1
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Yuan Y, Wang X, Jin J, Tang Z, Xian W, Zhang X, Fu J, He K, Liu X. The Salmonella Typhimurium Effector SpvB Subverts Host Membrane Trafficking by Targeting Clathrin and AP-1. Mol Cell Proteomics 2023; 22:100674. [PMID: 37924977 PMCID: PMC10696399 DOI: 10.1016/j.mcpro.2023.100674] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2023] [Revised: 10/21/2023] [Accepted: 11/01/2023] [Indexed: 11/06/2023] Open
Abstract
Salmonella enterica, the etiological agent of gastrointestinal and systemic diseases, translocates a plethora of virulence factors through its type III secretion systems to host cells during infection. Among them, SpvB has been reported to harbor an ADP-ribosyltransferase domain in its C terminus, which destabilizes host cytoskeleton by modifying actin. However, whether this effector targets other host factors as well as the function of its N terminus still remains to be determined. Here, we found that SpvB targets clathrin and its adaptor AP-1 (adaptor protein 1) via interactions with its N-terminal domain. Notably, our data suggest that SpvB-clathrin/AP-1 associations disrupt clathrin-mediated endocytosis and protein secretion pathway as well. In addition, knocking down of AP-1 promotes Salmonella intracellular survival and proliferation in host cells.
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Affiliation(s)
- Yi Yuan
- Department of Microbiology and Infectious Disease Center, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, China; NHC Key Laboratory of Medical Immunology, Peking University, Beijing, China
| | - Xinghao Wang
- State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, China; University of Chinese Academy of Sciences, Beijing, China
| | - Jie Jin
- Department of Microbiology and Infectious Disease Center, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, China; NHC Key Laboratory of Medical Immunology, Peking University, Beijing, China
| | - Zhiheng Tang
- Department of Microbiology and Infectious Disease Center, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, China; NHC Key Laboratory of Medical Immunology, Peking University, Beijing, China
| | - Wei Xian
- Department of Microbiology and Infectious Disease Center, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, China; NHC Key Laboratory of Medical Immunology, Peking University, Beijing, China
| | - Xinyi Zhang
- State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, China; University of Chinese Academy of Sciences, Beijing, China
| | - Jiaqi Fu
- Department of Respiratory Medicine, Infectious Diseases and Pathogen Biology Center, Key Laboratory of Organ Regeneration and Transplantation of the Ministry of Education, State Key Laboratory for Zoonotic Diseases, The First Hospital of Jilin University, Changchun, China.
| | - Kangmin He
- State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, China; University of Chinese Academy of Sciences, Beijing, China.
| | - Xiaoyun Liu
- Department of Microbiology and Infectious Disease Center, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, China; NHC Key Laboratory of Medical Immunology, Peking University, Beijing, China.
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2
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Tan C, Du Y, Zhu L, Jing S, Gao J, Qian Y, Yue X, Lee I. KDEL Receptor Trafficking to the Plasma Membrane Is Regulated by ACBD3 and Rab4A-GTP. Cells 2023; 12:cells12071079. [PMID: 37048152 PMCID: PMC10093020 DOI: 10.3390/cells12071079] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2022] [Revised: 03/01/2023] [Accepted: 03/14/2023] [Indexed: 04/07/2023] Open
Abstract
KDEL receptor-1 maintains homeostasis in the early secretory pathway by capturing and retrieving ER chaperones to the ER during heavy secretory activity. Unexpectedly, a fraction of the receptor is also known to reside in the plasma membrane (PM), although it is largely unknown exactly how the KDEL receptor gets exported from the Golgi and travels to the PM. We have previously shown that a Golgi scaffolding protein (ACBD3) facilitates KDEL receptor localization at the Golgi via the regulating cargo wave-induced cAMP/PKA-dependent signaling pathway. Upon endocytosis, surface-expressed KDEL receptor undergoes highly complex itineraries through the Golgi and the endo-lysosomal compartments, where the endocytosed receptor utilizes Rab14A- and Rab11A-positive recycling endosomes and clathrin-decorated tubulovesicular carriers. In this study, we sought to investigate the mechanism through which the KDEL receptor gets exported from the Golgi en route to the PM. We report here that ACBD3 depletion results in greatly increased trafficking of KDEL receptor to the PM via Rab4A-positive tubular carriers emanating from the Golgi. Expression of constitutively activated Rab4A mutant (Q72L) increases the surface expression of KDEL receptor up to 2~3-fold, whereas Rab4A knockdown or the expression of GDP-locked Rab4A mutant (S27N) inhibits KDEL receptor targeting of the PM. Importantly, KDELR trafficking from the Golgi to the PM is independent of PKA- and Src kinase-mediated mechanisms. Taken together, these results reveal that ACBD3 and Rab4A play a key role in regulating KDEL receptor trafficking to the cell surface.
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Affiliation(s)
- Chuanting Tan
- School of Life Science and Technology, ShanghaiTech University, Shanghai 201210, China
- University of Chinese Academy of Sciences, Beijing 101408, China
| | - Yulei Du
- School of Life Science and Technology, ShanghaiTech University, Shanghai 201210, China
- University of Chinese Academy of Sciences, Beijing 101408, China
| | - Lianhui Zhu
- School of Life Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Shuaiyang Jing
- School of Life Science and Technology, ShanghaiTech University, Shanghai 201210, China
- University of Chinese Academy of Sciences, Beijing 101408, China
| | - Jingkai Gao
- School of Life Science and Technology, ShanghaiTech University, Shanghai 201210, China
- University of Chinese Academy of Sciences, Beijing 101408, China
| | - Yi Qian
- School of Life Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Xihua Yue
- School of Life Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Intaek Lee
- School of Life Science and Technology, ShanghaiTech University, Shanghai 201210, China
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3
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Liu C, Li Z, Tian D, Xu M, Pan J, Wu H, Wang C, Otegui MS. AP1/2β-mediated exocytosis of tapetum-specific transporters is required for pollen development in Arabidopsis thaliana. THE PLANT CELL 2022; 34:3961-3982. [PMID: 35766888 PMCID: PMC9516047 DOI: 10.1093/plcell/koac192] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/02/2022] [Accepted: 06/21/2022] [Indexed: 06/15/2023]
Abstract
AP-1 and AP-2 adaptor protein (AP) complexes mediate clathrin-dependent trafficking at the trans-Golgi network (TGN) and the plasma membrane, respectively. Whereas AP-1 is required for trafficking to plasma membrane and vacuoles, AP-2 mediates endocytosis. These AP complexes consist of four subunits (adaptins): two large subunits (β1 and γ for AP-1 and β2 and α for AP-2), a medium subunit μ, and a small subunit σ. In general, adaptins are unique to each AP complex, with the exception of β subunits that are shared by AP-1 and AP-2 in some invertebrates. Here, we show that the two putative Arabidopsis thaliana AP1/2β adaptins co-assemble with both AP-1 and AP-2 subunits and regulate exocytosis and endocytosis in root cells, consistent with their dual localization at the TGN and plasma membrane. Deletion of both β adaptins is lethal in plants. We identified a critical role of β adaptins in pollen wall formation and reproduction, involving the regulation of membrane trafficking in the tapetum and pollen germination. In tapetal cells, β adaptins localize almost exclusively to the TGN and mediate exocytosis of the plasma membrane transporters such as ATP-binding cassette (ABC)G9 and ABCG16. This study highlights the essential role of AP1/2β adaptins in plants and their specialized roles in specific cell types.
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Affiliation(s)
- Chan Liu
- Ministry of Education Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou 730000, China
| | - Zhimin Li
- Ministry of Education Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou 730000, China
| | - Dan Tian
- Ministry of Education Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou 730000, China
| | - Mei Xu
- Ministry of Education Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou 730000, China
| | - Jianwei Pan
- Ministry of Education Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou 730000, China
| | - Haijun Wu
- Authors for correspondence: (M.S.O.); (C.W.); (H.W.)
| | - Chao Wang
- Authors for correspondence: (M.S.O.); (C.W.); (H.W.)
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4
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Li T, Guo Y. ADP-Ribosylation Factor Family of Small GTP-Binding Proteins: Their Membrane Recruitment, Activation, Crosstalk and Functions. Front Cell Dev Biol 2022; 10:813353. [PMID: 35186926 PMCID: PMC8850633 DOI: 10.3389/fcell.2022.813353] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2021] [Accepted: 01/14/2022] [Indexed: 11/13/2022] Open
Abstract
Members of the ADP-ribosylation factor (ARF) family of guanine-nucleotide binding proteins play critical roles in various cellular processes, especially in regulating the secretory, and endocytic pathways. The fidelity of intracellular vesicular trafficking depends on proper activations and precise subcellular distributions of ARF family proteins regulated by guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). Here we review recent progress in understanding the membrane recruitment, activation, crosstalk, and functions of ARF family proteins.
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Affiliation(s)
- Tiantian Li
- Division of Life Science and State Key Laboratory of Molecular Neuroscience, The Hong Kong University of Science and Technology, Kowloon, Hong Kong SAR, China
| | - Yusong Guo
- Division of Life Science and State Key Laboratory of Molecular Neuroscience, The Hong Kong University of Science and Technology, Kowloon, Hong Kong SAR, China
- Hong Kong University of Science and Technology, Shenzhen Research Institute, Shenzhen, China
- Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou, China
- *Correspondence: Yusong Guo,
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5
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Bell IJ, Horn MS, Van Raay TJ. Bridging the gap between non-canonical and canonical Wnt signaling through Vangl2. Semin Cell Dev Biol 2021; 125:37-44. [PMID: 34736823 DOI: 10.1016/j.semcdb.2021.10.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2021] [Revised: 09/30/2021] [Accepted: 10/05/2021] [Indexed: 12/29/2022]
Abstract
Non-canonical Wnt signaling (encompassing Wnt/PCP and WntCa2+) has a dual identity in the literature. One stream of research investigates its role in antagonizing canonical Wnt/β-catenin signaling in cancer, typically through Ca2+, while the other stream investigates its effect on polarity in development, typically through Vangl2. Rarely do these topics intersect or overlap. What has become clear is that Wnt5a can mobilize intracellular calcium stores to inhibit Wnt/β-catenin in cancer cells but there is no evidence that Vangl2 is involved in this process. Conversely, Wnt5a can independently activate Vangl2 to affect polarity and migration but the role of calcium in this process is also limited. Further, Vangl2 has also been implicated in inhibiting Wnt/β-catenin signaling in development. The consensus is that a cell can differentiate between canonical and non-canonical Wnt signaling when presented with a choice, always choosing non-canonical at the expense of canonical Wnt signaling. However, these are rare events in vivo. Given the shared resources between non-canonical and canonical Wnt signaling it is perplexing that there is not more in vivo evidence for cross talk between these two pathways. In this review we discuss the intersection of non-canonical Wnt, with a focus on Wnt/PCP, and Wnt/β-catenin signaling in an attempt to shed some light on pathways that rarely meet at a crossroads in vivo.
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Affiliation(s)
- Ian James Bell
- Department of Molecular and Cellular Biology, University of Guelph, 50 Stone Rd. E, Guelph, ON, Canada N1G 2W1
| | - Matthew Sheldon Horn
- Department of Molecular and Cellular Biology, University of Guelph, 50 Stone Rd. E, Guelph, ON, Canada N1G 2W1
| | - Terence John Van Raay
- Department of Molecular and Cellular Biology, University of Guelph, 50 Stone Rd. E, Guelph, ON, Canada N1G 2W1.
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6
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Tan JZA, Fourriere L, Wang J, Perez F, Boncompain G, Gleeson PA. Distinct anterograde trafficking pathways of BACE1 and amyloid precursor protein from the TGN and the regulation of amyloid-β production. Mol Biol Cell 2020; 31:27-44. [PMID: 31746668 PMCID: PMC6938271 DOI: 10.1091/mbc.e19-09-0487] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2019] [Revised: 11/01/2019] [Accepted: 11/15/2019] [Indexed: 01/08/2023] Open
Abstract
Processing of amyloid precursor protein (APP) by the β-secretase BACE1 is the initial step of the amyloidogenic pathway to generate amyloid-β (Aβ). Although newly synthesized BACE1 and APP are transported along the secretory pathway, it is not known whether BACE1 and APP share the same post-Golgi trafficking pathways or are partitioned into different transport routes. Here we demonstrate that BACE1 exits the Golgi in HeLa cells and primary neurons by a pathway distinct from the trafficking pathway for APP. By using the Retention Using Selective Hooks system, we show that BACE1 is transported from the trans-Golgi network to the plasma membrane in an AP-1- and Arf1/4-dependent manner. Subsequently, BACE1 is endocytosed to early and recycling endosomes. Perturbation of BACE1 post-Golgi trafficking results in an increase in BACE1 cleavage of APP and increased production of both Aβ40 and Aβ42. These findings reveal that Golgi exit of BACE1 and APP in primary neurons is tightly regulated, resulting in their segregation along different transport routes, which limits APP processing.
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Affiliation(s)
- Jing Zhi A. Tan
- Department of Biochemistry and Molecular Biology and Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Victoria 3010, Australia
| | - Lou Fourriere
- Department of Biochemistry and Molecular Biology and Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Victoria 3010, Australia
| | - Jingqi Wang
- Department of Biochemistry and Molecular Biology and Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Victoria 3010, Australia
| | - Franck Perez
- Dynamics of Intracellular Organization Laboratory, Institut Curie, PSL Research University, Sorbonne Université, Centre National de la Recherche Scientifique, UMR 144, 75248 Paris, France
| | - Gaelle Boncompain
- Dynamics of Intracellular Organization Laboratory, Institut Curie, PSL Research University, Sorbonne Université, Centre National de la Recherche Scientifique, UMR 144, 75248 Paris, France
| | - Paul A. Gleeson
- Department of Biochemistry and Molecular Biology and Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Victoria 3010, Australia
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7
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Huang Y, Ma T, Lau PK, Wang J, Zhao T, Du S, Loy MMT, Guo Y. Visualization of Protein Sorting at the Trans-Golgi Network and Endosomes Through Super-Resolution Imaging. Front Cell Dev Biol 2019; 7:181. [PMID: 31552246 PMCID: PMC6733968 DOI: 10.3389/fcell.2019.00181] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2019] [Accepted: 08/19/2019] [Indexed: 12/19/2022] Open
Abstract
The trans-Golgi network (TGN) and endosomes are essential protein sorting stations in the secretory transport pathway. Protein sorting is fundamentally a process of spatial segregation, but the spatial relationships among the proteins that constitute the sorting machinery have not been systematically analyzed at high resolution in mammalian cells. Here, using two-color STORM imaging, we show that the TGN/endosome-localized cargo adaptors, AP-1, GGA2 and epsinR, form elongated structures of over 250 nm in length at the juxta-nuclear Golgi area. Many of these structures are associated with clathrin. We found that AP-1 is spatially segregated from AP-3 and GGA2, whereas a fraction of AP-1 and GGA2 punctae are associated with epsinR. Moreover, we observed that the planar cell polarity cargo proteins, Vangl2 and Frizzled6 associate with different cargo adaptors—AP-1 and GGA2 or epsinR, respectively—when exiting the TGN. Knockdown analysis confirms the functional significance of this segregation. Our data indicates that TGN/endosome-localized cargo adaptors have distinct spatial relationships. The spatially segregated cargo adaptors GGA2 and AP-1 regulate sorting of Frizzled6 and Vangl2, respectively and spatially associated cargo adaptors can cooperatively regulate a specific sorting process.
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Affiliation(s)
- Yan Huang
- Division of Life Science, Hong Kong University of Science and Technology, Hong Kong, China
| | - Tianji Ma
- Division of Life Science, Hong Kong University of Science and Technology, Hong Kong, China
| | - Pik Ki Lau
- Division of Life Science, Hong Kong University of Science and Technology, Hong Kong, China
| | - Jinhui Wang
- Division of Life Science, Hong Kong University of Science and Technology, Hong Kong, China
| | - Teng Zhao
- Light Innovation Technology Limited, Hong Kong, China
| | - Shengwang Du
- Department of Chemical and Biological Engineering, Hong Kong University of Science and Technology, Hong Kong, China.,Department of Physics, Hong Kong University of Science and Technology, Hong Kong, China
| | - Michael M T Loy
- Department of Physics, Hong Kong University of Science and Technology, Hong Kong, China
| | - Yusong Guo
- Division of Life Science, Hong Kong University of Science and Technology, Hong Kong, China.,Hong Kong University of Science and Technology Shenzhen Research Institute, Shenzhen, China
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8
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Gilbert CE, Sztul E, Machamer CE. Commonly used trafficking blocks disrupt ARF1 activation and the localization and function of specific Golgi proteins. Mol Biol Cell 2018; 29:937-947. [PMID: 29467256 PMCID: PMC5896932 DOI: 10.1091/mbc.e17-11-0622] [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] [Indexed: 01/08/2023] Open
Abstract
Cold temperature blocks used to synchronize protein trafficking inhibit GBF1 function, leading to a decrease in ARF1-GTP levels and mislocalization of the ARF1 effector golgin-160. Several other, but not all, Golgi proteins including ARL1 also mislocalize. ARF1 activity and golgin-160 localization require more than 30 min to recover from these blocks. ADP-ribosylation factor (ARF) proteins are key regulators of the secretory pathway. ARF1, through interacting with its effectors, regulates protein trafficking by facilitating numerous events at the Golgi. One unique ARF1 effector is golgin-160, which promotes the trafficking of only a specific subset of cargo proteins through the Golgi. While studying this role of golgin-160, we discovered that commonly used cold temperature blocks utilized to synchronize cargo trafficking (20 and 16°C) caused golgin-160 dispersal from Golgi membranes. Here, we show that the loss of golgin-160 localization correlates with a decrease in the levels of activated ARF1, and that golgin-160 dispersal can be prevented by expression of a GTP-locked ARF1 mutant. Overexpression of the ARF1 activator Golgi brefeldin A–resistant guanine nucleotide exchange factor 1 (GBF1) did not prevent golgin-160 dispersal, suggesting that GBF1 may be nonfunctional at lower temperatures. We further discovered that several other Golgi resident proteins had altered localization at lower temperatures, including proteins recruited by ARF-like GTPase 1 (ARL1), a small GTPase that also became dispersed in the cold. Although cold temperature blocks are useful for synchronizing cargo trafficking through the Golgi, our data indicate that caution must be taken when interpreting results from these assays.
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Affiliation(s)
- Catherine E Gilbert
- Department of Cell Biology, The Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Elizabeth Sztul
- Department of Cell, Developmental and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL 35924
| | - Carolyn E Machamer
- Department of Cell Biology, The Johns Hopkins University School of Medicine, Baltimore, MD 21205
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9
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Saimani U, Kim K. Traffic from the endosome towards trans-Golgi network. Eur J Cell Biol 2017; 96:198-205. [PMID: 28256269 DOI: 10.1016/j.ejcb.2017.02.005] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2016] [Revised: 01/24/2017] [Accepted: 02/16/2017] [Indexed: 11/16/2022] Open
Abstract
Retrograde passage of a transport carrier entails cargo sorting at the endosome, generation of a cargo-laden carrier and its movement along cytoskeletal tracks towards trans-Golgi network (TGN), tethering at the TGN, and fusion with the Golgi membrane. Significant advances have been made in understanding this traffic system, revealing molecular requirements in each step and the functional connection between them as well as biomedical implication of the dysregulation of those important traffic factors. This review focuses on describing up-to-date action mechanisms for retrograde transport from the endosomal system to the TGN.
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Affiliation(s)
- Uma Saimani
- Department of Biology, Missouri State University, 901 S National, Springfield, MO 65807, United States
| | - Kyoungtae Kim
- Department of Biology, Missouri State University, 901 S National, Springfield, MO 65807, United States.
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10
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Seifert W, Posor Y, Schu P, Stenbeck G, Mundlos S, Klaassen S, Nürnberg P, Haucke V, Kornak U, Kühnisch J. The progressive ankylosis protein ANK facilitates clathrin- and adaptor-mediated membrane traffic at the trans-Golgi network-to-endosome interface. Hum Mol Genet 2016; 25:3836-3848. [PMID: 27466194 DOI: 10.1093/hmg/ddw230] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2016] [Revised: 07/01/2016] [Accepted: 07/01/2016] [Indexed: 12/19/2022] Open
Abstract
Dominant or recessive mutations in the progressive ankylosis gene ANKH have been linked to familial chondrocalcinosis (CCAL2), craniometaphyseal dysplasia (CMD), mental retardation, deafness and ankylosis syndrome (MRDA). The function of the encoded membrane protein ANK in cellular compartments other than the plasma membrane is unknown. Here, we show that ANK localizes to the trans-Golgi network (TGN), clathrin-coated vesicles and the plasma membrane. ANK functionally interacts with clathrin and clathrin associated adaptor protein (AP) complexes as loss of either protein causes ANK dispersion from the TGN to cytoplasmic endosome-like puncta. Consistent with its subcellular localization, loss of ANK results in reduced formation of tubular membrane carriers from the TGN, perinuclear accumulation of early endosomes and impaired transferrin endocytosis. Our data indicate that clathrin/AP-mediated cycling of ANK between the TGN, endosomes, and the cell surface regulates membrane traffic at the TGN/endosomal interface. These findings suggest that dysfunction of Golgi-endosomal membrane traffic may contribute to ANKH-associated pathologies.
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Affiliation(s)
- Wenke Seifert
- Institute of Vegetative Anatomy, Charité - Universitätsmedizin Berlin, Germany
| | - York Posor
- Department of Molecular Pharmacology and Cell Biology, Leibniz-Institut für Molekulare Pharmakologie (FMP), Berlin, Germany
| | - Peter Schu
- Department of Cellular Biochemistry, Universitätsmedizin Georg-August University, Göttingen, Germany
| | - Gudrun Stenbeck
- College of Health and Life Sciences, Brunel University, Uxbridge, United Kingdom
| | - Stefan Mundlos
- Institute for Medical and Human Genetics, Charité - Universitätsmedizin Berlin, Germany.,FG Development and Disease, Max-Planck-Institute for Molecular Genetics, Berlin, Germany.,Berlin-Brandenburg Center for Regenerative Therapies, Charité - Universitätsmedizin Berlin, Germany
| | - Sabine Klaassen
- Experimental and Clinical Research Center (ECRC)
- Max-Delbrück-Centrum for Molecular Medicine (MDC), Charité - Universitätsmedizin Berlin, Berlin, Germany.,Department of Pediatric Cardiology, Charité - Universitätsmedizin Berlin, Germany and
| | - Peter Nürnberg
- Cologne Center for Genomics (CCG), University of Cologne, Germany
| | - Volker Haucke
- Department of Molecular Pharmacology and Cell Biology, Leibniz-Institut für Molekulare Pharmakologie (FMP), Berlin, Germany
| | - Uwe Kornak
- Institute for Medical and Human Genetics, Charité - Universitätsmedizin Berlin, Germany.,FG Development and Disease, Max-Planck-Institute for Molecular Genetics, Berlin, Germany.,Berlin-Brandenburg Center for Regenerative Therapies, Charité - Universitätsmedizin Berlin, Germany
| | - Jirko Kühnisch
- Institute for Medical and Human Genetics, Charité - Universitätsmedizin Berlin, Germany .,FG Development and Disease, Max-Planck-Institute for Molecular Genetics, Berlin, Germany.,Experimental and Clinical Research Center (ECRC)
- Max-Delbrück-Centrum for Molecular Medicine (MDC), Charité - Universitätsmedizin Berlin, Berlin, Germany
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11
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Robinson MS. Forty Years of Clathrin-coated Vesicles. Traffic 2015; 16:1210-38. [PMID: 26403691 DOI: 10.1111/tra.12335] [Citation(s) in RCA: 230] [Impact Index Per Article: 25.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2015] [Revised: 09/16/2015] [Accepted: 09/16/2015] [Indexed: 12/11/2022]
Abstract
The purification of coated vesicles and the discovery of clathrin by Barbara Pearse in 1975 was a landmark in cell biology. Over the past 40 years, work from many labs has uncovered the molecular details of clathrin and its associated proteins, including how they assemble into a coated vesicle and how they select cargo. Unexpected connections have been found with signalling, development, neuronal transmission, infection, immunity and genetic disorders. But there are still a number of unanswered questions, including how clathrin-mediated trafficking is regulated and how the machinery evolved.
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Affiliation(s)
- Margaret S Robinson
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge, UK
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12
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Paczkowski JE, Richardson BC, Fromme JC. Cargo adaptors: structures illuminate mechanisms regulating vesicle biogenesis. Trends Cell Biol 2015; 25:408-16. [PMID: 25795254 DOI: 10.1016/j.tcb.2015.02.005] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2014] [Revised: 02/11/2015] [Accepted: 02/19/2015] [Indexed: 12/29/2022]
Abstract
Cargo adaptors sort transmembrane protein cargos into nascent vesicles by binding directly to their cytosolic domains. Recent studies have revealed previously unappreciated roles for cargo adaptors and regulatory mechanisms governing their function. The adaptor protein (AP)-1 and AP-2 clathrin adaptors switch between open and closed conformations that ensure they function at the right place at the right time. The exomer cargo adaptor has a direct role in remodeling the membrane for vesicle fission. Several different cargo adaptors functioning in distinct trafficking pathways at the Golgi are similarly regulated through bivalent binding to the ADP-ribosylation factor 1 (Arf1) GTPase, potentially enabling regulation by a threshold concentration of Arf1. Taken together, these studies highlight that cargo adaptors do more than just adapt cargos.
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Affiliation(s)
- Jon E Paczkowski
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY 14853, USA
| | - Brian C Richardson
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY 14853, USA
| | - J Christopher Fromme
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY 14853, USA.
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13
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Affiliation(s)
- Yusong Guo
- Department of Molecular and Cell Biology, Howard Hughes Medical Institute, University of California, Berkeley, California 94720-3200;
| | - Daniel W. Sirkis
- Department of Molecular and Cell Biology, Howard Hughes Medical Institute, University of California, Berkeley, California 94720-3200;
| | - Randy Schekman
- Department of Molecular and Cell Biology, Howard Hughes Medical Institute, University of California, Berkeley, California 94720-3200;
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14
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Renigunta V, Fischer T, Zuzarte M, Kling S, Zou X, Siebert K, Limberg MM, Rinné S, Decher N, Schlichthörl G, Daut J. Cooperative endocytosis of the endosomal SNARE protein syntaxin-8 and the potassium channel TASK-1. Mol Biol Cell 2014; 25:1877-91. [PMID: 24743596 PMCID: PMC4055267 DOI: 10.1091/mbc.e13-10-0592] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
SNARE proteins can have functions unrelated to membrane fusion. The unassembled form of the SNARE protein syntaxin-8 interacts with the K+ channel TASK-1; both proteins are internalized via clathrin-mediated endocytosis in a cooperative manner. This is a novel mechanism for the control of endocytosis by cargo proteins. The endosomal SNARE protein syntaxin-8 interacts with the acid-sensitive potassium channel TASK-1. The functional relevance of this interaction was studied by heterologous expression of these proteins (and mutants thereof) in Xenopus oocytes and in mammalian cell lines. Coexpression of syntaxin-8 caused a fourfold reduction in TASK-1 current, a corresponding reduction in the expression of TASK-1 at the cell surface, and a marked increase in the rate of endocytosis of the channel. TASK-1 and syntaxin-8 colocalized in the early endosomal compartment, as indicated by the endosomal markers 2xFYVE and rab5. The stimulatory effect of the SNARE protein on the endocytosis of the channel was abolished when both an endocytosis signal in TASK-1 and an endocytosis signal in syntaxin-8 were mutated. A syntaxin-8 mutant that cannot assemble with other SNARE proteins had virtually the same effect as wild-type syntaxin-8. Total internal reflection fluorescence microscopy showed formation and endocytosis of vesicles containing fluorescence-tagged clathrin, TASK-1, and/or syntaxin-8. Our results suggest that the unassembled form of syntaxin-8 and the potassium channel TASK-1 are internalized via clathrin-mediated endocytosis in a cooperative manner. This implies that syntaxin-8 regulates the endocytosis of TASK-1. Our study supports the idea that endosomal SNARE proteins can have functions unrelated to membrane fusion.
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Affiliation(s)
- Vijay Renigunta
- Institute of Physiology and Pathophysiology, Marburg University, 35037 Marburg, Germany
| | - Thomas Fischer
- Institute of Physiology and Pathophysiology, Marburg University, 35037 Marburg, Germany
| | - Marylou Zuzarte
- Institute of Physiology and Pathophysiology, Marburg University, 35037 Marburg, Germany
| | - Stefan Kling
- Institute of Physiology and Pathophysiology, Marburg University, 35037 Marburg, Germany
| | - Xinle Zou
- Institute of Physiology and Pathophysiology, Marburg University, 35037 Marburg, Germany
| | - Kai Siebert
- Institute of Physiology and Pathophysiology, Marburg University, 35037 Marburg, Germany
| | - Maren M Limberg
- Institute of Physiology and Pathophysiology, Marburg University, 35037 Marburg, Germany
| | - Susanne Rinné
- Institute of Physiology and Pathophysiology, Marburg University, 35037 Marburg, Germany
| | - Niels Decher
- Institute of Physiology and Pathophysiology, Marburg University, 35037 Marburg, Germany
| | - Günter Schlichthörl
- Institute of Physiology and Pathophysiology, Marburg University, 35037 Marburg, Germany
| | - Jürgen Daut
- Institute of Physiology and Pathophysiology, Marburg University, 35037 Marburg, Germany
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15
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Abstract
Polarized cells such as epithelial cells and neurons exhibit different plasma membrane domains with distinct protein compositions. Recent studies have shown that sorting of transmembrane proteins to the basolateral domain of epithelial cells and the somatodendritic domain of neurons is mediated by recognition of signals in the cytosolic domains of the proteins by adaptors. These adaptors are components of protein coats associated with the trans-Golgi network and/or recycling endosomes. The clathrin-associated adaptor protein 1 (AP-1) complex plays a preeminent role in this process, although other adaptors and coat proteins, such as AP-4, ARH, Numb, exomer, and retromer, have also been implicated.
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Affiliation(s)
- Juan S Bonifacino
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892
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16
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Guo X, Mattera R, Ren X, Chen Y, Retamal C, González A, Bonifacino JS. The adaptor protein-1 μ1B subunit expands the repertoire of basolateral sorting signal recognition in epithelial cells. Dev Cell 2014; 27:353-66. [PMID: 24229647 DOI: 10.1016/j.devcel.2013.10.006] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2012] [Revised: 07/15/2013] [Accepted: 10/10/2013] [Indexed: 01/05/2023]
Abstract
An outstanding question in protein sorting is why polarized epithelial cells express two isoforms of the μ1 subunit of the AP-1 clathrin adaptor complex: the ubiquitous μ1A and the epithelial-specific μ1B. Previous studies led to the notion that μ1A and μ1B mediate basolateral sorting predominantly from the trans-Golgi network (TGN) and recycling endosomes, respectively. Using improved analytical tools, however, we find that μ1A and μ1B largely colocalize with each other. They also colocalize to similar extents with TGN and recycling endosome markers, as well as with basolateral cargoes transiting biosynthetic and endocytic-recycling routes. Instead, the two isoforms differ in their signal-recognition specificity. In particular, μ1B preferentially binds a subset of signals from cargoes that are sorted basolaterally in a μ1B-dependent manner. We conclude that expression of distinct μ1 isoforms in epithelial cells expands the repertoire of signals recognized by AP-1 for sorting of a broader range of cargoes to the basolateral surface.
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Affiliation(s)
- Xiaoli Guo
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
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17
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PtdIns(4)P signalling and recognition systems. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2013; 991:59-83. [PMID: 23775691 DOI: 10.1007/978-94-007-6331-9_5] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The Golgi apparatus is a sorting platform that exchanges extensively with the endoplasmic reticulum (ER), endosomes (Es) and plasma membrane (PM) compartments. The last compartment of the Golgi, the trans-Golgi Network (TGN) is a large complex of highly deformed membranes from which vesicles depart to their targeted organelles but also are harbored from retrograde pathways. The phosphoinositide (PI) composition of the TGN is marked by an important contingent of phosphatidylinositol-4-phosphate (PtdIns(4)P). Although this PI is present throughout the Golgi, its proportion grows along the successive cisternae and peaks at the TGN. The levels of this phospholipid are controlled by a set of kinases and phosphatases that regulate its concentrations in the Golgi and maintain a dynamic gradient that determines the cellular localization of several interacting proteins. Though not exclusive to the Golgi, the synthesis of PtdIns(4)P in other membranes is relatively marginal and has unclear consequences. The significance of PtdIns(4)P within the TGN has been demonstrated for numerous cellular events such as vesicle formation, lipid metabolism, and membrane trafficking.
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18
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Traub LM, Bonifacino JS. Cargo recognition in clathrin-mediated endocytosis. Cold Spring Harb Perspect Biol 2013; 5:a016790. [PMID: 24186068 DOI: 10.1101/cshperspect.a016790] [Citation(s) in RCA: 214] [Impact Index Per Article: 19.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The endosomal system is expansive and complex, characterized by swift morphological transitions, dynamic remodeling of membrane constituents, and intracellular positioning changes. To properly navigate this ever-altering membrane labyrinth, transmembrane protein cargoes typically require specific sorting signals that are decoded by components of protein coats. The best-characterized sorting process within the endosomal system is the rapid internalization of select transmembrane proteins within clathrin-coated vesicles. Endocytic signals consist of linear motifs, conformational determinants, or covalent modifications in the cytosolic domains of transmembrane cargo. These signals are interpreted by a diverse set of clathrin-associated sorting proteins (CLASPs) that translocate from the cytosol to the inner face of the plasma membrane. Signal recognition by CLASPs is highly cooperative, involving additional interactions with phospholipids, Arf GTPases, other CLASPs, and clathrin, and is regulated by large conformational changes and covalent modifications. Related sorting events occur at other endosomal sorting stations.
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Affiliation(s)
- Linton M Traub
- Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261
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19
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Structural basis for recruitment and activation of the AP-1 clathrin adaptor complex by Arf1. Cell 2013; 152:755-67. [PMID: 23415225 DOI: 10.1016/j.cell.2012.12.042] [Citation(s) in RCA: 132] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2012] [Revised: 10/16/2012] [Accepted: 12/18/2012] [Indexed: 11/23/2022]
Abstract
AP-1 is a clathrin adaptor complex that sorts cargo between the trans-Golgi network and endosomes. AP-1 recruitment to these compartments requires Arf1-GTP. The crystal structure of the tetrameric core of AP-1 in complex with Arf1-GTP, together with biochemical analyses, shows that Arf1 activates cargo binding by unlocking AP-1. Unlocking is driven by two molecules of Arf1 that bridge two copies of AP-1 at two interaction sites. The GTP-dependent switch I and II regions of Arf1 bind to the N terminus of the β1 subunit of one AP-1 complex, while the back side of Arf1 binds to the central part of the γ subunit trunk of a second AP-1 complex. A third Arf1 interaction site near the N terminus of the γ subunit is important for recruitment, but not activation. These observations lead to a model for the recruitment and activation of AP-1 by Arf1.
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20
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Canagarajah BJ, Ren X, Bonifacino JS, Hurley JH. The clathrin adaptor complexes as a paradigm for membrane-associated allostery. Protein Sci 2013; 22:517-29. [PMID: 23424177 DOI: 10.1002/pro.2235] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2013] [Accepted: 02/13/2013] [Indexed: 11/12/2022]
Abstract
The clathrin-associated adaptor protein (AP) complexes AP-1 and AP-2 are two members of a family of heterotetrameric assemblies that connect transmembrane protein cargo to vesicular coats. Cargo binding by AP-1 is activated by the small GTPase Arf1, while AP-2 is activated by the phosphoinositide PI(4,5)P₂. The structures of both AP-1 and AP-2 have been determined in their locked and unlocked conformations. The structures show how different activators use different mechanisms to trigger similar large scale conformational rearrangements. The details of these mechanisms show how membrane docking and allosteric activation of AP complexes are intimately connected.
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Affiliation(s)
- Bertram J Canagarajah
- Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA
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21
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Niu YS, Cai ZZ, Lu Y, Wang MX, Liang S, Zhou F, Miao YG. Characterization of adaptor protein complex-1 in the silkworm, Bombyx mori. ARCHIVES OF INSECT BIOCHEMISTRY AND PHYSIOLOGY 2013; 82:84-95. [PMID: 23300124 DOI: 10.1002/arch.21077] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
To investigate the function of adaptor protein complex-1 (AP-1) in the silkworm, we characterized AP-1 in the silkworm by RNAi technique and co-localization methods. As a result, AP-1 was found to exist as cytosolic form and membrane-bound form distinguished by phosphate status, showing molecular mass difference. There was relatively more cytosolic form of AP-1 than its membrane-bound counterpart in the silkworm. However, AP-1 distributed predominantly as cytosolic form in BmN cells. Interruption of AP-1 expression via DsRNA was more efficient in BmN cells than in the insect larval, which led to a tendency to dissociation between subcellular organelles like the Golgi apparatus and the mitochondria. Environmental condition changes like relatively higher temperature and treatment with dimethyl sulfoxide can lead to expression variance of AP-1 both in mRNA and protein level. In BmN cells, both the heavy chain γ and light chain σ could clearly co-localize with AP-1 β, mostly forming pits in cytoplasm. Two isoforms of AP-1 σ corresponded to distinct subcellular distribution pattern, possibly due to C-terminal amino acids difference.
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Affiliation(s)
- Yan-shan Niu
- Key Laboratory of Animal Virology of Ministry of Agriculture, College of Animal Sciences, Zhejiang University, Hangzhou, P. R. China
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22
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Abstract
The assembly of clathrin/AP (adaptor protein)-1-coated vesicles on the trans-Golgi network and endosomes is much less studied than that of clathrin/AP-2 vesicles at the plasma membrane for endocytosis. In vitro, the association of AP-1 with protein-free liposomes had been shown to require phosphoinositides, Arf1 (ADP-ribosylation factor 1)–GTP and additional cytosolic factor(s). We have purified an active fraction from brain cytosol and found it to contain amphiphysin 1 and 2 and endophilin A1, three proteins known to be involved in the formation of AP-2/clathrin coats at the plasma membrane. Assays with bacterially expressed and purified proteins showed that AP-1 stabilization on liposomes depends on amphiphysin 2 or the amphiphysin 1/2 heterodimer. Activity is independent of the SH3 (Src homology 3) domain, but requires interaction of the WDLW motif with γ-adaptin. Endogenous amphiphysin in neurons and transfected protein in cell lines co-localize perinuclearly with AP-1 at the trans-Golgi network. This localization depends on interaction of clathrin and the adaptor sequence in the amphiphysins and is sensitive to brefeldin A, which inhibits Arf1-dependent AP-1 recruitment. Interaction between AP-1 and amphiphysin 1/2 in vivo was demonstrated by co-immunoprecipitation after cross-linking. These results suggest an involvement of amphiphysins not only with AP-2 at the plasma membrane, but also in AP-1/clathrin coat formation at the trans-Golgi network.
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23
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Guo Y, Zanetti G, Schekman R. A novel GTP-binding protein-adaptor protein complex responsible for export of Vangl2 from the trans Golgi network. eLife 2013; 2:e00160. [PMID: 23326640 PMCID: PMC3539332 DOI: 10.7554/elife.00160] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2012] [Accepted: 10/18/2012] [Indexed: 01/03/2023] Open
Abstract
Planar cell polarity (PCP) requires the asymmetric sorting of distinct signaling
receptors to distal and proximal surfaces of polarized epithelial cells. We have
examined the transport of one PCP signaling protein, Vangl2, from the
trans Golgi network (TGN) in mammalian cells. Using siRNA
knockdown experiments, we find that the GTP-binding protein, Arfrp1, and the clathrin
adaptor complex 1 (AP-1) are required for Vangl2 transport from the TGN. In contrast,
TGN export of Frizzled 6, which localizes to the opposing epithelial surface from
Vangl2, does not depend on Arfrp1 or AP-1. Mutagenesis studies identified a YYXXF
sorting signal in the C-terminal cytosolic domain of Vangl2 that is required for
Vangl2 traffic and interaction with the μ subunit of AP-1. We propose that
Arfrp1 exposes a binding site on AP-1 that recognizes the Vangl2 sorting motif for
capture into a transport vesicle destined for the proximal surface of a polarized
epithelial cell. DOI:http://dx.doi.org/10.7554/eLife.00160.001 Most cells in multicellular organisms possess a property known as polarity that is
reflected, in part, in the organization of the cell surface into distinct domains.
One well-known axis in epithelial cells, such as those in the skin, divides the cell
into an apical domain, which faces out, and a basal domain, which faces the
underlying tissue. These cells rely on the distribution of structural components
inside the cell, or within the cell membrane, to tell the difference between these
two directions. Epithelial cells also possess a second type of polarity, planar cell
polarity, that ensures that cells adjacent to each other in the plane parallel to the
skin tissue are oriented correctly with respect to each other during development.
This ensures, in turn, that hairs, scales, feathers and so on are all aligned. All eukaryotic cells sort and process proteins within an organelle called the Golgi
apparatus, and proteins that are required at a specific destination within the cell,
such as the cell surface membrane, carry specific molecular sorting signals that act
as address labels to convey the protein into and within the secretory pathway. As one
of these proteins moves through the Golgi apparatus, its sorting signals are
recognized by coat proteins, such as clathrin, that subsequently form a vesicle
around it. The assembly of this vesicle is initiated by an enzyme from the Arf
family, but the enzyme must first undergo a conformational change (by exchanging a
molecule of GDP for one of GTP) before formation can begin. The resulting vesicle can
then be sent on its way to the address indicated by its Golgi-to-cell-surface sorting
signal. These sorting signals also help to establish planar cell polarity in cells by
ensuring that proteins called signaling receptors are distributed asymmetrically
within the cell membrane. Guo et al. have now examined the mechanism behind the asymmetric sorting of two
proteins that are involved in planar cell polarity: Vangl2 and Frizzled 6. In an
effort to understand why these proteins are localized to opposite surfaces of
epithelial cells, Guo et al. used genetic techniques to reduce the expression of
Golgi-localized Arf proteins in epithelial cell cultures. They found that knockdown
of a protein called Arfrp1 caused Vangl2 to accumulate in the last station of the
Golgi complex instead of being transported to the cell surface membrane. Then, using
a technique called affinity chromatography, they demonstrated that a coat protein
called the clathrin adaptor complex (AP-1) had to be present for the formation of
vesicles around Vangl2. Moreover, disrupting AP-1 and Arfrp1 did not prevent Frizzled
6 being transported to the cell surface membrane. This suggests that cells use
several distinct adaptor proteins and coat complexes to ensure that proteins from the
Golgi apparatus go to specific locations on the cell surface and, thus, help to
establish planar cell polarity. DOI:http://dx.doi.org/10.7554/eLife.00160.002
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Affiliation(s)
- Yusong Guo
- Department of Molecular and Cell Biology , Howard Hughes Medical Institute, University of California-Berkeley , Berkeley , United States
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24
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Progida C, Nielsen MS, Koster G, Bucci C, Bakke O. Dynamics of Rab7b-dependent transport of sorting receptors. Traffic 2012; 13:1273-85. [PMID: 22708738 DOI: 10.1111/j.1600-0854.2012.01388.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2012] [Revised: 06/11/2012] [Accepted: 06/18/2012] [Indexed: 12/26/2022]
Abstract
The small GTPase Rab7b localizes to late endosomes-lysosomes and to the Golgi, regulating the transport between these two intracellular compartments. We have recently demonstrated that depletion of Rab7b causes missorting of the cation-independent mannose 6-phosphate receptor (CI-MPR), suggesting that Rab7b may control the trafficking of this receptor. Here we further investigated the function of this small GTPase with special attention to its role in the trafficking of sorting receptors and dynamics in living cells. Using endosome-to-Golgi retrieval assays we show that Rab7b is involved not only in CI-MPR transport but also in the MPRs independent pathway. Indeed, we find that it regulates and interacts with sortilin, a mannose 6-phosphate-independent sorting receptor. CI-MPR and sortilin are sorted from the trans-Golgi network (TGN) in tubular structures and the expression of Rab7b mutants or its silencing reduces CI-MPR and sortilin tubulation. In addition, the constitutively active mutant Rab7b Q67L impairs the formation of carriers from TGN. Collectively, our observations show for the first time that Rab7b is required for transport from endosomes to the TGN, not only of the CI-MPR, but also of sortilin, and that alterations in this transport result in impaired carrier formation from TGN.
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Affiliation(s)
- Cinzia Progida
- Centre for Immune Regulation, Department of Molecular Biosciences, University of Oslo, Blindernveien 31, 0371, Oslo, Norway
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25
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Yu X, Breitman M, Goldberg J. A structure-based mechanism for Arf1-dependent recruitment of coatomer to membranes. Cell 2012; 148:530-42. [PMID: 22304919 PMCID: PMC3285272 DOI: 10.1016/j.cell.2012.01.015] [Citation(s) in RCA: 88] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2011] [Revised: 09/02/2011] [Accepted: 01/06/2012] [Indexed: 11/19/2022]
Abstract
Budding of COPI-coated vesicles from Golgi membranes requires an Arf family G protein and the coatomer complex recruited from cytosol. Arf is also required with coatomer-related clathrin adaptor complexes to bud vesicles from the trans-Golgi network and endosomal compartments. To understand the structural basis for Arf-dependent recruitment of a vesicular coat to the membrane, we determined the structure of Arf1 bound to the γζ-COP subcomplex of coatomer. Structure-guided biochemical analysis reveals that a second Arf1-GTP molecule binds to βδ-COP at a site common to the γ- and β-COP subunits. The Arf1-binding sites on coatomer are spatially related to PtdIns4,5P(2)-binding sites on the endocytic AP2 complex, providing evidence that the orientation of membrane binding is general for this class of vesicular coat proteins. A bivalent GTP-dependent binding mode has implications for the dynamics of coatomer interaction with the Golgi and for the selection of cargo molecules.
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Affiliation(s)
- Xinchao Yu
- Howard Hughes Medical Institute and the Structural Biology Program, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, NY 10065, USA
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26
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Ma D, Taneja TK, Hagen BM, Kim BY, Ortega B, Lederer WJ, Welling PA. Golgi export of the Kir2.1 channel is driven by a trafficking signal located within its tertiary structure. Cell 2011; 145:1102-15. [PMID: 21703452 PMCID: PMC3139129 DOI: 10.1016/j.cell.2011.06.007] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2009] [Revised: 02/04/2011] [Accepted: 06/06/2011] [Indexed: 10/18/2022]
Abstract
Mechanisms that are responsible for sorting newly synthesized proteins for traffic to the cell surface from the Golgi are poorly understood. Here, we show that the potassium channel Kir2.1, mutations in which are associated with Andersen-Tawil syndrome, is selected as cargo into Golgi export carriers in an unusual signal-dependent manner. Unlike conventional trafficking signals, which are typically comprised of short linear peptide sequences, Golgi exit of Kir2.1 is dictated by residues that are embedded within the confluence of two separate domains. This signal patch forms a recognition site for interaction with the AP1 adaptor complex, thereby marking Kir2.1 for incorporation into clathrin-coated vesicles at the trans-Golgi. The identification of a trafficking signal in the tertiary structure of Kir2.1 reveals a quality control step that couples protein conformation to Golgi export and provides molecular insight into how mutations in Kir2.1 arrest the channels at the Golgi.
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Affiliation(s)
| | | | - Brian M. Hagen
- Department of Physiology, University of Maryland School of Medicine Baltimore, MD 21201
| | - Bo-Young Kim
- Department of Physiology, University of Maryland School of Medicine Baltimore, MD 21201
| | - Bernardo Ortega
- Department of Physiology, University of Maryland School of Medicine Baltimore, MD 21201
| | - W. Jonathan Lederer
- Department of Physiology, University of Maryland School of Medicine Baltimore, MD 21201
| | - Paul A. Welling
- Department of Physiology, University of Maryland School of Medicine Baltimore, MD 21201
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27
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Exit from the trans-Golgi network: from molecules to mechanisms. Curr Opin Cell Biol 2011; 23:443-51. [PMID: 21550789 DOI: 10.1016/j.ceb.2011.03.013] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2011] [Revised: 03/07/2011] [Accepted: 03/22/2011] [Indexed: 11/23/2022]
Abstract
The trans-Golgi network is a major sorting platform of the secretory pathway from which proteins and lipids, both newly synthesized and retrieved from endocytic compartments, are targeted to different destinations. These sorting processes occur during the formation of pleomorphic tubular-vesicular carriers. The past years have provided insights into basic mechanisms coordinating the spatial and temporal organization of machineries necessary for the segregation of membrane components into distinct microdomains, for the bending, elongation, and fission of corresponding membranes, thus revealing a complex interplay of protein-protein and protein-lipid interactions.
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28
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Anitei M, Wassmer T, Stange C, Hoflack B. Bidirectional transport between the trans-Golgi network and the endosomal system. Mol Membr Biol 2010; 27:443-56. [DOI: 10.3109/09687688.2010.522601] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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29
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Saint-Jean B, Seveno-Carpentier E, Alcon C, Neuhaus JM, Paris N. The cytosolic tail dipeptide Ile-Met of the pea receptor BP80 is required for recycling from the prevacuole and for endocytosis. THE PLANT CELL 2010; 22:2825-37. [PMID: 20807880 PMCID: PMC2947187 DOI: 10.1105/tpc.109.072215] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/16/2009] [Revised: 06/24/2010] [Accepted: 08/05/2010] [Indexed: 05/18/2023]
Abstract
Pea (Pisum sativum) BP80 is a vacuolar sorting receptor for soluble proteins and has a cytosolic domain essential for its intracellular trafficking between the trans-Golgi network and the prevacuole. Based on mammalian knowledge, we introduced point mutations in the cytosolic region of the receptor and produced chimeras of green fluorescent protein fused to the transmembrane domain of pea BP80 along with the modified cytosolic tails. By analyzing the subcellular location of these chimera, we found that mutating Glu-604, Asp-616, or Glu-620 had mild effects, whereas mutating the Tyr motif partially redistributed the chimera to the plasma membrane. Replacing both Ile-608 and Met-609 by Ala (IMAA) led to a massive redistribution of fluorescence to the vacuole, indicating that recycling is impaired. When the chimera uses the alternative route, the IMAA mutation led to a massive accumulation at the plasma membrane. Using Arabidopsis thaliana plants expressing a fluorescent reporter with the full-length sequence of At VSR4, we demonstrated that the receptor undergoes brefeldin A-sensitive endocytosis. We conclude that the receptors use two pathways, one leading directly to the lytic vacuole and the other going via the plasma membrane, and that the Ileu-608 Met-609 motif has a role in the retrieval step in both pathways.
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Affiliation(s)
- Bruno Saint-Jean
- Laboratoire de Physiologie et Biotechnologie des Algues, Institut Français de Recherche pour l'Exploitation de la Mer, 44311 Nantes Cedex 03, France
| | - Emilie Seveno-Carpentier
- Biochimie et Physiologie Moléculaire des Plantes, Institut de Biologie Intégrative des Plantes, Unité Mixte de Recherche 5004, Centre National de la Recherche Scientifique/Unité Mixte de Recherche 0386, Institut National de la Recherche Agronomique/Montpellier SupAgro/Université Montpellier 2, F-34060 Montpellier Cedex 1, France
| | - Carine Alcon
- Biochimie et Physiologie Moléculaire des Plantes, Institut de Biologie Intégrative des Plantes, Unité Mixte de Recherche 5004, Centre National de la Recherche Scientifique/Unité Mixte de Recherche 0386, Institut National de la Recherche Agronomique/Montpellier SupAgro/Université Montpellier 2, F-34060 Montpellier Cedex 1, France
| | - Jean-Marc Neuhaus
- Laboratoire de Biologie Moléculaire et Cellulaire, Université de Neuchâtel, CH-2009 Neuchâtel, Switzerland
| | - Nadine Paris
- Biochimie et Physiologie Moléculaire des Plantes, Institut de Biologie Intégrative des Plantes, Unité Mixte de Recherche 5004, Centre National de la Recherche Scientifique/Unité Mixte de Recherche 0386, Institut National de la Recherche Agronomique/Montpellier SupAgro/Université Montpellier 2, F-34060 Montpellier Cedex 1, France
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Jackson LP, Kelly BT, McCoy AJ, Gaffry T, James LC, Collins BM, Höning S, Evans PR, Owen DJ. A large-scale conformational change couples membrane recruitment to cargo binding in the AP2 clathrin adaptor complex. Cell 2010; 141:1220-9. [PMID: 20603002 PMCID: PMC3655264 DOI: 10.1016/j.cell.2010.05.006] [Citation(s) in RCA: 222] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2009] [Revised: 03/08/2010] [Accepted: 04/27/2010] [Indexed: 11/20/2022]
Abstract
The AP2 adaptor complex (α, β2, σ2, and μ2 subunits) crosslinks the endocytic clathrin scaffold to PtdIns4,5P2-containing membranes and transmembrane protein cargo. In the “locked” cytosolic form, AP2's binding sites for the two endocytic motifs, YxxΦ on the C-terminal domain of μ2 (C-μ2) and [ED]xxxL[LI] on σ2, are blocked by parts of β2. Using protein crystallography, we show that AP2 undergoes a large conformational change in which C-μ2 relocates to an orthogonal face of the complex, simultaneously unblocking both cargo-binding sites; the previously unstructured μ2 linker becomes helical and binds back onto the complex. This structural rearrangement results in AP2's four PtdIns4,5P2- and two endocytic motif-binding sites becoming coplanar, facilitating their simultaneous interaction with PtdIns4,5P2/cargo-containing membranes. Using a range of biophysical techniques, we show that the endocytic cargo binding of AP2 is driven by its interaction with PtdIns4,5P2-containing membranes.
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Affiliation(s)
- Lauren P Jackson
- Cambridge Institute for Medical Research, Department of Clinical Biochemistry, University of Cambridge, Hills Road, Cambridge CB2 0XY, UK
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31
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Spang A, Shiba Y, Randazzo PA. Arf GAPs: gatekeepers of vesicle generation. FEBS Lett 2010; 584:2646-51. [PMID: 20394747 DOI: 10.1016/j.febslet.2010.04.005] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2010] [Revised: 03/26/2010] [Accepted: 04/03/2010] [Indexed: 11/17/2022]
Abstract
Arf GAP proteins are a versatile and diverse group of proteins. They control the activity of the GTP-binding proteins of the ARF family by inducing the hydrolysis of GTP that is bound to Arf proteins. The best-studied role of Arf GAPs is in intracellular traffic. In this review, we will focus mainly on the Arf GAPs that play a role in vesicle formation, Arf GAP1, Arf GAP2 and Arf GAP3 and their yeast homologues, Gcs1p and Glo3p. We discuss the roles of Arf GAPs as regulators and effectors for Arf GTP-binding proteins.
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Affiliation(s)
- Anne Spang
- University of Basel, Growth and Development, Biozentrum, Switzerland.
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Protein complexes containing CYFIP/Sra/PIR121 coordinate Arf1 and Rac1 signalling during clathrin-AP-1-coated carrier biogenesis at the TGN. Nat Cell Biol 2010; 12:330-40. [PMID: 20228810 DOI: 10.1038/ncb2034] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2009] [Accepted: 02/19/2010] [Indexed: 12/12/2022]
Abstract
Actin dynamics is a tightly regulated process involved in various cellular events including biogenesis of clathrin-coated, AP-1 (adaptor protein 1)-coated transport carriers connecting the trans-Golgi network (TGN) and the endocytic pathway. However, the mechanisms coordinating coat assembly, membrane and actin remodelling during post-TGN transport remain poorly understood. Here we show that the Arf1 (ADP-ribosylation factor 1) GTPase synchronizes the TGN association of clathrin-AP-1 coats and protein complexes comprising CYFIP (cytoplasmic fragile-X mental retardation interacting protein; Sra, PIR121), a clathrin heavy chain binding protein associated with mental retardation. The Rac1 GTPase and its exchange factor beta-PIX (PAK-interacting exchange factor) activate these complexes, allowing N-WASP-dependent and Arp2/3-dependent actin polymerization towards membranes, thus promoting tubule formation. These phenomena can be recapitulated with synthetic membranes. This protein-network-based mechanism facilitates the sequential coordination of Arf1-dependent membrane priming, through the recruitment of coats and CYFIP-containing complexes, and of Rac1-dependent actin polymerization, and provides complementary but independent levels of regulation during early stages of clathrin-AP1-coated carrier biogenesis.
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Tickets to ride: selecting cargo for clathrin-regulated internalization. Nat Rev Mol Cell Biol 2009; 10:583-96. [PMID: 19696796 DOI: 10.1038/nrm2751] [Citation(s) in RCA: 414] [Impact Index Per Article: 27.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Clathrin-mediated endocytosis oversees the constitutive packaging of selected membrane cargoes into transport vesicles that fuse with early endosomes. The process is responsive to activation of signalling receptors and ion channels, promptly clearing post-translationally tagged forms of cargo off the plasma membrane. To accommodate the diverse array of transmembrane proteins that are variably gathered into forming vesicles, a dedicated sorting machinery cooperates to ensure that non-competitive uptake from the cell surface occurs within minutes. Recent structural and functional data reveal remarkable plasticity in how disparate sorting signals are recognized by cargo-selective clathrin adaptors, such as AP-2. Cargo loading also seems to govern whether coats ultimately bud or dismantle abortively at the cell surface.
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Luo R, Ha VL, Hayashi R, Randazzo PA. Arf GAP2 is positively regulated by coatomer and cargo. Cell Signal 2009; 21:1169-79. [PMID: 19296914 DOI: 10.1016/j.cellsig.2009.03.006] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2009] [Revised: 03/05/2009] [Accepted: 03/09/2009] [Indexed: 11/19/2022]
Abstract
Arf GAP2 is one of four Arf GAPs that function in the Golgi apparatus. We characterized the kinetics of Arf GAP2 and its regulation. Purified Arf GAP2 had little activity compared to purified Arf GAP1. Of the potential regulators we examined, coatomer had the greatest effect, stimulating activity one to two orders of magnitude. The effect was biphasic, with half-maximal activation observed at 50 nM coatomer and activation peaking at approximately 150 nM coatomer. Activation by coatomer was greater for Arf GAP2 than has been reported for Arf GAP1. The effects of phosphoinositides and changes in vesicle curvature on GAP activity were small compared to coatomer; however, both increased coatomer-dependent activity. Peptides from p24 cargo proteins increased Arf GAP2 activity by an additional 2- to 4-fold. The effect of cargo peptide was dependent on coatomer. Overexpressing the cargo protein p25 decreased cellular Arf1*GTP levels. The differential sensitivity of Arf GAP1 and Arf GAP2 to coatomer could coordinate their activities. Based on the common regulatory features of Arf GAP1 and 2, we propose a mechanism for cargo selection in which GTP hydrolysis triggered by cargo binding to the coat protein is coupled to coat polymerization.
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Affiliation(s)
- Ruibai Luo
- Laboratory of Cellular and Molecular Biology, National Cancer Institute, Bethesda, MD 20892, USA
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35
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Kelly BT, McCoy AJ, Späte K, Miller SE, Evans PR, Höning S, Owen DJ. A structural explanation for the binding of endocytic dileucine motifs by the AP2 complex. Nature 2008; 456:976-979. [PMID: 19140243 PMCID: PMC4340503 DOI: 10.1038/nature07422] [Citation(s) in RCA: 248] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Most transmembrane proteins are selected as transport vesicle cargo through the recognition of short, linear amino acid motifs in their cytoplasmic portions by vesicle coat proteins. In the case of clathrin-coated vesicles (CCVs) the motifs are recognised by clathrin adaptors. The AP2 adaptor complex (subunits α,β2,μ2,σ2) recognises both major endocytic motifs: YxxΦ motifs 1 and [DE]xxxL[LI] acidic dileucine motifs. Here we describe the binding of AP2 to the endocytic dileucine motif from CD4 2 . The major recognition events are the two leucine residues binding in hydrophobic pockets on σ2. The hydrophilic residue four residues upstream from the first leucine sits on a positively charged patch made from residues on σ2 and α subunits. Mutations in key residues inhibit the binding of AP2 to ‘acidic dileucine’ motifs displayed in liposomes containing PtdIns4,5P2, but do not affect binding to YxxΦ motifs via μ2. In the ‘inactive’ AP2 core structure 3 , both motif binding sites are blocked by different parts of the β2 subunit. To allow a dileucine motif to bind, the β2 N-terminus is displaced and becomes disordered; however, in this structure the YxxΦ binding site on μ2 remains blocked.
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Affiliation(s)
- Bernard T Kelly
- Cambridge Institute for Medical Research and Department of Clinical Biochemistry, University of Cambridge, Addenbrooke's Hospital, Hills Road, Cambridge. CB2 0XY, UK
| | - Airlie J McCoy
- Cambridge Institute for Medical Research and Department of Clinical Biochemistry, University of Cambridge, Addenbrooke's Hospital, Hills Road, Cambridge. CB2 0XY, UK
| | - Kira Späte
- Institute of Biochemistry I and Center for Molecular Medicine Cologne, University of Cologne, Joseph-Stelzmann-Str. 52, 50931 Cologne, GERMANY
| | - Sharon E Miller
- Cambridge Institute for Medical Research and Department of Clinical Biochemistry, University of Cambridge, Addenbrooke's Hospital, Hills Road, Cambridge. CB2 0XY, UK
| | - Philip R Evans
- Medical Research Council Laboratory of Molecular Biology, Hills Road, Cambridge CB2 0QH, UK
| | - Stefan Höning
- Institute of Biochemistry I and Center for Molecular Medicine Cologne, University of Cologne, Joseph-Stelzmann-Str. 52, 50931 Cologne, GERMANY
| | - David J Owen
- Cambridge Institute for Medical Research and Department of Clinical Biochemistry, University of Cambridge, Addenbrooke's Hospital, Hills Road, Cambridge. CB2 0XY, UK
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Sorting of lysosomal proteins. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2008; 1793:605-14. [PMID: 19046998 DOI: 10.1016/j.bbamcr.2008.10.016] [Citation(s) in RCA: 573] [Impact Index Per Article: 35.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/07/2008] [Revised: 10/07/2008] [Accepted: 10/30/2008] [Indexed: 11/24/2022]
Abstract
Lysosomes are composed of soluble and transmembrane proteins that are targeted to lysosomes in a signal-dependent manner. The majority of soluble acid hydrolases are modified with mannose 6-phosphate (M6P) residues, allowing their recognition by M6P receptors in the Golgi complex and ensuing transport to the endosomal/lysosomal system. Other soluble enzymes and non-enzymatic proteins are transported to lysosomes in an M6P-independent manner mediated by alternative receptors such as the lysosomal integral membrane protein LIMP-2 or sortilin. Sorting of cargo receptors and lysosomal transmembrane proteins requires sorting signals present in their cytosolic domains. These signals include dileucine-based motifs, DXXLL or [DE]XXXL[LI], and tyrosine-based motifs, YXXØ, which interact with components of clathrin coats such as GGAs or adaptor protein complexes. In addition, phosphorylation and lipid modifications regulate signal recognition and trafficking of lysosomal membrane proteins. The complex interaction of both luminal and cytosolic signals with recognition proteins guarantees the specific and directed transport of proteins to lysosomes.
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Lee I, Drake MT, Traub LM, Kornfeld S. Cargo-sorting signals promote polymerization of adaptor protein-1 in an Arf-1.GTP-independent manner. Arch Biochem Biophys 2008; 479:63-8. [PMID: 18762162 DOI: 10.1016/j.abb.2008.08.009] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2008] [Revised: 08/06/2008] [Accepted: 08/10/2008] [Indexed: 10/21/2022]
Abstract
Adaptor protein-1 (AP-1) is recruited onto the trans-Golgi network via binding to Arf-1.GTP, cargo-sorting signals and phosphoinositides, where it orchestrates the assembly of clathrin-coated vesicular carriers that transport cargo molecules to endosomes. Here we show that cytosolic AP-1 polymerizes when recruited onto enriched Golgi membranes and liposomes containing covalently attached cargo-sorting signal peptides. Incubation of cytosolic or purified AP-1 with soluble sorting signal peptides also resulted in AP-1 polymerization, showing that Arf-1.GTP and membranes are not required for this process. We propose that cargo-induced polymerization of AP-1 contributes to stabilization of the coat complex in the formation of clathrin-coated buds.
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Affiliation(s)
- Intaek Lee
- Department of Internal Medicine, Washington University School of Medicine, St. Louis, MO 63110, USA
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