Gene Summary

Gene:ATF6; activating transcription factor 6
Aliases: ATF6A
Summary:This gene encodes a transcription factor that activates target genes for the unfolded protein response (UPR) during endoplasmic reticulum (ER) stress. Although it is a transcription factor, this protein is unusual in that it is synthesized as a transmembrane protein that is embedded in the ER. It functions as an ER stress sensor/transducer, and following ER stress-induced proteolysis, it functions as a nuclear transcription factor via a cis-acting ER stress response element (ERSE) that is present in the promoters of genes encoding ER chaperones. This protein has been identified as a survival factor for quiescent but not proliferative squamous carcinoma cells. There have been conflicting reports about the association of polymorphisms in this gene with diabetes in different populations, but another polymorphism has been associated with increased plasma cholesterol levels. This gene is also thought to be a potential therapeutic target for cystic fibrosis. [provided by RefSeq, Aug 2011]
Databases:OMIM, VEGA, HGNC, Ensembl, GeneCard, Gene
Protein:cyclic AMP-dependent transcription factor ATF-6 alpha
Source:NCBIAccessed: 25 June, 2015


What does this gene/protein do?
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Cancer Overview

Research Indicators

Publications Per Year (1990-2015)
Graph generated 25 June 2015 using data from PubMed using criteria.

Literature Analysis

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Tag cloud generated 25 June, 2015 using data from PubMed, MeSH and CancerIndex

Specific Cancers (5)

Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Latest Publications: ATF6 (cancer-related)

Armengol S, Arretxe E, Enzunza L, et al.
The promoter of cell growth- and RNA protection-associated SND1 gene is activated by endoplasmic reticulum stress in human hepatoma cells.
BMC Biochem. 2014; 15:25 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Staphyloccocal nuclease domain-containing protein 1 (SND1) is involved in the regulation of gene expression and RNA protection. While numerous studies have established that SND1 protein expression is modulated by cellular stresses associated with tumor growth, hypoxia, inflammation, heat-shock and oxidative conditions, little is known about the factors responsible for SND1 expression. Here, we have approached this question by analyzing the transcriptional response of human SND1 gene to pharmacological endoplasmic reticulum (ER) stress in liver cancer cells.
RESULTS: We provide first evidence that SND1 promoter activity is increased in human liver cancer cells upon exposure to thapsigargin or tunicamycin or by ectopic expression of ATF6, a crucial transcription factor in the unfolded protein response triggered by ER stress. Deletion analysis of the 5'-flanking region of SND1 promoter identified maximal activation in fragment (-934, +221), which contains most of the predicted ER stress response elements in proximal promoter. Quantitative real-time PCR revealed a near 3 fold increase in SND1 mRNA expression by either of the stress-inducers; whereas SND1 protein was maximally upregulated (3.4-fold) in cells exposed to tunicamycin, a protein glycosylation inhibitor.
CONCLUSION: Promoter activity of the cell growth- and RNA-protection associated SND1 gene is up-regulated by ER stress in human hepatoma cells.

Jiang X, Kanda T, Nakamoto S, et al.
Knockdown of glucose-regulated protein 78 enhances poly(ADP-ribose) polymerase cleavage in human pancreatic cancer cells exposed to endoplasmic reticulum stress.
Oncol Rep. 2014; 32(6):2343-8 [PubMed] Free Access to Full Article Related Publications
The present study examined the expression of glucose‑regulated protein 78 (GRP78/Bip) in human pancreatic cancer cell lines and the effect of knockdown of GRP78 on the cleavage of poly(ADP-ribose) polymerase (PARP). Human pancreatic cancer cell lines (KP-2, MIAPaCa-2, Panc-1 and SUIT-2), constitutively expressed GRP78. We also demonstrated that ER stress induced by thapsigargin upregulated protein levels of GRP78. In the presence of thapsigargin, knockdown of GRP78 enhanced the PARP cleavage in the human pancreatic cancer cells. These results provide evidence that GRP78 is a potential therapeutic target for 'difficult-to-treat' pancreatic cancer, in which ER stress signaling in part falls into disorder.

Gong J, Fang L, Liu R, et al.
UPR decreases CD226 ligand CD155 expression and sensitivity to NK cell-mediated cytotoxicity in hepatoma cells.
Eur J Immunol. 2014; 44(12):3758-67 [PubMed] Related Publications
NK cells play important roles in anti-tumor immunity. CD226 is a major NK-cell activating receptor, which transduces activating signals after binding ligands CD155 and CD112. Here, we demonstrated that activated unfolded protein response (UPR) attenuated the sensitivity of human hepatocellular carcinoma cell (HCC) to NK-cell cytotoxicity by decreasing the expression level of CD226 ligand CD155 in HCC. The decreased expression level of CD155 was due to the involvement of the activating transcription factor 6 (ATF6) and inositol-requiring enzyme 1α (IRE1α) pathways. In addition, the IRE1α pathway contributed to the increased expression level of the ER-associated degradation (ERAD)-related molecule HRD1 and facilitated the degradation of CD155. Moreover, we found that low levels of CD155 expression were significantly associated with poor prognosis in patients with HCC. Thus, our results provide molecular, cellular, and clinical evidence demonstrating a novel NK cell-associated immune evasion mechanism, and indicate that targeting this immune evasion pathway may be meaningful in treating patients with HCC.

Howarth DL, Lindtner C, Vacaru AM, et al.
Activating transcription factor 6 is necessary and sufficient for alcoholic fatty liver disease in zebrafish.
PLoS Genet. 2014; 10(5):e1004335 [PubMed] Free Access to Full Article Related Publications
Fatty liver disease (FLD) is characterized by lipid accumulation in hepatocytes and is accompanied by secretory pathway dysfunction, resulting in induction of the unfolded protein response (UPR). Activating transcription factor 6 (ATF6), one of three main UPR sensors, functions to both promote FLD during acute stress and reduce FLD during chronic stress. There is little mechanistic understanding of how ATF6, or any other UPR factor, regulates hepatic lipid metabolism to cause disease. We addressed this using zebrafish genetics and biochemical analyses and demonstrate that Atf6 is necessary and sufficient for FLD. atf6 transcription is significantly upregulated in the liver of zebrafish with alcoholic FLD and morpholino-mediated atf6 depletion significantly reduced steatosis incidence caused by alcohol. Moreover, overexpression of active, nuclear Atf6 (nAtf6) in hepatocytes caused FLD in the absence of stress. mRNA-Seq and qPCR analyses of livers from five day old nAtf6 transgenic larvae revealed upregulation of genes promoting glyceroneogenesis and fatty acid elongation, including fatty acid synthase (fasn), and nAtf6 overexpression in both zebrafish larvae and human hepatoma cells increased the incorporation of 14C-acetate into lipids. Srebp transcription factors are key regulators of lipogenic enzymes, but reducing Srebp activation by scap morpholino injection neither prevented FLD in nAtf6 transgenics nor synergized with atf6 knockdown to reduce alcohol-induced FLD. In contrast, fasn morpholino injection reduced FLD in nAtf6 transgenic larvae and synergistically interacted with atf6 to reduce alcoholic FLD. Thus, our data demonstrate that Atf6 is required for alcoholic FLD and epistatically interacts with fasn to cause this disease, suggesting triglyceride biogenesis as the mechanism of UPR induced FLD.

Kosakowska-Cholody T, Lin J, Srideshikan SM, et al.
HKH40A downregulates GRP78/BiP expression in cancer cells.
Cell Death Dis. 2014; 5:e1240 [PubMed] Free Access to Full Article Related Publications
HKH40A, the 8-methoxy analog of WMC79, is a synthetic agent with promising in vitro and in vivo antitumor activity, especially against solid tumors. However, molecular mechanisms underlying its antitumor effects are poorly understood. Here, we report that HKH40A markedly reduces the level of GRP78/BiP protein in cancer cell lines of various origin. In this study, we show that HKH40A not only downregulates transcription of GRP78 but also directly binds to the isolated protein and induces its proteosomal degradation. Knockdown of BiP increased the efficacy of the drug and overexpression of BiP diminished its activity. BiP is generally highly elevated in solid tumors having a pivotal role in cancer cell survival and chemoresistance, and has been suggested as a novel target for therapeutic intervention. We show that reduction of BiP level by HKH40A impairs its function and induces unfolded protein response as evidenced by the activation of IRE1α, ATF6 and PERK. This leads to a series of downstream events, including sustained eIF2α phosphorylation, increased abundance of spliced XBP1 mRNA and protein levels of ATF4 and CHOP. We also demonstrate that HKH40A inhibited tumor formation in an in vivo xenograft tumor model. Collectively, our data show that HKH40A reduces BiP levels and this could have an important role in the activity of HKH40A against cancer cells.

Lu JW, Liao CY, Yang WY, et al.
Overexpression of endothelin 1 triggers hepatocarcinogenesis in zebrafish and promotes cell proliferation and migration through the AKT pathway.
PLoS One. 2014; 9(1):e85318 [PubMed] Free Access to Full Article Related Publications
Hepatocarcinogenesis commonly involves the gradual progression from hepatitis to fibrosis and cirrhosis, and ultimately to hepatocellular carcinoma (HCC). Endothelin 1 (Edn1) has been identified as a gene that is significantly up-regulated in HBx-induced HCC in mice. In this study, we further investigated the role of edn1 in hepatocarcinogenesis using a transgenic zebrafish model and a cell culture system. Liver-specific edn1 expression caused steatosis, fibrosis, glycogen accumulation, bile duct dilation, hyperplasia, and HCC in zebrafish. Overexpression of EDN1 in 293T cells enhanced cell proliferation and cell migration in in vitro and xenotransplantation assays and was accompanied with up-regulation of several cell cycle/proliferation- and migration-specific genes. Furthermore, expression of the unfolded protein response (UPR) pathway-related mediators, such as spliced XBP1, ATF6, IRE1, and PERK, was also up-regulated at both the RNA and protein levels. In the presence of an EDN1 inhibitor or an AKT inhibitor, these increases were diminished and the EDN1-induced migration ability also was disappeared, suggesting that the EDN1 effects act through activation of the AKT pathway to enhance the UPR and subsequently activate the expression of downstream genes. Additionally, p-AKT is enhanced in the edn1 transgenic fish compared to the GFP-mCherry control. The micro RNA miR-1 was found to inhibit the expression of EDN1. We also observed an inverse correlation between EDN1 and miR-1 expression in HCC patients. In conclusion, our data suggest that EDN1 plays an important role in HCC progression by activating the PI3K/AKT pathway and is regulated by miR-1.

Trondl R, Flocke LS, Kowol CR, et al.
Triapine and a more potent dimethyl derivative induce endoplasmic reticulum stress in cancer cells.
Mol Pharmacol. 2014; 85(3):451-9 [PubMed] Related Publications
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.

Scaiewicz V, Nahmias A, Chung RT, et al.
CCAAT/enhancer-binding protein homologous (CHOP) protein promotes carcinogenesis in the DEN-induced hepatocellular carcinoma model.
PLoS One. 2013; 8(12):e81065 [PubMed] Free Access to Full Article Related Publications
BACKGROUND AND AIMS: C/EBP homologous protein (CHOP) plays pro-apoptotic roles in the integrated stress response. Recently, a tumor suppressive role for CHOP was demonstrated in lung cancer via regulation of tumor metabolism. To explore the role of CHOP in hepatocarcinogenesis, we induced hepatocellular carcinoma (HCC) in wild type (wt) and CHOP knockout (KO) mice using the carcinogen N-diethylnitrosamine (DEN).
RESULTS: Analysis of tumor development showed reduced tumor load, with markedly smaller tumor nodules in the CHOP KO animals, suggesting oncogenic roles of CHOP in carcinogen-induced HCC. In wt tumors, CHOP was exclusively expressed in tumor tissue, with minimal expression in normal parenchyma. Analysis of human adenocarcinomas of various origins demonstrated scattered expression of CHOP in the tumors, pointing to relevance in human pathology. Characterization of pathways that may contribute to preferential expression of CHOP in the tumor identified ATF6 as a potential candidate. ATF6, a key member of the endoplasmic reticulum stress signaling machinery, exhibited a similar pattern of expression as CHOP and strong activation in wt but not CHOP KO tumors. Because HCC is induced by chronic inflammation, we assessed whether CHOP deficiency affects tumor-immune system crosstalk. We found that the number of macrophages and levels of IFNγ and CCL4 mRNA were markedly reduced in tumors from CHOP KO relative to wt mice, suggesting a role for CHOP in modulating tumor microenvironment and macrophage recruitment to the tumor.
CONCLUSION: Our data highlights a role for CHOP as a positive regulator of carcinogen-induced HCC progression through a complex mechanism that involves the immune system and modulation of stress signaling pathways.

Wu X, Xin Z, Zhang W, et al.
A missense polymorphism in ATF6 gene is associated with susceptibility to hepatocellular carcinoma probably by altering ATF6 level.
Int J Cancer. 2014; 135(1):61-8 [PubMed] Related Publications
Accumulated evidences indicate that single nucleotide polymorphisms (SNP) are associated with risk of hepatocellular carcinoma (HCC). Activating transcription factor 6 (ATF6) is an important modulator of the unfolded protein response (UPR), which is regarded to be involved in carcinogenesis. So we speculate that SNPs in ATF6 may be associated with susceptibility to HCC. We carried out a two-stage association study in three independent case-control groups in a total of 1,082 chronic hepatitis B (CHB) patients and 816 hepatitis B virus (HBV) related HCC patients in Han Chinese. Four SNPs which can represent all potential functional SNPs with MAF > 0.1 recorded in HapMap database in ATF6 gene were genotyped using TaqMan methods. Functional analyses were conducted to verify the biological significances of the associated SNP. We identified a missense SNP (rs2070150) was significantly associated with susceptibility to HCC (p = 0.008, 0.001 and 0.007 in Beijing_302, Beijing_You'an and Guangxi samples, respectively). This SNP was further validated in four independent groups of major HBV outcomes, indicating it may associate exclusively to HCC. ATF6 mRNA expression was significantly decreased as the disease progressed (p <0.001). Functional analyses show that the protective allele of rs2070150 could significantly increase the expression levels of ATF6 mRNA, as well as ATF6 regulated genes such as GRP78, XBP1 and CHOP. These findings indicate that a common missense SNP in ATF6 may contribute to susceptibility of HCC functionally.

Lacunza E, Rabassa ME, Canzoneri R, et al.
Identification of signaling pathways modulated by RHBDD2 in breast cancer cells: a link to the unfolded protein response.
Cell Stress Chaperones. 2014; 19(3):379-88 [PubMed] Free Access to Full Article Related Publications
Rhomboid domain containing 2 (RHBDD2) was previously observed overexpressed and amplified in breast cancer samples. In order to identify biological pathways modulated by RHBDD2, gene expression profiles of RHBDD2 silenced breast cancer cells were analyzed using whole genome human microarray. Among the statistically significant overrepresented biological processes, we found protein metabolism—with the associated ontological terms folding , ubiquitination, and proteosomal degradation—cell death, cell cycle, and oxidative phosphorylation. In addition, we performed an in silico analysis searching for RHBDD2 co-expressed genes in several human tissues. Interestingly, the functional analysis of these genes showed similar results to those obtained with the microarray data, with negative regulation of protein metabolism and oxidative phosphorylation as the most enriched gene ontology terms. These data led us to hypothesize that RHBDD2 might be involved in endoplasmic reticulum (ER) stress response. Thus, we specifically analyzed the unfolding protein response (UPR) of the ER stress process. We used a lentivirus-based approach for stable silencing of RHBDD2 mRNA in the T47D breast cancer cell line, and we examined the transcriptional consequences on UPR genes as well as the phenotypic effects on migration and proliferation processes. By employing dithiothreitol as an UPR inducer, we observed that cells with silenced RHBDD2 showed increased expression of ATF6, IRE1, PERK, CRT, BiP, ATF4, and CHOP (p <0.01). We also observed that RHBDD2 silencing inhibited colony formation and decreased cell migration. Based on these studies, we hypothesize that RHBDD2 overexpression in breast cancer could represent an adaptive phenotype to the stressful tumor microenvironment by modulating the ER stress response.

Weiß N, Stegemann A, Elsayed MA, et al.
Inhibition of the prohormone convertase subtilisin-kexin isoenzyme-1 induces apoptosis in human melanoma cells.
J Invest Dermatol. 2014; 134(1):168-75 [PubMed] Related Publications
Prohormone convertases (PCs) are endoproteases that process many substrates in addition to hormone precursors. Although overexpression of PCs is linked to carcinogenesis in some solid tumors, the role of subtilisin-kexin isoenzyme-1 (SKI-1) in this context is unknown. We show that SKI-1 is constitutively expressed in human pigment cells with higher SKI activity in seven out of eight melanoma cell lines compared with normal melanocytes. SKI-1 immunoreactivity is also detectable in tumor cells of melanoma metastases. Moreover, tissue samples of the latter display higher SKI-1 mRNA levels and activity than normal skin. From various stimuli tested, 12-O-tetradecanoylphorbol-13-acetate and tunicamycin affected SKI-1 expression. Importantly, SKI-1 inhibition by the cell-permeable enzyme inhibitor decanoyl-RRLL-chloromethylketone (dec-RRLL-CMK) not only suppressed proliferation and metabolic activity of melanoma cells in vitro but also reduced tumor growth of melanoma cells injected intracutaneously into immunodeficient mice. Mechanistic studies revealed that dec-RRLL-CMK induces classical apoptosis of melanoma cells in vitro and affects expression of several SKI-1 target genes including activating transcription factor 6 (ATF6). However, ATF6 gene silencing does not result in apoptosis of melanoma cells, suggesting that dec-RRLL-CMK induces cell death in an ATF6-independent manner. Our findings encourage further studies on SKI-1 as a potential target for melanoma therapy.

Vaeteewoottacharn K, Kariya R, Matsuda K, et al.
Perturbation of proteasome function by bortezomib leading to ER stress-induced apoptotic cell death in cholangiocarcinoma.
J Cancer Res Clin Oncol. 2013; 139(9):1551-62 [PubMed] Related Publications
PURPOSE: Cholangiocarcinoma (CCA) or cancer of the biliary tract is heterogeneous; however, chronic inflammatory-related features are unique in CCA. Moreover, the genes involved in proteasome functions are evidently increased in CCA. Hence, CCA might be vulnerable to endoplasmic reticulum (ER) stressors, particularly a proteasome inhibitor. Therefore, bortezomib (BTZ), a specific 26S proteasome inhibitor, was selected, and its antitumor effects against CCA were investigated.
METHODS: Liver fluke-associated CCA cell lines were used. Cell proliferation and apoptosis detection were determined by a tetrazolium-based assay, caspase detection and annexin V binding assay. The accumulations of proteasome substrates, the inductions of ER stress and unfolded protein response (UPR) proteins were demonstrated by western blot and reporter systems. The in vivo anti-proliferative effect was accessed in a subcutaneous transplantation mouse model.
RESULTS: BTZ inhibited CCA proliferation and induced caspase-dependent apoptosis, independently of the NF-κB pathway. Inhibition of protein degradation by BTZ led to the induction of UPR; induction of XBP1 splicing, ATF6 proteolysis and nuclear ATF4 as well as BiP and CHOP expressions were evident. Nevertheless, ER stress-induced UPR was overwhelming, leading to the activation of apoptosis demonstrated by proteolytic cleavages of ER-related caspase 4 and 12 as well as classical caspase 8, 9 and 3. The growth inhibitory effect of BTZ was supported by an in vivo model.
CONCLUSION: BTZ treatment could be a promising therapeutic approach for CCA treatment.

Liu H, Kurtoglu M, Cao Y, et al.
Conversion of 2-deoxyglucose-induced growth inhibition to cell death in normoxic tumor cells.
Cancer Chemother Pharmacol. 2013; 72(1):251-62 [PubMed] Related Publications
BACKGROUND: Inhibition of glucose metabolism has recently become an attractive target for cancer treatment. Accordingly, since 2-deoxyglucose (2-DG) competes effectively with glucose, it has come under increasing scrutiny as a therapeutic agent. The initial response of tumor cells to 2-DG is growth inhibition, which is thought to conserve energy and consequently protect cells from its ATP-lowering effects as a glycolytic inhibitor. However, since 2-DG also mimics mannose and thereby interferes with N-linked glycosylation, the question is raised of how this sugar analog inhibits tumor cell growth and whether the mechanism by which it protects cells can be manipulated to convert 2-DG-induced growth inhibition to cell death.
METHODS: Cell growth and death were measured via counting viable and dead cells based on trypan blue exclusion. Markers of ATP reduction and the unfolded protein response (UPR) were detected by Western blot. Protein functions were manipulated through chemical compounds, siRNA and the use of gene-specific wild-type and knock-out mouse embryonic fibroblasts (MEFs).
RESULTS: At 2-DG concentrations that can be achieved in human plasma without causing significant side effects, we find (a) It induces growth inhibition predominantly by interference with glycosylation, which leads to accumulation of unfolded proteins in the endoplasmic reticulum activating the UPR; (b) Inhibition of PERK (but not ATF6 or IRE1), a major component of the UPR, leads to conversion of 2-DG-induced growth inhibition to cell death and (c) secondarily to PERK, inhibition of GCN2, a kinase that is activated in response to low intracellular glutamine, increases 2-DG's cytotoxic effects in PERK -/- MEFs.
CONCLUSIONS: Overall, these findings present a novel anticancer strategy that can be translated into therapeutic gain as they uncover the metabolic target PERK, and to a lesser degree GCN2, that when inhibited convert 2-DG's static effect to a toxic one in tumor cells growing under normoxia.

Déry MA, Jodoin J, Ursini-Siegel J, et al.
Endoplasmic reticulum stress induces PRNP prion protein gene expression in breast cancer.
Breast Cancer Res. 2013; 15(2):R22 [PubMed] Free Access to Full Article Related Publications
INTRODUCTION: High prion protein (PrP) levels are associated with breast, colon and gastric cancer resistance to treatment and with a poor prognosis for the patients. However, little is known about the underlying molecular mechanism(s) regulating human PrP gene (PRNP) expression in cancers. Because endoplasmic reticulum (ER) stress is associated with solid tumors, we investigated a possible regulation of PRNP gene expression by ER stress.
METHODS: Published microarray databases of breast cancer tissues and breast carcinoma cell lines were analyzed for PrP mRNA and ER stress marker immunoglobulin heavy chain binding protein (BiP) levels. Breast cancer tissue microarrays (TMA) were immunostained for BiP and PrP. Breast carcinoma MCF-7, MDA-MB-231, HS578T and HCC1500 cells were treated with three different ER stressors - Brefeldin A, Tunicamycin, Thapsigargin - and levels of PrP mRNA or protein assessed by RT-PCR and Western blot analyses. A human PRNP promoter-luciferase reporter was used to assess transcriptional activation by ER stressors. Site-directed mutagenesis identified the ER stress response elements (ERSE). Chromatin immunoprecipitation (ChIP) analyses were done to identify the ER stress-mediated transcriptional regulators. The role of cleaved activating transcription factor 6α (ΔATF6α) and spliced X-box protein-1 (sXBP1) in PRNP gene expression was assessed with over-expression or silencing techniques. The role of PrP protection against ER stress was assessed with PrP siRNA and by using Prnp null cell lines.
RESULTS: We find that mRNA levels of BiP correlated with PrP transcript levels in breast cancer tissues and breast carcinoma cell lines. PrP mRNA levels were enriched in the basal subtype and were associated with poor prognosis in breast cancer patients. Higher PrP and BiP levels correlated with increasing tumor grade in TMA. ER stress was a positive regulator of PRNP gene transcription in MCF-7 cells and luciferase reporter assays identified one ER stress response element (ERSE) conserved among primates and rodents and three primate-specific ERSEs that regulated PRNP gene expression. Among the various transactivators of the ER stress-regulated unfolded protein response (UPR), ATF6α and XBP1 transactivated PRNP gene expression, but the ability of these varied in different cell types. Functionally, PrP delayed ER stress-induced cell death.
CONCLUSIONS: These results establish PRNP as a novel ER stress-regulated gene that could increase survival in breast cancers.

Vellanki RN, Zhang L, Volchuk A
OASIS/CREB3L1 is induced by endoplasmic reticulum stress in human glioma cell lines and contributes to the unfolded protein response, extracellular matrix production and cell migration.
PLoS One. 2013; 8(1):e54060 [PubMed] Free Access to Full Article Related Publications
OASIS is a transcription factor similar to ATF6 that is activated by endoplasmic reticulum stress. In this study we investigated the expression of OASIS in human glioma cell lines and the effect of OASIS knock-down on the ER stress response and cell migration. OASIS mRNA was detected in three distinct glioma cell lines (U373, A172 and U87) and expression levels were increased upon treatment with ER stress-inducing compounds in the U373 and U87 lines. OASIS protein, which is glycosylated on Asn-513, was detected in the U373 and U87 glioma lines at low levels in control cells and protein expression was induced by ER stress. Knock-down of OASIS in human glioma cell lines resulted in an attenuated unfolded protein response to ER stress (reduced GRP78/BiP and GRP94 induction) and decreased expression of chondroitin sulfate proteoglycan extracellular matrix proteins, but induction of the collagen gene Col1a1 was unaffected. Cells in which OASIS was knocked-down exhibited altered cell morphology and reduced cell migration. These results suggest that OASIS is important for the ER stress response and maintenance of some extracellular matrix proteins in human glioma cells.

Tsai HY, Yang YF, Wu AT, et al.
Endoplasmic reticulum ribosome-binding protein 1 (RRBP1) overexpression is frequently found in lung cancer patients and alleviates intracellular stress-induced apoptosis through the enhancement of GRP78.
Oncogene. 2013; 32(41):4921-31 [PubMed] Related Publications
Lung cancer is the leading cause of cancer deaths and is the most occurring malignancy worldwide. Unraveling the molecular mechanisms involved in lung tumorigenesis will greatly improve therapy. During early tumorigenesis, rapid proliferating tumor cells require increased activity of endoplasmic reticulum (ER) for protein synthesis, folding and secretion, thereby are subjected to ER stress. Ribosome-binding protein 1 (RRBP1) was originally identified as a ribosome-binding protein located on the rough ER and associated with unfolding protein response (UPR). In this report, we investigated the role of RRBP1 in lung cancer. RRBP1 was highly expressed in lung cancer tissue, as compared with adjacent normal tissues as assessed by immunohistochemistry (IHC) using lung cancer tissue array (n=87). Knockdown of RRBP1 by short-hairpin RNAs caused ER stress and significantly reduced cell viability and tumorigenicity. This effect was associated with a significant reduction in the expression of glucose-regulated protein 78 (GRP78). UPR regulator GRP78, an anti-apoptotic protein that is widely upregulated in cancer, has a critical role in chemotherapy resistance in some cancers. According to our results, cells with a higher level of RRBP1 were more resistant to ER stress. Ectopic expression of RRBP1 alleviated apoptosis that was induced by the ER-stress agent tunicamycin, 2-deoxy-D-glucose (2DG) or doxorubicin via enhancing GRP78 protein expression. A strong correlation was observed between the expression of RRBP1 and GRP78 in tumor biopsies using the database GSE10072. Our results also indicated that RRBP1 may involve in the regulation of mRNA stability of UPR components including ATF6 and GRP78. Taken together, RRBP1 could alleviate ER stress and help cancer cell survive. RRBP1 is critical for tumor cell survival, which may make it a useful target in lung cancer treatment and a candidate for the development of new targeted therapeutics.

Pan MY, Shen YC, Lu CH, et al.
Prodigiosin activates endoplasmic reticulum stress cell death pathway in human breast carcinoma cell lines.
Toxicol Appl Pharmacol. 2012; 265(3):325-34 [PubMed] Related Publications
Prodigiosin is a bacterial tripyrrole pigment with potent cytotoxicity against diverse human cancer cell lines. Endoplasmic reticulum (ER) stress is initiated by accumulation of unfolded or misfolded proteins in the ER lumen and may induce cell death when irremediable. In this study, the role of ER stress in prodigiosin-induced cytotoxicity was elucidated for the first time. Comparable to the ER stress inducer thapsigargin, prodigiosin up-regulated signature ER stress markers GRP78 and CHOP in addition to activating the IRE1, PERK and ATF6 branches of the unfolded protein response (UPR) in multiple human breast carcinoma cell lines, confirming prodigiosin as an ER stress inducer. Prodigiosin transcriptionally up-regulated CHOP, as evidenced by its promoting effect on the CHOP promoter activity. Of note, knockdown of CHOP effectively lowered prodigiosin's capacity to evoke PARP cleavage, reduce cell viability and suppress colony formation, highlighting an essential role of CHOP in prodigiosin-induced cytotoxic ER stress response. In addition, prodigiosin down-regulated BCL2 in a CHOP-dependent manner. Importantly, restoration of BCL2 expression blocked prodigiosin-induced PARP cleavage and greatly enhanced the survival of prodigiosin-treated cells, suggesting that CHOP-dependent BCL2 suppression mediates prodigiosin-elicited cell death. Moreover, pharmacological inhibition of JNK by SP600125 or dominant-negative blockade of PERK-mediated eIF2α phosphorylation impaired prodigiosin-induced CHOP up-regulation and PARP cleavage. Collectively, these results identified ER stress-mediated cell death as a mode-of-action of prodigiosin's tumoricidal effect. Mechanistically, prodigiosin engages the IRE1-JNK and PERK-eIF2α branches of the UPR signaling to up-regulate CHOP, which in turn mediates BCL2 suppression to induce cell death.

Booth L, Cazanave SC, Hamed HA, et al.
OSU-03012 suppresses GRP78/BiP expression that causes PERK-dependent increases in tumor cell killing.
Cancer Biol Ther. 2012; 13(4):224-36 [PubMed] Free Access to Full Article Related Publications
We have further defined mechanism(s) by which the drug OSU-03012 (OSU) kills tumor cells. OSU lethality was suppressed by knock down of PERK and enhanced by knock down of ATF6 and IRE1α. OSU treatment suppressed expression of the chaperone, BiP/GRP78, and did so through reduced stability of the protein. Knock down of BiP/GRP78 further enhanced OSU lethality. Overexpression of BiP/GRP78 abolished OSU toxicity. Pre-treatment of cells with OSU enhanced radiosensitivity to a greater extent than concomitant or sequential drug treatment with radiation exposure. Expression of a mutant active p110 PI3K, or mutant active forms of the EGFR in GBM cells did not differentially suppress OSU killing. In contrast loss of PTEN function reduced OSU lethality, without altering AKT, p70 S6K or mTOR activity, or the drug's ability to radiosensitize GBM cells. Knock down of PTEN protected cells from OSU and radiation treatment whereas re-expression of PTEN facilitated drug lethality and radiosensitization. In a dose-dependent fashion OSU prolonged the survival of mice carrying GBM tumors and interacted with radiotherapy to further prolong survival. Collectively, our data show that reduced BiP/GRP78 levels play a key role in OSU-3012 toxicity in GBM cells, and that this drug has in vivo activity against an invasive primary human GBM isolate.

Teodoro T, Odisho T, Sidorova E, Volchuk A
Pancreatic β-cells depend on basal expression of active ATF6α-p50 for cell survival even under nonstress conditions.
Am J Physiol Cell Physiol. 2012; 302(7):C992-1003 [PubMed] Related Publications
Activating transcription factor 6 (ATF6) is one of three principle endoplasmic reticulum (ER) stress response proteins and becomes activated when ER homeostasis is perturbed. ATF6 functions to increase ER capacity by stimulating transcription of ER-resident chaperone genes such as GRP78. Using an antibody that recognizes active ATF6α-p50, we found that active ATF6α was detected in insulinoma cells and rodent islets even under basal conditions and the levels were further increased by ER stress. To examine the function of ATF6α-p50, we depleted endogenous ATF6α-p50 levels using small interfering RNA in insulinoma cells. Knockdown of endogenous ATF6α-p50 levels by ∼60% resulted in a reduction in the steady-state levels of GRP78 mRNA and protein levels in nonstressed cells. Furthermore, ATF6α knockdown resulted in an apoptotic phenotype. We hypothesized that removal of the ATF6α branch of the unfolded protein response (UPR) would result in ER stress. However, neither the PKR-like endoplasmic reticulum kinase (PERK), nor the inositol requiring enzyme 1 (IRE1) pathways of the UPR were significantly activated in ATF6α knockdown cells, although these cells were more sensitive to ER stress-inducing compounds. Interestingly, phosphorylation of JNK, p38, and c-Jun were elevated in ATF6α knockdown cells and inhibition of JNK or p38 kinases prevented apoptosis. These results suggest that ATF6α may have a role in maintaining β-cell survival even in the absence of ER stress.

Rzymski T, Petry A, Kračun D, et al.
The unfolded protein response controls induction and activation of ADAM17/TACE by severe hypoxia and ER stress.
Oncogene. 2012; 31(31):3621-34 [PubMed] Related Publications
The family of ADAM (a disintegrin and metalloproteinase) proteins has been implicated in tumor initiation and progression. ADAM17/tumor necrosis factor-α (TNFα)-converting enzyme (TACE) has been initially recognized to release TNFα as well as its receptors (TNFRs) from the membrane. ADAM17, TNFα and TNFR have been found upregulated in cancer patients, although the underlying mechanisms remain largely unknown. As hypoxia is a hallmark of cancer that can lead to severe stress conditions accumulating in endoplasmic reticulum (ER) stress and the unfolded protein response (UPR), we investigated the role of these stress conditions in the regulation of ADAM17 and release of TNFR1.We found that severe hypoxia induced ADAM17 expression and activity. Although hypoxia-inducible factor 1α (HIF1α) was important to maintain basal ADAM17 mRNA levels during moderate hypoxia, it was not sufficient to induce ADAM17 levels under severe hypoxia. Instead, we found that ADAM17 induction by severe hypoxia can be mimicked by ER stressors such as Thapsigargin and occurs as a consequence of the activation of the PERK/eIF2α/ATF4 and activating transcription factor 6 (ATF6) arms of UPR in several tumor cell lines. ADAM17 expression was also increased in xenografts displaying ER stress because of treatment with the vascular endothelial growth factor (VEGF) inhibitory antibody Bevacizumab. Additionally, severe hypoxia and ER stress activated ADAM17 and ectodomain shedding of TNFR1 involving mitogen-activated protein (MAP) kinases and reactive oxygen species (ROS). Collectively, these results show that ADAM17 is a novel UPR-regulated gene in response to severe hypoxia and ER stress, which is actively involved in the release of TNFR1 under these conditions. These data provide a novel link between severe hypoxic stress conditions and inflammation in the tumor environment.

Michallet AS, Mondiere P, Taillardet M, et al.
Compromising the unfolded protein response induces autophagy-mediated cell death in multiple myeloma cells.
PLoS One. 2011; 6(10):e25820 [PubMed] Free Access to Full Article Related Publications
OBJECTIVE: To determine whether the Unfolded Protein Response (UPR) sensors (PERK, ATF6 and IRE-1) can be targeted to promote death of Multiple Myeloma (MM) cells.
METHODS: We have knocked-down separately each UPR stress sensor in human MM cell lines using RNA interference and followed MM cell death by monitoring the membrane, mitochondrial and nuclear alterations. Involvement of caspases in MM cell death consecutive to UPR sensor knock-down was analyzed by western blotting, measurement of their enzymatic activity using fluorigenic substrates and susceptibility to a pan-caspase inhibitor. Activation of the autophagic process was measured directly by detection of autophagosomes (electronic microscopy), monodansylcadaverine staining, production of the cleaved form of the microtubule-associated protein 1A/1B light chain 3 (LC3) and indirectly by analyzing the impact of pharmacological inhibitors of autophagy such as 3MA and bafilomycin A1.
RESULTS: We show that extinction of a single UPR stress sensor (PERK) induces a non-apoptotic form of cell death in MM cells that requires autophagy for its execution. We also show that this cytotoxic autophagic process represses the apoptosis program by reducing the cytosolic release of the apoptogenic factors Smac/DIABLO and cytochrome c.
INTERPRETATION: Altogether our findings suggest that autophagy can contribute to execution of death in mammalian cells that are exposed to mild ER stress. They also suggest that the autophagic process can regulate the intrinsic apoptotic pathway by inhibiting production of death effectors by the mitochondria, thus preventing formation of a functional apoptosome. Altogether these findings give credit to the idea that UPR sensors can be envisaged as therapeutic targets for the treatment of MM.

Lundemo AG, Pettersen CH, Berge K, et al.
Tetradecylthioacetic acid inhibits proliferation of human SW620 colon cancer cells--gene expression profiling implies endoplasmic reticulum stress.
Lipids Health Dis. 2011; 10:190 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Previous reports have shown an antiproliferative effect of the synthetic, 3-thia fatty acid tetradecylthioacetic acid (TTA) on different cancer cells in vitro and in vivo. The mechanisms behind the observed effects are poorly understood. We therefore wanted to explore the molecular mechanisms involved in TTA-induced growth inhibition of the human colon cancer cell line SW620 by gene expression profiling.
METHODS: An antiproliferative effect of TTA on SW620 cells in vitro was displayed in real time using the xCELLigence System (Roche). Affymetrix gene expression profiling was performed to elucidate the molecular mechanisms behind the antiproliferative effect of TTA. Changes in gene expression were verified at protein level by western blotting.
RESULTS: TTA reduced SW620 cell growth, measured as baseline cell index, by 35% and 55% after 48 h and 72 h, respectively. We show for the first time that TTA induces an endoplasmic reticulum (ER) stress response in cancer cells. Gene expression analysis revealed changes related to ER stress and unfolded protein response (UPR). This was verified at protein level by phosphorylation of eukaryote translation initiation factor 2 alpha (eIF2α) and downstream up-regulation of activating transcription factor 4 (ATF4). Transcripts for positive and negative cell cycle regulators were down- and up-regulated, respectively. This, together with a down-regulation of Cyclin D1 at protein level, indicates inhibition of cell cycle progression. TTA also affected transcripts involved in calcium homeostasis. Moreover, mRNA and protein level of the ER stress inducible C/EBP-homologous protein (CHOP), Tribbles homolog 3 (Drosophila) (TRIB3) and CCAAT/enhancer binding protein beta (C/EBPβ) were enhanced, and the C/EBPβ LIP/LAP ratio was significantly increased. These results indicate prolonged ER stress and a possible link to induction of cell death.
CONCLUSION: We find that TTA-induced growth inhibition of SW620 cells seems to be mediated through induction of ER stress and activation of the UPR pathway.

Ruan Q, Han S, Jiang WG, et al.
αB-crystallin, an effector of unfolded protein response, confers anti-VEGF resistance to breast cancer via maintenance of intracrine VEGF in endothelial cells.
Mol Cancer Res. 2011; 9(12):1632-43 [PubMed] Free Access to Full Article Related Publications
Effective inhibition of angiogenesis targeting the tumor endothelial cells requires identification of key cellular and molecular mechanisms associated with survival of vasculatures within the tumor microenvironment. Intracellular autocrine (intracrine) VEGF production by endothelial cells plays a critical role on the vasculature homeostasis. In vitro breast cancer cell-stimulated activation of the unfolded protein response (UPR) of the endothelial cells contributes to maintenance of the intracrine VEGF levels in the endothelial cells through the upregulation of a previous undescribed downstream effector- αB-crystallin (CRYAB). siRNA-mediated knockdown of two major UPR proteins-inositol requiring kinase 1 and ATF6, led to attenuated CRYAB expression of the endothelial cells. Finally, inhibition of CRYAB blocked the breast cancer cell-stimulated increase in the endogenous VEGF levels of the endothelial cells. A VEGF limited proteolysis assay further revealed that CRYAB protected VEGF for proteolytic degradation. Here, we report that the molecular chaperone-CRYAB was significantly increased and colocalized with tumor vessels in a breast cancer xenograft. Specifically, neutralization of VEGF induced higher levels of CRYAB expression in the endothelial cells cocultured with MDA-MB-231 or the breast cancer xenograft with a significant survival benefit. However, knockdown of CRYAB had a greater inhibitory effect on endothelial survival. These findings underscore the importance of defining a role for intracrine VEGF signaling in sustaining aberrant tumor angiogenesis and strongly implicate UPR/CRYAB as dichotomous parts of a crucial regulation pathway for maintaining intracrine VEGF signaling.

Tang L, Zhang Y, Jiang Y, et al.
Dietary wolfberry ameliorates retinal structure abnormalities in db/db mice at the early stage of diabetes.
Exp Biol Med (Maywood). 2011; 236(9):1051-63 [PubMed] Free Access to Full Article Related Publications
Hyperglycemia-linked oxidative stress and/or consequent endoplasmic reticulum (ER) stress are the causative factors of pathogenesis of diabetic retinopathy. Dietary bioactive components which mitigate oxidative stress may serve as potential chemopreventive agents to prevent or slow down the disease progression. Wolfberry is a traditional Asian fruit consumed for years to prevent aging eye diseases in Asian countries. Here we report that dietary wolfberry ameliorated mouse retinal abnormality at the early stage of type 2 diabetes in db/db mice. Male mice at six weeks of age were fed the control diet with or without 1% (kcal) wolfberry for eight weeks. Dietary wolfberry restored the thickness of the whole retina, in particular the inner nuclear layer and photoreceptor layer, and the integrity of the retinal pigment epithelia (RPE), and the ganglion cell number in db/db mice. Western blotting of whole retinal cell lysates revealed that addition of wolfberry lowered expression of ER stress biomarkers binding immunoglobulin protein (BiP), protein kinase RNA-like ER kinase (PERK), activating transcription factor 6 (ATF6) and caspase-12, and restored AMP-activated protein kinase (AMPK), thioredoxin, Mn superoxide dismutase (Mn SOD) and forkhead O transcription factor 3 α (FOXO3α) activities. To determine if our observations were due to the high contents of zeaxanthin and lutein in wolfberry, additional studies using these carotenoids were conducted. Using the human adult diploid RPE cell line ARPE-19, we demonstrated that both zeaxanthin and lutein could mimic the wolfberry preventive effect on activation of AMPK, thioredoxin, Mn SOD, FOXO3α activities, normalize cellular reactive oxygen species and attenuate ER stress in ARPE-19 cells exposed to a high glucose challenge. The zeaxanthin preventive effect was abolished by small interfering RNA knockdown of AMPKα. These results suggested that AMPK activation appeared to play a key role in upregulated expression of thioredoxin and Mn SOD, and mitigation of cellular oxidative stress and/or ER stress by wolfberry and zeaxanthin and/or lutein. Taken together, dietary wolfberry on retinal protection in diabetic mice is, at least partially, due to zeaxanthin and/or lutein.

Ravanan P, Sano R, Talwar P, et al.
Synthetic triterpenoid cyano enone of methyl boswellate activates intrinsic, extrinsic, and endoplasmic reticulum stress cell death pathways in tumor cell lines.
Mol Cancer Ther. 2011; 10(9):1635-43 [PubMed] Free Access to Full Article Related Publications
We explored the effect of a novel synthetic triterpenoid compound cyano enone of methyl boswellates (CEMB) on various prostate cancer and glioma cancer cell lines. CEMB displayed concentration-dependent cytotoxic activity with submicromolar lethal dose 50% (LD(50)) values in 10 of 10 tumor cell lines tested. CEMB-induced cytotoxicity is accompanied by activation of downstream effector caspases (caspases 3 and 7) and by upstream initiator caspases involved in both the extrinsic (caspase 8) and intrinsic (caspase 9) apoptotic pathways. By using short interfering RNAs (siRNA), we show evidence that knockdown of caspase 8, DR4, Apaf-1, and Bid impairs CEMB-induced cell death. Similar to other proapoptotic synthetic triterpenoid compounds, CEMB-induced apoptosis involved endoplasmic reticulum stress, as shown by partial rescue of tumor cells by siRNA-mediated knockdown of expression of genes involved in the unfolded protein response such as IRE1α, PERK, and ATF6. Altogether, our results suggest that CEMB stimulates several apoptotic pathways in cancer cells, suggesting that this compound should be evaluated further as a potential agent for cancer therapy.

Shirley CM, Chen J, Shamay M, et al.
Bortezomib induction of C/EBPβ mediates Epstein-Barr virus lytic activation in Burkitt lymphoma.
Blood. 2011; 117(23):6297-303 [PubMed] Free Access to Full Article Related Publications
Epstein-Barr virus (EBV) is associated with a variety of lymphoid malignancies. Bortezomib activates EBV lytic gene expression. Bortezomib, a proteasome inhibitor, leads to increased levels of CCAAT/enhancer-binding proteinβ (C/EBPβ) in a variety of tumor cell lines. C/EBPβ activates the promoter of the EBV lytic switch gene ZTA. Bortezomib treatment leads to increased binding of C/EBP to previously recognized binding sites in the ZTA promoter. Knockdown of C/EBPβ inhibits bortezomib activation of EBV lytic gene expression. Bortezomib also induces the unfolded protein response (UPR), as evidenced by increases in ATF4, CHOP10, and XBP1s and cleavage of ATF6. Thapsigargin, an inducer of the UPR that does not interfere with proteasome function, also induces EBV lytic gene expression. The effects of thapsigargin on EBV lytic gene expression are also inhibited by C/EBPβ knock-down. Therefore, C/EBPβ mediates the activation of EBV lytic gene expression associated with bortezomib and another UPR inducer.

Schardt JA, Mueller BU, Pabst T
Activation of the unfolded protein response in human acute myeloid leukemia.
Methods Enzymol. 2011; 489:227-43 [PubMed] Related Publications
There is accumulating evidence for the involvement of the unfolded protein response (UPR) in the pathogenesis of many tumor types in humans. This is particularly the case in rapidly growing solid tumors in which the demand for oxygen and nutrients can exceed the supply until new tumor-initiated blood vessels are formed. In contrast, the role of the UPR during leukemogenesis remains largely unknown. Acute myeloid leukemia (AML) is a genetically heterogeneous clonal disorder characterized by the accumulation of somatic mutations in hematopoietic progenitor cells that alter the physiological regulation of self-renewal, survival, proliferation, or differentiation. The CCAAT/enhancer-binding protein alpha (CEBPA) gene is a key myeloid transcription factor and a frequent target for disruption in AML. In particular, translation of CEBPA mRNA can be specifically blocked by binding of the chaperone calreticulin (CALR), a well-established effector of the UPR, to a stem loop structure within the 5' region of the CEBPA mRNA. The relevance of this mechanism was first elucidated in certain AML subtypes carrying the gene rearrangements t(3;21) or inv(16). In our recent work, we could demonstrate the induction of key effectors of the UPR in leukemic cells of AML patients comprising all subtypes (according to the French-American-British (FAB) classification for human AML). The formation of the spliced variant of the X-box binding protein (XBP1s) was detectable in 17.4% (17 of 105) of AML patients. Consistent with an activated UPR, this group had significantly increased expression of the UPR target genes CALR, the 78 kDa glucose-regulated protein (GRP78), and the CCAAT/enhancer-binding protein homologous protein (CHOP). Consistently, in vitro studies confirmed that calreticulin expression was upregulated via activation of the ATF6 pathway in myeloid leukemic cells. As a consequence, CEBPA protein expression was inhibited in vitro as well as in leukemic cells from patients with activated UPR. We therefore propose a model of the UPR being involved in leukemogenesis through induction of calreticulin along the ATF6 pathway, thereby ultimately suppressing CEBPA translation and contributing to the block in myeloid differentiation and cell-cycle deregulation which represent key features of the leukemic phenotype. From a more clinical point of view, the presence of activated UPR in AML patient samples was found to be associated with a favorable disease course.

Zhang XQ, Yang Z, Benedict WF
Direct gene transfer of adenoviral-mediated interferon α into human bladder cancer cells but not the bystander factors produced induces endoplasmic reticulum stress-related cytotoxicity.
Cancer Gene Ther. 2011; 18(4):260-4 [PubMed] Free Access to Full Article Related Publications
We have previously shown that adenoviral-mediated interferon α (Ad-IFNα) is cytotoxic both to cells that are sensitive to recombinant interferon α (IFNα) and to cells which are resistant to IFNα. The cancer cell-specific cytotoxic effects of Ad-IFNα involve three different mechanisms: 1. The direct effect of IFNα production causing cancer cell death in IFNα sensitive cells (1); 2. The direct effect of Ad-IFNα infection and high levels of IFNα expression in IFNα resistant cancer cells (2); and 3. The indirect effect of the Ad-IFNα bystander factors produced (2-4). After Ad-IFNα infection, the cells produce a large amount of perinuclear localized IFN protein. This protein over-load could be a major factor in the direct cancer cell death of those cells infected with Ad-IFNα compared with the indirect cytotoxic effects of the bystander factors produced. Here, we investigated whether a component of Ad-IFN-induced cell death involves protein overload-induced endoplasmic reticulum (ER) stress, using an IFNα-resistant human bladder cancer cell line (KU7), and the normal human urothelial cell line, TERT-NHUC, as preclinical models. We found that the two ER stress response pathways examined were activated in KU7 cells. In contrast, following treatment of the normal TERT-NHUC cells with Ad-IFNα, no ER stress signals were observed. In addition, no ER stress related changes were seen, when KU7 cells were exposed to conditioned medium from Ad-IFNα-treated KU7 cells, indicating that bystander produced cytotoxicity did not involve ER stress. After 24 h of Ad-IFNα infection, the KU7 cancer cells produced spliced X-box binding protein 1 and activating transcription factor 6 protein (ATF6), evoking an ER stress response that could contribute to Ad-IFNα induced apoptosis in these cancer cells. In addition, GADD153/CHOP, GADD34 and BAX were also subsequently modified following activation of the ER stress pathways, thereby signaling downstream effectors in a pro-apoptotic manner.

Dioufa N, Kassi E, Papavassiliou AG, Kiaris H
Atypical induction of the unfolded protein response by mifepristone.
Endocrine. 2010; 38(2):167-73 [PubMed] Related Publications
Mifepristone is a synthetic progesterone antagonist that is being used widely for the treatment of various conditions such as endometriosis, glaucoma, meningiomas, breast, ovarian and prostate cancer, as well as for research purposes, in the conditional induction of gene expression by using artificial plasmid-based systems. Here, we report that exposure of A549 human lung cancer cells to mifepristone caused an atypical induction of the cellular unfolded protein response, as evidenced by the time-dependent stimulation of RNA levels of the chaperone Grp94 and PDIa, as well as the endoplasmic reticulum stress-associated receptors ATF6, PERK and eIF2 but not of their downstream target, transcription factor ATF4. This profile was very different from that of progesterone, which at the same dose as mifepristone, failed to induce all of the ER-stress-related genes examined, apart from PERK. Furthermore, XBP1, a transcription factor that is regulated predominantly by alternative splicing by the IRE1 receptor, remains unspliced and therefore inactive either by mifepristone or progesterone treatment. Finally, the pro-apoptotic molecules CHOP and BIM are only induced in the presence of tunicamycin in the culture medium. Tunicamycin, the most commonly used pharmacologic inducer of ER stress that triggers the canonical ER stress response, was used for comparison purposes. Our results suggest that mifepristone can elicit an atypical ER stress response when used at different doses and for different time points. The subsequent induction of UPR should be taken into consideration when this agent is being used either for therapeutic or for experimental uses.

Wang H, Ye Y, Chu JH, et al.
Proteomic and functional analyses reveal the potential involvement of endoplasmic reticulum stress and α-CP1 in the anticancer activities of oridonin in HepG2 cells.
Integr Cancer Ther. 2011; 10(2):160-7 [PubMed] Related Publications
Oridonin has been shown to exhibit therapeutic effects against hepatocellular carcinoma (HCC) in vitro and in vivo. This study aimed to identify the anti-HCC mechanisms of oridonin in HepG2 cells using proteomic and functional analyses. MTT assay showed that oridonin treatment for 24 hours dose-dependently inhibited cell growth with an IC(50) value of 40.4 μM. Treatment with 40 μM oridonin for 24 hours induced apoptosis determined by nuclear morphologic changes of DAPI-stained cells and flow cytometric analysis of annexin V-FITC/PI-stained cells, which was accompanied by Grp78 upregulation and α-CP1 downregulation identified by proteomic analysis. Immunoblot analysis for the endoplasmic reticulum (ER) stress- related proteins demonstrated that the expression levels of phosphorylated PERK (p-PERK) and CHOP were increased, whereas PERK, ATF-6, and IRE-1 expression levels were decreased. Knockdown of α-CP1 expression with siRNA significantly increased cell death and apoptosis in control and oridonin-treated HepG2 cells. Together, these data provide proteomic and functional evidence for the potential involvement of ER stress and α-CP1 in the antiproliferative and apoptotic activities of oridonin in HepG2 cells, which shed new light on the action mechanisms of oridonin in HCC management.

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