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Mohr I, Mirzaiebadizi A, Sanyal SK, Chuenban P, Ahmadian MR, Ivanov R, Bauer P. Characterization of the small Arabidopsis thaliana GTPase and ADP-ribosylation factor-like 2 protein TITAN 5. J Cell Sci 2024; 137:jcs262315. [PMID: 39056156 PMCID: PMC11361645 DOI: 10.1242/jcs.262315] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2024] [Accepted: 06/03/2024] [Indexed: 07/28/2024] Open
Abstract
Small GTPases switch between GDP- and GTP-bound states during cell signaling. The ADP-ribosylation factor (ARF) family of small GTPases is involved in vesicle trafficking. Although evolutionarily well conserved, little is known about ARF and ARF-like GTPases in plants. We characterized biochemical properties and cellular localization of the essential small ARF-like GTPase TITAN 5 (TTN5; also known as HALLIMASCH, ARL2 and ARLC1) from Arabidopsis thaliana, and two TTN5 proteins with point mutants in conserved residues, TTN5T30N and TTN5Q70L, that were expected to be unable to perform nucleotide exchange and GTP hydrolysis, respectively. TTN5 exhibited very rapid intrinsic nucleotide exchange and remarkably low GTP hydrolysis activity, functioning as a non-classical small GTPase being likely present in a GTP-loaded active form. We analyzed signals from YFP-TTN5 and HA3-TTN5 by in situ immunolocalization in Arabidopsis seedlings and through use of a transient expression system. Colocalization with endomembrane markers and pharmacological treatments suggests that TTN5 can be present at the plasma membrane and that it dynamically associates with membranes of vesicles, Golgi stacks and multivesicular bodies. Although TTN5Q70L mirrored wild-type TTN5 behavior, the TTN5T30N mutant differed in some aspects. Hence, the unusual rapid nucleotide exchange activity of TTN5 is linked with its membrane dynamics, and TTN5 likely has a role in vesicle transport within the endomembrane system.
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Affiliation(s)
- Inga Mohr
- Institute of Botany, Heinrich Heine University, 40225 Düsseldorf, Germany
| | - Amin Mirzaiebadizi
- Institute of Biochemistry and Molecular Biology II, Medical Faculty and University Hospital Düsseldorf, Heinrich Heine University, 40225 Düsseldorf, Germany
| | - Sibaji K. Sanyal
- Institute of Botany, Heinrich Heine University, 40225 Düsseldorf, Germany
| | - Pichaporn Chuenban
- Institute of Botany, Heinrich Heine University, 40225 Düsseldorf, Germany
- Center for Plant Genome Engineering, Heinrich Heine University, 40225 Düsseldorf, Germany
| | - Mohammad R. Ahmadian
- Institute of Biochemistry and Molecular Biology II, Medical Faculty and University Hospital Düsseldorf, Heinrich Heine University, 40225 Düsseldorf, Germany
| | - Rumen Ivanov
- Institute of Botany, Heinrich Heine University, 40225 Düsseldorf, Germany
| | - Petra Bauer
- Institute of Botany, Heinrich Heine University, 40225 Düsseldorf, Germany
- Cluster of Excellence on Plant Sciences, Heinrich Heine University, 40225 Düsseldorf, Germany
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2
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Mohr I, Mirzaiebadizi A, Sanyal SK, Chuenban P, Ahmadian MR, Ivanov R, Bauer P. Characterization of the small Arabidopsis thaliana GTPase and ADP-ribosylation factor-like 2 protein TITAN 5. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.04.27.538563. [PMID: 37162876 PMCID: PMC10168340 DOI: 10.1101/2023.04.27.538563] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Small GTPases function by conformational switching ability between GDP- and GTP-bound states in rapid cell signaling events. The ADP-ribosylation factor (ARF) family is involved in vesicle trafficking. Though evolutionarily well conserved, little is known about ARF and ARF-like GTPases in plants. Here, we characterized biochemical properties and cellular localization of the essential small ARF-like GTPase TITAN 5/HALLIMASCH/ARL2/ARLC1 (hereafter termed TTN5) from Arabidopsis thaliana. Two TTN5 variants were included in the study with point mutations at conserved residues, suspected to be functional for nucleotide exchange and GTP hydrolysis, TTN5T30N and TTN5Q70L. We found that TTN5 had a very rapid intrinsic nucleotide exchange capacity with a conserved nucleotide switching mechanism. TTN5 acted as a non-classical small GTPase with a remarkably low GTP hydrolysis activity, suggesting it is likely present in GTP-loaded active form in the cell. We analyzed signals from yellow fluorescent protein (YFP)-tagged TTN5 and from in situ immunolocalization of hemagglutine-tagged HA3-TTN5 in Arabidopsis seedlings and in a transient expression system. Together with colocalization using endomembrane markers and pharmacological treatments the microscopic analysis suggests that TTN5 can be present at the plasma membrane and dynamically associated with membranes of vesicles, Golgi stacks and multivesicular bodies. While the TTN5Q70L variant showed similar GTPase activities and localization behavior as wild-type TTN5, the TTN5T30N mutant differed in some aspects. Hence, the unusual capacity of rapid nucleotide exchange activity of TTN5 is linked with cell membrane dynamics, likely associated with vesicle transport pathways in the endomembrane system.
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Affiliation(s)
- Inga Mohr
- Institute of Botany, Heinrich Heine University, 40225 Düsseldorf, Germany
| | - Amin Mirzaiebadizi
- Institute of Biochemistry and Molecular Biology II, Medical Faculty and University Hospital Düsseldorf, Heinrich Heine University, Düsseldorf, Germany
| | - Sibaji K Sanyal
- Institute of Botany, Heinrich Heine University, 40225 Düsseldorf, Germany
| | - Pichaporn Chuenban
- Institute of Botany, Heinrich Heine University, 40225 Düsseldorf, Germany
| | - Mohammad R Ahmadian
- Institute of Biochemistry and Molecular Biology II, Medical Faculty and University Hospital Düsseldorf, Heinrich Heine University, Düsseldorf, Germany
| | - Rumen Ivanov
- Institute of Botany, Heinrich Heine University, 40225 Düsseldorf, Germany
| | - Petra Bauer
- Institute of Botany, Heinrich Heine University, 40225 Düsseldorf, Germany
- Cluster of Excellence on Plant Sciences, Heinrich Heine University, 40225 Düsseldorf, Germany
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3
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Gerstner CD, Reed M, Dahl TM, Ying G, Frederick JM, Baehr W. Arf-like Protein 2 (ARL2) Controls Microtubule Neogenesis during Early Postnatal Photoreceptor Development. Cells 2022; 12:147. [PMID: 36611941 PMCID: PMC9818799 DOI: 10.3390/cells12010147] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2022] [Revised: 12/12/2022] [Accepted: 12/21/2022] [Indexed: 12/31/2022] Open
Abstract
Arf-like protein 2 (ARL2) is a ubiquitously expressed small GTPase with multiple functions. In a cell culture, ARL2 participates with tubulin cofactor D (TBCD) in the neogenesis of tubulin αβ-heterodimers, the building blocks of microtubules. To evaluate this function in the retina, we conditionally deleted ARL2 in mouse retina at two distinct stages, either during the embryonic development (retArl2-/-) or after ciliogenesis specifically in rods (rodArl2-/-). retArl2-/- retina sections displayed distorted nuclear layers and a disrupted microtubule cytoskeleton (MTC) as early as postnatal day 6 (P6). Rod and cone outer segments (OS) did not form. By contrast, the rod ARL2 knockouts were stable at postnatal day 35 and revealed normal ERG responses. Cytoplasmic dynein is reduced in retArl2-/- inner segments (IS), suggesting that dynein may be unstable in the absence of a normal MTC. We investigated the microtubular stability in the absence of either ARL2 (retARL2-/-) or DYNC1H1 (retDync1h1-/-), the dynein heavy chain, and found that both the retArl2-/- and retDync1h1-/- retinas exhibited reduced microtubules and nuclear layer distortion. The results suggest that ARL2 and dynein depend on each other to generate a functional MTC during the early photoreceptor development.
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Affiliation(s)
- Cecilia D. Gerstner
- Department of Ophthalmology, University of Utah Health Science Center, Salt Lake City, UT 84132, USA
| | - Michelle Reed
- Department of Ophthalmology, University of Utah Health Science Center, Salt Lake City, UT 84132, USA
| | - Tiffanie M. Dahl
- Department of Ophthalmology, University of Utah Health Science Center, Salt Lake City, UT 84132, USA
| | - Guoxin Ying
- Department of Ophthalmology, University of Utah Health Science Center, Salt Lake City, UT 84132, USA
| | - Jeanne M. Frederick
- Department of Ophthalmology, University of Utah Health Science Center, Salt Lake City, UT 84132, USA
| | - Wolfgang Baehr
- Department of Ophthalmology, University of Utah Health Science Center, Salt Lake City, UT 84132, USA
- Department of Neurobiology & Anatomy, University of Utah, Salt Lake City, UT 84112, USA
- Department of Biology, University of Utah, Salt Lake City, UT 84112, USA
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4
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Turn RE, Linnert J, Gigante ED, Wolfrum U, Caspary T, Kahn RA. Roles for ELMOD2 and Rootletin in ciliogenesis. Mol Biol Cell 2021; 32:800-822. [PMID: 33596093 PMCID: PMC8108518 DOI: 10.1091/mbc.e20-10-0635] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
ELMOD2 is a GTPase-activating protein with uniquely broad specificity for ARF family GTPases. We previously showed that it acts with ARL2 in mitochondrial fusion and microtubule stability and with ARF6 during cytokinesis. Mouse embryonic fibroblasts deleted for ELMOD2 also displayed changes in cilia-related processes including increased ciliation, multiciliation, ciliary morphology, ciliary signaling, centrin accumulation inside cilia, and loss of rootlets at centrosomes with loss of centrosome cohesion. Increasing ARL2 activity or overexpressing Rootletin reversed these defects, revealing close functional links between the three proteins. This was further supported by the findings that deletion of Rootletin yielded similar phenotypes, which were rescued upon increasing ARL2 activity but not ELMOD2 overexpression. Thus, we propose that ARL2, ELMOD2, and Rootletin all act in a common pathway that suppresses spurious ciliation and maintains centrosome cohesion. Screening a number of markers of steps in the ciliation pathway supports a model in which ELMOD2, Rootletin, and ARL2 act downstream of TTBK2 and upstream of CP110 to prevent spurious release of CP110 and to regulate ciliary vesicle docking. These data thus provide evidence supporting roles for ELMOD2, Rootletin, and ARL2 in the regulation of ciliary licensing.
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Affiliation(s)
- Rachel E Turn
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322.,Biochemistry, Cell & Developmental Biology Graduate Program, Emory University, Atlanta, GA 30322
| | - Joshua Linnert
- Institut für Molekulare Physiologie, Johannes Gutenberg-Universität, Mainz 655099, Germany
| | - Eduardo D Gigante
- Department of Human Genetics, Emory University School of Medicine, Atlanta, GA 30322.,Neuroscience Graduate Program, Emory University, Atlanta, GA 30322
| | - Uwe Wolfrum
- Institut für Molekulare Physiologie, Johannes Gutenberg-Universität, Mainz 655099, Germany
| | - Tamara Caspary
- Department of Human Genetics, Emory University School of Medicine, Atlanta, GA 30322
| | - Richard A Kahn
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322
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5
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ElMaghloob Y, Sot B, McIlwraith MJ, Garcia E, Yelland T, Ismail S. ARL3 activation requires the co-GEF BART and effector-mediated turnover. eLife 2021; 10:e64624. [PMID: 33438581 PMCID: PMC7817177 DOI: 10.7554/elife.64624] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2020] [Accepted: 01/12/2021] [Indexed: 12/28/2022] Open
Abstract
The ADP-ribosylation factor-like 3 (ARL3) is a ciliopathy G-protein which regulates the ciliary trafficking of several lipid-modified proteins. ARL3 is activated by its guanine exchange factor (GEF) ARL13B via an unresolved mechanism. BART is described as an ARL3 effector which has also been implicated in ciliopathies, although the role of its ARL3 interaction is unknown. Here, we show that, at physiological GTP:GDP levels, human ARL3GDP is weakly activated by ARL13B. However, BART interacts with nucleotide-free ARL3 and, in concert with ARL13B, efficiently activates ARL3. In addition, BART binds ARL3GTP and inhibits GTP dissociation, thereby stabilising the active G-protein; the binding of ARL3 effectors then releases BART. Finally, using live cell imaging, we show that BART accesses the primary cilium and colocalises with ARL13B. We propose a model wherein BART functions as a bona fide co-GEF for ARL3 and maintains the active ARL3GTP, until it is recycled by ARL3 effectors.
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Affiliation(s)
| | - Begoña Sot
- Fundación IMDEA-Nanociencia, Campus de CantoblancoMadridSpain
- Unidad Asociada de Nanobiotecnología (CNB-CSIC e IMDEA Nanociencia), Campus de CantoblancoMadridSpain
| | | | | | | | - Shehab Ismail
- CRUK- Beatson InstituteGlasgowUnited Kingdom
- Institute of Cancer Sciences, University of GlasgowGlasgowUnited Kingdom
- Department of Chemistry, KU Leuven, CelestijnenlaanHeverleeBelgium
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6
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Turn RE, East MP, Prekeris R, Kahn RA. The ARF GAP ELMOD2 acts with different GTPases to regulate centrosomal microtubule nucleation and cytokinesis. Mol Biol Cell 2020; 31:2070-2091. [PMID: 32614697 PMCID: PMC7543072 DOI: 10.1091/mbc.e20-01-0012] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
ELMOD2 is a ∼32 kDa protein first purified by its GTPase-activating protein (GAP) activity toward ARL2 and later shown to have uniquely broad specificity toward ARF family GTPases in in vitro assays. To begin the task of defining its functions in cells, we deleted ELMOD2 in immortalized mouse embryonic fibroblasts and discovered a number of cellular defects, which are reversed upon expression of ELMOD2-myc. We show that these defects, resulting from the loss of ELMOD2, are linked to two different pathways and two different GTPases: with ARL2 and TBCD to support microtubule nucleation from centrosomes and with ARF6 in cytokinesis. These data highlight key aspects of signaling by ARF family GAPs that contribute to previously underappreciated sources of complexity, including GAPs acting from multiple sites in cells, working with multiple GTPases, and contributing to the spatial and temporal control of regulatory GTPases by serving as both GAPs and effectors.
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Affiliation(s)
- Rachel E Turn
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322.,Biochemistry, Cell & Developmental Biology Graduate Program, Laney Graduate School, Emory University, Atlanta, GA 30307
| | - Michael P East
- Department of Pharmacology, University of North Carolina Chapel Hill, Chapel Hill, NC 27599
| | - Rytis Prekeris
- Department of Cell and Developmental Biology, University of Colorado, Aurora, CO 80045
| | - Richard A Kahn
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322
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7
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Moye AR, Bedoni N, Cunningham JG, Sanzhaeva U, Tucker ES, Mathers P, Peter VG, Quinodoz M, Paris LP, Coutinho-Santos L, Camacho P, Purcell MG, Winkelmann AC, Foster JA, Pugacheva EN, Rivolta C, Ramamurthy V. Mutations in ARL2BP, a protein required for ciliary microtubule structure, cause syndromic male infertility in humans and mice. PLoS Genet 2019; 15:e1008315. [PMID: 31425546 PMCID: PMC6715254 DOI: 10.1371/journal.pgen.1008315] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2019] [Revised: 08/29/2019] [Accepted: 07/17/2019] [Indexed: 12/30/2022] Open
Abstract
Cilia are evolutionarily conserved hair-like structures with a wide spectrum of key biological roles, and their dysfunction has been linked to a growing class of genetic disorders, known collectively as ciliopathies. Many strides have been made towards deciphering the molecular causes for these diseases, which have in turn expanded the understanding of cilia and their functional roles. One recently-identified ciliary gene is ARL2BP, encoding the ADP-Ribosylation Factor Like 2 Binding Protein. In this study, we have identified multiple ciliopathy phenotypes associated with mutations in ARL2BP in human patients and in a mouse knockout model. Our research demonstrates that spermiogenesis is impaired, resulting in abnormally shaped heads, shortened and mis-assembled sperm tails, as well as in loss of axonemal doublets. Additional phenotypes in the mouse included enlarged ventricles of the brain and situs inversus. Mouse embryonic fibroblasts derived from knockout animals revealed delayed depolymerization of primary cilia. Our results suggest that ARL2BP is required for the structural maintenance of cilia as well as of the sperm flagellum, and that its deficiency leads to syndromic ciliopathy. The flagellated tails of sperm cells require a stringent developmental process that is essential for motility and fertility. The components that comprise the sperm tail assemble in regulated steps with protein processing, transport, and structural assembly dependent on each other for sperm tail maturity. In this work, we have identified ARL2BP, a previously retinal-associated protein, to be essential for sperm tail development and assembly. We show that without functional ARL2BP in humans or mice, sperm tails fail to develop, starting with the assembly of the core microtubular structure within the tail. Loss of ARL2BP also effects other ciliated cells, indicating a unique role for ARL2BP in ciliary microtubule formation. This research on ARL2BP provides further understanding on the links between vision and fertility. This work also demonstrates how genomic studies for human patients and murine models can coincide to provide greater insight into disease.
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Affiliation(s)
- Abigail R. Moye
- Department of Ophthalmology, West Virginia University, Morgantown, United States of America
- Department of Biochemistry, West Virginia University, Morgantown, United States of America
| | - Nicola Bedoni
- Department of Computational Biology, Unit of Medical Genetics, University of Lausanne, Lausanne, Switzerland
| | - Jessica G. Cunningham
- Rockefeller Neurosciences Institute, West Virginia University, Morgantown, WV, United States of America
| | - Urikhan Sanzhaeva
- Department of Biochemistry, West Virginia University, Morgantown, United States of America
| | - Eric S. Tucker
- Rockefeller Neurosciences Institute, West Virginia University, Morgantown, WV, United States of America
| | - Peter Mathers
- Department of Ophthalmology, West Virginia University, Morgantown, United States of America
- Department of Biochemistry, West Virginia University, Morgantown, United States of America
- Rockefeller Neurosciences Institute, West Virginia University, Morgantown, WV, United States of America
| | - Virginie G. Peter
- Department of Computational Biology, Unit of Medical Genetics, University of Lausanne, Lausanne, Switzerland
| | - Mathieu Quinodoz
- Department of Computational Biology, Unit of Medical Genetics, University of Lausanne, Lausanne, Switzerland
| | - Liliana P. Paris
- Department of Ophthalmology, Instituto de Oftalmologia Dr Gama Pinto, Lisbon, Portugal
| | - Luísa Coutinho-Santos
- Department of Ophthalmology, Instituto de Oftalmologia Dr Gama Pinto, Lisbon, Portugal
| | - Pedro Camacho
- Department of Ophthalmology, Instituto de Oftalmologia Dr Gama Pinto, Lisbon, Portugal
| | - Madeleine G. Purcell
- Department of Biology, Randolph-Macon College, Ashland, VA, United States of America
| | - Abbie C. Winkelmann
- Department of Biology, Randolph-Macon College, Ashland, VA, United States of America
| | - James A. Foster
- Department of Biology, Randolph-Macon College, Ashland, VA, United States of America
| | - Elena N. Pugacheva
- Department of Biochemistry, West Virginia University, Morgantown, United States of America
| | - Carlo Rivolta
- Department of Computational Biology, Unit of Medical Genetics, University of Lausanne, Lausanne, Switzerland
- Department of Genetics and Genome Biology, University of Leicester, Leicester, United Kingdom
- Clinical Research Center, Institute of Molecular and Clinical Ophthalmology Basel (IOB), Basel, Switzerland
- Department of Ophthalmology, University Hospital Basel, Switzerland
- * E-mail: (CR); (VR)
| | - Visvanathan Ramamurthy
- Department of Ophthalmology, West Virginia University, Morgantown, United States of America
- Department of Biochemistry, West Virginia University, Morgantown, United States of America
- Rockefeller Neurosciences Institute, West Virginia University, Morgantown, WV, United States of America
- * E-mail: (CR); (VR)
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8
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Sztul E, Chen PW, Casanova JE, Cherfils J, Dacks JB, Lambright DG, Lee FJS, Randazzo PA, Santy LC, Schürmann A, Wilhelmi I, Yohe ME, Kahn RA. ARF GTPases and their GEFs and GAPs: concepts and challenges. Mol Biol Cell 2019; 30:1249-1271. [PMID: 31084567 PMCID: PMC6724607 DOI: 10.1091/mbc.e18-12-0820] [Citation(s) in RCA: 156] [Impact Index Per Article: 31.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2019] [Revised: 02/26/2019] [Accepted: 03/11/2019] [Indexed: 12/12/2022] Open
Abstract
Detailed structural, biochemical, cell biological, and genetic studies of any gene/protein are required to develop models of its actions in cells. Studying a protein family in the aggregate yields additional information, as one can include analyses of their coevolution, acquisition or loss of functionalities, structural pliability, and the emergence of shared or variations in molecular mechanisms. An even richer understanding of cell biology can be achieved through evaluating functionally linked protein families. In this review, we summarize current knowledge of three protein families: the ARF GTPases, the guanine nucleotide exchange factors (ARF GEFs) that activate them, and the GTPase-activating proteins (ARF GAPs) that have the ability to both propagate and terminate signaling. However, despite decades of scrutiny, our understanding of how these essential proteins function in cells remains fragmentary. We believe that the inherent complexity of ARF signaling and its regulation by GEFs and GAPs will require the concerted effort of many laboratories working together, ideally within a consortium to optimally pool information and resources. The collaborative study of these three functionally connected families (≥70 mammalian genes) will yield transformative insights into regulation of cell signaling.
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Affiliation(s)
- Elizabeth Sztul
- Department of Cell, Developmental and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL 35294
| | - Pei-Wen Chen
- Department of Biology, Williams College, Williamstown, MA 01267
| | - James E. Casanova
- Department of Cell Biology, University of Virginia, Charlottesville, VA 22908
| | - Jacqueline Cherfils
- Laboratoire de Biologie et Pharmacologie Appliquée, CNRS and Ecole Normale Supérieure Paris-Saclay, 94235 Cachan, France
| | - Joel B. Dacks
- Division of Infectious Disease, Department of Medicine, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - David G. Lambright
- Program in Molecular Medicine and Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Amherst, MA 01605
| | - Fang-Jen S. Lee
- Institute of Molecular Medicine, College of Medicine, National Taiwan University, Taipei 10002, Taiwan
| | | | - Lorraine C. Santy
- Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, PA 16802
| | - Annette Schürmann
- German Institute of Human Nutrition, 85764 Potsdam-Rehbrücke, Germany
| | - Ilka Wilhelmi
- German Institute of Human Nutrition, 85764 Potsdam-Rehbrücke, Germany
| | - Marielle E. Yohe
- Pediatric Oncology Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892
| | - Richard A. Kahn
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322-3050
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9
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Wright ZC, Loskutov Y, Murphy D, Stoilov P, Pugacheva E, Goldberg AFX, Ramamurthy V. ADP-Ribosylation Factor-Like 2 (ARL2) regulates cilia stability and development of outer segments in rod photoreceptor neurons. Sci Rep 2018; 8:16967. [PMID: 30446707 PMCID: PMC6240099 DOI: 10.1038/s41598-018-35395-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2018] [Accepted: 10/28/2018] [Indexed: 01/31/2023] Open
Abstract
Photoreceptor cells are specialized neurons with a sensory cilium carrying an elaborate membrane structure, the outer segment (OS). Inherited mutations in genes involved in ciliogenesis frequently result in OS malformation and blindness. ADP-ribosylation factor-like 2 (ARL2) has recently been implicated in OS formation through its association with Binder of ARL2 (BART or ARL2BP), a protein linked to inherited blinding disease. To test the role of ARL2 in vision we created a transgenic mouse model expressing a tagged-dominant active form of human ARL2 (ARL2-Q70L) under a rod-specific promoter. Transgenic ARL2-Q70L animals exhibit reduced photoreceptor cell function as early as post-natal day 16 and progressive rod degeneration. We attribute loss of photoreceptor function to the defective OS morphogenesis in the ARL2-Q70L transgenic model. ARL2-Q70L expression results in shortened inner and outer segments, shortened and mislocalized axonemes and cytoplasmic accumulation of rhodopsin. In conclusion, we show that ARL2-Q70L is crucial for photoreceptor neuron sensory cilium development. Future research will expand upon our hypothesis that ARL2-Q70L mutant interferes with microtubule maintenance and tubulin regulation resulting in impaired growth of the axoneme and elaboration of the photoreceptor outer segment.
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Affiliation(s)
- Zachary C Wright
- Departments of Ophthalmology, West Virginia University, Morgantown, West Virginia, 26506, USA
| | - Yuriy Loskutov
- Departments of Biochemistry, West Virginia University, Morgantown, West Virginia, 26506, USA
| | - Daniel Murphy
- Departments of Biochemistry, West Virginia University, Morgantown, West Virginia, 26506, USA
| | - Peter Stoilov
- Departments of Biochemistry, West Virginia University, Morgantown, West Virginia, 26506, USA
| | - Elena Pugacheva
- Departments of Biochemistry, West Virginia University, Morgantown, West Virginia, 26506, USA
| | | | - Visvanathan Ramamurthy
- Departments of Ophthalmology, West Virginia University, Morgantown, West Virginia, 26506, USA. .,Departments of Biochemistry, West Virginia University, Morgantown, West Virginia, 26506, USA. .,Center for Neuroscience, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, West Virginia, 26506, USA.
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10
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Schiavon CR, Griffin ME, Pirozzi M, Parashuraman R, Zhou W, Jinnah HA, Reines D, Kahn RA. Compositional complexity of rods and rings. Mol Biol Cell 2018; 29:2303-2316. [PMID: 30024290 PMCID: PMC6249804 DOI: 10.1091/mbc.e18-05-0274] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Rods and rings (RRs) are large linear- or circular-shaped structures typically described as polymers of IMPDH (inosine monophosphate dehydrogenase). They have been observed across a wide variety of cell types and species and can be induced to form by inhibitors of IMPDH. RRs are thought to play a role in the regulation of de novo guanine nucleotide synthesis; however, the function and regulation of RRs is poorly understood. Here we show that the regulatory GTPase, ARL2, a subset of its binding partners, and several resident proteins at the endoplasmic reticulum (ER) also localize to RRs. We also have identified two new inducers of RR formation: AICAR and glucose deprivation. We demonstrate that RRs can be disassembled if guanine nucleotides can be generated by salvage synthesis regardless of the inducer. Finally, we show that there is an ordered addition of components as RRs mature, with IMPDH first forming aggregates, followed by ARL2, and only later calnexin, a marker of the ER. These findings suggest that RRs are considerably more complex than previously thought and that the function(s) of RRs may include involvement of a regulatory GTPase, its effectors, and potentially contacts with intracellular membranes.
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Affiliation(s)
- Cara R Schiavon
- Cancer Biology Graduate Program, Graduate Division of Biomedical and Biological Sciences, Laney Graduate School, Atlanta, GA 30307
| | - Maxwell E Griffin
- Cancer Biology Graduate Program, Graduate Division of Biomedical and Biological Sciences, Laney Graduate School, Atlanta, GA 30307
| | - Marinella Pirozzi
- EuroBioImaging Facility, Institute of Protein Biochemistry, 80131 Naples, Italy
| | - Raman Parashuraman
- EuroBioImaging Facility, Institute of Protein Biochemistry, 80131 Naples, Italy
| | - Wei Zhou
- Department of Hematology and Medical Oncology, Emory University School of Medicine, Atlanta, GA 30322
| | - H A Jinnah
- Department of Neurology and Human Genetics, Emory University School of Medicine, Atlanta, GA 30322
| | - Daniel Reines
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322
| | - Richard A Kahn
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322
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11
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Moye AR, Singh R, Kimler VA, Dilan TL, Munezero D, Saravanan T, Goldberg AFX, Ramamurthy V. ARL2BP, a protein linked to retinitis pigmentosa, is needed for normal photoreceptor cilia doublets and outer segment structure. Mol Biol Cell 2018; 29:1590-1598. [PMID: 29718757 PMCID: PMC6080659 DOI: 10.1091/mbc.e18-01-0040] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The outer segment (OS) of photoreceptor cells is an elaboration of a primary cilium with organized stacks of membranous disks that contain the proteins needed for phototransduction and vision. Though ciliary formation and function has been well characterized, little is known about the role of cilia in the development of photoreceptor OS. Nevertheless, progress has been made by studying mutations in ciliary proteins, which often result in malformed OSs and lead to blinding diseases. To investigate how ciliary proteins contribute to OS formation, we generated a knockout (KO) mouse model for ARL2BP, a ciliary protein linked to retinitis pigmentosa. The KO mice display an early and progressive reduction in visual response. Before photoreceptor degeneration, we observed disorganization of the photoreceptor OS, with vertically aligned disks and shortened axonemes. Interestingly, ciliary doublet microtubule (MT) structure was also impaired, displaying open B-tubule doublets, paired with loss of singlet MTs. On the basis of results from this study, we conclude that ARL2BP is necessary for photoreceptor ciliary doublet formation and axoneme elongation, which is required for OS morphogenesis and vision.
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Affiliation(s)
- Abigail R Moye
- Department of Ophthalmology, West Virginia University, Morgantown, WV 26506.,Department of Biochemistry, West Virginia University, Morgantown, WV 26506
| | - Ratnesh Singh
- Department of Biochemistry, West Virginia University, Morgantown, WV 26506
| | | | - Tanya L Dilan
- Department of Ophthalmology, West Virginia University, Morgantown, WV 26506.,Department of Biochemistry, West Virginia University, Morgantown, WV 26506
| | - Daniella Munezero
- Department of Ophthalmology, West Virginia University, Morgantown, WV 26506.,Department of Biochemistry, West Virginia University, Morgantown, WV 26506
| | | | | | - Visvanathan Ramamurthy
- Department of Ophthalmology, West Virginia University, Morgantown, WV 26506.,Department of Biochemistry, West Virginia University, Morgantown, WV 26506.,Rockefeller Neurosciences Institute, West Virginia University, Morgantown, WV 26506
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12
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The abundance of the ARL2 GTPase and its GAP, ELMOD2, at mitochondria are modulated by the fusogenic activity of mitofusins and stressors. PLoS One 2017; 12:e0175164. [PMID: 28380071 PMCID: PMC5381910 DOI: 10.1371/journal.pone.0175164] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2016] [Accepted: 03/21/2017] [Indexed: 12/05/2022] Open
Abstract
Mitochondria are essential, dynamic organelles that respond to a number of stressors with changes in morphology that are linked to several mitochondrial functions, though the mechanisms involved are poorly understood. We show that the levels of the regulatory GTPase ARL2 and its GAP, ELMOD2, are specifically increased at mitochondria in immortalized mouse embryo fibroblasts deleted for Mitofusin 2 (MFN2), but not MFN1. Elevated ARL2 and ELMOD2 in MEFs deleted for MFN2 could be reversed by re-introduction of MFN2, but only when the mitochondrial fragmentation in these MEFs was also reversed, demonstrating that reversal of elevated ARL2 and ELMOD2 requires the fusogenic activity of MFN2. Other stressors with links to mitochondrial morphology were investigated and several, including glucose or serum deprivation, also caused increases in ARL2 and ELMOD2. In contrast, a number of pharmacological inhibitors of energy metabolism caused increases in ARL2 without affecting ELMOD2 levels. Together we interpret these data as evidence of two ARL2-sensitive pathways in mitochondria, one affecting ATP levels that is independent of ELMOD2 and the other leading to mitochondrial fusion involving MFN2 that does involve ELMOD2.
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13
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Francis JW, Newman LE, Cunningham LA, Kahn RA. A Trimer Consisting of the Tubulin-specific Chaperone D (TBCD), Regulatory GTPase ARL2, and β-Tubulin Is Required for Maintaining the Microtubule Network. J Biol Chem 2017; 292:4336-4349. [PMID: 28126905 DOI: 10.1074/jbc.m116.770909] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2016] [Revised: 01/24/2017] [Indexed: 11/06/2022] Open
Abstract
Microtubule dynamics involves the polymerization and depolymerization of tubulin dimers and is an essential and highly regulated process required for cell viability, architecture, and division. The regulation of the microtubule network also depends on the maintenance of a pool of αβ-tubulin heterodimers. These dimers are the end result of complex folding and assembly events, requiring the TCP1 Ring Complex (TriC or CCT) chaperonin and five tubulin-specific chaperones, tubulin binding cofactors A-E (TBCA-TBCE). However, models of the actions of these chaperones are incomplete or inconsistent. We previously purified TBCD from bovine tissues and showed that it tightly binds the small GTPase ARL2 but appears to be inactive. Here, in an effort to identify the functional form of TBCD and using non-denaturing gels and immunoblotting, we analyzed lysates from a number of mouse tissues and cell lines to identify the quaternary state(s) of TBCD and ARL2. We found that both proteins co-migrated in native gels in a complex of ∼200 kDa that also contained β-tubulin. Using human embryonic kidney cells enabled the purification of the TBCD·ARL2·β-tubulin trimer found in cell and tissue lysates as well as two other novel TBCD complexes. Characterization of ARL2 point mutants that disrupt binding to TBCD suggested that the ARL2-TBCD interaction is critical for proper maintenance of microtubule densities in cells. We conclude that the TBCD·ARL2·β-tubulin trimer represents a functional complex whose activity is fundamental to microtubule dynamics.
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Affiliation(s)
- Joshua W Francis
- From the Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322
| | - Laura E Newman
- From the Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322
| | - Leslie A Cunningham
- From the Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322
| | - Richard A Kahn
- From the Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322
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14
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Abstract
Arl2 and Arl3 are Arf-like small GTP-binding proteins of the Arf subfamily of the Ras superfamily. Despite their structural similarity and sharing of many interacting partners, Arl2 and Arl3 have different biochemical properties and biological functions. Growing evidence suggest that Arl2 and Arl3 play a fundamental role as regulators of trafficking of lipid modified proteins between different compartments. Here we highlight the similarities and differences between these 2 homologous proteins and discuss the sorting mechanism of lipidated cargo into the ciliary compartment through the carriers PDE6δ and Unc119 and the release factors Arl2 and Arl3.
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Affiliation(s)
- Eyad K Fansa
- a Max Planck Institute of Molecular Physiology , Dortmund , Germany
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15
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Francis JW, Turn RE, Newman LE, Schiavon C, Kahn RA. Higher order signaling: ARL2 as regulator of both mitochondrial fusion and microtubule dynamics allows integration of 2 essential cell functions. Small GTPases 2016; 7:188-196. [PMID: 27400436 PMCID: PMC5129891 DOI: 10.1080/21541248.2016.1211069] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2016] [Revised: 07/05/2016] [Accepted: 07/06/2016] [Indexed: 10/21/2022] Open
Abstract
ARL2 is among the most highly conserved proteins, predicted to be present in the last eukaryotic common ancestor, and ubiquitously expressed. Genetic screens in multiple model organisms identified ARL2, and its cytosolic binding partner cofactor D (TBCD), as important in tubulin folding and microtubule dynamics. Both ARL2 and TBCD also localize to centrosomes, making it difficult to dissect these effects. A growing body of evidence also has found roles for ARL2 inside mitochondria, as a regulator of mitochondrial fusion. Other studies have revealed roles for ARL2, in concert with its closest paralog ARL3, in the traffic of farnesylated cargos between membranes and specifically to cilia and photoreceptor cells. Details of each of these signaling processes continue to emerge. We summarize those data here and speculate about the potential for cross-talk or coordination of cell regulation, termed higher order signaling, based upon the use of a common GTPase in disparate cell functions.
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Affiliation(s)
- Joshua W. Francis
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA, USA
| | - Rachel E. Turn
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA, USA
| | - Laura E. Newman
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA, USA
| | - Cara Schiavon
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA, USA
| | - Richard A. Kahn
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA, USA
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16
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Togi S, Muromoto R, Hirashima K, Kitai Y, Okayama T, Ikeda O, Matsumoto N, Kon S, Sekine Y, Oritani K, Matsuda T. A New STAT3-binding Partner, ARL3, Enhances the Phosphorylation and Nuclear Accumulation of STAT3. J Biol Chem 2016; 291:11161-71. [PMID: 27048653 DOI: 10.1074/jbc.m116.724849] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2016] [Indexed: 01/05/2023] Open
Abstract
Signal transducer and activator of transcription 3 (STAT3) is involved in cell proliferation, differentiation, and cell survival during immune responses, hematopoiesis, neurogenesis, and other biological processes. STAT3 activity is regulated by a variety of mechanisms, including phosphorylation and nuclear translocation. To clarify the molecular mechanisms underlying the regulation of STAT3 activity, we performed yeast two-hybrid screening. We identified ARL3 (ADP-ribosylation factor-like 3) as a novel STAT3-binding partner. ARL3 recognizes the DNA-binding domain as well as the C-terminal region of STAT3 in vivo, and their binding was the strongest when both proteins were activated. Importantly, small interfering RNA-mediated reduction of endogenous ARL3 expression decreased IL-6-induced tyrosine phosphorylation, nuclear accumulation, and transcriptional activity of STAT3. These results indicate that ARL3 interacts with STAT3 and regulates the transcriptional activation of STAT3 by influencing its nuclear accumulation of STAT3.
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Affiliation(s)
- Sumihito Togi
- From the Department of Immunology, Graduate School of Pharmaceutical Sciences, Hokkaido University, Kita-12 Nishi-6, Kita-Ku, Sapporo, 060-0812 and
| | - Ryuta Muromoto
- From the Department of Immunology, Graduate School of Pharmaceutical Sciences, Hokkaido University, Kita-12 Nishi-6, Kita-Ku, Sapporo, 060-0812 and
| | - Koki Hirashima
- From the Department of Immunology, Graduate School of Pharmaceutical Sciences, Hokkaido University, Kita-12 Nishi-6, Kita-Ku, Sapporo, 060-0812 and
| | - Yuichi Kitai
- From the Department of Immunology, Graduate School of Pharmaceutical Sciences, Hokkaido University, Kita-12 Nishi-6, Kita-Ku, Sapporo, 060-0812 and
| | - Taichiro Okayama
- From the Department of Immunology, Graduate School of Pharmaceutical Sciences, Hokkaido University, Kita-12 Nishi-6, Kita-Ku, Sapporo, 060-0812 and
| | - Osamu Ikeda
- From the Department of Immunology, Graduate School of Pharmaceutical Sciences, Hokkaido University, Kita-12 Nishi-6, Kita-Ku, Sapporo, 060-0812 and
| | - Naoki Matsumoto
- From the Department of Immunology, Graduate School of Pharmaceutical Sciences, Hokkaido University, Kita-12 Nishi-6, Kita-Ku, Sapporo, 060-0812 and
| | - Shigeyuki Kon
- From the Department of Immunology, Graduate School of Pharmaceutical Sciences, Hokkaido University, Kita-12 Nishi-6, Kita-Ku, Sapporo, 060-0812 and
| | - Yuichi Sekine
- From the Department of Immunology, Graduate School of Pharmaceutical Sciences, Hokkaido University, Kita-12 Nishi-6, Kita-Ku, Sapporo, 060-0812 and
| | - Kenji Oritani
- the Department of Hematology and Oncology, Graduate School of Medicine, Osaka University, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan
| | - Tadashi Matsuda
- From the Department of Immunology, Graduate School of Pharmaceutical Sciences, Hokkaido University, Kita-12 Nishi-6, Kita-Ku, Sapporo, 060-0812 and
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17
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The Function of Arf-like Proteins ARL2 and ARL3 in Photoreceptors. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2016; 854:655-61. [PMID: 26427472 DOI: 10.1007/978-3-319-17121-0_87] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Arf-like proteins (ARLs) are ubiquitously expressed small G proteins of the RAS superfamily. In photoreceptors, ARL2 and ARL3 participate in the trafficking of lipidated membrane-associated proteins and colocalize in the inner segment with UNC119A and PDEδ. UNC119A and PDEδ are acyl- and prenyl-binding proteins, respectively, involved in trafficking of acylated (transducin-α subunit, nephrocystin NPHP3) and prenylated proteins (GRK1, PDE6). Germline Arl3 knockout mice do not survive beyond postnatal day 21 and display ciliary defects in multiple organs (kidney, liver and pancreas) as well as retinal degeneration. Conditional knockouts will be necessary to delineate mechanisms of protein transport in retina disease.
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18
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Lokaj M, Kösling SK, Koerner C, Lange SM, van Beersum SEC, van Reeuwijk J, Roepman R, Horn N, Ueffing M, Boldt K, Wittinghofer A. The Interaction of CCDC104/BARTL1 with Arl3 and Implications for Ciliary Function. Structure 2015; 23:2122-32. [PMID: 26455799 PMCID: PMC4635315 DOI: 10.1016/j.str.2015.08.016] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2015] [Revised: 08/26/2015] [Accepted: 08/29/2015] [Indexed: 01/23/2023]
Abstract
Cilia are small antenna-like cellular protrusions critical for many developmental signaling pathways. The ciliary protein Arl3 has been shown to act as a specific release factor for myristoylated and farnesylated ciliary cargo molecules by binding to the effectors Unc119 and PDE6δ. Here we describe a newly identified Arl3 binding partner, CCDC104/CFAP36. Biochemical and structural analyses reveal that the protein contains a BART-like domain and is called BARTL1. It recognizes an LLxILxxL motif at the N-terminal amphipathic helix of Arl3, which is crucial for the interaction with the BART-like domain but also for the ciliary localization of Arl3 itself. These results seem to suggest a ciliary role of BARTL1, and possibly link it to the Arl3 transport network. We thus speculate on a regulatory mechanism whereby BARTL1 aids the presentation of active Arl3 to its GTPase-activating protein RP2 or hinders Arl3 membrane binding in the area of the transition zone.
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Affiliation(s)
- Mandy Lokaj
- Max-Planck-Institute of Molecular Physiology, Emeritus Group, Otto-Hahn-Straße 15, 44227 Dortmund, Germany
| | - Stefanie K Kösling
- Max-Planck-Institute of Molecular Physiology, Emeritus Group, Otto-Hahn-Straße 15, 44227 Dortmund, Germany
| | - Carolin Koerner
- Max-Planck-Institute of Molecular Physiology, Emeritus Group, Otto-Hahn-Straße 15, 44227 Dortmund, Germany
| | - Sven M Lange
- Max-Planck-Institute of Molecular Physiology, Emeritus Group, Otto-Hahn-Straße 15, 44227 Dortmund, Germany
| | - Sylvia E C van Beersum
- Department of Human Genetics and Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Geert Grooteplein Zuid 10, 6525 GA Nijmegen, the Netherlands
| | - Jeroen van Reeuwijk
- Department of Human Genetics and Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Geert Grooteplein Zuid 10, 6525 GA Nijmegen, the Netherlands
| | - Ronald Roepman
- Department of Human Genetics and Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Geert Grooteplein Zuid 10, 6525 GA Nijmegen, the Netherlands
| | - Nicola Horn
- Medical Proteome Center, Institute for Ophthalmic Research, University of Tübingen, Nägelestrasse 5, 72074 Tübingen, Germany
| | - Marius Ueffing
- Medical Proteome Center, Institute for Ophthalmic Research, University of Tübingen, Nägelestrasse 5, 72074 Tübingen, Germany
| | - Karsten Boldt
- Medical Proteome Center, Institute for Ophthalmic Research, University of Tübingen, Nägelestrasse 5, 72074 Tübingen, Germany
| | - Alfred Wittinghofer
- Max-Planck-Institute of Molecular Physiology, Emeritus Group, Otto-Hahn-Straße 15, 44227 Dortmund, Germany.
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19
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Kapoor S, Fansa EK, Möbitz S, Ismail SA, Winter R, Wittinghofer A, Weise K. Effect of the N-Terminal Helix and Nucleotide Loading on the Membrane and Effector Binding of Arl2/3. Biophys J 2015; 109:1619-29. [PMID: 26488653 PMCID: PMC4624342 DOI: 10.1016/j.bpj.2015.08.033] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2015] [Revised: 08/05/2015] [Accepted: 08/10/2015] [Indexed: 01/02/2023] Open
Abstract
The small GTP-binding proteins Arl2 and Arl3, which are close homologs, share a number of interacting partners and act as displacement factors for prenylated and myristoylated cargo. Nevertheless, both proteins have distinct biological functions. Whereas Arl3 is considered a ciliary protein, Arl2 has been reported to be involved in tubulin folding, mitochondrial function, and Ras signaling. How these different roles are attained by the two homolog proteins is not fully understood. Recently, we showed that the N-terminal amphipathic helix of Arl3, but not that of Arl2, regulates the release of myristoylated ciliary proteins from the GDI-like solubilizing factor UNC119a/b. In the biophysical study presented here, both proteins are shown to exhibit a preferential localization and clustering in liquid-disordered domains of phase-separated membranes. However, the membrane interaction behavior differs significantly between both proteins with regard to their nucleotide loading. Whereas Arl3 and other Arf proteins with an N-terminal amphipathic helix require GTP loading for the interaction with membranes, Arl2 binds to membranes in a nucleotide-independent manner. In contrast to Arl2, the N-terminal helix of Arl3 increases the binding affinity to UNC119a. Furthermore, UNC119a impedes membrane binding of Arl3, but not of Arl2. Taken together, these results suggest an interplay among the nucleotide status of Arl3, the location of the N-terminal helix, membrane fluidity and binding, and the release of lipid modified cargos from carriers such as UNC119a. Since a specific Arl3-GEF is postulated to reside inside cilia, the N-terminal helix of Arl3•GTP would be available for allosteric regulation of UNC119a cargo release only inside cilia.
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Affiliation(s)
- Shobhna Kapoor
- Physical Chemistry I - Biophysical Chemistry, TU Dortmund University, Dortmund, Germany; Department of Chemical Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
| | - Eyad K Fansa
- Structural Biology Group, Max Planck Institute of Molecular Physiology, Dortmund, Germany
| | - Simone Möbitz
- Physical Chemistry I - Biophysical Chemistry, TU Dortmund University, Dortmund, Germany
| | - Shehab A Ismail
- Structural Biology Group, Max Planck Institute of Molecular Physiology, Dortmund, Germany; Structural Biology of Cilia, CR-UK Beatson Institute, Glasgow, United Kingdom
| | - Roland Winter
- Physical Chemistry I - Biophysical Chemistry, TU Dortmund University, Dortmund, Germany
| | - Alfred Wittinghofer
- Structural Biology Group, Max Planck Institute of Molecular Physiology, Dortmund, Germany.
| | - Katrin Weise
- Physical Chemistry I - Biophysical Chemistry, TU Dortmund University, Dortmund, Germany.
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20
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Newman LE, Zhou CJ, Mudigonda S, Mattheyses AL, Paradies E, Marobbio CMT, Kahn RA. The ARL2 GTPase is required for mitochondrial morphology, motility, and maintenance of ATP levels. PLoS One 2014; 9:e99270. [PMID: 24911211 PMCID: PMC4050054 DOI: 10.1371/journal.pone.0099270] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2014] [Accepted: 05/13/2014] [Indexed: 02/06/2023] Open
Abstract
ARF-like 2 (ARL2) is a member of the ARF family and RAS superfamily of regulatory GTPases, predicted to be present in the last eukaryotic common ancestor, and essential in a number of model genetic systems. Though best studied as a regulator of tubulin folding, we previously demonstrated that ARL2 partially localizes to mitochondria. Here, we show that ARL2 is essential to a number of mitochondrial functions, including mitochondrial morphology, motility, and maintenance of ATP levels. We compare phenotypes resulting from ARL2 depletion and expression of dominant negative mutants and use these to demonstrate that the mitochondrial roles of ARL2 are distinct from its roles in tubulin folding. Testing of current models for ARL2 actions at mitochondria failed to support them. Rather, we found that knockdown of the ARL2 GTPase activating protein (GAP) ELMOD2 phenocopies two of three phenotypes of ARL2 siRNA, making it a likely effector for these actions. These results add new layers of complexity to ARL2 signaling, highlighting the need to deconvolve these different cell functions. We hypothesize that ARL2 plays essential roles inside mitochondria along with other cellular functions, at least in part to provide coupling of regulation between these essential cell processes.
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Affiliation(s)
- Laura E. Newman
- Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia, United States of America
| | - Cheng-jing Zhou
- Department of Pediatrics, Emory University School of Medicine, Atlanta, Georgia, United States of America
| | - Samatha Mudigonda
- Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia, United States of America
| | - Alexa L. Mattheyses
- Department of Cell Biology, Emory University School of Medicine, Atlanta, Georgia, United States of America
| | - Eleonora Paradies
- Consiglio Nazionale delle Ricerche Institute of Biomembranes and Bioenergetics, Bari, Italy
| | | | - Richard A. Kahn
- Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia, United States of America
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21
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Abstract
The ARF-like (ARL) proteins, within the ARF family, are a collection of functionally diverse GTPases that share extensive (>40 %) identity with the ARFs and each other and are assumed to share basic mechanisms of regulation and a very incompletely documented degree of overlapping regulators. At least four ARLs were already present in the last eukaryotic common ancestor, along with one ARF, and these have been expanded to >20 members in mammals. We know little about the majority of these proteins so our review will focus on those about which the most is known, including ARL1, ARL2, ARL3, ARL4s, ARL6, ARL13s, and ARFRP1. From this fragmentary information we extract some generalizations and conclusions regarding the sources and extent of specificity and functions of the ARLs.
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Affiliation(s)
- Alfred Wittinghofer
- Max-Planck-Institute of Molecular Physiology, Dortmund, Nordrhein-Westfalen Germany
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22
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Davidson AE, Schwarz N, Zelinger L, Stern-Schneider G, Shoemark A, Spitzbarth B, Gross M, Laxer U, Sosna J, Sergouniotis PI, Waseem NH, Wilson R, Kahn RA, Plagnol V, Wolfrum U, Banin E, Hardcastle AJ, Cheetham ME, Sharon D, Webster AR. Mutations in ARL2BP, encoding ADP-ribosylation-factor-like 2 binding protein, cause autosomal-recessive retinitis pigmentosa. Am J Hum Genet 2013; 93:321-9. [PMID: 23849777 DOI: 10.1016/j.ajhg.2013.06.003] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2013] [Revised: 05/03/2013] [Accepted: 06/04/2013] [Indexed: 01/01/2023] Open
Abstract
Retinitis pigmentosa (RP) is a genetically heterogeneous retinal degeneration characterized by photoreceptor death, which results in visual failure. Here, we used a combination of homozygosity mapping and exome sequencing to identify mutations in ARL2BP, which encodes an effector protein of the small GTPases ARL2 and ARL3, as causative for autosomal-recessive RP (RP66). In a family affected by RP and situs inversus, a homozygous, splice-acceptor mutation, c.101-1G>C, which alters pre-mRNA splicing of ARLBP2 in blood RNA, was identified. In another family, a homozygous c.134T>G (p.Met45Arg) mutation was identified. In the mouse retina, ARL2BP localized to the basal body and cilium-associated centriole of photoreceptors and the periciliary extension of the inner segment. Depletion of ARL2BP caused cilia shortening. Moreover, depletion of ARL2, but not ARL3, caused displacement of ARL2BP from the basal body, suggesting that ARL2 is vital for recruiting or anchoring ARL2BP at the base of the cilium. This hypothesis is supported by the finding that the p.Met45Arg amino acid substitution reduced binding to ARL2 and caused the loss of ARL2BP localization at the basal body in ciliated nasal epithelial cells. These data demonstrate a role for ARL2BP and ARL2 in primary cilia function and that this role is essential for normal photoreceptor maintenance and function.
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23
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Mori R, Toda T. The dual role of fission yeast Tbc1/cofactor C orchestrates microtubule homeostasis in tubulin folding and acts as a GAP for GTPase Alp41/Arl2. Mol Biol Cell 2013; 24:1713-24, S1-8. [PMID: 23576550 PMCID: PMC3667724 DOI: 10.1091/mbc.e12-11-0792] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2012] [Revised: 02/22/2013] [Accepted: 03/29/2013] [Indexed: 11/11/2022] Open
Abstract
Supplying the appropriate amount of correctly folded α/β-tubulin heterodimers is critical for microtubule dynamics. Formation of assembly-competent heterodimers is remarkably elaborate at the molecular level, in which the α- and β-tubulins are separately processed in a chaperone-dependent manner. This sequential step is performed by the tubulin-folding cofactor pathway, comprising a specific set of regulatory proteins: cofactors A-E. We identified the fission yeast cofactor: the orthologue of cofactor C, Tbc1. In addition to its roles in tubulin folding, Tbc1 acts as a GAP in regulating Alp41/Arl2, a highly conserved small GTPase. Of interest, the expression of GDP- or GTP-bound Alp41 showed the identical microtubule loss phenotype, suggesting that continuous cycling between these forms is important for its functions. In addition, we found that Alp41 interacts with Alp1(D), the orthologue of cofactor D, specifically when in the GDP-bound form. Intriguingly, Alp1(D) colocalizes with microtubules when in excess, eventually leading to depolymerization, which is sequestered by co-overproducing GDP-bound Alp41. We present a model of the final stages of the tubulin cofactor pathway that includes a dual role for both Tbc1 and Alp1(D) in opposing regulation of the microtubule.
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Affiliation(s)
- Risa Mori
- Cell Regulation Laboratory, Cancer Research UK, London Research Institute, Lincoln's Inn Fields Laboratories, London WC2A 3LY, United Kingdom
| | - Takashi Toda
- Cell Regulation Laboratory, Cancer Research UK, London Research Institute, Lincoln's Inn Fields Laboratories, London WC2A 3LY, United Kingdom
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24
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BART inhibits pancreatic cancer cell invasion by Rac1 inactivation through direct binding to active Rac1. Neoplasia 2012; 14:440-50. [PMID: 22745590 DOI: 10.1593/neo.12352] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2012] [Revised: 04/06/2012] [Accepted: 04/09/2012] [Indexed: 12/16/2022] Open
Abstract
We report that Binder of Arl Two (BART) plays a role in inhibiting cell invasion by regulating the activity of the Rho small guanosine triphosphatase protein Rac1 in pancreatic cancer cells. BART was originally identified as a binding partner of ADP-ribosylation factor-like 2, a small G protein implicated as a regulator of microtubule dynamics and folding. BART interacts with active forms of Rac1, and the BART-Rac1 complex localizes at the leading edges of migrating cancer cells. Suppression of BART increases active Rac1, thereby increasing cell invasion. Treatment of pancreatic cancer cells in which BART is stably knocked down with a Rac1 inhibitor decreases invasiveness. Thus, BART-dependent inhibition of cell invasion is likely associated with decreased active Rac1. Suppression of BART induces membrane ruffling and lamellipodial protrusion and increases peripheral actin structures in membrane ruffles at the edges of lamellipodia. The Rac1 inhibitor inhibits the lamellipodia formation that is stimulated by suppression of BART. Our results imply that BART regulates actin-cytoskeleton rearrangements at membrane ruffles through modulation of the activity of Rac1, which, in turn, inhibits pancreatic cancer cell invasion.
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25
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Taniuchi K, Yokotani K, Saibara T. BART inhibits pancreatic cancer cell invasion by PKCα inactivation through binding to ANX7. PLoS One 2012; 7:e35674. [PMID: 22532868 PMCID: PMC3330813 DOI: 10.1371/journal.pone.0035674] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2012] [Accepted: 03/19/2012] [Indexed: 11/27/2022] Open
Abstract
A novel function for the binder of Arl two (BART) molecule in pancreatic cancer cells is reported. BART inhibits invasiveness of pancreatic cancer cells through binding to a Ca2+-dependent, phosphorylated, guanosine triphosphatase (GTPase) membrane fusion protein, annexin7 (ANX7). A tumor suppressor function for ANX7 was previously reported based on its prognostic role in human cancers and the cancer-prone mouse phenotype ANX7(+/−). Further investigation demonstrated that the BART–ANX7 complex is transported toward cell protrusions in migrating cells when BART supports the binding of ANX7 to the protein kinase C (PKC) isoform PKCα. Recent evidence has suggested that phosphorylation of ANX7 by PKC significantly potentiates ANX7-induced fusion of phospholipid vesicles; however, the current data suggest that the BART–ANX7 complex reduces PKCα activity. Knocking down endogenous BART and ANX7 increases activity of PKCα, and specific inhibitors of PKCα significantly abrogate invasiveness induced by BART and ANX7 knockdown. These results imply that BART contributes to regulating PKCα activity through binding to ANX7, thereby affecting the invasiveness of pancreatic cancer cells. Thus, it is possible that BART and ANX7 can distinctly regulate the downstream signaling of PKCα that is potentially relevant to cell invasion by acting as anti-invasive molecules.
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Affiliation(s)
- Keisuke Taniuchi
- Department of Pharmacology, School of Medicine, Kochi University, Nankoku, Kochi, Japan.
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26
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Wright KJ, Baye LM, Olivier-Mason A, Mukhopadhyay S, Sang L, Kwong M, Wang W, Pretorius PR, Sheffield VC, Sengupta P, Slusarski DC, Jackson PK. An ARL3-UNC119-RP2 GTPase cycle targets myristoylated NPHP3 to the primary cilium. Genes Dev 2011; 25:2347-60. [PMID: 22085962 DOI: 10.1101/gad.173443.111] [Citation(s) in RCA: 177] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The membrane of the primary cilium is a highly specialized compartment that organizes proteins to achieve spatially ordered signaling. Disrupting ciliary organization leads to diseases called ciliopathies, with phenotypes ranging from retinal degeneration and cystic kidneys to neural tube defects. How proteins are selectively transported to and organized in the primary cilium remains unclear. Using a proteomic approach, we identified the ARL3 effector UNC119 as a binding partner of the myristoylated ciliopathy protein nephrocystin-3 (NPHP3). We mapped UNC119 binding to the N-terminal 200 residues of NPHP3 and found the interaction requires myristoylation. Creating directed mutants predicted from a structural model of the UNC119-myristate complex, we identified highly conserved phenylalanines within a hydrophobic β sandwich to be essential for myristate binding. Furthermore, we found that binding of ARL3-GTP serves to release myristoylated cargo from UNC119. Finally, we showed that ARL3, UNC119b (but not UNC119a), and the ARL3 GAP Retinitis Pigmentosa 2 (RP2) are required for NPHP3 ciliary targeting and that targeting requires UNC119b myristoyl-binding activity. Our results uncover a selective, membrane targeting GTPase cycle that delivers myristoylated proteins to the ciliary membrane and suggest that other myristoylated proteins may be similarly targeted to specialized membrane domains.
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Affiliation(s)
- Kevin J Wright
- Genentech Inc., South San Francisco, California 94080, USA
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27
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Taniuchi K, Nishimori I, Hollingsworth MA. The N-terminal domain of G3BP enhances cell motility and invasion by posttranscriptional regulation of BART. Mol Cancer Res 2011; 9:856-66. [PMID: 21665939 DOI: 10.1158/1541-7786.mcr-10-0574] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The regulation of mRNA stability plays an important role in the control of gene expression during cell motility and invasion. We previously reported that GTPase-activating protein [Src homology 3 (SH3) domain] binding protein (G3BP), a marker of cytoplasmic stress granules that are formed in stressed cells and regulate mRNA stability, binds and degrades the mRNA of binder of Arl two (BART) that inhibits retroperitoneal invasion and hepatic metastasis of pancreatic cancer cells. Here, we report that overexpression of the amino (N)-terminal region of G3BP, including the binding region for BART mRNA, dominant-negatively inhibits formation of the complex between endogenous G3BP and BART mRNA, and increases the expression of BART. This, in turn, inhibits the invasiveness of pancreatic cancer cells. On the other hand, the carboxy (C)-terminal region of G3BP is associated with phosphorylation of eukaryotic translation initiation factor 2α (eIF2α) that initiates stress granule assembly but does not modulate the posttranscriptional regulation of BART mRNA. N-terminal G3BP also plays a role in regulating secreted matrix metalloproteinases, transcription factors, and a variety of genes involved in cell adhesion and motility. These results suggest that N-terminal G3BP contributes to posttranscriptional regulation of cell motility and invasive capacity of pancreatic cancer.
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Affiliation(s)
- Keisuke Taniuchi
- Eppley Institute for Research in Cancer and Allied Diseases, and Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, Nebraska, USA.
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28
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Chavrier P, Ménétrey J. Toward a structural understanding of arf family:effector specificity. Structure 2011; 18:1552-8. [PMID: 21134634 DOI: 10.1016/j.str.2010.11.004] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2010] [Revised: 11/15/2010] [Accepted: 11/17/2010] [Indexed: 11/17/2022]
Abstract
Arf family proteins are critical regulators of intracellular trafficking and actin cytoskeleton dynamics. To carry out their cellular functions, Arf family proteins interact with various effectors that differ in nature and structure. Understanding how these proteins interact with structurally different partners and are distinguished by specific effectors while being closely related requires a structural characterization and comparison of the various Arf family:effector complexes. Recent structural reports of Arf and Arl proteins in complex with different downstream effectors shed new light on general and specific structural recognition determinants characteristic of Arf family proteins.
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29
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Taniuchi K, Nishimori I, Hollingsworth MA. Intracellular CD24 Inhibits Cell Invasion by Posttranscriptional Regulation of BART through Interaction with G3BP. Cancer Res 2011; 71:895-905. [DOI: 10.1158/0008-5472.can-10-2743] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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30
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Abstract
The Arf-like (Arl) small GTPases have a diverse range of functions in the eukaryotic cell. Metazoan Arl2 acts as a regulator of microtubule biogenesis, binding to the tubulin-specific chaperone cofactor D. Arl2 also has a mitochondrial function through its interactions with BART and ANT-1, the only member of the Ras superfamily to be found in this organelle to date. In the present study, we describe characterization of the Arl2 orthologue in the protozoan parasite Trypanosoma brucei. Modulation of TbARL2 expression in bloodstream form parasites by RNA interference (RNAi) causes inhibition of cleavage furrow formation, resulting in a severe defect in cytokinesis and the accumulation of multinucleated cells. RNAi of TbARL2 also results in loss of acetylated alpha-tubulin but not of total -tubulin from cellular microtubules. While overexpression of TbARL2(myc) also leads to a defect in cytokinesis, an excess of untagged protein has no effect on cell division, demonstrating the importance of the extreme C-terminus in correct function. TbARL2 overexpressing cells (either myc-tagged or untagged) have an increase in acetylated -tubulin. Our data indicate that Arl2 has a fundamentally conserved role in trypanosome microtubule biogenesis that correlates with -tubulin acetylation.
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31
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Zhang T, Li S, Zhang Y, Zhong C, Lai Z, Ding J. Crystal structure of the ARL2-GTP-BART complex reveals a novel recognition and binding mode of small GTPase with effector. Structure 2009; 17:602-10. [PMID: 19368893 DOI: 10.1016/j.str.2009.01.014] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2008] [Revised: 01/02/2009] [Accepted: 01/16/2009] [Indexed: 11/17/2022]
Abstract
ARL2 is a member of the ADP-ribosylation factor family but has unique biochemical features. BART is an effector of ARL2 that is essential for nuclear retention of STAT3 and may also be involved in mitochondria transport and apoptosis. Here we report the crystal structure and biochemical characterization of human ARL2-GTP-BART complex. ARL2-GTP assumes a typical small GTPase fold with a unique N-terminal alpha helix conformation. BART consists of a six alpha helix bundle. The interactions between ARL2 and BART involve two interfaces: a conserved N-terminal LLXIL motif of ARL2 is embedded in a hydrophobic cleft of BART and the switch regions of ARL2 interact with helix alpha3 of BART. Both interfaces are essential for the binding as verified by mutagenesis study. This novel recognition and binding mode is different from that of other small GTPase-effector interactions and provides molecular basis for the high specificity of ARL2 for BART.
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Affiliation(s)
- Tianlong Zhang
- Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Shanghai 200031, China
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32
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Bailey LK, Campbell LJ, Evetts KA, Littlefield K, Rajendra E, Nietlispach D, Owen D, Mott HR. 1H, 13C and 15N resonance assignments for Binder of Arl2, BART. BIOMOLECULAR NMR ASSIGNMENTS 2009; 3:33-36. [PMID: 19636941 DOI: 10.1007/s12104-008-9135-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2008] [Accepted: 12/02/2008] [Indexed: 05/28/2023]
Abstract
We report (1)H, (13)C and (15)N resonance assignments for Binder of Arl Two (BART), an effector of the small G protein Arl2. The BMRB accession code is 15914.
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Affiliation(s)
- Laura K Bailey
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge, CB2 1GA, UK
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33
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Bailey LK, Campbell LJ, Evetts KA, Littlefield K, Rajendra E, Nietlispach D, Owen D, Mott HR. The structure of binder of Arl2 (BART) reveals a novel G protein binding domain: implications for function. J Biol Chem 2008; 284:992-9. [PMID: 18981177 DOI: 10.1074/jbc.m806167200] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The ADP-ribosylation factor-like (Arl) family of small G proteins are involved in the regulation of diverse cellular processes. Arl2 does not appear to be membrane localized and has been implicated as a regulator of microtubule dynamics. The downstream effector for Arl2, Binder of Arl 2 (BART) has no known function but, together with Arl2, can enter mitochondria and bind the adenine nucleotide transporter. We have solved the solution structure of BART and show that it forms a novel fold composed of six alpha-helices that form three interlocking "L" shapes. Analysis of the backbone dynamics reveals that the protein is highly anisotropic and that the loops between the central helices are dynamic. The regions involved in the binding of Arl2 were mapped onto the surface of BART and are found to localize to these loop regions. BART has faces of differing charge and structural elements, which may explain how it can interact with other proteins.
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Affiliation(s)
- Laura K Bailey
- Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, United Kingdom
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34
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Veltel S, Kravchenko A, Ismail S, Wittinghofer A. Specificity of Arl2/Arl3 signaling is mediated by a ternary Arl3-effector-GAP complex. FEBS Lett 2008; 582:2501-7. [PMID: 18588884 DOI: 10.1016/j.febslet.2008.05.053] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2008] [Revised: 05/09/2008] [Accepted: 05/13/2008] [Indexed: 10/21/2022]
Abstract
Arl2 and Arl3, members of the Arf subfamily of small G proteins, are believed to be involved in ciliary and microtubule-dependent processes. Recently, we could identify RP2, responsible for a variant of X-linked retinitis pigmentosa, as the Arl3-specific GAP. Here, we have characterized Arl2/3 interactions. We show the formation of a ternary complex between Arl3, its cognate GAP RP2 and its retinal effector HRG4. This complex seems to be important for photoreceptor function.
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Affiliation(s)
- Stefan Veltel
- Max-Planck-Institut für molekulare Physiologie, Abteilung Strukturelle Biologie, Otto-Hahn-Strasse 11, Dortmund, Germany
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35
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Muromoto R, Sekine Y, Imoto S, Ikeda O, Okayama T, Sato N, Matsuda T. BART is essential for nuclear retention of STAT3. Int Immunol 2008; 20:395-403. [DOI: 10.1093/intimm/dxm154] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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36
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Abstract
Mitochondrial disorders of oxidative phosphorylation (OXPHOS) comprise a growing list of potentially lethal diseases caused by mutations in either mitochondrial (mtDNA) or nuclear DNA (nDNA). Two such conditions, autosomal dominant progressive external ophthalmoplegia (adPEO) and Senger's Syndrome, are associated with dysfunction of the heart and muscle-specific isoform of the adenine nucleotide translocase (ANT1), a nDNA gene product that facilitates transport of ATP and ADP across the inner mitochondrial membrane. AdPEO is a mtDNA deletion disorder broadly characterized by pathology involving the eyes, skeletal muscle, and central nervous system. In addition to ANT1, mutations in at least two other nuclear genes, twinkle and POLG, have been shown to cause mtDNA destabilization associated with adPEO. Senger's syndrome is an autosomal recessive condition characterized by congenital heart defects, abnormalities of skeletal muscle mitochondria, cataracts, and elevated circulatory levels of lactic acid. This syndrome is associated with severe depletion of ANT1, which may be the result of an as yet unidentified ANT1-specific transcriptional or translational processing error. ANT1 has also been associated with a third condition, autosomal dominant facioscapulohumeral muscular dystrophy (FSHD), an adult onset disorder characterized by variable muscle weakness in the face, feet, shoulders, and hips. FSHD patients possess specific DNA deletions on chromosome 4, which appear to cause derepression of several nearby genes, including ANT1. Early development of FSHD may involve mitochondrial dysfunction and increased oxidative stress, possibly associated with overexpression of ANT1.
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Affiliation(s)
- J Daniel Sharer
- Department of Genetics, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA.
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37
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Hanzal-Bayer M, Linari M, Wittinghofer A. Properties of the interaction of Arf-like protein 2 with PDEdelta. J Mol Biol 2005; 350:1074-82. [PMID: 15979089 DOI: 10.1016/j.jmb.2005.05.036] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2005] [Revised: 05/04/2005] [Accepted: 05/18/2005] [Indexed: 02/06/2023]
Abstract
Arf-like proteins (Arl) share certain characteristic features with the Arf subfamily of Ras superfamily proteins, but their function is unknown. Here, we show by a variety of spectroscopic techniques that Arl2, unlike most other Ras-related proteins, has micromolar rather than picomolar affinity for nucleotides. As a consequence of low affinity, nucleotide dissociation rates are rather fast, arguing that it is not regulated by guanine nucleotide exchange factors. Arl2 is isolated as prey in a yeast double hybrid screen using phosphodiesterase 6delta (PDEdelta) as bait. This interaction is dependent on GTP, and the binding of PDEdelta substantially stabilizes GTP binding, increasing affinity and decreasing dissociation rates by a similar factor. Among all Arl proteins tested, PDEdelta only interacted with the closely related proteins Arl2 and Arl3, strongly suggesting that Arl2/3 are specific regulators of PDEdelta.
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Affiliation(s)
- Michael Hanzal-Bayer
- Max-Planck-Institute for Molecular Physiology, Department of Structural Biology, Otto-Hahn-Strasse 11, 44227 Dortmund, Germany
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38
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Abstract
Arl2 is a approximately 20 kDa GTPase in the ADP-ribosylation factor (Arf) family within the Ras superfamily with roles in microtubule dynamics that impact the cytoskeleton, cell division, and cytokinesis. Arl2 has been implicated as a regulator of the pathway responsible for formation of properly folded tubulin heterodimers and in adenine nucleotide transport in mitochondria. The identification and characterization of Arl2 binding partners and regulators of Arl2 activities are critical steps in the further dissection of these and likely other Arl2-dependent functions. This chapter describes methods for preparing recombinant Arl2, loading different radiolabeled guanine nucleotides onto the GTPase, identifying high-affinity Arl2 binding proteins, and assaying Arl2 GTPase activating proteins (GAPs). These methods may also prove useful for studies of other Arls or other GTPases.
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Affiliation(s)
- J Bradford Bowzard
- Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia, USA
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39
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Wu M, Lu L, Hong W, Song H. Structural basis for recruitment of GRIP domain golgin-245 by small GTPase Arl1. Nat Struct Mol Biol 2003; 11:86-94. [PMID: 14718928 DOI: 10.1038/nsmb714] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2003] [Accepted: 11/20/2003] [Indexed: 11/08/2022]
Abstract
Recruitment of the GRIP domain golgins to the trans-Golgi network is mediated by Arl1, a member of the ARF/Arl small GTPase family, through interaction between their GRIP domains and Arl1-GTP. The crystal structure of Arl1-GTP in complex with the GRIP domain of golgin-245 shows that Arl1-GTP interacts with the GRIP domain predominantly in a hydrophobic manner, with the switch II region conferring the main recognition surface. The involvement of the switch and interswitch regions in the interaction between Arl1-GTP and GRIP accounts for the specificity of GRIP domain for Arl1-GTP. Mutations that abolished the Arl1-mediated Golgi localization of GRIP domain golgins have been mapped on the interface between Arl1-GTP and GRIP. Notably, the GRIP domain forms a homodimer in which each subunit interacts separately with one Arl1-GTP. Mutations disrupting the GRIP domain dimerization also abrogated its Golgi targeting, suggesting that the dimeric form of GRIP domain is a functional unit.
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Affiliation(s)
- Mousheng Wu
- Laboratory of Macromolecular Structure, Institute of Molecular and Cell Biology, 30 Medical Drive, Singapore 117609
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40
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Shern JF, Sharer JD, Pallas DC, Bartolini F, Cowan NJ, Reed MS, Pohl J, Kahn RA. Cytosolic Arl2 is complexed with cofactor D and protein phosphatase 2A. J Biol Chem 2003; 278:40829-36. [PMID: 12912990 DOI: 10.1074/jbc.m308678200] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Arl2 is a member of the ADP-ribosylation factor family of 20-kDa GTPases that is highly conserved in eukaryotes. Recent results revealed that a portion of cellular Arl2 and its binding partner, BART, localize to mitochondria. Because approximately 90% of cellular Arl2 is cytosolic, we investigated properties of the soluble protein and found that it is stably bound in a complex that migrates in gel filtration medium with a predicted molecular mass of approximately 300 kDa. This complex was purified approximately 500-fold from the soluble fraction of bovine brain. Protein components were identified by mass spectroscopy and revealed the presence of four other proteins that include the tubulin folding cochaperone cofactor D and all three subunits of at least two protein phosphatase 2A (PP2A) protein phosphatase trimers. The presence of more than one PP2A B-type subunit and the low stoichiometry of Arl2 indicate that the purified preparation still contains a mixture of complexes that cannot currently be completely resolved. Thus, although all the soluble Arl2 in bovine brain is in high molecular mass complexes, only a portion of the total cellular cofactor D and PP2A are associated with the Arl2. We further show that the Arl2 in the complex cannot bind GTP and that complexed cofactor D does not efficiently participate in tubulin refolding reactions in a manner comparable with free cofactor D. Our data suggest functional roles for the cytosolic Arl2 complex in modulating tubulin and microtubule behavior as well as a possible role in apoptosis.
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Affiliation(s)
- Jack F Shern
- Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322, USA
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41
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Cuvillier A, Miranda JC, Ambit A, Barral A, Merlin G. Abortive infection of Lutzomyia longipalpis insect vectors by aflagellated LdARL-3A-Q70L overexpressing Leishmania amazonensis parasites. Cell Microbiol 2003; 5:717-28. [PMID: 12969377 DOI: 10.1046/j.1462-5822.2003.00316.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Leishmania donovani ADP-ribosylation factor-like protein 3A (LdARL-3A) is a small G protein isolated from the protozoan parasite L. donovani with no defined physiological function. Previously [Cuvillier, A., Redon, F., Antoine, J.-C., Chardin, P., DeVos, T., and Merlin, G. (2000) J Cell Sci 113: 2065-2074] we have shown that overexpression in L. amazonensis promastigotes of the mutated protein LdARL-3A-Q70L, which remains constitutively associated with GTP, leads to the disappearance of the flagellum but does not impair cell viability or growth. Here we report that parasites overexpressing LdARL-3A-Q70L can invade in vitro cultivated macrophages to the same extent as control cells, demonstrating that the flagellum is not necessary for attachment to or engulfment into macrophages. These infections are productive because amastigotes differentiate and multiply. However, aflagellated LdARL-3A-Q70L-overexpressing Leishmania promastigotes could not survive in experimentally infected Lutzomyia longipalpis insect vectors, in contrast to untransfected or native LdARL-3A-overexpressing cells. Overexpression of the native and mutated proteins did not modify in vitro procyclic to metacyclic lipophosphoglycan maturation or differentiation from procyclic to metacyclic promastigotes, nevertheless there is a block in transmission of Leishmania. Better understanding of LdARL-3A pathways, notably those regarding flagellum biogenesis, may lead to the future development of Leishmania-specific drugs, which may stop parasite transmission in nature without affecting other species.
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Affiliation(s)
- Armelle Cuvillier
- Laboratorio de Imunoparasitologia, FIOCRUZ, rua Waldemar Falcão, 121, 40295-001 Salvador, Bahia, Brazil
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42
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Kobayashi A, Kubota S, Mori N, McLaren MJ, Inana G. Photoreceptor synaptic protein HRG4 (UNC119) interacts with ARL2 via a putative conserved domain. FEBS Lett 2003; 534:26-32. [PMID: 12527357 DOI: 10.1016/s0014-5793(02)03766-3] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Human retinal gene 4 (HRG4) (UNC119) is a photoreceptor synaptic protein of unknown function, shown when mutated to cause retinal degeneration in a patient and in a confirmatory transgenic model. ADP-ribosylation factor-like protein 2 (ARL2) was identified as an interactor of HRG4 by the yeast two-hybrid strategy. The presence of ARL2 in the retina and co-localization with HRG4 was confirmed by Western blot and double immunofluorescence analysis, respectively. The interaction of ARL2 with HRG4 was further confirmed by co-immunoprecipitation and direct binding analysis. Phosphodiesterase delta (PDEdelta) is an ARL2-binding protein homologous to HRG4. Amino acid residues of PDEdelta involved in binding ARL2 and forming a hydrophobic pocket were shown to be highly conserved in HRG4, suggesting similarity in binding mechanism and function.
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Affiliation(s)
- Akira Kobayashi
- Bascom Palmer Eye Institute, University of Miami School of Medicine, 1638 N.W. 10th Avenue, Miami, FL 33136, USA
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43
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Chatterjee G, Rosner A, Han Y, Zelazny ET, Li B, Cardiff RD, Perkins AS. Acceleration of mouse mammary tumor virus-induced murine mammary tumorigenesis by a p53 172H transgene: influence of FVB background on tumor latency and identification of novel sites of proviral insertion. THE AMERICAN JOURNAL OF PATHOLOGY 2002; 161:2241-53. [PMID: 12466138 PMCID: PMC1850916 DOI: 10.1016/s0002-9440(10)64500-2] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
We previously showed that a mammary-specific dominant-negative p53 transgene (WAP-p53(172H)) could accelerate ErbB2-induced mammary tumorigenesis in mice, but was not tumorigenic on its own. To identify other genes that cooperate with WAP-p53(172H) in tumorigenesis, we performed mouse mammary tumor virus (MMTV) proviral mutagenesis. We derived F1, N2, and N4/N5 mice from p53(172H) transgenic FVB mice backcrossed onto MMTV+ C3H/He mice. Results show the latency of MMTV tumorigenesis is correlated with FVB contribution. F1 tumors had the shortest latency (217 days), had a higher rate of metastasis, and were less differentiated than the N2 and N4/N5 tumors. The latency was 269 days in N2 mice, and lengthened to 346 days in N4/N5 mice. p53(172H) significantly accelerated MMTV tumorigenesis only in N2 mice, indicating cooperativity between p53(172H) and MMTV in this cohort. To identify genes that may be causally involved in MMTV-induced mammary tumorigenesis, we identified 60 sites of proviral insertion in the N2 tumors. Among the insertions in p53(172H) transgenic tumors were 10 genes not previously found as sites of MMTV insertion including genes involved in signaling (Pdgfra, Pde1b, Cnk1), cell adhesion (Cd44), angiogenesis (Galgt1), and transcriptional regulation (Olig1, Olig2, and Uncx4.1). These may represent cellular functions that are likely not deregulated by mutation in p53.
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MESH Headings
- Animals
- Cell Transformation, Neoplastic
- DNA, Neoplasm/analysis
- Female
- Gene Expression Regulation, Neoplastic
- Genes, p53
- Humans
- Mammary Glands, Animal/pathology
- Mammary Glands, Animal/virology
- Mammary Neoplasms, Experimental/genetics
- Mammary Neoplasms, Experimental/pathology
- Mammary Neoplasms, Experimental/virology
- Mammary Tumor Virus, Mouse/genetics
- Mammary Tumor Virus, Mouse/metabolism
- Mice
- Mice, Inbred Strains
- Mice, Transgenic
- Mutagenesis
- Survival Rate
- Transgenes
- Tumor Suppressor Protein p53/genetics
- Virus Integration
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Affiliation(s)
- Gouri Chatterjee
- Department of Pathology, Yale University School of Medicine, New Haven, CT 06520-8023. USA
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44
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Jochum A, Jackson D, Schwarz H, Pipkorn R, Singer-Krüger B. Yeast Ysl2p, homologous to Sec7 domain guanine nucleotide exchange factors, functions in endocytosis and maintenance of vacuole integrity and interacts with the Arf-Like small GTPase Arl1p. Mol Cell Biol 2002; 22:4914-28. [PMID: 12052896 PMCID: PMC133889 DOI: 10.1128/mcb.22.13.4914-4928.2002] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We previously described the isolation of ysl2-1 due to its genetic interaction with Delta ypt51/vps21, a mutant with a deletion of the coding sequence for the yeast Rab5 homolog, which regulates endocytic traffic between early and late endosomes. Here we report that Ysl2p is a novel 186.8-kDa peripheral membrane protein homologous to members of the Sec7 family. We provide multiple genetic and biochemical evidence for an interaction between Ysl12p and the Arf-like protein Arl1p, consistent with a potential function as an Arf guanine nucleotide exchange factor (GEF). The temperature-sensitive alleles ysl2-307 and ysl2-316 are specifically defective in ligand-induced degradation of Ste2p and alpha-factor and exhibit vacuole fragmentation directly upon a shift to 37 degrees C. In living cells, green fluorescent protein (GFP)-Ysl2p colocalizes with endocytic elements that accumulate FM4-64. The GFP-Ysl2p staining is sensitive to a mutation in VPS27 resulting in the formation of an aberrant class E compartment, but it is not affected by a sec7 mutation. Consistent with the idea that Ysl2p and Arl1p have closely related functions, Delta arl1 cells are defective in endocytic transport and in vacuolar protein sorting.
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Affiliation(s)
- Alexandra Jochum
- Institute for Biochemistry, University of Stuttgart, D-70569 Stuttgart, Germany
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45
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Hanzal-Bayer M, Renault L, Roversi P, Wittinghofer A, Hillig RC. The complex of Arl2-GTP and PDE delta: from structure to function. EMBO J 2002; 21:2095-106. [PMID: 11980706 PMCID: PMC125981 DOI: 10.1093/emboj/21.9.2095] [Citation(s) in RCA: 196] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Arf-like (Arl) proteins are close relatives of the Arf regulators of vesicular transport, but their function is unknown. Here, we present the crystal structure of full-length Arl2-GTP in complex with its effector PDE delta solved in two crystal forms (Protein Data Bank codes 1KSG, 1KSH and 1KSJ). Arl2 shows a dramatic conformational change from the GDP-bound form, which suggests that it is reversibly membrane associated. PDE delta is structurally closely related to RhoGDI and contains a deep empty hydrophobic pocket. Further experiments show that H-Ras, Rheb, Rho6 and G alpha(i1) interact with PDE delta and that, at least for H-Ras, the intact C-terminus is required. We suggest PDE delta to be a specific soluble transport factor for certain prenylated proteins and Arl2-GTP a regulator of PDE delta-mediated transport.
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Affiliation(s)
- Michael Hanzal-Bayer
- Max-Planck-Institut für molekulare Physiologie, Abteilung Strukturelle Biologie, Otto-Hahn-Strasse 11, D-44227 Dortmund, Germany and GlobalPhasing Ltd, Sheraton House, Castle Park, Cambridge CB3 0AX, UK Present address: Laboratoire d’Enzymologie et Biochimie Structurales, CNRS, Avenue de la Terrasse, F-91198 Gif-sur-Yvette, France Present address: Schering AG Research Laboratories, D-13342 Berlin, Germany Corresponding authors e-mail: or
| | - Louis Renault
- Max-Planck-Institut für molekulare Physiologie, Abteilung Strukturelle Biologie, Otto-Hahn-Strasse 11, D-44227 Dortmund, Germany and GlobalPhasing Ltd, Sheraton House, Castle Park, Cambridge CB3 0AX, UK Present address: Laboratoire d’Enzymologie et Biochimie Structurales, CNRS, Avenue de la Terrasse, F-91198 Gif-sur-Yvette, France Present address: Schering AG Research Laboratories, D-13342 Berlin, Germany Corresponding authors e-mail: or
| | - Pietro Roversi
- Max-Planck-Institut für molekulare Physiologie, Abteilung Strukturelle Biologie, Otto-Hahn-Strasse 11, D-44227 Dortmund, Germany and GlobalPhasing Ltd, Sheraton House, Castle Park, Cambridge CB3 0AX, UK Present address: Laboratoire d’Enzymologie et Biochimie Structurales, CNRS, Avenue de la Terrasse, F-91198 Gif-sur-Yvette, France Present address: Schering AG Research Laboratories, D-13342 Berlin, Germany Corresponding authors e-mail: or
| | - Alfred Wittinghofer
- Max-Planck-Institut für molekulare Physiologie, Abteilung Strukturelle Biologie, Otto-Hahn-Strasse 11, D-44227 Dortmund, Germany and GlobalPhasing Ltd, Sheraton House, Castle Park, Cambridge CB3 0AX, UK Present address: Laboratoire d’Enzymologie et Biochimie Structurales, CNRS, Avenue de la Terrasse, F-91198 Gif-sur-Yvette, France Present address: Schering AG Research Laboratories, D-13342 Berlin, Germany Corresponding authors e-mail: or
| | - Roman C. Hillig
- Max-Planck-Institut für molekulare Physiologie, Abteilung Strukturelle Biologie, Otto-Hahn-Strasse 11, D-44227 Dortmund, Germany and GlobalPhasing Ltd, Sheraton House, Castle Park, Cambridge CB3 0AX, UK Present address: Laboratoire d’Enzymologie et Biochimie Structurales, CNRS, Avenue de la Terrasse, F-91198 Gif-sur-Yvette, France Present address: Schering AG Research Laboratories, D-13342 Berlin, Germany Corresponding authors e-mail: or
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46
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Bartolini F, Bhamidipati A, Thomas S, Schwahn U, Lewis SA, Cowan NJ. Functional overlap between retinitis pigmentosa 2 protein and the tubulin-specific chaperone cofactor C. J Biol Chem 2002; 277:14629-34. [PMID: 11847227 DOI: 10.1074/jbc.m200128200] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mutations in the X-linked retinitis pigmentosa 2 gene cause progressive degeneration of photoreceptor cells. The retinitis pigmentosa 2 protein (RP2) is similar in sequence to the tubulin-specific chaperone cofactor C. Together with cofactors D and E, cofactor C stimulates the GTPase activity of native tubulin, a reaction regulated by ADP-ribosylation factor-like 2 protein. Here we show that in the presence of cofactor D, RP2 protein also stimulates the GTPase activity of tubulin. We find that this function is abolished by mutation in an arginine residue that is conserved in both cofactor C and RP2. Notably, mutations that alter this arginine codon cause familial retinitis pigmentosa. Our data imply that this residue acts as an "arginine finger" to trigger the tubulin GTPase activity and suggest that loss of this function in RP2 contributes to retinal degeneration. We also show that in Saccharomyces cerevisiae, both cofactor C and RP2 partially complement the microtubule phenotype resulting from deletion of the cofactor C homolog, demonstrating their functional overlap in vivo. Finally, we find that RP2 interacts with GTP-bound ADP ribosylation factor-like 3 protein, providing a link between RP2 and several retinal-specific proteins, mutations in which also cause retinitis pigmentosa.
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Affiliation(s)
- Francesca Bartolini
- Department of Biochemistry, New York University Medical Center, New York, New York 10016, USA
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47
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Sharer JD, Shern JF, Van Valkenburgh H, Wallace DC, Kahn RA. ARL2 and BART enter mitochondria and bind the adenine nucleotide transporter. Mol Biol Cell 2002; 13:71-83. [PMID: 11809823 PMCID: PMC65073 DOI: 10.1091/mbc.01-05-0245] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The ADP-ribosylation factor-like 2 (ARL2) GTPase and its binding partner binder of ARL2 (BART) are ubiquitously expressed in rodent and human tissues and are most abundant in brain. Both ARL2 and BART are predominantly cytosolic, but a pool of each was found associated with mitochondria in a protease-resistant form. ARL2 was found to lack covalent N-myristoylation, present on all other members of the ARF family, thereby preserving the N-terminal amphipathic alpha-helix as a potential mitochondrial import sequence. An overlay assay was developed to identify binding partners for the BART.ARL2.GTP complex and revealed a specific interaction with a protein in bovine brain mitochondria. Purification and partial microsequencing identified the protein as an adenine nucleotide transporter (ANT). The overlay assay was performed on mitochondria isolated from five different tissues from either wild-type or transgenic mice deleted for ANT1. Results confirmed that ANT1 is the predominant binding partner for the BART.ARL2.GTP complex and that the structurally homologous ANT2 protein does not bind the complex. Cardiac and skeletal muscle mitochondria from ant1(-)/ant1(-) mice had increased levels of ARL2, relative to that seen in mitochondria from wild-type animals. We conclude that the amount of ARL2 in mitochondria is subject to regulation via an ANT1-sensitive pathway in muscle tissues.
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Affiliation(s)
- J Daniel Sharer
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322, USA
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48
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Lu L, Horstmann H, Ng C, Hong W. Regulation of Golgi structure and function by ARF-like protein 1 (Arl1). J Cell Sci 2001; 114:4543-55. [PMID: 11792819 DOI: 10.1242/jcs.114.24.4543] [Citation(s) in RCA: 113] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Arl1 is a member of the ARF-like protein (Arl) subfamily of small GTPases. Nothing is known about the function of Arl1 except for the fact that it is essential for normal development in Drosophila and that it is associated with the Golgi apparatus. In this study, we first demonstrate that Arl1 is enriched at the trans side of the Golgi, marked by AP-1. Association of Arl1 with the Golgi is saturable in intact cells and depends on N-terminal myristoylation. Over-expression of Arl1(T31N), which is expected to be restricted to the GDP-bound form and thus function as a dominant-negative mutant, causes the disappearance of the Golgi apparatus (marked by Golgi SNARE GS28), suggesting that Arl1 is necessary for maintaining normal Golgi structure. Overexpression of Arl1(Q71L), a mutant restricted primarily to the activated GTP-bound form, causes an expansion of the Golgi apparatus with massive and stable Golgi association of COPI and AP-1 coats. Interestingly, Golgi ARFs also become stably associated with the expanded Golgi. Transport of the envelope protein of vesicular stomatitis virus (VSV-G) along the secretory pathway is arrested at the expanded Golgi upon expression of Arl1(Q71L). The structure of stacked cisternae of the Golgi is disrupted in cells expressing Arl1(Q71L), resulting in the transformation of the Golgi into an extensive vesicule-tubule network. In addition, the GTP form of Arl1 interacts with arfaptin-2/POR1 but not GGA1, both of which interact with GTP-restricted ARF1, suggesting that Arl1 and ARF1 share some common effectors in regulating cellular events. On the basis of these observations, we propose that one of the mechanisms for the cell to regulate the structure and function of the Golgi apparatus is through the action of Arl1.
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Affiliation(s)
- L Lu
- Membrane Biology Laboratory, Institute of Molecular and Cell Biology, Singapore
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49
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Van Valkenburgh H, Shern JF, Sharer JD, Zhu X, Kahn RA. ADP-ribosylation factors (ARFs) and ARF-like 1 (ARL1) have both specific and shared effectors: characterizing ARL1-binding proteins. J Biol Chem 2001; 276:22826-37. [PMID: 11303027 DOI: 10.1074/jbc.m102359200] [Citation(s) in RCA: 126] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Despite the 40-60% identity between ADP-ribosylation factors (ARFs) and ARF-like (ARL) proteins, distinct functional roles have been inferred from findings that ARLs lack the biochemical or genetic activities characteristic of ARFs. The potential for functional overlap between ARFs and ARLs was examined by comparing effects of expression on intact cells and the ability to bind effectors. Expression of [Q71L]ARL1 in mammalian cells led to altered Golgi structure similar to, but less dramatic than, that reported previously for [Q71L]ARF1. Two previously identified partners of ARFs, MKLP1 and Arfaptin2/POR1, also bind ARL1 but not ARL2 or ARL3. Two-hybrid screens of human cDNA libraries with dominant active mutants of human ARL1, ARL2, and ARL3 identified eight different but overlapping sets of binding partners. Specific interactions between ARL1 and two binding proteins, SCOCO and Golgin-245, are defined and characterized in more detail. Like ARFs and ARL1, the binding of SCOCO to Golgi membranes is rapidly reversed by brefeldin A, suggesting the presence of a brefeldin A-sensitive ARL1 exchange factor. These data reveal a complex network of interactions between GTPases in the ARF family and their effectors and reveal a potential for cross-talk not demonstrated previously.
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Affiliation(s)
- H Van Valkenburgh
- Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322-3050, USA
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50
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Hillig RC, Hanzal-Bayer M, Linari M, Becker J, Wittinghofer A, Renault L. Structural and biochemical properties show ARL3-GDP as a distinct GTP binding protein. Structure 2000; 8:1239-45. [PMID: 11188688 DOI: 10.1016/s0969-2126(00)00531-1] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
BACKGROUND Based on sequence similarities, Arf-like (ARL) proteins have been assigned to the Arf subfamily of the superfamily of Ras-related GTP binding proteins. They have been identified in several isoforms in a wide variety of species. Their cellular function is unclear, but they are proposed to regulate intracellular transport. RESULTS The 1.7 A crystal structure of murine ARL3-GDP provides a first insight into the structural features of this subgroup of Ar proteins. The N-terminal extension of ARL3 folds into an elongated loop region that is hydrophobically anchored onto the surface by burying 1440 A2. The features observed suggest that ARL3 releases its N terminus and undergoes a beta sheet register shift upon the binding of GTP. The structure and kinetic experiments with fluorescent mGDP demonstrate that tight GDP (but not GTP) binding is achieved in the absence of a magnesium ion. This is due to a lysine residue in the active site, close to the canonical Mg2+ site found in other GTP binding proteins. This is a distinct feature separating ARL2 and ARL3 from Arf proteins. CONCLUSION The disturbed magnesium binding site and the independence of GDP coordination from the presence of Mg2+ separate ARL2 and ARL3 from Arf proteins. The D sheet register shift, which is similar to that of Arf, that is observed in the present structure, along with the postulated release of the N-terminal extension and the concomitant exposure of a patch of conserved hydrophobic residues in this region suggest that ARL proteins might be localized to target membranes upon exchange of GDP to GTP. Contrary to the situation in Arf, however, the conformational change to ARL-GTP does not require the presence of membranes and might thus be energetically unfavored. Together with the very low affinity described for the interaction of ARL3 with Mg-GTP, this suggests that ARL protein activation requires the presence of effectors stabilizing the GTP coordination rather than guanine nucleotide exchange factors (GEFs).
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Affiliation(s)
- R C Hillig
- Max-Planck-Institut für Molekulare Physiologie, Abteilung Strukturelle Biologie, Dortmund, Germany
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