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Kuruba B, Starks N, Josten MR, Naveh O, Wayman G, Mikhaylova M, Kostyukova AS. Effects of Tropomodulin 2 on Dendritic Spine Reorganization and Dynamics. Biomolecules 2023; 13:1237. [PMID: 37627302 PMCID: PMC10515316 DOI: 10.3390/biom13081237] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2023] [Revised: 08/01/2023] [Accepted: 08/03/2023] [Indexed: 08/27/2023] Open
Abstract
Dendritic spines are actin-rich protrusions that receive a signal from the axon at the synapse. Remodeling of cytoskeletal actin is tightly connected to dendritic spine morphology-mediated synaptic plasticity of the neuron. Remodeling of cytoskeletal actin is required for the formation, development, maturation, and reorganization of dendritic spines. Actin filaments are highly dynamic structures with slow-growing/pointed and fast-growing/barbed ends. Very few studies have been conducted on the role of pointed-end binding proteins in the regulation of dendritic spine morphology. In this study, we evaluated the role played by tropomodulin 2 (Tmod2)-a brain-specific isoform, on the dendritic spine re-organization. Tmod2 regulates actin nucleation and polymerization by binding to the pointed end via actin and tropomyosin (Tpm) binding sites. We studied the effects of Tmod2 overexpression in primary hippocampal neurons on spine morphology using confocal microscopy and image analysis. Tmod2 overexpression decreased the spine number and increased spine length. Destroying Tpm-binding ability increased the number of shaft synapses and thin spine motility. Eliminating the actin-binding abilities of Tmod2 increased the number of mushroom spines. Tpm-mediated pointed-end binding decreased F-actin depolymerization, which may positively affect spine stabilization; the nucleation ability of Tmod2 appeared to increase shaft synapses.
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Affiliation(s)
- Balaganesh Kuruba
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164, USA; (B.K.); (N.S.); (O.N.)
| | - Nickolas Starks
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164, USA; (B.K.); (N.S.); (O.N.)
| | - Mary Rose Josten
- Program in Neuroscience, Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, WA 99164, USA; (M.R.J.); (G.W.)
| | - Ori Naveh
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164, USA; (B.K.); (N.S.); (O.N.)
| | - Gary Wayman
- Program in Neuroscience, Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, WA 99164, USA; (M.R.J.); (G.W.)
| | - Marina Mikhaylova
- Center for Molecular Neurobiology, ZMNH, University Medical Center Hamburg-Eppendorf, 20251 Hamburg, Germany;
- AG Optobiology, Institute of Biology, Humboldt Universität zu Berlin, 10115 Berlin, Germany
| | - Alla S. Kostyukova
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164, USA; (B.K.); (N.S.); (O.N.)
- Center for Molecular Neurobiology, ZMNH, University Medical Center Hamburg-Eppendorf, 20251 Hamburg, Germany;
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Li N, Chen S, Xu K, He MT, Dong MQ, Zhang QC, Gao N. Structural basis of membrane skeleton organization in red blood cells. Cell 2023; 186:1912-1929.e18. [PMID: 37044097 DOI: 10.1016/j.cell.2023.03.017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2022] [Revised: 02/12/2023] [Accepted: 03/15/2023] [Indexed: 04/14/2023]
Abstract
The spectrin-based membrane skeleton is a ubiquitous membrane-associated two-dimensional cytoskeleton underneath the lipid membrane of metazoan cells. Mutations of skeleton proteins impair the mechanical strength and functions of the membrane, leading to several different types of human diseases. Here, we report the cryo-EM structures of the native spectrin-actin junctional complex (from porcine erythrocytes), which is a specialized short F-actin acting as the central organizational unit of the membrane skeleton. While an α-/β-adducin hetero-tetramer binds to the barbed end of F-actin as a flexible cap, tropomodulin and SH3BGRL2 together create an absolute cap at the pointed end. The junctional complex is strengthened by ring-like structures of dematin in the middle actin layers and by patterned periodic interactions with tropomyosin over its entire length. This work serves as a structural framework for understanding the assembly and dynamics of membrane skeleton and offers insights into mechanisms of various ubiquitous F-actin-binding factors in other F-actin systems.
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Affiliation(s)
- Ningning Li
- State Key Laboratory of Membrane Biology, Peking-Tsinghua Joint Center for Life Sciences, School of Life Sciences, Peking University, Beijing 100871, China; Changping Laboratory, Beijing 102206, China.
| | - Siyi Chen
- State Key Laboratory of Membrane Biology, Peking-Tsinghua Joint Center for Life Sciences, School of Life Sciences, Peking University, Beijing 100871, China; Changping Laboratory, Beijing 102206, China; Changping Laboratory Graduate Program, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing 100871, China
| | - Kui Xu
- MOE Key Laboratory of Bioinformatics, Center for Synthetic and Systems Biology, Beijing Advanced Innovation Center for Structural Biology & Frontier Research Center for Biological Structure, Tsinghua-Peking Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Meng-Ting He
- National Institute of Biological Sciences, Beijing 102206, China; Tsinghua Institute of Multidisciplinary Biomedical Research, Tsinghua University, Beijing 100084, China
| | - Meng-Qiu Dong
- National Institute of Biological Sciences, Beijing 102206, China; Tsinghua Institute of Multidisciplinary Biomedical Research, Tsinghua University, Beijing 100084, China
| | - Qiangfeng Cliff Zhang
- MOE Key Laboratory of Bioinformatics, Center for Synthetic and Systems Biology, Beijing Advanced Innovation Center for Structural Biology & Frontier Research Center for Biological Structure, Tsinghua-Peking Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Ning Gao
- State Key Laboratory of Membrane Biology, Peking-Tsinghua Joint Center for Life Sciences, School of Life Sciences, Peking University, Beijing 100871, China; Changping Laboratory, Beijing 102206, China; National Biomedical Imaging Center, Peking University, Beijing 100871, China.
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3
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Tolkatchev D, Gregorio CC, Kostyukova AS. The role of leiomodin in actin dynamics: a new road or a secret gate. FEBS J 2022; 289:6119-6131. [PMID: 34273242 PMCID: PMC8761783 DOI: 10.1111/febs.16128] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2021] [Revised: 05/10/2021] [Accepted: 07/16/2021] [Indexed: 12/29/2022]
Abstract
Leiomodin is an important emerging regulator of thin filaments. As novel molecular, cellular, animal model, and human data accumulate, the mechanisms of its action become clearer. Structural studies played a significant part in understanding the functional significance of leiomodin's interacting partners and functional domains. In this review, we present the current state of knowledge on the structural and cellular properties of leiomodin which has led to two proposed mechanisms of its function. Although it is known that leiomodin is essential for life, numerous domains within leiomodin remain unstudied and as such, we outline future directions for investigations that we predict will provide evidence that leiomodin is a multifunctional protein.
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Affiliation(s)
- Dmitri Tolkatchev
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164, USA
| | - Carol C. Gregorio
- Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, The University of Arizona, Tucson, AZ 85724, USA
| | - Alla S. Kostyukova
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164, USA
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4
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Shrestha MM, Lim CY, Bi X, Robinson RC, Han W. Tmod3 Phosphorylation Mediates AMPK-Dependent GLUT4 Plasma Membrane Insertion in Myoblasts. Front Endocrinol (Lausanne) 2021; 12:653557. [PMID: 33959097 PMCID: PMC8095187 DOI: 10.3389/fendo.2021.653557] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/14/2021] [Accepted: 03/22/2021] [Indexed: 12/28/2022] Open
Abstract
Insulin and muscle contractions mediate glucose transporter 4 (GLUT4) translocation and insertion into the plasma membrane (PM) for glucose uptake in skeletal muscles. Muscle contraction results in AMPK activation, which promotes GLUT4 translocation and PM insertion. However, little is known regarding AMPK effectors that directly regulate GLUT4 translocation. We aim to identify novel AMPK effectors in the regulation of GLUT4 translocation. We performed biochemical, molecular biology and fluorescent microscopy imaging experiments using gain- and loss-of-function mutants of tropomodulin 3 (Tmod3). Here we report Tmod3, an actin filament capping protein, as a novel AMPK substrate and an essential mediator of AMPK-dependent GLUT4 translocation and glucose uptake in myoblasts. Furthermore, Tmod3 plays a key role in AMPK-induced F-actin remodeling and GLUT4 insertion into the PM. Our study defines Tmod3 as a key AMPK effector in the regulation of GLUT4 insertion into the PM and glucose uptake in muscle cells, and offers new mechanistic insights into the regulation of glucose homeostasis.
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Affiliation(s)
- Man Mohan Shrestha
- Laboratory of Metabolic Medicine, Singapore Bioimaging Consortium, Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - Chun-Yan Lim
- Laboratory of Metabolic Medicine, Singapore Bioimaging Consortium, Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - Xuezhi Bi
- Bioprocessing Technology Institute, Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - Robert C. Robinson
- Institute of Molecular and Cell Biology, Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - Weiping Han
- Laboratory of Metabolic Medicine, Singapore Bioimaging Consortium, Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
- Institute of Molecular and Cell Biology, Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
- *Correspondence: Weiping Han,
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He Q, Yu F, Cong M, Ji Y, Zhang Q, Ding F. Comparative Proteomic Analysis of Differentially Expressed Proteins between Injured Sensory and Motor Nerves after Peripheral Nerve Transection. J Proteome Res 2020; 20:1488-1508. [PMID: 33284006 DOI: 10.1021/acs.jproteome.0c00639] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Peripheral nerve repair and functional recovery depend on the rate of nerve regeneration and the quality of target reinnervation. It is important to fully understand the cellular and molecular basis underlying the specificity of peripheral nerve regeneration, which means achieving corresponding correct pathfinding and accurate target reinnervation for regrowing motor and sensory axons. In this study, a quantitative proteomic technique, based on isobaric tags for relative and absolute quantitation (iTRAQ), was used to profile the protein expression pattern between single motor and sensory nerves at 14 days after peripheral nerve transection. Among a total of 1259 proteins identified, 176 proteins showed the differential expressions between injured motor and sensory nerves. Quantitative RT-PCR and western blot analysis were applied to validate the proteomic data on representative differentially expressed proteins. Functional categorization indicated that differentially expressed proteins were linked to a diverse array of molecular functions, including axonogenesis, response to axon injury, tissue remodeling, axon ensheathment, cell proliferation and adhesion, vesicle-mediated transport, response to oxidative stress, internal signal cascade, and macromolecular complex assembly, which might play an essential role in peripheral motor and sensory nerve regeneration. Overall, we hope that the proteomic database obtained in this study could serve as a solid foundation for the comprehensive investigation of differentially expressed proteins between injured motor and sensory nerves and for the mechanism elucidation of the specificity of peripheral nerve regeneration. Data are available via ProteomeXchange with identifier PXD022097.
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Affiliation(s)
- Qianru He
- Key Laboratory of Neuroregeneration of Jiangsu and Ministry of Education, Co-Innovation Center of Neuroregeneration, Jiangsu Clinical Medicine Center of Tissue Engineering and Nerve Injury Repair, Nantong University, Nantong, JS 226001, PR China
| | - Fanhui Yu
- Key Laboratory of Neuroregeneration of Jiangsu and Ministry of Education, Co-Innovation Center of Neuroregeneration, Jiangsu Clinical Medicine Center of Tissue Engineering and Nerve Injury Repair, Nantong University, Nantong, JS 226001, PR China
| | - Meng Cong
- Key Laboratory of Neuroregeneration of Jiangsu and Ministry of Education, Co-Innovation Center of Neuroregeneration, Jiangsu Clinical Medicine Center of Tissue Engineering and Nerve Injury Repair, Nantong University, Nantong, JS 226001, PR China
| | - Yuhua Ji
- Key Laboratory of Neuroregeneration of Jiangsu and Ministry of Education, Co-Innovation Center of Neuroregeneration, Jiangsu Clinical Medicine Center of Tissue Engineering and Nerve Injury Repair, Nantong University, Nantong, JS 226001, PR China
| | - Qi Zhang
- Key Laboratory of Neuroregeneration of Jiangsu and Ministry of Education, Co-Innovation Center of Neuroregeneration, Jiangsu Clinical Medicine Center of Tissue Engineering and Nerve Injury Repair, Nantong University, Nantong, JS 226001, PR China
| | - Fei Ding
- Key Laboratory of Neuroregeneration of Jiangsu and Ministry of Education, Co-Innovation Center of Neuroregeneration, Jiangsu Clinical Medicine Center of Tissue Engineering and Nerve Injury Repair, Nantong University, Nantong, JS 226001, PR China
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6
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Tolkatchev D, Smith GE, Schultz LE, Colpan M, Helms GL, Cort JR, Gregorio CC, Kostyukova AS. Leiomodin creates a leaky cap at the pointed end of actin-thin filaments. PLoS Biol 2020; 18:e3000848. [PMID: 32898131 PMCID: PMC7500696 DOI: 10.1371/journal.pbio.3000848] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2020] [Revised: 09/18/2020] [Accepted: 08/17/2020] [Indexed: 01/26/2023] Open
Abstract
Improper lengths of actin-thin filaments are associated with altered contractile activity and lethal myopathies. Leiomodin, a member of the tropomodulin family of proteins, is critical in thin filament assembly and maintenance; however, its role is under dispute. Using nuclear magnetic resonance data and molecular dynamics simulations, we generated the first atomic structural model of the binding interface between the tropomyosin-binding site of cardiac leiomodin and the N-terminus of striated muscle tropomyosin. Our structural data indicate that the leiomodin/tropomyosin complex only forms at the pointed end of thin filaments, where the tropomyosin N-terminus is not blocked by an adjacent tropomyosin protomer. This discovery provides evidence supporting the debated mechanism where leiomodin and tropomodulin regulate thin filament lengths by competing for thin filament binding. Data from experiments performed in cardiomyocytes provide additional support for the competition model; specifically, expression of a leiomodin mutant that is unable to interact with tropomyosin fails to displace tropomodulin at thin filament pointed ends and fails to elongate thin filaments. Together with previous structural and biochemical data, we now propose a molecular mechanism of actin polymerization at the pointed end in the presence of bound leiomodin. In the proposed model, the N-terminal actin-binding site of leiomodin can act as a "swinging gate" allowing limited actin polymerization, thus making leiomodin a leaky pointed-end cap. Results presented in this work answer long-standing questions about the role of leiomodin in thin filament length regulation and maintenance.
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Affiliation(s)
- Dmitri Tolkatchev
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, Washington, United States of America
| | - Garry E. Smith
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, Washington, United States of America
| | - Lauren E. Schultz
- Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, The University of Arizona, Tucson, Arizona, United States of America
| | - Mert Colpan
- Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, The University of Arizona, Tucson, Arizona, United States of America
| | - Gregory L. Helms
- The Center for NMR Spectroscopy, Washington State University, Pullman, Washington, United States of America
| | - John R. Cort
- Earth and Biological Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington, United States of America
- Institute of Biological Chemistry, Washington State University, Pullman, Washington, United States of America
| | - Carol C. Gregorio
- Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, The University of Arizona, Tucson, Arizona, United States of America
| | - Alla S. Kostyukova
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, Washington, United States of America
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7
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Role of intrinsic disorder in muscle sarcomeres. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2019; 166:311-340. [PMID: 31521234 DOI: 10.1016/bs.pmbts.2019.03.014] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The role and utility of intrinsically disordered regions (IDRs) is reviewed for two groups of sarcomeric proteins, such as members of tropomodulin/leiomodin (Tmod/Lmod) protein homology group and myosin binding protein C (MyBP-C). These two types of sarcomeric proteins represent very different but strongly interdependent functions, being responsible for maintaining structure and operation of the muscle sarcomere. The role of IDRs in the formation of complexes between thin filaments and Tmods/Lmods is discussed within the framework of current understanding of the thin filament length regulation. For MyBP-C, the function of IDRs is discussed in the context of MYBP-C-dependent sarcomere contraction and actomyosin activation.
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Gray KT, Stefen H, Ly TNA, Keller CJ, Colpan M, Wayman GA, Pate E, Fath T, Kostyukova AS. Tropomodulin's Actin-Binding Abilities Are Required to Modulate Dendrite Development. Front Mol Neurosci 2018; 11:357. [PMID: 30356860 PMCID: PMC6190845 DOI: 10.3389/fnmol.2018.00357] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2018] [Accepted: 09/11/2018] [Indexed: 01/22/2023] Open
Abstract
There are many unanswered questions about the roles of the actin pointed end capping and actin nucleation by tropomodulins (Tmod) in regulating neural morphology. Previous studies indicate that Tmod1 and Tmod2 regulate morphology of the dendritic arbor and spines. Tmod3, which is expressed in the brain, had only a minor influence on morphology. Although these studies established a defined role of Tmod in regulating dendritic and synaptic morphology, the mechanisms by which Tmods exert these effects are unknown. Here, we overexpressed a series of mutated forms of Tmod1 and Tmod2 with disrupted actin-binding sites in hippocampal neurons and found that Tmod1 and Tmod2 require both of their actin-binding sites to regulate dendritic morphology and dendritic spine shape. Proximity ligation assays (PLAs) indicate that these mutations impact the interaction of Tmod1 and Tmod2 with tropomyosins Tpm3.1 and Tpm3.2. This impact on Tmod/Tpm interaction may contribute to the morphological changes observed. Finally, we use molecular dynamics simulations (MDS) to characterize the structural changes, caused by mutations in the C-terminal helix of the leucine-rich repeat (LRR) domain of Tmod1 and Tmod2 alone and when bound onto actin monomers. Our results expand our understanding of how neurons utilize the different Tmod isoforms in development.
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Affiliation(s)
- Kevin T Gray
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA, United States.,Neurodegeneration and Repair Unit, School of Medical Sciences, University of New South Wales, Sydney, NSW, Australia.,Integrative Physiology and Neuroscience, Washington State University, Pullman, WA, United States
| | - Holly Stefen
- Neurodegeneration and Repair Unit, School of Medical Sciences, University of New South Wales, Sydney, NSW, Australia.,Neuronal Culture Core Facility, University of New South Wales, Sydney, NSW, Australia
| | - Thu N A Ly
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA, United States
| | - Christopher J Keller
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA, United States
| | - Mert Colpan
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA, United States
| | - Gary A Wayman
- Integrative Physiology and Neuroscience, Washington State University, Pullman, WA, United States
| | - Edward Pate
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA, United States
| | - Thomas Fath
- Neurodegeneration and Repair Unit, School of Medical Sciences, University of New South Wales, Sydney, NSW, Australia.,Neuronal Culture Core Facility, University of New South Wales, Sydney, NSW, Australia.,Dementia Research Centre, Department of Biomedical Sciences, Faculty of Medicine & Health Sciences, Macquarie University, Sydney, NSW, Australia
| | - Alla S Kostyukova
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA, United States
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Arslan B, Colpan M, Gray KT, Abu-Lail NI, Kostyukova AS. Characterizing interaction forces between actin and proteins of the tropomodulin family reveals the presence of the N-terminal actin-binding site in leiomodin. Arch Biochem Biophys 2017; 638:18-26. [PMID: 29223925 DOI: 10.1016/j.abb.2017.12.005] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2017] [Revised: 11/18/2017] [Accepted: 12/05/2017] [Indexed: 11/18/2022]
Abstract
Tropomodulin family of proteins includes several isoforms of tropomodulins (Tmod) and leiomodins (Lmod). These proteins can sequester actin monomers or nucleate actin polymerization. Although it is known that their actin-binding properties are isoform-dependent, knowledge on how they vary in strengths of interactions with G-actin is missing. While it is confirmed in many studies that Tmods have two actin-binding sites, information on number and location of actin-binding sites in Lmod2 is controversial. We used atomic force microscopy to study interactions between G-actin and proteins of the tropomodulin family. Unbinding forces between G-actin and Tmod1, Tmod2, Tmod3, or Lmod2 were quantified. Our results indicated that Tmod1 and Tmod3 had unimodal force distributions, Tmod2 had a bimodal distribution and Lmod2 had a trimodal distribution. The number of force distributions correlates with the proteins' abilities to sequester actin or to nucleate actin polymerization. We assigned specific unbinding forces to the individual actin-binding sites of Tmod2 and Lmod2 using mutations that destroy actin-binding sites of Tmod2 and truncated Lmod2. Our results confirm the existence of the N-terminal actin-binding site in Lmod2. Altogether, our data demonstrate how the differences between the number and the strength of actin-binding sites of Tmod or Lmod translate to their functional abilities.
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Affiliation(s)
- Baran Arslan
- The Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164-6515, United States
| | - Mert Colpan
- The Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164-6515, United States; Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson, AZ 85721, United States
| | - Kevin T Gray
- The Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164-6515, United States
| | - Nehal I Abu-Lail
- The Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164-6515, United States.
| | - Alla S Kostyukova
- The Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164-6515, United States.
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10
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Fowler VM, Dominguez R. Tropomodulins and Leiomodins: Actin Pointed End Caps and Nucleators in Muscles. Biophys J 2017; 112:1742-1760. [PMID: 28494946 DOI: 10.1016/j.bpj.2017.03.034] [Citation(s) in RCA: 52] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2017] [Revised: 03/27/2017] [Accepted: 03/30/2017] [Indexed: 12/29/2022] Open
Abstract
Cytoskeletal structures characterized by actin filaments with uniform lengths, including the thin filaments of striated muscles and the spectrin-based membrane skeleton, use barbed and pointed-end capping proteins to control subunit addition/dissociation at filament ends. While several proteins cap the barbed end, tropomodulins (Tmods), a family of four closely related isoforms in vertebrates, are the only proteins known to specifically cap the pointed end. Tmods are ∼350 amino acids in length, and comprise alternating tropomyosin- and actin-binding sites (TMBS1, ABS1, TMBS2, and ABS2). Leiomodins (Lmods) are related in sequence to Tmods, but display important differences, including most notably the lack of TMBS2 and the presence of a C-terminal extension featuring a proline-rich domain and an actin-binding WASP-Homology 2 domain. The Lmod subfamily comprises three somewhat divergent isoforms expressed predominantly in muscle cells. Biochemically, Lmods differ from Tmods, acting as powerful nucleators of actin polymerization, not capping proteins. Structurally, Lmods and Tmods display crucial differences that correlate well with their different biochemical activities. Physiologically, loss of Lmods in striated muscle results in cardiomyopathy or nemaline myopathy, whereas complete loss of Tmods leads to failure of myofibril assembly and developmental defects. Yet, interpretation of some of the in vivo data has led to the idea that Tmods and Lmods are interchangeable or, at best, different variants of two subfamilies of pointed-end capping proteins. Here, we review and contrast the existing literature on Tmods and Lmods, and propose a model of Lmod function that attempts to reconcile the in vitro and in vivo data, whereby Lmods nucleate actin filaments that are subsequently capped by Tmods during sarcomere assembly, turnover, and repair.
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Affiliation(s)
- Velia M Fowler
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, California.
| | - Roberto Dominguez
- Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
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11
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Colpan M, Ly T, Grover S, Tolkatchev D, Kostyukova AS. The cardiomyopathy-associated K15N mutation in tropomyosin alters actin filament pointed end dynamics. Arch Biochem Biophys 2017; 630:18-26. [PMID: 28732641 DOI: 10.1016/j.abb.2017.07.006] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2017] [Revised: 06/28/2017] [Accepted: 07/13/2017] [Indexed: 10/19/2022]
Abstract
Correct assembly of thin filaments composed of actin and actin-binding proteins is of crucial importance for properly functioning muscle cells. Tropomyosin (Tpm) mediates the binding of tropomodulin (Tmod) and leiomodin (Lmod) at the slow-growing, or pointed, ends of the thin filaments. Together these proteins regulate thin filament lengths and actin dynamics in cardiac muscle. The K15N mutation in the TPM1 gene is associated with familial dilated cardiomyopathy (DCM) but the effect of this mutation on Tpm's function is unknown. In this study, we introduced the K15N mutation in striated muscle α-Tpm (Tpm1.1) and investigated its interaction with actin, Tmod and Lmod. The mutation caused a ∼3-fold decrease in the affinity of Tpm1.1 for actin. The binding of Lmod and Tmod to Tpm1.1-covered actin filaments also decreased in the presence of the K15N mutation. Furthermore, the K15N mutation in Tpm1.1 disrupted the inhibition of actin polymerization and affected the competition between Tmod1 and Lmod2 for binding at the pointed ends. Our data demonstrate that the K15N mutation alters pointed end dynamics by affecting molecular interactions between Tpm1.1, Lmod2 and Tmod1.
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Affiliation(s)
- Mert Colpan
- Voiland School of Chemical Engineering & Bioengineering, Washington State University, Pullman, WA 99164-6515, United States; Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ 85721, United States.
| | - Thu Ly
- Voiland School of Chemical Engineering & Bioengineering, Washington State University, Pullman, WA 99164-6515, United States
| | - Samantha Grover
- Voiland School of Chemical Engineering & Bioengineering, Washington State University, Pullman, WA 99164-6515, United States
| | - Dmitri Tolkatchev
- Voiland School of Chemical Engineering & Bioengineering, Washington State University, Pullman, WA 99164-6515, United States
| | - Alla S Kostyukova
- Voiland School of Chemical Engineering & Bioengineering, Washington State University, Pullman, WA 99164-6515, United States.
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12
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Functional Actin Networks under Construction: The Cooperative Action of Actin Nucleation and Elongation Factors. Trends Biochem Sci 2017; 42:414-430. [DOI: 10.1016/j.tibs.2017.03.002] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2016] [Revised: 03/04/2017] [Accepted: 03/07/2017] [Indexed: 12/31/2022]
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13
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Gray KT, Kostyukova AS, Fath T. Actin regulation by tropomodulin and tropomyosin in neuronal morphogenesis and function. Mol Cell Neurosci 2017; 84:48-57. [PMID: 28433463 DOI: 10.1016/j.mcn.2017.04.002] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2016] [Revised: 04/06/2017] [Accepted: 04/11/2017] [Indexed: 12/26/2022] Open
Abstract
Actin is a profoundly influential protein; it impacts, among other processes, membrane morphology, cellular motility, and vesicle transport. Actin can polymerize into long filaments that push on membranes and provide support for intracellular transport. Actin filaments have polar ends: the fast-growing (barbed) end and the slow-growing (pointed) end. Depolymerization from the pointed end supplies monomers for further polymerization at the barbed end. Tropomodulins (Tmods) cap pointed ends by binding onto actin and tropomyosins (Tpms). Tmods and Tpms have been shown to regulate many cellular processes; however, very few studies have investigated their joint role in the nervous system. Recent data directly indicate that they can modulate neuronal morphology. Additional studies suggest that Tmod and Tpm impact molecular processes influential in synaptic signaling. To facilitate future research regarding their joint role in actin regulation in the nervous system, we will comprehensively discuss Tpm and Tmod and their known functions within molecular systems that influence neuronal development.
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Affiliation(s)
- Kevin T Gray
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, Washington, United States; School of Medical Sciences, University of New South Wales, Sydney, New South Wales, Australia
| | - Alla S Kostyukova
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, Washington, United States.
| | - Thomas Fath
- School of Medical Sciences, University of New South Wales, Sydney, New South Wales, Australia.
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14
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Duan Y, Zhou M, Xiao J, Wu C, Zhou L, Zhou F, Du C, Song Y. Prediction of key genes and miRNAs responsible for loss of muscle force in patients during an acute exacerbation of chronic obstructive pulmonary disease. Int J Mol Med 2016; 38:1450-1462. [PMID: 28025995 PMCID: PMC5065306 DOI: 10.3892/ijmm.2016.2761] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2015] [Accepted: 08/30/2016] [Indexed: 12/16/2022] Open
Abstract
The present study aimed to identify genes and microRNAs (miRNAs or miRs) that were abnormally expressed in the vastus lateralis muscle of patients with acute exacerbations of chronic obstructive pulmonary disease (AECOPD). The gene expression profile of GSE10828 was downloaded from the Gene Expression Omnibus database, and this dataset was comprised of 4 samples from patients with AECOPD and 5 samples from patients with stable COPD. Differentially expressed genes (DEGs) were screened using the Limma package in R. A protein-protein interaction (PPI) network of DEGs was built based on the STRING database. Module analysis of the PPI network was performed using the ClusterONE plugin and functional analysis of DEGs was conducted using DAVID. Additionally, key miRNAs were enriched using gene set enrichment analysis (GSEA) software and a miR-gene regulatory network was constructed using Cytoscape software. In total, 166 up- and 129 downregulated DEGs associated with muscle weakness in AECOPD were screened. Among them, NCL, GOT1, TMOD1, TSPO, SOD2, NCL and PA2G4 were observed in the modules consisting of upregulated or downregulated genes. The upregulated DEGs in modules (including KLF6 and XRCC5) were enriched in GO terms associated with immune system development, whereas the downregulated DEGs were enriched in GO terms associated with cell death and muscle contraction. Additionally, 39 key AECOPD-related miRNAs were also predicted, including miR-1, miR-9 and miR-23a, miR-16 and miR-15a. In conclusion, DEGs (NCL, GOT1, SOD2, KLF6, XRCC5, TSPO and TMOD1) and miRNAs (such as miR-1, miR-9 and miR-23a) may be associated with the loss of muscle force in patients during an acute exacerbation of COPD which also may act as therapeutic targets in the treatment of AECOPD.
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Affiliation(s)
- Yanhong Duan
- Department of Respiratory Medicine, Qingpu Branch of Zhongshan Hospital, Fudan University, Shanghai 201700, P.R. China
| | - Min Zhou
- Department of Respiratory Medicine, Jinshan Branch of The Sixth People's Hospital of Shanghai, Shanghai 201599, P.R. China
| | - Jian Xiao
- Department of Respiratory Medicine, Qingpu Branch of Zhongshan Hospital, Fudan University, Shanghai 201700, P.R. China
| | - Chaomin Wu
- Department of Respiratory Medicine, Qingpu Branch of Zhongshan Hospital, Fudan University, Shanghai 201700, P.R. China
| | - Lei Zhou
- Department of Respiratory Medicine, Qingpu Branch of Zhongshan Hospital, Fudan University, Shanghai 201700, P.R. China
| | - Feng Zhou
- Department of Respiratory Medicine, Qingpu Branch of Zhongshan Hospital, Fudan University, Shanghai 201700, P.R. China
| | - Chunling Du
- Department of Respiratory Medicine, Qingpu Branch of Zhongshan Hospital, Fudan University, Shanghai 201700, P.R. China
| | - Yuanlin Song
- Department of Respiratory Medicine, Zhongshan Hospital, Fudan University, Shanghai 201700, P.R. China
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15
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Ly T, Moroz N, Pappas CT, Novak SM, Tolkatchev D, Wooldridge D, Mayfield RM, Helms G, Gregorio CC, Kostyukova AS. The N-terminal tropomyosin- and actin-binding sites are important for leiomodin 2's function. Mol Biol Cell 2016; 27:2565-75. [PMID: 27307584 PMCID: PMC4985258 DOI: 10.1091/mbc.e16-03-0200] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2016] [Accepted: 06/10/2016] [Indexed: 11/11/2022] Open
Abstract
Leiomodin is a potent actin nucleator related to tropomodulin, a capping protein localized at the pointed end of the thin filaments. Mutations in leiomodin-3 are associated with lethal nemaline myopathy in humans, and leiomodin-2-knockout mice present with dilated cardiomyopathy. The arrangement of the N-terminal actin- and tropomyosin-binding sites in leiomodin is contradictory and functionally not well understood. Using one-dimensional nuclear magnetic resonance and the pointed-end actin polymerization assay, we find that leiomodin-2, a major cardiac isoform, has an N-terminal actin-binding site located within residues 43-90. Moreover, for the first time, we obtain evidence that there are additional interactions with actin within residues 124-201. Here we establish that leiomodin interacts with only one tropomyosin molecule, and this is the only site of interaction between leiomodin and tropomyosin. Introduction of mutations in both actin- and tropomyosin-binding sites of leiomodin affected its localization at the pointed ends of the thin filaments in cardiomyocytes. On the basis of our new findings, we propose a model in which leiomodin regulates actin poly-merization dynamics in myocytes by acting as a leaky cap at thin filament pointed ends.
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Affiliation(s)
- Thu Ly
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164-6515
| | - Natalia Moroz
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164-6515
| | - Christopher T Pappas
- Department of Cellular and Molecular Medicine, Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson, AZ 85721
| | - Stefanie M Novak
- Department of Cellular and Molecular Medicine, Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson, AZ 85721
| | - Dmitri Tolkatchev
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164-6515
| | - Dayton Wooldridge
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164-6515
| | - Rachel M Mayfield
- Department of Cellular and Molecular Medicine, Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson, AZ 85721
| | - Gregory Helms
- Center for NMR Spectroscopy, Washington State University, Pullman, WA 99164-4630
| | - Carol C Gregorio
- Department of Cellular and Molecular Medicine, Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson, AZ 85721
| | - Alla S Kostyukova
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164-6515
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16
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Gray KT, Suchowerska AK, Bland T, Colpan M, Wayman G, Fath T, Kostyukova AS. Tropomodulin isoforms utilize specific binding functions to modulate dendrite development. Cytoskeleton (Hoboken) 2016; 73:316-28. [PMID: 27126680 DOI: 10.1002/cm.21304] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2016] [Revised: 04/26/2016] [Accepted: 04/27/2016] [Indexed: 12/18/2022]
Abstract
Tropomodulins (Tmods) cap F-actin pointed ends and have altered expression in the brain in neurological diseases. The function of Tmods in neurons has been poorly studied and their role in neurological diseases is entirely unknown. In this article, we show that Tmod1 and Tmod2, but not Tmod3, are positive regulators of dendritic complexity and dendritic spine morphology. Tmod1 increases dendritic branching distal from the cell body and the number of filopodia/thin spines. Tmod2 increases dendritic branching proximal to the cell body and the number of mature dendritic spines. Tmods utilize two actin-binding sites and two tropomyosin (Tpm)-binding sites to cap F-actin. Overexpression of Tmods with disrupted Tpm-binding sites indicates that Tmod1 and Tmod2 differentially utilize their Tpm- and actin-binding sites to affect morphology. Disruption of Tmod1's Tpm-binding sites abolished the overexpression phenotype. In contrast, overexpression of the mutated Tmod2 caused the same phenotype as wild type overexpression. Proximity ligation assays indicate that the mutated Tmods are shuttled similarly to wild type Tmods. Our data begins to uncover the roles of Tmods in neural development and the mechanism by which Tmods alter neural morphology. These observations in combination with altered Tmod expression found in several neurological diseases also suggest that dysregulation of Tmod expression may be involved in the pathology of these diseases. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Kevin T Gray
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, Washington
| | - Alexandra K Suchowerska
- School of Medical Sciences, University of New South Wales, Sydney, New South Wales, Australia
| | - Tyler Bland
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, Washington
| | - Mert Colpan
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, Washington
| | - Gary Wayman
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, Washington
| | - Thomas Fath
- School of Medical Sciences, University of New South Wales, Sydney, New South Wales, Australia
| | - Alla S Kostyukova
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, Washington
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17
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Colpan M, Moroz NA, Gray KT, Cooper DA, Diaz CA, Kostyukova AS. Tropomyosin-binding properties modulate competition between tropomodulin isoforms. Arch Biochem Biophys 2016; 600:23-32. [PMID: 27091317 DOI: 10.1016/j.abb.2016.04.006] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2016] [Revised: 04/12/2016] [Accepted: 04/13/2016] [Indexed: 01/09/2023]
Abstract
The formation and fine-tuning of cytoskeleton in cells are governed by proteins that influence actin filament dynamics. Tropomodulin (Tmod) regulates the length of actin filaments by capping the pointed ends in a tropomyosin (TM)-dependent manner. Tmod1, Tmod2 and Tmod3 are associated with the cytoskeleton of non-muscle cells and their expression has distinct consequences on cell morphology. To understand the molecular basis of differences in the function and localization of Tmod isoforms in a cell, we compared the actin filament-binding abilities of Tmod1, Tmod2 and Tmod3 in the presence of Tpm3.1, a non-muscle TM isoform. Tmod3 displayed preferential binding to actin filaments when competing with other isoforms. Mutating the second or both TM-binding sites of Tmod3 destroyed its preferential binding. Our findings clarify how Tmod1, Tmod2 and Tmod3 compete for binding actin filaments. Different binding mechanisms and strengths of Tmod isoforms for Tpm3.1 contribute to their divergent functional capabilities.
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Affiliation(s)
- Mert Colpan
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164-6515, United States.
| | - Natalia A Moroz
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164-6515, United States
| | - Kevin T Gray
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164-6515, United States
| | - Dillon A Cooper
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164-6515, United States
| | - Christian A Diaz
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164-6515, United States
| | - Alla S Kostyukova
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164-6515, United States.
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18
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Suzuki T, Kasamatsu A, Miyamoto I, Saito T, Higo M, Endo-Sakamoto Y, Shiiba M, Tanzawa H, Uzawa K. Overexpression of TMOD1 is associated with enhanced regional lymph node metastasis in human oral cancer. Int J Oncol 2015; 48:607-12. [PMID: 26718916 DOI: 10.3892/ijo.2015.3305] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2015] [Accepted: 11/27/2015] [Indexed: 11/06/2022] Open
Abstract
Tropomodulin1 (TMOD1), which regulates the length and depolymerization of actin filaments by binding to the pointed end of the actin filament, has been reported to be a powerful diagnostic marker for ALK-negative anaplastic large-cell lymphoma; however, little is known about the relevance of TMOD1 in the behavior of oral squamous cell carcinoma (OSCC). We evaluated TMOD1 expression in OSCC-derived cell lines and primary OSCC samples (n=200) using quantitative reverse transcriptase-polymerase chain reaction, immunoblotting and semi-quantitative immunohistochemistry. We also analyzed the clinical correlation between TMOD1 expression status and clinical parameters in patients with OSCC and performed a prospective study using 40 primary OSCC samples. TMOD1 expression was upregulated significantly (p<0.05) in OSCC in vitro and in vivo compared with normal counterparts. TMOD1 expression also was correlated significantly (p=0.0199 and p=0.0064, respectively) with regional lymph node metastasis (RLNM) and 5-year survival rates. This prospective study also showed that high TMOD1 expression was seen in 12 (75%) of 16 cases in RLNM-positive patients and 9 (37.5%) of 24 cases in RLNM-negative patients. The current data provide the first evidence that TMOD1 expression is a critical biomarker for RLNM and prognosis of patients with OSCC.
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Affiliation(s)
- Toshikazu Suzuki
- Department of Oral Science, Graduate School of Medicine, Chiba University, Chuo-ku, Chiba, Japan
| | - Atsushi Kasamatsu
- Department of Dentistry and Oral-Maxillofacial Surgery, Chiba University Hospital, Chuo-ku, Chiba 260-8670, Japan
| | - Isao Miyamoto
- Department of Oral Science, Graduate School of Medicine, Chiba University, Chuo-ku, Chiba, Japan
| | - Tomoaki Saito
- Department of Oral Science, Graduate School of Medicine, Chiba University, Chuo-ku, Chiba, Japan
| | - Morihiro Higo
- Department of Dentistry and Oral-Maxillofacial Surgery, Chiba University Hospital, Chuo-ku, Chiba 260-8670, Japan
| | - Yosuke Endo-Sakamoto
- Department of Dentistry and Oral-Maxillofacial Surgery, Chiba University Hospital, Chuo-ku, Chiba 260-8670, Japan
| | - Masashi Shiiba
- Department of Medical Oncology, Graduate School of Medicine, Chiba University, Chuo-ku, Chiba, Japan
| | - Hideki Tanzawa
- Department of Oral Science, Graduate School of Medicine, Chiba University, Chuo-ku, Chiba, Japan
| | - Katsuhiro Uzawa
- Department of Oral Science, Graduate School of Medicine, Chiba University, Chuo-ku, Chiba, Japan
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19
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How Leiomodin and Tropomodulin use a common fold for different actin assembly functions. Nat Commun 2015; 6:8314. [PMID: 26370058 PMCID: PMC4571291 DOI: 10.1038/ncomms9314] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2015] [Accepted: 08/07/2015] [Indexed: 11/08/2022] Open
Abstract
How proteins sharing a common fold have evolved different functions is a fundamental question in biology. Tropomodulins (Tmods) are prototypical actin filament pointed-end-capping proteins, whereas their homologues, Leiomodins (Lmods), are powerful filament nucleators. We show that Tmods and Lmods do not compete biochemically, and display similar but distinct localization in sarcomeres. Changes along the polypeptide chains of Tmods and Lmods exquisitely adapt their functions for capping versus nucleation. Tmods have alternating tropomyosin (TM)- and actin-binding sites (TMBS1, ABS1, TMBS2 and ABS2). Lmods additionally contain a C-terminal extension featuring an actin-binding WH2 domain. Unexpectedly, the different activities of Tmods and Lmods do not arise from the Lmod-specific extension. Instead, nucleation by Lmods depends on two major adaptations-the loss of pointed-end-capping elements present in Tmods and the specialization of the highly conserved ABS2 for recruitment of two or more actin subunits. The WH2 domain plays only an auxiliary role in nucleation.
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20
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Cell type-restricted expression of erythrocyte tropomodulin Isoform41 in exon 1 knockout/LacZ knock-in heterozygous mice. Gene Expr Patterns 2015; 17:45-55. [PMID: 25721257 DOI: 10.1016/j.gep.2015.02.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2014] [Revised: 02/03/2015] [Accepted: 02/13/2015] [Indexed: 01/26/2023]
Abstract
Full-length erythrocyte tropomodulin (E-Tmod or Tmod1) isoform of 41 kDa is an actin nucleation protein and caps the pointed end of tropomyosin-coated actin filaments. It participates in the length control of short actin protofilaments in the erythrocyte membrane skeletal network as well as the organization of microfilaments in non-erythroid cells. Recently we discovered and characterized a truncated isoform of 29 kDa, which lacks the N-terminal sequence encoded by exons 1 and 2 required for nucleation and capping. Thus, it is important to study the expression pattern of solely the E-Tmod41 isoform in tissues. We utilized our exon 1 knockout (KO) mouse model with a knock-in lacZ reporter gene which reports the expression of E-Tmod41, but not E-Tmod29. Because this homozygous isoform-specific KO is an embryonic lethal mutation, we used heterozygous mice. X-gal staining localized specific signals at the single cell level and revealed a timed expression during embryonic development and restricted expression in adult mice. Our results showed that E-Tmod41 expressing cells include developing and young erythroid cells, developing somites, young fiber cells in the lens, certain subtype(s) of tubular cells in the kidney, smooth muscle cells in various tissues, and horizontal cells in the retina. A comparison with previous studies revealed that most if not all tissues known to express E-Tmod contained lacZ-expressing cells. Interestingly, some tubular cells were lacZ-positive while others in the same renal tubule were not, indicating heterogeneity within the tubular cells. Combined with double immunocytochemistry, we further localized E-Tmod41 to dendritic spines of horizontal cells. These timed and cell-type restricted expressions of E-Tmod41 suggest a role of actin nucleation and/or short actin protofilaments in these cell types and sub-cellular structures.
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21
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Nworu CU, Kraft R, Schnurr DC, Gregorio CC, Krieg PA. Leiomodin 3 and tropomodulin 4 have overlapping functions during skeletal myofibrillogenesis. J Cell Sci 2014; 128:239-50. [PMID: 25431137 DOI: 10.1242/jcs.152702] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Precise regulation of thin filament length is essential for optimal force generation during muscle contraction. The thin filament capping protein tropomodulin (Tmod) contributes to thin filament length uniformity by regulating elongation and depolymerization at thin filament ends. The leiomodins (Lmod1-3) are structurally related to Tmod1-4 and also localize to actin filament pointed ends, but in vitro biochemical studies indicate that Lmods act instead as robust nucleators. Here, we examined the roles of Tmod4 and Lmod3 during Xenopus skeletal myofibrillogenesis. Loss of Tmod4 or Lmod3 resulted in severe disruption of sarcomere assembly and impaired embryonic movement. Remarkably, when Tmod4-deficient embryos were supplemented with additional Lmod3, and Lmod3-deficient embryos were supplemented with additional Tmod4, sarcomere assembly was rescued and embryonic locomotion improved. These results demonstrate for the first time that appropriate levels of both Tmod4 and Lmod3 are required for embryonic myofibrillogenesis and, unexpectedly, both proteins can function redundantly during in vivo skeletal muscle thin filament assembly. Furthermore, these studies demonstrate the value of Xenopus for the analysis of contractile protein function during de novo myofibril assembly.
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Affiliation(s)
- Chinedu U Nworu
- Department of Cellular and Molecular Medicine, Sarver Molecular Cardiovascular Research Program, University of Arizona, 1656 E. Mabel St, Tucson, AZ 85724, USA
| | - Robert Kraft
- Department of Cellular and Molecular Medicine, Sarver Molecular Cardiovascular Research Program, University of Arizona, 1656 E. Mabel St, Tucson, AZ 85724, USA
| | - Daniel C Schnurr
- Department of Cellular and Molecular Medicine, Sarver Molecular Cardiovascular Research Program, University of Arizona, 1656 E. Mabel St, Tucson, AZ 85724, USA
| | - Carol C Gregorio
- Department of Cellular and Molecular Medicine, Sarver Molecular Cardiovascular Research Program, University of Arizona, 1656 E. Mabel St, Tucson, AZ 85724, USA
| | - Paul A Krieg
- Department of Cellular and Molecular Medicine, Sarver Molecular Cardiovascular Research Program, University of Arizona, 1656 E. Mabel St, Tucson, AZ 85724, USA
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22
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Rao JN, Madasu Y, Dominguez R. Mechanism of actin filament pointed-end capping by tropomodulin. Science 2014; 345:463-7. [PMID: 25061212 DOI: 10.1126/science.1256159] [Citation(s) in RCA: 86] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Proteins that cap the ends of the actin filament are essential regulators of cytoskeleton dynamics. Whereas several proteins cap the rapidly growing barbed end, tropomodulin (Tmod) is the only protein known to cap the slowly growing pointed end. The lack of structural information severely limits our understanding of Tmod's capping mechanism. We describe crystal structures of actin complexes with the unstructured amino-terminal and the leucine-rich repeat carboxy-terminal domains of Tmod. The structures and biochemical analysis of structure-inspired mutants showed that one Tmod molecule interacts with three actin subunits at the pointed end, while also contacting two tropomyosin molecules on each side of the filament. We found that Tmod achieves high-affinity binding through several discrete low-affinity interactions, which suggests a mechanism for controlled subunit exchange at the pointed end.
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Affiliation(s)
- Jampani Nageswara Rao
- Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Yadaiah Madasu
- Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Roberto Dominguez
- Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
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23
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Lewis RA, Yamashiro S, Gokhin DS, Fowler VM. Functional effects of mutations in the tropomyosin-binding sites of tropomodulin1 and tropomodulin3. Cytoskeleton (Hoboken) 2014; 71:395-411. [PMID: 24922351 DOI: 10.1002/cm.21179] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2014] [Accepted: 06/02/2014] [Indexed: 01/16/2023]
Abstract
Tropomodulins (Tmods) interact with tropomyosins (TMs) via two TM-binding sites and cap the pointed ends of TM-coated actin filaments. To study the functional interplay between TM binding and TM-actin filament capping by Tmods, we introduced disabling mutations into the first, second, or both TM-binding sites of full-length Tmod1 (Tmod1-L27G, Tmod1-I131D, and Tmod1-L27G/I131D, respectively) and full-length Tmod3 (Tmod3-L29G, Tmod3-L134D, and Tmod3-L29G/L134D, respectively). Tmod1 and Tmod3 showed somewhat different TM-binding site utilization, but nearly all TM binding was abolished in Tmod1-L27G/I131D and Tmod3-L29G/L134D. Disruption of Tmod-TM binding had a modest effect on Tmod1's ability and no effect on Tmod3's ability to stabilize TM-actin pointed ends against latrunculin A-induced depolymerization. However, disruption of Tmod-TM binding did significantly impair the ability of Tmod3 to reduce elongation rates at pointed ends with α/βTM, albeit less so with TM5NM1, and not at all with TM5b. For Tmod1, disruption of Tmod-TM binding only slightly impaired its ability to reduce elongation rates with α/βTM and TM5NM1, but not at all with TM5b. Thus, Tmod-TM binding has a greater influence on Tmods' ability to inhibit subunit association as compared to dissociation from TM-actin pointed ends, particularly for α/βTM, with Tmod3's activity being more dependent on TM binding than Tmod1's activity. Nevertheless, disruption of Tmod1-TM binding precluded Tmod1 targeting to thin filament pointed ends in cardiac myocytes, suggesting that the functional effects of Tmod-TM binding on TM-coated actin filament capping can be significantly modulated by the in vivo conformation of the pointed end or other factors in the intracellular environment.
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Affiliation(s)
- Raymond A Lewis
- Department of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, California
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24
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Bliss KT, Tsukada T, Novak SM, Dorovkov MV, Shah SP, Nworu C, Kostyukova AS, Gregorio CC. Phosphorylation of tropomodulin1 contributes to the regulation of actin filament architecture in cardiac muscle. FASEB J 2014; 28:3987-95. [PMID: 24891520 DOI: 10.1096/fj.13-246009] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2013] [Accepted: 05/19/2014] [Indexed: 01/09/2023]
Abstract
Tropomodulin1 (Tmod1) is an actin-capping protein that plays an important role in actin filament pointed-end dynamics and length in striated muscle. No mechanisms have been identified to explain how Tmod1's functional properties are regulated. The purpose of this investigation was to explore the functional significance of the phosphorylation of Tmod1 at previously identified Thr54. Rat cardiomyocytes were assessed for phosphorylation of Tmod1 using Pro-Q Diamond staining and (32)P labeling. Green fluorescent protein-tagged phosphorylation-mimic (T54E) and phosphorylation-deficient (T54A) versions of Tmod1 were expressed in cultured cardiomyocytes, and the ability of these mutants to assemble and restrict actin lengths was observed. We report for the first time that Tmod1 is phosphorylated endogenously in cardiomyocytes, and phosphorylation at Thr54 causes a significant reduction in the ability of Tmod1 to assemble to the pointed end compared with that of the wild type (WT; 48 vs. 78%, respectively). In addition, overexpression of Tmod1-T54E restricts actin filament lengths by only ∼3%, whereas Tmod1-WT restricts the lengths significantly by ∼8%. Finally, Tmod1-T54E altered the actin filament-capping activity in polymerization assays. Taken together, our data suggest that pointed-end assembly and Tmod1's thin filament length regulatory function are regulated by its phosphorylation state.
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Affiliation(s)
- Katherine T Bliss
- Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson, Arizona, USA
| | - Takehiro Tsukada
- Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson, Arizona, USA
| | - Stefanie Mares Novak
- Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson, Arizona, USA
| | | | - Samar P Shah
- Department of Neuroscience and Cell Biology, Robert Wood Johnson Medical School, Piscataway, New Jersey, USA; and
| | - Chinedu Nworu
- Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson, Arizona, USA
| | - Alla S Kostyukova
- Department of Neuroscience and Cell Biology, Robert Wood Johnson Medical School, Piscataway, New Jersey, USA; and School of Chemical Engineering and Bioengineering, Washington State University, Pullman, Washington, USA
| | - Carol C Gregorio
- Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson, Arizona, USA;
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Yamashiro S, Gokhin DS, Sui Z, Bergeron SE, Rubenstein PA, Fowler VM. Differential actin-regulatory activities of Tropomodulin1 and Tropomodulin3 with diverse tropomyosin and actin isoforms. J Biol Chem 2014; 289:11616-11629. [PMID: 24644292 DOI: 10.1074/jbc.m114.555128] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Tropomodulins (Tmods) are F-actin pointed end capping proteins that interact with tropomyosins (TMs) and cap TM-coated filaments with higher affinity than TM-free filaments. Here, we tested whether differences in recognition of TM or actin isoforms by Tmod1 and Tmod3 contribute to the distinct cellular functions of these Tmods. We found that Tmod3 bound ~5-fold more weakly than Tmod1 to α/βTM, TM5b, and TM5NM1. However, surprisingly, Tmod3 was as effective as Tmod1 at capping pointed ends of skeletal muscle α-actin (αsk-actin) filaments coated with α/βTM, TM5b, or TM5NM1. Tmod3 only capped TM-coated αsk-actin filaments more weakly than Tmod1 in the presence of recombinant αTM2, which is unacetylated at its NH2 terminus, binds F-actin weakly, and has a disabled Tmod-binding site. Moreover, both Tmod1 and Tmod3 were similarly effective at capping pointed ends of platelet β/cytoplasmic γ (γcyto)-actin filaments coated with TM5NM1. In the absence of TMs, both Tmod1 and Tmod3 had similarly weak abilities to nucleate β/γcyto-actin filament assembly, but only Tmod3 could sequester cytoplasmic β- and γcyto-actin (but not αsk-actin) monomers and prevent polymerization under physiological conditions. Thus, differences in TM binding by Tmod1 and Tmod3 do not appear to regulate the abilities of these Tmods to cap TM-αsk-actin or TM-β/γcyto-actin pointed ends and, thus, are unlikely to determine selective co-assembly of Tmod, TM, and actin isoforms in different cell types and cytoskeletal structures. The ability of Tmod3 to sequester β- and γcyto-actin (but not αsk-actin) monomers in the absence of TMs suggests a novel function for Tmod3 in regulating actin remodeling or turnover in cells.
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Affiliation(s)
- Sawako Yamashiro
- Department of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, California 92037; Laboratory of Single-Molecule Cell Biology, Tohoku University, Sendai, Miyagi 980-8578, Japan
| | - David S Gokhin
- Department of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, California 92037
| | - Zhenhua Sui
- Department of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, California 92037
| | - Sarah E Bergeron
- Department of Biochemistry, University of Iowa, Iowa City, Iowa 52242
| | | | - Velia M Fowler
- Department of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, California 92037.
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Colpan M, Moroz NA, Kostyukova AS. Tropomodulins and tropomyosins: working as a team. J Muscle Res Cell Motil 2013; 34:247-60. [PMID: 23828180 DOI: 10.1007/s10974-013-9349-6] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2013] [Accepted: 05/24/2013] [Indexed: 11/25/2022]
Abstract
Actin filaments are major components of the cytoskeleton in eukaryotic cells and are involved in vital cellular functions such as cell motility and muscle contraction. Tmod and TM are crucial constituents of the actin filament network, making their presence indispensable in living cells. Tropomyosin (TM) is an alpha-helical, coiled coil protein that covers the grooves of actin filaments and stabilizes them. Actin filament length is optimized by tropomodulin (Tmod), which caps the slow growing (pointed end) of thin filaments to inhibit polymerization or depolymerization. Tmod consists of two structurally distinct regions: the N-terminal and the C-terminal domains. The N-terminal domain contains two TM-binding sites and one TM-dependent actin-binding site, whereas the C-terminal domain contains a TM-independent actin-binding site. Tmod binds to two TM molecules and at least one actin molecule during capping. The interaction of Tmod with TM is a key regulatory factor for actin filament organization. The binding efficacy of Tmod to TM is isoform-dependent. The affinities of Tmod/TM binding influence the proper localization and capping efficiency of Tmod at the pointed end of actin filaments in cells. Here we describe how a small difference in the sequence of the TM-binding sites of Tmod may result in dramatic change in localization of Tmod in muscle cells or morphology of non-muscle cells. We also suggest most promising directions to study and elucidate the role of Tmod-TM interaction in formation and maintenance of sarcomeric and cytoskeletal structure.
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Affiliation(s)
- Mert Colpan
- The Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, 118 Dana Hall, Spokane St., Pullman, WA, 99164, USA
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27
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Fowler VM. The human erythrocyte plasma membrane: a Rosetta Stone for decoding membrane-cytoskeleton structure. CURRENT TOPICS IN MEMBRANES 2013; 72:39-88. [PMID: 24210427 DOI: 10.1016/b978-0-12-417027-8.00002-7] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The mammalian erythrocyte, or red blood cell (RBC), is a unique experiment of nature: a cell with no intracellular organelles, nucleus or transcellular cytoskeleton, and a plasma membrane with uniform structure across its entire surface. By virtue of these specialized properties, the RBC membrane has provided a template for discovery of the fundamental actin filament network machine of the membrane skeleton, now known to confer mechanical resilience, anchor membrane proteins, and organize membrane domains in all cells. This chapter provides a historical perspective and critical analysis of the biochemistry, structure, and physiological functions of this actin filament network in RBCs. The core units of this network are nodes of ~35-37 nm-long actin filaments, interconnected by long strands of (α1β1)₂-spectrin tetramers, forming a 2D isotropic lattice with quasi-hexagonal symmetry. Actin filament length and stability is critical for network formation, relying upon filament capping at both ends: tropomodulin-1 at pointed ends and αβ-adducin at barbed ends. Tropomodulin-1 capping is essential for precise filament lengths, and is enhanced by tropomyosin, which binds along the short actin filaments. αβ-adducin capping recruits spectrins to sites near barbed ends, promoting network formation. Accessory proteins, 4.1R and dematin, also promote spectrin binding to actin and, with αβ-adducin, link to membrane proteins, targeting actin nodes to the membrane. Dissection of the molecular organization within the RBC membrane skeleton is one of the paramount achievements of cell biological research in the past century. Future studies will reveal the structure and dynamics of actin filament capping, mechanisms of precise length regulation, and spectrin-actin lattice symmetry.
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Affiliation(s)
- Velia M Fowler
- Department of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, California, USA.
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28
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Wang TF, Lai NS, Huang KY, Huang HL, Lu MC, Lin YS, Chen CY, Liu SQ, Lin TH, Huang HB. Identification and characterization of the actin-binding motif of phostensin. Int J Mol Sci 2012; 13:15967-82. [PMID: 23443105 PMCID: PMC3546673 DOI: 10.3390/ijms131215967] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2012] [Revised: 11/15/2012] [Accepted: 11/19/2012] [Indexed: 11/16/2022] Open
Abstract
Phostensin, a protein phosphatase 1 F-actin cytoskeleton-targeting subunit encoded by KIAA1949, consists of 165 amino acids and caps the pointed ends of actin filaments. Sequence alignment analyses suggest that the C-terminal region of phostensin, spanning residues 129 to 155, contains a consensus actin-binding motif. Here, we have verified the existence of an actin-binding motif in the C-terminal domain of phostensin using colocalization, F-actin co-sedimentation and single filament binding assays. Our data indicate that the N-terminal region of phostensin (1-129) cannot bind to actin filaments and cannot retard the pointed end elongation of gelsolin-actin seeds. Furthermore, the C-terminal region of phostensin (125-165) multiply bind to the sides of actin filaments and lacks the ability to block the pointed end elongation, suggesting that the actin-binding motif is located in the C-terminal region of the phostensin. Further analyses indicate that phostensin binding to the pointed end of actin filament requires N-terminal residues 35 to 51. These results suggest that phostensin might fold into a rigid structure, allowing the N-terminus to sterically hinder the binding of C-terminus to the sides of actin filament, thus rendering phostensin binding to the pointed ends of actin filaments.
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Affiliation(s)
- Tzu-Fan Wang
- Department of Life Science and Institute of Molecular Biology, National Chung Cheng University, Chia-Yi 62102, Taiwan; E-Mails: (T.-F.W.); (Y.-S.L.); (C.-Y.C.)
| | - Ning-Sheng Lai
- College of Medicine, Tzu-Chi University, Hualien 97004, Taiwan; E-Mails: (N.-S.L.); (K.-Y.H.); (M.-C.L.)
- Section of Allergy, Immunology and Rheumatology, Department of Medicine, DaLin Tzu Chi Buddhist Hospital, Chia-Yi 62247, Taiwan; E-Mail:
| | - Kuang-Yung Huang
- College of Medicine, Tzu-Chi University, Hualien 97004, Taiwan; E-Mails: (N.-S.L.); (K.-Y.H.); (M.-C.L.)
- Section of Allergy, Immunology and Rheumatology, Department of Medicine, DaLin Tzu Chi Buddhist Hospital, Chia-Yi 62247, Taiwan; E-Mail:
| | - Hsien-Lu Huang
- Department of Nutrition and Health Science, Fooyin University, Kaohsiung 83102, Taiwan; E-Mail:
| | - Ming-Chi Lu
- College of Medicine, Tzu-Chi University, Hualien 97004, Taiwan; E-Mails: (N.-S.L.); (K.-Y.H.); (M.-C.L.)
- Section of Allergy, Immunology and Rheumatology, Department of Medicine, DaLin Tzu Chi Buddhist Hospital, Chia-Yi 62247, Taiwan; E-Mail:
| | - Yu-Shan Lin
- Department of Life Science and Institute of Molecular Biology, National Chung Cheng University, Chia-Yi 62102, Taiwan; E-Mails: (T.-F.W.); (Y.-S.L.); (C.-Y.C.)
| | - Chun-Yu Chen
- Department of Life Science and Institute of Molecular Biology, National Chung Cheng University, Chia-Yi 62102, Taiwan; E-Mails: (T.-F.W.); (Y.-S.L.); (C.-Y.C.)
| | - Su-Qin Liu
- Section of Allergy, Immunology and Rheumatology, Department of Medicine, DaLin Tzu Chi Buddhist Hospital, Chia-Yi 62247, Taiwan; E-Mail:
| | - Ta-Hsien Lin
- Institute of Biochemistry and Molecular Biology, National Yang-Ming University, Taipei 11221, Taiwan
- Department of Medical Research & Education, Taipei Veterans General Hospital, Taipei 11217, Taiwan
- Authors to whom correspondence should be addressed; E-Mails: (T.-H.L.); (H.-B.H.); Tel.: +886-2-2871-2121 (ext. 2703) (T.-H.L.); Fax: +886-2-2875-1562 (T.-H.L.); Tel.: +886-5-2720411 (ext. 53200) (H.-B.H.); Fax: +886-5-2722871 (H.-B.H.)
| | - Hsien-Bin Huang
- Department of Life Science and Institute of Molecular Biology, National Chung Cheng University, Chia-Yi 62102, Taiwan; E-Mails: (T.-F.W.); (Y.-S.L.); (C.-Y.C.)
- Authors to whom correspondence should be addressed; E-Mails: (T.-H.L.); (H.-B.H.); Tel.: +886-2-2871-2121 (ext. 2703) (T.-H.L.); Fax: +886-2-2875-1562 (T.-H.L.); Tel.: +886-5-2720411 (ext. 53200) (H.-B.H.); Fax: +886-5-2722871 (H.-B.H.)
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29
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Kryscio DR, Fleming MQ, Peppas NA. Protein conformational studies for macromolecularly imprinted polymers. Macromol Biosci 2012; 12:1137-44. [PMID: 22777744 DOI: 10.1002/mabi.201200068] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2012] [Indexed: 11/08/2022]
Abstract
CD is used to clearly show the negative impact of common ligands on the overall conformation of BSA, a typical protein template in macromolecularly imprinted polymers. This change occurs at concentrations far lower than those generally used in the literature. These findings are important as they offer insight into a potential fundamental reason for the lack of success in protein imprinting to date despite significant interest from the scientific community.
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Affiliation(s)
- David R Kryscio
- Fletcher Stuckey Pratt Chair in Engineering, Departments of Chemical Engineering and Biomedical Engineering, University of Texas at Austin, 1 University Station C0400, Austin, TX 78712-1062, USA
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30
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Mankelow TJ, Satchwell TJ, Burton NM. Refined views of multi-protein complexes in the erythrocyte membrane. Blood Cells Mol Dis 2012; 49:1-10. [PMID: 22465511 PMCID: PMC4443426 DOI: 10.1016/j.bcmd.2012.03.001] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2012] [Accepted: 02/27/2012] [Indexed: 12/20/2022]
Abstract
The erythrocyte membrane has been extensively studied, both as a model membrane system and to investigate its role in gas exchange and transport. Much is now known about the protein components of the membrane, how they are organised into large multi-protein complexes and how they interact with each other within these complexes. Many links between the membrane and the cytoskeleton have also been delineated and have been demonstrated to be crucial for maintaining the deformability and integrity of the erythrocyte. In this study we have refined previous, highly speculative molecular models of these complexes by including the available data pertaining to known protein-protein interactions. While the refined models remain highly speculative, they provide an evolving framework for visualisation of these important cellular structures at the atomic level.
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Affiliation(s)
- T J Mankelow
- Bristol Institute for Transfusion Sciences, N.H.S. Blood & Transplant, UK
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31
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Yamashiro S, Gokhin DS, Kimura S, Nowak RB, Fowler VM. Tropomodulins: pointed-end capping proteins that regulate actin filament architecture in diverse cell types. Cytoskeleton (Hoboken) 2012; 69:337-70. [PMID: 22488942 DOI: 10.1002/cm.21031] [Citation(s) in RCA: 96] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2011] [Revised: 03/23/2012] [Accepted: 03/26/2012] [Indexed: 01/31/2023]
Abstract
Tropomodulins are a family of four proteins (Tmods 1-4) that cap the pointed ends of actin filaments in actin cytoskeletal structures in a developmentally regulated and tissue-specific manner. Unique among capping proteins, Tmods also bind tropomyosins (TMs), which greatly enhance the actin filament pointed-end capping activity of Tmods. Tmods are defined by a TM-regulated/Pointed-End Actin Capping (TM-Cap) domain in their unstructured N-terminal portion, followed by a compact, folded Leucine-Rich Repeat/Pointed-End Actin Capping (LRR-Cap) domain. By inhibiting actin monomer association and dissociation from pointed ends, Tmods regulate actin dynamics and turnover, stabilizing actin filament lengths and cytoskeletal architecture. In this review, we summarize the genes, structural features, molecular and biochemical properties, actin regulatory mechanisms, expression patterns, and cell and tissue functions of Tmods. By understanding Tmods' functions in the context of their molecular structure, actin regulation, binding partners, and related variants (leiomodins 1-3), we can draw broad conclusions that can explain the diverse morphological and functional phenotypes that arise from Tmod perturbation experiments in vitro and in vivo. Tmod-based stabilization and organization of intracellular actin filament networks provide key insights into how the emergent properties of the actin cytoskeleton drive tissue morphogenesis and physiology.
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Affiliation(s)
- Sawako Yamashiro
- Department of Cell Biology, The Scripps Research Institute, La Jolla, California 92037, USA
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32
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Tropomodulin capping of actin filaments in striated muscle development and physiology. J Biomed Biotechnol 2011; 2011:103069. [PMID: 22013379 PMCID: PMC3196151 DOI: 10.1155/2011/103069] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2011] [Accepted: 08/18/2011] [Indexed: 11/17/2022] Open
Abstract
Efficient striated muscle contraction requires precise assembly and regulation of diverse actin filament systems, most notably the sarcomeric thin filaments of the contractile apparatus. By capping the pointed ends of actin filaments, tropomodulins (Tmods) regulate actin filament assembly, lengths, and stability. Here, we explore the current understanding of the expression patterns, localizations, and functions of Tmods in both cardiac and skeletal muscle. We first describe the mechanisms by which Tmods regulate myofibril assembly and thin filament lengths, as well as the roles of closely related Tmod family variants, the leiomodins (Lmods), in these processes. We also discuss emerging functions for Tmods in the sarcoplasmic reticulum. This paper provides abundant evidence that Tmods are key structural regulators of striated muscle cytoarchitecture and physiology.
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33
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Tsukada T, Kotlyanskaya L, Huynh R, Desai B, Novak SM, Kajava AV, Gregorio CC, Kostyukova AS. Identification of residues within tropomodulin-1 responsible for its localization at the pointed ends of the actin filaments in cardiac myocytes. J Biol Chem 2010; 286:2194-204. [PMID: 21078668 DOI: 10.1074/jbc.m110.186924] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Tropomodulin is a tropomyosin-dependent actin filament capping protein involved in the structural formation of thin filaments and in the regulation of their lengths through its localization at the pointed ends of actin filaments. The disordered N-terminal domain of tropomodulin contains three functional sites: two tropomyosin-binding and one tropomyosin-dependent actin-capping sites. The C-terminal half of tropomodulin consists of one compact domain containing a tropomyosin-independent actin-capping site. Here we determined the structural properties of tropomodulin-1 that affect its roles in cardiomyocytes. To explore the significance of individual tropomyosin-binding sites, GFP-tropomodulin-1 with single mutations that destroy each tropomyosin-binding site was expressed in cardiomyocytes. We demonstrated that both sites are necessary for the optimal localization of tropomodulin-1 at thin filament pointed ends, with site 2 acting as the major determinant. To investigate the functional properties of the tropomodulin C-terminal domain, truncated versions of GFP-tropomodulin-1 were expressed in cardiomyocytes. We discovered that the leucine-rich repeat (LRR) fold and the C-terminal helix are required for its proper targeting to the pointed ends. To investigate the structural significance of the LRR fold, we generated three mutations within the C-terminal domain (V232D, F263D, and L313D). Our results show that these mutations affect both tropomyosin-independent actin-capping activity and pointed end localization, most likely by changing local conformations of either loops or side chains of the surfaces involved in the interactions of the LRR domain. Studying the influence of these mutations individually, we concluded that, in addition to the tropomyosin-independent actin-capping site, there appears to be another regulatory site within the tropomodulin C-terminal domain.
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Affiliation(s)
- Takehiro Tsukada
- Department of Cell Biology and Anatomy and the Molecular Cardiovascular Research Program, University of Arizona, Tucson, Arizona 85724, USA
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34
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Yamashiro S, Speicher KD, Speicher DW, Fowler VM. Mammalian tropomodulins nucleate actin polymerization via their actin monomer binding and filament pointed end-capping activities. J Biol Chem 2010; 285:33265-33280. [PMID: 20650902 PMCID: PMC2963411 DOI: 10.1074/jbc.m110.144873] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2010] [Revised: 06/18/2010] [Indexed: 01/10/2023] Open
Abstract
Many actin-binding proteins have been shown to possess multiple activities to regulate filament dynamics. Tropomodulins (Tmod1-4) are a conserved family of actin filament pointed end-capping proteins. Our previous work has demonstrated that Tmod3 binds to monomeric actin in addition to capping pointed ends. Here, we show a novel actin-nucleating activity in mammalian Tmods. Comparison of Tmod isoforms revealed that Tmod1-3 but not Tmod4 nucleate actin filament assembly. All Tmods bind to monomeric actin, and Tmod3 forms a 1:1 complex with actin. By truncation and mutagenesis studies, we demonstrated that the second α-helix in the N-terminal domain of Tmod3 is essential for actin monomer binding. Chemical cross-linking and LC-MS/MS further indicated that residues in this second α-helix interact with actin subdomain 2, whereas Tmod3 N-terminal domain peptides distal to this α-helix interact with actin subdomain 1. Mutagenesis of Leu-73 to Asp, which disrupts the second α-helix of Tmod3, decreases both its actin monomer-binding and -nucleating activities. On the other hand, point mutations of residues in the C-terminal leucine-rich repeat domain of Tmod3 (Lys-317 in the fifth leucine-rich repeat β-sheet and Lys-344 or Arg-345/Arg-346 in the C-terminal α6-helix) significantly reduced pointed end-capping and nucleation without altering actin monomer binding. Taken together, our data indicate that Tmod3 binds actin monomers over an extended interface and that nucleating activity depends on actin monomer binding and pointed end-capping activities, contributed by N- and C-terminal domains of Tmod3, respectively. Tmod3 nucleation of actin assembly may regulate the cytoskeleton in dynamic cellular contexts.
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Affiliation(s)
- Sawako Yamashiro
- From the Department of Cell Biology, The Scripps Research Institute, La Jolla, California 92037.
| | - Kaye D Speicher
- Center for Systems and Computational Biology, The Wistar Institute, Philadelphia, Pennsylvania 19104
| | - David W Speicher
- Center for Systems and Computational Biology, The Wistar Institute, Philadelphia, Pennsylvania 19104
| | - Velia M Fowler
- From the Department of Cell Biology, The Scripps Research Institute, La Jolla, California 92037.
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35
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Tsukada T, Pappas CT, Moroz N, Antin PB, Kostyukova AS, Gregorio CC. Leiomodin-2 is an antagonist of tropomodulin-1 at the pointed end of the thin filaments in cardiac muscle. J Cell Sci 2010; 123:3136-45. [PMID: 20736303 DOI: 10.1242/jcs.071837] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Regulation of actin filament assembly is essential for efficient contractile activity in striated muscle. Leiomodin is an actin-binding protein and homolog of the pointed-end capping protein, tropomodulin. These proteins are structurally similar, sharing a common domain organization that includes two actin-binding sites. Leiomodin also contains a unique C-terminal extension that has a third actin-binding WH2 domain. Recently, the striated-muscle-specific isoform of leiomodin (Lmod2) was reported to be an actin nucleator in cardiomyocytes. Here, we have identified a function of Lmod2 in the regulation of thin filament lengths. We show that Lmod2 localizes to the pointed ends of thin filaments, where it competes for binding with tropomodulin-1 (Tmod1). Overexpression of Lmod2 results in loss of Tmod1 assembly and elongation of the thin filaments from their pointed ends. The Lmod2 WH2 domain is required for lengthening because its removal results in a molecule that caps the pointed ends similarly to Tmod1. Furthermore, Lmod2 transcripts are first detected in the heart after it has begun to beat, suggesting that the primary function of Lmod2 is to maintain thin filament lengths in the mature heart. Thus, Lmod2 antagonizes the function of Tmod1, and together, these molecules might fine-tune thin filament lengths.
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Affiliation(s)
- Takehiro Tsukada
- Department of Cell Biology and Anatomy, and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson, AZ 85724, USA
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36
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Skwarek-Maruszewska A, Boczkowska M, Zajac AL, Kremneva E, Svitkina T, Dominguez R, Lappalainen P. Different localizations and cellular behaviors of leiomodin and tropomodulin in mature cardiomyocyte sarcomeres. Mol Biol Cell 2010; 21:3352-61. [PMID: 20685966 PMCID: PMC2947471 DOI: 10.1091/mbc.e10-02-0109] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Leiomodin (Lmod) is a muscle-specific F-actin-nucleating protein that is related to the F-actin pointed-end-capping protein tropomodulin (Tmod). However, Lmod contains a unique ∼150-residue C-terminal extension that is required for its strong nucleating activity. Overexpression or depletion of Lmod compromises sarcomere organization, but the mechanism by which Lmod contributes to myofibril assembly is not well understood. We show that Tmod and Lmod localize through fundamentally different mechanisms to the pointed ends of two distinct subsets of actin filaments in myofibrils. Tmod localizes to two narrow bands immediately adjacent to M-lines, whereas Lmod displays dynamic localization to two broader bands, which are generally more separated from M-lines. Lmod's localization and F-actin nucleation activity are enhanced by interaction with tropomyosin. Unlike Tmod, the myofibril localization of Lmod depends on sustained muscle contraction and actin polymerization. We further show that Lmod expression correlates with the maturation of myofibrils in cultured cardiomyocytes and that it associates with sarcomeres only in differentiated myofibrils. Collectively, the data suggest that Lmod contributes to the final organization and maintenance of sarcomere architecture by promoting tropomyosin-dependent actin filament nucleation.
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Affiliation(s)
- Aneta Skwarek-Maruszewska
- Program in Cell and Molecular Biology, Institute of Biotechnology, University of Helsinki, Helsinki 00790, Finland
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Yao W, Sung LA. Erythrocyte tropomodulin isoforms with and without the N-terminal actin-binding domain. J Biol Chem 2010; 285:31408-17. [PMID: 20675374 DOI: 10.1074/jbc.m110.130278] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Erythrocyte tropomodulin (E-Tmod or Tmod1) of 41 kDa is a tropomyosin (TM)-binding protein that caps the slow-growing end of the actin filaments. Its N-terminal half is flexible, whereas the C-terminal half has a single domain structure. E-Tmod/TM5 complex may function as a "molecular ruler" generating actin protofilaments of ∼37 nm. Here we report the discovery of a short isoform of 29 kDa that lacks the N-terminal actin-binding domain (N-ABD) but retains the C-terminal actin-binding domain (C-ABD). E-Tmod29 can be generated by alternative splicing from an upstream promoter or by multiple transcriptional start sites from a downstream promoter. Promoter switching leads to a surge of E-Tmod41 in reticulocytes, which degrades quickly in the cytosol. We expressed recombinant isoforms in Escherichia coli and tested their binding toward TM5, G-actin, and F-actin. Solid-phase binding assays show that, without the N-terminal 102 residues, E-Tmod29 binds to TM5 or G-actin more strongly than E-Tmod41 does, but barely binds to F-actin after TM5 binding. Differential bindings explain the distinct localizations of E-Tmod29 in the cytosol and E-Tmod41 on the membrane. Sequential bindings and immunofluorescent staining further suggest that 1) TM5 binding to E-Tmod41 may open up the flexible N-terminal half, exposing N-ABD and unblocking C-ABD; 2) N-ABD binds to F-actin and C-ABD binds to G-actin; and 3) F-actin binding to N-ABD may prevent G-actin from binding to C-ABD. E-Tmod29 may thus modulate the availability of TM5 and G-actin for E-Tmod41 to construct the protofilament-based membrane skeletal network for circulating erythrocytes.
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Affiliation(s)
- Weijuan Yao
- Department of Bioengineering, University of California, San Diego, California 92093-0412, USA
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Gokhin DS, Lewis RA, McKeown CR, Nowak RB, Kim NE, Littlefield RS, Lieber RL, Fowler VM. Tropomodulin isoforms regulate thin filament pointed-end capping and skeletal muscle physiology. ACTA ACUST UNITED AC 2010; 189:95-109. [PMID: 20368620 PMCID: PMC2854367 DOI: 10.1083/jcb.201001125] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
In skeletal muscle fibers, tropomodulin 1 (Tmod1) can be compensated for, structurally but not functionally, by Tmod3 and -4. During myofibril assembly, thin filament lengths are precisely specified to optimize skeletal muscle function. Tropomodulins (Tmods) are capping proteins that specify thin filament lengths by controlling actin dynamics at pointed ends. In this study, we use a genetic targeting approach to explore the effects of deleting Tmod1 from skeletal muscle. Myofibril assembly, skeletal muscle structure, and thin filament lengths are normal in the absence of Tmod1. Tmod4 localizes to thin filament pointed ends in Tmod1-null embryonic muscle, whereas both Tmod3 and -4 localize to pointed ends in Tmod1-null adult muscle. Substitution by Tmod3 and -4 occurs despite their weaker interactions with striated muscle tropomyosins. However, the absence of Tmod1 results in depressed isometric stress production during muscle contraction, systemic locomotor deficits, and a shift to a faster fiber type distribution. Thus, Tmod3 and -4 compensate for the absence of Tmod1 structurally but not functionally. We conclude that Tmod1 is a novel regulator of skeletal muscle physiology.
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Affiliation(s)
- David S Gokhin
- Department of Cell Biology, The Scripps Research Institute, La Jolla, CA 92037, USA
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39
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Dominguez R. Actin filament nucleation and elongation factors--structure-function relationships. Crit Rev Biochem Mol Biol 2009; 44:351-66. [PMID: 19874150 DOI: 10.3109/10409230903277340] [Citation(s) in RCA: 124] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The spontaneous and unregulated polymerization of actin filaments is inhibited in cells by actin monomer-binding proteins such as profilin and Tbeta4. Eukaryotic cells and certain pathogens use filament nucleators to stabilize actin polymerization nuclei, whose formation is rate-limiting. Known filament nucleators include the Arp2/3 complex and its large family of nucleation promoting factors (NPFs), formins, Spire, Cobl, VopL/VopF, TARP and Lmod. These molecules control the time and location for polymerization, and additionally influence the structures of the actin networks that they generate. Filament nucleators are generally unrelated, but with the exception of formins they all use the WASP-Homology 2 domain (WH2 or W), a small and versatile actin-binding motif, for interaction with actin. A common architecture, found in Spire, Cobl and VopL/VopF, consists of tandem W domains that bind three to four actin subunits to form a nucleus. Structural considerations suggest that NPFs-Arp2/3 complex can also be viewed as a specialized form of tandem W-based nucleator. Formins are unique in that they use the formin-homology 2 (FH2) domain for interaction with actin and promote not only nucleation, but also processive barbed end elongation. In contrast, the elongation function among W-based nucleators has been "outsourced" to a dedicated family of proteins, Eva/VASP, which are related to WASP-family NPFs.
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Affiliation(s)
- Roberto Dominguez
- Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6085, USA.
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Kostyukova AS. Capping complex formation at the slow-growing end of the actin filament. BIOCHEMISTRY (MOSCOW) 2009; 73:1467-72. [PMID: 19216712 DOI: 10.1134/s0006297908130075] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Actin filaments are polar; their barbed (fast-growing) and pointed (slow-growing) ends differ in structure and dynamic properties. The slow-growing end is regulated by tropomodulins, a family of capping proteins that require tropomyosins for optimal function. There are four tropomodulin isoforms; their distributions vary depending on tissue type and change during development. The C-terminal half of tropomodulin contains one compact domain represented by alternating alpha-helices and beta-structures. The tropomyosin-independent actin-capping site is located at the C-terminus. The N-terminal half has no regular structure; however, it contains a tropomyosin-dependent actin-capping site and two tropomyosin-binding sites. One tropomodulin molecule can bind two tropomyosin molecules. Effectiveness of tropomodulin binding to tropomyosin depends on the tropomyosin isoform. Regulation of tropomodulin binding at the pointed end as well as capping effectiveness in the presence of specific tropomyosins may affect formation of local cytoskeleton and dynamics of actin filaments in cells.
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Affiliation(s)
- A S Kostyukova
- Institute of Protein Research, Russian Academy of Sciences, Pushchino, Moscow Region, 142290, Russia.
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41
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Qualmann B, Kessels MM. New players in actin polymerization--WH2-domain-containing actin nucleators. Trends Cell Biol 2009; 19:276-85. [PMID: 19406642 DOI: 10.1016/j.tcb.2009.03.004] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2008] [Revised: 02/24/2009] [Accepted: 03/09/2009] [Indexed: 01/07/2023]
Abstract
Actin nucleators promote the polymerization of the different types of actin arrays formed in a variety of cellular processes, such as cell migration, cellular morphogenesis and membrane trafficking processes. Several novel nucleators have been discovered recently. They all contain Wiskott-Aldrich syndrome protein (WASP) homology 2 (WH2 or W) domains for actin nucleation but seem to employ different molecular mechanisms and serve distinct cellular functions. Here, we summarize what is currently known about the different molecular mechanisms that Spire, Cordon-Bleu and Leiomodin seem to use and, also, the bacterial counterparts that mimic them (VopF, VopL and TARP). Recent studies on these WH2 proteins offer unique insight into the biological problem of actin-filament formation and how cells use specialized molecular machines to bring about so many different cytoskeletal structures.
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Affiliation(s)
- Britta Qualmann
- Institute for Biochemistry I, Friedrich-Schiller-University Jena, Nonnenplan 2, Jena, Germany
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42
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Disease severity and thin filament regulation in M9R TPM3 nemaline myopathy. J Neuropathol Exp Neurol 2008; 67:867-77. [PMID: 18716557 DOI: 10.1097/nen.0b013e318183a44f] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
The mechanism of muscle weakness was investigated in an Australian family with an M9R mutation in TPM3 (alpha-tropomyosin(slow)). Detailed protein analyses of 5 muscle samples from 2 patients showed that nemaline bodies are restricted to atrophied Type 1 (slow) fibers in which the TPM3 gene is expressed. Developmental expression studies showed that alpha-tropomyosin(slow) is not expressed at significant levels until after birth, thereby likely explaining the childhood (rather than congenital) disease onset in TPM3 nemaline myopathy. Isoelectric focusing demonstrated that alpha-tropomyosin(slow) dimers, composed of equal ratios of wild-type and M9R-alpha-tropomyosin(slow), are the dominant tropomyosin species in 3 separate muscle groups from an affected patient. These findings suggest that myopathy-related slow fiber predominance likely contributes to the severity of weakness in TPM3 nemaline myopathy because of increased proportions of fibers that express the mutant protein. Using recombinant proteins and far Western blot, we demonstrated a higher affinity of tropomodulin for alpha-tropomyosin(slow) compared with beta-tropomyosin; the M9R substitution within alpha-tropomyosin(slow) greatly reduced this interaction. Finally, transfection of the M9R mutated and wild-type alpha-tropomyosin(slow) into myoblasts revealed reduced incorporation into stress fibers and disruption of the filamentous actin network by the mutant protein. Collectively, these results provide insights into the clinical features and pathogenesis of M9R-TPM3 nemaline myopathy.
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Chereau D, Boczkowska M, Skwarek-Maruszewska A, Fujiwara I, Hayes DB, Rebowski G, Lappalainen P, Pollard TD, Dominguez R. Leiomodin is an actin filament nucleator in muscle cells. Science 2008; 320:239-43. [PMID: 18403713 DOI: 10.1126/science.1155313] [Citation(s) in RCA: 175] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Initiation of actin polymerization in cells requires nucleation factors. Here we describe an actin-binding protein, leiomodin, that acted as a strong filament nucleator in muscle cells. Leiomodin shared two actin-binding sites with the filament pointed end-capping protein tropomodulin: a flexible N-terminal region and a leucine-rich repeat domain. Leiomodin also contained a C-terminal extension of 150 residues. The smallest fragment with strong nucleation activity included the leucine-rich repeat and C-terminal extension. The N-terminal region enhanced the nucleation activity threefold and recruited tropomyosin, which weakly stimulated nucleation and mediated localization of leiomodin to the middle of muscle sarcomeres. Knocking down leiomodin severely compromised sarcomere assembly in cultured muscle cells, which suggests a role for leiomodin in the nucleation of tropomyosin-decorated filaments in muscles.
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Affiliation(s)
- David Chereau
- Boston Biomedical Research Institute, Watertown, MA 02472, USA
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44
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Shan SW, Tang MK, Chow PH, Maroto M, Cai DQ, Lee KKH. Induction of growth arrest and polycomb gene expression by reversine allows C2C12 cells to be reprogrammed to various differentiated cell types. Proteomics 2008; 7:4303-16. [PMID: 17973295 DOI: 10.1002/pmic.200700636] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Reversine is a small, cell permeable synthetic chemical that has the ability to reprogram C2C12 myogenic cells to become various differentiated cell types. However, we still do not know how reversine works or the genes and proteins involved. Hence, we have used comparative proteomic techniques to address this issue. We have identified several proteins that were associated with cell cycle progression which were downregulated by reversine. Simultaneously, there were proteins associated with the induction of growth arrest that were upregulated. Consequently, we investigated the effects of reversine on C2C12 cell growth and established that it inhibited cell growth. Reversine had little affects on cell survival. We also investigated whether expressions of the polycomb genes, polycomb repressive complex 1 (PHC1) and Ezh2, were affected by reversine. Polycomb group genes are normally involved in chromatin based gene silencing. We found that PHC1 and Ezh2 expressions were enhanced by reversine and that it correlated with the inhibition of muscle specific transcriptional factor genes, myogenin, MyoD, and Myf5. Therefore, we believe that reversine is able to reprogram C2C12 cells to various differentiated cell types by inducing cell growth arrest, and promoting PHC1 and Ezh2 expressions.
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Affiliation(s)
- Sze Wan Shan
- Department of Anatomy, Basic Medical Science Building, Chinese University of Hong Kong, Shatin, Hong Kong
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Tropomodulin/Tropomyosin Interactions Regulate Actin Pointed End Dynamics. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2008; 644:283-92. [DOI: 10.1007/978-0-387-85766-4_21] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
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46
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Greenfield NJ. Determination of the folding of proteins as a function of denaturants, osmolytes or ligands using circular dichroism. Nat Protoc 2007; 1:2733-41. [PMID: 17406529 PMCID: PMC2728349 DOI: 10.1038/nprot.2006.229] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Circular dichroism (CD) is an excellent tool for examining the interactions and stability of proteins. This protocol covers methods to obtain and analyze circular dichroism spectra to measure changes in the folding of proteins as a function of denaturants, osmolytes or ligands. Applications include determination of the free energy of folding of a protein, the effects of mutations on protein stability and the estimation of binding constants for the interactions of proteins with other proteins, DNA or ligands, such as substrates or inhibitors. The experiments require 2-5 h.
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Affiliation(s)
- Norma J Greenfield
- Department of Neuroscience and Cell Biology, Robert Wood Johnson Medical School, 675 Hoes Lane West, Piscataway, New Jersey 08854-8021, USA
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47
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Kostyukova AS. Leiomodin/tropomyosin interactions are isoform specific. Arch Biochem Biophys 2007; 465:227-30. [PMID: 17572376 DOI: 10.1016/j.abb.2007.05.012] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2007] [Revised: 05/17/2007] [Accepted: 05/17/2007] [Indexed: 10/23/2022]
Abstract
Leiomodins are larger homologs of tropomodulin, a tropomyosin-binding, actin-capping protein. There are several leiomodin isoforms, one of them found in smooth muscles (Lmod1) and another one found in cardiac and skeletal muscles (Lmod2). In this work, the tropomyosin-binding abilities of these two isoforms were studied. The tropomyosin-binding sites were localized in the N-terminal regions of Lmod1 and Lmod2. The affinities of the leiomodin fragments containing the tropomyosin-binding sites for tropomyosin peptides containing N-termini of different tropomyosin isoforms, alpha, gamma and delta, were determined and compared using non-denaturing gel-electrophoresis and circular dichroism. It was shown that leiomodin/tropomyosin binding is isoform-specific and differs almost 100-fold for different tropomyosin isoforms.
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Affiliation(s)
- Alla S Kostyukova
- Department of Neuroscience and Cell Biology, Robert Wood Johnson Medical School, 675 Hoes Lane, Piscataway, NJ 08854, USA.
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48
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Kostyukova AS, Hitchcock-Degregori SE, Greenfield NJ. Molecular basis of tropomyosin binding to tropomodulin, an actin-capping protein. J Mol Biol 2007; 372:608-18. [PMID: 17706248 PMCID: PMC2134803 DOI: 10.1016/j.jmb.2007.05.084] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2007] [Revised: 05/19/2007] [Accepted: 05/26/2007] [Indexed: 11/28/2022]
Abstract
The tropomodulin (Tmod) family of proteins that cap the pointed, slow-growing end of actin filaments require tropomyosin (TM) for optimal function. Earlier studies identified two regions in Tmod1 that bind the N terminus of TM, though the ability of different isoforms to bind the two sites is controversial. We used model peptides to determine the affinity and define the specificity of the highly conserved N termini of three short, non-muscle TMs (alpha, gamma, delta-TM) for the two Tmod1 binding sites using circular dichroism spectroscopy, native gel electrophoresis, and chemical crosslinking. All TM peptides have high affinity for the second Tmod1 binding site (within residues 109-144; alpha-TM, 2.5 nM; gamma-TM, delta-TM, 40-90 nM), but differ >100-fold for the first site (residues 1-38; alpha-TM, 90 nM; undetectable at 10 microM, gamma-TM, delta-TM). Residue 14 (R in alpha; Q in gamma and delta) and, to a lesser extent, residue 4 (S in alpha; T in gamma and delta) are primarily responsible for the differences. The functional consequence of the sequence differences is reflected in more effective inhibition of actin filament elongation by full-length alpha-TMs than gamma-TM in the presence of Tmod1. The binding sites of the two Tmod1 peptides on a model TM peptide differ, as defined by comparing (15)N,(1)H HSQC spectra of a (15)N-labeled model TM peptide in both the absence and presence of Tmod1 peptide. The NMR and CD studies show that there is an increase in alpha-helix upon Tmod1-TM complex formation, indicating that intrinsically disordered regions of the two proteins become ordered upon binding. A model proposed for the binding of Tmod to actin and TM at the pointed end of the filament shows how the Tmod-TM accentuates the asymmetry of the pointed end and suggests how subtle differences among TM isoforms may modulate actin filament dynamics.
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Affiliation(s)
- Alla S Kostyukova
- Department of Neuroscience and Cell Biology, Robert Wood Johnson Medical School, 675 Hoes Lane, Piscataway, NJ 08854, USA
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49
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Kostyukova AS, Choy A, Rapp BA. Tropomodulin binds two tropomyosins: a novel model for actin filament capping. Biochemistry 2006; 45:12068-75. [PMID: 17002306 PMCID: PMC2596622 DOI: 10.1021/bi060899i] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Tropomodulin, a tropomyosin-binding protein, caps the slow-growing (pointed) end of the actin filament regulating its dynamics. Tropomodulin, therefore, is important for determining cell morphology, cell movement, and muscle contraction. For the first time we show that one tropomodulin molecule simultaneously binds two tropomyosin molecules in a cooperative manner. On the basis of the tropomodulin solution structure and predicted secondary structure, we introduced a series of point mutations in regions important for tropomyosin binding and actin capping. Capping activity of these mutants was assayed by measuring actin polymerization using pyrene fluorescence. Using direct methods (circular dichroism and native gel electrophoresis) for detecting tropomodulin/tropomyosin binding, we localized the second tropomyosin-binding site to residues 109-144. Despite previous reports that the second binding site is for erythrocyte tropomyosin only, we found that both short nonmuscle and long muscle alpha-tropomyosins bind there as well, though with different affinities. We propose a model for actin capping where one tropomodulin molecule can bind to two tropomyosin molecules at the pointed end.
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Affiliation(s)
- Alla S Kostyukova
- Department of Neuroscience and Cell Biology, Robert Wood Johnson Medical School, 675 Hoes Lane, Piscataway, New Jersey 08854, USA.
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50
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Charras GT, Hu CK, Coughlin M, Mitchison TJ. Reassembly of contractile actin cortex in cell blebs. J Cell Biol 2006; 175:477-90. [PMID: 17088428 PMCID: PMC2064524 DOI: 10.1083/jcb.200602085] [Citation(s) in RCA: 439] [Impact Index Per Article: 24.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2006] [Accepted: 10/06/2006] [Indexed: 01/02/2023] Open
Abstract
Contractile actin cortex is involved in cell morphogenesis, movement, and cytokinesis, but its organization and assembly are poorly understood. During blebbing, the membrane detaches from the cortex and inflates. As expansion ceases, contractile cortex re-assembles under the membrane and drives bleb retraction. This cycle enabled us to measure the temporal sequence of protein recruitment to the membrane during cortex reassembly and to explore dependency relationships. Expanding blebs were devoid of actin, but proteins of the erythrocytic submembranous cytoskeleton were present. When expansion ceased, ezrin was recruited to the membrane first, followed by actin, actin-bundling proteins, and, finally, contractile proteins. Complete assembly of the contractile cortex, which was organized into a cagelike mesh of filaments, took approximately 30 s. Cytochalasin D blocked recruitment of actin and alpha-actinin, but had no effect on membrane association of ankyrin B and ezrin. Ezrin played no role in actin nucleation, but was essential for tethering the membrane to the cortex. The Rho pathway was important for cortex assembly in blebs.
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Affiliation(s)
- Guillaume T Charras
- Department of Systems Biology, Harvard Medical School, Boston, MA 02115, USA.
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