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Wang C, Sample KM, Gajendran B, Kapranov P, Liu W, Hu A, Zacksenhaus E, Li Y, Hao X, Ben-David Y. FLI1 Induces Megakaryopoiesis Gene Expression Through WAS/WIP-Dependent and Independent Mechanisms; Implications for Wiskott-Aldrich Syndrome. Front Immunol 2021; 12:607836. [PMID: 33717090 PMCID: PMC7953068 DOI: 10.3389/fimmu.2021.607836] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2020] [Accepted: 01/19/2021] [Indexed: 12/12/2022] Open
Abstract
Wiskott–Aldrich Syndrome, WAS/WAVE, is a rare, X-linked immune-deficiency disease caused by mutations in the WAS gene, which together with its homolog, N-WASP, regulates actin cytoskeleton remodeling and cell motility. WAS patients suffer from microthrombocytopenia, characterized by a diminished number and size of platelets, though the underlying mechanism is not fully understood. Here, we identified FLI1 as a direct transcriptional regulator of WAS and its binding partner WIP. Depletion of either WAS or WIP in human erythroleukemic cells accelerated cell proliferation, suggesting tumor suppressor function of both genes in leukemia. Depletion of WAS/WIP also led to a significant reduction in the percentage of CD41 and CD61 positive cells, which mark committed megakaryocytes. RNAseq analysis revealed common changes in megakaryocytic gene expression following FLI1 or WASP knockdown. However, in contrast to FLI1, WASP depletion did not alter expression of late-stage platelet-inducing genes. N-WASP was not regulated by FLI1, yet its silencing also reduced the percentage of CD41+ and CD61+ megakaryocytes. Moreover, combined knockdown of WASP and N-WASP further suppressed megakaryocyte differentiation, indicating a major cooperation of these related genes in controlling megakaryocytic cell fate. However, unlike WASP/WIP, N-WASP loss suppressed leukemic cell proliferation. WASP, WIP and N-WASP depletion led to induction of FLI1 expression, mediated by GATA1, and this may mitigate the severity of platelet deficiency in WAS patients. Together, these results uncover a crucial role for FLI1 in megakaryocyte differentiation, implicating this transcription factor in regulating microthrombocytopenia associated with Wiskott–Aldrich syndrome.
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Affiliation(s)
- Chunlin Wang
- State Key Laboratory for Functions and Applications of Medicinal Plants, Guizhou Medical University, Guiyang, China.,The Key Laboratory of Chemistry for Natural Products of Guizhou Province and Chinese Academic of Sciences, Guiyang, China
| | - Klarke M Sample
- The National Health Commission's Key Laboratory of Immunological Pulmonary Disease, Guizhou Provincial People's Hospital, The Affiliated Hospital of Guizhou University, Guiyang, China
| | - Babu Gajendran
- State Key Laboratory for Functions and Applications of Medicinal Plants, Guizhou Medical University, Guiyang, China.,The Key Laboratory of Chemistry for Natural Products of Guizhou Province and Chinese Academic of Sciences, Guiyang, China
| | - Philipp Kapranov
- School of Biomedical Sciences, Institute of Genomics, Huaqiao University, Xiamen, China
| | - Wuling Liu
- State Key Laboratory for Functions and Applications of Medicinal Plants, Guizhou Medical University, Guiyang, China.,The Key Laboratory of Chemistry for Natural Products of Guizhou Province and Chinese Academic of Sciences, Guiyang, China
| | - Anling Hu
- State Key Laboratory for Functions and Applications of Medicinal Plants, Guizhou Medical University, Guiyang, China.,The Key Laboratory of Chemistry for Natural Products of Guizhou Province and Chinese Academic of Sciences, Guiyang, China
| | - Eldad Zacksenhaus
- Department of Medicine, University of Toronto, Toronto, ON, Canada.,Division of Advanced Diagnostics, Toronto General Research Institute-University Health Network, Toronto, ON, Canada
| | - Yanmei Li
- State Key Laboratory for Functions and Applications of Medicinal Plants, Guizhou Medical University, Guiyang, China.,The Key Laboratory of Chemistry for Natural Products of Guizhou Province and Chinese Academic of Sciences, Guiyang, China
| | - Xiaojiang Hao
- State Key Laboratory for Functions and Applications of Medicinal Plants, Guizhou Medical University, Guiyang, China.,The Key Laboratory of Chemistry for Natural Products of Guizhou Province and Chinese Academic of Sciences, Guiyang, China
| | - Yaacov Ben-David
- State Key Laboratory for Functions and Applications of Medicinal Plants, Guizhou Medical University, Guiyang, China.,The Key Laboratory of Chemistry for Natural Products of Guizhou Province and Chinese Academic of Sciences, Guiyang, China
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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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Molecular difference between WASP and N-WASP critical for chemotaxis of T-cells towards SDF-1α. Sci Rep 2015; 5:15031. [PMID: 26463123 PMCID: PMC4604493 DOI: 10.1038/srep15031] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2015] [Accepted: 08/26/2015] [Indexed: 11/13/2022] Open
Abstract
Wiskott-Aldrich Syndrome protein (WASP) integrates cell signaling pathways to the actin cytoskeleton, which play a critical role in T-cell activation and migration. Hematopoietic cells express both WASP and neural-WASP (N-WASP) which share similar domain structure, yet WASP deficiency causes Wiskott-Aldrich syndrome, suggesting that N-WASP present in the cells is not able to carry out all the functions of WASP. We have identified a unique internal thirty amino acid region (I30) in WASP, which regulates its function in chemotaxis of Jurkat T-cells. Deletion of the I30 region altered the WASP’s closed conformation and impaired its ability to rescue the chemotactic defect of WASP-deficient (JurkatWKD) T-cells. Expression of N-WASP in JurkatWKD T-cells using WASP promoter restored the migration velocity without correcting the chemotactic defect. However, insertion of I30 region in N-WASP (N-WASP-I30) enabled N-WASP to rescue the chemotactic defect of JurkatWKD T-cells. N-WASP-I30-EGFP displayed a punctate localization in contrast to the predominant nuclear localization of N-WASP-EGFP. Thus, our study has demonstrated that the I30 region of WASP is critical for localization and chemotaxis. This suggests that N-WASP’s failure to compensate for WASP in rescuing chemotaxis could be due to the absence of this I30 region.
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Matalon O, Reicher B, Barda-Saad M. Wiskott-Aldrich syndrome protein - dynamic regulation of actin homeostasis: from activation through function and signal termination in T lymphocytes. Immunol Rev 2013; 256:10-29. [DOI: 10.1111/imr.12112] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Affiliation(s)
- Omri Matalon
- The Mina and Everard Goodman Faculty of Life Sciences; Bar-Ilan University; Ramat-Gan Israel
| | - Barak Reicher
- The Mina and Everard Goodman Faculty of Life Sciences; Bar-Ilan University; Ramat-Gan Israel
| | - Mira Barda-Saad
- The Mina and Everard Goodman Faculty of Life Sciences; Bar-Ilan University; Ramat-Gan Israel
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Emir S, Vezir E, Azkur D, Demir HA, Metin A. Characteristics of children with non-hodgkin lymphoma associated with primary immune deficiency diseases: descriptions of five patients. Pediatr Hematol Oncol 2013; 30:544-53. [PMID: 23647505 DOI: 10.3109/08880018.2013.792893] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
BACKGROUND An increased incidence of non-Hodgkin lymphoma (NHL) has been seen in various primary immune deficiency (PID) cases. The present study aimed to evaluate the clinical characteristics and treatment outcomes of five cases with NHL associated with primary immunodeficiency. METHODS We retrospectively evaluated five patients with primary immunodeficiency who developed NHL. Two patients had ataxia-telangiectasia (A-T), one patient had common variable immunodeficiency (CVID), one patient had Bloom's Syndrome, and one patient had Wiskott-Aldrich syndrome (WAS). RESULTS All patients were male (median age, 8 years). Stage distribution was stage III in three patients and stage IV in two patients. Three patients had B-cell lymphoma and two had T-cell lymphoma. Reduced doses of Berlin-Frankfurt-Münster (BFM) and French Society of Pediatric Oncology (SFOP) regimens were used in four patients according to histopathological subtype. The two patients with ataxia and one patient with Bloom's Syndrome died of progressive/relapsed disease at months 5, 19, and 6, respectively. The patient with CVID associated with T-cell lymphoma has been in remission for 7 years. A full-dosage regimen of rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) was successfully used in the patient with WAS and B-cell lymphoma; he was still in remission after 3 years. CONCLUSION Primary immunodeficiency diseases are one of the strongest known risk factors for the development of NHL. Management of these patients remains problematic. There is a great need to develop new therapeutic approaches in this group. The use of rituximab in combination with CHOP may provide a promising treatment option for B-cell lymphomas associated with immunodeficiency.
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Affiliation(s)
- Suna Emir
- Department of Pediatric Hematology Oncology, SB Ankara Children's Hematology Oncology Education and Research Hospital, Ankara, Turkey.
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6
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T-cell receptor ligation causes Wiskott-Aldrich syndrome protein degradation and F-actin assembly downregulation. J Allergy Clin Immunol 2013; 132:648-655.e1. [PMID: 23684068 DOI: 10.1016/j.jaci.2013.03.046] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2013] [Revised: 03/28/2013] [Accepted: 03/29/2013] [Indexed: 11/23/2022]
Abstract
BACKGROUND Wiskott-Aldrich syndrome protein (WASP) links T-cell receptor (TCR) signaling to the actin cytoskeleton. WASP is normally protected from degradation by the Ca(++)-dependent protease calpain and by the proteasome because of its interaction with the WASP-interacting protein. OBJECTIVE We investigated whether WASP is degraded after TCR ligation and whether its degradation downregulates F-actin assembly caused by TCR ligation. METHODS Primary T cells, Jurkat T cells, and transfected 293T cells were used in immunoprecipitation experiments. Intracellular F-actin content was measured in splenic T cells from wild-type, WASP-deficient, and c-Casitas B-lineage lymphoma (Cbl)-b-deficient mice by using flow cytometry. Calpeptin and MG-132 were used to inhibit calpain and the proteasome, respectively. RESULTS A fraction of WASP in T cells was degraded by calpain and by the ubiquitin-proteasome pathway after TCR ligation. The Cbl-b and c-Cbl E3 ubiquitin ligases associated with WASP after TCR signaling and caused its ubiquitination. Inhibition of calpain and lack of Cbl-b resulted in a significantly more sustained increase in F-actin content after TCR ligation in wild-type T cells but not in WASP-deficient T cells. CONCLUSION TCR ligation causes WASP to be degraded by calpain and to be ubiquitinated by Cbl family E3 ligases, which targets it for destruction by the proteasome. WASP degradation might provide a mechanism for regulating WASP-dependent TCR-driven assembly of F-actin.
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Massaad MJ, Ramesh N, Geha RS. Wiskott-Aldrich syndrome: a comprehensive review. Ann N Y Acad Sci 2013; 1285:26-43. [DOI: 10.1111/nyas.12049] [Citation(s) in RCA: 229] [Impact Index Per Article: 20.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
- Michel J. Massaad
- Division of Immunology, Boston Children's Hospital, and Department of Pediatrics; Harvard Medical School; Boston; Massachusetts
| | - Narayanaswamy Ramesh
- Division of Immunology, Boston Children's Hospital, and Department of Pediatrics; Harvard Medical School; Boston; Massachusetts
| | - Raif S. Geha
- Division of Immunology, Boston Children's Hospital, and Department of Pediatrics; Harvard Medical School; Boston; Massachusetts
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8
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Toscano MG, Anderson P, Muñoz P, Lucena G, Cobo M, Benabdellah K, Gregory PD, Holmes MC, Martin F. Use of zinc-finger nucleases to knock out the WAS gene in K562 cells: a human cellular model for Wiskott-Aldrich syndrome. Dis Model Mech 2013; 6:544-54. [PMID: 23324327 PMCID: PMC3597037 DOI: 10.1242/dmm.010652] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Mutations in the WAS gene cause Wiskott-Aldrich syndrome (WAS), which is characterized by eczema, immunodeficiency and microthrombocytopenia. Although the role of WASP in lymphocytes and myeloid cells is well characterized, its role on megakaryocyte (MK) development is poorly understood. In order to develop a human cellular model that mimics the megakaryocytic-derived defects observed in WAS patients we used K562 cells, a well-known model for study of megakaryocytic development. We knocked out the WAS gene in K562 cells using a zinc-finger nuclease (ZFN) pair targeting the WAS intron 1 and a homologous donor DNA that disrupted WASP expression. Knockout of WASP on K562 cells (K562WASKO cells) resulted in several megakaryocytic-related defects such as morphological alterations, lower expression of CD41ɑ, lower increments in F-actin polymerization upon stimulation, reduced CD43 expression and increased phosphatidylserine exposure. All these defects have been previously described either in WAS-knockout mice or in WAS patients, validating K562WASKO as a cell model for WAS. However, K562WASPKO cells showed also increased basal F-actin and adhesion, increased expression of CD61 and reduced expression of TGFβ and Factor VIII, defects that have never been described before for WAS-deficient cells. Interestingly, these phenotypic alterations correlate with different roles for WASP in megakaryocytic differentiation. All phenotypic alterations observed in K562WASKO cells were alleviated upon expression of WAS following lentiviral transduction, confirming the role of WASP in these phenotypes. In summary, in this work we have validated a human cellular model, K562WASPKO, that mimics the megakaryocytic-related defects found in WAS-knockout mice and have found evidences for a role of WASP as regulator of megakaryocytic differentiation. We propose the use of K562WASPKO cells as a tool to study the molecular mechanisms involved in the megakaryocytic-related defects observed in WAS patients and as a cellular model to study new therapeutic strategies.
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Affiliation(s)
- Miguel G Toscano
- Human DNA Variability Department, GENYO, Centre for Genomics and Oncological Research, Pfizer-University of Granada-Andalusian Regional Government, Parque Tecnológico Ciencias de la Salud, Av. de la Ilustracion 114, 18007 Granada, Spain
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9
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Ubiquitylation-dependent negative regulation of WASp is essential for actin cytoskeleton dynamics. Mol Cell Biol 2012; 32:3153-63. [PMID: 22665495 DOI: 10.1128/mcb.00161-12] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Wiskott-Aldrich syndrome protein (WASp) is a key regulator of actin dynamics during cell motility and adhesion, and mutations in its gene are responsible for Wiskott-Aldrich syndrome (WAS). Here, we demonstrate that WASp is ubiquitylated following T-cell antigen receptor (TCR) activation. WASp phosphorylation at tyrosine 291 results in recruitment of the E3 ligase Cbl-b, which, together with c-Cbl, carries out WASp ubiquitylation. Lysine residues 76 and 81, located at the WASp WH1 domain, which contains the vast majority of WASp gene mutations, serve as the ubiquitylation sites. Disruption of WASp ubiquitylation causes WASp accumulation and alters actin dynamics and the formation of actin-dependent structures. Our data suggest that regulated degradation of activated WASp might be an efficient strategy by which the duration and localization of actin rearrangement and the intensity of T-cell activation are controlled.
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10
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Dovas A, Cox D. Regulation of WASp by phosphorylation: Activation or other functions? Commun Integr Biol 2011; 3:101-5. [PMID: 20585499 DOI: 10.4161/cib.3.2.10759] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2009] [Accepted: 11/28/2009] [Indexed: 11/19/2022] Open
Abstract
Wiskott-Aldrich Syndrome protein (WASp) is an actin nucleation-promoting factor that regulates actin polymerisation via the Arp2/3 complex. Its mutation in human syndromes has led to extensive studies on the regulation and activities of this molecule. Several mechanisms for the regulation of WASp activity have been proposed, however, the role of tyrosine phosphorylation remains controversial, particularly due to inconsistencies between results obtained through biochemical and cell biological approaches. In this mini-review, we are addressing the major aspects of WASp regulation with an emphasis on the role of tyrosine phosphorylation on WASp activities.
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Isaac BM, Ishihara D, Nusblat LM, Gevrey JC, Dovas A, Condeelis J, Cox D. N-WASP has the ability to compensate for the loss of WASP in macrophage podosome formation and chemotaxis. Exp Cell Res 2010; 316:3406-16. [PMID: 20599953 DOI: 10.1016/j.yexcr.2010.06.011] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2010] [Revised: 06/09/2010] [Accepted: 06/10/2010] [Indexed: 10/24/2022]
Abstract
Wiskott-Aldrich syndrome protein (WASP) and its homologue neural-WASP (N-WASP) are nucleation promoting factors that integrate receptor signaling with actin cytoskeleton rearrangement. While hematopoietic cells express both WASP and N-WASP, WASP deficiency results in altered cell morphology, loss of podosomes and defective chemotaxis. It was determined that cells from a mouse derived monocyte/macrophage cell line and primary cells of myeloid lineage expressed approximately 15-fold higher levels of WASP relative to N-WASP. To test whether N-WASP can compensate for the loss of WASP and restore actin cytoskeleton integrity, N-WASP was overexpressed in macrophages, in which endogenous WASP expression was reduced by short hairpin RNA (shWASP cells). Many of the defects associated with the loss of WASP, such as podosome-dependent matrix degradation and chemotaxis were corrected when N-WASP was expressed at equimolar level to that of the wild-type WASP. Furthermore, the ability of N-WASP to partially compensate for the loss of WASP may be physiologically relevant since activated murine WASP-deficient peritoneal macrophages, which show enhanced N-WASP expression, also show an increase in matrix degradation. Our study suggests that expression levels of WASP and N-WASP may influence their roles in actin cytoskeleton rearrangement and shed light to the complex intertwining roles WASP and N-WASP play in macrophages.
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Affiliation(s)
- Beth M Isaac
- Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
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12
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CALLE Y, ANTÓN I, THRASHER A, JONES G. WASP and WIP regulate podosomes in migrating leukocytes. J Microsc 2008; 231:494-505. [DOI: 10.1111/j.1365-2818.2008.02062.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
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Eto K, Nishikii H, Ogaeri T, Suetsugu S, Kamiya A, Kobayashi T, Yamazaki D, Oda A, Takenawa T, Nakauchi H. The WAVE2/Abi1 complex differentially regulates megakaryocyte development and spreading: implications for platelet biogenesis and spreading machinery. Blood 2007; 110:3637-47. [PMID: 17664349 DOI: 10.1182/blood-2007-04-085860] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Abstract
Actin polymerization is crucial in throm-bopoiesis, platelet adhesion, and mega-karyocyte (MK) and platelet spreading. The Wiskott-Aldrich syndrome protein (WASp) homolog WAVE functions downstream of Rac and plays a pivotal role in lamellipodia formation. While MKs and platelets principally express WAVE1 and WAVE2, which are associated with Abi1, the physiologic significance of WAVE isoforms remains undefined. We generated WAVE2−/− embryonic stem (ES) cells because WAVE2-null mice die by embryonic day (E) 12.5. We found that while WAVE2−/− ES cells differentiated into immature MKs on OP9 stroma, they were severely impaired in terminal differentiation and in platelet production. WAVE2−/− MKs exhibited a defect in peripheral lamellipodia on fibrinogen even with phorbol 12-myristate 13-acetate (PMA) costimulation, indicating a requirement of WAVE2 for integrin αIIbβ3-mediated full spreading. MKs in which expression of Abi1 was reduced by small interfering RNA (siRNA) exhibited striking similarity to WAVE2−/− MKs in maturation and spreading. Interestingly, the knockdown of IRSp53, a Rac effector that preferentially binds to WAVE2, impaired the development of lamellipodia without affecting proplatelet production. In contrast, thrombopoiesis in vivo and platelet spreading on fibrinogen in vitro were intact in WAVE1-null mice. These observations clarify indispensable roles for the WAVE2/Abi1 complex in αIIbβ3-mediated lamellipodia by MKs and platelets through Rac and IRSp53, and additionally in thrombopoiesis independent of Rac and IRSp53.
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Affiliation(s)
- Koji Eto
- Laboratory of Stem Cell Therapy, Center for Experimental Medicine, The Institute of Medical Science, University of Tokyo, Japan.
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Lutskiy MI, Shcherbina A, Bachli ET, Cooley J, Remold-O'Donnell E. WASP localizes to the membrane skeleton of platelets. Br J Haematol 2007; 139:98-105. [PMID: 17854313 DOI: 10.1111/j.1365-2141.2007.06745.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
Patients with Wiskott-Aldrich syndrome (WAS), an X-linked blood cell disease, suffer from severe thrombocytopenia due to accelerated loss of defective platelets. The affected gene encodes WASP, an actin regulatory protein thought to reside in the cytoplasm of resting leucocytes. In contrast, this study showed that, for platelets, one-quarter of WASP molecules fractionate in the detergent-insoluble high speed pellet characterized as the membrane skeleton, the scaffold structure that underlies the lipid bilayer and stabilizes the surface membrane. Following treatment of platelets with thrombin and stirring, which induces cytoarchitectural remodelling, WASP and other membrane skeletal components sedimented at lower g force and partitioned in the low-speed pellet. Thrombin and stirring also induced WASP tyrosine phosphorylation, a rapid activating reaction, and proteolytic inactivation by cysteine protease calpain. Both the alteration of the sedimentation profile and the proteolytic inactivation were specific for the membrane skeletal pool of WASP and were abrogated in alphaIIb beta3 integrin-deficient platelets and in normal platelets treated with an integrin antagonist. The findings demonstrate that WASP is a component of the resting platelet membrane skeleton and participates in membrane skeletal rearrangements downstream of integrin outside-in signalling. The possible implications for the platelet defect in WAS are discussed.
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Affiliation(s)
- Maxim I Lutskiy
- The CBR Institute for Biomedical Research and the Department of Pediatrics, Harvard Medical School, Boston, MA 02115, USA
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15
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Hallett MB, Dewitt S. Ironing out the wrinkles of neutrophil phagocytosis. Trends Cell Biol 2007; 17:209-14. [DOI: 10.1016/j.tcb.2007.03.002] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2006] [Revised: 02/06/2007] [Accepted: 03/02/2007] [Indexed: 11/29/2022]
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16
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Dewitt S, Hallett M. Leukocyte membrane "expansion": a central mechanism for leukocyte extravasation. J Leukoc Biol 2007; 81:1160-4. [PMID: 17360954 DOI: 10.1189/jlb.1106710] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
The infiltration of inflamed tissues by leukocytes is a key event in the development and progression of inflammation. Although individual cytokines, which coordinate extravasation, have become the targets for therapy, a mechanism that is common to white cell extravasation, regardless of the specific molecular mechanism involved, would represent a more attractive therapeutic target. Such a target may be represented by the events underlying the spreading of leukocytes on the endothelium, which is a necessary prelude to extravasation. This leukocyte "spreading" involves an apparent increase in the cell surface area. The aim of this review is to examine whether the mechanism underlying the apparent expansion of plasma membrane surface area during leukocyte extravasation could be an "Achilles' heel," which is amenable to therapeutic intervention. In this short review, we evaluate the models proposed for the mechanism of membrane "expansion" and discuss recent data, which point to a mechanism of membrane "unwrinkling." The molecular pathway for the unwrinkling of the leukocyte plasma membrane may involve Ca2+ activation of mu-calpain and cleavage of cytoskeletal linkage molecules such as talin and ezrin. This route could be common to all extravasation signals and thus, represents a potential target for anti-inflammatory therapy.
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Affiliation(s)
- Sharon Dewitt
- Neutrophil Signalling Group, School of Medicine, Cardiff University, Heath Park, Cardiff, CF14 4XN, UK
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17
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Chou HC, Antón IM, Holt MR, Curcio C, Lanzardo S, Worth A, Burns S, Thrasher AJ, Jones GE, Calle Y. WIP regulates the stability and localization of WASP to podosomes in migrating dendritic cells. Curr Biol 2007; 16:2337-44. [PMID: 17141616 PMCID: PMC1885947 DOI: 10.1016/j.cub.2006.10.037] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2006] [Revised: 09/29/2006] [Accepted: 10/03/2006] [Indexed: 11/21/2022]
Abstract
The Wiskott-Aldrich Syndrome protein (WASP) is an adaptor protein that is essential for podosome formation in hematopoietic cells [1]. Given that 80% of identified Wiskott-Aldrich Syndrome patients result from mutations in the binding site for WASP-interacting-protein (WIP) [2], we examined the possible role of WIP in the regulation of podosome architecture and cell motility in dendritic cells (DCs). Our results show that WIP is essential both for the formation of actin cores containing WASP and cortactin and for the organization of integrin and integrin-associated proteins in circular arrays, specific characteristics of podosome structure. We also found that WIP is essential for the maintenance of the high turnover of adhesions and polarity in DCs. WIP exerts these functions by regulating calpain-mediated cleavage of WASP and by facilitating the localization of WASP to sites of actin polymerization at podosomes. Taken together, our results indicate that WIP is critical for the regulation of both the stability and localization of WASP in migrating DCs and suggest that WASP and WIP operate as a functional unit to control DC motility in response to changes in the extracellular environment.
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Affiliation(s)
- Hsiu-Chuan Chou
- Randall Division of Cell & Molecular Biophysics, King's College London, London SE1 1UL, United Kingdom
| | - Inés M. Antón
- Centro de Biología Molecular “Severo Ochoa”, CSIC-UAM, 28049 Madrid, Spain
| | - Mark R. Holt
- Randall Division of Cell & Molecular Biophysics, King's College London, London SE1 1UL, United Kingdom
| | - Claudia Curcio
- Department of Clinical and Biological Sciences, University of Turin, 10043 Orbassano, Turin, Italy
| | - Stefania Lanzardo
- Department of Clinical and Biological Sciences, University of Turin, 10043 Orbassano, Turin, Italy
| | - Austen Worth
- Molecular Immunology Unit, Institute of Child Health, University College London, London and GOSH NHS Trust WC1 1EH, United Kingdom
| | - Siobhan Burns
- Molecular Immunology Unit, Institute of Child Health, University College London, London and GOSH NHS Trust WC1 1EH, United Kingdom
| | - Adrian J. Thrasher
- Molecular Immunology Unit, Institute of Child Health, University College London, London and GOSH NHS Trust WC1 1EH, United Kingdom
| | - Gareth E. Jones
- Randall Division of Cell & Molecular Biophysics, King's College London, London SE1 1UL, United Kingdom
- Corresponding author
| | - Yolanda Calle
- Randall Division of Cell & Molecular Biophysics, King's College London, London SE1 1UL, United Kingdom
- Corresponding author
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18
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de la Fuente MA, Sasahara Y, Calamito M, Antón IM, Elkhal A, Gallego MD, Suresh K, Siminovitch K, Ochs HD, Anderson KC, Rosen FS, Geha RS, Ramesh N. WIP is a chaperone for Wiskott-Aldrich syndrome protein (WASP). Proc Natl Acad Sci U S A 2007; 104:926-31. [PMID: 17213309 PMCID: PMC1783416 DOI: 10.1073/pnas.0610275104] [Citation(s) in RCA: 121] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2006] [Indexed: 11/18/2022] Open
Abstract
Wiskott-Aldrich syndrome protein (WASP) is in a complex with WASP-interacting protein (WIP). WASP levels, but not mRNA levels, were severely diminished in T cells from WIP(-/-) mice and were increased by introduction of WIP in these cells. The WASP binding domain of WIP was shown to protect WASP from degradation by calpain in vitro. Treatment with the proteasome inhibitors MG132 and bortezomib increased WASP levels in T cells from WIP(-/-) mice and in T and B lymphocytes from two WAS patients with missense mutations (R86H and T45M) that disrupt WIP binding. The calpain inhibitor calpeptin increased WASP levels in activated T and B cells from the WASP patients, but not in primary T cells from the patients or from WIP(-/-) mice. Despite its ability to increase WASP levels proteasome inhibition did not correct the impaired IL-2 gene expression and low F-actin content in T cells from the R86H WAS patient. These results demonstrate that WIP stabilizes WASP and suggest that it may also be important for its function.
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Affiliation(s)
- Miguel A. de la Fuente
- *Division of Immunology, Children's Hospital Boston, and
- Department of Pediatrics, Harvard Medical School, Boston, MA 02115
| | - Yoji Sasahara
- *Division of Immunology, Children's Hospital Boston, and
- Department of Pediatrics, Harvard Medical School, Boston, MA 02115
| | - Marco Calamito
- *Division of Immunology, Children's Hospital Boston, and
| | - Inés M. Antón
- Centro de Biologia Molecular “Severo Ochoa,” CS IC, Universidad Autonoma de Madrid, 29049 Madrid, Spain
| | - Abdallah Elkhal
- *Division of Immunology, Children's Hospital Boston, and
- Department of Pediatrics, Harvard Medical School, Boston, MA 02115
| | - Maria D. Gallego
- *Division of Immunology, Children's Hospital Boston, and
- Department of Pediatrics, Harvard Medical School, Boston, MA 02115
| | - Koduru Suresh
- *Division of Immunology, Children's Hospital Boston, and
- Department of Pediatrics, Harvard Medical School, Boston, MA 02115
| | | | - Hans D. Ochs
- Division of Immunology, Infectious Diseases, and Rheumatology, Department of Pediatrics, University of Washington School of Medicine, Seattle, WA 98195; and
| | - Kenneth C. Anderson
- Department of Medical Oncology, Dana–Farber Cancer Institute, Boston, MA 02115
| | - Fred S. Rosen
- *Division of Immunology, Children's Hospital Boston, and
- Department of Pediatrics, Harvard Medical School, Boston, MA 02115
| | - Raif S. Geha
- *Division of Immunology, Children's Hospital Boston, and
- Department of Pediatrics, Harvard Medical School, Boston, MA 02115
| | - Narayanaswamy Ramesh
- *Division of Immunology, Children's Hospital Boston, and
- Department of Pediatrics, Harvard Medical School, Boston, MA 02115
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19
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Abstract
Cells offer different types of cytoskeletal anchorages: transitory structures such as focal contacts and perennial ones such as the sarcomeric cytoskeleton of muscle cells. The turnover of these structures is controlled with different timing by a family of cysteine proteases activated by calcium, the calpains. The large number of potential substrates present in each of these structures imposes fine tuning of the activity of the proteases to avoid excessive action. This phenomenon is thus guaranteed by various types of regulation, ranging from a relatively high calcium concentration necessary for activation, phosphorylation of substrates or the proteases themselves with either a favorable or inhibitory effect, possible intervention of phospholipids, and the presence of a specific inhibitor and its possible degradation before activation. Finally, formation of multiprotein complexes containing calpains offers a new method of regulation.
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20
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Kashiwagi H, Shiraga M, Kato H, Honda S, Sako M, Kurata Y, Kanakura Y, Tomiyama Y. Expression and subcellular localization of WAVE isoforms in the megakaryocyte/platelet lineage. J Thromb Haemost 2005; 3:361-8. [PMID: 15670045 DOI: 10.1111/j.1538-7836.2004.01082.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
WAVE isoforms, which consist of WAVE-1, WAVE-2 and WAVE-3, are members of the Wiskott-Aldrich syndrome protein (WASP) family. They are implicated in the regulation of actin-cytoskeletal reorganization downsteam of the small GTPase, Rac. Since platelet attachment to extracellular matrices leads to filopodial and lamellipodial extension, we examined the expression and subcellular localization of WAVEs in platelets. Employing primary megakaryocytic cells derived from cord blood as well as megakaryocytic cell lines, we also examined their expression during megakaryocytic differentiation. Immunoblotting and immunohistochemical analysis revealed that platelets expressed WAVE-1 and WAVE-2, whereas WAVE-3 expression was hardly to be detected. WAVE-1 expression was associated with megakaryocytic differentiation, whereas WAVE-2 and WAVE-3 expression was not changed by the differentiation. In adhered platelets both WAVE-1 and WAVE-2 were localized at the edge of the lamellipodia and at the tips of filopodia. In WASP-deficient platelets we found normal lamellipodial formation and localization of WAVE-1 and WAVE-2 at the edges of lamellipodia. Furthermore, we demonstrated that WAVE-1 and WAVE-2 moved from a detergent-soluble cytosolic fraction to insoluble cytoskeleton fraction after platelet aggregation. These results suggest that WAVE-1 and WAVE-2 regulate actin reorganization during platelet spreading and aggregate formation.
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Affiliation(s)
- H Kashiwagi
- Department of Hematology, Osaka University Graduate School of Medicine, 2-2, Yamada-oka, Suita, Osaka 565-0871, Japan.
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21
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Tian W, Dewitt S, Laffafian I, Hallett MB. Ca(2+), calpain and 3-phosphorylated phosphatidyl inositides; decision-making signals in neutrophils as potential targets for therapeutics. ACTA ACUST UNITED AC 2004; 56:565-71. [PMID: 15142332 DOI: 10.1211/0022357023466] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The chemical signals within neutrophils that control their behaviour are complex and these signals control the complex activity of neutrophils with precision. Failure of neutrophils to reform their antibacterial activity would lead to infection, while over-activity of neutrophils may lead to tissue damage and inflammatory disease. The identity of some of the intracellular signals is becoming clear and insights into the potential for interplay between them are being sought. Although it is well established that cytosolic free Ca(2+) plays a role, it is only recently that the importance of intracellular protease, calpain, and the 3-position phosphorylated phosphatidyl inositides is becoming recognised. In this review these three key signals are discussed as potential therapeutic targets for the modulation of neutrophil activity.
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Affiliation(s)
- Wei Tian
- Department of Surgery, University of Wales College of Medicine, Heath Park, Cardiff, CF14 4XN, UK
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22
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Carragher NO, Frame MC. Focal adhesion and actin dynamics: a place where kinases and proteases meet to promote invasion. Trends Cell Biol 2004; 14:241-9. [PMID: 15130580 DOI: 10.1016/j.tcb.2004.03.011] [Citation(s) in RCA: 281] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Integrin-linked focal adhesion complexes provide the main sites of cell adhesion to extracellular matrix and associate with the actin cytoskeleton to control cell movement. Dynamic regulation of focal adhesions and reorganization of the associated actin cytoskeleton are crucial determinants of cell migration. There are important roles for tyrosine kinases, extracellular signal-regulated protein kinase/mitogen-activated protein kinase signalling, and intracellular and extracellular proteases during actin and adhesion modulation. Dysregulation of these is associated with tumour cell invasion. In this article, we discuss established roles for these signalling pathways, as well as the functional interplay between them in controlling the migratory phenotype.
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Affiliation(s)
- Neil O Carragher
- The Beatson Institute for Cancer Research, Cancer Research UK, Glasgow G61 1BD, UK.
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23
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Lacout C, Haddad E, Sabri S, Svinarchouk F, Garçon L, Capron C, Foudi A, Mzali R, Snapper SB, Louache F, Vainchenker W, Duménil D. A defect in hematopoietic stem cell migration explains the nonrandom X-chromosome inactivation in carriers of Wiskott-Aldrich syndrome. Blood 2003; 102:1282-9. [PMID: 12730112 DOI: 10.1182/blood-2002-07-2099] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A defect in cell trafficking and chemotaxis plays an important role in the immune deficiency observed in Wiskott-Aldrich syndrome (WAS). In this report, we show that marrow cells from WAS protein (WASP)-deficient mice also have a defect in chemotaxis. Serial transplantation and competitive reconstitution experiments demonstrated that marrow cells, including hematopoietic progenitors and stem cells (HSCs), have decreased homing capacities that were associated with a defect in adhesion to collagen. During development, HSCs migrate from the liver to the marrow and the spleen, prompting us to ask if a defect in HSC homing during development may explain the skewed X-chromosome inactivation in WAS carriers. Preliminary evidence has shown that, in contrast to marrow progenitor cells, fetal liver progenitor cells from heterozygous females had a random X-chromosome inactivation. When fetal liver cells from WASP-carrier females were injected into irradiated recipients, a nonrandom inactivation of the X-chromosome was found at the level of hematopoietic progenitors and HSCs responsible for the short- and long-term hematopoietic reconstitution. Therefore, the mechanism of the skewed X-chromosomal inactivation observed in WAS carriers may be related to a migration defect of WASP-deficient HSCs.
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Affiliation(s)
- Catherine Lacout
- U362 Institut National de la Santé et de la Recherche Médicale (INSERM), Institut Gustave Roussy, Villejuif, France
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24
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Abstract
Abstract
Arp2/3 complex is believed to induce de novo nucleation of actin filaments at the edge of motile cells downstream of WASp family proteins. In this study, the signaling pathways leading to Arp2/3 complex activation, actin assembly, and shape change were investigated in platelets isolated from patients with Wiskott-Aldrich Syndrome (WAS), that is, who lack WASp, and in WASp-deficient mouse platelets. WASp-deficient human and mouse platelets elaborate filopodia, spread lamellae, and assemble actin, identical to control WASp-expressing platelets. Human platelets contain 2 μM Arp2/3 complex, or 8600 molecules/cell. Arp2/3 complex redistributes to the edge of the lamellae and to the Triton X-100–insoluble actin cytoskeleton of activated WASp-deficient platelets. Furthermore, the C-terminal CA domain of N-WASp, which sequesters Arp2/3 complex, inhibits by half the actin nucleation capacity of octylglucoside-permeabilized and activated WAS platelets, similar to its effect in WASp-expressing cells. Along with WASp, platelets express WAVE-2 as a physiologic activator of Arp2/3 complex and a small amount of N-WASp. Taken together, our findings show that platelets activate Arp2/3 complex, assemble actin, and change shape in the absence of WASp, indicating a more specialized role for WASp in these cells.
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25
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Abstract
Arp2/3 complex is believed to induce de novo nucleation of actin filaments at the edge of motile cells downstream of WASp family proteins. In this study, the signaling pathways leading to Arp2/3 complex activation, actin assembly, and shape change were investigated in platelets isolated from patients with Wiskott-Aldrich Syndrome (WAS), that is, who lack WASp, and in WASp-deficient mouse platelets. WASp-deficient human and mouse platelets elaborate filopodia, spread lamellae, and assemble actin, identical to control WASp-expressing platelets. Human platelets contain 2 μM Arp2/3 complex, or 8600 molecules/cell. Arp2/3 complex redistributes to the edge of the lamellae and to the Triton X-100–insoluble actin cytoskeleton of activated WASp-deficient platelets. Furthermore, the C-terminal CA domain of N-WASp, which sequesters Arp2/3 complex, inhibits by half the actin nucleation capacity of octylglucoside-permeabilized and activated WAS platelets, similar to its effect in WASp-expressing cells. Along with WASp, platelets express WAVE-2 as a physiologic activator of Arp2/3 complex and a small amount of N-WASp. Taken together, our findings show that platelets activate Arp2/3 complex, assemble actin, and change shape in the absence of WASp, indicating a more specialized role for WASp in these cells.
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26
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Li Z, Kim ES, Bearer EL. Arp2/3 complex is required for actin polymerization during platelet shape change. Blood 2002; 99:4466-74. [PMID: 12036877 PMCID: PMC3376088 DOI: 10.1182/blood.v99.12.4466] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Platelets undergo a series of actin-dependent morphologic changes when activated by thrombin receptor activating peptide (TRAP) or when spreading on glass. Polymerization of actin results in the sequential formation of filopodia, lamellipodia, and stress fibers, but the molecular mechanisms regulating this polymerization are unknown. The Arp2/3 complex nucleates actin polymerization in vitro and could perform this function inside cells as well. To test whether Arp2/3 regulated platelet actin polymerization, we used recombinant Arp2 protein (rArp2) to generate Arp2-specific antibodies (alpha Arp2). Intact and Fab fragments of alpha Arp2 inhibited TRAP-stimulated actin-polymerizing activity in platelet extracts as measured by the pyrene assay. Inhibition was reversed by the addition of rArp2 protein. To test the effect of Arp2/3 inhibition on the formation of specific actin structures, we designed a new method to permeabilize resting platelets while preserving their ability to adhere and to form filopodia and lamellipodia on exposure to glass. Inhibition of Arp2/3 froze platelets at the rounded, early stage of activation, before the formation of filopodia and lamellipodia. By morphometric analysis, the proportion of platelets in the rounded stage rose from 2.85% in untreated to 63% after treatment with alpha Arp2. This effect was also seen with Fab fragments and was reversed by the addition of rArp2 protein. By immunofluorescence of platelets at various stages of spreading, the Arp2/3 complex was found in filopodia and lamellipodia. These results suggest that activation of the Arp2/3 complex at the cortex by TRAP stimulation initiates an explosive polymerization of actin filaments that is required for all subsequent actin-dependent events.
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Affiliation(s)
- Zhi Li
- Department of Pathology and Laboratory Medicine, Brown University, Providence, RI 02912, USA
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27
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Abstract
The human blood platelet circulates in the blood as a non-adherent disk. Upon receiving signals of blood vessel damage, the platelet reorganizes its actin cytoskeleton which transforms it into a spiky dynamic adherent glue. This transformation involves a temporal sequence of four morphologically distinct steps which is reproducible in vitro. The actin dynamics underlying these shape changes depend on a large number of actin-binding proteins. Maintenance of the discoid shape requires actin-binding proteins that inhibit these reorganizations, whereas transformation involves other proteins, some to disassemble old filaments and others to polymerize new ones. F-Actin-affinity chromatography identified a large set of actin-binding proteins including VASP, Arp2 and 2E4/kaptin. Recent discoveries show that VASP inhibits filament disassembly and Arp2/3 is required to polymerize new filaments. Morphological analysis of the distribution of these actin-binding proteins in spread platelets together with biochemical measurements of their interactions with actin lead to a model of interactions with actin that mediate shape change.
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Affiliation(s)
- E L Bearer
- Department of Pathology and Laboratory Medicine, Brown University, Providence, Rhode Island 02912, USA
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