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Quistgaard EM. BAP31: Physiological functions and roles in disease. Biochimie 2021; 186:105-129. [PMID: 33930507 DOI: 10.1016/j.biochi.2021.04.008] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2021] [Revised: 04/20/2021] [Accepted: 04/21/2021] [Indexed: 12/22/2022]
Abstract
B-cell receptor-associated protein 31 (BAP31 or BCAP31) is a ubiquitously expressed transmembrane protein found mainly in the endoplasmic reticulum (ER), including in mitochondria-associated membranes (MAMs). It acts as a broad-specificity membrane protein chaperone and quality control factor, which can promote different fates for its clients, including ER retention, ER export, ER-associated degradation (ERAD), or evasion of degradation, and it also acts as a MAM tetherer and regulatory protein. It is involved in several cellular processes - it supports ER and mitochondrial homeostasis, promotes proliferation and migration, plays several roles in metabolism and the immune system, and regulates autophagy and apoptosis. Full-length BAP31 can be anti-apoptotic, but can also mediate activation of caspase-8, and itself be cleaved by caspase-8 into p20-BAP31, which promotes apoptosis by mobilizing ER calcium stores at MAMs. BAP31 loss-of-function mutations is the cause of 'deafness, dystonia, and central hypomyelination' (DDCH) syndrome, characterized by severe neurological symptoms and early death. BAP31 is furthermore implicated in a growing number of cancers and other diseases, and several viruses have been found to target it to promote their survival or life cycle progression. The purpose of this review is to provide an overview and examination of the basic properties, functions, mechanisms, and roles in disease of BAP31.
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Affiliation(s)
- Esben M Quistgaard
- Department of Molecular Biology and Genetics - DANDRITE, Aarhus University, Gustav Wieds Vej 10, DK-8000 Aarhus C, Denmark.
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2
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MCP-1/MCPIP-1 Signaling Modulates the Effects of IL-1β in Renal Cell Carcinoma through ER Stress-Mediated Apoptosis. Int J Mol Sci 2019; 20:ijms20236101. [PMID: 31816951 PMCID: PMC6928829 DOI: 10.3390/ijms20236101] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2019] [Revised: 11/21/2019] [Accepted: 11/29/2019] [Indexed: 01/07/2023] Open
Abstract
In renal cell carcinoma (RCC), interleukin (IL)-1β may be a pro-metastatic cytokine. However, we have not yet noted the clinical association between tumoral expression or serum level of IL-1β and RCC in our patient cohort. Herein, we investigate molecular mechanisms elicited by IL-1β in RCC. We found that IL-1β stimulates substantial monocyte chemoattractant protein (MCP)-1 production in RCC cells by activating NF-kB and AP-1. In our xenograft RCC model, intra-tumoral MCP-1 injection down-regulated Ki67 expression and reduced tumor size. Microarray analysis revealed that MCP-1 treatment altered protein-folding processes in RCC cells. MCP-1-treated RCC cells and xenograft tumors expressed MCP-1-induced protein (MCPIP) and molecules involved in endoplasmic reticulum (ER) stress-mediated apoptosis, namely C/EBP Homologous Protein (CHOP), protein kinase-like ER kinase (PERK), and calnexin (CNX). ER stress-mediated apoptosis in MCP-1-treated RCC cells was confirmed using Terminal deoxynucleotidyl transferase dUTP Nick-End Labeling (TUNEL) assay. Moreover, ectopic MCPIP expression increased PERK expression in Human embryonic kidney (HEK)293 cells. Our meta-analysis revealed that low MCP-1 levels reduce 1-year post-nephrectomy survival in patients with RCC. Immunohistochemistry indicated that in some RCC biopsy samples, the correlation between MCP-1 or MCPIP expression and tumor stages was inverse. Thus, MCP-1 and MCPIP potentially reduce the IL-1β-mediated oncogenic effect in RCC; our findings suggest that ER stress is a potential RCC treatment target.
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Mechanistic Connections between Endoplasmic Reticulum (ER) Redox Control and Mitochondrial Metabolism. Cells 2019; 8:cells8091071. [PMID: 31547228 PMCID: PMC6769559 DOI: 10.3390/cells8091071] [Citation(s) in RCA: 85] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2019] [Revised: 09/06/2019] [Accepted: 09/07/2019] [Indexed: 12/21/2022] Open
Abstract
The past decade has seen the emergence of endoplasmic reticulum (ER) chaperones as key determinants of contact formation between mitochondria and the ER on the mitochondria-associated membrane (MAM). Despite the known roles of ER–mitochondria tethering factors like PACS-2 and mitofusin-2, it is not yet entirely clear how they mechanistically interact with the ER environment to determine mitochondrial metabolism. In this article, we review the mechanisms used to communicate ER redox and folding conditions to the mitochondria, presumably with the goal of controlling mitochondrial metabolism at the Krebs cycle and at the electron transport chain, leading to oxidative phosphorylation (OXPHOS). To achieve this goal, redox nanodomains in the ER and the interorganellar cleft influence the activities of ER chaperones and Ca2+-handling proteins to signal to mitochondria. This mechanism, based on ER chaperones like calnexin and ER oxidoreductases like Ero1α, controls reactive oxygen production within the ER, which can chemically modify the proteins controlling ER–mitochondria tethering, or mitochondrial membrane dynamics. It can also lead to the expression of apoptotic or metabolic transcription factors. The link between mitochondrial metabolism and ER homeostasis is evident from the specific functions of mitochondria–ER contact site (MERC)-localized Ire1 and PERK. These functions allow these two transmembrane proteins to act as mitochondria-preserving guardians, a function that is apparently unrelated to their functions in the unfolded protein response (UPR). In scenarios where ER stress cannot be resolved via the activation of mitochondrial OXPHOS, MAM-localized autophagosome formation acts to remove defective portions of the ER. ER chaperones such as calnexin are again critical regulators of this MERC readout.
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Robin MJD, Appelman MD, Vos HR, van Es RM, Paton JC, Paton AW, Burgering B, Fickert P, Heijmans J, van de Graaf SFJ. Calnexin Depletion by Endoplasmic Reticulum Stress During Cholestasis Inhibits the Na +-Taurocholate Cotransporting Polypeptide. Hepatol Commun 2018; 2:1550-1566. [PMID: 30556041 PMCID: PMC6287483 DOI: 10.1002/hep4.1262] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/17/2018] [Accepted: 09/03/2018] [Indexed: 12/18/2022] Open
Abstract
Cholestasis‐induced accumulation of bile acids in the liver leads to farnesoid X receptor (FXR)‐mediated transcriptional down‐regulation of the bile acid importer Na+‐taurocholate cotransporting protein (NTCP) and to induction of endoplasmic reticulum (ER) stress. However, whether ER stress affects bile acid uptake is largely unknown. Here, we investigated the role of ER stress on the regulation and function of the bile acid transporter NTCP. ER stress was induced using thapsigargin or subtilase cytotoxin in human osteosarcoma (U2OS) and human hepatocellular carcinoma (HepG2) cells stably expressing NTCP. Cellular bile acid uptake was determined using radiolabeled taurocholate (TCA). NTCP plasma membrane expression was determined by cell surface biotinylation. Mice received a single injection of thapsigargin, and effects of ER stress on NTCP messenger RNA (mRNA) and protein were measured by reverse‐transcription polymerase chain reaction (RT‐PCR) and western blot analysis. Effects of cholestasis on NTCP and ER stress were assessed in response to 3, 5‐diethoxycarbonyl‐1, 4‐dihydrocollidine (DDC) feeding or bile duct ligation in FXR–/– mice after 7 or 3 days, respectively. Novel NTCP‐interacting proteins were identified by mass spectrometry (MS), interaction verified, and assessed by co‐immunoprecipitation and TCA uptake for functional relevance in relation to ER stress. ER stress induction strongly reduced NTCP protein expression, plasma membrane abundance, and NTCP‐mediated bile acid uptake. This was not controlled by FXR or through a single unfolded protein response (UPR) pathway but mainly depended on the interaction of NTCP with calnexin, an ER chaperone. In mice, expression of both NTCP and calnexin was reduced by thapsigargin or cholestasis‐induced ER stress. Calnexin down‐regulation in vitro recapitulated the effect of ER stress on NTCP. Conclusion: ER stress‐induced down‐regulation of calnexin provides an additional mechanism to dampen NTCP‐mediated bile acid uptake and protect hepatocytes against bile acid overload during cholestasis.
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Affiliation(s)
- Marion J D Robin
- Amsterdam UMC University of Amsterdam, Tytgat Institute for Liver and Intestinal Research, Amsterdam Gastroenterology and Metabolism Amsterdam the Netherlands
| | - Monique D Appelman
- Amsterdam UMC University of Amsterdam, Tytgat Institute for Liver and Intestinal Research, Amsterdam Gastroenterology and Metabolism Amsterdam the Netherlands
| | - Harmjan R Vos
- Center for Molecular Medicine, Molecular Cancer Research Section University Medical Center Utrecht the Netherlands
| | - Robert M van Es
- Center for Molecular Medicine, Molecular Cancer Research Section University Medical Center Utrecht the Netherlands
| | - James C Paton
- Research Centre for Infectious Diseases, Department of Molecular and Cellular Biology University of Adelaide Adelaide Australia
| | - Adrienne W Paton
- Research Centre for Infectious Diseases, Department of Molecular and Cellular Biology University of Adelaide Adelaide Australia
| | - Boudewijn Burgering
- Center for Molecular Medicine, Molecular Cancer Research Section University Medical Center Utrecht the Netherlands
| | - Peter Fickert
- Division of Gastroenterology and Hepatology, Department of Internal Medicine Medical University of Graz Graz Austria
| | - Jarom Heijmans
- Amsterdam UMC, University of Amsterdam Department of Gastroenterology and Hepatology, Amsterdam Gastroenterology and Metabolism Amsterdam the Netherlands
| | - Stan F J van de Graaf
- Amsterdam UMC University of Amsterdam, Tytgat Institute for Liver and Intestinal Research, Amsterdam Gastroenterology and Metabolism Amsterdam the Netherlands.,Amsterdam UMC, University of Amsterdam Department of Gastroenterology and Hepatology, Amsterdam Gastroenterology and Metabolism Amsterdam the Netherlands
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5
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Induction of ER and mitochondrial stress by the alkylphosphocholine erufosine in oral squamous cell carcinoma cells. Cell Death Dis 2018; 9:296. [PMID: 29463797 PMCID: PMC5833417 DOI: 10.1038/s41419-018-0342-2] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2017] [Revised: 01/04/2018] [Accepted: 01/24/2018] [Indexed: 12/11/2022]
Abstract
Endoplasmic reticulum (ER) plays an essential role in cell function and survival. Accumulation of unfolded or misfolded proteins in the lumen of the ER activates the unfolded protein response (UPR), resulting in ER stress and subsequent apoptosis. The alkylphosphocholine erufosine is a known Akt-mTOR inhibitor in oral squamous cell carcinoma (OSCC). In the present study, we evaluate erufosine’s role to induce ER and mitochondrial stress leading to autophagy, apoptosis, and ROS induction. The cellular toxicity of erufosine was determined in two OSCC cell lines and gene expression and enrichment analyses were performed. A positive enrichment of ER stress upon erufosine exposure was observed, which was verified at protein levels for the ER stress sensors and their downstream mediators. Knockdown and pharmacological inhibition of the ER stress sensors PERK and XBP1 revealed their involvement into erufosine’s cellular effects, including proliferation, apoptosis, and autophagy induction. Autophagy was confirmed by increased acidic vacuoles and LC3-B levels. Upon erufosine exposure, calcium influx into the cytoplasm of the two OSCC cell lines was seen. Apoptosis was confirmed by nuclear staining, Annexin-V, and immunoblotting of caspases. The induction of mitochondrial stress upon erufosine exposure was predicted by gene set enrichment analysis (GSEA) and shown by erufosine’s effect on mitochondrial membrane potential, ATP, and ROS production in OSCC cells. These data show that ER and mitochondrial targeting by erufosine represents a new facet of its mechanism of action as well as a promising new framework in the treatment of head and neck cancers.
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Vera CA, Oróstica L, Gabler F, Ferreira A, Selman A, Vega M, Romero CA. The nerve growth factor alters calreticulin translocation from the endoplasmic reticulum to the cell surface and its signaling pathway in epithelial ovarian cancer cells. Int J Oncol 2017; 50:1261-1270. [PMID: 28260038 DOI: 10.3892/ijo.2017.3892] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2016] [Accepted: 02/20/2017] [Indexed: 11/06/2022] Open
Abstract
Ovarian cancer is the seventh most common cancer among women worldwide, causing approximately 120,000 deaths every year. Immunotherapy, designed to boost the body's natural defenses against cancer, appears to be a promising option against ovarian cancer. Calreticulin (CRT) is an endoplasmic reticulum (ER) resident chaperone that, translocated to the cell membrane after ER stress, allows cancer cells to be recognized by the immune system. The nerve growth factor (NGF) is a pro-angiogenic molecule overexpressed in this cancer. In the present study, we aimed to determine weather NGF has an effect in CRT translocation induced by cytotoxic and ER stress. We treated A2780 ovarian cancer cells with NGF, thapsigargin (Tg), an ER stress inducer and mitoxantrone (Mtx), a chemotherapeutic drug; CRT subcellular localization was analyzed by immunofluorescence followed by confocal microscopy. In order to determine NGF effect on Mtx and Tg-induced CRT translocation from the ER to the cell membrane, cells were preincubated with NGF prior to Mtx or Tg treatment and CRT translocation to the cell surface was determined by flow cytometry. In addition, by western blot analyses, we evaluated proteins associated with the CRT translocation pathway, both in A2780 cells and human ovarian samples. We also measured NGF effect on cell apoptosis induced by Mtx. Our results indicate that Mtx and Tg, but not NGF, induce CRT translocation to the cell membrane. NGF, however, inhibited CRT translocation induced by Mtx, while it had no effect on Tg-induced CRT exposure. NGF also diminished cell death induced by Mtx. NGF effect on CRT translocation could have consequences in immunotherapy, potentially lessening the effectiveness of this type of treatment.
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Affiliation(s)
- Carolina Andrea Vera
- Laboratory of Endocrinology and Reproduction Biology, Clinical Hospital, University of Chile, Santiago, Chile
| | - Lorena Oróstica
- Laboratory of Endocrinology and Reproduction Biology, Clinical Hospital, University of Chile, Santiago, Chile
| | - Fernando Gabler
- Department of Pathology, School of Medicine, San Borja Arriarán Clinical Hospital, University of Chile, Santiago, Chile
| | - Arturo Ferreira
- Program of Immunology, Institute of Biomedical Sciences (ICBM), Faculty of Medicine, University of Chile, Santiago, Chile
| | - Alberto Selman
- Department of Obstetrics and Gynecology, School of Medicine, Clinical Hospital, University of Chile, Santiago, Chile
| | - Margarita Vega
- Laboratory of Endocrinology and Reproduction Biology, Clinical Hospital, University of Chile, Santiago, Chile
| | - Carmen Aurora Romero
- Laboratory of Endocrinology and Reproduction Biology, Clinical Hospital, University of Chile, Santiago, Chile
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Dudek E, Millott R, Liu WX, Beauchamp E, Berthiaume LG, Michalak M. N-Myristoyltransferase 1 interacts with calnexin at the endoplasmic reticulum. Biochem Biophys Res Commun 2015; 468:889-93. [PMID: 26603938 DOI: 10.1016/j.bbrc.2015.11.052] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2015] [Accepted: 11/11/2015] [Indexed: 11/28/2022]
Abstract
Calnexin is a type 1 integral endoplasmic reticulum (ER) membrane molecular chaperone with a highly conserved C-terminal domain oriented to the cytoplasm. Protein N-myristoylation plays an important role in a wide variety of cellular signal transduction pathways and it is catalyzed by N-myristoyltransferase (NMT), a cytoplasmic and ER associated enzyme. Here using yeast two-hybrid screen, Western blot analysis, immunoprecipitation, immunolocalization and cellular fractionation we discovered that N-myristoyltransferase 1 interacts with calnexin at the ER. These observations point at a previously unrecognized contribution of calnexin to the retention of NMT1 at the ER membrane.
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Affiliation(s)
- Elzbieta Dudek
- Departments of Biochemistry, University of Alberta, Edmonton, Alberta, T6G 2H7, Canada
| | - Robyn Millott
- Departments of Biochemistry, University of Alberta, Edmonton, Alberta, T6G 2H7, Canada
| | - Wen-Xin Liu
- Departments of Biochemistry, University of Alberta, Edmonton, Alberta, T6G 2H7, Canada
| | - Erwan Beauchamp
- Departments of Cell Biology, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Alberta, T6G 2H7, Canada
| | - Luc G Berthiaume
- Departments of Cell Biology, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Alberta, T6G 2H7, Canada
| | - Marek Michalak
- Departments of Biochemistry, University of Alberta, Edmonton, Alberta, T6G 2H7, Canada.
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Sabe AA, Sadek AA, Elmadhun NY, Dalal RS, Robich MP, Bianchi C, Sellke FW. Investigating the effects of resveratrol on chronically ischemic myocardium in a swine model of metabolic syndrome: a proteomics analysis. J Med Food 2015; 18:60-6. [PMID: 25089828 DOI: 10.1089/jmf.2014.0036] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Resveratrol has been shown to improve cardiac perfusion and ventricular function after chronic ischemic injury. Using proteomic analysis, we sought to objectively investigate potential mechanisms, by which resveratrol exerts its cardioprotective effects in the setting of metabolic syndrome and chronic myocardial ischemia. Yorkshire swine were divided into two groups based on diet: high cholesterol (n=7) or a high-cholesterol diet with supplemental resveratrol (n=6). Four weeks later, all animals underwent surgical placement of an ameroid constrictor to their left circumflex artery. Diets were continued for another 7 weeks, and then the ischemic myocardium was harvested for proteomics analysis. Proteomic analysis identified 669 common proteins between the two groups. Of these proteins, 76 were statistically different, of which 41 were characterized (P<.05). Pathway analysis demonstrated that in animals supplemented with resveratrol, there was a downregulation in several proteins involved with mitochondrial dysfunction, cell death, and unfavorable cardiac remodeling. Furthermore, there was an upregulation in proteins involved in free radical elimination. We conclude that resveratrol supplementation significantly alters several critical protein markers in the chronically ischemic myocardium. Further investigation of these proteins may help elucidate the mechanisms by which resveratrol exerts its cardioprotective effects.
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Affiliation(s)
- Ashraf A Sabe
- Division of Cardiothoracic Surgery, Cardiovascular Research Center, Warren Alpert School of Medicine, Brown University , Providence, Rhode Island, USA
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Benyair R, Ogen-Shtern N, Lederkremer GZ. Glycan regulation of ER-associated degradation through compartmentalization. Semin Cell Dev Biol 2015; 41:99-109. [DOI: 10.1016/j.semcdb.2014.11.006] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2014] [Revised: 11/13/2014] [Accepted: 11/14/2014] [Indexed: 12/20/2022]
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Coker-Gürkan A, Arisan ED, Obakan P, Akalın K, Özbey U, Palavan-Unsal N. Purvalanol induces endoplasmic reticulum stress-mediated apoptosis and autophagy in a time-dependent manner in HCT116 colon cancer cells. Oncol Rep 2015; 33:2761-70. [PMID: 25901510 DOI: 10.3892/or.2015.3918] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2014] [Accepted: 12/18/2014] [Indexed: 11/06/2022] Open
Abstract
Purvalanol, a novel cyclin-dependent kinase inhibitor, is referred to as a strong apoptotic inducer which causes cell cycle arrest in various cancer cells such as prostate, breast and colon cancer cell lines. Various physiological and pathological conditions such as glucose starvation, inhibition of protein glycosylation and oxidative stress may cause an accumulation of unfolded proteins in the endoplasmic reticulum (ER), leading to the unfolded protein response (UPR) and autophagy. Lacking proteosomal function on aggregates of unfolded proteins, ER stress may induce autophagic machinery. Autophagy, an evolutionarily conserved process, is characterized by massive degradation of cytosolic contents. In the present study, our aim was to determine the time-dependent, ER-mediated apoptotic and autophagy induction of purvalanol in HCT 116 colon cancer cells. Fifteen micromoles of purvalanol induced a reduction in cell viability by 20 and 35% within 24 and 48 h, respectively. HCT 116 colon cancer cells were exposed to purvalanol, which activated ER stress via upregulation of PERK, IRE1α gene expression, eIF-2α phosphorylation and ATF-6 cleavage at early time-points in the HCT 116 colon cancer cells. Moreover, we determined that during purvalanol-mediated ER stress, autophagic machinery was also activated prior to apoptotic cell death finalization. Beclin-1 and Atg-5 expression levels were upregulated and LC3 was cleaved after a 6 h purvalanol treatment. Purvalanol induced mitochondrial membrane potential loss, caspase-7 and caspase-3 activation and PARP cleavage following a 48 h treatment. Thus, we conclude that the anticancer effect of purvalanol in HCT 116 cells was due to ER stress-mediated apoptosis; however, purvalanol triggered autophagy, which functions as a cell survival mechanism at early time-points.
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Affiliation(s)
- Ajda Coker-Gürkan
- Department of Molecular Biology and Genetics, Science and Letters Faculty, Istanbul Kultur University, Atakoy Campus, Bakirkoy-Istanbul 34156, Turkey
| | - Elif Damla Arisan
- Department of Molecular Biology and Genetics, Science and Letters Faculty, Istanbul Kultur University, Atakoy Campus, Bakirkoy-Istanbul 34156, Turkey
| | - Pınar Obakan
- Department of Molecular Biology and Genetics, Science and Letters Faculty, Istanbul Kultur University, Atakoy Campus, Bakirkoy-Istanbul 34156, Turkey
| | - Kübra Akalın
- Department of Molecular Biology and Genetics, Science and Letters Faculty, Istanbul Kultur University, Atakoy Campus, Bakirkoy-Istanbul 34156, Turkey
| | - Utku Özbey
- Department of Molecular Biology and Genetics, Science and Letters Faculty, Istanbul Kultur University, Atakoy Campus, Bakirkoy-Istanbul 34156, Turkey
| | - Narcin Palavan-Unsal
- Department of Molecular Biology and Genetics, Science and Letters Faculty, Istanbul Kultur University, Atakoy Campus, Bakirkoy-Istanbul 34156, Turkey
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Núñez A, Dulude D, Jbel M, Rokeach LA. Calnexin is essential for survival under nitrogen starvation and stationary phase in Schizosaccharomyces pombe. PLoS One 2015; 10:e0121059. [PMID: 25803873 PMCID: PMC4372366 DOI: 10.1371/journal.pone.0121059] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2014] [Accepted: 02/06/2015] [Indexed: 12/04/2022] Open
Abstract
Cell fate is determined by the balance of conserved molecular mechanisms regulating death (apoptosis) and survival (autophagy). Autophagy is a process by which cells recycle their organelles and macromolecules through degradation within the vacuole in yeast and plants, and lysosome in metazoa. In the yeast Schizosaccharomyces pombe, autophagy is strongly induced under nitrogen starvation and in aging cells. Previously, we demonstrated that calnexin (Cnx1p), a highly conserved transmembrane chaperone of the endoplasmic reticulum (ER), regulates apoptosis under ER stress or inositol starvation. Moreover, we showed that in stationary phase, Cnx1p is cleaved into two moieties, L_Cnx1p and S_Cnx1p. Here, we show that the processing of Cnx1p is regulated by autophagy, induced by nitrogen starvation or cell aging. The cleavage of Cnx1p involves two vacuolar proteases: Isp6, which is essential for autophagy, and its paralogue Psp3. Blocking autophagy through the knockout of autophagy-related genes (atg) results in inhibition of both, the cleavage and the trafficking of Cnx1p from the ER to the vacuole. We demonstrate that Cnx1p is required for cell survival under nitrogen-starvation and in chronological aging cultures. The death of the mini_cnx1 mutant (overlapping S_cnx1p) cells is accompanied by accumulation of high levels of reactive-oxygen species (ROS), a slowdown in endocytosis and severe cell-wall defects. Moreover, mutant cells expressing only S_Cnx1p showed cell wall defects. Co-expressing mutant overlapping the L_Cnx1p and S_Cnx1p cleavage products reverses the death, ROS phenotype and cell wall defect to wild-type levels. As it is involved in both apoptosis and autophagy, Cnx1p could be a nexus for the crosstalk between these pro-death and pro-survival mechanisms. Ours, and observations in mammalian systems, suggest that the multiple roles of calnexin depend on its sub-cellular localization and on its cleavage. The use of S. pombe should assist in further shedding light on the multiple roles of calnexin.
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Affiliation(s)
- Andrés Núñez
- Department of Biochemistry and Molecular Medicine, Université de Montréal, Montréal, Québec, Canada
| | - Dominic Dulude
- Department of Biochemistry and Molecular Medicine, Université de Montréal, Montréal, Québec, Canada
| | - Mehdi Jbel
- Department of Biochemistry and Molecular Medicine, Université de Montréal, Montréal, Québec, Canada
| | - Luis A. Rokeach
- Department of Biochemistry and Molecular Medicine, Université de Montréal, Montréal, Québec, Canada
- * E-mail:
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Quantitative Proteomics and Lipidomics Analysis of Endoplasmic Reticulum of Macrophage Infected with Mycobacterium tuberculosis. INTERNATIONAL JOURNAL OF PROTEOMICS 2015; 2015:270438. [PMID: 25785198 PMCID: PMC4345262 DOI: 10.1155/2015/270438] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/26/2014] [Revised: 01/21/2015] [Accepted: 01/23/2015] [Indexed: 11/17/2022]
Abstract
Even though endoplasmic reticulum (ER) stress associated with mycobacterial infection has been well studied, the molecular basis of ER as a crucial organelle to determine the fate of Mtb is yet to be established. Here, we have studied the ability of Mtb to manipulate the ultrastructural architecture of macrophage ER and found that the ER-phenotypes associated with virulent (H37Rv) and avirulent (H37Ra) strains were different: a rough ER (RER) with the former against a smooth ER (SER) with the later. Further, the functional attributes of these changes were probed by MS-based quantitative proteomics (133 ER proteins) and lipidomics (8 phospholipids). Our omics approaches not only revealed the host pathogen cross-talk but also emphasized how precisely Mtb uses proteins and lipids in combination to give rise to characteristic ER-phenotypes. H37Ra-infected macrophages increased the cytosolic Ca2+ levels by attenuating the ATP2A2 protein and simultaneous induction of PC/PE expression to facilitate apoptosis. However, H37Rv inhibited apoptosis and further controlled the expression of EST-1 and AMRP proteins to disturb cholesterol homeostasis resulting in sustained infection. This approach offers the potential to decipher the specific roles of ER in understanding the cell biology of mycobacterial infection with special reference to the impact of host response.
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Jung J, Dudek E, Michalak M. The role of N-glycan in folding, trafficking and pathogenicity of myelin oligodendrocyte glycoprotein (MOG). BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2014; 1853:2115-21. [PMID: 25541284 DOI: 10.1016/j.bbamcr.2014.12.023] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2014] [Revised: 12/11/2014] [Accepted: 12/16/2014] [Indexed: 10/24/2022]
Abstract
Myelin oligodendrocyte glycoprotein (MOG) is a type I integral membrane protein that is expressed in the central nervous system. MOG has a single N-glycosylation site within its extracellular domain. MOG has been linked with pathogenesis of multiple sclerosis; anti-MOG antibodies have been detected in the sera of multiple sclerosis patients. N-glycosylation is an important post-translational modification of protein that might impact their folding, localization and function. However, the role of sugar in the biology of MOG is not well understood. In this study, we created a mutant MOG lacking N-linked glycan and tested its properties. We concluded that the lack of sugar did not impact on MOG abundance in the absence of endoplasmic reticulum molecular chaperone calnexin. We also show that the absence of N-glycan did not interfere with MOG's subcellular localization and it did not result in activation of endoplasmic reticulum stress. This article is part of a Special Issue entitled: 13th European Symposium on Calcium.
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Affiliation(s)
- Joanna Jung
- Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Elzbieta Dudek
- Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Marek Michalak
- Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada.
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Zhang Q, Wang XQ, Jiang HS, Jia WM, Zhao XF, Wang JX. Calnexin functions in antibacterial immunity of Marsupenaeus japonicus. DEVELOPMENTAL AND COMPARATIVE IMMUNOLOGY 2014; 46:356-363. [PMID: 24858031 DOI: 10.1016/j.dci.2014.05.009] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2014] [Revised: 05/04/2014] [Accepted: 05/04/2014] [Indexed: 06/03/2023]
Abstract
Calnexin (Cnx) is an endoplasmic reticulum membrane-bound lectin chaperone that comprises a dedicated maturation system with another lectin chaperone calreticulin (Crt). This maturation system is known as the Cnx/Crt cycle. The main functions of Cnx are Ca(2+) storage, glycoprotein folding, and quality control of synthesis. Recent studies have shown that Cnx is important in phagocytosis and in optimizing dendritic cell immunity. However, the functions of Cnx in invertebrate innate immunity remain unclear. In this research, we characterized Cnx in the kuruma shrimp Marsupenaeus japonicus (designated as MjCnx) and detected its function in shrimp immunity. The expression of MjCnx was upregulated in several tissues challenged with Vibrio anguillarum. Recombinant MjCnx could bind to bacteria by binding polysaccharides. MjCnx protein existed in the cytoplasm and on the membrane of hemocytes and was upregulated by bacterial challenge. The recombinant MjCnx enhanced the clearance of V. anguillarum in vivo, and the clearance effects were impaired after silencing MjCnx with RNA interference assay. Recombinant MjCnx promoted phagocytosis efficiency of hemocytes. These results suggest that MjCnx functions as one of the pattern recognition receptors and has crucial functions in shrimp antibacterial immunity.
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Affiliation(s)
- Qing Zhang
- MOE Key Laboratory of Plant Cell Engineering and Germplasm Innovation/Shandong Provincial Key Laboratory of Animal Cells and Developmental Biology, School of Life Sciences, Shandong University, Jinan, Shandong 250100, China
| | - Xiu-Qing Wang
- School of Clinical Laboratory of Medicine, Ningxia Medical University, Yinchuan, Ningxia 750004, China
| | - Hai-Shan Jiang
- MOE Key Laboratory of Plant Cell Engineering and Germplasm Innovation/Shandong Provincial Key Laboratory of Animal Cells and Developmental Biology, School of Life Sciences, Shandong University, Jinan, Shandong 250100, China
| | - Wen-Ming Jia
- MOE Key Laboratory of Plant Cell Engineering and Germplasm Innovation/Shandong Provincial Key Laboratory of Animal Cells and Developmental Biology, School of Life Sciences, Shandong University, Jinan, Shandong 250100, China
| | - Xiao-Fan Zhao
- MOE Key Laboratory of Plant Cell Engineering and Germplasm Innovation/Shandong Provincial Key Laboratory of Animal Cells and Developmental Biology, School of Life Sciences, Shandong University, Jinan, Shandong 250100, China
| | - Jin-Xing Wang
- MOE Key Laboratory of Plant Cell Engineering and Germplasm Innovation/Shandong Provincial Key Laboratory of Animal Cells and Developmental Biology, School of Life Sciences, Shandong University, Jinan, Shandong 250100, China.
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Sever L, Vo NT, Bols NC, Dixon B. Rainbow trout (Oncorhynchus mykiss) contain two calnexin genes which encode distinct proteins. DEVELOPMENTAL AND COMPARATIVE IMMUNOLOGY 2014; 42:211-9. [PMID: 24060503 PMCID: PMC7103213 DOI: 10.1016/j.dci.2013.09.005] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/15/2013] [Revised: 09/12/2013] [Accepted: 09/13/2013] [Indexed: 05/15/2023]
Abstract
Calnexin (IP90/P88) is an integral membrane protein of the endoplasmic reticulum that binds newly synthesized N-linked glycoproteins during their folding in the ER including MHC class I molecule. This manuscript reports the identification of two unique cDNA clones of calnexin in rainbow trout. Both encode putative mature proteins of 579 and 592 aa respectively in addition to a 24 aa signal peptide. Sequence analysis revealed that only one of the two cDNA clones encodes a putative ER retention signal, K/QEDDL, followed by a serine phosphorylation site conserved with mammalian homologs. Amino acid sequence alignment illustrated conservation of the calnexin luminal domain, which consists of a globular and a P domain, in both copies. Southern blotting revealed that there are at least two copies of the calnexin gene in the trout genome and northern blotting showed a wide tissue distribution of an estimated 3 kbp calnexin transcript with an additional minor transcript of 2.3 kbp expressed only in head kidney, spleen PBLs and strongly in RTS11. Importantly, the smaller transcript was predominantly upregulated in RTS11 after a 24h treatment with the calcium ionophore A23187. In western blots, calnexin was detected primarily as a 120 kDa protein and upon A23187 treatment; a 100 kDa band was most prominently expressed. These results suggest that in salmonids there are two differentiated versions of the calnexin gene which encode proteins that may have diverged to perform unique biological functions.
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Affiliation(s)
| | | | | | - Brian Dixon
- Corresponding author. Tel.: +1 (519)888 4567x32665.
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16
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Bousette N, Abbasi C, Chis R, Gramolini AO. Calnexin Silencing in Mouse Neonatal Cardiomyocytes Induces Ca2+Cycling Defects, ER Stress, and Apoptosis. J Cell Physiol 2013; 229:374-83. [DOI: 10.1002/jcp.24459] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2013] [Accepted: 08/21/2013] [Indexed: 01/20/2023]
Affiliation(s)
- Nicolas Bousette
- Department of Physiology; University of Toronto; Toronto Ontario Canada
- Heart and Stroke/Richard Lewar Centre of Excellence; University of Toronto; Toronto Ontario Canada
| | - Cynthia Abbasi
- Department of Physiology; University of Toronto; Toronto Ontario Canada
- Heart and Stroke/Richard Lewar Centre of Excellence; University of Toronto; Toronto Ontario Canada
| | - Roxana Chis
- Department of Physiology; University of Toronto; Toronto Ontario Canada
- Heart and Stroke/Richard Lewar Centre of Excellence; University of Toronto; Toronto Ontario Canada
| | - Anthony O. Gramolini
- Department of Physiology; University of Toronto; Toronto Ontario Canada
- Heart and Stroke/Richard Lewar Centre of Excellence; University of Toronto; Toronto Ontario Canada
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17
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Wakabayashi S, Yoshida H. The essential biology of the endoplasmic reticulum stress response for structural and computational biologists. Comput Struct Biotechnol J 2013; 6:e201303010. [PMID: 24688718 PMCID: PMC3962220 DOI: 10.5936/csbj.201303010] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2013] [Revised: 08/09/2013] [Accepted: 08/10/2013] [Indexed: 11/29/2022] Open
Abstract
The endoplasmic reticulum (ER) stress response is a cytoprotective mechanism that maintains homeostasis of the ER by upregulating the capacity of the ER in accordance with cellular demands. If the ER stress response cannot function correctly, because of reasons such as aging, genetic mutation or environmental stress, unfolded proteins accumulate in the ER and cause ER stress-induced apoptosis, resulting in the onset of folding diseases, including Alzheimer's disease and diabetes mellitus. Although the mechanism of the ER stress response has been analyzed extensively by biochemists, cell biologists and molecular biologists, many aspects remain to be elucidated. For example, it is unclear how sensor molecules detect ER stress, or how cells choose the two opposite cell fates (survival or apoptosis) during the ER stress response. To resolve these critical issues, structural and computational approaches will be indispensable, although the mechanism of the ER stress response is complicated and difficult to understand holistically at a glance. Here, we provide a concise introduction to the mammalian ER stress response for structural and computational biologists.
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Affiliation(s)
- Sadao Wakabayashi
- Department of Molecular Biochemistry, Graduate School of Life Science, University of Hyogo, Hyogo 678-1297, Japan
| | - Hiderou Yoshida
- Department of Molecular Biochemistry, Graduate School of Life Science, University of Hyogo, Hyogo 678-1297, Japan
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18
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Lakkaraju A, van der Goot F. Calnexin Controls the STAT3-Mediated Transcriptional Response to EGF. Mol Cell 2013; 51:386-96. [DOI: 10.1016/j.molcel.2013.07.009] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2013] [Revised: 06/10/2013] [Accepted: 06/26/2013] [Indexed: 01/05/2023]
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19
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Lynes EM, Raturi A, Shenkman M, Ortiz Sandoval C, Yap MC, Wu J, Janowicz A, Myhill N, Benson MD, Campbell RE, Berthiaume LG, Lederkremer GZ, Simmen T. Palmitoylation is the switch that assigns calnexin to quality control or ER Ca2+ signaling. J Cell Sci 2013; 126:3893-903. [PMID: 23843619 DOI: 10.1242/jcs.125856] [Citation(s) in RCA: 113] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
The palmitoylation of calnexin serves to enrich calnexin on the mitochondria-associated membrane (MAM). Given a lack of information on the significance of this finding, we have investigated how this endoplasmic reticulum (ER)-internal sorting signal affects the functions of calnexin. Our results demonstrate that palmitoylated calnexin interacts with sarcoendoplasmic reticulum (SR) Ca(2+) transport ATPase (SERCA) 2b and that this interaction determines ER Ca(2+) content and the regulation of ER-mitochondria Ca(2+) crosstalk. In contrast, non-palmitoylated calnexin interacts with the oxidoreductase ERp57 and performs its well-known function in quality control. Interestingly, our results also show that calnexin palmitoylation is an ER-stress-dependent mechanism. Following a short-term ER stress, calnexin quickly becomes less palmitoylated, which shifts its function from the regulation of Ca(2+) signaling towards chaperoning and quality control of known substrates. These changes also correlate with a preferential distribution of calnexin to the MAM under resting conditions, or the rough ER and ER quality control compartment (ERQC) following ER stress. Our results have therefore identified the switch that assigns calnexin either to Ca(2+) signaling or to protein chaperoning.
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Affiliation(s)
- Emily M Lynes
- Department of Cell Biology, University of Alberta, Edmonton, AB T6G 2H7, Canada
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20
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Cigna D, D'Anna C, Zizzo C, Francofonte D, Sorrentino I, Colomba P, Albeggiani G, Armini A, Bianchi L, Bini L, Duro G. Alteration of proteomic profiles in PBMC isolated from patients with Fabry disease: preliminary findings. MOLECULAR BIOSYSTEMS 2013; 9:1162-8. [PMID: 23385635 DOI: 10.1039/c3mb25402j] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Fabry disease (FD) is an X-linked progressive multisystem disease due to mutations in the gene encoding the lysosomal enzyme α-galactosidase A (α-GalA). The deficiency in α-GalA activity leads to an intra-lysosomal accumulation of neutral glycosphingolipids, mainly globotriaosylceramide (Gb3), in various organs and systems. Enzyme replacement therapy is available and alternative therapeutic approaches are being explored. No diagnostic test, other than sequencing of the α-galactosidase A gene, is available, no biomarker has been proven useful to screen for and predict the disease, and underlying mechanisms are still elusive. The aim of this study is to identify FD specific biomarkers and to better understand the pathophysiological changes that occur over time in FD. We compared peripheral blood mononuclear cells (PBMC) from FD patients (n = 8) with control PBMC from healthy individuals (n = 6), by two-dimensional electrophoresis (2DE) and the detected differentially expressed proteins were then subjected to matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS). In FD patients we identified, among the down-regulated proteins, Calnexin, Rho GDP-dissociation inhibitor 2, Rho GDP-dissociation inhibitor 1, Chloride intracellular channel protein 1; on the other hand γ-enolase, 14-3-3 protein theta, 14-3-3 protein zeta/delta, and galectin-1 were identified as up-regulated proteins. Calnexin and Rho GDP-dissociation inhibitor-1,2 are related to protein folding, signal transduction and cell proliferation. This is the first time that γ-enolase and galectin-1 are described to be up-regulated in Fabry patients. Levels of γ-enolase increase dramatically in cardiovascular accidents and cerebral trauma, whereas galectins are regulators of acute and chronic inflammation. These findings may improve our understanding of the molecular mechanisms underlying the pathology and provide new insight and knowledge for future studies in this field.
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Affiliation(s)
- Diego Cigna
- Laboratory of Proteomics, Institute of Biomedicine and Molecular Immunology (IBIM), CNR, Palermo, Italy
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21
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Bromfield EG, Nixon B. The function of chaperone proteins in the assemblage of protein complexes involved in gamete adhesion and fusion processes. Reproduction 2013; 145:R31-42. [PMID: 23166368 DOI: 10.1530/rep-12-0316] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The remarkable complexity of the molecular events governing adhesion and fusion of the male and female gametes is becoming apparent. Novel research suggests that these highly specific cellular interactions are facilitated by multiprotein complexes that are delivered to and/or assembled on the surface of the gametes by molecular chaperones in preparation for sperm-egg interaction. While the activation of these molecular chaperones and the mechanisms by which they shuttle proteins to the surface of the cell remain the subject of ongoing investigation, a compelling suggestion is that these processes are augmented by dynamic membrane microdomains or lipid rafts that migrate to the apical region of the sperm head after capacitation. Preliminary studies of the oocyte plasma membrane have also revealed the presence of lipid rafts comprising several molecular chaperones, raising the possibility that similar mechanisms may be involved in the activation of maternal fusion machinery and the regulation of oocyte plasma membrane integrity. Despite these findings, the analysis of oocyte surface multiprotein complexes is currently lacking. Further analyses of the intermediary proteins that facilitate the expression of key players in sperm-egg fusion are likely to deliver important insights into this unique event, which culminates in the cytoplasmic continuity of the male and female gametes.
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Affiliation(s)
- Elizabeth G Bromfield
- Priority Research Centre in Reproductive Science, School of Environmental and Life Sciences, Discipline of Biological Sciences, The University of Newcastle, Callaghan, New South Wales 2308, Australia
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22
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Raturi A, Simmen T. Where the endoplasmic reticulum and the mitochondrion tie the knot: the mitochondria-associated membrane (MAM). BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2012; 1833:213-24. [PMID: 22575682 DOI: 10.1016/j.bbamcr.2012.04.013] [Citation(s) in RCA: 343] [Impact Index Per Article: 28.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2012] [Revised: 04/12/2012] [Accepted: 04/25/2012] [Indexed: 01/01/2023]
Abstract
More than a billion years ago, bacterial precursors of mitochondria became endosymbionts in what we call eukaryotic cells today. The true significance of the word "endosymbiont" has only become clear to cell biologists with the discovery that the endoplasmic reticulum (ER) superorganelle dedicates a special domain for the metabolic interaction with mitochondria. This domain, identified in all eukaryotic cell systems from yeast to man and called the mitochondria-associated membrane (MAM), has a distinct proteome, specific tethers on the cytosolic face and regulatory proteins in the ER lumen of the ER. The MAM has distinct biochemical properties and appears as ER tubules closely apposed to mitochondria on electron micrographs. The functions of the MAM range from lipid metabolism and calcium signaling to inflammasome formation. Consistent with these functions, the MAM is enriched in lipid metabolism enzymes and calcium handling proteins. During cellular stress situations, like an altered cellular redox state, the MAM alters its set of regulatory proteins and thus alters MAM functions. Notably, this set prominently comprises ER chaperones and oxidoreductases that connect protein synthesis and folding inside the ER to mitochondrial metabolism. Moreover, ER membranes associated with mitochondria also accommodate parts of the machinery that determines mitochondrial membrane dynamics and connect mitochondria to the cytoskeleton. Together, these exciting findings demonstrate that the physiological interactions between the ER and mitochondria are so bilateral that we are tempted to compare their relationship to the one of a married couple: distinct, but inseparable and certainly dependent on each other. In this paradigm, the MAM stands for the intracellular location where the two organelles tie the knot. Resembling "real life", the happy marriage between the two organelles prevents the onset of diseases that are characterized by disrupted metabolism and decreased lifespan, including neurodegeneration and cancer. This article is part of a Special Issue entitled: Mitochondrial dynamics and physiology.
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Affiliation(s)
- Arun Raturi
- Department of Cell Biology, University of Alberta, Edmonton, Alberta, Canada
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23
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Tsai YY, Huang YH, Chao YL, Hu KY, Chin LT, Chou SH, Hour AL, Yao YD, Tu CS, Liang YJ, Tsai CY, Wu HY, Tan SW, Chen HM. Identification of the nanogold particle-induced endoplasmic reticulum stress by omic techniques and systems biology analysis. ACS NANO 2011; 5:9354-9369. [PMID: 22107733 DOI: 10.1021/nn2027775] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Growth inhibition and apoptotic/necrotic phenotype was observed in nanogold particle (AuNP)-treated human chronic myelogenous leukemia cells. To elucidate the underlying cellular mechanisms, proteomic techniques including two-dimensional electrophoresis/mass spectrometry and protein microarrays were utilized to study the differentially expressed proteome and phosphoproteome, respectively. Systems biology analysis of the proteomic data revealed that unfolded protein-associated endoplasmic reticulum (ER) stress response was the predominant event. Concomitant with transcriptomic analysis using mRNA expression, microarrays show ER stress response in the AuNP-treated cells. The ER stress protein markers' expression assay unveiled AuNPs as an efficient cellular ER stress elicitor. Upon ER stress, cellular responses, including reactive oxygen species increase, mitochondrial cytochrome c release, and mitochondria damage, chronologically occurred in the AuNP-treated cells. Conclusively, this study demonstrates that AuNPs cause cell death through induction of unmanageable ER stress.
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Affiliation(s)
- Yen-Yin Tsai
- Department of Life-Science, Fu-Jen Catholic University, Taipei, Taiwan
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24
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Romero-Fernandez W, Borroto-Escuela DO, Perez Alea M, Garcia-Mesa Y, Garriga P. Altered trafficking and unfolded protein response induction as a result of M3 muscarinic receptor impaired N-glycosylation. Glycobiology 2011; 21:1663-72. [DOI: 10.1093/glycob/cwr105] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
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25
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Lynes EM, Simmen T. Urban planning of the endoplasmic reticulum (ER): how diverse mechanisms segregate the many functions of the ER. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2011; 1813:1893-905. [PMID: 21756943 PMCID: PMC7172674 DOI: 10.1016/j.bbamcr.2011.06.011] [Citation(s) in RCA: 102] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/20/2011] [Revised: 06/22/2011] [Accepted: 06/23/2011] [Indexed: 12/21/2022]
Abstract
The endoplasmic reticulum (ER) is the biggest organelle in most cell types, but its characterization as an organelle with a continuous membrane belies the fact that the ER is actually an assembly of several, distinct membrane domains that execute diverse functions. Almost 20 years ago, an essay by Sitia and Meldolesi first listed what was known at the time about domain formation within the ER. In the time that has passed since, additional ER domains have been discovered and characterized. These include the mitochondria-associated membrane (MAM), the ER quality control compartment (ERQC), where ER-associated degradation (ERAD) occurs, and the plasma membrane-associated membrane (PAM). Insight has been gained into the separation of nuclear envelope proteins from the remainder of the ER. Research has also shown that the biogenesis of peroxisomes and lipid droplets occurs on specialized membranes of the ER. Several studies have shown the existence of specific marker proteins found on all these domains and how they are targeted there. Moreover, a first set of cytosolic ER-associated sorting proteins, including phosphofurin acidic cluster sorting protein 2 (PACS-2) and Rab32 have been identified. Intra-ER targeting mechanisms appear to be superimposed onto ER retention mechanisms and rely on transmembrane and cytosolic sequences. The crucial roles of ER domain formation for cell physiology are highlighted with the specific targeting of the tumor metastasis regulator gp78 to ERAD-mediating membranes or of the promyelocytic leukemia protein to the MAM.
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Affiliation(s)
- Emily M Lynes
- Department of Cell Biology, University of Alberta, Alberta, Canada
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Li HD, Liu WX, Michalak M. Enhanced clathrin-dependent endocytosis in the absence of calnexin. PLoS One 2011; 6:e21678. [PMID: 21747946 PMCID: PMC3128601 DOI: 10.1371/journal.pone.0021678] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2010] [Accepted: 06/08/2011] [Indexed: 12/24/2022] Open
Abstract
Background Calnexin, together with calreticulin, constitute the calnexin/calreticulin cycle. Calnexin is a type I endoplasmic reticulum integral membrane protein and molecular chaperone responsible for the folding and quality control of newly-synthesized (glyco)proteins. The endoplasmic reticulum luminal domain of calnexin is responsible for lectin-like activity and interaction with nascent polypeptide chains. The role of the C-terminal, cytoplasmic portion of calnexin is not clear. Methodology/Principal Findings Using yeast two hybrid screen and immunoprecipitation techniques, we showed that the Src homology 3-domain growth factor receptor-bound 2-like (Endophilin) interacting protein 1 (SGIP1), a neuronal specific regulator of endocytosis, forms complexes with the C-terminal cytoplasmic domain of calnexin. The calnexin cytoplasmic C-tail interacts with SGIP1 C-terminal domains containing the adaptor complexes medium subunit (Adap-Comp-Sub) region. Calnexin-deficient cells have enhanced clathrin-dependent endocytosis in neuronal cells and mouse neuronal system. This is reversed by expression of full length calnexin or calnexin C-tail. Conclusions/Significance We show that the effects of SGIP1 and calnexin C-tail on clathrin-dependent endocytosis are due to modulation of the internalization of the receptor-ligand complexes. Enhanced clathrin-dependent endocytosis in the absence of calnexin may contribute to the neurological phenotype of calnexin-deficient mice.
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Affiliation(s)
- Hao-Dong Li
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada
| | - Wen-Xin Liu
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada
| | - Marek Michalak
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada
- * E-mail:
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Jung J, Michalak M. Cell surface targeting of myelin oligodendrocyte glycoprotein (MOG) in the absence of endoplasmic reticulum molecular chaperones. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2010; 1813:1105-10. [PMID: 21172390 DOI: 10.1016/j.bbamcr.2010.12.014] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2010] [Revised: 12/07/2010] [Accepted: 12/08/2010] [Indexed: 11/15/2022]
Abstract
Myelin oligodendrocyte glycoprotein (MOG) is a type I integral membrane glycoprotein that localizes to myelin sheaths in the central nervous system. MOG has important implications in multiple sclerosis, as pathogenic anti-MOG antibodies have been detected in the sera of multiple sclerosis patients. As a membrane protein, MOG achieves its native structure in the endoplasmic reticulum where its folding is expected to be controlled by endoplasmic reticulum chaperones. Calnexin, calreticulin, and ERp57 are essential components of the endoplasmic reticulum quality control where they assist in the proper folding of newly synthesized glycoproteins. In this study, we show that expression of MOG is not affected by the absence of the endoplasmic reticulum quality control proteins calnexin, calreticulin, or ERp57. We also show that calnexin forms complexes with MOG and these interactions might be glycan-independent. Importantly, we show that cell surface targeting of MOG is not disrupted in the absence of the endoplasmic reticulum chaperones. This article is part of a special issue entitled: 11th European Symposium on Calcium.
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Affiliation(s)
- Joanna Jung
- Department of Biochemistry, School of Molecular and Systems Medicine, University of Alberta, Edmonton, Canada T6G 2H7.
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Gene expression in primary cultured astrocytes affected by aluminum: alteration of chaperons involved in protein folding. Environ Health Prev Med 2010; 16:16-24. [PMID: 21432213 DOI: 10.1007/s12199-010-0161-2] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2010] [Accepted: 05/31/2010] [Indexed: 12/20/2022] Open
Abstract
OBJECTIVES Aluminum is notorious as a neurotoxic metal. The aim of our study was to determine whether endoplasmic reticulum (ER) stress is involved in aluminum-induced apoptosis in astrocytes. METHODS Mitochondrial RNA (mRNA) was analyzed by reverse transcription (RT)-PCR following pulse exposure of aluminum glycinate to primary cultured astrocytes. Tunicamycin was used as a positive control. RESULTS Gene expression analysis revealed that Ire1β was up-regulated in astrocytes exposed to aluminum while Ire1α was up-regulated by tunicamycin. Exposure to aluminum glycinate, in contrast to tunicamycin, seemed to down-regulate mRNA expression of many genes, including the ER resident molecular chaperone BiP/Grp78 and Ca(2+)-binding chaperones (calnexin and calreticulin), as well as stanniocalcin 2 and OASIS. The down-regulation or non-activation of the molecular chaperons, whose expressions are known to be protective by increasing protein folding, may spell doom for the adaptive response. Exposure to aluminum did not have any significant effects on the expression of Bax and Bcl2 in astrocytes. CONCLUSIONS The results of this study demonstrate that aluminum may induce apoptosis in astrocytes via ER stress by impairing the protein-folding machinery.
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Lu Q, Jankowich M, Newton J, Harrington EO, Rounds S. Alterations in molecular chaperones and eIF2alpha during lung endothelial cell apoptosis. Am J Physiol Lung Cell Mol Physiol 2010; 298:L501-8. [PMID: 20097734 DOI: 10.1152/ajplung.00416.2009] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
We have previously demonstrated that inhibition of CAAX carboxyl methylation with AGGC caused redistribution and condensation of the ER molecular chaperones, glucose-regulated protein (GRP)-94 and calnexin; an effect that was attenuated by overexpression of dominant active RhoA. We have also shown that AGGC decreased GRP94 protein level; an effect that was dependent on caspase activity. In the present study, we tested the effects of inhibition of posttranslational processing of CAAX proteins on localization and protein levels of molecular chaperones and phosphorylation and protein level of eIF2alpha. We found that both AGGC, which inhibits CAAX carboxyl methylation, and simvastatin, which inhibits CAAX geranylgeranylation, caused relocalization of GRP94, calnexin, and calreticulin, effects that were not seen during endothelial apoptosis induced by TNF-alpha or ultraviolet (UV) irradiation. These results suggest that posttranslational processing of CAAX proteins is important in maintaining localization of molecular chaperones normally found in the ER. We also noted that AGGC, but not simvastatin, TNF-alpha, or UV irradiation, decreased protein levels of most molecular chaperones. Increased eIF2alpha phosphorylation was observed in the early stages of apoptosis, which was independent of the cause of apoptosis. These results suggest that eIF2alpha phosphorylation is a common early response to apoptosis-inducing stimuli. Interestingly, eIF2alpha protein level was decreased in the late stages of apoptosis induced by AGGC, TNF-alpha, and UV irradiation: an effect that was prevented by caspase inhibition. Thus we speculate that caspase(s)-dependent proteolysis of molecular chaperones and eIF2alpha may be novel signaling pathways of apoptosis. We also speculate that increased eIF2alpha phosphorylation is a defensive response against endothelial cell apoptosis.
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Affiliation(s)
- Qing Lu
- Department of Medicine, Vascular Research Laboratory, Providence Veterans Affairs Medical Center, Alpert Medical School of Brown University, Providence, Rhode Island 02908, USA
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30
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Guérin R, Turcotte C, Leroux A, Rokeach LA. The epigenetic calnexin-independent state is induced in response to environmental changes. FEMS Yeast Res 2009; 9:1250-9. [PMID: 19686339 DOI: 10.1111/j.1567-1364.2009.00554.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Yeasts have evolved numerous responsive pathways to survive in fluctuating and stressful environments. The endoplasmic reticulum (ER) is sensitive to adverse conditions, which are detected by response pathways to ensure correct protein folding. Calnexin is an ER transmembrane chaperone acting in both quality control of folding and response to persistent stress. Calnexin is a key protein required for viability in certain organisms such as mammals and the fission yeast Schizosaccharomyces pombe. Nevertheless, S. pombe calnexin-independent (Cin) cells were obtained after transient expression of a particular calnexin mutant. The Cin state is dominant, is stably propagated by an epigenetic mechanism and segregates in a non-Mendelian fashion to the meiotic progeny. The nucleolar protein Cif1p was identified as an inducer of the Cin state in a previous genetic screen. Here, we report the identification of novel inducers isolated in an overexpression genetic screen: pyruvate kinase (Pyk1p) and phosphoglycerate kinase (Pgk1p). Addition of pyruvate, the end product of pyruvate kinase and glycolysis, also induced calnexin independence in a dose-dependent manner. Remarkably, growth in respiration media or cold temperatures induced the appearance of Cin cells at high frequencies. Taken together, our results indicate that the Cin state can be triggered by extracellular changes, suggesting that this state represents an epigenetic adaptative response to environmental modifications.
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Affiliation(s)
- Renée Guérin
- Department of Biochemistry, Université de Montréal, Montréal, QC, Canada
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Guérin R, Beauregard PB, Leroux A, Rokeach LA. Calnexin regulates apoptosis induced by inositol starvation in fission yeast. PLoS One 2009; 4:e6244. [PMID: 19606215 PMCID: PMC2705804 DOI: 10.1371/journal.pone.0006244] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2009] [Accepted: 06/08/2009] [Indexed: 12/21/2022] Open
Abstract
Inositol is a precursor of numerous phospholipids and signalling molecules essential for the cell. Schizosaccharomyces pombe is naturally auxotroph for inositol as its genome does not have a homologue of the INO1 gene encoding inositol-1-phosphate synthase, the enzyme responsible for inositol biosynthesis. In this work, we demonstrate that inositol starvation in S. pombe causes cell death with apoptotic features. This apoptotic death is dependent on the metacaspase Pca1p and is affected by the UPR transducer Ire1p. Previously, we demonstrated that calnexin is involved in apoptosis induced by ER stress. Here, we show that cells expressing a lumenal version of calnexin exhibit a 2-fold increase in the levels of apoptosis provoked by inositol starvation. This increase is reversed by co-expression of a calnexin mutant spanning the transmembrane domain and C-terminal cytosolic tail. Coherently, calnexin is physiologically cleaved at the end of its lumenal domain, under normal growth conditions when cells approach stationary phase. This cleavage suggests that the two naturally produced calnexin fragments are needed to continue growth into stationary phase and to prevent cell death. Collectively, our observations indicate that calnexin takes part in at least two apoptotic pathways in S. pombe, and suggest that the cleavage of calnexin has regulatory roles in apoptotic processes involving calnexin.
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Affiliation(s)
- Renée Guérin
- Department of Biochemistry, Université de Montréal, Montréal, Québec, Canada
| | | | - Alexandre Leroux
- Department of Biochemistry, Université de Montréal, Montréal, Québec, Canada
| | - Luis A. Rokeach
- Department of Biochemistry, Université de Montréal, Montréal, Québec, Canada
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Patterson ST, Li J, Kang JA, Wickrema A, Williams DB, Reithmeier RAF. Loss of specific chaperones involved in membrane glycoprotein biosynthesis during the maturation of human erythroid progenitor cells. J Biol Chem 2009; 284:14547-57. [PMID: 19258325 PMCID: PMC2682903 DOI: 10.1074/jbc.m809076200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2008] [Revised: 02/23/2009] [Indexed: 11/06/2022] Open
Abstract
The production of erythrocytes requires the massive synthesis of red cell-specific proteins including hemoglobin, cytoskeletal proteins, as well as membrane glycoproteins glycophorin A (GPA) and anion exchanger 1 (AE1). We found that during the terminal differentiation of human CD34(+) erythroid progenitor cells in culture, key components of the endoplasmic reticulum (ER) protein translocation (Sec61alpha), glycosylation (OST48), and protein folding machinery, chaperones BiP, calreticulin (CRT), and Hsp90 were maintained to allow efficient red cell glycoprotein biosynthesis. Unexpected was the loss of calnexin (CNX), an ER glycoprotein chaperone, and ERp57, a protein-disulfide isomerase, as well as a major decrease of the cytosolic chaperones, Hsc70 and Hsp70, components normally involved in membrane glycoprotein folding and quality control. AE1 can traffic to the cell surface in mouse embryonic fibroblasts completely deficient in CNX or CRT, whereas disruption of the CNX/CRT-glycoprotein interactions in human K562 cells using castanospermine did not affect the cell-surface levels of endogenous GPA or expressed AE1. These results demonstrate that CNX and ERp57 are not required for major glycoprotein biosynthesis during red cell development, in contrast to their role in glycoprotein folding and quality control in other cells.
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Affiliation(s)
- Sian T Patterson
- Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada
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Beauregard PB, Guérin R, Turcotte C, Lindquist S, Rokeach LA. A nucleolar protein allows viability in the absence of the essential ER-residing molecular chaperone calnexin. J Cell Sci 2009; 122:1342-51. [PMID: 19351719 DOI: 10.1242/jcs.040949] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
In fission yeast, the ER-residing molecular chaperone calnexin is normally essential for viability. However, a specific mutant of calnexin that is devoid of chaperone function (Deltahcd_Cnx1p) induces an epigenetic state that allows growth of Schizosaccharomyces pombe without calnexin. This calnexin-independent (Cin) state was previously shown to be mediated via a non-chromosomal element exhibiting some prion-like features. Here, we report the identification of a gene whose overexpression induces the appearance of stable Cin cells. This gene, here named cif1(+) for calnexin-independence factor 1, encodes an uncharacterized nucleolar protein. The Cin cells arising from cif1(+) overexpression (Cin(cif1) cells) are genetically and phenotypically distinct from the previously characterized Cin(Deltahcd_cnx1) cells, which spontaneously appear in the presence of the Deltahcd_Cnx1p mutant. Moreover, cif1(+) is not required for the induction or maintenance of the Cin(Deltahcd_cnx1) state. These observations argue for different pathways of induction and/or maintenance of the state of calnexin independence. Nucleolar localization of Cif1p is required to induce the Cin(cif1) state, thus suggesting an unexpected interaction between the vital cellular role of calnexin and a function of the nucleolus.
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Affiliation(s)
- Pascale B Beauregard
- Department of Biochemistry, Université de Montréal, C.P. 6128, succursale Centre-ville, Montréal, Québec H3C 3J7, Canada
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Lebiedzinska M, Szabadkai G, Jones AWE, Duszynski J, Wieckowski MR. Interactions between the endoplasmic reticulum, mitochondria, plasma membrane and other subcellular organelles. Int J Biochem Cell Biol 2009; 41:1805-16. [PMID: 19703651 DOI: 10.1016/j.biocel.2009.02.017] [Citation(s) in RCA: 132] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2008] [Revised: 02/22/2009] [Accepted: 02/23/2009] [Indexed: 02/02/2023]
Abstract
Several recent works show structurally and functionally dynamic contacts between mitochondria, the plasma membrane, the endoplasmic reticulum, and other subcellular organelles. Many cellular processes require proper cooperation between the plasma membrane, the nucleus and subcellular vesicular/tubular networks such as mitochondria and the endoplasmic reticulum. It has been suggested that such contacts are crucial for the synthesis and intracellular transport of phospholipids as well as for intracellular Ca(2+) homeostasis, controlling fundamental processes like motility and contraction, secretion, cell growth, proliferation and apoptosis. Close contacts between smooth sub-domains of the endoplasmic reticulum and mitochondria have been shown to be required also for maintaining mitochondrial structure. The overall distance between the associating organelle membranes as quantified by electron microscopy is small enough to allow contact formation by proteins present on their surfaces, allowing and regulating their interactions. In this review we give a historical overview of studies on organelle interactions, and summarize the present knowledge and hypotheses concerning their regulation and (patho)physiological consequences.
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Mohan C, Lee GM. Calnexin overexpression sensitizes recombinant CHO cells to apoptosis induced by sodium butyrate treatment. Cell Stress Chaperones 2009; 14:49-60. [PMID: 18663604 PMCID: PMC2673906 DOI: 10.1007/s12192-008-0054-0] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2007] [Revised: 05/07/2008] [Accepted: 05/14/2008] [Indexed: 12/12/2022] Open
Abstract
Sodium butyrate (NaBu) can enhance the expression of foreign genes in recombinant Chinese hamster ovary (rCHO) cells, but it can also inhibit cell growth and induce cellular apoptosis. In this study, the potential role of calnexin (Cnx) expression in rCHO cells treated with 5 mM NaBu was investigated for rCHO cells producing tumor necrosis factor receptor FC. To regulate the Cnx expression level, a tetracycline-inducible system was used. Clones with different Cnx expression levels were selected and investigated. With regard to productivity per cell (q (p)), NaBu enhanced the q (p) by over twofold. Under NaBu treatment, Cnx overexpression further enhanced the q (p) by about 1.7-fold. However, under NaBu stress, the cells overexpressing Cnx showed a poorer viability profile with a consistent difference of over 25% in the viability when compared to the Cnx-repressed condition. This drop in the viability was attributed to increased apoptosis seen in these cells as evidenced by enhanced poly (ADP-ribose) polymerase cleavage and cytochrome C release. Ca(2+) localization staining and subsequent confocal imaging revealed elevated cytosolic Ca(2+) ([Ca(2+)](c)) in the Cnx-overexpressing cells when compared to the Cnx-repressed condition, thus endorsing the increased apoptosis observed in these cells. Taken together, Cnx overexpression not only improved the q (p) of cells treated with NaBu, but it also sensitized cells to apoptosis.
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Affiliation(s)
- Chaya Mohan
- Department of Biological Sciences, KAIST, 373-1 Kusong-Dong, Yusong-Gu, Daejon, 305-701 South Korea
| | - Gyun Min Lee
- Department of Biological Sciences, KAIST, 373-1 Kusong-Dong, Yusong-Gu, Daejon, 305-701 South Korea
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Guérin R, Arseneault G, Dumont S, Rokeach LA. Calnexin is involved in apoptosis induced by endoplasmic reticulum stress in the fission yeast. Mol Biol Cell 2008; 19:4404-20. [PMID: 18701708 DOI: 10.1091/mbc.e08-02-0188] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Stress conditions affecting the functions of the endoplasmic reticulum (ER) cause the accumulation of unfolded proteins. ER stress is counteracted by the unfolded-protein response (UPR). However, under prolonged stress the UPR initiates a proapoptotic response. Mounting evidence indicate that the ER chaperone calnexin is involved in apoptosis caused by ER stress. Here, we report that overexpression of calnexin in Schizosaccharomyces pombe induces cell death with apoptosis markers. Cell death was partially dependent on the Ire1p ER-stress transducer. Apoptotic death caused by calnexin overexpression required its transmembrane domain (TM), and involved sequences on either side of the ER membrane. Apoptotic death caused by tunicamycin was dramatically reduced in a strain expressing endogenous levels of calnexin lacking its TM and cytosolic tail. This demonstrates the involvement of calnexin in apoptosis triggered by ER stress. A genetic screen identified the S. pombe homologue of the human antiapoptotic protein HMGB1 as a suppressor of apoptotic death due to calnexin overexpression. Remarkably, overexpression of human calnexin in S. pombe also provoked apoptotic death. Our results argue for the conservation of the role of calnexin in apoptosis triggered by ER stress, and validate S. pombe as a model to elucidate the mechanisms of calnexin-mediated cell death.
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Affiliation(s)
- Renée Guérin
- Department of Biochemistry, Université de Montréal, Montréal, QC H3C 3J7, Canada
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Murphy N, Bonner HP, Ward MW, Murphy BM, Prehn JHM, Henshall DC. Depletion of 14-3-3 zeta elicits endoplasmic reticulum stress and cell death, and increases vulnerability to kainate-induced injury in mouse hippocampal cultures. J Neurochem 2008; 106:978-88. [PMID: 18466333 DOI: 10.1111/j.1471-4159.2008.05447.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
14-3-3 proteins are ubiquitous signalling molecules that regulate development and survival pathways in brain. Altered expression and cellular localization of 14-3-3 proteins has been implicated in neurodegenerative diseases and in neuronal death after acute neurological insults, including seizures. Presently, we examined expression and function of 14-3-3 isoforms in vitro using mouse organotypic hippocampal cultures. Treatment of cultures with the endoplasmic reticulum (ER) stressor tunicamycin caused an increase in levels of 14-3-3 zeta within the ER-containing microsomal fraction, along with up-regulation of Lys-Asp-Glu-Leu-containing proteins and calnexin, and the selective death of dentate granule cells. Depletion of 14-3-3 zeta levels using small interfering RNA induced both ER stress proteins and death of granule cells. Treatment of hippocampal cultures with the excitotoxin kainic acid increased levels of Lys-Asp-Glu-Leu-containing proteins and microsomal 14-3-3 zeta levels and caused cell death within the CA1, CA3 and dentate gyrus of the hippocampus. Kainic acid-induced damage was significantly increased in each hippocampal subfield of cultures treated with small interfering RNA targeting 14-3-3 zeta. The present data indicate a role for 14-3-3 zeta in survival responses following ER stress and possibly protection against seizure injury to the hippocampus.
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Affiliation(s)
- Niamh Murphy
- Department of Physiology & Medical Physics, Royal College of Surgeons in Ireland, Dublin, Ireland, UK
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Myhill N, Lynes EM, Nanji JA, Blagoveshchenskaya AD, Fei H, Carmine Simmen K, Cooper TJ, Thomas G, Simmen T. The subcellular distribution of calnexin is mediated by PACS-2. Mol Biol Cell 2008; 19:2777-88. [PMID: 18417615 DOI: 10.1091/mbc.e07-10-0995] [Citation(s) in RCA: 172] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Calnexin is an endoplasmic reticulum (ER) lectin that mediates protein folding on the rough ER. Calnexin also interacts with ER calcium pumps that localize to the mitochondria-associated membrane (MAM). Depending on ER homeostasis, varying amounts of calnexin target to the plasma membrane. However, no regulated sorting mechanism is so far known for calnexin. Our results now describe how the interaction of calnexin with the cytosolic sorting protein PACS-2 distributes calnexin between the rough ER, the MAM, and the plasma membrane. Under control conditions, more than 80% of calnexin localizes to the ER, with the majority on the MAM. PACS-2 knockdown disrupts the calnexin distribution within the ER and increases its levels on the cell surface. Phosphorylation by protein kinase CK2 of two calnexin cytosolic serines (Ser554/564) reduces calnexin binding to PACS-2. Consistent with this, a Ser554/564 Asp phosphomimic mutation partially reproduces PACS-2 knockdown by increasing the calnexin signal on the cell surface and reducing it on the MAM. PACS-2 knockdown does not reduce retention of other ER markers. Therefore, our results suggest that the phosphorylation state of the calnexin cytosolic domain and its interaction with PACS-2 sort this chaperone between domains of the ER and the plasma membrane.
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Affiliation(s)
- Nathan Myhill
- Department of Cell Biology, University of Alberta, Edmonton, Alberta, T6G2H7, Canada
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39
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Zhao X, Wang L, Sun Y, Ye L, Lu J, Yuan Y, Qian G, Ge S. The endoplasmic reticulum (ER)-target protein Bik induces Hep3B cells apoptosis by the depletion of the ER Ca2+ stores. Mol Cell Biochem 2008; 312:33-8. [DOI: 10.1007/s11010-008-9718-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2007] [Accepted: 01/29/2008] [Indexed: 12/01/2022]
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40
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Szabadkai G, Rizzuto R. Chaperones as Parts of Organelle Networks. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2007; 594:64-77. [PMID: 17205676 DOI: 10.1007/978-0-387-39975-1_7] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The efficiency, divergence, and specificity of virtually all intracellular metabolic and signalling pathways largely depend on their compartmentalized organization. A corollary of the requirement of compartmentalization is the dynamic structural partition of the intracellular space by endomembrane systems. A branch of these membranes communicate with the extracellular space through the endo- and exocytotic processes. Others, like the mitochondrial and endoplasmic reticulum networks accomplish a further role, being fundamental for the maintenance of cellular energy balance and for determination of cell fate under stress conditions. Recent structural and functional studies revealed that the interaction of these networks and the connectivity state of mitochondria controls metabolic flow, protein transport, intracellular Ca2+ signalling, and cell death. Moreover, reflecting the fact that the above processes are accomplished in a microdomain between collaborating organelle membranes, the existence of macromolecular complexes at their contact sites have also been revealed. Being not only assistants of nascent protein folding, chaperones are proposed to participate in assembling and maintaining the function of the above complexes. In this chapter we discuss recently found examples of such an assembly of protein interactions driven by chaperone proteins, and their role in regulating physiological and pathological processes.
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Affiliation(s)
- György Szabadkai
- Department of Experimental and Diagnostic Medicine, University of Ferrara, Via Borsari 46, Ferrara, 44100, Italy.
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41
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Abstract
Proteins synthesized in the endoplasmic reticulum (ER) are properly folded with the assistance of ER chaperones. Malfolded proteins are disposed of by ER-associated protein degradation (ERAD). When the amount of unfolded protein exceeds the folding capacity of the ER, human cells activate a defense mechanism called the ER stress response, which induces expression of ER chaperones and ERAD components and transiently attenuates protein synthesis to decrease the burden on the ER. It has been revealed that three independent response pathways separately regulate induction of the expression of chaperones, ERAD components, and translational attenuation. A malfunction of the ER stress response caused by aging, genetic mutations, or environmental factors can result in various diseases such as diabetes, inflammation, and neurodegenerative disorders including Alzheimer's disease, Parkinson's disease, and bipolar disorder, which are collectively known as 'conformational diseases'. In this review, I will summarize recent progress in this field. Molecules that regulate the ER stress response would be potential candidates for drug targets in various conformational diseases.
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Affiliation(s)
- Hiderou Yoshida
- Department of Biophysics, Graduate School of Science, Kyoto University, Japan.
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42
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Mukasa T, Santelli E, Reed JC, Pascual J. Preliminary structural studies on the leucine-zipper homology region of the human protein Bap31. Acta Crystallogr Sect F Struct Biol Cryst Commun 2007; 63:297-9. [PMID: 17401199 PMCID: PMC2330218 DOI: 10.1107/s1744309107008925] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2006] [Accepted: 02/22/2007] [Indexed: 11/10/2022]
Abstract
B-cell receptor-associated protein 31 (Bap31) is an integral membrane protein located in the endoplasmic reticulum (ER) that participates in the transport and quality control of membrane proteins and plays a role in determining cell sensitivity to ER stress and apoptosis. Its cytoplasmic region contains two target sites for caspase cleavage in certain apoptotic pathways. Here, the subcloning, expression, purification and crystallization of the Homo sapiens Bap31 leucine-zipper C-terminal fragment, which spans residues Gly160-Glu246, are reported. An N-terminally His-tagged protein was overexpressed in Escherichia coli and purified by chromatographic methods. X-ray diffraction data were collected in-house to 2.5 A resolution. Crystals belong to space group P6(1)22/P6(5)22, with unit-cell parameters a = b = 70.7, c = 80.6 A. Data analysis indicates the presence of one molecule per asymmetric unit.
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Affiliation(s)
- Takashi Mukasa
- Program on Infectious Diseases, Center for Inflammation and Infectious Diseases, The Burnham Institute for Medical Research, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - Eugenio Santelli
- Program on Infectious Diseases, Center for Inflammation and Infectious Diseases, The Burnham Institute for Medical Research, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - John C. Reed
- Program on Apoptosis, Cancer Center, The Burnham Institute for Medical Research, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - Jaime Pascual
- Program on Infectious Diseases, Center for Inflammation and Infectious Diseases, The Burnham Institute for Medical Research, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA
- Correspondence e-mail:
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Delom F, Fessart D, Chevet E. Regulation of calnexin sub-cellular localization modulates endoplasmic reticulum stress-induced apoptosis in MCF-7 cells. Apoptosis 2007; 12:293-305. [PMID: 17203246 DOI: 10.1007/s10495-006-0625-4] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The endoplasmic reticulum (ER) is the cellular compartment where proteins enter the secretory pathway, undergo post-translational modifications and acquire a correct conformation. If these functions are chronically altered, specific ER stress signals are triggered to promote cell death through the intrinsic apoptotic pathway. Here, we show that tunicamycin causes significant alteration of calnexin sub-cellular distribution in MCF-7 cells. Interestingly, this correlates with the absence of both tunicamycin-induced calnexin phosphorylation as well as tunicamycin-induced cell death. Under these conditions, calnexin-associated Bap31, an ER integral membrane protein, is subjected to a caspase-8 cleavage pattern within a specific sub-compartment of the ER. These results suggest that MCF-7 resistance to ER stress-induced apoptosis is partially mediated by the expression level of calnexin which in turn controls its sub-cellular localization, and its association with Bap31. These data may delineate a resistance mechanism to the ER stress-induced intrinsic apoptotic pathway.
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Affiliation(s)
- Frédéric Delom
- Department of Surgery, McGill University, 687 Pine Avenue West, Montreal, QC, H3A 1A1, Canada
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44
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Abstract
Small transmembrane proteins of the tetraspanin superfamily are believed to function as the main structural blocks of specialized membrane microdomains (referred to as tetraspanin-enriched microdomains, TERM or TEM). Through a multitude of homotypic and heterotypic interactions, tetraspanins regulate lateral clustering and, consequently, signalling involving adhesion and growth factor receptors as well as costimulatory proteins. The presence of major histocompatibility complex (MHC) I and MHCII molecules in TERM led to suggestion of tetraspanins' involvement in antigen presentation. In addition, certain tetraspanins function as viral co-receptors and may be important for viral egress from infected cells. It has recently become apparent that in addition to their purely structural function as organizers of TERM, tetraspanins also regulate various aspects of trafficking and biosynthetic processing of associated receptors. Here, we review recent studies, which specifically focus on this issue.
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Affiliation(s)
- Fedor Berditchevski
- Cancer Research UK Institute for Cancer Studies, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
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45
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Delom F, Emadali A, Cocolakis E, Lebrun JJ, Nantel A, Chevet E. Calnexin-dependent regulation of tunicamycin-induced apoptosis in breast carcinoma MCF-7 cells. Cell Death Differ 2006; 14:586-96. [PMID: 16858427 DOI: 10.1038/sj.cdd.4402012] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The endoplasmic reticulum (ER) has evolved specific mechanisms to ensure protein folding as well as the maintenance of its own homeostasis. When these functions are not achieved, specific ER stress signals are triggered to activate either adaptive or apoptotic responses. Here, we demonstrate that MCF-7 cells are resistant to tunicamycin-induced apoptosis. We show that the expression level of the ER chaperone calnexin can directly influence tunicamycin sensitivity in this cell line. Interestingly, the expression of a calnexin lacking the chaperone domain (DeltaE) partially restores their sensitivity to tunicamycin-induced apoptosis. Indeed, we show that DeltaE acts as a scaffold molecule to allow the cleavage of Bap31 and thus generate the proapoptotic p20 fragment. Utilizing the ability of MCF-7 cells to resist tunicamycin-induced apoptosis, we have characterized a molecular mechanism by which calnexin regulates ER-stress-mediated apoptosis in a manner independent of its chaperone functions but dependent of its binding to Bap31.
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Affiliation(s)
- F Delom
- Department of Surgery, McGill University, Montreal, Quebec, Canada
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46
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Zuppini A, Bugno V, Baldan B. Monitoring programmed cell death triggered by mild heat shock in soybean-cultured cells. FUNCTIONAL PLANT BIOLOGY : FPB 2006; 33:617-627. [PMID: 32689271 DOI: 10.1071/fp06015] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/17/2006] [Accepted: 03/29/2006] [Indexed: 06/11/2023]
Abstract
Programmed cell death (PCD) is a common form of cellular demise during plant response to environmental stresses. The pathway of PCD has been partially clarified in plants although the underlying molecular mechanisms are still poorly defined. We have investigated the signalling cascade induced by a mild heat treatment causing PCD in soybean cells (Glycine max L.). The data show that heat shock led to the onset of PCD in soybean cells involving H2O2 production and mitochondrial damage. Cytochrome c release accompanies the presence of caspase 9-like and caspase 3-like protease activities. Concomitantly, cells were severely damaged with a progressive cell shrinkage, chloroplast alteration and detachment of the plasma membrane from the cell wall. Chromatin condensation and DNA damage were observed. It is proposed that a mild heat stress induces PCD in soybean cells through a caspase-like-dependent pathway.
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Affiliation(s)
- Anna Zuppini
- Dipartimento di Biologia, Università di Padova, via U. Bassi 58/B, 35131 Padova, Italy
| | - Valentina Bugno
- Dipartimento di Biologia, Università di Padova, via U. Bassi 58/B, 35131 Padova, Italy
| | - Barbara Baldan
- Dipartimento di Biologia, Università di Padova, via U. Bassi 58/B, 35131 Padova, Italy
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47
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Zurgil N, Afrimzon E, Shafran Y, Shovman O, Gilburd B, Brikman H, Shoenfeld Y, Deutsch M. Lymphocyte resistance to lysophosphatidylcholine mediated apoptosis in atherosclerosis. Atherosclerosis 2006; 190:73-83. [PMID: 16564529 DOI: 10.1016/j.atherosclerosis.2006.02.013] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/02/2005] [Revised: 01/08/2006] [Accepted: 02/01/2006] [Indexed: 10/24/2022]
Abstract
OBJECTIVE Apoptosis is being increasingly regarded as a key component in the development and progression of atherosclerosis. Since it has become apparent that the immune system plays a predominant role in mediating atherogenesis, there has been a growing recognition that the evaluation of lymphocyte apoptosis may contribute to understanding a persistent altered immune and inflammatory response. The aim of the present study was to evaluate the apoptotic effect of lysophosphatidylcholine (LPC) on peripheral blood lymphocytes (PBL) derived from unstable angina (UA) patients, as compared to healthy donors. METHODS PBL isolated from 27 healthy donors and 25 age matched UA patients were examined. Early apoptotic events induced by LPC in resting and phytohemagglutinin (PHA)-activated lymphocytes were evaluated by several apoptotic assays. The levels of intracellular reactive oxygen species (ROS) and the expression of apoptotic regulated proteins (Bcl-2 and Bax) were measured. RESULTS LPC was found to induce apoptosis in normal activated lymphocytes, in a dose- and time-dependent manner, in association with an increase in intracellular ROS. In UA patients, an exposure of PHA-activated PBL to LPC triggered neither an increase in ROS generation, nor in the apoptotic manifestations, and was associated with a significantly lower ratio of Bax/Bcl-2 expression. CONCLUSION Our results indicate that PBL isolated from UA patients may be resistant to apoptosis induction by LPC, resulting from oxidative stress challenge and dysregulation of apoptosis-related protein expression.
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Affiliation(s)
- Naomi Zurgil
- The Biophysical Interdisciplinary Schottenstein Center for the Research and the Technology of the Cellome, Department of Physics, Bar Ilan University, Ramat Gan, Israel
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Szczesna-Skorupa E, Kemper B. BAP31 Is Involved in the Retention of Cytochrome P450 2C2 in the Endoplasmic Reticulum. J Biol Chem 2006; 281:4142-8. [PMID: 16332681 DOI: 10.1074/jbc.m509522200] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Microsomal cytochrome P450 2C2 is an integral endoplasmic reticulum (ER) membrane protein that is directly retained in the ER and excluded from transport vesicles. We have used bimolecular fluorescence complementation and co-immunoprecipitation to show that a ubiquitous ER membrane protein (BAP31) interacts with P450 2C2 in transfected COS-1 cells. A chimera containing only the N-terminal signal anchor of P450 2C1 (P450 2C1-(1-29)) also interacted with BAP31, which is consistent with interaction of the two proteins via their transmembrane domains. Down-regulation of BAP31 expression with small interfering RNA resulted in redistribution of green fluorescent protein-tagged P450 2C2 or P450 2C1-(1-29) from the ER into the nuclear membrane and compact perinuclear compartment structures as well as the cell surface in a small fraction of the cells. In Bap31-null embryonic stem cells, a significant fraction of P450 2C2 or P450 2C1-(1-29) was detected at the cell surface and nuclear envelope, but was redistributed to the ER by expression of BAP31. The expression level of P450 2C2 was significantly increased in COS-1 cells with repressed levels of BAP31. Formation of the pro-apoptotic p20 fragment of BAP31 was detected in transfected COS-1 cells expressing P450 2C2, and annexin V staining was consistent with the activation of an apoptotic pathway in these cells. Down-regulation of BAP31 with small interfering RNA partially reversed the apoptosis. These results suggest that interaction of P450 2C2 with BAP31 is important for its ER retention and expression level and that BAP31 may be involved in the regulation of apoptosis induced by the ER overload response to increased expression of P450.
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Affiliation(s)
- Elzbieta Szczesna-Skorupa
- Department of Molecular and Integrative Physiology, University of Illinois at Urbana-Champaign, 61801, USA
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Itoh K, Kawasaki S, Kawamoto S, Seishima M, Chiba H, Michibata H, Wakimoto K, Imai Y, Minesaki Y, Otsuji M, Okubo K. Identification of differentially expressed genes in psoriasis using expression profiling approaches. Exp Dermatol 2005; 14:667-74. [PMID: 16098126 DOI: 10.1111/j.0906-6705.2005.00338.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
To identify differentially expressed genes which play causal roles in pathogenesis and maintenance for psoriasis, we used BodyMapping and introduced amplified fragment length polymorphism approaches. From the BodyMap database, we selected 2007 genes which specifically expressed in epithelial tissues. Among 2007 genes, we surveyed genes which differentially expressed in involved or uninvolved psoriatic lesional skin samples compared with atopic dermatitis, mycosis fungoides, and normal skin samples. As a result of surveying 2007 genes, 241 genes were differentially expressed only in involved psoriatic skin but not in the other samples. Hierarchical cluster analysis of gene expression profiles showed that 13 independent psoriatic-involved skin samples clustered tightly together, reflecting highly similar expression profiles. Using the same 2007 gene set, we examined gene expression levels in five serial lesions from distal uninvolved psoriatic skin to involved psoriatic plaque. We identified seven genes such as alpha-1-microglobulin/bikunin precursor, calnexin, claudin 1, leucine zipper down-regulated in cancer 1, tyrosinase-related protein 1, Yes-associated protein 1, and unc-13-like protein (Coleonyx elegans) which show high-expression levels only in uninvolved psoriatic lesions. These seven genes, which were reported to be related to apoptosis or antiproliferation, might have causal roles in pathophysiology in psoriasis.
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Affiliation(s)
- K Itoh
- Laboratory for Gene-Expression Analysis, Center for Information Biology, National Institute of Genetics, Mishima, Shizuoka, Japan.
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Lee W, Lee TH, Park BJ, Chang JW, Yu JR, Koo HS, Park H, Yoo YJ, Ahnn J. Caenorhabditis elegans calnexin is N-glycosylated and required for stress response. Biochem Biophys Res Commun 2005; 338:1018-30. [PMID: 16256074 DOI: 10.1016/j.bbrc.2005.10.041] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2005] [Accepted: 10/08/2005] [Indexed: 11/27/2022]
Abstract
Calnexin, a type I integral Ca(2+)-binding protein in the endoplasmic reticulum (ER) membrane, has been implicated in various biological functions including chaperone activity, calcium homeostasis, phagocytosis, and ER stress-induced apoptosis. Caenorhabditis elegans CNX-1 is expressed in the H-shaped excretory cell, intestine, dorsal and ventral nerve cord, spermatheca, and head and tail neurons throughout development. A cnx-1 null mutant displays temperature-sensitive developmental and reproductive defects, and retarded growth under stress. Moreover, a double knockout mutant of calnexin and calreticulin exhibits additive severe defects. Interestingly, both cnx-1 transcript and protein levels are elevated under stress conditions suggesting that CNX-1 may be important for stress-induced chaperoning functions in C. elegans. Glycosidase treatment and site-directed mutagenesis confirmed that CeCNX-1 is N-glycosylated at two asparagine residues of Asn(203) and Asn(571). When transgenic animals from cnx-1 mutant were generated, a glycosylation defective construct failed to rescue phenotypes of cnx-1 mutant suggesting that glycosylation is important for calnexin's functions in C. elegans.
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Affiliation(s)
- Wonhae Lee
- Department of Life Science, Gwangju Institute of Science and Technology, Gwangju 500-712, Republic of Korea
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