Reduction of GRP78 expression with siRNA activates unfolded protein response leading to apoptosis in HeLa cells

Exploring the role of SWI/SNF complex subunit BAF60c in lipid metabolism and inflammation in fish

Chromatin remodeling plays an important role in regulating gene transcription, in which chromatin remodeling complex is a crucial aspect. Brg1/Brm-associated factor 60c (BAF60c) subunit forms a bridge between chromatin remodeling complexes and transcription factors in mammals; hence, it has received extensive attention. However, the roles of BAF60c in fish remain largely unexplored. In this study, we identified BAF60c-interacting proteins by using HIS-pull-down and LC-MS/MS analysis in fish. Subsequently, the RNA-seq analysis was performed to identify the overall effects of BAF60c. Then, the function of BAF60c was verified through BAF60c knockdown and overexpression experiments. We demonstrated for the first time that BAF60c interacts with glucose-regulated protein 78 (GRP78) and regulates lipid metabolism, endoplasmic reticulum (ER) stress, and inflammation. Knockdown of BAF60c reduces fatty acid biosynthesis, ER stress, and inflammation. In conclusion, the results enriched BAF60c-interacting protein network and explored the function of BAF60c in lipid metabolism and inflammation in fish.

Effects of GRP78 on Endoplasmic Reticulum Stress and Inflammatory Response in Macrophages of Large Yellow Croaker (Larimichthys crocea)

Endoplasmic reticulum (ER) homeostasis plays a vital role in cell physiological functions. Various factors can destroy the homeostasis of the ER and cause ER stress. Moreover, ER stress is often related to inflammation. Glucose-regulated protein 78 (GRP78) is an ER chaperone, which plays a vital role in maintaining cellular homeostasis. Nevertheless, the potential effects of GRP78 on ER stress and inflammation is still not fully elucidated in fish. In the present study, ER stress and inflammation was induced by tunicamycin (TM) or palmitic acid (PA) in the macrophages of large yellow croakers. GRP78 was treated with an agonist/inhibitor before or after the TM/PA treatment. The results showed that the TM/PA treatment could significantly induce ER stress and an inflammatory response in the macrophages of large yellow croakers whereas the incubation of the GRP78 agonist could reduce TM/PA-induced ER stress and an inflammatory response. Moreover, the incubation of the GRP78 inhibitor could further induce TM/PA-induced ER stress and an inflammatory response. These results provide an innovative idea to explain the relationship between GRP78 and TM/PA-induced ER stress or inflammation in large yellow croakers.

The function of the co-chaperone ERdj4 in diverse (patho-)physiological conditions

Accumulation of misfolded proteins in the endoplasmic reticulum (ER) induces a well-orchestrated cellular response to reduce the protein burden within the ER. This unfolded protein response (UPR) is controlled primarily by three transmembrane proteins, IRE1α, ATF6, and PERK, the activity of which is controlled by BiP, the ER-resident Hsp70 protein. Binding of BiP to co-chaperones via their highly conserved J-domains stimulates the intrinsic ATPase activity of BiP, thereby providing the energy necessary for (re-)folding of proteins, or for targeting of misfolded proteins to the degradation pathway, processes specified and controlled by the respective co-chaperone. In this review, our aim is to elucidate the function of the co-chaperone ERDJ4, also known as MDG1, MDJ7, or DNAJB9. Knockout and knockin experiments clearly point to the central role of ERDJ4 in controlling lipogenesis and protein synthesis by promoting degradation of SREBP1c and the assembly of the protein complex mTORC2. Accumulating data reveal that ERDJ4 controls epithelial-to-mesenchymal transition, a central process during embryogenesis, in wound healing, and tumor development. Overexpression of ERdj4 has been shown to improve engraftment of transplanted human stem cells, possibly due to its ability to promote cellular survival in stressed cells. High ERDJ4-plasma levels are specific for fibrillary glomerulonephritis and serve as a diagnostic marker. As outlined in this review, the functions of ERDJ4 are manifold, depending on the cellular (patho-) physiological state, the cellular protein repertoire, and the subcellular localization of ERDJ4.

Tonsil-derived mesenchymal stem cells incorporated in reactive oxygen species-releasing hydrogel promote bone formation by increasing the translocation of cell surface GRP78

Controlling the senescence of mesenchymal stem cells (MSCs) is essential for improving the efficacy of MSC-based therapies. Here, a model of MSC senescence was established by replicative subculture in tonsil-derived MSCs (TMSCs) using senescence-associated β-galactosidase, telomere-length related genes, stemness, and mitochondrial metabolism. Using transcriptomic and proteomic analyses, we identified glucose-regulated protein 78 (GRP78) as a unique MSC senescence marker. With increasing cell passage number, GRP78 gradually translocated from the cell surface and cytosol to the (peri)nuclear region of TMSCs. A gelatin-based hydrogel releasing a sustained, low level of reactive oxygen species (ROS-hydrogel) was used to improve TMSC quiescence and self-renewal. TMSCs expressing cell surface-specific GRP78 (csGRP78+), collected by magnetic sorting, showed better stem cell function and higher mitochondrial metabolism than unsorted cells. Implantation of csGRP78+ cells embedded in ROS-hydrogel in rats with calvarial defects resulted in increased bone regeneration. Thus, csGRP78 is a promising biomarker of senescent TMSCs, and the combined use of csGRP78+ cells and ROS-hydrogel improved the regenerative capacity of TMSCs by regulating GRP78 translocation.

Characterization of Endoplasmic Reticulum (ER) in Human Pluripotent Stem Cells Revealed Increased Susceptibility to Cell Death upon ER Stress

Human pluripotent stem cells (hPSCs), such as embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), have a well-orchestrated program for differentiation and self-renewal. However, the structural features of unique proteostatic-maintaining mechanisms in hPSCs and their features, distinct from those of differentiated cells, in response to cellular stress remain unclear. We evaluated and compared the morphological features and stress response of hPSCs and fibroblasts. Compared to fibroblasts, electron microscopy showed simpler/fewer structures with fewer networks in the endoplasmic reticulum (ER) of hPSCs, as well as lower expression of ER-related genes according to meta-analysis. As hPSCs contain low levels of binding immunoglobulin protein (BiP), an ER chaperone, thapsigargin treatment sharply increased the gene expression of the unfolded protein response. Thus, hPSCs with decreased chaperone function reacted sensitively to ER stress and entered apoptosis faster than fibroblasts. Such ER stress-induced apoptotic processes were abolished by tauroursodeoxycholic acid, an ER-stress reliever. Hence, our results revealed that as PSCs have an underdeveloped structure and express fewer BiP chaperone proteins than somatic cells, they are more susceptible to ER stress-induced apoptosis in response to stress.

Enhanced Cancer Theranostics with Self-Assembled, Multilabeled siRNAs

The integration of therapy and diagnostics, termed "theranostics", has recently gained widespread utility in the development of new and improved therapeutics that effectively diagnose and treat diseases, such as cancer. In this study, the covalent attachment of multiple fluorescent labels (i.e., fluorescein isothiocyanate (FITC)) to a wide range of siRNAs, including those adopting linear, V- and Y-shape nanostructures, was successfully accomplished by solid-phase bioconjugation for monitoring cell uptake, co-localization, and biological activity in cell culture. The FITC-labeled higher-order V- and Y-shape siRNAs maintained the requisite hybrid stabilities and A-type helical structures for invoking RNAi activity. The FITC-siRNA hybrids with sense-strand modifiers enabled efficient mRNA knockdown (∼50-90%), which also translated to increased cell death (∼20-95%) in a bone metastatic prostate cancer cell line, over a 72 h incubation period. Significantly, the Y-shaped siRNA containing three FITC probes enhanced fluorescent signaling relative to the siRNA constructs containing single and double fluorophores while retaining potent knockdown and cell death effects post-transfection. Taken together, this data highlights the theranostic utility of the multilabeled FITC-siRNA constructs for potential cancer gene therapy applications.

A mechanism underlies fish GRP78 protection against Pb2+ toxicity

Heavy metal exposure impacts basic cellular processes and results in serious toxicological effects. Pb²⁺ can activate the response to endoplasmic reticulum (ER) stress by protein denaturation, changing intracellular calcium homeostasis, and inducing cell death. As an ER retention protein, 78-kDa glucose-regulated protein (GRP78) can relieve the Pb²⁺-induced ER stress and enhance cell viability. We previously showed that heavy metal ions such as Pb²⁺ etc. are harmful to fish cell lines in a time- and dose-dependent manner. The phenomenon is accompanied by the increasing accumulation of grass carp GRP78 (CiGRP78), which can protect the cells from heavy metal ion cytotoxicity. Here, we investigated the mechanism in which CiGRP78 exerted its protective function. Using metal ions affinity elution method and fluorescent spectral analysis, we showed that CiGRP78 could respectively form a complex with Calcium, Lead and Cadmium ions, especially with Lead ion in vitro. However, another ER retention protein CiGRP94 could not bind to Pb²⁺, highlighting the functional differentiation might exist in CiGRP78 and CiGRP94 in regulating heavy metal cytotoxicity. Our results suggested that CiGRP78 might increase cellular tolerance to Pb²⁺ via the direct interaction with it.

RCAD/BiP pathway is necessary for the proper synthesis of digestive enzymes and secretory function of the exocrine pancreas

Alcoholism causes an imbalance of endoplasmic reticulum (ER) homeostasis in pancreatic acini. In those cells, the ER is involved in the synthesis and folding of pancreatic enzymes. Ubiquitin-fold modifier 1 (Ufm1) is part of a novel ubiquitin-like modification system involved in maintaining ER homeostasis. Among the components of the Ufm1 system, Regulator of C53 and DDRGK1 (RCAD) has recently been identified as a Ufm1-specific E3 ligase that promotes ufmylation of DDRGK1, an RCAD-interacting protein. We determined the importance of RCAD in the proper synthesis and secretion of pancreatic enzymes using mice with genetically deleted RCAD. The pancreas of RCAD-deficient mice was of normal size and histology. Using quantitative PCR and Western blotting, we found that amylase was upregulated in pancreas organs from RCAD-knockout (KO) mice. Constitutive amylase secretion was much higher in isolated pancreatic acini from RCAD KO mice, whereas CCK-stimulated amylase secretion was disturbed. RCAD deficiency caused a downregulation in expression of ER chaperone BiP, which affected ER homeostasis and activated both apoptosis and trypsin. We also found that both RCAD and DDRGK1 transcript levels were upregulated in pancreatic acini from alcohol-preferring rats. Elevated expression of RCAD and DDRGK1 was associated with increased ER stress and UPR activation. Because of the lack of BiP expression, caspase 3 and trypsin activation we enhanced in RCAD-deficient pancreatic acini upon treatment with ethanol and CCK. In conclusion, the RCAD/BiP pathway is required for proper synthesis and secretion of pancreatic enzymes. In alcoholism, increased levels of components of the Ufm1 system could prevent the deleterious effects of alcohol in the pancreas by regulating BiP levels.NEW & NOTEWORTHY RCAD/BiP pathway is required for the proper synthesis and secretion of amylase from pancreatic acini, as well as for the maintenance of the ER homeostasis. In alcoholism, the exocrine pancreas could increase the levels of components of the Ufm1 system to protect itself from alcohol's deleterious effects by regulating the expression of ER chaperone BiP.

RNAi Screening of the Glucose-Regulated Chaperones in Cancer with Self-Assembled siRNA Nanostructures

The emerging field of RNA nanotechnology has been used to design well-programmed, self-assembled nanostructures for applications in chemistry, biology, and medicine. At the forefront of its utility in cancer is the unrestricted ability to self-assemble multiple siRNAs within a single nanostructure formulation for the RNAi screening of a wide range of oncogenes while potentiating the gene therapy of malignant tumors. In our RNAi nanotechnology approach, V- and Y-shape RNA templates were designed and constructed for the self-assembly of discrete, higher-ordered siRNA nanostructures targeting the oncogenic glucose regulated chaperones. The GRP78-targeting siRNAs self-assembled into genetically encoded spheres, triangles, squares, pentagons and hexagons of discrete sizes and shapes according to TEM imaging. Furthermore, gel electrophoresis, thermal denaturation, and CD spectroscopy validated the prerequisite siRNA hybrids for their RNAi application. In a 24 sample siRNA screen conducted within the AN3CA endometrial cancer cells known to overexpress oncogenic GRP78 activity, the self-assembled siRNAs targeting multiple sites of GRP78 expression demonstrated more potent and long-lasting anticancer activity relative to their linear controls. Extending the scope of our RNAi screening approach, the self-assembled siRNA hybrids (5 nM) targeting of GRP-75, 78, and 94 resulted in significant (50-95%) knockdown of the glucose regulated chaperones, which led to synergistic effects in tumor cell cycle arrest (50-80%) and death (50-60%) within endometrial (AN3CA), cervical (HeLa), and breast (MDA-MB-231) cancer cell lines. Interestingly, a nontumorigenic lung (MRC5) cell line displaying normal glucose regulated chaperone levels was found to tolerate siRNA treatment and demonstrated less toxicity (5-20%) relative to the cancer cells that were found to be addicted to glucose regulated chaperones. These remarkable self-assembled siRNA nanostructures may thus encompass a new class of potent siRNAs that may be useful in screening important oncogene targets while improving siRNA therapeutic efficacy and specificity in cancer.

Effects of phycoerythrin from Gracilaria lemaneiformis in proliferation and apoptosis of SW480 cells

We studied phycoerythrin (PE) in human SW480 tumor cells and the underlying molecular mechanisms of action. PE inhibited cell proliferation as evidenced by CCK-8 assay. The IC50 values of phycoerythrin were 48.2 and 27.4 µg/ml for 24 and 48 h of exposure, respectively. PE induced apoptosis and cell cycle arrest in SW480 cells as observed under electron microscopy and with flow cytometry. Apoptosis increased from 5.1 (controls) to 39.0% in 80.0 µg/ml PE-treated cells. Differences in protein expression were identified using proteomic techniques. Protein spots (1018±60 and 1010±60) were resolved in PE-treated and untreated group. Forty differential protein spots were analyzed with MALDI-TOF-MS, including GRP78 and NPM1. The expression as measured by qPCR and western blotting agreed with data from two-dimensional electrophoresis. GRP78, NPM1, MTHSP75, Ezrin and Annexin A2 were decreased and HSP60 was increased after PE treatment, indicating that PE may target multiple proteins to induce apoptosis.

Transcriptome analysis of the unfolded protein response in hemocytes of Litopenaeus vannamei

In this study, Litopenaeus vannamei was injected with double-stranded RNA (dsRNA) against L. vannamei immunoglobulin heavy chain binding protein (LvBip) to activating UPR in the hemocytes, shirmps injected dsRNA against enhanced green fluorescence protein (eGFP) as control group. And genes expression in hemocytes of then were analyzed using Illumina Hiseq 2500 (PE100). By comparing the analyzed results, 1418 unigenes were significantly upregulated, and 596 unigenes were significantly down-regulated upon UPR. Analysis of the differentially expressed genes against known databases indicated that the distribution of gene pathways between the upregulated and down-regulated genes were substantially different. A total of 208 genes of UPR system were obtained, and 69 of them were differentially expressed between the two groups. Results also showed that L. vannamei UPR was involved in various metabolic processes, such as glycometabolism, lipid metabolism, amino acid metabolism, and nucleic acid metabolism. In addition, UPR was emgaged in immune-assicoated signaling pathways, such as NF-κB signaling pathway, NOD-like receptor signaling pathway, Hippo signaling pathway, p38 MAPK signaling pathway and Wnt signaling pathway in L. vannamei. These results improved our current understanding of the L. vannamei UPR, and highlighted its importance in cell homeostasis upon environmental stress.

Identification and functional characterization of a glucose regulated protein 94 gene in Litopenaeus vannamei and its responsiveness in WSSV infection

In the current study, a cDNA of glucose regulated protein 94 (LvGRP94) was cloned from Litopenaeus vannamei. Subcellular localization assay revealed that LvGRP94 expressed in endoplasmic reticulum (ER). And results of reported gene assays demonstrated that the promoter of LvGRP94 was activated by L. vannamei leucine zipper domain transcription factor X-box binding protein 1 (LvXBP1) or heat shock treatment. Furthermore, LvGRP94 was found to highly express in hemocytes as well as in epidermis by real-time RT-PCR. In addition, it was shown that LvGRP94 inhibited by LvXBP1 knocked-down in the hemocytes, was induced by white spot syndrome virus (WSSV) infection, or unfolded protein response (UPR) pathway activation. Importantly, decreasing LvGRP94 reduced the cumulative mortality of WSSV-infected shrimps and WSSV copies in shrimp muscle. These results suggested that LvGRP94 might involve in shrimp UPR pathway as well as WSSV infection.

Identification and functional characterization of an endoplasmic reticulum oxidoreductin 1-α gene in Litopenaeus vannamei

In the current study, full-length sequence of endoplasmic reticulum oxidoreductin 1-α (LvERO1-α) was cloned from Litopenaeus vannamei. Real-time RT-PCR results showed that LvERO1-α was highly expressed in hemocytes, gills, and intestines. White spot syndrome virus (WSSV) challenge was performed, and the expression of LvERO1-α and two other downstream genes of the double-stranded RNA-activated protein kinase-like ER kinase-eIF2α (PERK-α) pathway, namely, homocysteine-induced endoplasmic reticulum protein (LvHERP) and acylamino-acid-releasing enzyme (LvAARE), strongly increased in the hemocytes. Flow cytometry assay results indicated that the apoptosis rate of L. vannamei hemocytes in the LvERO1-α knockdown group was significantly lower than that of the controls. Moreover, shrimps with knockdown expression of LvERO1-α exhibited decreased cumulative mortality upon WSSV infection. Downregulation of L. vannamei immunoglobulin-binding protein (LvBip), which had been proven to induce unfolded protein response (UPR) in L. vannamei, did not only upregulate LvERO1-α, LvHERP, and LvAARE in hemocytes, but also increased their apoptosis rate, as well as the shrimp cumulative mortality. Furthermore, reporter gene assay results showed that the promoter of LvERO1-α was activated by L. vannamei activating transcription factor 4, thereby confirming that LvERO1-α was regulated by the PERK-eIF2α pathway. These results suggested that LvERO1-α plays a critical role in WSSV-induced apoptosis, which likely occurs through the WSSV-activated PERK-eIF2α pathway.

Cell-type variation in stress responses as a consequence of manipulating GRP78 expression in neuroectodermal cells

Glucose-regulated protein 78 (GRP78) is a stress sensor which interacts with unfolded protein response (UPR) activators in the endoplasmic reticulum (ER). The aim of this study was to test the hypothesis that GRP78 has distinct functional roles in mediating the effects of ER stress in neuroblastoma compared to other neuroectodermal cancer types. GRP78 was knocked down or overexpressed in neuroectodermal tumor cell lines. Protein and transcript expression were measured using Western blotting, confocal microscopy, and real-time polymerase chain reaction; cell stress was assessed by measurement of oxidative stress and accumulation of ubiquitinated proteins and cell response by measurement of apoptosis and cell viability. Neuroblastoma cells were more sensitive to ER stress than melanoma and glioblastoma cells. GRP78 knockdown increased stress sensitivity of melanoma and glioblastoma cells, but not neuroblastoma cells. Over-expression of GRP78 decreased the stress sensitivity of melanoma and glioblastoma cells but, in contrast, increased the stress sensitivity of neuroblastoma cells by activation of caspase-3-independent cell death and substantially increased the expression of UPR activators, particularly inositol-requiring element 1 (IRE1). The results from this study suggest that cell-type specific differences in the relationships between GRP78 and the UPR activators, particularly IRE1, may determine differential sensitivity to ER stress.

Inhibitory Effects of Verrucarin A on Tunicamycin-Induced ER Stress in FaO Rat Liver Cells

Endoplasmic reticulum (ER) stress is linked with development and maintenance of cancer, and serves as a therapeutic target for treatment of cancer. Verrucarin A, isolated from the broth of Fusarium sp. F060190, showed potential inhibitory activity on tunicamycin-induced ER stress in FaO rat liver cells. In addition, the compound decreased tunicamycin-induced GRP78 promoter activity in a dose dependent manner without inducing significant inhibition of luciferase activity and cell growth for 6 and 12 h. Moreover, the compound decreased the expression of GRP78, CHOP, XBP-1, and suppressed XBP-1, and reduced phosphorylation of IRE1α in FaO rat liver cells. This evidence suggests for the first time that verrucarin A inhibited tunicamycin-induced ER stress in FaO rat liver cells.

Pachymic acid inhibits growth and induces apoptosis of pancreatic cancer in vitro and in vivo by targeting ER stress

Pachymic acid (PA) is a purified triterpene extracted from medicinal fungus Poria cocos. In this paper, we investigated the anticancer effect of PA on human chemotherapy resistant pancreatic cancer. PA triggered apoptosis in gemcitabine-resistant pancreatic cancer cells PANC-1 and MIA PaCa-2. Comparative gene expression array analysis demonstrated that endoplasmic reticulum (ER) stress was induced by PA through activation of heat shock response and unfolded protein response related genes. Induced ER stress was confirmed by increasing expression of XBP-1s, ATF4, Hsp70, CHOP and phospho-eIF2α. Moreover, ER stress inhibitor tauroursodeoxycholic acid (TUDCA) blocked PA induced apoptosis. In addition, 25 mg kg-1 of PA significantly suppressed MIA PaCa-2 tumor growth in vivo without toxicity, which correlated with induction of apoptosis and expression of ER stress related proteins in tumor tissues. Taken together, growth inhibition and induction of apoptosis by PA in gemcitabine-resistant pancreatic cancer cells were associated with ER stress activation both in vitro and in vivo. PA may be potentially exploited for the use in treatment of chemotherapy resistant pancreatic cancer.

Knockdown of glucose-regulated protein 78/binding immunoglobulin heavy chain protein expression by asymmetric small interfering RNA induces apoptosis in prostate cancer cells and attenuates migratory capability

Glucose-regulated protein 78 [GRP78, also termed binding immunoglobulin heavy chain protein (Bip)] may be involved in cancer progression and metastasis. However, to date there has been minimal investigation into its potential role in human prostate cancer cells. Recent studies have demonstrated that asymmetric small interfering RNA (asiRNA)-mediated gene silencing is more effective and longer-lasting than conventional symmetric siRNA. Thus, the current study aimed to investigate the effects of GRP78-specific asiRNA on human prostate cancer cells. A series of asiRNAs was synthesized and their efficiency in silencing GRP78 expression in PC-3 human prostate cancer cells was evaluated. The effects of knockdown using asiRNAs were compared to those of knockdown using symmetric siRNAs. The effect of GRP78 silencing on PC-3 cell apoptosis and migration, and the possible mechanisms governing these biological processes were examined. Compared with the symmetric siRNA, transfection with the 15 base pair asiRNA (asiGRP78-3) resulted in greater downregulation of GRP78 expression. GRP78 depletion in PC-3 cells resulted in increased apoptosis and decreased migration of these cells. Experiments investigating the underlying mechanisms of these effects revealed that knockdown of GRP78 attenuated protein kinase B activation and decreased the expression of pro-caspase 9, pro-caspase 3 and vimentin. In conclusion, knockdown of GRP78/Bip expression with asymmetric siRNA led to increased prostate cancer cell apoptosis and reduced cellular migration.

Glucose-regulated protein 78 (Grp78) confers chemoresistance to tumor endothelial cells under acidic stress

OBJECTIVES

This study was designed to investigate the activation of the unfolded protein response (UPR) in tumor associated endothelial cells (TECs) and its association with chemoresistance during acidic pH stress.

MATERIALS AND METHODS

Endothelial cells from human oral squamous cell carcinomas (OSCC) were excised by laser capture microdissection (LCM) followed by analysis of UPR markers (Grp78, ATF4 and CHOP) using quantitative PCR. Grp78 expression was also determined by immunostaining. Acidic stress was induced in primary human dermal microvascular endothelial cells (HDMECs) by treatment with conditioned medium (CM) from tumor cells grown under hypoxic conditions or by adjusting medium pH to 6.4 or 7.0 using lactic acid or hydrochloric acid (HCl). HDMEC resistance to the anti-angiogenic drug Sunitinib was assessed with SRB assay.

RESULTS

UPR markers, Grp78, ATF4 and CHOP were significantly upregulated in TECs from OSCC compared to HDMECs. HDMECs cultured in acidic CM (pH 6.0-6.4) showed increased expression of the UPR markers. However, severe acidosis led to marked cell death in HDMECs. Alternatively, HDMECs were able to adapt when exposed to chronic acidosis at pH 7.0 for 7 days, with concomittant increase in Grp78 expression. Chronic acidosis also confers drug resistance to HDMECs against Sunitinib. Knockdown of Grp78 using shRNA resensitizes HDMECs to drug treatment.

CONCLUSIONS

UPR induction in ECs under acidic pH conditions is related to chemoresistance and may contribute to therapeutic failures in response to chemotherapy. Targeting Grp78, the key component of the UPR pathway, may provide a promising approach to overcome ECs resistance in cancer therapy.

ATF4 (activating transcription factor 4) from grass carp (Ctenopharyngodon idella) modulates the transcription initiation of GRP78 and GRP94 in CIK cells

GRP78 and GRP94, belong to GRP (glucose-regulated protein) family of endoplasmatic reticulum (ER) chaperone superfamily, are essential for cell survival under ER stress. ATF4 is a protective protein which regulates the adaptation of cells to ER stress by modulating the transcription of UPR (Unfolded Protein Response) target genes, including GRP78 and GRP94. To understand the molecular mechanism of ATF4 modulates the transcription initiation of CiGRP78 and CiGRP94, we cloned ATF4 ORF cDNA sequences (CiATF4) by homologous cloning techniques. The expression trend of CiATF4 was similar to CiGRP78 and CiGRP94 did under 37 °C thermal stress, namely, the expression of CiATF4 was up-regulated twice at 2 h post-thermal stress and at 18 h post recovery from thermal stress. In this paper, CiATF4 was expressed in BL21 Escherichia coli, and the expressed protein was purified by affinity chromatography with the Ni-NTA His-Bind Resin. On the basis of the cloned CiGRP78 and CiGRP94 cDNA in our laboratory previously, we cloned their promoter sequences by genomic walking approach. In vitro, gel mobility shift assays revealed that CiATF4 could bind to CiGRP78 and CiGRP94 promoter with high affinity. Subsequently, the recombinant plasmid of pGL3-CiGRPs and pcDNA3.1-CiATF4 were constructed and transiently co-transfected into Ctenopharyngodon idella kidney (CIK) cells. The impact of CiATF4 on CiGRP promoter sequences were measured by luciferase assays. These results demonstrated that CiATF4 could activate the transcription of CiGRP78 and CiGRP94. What's more, for better understanding the molecular mechanism of CiATF4 modulate the transcription initiation of CiGRP, three mutant fragments of CiGRP78 promoter recombinant plasmids (called CARE-mut/LUC, CRE1-mut/LUC and CRE2-mut/LUC) were constructed and transiently co-transfected with CiATF4 into CIK cells. The results indicated that CRE or CARE elements were the regulatory element for transcription initiation of CiGRP78. Between them, CRE element would play more important role in it.

Triapine and a more potent dimethyl derivative induce endoplasmic reticulum stress in cancer cells

Triapine (3-AP; 3-aminopyridine-2-carboxaldehyde thiosemicarbazone), a ribonucleotide reductase inhibitor, has been extensively evaluated in clinical trials in the last decade. This study addresses the role of endoplasmic reticulum (ER) stress in the anticancer activity of 3-AP and the derivative N(4),N(4)-dimethyl-triapine (3-AP-Me), differing from 3-AP only by dimethylation of the terminal nitrogen. Treatment of colon cancer cells with 3-AP or 3-AP-Me activated all three ER stress pathways (PERK, IRE1a, ATF6) by phosphorylation of eIF2α and upregulation of gene expression of activating transcription factors ATF4 and ATF6. In particular, 3-AP-Me led to an upregulation of the alternatively spliced mRNA variant XBP1 (16-fold). Moreover, 3-AP and 3-AP-Me activated the cellular stress kinases c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinases, and inhibition of JNK activity antagonized the cytotoxic effect of both compounds. Subsequent to induction of the unfolded protein response, a significant upregulation of proapoptotic proteins was detected, including the transcription factor CHOP and Bim, an essential factor for ER stress-related apoptosis. In correlation with the higher degree of ER stress after 3-AP-Me treatment, also a more potent depolarization of mitochondrial membranes was found. These data suggest that 3-AP and 3-AP-Me induce apoptosis via ER stress. This was further corroborated by showing that inhibition of protein biosynthesis with cycloheximide prior to 3-AP and 3-AP-Me treatment leads to a significant reduction of the antiproliferative properties of both compounds. Taken together, this study demonstrates that induction of ER stress contributes to the mode of action of 3-AP and that terminal dimethylation leads to an even more pronounced manifestation of this effect.

GRP78-targeting subtilase cytotoxin sensitizes cancer cells to photodynamic therapy

Glucose-regulated protein 78 (GRP78) is an endoplasmic reticulum (ER)-resident chaperone and a major regulator of the unfolded protein response (UPR). Accumulating evidence indicate that GRP78 is overexpressed in many cancer cell lines, and contributes to the invasion and metastasis in many human tumors. Besides, GRP78 upregulation is detected in response to different ER stress-inducing anticancer therapies, including photodynamic therapy (PDT). This study demonstrates that GRP78 mRNA and protein levels are elevated in response to PDT in various cancer cell lines. Stable overexpression of GRP78 confers resistance to PDT substantiating its cytoprotective role. Moreover, GRP78-targeting subtilase cytotoxin catalytic subunit fused with epidermal growth factor (EGF-SubA) sensitizes various cancer cells to Photofrin-mediated PDT. The combination treatment is cytotoxic to apoptosis-competent SW-900 lung cancer cells, as well as to Bax-deficient and apoptosis-resistant DU-145 prostate cancer cells. In these cells, PDT and EGF-SubA cytotoxin induce protein kinase R-like ER kinase and inositol-requiring enzyme 1 branches of UPR and also increase the level of C/EBP (CCAAT/enhancer-binding protein) homologous protein, an ER stress-associated apoptosis-promoting transcription factor. Although some apoptotic events such as disruption of mitochondrial membrane and caspase activation are detected after PDT, there is no phosphatidylserine plasma membrane externalization or DNA fragmentation, suggesting that in DU-145 cells the late apoptotic events are missing. Moreover, in SW-900 cells, EGF-SubA cytotoxin potentiates PDT-mediated cell death but attenuates PDT-induced apoptosis. In addition, the cell death cannot be reversed by caspase inhibitor z-VAD, confirming that apoptosis is not a major cell death mode triggered by the combination therapy. Moreover, no typical features of necrotic or autophagic cell death are recognized. Instead, an extensive cellular vacuolation of ER origin is observed. Altogether, these findings indicate that PDT and GRP78-targeting cytotoxin treatment can efficiently kill cancer cells independent on their apoptotic competence and triggers an atypical, non-apoptotic cell death.

BiP negatively affects ricin transport

The AB plant toxin ricin binds both glycoproteins and glycolipids at the cell surface via its B subunit. After binding, ricin is endocytosed and then transported retrogradely through the Golgi to the endoplasmic reticulum (ER). In the ER, the A subunit is retrotranslocated to the cytosol in a chaperone-dependent process, which is not fully explored. Recently two separate siRNA screens have demonstrated that ER chaperones have implications for ricin toxicity. ER associated degradation (ERAD) involves translocation of misfolded proteins from ER to cytosol and it is conceivable that protein toxins exploit this pathway. The ER chaperone BiP is an important ER regulator and has been implicated in toxicity mediated by cholera and Shiga toxin. In this study, we have investigated the role of BiP in ricin translocation to the cytosol. We first show that overexpression of BiP inhibited ricin translocation and protected cells against the toxin. Furthermore, shRNA-mediated depletion of BiP enhanced toxin translocation resulting in increased cytotoxicity. BiP-dependent inhibition of ricin toxicity was independent of ER stress. Our findings suggest that in contrast to what was shown with the Shiga toxin, the presence of BiP does not facilitate, but rather inhibits the entry of ricin into the cytosol.

GRP78 from grass carp (Ctenopharyngodon idella) provides cytoplasm protection against thermal and Pb2+ stress

Glucose regulated protein (GRP) located in endoplasmic reticulum (ER) was a member of heat shock protein (Hsp) family. The protective mechanism adapted to ER stimuli was closely related to GRP. GRP78, known as BiP, was one of central regulator responded to stress in ER. Grass carp (Ctenopharyngodon idella) GRP78 (CiGRP78) was up-regulated in almost tissues, especially in liver, under heat shock (34 °C), cold stress (4 °C) or lead nitrate (0.25 mmol/L) stress. In order to understand the function of CiGRP78 in cellular protection, CiGRP78 ORF cDNA was inserted into the plasmid of pET-32a(+) or pEGFP-C1 respectively, then the recombinant plasmids were transformed or transfected into Escherichia coli cells, mouse myeloma cells (SP2/0) or grass carp kidney cells (CIK). In the cells, CiGRP78 was over-expressed following thermal, cold or Pb(2+) stress. Results showed that CiGRP78 not only contributed to protecting prokaryotic cells against thermal or cold extremes, but also played the same role in SP2/0 and CIK cells. After treatment with heat stress at 42 °C for 1 h, although the viability of the cells declined a lot, CIK cells with pEGFP-C1/CiGRP78 exhibited a higher survival rate (28%) than wild-type cells (7%) or cells with only pEGFP-C1 (5.1%). When the time lag extended to 2.5 h, the survival rates were 19%, 5.7%, 4.8% respectively. In addition, CiGRP78 would also provide a transient cytoplasm protection against Pb(2+) stress in a dose- and time-dependent manner. After treatment with lead nitrate at concentration of 10 μmol/L for 12 h, 24 h or 36 h, the survival rates of cells with pEGFP-C1 or wild-type cells were 46.7% or 46.7% (12 h), 25% or 22% (24 h), 10% or 11% (36 h) respectively. When the cells were treated with lead nitrate at the concentration of 25 μmol/L, the survival rates of cells with pEGFP-C1 or wild-type cells were 45.5% or 30% (12 h), 16.7% or 25% (24 h), 6.5% or 8% (36 h), respectively. CiGRP78 provided a distinct protection in CIK cells at the low concentration for 24 h. The survival rates of CIK cells with pEGFP-C1/CiGRP78 treated with lead nitrate at concentration of 10 μmol/L or 25 μmol/L were 65.9% or 58.8% respectively. When the cells were treated with lead nitrate at concentration of 50 μmol/L for 24 h, the survival rate of the CIK cells was only about 30%. If the process-time was extended to 36 h, CiGRP78 could not provide any cytoplasm protection for CIK cells.

Endoplasmic reticulum stress: its role in disease and novel prospects for therapy

The endoplasmic reticulum (ER) is a multifunctional organelle required for lipid biosynthesis, calcium storage, and protein folding and processing. A number of physiological and pathological conditions, as well as a variety of pharmacological agents, are able to disturb proper ER function and thereby cause ER stress, which severely impairs protein folding and therefore poses the risk of proteotoxicity. Specific triggers for ER stress include, for example, particular intracellular alterations (e.g., calcium or redox imbalances), certain microenvironmental conditions (e.g., hypoglycemia, hypoxia, and acidosis), high-fat and high-sugar diet, a variety of natural compounds (e.g., thapsigargin, tunicamycin, and geldanamycin), and several prescription drugs (e.g., bortezomib/Velcade, celecoxib/Celebrex, and nelfinavir/Viracept). The cell reacts to ER stress by initiating a defensive process, called the unfolded protein response (UPR), which is comprised of cellular mechanisms aimed at adaptation and safeguarding cellular survival or, in cases of excessively severe stress, at initiation of apoptosis and elimination of the faulty cell. In recent years, this dichotomic stress response system has been linked to several human diseases, and efforts are underway to develop approaches to exploit ER stress mechanisms for therapy. For example, obesity and type 2 diabetes have been linked to ER stress-induced failure of insulin-producing pancreatic beta cells, and current research efforts are aimed at developing drugs that ameliorate cellular stress and thereby protect beta cell function. Other studies seek to pharmacologically aggravate chronic ER stress in cancer cells in order to enhance apoptosis and achieve tumor cell death. In the following, these principles will be presented and discussed.

A peptidic unconjugated GRP78/BiP ligand modulates the unfolded protein response and induces prostate cancer cell death

The molecular chaperone GRP78/BiP is a key regulator of protein folding in the endoplasmic reticulum, and it plays a pivotal role in cancer cell survival and chemoresistance. Inhibition of its function has therefore been an important strategy for inhibiting tumor cell growth in cancer therapy. Previous efforts to achieve this goal have used peptides that bind to GRP78/BiP conjugated to pro-drugs or cell-death-inducing sequences. Here, we describe a peptide that induces prostate tumor cell death without the need of any conjugating sequences. This peptide is a sequence derived from the cochaperone Bag-1. We have shown that this sequence interacts with and inhibits the refolding activity of GRP78/BiP. Furthermore, we have demonstrated that it modulates the unfolded protein response in ER stress resulting in PARP and caspase-4 cleavage. Prostate cancer cells stably expressing this peptide showed reduced growth and increased apoptosis in in vivo xenograft tumor models. Amino acid substitutions that destroyed binding of the Bag-1 peptide to GRP78/BiP or downregulation of the expression of GRP78 compromised the inhibitory effect of this peptide. This sequence therefore represents a candidate lead peptide for anti-tumor therapy.

Prevention of Doxorubicin cardiopathic changes by a benzyl styryl sulfone in mice

Cardiac toxicity is a major limitation in the use of doxorubicin (and related anthracyclins). ON 1910.Na (Estybon, Rogersitib, or 1910), a substituted benzyl styryl sulfone, is equally active as doxorubicin against MCF-7 human mammary carcinoma xenografted into nude mice. 1910 augments the antitumor activity of doxorubicin when given simultaneously. Furthermore, when given in combination, 1910 protects against cardiac weight loss and against morphological damage to cardiac tissues. Doxorubicin induces inactivation of glucose response protein 78 (GRP78), a principal chaperone that serves as the master regulator of the unfolded protein response (UPR). Inactivated GRP78 leads to an increase in misfolded proteins, endoplasmic reticulum (ER) stress, activation of UPR sensors, and increased CHOP expression. 1910 prevents the inactivation of GRP78 by doxorubicin, and the combination, while more active against the tumor, protects against cardiac weight loss.

The regulatory mechanism of 4-phenylbutyric acid against ER stress-induced autophagy in human gingival fibroblasts

Endoplasmic reticulum (ER) stress is closely connected to autophagy. When cells are exposed to ER stress, cells exhibit enhanced protein degradation and form autophagosomes. In this study, we demonstrate that the chemical chaperone, 4-phenylbutyric acid (4-PBA), regulates ER stressinduced cell death and autophagy in human gingival fibroblasts. We found that 4-PBA protected cells against thapsigargin-induced apoptotic cell death but did not affect the reduced cell proliferation. ER stress induced by thapsigargin was alleviated by 4-PBA through the regulation of several ER stress-inducible, unfolded protein response related proteins including GRP78, GRP94, C/EBP homologous protein, phospho-eIF-2α, eIF-2α, phospho-JNK1 (p46) and phospho-JNK2/3 (p54), JNK1, IRE-1α, PERK, and sXBP-1. Compared with cells treated with thapsigargin alone, cells treated with both 4-PBA and thapsigargin showed lower levels of Beclin-1, LC-3II and autophagic vacuoles, indicating that 4-PBA also inhibited autophagy induced by ER stress. This study suggests that 4-PBA may be a potential therapeutic agent against ER stress-associated pathologic situations.

Prospective impact of 5-FU in the induction of endoplasmic reticulum stress, modulation of GRP78 expression and autophagy in Sk-Hep1 cells

Hepatocellular carcinoma (HCC) is one of the most aggressive malignant diseases and is highly resistant to conventional chemotherapy. Therefore, HCC requires more effective prevention and treatment strategies. 5-fluorouracil (5-FU) remains the most widely used chemotherapeutic drug for the treatment of gastrointestinal, breast, head and neck, and ovarian cancers. In pursuit of a novel effective strategy, we have evaluated the potential of 5-FU to promote endoplasmic reticulum (ER) stress and autophagy in Sk-Hep1 HCC cells. We found that 5-FU profoundly induces ER stress in Sk-Hep1 cells and upregulates p53 and activates CHOP/GADD153 and caspase-12. Activation of CHOP/GADD153 and caspase-12 promotes mitochondrial cell death in Sk-Hep1 cells followed by ER stress. Changes in calcium homeostasis and the protein folding machinery cause stress in the ER, leading to apoptotic cell death. Stress in the ER activates autophagy to remove the misfolded protein aggregates and recover from the stress environment. Our study demonstrates that 5-FU-induced ER stress suppresses autophagy and also downregulates GRP78 expression. Activation of autophagy followed by ER stress facilitates the cell survival response. Therefore, the inhibition of protective autophagy may provide a useful pharmacological target. Taken together, these results indicate that 5-FU-induced ER stress activates the mitochondrial apoptotic cell death pathway by downregulating GRP78 and protective autophagy proteins in Sk-Hep1 cells, raising the possibility of using 5-FU as a therapeutic agent to target human HCC.

A novel epidermal growth factor receptor variant lacking multiple domains directly activates transcription and is overexpressed in tumors

The epidermal growth factor receptor (EGFR) is essential to multiple physiological and neoplastic processes via signaling by its tyrosine kinase domain and subsequent activation of transcription factors. EGFR overexpression and alteration, including point mutations and structural variants, contribute to oncogenesis in many tumor types. In this study, we identified an in-frame splice variant of the EGFR called mini-LEEK (mLEEK) that is more broadly expressed than the EGFR and is overexpressed in several cancers. Unlike previously characterized EGFR variants, mLEEK lacks the extracytoplasmic, transmembrane and tyrosine kinase domains. mLEEK localizes in the nucleus and functions as a transcription factor to regulate target genes involved in the cellular response to endoplasmic reticulum (ER) stress, including the master regulator of the unfolded protein response (UPR) pathways, molecular chaperone GRP78/Bip. We demonstrated that mLEEK regulates GRP78 transcription through direct interaction with a cis-regulatory element within the gene promoter. Several UPR pathways were interrogated and mLEEK expression was found to attenuate the induction of all pathways upon ER stress. Conversely, knockdown of mLEEK resulted in caspase-mediated cell death and sensitization to ER stress. These findings indicate that mLEEK levels determine cellular responses to unfavorable conditions that cause ER stress. This information, along with the overexpression of mLEEK in tumors, suggests unique strategies for therapeutic intervention. Furthermore, the identification of mLEEK expands the known mechanisms by which the EGFR gene contributes to oncogenesis and represents the first link between two previously disparate areas in cancer cell biology: EGFR signaling and the UPR.

Liver-specific loss of glucose-regulated protein 78 perturbs the unfolded protein response and exacerbates a spectrum of liver diseases in mice

The endoplasmic reticulum (ER) chaperone protein glucose-regulated protein 78 (GRP78)/binding immunoglobulin protein is a master regulator of ER homeostasis and stress responses, which have been implicated in the pathogenesis of metabolic disorders. By applying the locus of X-over P1-cyclization recombination strategy, we generated mice with liver-specific GRP78 loss. Our studies using this novel mouse model revealed that liver GRP78 was required for neonatal survival, and a loss of GRP78 in the adult liver greater than 50% caused an ER stress response and dilation of the ER compartment, which was accompanied by the onset of apoptosis. This suggested the critical involvement of GRP78 in maintaining hepatocyte ER homeostasis and viability. Furthermore, these mice exhibited elevations of serum alanine aminotransferase and fat accumulation in the liver, and they were sensitized to a variety of acute and chronic hepatic disorders by alcohol, a high-fat diet, drugs, and toxins. These disorders were alleviated by the simultaneous administration of the molecular chaperone 4-phenylbutyrate. A microarray analysis and a two-dimensional protein profile revealed major perturbations of unfolded protein response targets, common enzymes/factors in lipogenesis, and new factors possibly contributing to liver steatosis or fibrosis under ER stress (e.g., major urinary proteins in the liver, fatty acid binding proteins, adipose differentiation-related protein, cysteine-rich with epidermal growth factor-like domains 2, nuclear protein 1, and growth differentiation factor 15).

CONCLUSION

Our findings underscore the importance of GRP78 in managing the physiological client protein load and suppressing apoptosis in hepatocytes, and they support the pathological role of ER stress in the evolution of fatty liver disease under adverse conditions (i.e., drugs, diet, toxins, and alcohol).

Vanadyl bisacetylacetonate protects β cells from palmitate-induced cell death through the unfolded protein response pathway

Endoplasmic reticulum (ER) stress induced by free fatty acids (FFA) is important to β-cell loss during the development of type 2 diabetes. To test whether vanadium compounds could influence ER stress and the responses in their mechanism of antidiabetic effects, we investigated the effects and the mechanism of vanadyl bisacetylacetonate [VO(acac)(2)] on β cells upon treatment with palmitate, a typical saturated FFA. The experimental results showed that VO(acac)(2) could enhance FFA-induced signaling pathways of unfolded protein responses by upregulating the prosurvival chaperone immunoglobulin heavy-chain binding protein/78-kDa glucose-regulated protein and downregulating the expression of apoptotic C/EBP homologous protein, and consequently the reduction of insulin synthesis. VO(acac)(2) also ameliorated FFA-disturbed Ca(2+) homeostasis in β cells. Overall, VO(acac)(2) enhanced stress adaption, thus protecting β cells from palmitate-induced apoptosis. This study provides some new insights into the mechanisms of antidiabetic vanadium compounds.

Peptide-binding heat shock protein GRP78 protects cardiomyocytes from hypoxia-induced apoptosis

Myocardial ischemia is a severe stress condition that causes extensive biochemical changes triggering cardiac cell death. The 78-kDa glucose-regulated protein (GRP78), a heat shock protein present in all cells and a widely used marker of endoplasmic reticulum stress, functions in controlling the structural maturation of nascent glycoproteins. However, GRP78 was also found to be expressed on the cell surface of several cells such as endothelial cells, macrophages, and tumor cells where it functions as a receptor for a variety of ligands in signaling pathways. Recently, we have identified peptides from two different sources that specifically bind GRP78 protein. We have shown that binding of these peptides to endothelial cell surface GRP78 resulted in angiogenesis. In this study, we first established the presence of cell surface GRP78 on cardiac myocytes. Analysis of cardiomyocytes under hypoxia determined the significant increase in cell surface GRP78 in addition to gene expression and total protein. Apoptosis that was significantly increased in cardiomyocytes under hypoxic conditions was inhibited by the presence of the peptide-binding GRP78 during hypoxia. Inhibition of apoptosis was mediated by the binding of the peptide to cardiomyocytes cell surface GRP78 resulting in blocking caspase-3/7 activation. Silencing GRP78 RNA that reduced GRP78 receptor abrogated the peptide activity. Apoptosis of cardiac cells induced by myocardial infarction in a mouse model was also significantly inhibited by the administration of the peptide to mouse hearts. Our findings may make ADoPep1 a useful therapeutic tool for relieving of ischemia.

Cannabinoid receptor 1 mediates palmitic acid-induced apoptosis via endoplasmic reticulum stress in human renal proximal tubular cells

The endocannabinoid system (ECS) is activated at the onset of obesity and diverse metabolic diseases. Endocannabinoids mediate their physiological and behavioral effects by activating specific cannabinoid receptors, mainly cannabinoid receptor 1 (CB(1)R). Diabetic nephropathy (DN) is induced by hyperlipidemia, and renal proximal tubule cells are an important site for the onset of DN. However, the pathophysiology of CB(1)R, especially in the hyperlipidemia of DN, has not been elucidated. Therefore, we examined the effect of palmitic acid (PA) on CB(1)R expression and its related signal pathways in human renal proximal tubular cells (HK-2 cells). PA significantly increased CB(1)R mRNA and protein levels and induced CB(1)R internalization. PA-induced activation of CB(1)R is prevented by the treatment of AACOCF(3) (a cPLA(2) inhibitor), indomethacin and NS398 (a COX 2 inhibitors). Indeed, PA increased cPLA(2), and COX-2 but not COX-1. We also investigated whether the PA-induced activation of CB(1)R is linked to apoptosis. As a result, AM251 (a CB(1)R antagonist) attenuated PA-mediated apoptosis in a concentration-dependent manner. Furthermore, PA decreased GRP78 expression and induced increases in the endoplasmic reticulum (ER) stress signaling pathways p-PERK, p-eIF2α, p-ATF4, and CHOP, which were blocked by AM251 treatment. Moreover, PA increased the Bax/Bcl-2 ratio, cleaved PARP, and caspase-3 levels. The PA-induced apoptotic effects were decreased with CB(1)R-specific antagonist (AM251) treatment and CB1 si-RNA transfection. In conclusion, PA induced apoptosis through ER stress via CB(1)R expression in human proximal tubule cells. Our results provide evidence that CB(1)R blockade may be a potential anti-diabetic therapy for the treatment of DN.

Androgens modulate autophagy and cell death via regulation of the endoplasmic reticulum chaperone glucose-regulated protein 78/BiP in prostate cancer cells

Pro-survival signalling mediated by the androgen receptor (AR) is implicated as a key contributor to prostate carcinogenesis. As prostate tumours are characterized by nutrient-poor, hypoxic and acidified microenvironments, one mechanism whereby AR signalling may contribute to survival is by promoting adaptation to cellular stress. Here we have identified a novel role for AR in the inhibition of autophagy induced by serum withdrawal. This blockade is attributed to AR-mediated upregulation of the endoplasmic reticulum (ER) chaperone glucose-regulated protein 78/BiP (Grp78/BiP), and occurs independently of ER stress response pathway activation. Interestingly, AR activation did not affect serum starvation-induced mammalian target of rapamycin inhibition, illustrating that the adaptive role for androgens lies not in the ability to modulate nutrient sensing, but in the promotion of ER stability. Finally, we show that the adaptive advantage conferred by AR-mediated Grp78/BiP upregulation is temporary, as upon chronic serum starvation, AR activation delayed but did not suppress the onset of autophagy and cell death. This study reveals a novel mechanism whereby maintained AR signalling promotes temporary adaptation to cellular stress and in turn may contribute to the evasion of prostate tumour cell death.

Modulation of the unfolded protein response in prostate cancer cells by antibody-directed against the carboxyl-terminal domain of GRP78

Receptor-recognized forms of alpha(2)-macroglobulin (alpha(2)M*) bind to cancer cell surface GRP78, which functions as a signaling receptor promoting proliferation and survival. Patients with prostate, ovary, and skin cancer may develop auto-antibodies to the alpha(2)M* binding site which are receptor agonists whose presence indicates a poor prognosis. By contrast, antibodies directed against the COOH-terminal domain of GPR78 (anti-CTD antibody), are antagonists which down regulate pro-proliferative signaling and upregulate p53. Unfolded protein response (UPR) signaling plays an important role in cell survival and proliferation as well as apoptosis. We, therefore, studied the effect of anti-CTD antibody on UPR signaling in 1-LN and DU-145 prostate cancer cells. Treatment of these cells, which express GRP78 on their cell surface, with this antibody significantly downregulated IRE1-alpha, PERK, and ATF6alpha-dependent UPR signaling. By contrast, the pro-apoptotic protein GADD153 was elevated. Anti-CTD antibody treatment also elevated apoptotic components, cleaved PARP-1, and Erdj5. In general, a two to threefold effect was observed for the parameters which were studied. These studies suggest that anti-CTD antibody induces growth inhibitory and pro-apoptotic effects by modulating UPR signaling in human prostate cancer cells.

The role of endoplasmic reticulum stress-related unfolded protein response in the radiocontrast medium-induced renal tubular cell injury

Contrast medium (CM) induces a direct toxic effect on renal tubular cells. This toxic effect may have a role in the pathophysiology of CM-induced nephropathy. CM has been shown to affect the endoplasmic reticulum (ER)-related capacity. Unfolded protein response (UPR) is known as a prosurvival response to reduce the accumulation of unfolded proteins and restore normal ER function. However, the role of ER stress-related UPR in the CM-induced renal cell injury still remains unclear. In this study, we examined whether UPR participates in urografin (an ionic CM)-induced renal tubular cells apoptosis. Treatment with urografin in normal rat renal tubular cell line (NRK52E) markedly increased cell apoptosis and decreased cell viability with a dose- and time-dependent manner. The cell necrosis was not increased in urografin-treated cells. Urografin also enhance the induction of ER stress-related markers in NRK52E cells, including glucose-regulated protein (GRP)78 and GRP94 expressions, procaspase-12 cleavage, phosphorylation of PERK (PKR [double-stranded RNA-activated protein kinase]-like ER kinase), and eukaryotic initiation factor 2alpha (eIF2alpha). Salubrinal, a selective inhibitor of eIF2alpha dephosphorylation, effectively decreased urografin-induced cell apoptosis. Furthermore, transfection of GRP78-small interfering RNA in NRK52E cells significantly enhanced urografin-induced cell apoptosis. These results suggest that GRP78/eIF2alpha-related signals play a protective role during UPR, and the activation of ER stress-related UPR may play an important regulative role in urografin-induced renal tubular injury.

Hyperoxia augments ER-stress-induced cell death independent of BiP loss

Cytotoxic reactive oxygen species are constantly formed as a by-product of aerobic respiration and are thought to contribute to aging and disease. Cells respond to oxidative stress by activating various pathways, whose balance is important for adaptation or induction of cell death. Our lab recently reported that BiP (GRP78), a proposed negative regulator of the unfolded protein response (UPR), declines during hyperoxia, a model of chronic oxidative stress. Here, we investigate whether exposure to hyperoxia, and consequent loss of BiP, activates the UPR or sensitizes cells to ER stress. Evidence is provided that hyperoxia does not activate the three ER stress receptors IRE1, PERK, and ATF6. Although hyperoxia alone did not activate the UPR, it sensitized cells to tunicamycin-induced cell death. Conversely, overexpression of BiP did not block hyperoxia-induced ROS production or increased sensitivity to tunicamycin. These findings demonstrate that hyperoxia and loss of BiP alone are insufficient to activate the UPR. However, hyperoxia can sensitize cells to toxicity from unfolded proteins, implying that chronic ROS, such as that seen throughout aging, could augment the UPR and, moreover, suggesting that the therapeutic use of hyperoxia may be detrimental for lung diseases associated with ER stress.