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Garbett D, Bisaria A, Yang C, McCarthy DG, Hayer A, Moerner WE, Svitkina TM, Meyer T. T-Plastin reinforces membrane protrusions to bridge matrix gaps during cell migration. Nat Commun 2020; 11:4818. [PMID: 32968060 PMCID: PMC7511357 DOI: 10.1038/s41467-020-18586-3] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2020] [Accepted: 08/19/2020] [Indexed: 12/15/2022] Open
Abstract
Migrating cells move across diverse assemblies of extracellular matrix (ECM) that can be separated by micron-scale gaps. For membranes to protrude and reattach across a gap, actin filaments, which are relatively weak as single filaments, must polymerize outward from adhesion sites to push membranes towards distant sites of new adhesion. Here, using micropatterned ECMs, we identify T-Plastin, one of the most ancient actin bundling proteins, as an actin stabilizer that promotes membrane protrusions and enables bridging of ECM gaps. We show that T-Plastin widens and lengthens protrusions and is specifically enriched in active protrusions where F-actin is devoid of non-muscle myosin II activity. Together, our study uncovers critical roles of the actin bundler T-Plastin to promote protrusions and migration when adhesion is spatially-gapped. In vivo, cells migrate across a diverse landscape of extracellular matrix containing gaps which present a challenge for cells to protrude across. Here, the authors show that T-Plastin strengthens protrusive actin networks to promote protrusion, extracellular matrix gap-bridging, and cell migration.
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Affiliation(s)
- Damien Garbett
- Department of Chemical and Systems Biology, Stanford University, Stanford, CA, USA.
| | - Anjali Bisaria
- Department of Chemical and Systems Biology, Stanford University, Stanford, CA, USA
| | - Changsong Yang
- Department of Biology, University of Pennsylvania, Philadelphia, PA, USA
| | | | - Arnold Hayer
- Department of Chemical and Systems Biology, Stanford University, Stanford, CA, USA.,Department of Biology, McGill University, Montréal, Canada
| | - W E Moerner
- Department of Chemistry, Stanford University, Stanford, CA, USA
| | - Tatyana M Svitkina
- Department of Biology, University of Pennsylvania, Philadelphia, PA, USA
| | - Tobias Meyer
- Department of Chemical and Systems Biology, Stanford University, Stanford, CA, USA. .,Department of Cell and Developmental Biology, Weill Cornell Medicine, New York, NY, USA.
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2
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Bisaria A, Hayer A, Garbett D, Cohen D, Meyer T. Membrane-proximal F-actin restricts local membrane protrusions and directs cell migration. Science 2020; 368:1205-1210. [PMID: 32527825 DOI: 10.1126/science.aay7794] [Citation(s) in RCA: 82] [Impact Index Per Article: 20.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2019] [Revised: 02/24/2020] [Accepted: 04/09/2020] [Indexed: 12/14/2022]
Abstract
Cell migration is driven by local membrane protrusion through directed polymerization of F-actin at the front. However, F-actin next to the plasma membrane also tethers the membrane and thus resists outgoing protrusions. Here, we developed a fluorescent reporter to monitor changes in the density of membrane-proximal F-actin (MPA) during membrane protrusion and cell migration. Unlike the total F-actin concentration, which was high in the front of migrating cells, MPA density was low in the front and high in the back. Back-to-front MPA density gradients were controlled by higher cofilin-mediated turnover of F-actin in the front. Furthermore, nascent membrane protrusions selectively extended outward from areas where MPA density was reduced. Thus, locally low MPA density directs local membrane protrusions and stabilizes cell polarization during cell migration.
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Affiliation(s)
- Anjali Bisaria
- Department of Chemical and Systems Biology, Stanford University School of Medicine, Stanford, CA, USA.
| | - Arnold Hayer
- Department of Chemical and Systems Biology, Stanford University School of Medicine, Stanford, CA, USA
| | - Damien Garbett
- Department of Chemical and Systems Biology, Stanford University School of Medicine, Stanford, CA, USA
| | - Daniel Cohen
- Department of Biology, Stanford University, Stanford, CA, USA
| | - Tobias Meyer
- Department of Chemical and Systems Biology, Stanford University School of Medicine, Stanford, CA, USA. .,Department of Cell and Developmental Biology, Weill Cornell Medical College, New York, NY 10065, USA
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3
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Ponroy Bally B, Farmer WT, Jones EV, Jessa S, Kacerovsky JB, Mayran A, Peng H, Lefebvre JL, Drouin J, Hayer A, Ernst C, Murai KK. Human iPSC-derived Down syndrome astrocytes display genome-wide perturbations in gene expression, an altered adhesion profile, and increased cellular dynamics. Hum Mol Genet 2020; 29:785-802. [PMID: 31943018 PMCID: PMC7104679 DOI: 10.1093/hmg/ddaa003] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2019] [Revised: 12/31/2019] [Accepted: 01/10/2020] [Indexed: 12/15/2022] Open
Abstract
Down syndrome (DS), caused by the triplication of human chromosome 21, leads to significant alterations in brain development and is a major genetic cause of intellectual disability. While much is known about changes to neurons in DS, the effects of trisomy 21 on non-neuronal cells such as astrocytes are poorly understood. Astrocytes are critical for brain development and function, and their alteration may contribute to DS pathophysiology. To better understand the impact of trisomy 21 on astrocytes, we performed RNA-sequencing on astrocytes from newly produced DS human induced pluripotent stem cells (hiPSCs). While chromosome 21 genes were upregulated in DS astrocytes, we found consistent up- and down-regulation of genes across the genome with a strong dysregulation of neurodevelopmental, cell adhesion and extracellular matrix molecules. ATAC (assay for transposase-accessible chromatin)-seq also revealed a global alteration in chromatin state in DS astrocytes, showing modified chromatin accessibility at promoters of cell adhesion and extracellular matrix genes. Along with these transcriptomic and epigenomic changes, DS astrocytes displayed perturbations in cell size and cell spreading as well as modifications to cell-cell and cell-substrate recognition/adhesion, and increases in cellular motility and dynamics. Thus, triplication of chromosome 21 is associated with genome-wide transcriptional, epigenomic and functional alterations in astrocytes that may contribute to altered brain development and function in DS.
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Affiliation(s)
- Blandine Ponroy Bally
- Department of Neurology & Neurosurgery, Brain Repair and Integrative Neuroscience Program, Centre for Research in Neuroscience, Research Institute of the McGill University Health Centre, Montreal, QC H3G 1A4, Canada
| | - W Todd Farmer
- Department of Neurology & Neurosurgery, Brain Repair and Integrative Neuroscience Program, Centre for Research in Neuroscience, Research Institute of the McGill University Health Centre, Montreal, QC H3G 1A4, Canada
| | - Emma V Jones
- Department of Neurology & Neurosurgery, Brain Repair and Integrative Neuroscience Program, Centre for Research in Neuroscience, Research Institute of the McGill University Health Centre, Montreal, QC H3G 1A4, Canada
| | - Selin Jessa
- Department of Neurology & Neurosurgery, Brain Repair and Integrative Neuroscience Program, Centre for Research in Neuroscience, Research Institute of the McGill University Health Centre, Montreal, QC H3G 1A4, Canada
- Quantitative Life Sciences, McGill University, Montreal, QC H3A 2A7, Canada
| | - J Benjamin Kacerovsky
- Department of Neurology & Neurosurgery, Brain Repair and Integrative Neuroscience Program, Centre for Research in Neuroscience, Research Institute of the McGill University Health Centre, Montreal, QC H3G 1A4, Canada
| | - Alexandre Mayran
- Institut de Recherches Cliniques de Montréal (IRCM), Montreal, QC H2W 1R7, Canada
| | - Huashan Peng
- Department of Psychiatry, McGill University, Montreal, QC H4H 1R3, Canada
- Department of Human Genetics, McGill University, Montreal, QC H4H 1R3, Canada
- Douglas Hospital Research Institute, Verdun, QC H4H 1R3, Canada
| | - Julie L Lefebvre
- Department of Molecular Genetics, Program for Neuroscience and Mental Health, Hospital for Sick Children, University of Toronto, Toronto, ON M5G 0A4, Canada
| | - Jacques Drouin
- Institut de Recherches Cliniques de Montréal (IRCM), Montreal, QC H2W 1R7, Canada
| | - Arnold Hayer
- Department of Biology, McGill University, Bellini Life Sciences Complex, Montreal, QC H3G 0B1, Canada
| | - Carl Ernst
- Department of Psychiatry, McGill University, Montreal, QC H4H 1R3, Canada
- Department of Human Genetics, McGill University, Montreal, QC H4H 1R3, Canada
- Douglas Hospital Research Institute, Verdun, QC H4H 1R3, Canada
| | - Keith K Murai
- Department of Neurology & Neurosurgery, Brain Repair and Integrative Neuroscience Program, Centre for Research in Neuroscience, Research Institute of the McGill University Health Centre, Montreal, QC H3G 1A4, Canada
- Quantitative Life Sciences, McGill University, Montreal, QC H3A 2A7, Canada
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4
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Gan L, Seki A, Shen K, Iyer H, Han K, Hayer A, Wollman R, Ge X, Lin JR, Dey G, Talbot WS, Meyer T. The lysosomal GPCR-like protein GPR137B regulates Rag and mTORC1 localization and activity. Nat Cell Biol 2019; 21:614-626. [PMID: 31036939 PMCID: PMC6649673 DOI: 10.1038/s41556-019-0321-6] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2017] [Accepted: 03/27/2019] [Indexed: 12/13/2022]
Abstract
Cell growth is controlled by a lysosomal signaling complex containing Rag small GTPases and mTORC1 kinase. Here we carried out a microscopy-based genome-wide human siRNA screen and discovered a lysosome-localized G-protein coupled receptor (GPCR)-like protein, GPR137B, that interacts with Rag GTPases, increases Rag localization and activity, and thereby regulates mTORC1 translocation and activity. High GPR137B expression can recruit and activate mTORC1 in the absence of amino acids. Furthermore, GPR137B also regulates the dissociation of activated Rag from lysosomes, suggesting that GPR137B controls a cycle of Rag activation and dissociation from lysosomes. GPR137B knockout cells exhibited defective autophagy and an expanded lysosome compartment, similar to Rag knockout cells. Like zebrafish RagA mutants, GPR137B mutant zebrafish had upregulated TFEB target gene expression and an expanded lysosome compartment in microglia. Thus, GPR137B is a GPCR-like lysosomal regulatory protein that controls dynamic Rag and mTORC1 localization and activity as well as lysosome morphology.
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Affiliation(s)
- Lin Gan
- Department of Chemical and Systems Biology, Stanford University, Stanford, CA, USA
| | - Akiko Seki
- Department of Chemical and Systems Biology, Stanford University, Stanford, CA, USA
| | - Kimberle Shen
- Department of Developmental Biology, Stanford University, Stanford, CA, USA
| | - Harini Iyer
- Department of Developmental Biology, Stanford University, Stanford, CA, USA
| | - Kyuho Han
- Department of Chemical and Systems Biology, Stanford University, Stanford, CA, USA
| | - Arnold Hayer
- Department of Chemical and Systems Biology, Stanford University, Stanford, CA, USA
| | - Roy Wollman
- Department of Integrative Biology and Physiology and Department of Chemistry and Biochemistry, University of California, Los Angeles, CA, USA
| | - Xuecai Ge
- Department of Chemical and Systems Biology, Stanford University, Stanford, CA, USA
| | - Jerry R Lin
- Department of Chemical and Systems Biology, Stanford University, Stanford, CA, USA
| | - Gautam Dey
- Department of Chemical and Systems Biology, Stanford University, Stanford, CA, USA
| | - William S Talbot
- Department of Developmental Biology, Stanford University, Stanford, CA, USA
| | - Tobias Meyer
- Department of Chemical and Systems Biology, Stanford University, Stanford, CA, USA.
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5
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Hayer A, Shao L, Chung M, Joubert LM, Yang HW, Tsai FC, Bisaria A, Betzig E, Meyer T. Engulfed cadherin fingers are polarized junctional structures between collectively migrating endothelial cells. Nat Cell Biol 2016; 18:1311-1323. [PMID: 27842057 DOI: 10.1038/ncb3438] [Citation(s) in RCA: 161] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2015] [Accepted: 10/11/2016] [Indexed: 12/11/2022]
Abstract
The development and maintenance of tissues requires collective cell movement, during which neighbouring cells coordinate the polarity of their migration machineries. Here, we ask how polarity signals are transmitted from one cell to another across symmetrical cadherin junctions, during collective migration. We demonstrate that collectively migrating endothelial cells have polarized VE-cadherin-rich membrane protrusions, 'cadherin fingers', which leading cells extend from their rear and follower cells engulf at their front, thereby generating opposite membrane curvatures and asymmetric recruitment of curvature-sensing proteins. In follower cells, engulfment of cadherin fingers occurs along with the formation of a lamellipodia-like zone with low actomyosin contractility, and requires VE-cadherin/catenin complexes and Arp2/3-driven actin polymerization. Lateral accumulation of cadherin fingers in follower cells precedes turning, and increased actomyosin contractility can initiate cadherin finger extension as well as engulfment by a neighbouring cell, to promote follower behaviour. We propose that cadherin fingers serve as guidance cues that direct collective cell migration.
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Affiliation(s)
- Arnold Hayer
- Department of Chemical and Systems Biology, Stanford University School of Medicine, Stanford, California 94305, USA
| | - Lin Shao
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, Virginia 20147, USA
| | - Mingyu Chung
- Department of Chemical and Systems Biology, Stanford University School of Medicine, Stanford, California 94305, USA
| | - Lydia-Marie Joubert
- Cell Sciences Imaging Facility, Stanford University School of Medicine, Stanford, California 94305, USA
| | - Hee Won Yang
- Department of Chemical and Systems Biology, Stanford University School of Medicine, Stanford, California 94305, USA
| | - Feng-Chiao Tsai
- Department of Chemical and Systems Biology, Stanford University School of Medicine, Stanford, California 94305, USA
| | - Anjali Bisaria
- Department of Chemical and Systems Biology, Stanford University School of Medicine, Stanford, California 94305, USA
| | - Eric Betzig
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, Virginia 20147, USA
| | - Tobias Meyer
- Department of Chemical and Systems Biology, Stanford University School of Medicine, Stanford, California 94305, USA
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6
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Malmersjö S, Di Palma S, Diao J, Lai Y, Pfuetzner RA, Wang AL, McMahon MA, Hayer A, Porteus M, Bodenmiller B, Brunger AT, Meyer T. Phosphorylation of residues inside the SNARE complex suppresses secretory vesicle fusion. EMBO J 2016; 35:1810-21. [PMID: 27402227 PMCID: PMC5010044 DOI: 10.15252/embj.201694071] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2016] [Accepted: 06/09/2016] [Indexed: 12/22/2022] Open
Abstract
Membrane fusion is essential for eukaryotic life, requiring SNARE proteins to zipper up in an α‐helical bundle to pull two membranes together. Here, we show that vesicle fusion can be suppressed by phosphorylation of core conserved residues inside the SNARE domain. We took a proteomics approach using a PKCB knockout mast cell model and found that the key mast cell secretory protein VAMP8 becomes phosphorylated by PKC at multiple residues in the SNARE domain. Our data suggest that VAMP8 phosphorylation reduces vesicle fusion in vitro and suppresses secretion in living cells, allowing vesicles to dock but preventing fusion with the plasma membrane. Markedly, we show that the phosphorylation motif is absent in all eukaryotic neuronal VAMPs, but present in all other VAMPs. Thus, phosphorylation of SNARE domains is a general mechanism to restrict how much cells secrete, opening the door for new therapeutic strategies for suppression of secretion.
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Affiliation(s)
- Seth Malmersjö
- Department of Chemical and Systems Biology, Stanford University, Stanford, CA, USA
| | - Serena Di Palma
- Institute of Molecular Life Sciences, University of Zurich, Zurich, Switzerland Functional Genomics Center Zurich, ETH Zurich/University of Zurich, Zurich, Switzerland
| | - Jiajie Diao
- Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Photon Science, and Structural Biology, Stanford University, Stanford, CA, USA Howard Hughes Medical Institute, Stanford, CA, USA
| | - Ying Lai
- Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Photon Science, and Structural Biology, Stanford University, Stanford, CA, USA Howard Hughes Medical Institute, Stanford, CA, USA
| | - Richard A Pfuetzner
- Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Photon Science, and Structural Biology, Stanford University, Stanford, CA, USA Howard Hughes Medical Institute, Stanford, CA, USA
| | - Austin L Wang
- Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Photon Science, and Structural Biology, Stanford University, Stanford, CA, USA Howard Hughes Medical Institute, Stanford, CA, USA
| | - Moira A McMahon
- Department of Pediatrics, Stanford University, Stanford, CA, USA
| | - Arnold Hayer
- Department of Chemical and Systems Biology, Stanford University, Stanford, CA, USA
| | - Matthew Porteus
- Department of Pediatrics, Stanford University, Stanford, CA, USA
| | - Bernd Bodenmiller
- Institute of Molecular Life Sciences, University of Zurich, Zurich, Switzerland
| | - Axel T Brunger
- Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Photon Science, and Structural Biology, Stanford University, Stanford, CA, USA Howard Hughes Medical Institute, Stanford, CA, USA
| | - Tobias Meyer
- Department of Chemical and Systems Biology, Stanford University, Stanford, CA, USA
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7
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Rengarajan M, Hayer A, Theriot JA. Endothelial Cells Use a Formin-Dependent Phagocytosis-Like Process to Internalize the Bacterium Listeria monocytogenes. PLoS Pathog 2016; 12:e1005603. [PMID: 27152864 PMCID: PMC4859537 DOI: 10.1371/journal.ppat.1005603] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2015] [Accepted: 04/06/2016] [Indexed: 01/11/2023] Open
Abstract
Vascular endothelial cells act as gatekeepers that protect underlying tissue from blood-borne toxins and pathogens. Nevertheless, endothelial cells are able to internalize large fibrin clots and apoptotic debris from the bloodstream, although the precise mechanism of such phagocytosis-like uptake is unknown. We show that cultured primary human endothelial cells (HUVEC) internalize both pathogenic and non-pathogenic Listeria bacteria comparably, in a phagocytosis-like process. In contrast with previously studied host cell types, including intestinal epithelial cells and hepatocytes, we find that endothelial internalization of Listeria is independent of all known pathogenic bacterial surface proteins. Consequently, we exploited the internalization and intracellular replication of L. monocytogenes to identify distinct host cell factors that regulate phagocytosis-like uptake in HUVEC. Using siRNA screening and subsequent genetic and pharmacologic perturbations, we determined that endothelial infectivity was modulated by cytoskeletal proteins that normally modulate global architectural changes, including phosphoinositide-3-kinase, focal adhesions, and the small GTPase Rho. We found that Rho kinase (ROCK) is acutely necessary for adhesion of Listeria to endothelial cells, whereas the actin-nucleating formins FHOD1 and FMNL3 specifically regulate internalization of bacteria as well as inert beads, demonstrating that formins regulate endothelial phagocytosis-like uptake independent of the specific cargo. Finally, we found that neither ROCK nor formins were required for macrophage phagocytosis of L. monocytogenes, suggesting that endothelial cells have distinct requirements for bacterial internalization from those of classical professional phagocytes. Our results identify a novel pathway for L. monocytogenes uptake by human host cells, indicating that this wily pathogen can invade a variety of tissues by using a surprisingly diverse suite of distinct uptake mechanisms that operate differentially in different host cell types.
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Affiliation(s)
- Michelle Rengarajan
- Department of Biochemistry, Stanford University School of Medicine, Stanford, California, United States of America
| | - Arnold Hayer
- Department of Chemical and Systems Biology, Stanford University School of Medicine, Stanford, California, United States of America
| | - Julie A. Theriot
- Department of Biochemistry, Stanford University School of Medicine, Stanford, California, United States of America
- Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, California, United States of America
- Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, California, United States of America
- * E-mail:
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8
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Ritz D, Vuk M, Kirchner P, Bug M, Schütz S, Hayer A, Bremer S, Lusk C, Baloh RH, Lee H, Glatter T, Gstaiger M, Aebersold R, Weihl CC, Meyer H. Endolysosomal sorting of ubiquitylated caveolin-1 is regulated by VCP and UBXD1 and impaired by VCP disease mutations. Nat Cell Biol 2011; 13:1116-23. [PMID: 21822278 DOI: 10.1038/ncb2301] [Citation(s) in RCA: 175] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2011] [Accepted: 06/21/2011] [Indexed: 12/12/2022]
Abstract
The AAA-ATPase VCP (also known as p97) cooperates with distinct cofactors to process ubiquitylated proteins in different cellular pathways. VCP missense mutations cause a systemic degenerative disease in humans, but the molecular pathogenesis is unclear. We used an unbiased mass spectrometry approach and identified a VCP complex with the UBXD1 cofactor, which binds to the plasma membrane protein caveolin-1 (CAV1) and whose formation is specifically disrupted by disease-associated mutations. We show that VCP-UBXD1 targets mono-ubiquitylated CAV1 in SDS-resistant high-molecular-weight complexes on endosomes, which are en route to degradation in endolysosomes. Expression of VCP mutant proteins, chemical inhibition of VCP, or siRNA-mediated depletion of UBXD1 leads to a block of CAV1 transport at the limiting membrane of enlarged endosomes in cultured cells. In patient muscle, muscle-specific caveolin-3 accumulates in sarcoplasmic pools and specifically delocalizes from the sarcolemma. These results extend the cellular functions of VCP to mediating sorting of ubiquitylated cargo in the endocytic pathway and indicate that impaired trafficking of caveolin may contribute to pathogenesis in individuals with VCP mutations.
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Affiliation(s)
- Danilo Ritz
- Centre for Medical Biotechnology, University of Duisburg-Essen, 45117 Essen, Germany
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9
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Abstract
Although bovine pancreatic RNase is one of the best characterized proteins in respect to structure and in vitro refolding, little is known about its synthesis and maturation in the endoplasmic reticulum (ER) of live cells. We expressed the RNase in live cells and analyzed its folding, quality control, and secretion using pulse-chase analysis and other cell biological techniques. In contrast to the slow in vitro refolding, the protein folded almost instantly after translation and translocation into the ER lumen (t½ < 3 min). Despite high stability of the native protein, only about half of the RNase reached a secretion competent, monomeric form and was rapidly transported from the rough ER via the Golgi complex (t½ = 16 min) to the extracellular space (t½ = 35 min). The rest remained in the ER mainly in the form of dimers and was slowly degraded. The dimers were most likely formed by C-terminal domain swapping since mutation of Asn113, a residue that stabilizes such dimers, to Ser increased the efficiency of secretion from 59 to 75%. Consistent with stringent ER quality control in vivo, the secreted RNase in the bovine pancreas was mainly monomeric, whereas the enzyme present in the cells also contained 20% dimers. These results suggest that the efficiency of secretion is not only determined by the stability of the native protein but by multiple factors including the stability of secretion-incompetent side products of folding. The presence of N-glycans had little effect on the folding and secretion process.
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Affiliation(s)
- Roger Geiger
- Institute of Biochemistry, ETH Zürich, 8093 Zürich, Switzerland
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10
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Hayer A, Stoeber M, Ritz D, Engel S, Meyer HH, Helenius A. Caveolin-1 is ubiquitinated and targeted to intralumenal vesicles in endolysosomes for degradation. ACTA ACUST UNITED AC 2010; 191:615-29. [PMID: 21041450 PMCID: PMC3003328 DOI: 10.1083/jcb.201003086] [Citation(s) in RCA: 228] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Identification of the pathway by which caveolin-1 is degraded when caveolae assembly is compromised suggests that “caveosomes” may be endosomal accumulations of the protein awaiting degradation. Caveolae are long-lived plasma membrane microdomains composed of caveolins, cavins, and a cholesterol-rich membrane. Little is known about how caveolae disassemble and how their coat components are degraded. We studied the degradation of caveolin-1 (CAV1), a major caveolar protein, in CV1 cells. CAV1 was degraded very slowly, but turnover could be accelerated by compromising caveolae assembly. Now, CAV1 became detectable in late endosomes (LE) and lysosomes where it was degraded. Targeting to the degradative pathway required ubiquitination and the endosomal sorting complex required for transport (ESCRT) machinery for inclusion into intralumenal vesicles in endosomes. A dual-tag strategy allowed us to monitor exposure of CAV1 to the acidic lumen of individual, maturing LE in living cells. Importantly, we found that “caveosomes,” previously described by our group as independent organelles distinct from endosomes, actually correspond to late endosomal compartments modified by the accumulation of overexpressed CAV1 awaiting degradation. The findings led us to a revised model for endocytic trafficking of CAV1.
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Affiliation(s)
- Arnold Hayer
- Institute of Biochemistry, ETH Zurich, Zurich, Switzerland
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11
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Abstract
We analyzed the assembly of caveolae in CV1 cells by following the fate of newly synthesized caveolin-1 (CAV1), caveolin-2 and polymerase I and transcript release factor (PTRF)/cavin-1 biochemically and using live-cell imaging. Immediately after synthesis in the endoplasmic reticulum (ER), CAV1 assembled into 8S complexes that concentrated in ER exit sites, due to a DXE sequence in the N-terminal domain. The coat protein II (COPII) machinery allowed rapid transport to the Golgi complex. Accumulating in the medial Golgi, the caveolins lost their diffusional mobility, underwent conformational changes, associated with cholesterol, and eventually assembled into 70S complexes. Together with green fluorescent protein-glycosyl-phosphatidylinositol (GFP-GPI), the newly assembled caveolin scaffolds underwent transport to the plasma membrane in vesicular carriers distinct from those containing vesicular stomatitis virus (VSV) G-protein. After arrival, PTRF/cavin-1 was recruited to the caveolar domains over a period of 25 min or longer. PTRF/cavin-1 itself was present in 60S complexes that also formed in the absence of CAV1. Our study showed the existence of two novel large complexes containing caveolar coat components, and identified a hierarchy of events required for caveolae assembly occurring stepwise in three distinct locations--the ER, the Golgi complex and the plasma membrane.
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Affiliation(s)
- Arnold Hayer
- ETH Zurich, Institute of Biochemistry, HPM, 8093 Zurich, Switzerland
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12
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Abstract
We present a computational particle method for the simulation of isotropic and anisotropic diffusion on curved biological surfaces that have been reconstructed from image data. The method is capable of handling surfaces of high curvature and complex shape, which are often encountered in biology. The method is validated on simple benchmark problems and is shown to be second-order accurate in space and time and of high parallel efficiency. It is applied to simulations of diffusion on the membrane of endoplasmic reticula (ER) in live cells. Diffusion simulations are conducted on geometries reconstructed from real ER samples and are compared to fluorescence recovery after photobleaching experiments in the same ER samples using the transmembrane protein tsO45-VSV-G, C-terminally tagged with green fluorescent protein. Such comparisons allow derivation of geometry-corrected molecular diffusion constants for membrane components from fluorescence recovery after photobleaching data. The results of the simulations indicate that the diffusion behavior of molecules in the ER membrane differs significantly from the volumetric diffusion of soluble molecules in the lumen of the same ER. The apparent speed of recovery differs by a factor of approximately 4, even when the molecular diffusion constants of the two molecules are identical. In addition, the specific shape of the membrane affects the recovery half-time, which is found to vary by a factor of approximately 2 in different ER samples.
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Affiliation(s)
- Ivo F Sbalzarini
- Institute of Computational Science, and Institute of Biochemistry, ETH Zürich, Switzerland
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13
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Tagawa A, Mezzacasa A, Hayer A, Longatti A, Pelkmans L, Helenius A. Assembly and trafficking of caveolar domains in the cell: caveolae as stable, cargo-triggered, vesicular transporters. ACTA ACUST UNITED AC 2005; 170:769-79. [PMID: 16129785 PMCID: PMC2171342 DOI: 10.1083/jcb.200506103] [Citation(s) in RCA: 206] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Using total internal reflection fluorescence microscopy (TIR-FM), fluorescence recovery after photobleaching (FRAP), and other light microscopy techniques, we analyzed the dynamics, the activation, and the assembly of caveolae labeled with fluorescently tagged caveolin-1 (Cav1). We found that when activated by simian virus 40 (SV40), a non-enveloped DNA virus that uses caveolae for cell entry, the fraction of mobile caveolae was dramatically enhanced both in the plasma membrane (PM) and in the caveosome, an intracellular organelle that functions as an intermediate station in caveolar endocytosis. Activation also resulted in increased microtubule (MT)-dependent, long-range movement of caveolar vesicles. We generated heterokaryons that contained GFP- and RFP-tagged caveolae by fusing cells expressing Cav1-GFP and -RFP, respectively, and showed that even when activated, individual caveolar domains underwent little exchange of Cav1. Only when the cells were subjected to transient cholesterol depletion, did the caveolae domain exchange Cav1. Thus, in contrast to clathrin-, or other types of coated transport vesicles, caveolae constitute stable, cholesterol-dependent membrane domains that can serve as fixed containers through vesicle traffic. Finally, we identified the Golgi complex as the site where newly assembled caveolar domains appeared first.
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Affiliation(s)
- Akiko Tagawa
- Swiss Federal Institute of Technology (ETH) Zürich, ETH-Hönggerberg, 8093 Zürich, Switzerland
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Abstract
Changes in the synaptic connection strengths between neurons are believed to play a role in memory formation. An important mechanism for changing synaptic strength is through movement of neurotransmitter receptors and regulatory proteins to and from the synapse. Several activity-triggered biochemical events control these movements. Here we use computer models to explore how these putative memory-related changes can be stabilised long after the initial trigger, and beyond the lifetime of synaptic molecules. We base our models on published biochemical data and experiments on the activity-dependent movement of a glutamate receptor, AMPAR, and a calcium-dependent kinase, CaMKII. We find that both of these molecules participate in distinct bistable switches. These simulated switches are effective for long periods despite molecular turnover and biochemical fluctuations arising from the small numbers of molecules in the synapse. The AMPAR switch arises from a novel self-recruitment process where the presence of sufficient receptors biases the receptor movement cycle to insert still more receptors into the synapse. The CaMKII switch arises from autophosphorylation of the kinase. The switches may function in a tightly coupled manner, or relatively independently. The latter case leads to multiple stable states of the synapse. We propose that similar self-recruitment cycles may be important for maintaining levels of many molecules that undergo regulated movement, and that these may lead to combinatorial possible stable states of systems like the synapse. One of the key cellular changes that accompanies memory formation is a change in the efficacy of synaptic connections between nerve cells. Such changes may arise from long-lasting changes in the number of receptor ion channels at the synapse, and also from changes in their conductance. The authors ask how the cell maintains these changes despite molecular turnover, traffic, and biochemical noise. They use computer simulations as an “in silico” microscope to extrapolate biochemical and light microscopy measurements down to sub-synaptic volumes. Based on these computer models, the authors propose that there is a self-sustaining switch involving the movement of receptors (AMPA receptors) to and from the synaptic membrane. The switch works because the presence of sufficient receptors at the membrane biases the trafficking machinery to recruit still more receptors. This switch has suggestive parallels with experimental observations of the conversion of synapses from silent to active, which involves AMPA receptor insertion. The authors show that yet more conductance states may arise through interactions with a biochemical switch involving a synaptic kinase (CaMKII). This receptor switch illustrates how the cell may harness molecular turnover and traffic to maintain, rather than wash out, cellular structures and states.
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Affiliation(s)
- Arnold Hayer
- National Centre for Biological Sciences, Bangalore, India
- École Supérieure de Biotechnologie de Strasbourg, Strasbourg, France
| | - Upinder S Bhalla
- National Centre for Biological Sciences, Bangalore, India
- *To whom correspondence should be addressed. E-mail:
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Affiliation(s)
- A. Hayer
- Institut für Physikalische-, Kern- und Makromolekulare Chemie und Wissenschaftliches Zentrum für Materialwissenschaften, Philipps-Universität Marburg, Hans-Meerwein-Strasse, 35032 Marburg, Germany, and Institut für Dünnschichttechnologie und Mikrosensorik Teltow, Kantstrasse 55, D-14513 Teltow, Germany, and Institut für Physik, Lehrstuhl Physik kondensierter Materie, Universität Potsdam, Am Neuen Palais 10, 14469 Potsdam, Germany
| | - Bässler
- Institut für Physikalische-, Kern- und Makromolekulare Chemie und Wissenschaftliches Zentrum für Materialwissenschaften, Philipps-Universität Marburg, Hans-Meerwein-Strasse, 35032 Marburg, Germany, and Institut für Dünnschichttechnologie und Mikrosensorik Teltow, Kantstrasse 55, D-14513 Teltow, Germany, and Institut für Physik, Lehrstuhl Physik kondensierter Materie, Universität Potsdam, Am Neuen Palais 10, 14469 Potsdam, Germany
| | - B. Falk
- Institut für Physikalische-, Kern- und Makromolekulare Chemie und Wissenschaftliches Zentrum für Materialwissenschaften, Philipps-Universität Marburg, Hans-Meerwein-Strasse, 35032 Marburg, Germany, and Institut für Dünnschichttechnologie und Mikrosensorik Teltow, Kantstrasse 55, D-14513 Teltow, Germany, and Institut für Physik, Lehrstuhl Physik kondensierter Materie, Universität Potsdam, Am Neuen Palais 10, 14469 Potsdam, Germany
| | - S. Schrader
- Institut für Physikalische-, Kern- und Makromolekulare Chemie und Wissenschaftliches Zentrum für Materialwissenschaften, Philipps-Universität Marburg, Hans-Meerwein-Strasse, 35032 Marburg, Germany, and Institut für Dünnschichttechnologie und Mikrosensorik Teltow, Kantstrasse 55, D-14513 Teltow, Germany, and Institut für Physik, Lehrstuhl Physik kondensierter Materie, Universität Potsdam, Am Neuen Palais 10, 14469 Potsdam, Germany
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Hu Z, Kaindl G, Hayer A, Reinen D. Kantennahe Röntgenfeinstruktur-Untersuchungen an Oxidkeramiken von Chrom, Cobalt und Nickel in verschiedenen Oxidationsstufen und deren bindungschemische Interpretation. Z Anorg Allg Chem 2001. [DOI: 10.1002/1521-3749(200112)627:12%3c2647::aid-zaac2647%3e3.0.co;2-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Hu Z, Kaindl G, Hayer A, Reinen D. Kantennahe Röntgenfeinstruktur-Untersuchungen an Oxidkeramiken von Chrom, Cobalt und Nickel in verschiedenen Oxidationsstufen und deren bindungschemische Interpretation. Z Anorg Allg Chem 2001. [DOI: 10.1002/1521-3749(200112)627:12<2647::aid-zaac2647>3.0.co;2-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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