Sodium fluoride induces apoptosis through reactive oxygen species-mediated endoplasmic reticulum stress pathway in Sertoli cells

Excessive fluoride exposure is known to contribute to reproductive system dysfunction, ultimately leading to pathological damage and apoptosis in cells. Although both oxidative and endoplasmic reticulum (ER) stresses have been implicated in fluorosis, the signaling pathways and their roles in sodium fluoride (NaF)-induced apoptosis of Sertoli cells have been sparsely described. In this study, oxidative damage, ER stress, and apoptosis were analyzed after Sertoli cells were treated with varying doses of NaF for 24hr. Moreover, the antioxidant N-acetylcysteine (NAC) and pro-apoptotic transcription factor CHOP knockdown were used to clarify the precise interplay between reactive oxygen species (ROS), ER stress and their roles in NaF-induced apoptosis in Sertoli cells. The present study indicated that NaF significantly decreased cell viability and induced apoptosis in Sertoli cells. In addition, NaF exposure facilitated the accumulation of ROS and increased nuclear translocation of nuclear factor erythroid 2-related factor 2 (Nrf2) in Sertoli cells. Treatment with NAC caused remarkable recovery from these NaF-induced responses. Meanwhile, excessive NaF triggered ER stress as evidenced by up-regulated glucose-regulated protein 78 kDa (GRP78), PKR-like ER kinase (PERK), phosphorylation of eukaryotic translation initiation factor 2α (p-eIF2α) and CCAAT/enhancer-binding protein-homologous protein (CHOP), without affecting total eukaryotic translation initiation factor 2α (eIF2α). NAC effectively blocked the activation of ER stress, suggesting that NaF-induced ROS is an early event that triggers ER stress. Taken together, the results demonstrate that the ROS-mediated ER stress pathway is the crucial mechanistic event involved in NaF-induced apoptosis of Sertoli cells.

BRI2 ectodomain affects Aβ42 fibrillation and tau truncation in human neuroblastoma cells

Alzheimer's disease (AD) is pathologically characterized by the presence of misfolded proteins such as amyloid beta (Aβ) in senile plaques, and hyperphosphorylated tau and truncated tau in neurofibrillary tangles (NFT). The BRI2 protein inhibits Aβ aggregation via its BRICHOS domain and regulates critical proteins involved in initiating the amyloid cascade, which has been hypothesized to be central in AD pathogenesis. We recently detected the deposition of BRI2 ectodomain associated with Aβ plaques and concomitant changes in its processing enzymes in early stages of AD. Here, we aimed to investigate the effects of recombinant BRI2 ectodomain (rBRI276-266) on Aβ aggregation and on important molecular pathways involved in early stages of AD, including the unfolded protein response (UPR), phosphorylation and truncation of tau, as well as apoptosis. We found that rBRI276-266 delays Aβ fibril formation, although less efficiently than the BRI2 BRICHOS domain (BRI2 residues 113-231). In human neuroblastoma SH-SY5Y cells, rBRI276-266 slightly decreased cell viability and increased up to two-fold the Bax/Bcl-2 ratio and the subsequent activity of caspases 3 and 9, indicating activation of apoptosis. rBRI276-266 upregulated the chaperone BiP but did not modify the mRNA expression of other UPR markers (CHOP and Xbp-1). Strikingly, rBRI276-266 induced the activation of GSK3β but not the phosphorylation of tau. However, exposure to rBRI276-266 significantly induced the truncation of tau, indicating that BRI2 ectodomain can contribute to NFT formation. Since BRI2 can also regulate the metabolism of Aβ, the current data suggests that BRI2 ectodomain is a potential nexus between Aβ, tau pathology and neurodegeneration.

Activation of the UPR protects against cigarette smoke-induced RPE apoptosis through up-regulation of Nrf2

Recent studies have revealed a role of endoplasmic reticulum (ER) stress-induced unfolded protein response (UPR) in the regulation of RPE cell activity and survival. Herein, we examined the mechanisms by which the UPR modulates apoptotic signaling in human RPE cells challenged with cigarette smoking extract (CSE). Our results show that CSE exposure induced a dose- and time-dependent increase in ER stress markers, enhanced reactive oxygen species (ROS), mitochondrial fragmentation, and apoptosis of RPE cells. These changes were prevented by the anti-oxidant NAC or chemical chaperone TMAO, suggesting a close interaction between oxidative and ER stress in CSE-induced apoptosis. To decipher the role of the UPR, overexpression or down-regulation of XBP1 and CHOP genes was manipulated by adenovirus or siRNA. Overexpressing XBP1 protected against CSE-induced apoptosis by reducing CHOP, p-p38, and caspase-3 activation. In contrast, XBP1 knockdown sensitized the cells to CSE-induced apoptosis, which is likely through a CHOP-independent pathway. Surprisingly, knockdown of CHOP reduced p-eIF2α and Nrf2 resulting in a marked increase in caspase-3 activation and apoptosis. Furthermore, Nrf2 inhibition increased ER stress and exacerbated cell apoptosis, while Nrf2 overexpression reduced CHOP and protected RPE cells. Our data suggest that although CHOP may function as a pro-apoptotic gene during ER stress, it is also required for Nrf2 up-regulation and RPE cell survival. In addition, enhancing Nrf2 and XBP1 activity may help reduce oxidative and ER stress and protect RPE cells from cigarette smoke-induced damage.

Overexpression of 14-3-3ζ Increases Brain Levels of C/EBP Homologous Protein CHOP

Recent studies demonstrated that overexpression of the molecular chaperone 14-3-3ζ protects the brain against endoplasmic reticulum (ER) stress and prolonged seizures. The 14-3-3 targets responsible for improved neuronal survival after seizures remain unknown. Here we explored the mechanism, finding that protein levels of the ER-stress-associated transcription factor C/EBP homologous protein (CHOP) were significantly higher in 14-3-3ζ-overexpressing mice. Since previous studies by us demonstrated that loss of CHOP increased vulnerability to seizure damage, we explored whether elevated CHOP levels result from 14-3-3ζ overexpression and contribute to the protection. Pull-down experiments suggested that 14-3-3ζ could bind CHOP as well as sequester a CHOP-targeting microRNA. However, 14-3-3ζ overexpression remained protective against seizure-induced hippocampal injury in mice lacking CHOP. These studies reveal a novel function for 14-3-3ζ in regulating CHOP levels but show that this is not required for protection against seizure-induced neuronal death.

Cantharidins induce ER stress and a terminal unfolded protein response in OSCC

Mortality and morbidity associated with oral squamous cell carcinoma (OSCC) remain unacceptably high with disfiguring treatment options and a death rate of 1 per hour in the United States. The approval of cituximab for advanced OSCC has been the only new treatment for these patients since the 1970s, although it has not significantly increased overall survival. To address the paucity of effective new therapies, we undertook a high-throughput screen to discover small molecules and natural products that could induce endoplasmic reticulum (ER) stress and enforce a terminal unfolded protein response (UPR) in OSCC. The terpenoid cantharidin (CNT), previously used to treat various malignancies in culture-specific medical practices for over 2,000 y, emerged as a hit. CNT and its analog, cantharidic acid, potently induced protein and gene expression profiles consistent with the activation of ER stress, the UPR, and apoptosis in OSCC cells. Murine embryonic fibroblasts null for the UPR-associated transcription factors Atf4 or Chop were significantly protected from CNT, implicating a key role for the UPR in the death response. These data validate that our high-throughput screen can identify novel modulators of UPR signaling and that such compounds might provide a new therapeutic approach to treating patients with OSCC.

Dipeptidyl peptidase-4 inhibitor, vildagliptin, inhibits pancreatic beta cell apoptosis in association with its effects suppressing endoplasmic reticulum stress in db/db mice

AIMS

Vildagliptin promotes beta cell survival by inhibiting cell apoptosis. It has been suggested that chronic ER (endoplasmic reticulum) stress triggers beta cell apoptosis. The objective of the study is to explore whether the pro-survival effect of vildagliptin is associated with attenuation of endoplasmic reticulum stress in islets of db/db mice.

METHODS

Vildagliptin was orally administered to db/db mice for 6 weeks, followed by evaluation of beta cell apoptosis by caspase3 activity and TUNEL staining method. Endoplasmic reticulum stress markers were determined with quantitative RT-PCR, immunohistochemistry and immunoblot analysis.

RESULTS

After 6 weeks of treatment, vildagliptin treatment increased plasma active GLP-1 levels (22.63±1.19 vs. 11.69±0.44, P<0.001), inhibited beta cell apoptosis as demonstrated by lower amounts of TUNEL staining nuclei (0.37±0.03 vs. 0.55±0.03, P<0.01) as well as decreased caspase3 activity (1.48±0.11 vs. 2.67±0.13, P<0.01) in islets of diabetic mice compared with untreated diabetic group. Further, vildagliptin treatment down-regulated several genes related to endoplasmic reticulum stress including TRIB3 (tribbles homolog 3) (15.9±0.4 vs. 33.3±1.7, ×10⁻³, P<0.001), ATF-4(activating transcription factor 4) (0.83±0.06 vs. 1.42±0.02, P<0.001) and CHOP(C/EBP homologous protein) (0.07±0.01 vs. 0.16±0.01, P<0.001).

CONCLUSIONS

Vildagliptin promoted beta cell survival in db/db mice in association with down-regulating markers of endoplasmic reticulum stress including TRIB3, ATF-4 as well as CHOP.

Shiga toxin 2-induced endoplasmic reticulum stress is minimized by activated protein C but does not correlate with lethal kidney injury

Enterohemorrhagic Escherichia coli produce ribotoxic Shiga toxins (Stx), which are responsible for kidney injury and development of hemolytic uremic syndrome. The endoplasmic reticulum (ER) stress response is hypothesized to induce apoptosis contributing to organ injury; however, this process has been described only in vitro. ER stress marker transcripts of spliced XBP1 (1.78-fold), HSP40 (4.45-fold) and CHOP (7.69-fold) were up-regulated early in kidneys of Stx2 challenged mice compared to saline controls. Anti-apoptotic Bcl2 decreased (−2.41-fold vs. saline) and pro-apoptotic DR5 increased (6.38-fold vs. saline) at later time points. Cytoprotective activated protein C (APC) reduced early CHOP expression (−3.3-fold vs. untreated), increased later Bcl2 expression (5.8-fold vs. untreated), and had early effects on survival but did not alter DR5 expression. Changes in kidney ER stress and apoptotic marker transcripts were observed in Stx2-producing C. rodentium challenged mice compared to mice infected with a non-toxigenic control strain. CHOP (4.14-fold) and DR5 (2.81-fold) were increased and Bcl2 (−1.65-fold) was decreased. APC reduced CHOP expression and increased Bcl2 expression, but did not alter mortality. These data indicate that Stx2 induces renal ER stress and apoptosis in murine models of Stx2-induced kidney injury, but decreasing these processes alone was not sufficient to alter survival outcome.

Endoplasmic reticulum stress as a novel mechanism in amiodarone-induced destructive thyroiditis

CONTEXT

Amiodarone (AMIO) is one of the most effective antiarrhythmic drugs available; however, its use is limited by a serious side effect profile, including thyroiditis. The mechanisms underlying AMIO thyroid toxicity have been elusive; thus, identification of novel approaches in order to prevent thyroiditis is essential in patients treated with AMIO.

OBJECTIVE

Our aim was to evaluate whether AMIO treatment could induce endoplasmic reticulum (ER) stress in human thyroid cells and the possible implications of this effect in AMIO-induced destructive thyroiditis.

RESULTS

Here we report that AMIO, but not iodine, significantly induced the expression of ER stress markers including Ig heavy chain-binding protein (BiP), phosphoeukaryotic translation initiation factor 2α (eIF2α), CCAAT/enhancer-binding protein homologous protein (CHOP) and spliced X-box binding protein-1 (XBP-1) in human thyroid ML-1 cells and human primary thyrocytes. In both experimental systems AMIO down-regulated thyroglobulin (Tg) protein but had little effect on Tg mRNA levels, suggesting a mechanism involving Tg protein degradation. Indeed, pretreatment with the specific proteasome inhibitor MG132 reversed AMIO-induced down-regulation of Tg protein levels, confirming a proteasome-dependent degradation of Tg protein. Corroborating our findings, pretreatment of ML-1 cells and human primary thyrocytes with the chemical chaperone 4-phenylbutyric acid completely prevented the effect of AMIO on both ER stress induction and Tg down-regulation.

CONCLUSIONS

We identified ER stress as a novel mechanism contributing to AMIO-induced destructive thyroiditis. Our data establish that AMIO-induced ER stress impairs Tg expression via proteasome activation, providing a valuable therapeutic avenue for the treatment of AMIO-induced destructive thyroiditis.

Numerical and structural chromosomal anomalies in undifferentiated pleomorphic sarcoma

BACKGROUND

Malignant fibrous histiocytoma (MFH) or undifferentiated pleomorphic sarcoma (UPS) is the most common soft-tissue sarcoma of late adult life. Further advances in genetic characterization are warranted. The aim of this study was to search for numerical and structural chromosomal anomalies in UPS.

MATERIALS AND METHODS

We investigated five sarcoma-specific chromosomal translocations, five oncogene amplifications as well as the numerical karyotype of 19 UPS samples and one UPS/MFH cell line (U2197) using FISH probes on interphase nuclei.

RESULTS

Our results demonstrate that chromosomal translocations involving CHOP, SYT, EWS, FUS and FKHR genes are absent. Furthermore, amplification of ERBB2 (10.5%) and MDM2 (10.5%) was observed whereas the EGFR, C-MYC and N-MYC genes were not amplified. Interestingly, predominant aneuploidies were found in eight chromosomes.

CONCLUSION

The data demonstrate rarity of sarcoma-specific chromosomal breaks and oncogene amplifications in UPS, yet polysomic chromosomes appear more characteristically in this condition.

[Effect of glucose regulated protein 78 gene silencing on hyperoxia-induced apoptosis in alveolar epithelial cells]

OBJECTIVE

To investigate the effect and possible mechanism of small interfering RNA (siRNA)-mediated glucose regulated protein 78 (GRP78) gene silencing on hyperoxia-induced apoptosis of alveolar epithelial cells.

METHODS

Human lung adenocarcinoma A549 cells in vitro were transfected with siRNA by Lipofectamine(TM)2000. Cells were divided into untransfected group, scrambled siRNA group and GRP78-siRNA group. A model of hyperoxia-induced cell injury was established by 95% oxygen. After 48 hours, the mRNA and protein levels of GRP78 and C/EBP homologous protein (CHOP) were detected respectively by real-time PCR and Western blotting, and cell apoptosis was measured by flow cytometry.

RESULTS

By GRP78 siRNA interference, the mRNA and protein levels of GRP78 decreased significantly, while CHOP increased significantly. The apoptosis rate of A549 cells was elevated significantly.

CONCLUSION

GRP78 gene silencing may enhance the CHOP apoptotic pathway and promote apoptosis in alveolar epithelial cells induced by hyperoxia, suggesting the potential value of GRP78 as a therapeutic target for the clinical treatment of bronchopulmonary dysplasia.

[Effect of electroacupuncture pretreatment on apoptotic neurons and expression of GRP 78 and GADD 153 in the hippocampus in rats with global cerebral ischemia/reperfusion injury]

OBJECTIVE

To observe the effect of electroacupuncture (EA) pretreatment on the number of survival neurons and the expression of glucose regulated protein 78 (GRP 78) and growth arrest and DNA damage-inducible gene 153 (GADD 153) in the hippocampus in rats with global cerebral ischemia /reperfusion injury (CI/R), so as to study its underlying mechanism in neuroprotective action.

METHODS

SD male rats were randomly divided into 3 groups (n =48 each):sham operation,Cl/R model and EA pretreatment group. Global CI/R model was induced by 4-vessel occlusion (bilateral vertebral artery cauterization and bilateral carotid artery ligation for 5 min, followed by reperfusion). Before modeling, EA pretreatment of "Baihui" (GV 20) and "Dazhui" (GV 14, 2 Hz/15 Hz, 1 mA) was given to rats of the EA pretreatment group for 30 min, once daily for 5 days. At 6, 12, 24 and 48 h after CI/R, the hippocampus tissues of rats in different subgroups were separately sampled to be stained with H. E. method for detecting the number of the survived neurons, stained with TUNEL method for assaying the apoptotic neurons in the CA 1 region, and processed with Western blot (WB) for assaying the expression of GRP 78 and GADD 153 proteins.

RESULTS

Compared with the sham group, the number of hippocampal survival neurons was significantly decreased at the time-points of 12 h, 24 h and 48 h after CI/R in the model group (P<0. 05) and was apparently increased by EA pretreatment at 24 h and 48 h (P<0. 05). The number of the apoptotic neurons in the hippocampal CA 1 region at the time-points of 6 h, 12 h, 24 h and 48 h after CI/R was significantly bigger in the model group than in the sham group (P<0. 05), and was obviously decreased at 12 h, 24 h, 48 h after CI/R in the EA pretreatment group (P<0.05). WB detection showed that the expression levels of hippocampal GRP 78 and GADD 153 proteins at the four time-points after CI/R were significantly higher in the model group than in the sham group (P<0. 05). Compared with the model group, hippocampal GRP 78 protein expression levels at the 4 time-points were further markedly up-regulated (P<0.05), while GADD 153 protein expression levels at the 4 time-points were significantly suppressed in the EA pretreatment group (P<0.05).

CONCLUSION

EA pretreatment can effectively suppress the number of hippocampal apoptotic neurons and increase survival rate of neurons in CI/R rats, which may be closely associated with its effects in up-regulating the expression of GRP 78 protein and down-regulating the expression of GADD 153 protein in the hippocampus.

Development of a multifunctional luciferase reporters system for assessing endoplasmic reticulum-targeting photosensitive compounds

Photodynamic therapy (PDT) is a recently developed antitumor modality utilizing the generation of reactive oxygen species (ROS), through light irradiation of photosensitizers (PSs) localized in tumor. Interference with proper functioning of endoplasmic reticulum (ER) by ER-targeting PDT is a newly proposed strategy to achieve tumor cell death. The aim of this study is to establish a multifunctional model to screen and assess ER-targeting PSs based on luciferase reporters system. Upregulation of GRP78 is a biomarker for the onset of ER stress. CHOP is a key initiating player in ER stress-induced cell death. Here, the most sensitive fragments of GRP78 and CHOP promoters responding to ER-targeting PDT were mapped and cloned into pGL3-basic vector, forming -702/GRP78-Luc and -443/CHOP-Luc construct, respectively. We demonstrated that -702/GRP78-Luc expression can be used to indicate the ER-targeting of PSs, meanwhile estimate the ROS level induced by low-dose ER-targeting PDT. Moreover, the luciferase signaling of -443/CHOP-Luc showed highly consistence with apoptosis rate caused by ER-targeting PDT, suggesting that -443/CHOP-Luc can evaluate the antitumor properties of PSs. Hypericin, Foscan® and methylene blue were applied to verify the sensitivity and reliability of our model. These results proved that GRP78-CHOP model may be suitable to screen ER-targeting photosensitive compounds with lower cost and higher sensitivity than traditional ways.

Recombinant Clostridium difficile toxin B induces endoplasmic reticulum stress in mouse colonal carcinoma cells

Clostridium difficile is the main cause of antibiotic-associated diarrhea and pseudomembranous colitis in humans and animals. Its pathogenicity is primarily linked to the secretion of two exotoxins (TcdA and TcdB). Although great progress in the toxic mechanism of TcdA and TcdB has been achieved, there are many conflicting reports about the apoptotic mechanism. More importantly, apoptotic endoplasmic reticulum (ER) stress has been reported in cells treated with Shiga toxins-another kind of cytotoxins that can cause diarrhea and colitis. Herein we checked whether TcdB can induce ER stress. The results showed that recombinant TcdB (rTcdB) activated molecular markers of unfolded protein response, suggesting that rTcdB induced ER stress in CT26 cells. However, rTcdB did not induce the up-regulation of C/EBP homologous protein (CHOP), a classic mediator of apoptotic ER stress, but it activated the precursor of cysteine aspartic acid-specific protease 12 (caspase-12), a controversial mediator of apoptotic ER stress. Besides, glucosyltransferase activity-deficient mutant recombinant TcdB induced ER stress, though it has no cytotoxic or cytopathic effect on CT26 cells. Altogether, these data demonstrated that ER stress induced by rTcdB is glucosyltransferase-independent, indicating that ER stress induced by rTcdB is non-apoptotic. This work also offers us a new insight into the molecular mechanism of CHOP protein expression regulation and the role of CHOP expression in ER stress.

Chloroacetic acid triggers apoptosis in neuronal cells via a reactive oxygen species-induced endoplasmic reticulum stress signaling pathway

Chloroacetic acid (CA), a chlorinated analog of acetic acid and an environmental toxin that is more toxic than acetic, dichloroacetic, or trichloroacetic acids, is widely used in chemical industries. Furthermore, CA has been found to be the major disinfection by-products (DBPs) of drinking water. CA has been reported to be highly corrosive and to induce severe tissue injuries (including nervous system) that lead to death in mammals. However, the effects and underlying mechanisms of CA-induced neurotoxicity remain unknown. In the present study, we found that CA (0.5-2.0 mM) significantly increased LDH release, decreased the number of viable cells (cytotoxicity) and induced apoptotic events (including: increases in the numbers of apoptotic cells, the membrane externalization of phosphatidylserine (PS), and caspase-3/-7 activity) in Neuro-2a cells. CA (1.5 mM; the approximate to LD50) also triggered ER stress, which was identified by monitoring several key molecules that are involved in the unfolded protein responses (including the increase in the expressions of p-PERK, p-IRE-1, p-eIF2α, ATF-4, ATF-6, CHOP, XBP-1, GRP 78, GRP 94, and caspase-12) and calpain activity. Transfection of GRP 78- and GRP 94-specific si-RNA effectively abrogated CA-induced cytotoxicity, caspase-3/-7 and caspase-12 activity, and GRP 78 and GRP 94 expression in Neuro-2a cells. Additionally, pretreatment with 2.5 mM N-acetylcysteine (NAC; a glutathione (GSH) precursor) dramatically suppressed the increase in lipid peroxidation, cytotoxicity, apoptotic events, calpain and caspase-12 activity, and ER stress-related molecules in CA-exposed cells. Taken together, these results suggest that the higher concentration of CA exerts its cytotoxic effects in neuronal cells by triggering apoptosis via a ROS-induced ER stress signaling pathway.

Mmu-miR-615-3p regulates lipoapoptosis by inhibiting C/EBP homologous protein

Lipoapoptosis occurring due to an excess of saturated free fatty acids such as palmitate is a key pathogenic event in the initiation of nonalcoholic fatty liver disease. Palmitate loading of cells activates the endoplasmic reticulum stress response, including induction of the proapoptotic transcription factor C/EBP homologous protein (CHOP). Furthermore, the loss of microRNAs is implicated in regulating apoptosis under conditions of endoplasmic reticulum (ER) stress. The aim of this study was to identify specific microRNAs regulating CHOP expression during palmitate-induced ER stress. Five microRNAs were repressed under palmitate-induced endoplasmic reticulum stress conditions in hepatocyte cell lines (miR-92b-3p, miR-328-3p, miR-484, miR-574-5p, and miR-615-3p). We identified miR-615-3p as a candidate microRNA which was repressed by palmitate treatment and regulated CHOP protein expression, by RNA sequencing and in silico analyses, respectively. There is a single miR-615-3p binding site in the 3′untranslated region (UTR) of the Chop transcript. We characterized this as a functional binding site using a reporter gene-based assay. Augmentation of miR-615-3p levels, using a precursor molecule, repressed CHOP expression; and under these conditions palmitate- or tunicamycin-induced cell death were significantly reduced. Our results suggest that palmitate-induced apoptosis requires maximal expression of CHOP which is achieved via the downregulation of its repressive microRNA, miR-615-3p. We speculate that enhancement of miR-615-3p levels may be of therapeutic benefit by inhibiting palmitate-induced hepatocyte lipoapoptosis.

The immunosuppressive activity of MDSCs requires expression of CHOP

The stress sensor CHOP enhances the accumulation and inhibitory activity of MDSCs in tumors.

Modulation of the unfolded protein response impedes tumor cell adaptation to proteotoxic stress: a PERK for hepatocellular carcinoma therapy

Background

Functional disturbances of the endoplasmic reticulum (ER) lead to activation of the unfolded protein response (UPR), which is involved in the consecutive steps of carcinogenesis. In human hepatocellular carcinoma (HCC), the UPR is shown to be activated; however, little is known about the UPR kinetics and effects of UPR modulation in HCC.

Methods

We sequentially monitored the UPR over time in an orthotopic mouse model for HCC and explored the effects of UPR modulation on cell viability and proliferation in vitro and in the mouse model.

Results

The expression of ER-resident chaperones peaked during tumor initiation and increased further during tumor progression, predominantly within the nodules. A peak in Ire1 signaling was observed during tumor initiation. The Perk pathway was activated during tumor progression, and the proapoptotic target Chop was upregulated from week 5 and continued to rise, especially in the tumors. The Atf6 pathway was modestly activated only after tumor initiation. Consistent with the UPR activation, electron microscopy demonstrated ER expansion and reorganization in HCC cells in vivo. Strikingly, under ER stress or hypoxia, the Perk inhibitor and not the Ire1 inhibitor reduced cell viability and proliferation via escalating proteotoxic stress in vitro. Notably, the Perk inhibitor significantly decreased tumor burden in the mouse model.

Conclusion

We provide the first evaluation of the UPR dynamics in a long-term cancer model and identified a small molecule inhibitor of Perk as a promising strategy for HCC therapy.

Electronic supplementary material

The online version of this article (doi:10.1007/s12072-014-9582-0) contains supplementary material, which is available to authorized users.

Neurotoxin-induced pathway perturbation in human neuroblastoma SH-EP cells

The exact causes of cell death in Parkinson's disease (PD) remain unknown despite extensive studies on PD.The identification of signaling and metabolic pathways involved in PD might provide insight into the molecular mechanisms underlying PD. The neurotoxin 1-methyl-4-phenylpyridinium (MPP(+)) induces cellular changes characteristic of PD, and MPP(+)-based models have been extensively used for PD studies. In this study, pathways that were significantly perturbed in MPP(+)-treated human neuroblastoma SH-EP cells were identified from genome-wide gene expression data for five time points (1.5, 3, 9, 12, and 24 h) after treatment. The mitogen-activated protein kinase (MAPK) signaling pathway and endoplasmic reticulum (ER) protein processing pathway showed significant perturbation at all time points. Perturbation of each of these pathways resulted in the common outcome of upregulation of DNA-damage-inducible transcript 3 (DDIT3). Genes involved in ER protein processing pathway included ubiquitin ligase complex genes and ER-associated degradation (ERAD)-related genes. Additionally, overexpression of DDIT3 might induce oxidative stress via glutathione depletion as a result of overexpression of CHAC1. This study suggests that upregulation of DDIT3 caused by perturbation of the MAPK signaling pathway and ER protein processing pathway might play a key role in MPP(+)-induced neuronal cell death. Moreover, the toxicity signal of MPP(+) resulting from mitochondrial dysfunction through inhibition of complex I of the electron transport chain might feed back to the mitochondria via ER stress. This positive feedback could contribute to amplification of the death signal induced by MPP(+).

Protective effects of Hericium erinaceus mycelium and its isolated erinacine A against ischemia-injury-induced neuronal cell death via the inhibition of iNOS/p38 MAPK and nitrotyrosine

Hericium erinaceus, an edible mushroom, has been demonstrated to potentiate the effects of numerous biological activities. The aim of this study was to investigate whether H. erinaceus mycelium could act as an anti-inflammatory agent to bring about neuroprotection using a model of global ischemic stroke and the mechanisms involved. Rats were treated with H. erinaceus mycelium and its isolated diterpenoid derivative, erinacine A, after ischemia reperfusion brain injuries caused by the occlusion of the two common carotid arteries. The production of inflammatory cytokines in serum and the infracted volume of the brain were measured. The proteins from the stroke animal model (SAM) were evaluated to determine the effect of H. erinaceus mycelium. H. erinaceus mycelium reduced the total infarcted volumes by 22% and 44% at a concentration of 50 and 300 mg/kg, respectively, compared to the SAM group. The levels of acute inflammatory cytokines, including interleukin-1β, interleukin-6 and tumor necrosis factor á, were all reduced by erinacine A. Levels of nitrotyrosine-containing proteins, phosphorylation of p38 MAPK and CCAAT enhancer-binding protein (C/EBP) and homologous protein (CHOP) expression were attenuated by erinacine A. Moreover, the modulation of ischemia injury factors present in the SAM model by erinacine A seemed to result in the suppression of reactive nitrogen species and the downregulation of inducible NO synthase (iNOS), p38 MAPK and CHOP. These findings confirm the nerve-growth properties of Hericium erinaceus mycelium, which include the prevention of ischemic injury to neurons; this protective effect seems to be involved in the in vivo activity of iNOS, p38 MAPK and CHOP.

The effect of pioglitazone on aldosterone and cortisol production in HAC15 human adrenocortical carcinoma cells

Pioglitazone belongs to the class of drugs called thiazolidinediones (TZDs), which are widely used as insulin sensitizers in the treatment of diabetes. A major side effect of TZDs is fluid retention. The steroid hormone aldosterone also promotes sodium and fluid retention; however, the effect of pioglitazone on aldosterone production is controversial. We analyzed the effect of pioglitazone alone and in combination with angiotensin II (AngII) on the late rate-limiting step of adrenocortical steroidogenesis in human adrenocortical carcinoma HAC15 cells. Treatment with pioglitazone for 24 h significantly increased the expression of CYP11B2 and enhanced AngII-induced CYP11B2 expression. Despite the observed changes in mRNA levels, pioglitazone significantly inhibited AngII-induced aldosterone production and CYP11B2 protein levels. On the other hand, pioglitazone stimulated the expression of the unfolded protein response (UPR) marker DDIT3, with this effect occurring at early times and inhibitable by the PPARγ antagonist GW9962. The levels of DDIT3 (CHOP) and phospho-eIF2α (Ser51), a UPR-induced event that inhibits protein translation, were also increased. Thus, pioglitazone promotes CYP11B2 expression but nevertheless inhibits aldosterone production in AngII-treated HAC15 cells, likely by blocking global protein translation initiation through DDIT3 and phospho-eIF2α. In contrast, pioglitazone promoted AngII-induced CYP11B1 expression and cortisol production. Since cortisol enhances lipolysis, this result suggests the possibility that PPARs, activated by products of fatty acid oxidation, stimulate cortisol secretion to promote utilization of fatty acids during fasting. In turn, the ability of pioglitazone to stimulate cortisol production could potentially underlie the effects of this drug on fluid retention.

[Effects of acupuncture intervention on expression of glucose-regulated protein 78 and C/EBP homologous protein in hippocampal CA 1 region in rats with hyperspasmia]

OBJECTIVE

To observe the effect of acupuncture intervention on expression of glucose-regulated protein 78 (Grp 78) and C/EBP homologous protein (CHOP) in the hippocampus in epilepsy rats so as to explore its mechanism underlying improvement of hyperspasmia-induced brain injury.

METHODS

Forty-two SD rats were randomly divided into normal control group (n = 6), model group (n = 18), and acupuncture group (n = 18). The epileptic seizure model was established by intraperitonel injection of Pentylenetetrazol (50 mg/kg, 2 mL). Manual acupuncture stimulation of "Baihui" (GV 20) and "Dazhui" (GV 14) was conducted for rats of the acupuncture group for 30 min. Two hours (h), 12 h and 48 h after acupuncture intervention, the hippocampal tissue was sampled (6 rats at each time-point). The expression levels of Grp 78 and CHOP proteins in the hippocampal CA 1 region were detected by immunohistochemistry.

RESULTS

Compared with the normal group, the expression levels of Grp 78 protein at time-points of 2 h and 12 h, and those of CHOP protein at 2 h, 12 h and 48 h after epilpeptic seizure were significantly increased in the model group (P < 0.01). After acupuncture treatment, the expression levels of Grp 78 at 12 and 48 h were significantly increased, and those of CHOP protein at 2 h, 12 h and 24 h in the acupuncture group were considerably downregulated (P < 0.05, P < 0.01).

CONCLUSION

Acupuncture treatment can up-regulate Grp 78 protein expression and down-regulate CHOP protein expression level in epilepsy rats , which may contribute to its protective effect on seizure-induced brain injury.

New insights into the roles of CHOP-induced apoptosis in ER stress

Endoplasmic reticulum stress (ER stress) is triggered due to a loss of homeostasis in the ER, resulting in accumulation of misfolded proteins in the ER lumen. ER stress activates a series of adaptive mechanisms known as the unfolded protein response. Perturbation of the ER is a powerful inducer of the transcription factor C/EBP homologous protein (CHOP). Although it has been proved that excessive or adverse stress to the ER triggers apoptosis, the specific mechanisms underlying these processes induced by CHOP remain unclear. By now, CHOP-induced apoptosis in ER stress has been implicated in numerous human diseases, such as neurodegenerative diseases, diabetes, ischemic diseases, tumor, and so on. In this review, we summarized the current understanding of the roles of CHOP in the development of several diseases from the laboratory to the clinic.

Advanced glycation end-products induce endoplasmic reticulum stress in human aortic endothelial cells

BACKGROUND

Advanced glycation end products (AGEs), the final products of the Maillard reaction, have been shown to impair endothelial proliferation and function, thus contributing to endothelial cell injury present in diabetes, inflammatory and cardiovascular diseases. Endoplasmic reticulum (ER) stress triggered under hyperglycemic, hypoxic and oxidative conditions has been implicated in endothelial dysfunction through activation of the unfolded protein response (UPR). The present study investigates the role of AGEs in ER stress induction in human aortic endothelial cells exposed to variable AGE treatments.

METHODS

Human aortic endothelial cells (HAEC) were treated with increasing concentrations (100, 200 μg/mL) of AGE-bovine serum albumin (AGE-BSA) at different time-points (24, 48, 72 h). The induction of ER stress and the involved UPR components were investigated on mRNA and protein levels. Apoptosis was quantitatively determined by flow cytometry detecting propidium iodide expression and annexin V binding simultaneously.

RESULTS

AGEs administration significantly reduced HAEC proliferation in a time- and dose-dependent manner. An immediate induction of the ER chaperones GRP78, GRP94 and the transcriptional activator, XBP-1 was observed at 24 h and 48 h. A later induction of the phospho-elF2α and proapoptotic transcription factor CHOP was observed at 48 h and 72 h, being correlated with elevated early apoptotic cell numbers at the same time-points.

CONCLUSIONS

The present study demonstrates that AGEs directly induce ER stress in human aortic endothelial cells, playing an important role in endothelial cell apoptosis. Targeting AGEs signaling pathways in order to alleviate ER stress may prove of therapeutic potential to endothelial dysfunction-related disorders.

Protein degradation and quality control in cells from laforin and malin knockout mice

Lafora disease is a progressive myoclonus epilepsy caused by mutations in the EPM2A or EPM2B genes that encode a glycogen phosphatase, laforin, and an E3 ubiquitin ligase, malin, respectively. Lafora disease is characterized by accumulation of insoluble, poorly branched, hyperphosphorylated glycogen in brain, muscle, heart, and liver. The laforinmalin complex has been proposed to play a role in the regulation of glycogen metabolism and protein quality control. We evaluated three arms of the protein degradation/ quality control process (the autophago-lysosomal pathway, the ubiquitin-proteasomal pathway, and the endoplasmic reticulum (ER) stress response) in mouse embryonic fibroblasts from Epm2a(-/-), Epm2b(-/-), and Epm2a(-/-) Epm2b(-/-) mice. The levels of LC3-II, a marker of autophagy, were decreased in all knock-out cells as compared with wild type even though they still showed a slight response to starvation and rapamycin. Furthermore, ribosomal protein S6 kinase and S6 phosphorylation were increased. Under basal conditions there was no effect on the levels of ubiquitinated proteins in the knock-out cells, but ubiquitinated protein degradation was decreased during starvation or stress. Lack of malin (Epm2b(-/-) and Epm2a(-/-) Epm2b(-/-) cells) but not laforin (Epm2a(-/-) cells) decreased LAMP1, a lysosomal marker. CHOP expression was similar in wild type and knock-out cells under basal conditions or with ER stress-inducing agents. In conclusion, both laforin and malin knock-out cells display mTOR-dependent autophagy defects and reduced proteasomal activity but no defects in the ER stress response. We speculate that these defects may be secondary to glycogen overaccumulation. This study also suggests a malin function independent of laforin, possibly in lysosomal biogenesis and/or lysosomal glycogen disposal.

Chaperones ameliorate beta cell dysfunction associated with human islet amyloid polypeptide overexpression

In type 2 diabetes, beta-cell dysfunction is thought to be due to several causes, one being the formation of toxic protein aggregates called islet amyloid, formed by accumulations of misfolded human islet amyloid polypeptide (hIAPP). The process of hIAPP misfolding and aggregation is one of the factors that may activate the unfolded protein response (UPR), perturbing endoplasmic reticulum (ER) homeostasis. Molecular chaperones have been described to be important in regulating ER response to ER stress. In the present work, we evaluate the role of chaperones in a stressed cellular model of hIAPP overexpression. A rat pancreatic beta-cell line expressing hIAPP exposed to thapsigargin or treated with high glucose and palmitic acid, both of which are known ER stress inducers, showed an increase in ER stress genes when compared to INS1E cells expressing rat IAPP or INS1E control cells. Treatment with molecular chaperone glucose-regulated protein 78 kDa (GRP78, also known as BiP) or protein disulfite isomerase (PDI), and chemical chaperones taurine-conjugated ursodeoxycholic acid (TUDCA) or 4-phenylbutyrate (PBA), alleviated ER stress and increased insulin secretion in hIAPP-expressing cells. Our results suggest that the overexpression of hIAPP induces a stronger response of ER stress markers. Moreover, endogenous and chemical chaperones are able to ameliorate induced ER stress and increase insulin secretion, suggesting that improving chaperone capacity can play an important role in improving beta-cell function in type 2 diabetes.

Role of endoplasmic reticulum stress in atherosclerosis and diabetic macrovascular complications

Age-related changes in endoplasmic reticulum (ER) are associated with stress of this cell organelle. Unfolded protein response (UPR) is a normal physiological reaction of a cell in order to prevent accumulation of unfolded and misfolded proteins in the ER and improve the normal ER function. However, in pathologic conditions such as atherosclerosis, obesity, and diabetes, ER function becomes impaired, leading to the development of ER stress. In chronic ER stress, defective posttranslational protein folding results in deposits of aberrantly folded proteins in the ER and the induction of cell apoptosis mediated by UPR sensors C/EBPα-homologous protein (CHOP) and inositol requiring protein-1 (IRE1). Since ER stress and ER-induced cell death play a nonredundant role in the pathogenesis of atherosclerosis and diabetic macrovascular complications, pharmaceutical targeting of ER stress components and pathways may be beneficial in the treatment and prevention of cardiovascular pathology.

The effects and underlying mechanism of excessive iodide on excessive fluoride-induced thyroid cytotoxicity

In many regions, excessive fluoride and excessive iodide coexist in groundwater, which may lead to biphasic hazards to human thyroid. To explore fluoride-induced thyroid cytotoxicity and the mechanism underlying the effects of excessive iodide on fluoride-induced cytotoxicity, a thyroid cell line (Nthy-ori 3-1) was exposed to excessive fluoride and/or excessive iodide. Cell viability, lactate dehydrogenase (LDH) leakage, reactive oxygen species (ROS) formation, apoptosis, and the expression levels of inositol-requiring enzyme 1 (IRE1) pathway-related molecules were detected. Fluoride and/or iodide decreased cell viability and increased LDH leakage and apoptosis. ROS, the expression levels of glucose-regulated protein 78 (GRP78), IRE1, C/EBP homologous protein (CHOP), and spliced X-box-binding protein-1 (sXBP-1) were enhanced by fluoride or the combination of the two elements. Collectively, excessive fluoride and excessive iodide have detrimental influences on human thyroid cells. Furthermore, an antagonistic interaction between fluoride and excessive iodide exists, and cytotoxicity may be related to IRE1 pathway-induced apoptosis.

Dual role for CHOP in the crosstalk between autophagy and apoptosis to determine cell fate in response to amino acid deprivation

CHOP encodes a ubiquitous transcription factor that is one of the most important components in the network of stress-inducible transcription. In particular, this factor is known to mediate cell death in response to stress. The focus of this work is to study its pivotal role in the control of cell viability according to the duration of a stress like amino acid starvation. We show that during the first 6h of starvation, CHOP upregulates a number of autophagy genes but is not involved in the first steps of the autophagic process. By contrast, when the amino acid starvation is prolonged (16-48h), we demonstrated that CHOP has a dual role in both inducing apoptosis and limiting autophagy through the transcriptional control of specific target genes. Overall, this study reveals a novel regulatory role for CHOP in the crosstalk between autophagy and apoptosis in response to stress.

DHA-mediated enhancement of TRAIL-induced apoptosis in colon cancer cells is associated with engagement of mitochondria and specific alterations in sphingolipid metabolism

Docosahexaenoic acid (DHA), an n-3 polyunsaturated fatty acid present in fish oil, may exert cytotoxic and/or cytostatic effects on colon cancer cells when applied individually or in combination with some anticancer drugs. Here we demonstrate a selective ability of subtoxic doses of DHA to enhance antiproliferative and apoptotic effects of clinically useful cytokine TRAIL (tumor necrosis factor-related apoptosis inducing ligand) in cancer but not normal human colon cells. DHA-mediated stimulation of TRAIL-induced apoptosis was associated with extensive engagement of mitochondrial pathway (Bax/Bak activation, drop of mitochondrial membrane potential, cytochrome c release), activation of endoplasmic reticulum stress response (CHOP upregulation, changes in PERK level), decrease of cellular inhibitor of apoptosis protein (XIAP, cIAP1) levels and significant changes in sphingolipid metabolism (intracellular levels of ceramides, hexosyl ceramides, sphingomyelines, sphingosines; HPLC/MS/MS). Interestingly, we found significant differences in representation of various classes of ceramides (especially C16:0, C24:1) between the cancer and normal colon cells treated with DHA and TRAIL, and suggested their potential role in the regulation of the cell response to the drug combination. These study outcomes highlight the potential of DHA for a new combination therapy with TRAIL for selective elimination of colon cancer cells via simultaneous targeting of multiple steps in apoptotic pathways.

DDIT3 overexpression increases odontoblastic potential of human dental pulp cells

OBJECTIVES

Human dental pulp cells (HDPCs) with multi-potential differentiational capacity can undergo odontoblastic differentiation when stimulated with proinflammatory cytokines. However, factors linking proinflammatory stimuli and their odontoblastic differentiation have, as yet, not been completely understood. As an apoptotic transcription factor, DDIT3 plays a crucial role in the inflammatory reaction and in osteogenic differentiation. Thus, we hypothesized that DDIT3 may participate in odontoblastic differentiation of HDPCs.

MATERIALS AND METHODS

Immunofluorescent staining was used to detect expression of DDIT3 in HDPCs and effects of TNFα, on its nuclear accumulation. HDPCs that overexpressed DDIT3 were developed and their proliferation and odontoblastic differentiation abilities were examined. qRT-PCR was employed to detect mineralization-related genes, including ALP, runt-related transcription factor-2 (Runx2), osterix (OSX), dentin sialophosphoprotein (DSPP), dentin matrix acidic phosphoprotein 1 (DMP1) and osteocalcin (OCN). Western blot analysis was performed to detect expression of DSPP protein.

RESULTS

DDIT3 was expressed in HDPCs. TNFα treatment enhanced mRNA expression as well as nuclear accumulation of DDIT3 (slightly). DDIT3 overexpression reduced HDPC proliferation, however, it increased their calcium nodule formation and expression of OSX, DSPP, DMP1 and OCN.

CONCLUSIONS

DDIT3 may be a factor that links proinflammatory stimuli and differentiation of HDPCs.

The relationship between anticancer effect of metformin and the transcriptional regulation of certain genes (CHOP, CAV-1, HO-1, SGK-1 and Par-4) on MCF-7 cell line

BACKGROUND

1,1-dimethylbiguanide hydrochloride (biguanide metformin) is a hypoglycemic agent that is widely used in the treatment of Type 2 diabetes. Use of metformin was found to be associated with the lower risk of cancer. It is suggested that metformin has an anticancer and antiproliferative effect and affects the apoptosis by activating the AMPK and inhibiting the mammalian target of rapamycin (mTOR). Although the effects of metformin treatment of various types of cancers are defined with many mechanisms, the literature provides only sufficient information about how it affects the SGK-1, Par-4 and Cav-1 mRNA expressions and the impact of this effect on cytotoxicity. The breast cancer is globally one of the most important causes of cancer-related mortality for women. We, therefore investigated the possible effects of metmorfin on proliferation, cytotoxicity and some unfolded protein response (UPR) genes in the breast cancer cells (MCF-7).

MATERIALS AND METHODS

We administrated 0.31 mM, 2.5 mM and 10 mM of metformin alone and in combination with 2-DG to the MCF-7 cells and monitored the cell viability and proliferation with real-time cell analyzer system for 48 hours. We also measured CHOP, Cav-1, HO-1, SGK-1 and Par-4 genes mRNA expression levels using Real Time-Polymerase Chain Reaction (RT-PCR). We considered the GAPDH gene as reference gene and the control groups as calibrator. We performed an analysis for relative gene expressions of the study groups.

RESULTS

Metformin caused transcriptional regulation of UPR and tumor-related genes in MCF-7 cells and inhibited the proliferation depending on the dose, resulting in cytotoxic effect.

CONCLUSIONS

We consider that administration of metformin with chemotherapeutic agents could be an effective method in treatment of breast cancer through mechanisms such as reduced resistance to chemotherapy and increased cytotoxic activity.

Smoke exposure causes endoplasmic reticulum stress and lipid accumulation in retinal pigment epithelium through oxidative stress and complement activation

Age-related macular degeneration (AMD) is a complex disease caused by genetic and environmental factors, including genetic variants in complement components and smoking. Smoke exposure leads to oxidative stress, complement activation, endoplasmic reticulum (ER) stress, and lipid dysregulation, which have all been proposed to be associated with AMD pathogenesis. Here we examine the effects of smoke exposure on the retinal pigment epithelium (RPE). Mice were exposed to cigarette smoke or filtered air for 6 months. RPE cells grown as stable monolayers were exposed to 5% cigarette smoke extract (CSE). Effects of smoke were determined by biochemical, molecular, and histological measures. Effects of the alternative pathway (AP) of complement and complement C3a anaphylatoxin receptor signaling were analyzed using knock-out mice or specific inhibitors. ER stress markers were elevated after smoke exposure in RPE of intact mice, which was eliminated in AP-deficient mice. To examine this relationship further, RPE monolayers were exposed to CSE. Short term smoke exposure resulted in production and release of complement C3, the generation of C3a, oxidative stress, complement activation on the cell membrane, and ER stress. Long term exposure to CSE resulted in lipid accumulation, and secretion. All measures were reversed by blocking C3a complement receptor (C3aR), alternative complement pathway signaling, and antioxidant therapy. Taken together, our results provide clear evidence that smoke exposure results in oxidative stress and complement activation via the AP, resulting in ER stress-mediated lipid accumulation, and further suggesting that oxidative stress and complement act synergistically in the pathogenesis of AMD.

Luteolin modulates 6-hydroxydopamine-induced transcriptional changes of stress response pathways in PC12 cells

The neurotoxin 6-hydroxydopamine (6-OHDA), which causes transcriptional changes associated with oxidative and proteotoxic stress, has been widely used to generate an experimental model of Parkinson's disease. The food-derived compound luteolin has multi-target actions including antioxidant, anti-inflammatory and neurotrophic activities. The aim of this study is to investigate how luteolin affects 6-OHDA-mediated stress response pathways. The results showed that when PC12 cells were pre-treated with luteolin (20 µM) 30 min prior to 6-OHDA (100 µM) exposure, 6-OHDA-induced ROS overproduction, cytotoxicity, caspase-3 activation, and mRNA expression of BIM, TRB3 and GADD34 were significantly attenuated. Moreover, 6-OHDA-mediated cell cycle arrest and transcription of p53 target genes, p21, GADD45α and PUMA, were reduced by luteolin. Luteolin also significantly down-regulated 6-OHDA-mediated unfolded protein response (UPR), leading to decreases in phospho-eIF2α, ATF4, GRP78 and CHOP. In addition, luteolin attenuated 6-OHDA-induced Nrf2-mediated HO-1 and GCLC. Taken together, these results suggest that diminishing intracellular ROS formation and down-regulation of p53, UPR and Nrf2-ARE pathways may be involved in the neuroprotective effect of luteolin.

The transcription factor CHOP, a central component of the transcriptional regulatory network induced upon CCl4 intoxication in mouse liver, is not a critical mediator of hepatotoxicity

Since xenobiotics enter the organism via the liver, hepatocytes must cope with numerous perturbations, including modifications of proteins leading to endoplasmic reticulum stress (ER-stress). This triggers a signaling pathway termed unfolded protein response (UPR) that aims to restore homeostasis or to eliminate disturbed hepatocytes by apoptosis. In the present study, we used the well-established CCl4 hepatotoxicity model in mice to address the questions whether CCl4 induces ER-stress and, if so, whether the well-known ER-stress effector CHOP is responsible for CCl4-induced apoptosis. For this purpose, we treated mice with a high dose of CCl4 injected i.p. and followed gene expression profile over time using Affymetrix gene array analysis. This time resolved gene expression analysis allowed the identification of gene clusters with overrepresented binding sites for the three most important ER-stress induced transcription factors, CHOP, XBP1 and ATF4. Such result was confirmed by the demonstration of CCl4-induced XBP1 splicing, upregulation of CHOP at mRNA and protein levels, and translocation of CHOP to the nucleus. Two observations indicated that CHOP may be responsible for CCl4-induced cell death: (1) Nuclear translocation of CHOP was exclusively observed in the pericentral fraction of hepatocytes that deteriorate in response to CCl4 and (2) CHOP-regulated genes with previously reported pro-apoptotic function such as GADD34, TRB3 and ERO1L were induced in the pericentral zone as well. Therefore, we compared CCl4 induced hepatotoxicity in CHOP knockout versus wild-type mice. Surprisingly, genetic depletion of CHOP did not afford protection against CCl4-induced damage as evidenced by serum GOT and GPT as well as quantification of dead tissue areas. The negative result was obtained at several time points (8, 24 and 72 h) and different CCl4 doses (1.6 and 0.132 g/kg). Overall, our results demonstrate that all branches of the UPR are activated in mouse liver upon CCl4 treatment. However, CHOP does not play a critical role in CCl4-induced cell death and cannot be considered as a biomarker strictly linked to hepatotoxicity. The role of alternative UPR effectors such as XBP1 remains to be investigated.

Endoplasmic reticulum stress response as a possible mechanism of cyclooxygenase-2-independent anticancer effect of celecoxib

BACKGROUND

We investigated whether the endoplasmic reticulum (ER) stress response could be a cyclooxygenase-2 (COX2)-independent mechanism of growth inhibition by celecoxib in a head and neck squamous cell carcinoma (HNSCC) cell line.

MATERIALS AND METHODS

We performed western blotting and reverse transcription polymerase chain reaction to analyze the expression of ER stress response-associated proteins C/EBP homologous protein (CHOP), glucose-regulated protein (GRP)-78 and X-box binding protein-1 (XBP1), after treatment of celecoxib in the SNU-1041 cell line. A 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was performed to determine the change in growth inhibition by celecoxib after inhibition of the ER stress pathway by CHOP small-interfering RNA (siRNA).

RESULTS

Celecoxib triggered an ER stress response in this HNSCC cell line as shown by activation of CHOP, GRP78 and XBP1. The inhibition of cell proliferation by celecoxib was effectively hindered with CHOP siRNA.

CONCLUSION

ER stress response could be a COX2-independent anticancer mechanism of celecoxib.

Ocular-specific ER stress reduction rescues glaucoma in murine glucocorticoid-induced glaucoma

Administration of glucocorticoids induces ocular hypertension in some patients. If untreated, these patients can develop a secondary glaucoma that resembles primary open-angle glaucoma (POAG). The underlying pathology of glucocorticoid-induced glaucoma is not fully understood, due in part to lack of an appropriate animal model. Here, we developed a murine model of glucocorticoid-induced glaucoma that exhibits glaucoma features that are observed in patients. Treatment of WT mice with topical ocular 0.1% dexamethasone led to elevation of intraocular pressure (IOP), functional and structural loss of retinal ganglion cells, and axonal degeneration, resembling glucocorticoid-induced glaucoma in human patients. Furthermore, dexamethasone-induced ocular hypertension was associated with chronic ER stress of the trabecular meshwork (TM). Similar to patients, withdrawal of dexamethasone treatment reduced elevated IOP and ER stress in this animal model. Dexamethasone induced the transcriptional factor CHOP, a marker for chronic ER stress, in the anterior segment tissues, and Chop deletion reduced ER stress in these tissues and prevented dexamethasone-induced ocular hypertension. Furthermore, reduction of ER stress in the TM with sodium 4-phenylbutyrate prevented dexamethasone-induced ocular hypertension in WT mice. Our data indicate that ER stress contributes to glucocorticoid-induced ocular hypertension and suggest that reducing ER stress has potential as a therapeutic strategy for treating glucocorticoid-induced glaucoma.

[Effect of curcumin in inducing apoptosis of MDA-MB-213 cells by activating endoplasmic reticulum stress]

OBJECTIVE

To explore the possible mechanism of curcumin in inducing the apoptosis of breast cancer cell MDA-MB-231.

METHOD

Curcumin of different concentrations at 0, 10 25, 50, 100, 150, 200 micromol x L(-1) were used to intervene breast cancer cells MDA-MB-231 for 24 hours. MTT was used to observe its effect on the proliferation of breast cancer cells. The flow cytometry was used to detect its effect on the cell apoptosis. The real-time quantitative PCR and Western blot was used to assess the expression levels of GRP78 and CHOP in breast cancer cells.

RESULT

Curcumin could inhibit the proliferative ability of breast cancer cells by inducing them in a concentration-dependent manner. Curcumin could significantly increase the expression levels of GRP78 and CHOP in breast cancer cells.

CONCLUSION

Curcumin could induce the apoptosis of breast cancer cells MDA-MB-231 by activating endoplasmic reticulum stress.

Proteasome dysfunction mediates high glucose-induced apoptosis in rodent beta cells and human islets

The ubiquitin/proteasome system (UPS), a major cellular protein degradation machinery, plays key roles in the regulation of many cell functions. Glucotoxicity mediated by chronic hyperglycaemia is detrimental to the function and survival of pancreatic beta cells. The aim of our study was to determine whether proteasome dysfunction could be involved in beta cell apoptosis in glucotoxic conditions, and to evaluate whether such a dysfunction might be pharmacologically corrected. Therefore, UPS activity was measured in GK rats islets, INS-1E beta cells or human islets after high glucose and/or UPS inhibitor exposure. Immunoblotting was used to quantify polyubiquitinated proteins, endoplasmic reticulum (ER) stress through CHOP expression, and apoptosis through the cleavage of PARP and caspase-3, whereas total cell death was detected through histone-associated DNA fragments measurement. In vitro, we found that chronic exposure of INS-1E cells to high glucose concentrations significantly decreases the three proteasome activities by 20% and leads to caspase-3-dependent apoptosis. We showed that pharmacological blockade of UPS activity by 20% leads to apoptosis in a same way. Indeed, ER stress was involved in both conditions. These results were confirmed in human islets, and proteasome activities were also decreased in hyperglycemic GK rats islets. Moreover, we observed that a high glucose treatment hypersensitized beta cells to the apoptotic effect of proteasome inhibitors. Noteworthily, the decreased proteasome activity can be corrected with Exendin-4, which also protected against glucotoxicity-induced apoptosis. Taken together, our findings reveal an important role of proteasome activity in high glucose-induced beta cell apoptosis, potentially linking ER stress and glucotoxicity. These proteasome dysfunctions can be reversed by a GLP-1 analog. Thus, UPS may be a potent target to treat deleterious metabolic conditions leading to type 2 diabetes.

Abnormal chondrocyte apoptosis in the cartilage growth plate is influenced by genetic background and deletion of CHOP in a targeted mouse model of pseudoachondroplasia

Pseudoachondroplasia (PSACH) is an autosomal dominant skeletal dysplasia caused by mutations in cartilage oligomeric matrix protein (COMP) and characterised by short limbed dwarfism and early onset osteoarthritis. Mouse models of PSACH show variable retention of mutant COMP in the ER of chondrocytes, however, in each case a different stress pathway is activated and the underlying disease mechanisms remain largely unknown. T585M COMP mutant mice are a model of moderate PSACH and demonstrate a mild ER stress response. Although mutant COMP is not retained in significant quantities within the ER of chondrocytes, both BiP and the pro-apoptotic ER stress-related transcription factor CHOP are mildly elevated, whilst bcl-2 levels are decreased, resulting in increased and spatially dysregulated chondrocyte apoptosis. To determine whether the abnormal chondrocyte apoptosis observed in the growth plate of mutant mice is CHOP-mediated, we bred T585M COMP mutant mice with CHOP-null mice to homozygosity, and analysed the resulting phenotype. Although abnormal apoptosis was alleviated in the resting zone following CHOP deletion, the mutant growth plates were generally more disorganised. Furthermore, the bone lengths of COMP mutant CHOP null mice were significantly shorter at 9 weeks of age when compared to the COMP mutant mice, including a significant difference in the skull length. Overall, these data demonstrate that CHOP-mediated apoptosis is an early event in the pathobiology of PSACH and suggest that the lack of CHOP, in conjunction with a COMP mutation, may lead to aggravation of the skeletal phenotype via a potentially synergistic effect on endochondral ossification.

Hydrogen sulfide [corrected] increases survival during sepsis: protective effect of CHOP inhibition

Sepsis is a major cause of mortality, and dysregulation of the immune response plays a central role in this syndrome. H2S, a recently discovered gaso-transmitter, is endogenously generated by many cell types, regulating a number of physiologic processes and pathophysiologic conditions. We report that H2S increased survival after experimental sepsis induced by cecal ligation and puncture (CLP) in mice. Exogenous H2S decreased the systemic inflammatory response, reduced apoptosis in the spleen, and accelerated bacterial eradication. We found that C/EBP homologous protein 10 (CHOP), a mediator of the endoplasmic reticulum stress response, was elevated in several organs after CLP, and its expression was inhibited by H2S treatment. Using CHOP-knockout (KO) mice, we demonstrated for the first time, to our knowledge, that genetic deletion of Chop increased survival after LPS injection or CLP. CHOP-KO mice displayed diminished splenic caspase-3 activation and apoptosis, decreased cytokine production, and augmented bacterial clearance. Furthermore, septic CHOP-KO mice treated with H2S showed no additive survival benefit compared with septic CHOP-KO mice. Finally, we showed that H2S inhibited CHOP expression in macrophages by a mechanism involving Nrf2 activation. In conclusion, our findings show a protective effect of H2S treatment afforded, at least partially, by inhibition of CHOP expression. The data reveal a major negative role for the transcription factor CHOP in overall survival during sepsis and suggest a new target for clinical intervention, as well potential strategies for treatment.

Ampelopsin induces cell growth inhibition and apoptosis in breast cancer cells through ROS generation and endoplasmic reticulum stress pathway

Ampelopsin (AMP), a major bioactive constituent of Ampelopsis grossedentata, exerts a number of biological effects. In this study, we investigated its anti-cancer activity in human breast cancer cell lines, and explored the underlying mechanism of this action. Our results showed that treatment with AMP dose-dependently inhibited cell viability and induced apoptosis in MCF-7 and MDA-MB-231 breast cancer cells without cytotoxicity in human normal breast epithelial cells MCF-10A. Meanwhile, AMP dose- dependently triggered reactive oxygen species (ROS) generation in both breast cancer cells. The ROS scavenger N-acetyl-L-cysteine (NAC) strongly attenuated AMP-induced ROS production, along with cell growth inhibition and apoptosis. Furthermore, AMP was observed to activate endoplasmic reticulum (ER) stress, as evidenced by the up-regulation of ER stress-related proteins, including GRP78, p-PERK, p-elF2α, cleaved ATF6α and CHOP, while knockdown of ATF6α or PERK markedly down-regulated AMP-induced CHOP expression. Blocking ER stress using 4-phenylbutyric acid not only down-regulated AMP-induced GRP78 and CHOP expression, but also significantly decreased AMP-induced cell growth inhibition and apoptosis, whereas ER stress inducer thapsigargin played opposing effects. Additionally, NAC inhibited AMP-induced ER stress by down-regulating GRP78 and CHOP expression. Conversely, blocking ER stress using CHOP siRNA decreased AMP-induced ROS production and cell apoptosis. Taken together, these results demonstrate that AMP has anti-tumor effects against breast cancer cells through ROS generation and ER stress pathway, which therefore provide experimental evidences for developing AMP as a new therapeutic drug for breast cancer.

Anti-inflammatory effect of unsaturated fatty acids and Ergosta-7,22-dien-3-ol from Marthasterias glacialis: prevention of CHOP-mediated ER-stress and NF-κB activation

There has been increasing awareness to the potential interest of drug discovery from marine natural products to treat several pathological conditions, including inflammation. In this work we describe the anti-inflammatory activity of several compounds present in the echinoderm Marthasterias glacialis (spiny sea-star), using the inflammatory model RAW 264.7 cells challenged with LPS. Lipidomic profiling of the organism revealed two major classes of compounds: fatty acids and sterols. Among these, the predominant compounds cis 11-eicosenoic and cis 11,14 eicosadienoic acids and the unsaturated sterol ergosta-7,22-dien-3-ol were evaluated. The mechanism of action of the compounds was distinct as they modulated different levels of the inflammation pathway. Classical inflammatory markers, such as COX-2, iNOS, IL-6 and NF-κB, were evaluated. We also studied the contribution of the CHOP pathway-mediated ER-stress to the inflammatory process. Overall, the sterol ergosta-7,22-dien-3-ol was the most active compound, however maximum activity was obtained when all compounds were tested in combination, thus suggesting a potentially synergistic activity of both classes of metabolites. This work establishes the echinoderm M. glacialis as an interesting source of anti-inflammatory molecules.

Ablation of the proapoptotic genes CHOP or Ask1 does not prevent or delay loss of visual function in a P23H transgenic mouse model of retinitis pigmentosa

The P23H mutation in rhodopsin (Rho(P23H)) is a prevalent cause of autosomal dominant retinitis pigmentosa. We examined the role of the ER stress proteins, Chop and Ask1, in regulating the death of rod photoreceptors in a mouse line harboring the Rho(P23H) rhodopsin transgene (GHL(+)). We used knockout mice models to determine whether Chop and Ask1 regulate rod survival or retinal degeneration. Electrophysiological recordings showed similar retinal responses and sensitivities for GHL(+), GHL(+)/Chop(-/-) and GHL(+)/Ask1(-/-) animals between 4-28 weeks, by which time all three mouse lines exhibited severe loss of retinal function. Histologically, ablation of Chop and Ask1 did not rescue photoreceptor loss in young animals. However, in older mice, a regional protective effect was observed in the central retina of GHL(+)/Chop(-/-) and GHL(+)/Ask1(-/-), a region that was severely degenerated in GHL(+) mice. Our results show that in the presence of the Rho(P23H) transgene, the rate of decline in retinal sensitivity is similar in Chop or Ask1 ablated and wild-type retinas, suggesting that these proteins do not play a major role during the acute phase of photoreceptor loss in GHL(+) mice. Instead they may be involved in regulating secondary pathological responses such as inflammation that are upregulated during later stages of disease progression.

Bufalin induces the interplay between apoptosis and autophagy in glioma cells through endoplasmic reticulum stress

Malignant gliomas are common primary tumors of the central nervous system. The prognosis of patients with malignant glioma is poor in spite of current intensive therapy and thus novel therapeutic modalities are necessary. Bufalin is the major component of Chan-Su (a traditional Chinese medicine) extracts from the venom of Bufo gargarizan. In this study, we evaluated the growth inhibitory effect of bufalin on glioma cells and explored the underlying molecular mechanisms. Our results showed that bufalin inhibited the growth of glioma cells significantly. Mechanistic studies demonstrated that bufalin induced apoptosis through mitochondrial apoptotic pathway. In addition, bufalin was also found to induce ER stress-mediated apoptosis, which was supported by the up- regulation of ER stress markers, CHOP and GRP78, and augmented phosphorylation of PERK and eIF2α as well as cleavage of caspase-4. Downregulation of CHOP using siCHOP RNA attenuated bufalin-induced apoptosis, further confirming the role of ER stress response in mediating bufalin-induced apoptosis. Evidence of bufalin-induced autophagy included formation of the acidic vesicular organelles, increase of autophagolysosomes and LC3-II accumulation. Further experiments showed that the mechanism of bufalin-induced autophagy associated with ATP deleption involved an increase in the active form of AMPK, decreased phosphorylation levels of mTOR and its downstream targets 4EBP1 and p70S6K1. Furthermore, TUDC and silencing of eIF2α or CHOP partially blocked bufalin-induced accumulation of LC3-II, which indicated that ER stress preceded bufalin-induced autophagy and PERK/eIF2α/CHOP signaling pathway played a major part in the process. Blockage of autophagy increased expression of ER stress associated proteins and the ratio of apoptosis, indicating that autophagy played a cytoprotective role in bufalin induced ER stress and cell death. In conclusion, bufalin inhibits glioma cell growth and induces interplay between apoptosis and autophagy through endoplasmic reticulum stress. It will provide molecular bases for developing bufalin into a drug candidate for the treatment of maglinant glioma.

The role of thioredoxin-1 in suppression of endoplasmic reticulum stress in Parkinson disease

Endoplasmic reticulum (ER) stress has been implicated in Parkinson disease. We previously reported that thioredoxin 1 (Trx-1) suppressed the ER stress caused by 1-methy-4-phenyl-1,2,3,6-tetrahydropyridine; however, its molecular mechanism remains largely unknown. In the present study, we showed that 1-methyl-4-phenylpyridinium ion (MPP(+)) induced ER stress by activating glucose-regulated protein 78 (GRP78), inositol-requiring enzyme 1α (IRE1α), tumor necrosis factor receptor-associated factor 2 (TRAF2), c-Jun N-terminal kinase (JNK), caspase-12, and C/EBP homologous protein (CHOP) in PC12 cells. The downregulation of Trx-1 aggravated the ER stress and further increased the expression of the above molecules induced by MPP(+). In contrast, overexpression of Trx-1 attenuated the ER stress and repressed the expression of the above molecules induced by MPP(+). More importantly, the overexpression of Trx-1 in transgenic mice suppressed ER stress by inhibiting the activation of these molecules. We present, for the first time, the molecular mechanism of Trx-1 suppression of endoplasmic reticulum stress in Parkinson disease in vitro and in vivo. Based on our findings, we conclude that Trx-1 plays a neuroprotective role in Parkinson disease by suppressing ER stress by regulating the activation of GRP78, IRE1α, TRAF2, JNK, caspase-12, and CHOP.

Yessotoxin induces ER-stress followed by autophagic cell death in glioma cells mediated by mTOR and BNIP3

Yessotoxin at nanomolar concentrations can induce programmed cell death in different model systems. Paraptosis-like cell death induced by YTX in BC3H1 cells, which are insensitive to several caspase inhibitors,has also been reported. This makes yessotoxin of interest in the search of molecules that target cancer cells vulnerabilities when resistance to apoptosis is observed. To better understand the effect of this molecule at the molecular level on tumor cells, we conducted a transcriptomic analysis using 3 human glioma cell lines with different sensitivities to yessotoxin. We show that the toxin induces a deregulation of the lipid metabolism in glioma cells as a consequence of induction of endoplasmic reticulum stress. The endoplasmic reticulum stress in turn arrests the cell cycle and inhibits the protein synthesis. In the three cell lines used we show that YTX induces autophagy, which is involved in cell death. The sensibility of the cell lines used towards autophagic cell death was related to their doubling time, being the cell line with the lowest proliferation rate the most resistant.The involvement of mTOR and BNIP3 in the autophagy induction was also determined.

JNK1 protects against glucolipotoxicity-mediated beta-cell apoptosis

Pancreatic β-cell dysfunction is central to type 2 diabetes pathogenesis. Prolonged elevated levels of circulating free-fatty acids and hyperglycemia, also termed glucolipotoxicity, mediate β-cell dysfunction and apoptosis associated with increased c-Jun N-terminal Kinase (JNK) activity. Endoplasmic reticulum (ER) and oxidative stress are elicited by palmitate and high glucose concentrations further potentiating JNK activity. Our aim was to determine the role of the JNK subtypes JNK1, JNK2 and JNK3 in palmitate and high glucose-induced β-cell apoptosis. We established insulin-producing INS1 cell lines stably expressing JNK subtype specific shRNAs to understand the differential roles of the individual JNK isoforms. JNK activity was increased after 3 h of palmitate and high glucose exposure associated with increased expression of ER and mitochondrial stress markers. JNK1 shRNA expressing INS1 cells showed increased apoptosis and cleaved caspase 9 and 3 compared to non-sense shRNA expressing control INS1 cells when exposed to palmitate and high glucose associated with increased CHOP expression, ROS formation and Puma mRNA expression. JNK2 shRNA expressing INS1 cells did not affect palmitate and high glucose induced apoptosis or ER stress markers, but increased Puma mRNA expression compared to non-sense shRNA expressing INS1 cells. Finally, JNK3 shRNA expressing INS1 cells did not induce apoptosis compared to non-sense shRNA expressing INS1 cells when exposed to palmitate and high glucose but showed increased caspase 9 and 3 cleavage associated with increased DP5 and Puma mRNA expression. These data suggest that JNK1 protects against palmitate and high glucose-induced β-cell apoptosis associated with reduced ER and mitochondrial stress.

Mono-allelic and bi-allelic ENPP1 deficiency promote post-injury neointimal hyperplasia associated with increased C/EBP homologous protein expression

OBJECTIVE

Bi-allelic function-inactivating ENPP1 mutations cause artery media calcification (AMC) with associated severe myointimal hyperplasia in generalized arterial calcification of infancy (GACI), whereas mono-allelic ENPP1 deficiency is phenotypically normal. Here, we tested if ENPP1 deficiency promotes abnormal vascular smooth muscle cell (VSMC)-driven responses to injury, with or without calcification. The ER stress mediator C/EBP homologous protein (CHOP) affects neointimal hyperplasia and atherosclerosis, and has paradoxical effects on bone formation. Hence, we assessed relationships between ENPP1 and CHOP in VSMCs.

METHODS

We studied ENPP1-deficient mice and control littermates subjected to left carotid artery ligation, and isolated and studied VSMCs from these and Chop-/- mice, or with CHOP siRNA treatment.

RESULTS

Normal Enpp1-/+ mice, in addition to Enpp1-/- mice prior to AMC development, had accelerated neointimal hyperplasia in response to carotid artery ligation at 7-8 weeks age. Neointimal hyperplasia was linked with robust artery media CHOP expression in situ, but with marked AMC only in injured Enpp1-/- arteries. Cultured, ENPP1-deficient and CHOP-deficient VSMCs had increased migration and proliferation to PDGF. Cultured Chop-/- VSMCs demonstrated increased Pi donor-induced calcification. CHOP was significantly increased in Pi donor treated Enpp1-/- and Enpp1-/+ cultured VSMCs. CHOP siRNA treatment of Enpp1-/- VSMCs increased calcification, associated with elevated expression of tissue nonspecific alkaline phosphatase and the master osteoblastic transcription factor RUNX2.

CONCLUSIONS

Both mono-allelic and bi-allelic ENPP1 deficiency promote dysregulated VSMC function, with robust lesion CHOP expression and enhanced neointimal hyperplasia after injury in vivo, but marked post-injury calcification limited to Enpp1-/- mice. Intimal hyperplasia in GACI appears regulated by biologic effects of ENPP1 deficiency other than calcification, including ER stress. VSMC CHOP excess in ENPP1 deficiency may primarily function to limit VSMC calcification.

The inhibitory effect of quercetin on asymmetric dimethylarginine-induced apoptosis is mediated by the endoplasmic reticulum stress pathway in glomerular endothelial cells

Asymmetric dimethylarginine (ADMA) is considered an independent mortality and cardiovascular risk factor in chronic kidney disease (CKD) patients, and contributes to the development of renal fibrosis. Quercetin (QC), a natural component of foods, protects against renal injury. Here, we explored the possible mechanisms that are responsible for ADMA-induced renal fibrosis and the protective effect of QC. We found that ADMA treatment activated the endoplasmic reticulum (ER) stress sensor proteins phosphorylated protein kinase RNA-activated-like ER kinase (PERK) and inositol requiring-1α (IRE1), which correspondingly induced C/EBP homologous protein (CHOP) expression and phosphorylated c-Jun N-terminal kinase (JNK) phosphorylation in glomerular endothelial cells (GEnCs). Following this, ADMA promoted ER stress-induced apoptosis and resulted in transforming growth factor β (TGF-β) expression in GEnCs. SP600125, an inhibitor of JNK, and CHOP siRNA protected against ADMA-induced cell apoptosis and TGF-β expression. QC prevented ADMA-induced PERK and IRE1 apoptotic ER stress pathway activation. Also, ADMA-induced GEnCs apoptosis and TGF-β expression was reduced by QC. Overexpression of CHOP blocked QC-mediated protection from apoptosis in ER stressed cells. Overall, these observations indicate that ADMA may induce GEnCs apoptosis and TGF-β expression by targeting the PERK-CHOP and IRE1-JNK pathway. In addition, drugs such as QC targeting ER stress may hold great promise for the development of novel therapies against ADMA-induced renal fibrosis.