The Unfolded Protein Response (UPR) Is Activated in Human Acute Myeloid Leukemia (AML) and Suppresses Translation of the CCAAT/Enhancer Binding Protein-Alpha (CEBPA) by Induction of the RNA-Binding Protein Calreticulin

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 2934-2934
Author(s):  
Julian Schardt ◽  
Marianne Eyholzer ◽  
Beatrice U Mueller ◽  
Thomas Pabst
Keyword(s):  
Transcription Factor ◽  
Er Stress ◽  
Rna Binding ◽  
Binding Protein ◽  
Leukemic Cells ◽  
Protein Levels ◽  
Unfolded Protein ◽  
The Unfolded Protein Response ◽  
Protein Response ◽  
Spliced Variant

Abstract Deregulation of the myeloid key transcription factor CCAAT/enhancer binding protein alpha (CEBPA) is a common event in AML patients. We previously reported that the RNA-binding protein calreticulin efficiently blocks CEBPA translation and is specifically induced in core binding factor (CBF) leukemias. In addition, calreticulin is a crucial component of the unfolded protein response (UPR) which is triggered by the accumulation of misfolded proteins within the endoplasmic reticulum (ER). In vitro studies suggested that the UPR is activated in some solid cancers and thereby involved in tumor development. The role of the UPR during leukemogenesis has not been addressed so far. Here, we investigated the induction of the spliced variant of the X-box binding protein 1 (XBP1s) as a marker for activated ER stress and determined the expression of key mediators of the UPR such as calreticulin and the 78-kDa glucose-regulated protein (GRP78) in leukemic cells from 92 consecutive AML patients. Increased expression of the XBP1 spliced variant was detected in 16 of 92 AML patients. Consistently, this group also had increased mRNA and protein levels of calreticulin and GRP78. In patients expressing the XBP1 spliced variant, CEBPA protein was hardly detectable in contrast to AML patients not expressing the XBP1 spliced variant. Moreover, treatment of myeloid leukemic cells with compounds activating the UPR – such as thapsigargin - confirmed rapid induction of XBP1s, GRP78 and calreticulin in myeloid cells whereas CEBPA protein levels decreased. In addition, conditional expression of calreticulin in U937 cells suppressed CEBPA protein. At the molecular level, we identified two functional ER stress response elements (ERSE) in the calreticulin promoter, and both elements were found to be necessary for full induction of calreticulin following ER stress. The presence of the tripartite nuclear transcription factor Y (NFY) and activating transcription factor 6 (ATF6), as well as an intact binding site for the YY1 transcription factor (YY1) within these ERSE motifs appeared to be crucial for mediating sensitivity to ER stress. Finally, chromatin-immunoprecipitation assays indicated that binding of NFY and YY1 to the ERSE motifs is induced after induction of ER stress in vivo. Therefore, we conclude that the UPR is activated in a subgroup of AML patients. Activation of the UPR involves induction of calreticulin expression by the ATF6 pathway and ultimately leads to suppressed CEBPA translation, thus contributing to the block in myeloid differentiation in these leukemias.

scholarly journals Protein disulfide isomerase blocks CEBPA translation and is up-regulated during the unfolded protein response in AML

Blood ◽  
2011 ◽  
Vol 117 (22) ◽  
pp. 5931-5940 ◽  
Author(s):  
Simon Haefliger ◽  
Christiane Klebig ◽  
Kerstin Schaubitzer ◽  
Julian Schardt ◽  
Nikolai Timchenko ◽  
...  
Keyword(s):  
Er Stress ◽  
Unfolded Protein Response ◽  
Protein Disulfide Isomerase ◽  
Leukemic Cells ◽  
Stem Loop ◽  
Unfolded Protein ◽  
Loop Region ◽  
The Unfolded Protein Response ◽  
Protein Response ◽  
Protein Disulfide

Abstract Deregulation of the myeloid key transcription factor CEBPA is a common event in acute myeloid leukemia (AML). We previously reported that the chaperone calreticulin is activated in subgroups of AML patients and that calreticulin binds to the stem loop region of the CEBPA mRNA, thereby blocking CEBPA translation. In this study, we screened for additional CEBPA mRNA binding proteins and we identified protein disulfide isomerase (PDI), an endoplasmic reticulum (ER) resident protein, to bind to the CEBPA mRNA stem loop region. We found that forced PDI expression in myeloid leukemic cells in fact blocked CEBPA translation, but not transcription, whereas abolishing PDI function restored CEBPA protein. In addition, PDI protein displayed direct physical interaction with calreticulin. Induction of ER stress in leukemic HL60 and U937 cells activated PDI expression, thereby decreasing CEBPA protein levels. Finally, leukemic cells from 25.4% of all AML patients displayed activation of the unfolded protein response as a marker for ER stress, and these patients also expressed significantly higher PDI levels. Our results indicate a novel role of PDI as a member of the ER stress–associated complex mediating blocked CEBPA translation and thereby suppressing myeloid differentiation in AML patients with activated unfolded protein response (UPR).

scholarly journals Ceapins are a new class of unfolded protein response inhibitors, selectively targeting the ATF6α branch

eLife ◽  
2016 ◽  
Vol 5 ◽  
Author(s):  
Ciara M Gallagher ◽  
Carolina Garri ◽  
Erica L Cain ◽  
Kenny Kean-Hooi Ang ◽  
Christopher G Wilson ◽  
...  
Keyword(s):  
Transcription Factor ◽  
Er Stress ◽  
Unfolded Protein Response ◽  
Proteolytic Processing ◽  
Unfolded Protein ◽  
New Class ◽  
Cancer Models ◽  
Membrane Bound ◽  
The Unfolded Protein Response ◽  
Protein Response

The membrane-bound transcription factor ATF6α plays a cytoprotective role in the unfolded protein response (UPR), required for cells to survive ER stress. Activation of ATF6α promotes cell survival in cancer models. We used cell-based screens to discover and develop Ceapins, a class of pyrazole amides, that block ATF6α signaling in response to ER stress. Ceapins sensitize cells to ER stress without impacting viability of unstressed cells. Ceapins are highly specific inhibitors of ATF6α signaling, not affecting signaling through the other branches of the UPR, or proteolytic processing of its close homolog ATF6β or SREBP (a cholesterol-regulated transcription factor), both activated by the same proteases. Ceapins are first-in-class inhibitors that can be used to explore both the mechanism of activation of ATF6α and its role in pathological settings. The discovery of Ceapins now enables pharmacological modulation all three UPR branches either singly or in combination.

scholarly journals Activation of the ATF6 branch of the unfolded protein response in neurons improves stroke outcome

2016 ◽  
Vol 37 (3) ◽  
pp. 1069-1079 ◽  
Author(s):  
Zhui Yu ◽  
Huaxin Sheng ◽  
Shuai Liu ◽  
Shengli Zhao ◽  
Christopher C Glembotski ◽  
...  
Keyword(s):  
Transcription Factor ◽  
Er Stress ◽  
Unfolded Protein Response ◽  
Short Form ◽  
Infarct Volume ◽  
Stroke Outcome ◽  
Early Reperfusion ◽  
Unfolded Protein ◽  
The Unfolded Protein Response ◽  
Protein Response

Impaired function of the endoplasmic reticulum (ER stress) is a hallmark of many human diseases including stroke. To restore ER function in stressed cells, the unfolded protein response (UPR) is induced, which activates 3 ER stress sensor proteins including activating transcription factor 6 (ATF6). ATF6 is then cleaved by proteases to form the short-form ATF6 (sATF6), a transcription factor. To determine the extent to which activation of the ATF6 UPR branch defines the fate and function of neurons after stroke, we generated a conditional and tamoxifen-inducible sATF6 knock-in mouse. To express sATF6 in forebrain neurons, we crossed our sATF6 knock-in mouse line with Emx1-Cre mice to generate ATF6-KI mice. After the ATF6 branch was activated in ATF6-KI mice with tamoxifen, mice were subjected to transient middle cerebral artery occlusion. Forced activation of the ATF6 UPR branch reduced infarct volume and improved functional outcome at 24 h after stroke. Increased autophagic activity at early reperfusion time after stroke may contribute to the ATF6-mediated neuroprotection. We concluded that the ATF6 UPR branch is crucial to ischemic stroke outcome. Therefore, boosting UPR pro-survival pathways may be a promising therapeutic strategy for stroke.

scholarly journals The unfolded protein response in relation to mitochondrial biogenesis in skeletal muscle cells

2017 ◽  
Vol 312 (5) ◽  
pp. C583-C594 ◽  
Author(s):  
Zahra S. Mesbah Moosavi ◽  
David A. Hood
Keyword(s):  
Er Stress ◽  
Mitochondrial Biogenesis ◽  
Contractile Activity ◽  
Muscle Cells ◽  
Unfolded Proteins ◽  
Protein Levels ◽  
Unfolded Protein ◽  
The Unfolded Protein Response ◽  
Protein Response ◽  
Mitochondrial Adaptations

Mitochondria comprise both nuclear and mitochondrially encoded proteins requiring precise stoichiometry for their integration into functional complexes. The augmented protein synthesis associated with mitochondrial biogenesis results in the accumulation of unfolded proteins, thus triggering cellular stress. As such, the unfolded protein responses emanating from the endoplasmic reticulum (UPRER) or the mitochondrion (UPRMT) are triggered to ensure correct protein handling. Whether this response is necessary for mitochondrial adaptations is unknown. Two models of mitochondrial biogenesis were used: muscle differentiation and chronic contractile activity (CCA) in murine muscle cells. After 4 days of differentiation, our findings depict selective activation of the UPRMTin which chaperones decreased; however, Sirt3 and UPRERmarkers were elevated. To delineate the role of ER stress in mitochondrial adaptations, the ER stress inhibitor TUDCA was administered. Surprisingly, mitochondrial markers COX-I, COX-IV, and PGC-1α protein levels were augmented up to 1.5-fold above that of vehicle-treated cells. Similar results were obtained in myotubes undergoing CCA, in which biogenesis was enhanced by ~2–3-fold, along with elevated UPRMTmarkers Sirt3 and CPN10. To verify whether the findings were attributable to the terminal UPRERbranch directed by the transcription factor CHOP, cells were transfected with CHOP siRNA. Basally, COX-I levels increased (~20%) and COX-IV decreased (~30%), suggesting that CHOP influences mitochondrial composition. This effect was fully restored by CCA. Therefore, our results suggest that mitochondrial biogenesis is independent of the terminal UPRER. Under basal conditions, CHOP is required for the maintenance of mitochondrial composition, but not for differentiation- or CCA-induced mitochondrial biogenesis.

scholarly journals Staufen 1 amplifies pro-apoptotic activation of the unfolded protein response

2019 ◽  
Author(s):  
Mandi Gandelman ◽  
Warunee Dansithong ◽  
Karla P Figueroa ◽  
Sharan Paul ◽  
Daniel R Scoles ◽  
...  
Keyword(s):  
Unfolded Protein Response ◽  
Cortical Neurons ◽  
Rna Binding ◽  
Binding Protein ◽  
Unfolded Protein ◽  
Functional Consequences ◽  
Exogenous Expression ◽  
The Unfolded Protein Response ◽  
Protein Response

AbstractStaufen-1 (STAU1) is an RNA binding protein that becomes highly overabundant in numerous neurodegenerative disease models, including those carrying mutations in presenilin1 (PSEN1), microtubule associated protein tau (MAPT), huntingtin (HTT), TAR DNA-binding protein-43 gene (TARDBP) or C9orf72. We previously reported that elevations in STAU1 determine autophagy defects. Additional functional consequences of STAU1 overabundance, however, have not been investigated. We studied the role of STAU1 in the chronic activation of the Unfolded Protein Response (UPR), a common feature among the neurodegenerative diseases where STAU1 is increased, and is directly associated with neuronal death. Here we report that STAU1 is a novel modulator of the UPR, and is required for apoptosis induced by activation of the PERK-CHOP pathway. STAU1 levels increased in response to multiple ER stressors and exogenous expression of STAU1 was sufficient to cause apoptosis through the PERK-CHOP pathway of the UPR. Cortical neurons and skin fibroblasts derived from Stau1−/− mice showed reduced UPR and apoptosis when challenged with thapsigargin. In fibroblasts from SCA2 patients or with ALS-causing TDP-43 and C9ORF72 mutations we found highly increased STAU1 and CHOP levels in basal conditions. STAU1 knockdown restored CHOP levels to normal. Taken together, these results show STAU1 overabundance reduces cellular resistance to ER stress and precipitates apoptosis.

scholarly journals Transcription factor ATF4 directs basal and stress-induced gene expression in the unfolded protein response and cholesterol metabolism in the liver

2016 ◽  
Vol 27 (9) ◽  
pp. 1536-1551 ◽  
Author(s):  
Michael E. Fusakio ◽  
Jeffrey A. Willy ◽  
Yongping Wang ◽  
Emily T. Mirek ◽  
Rana J. T. Al Baghdadi ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Gene Expression ◽  
Transcription Factor ◽  
Er Stress ◽  
Unfolded Protein Response ◽  
Cholesterol Metabolism ◽  
Unfolded Protein ◽  
Expression Of Genes ◽  
The Unfolded Protein Response ◽  
Protein Response

Disturbances in protein folding and membrane compositions in the endoplasmic reticulum (ER) elicit the unfolded protein response (UPR). Each of three UPR sensory proteins—PERK (PEK/EIF2AK3), IRE1, and ATF6—is activated by ER stress. PERK phosphorylation of eIF2 represses global protein synthesis, lowering influx of nascent polypeptides into the stressed ER, coincident with preferential translation of ATF4 (CREB2). In cultured cells, ATF4 induces transcriptional expression of genes directed by the PERK arm of the UPR, including genes involved in amino acid metabolism, resistance to oxidative stress, and the proapoptotic transcription factor CHOP (GADD153/DDIT3). In this study, we characterize whole-body and tissue-specific ATF4-knockout mice and show in liver exposed to ER stress that ATF4 is not required for CHOP expression, but instead ATF6 is a primary inducer. RNA-Seq analysis indicates that ATF4 is responsible for a small portion of the PERK-dependent UPR genes and reveals a requirement for expression of ATF4 for expression of genes involved in oxidative stress response basally and cholesterol metabolism both basally and under stress. Consistent with this pattern of gene expression, loss of ATF4 resulted in enhanced oxidative damage, and increased free cholesterol in liver under stress accompanied by lowered cholesterol in sera.

Low-Dose Radiation Suppresses Pokemon Expression under Hypoxic Conditions

2014 ◽  
Vol 69 (1-2) ◽  
pp. 68-74
Author(s):  
Seung-Whan Kim ◽  
Kweon Yu ◽  
Kee-Sun Shin ◽  
Kisang Kwon ◽  
Tae-Sik Hwang ◽  
...  
Keyword(s):  
Transcription Factor ◽  
Er Stress ◽  
Low Dose ◽  
Differentially Expressed Gene ◽  
Low Dose Radiation ◽  
Unfolded Protein ◽  
Hypoxic Conditions ◽  
The Unfolded Protein Response ◽  
Protein Response ◽  
Dose Radiation

Our previous data demonstrated that CoCl2-induced hypoxia controls endoplasmic reticulum (ER) stress-associated and other intracellular factors. One of them, the transcription factor Pokemon, was differentially regulated by low-dose radiation (LDR). There are limited data regarding how this transcription factor is involved in expression of the unfolded protein response (UPR) under hypoxic conditions. The purpose of this study was to obtain clues on how Pokemon is involved in the UPR. Pokemon was selected as a differentially expressed gene under hypoxic conditions; however, its regulation was clearly repressed by LDR. It was also demonstrated that both expression of ER chaperones and ER stress sensors were affected by hypoxic conditions, and the same results were obtained when cells in which Pokemon was up- or down-regulated were used. The current state of UPR and LDR research associated with the Pokemon pathway offers an important opportunity to understand the oncogenesis, senescence, and differentiation of cells, as well as to facilitate introduction of new therapeutic radiopharmaceuticals

scholarly journals Coxsackievirus B3 Infection Activates the Unfolded Protein Response and Induces Apoptosis through Downregulation of p58IPK and Activation of CHOP and SREBP1

2010 ◽  
Vol 84 (17) ◽  
pp. 8446-8459 ◽  
Author(s):  
Huifang M. Zhang ◽  
Xin Ye ◽  
Yue Su ◽  
Ji Yuan ◽  
Zhen Liu ◽  
...  
Keyword(s):  
Transcription Factor ◽  
Er Stress ◽  
Unfolded Protein Response ◽  
Hela Cells ◽  
Coxsackievirus B3 ◽  
Unfolded Protein ◽  
Caspase 12 ◽  
Cvb3 Infection ◽  
The Unfolded Protein Response ◽  
Protein Response

ABSTRACT Cardiomyocyte apoptosis is a hallmark of coxsackievirus B3 (CVB3)-induced myocarditis. We used cardiomyocytes and HeLa cells to explore the cellular response to CVB3 infection, with a focus on pathways leading to apoptosis. CVB3 infection triggered endoplasmic reticulum (ER) stress and differentially regulated the three arms of the unfolded protein response (UPR) initiated by the proximal ER stress sensors ATF6a (activating transcription factor 6a), IRE1-XBP1 (X box binding protein 1), and PERK (PKR-like ER protein kinase). Upon CVB3 infection, glucose-regulated protein 78 expression was upregulated, and in turn ATF6a and XBP1 were activated via protein cleavage and mRNA splicing, respectively. UPR activity was further confirmed by the enhanced expression of UPR target genes ERdj4 and EDEM1. Surprisingly, another UPR-associated gene, p58IPK, which often is upregulated during infections with other types of viruses, was downregulated at both mRNA and protein levels after CVB3 infection. These findings were observed similarly for uninfected Tet-On HeLa cells induced to overexpress ATF6a or XBP1. In exploring potential connections between the three UPR pathways, we found that the ATF6a-induced downregulation of p58IPK was associated with the activation of PKR (PERK) and the phosphorylation of eIF2α, suggesting that p58IPK, a negative regulator of PERK and PKR, mediates cross-talk between the ATF6a/IRE1-XBP1 and PERK arms. Finally, we found that CVB3 infection eventually produced the induction of the proapoptoic transcription factor CHOP and the activation of SREBP1 and caspase-12. Taken together, these data suggest that CVB3 infection activates UPR pathways and induces ER stress-mediated apoptosis through the suppression of P58IPK and induction/activation of CHOP, SREBP1, and caspase-12.

scholarly journals Staufen 1 amplifies proapoptotic activation of the unfolded protein response

2020 ◽  
Vol 27 (10) ◽  
pp. 2942-2951 ◽  
Author(s):  
Mandi Gandelman ◽  
Warunee Dansithong ◽  
Karla P. Figueroa ◽  
Sharan Paul ◽  
Daniel R. Scoles ◽  
...  
Keyword(s):  
Neurodegenerative Diseases ◽  
Unfolded Protein Response ◽  
Cortical Neurons ◽  
Rna Binding ◽  
Binding Protein ◽  
Unfolded Protein ◽  
Functional Consequences ◽  
Exogenous Expression ◽  
The Unfolded Protein Response ◽  
Protein Response

AbstractStaufen-1 (STAU1) is an RNA-binding protein that becomes highly overabundant in numerous neurodegenerative disease models, including those carrying mutations in presenilin1 (PSEN1), microtubule-associated protein tau (MAPT), huntingtin (HTT), TAR DNA-binding protein-43 gene (TARDBP), or C9orf72. We previously reported that elevations in STAU1 determine autophagy defects and its knockdown is protective in models of several neurodegenerative diseases. Additional functional consequences of STAU1 overabundance, however, have not been investigated. We studied the role of STAU1 in the chronic activation of the unfolded protein response (UPR), a common feature among neurodegenerative diseases and often directly associated with neuronal death. Here we report that STAU1 is a novel modulator of the UPR, and is required for apoptosis induced by activation of the PERK–CHOP pathway. STAU1 levels increased in response to multiple endoplasmic reticulum (ER) stressors, and exogenous expression of STAU1 was sufficient to cause apoptosis through the PERK–CHOP pathway of the UPR. Cortical neurons and skin fibroblasts derived from Stau1−/− mice showed reduced UPR and apoptosis when challenged with thapsigargin. In fibroblasts from individuals with SCA2 or with ALS-causing TDP-43 and C9ORF72 mutations, we found highly increased STAU1 and CHOP levels in basal conditions, and STAU1 knockdown restored CHOP levels to normal. Taken together, these results show that STAU1 overabundance reduces cellular resistance to ER stress and precipitates apoptosis.

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