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Role of the Endocytosis of Caveolae in Intracellular Signaling and Metabolism. PROGRESS IN MOLECULAR AND SUBCELLULAR BIOLOGY 2019; 57:203-234. [PMID: 30097777 DOI: 10.1007/978-3-319-96704-2_8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Caveolae are 60-80 nm invaginated plasma membrane (PM) nanodomains, with a specific lipid and protein composition, which assist and regulate multiple processes in the plasma membrane-ranging from the organization of signalling complexes to the mechanical adaptation to changes in PM tension. However, since their initial descriptions, these structures have additionally been found tightly linked to internalization processes, mechanoadaptation, to the regulation of signalling events and of endosomal trafficking. Here, we review caveolae biology from this perspective, and its implications for cell physiology and disease.
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52
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Mendoza-Topaz C, Yeow I, Riento K, Nichols BJ. BioID identifies proteins involved in the cell biology of caveolae. PLoS One 2018; 13:e0209856. [PMID: 30589899 PMCID: PMC6307745 DOI: 10.1371/journal.pone.0209856] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2018] [Accepted: 12/12/2018] [Indexed: 01/20/2023] Open
Abstract
The mechanisms controlling the abundance and sub-cellular distribution of caveolae are not well described. A first step towards determining such mechanisms would be identification of relevant proteins that interact with known components of caveolae. Here, we applied proximity biotinylation (BioID) to identify a list of proteins that may interact with the caveolar protein cavin1. Screening of these candidates using siRNA to reduce their expression revealed that one of them, CSDE1, regulates the levels of mRNAs and protein expression for multiple components of caveolae. A second candidate, CD2AP, co-precipitated with cavin1. Caveolar proteins were observed in characteristic and previously un-described linear arrays adjacent to cell-cell junctions in both MDCK cells, and in HeLa cells overexpressing an active form of the small GTPase Rac1. CD2AP was required for the recruitment of caveolar proteins to these linear arrays. We conclude that BioID will be useful in identification of new proteins involved in the cell biology of caveolae, and that interaction between CD2AP and cavin1 may have an important role in regulating the sub-cellular distribution of caveolae.
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Affiliation(s)
| | - I. Yeow
- MRC Laboratory of Molecular Biology, Cambridge, United Kingdom
| | - K. Riento
- MRC Laboratory of Molecular Biology, Cambridge, United Kingdom
| | - B. J. Nichols
- MRC Laboratory of Molecular Biology, Cambridge, United Kingdom
- * E-mail:
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53
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Mendoza-Topaz C, Nelson G, Howard G, Hafner S, Rademacher P, Frick M, Nichols BJ. Cells respond to deletion of CAV1 by increasing synthesis of extracellular matrix. PLoS One 2018; 13:e0205306. [PMID: 30346954 PMCID: PMC6197626 DOI: 10.1371/journal.pone.0205306] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2018] [Accepted: 09/21/2018] [Indexed: 12/21/2022] Open
Abstract
A range of cellular functions have been attributed to caveolae, flask-like invaginations of the plasma membrane. Here, we have used RNA-seq to achieve quantitative transcriptional profiling of primary embryonic fibroblasts from caveolin 1 knockout mice (CAV1-/- MEFs), and thereby to gain hypothesis-free insight into how these cells respond to the absence of caveolae. Components of the extracellular matrix were decisively over-represented within the set of genes displaying altered expression in CAV1-/- MEFs when compared to congenic wild-type controls. This was confirmed biochemically and by imaging for selected examples. Up-regulation of components of the extracellular matrix was also observed in a second cell line, NIH-3T3 cells genome edited to delete CAV1. Up-regulation of components of the extracellular matrix was detected in vivo by assessing collagen deposition and compliance of CAV1-/- lungs. We discuss the implications of these findings in terms of the cellular function of caveolae.
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Affiliation(s)
- C. Mendoza-Topaz
- Medical Research Council Laboratory of Molecular Biology, Cambridge, United Kingdom
| | - G. Nelson
- Medical Research Council Laboratory of Molecular Biology, Cambridge, United Kingdom
| | - G. Howard
- Medical Research Council Laboratory of Molecular Biology, Cambridge, United Kingdom
| | - S. Hafner
- Institute of Pathophysiological Anesthesiology and Process Engineering, University of Ulm, Ulm, Germany
| | - P. Rademacher
- Institute of Pathophysiological Anesthesiology and Process Engineering, University of Ulm, Ulm, Germany
| | - M. Frick
- Institute of General Physiology, University of Ulm, Ulm, Germany
| | - B. J. Nichols
- Medical Research Council Laboratory of Molecular Biology, Cambridge, United Kingdom
- * E-mail:
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54
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Abstract
The plasma membrane of eukaryotic cells is not a simple sheet of lipids and proteins but is differentiated into subdomains with crucial functions. Caveolae, small pits in the plasma membrane, are the most abundant surface subdomains of many mammalian cells. The cellular functions of caveolae have long remained obscure, but a new molecular understanding of caveola formation has led to insights into their workings. Caveolae are formed by the coordinated action of a number of lipid-interacting proteins to produce a microdomain with a specific structure and lipid composition. Caveolae can bud from the plasma membrane to form an endocytic vesicle or can flatten into the membrane to help cells withstand mechanical stress. The role of caveolae as mechanoprotective and signal transduction elements is reviewed in the context of disease conditions associated with caveola dysfunction.
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Affiliation(s)
- Robert G. Parton
- Institute for Molecular Bioscience and Centre for Microscopy and Microanalysis, University of Queensland, Brisbane, Queensland 4060, Australia
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55
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Trávez A, Rabanal-Ruiz Y, López-Alcalá J, Molero-Murillo L, Díaz-Ruiz A, Guzmán-Ruiz R, Catalán V, Rodríguez A, Frühbeck G, Tinahones FJ, Gasman S, Vitale N, Jiménez-Gómez Y, Malagón MM. The caveolae-associated coiled-coil protein, NECC2, regulates insulin signalling in Adipocytes. J Cell Mol Med 2018; 22:5648-5661. [PMID: 30160359 PMCID: PMC6201366 DOI: 10.1111/jcmm.13840] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2017] [Revised: 07/10/2018] [Accepted: 07/13/2018] [Indexed: 02/06/2023] Open
Abstract
Adipocyte dysfunction in obesity is commonly associated with impaired insulin signalling in adipocytes and insulin resistance. Insulin signalling has been associated with caveolae, which are coated by large complexes of caveolin and cavin proteins, along with proteins with membrane-binding and remodelling properties. Here, we analysed the regulation and function of a component of caveolae involved in growth factor signalling in neuroendocrine cells, neuroendocrine long coiled-coil protein-2 (NECC2), in adipocytes. Studies in 3T3-L1 cells showed that NECC2 expression increased during adipogenesis. Furthermore, NECC2 co-immunoprecipitated with caveolin-1 (CAV1) and exhibited a distribution pattern similar to that of the components of adipocyte caveolae, CAV1, Cavin1, the insulin receptor and cortical actin. Interestingly, NECC2 overexpression enhanced insulin-activated Akt phosphorylation, whereas NECC2 downregulation impaired insulin-induced phosphorylation of Akt and ERK2. Finally, an up-regulation of NECC2 in subcutaneous and omental adipose tissue was found in association with human obesity and insulin resistance. This effect was also observed in 3T3-L1 adipocytes exposed to hyperglycaemia/hyperinsulinemia. Overall, the present study identifies NECC2 as a component of adipocyte caveolae that is regulated in response to obesity and associated metabolic complications, and supports the contribution of this protein as a molecular scaffold modulating insulin signal transduction at these membrane microdomains.
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Affiliation(s)
- Andrés Trávez
- Instituto Maimónides de Investigación Biomédica de Córdoba (IMIBIC), Córdoba, Spain.,Department of Cell Biology, Physiology, and Immunology, University of Córdoba, Córdoba, Spain.,Reina Sofía University Hospital, Córdoba, Spain.,CIBER Fisiopatología de la Obesidad y Nutrición (CIBERobn), Instituto de Salud Carlos III, Madrid, Spain
| | - Yoana Rabanal-Ruiz
- Instituto Maimónides de Investigación Biomédica de Córdoba (IMIBIC), Córdoba, Spain.,Department of Cell Biology, Physiology, and Immunology, University of Córdoba, Córdoba, Spain.,Reina Sofía University Hospital, Córdoba, Spain.,CIBER Fisiopatología de la Obesidad y Nutrición (CIBERobn), Instituto de Salud Carlos III, Madrid, Spain
| | - Jaime López-Alcalá
- Instituto Maimónides de Investigación Biomédica de Córdoba (IMIBIC), Córdoba, Spain.,Department of Cell Biology, Physiology, and Immunology, University of Córdoba, Córdoba, Spain.,Reina Sofía University Hospital, Córdoba, Spain
| | - Laura Molero-Murillo
- Instituto Maimónides de Investigación Biomédica de Córdoba (IMIBIC), Córdoba, Spain.,Department of Cell Biology, Physiology, and Immunology, University of Córdoba, Córdoba, Spain.,Reina Sofía University Hospital, Córdoba, Spain.,CIBER Fisiopatología de la Obesidad y Nutrición (CIBERobn), Instituto de Salud Carlos III, Madrid, Spain
| | - Alberto Díaz-Ruiz
- Instituto Maimónides de Investigación Biomédica de Córdoba (IMIBIC), Córdoba, Spain.,Department of Cell Biology, Physiology, and Immunology, University of Córdoba, Córdoba, Spain.,Reina Sofía University Hospital, Córdoba, Spain.,CIBER Fisiopatología de la Obesidad y Nutrición (CIBERobn), Instituto de Salud Carlos III, Madrid, Spain
| | - Rocío Guzmán-Ruiz
- Instituto Maimónides de Investigación Biomédica de Córdoba (IMIBIC), Córdoba, Spain.,Department of Cell Biology, Physiology, and Immunology, University of Córdoba, Córdoba, Spain.,Reina Sofía University Hospital, Córdoba, Spain.,CIBER Fisiopatología de la Obesidad y Nutrición (CIBERobn), Instituto de Salud Carlos III, Madrid, Spain
| | - Victoria Catalán
- CIBER Fisiopatología de la Obesidad y Nutrición (CIBERobn), Instituto de Salud Carlos III, Madrid, Spain.,Metabolic Research Laboratory, Department of Endocrinology & Nutrition, Clínica Universidad de Navarra, IdiSNA, Pamplona, Spain
| | - Amaia Rodríguez
- CIBER Fisiopatología de la Obesidad y Nutrición (CIBERobn), Instituto de Salud Carlos III, Madrid, Spain.,Metabolic Research Laboratory, Department of Endocrinology & Nutrition, Clínica Universidad de Navarra, IdiSNA, Pamplona, Spain
| | - Gema Frühbeck
- CIBER Fisiopatología de la Obesidad y Nutrición (CIBERobn), Instituto de Salud Carlos III, Madrid, Spain.,Metabolic Research Laboratory, Department of Endocrinology & Nutrition, Clínica Universidad de Navarra, IdiSNA, Pamplona, Spain
| | - Francisco J Tinahones
- CIBER Fisiopatología de la Obesidad y Nutrición (CIBERobn), Instituto de Salud Carlos III, Madrid, Spain.,Unidad de Gestion Clínica de Endocrinología y Nutrición, Laboratorio del Instituto de Investigación Biomédica de Málaga (IBIMA), Hospital Universitario de Málaga (Virgen de la Victoria), Universidad de Málaga, Málaga, Spain
| | - Stéphane Gasman
- Institut des Neurosciences Cellulaires et Intégratives (INCI), Centre National de la Recherche Scientifique (CNRS UPR 3212), Université de Strasbourg, Strasbourg, France
| | - Nicolas Vitale
- Institut des Neurosciences Cellulaires et Intégratives (INCI), Centre National de la Recherche Scientifique (CNRS UPR 3212), Université de Strasbourg, Strasbourg, France
| | - Yolanda Jiménez-Gómez
- Instituto Maimónides de Investigación Biomédica de Córdoba (IMIBIC), Córdoba, Spain.,Department of Cell Biology, Physiology, and Immunology, University of Córdoba, Córdoba, Spain.,Reina Sofía University Hospital, Córdoba, Spain
| | - María M Malagón
- Instituto Maimónides de Investigación Biomédica de Córdoba (IMIBIC), Córdoba, Spain.,Department of Cell Biology, Physiology, and Immunology, University of Córdoba, Córdoba, Spain.,Reina Sofía University Hospital, Córdoba, Spain.,CIBER Fisiopatología de la Obesidad y Nutrición (CIBERobn), Instituto de Salud Carlos III, Madrid, Spain
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56
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Shikanai M, Nishimura YV, Sakurai M, Nabeshima YI, Yuzaki M, Kawauchi T. Caveolin-1 Promotes Early Neuronal Maturation via Caveolae-Independent Trafficking of N-Cadherin and L1. iScience 2018; 7:53-67. [PMID: 30267686 PMCID: PMC6135901 DOI: 10.1016/j.isci.2018.08.014] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2018] [Revised: 07/31/2018] [Accepted: 08/16/2018] [Indexed: 12/03/2022] Open
Abstract
Axon specification is morphologically reproducible in vitro, whereas dendrite formation differs in vitro and in vivo. Cortical neurons initially develop immature neurites, but in vivo these are eliminated concurrently with the formation of a leading process, the future dendrite. However, the molecular mechanisms underlying these neuronal maturation events remain unclear. Here we show that caveolin-1, a major component of caveolae that are never observed in neurons, regulates in vivo-specific steps of neuronal maturation. Caveolin-1 is predominantly expressed in immature cortical neurons and regulates clathrin-independent endocytosis. In vivo knockdown of caveolin-1 disturbs immature neurite pruning, leading process elongation, and subsequent neuronal migration. Importantly, N-cadherin and L1, which are required for immature neurite formation, undergo caveolin-1-mediated endocytosis to eliminate immature neurites. Collectively, our findings indicate that caveolin-1 regulates N-cadherin and L1 trafficking independent of caveolae, which contributes to spatiotemporally restricted cellular events; immature neurite pruning and leading process elongation during early neuronal maturation. Clathrin-independent endocytosis regulates early neuronal maturation Caveolin-1 promotes immature neurite pruning and leading process elongation in vivo Caveolin-1 controls N-cadherin and L1 trafficking independent of caveolae Suppression of caveolin-1 results in defects in cortical neuronal migration
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Affiliation(s)
- Mima Shikanai
- Department of Physiology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan
| | - Yoshiaki V Nishimura
- Division of Neuroscience, Faculty of Medicine, Tohoku Medical and Pharmaceutical University, 1-15-1 Fukumuro, Miyaginoku, Sendai, Miyagi 983-8536, Japan
| | - Miwa Sakurai
- Laboratory of Molecular Life Science, Institute of Biomedical Research and Innovation, Foundation for Biomedical Research and Innovation at Kobe (FBRI), 2-2 Minatojima-Minamimachi Chuo-ku, Kobe 650-0047, Japan
| | - Yo-Ichi Nabeshima
- Laboratory of Molecular Life Science, Institute of Biomedical Research and Innovation, Foundation for Biomedical Research and Innovation at Kobe (FBRI), 2-2 Minatojima-Minamimachi Chuo-ku, Kobe 650-0047, Japan
| | - Michisuke Yuzaki
- Department of Physiology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan
| | - Takeshi Kawauchi
- Department of Physiology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan; Laboratory of Molecular Life Science, Institute of Biomedical Research and Innovation, Foundation for Biomedical Research and Innovation at Kobe (FBRI), 2-2 Minatojima-Minamimachi Chuo-ku, Kobe 650-0047, Japan; Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency (JST), Saitama 332-0012, Japan.
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57
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de Almeida CJG. Caveolin-1 and Caveolin-2 Can Be Antagonistic Partners in Inflammation and Beyond. Front Immunol 2017; 8:1530. [PMID: 29250058 PMCID: PMC5715436 DOI: 10.3389/fimmu.2017.01530] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2017] [Accepted: 10/27/2017] [Indexed: 12/26/2022] Open
Abstract
Caveolins, encoded by the CAV gene family, are the main protein components of caveolae. In most tissues, caveolin-1 (Cav-1) and caveolin-2 (Cav-2) are co-expressed, and Cav-2 targeting to caveolae depends on the formation of heterooligomers with Cav-1. Notwithstanding, Cav-2 has unpredictable activities, opposing Cav-1 in the regulation of some cellular processes. While the major roles of Cav-1 as a modulator of cell signaling in inflammatory processes and in immune responses have been extensively discussed elsewhere, the aim of this review is to focus on data revealing the distinct activity of Cav-1 and Cav-2, which suggest that these proteins act antagonistically to fine-tune a variety of cellular processes relevant to inflammation.
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58
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Yeow I, Howard G, Chadwick J, Mendoza-Topaz C, Hansen CG, Nichols BJ, Shvets E. EHD Proteins Cooperate to Generate Caveolar Clusters and to Maintain Caveolae during Repeated Mechanical Stress. Curr Biol 2017; 27:2951-2962.e5. [PMID: 28943089 PMCID: PMC5640515 DOI: 10.1016/j.cub.2017.07.047] [Citation(s) in RCA: 51] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2017] [Revised: 06/21/2017] [Accepted: 07/20/2017] [Indexed: 11/15/2022]
Abstract
Caveolae introduce flask-shaped convolutions into the plasma membrane and help to protect the plasma membrane from damage under stretch forces. The protein components that form the bulb of caveolae are increasingly well characterized, but less is known about the contribution of proteins that localize to the constricted neck. Here we make extensive use of multiple CRISPR/Cas9-generated gene knockout and knockin cell lines to investigate the role of Eps15 Homology Domain (EHD) proteins at the neck of caveolae. We show that EHD1, EHD2, and EHD4 are recruited to caveolae. Recruitment of the other EHDs increases markedly when EHD2, which has been previously detected at caveolae, is absent. Construction of knockout cell lines lacking EHDs 1, 2, and 4 confirms this apparent functional redundancy. Two striking sets of phenotypes are observed in EHD1,2,4 knockout cells: (1) the characteristic clustering of caveolae into higher-order assemblies is absent; and (2) when the EHD1,2,4 knockout cells are subjected to prolonged cycles of stretch forces, caveolae are destabilized and the plasma membrane is prone to rupture. Our data identify the first molecular components that act to cluster caveolae into a membrane ultrastructure with the potential to extend stretch-buffering capacity and support a revised model for the function of EHDs at the caveolar neck.
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Affiliation(s)
- Ivana Yeow
- MRC-Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 2QH, UK
| | - Gillian Howard
- MRC-Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 2QH, UK
| | - Jessica Chadwick
- MRC-Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 2QH, UK
| | | | - Carsten G Hansen
- MRC-Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 2QH, UK
| | - Benjamin J Nichols
- MRC-Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 2QH, UK.
| | - Elena Shvets
- MRC-Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 2QH, UK.
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59
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Tumor antigen glycosaminoglycan modification regulates antibody-drug conjugate delivery and cytotoxicity. Oncotarget 2017; 8:66960-66974. [PMID: 28978009 PMCID: PMC5620149 DOI: 10.18632/oncotarget.16921] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2017] [Accepted: 03/19/2017] [Indexed: 01/03/2023] Open
Abstract
Aggressive cancers are characterized by hypoxia, which is a key driver of tumor development and treatment resistance. Proteins specifically expressed in the hypoxic tumor microenvironment thus represent interesting candidates for targeted drug delivery strategies. Carbonic anhydrase (CAIX) has been identified as an attractive treatment target as it is highly hypoxia specific and expressed at the cell-surface to promote cancer cell aggressiveness. Here, we find that cancer cell internalization of CAIX is negatively regulated by post-translational modification with chondroitin or heparan sulfate glycosaminoglycan chains. We show that perturbed glycosaminoglycan modification results in increased CAIX endocytosis. We hypothesized that perturbation of CAIX glycosaminoglycan conjugation may provide opportunities for enhanced drug delivery to hypoxic tumor cells. In support of this concept, pharmacological inhibition of glycosaminoglycan biosynthesis with xylosides significantly potentiated the internalization and cytotoxic activity of an antibody-drug conjugate (ADC) targeted at CAIX. Moreover, cells expressing glycosaminoglycan-deficient CAIX were significantly more sensitive to ADC treatment as compared with cells expressing wild-type CAIX. We find that inhibition of CAIX endocytosis is associated with an increased localization of glycosaminoglycan-conjugated CAIX in membrane lipid raft domains stabilized by caveolin-1 clusters. The association of CAIX with caveolin-1 was partially attenuated by acidosis, i.e. another important feature of malignant tumors. Accordingly, we found increased internalization of CAIX at acidic conditions. These findings provide first evidence that intracellular drug delivery at pathophysiological conditions of malignant tumors can be attenuated by tumor antigen glycosaminoglycan modification, which is of conceptual importance in the future development of targeted cancer treatments.
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60
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Electron microscopy using the genetically encoded APEX2 tag in cultured mammalian cells. Nat Protoc 2017; 12:1792-1816. [PMID: 28796234 DOI: 10.1038/nprot.2017.065] [Citation(s) in RCA: 120] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Electron microscopy (EM) is the premiere technique for high-resolution imaging of cellular ultrastructure. Unambiguous identification of specific proteins or cellular compartments in electron micrographs, however, remains challenging because of difficulties in delivering electron-dense contrast agents to specific subcellular targets within intact cells. We recently reported enhanced ascorbate peroxidase 2 (APEX2) as a broadly applicable genetic tag that generates EM contrast on a specific protein or subcellular compartment of interest. This protocol provides guidelines for designing and validating APEX2 fusion constructs, along with detailed instructions for cell culture, transfection, fixation, heavy-metal staining, embedding in resin, and EM imaging. Although this protocol focuses on EM in cultured mammalian cells, APEX2 is applicable to many cell types and contexts, including intact tissues and organisms, and is useful for numerous applications beyond EM, including live-cell proteomic mapping. This protocol, which describes procedures for sample preparation from cell monolayers and cell pellets, can be completed in 10 d, including time for APEX2 fusion construct validation, cell growth, and solidification of embedding resins. Notably, the only additional steps required relative to a standard EM sample preparation are cell transfection and a 2- to 45-min staining period with 3,3-diaminobenzidine (DAB) and hydrogen peroxide (H2O2).
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61
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Blood-Brain Barrier Permeability Is Regulated by Lipid Transport-Dependent Suppression of Caveolae-Mediated Transcytosis. Neuron 2017; 94:581-594.e5. [PMID: 28416077 DOI: 10.1016/j.neuron.2017.03.043] [Citation(s) in RCA: 367] [Impact Index Per Article: 52.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2016] [Revised: 03/02/2017] [Accepted: 03/29/2017] [Indexed: 12/13/2022]
Abstract
The blood-brain barrier (BBB) provides a constant homeostatic brain environment that is essential for proper neural function. An unusually low rate of vesicular transport (transcytosis) has been identified as one of the two unique properties of CNS endothelial cells, relative to peripheral endothelial cells, that maintain the restrictive quality of the BBB. However, it is not known how this low rate of transcytosis is achieved. Here we provide a mechanism whereby the regulation of CNS endothelial cell lipid composition specifically inhibits the caveolae-mediated transcytotic route readily used in the periphery. An unbiased lipidomic analysis reveals significant differences in endothelial cell lipid signatures from the CNS and periphery, which underlie a suppression of caveolae vesicle formation and trafficking in brain endothelial cells. Furthermore, lipids transported by Mfsd2a establish a unique lipid environment that inhibits caveolae vesicle formation in CNS endothelial cells to suppress transcytosis and ensure BBB integrity.
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62
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Ludwig A, Nguyen TH, Leong D, Ravi LI, Tan BH, Sandin S, Sugrue RJ. Caveolae provide a specialized membrane environment for respiratory syncytial virus assembly. J Cell Sci 2017; 130:1037-1050. [PMID: 28154158 PMCID: PMC5358342 DOI: 10.1242/jcs.198853] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2016] [Accepted: 01/26/2017] [Indexed: 12/20/2022] Open
Abstract
Respiratory syncytial virus (RSV) is an enveloped virus that assembles into filamentous virus particles on the surface of infected cells. Morphogenesis of RSV is dependent upon cholesterol-rich (lipid raft) membrane microdomains, but the specific role of individual raft molecules in RSV assembly is not well defined. Here, we show that RSV morphogenesis occurs within caveolar membranes and that both caveolin-1 and cavin-1 (also known as PTRF), the two major structural and functional components of caveolae, are actively recruited to and incorporated into the RSV envelope. The recruitment of caveolae occurred just prior to the initiation of RSV filament assembly, and was dependent upon an intact actin network as well as a direct physical interaction between caveolin-1 and the viral G protein. Moreover, cavin-1 protein levels were significantly increased in RSV-infected cells, leading to a virus-induced change in the stoichiometry and biophysical properties of the caveolar coat complex. Our data indicate that RSV exploits caveolae for its assembly, and we propose that the incorporation of caveolae into the virus contributes to defining the biological properties of the RSV envelope.
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Affiliation(s)
- Alexander Ludwig
- School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore 637551
| | - Tra Huong Nguyen
- School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore 637551
| | - Daniel Leong
- Detection and Diagnostics Laboratory, DSO National Laboratories, 27 Medical Drive, Singapore 117510
| | - Laxmi Iyer Ravi
- School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore 637551
| | - Boon Huan Tan
- Detection and Diagnostics Laboratory, DSO National Laboratories, 27 Medical Drive, Singapore 117510
| | - Sara Sandin
- School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore 637551
| | - Richard J Sugrue
- School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore 637551
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63
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Martzoukou O, Amillis S, Zervakou A, Christoforidis S, Diallinas G. The AP-2 complex has a specialized clathrin-independent role in apical endocytosis and polar growth in fungi. eLife 2017; 6. [PMID: 28220754 PMCID: PMC5338921 DOI: 10.7554/elife.20083] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2016] [Accepted: 02/07/2017] [Indexed: 12/26/2022] Open
Abstract
Filamentous fungi provide excellent systems for investigating the role of the AP-2 complex in polar growth. Using Aspergillus nidulans, we show that AP-2 has a clathrin-independent essential role in polarity maintenance and growth. This is in line with a sequence analysis showing that the AP-2 β subunit (β2) of higher fungi lacks a clathrin-binding domain, and experiments showing that AP-2 does not co-localize with clathrin. We provide genetic and cellular evidence that AP-2 interacts with endocytic markers SlaBEnd4 and SagAEnd3 and the lipid flippases DnfA and DnfB in the sub-apical collar region of hyphae. The role of AP-2 in the maintenance of proper apical membrane lipid and cell wall composition is further supported by its functional interaction with BasA (sphingolipid biosynthesis) and StoA (apical sterol-rich membrane domains), and its essentiality in polar deposition of chitin. Our findings support that the AP-2 complex of dikarya has acquired, in the course of evolution, a specialized clathrin-independent function necessary for fungal polar growth. DOI:http://dx.doi.org/10.7554/eLife.20083.001
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Affiliation(s)
- Olga Martzoukou
- Department of Biology, National and Kapodistrian University of Athens, Athens, Greece
| | - Sotiris Amillis
- Department of Biology, National and Kapodistrian University of Athens, Athens, Greece
| | - Amalia Zervakou
- Department of Biology, National and Kapodistrian University of Athens, Athens, Greece
| | - Savvas Christoforidis
- Institute of Molecular Biology and Biotechnology-Biomedical Research, Foundation for Research and Technology, Ioannina, Greece.,Laboratory of Biological Chemistry, Department of Medicine, School of Health Sciences, University of Ioannina, Ioannina, Greece
| | - George Diallinas
- Department of Biology, National and Kapodistrian University of Athens, Athens, Greece
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64
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Modzel M, Lund FW, Wüstner D. Synthesis and Live-Cell Imaging of Fluorescent Sterols for Analysis of Intracellular Cholesterol Transport. Methods Mol Biol 2017; 1583:111-140. [PMID: 28205171 DOI: 10.1007/978-1-4939-6875-6_10] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
Abstract
Cellular cholesterol homeostasis relies on precise control of the sterol content of organelle membranes. Obtaining insight into cholesterol trafficking pathways and kinetics by live-cell imaging relies on two conditions. First, one needs to develop suitable analogs that resemble cholesterol as closely as possible with respect to their biophysical and biochemical properties. Second, the cholesterol analogs should have good fluorescence properties. This interferes, however, often with the first requirement, such that the imaging instrumentation must be optimized to collect photons from suboptimal fluorophores, but good cholesterol mimics, such as the intrinsically fluorescent sterols, cholestatrienol (CTL) or dehydroergosterol (DHE). CTL differs from cholesterol only in having two additional double bonds in the ring system, which is why it is slightly fluorescent in the ultraviolet (UV). In the first part of this protocol, we describe how to synthesize and image CTL in living cells relative to caveolin, a structural component of caveolae. In the second part, we explain in detail how to perform time-lapse experiments of commercially available BODIPY-tagged cholesterol (TopFluor-cholesterol®; TF-Chol) in comparison to DHE. Finally, using two-photon time-lapse imaging data of TF-Chol, we demonstrate how to use our imaging toolbox SpatTrack for tracking sterol rich vesicles in living cells over time.
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Affiliation(s)
- Maciej Modzel
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, Odense M, 5230, Denmark
| | - Frederik W Lund
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, Odense M, 5230, Denmark.,Department of Biochemistry, Weill Medical College of Cornell University, New York, NY, 10065, USA
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, Odense M, 5230, Denmark.
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65
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Gu X, Reagan AM, McClellan ME, Elliott MH. Caveolins and caveolae in ocular physiology and pathophysiology. Prog Retin Eye Res 2016; 56:84-106. [PMID: 27664379 DOI: 10.1016/j.preteyeres.2016.09.005] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2016] [Revised: 09/15/2016] [Accepted: 09/20/2016] [Indexed: 12/14/2022]
Abstract
Caveolae are specialized, invaginated plasma membrane domains that are defined morphologically and by the expression of signature proteins called, caveolins. Caveolae and caveolins are abundant in a variety of cell types including vascular endothelium, glia, and fibroblasts where they play critical roles in transcellular transport, endocytosis, mechanotransduction, cell proliferation, membrane lipid homeostasis, and signal transduction. Given these critical cellular functions, it is surprising that ablation of the caveolae organelle does not result in lethality suggesting instead that caveolae and caveolins play modulatory roles in cellular homeostasis. Caveolar components are also expressed in ocular cell types including retinal vascular cells, Müller glia, retinal pigment epithelium (RPE), conventional aqueous humor outflow cells, the corneal epithelium and endothelium, and the lens epithelium. In the eye, studies of caveolae and other membrane microdomains (i.e., "lipid rafts") have lagged behind what is a substantial body of literature outside vision science. However, interest in caveolae and their molecular components has increased with accumulating evidence of important roles in vision-related functions such as blood-retinal barrier homeostasis, ocular inflammatory signaling, pathogen entry at the ocular surface, and aqueous humor drainage. The recent association of CAV1/2 gene loci with primary open angle glaucoma and intraocular pressure has further enhanced the need to better understand caveolar functions in the context of ocular physiology and disease. Herein, we provide the first comprehensive review of literature on caveolae, caveolins, and other membrane domains in the context of visual system function. This review highlights the importance of caveolae domains and their components in ocular physiology and pathophysiology and emphasizes the need to better understand these important modulators of cellular function.
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Affiliation(s)
- Xiaowu Gu
- Department of Ophthalmology/Dean McGee Eye Institute, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA; Oklahoma Center for Neuroscience, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA
| | - Alaina M Reagan
- Department of Ophthalmology/Dean McGee Eye Institute, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA; Oklahoma Center for Neuroscience, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA
| | - Mark E McClellan
- Department of Ophthalmology/Dean McGee Eye Institute, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA
| | - Michael H Elliott
- Department of Ophthalmology/Dean McGee Eye Institute, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA; Oklahoma Center for Neuroscience, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA; Department of Physiology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA.
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66
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Han B, Copeland CA, Tiwari A, Kenworthy AK. Assembly and Turnover of Caveolae: What Do We Really Know? Front Cell Dev Biol 2016; 4:68. [PMID: 27446919 PMCID: PMC4921483 DOI: 10.3389/fcell.2016.00068] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2016] [Accepted: 06/13/2016] [Indexed: 11/13/2022] Open
Abstract
In addition to containing highly dynamic nanoscale domains, the plasma membranes of many cell types are decorated with caveolae, flask-shaped domains enriched in the structural protein caveolin-1 (Cav1). The importance of caveolae in numerous cellular functions and processes has become well-recognized, and recent years have seen dramatic advances in our understanding of how caveolae assemble and the mechanisms control the turnover of Cav1. At the same time, work from our lab and others have revealed that commonly utilized strategies such as overexpression and tagging of Cav1 have unexpectedly complex consequences on the trafficking and fate of Cav1. Here, we discuss the implications of these findings for current models of caveolae biogenesis and Cav1 turnover. In addition, we discuss how disease-associated mutants of Cav1 impact caveolae assembly and outline open questions in this still-emerging area.
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Affiliation(s)
- Bing Han
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine Nashville, TN, USA
| | - Courtney A Copeland
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine Nashville, TN, USA
| | - Ajit Tiwari
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine Nashville, TN, USA
| | - Anne K Kenworthy
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of MedicineNashville, TN, USA; Department of Cell and Developmental Biology, Vanderbilt University School of MedicineNashville, TN, USA; Epithelial Biology Program, Vanderbilt University School of MedicineNashville, TN, USA; Chemical and Physical Biology Program, Vanderbilt UniversityNashville, TN, USA
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67
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Blaas D. Viral entry pathways: the example of common cold viruses. Wien Med Wochenschr 2016; 166:211-26. [PMID: 27174165 PMCID: PMC4871925 DOI: 10.1007/s10354-016-0461-2] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2016] [Accepted: 04/12/2016] [Indexed: 02/02/2023]
Abstract
For infection, viruses deliver their genomes into the host cell. These nucleic acids are usually tightly packed within the viral capsid, which, in turn, is often further enveloped within a lipid membrane. Both protect them against the hostile environment. Proteins and/or lipids on the viral particle promote attachment to the cell surface and internalization. They are likewise often involved in release of the genome inside the cell for its use as a blueprint for production of new viruses. In the following, I shall cursorily discuss the early more general steps of viral infection that include receptor recognition, uptake into the cell, and uncoating of the viral genome. The later sections will concentrate on human rhinoviruses, the main cause of the common cold, with respect to the above processes. Much of what is known on the underlying mechanisms has been worked out by Renate Fuchs at the Medical University of Vienna.
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Affiliation(s)
- Dieter Blaas
- Max F. Perutz Laboratories, Department of Medical Biochemistry, Medical University of Vienna, Vienna Biocenter, Dr. Bohr Gasse 9/3, 1030, Vienna, Austria.
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68
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Kim DG, Bynoe MS. A2A adenosine receptor modulates drug efflux transporter P-glycoprotein at the blood-brain barrier. J Clin Invest 2016; 126:1717-33. [PMID: 27043281 PMCID: PMC4855938 DOI: 10.1172/jci76207] [Citation(s) in RCA: 60] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2015] [Accepted: 02/18/2016] [Indexed: 11/17/2022] Open
Abstract
The blood-brain barrier (BBB) protects the brain from toxic substances within the peripheral circulation. It maintains brain homeostasis and is a hurdle for drug delivery to the CNS to treat neurodegenerative diseases, including Alzheimer's disease and brain tumors. The drug efflux transporter P-glycoprotein (P-gp) is highly expressed on brain endothelial cells and blocks the entry of most drugs delivered to the brain. Here, we show that activation of the A2A adenosine receptor (AR) with an FDA-approved A2A AR agonist (Lexiscan) rapidly and potently decreased P-gp expression and function in a time-dependent and reversible manner. We demonstrate that downmodulation of P-gp expression and function coincided with chemotherapeutic drug accumulation in brains of WT mice and in primary mouse and human brain endothelial cells, which serve as in vitro BBB models. Lexiscan also potently downregulated the expression of BCRP1, an efflux transporter that is highly expressed in the CNS vasculature and other tissues. Finally, we determined that multiple pathways, including MMP9 cleavage and ubiquitinylation, mediated P-gp downmodulation. Based on these data, we propose that A2A AR activation on BBB endothelial cells offers a therapeutic window that can be fine-tuned for drug delivery to the brain and has potential as a CNS drug-delivery technology.
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MESH Headings
- ATP Binding Cassette Transporter, Subfamily B/biosynthesis
- ATP Binding Cassette Transporter, Subfamily B/genetics
- ATP Binding Cassette Transporter, Subfamily G, Member 2/biosynthesis
- ATP Binding Cassette Transporter, Subfamily G, Member 2/blood
- ATP Binding Cassette Transporter, Subfamily G, Member 2/genetics
- Adenosine A2 Receptor Agonists/pharmacology
- Animals
- Blood-Brain Barrier/metabolism
- Cell Line
- Endothelial Cells/metabolism
- Gene Expression Regulation
- Humans
- Matrix Metalloproteinase 9/genetics
- Matrix Metalloproteinase 9/metabolism
- Mice
- Neoplasm Proteins/blood
- Neoplasm Proteins/genetics
- Proteolysis/drug effects
- Purines/pharmacology
- Pyrazoles/pharmacology
- Receptor, Adenosine A2A/genetics
- Receptor, Adenosine A2A/metabolism
- Ubiquitination/drug effects
- Ubiquitination/genetics
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69
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Francavilla C, Papetti M, Rigbolt KTG, Pedersen AK, Sigurdsson JO, Cazzamali G, Karemore G, Blagoev B, Olsen JV. Multilayered proteomics reveals molecular switches dictating ligand-dependent EGFR trafficking. Nat Struct Mol Biol 2016; 23:608-18. [PMID: 27136326 DOI: 10.1038/nsmb.3218] [Citation(s) in RCA: 79] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2015] [Accepted: 04/01/2016] [Indexed: 12/30/2022]
Abstract
A fascinating conundrum in cell signaling is how stimulation of the same receptor tyrosine kinase with distinct ligands generates specific outcomes. To decipher the functional selectivity of EGF and TGF-α, which induce epidermal growth factor receptor (EGFR) degradation and recycling, respectively, we devised an integrated multilayered proteomics approach (IMPA). We analyzed dynamic changes in the receptor interactome, ubiquitinome, phosphoproteome, and late proteome in response to both ligands in human cells by quantitative MS and identified 67 proteins regulated at multiple levels. We identified RAB7 phosphorylation and RCP recruitment to EGFR as switches for EGF and TGF-α outputs, controlling receptor trafficking, signaling duration, proliferation, and migration. By manipulating RCP levels or phosphorylation of RAB7 in EGFR-positive cancer cells, we were able to switch a TGF-α-mediated response to an EGF-like response or vice versa as EGFR trafficking was rerouted. We propose IMPA as an approach to uncover fine-tuned regulatory mechanisms in cell signaling.
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Affiliation(s)
- Chiara Francavilla
- Proteomics Program, Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Moreno Papetti
- Proteomics Program, Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Kristoffer T G Rigbolt
- Center for Experimental Bioinformatics, Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark
| | - Anna-Kathrine Pedersen
- Proteomics Program, Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Jon O Sigurdsson
- Proteomics Program, Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Giuseppe Cazzamali
- Protein Structure and Function Program, Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Gopal Karemore
- Protein Imaging Platform, Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Blagoy Blagoev
- Center for Experimental Bioinformatics, Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark
| | - Jesper V Olsen
- Proteomics Program, Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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70
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Hypoxia regulates global membrane protein endocytosis through caveolin-1 in cancer cells. Nat Commun 2016; 7:11371. [PMID: 27094744 PMCID: PMC4842985 DOI: 10.1038/ncomms11371] [Citation(s) in RCA: 86] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2016] [Accepted: 03/18/2016] [Indexed: 01/12/2023] Open
Abstract
Hypoxia promotes tumour aggressiveness and resistance of cancers to oncological treatment. The identification of cancer cell internalizing antigens for drug targeting to the hypoxic tumour niche remains a challenge of high clinical relevance. Here we show that hypoxia down-regulates the surface proteome at the global level and, more specifically, membrane proteome internalization. We find that hypoxic down-regulation of constitutive endocytosis is HIF-independent, and involves caveolin-1-mediated inhibition of dynamin-dependent, membrane raft endocytosis. Caveolin-1 overexpression inhibits protein internalization, suggesting a general negative regulatory role of caveolin-1 in endocytosis. In contrast to this global inhibitory effect, we identify several proteins that can override caveolin-1 negative regulation, exhibiting increased internalization at hypoxia. We demonstrate antibody-mediated cytotoxin delivery and killing specifically of hypoxic cells through one of these proteins, carbonic anhydrase IX. Our data reveal that caveolin-1 modulates cell-surface proteome turnover at hypoxia with potential implications for specific targeting of the hypoxic tumour microenvironment. Hypoxia promotes tumour aggressiveness and resistance of cancers to oncological treatment. Here, the authors show that caveolin-1 can down-regulate global membrane protein endocytosis in hypoxic cells with potential implications for targeting the hypoxic 3microenvironment of aggressive tumours.
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71
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Imaging approaches for analysis of cholesterol distribution and dynamics in the plasma membrane. Chem Phys Lipids 2016; 199:106-135. [PMID: 27016337 DOI: 10.1016/j.chemphyslip.2016.03.003] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2016] [Accepted: 03/04/2016] [Indexed: 11/21/2022]
Abstract
Cholesterol is an important lipid component of the plasma membrane (PM) of mammalian cells, where it is involved in control of many physiological processes, such as endocytosis, cell migration, cell signalling and surface ruffling. In an attempt to explain these functions of cholesterol, several models have been put forward about cholesterol's lateral and transbilayer organization in the PM. In this article, we review imaging techniques developed over the last two decades for assessing the distribution and dynamics of cholesterol in the PM of mammalian cells. Particular focus is on fluorescence techniques to study the lateral and inter-leaflet distribution of suitable cholesterol analogues in the PM of living cells. We describe also several methods for determining lateral cholesterol dynamics in the PM including fluorescence recovery after photobleaching (FRAP), fluorescence correlation spectroscopy (FCS), single particle tracking (SPT) and spot variation FCS coupled to stimulated emission depletion (STED) microscopy. For proper interpretation of such measurements, we provide some background in probe photophysics and diffusion phenomena occurring in cell membranes. In particular, we show the equivalence of the reaction-diffusion approach, as used in FRAP and FCS, and continuous time random walk (CTRW) models, as often invoked in SPT studies. We also discuss mass spectrometry (MS) based imaging of cholesterol in the PM of fixed cells and compare this method with fluorescence imaging of sterols. We conclude that evidence from many experimental techniques converges towards a model of a homogeneous distribution of cholesterol with largely free and unhindered diffusion in both leaflets of the PM.
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72
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Cheng JPX, Mendoza-Topaz C, Howard G, Chadwick J, Shvets E, Cowburn AS, Dunmore BJ, Crosby A, Morrell NW, Nichols BJ. Caveolae protect endothelial cells from membrane rupture during increased cardiac output. J Cell Biol 2016; 211:53-61. [PMID: 26459598 PMCID: PMC4602045 DOI: 10.1083/jcb.201504042] [Citation(s) in RCA: 93] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
This study provides direct in vivo evidence that endothelial cell caveolae disassemble and hence flatten out under increased mechanical stress and that the presence of caveolae protects endothelial cell plasma membranes from damage. Caveolae are strikingly abundant in endothelial cells, yet the physiological functions of caveolae in endothelium and other tissues remain incompletely understood. Previous studies suggest a mechanoprotective role, but whether this is relevant under the mechanical forces experienced by endothelial cells in vivo is unclear. In this study we have sought to determine whether endothelial caveolae disassemble under increased hemodynamic forces, and whether caveolae help prevent acute rupture of the plasma membrane under these conditions. Experiments in cultured cells established biochemical assays for disassembly of caveolar protein complexes, and assays for acute loss of plasma membrane integrity. In vivo, we demonstrate that caveolae in endothelial cells of the lung and cardiac muscle disassemble in response to acute increases in cardiac output. Electron microscopy and two-photon imaging reveal that the plasma membrane of microvascular endothelial cells in caveolin 1−/− mice is much more susceptible to acute rupture when cardiac output is increased. These data imply that mechanoprotection through disassembly of caveolae is important for endothelial function in vivo.
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Affiliation(s)
- Jade P X Cheng
- Medical Research Council, Laboratory of Molecular Biology, University of Cambridge, Cambridge CB2 1TN, UK
| | - Carolina Mendoza-Topaz
- Medical Research Council, Laboratory of Molecular Biology, University of Cambridge, Cambridge CB2 1TN, UK
| | - Gillian Howard
- Medical Research Council, Laboratory of Molecular Biology, University of Cambridge, Cambridge CB2 1TN, UK
| | - Jessica Chadwick
- Medical Research Council, Laboratory of Molecular Biology, University of Cambridge, Cambridge CB2 1TN, UK
| | - Elena Shvets
- Medical Research Council, Laboratory of Molecular Biology, University of Cambridge, Cambridge CB2 1TN, UK
| | - Andrew S Cowburn
- Department of Physiology, University of Cambridge, Cambridge CB2 1TN, UK
| | | | - Alexi Crosby
- Department of Medicine, University of Cambridge, Cambridge CB2 1TN, UK
| | | | - Benjamin J Nichols
- Medical Research Council, Laboratory of Molecular Biology, University of Cambridge, Cambridge CB2 1TN, UK
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73
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Cheng JPX, Nichols BJ. Caveolae: One Function or Many? Trends Cell Biol 2015; 26:177-189. [PMID: 26653791 DOI: 10.1016/j.tcb.2015.10.010] [Citation(s) in RCA: 176] [Impact Index Per Article: 19.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2015] [Revised: 10/16/2015] [Accepted: 10/22/2015] [Indexed: 02/07/2023]
Abstract
Caveolae are small, bulb-shaped plasma membrane invaginations. Mutations that ablate caveolae lead to diverse phenotypes in mice and humans, making it challenging to uncover their molecular mechanisms. Caveolae have been described to function in endocytosis and transcytosis (a specialized form of endocytosis) and in maintaining membrane lipid composition, as well as acting as signaling platforms. New data also support a model in which the central function of caveolae could be related to the protection of cells from mechanical stress within the plasma membrane. We present evidence for these diverse roles and consider in vitro and in vivo experiments confirming a mechanoprotective role. We conclude by highlighting current gaps in our knowledge of how mechanical signals may be transduced by caveolae.
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Affiliation(s)
- Jade P X Cheng
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK.
| | - Benjamin J Nichols
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK.
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74
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Yamauchi Y, Iwamoto N, Rogers MA, Abe-Dohmae S, Fujimoto T, Chang CCY, Ishigami M, Kishimoto T, Kobayashi T, Ueda K, Furukawa K, Chang TY, Yokoyama S. Deficiency in the Lipid Exporter ABCA1 Impairs Retrograde Sterol Movement and Disrupts Sterol Sensing at the Endoplasmic Reticulum. J Biol Chem 2015. [PMID: 26198636 DOI: 10.1074/jbc.m115.662668] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cellular cholesterol homeostasis involves sterol sensing at the endoplasmic reticulum (ER) and sterol export from the plasma membrane (PM). Sterol sensing at the ER requires efficient sterol delivery from the PM; however, the macromolecules that facilitate retrograde sterol transport at the PM have not been identified. ATP-binding cassette transporter A1 (ABCA1) mediates cholesterol and phospholipid export to apolipoprotein A-I for the assembly of high density lipoprotein (HDL). Mutations in ABCA1 cause Tangier disease, a familial HDL deficiency. Several lines of clinical and experimental evidence suggest a second function of ABCA1 in cellular cholesterol homeostasis in addition to mediating cholesterol efflux. Here, we report the unexpected finding that ABCA1 also plays a key role in facilitating retrograde sterol transport from the PM to the ER for sterol sensing. Deficiency in ABCA1 delays sterol esterification at the ER and activates the SREBP-2 cleavage pathway. The intrinsic ATPase activity in ABCA1 is required to facilitate retrograde sterol transport. ABCA1 deficiency causes alternation of PM composition and hampers a clathrin-independent endocytic activity that is required for ER sterol sensing. Our finding identifies ABCA1 as a key macromolecule facilitating bidirectional sterol movement at the PM and shows that ABCA1 controls retrograde sterol transport by modulating a certain clathrin-independent endocytic process.
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Affiliation(s)
- Yoshio Yamauchi
- From the Department of Biochemistry II, Nagoya University Graduate School of Medicine, Nagoya 466-8550, Japan,
| | - Noriyuki Iwamoto
- the Department of Biochemistry, Nagoya City University Graduate School of Medical Sciences, Nagoya 467-8601, Japan
| | - Maximillian A Rogers
- the Department of Biochemistry, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire 03755
| | - Sumiko Abe-Dohmae
- the Department of Biochemistry, Nagoya City University Graduate School of Medical Sciences, Nagoya 467-8601, Japan
| | - Toyoshi Fujimoto
- the Department of Anatomy and Molecular Cell Biology, Nagoya University Graduate School of Medicine, Nagoya 466-8550, Japan
| | - Catherine C Y Chang
- the Department of Biochemistry, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire 03755
| | - Masato Ishigami
- the Institute for Integrated Cell-Material Sciences and Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan
| | - Takuma Kishimoto
- the Lipid Biology Laboratory, RIKEN, Wako, Saitama 351-0198, Japan, and
| | | | - Kazumitsu Ueda
- the Institute for Integrated Cell-Material Sciences and Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan
| | - Koichi Furukawa
- From the Department of Biochemistry II, Nagoya University Graduate School of Medicine, Nagoya 466-8550, Japan
| | - Ta-Yuan Chang
- the Department of Biochemistry, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire 03755,
| | - Shinji Yokoyama
- the Nutritional Health Science Research Center and Department of Food and Nutritional Sciences, Chubu University, Kasugai 487-8501, Japan
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