Dynamic changes in complexes of IRE1α, PERK, and ATF6α during endoplasmic reticulum stress

The endoplasmic reticulum (ER) localized unfolded protein response (UPR) sensors, IRE1α, PERK, and ATF6α, are activated by the accumulation of misfolded proteins in the ER. It is unclear how the endogenous UPR sensors are regulated by both ER stress and the ER luminal chaperone BiP, which is a negative regulator of UPR sensors. Here we simultaneously examined the changes in the endogenous complexes of UPR sensors by blue native PAGE immunoblotting in unstressed and stressed cells. We found that all three UPR sensors exist as preformed complexes even in unstressed cells. While PERK complexes shift to large complexes, ATF6α complexes are reduced to smaller complexes on ER stress. In contrast, IRE1α complexes were not significantly increased in size on ER stress, unless IRE1α is overexpressed. Surprisingly, depletion of BiP had little impact on the endogenous complexes of UPR sensors. In addition, overexpression of BiP did not significantly affect UPR complexes, but suppressed ER stress mediated activation of IRE1α, ATF6α and, to a lesser extent, PERK. Furthermore, we captured the interaction between IRE1α and misfolded secretory proteins in cells, which suggests that the binding of unfolded proteins to preformed complexes of UPR sensors may be crucial for activation.

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Dynamic changes in oligomeric complexes of UPR sensors induced by misfolded proteins in the ER

10.1101/189605 ◽

2017 ◽

Author(s):

Arunkumar Sundaram ◽

Suhila Appathurai ◽

Malaiyalam Mariappan

Keyword(s):

Endoplasmic Reticulum ◽

Er Stress ◽

Unfolded Protein Response ◽

Mammalian Cells ◽

Negative Regulator ◽

Misfolded Proteins ◽

Dynamic Changes ◽

Unfolded Protein ◽

Stressed Cells ◽

Protein Response

AbstractThe endoplasmic reticulum (ER) localized unfolded protein response (UPR) sensors, IRE1α, PERK, and ATF6α, are activated upon accumulation of misfolded proteins caused by ER stress. It is debated whether these UPR sensors are activated either by the release of their negative regulator BiP chaperone or directly binding to misfolded proteins during ER stress. Here we simultaneously examined oligomerization and activation of all three endogenous UPR sensors. We found that UPR sensors existed as preformed oligomers even in unstressed cells, which shifted to large oligomers for PERK and small oligomers for ATF6α, but little changed for IRE1α upon ER stress. Neither depletion nor overexpression of BiP had significant effects on oligomeric complexes of UPR sensors both in unstressed and stressed cells. Thus, our results find less evidence for the BiP-mediated activation of UPR sensors in mammalian cells and support that misfolded proteins bind and activate the preformed oligomers of UPR sensors.

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Proteostasis In The Endoplasmic Reticulum: Road to Cure

Cancers ◽

10.3390/cancers11111793 ◽

2019 ◽

Vol 11 (11) ◽

pp. 1793 ◽

Cited By ~ 7

Author(s):

Nam ◽

Jeon

Keyword(s):

Endoplasmic Reticulum ◽

Er Stress ◽

Unfolded Protein Response ◽

Protein Quality ◽

Tumor Development ◽

Therapeutic Interventions ◽

Secretory Proteins ◽

Unfolded Protein ◽

Stress Signals ◽

Protein Response

The endoplasmic reticulum (ER) is an interconnected organelle that is responsible for the biosynthesis, folding, maturation, stabilization, and trafficking of transmembrane and secretory proteins. Therefore, cells evolve protein quality-control equipment of the ER to ensure protein homeostasis, also termed proteostasis. However, disruption in the folding capacity of the ER caused by a large variety of pathophysiological insults leads to the accumulation of unfolded or misfolded proteins in this organelle, known as ER stress. Upon ER stress, unfolded protein response (UPR) of the ER is activated, integrates ER stress signals, and transduces the integrated signals to relive ER stress, thereby leading to the re-establishment of proteostasis. Intriguingly, severe and persistent ER stress and the subsequently sustained unfolded protein response (UPR) are closely associated with tumor development, angiogenesis, aggressiveness, immunosuppression, and therapeutic response of cancer. Additionally, the UPR interconnects various processes in and around the tumor microenvironment. Therefore, it has begun to be delineated that pharmacologically and genetically manipulating strategies directed to target the UPR of the ER might exhibit positive clinical outcome in cancer. In the present review, we summarize recent advances in our understanding of the UPR of the ER and the UPR of the ER–mitochondria interconnection. We also highlight new insights into how the UPR of the ER in response to pathophysiological perturbations is implicated in the pathogenesis of cancer. We provide the concept to target the UPR of the ER, eventually discussing the potential of therapeutic interventions for targeting the UPR of the ER for cancer treatment.

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Activation of Mammalian Unfolded Protein Response Is Compatible with the Quality Control System Operating in the Endoplasmic Reticulum

Molecular Biology of the Cell ◽

10.1091/mbc.e03-09-0693 ◽

2004 ◽

Vol 15 (6) ◽

pp. 2537-2548 ◽

Cited By ~ 64

Author(s):

Satomi Nadanaka ◽

Hiderou Yoshida ◽

Fumi Kano ◽

Masayuki Murata ◽

Kazutoshi Mori

Keyword(s):

Quality Control ◽

Endoplasmic Reticulum ◽

Control System ◽

Golgi Apparatus ◽

Er Stress ◽

Unfolded Protein Response ◽

Secretory Pathway ◽

Unfolded Proteins ◽

Unfolded Protein ◽

Protein Response

Newly synthesized secretory and transmembrane proteins are folded and assembled in the endoplasmic reticulum (ER) where an efficient quality control system operates so that only correctly folded molecules are allowed to move along the secretory pathway. The productive folding process in the ER has been thought to be supported by the unfolded protein response (UPR), which is activated by the accumulation of unfolded proteins in the ER. However, a dilemma has emerged; activation of ATF6, a key regulator of mammalian UPR, requires intracellular transport from the ER to the Golgi apparatus. This suggests that unfolded proteins might be leaked from the ER together with ATF6 in response to ER stress, exhibiting proteotoxicity in the secretory pathway. We show here that ATF6 and correctly folded proteins are transported to the Golgi apparatus via the same route and by the same mechanism under conditions of ER stress, whereas unfolded proteins are retained in the ER. Thus, activation of the UPR is compatible with the quality control in the ER and the ER possesses a remarkable ability to select proteins to be transported in mammalian cells in marked contrast to yeast cells, which actively utilize intracellular traffic to deal with unfolded proteins accumulated in the ER.

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Possible involvement of endoplasmic reticulum stress in the pathogenesis of Alzheimer’s disease

Endoplasmic Reticulum Stress in Diseases ◽

10.1515/ersc-2015-0008 ◽

2015 ◽

Vol 2 (1) ◽

Cited By ~ 2

Author(s):

Toru Hosoi ◽

Jun Nomura ◽

Koichiro Ozawa ◽

Akinori Nishi ◽

Yasuyuki Nomura

Keyword(s):

Alzheimer’S Disease ◽

Alzheimer's Disease ◽

Quality Control ◽

Endoplasmic Reticulum ◽

Er Stress ◽

Protein Quality ◽

Unfolded Proteins ◽

Unfolded Protein ◽

The Unfolded Protein Response ◽

Protein Response

AbstractThe endoplasmic reticulum (ER) is an organelle that plays a crucial role in protein quality control such as protein folding. Evidence to indicate the involvement of ER in maintaining cellular homeostasis is increasing. However, when cells are exposed to stressful conditions, which perturb ER function, unfolded proteins accumulate leading to ER stress. Cells then activate the unfolded protein response (UPR) to cope with this stressful condition. In the present review, we will discuss and summarize recent advances in research on the basic mechanisms of the UPR. We also discuss the possible involvement of ER stress in the pathogenesis of Alzheimer’s disease (AD). Potential therapeutic opportunities for diseases targeting ER stress is also described.

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The Sec61 translocon limits IRE1α signaling during the unfolded protein response

eLife ◽

10.7554/elife.27187 ◽

2017 ◽

Vol 6 ◽

Cited By ~ 24

Author(s):

Arunkumar Sundaram ◽

Rachel Plumb ◽

Suhila Appathurai ◽

Malaiyalam Mariappan

Keyword(s):

Er Stress ◽

Cell Fate ◽

Stress Conditions ◽

Native Page ◽

Cell Fate Decisions ◽

Unfolded Protein ◽

Blue Native Page ◽

Oligomeric Complex ◽

The Unfolded Protein Response ◽

Protein Response

IRE1α is an endoplasmic reticulum (ER) localized endonuclease activated by misfolded proteins in the ER. Previously, we demonstrated that IRE1α forms a complex with the Sec61 translocon, to which its substrate XBP1u mRNA is recruited for cleavage during ER stress (<xref ref-type="bibr" rid="bib39">Plumb et al., 2015</xref>). Here, we probe IRE1α complexes in cells with blue native PAGE immunoblotting. We find that IRE1α forms a hetero-oligomeric complex with the Sec61 translocon that is activated upon ER stress with little change in the complex. In addition, IRE1α oligomerization, activation, and inactivation during ER stress are regulated by Sec61. Loss of the IRE1α-Sec61 translocon interaction as well as severe ER stress conditions causes IRE1α to form higher-order oligomers that exhibit continuous activation and extended cleavage of XBP1u mRNA. Thus, we propose that the Sec61-IRE1α complex defines the extent of IRE1α activity and may determine cell fate decisions during ER stress conditions.

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Endoplasmic reticulum stress as target for treatment of hearing loss

STEMedicine ◽

10.37175/stemedicine.v1i3.21 ◽

2020 ◽

Vol 1 (3) ◽

pp. e21

Author(s):

Yanfei Wang ◽

Zhigang Xu

Keyword(s):

Endoplasmic Reticulum ◽

Hearing Loss ◽

Er Stress ◽

Protein Biosynthesis ◽

Unfolded Proteins ◽

Unfolded Protein ◽

Global Protein Synthesis ◽

Acquired Hearing Loss ◽

The Unfolded Protein Response ◽

Protein Response

The endoplasmic reticulum (ER) plays pivotal roles in coordinating protein biosynthesis and processing. Under ER stress, when excessive misfolded or unfolded proteins are accumulated in the ER, the unfolded protein response (UPR) is activated. The UPR blocks global protein synthesis while activates chaperone expression, eventually leading to the alleviation of ER stress. However, prolonged UPR induces cell death. ER stress has been associated with various types of diseases. Recently, increasing evidences suggest that ER stress and UPR are also involved in hearing loss. In the present review, we will discuss the role of ER stress in hereditary hearing loss as well as acquired hearing loss. Moreover, we will discuss the emerging ER stress-based treatment of hearing loss. Further investigations are warranted to understand the mechanisms in detail how ER stress contributes to hearing loss, which will help us develop better ER stress-related treatments.

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Endoplasmic reticulum stress in biological processing and disease

Journal of Investigative Medicine ◽

10.1136/jim-2020-001570 ◽

2021 ◽

Vol 69 (2) ◽

pp. 309-315

Author(s):

Ali Riza Koksal ◽

George Nicholas Verne ◽

QiQi Zhou

Keyword(s):

Endoplasmic Reticulum ◽

Er Stress ◽

Chronic Diseases ◽

Unfolded Proteins ◽

Unfolded Protein ◽

Inflammatory Bowel ◽

The Unfolded Protein Response ◽

Protein Response ◽

Er Homeostasis ◽

Multiple Signaling

The ability of translated cellular proteins to perform their functions requires their proper folding after synthesis. The endoplasmic reticulum (ER) is responsible for coordinating protein folding and maturation. Infections, genetic mutations, environmental factors and many other conditions can lead to challenges to the ER known as ER stress. Altering ER homeostasis results in accumulation of misfolded or unfolded proteins. To eliminate this problem, a response is initiated by the cell called the unfolded protein response (UPR), which involves multiple signaling pathways. Prolonged ER stress or a dysregulated UPR can lead to premature apoptosis and an exaggerated inflammatory response. Following these discoveries, ER stress was shown to be related to several chronic diseases, such as diabetes mellitus, neurodegenerative disorders, fatty liver disease and inflammatory bowel disease that have not yet been clearly demonstrated pathophysiologically. Here, we review the field and present up-to-date information on the relationship between biological processing, ER stress, UPR, and several chronic diseases.

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The proteasome biogenesis regulator Rpn4 cooperates with the unfolded protein response to promote resistance to endoplasmic reticulum stress

10.1101/457077 ◽

2018 ◽

Author(s):

Rolf M. Schmidt ◽

Sebastian Schuck

Keyword(s):

Endoplasmic Reticulum ◽

Er Stress ◽

Unfolded Protein Response ◽

Protein Misfolding ◽

Misfolded Proteins ◽

Secretory Proteins ◽

Unfolded Protein ◽

The Unfolded Protein Response ◽

Protein Response ◽

Multiple Signaling

ABSTRACTMisfolded proteins in the endoplasmic reticulum (ER) activate the unfolded protein response (UPR), which enhances protein folding to restore homeostasis. Additional pathways respond to ER stress, but how they help counteract protein misfolding is incompletely understood. Here, we develop a titratable system for the induction of ER stress in yeast to enable a genetic screen for factors that augment stress resistance independently of the UPR. We identify the proteasome biogenesis regulator Rpn4 and show that it cooperates with the UPR. Rpn4 abundance increases during ER stress, first by a post-transcriptional, then by a transcriptional mechanism. Induction of RPN4 transcription is triggered by cytosolic mislocalization of secretory proteins, is mediated by multiple signaling pathways and accelerates clearance of misfolded proteins from the cytosol. Thus, Rpn4 and the UPR are complementary elements of a modular cross-compartment response to ER stress.

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Methods for Monitoring Endoplasmic Reticulum Stress and the Unfolded Protein Response

International Journal of Cell Biology ◽

10.1155/2010/830307 ◽

2010 ◽

Vol 2010 ◽

pp. 1-11 ◽

Cited By ~ 132

Author(s):

Afshin Samali ◽

Una FitzGerald ◽

Shane Deegan ◽

Sanjeev Gupta

Keyword(s):

Endoplasmic Reticulum ◽

Er Stress ◽

Unfolded Protein Response ◽

Model Systems ◽

Unfolded Proteins ◽

Unfolded Protein ◽

Cellular Repair ◽

Standard Set ◽

The Unfolded Protein Response ◽

Protein Response

The endoplasmic reticulum (ER) is the site of folding of membrane and secreted proteins in the cell. Physiological or pathological processes that disturb protein folding in the endoplasmic reticulum cause ER stress and activate a set of signaling pathways termed the Unfolded Protein Response (UPR). The UPR can promote cellular repair and sustained survival by reducing the load of unfolded proteins through upregulation of chaperones and global attenuation of protein synthesis. Research into ER stress and the UPR continues to grow at a rapid rate as many new investigators are entering the field. There are also many researchers not working directly on ER stress, but who wish to determine whether this response is activated in the system they are studying: thus, it is important to list a standard set of criteria for monitoring UPR in different model systems. Here, we discuss approaches that can be used by researchers to plan and interpret experiments aimed at evaluating whether the UPR and related processes are activated. We would like to emphasize that no individual assay is guaranteed to be the most appropriate one in every situation and strongly recommend the use of multiple assays to verify UPR activation.

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Translational Regulations in Response to Endoplasmic Reticulum Stress in Cancers

Cells ◽

10.3390/cells9030540 ◽

2020 ◽

Vol 9 (3) ◽

pp. 540 ◽

Cited By ~ 1

Author(s):

Manon Jaud ◽

Céline Philippe ◽

Doriana Di Bella ◽

Weiwei Tang ◽

Stéphane Pyronnet ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Protein Synthesis ◽

Er Stress ◽

Unfolded Protein Response ◽

Translational Control ◽

Biological Processes ◽

Unfolded Proteins ◽

Unfolded Protein ◽

Wide Range ◽

Protein Response

During carcinogenesis, almost all the biological processes are modified in one way or another. Among these biological processes affected, anomalies in protein synthesis are common in cancers. Indeed, cancer cells are subjected to a wide range of stresses, which include physical injuries, hypoxia, nutrient starvation, as well as mitotic, oxidative or genotoxic stresses. All of these stresses will cause the accumulation of unfolded proteins in the Endoplasmic Reticulum (ER), which is a major organelle that is involved in protein synthesis, preservation of cellular homeostasis, and adaptation to unfavourable environment. The accumulation of unfolded proteins in the endoplasmic reticulum causes stress triggering an unfolded protein response in order to promote cell survival or to induce apoptosis in case of chronic stress. Transcription and also translational reprogramming are tightly controlled during the unfolded protein response to ensure selective gene expression. The majority of stresses, including ER stress, induce firstly a decrease in global protein synthesis accompanied by the induction of alternative mechanisms for initiating the translation of mRNA, later followed by a translational recovery. After a presentation of ER stress and the UPR response, we will briefly present the different modes of translation initiation, then address the specific translational regulatory mechanisms acting during reticulum stress in cancers and highlight the importance of translational control by ER stress in tumours.

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