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Wang M, Li S, Zhang H, Pei L, Zou S, Lee FJS, Wang YT, Liu F. Direct interaction between GluR2 and GAPDH regulates AMPAR-mediated excitotoxicity. Mol Brain 2012; 5:13. [PMID: 22537872 PMCID: PMC3407747 DOI: 10.1186/1756-6606-5-13] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2012] [Accepted: 04/26/2012] [Indexed: 12/30/2022] Open
Abstract
Over-activation of AMPARs (α−amino-3-hydroxy-5-methylisoxazole-4-propionic acid subtype glutamate receptors) is implicated in excitotoxic neuronal death associated with acute brain insults, such as ischemic stroke. However, the specific molecular mechanism by which AMPARs, especially the calcium-impermeable AMPARs, induce neuronal death remains poorly understood. Here we report the identification of a previously unrecognized molecular pathway involving a direct protein-protein interaction that underlies GluR2-containing AMPAR-mediated excitotoxicity. Agonist stimulation of AMPARs promotes GluR2/GAPDH (glyceraldehyde-3-phosphate dehydrogenase) complex formation and subsequent internalization. Disruption of GluR2/GAPDH interaction by administration of an interfering peptide prevents AMPAR-mediated excitotoxicity and protects against damage induced by oxygen-glucose deprivation (OGD), an in vitro model of brain ischemia.
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Affiliation(s)
- Min Wang
- Department of Neuroscience, Centre for Addiction and Mental Health, Toronto, Canada
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2
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Real-Hohn A, Zancan P, Da Silva D, Martins ER, Salgado LT, Mermelstein CS, Gomes AM, Sola-Penna M. Filamentous actin and its associated binding proteins are the stimulatory site for 6-phosphofructo-1-kinase association within the membrane of human erythrocytes. Biochimie 2010; 92:538-44. [DOI: 10.1016/j.biochi.2010.01.023] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2009] [Accepted: 01/29/2010] [Indexed: 01/16/2023]
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3
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Silva DD, Zancan P, Coelho WS, Gomez LS, Sola-Penna M. Metformin reverses hexokinase and 6-phosphofructo-1-kinase inhibition in skeletal muscle, liver and adipose tissues from streptozotocin-induced diabetic mouse. Arch Biochem Biophys 2010; 496:53-60. [DOI: 10.1016/j.abb.2010.01.013] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2009] [Revised: 01/22/2010] [Accepted: 01/25/2010] [Indexed: 12/25/2022]
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4
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Chuang DM, Hough C, Senatorov VV. Glyceraldehyde-3-phosphate dehydrogenase, apoptosis, and neurodegenerative diseases. Annu Rev Pharmacol Toxicol 2005; 45:269-90. [PMID: 15822178 DOI: 10.1146/annurev.pharmtox.45.120403.095902] [Citation(s) in RCA: 230] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Increasing evidence supports the notion that glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a protein with multiple functions, including its surprising role in apoptosis. GAPDH is overexpressed and accumulates in the nucleus during apoptosis induced by a variety of insults in diverse cell types. Knockdown of GAPDH using an antisense strategy demonstrates its involvement in the apoptotic cascade in which GAPDH nuclear translocation appears essential. Knowledge concerning the mechanisms underlying GAPDH nuclear translocation and subsequent cell death is growing. Additional evidence suggests that GAPDH may be an intracellular sensor of oxidative stress during early apoptosis. Abnormal expression, nuclear accumulation, changes in physical properties, and loss of glycolytic activity of GAPDH have been found in cellular and transgenic models as well as postmortem tissues of several neurodegenerative diseases. The interaction of GAPDH with disease-related proteins as well as drugs used to treat these diseases suggests that it is a potential molecular target for drug development.
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Affiliation(s)
- De-Maw Chuang
- Molecular Neurobiology Section, Mood and Anxiety Disorders Program, National Institute of Mental Health, National Institutes of Health, Bethesda, Maryland 20892-1363, USA.
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5
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Deveze-Alvarez M, Garcı A-Soto J, Martı Nez-Cadena G. Glyceraldehyde-3-phosphate dehydrogenase is negatively regulated by ADP-ribosylation in the fungus Phycomyces blakesleeanus. MICROBIOLOGY (READING, ENGLAND) 2001; 147:2579-2584. [PMID: 11535798 DOI: 10.1099/00221287-147-9-2579] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Dormant spores of Phycomyces blakesleeanus contain a 37 kDa protein that is endogenously mono-ADP-ribosylated. This protein was purified and identified as glyceraldehyde-3-phosphate dehydrogenase (GAPDH) by N-terminal sequencing and homology analysis. GAPDH enzymic activity changed dramatically upon spore germination, being maximal at stages where ADP-ribosylation was nearly undetectable. The presence of glyceraldehyde 3-phosphate in this reaction affected the [(32)P]ADP-ribosylation of the GAPDH. ADP-ribosylation of the GAPDH occurred by transfer of the ADP-ribose moiety from NAD to an arginine residue. A model for the regulation of GAPDH activity and its role in spore germination in P. blakesleeanus is proposed.
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Affiliation(s)
- Martha Deveze-Alvarez
- Instituto de Investigación en Biologı́a Experimental, Facultad de Quı́mica, Universidad de Guanajuato, Apdo. postal 187, Guanajuato, Gto, 36000, Mexico1
| | - Jesús Garcı A-Soto
- Instituto de Investigación en Biologı́a Experimental, Facultad de Quı́mica, Universidad de Guanajuato, Apdo. postal 187, Guanajuato, Gto, 36000, Mexico1
| | - Guadalupe Martı Nez-Cadena
- Instituto de Investigación en Biologı́a Experimental, Facultad de Quı́mica, Universidad de Guanajuato, Apdo. postal 187, Guanajuato, Gto, 36000, Mexico1
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6
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Yuan A, Mills RG, Bamburg JR, Bray JJ. Cotransport of glyceraldehyde-3-phosphate dehydrogenase and actin in axons of chicken motoneurons. Cell Mol Neurobiol 1999; 19:733-44. [PMID: 10456234 DOI: 10.1023/a:1006953022763] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
1. To study proteins transported with actin in axons, we pulse-labeled motoneurons in the chicken sciatic nerve with [35S]methionine and, 1-20 days later, isolated actin and its binding proteins by affinity chromatography of Triton soluble nerve extracts on DNase I-Sepharose. The DNase I-purified proteins were electrophoresed on two-dimensional gels and the specific activity of the radioactively labeled protein spots was estimated by fluorography. 2. In addition to actin, which binds specifically to DNase I, a small number of other proteins were labeled, including established actin monomer binding proteins and a protein of 36 kDa and pI 8.5. On the basis of its molecular mass, pI, amino acid composition, and immunostaining, the unrecognized protein was identified as the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH). 3. The high-affinity binding of GAPDH to actin was confirmed by incubation of Triton-soluble nerve extracts with either mouse anti-GAPDH (or antiactin) and indirect immunomagnetic separation with Dynabeads covalently linked to sheep anti-mouse antibody. Analysis by one-dimensional gel electrophoresis and immunoblotting showed that actin and GAPDH were the main proteins isolated by these methods. 4. Analysis of labeled nerves at 12 and 20 days after pulse labeling showed that GAPDH and actin were transported at the same rate, i.e., 3-5 mm/day, which corresponds to slow component b of axonal transport. These proteins were not associated with rapidly transported proteins that accumulated proximal to a ligation 7 cm from the spinal cord 9 hr after injection of radioactivity. 5. Our results indicate that GAPDH and actin are transported as a complex in axons and raise the possibility that GAPDH could act as a chaperone for monomeric actin, translocating it to intraaxonal sites for exchange with or assembly into actin filaments. Alternatively, actin could be involved in translocating and anchoring GAPDH to specialized sites in axons and nerve terminals that require a source of ATP by glycolysis.
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Affiliation(s)
- A Yuan
- Neuroscience Centre, University of Otago Medical School, Dunedin, New Zealand.
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7
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Ziegler U, Vinckier A, Kernen P, Zeisel D, Biber J, Semenza G, Murer H, Groscurth P. Preparation of basal cell membranes for scanning probe microscopy. FEBS Lett 1998; 436:179-84. [PMID: 9781674 DOI: 10.1016/s0014-5793(98)01118-1] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Scanning probe microscopy has the potential for investigating membranes in a physiological environment. We prepared with a lysis-squirting protocol basal cell membranes, that are suitable for scanning probe microscopy. Investigations using atomic force microscopy under liquid revealed cellular filaments which correlated perfectly with fluorescently stained actin filaments. Globular structures with a diameter as little as 10 nm could be resolved by stripping cytoplasmic components from the membranes. Therefore, cytoplasmic sides of supported basal cell membranes prove useful to gain high resolution with scanning probe microscopy in studies of plasma membrane associated structures and processes under buffer solution.
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Affiliation(s)
- U Ziegler
- Institute of Anatomy, University of Zurich, Switzerland.
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8
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Kusakabe T, Motoki K, Hori K. Mode of interactions of human aldolase isozymes with cytoskeletons. Arch Biochem Biophys 1997; 344:184-93. [PMID: 9244396 DOI: 10.1006/abbi.1997.0204] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Three isoforms of fructose-1,6-bisphosphate aldolase were found to bind specifically to the actin-containing filament of the cytoskeleton and to show tissue-specific binding patterns. Aldolase A (muscle type) bound more tightly to the skeletal muscle cytoskeleton among the three isozymes, while aldolase B (liver type) preferred the liver cytoskeleton to those of other tissues. The specific binding of aldolase A to the skeletal muscle cytoskeleton was inhibited strongly by the substrates fructose 1,6-bisphosphate and fructose 1-phosphate. Several mutant aldolases A were examined to identify the amino acid residues or regions that play a role in specific binding. Among the mutant aldolases tested, A-E34D, A-K41N, and A-Y363S exhibited remarkably reduced binding activities. Experiments using FITC-labeled enzymes and Rh-labeled phalloidin disclosed that aldolase A associated with the cytoskeleton. Specifically, when aldolase A was incubated with human fibroblast MRC-5 permeabilized with Triton X-100, aldolase A bound to the actin filaments in the stress fibers within the cell. Aldolase A reversibly inhibited the contraction of MRC-5 cells which usually occurred in the presence of Mg2(+)-ATP and Ca2+. These results provide direct evidence that aldolase binds specifically to the actin-containing stress fibers and suggest that aldolase may regulate cell contraction through its reversible binding to the filaments in the permeabilized MRC-5 fibroblast.
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Affiliation(s)
- T Kusakabe
- Department of Biochemistry, Saga Medical School, Nabeshima, Saga, Japan.
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9
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Ishitani R, Sunaga K, Tanaka M, Aishita H, Chuang DM. Overexpression of glyceraldehyde-3-phosphate dehydrogenase is involved in low K+-induced apoptosis but not necrosis of cultured cerebellar granule cells. Mol Pharmacol 1997; 51:542-50. [PMID: 9106617 DOI: 10.1124/mol.51.4.542] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
We have reported that overexpression of glyceraldehyde-3-phosphate dehydrogenase (GAPDH; EC 1.2.1.12) is involved in age-induced apoptosis of the cultured cerebellar granule cells that grow in a depolarizing concentration (25 mM) of KCI. The present study was undertaken to investigate whether GAPDH overexpression also occurs and participates in apoptosis of the cerebellar granule cells that result from switching the culturing conditions from high (25 mM) to low (5 mM) concentrations of KCl. We found that exposure of granule cells to low potassium (K+) for 24 hr induces not only apoptosis but also necrotic damage. The latter is supported by the morphological observations that a subpopulation of neurons showed cell swelling, extensive cytoplasmic vacuolization, damaged mitochondria, and apparently intact nuclei. Treatments with two antisense but not sense oligodeoxyribonucleotides directed against GAPDH attenuated low K+-induced neuronal death by approximately 50%. Morphological inspection revealed that GAPDH antisense oligonucleotides preferentially blocked low K+-induced apoptosis with little or no effect on necrotic damage. Similar to antisense oligonucleotides, actinomycin-D partially inhibited low K+-induced death of granule cells with a predominant effect on apoptosis. In contrast, cycloheximide almost completely blocked low K+-induced neuronal death and seemed to prevent both apoptotic and necrotic damage. The levels of GAPDH mRNA and protein were markedly increased in a time-dependent manner after low K+ exposure. The overexpression of GAPDH mRNA and protein was completely blocked by cycloheximide, actinomycin-D, and its antisense but not sense oligonucleotides. Taken together, these results lend credence to the view that exposure of cerebellar granule cells to low K+ induces both apoptosis and necrosis and that only the apoptotic component involves overexpression of GAPDH.
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Affiliation(s)
- R Ishitani
- Group on Cellular Neurobiology, Josai University, Sakado, Saitama, Japan
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10
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De Matteis MA, Di Girolamo M, Colanzi A, Pallas M, Di Tullio G, McDonald LJ, Moss J, Santini G, Bannykh S, Corda D. Stimulation of endogenous ADP-ribosylation by brefeldin A. Proc Natl Acad Sci U S A 1994; 91:1114-8. [PMID: 8302839 PMCID: PMC521464 DOI: 10.1073/pnas.91.3.1114] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Brefeldin A (BFA) is a fungal metabolite that exerts profound and generally inhibitory actions on membrane transport. At least some of the BFA effects are due to inhibition of the GDP-GTP exchange on the ADP-ribosylation factor (ARF) catalyzed by membrane protein(s). ARF activation is likely to be a key event in the association of non-clathrin coat components, including ARF itself, onto transport organelles. ARF, in addition to participating in membrane transport, is known to function as a cofactor in the enzymatic activity of cholera toxin, a bacterial ADP-ribosyltransferase. In this study we have examined whether BFA, in addition to inhibiting membrane transport, might affect endogenous ADP-ribosylation in eukaryotic cells. Two cytosolic proteins of 38 and 50 kDa were enzymatically ADP-ribosylated in the presence of BFA in cellular extracts. The 38-kDa substrate was tentatively identified as the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase. The BFA-binding components mediating inhibition of membrane traffic and stimulation of ADP-ribosylation appear to have the same ligand specificity. These data demonstrate the existence of a BFA-sensitive mono(ADP-ribosyl)transferase that may play a role in membrane movements.
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Affiliation(s)
- M A De Matteis
- Unit of Physiopathology of Secretion, Istituto di Ricerche Farmacologiche Mario Negri, Consorzio Mario Negri Sud, S. Maria Imbaro (Chieti), Italy
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11
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Schulze H, Schuler A, Stüber D, Döbeli H, Langen H, Huber G. Rat brain glyceraldehyde-3-phosphate dehydrogenase interacts with the recombinant cytoplasmic domain of Alzheimer's beta-amyloid precursor protein. J Neurochem 1993; 60:1915-22. [PMID: 8473906 DOI: 10.1111/j.1471-4159.1993.tb13420.x] [Citation(s) in RCA: 96] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Abundant senile plaques are a histological hallmark in the brain of Alzheimer's disease patients. Such plaques consist of, among many other constituents, aggregated beta A4 amyloid peptide. This peptide is derived from an amyloid precursor protein (APP) by irregular proteolytic processing and is considered to be involved in the development of Alzheimer's disease. To study possible interactions of brain proteins with beta A4 amyloid or other fragments of APP, beta A4 amyloid and beta A4 amyloid extended to the C-terminus of APP were recombinantly produced as fusion proteins termed "Amy" and "AmyC," respectively. Using Amy and AmyC affinity chromatography, a 35-kDa protein from rat brain was isolated that bound tightly to AmyC but not to Amy, thus indicating an interaction of the protein with the C-terminus of APP. This 35-kDa protein was identified as the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Binding of GAPDH to AmyC but not to Amy was confirmed by gel filtration. Although AmyC slightly reduced the Vmax of GAPDH, the same reduction was observed in the presence of Amy. These findings suggest that the interaction of the cytoplasmic domain of APP with GAPDH is unlikely to influence directly the rate of glycolysis but may serve another function.
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Affiliation(s)
- H Schulze
- Pharma Division, Preclinical Research and New Technologies, F. Hoffman-LaRoche Ltd., Basel, Switzerland
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12
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Nermut MV, Burt JS, Hirst EM, Larjava H. Distribution of avian integrin during the lifetime of chicken embryo fibroblasts in vitro: Study by immunofluorescence and immuno electron microscopy. Micron 1993. [DOI: 10.1016/0968-4328(93)90002-i] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
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13
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Association of Glyceraldehyde-3-phosphate Dehydrogenase with the Plasma Membrane of the Intact Human Red Blood Cell. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(18)83368-3] [Citation(s) in RCA: 80] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
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14
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Blum JJ, Reed MC. A model for slow axonal transport and its application to neurofilamentous neuropathies. CELL MOTILITY AND THE CYTOSKELETON 1989; 12:53-65. [PMID: 2468419 DOI: 10.1002/cm.970120107] [Citation(s) in RCA: 32] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
A model for slow axonal transport is developed in which the essential features are reversible binding of cytoskeletal elements and of soluble cytosolic proteins to each other and to motile elements such as actin microfilaments. Computer simulation of the equations of the model demonstrate that the model can account for many of the features of the SCa and SCb waves observed in pulse experiments. The model also provides a unified explanation for the increase and decrease of neurofilament transport rates observed in various toxicant-induced neuropathies.
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Affiliation(s)
- J J Blum
- Department of Physiology, Duke University, Durham, North Carolina
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15
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Rogers SW, Rechsteiner M. Degradation of structurally characterized proteins injected into HeLa cells. Effects of intracellular location and the involvement of lysosomes. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(19)77712-6] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
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16
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Faulstich H, Zobeley S, Rinnerthaler G, Small JV. Fluorescent phallotoxins as probes for filamentous actin. J Muscle Res Cell Motil 1988; 9:370-83. [PMID: 3063723 DOI: 10.1007/bf01774064] [Citation(s) in RCA: 120] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Affiliation(s)
- H Faulstich
- Max-Planck-Institut für Medizinische Forschung, Abteilung Physiologie, Heidelberg, F.R.G
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Buss F, Hinssen H, Jockusch BM. Immunological and biochemical studies on the relationship between two actin-binding proteins, phosphofructokinase and gelsolin. EUROPEAN JOURNAL OF BIOCHEMISTRY 1988; 175:251-7. [PMID: 2841131 DOI: 10.1111/j.1432-1033.1988.tb14190.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Phosphofructokinase and gelsolin-like proteins coexist in many muscle and non-muscle tissues. They are both actin-binding proteins, and some of their biochemical parameters are remarkably similar. In a previous report [Füchtbauer, A., Jockusch, B. M., Leberer, E. & Pette, D. (1986) Proc. Natl Acad. Sci. USA 83, 9502-9506] it was shown that phosphofructokinase preparations contained actin-filament-severin activities characteristic for gelsolin. Therefore, we investigated a possible relationship between these proteins with respect to their actin-binding properties. Immunoblotting experiments with specific and non-cross-reacting antibodies to both proteins revealed two distinct polypeptides with slightly different molecular mass in SDS-PAGE of crude extracts from rabbit skeletal muscle, indicating that phosphofructokinase and gelsolin are not identical. An actin-filament-severing activity as well as the component detected by anti-gelsolin were found to copurify with phosphofructokinase during its preparation. However, the presumptive gelsolin was completely eliminated after a heat-denaturation step leaving the phosphofructokinase activity unaffected. Purified phosphofructokinase had no effects on the polymer state of preformed actin filaments. Unlike gelsolin, phosphofructokinase did not promote nucleation of actin polymerization but delayed the nucleation step. We therefore conclude that phosphofructokinase and gelsolin are functionally and structurally distinct proteins.
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Affiliation(s)
- F Buss
- Developmental Biology Unit, University of Bielefeld, Federal Republic of Germany
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18
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Cooper JA, Bryan J, Schwab B, Frieden C, Loftus DJ, Elson EL. Microinjection of gelsolin into living cells. J Cell Biol 1987; 104:491-501. [PMID: 3029140 PMCID: PMC2114549 DOI: 10.1083/jcb.104.3.491] [Citation(s) in RCA: 123] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Gelsolins are actin-binding proteins that cap, nucleate, and sever actin filaments. Microinjection of cytoplasmic or plasma gelsolin into living fibroblasts and macrophages did not affect the shape, actin distribution, deformability, or ruffling activity of the cells. Gelsolin requires calcium for activity, but the NH2-terminal half is active without calcium. Microinjection of this proteolytic fragment had marked effects: the cells rounded up, stopped ruffling, became soft, and stress fibers disappeared. These changes are similar to those seen with cytochalasin, which also caps barbed ends of actin filaments. Attempts to raise the cytoplasmic calcium concentration and thereby activate the injected gelsolin were unsuccessful, but the increases in calcium concentration were minimal or transient and may not have been sufficient. Our interpretation of these results is that at the low calcium concentrations normally found in cells, gelsolin does not express the activities observed in vitro at higher calcium concentrations. We presume that gelsolin may be active at certain times or places if the calcium concentration is elevated to a sufficient level, but we cannot exclude the existence of another molecule that inhibits gelsolin. Microinjection of a 1:1 gelsolin/actin complex had no effect on the cells. This complex is stable in the absence of calcium and has capping activity but no severing and less nucleation activity as compared with either gelsolin in calcium or the NH2-terminal fragment. The NH2-terminal fragment-actin complex also has capping and nucleating activity but no severing activity. On microinjection it had the same effects as the fragment alone. The basis for the difference between the two complexes is unknown. The native molecular weight of rabbit plasma gelsolin is 82,500, and the extinction coefficient at 280 nm is 1.68 cm2/mg. A new simple procedure for purification of plasma gelsolin is described.
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