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Chu A, Yao Y, Glibowicka M, Deber CM, Manolson MF. The Human Mutation K237_V238del in a Putative Lipid Binding Motif within the V-ATPase a2 Isoform Suggests a Molecular Mechanism Underlying Cutis Laxa. Int J Mol Sci 2024; 25:2170. [PMID: 38396846 PMCID: PMC10889665 DOI: 10.3390/ijms25042170] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2023] [Revised: 01/19/2024] [Accepted: 02/01/2024] [Indexed: 02/25/2024] Open
Abstract
Vacuolar ATPases (V-ATPases), proton pumps composed of 16 subunits, are necessary for a variety of cellular functions. Subunit "a" has four isoforms, a1-a4, each with a distinct cellular location. We identified a phosphoinositide (PIP) interaction motif, KXnK(R)IK(R), conserved in all four isoforms, and hypothesize that a/PIP interactions regulate V-ATPase recruitment/retention to different organelles. Among the four isoforms, a2 is enriched on Golgi with a2 mutations in the PIP motif resulting in cutis laxa. We hypothesize that the hydrophilic N-terminal (NT) domain of a2 contains a lipid-binding domain, and mutations in this domain prevent interaction with Golgi-enriched PIPs, resulting in cutis laxa. We recreated the cutis laxa-causing mutation K237_V238del, and a double mutation in the PIP-binding motif, K237A/V238A. Circular dichroism confirmed that there were no protein structure alterations. Pull-down assays with PIP-enriched liposomes revealed that wildtype a2NT preferentially binds phosphatidylinositol 4-phosphate (PI(4)P), while mutants decreased binding to PI(4)P. In HEK293 cells, wildtype a2NT was localized to Golgi and co-purified with microsomal membranes. Mutants reduced Golgi localization and membrane association. Rapamycin depletion of PI(4)P diminished a2NT-Golgi localization. We conclude that a2NT is sufficient for Golgi retention, suggesting the lipid-binding motif is involved in V-ATPase targeting and/or retention. Mutational analyses suggest a molecular mechanism underlying how a2 mutations result in cutis laxa.
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Affiliation(s)
- Anh Chu
- Faculty of Dentistry, University of Toronto, Toronto M5G 1G6, ON, Canada; (A.C.); (Y.Y.)
| | - Yeqi Yao
- Faculty of Dentistry, University of Toronto, Toronto M5G 1G6, ON, Canada; (A.C.); (Y.Y.)
| | - Miroslawa Glibowicka
- Division of Molecular Medicine, Research Institute, Hospital for Sick Children, Toronto M5G 0A4, ON, Canada; (M.G.); (C.M.D.)
| | - Charles M. Deber
- Division of Molecular Medicine, Research Institute, Hospital for Sick Children, Toronto M5G 0A4, ON, Canada; (M.G.); (C.M.D.)
- Department of Biochemistry, Faculty of Medicine, University of Toronto, Toronto M5S 1A8, ON, Canada
| | - Morris F. Manolson
- Faculty of Dentistry, University of Toronto, Toronto M5G 1G6, ON, Canada; (A.C.); (Y.Y.)
- Department of Biochemistry, Faculty of Medicine, University of Toronto, Toronto M5S 1A8, ON, Canada
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Polanco CM, Cavieres VA, Galarza AJ, Jara C, Torres AK, Cancino J, Varas-Godoy M, Burgos PV, Tapia-Rojas C, Mardones GA. GOLPH3 Participates in Mitochondrial Fission and Is Necessary to Sustain Bioenergetic Function in MDA-MB-231 Breast Cancer Cells. Cells 2024; 13:316. [PMID: 38391929 PMCID: PMC10887169 DOI: 10.3390/cells13040316] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2023] [Revised: 02/03/2024] [Accepted: 02/05/2024] [Indexed: 02/24/2024] Open
Abstract
In this study, we investigated the inter-organelle communication between the Golgi apparatus (GA) and mitochondria. Previous observations suggest that GA-derived vesicles containing phosphatidylinositol 4-phosphate (PI(4)P) play a role in mitochondrial fission, colocalizing with DRP1, a key protein in this process. However, the functions of these vesicles and potentially associated proteins remain unknown. GOLPH3, a PI(4)P-interacting GA protein, is elevated in various types of solid tumors, including breast cancer, yet its precise role is unclear. Interestingly, GOLPH3 levels influence mitochondrial mass by affecting cardiolipin synthesis, an exclusive mitochondrial lipid. However, the mechanism by which GOLPH3 influences mitochondria is not fully understood. Our live-cell imaging analysis showed GFP-GOLPH3 associating with PI(4)P vesicles colocalizing with YFP-DRP1 at mitochondrial fission sites. We tested the functional significance of these observations with GOLPH3 knockout in MDA-MB-231 cells of breast cancer, resulting in a fragmented mitochondrial network and reduced bioenergetic function, including decreased mitochondrial ATP production, mitochondrial membrane potential, and oxygen consumption. Our findings suggest a potential negative regulatory role for GOLPH3 in mitochondrial fission, impacting mitochondrial function and providing insights into GA-mitochondria communication.
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Affiliation(s)
- Catalina M. Polanco
- Centro de Biología Celular y Biomedicina (CEBICEM), Facultad de Medicina y Ciencia, Universidad San Sebastián, Providencia, Santiago 7510156, Chile; (C.M.P.); (V.A.C.); (C.J.); (A.K.T.); (J.C.); (M.V.-G.); (P.V.B.)
| | - Viviana A. Cavieres
- Centro de Biología Celular y Biomedicina (CEBICEM), Facultad de Medicina y Ciencia, Universidad San Sebastián, Providencia, Santiago 7510156, Chile; (C.M.P.); (V.A.C.); (C.J.); (A.K.T.); (J.C.); (M.V.-G.); (P.V.B.)
- Departamento de Ciencias Biológicas y Químicas, Facultad de Medicina y Ciencia, Universidad San Sebastián, Campus Los Leones, Providencia, Santiago 7510156, Chile
| | - Abigail J. Galarza
- Escuela de Medicina, Facultad de Medicina y Ciencia, Universidad San Sebastián, Valdivia 5110693, Chile;
| | - Claudia Jara
- Centro de Biología Celular y Biomedicina (CEBICEM), Facultad de Medicina y Ciencia, Universidad San Sebastián, Providencia, Santiago 7510156, Chile; (C.M.P.); (V.A.C.); (C.J.); (A.K.T.); (J.C.); (M.V.-G.); (P.V.B.)
- Centro Científico y Tecnológico de Excelencia Ciencia & Vida, Fundación Ciencia & Vida, Huechuraba, Santiago 8580702, Chile
| | - Angie K. Torres
- Centro de Biología Celular y Biomedicina (CEBICEM), Facultad de Medicina y Ciencia, Universidad San Sebastián, Providencia, Santiago 7510156, Chile; (C.M.P.); (V.A.C.); (C.J.); (A.K.T.); (J.C.); (M.V.-G.); (P.V.B.)
- Centro de Excelencia en Biomedicina de Magallanes (CEBIMA), Universidad de Magallanes, Punta Arenas 6210427, Chile
| | - Jorge Cancino
- Centro de Biología Celular y Biomedicina (CEBICEM), Facultad de Medicina y Ciencia, Universidad San Sebastián, Providencia, Santiago 7510156, Chile; (C.M.P.); (V.A.C.); (C.J.); (A.K.T.); (J.C.); (M.V.-G.); (P.V.B.)
- Escuela de Medicina, Facultad de Medicina y Ciencia, Universidad San Sebastián, Valdivia 5110693, Chile;
| | - Manuel Varas-Godoy
- Centro de Biología Celular y Biomedicina (CEBICEM), Facultad de Medicina y Ciencia, Universidad San Sebastián, Providencia, Santiago 7510156, Chile; (C.M.P.); (V.A.C.); (C.J.); (A.K.T.); (J.C.); (M.V.-G.); (P.V.B.)
- Escuela de Medicina, Facultad de Medicina y Ciencia, Universidad San Sebastián, Valdivia 5110693, Chile;
- Centro Científico y Tecnológico de Excelencia Ciencia & Vida, Fundación Ciencia & Vida, Huechuraba, Santiago 8580702, Chile
| | - Patricia V. Burgos
- Centro de Biología Celular y Biomedicina (CEBICEM), Facultad de Medicina y Ciencia, Universidad San Sebastián, Providencia, Santiago 7510156, Chile; (C.M.P.); (V.A.C.); (C.J.); (A.K.T.); (J.C.); (M.V.-G.); (P.V.B.)
- Escuela de Medicina, Facultad de Medicina y Ciencia, Universidad San Sebastián, Valdivia 5110693, Chile;
- Centro Científico y Tecnológico de Excelencia Ciencia & Vida, Fundación Ciencia & Vida, Huechuraba, Santiago 8580702, Chile
| | - Cheril Tapia-Rojas
- Centro de Biología Celular y Biomedicina (CEBICEM), Facultad de Medicina y Ciencia, Universidad San Sebastián, Providencia, Santiago 7510156, Chile; (C.M.P.); (V.A.C.); (C.J.); (A.K.T.); (J.C.); (M.V.-G.); (P.V.B.)
- Centro Científico y Tecnológico de Excelencia Ciencia & Vida, Fundación Ciencia & Vida, Huechuraba, Santiago 8580702, Chile
| | - Gonzalo A. Mardones
- Escuela de Medicina, Facultad de Medicina y Ciencia, Universidad San Sebastián, Valdivia 5110693, Chile;
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Ovejero S, Kumanski S, Soulet C, Azarli J, Pardo B, Santt O, Constantinou A, Pasero P, Moriel-Carretero M. A sterol- PI(4)P exchanger modulates the Tel1/ATM axis of the DNA damage response. EMBO J 2023:e112684. [PMID: 37303233 PMCID: PMC10390878 DOI: 10.15252/embj.2022112684] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2022] [Revised: 05/15/2023] [Accepted: 05/26/2023] [Indexed: 06/13/2023] Open
Abstract
Upon DNA damage, cells activate the DNA damage response (DDR) to coordinate proliferation and DNA repair. Dietary, metabolic, and environmental inputs are emerging as modulators of how DNA surveillance and repair take place. Lipids hold potential to convey these cues, although little is known about how. We observed that lipid droplet (LD) number specifically increased in response to DNA breaks. Using Saccharomyces cerevisiae and cultured human cells, we show that the selective storage of sterols into these LD concomitantly stabilizes phosphatidylinositol-4-phosphate (PI(4)P) at the Golgi, where it binds the DDR kinase ATM. In turn, this titration attenuates the initial nuclear ATM-driven response to DNA breaks, thus allowing processive repair. Furthermore, manipulating this loop impacts the kinetics of DNA damage signaling and repair in a predictable manner. Thus, our findings have major implications for tackling genetic instability pathologies through dietary and pharmacological interventions.
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Affiliation(s)
- Sara Ovejero
- Institut de Génétique Humaine (IGH), Université de Montpellier-Centre National de la Recherche Scientifique, Montpellier Cedex 5, France
- Department of Biological Haematology, CHU Montpellier, Montpellier Cedex 5, France
| | - Sylvain Kumanski
- Centre de Recherche en Biologie cellulaire de Montpellier (CRBM), Université de Montpellier-Centre National de la Recherche Scientifique, Montpellier Cedex 5, France
| | - Caroline Soulet
- Centre de Recherche en Biologie cellulaire de Montpellier (CRBM), Université de Montpellier-Centre National de la Recherche Scientifique, Montpellier Cedex 5, France
| | - Julie Azarli
- Centre de Recherche en Biologie cellulaire de Montpellier (CRBM), Université de Montpellier-Centre National de la Recherche Scientifique, Montpellier Cedex 5, France
| | - Benjamin Pardo
- Institut de Génétique Humaine (IGH), Université de Montpellier-Centre National de la Recherche Scientifique, Montpellier Cedex 5, France
| | - Olivier Santt
- Centre de Recherche en Biologie cellulaire de Montpellier (CRBM), Université de Montpellier-Centre National de la Recherche Scientifique, Montpellier Cedex 5, France
| | - Angelos Constantinou
- Institut de Génétique Humaine (IGH), Université de Montpellier-Centre National de la Recherche Scientifique, Montpellier Cedex 5, France
| | - Philippe Pasero
- Institut de Génétique Humaine (IGH), Université de Montpellier-Centre National de la Recherche Scientifique, Montpellier Cedex 5, France
| | - María Moriel-Carretero
- Centre de Recherche en Biologie cellulaire de Montpellier (CRBM), Université de Montpellier-Centre National de la Recherche Scientifique, Montpellier Cedex 5, France
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4
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Zhang Y, Tao X, MacKinnon R. Correlation between structure and function in phosphatidylinositol lipid-dependent Kir2.2 gating. Proc Natl Acad Sci U S A 2022; 119:e2114046119. [PMID: 35286194 DOI: 10.1073/pnas.2114046119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) levels regulate cell membrane voltage by gluing two halves of a K+ channel together and opening the pore. PI(4)P competes with this process. Because both of these lipids are relatively abundant in the plasma membrane and are directly interconvertible through the action of specific enzymes, they may function together to regulate channel activity. Inward rectifier K+(Kir) channels regulate cell membrane potential. Different Kir channels respond to unique ligands, but all are regulated by phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2). Using planar lipid bilayers, we show that Kir2.2 exhibits bursts of openings separated by long quiescent interburst periods. Increasing PI(4,5)P2 concentration shortens the Kir2.2 interburst duration and lengthens the burst duration without affecting dwell times within a burst. From this, we propose that burst and interburst durations correspond to the cytoplasmic domain (CTD)–docked and CTD-undocked conformations observed in the presence and absence of PI(4,5)P2 in atomic structures. We also studied the effect of different phosphatidylinositol lipids on Kir2.2 activation and conclude that the 5′ phosphate is essential to Kir2.2 pore opening. Other phosphatidylinositol lipids can compete with PI(4,5)P2 but cannot activate Kir2.2 without the 5′ phosphate. PI(4)P, which is directly interconvertible to and from PI(4,5)P2, might thus be a regulator of Kir channels in the plasma membrane.
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5
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Batrouni AG, Bag N, Phan HT, Baird BA, Baskin JM. A palmitoylation code controls PI4KIIIα complex formation and PI(4,5)P2 homeostasis at the plasma membrane. J Cell Sci 2022; 135:272297. [PMID: 34569608 DOI: 10.1242/jcs.259365] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2021] [Accepted: 09/14/2021] [Indexed: 12/12/2022] Open
Abstract
Phosphatidylinositol 4-kinase IIIα (PI4KIIIα) is the major enzyme responsible for generating phosphatidylinositol (4)-phosphate [PI(4)P] at the plasma membrane. This lipid kinase forms two multicomponent complexes, both including a palmitoylated anchor, EFR3. Whereas both PI4KIIIα complexes support production of PI(4)P, the distinct functions of each complex and mechanisms underlying the interplay between them remain unknown. Here, we present roles for differential palmitoylation patterns within a tri-cysteine motif in EFR3B (Cys5, Cys7 and Cys8) in controlling the distribution of PI4KIIIα between these two complexes at the plasma membrane and corresponding functions in phosphoinositide homeostasis. Spacing of palmitoyl groups within three doubly palmitoylated EFR3B 'lipoforms' affects both interactions between EFR3B and TMEM150A, a transmembrane protein governing formation of a PI4KIIIα complex functioning in rapid phosphatidylinositol (4,5)-bisphosphate [PI(4,5)P2] resynthesis following phospholipase C signaling, and EFR3B partitioning within liquid-ordered and -disordered regions of the plasma membrane. This work identifies a palmitoylation code involved in controlling protein-protein and protein-lipid interactions that affect a plasma membrane-resident lipid biosynthetic pathway.
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Affiliation(s)
- Alex G Batrouni
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA.,Weill Institute for Molecular and Cell Biology, Cornell University, Ithaca, NY 14853, USA
| | - Nirmalya Bag
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA
| | - Henry T Phan
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA
| | - Barbara A Baird
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA
| | - Jeremy M Baskin
- Weill Institute for Molecular and Cell Biology, Cornell University, Ithaca, NY 14853, USA.,Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA
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6
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Dickson EJ. Phosphoinositide transport and metabolism at membrane contact sites. Biochim Biophys Acta Mol Cell Biol Lipids 2022; 1867:159107. [PMID: 34995791 DOI: 10.1016/j.bbalip.2021.159107] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2021] [Revised: 12/06/2021] [Accepted: 12/09/2021] [Indexed: 11/18/2022]
Abstract
Phosphoinositides are a family of signaling lipids that play a profound role in regulating protein function at the membrane-cytosol interface of all cellular membranes. Underscoring their importance, mutations or alterations in phosphoinositide metabolizing enzymes lead to host of developmental, neurodegenerative, and metabolic disorders that are devastating for human health. In addition to lipid enzymes, phosphoinositide metabolism is regulated and controlled at membrane contact sites (MCS). Regions of close opposition typically between the ER and other cellular membranes, MCS are non-vesicular lipid transport portals that engage in extensive communication to influence organelle homeostasis. This review focuses on lipid transport, specifically phosphoinositide lipid transport and metabolism at MCS.
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Affiliation(s)
- Eamonn J Dickson
- Department of Physiology and Membrane Biology, University of California, Davis, CA 95616, United States of America.
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7
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Liu K, Kong L, Graham DB, Carey KL, Xavier RJ. SAC1 regulates autophagosomal phosphatidylinositol-4-phosphate for xenophagy-directed bacterial clearance. Cell Rep 2021; 36:109434. [PMID: 34320354 PMCID: PMC8327279 DOI: 10.1016/j.celrep.2021.109434] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2020] [Revised: 12/21/2020] [Accepted: 07/01/2021] [Indexed: 02/07/2023] Open
Abstract
Phosphoinositides are important molecules in lipid signaling, membrane identity, and trafficking that are spatiotemporally controlled by factors from both mammalian cells and intracellular pathogens. Here, using small interfering RNA (siRNA) directed against phosphoinositide kinases and phosphatases, we screen for regulators of the host innate defense response to intracellular bacterial replication. We identify SAC1, a transmembrane phosphoinositide phosphatase, as an essential regulator of xenophagy. Depletion or inactivation of SAC1 compromises fusion between Salmonella-containing autophagosomes and lysosomes, leading to increased bacterial replication. Mechanistically, the loss of SAC1 results in aberrant accumulation of phosphatidylinositol-4-phosphate [PI(4)P] on Salmonella-containing autophagosomes, thus facilitating recruitment of SteA, a PI(4)P-binding Salmonella effector protein, which impedes lysosomal fusion. Replication of Salmonella lacking SteA is suppressed by SAC-1-deficient cells, however, demonstrating bacterial adaptation to xenophagy. Our findings uncover a paradigm in which a host protein regulates the level of its substrate and impairs the function of a bacterial effector during xenophagy.
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Affiliation(s)
- Kai Liu
- Center for Computational and Integrative Biology, Department of Molecular Biology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA
| | - Lingjia Kong
- Center for Computational and Integrative Biology, Department of Molecular Biology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA
| | - Daniel B Graham
- Center for Computational and Integrative Biology, Department of Molecular Biology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA; Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA; Center for the Study of Inflammatory Bowel Disease, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA; Klarman Cell Observatory, Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA
| | | | - Ramnik J Xavier
- Center for Computational and Integrative Biology, Department of Molecular Biology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA; Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA; Center for the Study of Inflammatory Bowel Disease, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA; Klarman Cell Observatory, Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA.
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8
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Batrouni AG, Baskin JM. The chemistry and biology of phosphatidylinositol 4-phosphate at the plasma membrane. Bioorg Med Chem 2021; 40:116190. [PMID: 33965837 DOI: 10.1016/j.bmc.2021.116190] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2021] [Revised: 04/24/2021] [Accepted: 04/26/2021] [Indexed: 12/29/2022]
Abstract
Phosphoinositides are an important class of anionic, low abundance signaling lipids distributed throughout intracellular membranes. The plasma membrane contains three phosphoinositides: PI(4)P, PI(4,5)P2, and PI(3,4,5)P3. Of these, PI(4)P has remained the most mysterious, despite its characterization in this membrane more than a half-century ago. Fortunately, recent methodological innovations at the chemistry-biology interface have spurred a renaissance of interest in PI(4)P. Here, we describe these new toolsets and how they have revealed novel functions for the plasma membrane PI(4)P pool. We examine high-resolution structural characterization of the plasma membrane PI 4-kinase complex that produces PI(4)P, tools for modulating PI(4)P levels including isoform-selective PI 4-kinase inhibitors, and fluorescent probes for visualizing PI(4)P. Collectively, these chemical and biochemical approaches have revealed insights into how cells regulate synthesis of PI(4)P and its downstream metabolites as well as new roles for plasma membrane PI(4)P in non-vesicular lipid transport, membrane homeostasis and trafficking, and cell signaling pathways.
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Affiliation(s)
- Alex G Batrouni
- Department of Chemistry and Chemical Biology and Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY 14853, USA
| | - Jeremy M Baskin
- Department of Chemistry and Chemical Biology and Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY 14853, USA.
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9
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Sasvari Z, Lin W, Inaba JI, Xu K, Kovalev N, Nagy PD. Co-opted Cellular Sac1 Lipid Phosphatase and PI(4)P Phosphoinositide Are Key Host Factors during the Biogenesis of the Tombusvirus Replication Compartment. J Virol 2020; 94:e01979-19. [PMID: 32269127 PMCID: PMC7307105 DOI: 10.1128/jvi.01979-19] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2019] [Accepted: 04/02/2020] [Indexed: 12/19/2022] Open
Abstract
Positive-strand RNA [(+)RNA] viruses assemble numerous membrane-bound viral replicase complexes (VRCs) with the help of viral replication proteins and co-opted host proteins within large viral replication compartments in the cytosol of infected cells. In this study, we found that deletion or depletion of Sac1 phosphatidylinositol 4-phosphate [PI(4)P] phosphatase reduced tomato bushy stunt virus (TBSV) replication in yeast (Saccharomyces cerevisiae) and plants. We demonstrate a critical role for Sac1 in TBSV replicase assembly in a cell-free replicase reconstitution assay. The effect of Sac1 seems to be direct, based on its interaction with the TBSV p33 replication protein, its copurification with the tombusvirus replicase, and its presence in the virus-induced membrane contact sites and within the TBSV replication compartment. The proviral functions of Sac1 include manipulation of lipid composition, sterol enrichment within the VRCs, and recruitment of additional host factors into VRCs. Depletion of Sac1 inhibited the recruitment of Rab5 GTPase-positive endosomes and enrichment of phosphatidylethanolamine in the viral replication compartment. We propose that Sac1 might be a component of the assembly hub for VRCs, likely in collaboration with the co-opted the syntaxin18-like Ufe1 SNARE protein within the TBSV replication compartments. This work also led to demonstration of the enrichment of PI(4)P phosphoinositide within the replication compartment. Reduction in the PI(4)P level due to chemical inhibition in plant protoplasts; depletion of two PI(4)P kinases, Stt4p and Pik1p; or sequestration of free PI(4)P via expression of a PI(4)P-binding protein in yeast strongly inhibited TBSV replication. Altogether, Sac1 and PI(4)P play important proviral roles during TBSV replication.IMPORTANCE Replication of positive-strand RNA viruses depends on recruitment of host components into viral replication compartments or organelles. Using TBSV, we uncovered the critical roles of Sac1 PI(4)P phosphatase and its substrate, PI(4)P phosphoinositide, in promoting viral replication. Both Sac1 and PI(4)P are recruited to the site of viral replication to facilitate the assembly of the viral replicase complexes, which perform viral RNA replication. We found that Sac1 affects the recruitment of other host factors and enrichment of phosphatidylethanolamine and sterol lipids within the subverted host membranes to promote optimal viral replication. In summary, this work demonstrates the novel functions of Sac1 and PI(4)P in TBSV replication in the model host yeast and in plants.
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Affiliation(s)
- Zsuzsanna Sasvari
- Department of Plant Pathology, University of Kentucky, Lexington, Kentucky, USA
| | - Wenwu Lin
- Department of Plant Pathology, University of Kentucky, Lexington, Kentucky, USA
| | - Jun-Ichi Inaba
- Department of Plant Pathology, University of Kentucky, Lexington, Kentucky, USA
| | - Kai Xu
- Department of Plant Pathology, University of Kentucky, Lexington, Kentucky, USA
| | - Nikolay Kovalev
- Department of Plant Pathology, University of Kentucky, Lexington, Kentucky, USA
| | - Peter D Nagy
- Department of Plant Pathology, University of Kentucky, Lexington, Kentucky, USA
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10
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De Tito S, Hervás JH, van Vliet AR, Tooze SA. The Golgi as an Assembly Line to the Autophagosome. Trends Biochem Sci 2020; 45:484-496. [PMID: 32307224 DOI: 10.1016/j.tibs.2020.03.010] [Citation(s) in RCA: 54] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2019] [Revised: 03/05/2020] [Accepted: 03/17/2020] [Indexed: 12/11/2022]
Abstract
Autophagy is traditionally depicted as a signaling cascade that culminates in the formation of an autophagosome that degrades cellular cargo. However, recent studies have identified myriad pathways and cellular organelles underlying the autophagy process, be it as signaling platforms or through the contribution of proteins and lipids. The Golgi complex is recognized as being a central transport hub in the cell, with a critical role in endocytic trafficking and endoplasmic reticulum (ER) to plasma membrane (PM) transport. However, the Golgi is also an important site of key autophagy regulators, including the protein autophagy-related (ATG)-9A and the lipid, phosphatidylinositol-4-phosphate [PI(4)P]. In this review, we highlight the central function of this organelle in autophagy as a transport hub supplying various components of autophagosome formation.
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Affiliation(s)
- Stefano De Tito
- The Molecular Cell Biology of Autophagy, The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK
| | - Javier H Hervás
- The Molecular Cell Biology of Autophagy, The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK; Instituto Biofisika (CSIC, UPV/EHU), Departamento de Bioquímica y Biología Molecular, Universidad del País Vasco, Bilbao, Spain
| | - Alexander R van Vliet
- The Molecular Cell Biology of Autophagy, The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK
| | - Sharon A Tooze
- The Molecular Cell Biology of Autophagy, The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK.
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11
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Fáberová V, Kalasová I, Krausová A, Hozák P. Super-Resolution Localisation of Nuclear PI(4)P and Identification of Its Interacting Proteome. Cells 2020; 9:E1191. [PMID: 32403279 DOI: 10.3390/cells9051191] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2020] [Revised: 05/03/2020] [Accepted: 05/05/2020] [Indexed: 12/23/2022] Open
Abstract
Phosphoinositides are glycerol-based phospholipids, and they play essential roles in cellular signalling, membrane and cytoskeletal dynamics, cell movement, and the modulation of ion channels and transporters. Phosphoinositides are also associated with fundamental nuclear processes through their nuclear protein-binding partners, even though membranes do not exist inside of the nucleus. Phosphatidylinositol 4-phosphate (PI(4)P) is one of the most abundant cellular phosphoinositides; however, its functions in the nucleus are still poorly understood. In this study, we describe PI(4)P localisation in the cell nucleus by super-resolution light and electron microscopy, and employ immunoprecipitation with a specific anti-PI(4)P antibody and subsequent mass spectrometry analysis to determine PI(4)P’s interaction partners. We show that PI(4)P is present at the nuclear envelope, in nuclear lamina, in nuclear speckles and in nucleoli and also forms multiple small foci in the nucleoplasm. Nuclear PI(4)P undergoes re-localisation to the cytoplasm during cell division; it does not localise to chromosomes, nucleolar organising regions or mitotic interchromatin granules. When PI(4)P and PI(4,5)P2 are compared, they have different nuclear localisations during interphase and mitosis, pointing to their functional differences in the cell nucleus. Mass spectrometry identified hundreds of proteins, including 12 potentially novel PI(4)P interactors, most of them functioning in vital nuclear processes such as pre-mRNA splicing, transcription or nuclear transport, thus extending the current knowledge of PI(4)P’s interaction partners. Based on these data, we propose that PI(4)P also plays a role in essential nuclear processes as a part of protein–lipid complexes. Altogether, these observations provide a novel insight into the role of PI(4)P in nuclear functions and provide a direction for further investigation.
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12
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Abstract
To maintain an asymmetric distribution of ions across membranes, protein pumps displace ions against their concentration gradient by using chemical energy. Here, we describe a functionally analogous but topologically opposite process that applies to the lipid transfer protein (LTP) oxysterol-binding protein (OSBP). This multidomain protein exchanges cholesterol for the phosphoinositide phosphatidylinositol 4-phosphate [PI(4)P] between two apposed membranes. Because of the subsequent hydrolysis of PI(4)P, this counterexchange is irreversible and contributes to the establishment of a cholesterol gradient along organelles of the secretory pathway. The facts that some natural anti-cancer molecules block OSBP and that many viruses hijack the OSBP cycle for the formation of intracellular replication organelles highlight the importance and potency of OSBP-mediated lipid exchange. The architecture of some LTPs is similar to that of OSBP, suggesting that the principles of the OSBP cycle-burning PI(4)P for the vectorial transfer of another lipid-might be general.
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Affiliation(s)
- Bruno Antonny
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS UMR 7275, Université Côte d'Azur, 06560 Valbonne, France;
| | - Joëlle Bigay
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS UMR 7275, Université Côte d'Azur, 06560 Valbonne, France;
| | - Bruno Mesmin
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS UMR 7275, Université Côte d'Azur, 06560 Valbonne, France;
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13
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Yamamoto W, Wada S, Nagano M, Aoshima K, Siekhaus DE, Toshima JY, Toshima J. Distinct roles for plasma membrane PtdIns(4)P and PtdIns(4,5)P 2 during receptor-mediated endocytosis in yeast. J Cell Sci 2018; 131:jcs.207696. [PMID: 29192062 DOI: 10.1242/jcs.207696] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2017] [Accepted: 11/14/2017] [Indexed: 01/15/2023] Open
Abstract
Clathrin-mediated endocytosis requires the coordinated assembly of various endocytic proteins and lipids at the plasma membrane. Accumulating evidence demonstrates a crucial role for phosphatidylinositol-4,5-bisphosphate [PtdIns(4,5)P2] in endocytosis but specific roles for phosphatidylinositol-4-phosphate [PtdIns(4)P], other than as the biosynthetic precursor of PtdIns(4,5)P2, have not been clarified. In this study we investigated the roles of PtdIns(4)P and PtdIns(4,5)P2 in receptor-mediated endocytosis through the construction of temperature-sensitive (ts) mutants for the phosphatidylinositol 4-kinases (PI4-kinases) Stt4p and Pik1p and the 1-phosphatidylinositol-4-phosphate 5-kinase [PtdIns(4) 5-kinase] Mss4p. Quantitative analyses of endocytosis revealed that both the stt4tspik1ts and mss4ts mutants have a severe defect in endocytic internalization. Live-cell imaging of endocytic protein dynamics in stt4tspik1ts and mss4ts mutants revealed that PtdIns(4)P is required for the recruitment of the α-factor receptor Ste2p to clathrin-coated pits, whereas PtdIns(4,5)P2 is required for membrane internalization. We also found that the localization to endocytic sites of the ENTH/ANTH domain-bearing clathrin adaptors, Ent1p, Ent2p, Yap1801p and Yap1802p, is significantly impaired in the stt4tspik1ts mutant but not in the mss4ts mutant. These results suggest distinct roles in successive steps for PtdIns(4)P and PtdIns(4,5)P2 during receptor-mediated endocytosis.
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Affiliation(s)
- Wataru Yamamoto
- Department of Biological Science and Technology, Tokyo University of Science, 6-3-1 Niijyuku, Katsushika-ku, Tokyo 125-8585, Japan
| | - Suguru Wada
- Department of Biological Science and Technology, Tokyo University of Science, 6-3-1 Niijyuku, Katsushika-ku, Tokyo 125-8585, Japan
| | - Makoto Nagano
- Department of Biological Science and Technology, Tokyo University of Science, 6-3-1 Niijyuku, Katsushika-ku, Tokyo 125-8585, Japan
| | - Kaito Aoshima
- Department of Biological Science and Technology, Tokyo University of Science, 6-3-1 Niijyuku, Katsushika-ku, Tokyo 125-8585, Japan
| | | | - Junko Y Toshima
- School of Health Science, Tokyo University of Technology, 5-23-22 Nishikamata, Ota-ku, Tokyo 144-8535, Japan
| | - Jiro Toshima
- Department of Biological Science and Technology, Tokyo University of Science, 6-3-1 Niijyuku, Katsushika-ku, Tokyo 125-8585, Japan
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14
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Mani M, Lee UH, Yoon NA, Yoon EH, Lee BJ, Cho WJ, Park JW. Developmentally regulated GTP-binding protein 2 is required for stabilization of Rac1-positive membrane tubules. Biochem Biophys Res Commun 2017; 493:758-764. [PMID: 28865956 DOI: 10.1016/j.bbrc.2017.08.110] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Accepted: 08/27/2017] [Indexed: 01/07/2023]
Abstract
Previously we have reported that developmentally regulated GTP-binding protein 2 (DRG2) localizes on Rab5 endosomes and plays an important role in transferrin (Tfn) recycling. We here identified DRG2 as a key regulator of membrane tubule stability. At 30 min after Tfn treatment, DRG2 localized to membrane tubules which were enriched with phosphatidylinositol 4-monophosphate [PI(4)P] and did not contain Rab5. DRG2 interacted with Rac1 more strongly with GTP-bound Rac1 and tubular localization of DRG2 depended on Rac1 activity. DRG2 depletion led to destabilization of membrane tubules, while ectopic expression of DRG2 rescued the stability of the membrane tubules in DRG2-depleted cells. Our results reveal a novel mechanism for regulation of membrane tubule stability mediated by DRG2.
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Affiliation(s)
- Muralidharan Mani
- Department of Biological Sciences, University of Ulsan, Ulsan 680-749, South Korea
| | - Unn Hwa Lee
- Department of Biological Sciences, University of Ulsan, Ulsan 680-749, South Korea
| | - Nal Ae Yoon
- Department of Biological Sciences, University of Ulsan, Ulsan 680-749, South Korea
| | - Eun Hye Yoon
- Department of Biological Sciences, University of Ulsan, Ulsan 680-749, South Korea
| | - Byung Ju Lee
- Department of Biological Sciences, University of Ulsan, Ulsan 680-749, South Korea
| | - Wha Ja Cho
- Metainflammation Research Center, University of Ulsan, Ulsan 680-749, South Korea
| | - Jeong Woo Park
- Department of Biological Sciences, University of Ulsan, Ulsan 680-749, South Korea.
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15
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Aksnes H, Goris M, Strømland Ø, Drazic A, Waheed Q, Reuter N, Arnesen T. Molecular determinants of the N-terminal acetyltransferase Naa60 anchoring to the Golgi membrane. J Biol Chem 2017; 292:6821-6837. [PMID: 28196861 DOI: 10.1074/jbc.m116.770362] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2016] [Revised: 01/29/2017] [Indexed: 11/06/2022] Open
Abstract
Nα-Acetyltransferase 60 (Naa60 or NatF) was recently identified as an unconventional N-terminal acetyltransferase (NAT) because it localizes to organelles, in particular the Golgi apparatus, and has a preference for acetylating N termini of the transmembrane proteins. This knowledge challenged the prevailing view of N-terminal acetylation as a co-translational ribosome-associated process and suggested a new mechanistic functioning for the enzymes responsible for this increasingly recognized protein modification. Crystallography studies on Naa60 were unable to resolve the C-terminal tail of Naa60, which is responsible for the organellar localization. Here, we combined modeling, in vitro assays, and cellular localization studies to investigate the secondary structure and membrane interacting capacity of Naa60. The results show that Naa60 is a peripheral membrane protein. Two amphipathic helices within the Naa60 C terminus bind the membrane directly in a parallel position relative to the lipid bilayer via hydrophobic and electrostatic interactions. A peptide corresponding to the C terminus was unstructured in solution and only folded into an α-helical conformation in the presence of liposomes. Computational modeling and cellular mutational analysis revealed the hydrophobic face of two α-helices to be critical for membranous localization. Furthermore, we found a strong and specific binding preference of Naa60 toward membranes containing the phosphatidylinositol PI(4)P, thus possibly explaining the primary residency of Naa60 at the PI(4)P-rich Golgi. In conclusion, we have defined the mode of cytosolic Naa60 anchoring to the Golgi apparatus, most likely occurring post-translationally and specifically facilitating post-translational N-terminal acetylation of many transmembrane proteins.
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Affiliation(s)
- Henriette Aksnes
- From the Department of Molecular Biology, University of Bergen, N-5020 Bergen
| | - Marianne Goris
- From the Department of Molecular Biology, University of Bergen, N-5020 Bergen
| | - Øyvind Strømland
- From the Department of Molecular Biology, University of Bergen, N-5020 Bergen
| | - Adrian Drazic
- From the Department of Molecular Biology, University of Bergen, N-5020 Bergen
| | - Qaiser Waheed
- From the Department of Molecular Biology, University of Bergen, N-5020 Bergen.,the Computational Biology Unit, Department of Informatics, University of Bergen, N-5020 Bergen, and
| | - Nathalie Reuter
- From the Department of Molecular Biology, University of Bergen, N-5020 Bergen.,the Computational Biology Unit, Department of Informatics, University of Bergen, N-5020 Bergen, and
| | - Thomas Arnesen
- From the Department of Molecular Biology, University of Bergen, N-5020 Bergen, .,the Department of Surgery, Haukeland University Hospital, N-5021 Bergen, Norway
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16
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Jeschke A, Haas A. Deciphering the roles of phosphoinositide lipids in phagolysosome biogenesis. Commun Integr Biol 2016; 9:e1174798. [PMID: 27489580 DOI: 10.1080/19420889.2016.1174798] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2016] [Revised: 03/29/2016] [Accepted: 03/31/2016] [Indexed: 01/01/2023] Open
Abstract
Professional phagocytes engulf microbial invaders into plasma membrane-derived phagosomes. These mature into microbicidal phagolysosomes, leading to killing of the ingested microbe. Phagosome maturation involves sequential fusion of the phagosome with early endosomes, late endosomes, and the main degradative compartments in cells, lysosomes. Some bacterial pathogens manipulate the phosphoinositide (PIP) composition of phagosome membranes and are not delivered to phagolysosomes, pointing at a role of PIPs in phagosome maturation. This hypothesis is supported by comprehensive microscopic studies. Recently, cell-free reconstitution of fusion between phagosomes and endo(lyso)somes identified phosphatidylinositol 4-phosphate [PI(4)P] and phosphatidylinositol 3-phosphate [PI(3)P] as key regulators of phagolysosome biogenesis. Here, we describe the emerging roles of PIPs in phagosome maturation and we present tools to study PIP involvement in phagosome trafficking using intact cells or purified compartments.
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17
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Abstract
During recent decades, PI(4)P (phosphoinositol-4-phosphate) has been described as a key regulator of a wide range of cellular functions such as organelle biogenesis, lipid metabolism and distribution, membrane trafficking, ion channels, pumps, and transporter activities. In this review we will focus on the multiple mechanisms that regulate PI(4)P homeostasis ranging from those responsible for the spatial distribution of the PI4 kinases and PI(4)P phosphatase to those controlling their enzymatic activity or the delivery/presentation of the substrate, i.e. PI or PI(4)P, to the PI4Ks or PI(4)P phosphatase, respectively. We will also highlight the open questions in the field mainly dealing with the existence and mode of action of PI(4)P sensors that monitor its amount and can act as a rheostat tuning PI(4)P levels in different compartments and adapting them to the different needs of the cell.
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Affiliation(s)
- Rossella Venditti
- Telethon Institute of Genetics and Medicine, Via Campi Flegrei 34, 80078 Pozzuoli, Naples, Italy
| | - Maria Chiara Masone
- Telethon Institute of Genetics and Medicine, Via Campi Flegrei 34, 80078 Pozzuoli, Naples, Italy
| | - Cathal Wilson
- Telethon Institute of Genetics and Medicine, Via Campi Flegrei 34, 80078 Pozzuoli, Naples, Italy
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18
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Wasilko DJ, Mao Y. Exploiting the ubiquitin and phosphoinositide pathways by the Legionella pneumophila effector, SidC. Curr Genet 2015; 62:105-8. [PMID: 26433729 DOI: 10.1007/s00294-015-0521-y] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2015] [Revised: 09/13/2015] [Accepted: 09/14/2015] [Indexed: 01/29/2023]
Abstract
Intracellular bacterial pathogens use secreted effector proteins to alter host cellular processes, with the goal of subverting host defenses and allowing the infection to progress. One such pathogen, Legionella pneumophila, secretes ~300 proteins into its host to alter a number of pathways including intracellular trafficking, phosphoinositide metabolism, and cell signaling. The Legionella effector SidC was previously found to bind to PI(4)P and was responsible for the enrichment of ER proteins and ubiquitinated species on the Legionella-containing vacuoles. Through our recent work, we have discovered that SidC contains a unique N-terminal E3 ubiquitin ligase domain and a C-terminal novel PI(4)P-binding domain. Our results demonstrate that SidC serves to link two distinct cellular pathways, ubiquitin and phosphoinositide. However, how the ubiquitin ligase activity regulates host membrane trafficking events remains to be investigated.
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Affiliation(s)
- David J Wasilko
- Weill Institute for Cell and Molecular Biology and Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY, 14853, USA
| | - Yuxin Mao
- Weill Institute for Cell and Molecular Biology and Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY, 14853, USA.
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Miller MB, Vishwanatha KS, Mains RE, Eipper BA. An N-terminal Amphipathic Helix Binds Phosphoinositides and Enhances Kalirin Sec14 Domain-mediated Membrane Interactions. J Biol Chem 2015; 290:13541-55. [PMID: 25861993 DOI: 10.1074/jbc.m115.636746] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2015] [Indexed: 11/06/2022] Open
Abstract
Previous studies revealed an essential role for the lipid-binding Sec14 domain of kalirin (KalSec14), but its mechanism of action is not well understood. Because alternative promoter usage appends unique N-terminal peptides to the KalSec14 domain, we used biophysical, biochemical, and cell biological approaches to examine the two major products, bKalSec14 and cKalSec14. Promoter B encodes a charged, unstructured peptide, whereas promoter C encodes an amphipathic helix (Kal-C-helix). Both bKalSec14 and cKalSec14 interacted with lipids in PIP strip and liposome flotation assays, with significantly greater binding by cKalSec14 in both assays. Disruption of the hydrophobic face of the Kal-C-helix in cKalSec14KKED eliminated its increased liposome binding. Although cKalSec14 showed significantly reduced binding to liposomes lacking phosphatidylinositol phosphates or cholesterol, liposome binding by bKalSec14 and cKalSec14KKED was not affected. When expressed in AtT-20 cells, bKalSec14-GFP was diffusely localized, whereas cKalSec14-GFP localized to the trans-Golgi network and secretory granules. The amphipathic C-helix was sufficient for this localization. When AtT-20 cells were treated with a cell-permeant derivative of the Kal-C-helix (Kal-C-helix-Arg9), we observed increased secretion of a product stored in mature secretory granules, with no effect on basal secretion; a cell-permeant control peptide (Kal-C-helixKKED-Arg9) did not have this effect. Through its ability to control expression of a novel, phosphoinositide-binding amphipathic helix, Kalrn promoter usage is expected to affect function.
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Affiliation(s)
| | | | | | - Betty A Eipper
- From the Departments of Neuroscience and Molecular Biology and Biophysics, University of Connecticut Health Center, Farmington, Connecticut 06030
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