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König C, Shvarev D, Gao J, Haar E, Susan N, Auffarth K, Langemeyer L, Moeller A, Ungermann C. Vps41 functions as a molecular ruler for HOPS tethering complex-mediated membrane fusion. J Cell Sci 2025; 138:jcs263788. [PMID: 40159992 DOI: 10.1242/jcs.263788] [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: 12/10/2024] [Accepted: 03/24/2025] [Indexed: 04/02/2025] Open
Abstract
Fusion at the lysosome (or the yeast vacuole) requires the conserved hexameric HOPS tethering complex. In the yeast Saccharomyces cerevisiae, HOPS binds to the vacuolar Rab7-like GTPase Ypt7 via its subunits Vps41 and Vps39 and supports fusion by promoting SNARE assembly. In contrast to its sister complex CORVET, the Ypt7-interacting domain of Vps41 in the HOPS complex is connected to the core by a long, extended α-solenoid domain. Here, we show that this solenoid acts as a molecular ruler to position the Ypt7-interacting region of Vps41 relative to the core of HOPS to support function. Mutant complexes with a shortened or extended α-solenoid region in Vps41 still tethered membranes, but failed to efficiently support their fusion. In vivo, Vps41 mutants grew poorly and showed defects in vacuolar morphology, endolysosomal sorting and autophagy. Importantly, when a length-compensating linker was inserted instead of the shortened α-solenoid domain, these defects were rescued. This suggests that the Rab-specific Vps41 subunit requires the exact length of the α-solenoid domain but not the α-solenoid architecture for functionality, suggesting a revised model of how HOPS supports fusion.
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Affiliation(s)
- Caroline König
- Department of Biology/Chemistry, Biochemistry section, Osnabrück University, 49076 Osnabrück, Germany
| | - Dmitry Shvarev
- Department of Biology/Chemistry, Structural Biology section, Osnabrück University, 49076 Osnabrück, Germany
| | - Jieqiong Gao
- Department of Biology/Chemistry, Biochemistry section, Osnabrück University, 49076 Osnabrück, Germany
| | - Eduard Haar
- Department of Biology/Chemistry, Biochemistry section, Osnabrück University, 49076 Osnabrück, Germany
| | - Nicole Susan
- Department of Biology/Chemistry, Biochemistry section, Osnabrück University, 49076 Osnabrück, Germany
| | - Kathrin Auffarth
- Department of Biology/Chemistry, Biochemistry section, Osnabrück University, 49076 Osnabrück, Germany
| | - Lars Langemeyer
- Department of Biology/Chemistry, Biochemistry section, Osnabrück University, 49076 Osnabrück, Germany
- Center of Cellular Nanoanalytics (CellNanOs), Osnabrück University, 49076 Osnabrück, Germany
| | - Arne Moeller
- Department of Biology/Chemistry, Structural Biology section, Osnabrück University, 49076 Osnabrück, Germany
- Center of Cellular Nanoanalytics (CellNanOs), Osnabrück University, 49076 Osnabrück, Germany
| | - Christian Ungermann
- Department of Biology/Chemistry, Biochemistry section, Osnabrück University, 49076 Osnabrück, Germany
- Center of Cellular Nanoanalytics (CellNanOs), Osnabrück University, 49076 Osnabrück, Germany
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2
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Zhang S, Gu M, Yin H, Pan S, Xie H, Chen W, Gul S, Zhao Y, Wang Z, Zheng W, You Y, You B. IGF2BP1-HAX-1 positive feedback loop-mediated HAX-1 overexpression blocks autophagic flux and promotes chemoresistance in nasopharyngeal carcinoma. Cell Mol Life Sci 2025; 82:105. [PMID: 40055185 PMCID: PMC11889316 DOI: 10.1007/s00018-025-05604-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2024] [Revised: 10/10/2024] [Accepted: 01/22/2025] [Indexed: 05/13/2025]
Abstract
Autophagy is associated with chemoresistance, which is the leading cause of failure in chemotherapeutic treatments. Among the various aspects of autophagy, autophagic flux serves as a critical indicator for evaluating the dynamic processes involved.We report herein that the multifunctional protein HAX-1 promotes chemoresistance by effectively blocking the fusion of autophagosomes with lysosomes. Complementary mass spectrometric and functional studies also demonstrated that HAX-1 recruits NEDD4 to promote Rab7a degradation and inhibits binding of Rab7a with SNAREs by competitively binding to it. Furthermore, HAX-1 binds IGF2BP1 mRNA, thereby contributing to its stability and translation. Moreover, IGF2BP1 enhanced HAX-1 m6A methylation, thereby enhancing its stability. By way of in-vivo and in-vitro experiments, we confirmed the positive role of the IGF2BP1-HAX-1 feedback loop in chemoresistance. Taken together, our findings provide evidence that monitoring of HAX-1, IGF2BP1, and SQSTM1 levels can serve as useful predictors of clinical outcome and chemoresistance risk. In addition, our data provide new insights into the clinical applications of therapies related to autophagic flux and its associated molecular network in targeting cisplatin chemoresistance in nasopharyngeal carcinoma.
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Affiliation(s)
- Siyu Zhang
- Department of Otorhinolaryngology Head and Neck Surgery, Affiliated Hospital of Nantong University, Xisi Road 20, Nantong, 226019, Jiangsu Province, China
- Institute of Otolaryngology Head and Neck Surgery, Affiliated Hospital of Nantong University, Xisi Road 20, Nantong, 226019, Jiangsu Province, China
| | - Miao Gu
- Department of Otorhinolaryngology Head and Neck Surgery, Affiliated Hospital of Nantong University, Xisi Road 20, Nantong, 226019, Jiangsu Province, China
- Institute of Otolaryngology Head and Neck Surgery, Affiliated Hospital of Nantong University, Xisi Road 20, Nantong, 226019, Jiangsu Province, China
| | - Haimeng Yin
- Department of Otorhinolaryngology Head and Neck Surgery, Affiliated Hospital of Nantong University, Xisi Road 20, Nantong, 226019, Jiangsu Province, China
- Institute of Otolaryngology Head and Neck Surgery, Affiliated Hospital of Nantong University, Xisi Road 20, Nantong, 226019, Jiangsu Province, China
| | - Si Pan
- Department of Otorhinolaryngology Head and Neck Surgery, Affiliated Hospital of Nantong University, Xisi Road 20, Nantong, 226019, Jiangsu Province, China
- Institute of Otolaryngology Head and Neck Surgery, Affiliated Hospital of Nantong University, Xisi Road 20, Nantong, 226019, Jiangsu Province, China
| | - Haijing Xie
- Department of Otorhinolaryngology Head and Neck Surgery, Affiliated Hospital of Nantong University, Xisi Road 20, Nantong, 226019, Jiangsu Province, China
- Institute of Otolaryngology Head and Neck Surgery, Affiliated Hospital of Nantong University, Xisi Road 20, Nantong, 226019, Jiangsu Province, China
| | - Wenhui Chen
- Department of Otorhinolaryngology Head and Neck Surgery, Affiliated Hospital of Nantong University, Xisi Road 20, Nantong, 226019, Jiangsu Province, China
- Institute of Otolaryngology Head and Neck Surgery, Affiliated Hospital of Nantong University, Xisi Road 20, Nantong, 226019, Jiangsu Province, China
| | - Sheraz Gul
- Fraunhofer Institute for Translational Medicine and Pharmacology (ITMP), Hamburg, Germany
- Fraunhofer Cluster of Excellence for Immune-Mediated Diseases (CIMD), Hamburg, Germany
| | - Yue Zhao
- Department of General, Visceral and Cancer Surgery, Faculty of Medicine and University Hospital Cologne, University of Cologne, Cologne, Germany
| | - Zhefang Wang
- Department of Plastic and Reconstructive Surgery, Second Affiliated Hospital of Zhejiang University School of Medicine, Jiefang Road 88, Hangzhou, Zhejiang, P. R. China
| | - Wenjie Zheng
- Research Center of Clinical Medicine, Nantong University Medical School, Affiliated Hospital of Nantong University, Nantong, 226019, Jiangsu Province, China.
| | - Yiwen You
- Department of Otorhinolaryngology Head and Neck Surgery, Affiliated Hospital of Nantong University, Xisi Road 20, Nantong, 226019, Jiangsu Province, China.
- Institute of Otolaryngology Head and Neck Surgery, Affiliated Hospital of Nantong University, Xisi Road 20, Nantong, 226019, Jiangsu Province, China.
| | - Bo You
- Department of Otorhinolaryngology Head and Neck Surgery, Affiliated Hospital of Nantong University, Xisi Road 20, Nantong, 226019, Jiangsu Province, China.
- Institute of Otolaryngology Head and Neck Surgery, Affiliated Hospital of Nantong University, Xisi Road 20, Nantong, 226019, Jiangsu Province, China.
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3
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Zhang C, Calderin JD, Hurst LR, Gokbayrak ZD, Hrabak MR, Balutowski A, Rivera-Kohr DA, Kazmirchuk TDD, Brett CL, Fratti RA. Sphingolipids containing very long-chain fatty acids regulate Ypt7 function during the tethering stage of vacuole fusion. J Biol Chem 2024; 300:107808. [PMID: 39307308 PMCID: PMC11530833 DOI: 10.1016/j.jbc.2024.107808] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2024] [Revised: 08/22/2024] [Accepted: 09/15/2024] [Indexed: 10/20/2024] Open
Abstract
Sphingolipids are essential in membrane trafficking and cellular homeostasis. Here, we show that sphingolipids containing very long-chain fatty acids (VLCFAs) promote homotypic vacuolar fusion in Saccharomyces cerevisiae. The elongase Elo3 adds the last two carbons to VLCFAs that are incorporated into sphingolipids. Cells lacking Elo3 have fragmented vacuoles, which is also seen when WT cells are treated with the sphingolipid synthesis inhibitor Aureobasidin-A. Isolated elo3Δ vacuoles show acidification defects and increased membrane fluidity, and this correlates with deficient fusion. Fusion arrest occurs at the tethering stage as elo3Δ vacuoles fail to cluster efficiently in vitro. Unlike HOPS and fusogenic lipids, GFP-Ypt7 does not enrich at elo3Δ vertex microdomains, a hallmark of vacuole docking prior to fusion. Pulldown assays using bacterially expressed GST-Ypt7 showed that HOPS from elo3Δ vacuole extracts failed to bind GST-Ypt7 while HOPS from WT extracts interacted strongly with GST-Ypt7. Treatment of WT vacuoles with the fluidizing anesthetic dibucaine recapitulates the elo3Δ phenotype and shows increased membrane fluidity, mislocalized GFP-Ypt7, inhibited fusion, and attenuated acidification. Together these data suggest that sphingolipids contribute to Rab-mediated tethering and docking required for vacuole fusion.
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Affiliation(s)
- Chi Zhang
- Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, Illinois, USA
| | - Jorge D Calderin
- Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, Illinois, USA
| | - Logan R Hurst
- Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, Illinois, USA
| | | | - Michael R Hrabak
- Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, Illinois, USA
| | - Adam Balutowski
- Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, Illinois, USA
| | - David A Rivera-Kohr
- Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, Illinois, USA
| | | | | | - Rutilio A Fratti
- Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, Illinois, USA; Center for Biophysics & Quantitative Biology, University of Illinois Urbana-Champaign, Urbana, Illinois, USA.
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4
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Füllbrunn N, Nicastro R, Mari M, Griffith J, Herrmann E, Rasche R, Borchers AC, Auffarth K, Kümmel D, Reggiori F, De Virgilio C, Langemeyer L, Ungermann C. The GTPase activating protein Gyp7 regulates Rab7/Ypt7 activity on late endosomes. J Cell Biol 2024; 223:e202305038. [PMID: 38536036 PMCID: PMC10978497 DOI: 10.1083/jcb.202305038] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2023] [Revised: 01/22/2024] [Accepted: 03/08/2024] [Indexed: 04/01/2024] Open
Abstract
Organelles of the endomembrane system contain Rab GTPases as identity markers. Their localization is determined by guanine nucleotide exchange factors (GEFs) and GTPase activating proteins (GAPs). It remains largely unclear how these regulators are specifically targeted to organelles and how their activity is regulated. Here, we focus on the GAP Gyp7, which acts on the Rab7-like Ypt7 protein in yeast, and surprisingly observe the protein exclusively in puncta proximal to the vacuole. Mistargeting of Gyp7 to the vacuole strongly affects vacuole morphology, suggesting that endosomal localization is needed for function. In agreement, efficient endolysosomal transport requires Gyp7. In vitro assays reveal that Gyp7 requires a distinct lipid environment for membrane binding and activity. Overexpression of Gyp7 concentrates Ypt7 in late endosomes and results in resistance to rapamycin, an inhibitor of the target of rapamycin complex 1 (TORC1), suggesting that these late endosomes are signaling endosomes. We postulate that Gyp7 is part of regulatory machinery involved in late endosome function.
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Affiliation(s)
- Nadia Füllbrunn
- Department of Biology/Chemistry, Biochemistry Section, Osnabrück University, Osnabrück, Germany
- Center of Cellular Nanoanalytics, Osnabrück University, Osnabrück, Germany
| | - Raffaele Nicastro
- Department of Biology, University of Fribourg, Fribourg, Switzerland
| | - Muriel Mari
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
| | - Janice Griffith
- Department of Cell Biology, University Medical Center Utrecht, Utrecht, Netherlands
| | - Eric Herrmann
- Institute of Biochemistry, University of Münster, Münster, Germany
| | - René Rasche
- Institute of Biochemistry, University of Münster, Münster, Germany
| | - Ann-Christin Borchers
- Department of Biology/Chemistry, Biochemistry Section, Osnabrück University, Osnabrück, Germany
| | - Kathrin Auffarth
- Department of Biology/Chemistry, Biochemistry Section, Osnabrück University, Osnabrück, Germany
| | - Daniel Kümmel
- Institute of Biochemistry, University of Münster, Münster, Germany
| | - Fulvio Reggiori
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
- Department of Cell Biology, University Medical Center Utrecht, Utrecht, Netherlands
| | | | - Lars Langemeyer
- Department of Biology/Chemistry, Biochemistry Section, Osnabrück University, Osnabrück, Germany
- Center of Cellular Nanoanalytics, Osnabrück University, Osnabrück, Germany
| | - Christian Ungermann
- Department of Biology/Chemistry, Biochemistry Section, Osnabrück University, Osnabrück, Germany
- Center of Cellular Nanoanalytics, Osnabrück University, Osnabrück, Germany
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5
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Klössel S, Zhu Y, Amado L, Bisinski DD, Ruta J, Liu F, González Montoro A. Yeast TLDc domain proteins regulate assembly state and subcellular localization of the V-ATPase. EMBO J 2024; 43:1870-1897. [PMID: 38589611 PMCID: PMC11066047 DOI: 10.1038/s44318-024-00097-2] [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: 01/18/2024] [Revised: 03/06/2024] [Accepted: 03/08/2024] [Indexed: 04/10/2024] Open
Abstract
Yeast vacuoles perform crucial cellular functions as acidic degradative organelles, storage compartments, and signaling hubs. These functions are mediated by important protein complexes, including the vacuolar-type H+-ATPase (V-ATPase), responsible for organelle acidification. To gain a more detailed understanding of vacuole function, we performed cross-linking mass spectrometry on isolated vacuoles, detecting many known as well as novel protein-protein interactions. Among these, we identified the uncharacterized TLDc-domain-containing protein Rtc5 as a novel interactor of the V-ATPase. We further analyzed the influence of Rtc5 and of Oxr1, the only other yeast TLDc-domain-containing protein, on V-ATPase function. We find that both Rtc5 and Oxr1 promote the disassembly of the vacuolar V-ATPase in vivo, counteracting the role of the RAVE complex, a V-ATPase assembly chaperone. Furthermore, Oxr1 is necessary for the retention of a Golgi-specific subunit of the V-ATPase in this compartment. Collectively, our results shed light on the in vivo roles of yeast TLDc-domain proteins as regulators of the V-ATPase, highlighting the multifaceted regulation of this crucial protein complex.
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Affiliation(s)
- Samira Klössel
- Osnabrück University, Department of Biology/Chemistry, Cellular Communication Laboratory, Barbarastrasse 13, 49076, Osnabrück, Germany
| | - Ying Zhu
- Department of Structural Biology, Leibniz - Forschungsinstitut für Molekulare Pharmakologie (FMP), Robert-Roessle-Str. 10, Berlin, 13125, Germany
| | - Lucia Amado
- Osnabrück University, Department of Biology/Chemistry, Cellular Communication Laboratory, Barbarastrasse 13, 49076, Osnabrück, Germany
| | - Daniel D Bisinski
- Osnabrück University, Department of Biology/Chemistry, Cellular Communication Laboratory, Barbarastrasse 13, 49076, Osnabrück, Germany
| | - Julia Ruta
- Department of Structural Biology, Leibniz - Forschungsinstitut für Molekulare Pharmakologie (FMP), Robert-Roessle-Str. 10, Berlin, 13125, Germany
| | - Fan Liu
- Department of Structural Biology, Leibniz - Forschungsinstitut für Molekulare Pharmakologie (FMP), Robert-Roessle-Str. 10, Berlin, 13125, Germany
- Charité - Universitätsmedizin Berlin, Charitépl. 1, 10117, Berlin, Germany
| | - Ayelén González Montoro
- Osnabrück University, Department of Biology/Chemistry, Cellular Communication Laboratory, Barbarastrasse 13, 49076, Osnabrück, Germany.
- Osnabrück University, Center of Cellular Nanoanalytic Osnabrück (CellNanOs), Barbarastrasse 11, 49076, Osnabrück, Germany.
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6
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Kimura Y, Tsuji T, Shimizu Y, Watanabe Y, Kimura M, Fujimoto T, Higuchi M. Physicochemical properties of the vacuolar membrane and cellular factors determine formation of vacuolar invaginations. Sci Rep 2023; 13:16187. [PMID: 37759072 PMCID: PMC10533490 DOI: 10.1038/s41598-023-43232-5] [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: 02/26/2023] [Accepted: 09/21/2023] [Indexed: 09/29/2023] Open
Abstract
Vacuoles change their morphology in response to stress. In yeast exposed to chronically high temperatures, vacuolar membranes get deformed and invaginations are formed. We show that phase-separation of vacuolar membrane occurred after heat stress leading to the formation of the invagination. In addition, Hfl1, a vacuolar membrane-localized Atg8-binding protein, was found to suppress the excess vacuolar invaginations after heat stress. At that time, Hfl1 formed foci at the neck of the invaginations in wild-type cells, whereas it was efficiently degraded in the vacuole in the atg8Δ mutant. Genetic analysis showed that the endosomal sorting complex required for transport machinery was necessary to form the invaginations irrespective of Atg8 or Hfl1. In contrast, a combined mutation with the vacuole BAR domain protein Ivy1 led to vacuoles in hfl1Δivy1Δ and atg8Δivy1Δ mutants having constitutively invaginated structures; moreover, these mutants showed stress-sensitive phenotypes. Our findings suggest that vacuolar invaginations result from the combination of changes in the physiochemical properties of the vacuolar membrane and other cellular factors.
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Affiliation(s)
- Yoko Kimura
- Graduate School of Integrated Science and Technology, Shizuoka University, Shizuoka, 422-8529, Japan.
- Department of Agriculture, Shizuoka University, Shizuoka, 422-8529, Japan.
| | - Takuma Tsuji
- Laboratory of Molecular Cell Biology, Research Institute for Diseases of Old Age, Juntendo University Graduate School of Medicine, Tokyo, Japan
| | - Yosuke Shimizu
- Graduate School of Integrated Science and Technology, Shizuoka University, Shizuoka, 422-8529, Japan
| | - Yuki Watanabe
- Graduate School of Integrated Science and Technology, Shizuoka University, Shizuoka, 422-8529, Japan
| | - Masafumi Kimura
- Graduate School of Integrated Science and Technology, Shizuoka University, Shizuoka, 422-8529, Japan
| | - Toyoshi Fujimoto
- Laboratory of Molecular Cell Biology, Research Institute for Diseases of Old Age, Juntendo University Graduate School of Medicine, Tokyo, Japan
| | - Miyuki Higuchi
- Department of Agriculture, Shizuoka University, Shizuoka, 422-8529, Japan
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7
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Fairman G, Ouimet M. Lipophagy pathways in yeast are controlled by their distinct modes of induction. Yeast 2022; 39:429-439. [PMID: 35652813 DOI: 10.1002/yea.3705] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2021] [Revised: 03/18/2022] [Accepted: 04/04/2022] [Indexed: 11/06/2022] Open
Abstract
Lipid droplet (LD) autophagy (lipophagy) is a recently discovered selective form of autophagy and is a pathway for LD catabolism. This ubiquitous process has been an ongoing area of research within the budding yeast, Saccharomyces cerevisiae. Yeast lipophagy phenotypically resembles microautophagy, although it has a distinct set of genetic requirements depending on the mode of induction. This review highlights the similarities and differences between different forms of yeast lipophagy and offers perspectives on how our knowledge of lipophagy in yeast may guide our understanding of this process within mammalian cells to ultimately inform future applications of lipophagy.
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Affiliation(s)
- Garrett Fairman
- University of Ottawa Heart Institute, Ottawa, Ontario, Canada.,Department of Biochemistry, Microbiology and Immunology, Faculty of Medicine, University of Ottawa, Ottawa, Ontario, Canada
| | - Mireille Ouimet
- University of Ottawa Heart Institute, Ottawa, Ontario, Canada.,Department of Biochemistry, Microbiology and Immunology, Faculty of Medicine, University of Ottawa, Ottawa, Ontario, Canada
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8
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Schmidt O, de Araujo ME. Establishing spatial control over TORC1 signaling. J Cell Biol 2022; 221:e202203136. [PMID: 35404386 PMCID: PMC9007745 DOI: 10.1083/jcb.202203136] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Target-of-rapamycin complex 1 resides on lysosomes/vacuoles and additionally on signaling endosomes. Gao et al. (2022. J. Cell Biol.https://doi.org/10.1083/jcb.202109084) set out to define the molecular identity of signaling endosomes, along with players required for the formation and maintenance of this endosomal subpopulation.
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Affiliation(s)
- Oliver Schmidt
- Institute of Cell Biology, Biocenter Innsbruck, Medical University of Innsbruck, Innsbruck, Austria
| | - Mariana E.G. de Araujo
- Institute of Cell Biology, Biocenter Innsbruck, Medical University of Innsbruck, Innsbruck, Austria
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9
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Gao J, Nicastro R, Péli-Gulli MP, Grziwa S, Chen Z, Kurre R, Piehler J, De Virgilio C, Fröhlich F, Ungermann C. The HOPS tethering complex is required to maintain signaling endosome identity and TORC1 activity. J Biophys Biochem Cytol 2022; 221:213121. [PMID: 35404387 PMCID: PMC9011323 DOI: 10.1083/jcb.202109084] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2021] [Revised: 01/27/2022] [Accepted: 02/28/2022] [Indexed: 12/04/2022] Open
Abstract
The endomembrane system of eukaryotic cells is essential for cellular homeostasis during growth and proliferation. Previous work showed that a central regulator of growth, namely the target of rapamycin complex 1 (TORC1), binds both membranes of vacuoles and signaling endosomes (SEs) that are distinct from multivesicular bodies (MVBs). Interestingly, the endosomal TORC1, which binds membranes in part via the EGO complex, critically defines vacuole integrity. Here, we demonstrate that SEs form at a branch point of the biosynthetic and endocytic pathways toward the vacuole and depend on MVB biogenesis. Importantly, function of the HOPS tethering complex is essential to maintain the identity of SEs and proper endosomal and vacuolar TORC1 activities. In HOPS mutants, the EGO complex redistributed to the Golgi, which resulted in a partial mislocalization of TORC1. Our study uncovers that SE function requires a functional HOPS complex and MVBs, suggesting a tight link between trafficking and signaling along the endolysosomal pathway.
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Affiliation(s)
- Jieqiong Gao
- Department of Biology/Chemistry, Biochemistry Section, Osnabrück University, Osnabrück, Germany
| | - Raffaele Nicastro
- Department of Biology, University of Fribourg, Chemin du Musée, Fribourg, Switzerland
| | | | - Sophie Grziwa
- Department of Biology/Chemistry, Biochemistry Section, Osnabrück University, Osnabrück, Germany
| | - Zilei Chen
- Department of Biology/Chemistry, Biochemistry Section, Osnabrück University, Osnabrück, Germany
| | - Rainer Kurre
- Center of Cellular Nanoanalytic Osnabrück (CellNanOs), Osnabrück University, Osnabrück, Germany
| | - Jacob Piehler
- Center of Cellular Nanoanalytic Osnabrück (CellNanOs), Osnabrück University, Osnabrück, Germany
- Department of Biology/Chemistry, Biophysics Section, Osnabrück University, Osnabrück, Germany
| | - Claudio De Virgilio
- Department of Biology, University of Fribourg, Chemin du Musée, Fribourg, Switzerland
| | - Florian Fröhlich
- Center of Cellular Nanoanalytic Osnabrück (CellNanOs), Osnabrück University, Osnabrück, Germany
- Department of Biology/Chemistry, Molecular Membrane Biology Section, Osnabrück University, Osnabrück, Germany
| | - Christian Ungermann
- Department of Biology/Chemistry, Biochemistry Section, Osnabrück University, Osnabrück, Germany
- Center of Cellular Nanoanalytic Osnabrück (CellNanOs), Osnabrück University, Osnabrück, Germany
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10
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Liao PC, Yang EJ, Borgman T, Boldogh IR, Sing CN, Swayne TC, Pon LA. Touch and Go: Membrane Contact Sites Between Lipid Droplets and Other Organelles. Front Cell Dev Biol 2022; 10:852021. [PMID: 35281095 PMCID: PMC8908909 DOI: 10.3389/fcell.2022.852021] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2022] [Accepted: 02/03/2022] [Indexed: 12/26/2022] Open
Abstract
Lipid droplets (LDs) have emerged not just as storage sites for lipids but as central regulators of metabolism and organelle quality control. These critical functions are achieved, in part, at membrane contact sites (MCS) between LDs and other organelles. MCS are sites of transfer of cellular constituents to or from LDs for energy mobilization in response to nutrient limitations, as well as LD biogenesis, expansion and autophagy. Here, we describe recent findings on the mechanisms underlying the formation and function of MCS between LDs and mitochondria, ER and lysosomes/vacuoles and the role of the cytoskeleton in promoting LD MCS through its function in LD movement and distribution in response to environmental cues.
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Affiliation(s)
- Pin-Chao Liao
- Department of Pathology and Cell Biology, Columbia University Irving Medical Center, New York, NY, United States
- Institute of Molecular Medicine, National Tsing Hua University, Hsinchu, Taiwan
| | - Emily J. Yang
- Department of Pathology and Cell Biology, Columbia University Irving Medical Center, New York, NY, United States
| | - Taylor Borgman
- Institute of Human Nutrition, Columbia University Irving Medical Center, New York, NY, United States
| | - Istvan R. Boldogh
- Department of Pathology and Cell Biology, Columbia University Irving Medical Center, New York, NY, United States
- Herbert Irving Comprehensive Cancer Center, Columbia University Irving Medical Center, New York, NY, United States
| | - Cierra N. Sing
- Institute of Human Nutrition, Columbia University Irving Medical Center, New York, NY, United States
| | - Theresa C. Swayne
- Herbert Irving Comprehensive Cancer Center, Columbia University Irving Medical Center, New York, NY, United States
| | - Liza A. Pon
- Department of Pathology and Cell Biology, Columbia University Irving Medical Center, New York, NY, United States
- Institute of Human Nutrition, Columbia University Irving Medical Center, New York, NY, United States
- *Correspondence: Liza A. Pon,
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11
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Liao PC, Garcia EJ, Tan G, Tsang CA, Pon LA. Roles for L o microdomains and ESCRT in ER stress-induced lipid droplet microautophagy in budding yeast. Mol Biol Cell 2021; 32:br12. [PMID: 34668753 PMCID: PMC8694086 DOI: 10.1091/mbc.e21-04-0179] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Microlipophagy (µLP), degradation of lipid droplets (LDs) by microautophagy, occurs by autophagosome-independent direct uptake of LDs at lysosomes/vacuoles in response to nutrient limitations and ER stressors in Saccharomyces cerevisiae. In nutrient-limited yeast, liquid-ordered (Lo) microdomains, sterol-rich raftlike regions in vacuolar membranes, are sites of membrane invagination during LD uptake. The endosome sorting complex required for transport (ESCRT) is required for sterol transport during Lo formation under these conditions. However, ESCRT has been implicated in mediating membrane invagination during µLP induced by ER stressors or the diauxic shift from glycolysis- to respiration-driven growth. Here we report that ER stress induced by lipid imbalance and other stressors induces Lo microdomain formation. This process is ESCRT independent and dependent on Niemann-Pick type C sterol transfer proteins. Inhibition of ESCRT or Lo microdomain formation partially inhibits lipid imbalance-induced µLP, while inhibition of both blocks this µLP. Finally, although the ER stressors dithiothreitol or tunicamycin induce Lo microdomains, µLP in response to these stressors is ESCRT dependent and Lo microdomain independent. Our findings reveal that Lo microdomain formation is a yeast stress response, and stress-induced Lo microdomain formation occurs by stressor-specific mechanisms. Moreover, ESCRT and Lo microdomains play functionally distinct roles in LD uptake during stress-induced µLP.
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Affiliation(s)
- Pin-Chao Liao
- Department of Pathology and Cell Biology, Columbia University, New York, NY 10032
| | - Enrique J Garcia
- Department of Pathology and Cell Biology, Columbia University, New York, NY 10032
| | - Gary Tan
- Department of Pathology and Cell Biology, Columbia University, New York, NY 10032
| | - Catherine A Tsang
- Department of Pathology and Cell Biology, Columbia University, New York, NY 10032
| | - Liza A Pon
- Department of Pathology and Cell Biology, Columbia University, New York, NY 10032
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12
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Chen Z, Malia PC, Hatakeyama R, Nicastro R, Hu Z, Péli-Gulli MP, Gao J, Nishimura T, Eskes E, Stefan CJ, Winderickx J, Dengjel J, De Virgilio C, Ungermann C. TORC1 Determines Fab1 Lipid Kinase Function at Signaling Endosomes and Vacuoles. Curr Biol 2020; 31:297-309.e8. [PMID: 33157024 DOI: 10.1016/j.cub.2020.10.026] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2020] [Revised: 09/25/2020] [Accepted: 10/08/2020] [Indexed: 01/17/2023]
Abstract
Organelles of the endomembrane system maintain their identity and integrity during growth or stress conditions by homeostatic mechanisms that regulate membrane flux and biogenesis. At lysosomes and endosomes, the Fab1 lipid kinase complex and the nutrient-regulated target of rapamycin complex 1 (TORC1) control the integrity of the endolysosomal homeostasis and cellular metabolism. Both complexes are functionally connected as Fab1-dependent generation of PI(3,5)P2 supports TORC1 activity. Here, we identify Fab1 as a target of TORC1 on signaling endosomes, which are distinct from multivesicular bodies, and provide mechanistic insight into their crosstalk. Accordingly, TORC1 can phosphorylate Fab1 proximal to its PI3P-interacting FYVE domain, which causes Fab1 to shift to signaling endosomes, where it generates PI(3,5)P2. This, in turn, regulates (1) vacuole morphology, (2) recruitment of TORC1 and the TORC1-regulatory Rag GTPase-containing EGO complex to signaling endosomes, and (3) TORC1 activity. Thus, our study unravels a regulatory feedback loop between TORC1 and the Fab1 complex that controls signaling at endolysosomes.
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Affiliation(s)
- Zilei Chen
- Department of Biology/Chemistry, Biochemistry Section, University of Osnabrück, Barbarastrasse 13, 49076 Osnabrück, Germany
| | - Pedro Carpio Malia
- Department of Biology/Chemistry, Biochemistry Section, University of Osnabrück, Barbarastrasse 13, 49076 Osnabrück, Germany
| | - Riko Hatakeyama
- Department of Biology, University of Fribourg, Chemin du Musée, CH-1700 Fribourg, Switzerland
| | - Raffaele Nicastro
- Department of Biology, University of Fribourg, Chemin du Musée, CH-1700 Fribourg, Switzerland
| | - Zehan Hu
- Department of Biology, University of Fribourg, Chemin du Musée, CH-1700 Fribourg, Switzerland
| | - Marie-Pierre Péli-Gulli
- Department of Biology, University of Fribourg, Chemin du Musée, CH-1700 Fribourg, Switzerland
| | - Jieqiong Gao
- Department of Biology/Chemistry, Biochemistry Section, University of Osnabrück, Barbarastrasse 13, 49076 Osnabrück, Germany
| | - Taki Nishimura
- MRC Laboratory for Molecular Cell Biology, University College London, Gower Street, London WC1E 6BT, UK
| | - Elja Eskes
- Functional Biology, KU Leuven, Kasteelpark Arensberg 31, 3000 Leuven, Belgium
| | - Christopher J Stefan
- MRC Laboratory for Molecular Cell Biology, University College London, Gower Street, London WC1E 6BT, UK
| | - Joris Winderickx
- Functional Biology, KU Leuven, Kasteelpark Arensberg 31, 3000 Leuven, Belgium
| | - Jörn Dengjel
- Department of Biology, University of Fribourg, Chemin du Musée, CH-1700 Fribourg, Switzerland
| | - Claudio De Virgilio
- Department of Biology, University of Fribourg, Chemin du Musée, CH-1700 Fribourg, Switzerland.
| | - Christian Ungermann
- Department of Biology/Chemistry, Biochemistry Section, University of Osnabrück, Barbarastrasse 13, 49076 Osnabrück, Germany; Center of Cellular Nanoanalytics Osnabrück (CellNanOs), University of Osnabrück, Barbarastrasse 11, 49076 Osnabrück, Germany.
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13
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Hurst LR, Fratti RA. Lipid Rafts, Sphingolipids, and Ergosterol in Yeast Vacuole Fusion and Maturation. Front Cell Dev Biol 2020; 8:539. [PMID: 32719794 PMCID: PMC7349313 DOI: 10.3389/fcell.2020.00539] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2020] [Accepted: 06/09/2020] [Indexed: 01/15/2023] Open
Abstract
The Saccharomyces cerevisiae lysosome-like vacuole is a useful model for studying membrane fusion events and organelle maturation processes utilized by all eukaryotes. The vacuolar membrane is capable of forming micrometer and nanometer scale domains that can be visualized using microscopic techniques and segregate into regions with surprisingly distinct lipid and protein compositions. These lipid raft domains are liquid-ordered (L o ) like regions that are rich in sphingolipids, phospholipids with saturated acyl chains, and ergosterol. Recent studies have shown that these lipid rafts contain an enrichment of many different proteins that function in essential activities such as nutrient transport, organelle contact, membrane trafficking, and homotypic fusion, suggesting that they are biologically relevant regions within the vacuole membrane. Here, we discuss recent developments and the current understanding of sphingolipid and ergosterol function at the vacuole, the composition and function of lipid rafts at this organelle and how the distinct lipid and protein composition of these regions facilitates the biological processes outlined above.
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Affiliation(s)
- Logan R Hurst
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL, United States
| | - Rutilio A Fratti
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL, United States.,Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL, United States
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14
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Multi-model functionalization of disease-associated PTEN missense mutations identifies multiple molecular mechanisms underlying protein dysfunction. Nat Commun 2020; 11:2073. [PMID: 32350270 PMCID: PMC7190743 DOI: 10.1038/s41467-020-15943-0] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2019] [Accepted: 04/03/2020] [Indexed: 01/16/2023] Open
Abstract
Functional variomics provides the foundation for personalized medicine by linking genetic variation to disease expression, outcome and treatment, yet its utility is dependent on appropriate assays to evaluate mutation impact on protein function. To fully assess the effects of 106 missense and nonsense variants of PTEN associated with autism spectrum disorder, somatic cancer and PTEN hamartoma syndrome (PHTS), we take a deep phenotypic profiling approach using 18 assays in 5 model systems spanning diverse cellular environments ranging from molecular function to neuronal morphogenesis and behavior. Variants inducing instability occur across the protein, resulting in partial-to-complete loss-of-function (LoF), which is well correlated across models. However, assays are selectively sensitive to variants located in substrate binding and catalytic domains, which exhibit complete LoF or dominant negativity independent of effects on stability. Our results indicate that full characterization of variant impact requires assays sensitive to instability and a range of protein functions. Mutations in PTEN have been associated with various human disease, including autism spectrum disorder (ASD) and cancer. Here, the authors assess the function of 106 PTEN variants in yeast, invertebrate models and cell culture and report that PTEN variants generally decrease protein stability.
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15
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Sinha A, Israeli R, Cirigliano A, Gihaz S, Trabelcy B, Braus GH, Gerchman Y, Fishman A, Negri R, Rinaldi T, Pick E. The COP9 signalosome mediates the Spt23 regulated fatty acid desaturation and ergosterol biosynthesis. FASEB J 2020; 34:4870-4889. [PMID: 32077151 DOI: 10.1096/fj.201902487r] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2019] [Revised: 01/02/2020] [Accepted: 01/14/2020] [Indexed: 02/06/2023]
Abstract
The COP9 signalosome (CSN) is a conserved eukaryotic complex, essential for vitality in all multicellular organisms and critical for the turnover of key cellular proteins through catalytic and non-catalytic activities. Saccharomyces cerevisiae is a powerful model organism for studying fundamental aspects of the CSN complex, since it includes a conserved enzymatic core but lacks non-catalytic activities, probably explaining its non-essentiality for life. A previous transcriptomic analysis of an S. cerevisiae strain deleted in the CSN5/RRI1 gene, encoding to the CSN catalytic subunit, revealed a downregulation of genes involved in lipid metabolism. We now show that the S. cerevisiae CSN holocomplex is essential for cellular lipid homeostasis. Defects in CSN assembly or activity lead to decreased quantities of ergosterol and unsaturated fatty acids (UFA); vacuole defects; diminished lipid droplets (LDs) size; and to accumulation of endoplasmic reticulum (ER) stress. The molecular mechanism behind these findings depends on CSN involvement in upregulating mRNA expression of SPT23. Spt23 is a novel activator of lipid desaturation and ergosterol biosynthesis. Our data reveal for the first time a functional link between the CSN holocomplex and Spt23. Moreover, CSN-dependent upregulation of SPT23 transcription is necessary for the fine-tuning of lipid homeostasis and for cellular health.
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Affiliation(s)
- Abhishek Sinha
- Department of Biology and Environment, Faculty of Natural Sciences, University of Haifa, Oranim, Israel
| | - Ran Israeli
- Department of Biology and Environment, Faculty of Natural Sciences, University of Haifa, Oranim, Israel
| | - Angela Cirigliano
- Department of Biology and Biotechnology "Charles Darwin", Sapienza University of Rome, Rome, Italy
| | - Shalev Gihaz
- Department of Biotechnology and Food Engineering, Technion-Israel Institute of Technology, Haifa, Israel
| | - Beny Trabelcy
- Department of Biology and Environment, Faculty of Natural Sciences, University of Haifa, Oranim, Israel
| | - Gerhard H Braus
- Department of Molecular Microbiology and Genetics, Institute of Microbiology and Genetics, Goettingen Center for Molecular Biosciences (GZMB), University of Goettingen, Goettingen, Germany
| | - Yoram Gerchman
- Department of Biology and Environment, Faculty of Natural Sciences, University of Haifa, Oranim, Israel
| | - Ayelet Fishman
- Department of Biotechnology and Food Engineering, Technion-Israel Institute of Technology, Haifa, Israel
| | - Rodolfo Negri
- Department of Biology and Biotechnology "Charles Darwin", Sapienza University of Rome, Rome, Italy
| | - Teresa Rinaldi
- Department of Biology and Biotechnology "Charles Darwin", Sapienza University of Rome, Rome, Italy
| | - Elah Pick
- Department of Biology and Environment, Faculty of Natural Sciences, University of Haifa, Oranim, Israel
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16
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Ishii A, Kurokawa K, Hotta M, Yoshizaki S, Kurita M, Koyama A, Nakano A, Kimura Y. Role of Atg8 in the regulation of vacuolar membrane invagination. Sci Rep 2019; 9:14828. [PMID: 31616012 PMCID: PMC6794316 DOI: 10.1038/s41598-019-51254-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2019] [Accepted: 09/26/2019] [Indexed: 01/23/2023] Open
Abstract
Cellular heat stress can cause damage, and significant changes, to a variety of cellular structures. When exposed to chronically high temperatures, yeast cells invaginate vacuolar membranes. In this study, we found that the expression of Atg8, an essential autophagy factor, is induced after chronic heat stress. In addition, without Atg8, vacuolar invaginations are induced conspicuously, beginning earlier and invaginating vacuoles more frequently after heat stress. Our results indicate that Atg8's invagination-suppressing functions do not require Atg8 lipidation, in contrast with autophagy, which requires Atg8 lipidation. Genetic analyses of vps24 and vps23 further suggest that full ESCRT machinery is necessary to form vacuolar invaginations irrespective of Atg8. In contrast, through a combined mutation with the vacuole BAR domain protein Ivy1, vacuoles show constitutively enhanced invaginated structures. Finally, we found that the atg8Δivy1Δ mutant is sensitive against agents targeting functions of the vacuole and/or plasma membrane (cell wall). Collectively, our findings revealed that Atg8 maintains vacuolar membrane homeostasis in an autophagy-independent function by coordinating with other cellular factors.
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Affiliation(s)
- Ayane Ishii
- Graduate School of Integrated Science and Technology, Shizuoka University, Shizuoka, 422-8529, Japan
| | - Kazuo Kurokawa
- Live Cell Super-Resolution Imaging Research Team, RIKEN Center for Advanced Photonics, Wako, Saitama, 351-0198, Japan
| | - Miyuu Hotta
- Department of Agriculture, Shizuoka University, Shizuoka, 422-8529, Japan
| | - Suzuka Yoshizaki
- Department of Agriculture, Shizuoka University, Shizuoka, 422-8529, Japan
| | - Maki Kurita
- Graduate School of Integrated Science and Technology, Shizuoka University, Shizuoka, 422-8529, Japan
| | - Aya Koyama
- Department of Agriculture, Shizuoka University, Shizuoka, 422-8529, Japan
| | - Akihiko Nakano
- Live Cell Super-Resolution Imaging Research Team, RIKEN Center for Advanced Photonics, Wako, Saitama, 351-0198, Japan
| | - Yoko Kimura
- Graduate School of Integrated Science and Technology, Shizuoka University, Shizuoka, 422-8529, Japan. .,Department of Agriculture, Shizuoka University, Shizuoka, 422-8529, Japan.
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17
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Li L, Baxter SS, Zhao P, Gu N, Zhan X. Differential interactions of missing in metastasis and insulin receptor tyrosine kinase substrate with RAB proteins in the endocytosis of CXCR4. J Biol Chem 2019; 294:6494-6505. [PMID: 30808710 DOI: 10.1074/jbc.ra118.006071] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2018] [Revised: 02/15/2019] [Indexed: 12/26/2022] Open
Abstract
Missing in metastasis (MIM), an inverse Bin-Amphiphysin-Rvs (I-BAR) domain protein, promotes endocytosis of C-X-C chemokine receptor 4 (CXCR4) in mammalian cells. In response to the CXCR4 ligand stromal cell-derived factor 1 (SDF-1 or CXCL12), MIM associates with RAS-related GTP-binding protein 7 (RAB7) 30 min after stimulation. However, RAB7's role in MIM function remains undefined. Here we show that RNAi-mediated suppression of RAB7 expression in human HeLa cells has little effect on the binding of MIM to RAB5 and on the recruitment of CXCR4 to early endosomes but effectively abolishes MIM-mediated CXCR4 degradation, chemotactic response, and sorting into late endosomes and lysosomes. To determine whether I-BAR domain proteins interact with RAB7, we examined cells expressing insulin receptor tyrosine kinase substrate (IRTKS), an I-BAR domain protein bearing an Src homology 3 (SH3) domain. We observed that both MIM and IRTKS interact with RAB5 at an early response to SDF-1 and that IRTKS binds poorly to RAB7 but strongly to RAB11 at a later time point. Moreover, IRTKS overexpression reduced CXCR4 internalization and enhanced the chemotactic response to SDF-1. Interestingly, deletion of the SH3 domain in IRTKS abolished the IRTKS-RAB11 interaction and promoted CXCR4 degradation. Furthermore, the SH3 domain was required for selective targeting of MIM-IRTKS fusion proteins by both RAB7 and RAB11. Hence, to the best of our knowledge, our results provide first evidence that the SH3 domain is critical in the regulation of specific endocytic pathways by I-BAR domain proteins.
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Affiliation(s)
- Lushen Li
- From the Center for Vascular and Inflammatory Diseases
| | | | - Peng Zhao
- the State Key Laboratory of Bioelectronics, Jiangsu Key Laboratory for Biomaterials and Devices, School of Biological Science and Medical Engineering, Southeast University, Nanjing 210096, China
| | - Ning Gu
- the State Key Laboratory of Bioelectronics, Jiangsu Key Laboratory for Biomaterials and Devices, School of Biological Science and Medical Engineering, Southeast University, Nanjing 210096, China
| | - Xi Zhan
- From the Center for Vascular and Inflammatory Diseases, .,Department of Pathology, and.,University of Maryland Marlene and Stewart Greenebaum Comprehensive Cancer Center, University of Maryland School of Medicine, Baltimore, Maryland 21201 and
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18
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Stroupe C. This Is the End: Regulation of Rab7 Nucleotide Binding in Endolysosomal Trafficking and Autophagy. Front Cell Dev Biol 2018; 6:129. [PMID: 30333976 PMCID: PMC6176412 DOI: 10.3389/fcell.2018.00129] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2018] [Accepted: 09/14/2018] [Indexed: 01/07/2023] Open
Abstract
Rab7 – or in yeast, Ypt7p – governs membrane trafficking in the late endocytic and autophagic pathways. Rab7 also regulates mitochondrion-lysosome contacts, the sites of mitochondrial fission. Like all Rab GTPases, Rab7 cycles between an “active” GTP-bound form that binds downstream effectors – e.g., the HOPS and retromer complexes and the dynactin-binding Rab-interacting lysosomal protein (RILP) – and an “inactive” GDP-bound form that cannot bind effectors. Accessory proteins regulate the nucleotide binding state of Rab7: guanine nucleotide exchange factors (GEFs) stimulate exchange of bound GDP for GTP, resulting in Rab7 activation, whereas GTPase activating proteins (GAPs) boost Rab7’s GTP hydrolysis activity, thereby inactivating Rab7. This review will discuss the GEF and GAPs that control Rab7 nucleotide binding, and thus regulate Rab7’s activity in endolysosomal trafficking and autophagy. It will also consider how bacterial pathogens manipulate Rab7 nucleotide binding to support intracellular invasion and immune evasion.
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Affiliation(s)
- Christopher Stroupe
- Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville, VA, United States
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19
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Lipids and lipid domains of the yeast vacuole. Biochem Soc Trans 2018; 46:1047-1054. [PMID: 30242116 DOI: 10.1042/bst20180120] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2018] [Revised: 07/30/2018] [Accepted: 08/01/2018] [Indexed: 11/17/2022]
Abstract
The membrane raft has been a focus of intensive research for the past two decades. Liquid-ordered domains form in artificial liposomes containing sterol and saturated lipids, but their presence in living cell membranes has been controversial. The yeast vacuole is exceptional in that micron-sized raft-like domains form in the stationary phase and under several other conditions. The sterol content of the vacuole in the log phase is much lower than that of liposomes showing liquid-ordered domains, suggesting that sterols may need to be supplied to the vacuole for the raft-like domain formation. We will discuss how lipids and lipid domains are organized in the vacuolar membrane and examine whether evidence is strong enough to conclude that the observed micron-sized domains are rafts.
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20
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Varlakhanova NV, Tornabene BA, Ford MGJ. Ivy1 is a negative regulator of Gtr-dependent TORC1 activation. J Cell Sci 2018; 131:jcs.218305. [PMID: 30097557 DOI: 10.1242/jcs.218305] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2018] [Accepted: 07/27/2018] [Indexed: 11/20/2022] Open
Abstract
The highly conserved TORC1 complex controls cell growth in response to nutrients, especially amino acids. The EGO complex activates TORC1 in response to glutamine and leucine. Here, we demonstrate that the I-BAR domain-containing protein Ivy1 colocalizes with Gtr1 and Gtr2, a heterodimer of small GTPases that are part of the EGO complex. Ivy1 is a negative regulator of Gtr-induced TORC1 activation, and is contained within puncta associated with the vacuolar membrane in cells grown in nutrient-rich medium or after brief nitrogen starvation. Addition of glutamine to nitrogen-starved cells leads to dissipation of Ivy1 puncta and redistribution of Ivy1 throughout the vacuolar membrane. Continued stimulation with glutamine results in concentration of Ivy1 within vacuolar membrane invaginations and its spatial separation from the EGO complex components Gtr1 and Gtr2. Disruption of vacuolar membrane invagination is associated with persistent mislocalization of Ivy1 across the vacuolar membrane and inhibition of TORC1 activity. Together, our findings illustrate a novel negative-feedback pathway that is exerted by Ivy1 on Gtr-dependent TORC1 signaling and provide insight into a potential molecular mechanism underlying TORC1 activation by vacuolar membrane remodeling.
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Affiliation(s)
- Natalia V Varlakhanova
- Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, United States of America
| | - Bryan A Tornabene
- Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, United States of America
| | - Marijn G J Ford
- Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, United States of America
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21
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Langemeyer L, Fröhlich F, Ungermann C. Rab GTPase Function in Endosome and Lysosome Biogenesis. Trends Cell Biol 2018; 28:957-970. [PMID: 30025982 DOI: 10.1016/j.tcb.2018.06.007] [Citation(s) in RCA: 266] [Impact Index Per Article: 38.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2018] [Revised: 06/15/2018] [Accepted: 06/25/2018] [Indexed: 10/28/2022]
Abstract
Eukaryotic cells maintain a highly organized endolysosomal system. This system regulates the protein and lipid content of the plasma membrane, it participates in the intracellular quality control machinery and is needed for the efficient removal of damaged organelles. This complex network comprises an endosomal membrane system that feeds into the lysosomes, yet also allows recycling of membrane proteins, and probably lipids. Moreover, lysosomal degradation provides the cell with macromolecules for further growth. In this review, we focus primarily on the role of the small Rab GTPases Rab5 and Rab7 as organelle markers and interactors of multiple effectors on endosomes and lysosomes and highlight their role in membrane dynamics, particularly fusion along the endolysosomal pathway.
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Affiliation(s)
- Lars Langemeyer
- Department of Biology/Chemistry, Biochemistry Section, University of Osnabrück, Barbarastrasse 13, 49076 Osnabrück, Germany
| | - Florian Fröhlich
- Department of Biology/Chemistry, Molecular Membrane Biology Group, University of Osnabrück, Barbarastrasse 13, 49076 Osnabrück, Germany; Center of Cellular Nanoanalytics of the University of Osnabrück (CellNanOs), Barbarastrasse 11, 49076 Osnabrück, Germany
| | - Christian Ungermann
- Department of Biology/Chemistry, Biochemistry Section, University of Osnabrück, Barbarastrasse 13, 49076 Osnabrück, Germany; Department of Biology/Chemistry, Molecular Membrane Biology Group, University of Osnabrück, Barbarastrasse 13, 49076 Osnabrück, Germany; Center of Cellular Nanoanalytics of the University of Osnabrück (CellNanOs), Barbarastrasse 11, 49076 Osnabrück, Germany.
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22
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Abstract
The lysosome-like vacuole is the main organelle to degrade membrane proteins and organelles and, thus, provides amino acids, but also ions to the cytosol for cellular survival. Maintenance of vacuole membrane integrity is thus important for cellular adaptations. The vacuole contains several protein complexes on its surface to maintain the vacuole functional, and one such complex is a lipid kinase named Fab1 (of PIKfyve in human cells). Fab1 is part of a protein complex that produces a phosphorylated lipid, PI-3,5-P2. Other proteins bind PI-3,5-P2 and can fragment the vacuole to balance volume vs. membrane during stress. We now identify Ivy1 as a protein that binds Fab1 and controls its activity. Lysosomes have an important role in cellular protein and organelle quality control, metabolism, and signaling. On the surface of lysosomes, the PIKfyve/Fab1 complex generates phosphatidylinositol 3,5-bisphosphate, PI-3,5-P2, which is critical for lysosomal membrane homeostasis during acute osmotic stress and for lysosomal signaling. Here, we identify the inverted BAR protein Ivy1 as an inhibitor of the Fab1 complex with a direct influence on PI-3,5-P2 levels and vacuole homeostasis. Ivy1 requires Ypt7 binding for its function, binds PI-3,5-P2, and interacts with the Fab1 kinase. Colocalization of Ivy1 and Fab1 is lost during osmotic stress. In agreement with Ivy1’s role as a Fab1 regulator, its overexpression blocks Fab1 activity during osmotic shock and vacuole fragmentation. Conversely, loss of Ivy1, or lateral relocalization of Ivy1 on vacuoles away from Fab1, results in vacuole fragmentation and poor growth. Our data suggest that Ivy1 modulates Fab1-mediated PI-3,5-P2 synthesis during membrane stress and may allow adjustment of the vacuole membrane environment.
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23
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Tekirdag K, Cuervo AM. Chaperone-mediated autophagy and endosomal microautophagy: Joint by a chaperone. J Biol Chem 2018; 293:5414-5424. [PMID: 29247007 PMCID: PMC5900761 DOI: 10.1074/jbc.r117.818237] [Citation(s) in RCA: 256] [Impact Index Per Article: 36.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
A variety of mechanisms deliver cytosolic materials to the lysosomal compartment for degradation through autophagy. Here, we focus on two autophagic pathways, the chaperone-mediated autophagy and the endosomal microautophagy that rely on the cytosolic chaperone hsc70 for substrate targeting. Although hsc70 participates in the triage of proteins for degradation by different proteolytic systems, the common characteristic shared by these two forms of autophagy is that hsc70 binds directly to a specific five-amino acid motif in the cargo protein for its autophagic targeting. We summarize the current understanding of the molecular machineries behind each of these types of autophagy.
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Affiliation(s)
- Kumsal Tekirdag
- From the Department of Developmental and Molecular Biology, Institute for Aging Studies, Albert Einstein College of Medicine, Bronx, New York 10461
| | - Ana Maria Cuervo
- From the Department of Developmental and Molecular Biology, Institute for Aging Studies, Albert Einstein College of Medicine, Bronx, New York 10461
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24
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Accelerated invagination of vacuoles as a stress response in chronically heat-stressed yeasts. Sci Rep 2018; 8:2644. [PMID: 29422608 PMCID: PMC5805771 DOI: 10.1038/s41598-018-20781-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2017] [Accepted: 01/24/2018] [Indexed: 01/01/2023] Open
Abstract
When exposed to sublethal high temperatures, budding yeast cells can survive for a period of time; however, a sufficient amount of ubiquitin is necessary for this survival. To understand the nature of the stress, we examined the morphological changes in yeast cells, focusing on the vacuoles. Changes in vacuolar morphology were notable, and ruffled vacuolar membranes, accelerated invaginations of vacuolar membranes, and vesicle-like formations were observed. These changes occurred in the absence of Atg1, Atg9 or Ivy1 but appeared to require endosomal sorting proteins, such as Vps23, Vps24 or Pep12. Furthermore, the serial sections of the vacuoles analysed using an electron microscopic analysis revealed that spherical invaginated structures were linked together in a vacuole. Because degradation of cell surface proteins is induced from heat stress, fusion of endosomal and vacuolar membranes might occur frequently in heat-stressed cells, and yeast cells might be able to cope with a rapid increase in vacuolar surface area by such invaginations.
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Murley A, Yamada J, Niles BJ, Toulmay A, Prinz WA, Powers T, Nunnari J. Sterol transporters at membrane contact sites regulate TORC1 and TORC2 signaling. J Cell Biol 2017; 216:2679-2689. [PMID: 28774891 PMCID: PMC5584152 DOI: 10.1083/jcb.201610032] [Citation(s) in RCA: 57] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2016] [Revised: 03/20/2017] [Accepted: 06/26/2017] [Indexed: 12/15/2022] Open
Abstract
Membrane contact sites (MCSs) function to facilitate the formation of membrane domains composed of specialized lipids, proteins, and nucleic acids. In cells, membrane domains regulate membrane dynamics and biochemical and signaling pathways. We and others identified a highly conserved family of sterol transport proteins (Ltc/Lam) localized at diverse MCSs. In this study, we describe data indicating that the yeast family members Ltc1 and Ltc3/4 function at the vacuole and plasma membrane, respectively, to create membrane domains that partition upstream regulators of the TORC1 and TORC2 signaling pathways to coordinate cellular stress responses with sterol homeostasis.
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Affiliation(s)
- Andrew Murley
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA
| | - Justin Yamada
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA
| | - Bradley J Niles
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA
| | - Alexandre Toulmay
- National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD
| | - William A Prinz
- National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD
| | - Ted Powers
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA
| | - Jodi Nunnari
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA
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26
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Mitochondria-organelle contact sites: the plot thickens. Biochem Soc Trans 2017; 45:477-488. [PMID: 28408488 DOI: 10.1042/bst20160130] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2016] [Revised: 02/07/2017] [Accepted: 02/13/2017] [Indexed: 01/30/2023]
Abstract
Membrane contact sites (MCSs) are areas of close apposition between the membranes of two different organelles that enable non-vesicular transfer of ions and lipids. Recent studies reveal that mitochondria maintain contact sites with organelles other than the endoplasmic reticulum such as the vacuole, plasma membrane and peroxisomes. This review focuses on novel findings achieved mainly in yeast regarding tethers, function and regulation of mitochondria-organelle contact sites. The emerging network of MCSs linking virtually all cellular organelles is highly dynamic and integrated with cellular metabolism.
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Li L, Baxter SS, Gu N, Ji M, Zhan X. Missing-in-metastasis protein downregulates CXCR4 by promoting ubiquitylation and interaction with small Rab GTPases. J Cell Sci 2017; 130:1475-1485. [PMID: 28264927 DOI: 10.1242/jcs.198937] [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: 10/25/2016] [Accepted: 02/27/2017] [Indexed: 01/09/2023] Open
Abstract
Surface expression of chemokine receptor CXCR4 is downregulated by missing-in-metastasis protein (MIM; also known as MTSS1), a member of the inverse BAR (I-BAR)-domain protein family that recognizes and generates membranes with negative curvature. Yet, the mechanism for the regulation is unknown. Here, we show that MIM forms a complex with CXCR4 by binding to E3 ubiquitin ligase AIP4 (also known as ITCH) in response to stromal cell-derived factor 1 (SDF-1; also known as CXCL12). Overexpression of MIM promoted CXCR4 ubiquitylation, inhibited cellular response to SDF-1, caused accumulation and aggregation of multivesicular bodies (MVBs) in the cytoplasm, and promoted CXCR4 sorting into MVBs in a manner depending on binding to AIP4. In response to SDF-1, MIM also bound transiently to the small GTPase Rab5 at 5 min and to Rab7 at 30 min. Binding to Rab7 requires an N-terminal coiled-coil motif, deletion of which abolished MIM-mediated MVB formation and CXCR4 internalization. Our results unveil a previously unknown property of MIM that establishes the linkage of protein ubiquitylation with Rab-guided trafficking of CXCR4 in endocytic vesicles.
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Affiliation(s)
- Lushen Li
- School of Biological Science and Medical Engineering, Southeast University, Nanjing 210096, China.,Center for Vascular and Inflammatory Diseases, University of Maryland School of Medicine, Baltimore, MD 21201, USA
| | - Shaneen S Baxter
- Center for Vascular and Inflammatory Diseases, University of Maryland School of Medicine, Baltimore, MD 21201, USA
| | - Ning Gu
- School of Biological Science and Medical Engineering, Southeast University, Nanjing 210096, China
| | - Min Ji
- School of Biological Science and Medical Engineering, Southeast University, Nanjing 210096, China
| | - Xi Zhan
- Center for Vascular and Inflammatory Diseases, University of Maryland School of Medicine, Baltimore, MD 21201, USA .,Department of Pathology, University of Maryland School of Medicine, Baltimore, MD 21201, USA.,University of Maryland Marlene and Stewart Greenebaum Comprehensive Cancer Center, Baltimore, MD 21201, USA
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Yang S, Rosenwald A. A High Copy Suppressor Screen for Autophagy Defects in Saccharomyces arl1Δ and ypt6Δ Strains. G3 (BETHESDA, MD.) 2017; 7:333-341. [PMID: 27974437 PMCID: PMC5295583 DOI: 10.1534/g3.116.035998] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/27/2016] [Accepted: 11/17/2016] [Indexed: 11/26/2022]
Abstract
In Saccharomyces cerevisiae, Arl1 and Ypt6, two small GTP-binding proteins that regulate membrane traffic in the secretory and endocytic pathways, are also necessary for autophagy. To gain information about potential partners of Arl1 and Ypt6 specifically in autophagy, we carried out a high copy number suppressor screen to identify genes that when overexpressed suppress the rapamycin sensitivity phenotype of arl1Δ and ypt6Δ strains at 37°. From the screen results, we selected COG4, SNX4, TAX4, IVY1, PEP3, SLT2, and ATG5, either membrane traffic or autophagy regulators, to further test whether they can suppress the specific autophagy defects of arl1Δ and ypt6Δ strains. As a result, we identified COG4, SNX4, and TAX4 to be specific suppressors for the arl1Δ strain, and IVY1 and ATG5 for the ypt6Δ strain. Through this screen, we were able to confirm several membrane traffic and autophagy regulators that have novel relationships with Arl1 and Ypt6 during autophagy.
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Affiliation(s)
- Shu Yang
- Department of Biology, Georgetown University, Washington, DC 20057
| | - Anne Rosenwald
- Department of Biology, Georgetown University, Washington, DC 20057
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29
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Purushothaman LK, Arlt H, Kuhlee A, Raunser S, Ungermann C. Retromer-driven membrane tubulation separates endosomal recycling from Rab7/Ypt7-dependent fusion. Mol Biol Cell 2017; 28:783-791. [PMID: 28100638 PMCID: PMC5349785 DOI: 10.1091/mbc.e16-08-0582] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2016] [Revised: 12/21/2016] [Accepted: 01/10/2017] [Indexed: 12/31/2022] Open
Abstract
How does a Rab function in both recycling and fusion? An endosomal subcomplex of the SNX-BAR retromer can bind to Ypt7 and compete with the HOPS complex. Assembly of the full retromer then results in displacement of Ypt7. These data explain how domain formation and Ypt7 participation can be coordinated. Endosomes are the major protein-sorting hubs of the endocytic pathway. They sort proteins destined for degradation into internal vesicles while in parallel recycling receptors via tubular carriers back to the Golgi. Tubule formation depends on the Rab7/Ypt7-interacting retromer complex, consisting of the sorting nexin dimer (SNX-BAR) and the trimeric cargo selection complex (CSC). Fusion of mature endosomes with the lysosome-like vacuole also requires Rab7/Ypt7. Here we solve a major problem in understanding this dual function of endosomal Rab7/Ypt7, using a fully reconstituted system, including purified, full-length yeast SNX-BAR and CSC, whose overall structure we present. We reveal that the membrane-active SNX-BAR complex displaces Ypt7 from cargo-bound CSC during formation of recycling tubules. This explains how a single Rab can coordinate recycling and fusion on endosomes.
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Affiliation(s)
- Latha Kallur Purushothaman
- Department of Biology/Chemistry, Biochemistry Section, University of Osnabrück, 49076 Osnabrück, Germany
| | - Henning Arlt
- Department of Biology/Chemistry, Biochemistry Section, University of Osnabrück, 49076 Osnabrück, Germany
| | - Anne Kuhlee
- Department of Structural Biochemistry, Max-Planck Institute of Molecular Physiology, 44227 Dortmund, Germany
| | - Stefan Raunser
- Department of Structural Biochemistry, Max-Planck Institute of Molecular Physiology, 44227 Dortmund, Germany
| | - Christian Ungermann
- Department of Biology/Chemistry, Biochemistry Section, University of Osnabrück, 49076 Osnabrück, Germany
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Abstract
Macroautophagy, a highly conserved process in eukaryotic cells, is initiated in response to stress, especially nutrient starvation. Macroautophagy helps cells survive by engulfing proteins and organelles into an unusual double-membraned structure called the autophagosome, which then fuses with the lysosome. Upon degradation of the engulfed contents, the building blocks are recycled for synthesis of new macromolecules. Recent work has demonstrated that construction of the autophagosome requires a variety of small GTPases in variations of their normal roles in membrane traffic. In this Commentary, we review our own recent findings with respect to 2 different GTPases, Arl1, a member of the Arf/Arl/Sar family, and Ypt6, a member of the Rab family, in the yeast S. cerevisiae in light of other information from the literature and discuss future directions for further discerning the roles of small GTPases in autophagy.
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Affiliation(s)
- Shu Yang
- a Department of Biology , Georgetown University , Washington, DC , USA
| | - Anne Rosenwald
- a Department of Biology , Georgetown University , Washington, DC , USA
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Kikuma T, Tadokoro T, Maruyama JI, Kitamoto K. AoAtg26, a putative sterol glucosyltransferase, is required for autophagic degradation of peroxisomes, mitochondria, and nuclei in the filamentous fungus Aspergillus oryzae. Biosci Biotechnol Biochem 2016; 81:384-395. [PMID: 27696999 DOI: 10.1080/09168451.2016.1240603] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Autophagy is a conserved process in eukaryotic cells for degradation of cellular proteins and organelles. In filamentous fungi, autophagic degradation of organelles such as peroxisomes, mitochondria, and nuclei occurs in basal cells after the prolonged culture, but its mechanism is not well understood. Here, we functionally analyzed the filamentous fungus Aspergillus oryzae AoAtg26, an ortholog of the sterol glucosyltransferase PpAtg26 involved in pexophagy in the yeast Pichia pastoris. Deletion of Aoatg26 caused a severe decrease in conidiation and aerial hyphae formation, which is typically observed in the autophagy-deficient A. oryzae strains. In addition, cup-shaped AoAtg8-positive membrane structures were accumulated in the Aoatg26 deletion strain, indicating that autophagic process is impaired. Indeed, the Aoatg26 deletion strain was defective in the degradation of peroxisomes, mitochondria, and nuclei. Taken together, AoAtg26 plays an important role for autophagic degradation of organelles in A. oryzae, which may physiologically contribute to the differentiation in filamentous fungi.
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Affiliation(s)
- Takashi Kikuma
- a Department of Biotechnology , The University of Tokyo , Tokyo , Japan
| | - Takayuki Tadokoro
- a Department of Biotechnology , The University of Tokyo , Tokyo , Japan
| | - Jun-Ichi Maruyama
- a Department of Biotechnology , The University of Tokyo , Tokyo , Japan
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32
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Lystad AH, Simonsen A. Phosphoinositide-binding proteins in autophagy. FEBS Lett 2016; 590:2454-68. [PMID: 27391591 DOI: 10.1002/1873-3468.12286] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2016] [Revised: 06/28/2016] [Accepted: 07/05/2016] [Indexed: 12/21/2022]
Abstract
Phosphoinositides represent a very small fraction of membrane phospholipids, having fast turnover rates and unique subcellular distributions, which make them perfect for initiating local temporal effects. Seven different phosphoinositide species are generated through reversible phosphorylation of the inositol ring of phosphatidylinositol (PtdIns). The negative charge generated by the phosphates provides specificity for interaction with various protein domains that commonly contain a cluster of basic residues. Examples of domains that bind phosphoinositides include PH domains, WD40 repeats, PX domains, and FYVE domains. Such domains often display specificity toward a certain species or subset of phosphoinositides. Here we will review the current literature of different phosphoinositide-binding proteins involved in autophagy.
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Affiliation(s)
- Alf Håkon Lystad
- Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, Norway
| | - Anne Simonsen
- Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, Norway
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33
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Abstract
The target of rapamycin complex 1 (TORC1) plays a central role in controlling eukaryotic cell growth by fine-tuning anabolic and catabolic processes to the nutritional status of organisms and individual cells. Amino acids represent essential and primordial signals that modulate TORC1 activity through the conserved Rag family GTPases. These assemble, as part of larger lysosomal/vacuolar membrane-associated complexes, into heterodimeric sub-complexes, which typically comprise two paralogous Rag GTPases of opposite GTP-/GDP-loading status. The TORC1-stimulating/inhibiting states of these heterodimers are controlled by various guanine nucleotide exchange factor (GEF) and GTPase-activating protein (GAP) complexes, which are remarkably conserved in various eukaryotic model systems. Among the latter, the budding yeast Saccharomyces cerevisiae has been instrumental for the elucidation of basic aspects of Rag GTPase regulation and function. Here, we discuss the current state of the respective research, focusing on the major unsolved issues regarding the architecture, regulation, and function of the Rag GTPase containing complexes in yeast. Decoding these mysteries will undoubtedly further shape our understanding of the conserved and divergent principles of nutrient signaling in eukaryotes.
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Affiliation(s)
- Riko Hatakeyama
- a Department of Biology , University of Fribourg , Fribourg , Switzerland
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34
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Vacuole membrane contact sites and domains: emerging hubs to coordinate organelle function with cellular metabolism. Biochem Soc Trans 2016; 44:528-33. [DOI: 10.1042/bst20150277] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2016] [Indexed: 02/07/2023]
Abstract
Eukaryotic cells rely on a set of membrane-enclosed organelles to perform highly efficient reactions in an optimized environment. Trafficking of molecules via vesicular carriers and membrane contact sites (MCS) allow the coordination between these compartments, though the precise mechanisms are still enigmatic. Among the cellular organelles, the lysosome/vacuole stands out as a central hub, where multiple pathways merge. Importantly, the delivered material is degraded and the monomers are recycled for further usage, which explains its wide variety of roles in controlling cellular metabolism. We will highlight recent advances in the field by focusing on the yeast vacuole as a model system to understand lysosomal function in general.
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35
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Koch D, Rai A, Ali I, Bleimling N, Friese T, Brockmeyer A, Janning P, Goud B, Itzen A, Müller MP, Goody RS. A pull-down procedure for the identification of unknown GEFs for small GTPases. Small GTPases 2016; 7:93-106. [PMID: 26918858 PMCID: PMC4905258 DOI: 10.1080/21541248.2016.1156803] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Members of the family of small GTPases regulate a variety of important cellular functions. In order to accomplish this, tight temporal and spatial regulation is absolutely necessary. The two most important factors for this regulation are GTPase activating proteins (GAPs) and guanine nucleotide exchange factors (GEFs), the latter being responsible for the activation of the GTPase downstream pathways at the correct location and time. Although a large number of exchange factors have been identified, it is likely that a similarly large number remains unidentified. We have therefore developed a procedure to specifically enrich GEF proteins from biological samples making use of the high affinity binding of GEFs to nucleotide-free GTPases. In order to verify the results of these pull-down experiments, we have additionally developed two simple validation procedures: An in vitro transcription/translation system coupled with a GEF activity assay and a yeast two-hybrid screen for detection of GEFs. Although the procedures were established and tested using the Rab protein Sec4, the similar basic principle of action of all nucleotide exchange factors will allow the method to be used for identification of unknown GEFs of small GTPases in general.
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Affiliation(s)
- Daniel Koch
- a Department of Structural Biochemistry , Max Planck Institute of Molecular Physiology , Dortmund , Germany
| | - Amrita Rai
- a Department of Structural Biochemistry , Max Planck Institute of Molecular Physiology , Dortmund , Germany
| | - Imtiaz Ali
- a Department of Structural Biochemistry , Max Planck Institute of Molecular Physiology , Dortmund , Germany
| | - Nathalie Bleimling
- a Department of Structural Biochemistry , Max Planck Institute of Molecular Physiology , Dortmund , Germany
| | - Timon Friese
- a Department of Structural Biochemistry , Max Planck Institute of Molecular Physiology , Dortmund , Germany
| | - Andreas Brockmeyer
- b Department of Chemical Biology , Max Planck Institute of Molecular Physiology , Dortmund , Germany
| | - Petra Janning
- b Department of Chemical Biology , Max Planck Institute of Molecular Physiology , Dortmund , Germany
| | - Bruno Goud
- c Institut Curie, PSL Research University, CNRS UMR 144 , Paris , France
| | - Aymelt Itzen
- d Center for Integrated Protein Science Munich (CIPSM), Department of Chemistry, Technische Universität München , Garching , Germany
| | - Matthias P Müller
- a Department of Structural Biochemistry , Max Planck Institute of Molecular Physiology , Dortmund , Germany
| | - Roger S Goody
- a Department of Structural Biochemistry , Max Planck Institute of Molecular Physiology , Dortmund , Germany
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36
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Suetsugu S. Higher-order assemblies of BAR domain proteins for shaping membranes. Microscopy (Oxf) 2016; 65:201-10. [DOI: 10.1093/jmicro/dfw002] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2015] [Accepted: 01/09/2016] [Indexed: 02/07/2023] Open
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Itoh Y, Kida K, Hanawa-Suetsugu K, Suetsugu S. Yeast Ivy1p Is a Putative I-BAR-domain Protein with pH-sensitive Filament Forming Ability in vitro. Cell Struct Funct 2015; 41:1-11. [PMID: 26657738 DOI: 10.1247/csf.15014] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Bin-Amphiphysin-Rvs161/167 (BAR) domains mold lipid bilayer membranes into tubules, by forming a spiral polymer on the membrane. Most BAR domains are thought to be involved in forming membrane invaginations through their concave membrane binding surfaces, whereas some members have convex membrane binding surfaces, and thereby mold membranes into protrusions. The BAR domains with a convex surface form a subtype called the inverse BAR (I-BAR) domain or IRSp53-MIM-homology domain (IMD). Although the mammalian I-BAR domains have been studied, those from other organisms remain elusive. Here, we found putative I-BAR domains in Fungi and animal-like unicellular organisms. The fungal protein containing the putative I-BAR-domain is known as Ivy1p in yeast, and is reportedly localized in the vacuole. The phylogenetic analysis of the I-BAR domains revealed that the fungal I-BAR-domain containing proteins comprise a distinct group from those containing IRSp53 or MIM. Importantly, Ivy1p formed a polymer with a diameter of approximately 20 nm in vitro, without a lipid membrane. The filaments were formed at neutral pH, but disassembled when pH was reverted to basic. Moreover, Ivy1p and the I-BAR domain expressed in mammalian HeLa cells was localized at a vacuole-like structure as filaments as revealed by super-resolved microscopy. These data indicate the pH-sensitive polymer forming ability and the functional conservation of Ivy1p in eukaryotic cells.
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Affiliation(s)
- Yuzuru Itoh
- Laboratory of Membrane and Cytoskeleton Dynamics, Institute of Molecular and Cellular Biosciences, The University of Tokyo
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38
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Kira S, Kumano Y, Ukai H, Takeda E, Matsuura A, Noda T. Dynamic relocation of the TORC1-Gtr1/2-Ego1/2/3 complex is regulated by Gtr1 and Gtr2. Mol Biol Cell 2015; 27:382-96. [PMID: 26609069 PMCID: PMC4713139 DOI: 10.1091/mbc.e15-07-0470] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2015] [Accepted: 11/19/2015] [Indexed: 11/29/2022] Open
Abstract
Ego2 is characterized as a new subunit of Ego protein complex (the yeast Ragulaor counterpart) that is a scaffold of Gtr (the yeast Rag counterpart) and TORC1. Gtr1 and Gtr2 regulate the dynamic translocation of the Ego/Gtr/TORC1 supercomplex between the vacuolar limiting membrane and perivacuolar foci. This localization shift is closely associated with the TORC1 activity level. TORC1 regulates cellular growth, metabolism, and autophagy by integrating various signals, including nutrient availability, through the small GTPases RagA/B/C/D in mammals and Gtr1/2 in budding yeast. Rag/Gtr is anchored to the lysosomal/vacuolar membrane by the scaffold protein complex Ragulator/Ego. Here we show that Ego consists of Ego1 and Ego3, and novel subunit Ego2. The ∆ego2 mutant exhibited only partial defects both in Gtr1-dependent TORC1 activation and Gtr1 localization on the vacuole. Ego1/2/3, Gtr1/2, and Tor1/Tco89 were colocalized on the vacuole and associated puncta. When Gtr1 was in its GTP-bound form and TORC1 was active, these proteins were preferentially localized on the vacuolar membrane, whereas when Gtr1 was in its GDP-bound form, they were mostly localized on the puncta. The localization of TORC1 to puncta was further facilitated by direct binding to Gtr2, which is involved in suppression of TORC1 activity. Thus regulation of TORC1 activity through Gtr1/Gtr2 is tightly coupled to the dynamic relocation of these proteins.
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Affiliation(s)
- Shintaro Kira
- Center for Frontier Oral Science, Graduate School of Dentistry, Osaka University, Osaka 565-0871, Japan
| | - Yuri Kumano
- Graduate School of Frontier BioSciences, Osaka University, Osaka 565-0871, Japan
| | - Hirofumi Ukai
- Graduate School of Frontier BioSciences, Osaka University, Osaka 565-0871, Japan
| | - Eigo Takeda
- Department of Nanobiology, Graduate School of Advanced Integration Science, Chiba University, Chiba 263-8522, Japan
| | - Akira Matsuura
- Department of Nanobiology, Graduate School of Advanced Integration Science, Chiba University, Chiba 263-8522, Japan
| | - Takeshi Noda
- Center for Frontier Oral Science, Graduate School of Dentistry, Osaka University, Osaka 565-0871, Japan Graduate School of Frontier BioSciences, Osaka University, Osaka 565-0871, Japan
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