101
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Kucharz K, Wieloch T, Toresson H. Fission and Fusion of the Neuronal Endoplasmic Reticulum. Transl Stroke Res 2013; 4:652-62. [DOI: 10.1007/s12975-013-0279-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2013] [Accepted: 07/24/2013] [Indexed: 10/26/2022]
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102
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Iber D, Geyter CD. Computational modelling of bovine ovarian follicle development. BMC SYSTEMS BIOLOGY 2013; 7:60. [PMID: 23856357 PMCID: PMC3726369 DOI: 10.1186/1752-0509-7-60] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/22/2012] [Accepted: 07/11/2013] [Indexed: 11/23/2022]
Abstract
Background The development of ovarian follicles hinges on the timely exposure to the appropriate combination of hormones. Follicle stimulating hormone (FSH) and luteinizing hormone (LH) are both produced in the pituitary gland and are transported via the blood circulation to the thecal layer surrounding the follicle. From there both hormones are transported into the follicle by diffusion. FSH-receptors are expressed mainly in the granulosa while LH-receptors are expressed in a gradient with highest expression in the theca. How this spatial organization is achieved is not known. Equally it is not understood whether LH and FSH trigger distinct signalling programs or whether the distinct spatial localization of their G-protein coupled receptors is sufficient to convey their distinct biological function. Results We have developed a data-based computational model of the spatio-temporal signalling processes within the follicle and (i) predict that FSH and LH form a gradient inside the follicle, (ii) show that the spatial distribution of FSH- and LH-receptors can arise from the well known regulatory interactions, and (iii) find that the differential activity of FSH and LH may well result from the distinct spatial localisation of their receptors, even when both receptors respond with the same intracellular signalling cascade to their ligand. Conclusion The model integrates the large amount of published data into a consistent framework that can now be used to better understand how observed defects translate into failed follicle maturation.
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Affiliation(s)
- Dagmar Iber
- Department for Biosystems Science and Engineering-D-BSSE, ETH Zurich, Swiss Institute of Bioinformatics, Basel, Switzerland.
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103
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Loison P, Hosny NA, Gervais P, Champion D, Kuimova MK, Perrier-Cornet JM. Direct investigation of viscosity of an atypical inner membrane of Bacillus spores: a molecular rotor/FLIM study. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1828:2436-43. [PMID: 23831602 DOI: 10.1016/j.bbamem.2013.06.028] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2013] [Revised: 06/05/2013] [Accepted: 06/25/2013] [Indexed: 10/26/2022]
Abstract
We utilize the fluorescent molecular rotor Bodipy-C12 to investigate the viscoelastic properties of hydrophobic layers of bacterial spores Bacillus subtilis. The molecular rotor shows a marked increase in fluorescence lifetime, from 0.3 to 4ns, upon viscosity increase from 1 to 1500cP and can be incorporated into the hydrophobic layers within the spores from dormant state through to germination. We use fluorescence lifetime imaging microscopy to visualize the viscosity inside different compartments of the bacterial spore in order to investigate the inner membrane and relate its compaction to the extreme resistance observed during exposure of spores to toxic chemicals. We demonstrate that the bacterial spores possess an inner membrane that is characterized by a very high viscosity, exceeding 1000cP, where the lipid bilayer is likely in a gel state. We also show that this membrane evolves during germination to reach a viscosity value close to that of a vegetative cell membrane, ca. 600cP. The present study demonstrates quantitative imaging of the microscopic viscosity in hydrophobic layers of bacterial spores Bacillus subtilis and shows the potential for further investigation of spore membranes under environmental stress.
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Affiliation(s)
- Pauline Loison
- UMR PAM/Equipe PMB Université de Bourgogne/Agrosup Dijon Nord, 1 Esplanade Erasme 21000 Dijon, France
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104
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Vélez Pérez JA, Guzmán O, Navarro-García F. Steric contribution of macromolecular crowding to the time and activation energy for preprotein translocation across the endoplasmic reticulum membrane. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2013; 88:012725. [PMID: 23944508 DOI: 10.1103/physreve.88.012725] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2012] [Indexed: 06/02/2023]
Abstract
Protein translocation from the cytosol to the endoplasmic reticulum (ER) or vice versa, an essential process for cell function, includes the transport of preproteins destined to become secretory, luminal, or integral membrane proteins (translocation) or misfolded proteins returned to the cytoplasm to be degraded (retrotranslocation). An important aspect in this process that has not been fully studied is the molecular crowding at both sides of the ER membrane. By using models of polymers crossing a membrane through a pore, in an environment crowded by either static or dynamic spherical agents, we computed the following transport properties: the free energy, the activation energy, the force, and the transport times for translocation and retrotranslocation. Using experimental protein crowding data for the cytoplasm and ER sides, we showed that dynamic crowding, which resembles biological environments where proteins are translocated or retrotranslocated, increases markedly all the physical properties of translocation and retrotranslocation as compared with translocation in a diluted system. By contrast, transport properties in static crowded systems were similar to those in diluted conditions. In the dynamic regime, the effects of crowding were more notorious in the transport times, leading to a huge difference for large chains. We indicate that this difference is the result of the synergy between the free energy and the diffusivity of the translocating chain. That synergy leads to translocation rates similar to experimental measures in diluted systems, which indicates that the effects of crowding can be measured. Our data also indicate that effects of crowding cannot be neglected when studying translocation because protein dynamic crowding has a relevant steric contribution, which changes the properties of translocation.
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Affiliation(s)
- José Antonio Vélez Pérez
- Departamento de Física, Universidad Autónoma Metropolitana-Iztapalapa, 09340 México, DF, México.
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105
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Tang YQ, Liang P, Zhou J, Lu Y, Lei L, Bian X, Wang K. Auxiliary KChIP4a suppresses A-type K+ current through endoplasmic reticulum (ER) retention and promoting closed-state inactivation of Kv4 channels. J Biol Chem 2013; 288:14727-41. [PMID: 23576435 DOI: 10.1074/jbc.m113.466052] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
In the brain and heart, auxiliary Kv channel-interacting proteins (KChIPs) co-assemble with pore-forming Kv4 α-subunits to form a native K(+) channel complex and regulate the expression and gating properties of Kv4 currents. Among the KChIP1-4 members, KChIP4a exhibits a unique N terminus that is known to suppress Kv4 function, but the underlying mechanism of Kv4 inhibition remains unknown. Using a combination of confocal imaging, surface biotinylation, and electrophysiological recordings, we identified a novel endoplasmic reticulum (ER) retention motif, consisting of six hydrophobic and aliphatic residues, 12-17 (LIVIVL), within the KChIP4a N-terminal KID, that functions to reduce surface expression of Kv4-KChIP complexes. This ER retention capacity is transferable and depends on its flanking location. In addition, adjacent to the ER retention motif, the residues 19-21 (VKL motif) directly promote closed-state inactivation of Kv4.3, thus leading to an inhibition of channel current. Taken together, our findings demonstrate that KChIP4a suppresses A-type Kv4 current via ER retention and enhancement of Kv4 closed-state inactivation.
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Affiliation(s)
- Yi-Quan Tang
- Department of Neurobiology, Neuroscience Research Institute, Peking University Health Science Center, Peking University School of Pharmaceutical Sciences, Beijing 100191, China
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106
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English AR, Voeltz GK. Endoplasmic reticulum structure and interconnections with other organelles. Cold Spring Harb Perspect Biol 2013; 5:a013227. [PMID: 23545422 DOI: 10.1101/cshperspect.a013227] [Citation(s) in RCA: 226] [Impact Index Per Article: 20.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The endoplasmic reticulum (ER) is a large, continuous membrane-bound organelle comprised of functionally and structurally distinct domains including the nuclear envelope, peripheral tubular ER, peripheral cisternae, and numerous membrane contact sites at the plasma membrane, mitochondria, Golgi, endosomes, and peroxisomes. These domains are required for multiple cellular processes, including synthesis of proteins and lipids, calcium level regulation, and exchange of macromolecules with various organelles at ER-membrane contact sites. The ER maintains its unique overall structure regardless of dynamics or transfer at ER-organelle contacts. In this review, we describe the numerous factors that contribute to the structure of the ER.
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Affiliation(s)
- Amber R English
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, CO 80309, USA
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107
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Bouxsein NF, Carroll-Portillo A, Bachand M, Sasaki DY, Bachand GD. A continuous network of lipid nanotubes fabricated from the gliding motility of kinesin powered microtubule filaments. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:2992-2999. [PMID: 23391254 DOI: 10.1021/la304238u] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Synthetic interconnected lipid nanotube networks were fabricated on the millimeter scale based on the simple, cooperative interaction between phospholipid vesicles and kinesin-microtubule (MT) transport systems. More specifically, taxol-stabilized MTs, in constant 2D motion via surface absorbed kinesin, extracted and extended lipid nanotube networks from large Lα phase multilamellar liposomes (5-25 μm). Based on the properties of the inverted motility geometry, the total size of these nanofluidic networks was limited by MT surface density, molecular motor energy source (ATP), and total amount and physical properties of lipid source material. Interactions between MTs and extended lipid nanotubes resulted in bifurcation of the nanotubes and ultimately the generation of highly branched networks of fluidically connected nanotubes. The network bifurcation was easily tuned by changing the density of microtubules on the surface to increase or decrease the frequency of branching. The ability of these networks to capture nanomaterials at the membrane surface with high fidelity was subsequently demonstrated using quantum dots as a model system. The diffusive transport of quantum dots was also characterized with respect to using these nanotube networks for mass transport applications.
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Affiliation(s)
- Nathan F Bouxsein
- Center for Integrated Nanotechnology, Sandia National Laboratories, Albuquerque, New Mexico 87123, USA
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108
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Day CA, Kraft LJ, Kang M, Kenworthy AK. Analysis of protein and lipid dynamics using confocal fluorescence recovery after photobleaching (FRAP). ACTA ACUST UNITED AC 2013; Chapter 2:Unit2.19. [PMID: 23042527 DOI: 10.1002/0471142956.cy0219s62] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Fluorescence recovery after photobleaching (FRAP) is a powerful, versatile, and widely accessible tool to monitor molecular dynamics in living cells that can be performed using modern confocal microscopes. Although the basic principles of FRAP are simple, quantitative FRAP analysis requires careful experimental design, data collection, and analysis. In this unit, we discuss the theoretical basis for confocal FRAP, followed by step-by-step protocols for FRAP data acquisition using a laser-scanning confocal microscope for (1) measuring the diffusion of a membrane protein, (2) measuring the diffusion of a soluble protein, and (3) analysis of intracellular trafficking. Finally, data analysis procedures are discussed, and an equation for determining the diffusion coefficient of a molecular species undergoing pure diffusion is presented.
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Affiliation(s)
- Charles A Day
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN, USA
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109
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Abstract
Co-chaperones regulate chaperone activities and are likely to impact a protein-folding environment as much as the chaperone itself. As co-chaperones are expressed substoichiometrically, the ability of co-chaperones to encounter a chaperone is crucial for chaperone activity. ERdj3, an abundant soluble endoplasmic reticulum (ER) co-chaperone of the Hsp70 BiP, stimulates the ATPase activity of BiP to increase BiP's affinity for client (or substrate) proteins. We investigated ERdj3 availability, how ERdj3 levels impact BiP availability, and the significance of J proteins for regulating BiP binding of clients in living cells. FRAP analysis revealed that overexpressed ERdj3-sfGFP dramatically decreases BiP-GFP mobility in a client-dependent manner. By contrast, ERdj3-GFP mobility remains low regardless of client protein levels. Native gels and co-immunoprecipitations established that ERdj3 associates with a large complex including Sec61α. Translocon binding probably ensures rapid encounters between emerging nascent peptides and stimulates BiP activity in the crucial early stages of secretory protein folding. Importantly, mutant BiP exhibited significantly increased mobility when it could not interact with any ERdjs. Thus, ERdjs appear to play the dual roles of increasing BiP affinity for clients and regulating delivery of clients to BiP. Our data suggest that BiP engagement of clients is enhanced in ER subdomains enriched in ERdj proteins.
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Affiliation(s)
- Feng Guo
- Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA
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110
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Ohshima D, Inoue JI, Ichikawa K. Roles of spatial parameters on the oscillation of nuclear NF-κB: computer simulations of a 3D spherical cell. PLoS One 2012; 7:e46911. [PMID: 23056526 PMCID: PMC3463570 DOI: 10.1371/journal.pone.0046911] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2012] [Accepted: 09/06/2012] [Indexed: 01/04/2023] Open
Abstract
Transcription factor NF-κB resides in the cytoplasm and translocates to the nucleus by application of extracellular stimuli. It is known that the nuclear NF-κB oscillates and different oscillation patterns lead to different gene expression. Nearly forty reports on modeling and simulation of nuclear NF-κB have been published to date. The computational models reported so far are temporal or two-dimensional, and the discussions on spatial parameters have not been involved or limited. Since spatial parameters in cancer cells such as nuclear to cytoplasmic volume (N/C) ratio are different from normal cells, it is important to understand the relationship between oscillation patterns and spatial parameters. Here we report simulations of a 3D computational model for the oscillation of nuclear NF-κB using A-Cell software. First, we found that the default biochemical kinetic constants used in the temporal model cannot replicate the experimentally observed oscillation in the 3D model. Thus, the default parameters should be changed in the 3D model. Second, spatial parameters such as N/C ratio, nuclear transport, diffusion coefficients, and the location of IκB synthesis were found to alter the oscillation pattern. Third, among them, larger N/C ratios resulted in persistent oscillation of nuclear NF-κB, and larger nuclear transport resulted in faster oscillation frequency. Our simulation results suggest that the changes in spatial parameters seen in cancer cells is one possible mechanism for alteration in the oscillation pattern of nuclear NF-κB and lead to the altered gene expression in these cells.
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Affiliation(s)
- Daisuke Ohshima
- Division of Mathematical Oncology, The Institute of Medical Science, The University of Tokyo, Minato-ku, Tokyo, Japan
| | - Jun-ichiro Inoue
- Division of Cellular and Molecular Biology, The Institute of Medical Science, The University of Tokyo, Minato-ku, Tokyo, Japan
| | - Kazuhisa Ichikawa
- Division of Mathematical Oncology, The Institute of Medical Science, The University of Tokyo, Minato-ku, Tokyo, Japan
- * E-mail:
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111
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Athanasiou D, Kosmaoglou M, Kanuga N, Novoselov SS, Paton AW, Paton JC, Chapple JP, Cheetham ME. BiP prevents rod opsin aggregation. Mol Biol Cell 2012; 23:3522-31. [PMID: 22855534 PMCID: PMC3442401 DOI: 10.1091/mbc.e12-02-0168] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2012] [Revised: 07/18/2012] [Accepted: 07/24/2012] [Indexed: 11/24/2022] Open
Abstract
Mutations in rod opsin-the light-sensitive protein of rod cells-cause retinitis pigmentosa. Many rod opsin mutations lead to protein misfolding, and therefore it is important to understand the role of molecular chaperones in rod opsin biogenesis. We show that BiP (HSPA5) prevents the aggregation of rod opsin. Cleavage of BiP with the subtilase cytotoxin SubAB results in endoplasmic reticulum (ER) retention and ubiquitylation of wild-type (WT) rod opsin (WT-green fluorescent protein [GFP]) at the ER. Fluorescence recovery after photobleaching reveals that WT-GFP is usually mobile in the ER. By contrast, depletion of BiP activity by treatment with SubAB or coexpression of a BiP ATPase mutant, BiP(T37G), decreases WT-GFP mobility to below that of the misfolding P23H mutant of rod opsin (P23H-GFP), which is retained in the ER and can form cytoplasmic ubiquitylated inclusions. SubAB treatment of P23H-GFP-expressing cells decreases the mobility of the mutant protein further and leads to ubiquitylation throughout the ER. Of interest, BiP overexpression increases the mobility of P23H-GFP, suggesting that it can reduce mutant rod opsin aggregation. Therefore inhibition of BiP function results in aggregation of rod opsin in the ER, which suggests that BiP is important for maintaining the solubility of rod opsin in the ER.
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Affiliation(s)
| | | | - Naheed Kanuga
- UCL Institute of Ophthalmology, London EC1V 9EL, United Kingdom
| | | | - Adrienne W. Paton
- Research Centre for Infectious Diseases, School of Molecular and Biomedical Science, University of Adelaide, Adelaide 5005, Australia
| | - James C. Paton
- Research Centre for Infectious Diseases, School of Molecular and Biomedical Science, University of Adelaide, Adelaide 5005, Australia
| | - J. Paul Chapple
- Centre for Endocrinology, William Harvey Research Institute, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, London EC1M 6BQ, United Kingdom
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112
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Abstract
In January of 2011, the Biomedical Engineering Society (BMES) and the Society for Physical Regulation in Biology and Medicine (SPRBM) held its inaugural Cellular and Molecular Bioengineering (CMBE) conference. The CMBE conference assembled worldwide leaders in the field of CMBE and held a very successful Round Table discussion among leaders. One of the action items was to collectively construct a white paper regarding the future of CMBE. Thus, the goal of this report is to emphasize the impact of CMBE as an emerging field, identify critical gaps in research that may be answered by the expertise of CMBE, and provide perspectives on enabling CMBE to address challenges in improving human health. Our goal is to provide constructive guidelines in shaping the future of CMBE.
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113
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Li HY, Zheng XM, Che MX, Hu HY. A redox-sensitive luciferase assay for determining the localization and topology of endoplasmic reticulum proteins. PLoS One 2012; 7:e35628. [PMID: 22530060 PMCID: PMC3329452 DOI: 10.1371/journal.pone.0035628] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2011] [Accepted: 03/19/2012] [Indexed: 11/19/2022] Open
Abstract
Correct localization and transmembrane topology are crucial for the proteins residing and functioning in the endoplasmic reticulum (ER). We have developed a rapid and convenient assay, based on the redox-sensitive luciferase from Gaussia princeps (Gluc) and green fluorescence protein (GFP), to determine the localization or topology of ER proteins. Using the tandem Gluc-GFP reporter fused to different positions of a target protein, we successfully characterized the topologies of two ER transmembrane proteins Herp and HRD1 that are involved in the ER quality control system. This assay method may also be applicable to the proteins in secretory pathway, plasma membrane, and other compartments of cells.
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Affiliation(s)
- Hai-Yin Li
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Xue-Ming Zheng
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Mei-Xia Che
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Hong-Yu Hu
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
- * E-mail:
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114
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Mueller F, Morisaki T, Mazza D, McNally JG. Minimizing the impact of photoswitching of fluorescent proteins on FRAP analysis. Biophys J 2012; 102:1656-65. [PMID: 22500766 DOI: 10.1016/j.bpj.2012.02.029] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2011] [Revised: 02/07/2012] [Accepted: 02/13/2012] [Indexed: 11/30/2022] Open
Abstract
Fluorescence recovery after photobleaching (FRAP) is a widely used imaging technique for measuring the mobility of fluorescently tagged proteins in living cells. Although FRAP presumes that high-intensity illumination causes only irreversible photobleaching, reversible photoswitching of many fluorescent molecules, including GFP, can also occur. Here, we show that this photoswitching is likely to contaminate many FRAPs of GFP, and worse, the size of its contribution can be up to 60% under different experimental conditions, making it difficult to compare FRAPs from different studies. We develop a procedure to correct FRAPs for photoswitching and apply it to FRAPs of the GFP-tagged histone H2B, which, depending on the precise photobleaching conditions exhibits apparent fast components ranging from 9-36% before correction and ∼1% after correction. We demonstrate how this ∼1% fast component of H2B-GFP can be used as a benchmark both to estimate the role of photoswitching in previous FRAP studies of TATA binding proteins (TBP) and also as a tool to minimize the contribution of photoswitching to tolerable levels in future FRAP experiments. In sum, we show how the impact of photoswitching on FRAP can be identified, minimized, and corrected.
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Affiliation(s)
- Florian Mueller
- Laboratory of Receptor Biology and Gene Expression, National Cancer Institute, Bethesda, Maryland, USA
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115
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Costantini LM, Fossati M, Francolini M, Snapp EL. Assessing the tendency of fluorescent proteins to oligomerize under physiologic conditions. Traffic 2012; 13:643-9. [PMID: 22289035 DOI: 10.1111/j.1600-0854.2012.01336.x] [Citation(s) in RCA: 161] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2011] [Revised: 01/27/2012] [Accepted: 01/30/2012] [Indexed: 11/28/2022]
Abstract
Several fluorescent proteins (FPs) are prone to forming low-affinity oligomers. This undesirable tendency is exacerbated when FPs are confined to membranes or when fused to naturally oligomeric proteins. Oligomerization of FPs limits their suitability for creating fusions with proteins of interest. Unfortunately, no standardized method evaluates the biologically relevant oligomeric state of FPs. Here, we describe a quantitative visual assay for assessing whether FPs are sufficiently monomeric under physiologic conditions. Membrane-associated FP-fusion proteins, by virtue of their constrained planar geometry, achieve high effective concentrations. We exploited this propensity to develop an assay to measure FP tendencies to oligomerize in cells. FPs were fused on the cytoplasmic end of an endoplasmic reticulum (ER) signal-anchor membrane protein (CytERM) and expressed in cells. Cells were scored based on the ability of CytERM to homo-oligomerize with proteins on apposing membranes and restructure the ER from a tubular network into organized smooth ER (OSER) whorl structures. The ratio of nuclear envelope and OSER structures mean fluorescent intensities for cells expressing enhanced green fluorescent protein (EGFP) or monomeric green fluorescent protein (mGFP) CytERM established standards for comparison of uncharacterized FPs. We tested three FPs and identified two as sufficiently monomeric, while a third previously reported as monomeric was found to strongly oligomerize.
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Affiliation(s)
- Lindsey M Costantini
- Department of Anatomy and Structural Biology, Albert Einstein College of Medicine of Yeshiva University, 1300 Morris Park Avenue, Bronx, NY 10461, USA
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116
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Ohta S, Shen P, Inasawa S, Yamaguchi Y. Size- and surface chemistry-dependent intracellular localization of luminescent silicon quantum dot aggregates. ACTA ACUST UNITED AC 2012. [DOI: 10.1039/c2jm31112g] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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117
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118
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Human herpesvirus 8 viral interleukin-6 interacts with splice variant 2 of vitamin K epoxide reductase complex subunit 1. J Virol 2011; 86:1577-88. [PMID: 22130532 DOI: 10.1128/jvi.05782-11] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Viral interleukin-6 (vIL-6) specified by human herpesvirus 8 is, unlike its cellular counterpart, secreted very inefficiently and can signal via vIL-6(2):gp130(2) signaling complexes from the endoplasmic reticulum (ER) compartment. Intracellular, autocrine activities of vIL-6 are important for proproliferative and prosurvival activities of the viral cytokine in latently infected primary effusion lymphoma (PEL) cells. However, the molecular determinants of vIL-6 ER localization and function are unclear. Using yeast two-hybrid analysis, we identified the database-documented but uncharacterized splice variant of vitamin K epoxide reductase complex subunit 1 (VKORC1), termed VKORC1 variant 2 (VKORC1v2), as a potential interaction partner of vIL-6. In transfected cells, epitope-tagged VKORC1v2 was found to localize to the ER, to adopt a single-transmembrane (TM) topology placing the C tail in the ER lumen, and to bind vIL-6 via these sequences. Deletion mutagenesis and coprecipitation assays mapped the vIL-6-binding domain (vBD) of VKORC1v2 to TM-proximal residues 31 to 39. However, while sufficient to confer vIL-6 binding to a heterologous protein, vBD was unable to induce vIL-6 secretion when fused to (secreted) hIL-6, suggesting a VKORC1v2-independent mechanism of vIL-6 ER retention. In functional assays, overexpression of ER-directed vBD led to suppression of PEL cell proliferation and viability, effects also mediated by VKORC1v2 depletion and, as reported previously, by vIL-6 suppression. The growth-inhibitory and proapoptotic effects of VKORC1v2 depletion could be rescued by transduced wild-type VKORC1v2 but not by a vIL-6-refractory vBD-altered variant, indicating the functional relevance of the vIL-6-VKORC1v2 interaction. Notably, gp130 signaling was unaffected by VKORC1v2 or vBD overexpression or by VKORC1v2 depletion, suggesting an alternative pathway of vIL-6 activity via VKORC1v2. Combined, our data identify a novel and functionally significant interaction partner of vIL-6 that could potentially be targeted for therapeutic benefit.
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119
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Biess A, Korkotian E, Holcman D. Barriers to diffusion in dendrites and estimation of calcium spread following synaptic inputs. PLoS Comput Biol 2011; 7:e1002182. [PMID: 22022241 PMCID: PMC3192802 DOI: 10.1371/journal.pcbi.1002182] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2011] [Accepted: 07/17/2011] [Indexed: 11/18/2022] Open
Abstract
The motion of ions, molecules or proteins in dendrites is restricted by cytoplasmic obstacles such as organelles, microtubules and actin network. To account for molecular crowding, we study the effect of diffusion barriers on local calcium spread in a dendrite. We first present a model based on a dimension reduction approach to approximate a three dimensional diffusion in a cylindrical dendrite by a one-dimensional effective diffusion process. By comparing uncaging experiments of an inert dye in a spiny dendrite and in a thin glass tube, we quantify the change in diffusion constants due to molecular crowding as D(cyto)/D(water) = 1/20. We validate our approach by reconstructing the uncaging experiments using Brownian simulations in a realistic 3D model dendrite. Finally, we construct a reduced reaction-diffusion equation to model calcium spread in a dendrite under the presence of additional buffers, pumps and synaptic input. We find that for moderate crowding, calcium dynamics is mainly regulated by the buffer concentration, but not by the cytoplasmic crowding, dendritic spines or synaptic inputs. Following high frequency stimulations, we predict that calcium spread in dendrites is limited to small microdomains of the order of a few microns (<5 μm).
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Affiliation(s)
- Armin Biess
- Bernstein Center for Computational Neuroscience, Göttingen, Germany
- Max-Planck-Institute for Dynamics and Self-Organization, Göttingen, Germany
- * E-mail: (AB); (DH)
| | - Eduard Korkotian
- Department of Neurobiology, Weizmann Institute of Science, Rehovot, Israel
| | - David Holcman
- Department of Computational Biology, Ecole Normale Supérieure, Paris, France
- * E-mail: (AB); (DH)
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120
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Proteins on the move: insights gained from fluorescent protein technologies. Nat Rev Mol Cell Biol 2011; 12:656-68. [PMID: 21941275 DOI: 10.1038/nrm3199] [Citation(s) in RCA: 96] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Proteins are always on the move, and this may occur through diffusion or active transport. The realization that the regulation of signal transduction is highly dynamic in space and time has stimulated intense interest in the movement of proteins. Over the past decade, numerous new technologies using fluorescent proteins have been developed, allowing us to observe the spatiotemporal dynamics of proteins in living cells. These technologies have greatly advanced our understanding of protein dynamics, including protein movement and protein interactions.
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121
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Rapid fragmentation of the endoplasmic reticulum in cortical neurons of the mouse brain in situ following cardiac arrest. J Cereb Blood Flow Metab 2011; 31:1663-7. [PMID: 21468089 PMCID: PMC3170944 DOI: 10.1038/jcbfm.2011.37] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Neuronal endoplasmic reticulum (ER), continuous from soma to dendritic spines, undergoes rapid fragmentation in response to N-methyl-D-aspartate (NMDA) receptor stimulation in hippocampal slices and neuronal primary cultures. Here, we show that ER fragments in the mouse brain following cardiac arrest (CA) induced brain ischemia. The ER structure was assessed in vivo in cortical pyramidal neurons in transgenic mice expressing ER-targeted GFP using two-photon laser scanning microscopy with fluorescence recovery after photobleaching (FRAP). Endoplasmic reticulum fragmentation occurred 1 to 2 minutes after CA and once induced, fragmentation was rapid (<15 seconds). We propose that acute ER fragmentation may be a protective response against severe ischemic stress.
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122
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Howarth DL, Vacaru AM, Tsedensodnom O, Mormone E, Nieto N, Costantini LM, Snapp EL, Sadler KC. Alcohol disrupts endoplasmic reticulum function and protein secretion in hepatocytes. Alcohol Clin Exp Res 2011; 36:14-23. [PMID: 21790674 DOI: 10.1111/j.1530-0277.2011.01602.x] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
BACKGROUND Many alcoholic patients have serum protein deficiency that contributes to their systemic problems. The unfolded protein response (UPR) is induced in response to disequilibrium in the protein folding capability of the endoplasmic reticulum (ER) and is implicated in hepatocyte lipid accumulation and apoptosis, which are associated with alcoholic liver disease (ALD). We investigated whether alcohol affects ER structure, function, and UPR activation in hepatocytes in vitro and in vivo. METHODS HepG2 cells expressing human cytochrome P450 2E1 and mouse alcohol dehydrogenase (VL-17A) were treated for up to 48 hours with 50 and 100 mM ethanol. Zebrafish larvae at 4 days postfertilization were exposed to 350 mM ethanol for 32 hours. ER morphology was visualized by fluorescence in cells and transmission electron microscopy in zebrafish. UPR target gene activation was assessed using quantitative PCR, in situ hybridization, and Western blotting. Mobility of the major ER chaperone, BIP, was monitored in cells by fluorescence recovery after photobleaching (FRAP). RESULTS VL-17A cells metabolized alcohol yet only had slight activation of some UPR target genes following ethanol treatment. However, ER fragmentation, crowding, and accumulation of unfolded proteins as detected by immunofluorescence and FRAP demonstrate that alcohol induced some ER dysfunction despite the lack of UPR activation. Zebrafish treated with alcohol, however, showed modest ER dilation, and several UPR targets were significantly induced. CONCLUSIONS Ethanol metabolism directly impairs ER structure and function in hepatocytes. Zebrafish are a novel in vivo system for studying ALD.
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Affiliation(s)
- Deanna L Howarth
- Division of Liver Diseases, Department of Medicine, Mount Sinai School of Medicine, New York, New York, USA
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123
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Valenzuela JI, Jaureguiberry-Bravo M, Couve A. Neuronal protein trafficking: emerging consequences of endoplasmic reticulum dynamics. Mol Cell Neurosci 2011; 48:269-77. [PMID: 21782949 DOI: 10.1016/j.mcn.2011.07.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2011] [Revised: 06/23/2011] [Accepted: 07/07/2011] [Indexed: 01/16/2023] Open
Abstract
The highly polarized morphology and complex geometry of neurons is determined to a great extent by the structural and functional organization of the secretory pathway. It is intuitive to propose that the spatial arrangement of secretory organelles and their dynamic behavior impinge on protein trafficking and neuronal function, but these phenomena and their consequences are not well delineated. Here we analyze the architecture and motility of the archetypal endoplasmic reticulum (ER), and their relationship to the microtubule cytoskeleton and post-translational modifications of tubulin. We also review the dynamics of the ER in axons, dendrites and spines, and discuss the role of ER dynamics on protein mobility and trafficking in neurons.
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Affiliation(s)
- José Ignacio Valenzuela
- Programa de Fisiología y Biofísica, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Santiago, Chile
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124
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Lynes EM, Simmen T. Urban planning of the endoplasmic reticulum (ER): how diverse mechanisms segregate the many functions of the ER. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2011; 1813:1893-905. [PMID: 21756943 PMCID: PMC7172674 DOI: 10.1016/j.bbamcr.2011.06.011] [Citation(s) in RCA: 102] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/20/2011] [Revised: 06/22/2011] [Accepted: 06/23/2011] [Indexed: 12/21/2022]
Abstract
The endoplasmic reticulum (ER) is the biggest organelle in most cell types, but its characterization as an organelle with a continuous membrane belies the fact that the ER is actually an assembly of several, distinct membrane domains that execute diverse functions. Almost 20 years ago, an essay by Sitia and Meldolesi first listed what was known at the time about domain formation within the ER. In the time that has passed since, additional ER domains have been discovered and characterized. These include the mitochondria-associated membrane (MAM), the ER quality control compartment (ERQC), where ER-associated degradation (ERAD) occurs, and the plasma membrane-associated membrane (PAM). Insight has been gained into the separation of nuclear envelope proteins from the remainder of the ER. Research has also shown that the biogenesis of peroxisomes and lipid droplets occurs on specialized membranes of the ER. Several studies have shown the existence of specific marker proteins found on all these domains and how they are targeted there. Moreover, a first set of cytosolic ER-associated sorting proteins, including phosphofurin acidic cluster sorting protein 2 (PACS-2) and Rab32 have been identified. Intra-ER targeting mechanisms appear to be superimposed onto ER retention mechanisms and rely on transmembrane and cytosolic sequences. The crucial roles of ER domain formation for cell physiology are highlighted with the specific targeting of the tumor metastasis regulator gp78 to ERAD-mediating membranes or of the promyelocytic leukemia protein to the MAM.
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Affiliation(s)
- Emily M Lynes
- Department of Cell Biology, University of Alberta, Alberta, Canada
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125
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Pantazaka E, Taylor CW. Differential distribution, clustering, and lateral diffusion of subtypes of the inositol 1,4,5-trisphosphate receptor. J Biol Chem 2011; 286:23378-87. [PMID: 21550988 PMCID: PMC3123102 DOI: 10.1074/jbc.m111.236372] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2011] [Revised: 04/27/2011] [Indexed: 01/19/2023] Open
Abstract
Regulation of inositol 1,4,5-trisphosphate (IP(3)) receptors (IP(3)R) by IP(3) and Ca(2+) allows them to initiate and regeneratively propagate intracellular Ca(2+) signals. The distribution and mobility of IP(3)R determines the spatial organization of these Ca(2+) signals. Until now, there has been no systematic comparison of the distribution and mobility of the three mammalian IP(3)R subtypes in a uniform background. We used confocal microscopy and fluorescence recovery after photobleaching to define these properties for each IP(3)R subtype expressed heterologously in COS-7 cells. IP(3)R1 and IP(3)R3 were uniformly distributed within the membranes of the endoplasmic reticulum (ER), but the distribution of IP(3)R2 was punctate. The mobile fractions (M(f) = 84 ± 2 and 80 ± 2%) and diffusion coefficients (D = 0.018 ± 0.001 and 0.016 ± 0.002 μm(2)/s) of IP(3)R1 and IP(3)R3 were similar. Other ER membrane proteins (ryanodine receptor type 1 and sarco/endoplasmic reticulum Ca(2+)-ATPase type 1) and a luminal protein (enhanced GFP with a KDEL retrieval sequence) had similar mobile fractions, suggesting that IP(3)R1 and IP(3)R3 move freely within an ER that is largely, although not entirely, continuous. IP(3)R2 was less mobile, but IP(3)R2 mobility differed between perinuclear (M(f) = 47 ± 4% and D = 0.004 ± 0.001 μm(2)/s) and near-plasma membrane (M(f) = 64 ± 6% and D = 0.013 ± 0.004 μm(2)/s) regions, whereas IP(3)R3 behaved similarly in both regions. We conclude that IP(3)R1 and IP(3)R3 diffuse freely within a largely continuous ER, but IP(3)R2 is more heterogeneously distributed and less mobile, and its mobility differs between regions of the cell.
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Affiliation(s)
- Evangelia Pantazaka
- From the Department of Pharmacology, University of Cambridge, Cambridge CB2 1PD, United Kingdom
| | - Colin W. Taylor
- From the Department of Pharmacology, University of Cambridge, Cambridge CB2 1PD, United Kingdom
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126
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Measuring immune receptor mobility by fluorescence recovery after photobleaching. Methods Mol Biol 2011. [PMID: 21701973 DOI: 10.1007/978-1-61779-139-0_11] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
Abstract
The coordinated effort of cells in the immune system relies heavily on surface receptor interactions. Immune receptor mobility provides vital information on the function and responses of immune cells, and these measurements shed light on their interactions with other membrane, cytosolic, and extracellular matrix proteins. These measurements can be obtained using the fluorescence recovery after photobleaching (FRAP) technique in living cells. We describe here general approaches for FRAP using green fluorescent protein fusion proteins.
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127
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Koivusalo M, Steinberg BE, Mason D, Grinstein S. In situ Measurement of the Electrical Potential Across the Lysosomal Membrane Using FRET. Traffic 2011; 12:972-82. [DOI: 10.1111/j.1600-0854.2011.01215.x] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
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128
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Quantity control of the ErbB3 receptor tyrosine kinase at the endoplasmic reticulum. Mol Cell Biol 2011; 31:3009-18. [PMID: 21576364 DOI: 10.1128/mcb.05105-11] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The ErbB3 receptor tyrosine kinase contributes to a variety of developmental processes, and its overexpression and aberrant activation promote tumor progression and therapeutic resistance. Accumulating evidence suggests that tumor overexpression may be mediated by the loss of posttranscriptional negative regulatory mechanisms, such as protein degradation, that normally keep receptor levels in check. Our previous studies indicate that the RING finger E3 ubiquitin ligase Nrdp1, a protein lost in breast and other tumor types, suppresses ErbB3 levels by mediating ligand-independent receptor ubiquitination and degradation. Here we demonstrate that Nrdp1 preferentially associates with the nascent form of ErbB3 to accelerate its degradation, and we show that the two proteins colocalize at the endoplasmic reticulum (ER). Blocking the exit of ErbB3 from the ER does not affect the ability of Nrdp1 to mediate receptor ubiquitination or degradation, while functional disruption of the conserved ER-associated degradation (ERAD) pathway ATPase VCP/p97 leads to the Nrdp1-dependent accumulation of ubiquitinated ErbB3 but blocks receptor degradation. Further evidence indicates that the ErbB3 targeted by Nrdp1 for degradation is properly folded and fully functional. Collectively, these observations point to a novel mechanism of receptor tyrosine kinase quantity control wherein steady-state levels of signaling-competent receptor are dictated by an ER-localized degradation pathway.
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129
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Abstract
Intracellular chemical reactions generally constitute reaction-diffusion systems located inside nanostructured compartments like the cytosol, nucleus, endoplasmic reticulum, Golgi, and mitochondrion. Understanding the properties of such systems requires quantitative information about solute diffusion. Here we present a novel approach that allows determination of the solvent-dependent solute diffusion constant (D(solvent)) inside cell compartments with an experimentally quantifiable nanostructure. In essence, our method consists of the matching of synthetic fluorescence recovery after photobleaching (FRAP) curves, generated by a mathematical model with a realistic nanostructure, and experimental FRAP data. As a proof of principle, we assessed D(solvent) of a monomeric fluorescent protein (AcGFP1) and its tandem fusion (AcGFP1(2)) in the mitochondrial matrix of HEK293 cells. Our results demonstrate that diffusion of both proteins is substantially slowed by barriers in the mitochondrial matrix (cristae), suggesting that cells can control the dynamics of biochemical reactions in this compartment by modifying its nanostructure.
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130
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Kucharz K, Wieloch T, Toresson H. Potassium-induced structural changes of the endoplasmic reticulum in pyramidal neurons in murine organotypic hippocampal slices. J Neurosci Res 2011; 89:1150-9. [PMID: 21538461 DOI: 10.1002/jnr.22646] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2010] [Revised: 02/08/2011] [Accepted: 02/09/2011] [Indexed: 12/15/2022]
Abstract
The endoplasmic reticulum (ER) structure is of central importance for the regulation of cellular anabolism, stress response, and signal transduction. Generally continuous, the ER can temporarily undergo dramatic structural rearrangements resulting in a fragmented appearance. In this study we assess the dynamic nature of ER fission in pyramidal neurons in organotypic hippocampal slice cultures stimulated by depolarizing concentration of potassium (50 mM). The slices were obtained from transgenic mice expressing fluorescent ER-targeted DsRed2 protein. We employed live tissue confocal microscopy imaging with fluorescence recovery after photobleaching (FRAP) to monitor the extent of structural rearrangements of the ER. In control slices, the ER structure was continuous. Potassium stimulation resulted in extensive fragmentation (fission), whereas return to basal potassium levels (2.5 mM) led to ER fusion and normalization of ER structure. This ER fission/fusion could be repeated several times in the same neuron, demonstrating the reversibility of the process. Blockade of the N-methyl-D-aspartate receptor (NMDAR) with the antagonist D-AP5 or removal of extracellular Ca(2+) prevented depolarization-induced ER fission. ER fission is sensitive to temperature, and decreasing temperature from 35°C to 30°C augments fission, implying that the altering of ER continuity may be a protective response against damage. We conclude that events that generate membrane depolarisation in brain tissue lead to the release of endogenous glutamate that may regulate neuronal ER continuity. The rapid and reversible NMDAR-mediated changes in ER structure reflect an adaptive, innate property of the ER for synaptic activation as well as response to tissue stress, injury, and disease.
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Affiliation(s)
- Krzysztof Kucharz
- Laboratory for Experimental Brain Research, Department of Clinical Sciences Lund, Lund University, Lund, Sweden
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131
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Ramírez OA, Couve A. The endoplasmic reticulum and protein trafficking in dendrites and axons. Trends Cell Biol 2011; 21:219-27. [DOI: 10.1016/j.tcb.2010.12.003] [Citation(s) in RCA: 99] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2010] [Revised: 11/24/2010] [Accepted: 12/02/2010] [Indexed: 12/12/2022]
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132
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Design principles of nuclear receptor signaling: how complex networking improves signal transduction. Mol Syst Biol 2011; 6:446. [PMID: 21179018 PMCID: PMC3018161 DOI: 10.1038/msb.2010.102] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2010] [Accepted: 10/21/2010] [Indexed: 12/29/2022] Open
Abstract
Nuclear receptors often function in the cytoplasm. A triple conveyor belt pumps ligand (signal) into the nucleus and onto the DNA. The active export of importins enhances signaling to the nucleus. Sharing a single nuclear pore may reduce rather than increase crosstalk.
Nuclear receptors (NRs) derive their family name from the early observation that they are located in the nucleus, despite responding to extracellular signals such as hormones (e.g., cortisol) (Fanestil and Edelman, 1966). According to the ‘classical' paradigm of NR signaling, the NR resides in the nucleus, attached to a DNA response element, waiting for its ligand to bind. The actual systems have multiple additional features (reviewed in Cutress et al, 2008; Cao et al, 2009; Levin, 2009a; Bunce and Campbell, 2010), such as that NRs shuttle between the nucleus and the cytoplasm (Von Knethen et al, 2010) and ligand addition changes receptor location dynamically (Pratt et al, 1989; Liu and DeFranco, 2000; Kumar et al, 2004, 2006; Tanaka et al, 2005; Heitzer et al, 2007; Prüfer and Boudreaux, 2007; Ricketson et al, 2007; Cutress et al, 2008): Figure 1 summarizes the current understanding of the topology of the reaction networks involved in NR signaling, in systems biological graphical notation (SBGN), with NR activation, importin-α and -β binding, nuclear pore complex (NPC)-mediated import, recycling of importins, NR binding to target promoter sequences, exportin-mediated nuclear export of the NR, exportin cycling and free energy-driven Ran recycling. This topology is surprisingly complex when compared with the ‘classical' paradigm. To address to what extent this extra complexity is just detail or contributes essential functionality, we have simulated the dynamics of the NR transcriptional response in maximally realistic mathematical models of increasingly complex designs. The calculations revealed significant disadvantages of the classical and simplest mechanism for endocrine NR-mediated signaling, i.e., the one with localization of the NR exclusively on the DNA (design 1 in Figure 2A): the transcriptional response was very low (Figure 2B). A high concentration of free NR in the nucleus (design 2) improved sensitivity, but made the responsiveness much slower (Figure 2B). If the NR was equally distributed between the nucleus and the cytoplasm without the NR being able to traverse the nucleocytoplasmic membrane (design 3), then, although the NR diffuses more slowly than the much smaller ligand molecule, the higher concentration of the NR increased flux from the plasma membrane to the nuclear membrane; the steady state was reached faster (Figure 2B and C; compare design 3 relative to design 2). Enabling the NR to traverse the nucleocytoplasmic membrane (design 4), further accelerated the response (Figure 2B and C). Designs 1–4 considered the permeation of the NR through the nuclear membrane to be passive, implying an import/export activity ratio of 1. When varying the import to export activity ratio (design 5), a trade-off between the fast responsiveness of design 4 and the high sensitivity of design 2 was calculated (Figure 2B). In order to maximize responsiveness, core-NR should be concentrated in the cytoplasm, whereas to gain sensitivity, liganded NR should be concentrated in the nucleus. This suggested that performance could be improved by making nuclear import and export selective for liganded over unliganded NR (design 6; Figure 2A). Indeed, retention of core-NR in the cytoplasm provided high influx of ligand into the nucleus (Figure 2D), and also the highest concentration of ligand in the nucleus (Figure 2C): Apart from its classical receptor role in transcription regulation, the NR may function as (part of) an active pump for its ligand, resembling a triple conveyor belt: importins and exportins cycle as conveyor belts and drive the cycling of the third conveyor belt consisting of the NR that pumps ligand into the nucleus. Two other striking features of the NR signaling network (Figure 1) are related to the facts that the energy of GTP hydrolysis is coupled to an active export of importins rather than to direct active import of NR and that the same NPC is used for all transport processes. At first sight, the former may waste free energy and the latter might cause fragility due to interferences between different NRs and other signaling pathways. However, our models show that active nuclear export of importins is a design preventing NR sequestration in the nucleus by nuclear importins and, equally paradoxically, the transport of all cargo through the same NPC makes the transport of any particular cargo robust with respect to perturbations in the availability of any other cargo. Our calculations also predict that there is an optimal ratio of nuclear to cytoplasmic fractions of the NR (Figure 2G) that depends on the specific properties of the ligand and on the transcription activation requirements. This may help to explain the observation that different NRs have different predominant intracellular localizations. Our model calculations are thereby in line with many experimental observations, but specific cases of NR signaling may only exhibit a subset of all features. Our models can aid in identifying which subsets are important in any particular case of NR signaling, as we demonstrate for an example. In this study, we have shown that complex networks of biochemical and signaling reactions can harbor subtle design principles that can be understood rationally in terms of simplified but not simple models (which are available to the reader). The topology of nuclear receptor (NR) signaling is captured in a systems biological graphical notation. This enables us to identify a number of ‘design' aspects of the topology of these networks that might appear unnecessarily complex or even functionally paradoxical. In realistic kinetic models of increasing complexity, calculations show how these features correspond to potentially important design principles, e.g.: (i) cytosolic ‘nuclear' receptor may shuttle signal molecules to the nucleus, (ii) the active export of NRs may ensure that there is sufficient receptor protein to capture ligand at the cytoplasmic membrane, (iii) a three conveyor belts design dissipating GTP-free energy, greatly aids response, (iv) the active export of importins may prevent sequestration of NRs by importins in the nucleus and (v) the unspecific nature of the nuclear pore may ensure signal-flux robustness. In addition, the models developed are suitable for implementation in specific cases of NR-mediated signaling, to predict individual receptor functions and differential sensitivity toward physiological and pharmacological ligands.
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133
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Brodbeck J, McGuire J, Liu Z, Meyer-Franke A, Balestra ME, Jeong DE, Pleiss M, McComas C, Hess F, Witter D, Peterson S, Childers M, Goulet M, Liverton N, Hargreaves R, Freedman S, Weisgraber KH, Mahley RW, Huang Y. Structure-dependent impairment of intracellular apolipoprotein E4 trafficking and its detrimental effects are rescued by small-molecule structure correctors. J Biol Chem 2011; 286:17217-26. [PMID: 21454574 DOI: 10.1074/jbc.m110.217380] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Apolipoprotein (apo) E4 is the major genetic risk factor for Alzheimer disease (AD) and likely contributes to neuropathology through various pathways. Here we report that the intracellular trafficking of apoE4 is impaired in Neuro-2a cells and primary neurons, as shown by measuring fluorescence recovery after photobleaching. In Neuro-2a cells, more apoE4 than apoE3 molecules remained immobilized in the endoplasmic reticulum (ER) and the Golgi apparatus, and the lateral motility of apoE4 was significantly lower in the Golgi apparatus (but not in the ER) than that of apoE3. Likewise, the immobile fraction was larger, and the lateral motility was lower for apoE4 than apoE3 in mouse primary hippocampal neurons. ApoE4 with the R61T mutation, which abolishes apoE4 domain interaction, was less immobilized, and its lateral motility was comparable with that of apoE3. The trafficking impairment of apoE4 was also rescued by disrupting domain interaction with the small-molecule structure correctors GIND25 and PH002. PH002 also rescued apoE4-induced impairments of neurite outgrowth in Neuro-2a cells and dendritic spine development in primary neurons. ApoE4 did not affect trafficking of amyloid precursor protein, another AD-related protein, through the secretory pathway. Thus, domain interaction renders more newly synthesized apoE4 molecules immobile and slows their trafficking along the secretory pathway. Correcting the pathological structure of apoE4 by disrupting domain interaction is a potential therapeutic approach to treat or prevent AD related to apoE4.
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Affiliation(s)
- Jens Brodbeck
- Gladstone Institute of Neurological Disease, University of California, San Francisco, California 94158, USA
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Aronson DE, Costantini LM, Snapp EL. Superfolder GFP is fluorescent in oxidizing environments when targeted via the Sec translocon. Traffic 2011; 12:543-8. [PMID: 21255213 DOI: 10.1111/j.1600-0854.2011.01168.x] [Citation(s) in RCA: 100] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
The ability to study proteins in live cells using genetically encoded fluorescent proteins (FPs) has revolutionized cell biology (1-3). Researchers have created numerous FP biosensors and optimized FPs for specific organisms and subcellular environments in a rainbow of colors (4,5). However, expressing FPs in oxidizing environments such as the eukaryotic endoplasmic reticulum (ER) or the bacterial periplasm can impair folding, thereby preventing fluorescence (6,7). A substantial fraction of enhanced green fluorescent protein (EGFP) oligomerizes to form non-fluorescent mixed disulfides in the ER (6) and EGFP does not fluoresce in the periplasm when targeted via the SecYEG translocon (7). To overcome these obstacles, we exploited the highly efficient folding capability of superfolder GFP (sfGFP) (8). Here, we report sfGFP does not form disulfide-linked oligomers in the ER and maltose-binding protein (MBP) signal sequence (peri)-sfGFP (9) is brightly fluorescent in the periplasm of Escherichia coli. Thus, sfGFP represents an important research tool for studying resident proteins of oxidizing environments.
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Affiliation(s)
- Deborah E Aronson
- Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA
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135
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Kiskin NI, Hellen N, Babich V, Hewlett L, Knipe L, Hannah MJ, Carter T. Protein mobilities and P-selectin storage in Weibel-Palade bodies. J Cell Sci 2011; 123:2964-75. [PMID: 20720153 DOI: 10.1242/jcs.073593] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Using fluorescence recovery after photobleaching (FRAP) we measured the mobilities of EGFP-tagged soluble secretory proteins in the endoplasmic reticulum (ER) and in individual Weibel-Palade bodies (WPBs) at early (immature) and late (mature) stages in their biogenesis. Membrane proteins (P-selectin, CD63, Rab27a) were also studied in individual WPBs. In the ER, soluble secretory proteins were mobile; however, following insertion into immature WPBs larger molecules (VWF, Proregion, tPA) and P-selectin became immobilised, whereas small proteins (ssEGFP, eotaxin-3) became less mobile. WPB maturation led to further decreases in mobility of small proteins and CD63. Acute alkalinisation of mature WPBs selectively increased the mobilities of small soluble proteins without affecting larger molecules and the membrane proteins. Disruption of the Proregion-VWF paracrystalline core by prolonged incubation with NH(4)Cl rendered P-selectin mobile while VWF remained immobile. FRAP of P-selectin mutants revealed that immobilisation most probably involves steric entrapment of the P-selectin extracellular domain by the Proregion-VWF paracrystal. Significantly, immobilisation contributed to the enrichment of P-selectin in WPBs; a mutation of P-selectin preventing immobilisation led to a failure of enrichment. Together these data shed new light on the transitions that occur for soluble and membrane proteins following their entry and storage into post-Golgi-regulated secretory organelles.
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Affiliation(s)
- Nikolai I Kiskin
- Division of Molecular Neuroendocrinology, MRC National Institute for Medical Research, Mill Hill, London NW7 1AA, UK.
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136
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Jandt U, Zeng AP. Modeling of intracellular transport and compartmentation. ADVANCES IN BIOCHEMICAL ENGINEERING/BIOTECHNOLOGY 2011; 127:221-49. [PMID: 22210243 DOI: 10.1007/10_2011_104] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The complexity and internal organization of mammalian cells as well as the regulation of intracellular transport processes has increasingly moved into the focus of investigation during the past two decades. Advanced staining and microscopy techniques help to shed light onto spatial cellular compartmentation and regulation, increasing the demand for improved modeling techniques. In this chapter, we summarize recent developments in the field of quantitative simulation approaches and frameworks for the description of intracellular transport processes. Special focus is therefore laid on compartmented and spatiotemporally resolved simulation approaches. The processes considered include free and facilitated diffusion of molecules, active transport via the microtubule and actin filament network, vesicle distribution, membrane transport, cell cycle-dependent cell growth and morphology variation, and protein production. Commercially and freely available simulation packages are summarized as well as model data exchange and harmonization issues.
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Affiliation(s)
- Uwe Jandt
- Institute of Bioprocess and Biosystems Engineering, Hamburg University of Technology, Denickestreet 15, D-21071, Hamburg, Germany,
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137
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Yamaguchi H, Miyazaki M, Briones-Nagata MP, Maeda H. Refolding of difficult-to-fold proteins by a gradual decrease of denaturant using microfluidic chips. ACTA ACUST UNITED AC 2010; 147:895-903. [DOI: 10.1093/jb/mvq024] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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138
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Calvert PD, Schiesser WE, Pugh EN. Diffusion of a soluble protein, photoactivatable GFP, through a sensory cilium. ACTA ACUST UNITED AC 2010; 135:173-96. [PMID: 20176852 PMCID: PMC2828910 DOI: 10.1085/jgp.200910322] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Transport of proteins to and from cilia is crucial for normal cell function and
survival, and interruption of transport has been implicated in degenerative and
neoplastic diseases. It has been hypothesized that the ciliary axoneme and
structures adjacent to and including the basal bodies of cilia impose selective
barriers to the movement of proteins into and out of the cilium. To examine this
hypothesis, using confocal and multiphoton microscopy we determined the mobility
of the highly soluble photoactivatable green fluorescent protein (PAGFP) in the
connecting cilium (CC) of live Xenopus retinal rod
photoreceptors, and in the contiguous subcellular compartments bridged by the
CC, the inner segment (IS) and the outer segment (OS). The estimated axial
diffusion coefficients are DCC = 2.8 ±
0.3, DIS = 5.2 ± 0.6, and
DOS = 0.079 ± 0.009
µm2 s−1. The results establish that the
CC does not pose a major barrier to protein diffusion within the rod cell.
However, the results also reveal that axial diffusion in each of the
rod’s compartments is substantially retarded relative to aqueous
solution: the axial diffusion of PAGFP was retarded ∼18-, 32- and
1,000-fold in the IS, CC, and OS, respectively, with ∼20-fold of the
reduction in the OS attributable to tortuosity imposed by the lamellar disc
membranes. Previous investigation of PAGFP diffusion in passed, spherical
Chinese hamster ovary cells yielded DCHO = 20
µm2 s−1, and estimating cytoplasmic
viscosity as Daq/DCHO
= 4.5, the residual 3- to 10-fold reduction in PAGFP diffusion is
ascribed to sub-optical resolution structures in the IS, CC, and OS
compartments.
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Affiliation(s)
- Peter D Calvert
- Department of Ophthalmology, SUNY Upstate Medical University, Syracuse, NY 13210, USA.
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139
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Lai CW, Aronson DE, Snapp EL. BiP availability distinguishes states of homeostasis and stress in the endoplasmic reticulum of living cells. Mol Biol Cell 2010; 21:1909-21. [PMID: 20410136 PMCID: PMC2883936 DOI: 10.1091/mbc.e09-12-1066] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
BiP availability represents a powerful tool for reporting global secretory protein misfolding levels and investigating the molecular events of ER stress in single cells, independent of traditional UPR markers. Accumulation of misfolded secretory proteins causes cellular stress and induces the endoplasmic reticulum (ER) stress pathway, the unfolded protein response (UPR). Although the UPR has been extensively studied, little is known about the molecular changes that distinguish the homeostatic and stressed ER. The increase in levels of misfolded proteins and formation of complexes with chaperones during ER stress are predicted to further crowd the already crowded ER lumen. Surprisingly, using live cell fluorescence microscopy and an inert ER reporter, we find the crowdedness of stressed ER, treated acutely with tunicamycin or DTT, either is comparable to homeostasis or significantly decreases in multiple cell types. In contrast, photobleaching experiments revealed a GFP-tagged variant of the ER chaperone BiP rapidly undergoes a reversible quantitative decrease in diffusion as misfolded proteins accumulate. BiP mobility is sensitive to exceptionally low levels of misfolded protein stressors and can detect intermediate states of BiP availability. Decreased BiP availability temporally correlates with UPR markers, but restoration of BiP availability correlates less well. Thus, BiP availability represents a novel and powerful tool for reporting global secretory protein misfolding levels and investigating the molecular events of ER stress in single cells, independent of traditional UPR markers.
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Affiliation(s)
- Chun Wei Lai
- Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA
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140
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Kang M, Day CA, Drake K, Kenworthy AK, DiBenedetto E. A generalization of theory for two-dimensional fluorescence recovery after photobleaching applicable to confocal laser scanning microscopes. Biophys J 2009; 97:1501-11. [PMID: 19720039 DOI: 10.1016/j.bpj.2009.06.017] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2008] [Revised: 06/05/2009] [Accepted: 06/16/2009] [Indexed: 11/25/2022] Open
Abstract
Fluorescence recovery after photobleaching (FRAP) using confocal laser scanning microscopes (confocal FRAP) has become a valuable technique for studying the diffusion of biomolecules in cells. However, two-dimensional confocal FRAP sometimes yields results that vary with experimental setups, such as different bleaching protocols and bleaching spot sizes. In addition, when confocal FRAP is used to measure diffusion coefficients (D) for fast diffusing molecules, it often yields D-values that are one or two orders-of-magnitude smaller than that predicted theoretically or measured by alternative methods such as fluorescence correlation spectroscopy. Recently, it was demonstrated that this underestimation of D can be corrected by taking diffusion during photobleaching into consideration. However, there is currently no consensus on confocal FRAP theory, and no efforts have been made to unify theories on conventional and confocal FRAP. To this end, we generalized conventional FRAP theory to incorporate diffusion during photobleaching so that analysis by conventional FRAP theory for a circular region of interest is easily applicable to confocal FRAP. Finally, we demonstrate the accuracy of these new (to our knowledge) formulae by measuring D for soluble enhanced green fluorescent protein in aqueous glycerol solution and in the cytoplasm and nucleus of COS7 cells.
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Affiliation(s)
- Minchul Kang
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
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141
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The sarcoplasmic reticulum Ca2+ store arrangement in vascular smooth muscle. Cell Calcium 2009; 46:313-22. [DOI: 10.1016/j.ceca.2009.09.001] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2009] [Revised: 08/28/2009] [Accepted: 09/03/2009] [Indexed: 01/01/2023]
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142
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Schmit JD, Kamber E, Kondev J. Lattice model of diffusion-limited bimolecular chemical reactions in confined environments. PHYSICAL REVIEW LETTERS 2009; 102:218302. [PMID: 19519142 DOI: 10.1103/physrevlett.102.218302] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/31/2008] [Indexed: 05/27/2023]
Abstract
We study the effect of confinement on diffusion-limited bimolecular reactions within a lattice model where a small number of reactants diffuse among a much larger number of inert particles. When the number of inert particles is held constant, the rate of the reaction is slow for small reaction volumes due to limited mobility from crowding and for large reaction volumes due to the reduced concentration of the reactants. The reaction rate proceeds fastest at an intermediate confinement corresponding to a volume fraction near 50%. We generalize the model to off-lattice systems with hydrodynamic coupling and predict that the optimal reaction rate for monodisperse colloidal systems occurs when the volume fraction is approximately 19%. Finally, we discuss the implications of our model for bimolecular reactions inside cells and the dynamics of confined polymers.
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Affiliation(s)
- Jeremy D Schmit
- Department of Physics, Brandeis University, Waltham, Massachusetts 02454, USA.
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143
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Testerink N, van der Sanden MHM, Houweling M, Helms JB, Vaandrager AB. Depletion of phosphatidylcholine affects endoplasmic reticulum morphology and protein traffic at the Golgi complex. J Lipid Res 2009; 50:2182-92. [PMID: 19458387 DOI: 10.1194/jlr.m800660-jlr200] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The mutant Chinese hamster ovary cell line MT58 contains a thermosensitive mutation in CTP:phosphocholine cytidylyltransferase, the regulatory enzyme in the CDP-choline pathway. As a result, MT58 cells have a 50% decrease in their phosphatidylcholine (PC) level within 24 h when cultured at the nonpermissive temperature (40 degrees C). This is due to a relative rapid breakdown of PC that is not compensated for by the inhibition of de novo PC synthesis. Despite this drastic decrease in cellular PC content, cells are viable and can proliferate by addition of lysophosphatidylcholine. By [(3)H]oleate labeling, we found that the FA moiety of the degraded PC is recovered in triacylglycerol. In accordance with this finding, an accumulation of lipid droplets is seen in MT58 cells. Analysis of PC-depleted MT58 cells by electron and fluorescence microscopy revealed a partial dilation of the rough endoplasmic reticulum, resulting in spherical structures on both sites of the nucleus, whereas the morphology of the plasma membrane, mitochondria, and Golgi complex was unaffected. In contrast to these morphological observations, protein transport from the ER remains intact. Surprisingly, protein transport at the level of the Golgi complex is impaired. Our data suggest that the transport processes at the Golgi complex are regulated by distal changes in lipid metabolism.
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Affiliation(s)
- Nicole Testerink
- Department of Biochemistry and Cell Biology, Faculty of Veterinary Medicine, and Institute of Biomembranes, University of Utrecht, 3584 CM, The Netherlands
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144
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Kucharz K, Krogh M, Ng AN, Toresson H. NMDA receptor stimulation induces reversible fission of the neuronal endoplasmic reticulum. PLoS One 2009; 4:e5250. [PMID: 19381304 PMCID: PMC2668765 DOI: 10.1371/journal.pone.0005250] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2009] [Accepted: 03/19/2009] [Indexed: 12/02/2022] Open
Abstract
With few exceptions the endoplasmic reticulum (ER) is considered a continuous system of endomembranes within which proteins and ions can move. We have studied dynamic structural changes of the ER in hippocampal neurons in primary culture and organotypic slices. Fluorescence recovery after photobleaching (FRAP) was used to quantify and model ER structural dynamics. Ultrastructure was assessed by electron microscopy. In live cell imaging experiments we found that, under basal conditions, the ER of neuronal soma and dendrites was continuous. The smooth and uninterrupted appearance of the ER changed dramatically after glutamate stimulation. The ER fragmented into isolated vesicles in a rapid fission reaction that occurred prior to overt signs of neuronal damage. ER fission was found to be independent of ER calcium levels. Apart from glutamate, the calcium ionophore ionomycin was able to induce ER fission. The N-methyl, D-aspartate (NMDA) receptor antagonist MK-801 inhibited ER fission induced by glutamate as well as by ionomycin. Fission was not blocked by either ifenprodil or kinase inhibitors. Interestingly, sub-lethal NMDA receptor stimulation caused rapid ER fission followed by fusion. Hence, ER fission is not strictly associated with cellular damage or death. Our results thus demonstrate that neuronal ER structure is dynamically regulated with important consequences for protein mobility and ER luminal calcium tunneling.
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Affiliation(s)
- Krzysztof Kucharz
- Laboratory for Experimental Brain Research, Wallenberg Neuroscience Centre, Department of Clinical Sciences Lund, Lund University, Lund, Sweden
| | - Morten Krogh
- Computational Biology and Biological Physics, Department of Theoretical Physics, Lund University, Lund, Sweden
| | - Ai Na Ng
- Laboratory for Experimental Brain Research, Wallenberg Neuroscience Centre, Department of Clinical Sciences Lund, Lund University, Lund, Sweden
| | - Håkan Toresson
- Laboratory for Experimental Brain Research, Wallenberg Neuroscience Centre, Department of Clinical Sciences Lund, Lund University, Lund, Sweden
- * E-mail:
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145
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Mirkovic T, Wilk KE, Curmi PMG, Scholes GD. Phycobiliprotein diffusion in chloroplasts of cryptophyte Rhodomonas CS24. PHOTOSYNTHESIS RESEARCH 2009; 100:7-17. [PMID: 19224391 DOI: 10.1007/s11120-009-9412-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2008] [Accepted: 02/04/2009] [Indexed: 05/27/2023]
Abstract
Unicellular cryptophyte algae employ antenna proteins with phycobilin chromophores in their photosynthetic machinery. The mechanism of light harvesting in these organisms is significantly different than the energy funneling processes in phycobilisomes utilized by cyanobacteria and red algae. One of the most striking features of cryptophytes is the location of the water-soluble phycobiliproteins, which are contained within the intrathylakoid spaces and are not on the stromal side of the lamellae as in the red algae and cyanobacteria. Studies of mobility of phycobiliproteins at the lumenal side of the thylakoid membranes and how their diffusional behavior may influence the energy funneling steps in light harvesting are reported. Confocal microscopy and fluorescence recovery after photobleaching (FRAP) are used to measure the diffusion coefficient of phycoerythrin 545 (PE545), the primary light harvesting protein of Rhodomonas CS24, in vivo. It is concluded that the diffusion of PE545 in the lumen is inhibited, suggesting possible membrane association or aggregation as a potential source of mobility hindrance.
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Affiliation(s)
- Tihana Mirkovic
- Department of Chemistry, Institute for Optical Sciences, Centre for Quantum Information and Quantum Control, University of Toronto, 80 St. George Street, Toronto, Ontario, Canada
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146
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Wang Y, Shyy JYJ, Chien S. Fluorescence proteins, live-cell imaging, and mechanobiology: seeing is believing. Annu Rev Biomed Eng 2008; 10:1-38. [PMID: 18647110 DOI: 10.1146/annurev.bioeng.010308.161731] [Citation(s) in RCA: 199] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Fluorescence proteins (FPs) have been widely used for live-cell imaging in the past decade. This review summarizes the recent advances in FP development and imaging technologies using FPs to monitor molecular localization and activities and gene expressions in live cells. We also discuss the utilization of FPs to develop molecular biosensors and the principles and application of advanced technologies such as fluorescence resonance energy transfer (FRET), fluorescence recovery after photobleaching (FRAP), fluorescence lifetime imaging microscopy (FLIM), and chromophore-assisted light inactivation (CALI). We present examples of the application of FPs and biosensors to visualize mechanotransduction events with high spatiotemporal resolutions in live cells. These live-cell imaging technologies, which represent a frontier area in biomedical engineering, can shed new light on the mechanisms regulating mechanobiology at cellular and molecular levels in normal and pathophysiological conditions.
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Affiliation(s)
- Yingxiao Wang
- Department of Bioengineering and Beckman Institute for Advanced Science and Technology, University of Illinois, Urbana-Champaign, Urbana, IL 61801, USA.
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147
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Lustyik G. Photobleaching measurements of diffusion in cell membranes and aqueous cell compartments. CURRENT PROTOCOLS IN CYTOMETRY 2008; Chapter 2:Unit 2.12. [PMID: 18770695 DOI: 10.1002/0471142956.cy0212s16] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
This commentary unit discusses in great detail the theoretical nature of fluorescence recovery after photobleaching (FRAP). This information is crucial to an understanding of how and why FRAP works in a cell system. Further, understanding how to interpret the data sets requires a sound knowledge of the processes involved. Of primary importance are the nature of membrane diffusion and the nature of the multiple compartments into which fluorescent dyes can enter. The unit provides a complete discussion of all aspects of FRAP from the perspective of cellular measurements.
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Affiliation(s)
- G Lustyik
- University of Pécs, Faculty of Medicine, Pécs, Hungary
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148
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Affiliation(s)
- Soohyung Park
- Institute of Chemistry and the Fritz Haber Research Center, The Hebrew University, Jerusalem 91904, Israel
| | - Noam Agmon
- Institute of Chemistry and the Fritz Haber Research Center, The Hebrew University, Jerusalem 91904, Israel
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149
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Krasnenko V, Tkaczyk AH, Tkaczyk ER, Mauring K. Physicochemical properties of blue fluorescent protein determined via molecular dynamics simulation. Biopolymers 2008; 89:1136-43. [DOI: 10.1002/bip.21065] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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150
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Abstract
We review the effects of molecular crowding on solute diffusion in solution and in cellular aqueous compartments and membranes. Anomalous diffusion, in which mean squared displacement does not increase linearly with time, is predicted in simulations of solute diffusion in media crowded with fixed or mobile obstacles, or when solute diffusion is restricted or accelerated by a variety of geometric or active transport processes. Experimental measurements of solute diffusion in solutions and cellular aqueous compartments, however, generally show Brownian diffusion. In cell membranes, there are examples of both Brownian and anomalous diffusion, with the latter likely produced by lipid-protein and protein-protein interactions. We conclude that the notion of universally anomalous diffusion in cells as a consequence of molecular crowding is not correct and that slowing of diffusion in cells is less marked than has been generally assumed.
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Affiliation(s)
- James A Dix
- Department of Chemistry, State University of New York, Binghamton, New York 13902, USA
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