XBP1

Gene Summary

Gene:XBP1; X-box binding protein 1
Aliases: XBP2, TREB5, XBP-1, TREB-5
Location:22q12.1
Summary:This gene encodes a transcription factor that regulates MHC class II genes by binding to a promoter element referred to as an X box. This gene product is a bZIP protein, which was also identified as a cellular transcription factor that binds to an enhancer in the promoter of the T cell leukemia virus type 1 promoter. It may increase expression of viral proteins by acting as the DNA binding partner of a viral transactivator. It has been found that upon accumulation of unfolded proteins in the endoplasmic reticulum (ER), the mRNA of this gene is processed to an active form by an unconventional splicing mechanism that is mediated by the endonuclease inositol-requiring enzyme 1 (IRE1). The resulting loss of 26 nt from the spliced mRNA causes a frame-shift and an isoform XBP1(S), which is the functionally active transcription factor. The isoform encoded by the unspliced mRNA, XBP1(U), is constitutively expressed, and thought to function as a negative feedback regulator of XBP1(S), which shuts off transcription of target genes during the recovery phase of ER stress. A pseudogene of XBP1 has been identified and localized to chromosome 5. [provided by RefSeq, Jul 2008]
Databases:VEGA, OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:X-box-binding protein 1
Source:NCBIAccessed: 13 March, 2017

Ontology:

What does this gene/protein do?
Show (16)

Cancer Overview

Research Indicators

Publications Per Year (1992-2017)
Graph generated 13 March 2017 using data from PubMed using criteria.

Literature Analysis

Mouse over the terms for more detail; many indicate links which you can click for dedicated pages about the topic.

  • regulatory factor X transcription factors
  • Neoplasm Proteins
  • Endoribonucleases
  • Protein-Serine-Threonine Kinases
  • Molecular Sequence Data
  • Breast Cancer
  • Up-Regulation
  • Transcription Factor CHOP
  • Neoplastic Cell Transformation
  • Unfolded Protein Response
  • Chromosome 22
  • B-Lymphocytes
  • eIF-2 Kinase
  • RTPCR
  • Multiple Myeloma
  • Transfection
  • Liver Cancer
  • Cancer Gene Expression Regulation
  • Cell Survival
  • Regulatory Elements, Transcriptional
  • Antineoplastic Agents
  • RNA Splicing
  • Plasma Cells
  • Gene Expression
  • Mutation
  • Apoptosis
  • Endoplasmic Reticulum
  • Oligonucleotide Array Sequence Analysis
  • Signal Transduction
  • Nuclear Proteins
  • Messenger RNA
  • Gene Expression Profiling
  • Cell Differentiation
  • Cell Proliferation
  • Xenograft Models
  • DNA-Binding Proteins
  • Endoplasmic Reticulum Stress
  • Immunohistochemistry
  • Young Adult
  • Activating Transcription Factor 6
  • Western Blotting
Tag cloud generated 13 March, 2017 using data from PubMed, MeSH and CancerIndex

Specific Cancers (4)

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: XBP1 (cancer-related)

Ruwan Kumara MH, Piao MJ, Kang KA, et al.
Non-thermal gas plasma-induced endoplasmic reticulum stress mediates apoptosis in human colon cancer cells.
Oncol Rep. 2016; 36(4):2268-74 [PubMed] Related Publications
Colorectal cancer is a common type of tumor among both men and women worldwide. Conventional remedies such as chemotherapies pose the risk of side‑effects, and in many cases cancer cells develop chemoresistance to these treatments. Non‑thermal gas plasma (NTGP) was recently identified as a potential tool for cancer treatment. In this study, we investigated the potential use of NTGP to control SNUC5 human colon carcinoma cells. We hypothesized that NTGP would generate reactive oxygen species (ROS) in these cells, resulting in induction of endoplasmic reticulum (ER) stress. ROS generation, expression of ER stress‑related proteins and mitochondrial calcium levels were analyzed. Our results confirmed that plasma‑generated ROS induce apoptosis in SNUC5 cells. Furthermore, we found that plasma exposure resulted in mitochondrial calcium accumulation and expression of unfolded protein response (UPR) proteins such as glucose‑related protein 78 (GRP78), protein kinase R (PKR)‑like ER kinase (PERK), and inositol‑requiring enzyme 1 (IRE1). Elevated expression of spliced X‑box binding protein 1 (XBP1) and CCAAT/enhancer‑binding protein homologous protein (CHOP) further confirmed that ROS generated by NTGP induces apoptosis through the ER stress signaling pathway.

Wu CF, Seo EJ, Klauck SM, Efferth T
Cryptotanshinone deregulates unfolded protein response and eukaryotic initiation factor signaling in acute lymphoblastic leukemia cells.
Phytomedicine. 2016; 23(2):174-80 [PubMed] Related Publications
BACKGROUND: Unfolded protein responses (UPR) determine cell fate and are recognized as anticancer targets. In a previous research, we reported that cryptotanshinone (CPT) exerted cytotoxic effects toward acute lymphoblastic leukemia cells through mitochondria-mediated apoptosis.
PURPOSE: In the present study, we further investigated the role of UPR in CPT-induced cytotoxicity on acute lymphoblastic leukemia cells by applying tools of pharmacogenomics and bioinformatics.
METHODS: Gene expression profiling was performed by mRNA microarray hybridization. Potential transcription factor binding motifs were identified in the promoter regions of the deregulated genes by Cistrome software. Molecular docking on eIF-4A and PI3K was performed to investigate the inhibitory activity of CPT on translation initiation.
RESULTS: CPT regulated genes related to UPR and eIF2 signaling pathways. The DNA-Damage-Inducible Transcript 3 (DDIT3) gene, which is activated as consequence of UPR malfunction during apoptosis, was induced and validated by in vitro experiments. Transcription factor binding motif analysis of the microarrary-retrieved deregulated genes in the promoter region emphasized the relevance of transcription factors, such as ATF2, ATF4 and XBP1, regulating UPR and cell apoptosis. Molecular docking suggested inhibitory effects of CPT by binding to eIF-4A and PI3K providing evidence for a role of CPT's in the disruption of protein synthesis.
CONCLUSION: CPT triggered UPR and inhibited protein synthesis via eIF-mediated translation initiation, potentially supporting CPT-induced cytotoxic effects toward acute leukemia cells.

Willis S, Villalobos VM, Gevaert O, et al.
Single Gene Prognostic Biomarkers in Ovarian Cancer: A Meta-Analysis.
PLoS One. 2016; 11(2):e0149183 [PubMed] Free Access to Full Article Related Publications
PURPOSE: To discover novel prognostic biomarkers in ovarian serous carcinomas.
METHODS: A meta-analysis of all single genes probes in the TCGA and HAS ovarian cohorts was performed to identify possible biomarkers using Cox regression as a continuous variable for overall survival. Genes were ranked by p-value using Stouffer's method and selected for statistical significance with a false discovery rate (FDR) <.05 using the Benjamini-Hochberg method.
RESULTS: Twelve genes with high mRNA expression were prognostic of poor outcome with an FDR <.05 (AXL, APC, RAB11FIP5, C19orf2, CYBRD1, PINK1, LRRN3, AQP1, DES, XRCC4, BCHE, and ASAP3). Twenty genes with low mRNA expression were prognostic of poor outcome with an FDR <.05 (LRIG1, SLC33A1, NUCB2, POLD3, ESR2, GOLPH3, XBP1, PAXIP1, CYB561, POLA2, CDH1, GMNN, SLC37A4, FAM174B, AGR2, SDR39U1, MAGT1, GJB1, SDF2L1, and C9orf82).
CONCLUSION: A meta-analysis of all single genes identified thirty-two candidate biomarkers for their possible role in ovarian serous carcinoma. These genes can provide insight into the drivers or regulators of ovarian cancer and should be evaluated in future studies. Genes with high expression indicating poor outcome are possible therapeutic targets with known antagonists or inhibitors. Additionally, the genes could be combined into a prognostic multi-gene signature and tested in future ovarian cohorts.

Wang CY, Guo ST, Wang JY, et al.
Inhibition of HSP90 by AUY922 Preferentially Kills Mutant KRAS Colon Cancer Cells by Activating Bim through ER Stress.
Mol Cancer Ther. 2016; 15(3):448-59 [PubMed] Related Publications
Oncogenic mutations of KRAS pose a great challenge in the treatment of colorectal cancer. Here we report that mutant KRAS colon cancer cells are nevertheless more susceptible to apoptosis induced by the HSP90 inhibitor AUY922 than those carrying wild-type KRAS. Although AUY922 inhibited HSP90 activity with comparable potency in colon cancer cells irrespective of their KRAS mutational statuses, those with mutant KRAS were markedly more sensitive to AUY922-induced apoptosis. This was associated with upregulation of the BH3-only proteins Bim, Bik, and PUMA. However, only Bim appeared essential, in that knockdown of Bim abolished, whereas knockdown of Bik or PUMA only moderately attenuated apoptosis induced by AUY922. Mechanistic investigations revealed that endoplasmic reticulum (ER) stress was responsible for AUY922-induced upregulation of Bim, which was inhibited by a chemical chaperone or overexpression of GRP78. Conversely, siRNA knockdown of GRP78 or XBP-1 enhanced AUY922-induced apoptosis. Remarkably, AUY922 inhibited the growth of mutant KRAS colon cancer xenografts through activation of Bim that was similarly associated with ER stress. Taken together, these results suggest that AUY922 is a promising drug in the treatment of mutant KRAS colon cancers, and the agents that enhance the apoptosis-inducing potential of Bim may be useful to improve the therapeutic efficacy.

Chen H, Yang H, Pan L, et al.
The molecular mechanisms of XBP-1 gene silencing on IRE1α-TRAF2-ASK1-JNK pathways in oral squamous cell carcinoma under endoplasmic reticulum stress.
Biomed Pharmacother. 2016; 77:108-13 [PubMed] Related Publications
BACKGROUND: Proteasome inhibitor Carbobenzoxy-Leu-Leu-leucinal (MG132) induces the unfolded protein response (UPR) in oral squamous cell carcinoma (OSCC). X-box binding protein 1 (XBP1) is a key UPR component that regulates endoplasmic reticulum stress (ER) homeostasis. This study was aimed to investigate the activation of IRE1α-TRAF2-ASK1-JNK pathway by silencing the XBP1 expression in an OSCC cell line.
METHODS: The XBP1 specific short hairpin RNA (shRNA) plasmid vector was constructed and then transfected into the Tca-8113 cells. The effect of XBP-1 gene silencing on IRE1α-TRAF2-ASK1-JNK pathway under MG132 induced endoplasmic reticulum stress in Tca-8113 were investigated by real-time RT-PCR or western blot. Cell apoptosis was detected by flow cytometry.
RESULTS: XBP1 expression was reduced in transfected groups and MG132 groups. shRNA-XBP1 induces IRE1α-TRAF2-ASK1 signaling activation to activate pro-apoptotic ASK1-JNK signaling. Moreover, combined shRNA-XBP1 with MG132 further enhanced downregulated XBP1 expression and upregulated activation of ASK1-JNK signaling.
CONCLUSIONS: Silencing XBP1 expression under MG132 induced ER stress block the XBP1 survival pathway and synergism with MG132 to promote Tca8113 cell apoptosis. These findings provide a therapeutic option in oral squamous cell carcinoma by inhibition of proteasome and XBP1 splicing.

Liu Y, Hou X, Liu M, et al.
XBP1 silencing decreases glioma cell viability and glycolysis possibly by inhibiting HK2 expression.
J Neurooncol. 2016; 126(3):455-62 [PubMed] Related Publications
Glioma cells rely on glycolysis to obtain energy and sustain their survival under microenvironmental stress in vivo. The mechanisms of regulation of glycolysis in glioma cells are unclear. Signaling pathway mediated by the transcription factor X box-binding protein 1 (XBP1) is one of the most important pathways of unfolded protein response which is comprehensively activated in cancer cells upon the microenvironmental stress. Here we showed that XBP1 was significantly activated in glioma tissues in vivo. XBP1 silencing resulted in decreasing of glioma cell viability and ATP/lactate production under hypoxia, which is possibly mediated by inhibition of Hexokinase II (HK2)'s expression. More importantly, XBP1 silenced glioma cells showed the decrease of tumor formation capacity. Our results revealed that XBP1s activation was involved in glioma glycolysis regulation and might be a potential molecular target for glioma treatment.

Cui C, Ye L, Huang Z, et al.
FAM172A is a tumor suppressor in colorectal carcinoma.
Tumour Biol. 2016; 37(5):6501-10 [PubMed] Related Publications
The present study was designed to elucidate the regulatory role of a novel protein FAM172A in carcinogenesis of colorectal carcinoma (CRC). Investigation of clinical samples using Western blotting showed that expression of FAM172A is significantly lower in cancerous tissues than in adjacent tissues. Furthermore, we constructed in vitro model for continuous overexpression and silencing of FAM172A with a retroviral vector system. FAM172A suppressed the proliferative and invasive potentials of LOVO cells as shown in MTT test, transwell migration assay, wound healing assay, 3D-culture morphologic study, and xenograft experiment. RT-PCR and Western blotting showed that FAM172A overexpression inhibited expressions of Cyclin D1, CDK2, MMP-2, MMP-9, PERK, elF2α, ATF6, XBP1, and GRP78, while FAM172A silencing induced their expressions. FAM172A might regulate ERS through PERK-elF2α, ATF6-XBP1-GRP78 signal pathway. The results implicated that FAM172A functioned as a tumor suppressor in colorectal carcinoma.

Yang J, Cheng D, Zhou S, et al.
Overexpression of X-Box Binding Protein 1 (XBP1) Correlates to Poor Prognosis and Up-Regulation of PI3K/mTOR in Human Osteosarcoma.
Int J Mol Sci. 2015; 16(12):28635-46 [PubMed] Free Access to Full Article Related Publications
Increasing evidence demonstrates that dysregulation of XBP1 function contributes to tumorigenesis in some cancers. However, little is known about the role of XBP1 in the progression of osteosarcoma (OS). The expression of XBP1 in OS samples was measured by quantitative RT-PCR and Western blotting assays. Cell cycle analysis and cell counting kit 8 (CCK8) assays were performed to determine the effects of XBP1 expression on cells growth capacity. Cell apoptosis coassay was applied to determine cell survival. The expression of genes affected by XBP1 was examined by quantitative RT-RCR and validated by Western blotting assays. XBP1 was overexpressed in OS clinical samples compared with corresponding non-cancerous tissues. Overexpression of XBP1 was significantly associated with advanced clinical stages, high degree of malignancy and low tumor necrosis rate. Furthermore, hypoxia activated XBP1, and silencing XBP1 significantly enhanced OS cell apoptosis. Knock-down of XBP1 resulted in inhibition of OS growth. Most importantly, knockdown of XBP1 led to down-regulation of PIK3R3 and mTOR. Taken together, XBP1 is up-regulated and has a pro-tumor effect in OS with activation of PI3K/mTOR signaling. Thus, targeting XBP1 may provide a new potential therapeutic method for OS.

Yu L, Andruska N, Zheng X, Shapiro DJ
Anticipatory activation of the unfolded protein response by epidermal growth factor is required for immediate early gene expression and cell proliferation.
Mol Cell Endocrinol. 2016; 422:31-41 [PubMed] Free Access to Full Article Related Publications
The onco-protein epidermal growth factor (EGF) initiates a cascade that includes activation of the ERK and AKT signaling pathways and alters gene expression. We describe a new action of EGF-EGF receptor (EGFR), rapid anticipatory activation of the endoplasmic reticulum stress sensor, the unfolded protein response (UPR). Within 2 min, EGF elicits EGFR dependent activation of phospholipase C γ (PLCγ), producing inositol triphosphate (IP3), which binds to IP3 receptor (IP3R), opening the endoplasmic reticulum IP3R Ca(2+) channels, resulting in increased intracellular Ca(2+). This calcium release leads to transient and moderate activation of the IRE1α and ATF6α arms of the UPR, resulting in induction of BiP chaperone. Knockdown or inhibition of EGFR, PLCγ or IP3R blocks the increase in intracellular Ca(2+). While blocking the increase in intracellular Ca(2+) by locking the IP3R calcium channel with 2-APB had no effect on EGF activation of the ERK or AKT signaling pathways, it abolished the rapid EGF-mediated induction and repression of gene expression. Knockdown of ATF6α or XBP1, which regulate UPR-induced chaperone production, inhibited EGF stimulated cell proliferation. Supporting biological relevance, increased levels of EGF receptor during tumor progression were correlated with increased expression of the UPR gene signature. Anticipatory activation of the UPR is a new role for EGF. Since UPR activation occurs in <2 min, it is an initial cell response when EGF binds EGFR.

Ming J, Ruan S, Wang M, et al.
A novel chemical, STF-083010, reverses tamoxifen-related drug resistance in breast cancer by inhibiting IRE1/XBP1.
Oncotarget. 2015; 6(38):40692-703 [PubMed] Free Access to Full Article Related Publications
Recent studies show that the unfolded protein response (UPR) within the endoplasmic reticulum is correlated with breast cancer drug resistance. In particular, human X-box binding protein-1(XBP1), a transcription factor which participates in UPR stress signaling, is reported to correlate with poor clinical responsiveness to tamoxifen. In this study, we develop a tamoxifen-resistant MCF-7 cell line by treating the cell line with low concentration of tamoxifen, and we find that XBP1 is indeed up-regulated at both the mRNA and protein levels compared to normal MCF-7 cells. STF-083010, a novel inhibitor which specifically blocks the XBP1 splicing, reestablishes tamoxifen sensitivity to resistant MCF-7 cells. Moreover, co-treatment with STF-083010 and tamoxifen can significantly delay breast cancer progression in a xenograft mammary tumor model. We next investigate the expression of XBP1s in over 170 breast cancer patients' samples and the results demonstrate that XBP1s expression level is highly correlated with overall survival in the ER+ subgroup, but not in the ER- subgroup, suggesting a potential therapeutic application of XBP1 inhibitors in ER+breast cancer treatment.

Zheng Y, Xu B, Zhao Y, et al.
CA1 contributes to microcalcification and tumourigenesis in breast cancer.
BMC Cancer. 2015; 15:679 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Although mammary microcalcification is frequently observed and has been associated with poor survival in patients with breast cancer, the genesis of calcification remains unclear. Carbonic anhydrase I (CA1) has been shown to promote calcification by catalysing the hydration of CO2. This study aimed to determine whether CA1 was correlated with microcalcification and with other processes that are involved in breast cancer tumourigenesis.
METHODS: CA1 expression in breast cancer tissues and blood samples was detected using western blotting, real-time PCR, immunohistochemistry and ELISA. Calcification was induced in the cultured 4T1 cell line originating from mouse breast tumours, using ascorbic acid and β-glycerophosphate. Acetazolamide, a chemical inhibitor of CA1, was also added to the culture to determine the role of CA1 in calcification. The MCF-7 human breast cancer cell line was treated with anti-CA1 siRNA and was assessed using a CCK-8 cell proliferation assay, an annexin V cell apoptosis assay, transwell migration assay and a human breast cancer PCR array. The tag SNP rs725605, which is located in the CA1 locus, was genotyped using TaqMan® genotyping.
RESULTS: Increased CA1 expression was detected in samples of breast carcinoma tissues and blood obtained from patients with breast cancer. A total of 15.3 % of these blood samples exhibited a 2.1-fold or higher level of CA1 expression, compared to the average level of CA1 expression in samples from healthy controls. Following the induction of calcification of 4T1 cells, both the number of calcium-rich deposits and the expression of CA1 increased, whereas the calcification and CA1 expression were significantly supressed in the presence of acetazolamide. Increased migration and apoptosis were observed in MCF-7 cells that were treated with anti-CA1 siRNA. The PCR array detected up-regulation of the androgen receptor (AR) and down-regulation of X-box binding protein 1 (XBP1) in the treated MCF-7 cells. Significant differences in the allele and genotype frequencies of rs725605 were detected in the cohort of patients with breast cancer but not in other tumours.
CONCLUSION: The results of this study suggested that CA1 is a potential oncogene and that it contributes to abnormal cell calcification, apoptosis and migration in breast cancer.

Bazi A, Keramati MR, Gholamin M
Role of Oxidative Stress in Modulating Unfolded Protein Response Activity in Chronic Myeloid Leukemia Cell Line.
Iran Biomed J. 2016; 20(1):63-7 [PubMed] Free Access to Full Article Related Publications
UNLABELLED: Recently, it has been revealed that tyrosine kinase inhibitors (TKIs) act through inducing both oxidative and endoplasmic reticulum (ER) stress in chronic myeloid leukemia cells. However, ER stress signaling triggers both apoptotic and survival processes within cells. Nevertheless, mechanisms by which TKIs avoid the pro-survival effects are not clear. The aim of this study was to evaluate the potential role of oxidative stress in activity of unfolded protein response (UPR) survival pathway within K562 cell line.
METHODS: The expression of UPR survival target genes, Xbp1, and Grp94 (glucose requiring protein 94) was studied in single and combined exposure to oxidative and ER stress in K562 cell line by quantitative and qualitative PCR.
RESULTS: The expression of UPR-related survival gene Grp94 was hampered by exposing to oxidative stress in cell induced with ER stress.
CONCLUSION: Interaction of oxidative and ER stress may role as a mediator influencing UPR signaling activity.

Marquitz AR, Mathur A, Edwards RH, Raab-Traub N
Host Gene Expression Is Regulated by Two Types of Noncoding RNAs Transcribed from the Epstein-Barr Virus BamHI A Rightward Transcript Region.
J Virol. 2015; 89(22):11256-68 [PubMed] Free Access to Full Article Related Publications
UNLABELLED: In Epstein-Barr virus-infected epithelial cancers, the alternatively spliced BamHI A rightward transcripts (BARTs) are the most abundant viral polyadenylated RNA. The BART introns form the template for the production of 44 microRNAs (miRNAs), and the spliced and polyadenylated exons form nuclear non-protein-coding RNAs. Analysis of host cell transcription by RNA-seq during latency in AGS cells identified a large number of reproducibly changed genes. Genes that were downregulated were enriched for BART miRNA targets. Bioinformatics analysis predicted activation of the myc pathway and downregulation of XBP1 as likely mediators of the host transcriptional changes. Effects on XBP1 activity were not detected in these cells; however, myc activation was confirmed through use of a myc-responsive luciferase reporter. To identify potential regulatory properties of the spliced, polyadenylated BART RNAs, a full-length cDNA clone of one of the BART isoforms was obtained and expressed in the Epstein-Barr virus (EBV)-negative AGS cells. The BART cDNA transcript remained primarily nuclear yet induced considerable and consistent changes in cellular transcription, as profiled by RNA-seq. These transcriptional changes significantly overlapped the transcriptional changes induced during latent EBV infection of these same cells, where the BARTs are exclusively nuclear and do not encode proteins. These data suggest that the nuclear BART RNAs are functional long noncoding RNAs (lncRNAs). The abundant expression of multiple forms of noncoding RNAs that contribute to growth regulation without expression of immunogenic proteins would be an important mechanism for viral oncogenesis in the presence of a functional immune system.
IMPORTANCE: Infection with Epstein-Barr virus (EBV) is nearly ubiquitous in the human population; however, it does contribute to the formation of multiple types of cancer. In immunocompromised patients, EBV causes multiple types of lymphomas by expressing viral oncogenes that promote growth and survival of infected B lymphocytes. EBV-positive gastric carcinoma does not require immune suppression, and the viral oncoproteins that are frequent targets for an immunological response are not expressed. This study demonstrates using transcriptional analysis that the expression of various classes of viral non-protein-coding RNAs likely contribute to the considerable changes in the host transcriptional profile in the AGS gastric cancer cell line. This is the first report to show that the highly expressed polyadenylated BamHI A rightward transcripts (BART) viral transcript in gastric carcinoma is in fact a functional viral long noncoding RNA. These studies provide new insight into how EBV can promote transformation in the absence of viral protein expression.

Sbiera S, Leich E, Liebisch G, et al.
Mitotane Inhibits Sterol-O-Acyl Transferase 1 Triggering Lipid-Mediated Endoplasmic Reticulum Stress and Apoptosis in Adrenocortical Carcinoma Cells.
Endocrinology. 2015; 156(11):3895-908 [PubMed] Related Publications
Adrenocortical carcinoma (ACC) is a rare malignancy that harbors a dismal prognosis in advanced stages. Mitotane is approved as an orphan drug for treatment of ACC and counteracts tumor growth and steroid hormone production. Despite serious adverse effects, mitotane has been clinically used for decades. Elucidation of its unknown molecular mechanism of action seems essential to develop better ACC therapies. Here, we set out to identify the molecular target of mitotane and altered downstream mechanisms by combining expression genomics and mass spectrometry technology in the NCI-H295 ACC model cell line. Pathway analyses of expression genomics data demonstrated activation of endoplasmic reticulum (ER) stress and profound alteration of lipid-related genes caused by mitotane treatment. ER stress marker CHOP was strongly induced and the two upstream ER stress signalling events XBP1-mRNA splicing and eukaryotic initiation factor 2 A (eIF2α) phosphorylation were activated by mitotane in NCI-H295 cells but to a much lesser extent in four nonsteroidogenic cell lines. Lipid mass spectrometry revealed mitotane-induced increase of free cholesterol, oxysterols, and fatty acids specifically in NCI-H295 cells as cause of ER stress. We demonstrate that mitotane is an inhibitor of sterol-O-acyl-transferase 1 (SOAT1) leading to accumulation of these toxic lipids. In ACC tissue samples we show variable SOAT1 expression correlating with the response to mitotane treatment. In conclusion, mitotane confers adrenal-specific cytotoxicity and down-regulates steroidogenesis by inhibition of SOAT1 leading to lipid-induced ER stress. Targeting of cancer-specific lipid metabolism opens new avenues for treatment of ACC and potentially other types of cancer.

Joo JH, Ueda E, Bortner CD, et al.
Farnesol activates the intrinsic pathway of apoptosis and the ATF4-ATF3-CHOP cascade of ER stress in human T lymphoblastic leukemia Molt4 cells.
Biochem Pharmacol. 2015; 97(3):256-68 [PubMed] Free Access to Full Article Related Publications
In this study, we demonstrate that treatment of T lymphoblastic leukemic Molt4 cells with farnesol activates the apoptosome via the intrinsic pathway of apoptosis. This induction was associated with changes in the level of intracellular potassium and calcium, the dissipation of the mitochondrial and plasma membrane potential, release of cytochrome c, activation of several caspases, and PARP cleavage. The induction of apoptosis by farnesol was inhibited by the addition of the pan-caspase inhibitor Z-VAD-fmk and by the exogenous expression of the anti-apoptotic protein Bcl2. Analysis of the gene expression profiles by microarray analysis revealed that farnesol increased the expression of several genes related to the unfolded protein response (UPR), including CHOP and CHAC1. This induction was associated with the activation of the PERK-eIF2α-ATF3/4 cascade, but not the XBP-1 branch of the UPR. Although farnesol induced activation of the ERK1/2, p38, and JNK pathways, inhibition of these MAPKs had little effect on farnesol-induced apoptosis or the induction of UPR-related genes. Our data indicate that the induction of apoptosis in leukemic cells by farnesol is mediated through a pathway that involves activation of the apoptosome via the intrinsic pathway and induction of the PERK-eIF2α-ATF3/4 cascade in a manner that is independent of the farnesol-induced activation of MAPKs.

Sakabe I, Hu R, Jin L, et al.
TMEM33: a new stress-inducible endoplasmic reticulum transmembrane protein and modulator of the unfolded protein response signaling.
Breast Cancer Res Treat. 2015; 153(2):285-97 [PubMed] Free Access to Full Article Related Publications
Endoplasmic reticulum (ER) stress leads to activation of the unfolded protein response (UPR) signaling cascade and induction of an apoptotic cell death, autophagy, oncogenesis, metastasis, and/or resistance to cancer therapies. Mechanisms underlying regulation of ER transmembrane proteins PERK, IRE1α, and ATF6α/β, and how the balance of these activities determines outcome of the activated UPR, remain largely unclear. Here, we report a novel molecule transmembrane protein 33 (TMEM33) and its actions in UPR signaling. Immunoblotting and northern blot hybridization assays were used to determine the effects of ER stress on TMEM33 expression levels in various cell lines. Transient transfections, immunofluorescence, subcellular fractionation, immunoprecipitation, and immunoblotting were used to study the subcellular localization of TMEM33, the binding partners of TMEM33, and the expression of downstream effectors of PERK and IRE1α. Our data demonstrate that TMEM33 is a unique ER stress-inducible and ER transmembrane molecule, and a new binding partner of PERK. Exogenous expression of TMEM33 led to increased expression of p-eIF2α and p-IRE1α and their known downstream effectors, ATF4-CHOP and XBP1-S, respectively, in breast cancer cells. TMEM33 overexpression also correlated with increased expression of apoptotic signals including cleaved caspase-7 and cleaved PARP, and an autophagosome protein LC3II, and reduced expression of the autophagy marker p62. TMEM33 is a novel regulator of the PERK-eIE2α-ATF4 and IRE1-XBP1 axes of the UPR signaling. Therefore, TMEM33 may function as a determinant of the ER stress-responsive events in cancer cells.

Wang LL, Hu RC, Dai AG, Tan SX
Bevacizumab induces A549 cell apoptosis through the mechanism of endoplasmic reticulum stress in vitro.
Int J Clin Exp Pathol. 2015; 8(5):5291-9 [PubMed] Free Access to Full Article Related Publications
AIMS: To observe the effect of bevacizumab on human A549 cells and explore its mechanism.
METHODS: After different concentrations (0 μM, 1 μM, 5 μM, 25 μM) of bevacizumab treating in A549 cells, CCK8 assay detect the impact of bevacizumab on A549 cell proliferation and flow cytometry determine the effect of bevacizumab on human A549 cells apoptosis. Real-time PCR and Western blotting detect the changing expression of the target gene (CHOP, caspase-4, IRE1, XBP-1) on mRNA and Protein level.
RESULTS: Treatment with bevacizumab for 24-hr have induced cell death in a does-dependent manner dramatically (P<0.05). In terms of the mRNA level, expression of XBP-1 has increased obviously in each group (1 μM, 5 μM, 25 μM) (P<0.01); the expression of CHOP (25 μM) and caspase-4 (5 μM) have increased slightly (P<0.05). In terms of the protein level, the expression of CHOP has increased obviously in each group (1 μM, 5 μM, 25 μM) when compared with the control group (0 μM) (P<0.05). As for caspase-4 (5 μM, 25 μM), the expression have increased slightly when compared with the control group (0 μM) (P<0.05).
CONCLUSION: Bevacizumab can induce A549 cell apoptosis through the mechanism of endoplasmic reticulum stress.

Jang JH, Min KJ, Kim S, et al.
RU486 Induces Pro-Apoptotic Endoplasmic Reticulum Stress Through the Induction of CHOP Expression by Enhancing C/EBPδ Expression in Human Renal Carcinoma Caki Cells.
J Cell Biochem. 2016; 117(2):361-9 [PubMed] Related Publications
RU486 (Mifepristone) is known as an antagonist of the progesterone receptor and glucocorticoid receptor. Here, we investigated the mechanism underlying anti-tumor activity of RU486 in renal carcinoma Caki cells. Treatment of Caki cells with RU486 was found to induce several signature ER stress markers; including ER stress-specific XBP1 splicing, and the up-regulation of glucose-regulated protein (GRP)-78 and CCAAT/enhancer-binding protein homologous protein (CHOP) expression. RU486-induced expression of CHOP involves the putative C/EBPδ site within the CHOP promoter region. Using a combination of C/EBPδ cDNA transfection, the luciferase assay with a mutated C/EBPδ binding site and siRNA-mediated C/EBPδ knockdown, we found that the C/EBPδ site is required for RU486-mediated activation of the CHOP promoter. In addition, RU486-induced CHOP expression is down-regulated by inhibition of the p38 MAPK and JNK signaling pathways at the post-translational levels. RU486 dose-dependently induced apoptotic cell death in renal carcinoma cells. Suppression of CHOP expression by CHOP siRNA attenuated RU486-induced apoptosis. Taken together, RU486 induces pro-apoptotic ER stress through the induction of CHOP expression.

Zhu H, Abulimiti M, Liu H, et al.
RITA enhances irradiation-induced apoptosis in p53-defective cervical cancer cells via upregulation of IRE1α/XBP1 signaling.
Oncol Rep. 2015; 34(3):1279-88 [PubMed] Related Publications
Radiation therapy is the most widely used treatment for patients with cervical cancer. Recent studies have shown that endoplasmic reticulum (ER) stress induces apoptosis and sensitizes tumor cells to radiotherapy, which reportedly induces ER stress in cells. Classical key tumor suppressor p53 is involved in the response to a variety of cellular stresses, including those incurred by ionizing irradiation. A recent study demonstrated that small-molecule RITA (reactivation of p53 and induction of tumor cell apoptosis) increased the radiosensitivity of tumor cells expressing mutant p53 (mtp53). In the present study, we explored the effects and the underlying mechanisms of RITA in regards to the radiosensitivity and ER stress in mtp53-expressing human cervix cancer cells. Treatment with 1 µM of RITA for 24 h before irradiation markedly decreased survival and increased apoptosis in C-33A and HT-3 cells; the effects were not significantly altered by knockdown of p53. In the irradiated C-33A and HT-3 cells, RITA significantly increased the expression of IRE1α, the spliced XBP1 mRNA level, as well as apoptosis; the effects were abolished by knockdown of IRE1α. Transcriptional pulse-chase assays revealed that RITA significantly increased the stability of IRE1α mRNA in the irradiated C-33A and HT-3 cells. In contrast, the same RITA treatment did not show any significant effect on sham-irradiated cells. In conclusion, the present study provides initial evidence that RITA upregulates the expression level of IRE1α by increasing the stability of IRE1α mRNA in irradiated mtp53-expressing cervical cancer cells; the effect leads to enhanced IRE1α/XBP1 ER stress signaling and increased apoptosis in the cells. The present study offers novel insight into the pharmacological potential of RITA in the radiotherapy for cervical cancer.

Luan Q, Jin L, Jiang CC, et al.
RIPK1 regulates survival of human melanoma cells upon endoplasmic reticulum stress through autophagy.
Autophagy. 2015; 11(7):975-94 [PubMed] Free Access to Full Article Related Publications
Although RIPK1 (receptor [TNFRSF]-interacting protein kinase 1) is emerging as a critical determinant of cell fate in response to cellular stress resulting from activation of death receptors and DNA damage, its potential role in cell response to endoplasmic reticulum (ER) stress remains undefined. Here we report that RIPK1 functions as an important prosurvival mechanism in melanoma cells undergoing pharmacological ER stress induced by tunicamycin (TM) or thapsigargin (TG) through activation of autophagy. While treatment with TM or TG upregulated RIPK1 and triggered autophagy in melanoma cells, knockdown of RIPK1 inhibited autophagy and rendered the cells sensitive to killing by TM or TG, recapitulating the effect of inhibition of autophagy. Consistently, overexpression of RIPK1 enhanced induction of autophagy and conferred resistance of melanoma cells to TM- or TG-induced cell death. Activation of MAPK8/JNK1 or MAPK9/JNK2, which phosphorylated BCL2L11/BIM leading to its dissociation from BECN1/Beclin 1, was involved in TM- or TG-induced, RIPK1-mediated activation of autophagy; whereas, activation of the transcription factor HSF1 (heat shock factor protein 1) downstream of the ERN1/IRE1-XBP1 axis of the unfolded protein response was responsible for the increase in RIPK1 in melanoma cells undergoing pharmacological ER stress. Collectively, these results identify upregulation of RIPK1 as an important resistance mechanism of melanoma cells to TM- or TG-induced ER stress by protecting against cell death through activation of autophagy, and suggest that targeting the autophagy-activating mechanism of RIPK1 may be a useful strategy to enhance sensitivity of melanoma cells to therapeutic agents that induce ER stress.

Liu R, Zhang L, Yang J, et al.
HIV Protease Inhibitors Sensitize Human Head and Neck Squamous Carcinoma Cells to Radiation by Activating Endoplasmic Reticulum Stress.
PLoS One. 2015; 10(5):e0125928 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Human head and neck squamous cell carcinoma (HNSCC) is the sixth most malignant cancer worldwide. Despite significant advances in the delivery of treatment and surgical reconstruction, there is no significant improvement of mortality rates for this disease in the past decades. Radiotherapy is the core component of the clinical combinational therapies for HNSCC. However, the tumor cells have a tendency to develop radiation resistance, which is a major barrier to effective treatment. HIV protease inhibitors (HIV PIs) have been reported with radiosensitizing activities in HNSCC cells, but the underlying cellular/molecular mechanisms remain unclear. Our previous study has shown that HIV PIs induce cell apoptosis via activation of endoplasmic reticulum (ER) stress. The aim of this study was to examine the role of ER stress in HIV PI-induced radiosensitivity in human HNSCC.
METHODOLOGY AND PRINCIPAL FINDINGS: HNSCC cell lines, SQ20B and FaDu, and the most commonly used HIV PIs, lopinavir and ritonavir (L/R), were used in this study. Clonogenic assay was used to assess the radiosensitivity. Cell viability, apoptosis and cell cycle were analyzed using Cellometer Vision CBA. The mRNA and protein levels of ER stress-related genes (eIF2α, CHOP, ATF-4, and XBP-1), as well as cell cycle related protein, cyclin D1, were detected by real time RT-PCR and Western blot analysis, respectively. The results demonstrated that L/R dose-dependently sensitized HNSCC cells to irradiation and inhibited cell growth. L/R-induced activation of ER stress was correlated to down-regulation of cyclin D1 expression and cell cycle arrest under G0/G1 phase.
CONCLUSION AND SIGNIFICANCE: HIV PIs sensitize HNSCC cells to radiotherapy by activation of ER stress and induction of cell cycle arrest. Our results provided evidence that HIV PIs can be potentially used in combination with radiation in the treatment of HNSCC.

Cheng S, Swanson K, Eliaz I, et al.
Pachymic acid inhibits growth and induces apoptosis of pancreatic cancer in vitro and in vivo by targeting ER stress.
PLoS One. 2015; 10(4):e0122270 [PubMed] Free Access to Full Article Related Publications
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.

Zhou T, Lv X, Guo X, et al.
RACK1 modulates apoptosis induced by sorafenib in HCC cells by interfering with the IRE1/XBP1 axis.
Oncol Rep. 2015; 33(6):3006-14 [PubMed] Related Publications
Sorafenib is one of the preferred drugs for the treatment of advanced primary hepatocellular carcinoma (HCC). However, its side-effects and acquired resistance limit its use. The unfolded protein response (UPR) induced by chemotherapeutics has been demonstrated to be required for tumor cells to maintain malignancy and therapy resistance. Activation of the IRE1/XBP1 pathway during the UPR is important for tumor survival under pathophysiological conditions. In the present study, we found that the UPR was activated and RACK1 was overexpressed in three human HCC cell lines and in HCC samples. Activation of the IRE1/XBP1 signaling pathway plays a protective role when HCC cells encounter endoplasmic reticulum (ER) stress due to in vitro sorafenib treatment. We then found that the interaction between IRE1 and RACK1 was essential for the activation of IRE1 signaling in sorafenib-treated cells. Exogenous overexpression of RACK1 enhanced the phosphorylation level of IRE1 and increased XBP1 mRNA splicing activity, which protected the HCC cells from sorafenib-induced apoptosis. However, the re-expression of RACK1 led HCC cells to regain susceptibility to sorafenib-induced apoptosis. Taken together, the present study suggests that the RACK1/IRE1 complex may contribute to activation of the UPR in HCC cells. Targeting RACK1 in combination with sorafenib administration is a potential strategy for clinical trials of advanced HCC treatment.

Granados-Principal S, Liu Y, Guevara ML, et al.
Inhibition of iNOS as a novel effective targeted therapy against triple-negative breast cancer.
Breast Cancer Res. 2015; 17:25 [PubMed] Free Access to Full Article Related Publications
INTRODUCTION: Triple-negative breast cancer (TNBC) is an aggressive form of breast cancer with no effective targeted therapy. Inducible nitric oxide synthase (iNOS) is associated with poor survival in patients with breast cancer by increasing tumor aggressiveness. This work aimed to investigate the potential of iNOS inhibitors as a targeted therapy for TNBC. We hypothesized that inhibition of endogenous iNOS would decrease TNBC aggressiveness by reducing tumor initiation and metastasis through modulation of epithelial-mesenchymal transition (EMT)-inducing factors.
METHODS: iNOS protein levels were determined in 83 human TNBC tissues and correlated with clinical outcome. Proliferation, mammosphere-forming efficiency, migration, and EMT transcription factors were assessed in vitro after iNOS inhibition. Endogenous iNOS targeting was evaluated as a potential therapy in TNBC mouse models.
RESULTS: High endogenous iNOS expression was associated with worse prognosis in patients with TNBC by gene expression as well as immunohistochemical analysis. Selective iNOS (1400 W) and pan-NOS (L-NMMA and L-NAME) inhibitors diminished cell proliferation, cancer stem cell self-renewal, and cell migration in vitro, together with inhibition of EMT transcription factors (Snail, Slug, Twist1, and Zeb1). Impairment of hypoxia-inducible factor 1α, endoplasmic reticulum stress (IRE1α/XBP1), and the crosstalk between activating transcription factor 3/activating transcription factor 4 and transforming growth factor β was observed. iNOS inhibition significantly reduced tumor growth, the number of lung metastases, tumor initiation, and self-renewal.
CONCLUSIONS: Considering the effectiveness of L-NMMA in decreasing tumor growth and enhancing survival rate in TNBC, we propose a targeted therapeutic clinical trial by re-purposing the pan-NOS inhibitor L-NMMA, which has been extensively investigated for cardiogenic shock as an anti-cancer therapeutic.

Kim H, Bhattacharya A, Qi L
Endoplasmic reticulum quality control in cancer: Friend or foe.
Semin Cancer Biol. 2015; 33:25-33 [PubMed] Free Access to Full Article Related Publications
Quality control systems in the endoplasmic reticulum (ER) mediated by unfolded protein response (UPR) and endoplasmic reticulum associated degradation (ERAD) ensure cellular function and organismal survival. Recent studies have suggested that ER quality-control systems in cancer cells may serve as a double-edged sword that aids progression as well as prevention of tumor growth in a context-dependent manner. Here we review recent advances in our understanding of the complex relationship between ER proteostasis and cancer pathology, with a focus on the two most conserved ER quality-control mechanisms--the IRE1α-XBP1 pathway of the UPR and SEL1L-HRD1 complex of the ERAD.

Kortüm KM, Langer C, Monge J, et al.
Longitudinal analysis of 25 sequential sample-pairs using a custom multiple myeloma mutation sequencing panel (M(3)P).
Ann Hematol. 2015; 94(7):1205-11 [PubMed] Free Access to Full Article Related Publications
Recent advances in genomic sequencing technologies now allow results from deep next-generation sequencing to be obtained within clinically meaningful timeframes, making this an attractive approach to better guide personalized treatment strategies. No multiple myeloma-specific gene panel has been established so far; we therefore designed a 47-gene-targeting gene panel, containing 39 genes known to be mutated in ≥3 % of multiple myeloma cases and eight genes in pathways therapeutically targeted in multiple myeloma (MM). We performed targeted sequencing on tumor/germline DNA of 25 MM patients in which we also had a sequential sample post treatment. Mutation analysis revealed KRAS as the most commonly mutated gene (36 % in each time point), followed by NRAS (20 and 16 %), TP53 (16 and 16 %), DIS3 (16 and 16 %), FAM46C (12 and 16 %), and SP140 (12 and 12 %). We successfully tracked clonal evolution and identified mutation acquisition and/or loss in FAM46C, FAT1, KRAS, NRAS, SPEN, PRDM1, NEB, and TP53 as well as two mutations in XBP1, a gene associated with bortezomib resistance. Thus, we present the first longitudinal analysis of a MM-specific targeted sequencing gene panel that can be used for individual tumor characterization and for tracking clonal evolution over time.

Mhaidat NM, Alzoubi KH, Abushbak A
X-box binding protein 1 (XBP-1) enhances colorectal cancer cell invasion.
J Chemother. 2015; 27(3):167-73 [PubMed] Related Publications
In this study, we investigated the role of X-box binding protein 1 (XBP-1) and vascular endothelial growth factor receptor-2 (VEGF-R2) signalling in colorectal cancer (CRC) cells invasion by evaluating their extent of activation in CRC tissues and cell lines using immunohistochemistry, western blotting, and invasion assays. Results showed that XBP-1 is expressed at high levels in metastatic and poorly differentiated tissue samples, whereas it appeared relatively low in moderately and well-differentiated tissue samples compared to those in normal colon tissue. The XBP-1 immunoreactivity score (IRS) was positively associated with increasing tumour invasion. In vitro studies showed that overexpression of XBP-1 promoted cancer cell invasion, which was suppressed by inhibition of XBP-1 using small interfering RNA molecules (siRNA). Inhibition of XBP-1 expression significantly decreased levels of VEGF-R2.In conclusion, XBP-1 might be regarded as a novel predictive biomarker in CRC invasion and metastasis.

Pagliarini V, Giglio P, Bernardoni P, et al.
Downregulation of E2F1 during ER stress is required to induce apoptosis.
J Cell Sci. 2015; 128(6):1166-79 [PubMed] Related Publications
The endoplasmic reticulum (ER) has recently emerged as an alternative target to induce cell death in tumours, because prolonged ER stress results in the induction of apoptosis even in chemoresistant transformed cells. Here, we show that the DNA-damage-responsive pro-apoptotic factor E2F1 is unexpectedly downregulated during the ER stress-mediated apoptotic programme. E2F1 decline is a late event during the ER response and is mediated by the two unfolded protein response (UPR) sensors ATF6 and IRE1 (also known as ERN1). Whereas ATF6 directly interacts with the E2F1 promoter, IRE1 requires the involvement of the known E2F1 modulator E2F7, through the activation of its main target Xbp-1. Importantly, inhibition of the E2F1 decrease prevents ER-stress-induced apoptosis, whereas E2F1 knockdown efficiently sensitises cells to ER stress-dependent apoptosis, leading to the upregulation of two main factors in the UPR pro-apoptotic execution phase, Puma and Noxa (also known as BBC3 and PMAIP1, respectively). Our results point to a novel key role of E2F1 in the cell survival/death decision under ER stress, and unveil E2F1 inactivation as a valuable novel potential therapeutic strategy to increase the response of tumour cells to ER stress-based anticancer treatments.

Booth L, Cruickshanks N, Tavallai S, et al.
Regulation of dimethyl-fumarate toxicity by proteasome inhibitors.
Cancer Biol Ther. 2014; 15(12):1646-57 [PubMed] Free Access to Full Article Related Publications
The present studies examined the biology of the multiple sclerosis drug dimethyl-fumarate (DMF) or its in vivo breakdown product and active metabolite mono-methyl-fumarate (MMF), alone or in combination with proteasome inhibitors, in primary human glioblastoma (GBM) cells. MMF enhanced velcade and carfilzomib toxicity in multiple primary GBM isolates. Similar data were obtained in breast and colon cancer cells. MMF reduced the invasiveness of GBM cells, and enhanced the toxicity of ionizing radiation and temozolomide. MMF killed freshly isolated activated microglia which was associated with reduced IL-6, TGFβ and TNFα production. The combination of MMF and the multiple sclerosis drug Gilenya further reduced both GBM and activated microglia viability and cytokine production. Over-expression of c-FLIP-s or BCL(-)XL protected GBM cells from MMF and velcade toxicity. MMF and velcade increased plasma membrane localization of CD95, and knock down of CD95 or FADD blocked the drug interaction. The drug combination inactivated AKT, ERK1/2 and mTOR. Molecular inhibition of AKT/ERK/mTOR signaling enhanced drug combination toxicity whereas molecular activation of these pathways suppressed killing. MMF and velcade increased the levels of autophagosomes and autolysosomes and knock down of ATG5 or Beclin1 protected cells. Inhibition of the eIF2α/ATF4 arm or the IRE1α/XBP1 arm of the ER stress response enhanced drug combination lethality. This was associated with greater production of reactive oxygen species and quenching of ROS suppressed cell killing.

Kim HS, Jung G
Reactive oxygen species increase HEPN1 expression via activation of the XBP1 transcription factor.
FEBS Lett. 2014; 588(23):4413-21 [PubMed] Related Publications
Hepatocellular carcinoma downregulated 1 (HEPN1), a cell growth arrest- and apoptosis-related gene, is suppressed in hepatocellular carcinoma (HCC). However, transcriptional control of HEPN1 has not been characterized. Here, we show that exposure to reactive oxygen species (ROS) leads to upregulation of the mRNA expression of HEPN1 in HCC cell lines. Mechanistically, ROS increase production of an alternately spliced form of X-box binding protein 1 (XBP1s) and XBP1s increases HEPN1 expression by binding to the HEPN1 promoter, thereby acting as a transcriptional activator. Finally, HEPN1 overexpression increases the expression of p53, p21, and Bax, all of which are ROS-upregulated proteins.

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