1
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Tseng CC, Zheng RH, Lin TW, Chou CC, Shih YC, Liang SW, Lee HH. α-Actinin-4 recruits Shp2 into focal adhesions to potentiate ROCK2 activation in podocytes. Life Sci Alliance 2022; 5:5/11/e202201557. [PMID: 36096674 PMCID: PMC9468603 DOI: 10.26508/lsa.202201557] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2022] [Revised: 08/20/2022] [Accepted: 08/22/2022] [Indexed: 11/24/2022] Open
Abstract
α-Actinin-4 is crucial in the regulation of Shp2 FA targeting to enhance ROCK2-mediated actomyosin contractility and thereby strengthening cell adhesion and cytoskeletal architecture in podocytes. Cell–matrix adhesions are mainly provided by integrin-mediated focal adhesions (FAs). We previously found that Shp2 is essential for FA maturation by promoting ROCK2 activation at FAs. In this study, we further delineated the role of α-actinin-4 in the FA recruitment and activation of Shp2. We used the conditional immortalized mouse podocytes to examine the role of α-actinin-4 in the regulation of Shp2 and ROCK2 signaling. After the induction of podocyte differentiation, Shp2 and ROCK2 were strongly activated, concomitant with the formation of matured FAs, stress fibers, and interdigitating intracellular junctions in a ROCK-dependent manner. Gene knockout of α-actinin-4 abolished the Shp2 activation and subsequently reduced matured FAs in podocytes. We also demonstrated that gene knockout of ROCK2 impaired the generation of contractility and interdigitating intercellular junctions. Our results reveal the role of α-actinin-4 in the recruitment of Shp2 at FAs to potentiate ROCK2 activation for the maintenance of cellular contractility and cytoskeletal architecture in the cultured podocytes.
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Affiliation(s)
- Chien-Chun Tseng
- Department of Life Sciences and Institute of Genome Sciences, National Yang Ming Chiao Tung University, Taipei, Taiwan
| | - Ru-Hsuan Zheng
- Department of Life Sciences and Institute of Genome Sciences, National Yang Ming Chiao Tung University, Taipei, Taiwan
| | - Ting-Wei Lin
- Department of Life Sciences and Institute of Genome Sciences, National Yang Ming Chiao Tung University, Taipei, Taiwan
| | - Chih-Chiang Chou
- Department of Life Sciences and Institute of Genome Sciences, National Yang Ming Chiao Tung University, Taipei, Taiwan
| | - Yu-Chia Shih
- Department of Life Sciences and Institute of Genome Sciences, National Yang Ming Chiao Tung University, Taipei, Taiwan
| | - Shao-Wei Liang
- Department of Life Sciences and Institute of Genome Sciences, National Yang Ming Chiao Tung University, Taipei, Taiwan
| | - Hsiao-Hui Lee
- Department of Life Sciences and Institute of Genome Sciences, National Yang Ming Chiao Tung University, Taipei, Taiwan .,Center for Intelligent Drug Systems and Smart Bio-Devices (IDS2B), National Yang Ming Chiao Tung University, Taipei, Taiwan
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2
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Protein friction and filament bending facilitate contraction of disordered actomyosin networks. Biophys J 2021; 120:4029-4040. [PMID: 34390686 DOI: 10.1016/j.bpj.2021.08.012] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2021] [Revised: 06/21/2021] [Accepted: 08/06/2021] [Indexed: 12/23/2022] Open
Abstract
We use mathematical modeling and computation to investigate how protein friction facilitates contraction of disordered actomyosin networks. We simulate two-dimensional networks using an agent-based model, consisting of a system of force-balance equations for myosin motor proteins and semiflexible actin filaments. A major advantage of our approach is that it enables direct calculation of the network stress tensor, which provides a quantitative measure of contractility. Exploiting this, we use repeated simulations of disordered networks to confirm that both protein friction and actin filament bending are required for contraction. We then use simulations of elementary two-filament systems to show that filament bending flexibility can facilitate contraction on the microscopic scale. Finally, we show that actin filament turnover is necessary to sustain contraction and prevent filament aggregation. Simulations with and without turnover also exhibit contractile pulses. However, these pulses are aperiodic, suggesting that periodic pulsation can only arise because of additional regulatory mechanisms or more complex mechanical behavior.
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3
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Determining the domain-level reaction-diffusion properties of an actin-binding protein transgelin-2 within cells. Exp Cell Res 2021; 404:112619. [PMID: 33965400 DOI: 10.1016/j.yexcr.2021.112619] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2021] [Revised: 03/18/2021] [Accepted: 04/19/2021] [Indexed: 11/21/2022]
Abstract
Proteins in cells undergo repeated binding to other molecules, thereby reducing the apparent extent of their intracellular diffusion. While much effort has been made to analytically decouple these combined effects of pure diffusion and chemical binding, it is difficult with conventional approaches to attribute the measured quantities to the nature of specific domains of the proteins. Motivated by the common goal in cell signaling research aimed at identifying the domains responsible for particular intermolecular interactions, here we describe a framework for determining the local physicochemical properties of cellular proteins associated with immobile scaffolds. To validate this new approach, we apply it to transgelin-2, an actin-binding protein whose intracellular dynamics remains elusive. We develop a fluorescence recovery after photobleaching (FRAP)-based framework, in which comprehensive combinations of domain-deletion mutants are created, and the difference among them in FRAP response is analyzed. We demonstrate that transgelin-2 in actin stress fibers (SFs) interacts with F-actin via two separate domains, and the chemical properties are determined for the individual domains. Its pure diffusion properties independent of the association to F-actin is also obtained. Our approach will thus be useful, as presented here for transgelin-2, in addressing the signaling mechanism of cellular proteins associated with SFs.
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4
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Anderson SJ, Garamella J, Adalbert S, McGorty RJ, Robertson-Anderson RM. Subtle changes in crosslinking drive diverse anomalous transport characteristics in actin-microtubule networks. SOFT MATTER 2021; 17:4375-4385. [PMID: 33908593 PMCID: PMC8189643 DOI: 10.1039/d1sm00093d] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Anomalous diffusion in crowded and complex environments is widely studied due to its importance in intracellular transport, fluid rheology and materials engineering. Specifically, diffusion through the cytoskeleton, a network comprised of semiflexible actin filaments and rigid microtubules that interact both sterically and via crosslinking, plays a principal role in viral infection, vesicle transport and targeted drug delivery. Here, we elucidate the impact of crosslinking on particle diffusion in composites of actin and microtubules with actin-actin, microtubule-microtubule and actin-microtubule crosslinking. We analyze a suite of transport metrics by coupling single-particle tracking and differential dynamic microscopy. Using these complementary techniques, we find that particles display non-Gaussian and non-ergodic subdiffusion that is markedly enhanced by cytoskeletal crosslinking, which we attribute to suppressed microtubule mobility. However, the extent to which transport deviates from normal Brownian diffusion depends strongly on the crosslinking motif - with actin-microtubule crosslinking inducing the most pronounced anomalous characteristics. Our results reveal that subtle changes to actin-microtubule interactions can have complex impacts on particle diffusion in cytoskeleton composites, and suggest that a combination of reduced filament mobility and more variance in actin mobilities leads to more strongly anomalous particle transport.
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Affiliation(s)
- S J Anderson
- Department of Physics & Biophysics, University of San Diego, San Diego, CA 92110, USA.
| | - J Garamella
- Department of Physics & Biophysics, University of San Diego, San Diego, CA 92110, USA.
| | - S Adalbert
- Department of Physics & Biophysics, University of San Diego, San Diego, CA 92110, USA.
| | - R J McGorty
- Department of Physics & Biophysics, University of San Diego, San Diego, CA 92110, USA.
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5
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Chaubet L, Chaudhary AR, Heris HK, Ehrlicher AJ, Hendricks AG. Dynamic actin cross-linking governs the cytoplasm's transition to fluid-like behavior. Mol Biol Cell 2020; 31:1744-1752. [PMID: 32579489 PMCID: PMC7521843 DOI: 10.1091/mbc.e19-09-0504] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2019] [Revised: 06/05/2020] [Accepted: 06/16/2020] [Indexed: 12/21/2022] Open
Abstract
Cells precisely control their mechanical properties to organize and differentiate into tissues. The architecture and connectivity of cytoskeletal filaments change in response to mechanical and biochemical cues, allowing the cell to rapidly tune its mechanics from highly cross-linked, elastic networks to weakly cross-linked viscous networks. While the role of actin cross-linking in controlling actin network mechanics is well-characterized in purified actin networks, its mechanical role in the cytoplasm of living cells remains unknown. Here, we probe the frequency-dependent intracellular viscoelastic properties of living cells using multifrequency excitation and in situ optical trap calibration. At long timescales in the intracellular environment, we observe that the cytoskeleton becomes fluid-like. The mechanics are well-captured by a model in which actin filaments are dynamically connected by a single dominant cross-linker. A disease-causing point mutation (K255E) of the actin cross-linker α-actinin 4 (ACTN4) causes its binding kinetics to be insensitive to tension. Under normal conditions, the viscoelastic properties of wild-type (WT) and K255E+/- cells are similar. However, when tension is reduced through myosin II inhibition, WT cells relax 3× faster to the fluid-like regime while K255E+/- cells are not affected. These results indicate that dynamic actin cross-linking enables the cytoplasm to flow at long timescales.
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Affiliation(s)
- Loïc Chaubet
- Department of Bioengineering, McGill University, Montreal, QC H3A 0C3, Canada
| | | | - Hossein K. Heris
- Department of Bioengineering, McGill University, Montreal, QC H3A 0C3, Canada
| | - Allen J. Ehrlicher
- Department of Bioengineering, McGill University, Montreal, QC H3A 0C3, Canada
| | - Adam G. Hendricks
- Department of Bioengineering, McGill University, Montreal, QC H3A 0C3, Canada
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6
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Kothari P, Johnson C, Sandone C, Iglesias PA, Robinson DN. How the mechanobiome drives cell behavior, viewed through the lens of control theory. J Cell Sci 2019; 132:jcs234476. [PMID: 31477578 PMCID: PMC6771144 DOI: 10.1242/jcs.234476] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Cells have evolved sophisticated systems that integrate internal and external inputs to coordinate cell shape changes during processes, such as development, cell identity determination, and cell and tissue homeostasis. Cellular shape-change events are driven by the mechanobiome, the network of macromolecules that allows cells to generate, sense and respond to externally imposed and internally generated forces. Together, these components build the cellular contractility network, which is governed by a control system. Proteins, such as non-muscle myosin II, function as both sensors and actuators, which then link to scaffolding proteins, transcription factors and metabolic proteins to create feedback loops that generate the foundational mechanical properties of the cell and modulate cellular behaviors. In this Review, we highlight proteins that establish and maintain the setpoint, or baseline, for the control system and explore the feedback loops that integrate different cellular processes with cell mechanics. Uncovering the genetic, biophysical and biochemical interactions between these molecular components allows us to apply concepts from control theory to provide a systems-level understanding of cellular processes. Importantly, the actomyosin network has emerged as more than simply a 'downstream' effector of linear signaling pathways. Instead, it is also a significant driver of cellular processes traditionally considered to be 'upstream'.
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Affiliation(s)
- Priyanka Kothari
- Departments of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Cecilia Johnson
- Art as Applied to Medicine, Johns Hopkins University School of Medicine, Baltimore, M 21205, USA
| | - Corinne Sandone
- Art as Applied to Medicine, Johns Hopkins University School of Medicine, Baltimore, M 21205, USA
| | - Pablo A Iglesias
- Departments of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
- Department of Electrical and Computer Engineering, Johns Hopkins University, Baltimore, MD 21218, USA
| | - Douglas N Robinson
- Departments of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
- Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, MD 21218, USA
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7
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Mulla Y, Wierenga H, Alkemade C, Ten Wolde PR, Koenderink GH. Frustrated binding of biopolymer crosslinkers. SOFT MATTER 2019; 15:3036-3042. [PMID: 30900710 DOI: 10.1039/c8sm02429d] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
Transiently crosslinked actin filament networks allow cells to combine elastic rigidity with the ability to deform viscoelastically. Theoretical models of semiflexible polymer networks predict that the crosslinker unbinding rate governs the timescale beyond which viscoelastic flow occurs. However a direct comparison between network and crosslinker dynamics is lacking. Here we measure the network's stress relaxation timescale using rheology and the lifetime of bound crosslinkers using fluorescence recovery after photobleaching (FRAP). Intriguingly, we observe that the crosslinker unbinding rate measured by FRAP is more than an order of magnitude slower than the rate measured by rheology. We rationalize this difference with a three-state model where crosslinkers are bound to either 0, 1 or 2 filaments, which allows us to extract crosslinker transition rates that are otherwise difficult to access. We find that the unbinding rate of singly bound crosslinkers is nearly two orders of magnitude slower than for doubly bound ones. We attribute the increased unbinding rate of doubly bound crosslinkers to the high stiffness of biopolymers, which frustrates crosslinker binding.
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Affiliation(s)
- Yuval Mulla
- Living Matter Department, AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands.
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8
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Hayakawa K, Sekiguchi C, Sokabe M, Ono S, Tatsumi H. Real-Time Single-Molecule Kinetic Analyses of AIP1-Enhanced Actin Filament Severing in the Presence of Cofilin. J Mol Biol 2018; 431:308-322. [PMID: 30439520 DOI: 10.1016/j.jmb.2018.11.010] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2018] [Revised: 11/08/2018] [Accepted: 11/08/2018] [Indexed: 11/17/2022]
Abstract
Rearrangement of actin filaments by polymerization, depolymerization, and severing is important for cell locomotion, membrane trafficking, and many other cellular functions. Cofilin and actin-interacting protein 1 (AIP1; also known as WDR1) are evolutionally conserved proteins that cooperatively sever actin filaments. However, little is known about the biophysical basis of the actin filament severing by these proteins. Here, we performed single-molecule kinetic analyses of fluorescently labeled AIP1 during the severing process of cofilin-decorated actin filaments. Results demonstrated that binding of a single AIP molecule was sufficient to enhance filament severing. After AIP1 binding to a filament, severing occurred with a delay of 0.7 s. Kinetics of binding and dissociation of a single AIP1 molecule to/from actin filaments followed a second-order and a first-order kinetics scheme, respectively. AIP1 binding and severing were detected preferentially at the boundary between the cofilin-decorated and bare regions on actin filaments. Based on the kinetic parameters explored in this study, we propose a possible mechanism behind the enhanced severing by AIP1.
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Affiliation(s)
- Kimihide Hayakawa
- Mechanobiology Laboratory, Nagoya University Graduate School of Medicine, 65 Tsurumai, Nagoya 466-8550, Japan
| | - Carina Sekiguchi
- Department of Physiology, Nagoya University Graduate School of Medicine, 65 Tsurumai, Nagoya 466-8550, Japan
| | - Masahiro Sokabe
- Mechanobiology Laboratory, Nagoya University Graduate School of Medicine, 65 Tsurumai, Nagoya 466-8550, Japan
| | - Shoichiro Ono
- Department of Pathology, Emory University School of Medicine, Atlanta, GA 30322, USA
| | - Hitoshi Tatsumi
- Department of Applied Bioscience, Kanazawa Institute of Technology (KIT), Ishikawa 924-0838, Japan.
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9
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Majumdar S, Foucard LC, Levine AJ, Gardel ML. Mechanical hysteresis in actin networks. SOFT MATTER 2018; 14:2052-2058. [PMID: 29479596 DOI: 10.1039/c7sm01948c] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Understanding the response of complex materials to external force is central to fields ranging from materials science to biology. Here, we describe a novel type of mechanical adaptation in cross-linked networks of F-actin, a ubiquitous protein found in eukaryotic cells. We show that shear stress changes the network's nonlinear mechanical response even long after that stress is removed. The duration, magnitude and direction of forcing history all change this mechanical response. While the mechanical hysteresis is long-lived, it can be simply erased by force application in the opposite direction. We further show that the observed mechanical adaptation is consistent with stress-dependent changes in the nematic order of the constituent filaments. Thus, this mechanical hysteresis arises from the changes in non-linear response that originates from stress-induced changes to filament orientation. This demonstrates that F-actin networks can exhibit analog read-write mechanical hysteretic properties, which can be used for adaptation to mechanical stimuli.
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Affiliation(s)
- Sayantan Majumdar
- James Franck Institute, The University of Chicago, Chicago, IL 60637, USA.
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10
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Alvarado J, Sheinman M, Sharma A, MacKintosh FC, Koenderink GH. Force percolation of contractile active gels. SOFT MATTER 2017; 13:5624-5644. [PMID: 28812094 DOI: 10.1039/c7sm00834a] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Living systems provide a paradigmatic example of active soft matter. Cells and tissues comprise viscoelastic materials that exert forces and can actively change shape. This strikingly autonomous behavior is powered by the cytoskeleton, an active gel of semiflexible filaments, crosslinks, and molecular motors inside cells. Although individual motors are only a few nm in size and exert minute forces of a few pN, cells spatially integrate the activity of an ensemble of motors to produce larger contractile forces (∼nN and greater) on cellular, tissue, and organismal length scales. Here we review experimental and theoretical studies on contractile active gels composed of actin filaments and myosin motors. Unlike other active soft matter systems, which tend to form ordered patterns, actin-myosin systems exhibit a generic tendency to contract. Experimental studies of reconstituted actin-myosin model systems have long suggested that a mechanical interplay between motor activity and the network's connectivity governs this contractile behavior. Recent theoretical models indicate that this interplay can be understood in terms of percolation models, extended to include effects of motor activity on the network connectivity. Based on concepts from percolation theory, we propose a state diagram that unites a large body of experimental observations. This framework provides valuable insights into the mechanisms that drive cellular shape changes and also provides design principles for synthetic active materials.
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Affiliation(s)
- José Alvarado
- Systems Biophysics Department, AMOLF, 1098 XG Amsterdam, The Netherlands.
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11
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Thomas DG, Robinson DN. The fifth sense: Mechanosensory regulation of alpha-actinin-4 and its relevance for cancer metastasis. Semin Cell Dev Biol 2017; 71:68-74. [PMID: 28579451 DOI: 10.1016/j.semcdb.2017.05.024] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2017] [Revised: 05/26/2017] [Accepted: 05/30/2017] [Indexed: 12/18/2022]
Abstract
Metastatic cancer cells invading through dense tumor stroma experience internal and external forces that are sensed through a variety of mechanosensory proteins that drive adaptations for specific environments. Alpha-actinin-4 (ACTN4) is a member of the α-actinin family of actin crosslinking proteins that is upregulated in several types of cancers. It shares 86% protein similarity with α-actinin-1, another non-muscle ACTN isoform, which appears to have a more modest role, if any, in cancer progression. While they share regulatory mechanisms, such as phosphorylation, calcium binding, phosphatidyl inositol binding, and calpain cleavage, α-actinin-4 exhibits a unique mechanosensory regulation that α-actinin-1 does not. This behavior is mediated, at least in part, by each protein's actin-binding affinity as well as the catch-slip-bond behavior of the actin binding domains. We will discuss currently known modes of ACTN4 regulation, their interactions, and how mechanosensation may provide major therapeutic targeting potential for cancer metastasis.
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Affiliation(s)
- Dustin G Thomas
- Department of Cell Biology, Johns Hopkins University, Baltimore, MD, 21205, USA.
| | - Douglas N Robinson
- Department of Cell Biology, Johns Hopkins University, Baltimore, MD, 21205, USA; Department of Pharmacology and Molecular Science, Johns Hopkins University,Baltimore, MD, 21205, USA; Department of Medicine, School of Medicine, Johns Hopkins University, Baltimore, MD, 21205, USA; Department of Chemical and Biomolecular Engineering, Whiting School of Engineering, Johns Hopkins University, Baltimore, MD, 21218, USA.
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12
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Plaza GR, Uyeda TQP, Mirzaei Z, Simmons CA. Study of the influence of actin-binding proteins using linear analyses of cell deformability. SOFT MATTER 2015; 11:5435-5446. [PMID: 26059185 DOI: 10.1039/c5sm00125k] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The actin cytoskeleton plays a key role in the deformability of the cell and in mechanosensing. Here we analyze the contributions of three major actin cross-linking proteins, myosin II, α-actinin and filamin, to cell deformability, by using micropipette aspiration of Dictyostelium cells. We examine the applicability of three simple mechanical models: for small deformation, linear viscoelasticity and drop of liquid with a tense cortex; and for large deformation, a Newtonian viscous fluid. For these models, we have derived linearized equations and we provide a novel, straightforward methodology to analyze the experiments. This methodology allowed us to differentiate the effects of the cross-linking proteins in the different regimes of deformation. Our results confirm some previous observations and suggest important relations between the molecular characteristics of the actin-binding proteins and the cell behavior: the effect of myosin is explained in terms of the relation between the lifetime of the bond to actin and the resistive force; the presence of α-actinin obstructs the deformation of the cytoskeleton, presumably mainly due to the higher molecular stiffness and to the lower dissociation rate constants; and filamin contributes critically to the global connectivity of the network, possibly by rapidly turning over cross-links during the remodeling of the cytoskeletal network, thanks to the higher rate constants, flexibility and larger size. The results suggest a sophisticated relationship between the expression levels of actin-binding proteins, deformability and mechanosensing.
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Affiliation(s)
- Gustavo R Plaza
- Departamento de Ciencia de Materiales, ETSI de Caminos, Canales y Puertos, Universidad Politécnica de Madrid, 28040 Madrid, Spain.
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13
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Abstract
Actomyosin-mediated contractility is a highly conserved mechanism for generating mechanical stress in animal cells and underlies muscle contraction, cell migration, cell division and tissue morphogenesis. Whereas actomyosin-mediated contractility in striated muscle is well understood, the regulation of such contractility in non-muscle and smooth muscle cells is less certain. Our increased understanding of the mechanics of actomyosin arrays that lack sarcomeric organization has revealed novel modes of regulation and force transmission. This work also provides an example of how diverse mechanical behaviours at cellular scales can arise from common molecular components, underscoring the need for experiments and theories to bridge the molecular to cellular length scales.
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14
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Pritchard RH, Huang YYS, Terentjev EM. Mechanics of biological networks: from the cell cytoskeleton to connective tissue. SOFT MATTER 2014; 10:1864-84. [PMID: 24652375 DOI: 10.1039/c3sm52769g] [Citation(s) in RCA: 107] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
From the cell cytoskeleton to connective tissues, fibrous networks are ubiquitous in metazoan life as the key promoters of mechanical strength, support and integrity. In recent decades, the application of physics to biological systems has made substantial strides in elucidating the striking mechanical phenomena observed in such networks, explaining strain stiffening, power law rheology and cytoskeletal fluidisation - all key to the biological function of individual cells and tissues. In this review we focus on the current progress in the field, with a primer into the basic physics of individual filaments and the networks they form. This is followed by a discussion of biological networks in the context of a broad spread of recent in vitro and in vivo experiments.
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Affiliation(s)
- Robyn H Pritchard
- Cavendish Laboratory, University of Cambridge, Cambridge, CB3 0HE, UK.
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15
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Oelz D, Schmeiser C. Simulation of lamellipodial fragments. J Math Biol 2011; 64:513-28. [DOI: 10.1007/s00285-011-0421-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2010] [Revised: 01/13/2011] [Indexed: 02/05/2023]
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16
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Lee H, Ferrer JM, Lang MJ, Kamm RD. Molecular origin of strain softening in cross-linked F-actin networks. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2010; 82:011919. [PMID: 20866660 PMCID: PMC3870339 DOI: 10.1103/physreve.82.011919] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/12/2009] [Revised: 03/03/2010] [Indexed: 05/09/2023]
Abstract
Two types of measurement are presented that relate molecular events to macroscopic behavior of F-actin networks. First, shear modulus is measured by oscillating an embedded microbead. Second, a microbead is translated at constant rate and transitions in the resisting force are observed. The loading rate dependence of the force at the transitions is similar to that of the molecular unbinding force, suggesting that they share a common origin. Reversibility tests of shear modulus provide further evidence that strain softening of F-actin networks is caused by force-induced rupture of cross-links.
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Affiliation(s)
- Hyungsuk Lee
- Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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17
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Greenberg MJ, Moore JR. The molecular basis of frictional loads in the in vitro motility assay with applications to the study of the loaded mechanochemistry of molecular motors. Cytoskeleton (Hoboken) 2010; 67:273-85. [PMID: 20191566 PMCID: PMC2861725 DOI: 10.1002/cm.20441] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2009] [Accepted: 02/05/2010] [Indexed: 11/05/2022]
Abstract
Molecular motors convert chemical energy into mechanical movement, generating forces necessary to accomplish an array of cellular functions. Since molecular motors generate force, they typically work under loaded conditions where the motor mechanochemistry is altered by the presence of a load. Several biophysical techniques have been developed to study the loaded behavior and force generating capabilities of molecular motors yet most of these techniques require specialized equipment. The frictional loading assay is a modification to the in vitro motility assay that can be performed on a standard epifluorescence microscope, permitting the high-throughput measurement of the loaded mechanochemistry of molecular motors. Here, we describe a model for the molecular basis of the frictional loading assay by modeling the load as a series of either elastic or viscoelastic elements. The model, which calculates the frictional loads imposed by different binding proteins, permits the measurement of isotonic kinetics, force-velocity relationships, and power curves in the motility assay. We show computationally and experimentally that the frictional load imposed by alpha-actinin, the most widely employed actin binding protein in frictional loading experiments, behaves as a viscoelastic rather than purely elastic load. As a test of the model, we examined the frictional loading behavior of rabbit skeletal muscle myosin under normal and fatigue-like conditions using alpha-actinin as a load. We found that, consistent with fiber studies, fatigue-like conditions cause reductions in myosin isometric force, unloaded sliding velocity, maximal power output, and shift the load at which peak power output occurs.
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Affiliation(s)
- Michael J. Greenberg
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA, USA
| | - Jeffrey R. Moore
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA, USA
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18
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Lieleg O, Schmoller KM, Claessens MMAE, Bausch AR. Cytoskeletal polymer networks: viscoelastic properties are determined by the microscopic interaction potential of cross-links. Biophys J 2009; 96:4725-32. [PMID: 19486695 DOI: 10.1016/j.bpj.2009.03.038] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2008] [Revised: 02/02/2009] [Accepted: 03/11/2009] [Indexed: 11/30/2022] Open
Abstract
Although the structure of cross-linking molecules mainly determines the structural organization of actin filaments and with that the static elastic properties of the cytoskeleton, it is largely unknown how the biochemical characteristics of transiently cross-linking proteins (actin-binding proteins (ABPs)) affect the viscoelasticity of actin networks. In this study, we show that the macroscopic network response of reconstituted actin networks can be traced back to the microscopic interaction potential of an individual actin/ABP bond. The viscoelastic response of cross-linked actin networks is set by the cross-linker off-rate, the binding energy, and the characteristic bond length of individual actin/ABP interactions.
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Affiliation(s)
- O Lieleg
- Lehrstuhl für Zellbiophysik E27, Technische Universität München, Garching, Germany
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19
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Oelz D, Schmeiser C, Small JV. Modeling of the actin-cytoskeleton in symmetric lamellipodial fragments. Cell Adh Migr 2009; 2:117-26. [PMID: 19271354 DOI: 10.4161/cam.2.2.6373] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The pushing structures of cells include laminar sheets, termed lamellipodia, made up of a meshwork of actin filaments that grow at the front and depolymerise at the rear, in a treadmilling mode.We here develop a mathematical model to describe the turnover and the mechanical properties of this network.Our basic modeling assumptions are that the lamellipodium is idealised as a two-dimensional structure, and that the actin network consists of two families of possibly bent, but locally parallel filaments. Instead of dealing with individual polymers, the filaments are assumed to be continuously distributed.The model includes (de)polymerization, of the mechanical effects of cross-linking, cell-substrate adhesion, as well as of the leading edge of the membrane.In the first version presented here, the total amount of F-actin is prescribed by assuming a constant polymerisation speed at the leading edge and a fixed total number and length distribution of filaments. We assume that cross-links at filament crossing points as well as integrin linkages with the matrix break and reform in response to incremental changes in network organization. In this first treatment, the model successfully simulates the persistence of the treadmilling network in radially spread cells.
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20
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Cytoskeletal Deformation at High Strains and the Role of Cross-link Unfolding or Unbinding. Cell Mol Bioeng 2009. [DOI: 10.1007/s12195-009-0048-8] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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21
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Esue O, Tseng Y, Wirtz D. Alpha-actinin and filamin cooperatively enhance the stiffness of actin filament networks. PLoS One 2009; 4:e4411. [PMID: 19198659 PMCID: PMC2635933 DOI: 10.1371/journal.pone.0004411] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2008] [Accepted: 01/09/2009] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND The close subcellular proximity of different actin filament crosslinking proteins suggests that these proteins may cooperate to organize F-actin structures to drive complex cellular functions during cell adhesion, motility and division. Here we hypothesize that alpha-actinin and filamin, two major F-actin crosslinking proteins that are both present in the lamella of adherent cells, display synergistic mechanical functions. METHODOLOGY/PRINCIPAL FINDINGS Using quantitative rheology, we find that combining alpha-actinin and filamin is much more effective at producing elastic, solid-like actin filament networks than alpha-actinin and filamin separately. Moreover, F-actin networks assembled in the presence of alpha-actinin and filamin strain-harden more readily than networks in the presence of either alpha-actinin or filamin. SIGNIFICANCE These results suggest that cells combine auxiliary proteins with similar ability to crosslink filaments to generate stiff cytoskeletal structures, which are required for the production of internal propulsive forces for cell migration, and that these proteins do not have redundant mechanical functions.
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Affiliation(s)
- Osigwe Esue
- Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland, United States of America
- Department of Early Stage Pharmaceutical Development, Genentech, Inc., South San Francisco, California, United States of America
| | - Yiider Tseng
- Department of Chemical Engineering, University of Florida, Gainesville, Florida, United States of America
| | - Denis Wirtz
- Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland, United States of America
- * E-mail:
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22
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Abstract
Stress fibres are contractile acto-myosin structures found from many types of non-muscle cells, where they are involved in adhesion, motility and morphogenesis. Stress fibres typically display a periodic alpha-actinin-myosin II pattern and are thus suggested to resemble the sarcomeric actin filament structures of muscle cells. Mammalian cells contain three categories of stress fibres: ventral stress fibres that are attached to focal adhesions at both ends, dorsal stress fibres that are attached to focal adhesions typically at one end and transverse arcs that are curved acto-myosin bundles, which do not directly attach to focal adhesions. In this review, we discuss the definition of stress fibres, organization of actin filaments and other components within these contractile structures, and the mechanisms of stress fibre assembly.
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Affiliation(s)
- P Naumanen
- Institute of Biotechnology, PO Box 56, 00014 University of Helsinki, Finland
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23
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Protein localization by actin treadmilling and molecular motors regulates stereocilia shape and treadmilling rate. Biophys J 2008; 95:5706-18. [PMID: 18936243 DOI: 10.1529/biophysj.108.143453] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We present a physical model that describes the active localization of actin-regulating proteins inside stereocilia during steady-state conditions. The mechanism of localization is through the interplay of free diffusion and directed motion, which is driven by coupling to the treadmilling actin filaments and to myosin motors that move along the actin filaments. The resulting localization of both the molecular motors and their cargo is calculated, and is found to have an exponential (or steeper) profile. This localization can be at the base (driven by actin retrograde flow and minus-end myosin motors), or at the stereocilia tip (driven by plus-end myosin motors). The localization of proteins that influence the actin depolymerization and polymerization rates allow us to describe the narrow shape of the stereocilia base, and the observed increase of the actin polymerization rate with the stereocilia height.
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24
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Measuring molecular rupture forces between single actin filaments and actin-binding proteins. Proc Natl Acad Sci U S A 2008; 105:9221-6. [PMID: 18591676 DOI: 10.1073/pnas.0706124105] [Citation(s) in RCA: 135] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Actin-binding proteins (ABPs) regulate the assembly of actin filaments (F-actin) into networks and bundles that provide the structural integrity of the cell. Two of these ABPs, filamin and alpha-actinin, have been extensively used to model the mechanical properties of actin networks grown in vitro; however, there is a lack in the understanding of how the molecular interactions between ABPs and F-actin regulate the dynamic properties of the cytoskeleton. Here, we present a native-like assay geometry to test the rupture force of a complex formed by an ABP linking two quasiparallel actin filaments. We readily demonstrate the adaptability of this assay by testing it with two different ABPs: filamin and alpha-actinin. For filamin/actin and alpha-actinin/actin, we measured similar rupture forces of 40-80 pN for loading rates between 4 and 50 pN/s. Both ABP unfolding and conformational transition events were observed, demonstrating that both are important and may be a significant mechanism for the temporal regulation of the mechanical properties of the actin cytoskeleton. With this modular, single-molecule assay, a wide range of ABP/actin interactions can be studied to better understand cytoskeletal and cell dynamics.
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25
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Lele TP, Thodeti CK, Pendse J, Ingber DE. Investigating complexity of protein-protein interactions in focal adhesions. Biochem Biophys Res Commun 2008; 369:929-34. [PMID: 18331831 DOI: 10.1016/j.bbrc.2008.02.137] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2008] [Accepted: 02/26/2008] [Indexed: 11/25/2022]
Abstract
The formation of focal adhesions governs cell shape and function; however, there are few measurements of the binding kinetics of focal adhesion proteins in living cells. Here, we used the fluorescence recovery after photobleaching (FRAP) technique, combined with mathematical modeling and scaling analysis to quantify dissociation kinetics of focal adhesion proteins in capillary endothelial cells. Novel experimental protocols based on mathematical analysis were developed to discern the rate-limiting step during FRAP. Values for the dissociation rate constant k(OFF) ranged over an order of magnitude from 0.009+/-0.001/s for talin to 0.102+/-0.010/s for FAK, indicating that talin is bound more strongly than other proteins in focal adhesions. Comparisons with in vitro measurements reveal that multiple focal adhesion proteins form a network of bonds, rather than binding in a pair-wise manner in these anchoring structures in living cells.
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Affiliation(s)
- Tanmay P Lele
- Department of Chemical Engineering, University of Florida, Gainesville, FL 32611, USA
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26
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Thermodynamic evidence of non-muscle myosin II–lipid-membrane interaction. Biochem Biophys Res Commun 2008; 366:500-5. [DOI: 10.1016/j.bbrc.2007.11.170] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2007] [Accepted: 11/29/2007] [Indexed: 11/19/2022]
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27
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Abstract
Animal cell movement is effected through a combination of protrusive and contractile events. Non-muscle cells contain stress fibres - bundles of actomyosin that are the major mediators of cell contraction and that can be compared to the highly organised actomyosin arrays of muscle cells. Recent studies have defined regulatory mechanisms that control stress fibre formation, placing the ROCK protein kinase at the centre of a complex signalling network controlling actomyosin contractility and stress fibre assembly. As we uncover the details of stress fibre construction, it is becoming clear that different categories of stress fibres exist. Some of these structures are less suited for cell motility and more suited to static contraction. In keeping with this, many specialised contractile cell types use stress fibres to remodel tissues and extracellular matrix.
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Affiliation(s)
- Stéphanie Pellegrin
- Department of Biochemistry, School of Medical Sciences, University of Bristol, BS8 1TD, UK.
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28
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Nakamura F, Osborn TM, Hartemink CA, Hartwig JH, Stossel TP. Structural basis of filamin A functions. ACTA ACUST UNITED AC 2007; 179:1011-25. [PMID: 18056414 PMCID: PMC2099194 DOI: 10.1083/jcb.200707073] [Citation(s) in RCA: 208] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Filamin A (FLNa) can effect orthogonal branching of F-actin and bind many cellular constituents. FLNa dimeric subunits have N-terminal spectrin family F-actin binding domains (ABDs) and an elongated flexible segment of 24 immunoglobulin (Ig) repeats. We generated a library of FLNa fragments to examine their F-actin binding to define the structural properties of FLNa that enable its various functions. We find that Ig repeats 9–15 contain an F-actin–binding domain necessary for high avidity F-actin binding. Ig repeats 16–24, where most FLNa-binding partners interact, do not bind F-actin, and thus F-actin does not compete with Ig repeat 23 ligand, FilGAP. Ig repeats 16–24 have a compact structure that suggests their unfolding may accommodate pre-stress–mediated stiffening of F-actin networks, partner binding, mechanosensing, and mechanoprotection properties of FLNa. Our results also establish the orientation of FLNa dimers in F-actin branching. Dimerization, mediated by FLNa Ig repeat 24, accounts for rigid high-angle FLNa/F-actin branching resistant to bending by thermal forces, and high avidity F-actin binding and cross-linking.
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Affiliation(s)
- Fumihiko Nakamura
- Translational Medicine Division, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA.
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29
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Abstract
The mechanical properties of cytoskeletal actin bundles play an essential role in numerous physiological processes, including hearing, fertilization, cell migration, and growth. Cells employ a multitude of actin-binding proteins to actively regulate bundle dimensions and cross-linking properties to suit biological function. The mechanical properties of actin bundles vary by orders of magnitude depending on diameter and length, cross-linking protein type and concentration, and constituent filament properties. Despite their importance to cell function, the molecular design principles responsible for this mechanical behavior remain unknown. Here, we examine the mechanics of cytoskeletal bundles using a molecular-based model that accounts for the discrete nature of constituent actin filaments and their distinct cross-linking proteins. A generic competition between filament stretching and cross-link shearing determines three markedly different regimes of mechanical response that are delineated by the relative values of two simple design parameters, revealing the universal nature of bundle-bending mechanics. In each regime, bundle-bending stiffness displays distinct scaling behavior with respect to bundle dimensions and molecular composition, as observed in reconstituted actin bundles in vitro. This mechanical behavior has direct implications on the physiological bending, buckling, and entropic stretching behavior of cytoskeletal processes, as well as reconstituted actin systems. Results are used to predict the bending regimes of various in vivo cytoskeletal bundles that are not easily accessible to experiment and to generate hypotheses regarding implications of the isolated behavior on in vivo bundle function.
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30
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Hoffman BD, Massiera G, Crocker JC. Fragility and mechanosensing in a thermalized cytoskeleton model with forced protein unfolding. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2007; 76:051906. [PMID: 18233686 DOI: 10.1103/physreve.76.051906] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2007] [Indexed: 05/25/2023]
Abstract
We describe a model of cytoskeletal mechanics based on the force-induced conformational change of protein cross-links in a stressed polymer network. Slow deformation of simulated networks containing cross-links that undergo repeated, serial domain unfolding leads to an unusual state-with many cross-links accumulating near the critical force for further unfolding. This state is robust to thermalization and does not occur in similar protein unbinding based simulations. Moreover, we note that the unusual configuration of near-critical protein cross-links in the fragile state provides a physical mechanism for the chemical transduction of cell-level mechanical strain and extra-cellular matrix stiffness.
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Affiliation(s)
- Brenton D Hoffman
- Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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31
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Ananthakrishnan R, Guck J, Wottawah F, Schinkinger S, Lincoln B, Romeyke M, Moon T, Käs J. Quantifying the contribution of actin networks to the elastic strength of fibroblasts. J Theor Biol 2006; 242:502-16. [DOI: 10.1016/j.jtbi.2006.03.021] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2005] [Revised: 03/16/2006] [Accepted: 03/22/2006] [Indexed: 01/13/2023]
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32
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Hotulainen P, Lappalainen P. Stress fibers are generated by two distinct actin assembly mechanisms in motile cells. ACTA ACUST UNITED AC 2006; 173:383-94. [PMID: 16651381 PMCID: PMC2063839 DOI: 10.1083/jcb.200511093] [Citation(s) in RCA: 646] [Impact Index Per Article: 35.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Stress fibers play a central role in adhesion, motility, and morphogenesis of eukaryotic cells, but the mechanism of how these and other contractile actomyosin structures are generated is not known. By analyzing stress fiber assembly pathways using live cell microscopy, we revealed that these structures are generated by two distinct mechanisms. Dorsal stress fibers, which are connected to the substrate via a focal adhesion at one end, are assembled through formin (mDia1/DRF1)–driven actin polymerization at focal adhesions. In contrast, transverse arcs, which are not directly anchored to substrate, are generated by endwise annealing of myosin bundles and Arp2/3-nucleated actin bundles at the lamella. Remarkably, dorsal stress fibers and transverse arcs can be converted to ventral stress fibers anchored to focal adhesions at both ends. Fluorescence recovery after photobleaching analysis revealed that actin filament cross-linking in stress fibers is highly dynamic, suggesting that the rapid association–dissociation kinetics of cross-linkers may be essential for the formation and contractility of stress fibers. Based on these data, we propose a general model for assembly and maintenance of contractile actin structures in cells.
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Affiliation(s)
- Pirta Hotulainen
- Institute of Biotechnology, University of Helsinki, Helsinki FI-00014, Finland
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33
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van der Gucht J, Paluch E, Plastino J, Sykes C. Stress release drives symmetry breaking for actin-based movement. Proc Natl Acad Sci U S A 2005; 102:7847-52. [PMID: 15911773 PMCID: PMC1142378 DOI: 10.1073/pnas.0502121102] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
By using a simple assay composed of purified proteins, we studied the spontaneous polarization of actin networks polymerizing on spherical beads, which subsequently undergo movement. We show evidence that this symmetry breaking is based on the release of elastic energy, analogous to the fracture of polymer gels. The dynamics of this process and the thickness at which it occurs depend on the growth rate and mechanical properties of the actin gel. We explain our experimental results with a model based on elasticity theory and fracture mechanics.
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Affiliation(s)
- Jasper van der Gucht
- Laboratoire Physico-Chimie Curie, Unité Mixte de Recherche 168, Institut Curie, 11 Rue Pierre et Marie Curie, 75231 Paris, Cedex 5, France.
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34
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Wottawah F, Schinkinger S, Lincoln B, Ebert S, Müller K, Sauer F, Travis K, Guck J. Characterizing single suspended cells by optorheology. Acta Biomater 2005; 1:263-71. [PMID: 16701805 DOI: 10.1016/j.actbio.2005.02.010] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2005] [Revised: 02/11/2005] [Accepted: 02/13/2005] [Indexed: 10/25/2022]
Abstract
The measurement of the mechanical properties of individual cells has received much attention in recent years. In this paper we describe the application of optically induced forces with an optical stretcher to perform step-stress experiments on individual suspended fibroblasts. The conversion from creep-compliance to frequency-dependent complex shear modulus reveals characteristic viscoelastic signatures of the underlying cytoskeleton and its dynamic molecular properties. Both normal and cancerous fibroblasts display a single stress relaxation time in the observed time and frequency space that can be related to the transient binding of actin crosslinking proteins. In addition, shear modulus and steady-state viscosity of the shell-like actin cortex as the main module resisting small deformations are extracted. These values in combination with insight into the cells' architecture are used to explain their different deformability. This difference can then be exploited to distinguish normal from cancerous cells. The nature of the optical stretcher as an optical trap allows easy incorporation in a microfluidic system with automatic trapping and alignment of the cells, and thus a high measurement throughput. This carries the potential for using the microfluidic optical stretcher to investigate cellular processes involving the cytoskeleton and to diagnose diseases related to cytoskeletal alterations.
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Affiliation(s)
- Falk Wottawah
- Institute for Soft Matter Physics, Department of Physics and Geosciences, University of Leipzig, Linnéstrasse 5, 04103 Leipzig, Germany
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35
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Wottawah F, Schinkinger S, Lincoln B, Ananthakrishnan R, Romeyke M, Guck J, Käs J. Optical rheology of biological cells. PHYSICAL REVIEW LETTERS 2005; 94:098103. [PMID: 15784006 DOI: 10.1103/physrevlett.94.098103] [Citation(s) in RCA: 108] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/06/2004] [Indexed: 05/22/2023]
Abstract
A step stress deforming suspended cells causes a passive relaxation, due to a transiently cross-linked isotropic actin cortex underlying the cellular membrane. The fluid-to-solid transition occurs at a relaxation time coinciding with unbinding times of actin cross-linking proteins. Elastic contributions from slowly relaxing entangled filaments are negligible. The symmetric geometry of suspended cells ensures minimal statistical variability in their viscoelastic properties in contrast with adherent cells and thus is defining for different cell types. Mechanical stimuli on time scales of minutes trigger active structural responses.
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Affiliation(s)
- Falk Wottawah
- Institute for Soft Matter Physics, University of Leipzig, Linnéstrasse 5, 04103 Leipzig, Germany
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36
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Abstract
Cell-extracellular matrix (ECM) adhesion is crucial for control of cell behavior. It connects the ECM to the intracellular cytoskeleton and transduces bidirectional signals between the extracellular and intracellular compartments. The subcellular machinery that mediates cell-ECM adhesion and signaling is complex. It consists of transmembrane proteins (e.g., integrins) and at least several dozens of membrane-proximal proteins that assemble into a network through multiple protein interactions. Furthermore, despite sharing certain common components, cell-ECM adhesions exhibit considerable heterogeneity in different types of cells (e.g., the cell-ECM adhesions in cardiac myocytes are considerably different from those in fibroblasts). Here, we will first briefly describe the general properties of the integrin-mediated cell-ECM adhesion and signal transduction. Next, we will focus on one of the recently discovered cell-ECM adhesion protein complexes consisting of PINCH, integrin-linked kinase (ILK), and Parvin and use it as an example to illustrate the molecular basis underlying the assembly and functions of cell-ECM adhesions. Finally, we will discuss in detail the structure and regulation of cell-ECM adhesion complexes in cardiac myocytes, which illustrate the importance and complexity of the cell-ECM adhesion structures in organogenesis and diseases.
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Affiliation(s)
- Jorge L Sepulveda
- Department of Pathology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA
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37
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Limozin L, Sackmann E. Polymorphism of cross-linked actin networks in giant vesicles. PHYSICAL REVIEW LETTERS 2002; 89:168103. [PMID: 12398759 DOI: 10.1103/physrevlett.89.168103] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/2002] [Indexed: 05/23/2023]
Abstract
Actin networks cross-linked by natural linkers alpha-actinin and filamin are generated in giant vesicles by polymerization through ionophore-mediated influx of Mg2+. alpha-actinin induces the formation of randomly linked networks at 25 degrees C which transform at <15 degrees C into spiderweblike gels or ringlike bundles depending on the vesicle size. Muscle filamin forms ringlike structures under all experimental conditions which can supercoil by subsequent Mg2+ addition. The polymorphism is rationalized in terms of recent models of bivalent ion coupled semiflexible polyelectrolytes and by considering the topology of the linkers.
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Affiliation(s)
- Laurent Limozin
- E22-Biophysics, Physics Department, Technical University Munich, James Franck Strasse, 85748 Garching, Germany.
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38
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Nakamura F, Osborn E, Janmey PA, Stossel TP. Comparison of filamin A-induced cross-linking and Arp2/3 complex-mediated branching on the mechanics of actin filaments. J Biol Chem 2002; 277:9148-54. [PMID: 11786548 DOI: 10.1074/jbc.m111297200] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We compared the effects of human filamin A (FLNa) and the activated human Arp2/3 complex on mechanical properties of actin filaments. As little as 1 FLNa to 800 polymerizing actin monomers induces a sharp concentration-dependent increase in the apparent viscosity of 24 microm actin, a parameter classically defined as a gel point. The activated Arp2/3 complex, at concentrations up to 1:25 actins had no detectable actin gelation activity, even in the presence of phalloidin, to stabilize actin filaments against debranching. Increasing the activated Arp2/3 complex to actin ratio raises the FLNa concentration required to induce actin gelation, an effect ascribable to Arp2/3-mediated actin nucleation resulting in actin filament length diminution. Time lapse video microscopy of microparticles attached to actin filaments or photoactivation of fluorescence revealed actin filament immobilization by FLNa in contrast to diffusion of Arp2/3-branched actin filaments. The experimental results support theories predicting that polymer branching absent cross-linking does not lead to polymer gelation and are consistent with the observation that cells deficient in actin filament cross-linking activity have unstable surfaces. They suggest complementary roles for actin branching and cross-linking in cellular actin mechanics in vivo.
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Affiliation(s)
- Fumihiko Nakamura
- Hematology Division, Brigham and Women's Hospital, Department of Medicine, Harvard Medical School, Boston, Massachusetts 02115, USA
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39
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Stossel TP, Condeelis J, Cooley L, Hartwig JH, Noegel A, Schleicher M, Shapiro SS. Filamins as integrators of cell mechanics and signalling. Nat Rev Mol Cell Biol 2001; 2:138-45. [PMID: 11252955 DOI: 10.1038/35052082] [Citation(s) in RCA: 774] [Impact Index Per Article: 33.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Filamins are large actin-binding proteins that stabilize delicate three-dimensional actin webs and link them to cellular membranes. They integrate cellular architectural and signalling functions and are essential for fetal development and cell locomotion. Here, we describe the history, structure and function of this group of proteins.
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Affiliation(s)
- T P Stossel
- Brigham and Women's Hospital, Boston, Massachusetts 02115, USA.
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40
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Abstract
I examined the binding kinetics between integrin (alpha(IIb)beta(3)) and purified focal adhesion proteins, including alpha-actinin, filamin, vinculin, talin, and F-actin. Using static light-scatter technique, I observed affinities of the order talin > filamin > F-actin > alpha-actinin > (talin when bound to vinculin) which were lower when integrin was complexed with fibronectin. No binding between integrin and vinculin was detected. The calculated dissociation constants (K(d)) ranged between 0.4 microM and 5 microM. These results in part confirm previously published data using different methods. The modest affinity with which the focal adhesion proteins interact in vitro might be indicative of how cells, e.g., thrombocytes, gain a high degree of versatility and velocity.
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Affiliation(s)
- W H Goldmann
- Department of Pathology and Department of Surgery, Harvard Medical School, Boston, Massachusetts, 02115, USA
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41
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Leinweber B, Tang JX, Stafford WF, Chalovich JM. Calponin interaction with alpha-actinin-actin: evidence for a structural role for calponin. Biophys J 1999; 77:3208-17. [PMID: 10585942 PMCID: PMC1289132 DOI: 10.1016/s0006-3495(99)77151-1] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
The purpose of this study was to address the paradox of calponin localization with alpha-actinin and filamin, two proteins with tandem calponin homology (CH) domains, by determining the effect of these proteins on the binding of calponin to actin. The results show that actin can accommodate near-saturating concentrations of either calponin and alpha-actinin or calponin and filamin with little change or no change in ligand affinity. Little direct interaction occurred between alpha-actinin and calponin in the absence of actin, so this effect is not likely to explain the co-distribution of these proteins. Calponin, like alpha-actinin, induced elastic gel formation when added to actin. When alpha-actinin was added to newly formed calponin/actin gels, no change was seen in the mechanical properties of the gel compared to calponin and actin alone. However, when calponin was added to newly formed alpha-actinin/actin gels, the resulting gel was much stronger than the gels formed by either ligand alone. Furthermore, gels formed by the addition of calponin to alpha-actinin/actin exhibited a phenomenon known as strain hardening, a characteristic of mechanically resilient gels. These results add weight to the concept that one of the functions of calponin is to stabilize the actin cytoskeleton.
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Affiliation(s)
- B Leinweber
- Department of Physiology, East Carolina University School of Medicine, Greenville, North Carolina 27834, USA
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Goldmann WH, Teodoridis JM, Sharma CP, Alonso JL, Isenberg G. Fragments from alpha-actinin insert into reconstituted lipid bilayers. Biochem Biophys Res Commun 1999; 264:225-9. [PMID: 10527869 DOI: 10.1006/bbrc.1999.1495] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Recent experiments have indicated that alpha-actinin interacts with phospholipid membranes. Using computer analysis methods we determined two possible lipid binding sites capable of membrane attachment/insertion, residues 281-300 and 720-739 of the primary amino acid sequence on smooth muscle alpha-actinin. Having expressed these regions as fusion proteins with schistosomal GST (glutathione S-transferase), we used differential scanning calorimetry (DSC) to investigate their interaction with mixtures of zwitterionic (dimyristoyl-l-alpha-phosphatidylcholine, DMPC) and anionic (dimyristoyl-l-alpha-phosphatidylglycerol, DMPG) phospholipids in reconstituted lipid bilayers. Calorimetric measurements showed that as fusion protein concentration increased, the main chain transition enthalpy decreased and chain melting temperatures shifted, which is indicative of partial protein insertion into the hydrophobic region of the lipid membranes. Centrifugation assay and subsequent SDS/Page chromatography confirmed this finding.
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Affiliation(s)
- W H Goldmann
- Department of Pathology, Children's Hospital, Boston, Massachusetts, 02115, USA.
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Abstract
In the current study, the process of alpha-actinin binding to the myofibrillar Z-line was investigated to determine its mechanism. Pretreatment of rigor myofibrils with unlabeled alpha-actinin did not prevent or slow the incorporation of fluorescein skeletal alpha-actinin into myofibrils suggesting that incorporation was not the filling of empty binding sites but rather an exchange reaction. Further support for this was obtained using quantitative measures of labeled alpha-actinin incorporation and measures of total myofibrillar alpha-actinin. These results showed that there was no change in myofibrillar alpha-actinin content when up to 15% of the total alpha-actinin was the labeled protein. Measurement of the time-course of fluorescein alpha-actinin incorporation by quantitative fluorescence microscopy showed that the increase in Z-line fluorescence was well described by a rapid (unresolved) incorporation of fluorescence followed by a much slower phase. The slower phase was independent of fluorescein alpha-actinin concentration (2.5-160 nM) and had an apparent rate of 0.008-0.016 min(-1). Pretreatment of myofibrils with fluorescein alpha-actinin followed by incubation with unlabeled alpha-actinin resulted in a decrease in Z-line fluorescence with an apparent rate of 0.021 min(-1). The slow phase was interpreted as representing the dissociation rate of intrinsic Z-line alpha-actinin. Thus, the dissociation rate for the in situ interaction of alpha-actinin with actin appears to be three orders of magnitude slower than that determined from solution studies.
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Affiliation(s)
- D R Swartz
- Anatomy Department, Indiana University Medical School, Indianapolis 46202, USA.
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Goldmann WH, Teodoridis JM, Sharma CP, Hu B, Isenberg G. Fragments from actin binding protein (ABP-280; filamin) insert into reconstituted lipid layers. Biochem Biophys Res Commun 1999; 259:108-12. [PMID: 10334924 DOI: 10.1006/bbrc.1999.0735] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Previous computer analyses suggested two possible lipid binding sites, residues 49-71 and 131-155, of the primary amino acid sequence on ABP-280 (filamin), which could facilitate membrane attachment/insertion. We expressed these regions as fusion proteins with schistosomal GST and investigated their interaction with mixtures of zwitterionic (dimyristoyl-l-alpha-phosphatidylcholine, DMPC) and anionic (dimyristoyl-l-alpha-phosphatidylglycerol, DMPG) phospholipids in reconstituted lipid bilayers by differential scanning calorimetry (DSC). Using vesicles of mixed DMPC/DMPG with increasing fusion protein concentrations, we established in calorimetric assays a decrease of the main chain transition enthalpy, DeltaH, and a shift in chain melting temperature. This is indicative of the insertion of these fragments into the hydrophobic region of lipid membranes. We confirmed these findings by the film balance technique using lipid monolayers (DMPG). The binding judged from both methods was of moderate affinity.
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Affiliation(s)
- W H Goldmann
- Department of Surgery, Children's Hospital, Boston, Massachusetts, USA.
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Xu J, Wirtz D, Pollard TD. Dynamic cross-linking by alpha-actinin determines the mechanical properties of actin filament networks. J Biol Chem 1998; 273:9570-6. [PMID: 9545287 DOI: 10.1074/jbc.273.16.9570] [Citation(s) in RCA: 140] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We used smooth muscle alpha-actinin to evaluate the contribution of cross-linker dynamics to the mechanical properties of actin filament networks. Recombinant actin-binding domain (residues 2-269) binds actin filaments with a Kd of 1 microM at 25 degrees C, 20 times stronger than actin-binding domain produced by thermolysin digestion of native alpha-actinin (residues 25-257). Between 8 and 25 degrees C the rate constants for recombinant actin-binding domain to bind to (0.8-2.7 microM-1 s-1) and dissociate from (0.2-2.4 s-1) actin filaments depend on temperature. At 8 degrees C actin filaments cross-linked with alpha-actinin are stiff and nearly solid, whereas at 25 degrees C the mechanical properties approach those of actin filaments alone. In these experiments, high actin concentrations kept most of the alpha-actinin bound to actin and temperature varied a single parameter, cross-linker dynamics, because the mechanical properties of pure actin filaments (a viscoelastic gel) or biotinylated actin filaments cross-linked irreversibly by avidin (a stiff viscoelastic solid) depend little on temperature. These results show that the rate of exchange of dynamic cross-links between actin filaments is an important determinant of the mechanical properties of the networks.
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Affiliation(s)
- J Xu
- Department of Biophysics and Biophysical Chemistry, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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Goldmann WH, Guttenberg Z. Examination of temperature-induced 'gel-sol' transformation of alpha-actinin/cross-linked actin networks by static light scattering. FEBS Lett 1998; 426:255-9. [PMID: 9599019 DOI: 10.1016/s0014-5793(98)00353-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
We studied the gel-sol transformation of F-actin/alpha-actinin solutions. Cross-linking of actin filaments by alpha-actinin shows a temperature-dependent increase in light scatter signal, (I)T. Higher F-actin/alpha-actinin molar ratios, r(A alpha) as well as increases in F-actin concentration, [A], and reduction of actin filament lengths, rAG, augment the maximal light intensity, I and shift the gel-sol transition point, Tg to higher temperatures. This behavior is interpreted in terms of the model developed by Tempel, M., Isenberg, G. and Sackmann, E. (1996) (Physical Review E 54, 1802-1810) based on the percolation theory. Using the temperature-dependent binding model of this theory allows instant prediction of the equilibrium constant, K for F-actin/alpha-actinin solutions at temperatures T < Tg.
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Affiliation(s)
- W H Goldmann
- Surgery Research Laboratories, Massachusetts General Hospital, Harvard Medical School, Charlestown 02129, USA.
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Isenberg G, Niggli V. Interaction of cytoskeletal proteins with membrane lipids. INTERNATIONAL REVIEW OF CYTOLOGY 1997; 178:73-125. [PMID: 9348669 DOI: 10.1016/s0074-7696(08)62136-1] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Rapid and significant progress has been made in understanding lipid/protein interactions involving cytoskeletal components and the plasma membrane. Covalent and noncovalent lipid modifications of cytoskeletal proteins mediate their interaction with lipid bilayers. The application of biophysical techniques such as differential scanning colorimetry, neutron reflection, electron spin resonance, CD spectroscopy, nuclear magnetic resonance, and hydrophobic photolabeling, allow various folding stages of proteins during electrostatic adsorption and hydrophobic insertion into lipid bilayers to be analyzed. Reconstitution of proteins into planar lipid films and liposomes help to understand the architecture of biological interfaces. During signaling events at plasma membrane interfaces, lipids are important for the regulation of catalytic protein functions. Protein/lipid interactions occur selectively and with a high degree of specificity and thus have to be considered as physiologically relevant processes with gaining impact on cell functions.
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Affiliation(s)
- G Isenberg
- Biophysics Department, Technical University of Munich, Garching, Germany
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Goldmann WH, Tempel M, Sprenger I, Isenberg G, Ezzell RM. Viscoelasticity of actin-gelsolin networks in the presence of filamin. EUROPEAN JOURNAL OF BIOCHEMISTRY 1997; 246:373-9. [PMID: 9208927 DOI: 10.1111/j.1432-1033.1997.00373.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Cross-linking of actin filaments by filamin by means of frequency-dependent rheology yields an increase in the filament's elasticity and stiffness. Higher cross-linker (filamin) ratios are required for mean actin-filament lengths of 5-6 microm than for random-length distribution of actin filaments. The loss modulus (i.e. the viscous portion) in the region of the internal-chain dynamics [G"(omega) approximately omega(alpha)] is influenced by the cross-linking of filaments, and with an increasing molar ratio of filamin/actin a reduction of alpha is observed. Rheological measurements reveal that actin networks are already formed at the polymerizing stage at a molar ratio of filamin/actin of less than 1:100, and electron micrographs show phase separation of actin/filament networks of low density and of actin/filament bundles.
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Affiliation(s)
- W H Goldmann
- Surgery Research Laboratories, Massachusetts General Hospital, Harvard Medical School, Charlestown 02129, USA.
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Tempel M, Isenberg G, Sackmann E. Temperature-induced sol-gel transition and microgel formation in alpha -actinin cross-linked actin networks: A rheological study. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1996; 54:1802-1810. [PMID: 9965260 DOI: 10.1103/physreve.54.1802] [Citation(s) in RCA: 71] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
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Tempel M, Goldmann WH, Isenberg G. Computer analyses suggest interactions of non-muscle filamin with lipid membranes. FEBS Lett 1994; 350:169-72. [PMID: 8070558 DOI: 10.1016/0014-5793(94)00697-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
It is concluded from structure predictions of the primary amino acid sequence by computer analyses that two segments of non-muscle filamin could facilitate lipid membrane attachment or anchoring. Residues 49-71 of the amino-terminal may attach to phospholipid membranes, and residues 131-155 may anchor in the hydrophobic region of lipid membranes.
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Affiliation(s)
- M Tempel
- Technical University of Munich, Garching, Germany
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