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van Zwam MC, Dhar A, Bosman W, van Straaten W, Weijers S, Seta E, Joosten B, van Haren J, Palani S, van den Dries K. IntAct: A nondisruptive internal tagging strategy to study the organization and function of actin isoforms. PLoS Biol 2024; 22:e3002551. [PMID: 38466773 PMCID: PMC10957077 DOI: 10.1371/journal.pbio.3002551] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2023] [Revised: 03/21/2024] [Accepted: 02/16/2024] [Indexed: 03/13/2024] Open
Abstract
Mammals have 6 highly conserved actin isoforms with nonredundant biological functions. The molecular basis of isoform specificity, however, remains elusive due to a lack of tools. Here, we describe the development of IntAct, an internal tagging strategy to study actin isoforms in fixed and living cells. We identified a residue pair in β-actin that permits tag integration and used knock-in cell lines to demonstrate that IntAct β-actin expression and filament incorporation is indistinguishable from wild type. Furthermore, IntAct β-actin remains associated with common actin-binding proteins (ABPs) and can be targeted in living cells. We demonstrate the usability of IntAct for actin isoform investigations by showing that actin isoform-specific distribution is maintained in human cells. Lastly, we observed a variant-dependent incorporation of tagged actin variants into yeast actin patches, cables, and cytokinetic rings demonstrating cross species applicability. Together, our data indicate that IntAct is a versatile tool to study actin isoform localization, dynamics, and molecular interactions.
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Affiliation(s)
- Maxime C. van Zwam
- Department of Medical BioSciences, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Anubhav Dhar
- Department of Biochemistry, Division of Biological Sciences, Indian Institute of Science, Bangalore, India
| | - Willem Bosman
- Department of Medical BioSciences, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Wendy van Straaten
- Department of Medical BioSciences, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Suzanne Weijers
- Department of Medical BioSciences, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Emiel Seta
- Department of Medical BioSciences, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Ben Joosten
- Department of Medical BioSciences, Radboud University Medical Center, Nijmegen, the Netherlands
| | | | - Saravanan Palani
- Department of Biochemistry, Division of Biological Sciences, Indian Institute of Science, Bangalore, India
| | - Koen van den Dries
- Department of Medical BioSciences, Radboud University Medical Center, Nijmegen, the Netherlands
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2
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Schroeder CM, Tomlin SA, Mejia Natividad I, Valenzuela JR, Young JM, Malik HS. An actin-related protein that is most highly expressed in Drosophila testes is critical for embryonic development. eLife 2021; 10:71279. [PMID: 34282725 PMCID: PMC8291977 DOI: 10.7554/elife.71279] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2021] [Accepted: 06/20/2021] [Indexed: 12/25/2022] Open
Abstract
Most actin-related proteins (Arps) are highly conserved and carry out well-defined cellular functions in eukaryotes. However, many lineages like Drosophila and mammals encode divergent non-canonical Arps whose roles remain unknown. To elucidate the function of non-canonical Arps, we focus on Arp53D, which is highly expressed in testes and retained throughout Drosophila evolution. We show that Arp53D localizes to fusomes and actin cones, two germline-specific actin structures critical for sperm maturation, via a unique N-terminal tail. Surprisingly, we find that male fertility is not impaired upon Arp53D loss, yet population cage experiments reveal that Arp53D is required for optimal fitness in Drosophila melanogaster. To reconcile these findings, we focus on Arp53D function in ovaries and embryos where it is only weakly expressed. We find that under heat stress Arp53D-knockout (KO) females lay embryos with reduced nuclear integrity and lower viability; these defects are further exacerbated in Arp53D-KO embryos. Thus, despite its relatively recent evolution and primarily testis-specific expression, non-canonical Arp53D is required for optimal embryonic development in Drosophila.
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Affiliation(s)
- Courtney M Schroeder
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, United States
| | - Sarah A Tomlin
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, United States.,Howard Hughes Medical Institute, Fred Hutchinson Cancer Research Center, Seattle, United States
| | - Isabel Mejia Natividad
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, United States.,Howard Hughes Medical Institute, Fred Hutchinson Cancer Research Center, Seattle, United States
| | - John R Valenzuela
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, United States
| | - Janet M Young
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, United States
| | - Harmit S Malik
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, United States.,Howard Hughes Medical Institute, Fred Hutchinson Cancer Research Center, Seattle, United States
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3
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Parker F, Baboolal TG, Peckham M. Actin Mutations and Their Role in Disease. Int J Mol Sci 2020; 21:ijms21093371. [PMID: 32397632 PMCID: PMC7247010 DOI: 10.3390/ijms21093371] [Citation(s) in RCA: 34] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2020] [Revised: 05/06/2020] [Accepted: 05/07/2020] [Indexed: 12/15/2022] Open
Abstract
Actin is a widely expressed protein found in almost all eukaryotic cells. In humans, there are six different genes, which encode specific actin isoforms. Disease-causing mutations have been described for each of these, most of which are missense. Analysis of the position of the resulting mutated residues in the protein reveals mutational hotspots. Many of these occur in regions important for actin polymerization. We briefly discuss the challenges in characterizing the effects of these actin mutations, with a focus on cardiac actin mutations.
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4
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A peptide tag-specific nanobody enables high-quality labeling for dSTORM imaging. Nat Commun 2018; 9:930. [PMID: 29500346 PMCID: PMC5834503 DOI: 10.1038/s41467-018-03191-2] [Citation(s) in RCA: 107] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2017] [Accepted: 01/26/2018] [Indexed: 11/08/2022] Open
Abstract
Dense fluorophore labeling without compromising the biological target is crucial for genuine super-resolution microscopy. Here we introduce a broadly applicable labeling strategy for fixed and living cells utilizing a short peptide tag-specific nanobody (BC2-tag/bivBC2-Nb). BC2-tagging of ectopically introduced or endogenous proteins does not interfere with the examined structures and bivBC2-Nb staining results in a close-grained fluorophore labeling with minimal linkage errors. This allowed us to perform high-quality dSTORM imaging of various targets in mammalian and yeast cells. We expect that this versatile strategy will render many more demanding cellular targets amenable to dSTORM imaging.
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5
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Abstract
Striated cardiac and skeletal muscles play very different roles in the body, but they are similar at the molecular level. In particular, contraction, regardless of the type of muscle, is a precise and complex process involving the integral protein myofilaments and their associated regulatory components. The smallest functional unit of muscle contraction is the sarcomere. Within the sarcomere can be found a sophisticated ensemble of proteins associated with the thick filaments (myosin, myosin binding protein-C, titin, and obscurin) and thin myofilaments (actin, troponin, tropomyosin, nebulin, and nebulette). These parallel thick and thin filaments slide across one another, pulling the two ends of the sarcomere together to regulate contraction. More specifically, the regulation of both timing and force of contraction is accomplished through an intricate network of intra- and interfilament interactions belonging to each myofilament. This review introduces the sarcomere proteins involved in striated muscle contraction and places greater emphasis on the more recently identified and less well-characterized myofilaments: cardiac myosin binding protein-C, titin, nebulin, and obscurin. © 2017 American Physiological Society. Compr Physiol 7:675-692, 2017.
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Affiliation(s)
- Brian Leei Lin
- Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Illinois, USA
| | - Taejeong Song
- Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Illinois, USA.,Department of Internal Medicine, Heart, Lung and Vascular Institute, Division of Cardiovascular Health and Sciences, University of Cincinnati College of Medicine, Cincinnati, Ohio, USA
| | - Sakthivel Sadayappan
- Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Illinois, USA.,Department of Internal Medicine, Heart, Lung and Vascular Institute, Division of Cardiovascular Health and Sciences, University of Cincinnati College of Medicine, Cincinnati, Ohio, USA
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6
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Simiczyjew A, Mazur AJ, Popow-Woźniak A, Malicka-Błaszkiewicz M, Nowak D. Effect of overexpression of β- and γ-actin isoforms on actin cytoskeleton organization and migration of human colon cancer cells. Histochem Cell Biol 2014; 142:307-22. [PMID: 24682235 PMCID: PMC4133152 DOI: 10.1007/s00418-014-1199-9] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/09/2014] [Indexed: 01/26/2023]
Abstract
Actins are eukaryotic proteins, which are involved in diverse cellular functions including muscle contraction, cell motility, adhesion and maintenance of cell shape. Cytoplasmic actin isoforms β and γ are ubiquitously expressed and essential for cell functioning. However, their unique contributions are not very well understood. The aim of this study was to determine the effect of β- and γ-actin overexpression on the migration capacity and actin cytoskeleton organization of human colon adenocarcinoma BE cells. In cells overexpressing β- or γ-actin, distinct cytoskeletal actin rearrangements were observed under the laser scanning confocal microscope. Overexpressed actins localized at the submembranous region of the cell body, especially near to the leading edge and on the tips of pseudopodia. The cells transfected with plasmids containing cDNA for β- or γ-actin were characterized by increased migration and invasion capacities. However, the migration velocity was statistically significantly higher only in the case of γ-actin overexpressing cells. In conclusion, the increased level of β- or γ-actin leads to actin cytoskeletal remodeling followed by an increase in migration and invasion capacities of human colon BE cells. These data suggest that expression of both actin isoforms has an impact on cancer cell motility, with the subtle predominance of γ-actin, and may influence invasiveness of human colon cancer.
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Affiliation(s)
- Aleksandra Simiczyjew
- Department of Cell Pathology, Faculty of Biotechnology, University of Wrocław, Joliot-Curie 14a, 50-383 Wrocław, Poland
| | - Antonina Joanna Mazur
- Department of Cell Pathology, Faculty of Biotechnology, University of Wrocław, Joliot-Curie 14a, 50-383 Wrocław, Poland
| | - Agnieszka Popow-Woźniak
- Department of Cell Pathology, Faculty of Biotechnology, University of Wrocław, Joliot-Curie 14a, 50-383 Wrocław, Poland
| | - Maria Malicka-Błaszkiewicz
- Department of Cell Pathology, Faculty of Biotechnology, University of Wrocław, Joliot-Curie 14a, 50-383 Wrocław, Poland
| | - Dorota Nowak
- Department of Cell Pathology, Faculty of Biotechnology, University of Wrocław, Joliot-Curie 14a, 50-383 Wrocław, Poland
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7
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Grantham J, Lassing I, Karlsson R. Controlling the cortical actin motor. PROTOPLASMA 2012; 249:1001-1015. [PMID: 22526202 PMCID: PMC3459087 DOI: 10.1007/s00709-012-0403-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/06/2012] [Accepted: 03/21/2012] [Indexed: 05/31/2023]
Abstract
Actin is the essential force-generating component of the microfilament system, which powers numerous motile processes in eukaryotic cells and undergoes dynamic remodeling in response to different internal and external signaling. The ability of actin to polymerize into asymmetric filaments is the inherent property behind the site-directed force-generating capacity that operates during various intracellular movements and in surface protrusions. Not surprisingly, a broad variety of signaling pathways and components are involved in controlling and coordinating the activities of the actin microfilament system in a myriad of different interactions. The characterization of these processes has stimulated cell biologists for decades and has, as a consequence, resulted in a huge body of data. The purpose here is to present a cellular perspective on recent advances in our understanding of the microfilament system with respect to actin polymerization, filament structure and specific folding requirements.
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Affiliation(s)
- Julie Grantham
- Department of Chemistry and Molecular Biology, University of Gothenburg, Gothenburg, Sweden
| | - Ingrid Lassing
- Department of Cell Biology, Wenner-Gren Institute, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Roger Karlsson
- Department of Cell Biology, Wenner-Gren Institute, Stockholm University, SE-106 91 Stockholm, Sweden
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8
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Chen Q, Nag S, Pollard TD. Formins filter modified actin subunits during processive elongation. J Struct Biol 2011; 177:32-9. [PMID: 22056467 DOI: 10.1016/j.jsb.2011.10.005] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2011] [Revised: 10/18/2011] [Accepted: 10/19/2011] [Indexed: 12/19/2022]
Abstract
Fission yeast cells reject actin subunits tagged with a fluorescent protein from the cytokinetic contractile ring, so cytokinesis fails and the cells die when the native actin gene is replaced by GFP-actin. The lack of a fluorescent actin probe has prevented a detailed study of actin filament dynamics in contractile rings, and left open questions regarding the mechanism of cytokinesis. To incorporate fluorescent actin into the contractile ring to study its dynamics, we introduced the coding sequence for a tetracysteine motif (FLNCCPGCCMEP) at 10 locations in the fission yeast actin gene and expressed the mutant proteins from the native actin locus in diploid cells with wild-type actin on the other chromosome. We labeled these tagged actins inside live cells with the FlAsH reagent. Cells incorporated some of these labeled actins into actin patches at sites of endocytosis, where Arp2/3 complex nucleates all of the actin filaments. However, the cells did not incorporate any of the FlAsH-actins into the contractile ring. Therefore, formin Cdc12p rejects actin subunits with a tag of ~2 kDa, illustrating the stringent structural requirements for this formin to promote the elongation of actin filament barbed ends as it moves processively along the end of a growing filament.
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Affiliation(s)
- Qian Chen
- Department of Molecular Cellular and Developmental Biology, Yale University, P.O. Box 208103, New Haven, CT 06520-8103, USA
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9
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Feng JJ, Marston S. Genotype–phenotype correlations in ACTA1 mutations that cause congenital myopathies. Neuromuscul Disord 2009; 19:6-16. [DOI: 10.1016/j.nmd.2008.09.005] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2008] [Revised: 09/08/2008] [Accepted: 09/09/2008] [Indexed: 12/01/2022]
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10
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Miller BM, Trybus KM. Functional effects of nemaline myopathy mutations on human skeletal alpha-actin. J Biol Chem 2008; 283:19379-88. [PMID: 18477565 DOI: 10.1074/jbc.m801963200] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mutations in human alpha-skeletal actin have been implicated in causing congenital nemaline myopathy, a disease characterized histopathologically by nemaline bodies in skeletal muscle and manifested in the patient as skeletal muscle weakness. Here we investigate the functional effects of three severe nemaline myopathy mutations (V43F, A138P, and R183G) in human alpha-skeletal actin. Wild-type and mutant actins were expressed and purified from the baculovirus/insect cell expression system. The mutations are located in different subdomains of actin; Val-43 is located in a flexible loop of subdomain 2, Ala-138 is near a hydrophobic cleft in the "hinge" region between subdomains 1 and 3, and Arg-183 is near the nucleotide-binding site. None of the three mutations affected the folding of the actin monomer, the velocity at which skeletal myosin moves actin in an in vitro motility assay, or the relative average isometric force supported by F-actin. Defects in fundamental actomyosin interactions are, therefore, unlikely to account for the muscle weakness observed in affected patients. There were, however, significant changes observed in the polymerization kinetics of V43F and A138P and in the rate of nucleotide release for V43F. No detectable defect was found for R183G. If these subtle changes in polymerization observed in vitro are amplified in the context of the sarcomere, it could in principle be one of the primary insults that triggers the development of nemaline myopathy.
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Affiliation(s)
- Becky M Miller
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont 05405, USA
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11
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Röper K, Mao Y, Brown NH. Contribution of sequence variation inDrosophilaactins to their incorporation into actin-based structures in vivo. J Cell Sci 2005; 118:3937-48. [PMID: 16105877 DOI: 10.1242/jcs.02517] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Actin is a highly conserved protein important for many cellular functions including motility, contraction in muscles and intracellular transport. Many eukaryotic genomes encode multiple actin protein isoforms that differ from each other by only a few residues. We addressed whether the sequence differences between actin paralogues in one species affect their ability to integrate into the large variety of structures generated by filamentous actin. We thus ectopically expressed all six Drosophila actins as fusion proteins with green fluorescent protein (GFP) in a variety of embryonic, larval and adult fly tissues. We found that each actin was able to integrate into most actin structures analysed. For example, in contrast to studies in mammalian cells, the two Drosophila cytoplasmic actins were incorporated into muscle sarcomeres. However, there were differences in the efficiency with which each actin was incorporated into specific actin structures. The most striking difference was observed within the Z-lines of the sarcomeres: one actin was specifically excluded and we mapped this feature to one or both of two residues within the C-terminal half of the protein. Thus, in Drosophila, the primary sequence of different actins does affect their ability to incorporate into actin structures, and so specific GFPactins may be used to label certain actin structures particularly well.
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Affiliation(s)
- Katja Röper
- Wellcome Trust/Cancer Research UK Gurdon Institute and Department of Anatomy, University of Cambridge, Tennis Court Road, Cambridge CB2 1QN, UK
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12
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Abstract
This is the first of a projected series of canonic reviews covering all invertebrate muscle literature prior to 2005 and covers muscle genes and proteins except those involved in excitation-contraction coupling (e.g., the ryanodine receptor) and those forming ligand- and voltage-dependent channels. Two themes are of primary importance. The first is the evolutionary antiquity of muscle proteins. Actin, myosin, and tropomyosin (at least, the presence of other muscle proteins in these organisms has not been examined) exist in muscle-like cells in Radiata, and almost all muscle proteins are present across Bilateria, implying that the first Bilaterian had a complete, or near-complete, complement of present-day muscle proteins. The second is the extraordinary diversity of protein isoforms and genetic mechanisms for producing them. This rich diversity suggests that studying invertebrate muscle proteins and genes can be usefully applied to resolve phylogenetic relationships and to understand protein assembly coevolution. Fully achieving these goals, however, will require examination of a much broader range of species than has been heretofore performed.
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Affiliation(s)
- Scott L Hooper
- Neuroscience Program, Department of Biological Sciences, Irvine Hall, Ohio University, Athens, Ohio 45701, USA.
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13
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Clément S, Hinz B, Dugina V, Gabbiani G, Chaponnier C. The N-terminal Ac-EEED sequence plays a role in alpha-smooth-muscle actin incorporation into stress fibers. J Cell Sci 2005; 118:1395-404. [PMID: 15769852 DOI: 10.1242/jcs.01732] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We have previously shown that the N-terminal sequence AcEEED of alpha-smooth-muscle actin causes the loss of alpha-smooth-muscle actin from stress fibers and a decrease in cell contractility when introduced in myofibroblasts as a cell-penetrating fusion peptide. Here, we have investigated the function of this sequence on stress fiber organization in living cells, using enhanced green fluorescent protein (EGFP)-tagged alpha-smooth-muscle actin. The fusion peptide provokes the gradual disappearance of EGFP fluorescence of alpha-smooth-muscle actin from stress fibers and the formation of hitherto unknown rod-like structures. In addition to alpha-smooth-muscle actin, these structures contain cytoplasmic actins, gelsolin and cofilin but not other major actin-binding proteins. These rod-like structures are also visible in wild-type fibroblasts during normal cell spreading, suggesting that they represent a physiological step in the organization of alpha-smooth-muscle actin in stress fibers. Fluorescence-recovery-after-photobleaching experiments suggest that the fusion peptide reduces the dynamics of alpha-smooth-muscle actin and its incorporation in stress fibers. Here, we propose a new mechanism of how alpha-smooth-muscle actin is incorporated in stress fibers involving the sequence Ac-EEED.
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Affiliation(s)
- Sophie Clément
- Department of Pathology and Immunology, CMU, Geneva, Switzerland
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14
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Rommelaere H, Waterschoot D, Neirynck K, Vandekerckhove J, Ampe C. A method for rapidly screening functionality of actin mutants and tagged actins. Biol Proced Online 2004; 6:235-249. [PMID: 15514698 PMCID: PMC524212 DOI: 10.1251/bpo94] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2004] [Revised: 09/23/2004] [Accepted: 10/01/2004] [Indexed: 11/26/2022] Open
Abstract
Recombinant production and biochemical analysis of actin mutants has been hampered by the fact that actin has an absolute requirement for the eukaryotic chaperone CCT to reach its native state. We therefore have developed a method to rapidly screen the folding capacity and functionality of actin variants, by combining in vitro expression of labelled actin with analysis on native gels, band shift assays or copolymerization tests. Additionally, we monitor, using immuno-fluorescence, incorporation of actin variants in cytoskeletal structures in transfected cells. We illustrate the method by two examples. In one we show that tagged versions of actin do not always behave native-like and in the other we study some of the molecular defects of three beta-actin mutants that have been associated with diseases.
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Affiliation(s)
- Heidi Rommelaere
- Flanders Interuniversity Institute for Biotechnology (VIB 09) and Department of Biochemistry, Faculty of Medicine and Health Sciences, Ghent University. B-9000 Gent. Belgium
| | - Davy Waterschoot
- Flanders Interuniversity Institute for Biotechnology (VIB 09) and Department of Biochemistry, Faculty of Medicine and Health Sciences, Ghent University. B-9000 Gent. Belgium
| | - Katrien Neirynck
- Flanders Interuniversity Institute for Biotechnology (VIB 09) and Department of Biochemistry, Faculty of Medicine and Health Sciences, Ghent University. B-9000 Gent. Belgium
| | - Joël Vandekerckhove
- Flanders Interuniversity Institute for Biotechnology (VIB 09) and Department of Biochemistry, Faculty of Medicine and Health Sciences, Ghent University. B-9000 Gent. Belgium
| | - Christophe Ampe
- Flanders Interuniversity Institute for Biotechnology (VIB 09) and Department of Biochemistry, Faculty of Medicine and Health Sciences, Ghent University. B-9000 Gent. Belgium
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15
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Arredondo JJ, Mardahl-Dumesnil M, Cripps RM, Cervera M, Bernstein SI. Overexpression of miniparamyosin causes muscle dysfunction and age-dependant myofibril degeneration in the indirect flight muscles of Drosophila melanogaster. J Muscle Res Cell Motil 2002; 22:287-99. [PMID: 11763201 DOI: 10.1023/a:1012431725009] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Miniparamyosin (mPM) is a protein of invertebrate muscle thick filaments. Its similarity to paramyosin (PM) suggests that it regulates thick filament and myofibril assembly. To determine its role in muscle structure and function we overexpressed mPM in muscles of Drosophila melanogaster. Surprisingly, myofibrils accumulating excess mPM assemble nearly normally, with thick filament electron density and sarcomere length unaffected. Myofibrils in some indirect flight muscle groups are misaligned and young flies exhibit a moderate level of flight impairment. This phenotype is exacerbated with age. Transgenic flies undergo progressive myofibril deterioration that increases flight muscle dysfunction. Our observations indicate that the correct stoichiometry of mPM is important for maintenance of myofibril integrity and for the proper function of the flight musculature.
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Affiliation(s)
- J J Arredondo
- Departamento de Bioquímica and Instituto Investigaciones Biomédicas, CSIC, Facultad de Medicina, Universidad Autónoma de Madrid, Spain
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16
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Abstract
Actin, one of the main proteins of muscle and cytoskeleton, exists as a variety of highly conserved isoforms whose distribution in vertebrates is tissue-specific. Synthesis of specific actin isoforms is accompanied by their subcellular compartmentalization, with both processes being regulated by factors of cell proliferation and differentiation. Actin isoforms cannot substitute for each other, and the high-level synthesis of exogenous actins leads to alterations in cell organization and morphology. This indicates that the highly conserved actins are functionally specialized for the tissues in which they predominate. The first goal of this review is to analyze the data on the polymerizability of actin isoforms to show that cytoskeleton isoactins form less stable polymers than skeletal muscle actin. This difference correlates with the dynamics of actin microfilaments versus the stability of myofibrillar systems. The three-dimensional actin structure as well as progress in the analysis of conformational changes in both the actin monomer and the filament allows us to view the data on the structure and polymerization of isoactins in terms of structure-function relationships within the actin molecule. Most of the amino acid substitutions that distinguish actin isoforms are located apart from actin-actin contact sites in the polymer. We suggest that these substitutions can modulate the ability of actin monomers to form more or less stable polymers by long-range (allosteric) regulation of the contact sites.
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Affiliation(s)
- S Y Khaitlina
- Institute of Cytology, Russian Academy of Sciences, St. Petersburg
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17
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Schmitz S, Clayton J, Nongthomba U, Prinz H, Veigel C, Geeves M, Sparrow J. Drosophila ACT88F indirect flight muscle-specific actin is not N-terminally acetylated: a mutation in N-terminal processing affects actin function. J Mol Biol 2000; 295:1201-10. [PMID: 10653697 DOI: 10.1006/jmbi.1999.3407] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Many eukaryotic proteins are co and post-translationally modified at their N termini by removal of one or two amino acid residues and N(alpha)-acetylation. Actins show two different forms of N-terminal processing dependent on their N-terminal sequence. In class II actins, which include muscle actins, the common primary sequence of Met-Cys-Asp-actin is processed to acetyl-Asp-actin. The functional significance of this in vivo is unknown. We have studied the indirect flight muscle-specific actin, ACT88F, of Drosophila melanogaster. Our results show that ACT88F is N-terminally processed in vivo as a class II actin by removal of the first two amino acid residues (Met and Cys), but that uniquely the N terminus is not acetylated. In addition we show that ACT88F is methylated, probably at His73. Flies carrying the mod(-) mutation fail to complete post-translational processing of ACT88F. We propose that the mod gene product is normally responsible for removing N-acetyl-cysteine from actin. The biological significance of this process is demonstrated by observations that retention of the N-acetyl-cysteine in ACT88F affects the flight muscle function of mod(-) flies. This suggests that the extreme N terminus affects actomyosin interactions in vivo, a proposal we have examined by in vitro motility assays of ACT88F F-actin from mod(-) flies. The mod(-) actin only moves in the presence of methylcellulose, a viscosity-enhancing agent, where it moves at velocities slightly, but significantly, reduced compared to wild-type. These data confirm that N-acetyl-cysteine at the N terminus affects actomyosin interactions, probably by reducing formation of the initial actomyosin collision complex, a process known to involve the actin N terminus.
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Affiliation(s)
- S Schmitz
- Department of Biology, University of York, York, Y010 5YW, UK
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Ojima K, Lin ZX, Zhang ZQ, Hijikata T, Holtzer S, Labeit S, Sweeney HL, Holtzer H. Initiation and maturation of I-Z-I bodies in the growth tips of transfected myotubes. J Cell Sci 1999; 112 ( Pt 22):4101-12. [PMID: 10547369 DOI: 10.1242/jcs.112.22.4101] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
While over a dozen I-Z-I proteins are expressed in postmitotic myoblasts and myotubes it is unclear how, when, or where these first assemble into transitory I-Z-I bodies (thin filament/Z-band precursors) and, a short time later, into definitive I-Z-I bands. By double-staining the growth tips of transfected myotubes expressing (a) MYC-tagged s-alpha-actinins (MYC/s-alpha-actinins) or (b) green fluorescent protein-tagged titin cap (GFP/T-cap) with antibodies against MYC and I-Z-I band proteins, we found that the de novo assembly of I-Z-I bodies and their maturation into I-Z-I bands involved relatively concurrent, cooperative binding and reconfiguration of, at a minimum, 5 integral Z-band molecules. These included s-alpha-actinin, nebulin, titin, T-cap and alpha-actin. Resolution of the approximately 1.0 microm polarized alpha-actin/nebulin/tropomyosin/troponin thin filament complexes occurred subsequent to the maturation of Z-bands into a dense tetragonal configuration. Of particular interest is finding that mutant MYC/s-alpha-actinin peptides (a) lacking spectrin-like repeats 1–4, or consisting of spectrin-like repeats 1–4 only, as well as (b) mutants/fragments lacking titin or alpha-actin binding sites, were promptly and exclusively incorporated into de novo assembling I-Z-I bodies and definitive I-Z-I bands as was exogenous full length MYC/s-alpha-actinin or GFP/T-cap.
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Affiliation(s)
- K Ojima
- Department of Physiology and Cell and Developmental Biology, The School of Medicine, University of Pennsylvania, Philadelphia, PA l9l04, USA
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Brault V, Reedy MC, Sauder U, Kammerer RA, Aebi U, Schoenenberger C. Substitution of flight muscle-specific actin by human (beta)-cytoplasmic actin in the indirect flight muscle of Drosophila. J Cell Sci 1999; 112 ( Pt 21):3627-39. [PMID: 10523499 DOI: 10.1242/jcs.112.21.3627] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The human (beta)-cytoplasmic actin differs by only 15 amino acids from Act88F actin which is the only actin expressed in the indirect flight muscle (IFM) of Drosophila melanogaster. To test the structural and functional significance of this difference, we ectopically expressed (beta)-cytoplasmic actin in the IFM of Drosophila that lack endogenous Act88F. When expression of the heterologous actin was regulated by approximately 1.5 kb of the 5′ promoter region of the Act88F gene, little (beta)-cytoplasmic actin accumulated in the IFM of the flightless transformants. Including Act88F-specific 5′ and 3′ untranslated regions (UTRs) yielded transformants that expressed wild-type amounts of (beta)-cytoplasmic actin. Despite the assembly of (beta)-cytoplasmic actin containing thin filaments to which endogenous myosin crossbridges attached, sarcomere organization was deficient, leaving the transformants flightless. Rather than affecting primarily actin-myosin interactions, our findings suggest that the (beta)-cytoplasmic actin isoform is not competent to interact with other actin-binding proteins in the IFM that are involved in the organization of functional myofibrils.
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Affiliation(s)
- V Brault
- M.E. Müller Institute, Biozentrum, University of Basel, CH-4056 Basel, Switzerland
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Schoenenberger CA, Steinmetz MO, Stoffler D, Mandinova A, Aebi U. Structure, assembly, and dynamics of actin filaments in situ and in vitro. Microsc Res Tech 1999; 47:38-50. [PMID: 10506760 DOI: 10.1002/(sici)1097-0029(19991001)47:1<38::aid-jemt4>3.0.co;2-5] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Actin, though highly conserved, exhibits a myriad of diverse functions, most of which ultimately depend on its intrinsic ability to rapidly assemble and disassemble filamentous structures. Many organisms synthesize multiple actin isoforms even within the same cell. Tissue-specific expression patterns and tight developmental regulation as well as a high conservation across species emphasize the functional importance of isoforms. The detailed knowledge of the structure, assembly, and dynamic behavior of actin provides important pieces in solving the puzzle of how the different isoforms can be so versatile despite their extremely high sequence identity.
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Affiliation(s)
- C A Schoenenberger
- M.E. Müller Institute for Structural Biology, Biozentrum, University of Basel, CH-4506 Basel, Switzerland.
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