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Todd TW, Shao W, Zhang YJ, Petrucelli L. The endolysosomal pathway and ALS/FTD. Trends Neurosci 2023; 46:1025-1041. [PMID: 37827960 PMCID: PMC10841821 DOI: 10.1016/j.tins.2023.09.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2023] [Revised: 08/23/2023] [Accepted: 09/19/2023] [Indexed: 10/14/2023]
Abstract
Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are considered to be part of a disease spectrum that is associated with causative mutations and risk variants in a wide range of genes. Mounting evidence indicates that several of these genes are linked to the endolysosomal system, highlighting the importance of this pathway in ALS/FTD. Although many studies have focused on how disruption of this pathway impacts on autophagy, recent findings reveal that this may not be the whole picture: specifically, disrupting autophagy may not be sufficient to induce disease, whereas disrupting the endolysosomal system could represent a crucial pathogenic driver. In this review we discuss the connections between ALS/FTD and the endolysosomal system, including a breakdown of how disease-associated genes are implicated in this pathway. We also explore the potential downstream consequences of disrupting endolysosomal activity in the brain, outside of an effect on autophagy.
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Affiliation(s)
- Tiffany W Todd
- Department of Neuroscience, Mayo Clinic, Jacksonville, FL, USA
| | - Wei Shao
- Department of Neuroscience, Mayo Clinic, Jacksonville, FL, USA
| | - Yong-Jie Zhang
- Department of Neuroscience, Mayo Clinic, Jacksonville, FL, USA; Neurobiology of Disease Graduate Program, Mayo Graduate School, Mayo Clinic College of Medicine, Rochester, MN, USA
| | - Leonard Petrucelli
- Department of Neuroscience, Mayo Clinic, Jacksonville, FL, USA; Neurobiology of Disease Graduate Program, Mayo Graduate School, Mayo Clinic College of Medicine, Rochester, MN, USA.
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2
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Lenk GM, Szymanska K, Debska-Vielhaber G, Rydzanicz M, Walczak A, Bekiesinska-Figatowska M, Vielhaber S, Hallmann K, Stawinski P, Buehring S, Hsu DA, Kunz WS, Meisler MH, Ploski R. Biallelic Mutations of VAC14 in Pediatric-Onset Neurological Disease. Am J Hum Genet 2016; 99:188-94. [PMID: 27292112 DOI: 10.1016/j.ajhg.2016.05.008] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2016] [Accepted: 05/02/2016] [Indexed: 01/29/2023] Open
Abstract
In the PI(3,5)P2 biosynthetic complex, the lipid kinase PIKFYVE and the phosphatase FIG4 are bound to the dimeric scaffold protein VAC14, which is composed of multiple heat-repeat domains. Mutations of FIG4 result in the inherited disorders Charcot-Marie-Tooth disease type 4J, Yunis-Varón syndrome, and polymicrogyria with seizures. We here describe inherited variants of VAC14 in two unrelated children with sudden onset of a progressive neurological disorder and regression of developmental milestones. Both children developed impaired movement with dystonia, became nonambulatory and nonverbal, and exhibited striatal abnormalities on MRI. A diagnosis of Leigh syndrome was rejected due to normal lactate profiles. Exome sequencing identified biallelic variants of VAC14 that were inherited from unaffected heterozygous parents in both families. Proband 1 inherited a splice-site variant that results in skipping of exon 13, p.Ile459Profs(∗)4 (not reported in public databases), and the missense variant p.Trp424Leu (reported in the ExAC database in a single heterozygote). Proband 2 inherited two missense variants in the dimerization domain of VAC14, p.Ala582Ser and p.Ser583Leu, that have not been previously reported. Cultured skin fibroblasts exhibited the accumulation of vacuoles that is characteristic of PI(3,5)P2 deficiency. Vacuolization of fibroblasts was rescued by transfection of wild-type VAC14 cDNA. The similar age of onset and neurological decline in the two unrelated children define a recessive disorder resulting from compound heterozygosity for deleterious variants of VAC14.
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Affiliation(s)
- Guy M Lenk
- Department of Human Genetics, University of Michigan, Ann Arbor, MI 48109-5618, USA
| | - Krystyna Szymanska
- Department of Child Psychiatry, Warsaw Medical University, 02-106 Warsaw, Poland; Department of Experimental and Clinical Neuropathology, Medical Research Center, Polish Academy of Sciences, 02-106 Warsaw, Poland
| | | | - Malgorzata Rydzanicz
- Department of Medical Genetics, Warsaw Medical University, 02-106 Warsaw, Poland
| | - Anna Walczak
- Department of Medical Genetics, Warsaw Medical University, 02-106 Warsaw, Poland
| | | | - Stefan Vielhaber
- Klinik für Neurologie, Universitätsklinikum Magdeburg, 39120 Magdeburg, Germany
| | - Kerstin Hallmann
- Klinik für Epileptologie and Life&Brain Center, Universitätsklinikum Bonn, 53105 Bonn, Germany
| | - Piotr Stawinski
- Department of Medical Genetics, Warsaw Medical University, 02-106 Warsaw, Poland; Institute of Physiology and Pathology of Hearing, 05-830 Nadarzyn, Poland
| | | | - David A Hsu
- Department of Neurology, University of Wisconsin-Madison, Madison, WI 53705, USA
| | - Wolfram S Kunz
- Klinik für Epileptologie and Life&Brain Center, Universitätsklinikum Bonn, 53105 Bonn, Germany
| | - Miriam H Meisler
- Department of Human Genetics, University of Michigan, Ann Arbor, MI 48109-5618, USA.
| | - Rafal Ploski
- Department of Medical Genetics, Warsaw Medical University, 02-106 Warsaw, Poland.
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3
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Ueda Y. The Role of Phosphoinositides in Synapse Function. Mol Neurobiol 2014; 50:821-38. [DOI: 10.1007/s12035-014-8768-8] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2013] [Accepted: 06/01/2014] [Indexed: 11/30/2022]
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García-Beltrán O, Yañez O, Caballero J, Galdámez A, Mena N, Nuñez MT, Cassels BK. Synthesis of coumarin derivatives as fluorescent probes for membrane and cell dynamics studies. Eur J Med Chem 2014; 76:79-86. [PMID: 24576613 DOI: 10.1016/j.ejmech.2014.02.016] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2013] [Revised: 11/13/2013] [Accepted: 02/08/2014] [Indexed: 01/07/2023]
Abstract
Three coumarin-derived fluorescent probes, 3-acetyl-7-[(6-bromohexyl)oxy]-2H-chromen-2-one (FM1), 7-[(6-bromohexyl)oxy]-4-methyl-2H-chromen-2-one (FM2) and ethyl 2-{7-[(6-bromohexyl)oxy]-2-oxo-2H-chromen-4-yl}acetate (FM3), are described, with their photophysical constants. The compounds were tested in preliminary studies employing epifluorescence microscopy demonstrating that they allow the imaging of human neuroblastoma SH-SY5Y cell membranes. The structure of FM3 was confirmed by X-ray crystallographic analysis. Molecular dynamics (MD) simulations were used to characterize the localization and interactions of the studied compounds with a lipid bilayer model of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC).
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Affiliation(s)
- Olimpo García-Beltrán
- Department of Chemistry, Faculty of Sciences, University of Chile, Santiago, Chile; Facultad de Ciencias Naturales y Matemáticas, Universidad de Ibagué, Carrera 22 Calle 67, Ibagué, Colombia.
| | - Osvaldo Yañez
- Centro de Bioinformática y Simulación Molecular, Facultad de Ingeniería, Universidad de Talca, 2 Norte 685, Casilla 721, Talca, Chile
| | - Julio Caballero
- Centro de Bioinformática y Simulación Molecular, Facultad de Ingeniería, Universidad de Talca, 2 Norte 685, Casilla 721, Talca, Chile
| | - Antonio Galdámez
- Department of Chemistry, Faculty of Sciences, University of Chile, Santiago, Chile
| | - Natalia Mena
- Department of Biology, Faculty of Sciences, University of Chile, Santiago, Chile
| | - Marco T Nuñez
- Department of Biology, Faculty of Sciences, University of Chile, Santiago, Chile
| | - Bruce K Cassels
- Department of Chemistry, Faculty of Sciences, University of Chile, Santiago, Chile
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5
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Michell RH. Inositol lipids: from an archaeal origin to phosphatidylinositol 3,5-bisphosphate faults in human disease. FEBS J 2013; 280:6281-94. [PMID: 23902363 DOI: 10.1111/febs.12452] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2013] [Revised: 07/22/2013] [Accepted: 07/23/2013] [Indexed: 01/12/2023]
Abstract
The last couple of decades have seen an extraordinary transformation in our knowledge and understanding of the multifarious biological roles of inositol phospholipids. Herein, I briefly consider two topics. The first is the role that recently acquired biochemical and genomic information - especially from archaeons - has played in illuminating the possible evolutionary origins of the biological employment of inositol in lipids, and some questions that these studies raise about the 'classical' biosynthetic route to phosphatidylinositol. The second is the growing recognition of the importance in eukaryotic cells of phosphatidylinositol 3,5-bisphosphate. Phosphatidylinositol 3,5-bisphosphate only entered our phosphoinositide consciousness quite recently, but it is speedily gathering a plethora of roles in diverse cellular processes and diseases thereof. These include: control of endolysosomal vesicular trafficking and of the activity of ion channels and pumps in the endolysosomal compartment; control of constitutive and stimulated protein traffic to and from plasma membrane subdomains; control of the nutrient and stress-sensing target of rapamycin complex 1 pathway (TORC1); and regulation of key genes in some central metabolic pathways.
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Abstract
Phosphoinositides are important regulators of cellular homoeostasis and numerous signal-transduction pathways. One of their major features is their ability to recruit signalling proteins to membranes by direct interaction with phosphoinositide-binding modules. The distribution and dynamics of membrane phosphoinositides are therefore major determinants in the spatiotemporal control of cell signalling and membrane trafficking. However, standard biochemical approaches cannot reveal the dynamics of phosphoinositides at the single-cell level. A major technical advance has been the development of genetically encoded fluorescent phosphoinositide probes on the basis of the phosphoinositide-binding domains found in signalling proteins, such as the PH (pleckstrin homology) domain. This review describes the diverse fluorescent phosphoinositide probes available for imaging specific phosphoinositide species and how their use has improved the understanding of phosphoinositide signalling at the single-cell level.
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Affiliation(s)
- Guillaume Halet
- Department of Physiology, University College London, Gower Street, London WC1E 6BT, UK.
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7
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Abstract
Phosphoinositides play an important role in organelle identity by recruiting effector proteins to the host membrane organelle, thus decorating that organelle with molecular identity. Phosphatidylinositol-3,5-bisphos- phate [PtdIns(3,5)P(2) ] is a low-abundance phosphoinositide that predominates in endolysosomes in higher eukaryotes and in the yeast vacuole. Compared to other phosphoinositides such as PtdIns(4,5)P(2) , our understanding of the regulation and function of PtdIns(3,5)P(2) remained rudimentary until more recently. Here, we review many of the recent developments in PtdIns(3,5)P(2) function and regulation. PtdIns(3,5)P(2) is now known to espouse functions, not only in the regulation of endolysosome morphology, trafficking and acidification, but also in autophagy, signaling mediation in response to stresses and hormonal cues and control of membrane and ion transport. In fact, PtdIns(3,5)P(2) misregulation is now linked with several human neuropathologies including Charcot-Marie-Tooth disease and amyotrophic lateral sclerosis. Given the functional versatility of PtdIns(3,5)P(2) , it is not surprising that regulation of PtdIns(3,5)P(2) metabolism is proving rather elaborate. PtdIns(3,5)P(2) synthesis and turnover are tightly coupled via a protein complex that includes the Fab1/PIKfyve lipid kinase and its antagonistic Fig4/Sac3 lipid phosphatase. Most interestingly, many PtdIns(3,5)P(2) regulators play simultaneous roles in its synthesis and turnover.
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Affiliation(s)
- Cheuk Y Ho
- Department of Chemistry and Biology, Ryerson University, Toronto, Ontario, Canada
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Wywial E, Singh SM. Identification and structural characterization of FYVE domain-containing proteins of Arabidopsis thaliana. BMC PLANT BIOLOGY 2010; 10:157. [PMID: 20678208 PMCID: PMC3017826 DOI: 10.1186/1471-2229-10-157] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/22/2010] [Accepted: 08/02/2010] [Indexed: 05/02/2023]
Abstract
BACKGROUND FYVE domains have emerged as membrane-targeting domains highly specific for phosphatidylinositol 3-phosphate (PtdIns(3)P). They are predominantly found in proteins involved in various trafficking pathways. Although FYVE domains may function as individual modules, dimers or in partnership with other proteins, structurally, all FYVE domains share a fold comprising two small characteristic double-stranded beta-sheets, and a C-terminal alpha-helix, which houses eight conserved Zn2+ ion-binding cysteines. To date, the structural, biochemical, and biophysical mechanisms for subcellular targeting of FYVE domains for proteins from various model organisms have been worked out but plant FYVE domains remain noticeably under-investigated. RESULTS We carried out an extensive examination of all Arabidopsis FYVE domains, including their identification, classification, molecular modeling and biophysical characterization using computational approaches. Our classification of fifteen Arabidopsis FYVE proteins at the outset reveals unique domain architectures for FYVE containing proteins, which are not paralleled in other organisms. Detailed sequence analysis and biophysical characterization of the structural models are used to predict membrane interaction mechanisms previously described for other FYVE domains and their subtle variations as well as novel mechanisms that seem to be specific to plants. CONCLUSIONS Our study contributes to the understanding of the molecular basis of FYVE-based membrane targeting in plants on a genomic scale. The results show that FYVE domain containing proteins in plants have evolved to incorporate significant differences from those in other organisms implying that they play a unique role in plant signaling pathways and/or play similar/parallel roles in signaling to other organisms but use different protein players/signaling mechanisms.
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Affiliation(s)
- Ewa Wywial
- Department of Biology, The Graduate Center of the City University of New York, 365 Fifth Avenue, New York, NY 10016, USA
- Department of Biology, Brooklyn College, City University of New York, 2900 Bedford Avenue, Brooklyn, NY 11210, USA
| | - Shaneen M Singh
- Department of Biology, The Graduate Center of the City University of New York, 365 Fifth Avenue, New York, NY 10016, USA
- Department of Biology, Brooklyn College, City University of New York, 2900 Bedford Avenue, Brooklyn, NY 11210, USA
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9
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Barucha-Kraszewska J, Kraszewski S, Jurkiewicz P, Ramseyer C, Hof M. Numerical studies of the membrane fluorescent dyes dynamics in ground and excited states. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1798:1724-34. [PMID: 20510669 DOI: 10.1016/j.bbamem.2010.05.020] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/07/2010] [Revised: 05/17/2010] [Accepted: 05/19/2010] [Indexed: 11/18/2022]
Abstract
Fluorescence methods are widely used in studies of biological and model membranes. The dynamics of membrane fluorescent markers in their ground and excited electronic states and correlations with their molecular surrounding within the fully hydrated phospholipid bilayer are still not well understood. In the present work, Quantum Mechanical (QM) calculations and Molecular Dynamics (MD) simulations are used to characterize location and interactions of two membrane polarity probes (Prodan; 6-propionyl-2-dimethylaminonaphthalene and its derivative Laurdan; 2-dimethylamino-6-lauroylnaphthalene) with the dioleoylphosphatidylcholine (DOPC) lipid bilayer model. MD simulations with fluorophores in ground and excited states are found to be a useful tool to analyze the fluorescent dye dynamics and their immediate vicinity. The results of QM calculations and MD simulations are in excellent agreement with available experimental data. The calculation shows that the two amphiphilic dyes initially placed in bulk water diffuse within 10 ns towards their final location in the lipid bilayer. Analysis of solvent relaxation process in the aqueous phase occurs on the picoseconds timescale whereas it takes nanoseconds at the lipid/water interface. Four different relaxation time constants, corresponding to different relaxation processes, where observed when the dyes were embedded into the membrane.
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10
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Inhibition of the PtdIns(5) kinase PIKfyve disrupts intracellular replication of Salmonella. EMBO J 2010; 29:1331-47. [PMID: 20300065 DOI: 10.1038/emboj.2010.28] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2009] [Accepted: 02/10/2010] [Indexed: 01/15/2023] Open
Abstract
3-phosphorylated phosphoinositides (3-PtdIns) orchestrate endocytic trafficking pathways exploited by intracellular pathogens such as Salmonella to gain entry into the cell. To infect the host, Salmonellae subvert its normal macropinocytic activity, manipulating the process to generate an intracellular replicative niche. Disruption of the PtdIns(5) kinase, PIKfyve, be it by interfering mutant, siRNA-mediated knockdown or pharmacological means, inhibits the intracellular replication of Salmonella enterica serovar typhimurium in epithelial cells. Monitoring the dynamics of macropinocytosis by time-lapse 3D (4D) videomicroscopy revealed a new and essential role for PI(3,5)P(2) in macropinosome-late endosome/lysosome fusion, which is distinct from that of the small GTPase Rab7. This PI(3,5)P(2)-dependent step is required for the proper maturation of the Salmonella-containing vacuole (SCV) through the formation of Salmonella-induced filaments (SIFs) and for the engagement of the Salmonella pathogenicity island 2-encoded type 3 secretion system (SPI2-T3SS). Finally, although inhibition of PIKfyve in macrophages did inhibit Salmonella replication, it also appears to disrupt the macrophage's bactericidal response.
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11
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Anand VC, Daboussi L, Lorenz TC, Payne GS. Genome-wide analysis of AP-3-dependent protein transport in yeast. Mol Biol Cell 2008; 20:1592-604. [PMID: 19116312 DOI: 10.1091/mbc.e08-08-0819] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The evolutionarily conserved adaptor protein-3 (AP-3) complex mediates cargo-selective transport to lysosomes and lysosome-related organelles. To identify proteins that function in AP-3-mediated transport, we performed a genome-wide screen in Saccharomyces cerevisiae for defects in the vacuolar maturation of alkaline phosphatase (ALP), a cargo of the AP-3 pathway. Forty-nine gene deletion strains were identified that accumulated precursor ALP, many with established defects in vacuolar protein transport. Maturation of a vacuolar membrane protein delivered via a separate, clathrin-dependent pathway, was affected in all strains except those with deletions of YCK3, encoding a vacuolar type I casein kinase; SVP26, encoding an endoplasmic reticulum (ER) export receptor for ALP; and AP-3 subunit genes. Subcellular fractionation and fluorescence microscopy revealed ALP transport defects in yck3Delta cells. Characterization of svp26Delta cells revealed a role for Svp26p in ER export of only a subset of type II membrane proteins. Finally, ALP maturation kinetics in vac8Delta and vac17Delta cells suggests that vacuole inheritance is important for rapid generation of proteolytically active vacuolar compartments in daughter cells. We propose that the cargo-selective nature of the AP-3 pathway in yeast is achieved by AP-3 and Yck3p functioning in concert with machinery shared by other vacuolar transport pathways.
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Affiliation(s)
- Vikram C Anand
- Department of Biological Chemistry, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095, USA
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12
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Osborne SL, Wen PJ, Boucheron C, Nguyen HN, Hayakawa M, Kaizawa H, Parker PJ, Vitale N, Meunier FA. PIKfyve Negatively Regulates Exocytosis in Neurosecretory Cells. J Biol Chem 2008; 283:2804-13. [DOI: 10.1074/jbc.m704856200] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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Cao C, Laporte J, Backer JM, Wandinger-Ness A, Stein MP. Myotubularin lipid phosphatase binds the hVPS15/hVPS34 lipid kinase complex on endosomes. Traffic 2007; 8:1052-67. [PMID: 17651088 DOI: 10.1111/j.1600-0854.2007.00586.x] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Myotubularins constitute a ubiquitous family of phosphatidylinositol (PI) 3-phosphatases implicated in several neuromuscular disorders. Myotubularin [myotubular myopathy 1 (MTM1)] PI 3-phosphatase is shown associated with early and late endosomes. Loss of endosomal phosphatidylinositol 3-phosphate [PI(3)P] upon overexpression of wild-type MTM1, but not a phosphatase-dead MTM1C375S mutant, resulted in altered early and late endosomal PI(3)P levels and rapid depletion of early endosome antigen-1. Membrane-bound MTM1 was directly complexed to the hVPS15/hVPS34 [vacuolar protein sorting (VPS)] PI 3-kinase complex with binding mediated by the WD40 domain of the hVPS15 (p150) adapter protein and independent of a GRAM-domain point mutation that blocks PI(3,5)P(2) binding. The WD40 domain of hVPS15 also constitutes the binding site for Rab7 and, as shown previously, contributes to Rab5 binding. In vivo, the hVPS15/hVPS34 PI 3-kinase complex forms mutually exclusive complexes with the Rab GTPases (Rab5 or Rab7) or with MTM1, suggesting a competitive binding mechanism. Thus, the Rab GTPases together with MTM1 likely serve as molecular switches for controlling the sequential synthesis and degradation of endosomal PI(3)P. Normal levels of endosomal PI(3)P and PI(3,5)P(2) are crucial for both endosomal morphology and function, suggesting that disruption of endosomal sorting and trafficking in skeletal muscle when MTM1 is mutated may be a key factor in precipitating X-linked MTM.
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Affiliation(s)
- Canhong Cao
- Molecular Trafficking Laboratory, Department of Pathology, University of New Mexico School of Medicine, Albuquerque, NM 87131, USA
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Phelan JP, Millson SH, Parker PJ, Piper PW, Cooke FT. Fab1p and AP-1 are required for trafficking of endogenously ubiquitylated cargoes to the vacuole lumen in S. cerevisiae. J Cell Sci 2006; 119:4225-34. [PMID: 17003107 DOI: 10.1242/jcs.03188] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In S. cerevisiae synthesis of phosphatidylinositol (3,5)-bisphosphate [PtdIns(3,5)P2] by Fab1p is required for several cellular events, including an as yet undefined step in the ubiquitin-dependent trafficking of some integral membrane proteins from the trans-Golgi network to the vacuole lumen. AP-1 is a heterotetrameric clathrin adaptor protein complex that binds cargo proteins and clathrin coats, and regulates bi-directional protein trafficking between the trans-Golgi network and the endocytic/secretory pathway. Like fab1Δ cells, AP-1 complex component mutants have lost the ability to traffic ubiquitylated cargoes to the vacuole lumen – the first demonstration that AP-1 is required for this process. Deletion mutants of AP-1 complex components are compromised in their ability to synthesize PtdIns(3,5)P2, indicating that AP-1 is required for correct in vivo activation of Fab1p. Furthermore, wild-type protein sorting can be restored in AP-1 mutants by overexpression of Fab1p, implying that the protein-sorting defect in these cells is as a result of disruption of PtdIns(3,5)P2 synthesis. Finally, we show that Fab1p and Vac14p, an activator of Fab1p, are also required for another AP-1-dependent process: chitin-ring deposition in chs6Δ cells. Our data imply that AP-1 is required for some Fab1p and PtdIns(3,5)P2-dependent processes.
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Affiliation(s)
- John P Phelan
- Department of Biochemistry and Molecular Biology, University College London, Darwin Building, Gower Street, London, WC1E 6BT, UK
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15
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Jurkiewicz P, Olzyńska A, Langner M, Hof M. Headgroup hydration and mobility of DOTAP/DOPC bilayers: a fluorescence solvent relaxation study. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2006; 22:8741-9. [PMID: 17014112 DOI: 10.1021/la061597k] [Citation(s) in RCA: 108] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
The biophysical properties of liposome surfaces are critical for interactions between lipid aggregates and macromolecules. Liposomes formed from cationic lipids, commonly used to deliver genes into cells in vitro and in vivo, are an example of such a system. We apply the fluorescence solvent relaxation technique to study the structure and dynamics of fully hydrated liquid crystalline lipid bilayers composed of mixtures of cationic dioleoyltrimethylammoniumpropane (DOTAP) and neutral dioleoylphosphatidylcholine (DOPC). Using three different naphthalene derivatives as fluorescent dyes (Patman, Laurdan and Prodan) allowed different parts of the headgroup region to be probed. Wavelength-dependent parallax quenching measurements resulted in the precise determination of Laurdan and Patman locations within the DOPC bilayer. Acrylamide quenching experiments were used to examine DOTAP-induced dye relocalization. The nonmonotonic dependence of dipolar relaxation kinetics (occurring exclusively on the nanosecond time scale) on DOTAP content in the membrane was found to exhibit a maximum mean solvent relaxation time at 30 mol % of DOTAP. Up to 30 mol %, addition of DOTAP does not influence the amount of bound water at the level of the sn(1) carbonyls, but leads to an increased packing of phospholipid headgroups. Above this concentration, elevated lipid bilayer water penetration was observed.
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Affiliation(s)
- Piotr Jurkiewicz
- J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejskova 3, CZ-18223 Prague 8, Czech Republic
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16
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Rusten TE, Rodahl LM, Pattni K, Englund C, Samakovlis C, Dove S, Brech A, Stenmark H. Fab1 phosphatidylinositol 3-phosphate 5-kinase controls trafficking but not silencing of endocytosed receptors. Mol Biol Cell 2006; 17:3989-4001. [PMID: 16837550 PMCID: PMC1556381 DOI: 10.1091/mbc.e06-03-0239] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2006] [Revised: 06/13/2006] [Accepted: 07/03/2006] [Indexed: 11/11/2022] Open
Abstract
The trafficking of endocytosed receptors through phosphatidylinositol 3-phosphate [PtdIns(3)P]-containing endosomes is thought to attenuate their signaling. Here, we show that the PtdIns(3)P 5-kinase Fab1/PIKfyve controls trafficking but not silencing of endocytosed receptors. Drosophila fab1 mutants contain undetectable phosphatidylinositol 3,5-bisphosphate levels, show profound increases in cell and organ size, and die at the pupal stage. Mutant larvae contain highly enlarged multivesicular bodies and late endosomes that are inefficiently acidified. Clones of fab1 mutant cells accumulate Wingless and Notch, similarly to cells lacking Hrs, Vps25, and Tsg101, components of the endosomal sorting machinery for ubiquitinated membrane proteins. However, whereas hrs, vps25, and tsg101 mutant cell clones accumulate ubiquitinated cargo, this is not the case with fab1 mutants. Even though endocytic receptor trafficking is impaired in fab1 mutants, Notch, Wingless, and Dpp signaling is unaffected. We conclude that Fab1, despite its importance for endosomal functions, is not required for receptor silencing. This is consistent with the possibility that Fab1 functions at a late stage in endocytic receptor trafficking, at a point when signal termination has occurred.
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Affiliation(s)
- Tor Erik Rusten
- *Department of Biochemistry, The Norwegian Radium Hospital and the University of Oslo, Montebello, N-0310 Oslo, Norway
| | - Lina M.W. Rodahl
- *Department of Biochemistry, The Norwegian Radium Hospital and the University of Oslo, Montebello, N-0310 Oslo, Norway
| | - Krupa Pattni
- *Department of Biochemistry, The Norwegian Radium Hospital and the University of Oslo, Montebello, N-0310 Oslo, Norway
| | - Camilla Englund
- Department of Developmental Biology, Wenner-Gren Institute, Stockholm University, S-106 91 Stockholm, Sweden; and
| | - Christos Samakovlis
- Department of Developmental Biology, Wenner-Gren Institute, Stockholm University, S-106 91 Stockholm, Sweden; and
| | - Stephen Dove
- Department of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
| | - Andreas Brech
- *Department of Biochemistry, The Norwegian Radium Hospital and the University of Oslo, Montebello, N-0310 Oslo, Norway
| | - Harald Stenmark
- *Department of Biochemistry, The Norwegian Radium Hospital and the University of Oslo, Montebello, N-0310 Oslo, Norway
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17
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Mollapour M, Phelan J, Millson S, Piper P, Cooke F. Weak acid and alkali stress regulate phosphatidylinositol bisphosphate synthesis in Saccharomyces cerevisiae. Biochem J 2006; 395:73-80. [PMID: 16316315 PMCID: PMC1409697 DOI: 10.1042/bj20051765] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Weak organic acids are used as food preservatives to inhibit the growth of spoilage yeasts, including Saccharomyces cerevisiae. Long-term adaptation to weak acids requires the increased expression of the ATP-binding cassette transporter Pdr12p, which catalyses the active efflux of the weak acids from the cytosol; however, very little is known about the signalling events immediately following application of weak acid stress. We have investigated the effects of weak acids on two stress-responsive signalling molecules, PtdIns(3,5)P2 and PtdIns(4,5)P2, which in S. cerevisiae are synthesized by Fab1p and Mss4p respectively. At low extracellular pH, benzoic acid, sorbic acid and acetic acid all cause a transient reduction in PtdIns(3,5)P2 accumulation and a more persistent rise in PtdIns(4,5)P2 levels. The increase in PtdIns(4,5)P2 levels is accompanied by a reorganization of the actin cytoskeleton. However, changes in PtdInsP2 levels are independent of weak acid-induced Pdr12p expression. In contrast, changing the extracellular medium to alkaline pH provokes a prolonged and substantial rise in PtdIns(3,5)P2 levels. As PtdIns(3,5)P2 synthesis is required for correct vacuole acidification, it is possible that levels of this molecule are modulated to maintain intracellular pH homoeostasis in response to weak acid and alkali stresses. In conclusion, we have expanded the repertoire of stress responses that affect PtdInsP2 levels to include weak acid and alkali stresses.
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Affiliation(s)
- Mehdi Mollapour
- *Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, U.K
| | - John P. Phelan
- †Department of Biochemistry and Molecular Biology, University College London, Darwin Building, Gower Street, London WC1E 6BT, U.K
| | - Stefan H. Millson
- *Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, U.K
| | - Peter W. Piper
- *Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, U.K
| | - Frank T. Cooke
- †Department of Biochemistry and Molecular Biology, University College London, Darwin Building, Gower Street, London WC1E 6BT, U.K
- To whom correspondence should be addressed (email )
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18
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Cabezas A, Pattni K, Stenmark H. Cloning and subcellular localization of a human phosphatidylinositol 3-phosphate 5-kinase, PIKfyve/Fab1. Gene 2006; 371:34-41. [PMID: 16448788 DOI: 10.1016/j.gene.2005.11.009] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2005] [Revised: 10/21/2005] [Accepted: 11/04/2005] [Indexed: 01/08/2023]
Abstract
Yeast Fab1 is a phosphatidylinositol 3-phosphate 5-kinase involved in endocytic membrane traffic and vacuole homeostasis. Here we have cloned and sequenced the cDNA for the human homologue of Fab1, PIKfyve. The cDNA has an open reading frame of 6294 bp and encodes a 2098-amino acid protein with a calculated molecular mass of 237 kDa, containing a phosphatidylinositol 3-phosphate-binding FYVE domain, a DEP domain, a chaperonin-like domain, and a phosphoinositide kinase domain. The human genome contains a single PIKfyve gene, which comprises 38 exons on chromosomal locus 2q34. PIKfyve is expressed as a single molecular species in a number of human cell lines derived from different tissues. The exogenously expressed protein was found to localize mainly to early endosomes containing two other FYVE domain proteins, EEA1 and Hrs. The endosomal membrane localization of PIKfyve was studied in more detail by examining cells transfected with a constitutively active mutant of the small GTPase Rab5, whose expression results in the enlargement of early endosomes. We show that PIKfyve is distributed in microdomains that are distinct from those occupied by EEA1 and Hrs.
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Affiliation(s)
- Alicia Cabezas
- Department of Biochemistry, The Norwegian Radium Hospital, Montebello, N-0310 Oslo, Norway
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19
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Michell RH, Heath VL, Lemmon MA, Dove SK. Phosphatidylinositol 3,5-bisphosphate: metabolism and cellular functions. Trends Biochem Sci 2005; 31:52-63. [PMID: 16364647 DOI: 10.1016/j.tibs.2005.11.013] [Citation(s) in RCA: 180] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2005] [Revised: 10/26/2005] [Accepted: 11/25/2005] [Indexed: 11/16/2022]
Abstract
Polyphosphoinositides (PPIn) are low-abundance membrane phospholipids that each bind to a distinctive set of effector proteins and, thereby, regulate a characteristic suite of cellular processes. Major functions of phosphatidylinositol 3,5-bisphosphate [PtdIns(3,5)P(2)] are in membrane and protein trafficking, and in pH control in the endosome-lysosome axis. Recently identified PtdIns(3,5)P(2) effectors include a family of novel beta-propeller proteins, for which we propose the name PROPPINs [for beta-propeller(s) that binds PPIn], and possibly proteins of the epsin and CHMP (charged multi-vesicular body proteins) families. All eukaryotes, with the exception of some pathogenic protists and microsporidians, possess proteins needed for the formation, metabolism and functions of PtdIns(3,5)P(2). The importance of PtdIns(3,5)P(2) for normal cell function is underscored by recent evidence for its involvement in mammalian cell responses to insulin and for PtdIns(3,5)P(2) dysfunction in the human genetic conditions X-linked myotubular myopathy, Type-4B Charcot-Marie-Tooth disease and fleck corneal dystrophy.
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Affiliation(s)
- Robert H Michell
- School of Biosciences, University of Birmingham, Birmingham B15 2TT, UK.
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20
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Robinson FL, Dixon JE. The Phosphoinositide-3-phosphatase MTMR2 Associates with MTMR13, a Membrane-associated Pseudophosphatase Also Mutated in Type 4B Charcot-Marie-Tooth Disease. J Biol Chem 2005; 280:31699-707. [PMID: 15998640 DOI: 10.1074/jbc.m505159200] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Charcot-Marie-Tooth disease type 4B (CMT4B) is a severe, demyelinating peripheral neuropathy characterized by distinctive, focally folded myelin sheaths. CMT4B is caused by recessively inherited mutations in either myotubularin-related 2 (MTMR2) or MTMR13 (also called SET-binding factor 2). MTMR2 encodes a member of the myotubularin family of phosphoinositide-3-phosphatases, which dephosphorylate phosphatidylinositol 3-phosphate (PI(3)P) and bisphosphate PI(3,5)P2. MTMR13 encodes a large, uncharacterized member of the myotubularin family. The MTMR13 phosphatase domain is catalytically inactive because the essential Cys and Arg residues are absent. Given the genetic association of both MTMR2 and MTMR13 with CMT4B, we investigated the biochemical relationship between these two proteins. We found that the endogenous MTMR2 and MTMR13 proteins are associated in human embryonic kidney 293 cells. MTMR2-MTMR13 association is mediated by coiled-coil sequences present in each protein. We also examined the cellular localization of MTMR2 and MTMR13 using fluorescence microscopy and subcellular fractionation. We found that (i) MTMR13 is a predominantly membrane-associated protein; (ii) MTMR2 and MTMR13 cofractionate in both a light membrane fraction and a cytosolic fraction; and (iii) MTMR13 membrane association is mediated by the segment of the protein which contains the pseudophosphatase domain. This work, which describes the first cellular or biochemical investigation of the MTMR13 pseudophosphatase protein, suggests that MTMR13 functions in association with MTMR2. Loss of MTMR13 function in CMT4B2 patients may lead to alterations in MTMR2 function and subsequent alterations in 3-phosphoinositide signaling. Such a mechanism would explain the strikingly similar phenotypes of patients with recessive mutations in either MTMR2 or MTMR13.
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Affiliation(s)
- Fred L Robinson
- Department of Pharmacology, The University of California San Diego, La Jolla, California 92093, USA
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21
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Abstract
In this article, we consider the functions of the myotubularins - a large family of phosphoinositide 3-phosphatases. By analogy with the phosphatidylinositol 3-phosphatase PTEN (phosphatase and tensin homolog deleted in chromosome ten) and many protein phosphatases, it has been proposed that the primary function of this protein family is to regulate substrate levels, in this case phosphatidylinositol (3)-phosphate. We propose an alternate, or additional, function that is analogous to the G-protein family of phosphatases, which use nucleotide-dependent conformational changes to transduce signals or do mechanical work.
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Affiliation(s)
- Michael J Clague
- Physiological Laboratory, University of Liverpool, Crown Street, Liverpool L69 3BX, UK.
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22
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Abstract
Phosphoinositides are minor components of biological membranes, which have emerged as essential regulators of a variety of cellular processes, both on the plasma membrane and on several intracellular organelles. The versatility of these lipids stems from their ability to function either as substrates for the generation of second messengers, as membrane-anchoring sites for cytosolic proteins or as regulators of the actin cytoskeleton. Despite a vast literature demonstrating the presence of phosphoinositides in the nucleus, only recently has the function(s) of the nuclear pool of these lipids and their soluble analogues, inositol polyphosphates, started to emerge. These compounds have been shown to serve as essential co-factors for several nuclear processes, including DNA repair, transcription regulation and RNA dynamics. In this light, phosphoinositides and inositol polyphosphates might represent high turnover activity switches for nuclear complexes responsible for these processes. The regulation of these large machineries would be linked to the phosphorylation state of the inositol ring and limited temporally and spatially based on the synthesis and degradation of these molecules.
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Affiliation(s)
- G Hammond
- Molecular NeuroPathoBiology Laboratory, Lincoln's Inn Fields Laboratories, Cancer Research UK London Research Institute, 44 Lincoln's Inn Fields, London WC2A 3PX, UK
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23
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Abstract
Phosphatidylinositol-3,5-bisphosphate (PtdIns(3,5)P(2)) is required for the sorting of a subset of membrane proteins at the late endosome. Unlike other phosphoinositides, binding partners for PtdIns(3,5)P(2) and its mechanism of action have not been characterized. New work by in this issue of Developmental Cell describes the identification of a yeast epsin-like protein that binds PtdIns(3,5)P(2) and functions in the transport of proteins through late endosomes to the lysosome-like vacuole.
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Affiliation(s)
- Linda Hicke
- Department of Biochemistry, Molecular Biology, and Cell Biology, Northwestern University, Evanston, IL 60208, USA
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