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Ernst R, Renne MF, Jain A, von der Malsburg A. Endoplasmic Reticulum Membrane Homeostasis and the Unfolded Protein Response. Cold Spring Harb Perspect Biol 2024; 16:a041400. [PMID: 38253414 DOI: 10.1101/cshperspect.a041400] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2024]
Abstract
The endoplasmic reticulum (ER) is the key organelle for membrane biogenesis. Most lipids are synthesized in the ER, and most membrane proteins are first inserted into the ER membrane before they are transported to their target organelle. The composition and properties of the ER membrane must be carefully controlled to provide a suitable environment for the insertion and folding of membrane proteins. The unfolded protein response (UPR) is a powerful signaling pathway that balances protein and lipid production in the ER. Here, we summarize our current knowledge of how aberrant compositions of the ER membrane, referred to as lipid bilayer stress, trigger the UPR.
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Affiliation(s)
- Robert Ernst
- Medical Biochemistry and Molecular Biology, Medical Faculty, Saarland University, 66421 Homburg, Germany
- Preclinical Center for Molecular Signaling (PZMS), Medical Faculty, Saarland University, 66421 Homburg, Germany
| | - Mike F Renne
- Medical Biochemistry and Molecular Biology, Medical Faculty, Saarland University, 66421 Homburg, Germany
- Preclinical Center for Molecular Signaling (PZMS), Medical Faculty, Saarland University, 66421 Homburg, Germany
| | - Aamna Jain
- Medical Biochemistry and Molecular Biology, Medical Faculty, Saarland University, 66421 Homburg, Germany
- Preclinical Center for Molecular Signaling (PZMS), Medical Faculty, Saarland University, 66421 Homburg, Germany
| | - Alexander von der Malsburg
- Medical Biochemistry and Molecular Biology, Medical Faculty, Saarland University, 66421 Homburg, Germany
- Preclinical Center for Molecular Signaling (PZMS), Medical Faculty, Saarland University, 66421 Homburg, Germany
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Ishiwata-Kimata Y, Kimata Y. Fundamental and Applicative Aspects of the Unfolded Protein Response in Yeasts. J Fungi (Basel) 2023; 9:989. [PMID: 37888245 PMCID: PMC10608004 DOI: 10.3390/jof9100989] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2023] [Revised: 10/03/2023] [Accepted: 10/04/2023] [Indexed: 10/28/2023] Open
Abstract
Upon the dysfunction or functional shortage of the endoplasmic reticulum (ER), namely, ER stress, eukaryotic cells commonly provoke a protective gene expression program called the unfolded protein response (UPR). The molecular mechanism of UPR has been uncovered through frontier genetic studies using Saccharomyces cerevisiae as a model organism. Ire1 is an ER-located transmembrane protein that directly senses ER stress and is activated as an RNase. During ER stress, Ire1 promotes the splicing of HAC1 mRNA, which is then translated into a transcription factor that induces the expression of various genes, including those encoding ER-located molecular chaperones and protein modification enzymes. While this mainstream intracellular UPR signaling pathway was elucidated in the 1990s, new intriguing insights have been gained up to now. For instance, various additional factors allow UPR evocation strictly in response to ER stress. The UPR machineries in other yeasts and fungi, including pathogenic species, are another important research topic. Moreover, industrially beneficial yeast strains carrying an enforced and enlarged ER have been produced through the artificial and constitutive induction of the UPR. In this article, we review canonical and up-to-date insights concerning the yeast UPR, mainly from the viewpoint of the functions and regulation of Ire1 and HAC1.
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Affiliation(s)
| | - Yukio Kimata
- Division of Biological Science, Graduate School of Science and Technology, Nara Institute of Science and Technology, Nara 630-0192, Japan
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Fauzee YNBM, Yoshida Y, Kimata Y. Endoplasmic stress sensor Ire1 is involved in cytosolic/nuclear protein quality control in Pichia pastoris cells independent of HAC1. Front Microbiol 2023; 14:1157146. [PMID: 37415818 PMCID: PMC10321714 DOI: 10.3389/fmicb.2023.1157146] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2023] [Accepted: 05/31/2023] [Indexed: 07/08/2023] Open
Abstract
In eukaryotic species, dysfunction of the endoplasmic reticulum (ER), namely, ER stress, provokes a cytoprotective transcription program called the unfolded protein response (UPR). The UPR is triggered by transmembrane ER-stress sensors, including Ire1, which acts as an endoribonuclease to splice and mature the mRNA encoding the transcription factor Hac1 in many fungal species. Through analyses of the methylotrophic yeast Pichia pastoris (syn. Komagataella phaffii), we revealed a previously unknown function of Ire1. In P. pastoris cells, the IRE1 knockout mutation (ire1Δ) and HAC1 knockout mutation (hac1Δ) caused only partially overlapping gene expression changes. Protein aggregation and the heat shock response (HSR) were induced in ire1Δ cells but not in hac1Δ cells even under non-stress conditions. Moreover, Ire1 was further activated upon high-temperature culturing and conferred heat stress resistance to P. pastoris cells. Our findings cumulatively demonstrate an intriguing case in which the UPR machinery controls cytosolic protein folding status and the HSR, which is known to be activated upon the accumulation of unfolded proteins in the cytosol and/or nuclei.
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Das E, Sahu KK, Roy I. The functional role of Ire1 in regulating autophagy and proteasomal degradation under prolonged proteotoxic stress. FEBS J 2023. [PMID: 36757110 DOI: 10.1111/febs.16747] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2022] [Revised: 12/23/2022] [Accepted: 02/08/2023] [Indexed: 02/10/2023]
Abstract
Inhibition of endoribonuclease/kinase Ire1 has shown beneficial effects in many proteotoxicity-induced pathology models. The mechanism by which this occurs has not been elucidated completely. Using a proteotoxic yeast model of Huntington's disease, we show that the deletion of Ire1 led to lower protein aggregation at longer time points. The rate of protein degradation was higher in ΔIre1 cells. We monitored the two major protein degradation mechanisms in the cell. The increase in expression of Rpn4, coding for the transcription factor controlling proteasome biogenesis, was higher in ΔIre1 cells. The chymotrypsin-like proteasomal activity was also significantly enhanced in these cells at later time points of aggregation. The gene and protein expression levels of the autophagy gene Atg8 were higher in ΔIre1 than in wild-type cells. Significant increase in autophagy flux was also seen in ΔIre1 cells at later time points of aggregation. The results suggest that the deletion of Ire1 activates UPR-independent arms of the proteostasis network, especially under conditions of aggravated stress. Thus, the inhibition of Ire1 may regulate UPR-independent cellular stress-response pathways under prolonged stress.
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Affiliation(s)
- Eshita Das
- Department of Biotechnology, National Institute of Pharmaceutical Education and Research, S.A.S. Nagar, India
| | - Kiran Kumari Sahu
- Department of Biotechnology, National Institute of Pharmaceutical Education and Research, S.A.S. Nagar, India
| | - Ipsita Roy
- Department of Biotechnology, National Institute of Pharmaceutical Education and Research, S.A.S. Nagar, India
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Papaioannou A, Centonze F, Metais A, Maurel M, Negroni L, Gonzalez-Quiroz M, Mahdizadeh SJ, Svensson G, Zare E, Blondel A, Koong AC, Hetz C, Pedeux R, Tremblay ML, Eriksson LA, Chevet E. Stress-induced tyrosine phosphorylation of RtcB modulates IRE1 activity and signaling outputs. Life Sci Alliance 2022; 5:5/5/e202201379. [PMID: 35193953 PMCID: PMC8899846 DOI: 10.26508/lsa.202201379] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2022] [Revised: 01/27/2022] [Accepted: 01/31/2022] [Indexed: 12/18/2022] Open
Abstract
ER stress is mediated by three sensors and the most evolutionary conserved IRE1α signals through its cytosolic kinase and endoribonuclease (RNase) activities. IRE1α RNase activity can either catalyze the initial step of XBP1 mRNA unconventional splicing or degrade a number of RNAs through regulated IRE1-dependent decay. Until now, the biochemical and biological outputs of IRE1α RNase activity have been well documented; however, the precise mechanisms controlling whether IRE1α signaling is adaptive or pro-death (terminal) remain unclear. We investigated those mechanisms and hypothesized that XBP1 mRNA splicing and regulated IRE1-dependent decay activity could be co-regulated by the IRE1α RNase regulatory network. We identified that RtcB, the tRNA ligase responsible for XBP1 mRNA splicing, is tyrosine-phosphorylated by c-Abl and dephosphorylated by PTP1B. Moreover, we show that the phosphorylation of RtcB at Y306 perturbs RtcB interaction with IRE1α, thereby attenuating XBP1 mRNA splicing. Our results demonstrate that the IRE1α RNase regulatory network is dynamically fine-tuned by tyrosine kinases and phosphatases upon various stresses and that the extent of RtcB tyrosine phosphorylation determines cell adaptive or death outputs.
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Affiliation(s)
- Alexandra Papaioannou
- INSERM U1242, University of Rennes, Rennes, France.,Centre Eugène Marquis, Rennes, France
| | - Federica Centonze
- INSERM U1242, University of Rennes, Rennes, France.,Centre Eugène Marquis, Rennes, France
| | - Alice Metais
- INSERM U1242, University of Rennes, Rennes, France.,Centre Eugène Marquis, Rennes, France
| | - Marion Maurel
- INSERM U1242, University of Rennes, Rennes, France.,Centre Eugène Marquis, Rennes, France
| | - Luc Negroni
- Centre National de la Recherche Scientifique, UMR7104, Illkirch, France.,Institut National de la Santé et de la Recherche Médicale, U1258, Illkirch, France.,Université de Strasbourg, Illkirch, France
| | - Matías Gonzalez-Quiroz
- INSERM U1242, University of Rennes, Rennes, France.,Biomedical Neuroscience Institute, Faculty of Medicine, University of Chile, Santiago, Chile.,Center for Geroscience, Brain Health and Metabolism (GERO), Santiago, Chile.,Program of Cellular and Molecular Biology, Institute of Biomedical Sciences, University of Chile, Santiago, Chile
| | | | - Gabriella Svensson
- Department of Chemistry and Molecular Biology, University of Gothenburg, Göteborg, Sweden
| | - Ensieh Zare
- Department of Chemistry and Molecular Biology, University of Gothenburg, Göteborg, Sweden
| | - Alice Blondel
- INSERM U1242, University of Rennes, Rennes, France.,Centre Eugène Marquis, Rennes, France
| | - Albert C Koong
- Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Claudio Hetz
- Biomedical Neuroscience Institute, Faculty of Medicine, University of Chile, Santiago, Chile.,Center for Geroscience, Brain Health and Metabolism (GERO), Santiago, Chile.,Program of Cellular and Molecular Biology, Institute of Biomedical Sciences, University of Chile, Santiago, Chile
| | - Rémy Pedeux
- INSERM U1242, University of Rennes, Rennes, France.,Centre Eugène Marquis, Rennes, France
| | - Michel L Tremblay
- Goodman Cancer Research Centre, McGill University, Montreal, Canada.,Department of Biochemistry, McGill University, Montreal, Canada
| | - Leif A Eriksson
- Department of Chemistry and Molecular Biology, University of Gothenburg, Göteborg, Sweden
| | - Eric Chevet
- INSERM U1242, University of Rennes, Rennes, France .,Centre Eugène Marquis, Rennes, France
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Decoding non-canonical mRNA decay by the endoplasmic-reticulum stress sensor IRE1α. Nat Commun 2021; 12:7310. [PMID: 34911951 PMCID: PMC8674358 DOI: 10.1038/s41467-021-27597-7] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2021] [Accepted: 11/24/2021] [Indexed: 12/21/2022] Open
Abstract
Inositol requiring enzyme 1 (IRE1) mitigates endoplasmic-reticulum (ER) stress by orchestrating the unfolded-protein response (UPR). IRE1 spans the ER membrane, and signals through a cytosolic kinase-endoribonuclease module. The endoribonuclease generates the transcription factor XBP1s by intron excision between similar RNA stem-loop endomotifs, and depletes select cellular mRNAs through regulated IRE1-dependent decay (RIDD). Paradoxically, in mammals RIDD seems to target only mRNAs with XBP1-like endomotifs, while in flies RIDD exhibits little sequence restriction. By comparing nascent and total IRE1α-controlled mRNAs in human cells, we identify not only canonical endomotif-containing RIDD substrates, but also targets without such motifs-degraded by a process we coin RIDDLE, for RIDD lacking endomotif. IRE1α displays two basic endoribonuclease modalities: highly specific, endomotif-directed cleavage, minimally requiring dimers; and more promiscuous, endomotif-independent processing, requiring phospho-oligomers. An oligomer-deficient IRE1α mutant fails to support RIDDLE in vitro and in cells. Our results advance current mechanistic understanding of the UPR.
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Structural and molecular bases to IRE1 activity modulation. Biochem J 2021; 478:2953-2975. [PMID: 34375386 DOI: 10.1042/bcj20200919] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2021] [Revised: 07/06/2021] [Accepted: 07/12/2021] [Indexed: 12/13/2022]
Abstract
The Unfolded Protein response is an adaptive pathway triggered upon alteration of endoplasmic reticulum (ER) homeostasis. It is transduced by three major ER stress sensors, among which the Inositol Requiring Enzyme 1 (IRE1) is the most evolutionarily conserved. IRE1 is an ER-resident type I transmembrane protein exhibiting an ER luminal domain that senses the protein folding status and a catalytic kinase and RNase cytosolic domain. In recent years, IRE1 has emerged as a relevant therapeutic target in various diseases including degenerative, inflammatory and metabolic pathologies and cancer. As such several drugs altering IRE1 activity were developed that target either catalytic activity and showed some efficacy in preclinical pathological mouse models. In this review, we describe the different drugs identified to target IRE1 activity as well as their mode of action from a structural perspective, thereby identifying common and different modes of action. Based on this information we discuss on how new IRE1-targeting drugs could be developed that outperform the currently available molecules.
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