1
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Cuentas-Condori A, Chen S, Krout M, Gallik KL, Tipps J, Gailey C, Flautt L, Kim H, Mulcahy B, Zhen M, Richmond JE, Miller DM. The epithelial Na + channel UNC-8 promotes an endocytic mechanism that recycles presynaptic components to new boutons in remodeling neurons. Cell Rep 2023; 42:113327. [PMID: 37906594 PMCID: PMC10921563 DOI: 10.1016/j.celrep.2023.113327] [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: 08/18/2022] [Revised: 06/01/2023] [Accepted: 10/06/2023] [Indexed: 11/02/2023] Open
Abstract
Circuit refinement involves the formation of new presynaptic boutons as others are dismantled. Nascent presynaptic sites can incorporate material from recently eliminated synapses, but the recycling mechanisms remain elusive. In early-stage C. elegans larvae, the presynaptic boutons of GABAergic DD neurons are removed and new outputs established at alternative sites. Here, we show that developmentally regulated expression of the epithelial Na+ channel (ENaC) UNC-8 in remodeling DD neurons promotes a Ca2+ and actin-dependent mechanism, involving activity-dependent bulk endocytosis (ADBE), that recycles presynaptic material for reassembly at nascent DD synapses. ADBE normally functions in highly active neurons to accelerate local recycling of synaptic vesicles. In contrast, we find that an ADBE-like mechanism results in the distal recycling of synaptic material from old to new synapses. Thus, our findings suggest that a native mechanism (ADBE) can be repurposed to dismantle presynaptic terminals for reassembly at new, distant locations.
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Affiliation(s)
- Andrea Cuentas-Condori
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN 37240, USA
| | - Siqi Chen
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN 37240, USA
| | - Mia Krout
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Kristin L Gallik
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - John Tipps
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN 37240, USA
| | - Casey Gailey
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN 37240, USA
| | - Leah Flautt
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN 37240, USA
| | - Hongkyun Kim
- Department of Cell Biology and Anatomy, Chicago Medical School, Rosalind Franklin University of Medicine and Science, North Chicago, IL 60064, USA
| | - Ben Mulcahy
- Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, ON M5G 1X5, Canada
| | - Mei Zhen
- Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, ON M5G 1X5, Canada
| | - Janet E Richmond
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - David M Miller
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN 37240, USA; Neurosience Program, Vanderbilt University, Nashville, TN 37240, USA.
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2
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Nurden AT. Molecular basis of clot retraction and its role in wound healing. Thromb Res 2023; 231:159-169. [PMID: 36008192 DOI: 10.1016/j.thromres.2022.08.010] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2022] [Revised: 08/08/2022] [Accepted: 08/10/2022] [Indexed: 11/30/2022]
Abstract
Clot retraction is important for the prevention of bleeding, in the manifestations of thrombosis and for tissue repair. The molecular mechanisms behind clot formation are complex. Platelet involvement begins with adhesion at sites of vessel injury followed by platelet aggregation, thrombin generation and fibrin production. Other blood cells incorporate into a fibrin mesh that is consolidated by FXIIIa-mediated crosslinking and platelet contractile activity. The latter results in the asymmetric redistribution of erythrocytes into a tighter central mass providing the clot with stability and resistance to fibrinolysis. Integrin αIIbβ3 on platelets is the key player in these events, bridging fibrin and the platelet cytoskeleton. Glycoprotein VI participates in thrombus formation but not in the retraction. Rheological and environmental factors influence clot construction with retraction driven by the platelet cytoskeleton with actomyosin acting as the motor. Activated platelets provide procoagulant activity stimulating thrombin generation together with the release of a plethora of biologically active proteins and substances from storage pools; many form chemotactic gradients within the fibrin or the underlying matrix. Also released are newly synthesized metabolites and lipid-rich vesicles that circulate within the vasculature and mimic platelet functions. Platelets and their released elements play key roles in wound healing. This includes promoting stem cell and mesenchymal stromal cell recruitment, fibroblast and endothelial cell migration, angiogenesis and matrix formation. These properties have led to the use of autologous clots in therapies designed to accelerate tissue repair while offering the potential for genetic manipulation in both inherited and acquired diseases.
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Affiliation(s)
- Alan T Nurden
- Institut Hospitalo-Universitaire LIRYC, Pessac, France.
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3
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Pontarollo G, Reinhardt C. The hemorrhage risk of dasatinib therapy. Blood 2023; 141:2917-2918. [PMID: 37318908 DOI: 10.1182/blood.2023020399] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/17/2023] Open
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4
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Paul M, Golla K, Kim H. Gelsolin Modulates Platelet Dense Granule Secretion and Hemostasis via the Actin Cytoskeleton. Thromb Haemost 2023; 123:219-230. [PMID: 36522181 DOI: 10.1055/s-0042-1758800] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
BACKGROUND AND OBJECTIVE The mechanisms underlying platelet granule release are not fully understood. The actin cytoskeleton serves as the platelet's structural framework that is remodeled upon platelet activation. Gelsolin is a calcium-dependent protein that severs and caps existing actin filaments although its role in modulating platelet granule exocytosis is unknown. METHODS The hemostatic function of wild-type (WT) and gelsolin null (Gsn-/- ) mice was measured ex vivo by rotational thromboelastometry analysis of whole blood. Platelets were purified from WT and Gsn-/- mouse blood and activated with thrombin. Platelet aggregation was assessed by light-transmission aggregometry. Clot retraction was measured to assess outside-in integrin signaling. Adenosine triphosphate (ATP) release and surface P-selectin were measured as markers of dense- and α-granule secretion, respectively. RESULTS The kinetics of agonist-induced aggregation, clot retraction, and ATP release were accelerated in Gsn-/- platelets relative to WT. However, levels of surface P-selectin were diminished in Gsn-/- platelets. ATP release was also accelerated in WT platelets pretreated with the actin-depolymerizing drug cytochalasin D, thus mimicking the kinetics observed in Gsn-/- platelets. Conversely, ATP release kinetics were normalized in Gsn-/- platelets treated with the actin polymerization agonist jasplakinolide. Rab27b and Munc13-4 are vesicle-priming proteins known to promote dense granule secretion. Co-immunoprecipitation indicates that the association between Rab27b and Munc13-4 is enhanced in Gsn-/- platelets. CONCLUSIONS Gelsolin regulates the kinetics of hemostasis by modulating the platelet's actin cytoskeleton and the protein machinery of dense granule exocytosis.
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Affiliation(s)
- Manoj Paul
- Centre for Blood Research, University of British Columbia, Vancouver, British Columbia, Canada.,Department of Oral Biological and Medical Sciences, University of British Columbia, Vancouver, British Columbia, Canada
| | - Kalyan Golla
- Centre for Blood Research, University of British Columbia, Vancouver, British Columbia, Canada.,Department of Oral Biological and Medical Sciences, University of British Columbia, Vancouver, British Columbia, Canada
| | - Hugh Kim
- Centre for Blood Research, University of British Columbia, Vancouver, British Columbia, Canada.,Department of Oral Biological and Medical Sciences, University of British Columbia, Vancouver, British Columbia, Canada.,Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada
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5
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Dandamudi A, Akbar H, Cancelas J, Zheng Y. Rho GTPase Signaling in Platelet Regulation and Implication for Antiplatelet Therapies. Int J Mol Sci 2023; 24:ijms24032519. [PMID: 36768837 PMCID: PMC9917354 DOI: 10.3390/ijms24032519] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2022] [Revised: 01/16/2023] [Accepted: 01/21/2023] [Indexed: 01/31/2023] Open
Abstract
Platelets play a vital role in regulating hemostasis and thrombosis. Rho GTPases are well known as molecular switches that control various cellular functions via a balanced GTP-binding/GTP-hydrolysis cycle and signaling cascade through downstream effectors. In platelets, Rho GTPases function as critical regulators by mediating signal transduction that drives platelet activation and aggregation. Mostly by gene targeting and pharmacological inhibition approaches, Rho GTPase family members RhoA, Rac1, and Cdc42 have been shown to be indispensable in regulating the actin cytoskeleton dynamics in platelets, affecting platelet shape change, spreading, secretion, and aggregation, leading to thrombus formation. Additionally, studies of Rho GTPase function using platelets as a non-transformed model due to their anucleated nature have revealed valuable information on cell signaling principles. This review provides an updated summary of recent advances in Rho GTPase signaling in platelet regulation. We also highlight pharmacological approaches that effectively inhibited platelet activation to explore their possible development into future antiplatelet therapies.
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Affiliation(s)
- Akhila Dandamudi
- Division of Experimental Hematology and Cancer Biology, Cincinnati Children’s Hospital Medical Center, 3333 Burnet Avenue, Cincinnati, OH 45229, USA
- Department of Pathology, University of Cincinnati Graduate School, Cincinnati, OH 45267, USA
| | - Huzoor Akbar
- Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, Athens, OH 45701, USA
| | - Jose Cancelas
- Division of Experimental Hematology and Cancer Biology, Cincinnati Children’s Hospital Medical Center, 3333 Burnet Avenue, Cincinnati, OH 45229, USA
- Hoxworth Blood Center, College of Medicine, University of Cincinnati, Cincinnati, OH 45229, USA
| | - Yi Zheng
- Division of Experimental Hematology and Cancer Biology, Cincinnati Children’s Hospital Medical Center, 3333 Burnet Avenue, Cincinnati, OH 45229, USA
- Department of Pathology, University of Cincinnati Graduate School, Cincinnati, OH 45267, USA
- Correspondence: ; Tel.: +1-513-636-0595
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6
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Myers KR, Fan Y, McConnell P, Cooper JA, Zheng JQ. Actin capping protein regulates postsynaptic spine development through CPI-motif interactions. Front Mol Neurosci 2022; 15:1020949. [PMID: 36245917 PMCID: PMC9557104 DOI: 10.3389/fnmol.2022.1020949] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2022] [Accepted: 09/12/2022] [Indexed: 12/02/2022] Open
Abstract
Dendritic spines are small actin-rich protrusions essential for the formation of functional circuits in the mammalian brain. During development, spines begin as dynamic filopodia-like protrusions that are then replaced by relatively stable spines containing an expanded head. Remodeling of the actin cytoskeleton plays a key role in the formation and modification of spine morphology, however many of the underlying regulatory mechanisms remain unclear. Capping protein (CP) is a major actin regulating protein that caps the barbed ends of actin filaments, and promotes the formation of dense branched actin networks. Knockdown of CP impairs the formation of mature spines, leading to an increase in the number of filopodia-like protrusions and defects in synaptic transmission. Here, we show that CP promotes the stabilization of dendritic protrusions, leading to the formation of stable mature spines. However, the localization and function of CP in dendritic spines requires interactions with proteins containing a capping protein interaction (CPI) motif. We found that the CPI motif-containing protein Twinfilin-1 (Twf1) also localizes to spines where it plays a role in CP spine enrichment. The knockdown of Twf1 leads to an increase in the density of filopodia-like protrusions and a decrease in the stability of dendritic protrusions, similar to CP knockdown. Finally, we show that CP directly interacts with Shank and regulates its spine accumulation. These results suggest that spatiotemporal regulation of CP in spines not only controls the actin dynamics underlying the formation of stable postsynaptic spine structures, but also plays an important role in the assembly of the postsynaptic apparatus underlying synaptic function.
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Affiliation(s)
- Kenneth R. Myers
- Department of Cell Biology, Emory University School of Medicine, Atlanta, GA, United States
| | - Yanjie Fan
- Department of Cell Biology, Emory University School of Medicine, Atlanta, GA, United States
| | - Patrick McConnell
- Department of Biochemistry and Molecular Biophysics, Washington University in St. Louis, St. Louis, MO, United States
| | - John A. Cooper
- Department of Biochemistry and Molecular Biophysics, Washington University in St. Louis, St. Louis, MO, United States
| | - James Q. Zheng
- Department of Cell Biology, Emory University School of Medicine, Atlanta, GA, United States
- Department of Neurology, Emory University School of Medicine, Atlanta, GA, United States
- Center for Neurodegenerative Diseases, Emory University School of Medicine, Atlanta, GA, United States
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7
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Duan X, Perveen R, Dandamudi A, Adili R, Johnson J, Funk K, Berryman M, Davis AK, Holinstat M, Zheng Y, Akbar H. Pharmacologic targeting of Cdc42 GTPase by a small molecule Cdc42 activity-specific inhibitor prevents platelet activation and thrombosis. Sci Rep 2021; 11:13170. [PMID: 34162972 PMCID: PMC8222210 DOI: 10.1038/s41598-021-92654-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2020] [Accepted: 05/27/2021] [Indexed: 01/14/2023] Open
Abstract
Gene targeting of Cdc42 GTPase has been shown to inhibit platelet activation. In this study, we investigated a hypothesis that inhibition of Cdc42 activity by CASIN, a small molecule Cdc42 Activity-Specific INhibitor, may down regulate platelet activation and thrombus formation. We investigated the effects of CASIN on platelet activation in vitro and thrombosis in vivo. In human platelets, CASIN, but not its inactive analog Pirl7, blocked collagen induced activation of Cdc42 and inhibited phosphorylation of its downstream effector, PAK1/2. Moreover, addition of CASIN to washed human platelets inhibited platelet spreading on immobilized fibrinogen. Treatment of human platelets with CASIN inhibited collagen or thrombin induced: (a) ATP secretion and platelet aggregation; and (b) phosphorylation of Akt, ERK and p38-MAPK. Pre-incubation of platelets with Pirl7, an inactive analog of CASIN, failed to inhibit collagen induced aggregation. Washing of human platelets after incubation with CASIN eliminated its inhibitory effect on collagen induced aggregation. Intraperitoneal administration of CASIN to wild type mice inhibited ex vivo aggregation induced by collagen but did not affect the murine tail bleeding times. CASIN administration, prior to laser-induced injury in murine cremaster muscle arterioles, resulted in formation of smaller and unstable thrombi compared to control mice without CASIN treatment. These data suggest that pharmacologic targeting of Cdc42 by specific and reversible inhibitors may lead to the discovery of novel antithrombotic agents.
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Affiliation(s)
- Xin Duan
- Division of Experimental Hematology and Cancer Biology, Children's Hospital Medical Center, University of Cincinnati, Cincinnati, OH, 45229, USA
| | - Rehana Perveen
- Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, Athens, OH, 45701, USA
| | - Akhila Dandamudi
- Division of Experimental Hematology and Cancer Biology, Children's Hospital Medical Center, University of Cincinnati, Cincinnati, OH, 45229, USA
| | - Reheman Adili
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI, 48109, USA
| | - James Johnson
- Division of Experimental Hematology and Cancer Biology, Children's Hospital Medical Center, University of Cincinnati, Cincinnati, OH, 45229, USA
| | - Kevin Funk
- Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, Athens, OH, 45701, USA
| | - Mark Berryman
- Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, Athens, OH, 45701, USA
| | - Ashley Kuenzi Davis
- Division of Experimental Hematology and Cancer Biology, Children's Hospital Medical Center, University of Cincinnati, Cincinnati, OH, 45229, USA
| | - Michael Holinstat
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI, 48109, USA
| | - Yi Zheng
- Division of Experimental Hematology and Cancer Biology, Children's Hospital Medical Center, University of Cincinnati, Cincinnati, OH, 45229, USA.
| | - Huzoor Akbar
- Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, Athens, OH, 45701, USA.
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8
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Bender M, Palankar R. Platelet Shape Changes during Thrombus Formation: Role of Actin-Based Protrusions. Hamostaseologie 2021; 41:14-21. [PMID: 33588449 DOI: 10.1055/a-1325-0993] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Platelet activation and aggregation are essential to limit blood loss at sites of vascular injury but may also lead to occlusion of diseased vessels. The platelet cytoskeleton is a critical component for proper hemostatic function. Platelets change their shape after activation and their contractile machinery mediates thrombus stabilization and clot retraction. In vitro studies have shown that platelets, which come into contact with proteins such as fibrinogen, spread and first form filopodia and then lamellipodia, the latter being plate-like protrusions with branched actin filaments. However, the role of platelet lamellipodia in hemostasis and thrombus formation has been unclear until recently. This short review will briefly summarize the recent findings on the contribution of the actin cytoskeleton and lamellipodial structures to platelet function.
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Affiliation(s)
- Markus Bender
- Institute of Experimental Biomedicine - Chair I, University Hospital and Rudolf Virchow Center, Würzburg, Germany
| | - Raghavendra Palankar
- Department of Transfusion Medicine, Institute for Immunology and Transfusion Medicine, University Medicine Greifswald, Greifswald, Germany
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9
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10
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Sensitized mutagenesis screen in Factor V Leiden mice identifies thrombosis suppressor loci. Proc Natl Acad Sci U S A 2017; 114:9659-9664. [PMID: 28827327 DOI: 10.1073/pnas.1705762114] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Factor V Leiden (F5L ) is a common genetic risk factor for venous thromboembolism in humans. We conducted a sensitized N-ethyl-N-nitrosourea (ENU) mutagenesis screen for dominant thrombosuppressor genes based on perinatal lethal thrombosis in mice homozygous for F5L (F5L/L ) and haploinsufficient for tissue factor pathway inhibitor (Tfpi+/- ). F8 deficiency enhanced the survival of F5L/LTfpi+/- mice, demonstrating that F5L/LTfpi+/- lethality is genetically suppressible. ENU-mutagenized F5L/L males and F5L/+Tfpi+/- females were crossed to generate 6,729 progeny, with 98 F5L/LTfpi+/- offspring surviving until weaning. Sixteen lines, referred to as "modifier of Factor 5 Leiden (MF5L1-16)," exhibited transmission of a putative thrombosuppressor to subsequent generations. Linkage analysis in MF5L6 identified a chromosome 3 locus containing the tissue factor gene (F3). Although no ENU-induced F3 mutation was identified, haploinsufficiency for F3 (F3+/- ) suppressed F5L/LTfpi+/- lethality. Whole-exome sequencing in MF5L12 identified an Actr2 gene point mutation (p.R258G) as the sole candidate. Inheritance of this variant is associated with suppression of F5L/LTfpi+/- lethality (P = 1.7 × 10-6), suggesting that Actr2p.R258G is thrombosuppressive. CRISPR/Cas9 experiments to generate an independent Actr2 knockin/knockout demonstrated that Actr2 haploinsufficiency is lethal, supporting a hypomorphic or gain-of-function mechanism of action for Actr2p.R258G Our findings identify F8 and the Tfpi/F3 axis as key regulators in determining thrombosis balance in the setting of F5L and also suggest a role for Actr2 in this process.
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11
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Xu Q, Huff LP, Fujii M, Griendling KK. Redox regulation of the actin cytoskeleton and its role in the vascular system. Free Radic Biol Med 2017; 109:84-107. [PMID: 28285002 PMCID: PMC5497502 DOI: 10.1016/j.freeradbiomed.2017.03.004] [Citation(s) in RCA: 78] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/22/2016] [Revised: 02/17/2017] [Accepted: 03/06/2017] [Indexed: 12/17/2022]
Abstract
The actin cytoskeleton is critical for form and function of vascular cells, serving mechanical, organizational and signaling roles. Because many cytoskeletal proteins are sensitive to reactive oxygen species, redox regulation has emerged as a pivotal modulator of the actin cytoskeleton and its associated proteins. Here, we summarize work implicating oxidants in altering actin cytoskeletal proteins and focus on how these alterations affect cell migration, proliferation and contraction of vascular cells. Finally, we discuss the role of oxidative modification of the actin cytoskeleton in vivo and highlight its importance for vascular diseases.
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Affiliation(s)
- Qian Xu
- Division of Cardiology, Department of Medicine, Emory University, 101 Woodruff Circle, 308a WMB, Atlanta, GA 30322, United States; Department of Cardiovascular Medicine, Xiangya Hospital, Central South University, Changsha, China
| | - Lauren P Huff
- Division of Cardiology, Department of Medicine, Emory University, 101 Woodruff Circle, 308a WMB, Atlanta, GA 30322, United States
| | - Masakazu Fujii
- Department of Medicine and Bioregulatory Science, Graduate School of Medical Sciences, Kyushu University, Japan
| | - Kathy K Griendling
- Division of Cardiology, Department of Medicine, Emory University, 101 Woodruff Circle, 308a WMB, Atlanta, GA 30322, United States.
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12
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Abstract
Actin reorganization regulates key processes in platelet activation. Here we examined the role of the Arp2/3 complex, an essential component in actin filament branching, in platelet function. The Arpc2 gene, encoding the p34 subunit of the Arp2/3 complex, was deleted in the megakaryocyte lineage (Arpc2fl/flPF4-Cre). Deletion of the Arp2/3 complex resulted in marked microthrombocytopenia in mice, caused by premature platelet release into the bone marrow compartment and impaired platelet survival in circulation. Arpc2fl/flPF4-Cre platelets exhibited alterations in their actin cytoskeleton and their peripheral microtubule coil. Thrombocytopenia was alleviated following clodronate liposome-induced macrophage depletion in Arpc2fl/flPF4-Cre mice. Arpc2fl/flPF4-Cre platelets failed to spread and showed a mild defect in integrin activation and aggregation. However, no significant differences in hemostasis or thrombosis were observed between Arpc2fl/flPF4-Cre and control mice. Thus, Arp2/3 is critical for platelet homeostasis but plays only a minor role for vascular hemostasis.
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13
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Loss of the Arp2/3 complex component ARPC1B causes platelet abnormalities and predisposes to inflammatory disease. Nat Commun 2017. [PMID: 28368018 DOI: 10.1038/ncomms14816)] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022] Open
Abstract
Human actin-related protein 2/3 complex (Arp2/3), required for actin filament branching, has two ARPC1 component isoforms, with ARPC1B prominently expressed in blood cells. Here we show in a child with microthrombocytopenia, eosinophilia and inflammatory disease, a homozygous frameshift mutation in ARPC1B (p.Val91Trpfs*30). Platelet lysates reveal no ARPC1B protein and greatly reduced Arp2/3 complex. Missense ARPC1B mutations are identified in an unrelated patient with similar symptoms and ARPC1B deficiency. ARPC1B-deficient platelets are microthrombocytes similar to those seen in Wiskott-Aldrich syndrome that show aberrant spreading consistent with loss of Arp2/3 function. Knockout of ARPC1B in megakaryocytic cells results in decreased proplatelet formation, and as observed in platelets from patients, increased ARPC1A expression. Thus loss of ARPC1B produces a unique set of platelet abnormalities, and is associated with haematopoietic/immune symptoms affecting cell lineages where this isoform predominates. In agreement with recent experimental studies, our findings suggest that ARPC1 isoforms are not functionally interchangeable.
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14
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Kahr WHA, Pluthero FG, Elkadri A, Warner N, Drobac M, Chen CH, Lo RW, Li L, Li R, Li Q, Thoeni C, Pan J, Leung G, Lara-Corrales I, Murchie R, Cutz E, Laxer RM, Upton J, Roifman CM, Yeung RSM, Brumell JH, Muise AM. Loss of the Arp2/3 complex component ARPC1B causes platelet abnormalities and predisposes to inflammatory disease. Nat Commun 2017; 8:14816. [PMID: 28368018 PMCID: PMC5382316 DOI: 10.1038/ncomms14816] [Citation(s) in RCA: 147] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2016] [Accepted: 01/31/2017] [Indexed: 12/19/2022] Open
Abstract
Human actin-related protein 2/3 complex (Arp2/3), required for actin filament branching, has two ARPC1 component isoforms, with ARPC1B prominently expressed in blood cells. Here we show in a child with microthrombocytopenia, eosinophilia and inflammatory disease, a homozygous frameshift mutation in ARPC1B (p.Val91Trpfs*30). Platelet lysates reveal no ARPC1B protein and greatly reduced Arp2/3 complex. Missense ARPC1B mutations are identified in an unrelated patient with similar symptoms and ARPC1B deficiency. ARPC1B-deficient platelets are microthrombocytes similar to those seen in Wiskott–Aldrich syndrome that show aberrant spreading consistent with loss of Arp2/3 function. Knockout of ARPC1B in megakaryocytic cells results in decreased proplatelet formation, and as observed in platelets from patients, increased ARPC1A expression. Thus loss of ARPC1B produces a unique set of platelet abnormalities, and is associated with haematopoietic/immune symptoms affecting cell lineages where this isoform predominates. In agreement with recent experimental studies, our findings suggest that ARPC1 isoforms are not functionally interchangeable. ARPC1B is a component of the actin-related protein 2/3 complex (Arp2/3), which is required for actin filament branching. Kahr et al. show that ARPC1B deficiency in humans is associated with severe multisystem disease that includes platelet abnormalities, eosinophilia, eczema and other indicators of immune disease.
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Affiliation(s)
- Walter H A Kahr
- Cell Biology Program, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada M5G 0A4.,Division of Haematology/Oncology, Department of Paediatrics, University of Toronto and The Hospital for Sick Children, Toronto, Ontario, Canada M5G 1X8.,Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada M5S 1A8
| | - Fred G Pluthero
- Cell Biology Program, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada M5G 0A4
| | - Abdul Elkadri
- Cell Biology Program, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada M5G 0A4.,SickKids Inflammatory Bowel Disease Center and Division of Gastroenterology, Hepatology, and Nutrition, Department of Paediatrics, University of Toronto, Hospital for Sick Children, Toronto, Ontario, Canada M5G 1X8.,Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada M5S 1A8
| | - Neil Warner
- Cell Biology Program, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada M5G 0A4.,SickKids Inflammatory Bowel Disease Center and Division of Gastroenterology, Hepatology, and Nutrition, Department of Paediatrics, University of Toronto, Hospital for Sick Children, Toronto, Ontario, Canada M5G 1X8
| | - Marko Drobac
- Cell Biology Program, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada M5G 0A4.,Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada M5S 1A8
| | - Chang Hua Chen
- Cell Biology Program, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada M5G 0A4.,Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada M5S 1A8
| | - Richard W Lo
- Cell Biology Program, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada M5G 0A4.,Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada M5S 1A8
| | - Ling Li
- Cell Biology Program, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada M5G 0A4
| | - Ren Li
- Cell Biology Program, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada M5G 0A4
| | - Qi Li
- Cell Biology Program, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada M5G 0A4.,SickKids Inflammatory Bowel Disease Center and Division of Gastroenterology, Hepatology, and Nutrition, Department of Paediatrics, University of Toronto, Hospital for Sick Children, Toronto, Ontario, Canada M5G 1X8
| | - Cornelia Thoeni
- Cell Biology Program, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada M5G 0A4.,SickKids Inflammatory Bowel Disease Center and Division of Gastroenterology, Hepatology, and Nutrition, Department of Paediatrics, University of Toronto, Hospital for Sick Children, Toronto, Ontario, Canada M5G 1X8
| | - Jie Pan
- Cell Biology Program, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada M5G 0A4.,SickKids Inflammatory Bowel Disease Center and Division of Gastroenterology, Hepatology, and Nutrition, Department of Paediatrics, University of Toronto, Hospital for Sick Children, Toronto, Ontario, Canada M5G 1X8
| | - Gabriella Leung
- Cell Biology Program, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada M5G 0A4.,SickKids Inflammatory Bowel Disease Center and Division of Gastroenterology, Hepatology, and Nutrition, Department of Paediatrics, University of Toronto, Hospital for Sick Children, Toronto, Ontario, Canada M5G 1X8
| | - Irene Lara-Corrales
- Division of Pathology, The Hospital for Sick Children, Toronto, Ontario, Canada M5G 1X8
| | - Ryan Murchie
- Cell Biology Program, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada M5G 0A4.,SickKids Inflammatory Bowel Disease Center and Division of Gastroenterology, Hepatology, and Nutrition, Department of Paediatrics, University of Toronto, Hospital for Sick Children, Toronto, Ontario, Canada M5G 1X8
| | - Ernest Cutz
- Division of Pathology, The Hospital for Sick Children, Toronto, Ontario, Canada M5G 1X8
| | - Ronald M Laxer
- Division of Rheumatology, Department of Paediatrics, University of Toronto, The Hospital for Sick Children, Toronto, Ontario, Canada M5G 1X8.,Department of Medicine, University of Toronto, Toronto, Ontario, Canada M5S 1A8
| | - Julia Upton
- Division of Immunology, Department of Paediatrics, University of Toronto, The Hospital for Sick Children, Toronto, Ontario, Canada M5G 1X8
| | - Chaim M Roifman
- Division of Immunology, Department of Paediatrics, University of Toronto, The Hospital for Sick Children, Toronto, Ontario, Canada M5G 1X8
| | - Rae S M Yeung
- Cell Biology Program, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada M5G 0A4.,Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada M5S 1A8.,Division of Rheumatology, Department of Paediatrics, University of Toronto, The Hospital for Sick Children, Toronto, Ontario, Canada M5G 1X8.,Department of Immunology, University of Toronto, Toronto, Ontario, Canada M5S 1A8
| | - John H Brumell
- Cell Biology Program, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada M5G 0A4.,SickKids Inflammatory Bowel Disease Center and Division of Gastroenterology, Hepatology, and Nutrition, Department of Paediatrics, University of Toronto, Hospital for Sick Children, Toronto, Ontario, Canada M5G 1X8.,Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada M5S 1A8.,Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada M5S 1A8
| | - Aleixo M Muise
- Cell Biology Program, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada M5G 0A4.,Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada M5S 1A8.,SickKids Inflammatory Bowel Disease Center and Division of Gastroenterology, Hepatology, and Nutrition, Department of Paediatrics, University of Toronto, Hospital for Sick Children, Toronto, Ontario, Canada M5G 1X8.,Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada M5S 1A8
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15
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Palazzo A, Bluteau O, Messaoudi K, Marangoni F, Chang Y, Souquere S, Pierron G, Lapierre V, Zheng Y, Vainchenker W, Raslova H, Debili N. The cell division control protein 42-Src family kinase-neural Wiskott-Aldrich syndrome protein pathway regulates human proplatelet formation. J Thromb Haemost 2016; 14:2524-2535. [PMID: 27685868 DOI: 10.1111/jth.13519] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2016] [Indexed: 12/31/2022]
Abstract
Essentials The role of the cytoskeleton during megakaryocyte differentiation was examined. Human megakaryocytes are derived from in vitro cultured CD34+ cells. Cell division control protein 42 (CDC42) positively regulates proplatelet formation (PPF). Neural Wiskott-Aldrich syndrome protein, the main effector of CDC42 with Src positively regulates PPF. SUMMARY Background Cytoskeletal rearrangements are essential for platelet release. The RHO small GTPase family, as regulators of the actin cytoskeleton, play an important role in proplatelet formation (PPF). In the neuronal system, CDC42 is involved in axon formation, a process that combines elongation and branching as for PPF. Objective To analyze the role of CDC42 and its effectors of the Wiskott-Aldrich syndrome protein (WASP) family in PPF. Methods Human megakaryocytes (MKs) were obtained from CD34+ cells. Inhibition of CDC42 in MKs was performed with the chemical inhibitor CASIN or with an active or a dominant-negative form of CDC42. The knock-down of N-WASP was obtained with a small hairpin RNA strategy Results Herein, we show that CDC42 activity increased during MK differentiation. The use of the chemical inhibitor CASIN or of an active or a dominant-negative form of CDC42 demonstrated that CDC42 positively regulated PPF in vitro. We determined that N-WASP, but not WASP, regulated PPF. We found that N-WASP knockdown led to a marked decrease in PPF, owing to a defect in the demarcation membrane system (DMS). This was associated with RHOA activation, and a concomitant augmentation in the phosphorylation of mysosin light chain 2. Phosphorylation of N-WASP, creating a primed form of N-WASP, increased during MK differentiation. Phosphorylation inhibition by two Src family kinase inhibitors decreased PPF. Conclusions We conclude that N-WASP positively regulates DMS development and PPF, and that the Src family kinases in association with CDC42 regulate PPF through N-WASP.
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Affiliation(s)
- A Palazzo
- Institut National de la Santé et de la Recherche Médicale, UMR 1170, Equipe labellisée Ligue Contre le Cancer, Laboratoire d'Excellence GR-Ex, Villejuif, France
- Université Paris-Saclay, UMR 1170, Villejuif, France
- Gustave Roussy, UMR 1170, Villejuif, France
| | - O Bluteau
- Institut National de la Santé et de la Recherche Médicale, UMR 1170, Equipe labellisée Ligue Contre le Cancer, Laboratoire d'Excellence GR-Ex, Villejuif, France
- Université Paris-Saclay, UMR 1170, Villejuif, France
- Gustave Roussy, UMR 1170, Villejuif, France
| | - K Messaoudi
- Institut National de la Santé et de la Recherche Médicale, UMR 1170, Equipe labellisée Ligue Contre le Cancer, Laboratoire d'Excellence GR-Ex, Villejuif, France
- Université Paris-Saclay, UMR 1170, Villejuif, France
- Gustave Roussy, UMR 1170, Villejuif, France
| | - F Marangoni
- Institut National de la Santé et de la Recherche Médicale, UMR 1170, Equipe labellisée Ligue Contre le Cancer, Laboratoire d'Excellence GR-Ex, Villejuif, France
- Université Paris-Saclay, UMR 1170, Villejuif, France
- Gustave Roussy, UMR 1170, Villejuif, France
| | - Y Chang
- Institut National de la Santé et de la Recherche Médicale, UMR 1170, Equipe labellisée Ligue Contre le Cancer, Laboratoire d'Excellence GR-Ex, Villejuif, France
- Université Paris-Saclay, UMR 1170, Villejuif, France
- Gustave Roussy, UMR 1170, Villejuif, France
| | - S Souquere
- Gustave Roussy, Centre Nationale de la Recherche Scientifique, UMR 8122, Gustave Roussy, Villejuif, France
| | - G Pierron
- Gustave Roussy, Centre Nationale de la Recherche Scientifique, UMR 8122, Gustave Roussy, Villejuif, France
| | - V Lapierre
- Gustave Roussy, Unité de Thérapie Cellulaire, Villejuif, France
| | - Y Zheng
- Division of Experimental Hematology and Cancer Biology, Cincinnati Children's Hospital Medical Center, University of Cincinnati College of Medicine, Cincinnati, OH, USA
| | - W Vainchenker
- Institut National de la Santé et de la Recherche Médicale, UMR 1170, Equipe labellisée Ligue Contre le Cancer, Laboratoire d'Excellence GR-Ex, Villejuif, France
- Université Paris-Saclay, UMR 1170, Villejuif, France
- Gustave Roussy, UMR 1170, Villejuif, France
| | - H Raslova
- Institut National de la Santé et de la Recherche Médicale, UMR 1170, Equipe labellisée Ligue Contre le Cancer, Laboratoire d'Excellence GR-Ex, Villejuif, France
- Université Paris-Saclay, UMR 1170, Villejuif, France
- Gustave Roussy, UMR 1170, Villejuif, France
| | - N Debili
- Institut National de la Santé et de la Recherche Médicale, UMR 1170, Equipe labellisée Ligue Contre le Cancer, Laboratoire d'Excellence GR-Ex, Villejuif, France
- Université Paris-Saclay, UMR 1170, Villejuif, France
- Gustave Roussy, UMR 1170, Villejuif, France
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16
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Rondina MT, Freitag M, Pluthero FG, Kahr WHA, Rowley JW, Kraiss LW, Franks Z, Zimmerman GA, Weyrich AS, Schwertz H. Non-genomic activities of retinoic acid receptor alpha control actin cytoskeletal events in human platelets. J Thromb Haemost 2016; 14:1082-94. [PMID: 26848712 PMCID: PMC5497578 DOI: 10.1111/jth.13281] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2015] [Indexed: 12/29/2022]
Abstract
UNLABELLED Essentials Platelets employ proteins/signaling pathways traditionally thought reserved for nuclear niche. We determined retinoic-acid-receptor alpha (RARα) expression and function in human platelets. RARα/actin-related protein-2/3 complex (Arp2/3) interact via non-genomic signaling in platelets. RARα regulates Arp2/3-mediated actin cytoskeletal dynamics and platelet spreading. SUMMARY Background Platelets utilize proteins and pathways classically reserved for the nuclear niche. Methods We determined whether human platelets express retinoic-acid-receptor family members, traditionally thought of as nuclear transcription factors, and deciphered the function of RARα. Results We found that RARα is robustly expressed in human platelets and megakaryocytes and interacts directly with actin-related protein-2/3 complex (Arp2/3) subunit 5 (Arp2/3s5). Arp2/3s5 co-localized with RARα in situ and regulated platelet cytoskeletal processes. The RARα ligand all-trans retinoic acid (atRA) disrupted RARα-Arp2/3 interactions. When isolated human platelets were treated with atRA, rapid cytoskeletal events (e.g. platelet spreading) were inhibited. In addition, when platelets were cultured for 18 h in the presence of atRA, actin-dependent morphological changes (e.g. extended cell body formation) were similarly inhibited. Using in vitro actin branching assays, RARα and Arp2/3-regulated complex actin branch formation was demonstrated. Consistent with inhibition of cytoskeletal processes in platelets, atRA, when added to this branching assay, resulted in dysregulated actin branching. Conclusion Our findings identify a previously unknown mechanism by which RARα regulates Arp2/3-mediated actin cytoskeletal dynamics through a non-genomic signaling pathway. These findings have broad implications in both nucleated and anucleate cells, where actin cytoskeletal events regulate cell morphology, movement and division.
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Affiliation(s)
- M T Rondina
- Molecular Medicine Program, University of Utah, Salt Lake City, UT, USA
- Department of Internal Medicine, University of Utah, Salt Lake City, UT, USA
- Department of Internal Medicine, George E. Wahlen Salt Lake City VAMC, Salt Lake City, UT, USA
| | - M Freitag
- Department of Immunology and Transfusion Medicine, University of Greifswald, Greifswald, Germany
| | - F G Pluthero
- Program in Cell Biology, Research Institute, Hospital for Sick Children, Toronto, ON, Canada
| | - W H A Kahr
- Program in Cell Biology, Research Institute, Hospital for Sick Children, Toronto, ON, Canada
- Departments of Paediatrics and Biochemistry, University of Toronto, Toronto, ON, Canada
| | - J W Rowley
- Molecular Medicine Program, University of Utah, Salt Lake City, UT, USA
| | - L W Kraiss
- Molecular Medicine Program, University of Utah, Salt Lake City, UT, USA
- Division of Vascular Surgery, Department of Surgery, University of Utah, Salt Lake City, UT, USA
| | - Z Franks
- Molecular Medicine Program, University of Utah, Salt Lake City, UT, USA
| | - G A Zimmerman
- Molecular Medicine Program, University of Utah, Salt Lake City, UT, USA
- Department of Internal Medicine, University of Utah, Salt Lake City, UT, USA
| | - A S Weyrich
- Molecular Medicine Program, University of Utah, Salt Lake City, UT, USA
- Department of Internal Medicine, University of Utah, Salt Lake City, UT, USA
| | - H Schwertz
- Molecular Medicine Program, University of Utah, Salt Lake City, UT, USA
- Department of Immunology and Transfusion Medicine, University of Greifswald, Greifswald, Germany
- Division of Vascular Surgery, Department of Surgery, University of Utah, Salt Lake City, UT, USA
- Lichtenberg-Professor for Experimental Hemostasis, University of Greifswald, Greifswald, Germany
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17
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Poulter NS, Pollitt AY, Davies A, Malinova D, Nash GB, Hannon MJ, Pikramenou Z, Rappoport JZ, Hartwig JH, Owen DM, Thrasher AJ, Watson SP, Thomas SG. Platelet actin nodules are podosome-like structures dependent on Wiskott-Aldrich syndrome protein and ARP2/3 complex. Nat Commun 2015; 6:7254. [PMID: 26028144 PMCID: PMC4458878 DOI: 10.1038/ncomms8254] [Citation(s) in RCA: 69] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Accepted: 04/21/2015] [Indexed: 11/09/2022] Open
Abstract
The actin nodule is a novel F-actin structure present in platelets during early spreading. However, only limited detail is known regarding nodule organization and function. Here we use electron microscopy, SIM and dSTORM super-resolution, and live-cell TIRF microscopy to characterize the structural organization and signalling pathways associated with nodule formation. Nodules are composed of up to four actin-rich structures linked together by actin bundles. They are enriched in the adhesion-related proteins talin and vinculin, have a central core of tyrosine phosphorylated proteins and are depleted of integrins at the plasma membrane. Nodule formation is dependent on Wiskott–Aldrich syndrome protein (WASp) and the ARP2/3 complex. WASp−/− mouse blood displays impaired platelet aggregate formation at arteriolar shear rates. We propose actin nodules are platelet podosome-related structures required for platelet–platelet interaction and their absence contributes to the bleeding diathesis of Wiskott–Aldrich syndrome. During early platelet spreading a novel F-actin structure forms, called the actin nodule. Here Poulter et al. demonstrate that actin nodule formation depends on WASp and the Arp2/3 complex, and using super-resolution microscopy they show that nodules bear a structural resemblance to podosomes.
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Affiliation(s)
- Natalie S Poulter
- Centre for Cardiovascular Sciences, The Medical School, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
| | - Alice Y Pollitt
- Centre for Cardiovascular Sciences, The Medical School, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
| | - Amy Davies
- PSIBS doctoral training centre, School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
| | - Dessislava Malinova
- Molecular Immunology Unit, UCL Institute of Child Health, 30 Guilford Street, London WC1N 1EH, UK
| | - Gerard B Nash
- Centre for Cardiovascular Sciences, The Medical School, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
| | - Mike J Hannon
- PSIBS doctoral training centre, School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
| | - Zoe Pikramenou
- School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
| | - Joshua Z Rappoport
- The Center for Advanced Microscopy and Nikon Imaging Center, Morton 2-681, Northwestern University Feinberg School of Medicine, 303 E. Chicago Avenue, Chicago, Illinois 60611, USA
| | - John H Hartwig
- Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA
| | - Dylan M Owen
- Randall Division of Cell and Molecular Biophysics, New Hunt's House, King's College London, Guy's Campus, London SE1 1UL, UK
| | - Adrian J Thrasher
- Molecular Immunology Unit, UCL Institute of Child Health, 30 Guilford Street, London WC1N 1EH, UK
| | - Stephen P Watson
- Centre for Cardiovascular Sciences, The Medical School, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
| | - Steven G Thomas
- Centre for Cardiovascular Sciences, The Medical School, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
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18
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VAMP-7 links granule exocytosis to actin reorganization during platelet activation. Blood 2015; 126:651-60. [PMID: 25999457 DOI: 10.1182/blood-2014-12-618744] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2014] [Accepted: 05/09/2015] [Indexed: 01/30/2023] Open
Abstract
Platelet activation results in profound morphologic changes accompanied by release of granule contents. Recent evidence indicates that fusion of granules with the plasma membrane during activation provides auxiliary membrane to cover growing actin structures. Yet little is known about how membrane fusion is coupled with actin reorganization. Vesicle-associated membrane protein (VAMP)-7 is found on platelet vesicles and possesses an N-terminal longin domain capable of linking exocytosis to cytoskeletal remodeling. We have evaluated platelets from VAMP-7(-/-) mice to determine whether this VAMP isoform contributes to granule release and platelet spreading. VAMP-7(-/-) platelets demonstrated a partial defect in dense granule exocytosis and impaired aggregation. α Granule exocytosis from VAMP-7(-/-) platelets was diminished both in vitro and in vivo during thrombus formation. Consistent with a role of VAMP-7 in cytoskeletal remodeling, spreading on matrices was decreased in VAMP-7(-/-) platelets compared to wild-type controls. Immunoprecipitation of VAMP-7 revealed an association with VPS9-domain ankyrin repeat protein (VARP), an adaptor protein that interacts with both membrane-bound and cytoskeleton proteins and with Arp2/3. VAMP-7, VARP, and Arp2/3 localized to the platelet periphery during spreading. These studies demonstrate that VAMP-7 participates in both platelet granule secretion and spreading and suggest a mechanism whereby VAMP-7 links granule exocytosis with actin reorganization.
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19
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FlnA binding to PACSIN2 F-BAR domain regulates membrane tubulation in megakaryocytes and platelets. Blood 2015; 126:80-8. [PMID: 25838348 DOI: 10.1182/blood-2014-07-587600] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2014] [Accepted: 03/30/2015] [Indexed: 11/20/2022] Open
Abstract
Bin-Amphiphysin-Rvs (BAR) and Fes-CIP4 homology BAR (F-BAR) proteins generate tubular membrane invaginations reminiscent of the megakaryocyte (MK) demarcation membrane system (DMS), which provides membranes necessary for future platelets. The F-BAR protein PACSIN2 is one of the most abundant BAR/F-BAR proteins in platelets and the only one reported to interact with the cytoskeletal and scaffold protein filamin A (FlnA), an essential regulator of platelet formation and function. The FlnA-PACSIN2 interaction was therefore investigated in MKs and platelets. PACSIN2 associated with FlnA in human platelets. The interaction required FlnA immunoglobulin-like repeat 20 and the tip of PACSIN2 F-BAR domain and enhanced PACSIN2 F-BAR domain membrane tubulation in vitro. Most human and wild-type mouse platelets had 1 to 2 distinct PACSIN2 foci associated with cell membrane GPIbα, whereas Flna-null platelets had 0 to 4 or more foci. Endogenous PACSIN2 and transfected enhanced green fluorescent protein-PACSIN2 were concentrated in midstage wild-type mouse MKs in a well-defined invagination of the plasma membrane reminiscent of the initiating DMS and dispersed in the absence of FlnA binding. The DMS appeared less well defined, and platelet territories were not readily visualized in Flna-null MKs. We conclude that the FlnA-PACSIN2 interaction regulates membrane tubulation in MKs and platelets and likely contributes to DMS formation.
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20
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Roll, adhere, spread and contract: structural mechanics of platelet function. Eur J Cell Biol 2015; 94:129-38. [PMID: 25655000 DOI: 10.1016/j.ejcb.2015.01.001] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2014] [Revised: 12/26/2014] [Accepted: 01/07/2015] [Indexed: 12/31/2022] Open
Abstract
Platelets are involved in life-sustaining processes such as hemostasis, wound healing, atherothrombosis and angiogenesis. Mechanical trauma to blood vessels causes platelet activation resulting in their adherence and clot formation at the damaged site, culminating in clot retraction and tissue repair. Two of the major players underlying this process are the cytoskeleton, i.e., actin and microtubules, and the membrane integrin receptors. Rare congenital bleeding disorders such as Glanzmann thrombasthenia and Bernard-Soulier syndrome are associated with genetic alterations of platelet surface receptors, also affecting the platelet cytoskeletal structure. In this review, we summarize the current knowledge about platelet structure and adhesion, and delve into the mechanical aspects of platelet function. Platelets lack a nucleus, and can thus provide a minimal model of a biological cell. New biophysical tools may help to scrutinize platelets anew and to extend the existing knowledge on cell biology.
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21
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Kim H, Falet H, Hoffmeister KM, Hartwig JH. Wiskott-Aldrich syndrome protein (WASp) controls the delivery of platelet transforming growth factor-β1. J Biol Chem 2013; 288:34352-63. [PMID: 24133214 DOI: 10.1074/jbc.m113.459750] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Platelets are immunologically competent cells containing cytokines such as TGF-β1 that regulate cell-mediated immunity. However, the mechanisms underlying cytokine secretion from platelets are undefined. The Wiskott-Aldrich syndrome protein (WASp) regulates actin polymerization in nucleated hematopoietic cells but has other role(s) in platelets. WASp-null (WASp(-/-)) platelets stimulated with a PAR-4 receptor agonist had increased TGF-β1 release compared with WT platelets; inhibiting WASp function with wiskostatin augmented TRAP-induced TGF-β1 release in human platelets. TGF-β1 release is dissociated from α-granule secretion (P-selectin up-regulation) and occurs more gradually, with ∼10-15% released after 30-60 min. Blockade of Src family kinase-mediated WASp Tyr-291/Tyr-293 phosphorylation increased TGF-β1 release, with no additive effect in WASp(-/-) platelets, signifying that phosphorylation is critical for WASp-limited TGF-β1 secretion. Inhibiting F-actin assembly with cytochalasin D enhanced secretion in WT platelets and further increased TGF-β1 release in WASp(-/-) platelets, indicating that WASp and actin assembly independently regulate TGF-β1 release. A permeabilized platelet model was used to test the role of upstream small GTPases in TGF-β1 release. N17Cdc42, but not Rac1 mutants, increased TGF-β1 secretion and abrogated WASp phosphorylation. We conclude that WASp function restricts TGF-β1 secretion in a Cdc42- and Src family kinase-dependent manner and independently of actin assembly.
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Affiliation(s)
- Hugh Kim
- From the Division of Translational Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts 02115
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22
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Abstract
The Rho family of GTP binding proteins, also commonly referred to as the Rho GTPases, are master regulators of the platelet cytoskeleton and platelet function. These low-molecular-weight or 'small' GTPases act as signaling switches in the spatial and temporal transduction, and amplification of signals from platelet cell surface receptors to the intracellular signaling pathways that drive platelet function. The Rho GTPase family members RhoA, Cdc42 and Rac1 have emerged as key regulators in the dynamics of the actin cytoskeleton in platelets and play key roles in platelet aggregation, secretion, spreading and thrombus formation. Rho GTPase regulators, including GEFs and GAPs and downstream effectors, such as the WASPs, formins and PAKs, may also regulate platelet activation and function. In this review, we provide an overview of Rho GTPase signaling in platelet physiology. Previous studies of Rho GTPases and platelets have had a shared history, as platelets have served as an ideal, non-transformed cellular model to characterize Rho function. Likewise, recent studies of the cell biology of Rho GTPase family members have helped to build an understanding of the molecular regulation of platelet function and will continue to do so through the further characterization of Rho GTPases as well as Rho GAPs, GEFs, RhoGDIs and Rho effectors in actin reorganization and other Rho-driven cellular processes.
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Affiliation(s)
- J E Aslan
- Department of Biomedical Engineering and Cell & Developmental Biology, School of Medicine, Oregon Health & Science University, Portland, OR 97239, USA.
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23
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24
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Mouneimne G, Hansen SD, Selfors LM, Petrak L, Hickey MM, Gallegos LL, Simpson KJ, Lim J, Gertler FB, Hartwig JH, Mullins RD, Brugge JS. Differential remodeling of actin cytoskeleton architecture by profilin isoforms leads to distinct effects on cell migration and invasion. Cancer Cell 2012; 22:615-30. [PMID: 23153535 PMCID: PMC3500527 DOI: 10.1016/j.ccr.2012.09.027] [Citation(s) in RCA: 118] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/25/2012] [Revised: 09/06/2012] [Accepted: 09/28/2012] [Indexed: 01/17/2023]
Abstract
Dynamic actin cytoskeletal reorganization is integral to cell motility. Profilins are well-characterized regulators of actin polymerization; however, functional differences among coexpressed profilin isoforms are not well defined. Here, we demonstrate that profilin-1 and profilin-2 differentially regulate membrane protrusion, motility, and invasion; these processes are promoted by profilin-1 and suppressed by profilin-2. Compared to profilin-1, profilin-2 preferentially drives actin polymerization by the Ena/VASP protein, EVL. Profilin-2 and EVL suppress protrusive activity and cell motility by an actomyosin contractility-dependent mechanism. Importantly, EVL or profilin-2 downregulation enhances invasion in vitro and in vivo. In human breast cancer, lower EVL expression correlates with high invasiveness and poor patient outcome. We propose that profilin-2/EVL-mediated actin polymerization enhances actin bundling and suppresses breast cancer cell invasion.
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Affiliation(s)
- Ghassan Mouneimne
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115
| | - Scott D. Hansen
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, CA 94158
| | - Laura M. Selfors
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115
| | - Lara Petrak
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115
| | - Michele M. Hickey
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115
| | - Lisa L. Gallegos
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115
| | - Kaylene J. Simpson
- Victorian Centre for Functional Genomics, Peter MacCallum Cancer Centre, East Melbourne, 3002
- Sir Peter MacCallum Department of Oncology, University of Melbourne, Parkville, 3050
| | - James Lim
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115
| | - Frank B. Gertler
- The Koch Institute for integrative Cancer Research at MIT, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - John H. Hartwig
- Division of Translational Medicine at Brigham and Women’s Hospital, Harvard Medical School, Boston, MA 02115
| | - R. Dyche Mullins
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, CA 94158
| | - Joan S. Brugge
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115
- Corresponding author: , Phone: 617 432 3974, Fax: 617 432 3969
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25
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Delaney MK, Liu J, Zheng Y, Berndt MC, Du X. The role of Rac1 in glycoprotein Ib-IX-mediated signal transduction and integrin activation. Arterioscler Thromb Vasc Biol 2012; 32:2761-8. [PMID: 22995516 DOI: 10.1161/atvbaha.112.254920] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
OBJECTIVE The platelet receptor for von Willebrand factor, the glycoprotein Ib-IX (GPIb-IX) complex, mediates platelet adhesion at sites of vascular injury and transmits signals leading to platelet activation. von Willebrand factor/GPIb-IX interaction sequentially activates the Src family kinase Lyn (SFK), phosphoinositide 3-kinase (PI3K), and Akt, leading to activation of integrin α(IIb)β(3) and integrin-dependent stable platelet adhesion and aggregation. It remains unclear how Lyn activates the PI3K/Akt pathway after ligand binding to GPIb-IX. METHODS AND RESULTS Using platelet-specific Rac1(-/-) mice and the Rac1 inhibitor NSC23766, we examined the role of Rac1 in GPIb-IX-dependent platelet activation. Rac1(-/-) mouse platelets and NSC23766-treated human platelets were defective in GPIb-dependent stable adhesion to von Willebrand factor under shear stress, integrin activation, thromboxane A(2) synthesis, and platelet aggregation. Interestingly, GPIb-induced activation of Rac1 and the guanine nucleotide exchange factor for Rac1, Vav, was abolished in both Lyn(-/-) and SFK inhibitor-treated platelets but was unaffected by the PI3K inhibitor LY294002, indicating that Lyn mediates activation of Vav and Rac1 independently of PI3K. Furthermore, GPIb-induced activation of Akt was abolished in Rac1-deficient platelets, suggesting that Rac1 is upstream of the PI3K/Akt pathway. CONCLUSIONS A Lyn-Vav-Rac1-PI3K-Akt pathway mediates von Willebrand factor-induced activation of integrin α(IIb)β(3) to promote GPIb-IX-dependent platelet activation.
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Affiliation(s)
- M Keegan Delaney
- Department of Pharmacology, University of Illinois College of Medicine, 835 South Wolcott Ave, Chicago, IL 60612, USA
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26
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Abstract
Platelet (PLT) production represents the final stage of megakaryocyte (MK) development. During differentiation, bone marrow MKs extend and release long, branched proPLTs into sinusoidal blood vessels, which undergo repeated abscissions to yield circulating PLTs. Circular-prePLTs are dynamic intermediate structures in this sequence that have the capacity to reversibly convert into barbell-proPLTs and may be related to "young PLTs" and "large PLTs" of both inherited and acquired macrothrombocytopenias. Conversion is regulated by the diameter and thickness of the peripheral microtubule coil, and PLTs are capable of enlarging in culture to generate barbell-proPLTs that divide to yield 2 smaller PLT products. Because PLT number and size are inversely proportional, this raises the question: do macrothrombocytopenias represent a failure in the intermediate stages of PLT production? This review aims to bring together and contextualize our current understanding of terminal PLT production against the backdrop of human macrothrombocytopenias to establish how "large PLTs" observed in both conditions are similar, how they are different, and what they can teach us about PLT formation. A better understanding of the cytoskeletal mechanisms that regulate PLT formation and determine PLT size offers the promise of improved therapies for clinical disorders of PLT production and an important source of PLTs for infusion.
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27
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Penzes P, Cahill ME. Deconstructing signal transduction pathways that regulate the actin cytoskeleton in dendritic spines. Cytoskeleton (Hoboken) 2012; 69:426-41. [PMID: 22307832 DOI: 10.1002/cm.21015] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2011] [Revised: 01/29/2012] [Accepted: 01/30/2012] [Indexed: 11/10/2022]
Abstract
Dendritic spines are the sites of most excitatory synapses in the central nervous system. Recent studies have shown that spines function independently of each other, and they are currently the smallest known processing units in the brain. Spines exist in an array of morphologies, and spine structure helps dictate synaptic function. Dendritic spines are rich in actin, and actin rearrangements are critical regulators of spine morphology and density. In this review, we discuss the importance of actin in regulating dendritic spine morphogenesis, and discuss the upstream signal transduction pathways that either foster or inhibit actin polymerization. The understanding of actin regulatory pathways is best conceptualized as a hierarchical network in which molecules function in discrete levels defined by their molecular distance to actin. To this end, we focus on several classes of molecules, including guanine nucleotide exchange factors, small GTPases, small GTPase effectors, and actin binding proteins. We discuss how individual proteins in these molecular classes impact spine morphogenesis, and reveal the biochemical interactions in these networks that are responsible for shaping actin polymerization. Finally, we discuss the importance of these actin regulatory pathways in neuropsychiatric disorders.
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Affiliation(s)
- Peter Penzes
- Department of Physiology, Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA.
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28
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Chen CL, Lin YP, Lai YC, Chen HC. α-Adducin translocates to the nucleus upon loss of cell-cell adhesions. Traffic 2011; 12:1327-40. [PMID: 21736685 DOI: 10.1111/j.1600-0854.2011.01245.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The F-actin binding protein adducin plays an important role in plasma membrane stability, cell motility and cell-cell junctions. In this study, we demonstrate that α-adducin is mainly localized in the nucleus of sparsely cultured epithelial cells, whereas it is localized at cell-cell junctions when the cells are grown to confluence. Disruption of cell-cell adhesions induces a nuclear translocation of α-adducin. Conversely, α-adducin is redistributed to the cytoplasm and cell-cell junctions in the process of establishing cell-cell adhesions. We identify that α-adducin contains a bipartite nuclear localization signal (NLS) in its COOH-terminal tail domain and a nuclear export signal in its neck region. The phosphorylation of α-adducin at Ser716 that is immediately adjacent to the NLS appears to antagonize the function of the NLS. Moreover, we show that depletion of α-adducin has adverse effects on cell-cell adhesions and, to our surprise, cell proliferation. The impaired cell proliferation is associated with mitotic defects characterized by disorganized mitotic spindles, aberrant chromosomal congregation/segregation and abnormal centrosomes. Taken together, our results not only reveal the mechanism for α-adducin to shuttle between the cytoplasm and nucleus, but also highlight a potential role for α-adducin in mitosis.
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Affiliation(s)
- Chien-Lin Chen
- Department of Life Sciences, National Chung Hsing University, Taichung, Taiwan
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29
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Falet H, Pollitt AY, Begonja AJ, Weber SE, Duerschmied D, Wagner DD, Watson SP, Hartwig JH. A novel interaction between FlnA and Syk regulates platelet ITAM-mediated receptor signaling and function. ACTA ACUST UNITED AC 2010; 207:1967-79. [PMID: 20713593 PMCID: PMC2931168 DOI: 10.1084/jem.20100222] [Citation(s) in RCA: 94] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Filamin A (FlnA) cross-links actin filaments and connects the Von Willebrand factor receptor GPIb-IX-V to the underlying cytoskeleton in platelets. Because FlnA deficiency is embryonic lethal, mice lacking FlnA in platelets were generated by breeding FlnAloxP/loxP females with GATA1-Cre males. FlnAloxP/y GATA1-Cre males have a macrothrombocytopenia and increased tail bleeding times. FlnA-null platelets have decreased expression and altered surface distribution of GPIbα because they lack the normal cytoskeletal linkage of GPIbα to underlying actin filaments. This results in ∼70% less platelet coverage on collagen-coated surfaces at shear rates of 1,500/s, compared with wild-type platelets. Unexpectedly, however, immunoreceptor tyrosine-based activation motif (ITAM)- and ITAM-like–mediated signals are severely compromised in FlnA-null platelets. FlnA-null platelets fail to spread and have decreased α-granule secretion, integrin αIIbβ3 activation, and protein tyrosine phosphorylation, particularly that of the protein tyrosine kinase Syk and phospholipase C–γ2, in response to stimulation through the collagen receptor GPVI and the C-type lectin-like receptor 2. This signaling defect was traced to the loss of a novel FlnA–Syk interaction, as Syk binds to FlnA at immunoglobulin-like repeat 5. Our findings reveal that the interaction between FlnA and Syk regulates ITAM- and ITAM-like–containing receptor signaling and platelet function.
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Affiliation(s)
- Hervé Falet
- Division of Translational Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA.
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30
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Abstract
Recent advances in structural, biochemical, biophysical, and live cell imaging approaches have furthered our understanding of the molecular mechanisms by which regulated assembly dynamics of actin filaments drive motile processes. Attention is focused on lamellipodium protrusion, powered by the turnover of a branched filament array. ATP hydrolysis on actin is the key reaction that allows filament treadmilling. It regulates barbed-end dynamics and length fluctuations at steady state and specifies the functional interaction of actin with essential regulatory proteins such as profilin and ADF/cofilin. ATP hydrolysis on actin and Arp2/3 acts as a timer, regulating the assembly and disassembly of the branched array to generate tropomyosin-mediated heterogeneity in the structure and dynamics of the lamellipodial network. The detailed molecular mechanisms of ATP hydrolysis/Pi release on F-actin remain elusive, as well as the mechanism of filament branching with Arp2/3 complex or that of the formin-driven processive actin assembly. Novel biophysical methods involving single-molecule measurements should foster progress in these crucial issues.
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Affiliation(s)
- Beáta Bugyi
- Cytoskeleton Dynamics and Cell Motility Group, CNRS, UPR 3082, Laboratoire d'Enzymologie et Biochimie Structurales, 91198 Gif-sur-Yvette, France
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31
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Frantz C, Barreiro G, Dominguez L, Chen X, Eddy R, Condeelis J, Kelly MJS, Jacobson MP, Barber DL. Cofilin is a pH sensor for actin free barbed end formation: role of phosphoinositide binding. ACTA ACUST UNITED AC 2008; 183:865-79. [PMID: 19029335 PMCID: PMC2592832 DOI: 10.1083/jcb.200804161] [Citation(s) in RCA: 154] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Newly generated actin free barbed ends at the front of motile cells provide sites for actin filament assembly driving membrane protrusion. Growth factors induce a rapid biphasic increase in actin free barbed ends, and we found both phases absent in fibroblasts lacking H(+) efflux by the Na-H exchanger NHE1. The first phase is restored by expression of mutant cofilin-H133A but not unphosphorylated cofilin-S3A. Constant pH molecular dynamics simulations and nuclear magnetic resonance (NMR) reveal pH-sensitive structural changes in the cofilin C-terminal filamentous actin binding site dependent on His133. However, cofilin-H133A retains pH-sensitive changes in NMR spectra and severing activity in vitro, which suggests that it has a more complex behavior in cells. Cofilin activity is inhibited by phosphoinositide binding, and we found that phosphoinositide binding is pH-dependent for wild-type cofilin, with decreased binding at a higher pH. In contrast, phosphoinositide binding by cofilin-H133A is attenuated and pH insensitive. These data suggest a molecular mechanism whereby cofilin acts as a pH sensor to mediate a pH-dependent actin filament dynamics.
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Affiliation(s)
- Christian Frantz
- Department of Cell and Tissue Biology, University of California, San Francisco, CA 94143, USA
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32
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Chhabra ES, Higgs HN. The many faces of actin: matching assembly factors with cellular structures. Nat Cell Biol 2008; 9:1110-21. [PMID: 17909522 DOI: 10.1038/ncb1007-1110] [Citation(s) in RCA: 542] [Impact Index Per Article: 33.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Actin filaments are major components of at least 15 distinct structures in metazoan cells. These filaments assemble from a common pool of actin monomers, but do so at different times and places, and in response to different stimuli. All of these structures require actin-filament assembly factors. To date, many assembly factors have been identified, including Arp2/3 complex, multiple formin isoforms and spire. Now, a major task is to figure out which factors assemble which actin-based structures. Here, we focus on structures at the plasma membrane, including both sheet-like protrusive structures (such as lamellipodia and ruffles) and finger-like protrusions (such as filopodia and microvilli). Insights gained from studies of adherens junctions and the immunological synapse are also considered.
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Affiliation(s)
- Ekta Seth Chhabra
- Department of Biochemistry, Dartmouth Medical School, Hanover, NH 03755, USA
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Akbar H, Kim J, Funk K, Cancelas JA, Shang X, Chen L, Johnson JF, Williams DA, Zheng Y. Genetic and pharmacologic evidence that Rac1 GTPase is involved in regulation of platelet secretion and aggregation. J Thromb Haemost 2007; 5:1747-55. [PMID: 17663742 DOI: 10.1111/j.1538-7836.2007.02646.x] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
BACKGROUND Rac1 GTPase, a member of the Ras-related Rho GTPase family, is the major Rac isoform present in platelets and has been shown to be involved in cell actin cytoskeleton reorganization and adhesion. Agonists that induce platelet secretion and aggregation also activate Rac1 GTPase, raising the possibility that Rac1 GTPase may be involved in regulation of platelet function. OBJECTIVES To rigorously define the role of Rac1 in platelet regulation. METHODS We have used a dual approach of gene targeting in mice and pharmacologic inhibition of Rac1 by NSC23766, a rationally designed specific small molecule inhibitor, to study the role of Rac1 in platelet function. RESULTS Platelets from mice as well as human platelets treated with NSC23766 exhibited a significant decrease in: (i) active Rac1 species and phosphorylation of the Rac effector, p21-activated kinase; (ii) expression of P-selectin and secretion of adenosine triphosphate induced by thrombin or U46619; and (iii) aggregation induced by adenosine 5'-diphosphate, collagen, thrombin and U46619, a stable analog of thromboxane A(2). NSC23766 did not alter the cAMP or cGMP levels in platelets. Consistent with the requirement of Rac1 for normal platelet function, the bleeding times in Rac1(-/-) mice or mice given NSC23766 were significantly prolonged. CONCLUSIONS Our data show that deficiency or inhibition of Rac1 GTPase blocks platelet secretion. The inhibition of secretion, at least in part, is responsible for diminished platelet aggregation and prolonged bleeding times observed in Rac1 knockout or Rac1 inhibitor-treated mice.
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Affiliation(s)
- H Akbar
- Division of Experimental Hematology, Cincinnati Children's Research Foundation, University of Cincinnati, Cincinnati, OH, USA
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34
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Chan MWC, Arora PD, McCulloch CA. Cyclosporin inhibition of collagen remodeling is mediated by gelsolin. Am J Physiol Cell Physiol 2007; 293:C1049-58. [PMID: 17615162 DOI: 10.1152/ajpcell.00027.2007] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cyclosporin A (CsA) inhibits collagen remodeling by interfering with the collagen-binding step of phagocytosis. In rapidly remodeling connective tissues such as human periodontium this interference manifests as marked tissue overgrowth and loss of function. Previous data have shown that CsA inhibits integrin-induced release of Ca(2+) from internal stores, which is required for the binding step of collagen phagocytosis. Because gelsolin is a Ca(2+)-dependent actin-severing protein that mediates collagen phagocytosis, we determined whether gelsolin is a CsA target. Compared with vehicle controls, CsA treatment of wild-type mice increased collagen accumulation by 60% in periodontal tissues; equivalent increases were seen in vehicle-treated gelsolin-null mice. Collagen degradation by phagocytosis in cultured gelsolin wild-type fibroblasts was blocked by CsA, comparable to levels of vehicle-treated gelsolin-null fibroblasts. In wild-type cells treated with CsA, collagen binding was similar to that of gelsolin-null fibroblasts transfected with a gelsolin-severing mutant and treated with vehicle. CsA blocked collagen-induced Ca(2+) fluxes subjacent to bound collagen beads, gelsolin recruitment, and actin assembly at bead sites. CsA reduced gelsolin-dependent severing of actin in wild-type cells to levels similar to those in gelsolin-null fibroblasts. We conclude that CsA-induced accumulation of collagen in the extracellular matrix involves disruption of the actin-severing properties of gelsolin, thereby inhibiting the binding step of collagen phagocytosis.
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Affiliation(s)
- Marie-France Carlier
- Cytoskeleton Dynamics and Motility Group, Laboratoire d'Enzymologie et Biochimie Structurale, CNRS, Gif-sur-Yvette 91198, France.
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36
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Bindschadler M, McGrath JL. Relationships between actin regulatory mechanisms and measurable state variables. Ann Biomed Eng 2007; 35:995-1011. [PMID: 17380395 DOI: 10.1007/s10439-007-9267-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2006] [Accepted: 01/25/2007] [Indexed: 12/24/2022]
Abstract
In this report we extend our recent mathematical formulation of the actin cycle model [Bindschadler et al. Biophys. J. 86 (2004) 2720] to predict the influence of key regulatory mechanisms on network-scale state variables estimable in live cell experiments. Specifically, we examine the influence of regulation by cofilin, profilin, capping protein and proteins that adjust filament number through nucleation and/or filament severing, on the higher order variables of average filament length, polymer fraction, and filament turnover rate. Importantly, we find that severing/nucleation, the acceleration of ADP-subunit disassembly by cofilin, and the catalytic and shuttle functions of profilin have 'signature' effects on the higher order state variables. In this way, measurement of the state variables in live cells can allow inference of regulatory mechanism(s) underlying changes in cell state. Our results compare favorably to published data for endothelial cells undergoing a transition from non-motile confluent cells to highly motile subconfluent cells. The extension of our model to higher order state variables allows us to investigate other important issues such as the distinction between basic and higher order measures of filament dynamics, the influence of thymosin beta4 on network state variables, the interplay between thymosin beta4 and profilin, and the synergystic effects of cofilin and profilin.
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Affiliation(s)
- Michael Bindschadler
- Department of Biomedical Engineering, University of Rochester, Rochester, NY 14642, USA
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37
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Chen CL, Hsieh YT, Chen HC. Phosphorylation of adducin by protein kinase Cdelta promotes cell motility. J Cell Sci 2007; 120:1157-67. [PMID: 17341583 DOI: 10.1242/jcs.03408] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Protein kinase Cdelta (PKCdelta) has been implicated to play a crucial role in cell proliferation, differentiation and apoptosis. In this study, we have investigated the role of PKCdelta in cell motility using Madin-Darby canine kidney cells. Overexpression of PKCdelta promoted membrane protrusions, concomitant with increased cell motility. By contrast, suppression of PKCdelta expression by RNA interference inhibited cell motility. Moreover, a fraction of PKCdelta was detected at the edge of membrane protrusions in which it colocalized with adducin, a membrane skeletal protein whose phosphorylation state is important for remodeling of the cortical actin cytoskeleton. Elevated expression of PKCdelta correlated with increased phosphorylation of adducin at Ser726 in intact cells. In vitro, PKCdelta, but not PKCalpha, directly phosphorylated the Ser726 of adducin. Finally, we demonstrated that overexpression of both adducin and PKCdelta could generate a synergistic effect on promoting cell spreading and cell migration. Our results support a positive role for PKCdelta in cell motility and strongly suggest a link between PKCdelta activity, adducin phosphorylation and cell motility.
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Affiliation(s)
- Chien-Lin Chen
- Department of Life Science and the Graduate Institute of Biomedical Sciences, National Chung Hsing University, Taichung 40227, Taiwan
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Calaminus SD, McCarty OJ, Auger JM, Pearce AC, Insall RH, Watson SP, Machesky LM. A major role for Scar/WAVE-1 downstream of GPVI in platelets. J Thromb Haemost 2007; 5:535-41. [PMID: 17319906 PMCID: PMC1880834 DOI: 10.1111/j.1538-7836.2007.02377.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
BACKGROUND The small GTPase Rac1 plays a critical role in lamellipodia assembly in platelets on matrix proteins in the absence or presence of G protein-coupled receptor (GPCR) agonists. Rac mediates actin assembly via Scar/WAVE, a family of scaffolding proteins that direct actin reorganization by relaying signals from Rac to the Arp2/3 complex. OBJECTIVE To evaluate the role of Scar/WAVE-1 in mediating platelet activation and cytoskeletal reorganization. METHODS AND RESULTS Using specific antibodies, we demonstrate that murine platelets, like human platelets, express Scar/WAVE-1 and Scar/WAVE-2. Lamellipodia formation in Scar/WAVE-1(-/-) platelets is markedly inhibited on immobilized collagen-related peptide (CRP) and on laminin, both of which signal through the collagen receptor GPVI. In contrast, lamellipodia formation on collagen, which requires release of the GPCR agonists ADP and thromboxane A(2), is not altered. Immobilized fibrinogen supports limited formation of lamellipodia in murine platelets, which is not altered in Scar/WAVE-1(-/-) platelets. As with Rac1(-/-) platelets, Scar/WAVE-1(-/-) platelets exhibit a marked inhibition of aggregation in response to CRP, whereas the response to the GPCR agonist thrombin is not altered. Platelet aggregation on immobilized collagen under shear, which is dependent on signaling by matrix and GPCR agonists, was unaltered in the absence of Scar/WAVE-1. CONCLUSION This study demonstrates a major role for Scar/WAVE-1 in mediating platelet cytoskeletal reorganization and aggregate formation downstream of activation by GPVI but not by GPCR agonists.
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Affiliation(s)
- Simon D.J. Calaminus
- Centre for Cardiovascular Sciences, Institute of Biomedical Research, The Medical School, University of Birmingham, Birmingham B15 2TT, UK
| | - Owen J.T. McCarty
- Centre for Cardiovascular Sciences, Institute of Biomedical Research, The Medical School, University of Birmingham, Birmingham B15 2TT, UK
- Department of Biomedical Engineering, Oregon Health & Science University, Portland, OR 97239, USA
| | - Jocelyn M. Auger
- Centre for Cardiovascular Sciences, Institute of Biomedical Research, The Medical School, University of Birmingham, Birmingham B15 2TT, UK
| | - Andrew C. Pearce
- Centre for Cardiovascular Sciences, Institute of Biomedical Research, The Medical School, University of Birmingham, Birmingham B15 2TT, UK
| | - Robert H. Insall
- School of Biosciences, University of Birmingham, Birmingham B15 2TT, UK
| | - Steve P. Watson
- Centre for Cardiovascular Sciences, Institute of Biomedical Research, The Medical School, University of Birmingham, Birmingham B15 2TT, UK
| | - Laura M. Machesky
- School of Biosciences, University of Birmingham, Birmingham B15 2TT, UK
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El Sayegh TY, Kapus A, McCulloch CA. Beyond the epithelium: Cadherin function in fibrous connective tissues. FEBS Lett 2007; 581:167-74. [PMID: 17217950 DOI: 10.1016/j.febslet.2006.12.029] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2006] [Revised: 12/04/2006] [Accepted: 12/12/2006] [Indexed: 11/18/2022]
Abstract
In fibrous connective tissues, fibroblasts are organized into syncytia, cellular networks that enable matrix remodeling and that are interconnected by intercellular adherens junctions (AJs). The AJs of fibroblasts are mediated by N-cadherin, a broadly expressed classical cadherin that is critically involved in developmental processes, wound healing and several diseases of mesenchymal tissues. In contrast to E-cadherin-dependent junctions of epithelia, the formation of AJs in fibrous connective tissues is relatively uncharacterized. Work over the last several years has documented an expanding list of molecules which function to regulate N-cadherin mediated junctions such as: Fer, PTP1B, cortactin, calcium, gelsolin, PIP5KIgamma, PIP2, and the Rho family of GTPases. We present an overview on the regulation of N-cadherin-mediated junction formation that highlights recent molecular advances in the field and rationalizes the roles of N-cadherin in connective tissue function.
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Affiliation(s)
- T Y El Sayegh
- CIHR Group in Matrix Dynamics, University of Toronto, Room 243, Fitzgerald Building, 150 College Street, Toronto, Ont., Canada M5S 3E2.
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Ono S. Mechanism of depolymerization and severing of actin filaments and its significance in cytoskeletal dynamics. INTERNATIONAL REVIEW OF CYTOLOGY 2007; 258:1-82. [PMID: 17338919 DOI: 10.1016/s0074-7696(07)58001-0] [Citation(s) in RCA: 212] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The actin cytoskeleton is one of the major structural components of the cell. It often undergoes rapid reorganization and plays crucial roles in a number of dynamic cellular processes, including cell migration, cytokinesis, membrane trafficking, and morphogenesis. Actin monomers are polymerized into filaments under physiological conditions, but spontaneous depolymerization is too slow to maintain the fast actin filament dynamics observed in vivo. Gelsolin, actin-depolymerizing factor (ADF)/cofilin, and several other actin-severing/depolymerizing proteins can enhance disassembly of actin filaments and promote reorganization of the actin cytoskeleton. This review presents advances as well as a historical overview of studies on the biochemical activities and cellular functions of actin-severing/depolymerizing proteins.
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Affiliation(s)
- Shoichiro Ono
- Department of Pathology, Emory University, Atlanta, GA 30322, USA
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42
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Dawes AT, Edelstein-Keshet L. Phosphoinositides and Rho proteins spatially regulate actin polymerization to initiate and maintain directed movement in a one-dimensional model of a motile cell. Biophys J 2006; 92:744-68. [PMID: 17098793 PMCID: PMC1779977 DOI: 10.1529/biophysj.106.090514] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Gradient sensing, polarization, and chemotaxis of motile cells involve the actin cytoskeleton, and regulatory modules, including the phosphoinositides (PIs), their kinases/phosphatases, and small GTPases (Rho proteins). Here we model their individual components (PIP1, PIP2, PIP3; PTEN, PI3K, PI5K; Cdc42, Rac, Rho; Arp2/3, and actin), their interconversions, interactions, and modular functions in the context of a one-dimensional dynamic model for protrusive cell motility, with parameter values derived from in vitro and in vivo studies. In response to a spatially graded stimulus, the model produces stable amplified internal profiles of regulatory components, and initiates persistent motility (consistent with experimental observations). By connecting the modules, we find that Rho GTPases work as a spatial switch, and that the PIs filter noise, and define the front versus back. Relatively fast PI diffusion also leads to selection of a unique pattern of Rho distribution from a collection of possible patterns. We use the model to explore the importance of specific hypothesized interactions, to explore mutant phenotypes, and to study the role of actin polymerization in the maintenance of the PI asymmetry. We also suggest a mechanism to explain the spatial exclusion of Cdc42 and PTEN and the inability of cells lacking active Cdc42 to properly detect chemoattractant gradients.
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Affiliation(s)
- Adriana T Dawes
- Institute of Applied Mathematics and Department of Mathematics, University of British Columbia, Vancouver, British Columbia, Canada.
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43
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Abstract
The cellular functions of the actin cytoskeleton require precise regulation of both the initiation of actin polymerization and the organization of the resulting filaments. The actin-related protein-2/3 (ARP2/3) complex is a central player in this regulation. A decade of study has begun to shed light on the molecular mechanisms by which this powerful machine controls the polymerization, organization and recycling of actin-filament networks, both in vitro and in the living cell.
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Affiliation(s)
- Erin D Goley
- Department of Molecular and Cell Biology, University of California, Berkeley, California 94720, USA
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44
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Shao D, Forge A, Munro PMG, Bailly M. Arp2/3 complex-mediated actin polymerisation occurs on specific pre-existing networks in cells and requires spatial restriction to sustain functional lamellipod extension. ACTA ACUST UNITED AC 2006; 63:395-414. [PMID: 16619224 PMCID: PMC7611918 DOI: 10.1002/cm.20131] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The classical Arp2/3-mediated dendritic network defines the cytoskeleton at the leading edge of crawling cells, and it is generally assumed that Arp2/3-mediated actin polymerization generates the force necessary to extend lamellipods. Our previous work suggested that successful lamellipod extension required not only free barbed ends for actin polymerization but also a proper ultrastructural organization of the cytoskeleton. To further explore the structural role of the Arp2/3 complex-mediated networks in lamellipod morphology and function, we performed a detailed analysis of the ultrastructure of the Arp2/3-mediated networks, using the WA domains of Scar and WASp to generate mislocalised Arp2/3 networks in vivo, and to reconstruct de novo Arp2/3-mediated actin nucleation and polymerization on extracted cytoskeletons. We present here evidence that spatially unrestricted Arp2/3-mediated networks are intrinsically three-dimensional and multilayered by nature and, as such, cannot sustain significant polarized extension. Furthermore, such networks polymerize only at preferred locations in extracted cells, corresponding to pre-existing Arp2/3 networks, suggesting that the specific molecular organization of the actin cytoskeleton, in terms of structure and/or biochemical composition, dictates the location of Arp2/3 complex-mediated actin polymerization. We propose that successful lamellipod extension depends not only on localized actin polymerization mediated through local signalling, but also on spatial restriction of the Arp2/3 complex-mediated nucleation of actin polymerization, both in terms of location within the cell and ultrastructural organization of the resulting network.
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Affiliation(s)
- D Shao
- Division of Cell Biology, UCL Institute of Ophthalmology, London, United Kingdom
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Marée AFM, Jilkine A, Dawes A, Grieneisen VA, Edelstein-Keshet L. Polarization and Movement of Keratocytes: A Multiscale Modelling Approach. Bull Math Biol 2006; 68:1169-211. [PMID: 16794915 DOI: 10.1007/s11538-006-9131-7] [Citation(s) in RCA: 151] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2005] [Accepted: 03/31/2006] [Indexed: 02/05/2023]
Abstract
Eukariotic cell motility is a complex phenomenon, in which the cytoskeleton and its major constituent, actin, play an essential role. Actin forms polymers of long, stiff filaments that are cross-linked into an anisotropic network inside a thin sheet-like cellular protrusion, the lamellipod. At the leading edge of this structure, polymerization of actin filaments creates the force that pushes out the membrane and leads to translocation of a motile cell. Dynamics of the actin network account for changes in cell shape, crawling motion and turning of the cell in response to external cues. Regulating the dynamics of the cytoskeleton, and playing a central role in signal transduction in the cell, are Cdc42, Rac and Rho (GTPases of the rho family, collectively known as the small G-proteins) and the actin nucleating complex, Arp2/3. In this paper, we use a multiscale modelling approach in a 2D model of a motile cell. We describe the mutual interactions of the small G-proteins, and their effects on capping and side-branching of actin filaments. We incorporate the pushing exerted by oriented actin filament ends on the cell edge, and a Rho-dependent contraction force. Combining these biochemical and mechanical aspects, we investigate the dynamics of a model epidermal fish keratocyte through in silico experiments. Our model gives insight into how, in response to some cue, a cell can polarize, form a leading edge, and move; concomitantly it explains how a keratocyte cell can maintain its shape and polarity, even after removal of the initial stimulus, and how it can change direction quickly in response to changes in its environment. We show that establishment of polarity stems from interactions of Cdc42, Rac and Rho, while maintenance and robustness of polarity is due to the rapid cytosolic diffusion of the inactive (GDI-bound) forms of the small G-proteins. Our model produces a cell shape that closely resembles the keratocytes and correct speeds for biologically reasonable parameter values. Movies of the simulations can be obtained from http://theory.bio.uu.nl/stan/keratocyte.
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Affiliation(s)
- Athanasius F M Marée
- Theoretical Biology/Bioinformatics, Utrecht University, Utrecht, The Netherlands.
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Abstract
Platelets are small subcellular fragments that are released from megakaryocytes. They are composed of a concentrate of megakaryocyte membrane, cytoplasm, granules, and organelles, and circulate throughout blood vessels and survey the integrity of the vascular system. They circulate as discs, a form specified by their internal microtubule and actin cytoskeleton. When encountering vascular damage, platelets rapidly convert into their active forms, which function to seal off the injury and prevent fluid loss. To assume the active shape, the internal cytoskeleton of each platelet is rapidly disassembled and replaced. New actin filament assembly provides the force that spreads platelets across damaged surfaces and allows the formation of filopodia, which are used to interconnect platelets in solution. In this review, we discuss the role of the cytoskeleton in defining the resting and active forms of the platelet.
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Affiliation(s)
- John H Hartwig
- Division of Hematology, Karp Family Research Laboratories, Brigham and Women's Hospital, Boston, MA 02115, USA.
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Actin filament branching and protrusion velocity in a simple 1D model of a motile cell. J Theor Biol 2006; 242:265-79. [PMID: 16600307 DOI: 10.1016/j.jtbi.2006.02.017] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2005] [Revised: 02/17/2006] [Accepted: 02/22/2006] [Indexed: 11/19/2022]
Abstract
We formulate and analyse a 1D model for the spatial distribution of actin density at the leading edge of a motile cell. The model incorporates nucleation, capping, growth and decay of actin filaments, as well as retrograde flow of the actin meshwork and known parameter values based on the literature. Using a simplified geometry, and reasonable assumptions about the biochemical processes, we derive PDEs for the density of actin filaments and their tips. Analytic travelling wave solutions are used to predict how the speed of the cell depends on rates of nucleation, capping, polymerization and membrane resistance. Analysis and simulations agree with experimental profiles for measured actin distributions. Extended versions of the model are studied numerically. We find that our model produces stable travelling wave solutions with reasonable cell speeds. Increasing the rate of nucleation of filaments (by the actin related protein Arp2/3) or the rate of actin polymerization leads to faster cell speed, whereas increasing the rate of capping or the membrane resistance reduces cell speed. We consider several variants of nucleation (spontaneous, tip, and side branching) and find best agreement with experimentally measured spatial profiles of filament and tip density in the side branching case.
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McCarty OJT, Larson MK, Auger JM, Kalia N, Atkinson BT, Pearce AC, Ruf S, Henderson RB, Tybulewicz VLJ, Machesky LM, Watson SP. Rac1 is essential for platelet lamellipodia formation and aggregate stability under flow. J Biol Chem 2005; 280:39474-84. [PMID: 16195235 PMCID: PMC1395485 DOI: 10.1074/jbc.m504672200] [Citation(s) in RCA: 179] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The role of Rac family proteins in platelet spreading on matrix proteins under static and flow conditions has been investigated by using Rac-deficient platelets. Murine platelets form filopodia and undergo limited spreading on fibrinogen independent of Rac1 and Rac2. In the presence of thrombin, marked lamellipodia formation is observed on fibrinogen, which is abrogated in the absence of Rac1. However, Rac1 is not required for thrombin-induced aggregation or elevation of F-actin levels. Formation of lamellipodia on collagen and laminin is also Rac1-dependent. Analysis of platelet adhesion dynamics on collagen under flow conditions in vitro revealed that Rac1 is required for platelet aggregate stability at arterial rates of shear, as evidenced by a dramatic increase in platelet embolization. Furthermore, studies employing intravital microscopy demonstrated that Rac1 plays a critical role in the development of stable thrombi at sites of vascular injury in vivo. Thus, our data demonstrated that Rac1 is essential for lamellipodia formation in platelets and indicated that Rac1 is required for aggregate integrity leading to thrombus formation under physiologically relevant levels of shear both in vitro and in vivo.
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Affiliation(s)
- Owen J T McCarty
- Centre for Cardiovascular Sciences, the Institute of Biomedical Research, School of Biosciences, University of Birmingham, United Kingdom.
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Di Nardo A, Cicchetti G, Falet H, Hartwig JH, Stossel TP, Kwiatkowski DJ. Arp2/3 complex-deficient mouse fibroblasts are viable and have normal leading-edge actin structure and function. Proc Natl Acad Sci U S A 2005; 102:16263-8. [PMID: 16254049 PMCID: PMC1283463 DOI: 10.1073/pnas.0508228102] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
RNA interference silencing of up to 90% of Arp3 protein expression, a major subunit of the Arp2/3 complex, proportionately decreases the intracellular motility of Listeria monocytogenes and actin nucleation activity ascribable to the Arp2/3 complex in mouse embryonic fibroblasts. However, the Arp2/3-deficient cells exhibit unimpaired lamellipodial actin network structure, translational locomotion, spreading, actin assembly, and ruffling responses. In addition, Arp3-silenced cells expressing neural Wiskott-Aldrich syndrome protein-derived peptides that inhibit Arp2/3 complex function in wild-type cells retained normal PDGF-induced ruffling. The Arp2/3 complex can be dispensable for leading-edge actin remodeling.
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Affiliation(s)
- Alessia Di Nardo
- Division of Hematology, Brigham and Women's Hospital, and Department of Medicine, Harvard Medical School, One Blackfan Circle, Boston, MA 02115, USA
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Falet H, Chang G, Brohard-Bohn B, Rendu F, Hartwig JH. Integrin αIIbβ3signals lead cofilin to accelerate platelet actin dynamics. Am J Physiol Cell Physiol 2005; 289:C819-25. [PMID: 15901596 DOI: 10.1152/ajpcell.00587.2004] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Cofilin, in its Ser3 dephosphorylated form, accelerates actin filament turnover in cells. We report here the role of cofilin in platelet actin assembly. Cofilin is primarily phosphorylated in the resting platelet as evidenced by a specific antibody directed against its Ser3 phosphorylated form. After stimulation with thrombin under nonstirring conditions, cofilin is reversibly dephosphorylated and transiently incorporates into the actin cytoskeleton. Its dephosphorylation is maximal 1–2 min after platelet stimulation, shortly after the peak of actin assembly occurs. Cofilin rephosphorylation begins 2 min after activation and exceeds resting levels by 5–10 min. Cofilin is dephosphorylated with identical kinetics but fails to become rephosphorylated when platelets are stimulated under stirring conditions. Cofilin is normally rephosphorylated when platelets are stimulated in the presence of Arg-Gly-Asp-Ser (RGDS) peptide or wortmannin to block αIIbβ3cross-linking and signaling or in platelets isolated from a patient with Glanzmann thrombasthenia, which express only 2–3% of normal αIIbβ3levels. Furthermore, actin assembly and Arp2/3 complex incorporation in the platelet actin cytoskeleton are decreased when αIIbβ3is engaged. Our results suggest that cofilin is essential for actin dynamics mediated by outside-in signals in activated platelets.
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Affiliation(s)
- Hervé Falet
- Division of Hematology, Brigham and Women's Hospital, Department of Medicine, Harvard Medical School, One Blackfan Circle, Karp 6, Boston, Massachusetts 02115, USA.
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