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Kervin TA, Overduin M. Regulation of the Phosphoinositide Code by Phosphorylation of Membrane Readers. Cells 2021; 10:cells10051205. [PMID: 34069055 PMCID: PMC8156045 DOI: 10.3390/cells10051205] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2021] [Revised: 05/07/2021] [Accepted: 05/09/2021] [Indexed: 02/07/2023] Open
Abstract
The genetic code that dictates how nucleic acids are translated into proteins is well known, however, the code through which proteins recognize membranes remains mysterious. In eukaryotes, this code is mediated by hundreds of membrane readers that recognize unique phosphatidylinositol phosphates (PIPs), which demark organelles to initiate localized trafficking and signaling events. The only superfamily which specifically detects all seven PIPs are the Phox homology (PX) domains. Here, we reveal that throughout evolution, these readers are universally regulated by the phosphorylation of their PIP binding surfaces based on our analysis of existing and modelled protein structures and phosphoproteomic databases. These PIP-stops control the selective targeting of proteins to organelles and are shown to be key determinants of high-fidelity PIP recognition. The protein kinases responsible include prominent cancer targets, underscoring the critical role of regulated membrane readership.
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2
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Makaraci P, Kim K. trans-Golgi network-bound cargo traffic. Eur J Cell Biol 2018; 97:137-149. [PMID: 29398202 DOI: 10.1016/j.ejcb.2018.01.003] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2017] [Revised: 12/15/2017] [Accepted: 01/16/2018] [Indexed: 12/19/2022] Open
Abstract
Cargo following the retrograde trafficking are sorted at endosomes to be targeted the trans-Golgi network (TGN), a central receiving organelle. Though molecular requirements and their interaction networks have been somewhat established, the complete understanding of the intricate nature of their action mechanisms in every step of the retrograde traffic pathway remains unachieved. This review focuses on elucidating known functions of key regulators, including scission factors at the endosome and tethering/fusion mediators at the receiving dock, TGN, as well as a diverse range of cargo.
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Affiliation(s)
- Pelin Makaraci
- Department of Biology, Missouri State University, 901 S National Ave., Springfield, MO 65807, USA
| | - Kyoungtae Kim
- Department of Biology, Missouri State University, 901 S National Ave., Springfield, MO 65807, USA.
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3
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Brown C, Szpryngiel S, Kuang G, Srivastava V, Ye W, McKee LS, Tu Y, Mäler L, Bulone V. Structural and functional characterization of the microtubule interacting and trafficking domains of two oomycete chitin synthases. FEBS J 2016; 283:3072-88. [PMID: 27363606 DOI: 10.1111/febs.13794] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2016] [Revised: 05/31/2016] [Accepted: 06/28/2016] [Indexed: 12/18/2022]
Abstract
UNLABELLED Chitin synthases (Chs) are responsible for the synthesis of chitin, a key structural cell wall polysaccharide in many organisms. They are essential for growth in certain oomycete species, some of which are pathogenic to diverse higher organisms. Recently, a microtubule interacting and trafficking (MIT) domain, which is not found in any fungal Chs, has been identified in some oomycete Chs proteins. Based on experimental data relating to the binding specificity of other eukaryotic MIT domains, there was speculation that this domain may be involved in the intracellular trafficking of Chs proteins. However, there is currently no evidence for this or any other function for the MIT domain in these enzymes. To attempt to elucidate their function, MIT domains from two Chs enzymes from the oomycete Saprolegnia monoica were cloned, expressed, and characterized. Both were shown to interact strongly with the plasma membrane component, phosphatidic acid, and to have additional putative interactions with proteins thought to be involved in protein transport and localization. Aiding our understanding of these data, the structure of the first MIT domain from a carbohydrate-active enzyme (MIT1) was solved by NMR, and a model structure of a second MIT domain (MIT2) was built by homology modeling. Our results suggest a potential function for these MIT domains in the intracellular transport and/or regulation of Chs enzymes in the oomycetes. DATABASE Structural data are available in the Biological Magnetic Resonance Bank (BMRB) database under the accession number 19987 and the PDB database under the accession number 2MPK.
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Affiliation(s)
- Christian Brown
- Division of Glycoscience, School of Biotechnology, Royal Institute of Technology (KTH), AlbaNova University Centre, Stockholm, Sweden
| | - Scarlett Szpryngiel
- Department of Biochemistry and Biophysics, The Arrhenius Laboratory, Stockholm University, Sweden
| | - Guanglin Kuang
- Division of Theoretical Chemistry and Biology, School of Biotechnology, Royal Institute of Technology (KTH), Stockholm, Sweden
| | - Vaibhav Srivastava
- Division of Glycoscience, School of Biotechnology, Royal Institute of Technology (KTH), AlbaNova University Centre, Stockholm, Sweden
| | - Weihua Ye
- Department of Biochemistry and Biophysics, The Arrhenius Laboratory, Stockholm University, Sweden
| | - Lauren S McKee
- Division of Glycoscience, School of Biotechnology, Royal Institute of Technology (KTH), AlbaNova University Centre, Stockholm, Sweden
| | - Yaoquan Tu
- Division of Theoretical Chemistry and Biology, School of Biotechnology, Royal Institute of Technology (KTH), Stockholm, Sweden
| | - Lena Mäler
- Department of Biochemistry and Biophysics, The Arrhenius Laboratory, Stockholm University, Sweden
| | - Vincent Bulone
- Division of Glycoscience, School of Biotechnology, Royal Institute of Technology (KTH), AlbaNova University Centre, Stockholm, Sweden.,ARC Centre of Excellence in Plant Cell Walls, School of Agriculture, Food and Wine, The University of Adelaide, Waite Campus, Urrbrae, South Australia, Australia
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4
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Feng T, Niu M, Ji C, Gao Y, Wen J, Bu G, Xu H, Zhang YW. SNX15 Regulates Cell Surface Recycling of APP and Aβ Generation. Mol Neurobiol 2015; 53:3690-3701. [PMID: 26115702 DOI: 10.1007/s12035-015-9306-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2015] [Accepted: 06/16/2015] [Indexed: 12/31/2022]
Abstract
Amyloid-β (Aβ) peptide plays an essential role in the pathogenesis of Alzheimer's disease (AD) and is generated from amyloid-β precursor protein (APP) through sequential proteolytic cleavages by β-site APP cleaving enzyme 1 (BACE1) and γ-secretase. Trafficking dysregulation of APP, BACE1, and γ-secretase may affect Aβ generation and disease pathogenesis. Sorting nexin 15 (SNX15) is known to regulate protein trafficking. Here, we report that SNX15 is abundantly expressed in mouse neurons and astrocytes. In addition, we show that although not affecting the protein levels of APP, BACE1, and γ-secretase components and the activity of BACE1 and γ-secretase, overexpression and downregulation of SNX15 reduce and promote Aβ production, respectively. Furthermore, we find that overexpression of SNX15 increases APP protein levels in cell surface through accelerating APP recycling, whereas downregulation of SNX15 has an opposite effect. Finally, we show that exogenous expression of human SNX15 in the hippocampal dentate gyrus by adeno-associated virus (AAV) infection can significantly reduce Aβ pathology in the hippocampus and improve short-term working memory in the APPswe/PSEN1dE9 double transgenic AD model mice. Together, our results suggest that SNX15 regulates the recycling of APP to cell surface and, thus, its processing for Aβ generation.
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Affiliation(s)
- Tuancheng Feng
- Fujian Provincial Key Laboratory of Neurodegenerative Disease and Aging Research, Institute of Neuroscience, School of Pharmaceutical Sciences, College of Medicine, Xiamen University, Xiamen, 361102, China
| | - Mengmeng Niu
- Fujian Provincial Key Laboratory of Neurodegenerative Disease and Aging Research, Institute of Neuroscience, School of Pharmaceutical Sciences, College of Medicine, Xiamen University, Xiamen, 361102, China
| | - Chengxiang Ji
- Fujian Provincial Key Laboratory of Neurodegenerative Disease and Aging Research, Institute of Neuroscience, School of Pharmaceutical Sciences, College of Medicine, Xiamen University, Xiamen, 361102, China
| | - Yuehong Gao
- Fujian Provincial Key Laboratory of Neurodegenerative Disease and Aging Research, Institute of Neuroscience, School of Pharmaceutical Sciences, College of Medicine, Xiamen University, Xiamen, 361102, China
| | - Jing Wen
- Fujian Provincial Key Laboratory of Neurodegenerative Disease and Aging Research, Institute of Neuroscience, School of Pharmaceutical Sciences, College of Medicine, Xiamen University, Xiamen, 361102, China
| | - Guojun Bu
- Fujian Provincial Key Laboratory of Neurodegenerative Disease and Aging Research, Institute of Neuroscience, School of Pharmaceutical Sciences, College of Medicine, Xiamen University, Xiamen, 361102, China
| | - Huaxi Xu
- Fujian Provincial Key Laboratory of Neurodegenerative Disease and Aging Research, Institute of Neuroscience, School of Pharmaceutical Sciences, College of Medicine, Xiamen University, Xiamen, 361102, China
- Degenerative Disease Research Program, Sanford-Burnham Medical Research Institute, La Jolla, CA, 92037, USA
| | - Yun-Wu Zhang
- Fujian Provincial Key Laboratory of Neurodegenerative Disease and Aging Research, Institute of Neuroscience, School of Pharmaceutical Sciences, College of Medicine, Xiamen University, Xiamen, 361102, China.
- Degenerative Disease Research Program, Sanford-Burnham Medical Research Institute, La Jolla, CA, 92037, USA.
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5
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Danson C, Brown E, Hemmings OJ, McGough IJ, Yarwood S, Heesom KJ, Carlton JG, Martin-Serrano J, May MT, Verkade P, Cullen PJ. SNX15 links clathrin endocytosis to the PtdIns3P early endosome independently of the APPL1 endosome. J Cell Sci 2013; 126:4885-99. [PMID: 23986476 DOI: 10.1242/jcs.125732] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Sorting nexins (SNXs) are key regulators of the endosomal network. In designing an RNAi-mediated loss-of-function screen, we establish that of 30 human SNXs only SNX3, SNX5, SNX9, SNX15 and SNX21 appear to regulate EGF receptor degradative sorting. Suppression of SNX15 results in a delay in receptor degradation arising from a defect in movement of newly internalised EGF-receptor-labelled vesicles into early endosomes. Besides a phosphatidylinositol 3-phosphate- and PX-domain-dependent association to early endosomes, SNX15 also associates with clathrin-coated pits and clathrin-coated vesicles by direct binding to clathrin through a non-canonical clathrin-binding box. From live-cell imaging, it was identified that the activated EGF receptor enters distinct sub-populations of SNX15- and APPL1-labelled peripheral endocytic vesicles, which do not undergo heterotypic fusion. The SNX15-decorated receptor-containing sub-population does, however, undergo direct fusion with the Rab5-labelled early endosome. Our data are consistent with a model in which the EGF receptor enters the early endosome following clathrin-mediated endocytosis through at least two parallel pathways: maturation through an APPL1-intermediate compartment and an alternative more direct fusion between SNX15-decorated endocytic vesicles and the Rab5-positive early endosome.
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Affiliation(s)
- Chris Danson
- The Henry Wellcome Integrated Signalling Laboratories, School of Biochemistry, Medical Sciences Building, University of Bristol, Bristol BS8 1TD, UK
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6
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Snx3 regulates recycling of the transferrin receptor and iron assimilation. Cell Metab 2013; 17:343-52. [PMID: 23416069 PMCID: PMC3595351 DOI: 10.1016/j.cmet.2013.01.013] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/09/2012] [Revised: 10/21/2012] [Accepted: 01/23/2013] [Indexed: 11/23/2022]
Abstract
Sorting of endocytic ligands and receptors is critical for diverse cellular processes. The physiological significance of endosomal sorting proteins in vertebrates, however, remains largely unknown. Here we report that sorting nexin 3 (Snx3) facilitates the recycling of transferrin receptor (Tfrc) and thus is required for the proper delivery of iron to erythroid progenitors. Snx3 is highly expressed in vertebrate hematopoietic tissues. Silencing of Snx3 results in anemia and hemoglobin defects in vertebrates due to impaired transferrin (Tf)-mediated iron uptake and its accumulation in early endosomes. This impaired iron assimilation can be complemented with non-Tf iron chelates. We show that Snx3 and Vps35, a component of the retromer, interact with Tfrc to sort it to the recycling endosomes. Our findings uncover a role of Snx3 in regulating Tfrc recycling, iron homeostasis, and erythropoiesis. Thus, the identification of Snx3 provides a genetic tool for exploring erythropoiesis and disorders of iron metabolism.
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7
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Pons V, Ustunel C, Rolland C, Torti E, Parton RG, Gruenberg J. SNX12 role in endosome membrane transport. PLoS One 2012; 7:e38949. [PMID: 22719997 PMCID: PMC3376135 DOI: 10.1371/journal.pone.0038949] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2011] [Accepted: 05/16/2012] [Indexed: 12/03/2022] Open
Abstract
In this paper, we investigated the role of sorting nexin 12 (SNX12) in the endocytic pathway. SNX12 is a member of the PX domain-containing sorting nexin family and shares high homology with SNX3, which plays a central role in the formation of intralumenal vesicles within multivesicular endosomes. We found that SNX12 is expressed at very low levels compared to SNX3. SNX12 is primarily associated with early endosomes and this endosomal localization depends on the binding to 3-phosphoinositides. We find that overexpression of SNX12 prevents the detachment (or maturation) of multivesicular endosomes from early endosomes. This in turn inhibits the degradative pathway from early to late endosomes/lysosomes, much like SNX3 overexpression, without affecting endocytosis, recycling and retrograde transport. In addition, while previous studies showed that Hrs knockdown prevents EGF receptor sorting into multivesicular endosomes, we find that overexpression of SNX12 restores the sorting process in an Hrs knockdown background. Altogether, our data show that despite lower expression level, SNX12 shares redundant functions with SNX3 in the biogenesis of multivesicular endosomes.
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Affiliation(s)
- Véronique Pons
- Department of Biochemistry, University of Geneva, Geneva, Switzerland
- INSERM, UMR 1048, Institut Maladies Métaboliques et Cardiovasculaires, Université de Toulouse III, Toulouse, France
| | - Cansel Ustunel
- Department of Biochemistry, University of Geneva, Geneva, Switzerland
| | - Corinne Rolland
- INSERM, U1043, UPS, Centre de Physiopathologie de Toulouse Purpan (CPTP), Toulouse, France
| | - Eleonora Torti
- Department of Biochemistry, University of Geneva, Geneva, Switzerland
| | - Robert G. Parton
- Institute for Molecular Bioscience and Center for Microscopy and Microanalysis, University of Queensland, Brisbane, Australia
| | - Jean Gruenberg
- Department of Biochemistry, University of Geneva, Geneva, Switzerland
- * E-mail:
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8
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Insights into the PX (phox-homology) domain and SNX (sorting nexin) protein families: structures, functions and roles in disease. Biochem J 2011; 441:39-59. [DOI: 10.1042/bj20111226] [Citation(s) in RCA: 212] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The mammalian genome encodes 49 proteins that possess a PX (phox-homology) domain, responsible for membrane attachment to organelles of the secretory and endocytic system via binding of phosphoinositide lipids. The PX domain proteins, most of which are classified as SNXs (sorting nexins), constitute an extremely diverse family of molecules that play varied roles in membrane trafficking, cell signalling, membrane remodelling and organelle motility. In the present review, we present an overview of the family, incorporating recent functional and structural insights, and propose an updated classification of the proteins into distinct subfamilies on the basis of these insights. Almost all PX domain proteins bind PtdIns3P and are recruited to early endosomal membranes. Although other specificities and localizations have been reported for a select few family members, the molecular basis for binding to other lipids is still not clear. The PX domain is also emerging as an important protein–protein interaction domain, binding endocytic and exocytic machinery, transmembrane proteins and many other molecules. A comprehensive survey of the molecular interactions governed by PX proteins highlights the functional diversity of the family as trafficking cargo adaptors and membrane-associated scaffolds regulating cell signalling. Finally, we examine the mounting evidence linking PX proteins to different disorders, in particular focusing on their emerging importance in both pathogen invasion and amyloid production in Alzheimer's disease.
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9
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Gonçalves JP, Grãos M, Valente AX. POLAR MAPPER: a computational tool for integrated visualization of protein interaction networks and mRNA expression data. J R Soc Interface 2009; 6:881-96. [PMID: 19091689 PMCID: PMC2684442 DOI: 10.1098/rsif.2008.0407] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2008] [Accepted: 11/04/2008] [Indexed: 11/25/2022] Open
Abstract
Polar Mapper is a computational application for exposing the architecture of protein interaction networks. It facilitates the system-level analysis of mRNA expression data in the context of the underlying protein interaction network. Preliminary analysis of a human protein interaction network and comparison of the yeast oxidative stress and heat shock gene expression responses are addressed as case studies.
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Affiliation(s)
- Joana P. Gonçalves
- Unidade de Sistemas Biológicos, Biocant, 3060-197 Cantanhede, Portugal
- KDBIO Group, INESC-ID, 1000-029 Lisbon, Portugal
- IST, Technical University of Lisbon, 1169-047 Lisbon, Portugal
| | - Mário Grãos
- Unidade de Biologia Celular, Biocant, 3060-197 Cantanhede, Portugal
| | - André X.C.N. Valente
- Unidade de Sistemas Biológicos, Biocant, 3060-197 Cantanhede, Portugal
- Centro de Neurociências e Biologia Celular, Universidade de Coimbra, 3004-517 Coimbra, Portugal
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10
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Dyve AB, Bergan J, Utskarpen A, Sandvig K. Sorting nexin 8 regulates endosome-to-Golgi transport. Biochem Biophys Res Commun 2009; 390:109-14. [PMID: 19782049 DOI: 10.1016/j.bbrc.2009.09.076] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2009] [Accepted: 09/20/2009] [Indexed: 11/25/2022]
Abstract
Sorting nexin 8 (SNX8) belongs to the sorting nexin protein family, whose members are involved in endocytosis and endosomal sorting and signaling. The function of SNX8 has so far been unknown. Here, we have investigated the role of SNX8 in intracellular transport of the bacterial toxin Shiga toxin (Stx) and the plant toxin ricin. After being endocytosed, these toxins are transported retrogradely from endosomes, via the Golgi apparatus and the endoplasmic reticulum (ER), into the cytosol, where they exert their toxic effect. Interestingly, our experiments show that SNX8 regulates the transport of Stx and ricin differently; siRNA-mediated knockdown of SNX8 significantly increased the Stx transport to the trans-Golgi network (TGN), whereas ricin transport was slightly inhibited. We also found that SNX8 colocalizes with early endosome antigen 1 (EEA1) and with retromer components, suggesting an endosomal localization of SNX8 and supporting our finding that SNX8 is involved in endosomal sorting.
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Affiliation(s)
- Anne Berit Dyve
- Faculty Division The Norwegian Radium Hospital, Centre for Cancer Biomedicine, University of Oslo, 0316 Oslo, Norway
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11
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Phan NQ, Kim SJ, Bassham DC. Overexpression of Arabidopsis sorting nexin AtSNX2b inhibits endocytic trafficking to the vacuole. MOLECULAR PLANT 2008; 1:961-976. [PMID: 19825596 DOI: 10.1093/mp/ssn057] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Sorting nexins are conserved proteins that function in vesicular trafficking and contain a characteristic phox homology (PX) domain. Here, we characterize the ubiquitously expressed Arabidopsis thaliana sorting nexin AtSNX2b. Sub-cellular fractionation studies indicate that AtSNX2b is peripherally associated with membranes. The AtSNX2b PX domain binds to phosphatidylinositol 3-phosphate in vitro and this association is required for the localization of GFP-AtSNX2b to punctate structures in vivo, identified as the trans-Golgi network, prevacuolar compartment and endosomes. Overexpression of GFP-tagged AtSNX2b produces enlarged GFP-labeled compartments that can also be labeled by the endocytic tracer FM4-64. Endocytic trafficking of FM4-64 to the vacuole is arrested in these GFP-AtSNX2b compartments, and similar FM4-64-accumulating compartments are seen upon overexpression of untagged AtSNX2b. This suggests that exit of membrane components from these enlarged or aggregated endosomes is inhibited. Vacuolar proteins containing an N-terminal propeptide, but not those with a C-terminal propeptide, are also present in these enlarged compartments. We hypothesize that AtSNX2b is involved in vesicular trafficking from endosomes to the vacuole.
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Affiliation(s)
- Nguyen Q Phan
- Department of Genetics, Development and Cell Biology, Iowa State University, Ames, IA 50011, USA
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12
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Rojas R, Kametaka S, Haft CR, Bonifacino JS. Interchangeable but essential functions of SNX1 and SNX2 in the association of retromer with endosomes and the trafficking of mannose 6-phosphate receptors. Mol Cell Biol 2006; 27:1112-24. [PMID: 17101778 PMCID: PMC1800681 DOI: 10.1128/mcb.00156-06] [Citation(s) in RCA: 179] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The retromer is a cytosolic/peripheral membrane protein complex that mediates the retrieval of the cation-independent mannose 6-phosphate receptor from endosomes to the trans-Golgi network (TGN) in mammalian cells. Previous studies showed that the mammalian retromer comprises three proteins, named Vps26, Vps29, and Vps35, plus the sorting nexin, SNX1. There is conflicting evidence, however, as to whether a homologous sorting nexin, SNX2, is truly a component of the retromer. In addition, the nature of the subunit interactions and assembly of the mammalian retromer complex are poorly understood. We have addressed these issues by performing biochemical and functional analyses of endogenous retromers in the human cell line HeLa. We found that the mammalian retromer complex consists of two autonomously assembling subcomplexes, namely, a Vps26-Vps29-Vps35 obligate heterotrimer and a SNX1/2 alternative heterodimer or homodimer. The association of Vps26-Vps29-Vps35 with endosomes requires the presence of either SNX1 or SNX2, whereas SNX1/2 can be recruited to endosomes independently of Vps26-Vps29-Vps35. We also found that the presence of either SNX1 or SNX2 is essential for the retrieval of the cation-independent mannose 6-phosphate receptor to the TGN. These observations indicate that the mammalian retromer complex assembles by sequential association of SNX1/2 and Vps26-Vps29-Vps35 subcomplexes on endosomal membranes and that SNX1 and SNX2 play interchangeable but essential roles in retromer structure and function.
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Affiliation(s)
- Raul Rojas
- Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, Building 18T/Room 101, National Institutes of Health, Bethesda, MD 20892, USA
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13
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Carlton JG, Bujny MV, Peter BJ, Oorschot VMJ, Rutherford A, Arkell RS, Klumperman J, McMahon HT, Cullen PJ. Sorting nexin-2 is associated with tubular elements of the early endosome, but is not essential for retromer-mediated endosome-to-TGN transport. J Cell Sci 2006; 118:4527-39. [PMID: 16179610 PMCID: PMC1904489 DOI: 10.1242/jcs.02568] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Sorting nexins are a large family of phox-homology-domain-containing proteins that have been implicated in the control of endosomal sorting. Sorting nexin-1 is a component of the mammalian retromer complex that regulates retrieval of the cation-independent mannose 6-phosphate receptor from endosomes to the trans-Golgi network. In yeast, retromer is composed of Vps5p (the orthologue of sorting nexin-1), Vps17p (a related sorting nexin) and a cargo selective subcomplex composed of Vps26p, Vps29p and Vps35p. With the exception of Vps17p, mammalian orthologues of all yeast retromer components have been identified. For Vps17p, one potential mammalian orthologue is sorting nexin-2. Here we show that, like sorting nexin-1, sorting nexin-2 binds phosphatidylinositol 3-monophosphate and phosphatidylinositol 3,5-bisphosphate, and possesses a Bin/Amphiphysin/Rvs domain that can sense membrane curvature. However, in contrast to sorting nexin-1, sorting nexin-2 could not induce membrane tubulation in vitro or in vivo. Functionally, we show that endogenous sorting nexin-1 and sorting nexin-2 co-localise on high curvature tubular elements of the 3-phosphoinositide-enriched early endosome, and that suppression of sorting nexin-2 does not perturb the degradative sorting of receptors for epidermal growth factor or transferrin, nor the steady-state distribution of the cation-independent mannose 6-phosphate receptor. However, suppression of sorting nexin-2 results in a subtle alteration in the kinetics of cation-independent mannose 6-phosphate receptor retrieval. These data suggest that although sorting nexin-2 may be a component of the retromer complex, its presence is not essential for the regulation of endosome-to-trans Golgi network retrieval of the cation-independent mannose 6-phosphate receptor.
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Affiliation(s)
- Jez G. Carlton
- Henry Wellcome Integrated Signalling Laboratories, Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK
| | - Miriam V. Bujny
- Henry Wellcome Integrated Signalling Laboratories, Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK
| | - Brian J. Peter
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK
| | - Viola M. J. Oorschot
- Cell Microscopy Center, Department of Cell Biology and Institute for Biomembranes, University Medical Centre Utrecht, Utrecht, The Netherlands
| | - Anna Rutherford
- Henry Wellcome Integrated Signalling Laboratories, Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK
| | - Rebecca S. Arkell
- Signalling Programme, The Babraham Institute, Babraham Hall, Cambridge CB2 4AT, UK
| | - Judith Klumperman
- Cell Microscopy Center, Department of Cell Biology and Institute for Biomembranes, University Medical Centre Utrecht, Utrecht, The Netherlands
| | - Harvey T. McMahon
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK
| | - Peter J. Cullen
- Henry Wellcome Integrated Signalling Laboratories, Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK
- Author for correspondence (e-mail: )
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14
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Yokoi K, Akiyama M, Yanagisawa T, Yoshino M, Nakazaki H, Takahashi K, Takahashi-Fujigasaki J, Kanetsuna Y, Yamada H, Oi S, Eto Y. RNA expression analysis of a congenital intracranial teratoma. Pediatr Blood Cancer 2005; 44:516-20. [PMID: 15558703 DOI: 10.1002/pbc.20274] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Congenital intracranial tumors are extremely rare and account only for 0.5%-1.5% of brain tumors in children. We report a large intrauterine congenital teratoma in a female fetus at gestation weeks 37, which was diagnosed by detecting the tumor and associated craniomegaly with ultrasonography (US) and magnetic resonance (MR) imaging. The tumor had replaced the cerebral hemispheres and produced prenatal manifestations. Pathologic examination showed an immature teratoma, which was differentiated from all three germ layers. Microarray analysis revealed upregulation of ten genes and downregulation of three genes, as well as upregulation of 41 genes of ribosomal proteins in teratoma cells, compared to normal brain tissue of the patient. The data from the microarray analysis offer not only the potential to help define disease pathogenesis but may also provide clues to identify potential molecular therapeutic targets.
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Affiliation(s)
- Kentaro Yokoi
- Department of Pediatrics, Institute of DNA Medicine, Jikei University School of Medicine, Tokyo, Japan
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15
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Knauth P, Schlüter T, Czubayko M, Kirsch C, Florian V, Schreckenberger S, Hahn H, Bohnensack R. Functions of sorting nexin 17 domains and recognition motif for P-selectin trafficking. J Mol Biol 2005; 347:813-25. [PMID: 15769472 DOI: 10.1016/j.jmb.2005.02.004] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2004] [Revised: 01/31/2005] [Accepted: 02/01/2005] [Indexed: 01/16/2023]
Abstract
SNX17 is a member of the sorting nexin family (SNX), a group of hydrophilic proteins whose common characteristic property is a phox homology (PX) domain. The PX domain directs SNXs to phosphatidylinositides containing membranes of the endosomal compartment, where the SNXs are involved in the sorting of transmembrane proteins. SNX17 is known to interact with P-selectin and the LDL receptor family. Here, we report that the PX domain of SNX17 specifically binds to phosphatidylinositol 3-phosphate-containing membranes. The functional part of SNX17 that binds P-selectin or Patched (PTCH) consists of a truncated FERM domain and a unique C terminus together (FC-unit). In a yeast two-hybrid analysis a putative recognition motif for the FC-unit was revealed within P-selectin as FxNaa(F/Y). When HepG2 cells overexpress P-selectin together with SNX17, SNX17 changes its distribution from early endosomes to lysobisphosphatidic acid-containing late endosomes. Furthermore, overexpressed SNX17 restrains P-selectin in the outer membrane of the late endosomal compartment, thus preventing the normal lysosomal accumulation of P-selectin. These results suggest that the PX domain is necessary for the intracellular localisation, while the FC-unit is required for cargo recognition. We hypothesise that the expression level of SNX17 may regulate the lysosomal degradation, at least for P-selectin, by suppressing its entry into the inner vesicles of the multi-vesicular bodies (MVBs).
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Affiliation(s)
- Peter Knauth
- Centro de Investigación y Asistencia en Tecnología y Diseño del Estado de Jalisco (CIATEJ), Av. Normalistas 800, 44270 Guadalajara, México.
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16
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Zhong Q, Watson MJ, Lazar CS, Hounslow AM, Waltho JP, Gill GN. Determinants of the endosomal localization of sorting nexin 1. Mol Biol Cell 2005; 16:2049-57. [PMID: 15673616 PMCID: PMC1073682 DOI: 10.1091/mbc.e04-06-0504] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The sorting nexin (SNX) family of proteins is characterized by sequence-related phox homology (PX) domains. A minority of PX domains bind with high affinity to phosphatidylinositol 3-phosphate [PI(3)P], whereas the majority of PX domains exhibit low affinity that is insufficient to target them to vesicles. SNX1 is located on endosomes, but its low affinity PX domain fails to localize in vivo. The NMR structure of the PX domain of SNX1 reveals an overall fold that is similar to high-affinity PX domains. However, the phosphatidylinositol (PI) binding pocket of the SNX1 PX domain is incomplete; regions of the pocket that are well defined in high-affinity PX domains are highly mobile in SNX1. Some of this mobility is lost upon binding PI(3)P. The C-terminal domain of SNX1 is a long helical dimer that localizes to vesicles but not to the early endosome antigen-1-containing vesicles where endogenous SNX1 resides. Thus, the obligate dimerization of SNX1 that is driven by the C-terminal domain creates a high-affinity PI binding species that properly targets the holo protein to endosomes.
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Affiliation(s)
- Qi Zhong
- Department of Medicine and Cellular, University of California, San Diego, La Jolla, 92093-0650, USA
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17
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Abstract
The sorting nexins (SNXs) are a family of PX domain-containing proteins found in yeast and mammalian cells that have been proposed to regulate intracellular trafficking. Mammalian SNXs have been suggested to function variously in pro-degradative sorting, internalization, endosomal recycling, or simply in endosomal sorting. In yeast, the defining function for these proteins is a regulation of cargo retrieval. Here we examine recent data on the SNX family of proteins and attempt to draw out unifying themes between the work performed in yeast and mammalian systems.
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Affiliation(s)
- Jez Carlton
- Department of Biochemistry, School of Medical Sciences, University Walk, Clifton, Bristol, BS8 1TD, UK
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18
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Merino-Trigo A, Kerr MC, Houghton F, Lindberg A, Mitchell C, Teasdale RD, Gleeson PA. Sorting nexin 5 is localized to a subdomain of the early endosomes and is recruited to the plasma membrane following EGF stimulation. J Cell Sci 2004; 117:6413-24. [PMID: 15561769 DOI: 10.1242/jcs.01561] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Sorting nexins are a large family of proteins that contain the phosphoinositide-binding Phox homology (PX) domain. A number of sorting nexins are known to bind to PtdIns3P, which mediates their localization to membranes of the endocytic pathway. We show here that sorting nexin 5 (SNX5) can be recruited to two distinct membrane compartments. In non-stimulated cells, the PX domain was independently targeted to endosomal structures and colocalized with full-length SNX5. The membrane binding of the PX domain was inhibited by the PI 3-kinase inhibitor, wortmannin. Although SNX5 colocalized with a fluid-phase marker and was found predominantly within a PtdIns3P-rich endosomal domain, very little colocalization was observed between SNX5 and the PtdIns3P-binding protein, EEA1. Using liposome-based binding assays, we have shown that the PX domain of SNX5 interacts not only with PtdIns3P but also with PtdIns3,4P2. In response to EGF stimulation, either the SNX5-PX domain or full-length SNX5 was rapidly recruited to the plasma membrane. The localization of SNX1, which does not bind PtdIns3,4P2, was unaffected by EGF signalling. Therefore, SNX5 is localized to a subdomain of the early endosome distinct from EEA1 and, following EGF stimulation and elevation of PtdIns3,4P2, is also transiently recruited to the plasma membrane. These results indicate that SNX5 may have functions not only associated with endosomal sorting but also with the phosphoinositide-signalling pathway.
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Affiliation(s)
- Ana Merino-Trigo
- The Russell Grimwade School of Biochemistry and Molecular Biology, The University of Melbourne, Melbourne, Victoria, 3010, Australia
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19
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Abstract
Proteins that make, consume, and bind to phosphoinositides are important for constitutive membrane traffic. Different phosphoinositides are concentrated in different parts of the central vacuolar pathway, with phosphatidylinositol 4-phosphate predominate on Golgi, phosphatidylinositol 4,5-bisphosphate predominate at the plasma membrane, phosphatidylinositol 3-phosphate the major phosphoinositide on early endosomes, and phosphatidylinositol 3,5-bisphosphate found on late endocytic organelles. This spatial segregation may be the mechanism by which the direction of membrane traffic is controlled. Phosphoinositides increase the affinity of membranes for peripheral membrane proteins that function for sorting protein cargo or for the docking and fusion of transport vesicles. This implies that constitutive membrane traffic may be regulated by the mechanisms that control the activity of the enzymes that produce and consume phosphoinositides. Although the lipid kinases and phosphatases that function in constitutive membrane traffic are beginning to be identified, their regulation is poorly understood.
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Affiliation(s)
- Michael G Roth
- Dept. of Biochemistry, Univ. of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Blvd., Dallas, TX 75390-9038, USA.
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20
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Williams R, Schlüter T, Roberts MS, Knauth P, Bohnensack R, Cutler DF. Sorting nexin 17 accelerates internalization yet retards degradation of P-selectin. Mol Biol Cell 2004; 15:3095-105. [PMID: 15121882 PMCID: PMC452567 DOI: 10.1091/mbc.e04-02-0143] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The transient appearance of P-selectin on the surface of endothelial cells helps recruit leukocytes into sites of inflammation. The tight control of cell surface P-selectin on these cells depends on regulated exocytosis of Weibel-Palade bodies where the protein is stored and on its rapid endocytosis. After endocytosis, P-selectin is either sorted via endosomes and the Golgi apparatus for storage in Weibel-Palade bodies or targeted to lysosomes for degradation. A potential player in this complex endocytic itinerary is SNX17, a member of the sorting nexin family, which has been shown in a yeast two-hybrid assay to bind P-selectin. Here, we show that overexpression of SNX17 in mammalian cells can influence two key steps in the endocytic trafficking of P-selectin. First, it promotes the endocytosis of P-selectin from the plasma membrane. Second, it inhibits the movement of P-selectin into lysosomes, thereby reducing its degradation.
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Affiliation(s)
- Ross Williams
- MRC Laboratory for Molecular Cell Biology, Cell Biology Unit and Department of Biochemistry and Molecular Biology, University College London, London, United Kingdom
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21
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Abstract
After endocytosis, most membrane proteins and lipids return to the cell surface, but some membrane components are delivered to late endosomes or the Golgi. We now understand that the pathways taken by internalized molecules that eventually recycle to the cell surface can be surprisingly complex and can involve a series of sorting events that occur in several organelles. The molecular basis for many of these sorting processes is only partly understood.
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Affiliation(s)
- Frederick R Maxfield
- Department of Biochemistry, Weill Medical College of Cornell University, 1300 York Avenue, New York, New York 10021, USA.
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22
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Burden JJ, Sun XM, García ABG, Soutar AK. Sorting motifs in the intracellular domain of the low density lipoprotein receptor interact with a novel domain of sorting nexin-17. J Biol Chem 2004; 279:16237-45. [PMID: 14739284 DOI: 10.1074/jbc.m313689200] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The low density lipoprotein (LDL) receptor plays a major role in maintaining human plasma cholesterol levels and mutations in the gene cause familial hypercholesterolemia. The LDL receptor (LDLR) pathway has been well characterized, but little is known of proteins involved in its complex intracellular sorting and trafficking. Sorting nexin 17 (SNX17) has recently been implicated in LDLR intracellular trafficking. We show here that endogenous SNX17 is highly expressed in several cell types and is localized partially in early endosomes. We found that the PX domain of SNX17 is required for its endosomal localization but does not interact directly with the LDL receptor. A novel domain containing a FERM-like domain of SNX17 is needed for its interaction with the LDL receptor. Mutations in the NPXY motif of the LDL-receptor cytoplasmic tail that disrupt internalization also disrupt its interaction with SNX17, whereas mutations elsewhere had little effect. When transiently overexpressed in Chinese hamster ovary cells, SNX17 localized to large vesicular structures and disrupted normal trafficking of the LDL receptor in a PX domain-dependent manner. These results suggest that SNX17 plays a role in the cellular trafficking of the LDL receptor through interaction with the NPVY motif in its cytoplasmic domain and interaction of the PX domain with subcellular membrane compartments.
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Affiliation(s)
- Jemima J Burden
- Lipoprotein Group, Medical Research Council Clinical Sciences Centre, Imperial College School of Medicine, Hammersmith Hospital, Ducane Road, London W12 ONN, United Kingdom
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23
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Birkeland HCG, Stenmark H. Protein targeting to endosomes and phagosomes via FYVE and PX domains. Curr Top Microbiol Immunol 2004; 282:89-115. [PMID: 14594215 DOI: 10.1007/978-3-642-18805-3_4] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Phosphatidylinositol 3-phosphate (PI3P) is generated on early endosomal and phagosomal membranes by PI 3-kinases. This lipid serves important regulatory functions in phagocytosis, endocytic traffic, receptor signalling and microbial killing through the recruitment and activation of a number of effector proteins. Almost all of these effectors contain FYVE or PX domains, functional protein modules which are conserved from yeast to mammals. Structural information is available regarding the binding of FYVE and PX domains to PI3P. The two domains are highly different, but they have in common that clusters of basic residues mediate ligand binding through interactions with the phosphate groups of PI3P. Most proteins that contain FYVE or PX domains serve as regulators of endocytic membrane trafficking, whereas others function as regulators of phagosome maturation, signal transduction, microbial killing and other cellular activities of relevance for the immune system.
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Affiliation(s)
- H C G Birkeland
- Department of Biochemistry, Norwegian Radium Hospital, Montebello, 0310 Oslo, Norway
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24
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Hanson BJ, Hong W. Evidence for a role of SNX16 in regulating traffic between the early and later endosomal compartments. J Biol Chem 2003; 278:34617-30. [PMID: 12813048 DOI: 10.1074/jbc.m300143200] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Sorting nexins (SNXs) are a growing family of proteins characterized by the presence of a PX domain. The PX domain mediates membrane association by interaction with phosphoinositides. The SNXs are generally believed to participate in membrane trafficking, but information regarding the function of individual proteins is limited. In this report, we describe the major characteristics of one member, SNX16. SNX16 is a novel 343-amino acid protein consisting of a central PX domain followed by a potential coiled-coil domain and a C-terminal region. Like other sorting nexins, SNX16 associates with the membrane via the PX domain which interacts with the phospholipid phosphatidylinositol 3-phosphate. We show via biochemical and cellular studies that SNX16 is distributed in both early and late endosome/lysosome structures. The coiled-coil domain is necessary for localization to the later endosomal structures, as mutant SNX16 lacking this domain was found only in early endosomes. Trafficking of internalized epidermal growth factor was also delayed by this SNX16 mutant, as these cells showed a delay in the segregation of epidermal growth factor in the early endosome for its delivery to later compartments. In addition, the coiled-coil domain is shown here to be important for homo-oligomerization of SNX16. Taken together, these results suggest that SNX16 is a sorting nexin that may function in the trafficking of proteins between the early and late endosomal compartments.
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MESH Headings
- Amino Acid Sequence
- Animals
- Blotting, Western
- Carrier Proteins/chemistry
- Carrier Proteins/physiology
- Centrifugation, Density Gradient
- Cloning, Molecular
- DNA, Complementary/metabolism
- Endosomes/metabolism
- Epidermal Growth Factor/metabolism
- Fluorescent Antibody Technique, Indirect
- Glutathione Transferase/metabolism
- Humans
- Lipid Metabolism
- Lysosomes/metabolism
- Membrane Proteins/chemistry
- Membrane Proteins/physiology
- Microscopy, Fluorescence
- Models, Genetic
- Molecular Sequence Data
- Phosphorylation
- Polymerase Chain Reaction
- Precipitin Tests
- Protein Binding
- Protein Structure, Tertiary
- Proteins/metabolism
- RNA, Messenger/metabolism
- Rats
- Sequence Homology, Amino Acid
- Sorting Nexins
- Sucrose/pharmacology
- Tissue Distribution
- Transfection
- Tumor Cells, Cultured
- Vesicular Transport Proteins
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Affiliation(s)
- Brendon J Hanson
- Membrane Biology Laboratory, Institute of Molecular and Cell Biology, Singapore 117609, Singapore
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25
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Abstract
Hereditary spastic paraplegias (HSP) are characterised by symmetric spastic paraplegia, pallhypaesthesia, and urinary dysfunction (uncomplicated HSP). Complicated HSP is present if uncomplicated HSP additionally presents with epilepsy, dementia, cataract, extrapyramidal dysfunction, amyotrophy, polyneuropathy, or ichthyosis. Clinically, HSP are similar but genetically even more heterogeneous. The disease course is slowly progressive and, the earlier the disease onset, the slower the course. Causes of HSP are mutations in 20 different genes, of which eight have been identified so far. A single mutation can cause complicated and uncomplicated HSP. Onset and severity can be quite variable between both groups and within families. Despite molecular genetic advances, diagnosis of HSP still relies on clinical features and the exclusion of various differential diagnoses. Neuropathologically, there is degeneration of corticospinal, posterior column, and spinocerebellar axons. Most likely, degeneration of the longest CNS axons is due to an impaired energy supply of the anterograde and retrograde axonal transport.
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Affiliation(s)
- J Finsterer
- Neurologische Abteilung, Krankenanstalt Rudolfstiftung, Vienna.
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26
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Leprince C, Le Scolan E, Meunier B, Fraisier V, Brandon N, De Gunzburg J, Camonis J. Sorting nexin 4 and amphiphysin 2, a new partnership between endocytosis and intracellular trafficking. J Cell Sci 2003; 116:1937-48. [PMID: 12668730 DOI: 10.1242/jcs.00403] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Endocytosis is a regulated physiological process by which membrane receptors and their extracellular ligands are internalized. After internalization, they enter the endosomal trafficking pathway for sorting and processing. Amphiphysins consist of a family of proteins conserved throughout evolution that are crucial elements of the endocytosis machinery in mammalian cells. They act as adaptors for a series of proteins important for the endocytic process, such as dynamin. In order to improve our knowledge of amphiphysin function, we performed a two-hybrid screen with the N-terminal part of murine amphiphysin 2 (residues 1-304). One of the interacting clones corresponded to sorting nexin 4 (SNX4), a member of the SNX family of proteins which are suspected to regulate vesicular trafficking. This interaction was confirmed in vivo by co-immunoprecipitation. Immunofluorescence analysis revealed that amphiphysin 2 might bind reticulo-vesicular structures present throughout the cell body and be associated with SNX4 on these structures. In an endocytosis assay, overexpressed C-terminal or full-length SNX4 was able to inhibit transferrin receptor endocytosis as efficiently as the SH3 domain of amphiphysin 2. At lower levels of expression, SNX4 colocalized with transferrin-containing vesicles, some of which were also positive for amphiphysin 2. These results indicate that SNX4 may be part of the endocytic machinery or, alternatively, that SNX4 may associate with key elements of endocytosis such as amphiphysin 2 and sequester them when overexpressed. The presence of amphiphysin 2 on intracellular vesicles and its interplay with SNX4, which is likely to take part in intracellular trafficking, suggest that amphiphysin 2 is not only a regulator of the early steps of endocytosis. It could also play a role at the surface of the endocytic vesicle that has just been formed and of the future endosomes, in order to regulate intracellular trafficking.
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Affiliation(s)
- Corinne Leprince
- INSERM U528, Institut Curie Section de Recherche, 26 rue d'Ulm, 75248 Paris Cedex 05, France.
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27
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Zeng W, Yuan W, Wang Y, Jiao W, Zhu Y, Huang C, Li D, Li Y, Zhu C, Wu X, Liu M. Expression of a novel member of sorting nexin gene family, SNX-L, in human liver development. Biochem Biophys Res Commun 2002; 299:542-8. [PMID: 12459172 DOI: 10.1016/s0006-291x(02)02695-5] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The sorting nexin (SNX) protein family is implicated in the regulation of receptor degradation and membrane traffic in the cell. With the aim of identifying novel genes involved in receptor degradation and recycling, we have cloned a new member of the sorting nexin gene family, human sorting nexin L, SNX-L (or SNX21). This gene includes 4 exons and 3 introns, and is located on chromosome 20q12-13.1 region, encompassing 8 kb. The full-length cDNA of SNX-L is 1,811 bp, with an open reading frame of 1,092 bp. The protein consists of 364 amino acids and encodes a 40 kDa protein. The SNX-L protein has a common PX domain shared by all SNX family members. The similarity of SNX-L PX domain to the PX consensus sequence is over 40%. PX domains have been shown to associate with specific phospholipids and membrane compartments. Expression analysis of SNX-L mRNA indicates that SNX-L is distinctly and highly expressed in fetus liver, but only weakly expressed in brain, muscle (skeleton muscle, smooth muscle, and cardiac muscle), kidney, and adrenal gland. Strong liver expression of SNX-L is maintained from 12 to 25 weeks during human fetus development, suggesting that SNX-L may be a regulatory gene involved in receptor protein degradation during embryonic liver development.
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Affiliation(s)
- Weiqi Zeng
- College of Life Sciences, Hunan Normal University, Changsha, 410081 Hunan, People's Republic of China
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28
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Abstract
Sorting nexins are a diverse group of cellular trafficking proteins that are unified by the presence of a phospholipid-binding motif - the PX domain. The ability of these proteins to bind specific phospholipids, as well as their propensity to form protein-protein complexes, points to a role for these proteins in membrane trafficking and protein sorting. It will be interesting to determine whether the various sorting nexins have specialized or generalized roles in protein trafficking.
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Affiliation(s)
- Carolyn A Worby
- Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA.
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29
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Crosby AH, Proukakis C. Is the transportation highway the right road for hereditary spastic paraplegia? Am J Hum Genet 2002; 71:1009-16. [PMID: 12355399 PMCID: PMC385081 DOI: 10.1086/344206] [Citation(s) in RCA: 102] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2002] [Accepted: 07/29/2002] [Indexed: 12/11/2022] Open
Abstract
The term "hereditary spastic paraplegia" (HSP) refers to a genetically and clinically diverse group of disorders whose primary feature is progressive spasticity of the lower extremities. The condition arises because of degeneration of the longest motor and sensory axons on the spinal cord, which appear to be most sensitive to the underlying mutations. The marked genetic heterogeneity in HSP, with 20 loci chromosomally mapped and eight genes now identified, suggests that a number of defective cellular processes may be shown to result in the disease. Although previous studies have suggested a mitochondrial basis for at least one form of the disease, a mechanism common to a number of the other genes mutated in HSP has remained elusive until now. The identification of the most recent genes for the condition suggests that aberrant cellular-trafficking dynamics may be a common process responsible for the specific pattern of neurodegeneration seen in HSP.
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30
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Thomas G. Furin at the cutting edge: from protein traffic to embryogenesis and disease. Nat Rev Mol Cell Biol 2002; 3:753-66. [PMID: 12360192 PMCID: PMC1964754 DOI: 10.1038/nrm934] [Citation(s) in RCA: 893] [Impact Index Per Article: 40.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Furin catalyses a simple biochemical reaction--the proteolytic maturation of proprotein substrates in the secretory pathway. But the simplicity of this reaction belies furin's broad and important roles in homeostasis, as well as in diseases ranging from Alzheimer's disease and cancer to anthrax and Ebola fever. This review summarizes various features of furin--its structural and enzymatic properties, intracellular localization, trafficking, substrates, and roles in vivo.
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Affiliation(s)
- Gary Thomas
- Vollum Institute, 3181 SW Sam Jackson Park Road, Portland, Oregon 97239, USA.
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31
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Patel H, Cross H, Proukakis C, Hershberger R, Bork P, Ciccarelli FD, Patton MA, McKusick VA, Crosby AH. SPG20 is mutated in Troyer syndrome, an hereditary spastic paraplegia. Nat Genet 2002; 31:347-8. [PMID: 12134148 DOI: 10.1038/ng937] [Citation(s) in RCA: 176] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Troyer syndrome (TRS) is an autosomal recessive complicated hereditary spastic paraplegia (HSP) that occurs with high frequency in the Old Order Amish. We report mapping of the TRS locus to chromosome 13q12.3 and identify a frameshift mutation in SPG20, encoding spartin. Comparative sequence analysis indicates that spartin shares similarity with molecules involved in endosomal trafficking and with spastin, a molecule implicated in microtubule interaction that is commonly mutated in HSP.
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Affiliation(s)
- Heema Patel
- Department of Medical Genetics, St. George's Hospital Medical School, University of London, Cranmer Terrace, London SW17 0RE, UK
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32
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Zhong Q, Lazar CS, Tronchère H, Sato T, Meerloo T, Yeo M, Songyang Z, Emr SD, Gill GN. Endosomal localization and function of sorting nexin 1. Proc Natl Acad Sci U S A 2002; 99:6767-72. [PMID: 11997453 PMCID: PMC124477 DOI: 10.1073/pnas.092142699] [Citation(s) in RCA: 123] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2001] [Accepted: 03/12/2002] [Indexed: 11/18/2022] Open
Abstract
There are 17 human members of the sorting nexin (SNX) family of proteins that contain Phox (PX) domains. Yeast orthologs function in vesicular trafficking and mammalian proteins have been implicated in endocytic trafficking of cell surface receptors. The first member of this family, SNX1, was identified via interaction with the epidermal growth factor receptor. The present studies indicate that SNX1 and SNX2 are colocalized to tubulovesicular endosomal membranes and this localization depends on PI 3-kinase activity. Point mutations in the PX domain that abolish recognition of phosphorylated phosphatidylinositol (PtdIns) in vitro abolish vesicle localization in vivo indicating that lipid binding by the PX domain is necessary for localization to vesicle membranes. Deletion of a predicted coiled-coil region in the COOH terminus of SNX1 also abolished vesicle localization, indicating that this helical domain, too, is necessary for SNX1 localization. Thus, both PX domain recognition of PtdIns and COOH terminal helical domains are necessary for localization of SNX1 with neither alone being sufficient. Regulated overexpression of the NH(2) terminus of SNX1 containing the PX domain decreased the rate of ligand-induced epidermal growth factor receptor degradation, an effect consistent with inhibition of endogenous SNX1 function in the endosome compartment. SNX1 thus functions in regulating trafficking in the endosome compartment via PX domain recognition of phosphorylated PtdIns and via interaction with other protein components.
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Affiliation(s)
- Qi Zhong
- Department of Medicine, University of California at San Diego School of Medicine, La Jolla, CA 92093-0650, USA
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33
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Lin Q, Lo CG, Cerione RA, Yang W. The Cdc42 target ACK2 interacts with sorting nexin 9 (SH3PX1) to regulate epidermal growth factor receptor degradation. J Biol Chem 2002; 277:10134-8. [PMID: 11799118 DOI: 10.1074/jbc.m110329200] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Activated Cdc42-associated kinase-2 (ACK2) is a non-receptor tyrosine kinase that serves as a specific effector for Cdc42, a Rho family small G-protein. Recently, we have found that ACK2 directly interacts with clathrin heavy chain through a clathrin-binding motif that is conserved in all endocytic adaptor proteins and regulates clathrin assembly, suggesting that ACK2 plays a role in clathrin-coated vesicle endocytosis (Yang, W., Lo, C. G., Dispenza, T., and Cerione, R. A. (2001) J. Biol. Chem. 276, 17468-17473). Here we report the identification of another binding partner for ACK2 that has previously been implicated in endocytosis, namely the sorting nexin protein SH3PX1 (sorting nexin 9). The interaction occurs between a proline-rich domain of ACK2 and the Src homology 3 domain (SH3) of SH3PX1. Co-immunoprecipitation studies indicate that ACK2, clathrin, and SH3PX1 form a complex in cells. Epidermal growth factor (EGF) stimulated the tyrosine phosphorylation of SH3PX1, whereas co-transfection of ACK2 with SH3PX1 resulted in the constitutive phosphorylation of SH3PX1. However, co-transfection of the kinase-dead mutant ACK2(K158R) with SH3PX1 blocked EGF-induced tyrosine phosphorylation of SH3PX1, indicating that the EGF-stimulated phosphorylation of SH3PX1 is mediated by ACK2. EGF receptor levels were significantly decreased following EGF stimulation of cells co-expressing ACK2 and SH3PX1, thus highlighting a novel role for ACK2, working together with SH3PX1 to promote the degradation of the EGF receptor.
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Affiliation(s)
- Qiong Lin
- Department of Molecular Medicine and Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, USA
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Xu Y, Seet LF, Hanson B, Hong W. The Phox homology (PX) domain, a new player in phosphoinositide signalling. Biochem J 2001; 360:513-30. [PMID: 11736640 PMCID: PMC1222253 DOI: 10.1042/0264-6021:3600513] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Phosphoinositides are key regulators of diverse cellular processes. The pleckstrin homology (PH) domain mediates the action of PtdIns(3,4)P(2), PtdIns(4,5)P(2) and PtdIns(3,4,5)P(3), while the FYVE domain relays the pulse of PtdIns3P. The recent establishment that the Phox homology (PX) domain interacts with PtdIns3P and other phosphoinositides suggests another mechanism by which phosphoinositides can regulate/integrate multiple cellular events via a spectrum of PX domain-containing proteins. Together with the recent discovery that the epsin N-terminal homologue (ENTH) domain interacts with PtdIns(4,5)P(2), it is becoming clear that phosphoinositides regulate diverse cellular events through interactions with several distinct structural motifs present in many different proteins.
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Affiliation(s)
- Y Xu
- Membrane Biology Laboratory, Institute of Molecular and Cell Biology, 30 Medical Drive, Singapore 117609, Singapore
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Corvera S. Phosphatidylinositol 3-kinase and the control of endosome dynamics: new players defined by structural motifs. Traffic 2001; 2:859-66. [PMID: 11737823 DOI: 10.1034/j.1600-0854.2001.21201.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Phosphatidylinositol (PtdIns) 3-kinase (PI 3-kinase) activity has been implicated in fundamental cellular functions such as endosomal trafficking, growth-factor receptor signal transduction, and cell survival. This multiplicity of actions can be attributed to the existence of three classes of PI 3-kinases in mammalian cells, which can together lead to the production of four known distinct end products: PtdIns(3)P, PtdIns(3,4)P2, PtdIns(3,4,5)P3 and PtdIns(3,5)P2. The challenge of deciphering the connection between PI 3-kinase activity, the production of specific phosphoinositides and the control of specific cellular events is being met with the discovery of novel structural motifs that interact specifically with distinct PI 3-kinase products.
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Affiliation(s)
- S Corvera
- Program in Molecular Medicine, University of Massachusetts Medical School, 373 Plantation Street, Worcester, MA 01615, USA.
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Worby CA, Simonson-Leff N, Clemens JC, Kruger RP, Muda M, Dixon JE. The sorting nexin, DSH3PX1, connects the axonal guidance receptor, Dscam, to the actin cytoskeleton. J Biol Chem 2001; 276:41782-9. [PMID: 11546816 DOI: 10.1074/jbc.m107080200] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Dock, an adaptor protein that functions in Drosophila axonal guidance, consists of three tandem Src homology 3 (SH3) domains preceding an SH2 domain. To develop a better understanding of axonal guidance at the molecular level, we used the SH2 domain of Dock to purify a protein complex from fly S2 cells. Five proteins were obtained in pure form from this protein complex. The largest protein in the complex was identified as Dscam (Down syndrome cell adhesion molecule), which was subsequently shown to play a key role in directing neurons of the fly embryo to correct positions within the nervous system (Schmucker, D., Clemens, J. C., Shu, H., Worby, C. A., Xiao, J., Muda, M., Dixon, J. E., and Zipursky, S. L. (2000) Cell 101, 671-684). The smallest protein in this complex (p63) has now been identified. We have named p63 DSH3PX1 because it appears to be the Drosophila orthologue of the human protein known as SH3PX1. DSH3PX1 is comprised of an NH(2)-terminal SH3 domain, an internal PHOX homology (PX) domain, and a carboxyl-terminal coiled-coil region. Because of its PX domain, DSH3PX1 is considered to be a member of a growing family of proteins known collectively as sorting nexins, some of which have been shown to be involved in vesicular trafficking. We demonstrate that DSH3PX1 immunoprecipitates with Dock and Dscam from S2 cell extracts. The domains responsible for the in vitro interaction between DSH3PX1 and Dock were also identified. We further show that DSH3PX1 interacts with the Drosophila orthologue of Wasp, a protein component of actin polymerization machinery, and that DSH3PX1 co-immunoprecipitates with AP-50, the clathrin-coat adapter protein. This evidence places DSH3PX1 in a complex linking cell surface receptors like Dscam to proteins involved in cytoskeletal rearrangements and/or receptor trafficking.
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Affiliation(s)
- C A Worby
- Life Sciences Institute and the Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan 48109-0606, USA
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McCabe JB, Berthiaume LG. N-terminal protein acylation confers localization to cholesterol, sphingolipid-enriched membranes but not to lipid rafts/caveolae. Mol Biol Cell 2001; 12:3601-17. [PMID: 11694592 PMCID: PMC60279 DOI: 10.1091/mbc.12.11.3601] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
When variably fatty acylated N-terminal amino acid sequences were appended to a green fluorescent reporter protein (GFP), chimeric GFPs were localized to different membranes in a fatty acylation-dependent manner. To explore the mechanism of localization, the properties of acceptor membranes and their interaction with acylated chimeric GFPs were analyzed in COS-7 cells. Myristoylated GFPs containing a palmitoylated or polybasic region colocalized with cholesterol and ganglioside GM(1), but not with caveolin, at the plasma membrane and endosomes. A dipalmitoylated GFP chimera colocalized with cholesterol and GM(1) at the plasma membrane and with caveolin in the Golgi region. Acylated GFP chimeras did not cofractionate with low-density caveolin-rich lipid rafts prepared with Triton X-100 or detergent-free methods. All GFP chimeras, but not full-length p62(c-yes) and caveolin, were readily solubilized from membranes with various detergents. These data suggest that, although N-terminal acylation can bring GFP to cholesterol and sphingolipid-enriched membranes, protein-protein interactions are required to localize a given protein to detergent-resistant membranes or caveolin-rich membranes. In addition to restricting acceptor membrane localization, N-terminal fatty acylation could represent an efficient means to enrich the concentration of signaling proteins in the vicinity of detergent-resistant membranes and facilitate protein-protein interactions mediating transfer to a detergent-resistant lipid raft core.
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Affiliation(s)
- J B McCabe
- M.D./Ph.D. Program, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
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Abstract
Organelles in the endocytic pathway are composed of a mosaic of structural and functional regions. These regions consist, at least in part, of specialized protein-lipid domains within the plane of the membrane, or of protein complexes associated with specific membrane lipids. Whereas some of these molecular assemblies can be found in more than one compartment, a given combination seems to be unique to each compartment, indicating that membrane organization might be modular.
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Affiliation(s)
- J Gruenberg
- Department of Biochemistry, University of Geneva, 1211-Geneva-4, Switzerland.
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Rocca A, Lamaze C, Subtil A, Dautry-Varsat A. Involvement of the ubiquitin/proteasome system in sorting of the interleukin 2 receptor beta chain to late endocytic compartments. Mol Biol Cell 2001; 12:1293-301. [PMID: 11359922 PMCID: PMC34584 DOI: 10.1091/mbc.12.5.1293] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Down-regulation of cell surface growth factor receptors plays a key role in the tight control of cellular responses. Recent reports suggest that the ubiquitin system, in addition to participating in degradation by the proteasome of cytosolic and nuclear proteins, might also be involved in the down-regulation of various membrane receptors. We have previously characterized a signal in the cytosolic part of the interleukin 2 receptor beta chain (IL2Rbeta) responsible for its targeting to late endosomes/lysosomes. In this report, the role of the ubiquitin/proteasome system on the intracellular fate of IL2Rbeta was investigated. Inactivation of the cellular ubiquitination machinery in ts20 cells, which express a thermolabile ubiquitin-activating enzyme E1, leads to a significant decrease in the degradation rate of IL2Rbeta, with little effect on its internalization. In addition, we show that a fraction of IL2Rbeta can be monoubiquitinated. Furthermore, mutation of the lysine residues of the cytosolic region of a chimeric receptor carrying the IL2Rbeta targeting signal resulted in a decreased degradation rate. When cells expressing IL2Rbeta were treated either by proteasome or lysosome inhibitors, a significant decrease in receptor degradation was observed. Our data show that ubiquitination is required for the sorting of IL2Rbeta toward degradation. They also indicate that impairment of proteasome function might more generally affect intracellular routing.
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Affiliation(s)
- A Rocca
- Unité de Biologie des Interactions Cellulaires, Unité de Recherche Associée Centre National de la Recherche Scientifique 1960, Institut Pasteur, 75724 Paris Cedex 15, France
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Teasdale RD, Loci D, Houghton F, Karlsson L, Gleeson PA. A large family of endosome-localized proteins related to sorting nexin 1. Biochem J 2001; 358:7-16. [PMID: 11485546 PMCID: PMC1222026 DOI: 10.1042/0264-6021:3580007] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Sorting nexin 1 (SNX1), a peripheral membrane protein, has previously been shown to regulate the cell-surface expression of the human epidermal growth factor receptor [Kurten, Cadena and Gill (1996) Science 272, 1008-1010]. Searches of human expressed sequence tag databases with SNX1 revealed eleven related human cDNA sequences, termed SNX2 to SNX12, eight of them novel. Analysis of SNX1-related sequences in the Saccharomyces cerevisiae genome clearly shows a greatly expanded SNX family in humans in comparison with yeast. On the basis of the predicted protein sequences, all members of this family of hydrophilic molecules contain a conserved 70-110-residue Phox homology (PX) domain, referred to as the SNX-PX domain. Within the SNX family, subgroups were identified on the basis of the sequence similarities of the SNX-PX domain and the overall domain structure of each protein. The members of one subgroup, which includes human SNX1, SNX2, SNX4, SNX5 and SNX6 and the yeast Vps5p and YJL036W, all contain coiled-coil regions within their large C-terminal domains and are found distributed in both membrane and cytosolic fractions, typical of hydrophilic peripheral membrane proteins. Localization of the human SNX1 subgroup members in HeLa cells transfected with the full-length cDNA species revealed a similar intracellular distribution that in all cases overlapped substantially with the early endosome marker, early endosome autoantigen 1. The intracellular localization of deletion mutants and fusions with green fluorescent protein showed that the C-terminal regions of SNX1 and SNX5 are responsible for their endosomal localization. On the basis of these results, the functions of these SNX molecules are likely to be unique to endosomes, mediated in part by interactions with SNX-specific C-terminal sequences and membrane-associated determinants.
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Affiliation(s)
- R D Teasdale
- R.W. Johnson Pharmaceutical Research Institute, 3210 Merryfield Row, San Diego, CA 92121, USA.
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Phillips SA, Barr VA, Haft DH, Taylor SI, Haft CR. Identification and characterization of SNX15, a novel sorting nexin involved in protein trafficking. J Biol Chem 2001; 276:5074-84. [PMID: 11085978 DOI: 10.1074/jbc.m004671200] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Sorting nexins are a family of phox homology domain containing proteins that are homologous to yeast proteins involved in protein trafficking. We have identified a novel 342-amino acid residue sorting nexin, SNX15, and a 252-amino acid splice variant, SNX15A. Unlike many sorting nexins, a SNX15 ortholog has not been identified in yeast or Caenorhabditis elegans. By Northern blot analysis, SNX15 mRNA is widely expressed. Although predicted to be a soluble protein, both endogenous and overexpressed SNX15 are found on membranes and in the cytosol. The phox homology domain of SNX15 is required for its membrane association and for association with the platelet-derived growth factor receptor. We did not detect association of SNX15 with receptors for epidermal growth factor or insulin. However, overexpression of SNX15 led to a decrease in the processing of insulin and hepatocyte growth factor receptors to their mature subunits. Immunofluorescence studies showed that SNX15 overexpression resulted in mislocalization of furin, the endoprotease responsible for cleavage of insulin and hepatocyte growth factor receptors. Based on our data and the existing findings with yeast orthologs of other sorting nexins, we propose that overexpression of SNX15 disrupts the normal trafficking of proteins from the plasma membrane to recycling endosomes or the trans-Golgi network.
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Affiliation(s)
- S A Phillips
- Diabetes Branch, NIDDK/National Institutes of Health, Bethesda, MD 20892, USA
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