1
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Xu XP, Cao W, Swift MF, Pandit NG, Huehn AE, Sindelar CV, De La Cruz EM, Hanein D, Volkmann N. High-resolution yeast actin structures indicate the molecular mechanism of actin filament stiffening by cations. Commun Chem 2024; 7:164. [PMID: 39079963 PMCID: PMC11289367 DOI: 10.1038/s42004-024-01243-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2024] [Accepted: 07/10/2024] [Indexed: 08/02/2024] Open
Abstract
Actin filament assembly and the regulation of its mechanical properties are fundamental processes essential for eukaryotic cell function. Residue E167 in vertebrate actins forms an inter-subunit salt bridge with residue K61 of the adjacent subunit. Saccharomyces cerevisiae actin filaments are more flexible than vertebrate filaments and have an alanine at this position (A167). Substitution of this alanine for a glutamic acid (A167E) confers Saccharomyces cerevisiae actin filaments with salt-dependent stiffness similar to vertebrate actins. We developed an optimized cryogenic electron microscopy workflow refining sample preparation and vitrification to obtain near-atomic resolution structures of wild-type and A167E mutant Saccharomyces cerevisiae actin filaments. The difference between these structures allowed us to pinpoint the potential binding site of a filament-associated cation that controls the stiffness of the filaments in vertebrate and A167E Saccharomyces cerevisiae actins. Through an analysis of previously published high-resolution reconstructions of vertebrate actin filaments, along with a newly determined high-resolution vertebrate actin structure in the absence of potassium, we identified a unique peak near residue 167 consistent with the binding of a magnesium ion. Our findings show how magnesium can contribute to filament stiffening by directly bridging actin subunits and allosterically affecting the orientation of the DNase-I binding loop of actin, which plays a regulatory role in modulating actin filament stiffness and interactions with regulatory proteins.
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Affiliation(s)
- Xiao-Ping Xu
- Scintillon Institute, 6868 Nancy Ridge Drive, San Diego, CA, 92121, USA
| | - Wenxiang Cao
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, 06520, USA
| | - Mark F Swift
- Scintillon Institute, 6868 Nancy Ridge Drive, San Diego, CA, 92121, USA
| | - Nandan G Pandit
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, 06520, USA
| | - Andrew E Huehn
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, 06520, USA
| | - Charles V Sindelar
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, 06520, USA
| | - Enrique M De La Cruz
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, 06520, USA
| | - Dorit Hanein
- Department of Chemistry and Biochemistry and Department of Biological Engineering, University of California, Santa Barbara, CA, 93106, USA.
| | - Niels Volkmann
- Department of Biological Engineering, Department of Electrical and Computer Engineering, Biomolecular Science and Engineering Program, University of California, Santa Barbara, CA, 93106, USA.
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2
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Zsolnay V, Gardel ML, Kovar DR, Voth GA. Cracked actin filaments as mechanosensitive receptors. Biophys J 2024:S0006-3495(24)00411-9. [PMID: 38894540 DOI: 10.1016/j.bpj.2024.06.014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2023] [Revised: 05/10/2024] [Accepted: 06/14/2024] [Indexed: 06/21/2024] Open
Abstract
Actin filament networks are exposed to mechanical stimuli, but the effect of strain on actin filament structure has not been well established in molecular detail. This is a critical gap in understanding because the activity of a variety of actin-binding proteins has recently been determined to be altered by actin filament strain. We therefore used all-atom molecular dynamics simulations to apply tensile strains to actin filaments and find that changes in actin subunit organization are minimal in mechanically strained, but intact, actin filaments. However, a conformational change disrupts the critical D-loop to W-loop connection between longitudinal neighboring subunits, which leads to a metastable cracked conformation of the actin filament whereby one protofilament is broken prior to filament severing. We propose that the metastable crack presents a force-activated binding site for actin regulatory factors that specifically associate with strained actin filaments. Through protein-protein docking simulations, we find that 43 evolutionarily diverse members of the dual zinc-finger-containing LIM-domain family, which localize to mechanically strained actin filaments, recognize two binding sites exposed at the cracked interface. Furthermore, through its interactions with the crack, LIM domains increase the length of time damaged filaments remain stable. Our findings propose a new molecular model for mechanosensitive binding to actin filaments.
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Affiliation(s)
- Vilmos Zsolnay
- Graduate Program in Biophysical Sciences, University of Chicago, Chicago, Illinois
| | - Margaret L Gardel
- Department of Physics & Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois; Institute for Biophysical Dynamics and James Franck Institute, University of Chicago, Chicago, Illinois
| | - David R Kovar
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, Illinois; Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois.
| | - Gregory A Voth
- Institute for Biophysical Dynamics and James Franck Institute, University of Chicago, Chicago, Illinois; Department of Chemistry and Chicago Center for Theoretical Chemistry, University of Chicago, Chicago, Illinois.
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3
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Rottner K, Bieling P. Illuminating cortactin structure and function at actin filament branches. Nat Struct Mol Biol 2024; 31:739-741. [PMID: 38714891 DOI: 10.1038/s41594-024-01297-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/21/2024]
Affiliation(s)
- Klemens Rottner
- Department of Cell Biology, Helmholtz Centre for Infection Research, Braunschweig, Germany.
- Division of Molecular Cell Biology, Zoological Institute, Technische Universität Braunschweig, Braunschweig, Germany.
| | - Peter Bieling
- Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany.
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4
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Zheng Y, Liu M, Yu Q, Wang R, Yao Y, Jiang L. Release of extracellular vesicles triggered by low-intensity pulsed ultrasound: immediate and delayed reactions. NANOSCALE 2024; 16:6017-6032. [PMID: 38410045 DOI: 10.1039/d4nr00277f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/28/2024]
Abstract
Previous studies have shown that ultrasound may stimulate the release of extracellular vesicles, improving the efficiency of tumor detection. However, it is unclear whether ultrasonic stimulation affects the distribution of extracellular vesicles, and the duration of such stimulation release has not been extensively studied. In this study, we stimulated cells with low-intensity pulsed ultrasound and used liposomes containing black hole quenchers to simulate natural extracellular vesicles, confirming that ultrasound has a destructive effect on vesicles and thus affects particle size distribution. Furthermore, we used proteomics technology to examine the protein expression profile of small vesicles and discovered that the expression of proteins involved in exosome biogenesis was down-regulated. We then looked into the regulation of the actin cytoskeleton and endocytosis pathways, which are required for intracellular vesicle transport, and discovered that ultrasound might induce F-actin depolymerization. The intracellular transport of the cation-independent mannose-6-phosphate receptor (CI-MPR) in the trans-Golgi network (TGN) and the amount of Rab7a protein were proportional to the culture time after LIPUS treatment.
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Affiliation(s)
- Yiwen Zheng
- Department of Medical Ultrasound, Renji Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200127, China.
| | - Mengyao Liu
- Department of Medical Ultrasound, Renji Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200127, China.
| | - Qian Yu
- Department of Medical Ultrasound, Renji Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200127, China.
| | - Rui Wang
- Department of Medical Ultrasound, Renji Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200127, China.
| | - Yijing Yao
- Department of Medical Ultrasound, Renji Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200127, China.
| | - Lixin Jiang
- Department of Medical Ultrasound, Renji Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200127, China.
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5
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Chavali SS, Chou SZ, Cao W, Pollard TD, De La Cruz EM, Sindelar CV. Cryo-EM structures reveal how phosphate release from Arp3 weakens actin filament branches formed by Arp2/3 complex. Nat Commun 2024; 15:2059. [PMID: 38448439 PMCID: PMC10918085 DOI: 10.1038/s41467-024-46179-x] [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: 07/11/2023] [Accepted: 02/16/2024] [Indexed: 03/08/2024] Open
Abstract
Arp2/3 complex nucleates branched actin filaments for cell and organelle movements. Here we report a 2.7 Å resolution cryo-EM structure of the mature branch junction formed by S. pombe Arp2/3 complex that provides details about interactions with both mother and daughter filaments. We determine a second structure at 3.2 Å resolution with the phosphate analog BeFx bound with ADP to Arp3 and ATP bound to Arp2. In this ADP-BeFx transition state the outer domain of Arp3 is rotated 2° toward the mother filament compared with the ADP state and makes slightly broader contacts with actin in both the mother and daughter filaments. Thus, dissociation of Pi from the ADP-Pi transition state reduces the interactions of Arp2/3 complex with the actin filaments and may contribute to the lower mechanical stability of mature branch junctions with ADP bound to the Arps. Our structures also reveal that the mother filament in contact with Arp2/3 complex is slightly bent and twisted, consistent with the preference of Arp2/3 complex binding curved actin filaments. The small degree of twisting constrains models of actin filament mechanics.
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Affiliation(s)
- Sai Shashank Chavali
- Department of Molecular Biophysics and Biochemistry, Yale University, PO Box 208103, New Haven, CT, 06520-8103, USA
| | - Steven Z Chou
- Department of Molecular Cellular and Developmental Biology, Yale University, PO Box 208103, New Haven, CT, 06520-8103, USA
- Department of Molecular Biology and Biophysics, University of Connecticut Health Center, Farmington, CT, 06030, USA
| | - Wenxiang Cao
- Department of Molecular Biophysics and Biochemistry, Yale University, PO Box 208103, New Haven, CT, 06520-8103, USA
| | - Thomas D Pollard
- Department of Molecular Biophysics and Biochemistry, Yale University, PO Box 208103, New Haven, CT, 06520-8103, USA.
- Department of Molecular Cellular and Developmental Biology, Yale University, PO Box 208103, New Haven, CT, 06520-8103, USA.
- Department of Cell Biology, Yale University, PO Box 208103, New Haven, CT, 06520-8103, USA.
- Department of Molecular and Cell Biology, University of California, 638 Barker Hall, Berkeley, CA, 94720-3200, USA.
| | - Enrique M De La Cruz
- Department of Molecular Biophysics and Biochemistry, Yale University, PO Box 208103, New Haven, CT, 06520-8103, USA.
| | - Charles V Sindelar
- Department of Molecular Biophysics and Biochemistry, Yale University, PO Box 208103, New Haven, CT, 06520-8103, USA.
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6
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McGuirk ER, Koundinya N, Nagarajan P, Padrick SB, Goode BL. Direct observation of cortactin protecting Arp2/3-actin filament branch junctions from GMF-mediated destabilization. Eur J Cell Biol 2024; 103:151378. [PMID: 38071835 PMCID: PMC10843626 DOI: 10.1016/j.ejcb.2023.151378] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2023] [Revised: 12/02/2023] [Accepted: 12/02/2023] [Indexed: 01/28/2024] Open
Abstract
How cells tightly control the formation and turnover of branched actin filament arrays to drive cell motility, endocytosis, and other cellular processes is still not well understood. Here, we investigated the mechanistic relationship between two binding partners of the Arp2/3 complex, glia maturation factor (GMF) and cortactin. Individually, GMF and cortactin have opposite effects on the stability of actin filament branches, but it is unknown how they work in concert with each other to govern branch turnover. Using TIRF microscopy, we observe that GMF's branch destabilizing activities are potently blocked by cortactin (IC50 = 1.3 nM) and that this inhibition requires direct interactions of cortactin with Arp2/3 complex. The simplest model that would explain these results is competition for binding Arp2/3 complex. However, we find that cortactin and GMF do not compete for free Arp2/3 complex in solution. Further, we use single molecule analysis to show that cortactin's on-rate (3 ×107 s-1 M-1) and off-rate (0.03 s-1) at branch junctions are minimally affected by excess GMF. Together, these results show that cortactin binds with high affinity to branch junctions, where it blocks the destabilizing effects of GMF, possibly by a mechanism that is allosteric in nature. In addition, the affinities we measure for cortactin at actin filament branch junctions (Kd = 0.9 nM) and filament sides (Kd = 206 nM) are approximately 20-fold stronger than previously reported. These observations contribute to an emerging view of molecular complexity in how Arp2/3 complex is regulated through the integration of multiple inputs.
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Affiliation(s)
- Emma R McGuirk
- Department of Biology, Rosenstiel Basic Medical Science Research Center, Brandeis University, 415 South Street, Waltham, MA 02454, USA
| | - Neha Koundinya
- Department of Biology, Rosenstiel Basic Medical Science Research Center, Brandeis University, 415 South Street, Waltham, MA 02454, USA
| | - Priyashree Nagarajan
- Department of Biochemistry and Molecular Biology, Drexel University, Philadelphia, PA 19104, USA
| | - Shae B Padrick
- Department of Biochemistry and Molecular Biology, Drexel University, Philadelphia, PA 19104, USA
| | - Bruce L Goode
- Department of Biology, Rosenstiel Basic Medical Science Research Center, Brandeis University, 415 South Street, Waltham, MA 02454, USA.
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7
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Cao L, Way M. The stabilization of Arp2/3 complex generated actin filaments. Biochem Soc Trans 2024; 52:343-352. [PMID: 38288872 PMCID: PMC10903444 DOI: 10.1042/bst20230638] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2023] [Revised: 12/21/2023] [Accepted: 01/02/2024] [Indexed: 02/29/2024]
Abstract
The Arp2/3 complex, which generates both branched but also linear actin filaments via activation of SPIN90, is evolutionarily conserved in eukaryotes. Several factors regulate the stability of filaments generated by the Arp2/3 complex to maintain the dynamics and architecture of actin networks. In this review, we summarise recent studies on the molecular mechanisms governing the tuning of Arp2/3 complex nucleated actin filaments, which includes investigations using microfluidics and single-molecule imaging to reveal the mechanosensitivity, dissociation and regeneration of actin branches. We also discuss the high-resolution cryo-EM structure of cortactin bound to actin branches, as well as the differences and similarities between the stability of Arp2/3 complex nucleated branches and linear filaments. These new studies provide a clearer picture of the stabilisation of Arp2/3 nucleated filaments at the molecular level. We also identified gaps in our understanding of how different factors collectively contribute to the stabilisation of Arp2/3 complex-generated actin networks.
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Affiliation(s)
- LuYan Cao
- Cellular Signalling and Cytoskeletal Function Laboratory, The Francis Crick Institute, 1 Midland Road, London NW1 1AT, U.K
| | - Michael Way
- Cellular Signalling and Cytoskeletal Function Laboratory, The Francis Crick Institute, 1 Midland Road, London NW1 1AT, U.K
- Department of Infectious Disease, Imperial College, London W2 1PG, U.K
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8
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Xu M, Rutkowski DM, Rebowski G, Boczkowska M, Pollard LW, Dominguez R, Vavylonis D, Ostap EM. Myosin-I Synergizes with Arp2/3 Complex to Enhance Pushing Forces of Branched Actin Networks. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.02.09.579714. [PMID: 38405741 PMCID: PMC10888859 DOI: 10.1101/2024.02.09.579714] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/27/2024]
Abstract
Myosin-Is colocalize with Arp2/3 complex-nucleated actin networks at sites of membrane protrusion and invagination, but the mechanisms by which myosin-I motor activity coordinates with branched actin assembly to generate force are unknown. We mimicked the interplay of these proteins using the "comet tail" bead motility assay, where branched actin networks are nucleated by Arp2/3 complex on the surface of beads coated with myosin-I and the WCA domain of N-WASP. We observed that myosin-I increased bead movement efficiency by thinning actin networks without affecting growth rates. Remarkably, myosin-I triggered symmetry breaking and comet-tail formation in dense networks resistant to spontaneous fracturing. Even with arrested actin assembly, myosin-I alone could break the network. Computational modeling recapitulated these observations suggesting myosin-I acts as a repulsive force shaping the network's architecture and boosting its force-generating capacity. We propose that myosin-I leverages its power stroke to amplify the forces generated by Arp2/3 complex-nucleated actin networks.
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Affiliation(s)
- Mengqi Xu
- Department of Physiology, Pennsylvania Muscle Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104
| | | | - Grzegorz Rebowski
- Department of Physiology, Pennsylvania Muscle Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104
| | - Malgorzata Boczkowska
- Department of Physiology, Pennsylvania Muscle Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104
| | - Luther W Pollard
- Department of Physiology, Pennsylvania Muscle Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104
| | - Roberto Dominguez
- Department of Physiology, Pennsylvania Muscle Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104
| | | | - E Michael Ostap
- Department of Physiology, Pennsylvania Muscle Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104
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9
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Mukadum F, Ccoa WJP, Hocky GM. Molecular simulation approaches to probing the effects of mechanical forces in the actin cytoskeleton. Cytoskeleton (Hoboken) 2024:10.1002/cm.21837. [PMID: 38334204 PMCID: PMC11310368 DOI: 10.1002/cm.21837] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2023] [Revised: 01/24/2024] [Accepted: 01/25/2024] [Indexed: 02/10/2024]
Abstract
In this article we give our perspective on the successes and promise of various molecular and coarse-grained simulation approaches to probing the effect of mechanical forces in the actin cytoskeleton.
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Affiliation(s)
- Fatemah Mukadum
- Department of Chemistry, New York University, New York, NY 10003, USA
| | | | - Glen M. Hocky
- Department of Chemistry, New York University, New York, NY 10003, USA
- Simons Center for Computational Physical Chemistry, New York, NY 10003, USA
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10
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Ghasemi F, Cao L, Mladenov M, Guichard B, Way M, Jégou A, Romet-Lemonne G. Regeneration of actin filament branches from the same Arp2/3 complex. SCIENCE ADVANCES 2024; 10:eadj7681. [PMID: 38277459 PMCID: PMC10816697 DOI: 10.1126/sciadv.adj7681] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2023] [Accepted: 12/27/2023] [Indexed: 01/28/2024]
Abstract
Branched actin filaments are found in many key cellular structures. Branches are nucleated by the Arp2/3 complex activated by nucleation-promoting factor (NPF) proteins and bound to the side of preexisting "mother" filaments. Over time, branches dissociate from their mother filament, leading to network reorganization and turnover, but this mechanism is less understood. Here, using microfluidics and purified proteins, we examined the dissociation of individual branches under controlled biochemical and mechanical conditions. We observe that the Arp2/3 complex remains bound to the mother filament after most debranching events, even when accelerated by force. Strikingly, this surviving Arp2/3 complex readily nucleates a new actin filament branch, without being activated anew by an NPF: It simply needs to exchange its nucleotide and bind an actin monomer. The protein glia maturation factor (GMF), which accelerates debranching, prevents branch renucleation. Our results suggest that actin filament renucleation can provide a self-repair mechanism, helping branched networks to sustain mechanical stress in cells over extended periods of time.
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Affiliation(s)
- Foad Ghasemi
- Université Paris Cité, CNRS, Institut Jacques Monod, F-75013 Paris, France
| | - LuYan Cao
- The Francis Crick Institute, London, UK
| | | | - Bérengère Guichard
- Université Paris Cité, CNRS, Institut Jacques Monod, F-75013 Paris, France
| | - Michael Way
- The Francis Crick Institute, London, UK
- Department of Infectious Disease, Imperial College, London, UK
| | - Antoine Jégou
- Université Paris Cité, CNRS, Institut Jacques Monod, F-75013 Paris, France
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11
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Goode BL, Eskin J, Shekhar S. Mechanisms of actin disassembly and turnover. J Cell Biol 2023; 222:e202309021. [PMID: 37948068 PMCID: PMC10638096 DOI: 10.1083/jcb.202309021] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2023] [Revised: 10/21/2023] [Accepted: 10/23/2023] [Indexed: 11/12/2023] Open
Abstract
Cellular actin networks exhibit a wide range of sizes, shapes, and architectures tailored to their biological roles. Once assembled, these filamentous networks are either maintained in a state of polarized turnover or induced to undergo net disassembly. Further, the rates at which the networks are turned over and/or dismantled can vary greatly, from seconds to minutes to hours or even days. Here, we review the molecular machinery and mechanisms employed in cells to drive the disassembly and turnover of actin networks. In particular, we highlight recent discoveries showing that specific combinations of conserved actin disassembly-promoting proteins (cofilin, GMF, twinfilin, Srv2/CAP, coronin, AIP1, capping protein, and profilin) work in concert to debranch, sever, cap, and depolymerize actin filaments, and to recharge actin monomers for new rounds of assembly.
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Affiliation(s)
- Bruce L. Goode
- Department of Biology, Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, MA, USA
| | - Julian Eskin
- Department of Biology, Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, MA, USA
| | - Shashank Shekhar
- Departments of Physics, Cell Biology and Biochemistry, Emory University, Atlanta, GA, USA
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12
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Asante-Asamani E, Dalton M, Brazill D, Strychalski W. Modeling the dynamics of actin and myosin during bleb stabilization. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.10.26.564082. [PMID: 37961169 PMCID: PMC10634845 DOI: 10.1101/2023.10.26.564082] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2023]
Abstract
The actin cortex is very dynamic during migration of eukaryotes. In cells that use blebs as leading-edge protrusions, the cortex reforms beneath the cell membrane (bleb cortex) and completely disassembles at the site of bleb initiation. Remnants of the actin cortex at the site of bleb nucleation are referred to as the actin scar. We refer to the combined process of cortex reformation along with the degradation of the actin scar during bleb-based cell migration as bleb stabilization. The molecular factors that regulate the dynamic reorganization of the cortex are not fully understood. Myosin motor protein activity has been shown to be necessary for blebbing, with its major role associated with pressure generation to drive bleb expansion. Here, we examine the role of myosin in regulating cortex dynamics during bleb stabilization. Analysis of microscopy data from protein localization experiments in Dictyostelium discoideum cells reveals a rapid formation of the bleb's cortex with a delay in myosin accumulation. In the degrading actin scar, myosin is observed to accumulate before active degradation of the cortex begins. Through a combination of mathematical modeling and data fitting, we identify that myosin helps regulate the equilibrium concentration of actin in the bleb cortex during its reformation by increasing its dissasembly rate. Our modeling and analysis also suggests that cortex degradation is driven primarily by an exponential decrease in actin assembly rate rather than increased myosin activity. We attribute the decrease in actin assembly to the separation of the cell membrane from the cortex after bleb nucleation.
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Affiliation(s)
| | - Mackenzie Dalton
- Department of Mathematics, Clarkson University, Clarkson, Potsdam, NY 13699
| | | | - Wanda Strychalski
- Department of Mathematics, Applied Mathematics, and Statistics, Case Western Reserve University, Cleveland, OH 44106
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13
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Levin JT, Pan A, Barrett MT, Alushin GM. A platform for dissecting force sensitivity and multivalency in actin networks. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.08.15.553463. [PMID: 37645911 PMCID: PMC10462062 DOI: 10.1101/2023.08.15.553463] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/31/2023]
Abstract
The physical structure and dynamics of cells are supported by micron-scale actin networks with diverse geometries, protein compositions, and mechanical properties. These networks are composed of actin filaments and numerous actin binding proteins (ABPs), many of which engage multiple filaments simultaneously to crosslink them into specific functional architectures. Mechanical force has been shown to modulate the interactions between several ABPs and individual actin filaments, but it is unclear how this phenomenon contributes to the emergent force-responsive functional dynamics of actin networks. Here, we engineer filament linker complexes and combine them with photo-micropatterning of myosin motor proteins to produce an in vitro reconstitution platform for examining how force impacts the behavior of ABPs within multi-filament assemblies. Our system enables the monitoring of dozens of actin networks with varying architectures simultaneously using total internal reflection fluorescence microscopy, facilitating detailed dissection of the interplay between force-modulated ABP binding and network geometry. We apply our system to study a dimeric form of the critical cell-cell adhesion protein α-catenin, a model force-sensitive ABP. We find that myosin forces increase α-catenin's engagement of small filament bundles embedded within networks. This activity is absent in a force-sensing deficient mutant, whose binding scales linearly with bundle size in both the presence and absence of force. These data are consistent with filaments in smaller bundles bearing greater per-filament loads that enhance α-catenin binding, a mechanism that could equalize α-catenin's distribution across actin-myosin networks of varying sizes in cells to regularize their stability and composition.
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Affiliation(s)
- Joseph T. Levin
- Laboratory of Structural Biophysics and Mechanobiology, The Rockefeller University, New York, New York, USA
| | - Ariel Pan
- Laboratory of Structural Biophysics and Mechanobiology, The Rockefeller University, New York, New York, USA
| | - Michael T. Barrett
- Laboratory of Structural Biophysics and Mechanobiology, The Rockefeller University, New York, New York, USA
| | - Gregory M. Alushin
- Laboratory of Structural Biophysics and Mechanobiology, The Rockefeller University, New York, New York, USA
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14
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Zsolnay V, Gardel ML, Kovar DR, Voth GA. Cracked actin filaments as mechanosensitive receptors. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.06.26.546553. [PMID: 37425801 PMCID: PMC10327158 DOI: 10.1101/2023.06.26.546553] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/11/2023]
Abstract
Actin filament networks are exposed to mechanical stimuli, but the effect of strain on actin filament structure has not been well-established in molecular detail. This is a critical gap in understanding because the activity of a variety of actin-binding proteins have recently been determined to be altered by actin filament strain. We therefore used all-atom molecular dynamics simulations to apply tensile strains to actin filaments and find that changes in actin subunit organization are minimal in mechanically strained, but intact, actin filaments. However, a conformational change disrupts the critical D-loop to W-loop connection between longitudinal neighboring subunits, which leads to a metastable cracked conformation of the actin filament, whereby one protofilament is broken prior to filament severing. We propose that the metastable crack presents a force-activated binding site for actin regulatory factors that specifically associate with strained actin filaments. Through protein-protein docking simulations, we find that 43 evolutionarily-diverse members of the dual zinc finger containing LIM domain family, which localize to mechanically strained actin filaments, recognize two binding sites exposed at the cracked interface. Furthermore, through its interactions with the crack, LIM domains increase the length of time damaged filaments remain stable. Our findings propose a new molecular model for mechanosensitive binding to actin filaments.
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Affiliation(s)
- Vilmos Zsolnay
- Graduate Program in Biophysical Sciences, University of Chicago, Chicago, IL
| | - Margaret L. Gardel
- Department of Physics & Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL
- Institute for Biophysical Dynamics and James Franck Institute, University of Chicago, Chicago, IL
| | - David R. Kovar
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL
| | - Gregory A. Voth
- Institute for Biophysical Dynamics and James Franck Institute, University of Chicago, Chicago, IL
- Department of Chemistry and Chicago Center for Theoretical Chemistry, University of Chicago, Chicago, IL
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15
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Wagner EL, Im JS, Sala S, Nakahata MI, Imbery TE, Li S, Chen D, Nimchuk K, Noy Y, Archer DW, Xu W, Hashisaki G, Avraham KB, Oakes PW, Shin JB. Repair of noise-induced damage to stereocilia F-actin cores is facilitated by XIRP2 and its novel mechanosensor domain. eLife 2023; 12:e72681. [PMID: 37294664 PMCID: PMC10259482 DOI: 10.7554/elife.72681] [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: 08/01/2021] [Accepted: 05/17/2023] [Indexed: 06/11/2023] Open
Abstract
Prolonged exposure to loud noise has been shown to affect inner ear sensory hair cells in a variety of deleterious manners, including damaging the stereocilia core. The damaged sites can be visualized as 'gaps' in phalloidin staining of F-actin, and the enrichment of monomeric actin at these sites, along with an actin nucleator and crosslinker, suggests that localized remodeling occurs to repair the broken filaments. Herein, we show that gaps in mouse auditory hair cells are largely repaired within 1 week of traumatic noise exposure through the incorporation of newly synthesized actin. We provide evidence that Xin actin binding repeat containing 2 (XIRP2) is required for the repair process and facilitates the enrichment of monomeric γ-actin at gaps. Recruitment of XIRP2 to stereocilia gaps and stress fiber strain sites in fibroblasts is force-dependent, mediated by a novel mechanosensor domain located in the C-terminus of XIRP2. Our study describes a novel process by which hair cells can recover from sublethal hair bundle damage and which may contribute to recovery from temporary hearing threshold shifts and the prevention of age-related hearing loss.
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Affiliation(s)
- Elizabeth L Wagner
- Department of Neuroscience, University of VirginiaCharlottesvilleUnited States
- Department of Biochemistry & Molecular Genetics, University of VirginiaCharlottesvilleUnited States
| | - Jun-Sub Im
- Department of Neuroscience, University of VirginiaCharlottesvilleUnited States
| | - Stefano Sala
- Department of Cell & Molecular Physiology, Stritch School of Medicine, Loyola University ChicagoChicagoUnited States
| | - Maura I Nakahata
- Department of Neuroscience, University of VirginiaCharlottesvilleUnited States
| | - Terence E Imbery
- Department of Neuroscience, University of VirginiaCharlottesvilleUnited States
- Department of Otolaryngology-Head & Neck Surgery, University of VirginiaCharlottesvilleUnited States
| | - Sihan Li
- Department of Neuroscience, University of VirginiaCharlottesvilleUnited States
- Department of Biochemistry & Molecular Genetics, University of VirginiaCharlottesvilleUnited States
| | - Daniel Chen
- Department of Neuroscience, University of VirginiaCharlottesvilleUnited States
| | - Katherine Nimchuk
- Department of Neuroscience, University of VirginiaCharlottesvilleUnited States
| | - Yael Noy
- Department of Human Molecular Genetics and Biochemistry, Faculty of Medicine and Sagol School of Neuroscience, Tel Aviv UniversityTel AvivIsrael
| | - David W Archer
- Department of Neuroscience, University of VirginiaCharlottesvilleUnited States
| | - Wenhao Xu
- Genetically Engineered Murine Model (GEMM) Core, University of VirginiaCharlottesvilleUnited States
| | - George Hashisaki
- Department of Otolaryngology-Head & Neck Surgery, University of VirginiaCharlottesvilleUnited States
| | - Karen B Avraham
- Department of Human Molecular Genetics and Biochemistry, Faculty of Medicine and Sagol School of Neuroscience, Tel Aviv UniversityTel AvivIsrael
| | - Patrick W Oakes
- Department of Cell & Molecular Physiology, Stritch School of Medicine, Loyola University ChicagoChicagoUnited States
| | - Jung-Bum Shin
- Department of Neuroscience, University of VirginiaCharlottesvilleUnited States
- Department of Biochemistry & Molecular Genetics, University of VirginiaCharlottesvilleUnited States
- Department of Otolaryngology-Head & Neck Surgery, University of VirginiaCharlottesvilleUnited States
- Department of Cell Biology, University of VirginiaCharlottesvilleUnited States
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16
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Cao L, Ghasemi F, Way M, Jégou A, Romet‐Lemonne G. Regulation of branched versus linear Arp2/3-generated actin filaments. EMBO J 2023; 42:e113008. [PMID: 36939020 PMCID: PMC10152144 DOI: 10.15252/embj.2022113008] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2022] [Revised: 02/01/2023] [Accepted: 03/01/2023] [Indexed: 03/21/2023] Open
Abstract
Activation of the Arp2/3 complex by VCA-motif-bearing actin nucleation-promoting factors results in the formation of "daughter" actin filaments branching off the sides of pre-existing "mother" filaments. Alternatively, when stimulated by SPIN90, Arp2/3 directly nucleates "linear" actin filaments. Uncovering the similarities and differences between these two mechanisms is fundamental to understanding how actin cytoskeleton dynamics are regulated. Here, analysis of individual filaments reveals that, unexpectedly, the VCA motifs of WASP, N-WASP, and WASH destabilize existing branches, as well as SPIN90-Arp2/3 at linear filament ends. Furthermore, branch stabilizer cortactin and destabilizer GMF each have a similar impact on SPIN90-activated Arp2/3. However, unlike branch junctions, SPIN90-Arp2/3 at the ends of linear filaments is not destabilized by piconewton forces and does not become less stable with time. It thus appears that linear and branched Arp2/3-generated filaments respond similarly to the regulatory proteins we have tested, albeit with some differences, but significantly differ in their responses to aging and mechanical stress. These kinetic differences likely reflect the small conformational differences recently reported between Arp2/3 in branch junctions and linear filaments and suggest that their turnover in cells may be differently regulated.
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Affiliation(s)
- Luyan Cao
- Université Paris Cité, CNRS, Institut Jacques MonodParisFrance
- The Francis Crick InstituteLondonUK
| | - Foad Ghasemi
- Université Paris Cité, CNRS, Institut Jacques MonodParisFrance
| | - Michael Way
- The Francis Crick InstituteLondonUK
- Department of Infectious DiseaseImperial CollegeLondonUK
| | - Antoine Jégou
- Université Paris Cité, CNRS, Institut Jacques MonodParisFrance
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17
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Splitt RL, DeMali KA. Metabolic reprogramming in response to cell mechanics. Biol Cell 2023; 115:e202200108. [PMID: 36807920 PMCID: PMC10192020 DOI: 10.1111/boc.202200108] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2022] [Revised: 02/02/2023] [Accepted: 02/03/2023] [Indexed: 02/20/2023]
Abstract
Much attention has been dedicated to understanding how cells sense and respond to mechanical forces. The types of forces cells experience as well as the repertoire of cell surface receptors that sense these forces have been identified. Key mechanisms for transmitting that force to the cell interior have also emerged. Yet, how cells process mechanical information and integrate it with other cellular events remains largely unexplored. Here we review the mechanisms underlying mechanotransduction at cell-cell and cell-matrix adhesions, and we summarize the current understanding of how cells integrate information from the distinct adhesion complexes with cell metabolism.
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Affiliation(s)
- Rebecca L. Splitt
- Department of Biochemistry and Molecular Biology, University of Iowa Roy J. and Lucille A. Carver College of Medicine, Iowa City, IA 52242
| | - Kris A. DeMali
- Department of Biochemistry and Molecular Biology, University of Iowa Roy J. and Lucille A. Carver College of Medicine, Iowa City, IA 52242
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18
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Nunes Vicente F, Chen T, Rossier O, Giannone G. Novel imaging methods and force probes for molecular mechanobiology of cytoskeleton and adhesion. Trends Cell Biol 2023; 33:204-220. [PMID: 36055943 DOI: 10.1016/j.tcb.2022.07.008] [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: 05/06/2022] [Revised: 07/26/2022] [Accepted: 07/27/2022] [Indexed: 12/01/2022]
Abstract
Detection and conversion of mechanical forces into biochemical signals is known as mechanotransduction. From cells to tissues, mechanotransduction regulates migration, proliferation, and differentiation in processes such as immune responses, development, and cancer progression. Mechanosensitive structures such as integrin adhesions, the actin cortex, ion channels, caveolae, and the nucleus sense and transmit forces. In vitro approaches showed that mechanosensing is based on force-dependent protein deformations and reorganizations. However, the mechanisms in cells remained unclear since cell imaging techniques lacked molecular resolution. Thanks to recent developments in super-resolution microscopy (SRM) and molecular force sensors, it is possible to obtain molecular insight of mechanosensing in live cells. We discuss how understanding of molecular mechanotransduction was revolutionized by these innovative approaches, focusing on integrin adhesions, actin structures, and the plasma membrane.
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Affiliation(s)
- Filipe Nunes Vicente
- University Bordeaux, CNRS, Interdisciplinary Institute for Neuroscience, IINS, UMR 5297, Bordeaux, France; Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Tianchi Chen
- University Bordeaux, CNRS, Interdisciplinary Institute for Neuroscience, IINS, UMR 5297, Bordeaux, France
| | - Olivier Rossier
- University Bordeaux, CNRS, Interdisciplinary Institute for Neuroscience, IINS, UMR 5297, Bordeaux, France
| | - Grégory Giannone
- University Bordeaux, CNRS, Interdisciplinary Institute for Neuroscience, IINS, UMR 5297, Bordeaux, France.
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19
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Qi J, Cheng W, Gao Z, Chen Y, Shipton ML, Furkert D, Chin AC, Riley AM, Fiedler D, Potter BVL, Fu C. Itraconazole inhibits endothelial cell migration by disrupting inositol pyrophosphate-dependent focal adhesion dynamics and cytoskeletal remodeling. Biomed Pharmacother 2023; 161:114449. [PMID: 36857911 PMCID: PMC7614367 DOI: 10.1016/j.biopha.2023.114449] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2022] [Revised: 02/21/2023] [Accepted: 02/23/2023] [Indexed: 03/03/2023] Open
Abstract
The antifungal drug itraconazole has been repurposed to anti-angiogenic agent, but the mechanisms of action have been elusive. Here we report that itraconazole disrupts focal adhesion dynamics and cytoskeletal remodeling, which requires 5-diphosphoinositol 1,2,3,4,6-pentakisphosphate (5-InsP7). We find that inositol hexakisphosphate kinase 1 (IP6K1) binds Arp2 and generates 5-InsP7 to recruit coronin, a negative regulator of the Arp2/3 complex. IP6K1 also produces focal adhesion-enriched 5-InsP7, which binds focal adhesion kinase (FAK) at the FERM domain to promote its dimerization and phosphorylation. Itraconazole treatment elicits displacement of IP6K1/5-InsP7, thus augments 5-InsP7-mediated inhibition of Arp2/3 complex and reduces 5-InsP7-mediated FAK dimerization. Itraconazole-treated cells display reduced focal adhesion dynamics and actin cytoskeleton remodeling. Accordingly, itraconazole severely disrupts cell motility, an essential component of angiogenesis. These results demonstrate critical roles of IP6K1-generated 5-InsP7 in regulating focal adhesion dynamics and actin cytoskeleton remodeling and reveal functional mechanisms by which itraconazole inhibits cell motility.
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Affiliation(s)
- Ji Qi
- The province and ministry co-sponsored collaborative innovation center for medical epigenetics, Tianjin Key Laboratory of Metabolic Diseases, Department of Physiology and Pathophysiology, Tianjin Medical University, Tianjin 300070, China
| | - Weiwei Cheng
- Institute for Developmental and Regenerative Cardiovascular Medicine, Xinhua Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200092, China
| | - Zhe Gao
- School of Integrative Medicine, Tianjin University of Traditional Chinese Medicine, Tianjin 301617, China
| | - Yuanyuan Chen
- Institute for Developmental and Regenerative Cardiovascular Medicine, Xinhua Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200092, China
| | - Megan L Shipton
- Medicinal Chemistry & Drug Discovery, Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, UK
| | - David Furkert
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Berlin, Germany
| | - Alfred C Chin
- Weill Cornell/Rockefeller/Sloan Kettering Tri-Institutional MD-PhD Program, New York, NY, USA
| | - Andrew M Riley
- Medicinal Chemistry & Drug Discovery, Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, UK
| | - Dorothea Fiedler
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Berlin, Germany
| | - Barry V L Potter
- Medicinal Chemistry & Drug Discovery, Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, UK
| | - Chenglai Fu
- The province and ministry co-sponsored collaborative innovation center for medical epigenetics, Tianjin Key Laboratory of Metabolic Diseases, Department of Physiology and Pathophysiology, Tianjin Medical University, Tianjin 300070, China; Institute for Developmental and Regenerative Cardiovascular Medicine, Xinhua Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200092, China.
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20
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Abstract
Actin cytoskeleton force generation, sensing, and adaptation are dictated by the bending and twisting mechanics of filaments. Here, we use magnetic tweezers and microfluidics to twist and pull individual actin filaments and evaluate their response to applied loads. Twisted filaments bend and dissipate torsional strain by adopting a supercoiled plectoneme. Pulling prevents plectoneme formation, which causes twisted filaments to sever. Analysis over a range of twisting and pulling forces and direct visualization of filament and single subunit twisting fluctuations yield an actin filament torsional persistence length of ~10 µm, similar to the bending persistence length. Filament severing by cofilin is driven by local twist strain at boundaries between bare and decorated segments and is accelerated by low pN pulling forces. This work explains how contractile forces generated by myosin motors accelerate filament severing by cofilin and establishes a role for filament twisting in the regulation of actin filament stability and assembly dynamics.
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21
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Lappalainen P, Kotila T, Jégou A, Romet-Lemonne G. Biochemical and mechanical regulation of actin dynamics. Nat Rev Mol Cell Biol 2022; 23:836-852. [PMID: 35918536 DOI: 10.1038/s41580-022-00508-4] [Citation(s) in RCA: 77] [Impact Index Per Article: 38.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/13/2022] [Indexed: 12/30/2022]
Abstract
Polymerization of actin filaments against membranes produces force for numerous cellular processes, such as migration, morphogenesis, endocytosis, phagocytosis and organelle dynamics. Consequently, aberrant actin cytoskeleton dynamics are linked to various diseases, including cancer, as well as immunological and neurological disorders. Understanding how actin filaments generate forces in cells, how force production is regulated by the interplay between actin-binding proteins and how the actin-regulatory machinery responds to mechanical load are at the heart of many cellular, developmental and pathological processes. During the past few years, our understanding of the mechanisms controlling actin filament assembly and disassembly has evolved substantially. It has also become evident that the activities of key actin-binding proteins are not regulated solely by biochemical signalling pathways, as mechanical regulation is critical for these proteins. Indeed, the architecture and dynamics of the actin cytoskeleton are directly tuned by mechanical load. Here we discuss the general mechanisms by which key actin regulators, often in synergy with each other, control actin filament assembly, disassembly, and monomer recycling. By using an updated view of actin dynamics as a framework, we discuss how the mechanics and geometry of actin networks control actin-binding proteins, and how this translates into force production in endocytosis and mesenchymal cell migration.
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Affiliation(s)
- Pekka Lappalainen
- Institute of Biotechnology and Helsinki Institute of Life Sciences, University of Helsinki, Helsinki, Finland.
| | - Tommi Kotila
- Institute of Biotechnology and Helsinki Institute of Life Sciences, University of Helsinki, Helsinki, Finland
| | - Antoine Jégou
- Université Paris Cité, CNRS, Institut Jacques Monod, Paris, France
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22
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Muresan CG, Sun ZG, Yadav V, Tabatabai AP, Lanier L, Kim JH, Kim T, Murrell MP. F-actin architecture determines constraints on myosin thick filament motion. Nat Commun 2022; 13:7008. [PMID: 36385016 PMCID: PMC9669029 DOI: 10.1038/s41467-022-34715-6] [Citation(s) in RCA: 19] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2022] [Accepted: 11/03/2022] [Indexed: 11/17/2022] Open
Abstract
Active stresses are generated and transmitted throughout diverse F-actin architectures within the cell cytoskeleton, and drive essential behaviors of the cell, from cell division to migration. However, while the impact of F-actin architecture on the transmission of stress is well studied, the role of architecture on the ab initio generation of stresses remains less understood. Here, we assemble F-actin networks in vitro, whose architectures are varied from branched to bundled through F-actin nucleation via Arp2/3 and the formin mDia1. Within these architectures, we track the motions of embedded myosin thick filaments and connect them to the extent of F-actin network deformation. While mDia1-nucleated networks facilitate the accumulation of stress and drive contractility through enhanced actomyosin sliding, branched networks prevent stress accumulation through the inhibited processivity of thick filaments. The reduction in processivity is due to a decrease in translational and rotational motions constrained by the local density and geometry of F-actin.
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Affiliation(s)
- Camelia G Muresan
- Department of Biomedical Engineering, Yale University, 55 Prospect Street, New Haven, CT, 06511, USA
- Systems Biology Institute, Yale University, 850 West Campus Drive, West Haven, CT, 06516, USA
| | - Zachary Gao Sun
- Systems Biology Institute, Yale University, 850 West Campus Drive, West Haven, CT, 06516, USA
- Department of Physics, Yale University, 217 Prospect Street, New Haven, CT, 06511, USA
| | - Vikrant Yadav
- Department of Biomedical Engineering, Yale University, 55 Prospect Street, New Haven, CT, 06511, USA
- Systems Biology Institute, Yale University, 850 West Campus Drive, West Haven, CT, 06516, USA
| | - A Pasha Tabatabai
- Department of Biomedical Engineering, Yale University, 55 Prospect Street, New Haven, CT, 06511, USA
- Systems Biology Institute, Yale University, 850 West Campus Drive, West Haven, CT, 06516, USA
| | - Laura Lanier
- Department of Biomedical Engineering, Yale University, 55 Prospect Street, New Haven, CT, 06511, USA
- Systems Biology Institute, Yale University, 850 West Campus Drive, West Haven, CT, 06516, USA
| | - June Hyung Kim
- Weldon School of Biomedical Engineering, Purdue University, 206S. Martin Jischke Drive, West Lafayette, IN, 47907, USA
| | - Taeyoon Kim
- Weldon School of Biomedical Engineering, Purdue University, 206S. Martin Jischke Drive, West Lafayette, IN, 47907, USA
| | - Michael P Murrell
- Department of Biomedical Engineering, Yale University, 55 Prospect Street, New Haven, CT, 06511, USA.
- Systems Biology Institute, Yale University, 850 West Campus Drive, West Haven, CT, 06516, USA.
- Department of Physics, Yale University, 217 Prospect Street, New Haven, CT, 06511, USA.
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23
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Reynolds MJ, Hachicho C, Carl AG, Gong R, Alushin GM. Bending forces and nucleotide state jointly regulate F-actin structure. Nature 2022; 611:380-386. [PMID: 36289330 PMCID: PMC9646526 DOI: 10.1038/s41586-022-05366-w] [Citation(s) in RCA: 39] [Impact Index Per Article: 19.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2022] [Accepted: 09/20/2022] [Indexed: 02/05/2023]
Abstract
ATP-hydrolysis-coupled actin polymerization is a fundamental mechanism of cellular force generation1-3. In turn, force4,5 and actin filament (F-actin) nucleotide state6 regulate actin dynamics by tuning F-actin's engagement of actin-binding proteins through mechanisms that are unclear. Here we show that the nucleotide state of actin modulates F-actin structural transitions evoked by bending forces. Cryo-electron microscopy structures of ADP-F-actin and ADP-Pi-F-actin with sufficient resolution to visualize bound solvent reveal intersubunit interfaces bridged by water molecules that could mediate filament lattice flexibility. Despite extensive ordered solvent differences in the nucleotide cleft, these structures feature nearly identical lattices and essentially indistinguishable protein backbone conformations that are unlikely to be discriminable by actin-binding proteins. We next introduce a machine-learning-enabled pipeline for reconstructing bent filaments, enabling us to visualize both continuous structural variability and side-chain-level detail. Bent F-actin structures reveal rearrangements at intersubunit interfaces characterized by substantial alterations of helical twist and deformations in individual protomers, transitions that are distinct in ADP-F-actin and ADP-Pi-F-actin. This suggests that phosphate rigidifies actin subunits to alter the bending structural landscape of F-actin. As bending forces evoke nucleotide-state dependent conformational transitions of sufficient magnitude to be detected by actin-binding proteins, we propose that actin nucleotide state can serve as a co-regulator of F-actin mechanical regulation.
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Affiliation(s)
- Matthew J Reynolds
- Laboratory of Structural Biophysics and Mechanobiology, The Rockefeller University, New York, NY, USA
| | - Carla Hachicho
- Laboratory of Structural Biophysics and Mechanobiology, The Rockefeller University, New York, NY, USA
| | - Ayala G Carl
- Laboratory of Structural Biophysics and Mechanobiology, The Rockefeller University, New York, NY, USA
- Tri-Institutional Program in Chemical Biology, The Rockefeller University, New York, NY, USA
| | - Rui Gong
- Laboratory of Structural Biophysics and Mechanobiology, The Rockefeller University, New York, NY, USA
| | - Gregory M Alushin
- Laboratory of Structural Biophysics and Mechanobiology, The Rockefeller University, New York, NY, USA.
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24
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Abstract
One of the major challenges of bottom-up synthetic biology is rebuilding a minimal cell division machinery. From a reconstitution perspective, the animal cell division apparatus is mechanically the simplest and therefore attractive to rebuild. An actin-based ring produces contractile force to constrict the membrane. By contrast, microbes and plant cells have a cell wall, so division requires concerted membrane constriction and cell wall synthesis. Furthermore, reconstitution of the actin division machinery helps in understanding the physical and molecular mechanisms of cytokinesis in animal cells and thus our own cells. In this review, we describe the state-of-the-art research on reconstitution of minimal actin-mediated cytokinetic machineries. Based on the conceptual requirements that we obtained from the physics of the shape changes involved in cell division, we propose two major routes for building a minimal actin apparatus capable of division. Importantly, we acknowledge both the passive and active roles that the confining lipid membrane can play in synthetic cytokinesis. We conclude this review by identifying the most pressing challenges for future reconstitution work, thereby laying out a roadmap for building a synthetic cell equipped with a minimal actin division machinery.
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25
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Chandrasekaran A, Clarke A, McQueen P, Fang HY, Papoian GA, Giniger E. Computational simulations reveal that Abl activity controls cohesiveness of actin networks in growth cones. Mol Biol Cell 2022; 33:ar92. [PMID: 35857718 DOI: 10.1091/mbc.e21-11-0535] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Extensive studies of growing axons have revealed many individual components and protein interactions that guide neuronal morphogenesis. Despite this, however, we lack any clear picture of the emergent mechanism by which this nanometer-scale biochemistry generates the multimicron-scale morphology and cell biology of axon growth and guidance in vivo. To address this, we studied the downstream effects of the Abl signaling pathway using a computer simulation software (MEDYAN) that accounts for mechanochemical dynamics of active polymers. Previous studies implicate two Abl effectors, Arp2/3 and Enabled, in Abl-dependent axon guidance decisions. We now find that Abl alters actin architecture primarily by activating Arp2/3, while Enabled plays a more limited role. Our simulations show that simulations mimicking modest levels of Abl activity bear striking similarity to actin profiles obtained experimentally from live imaging of actin in wild-type axons in vivo. Using a graph theoretical filament-filament contact analysis, moreover, we find that networks mimicking hyperactivity of Abl (enhanced Arp2/3) are fragmented into smaller domains of actin that interact weakly with each other, consistent with the pattern of actin fragmentation observed upon Abl overexpression in vivo. Two perturbative simulations further confirm that high-Arp2/3 actin networks are mechanically disconnected and fail to mount a cohesive response to perturbation. Taken together, these data provide a molecular-level picture of how the large-scale organization of the axonal cytoskeleton arises from the biophysics of actin networks.
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Affiliation(s)
- Aravind Chandrasekaran
- Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742.,National Institute of Neurological Diseases and Stroke, Bethesda, MD 20892
| | - Akanni Clarke
- National Institute of Neurological Diseases and Stroke, Bethesda, MD 20892.,Department of Biochemistry and Molecular Medicine, George Washington University School of Medicine/National Institutes of Health Graduate Partnerships Program, Washington, DC 20037
| | - Philip McQueen
- Center for Information Technology, National Institutes of Health, Bethesda, MD 20892
| | - Hsiao Yu Fang
- National Institute of Neurological Diseases and Stroke, Bethesda, MD 20892
| | - Garegin A Papoian
- Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742.,Institute for Physical Science and Technology, University of Maryland, College Park, MD 20742
| | - Edward Giniger
- National Institute of Neurological Diseases and Stroke, Bethesda, MD 20892
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26
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Abstract
Eukaryotic cells contain branched actin networks that are essential for endocytosis, motility, and other key cellular processes. These networks, which are formed by filamentous actin and the Arp2/3 complex, must subsequently be debranched to allow network remodeling and to recycle the Arp2/3 complex. Debranching appears to be catalyzed by two different members of the actin depolymerizing factor homology protein family: cofilin and glial maturation factor (GMF). However, their mechanisms of debranching are only partially understood. Here, we used single-molecule fluorescence imaging of Arp2/3 complex and actin filaments under physiological ionic conditions to observe debranching by GMF and cofilin. We demonstrate that cofilin, like GMF, is an authentic debrancher independent of its filament-severing activity and that the debranching activities of the two proteins are additive. While GMF binds directly to the Arp2/3 complex, cofilin selectively accumulates on branch-junction daughter filaments in tropomyosin-decorated networks just prior to debranching events. Quantitative comparison of debranching rates with the known kinetics of cofilin-actin binding suggests that cofilin occupancy of a particular single actin site at the branch junction is sufficient to trigger debranching. In rare cases in which the order of departure could be resolved during GMF- or cofilin-induced debranching, the Arp2/3 complex left the branch junction bound to the pointed end of the daughter filament, suggesting that both GMF and cofilin can work by destabilizing the mother filament-Arp2/3 complex interface. Taken together, these observations suggest that GMF and cofilin promote debranching by distinct yet complementary mechanisms.
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27
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Sun X, Alushin GM. Cellular force-sensing through actin filaments. FEBS J 2022; 290:2576-2589. [PMID: 35778931 PMCID: PMC9945651 DOI: 10.1111/febs.16568] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2022] [Revised: 06/17/2022] [Accepted: 06/30/2022] [Indexed: 02/05/2023]
Abstract
The actin cytoskeleton orchestrates cell mechanics and facilitates the physical integration of cells into tissues, while tissue-scale forces and extracellular rigidity in turn govern cell behaviour. Here, we discuss recent evidence that actin filaments (F-actin), the core building blocks of the actin cytoskeleton, also serve as molecular force sensors. We delineate two classes of proteins, which interpret forces applied to F-actin through enhanced binding interactions: 'mechanically tuned' canonical actin-binding proteins, whose constitutive F-actin affinity is increased by force, and 'mechanically switched' proteins, which bind F-actin only in the presence of force. We speculate mechanically tuned and mechanically switched actin-binding proteins are biophysically suitable for coordinating cytoskeletal force-feedback and mechanical signalling processes, respectively. Finally, we discuss potential mechanisms mediating force-activated actin binding, which likely occurs both through the structural remodelling of F-actin itself and geometric rearrangements of higher-order actin networks. Understanding the interplay of these mechanisms will enable the dissection of force-activated actin binding's specific biological functions.
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Affiliation(s)
- Xiaoyu Sun
- Laboratory of Structural Biophysics and Mechanobiology, The Rockefeller University. New York, NY, USA.,Correspondence: ;
| | - Gregory M. Alushin
- Laboratory of Structural Biophysics and Mechanobiology, The Rockefeller University. New York, NY, USA.,Correspondence: ;
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Li TD, Bieling P, Weichsel J, Mullins RD, Fletcher DA. The molecular mechanism of load adaptation by branched actin networks. eLife 2022; 11:e73145. [PMID: 35748355 PMCID: PMC9328761 DOI: 10.7554/elife.73145] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2021] [Accepted: 06/07/2022] [Indexed: 11/13/2022] Open
Abstract
Branched actin networks are self-assembling molecular motors that move biological membranes and drive many important cellular processes, including phagocytosis, endocytosis, and pseudopod protrusion. When confronted with opposing forces, the growth rate of these networks slows and their density increases, but the stoichiometry of key components does not change. The molecular mechanisms governing this force response are not well understood, so we used single-molecule imaging and AFM cantilever deflection to measure how applied forces affect each step in branched actin network assembly. Although load forces are observed to increase the density of growing filaments, we find that they actually decrease the rate of filament nucleation due to inhibitory interactions between actin filament ends and nucleation promoting factors. The force-induced increase in network density turns out to result from an exponential drop in the rate constant that governs filament capping. The force dependence of filament capping matches that of filament elongation and can be explained by expanding Brownian Ratchet theory to cover both processes. We tested a key prediction of this expanded theory by measuring the force-dependent activity of engineered capping protein variants and found that increasing the size of the capping protein increases its sensitivity to applied forces. In summary, we find that Brownian Ratchets underlie not only the ability of growing actin filaments to generate force but also the ability of branched actin networks to adapt their architecture to changing loads.
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Affiliation(s)
- Tai-De Li
- Department of Bioengineering & Biophysics Program, University of California, BerkeleyBerkeleyUnited States
- Division of Biological Systems & Engineering, Lawrence Berkeley National LaboratoryBerkeleyUnited States
- Advanced Science Research Center, City University of New YorkNew YorkUnited States
| | - Peter Bieling
- Division of Biological Systems & Engineering, Lawrence Berkeley National LaboratoryBerkeleyUnited States
- Department of Cellular and Molecular Pharmacology and Howard Hughes Medical Institute, University of California, San FranciscoSan FranciscoUnited States
- Department of Systemic Cell Biology, Max Planck Institute of Molecular PhysiologyDortmundGermany
| | - Julian Weichsel
- Department of Chemistry, University of California, BerkeleyBerkeleyUnited States
| | - R Dyche Mullins
- Department of Cellular and Molecular Pharmacology and Howard Hughes Medical Institute, University of California, San FranciscoSan FranciscoUnited States
| | - Daniel A Fletcher
- Department of Bioengineering & Biophysics Program, University of California, BerkeleyBerkeleyUnited States
- Division of Biological Systems & Engineering, Lawrence Berkeley National LaboratoryBerkeleyUnited States
- Chan Zuckerberg BiohubSan FranciscoUnited States
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29
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Zhao T, Wu D, Du J, Liu G, Ji G, Wang Z, Peng F, Man L, Zhou W, Hao A. Folic Acid Attenuates Glial Activation in Neonatal Mice and Improves Adult Mood Disorders Through Epigenetic Regulation. Front Pharmacol 2022; 13:818423. [PMID: 35197855 PMCID: PMC8859176 DOI: 10.3389/fphar.2022.818423] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2021] [Accepted: 01/10/2022] [Indexed: 01/08/2023] Open
Abstract
Growing evidence indicates that postnatal immune activation (PIA) can adversely increase the lifetime risk for several neuropsychiatric disorders, including anxiety and depression, which involve the activation of glial cells and early neural developmental events. Several glia-targeted agents are required to protect neonates. Folic acid (FA), a clinical medication used during pregnancy, has been reported to have neuroprotective properties. However, the effects and mechanisms of FA in PIA-induced neonatal encephalitis and mood disorders remain unclear. Here, we investigated the roles of FA in a mouse model of PIA, and found that FA treatment improved depressive- and anxiety-like behaviors in adults, accompanied by a decrease in the number of activated microglia and astrocytes, as well as a reduction in the inflammatory response in the cortex and hippocampus of neonatal mice. Furthermore, we offer new evidence describing the functional differences in FA between microglia and astrocytes. Our data show that epigenetic regulation plays an essential role in FA-treated glial cells following PIA stimulation. In astrocytes, FA promoted the expression of IL-10 by decreasing the level of EZH2-mediated H3K27me3 at its promoter, whereas FA promoted the expression of IL-13 by reducing the promoter binding of H3K9me3 mediated by KDM4A in microglia. Importantly, FA specifically regulated the expression level of BDNF in astrocytes through H3K27me3. Overall, our data supported that FA may be an effective treatment for reducing mood disorders induced by PIA, and we also demonstrated significant functional differences in FA between the two cell types following PIA stimulation.
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Affiliation(s)
- Tiantian Zhao
- Key Laboratory for Experimental Teratology of Ministry of Education, Shandong Key Laboratory of Mental Disorders, Key Laboratory of Birth Regulation and Control Technology of National Health Commission of China, Department of Anatomy and Histoembryology, School of Basic Medical Sciences, Cheeloo College of Medicine, Shandong University, Jinan, China
| | - Dong Wu
- Key Laboratory for Experimental Teratology of Ministry of Education, Shandong Key Laboratory of Mental Disorders, Key Laboratory of Birth Regulation and Control Technology of National Health Commission of China, Department of Anatomy and Histoembryology, School of Basic Medical Sciences, Cheeloo College of Medicine, Shandong University, Jinan, China
| | - Jingyi Du
- Key Laboratory for Experimental Teratology of Ministry of Education, Shandong Key Laboratory of Mental Disorders, Key Laboratory of Birth Regulation and Control Technology of National Health Commission of China, Department of Anatomy and Histoembryology, School of Basic Medical Sciences, Cheeloo College of Medicine, Shandong University, Jinan, China
| | - Guowei Liu
- Department of Neurosurgery, Cheeloo College of Medicine, Qilu Hospital of Shandong University and Institute of Brain and Brain-Inspired Science, Shandong University, Jinan, China
| | - Guangyu Ji
- Key Laboratory for Experimental Teratology of Ministry of Education, Shandong Key Laboratory of Mental Disorders, Key Laboratory of Birth Regulation and Control Technology of National Health Commission of China, Department of Anatomy and Histoembryology, School of Basic Medical Sciences, Cheeloo College of Medicine, Shandong University, Jinan, China
| | - Zixiao Wang
- Key Laboratory for Experimental Teratology of Ministry of Education, Shandong Key Laboratory of Mental Disorders, Key Laboratory of Birth Regulation and Control Technology of National Health Commission of China, Department of Anatomy and Histoembryology, School of Basic Medical Sciences, Cheeloo College of Medicine, Shandong University, Jinan, China
| | - Fan Peng
- Key Laboratory for Experimental Teratology of Ministry of Education, Shandong Key Laboratory of Mental Disorders, Key Laboratory of Birth Regulation and Control Technology of National Health Commission of China, Department of Anatomy and Histoembryology, School of Basic Medical Sciences, Cheeloo College of Medicine, Shandong University, Jinan, China
| | - Lajie Man
- Key Laboratory for Experimental Teratology of Ministry of Education, Shandong Key Laboratory of Mental Disorders, Key Laboratory of Birth Regulation and Control Technology of National Health Commission of China, Department of Anatomy and Histoembryology, School of Basic Medical Sciences, Cheeloo College of Medicine, Shandong University, Jinan, China
| | - Wenjuan Zhou
- Key Laboratory for Experimental Teratology of Ministry of Education, Shandong Key Laboratory of Mental Disorders, Key Laboratory of Birth Regulation and Control Technology of National Health Commission of China, Department of Anatomy and Histoembryology, School of Basic Medical Sciences, Cheeloo College of Medicine, Shandong University, Jinan, China
- *Correspondence: Wenjuan Zhou, ; Aijun Hao,
| | - Aijun Hao
- Key Laboratory for Experimental Teratology of Ministry of Education, Shandong Key Laboratory of Mental Disorders, Key Laboratory of Birth Regulation and Control Technology of National Health Commission of China, Department of Anatomy and Histoembryology, School of Basic Medical Sciences, Cheeloo College of Medicine, Shandong University, Jinan, China
- *Correspondence: Wenjuan Zhou, ; Aijun Hao,
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30
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Abstract
The precise assembly and disassembly of actin filaments is required for several cellular processes, and their regulation has been scrutinized for decades. Twenty years ago, a handful of studies marked the advent of a new type of experiment to study actin dynamics: using optical microscopy to look at individual events, taking place on individual filaments in real time. Here, we summarize the main characteristics of this approach and how it has changed our ability to understand actin assembly dynamics. We also highlight some of its caveats and reflect on what we have learned over the past 20 years, leading us to propose a set of guidelines, which we hope will contribute to a better exploitation of this powerful tool.
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31
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Dynamics of the Actin Cytoskeleton at Adhesion Complexes. BIOLOGY 2021; 11:biology11010052. [PMID: 35053050 PMCID: PMC8773209 DOI: 10.3390/biology11010052] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Revised: 12/22/2021] [Accepted: 12/24/2021] [Indexed: 01/06/2023]
Abstract
The shape of cells is altered to allow cells to adapt to their changing environments, including responding to internally generated and externally applied force. Force is sensed by cell surface adhesion proteins that are enriched in sites where cells bind to the extracellular matrix (focal adhesions) and neighboring cells (cell-cell or adherens junctions). Receptors at these adhesion sites stimulate intracellular signal transduction cascades that culminate in dramatic changes in the actin cytoskeleton. New actin filaments form, and/or new and existing filaments can be cleaved, branched, or bundled. Here, we discuss the actin cytoskeleton and its functions. We will examine the current understanding for how the actin cytoskeleton is tethered to adhesion sites. Finally, we will highlight recent studies describing how the actin cytoskeleton at these adhesion sites is remodeled in response to force.
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32
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Gautreau AM, Fregoso FE, Simanov G, Dominguez R. Nucleation, stabilization, and disassembly of branched actin networks. Trends Cell Biol 2021; 32:421-432. [PMID: 34836783 PMCID: PMC9018471 DOI: 10.1016/j.tcb.2021.10.006] [Citation(s) in RCA: 62] [Impact Index Per Article: 20.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2021] [Revised: 10/19/2021] [Accepted: 10/22/2021] [Indexed: 12/18/2022]
Abstract
Arp2/3 complex is an actin filament nucleation and branching machinery conserved in all eukaryotes from yeast to human. Arp2/3 complex branched networks generate pushing forces that drive cellular processes ranging from membrane remodeling to cell and organelle motility. Several molecules regulate these processes by directly inhibiting or activating Arp2/3 complex and by stabilizing or disassembling branched networks. Here, we review recent advances in our understanding of Arp2/3 complex regulation, including high-resolution cryoelectron microscopy (cryo-EM) structures that illuminate the mechanisms of Arp2/3 complex activation and branch formation, and novel cellular pathways of branch formation, stabilization, and debranching. We also identify major gaps in our understanding of Arp2/3 complex inhibition and branch stabilization and disassembly.
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Affiliation(s)
- Alexis M Gautreau
- Laboratoire de Biologie Structurale de la Cellule, CNRS, École Polytechnique, Institut Polytechnique de Paris, 91128 Palaiseau, France.
| | - Fred E Fregoso
- Department of Physiology and Biochemistry and Molecular Biophysics Graduate Group, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Gleb Simanov
- Laboratoire de Biologie Structurale de la Cellule, CNRS, École Polytechnique, Institut Polytechnique de Paris, 91128 Palaiseau, France
| | - Roberto Dominguez
- Department of Physiology and Biochemistry and Molecular Biophysics Graduate Group, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
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33
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Rutkowski DM, Vavylonis D. Discrete mechanical model of lamellipodial actin network implements molecular clutch mechanism and generates arcs and microspikes. PLoS Comput Biol 2021; 17:e1009506. [PMID: 34662335 PMCID: PMC8553091 DOI: 10.1371/journal.pcbi.1009506] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2021] [Revised: 10/28/2021] [Accepted: 09/30/2021] [Indexed: 01/03/2023] Open
Abstract
Mechanical forces, actin filament turnover, and adhesion to the extracellular environment regulate lamellipodial protrusions. Computational and mathematical models at the continuum level have been used to investigate the molecular clutch mechanism, calculating the stress profile through the lamellipodium and around focal adhesions. However, the forces and deformations of individual actin filaments have not been considered while interactions between actin networks and actin bundles is not easily accounted with such methods. We develop a filament-level model of a lamellipodial actin network undergoing retrograde flow using 3D Brownian dynamics. Retrograde flow is promoted in simulations by pushing forces from the leading edge (due to actin polymerization), pulling forces (due to molecular motors), and opposed by viscous drag in cytoplasm and focal adhesions. Simulated networks have densities similar to measurements in prior electron micrographs. Connectivity between individual actin segments is maintained by permanent and dynamic crosslinkers. Remodeling of the network occurs via the addition of single actin filaments near the leading edge and via filament bond severing. We investigated how several parameters affect the stress distribution, network deformation and retrograde flow speed. The model captures the decrease in retrograde flow upon increase of focal adhesion strength. The stress profile changes from compression to extension across the leading edge, with regions of filament bending around focal adhesions. The model reproduces the observed reduction in retrograde flow speed upon exposure to cytochalasin D, which halts actin polymerization. Changes in crosslinker concentration and dynamics, as well as in the orientation pattern of newly added filaments demonstrate the model's ability to generate bundles of filaments perpendicular (actin arcs) or parallel (microspikes) to the protruding direction.
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34
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Deretic N, Bolger-Munro M, Choi K, Abraham L, Gold MR. The Actin-Disassembly Protein Glia Maturation Factor γ Enhances Actin Remodeling and B Cell Antigen Receptor Signaling at the Immune Synapse. Front Cell Dev Biol 2021; 9:647063. [PMID: 34336818 PMCID: PMC8318000 DOI: 10.3389/fcell.2021.647063] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2020] [Accepted: 06/07/2021] [Indexed: 11/16/2022] Open
Abstract
Signaling by the B cell antigen receptor (BCR) initiates actin remodeling. The assembly of branched actin networks that are nucleated by the Arp2/3 complex exert outward force on the plasma membrane, allowing B cells to form membrane protrusions that can scan the surface of antigen-presenting cells (APCs). The resulting Arp2/3 complex-dependent actin retrograde flow promotes the centripetal movement and progressive coalescence of BCR microclusters, which amplifies BCR signaling. Glia maturation factor γ (GMFγ) is an actin disassembly-protein that releases Arp2/3 complex-nucleated actin filaments from actin networks. By doing so, GMFγ could either oppose the actions of the Arp2/3 complex or support Arp2/3 complex-nucleated actin polymerization by contributing to the recycling of actin monomers and Arp2/3 complexes. We now show that reducing the levels of GMFγ in human B cell lines via transfection with a specific siRNA impairs the ability of B cells to spread on antigen-coated surfaces, decreases the velocity of actin retrograde flow, diminishes the coalescence of BCR microclusters into a central cluster at the B cell-APC contact site, and decreases APC-induced BCR signaling. These effects of depleting GMFγ are similar to what occurs when the Arp2/3 complex is inhibited. This suggests that GMFγ cooperates with the Arp2/3 complex to support BCR-induced actin remodeling and amplify BCR signaling at the immune synapse.
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Affiliation(s)
- Nikola Deretic
- Department of Microbiology and Immunology, Life Sciences Institute, University of British Columbia, Vancouver, BC, Canada
| | - Madison Bolger-Munro
- Department of Microbiology and Immunology, Life Sciences Institute, University of British Columbia, Vancouver, BC, Canada
| | - Kate Choi
- Department of Microbiology and Immunology, Life Sciences Institute, University of British Columbia, Vancouver, BC, Canada
| | - Libin Abraham
- Department of Microbiology and Immunology, Life Sciences Institute, University of British Columbia, Vancouver, BC, Canada
| | - Michael R Gold
- Department of Microbiology and Immunology, Life Sciences Institute, University of British Columbia, Vancouver, BC, Canada
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35
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Anderson CA, Kovar DR, Gardel ML, Winkelman JD. LIM domain proteins in cell mechanobiology. Cytoskeleton (Hoboken) 2021; 78:303-311. [PMID: 34028199 DOI: 10.1002/cm.21677] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2021] [Revised: 05/06/2021] [Accepted: 05/07/2021] [Indexed: 12/13/2022]
Abstract
The actin cytoskeleton is important for maintaining mechanical homeostasis in adherent cells, largely through its regulation of adhesion and cortical tension. The LIM (Lin-11, Isl1, MEC-3) domain-containing proteins are involved in a myriad of cellular mechanosensitive pathways. Recent work has discovered that LIM domains bind to mechanically stressed actin filaments, suggesting a novel and widely conserved mechanism of mechanosensing. This review summarizes the current state of knowledge of LIM protein mechanosensitivity.
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Affiliation(s)
- Caitlin A Anderson
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, Illinois, USA
| | - David R Kovar
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, Illinois, USA.,Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois, USA
| | - Margaret L Gardel
- Institute for Biophysical Dynamics, University of Chicago, Chicago, Illinois, USA.,James Franck Institute, University of Chicago, Chicago, Illinois, USA.,Department of Physics, University of Chicago, Chicago, Illinois, USA.,Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois, USA
| | - Jonathan D Winkelman
- Institute for Biophysical Dynamics, University of Chicago, Chicago, Illinois, USA
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36
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Papalazarou V, Machesky LM. The cell pushes back: The Arp2/3 complex is a key orchestrator of cellular responses to environmental forces. Curr Opin Cell Biol 2021; 68:37-44. [PMID: 32977244 PMCID: PMC7938217 DOI: 10.1016/j.ceb.2020.08.012] [Citation(s) in RCA: 55] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2020] [Revised: 08/14/2020] [Accepted: 08/17/2020] [Indexed: 12/21/2022]
Abstract
The Arp2/3 complex orchestrates the formation of branched actin networks at the interface between the cytoplasm and membranes. Although it is widely appreciated that these networks are useful for scaffolding, creating pushing forces and delineating zones at the membrane interface, it has only recently come to light that branched actin networks are mechanosensitive, giving them special properties. Here, we discuss recent advances in our understanding of how Arp2/3-generated actin networks respond to load forces and thus allow cells to create pushing forces in responsive and tuneable ways to effect cellular processes such as migration, invasion, phagocytosis, adhesion and even nuclear and DNA damage repair.
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Affiliation(s)
- Vassilis Papalazarou
- CRUK Beatson Institute for Cancer Research, Garscube Estate, Switchback Road, Glasgow, G61 1BD, UK
| | - Laura M Machesky
- CRUK Beatson Institute for Cancer Research, Garscube Estate, Switchback Road, Glasgow, G61 1BD, UK; Institute of Cancer Sciences, Garscube Estate, University of Glasgow, Glasgow, G61 1BD, UK.
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37
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Bibeau JP, Gray S, De La Cruz EM. Clusters of a Few Bound Cofilins Sever Actin Filaments. J Mol Biol 2021; 433:166833. [PMID: 33524412 DOI: 10.1016/j.jmb.2021.166833] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2020] [Revised: 01/12/2021] [Accepted: 01/14/2021] [Indexed: 02/06/2023]
Abstract
Cofilin is an essential actin filament severing protein that accelerates the assembly dynamics and turnover of actin networks by increasing the number of filament ends where subunits add and dissociate. It binds filament subunits stoichiometrically and cooperatively, forming clusters of contiguously-bound cofilin at sub-saturating occupancies. Filaments partially occupied with cofilin sever at boundaries between bare and cofilin-decorated segments. Imaging studies concluded that bound clusters must reach a critical size (Cc) of 13-100 cofilins to sever filaments. In contrast, structural and modeling studies suggest that a few or even a single cofilin can sever filaments, possibly with different severing rate constants. How clusters grow through the cooperative incorporation of additional cofilin molecules, specifically if they elongate asymmetrically or uniformly from both ends and if they are modulated by filament shape and external force, also lacks consensus. Here, using hydrodynamic flow to visualize individual actin filaments with TIRF microscopy, we found that neither flow-induced filament bending, tension, nor surface attachment conditions substantially affected the kinetics of cofilin binding to actin filaments. Clusters of bound cofilin preferentially extended toward filament pointed ends and displayed severing competency at small sizes (Cc < 3), with no detectable severing dependence on cluster size. These data support models in which small clusters of cofilin introduce local, but asymmetric, structural changes in actin filaments that promote filament severing with a rate constant that depends weakly on the size of the cluster.
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Affiliation(s)
- Jeffrey P Bibeau
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, United States
| | - Shawn Gray
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, United States
| | - Enrique M De La Cruz
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, United States.
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38
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Mechanically tuning actin filaments to modulate the action of actin-binding proteins. Curr Opin Cell Biol 2020; 68:72-80. [PMID: 33160108 DOI: 10.1016/j.ceb.2020.09.002] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2020] [Revised: 09/07/2020] [Accepted: 09/10/2020] [Indexed: 12/16/2022]
Abstract
In cells, the actin cytoskeleton is regulated by an interplay between mechanics and biochemistry. A key mechanism, which has emerged based on converging indications from structural, cellular, and biophysical data, depicts the actin filament as a mechanically tunable substrate: mechanical stress applied to an actin filament induces conformational changes, which modify the binding and the regulatory action of actin-binding proteins. For a long time, however, direct evidence of this mechanotransductive mechanism was very scarce. This situation is changing rapidly, and recent in vitro single-filament studies using different techniques have revealed that several actin-binding proteins are able to sense tension, curvature, and/or torsion, applied to actin filaments. Here, we discuss these recent advances and their possible implications.
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39
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Pernier J, Morchain A, Caorsi V, Bertin A, Bousquet H, Bassereau P, Coudrier E. Myosin 1b flattens and prunes branched actin filaments. J Cell Sci 2020; 133:jcs247403. [PMID: 32895245 PMCID: PMC7522023 DOI: 10.1242/jcs.247403] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2020] [Accepted: 08/18/2020] [Indexed: 01/29/2023] Open
Abstract
Motile and morphological cellular processes require a spatially and temporally coordinated branched actin network that is controlled by the activity of various regulatory proteins, including the Arp2/3 complex, profilin, cofilin and tropomyosin. We have previously reported that myosin 1b regulates the density of the actin network in the growth cone. Here, by performing in vitro F-actin gliding assays and total internal reflection fluorescence (TIRF) microscopy, we show that this molecular motor flattens (reduces the branch angle) in the Arp2/3-dependent actin branches, resulting in them breaking, and reduces the probability of new branches forming. This experiment reveals that myosin 1b can produce force sufficient enough to break up the Arp2/3-mediated actin junction. Together with the former in vivo studies, this work emphasizes the essential role played by myosins in the architecture and dynamics of actin networks in different cellular regions.This article has an associated First Person interview with the first author of the paper.
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Affiliation(s)
- Julien Pernier
- Laboratoire Physico-Chimie Curie, Institut Curie, PSL Research University, CNRS UMR168, 75005 Paris, France
- Sorbonne Université, 75005 Paris, France
- Laboratory Cell Biology and Cancer, Institut Curie, PSL Research University, C.N.R.S. UMR 144, 26 rue d'Ulm, Paris, France
| | - Antoine Morchain
- Laboratoire Physico-Chimie Curie, Institut Curie, PSL Research University, CNRS UMR168, 75005 Paris, France
- Sorbonne Université, 75005 Paris, France
| | | | - Aurélie Bertin
- Laboratoire Physico-Chimie Curie, Institut Curie, PSL Research University, CNRS UMR168, 75005 Paris, France
- Sorbonne Université, 75005 Paris, France
| | - Hugo Bousquet
- Sorbonne Université, 75005 Paris, France
- Laboratory Cell Biology and Cancer, Institut Curie, PSL Research University, C.N.R.S. UMR 144, 26 rue d'Ulm, Paris, France
| | - Patricia Bassereau
- Laboratoire Physico-Chimie Curie, Institut Curie, PSL Research University, CNRS UMR168, 75005 Paris, France
- Sorbonne Université, 75005 Paris, France
| | - Evelyne Coudrier
- Sorbonne Université, 75005 Paris, France
- Laboratory Cell Biology and Cancer, Institut Curie, PSL Research University, C.N.R.S. UMR 144, 26 rue d'Ulm, Paris, France
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