51
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Amyotrophic Lateral Sclerosis Pathogenesis Converges on Defects in Protein Homeostasis Associated with TDP-43 Mislocalization and Proteasome-Mediated Degradation Overload. Curr Top Dev Biol 2017; 121:111-171. [DOI: 10.1016/bs.ctdb.2016.07.004] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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52
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Liu QN, Xin ZZ, Chai XY, Jiang SH, Li CF, Zhang DZ, Zhou CL, Tang BP. Identification of differentially expressed genes in the spleens of polyriboinosinic polyribocytidylic acid (poly I:C)-stimulated yellow catfish Pelteobagrus fulvidraco. FISH & SHELLFISH IMMUNOLOGY 2016; 56:278-285. [PMID: 27368543 DOI: 10.1016/j.fsi.2016.06.041] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2016] [Revised: 06/16/2016] [Accepted: 06/27/2016] [Indexed: 06/06/2023]
Abstract
The yellow catfish, Pelteobagrus fulvidraco (Siluriformes: Bagridae) is an economically important fish in China. However, genomic research and resources on this species are largely unavailable and still in infancy. In the present study, we constructed a cDNA library following poly I:C injection to screen for immune response genes in the spleens of P. fulvidraco using suppression subtractive hybridization (SSH). A total of 420 putative expressed sequence tag (EST) clones were identified at 24 h post-injection, which contain 103 genes consisting of 25 immune response genes, 12 cytoskeleton genes, 7 cell cycle and apoptosis genes, 7 respiration and energy metabolism genes, 7 transport genes, 26 metabolism genes, 10 stress response genes, 9 translational regulation genes, and 71 unknown genes. Real-time quantitative reverse transcription-PCR (qRT-PCR) results revealed that a set of randomly selected immune response genes were identified to be up-regulated after 24 h of poly I:C stimulation compared to controls. Our study provides an annotation of immune genes in detail and insight into fish immunity.
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Affiliation(s)
- Qiu-Ning Liu
- Jiangsu Key Laboratory for Bioresources of Saline Soils, Jiangsu Synthetic Innovation Center for Coastal Bio-agriculture, Jiangsu Provincial Key Laboratory of Coastal Wetland Bioresources and Environmental Protection, School of Ocean and Biological Engineering, Yancheng Teachers University, Yancheng 224001, PR China
| | - Zhao-Zhe Xin
- Jiangsu Key Laboratory for Bioresources of Saline Soils, Jiangsu Synthetic Innovation Center for Coastal Bio-agriculture, Jiangsu Provincial Key Laboratory of Coastal Wetland Bioresources and Environmental Protection, School of Ocean and Biological Engineering, Yancheng Teachers University, Yancheng 224001, PR China
| | - Xin-Yue Chai
- Jiangsu Key Laboratory for Bioresources of Saline Soils, Jiangsu Synthetic Innovation Center for Coastal Bio-agriculture, Jiangsu Provincial Key Laboratory of Coastal Wetland Bioresources and Environmental Protection, School of Ocean and Biological Engineering, Yancheng Teachers University, Yancheng 224001, PR China
| | - Sen-Hao Jiang
- Jiangsu Key Laboratory for Bioresources of Saline Soils, Jiangsu Synthetic Innovation Center for Coastal Bio-agriculture, Jiangsu Provincial Key Laboratory of Coastal Wetland Bioresources and Environmental Protection, School of Ocean and Biological Engineering, Yancheng Teachers University, Yancheng 224001, PR China
| | - Chao-Feng Li
- Jiangsu Key Laboratory for Bioresources of Saline Soils, Jiangsu Synthetic Innovation Center for Coastal Bio-agriculture, Jiangsu Provincial Key Laboratory of Coastal Wetland Bioresources and Environmental Protection, School of Ocean and Biological Engineering, Yancheng Teachers University, Yancheng 224001, PR China
| | - Dai-Zhen Zhang
- Jiangsu Key Laboratory for Bioresources of Saline Soils, Jiangsu Synthetic Innovation Center for Coastal Bio-agriculture, Jiangsu Provincial Key Laboratory of Coastal Wetland Bioresources and Environmental Protection, School of Ocean and Biological Engineering, Yancheng Teachers University, Yancheng 224001, PR China
| | - Chun-Lin Zhou
- Jiangsu Key Laboratory for Bioresources of Saline Soils, Jiangsu Synthetic Innovation Center for Coastal Bio-agriculture, Jiangsu Provincial Key Laboratory of Coastal Wetland Bioresources and Environmental Protection, School of Ocean and Biological Engineering, Yancheng Teachers University, Yancheng 224001, PR China
| | - Bo-Ping Tang
- Jiangsu Key Laboratory for Bioresources of Saline Soils, Jiangsu Synthetic Innovation Center for Coastal Bio-agriculture, Jiangsu Provincial Key Laboratory of Coastal Wetland Bioresources and Environmental Protection, School of Ocean and Biological Engineering, Yancheng Teachers University, Yancheng 224001, PR China.
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53
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Gallo A, Vannier C, Galli T. Endoplasmic Reticulum-Plasma Membrane Associations:Structures and Functions. Annu Rev Cell Dev Biol 2016; 32:279-301. [PMID: 27298092 DOI: 10.1146/annurev-cellbio-111315-125024] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Inside eukaryotic cells, membrane contact sites (MCSs), regions where two membrane-bound organelles are apposed at less than 30 nm, generate regions of important lipid and calcium exchange. This review principally focuses on the structure and the function of MCSs between the endoplasmic reticulum (ER) and the plasma membrane (PM). Here we describe how tethering structures form and maintain these junctions and, in some instances, participate in their function. We then discuss recent insights into the mechanisms by which specific classes of proteins mediate nonvesicular lipid exchange between the ER and PM and how such phenomena, already known to be crucial for maintaining organelle identity, are also emerging as regulators of cell growth and development.
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Affiliation(s)
- Alessandra Gallo
- Membrane Traffic in Health & Disease Group (INSERM ERL U950), F-75013 Paris, France;
| | - Christian Vannier
- Membrane Traffic in Health & Disease Group (INSERM ERL U950), F-75013 Paris, France;
| | - Thierry Galli
- Membrane Traffic in Health & Disease Group (INSERM ERL U950), F-75013 Paris, France;
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54
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Darbyson A, Ngsee JK. Oxysterol-binding protein ORP3 rescues the Amyotrophic Lateral Sclerosis-linked mutant VAPB phenotype. Exp Cell Res 2016; 341:18-31. [PMID: 26812496 DOI: 10.1016/j.yexcr.2016.01.013] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2015] [Revised: 01/21/2016] [Accepted: 01/22/2016] [Indexed: 12/13/2022]
Abstract
A mutation in VAPB causes a familial form of Amyotrophic Lateral Sclerosis. The mutant protein (VAPB-P56S) is aggregate prone and blocks retrograde traffic from the endoplasmic reticulum (ER) Golgi intermediate compartment (ERGIC) including trafficking to the nuclear envelope (NE). Here we report a morphological screen where overexpression of oxysterol binding protein-related protein-3 (ORP3) rescued the mutant VAPB phenotype. It resolved the mutant VAPB-induced membrane expansions, restored solubility of the mutant protein in non-ionic detergent, and restored trafficking of Emerin to the NE. Knockdown of ORP3 or VAPB increased the intracellular level of phosphatidylinositol 4-phosphate (PtdIns4P). Decreasing PtdIns4P levels by inhibiting its synthesis reduced the severity of the mutant VAPB-induced membrane expansions and restored Emerin trafficking to the NE. Thus, VAPB and its interacting partners cooperatively regulate protein trafficking through the ERGIC by modulating PtdIns4P levels.
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Affiliation(s)
- Angie Darbyson
- Ottawa Hospital Research Institute Department of Cellular and Molecular Medicine, University of Ottawa, 451 Smyth Road, Ottawa, Ontario, Canada K1H 8M5
| | - Johnny K Ngsee
- Ottawa Hospital Research Institute Department of Cellular and Molecular Medicine, University of Ottawa, 451 Smyth Road, Ottawa, Ontario, Canada K1H 8M5.
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55
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Spalloni A, Longone P. Cognitive impairment in amyotrophic lateral sclerosis, clues from the SOD1 mouse. Neurosci Biobehav Rev 2016; 60:12-25. [DOI: 10.1016/j.neubiorev.2015.11.006] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2015] [Revised: 11/09/2015] [Accepted: 11/16/2015] [Indexed: 12/11/2022]
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56
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Wakana Y, Kotake R, Oyama N, Murate M, Kobayashi T, Arasaki K, Inoue H, Tagaya M. CARTS biogenesis requires VAP-lipid transfer protein complexes functioning at the endoplasmic reticulum-Golgi interface. Mol Biol Cell 2015; 26:4686-99. [PMID: 26490117 PMCID: PMC4678024 DOI: 10.1091/mbc.e15-08-0599] [Citation(s) in RCA: 207] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2015] [Accepted: 10/14/2015] [Indexed: 11/24/2022] Open
Abstract
Biogenesis of the TGN-derived transport carriers CARTS requires the ER protein VAP and Golgi lipid transfer proteins, ceramide transfer protein and OSBP. Sac1 lipid phosphatase is recruited to a VAP–OSBP complex formed at an ER subdomain closely apposed to the trans-Golgi/TGN. Association–dissociation dynamics of ER–Golgi contacts are important for CARTS formation. Vesicle-associated membrane protein–associated protein (VAP) is an endoplasmic reticulum (ER)-resident integral membrane protein that controls a nonvesicular mode of ceramide and cholesterol transfer from the ER to the Golgi complex by interacting with ceramide transfer protein and oxysterol-binding protein (OSBP), respectively. We report that VAP and its interacting proteins are required for the processing and secretion of pancreatic adenocarcinoma up-regulated factor, whose transport from the trans-Golgi network (TGN) to the cell surface is mediated by transport carriers called “carriers of the trans-Golgi network to the cell surface” (CARTS). In VAP-depleted cells, diacylglycerol level at the TGN was decreased and CARTS formation was impaired. We found that VAP forms a complex with not only OSBP but also Sac1 phosphoinositide phosphatase at specialized ER subdomains that are closely apposed to the trans-Golgi/TGN, most likely reflecting membrane contact sites. Immobilization of ER–Golgi contacts dramatically reduced CARTS production, indicating that association–dissociation dynamics of the two membranes are important. On the basis of these findings, we propose that the ER–Golgi contacts play a pivotal role in lipid metabolism to control the biogenesis of transport carriers from the TGN.
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Affiliation(s)
- Yuichi Wakana
- School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, Hachioji, Tokyo 192-0392, Japan
| | - Richika Kotake
- School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, Hachioji, Tokyo 192-0392, Japan
| | - Nanako Oyama
- School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, Hachioji, Tokyo 192-0392, Japan
| | - Motohide Murate
- Lipid Biology Laboratory, RIKEN, Wako, Saitama 351-0198, Japan
| | | | - Kohei Arasaki
- School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, Hachioji, Tokyo 192-0392, Japan
| | - Hiroki Inoue
- School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, Hachioji, Tokyo 192-0392, Japan
| | - Mitsuo Tagaya
- School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, Hachioji, Tokyo 192-0392, Japan
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57
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Larroquette F, Seto L, Gaub PL, Kamal B, Wallis D, Larivière R, Vallée J, Robitaille R, Tsuda H. Vapb/Amyotrophic lateral sclerosis 8 knock-in mice display slowly progressive motor behavior defects accompanying ER stress and autophagic response. Hum Mol Genet 2015; 24:6515-29. [PMID: 26362257 DOI: 10.1093/hmg/ddv360] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2015] [Accepted: 09/01/2015] [Indexed: 12/12/2022] Open
Abstract
Missense mutations (P56S) in Vapb are associated with autosomal dominant motor neuron diseases: amyotrophic lateral sclerosis and lower motor neuron disease. Although transgenic mice overexpressing the mutant vesicle-associated membrane protein-associated protein B (VAPB) protein with neuron-specific promoters have provided some insight into the toxic properties of the mutant proteins, their role in pathogenesis remains unclear. To identify pathological defects in animals expressing the P56S mutant VAPB protein at physiological levels in the appropriate tissues, we have generated Vapb knock-in mice replacing wild-type Vapb gene with P56S mutant Vapb gene and analyzed the resulting pathological phenotypes. Heterozygous P56S Vapb knock-in mice show mild age-dependent defects in motor behaviors as characteristic features of the disease. The homozygous P56S Vapb knock-in mice show more severe defects compared with heterozygous mice reflecting the dominant and dose-dependent effects of P56S mutation. Significantly, the knock-in mice demonstrate accumulation of P56S VAPB protein and ubiquitinated proteins in cytoplasmic inclusions, selectively in motor neurons. The mutant mice demonstrate induction of ER stress and autophagic response in motor neurons before obvious onset of behavioral defects, suggesting that these cellular biological defects might contribute to the initiation of the disease. The P56S Vapb knock-in mice could be a valuable tool to gain a better understanding of the mechanisms by which the disease arises.
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Affiliation(s)
- Frédérique Larroquette
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada H3A 2B4
| | - Lesley Seto
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada H3A 2B4
| | - Perrine L Gaub
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada H3A 2B4
| | - Brishna Kamal
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada H3A 2B4
| | - Deeann Wallis
- Department of Biochemistry and Biophysics, Texas A&M University, Cypress, TX, USA and
| | - Roxanne Larivière
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada H3A 2B4
| | - Joanne Vallée
- Departement of Neurosciences, University of Montreal, Montreal, Quebec, Canada
| | - Richard Robitaille
- Departement of Neurosciences, University of Montreal, Montreal, Quebec, Canada
| | - Hiroshi Tsuda
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada H3A 2B4,
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58
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Kentala H, Pfisterer SG, Olkkonen VM, Weber-Boyvat M. Sterol liganding of OSBP-related proteins (ORPs) regulates the subcellular distribution of ORP-VAPA complexes and their impacts on organelle structure. Steroids 2015; 99:248-58. [PMID: 25681634 DOI: 10.1016/j.steroids.2015.01.027] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/28/2014] [Revised: 01/21/2015] [Accepted: 01/22/2015] [Indexed: 01/20/2023]
Abstract
Oxysterol-binding protein (OSBP) and its homologues (ORPs) are lipid-binding/transfer proteins with affinity for oxysterols, cholesterol and glycerophospholipids. In addition to a ligand-binding domain, a majority of the ORPs carry a pleckstrin homology domain that targets organelle membranes via phosphoinositides, and a motif targeting the endoplasmic reticulum (ER) via VAMP-associated proteins (VAPs). We employed here Bimolecular Fluorescence Complementation (BiFC) to systematically assess the effects of sterol manipulation of HuH7 cells on complexes of established sterol-binding ORPs with their ER receptor, VAMP-associated protein A (VAPA). Depletion of cellular cholesterol with lipoprotein-deficient medium and Mevastatin caused concentration of OSBP-VAPA complexes and Golgi complex markers at a juxtanuclear position, an effect reversed by low-density lipoprotein treatment. A similar redistribution of OSBP-VAPA but not of sterol-binding deficient mutant OSBP(ΔELSK)-VAPA, occurred upon treatment with the high-affinity ligand, 25-hydroxycholesterol (25OHC), which reduced total and free cholesterol. ORP2-VAPA complexes, which localize in untreated cells at blob-like ER structures with associated lipid droplets, were redistributed upon treatment with the ORP2 ligand 22(R)OHC to a diffuse cytoplasmic/ER pattern and the plasma membrane. Analogously, distribution of ORP4L-VAPA complexes between the plasma membrane and vimentin intermediate filament associated compartments was modified by statin or 25OHC treatment. The treatments resulted in loss of vimentin co-localization, and sterol-binding deficient ORP4L(ΔELSR)-VAPA localized predominantly to the plasma membrane. In conclusion, treatment with statin or oxysterol ligands modify the subcellular targeting of ORP-VAPA complexes, consistent with the notion that this machinery controls lipid homeostasis and signaling at organelle interfaces.
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Affiliation(s)
- Henriikka Kentala
- Minerva Foundation Institute for Medical Research, Biomedicum 2U, FI-00290 Helsinki, Finland
| | - Simon G Pfisterer
- Institute of Biomedicine, Anatomy, FI-00014 University of Helsinki, Finland
| | - Vesa M Olkkonen
- Minerva Foundation Institute for Medical Research, Biomedicum 2U, FI-00290 Helsinki, Finland; Institute of Biomedicine, Anatomy, FI-00014 University of Helsinki, Finland
| | - Marion Weber-Boyvat
- Minerva Foundation Institute for Medical Research, Biomedicum 2U, FI-00290 Helsinki, Finland.
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59
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Weber-Boyvat M, Kentala H, Peränen J, Olkkonen VM. Ligand-dependent localization and function of ORP-VAP complexes at membrane contact sites. Cell Mol Life Sci 2015; 72:1967-87. [PMID: 25420878 PMCID: PMC11114005 DOI: 10.1007/s00018-014-1786-x] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2014] [Revised: 10/17/2014] [Accepted: 11/17/2014] [Indexed: 01/08/2023]
Abstract
Oxysterol-binding protein/OSBP-related proteins (ORPs) constitute a conserved family of sterol/phospholipid-binding proteins with lipid transporter or sensor functions. We investigated the spatial occurrence and regulation of the interactions of human OSBP/ORPs or the S. cerevisiae orthologs, the Osh (OSBP homolog) proteins, with their endoplasmic reticulum (ER) anchors, the VAMP-associated proteins (VAPs), by employing bimolecular fluorescence complementation and pull-down set-ups. The ORP-VAP interactions localize frequently at distinct subcellular sites, shown in several cases to represent membrane contact sites (MCSs). Using established ORP ligand-binding domain mutants and pull-down assays with recombinant proteins, we show that ORP liganding regulates the ORP-VAP association, alters the subcellular targeting of ORP-VAP complexes, or modifies organelle morphology. There is distinct protein specificity in the effects of the mutants on subcellular targeting of ORP-VAP complexes. We provide evidence that complexes of human ORP2 and VAPs at ER-lipid droplet interfaces regulate the hydrolysis of triglycerides and lipid droplet turnover. The data suggest evolutionarily conserved, complex ligand-dependent functions of ORP-VAP complexes at MCSs, with implications for cellular lipid homeostasis and signaling.
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Affiliation(s)
- Marion Weber-Boyvat
- Minerva Foundation Institute for Medical Research, Biomedicum 2U, Tukholmankatu 8, 00290 Helsinki, Finland
| | - Henriikka Kentala
- Minerva Foundation Institute for Medical Research, Biomedicum 2U, Tukholmankatu 8, 00290 Helsinki, Finland
| | - Johan Peränen
- Cell and Molecular Biology Program, Institute of Biotechnology, University of Helsinki, 00014 Helsinki, Finland
| | - Vesa M. Olkkonen
- Minerva Foundation Institute for Medical Research, Biomedicum 2U, Tukholmankatu 8, 00290 Helsinki, Finland
- Institute of Biomedicine, Anatomy, University of Helsinki, 00014 Helsinki, Finland
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60
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Deivasigamani S, Verma HK, Ueda R, Ratnaparkhi A, Ratnaparkhi GS. A genetic screen identifies Tor as an interactor of VAPB in a Drosophila model of amyotrophic lateral sclerosis. Biol Open 2014; 3:1127-38. [PMID: 25361581 PMCID: PMC4232771 DOI: 10.1242/bio.201410066] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Amyotrophic Lateral Sclerosis (ALS) is a progressive neurodegenerative disorder characterized by selective death of motor neurons. In 5–10% of the familial cases, the disease is inherited because of mutations. One such mutation, P56S, was identified in human VAPB that behaves in a dominant negative manner, sequestering wild type protein into cytoplasmic inclusions. We have conducted a reverse genetic screen to identify interactors of Drosophila VAPB. We screened 2635 genes and identified 103 interactors, of which 45 were enhancers and 58 were suppressors of VAPB function. Interestingly, the screen identified known ALS loci – TBPH, alsin2 and SOD1. Also identified were genes involved in cellular energetics and homeostasis which were used to build a gene regulatory network of VAPB modifiers. One key modifier identified was Tor, whose knockdown reversed the large bouton phenotype associated with VAP(P58S) expression in neurons. A similar reversal was seen by over-expressing Tuberous Sclerosis Complex (Tsc1,2) that negatively regulates TOR signaling as also by reduction of S6K activity. In comparison, the small bouton phenotype associated with VAP(wt) expression was reversed with Tsc1 knock down as well as S6K-CA expression. Tor therefore interacts with both VAP(wt) and VAP(P58S), but in a contrasting manner. Reversal of VAP(P58S) bouton phenotypes in larvae fed with the TOR inhibitor Rapamycin suggests upregulation of TOR signaling in response to VAP(P58S) expression. The VAPB network and further mechanistic understanding of interactions with key pathways, such as the TOR cassette, will pave the way for a better understanding of the mechanisms of onset and progression of motor neuron disease.
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Affiliation(s)
| | | | - Ryu Ueda
- National Institute of Genetics, Mishima, Shizuoka 411-8540, Japan
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61
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Weber-Boyvat M, Kentala H, Lilja J, Vihervaara T, Hanninen R, Zhou Y, Peränen J, Nyman TA, Ivaska J, Olkkonen VM. OSBP-related protein 3 (ORP3) coupling with VAMP-associated protein A regulates R-Ras activity. Exp Cell Res 2014; 331:278-91. [PMID: 25447204 DOI: 10.1016/j.yexcr.2014.10.019] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2014] [Revised: 10/20/2014] [Accepted: 10/21/2014] [Indexed: 12/20/2022]
Abstract
ORP3 is an R-Ras interacting oxysterol-binding protein homolog that regulates cell adhesion and is overexpressed in several cancers. We investigated here a novel function of ORP3 dependent on its targeting to both the endoplasmic reticulum (ER) and the plasma membrane (PM). Using biochemical and cell imaging techniques we demonstrate the mechanistic requirements for the subcellular targeting and function of ORP3 in control of R-Ras activity. We show that hyperphosphorylated ORP3 (ORP3-P) selectively interacts with the ER membrane protein VAPA, and ORP3-VAPA complexes are targeted to PM sites via the ORP3 pleckstrin homology (PH) domain. A novel FFAT (two phenylalanines in an acidic tract)-like motif was identified in ORP3; only disruption of both the FFAT-like and canonical FFAT motif abolished the phorbol-12-myristate-13-acetate (PMA) stimulated interaction of ORP3-P with VAPA. Co-expression of ORP3 and VAPA induced R-Ras activation, dependent on the interactions of ORP3 with VAPA and the PM. Consistently, downstream AktS473 phosphorylation and β1-integrin activity were enhanced by ORP3-VAPA. To conclude, phosphorylation of ORP3 controls its association with VAPA. Furthermore, we present evidence that ORP3-VAPA complexes stimulate R-Ras signaling.
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Affiliation(s)
- Marion Weber-Boyvat
- Minerva Foundation Institute for Medical Research, Biomedicum 2U, FI-00290 Helsinki, Finland
| | - Henriikka Kentala
- Minerva Foundation Institute for Medical Research, Biomedicum 2U, FI-00290 Helsinki, Finland
| | - Johanna Lilja
- VTT Medical Biotechnology and Turku Centre for Biotechnology, University of Turku, FI-20520 Turku, Finland
| | - Terhi Vihervaara
- Minerva Foundation Institute for Medical Research, Biomedicum 2U, FI-00290 Helsinki, Finland
| | - Raisa Hanninen
- National Institute for Health and Welfare, Biomedicum 1, FI-00290 Helsinki, Finland
| | - You Zhou
- Minerva Foundation Institute for Medical Research, Biomedicum 2U, FI-00290 Helsinki, Finland
| | - Johan Peränen
- Institute of Biotechnology, FI-00014 University of Helsinki, Finland
| | - Tuula A Nyman
- Institute of Biotechnology, FI-00014 University of Helsinki, Finland
| | - Johanna Ivaska
- VTT Medical Biotechnology and Turku Centre for Biotechnology, University of Turku, FI-20520 Turku, Finland
| | - Vesa M Olkkonen
- Minerva Foundation Institute for Medical Research, Biomedicum 2U, FI-00290 Helsinki, Finland; Institute of Biomedicine/Anatomy, FI-00014 University of Helsinki, Finland.
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62
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Sandström von Tobel J, Zoia D, Althaus J, Antinori P, Mermoud J, Pak HS, Scherl A, Monnet-Tschudi F. Immediate and delayed effects of subchronic Paraquat exposure during an early differentiation stage in 3D-rat brain cell cultures. Toxicol Lett 2014; 230:188-97. [DOI: 10.1016/j.toxlet.2014.02.001] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2013] [Revised: 01/30/2014] [Accepted: 02/02/2014] [Indexed: 11/28/2022]
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63
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Wang P, Hawkins TJ, Richardson C, Cummins I, Deeks MJ, Sparkes I, Hawes C, Hussey PJ. The plant cytoskeleton, NET3C, and VAP27 mediate the link between the plasma membrane and endoplasmic reticulum. Curr Biol 2014; 24:1397-1405. [PMID: 24909329 DOI: 10.1016/j.cub.2014.05.003] [Citation(s) in RCA: 105] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2014] [Revised: 04/04/2014] [Accepted: 05/02/2014] [Indexed: 02/03/2023]
Abstract
The cortical endoplasmic reticulum (ER) network in plants is a highly dynamic structure, and it contacts the plasma membrane (PM) at ER-PM anchor/contact sites. These sites are known to be essential for communication between the ER and PM for lipid transport, calcium influx, and ER morphology in mammalian and fungal cells. The nature of these contact sites is unknown in plants, and here, we have identified a complex that forms this bridge. This complex includes (1) NET3C, which belongs to a plant-specific superfamily (NET) of actin-binding proteins, (2) VAP27, a plant homolog of the yeast Scs2 ER-PM contact site protein, and (3) the actin and microtubule networks. We demonstrate that NET3C and VAP27 localize to puncta at the PM and that NET3C and VAP27 form homodimers/oligomers and together form complexes with actin and microtubules. We show that F-actin modulates the turnover of NET3C at these puncta and microtubules regulate the exchange of VAP27 at the same sites. Based on these data, we propose a model for the structure of the plant ER-PM contact sites.
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Affiliation(s)
- Pengwei Wang
- School of Biological and Biomedical Sciences, University of Durham, South Road, Durham DH1 3LE, UK
| | - Timothy J Hawkins
- School of Biological and Biomedical Sciences, University of Durham, South Road, Durham DH1 3LE, UK
| | - Christine Richardson
- School of Biological and Biomedical Sciences, University of Durham, South Road, Durham DH1 3LE, UK
| | - Ian Cummins
- School of Biological and Biomedical Sciences, University of Durham, South Road, Durham DH1 3LE, UK
| | - Michael J Deeks
- School of Biological and Biomedical Sciences, University of Durham, South Road, Durham DH1 3LE, UK
| | - Imogen Sparkes
- Department of Biological and Medical Sciences, Oxford Brookes University, Gipsy Lane, Headington, Oxford OX3 0BP, UK
| | - Chris Hawes
- Department of Biological and Medical Sciences, Oxford Brookes University, Gipsy Lane, Headington, Oxford OX3 0BP, UK
| | - Patrick J Hussey
- School of Biological and Biomedical Sciences, University of Durham, South Road, Durham DH1 3LE, UK.
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64
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Baron Y, Pedrioli PG, Tyagi K, Johnson C, Wood NT, Fountaine D, Wightman M, Alexandru G. VAPB/ALS8 interacts with FFAT-like proteins including the p97 cofactor FAF1 and the ASNA1 ATPase. BMC Biol 2014; 12:39. [PMID: 24885147 PMCID: PMC4068158 DOI: 10.1186/1741-7007-12-39] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2014] [Accepted: 05/12/2014] [Indexed: 11/10/2022] Open
Abstract
Background FAF1 is a ubiquitin-binding adaptor for the p97 ATPase and belongs to the UBA-UBX family of p97 cofactors. p97 converts the energy derived from ATP hydrolysis into conformational changes of the p97 hexamer, which allows the dissociation of its targets from cellular structures or from larger protein complexes to facilitate their ubiquitin-dependent degradation. VAPB and the related protein VAPA form homo- and heterodimers that are anchored in the endoplasmic reticulum membrane and can interact with protein partners carrying a FFAT motif. Mutations in either VAPB or p97 can cause amyotrophic lateral sclerosis, a neurodegenerative disorder that affects upper and lower motor neurons. Results We show that FAF1 contains a non-canonical FFAT motif that allows it to interact directly with the MSP domain of VAPB and, thereby, to mediate VAPB interaction with p97. This finding establishes a link between two proteins that can cause amyotrophic lateral sclerosis when mutated, VAPB/ALS8 and p97/ALS14. Subsequently, we identified a similar FFAT-like motif in the ASNA1 subunit of the transmembrane-domain recognition complex (TRC), which in turn mediates ASNA1 interaction with the MSP domain of VAPB. Proteasome inhibition leads to the accumulation of ubiquitinated species in VAPB immunoprecipitates and this correlates with an increase in FAF1 and p97 binding. We found that VAPB interaction with ubiquitinated proteins is strongly reduced in cells treated with FAF1 siRNA. Our efforts to determine the identity of the ubiquitinated targets common to VAPB and FAF1 led to the identification of RPN2, a subunit of an oligosaccharyl-transferase located at the endoplasmic reticulum, which may be regulated by ubiquitin-mediated degradation. Conclusions The FFAT-like motifs we identified in FAF1 and ASNA1 demonstrate that sequences containing a single phenylalanine residue with the consensus (D/E)(D/E)FEDAx(D/E) are also proficient to mediate interaction with VAPB. Our findings indicate that the repertoire of VAPB interactors is more diverse than previously anticipated and link VAPB to the function of ATPase complexes such as p97/FAF1 and ASNA1/TRC.
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Affiliation(s)
| | | | | | | | | | | | | | - Gabriela Alexandru
- Medical Research Council Protein Phosphorylation and Ubiquitylation Unit (MRC-PPU), College of Life Sciences, University of Dundee, Dow St, Dundee DD1 5EH, UK.
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Maximino JR, de Oliveira GP, Alves CJ, Chadi G. Deregulated expression of cytoskeleton related genes in the spinal cord and sciatic nerve of presymptomatic SOD1(G93A) Amyotrophic Lateral Sclerosis mouse model. Front Cell Neurosci 2014; 8:148. [PMID: 24904291 PMCID: PMC4033281 DOI: 10.3389/fncel.2014.00148] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2014] [Accepted: 05/08/2014] [Indexed: 12/11/2022] Open
Abstract
Early molecular events related to cytoskeleton are poorly described in Amyotrophic Lateral Sclerosis (ALS), especially in the Schwann cell (SC), which offers strong trophic support to motor neurons. Database for Annotation, Visualization and Integrated Discovery (DAVID) tool identified cytoskeleton-related genes by employing the Cellular Component Ontology (CCO) in a large gene profiling of lumbar spinal cord and sciatic nerve of presymptomatic SOD1(G93A) mice. One and five CCO terms related to cytoskeleton were described from the spinal cord deregulated genes of 40 days (actin cytoskeleton) and 80 days (microtubule cytoskeleton, cytoskeleton part, actin cytoskeleton, neurofilament cytoskeleton, and cytoskeleton) old transgene mice, respectively. Also, four terms were depicted from the deregulated genes of sciatic nerve of 60 days old transgenes (actin cytoskeleton, cytoskeleton part, microtubule cytoskeleton and cytoskeleton). Kif1b was the unique deregulated gene in more than one studied region or presymptomatic age. The expression of Kif1b [quantitative polymerase chain reaction (qPCR)] elevated in the lumbar spinal cord (40 days old) and decreased in the sciatic nerve (60 days old) of presymptomatic ALS mice, results that were in line to microarray findings. Upregulation (24.8 fold) of Kif1b was seen in laser microdissected enriched immunolabeled motor neurons from the spinal cord of 40 days old presymptomatic SOD1(G93A) mice. Furthermore, Kif1b was dowregulated in the sciatic nerve Schwann cells of presymptomatic ALS mice (60 days old) that were enriched by means of cell microdissection (6.35 fold), cell sorting (3.53 fold), and primary culture (2.70 fold) technologies. The gene regulation of cytoskeleton molecules is an important occurrence in motor neurons and Schwann cells in presymptomatic stages of ALS and may be relevant in the dying back mechanisms of neuronal death. Furthermore, a differential regulation of Kif1b in the spinal cord and sciatic nerve cells emerged as key event in ALS.
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Affiliation(s)
- Jessica R Maximino
- Department of Neurology, Neuroregeneration Research Center, University of São Paulo School of Medicine São Paulo, Brazil
| | - Gabriela P de Oliveira
- Department of Neurology, Neuroregeneration Research Center, University of São Paulo School of Medicine São Paulo, Brazil
| | - Chrystian J Alves
- Department of Neurology, Neuroregeneration Research Center, University of São Paulo School of Medicine São Paulo, Brazil
| | - Gerson Chadi
- Department of Neurology, Neuroregeneration Research Center, University of São Paulo School of Medicine São Paulo, Brazil
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Vinay Kumar C, Kumar KM, Swetha R, Ramaiah S, Anbarasu A. Protein aggregation due to nsSNP resulting in P56S VABP protein is associated with amyotrophic lateral sclerosis. J Theor Biol 2014; 354:72-80. [PMID: 24681403 DOI: 10.1016/j.jtbi.2014.03.027] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2014] [Revised: 03/14/2014] [Accepted: 03/16/2014] [Indexed: 12/13/2022]
Abstract
Mutations in the gene encoding vesicle-associated membrane protein (VAPB) cause amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disorder. The VAPB gene is mapped to chromosome number 20 and can be found at cytogenetic location 20q13.33 of the chromosome. VAPB is seen to play a significant role in the unfolded protein response (UPR), which is a process that suppresses the accumulation of unfolded proteins in the endoplasmic reticulum. Earlier studies have reported two points; which we have analyzed in our study. Firstly, the mutation P56S in the VAPB is seen to increase the stability of the protein and secondly, the mutation P56S in VAPB is seen to interrupt the functioning of the gene and loses its ability to be involved in the activation of the IRE1/XBP1 pathway which leads to ALS. With correlation on the previous research studies on the stability of this protein, we carried out Molecular dynamics (MD) simulation. We analyzed the SNP results of 17 nsSNPs obtained from dbSNP using SIFT, polyphen, I-Mutant, SNP&GO, PhDSNP and Mutpred to predict the role of nsSNPs in VAPB. MD simulation is carried out and plots for RMSD, RMSF, Rg, SASA, H-bond and PCA are obtained to check and prove the stability of the wild type and the mutant protein structure. The protein is checked for its aggregation and the results obtained show changes in the protein structure that might result in the loss of function.
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Affiliation(s)
- Chundi Vinay Kumar
- School of Biosciences and Technology, VIT University, Vellore 632014, Tamil Nadu, India
| | - K M Kumar
- School of Biosciences and Technology, VIT University, Vellore 632014, Tamil Nadu, India
| | - Rayapadi Swetha
- School of Biosciences and Technology, VIT University, Vellore 632014, Tamil Nadu, India
| | - Sudha Ramaiah
- School of Biosciences and Technology, VIT University, Vellore 632014, Tamil Nadu, India
| | - Anand Anbarasu
- School of Biosciences and Technology, VIT University, Vellore 632014, Tamil Nadu, India.
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Sanhueza M, Zechini L, Gillespie T, Pennetta G. Gain-of-function mutations in the ALS8 causative gene VAPB have detrimental effects on neurons and muscles. Biol Open 2014; 3:59-71. [PMID: 24326187 PMCID: PMC3892161 DOI: 10.1242/bio.20137070] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Amyotrophic Lateral Sclerosis (ALS) is a motor neuron degenerative disease characterized by a progressive, and ultimately fatal, muscle paralysis. The human VAMP-Associated Protein B (hVAPB) is the causative gene of ALS type 8. Previous studies have shown that a loss-of-function mechanism is responsible for VAPB-induced ALS. Recently, a novel mutation in hVAPB (V234I) has been identified but its pathogenic potential has not been assessed. We found that neuronal expression of the V234I mutant allele in Drosophila (DVAP-V260I) induces defects in synaptic structure and microtubule architecture that are opposite to those associated with DVAP mutants and transgenic expression of other ALS-linked alleles. Expression of DVAP-V260I also induces aggregate formation, reduced viability, wing postural defects, abnormal locomotion behavior, nuclear abnormalities, neurodegeneration and upregulation of the heat-shock-mediated stress response. Similar, albeit milder, phenotypes are associated with the overexpression of the wild-type protein. These data show that overexpressing the wild-type DVAP is sufficient to induce the disease and that DVAP-V260I is a pathogenic allele with increased wild-type activity. We propose that a combination of gain- and loss-of-function mechanisms is responsible for VAPB-induced ALS.
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Affiliation(s)
- Mario Sanhueza
- Centre for Integrative Physiology, Euan MacDonald Centre for Motor Neuron Disease Research, School of Biomedical Sciences, University of Edinburgh, Edinburgh EH8 9XD, UK
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Deidda I, Galizzi G, Passantino R, Cascio C, Russo D, Colletti T, La Bella V, Guarneri P. Expression of vesicle-associated membrane-protein-associated protein B cleavage products in peripheral blood leukocytes and cerebrospinal fluid of patients with sporadic amyotrophic lateral sclerosis. Eur J Neurol 2013; 21:478-85. [PMID: 24372953 DOI: 10.1111/ene.12334] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2013] [Accepted: 11/18/2013] [Indexed: 02/06/2023]
Abstract
BACKGROUND AND PURPOSE Vesicle-associated membrane-protein-associated protein B (VAPB) is an endoplasmic reticulum (ER) resident protein participating in ER function, vesicle trafficking, calcium homeostasis and lipid transport. Its N-terminal domain, named MSP, is cleaved and secreted, serving as an extracellular ligand. VAPB mutations are linked to autosomal-dominant motor neuron diseases, including amyotrophic lateral sclerosis (ALS) type 8. An altered VAPB function is also suspected in sporadic ALS (SALS). METHODS The expression pattern of VAPB cleavage and secreted products in the peripheral blood leukocytes (PBL) and cerebrospinal fluid (CSF) of SALS patients and neurological controls was assessed. PBL from healthy controls were also analyzed. Assays were carried out through western blotting, using an anti-VAPB (N-terminal) antibody. RESULTS Two VAPB fragments containing the MSP domain (17 kDa and 14 kDa molecular sizes) were identified in PBL of SALS and controls, with no significant differences amongst groups. In CSF, only the 14 kDa VAPB MSP fragment was expressed and a corresponding VAPA fragment was not detected. The CSF VAPB fragment was absent in 58.7% of SALS patients, of whom 79.2% were bulbar onset (P = 0.001, bulbar versus spinal). CONCLUSIONS The absence of the CSF VAPB MSP fragment from most bulbar-onset SALS patients suggests a specific alteration of brain-derived VAPB cleavage and secretion in this group of patients, and hints at a role of VAPB in the pathophysiology of this motor neuron disease.
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Affiliation(s)
- I Deidda
- Neuroscience Unit, CNR Institute of Biomedicine and Molecular Immunology, Palermo, Italy
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69
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Moustaqim-Barrette A, Lin YQ, Pradhan S, Neely GG, Bellen HJ, Tsuda H. The amyotrophic lateral sclerosis 8 protein, VAP, is required for ER protein quality control. Hum Mol Genet 2013; 23:1975-89. [PMID: 24271015 DOI: 10.1093/hmg/ddt594] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
A familial form of Amyotrophic lateral sclerosis (ALS8) is caused by a point mutation (P56S) in the vesicle-associated membrane protein associated protein B (VapB). Human VapB and Drosophila Vap-33-1 (Vap) are homologous type II transmembrane proteins that are localized to the ER. However, the precise consequences of the defects associated with the P56S mutation in the endoplasmic reticulum (ER) and its role in the pathology of ALS are not well understood. Here we show that Vap is required for ER protein quality control (ERQC). Loss of Vap in flies shows various ERQC associated defects, including protein accumulation, ER expansion, and ER stress. We also show that wild type Vap, but not the ALS8 mutant Vap, interacts with a lipid-binding protein, Oxysterol binding protein (Osbp), and that Vap is required for the proper localization of Osbp to the ER. Restoring the expression of Osbp in the ER suppresses the defects associated with loss of Vap and the ALS8 mutant Vap. Hence, we propose that the ALS8 mutation impairs the interaction of Vap with Osbp, resulting in hypomorphic defects that might contribute to the pathology of ALS8.
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Affiliation(s)
- Amina Moustaqim-Barrette
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal H3A 2B4 Canada
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Alpy F, Rousseau A, Schwab Y, Legueux F, Stoll I, Wendling C, Spiegelhalter C, Kessler P, Mathelin C, Rio MC, Levine TP, Tomasetto C. STARD3 or STARD3NL and VAP form a novel molecular tether between late endosomes and the ER. J Cell Sci 2013; 126:5500-12. [PMID: 24105263 DOI: 10.1242/jcs.139295] [Citation(s) in RCA: 172] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Inter-organelle membrane contacts sites (MCSs) are specific subcellular regions favoring the exchange of metabolites and information. We investigated the potential role of the late-endosomal membrane-anchored proteins StAR related lipid transfer domain-3 (STARD3) and STARD3 N-terminal like (STARD3NL) in the formation of MCSs involving late-endosomes (LEs). We demonstrate that both STARD3 and STARD3NL create MCSs between LEs and the endoplasmic reticulum (ER). STARD3 and STARD3NL use a conserved two phenylalanines in an acidic tract (FFAT)-motif to interact with ER-anchored VAP proteins. Together, they form an LE-ER tethering complex allowing heterologous membrane apposition. This LE-ER tethering complex affects organelle dynamics by altering the formation of endosomal tubules. An in situ proximity ligation assay between STARD3, STARD3NL and VAP proteins identified endogenous LE-ER MCS. Thus, we report here the identification of proteins involved in inter-organellar interaction.
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Affiliation(s)
- Fabien Alpy
- Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Functional Genomics and Cancer Department, 1 rue Laurent Fries, Illkirch, 67404, France
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Ingre C, Pinto S, Birve A, Press R, Danielsson O, de Carvalho M, Guđmundsson G, Andersen PM. No association between VAPB mutations and familial or sporadic ALS in Sweden, Portugal and Iceland. Amyotroph Lateral Scler Frontotemporal Degener 2013; 14:620-7. [PMID: 23971766 DOI: 10.3109/21678421.2013.822515] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Linkage analysis in Brazilian families with amyotrophic lateral sclerosis (ALS) revealed that a missense mutation p.Pro56Ser in a conserved gene VAMP-associated protein type B and C (VAPB) cosegregates with disease. Blood samples were studied from 973 Swedish, 126 Portuguese and 19 Icelandic ALS patients, and from 644 control subjects. We identified five VAPB mutations, two of which are novel, in 14 Swedish ALS patients and in nine control individuals from Sweden and Portugal. The 14 patients with VAPB mutations all carried a diagnosis of sporadic ALS. Mutations were also found in healthy adult relatives. The p.Asp130Glu VAPB mutation was also found in two patients from an Icelandic ALS family, but the mutation did not cosegregate with disease. All patients were instead found to be heterozygous for a p.Gly93Ser SOD1 mutation. There were no clinical differences between them, suggesting that the p.Asp130Glu VAPB mutation is unrelated to the disease process. In conclusion, the VAPB mutations were as frequent in control individuals as in patients. This observation, in combination with the finding of several healthy relatives carrying the VAPB mutations and no ancestors with ALS disease, suggests that it is unlikely that these VAPB mutations are pathogenic.
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Affiliation(s)
- Caroline Ingre
- Department of Pharmacology and Clinical Neuroscience, Umeå University , Umeå
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Aliaga L, Lai C, Yu J, Chub N, Shim H, Sun L, Xie C, Yang WJ, Lin X, O'Donovan MJ, Cai H. Amyotrophic lateral sclerosis-related VAPB P56S mutation differentially affects the function and survival of corticospinal and spinal motor neurons. Hum Mol Genet 2013; 22:4293-305. [PMID: 23771029 DOI: 10.1093/hmg/ddt279] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The substitution of Proline with Serine at residue 56 (P56S) of vesicle-associated membrane protein-associated protein B (VAPB) has been linked to an atypical autosomal dominant form of familial amyotrophic lateral sclerosis 8 (ALS8). To investigate the pathogenic mechanism of P56S VAPB in ALS, we generated transgenic (Tg) mice that heterologously express human wild-type (WT) and P56S VAPB under the control of a pan-neuronal promoter Thy1.2. While WT VAPB Tg mice did not exhibit any overt motor behavioral phenotypes, P56S VAPB Tg mice developed progressive hyperactivities and other motor abnormalities. VAPB protein was accumulated as large punctate in the soma and proximal dendrites of both corticospinal motor neurons (CSMNs) and spinal motor neurons (SMNs) in P56S VAPB Tg mice. Concomitantly, a significant increase of endoplasmic reticulum stress and unfolded protein response and the resulting up-regulation of pro-apoptotic factor CCAAT/enhancer-binding protein homologous protein expression were observed in the CSMNs and SMNs of P56S VAPB Tg mice. However, only a progressive loss of CSMNs but not SMNs was found in P56S VAPB Tg mice. In SMNs, P56S VAPB promoted a rather selective translocation of VAPB protein onto the postsynaptic site of C-boutons that altered the morphology of C-boutons and impaired the spontaneous rhythmic discharges of SMNs. Therefore, these findings provide new pathophysiological mechanisms of P56S VAPB that differentially affect the function and survival of CSMNs and SMNs in ALS8.
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Affiliation(s)
- Leonardo Aliaga
- Transgenics Section, Laboratory of Neurogenetics, National Institute on Aging, Bethesda, MD 20892, USA and
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Kuijpers M, van Dis V, Haasdijk ED, Harterink M, Vocking K, Post JA, Scheper W, Hoogenraad CC, Jaarsma D. Amyotrophic lateral sclerosis (ALS)-associated VAPB-P56S inclusions represent an ER quality control compartment. Acta Neuropathol Commun 2013; 1:24. [PMID: 24252306 PMCID: PMC3893532 DOI: 10.1186/2051-5960-1-24] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2013] [Accepted: 06/01/2013] [Indexed: 12/14/2022] Open
Abstract
BACKGROUND Protein aggregation and the formation of intracellular inclusions are a central feature of many neurodegenerative disorders, but precise knowledge about their pathogenic role is lacking in most instances. Here we have characterized inclusions formed in transgenic mice carrying the P56S mutant form of VAPB that causes various motor neuron syndromes including ALS8. RESULTS Inclusions in motor neurons of VAPB-P56S transgenic mice are characterized by the presence of smooth ER-like tubular profiles, and are immunoreactive for factors that operate in the ER associated degradation (ERAD) pathway, including p97/VCP, Derlin-1, and the ER membrane chaperone BAP31. The presence of these inclusions does not correlate with signs of axonal and neuronal degeneration, and axotomy leads to their gradual disappearance, indicating that they represent reversible structures. Inhibition of the proteasome and knockdown of the ER membrane chaperone BAP31 increased the size of mutant VAPB inclusions in primary neuron cultures, while knockdown of TEB4, an ERAD ubiquitin-protein ligase, reduced their size. Mutant VAPB did not codistribute with mutant forms of seipin that are associated with an autosomal dominant motor neuron disease, and accumulate in a protective ER derived compartment termed ERPO (ER protective organelle) in neurons. CONCLUSIONS The data indicate that the VAPB-P56S inclusions represent a novel reversible ER quality control compartment that is formed when the amount of mutant VAPB exceeds the capacity of the ERAD pathway and that isolates misfolded and aggregated VAPB from the rest of the ER. The presence of this quality control compartment reveals an additional level of flexibility of neurons to cope with misfolded protein stress in the ER.
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Kuijpers M, Yu KL, Teuling E, Akhmanova A, Jaarsma D, Hoogenraad CC. The ALS8 protein VAPB interacts with the ER-Golgi recycling protein YIF1A and regulates membrane delivery into dendrites. EMBO J 2013; 32:2056-72. [PMID: 23736259 DOI: 10.1038/emboj.2013.131] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2012] [Accepted: 05/07/2013] [Indexed: 02/06/2023] Open
Abstract
The vesicle-associated membrane protein (VAMP) associated protein B (VAPB) is an integral membrane protein localized to the endoplasmic reticulum (ER). The P56S mutation in VAPB has been linked to motor neuron degeneration in amyotrophic lateral sclerosis type 8 (ALS8) and forms ER-like inclusions in various model systems. However, the role of wild-type and mutant VAPB in neurons is poorly understood. Here, we identified Yip1-interacting factor homologue A (YIF1A) as a new VAPB binding partner and important component in the early secretory pathway. YIF1A interacts with VAPB via its transmembrane regions, recycles between the ER and Golgi and is mainly localized to the ER-Golgi intermediate compartments (ERGICs) in rat hippocampal neurons. VAPB strongly affects the distribution of YIF1A and is required for intracellular membrane trafficking into dendrites and normal dendritic morphology. When VAPB-P56S is present, YIF1A is recruited to the VAPB-P56S clusters and loses its ERGIC localization. These data suggest that both VAPB and YIF1A are important for ER-to-Golgi transport and that missorting of YIF1A may contribute to VAPB-associated motor neuron disease.
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Affiliation(s)
- Marijn Kuijpers
- Division of Cell Biology, Department of Biology, Faculty of Science, Utrecht University, Utrecht, The Netherlands
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New putative chloroplast vesicle transport components and cargo proteins revealed using a bioinformatics approach: an Arabidopsis model. PLoS One 2013; 8:e59898. [PMID: 23573218 PMCID: PMC3613420 DOI: 10.1371/journal.pone.0059898] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2012] [Accepted: 02/19/2013] [Indexed: 11/23/2022] Open
Abstract
Proteins and lipids are known to be transported to targeted cytosolic compartments in vesicles. A similar system in chloroplasts is suggested to transfer lipids from the inner envelope to the thylakoids. However, little is known about both possible cargo proteins and the proteins required to build a functional vesicle transport system in chloroplasts. A few components have been suggested, but only one (CPSAR1) has a verified location in chloroplast vesicles. This protein is localized in the donor membrane (envelope) and vesicles, but not in the target membrane (thylakoids) suggesting it plays a similar role to a cytosolic homologue, Sar1, in the secretory pathway. Thus, we hypothesized that there may be more similarities, in addition to lipid transport, between the vesicle transport systems in the cytosol and chloroplast, i.e. similar vesicle transport components, possible cargo proteins and receptors. Therefore, using a bioinformatics approach we searched for putative chloroplast components in the model plant Arabidopsis thaliana, corresponding mainly to components of the cytosolic vesicle transport system that may act in coordination with previously proposed COPII chloroplast homologues. We found several additional possible components, supporting the notion of a fully functional vesicle transport system in chloroplasts. Moreover, we found motifs in thylakoid-located proteins similar to those of COPII vesicle cargo proteins, supporting the hypothesis that chloroplast vesicles may transport thylakoid proteins from the envelope to the thylakoid membrane. Several putative cargo proteins are involved in photosynthesis, thus we propose the existence of a novel thylakoid protein pathway that is important for construction and maintenance of the photosynthetic machinery.
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Qin H, Wang W, Song J. ALS-causing P56S mutation and splicing variation on the hVAPB MSP domain transform its β-sandwich fold into lipid-interacting helical conformations. Biochem Biophys Res Commun 2013; 431:398-403. [DOI: 10.1016/j.bbrc.2013.01.039] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2013] [Accepted: 01/07/2013] [Indexed: 10/27/2022]
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VAMP-associated protein B (VAPB) promotes breast tumor growth by modulation of Akt activity. PLoS One 2012; 7:e46281. [PMID: 23049696 PMCID: PMC3462209 DOI: 10.1371/journal.pone.0046281] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2012] [Accepted: 08/28/2012] [Indexed: 12/31/2022] Open
Abstract
VAPB (VAMP- associated protein B) is an ER protein that regulates multiple biological functions. Although aberrant expression of VAPB is associated with breast cancer, its function in tumor cells is poorly understood. In this report, we provide evidence that VAPB regulates breast tumor cell proliferation and AKT activation. VAPB protein expression is elevated in primary and metastatic tumor specimens, and VAPB mRNA expression levels correlated negatively with patient survival in two large breast tumor datasets. Overexpression of VAPB in mammary epithelial cells increased cell growth, whereas VAPB knockdown in tumor cells inhibited cell proliferation in vitro and suppressed tumor growth in orthotopic mammary gland allografts. The growth regulation of mammary tumor cells controlled by VAPB appears to be mediated, at least in part, by modulation of AKT activity. Overexpression of VAPB in MCF10A-HER2 cells enhances phosphorylation of AKT. In contrast, knockdown of VAPB in MMTV-Neu tumor cells inhibited pAKT levels. Pharmacological inhibition of AKT significantly reduced three-dimensional spheroid growth induced by VAPB. Collectively, the genetic, functional and mechanistic analyses suggest a role of VAPB in tumor promotion in human breast cancer.
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Goyal S, Gupta G, Qin H, Upadya MH, Tan YJ, Chow VTK, Song J. VAPC, an human endogenous inhibitor for hepatitis C virus (HCV) infection, is intrinsically unstructured but forms a "fuzzy complex" with HCV NS5B. PLoS One 2012; 7:e40341. [PMID: 22815741 PMCID: PMC3398895 DOI: 10.1371/journal.pone.0040341] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2012] [Accepted: 06/04/2012] [Indexed: 01/11/2023] Open
Abstract
Nearly 200 million people are infected by hepatitis C virus (HCV) worldwide. For replicating the HCV genome, the membrane-associated machinery needs to be formed by both HCV non-structural proteins (including NS5B) and human host factors such as VAPB. Recently, the 99-residue VAPC, a splicing variant of VAPB, was demonstrated to inhibit HCV replication via binding to NS5B, thus acting as an endogenous inhibitor of HCV infection. So far, the structure of VAPC remains unknown, and its interaction with NS5B has not been biophysically characterized. In this study, we conducted extensive CD and NMR investigations on VAPC which led to several striking findings: 1) although the N-terminal 70 residues are identical in VAPC and VAPB, they constitute the characteristic β-barrel MSP fold in VAPB, while VAPC is entirely unstructured in solution, only with helical-like conformations weakly populated. 2) VAPC is indeed capable of binding to NS5B, with an average dissociation constant (Kd) of ∼20 µM. Intriguingly, VAPC remains dynamic even in the complex, suggesting that the VAPC-NS5B is a “fuzzy complex”. 3) NMR mapping revealed that the major binding region for NS5B is located over the C-terminal half of VAPC, which is composed of three discrete clusters, of which only the first contains the region identical in VAPC and VAPB. The second region containing ∼12 residues appears to play a key role in binding since mutation of 4 residues within this region leads to almost complete loss of the binding activity. 4) A 14-residue mimetic, VAPC-14 containing the second region, only has a ∼3-fold reduction of the affinity. Our study not only provides critical insights into how a human factor mediates the formation of the HCV replication machinery, but also leads to design of VAPC-14 which may be further used to explore the function of VAPC and to develop anti-HCV molecules.
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Affiliation(s)
- Shaveta Goyal
- Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Republic of Singapore
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79
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Gupta G, Qin H, Song J. Intrinsically unstructured domain 3 of hepatitis C Virus NS5A forms a "fuzzy complex" with VAPB-MSP domain which carries ALS-causing mutations. PLoS One 2012; 7:e39261. [PMID: 22720086 PMCID: PMC3374797 DOI: 10.1371/journal.pone.0039261] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2012] [Accepted: 05/22/2012] [Indexed: 01/26/2023] Open
Abstract
Hepatitis C virus (HCV) affects nearly 200 million people worldwide and is a leading factor for serious chronic liver diseases. For replicating HCV genome, the membrane-associated replication machinery needs to be formed by both HCV non-structural proteins including NS5A and human host factors. Recently NS5A has been identified to bind ER-anchored human VAP proteins and consequently this interaction may serve as a novel target for design of anti-HCV drugs. So far no biophysical characterization of this interaction has been reported. Here, we dissected the 243-residue VAPB into 4 and 447-residue NS5A into 10 fragments, followed by CD and NMR characterization of their structural properties. Subsequently, binding interactions between these fragments have been extensively assessed by NMR HSQC titration which is very powerful in detecting even very weak binding. The studies lead to three important findings: 1). a "fuzzy complex" is formed between the intrinsically-unstructured third domain (D3) of NS5A and the well-structured MSP domain of VAPB, with an average dissociation constant (Kd) of ~5 µM. 2). The binding-important residues on both NS5A-D3 and VAPB-MSP have been successfully mapped out, which provided experimental constraints for constructing the complex structure. In the complex, unstructured D3 binds to three surface pockets on one side of the MSP structure. Interestingly, two ALS-causing mutations T46I and P56S are also located on the D3-MSP interface. Moreover, NS5A-D3, FFAT-containing proteins and EphA4 appear to have overlapped binding interfaces on the MSP domain. 3). NS5A-D3 has been experimentally confirmed to competes with EphA4 in binding to the MSP domain, and T46I mutation of MSP dramatically abolishes its binding ability to D3. Our study not only provides essential foundation for further deciphering structure and function of the HCV replication machinery, but may also shed light on rationalizing a recent observation that a chronic HCV patient surprisingly developed ALS-like syndrome.
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Affiliation(s)
- Garvita Gupta
- Department of Biological Sciences, Faculty of Science, National University of Singapore, Singapore, Republic of Singapore
| | - Haina Qin
- Department of Biological Sciences, Faculty of Science, National University of Singapore, Singapore, Republic of Singapore
| | - Jianxing Song
- Department of Biological Sciences, Faculty of Science, National University of Singapore, Singapore, Republic of Singapore
- Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Republic of Singapore
- * E-mail:
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80
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Moriishi K, Matsuura Y. Exploitation of lipid components by viral and host proteins for hepatitis C virus infection. Front Microbiol 2012; 3:54. [PMID: 22347882 PMCID: PMC3278987 DOI: 10.3389/fmicb.2012.00054] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2011] [Accepted: 01/31/2012] [Indexed: 12/13/2022] Open
Abstract
Hepatitis C virus (HCV), which is a major causative agent of blood-borne hepatitis, has chronically infected about 170 million individuals worldwide and leads to chronic infection, resulting in development of steatosis, cirrhosis, and eventually hepatocellular carcinoma. Hepatocellular carcinoma associated with HCV infection is not only caused by chronic inflammation, but also by the biological activity of HCV proteins. HCV core protein is known as a main component of the viral nucleocapsid. It cooperates with host factors and possesses biological activity causing lipid alteration, oxidative stress, and progression of cell growth, while other viral proteins also interact with host proteins including molecular chaperones, membrane-anchoring proteins, and enzymes associated with lipid metabolism to maintain the efficiency of viral replication and production. HCV core protein is localized on the surface of lipid droplets in infected cells. However, the role of lipid droplets in HCV infection has not yet been elucidated. Several groups recently reported that other viral proteins also support viral infection by regulation of lipid droplets and core localization in infected cells. Furthermore, lipid components are required for modification of host factors and the intracellular membrane to maintain or up-regulate viral replication. In this review, we summarize the current status of knowledge regarding the exploitation of lipid components by viral and host proteins in HCV infection.
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Affiliation(s)
- Kohji Moriishi
- Department of Microbiology, Faculty of Medicine, University of Yamanashi Chuo-shi, Yamanashi, Japan
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81
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Lacomble S, Vaughan S, Deghelt M, Moreira-Leite FF, Gull K. A Trypanosoma brucei protein required for maintenance of the flagellum attachment zone and flagellar pocket ER domains. Protist 2011; 163:602-15. [PMID: 22186015 PMCID: PMC3405529 DOI: 10.1016/j.protis.2011.10.010] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2011] [Revised: 10/31/2011] [Accepted: 10/31/2011] [Indexed: 01/24/2023]
Abstract
Trypanosomes and Leishmanias are important human parasites whose cellular architecture is centred on the single flagellum. In trypanosomes, this flagellum is attached to the cell along a complex flagellum attachment zone (FAZ), comprising flagellar and cytoplasmic components, the integrity of which is required for correct cell morphogenesis and division. The cytoplasmic FAZ cytoskeleton is conspicuously associated with a sheet of endoplasmic reticulum termed the ‘FAZ ER’. In the present work, 3D electron tomography of bloodstream form trypanosomes was used to clarify the nature of the FAZ ER. We also identified TbVAP, a T. brucei protein whose knockdown by RNAi in procyclic form cells leads to a dramatic reduction in the FAZ ER, and in the ER associated with the flagellar pocket. TbVAP is an orthologue of VAMP-associated proteins (VAPs), integral ER membrane proteins whose mutation in humans has been linked to familial motor neuron disease. The localisation of tagged TbVAP and the phenotype of TbVAP RNAi in procyclic form trypanosomes are consistent with a function for TbVAP in the maintenance of sub-populations of the ER associated with the FAZ and the flagellar pocket. Nevertheless, depletion of TbVAP did not affect cell viability or cell cycle progression.
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Affiliation(s)
- Sylvain Lacomble
- Sir William Dunn School of Pathology, University of Oxford, Oxford OX1 3RE, United Kingdom
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82
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Lua S, Qin H, Lim L, Shi J, Gupta G, Song J. Structural, stability, dynamic and binding properties of the ALS-causing T46I mutant of the hVAPB MSP domain as revealed by NMR and MD simulations. PLoS One 2011; 6:e27072. [PMID: 22069488 PMCID: PMC3206076 DOI: 10.1371/journal.pone.0027072] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2011] [Accepted: 10/09/2011] [Indexed: 12/31/2022] Open
Abstract
T46I is the second mutation on the hVAPB MSP domain which was recently identified from non-Brazilian kindred to cause a familial amyotrophic lateral sclerosis (ALS). Here using CD, NMR and molecular dynamics (MD) simulations, we characterized the structure, stability, dynamics and binding capacity of the T46I-MSP domain. The results reveal: 1) unlike P56S which we previously showed to completely eliminate the native MSP structure, T46I leads to no significant disruption of the native secondary and tertiary structures, as evidenced from its far-UV CD spectrum, as well as Cα and Cβ NMR chemical shifts. 2) Nevertheless, T46I does result in a reduced thermodynamic stability and loss of the cooperative urea-unfolding transition. As such, the T46I-MSP domain is more prone to aggregation than WT at high protein concentrations and temperatures in vitro, which may become more severe in the crowded cellular environments. 3) T46I only causes a 3-fold affinity reduction to the Nir2 peptide, but a significant elimination of its binding to EphA4. 4) EphA4 and Nir2 peptide appear to have overlapped binding interfaces on the MSP domain, which strongly implies that two signaling networks may have a functional interplay in vivo. 5) As explored by both H/D exchange and MD simulations, the MSP domain is very dynamic, with most loop residues and many residues on secondary structures highly fluctuated or/and exposed to bulk solvent. Although T46I does not alter overall dynamics, it does trigger increased dynamics of several local regions of the MSP domain which are implicated in binding to EphA4 and Nir2 peptide. Our study provides the structural and dynamic understanding of the T46I-causing ALS; and strongly highlights the possibility that the interplay of two signaling networks mediated by the FFAT-containing proteins and Eph receptors may play a key role in ALS pathogenesis.
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Affiliation(s)
- Shixiong Lua
- Department of Biological Sciences, Faculty of Science, National University of Singapore, Singapore, Singapore
| | - Haina Qin
- Department of Biological Sciences, Faculty of Science, National University of Singapore, Singapore, Singapore
| | - Liangzhong Lim
- Department of Biological Sciences, Faculty of Science, National University of Singapore, Singapore, Singapore
| | - Jiahai Shi
- Department of Biological Sciences, Faculty of Science, National University of Singapore, Singapore, Singapore
| | - Garvita Gupta
- Department of Biological Sciences, Faculty of Science, National University of Singapore, Singapore, Singapore
| | - Jianxing Song
- Department of Biological Sciences, Faculty of Science, National University of Singapore, Singapore, Singapore
- Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
- * E-mail:
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83
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Mitne-Neto M, Machado-Costa M, Marchetto MCN, Bengtson MH, Joazeiro CA, Tsuda H, Bellen HJ, Silva HCA, Oliveira ASB, Lazar M, Muotri AR, Zatz M. Downregulation of VAPB expression in motor neurons derived from induced pluripotent stem cells of ALS8 patients. Hum Mol Genet 2011; 20:3642-52. [PMID: 21685205 PMCID: PMC3159551 DOI: 10.1093/hmg/ddr284] [Citation(s) in RCA: 167] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Amyotrophic lateral sclerosis (ALS) is an incurable neuromuscular disease that leads to a profound loss of life quality and premature death. Around 10% of the cases are inherited and ALS8 is an autosomal dominant form of familial ALS caused by mutations in the vamp-associated protein B/C (VAPB) gene. The VAPB protein is involved in many cellular processes and it likely contributes to the pathogenesis of other forms of ALS besides ALS8. A number of successful drug tests in ALS animal models could not be translated to humans underscoring the need for novel approaches. The induced pluripotent stem cells (iPSC) technology brings new hope, since it can be used to model and investigate diseases in vitro. Here we present an additional tool to study ALS based on ALS8-iPSC. Fibroblasts from ALS8 patients and their non-carrier siblings were successfully reprogrammed to a pluripotent state and differentiated into motor neurons. We show for the first time that VAPB protein levels are reduced in ALS8-derived motor neurons but, in contrast to over-expression systems, cytoplasmic aggregates could not be identified. Our results suggest that optimal levels of VAPB may play a central role in the pathogenesis of ALS8, in agreement with the observed reduction of VAPB in sporadic ALS.
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Affiliation(s)
- Miguel Mitne-Neto
- University of California San Diego, School of Medicine, Department of Pediatrics/Rady Children’s Hospital San Diego, Department of Cellular & Molecular Medicine, Stem Cell Program, 9500 Gilman Dr, La Jolla, CA 92093, MC 0695, USA
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84
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Gkogkas C, Wardrope C, Hannah M, Skehel P. The ALS8-associated mutant VAPB(P56S) is resistant to proteolysis in neurons. J Neurochem 2011; 117:286-94. [PMID: 21275991 DOI: 10.1111/j.1471-4159.2011.07201.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
VAMP/synaptobrevin associated proteins A and B (VAPA and VAPB), are type IV membrane proteins enriched on ER and Golgi membranes. Both VAPA and B interact with cytoplasmic lipid transport proteins and cytoskeletal elements to maintain the structure and composition of ER and Golgi membranes. Truncated forms of both proteins are present in some tissues but the functional significance of this is not clear. In rodents processing of VAPA occurs in most tissues, however, truncated forms of VAPB have only been reported in brain tissue. It is demonstrated here that the extent of VAPB processing in rat increases during postnatal development and that it is restricted to neurons. The C-terminal polypeptide generated by this cleavage reaction remains associated with cell membranes, but its subcellular distribution is distinct from the full-length protein. A mutant form of VAPB is associated with a familial form of neurodegenerative disease, amyotrophic lateral sclerosis type 8. The mutant protein, VAPB(P56S) , is resistant to truncation in primary neuronal cultures, although remains sensitive to some form of proteolysis when over-expressed in HEK293 cells. These data suggest that neuronal cells have a particular requirement for VAPB proteolysis and that reduced levels of processed polypeptides may contribute to the neurodegeneration associated with amyotrophic lateral sclerosis type 8.
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Affiliation(s)
- Christos Gkogkas
- Centre for Integrative Physiology, The University of Edinburgh, Edinburgh, UK
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85
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Vu HT, Ondar UN, Soldatova OP. Expression of new mutant alleles of AS1 and AS2 genes controlling leaf morphogenesis in Arabidopsis thaliana. Russ J Dev Biol 2011. [DOI: 10.1134/s1062360408010037] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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86
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Nakamichi S, Yamanaka K, Suzuki M, Watanabe T, Kagiwada S. Human VAPA and the yeast VAP Scs2p with an altered proline distribution can phenocopy amyotrophic lateral sclerosis-associated VAPB(P56S). Biochem Biophys Res Commun 2010; 404:605-9. [PMID: 21144830 DOI: 10.1016/j.bbrc.2010.12.011] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2010] [Accepted: 12/02/2010] [Indexed: 10/18/2022]
Abstract
A human isoform of the vesicle-associated membrane protein-associated proteins (VAPs), VAPB, causes amyotrophic lateral sclerosis eight due to the missense mutation of Pro-56, whereas human VAPA and the yeast VAP Scs2p proteins are not significantly affected by similar mutations. We have found that VAPA and Scs2p have three prolines present in a conserved region however VAPB has only two prolines in this region. Consequently, this mutation in VAPB (VAPB(P56S)) leaves a single proline in this region whereas other VAPs can retain two proline residues even if the proline equivalent to the Pro-56 is substituted. When Scs2p and VAPA were mutated to be equivalent to VAPB(P56S) in terms of the distribution of proline residues in this region, Scs2p became inactive and aggregated, and VAPA localize to membranous aggregates indistinguishable from those induced by VAPB(P56S). This suggests that the appropriate distribution of three conserved prolines, not the existence of a particular proline, confers VAPA and Scs2p resistance to the Pro-56 mutation and, therefore, is critical for VAP activities.
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Affiliation(s)
- Shoko Nakamichi
- Department of Biological Science and Environment, Graduate School of Humanities and Sciences, Nara Women's University, Nara 630-8506, Japan
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87
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Markaki M, Tavernarakis N. Modeling human diseases in Caenorhabditis elegans. Biotechnol J 2010; 5:1261-76. [PMID: 21154667 DOI: 10.1002/biot.201000183] [Citation(s) in RCA: 139] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2010] [Revised: 10/22/2010] [Accepted: 10/25/2010] [Indexed: 01/15/2023]
Abstract
Genes linked to human diseases often function in evolutionarily conserved pathways, which can be readily dissected in simple model organisms. Because of its short lifespan and well-known biology, coupled with a completely sequenced genome that shares extensive homology with that of mammals, Caenorhabditis elegans is one of the most versatile and powerful model organisms. Research in C. elegans has been instrumental for the elucidation of molecular pathways implicated in many human diseases. In this review, we introduce C. elegans as a model organism for biomedical research and we survey recent relevant findings that shed light on the basic molecular determinants of human disease pathophysiology. The nematode holds promise of providing clear leads towards the identification of potential targets for the development of new therapeutic interventions against human diseases.
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Affiliation(s)
- Maria Markaki
- Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology-Hellas, N. Plastira 100, Vassilika Vouton, Heraklion, Crete, Greece
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88
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Han SM, Cottee PA, Miller MA. Sperm and oocyte communication mechanisms controlling C. elegans fertility. Dev Dyn 2010; 239:1265-81. [PMID: 20034089 DOI: 10.1002/dvdy.22202] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
During sexual reproduction in many species, sperm and oocyte secrete diffusible signaling molecules to help orchestrate the biological symphony of fertilization. In the Caenorhabditis elegans gonad, bidirectional signaling between sperm and oocyte is important for guiding sperm to the fertilization site and inducing oocyte maturation. The molecular mechanisms that regulate sperm guidance and oocyte maturation are being delineated. Unexpectedly, these mechanisms are providing insight into human diseases, such as amyotrophic lateral sclerosis, spinal muscular atrophy, and cancer. Here we review sperm and oocyte communication in C. elegans and discuss relationships to human disorders.
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Affiliation(s)
- Sung Min Han
- Department of Cell Biology, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA
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89
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Suzuki H, Kanekura K, Levine TP, Kohno K, Olkkonen VM, Aiso S, Matsuoka M. ALS-linked P56S-VAPB, an aggregated loss-of-function mutant of VAPB, predisposes motor neurons to ER stress-related death by inducing aggregation of co-expressed wild-type VAPB. J Neurochem 2010. [DOI: 10.1111/j.0022-3042.2008.05857.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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90
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Functional implications of sterol transport by the oxysterol-binding protein gene family. Biochem J 2010; 429:13-24. [PMID: 20545625 DOI: 10.1042/bj20100263] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Cholesterol and its numerous oxygenated derivatives (oxysterols) profoundly affect the biophysical properties of membranes, and positively and negatively regulate sterol homoeostasis through interaction with effector proteins. As the bulk of cellular sterols are segregated from the sensory machinery that controls homoeostatic responses, an important regulatory step involves sterol transport or signalling between membrane compartments. Evidence for rapid, energy-independent transport between organelles has implicated transport proteins, such as the eukaryotic family of OSBP (oxysterol-binding protein)/ORPs (OSBP-related proteins). Since the founding member of this family was identified more than 25 years ago, accumulated evidence has implicated OSBP/ORPs in sterol signalling and/or sterol transport functions. However, recent evidence of sterol transfer activity by OSBP/ORPs suggests that other seemingly disparate functions could be the result of alterations in membrane sterol distribution or ancillary to this primary activity.
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91
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Vesicle associated membrane protein B (VAPB) is decreased in ALS spinal cord. Neurobiol Aging 2010; 31:969-85. [DOI: 10.1016/j.neurobiolaging.2008.07.005] [Citation(s) in RCA: 105] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2008] [Revised: 07/02/2008] [Accepted: 07/03/2008] [Indexed: 11/21/2022]
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92
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Shi J, Lua S, Tong JS, Song J. Elimination of the native structure and solubility of the hVAPB MSP domain by the Pro56Ser mutation that causes amyotrophic lateral sclerosis. Biochemistry 2010; 49:3887-97. [PMID: 20377183 DOI: 10.1021/bi902057a] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The Pro56Ser mutation in the human VAPB MSP domain causes a familial amyotrophic lateral sclerosis. Here we present the first structural investigation of both wild-type and Pro56Ser mutant MSP domains. The results reveal that the wild-type MSP domain is well-folded at neutral pH but can undergo acid-induced unfolding reversibly. It has a thermodynamic stability energy (DeltaG degrees (N-U)) of 7.40 kcal/mol and is also active in binding to a Nir2 peptide with a K(D) of 0.65 muM. Further determination of its crystal structure reveals that it adopts a seven-strand immunoglobulin-like beta sandwich in which Pro56 adopts the unusual cis-peptide bond conformation that appears to be critical in maintaining the characteristic S-shaped loop. Markedly, the Pro56Ser mutation renders the MSP domain insoluble in buffer. Nevertheless, as facilitated by our recent discovery that "insoluble proteins" can be solubilized in salt-free water, we have successfully characterized the residue-specific conformation of the Pro56Ser mutant by CD and heteronuclear NMR spectroscopy. The Pro56Ser mutant remains lacking of the native tight packing and secondary structures under various conditions and was further characterized as having a non-native helical conformation weakly populated at pH 3.5. Intriguingly, Pro12 located in another S-shaped loop also adopts the cis-peptide bond conformation, and its mutation to Ser is able to make the MSP domain highly insoluble and unfolded like the Pro56Ser mutant. Our study thus implies that the Pro56Ser mutation might lead to ALS by eliminating the native MSP structure, which consequently leads to aggregation and loss of functions under physiological conditions.
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Affiliation(s)
- Jiahai Shi
- Department of Biological Sciences, Faculty of Science, National University of Singapore, Singapore
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93
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Sengupta S, Miller KK, Homma K, Edge R, Cheatham MA, Dallos P, Zheng J. Interaction between the motor protein prestin and the transporter protein VAPA. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2010; 1803:796-804. [PMID: 20359505 DOI: 10.1016/j.bbamcr.2010.03.017] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/12/2009] [Revised: 03/19/2010] [Accepted: 03/23/2010] [Indexed: 01/25/2023]
Abstract
Prestin is the motor protein responsible for cochlear outer hair cell (OHC) somatic electromotility. Eliminating this abundant basolateral membrane protein not only causes loss of frequency selectivity and hearing sensitivity, but also leads to OHC death. A membrane-based yeast two-hybrid approach was used to screen an OHC-enriched cDNA (complementary Deoxyribonucleic Acid) library in order to identify prestin-associated proteins. Several proteins were recognized as potential prestin partners, including vesicle-associated membrane protein associated protein A (VAPA or VAP-33). VAPA is an integral membrane protein that plays an important role in membrane trafficking, endoplasmic reticulum homeostasis, and the stress-signaling system. The connection between VAPA and prestin was confirmed through co-immunoprecipitation experiments. This new finding prompted the investigation of the interaction between VAPA and prestin in outer hair cells. By comparing VAPA expression between wild-type OHCs and OHCs derived from prestin-knockout mice, we found that VAPA is expressed in OHCs and the quantity of VAPA expressed is related to the presence of prestin. In other words, less VAPA protein is found in OHCs lacking prestin. Thus, prestin appears to modify the expression of VAPA protein in OHCs. Intriguingly, more prestin protein appears at the plasma membrane when VAPA is co-expressed with prestin. These data suggest that VAPA could be involved in prestin's transportation inside OHCs and may facilitate the targeting of this abundant OHC protein to the plasma membrane.
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Affiliation(s)
- Soma Sengupta
- Department of Otolaryngology, Feinberg School of Medicine, Northwestern University, 303 East Chicago Avenue, Chicago, IL 60611, USA
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94
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Nachreiner T, Esser M, Tenten V, Troost D, Weis J, Krüttgen A. Novel splice variants of the amyotrophic lateral sclerosis-associated gene VAPB expressed in human tissues. Biochem Biophys Res Commun 2010; 394:703-8. [PMID: 20227395 DOI: 10.1016/j.bbrc.2010.03.055] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2010] [Accepted: 03/09/2010] [Indexed: 02/03/2023]
Abstract
VAPB is a highly conserved integral membrane protein that is ubiquitously expressed in all eukaryotic organisms and located within the membranes of the endoplasmic reticulum (ER). The P56S missense mutation of the VAPB protein is linked to a hereditary form of amyotrophic lateral sclerosis (ALS8), and the pathogenesis of ALS8 has remained enigmatic. We report the cloning of five novel splice variants of the human VAPB gene, all of which are expressed at the mRNA level in the human nervous system. When transfected into human HEK293 or SH-SY5Y cells, two of these variants (VAPB-2 and VAPB-4,5) were readily detectable by immunoblotting whereas two variants (VAPB-3 and VAPB-3,4) became detectable after proteasomal inhibition, a condition commonly found in neurodegenerative diseases. Interestingly, one of these novel VAPB variants, VAPB-2, co-immunoprecipitated with wt-VAPB. However, so far none of these splice variants could be detected by immunoblotting of lysates from selected human tissues, suggesting that in vivo, the proteins translated from the variant VAPB mRNAs are quickly degraded or, alternatively, the expressed proteins are below detection limit of the available antibodies. We speculate that under conditions of proteasomal inhibition, as encountered in many neurodegenerative diseases including ALS, variant VAPB proteins might accumulate in affected cells and contribute to ALS pathogenesis.
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Affiliation(s)
- T Nachreiner
- Institute of Neuropathology, Medical Faculty, RWTH Aachen University, Aachen, Germany
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95
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Kim S, Leal SS, Ben Halevy D, Gomes CM, Lev S. Structural requirements for VAP-B oligomerization and their implication in amyotrophic lateral sclerosis-associated VAP-B(P56S) neurotoxicity. J Biol Chem 2010; 285:13839-49. [PMID: 20207736 DOI: 10.1074/jbc.m109.097345] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The integral endoplasmic reticulum (ER)-membrane protein VAP-B interacts with various lipid-transfer/binding proteins containing an FFAT motif through its N-terminal MSP domain. A genetic mutation within its MSP domain, P56S, was identified in familial forms of motor neuron diseases. This mutation induces the formation of insoluble VAP-B(P56S) protein aggregates by an unknown mechanism. In this study, we defined the structural requirements for VAP-B oligomerization and demonstrated their contribution for VAP-B(P56S) aggregation and neurotoxicity. We show that the oligomerization of VAP-B is mainly mediated by its coiled-coil domain and that the GXXXG dimerization motif within the transmembrane domain mediates transmembrane domains self-association but is insufficient to drive VAP-B oligomerization. We further show that the oligomerization of the wild-type VAP-B is independent of its MSP domain. However, we found that the P56S mutation induces conformational changes within the MSP domain and facilitates its propensity to aggregate by exposing hydrophobic patches to the solvent. These conformational changes have no direct effect on FFAT binding. Rather, they enhance VAP-B(P56S) oligomerization driven by the combined contributions of the coiled-coil and the transmembrane domains, thereby preventing accessibility to FFAT-binding site, facilitating the production of VAP-B(P56S)-insoluble aggregates and consequently its neurotoxicity. These results shed light on the mechanism by which VAP-B(P56S) aggregates are formed and induce familial motor neuron diseases.
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Affiliation(s)
- SoHui Kim
- Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot 76100, Israel
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96
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Furuita K, Jee J, Fukada H, Mishima M, Kojima C. Electrostatic interaction between oxysterol-binding protein and VAMP-associated protein A revealed by NMR and mutagenesis studies. J Biol Chem 2010; 285:12961-70. [PMID: 20178991 DOI: 10.1074/jbc.m109.082602] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Oxysterol-binding protein (OSBP), a cytosolic receptor of cholesterol and oxysterols, is recruited to the endoplasmic reticulum by binding to the cytoplasmic major sperm protein (MSP) domain of integral endoplasmic reticulum protein VAMP-associated protein-A (VAP-A), a process essential for the stimulation of sphingomyelin synthesis by 25-hydroxycholesterol. To delineate the interaction mechanism between VAP-A and OSBP, we determined the complex structure between the VAP-A MSP domain (VAP-A(MSP)) and the OSBP fragment containing a VAP-A binding motif FFAT (OSBP(F)) by NMR. This solution structure explained that five of six conserved residues in the FFAT motif are required for the stable complex formation, and three of five, including three critical intermolecular electrostatic interactions, were not explained before. By combining NMR relaxation and titration, isothermal titration calorimetry, and mutagenesis experiments with structural information, we further elucidated the detailed roles of the FFAT motif and underlying motions of VAP-A(MSP), OSBP(F), and the complex. Our results show that OSBP(F) is disordered in the free state, and VAP-A(MSP) and OSBP(F) form a final complex by means of intermediates, where electrostatic interactions through acidic residues, including an acid patch preceding the FFAT motif, probably play a collective role. Additionally, we report that the mutation that causes the familial motor neuron disease decreases the stability of the MSP domain.
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Affiliation(s)
- Kyoko Furuita
- Graduate School of Biological Sciences, Nara Institute of Science and Technology, Nara 630-0192, Japan
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97
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Pumplin N, Mondo SJ, Topp S, Starker CG, Gantt JS, Harrison MJ. Medicago truncatula Vapyrin is a novel protein required for arbuscular mycorrhizal symbiosis. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2010; 61:482-94. [PMID: 19912567 DOI: 10.1111/j.1365-313x.2009.04072.x] [Citation(s) in RCA: 120] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Arbuscular mycorrhizal (AM) symbiosis is a widespread mutualism formed between vascular plants and fungi of the Glomeromycota. In this endosymbiosis, fungal hyphae enter the roots, growing through epidermal cells to the cortex where they establish differentiated hyphae called arbuscules in the cortical cells. Reprogramming of the plant epidermal and cortical cells occurs to enable intracellular growth of the fungal symbiont; however, the plant genes underlying this process are largely unknown. Here, through the use of RNAi, we demonstrate that the expression of a Medicago truncatula gene named Vapyrin is essential for arbuscule formation, and also for efficient epidermal penetration by AM fungi. Vapyrin is induced transiently in the epidermis coincident with hyphal penetration, and then in the cortex during arbuscule formation. The Vapyrin protein is cytoplasmic, and in cells containing AM fungal hyphae, the protein accumulates in small puncta that move through the cytoplasm. Vapyrin is a novel protein composed of two domains that mediate protein-protein interactions: an N-terminal VAMP-associated protein (VAP)/major sperm protein (MSP) domain and a C-terminal ankyrin-repeat domain. Putative Vapyrin orthologs exist widely in the plant kingdom, but not in Arabidopsis, or in non-plant species. The data suggest a role for Vapyrin in cellular remodeling to support the intracellular development of fungal hyphae during AM symbiosis.
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Affiliation(s)
- Nathan Pumplin
- Boyce Thompson Institute for Plant Research, Tower Road, Ithaca, NY 14853, USA
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98
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The glycolipid transfer protein interacts with the vesicle-associated membrane protein-associated protein VAP-A. Biochem Biophys Res Commun 2009; 388:395-9. [DOI: 10.1016/j.bbrc.2009.08.023] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2009] [Accepted: 08/04/2009] [Indexed: 12/18/2022]
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99
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Rocha N, Kuijl C, van der Kant R, Janssen L, Houben D, Janssen H, Zwart W, Neefjes J. Cholesterol sensor ORP1L contacts the ER protein VAP to control Rab7-RILP-p150 Glued and late endosome positioning. ACTA ACUST UNITED AC 2009; 185:1209-25. [PMID: 19564404 PMCID: PMC2712958 DOI: 10.1083/jcb.200811005] [Citation(s) in RCA: 520] [Impact Index Per Article: 34.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Late endosomes (LEs) have characteristic intracellular distributions determined by their interactions with various motor proteins. Motor proteins associated to the dynactin subunit p150(Glued) bind to LEs via the Rab7 effector Rab7-interacting lysosomal protein (RILP) in association with the oxysterol-binding protein ORP1L. We found that cholesterol levels in LEs are sensed by ORP1L and are lower in peripheral vesicles. Under low cholesterol conditions, ORP1L conformation induces the formation of endoplasmic reticulum (ER)-LE membrane contact sites. At these sites, the ER protein VAP (VAMP [vesicle-associated membrane protein]-associated ER protein) can interact in trans with the Rab7-RILP complex to remove p150(Glued) and associated motors. LEs then move to the microtubule plus end. Under high cholesterol conditions, as in Niemann-Pick type C disease, this process is prevented, and LEs accumulate at the microtubule minus end as the result of dynein motor activity. These data explain how the ER and cholesterol control the association of LEs with motor proteins and their positioning in cells.
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Affiliation(s)
- Nuno Rocha
- Division of Cell Biology, The Netherlands Cancer Institute, 1066CX Amsterdam, Netherlands
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100
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Abstract
Human vesicle-associated membrane protein-associated protein (VAP) subtype A (VAP-A) and subtype B (VAP-B) are involved in the regulation of membrane trafficking, lipid transport and metabolism, and the unfolded protein response. VAP-A and VAP-B consist of the major sperm protein (MSP) domain, the coiled-coil motif, and the C-terminal transmembrane anchor and form homo- and heterodimers through the transmembrane domain. VAP-A and VAP-B interact with NS5B and NS5A of hepatitis C virus (HCV) through the MSP domain and the coiled-coil motif, respectively, and participate in the replication of HCV. VAP-C is a splicing variant of VAP-B consisting of the N-terminal half of the MSP domain of VAP-B followed by the subtype-specific frameshift sequences, and its biological function has not been well characterized. In this study, we have examined the biological functions of VAP-C in the propagation of HCV. VAP-C interacted with NS5B but not with VAP-A, VAP-B, or NS5A in immunoprecipitation analyses, and the expression of VAP-C inhibited the interaction of NS5B with VAP-A or VAP-B. Overexpression of VAP-C impaired the RNA replication of the HCV replicon and the propagation of the HCV JFH1 strain, whereas overexpression of VAP-A and VAP-B enhanced the replication. Furthermore, the expression of VAP-C was observed in various tissues, whereas it was barely detected in the liver. These results suggest that VAP-C acts as a negative regulator of HCV propagation and that the expression of VAP-C may participate in the determination of tissue tropism of HCV propagation.
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