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Welters A, Nortmann O, Wörmeyer L, Freiberg C, Eberhard D, Bachmann N, Bergmann C, Mayatepek E, Meissner T, Kummer S. Congenital Hyperinsulinism in Humans and Insulin Secretory Dysfunction in Mice Caused by Biallelic DNAJC3 Variants. Int J Mol Sci 2024; 25:1270. [PMID: 38279270 PMCID: PMC10816850 DOI: 10.3390/ijms25021270] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2023] [Revised: 12/29/2023] [Accepted: 01/12/2024] [Indexed: 01/28/2024] Open
Abstract
The BiP co-chaperone DNAJC3 protects cells during ER stress. In mice, the deficiency of DNAJC3 leads to beta-cell apoptosis and the gradual onset of hyperglycemia. In humans, biallelic DNAJC3 variants cause a multisystem disease, including early-onset diabetes mellitus. Recently, hyperinsulinemic hypoglycemia (HH) has been recognized as part of this syndrome. This report presents a case study of an individual with HH caused by DNAJC3 variants and provides an overview of the metabolic phenotype of individuals with HH and DNAJC3 variants. The study demonstrates that HH may be a primary symptom of DNAJC3 deficiency and can persist until adolescence. Additionally, glycemia and insulin release were analyzed in young DNACJ3 knockout (K.O.) mice, which are equivalent to human infants. In the youngest experimentally accessible age group of 4-week-old mice, the in vivo glycemic phenotype was already dominated by a reduced total insulin secretion capacity. However, on a cellular level, the degree of insulin release of DNAJC3 K.O. islets was higher during periods of increased synthetic activity (high-glucose stimulation). We propose that calcium leakage from the ER into the cytosol, due to disrupted DNAJC3-controlled gating of the Sec61 channel, is the most likely mechanism for HH. This is the first genetic mechanism explaining HH solely by the disruption of intracellular calcium homeostasis. Clinicians should screen for HH in DNAJC3 deficiency and consider DNAJC3 variants in the differential diagnosis of congenital hyperinsulinism.
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Affiliation(s)
- Alena Welters
- Department of General Pediatrics, Neonatology and Pediatric Cardiology, Medical Faculty and University Hospital Düsseldorf, Heinrich Heine University Düsseldorf, D-40225 Düsseldorf, Germany; (O.N.); (E.M.); (T.M.); (S.K.)
- Institute of Metabolic Physiology, Heinrich Heine University Düsseldorf, D-40225 Düsseldorf, Germany;
| | - Oliver Nortmann
- Department of General Pediatrics, Neonatology and Pediatric Cardiology, Medical Faculty and University Hospital Düsseldorf, Heinrich Heine University Düsseldorf, D-40225 Düsseldorf, Germany; (O.N.); (E.M.); (T.M.); (S.K.)
- Institute of Metabolic Physiology, Heinrich Heine University Düsseldorf, D-40225 Düsseldorf, Germany;
| | - Laura Wörmeyer
- Department of General Pediatrics, Neonatology and Pediatric Cardiology, Medical Faculty and University Hospital Düsseldorf, Heinrich Heine University Düsseldorf, D-40225 Düsseldorf, Germany; (O.N.); (E.M.); (T.M.); (S.K.)
- Institute of Metabolic Physiology, Heinrich Heine University Düsseldorf, D-40225 Düsseldorf, Germany;
| | - Clemens Freiberg
- Department of Pediatrics and Adolescent Medicine, Pediatric Endocrinology, University Medicine Göttingen, D-37075 Göttingen, Germany;
| | - Daniel Eberhard
- Institute of Metabolic Physiology, Heinrich Heine University Düsseldorf, D-40225 Düsseldorf, Germany;
| | - Nadine Bachmann
- Medizinische Genetik Mainz, Limbach Genetics, D-55128 Mainz, Germany; (N.B.); (C.B.)
| | - Carsten Bergmann
- Medizinische Genetik Mainz, Limbach Genetics, D-55128 Mainz, Germany; (N.B.); (C.B.)
| | - Ertan Mayatepek
- Department of General Pediatrics, Neonatology and Pediatric Cardiology, Medical Faculty and University Hospital Düsseldorf, Heinrich Heine University Düsseldorf, D-40225 Düsseldorf, Germany; (O.N.); (E.M.); (T.M.); (S.K.)
| | - Thomas Meissner
- Department of General Pediatrics, Neonatology and Pediatric Cardiology, Medical Faculty and University Hospital Düsseldorf, Heinrich Heine University Düsseldorf, D-40225 Düsseldorf, Germany; (O.N.); (E.M.); (T.M.); (S.K.)
| | - Sebastian Kummer
- Department of General Pediatrics, Neonatology and Pediatric Cardiology, Medical Faculty and University Hospital Düsseldorf, Heinrich Heine University Düsseldorf, D-40225 Düsseldorf, Germany; (O.N.); (E.M.); (T.M.); (S.K.)
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Xu S, Li X, Geng J, Cao Y, Yu Y, Qi L. Sec61γ is a vital protein in the endoplasmic reticulum membrane promoting tumor metastasis and invasion in lung adenocarcinoma. Br J Cancer 2023; 128:1478-1490. [PMID: 36759724 PMCID: PMC10070493 DOI: 10.1038/s41416-023-02150-z] [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: 06/16/2021] [Revised: 12/01/2022] [Accepted: 01/11/2023] [Indexed: 02/11/2023] Open
Abstract
BACKGROUND Lung adenocarcinoma (LUAD) is one of the most common malignant tumors worldwide. Finding effective prognostic markers and therapeutic targets is of great significance for controlling metastasis and invasion clinically. METHODS The open copy-number aberrations and gene expression datasets were analysed, and the data of 102 LUAD patients was used for further validation. The cell proliferation, colony formation, migration, invasion assays and mice tumor models were used to detect the function of SEC61G. The epidermal growth factor receptor (EGFR) pathway was also detected to find the mechanism of Sec61γ. RESULTS Based on the open datasets, we found that the high level of SEC61G mRNA may drive LUAD metastasis. Furthermore, the overexpression of Sec61γ protein was significantly associated with poor prognosis and greater tumor cell proliferation and metastasis. The SEC61G knockdown could inhibit the EGFR pathway, including STAT3, AKT and PI3K, which can be reversed by Sec61γ overexpression and epithelial growth factor (EGF) supplement. CONCLUSIONS Sec61γ promoted the proliferation, metastasis, and invasion of LUAD through EGFR pathways. Sec61γ might be a potential target for the treatment of LUAD metastases.
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Affiliation(s)
- Shanqi Xu
- Department of Medical Oncology, Harbin Medical University Cancer Hospital, Harbin, China
| | - Xin Li
- College of Bioinformatics Science and Technology, Harbin Medical University, Harbin, China
| | - Jianxiong Geng
- Department of Medical Oncology, Harbin Medical University Cancer Hospital, Harbin, China
| | - Yingyue Cao
- Department of Medical Oncology, Harbin Medical University Cancer Hospital, Harbin, China
| | - Yan Yu
- Department of Medical Oncology, Harbin Medical University Cancer Hospital, Harbin, China.
| | - Lishuang Qi
- College of Bioinformatics Science and Technology, Harbin Medical University, Harbin, China.
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Cavalié A, Zimmermann R. Editorial: The evolving picture of Ca 2+ leak from endoplasmic reticulum in health and diseases. Front Physiol 2023; 14:1182455. [PMID: 37051023 PMCID: PMC10083479 DOI: 10.3389/fphys.2023.1182455] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2023] [Accepted: 03/20/2023] [Indexed: 03/29/2023] Open
Affiliation(s)
- Adolfo Cavalié
- Experimental and Clinical Pharmacology and Toxicology, Pre-clinical Center for Molecular Signalling (PZMS), Saarland University, Homburg, Germany
| | - Richard Zimmermann
- Competence Center for Molecular Medicine, Saarland University, Homburg, Germany
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Melnyk A, Lang S, Sicking M, Zimmermann R, Jung M. Co-chaperones of the Human Endoplasmic Reticulum: An Update. Subcell Biochem 2023; 101:247-291. [PMID: 36520310 DOI: 10.1007/978-3-031-14740-1_9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
In mammalian cells, the rough endoplasmic reticulum (ER) plays central roles in the biogenesis of extracellular plus organellar proteins and in various signal transduction pathways. For these reasons, the ER comprises molecular chaperones, which are involved in import, folding, assembly, export, plus degradation of polypeptides, and signal transduction components, such as calcium channels, calcium pumps, and UPR transducers plus adenine nucleotide carriers/exchangers in the ER membrane. The calcium- and ATP-dependent ER lumenal Hsp70, termed immunoglobulin heavy-chain-binding protein or BiP, is the central player in all these activities and involves up to nine different Hsp40-type co-chaperones, i.e., ER membrane integrated as well as ER lumenal J-domain proteins, termed ERj or ERdj proteins, two nucleotide exchange factors or NEFs (Grp170 and Sil1), and NEF-antagonists, such as MANF. Here we summarize the current knowledge on the ER-resident BiP/ERj chaperone network and focus on the interaction of BiP with the polypeptide-conducting and calcium-permeable Sec61 channel of the ER membrane as an example for BiP action and how its functional cycle is linked to ER protein import and various calcium-dependent signal transduction pathways.
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Affiliation(s)
- Armin Melnyk
- Medical Biochemistry & Molecular Biology, Saarland University, Homburg, Germany
| | - Sven Lang
- Medical Biochemistry & Molecular Biology, Saarland University, Homburg, Germany
| | - Mark Sicking
- Medical Biochemistry & Molecular Biology, Saarland University, Homburg, Germany
| | - Richard Zimmermann
- Medical Biochemistry & Molecular Biology, Saarland University, Homburg, Germany.
| | - Martin Jung
- Medical Biochemistry & Molecular Biology, Saarland University, Homburg, Germany
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Parys JB, Van Coppenolle F. Sec61 complex/translocon: The role of an atypical ER Ca 2+-leak channel in health and disease. Front Physiol 2022; 13:991149. [PMID: 36277220 PMCID: PMC9582130 DOI: 10.3389/fphys.2022.991149] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2022] [Accepted: 09/20/2022] [Indexed: 11/02/2023] Open
Abstract
The heterotrimeric Sec61 protein complex forms the functional core of the so-called translocon that forms an aqueous channel in the endoplasmic reticulum (ER). The primary role of the Sec61 complex is to allow protein import in the ER during translation. Surprisingly, a completely different function in intracellular Ca2+ homeostasis has emerged for the Sec61 complex, and the latter is now accepted as one of the major Ca2+-leak pathways of the ER. In this review, we first discuss the structure of the Sec61 complex and focus on the pharmacology and regulation of the Sec61 complex as a Ca2+-leak channel. Subsequently, we will pay particular attention to pathologies that are linked to Sec61 mutations, such as plasma cell deficiency and congenital neutropenia. Finally, we will explore the relevance of the Sec61 complex as a Ca2+-leak channel in various pathophysiological (ER stress, apoptosis, ischemia-reperfusion) and pathological (type 2 diabetes, cancer) settings.
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Affiliation(s)
- Jan B. Parys
- Laboratory for Molecular and Cellular Signaling, Department of Cellular and Molecular Medicine & Leuven Kanker Instituut, KU Leuven, Leuven, Belgium
| | - Fabien Van Coppenolle
- CarMeN Laboratory, INSERM, INRA, INSA Lyon, Université Claude Bernard Lyon 1, Lyon, France
- Groupement Hospitalier EST, Department of Cardiology, Hospices Civils de Lyon, Lyon, France
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Zimmermann JSM, Linxweiler J, Radosa JC, Linxweiler M, Zimmermann R. The endoplasmic reticulum membrane protein Sec62 as potential therapeutic target in SEC62 overexpressing tumors. Front Physiol 2022; 13:1014271. [PMID: 36262254 PMCID: PMC9574383 DOI: 10.3389/fphys.2022.1014271] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2022] [Accepted: 09/16/2022] [Indexed: 11/30/2022] Open
Abstract
The human SEC62 gene is located on chromosome 3q, was characterized as a tumor driver gene and is found to be overexpressed in an ever-growing number of tumors, particularly those with 3q26 amplification. Where analyzed, SEC62 overexpression was associated with poor prognosis. Sec62 protein is a membrane protein of the endoplasmic reticulum (ER) and has functions in endoplasmic reticulum protein import, endoplasmic reticulum-phagy and -in cooperation with the cytosolic protein calmodulin- the maintenance of cellular calcium homeostasis. Various human tumors show SEC62 overexpression in immunohistochemistry and corresponding cell lines confirm this phenomenon in western blots and immunofluorescence. Furthermore, these tumor cells are characterized by increased stress tolerance and migratory as well as invasive potential, three hallmarks of cancer cells. Strikingly, plasmid-driven overexpression of SEC62 in non-SEC62 overexpressing cells introduces the same three hallmarks of cancer into the transfected cells. Depletion of Sec62 from either type of SEC62 overexpressing tumor cells by treatment with SEC62-targeting siRNAs leads to reduced stress tolerance and reduced migratory as well as invasive potential. Where tested, treatment of SEC62 overexpressing tumor cells with the small molecule/calmodulin antagonist trifluoperazine (TFP) phenocopied the effect of SEC62-targeting siRNAs. Recently, first phase II clinical trials with the prodrug mipsagargin/G202, which targets cellular calcium homeostasis in prostate cells as well as neovascular tissue in various tumors were started. According to experiments with tumor cell lines, however, SEC62 overexpressing tumor cells may be less responsive or resistant against such treatment. Therefore, murine tumor models for tumor growth or metastasis were evaluated with respect to their responsiveness to treatment with a mipsagargin analog (thapsigargin), or trifluoperazine, which had previously been in clinical use for the treatment of schizophrenia, or with the combination of both drugs. So far, no additive effect of the two drugs was observed but trifluoperazine had an inhibitory effect on tumor growth and metastatic potential in the models. Here, we review the state of affairs.
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Affiliation(s)
- Julia S. M. Zimmermann
- Department of Gynecology, Obstetrics and Reproductive Medicine, Saarland University, Homburg, Germany
| | - Johannes Linxweiler
- Department of Urology and Pediatric Urology, Saarland University, Homburg, Germany
| | - Julia C. Radosa
- Department of Gynecology, Obstetrics and Reproductive Medicine, Saarland University, Homburg, Germany
| | - Maximilian Linxweiler
- Department of Otorhinolaryngology, Head and Neck Surgery, Saarland University, Homburg, Germany
| | - Richard Zimmermann
- Competence Center for Molecular Medicine, Saarland University, Homburg, Germany
- *Correspondence: Richard Zimmermann,
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Lang S, Nguyen D, Bhadra P, Jung M, Helms V, Zimmermann R. Signal Peptide Features Determining the Substrate Specificities of Targeting and Translocation Components in Human ER Protein Import. Front Physiol 2022; 13:833540. [PMID: 35899032 PMCID: PMC9309488 DOI: 10.3389/fphys.2022.833540] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2021] [Accepted: 05/17/2022] [Indexed: 12/11/2022] Open
Abstract
In human cells, approximately 30% of all polypeptides enter the secretory pathway at the level of the endoplasmic reticulum (ER). This process involves cleavable amino-terminal signal peptides (SPs) or more or less amino-terminal transmembrane helices (TMHs), which serve as targeting determinants, at the level of the precursor polypeptides and a multitude of cytosolic and ER proteins, which facilitate their ER import. Alone or in combination SPs and TMHs guarantee the initial ER targeting as well as the subsequent membrane integration or translocation. Cytosolic SRP and SR, its receptor in the ER membrane, mediate cotranslational targeting of most nascent precursor polypeptide chains to the polypeptide-conducting Sec61 complex in the ER membrane. Alternatively, fully-synthesized precursor polypeptides and certain nascent precursor polypeptides are targeted to the ER membrane by either the PEX-, SND-, or TRC-pathway. Although these targeting pathways may have overlapping functions, the question arises how relevant this is under cellular conditions and which features of SPs and precursor polypeptides determine preference for a certain pathway. Irrespective of their targeting pathway(s), most precursor polypeptides are integrated into or translocated across the ER membrane via the Sec61 channel. For some precursor polypeptides specific Sec61 interaction partners have to support the gating of the channel to the open state, again raising the question why and when this is the case. Recent progress shed light on the client spectrum and specificities of some auxiliary components, including Sec62/Sec63, TRAM1 protein, and TRAP. To address the question which precursors use a certain pathway or component in intact human cells, i.e., under conditions of fast translation rates and molecular crowding, in the presence of competing precursors, different targeting organelles, and relevant stoichiometries of the involved components, siRNA-mediated depletion of single targeting or transport components in HeLa cells was combined with label-free quantitative proteomics and differential protein abundance analysis. Here, we present a summary of the experimental approach as well as the resulting differential protein abundance analyses and discuss their mechanistic implications in light of the available structural data.
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Affiliation(s)
- Sven Lang
- Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
- *Correspondence: Sven Lang, ; Richard Zimmermann,
| | - Duy Nguyen
- Center for Bioinformatics, Saarland University, Saarbrücken, Germany
| | - Pratiti Bhadra
- Center for Bioinformatics, Saarland University, Saarbrücken, Germany
| | - Martin Jung
- Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
| | - Volkhard Helms
- Center for Bioinformatics, Saarland University, Saarbrücken, Germany
| | - Richard Zimmermann
- Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
- *Correspondence: Sven Lang, ; Richard Zimmermann,
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Calabrese G, Molzahn C, Mayor T. Protein interaction networks in neurodegenerative diseases: from physiological function to aggregation. J Biol Chem 2022; 298:102062. [PMID: 35623389 PMCID: PMC9234719 DOI: 10.1016/j.jbc.2022.102062] [Citation(s) in RCA: 23] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2022] [Revised: 04/26/2022] [Accepted: 05/18/2022] [Indexed: 11/25/2022] Open
Abstract
The accumulation of protein inclusions is linked to many neurodegenerative diseases that typically develop in older individuals, due to a combination of genetic and environmental factors. In rare familial neurodegenerative disorders, genes encoding for aggregation-prone proteins are often mutated. While the underlying mechanism leading to these diseases still remains to be fully elucidated, efforts in the past 20 years revealed a vast network of protein–protein interactions that play a major role in regulating the aggregation of key proteins associated with neurodegeneration. Misfolded proteins that can oligomerize and form insoluble aggregates associate with molecular chaperones and other elements of the proteolytic machineries that are the frontline workers attempting to protect the cells by promoting clearance and preventing aggregation. Proteins that are normally bound to aggregation-prone proteins can become sequestered and mislocalized in protein inclusions, leading to their loss of function. In contrast, mutations, posttranslational modifications, or misfolding of aggregation-prone proteins can lead to gain of function by inducing novel or altered protein interactions, which in turn can impact numerous essential cellular processes and organelles, such as vesicle trafficking and the mitochondria. This review examines our current knowledge of protein–protein interactions involving several key aggregation-prone proteins that are associated with Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, or amyotrophic lateral sclerosis. We aim to provide an overview of the protein interaction networks that play a central role in driving or mitigating inclusion formation, while highlighting some of the key proteomic studies that helped to uncover the extent of these networks.
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Affiliation(s)
- Gaetano Calabrese
- Michael Smith Laboratories, University of British Columbia, V6T 1Z4 Vancouver BC, Canada.
| | - Cristen Molzahn
- Michael Smith Laboratories, University of British Columbia, V6T 1Z4 Vancouver BC, Canada
| | - Thibault Mayor
- Michael Smith Laboratories, University of British Columbia, V6T 1Z4 Vancouver BC, Canada.
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Regulation of calcium homeostasis and flux between the endoplasmic reticulum and the cytosol. J Biol Chem 2022; 298:102061. [PMID: 35609712 PMCID: PMC9218512 DOI: 10.1016/j.jbc.2022.102061] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2021] [Revised: 05/17/2022] [Accepted: 05/18/2022] [Indexed: 12/20/2022] Open
Abstract
The concentration of Ca2+ in the endoplasmic reticulum (ER) is critically important for maintaining its oxidizing environment as well as for maintaining luminal ATP levels required for chaperone activity. Therefore, local luminal Ca2+ concentrations and the dynamic Ca2+ flux between the different subcellular compartments are tightly controlled. Influx of Ca2+ into the ER is enabled by a reductive shift, which opens the sarcoendoplasmic reticulum calcium transport ATPase pump, building the Ca2+ gradient across the ER membrane required for ATP import. Meanwhile, Ca2+ leakage from the ER has been reported to occur via the Sec61 translocon following protein translocation. In this review, we provide an overview of the complex regulation of Ca2+ homeostasis, Ca2+ flux between subcellular compartments, and the cellular stress response (the unfolded protein response) induced upon dysregulated luminal Ca2+ metabolism. We also provide insight into the structure and gating mechanism at the Sec61 translocon and examine the role of ER-resident cochaperones in assisting the central ER-resident chaperone BiP in the control of luminal Ca2+ concentrations.
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Regulation of Translation, Translocation, and Degradation of Proteins at the Membrane of the Endoplasmic Reticulum. Int J Mol Sci 2022; 23:ijms23105576. [PMID: 35628387 PMCID: PMC9147092 DOI: 10.3390/ijms23105576] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2022] [Revised: 05/10/2022] [Accepted: 05/13/2022] [Indexed: 11/21/2022] Open
Abstract
The endoplasmic reticulum (ER) of mammalian cells is the central organelle for the maturation and folding of transmembrane proteins and for proteins destined to be secreted into the extracellular space. The proper folding of target proteins is achieved and supervised by a complex endogenous chaperone machinery. BiP, a member of the Hsp70 protein family, is the central chaperone in the ER. The chaperoning activity of BiP is assisted by ER-resident DnaJ (ERdj) proteins due to their ability to stimulate the low, intrinsic ATPase activity of BiP. Besides their co-chaperoning activity, ERdj proteins also regulate and tightly control the translation, translocation, and degradation of proteins. Disturbances in the luminal homeostasis result in the accumulation of unfolded proteins, thereby eliciting a stress response, the so-called unfolded protein response (UPR). Accumulated proteins are either deleterious due to the functional loss of the respective protein and/or due to their deposition as intra- or extracellular protein aggregates. A variety of metabolic diseases are known to date, which are associated with the dysfunction of components of the chaperone machinery. In this review, we will delineate the impact of ERdj proteins in controlling protein synthesis and translocation under physiological and under stress conditions. A second aspect of this review is dedicated to the role of ERdj proteins in the ER-associated degradation pathway, by which unfolded or misfolded proteins are discharged from the ER. We will refer to some of the most prominent diseases known to be based on the dysfunction of ERdj proteins.
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Sun R, Yang L, Wang Y, Zhang Y, Ke J, Zhao D. DNAJB11 predicts a poor prognosis and is associated with immune infiltration in thyroid carcinoma: a bioinformatics analysis. J Int Med Res 2021; 49:3000605211053722. [PMID: 34727750 PMCID: PMC8573516 DOI: 10.1177/03000605211053722] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Objective To investigate the prognostic value of the co-chaperone protein DnaJ Heat Shock Protein Family (Hsp40) Member B11 (DNAJB11) in thyroid carcinoma (THCA). Methods This bioinformatics analysis study evaluated the prognostic value of DNAJB11 mRNA levels in THCA based on data from The Cancer Genome Atlas (TCGA). The levels of DNAJB11 mRNA in THCA and normal tissues were compared with Wilcoxon signed rank test. Kaplan–Meier survival curve analysis and Cox regression analysis were performed to evaluate the correlation between DNAJB11 mRNA levels and survival. Gene Ontology (GO) enrichment analysis was used to elucidate the functional enrichment difference. Results Data from the 502 patients with THCA from the TCGA database were analysed. DNAJB11 mRNA was downregulated in THCA tissues compared with normal tissues. Decreased levels of DNAJB11 mRNA were significantly correlated with T stage, N stage, pathological stage, histological type, extrathyroidal extension and BRAF gene status. The low levels of DNAJB11 mRNA were associated with a shorter progression-free interval. GO enrichment analysis showed that DNAJB11 was involved in immune-related biological processes. Conclusion Low levels of DNAJB11 mRNA were associated with poor prognosis in THCA.
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Affiliation(s)
- Rongxin Sun
- Centre for Endocrine Metabolism and Immune Diseases, Beijing Luhe Hospital, Capital Medical University, Beijing, China.,Beijing Key Laboratory of Diabetes Research and Care, Beijing, China
| | - Longyan Yang
- Centre for Endocrine Metabolism and Immune Diseases, Beijing Luhe Hospital, Capital Medical University, Beijing, China.,Beijing Key Laboratory of Diabetes Research and Care, Beijing, China
| | - Yan Wang
- Centre for Endocrine Metabolism and Immune Diseases, Beijing Luhe Hospital, Capital Medical University, Beijing, China.,Beijing Key Laboratory of Diabetes Research and Care, Beijing, China
| | - Yuanyuan Zhang
- Centre for Endocrine Metabolism and Immune Diseases, Beijing Luhe Hospital, Capital Medical University, Beijing, China.,Beijing Key Laboratory of Diabetes Research and Care, Beijing, China
| | - Jing Ke
- Centre for Endocrine Metabolism and Immune Diseases, Beijing Luhe Hospital, Capital Medical University, Beijing, China.,Beijing Key Laboratory of Diabetes Research and Care, Beijing, China
| | - Dong Zhao
- Centre for Endocrine Metabolism and Immune Diseases, Beijing Luhe Hospital, Capital Medical University, Beijing, China.,Beijing Key Laboratory of Diabetes Research and Care, Beijing, China
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Jennings MJ, Hathazi D, Nguyen CDL, Munro B, Münchberg U, Ahrends R, Schenck A, Eidhof I, Freier E, Synofzik M, Horvath R, Roos A. Intracellular Lipid Accumulation and Mitochondrial Dysfunction Accompanies Endoplasmic Reticulum Stress Caused by Loss of the Co-chaperone DNAJC3. Front Cell Dev Biol 2021; 9:710247. [PMID: 34692675 PMCID: PMC8526738 DOI: 10.3389/fcell.2021.710247] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2021] [Accepted: 09/02/2021] [Indexed: 12/25/2022] Open
Abstract
Recessive mutations in DNAJC3, an endoplasmic reticulum (ER)-resident BiP co-chaperone, have been identified in patients with multisystemic neurodegeneration and diabetes mellitus. To further unravel these pathomechanisms, we employed a non-biased proteomic approach and identified dysregulation of several key cellular pathways, suggesting a pathophysiological interplay of perturbed lipid metabolism, mitochondrial bioenergetics, ER-Golgi function, and amyloid-beta processing. Further functional investigations in fibroblasts of patients with DNAJC3 mutations detected cellular accumulation of lipids and an increased sensitivity to cholesterol stress, which led to activation of the unfolded protein response (UPR), alterations of the ER-Golgi machinery, and a defect of amyloid precursor protein. In line with the results of previous studies, we describe here alterations in mitochondrial morphology and function, as a major contributor to the DNAJC3 pathophysiology. Hence, we propose that the loss of DNAJC3 affects lipid/cholesterol homeostasis, leading to UPR activation, β-amyloid accumulation, and impairment of mitochondrial oxidative phosphorylation.
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Affiliation(s)
- Matthew J. Jennings
- Department of Clinical Neuroscience, University of Cambridge, Cambridge, United Kingdom
| | - Denisa Hathazi
- Department of Clinical Neuroscience, University of Cambridge, Cambridge, United Kingdom
- Leibniz-Institut für Analytische Wissenschaften – ISAS – e.V., Dortmund, Germany
| | - Chi D. L. Nguyen
- Leibniz-Institut für Analytische Wissenschaften – ISAS – e.V., Dortmund, Germany
| | - Benjamin Munro
- Department of Clinical Neuroscience, University of Cambridge, Cambridge, United Kingdom
| | - Ute Münchberg
- Leibniz-Institut für Analytische Wissenschaften – ISAS – e.V., Dortmund, Germany
| | - Robert Ahrends
- Leibniz-Institut für Analytische Wissenschaften – ISAS – e.V., Dortmund, Germany
| | - Annette Schenck
- Department of Human Genetics, Donders Institute for Brain, Cognition and Behavior, Radboud University Medical Center, Nijmegen, Netherlands
| | - Ilse Eidhof
- Department of Human Genetics, Donders Institute for Brain, Cognition and Behavior, Radboud University Medical Center, Nijmegen, Netherlands
| | - Erik Freier
- Leibniz-Institut für Analytische Wissenschaften – ISAS – e.V., Dortmund, Germany
| | - Matthis Synofzik
- Department of Neurodegenerative Diseases, Hertie Institute for Clinical Brain Research, University of Tübingen, Tübingen, Germany
- German Centre for Neurodegenerative Diseases (DZNE), Tübingen, Germany
| | - Rita Horvath
- Department of Clinical Neuroscience, University of Cambridge, Cambridge, United Kingdom
| | - Andreas Roos
- Leibniz-Institut für Analytische Wissenschaften – ISAS – e.V., Dortmund, Germany
- Department of Pediatric Neurology, Developmental Neurology and Social Pediatrics, Children’s Hospital University of Essen, Essen, Germany
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13
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Pick T, Beck A, Gamayun I, Schwarz Y, Schirra C, Jung M, Krause E, Niemeyer BA, Zimmermann R, Lang S, Anken EV, Cavalié A. Remodelling of Ca 2+ homeostasis is linked to enlarged endoplasmic reticulum in secretory cells. Cell Calcium 2021; 99:102473. [PMID: 34560367 DOI: 10.1016/j.ceca.2021.102473] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2021] [Revised: 08/27/2021] [Accepted: 09/08/2021] [Indexed: 11/30/2022]
Abstract
The endoplasmic reticulum (ER) is extensively remodelled during the development of professional secretory cells to cope with high protein production. Since ER is the principal Ca2+ store in the cell, we characterised the Ca2+ homeostasis in NALM-6 and RPMI 8226 cells, which are commonly used as human pre-B and antibody secreting plasma cell models, respectively. Expression levels of Sec61 translocons and the corresponding Sec61-mediated Ca2+ leak from ER, Ca2+ storage capacity and store-operated Ca2+ entry were significantly enlarged in the secretory RPMI 8226 cell line. Using an immunoglobulin M heavy chain producing HeLa cell model, we found that the enlarged Ca2+ storage capacity and Ca2+ leak from ER are linked to ER expansion. Our data delineates a developmental remodelling of Ca2+ homeostasis in professional secretory cells in which a high Sec61-mediated Ca2+ leak and, thus, a high Ca2+ turnover in the ER is backed up by enhanced store-operated Ca2+ entry.
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Affiliation(s)
- Tillman Pick
- Experimental and Clinical Pharmacology and Toxicology, Pre-clinical Center for Molecular Signalling (PZMS), Saarland University, 66421 Homburg, Germany.
| | - Andreas Beck
- Experimental and Clinical Pharmacology and Toxicology, Pre-clinical Center for Molecular Signalling (PZMS), Saarland University, 66421 Homburg, Germany
| | - Igor Gamayun
- Experimental and Clinical Pharmacology and Toxicology, Pre-clinical Center for Molecular Signalling (PZMS), Saarland University, 66421 Homburg, Germany
| | - Yvonne Schwarz
- Molecular Neurophysiology, Center for Integrative Physiology and Molecular Medicine (CIPMM), Saarland University, 66421 Homburg, Germany
| | - Claudia Schirra
- Cellular Neurophysiology, Center for Integrative Physiology and Molecular Medicine (CIPMM), Saarland University, 66421 Homburg, Germany
| | - Martin Jung
- Medical Biochemistry and Molecular Biology, Pre-clinical Centre for Molecular Signalling (PZMS), Saarland University, 66421 Homburg, Germany
| | - Elmar Krause
- Cellular Neurophysiology, Center for Integrative Physiology and Molecular Medicine (CIPMM), Saarland University, 66421 Homburg, Germany
| | - Barbara A Niemeyer
- Molecular Biophysics, Center for Integrative Physiology and Molecular Medicine (CIPMM), Saarland University, 66421 Homburg, Germany
| | - Richard Zimmermann
- Medical Biochemistry and Molecular Biology, Pre-clinical Centre for Molecular Signalling (PZMS), Saarland University, 66421 Homburg, Germany
| | - Sven Lang
- Medical Biochemistry and Molecular Biology, Pre-clinical Centre for Molecular Signalling (PZMS), Saarland University, 66421 Homburg, Germany
| | - Eelco van Anken
- Division of Genetics and Cell Biology, San Raffaele Scientific Institute and Università Vita-Salute San Raffaele, Milan, Italy
| | - Adolfo Cavalié
- Experimental and Clinical Pharmacology and Toxicology, Pre-clinical Center for Molecular Signalling (PZMS), Saarland University, 66421 Homburg, Germany.
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14
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Sicking M, Lang S, Bochen F, Roos A, Drenth JPH, Zakaria M, Zimmermann R, Linxweiler M. Complexity and Specificity of Sec61-Channelopathies: Human Diseases Affecting Gating of the Sec61 Complex. Cells 2021; 10:1036. [PMID: 33925740 PMCID: PMC8147068 DOI: 10.3390/cells10051036] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2021] [Revised: 04/15/2021] [Accepted: 04/17/2021] [Indexed: 12/14/2022] Open
Abstract
The rough endoplasmic reticulum (ER) of nucleated human cells has crucial functions in protein biogenesis, calcium (Ca2+) homeostasis, and signal transduction. Among the roughly one hundred components, which are involved in protein import and protein folding or assembly, two components stand out: The Sec61 complex and BiP. The Sec61 complex in the ER membrane represents the major entry point for precursor polypeptides into the membrane or lumen of the ER and provides a conduit for Ca2+ ions from the ER lumen to the cytosol. The second component, the Hsp70-type molecular chaperone immunoglobulin heavy chain binding protein, short BiP, plays central roles in protein folding and assembly (hence its name), protein import, cellular Ca2+ homeostasis, and various intracellular signal transduction pathways. For the purpose of this review, we focus on these two components, their relevant allosteric effectors and on the question of how their respective functional cycles are linked in order to reconcile the apparently contradictory features of the ER membrane, selective permeability for precursor polypeptides, and impermeability for Ca2+. The key issues are that the Sec61 complex exists in two conformations: An open and a closed state that are in a dynamic equilibrium with each other, and that BiP contributes to its gating in both directions in cooperation with different co-chaperones. While the open Sec61 complex forms an aqueous polypeptide-conducting- and transiently Ca2+-permeable channel, the closed complex is impermeable even to Ca2+. Therefore, we discuss the human hereditary and tumor diseases that are linked to Sec61 channel gating, termed Sec61-channelopathies, as disturbances of selective polypeptide-impermeability and/or aberrant Ca2+-permeability.
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Affiliation(s)
- Mark Sicking
- Department of Medical Biochemistry & Molecular Biology, Saarland University, D-66421 Homburg, Germany;
| | - Sven Lang
- Department of Medical Biochemistry & Molecular Biology, Saarland University, D-66421 Homburg, Germany;
| | - Florian Bochen
- Department of Otorhinolaryngology, Head and Neck Surgery, Saarland University Medical Center, D-66421 Homburg, Germany; (F.B.); (M.L.)
| | - Andreas Roos
- Department of Neuropediatrics, Essen University Hospital, D-45147 Essen, Germany;
| | - Joost P. H. Drenth
- Department of Molecular Gastroenterology and Hepatology, Radboud University Medical Center, 6525 GA Nijmegen, The Netherlands;
| | - Muhammad Zakaria
- Department of Genetics, Hazara University, Mansehra 21300, Pakistan;
| | - Richard Zimmermann
- Department of Medical Biochemistry & Molecular Biology, Saarland University, D-66421 Homburg, Germany;
| | - Maximilian Linxweiler
- Department of Otorhinolaryngology, Head and Neck Surgery, Saarland University Medical Center, D-66421 Homburg, Germany; (F.B.); (M.L.)
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15
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Lemos FO, Bultynck G, Parys JB. A comprehensive overview of the complex world of the endo- and sarcoplasmic reticulum Ca 2+-leak channels. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2021; 1868:119020. [PMID: 33798602 DOI: 10.1016/j.bbamcr.2021.119020] [Citation(s) in RCA: 33] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 01/23/2021] [Revised: 03/09/2021] [Accepted: 03/13/2021] [Indexed: 12/11/2022]
Abstract
Inside cells, the endoplasmic reticulum (ER) forms the largest Ca2+ store. Ca2+ is actively pumped by the SERCA pumps in the ER, where intraluminal Ca2+-binding proteins enable the accumulation of large amount of Ca2+. IP3 receptors and the ryanodine receptors mediate the release of Ca2+ in a controlled way, thereby evoking complex spatio-temporal signals in the cell. The steady state Ca2+ concentration in the ER of about 500 μM results from the balance between SERCA-mediated Ca2+ uptake and the passive leakage of Ca2+. The passive Ca2+ leak from the ER is often ignored, but can play an important physiological role, depending on the cellular context. Moreover, excessive Ca2+ leakage significantly lowers the amount of Ca2+ stored in the ER compared to normal conditions, thereby limiting the possibility to evoke Ca2+ signals and/or causing ER stress, leading to pathological consequences. The so-called Ca2+-leak channels responsible for Ca2+ leakage from the ER are however still not well understood, despite over 20 different proteins have been proposed to contribute to it. This review has the aim to critically evaluate the available evidence about the various channels potentially involved and to draw conclusions about their relative importance.
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Affiliation(s)
- Fernanda O Lemos
- KU Leuven, Laboratory of Molecular and Cellular Signaling, Department of Cellular and Molecular Medicine and Leuven Kanker Instituut, Campus Gasthuisberg O/N-1 B-802, Herestraat 49, B-3000 Leuven, Belgium
| | - Geert Bultynck
- KU Leuven, Laboratory of Molecular and Cellular Signaling, Department of Cellular and Molecular Medicine and Leuven Kanker Instituut, Campus Gasthuisberg O/N-1 B-802, Herestraat 49, B-3000 Leuven, Belgium
| | - Jan B Parys
- KU Leuven, Laboratory of Molecular and Cellular Signaling, Department of Cellular and Molecular Medicine and Leuven Kanker Instituut, Campus Gasthuisberg O/N-1 B-802, Herestraat 49, B-3000 Leuven, Belgium.
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16
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Schorr S, Nguyen D, Haßdenteufel S, Nagaraj N, Cavalié A, Greiner M, Weissgerber P, Loi M, Paton AW, Paton JC, Molinari M, Förster F, Dudek J, Lang S, Helms V, Zimmermann R. Identification of signal peptide features for substrate specificity in human Sec62/Sec63-dependent ER protein import. FEBS J 2020; 287:4612-4640. [PMID: 32133789 DOI: 10.1111/febs.15274] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2019] [Revised: 01/22/2020] [Accepted: 03/02/2020] [Indexed: 02/06/2023]
Abstract
In mammalian cells, one-third of all polypeptides are integrated into the membrane or translocated into the lumen of the endoplasmic reticulum (ER) via the Sec61 channel. While the Sec61 complex facilitates ER import of most precursor polypeptides, the Sec61-associated Sec62/Sec63 complex supports ER import in a substrate-specific manner. So far, mainly posttranslationally imported precursors and the two cotranslationally imported precursors of ERj3 and prion protein were found to depend on the Sec62/Sec63 complex in vitro. Therefore, we determined the rules for engagement of Sec62/Sec63 in ER import in intact human cells using a recently established unbiased proteomics approach. In addition to confirming ERj3, we identified 22 novel Sec62/Sec63 substrates under these in vivo-like conditions. As a common feature, those previously unknown substrates share signal peptides (SP) with comparatively longer but less hydrophobic hydrophobic region of SP and lower carboxy-terminal region of SP (C-region) polarity. Further analyses with four substrates, and ERj3 in particular, revealed the combination of a slowly gating SP and a downstream translocation-disruptive positively charged cluster of amino acid residues as decisive for the Sec62/Sec63 requirement. In the case of ERj3, these features were found to be responsible for an additional immunoglobulin heavy-chain binding protein (BiP) requirement and to correlate with sensitivity toward the Sec61-channel inhibitor CAM741. Thus, the human Sec62/Sec63 complex may support Sec61-channel opening for precursor polypeptides with slowly gating SPs by direct interaction with the cytosolic amino-terminal peptide of Sec61α or via recruitment of BiP and its interaction with the ER-lumenal loop 7 of Sec61α. These novel insights into the mechanism of human ER protein import contribute to our understanding of the etiology of SEC63-linked polycystic liver disease. DATABASES: The mass spectrometry proteomics data have been deposited to the ProteomeXchange Consortium via the PRIDE partner repository (http://www.ebi.ac.uk/pride/archive/projects/Identifiers) with the dataset identifiers: PXD008178, PXD011993, and PXD012078. Supplementary information was deposited at Mendeley Data (https://data.mendeley.com/datasets/6s5hn73jcv/2).
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Affiliation(s)
- Stefan Schorr
- Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
| | - Duy Nguyen
- Center for Bioinformatics, Saarland University, Saarbrücken, Germany
| | - Sarah Haßdenteufel
- Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
| | - Nagarjuna Nagaraj
- Core Facility, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Adolfo Cavalié
- Experimental and Clinical Pharmacology and Toxicology, Saarland University, Homburg, Germany
| | - Markus Greiner
- Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
| | - Petra Weissgerber
- Experimental and Clinical Pharmacology and Toxicology, Saarland University, Homburg, Germany
| | - Marisa Loi
- Faculty of Biomedical Sciences, Institute for Research in Biomedicine, Università della Svizzera italiana, Bellinzona, Switzerland
| | - Adrienne W Paton
- Research Centre for Infectious Diseases, University of Adelaide, SA, Australia
| | - James C Paton
- Research Centre for Infectious Diseases, University of Adelaide, SA, Australia
| | - Maurizio Molinari
- Faculty of Biomedical Sciences, Institute for Research in Biomedicine, Università della Svizzera italiana, Bellinzona, Switzerland
| | - Friedrich Förster
- Bijvoet Center for Biomolecular Research, Utrecht University, The Netherlands
| | - Johanna Dudek
- Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
| | - Sven Lang
- Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
| | - Volkhard Helms
- Center for Bioinformatics, Saarland University, Saarbrücken, Germany
| | - Richard Zimmermann
- Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
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17
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Muncanovic D, Justesen MH, Preisler SS, Pedersen PA. Characterization of Hailey-Hailey Disease-mutants in presence and absence of wild type SPCA1 using Saccharomyces cerevisiae as model organism. Sci Rep 2019; 9:12442. [PMID: 31455819 PMCID: PMC6712213 DOI: 10.1038/s41598-019-48866-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2018] [Accepted: 08/12/2019] [Indexed: 01/07/2023] Open
Abstract
Hailey-Hailey disease is an autosomal genetic disease caused by mutations in one of the two ATP2C1 alleles encoding the secretory pathway Ca2+/Mn2+-ATPase, hSPCA1. The disease almost exclusively affects epidermis, where it mainly results in acantholysis of the suprabasal layers. The etiology of the disease is complex and not well understood. We applied a yeast based complementation system to characterize fourteen disease-causing ATP2C1 missense mutations in presence or absence of wild type ATP2C1 or ATP2A2, encoding SERCA2. In our yeast model system, mutations in ATP2C1 affected Mn2+ transport more than Ca2+ transport as twelve out of fourteen mutations were unable to complement Mn2+ sensitivity while thirteen out of fourteen to some extent complemented the high Ca2+requirement. Nine out of fourteen mutations conferred a cold sensitive complementation capacity. In absence of a wild type ATP2C1 allele, twelve out of fourteen mutations induced an unfolded protein response indicating that in vivo folding of hSPCA1 is sensitive to disease causing amino acid substitutions and four of the fourteen mutations caused the hSPCA1 protein to accumulate in the vacuolar membrane. Co-expression of either wild type ATP2C1 or ATP2A2 prevented induction of the unfolded protein response and hSPCA1 mis-localization.
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Affiliation(s)
- Daniel Muncanovic
- Department of Biology, August Krogh Building, University of Copenhagen, Universitetsparken 13, 2100, Copenhagen, OE, Denmark
| | - Mette Heberg Justesen
- Department of Biology, August Krogh Building, University of Copenhagen, Universitetsparken 13, 2100, Copenhagen, OE, Denmark
| | - Sarah Spruce Preisler
- Department of Biology, August Krogh Building, University of Copenhagen, Universitetsparken 13, 2100, Copenhagen, OE, Denmark
| | - Per Amstrup Pedersen
- Department of Biology, August Krogh Building, University of Copenhagen, Universitetsparken 13, 2100, Copenhagen, OE, Denmark.
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18
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Needham PG, Guerriero CJ, Brodsky JL. Chaperoning Endoplasmic Reticulum-Associated Degradation (ERAD) and Protein Conformational Diseases. Cold Spring Harb Perspect Biol 2019; 11:cshperspect.a033928. [PMID: 30670468 DOI: 10.1101/cshperspect.a033928] [Citation(s) in RCA: 81] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Misfolded proteins compromise cellular homeostasis. This is especially problematic in the endoplasmic reticulum (ER), which is a high-capacity protein-folding compartment and whose function requires stringent protein quality-control systems. Multiprotein complexes in the ER are able to identify, remove, ubiquitinate, and deliver misfolded proteins to the 26S proteasome for degradation in the cytosol, and these events are collectively termed ER-associated degradation, or ERAD. Several steps in the ERAD pathway are facilitated by molecular chaperone networks, and the importance of ERAD is highlighted by the fact that this pathway is linked to numerous protein conformational diseases. In this review, we discuss the factors that constitute the ERAD machinery and detail how each step in the pathway occurs. We then highlight the underlying pathophysiology of protein conformational diseases associated with ERAD.
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Affiliation(s)
- Patrick G Needham
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
| | | | - Jeffrey L Brodsky
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
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19
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Haßdenteufel S, Nguyen D, Helms V, Lang S, Zimmermann R. ER import of small human presecretory proteins: components and mechanisms. FEBS Lett 2019; 593:2506-2524. [PMID: 31325177 DOI: 10.1002/1873-3468.13542] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2019] [Revised: 07/10/2019] [Accepted: 07/13/2019] [Indexed: 11/12/2022]
Abstract
Protein transport into the mammalian endoplasmic reticulum (ER) used to be seen as strictly cotranslational, that is temporarily and mechanistically coupled to protein synthesis. In the course of the last decades, however, several classes of precursors of soluble and membrane proteins were found to be post-translationally imported into the ER, without any involvement of the ribosome. The first such class to be identified were the small presecretory proteins; tail-anchored membrane proteins followed next. In both classes, the inherent address tag is released from the translating ribosome before the initiation of ER import, as part of the fully synthesized precursor. In small presecretory proteins, the information for ER targeting and -translocation via the polypeptide-conducting Sec61-channel is encoded by a classical N-terminal signal peptide, which is released from the ribsosome before targeting due to the small size of the full-length precursor. Here, we discuss the current state of research on targeting and translocation of small presecretory proteins into the mammalian ER. In closing, we present a unifying hypothesis for ER protein translocation in terms of an energy diagram for Sec61-channel gating.
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Affiliation(s)
- Sarah Haßdenteufel
- Department of Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
| | - Duy Nguyen
- Center for Bioinformatics, Saarland University, Saarbrücken, Germany
| | - Volkhard Helms
- Center for Bioinformatics, Saarland University, Saarbrücken, Germany
| | - Sven Lang
- Department of Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
| | - Richard Zimmermann
- Department of Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
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20
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Ziska A, Tatzelt J, Dudek J, Paton AW, Paton JC, Zimmermann R, Haßdenteufel S. The signal peptide plus a cluster of positive charges in prion protein dictate chaperone-mediated Sec61 channel gating. Biol Open 2019; 8:bio.040691. [PMID: 30745438 PMCID: PMC6451349 DOI: 10.1242/bio.040691] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
The Sec61-complex as a dynamic polypeptide-conducting channel mediates protein transport into the human endoplasmic reticulum (ER) with the help of additional components. ER membrane resident Hsp40-type co-chaperone Sec63 as well as the ER lumenal Hsp70-type chaperone BiP were proposed to facilitate channel opening in a precursor-specific fashion. Here, we report on their rules of engagement in ER import of the prion protein (PrP) by addressing sixteen PrP-related variants which differ in their signal peptides and mature parts, respectively. Transport into the ER of semi-permeabilized human cells was analyzed upon depletion of the components by siRNA- or toxin-treatment. The results are consistent with the view of separate functions of BiP and Sec63 and strongly suggest that the co-chaperone/chaperone-pair facilitates Sec61 channel gating to the open state when precursor polypeptides with weak signal peptides in combination with detrimental features in the adjacent mature part were targeted. Thus, we expand the view of chaperone-mediated Sec61 channel gating by providing a novel example of a polybasic motif that interferes with signal peptide-mediated Sec61 channel gating. This article has an associated First Person interview with the first author of the paper.
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Affiliation(s)
- Anke Ziska
- Department of Medical Biochemistry and Molecular Biology, Saarland University, 66421 Homburg, Germany
| | - Jörg Tatzelt
- Department Biochemistry of Neurodegenerative Diseases, Institute of Biochemistry and Pathobiochemistry, Ruhr University, 44801 Bochum, Germany
| | - Johanna Dudek
- Department of Medical Biochemistry and Molecular Biology, Saarland University, 66421 Homburg, Germany
| | - Adrienne W Paton
- School of Molecular and Biomedical Sciences, Research Centre for Infectious Disease, University of Adelaide, Adelaide, South Australia 5005, Australia
| | - James C Paton
- School of Molecular and Biomedical Sciences, Research Centre for Infectious Disease, University of Adelaide, Adelaide, South Australia 5005, Australia
| | - Richard Zimmermann
- Department of Medical Biochemistry and Molecular Biology, Saarland University, 66421 Homburg, Germany
| | - Sarah Haßdenteufel
- Department of Medical Biochemistry and Molecular Biology, Saarland University, 66421 Homburg, Germany
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21
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Lang S, Nguyen D, Pfeffer S, Förster F, Helms V, Zimmermann R. Functions and Mechanisms of the Human Ribosome-Translocon Complex. Subcell Biochem 2019; 93:83-141. [PMID: 31939150 DOI: 10.1007/978-3-030-28151-9_4] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The membrane of the endoplasmic reticulum (ER) in human cells harbors the protein translocon, which facilitates membrane insertion and translocation of almost every newly synthesized polypeptide targeted to organelles of the secretory pathway. The translocon comprises the polypeptide-conducting Sec61 channel and several additional proteins, which are associated with the heterotrimeric Sec61 complex. This ensemble of proteins facilitates ER targeting of precursor polypeptides, Sec61 channel opening and closing, and modification of precursor polypeptides in transit through the Sec61 complex. Recently, cryoelectron tomography of translocons in native ER membranes has given unprecedented insights into the architecture and dynamics of the native, ribosome-associated translocon and the Sec61 channel. These structural data are discussed in light of different Sec61 channel activities including ribosome receptor function, membrane insertion or translocation of newly synthesized polypeptides as well as the possible roles of the Sec61 channel as a passive ER calcium leak channel and regulator of ATP/ADP exchange between cytosol and ER.
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Affiliation(s)
- Sven Lang
- Competence Center for Molecular Medicine, Saarland University Medical School, Building 44, 66421, Homburg, Germany.
| | - Duy Nguyen
- Center for Bioinformatics, Saarland University, 66041, Saarbrücken, Germany
| | - Stefan Pfeffer
- Department of Molecular Structural Biology, Max-Planck Institute of Biochemistry, 82152, Martinsried, Germany
- ZMBH, 69120, Heidelberg, Germany
| | - Friedrich Förster
- Department of Molecular Structural Biology, Max-Planck Institute of Biochemistry, 82152, Martinsried, Germany
- Center for Biomolecular Research, Utrecht University, 3584 CH, Utrecht, The Netherlands
| | - Volkhard Helms
- Center for Bioinformatics, Saarland University, 66041, Saarbrücken, Germany
| | - Richard Zimmermann
- Competence Center for Molecular Medicine, Saarland University Medical School, Building 44, 66421, Homburg, Germany
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22
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AXER is an ATP/ADP exchanger in the membrane of the endoplasmic reticulum. Nat Commun 2018; 9:3489. [PMID: 30154480 PMCID: PMC6113206 DOI: 10.1038/s41467-018-06003-9] [Citation(s) in RCA: 48] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2017] [Accepted: 08/06/2018] [Indexed: 12/11/2022] Open
Abstract
To fulfill its role in protein biogenesis, the endoplasmic reticulum (ER) depends on the Hsp70-type molecular chaperone BiP, which requires a constant ATP supply. However, the carrier that catalyzes ATP uptake into the ER was unknown. Here, we report that our screen of gene expression datasets for member(s) of the family of solute carriers that are co-expressed with BiP and are ER membrane proteins identifies SLC35B1 as a potential candidate. Heterologous expression of SLC35B1 in E. coli reveals that SLC35B1 is highly specific for ATP and ADP and acts in antiport mode. Moreover, depletion of SLC35B1 from HeLa cells reduces ER ATP levels and, as a consequence, BiP activity. Thus, human SLC35B1 may provide ATP to the ER and was named AXER (ATP/ADP exchanger in the ER membrane). Furthermore, we propose an ER to cytosol low energy response regulatory axis (termed lowER) that appears as central for maintaining ER ATP supply.
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23
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Kim MJ, Min SH, Shin SY, Kim MN, Lee H, Jang JY, Kim SW, Park KS, Jung HS. Attenuation of PERK enhances glucose-stimulated insulin secretion in islets. J Endocrinol 2018; 236:125-136. [PMID: 29273589 DOI: 10.1530/joe-17-0497] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/30/2017] [Accepted: 12/22/2017] [Indexed: 01/18/2023]
Abstract
PERK is a pancreatic endoplasmic reticulum (ER) kinase. Its complete deletion in pancreatic β cells induces insulin deficiency; however, the effects of partial Perk suppression are unclear. We investigated the effect of partial PERK suppression using the specific PERK inhibitors GSK2606414 and GSK2656157. Low-dose GSK2606414 treatment for 24 h enhanced glucose-stimulated insulin secretion (GSIS), islet insulin content and calcium transit in mouse (at 40 nM) and human (at 50-100 nM) pancreatic islets. GSK2606414 also induced the expression of the ER chaperone BiP and the release of calcium from the ER. When Bip expression was inhibited using a Bip siRNA, the GSK2606414-induced augmentation of the ER calcium level, islet insulin contents, glucose-stimulated cytosolic calcium transit and GSIS were abrogated. In both wild-type and insulin-deficient Atg7-knockout mice, 8 weeks of GSK2656157 treatment enhanced GSIS and improved hyperglycemia without affecting body weight. In conclusion, partial PERK inhibition induced BiP expression in islets, increased glucose-stimulated calcium transit and islet insulin contents and enhanced GSIS, suggesting that low-dose PERK inhibitors could potentially be used to treat insulin deficiency.
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Affiliation(s)
- Min Joo Kim
- Department of Internal MedicineSeoul National University College of Medicine, Seoul, Republic of Korea
| | - Se Hee Min
- Department of Internal MedicineSeoul National University College of Medicine, Seoul, Republic of Korea
| | - Seon Young Shin
- Innovative Research Institute for Cell TherapySeoul, Republic of Korea
| | - Mi Na Kim
- Innovative Research Institute for Cell TherapySeoul, Republic of Korea
| | - Hakmo Lee
- Innovative Research Institute for Cell TherapySeoul, Republic of Korea
| | - Jin Young Jang
- Department of SurgerySeoul National University College of Medicine, Seoul, Republic of Korea
| | - Sun-Whe Kim
- Department of SurgerySeoul National University College of Medicine, Seoul, Republic of Korea
| | - Kyong Soo Park
- Department of Internal MedicineSeoul National University College of Medicine, Seoul, Republic of Korea
- Innovative Research Institute for Cell TherapySeoul, Republic of Korea
| | - Hye Seung Jung
- Department of Internal MedicineSeoul National University College of Medicine, Seoul, Republic of Korea
- Innovative Research Institute for Cell TherapySeoul, Republic of Korea
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Lang S, Pfeffer S, Lee PH, Cavalié A, Helms V, Förster F, Zimmermann R. An Update on Sec61 Channel Functions, Mechanisms, and Related Diseases. Front Physiol 2017; 8:887. [PMID: 29163222 PMCID: PMC5672155 DOI: 10.3389/fphys.2017.00887] [Citation(s) in RCA: 95] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2017] [Accepted: 10/19/2017] [Indexed: 12/18/2022] Open
Abstract
The membrane of the endoplasmic reticulum (ER) of nucleated human cells harbors the protein translocon, which facilitates membrane integration or translocation of almost every newly synthesized polypeptide targeted to organelles of the endo- and exocytotic pathway. The translocon comprises the polypeptide-conducting Sec61 channel and several additional proteins and complexes that are permanently or transiently associated with the heterotrimeric Sec61 complex. This ensemble of proteins facilitates ER targeting of precursor polypeptides, modification of precursor polypeptides in transit through the Sec61 complex, and Sec61 channel gating, i.e., dynamic regulation of the pore forming subunit to mediate precursor transport and calcium efflux. Recently, cryoelectron tomography of translocons in native ER membrane vesicles, derived from human cell lines or patient fibroblasts, and even intact cells has given unprecedented insights into the architecture and dynamics of the native translocon and the Sec61 channel. These structural data are discussed in light of different Sec61 channel activities including ribosome receptor function, membrane insertion, and translocation of newly synthesized polypeptides as well as the putative physiological roles of the Sec61 channel as a passive ER calcium leak channel. Furthermore, the structural insights into the Sec61 channel are incorporated into an overview and update on Sec61 channel-related diseases—the Sec61 channelopathies—and novel therapeutic concepts for their treatment.
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Affiliation(s)
- Sven Lang
- Competence Center for Molecular Medicine, Saarland University Medical School, Homburg, Germany
| | - Stefan Pfeffer
- Department of Molecular Structural Biology, Max-Planck Institute of Biochemistry, Martinsried, Germany
| | - Po-Hsien Lee
- Center for Bioinformatics, Saarland University, Saarbrücken, Germany
| | - Adolfo Cavalié
- Experimental and Clinical Pharmacology and Toxicology, Saarland University, Homburg, Germany
| | - Volkhard Helms
- Center for Bioinformatics, Saarland University, Saarbrücken, Germany
| | - Friedrich Förster
- Bijvoet Center for Biomolecular Research, Utrecht University, Utrecht, Netherlands
| | - Richard Zimmermann
- Competence Center for Molecular Medicine, Saarland University Medical School, Homburg, Germany
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Disruption of Protein Processing in the Endoplasmic Reticulum of DYT1 Knock-in Mice Implicates Novel Pathways in Dystonia Pathogenesis. J Neurosci 2017; 36:10245-10256. [PMID: 27707963 DOI: 10.1523/jneurosci.0669-16.2016] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2016] [Accepted: 07/13/2016] [Indexed: 11/21/2022] Open
Abstract
Dystonia type 1 (DYT1) is a dominantly inherited neurological disease caused by mutations in TOR1A, the gene encoding the endoplasmic reticulum (ER)-resident protein torsinA. Previous work mostly completed in cell-based systems suggests that mutant torsinA alters protein processing in the secretory pathway. We hypothesized that inducing ER stress in the mammalian brain in vivo would trigger or exacerbate mutant torsinA-induced dysfunction. To test this hypothesis, we crossed DYT1 knock-in with p58(IPK)-null mice. The ER co-chaperone p58(IPK) interacts with BiP and assists in protein maturation by helping to fold ER cargo. Its deletion increases the cellular sensitivity to ER stress. We found a lower generation of DYT1 knock-in/p58 knock-out mice than expected from this cross, suggesting a developmental interaction that influences viability. However, surviving animals did not exhibit abnormal motor function. Analysis of brain tissue uncovered dysregulation of eiF2α and Akt/mTOR translational control pathways in the DYT1 brain, a finding confirmed in a second rodent model and in human brain. Finally, an unbiased proteomic analysis identified relevant changes in the neuronal protein landscape suggesting abnormal ER protein metabolism and calcium dysregulation. Functional studies confirmed the interaction between the DYT1 genotype and neuronal calcium dynamics. Overall, these findings advance our knowledge on dystonia, linking translational control pathways and calcium physiology to dystonia pathogenesis and identifying potential new pharmacological targets. SIGNIFICANCE STATEMENT Dystonia type 1 (DYT1) is one of the different forms of inherited dystonia, a neurological disorder characterized by involuntary, disabling movements. DYT1 is caused by mutations in the gene that encodes the endoplasmic reticulum (ER)-resident protein torsinA. How mutant torsinA causes neuronal dysfunction remains unknown. Here, we show the behavioral and molecular consequences of stressing the ER in DYT1 mice by increasing the amount of misfolded proteins. This resulted in the generation of a reduced number of animals, evidence of abnormal ER protein processing and dysregulation of translational control pathways. The work described here proposes a shared mechanism for different forms of dystonia, links for the first time known biological pathways to dystonia pathogenesis, and uncovers potential pharmacological targets for its treatment.
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26
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Chen KC, Qu S, Chowdhury S, Noxon IC, Schonhoft JD, Plate L, Powers ET, Kelly JW, Lander GC, Wiseman RL. The endoplasmic reticulum HSP40 co-chaperone ERdj3/DNAJB11 assembles and functions as a tetramer. EMBO J 2017; 36:2296-2309. [PMID: 28655754 DOI: 10.15252/embj.201695616] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2016] [Revised: 05/15/2017] [Accepted: 05/22/2017] [Indexed: 11/09/2022] Open
Abstract
ERdj3/DNAJB11 is an endoplasmic reticulum (ER)-targeted HSP40 co-chaperone that performs multifaceted functions involved in coordinating ER and extracellular proteostasis. Here, we show that ERdj3 assembles into a native tetramer that is distinct from the dimeric structure observed for other HSP40 co-chaperones. An electron microscopy structural model of full-length ERdj3 shows that these tetramers are arranged as a dimer of dimers formed by distinct inter-subunit interactions involving ERdj3 domain II and domain III Targeted deletion of residues 175-190 within domain II renders ERdj3 a stable dimer that is folded and efficiently secreted from mammalian cells. This dimeric ERdj3 shows impaired substrate binding both in the ER and extracellular environments and reduced interactions with the ER HSP70 chaperone BiP. Furthermore, we show that overexpression of dimeric ERdj3 exacerbates ER stress-dependent reductions in the secretion of a destabilized, aggregation-prone protein and increases its accumulation as soluble oligomers in extracellular environments. These results reveal ERdj3 tetramerization as an important structural framework for ERdj3 functions involved in coordinating ER and extracellular proteostasis in the presence and absence of ER stress.
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Affiliation(s)
- Kai-Chun Chen
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA, USA
| | - Song Qu
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA, USA
| | - Saikat Chowdhury
- Department of Integrative, Structural, and Computational Biology, The Scripps Research Institute, La Jolla, CA, USA
| | - Isabelle C Noxon
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA, USA
| | - Joseph D Schonhoft
- Department of Chemistry, The Scripps Research Institute, La Jolla, CA, USA
| | - Lars Plate
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA, USA.,Department of Chemistry, The Scripps Research Institute, La Jolla, CA, USA
| | - Evan T Powers
- Department of Chemistry, The Scripps Research Institute, La Jolla, CA, USA
| | - Jeffery W Kelly
- Department of Chemistry, The Scripps Research Institute, La Jolla, CA, USA.,Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, CA, USA
| | - Gabriel C Lander
- Department of Integrative, Structural, and Computational Biology, The Scripps Research Institute, La Jolla, CA, USA
| | - R Luke Wiseman
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA, USA
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27
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Gutiérrez T, Simmen T. Endoplasmic reticulum chaperones tweak the mitochondrial calcium rheostat to control metabolism and cell death. Cell Calcium 2017; 70:64-75. [PMID: 28619231 DOI: 10.1016/j.ceca.2017.05.015] [Citation(s) in RCA: 73] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2017] [Revised: 05/24/2017] [Accepted: 05/24/2017] [Indexed: 12/16/2022]
Abstract
The folding of secretory proteins is a well-understood mechanism, based on decades of research on endoplasmic reticulum (ER) chaperones. These chaperones interact with newly imported polypeptides close to the ER translocon. Classic examples for these proteins include the immunoglobulin binding protein (BiP/GRP78), and the lectins calnexin and calreticulin. Although not considered chaperones per se, the ER oxidoreductases of the protein disulfide isomerase (PDI) family complete the folding job by catalyzing the formation of disulfide bonds through cysteine oxidation. Research from the past decade has demonstrated that ER chaperones are multifunctional proteins. The regulation of ER-mitochondria Ca2+ crosstalk is one of their additional functions, as shown for calnexin, BiP/GRP78 or the oxidoreductases Ero1α and TMX1. This function depends on interactions of this group of proteins with the ER Ca2+ handling machinery. This novel function makes perfect sense for two reasons: i. It allows ER chaperones to control mitochondrial apoptosis instantly without a lengthy bypass involving the upregulation of pro-apoptotic transcription factors via the unfolded protein response (UPR); and ii. It allows the ER protein folding machinery to fine-tune ATP import via controlling the speed of mitochondrial oxidative phosphorylation. Therefore, the role of ER chaperones in regulating ER-mitochondria Ca2+ flux identifies the progression of secretory protein folding as a central regulator of cell survival and death, at least in cell types that secrete large amount of proteins. In other cell types, ER protein folding might serve as a sentinel mechanism that monitors cellular well-being to control cell metabolism and apoptosis. The selenoprotein SEPN1 is a classic example for such a role. Through the control of ER-mitochondria Ca2+-flux, ER chaperones and folding assistants guide cellular apoptosis and mitochondrial metabolism.
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Affiliation(s)
- Tomas Gutiérrez
- Faculty of Medicine and Dentistry, Department of Cell Biology, University of Alberta, Edmonton, T6G2H7, Canada
| | - Thomas Simmen
- Faculty of Medicine and Dentistry, Department of Cell Biology, University of Alberta, Edmonton, T6G2H7, Canada,.
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28
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Zimmermann R. Components and Mechanisms of Import, Modification, Folding, and Assembly of Immunoglobulins in the Endoplasmic Reticulum. J Clin Immunol 2016; 36 Suppl 1:5-11. [PMID: 26923573 DOI: 10.1007/s10875-016-0250-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2016] [Accepted: 02/19/2016] [Indexed: 11/27/2022]
Abstract
In mammalian cells, the endoplasmic reticulum (ER) plays a central role in biogenesis of secretory- and plasma membrane proteins as well as in cellular calcium (Ca(2+)) homeostasis. The protein biogenesis function involves an aqueous polypeptide conducting channel in the ER membrane, which is formed by the heterotrimeric Sec61 complex; the store- and receptor-controlled Ca(2+)- release function requires a steep ER to cytosol gradient, with more than 500 μM free Ca(2+) in the ER and 50 nM Ca(2+) in the cytosol. Recent work demonstrated that the Sec61 complex can transiently allow passive ER Ca(2+) efflux. Therefore, gating of the Sec61 channel has to be tightly regulated by substrates as well as allosteric effectors. The ER lumenal Hsp70-type molecular chaperone, immunoglobulin heavy-chain binding protein (BiP), together with its membrane resident co-chaperone Sec63 facilitates channel opening in a precursor specific manner. In addition, BiP, together with its lumenal co-chaperones, ERj3 and ERj6, as well as cytosolic Ca(2+)-calmodulin (CaM) in collaboration with the membrane resident Sec62 protein represent allosteric effectors for channel closure. In the course of the last couple of years several human diseases were linked to the Sec61 complex and its effectors and were termed Sec61-channelopathies.
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Affiliation(s)
- Richard Zimmermann
- Competence Center for Molecular Medicine, Saarland University Medical School, Building 44, D-66421, Homburg, Germany.
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