Endoplasmic Reticulum Stress Sensor Research Articles

A chimeric mutant analysis in yeast cells suggests BiP independent regulation of the mammalian endoplasmic reticulum-stress sensor IRE1α

An endoplasmic reticulum (ER)-located transmembrane protein, Ire1, triggers cytoprotective events upon ER stress. Chimeric yeast Ire1 carrying the luminal domain of the mammalian major Ire1 paralogue IRE1α is upregulated in ER-stressed yeast cells, but is poorly associated with the ER-located chaperone BiP even under non-stressed conditions. This observation contradicts the theory that BiP is the master regulator of IRE1α.

Inhibition of IRE1 RNase activity modulates the tumor cell secretome and enhances response to chemotherapy

Triple-negative breast cancer (TNBC) lacks targeted therapies and has a worse prognosis than other breast cancer subtypes, underscoring an urgent need for new therapeutic targets and strategies. IRE1 is an endoplasmic reticulum (ER) stress sensor, whose activation is predominantly linked to the resolution of ER stress and, in the case of severe stress, to cell death. Here we demonstrate that constitutive IRE1 RNase activity contributes to basal production of pro-tumorigenic factors IL-6, IL-8, CXCL1, GM-CSF, and TGFβ2 in TNBC cells. We further show that the chemotherapeutic drug, paclitaxel, enhances IRE1 RNase activity and this contributes to paclitaxel-mediated expansion of tumor-initiating cells. In a xenograft mouse model of TNBC, inhibition of IRE1 RNase activity increases paclitaxel-mediated tumor suppression and delays tumor relapse post therapy. We therefore conclude that inclusion of IRE1 RNase inhibition in therapeutic strategies can enhance the effectiveness of current chemotherapeutics.

Expression analysis and functional characterization of the mouse cysteine-rich with EGF-like domains 2

We have previously identified a novel endoplasmic reticulum (ER) stress-inducible protein, namely, cysteine-rich with EGF-like domains 2 (CRELD2), which is predominantly regulated by ATF6. However, few studies on intrinsic CRELD2 have been published. In the present study, we elucidated the expression of intrinsic CRELD2 in mouse tissues and ER stress- treated Neuro2a cells. Among nine tissues we tested, CRELD2 protein in the heart and skeletal muscles was negligible. CRELD2 expression in Neuro2a cells was induced at the late phase after treatment with tunicamycin (Tm) compared with rapid induction of growth arrest and DNA damage inducible gene 153 (GADD153). On the other hand, another ER stress inducer, thapsigargin, increased the intrinsic CRELD2 secretion from Neuro2a cells. We furthermore established CRELD2-deficient Neuro2a cells to evaluate their features. In combination with the NanoLuc complementary reporter system, which was designed to detect protein-protein interaction in living cells, CRELD2 interacted with not only CRELD2 itself but also with ER localizing proteins in Neuro2a cells. Finally, we investigated the responsiveness of CRELD2-deficient cells against Tm-treatment and found that CRELD2 deficiency did not affect the expression of genes triggered by three canonical ER stress sensors but rendered Neuro2a cells vulnerable to Tm-stimulation. Taken together, these findings provide the novel molecular features of CRELD2, and its further characterization would give new insights into understanding the ER homeostasis and ER stress-induced cellular dysfunctions.

Inhibition of ER stress-related IRE1α/CREB/NLRP1 pathway promotes the apoptosis of human chronic myelogenous leukemia cell

Endoplasmic reticulum (ER) stress is induced in chronic myelogenous leukemia (CML) cells. As an important sensor of ER stress, inositol-requiring protein-1α (IRE1α) promotes the survival of acute myeloid leukemia. NLRP1 inflammasome activation promotes metastatic melanoma growth and that IRE1α can increase NLRP1 inflammasome gene expression. This study aimed to investigate the role and molecular mechanism of IRE1α in CML cell growth. We found that overexpression of IRE1α or NLRP1 significantly promoted the proliferation and decreased the apoptosis of CML cells, whereas downregulation of these two genes showed the opposite effects. 4-phenylbutyric acid (4-PBA), an ER stress inhibitor, reduced the expression of IRE1α and NLRP1. IRE1α elevated NLRP1 expression via cAMP responsive element binding protein (CREB) phosphorylation. NLRP1 inflammasome was activated in CML cells and its activation partly reversed ER stress inhibitor-induced cell apoptosis. Furthermore, inhibition of IRE1α/NLRP1 pathway sensitized CML cells to imatinib-mediated apoptosis. Additionally, IRE1α expression was elevated and NLRP1 inflammasome was activated in primary cells from CML patients. Downregulation of IRE1α or NLRP1 suppressed the proliferation and elevated the apoptosis of primary CML cells. Collectively, this study demonstrated that the IRE1α/CREB/NLRP1 pathway contributes to the progression of CML and the development of imatinib resistance. Hence, targeting ER stress-related IRE1α expression or NLRP1 inflammasome activation may block CML development.

Hyperthermia induces therapeutic effectiveness and potentiates adjuvant therapy with non-targeted and targeted drugs in an in vitro model of human malignant melanoma

In the present study, we have aimed to characterize the intrinsic, extrinsic and ER-mediated apoptotic induction by hyperthermia in an in vitro model of human malignant melanoma and furthermore, to evaluate its therapeutic effectiveness in an adjuvant therapeutic setting characterized by combinational treatments with non-targeted (Dacarbazine & Temozolomide) and targeted (Dabrafenib & Vemurafenib) drugs. Overall, our data showed that both low (43 °C) and high (45 °C) hyperthermic exposures were capable of inducing cell death by activating all apoptotic pathways but in a rather distinct manner. More specifically, low hyperthermia induced extrinsic and intrinsic apoptotic pathways both of which activated caspase 6 only as opposed to high hyperthermia which was mediated by the combined effects of caspases 3, 7 and 6. Furthermore, significant involvement of the ER was evident (under both hyperthermic conditions) suggesting its role in regulating apoptosis via activation of CHOP. Our data revealed that while low hyperthermia activated IRE-1 and ATF6 only, high hyperthermia induced activation of PERK as well suggesting that ultimately these ER stress sensors can lead to the induction of CHOP via different pathways of transmitted signals. Finally, combinational treatment protocols revealed an effect of hyperthermia in potentiating the therapeutic effectiveness of non-targeted as well as targeted drugs utilized in the clinical setting. Overall, our findings support evidence into hyperthermia’s therapeutic potential in treating human malignant melanoma by elucidating the underlying mechanisms of its complex apoptotic induction.

Pre-pregnancy maternal obesity associates with endoplasmic reticulum stress in human umbilical vein endothelium

Obesity associates with the endoplasmic reticulum (ER) stress-induced endothelial dysfunction. Pregnant women with pre-pregnancy maternal obesity (PGMO) may transfer this potential risk to their offspring; however, whether ER stress occurs and associates with foetoplacental endothelial dysfunction in PGMO is unknown. We studied the l-arginine transport and nitric oxide (NO) synthesis in human umbilical vein endothelial cells (HUVECs) from women with PGMO or with a normal pre-pregnancy weight. We analysed the expression and activation of the ER stress sensors protein kinase RNA-like endoplasmic reticulum kinase (PERK), inositol-requiring enzyme 1α (IRE1α), and activating transcription factor 6 (ATF6). PGMO associated with lower endothelial NO synthase activity due to increased Thr495-inhibitor and decreased Ser1177-stimulator phosphorylation. However, higher expression and activity of the human cationic amino acid transporter 1 was found. PGMO caused activation of PERK and its downstream targets eukaryotic initiation factor 2 (eIF2α), C/EBP homologous protein 10 (CHOP), and tribbles-like protein 3 (TRB3). Increased IRE1α protein abundance (but not its phosphorylation or X-box binding protein 1-mRNA splicing) and increased c-Jun N-terminal kinase 1 phosphorylation was seen in PGMO. A preferential nuclear location of the activating transcription factor 6 (ATF6) was found in HUVECs from PGMO. All the changes seen in PGMO were blocked by TUDCA but unaltered by tunicamycin. Thus, PGMO may determine a state of ER stress via upregulation of the PERK–eIF2α–CHOP–TRB3 axis signalling in HUVECs. This phenomenon results in foetoplacental vascular endothelial dysfunction at birth.

The synthetic chalcone derivative 2-hydroxy-3′,5,5′-trimethoxychalcone induces unfolded protein response-mediated apoptosis in A549 lung cancer cells

The synthetic chalcone derivative 2-hydroxy-3′,5,5′-trimenthoxyochalcone (named DK-139) exhibits anti-inflammatory and anti-tumor invasion properties. However, effects of DK-139 on tumor cell growth remain unknown. In the present study, we evaluated the inhibitory activity of DK-139 against human lung cancer cells. Treatment with DK-139 inhibited clonogenicity in various lung cancers and stimulated the caspase cascade, leading to the apoptosis of A549 lung cancer cells. To investigate the mode of action of DK-139-induced apoptosis, we analyzed the effect of DK-139 on the endoplasmic reticulum (ER) stress response. DK-139 increased expression of ER stress sensors, including p-PERK, GRP78/BiP, and IRE1α. IRE1α-regulated XBP-1 mRNA splicing and PERK-induced ATF4 expression was also upregulated following DK-139 treatment. In addition, expression levels of the pro-apoptotic transcription factor CHOP and its downstream target Bim, which is involved in mitochondria-mediated apoptosis, were increased by DK-139 treatment. These results suggest that DK-139 triggers caspase-mediated apoptosis via the ER stress-activated unfolded protein response (UPR) pathway. We propose that the synthetic chalcone derivative DK-139 may be used as a potential agent for the prevention and/or treatment of human lung cancer.

Abstract 448: The novel role of ecdysoneless (ECD) in maintain ER Ca2+ homeostasis

Abstract Background and Significance: Calcium (Ca2+) is an essential signal transduction element involved in the regulation of several cellular activities such as gene transcription, proliferation and apoptosis. Endoplasmic Reticulum (ER) is the Ca2+ reservoir inside the cell that strictly orchestrate Ca2+ gradient across the Plasma Membrane(PM). Importantly, intracellular Ca2+ flux, is a key to orderly regulate cell proliferation, if altered can promote uncontrolled proliferation leading to cancer. Ca2+ entry through the [Ca2+]PM channels during [Ca2+]ER depletion is called the Store Operated Ca2+ Entry (SOCE). Impairment of endogenous SOCE leads to sustained [Ca2+]ER depletion and results in accumulation of unfolded proteins in the ER (known as ER stress). Understanding the basic molecular mechanism regulating PM to ER Ca2+ flow and developing novel strategies to target ER Ca2+ signaling could be beneficial from cancer therapeutic perspective. We have identified Ecdysoneless (ECD), an evolutionary conserved novel cell cycle regulator protein. ECD is overexpressed in several cancers, including breast and pancreatic cancers and its overexpression in breast cancer correlates with poor prognosis and short survival of patients. Recently our lab demonstrates that ECD is a negative regulator of ER stress; however, there is no mechanistic insights of how ECD senses and acts to maintain ER homeostasis. Experimental Design: We have utilized mouse embryonic fibroblasts (MEFs) from Tet(O)-FhECD-IRES-eGFP-rtTA and Ecdflox/flox mice transgenic mice to regulate ECD levels in cells to assess the role of ECD in Ca2+ signaling in a highly controlled system. Structured illumination microscopy(SIM) and biochemical fractionation techniques were performed to identify localization of ECD. Live cell imaging of cells stained with Ca2+ binding dyes like Fluo4-AM and Fluo5N-AM were used to access [Ca2+]Cyto and [Ca2+]ER levels respectively. Fluorescence resonance energy transfer (FRET) and immunoprecipitation methods were conducted to analyze SOCE pathway. Western blotting was used to assess the levels of various proteins involved in Ca2+ signaling. Results: We demonstrate several novel findings: (i) ECD is a smooth ER associated protein; (ii) ECD regulates assembly of ER-PM protein complex to drive Ca2+ entry through SOCE into the ER, maintaining [Ca2+]ER homeostasis; iii) ECD is overexpressed upon Ca2+ depletion and provides survival benefit to cells; v) ECD regulates Ca2+ mediated cell proliferation via CaMKII phosphorylation. Conclusion: Our results demonstrate ECD is a sensor of ER stress, induced by Ca2+deprivation, and overexpressed ECD promotes cell proliferation and survival under ER stress. These findings suggest ECD could be a potential target of Cancer therapy. Citation Format: Aniruddha Sarkar, Irfana Saleem, Sameer Mirza, Keshore Bidasee, Rajini Rao, Hamid Band, Vimla Band. The novel role of ecdysoneless (ECD) in maintain ER Ca2+ homeostasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 448.

Abstract 1255: Delta-tocopherol induced endoplasmic reticulum stress causes autophagic degradation of ER and cell death in bladder cancer models

Abstract Vitamin E has been the subject of numerous basic and clinical studies, which have demonstrated a range of results that necessitate the further analysis of its individual components. We demonstrate that of the major tocopherol components of Vitamin E, Delta tocopherol (δ-T) is significantly more effective than the more common Alpha- and Gamma- tocopherols at inducing bladder cancer cell death in vitro and reduces tumor growth and burden in vivo. As a major site of protein synthesis and folding the endoplasmic reticulum (ER) is highly sensitive to stress induced by increased unfolded protein load, which induces both pro-survival and ultimately pro-apoptotic responses via the different branches of the unfolded protein response (UPR). δ-T induces the UPR in human bladder cancer cells and ultimately results in cell death, inducing both apoptosis and autophagic cell death. Analysis of bladder cancer cells treated with δ-T revealed strong evidence of UPR activation in the form of upregulation and activation of ER stress sensors PERK and IRE1α, and the upregulation of folding chaperone GRP78 and transcription factors ATF4 and CHOP. These changes in turn induced downstream effects including Death Receptor 5 (DR5)-mediated apoptosis and visible induction of autophagy. In addition to the observation of autophagosome formation, induction of autophagy was further confirmed by upregulation of protein expression of components of the autophagic machinery LC3B and Atg family members. Electron Microscope imaging of treated cells revealed the presence of ER-whorls within the large autophagosomes which were themselves visible under conventional light microscopy, which has to our knowledge not been previously observed in cancer models. This observation is supported by the ER stress-based mechanism of action exhibited by δ-T on bladder cancer cells, which recapitulates the observations of the few previous reports of “ER-phagy” described in yeast models. ER stress induced expansion of the ER is believed to aid in the improvement of stressed cells' protein folding capacity, and selective degradation of the ER-whorls formed in this manner by a previously undescribed mechanism of autophagy was first described in yeast and remains unexplored in human cancer models. These findings may provide new insights into δ-T's mechanism of action and inform new approaches to the development of tocopherols as novel chemopreventive agents. Citation Format: Christopher A. Blair, Hanze Hu, Tim Huynh, Maggie Wu, Chung S. Yang, Xiaolin Zi. Delta-tocopherol induced endoplasmic reticulum stress causes autophagic degradation of ER and cell death in bladder cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1255.

PO-046 The antiproliferative activity and cell death effects of four marine invertebrate extracts in colon cancer cells

IntroductionFast-growing tumour cells show enhanced protein synthesis and therefore depend on efficient folding for nascent export proteins in the endoplasmic reticulum (ER). Herein, the two most prominent ER resident thiol oxidoreductases ERp57 and PDI play important parts in formation of disulfide bonds in client proteins. This and the finding that both proteins fulfil various roles also in other compartments (i.e. cytoplasm, nucleus, cell membrane) encouraged us to investigate the impact of their depletion on colorectal cancer cells.Material and methodsUsing an inducible knockdown (KD) system we tested ERp57 and PDI deficiency in long term survival assays in normoxia and hypoxia combined with irradiation.Results and discussionsKD of ERp57 or PDI triggered a severe attenuation of proliferation, but only ERp57 deficiency led to activation of the PERK-dependent UPR and apoptosis. When combined with an ERp57 KD, irradiation displayed the most dramatic growth reduction even under 1% oxygen. The absence of ERp57 reduced expression of cellular proliferation factors like c-Myc, PLK-1, AKT, PDPK1, ERK1,2 and others. Further, we demonstrated for the first time that PDI is an essential activator of the ER stress sensor PERK that enforces cancer cell survival under global ER stress in hypoxia. In the absense of ER stress, ERp57 functions as a reductase for PDI that keeps PERK in an inactive state.ConclusionOur data identified ERp57 and PDI as promising new targets for a mono- and combination anti-cancer therapy due to multiple cellular points of attack.

PO-043 Targeting the thiol oxidoreductases ERp57 and PDI hits cancer cells on multiple fronts: proliferation, radioresistance and ER stress response (UPR)

IntroductionFast-growing tumour cells show enhanced protein synthesis and therefore depend on efficient folding for nascent export proteins in the endoplasmic reticulum (ER). Herein, the two most prominent ER resident thiol oxidoreductases ERp57 and PDI play important parts in formation of disulfide bonds in client proteins. This and the finding that both proteins fulfil various roles also in other compartments (i.e. cytoplasm, nucleus, cell membrane) encouraged us to investigate the impact of their depletion on colorectal cancer cells.Material and methodsUsing an inducible knockdown (KD) system we tested ERp57 and PDI deficiency in long term survival assays in normoxia and hypoxia combined with irradiation.Results and discussionsKD of ERp57 or PDI triggered a severe attenuation of proliferation, but only ERp57 deficiency led to activation of the PERK-dependent UPR and apoptosis. When combined with an ERp57 KD, irradiation displayed the most dramatic growth reduction even under 1% oxygen. The absence of ERp57 reduced expression of cellular proliferation factors like c-Myc, PLK-1, AKT, PDPK1, ERK1,2 and others. Further, we demonstrated for the first time that PDI is an essential activator of the ER stress sensor PERK that enforces cancer cell survival under global ER stress in hypoxia. In the absense of ER stress, ERp57 functions as a reductase for PDI that keeps PERK in an inactive state.ConclusionOur data identified ERp57 and PDI as promising new targets for a mono- and combination anti-cancer therapy due to multiple cellular points of attack.

Abstract 3938: The alkylphosphocholine erufosine induces ER and mitochondrial stress in OSCC cells

Abstract Endoplasmic reticulum (ER) plays an essential role in cell function and survival. Accumulation of unfolded or misfolded proteins in the lumen of the ER activates the unfolded protein response (UPR), resulting in ER-stress and subsequent apoptosis. The alkylphosphocholine erufosine is a known Akt-mTOR inhibitor in oral squamous cell carcinoma (OSCC). In the present study we decipher a new facet of erufosine's mechanism of action and evaluate its role to induce ER and mitochondrial stress leading to autophagy, apoptosis and ROS induction. The cellular toxicity of erufosine was determined by MTT assay after 24h, 48h and 72h exposure in two OSCC cell lines, HN-5 and SCC-61. Based on these results, HN-5 cells were exposed to erufosine at concentrations corresponding to IC25, IC50 and IC75 concentrations, and then their mRNA was isolated and analyzed by Illumina Chip array. Gene expression and gene set enrichment analyses were performed to identify core KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways and GO (Gene Ontology) terms. A positive enrichment of ER stress upon erufosine exposure was observed, which was verified at protein level for the ER stress sensors and their downstream mediators. Upon erufosine exposure, calcium influx into the cytoplasm of the two OSCC cell lines was also observed. A differential regulation of genes and positive enrichment of processes pertaining to autophagy and apoptosis was also observed upon erufosine exposure. Autophagy was confirmed by increased acidic vacuoles and LC3-B levels. Apoptosis was confirmed by nuclear staining, annexin-V and immuno-blotting of caspases. The induction of mitochondrial stress upon erufosine exposure was predicted by gene enrichment analysis and shown by erufosine's effect on mitochondrial membrane potential, ATP and ROS production in OSCC cells. These data show that ER and mitochondrial targeting by erufosine represents a new facet of its mechanism of action as well as a promising new framework in the treatment of head and neck cancers. They furthermore support the future evaluation of erufosine as a therapeutic approach in cancer treatment alone, or in combination. Citation Format: Shariq S. Ansari, Ashwini Sharma, Doaa M. Ali, Rainer Köng, Martin R. Berger. The alkylphosphocholine erufosine induces ER and mitochondrial stress in OSCC cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3938.

Activation of the endoplasmic reticulum stress sensor IRE1\u03b1 by the vaccine adjuvant AS03 contributes to its immunostimulatory properties

The oil-in-water emulsion Adjuvant System 03 (AS03) is one of the few adjuvants used in licensed vaccines. Previous work indicates that AS03 induces a local and transient inflammatory response that contributes to its adjuvant effect. However, the molecular mechanisms involved in its immunostimulatory properties are ill-defined. Upon intramuscular injection in mice, AS03 elicited a rapid and transient downregulation of lipid metabolism-related genes in the draining lymph node. In vitro, these modifications were associated with profound changes in lipid composition, alteration of endoplasmic reticulum (ER) morphology and activation of the unfolded protein response pathway. In vivo, treatment with a chemical chaperone or deletion of the ER stress sensor kinase IRE1α in myeloid cells decreased AS03-induced cytokine production and its capacity to elicit high affinity antigen-specific antibodies. In summary, our results indicate that IRE1α is a sensor for the metabolic changes induced by AS03 in monocytic cells and may constitute a canonical pathway that could be exploited for the design of novel vaccine adjuvants.

Ethyl Acetate Extract of Scindapsus cf. hederaceus Exerts the Inhibitory Bioactivity on Human Non-Small Cell Lung Cancer Cells through Modulating ER Stress.

Unfolded protein response (UPR) is a cytoprotective mechanism that alleviates the protein-folding burden in eukaryotic organisms. Moderate activation of UPR is required for maintaining endoplasmic reticulum (ER) homeostasis and profoundly contributes to tumorigenesis. Defects in UPR signaling are implicated in the attenuation of various malignant phenotypes including cell proliferation, migration, and invasion, as well as angiogenesis. This suggests UPR as a promising target in cancer therapy. The pharmacological effects of the plant Scindapsus cf. hederaceus on human cancer cell lines is not understood. In this study, we identified an ethyl acetate extract from Scindapsus cf. hederaceus (SH-EAE), which markedly altered the protein expression of UPR-related genes in human non-small cell lung cancer (NSCLC) cells. Treatment with the SH-EAE led to the dose-dependent suppression of colony forming ability of both H1299 and H460 cells, but not markedly in normal bronchial epithelial BEAS-2B cells. SH-EAE treatment also attenuated the migration and invasion ability of H1299 and H460 cells. Moreover, SH-EAE strikingly suppressed the protein expression of two ER stress sensors, including inositol requiring enzyme-1α (IRE-1α) and protein kinase R-like ER kinase (PERK), and antagonized the induction of C/EBP homologous protein (CHOP) expression by thapsigargin, an ER stress inducer. SH-EAE induced the formation of massive vacuoles which are probably derived from ER. Importantly, SH-EAE impaired the formation of intersegmental vessels (ISV) in zebrafish larvae, an index of angiogenesis, but had no apparent effect on the rate of larval development. Together, our findings demonstrate, for the first time, that the ability of SH-EAE specifically targets the two sensors of UPR, with significant anti-proliferation and anti-migration activities as a crude extract in human NSCLC cells. Our finding also indicates potential applications of SH-EAE in preventing UPR activation in response to Tg-induced ER stress. We suggest that SH-EAE attenuates UPR adaptive pathways for rendering the NSCLC cells intolerant to ER stress.

A New Role for Estrogen Receptor α in Cell Proliferation and Cancer: Activating the Anticipatory Unfolded Protein Response.

Cells react to a variety of stresses, including accumulation of unfolded or misfolded protein, by activating the endoplasmic reticulum (EnR) stress sensor, the unfolded protein response (UPR). The UPR is highly conserved and plays a key role in the maintenance of protein folding quality control and homeostasis. In contrast to the classical reactive mode of UPR activation, recent studies describe a hormone-activated anticipatory UPR. In this pathway, mitogenic hormones, such as estrogen (E2), epidermal growth factor, and vascular endothelial growth factor rapidly activate the UPR in anticipation of a future need for increased protein folding capacity upon cell proliferation. Here, we focus on this recently unveiled pathway of E2-estrogen receptor α (ERα) action. Notably, rapid activation of the anticipatory UPR pathway is essential for subsequent activation of the E2-ERα regulated transcription program. Moreover, activation of the UPR at diagnosis is a powerful prognostic marker in ERα positive breast cancer. Furthermore, in cells containing ERα mutations that confer estrogen independence and are common in metastatic breast cancer, the UPR is constitutively activated and linked to antiestrogen resistance. Lethal ERα-dependent hyperactivation of the anticipatory UPR represents a promising therapeutic approach exploited by a new class of small molecule ERα biomodulator.

Strong and sustained activation of the anticipatory unfolded protein response induces necrotic cell death.

The endoplasmic reticulum stress sensor, the unfolded protein response (UPR), regulates intracellular protein homeostasis. While transient activation of the reactive UPR by unfolded protein is protective, prolonged and sustained activation of the reactive UPR triggers CHOP-mediated apoptosis. In the recently characterized, evolutionarily conserved anticipatory UPR, mitogenic hormones and other effectors pre-activate the UPR; how strong and sustained activation of the anticipatory UPR induces cell death was unknown. To characterize this cell death pathway, we used BHPI, a small molecule that activates the anticipatory UPR through estrogen receptor α (ERα) and induces death of ERα+ cancer cells. We show that sustained activation of the anticipatory UPR by BHPI kills cells by inducing depletion of intracellular ATP, resulting in classical necrosis phenotypes, including plasma membrane disruption and leakage of intracellular contents. Unlike reactive UPR activation, BHPI-induced hyperactivation of the anticipatory UPR does not induce apoptosis or sustained autophagy. BHPI does not induce CHOP protein or PARP cleavage, and two pan-caspase inhibitors, or Bcl2 overexpression, have no effect on BHPI-induced cell death. Moreover, BHPI does not increase expression of autophagy markers, or work through recently identified programmed-necrosis pathways, such as necroptosis. Opening of endoplasmic reticulum IP3R calcium channels stimulates cell swelling, cPLA2 activation, and arachidonic acid release. Notably, cPLA2 activation requires ATP depletion. Importantly, blocking rapid cell swelling or production of arachidonic acid does not prevent necrotic cell death. Rapid cell death is upstream of PERK activation and protein synthesis inhibition, and results from strong and sustained activation of early steps in the anticipatory UPR. Supporting a central role for ATP depletion, reversing ATP depletion blocks rapid cell death, and the onset of necrotic cell death is correlated with ATP depletion. Necrotic cell death initiated by strong and sustained activation of the anticipatory UPR is a newly discovered role of the UPR.

Betulinic acid chemosensitizes breast cancer by triggering ER stress-mediated apoptosis by directly targeting GRP78

Stress-induced cellular defense machinery has a critical role in mediating cancer drug resistance, and targeting stress-related signaling has become a novel strategy to improve chemosensitivity. Betulinic acid (BA) is a naturally occurring pentacyclic triterpenoid with potent anticancer bioactivities in multiple malignancies, whereas its underlying mechanisms remain unclear. Here in, we found that BA has synergistic effects with taxol to induce breast cancer cells G2/M checkpoint arrest and apoptosis induction, but had little cytotoxicity effects on normal mammary epithelial cells. Drug affinity responsive target stability (DARTS) strategy further identified glucose-regulated protein 78 (GRP78) as the direct interacting target of BA. BA administration significantly elevated GRP78-mediated endoplasmic reticulum (ER) stress and resulted in the activation of protein kinase R-like ER kinase (PERK)/eukaryotic initiation factor 2a/CCAAT/enhancer-binding protein homologous protein apoptotic pathway. GRP78 silencing or ER stress inhibitor salubrinal administration was revealed to abolish the anticancer effects of BA, indicating the critical role of GRP78 in mediating the bioactivity of BA. Molecular docking and coimmunoprecipitation assay further demonstrated that BA might competitively bind with ATPase domain of GRP78 to interrupt its interaction with ER stress sensor PERK, thereby initiating the downstream apoptosis cascade. In vivo breast cancer xenografts finally validated the chemosensitizing effects of BA and its biofunction in activating GRP78 to trigger ER stress-mediated apoptosis. Taken together, our study not only uncovers GRP78 as a novel target underlying the chemosensitizing effects of BA, but also highlights GRP78-based targeting strategy as a promising approach to improve breast cancer prognosis.

Diphenyleneiodonium enhances oxidative stress and inhibits Japanese encephalitis virus induced autophagy and ER stress pathways

Diphenyleneiodonium (DPI) and N-acetyl-l-cysteine (NAC), two widely used anti-oxidants, were employed to evaluate the role of oxidative stress in Japanese encephalitis virus (JEV) induced autophagy, stress responses and replication. DPI and NAC exerted opposite effects on ROS levels in JEV infected mouse neuronal cells (Neuro2a), mouse embryonic fibroblasts (MEFs) and human epithelial cells (HeLa). While NAC effectively quenched ROS, DPI enhanced ROS levels, suggesting that DPI induces oxidative stress in JEV infected cells. DPI treatment of JEV infected Neuro2a cells further blocked autophagy induction and activation of all three arms of the ER stress pathway, and, inhibited virus particle release. Autophagy induction in JEV infection has been previously shown to be linked to the activation of XBP1 and ATF6 ER stress sensors. Our data suggests that DPI mediated block of autophagy is a result of inhibition of ER stress responses and is not associated with an anti-oxidative effect. Since DPI has a wide inhibitory potential for all Flavin dependent enzymes, it is likely that the signalling pathways for ER stress and autophagy during JEV infection are modulated by DPI sensitive enzymes.

Bax inhibitor-1 protects from nonalcoholic steatohepatitis by limiting inositol-requiring enzyme 1 alpha signaling in mice.

Targeting IRE1α-dependent NLRP3 inflammasome signaling with pharmacological agents or by BI-1 may represent a tangible therapeutic strategy for NASH. (Hepatology 2018).

Oxymatrine Causes Hepatotoxicity by Promoting the Phosphorylation of JNK and Induction of Endoplasmic Reticulum Stress Mediated by ROS in LO2 Cells.

Oxymatrine (OMT) often used in treatment for chronic hepatitis B virus infection in clinic. However, OMT–induced liver injury has been reported. In this study, we aim to investigate the possible mechanism of OMT-induced hepatotoxicity in human normal liver cells (L02). Exposed cells to OMT, the cell viability was decreased and apoptosis rate increased, the intracellular markers of oxidative stress were changed. Simultaneously, OMT altered apoptotic related proteins levels, including Bcl-2, Bax and pro-caspase-8/-9/-3. In addition, OMT enhanced the protein levels of endoplasmic reticulum (ER) stress makers (GRP78/Bip, CHOP, and cleaved-Caspase-4) and phosphorylation of c-Jun N-terminal kinase (p-JNK), as well as the mRNA levels of GRP78/Bip, CHOP, caspase-4, and ER stress sensors (IREI, ATF6, and PERK). Pre-treatment with Z-VAD-fmk, JNK inhibitor SP600125 and N-acetyl-l-cysteine (NAC), a ROS scavenger, partly improved the survival rates and restored OMT-induced cellular damage, and reduced caspase-3 cleavage. SP600125 or NAC reduced OMT-induced p-JNK and NAC significantly lowered caspase-4. Furthermore, 4-PBA, the ER stress inhibitor, weakened inhibitory effect of OMT on cells, on the contrary, TM worsen. 4-PBA also reduced the levels of p-JNK and cleaved-caspase-3 proteins. Therefore, OMT-induced injury in L02 cells was related to ROS mediated p-JNK and ER stress induction. Antioxidant, by inhibition of p-JNK or ER stress, may be a feasible method to alleviate OMT-induced liver injury.