dependent functions of OTUD3.

Protective role of PERK-eIF2α-ATF4 pathway in chronic renal failure induced injury of rat hippocampal neurons

PURPOSE

Chronic renal failure (CRF) is associated with impairment of hippocampal neurons. This study investigated the effect of PERK-eIF2α-ATF4 pathway in CRF.

METHODS

Rat CRF model was established and rat hippocampal neurons were separated. Xanthine Oxidase method, fluorescence spectrophotometry and flow cytometry were applied to detect superoxide dismutase (SOD) content, reactive oxygen species (ROS) level and apoptosis in hippocampal neurons, respectively. The levels of phosphorylated (p)-PERK, phosphorylated (p)-eIF2α, CHOP, Bax, C-Caspase-3 and Bcl-2 in rats were measured using Western blot. Then, the neurotoxicity of serum from CRF rats was assessed in rat hippocampal neurons after treatment with rat CRF serum and transfection with or without PERK overexpression or knockdown plasmid.

RESULTS

SOD activity was reduced, while ROS level and apoptosis rate were increased in hippocampal tissues of CRF rats. PERK-eIF2α-ATF4 and apoptosis pathways were activated in CRF rats. Cells treated with serum from CRF rats showed increases in apoptosis rate and LDH and ROS levels, and decreases in cell viability and SOD activity. However, overexpressed PERK could reverse the cytotoxic effect of serum from CRF rats. PERK overexpression could enhance the activation of PERK-eIF2α-ATF4 pathway in hippocampal neurons induced by serum from CRF rats. Furthermore, PERK overexpression could alleviate the increases in CHOP, Bax, C-Caspase-3 expressions and the reduction of Bcl-2 expression in hippocampal neurons induced by serum from CRF rats.

CONCLUSION

PERK-eIF2α-ATF4 pathway induced by increased endoplasmic reticulum stress may alleviate CRF-induced hippocampal neuronal damage.

ROS and Endoplasmic Reticulum Stress in Pulmonary Disease

Pulmonary diseases are main causes of morbidity and mortality worldwide. Current studies show that though specific pulmonary diseases and correlative lung-metabolic deviance own unique pathophysiology and clinical manifestations, they always tend to exhibit common characteristics including reactive oxygen species (ROS) signaling and disruptions of proteostasis bringing about accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER). ER is generated by the unfolded protein response. When the adaptive unfolded protein response (UPR) fails to preserve ER homeostasis, a maladaptive or terminal UPR is engaged, leading to the disruption of ER integrity and to apoptosis, which is called ER stress. The ER stress mainly includes the accumulation of misfolded and unfolded proteins in lumen and the disorder of Ca²⁺ balance. ROS mediates several critical aspects of the ER stress response. We summarize the latest advances in of the UPR and ER stress in the pathogenesis of pulmonary disease and discuss potential therapeutic strategies aimed at restoring ER proteostasis in pulmonary disease.

The PERK-Dependent Molecular Mechanisms as a Novel Therapeutic Target for Neurodegenerative Diseases

Higher prevalence of neurodegenerative diseases is strictly connected with progressive aging of the world population. Interestingly, a broad range of age-related, neurodegenerative diseases is characterized by a common pathological mechanism-accumulation of misfolded and unfolded proteins within the cells. Under certain circumstances, such protein aggregates may evoke endoplasmic reticulum (ER) stress conditions and subsequent activation of the unfolded protein response (UPR) signaling pathways via the protein kinase RNA-like endoplasmic reticulum kinase (PERK)-dependent manner. Under mild to moderate ER stress, UPR has a pro-adaptive role. However, severe or long-termed ER stress conditions directly evoke shift of the UPR toward its pro-apoptotic branch, which is considered to be a possible cause of neurodegeneration. To this day, there is no effective cure for Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), or prion disease. Currently available treatment approaches for these diseases are only symptomatic and cannot affect the disease progression. Treatment strategies, currently under detailed research, include inhibition of the PERK-dependent UPR signaling branches. The newest data have reported that the use of small-molecule inhibitors of the PERK-mediated signaling branches may contribute to the development of a novel, ground-breaking therapeutic approach for neurodegeneration. In this review, we critically describe all the aspects associated with such targeted therapy against neurodegenerative proteopathies.

Diterpenoid Tanshinones, the extract from Danshen (Radix Salviae Miltiorrhizae) induced apoptosis in nine human cancer cell lines

OBJECTIVE

To identify the active anti-tumor constituents in the extract from Danshen (Radix Salviae Miltiorrhizae) and investigate the mechanisms underlying the actions.

METHODS

First, we introduced a two-step counter- current chromatography to extract the therapeutically active diterpenoid, tanshinone from Danshen (Radix Salviae Miltiorrhizae). The cholecystokinin (CCK-8) method was used to evaluate the inhibitory effect of diterpenoid tanshinone in liver cancer QGY-7703, lung cancer PC9, lung cancer A549, gastric cancer MKN-45, gastric cancer HGC-27, colon cancer HCT116, myeloma cellU266/ RPMI8226, and human breast cancer MCF-7 in vitro. Fluorescence staining was used to observe the cytotoxicity ofditerpenoid tanshinone on PC9 cells. The Western blot was used to detect apoptosis- related protein poly ADP-ribose polymerase (PARP), cysteinyl aspartate specific proteinase3/9 (caspase3/9), and cleaved-cysteinyl aspartate specific proteinase3/9 (cleaved-caspase3/9). The endoplasmic reticulum stress-related activating transcription factor 4 (ATF4), phosphorylated eukaryotic initiation factor 2α (p-eIF2α), and phosphorylated jun amino-terminal kinase (p-JNK), and caspase- 12 were also analyzed using the Western blot.

RESULTS

Diterpenoid tanshinone inhibited the nine human tumor cell lines, with an IC50 of 4.37-29 μg/mL, with the PC9 and MCF-7 displaying the lowest values. Fluorescence staining showed a lethal effect of diterpenoid tanshinone on PC9 cells. The Western blot showed that the expression of caspase3/9 protein and ATF-4 protein decreased gradually. However, the PARP, cleaved-caspase 3/9 and the expression of p-eIF2 α, P-JNK, and caspase- 12 increased gradually, in a dose-dependent fashion.

CONCLUSION

We successfully introduced a two-step counter-current chromatography method to extract diterpenoid tanshinone, and demonstrated its antitumor activity. Diterpenoid tanshinone can induce apoptosis in nine human cancer cell lines.

Endoplasmic Reticulum Stress PERK-ATF4-CHOP Pathway Is Associated with Hypothalamic Neuronal Injury in Different Durations of Stress in Rats

The hypothalamus, which is the initial part of the hypothalamic-pituitary-adrenal (HPA) axis, plays a critical role in regulating stress in the central nervous system. The present study aimed to determine whether endoplasmic reticulum stress in hypothalamic neurons is differentially stimulated by varying durations of stress exposure, which ultimately leads to pathological changes in neurons by affecting HPA axis function. There is a need for better morphological evidence of the mechanisms involved in stress-induced neuron injury. A stress model was established in rats by restraining for 8 h and forced ice-water swimming for 5 min each day. The stress-inducing process lasted for 1, 3, 7, 14, and 21 days. Enzyme-linked immunosorbent assay (ELISA) was used to assay serum glucocorticoid levels. Thionine staining was used to observe morphological changes in hypothalamic neurons. Immunohistochemistry and microscopy-based multicolor tissue cytometry (MMTC) was used to detect changes in expression of endoplasmic reticulum stress protein GRP78, ATF4, and CHOP. Serum glucocorticoid levels significantly increased after 3 days of stress exposure and the levels peaked by 7 days. By 21 days, however, the levels were significantly decreased. Thionine staining revealed that prolonged stress exposure resulted in hypothalamic neurons with edema, a lack of Nissl bodies, and pyknotic neurons. Immunohistochemistry and MMTC showed that increasing stress periods significantly decreased GRP78 expression, although ATF4 and CHOP protein expression significantly increased. Stress resulted in pathological changes and significant dynamic changes because of endoplasmic reticulum stress in rat hypothalamic neurons. These results suggested that the endoplasmic reticulum stress PERK-ATF4-CHOP pathway may be associated with hypothalamic neuronal injury.

Transcriptome analysis of blood stasis syndrome in subjects with hypertension

OBJECTIVE

To screen for mRNAs associated with blood stasis syndrome and to explore the genetic mechanisms of blood stasis syndrome in hypertension.

METHODS

This study involved groups of patients with hypertension and blood stasis, including those with Qi deficiency, Qi stagnation, cold retention and heat retention; as well as hypertensive patients without blood stasis and healthy individuals. Human umbilical vein endothelial cells were co-cultured with the sera of these healthy individuals and patients with blood stasis syndrome. Total RNA was extracted from these cells and assessed by a high-throughput sequencing method (Solexa) and digital gene expression. Differentially expressed genes among these six groups were compared using whole genome sequences, and mRNAs associated with blood stasis syndrome identified. Differences in gene use and gene ontology function were analyzed. Genes enriched significantly and their pathways were determined, as were network interactions, and encoded proteins. Gene identities were confirmed by real-time polymerase chain reactions.

RESULTS

Compared with cells cultured in sera of the blood stasis groups, those culture in sera of healthy individuals and of the non-blood stasis group showed 11 and 301 differences, respectively in stasis-related genes. Genes identified as differing between the blood stasis and healthy groups included activating transcription factor 4, activating transcription factor 3, DNA-damage inducible transcription factor 3, Tribbles homolog 3, CCAAT/enhancer binding protein-β, and Jun proto-oncogene (JUN). Pathway and protein interaction network analyses showed that these genes were associated with endoplasmic reticulum stress. Cells cultured in sera of patients with blood stasis and Qi deficiency, Qi stagnation, heat retention, and cold retention were compared with cells cultured in sera of patients with the other types blood stasis syndrome. The comparison showed differences in expression of 28, 28, 34, and 32 specific genes, respectively.

CONCLUSION

The pathogenesis of blood stasis syndrome in hypertension is related to endoplasmic reticulum stress and involves the differential expression of the activating transcription factor 4, activating transcription factor 3, DNA-damage inducible transcription factor 3, Tribbles homolog 3, CCAAT/enhancer binding protein-β, and JUN genes.

Protective effect of kaempferol on endoplasmic reticulum stress-induced hepatocyte apoptosis and underlying mechanism

AIM: To explore the protective effect of kaempferol on human normal hepatocyte line HL-7702 cells under the endoplasmic reticulum stress and the underlying mechanism.

METHODS: In order to develop a hepatocyte apoptosis model, endoplasmic reticulum stress inducer tunicamycin was used to induce HL-7702 cell apoptosis. After HL-7702 cells were incubated with different concentrations of kaempferol (0.01, 0.1, 1 μmol/L), cell morphological changes were observed by microscopy, cell viability was measured by MTT assay, lactate dehydrogenase (LDH) activity in cell supernatants was determined with an LDH assay kit, apoptosis was measured by flow cytometry, and the protein expression of CHOP, a special marker of apoptosis induced by endoplasmic reticulum stress, was detected by Western blot.

RESULTS: Compared with the tunicamycin-induced hepatocyte apoptosis group, low concentrations of kaempferol (0.01, 0.1, 1 μmol/L) significantly inhibited endoplasmic reticulum stress-induced hepatocyte apoptosis. Kaempferol improved cell morphology, increased liver cell survival (tunicamycin model group, 80.14% ± 8.00%; 0.01 μmol/L kaempferol group, 96.16% ± 10.00%, P < 0.01; 0.1 μmol/L kaempferol, 91.43% ± 9.10%, P < 0.01; 1 μmol/L kaempferol, 87.84% ± 6.90%, P < 0.01), and reduced the levels of LDH released from HL-7702 cells (tunicamycin model group, 398.5 U ± 30.8 U; 0.01 μmol/L kaempferol, 89.9 U ± 21.4 U, P < 0.05; 0.1 μmol/L kaempferol, 95.1 U ± 8.9 U, P < 0.05; 1 μmol/L kaempferol, 120.5 U ± 24.2 U, P < 0.05), the apoptosis rates (tunicamycin model group, 4.58% ± 0.90%; 0.01 μmol/L kaempferol, 1.18% ± 0.48%, P < 0.05; 0.1 μmol/L kaempferol, 1.97% ± 0.32%, P < 0.05; 1 μmol/L kaempferol, 2.63% ± 0.16%, P < 0.05) and significantly reduced the expression of CHOP protein.

CONCLUSION: Low concentrations of kaempferol may inhibit endoplasmic reticulum stress-induced hepatocyte apoptosis by decreasing the expression of CHOP. Kaempferol may be a new drug to protect against liver injury induced by liver disease.

Liraglutide alleviates diabetic cardiomyopathy by blocking CHOP-triggered apoptosis via the inhibition of the IRE-α pathway

Clinically, diabetes mellitus is closely associated with and induces certain cardiovascular diseases. The aim of this study was to investigate endoplasmic reticulum (ER) stress-associated apoptosis of diabetic cardiomyopathy (DCM), and explore the protective mechanism of liraglutide. The DCM model was established with a high-fat diet and streptozotocin (STZ). Cardiac function was detected by echocardiogram examination and hematoxylin-eosin staining. ER stress unfolded protein response (UPR) hallmarks [inositol-requiring enzyme-α (IRE-α), p-Perk and ATF6] and transcription factors were detected with western blotting. Apoptosis inducers CHOP, c-Jun amino terminal kinase (JNK) and casapse-12 were also examined with western blotting. The results indicated that liraglutide is capable of improving cardiac function in DCM rats (P<0.05). IRE-α expression was significantly increased in the DCM group compared with the control group (P<0.05), and liraglutide is capable of decreasing IRE-α expression. X-box transcription factor-1 (XBP-1) was significantly spliced in the model group, and downregulated in the liraglutide-treated group. CHOP protein was upregulated in the DCM group, but inactivated by liraglutide treatment. In conclusion, liraglutide is capable of protecting DCM and blocking CHOP-mediated ER stress by inhibiting the IRE-α UPR pathway.

Endoplasmic reticulum stress signaling is involved in silver nanoparticles-induced apoptosis

Although silver nanoparticles (AgNPs) have been reported to exert strong acute toxic effects on various cultured cells by inducing oxidative stress, the molecular mechanisms by which AgNPs-damaged cells are unknown. Because the endoplasmic reticulum (ER) may play an important role in the response to oxidative stress-induced damage and is quite sensitive to oxidative damage, we hypothesized that AgNPs may exert cytotoxic effects on cells by modulating ER stress. In our study, AgNPs resulted in cytotoxicity and apoptotic cell death when analyzing cell viability, DNA fragmentation and the apoptotic sub-G(1) population. Flow cytometry and confocal microscopy indicated that the cells were sensitive to AgNPs with respect to the induction of mitochondrial Ca(2+) overloading and enhancement of ER stress. AgNPs induced a number of signature ER stress markers, including phosphorylation of RNA-dependent protein kinase-like ER kinase (PERK) and its downstream eukaryotic initiation factor 2α, phosphorylation of inositol-requiring protein 1 (IRE1), splicing of ER stress-specific X-box transcription factor-1, cleavage of activating transcription factor 6 (ATF6) and up-regulation of glucose-regulated protein-78 and CCAAT/enhancer-binding protein-homologous protein (CHOP/GADD153). Down-regulation of PERK, IRE1 and ATF6 expression using siRNA significantly decreased AgNPs-induced the enhancement of ER stress. In addition, down-regulation of CHOP expression with siRNA CHOP attenuated AgNPs-induced apoptosis. Taken together, the present study supports an important role for the ER stress response in mediating AgNPs-induced apoptosis.

Identification of novel myeloma-specific XBP1 peptides able to generate cytotoxic T lymphocytes: a potential therapeutic application in multiple myeloma

The purpose of these studies was to identify HLA-A2⁺ immunogenic peptides derived from XBP1 antigens to induce a multiple myeloma (MM)-specific immune response. Six native peptides from non-spliced XBP1 antigen and three native peptides from spliced XBP1 antigen were selected and evaluated for their HLA-A2 specificity. Among them, XBP1_184–192, XBP1 SP_196–204 and XBP1 SP_367–375 peptides showed the highest level of binding affinity, but not stability to HLA-A2 molecules. Novel heteroclitic XBP1 peptides, YISPWILAV or YLFPQLISV, demonstrated a significant improvement in HLA-A2 stability from their native XBP1_184–192 or XBP1 SP_367–375 peptide, respectively. Cytotoxic T lymphocytes generated by repeated stimulation of CD3⁺ T cells with each HLA-A2-specific heteroclitic peptide showed an increased percentage of CD8⁺ (cytotoxic) and CD69⁺/CD45RO⁺ (activated memory) T cells and a lower percentage of CD4⁺ (helper) and CD45RA⁺/CCR7⁺ (naïve) T cells, which were distinct from the control T cells. Functionally, the CTLs demonstrated MM-specific and HLA-A2-restricted proliferation, IFN-γ secretion and cytotoxic acivity in response to MM cell lines and importantly, cytotoxicty against primary MM cells. These data demonstrate the distinct immunogenic characteristics of unique heteroclitic XBP1 peptides which induce MM-specific CTLs and highlights their potential application for immunotherapy to treat the patients with MM or its pre-malignant condition.

Berberine-induced apoptosis in human glioblastoma T98G cells is mediated by endoplasmic reticulum stress accompanying reactive oxygen species and mitochondrial dysfunction

Berberine has a wide range of biochemical and pharmacologic effects, including antitumor activity, but the mechanisms involved in berberine-induced apoptosis remain unclear. The purpose of the present study was to investigate the changes in oxidative stress and endoplasmic reticulum (ER)-related molecules, which are closely associated with cell death-signaling transduction pathways, in human glioblastoma T98G cells treated with berberine. Berberine significantly decreased the cell viability of T98G cells in a dose-dependent manner. Berberine increased the production of reactive oxygen species (ROS) and level of intracellular Ca(2+). Berberine induced ER stress as evidenced by the detection of ER stress-associated molecules such as phosphorylated protein kinase-like ER kinase, eukaryotic translation initiation factor-2α, glucose-regulated protein 78/immunoglobulin heavy chain-binding protein, and CCAAT/enhancer-binding protein (C/EBP)-homologous protein/growth arrest and DNA damage-inducible gene 153, which was associated with the activation of caspase-3. Furthermore, the administration of the antioxidants, N-acetylcysteine and glutathione, reversed berberine-induced apoptosis. Berberine also markedly enhanced apoptosis in T98G cells through the induction of a higher ratio of Bax/Bcl-2 proteins, disruption of the mitochondrial membrane potential, activation of caspase-9 and -3, and cleavage of the poly(ADP-ribose) polymerase (PARP). The inhibition of ER stress using salubrinal led to an increased the level of Bcl-2, whereas the level of Bax, cleavage of procaspase-9 and -3, and PARP were decreased when compared with cells treated with berberine alone, indicating that berberine-induced apoptosis is associated with mitochondrial dysfunction. These results demonstrate that berberine induces apoptosis via ER stress through the elevation of ROS and mitochondrial-dependent pathway in human glioblastoma T98G cells.

Oxidative and endoplasmic reticulum stress signaling are involved in dehydrocostuslactone-mediated apoptosis in human non-small cell lung cancer cells

This study investigates the anticancer effect of dehydrocostuslactone (DHE), a medicinal plant-derived sesquiterpene lactone, on human non-small cell lung cancer cell lines, A549, NCI-H460 and NCI-H520. Our results show that DHE inhibits the proliferation of A549, NCI-H460 and NCI-H520 cells. DHE-induced apoptosis in both A549 and NCI-H460 cells. DHE triggered endoplasmic reticulum (ER) stress, as indicated by changes in cytosol-calcium levels, PKR-like ER kinase (PERK) phosphorylation, inositol requiring protein 1 (IRE1) and CHOP/GADD153 upregulation, X-box transcription factor-1 (XBP-1) mRNA splicing, and caspase-4 activation. The release of calcium triggered the production of ROS, which further enhances calcium overloading and subsequently activates p38, JNK and ERK1/2. Both IRE1 miRNA transfection and BAPTA-AM pretreatment inhibit DHE-mediated apoptosis, supporting the hypothesis that DHE induces cell death through ER stress. Importantly, a novel anticancer agent for the treatment of non-small cell lung cancer, and is supported by animal studies which have shown a dramatic 50% reduction in tumor size after 28 days of treatment. This study demonstrates that DHE may be a novel anticancer agent for the treatment of non-small cell lung cancer.