201
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Arp3 is required during preimplantation development of the mouse embryo. FEBS Lett 2007; 581:5691-7. [PMID: 18035060 DOI: 10.1016/j.febslet.2007.11.031] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2007] [Revised: 11/09/2007] [Accepted: 11/12/2007] [Indexed: 12/11/2022]
Abstract
The role of Arp3 in mouse development was investigated utilizing a gene trap mutation in the Arp3 gene. Heterozygous Arp3(WT/GT) mice are normal, however, homozygous Arp3(GT/GT) embryos die at blastocyst stage. Earlier embryonic stages appear unaffected by the mutation, probably due to maternal Arp3 protein. Mutant blastocysts isolated at E3.5 fail to continue development in vitro, lack outgrowth of trophoblast-like cells in culture and express reduced levels of the trophoblast marker Cdx2, while markers for inner cell mass continue to be present. The recessive embryonic lethal phenotype indicates that Arp3 plays a vital role for early mouse development, possibly when trophoblast cells become critical for implantation.
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202
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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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203
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Richardson BE, Beckett K, Nowak SJ, Baylies MK. SCAR/WAVE and Arp2/3 are crucial for cytoskeletal remodeling at the site of myoblast fusion. Development 2007; 134:4357-67. [PMID: 18003739 DOI: 10.1242/dev.010678] [Citation(s) in RCA: 132] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Myoblast fusion is crucial for formation and repair of skeletal muscle. Here we show that active remodeling of the actin cytoskeleton is essential for fusion in Drosophila. Using live imaging, we have identified a dynamic F-actin accumulation (actin focus) at the site of fusion. Dissolution of the actin focus directly precedes a fusion event. Whereas several known fusion components regulate these actin foci, others target additional behaviors required for fusion. Mutations in kette/Nap1, an actin polymerization regulator, lead to enlarged foci that do not dissolve, consistent with the observed block in fusion. Kette is required to positively regulate SCAR/WAVE, which in turn activates the Arp2/3 complex. Mutants in SCAR and Arp2/3 have a fusion block and foci phenotype, suggesting that Kette-SCAR-Arp2/3 participate in an actin polymerization event required for focus dissolution. Our data identify a new paradigm for understanding the mechanisms underlying fusion in myoblasts and other tissues.
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Affiliation(s)
- Brian E Richardson
- Program in Developmental Biology, Sloan Kettering Institute, New York, NY 10021, USA
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204
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Huang CH, Lin TY, Pan RL, Juang JL. The Involvement of Abl and PTP61F in the Regulation of Abi Protein Localization and Stability and Lamella Formation in Drosophila S2 Cells. J Biol Chem 2007; 282:32442-52. [PMID: 17804420 DOI: 10.1074/jbc.m702583200] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Most aspects of cellular events are regulated by a series of protein phosphorylation and dephosphorylation processes. Abi (Abl interactor protein) functions as a substrate adaptor protein for Abl and a core member of the WAVE complex, relaying signals from Rac to Arp2/3 complex and regulating actin dynamics. It is known that the recruitment of Abi into the lamella promotes polymerization of actin, although how it does this is unclear. In this study, we found PTP61F, a Drosophila homolog of mammalian PTP1B, can reverse the Abl phosphorylation of Abi and colocalizes with Abi in Drosophila S2 cells. Abi can be translocalized from the cytosol to the cell membrane by either increasing Abl or reducing endogenous PTP61F. This reciprocal regulation of Abi phosphorylation is also involved in modulating Abi protein level, which is thought to affect the stability of the WAVE complex. Using mass spectrometry, we identified several important tyrosine phosphorylation sites in Abi. We compared the translocalization and protein half-life of wild type (wt) and phosphomutant Abi and their abilities to restore the lamellipodia structure of the Abi-reduced cells. We found the phosphomutant to have reduced ability to translocalize and to have a protein half-life shorter than that of wt Abi. We also found that although the wt Abi could fully restore the lamellipodia structure, the phosphomutant could not. Together, these findings suggest that the reciprocal regulation of Abi phosphorylation by Abl and PTP61F may regulate the localization and stability of Abi and may regulate the formation of lamella.
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Affiliation(s)
- Chiu-Hui Huang
- Division of Molecular and Genomic Medicine, National Health Research Institutes, Zhunan, Miaoli 35053, Taiwan
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205
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Qurashi A, Sahin HB, Carrera P, Gautreau A, Schenck A, Giangrande A. HSPC300 and its role in neuronal connectivity. Neural Dev 2007; 2:18. [PMID: 17894861 PMCID: PMC2098765 DOI: 10.1186/1749-8104-2-18] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2007] [Accepted: 09/25/2007] [Indexed: 11/12/2022] Open
Abstract
Background The WAVE/SCAR complex, consisting of CYFIP (PIR121 or Sra1), Kette (Nap1), Abi, SCAR (WAVE) and HSPC300, is known to regulate the actin nucleating Arp2/3 complex in a Rac1-dependent manner. While in vitro and in vivo studies have demonstrated that CYFIP, Kette, Abi and SCAR work as subunits of the complex, the role of the small protein HSPC300 remains unclear. Results In the present study, we identify the HSPC300 gene and characterize its interaction with the WAVE/SCAR complex in the Drosophila animal model. On the basis of several lines of evidence, we demonstrate that HSPC300 is an indispensable component of the complex controlling axonal and neuromuscular junction (NMJ) growth. First, the Drosophila HSPC300 expression profile resembles that of other members of the WAVE/SCAR complex. Second, HSPC300 mutation, as well as mutations in the other complex subunits, results in identical axonal and NMJ growth defects. Third, like with other complex subunits, defects in NMJ architecture are rescued by presynaptic expression of the respective wild-type gene. Fourth, HSPC300 genetically interacts with another subunit of the WAVE/SCAR complex. Fifth, HSPC300 physically associates with CYFIP and SCAR. Conclusion Present data provide the first evidence for HSPC300 playing a role in nervous system development and demonstrate in vivo that this small protein works in the context of the WAVE/SCAR complex.
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Affiliation(s)
- Abrar Qurashi
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP, BP 10142, 67404 Illkirch, CU de Strasbourg, France
- Department of Human Genetics, Emory University School of Medicine, Atlanta, GA 30322, USA
| | - H Bahar Sahin
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP, BP 10142, 67404 Illkirch, CU de Strasbourg, France
| | - Pilar Carrera
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP, BP 10142, 67404 Illkirch, CU de Strasbourg, France
- Abteilung für Molekulare Entwicklungsbiologie, Institut für Molekulare Physiologie und Entwicklungsbiologie, Universität Bonn, D-53115 Bonn, Germany
| | - Alexis Gautreau
- Laboratoire de Morphogenèse et Signalisation Cellulaires, UMR 144 CNRS/Institut Curie, 75248 Paris Cedex 05, France
| | - Annette Schenck
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP, BP 10142, 67404 Illkirch, CU de Strasbourg, France
- Department of Human Genetics (855), Nijmegen Centre for Molecular Life Science, Radboud University Nijmegen Medical Centre, Box 9101, 6500 HB Nijmegen, The Netherlands
| | - Angela Giangrande
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP, BP 10142, 67404 Illkirch, CU de Strasbourg, France
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206
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Abstract
This review summarizes what is known about the biochemical and biophysical mechanisms that initiate the assembly of actin filaments in cells. Assembly and disassembly of these filaments contribute to many types of cellular movements. Numerous proteins regulate actin assembly, but Arp2/3 complex and formins are the focus of this review because more is known about them than other proteins that stimulate the formation of new filaments. Arp2/3 complex is active at the leading edge of motile cells, where it produces branches on the sides of existing filaments. Growth of these filaments produces force to protrude the membrane. Crystal structures, reconstructions from electron micrographs, and biophysical experiments have started to map out the steps through which proteins called nucleation-promoting factors stimulate the formation of branches. Formins nucleate and support the elongation of unbranched actin filaments for cytokinesis and various types of actin filament bundles. Formins associate processively with the fast-growing ends of filaments and protect them from capping.
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Affiliation(s)
- Thomas D Pollard
- Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Connecticut 06520-8103, USA.
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207
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Sakata D, Taniguchi H, Yasuda S, Adachi-Morishima A, Hamazaki Y, Nakayama R, Miki T, Minato N, Narumiya S. Impaired T lymphocyte trafficking in mice deficient in an actin-nucleating protein, mDia1. ACTA ACUST UNITED AC 2007; 204:2031-8. [PMID: 17682067 PMCID: PMC2118705 DOI: 10.1084/jem.20062647] [Citation(s) in RCA: 106] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Trafficking of immune cells is controlled by directed migration of relevant cells toward chemotactic signals. Actin cytoskeleton undergoes continuous remodeling and serves as machinery for cell migration. The mDia family of formins and the Wiskott-Aldrich syndrome protein (WASP)-Arp2/3 system are two major actin nucleating-polymerizing systems in mammalian cells, with the former producing long straight actin filaments and the latter producing branched actin meshwork. Although much is known about the latter, the physiological functions of mDia proteins are unclear. We generated mice deficient in one mDia isoform, mDia1. Although mDia1(-/-) mice were born and developed without apparent abnormality, mDia1(-/-) T lymphocytes exhibited impaired trafficking to secondary lymphoid organs in vivo and showed reduced chemotaxis, little actin filament formation, and impaired polarity in response to chemotactic stimuli in vitro. Similarly, mDia1(-/-) thymocytes showed reduced chemotaxis and impaired egression from the thymus. These results suggest that mDia1 plays a distinct role in chemotaxis in T lymphocyte trafficking.
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Affiliation(s)
- Daiji Sakata
- Department of Pharmacology,Kyoto University Faculty of Medicine, Kyoto 606-8501, Japan
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208
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Kondylis V, van Nispen tot Pannerden HE, Herpers B, Friggi-Grelin F, Rabouille C. The golgi comprises a paired stack that is separated at G2 by modulation of the actin cytoskeleton through Abi and Scar/WAVE. Dev Cell 2007; 12:901-15. [PMID: 17543863 DOI: 10.1016/j.devcel.2007.03.008] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2006] [Revised: 02/02/2007] [Accepted: 03/09/2007] [Indexed: 11/19/2022]
Abstract
During the cell cycle, the Golgi, like other organelles, has to be duplicated in mass and number to ensure its correct segregation between the two daughter cells. It remains unclear, however, when and how this occurs. Here we show that in Drosophila S2 cells, the Golgi likely duplicates in mass to form a paired structure during G1/S phase and remains so until G2 when the two stacks separate, ready for entry into mitosis. We show that pairing requires an intact actin cytoskeleton which in turn depends on Abi/Scar but not WASP. This actin-dependent pairing is not limited to flies but also occurs in mammalian cells. We further show that preventing the Golgi stack separation at G2 blocks entry into mitosis, suggesting that this paired organization is part of the mitotic checkpoint, similar to what has been proposed in mammalian cells.
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Affiliation(s)
- Vangelis Kondylis
- The Cell Microscopy Centre, Department of Cell Biology, Institute of Biomembranes, University Medical Centre Utrecht, Heidelberglaan 100, 3584 CX Utrecht, The Netherlands
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209
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Sossey-Alaoui K, Li X, Cowell JK. c-Abl-mediated phosphorylation of WAVE3 is required for lamellipodia formation and cell migration. J Biol Chem 2007; 282:26257-65. [PMID: 17623672 DOI: 10.1074/jbc.m701484200] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The activity of the Wiskott-Aldrich syndrome-related WAVE3 protein is critical for the regulation of the Arp2/3-dependent cytoskeleton organization downstream of Rac-GTPase. The Ableson (Abl) non-receptor tyrosine kinase is also involved in the remolding of actin cytoskeleton in response to extracellular stimuli. Here we show that platelet-derived growth factor stimulation of cultured cells results in WAVE3-Abl interaction and localization to the cell periphery. WAVE3-Abl interaction promotes the tyrosine phosphorylation of WAVE3 by Abl, and STI-571, a specific inhibitor of Abl kinase activity, abrogates the Abl-mediated phosphorylation of WAVE3. We have also shown that Abl targets and phosphorylates four tyrosine residues in WAVE3 and that the Abl-dependent phosphorylation of WAVE3 is critical for the stimulation of lamellipodia formation and cell migration. Our results show that the activation of WAVE3 to promote actin remodeling is enhanced by the c-Abl-mediated tyrosine phosphorylation of WAVE3.
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Affiliation(s)
- Khalid Sossey-Alaoui
- Department of Cancer Genetics, Roswell Park Cancer Institute, Buffalo, New York 14263, USA.
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210
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Bakal C, Aach J, Church G, Perrimon N. Quantitative Morphological Signatures Define Local Signaling Networks Regulating Cell Morphology. Science 2007; 316:1753-6. [PMID: 17588932 DOI: 10.1126/science.1140324] [Citation(s) in RCA: 252] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Although classical genetic and biochemical approaches have identified hundreds of proteins that function in the dynamic remodeling of cell shape in response to upstream signals, there is currently little systems-level understanding of the organization and composition of signaling networks that regulate cell morphology. We have developed quantitative morphological profiling methods to systematically investigate the role of individual genes in the regulation of cell morphology in a fast, robust, and cost-efficient manner. We analyzed a compendium of quantitative morphological signatures and described the existence of local signaling networks that act to regulate cell protrusion, adhesion, and tension.
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Affiliation(s)
- Chris Bakal
- Department of Genetics, Harvard Medical School, Boston, MA 02115, USA
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211
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Jovceva E, Larsen MR, Waterfield MD, Baum B, Timms JF. Dynamic cofilin phosphorylation in the control of lamellipodial actin homeostasis. J Cell Sci 2007; 120:1888-97. [PMID: 17504806 DOI: 10.1242/jcs.004366] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
During animal cell chemotaxis, signalling at the plasma membrane induces actin polymerisation to drive forward cell movement. Since the cellular pool of actin is limited, efficient protrusion formation also requires the coordinated disassembly of pre-existing actin filaments. To search for proteins that can monitor filamentous and globular actin levels to maintain the balance of polymerisation and disassembly, we followed changes in the proteome induced by RNA interference (RNAi)-mediated alterations in actin signalling. This unbiased approach revealed an increase in the levels of an inactive, phosphorylated form of the actin-severing protein cofilin in cells unable to generate actin-based lamellipodia. Conversely, an increase in F-actin levels induced the dephosphorylation and activation of cofilin via activation of the Ssh phosphatase. Similarly, in the context of acute phosphoinositide 3-kinase (PI3K) signalling, dynamic changes in cofilin phosphorylation were found to depend on the Ssh phosphatase and on changes in lamellipodial F-actin. These results indicate that changes in the extent of cofilin phosphorylation are regulated by Ssh in response to changes in the levels and/or organisation of F-actin. Together with the recent finding that Ssh phosphatase activity is augmented by F-actin binding, these results identify Ssh-dependent regulation of phosphorylated cofilin levels as an important feedback control mechanism that maintains actin filament homeostasis during actin signalling.
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Affiliation(s)
- Eleonora Jovceva
- Ludwig Institute for Cancer Research, UCL Branch, London, W1W 7BS, UK
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212
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Carabeo RA, Dooley CA, Grieshaber SS, Hackstadt T. Rac interacts with Abi-1 and WAVE2 to promote an Arp2/3-dependent actin recruitment during chlamydial invasion. Cell Microbiol 2007; 9:2278-88. [PMID: 17501982 DOI: 10.1111/j.1462-5822.2007.00958.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Chlamydiae are Gram-negative obligate intracellular pathogens to which access to an intracellular environment is fundamental to their development. Chlamydial attachment to host cells induces the activation of the Rac GTPase, which is required for the localization of WAVE2 at the sites of chlamydial entry. Co-immunoprecipitation experiments demonstrated that Chlamydia trachomatis infection promoted the interaction of Rac with WAVE2 and Abi-1, but not with IRSp53. siRNA depletion of WAVE2 and Abi-1 abrogated chlamydia-induced actin recruitment and significantly reduced the uptake of the pathogen by the depleted cells. Chlamydia invasion also requires the Arp2/3 complex as demonstrated by its localization to the sites of chlamydial attachment and the reduced efficiency of chlamydial invasion in cells overexpressing the VCA domain of the neural Wiskott-Aldrich syndrome protein. Thus, C. trachomatis activates Rac and promotes its interaction with WAVE2 and Abi-1 to activate the Arp2/3 complex resulting in the induction of actin cytoskeletal rearrangements that are required for invasion.
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Affiliation(s)
- Rey A Carabeo
- Department of Microbiology and Immunology, University of Louisville School of Medicine, Louisville, KY, USA
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213
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Yokota Y, Ring C, Chong R, Pevny L, Anton ES. Nap1-regulated neuronal cytoskeletal dynamics is essential for the final differentiation of neurons in cerebral cortex. Neuron 2007; 54:429-45. [PMID: 17481396 PMCID: PMC3443617 DOI: 10.1016/j.neuron.2007.04.016] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2006] [Revised: 03/26/2007] [Accepted: 04/18/2007] [Indexed: 10/23/2022]
Abstract
The cytoskeletal regulators that mediate the change in the neuronal cytoskeletal machinery from one that promotes oriented motility to one that facilitates differentiation at the appropriate locations in the developing neocortex remain unknown. We found that Nck-associated protein 1 (Nap1), an adaptor protein thought to modulate actin nucleation, is selectively expressed in the developing cortical plate, where neurons terminate their migration and initiate laminar-specific differentiation. Loss of Nap1 function disrupts neuronal differentiation. Premature expression of Nap1 in migrating neurons retards migration and promotes postmigratory differentiation. Nap1 gene mutation in mice leads to neural tube and neuronal differentiation defects. Disruption of Nap1 retards the ability to localize key actin cytoskeletal regulators such as WAVE1 to the protrusive edges where they are needed to elaborate process outgrowth. Thus, Nap1 plays an essential role in facilitating neuronal cytoskeletal changes underlying the postmigratory differentiation of cortical neurons, a critical step in functional wiring of the cortex.
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Affiliation(s)
- Yukako Yokota
- UNC Neuroscience Center, Department of Cell and Molecular Physiology, University of North Carolina School of Medicine, Chapel Hill, NC 27599, USA
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214
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Sánchez-Soriano N, Tear G, Whitington P, Prokop A. Drosophila as a genetic and cellular model for studies on axonal growth. Neural Dev 2007; 2:9. [PMID: 17475018 PMCID: PMC1876224 DOI: 10.1186/1749-8104-2-9] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2007] [Accepted: 05/02/2007] [Indexed: 11/10/2022] Open
Abstract
One of the most fascinating processes during nervous system development is the establishment of stereotypic neuronal networks. An essential step in this process is the outgrowth and precise navigation (pathfinding) of axons and dendrites towards their synaptic partner cells. This phenomenon was first described more than a century ago and, over the past decades, increasing insights have been gained into the cellular and molecular mechanisms regulating neuronal growth and navigation. Progress in this area has been greatly assisted by the use of simple and genetically tractable invertebrate model systems, such as the fruit fly Drosophila melanogaster. This review is dedicated to Drosophila as a genetic and cellular model to study axonal growth and demonstrates how it can and has been used for this research. We describe the various cellular systems of Drosophila used for such studies, insights into axonal growth cones and their cytoskeletal dynamics, and summarise identified molecular signalling pathways required for growth cone navigation, with particular focus on pathfinding decisions in the ventral nerve cord of Drosophila embryos. These Drosophila-specific aspects are viewed in the general context of our current knowledge about neuronal growth.
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Affiliation(s)
- Natalia Sánchez-Soriano
- The Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, The University of Manchester, Manchester, UK
| | - Guy Tear
- MRC Centre for Developmental Neurobiology, Guy's Campus, King's College, London, UK
| | - Paul Whitington
- Department of Anatomy and Cell Biology, University of Melbourne, Victoria, Australia
| | - Andreas Prokop
- The Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, The University of Manchester, Manchester, UK
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215
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Li Y, Clough N, Sun X, Yu W, Abbott BL, Hogan CJ, Dai Z. Bcr-Abl induces abnormal cytoskeleton remodeling, beta1 integrin clustering and increased cell adhesion to fibronectin through the Abl interactor 1 pathway. J Cell Sci 2007; 120:1436-46. [PMID: 17389688 PMCID: PMC1950936 DOI: 10.1242/jcs.03430] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Hematopoietic cells isolated from patients with Bcr-Abl-positive leukemia exhibit multiple abnormalities of cytoskeletal and integrin function. These abnormalities are thought to play a role in the pathogenesis of leukemia; however, the molecular events leading to these abnormalities are not fully understood. We show here that the Abi1 pathway is required for Bcr-Abl to stimulate actin cytoskeleton remodeling, integrin clustering and cell adhesion. Expression of Bcr-Abl induces tyrosine phosphorylation of Abi1. This is accompanied by a subcellular translocation of Abi1/WAVE2 to a site adjacent to membrane, where an F-actin-enriched structure containing the adhesion molecules such as beta1-integrin, paxillin and vinculin is assembled. Bcr-Abl-induced membrane translocation of Abi1/WAVE2 requires direct interaction between Abi1 and Bcr-Abl, but is independent of the phosphoinositide 3-kinase pathway. Formation of the F-actin-rich complex correlates with an increased cell adhesion to fibronectin. More importantly, disruption of the interaction between Bcr-Abl and Abi1 by mutations either in Bcr-Abl or Abi1 not only abolished tyrosine phosphorylation of Abi1 and membrane translocation of Abi1/WAVE2, but also inhibited Bcr-Abl-stimulated actin cytoskeleton remodeling, integrin clustering and cell adhesion to fibronectin. Together, these data define Abi1/WAVE2 as a downstream pathway that contributes to Bcr-Abl-induced abnormalities of cytoskeletal and integrin function.
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Affiliation(s)
- Yingzhu Li
- Department of Medicine, University of Colorado at Denver and Health Sciences Center, Aurora, CO 80045
| | - Nancy Clough
- Department of Medicine, University of Colorado at Denver and Health Sciences Center, Aurora, CO 80045
| | - Xiaolin Sun
- Department of Medicine, University of Colorado at Denver and Health Sciences Center, Aurora, CO 80045
| | - Weidong Yu
- Department of Medicine, University of Colorado at Denver and Health Sciences Center, Aurora, CO 80045
| | - Brian L. Abbott
- Department of Medicine, University of Colorado at Denver and Health Sciences Center, Aurora, CO 80045
| | - Christopher J. Hogan
- Department of Medicine, University of Colorado at Denver and Health Sciences Center, Aurora, CO 80045
- University of Colorado Cancer Center, University of Colorado at Denver and Health Sciences Center, Aurora, CO 80045
| | - Zonghan Dai
- Department of Medicine, University of Colorado at Denver and Health Sciences Center, Aurora, CO 80045
- Cell and Developmental Biology, University of Colorado at Denver and Health Sciences Center, Aurora, CO 80045
- University of Colorado Cancer Center, University of Colorado at Denver and Health Sciences Center, Aurora, CO 80045
- Correspondence author: 1400 Wallace Boulevard, Texas Tech University Health Sciences Center, Amarillo, TX 79106, Tel. 806-354-5719, Fax. 806-354-5764, E-mail:
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216
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Bouslama-Oueghlani L, Echard A, Louvard D, Gautreau A. RNAi depleted Drosophila cell extracts to dissect signaling pathways leading to actin polymerization. ACTA ACUST UNITED AC 2007; 70:663-9. [PMID: 17434595 DOI: 10.1016/j.jbbm.2007.03.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2006] [Revised: 03/06/2007] [Accepted: 03/12/2007] [Indexed: 11/24/2022]
Abstract
Dissection of signal transduction pathways leading to actin polymerization has been performed in cytosolic extracts. In such assays, the implication of an effector molecule is demonstrated by the loss of actin polymerization upon its depletion and the restoration of actin polymerization upon its add-back. Two major limitations in the wide use of this approach have been the availability of immunodepleting antibodies and the functional redundancy for many classes of effector molecules encoded by vertebrate genomes. To circumvent these limitations, we developed extracts derived from S2 Drosophila cells, which are competent for actin polymerization. In this system, depleted extracts are simply obtained from cells cultured with long double stranded RNAs in the medium. We validated the method by showing that beads coated with the C-terminal domain of Wave2 were no longer able to trigger actin polymerization in an extract depleted of the Arp2/3 complex. We also examined the complete set of Drosophila small GTPases of the Rho family for their ability to polymerize actin in such extracts, and found that only dCdc42 was able to induce actin polymerization. Using RNAi depleted extract, we confirmed that dCdc42 triggers actin polymerization in a Wasp dependent manner.
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Affiliation(s)
- Lamia Bouslama-Oueghlani
- Lab. of "Morphogenesis and Cell Signaling", UMR 144 CNRS/Institut Curie, 26 rue d'Ulm 75248 Paris Cedex 05, France
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217
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Iwaya K, Norio K, Mukai K. Coexpression of Arp2 and WAVE2 predicts poor outcome in invasive breast carcinoma. Mod Pathol 2007; 20:339-43. [PMID: 17277766 DOI: 10.1038/modpathol.3800741] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Breast carcinoma with a high histologic grade is highly invasive and metastatic. One reason for its irregular morphology is the formation of excessive protrusions due to assemblages of branched actin filament networks. In mammalian cells, the actin-related protein 2 and 3 (Arp2/3) complex initiates actin assembly to form lamellipodial protrusions by binding to the Wiskott-Aldrich syndrome (WASP)/WASP family verproline-homologous protein2 (WAVE2), a member of the WASP protein family. In this study, the localization Arp2 and WAVE2 in breast carcinoma was investigated to clarify whether coexpression of the two proteins is associated with histologic grade or patient outcome. Immunohistochemical staining of Arp2 and WAVE2 was performed on mirror specimens of 197 breast carcinomas, and the association between coexpression of the two proteins and clinicopathologic factors was examined. Kaplan-Meier disease-free survival and overall survival curves were analyzed to determine the prognostic significance of Arp2 and WAVE2 coexpression in breast carcinoma. Coexpression of Arp2 and WAVE2 was detected in 64 (36%) of 179 invasive ductal carcinomas and in 2 (11%) of 18 ductal carcinomas in situ, but was not detected in any adjacent non-cancerous tissue. The proportion of cancer cells expressing both Arp2 and WAVE2 was significantly higher in cases with high histologic grade (P<0.0001), and cases with lymph node metastasis (P=0.0150). The patients whose cancer cells showed such coexpression had shorter disease-free (P=0.0002) and overall survival (P=0.0122) than patients whose cancer cells expressed only one or none of Arp2 and WAVE2. Multivariate Cox regression analysis revealed that coexpression of Arp2 and WAVE2 is an independent factor for both tumor recurrence (P=0.0308) and death (P=0.0455). These results indicate that coexpression of Arp2 and WAVE2 is a significant prognostic factor that is closely associated with aggressive morphology of invasive ductal carcinoma of the breast.
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Affiliation(s)
- Keiichi Iwaya
- Department of Diagnostic Pathology, Tokyo Medical University, Shinjuku-ku, Tokyo, Japan.
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218
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Caracino D, Jones C, Compton M, Saxe CL. The N-terminus of Dictyostelium Scar interacts with Abi and HSPC300 and is essential for proper regulation and function. Mol Biol Cell 2007; 18:1609-20. [PMID: 17314411 PMCID: PMC1855017 DOI: 10.1091/mbc.e06-06-0518] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Scar/WAVE proteins, members of the conserved Wiskott-Aldrich syndrome (WAS) family, promote actin polymerization by activating the Arp2/3 complex. A number of proteins, including a complex containing Nap1, PIR121, Abi1/2, and HSPC300, interact with Scar/WAVE, though the role of this complex in regulating Scar function remains unclear. Here we identify a short N-terminal region of Dictyostelium Scar that is necessary and sufficient for interaction with HSPC300 and Abi in vitro. Cells expressing Scar lacking this N-terminal region show abnormalities in F-actin distribution, cell morphology, movement, and cytokinesis. This is true even in the presence of wild-type Scar. The data suggest that the first 96 amino acids of Scar are necessary for participation in a large-molecular-weight protein complex, and that this Scar-containing complex is responsible for the proper localization and regulation of Scar. The presence of mis-regulated or unregulated Scar has significant deleterious effects on cells and may explain the need to keep Scar activity tightly controlled in vivo either by assembly in a complex or by rapid degradation.
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Affiliation(s)
- Diana Caracino
- *Department of Cell Biology and
- Graduate Program in Microbiology and Molecular Genetics, Emory University School of Medicine, Atlanta, GA 30322; and
| | | | - Mark Compton
- Department of Poultry Science, School of Agriculture, University of Georgia, Athens, GA 30602
| | - Charles L. Saxe
- *Department of Cell Biology and
- Graduate Program in Microbiology and Molecular Genetics, Emory University School of Medicine, Atlanta, GA 30322; and
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219
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Takenawa T, Suetsugu S. The WASP-WAVE protein network: connecting the membrane to the cytoskeleton. Nat Rev Mol Cell Biol 2007; 8:37-48. [PMID: 17183359 DOI: 10.1038/nrm2069] [Citation(s) in RCA: 698] [Impact Index Per Article: 41.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Wiskott-Aldrich syndrome protein (WASP) and WASP-family verprolin-homologous protein (WAVE) family proteins are scaffolds that link upstream signals to the activation of the ARP2/3 complex, leading to a burst of actin polymerization. ARP2/3-complex-mediated actin polymerization is crucial for the reorganization of the actin cytoskeleton at the cell cortex for processes such as cell movement, vesicular trafficking and pathogen infection. Large families of membrane-binding proteins were recently found to interact with WASP and WAVE family proteins, therefore providing a new layer of membrane-dependent regulation of actin polymerization.
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Affiliation(s)
- Tadaomi Takenawa
- Department of Biochemistry, Institute of Medical Science, University of Tokyo, 4-6-1, Shirokane-dai, Minato-ku, Tokyo 108-8639, Japan.
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220
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Bacon C, Lakics V, Machesky L, Rumsby M. N-WASP regulates extension of filopodia and processes by oligodendrocyte progenitors, oligodendrocytes, and Schwann cells—implications for axon ensheathment at myelination. Glia 2007; 55:844-58. [PMID: 17405146 DOI: 10.1002/glia.20505] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
The molecular mechanisms used by oligodendrocyte precursor cells (OPCs), oligodendrocytes (OLs), and Schwann cells (SCs) to advance processes for motility in the developing nervous system and to ensheath axons at myelination are currently not well defined. Here we demonstrate that OPCs, OLs, and SCs express the major proteins involved in actin polymerization-driven protrusion; these key proteins including F-actin, the Arp2/3 complex, neural-Wiskott Aldrich Syndrome protein (N-WASP) and WAVE proteins, and the RhoGTPases Rac and Cdc42 are present at the leading edges of processes being extended by OPCs, OLs, and SCs. We reveal by real-time PCR that OLs and SCs have different dominant WAVE isoforms. Inhibition of the WASP/WAVE protein, N-WASP, with wiskostatin that prevents activation of the Arp2/3 complex, blocks process extension by OPCs and SCs. Inhibition of N-WASP also causes OPC and SC process retraction, which is preceded by retraction of filopodia. This implicates filopodia in OPC and SC process stability and also of N-WASP in OPC and SC process dynamics. We also demonstrate that p34 (a component of the Arp2/3 complex), WASP/WAVE proteins, actin, alpha-tubulin, Rac, Cdc42, vinculin, and focal adhesion kinase are detected in water-shocked myelin purified from brain. Inhibition of N-WASP with wiskostatin decreases the number of axons undergoing initial ensheathment in intact optic nerve samples and reduces the Po content of dorsal root ganglia:SC co-cultures. Our findings indicate that OPCs, OLs, and SCs extend processes using actin polymerization-driven protrusion dependent on N-WASP. We hypothesize that inner mesaxons of OLs and SCs use the same mechanism to ensheath axons at myelination.
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Affiliation(s)
- Claire Bacon
- Department of Biology, University of York, York, United Kingdom
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221
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Yamazaki D, Oikawa T, Takenawa T. Rac-WAVE-mediated actin reorganization is required for organization and maintenance of cell-cell adhesion. J Cell Sci 2007; 120:86-100. [PMID: 17164293 DOI: 10.1242/jcs.03311] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
During cadherin-dependent cell-cell adhesion, the actin cytoskeleton undergoes dynamic reorganization in epithelial cells. Rho-family small GTPases, which regulate actin dynamics, play pivotal roles in cadherin-dependent cell-cell adhesion; however, the precise molecular mechanisms that underlie cell-cell adhesion formation remain unclear. Here we show that Wiskott-Aldrich syndrome protein family verprolin-homologous protein (WAVE)-mediated reorganization of actin, downstream of Rac plays an important role in normal development of cadherin-dependent cell-cell adhesions in MDCK cells. Rac-induced development of cadherin-dependent adhesions required WAVE2-dependent actin reorganization. The process of cell-cell adhesion is divided into three steps: formation of new cell-cell contacts, stabilization of these new contacts and junction maturation. WAVE1 and WAVE2 were expressed in MDCK cells. The functions of WAVE1 and WAVE2 were redundant in this system but WAVE2 appeared to play a more significant role. During the first step, WAVE2-dependent lamellipodial protrusions facilitated formation of cell-cell contacts. During the second step, WAVE2 recruited actin filaments to new cell-cell contacts and stabilized newly formed cadherin clusters. During the third step, WAVE2-dependent actin reorganization was required for organization and maintenance of mature cell-cell adhesions. Thus, Rac-WAVE-dependent actin reorganization is not only involved in formation of cell-cell adhesions but is also required for their maintenance.
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Affiliation(s)
- Daisuke Yamazaki
- Department of Biochemistry, Institute of Medical Science, University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan
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222
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Hirao N, Sato S, Gotoh T, Maruoka M, Suzuki J, Matsuda S, Shishido T, Tani K. NESH (Abi-3) is present in the Abi/WAVE complex but does not promote c-Abl-mediated phosphorylation. FEBS Lett 2006; 580:6464-70. [PMID: 17101133 DOI: 10.1016/j.febslet.2006.10.065] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2006] [Revised: 09/26/2006] [Accepted: 10/29/2006] [Indexed: 01/21/2023]
Abstract
Abl interactor (Abi) was identified as an Abl tyrosine kinase-binding protein and subsequently shown to be a component of the macromolecular Abi/WAVE complex, which is a key regulator of Rac-dependent actin polymerization. Previous studies showed that Abi-1 promotes c-Abl-mediated phosphorylation of Mammalian Enabled (Mena) and WAVE2. In addition to Abi-1, mammals possess Abi-2 and NESH (Abi-3). In this study, we compared the three Abi proteins in terms of the promotion of c-Abl-mediated phosphorylation and the formation of Abi/WAVE complex. Although Abi-2, like Abi-1, promoted the c-Abl-mediated phosphorylation of Mena and WAVE2, NESH (Abi-3) had no such effect. This difference was likely due to their binding abilities as to c-Abl. Immunoprecipitation revealed that NESH (Abi-3) is present in the Abi/WAVE complex. Our results suggest that NESH (Abi-3), like Abi-1 and Abi-2, is a component of the Abi/WAVE complex, but likely plays a different role in the regulation of c-Abl.
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Affiliation(s)
- Noriko Hirao
- School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, Hachioji, Tokyo 192-0392, Japan
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223
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Ibarra N, Blagg SL, Vazquez F, Insall RH. Nap1 regulates Dictyostelium cell motility and adhesion through SCAR-dependent and -independent pathways. Curr Biol 2006; 16:717-22. [PMID: 16581519 DOI: 10.1016/j.cub.2006.02.068] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2005] [Revised: 02/14/2006] [Accepted: 02/17/2006] [Indexed: 11/17/2022]
Abstract
SCAR--also known as WAVE--is a key regulator of actin dynamics. Activation of SCAR enhances the nucleation of new actin filaments through the Arp2/3 complex, causing a localized increase in the rate of actin polymerization . In vivo, SCAR is held in a large regulatory complex, which includes PIR121 and Nap1 proteins, whose precise role is unclear. It was initially thought to hold SCAR inactive until needed , but recent data suggest that it is essential for SCAR function . Here, we show that disruption of the gene that encodes Nap1 (napA) causes loss of SCAR function. Cells lacking Nap1 are small and rounded, with diminished actin polymerization and small pseudopods. Furthermore, several aspects of the napA phenotype are more severe than those evoked by the absence of SCAR alone. In particular, napA mutants have defects in cell-substrate adhesion and multicellular development. Despite these defects, napA(-) cells move and chemotax surprisingly effectively. Our results show that the members of the complex have unexpectedly diverse biological roles.
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Affiliation(s)
- Neysi Ibarra
- School of Biosciences, University of Birmingham, Edgbaston, UK
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224
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Deshpande G, Calhoun G, Schedl P. The drosophila fragile X protein dFMR1 is required during early embryogenesis for pole cell formation and rapid nuclear division cycles. Genetics 2006; 174:1287-98. [PMID: 16888325 PMCID: PMC1667070 DOI: 10.1534/genetics.106.062414] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The FMR family of KH domain RNA-binding proteins is conserved from invertebrates to humans. In humans, inactivation of the X-linked FMR gene fragile X is the most common cause of mental retardation and leads to defects in neuronal architecture. While there are three FMR family members in humans, there is only a single gene, dfmr1, in flies. As in humans, inactivation of dfmr1 causes defects in neuronal architecture and in behavior. dfmr1 has other functions in the fly in addition to neurogenesis. Here we have analyzed its role during early embryonic development. We found that dfmr1 embryos display defects in the rapid nuclear division cycles that precede gastrulation in nuclear migration and in pole cell formation. While the aberrations in nuclear division are correlated with a defect in the assembly of centromeric/centric heterochromatin, the defects in pole cell formation are associated with alterations in the actin-myosin cytoskeleton.
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Affiliation(s)
- Girish Deshpande
- Department of Molecular Biology, Princeton University, Princeton, New Jersey 08540, USA
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225
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Pollitt AY, Blagg SL, Ibarra N, Insall RH. Cell motility and SCAR localisation in axenically growing Dictyostelium cells. Eur J Cell Biol 2006; 85:1091-8. [PMID: 16822579 DOI: 10.1016/j.ejcb.2006.05.014] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Dictyostelium is a popular experimental organism, in particular for studies of actin dynamics, cell motility and chemotaxis. We find that the motility of axenic cells is unexpectedly different from other strains during growth. In particular, vegetative AX3 cells do not show detectable localisation of SCAR and its regulatory complex to actin-rich protrusions such as filopodia and pseudopodia. Similarly, a range of different mutations, in particular knockouts of members of the SCAR complex and Ras proteins, cause different phenotypes during vegetative growth in different parental strains. Development reverses this unusual behaviour; aggregation-competent AX3 cells localise SCAR in the same way as cells of other strains and species. Studies on cell motility using vegetative cells should therefore be interpreted with caution.
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Affiliation(s)
- Alice Y Pollitt
- School of Biosciences, Birmingham University, Edgbaston, Birmingham B15 2TT, UK
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226
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Wheeler AP, Wells CM, Smith SD, Vega FM, Henderson RB, Tybulewicz VL, Ridley AJ. Rac1 and Rac2 regulate macrophage morphology but are not essential for migration. J Cell Sci 2006; 119:2749-57. [PMID: 16772332 DOI: 10.1242/jcs.03024] [Citation(s) in RCA: 150] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Rac GTPases are believed to contribute to migration in leukocytes by transducing signals from cell surface receptors to the actin and microtubule cytoskeletons. Mammals have three closely related Rac isoforms, Rac1, Rac2 and Rac3, and it is widely assumed that cell migration requires the activity of these Rac GTPases. We have previously shown that Rac1-null mouse macrophages have altered cell shape and reduced membrane ruffling but normal migration speed. Here we investigate the behaviour of macrophages lacking Rac2 (Rac2(-/-)) or Rac1 and Rac2 (Rac1/2(-/-)). Rac2(-/-) macrophages have reduced F-actin levels and lack podosomes, which are integrin-based adhesion sites, and their migration speed is similar to or slightly slower than wild-type macrophages, depending on the substrate. Unexpectedly, Rac1/2(-/-) macrophages, which do not express Rac1, Rac2 or Rac3, migrate at a similar speed to wild-type macrophages on a variety of substrates and perform chemotaxis normally, although their morphology and mode of migration is altered. However, Rac1(-/-) and Rac1/2(-/-) but not Rac2(-/-) macrophages are impaired in their ability to invade through Matrigel. Together, these data show that Rac1 and Rac2 have distinct roles in regulating cell morphology, migration and invasion, but are not essential for macrophage migration or chemotaxis.
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Affiliation(s)
- Ann P Wheeler
- Ludwig Institute for Cancer Research, Royal Free and University College School of Medicine, 91 Riding House Street, London, W1W 7BS, UK
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227
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ten Klooster J, Evers E, Janssen L, Machesky L, Michiels F, Hordijk P, Collard J. Interaction between Tiam1 and the Arp2/3 complex links activation of Rac to actin polymerization. Biochem J 2006; 397:39-45. [PMID: 16599904 PMCID: PMC1479755 DOI: 10.1042/bj20051957] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2005] [Revised: 03/27/2006] [Accepted: 04/07/2006] [Indexed: 12/22/2022]
Abstract
The Rac-specific GEF (guanine-nucleotide exchange factor) Tiam1 (T-lymphoma invasion and metastasis 1) regulates migration, cell-matrix and cell-cell adhesion by modulating the actin cytoskeleton through the GTPase, Rac1. Using yeast two-hybrid screening and biochemical assays, we found that Tiam1 interacts with the p21-Arc [Arp (actin-related protein) complex] subunit of the Arp2/3 complex. Association occurred through the N-terminal pleckstrin homology domain and the adjacent coiled-coil region of Tiam1. As a result, Tiam1 co-localizes with the Arp2/3 complex at sites of actin polymerization, such as epithelial cell-cell contacts and membrane ruffles. Deletion of the p21-Arc-binding domain in Tiam1 impairs its subcellular localization and capacity to activate Rac1, suggesting that binding to the Arp2/3 complex is important for the function of Tiam1. Indeed, blocking Arp2/3 activation with a WASP (Wiskott-Aldrich syndrome protein) inhibitor leads to subcellular relocalization of Tiam1 and decreased Rac activation. Conversely, functionally active Tiam1, but not a GEF-deficient mutant, promotes activation of the Arp2/3 complex and its association with cytoskeletal components, indicating that Tiam1 and Arp2/3 are mutually dependent for their correct localization and signalling. Our data suggests a model in which the Arp2/3 complex acts as a scaffold to localize Tiam1, and thereby Rac activity, which are both required for activation of the Arp2/3 complex and further Arp2/3 recruitment. This 'self-amplifying' signalling module involving Tiam1, Rac and the Arp2/3 complex could thus drive actin polymerization at specific sites in cells that are required for dynamic morphological changes.
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Key Words
- actin
- arp2/3 complex
- wiskott–aldrich syndrome protein (wasp)
- p21-arc
- rac1
- t-lymphoma invasion and metastasis 1 (tiam1)
- 3at, 3-aminotriazole
- arc, arp complex
- arp, actin-related protein
- cc, coiled-coil
- cdc42, cell division cycle 42
- crib, cdc42/rac interacting binding
- dh, dbl homology
- ex, extended
- fl, full-length
- gef, guanine-nucleotide exchange factor
- gst, glutathione s-transferase
- ha, haemagglutinin
- irsp53, insulin receptor substrate p53
- jip, c-jun n-terminal kinase-interacting protein
- mdck, madin–darby canine kidney cells
- pak, p21-activated kinase
- ph, pleckstrin homology
- phn, n-terminal ph domain
- pir121, p53-inducible mrna with an mr of 140000
- tiam1, t-lymphoma invasion and metastasis
- wasp, wiskott–aldrich syndrome protein
- wave, wasp-family verprolin homologous protein
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Affiliation(s)
- Jean Paul ten Klooster
- *The Netherlands Cancer Institute, Division of Cell Biology, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands
| | - Eva E. Evers
- *The Netherlands Cancer Institute, Division of Cell Biology, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands
| | - Lennert Janssen
- *The Netherlands Cancer Institute, Division of Cell Biology, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands
| | - Laura M. Machesky
- †Division of Molecular Cell Biology, School of Biosciences, University of Birmingham, Birmingham B15 2TT, U.K
| | - Frits Michiels
- *The Netherlands Cancer Institute, Division of Cell Biology, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands
| | - Peter Hordijk
- ‡Sanquin Research and Landsteiner Laboratorium, Academic Medical Center, University of Amsterdam, Plesmanlaan 125, 1066 CX Amsterdam, The Netherlands
| | - John G. Collard
- *The Netherlands Cancer Institute, Division of Cell Biology, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands
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228
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Sasaki AT, Firtel RA. Regulation of chemotaxis by the orchestrated activation of Ras, PI3K, and TOR. Eur J Cell Biol 2006; 85:873-95. [PMID: 16740339 DOI: 10.1016/j.ejcb.2006.04.007] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Directed cell migration and cell polarity are crucial in many facets of biological processes. Cellular motility requires a complex array of signaling pathways, in which orchestrated cross-talk, a feedback loop, and multi-component signaling recur. Almost every signaling molecule requires several regulatory processes to be functionally activated, and a lack of a signaling molecule often leads to chemotaxis defects, suggesting an integral role for each component in the pathway. We outline our current understanding of the signaling event that regulates chemotaxis with an emphasis on recent findings associated with the Ras, PI3K, and target of rapamycin (TOR) pathways and the interplay of these pathways. Ras, PI3K, and TOR are known as key regulators of cellular growth. Deregulation of those pathways is associated with many human diseases, such as cancer, developmental disorders, and immunological deficiency. Recent studies in yeast, mammalian cells, and Dictyostelium discoideum reveal another critical role of Ras, PI3K, and TOR in regulating the actin cytoskeleton, cell polarity, and cellular movement. These findings shed light on the mechanism by which eukaryotic cells maintain cell polarity and directed cell movement, and also demonstrate that multiple steps in the signal transduction pathway coordinately regulate cell motility.
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Affiliation(s)
- Atsuo T Sasaki
- Section of Cell and Developmental Biology, Division of Biological Sciences, Center for Molecular Genetics, University of California, San Diego, Natural Sciences Building, Room 6316, 9500 Gilman Drive, La Jolla, CA 92093-0380, USA
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229
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Suetsugu S, Kurisu S, Oikawa T, Yamazaki D, Oda A, Takenawa T. Optimization of WAVE2 complex-induced actin polymerization by membrane-bound IRSp53, PIP(3), and Rac. ACTA ACUST UNITED AC 2006; 173:571-85. [PMID: 16702231 PMCID: PMC2063866 DOI: 10.1083/jcb.200509067] [Citation(s) in RCA: 140] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
WAVE2 activates the actin-related protein (Arp) 2/3 complex for Rac-induced actin polymerization during lamellipodium formation and exists as a large WAVE2 protein complex with Sra1/PIR121, Nap1, Abi1, and HSPC300. IRSp53 binds to both Rac and Cdc42 and is proposed to link Rac to WAVE2. We found that the knockdown of IRSp53 by RNA interference decreased lamellipodium formation without a decrease in the amount of WAVE2 complex. Localization of WAVE2 at the cell periphery was retained in IRSp53 knockdown cells. Moreover, activated Cdc42 but not Rac weakened the association between WAVE2 and IRSp53. When we measured Arp2/3 activation in vitro, the WAVE2 complex isolated from the membrane fraction of cells was fully active in an IRSp53-dependent manner but WAVE2 isolated from the cytosol was not. Purified WAVE2 and purified WAVE2 complex were activated by IRSp53 in a Rac-dependent manner with PIP3-containing liposomes. Therefore, IRSp53 optimizes the activity of the WAVE2 complex in the presence of activated Rac and PIP3.
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Affiliation(s)
- Shiro Suetsugu
- Department of Biochemistry, Institute of Medical Science, University of Tokyo, Minato-ku, Tokyo 108-8639, Japan
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230
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Stradal TEB, Pusch R, Kliche S. Molecular regulation of cytoskeletal rearrangements during T cell signalling. Results Probl Cell Differ 2006; 43:219-44. [PMID: 17068974 DOI: 10.1007/400_022] [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] [Indexed: 12/18/2022]
Abstract
Regulation of the cytoskeleton in cells of the haematopoietic system is essential for fulfilling diverse tasks such as migration towards a chemoattractant, phagocytosis or cell-cell communication. This is particularly true for the many types of T cells, which are at the foundation of the adaptive immune system in vertebrates. Deregulation of actin filament turnover is known to be involved in the development of severe immunodeficiencies or immunoproliferative diseases. Therefore, molecular dissection of signalling complexes and effector molecules, which leads to controlled cytoskeletal assembly, has been the focus of immunological research in the last decade. In the past, cytoskeletal remodelling was frequently understood as the finish line of signalling, while today it becomes increasingly evident that actin and microtubule dynamics are required for proper signal transmission in many processes such as T cell activation. Significant effort is made in many laboratories to further elucidate the contribution of cytoskeletal remodelling to immune function. The objective of this article is to summarise the current knowledge on how actin and microtubules are reorganised to support the formation of structures as diverse as the immunological synapse and peripheral protrusions during cell migration.
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Affiliation(s)
- Theresia E B Stradal
- Signalling and Motility Group, German Research Centre for Biotechnology (GBF), Braunschweig, Germany
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231
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Le J, Mallery EL, Zhang C, Brankle S, Szymanski DB. Arabidopsis BRICK1/HSPC300 Is an Essential WAVE-Complex Subunit that Selectively Stabilizes the Arp2/3 Activator SCAR2. Curr Biol 2006; 16:895-901. [PMID: 16584883 DOI: 10.1016/j.cub.2006.03.061] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2006] [Revised: 03/06/2006] [Accepted: 03/07/2006] [Indexed: 11/24/2022]
Abstract
The actin cytoskeleton dynamically reorganizes the cytoplasm during cell morphogenesis. The actin-related protein (Arp)2/3 complex is a potent nucleator of actin filaments that controls a variety of endomembrane functions including the endocytic internalization of plasma membrane , vacuole biogenesis , plasma-membrane protrusion in crawling cells , and membrane trafficking from the Golgi . Therefore, Arp2/3 is an important signaling target during morphogenesis. The evolutionarily conserved Rac-WAVE-Arp2/3 pathway links actin filament nucleation to cell morphogenesis . WAVE translates Rac-GTP signals into Arp2/3 activation by regulating the stability and/or localization of the activator subunit Scar/WAVE . The WAVE complex includes Sra1/PIR121/CYFIP1, Nap1/NAP125, Abi-1/Abi-2, Brick1(Brk1)/HSPC300, and Scar/WAVE : Defining the in vivo function of each subunit is an important step toward understanding this complicated signaling pathway. Brk1/HSPC300 has been the most recalcitrant WAVE-complex protein and has no known function. In this paper, we report that Arabidopsis brick1 (brk1) is a member of the "distorted group" of trichome morphology mutants, a group that defines a WAVE-ARP2/3 morphogenesis pathway . In this paper we provide the first strong genetic and biochemical evidence that BRK1 is a critical WAVE-complex subunit that selectively stabilizes the Arp2/3 activator SCAR2.
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Affiliation(s)
- Jie Le
- Department of Agronomy, Purdue University, Lilly Hall, 915 W. State Street, West Lafayette, Indiana 47907, USA
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232
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Williams MJ, Wiklund ML, Wikman S, Hultmark D. Rac1 signalling in the Drosophila larval cellular immune response. J Cell Sci 2006; 119:2015-24. [PMID: 16621891 DOI: 10.1242/jcs.02920] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
The Drosophila larval cellular immune response involves cells (hemocytes) that can be recruited from a hematopoietic organ located behind the brain, as well as a sessile population of cells found just underneath the larval cuticle arranged in a segmental pattern. By using two Rac1 GTPase effector-loop mutants together with epistasis studies, we show that Rac1 requires the Drosophila melanogaster Jun N-terminal kinase Basket (Bsk), as well as stable actin formation to recruit the sessile hemocyte population. We show that actin stabilization is necessary for Rac1-induced hemocyte activation by lowering cofilin (encoded by the twinstar gene tsr) expression in blood cells. Removing Bsk by RNAi suppressed Rac1-induced release of sessile hemocytes. RNAi against Bsk also suppressed Rac1 induction of lamellocytes, a specialized population of hemocytes necessary for the encapsulation of invading pathogens. Furthermore, Rac1 and Bsk are involved in regulating the formation of actin- and focal adhesion kinase (FAK)-rich placodes in hemocytes. Lastly, Rac1 and Bsk are both required for the proper encapsulation of eggs from the parasitoid wasp Leptipolina boulardi. From these data we conclude that Rac1 induces Bsk activity and stable actin formation for cellular immune activation, leading to sessile hemocyte release and an increase in the number of circulating hemocytes.
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Affiliation(s)
- Michael J Williams
- Umeå Centre for Molecular Pathogenesis (UCMP), Umeå University, S-901 87, Umeå, Sweden.
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233
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Steffen A, Faix J, Resch GP, Linkner J, Wehland J, Small JV, Rottner K, Stradal TE. Filopodia formation in the absence of functional WAVE- and Arp2/3-complexes. Mol Biol Cell 2006; 17:2581-91. [PMID: 16597702 PMCID: PMC1474932 DOI: 10.1091/mbc.e05-11-1088] [Citation(s) in RCA: 188] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Cell migration is initiated by plasma membrane protrusions, in the form of lamellipodia and filopodia. The latter rod-like projections may exert sensory functions and are found in organisms as distant in evolution as mammals and amoeba such as Dictyostelium discoideum. In mammals, lamellipodia protrusion downstream of the small GTPase Rac1 requires a multimeric protein assembly, the WAVE-complex, which activates Arp2/3-mediated actin filament nucleation and actin network assembly. A current model of filopodia formation postulates that these structures arise from a dendritic network of lamellipodial actin filaments by selective elongation and bundling. Here, we have analyzed filopodia formation in mammalian cells abrogated in expression of essential components of the lamellipodial actin polymerization machinery. Cells depleted of the WAVE-complex component Nck-associated protein 1 (Nap1), and, in consequence, of lamellipodia, exhibited normal filopodia protrusion. Likewise, the Arp2/3-complex, which is essential for lamellipodia protrusion, is dispensable for filopodia formation. Moreover, genetic disruption of nap1 or the WAVE-orthologue suppressor of cAMP receptor (scar) in Dictyostelium was also ineffective in preventing filopodia protrusion. These data suggest that the molecular mechanism of filopodia formation is conserved throughout evolution from Dictyostelium to mammals and show that lamellipodia and filopodia formation are functionally separable.
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Affiliation(s)
| | - Jan Faix
- Institute of Biophysical Chemistry, Hannover Medical School, D-30623 Hannover, Germany; and
| | - Guenter P. Resch
- Institute of Molecular Biotechnology, Austrian Academy of Sciences, A-1030 Vienna, Austria
| | - Joern Linkner
- Institute of Biophysical Chemistry, Hannover Medical School, D-30623 Hannover, Germany; and
| | - Juergen Wehland
- Department of Cell Biology, German Research Centre for Biotechnology, D-38124 Braunschweig, Germany
| | - J. Victor Small
- Institute of Molecular Biotechnology, Austrian Academy of Sciences, A-1030 Vienna, Austria
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234
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Abstract
The small GTPases Rho, Rac and Cdc42 (cell-division cycle 42) function as molecular switches to modulate the actin cytoskeleton. They achieve this by modulating the activity of downstream cellular targets. One group of Rho GTPase effectors, WAVE (Wiskott-Aldrich syndrome protein verprolin homologous)-1, WAVE-2 and WAVE-3, function as scaffolds for actin-based signalling complexes. The present review highlights current knowledge regarding the biochemistry of the WAVE signalling complexes and their biological significance.
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Affiliation(s)
- S H Soderling
- Howard Hughes Medical Institute, Vollum Institute, Oregon Health and Science University, Portland, OR 97239, USA
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235
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Djakovic S, Dyachok J, Burke M, Frank MJ, Smith LG. BRICK1/HSPC300 functions with SCAR and the ARP2/3 complex to regulate epidermal cell shape in Arabidopsis. Development 2006; 133:1091-100. [PMID: 16481352 DOI: 10.1242/dev.02280] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The Arp2/3 complex, a highly conserved nucleator of F-actin polymerization,is essential for a variety of eukaryotic cellular processes, including epidermal cell morphogenesis in Arabidopsis thaliana. Efficient nucleation of actin filaments by the Arp2/3 complex requires the presence of an activator such as a member of the Scar/WAVE family. In mammalian cells, a multiprotein complex consisting of WAVE, PIR121/Sra-1, Nap1, Abi-2 and HSPC300 mediates responsiveness of WAVE to upstream regulators such as Rac. Essential roles in WAVE complex assembly or function have been demonstrated for PIR121/Sra-1, Nap1 and Abi-2, but the significance of HSPC300 in this complex is unclear. Plant homologs of all mammalian WAVE complex components have been identified, including HSPC300, the mammalian homolog of maize BRICK1 (BRK1). We show that, like mutations disrupting the Arabidopsis homologs of PIR121/Sra-1, Nap1 and Scar/WAVE, mutations in the Arabidopsis BRK1gene result in trichome and pavement cell morphology defects (and associated alterations in the F-actin cytoskeleton of expanding cells) similar to those caused by mutations disrupting the ARP2/3 complex itself. Analysis of double mutants provides genetic evidence that BRK1 functions in a pathway with the ARP2/3 complex. BRK1 is required for accumulation of SCAR1 protein in vivo,potentially explaining the apparently essential role of BRK1 in ARP2/3 complex function.
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Affiliation(s)
- Stevan Djakovic
- Section of Cell and Developmental Biology, Division of Biological Sciences, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0116, USA
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236
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Nolz JC, Gomez TS, Zhu P, Li S, Medeiros RB, Shimizu Y, Burkhardt JK, Freedman BD, Billadeau DD. The WAVE2 complex regulates actin cytoskeletal reorganization and CRAC-mediated calcium entry during T cell activation. Curr Biol 2006; 16:24-34. [PMID: 16401421 PMCID: PMC1779663 DOI: 10.1016/j.cub.2005.11.036] [Citation(s) in RCA: 190] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2005] [Revised: 10/19/2005] [Accepted: 11/08/2005] [Indexed: 11/15/2022]
Abstract
BACKGROUND The engagement of the T cell receptor results in actin cytoskeletal reorganization at the immune synapse (IS) and the triggering of biochemical signaling cascades leading to gene regulation and, ultimately, cellular activation. Recent studies have identified the WAVE family of proteins as critical mediators of Rac1-induced actin reorganization in other cell types. However, whether these proteins participate in actin reorganization at the IS or signaling pathways in T cells has not been investigated. RESULTS By using a combination of biochemical, genetic, and cell biology approaches, we provide evidence that WAVE2 is recruited to the IS, is biochemically modified, and is required for actin reorganization and beta-integrin-mediated adhesion after TCR crosslinking. Moreover, we show that WAVE2 regulates calcium entry at a point distal to PLCgamma1 activation and IP(3)-mediated store release. CONCLUSIONS These data reveal a role for WAVE2 in regulating multiple pathways leading to T cell activation. In particular, this work shows that WAVE2 is a key component of the actin regulatory machinery in T cells and that it also participates in linking intracellular calcium store depletion to calcium release-activated calcium (CRAC) channel activation.
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Affiliation(s)
| | | | - Peimin Zhu
- Department of Pathobiology School of Veterinary Medicine
University of Pennsylvania Philadelphia, Pennsylvania 19104
| | - Shuixing Li
- Department of Pathology Children’s Hospital of
Philadelphia University of Pennsylvania Philadelphia, Pennsylvania 19104
| | - Ricardo B. Medeiros
- Department of Laboratory Medicine and Pathology Center for
Immunology Cancer Center University of Minnesota Medical School Minneapolis,
Minnesota 55455
| | - Yoji Shimizu
- Department of Laboratory Medicine and Pathology Center for
Immunology Cancer Center University of Minnesota Medical School Minneapolis,
Minnesota 55455
| | - Janis K. Burkhardt
- Department of Pathology Children’s Hospital of
Philadelphia University of Pennsylvania Philadelphia, Pennsylvania 19104
| | - Bruce D. Freedman
- Department of Pathobiology School of Veterinary Medicine
University of Pennsylvania Philadelphia, Pennsylvania 19104
| | - Daniel D. Billadeau
- Department of Immunology
- Division of Oncology Research Mayo Clinic College of Medicine
Rochester, Minnesota 55905
- Correspondence:
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237
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Zipfel PA, Bunnell SC, Witherow DS, Gu JJ, Chislock EM, Ring C, Pendergast AM. Role for the Abi/wave protein complex in T cell receptor-mediated proliferation and cytoskeletal remodeling. Curr Biol 2006; 16:35-46. [PMID: 16401422 DOI: 10.1016/j.cub.2005.12.024] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2005] [Revised: 12/12/2005] [Accepted: 12/13/2005] [Indexed: 12/11/2022]
Abstract
BACKGROUND The molecular reorganization of signaling molecules after T cell receptor (TCR) activation is accompanied by polymerization of actin at the site of contact between a T cell and an antigen-presenting cell (APC), as well as extension of actin-rich lamellipodia around the APC. Actin polymerization is critical for the fidelity and efficiency of the T cell response to antigen. The ability of T cells to polymerize actin is critical for several steps in T cell activation including TCR clustering, mature immunological synapse formation, calcium flux, IL-2 production, and proliferation. Activation of the Rac GTPase has been linked to regulation of actin polymerization after TCR stimulation. However, the molecules required for TCR-mediated actin polymerization downstream of activated Rac have remained elusive. Here we identify a novel role for the Abi/Wave protein complex, which signals downstream of activated Rac, in the regulation of actin polymerization and T cell activation in response to TCR stimulation. RESULTS Here we show that Abi and Wave rapidly translocate from the T cell cytoplasm to the T cell:B cell contact site in the presence of antigen. Abi and Wave colocalize with actin at the T cell:B cell conjugation site. Moreover, Wave and Abi are necessary for actin polymerization after T cell activation, and loss of Abi proteins in mice impairs TCR-induced cell proliferation and IL-2 production in primary T cells. Significantly, the impairment in actin polymerization in cells lacking Abi proteins is due to the inability of Wave proteins to localize to the T cell:B cell contact site in the presence of antigen, rather than the destabilization of the components of the Wave protein complex. CONCLUSIONS The Abi/Wave complex is a novel regulator of TCR-mediated actin dynamics, IL-2 production, and proliferation.
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Affiliation(s)
- Patricia A Zipfel
- Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina 27710, USA
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238
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Mitsushima M, Sezaki T, Akahane R, Ueda K, Suetsugu S, Takenawa T, Kioka N. Protein kinase A-dependent increase in WAVE2 expression induced by the focal adhesion protein vinexin. Genes Cells 2006; 11:281-92. [PMID: 16483316 DOI: 10.1111/j.1365-2443.2006.00932.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The focal adhesion protein vinexin is a member of a family of adaptor proteins that are thought to participate in the regulation of cell adhesion, cytoskeletal reorganization, and growth factor signaling. Here, we show that vinexin beta increases the amount of and reduces the mobility on SDS-PAGE of Wiskott-Aldrich syndrome protein family verprolin-homologous protein (WAVE) 2 protein, which is a key factor modulating actin polymerization in migrating cells. This mobility retardation disappeared after in vitro phosphatase treatment. Co-immunoprecipitation assays revealed the interaction of vinexin beta with WAVE2 as well as WAVE1 and N-WASP. Vinexin beta interacts with the proline-rich region of WAVE2 through the first and second SH3 domains of vinexin beta. Mutations disrupting the interaction impaired the ability of vinexin beta to increase the amount of WAVE2 protein. Treatments with proteasome inhibitors increased the amount of WAVE2, but did not have an additive effect with vinexin beta. Inhibition of protein kinase A (PKA) activity suppressed the vinexin-induced increase in WAVE2 protein, while activation of PKA increased WAVE2 expression without vinexin beta. These results suggest that vinexin beta regulates the proteasome-dependent degradation of WAVE2 in a PKA-dependent manner.
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Affiliation(s)
- Masaru Mitsushima
- Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
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239
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Kheir WA, Gevrey JC, Yamaguchi H, Isaac B, Cox D. A WAVE2-Abi1 complex mediates CSF-1-induced F-actin-rich membrane protrusions and migration in macrophages. J Cell Sci 2006; 118:5369-79. [PMID: 16280551 DOI: 10.1242/jcs.02638] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Colony-stimulating factor 1 (CSF-1) is an important physiological chemoattractant for macrophages. The mechanisms by which CSF-1 elicits the formation of filamentous actin (F-actin)-rich membrane protrusions and induces macrophage migration are not fully understood. In particular, very little is known regarding the contribution of the different members of the Wiskott-Aldrich Syndrome protein (WASP) family of actin regulators in response to CSF-1. Although a role for WASP itself in macrophage chemotaxis has been previously identified, no data was available regarding the function of WASP family verprolin-homologous (WAVE) proteins in this cell type. We found that WAVE2 was the predominant isoform to be expressed in primary macrophages and in cells derived from the murine monocyte/macrophage RAW264.7 cell line (RAW/LR5). CSF-1 treatment of macrophages resulted in WAVE2 accumulation in F-actin-rich protrusions induced by CSF-1. Inhibition of WAVE2 function by expressing a dominant-negative mutant or introducing anti-WAVE2 antibodies in RAW/LR5 cells, as well as reduction of endogenous WAVE2 expression by RNA-mediated interference (RNAi), resulted in a significant reduction of CSF-1-elicited F-actin protrusions. WAVE2 was found in a protein complex together with Abelson kinase interactor 1 (Abi1) in resting or stimulated cells. Both WAVE2 and Abi1 were recruited to and necessary for the formation of F-actin protrusions in response to CSF-1. Reducing the levels of WAVE2, directly or by targeting Abi1, resulted in an impaired cell migration to CSF-1. Altogether these data identify a WAVE2-Abi1 complex crucial for the normal actin cytoskeleton reorganization and migration of macrophages in response to CSF-1.
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Affiliation(s)
- Wassim Abou Kheir
- Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, Bronx, New York City, NY 10461, USA
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240
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Luo X, Levens E, Williams RS, Chegini N. The expression of Abl interactor 2 in leiomyoma and myometrium and regulation by GnRH analogue and transforming growth factor-β. Hum Reprod 2006; 21:1380-6. [PMID: 16488906 DOI: 10.1093/humrep/del011] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
BACKGROUND Abelson (Abl) interactor 2 (Abi-2) has been considered as a key regulator of cell/tissue structural organization and is differentially expressed in leiomyomas. The objective of this study was to evaluate the expression of Abi-2 in leiomyoma/myometrium during the menstrual cycle and following GnRH analogue (GnRHa) therapy, as well as regulation by transforming growth factor (TGF)-beta1 in leiomyoma and myometrial smooth muscle cells (LSMC and MSMC). METHODS We used real-time PCR, Western blotting and immunohistochemistry to determine the expression of Abi-2 in paired leiomyoma and myometrium (n = 27) from proliferative (n = 8) and secretory (n = 12) phases of the menstrual cycle and from patients who received GnRHa therapy (n = 7). Time-dependent action of TGF-beta1 (2.5 ng/ml) and GnRHa (0.1 microM) on Abi-2 expression was determined in LSMC and MSMC. RESULTS Leiomyomas express elevated levels of Abi-2 as compared with myometrium from the proliferative but not the secretory phase of the menstrual cycle, with a significant reduction following GnRHa therapy (P < 0.05). Western blotting showed a similar trend in Abi-2 protein expression in leiomyoma/myometrial tissue extracts, which was immunolocalized in LSMC and MSMC, connective tissue fibroblasts and arterial walls. The expression of Abi-2 in LSMC and MSMC was increased by TGF-beta1 (2.5 ng/ml) and was inhibited by GnRHa (0.1 microM) in a time- and cell-dependent manner, and pretreatment with Smad3 SiRNA and U0126, an MEK-1/2 inhibitor, respectively, reversed their actions. CONCLUSION Based on the menstrual cycle-dependent expression, the influence of GnRHa therapy, and regulation by TGF-beta in LSMC/MSMC, we conclude that Abi-2 may have a key regulatory function in leiomyomas cellular/tissue structural organization during growth and regression.
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Affiliation(s)
- Xiaoping Luo
- Department of Obstetrics and Gynecology, University of Florida, Gainesville, FL, USA
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241
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Weiner OD, Rentel MC, Ott A, Brown GE, Jedrychowski M, Yaffe MB, Gygi SP, Cantley LC, Bourne HR, Kirschner MW. Hem-1 complexes are essential for Rac activation, actin polymerization, and myosin regulation during neutrophil chemotaxis. PLoS Biol 2006; 4:e38. [PMID: 16417406 PMCID: PMC1334198 DOI: 10.1371/journal.pbio.0040038] [Citation(s) in RCA: 138] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2005] [Accepted: 12/01/2005] [Indexed: 12/30/2022] Open
Abstract
Migrating cells need to make different actin assemblies at the cell's leading and trailing edges and to maintain physical separation of signals for these assemblies. This asymmetric control of activities represents one important form of cell polarity. There are significant gaps in our understanding of the components involved in generating and maintaining polarity during chemotaxis. Here we characterize a family of complexes (which we term leading edge complexes), scaffolded by hematopoietic protein 1 (Hem-1), that organize the neutrophil's leading edge. The Wiskott-Aldrich syndrome protein family Verprolin-homologous protein (WAVE)2 complex, which mediates activation of actin polymerization by Rac, is only one member of this family. A subset of these leading edge complexes are biochemically separable from the WAVE2 complex and contain a diverse set of potential polarity-regulating proteins. RNA interference-mediated knockdown of Hem-1-containing complexes in neutrophil-like cells: (a) dramatically impairs attractant-induced actin polymerization, polarity, and chemotaxis; (b) substantially weakens Rac activation and phosphatidylinositol-(3,4,5)-tris-phosphate production, disrupting the (phosphatidylinositol-(3,4,5)-tris-phosphate)/Rac/F-actin-mediated feedback circuit that organizes the leading edge; and (c) prevents exclusion of activated myosin from the leading edge, perhaps by misregulating leading edge complexes that contain inhibitors of the Rho-actomyosin pathway. Taken together, these observations show that versatile Hem-1-containing complexes coordinate diverse regulatory signals at the leading edge of polarized neutrophils, including but not confined to those involving WAVE2-dependent actin polymerization.
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Affiliation(s)
- Orion D Weiner
- 1Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America
- 6Cardivascular Research Institute, University of California San Francisco, California, United States of America
| | - Maike C Rentel
- 2Department of Cellular and Molecular Pharmacology, University of California, San Francisco, California, United States of America
| | - Alex Ott
- 2Department of Cellular and Molecular Pharmacology, University of California, San Francisco, California, United States of America
| | - Glenn E Brown
- 3Center for Cancer Research, Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States of America
| | - Mark Jedrychowski
- 4Department of Cell Biology and Taplin Biological Mass Spectrometry Facility, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Michael B Yaffe
- 3Center for Cancer Research, Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States of America
| | - Steven P Gygi
- 4Department of Cell Biology and Taplin Biological Mass Spectrometry Facility, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Lewis C Cantley
- 5Department of Systems Biology, Harvard Medical School, Division of Signal Transduction, Beth Israel Deaconess Medical Center, Boston, Massachusetts, United States of America
| | - Henry R Bourne
- 2Department of Cellular and Molecular Pharmacology, University of California, San Francisco, California, United States of America
| | - Marc W Kirschner
- 1Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America
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242
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Sawa M, Takenawa T. Caenorhabditis elegans WASP-interacting protein homologue WIP-1 is involved in morphogenesis through maintenance of WSP-1 protein levels. Biochem Biophys Res Commun 2005; 340:709-17. [PMID: 16378591 DOI: 10.1016/j.bbrc.2005.12.056] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2005] [Accepted: 12/06/2005] [Indexed: 11/25/2022]
Abstract
Mammalian WASP and N-WASP are involved in reorganization of the actin cytoskeleton through activation of the Arp2/3 complex and in regulation of cell motility or cell shape changes. In the present study, we identified WASP-interacting protein homologue (WIP)-1 in Caenorhabditis elegans. WIP-1 contains the domains and sequences conserved among mammalian WIP family proteins. Yeast two-hybrid analysis detected a physical interaction between WIP-1 and WSP-1, the sole homologue of WASP/N-WASP in C. elegans. Western analysis of embryo lysates showed that RNA interference (RNAi) treatment for wip-1 decreased levels of WSP-1 protein, and wsp-1(RNAi) treatment decreased levels of WIP-1 protein. However, wsp-1 mRNA levels were not decreased in wip-1(RNAi)-treated embryos, and wip-1 mRNA levels were not decreased in wsp-1(RNAi)-treated embryos. Furthermore, disruption of WIP-1 by RNAi resulted in embryonic lethality with morphologic defects in hypodermal cell migration, a process known as ventral enclosure. This phenotype was similar to that observed in RNAi experiments for wsp-1. Immunostaining showed that WIP-1 was expressed by migrating hypodermal cells, as was WSP-1. This expression during ventral enclosure was reduced in wip-1(RNAi)-treated embryos and wsp-1(RNAi)-treated embryos. Our results suggest that C. elegans WIP-1 may function in hypodermal cell migration during ventral enclosure by maintaining levels of WSP-1.
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Affiliation(s)
- Mariko Sawa
- Department of Biochemistry, Institute of Medical Science, University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan
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243
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Stradal TEB, Scita G. Protein complexes regulating Arp2/3-mediated actin assembly. Curr Opin Cell Biol 2005; 18:4-10. [PMID: 16343889 DOI: 10.1016/j.ceb.2005.12.003] [Citation(s) in RCA: 202] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2005] [Accepted: 12/01/2005] [Indexed: 10/25/2022]
Abstract
Key steps in regulating actin dynamics are the de novo nucleation and elongation of actin filaments, which can be catalysed by a limited number of proteins and protein complexes. Among these, Arp2/3 complex and formins are the best studied. Arp2/3-complex activity is controlled through signalling-dependent association with nucleation-promoting factors, such as the WASP/WAVE family proteins. A common theme for these molecules, which is well established for WAVEs but is only just beginning to emerge for WASPs, is that they act as coincident detectors of a variety of signalling pathways through the formation of large multi-molecular complexes.
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Affiliation(s)
- Theresia E B Stradal
- Signalling and Motility Group, German Research Centre for Biotechnology (GBF), Mascheroder Weg 1, D-38124 Braunschweig, Germany.
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244
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Abstract
Actin reorganization is a tightly regulated process that co-ordinates complex cellular events, such as cell migration, chemotaxis, phagocytosis and adhesion, but the molecular mechanisms that underlie these processes are not well understood. SCAR (suppressor of cAMP receptor)/WAVE [WASP (Wiskott-Aldrich syndrome protein)-family verprolin homology protein] proteins are members of the conserved WASP family of cytoskeletal regulators, which play a critical role in actin dynamics by triggering Arp2/3 (actin-related protein 2/3)-dependent actin nucleation. SCAR/WAVEs are thought to be regulated by a pentameric complex which also contains Abi (Abl-interactor), Nap (Nck-associated protein), PIR121 (p53-inducible mRNA 121) and HSPC300 (haematopoietic stem progenitor cell 300), but the structural organization of the complex and the contribution of its individual components to the regulation of SCAR/WAVE function remain unclear. Additional features of SCAR/WAVE regulation are highlighted by the discovery of other interactors and distinct complexes. It is likely that the combinatorial assembly of different components of SCAR/WAVE complexes will prove to be vital for their roles at the centre of dynamic actin reorganization.
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245
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Abstract
The actin-nucleating Arp2/3 complex is essential for life in yeast and animals, but not in plants, in which mutants of Arp2/3 complex components show relatively minor developmental abnormalities. Animal cells control the activity of the Arp2/3 complex through the suppressor of cyclic AMP receptor (SCAR) complex to achieve cell motility. Amazingly, plants have also retained the SCAR cell-motility pathway, and now provide a unique model for the study of new aspects of SCAR function in the absence of cell motility.
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Affiliation(s)
- Michael J Deeks
- The Integrative Cell Biology Laboratory, School of Biological and Biomedical Sciences, University of Durham, South Road, Durham, DH1 3LE, UK
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Bogdan S, Stephan R, Löbke C, Mertens A, Klämbt C. Abi activates WASP to promote sensory organ development. Nat Cell Biol 2005; 7:977-84. [PMID: 16155589 DOI: 10.1038/ncb1305] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2005] [Accepted: 08/12/2005] [Indexed: 11/08/2022]
Abstract
Actin polymerization is a key process for many cellular events during development. To a large extent, the formation of filamentous actin is controlled by the WASP and WAVE proteins that activate the Arp2/3 complex in different developmental processes. WAVE function is regulated through a protein complex containing Sra1, Kette and Abi. Using biochemical, cell biological and genetic tools, we show here that the Abi protein also has a central role in activating WASP-mediated processes. Abi binds WASP through its carboxy-terminal domain and acts as a potent stimulator of WASP-dependent F-actin formation. To elucidate the biological function of abi in Drosophila melanogaster, we studied bristle development, a process known to require wasp function. Reduction of abi function leads to a loss of bristles similar to that observed in wasp mutants. Activation of Abi results in the formation of ectopic bristles, a phenotype that is suppressed by a reduction of wasp activity but is not affected by the reduction of wave function. Thus, in vivo Abi may set the balance between WASP and WAVE in different actin-based developmental processes.
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Affiliation(s)
- Sven Bogdan
- Institut für Neurobiologie, Universität Münster, Badestr. 9, D-48149 Münster, Germany
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247
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Innocenti M, Gerboth S, Rottner K, Lai FPL, Hertzog M, Stradal TEB, Frittoli E, Didry D, Polo S, Disanza A, Benesch S, Di Fiore PP, Carlier MF, Scita G. Abi1 regulates the activity of N-WASP and WAVE in distinct actin-based processes. Nat Cell Biol 2005; 7:969-76. [PMID: 16155590 DOI: 10.1038/ncb1304] [Citation(s) in RCA: 169] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2005] [Accepted: 08/18/2005] [Indexed: 11/09/2022]
Abstract
Neural Wiskott-Aldrich syndrome protein (N-WASP) and WAVE are members of a family of proteins that use the Arp2/3 complex to stimulate actin assembly in actin-based motile processes. By entering into distinct macromolecular complexes, they act as convergent nodes of different signalling pathways. The role of WAVE in generating lamellipodial protrusion during cell migration is well established. Conversely, the precise cellular functions of N-WASP have remained elusive. Here, we report that Abi1, an essential component of the WAVE protein complex, also has a critical role in regulating N-WASP-dependent function. Consistently, Abi1 binds to N-WASP with nanomolar affinity and, cooperating with Cdc42, potently induces N-WASP activity in vitro. Molecular genetic approaches demonstrate that Abi1 and WAVE, but not N-WASP, are essential for Rac-dependent membrane protrusion and macropinocytosis. Conversely, Abi1 and N-WASP, but not WAVE, regulate actin-based vesicular transport, epidermal growth factor receptor (EGFR) endocytosis, and EGFR and transferrin receptor (TfR) cell-surface distribution. Thus, Abi1 is a dual regulator of WAVE and N-WASP activities in specific processes that are dependent on actin dynamics.
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Affiliation(s)
- Metello Innocenti
- IFOM, Istituto FIRC di Oncologia Molecolare, Via Adamello 16, 20134, Milan, Italy
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248
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Williams MJ, Ando I, Hultmark D. Drosophila melanogaster Rac2 is necessary for a proper cellular immune response. Genes Cells 2005; 10:813-23. [PMID: 16098145 DOI: 10.1111/j.1365-2443.2005.00883.x] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
It has been reported that during Drosophila embryonic development, and in cell culture, that the Rac GTPases are redundant. To better elucidate Rac function in Drosophila, we decided to study the role of Rac2 in larval cellular defense reactions against the parasitiod Leptopilina boulardi. Here we show a dramatic effect in the context of cellular immunity where, unlike embryonic development, Rac2 appears to have a non-redundant function. When an invading parasitoid is recognized as foreign, circulating hemocytes (blood cells) should recognize and attach to the egg chorion. After attachment the hemocytes should then spread to form a multilayered capsule surrounding the invader. In Rac2 mutants this process is disrupted. Immune surveillance cells, known as plasmatocytes, adhere to the parasitoid egg but fail to spread, and septate junctions do not assemble, possibly due to mislocalization of the Protein 4.1 homolog Coracle. Finally, larger cells known as lamellocytes attach to the capsule but also fail to spread, and there is a lack of melanization. From these results it appears that Rac2 is necessary for the larval cellular immune response.
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Affiliation(s)
- Michael J Williams
- Umeå Centre for Molecular Pathogenesis, Umeå University, S-901 87 Umeå, Sweden.
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249
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Yang Y, Lundquist EA. The actin-binding protein UNC-115/abLIM controls formation of lamellipodia and filopodia and neuronal morphogenesis in Caenorhabditis elegans. Mol Cell Biol 2005; 25:5158-70. [PMID: 15923631 PMCID: PMC1140600 DOI: 10.1128/mcb.25.12.5158-5170.2005] [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: 11/20/2022] Open
Abstract
The roles of actin-binding proteins in development and morphogenesis are not well understood. The actin-binding protein UNC-115 has been implicated in cytoskeletal signaling downstream of Rac in Caenorhabditis elegans axon pathfinding, but the cellular role of UNC-115 in this process remains undefined. Here we report that UNC-115 overactivity in C. elegans neurons promotes the formation of neurites and lamellipodial and filopodial extensions similar to those induced by activated Rac and normally found in C. elegans growth cones. We show that UNC-115 activity in neuronal morphogenesis is enhanced by two molecular mechanisms: when ectopically driven to the plasma membrane by the myristoylation sequence of c-Src, and by mutation of a putative serine phosphorylation site in the actin-binding domain of UNC-115. In support of the hypothesis that UNC-115 modulates actin cytoskeletal organization, we show that UNC-115 activity in serum-starved NIH 3T3 fibroblasts results in the formation of lamellipodia and filopodia. We conclude that UNC-115 is a novel regulator of the formation of lamellipodia and filopodia in neurons, possibly in the growth cone during axon pathfinding.
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Affiliation(s)
- Yieyie Yang
- Department of Molecular Biosciences, 5049 Haworth Hall, 1200 Sunnyside Avenue, University of Kansas, Lawrence, KS 66045, USA
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250
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Shi J, Scita G, Casanova JE. WAVE2 signaling mediates invasion of polarized epithelial cells by Salmonella typhimurium. J Biol Chem 2005; 280:29849-55. [PMID: 15929989 DOI: 10.1074/jbc.m500617200] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
The bacterial pathogen Salmonella penetrates the intestinal epithelium by inducing its own phagocytosis into epithelial cells. The dramatic reorganization of the actin cytoskeleton required for internalization is driven by bacterial manipulation of host signaling pathways, including activation of the Rho family GTPase Rac1 and subsequent activation of the Arp2/3 complex. However, the mechanisms linking these two events remain poorly understood. Rac1 is thought to promote activation of the Arp2/3 complex through its interaction with suppressor of cAMP receptor/WASP family verprolin-homologous (SCAR/WAVE) family proteins, but this interaction is apparently indirect. Two different Rac1 effectors have been shown to bind WAVE2: IRSp53, the SH3 domain of which binds the WAVE2 proline-rich domain, and PIR121/Sra-1, which forms a pentameric complex containing WAVE, Abi1, Nap1, and HSPC300. However, the extent to which each of these complexes contributes to Arp2/3 complex activation in the context of Salmonella infection is unclear. Here, we show that WAVE2 is necessary for efficient invasion of epithelial cells by Salmonella typhimurium. We found that although Salmonella infection strongly promotes the formation of an IRSp53/WAVE2 complex, IRSp53 is not necessary for bacterial internalization. In contrast, disruption of the PIR121/Nap1/Abi1/WAVE2/HSPC300 complex potently inhibits bacterial uptake. These results indicate that WAVE2 is an important component in signaling pathways leading to Salmonella invasion. Although infection leads to the formation of an IRSp53/WAVE2 complex, it is the association of WAVE2 with the Abi1/Nap1/PIR121/HSPC300 complex that regulates bacterial internalization.
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Affiliation(s)
- Jing Shi
- Department of Cell Biology, University of Virginia Health Sciences Center, Charlottesville, 22908-0732, USA
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