1
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Schneider R, Deutsch K, Hoeprich GJ, Marquez J, Hermle T, Braun DA, Seltzsam S, Kitzler TM, Mao Y, Buerger F, Majmundar AJ, Onuchic-Whitford AC, Kolvenbach CM, Schierbaum L, Schneider S, Halawi AA, Nakayama M, Mann N, Connaughton DM, Klämbt V, Wagner M, Riedhammer KM, Renders L, Katsura Y, Thumkeo D, Soliman NA, Mane S, Lifton RP, Shril S, Khokha MK, Hoefele J, Goode BL, Hildebrandt F. DAAM2 Variants Cause Nephrotic Syndrome via Actin Dysregulation. Am J Hum Genet 2020; 107:1113-1128. [PMID: 33232676 DOI: 10.1016/j.ajhg.2020.11.008] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2020] [Accepted: 11/05/2020] [Indexed: 01/10/2023] Open
Abstract
The discovery of >60 monogenic causes of nephrotic syndrome (NS) has revealed a central role for the actin regulators RhoA/Rac1/Cdc42 and their effectors, including the formin INF2. By whole-exome sequencing (WES), we here discovered bi-allelic variants in the formin DAAM2 in four unrelated families with steroid-resistant NS. We show that DAAM2 localizes to the cytoplasm in podocytes and in kidney sections. Further, the variants impair DAAM2-dependent actin remodeling processes: wild-type DAAM2 cDNA, but not cDNA representing missense variants found in individuals with NS, rescued reduced podocyte migration rate (PMR) and restored reduced filopodia formation in shRNA-induced DAAM2-knockdown podocytes. Filopodia restoration was also induced by the formin-activating molecule IMM-01. DAAM2 also co-localizes and co-immunoprecipitates with INF2, which is intriguing since variants in both formins cause NS. Using in vitro bulk and TIRF microscopy assays, we find that DAAM2 variants alter actin assembly activities of the formin. In a Xenopus daam2-CRISPR knockout model, we demonstrate actin dysregulation in vivo and glomerular maldevelopment that is rescued by WT-DAAM2 mRNA. We conclude that DAAM2 variants are a likely cause of monogenic human SRNS due to actin dysregulation in podocytes. Further, we provide evidence that DAAM2-associated SRNS may be amenable to treatment using actin regulating compounds.
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2
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Fischer RS, Lam PY, Huttenlocher A, Waterman CM. Filopodia and focal adhesions: An integrated system driving branching morphogenesis in neuronal pathfinding and angiogenesis. Dev Biol 2018; 451:86-95. [PMID: 30193787 DOI: 10.1016/j.ydbio.2018.08.015] [Citation(s) in RCA: 46] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2018] [Revised: 08/08/2018] [Accepted: 08/29/2018] [Indexed: 12/31/2022]
Abstract
Single cell branching during development in vertebrates is typified by neuronal branching to form neurites and vascular branches formed by sprouting angiogenesis. Neurons and endothelial tip cells possess subcellular protrusions that share many common features from the morphological to the molecular level. Both systems utilize filopodia as their cellular protrusion organelles and depend on specific integrin-mediated adhesions to the local extracellular matrix for guidance in their pathfinding. We discuss the similar molecular machineries involved in these two types of cell branch formation and use their analogy to propose a new mechanism for angiogenic filopodia function, namely as adhesion assembly sites. In support of this model we provide primary data of angiogenesis in zebrafish in vivo showing that the actin assembly factor VASP participates in both filopodia formation and adhesion assembly at the base of the filopodia, enabling forward progress of the tip cell. The use of filopodia and their associated adhesions provide a common mechanism for neuronal and endothelial pathfinding during development in response to extracellular matrix cues.
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Affiliation(s)
- Robert S Fischer
- Cell and Developmental Biology Center, National Heart Lung and Blood Institute, National Institutes of Health, United States
| | - Pui-Ying Lam
- Department of Pharmacology and Toxicology, College of Pharmacy, University of Utah, United States
| | - Anna Huttenlocher
- Departments of Pediatrics and Medical Microbiology and Immunology, School of Medicine and Public Health, University of Wisconsin, United States
| | - Clare M Waterman
- Cell and Developmental Biology Center, National Heart Lung and Blood Institute, National Institutes of Health, United States.
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3
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Weck ML, Grega-Larson NE, Tyska MJ. MyTH4-FERM myosins in the assembly and maintenance of actin-based protrusions. Curr Opin Cell Biol 2016; 44:68-78. [PMID: 27836411 DOI: 10.1016/j.ceb.2016.10.002] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2016] [Accepted: 10/12/2016] [Indexed: 12/13/2022]
Abstract
Unconventional myosins are actin-based molecular motors that serve a multitude of roles within the cell. One group of myosin motors, the MyTH4-FERM myosins, play an integral part in building and maintaining finger-like protrusions, which allow cells to interact with their external environment. Suggested to act primarily as transporters, these motor proteins enrich adhesion molecules, actin-regulatory proteins and other factors at the tips of filopodia, microvilli, and stereocilia. Below we review data from biophysical, biochemical, and cell biological studies, which implicate these myosins as central players in the assembly, maintenance and function of actin-based protrusions.
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Affiliation(s)
- Meredith L Weck
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, 3154 MRB III, PMB 407935, 465 21st Avenue South, Nashville, TN 37240-7935, United States
| | - Nathan E Grega-Larson
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, 3154 MRB III, PMB 407935, 465 21st Avenue South, Nashville, TN 37240-7935, United States
| | - Matthew J Tyska
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, 3154 MRB III, PMB 407935, 465 21st Avenue South, Nashville, TN 37240-7935, United States.
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4
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Skau CT, Plotnikov SV, Doyle AD, Waterman CM. Inverted formin 2 in focal adhesions promotes dorsal stress fiber and fibrillar adhesion formation to drive extracellular matrix assembly. Proc Natl Acad Sci U S A 2015; 112:E2447-56. [PMID: 25918420 PMCID: PMC4434736 DOI: 10.1073/pnas.1505035112] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Actin filaments and integrin-based focal adhesions (FAs) form integrated systems that mediate dynamic cell interactions with their environment or other cells during migration, the immune response, and tissue morphogenesis. How adhesion-associated actin structures obtain their functional specificity is unclear. Here we show that the formin-family actin nucleator, inverted formin 2 (INF2), localizes specifically to FAs and dorsal stress fibers (SFs) in fibroblasts. High-resolution fluorescence microscopy and manipulation of INF2 levels in cells indicate that INF2 plays a critical role at the SF-FA junction by promoting actin polymerization via free barbed end generation and centripetal elongation of an FA-associated actin bundle to form dorsal SF. INF2 assembles into FAs during maturation rather than during their initial generation, and once there, acts to promote rapid FA elongation and maturation into tensin-containing fibrillar FAs in the cell center. We show that INF2 is required for fibroblasts to organize fibronectin into matrix fibers and ultimately 3D matrices. Collectively our results indicate an important role for the formin INF2 in specifying the function of fibrillar FAs through its ability to generate dorsal SFs. Thus, dorsal SFs and fibrillar FAs form a specific class of integrated adhesion-associated actin structure in fibroblasts that mediates generation and remodeling of ECM.
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Affiliation(s)
- Colleen T Skau
- Cell Biology and Physiology Center, National Heart Lung and Blood Institute, and
| | - Sergey V Plotnikov
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada M5S 3G5
| | - Andrew D Doyle
- Cell Biology Section, Laboratory of Cell and Developmental Biology, National Institute of Dental and Craniofacial Research, NIH, Bethesda, MD 20892; and
| | - Clare M Waterman
- Cell Biology and Physiology Center, National Heart Lung and Blood Institute, and
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5
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Chen CJ, Shih CH, Chang YJ, Hong SJ, Li TN, Wang LHC, Chen L. SH2B1 and IRSp53 proteins promote the formation of dendrites and dendritic branches. J Biol Chem 2015; 290:6010-21. [PMID: 25586189 DOI: 10.1074/jbc.m114.603795] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
SH2B1 is an adaptor protein known to enhance neurite outgrowth. In this study, we provide evidence suggesting that the SH2B1 level is increased during in vitro culture of hippocampal neurons, and the β isoform (SH2B1β) is the predominant isoform. The fact that formation of filopodia is prerequisite for neurite initiation suggests that SH2B1 may regulate filopodium formation and thus neurite initiation. To investigate whether SH2B1 may regulate filopodium formation, the effect of SH2B1 and a membrane and actin regulator, IRSp53 (insulin receptor tyrosine kinase substrate p53), is investigated. Overexpressing both SH2B1β and IRSp53 significantly enhances filopodium formation, neurite outgrowth, and branching. Both in vivo and in vitro data show that SH2B1 interacts with IRSp53 in hippocampal neurons. This interaction depends on the N-terminal proline-rich domains of SH2B1. In addition, SH2B1 and IRSp53 co-localize at the plasma membrane, and their levels increase in the Triton X-100-insoluble fraction of developing neurons. These findings suggest that SH2B1-IRSp53 complexes promote the formation of filopodia, neurite initiation, and neuronal branching.
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Affiliation(s)
| | | | | | | | | | - Lily Hui-Ching Wang
- Institute of Molecular and Cellular Biology, Department of Medical Science, National Tsing Hua University, Hsinchu, Taiwan 30013, China
| | - Linyi Chen
- From the Institute of Molecular Medicine, Department of Medical Science, National Tsing Hua University, Hsinchu, Taiwan 30013, China
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6
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Barzik M, McClain LM, Gupton SL, Gertler FB. Ena/VASP regulates mDia2-initiated filopodial length, dynamics, and function. Mol Biol Cell 2014; 25:2604-19. [PMID: 24989797 PMCID: PMC4148250 DOI: 10.1091/mbc.e14-02-0712] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Filopodia are long plasma membrane extensions involved in the formation of adhesive, contractile, and protrusive actin-based structures in spreading and migrating cells. Whether filopodia formed by different molecular mechanisms equally support these cellular functions is unresolved. We used Enabled/vasodilator-stimulated phosphoprotein (Ena/VASP)-deficient MV(D7) fibroblasts, which are also devoid of endogenous mDia2, as a model system to investigate how these different actin regulatory proteins affect filopodia morphology and dynamics independently of one another. Filopodia initiated by either Ena/VASP or mDia2 contained similar molecular inventory but differed significantly in parameters such as number, length, F-actin organization, lifetime, and protrusive persistence. Moreover, in the absence of Ena/VASP, filopodia generated by mDia2 did not support initiation of integrin-dependent signaling cascades required for adhesion and subsequent lamellipodial extension, thereby causing a defect in early cell spreading. Coexpression of VASP with constitutively active mDia2(M/A) rescued these early adhesion defects. We conclude that Ena/VASP and mDia2 support the formation of filopodia with significantly distinct properties and that Ena/VASP regulates mDia2-initiated filopodial morphology, dynamics, and function.
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Affiliation(s)
- Melanie Barzik
- David H. Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Leslie M McClain
- David H. Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Stephanie L Gupton
- Department of Cell Biology and Physiology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Frank B Gertler
- David H. Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, MA 02139
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7
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Heuzé ML, Vargas P, Chabaud M, Le Berre M, Liu YJ, Collin O, Solanes P, Voituriez R, Piel M, Lennon-Duménil AM. Migration of dendritic cells: physical principles, molecular mechanisms, and functional implications. Immunol Rev 2014; 256:240-54. [PMID: 24117825 DOI: 10.1111/imr.12108] [Citation(s) in RCA: 86] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Dendritic cells (DCs) constitute a complex cell population that resides in both peripheral tissues and lymphoid organs. Their major function in tissues is to patrol their environment in search of danger-associated antigens to transport to lymph nodes and present to T lymphocytes. This process constitutes the first step of the adaptive immune response and relies on specific DC properties, including a high endocytic capacity as well as efficient motility in confined three-dimensional environments. Although cell motility has been widely studied, little is known on how the geometric characteristics of the environment influence DC migration and function. In this review, we give an overview of the basic physical principles and molecular mechanisms that control DC migration under confinement and discuss how such mechanisms impact the environment-patrolling capacity of DCs.
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8
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CDC42 switches IRSp53 from inhibition of actin growth to elongation by clustering of VASP. EMBO J 2013; 32:2735-50. [PMID: 24076653 DOI: 10.1038/emboj.2013.208] [Citation(s) in RCA: 89] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2013] [Accepted: 08/30/2013] [Indexed: 12/21/2022] Open
Abstract
Filopodia explore the environment, sensing soluble and mechanical cues during directional motility and tissue morphogenesis. How filopodia are initiated and spatially restricted to specific sites on the plasma membrane is still unclear. Here, we show that the membrane deforming and curvature sensing IRSp53 (Insulin Receptor Substrate of 53 kDa) protein slows down actin filament barbed end growth. This inhibition is relieved by CDC42 and counteracted by VASP, which also binds to IRSp53. The VASP:IRSp53 interaction is regulated by activated CDC42 and promotes high-density clustering of VASP, which is required for processive actin filament elongation. The interaction also mediates VASP recruitment to liposomes. In cells, IRSp53 and VASP accumulate at discrete foci at the leading edge, where filopodia are initiated. Genetic removal of IRSp53 impairs the formation of VASP foci, filopodia and chemotactic motility, while IRSp53 null mice display defective wound healing. Thus, IRSp53 dampens barbed end growth. CDC42 activation inhibits this activity and promotes IRSp53-dependent recruitment and clustering of VASP to drive actin assembly. These events result in spatial restriction of VASP filament elongation for initiation of filopodia during cell migration, invasion, and tissue repair.
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9
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Schäfer C, Faust U, Kirchgessner N, Merkel R, Hoffmann B. The filopodium: a stable structure with highly regulated repetitive cycles of elongation and persistence depending on the actin cross-linker fascin. Cell Adh Migr 2012; 5:431-8. [PMID: 21975552 DOI: 10.4161/cam.5.5.17400] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
The ability of mammalian cells to adhere and to migrate is an essential prerequisite to form higher organisms. Early migratory events include substrate sensing, adhesion formation, actin bundle assembly and force generation. Latest research revealed that filopodia are important not only for sensing the substrate but for all of the aforementioned highly regulated processes. However, the exact regulatory mechanisms are still barely understood. Here, we demonstrate that filopodia of human keratinocytes exhibit distinct cycles of repetitive elongation and persistence. A single filopodium thereby is able to initiate the formation of several stable adhesions. Every single filopodial cycle is characterized by an elongation phase, followed by a stabilization time and in many cases a persistence phase. The whole process is strongly connected to the velocity of the lamellipodial leading edge, characterized by a similar phase behavior with a slight time shift compared to filopodia and a different velocity. Most importantly, re-growth of existing filopodia is induced at a sharply defined distance between the filopodial tip and the lamellipodial leading edge. On the molecular level this re-growth is preceded by a strong filopodial reduction of the actin bundling protein fascin. This reduction is achieved by a switch to actin polymerization without fascin incorporation at the filopodial tip and therefore subsequent out-transport of the cross-linker by actin retrograde flow.
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Affiliation(s)
- Claudia Schäfer
- Institute of Complex Systems, Biomechanics, Forschungszentrum Jülich, Jülich, Germany
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10
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Abstract
Eukaryotic cells generate a diversity of actin filament networks in a common cytoplasm to optimally perform functions such as cell motility, cell adhesion, endocytosis and cytokinesis. Each of these networks maintains precise mechanical and dynamic properties by autonomously controlling the composition of its interacting proteins and spatial organization of its actin filaments. In this review, we discuss the chemical and physical mechanisms that target distinct sets of actin-binding proteins to distinct actin filament populations after nucleation, resulting in the assembly of actin filament networks that are optimized for specific functions.
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Affiliation(s)
- Alphée Michelot
- Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720-3202, USA.
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11
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Barkó S, Bugyi B, Carlier MF, Gombos R, Matusek T, Mihály J, Nyitrai M. Characterization of the biochemical properties and biological function of the formin homology domains of Drosophila DAAM. J Biol Chem 2010; 285:13154-69. [PMID: 20177055 PMCID: PMC2857102 DOI: 10.1074/jbc.m109.093914] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2009] [Revised: 02/04/2010] [Indexed: 11/06/2022] Open
Abstract
We characterized the properties of Drosophila melanogaster DAAM-FH2 and DAAM-FH1-FH2 fragments and their interactions with actin and profilin by using various biophysical methods and in vivo experiments. The results show that although the DAAM-FH2 fragment does not have any conspicuous effect on actin assembly in vivo, in cells expressing the DAAM-FH1-FH2 fragment, a profilin-dependent increase in the formation of actin structures is observed. The trachea-specific expression of DAAM-FH1-FH2 also induces phenotypic effects, leading to the collapse of the tracheal tube and lethality in the larval stages. In vitro, both DAAM fragments catalyze actin nucleation but severely decrease both the elongation and depolymerization rate of the filaments. Profilin acts as a molecular switch in DAAM function. DAAM-FH1-FH2, remaining bound to barbed ends, drives processive assembly of profilin-actin, whereas DAAM-FH2 forms an abortive complex with barbed ends that does not support profilin-actin assembly. Both DAAM fragments also bind to the sides of the actin filaments and induce actin bundling. These observations show that the D. melanogaster DAAM formin represents an extreme class of barbed end regulators gated by profilin.
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Affiliation(s)
- Szilvia Barkó
- From the
Faculty of Medicine, Department of Biophysics, University of Pécs, Szigeti Str. 12, Pécs H-7624, Hungary
| | - Beáta Bugyi
- Cytoskeleton Dynamics and Motility, Laboratoire d'Enzymologie et Biochemie Structurales, Centre National de la Recherche Scientifique, 1 Avenue de la Terrasse, 91198 Gif-sur-Yvette, France, and
| | - Marie-France Carlier
- Cytoskeleton Dynamics and Motility, Laboratoire d'Enzymologie et Biochemie Structurales, Centre National de la Recherche Scientifique, 1 Avenue de la Terrasse, 91198 Gif-sur-Yvette, France, and
| | - Rita Gombos
- the
Institute of Genetics, Biological Research Center of the Hungarian Academy of Sciences, Temesvári Krt. 62, Szeged H-6726, Hungary
| | - Tamás Matusek
- the
Institute of Genetics, Biological Research Center of the Hungarian Academy of Sciences, Temesvári Krt. 62, Szeged H-6726, Hungary
| | - József Mihály
- the
Institute of Genetics, Biological Research Center of the Hungarian Academy of Sciences, Temesvári Krt. 62, Szeged H-6726, Hungary
| | - Miklós Nyitrai
- From the
Faculty of Medicine, Department of Biophysics, University of Pécs, Szigeti Str. 12, Pécs H-7624, Hungary
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12
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Homem CCF, Peifer M. Exploring the roles of diaphanous and enabled activity in shaping the balance between filopodia and lamellipodia. Mol Biol Cell 2010; 20:5138-55. [PMID: 19846663 DOI: 10.1091/mbc.e09-02-0144] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
During migration cell protrusions power cell extension and sample the environment. Different cells produce different protrusions, from keratocytes dominated by lamellipodia, to growth cones combining filopodia and lamellipodia, to dendritic spines. One key challenge is to determine how the toolkit of actin regulators are coordinated to generate these diverse protrusive arrays. Here we use Drosophila leading-edge (LE) cells to explore how Diaphanous (Dia)-related formins and Ena/VASP proteins cooperate in this process. We first dissect the Dia regulatory region, revealing novel roles for the GTPase-binding and FH3 domains in cortical localization, filopodial initiation, and lengthening. Second, we provide evidence that activating Dia mobilizes Ena from storage places near the LE to act at the LE. Further, Dia and Ena coIP and can recruit one another to new locations, suggesting cooperation is key to their mechanisms of action. Third, we directly explore the functional relationship between Dia and Ena, varying their levels and activity separately in the same cell type. Surprisingly, although each is sufficient to induce filopodia, together they induce lamellipodia. Our data suggest they work together in a complex and nonadditive way, with the ratio between active Dia and Ena being one factor that modulates the balance between filopodia and lamellipodia.
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Affiliation(s)
- Catarina C F Homem
- Department of Biology and Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3280, USA
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13
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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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14
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Menna E, Disanza A, Cagnoli C, Schenk U, Gelsomino G, Frittoli E, Hertzog M, Offenhauser N, Sawallisch C, Kreienkamp HJ, Gertler FB, Di Fiore PP, Scita G, Matteoli M. Eps8 regulates axonal filopodia in hippocampal neurons in response to brain-derived neurotrophic factor (BDNF). PLoS Biol 2009; 7:e1000138. [PMID: 19564905 PMCID: PMC2696597 DOI: 10.1371/journal.pbio.1000138] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2009] [Accepted: 05/15/2009] [Indexed: 12/17/2022] Open
Abstract
A novel signaling cascade controlling actin polymerization in response to extracellular signals regulates filopodia formation and likely also neuronal synapse formation. The regulation of filopodia plays a crucial role during neuronal development and synaptogenesis. Axonal filopodia, which are known to originate presynaptic specializations, are regulated in response to neurotrophic factors. The structural components of filopodia are actin filaments, whose dynamics and organization are controlled by ensembles of actin-binding proteins. How neurotrophic factors regulate these latter proteins remains, however, poorly defined. Here, using a combination of mouse genetic, biochemical, and cell biological assays, we show that genetic removal of Eps8, an actin-binding and regulatory protein enriched in the growth cones and developing processes of neurons, significantly augments the number and density of vasodilator-stimulated phosphoprotein (VASP)-dependent axonal filopodia. The reintroduction of Eps8 wild type (WT), but not an Eps8 capping-defective mutant, into primary hippocampal neurons restored axonal filopodia to WT levels. We further show that the actin barbed-end capping activity of Eps8 is inhibited by brain-derived neurotrophic factor (BDNF) treatment through MAPK-dependent phosphorylation of Eps8 residues S624 and T628. Additionally, an Eps8 mutant, impaired in the MAPK target sites (S624A/T628A), displays increased association to actin-rich structures, is resistant to BDNF-mediated release from microfilaments, and inhibits BDNF-induced filopodia. The opposite is observed for a phosphomimetic Eps8 (S624E/T628E) mutant. Thus, collectively, our data identify Eps8 as a critical capping protein in the regulation of axonal filopodia and delineate a molecular pathway by which BDNF, through MAPK-dependent phosphorylation of Eps8, stimulates axonal filopodia formation, a process with crucial impacts on neuronal development and synapse formation. Neurons communicate with each other via specialized cell–cell junctions called synapses. The proper formation of synapses (“synaptogenesis”) is crucial to the development of the nervous system, but the molecular pathways that regulate this process are not fully understood. External cues, such as brain-derived neurotrophic factor (BDNF), trigger synaptogenesis by promoting the formation of axonal filopodia, thin extensions projecting outward from a growing axon. Filopodia are formed by elongation of actin filaments, a process that is regulated by a complex set of actin-binding proteins. Here, we reveal a novel molecular circuit underlying BDNF-stimulated filopodia formation through the regulated inhibition of actin-capping factor activity. We show that the actin-capping protein Eps8 down-regulates axonal filopodia formation in neurons in the absence of neurotrophic factors. In contrast, in the presence of BDNF, the kinase MAPK becomes activated and phosphorylates Eps8, leading to inhibition of its actin-capping function and stimulation of filopodia formation. Our study, therefore, identifies actin-capping factor inhibition as a critical step in axonal filopodia formation and likely in new synapse formation.
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Affiliation(s)
- Elisabetta Menna
- Department of Medical Pharmacology, National Research Council (CNR) Institute of Neuroscience, University of Milan, Milan, Italy
- Filarete Foundation, Milan, Italy
| | - Andrea Disanza
- IFOM Foundation – FIRC (Italian Foundation for Cancer Research) Institute of Molecular Oncology, Milan, Itlay
| | - Cinzia Cagnoli
- Department of Medical Pharmacology, National Research Council (CNR) Institute of Neuroscience, University of Milan, Milan, Italy
| | - Ursula Schenk
- Department of Medical Pharmacology, National Research Council (CNR) Institute of Neuroscience, University of Milan, Milan, Italy
| | - Giuliana Gelsomino
- Department of Medical Pharmacology, National Research Council (CNR) Institute of Neuroscience, University of Milan, Milan, Italy
| | - Emanuela Frittoli
- IFOM Foundation – FIRC (Italian Foundation for Cancer Research) Institute of Molecular Oncology, Milan, Itlay
| | - Maud Hertzog
- IFOM Foundation – FIRC (Italian Foundation for Cancer Research) Institute of Molecular Oncology, Milan, Itlay
| | - Nina Offenhauser
- IFOM Foundation – FIRC (Italian Foundation for Cancer Research) Institute of Molecular Oncology, Milan, Itlay
| | - Corinna Sawallisch
- Institut für Humangenetik, Universitätsklinikum Hamburg-Eppendorf, Hamburg, Germany
| | | | - Frank B. Gertler
- Massachusetts Institute of Technology, Koch Institute, Cambridge, Massachusetts, United States of America
| | - Pier Paolo Di Fiore
- IFOM Foundation – FIRC (Italian Foundation for Cancer Research) Institute of Molecular Oncology, Milan, Itlay
- Department of Experimental Oncology, Istituto Europeo di Oncologia, Milan, Italy
- University of Milan Medical School, Milan, Italy
| | - Giorgio Scita
- IFOM Foundation – FIRC (Italian Foundation for Cancer Research) Institute of Molecular Oncology, Milan, Itlay
- University of Milan Medical School, Milan, Italy
- * E-mail: (GS); (MM)
| | - Michela Matteoli
- Department of Medical Pharmacology, National Research Council (CNR) Institute of Neuroscience, University of Milan, Milan, Italy
- Filarete Foundation, Milan, Italy
- Institute for Hospitalisation and Scientific Care (IRCCS) Don Gnocchi, Milan, Italy
- * E-mail: (GS); (MM)
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15
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One step ahead: role of filopodia in adhesion formation during cell migration of keratinocytes. Exp Cell Res 2008; 315:1212-24. [PMID: 19100734 DOI: 10.1016/j.yexcr.2008.11.008] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2008] [Revised: 11/14/2008] [Accepted: 11/15/2008] [Indexed: 01/09/2023]
Abstract
Cell adhesion is an essential prerequisite for cell function and movement. It depends strongly on focal adhesion complexes connecting the extracellular matrix to the actin cytoskeleton. Especially in moving cells focal adhesions are highly dynamic and believed to be formed closely behind the leading edge. Filopodia were thought to act mainly as guiding cues using their tip complexes for elongation. Here we show for keratinocytes a strong dependence of lamellipodial adhesion sites on filopodia. Upon stable contact of the VASP-containing tip spot to the substrate, a filopodial focal complex (filopodial FX) is formed right behind along the filopodia axis. These filopodial FXs are fully assembled, yet small adhesions containing all adhesion markers tested. Filopodial FXs when reached by the lamellipodium are just increased in size resulting in classical focal adhesions. At the same time most filopodia regain their elongation ability. Blocking filopodia inhibits development of new focal adhesions in the lamellipodium, while focal adhesion maturation in terms of vinculin exchange dynamics remains active. Our data therefore argue for a strong spatial and temporal dependence of focal adhesions on filopodial focal complexes in keratinocytes with filopodia not permanently initiated via new clustering of actin filaments to induce elongation.
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16
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Esue O, Harris ES, Higgs HN, Wirtz D. The filamentous actin cross-linking/bundling activity of mammalian formins. J Mol Biol 2008; 384:324-34. [PMID: 18835565 DOI: 10.1016/j.jmb.2008.09.043] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2008] [Revised: 09/14/2008] [Accepted: 09/15/2008] [Indexed: 01/17/2023]
Abstract
Formins are multidomain proteins that regulate actin filament dynamics and are defined by the formin homology 2 domain. Biochemical assays suggest that mammalian formins display actin-filament nucleation, severing, and bundling activities. Whether formins can cross-link actin filaments into viscoelastic arrays and the effectiveness of formins' bundling activity compared with that of important filamentous actin (F-actin) cross-linking/bundling proteins are unknown. Here, we used rigorous in vitro rheologic assays to deconvolve the dynamic cross-linking activity from the bundling activity of formin FRL1 and the closely related mDia1 and mDia2. In addition, we compared these formins with the canonical F-actin bundling protein fascin and cross-linking/bundling proteins alpha-actinin and filamin. We found that FRL1 and mDia2, but not mDia1, can help F-actin form highly elastic networks. FRL1 and mDia2 mediate the formation of highly elastic F-actin networks as effectively and rapidly as alpha-actinin and filamin but only past a relatively high actin-to-formin molar ratio of 50:1. Past that threshold molar ratio, the mechanical properties of F-actin/formin networks are independent of formin concentration, similar to fascin. Moreover, unlike those for alpha-actinin and filamin but similar to those for fascin, F-actin/formin networks show no strain-induced hardening. mDia1 cannot bundle F-actin but can weakly cross-link filaments at high concentrations. Point mutagenesis reveals that reducing the barbed-end binding activity of FRL1 and mDia2 greatly enhances the rate of formation of F-actin gels but does not significantly affect the mechanical properties of the resulting networks at steady state. Together, these results suggest that the mechanical behaviors of FRL1 and mDia2 are fundamentally different from those of cross-linking/bundling proteins alpha-actinin and filamin but qualitatively similar to the mechanical behavior of the bundling protein fascin, albeit with a dramatically increased (>10-fold) threshold concentration for transition to bundling, which nevertheless leads to much stiffer F-actin networks than fascin.
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Affiliation(s)
- Osigwe Esue
- Department of Chemical and Biomolecular Engineering, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA.
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17
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Jiang H, Powers TR. Curvature-driven lipid sorting in a membrane tubule. PHYSICAL REVIEW LETTERS 2008; 101:018103. [PMID: 18764156 DOI: 10.1103/physrevlett.101.018103] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/11/2008] [Indexed: 05/26/2023]
Abstract
Motivated by recent experiments that implicate the mechanical properties of membranes in lipid sorting, we examine the interplay of lipid composition and curvature in membrane tubules. We study how the coupling between membrane composition and membrane bending stiffness and tension affects tubule formation. Drawing a tubule from a vesicle leads to a rearrangement of composition in which the phase of higher flexibility segregates into the highly curved tubule. For point forcing, the force vs extension curve can have a sharp drop just as the tubule begins to form.
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Affiliation(s)
- Hongyuan Jiang
- Division of Engineering, Box D, Brown University, Providence, Rhode Island 02912, USA
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18
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The actin cytoskeleton in cancer cell motility. Clin Exp Metastasis 2008; 26:273-87. [PMID: 18498004 DOI: 10.1007/s10585-008-9174-2] [Citation(s) in RCA: 411] [Impact Index Per Article: 25.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2008] [Accepted: 04/25/2008] [Indexed: 01/01/2023]
Abstract
Cancer cell metastasis is a multi-stage process involving invasion into surrounding tissue, intravasation, transit in the blood or lymph, extravasation, and growth at a new site. Many of these steps require cell motility, which is driven by cycles of actin polymerization, cell adhesion and acto-myosin contraction. These processes have been studied in cancer cells in vitro for many years, often with seemingly contradictory results. The challenge now is to understand how the multitude of in vitro observations relates to the movement of cancer cells in living tumour tissue. In this review we will concentrate on actin protrusion and acto-myosin contraction. We will begin by presenting some general principles summarizing the widely-accepted mechanisms for the co-ordinated regulation of actin polymerization and contraction. We will then discuss more recent studies that investigate how experimental manipulation of actin dynamics affects cancer cell invasion in complex environments and in vivo.
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19
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Pasic L, Kotova T, Schafer DA. Ena/VASP proteins capture actin filament barbed ends. J Biol Chem 2008; 283:9814-9. [PMID: 18283104 DOI: 10.1074/jbc.m710475200] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Ena/VASP (vasodialator-stimulated protein) proteins regulate many actin-dependent events, including formation of protrusive structures, fibroblast migration, neurite extension, cell-cell adhesion, and Listeria pathogenesis. In vitro, Ena/VASP activities on actin are complex and varied. They promote actin assembly, protect filaments from cappers, bundle filaments, and inhibit filament branching. To determine the mechanisms by which Ena/VASP proteins regulate actin dynamics at barbed ends, we monitored individual actin filaments growing in the presence of VASP and profilin using total internal reflection fluorescence microscopy. Filament growth was unchanged by VASP, but filaments grew faster in profilin-actin and VASP than with profilin-actin alone. Actin filaments were captured directly by VASP-coated surfaces via interactions with growing barbed ends. End-attached filaments transiently paused but resumed growth after becoming bound to the surface via a filament side attachment. Thus, Ena/VASP proteins promote actin assembly by interacting directly with actin filament barbed ends, recruiting profilin-actin, and blocking capping.
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Affiliation(s)
- Lejla Pasic
- Departments of Biology and Cell Biology, University of Virginia, Charlottesville, VA 22903, USA
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20
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Scita G, Confalonieri S, Lappalainen P, Suetsugu S. IRSp53: crossing the road of membrane and actin dynamics in the formation of membrane protrusions. Trends Cell Biol 2008; 18:52-60. [DOI: 10.1016/j.tcb.2007.12.002] [Citation(s) in RCA: 208] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2007] [Revised: 12/04/2007] [Accepted: 12/04/2007] [Indexed: 11/16/2022]
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21
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Abstract
A filopodium is a cytoplasmic projection, exquisitely built and regulated, which extends from the leading edge of the migrating cell, exploring the cell's neighborhood. Commonly, filopodia grow and retract after their initiation, exhibiting rich dynamical behaviors. We model the growth of a filopodium based on a stochastic description which incorporates mechanical, physical, and biochemical components. Our model provides a full stochastic treatment of the actin monomer diffusion and polymerization of each individual actin filament under stress of the fluctuating membrane. We investigated the length distribution of individual filaments in a growing filopodium and studied how it depends on various physical parameters. The distribution of filament lengths turned out to be narrow, which we explained by the negative feedback created by the membrane load and monomeric G-actin gradient. We also discovered that filopodial growth is strongly diminished upon increasing retrograde flow, suggesting that regulating the retrograde flow rate would be a highly efficient way to control filopodial extension dynamics. The filopodial length increases as the membrane fluctuations decrease, which we attributed to the unequal loading of the membrane force among individual filaments, which, in turn, results in larger average polymerization rates. We also observed significant diffusional noise of G-actin monomers, which leads to smaller G-actin flux along the filopodial tube compared with the prediction using the diffusion equation. Overall, partial cancellation of these two fluctuation effects allows a simple mean field model to rationalize most of our simulation results. However, fast fluctuations significantly renormalize the mean field model parameters. The biological significance of our filopodial model and avenues for future development are also discussed.
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22
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Faul C, Asanuma K, Yanagida-Asanuma E, Kim K, Mundel P. Actin up: regulation of podocyte structure and function by components of the actin cytoskeleton. Trends Cell Biol 2007; 17:428-37. [PMID: 17804239 DOI: 10.1016/j.tcb.2007.06.006] [Citation(s) in RCA: 412] [Impact Index Per Article: 24.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2007] [Revised: 06/15/2007] [Accepted: 06/15/2007] [Indexed: 12/18/2022]
Abstract
Podocytes of the renal glomerulus are unique cells with a complex cellular organization consisting of a cell body, major processes and foot processes. Podocyte foot processes form a characteristic interdigitating pattern with foot processes of neighboring podocytes, leaving in between the filtration slits that are bridged by the glomerular slit diaphragm. The highly dynamic foot processes contain an actin-based contractile apparatus comparable to that of smooth muscle cells or pericytes. Mutations affecting several podocyte proteins lead to rearrangement of the actin cytoskeleton, disruption of the filtration barrier and subsequent renal disease. The fact that the dynamic regulation of the podocyte cytoskeleton is vital to kidney function has led to podocytes emerging as an excellent model system for studying actin cytoskeleton dynamics in a physiological context.
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Affiliation(s)
- Christian Faul
- Department of Medicine, Mount Sinai School of Medicine, New York, NY 10029, USA
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23
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Abstract
Formation of protrusions and protein segregation on the membrane is of a great importance for the functioning of the living cell. This is most evident in recent experiments that show the effects of the mechanical properties of the surrounding substrate on cell morphology. We propose a mechanism for the formation of membrane protrusions and protein phase separation, which may lay behind this effect. In our model, the fluid cell membrane has a mobile but constant population of proteins with a convex spontaneous curvature. Our basic assumption is that these membrane proteins represent small adhesion complexes, and also include proteins that activate actin polymerization. Such a continuum model couples the membrane and protein dynamics, including cell-substrate adhesion and protrusive actin force. Linear stability analysis shows that sufficiently strong adhesion energy and actin polymerization force can bring about phase separation of the membrane protein and the appearance of protrusions. Specifically, this occurs when the spontaneous curvature and aggregation potential alone (passive system) do not cause phase separation. Finite-size patterns may appear in the regime where the spontaneous curvature energy is a strong factor. Different instability characteristics are calculated for the various regimes, and are compared to various types of observed protrusions and phase separations, both in living cells and in artificial model systems. A number of testable predictions are proposed.
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Affiliation(s)
- Alex Veksler
- Department of Chemical Physics, The Weizmann Institute of Science, Rehovot, Israel.
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24
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Applewhite DA, Barzik M, Kojima SI, Svitkina TM, Gertler FB, Borisy GG. Ena/VASP proteins have an anti-capping independent function in filopodia formation. Mol Biol Cell 2007; 18:2579-91. [PMID: 17475772 PMCID: PMC1924831 DOI: 10.1091/mbc.e06-11-0990] [Citation(s) in RCA: 164] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Filopodia have been implicated in a number of diverse cellular processes including growth-cone path finding, wound healing, and metastasis. The Ena/VASP family of proteins has emerged as key to filopodia formation but the exact mechanism for how they function has yet to be fully elucidated. Using cell spreading as a model system in combination with small interfering RNA depletion of Capping Protein, we determined that Ena/VASP proteins have a role beyond anticapping activity in filopodia formation. Analysis of mutant Ena/VASP proteins demonstrated that the entire EVH2 domain was the minimal domain required for filopodia formation. Fluorescent recovery after photobleaching data indicate that Ena/VASP proteins rapidly exchange at the leading edge of lamellipodia, whereas virtually no exchange occurred at filopodial tips. Mutation of the G-actin-binding motif (GAB) partially compromised stabilization of Ena/VASP at filopodia tips. These observations led us to propose a model where the EVH2 domain of Ena/VASP induces and maintains clustering of the barbed ends of actin filaments, which putatively corresponds to a transition from lamellipodial to filopodial localization. Furthermore, the EVH1 domain, together with the GAB motif in the EVH2 domain, helps to maintain Ena/VASP at the growing barbed ends.
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Affiliation(s)
- Derek A. Applewhite
- *Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611
| | - Melanie Barzik
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Shin-ichiro Kojima
- *Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611
| | - Tatyana M. Svitkina
- Department of Biology, University of Pennsylvania, Philadelphia, PA 19104; and
| | - Frank B. Gertler
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Gary G. Borisy
- *Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611
- Marine Biological Laboratory, Woods Hole, MA 02453
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25
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van der Honing HS, Emons AMC, Ketelaar T. Actin based processes that could determine the cytoplasmic architecture of plant cells. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2007; 1773:604-14. [PMID: 16962185 DOI: 10.1016/j.bbamcr.2006.07.009] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2006] [Revised: 06/09/2006] [Accepted: 07/21/2006] [Indexed: 10/24/2022]
Abstract
Actin polymerisation can generate forces that are necessary for cell movement, such as the propulsion of a class of bacteria, including Listeria, and the protrusion of migrating animal cells. Force generation by the actin cytoskeleton in plant cells has not been studied. One process in plant cells that is likely to depend on actin-based force generation is the organisation of the cytoplasm. We compare the function of actin binding proteins of three well-studied mammalian models that depend on actin-based force generation with the function of their homologues in plants. We predict the possible role of these proteins, and thus the role of actin-based force generation, in the production of cytoplasmic organisation in plant cells.
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Affiliation(s)
- Hannie S van der Honing
- Laboratory of Plant Cell Biology, Wageningen University, Arboretumlaan 4, 6703BD Wageningen, The Netherlands
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26
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Abstract
A new study has found that retrograde flow of budding yeast actin cables is facilitated by myosin II but is inhibited by a specific tropomyosin isoform (Tpm2p). Budding yeast therefore contains a minimal component system for elucidating the mechanistic details of retrograde actin flow.
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Affiliation(s)
- David R Kovar
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637, USA.
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27
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Radha V, Rajanna A, Mitra A, Rangaraj N, Swarup G. C3G is required for c-Abl-induced filopodia and its overexpression promotes filopodia formation. Exp Cell Res 2007; 313:2476-92. [PMID: 17475248 DOI: 10.1016/j.yexcr.2007.03.019] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2006] [Revised: 02/27/2007] [Accepted: 03/18/2007] [Indexed: 01/26/2023]
Abstract
The Rap1 guanine nucleotide exchange factor, C3G (also known as Rap1GEF-1) is involved in signaling from growth factors, cytokines and integrins and plays a role in cell adhesion and migration, but the mechanism by which C3G regulates various cellular functions is poorly understood. We, therefore, investigated the ability of C3G to affect actin cytoskeleton-dependent morphological changes in cells. Using RNA interference, we provide evidence that C3G is required for c-Abl-induced filopodia during cell spreading on fibronectin. C3G expression induces actin cytoskeletal reorganization and promotes filopodia formation independent of its catalytic activity. It showed enrichment at filopodia tips characteristic of molecules involved in filopodia dynamics. C3G-induced filopodia were not inhibited by dominant negative mutants of Rho, Rac and Cdc42, but required Abl catalytic activity. Coexpression of N-Wasp-Crib inhibited C3G induced as well as c-Abl-induced filopodia and wiskostatin, a pharmacological inhibitor of N-Wasp attenuates C3G-induced filopodia. Cellular C3G interacts with c-Abl and C3G expression results in enhanced localization of endogenous c-Abl in the cytoplasm. We suggest that C3G and c-Abl function in an interdependent manner, in linking external signals to remodeling the cytoskeleton to induce filopodia.
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Affiliation(s)
- Vegesna Radha
- Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad, India.
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28
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Arasada R, Gloss A, Tunggal B, Joseph JM, Rieger D, Mondal S, Faix J, Schleicher M, Noegel AA. Profilin isoforms in Dictyostelium discoideum. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2007; 1773:631-41. [PMID: 17467078 DOI: 10.1016/j.bbamcr.2007.03.009] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/09/2006] [Revised: 03/13/2007] [Accepted: 03/14/2007] [Indexed: 11/21/2022]
Abstract
Eukaryotic cells contain a large number of actin binding proteins of different functions, locations and concentrations. They bind either to monomeric actin (G-actin) or to actin filaments (F-actin) and thus regulate the dynamic rearrangement of the actin cytoskeleton. The Dictyostelium discoideum genome harbors representatives of all G-actin binding proteins including actobindin, twinfilin, and profilin. A phylogenetic analysis of all profilins suggests that two distinguishable groups emerged very early in evolution and comprise either vertebrate and viral profilins or profilins from all other organisms. The newly discovered profilin III isoform in D. discoideum shows all functions that are typical for a profilin. However, the concentration of the third isoform in wild type cells reaches only about 0.5% of total profilin. In a yeast-2-hybrid assay profilin III was found to bind specifically to the proline-rich region of the cytoskeleton-associated vasodilator-stimulated phosphoprotein (VASP). Immunolocalization studies showed similar to VASP the profilin III isoform in filopodia and an enrichment at their tips. Cells lacking the profilin III isoform show defects in cell motility during chemotaxis. The low abundance and the specific interaction with VASP argue against a significant actin sequestering function of the profilin III isoform.
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Affiliation(s)
- Rajesh Arasada
- Adolf-Butenandt-Inst.-Zellbiologie, Ludwig-Maximilians-Universität, Schillerstrasse 42, 80336 München, Germany
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29
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Mège RM, Gavard J, Lambert M. Regulation of cell–cell junctions by the cytoskeleton. Curr Opin Cell Biol 2006; 18:541-8. [PMID: 16905303 DOI: 10.1016/j.ceb.2006.08.004] [Citation(s) in RCA: 211] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2006] [Accepted: 08/02/2006] [Indexed: 11/29/2022]
Abstract
A major form of animal cell-cell adhesion results from the dynamic association of cadherin molecules, cytosolic catenins and actin microfilaments. Cadherins dynamically regulate the cytoskeleton. In turn, the actin cytoskeleton contributes to cadherin molecule oligomerization at cell contacts and to cell reshaping in response to environmental changes. Over the past two years, this evolutionarily conserved adhesion system has been intensively revisited in both its structural and functional aspects; this is illustrated by the remarkable progress in the determination of physical parameters of cadherin bonds (including force measurement) and the new insights into the role of alpha-catenin and the regulation of actin dynamics at cadherin contacts. Other recent studies uncover the important contribution of acto-myosin, microtubules and cell tension to adherens junction formation, cell differentiation and tissue reshaping/remodeling. An open challenge is now to integrate these new data with the diversity of cadherin adhesive complexes.
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Affiliation(s)
- René-Marc Mège
- INSERM, U 706, Institut du Fer à Moulin, 75005 Paris, France.
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30
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Ridley AJ. Rho GTPases and actin dynamics in membrane protrusions and vesicle trafficking. Trends Cell Biol 2006; 16:522-9. [PMID: 16949823 DOI: 10.1016/j.tcb.2006.08.006] [Citation(s) in RCA: 870] [Impact Index Per Article: 48.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2006] [Revised: 08/14/2006] [Accepted: 08/24/2006] [Indexed: 02/08/2023]
Abstract
Rho GTPases are well known to regulate actin dynamics. They activate two types of actin nucleators, WASP/WAVE proteins and Diaphanous-related formins (DRFs), which induce different types of actin organization. Their ability to interact with membranes allows them to target actin polymerization to discrete sites on the plasma membrane and to intracellular membrane compartments and thereby induce membrane protrusions or regulate vesicle movement. Most studies have concentrated on just three of the 22 mammalian Rho proteins, RhoA, Rac1 and Cdc42. However, recent research indicates that several other members of the Rho family, including Rif, RhoD, TC10 and Wrch1, and also related Rho-of-plants proteins (ROPs) in plants, stimulate actin polymerization and affect plasma membrane protrusion and/or vesicular traffic.
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Affiliation(s)
- Anne J Ridley
- Ludwig Institute for Cancer Research, Royal Free and University College School of Medicine, 91 Riding House Street, London W1W 7BS, UK.
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31
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Dormann D, Weijer CJ. Chemotactic cell movement during Dictyostelium development and gastrulation. Curr Opin Genet Dev 2006; 16:367-73. [PMID: 16782325 DOI: 10.1016/j.gde.2006.06.003] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2006] [Accepted: 06/08/2006] [Indexed: 11/26/2022]
Abstract
Many developmental processes involve chemotactic cell movement up or down dynamic chemical gradients. Studies of the molecular mechanisms of chemotactic movement of Dictyostelium amoebae up cAMP gradients highlight the importance of PIP3 signaling in the control of cAMP-dependent actin polymerization, which drives the protrusion of lamellipodia and filopodia at the leading edge of the cell, but also emphasize the need for myosin thick filament assembly and motor activation for the contraction of the back of the cell. These process become even more important during the multicellular stages of development, when propagating waves of cAMP coordinate the chemotactic movement of tens of thousands of cells, resulting in multicellular morphogenesis. Recent experiments show that chemotaxis, especially in response to members of the FGF, PDGF and VEGF families of growth factors, plays a key role in the guidance of mesoderm cells during gastrulation in chick, mouse and frog embryos. The molecular mechanisms of signal detection and signaling to the actin-myosin cytoskeleton remain to be elucidated.
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Affiliation(s)
- Dirk Dormann
- Division of Cell and Developmental Biology, School of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
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