PERK Signaling Regulates Extracellular Proteostasis of an Amyloidogenic Protein During Endoplasmic Reticulum Stress

Stress Dependent ◽

Protein Response ◽

The Impact

ABSTRACTThe PERK arm of the unfolded protein response (UPR) regulates cellular proteostasis and survival in response to endoplasmic reticulum (ER) stress. However, the impact of PERK signaling on extracellular proteostasis is poorly understood. We define how PERK signaling influences extracellular proteostasis during ER stress using a conformational reporter of the secreted amyloidogenic protein transthyretin (TTR). We show that inhibiting PERK signaling impairs ER stress-dependent secretion of destabilized TTR by increasing its ER retention in chaperone-bound complexes. Interestingly, PERK inhibition promotes the ER stress-dependent secretion of TTR in non-native conformations that accumulate extracellularly as soluble oligomers. Pharmacologic or genetic TTR stabilization partially restores secretion of native TTR tetramers. However, PERK inhibition still increases the ER stress-dependent secretion of TTR in non-native conformations under these conditions, indicating that the conformation of stable secreted proteins can also be affected by inhibiting PERK. Our results define a role for PERK in regulating extracellular proteostasis during ER stress and indicate that genetic or aging-related alterations in PERK signaling can exacerbate ER stress-related imbalances in extracellular proteostasis implicated in diverse diseases.

The Impact of Endoplasmic Reticulum-Associated Protein Modifications, Folding and Degradation on Lung Structure and Function

Frontiers in Physiology ◽

10.3389/fphys.2021.665622 ◽

2021 ◽

Vol 12 ◽

Author(s):

Emily M. Nakada ◽

Rui Sun ◽

Utako Fujii ◽

James G. Martin

Keyword(s):

Endoplasmic Reticulum ◽

Er Stress ◽

Unfolded Protein ◽

Lung Structure ◽

Selective Translation ◽

And Function ◽

Protein Response ◽

Er Homeostasis ◽

The Impact

The accumulation of unfolded/misfolded proteins in the endoplasmic reticulum (ER) causes ER stress and induces the unfolded protein response (UPR) and other mechanisms to restore ER homeostasis, including translational shutdown, increased targeting of mRNAs for degradation by the IRE1-dependent decay pathway, selective translation of proteins that contribute to the protein folding capacity of the ER, and activation of the ER-associated degradation machinery. When ER stress is excessive or prolonged and these mechanisms fail to restore proteostasis, the UPR triggers the cell to undergo apoptosis. This review also examines the overlooked role of post-translational modifications and their roles in protein processing and effects on ER stress and the UPR. Finally, these effects are examined in the context of lung structure, function, and disease.

Endoplasmic reticulum stress differentially modulates the IL-6 family of cytokines in murine astrocytes and macrophages

Scientific Reports ◽

10.1038/s41598-019-51481-6 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 4

Author(s):

Cristina L. Sanchez ◽

Savannah G. Sims ◽

John D. Nowery ◽

Gordon P. Meares

Keyword(s):

Endoplasmic Reticulum ◽

Er Stress ◽

Cell Types ◽

Janus Kinase ◽

Unfolded Protein ◽

Leukemia Inhibitor Factor ◽

Protein Response ◽

The Impact ◽

Dependent Mechanism

Abstract In many diseases, misfolded proteins accumulate within the endoplasmic reticulum (ER), leading to ER stress. In response, the cell initiates the unfolded protein response (UPR) to reestablish homeostasis. Additionally, in response to ER stress, various cell types mount an inflammatory response involving interleukin (IL)-6. While IL-6 has been widely studied, the impact of ER stress on other members of the IL-6 cytokine family, including oncostatin (OSM), IL-11, ciliary neurotrophic factor (CNTF), and leukemia inhibitor factor (LIF) remains to be elucidated. Here, we have examined the expression of the IL-6 family cytokines in response to pharmacologically-induced ER stress in astrocytes and macrophages, which express IL-6 in response to ER stress through different mechanisms. Our findings indicate that, in astrocytes, ER stress regulates mRNA expression of the IL-6 family of cytokines that is, in part, mediated by PKR-like ER kinase (PERK) and Janus kinase (JAK) 1. Additionally, in astrocytes, CNTF expression was suppressed through a PERK-dependent mechanism. Macrophages display a different profile of expression of the IL-6 family that is largely independent of PERK. However, IL-6 expression in macrophages was dependent on JAK signaling. Overall, this study demonstrates the cell-specific and differential mechanisms controlling expression of the IL-6 family of cytokines in response to ER stress.

IreA controls endoplasmic reticulum stress-induced autophagy and survival through homeostasis recovery

Molecular and Cellular Biology ◽

10.1128/mcb.00054-18 ◽

2018 ◽

pp. MCB.00054-18 ◽

Cited By ~ 6

Author(s):

Eunice Domínguez-Martín ◽

Laura Ongay-Larios ◽

Laura Kawasaki ◽

Olivier Vincent ◽

Gerardo Coello ◽

...

Keyword(s):

Gene Expression ◽

Endoplasmic Reticulum ◽

Er Stress ◽

Cell Survival ◽

Eukaryotic Cell ◽

Functional Link ◽

Unfolded Protein ◽

Transcriptional Changes ◽

The Unfolded Protein Response (UPR) is an adaptive pathway that restores cellular homeostasis after endoplasmic reticulum (ER) stress. The ER-resident kinase/ribonuclease Ire1 is the only UPR sensor conserved during evolution. Autophagy, a lysosomal degradative pathway, also contributes to the recovery of cell homeostasis after ER-stress but the interplay between these two pathways is still poorly understood. We describe the Dictyostelium discoideum ER-stress response and characterize its single bonafide Ire1 orthologue, IreA. We found that tunicamycin (TN) triggers a gene-expression reprogramming that increases the protein folding capacity of the ER and alleviates ER protein load. Further, IreA is required for cell-survival after TN-induced ER-stress and is responsible for nearly 40% of the transcriptional changes induced by TN. The response of Dictyostelium cells to ER-stress involves the combined activation of an IreA-dependent gene expression program and the autophagy pathway. These two pathways are independently activated in response to ER-stress but, interestingly, autophagy requires IreA at a later stage for proper autophagosome formation. We propose that unresolved ER-stress in cells lacking IreA causes structural alterations of the ER, leading to a late-stage blockade of autophagy clearance. This unexpected functional link may critically affect eukaryotic cell survival under ER-stress.

ER stress in neurodegenerative disease: from disease mechanisms to therapeutic interventions

Endoplasmic Reticulum Stress in Diseases ◽

10.1515/ersc-2017-0002 ◽

2017 ◽

Vol 4 (1) ◽

Cited By ~ 2

Author(s):

Felipe Cabral-Miranda ◽

Claudio Hetz

Keyword(s):

Endoplasmic Reticulum ◽

Neurodegenerative Diseases ◽

Er Stress ◽

Major Element ◽

Neuronal Loss ◽

Therapeutic Interventions ◽

Unfolded Protein ◽

Disease Mechanisms ◽

AbstractThe conception that protein aggregates composed by misfolded proteins underlies the occurrence of several neurodegenerative diseases suggests that this phenomenon may have a common origin, ultimately driven by disruption of proteostasis control. The unfolded protein response (UPR) embodies a major element of the proteostasis network, which is engaged by endoplasmic reticulum (ER) stress. Chronic ER stress may operate as a possible mechanism of neurodegeneration, contributing to synaptic alterations, neuroinflammation and neuronal loss. In this review we discuss most recent findings relating ER stress and the development of distinct neurodegenerative diseases, and the possible strategies for disease intervention.

The PGRS Domain of Mycobacterium tuberculosis PE_PGRS Protein Rv0297 Is Involved in Endoplasmic Reticulum Stress-Mediated Apoptosis through Toll-Like Receptor 4

mBio ◽

10.1128/mbio.01017-18 ◽

2018 ◽

Vol 9 (3) ◽

Cited By ~ 19

Author(s):

Sonam Grover ◽

Tarina Sharma ◽

Yadvir Singh ◽

Sakshi Kohli ◽

Manjunath P. ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Mycobacterium Tuberculosis ◽

Er Stress ◽

Toll Like Receptor ◽

Toll Like Receptor 4 ◽

Content Type ◽

Unfolded Protein ◽

ABSTRACT The genome of Mycobacterium tuberculosis , the causal organism of tuberculosis (TB), encodes a unique protein family known as the PE/PPE/PGRS family, present exclusively in the genus Mycobacterium and nowhere else in the living kingdom, with largely unexplored functions. We describe the functional significance of the PGRS domain of Rv0297, a member of this family. In silico analyses revealed the presence of intrinsically disordered stretches and putative endoplasmic reticulum (ER) localization signals in the PGRS domain of Rv0297 (Rv0297PGRS). The PGRS domain aids in ER localization, which was shown by infecting macrophage cells with M. tuberculosis and by overexpressing the protein by transfection in macrophage cells followed by activation of the unfolded protein response, as evident from increased expression of GRP78/GRP94 and CHOP/ATF4, leading to disruption of intracellular Ca 2+ homeostasis and increased nitric oxide (NO) and reactive oxygen species (ROS) production. The consequent activation of the effector caspase-8 resulted in apoptosis of macrophages, which was Toll-like receptor 4 (TLR4) dependent. Administration of recombinant Rv0297PGRS (rRv0297PGRS) also exhibited similar effects. These results implicate a hitherto-unknown role of the PGRS domain of the PE_PGRS protein family in ER stress-mediated cell death through TLR4. Since this protein is already known to be present at later stages of infection in human granulomas it points to the possibility of it being employed by M. tuberculosis for its dissemination via an apoptotic mechanism. IMPORTANCE Apoptosis is generally thought to be a defense mechanism in protecting the host against Mycobacterium tuberculosis in early stages of infection. However, apoptosis during later stages in lung granulomas may favor the bacterium in disseminating the disease. ER stress has been found to induce apoptosis in TB granulomas, in zones where apoptotic macrophages accumulate in mice and humans. In this study, we report ER stress-mediated apoptosis of host cells by the Rv0297-encoded PE_PGRS5 protein of M. tuberculosis exceptionally present in the pathogenic Mycobacterium genus. The PGRS domain of Rv0297 aids the protein in localizing to the ER and induces the unfolded protein response followed by apoptosis of macrophages. The effect of the Rv0297PGRS domain was found to be TLR4 dependent. This study presents novel insights on the strategies employed by M. tuberculosis to disseminate the disease.

Endoplasmic Reticulum Stress and Unfolded Protein Response in Breast Cancer: The Balance between Apoptosis and Autophagy and Its Role in Drug Resistance

International Journal of Molecular Sciences ◽

10.3390/ijms20040857 ◽

2019 ◽

Vol 20 (4) ◽

pp. 857 ◽

Cited By ~ 20

Author(s):

Lorenza Sisinni ◽

Michele Pietrafesa ◽

Silvia Lepore ◽

Francesca Maddalena ◽

Valentina Condelli ◽

...

Keyword(s):

Breast Cancer ◽

Endoplasmic Reticulum ◽

Er Stress ◽

Inflammatory Diseases ◽

Unfolded Protein ◽

Chronic Activation ◽

Protein Response ◽

The Relationship

The unfolded protein response (UPR) is a stress response activated by the accumulation of unfolded or misfolded proteins in the lumen of the endoplasmic reticulum (ER) and its uncontrolled activation is mechanistically responsible for several human pathologies, including metabolic, neurodegenerative, and inflammatory diseases, and cancer. Indeed, ER stress and the downstream UPR activation lead to changes in the levels and activities of key regulators of cell survival and autophagy and this is physiologically finalized to restore metabolic homeostasis with the integration of pro-death or/and pro-survival signals. By contrast, the chronic activation of UPR in cancer cells is widely considered a mechanism of tumor progression. In this review, we focus on the relationship between ER stress, apoptosis, and autophagy in human breast cancer and the interplay between the activation of UPR and resistance to anticancer therapies with the aim to disclose novel therapeutic scenarios. The hypothesis that autophagy and UPR may provide novel molecular targets in human malignancies is discussed.

Endoplasmic reticulum stress and the unfolded protein response in pancreatic islet inflammation

Journal of Molecular Endocrinology ◽

10.1530/jme-15-0306 ◽

2016 ◽

Vol 57 (1) ◽

pp. R1-R17 ◽

Cited By ~ 31

Author(s):

Kira Meyerovich ◽

Fernanda Ortis ◽

Florent Allagnat ◽

Alessandra K Cardozo

Keyword(s):

Endoplasmic Reticulum ◽

Er Stress ◽

Diabetic Patients ◽

Β Cells ◽

Β Cell ◽

Unfolded Protein ◽

Islet Inflammation ◽

Insulin-secreting pancreatic β-cells are extremely dependent on their endoplasmic reticulum (ER) to cope with the oscillatory requirement of secreted insulin to maintain normoglycemia. Insulin translation and folding rely greatly on the unfolded protein response (UPR), an array of three main signaling pathways designed to maintain ER homeostasis and limit ER stress. However, prolonged or excessive UPR activation triggers alternative molecular pathways that can lead to β-cell dysfunction and apoptosis. An increasing number of studies suggest a role of these pro-apoptotic UPR pathways in the downfall of β-cells observed in diabetic patients. Particularly, the past few years highlighted a cross talk between the UPR and inflammation in the context of both type 1 (T1D) and type 2 diabetes (T2D). In this article, we describe the recent advances in research regarding the interplay between ER stress, the UPR, and inflammation in the context of β-cell apoptosis leading to diabetes.

Endoplasmic reticulum stress regulation of the Kar2p/BiP chaperone alleviates proteotoxicity via dual degradation pathways

Molecular Biology of the Cell ◽

10.1091/mbc.e11-04-0297 ◽

2012 ◽

Vol 23 (4) ◽

pp. 630-641 ◽

Cited By ~ 6

Author(s):

Chia-Ling Hsu ◽

Rupali Prasad ◽

Christie Blackman ◽

Davis T. W. Ng

Keyword(s):

Endoplasmic Reticulum ◽

Er Stress ◽

Target Genes ◽

Regulatory Element ◽

Unfolded Protein ◽

Single Target ◽

Transcriptional Regulatory ◽

Protein Response ◽

Stress Activation

The unfolded protein response (UPR) monitors and maintains protein homeostasis in the endoplasmic reticulum (ER). In budding yeast, the UPR is a transcriptional regulatory pathway that is quiescent under normal conditions. Under conditions of acute ER stress, activation of UPR targets is essential for cell viability. How individual target genes contribute to stress tolerance is unclear. Uncovering these roles is hampered because most targets also play important functions in the absence of stress. To differentiate stress-specific roles from everyday functions, a single target gene was uncoupled from UPR control by eliminating its UPR-specific regulatory element. Through this approach, the UPR remains intact, aside from its inability to induce the designated target. Applying the strategy to the major ER chaperone Kar2p/BiP revealed the physiological function of increasing its cellular concentration. Despite hundreds of target genes under UPR control, we show that activation of KAR2 is indispensable to alleviate some forms of ER stress. Specifically, activation is essential to dispose misfolded proteins that are otherwise toxic. Surprisingly, induced BiP/Kar2p molecules are dedicated to alleviating stress. The inability to induce KAR2 under stress had no effect on its known housekeeping functions.

Cu, Zn Superoxide Dismutase and NADP(H) Homeostasis Are Required for Tolerance of Endoplasmic Reticulum Stress inSaccharomyces cerevisiae

Molecular Biology of the Cell ◽

10.1091/mbc.e08-07-0697 ◽

2009 ◽

Vol 20 (5) ◽

pp. 1493-1508 ◽

Cited By ~ 44

Author(s):

Shi-Xiong Tan ◽

Mariati Teo ◽

Yuen T. Lam ◽

Ian W. Dawes ◽

Gabriel G. Perrone

Keyword(s):

Endoplasmic Reticulum ◽

Superoxide Dismutase ◽

Er Stress ◽

Stress Sensitivity ◽

Pentose Phosphate ◽

Unfolded Protein ◽

Genome Wide ◽

Genome-wide screening for sensitivity to chronic endoplasmic reticulum (ER) stress induced by dithiothreitol and tunicamycin (TM) identified mutants deleted for Cu, Zn superoxide dismutase (SOD) function (SOD1, CCS1) or affected in NADPH generation via the pentose phosphate pathway (TKL1, RPE1). TM-induced ER stress led to an increase in cellular superoxide accumulation and an increase in SOD1 expression and Sod1p activity. Prior adaptation of the hac1 mutant deficient in the unfolded protein response (UPR) to the superoxide-generating agent paraquat reduced cell death under ER stress. Overexpression of the ER oxidoreductase Ero1p known to generate hydrogen peroxide in vitro, did not lead to increased superoxide levels in cells subjected to ER stress. The mutants lacking SOD1, TKL1, or RPE1 exhibited decreased UPR induction under ER stress. Sensitivity of the sod1 mutant to ER stress and decreased UPR induction was partially rescued by overexpression of TKL1 encoding transketolase. These data indicate an important role for SOD and cellular NADP(H) in cell survival during ER stress, and it is proposed that accumulation of superoxide affects NADP(H) homeostasis, leading to reduced UPR induction during ER stress.

Ratiometric sensing of BiP-client versus BiP levels by the unfolded protein response determines its signaling amplitude

eLife ◽

10.7554/elife.27518 ◽

2017 ◽

Vol 6 ◽

Cited By ~ 26

Author(s):

Anush Bakunts ◽

Andrea Orsi ◽

Milena Vitale ◽

Angela Cattaneo ◽

Federica Lari ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Er Stress ◽

Heavy Chain ◽

Immunoglobulin M ◽

Unfolded Protein ◽

Er Chaperone ◽

Ideal System ◽

Insufficient folding capacity of the endoplasmic reticulum (ER) activates the unfolded protein response (UPR) to restore homeostasis. Yet, how the UPR achieves ER homeostatic readjustment is poorly investigated, as in most studies the ER stress that is elicited cannot be overcome. Here we show that a proteostatic insult, provoked by persistent expression of the secretory heavy chain of immunoglobulin M (µs), is well-tolerated in HeLa cells. Upon µs expression, its levels temporarily eclipse those of the ER chaperone BiP, leading to acute, full-geared UPR activation. Once BiP is in excess again, the UPR transitions to chronic, submaximal activation, indicating that the UPR senses ER stress in a ratiometric fashion. In this process, the ER expands about three-fold and becomes dominated by BiP. As the UPR is essential for successful ER homeostatic readjustment in the HeLa-µs model, it provides an ideal system for dissecting the intricacies of how the UPR evaluates and alleviates ER stress.