1
|
Zhang SX, Wang JJ, Starr CR, Lee EJ, Park KS, Zhylkibayev A, Medina A, Lin JH, Gorbatyuk M. The endoplasmic reticulum: Homeostasis and crosstalk in retinal health and disease. Prog Retin Eye Res 2024; 98:101231. [PMID: 38092262 PMCID: PMC11056313 DOI: 10.1016/j.preteyeres.2023.101231] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2023] [Revised: 12/05/2023] [Accepted: 12/06/2023] [Indexed: 12/19/2023]
Abstract
The endoplasmic reticulum (ER) is the largest intracellular organelle carrying out a broad range of important cellular functions including protein biosynthesis, folding, and trafficking, lipid and sterol biosynthesis, carbohydrate metabolism, and calcium storage and gated release. In addition, the ER makes close contact with multiple intracellular organelles such as mitochondria and the plasma membrane to actively regulate the biogenesis, remodeling, and function of these organelles. Therefore, maintaining a homeostatic and functional ER is critical for the survival and function of cells. This vital process is implemented through well-orchestrated signaling pathways of the unfolded protein response (UPR). The UPR is activated when misfolded or unfolded proteins accumulate in the ER, a condition known as ER stress, and functions to restore ER homeostasis thus promoting cell survival. However, prolonged activation or dysregulation of the UPR can lead to cell death and other detrimental events such as inflammation and oxidative stress; these processes are implicated in the pathogenesis of many human diseases including retinal disorders. In this review manuscript, we discuss the unique features of the ER and ER stress signaling in the retina and retinal neurons and describe recent advances in the research to uncover the role of ER stress signaling in neurodegenerative retinal diseases including age-related macular degeneration, inherited retinal degeneration, achromatopsia and cone diseases, and diabetic retinopathy. In some chapters, we highlight the complex interactions between the ER and other intracellular organelles focusing on mitochondria and illustrate how ER stress signaling regulates common cellular stress pathways such as autophagy. We also touch upon the integrated stress response in retinal degeneration and diabetic retinopathy. Finally, we provide an update on the current development of pharmacological agents targeting the UPR response and discuss some unresolved questions and knowledge gaps to be addressed by future research.
Collapse
Affiliation(s)
- Sarah X Zhang
- Department of Ophthalmology and Ross Eye Institute, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, State University of New York, Buffalo, NY, United States; Department of Biochemistry, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, State University of New York, Buffalo, NY, United States.
| | - Josh J Wang
- Department of Ophthalmology and Ross Eye Institute, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, State University of New York, Buffalo, NY, United States
| | - Christopher R Starr
- Department of Optometry and Vision Science, University of Alabama at Birmingham, Birmingham, AL, United States
| | - Eun-Jin Lee
- Department of Ophthalmology and Byers Eye Institute, Stanford University, Stanford, CA, United States; VA Palo Alto Healthcare System, Palo Alto, CA, United States; Department of Pathology, Stanford University, Stanford, CA, United States
| | - Karen Sophia Park
- Department of Ophthalmology and Ross Eye Institute, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, State University of New York, Buffalo, NY, United States
| | - Assylbek Zhylkibayev
- Department of Optometry and Vision Science, University of Alabama at Birmingham, Birmingham, AL, United States
| | - Andy Medina
- Department of Ophthalmology and Ross Eye Institute, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, State University of New York, Buffalo, NY, United States
| | - Jonathan H Lin
- Department of Ophthalmology and Byers Eye Institute, Stanford University, Stanford, CA, United States; VA Palo Alto Healthcare System, Palo Alto, CA, United States; Department of Pathology, Stanford University, Stanford, CA, United States
| | - Marina Gorbatyuk
- Department of Optometry and Vision Science, University of Alabama at Birmingham, Birmingham, AL, United States
| |
Collapse
|
2
|
Lee EJ, Diaz-Aguilar MS, Min H, Choi J, Valdez Duran DA, Grandjean JM, Wiseman RL, Kroeger H, Lin JH. Mitochondria and Endoplasmic Reticulum Stress in Retinal Organoids from Patients with Vision Loss. THE AMERICAN JOURNAL OF PATHOLOGY 2023; 193:1721-1739. [PMID: 36535406 PMCID: PMC10616714 DOI: 10.1016/j.ajpath.2022.12.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/19/2022] [Revised: 11/10/2022] [Accepted: 12/05/2022] [Indexed: 12/23/2022]
Abstract
Activating transcription factor 6 (ATF6), a key regulator of the unfolded protein response, plays a key role in endoplasmic reticulum function and protein homeostasis. Variants of ATF6 that abrogate transcriptional activity cause morphologic and molecular defects in cones, clinically manifesting as the human vision loss disease achromatopsia (ACHM). ATF6 is expressed in all retinal cells. However, the effect of disease-associated ATF6 variants on other retinal cell types remains unclear. Herein, this was investigated by analyzing bulk RNA-sequencing transcriptomes from retinal organoids generated from patients with ACHM, carrying homozygous loss-of-function ATF6 variants. Marked dysregulation in mitochondrial respiratory complex gene expression and disrupted mitochondrial morphology in ACHM retinal organoids were identified. This indicated that loss of ATF6 leads to previously unappreciated mitochondrial defects in the retina. Next, gene expression from control and ACHM retinal organoids were compared with transcriptome profiles of seven major retinal cell types generated from recent single-cell transcriptomic maps of nondiseased human retina. This indicated pronounced down-regulation of cone genes and up-regulation in Müller glia genes, with no significant effects on other retinal cells. Overall, the current analysis of ACHM patient retinal organoids identified new cellular and molecular phenotypes in addition to cone dysfunction: activation of Müller cells, increased endoplasmic reticulum stress, disrupted mitochondrial structure, and elevated respiratory chain activity gene expression.
Collapse
Affiliation(s)
- Eun-Jin Lee
- Department of Ophthalmology, Stanford University, Stanford, California; Department of Pathology, VA Palo Alto Healthcare System, Palo Alto, California; Department of Pathology, Stanford University, Stanford, California
| | - Monica S Diaz-Aguilar
- Department of Ophthalmology, Stanford University, Stanford, California; Department of Pathology, VA Palo Alto Healthcare System, Palo Alto, California; Department of Pathology, Stanford University, Stanford, California; Department of Medicine, Rush University Medical College, Chicago, Illinois
| | - Hyejung Min
- Department of Pathology, VA Palo Alto Healthcare System, Palo Alto, California; Department of Pathology, Stanford University, Stanford, California
| | - Jihee Choi
- Department of Pathology, Stanford University, Stanford, California
| | | | - Julia M Grandjean
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, California
| | - R Luke Wiseman
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, California
| | - Heike Kroeger
- Department of Cellular Biology, University of Georgia, Athens, Georgia
| | - Jonathan H Lin
- Department of Ophthalmology, Stanford University, Stanford, California; Department of Pathology, VA Palo Alto Healthcare System, Palo Alto, California; Department of Pathology, Stanford University, Stanford, California.
| |
Collapse
|
3
|
Ricci D, Gidalevitz T, Argon Y. The special unfolded protein response in plasma cells. Immunol Rev 2021; 303:35-51. [PMID: 34368957 DOI: 10.1111/imr.13012] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2021] [Accepted: 06/08/2021] [Indexed: 12/11/2022]
Abstract
The high rate of antibody production places considerable metabolic and folding stress on plasma cells (PC). Not surprisingly, they rely on the unfolded protein response (UPR), a universal signaling, and transcriptional network that monitors the health of the secretory pathway and mounts cellular responses to stress. Typically, the UPR utilizes three distinct stress sensors in the ER membrane, each regulating a subset of targets to re-establish homeostasis. PC use a specialized UPR scheme-they preemptively trigger the UPR via developmental signals and suppress two of the sensors, PERK and ATF6, relying on IRE1 alone. The specialized PC UPR program is tuned to the specific needs at every stage of development-from early biogenesis of secretory apparatus, to massive immunoglobulin expression later. Furthermore, the UPR in PC integrates with other pathways essential in a highly secretory cell-mTOR pathway that ensures efficient synthesis, autophagosomes that recycle components of the synthetic machinery, and apoptotic signaling that controls cell fate in the face of excessive folding stress. This specialized PC program is not shared with other secretory cells, for reasons yet to be defined. In this review, we give a perspective into how and why PC need such a unique UPR program.
Collapse
Affiliation(s)
- Daniela Ricci
- Department of Pathology and Lab Medicine, The Childrens' Hospital of Philadelphia and the University of Pennsylvania, Philadelphia, PA, USA
| | - Tali Gidalevitz
- Department of Biology, Drexel University, Philadelphia, PA, USA
| | - Yair Argon
- Department of Pathology and Lab Medicine, The Childrens' Hospital of Philadelphia and the University of Pennsylvania, Philadelphia, PA, USA
| |
Collapse
|
4
|
Unfolded protein response during cardiovascular disorders: a tilt towards pro-survival and cellular homeostasis. Mol Cell Biochem 2021; 476:4061-4080. [PMID: 34259975 DOI: 10.1007/s11010-021-04223-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2021] [Accepted: 07/08/2021] [Indexed: 12/13/2022]
Abstract
The endoplasmic reticulum (ER) is an organelle that orchestrates the production and proper assembly of an extensive types of secretory and membrane proteins. Endoplasmic reticulum stress is conventionally related to prolonged disruption in the protein folding machinery resulting in the accumulation of unfolded proteins in the ER. This disruption is often manifested due to oxidative stress, Ca2+ leakage, iron imbalance, disease conditions which in turn hampers the cellular homeostasis and induces cellular apoptosis. A mild ER stress is often reverted back to normal. However, cells retaliate to acute ER stress by activating the unfolded protein response (UPR) which comprises three signaling pathways, Activating transcription factor 6 (ATF6), inositol requiring enzyme 1 alpha (IRE1α), and protein kinase RNA-activated-like ER kinase (PERK). The UPR response participates in both protective and pro-apoptotic responses and not much is known about the mechanistic aspects of the switch from pro-survival to pro-apoptosis. When ER stress outpaces UPR response then cell apoptosis prevails which often leads to the development of various diseases including cardiomyopathies. Therefore, it is important to identify molecules that modulate the UPR that may serve as promising tools towards effective treatment of cardiovascular diseases. In this review, we elucidated the latest advances in construing the contribution imparted by the three arms of UPR to combat the adverse environment in the ER to restore cellular homeostasis during cardiomyopathies. We also summarized the various therapeutic agents that plays crucial role in tilting the UPR response towards pro-survival.
Collapse
|
5
|
Rius B, Mesgarzadeh JS, Romine IC, Paxman RJ, Kelly JW, Wiseman RL. Pharmacologic targeting of plasma cell endoplasmic reticulum proteostasis to reduce amyloidogenic light chain secretion. Blood Adv 2021; 5:1037-1049. [PMID: 33599742 PMCID: PMC7903236 DOI: 10.1182/bloodadvances.2020002813] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2020] [Accepted: 01/05/2021] [Indexed: 02/08/2023] Open
Abstract
Light chain (LC) amyloidosis (AL) involves the toxic aggregation of amyloidogenic immunoglobulin LCs secreted from a clonal expansion of diseased plasma cells. Current AL treatments use chemotherapeutics to ablate the AL plasma cell population. However, no treatments are available that directly reduce the toxic LC aggregation involved in AL pathogenesis. An attractive strategy to reduce toxic LC aggregation in AL involves enhancing endoplasmic reticulum (ER) proteostasis in plasma cells to reduce the secretion and subsequent aggregation of amyloidogenic LCs. Here, we show that the ER proteostasis regulator compound 147 reduces secretion of an amyloidogenic LC as aggregation-prone monomers and dimers in AL patient-derived plasma cells. Compound 147 was established to promote ER proteostasis remodeling by activating the ATF6 unfolded protein response signaling pathway through a mechanism involving covalent modification of ER protein disulfide isomerases (PDIs). However, we show that 147-dependent reductions in amyloidogenic LCs are independent of ATF6 activation. Instead, 147 reduces amyloidogenic LC secretion through the selective, on-target covalent modification of ER proteostasis factors, including PDIs, revealing an alternative mechanism by which this compound can influence ER proteostasis of amyloidogenic proteins. Importantly, compound 147 does not interfere with AL plasma cell toxicity induced by bortezomib, a standard chemotherapeutic used to ablate the underlying diseased plasma cells in AL. This shows that pharmacologic targeting of ER proteostasis through selective covalent modification of ER proteostasis factors is a strategy that can be used in combination with chemotherapeutics to reduce the LC toxicity associated with AL pathogenesis.
Collapse
Affiliation(s)
| | | | | | | | - Jeffery W Kelly
- Department of Chemistry, and
- Skaggs Institute for Chemical Biology, Scripps Research Institute, La Jolla, CA
| | | |
Collapse
|
6
|
Grandjean JMD, Wiseman RL. Small molecule strategies to harness the unfolded protein response: where do we go from here? J Biol Chem 2020; 295:15692-15711. [PMID: 32887796 PMCID: PMC7667976 DOI: 10.1074/jbc.rev120.010218] [Citation(s) in RCA: 52] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2020] [Revised: 09/02/2020] [Indexed: 12/31/2022] Open
Abstract
The unfolded protein response (UPR) plays a central role in regulating endoplasmic reticulum (ER) and global cellular physiology in response to pathologic ER stress. The UPR is comprised of three signaling pathways activated downstream of the ER membrane proteins IRE1, ATF6, and PERK. Once activated, these proteins initiate transcriptional and translational signaling that functions to alleviate ER stress, adapt cellular physiology, and dictate cell fate. Imbalances in UPR signaling are implicated in the pathogenesis of numerous, etiologically-diverse diseases, including many neurodegenerative diseases, protein misfolding diseases, diabetes, ischemic disorders, and cancer. This has led to significant interest in establishing pharmacologic strategies to selectively modulate IRE1, ATF6, or PERK signaling to both ameliorate pathologic imbalances in UPR signaling implicated in these different diseases and define the importance of the UPR in diverse cellular and organismal contexts. Recently, there has been significant progress in the identification and characterization of UPR modulating compounds, providing new opportunities to probe the pathologic and potentially therapeutic implications of UPR signaling in human disease. Here, we describe currently available UPR modulating compounds, specifically highlighting the strategies used for their discovery and specific advantages and disadvantages in their application for probing UPR function. Furthermore, we discuss lessons learned from the application of these compounds in cellular and in vivo models to identify favorable compound properties that can help drive the further translational development of selective UPR modulators for human disease.
Collapse
Affiliation(s)
- Julia M D Grandjean
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, California, USA
| | - R Luke Wiseman
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, California, USA.
| |
Collapse
|
7
|
Kelly JW. Pharmacologic Approaches for Adapting Proteostasis in the Secretory Pathway to Ameliorate Protein Conformational Diseases. Cold Spring Harb Perspect Biol 2020; 12:a034108. [PMID: 31088828 PMCID: PMC7197434 DOI: 10.1101/cshperspect.a034108] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Maintenance of the proteome, ensuring the proper locations, proper conformations, appropriate concentrations, etc., is essential to preserve the health of an organism in the face of environmental insults, infectious diseases, and the challenges associated with aging. Maintaining the proteome is even more difficult in the background of inherited mutations that render a given protein and others handled by the same proteostasis machinery misfolding prone and/or aggregation prone. Maintenance of the proteome or maintaining proteostasis requires the orchestration of protein synthesis, folding, trafficking, and degradation by way of highly conserved, interacting, and competitive proteostasis pathways. Each subcellular compartment has a unique proteostasis network compromising common and specialized proteostasis maintenance pathways. Stress-responsive signaling pathways detect the misfolding and/or aggregation of proteins in specific subcellular compartments using stress sensors and respond by generating an active transcription factor. Subsequent transcriptional programs up-regulate proteostasis network capacity (i.e., ability to fold and degrade proteins in that compartment). Stress-responsive signaling pathways can also be linked by way of signaling cascades to nontranscriptional means to reestablish proteostasis (e.g., by translational attenuation). Proteostasis is also strongly influenced by the inherent kinetics and thermodynamics of the folding, misfolding, and aggregation of individual proteins, and these sequence-based attributes in combination with proteostasis network capacity together influence proteostasis. In this review, we will focus on the growing body of evidence that proteostasis deficits leading to human pathology can be reversed by pharmacologic adaptation of proteostasis network capacity through stress-responsive signaling pathway activation. The power of this approach will be exemplified by focusing on the ATF6 arm of the unfolded protein response stress responsive-signaling pathway that regulates proteostasis network capacity of the secretory pathway.
Collapse
Affiliation(s)
- Jeffery W Kelly
- Departments of Chemistry and Molecular Medicine; and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, California 92037
| |
Collapse
|
8
|
Lee EJ, Chiang WCJ, Kroeger H, Bi CX, Chao DL, Skowronska-Krawczyk D, Mastey RR, Tsang SH, Chea L, Kim K, Lambert SR, Grandjean JM, Baumann B, Audo I, Kohl S, Moore AT, Wiseman RL, Carroll J, Lin JH. Multiexon deletion alleles of ATF6 linked to achromatopsia. JCI Insight 2020; 5:136041. [PMID: 32271167 PMCID: PMC7205249 DOI: 10.1172/jci.insight.136041] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2019] [Accepted: 03/04/2020] [Indexed: 12/20/2022] Open
Abstract
Achromatopsia (ACHM) is an autosomal recessive disease that results in severe visual loss. Symptoms of ACHM include impaired visual acuity, nystagmus, and photoaversion starting from infancy; furthermore, ACHM is associated with bilateral foveal hypoplasia and absent or severely reduced cone photoreceptor function on electroretinography. Here, we performed genetic sequencing in 3 patients from 2 families with ACHM, identifying and functionally characterizing 2 mutations in the activating transcription factor 6 (ATF6) gene. We identified a homozygous deletion covering exons 8-14 of the ATF6 gene from 2 siblings from the same family. In another patient from a different family, we identified a heterozygous deletion covering exons 2 and 3 of the ATF6 gene found in trans with a previously identified ATF6 c.970C>T (p.Arg324Cys) ACHM disease allele. Recombinant ATF6 proteins bearing these exon deletions showed markedly impaired transcriptional activity by qPCR and RNA-Seq analysis compared with WT-ATF6. Finally, RNAscope revealed that ATF6 and the related ATF6B transcripts were expressed in cones as well as in all retinal layers in normal human retina. Overall, our data identify loss-of-function ATF6 disease alleles that cause human foveal disease.
Collapse
Affiliation(s)
- Eun-Jin Lee
- Department of Ophthalmology, Shiley Eye Institute, and
- Department of Pathology, UCSD, San Diego, California, USA
- Department of Ophthalmology, Stanford University, Stanford, California, USA
| | - Wei-Chieh Jerry Chiang
- Department of Pathology, UCSD, San Diego, California, USA
- Developmental Neurobiology Unit, Okinawa Institute of Science and Technology Graduate University, Okinawa, Japan
| | - Heike Kroeger
- Department of Pathology, UCSD, San Diego, California, USA
- Department of Cellular Biology, University of Georgia, Athens, Georgia, USA
| | | | | | | | - Rebecca R. Mastey
- Department of Ophthalmology and Visual Sciences, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
| | - Stephen H. Tsang
- Departments of Ophthalmology and Pathology and Cell Biology, Vagelos College of Physicians and Surgeons, Columbia University, New York, New York, USA
| | - Leon Chea
- Department of Pathology, Stanford University, Stanford, California, USA
| | - Kyle Kim
- Department of Pathology, UCSD, San Diego, California, USA
| | - Scott R. Lambert
- Department of Ophthalmology, Stanford University, Stanford, California, USA
| | - Julia M.D. Grandjean
- Department of Molecular Medicine, The Scripps Research Institute, San Diego, California, USA
| | - Britta Baumann
- Institute for Ophthalmic Research, Centre for Ophthalmology, University of Tübingen, Tübingen, Germany
| | - Isabelle Audo
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, Paris, France
- CHNO des Quinze-Vingts, DHU Sight Restore, INSERM-DGOS CIC1423, Paris, France
| | - Susanne Kohl
- Institute for Ophthalmic Research, Centre for Ophthalmology, University of Tübingen, Tübingen, Germany
| | - Anthony T. Moore
- Department of Ophthalmology, UCSF, San Francisco, California, USA
| | - R. Luke Wiseman
- Department of Molecular Medicine, The Scripps Research Institute, San Diego, California, USA
| | - Joseph Carroll
- Department of Ophthalmology and Visual Sciences, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
| | - Jonathan H. Lin
- Department of Ophthalmology, Stanford University, Stanford, California, USA
- Department of Pathology, Stanford University, Stanford, California, USA
- VA Palo Alto Healthcare System, Palo Alto, California, USA
| |
Collapse
|
9
|
Sledgehammer to Scalpel: Broad Challenges to the Heart and Other Tissues Yield Specific Cellular Responses via Transcriptional Regulation of the ER-Stress Master Regulator ATF6α. Int J Mol Sci 2020; 21:ijms21031134. [PMID: 32046286 PMCID: PMC7037772 DOI: 10.3390/ijms21031134] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2019] [Revised: 02/04/2020] [Accepted: 02/06/2020] [Indexed: 12/28/2022] Open
Abstract
There are more than 2000 transcription factors in eukaryotes, many of which are subject to complex mechanisms fine-tuning their activity and their transcriptional programs to meet the vast array of conditions under which cells must adapt to thrive and survive. For example, conditions that impair protein folding in the endoplasmic reticulum (ER), sometimes called ER stress, elicit the relocation of the ER-transmembrane protein, activating transcription factor 6α (ATF6α), to the Golgi, where it is proteolytically cleaved. This generates a fragment of ATF6α that translocates to the nucleus, where it regulates numerous genes that restore ER protein-folding capacity but is degraded soon after. Thus, upon ER stress, ATF6α is converted from a stable, transmembrane protein, to a rapidly degraded, nuclear protein that is a potent transcription factor. This review focuses on the molecular mechanisms governing ATF6α location, activity, and stability, as well as the transcriptional programs ATF6α regulates, whether canonical genes that restore ER protein-folding or unexpected, non-canonical genes affecting cellular functions beyond the ER. Moreover, we will review fascinating roles for an ATF6α isoform, ATF6β, which has a similar mode of activation but, unlike ATF6α, is a long-lived, weak transcription factor that may moderate the genetic effects of ATF6α.
Collapse
|
10
|
Karagöz GE, Acosta-Alvear D, Walter P. The Unfolded Protein Response: Detecting and Responding to Fluctuations in the Protein-Folding Capacity of the Endoplasmic Reticulum. Cold Spring Harb Perspect Biol 2019; 11:cshperspect.a033886. [PMID: 30670466 DOI: 10.1101/cshperspect.a033886] [Citation(s) in RCA: 173] [Impact Index Per Article: 34.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Most of the secreted and plasma membrane proteins are synthesized on membrane-bound ribosomes on the endoplasmic reticulum (ER). They require engagement of ER-resident chaperones and foldases that assist in their folding and maturation. Since protein homeostasis in the ER is crucial for cellular function, the protein-folding status in the organelle's lumen is continually surveyed by a network of signaling pathways, collectively called the unfolded protein response (UPR). Protein-folding imbalances, or "ER stress," are detected by highly conserved sensors that adjust the ER's protein-folding capacity according to the physiological needs of the cell. We review recent developments in the field that have provided new insights into the ER stress-sensing mechanisms used by UPR sensors and the mechanisms by which they integrate various cellular inputs to adjust the folding capacity of the organelle to accommodate to fluctuations in ER protein-folding demands.
Collapse
Affiliation(s)
- G Elif Karagöz
- Howard Hughes Medical Institute and Department of Biochemistry and Biophysics, University of California at San Francisco, San Francisco, California 94143
| | - Diego Acosta-Alvear
- Department of Molecular, Cellular, and Developmental Biology, University of California at Santa Barbara, Santa Barbara, California 93106
| | - Peter Walter
- Howard Hughes Medical Institute and Department of Biochemistry and Biophysics, University of California at San Francisco, San Francisco, California 94143
| |
Collapse
|
11
|
Glembotski CC, Rosarda JD, Wiseman RL. Proteostasis and Beyond: ATF6 in Ischemic Disease. Trends Mol Med 2019; 25:538-550. [PMID: 31078432 DOI: 10.1016/j.molmed.2019.03.005] [Citation(s) in RCA: 61] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2019] [Revised: 03/16/2019] [Accepted: 03/25/2019] [Indexed: 12/28/2022]
Abstract
Endoplasmic reticulum (ER) stress is a pathological hallmark of numerous ischemic diseases, including stroke and myocardial infarction (MI). In these diseases, ER stress leads to activation of the unfolded protein response (UPR) and subsequent adaptation of cellular physiology in ways that dictate cellular fate following ischemia. Recent evidence highlights a protective role for the activating transcription factor 6 (ATF6) arm of the UPR in mitigating adverse outcomes associated with ischemia/reperfusion (I/R) injury in multiple disease models. This suggests ATF6 as a potential therapeutic target for intervening in diverse ischemia-related disorders. Here, we discuss the evidence demonstrating the importance of ATF6 signaling in protecting different tissues against ischemic damage and discuss preclinical results focused on defining the potential for pharmacologically targeting ATF6 to intervene in such diseases.
Collapse
Affiliation(s)
- Christopher C Glembotski
- San Diego State University Heart Institute and the Department of Biology, San Diego State University, San Diego, CA 92182, USA
| | - Jessica D Rosarda
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA 92037, USA
| | - R Luke Wiseman
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA 92037, USA.
| |
Collapse
|
12
|
Fun XH, Thibault G. Lipid bilayer stress and proteotoxic stress-induced unfolded protein response deploy divergent transcriptional and non-transcriptional programmes. Biochim Biophys Acta Mol Cell Biol Lipids 2019; 1865:158449. [PMID: 31028913 DOI: 10.1016/j.bbalip.2019.04.009] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2019] [Revised: 04/14/2019] [Accepted: 04/22/2019] [Indexed: 12/13/2022]
Abstract
The unfolded protein response (UPR) is activated by endoplasmic reticulum (ER) stress and is designed to restore cellular homeostasis through multiple intracellular signalling pathways. In mammals, the UPR programme regulates the expression of hundreds of genes in response to signalling from ATF6, IRE1, and PERK. These three highly conserved stress sensors are activated by the accumulation of unfolded proteins within the ER. Alternatively, IRE1 and PERK sense generalised lipid bilayer stress (LBS) at the ER while ATF6 is activated by an increase of specific sphingolipids. As a result, the UPR supports cellular robustness as a broad-spectrum compensatory pathway that is achieved by deploying a tailored transcriptional programme adapted to the source of ER stress. This review summarises the current understanding of the three ER stress transducers in sensing proteotoxic stress and LBS. The plasticity of the UPR programme in the context of different sources of ER stress will also be discussed.
Collapse
Affiliation(s)
- Xiu Hui Fun
- School of Biological Sciences, Nanyang Technological University, Singapore 637551, Singapore
| | - Guillaume Thibault
- School of Biological Sciences, Nanyang Technological University, Singapore 637551, Singapore.
| |
Collapse
|
13
|
Papaioannou A, Higa A, Jégou G, Jouan F, Pineau R, Saas L, Avril T, Pluquet O, Chevet E. Alterations of
EDEM
1 functions enhance
ATF
6 pro‐survival signaling. FEBS J 2018; 285:4146-4164. [DOI: 10.1111/febs.14669] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2017] [Revised: 08/31/2018] [Accepted: 09/28/2018] [Indexed: 12/17/2022]
Affiliation(s)
- Alexandra Papaioannou
- INSERM U1242 Université de Rennes France
- Centre de Lutte Contre le Cancer Eugène Marquis Rennes France
| | - Arisa Higa
- INSERM U1242 Université de Rennes France
| | - Gwénaële Jégou
- INSERM U1242 Université de Rennes France
- Centre de Lutte Contre le Cancer Eugène Marquis Rennes France
| | - Florence Jouan
- INSERM U1242 Université de Rennes France
- Centre de Lutte Contre le Cancer Eugène Marquis Rennes France
| | - Raphael Pineau
- INSERM U1242 Université de Rennes France
- Centre de Lutte Contre le Cancer Eugène Marquis Rennes France
| | - Laure Saas
- CNRS Institut Pasteur de Lille UMR8161 – M3T – Mechanisms of Tumorigenesis and Targeted Therapies Univ. Lille France
| | - Tony Avril
- INSERM U1242 Université de Rennes France
- Centre de Lutte Contre le Cancer Eugène Marquis Rennes France
| | - Olivier Pluquet
- CNRS Institut Pasteur de Lille UMR8161 – M3T – Mechanisms of Tumorigenesis and Targeted Therapies Univ. Lille France
| | - Eric Chevet
- INSERM U1242 Université de Rennes France
- Centre de Lutte Contre le Cancer Eugène Marquis Rennes France
- CNRS Institut Pasteur de Lille UMR8161 – M3T – Mechanisms of Tumorigenesis and Targeted Therapies Univ. Lille France
| |
Collapse
|
14
|
Paxman R, Plate L, Blackwood EA, Glembotski C, Powers ET, Wiseman RL, Kelly JW. Pharmacologic ATF6 activating compounds are metabolically activated to selectively modify endoplasmic reticulum proteins. eLife 2018; 7:37168. [PMID: 30084354 PMCID: PMC6080950 DOI: 10.7554/elife.37168] [Citation(s) in RCA: 71] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2018] [Accepted: 07/24/2018] [Indexed: 12/15/2022] Open
Abstract
Pharmacologic arm-selective unfolded protein response (UPR) signaling pathway activation is emerging as a promising strategy to ameliorate imbalances in endoplasmic reticulum (ER) proteostasis implicated in diverse diseases. The small molecule N-(2-hydroxy-5-methylphenyl)-3-phenylpropanamide (147) was previously identified (Plate et al., 2016) to preferentially activate the ATF6 arm of the UPR, promoting protective remodeling of the ER proteostasis network. Here we show that 147-dependent ATF6 activation requires metabolic oxidation to form an electrophile that preferentially reacts with ER proteins. Proteins covalently modified by 147 include protein disulfide isomerases (PDIs), known to regulate ATF6 activation. Genetic depletion of PDIs perturbs 147-dependent induction of the ATF6-target gene, BiP, implicating covalent modifications of PDIs in the preferential activation of ATF6 afforded by treatment with 147. Thus, 147 is a pro-drug that preferentially activates ATF6 signaling through a mechanism involving localized metabolic activation and selective covalent modification of ER resident proteins that regulate ATF6 activity.
Collapse
Affiliation(s)
- Ryan Paxman
- Department of Chemistry, The Scripps Research Institute, La Jolla, United States
| | - Lars Plate
- Department of Chemistry, The Scripps Research Institute, La Jolla, United States.,Department of Molecular Medicine, The Scripps Research Institute, La Jolla, United States
| | - Erik A Blackwood
- Department of Biology, San Diego State University, San Diego, United States.,San Diego State University Heart Institute, San Diego State University, San Diego, United States
| | - Chris Glembotski
- Department of Biology, San Diego State University, San Diego, United States.,San Diego State University Heart Institute, San Diego State University, San Diego, United States
| | - Evan T Powers
- Department of Chemistry, The Scripps Research Institute, La Jolla, United States
| | - R Luke Wiseman
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, United States
| | - Jeffery W Kelly
- Department of Chemistry, The Scripps Research Institute, La Jolla, United States.,Department of Molecular Medicine, The Scripps Research Institute, La Jolla, United States.,The Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, United States
| |
Collapse
|
15
|
Ellgaard L, Sevier CS, Bulleid NJ. How Are Proteins Reduced in the Endoplasmic Reticulum? Trends Biochem Sci 2018; 43:32-43. [PMID: 29153511 PMCID: PMC5751730 DOI: 10.1016/j.tibs.2017.10.006] [Citation(s) in RCA: 71] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2017] [Revised: 10/23/2017] [Accepted: 10/24/2017] [Indexed: 12/16/2022]
Abstract
The reversal of thiol oxidation in proteins within the endoplasmic reticulum (ER) is crucial for protein folding, degradation, chaperone function, and the ER stress response. Our understanding of this process is generally poor but progress has been made. Enzymes performing the initial reduction of client proteins, as well as the ultimate electron donor in the pathway, have been identified. Most recently, a role for the cytosol in ER protein reduction has been revealed. Nevertheless, how reducing equivalents are transferred from the cytosol to the ER lumen remains an open question. We review here why proteins are reduced in the ER, discuss recent data on catalysis of steps in the pathway, and consider the implications for redox homeostasis within the early secretory pathway.
Collapse
Affiliation(s)
- Lars Ellgaard
- Department of Biology, University of Copenhagen, 2200 Copenhagen, Denmark.
| | - Carolyn S Sevier
- Department of Molecular Medicine, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853-2703, USA.
| | - Neil J Bulleid
- Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK.
| |
Collapse
|
16
|
Morales-Prieto N, López de Lerma N, Pacheco IL, Pérez J, Peinado RA, Abril N. Redox proteomics reveals the hepatoprotective effect of must from Pedro Ximénez dried grapes in aged Mus spretus mice. J Funct Foods 2017. [DOI: 10.1016/j.jff.2017.04.025] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
|
17
|
Ariyasu D, Yoshida H, Hasegawa Y. Endoplasmic Reticulum (ER) Stress and Endocrine Disorders. Int J Mol Sci 2017; 18:ijms18020382. [PMID: 28208663 PMCID: PMC5343917 DOI: 10.3390/ijms18020382] [Citation(s) in RCA: 70] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2016] [Revised: 01/24/2017] [Accepted: 02/03/2017] [Indexed: 12/15/2022] Open
Abstract
The endoplasmic reticulum (ER) is the organelle where secretory and membrane proteins are synthesized and folded. Unfolded proteins that are retained within the ER can cause ER stress. Eukaryotic cells have a defense system called the “unfolded protein response” (UPR), which protects cells from ER stress. Cells undergo apoptosis when ER stress exceeds the capacity of the UPR, which has been revealed to cause human diseases. Although neurodegenerative diseases are well-known ER stress-related diseases, it has been discovered that endocrine diseases are also related to ER stress. In this review, we focus on ER stress-related human endocrine disorders. In addition to diabetes mellitus, which is well characterized, several relatively rare genetic disorders such as familial neurohypophyseal diabetes insipidus (FNDI), Wolfram syndrome, and isolated growth hormone deficiency type II (IGHD2) are discussed in this article.
Collapse
Affiliation(s)
- Daisuke Ariyasu
- Division of Developmental Genetics, Institute of Resource Development and Analysis, Kumamoto University, Kumamoto 860-0811, Japan.
| | - Hiderou Yoshida
- Department of Biochemistry and Molecular Biology, Graduate School of Life Science, University of Hyogo, Hyogo 678-1297, Japan.
| | - Yukihiro Hasegawa
- Division of Endocrinology and Metabolism, Tokyo Metropolitan Children's Medical Center, Tokyo 183-8561, Japan.
| |
Collapse
|
18
|
|
19
|
Targeting the angio-proteostasis network: Combining the forces against cancer. Pharmacol Ther 2016; 167:1-12. [DOI: 10.1016/j.pharmthera.2016.07.007] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2016] [Accepted: 07/14/2016] [Indexed: 01/24/2023]
|
20
|
ERp29 deficiency affects sensitivity to apoptosis via impairment of the ATF6-CHOP pathway of stress response. Apoptosis 2014; 19:801-15. [PMID: 24370996 DOI: 10.1007/s10495-013-0961-0] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Endoplasmic reticulum protein 29 (ERp29) belongs to the redox-inactive PDI-Dβ-subfamily of PDI-proteins. ERp29 is expressed in all mammalian tissues examined. Especially high levels of expression were observed in secretory tissues and in some tumors. However, the biological role of ERp29 remains unclear. In the present study we show, by using thyrocytes and primary dermal fibroblasts from adult ERp29(-/-) mice, that ERp29 deficiency affects the activation of the ATF6-CHOP-branch of unfolded protein response (UPR) without influencing the function of other UPR branches, like the ATF4-eIF2α-XBP1 signaling pathway. As a result of impaired ATF6 activation, dermal fibroblasts and adult thyrocytes from ERp29(-/-) mice display significantly lower apoptosis sensitivities when treated with tunicamycin and hydrogen peroxide. However, in contrast to previous reports, we could demonstrate that ERp29 deficiency does not alter thyroglobulin expression levels. Therefore, our study suggests that ERp29 acts as an escort factor for ATF6 and promotes its transport from ER to Golgi apparatus under ER stress conditions.
Collapse
|
21
|
Endoplasmic reticulum stress-activated transcription factor ATF6α requires the disulfide isomerase PDIA5 to modulate chemoresistance. Mol Cell Biol 2014; 34:1839-49. [PMID: 24636989 DOI: 10.1128/mcb.01484-13] [Citation(s) in RCA: 149] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
ATF6α, a membrane-anchored transcription factor from the endoplasmic reticulum (ER) that modulates the cellular response to stress as an effector of the unfolded-protein response (UPR), is a key player in the development of tumors of different origin. ATF6α activation has been linked to oncogenic transformation and tumor maintenance; however, the mechanism(s) underlying this phenomenon remains elusive. Here, using a phenotypic small interfering RNA (siRNA) screening, we identified a novel role for ATF6α in chemoresistance and defined the protein disulfide isomerase A5 (PDIA5) as necessary for ATF6α activation upon ER stress. PDIA5 contributed to disulfide bond rearrangement in ATF6α under stress conditions, thereby leading to ATF6α export from the ER and activation of its target genes. Further analysis of the mechanism demonstrated that PDIA5 promotes ATF6α packaging into coat protein complex II (COPII) vesicles and that the PDIA5/ATF6α activation loop is essential to confer chemoresistance on cancer cells. Genetic and pharmacological inhibition of the PDIA5/ATF6α axis restored sensitivity to the drug treatment. This work defines the mechanisms underlying the role of ATF6α activation in carcinogenesis and chemoresistance; furthermore, it identifies PDIA5 as a key regulator ATF6α-mediated cellular functions in cancer.
Collapse
|
22
|
Rabhi N, Salas E, Froguel P, Annicotte JS. Role of the unfolded protein response in β cell compensation and failure during diabetes. J Diabetes Res 2014; 2014:795171. [PMID: 24812634 PMCID: PMC4000654 DOI: 10.1155/2014/795171] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/15/2014] [Revised: 03/12/2014] [Accepted: 03/13/2014] [Indexed: 02/06/2023] Open
Abstract
Pancreatic β cell failure leads to diabetes development. During disease progression, β cells adapt their secretory capacity to compensate the elevated glycaemia and the peripheral insulin resistance. This compensatory mechanism involves a fine-tuned regulation to modulate the endoplasmic reticulum (ER) capacity and quality control to prevent unfolded proinsulin accumulation, a major protein synthetized within the β cell. These signalling pathways are collectively termed unfolded protein response (UPR). The UPR machinery is required to preserve ER homeostasis and β cell integrity. Moreover, UPR actors play a key role by regulating ER folding capacity, increasing the degradation of misfolded proteins, and limiting the mRNA translation rate. Recent genetic and biochemical studies on mouse models and human UPR sensor mutations demonstrate a clear requirement of the UPR machinery to prevent β cell failure and increase β cell mass and adaptation throughout the progression of diabetes. In this review we will highlight the specific role of UPR actors in β cell compensation and failure during diabetes.
Collapse
Affiliation(s)
- Nabil Rabhi
- European Genomic Institute for Diabetes (EGID), CNRS UMR 8199, Lille 2 University of Health and Law, 59000 Lille, France
| | - Elisabet Salas
- European Genomic Institute for Diabetes (EGID), CNRS UMR 8199, Lille 2 University of Health and Law, 59000 Lille, France
| | - Philippe Froguel
- European Genomic Institute for Diabetes (EGID), CNRS UMR 8199, Lille 2 University of Health and Law, 59000 Lille, France
- Departments of Genomics of Common Disease, Hammersmith Hospital, Imperial College London, London, UK
| | - Jean-Sébastien Annicotte
- European Genomic Institute for Diabetes (EGID), CNRS UMR 8199, Lille 2 University of Health and Law, 59000 Lille, France
- Laboratoire Bases Moléculaires et Modélisation du Diabète et de l'Obésité, Faculté de Médecine, Pôle Recherche, 59045 Lille, France
- *Jean-Sébastien Annicotte:
| |
Collapse
|
23
|
Wakabayashi S, Yoshida H. The essential biology of the endoplasmic reticulum stress response for structural and computational biologists. Comput Struct Biotechnol J 2013; 6:e201303010. [PMID: 24688718 PMCID: PMC3962220 DOI: 10.5936/csbj.201303010] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2013] [Revised: 08/09/2013] [Accepted: 08/10/2013] [Indexed: 11/29/2022] Open
Abstract
The endoplasmic reticulum (ER) stress response is a cytoprotective mechanism that maintains homeostasis of the ER by upregulating the capacity of the ER in accordance with cellular demands. If the ER stress response cannot function correctly, because of reasons such as aging, genetic mutation or environmental stress, unfolded proteins accumulate in the ER and cause ER stress-induced apoptosis, resulting in the onset of folding diseases, including Alzheimer's disease and diabetes mellitus. Although the mechanism of the ER stress response has been analyzed extensively by biochemists, cell biologists and molecular biologists, many aspects remain to be elucidated. For example, it is unclear how sensor molecules detect ER stress, or how cells choose the two opposite cell fates (survival or apoptosis) during the ER stress response. To resolve these critical issues, structural and computational approaches will be indispensable, although the mechanism of the ER stress response is complicated and difficult to understand holistically at a glance. Here, we provide a concise introduction to the mammalian ER stress response for structural and computational biologists.
Collapse
Affiliation(s)
- Sadao Wakabayashi
- Department of Molecular Biochemistry, Graduate School of Life Science, University of Hyogo, Hyogo 678-1297, Japan
| | - Hiderou Yoshida
- Department of Molecular Biochemistry, Graduate School of Life Science, University of Hyogo, Hyogo 678-1297, Japan
| |
Collapse
|
24
|
Higa A, Chevet E. Redox signaling loops in the unfolded protein response. Cell Signal 2012; 24:1548-55. [DOI: 10.1016/j.cellsig.2012.03.011] [Citation(s) in RCA: 135] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2012] [Accepted: 03/20/2012] [Indexed: 12/30/2022]
|
25
|
Abstract
This chapter provides an overview of our present understanding of mechanisms of sensing protein folding status and endoplasmic reticulum (ER) stress in eukaryotic cells. The ER folds and matures most secretory and transmembrane proteins. Mis- or unfolded proteins are sensed by specialized ER stress sensors, such as IRE1, PERK and ATF6, which initiate several cellular responses and signaling pathways to restore ER homeostasis. These intracellular signaling events are called the unfolded protein response (UPR). Here we focus on how ER stress and protein folding status in the ER are sensed by the ER stress sensors by summarizing results from recent structural, biochemical and genetic approaches.
Collapse
|
26
|
Abstract
The efficient functioning of the ER is indispensable for most of the cellular activities and survival. Disturbances in the physiological functions of the ER result in the activation of a complex set of signaling pathways from the ER to the cytosol and nucleus, and these are collectively known as unfolded protein response (UPR), which is aimed to compensate damage and can eventually trigger cell death if ER stress is severe or persists for a longer period. The precise molecular mechanisms that facilitate this switch in brain damage have yet to be understood completely with multiple potential participants involved. The ER stress-associated cell death pathways have been recognized in the numerous pathophysiological conditions, such as diabetes, hypoxia, ischemia/reperfusion injury, and neurodegenerative disorders, including Alzheimer's disease, Parkinson's disease, and bipolar disorder. Hence, there is an emerging need to study the basic molecular mechanisms of ER stress-mediating multiple cell survival/death signaling pathways. These molecules that regulate the ER stress response would be potential drug targets in brain diseases.
Collapse
Affiliation(s)
- Ram Raghubir
- Division of Pharmacology, Central Drug Research Institute, (CSIR), Chatter Manzil Palace, Lucknow, India
| | | | | |
Collapse
|
27
|
Sato Y, Nadanaka S, Okada T, Okawa K, Mori K. Luminal domain of ATF6 alone is sufficient for sensing endoplasmic reticulum stress and subsequent transport to the Golgi apparatus. Cell Struct Funct 2010; 36:35-47. [PMID: 21150130 DOI: 10.1247/csf.10010] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The transcription factor ATF6 is constitutively synthesized as a type II transmembrane protein embedded in the endoplasmic reticulum (ER). When unfolded proteins accumulate in the ER, ATF6 senses such ER stress via an as yet undetermined mechanism and relocates to the Golgi apparatus where it is cleaved by sequential action of Site-1 and Site-2 proteases, allowing liberated N-terminal fragments to translocate into the nucleus. This ATF6-mediated transcriptional induction of ER-localized molecular chaperones and folding enzymes together with components of ER-associated degradation leads to the maintenance of ER homeostasis in mammals. Here, we demonstrated that the luminal domain of ATF6 alone is sufficient for sensing ER stress and subsequent transportation to the Golgi apparatus. This domain of ATF6 was inserted between the N-terminal signal sequence and C-terminal tandem affinity purification tag. The resulting ATF6(C)-TAP translocated into the ER, where it was glycosylated and disulfide bonded. ATF6(C)-TAP occurred as monomer and dimer, and exhibited a relatively short half-life, similar to full-length ATF6. On application of dithiothreitol- or thapsigargin-induced ER stress, the ER chaperone BiP dissociated from ATF6(C)-TAP, and ATF6(C)-TAP was transported to the Golgi apparatus and then secreted into medium. Calnexin and protein disulfide isomerase were identified as cellular proteins capable of binding to ATF6(C)-TAP in addition to BiP, and subsequent analysis revealed that protein disulfide isomerase was bound to ATF6(C)-TAP with chaperone activity. These findings indicate that ATF6(C)-TAP can be used as a tool to isolate protein(s) that escort ATF6 from the ER to the Golgi apparatus in response to ER stress.
Collapse
Affiliation(s)
- Yoshimi Sato
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
| | | | | | | | | |
Collapse
|
28
|
Kimata Y, Kohno K. Endoplasmic reticulum stress-sensing mechanisms in yeast and mammalian cells. Curr Opin Cell Biol 2010; 23:135-42. [PMID: 21093243 DOI: 10.1016/j.ceb.2010.10.008] [Citation(s) in RCA: 149] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2010] [Revised: 09/30/2010] [Accepted: 10/21/2010] [Indexed: 01/12/2023]
Abstract
Upon endoplasmic reticulum (ER) stress, ER-located transmembrane stress sensors evoke diverse protective responses. Although ER stress-dependent activation of the sensor proteins is partly explained through their negative regulation by the ER-located chaperone BiP under non-stress conditions, each of the sensors is also regulated by distinct mechanism(s). For instance, yeast Ire1 is fully activated via its direct interaction with unfolded proteins accumulated in the ER. This insight is consistent with a classical notion that unfolded proteins per se trigger ER-stress responses, while various stress stimuli also seem to activate individual sensors independently of unfolded proteins and in a stimuli-specific manner. These properties may account for the different responses observed under different conditions in mammalian cells, which carry multiple ER-stress sensors.
Collapse
Affiliation(s)
- Yukio Kimata
- Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192, Japan
| | | |
Collapse
|
29
|
Rutkowski DT, Hegde RS. Regulation of basal cellular physiology by the homeostatic unfolded protein response. ACTA ACUST UNITED AC 2010; 189:783-94. [PMID: 20513765 PMCID: PMC2878945 DOI: 10.1083/jcb.201003138] [Citation(s) in RCA: 299] [Impact Index Per Article: 21.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The extensive membrane network of the endoplasmic reticulum (ER) is physically juxtaposed to and functionally entwined with essentially all other cellular compartments. Therefore, the ER must sense diverse and constantly changing physiological inputs so it can adjust its numerous functions to maintain cellular homeostasis. A growing body of new work suggests that the unfolded protein response (UPR), traditionally charged with signaling protein misfolding stress from the ER, has been co-opted for the maintenance of basal cellular homeostasis. Thus, the UPR can be activated, and its output modulated, by signals far outside the realm of protein misfolding. These findings are revealing that the UPR causally contributes to disease not just by its role in protein folding but also through its broad influence on cellular physiology.
Collapse
Affiliation(s)
- D Thomas Rutkowski
- Department of Anatomy and Cell Biology, Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA.
| | | |
Collapse
|
30
|
Abstract
The lumen of the endoplasmic reticulum constitutes a separate intracellular compartment with a special proteome and metabolome. The redox conditions of the organelle are also characteristically different from those of the other subcellular compartments. The luminal environment has been considered more oxidizing than the cytosol due to the presence of oxidative protein folding. However, recent observations suggest that redox systems in reduced and oxidized states are present simultaneously. The concerted action of membrane transporters and oxidoreductase enzymes maintains the oxidized state of the thiol-disulfide and the reduced state of the pyridine nucleotide redox systems, which are prerequisites for the normal redox reactions localized in the organelle. The powerful thiol-oxidizing machinery of oxidative protein folding continuously challenges the local antioxidant defense. Alterations of the luminal redox conditions, either in oxidizing or reducing direction, affect protein processing, are sensed by the accumulation of misfolded/unfolded proteins, and may induce endoplasmic reticulum stress and unfolded protein response. The activated signaling pathways attempt to restore the balance between protein loading and processing and induce programmed cell death if these attempts fail. Recent findings strongly support the involvement of redox-based endoplasmic reticulum stress in a plethora of human diseases, either as causative agents or as complications.
Collapse
Affiliation(s)
- Miklós Csala
- Department of Medical Chemistry, Molecular Biology and Pathobiochemistry, Semmelweis University, Budapest, Hungary
| | | | | |
Collapse
|
31
|
Kohno K. Stress-sensing mechanisms in the unfolded protein response: similarities and differences between yeast and mammals. J Biochem 2009; 147:27-33. [PMID: 19942680 DOI: 10.1093/jb/mvp196] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
The unfolded protein response is an adaptive stress response that responds to the imbalance between the entry of newly synthesized unfolded proteins and the inherent folding capacity in the endoplasmic reticulum (ER). Various environmental stresses and changes in physiological conditions can result in the accumulation of unfolded proteins in the ER, which is sensed through ER transmembrane protein sensors named inositol requiring enzyme 1 (IRE1), PKR-like ER kinase (PERK) and activating transcription factor 6 (ATF6), and the sensed signals are transduced to the cytosol and the nucleus. IRE1 is a prototype ER stress sensor that is evolutionarily conserved from yeast to humans. Higher eukaryotes have evolved two other sensors, PERK and ATF6. This review focuses on the current progress in our understanding of stress-sensing mechanisms, in particular, the similarities and differences between yeast and mammals.
Collapse
Affiliation(s)
- Kenji Kohno
- Laboratory of Molecular and Cell Genetics, Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192 Japan.
| |
Collapse
|
32
|
Szegezdi E, MacDonald DC, Ní Chonghaile T, Gupta S, Samali A. Bcl-2 family on guard at the ER. Am J Physiol Cell Physiol 2009; 296:C941-53. [DOI: 10.1152/ajpcell.00612.2008] [Citation(s) in RCA: 199] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The endoplasmic reticulum (ER) is the main site for protein folding, lipid biosynthesis, and calcium storage in the cell. Disturbances of these critical cellular functions lead to ER stress. The ER responds to disturbances in its homeostasis by launching an adaptive signal transduction pathway, known as the unfolded protein response (UPR). The UPR strives to maintain ER function during stress; however, if the stress is not resolved, apoptotic responses are activated that involve cross talk between the ER and mitochondria. In addition, ER stress is also known to induce autophagy to counteract XBP-1-mediated ER expansion and assist in the degradation of unfolded proteins. One family of proteins involved in the regulation of apoptosis is that of B-cell lymphoma protein 2 (Bcl-2). Complex interactions among the three subgroups within the Bcl-2 family [the antiapoptotic, the multidomain proapoptotic, and the Bcl-2 homology domain 3 (BH3)-only members] control the signaling events of apoptosis upstream of mitochondrial outer membrane permeabilization. These proteins were found to have diverse subcellular locations to aid in the response to varied intrinsic and extrinsic stimuli. Of recent interest is the presence of the Bcl-2 family at the ER. Here, we review the involvement of proteins from each of the three Bcl-2 family subgroups in the maintenance of ER homeostasis and their participation in ER stress signal transduction pathways.
Collapse
|
33
|
Gonzales JC, Gentile CL, Pfaffenbach KT, Wei Y, Wang D, Pagliassotti MJ. Chemical induction of the unfolded protein response in the liver increases glucose production and is activated during insulin-induced hypoglycaemia in rats. Diabetologia 2008; 51:1920-9. [PMID: 18651128 PMCID: PMC2597049 DOI: 10.1007/s00125-008-1094-9] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/16/2008] [Accepted: 06/06/2008] [Indexed: 01/28/2023]
Abstract
AIMS/HYPOTHESIS Endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) can regulate insulin secretion, insulin action and in vitro hepatocyte glucose release. The aims of this study were to determine whether chemical agents that induce ER stress regulate glucose production in vivo and to identify a physiological setting in which this may be important. METHODS A pancreatic clamp test was performed in anaesthetised rats, and insulin and glucagon were replaced at basal levels. [6,6-(2)H(2)]Glucose was infused in the absence (CON, n = 10) or presence of ER stress-inducing agents, namely, tunicamycin (Tun, n = 10) or thapsigargin (Thap, n = 10). RESULTS Arterial insulin, glucagon, corticosterone and NEFA concentrations were constant throughout experiments and not different among groups. After 1 h, the glucose concentration was significantly increased in Tun and Thap rats (1.5 +/- 0.2 and 2.1 +/- 0.3 mmol/l, respectively; mean +/- SD), but did not change in CON rats. Glucose production increased (p < 0.05) by 11.0 +/- 1.6 and 13.2 +/- 2.2 micromol kg(-1) min(-1) in Tun and Thap rats, respectively, but did not change in CON rats. When glucose was infused in a fourth group (HYPER) to match the increase in glucose observed in the Tun and Thap rats, glucose production decreased by approximately 22 micromol kg(-1) min(-1). Liver phosphorylase activity was increased and glycogen decreased in the Tun and Thap groups compared with the CON and HYPER groups. Given that glucose deprivation induces ER stress in cells, we hypothesised that hypoglycaemia, a condition that elicits increased glucose production, would activate the UPR in the liver. Three hour hyperinsulinaemic (5 mU kg(-1) min(-1)) -euglycaemic (EUG, approximately 7.2 mmol/l, n = 6) or -hypoglycaemic (HYPO, approximately 2.8 mmol/l, n = 6) clamps were performed in conscious rats. Several biochemical markers of the UPR were significantly increased in the liver, but not in kidney or pancreas, in HYPO vs EUG rats. CONCLUSIONS/INTERPRETATION Based on our findings that the chemical induction of the UPR increased glucose production and that prolonged hypoglycaemia activated the UPR in the liver, we propose that the UPR in the liver may contribute to the regulation of glucose production during prolonged hypoglycaemia.
Collapse
Affiliation(s)
- J. C. Gonzales
- Department of Food Science and Human Nutrition, Colorado State University, Gifford 234, Fort Collins, CO 80523-1571, USA
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO, USA
| | - C. L. Gentile
- Department of Food Science and Human Nutrition, Colorado State University, Gifford 234, Fort Collins, CO 80523-1571, USA
| | - K. T. Pfaffenbach
- Department of Food Science and Human Nutrition, Colorado State University, Gifford 234, Fort Collins, CO 80523-1571, USA
| | - Y. Wei
- Department of Food Science and Human Nutrition, Colorado State University, Gifford 234, Fort Collins, CO 80523-1571, USA
| | - D. Wang
- Department of Food Science and Human Nutrition, Colorado State University, Gifford 234, Fort Collins, CO 80523-1571, USA
| | - M. J. Pagliassotti
- Department of Food Science and Human Nutrition, Colorado State University, Gifford 234, Fort Collins, CO 80523-1571, USA, e-mail:
| |
Collapse
|
34
|
Christis C, Lubsen NH, Braakman I. Protein folding includes oligomerization - examples from the endoplasmic reticulum and cytosol. FEBS J 2008; 275:4700-27. [DOI: 10.1111/j.1742-4658.2008.06590.x] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
|
35
|
Bánhegyi G, Mandl J, Csala M. Redox-based endoplasmic reticulum dysfunction in neurological diseases. J Neurochem 2008; 107:20-34. [PMID: 18643792 DOI: 10.1111/j.1471-4159.2008.05571.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The redox homeostasis of the endoplasmic reticulum lumen is characteristically different from that of the other subcellular compartments. The concerted action of membrane transport processes and oxidoreductase enzymes maintain the oxidized state of the thiol-disulfide and the reducing state of the pyridine nucleotide redox systems, which are prerequisites for the normal functions of the organelle. The powerful thiol-oxidizing machinery allows oxidative protein folding but continuously challenges the local antioxidant defense. Alterations of the cellular redox environment either in oxidizing or reducing direction affect protein processing and may induce endoplasmic reticulum stress and unfolded protein response. The activated signaling pathways attempt to restore the balance between protein loading and processing and induce apoptosis if the attempt fails. Recent findings strongly support the involvement of this mechanism in brain ischemia, neuronal degenerative diseases and traumatic injury. The redox changes in the endoplasmic reticulum are integral parts of the pathomechanism of neurological diseases, either as causative agents, or as complications.
Collapse
Affiliation(s)
- Gábor Bánhegyi
- Department of Medical Chemistry, Molecular Biology and Pathobiochemistry, Semmelweis University, Budapest, Hungary
| | | | | |
Collapse
|
36
|
Kubisch CH, Logsdon CD. Endoplasmic reticulum stress and the pancreatic acinar cell. Expert Rev Gastroenterol Hepatol 2008; 2:249-60. [PMID: 19072360 DOI: 10.1586/17474124.2.2.249] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The pancreas is the primary organ responsible for the digestion of food. Pancreatic acinar cells are specialized for the production of digestive enzymes, and these cells have a higher rate of protein synthesis than all other adult human tissues. Digestive enzymes are produced in the endoplasmic reticulum (ER), a multifunctional organelle responsible for the synthesis and correct folding of proteins in the secretory pathway. Disturbances of ER function lead to stress-response mechanisms that can restore homeostasis but can also, if uncontrolled, cause disease. Pancreatic acinar cells are particularly susceptible to ER perturbations, and mechanisms that relieve ER stress are necessary for normal pancreatic development. Furthermore, ER stress occurs during acute pancreatitis, and may also be present in pancreatic cancer. However, the specific roles of ER stress-response mechanisms in these diseases are unknown.
Collapse
Affiliation(s)
- Constanze H Kubisch
- Department of Internal Medicine/Gastroenterology, University of Munich, Marchioninistrasse 15, 81377 Munich, Germany.
| | | |
Collapse
|
37
|
Abstract
The unfolded protein response (UPR) is an adaptive stress response in which cells recover from the accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER) by increasing its protein-folding capacity. The IRE1 pathway in the UPR is evolutionarily conserved from yeast to human, and two other pathways involving PERK and ATF6 have also evolved in higher eukaryotes. These three intracellular signaling pathways originate in the ER lumen, where unfolded or misfolded proteins are recognized by the three transmembrane ER stress sensors IRE1, PERK, and ATF6. This review focuses on current progress with efforts to elucidate how stress sensors recognize the accumulation of unfolded proteins.
Collapse
Affiliation(s)
- Kenji Kohno
- Department of Cell Biology, Graduate School of Biological Sciences, Nara Institute of Science and Technology (NAIST), 8916-5 Takayama, Ikoma, Nara, Japan.
| |
Collapse
|
38
|
Wu J, Rutkowski DT, Dubois M, Swathirajan J, Saunders T, Wang J, Song B, Yau GDY, Kaufman RJ. ATF6alpha optimizes long-term endoplasmic reticulum function to protect cells from chronic stress. Dev Cell 2007; 13:351-64. [PMID: 17765679 DOI: 10.1016/j.devcel.2007.07.005] [Citation(s) in RCA: 531] [Impact Index Per Article: 31.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2007] [Revised: 06/11/2007] [Accepted: 07/10/2007] [Indexed: 12/18/2022]
Abstract
In vertebrates, three proteins--PERK, IRE1alpha, and ATF6alpha--sense protein-misfolding stress in the ER and initiate ER-to-nucleus signaling cascades to improve cellular function. The mechanism by which this unfolded protein response (UPR) protects ER function during stress is not clear. To address this issue, we have deleted Atf6alpha in the mouse. ATF6alpha is neither essential for basal expression of ER protein chaperones nor for embryonic or postnatal development. However, ATF6alpha is required in both cells and tissues to optimize protein folding, secretion, and degradation during ER stress and thus to facilitate recovery from acute stress and tolerance to chronic stress. Challenge of Atf6alpha null animals in vivo compromises organ function and survival despite functional overlap between UPR sensors. These results suggest that the vertebrate ATF6alpha pathway evolved to maintain ER function when cells are challenged with chronic stress and provide a rationale for the overlap among the three UPR pathways.
Collapse
Affiliation(s)
- Jun Wu
- Department of Biological Chemistry, University of Michigan Medical Center, Ann Arbor, MI 48109, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
39
|
Yamamoto K, Sato T, Matsui T, Sato M, Okada T, Yoshida H, Harada A, Mori K. Transcriptional induction of mammalian ER quality control proteins is mediated by single or combined action of ATF6alpha and XBP1. Dev Cell 2007; 13:365-76. [PMID: 17765680 DOI: 10.1016/j.devcel.2007.07.018] [Citation(s) in RCA: 786] [Impact Index Per Article: 46.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2007] [Revised: 06/21/2007] [Accepted: 07/31/2007] [Indexed: 11/29/2022]
Abstract
Metazoans express three unfolded protein response transducers (IRE1, PERK, and ATF6) ubiquitously to cope with endoplasmic reticulum (ER) stress. ATF6 is an ER membrane-bound transcription factor activated by ER stress-induced proteolysis and has been duplicated in mammals. Here, we generated ATF6alpha- and ATF6beta-knockout mice, which developed normally, and then found that their double knockout caused embryonic lethality. Analysis of mouse embryonic fibroblasts (MEFs) deficient in ATF6alpha or ATF6beta revealed that ATF6alpha is solely responsible for transcriptional induction of ER chaperones and that ATF6alpha heterodimerizes with XBP1 for the induction of ER-associated degradation components. ATF6alpha(-/-) MEFs are sensitive to ER stress. Unaltered responses observed in ATF6beta(-/-) MEFs indicate that ATF6beta is not a negative regulator of ATF6alpha. These results demonstrate that ATF6alpha functions as a critical regulator of ER quality control proteins in mammalian cells, in marked contrast to worm and fly cells in which IRE1 is responsible.
Collapse
Affiliation(s)
- Keisuke Yamamoto
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
| | | | | | | | | | | | | | | |
Collapse
|
40
|
Rutkowski DT, Kaufman RJ. That which does not kill me makes me stronger: adapting to chronic ER stress. Trends Biochem Sci 2007; 32:469-76. [DOI: 10.1016/j.tibs.2007.09.003] [Citation(s) in RCA: 314] [Impact Index Per Article: 18.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2007] [Revised: 07/20/2007] [Accepted: 09/24/2007] [Indexed: 11/29/2022]
|
41
|
Bánhegyi G, Benedetti A, Csala M, Mandl J. Stress on redox. FEBS Lett 2007; 581:3634-40. [PMID: 17467703 DOI: 10.1016/j.febslet.2007.04.028] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2007] [Revised: 04/11/2007] [Accepted: 04/12/2007] [Indexed: 01/12/2023]
Abstract
Redox imbalance in the endoplasmic reticulum lumen is the most frequent cause of endoplasmic reticulum stress and consequent apoptosis. The mechanism involves the impairment of oxidative protein folding, the accumulation of unfolded/misfolded proteins in the lumen and the initiation of the unfolded protein response. The participation of several redox systems (glutathione, ascorbate, FAD, tocopherol, vitamin K) has been demonstrated in the process. Recent findings have attracted attention to the possible mechanistic role of luminal pyridine nucleotides in the endoplasmic reticulum stress. The aim of this minireview is to summarize the luminal redox systems and the redox sensing mechanisms of the endoplasmic reticulum.
Collapse
Affiliation(s)
- Gábor Bánhegyi
- Department of Medical Chemistry, Molecular Biology and Pathobiochemistry, Semmelweis University, 1444 Budapest, POB 260, Hungary.
| | | | | | | |
Collapse
|