G2Cdb::Gene report

Gene id
Gene symbol
Homo sapiens
ARP2 actin-related protein 2 homolog (yeast)
G00000539 (Mus musculus)

Databases (8)

ENSG00000138071 (Ensembl human gene)
10097 (Entrez Gene)
959 (G2Cdb plasticity & disease)
ACTR2 (GeneCards)
604221 (OMIM)
Marker Symbol
Protein Expression
5083 (human protein atlas)
Protein Sequence
P61160 (UniProt)

Synonyms (1)

  • ARP2

Literature (55)

Pubmed - other

  • Distinct roles for the actin nucleators Arp2/3 and hDia1 during NK-mediated cytotoxicity.

    Butler B and Cooper JA

    Department of Cell Biology and Physiology, Washington University in St. Louis, MO 63110, USA. boyd.butler@wustl.edu

    Background: Several actin nucleators, including Arp2/3 and various formins, control numerous cytoskeletal-based functions in vivo.

    Results: We investigated the relative roles of these nucleators. As a model system, we used natural killer (NK) lymphocytes, which display a wide range of cytoskeletal-based functions that culminate in the lysis of target cells. NK cells lacking either Arp2/3 or the formin hDia1 were ineffective in target cell lysis, but for distinct reasons. Loss of Arp2/3 function led to defects in cell adhesion and actin assembly at the junction with the target cell (the lytic synapse). In contrast, loss of hDia1 did not disrupt actin assembly at the lytic synapse. Instead, loss of hDia1 led to perturbations in the microtubule cytoskeleton, including the targeting of microtubules to the lytic synapse.

    Conclusions: These studies reveal novel distinctions and relationships among the functions of Arp2/3, formins, and microtubules in cells. Notably, a formin mediates the capture of microtubules at the cell periphery.

    Funded by: NCI NIH HHS: P30 CA091842, P30 CA91842; NIAID NIH HHS: AI071429, F32 AI071429; NIGMS NIH HHS: GM38542, R01 GM038542, R01 GM038542-21

    Current biology : CB 2009;19;22;1886-96

  • Local network topology in human protein interaction data predicts functional association.

    Li H and Liang S

    Department of Bioinformatics & Computational Biology, The University of Texas M. D. Anderson Cancer Center, Houston, Texas, United States of America.

    The use of high-throughput techniques to generate large volumes of protein-protein interaction (PPI) data has increased the need for methods that systematically and automatically suggest functional relationships among proteins. In a yeast PPI network, previous work has shown that the local connection topology, particularly for two proteins sharing an unusually large number of neighbors, can predict functional association. In this study we improved the prediction scheme by developing a new algorithm and applied it on a human PPI network to make a genome-wide functional inference. We used the new algorithm to measure and reduce the influence of hub proteins on detecting function-associated protein pairs. We used the annotations of the Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) as benchmarks to compare and evaluate the function relevance. The application of our algorithms to human PPI data yielded 4,233 significant functional associations among 1,754 proteins. Further functional comparisons between them allowed us to assign 466 KEGG pathway annotations to 274 proteins and 123 GO annotations to 114 proteins with estimated false discovery rates of <21% for KEGG and <30% for GO. We clustered 1,729 proteins by their functional associations and made functional inferences from detailed analysis on one subcluster highly enriched in the TGF-beta signaling pathway (P<10(-50)). Analysis of another four subclusters also suggested potential new players in six signaling pathways worthy of further experimental investigations. Our study gives clear insight into the common neighbor-based prediction scheme and provides a reliable method for large-scale functional annotation in this post-genomic era.

    Funded by: NCI NIH HHS: K25 CA123344

    PloS one 2009;4;7;e6410

  • Host cell entry by apicomplexa parasites requires actin polymerization in the host cell.

    Gonzalez V, Combe A, David V, Malmquist NA, Delorme V, Leroy C, Blazquez S, Ménard R and Tardieux I

    Institut Cochin, Université Paris Descartes, CNRS (UMR 8104), Paris, France.

    Apicomplexa are obligate intracellular parasites that actively invade host cells using their membrane-associated, actin-myosin motor. The current view is that host cell invasion by Apicomplexa requires the formation of a parasite-host cell junction, which has been termed the moving junction, but does not require the active participation of host actin. Using Toxoplasma gondii tachyzoites and Plasmodium berghei sporozoites, we show that host actin participates in parasite entry. Parasites induce the formation of a ring-shaped F-actin structure in the host cell at the parasite-cell junction, which remains stable during parasite entry. The Arp2/3 complex, an actin-nucleating factor, is recruited at the ring structure and is important for parasite entry. We propose that Apicomplexa invasion of host cells requires not only the parasite motor but also de novo polymerization of host actin at the entry site for anchoring the junction on which the parasite pulls to penetrate the host cell.

    Funded by: Howard Hughes Medical Institute

    Cell host & microbe 2009;5;3;259-72

  • The rate of N-WASP exchange limits the extent of ARP2/3-complex-dependent actin-based motility.

    Weisswange I, Newsome TP, Schleich S and Way M

    Cell Motility Laboratory, Cancer Research UK, London Research Institute, 44 Lincoln's Inn Fields, London WC2A 3PX, UK.

    Understanding cell motility will require detailed knowledge not only of the localization of signalling networks regulating actin polymerization, but also of their dynamics. Unfortunately, many signalling networks are not amenable to such analysis, as they are frequently transient and dispersed. By contrast, the signalling pathways used by pathogens undergoing actin-based motility are highly localized and operate in a constitutive fashion. Taking advantage of this, we have analysed the dynamics of neuronal Wiskott-Aldrich syndrome protein (N-WASP), WASP-interacting protein (WIP), GRB2 and NCK, which are required to stimulate actin-related protein (ARP)2/3-complex-dependent actin-based motility of vaccinia virus, using fluorescence recovery after photobleaching. Here we show that all four proteins are rapidly exchanging, albeit at different rates, and that the turnover of N-WASP depends on its ability to stimulate ARP2/3-complex-mediated actin polymerization. Conversely, disruption of the interaction of N-WASP with GRB2 and/or the barbed ends of actin filaments increases its exchange rate and results in a faster rate of virus movement. We suggest that the exchange rate of N-WASP controls the rate of ARP2/3-complex-dependent actin-based motility by regulating the extent of actin polymerization by antagonizing filament capping.

    Funded by: Cancer Research UK

    Nature 2009;458;7234;87-91

  • Arp2 depletion inhibits sheet-like protrusions but not linear protrusions of fibroblasts and lymphocytes.

    Nicholson-Dykstra SM and Higgs HN

    Department of Biochemistry, Dartmouth Medical School, Hanover, NH 03755, USA.

    The Arp2/3 complex-mediated assembly and protrusion of a branched actin network at the leading edge occurs during cell migration, although some studies suggest it is not essential. In order to test the role of Arp2/3 complex in leading edge protrusion, Swiss 3T3 fibroblasts and Jurkat T cells were depleted of Arp2 and evaluated for defects in cell morphology and spreading efficiency. Arp2-depleted fibroblasts exhibit severe defects in formation of sheet-like protrusions at early time points of cell spreading, with sheet-like protrusions limited to regions along the length of linear protrusions. However, Arp2-depleted cells are able to spread fully after extended times. Similarly, Arp2-depleted Jurkat T lymphocytes exhibit defects in spreading on anti-CD3. Interphase Jurkats in suspension are covered with large ruffle structures, whereas mitotic Jurkats are covered by finger-like linear protrusions. Arp2-depleted Jurkats exhibit defects in ruffle assembly but not in assembly of mitotic linear protrusions. Similarly, Arp2-depletion has no effect on the highly dynamic linear protrusion of another suspended lymphocyte line. We conclude that Arp2/3 complex plays a significant role in assembly of sheet-like protrusions, especially during early stages of cell spreading, but is not required for assembly of a variety of linear actin-based protrusions.

    Funded by: NIGMS NIH HHS: R01 GM069818, R01 GM069818-05

    Cell motility and the cytoskeleton 2008;65;11;904-22

  • WAVE and Arp2/3 jointly inhibit filopodium formation by entering into a complex with mDia2.

    Beli P, Mascheroni D, Xu D and Innocenti M

    Institute of Biochemistry II, Goethe University Medical School, Theodor-Stern-Kai 7, 60590 Frankfurt, Germany.

    Lamellipodia/ruffles and filopodia are protruding organelles containing short and highly branched or long and unbranched actin filaments, respectively. The microscopic morphology, dynamic development and protein signature of both lamellipodia/ruffles and filopodia have been investigated; however, little is known about the mechanisms by which cells coordinate the formation of these actin-based extensions. Here, we show that WAVE holds mDia2 and the Arp2/3 complex in a multimolecular complex. WAVE- and Arp2/3-dependent ruffling induced by EGF does not require mDia2. Conversely, the emission of mDia2-dependent filopodia correlates with its disengagement from WAVE. Consistently, the ability of EGF, Cdc42 and serum to induce mDia2-dependent formation of filopodia is increased in the absence of either the WAVE/Abi1/Nap1/PIR121 (WANP) or the Arp2/3 complex. Reintroduction of WAVE2 into WANP-complex knockdown cells markedly reduces filopodia formation independently of actin polymerization. Thus, WAVE and the Arp2/3 complex jointly orchestrate different types of actin-based plasma membrane protrusions by promoting ruffling and inhibiting mDia2-induced filopodia.

    Nature cell biology 2008;10;7;849-57

  • Rac interacts with Abi-1 and WAVE2 to promote an Arp2/3-dependent actin recruitment during chlamydial invasion.

    Carabeo RA, Dooley CA, Grieshaber SS and Hackstadt T

    Department of Microbiology and Immunology, University of Louisville School of Medicine, Louisville, KY, USA.

    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.

    Funded by: Intramural NIH HHS; NIAID NIH HHS: AI065545, K22 AI052252, K22 AI052252-02, R01 AI065545, R01 AI065545-01

    Cellular microbiology 2007;9;9;2278-88

  • Correlation between liver metastasis of the colocalization of actin-related protein 2 and 3 complex and WAVE2 in colorectal carcinoma.

    Iwaya K, Oikawa K, Semba S, Tsuchiya B, Mukai Y, Otsubo T, Nagao T, Izumi M, Kuroda M, Domoto H and Mukai K

    Department of Diagnostic Pathology, Tokyo Medical University, Tokyo, Japan. kiwaya@tokyo-med.ac.jp

    Directed movement of normal cells occurs when actin-related protein 2 and 3 complex (Arp2/3 complex) triggers the actin polymerization that forms lamellipodia immediately after binding to WAVE2. In order to determine whether the same mechanism correlates with liver metastasis from colorectal cancer, paired mirror sections of 154 cancer specimens (29 cases with liver metastasis and 125 cases without liver metastasis in which T factor, gender, primary tumor site, and age at operation were matched) were examined immunohistochemically for the localization of Arp2 and WAVE2. Expression of both Arp2 and WAVE2 was detected in the same cancer cells in 55 (35.7%) of the 154 cases, but not detected in the normal colonic epithelial cells. Univariate analysis showed that the colocalization was significantly predictive of liver metastasis (risk ratio [RR] 8.760. Likewise, histological grade (RR 2.46), lymphatic invasion (RR 9.95), and tumor budding (RR 4.00) were significant predictors. Among these, colocalization and lymphatic invasion were shown to be independent risk factors by multivariate analysis. Another 59 colorectal specimens were examined for mRNA expression of Arp2 by real time polymerase chain reaction. High mRNA levels of Arp2, that in situ hybridization revealed to be expressed by the cancer cells, were significantly associated with liver metastasis. However, its effect was absorbed by the influence of risk of the colocalization that is closely related to high expression of Arp2. These results indicate that the colocalization of Arp2 and WAVE2 is an independent risk factor for liver metastasis of colorectal carcinoma.

    Cancer science 2007;98;7;992-9

  • IQGAP1 stimulates actin assembly through the N-WASP-Arp2/3 pathway.

    Le Clainche C, Schlaepfer D, Ferrari A, Klingauf M, Grohmanova K, Veligodskiy A, Didry D, Le D, Egile C, Carlier MF and Kroschewski R

    Dynamics of Cytoskeleton and Motility Group, CNRS, Gif-sur-Yvette, France.

    IQGAP1 is a conserved modular protein overexpressed in cancer and involved in organizing actin and microtubules in motile processes such as adhesion, migration, and cytokinesis. A variety of proteins have been shown to interact with IQGAP1, including the small G proteins Rac1 and Cdc42, actin, calmodulin, beta-catenin, the microtubule plus end-binding proteins CLIP170 (cytoplasmic linker protein) and adenomatous polyposis coli. However, the molecular mechanism by which IQGAP1 controls actin dynamics in cell motility is not understood. Quantitative co-localization analysis and down-regulation of IQGAP1 revealed that IQGAP1 controls the co-localization of N-WASP with the Arp2/3 complex in lamellipodia. Co-immunoprecipitation supports an in vivo link between IQGAP1 and N-WASP. Pull-down experiments and kinetic assays of branched actin polymerization with N-WASP and Arp2/3 complex demonstrated that the C-terminal half of IQGAP1 activates N-WASP by interacting with its BR-CRIB domain in a Cdc42-like manner, whereas the N-terminal half of IQGAP1 antagonizes this activation by association with a C-terminal region of IQGAP1. We propose that signal-induced relief of the autoinhibited fold of IQGAP1 allows activation of N-WASP to stimulate Arp2/3-dependent actin assembly.

    The Journal of biological chemistry 2007;282;1;426-35

  • Large-scale mapping of human protein-protein interactions by mass spectrometry.

    Ewing RM, Chu P, Elisma F, Li H, Taylor P, Climie S, McBroom-Cerajewski L, Robinson MD, O'Connor L, Li M, Taylor R, Dharsee M, Ho Y, Heilbut A, Moore L, Zhang S, Ornatsky O, Bukhman YV, Ethier M, Sheng Y, Vasilescu J, Abu-Farha M, Lambert JP, Duewel HS, Stewart II, Kuehl B, Hogue K, Colwill K, Gladwish K, Muskat B, Kinach R, Adams SL, Moran MF, Morin GB, Topaloglou T and Figeys D

    Protana, Toronto, Ontario, Canada.

    Mapping protein-protein interactions is an invaluable tool for understanding protein function. Here, we report the first large-scale study of protein-protein interactions in human cells using a mass spectrometry-based approach. The study maps protein interactions for 338 bait proteins that were selected based on known or suspected disease and functional associations. Large-scale immunoprecipitation of Flag-tagged versions of these proteins followed by LC-ESI-MS/MS analysis resulted in the identification of 24,540 potential protein interactions. False positives and redundant hits were filtered out using empirical criteria and a calculated interaction confidence score, producing a data set of 6463 interactions between 2235 distinct proteins. This data set was further cross-validated using previously published and predicted human protein interactions. In-depth mining of the data set shows that it represents a valuable source of novel protein-protein interactions with relevance to human diseases. In addition, via our preliminary analysis, we report many novel protein interactions and pathway associations.

    Molecular systems biology 2007;3;89

  • Coexpression of actin-related protein 2 and Wiskott-Aldrich syndrome family verproline-homologous protein 2 in adenocarcinoma of the lung.

    Semba S, Iwaya K, Matsubayashi J, Serizawa H, Kataba H, Hirano T, Kato H, Matsuoka T and Mukai K

    Department of Diagnostic Pathology, Tokyo Medical University, Tokyo, Japan.

    Purpose: Highly invasive and metastatic cancer cells, such as adenocarcinoma of the lung cells, form irregular protrusions by assembling a branched network of actin filaments. In mammalian cells, the actin-related protein 2 and 3 (Arp2/3) complex initiates actin assembly to form lamellipodial protrusions by binding to Wiskott-Aldrich syndrome (WASP)/WASP family verproline-homologous protein 2 (WAVE2). In this study, colocalization of Arp2 and WAVE2 in adenocarcinoma of the lung was investigated to elucidate its prognostic value.

    Immunohistochemical staining of Arp2 and WAVE2 was done on mirror sections of 115 adenocarcinomas of the lung from pathologic stage IA to IIIA classes. Kaplan-Meier disease-free survival and overall survival curves were analyzed to determine the prognostic significance of the coexpression of Arp2 and WAVE2.

    Results: Immunoreactivity for both Arp2 and WAVE2 was detected in the same cancer cells in 78 (67.8%) of the 115 lung cancer specimens. The proportion of cancer cells expressing both Arp2 and WAVE2 was significantly higher in cases with lymph-node metastasis (P = 0.0046), and significantly lower in bronchioloalveolar carcinomas (P < 0.0001). The patients whose cancer cells coexpressed them had a shorter disease-free survival time (P < 0.0001) and overall survival time (P < 0.0001). Multivariate Cox regression analysis revealed that coexpression of Arp2 and WAVE2 is an independent risk factor for tumor recurrence.

    Conclusions: Coexpression of Arp2 and WAVE2 is correlated with poorer patient outcome, and may be involved in the mechanism of cancer metastasis.

    Clinical cancer research : an official journal of the American Association for Cancer Research 2006;12;8;2449-54

  • Actin binding to the central domain of WASP/Scar proteins plays a critical role in the activation of the Arp2/3 complex.

    Kelly AE, Kranitz H, Dötsch V and Mullins RD

    Graduate Group in Biophysics and Department of Cellular & Molecular Pharmacology, University of California-San Francisco, San Francisco, CA 94143, USA.

    The Arp2/3 complex nucleates and cross-links actin filaments at the leading edge of motile cells, and its activity is stimulated by C-terminal regions of WASP/Scar proteins, called VCA domains. VCA domains contain a verprolin homology sequence (V) that binds monomeric actin and central (C) and acidic sequences (A) that bind the Arp2/3 complex. Here we show that the C domain binds to monomeric actin with higher affinity (K(d) = 10 microm) than to the Arp2/3 complex (K(d) > 200 microm). Nuclear magnetic resonance spectroscopy reveals that actin binds to the N-terminal half of the C domain and that both the V and C domains can bind actin independently and simultaneously, indicating that they interact with different sites. Mutation of conserved hydrophobic residues in the actin-binding interface of the C domain disrupts activation of the Arp2/3 complex but does not alter affinity for the complex. By chemical cross-linking the C domain interacts with the p40 subunit of the Arp2/3 complex and, by fluorescence polarization anisotropy, the binding of actin and the Arp2/3 complex are mutually exclusive. Our results indicate that both actin and Arp2/3 binding are important for C domain function but that the C domain does not form a static bridge between the two. We propose a model for activation of the Arp2/3 complex in which the C domain first primes the complex by inducing a necessary conformational change and then initiates nucleus assembly by bringing an actin monomer into proximity of the primed complex.

    Funded by: NIGMS NIH HHS: R01 GM 61010, R01 GM061010, R01 GM061010-06

    The Journal of biological chemistry 2006;281;15;10589-97

  • Interaction of SPIN90 with the Arp2/3 complex mediates lamellipodia and actin comet tail formation.

    Kim DJ, Kim SH, Lim CS, Choi KY, Park CS, Sung BH, Yeo MG, Chang S, Kim JK and Song WK

    Department of Life Science and Molecular Disease Research Center, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea.

    The appropriate regulation of the actin cytoskeleton is essential for cell movement, changes in cell shape, and formation of membrane protrusions like lamellipodia and filopodia. Moreover, several regulatory proteins affecting actin dynamics have been identified in the motile regions of cells. Here, we provide evidence for the involvement of SPIN90 in the regulation of actin cytoskeleton and actin comet tail formation. SPIN90 was distributed throughout the cytoplasm in COS-7 cells, but exposing the cells to platelet-derived growth factor (PDGF) caused a redistribution of SPIN90 to the cell cortex and the formation of lamellipodia (or membrane ruffles), both of which were dramatically inhibited in SPIN90-knockdown cells. In addition, the binding of the C terminus of SPIN90 with both the Arp2/3 complex (actin-related proteins Arp 2 and Arp 3) and G-actin activates the former, leading to actin polymerization in vitro. And when coexpressed with phosphatidylinositol 4-phosphate 5 kinase, SPIN90 was observed within actin comet tails. Taken these findings suggest that SPIN90 participates in reorganization of the actin cytoskeleton and in actin-based cell motility.

    The Journal of biological chemistry 2006;281;1;617-25

  • Towards a proteome-scale map of the human protein-protein interaction network.

    Rual JF, Venkatesan K, Hao T, Hirozane-Kishikawa T, Dricot A, Li N, Berriz GF, Gibbons FD, Dreze M, Ayivi-Guedehoussou N, Klitgord N, Simon C, Boxem M, Milstein S, Rosenberg J, Goldberg DS, Zhang LV, Wong SL, Franklin G, Li S, Albala JS, Lim J, Fraughton C, Llamosas E, Cevik S, Bex C, Lamesch P, Sikorski RS, Vandenhaute J, Zoghbi HY, Smolyar A, Bosak S, Sequerra R, Doucette-Stamm L, Cusick ME, Hill DE, Roth FP and Vidal M

    Center for Cancer Systems Biology and Department of Cancer Biology, Dana-Farber Cancer Institute, Harvard Medical School, 44 Binney Street, Boston, Massachusetts 02115, USA.

    Systematic mapping of protein-protein interactions, or 'interactome' mapping, was initiated in model organisms, starting with defined biological processes and then expanding to the scale of the proteome. Although far from complete, such maps have revealed global topological and dynamic features of interactome networks that relate to known biological properties, suggesting that a human interactome map will provide insight into development and disease mechanisms at a systems level. Here we describe an initial version of a proteome-scale map of human binary protein-protein interactions. Using a stringent, high-throughput yeast two-hybrid system, we tested pairwise interactions among the products of approximately 8,100 currently available Gateway-cloned open reading frames and detected approximately 2,800 interactions. This data set, called CCSB-HI1, has a verification rate of approximately 78% as revealed by an independent co-affinity purification assay, and correlates significantly with other biological attributes. The CCSB-HI1 data set increases by approximately 70% the set of available binary interactions within the tested space and reveals more than 300 new connections to over 100 disease-associated proteins. This work represents an important step towards a systematic and comprehensive human interactome project.

    Funded by: NCI NIH HHS: R33 CA132073; NHGRI NIH HHS: P50 HG004233, R01 HG001715, RC4 HG006066, U01 HG001715; NHLBI NIH HHS: U01 HL098166

    Nature 2005;437;7062;1173-8

  • Involvement of Arp2/3 complex in MCP-1-induced chemotaxis.

    Mukai Y, Iwaya K, Ogawa H and Mukai K

    Department of Diagnostic Pathology, Tokyo Medical University, Tokyo, Japan.

    The migrating monocyte shows dynamic actin polymerization in response to MCP-1. We investigated the involvement of the actin-related protein 2 and 3 complex (Arp2/3 complex) during chemotaxis of a human monocyte cell line (THP-1). To clarify whether the Arp2/3 complex directly polymerizes actin in response to MCP-1 stimulation, THP-1 cells were transfected with complementary DNA constructs encoding ScarWA. In ScarWA-transfected cells, neither recruitment of Arp2/3 complex at the leading edge nor actin polymerization was detected. Indeed, migration induced by MCP-1 was almost completely blocked. At the same time, transfection also interfered with the recruitment of integrin beta-1 at the leading edge and reduced affinity binding to fibronectin. Immunoprecipitation with an anti-Arp2 antibody showed that integrin beta-1 and WASP were co-precipitated under the condition of MCP-1 stimulation. These results indicate that interaction between the Arp2/3 complex and WASP stimulates actin polymerization and integrin beta-1-mediated adhesion during MCP-1-induced chemotaxis of THP-1 cells.

    Biochemical and biophysical research communications 2005;334;2;395-402

  • The adapter protein CrkII regulates neuronal Wiskott-Aldrich syndrome protein, actin polymerization, and tension development during contractile stimulation of smooth muscle.

    Tang DD, Zhang W and Gunst SJ

    Department of Cellular and Integrative Physiology, School of Medicine, Indiana University, Indianapolis, 46202, USA.

    Actin polymerization has been shown to occur in tracheal smooth muscle tissues and cells in response to contractile stimulation, and there is evidence that the polymerization of actin is required for contraction. In tracheal smooth muscle, agonist-induced actin polymerization is mediated by activation of neuronal Wiskott-Aldrich syndrome protein (N-WASp) and the Arp (actin-related protein) 2/3 complex, and activation of the small GTPase Cdc42 regulates the activation of N-WASp. In the present study, the role of the adapter protein CrkII in the regulation of N-WASp and Cdc42 activation, actin polymerization, and tension development in smooth muscle tissues was evaluated. Stimulation of tracheal smooth muscle tissues with acetylcholine increased the association of CrkII with N-WASp. Plasmids encoding wild type CrkII or a CrkII mutant lacking the SH3 effector-binding ability, CrkII SH3N, were introduced into tracheal smooth muscle tissues, and the tissues were incubated for 2 days to allow for protein expression. Expression of the CrkII SH3N mutant in smooth muscle tissues inhibited the association of CrkII with N-WASp and the activation of Cdc42. The CrkII SH3N mutant also inhibited the increase in the association of N-WASp with Arp2, a major component of the Arp2/3 complex, in response to contractile stimulation, indicating inhibition of N-WASp activation. Expression of the CrkII SH3N mutant also inhibited tension generation and actin polymerization in response to contractile stimulation; however, it did not inhibit myosin light chain phosphorylation. These results suggest that CrkII plays a critical role in the regulation of N-WASp activation, perhaps by regulating the activation of Cdc42, and that it thereby regulates actin polymerization and active tension generation in tracheal smooth muscle. These studies suggest a novel signaling pathway for the regulation of N-WASp activation and active contraction in smooth muscle tissues.

    Funded by: NHLBI NIH HHS: HL-29289, HL-74099, HL-75388, R01 HL029289, R01 HL029289-19, R01 HL074099, R01 HL074099-03, R01 HL075388

    The Journal of biological chemistry 2005;280;24;23380-9

  • Actin-filament cross-linking protein T-plastin increases Arp2/3-mediated actin-based movement.

    Giganti A, Plastino J, Janji B, Van Troys M, Lentz D, Ampe C, Sykes C and Friederich E

    Laboratoire de Biologie Moléculaire, d'Analyse Génique et de Modélisation, Centre de Recherche Public-Santé, 42, rue du Laboratoire, L-1911, Luxembourg.

    Increasing evidence suggests that actin cross-linking or bundling proteins might not only structure the cortical actin cytoskeleton but also control actin dynamics. Here, we analyse the effects of T-plastin/T-fimbrin, a representative member of an important actin-filament cross-linking protein by combining a quantitative biomimetic motility assay with biochemical and cell-based approaches. Beads coated with the VCA domain of the Wiskott/Aldrich-syndrome protein (WASP) recruit the actin-nucleating Arp2/3 complex, polymerize actin at their surface and undergo movement when placed in cell-free extracts. T-Plastin increased the velocity of VCA beads 1.5 times, stabilized actin comets and concomitantly displaced cofilin, an actin-depolymerizing protein. T-Plastin also decreased the F-actin disassembly rate and inhibited cofilin-mediated depolymerization of actin filaments in vitro. Importantly, a bundling-incompetent variant comprising the first actin-binding domain (ABD1) had similar effects. In cells, this domain induced the formation of long actin cables to which other actin-regulating proteins were recruited. Altogether, these results favor a mechanism in which binding of ABD1 controls actin turnover independently of cross-link formation. In vivo, this activity might contribute to the assembly and maintenance of the actin cytoskeleton of plasma-membrane protrusions.

    Journal of cell science 2005;118;Pt 6;1255-65

  • Inhibiting the Arp2/3 complex limits infection of both intracellular mature vaccinia virus and primate lentiviruses.

    Komano J, Miyauchi K, Matsuda Z and Yamamoto N

    Laboratory of Virology and Pathogenesis, AIDS Research Center, National Institute of Infectious Diseases, Tokyo 208-0011, Japan. ajkomano@nih.go.jp

    Characterizing cellular factors involved in the life cycle of human immunodeficiency virus type 1 (HIV-1) is an initial step toward controlling replication of HIV-1. Actin polymerization mediated by the Arp2/3 complex has been found to play a critical role in some pathogens' intracellular motility. We have asked whether this complex also contributes to the viral life cycles including that of HIV-1. We have used both the acidic domains from actin-related protein (Arp) 2/3 complex-binding proteins such as the Wiscott-Aldrich syndrome protein (N-WASP) or cortactin, and siRNA directing toward Arp2 to inhibit viral infection. HIV-1, simian immunodeficiency virus (SIV), and intracellular mature vaccinia virus (IMV) were sensitive to inhibition of the Arp2/3 complex, whereas MLV, HSV-1, and adenovirus were not. Interestingly, pseudotyping HIV-1 with vesicular stomatitis virus G protein (VSV-G) overcame this inhibition. Constitutive inhibition of the Arp2/3 complex in the T-cell line H9 also blocked replication of HIV-1. These data suggested the existence of an Arp2/3 complex-dependent event during the early phase of the life cycles of both primate lentiviruses and IMV. Inhibiting the HIV-1's ability to activate Arp2/3 complex could be a potential chemotherapeutic intervention for acquired immunodeficiency syndrome (AIDS).

    Molecular biology of the cell 2004;15;12;5197-207

  • Analysis of the mechanisms of Salmonella-induced actin assembly during invasion of host cells and intracellular replication.

    Unsworth KE, Way M, McNiven M, Machesky L and Holden DW

    Centre for Molecular Microbiology and Infection, Department of Infectious Diseases, Imperial College London, Armstrong Road, London SW7 2AZ, UK.

    Salmonella enterica serovar Typhimurium (S. typhimurium) induces actin assembly both during invasion of host cells and during the course of intracellular bacterial replication. In this study, we investigated the involvement in these processes of host cell signalling pathways that are frequently utilized by bacterial pathogens to manipulate the eukaryotic actin cytoskeleton. We confirmed that Cdc42, Rac, and Arp3 are involved in S. typhimurium invasion of HeLa cells, and found that N-WASP and Scar/WAVE also play a role in this process. However, we found no evidence for the involvement of these proteins in actin assembly during intracellular replication. Cortactin was recruited by Salmonella during both invasion and intracellular replication. However, RNA interference directed against cortactin did not inhibit either invasion or intracellular actin assembly, although it resulted in increased cell spreading and a greater number of lamellipodia. We also found no role for either the GTPase dynamin or the formin family member mDia1 in actin assembly by intracellular bacteria. Collectively, these data provide evidence that signalling pathways leading to Arp2/3-dependent actin nucleation play an important role in S. typhimurium invasion, but are not involved in intracellular Salmonella-induced actin assembly, and suggest that actin assembly by intracellular S. typhimurium may proceed by a novel mechanism.

    Cellular microbiology 2004;6;11;1041-55

  • The status, quality, and expansion of the NIH full-length cDNA project: the Mammalian Gene Collection (MGC).

    Gerhard DS, Wagner L, Feingold EA, Shenmen CM, Grouse LH, Schuler G, Klein SL, Old S, Rasooly R, Good P, Guyer M, Peck AM, Derge JG, Lipman D, Collins FS, Jang W, Sherry S, Feolo M, Misquitta L, Lee E, Rotmistrovsky K, Greenhut SF, Schaefer CF, Buetow K, Bonner TI, Haussler D, Kent J, Kiekhaus M, Furey T, Brent M, Prange C, Schreiber K, Shapiro N, Bhat NK, Hopkins RF, Hsie F, Driscoll T, Soares MB, Casavant TL, Scheetz TE, Brown-stein MJ, Usdin TB, Toshiyuki S, Carninci P, Piao Y, Dudekula DB, Ko MS, Kawakami K, Suzuki Y, Sugano S, Gruber CE, Smith MR, Simmons B, Moore T, Waterman R, Johnson SL, Ruan Y, Wei CL, Mathavan S, Gunaratne PH, Wu J, Garcia AM, Hulyk SW, Fuh E, Yuan Y, Sneed A, Kowis C, Hodgson A, Muzny DM, McPherson J, Gibbs RA, Fahey J, Helton E, Ketteman M, Madan A, Rodrigues S, Sanchez A, Whiting M, Madari A, Young AC, Wetherby KD, Granite SJ, Kwong PN, Brinkley CP, Pearson RL, Bouffard GG, Blakesly RW, Green ED, Dickson MC, Rodriguez AC, Grimwood J, Schmutz J, Myers RM, Butterfield YS, Griffith M, Griffith OL, Krzywinski MI, Liao N, Morin R, Morrin R, Palmquist D, Petrescu AS, Skalska U, Smailus DE, Stott JM, Schnerch A, Schein JE, Jones SJ, Holt RA, Baross A, Marra MA, Clifton S, Makowski KA, Bosak S, Malek J and MGC Project Team

    The National Institutes of Health's Mammalian Gene Collection (MGC) project was designed to generate and sequence a publicly accessible cDNA resource containing a complete open reading frame (ORF) for every human and mouse gene. The project initially used a random strategy to select clones from a large number of cDNA libraries from diverse tissues. Candidate clones were chosen based on 5'-EST sequences, and then fully sequenced to high accuracy and analyzed by algorithms developed for this project. Currently, more than 11,000 human and 10,000 mouse genes are represented in MGC by at least one clone with a full ORF. The random selection approach is now reaching a saturation point, and a transition to protocols targeted at the missing transcripts is now required to complete the mouse and human collections. Comparison of the sequence of the MGC clones to reference genome sequences reveals that most cDNA clones are of very high sequence quality, although it is likely that some cDNAs may carry missense variants as a consequence of experimental artifact, such as PCR, cloning, or reverse transcriptase errors. Recently, a rat cDNA component was added to the project, and ongoing frog (Xenopus) and zebrafish (Danio) cDNA projects were expanded to take advantage of the high-throughput MGC pipeline.

    Funded by: PHS HHS: N01-C0-12400

    Genome research 2004;14;10B;2121-7

  • Role of EHD1 and EHBP1 in perinuclear sorting and insulin-regulated GLUT4 recycling in 3T3-L1 adipocytes.

    Guilherme A, Soriano NA, Furcinitti PS and Czech MP

    Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA.

    Insulin stimulates glucose transport in muscle and adipose tissues by recruiting intracellular membrane vesicles containing the glucose transporter GLUT4 to the plasma membrane. The mechanisms involved in the biogenesis of these vesicles and their translocation to the cell surface are poorly understood. Here, we report that an Eps15 homology (EH) domain-containing protein, EHD1, controls the normal perinuclear localization of GLUT4-containing membranes and is required for insulin-stimulated recycling of these membranes in cultured adipocytes. EHD1 is a member of a family of four closely related proteins (EHD1, EHD2, EHD3, and EHD4), which also contain a P-loop near the N terminus and a central coiled-coil domain. Analysis of cultured adipocytes stained with anti-GLUT4, anti-EHD1, and anti-EHD2 antibodies revealed that EHD1, but not EHD2, partially co-localizes with perinuclear GLUT4. Expression of a dominant-negative construct of EHD1 missing the EH domain (DeltaEH-EHD1) markedly enlarged endosomes, dispersed perinuclear GLUT4-containing membranes throughout the cytoplasm, and inhibited GLUT4 translocation to the plasma membranes of 3T3-L1 adipocytes stimulated with insulin. Similarly, small interfering RNA-mediated depletion of endogenous EHD1 protein also markedly dispersed perinuclear GLUT4 in cultured adipocytes. Moreover, EHD1 is shown to interact through its EH domain with the protein EHBP1, which is also required for insulin-stimulated GLUT4 movements and hexose transport. In contrast, disruption of EHD2 function was without effect on GLUT4 localization or translocation to the plasma membrane. Taken together, these results show that EHD1 and EHBP1, but not EHD2, are required for perinuclear localization of GLUT4 and reveal that loss of EHBP1 disrupts insulin-regulated GLUT4 recycling in cultured adipocytes.

    Funded by: NIDDK NIH HHS: DK30898

    The Journal of biological chemistry 2004;279;38;40062-75

  • Interaction of cortactin and Arp2/3 complex is required for sphingosine-1-phosphate-induced endothelial cell remodeling.

    Li Y, Uruno T, Haudenschild C, Dudek SM, Garcia JG and Zhan X

    Department of Experimental Pathology, Jerome H. Holland Laboratory for the Biomedical Sciences, American Red Cross, Rockville, MD 20855, USA.

    Sphingosine-1-phosphate (S1P) induces capillary formation of endothelial cells on Matrigel in accompany with actin assembly and accumulation of cortactin and Arp2/3 complex at the cell-leading edge. Suppression of cortactin expression with a cortactin antisense oligo significantly impaired S1P-induced capillary formation, migration of endothelial cells, and actin assembly at the cell periphery. Overexpression of wild-type cortactin tagged by green fluorescent protein (GFP) increased the S1P-induced tube formation and cell motility, whereas the cells overexpressing the mutant formed poorly capillary network and became less motile in response to S1P. Analysis of distribution in Triton X-100 insoluble fractions demonstrated that the cortactin mutant inhibited the association of wild-type cortactin and Arp2/3 complex with the actin-enriched complex. Furthermore, actin polymerization at and distribution of Arp2/3 complex as well as endogenous cortactin into the cell-leading edge mediated by S1P was disturbed. These data suggest that the interaction between cortactin and Arp2/3 complex plays an important role in S1P-mediated remodeling of endothelial cells.

    Funded by: NCI NIH HHS: R01 CA 91984-01; NHLBI NIH HHS: HL 10403, KO8 HL70013-01, P01 HL 58064, R01 HL 52753-09; PHS HHS: R01 50533, R01 68071

    Experimental cell research 2004;298;1;107-21

  • Transcriptome characterization elucidates signaling networks that control human ES cell growth and differentiation.

    Brandenberger R, Wei H, Zhang S, Lei S, Murage J, Fisk GJ, Li Y, Xu C, Fang R, Guegler K, Rao MS, Mandalam R, Lebkowski J and Stanton LW

    Geron Corporation, Menlo Park, California 94025, USA. rbrandenberger@geron.com

    Human embryonic stem (hES) cells hold promise for generating an unlimited supply of cells for replacement therapies. To characterize hES cells at the molecular level, we obtained 148,453 expressed sequence tags (ESTs) from undifferentiated hES cells and three differentiated derivative subpopulations. Over 32,000 different transcripts expressed in hES cells were identified, of which more than 16,000 do not match closely any gene in the UniGene public database. Queries to this EST database revealed 532 significantly upregulated and 140 significantly downregulated genes in undifferentiated hES cells. These data highlight changes in the transcriptional network that occur when hES cells differentiate. Among the differentially regulated genes are several components of signaling pathways and transcriptional regulators that likely play key roles in hES cell growth and differentiation. The genomic data presented here may facilitate the derivation of clinically useful cell types from hES cells.

    Nature biotechnology 2004;22;6;707-16

  • A conserved amphipathic helix in WASP/Scar proteins is essential for activation of Arp2/3 complex.

    Panchal SC, Kaiser DA, Torres E, Pollard TD and Rosen MK

    Department of Biochemistry, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, Texas 75390, USA.

    Members of the Wiskott-Aldrich syndrome protein (WASP) family link Rho GTPase signaling pathways to the cytoskeleton through a multiprotein assembly called Arp2/3 complex. The C-terminal VCA regions (verprolin-homology, central hydrophobic, and acidic regions) of WASP and its relatives stimulate Arp2/3 complex to nucleate actin filament branches. Here we show by differential line broadening in NMR spectra that the C (central) and A (acidic) segments of VCA domains from WASP, N-WASP and Scar bind Arp2/3 complex. The C regions of these proteins have a conserved sequence motif consisting of hydrophobic residues and an arginine residue. Point mutations in this conserved sequence motif suggest that it forms an amphipathic helix that is required in biochemical assays for activation of Arp2/3 complex. Key residues in this motif are buried through contacts with the GTPase binding domain in the autoinhibited structure of WASP and N-WASP, indicating that sequestration of these residues is an important aspect of autoinhibition.

    Nature structural biology 2003;10;8;591-8

  • A Cortactin-CD2-associated protein (CD2AP) complex provides a novel link between epidermal growth factor receptor endocytosis and the actin cytoskeleton.

    Lynch DK, Winata SC, Lyons RJ, Hughes WE, Lehrbach GM, Wasinger V, Corthals G, Cordwell S and Daly RJ

    Cancer Research Program, Garvan Institute of Medical Research, St. Vincent's Hospital, Sydney, New South Wales 2010, Australia.

    Growth factor regulation of the cortical actin cytoskeleton is fundamental to a wide variety of cellular processes. The cortical actin-associated protein, cortactin, regulates the formation of dynamic actin networks via the actin-related protein (Arp)2/3 complex and hence is a key mediator of such responses. In order to reveal novel roles for this versatile protein, we used a proteomics-based approach to isolate cortactin-interacting proteins. This identified several proteins, including CD2-associated protein (CD2AP), as targets for the cortactin Src homology 3 domain. Co-immunoprecipitation of CD2AP with cortactin occurred at endogenous expression levels, was transiently induced by epidermal growth factor (EGF) treatment, and required the cortactin Src homology 3 domain. The CD2AP-binding site for cortactin mapped to the second of three proline-rich regions. Because CD2AP is closely related to Cbl-interacting protein of 85 kDa (CIN85), which regulates growth factor receptor down-regulation via complex formation with Cbl and endophilin, we investigated whether the CD2AP-cortactin complex performs a similar function. EGF treatment of cells led to transient association of Cbl and the epidermal growth factor receptor (EGFR) with a constitutive CD2AP-endophilin complex. Cortactin was recruited into this complex with slightly delayed kinetics compared with Cbl and the EGFR. Immunofluorescence analysis revealed that the EGFR, CD2AP, and cortactin co-localized in regions of EGF-induced membrane ruffles. Therefore, by binding both CD2AP and the Arp2/3 complex, cortactin links receptor endocytosis to actin polymerization, which may facilitate the trafficking of internalized growth factor receptors.

    The Journal of biological chemistry 2003;278;24;21805-13

  • Regulation by phosphorylation. Yet another twist in the WASP story.

    Caron E

    Centre for Molecular Microbiology and Infection and Department of Biological Sciences, The Flowers Building, Armstrong Road, Imperial College London, SW7 2AZ, London, United Kingdom.

    Cell migration and other complex cellular processes involve a variety of signaling molecules and require the integration of multiple signals into a coherent cytoskeletal response. Two papers in the May issue of Molecular Cell now demonstrate that phosphorylation plays a critical role in WASP function as a regulator of Arp2/3-mediated actin polymerization.

    Developmental cell 2003;4;6;772-3

  • Haematopoietic lineage cell-specific protein 1 (HS1) promotes actin-related protein (Arp) 2/3 complex-mediated actin polymerization.

    Uruno T, Zhang P, Liu J, Hao JJ and Zhan X

    Department of Experimental Pathology, Jerome H. Holland Laboratory for the Biomedical Sciences, American Red Cross, 15601 Crabbs Branch Way, Rockville, MD 20855, USA.

    HS1 (haematopoietic lineage cell-specific gene protein 1), a prominent substrate of intracellular protein tyrosine kinases in haematopoietic cells, is implicated in the immune response to extracellular stimuli and in cell differentiation induced by cytokines. Although HS1 contains a 37-amino acid tandem repeat motif and a C-terminal Src homology 3 domain and is closely related to the cortical-actin-associated protein cortactin, it lacks the fourth repeat that has been shown to be essential for cortactin binding to filamentous actin (F-actin). In this study, we examined the possible role of HS1 in the regulation of the actin cytoskeleton. Immunofluorescent staining demonstrated that HS1 co-localizes in the cytoplasm of cells with actin-related protein (Arp) 2/3 complex, the primary component of the cellular machinery responsible for de novo actin assembly. Furthermore, recombinant HS1 binds directly to Arp2/3 complex with an equilibrium dissociation constant (K(d)) of 880 nM. Although HS1 is a modest F-actin-binding protein with a K(d) of 400 nM, it increases the rate of the actin assembly mediated by Arp2/3 complex, and promotes the formation of branched actin filaments induced by Arp2/3 complex and a constitutively activated peptide of N-WASP (neural Wiskott-Aldrich syndrome protein). Our data suggest that HS1, like cortactin, plays an important role in the modulation of actin assembly.

    Funded by: NHLBI NIH HHS: R01 HL 52753-09

    The Biochemical journal 2003;371;Pt 2;485-93

  • IQGAP2 functions as a GTP-dependent effector protein in thrombin-induced platelet cytoskeletal reorganization.

    Schmidt VA, Scudder L, Devoe CE, Bernards A, Cupit LD and Bahou WF

    Department of Medicine and the Program in Genetics, State University of New York, Stony Brook, 11794, USA.

    Human blood platelets are anucleate cells whose response to extracellular stimuli results in actin cytoskeleton rearrangements, thereby providing the critical initial step in the regulation of hemostasis. The serine protease alpha-thrombin, known to activate platelets by cleavage of a family of protease-activated receptors (PARs), is the most potent physiologic activator of human platelets, though downstream effector proteins uniquely linked to platelet cytoskeletal actin polymerization remain largely uncharacterized. The gene encoding the putative rac1/cdc42 effector protein IQGAP2 was identified within the PAR gene cluster at 5q13, flanked telomeric by PAR1 and encompassing PAR3. Immunofluorescence microscopy demonstrated IQGAP2 expression in filopodial extensions of activated platelets and colocalized with F-actin in lamellipodia and filopodia of IQGAP2-transfected COS1 cells. Platelet activation by alpha-thrombin, but not saturating concentrations of fibrillar collagen or adenosine 5'-diphosphate, uniquely assemble an IQGAP2/arp2/3-actin cytoplasmic complex, an association regulated by guanosine triphosphate rac1 ([GTP]rac1) but not by [GTP]cdc42. Likewise, only thrombin-activated platelets resulted in rapid translocation of IQGAP2 to the platelet cytoskeleton. These observations identify a physiologic scaffolding function for IQGAP2 and establish the presence of a functional genomic unit in humans uniquely evolved to regulate thrombin-induced platelet cytoskeletal actin reorganization.

    Funded by: NHLBI NIH HHS: HL49141, HL53665; NIDDK NIH HHS: DDK62040

    Blood 2003;101;8;3021-8

  • Importance of free actin filament barbed ends for Arp2/3 complex function in platelets and fibroblasts.

    Falet H, Hoffmeister KM, Neujahr R, Italiano JE, Stossel TP, Southwick FS and Hartwig JH

    Division of Hematology, Brigham and Women's Hospital, Department of Medicine, Harvard Medical School, 221 Longwood Avenue, LMRC 301, Boston, MA 02115, USA. hfalet@rics.bwh.harvard.edu

    We investigated the effect of actin filament barbed end uncapping on Arp23 complex function both in vivo and in vitro. Arp23 complex redistributes rapidly and uniformly to the lamellar edge of activated wild-type platelets and fibroblasts but clusters in marginal actin filament clumps in gelsolin-null cells. Treatment of gelsolin-null platelets with the negative dominant N-WASp C-terminal CA domain has no effect on their residual actin nucleation activity, placing gelsolin actin filament severing, capping, and uncapping function upstream of Arp23 complex nucleation. Actin filaments capped by gelsolin or the gelsolin homolog CapG fail to enhance Arp23 complex nucleation in vitro, but uncapping of the barbed ends of these actin filaments restores their ability to potentiate Arp23 complex nucleation. We conclude that Arp23 complex contribution to actin filament nucleation in platelets and fibroblasts importantly requires free barbed ends generated by severing and uncapping.

    Funded by: NHLBI NIH HHS: HL-56252, HL-56949, P01 HL056949, R01 HL056252; NIAID NIH HHS: AI-32634, R01 AI023262

    Proceedings of the National Academy of Sciences of the United States of America 2002;99;26;16782-7

  • Recruitment of the Arp2/3 complex to vinculin: coupling membrane protrusion to matrix adhesion.

    DeMali KA, Barlow CA and Burridge K

    Department of Cell and Developmental Biology, Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, NC 27599, USA. kdemali@med.unc.edu

    Cell migration involves many steps, including membrane protrusion and the development of new adhesions. Here we have investigated whether there is a link between actin polymerization and integrin engagement. In response to signals that trigger membrane protrusion, the actin-related protein (Arp)2/3 complex transiently binds to vinculin, an integrin-associated protein. The interaction is regulated, requiring phosphatidylinositol-4,5-bisphosphate and Rac1 activation, and is sufficient to recruit the Arp2/3 complex to new sites of integrin aggregation. Binding of the Arp2/3 complex to vinculin is direct and does not depend on the ability of vinculin to associate with actin. We have mapped the binding site for the Arp2/3 complex to the hinge region of vinculin, and a point mutation in this region selectively blocks binding to the Arp2/3 complex. Compared with WT vinculin, expression of this mutant in vinculin-null cells results in diminished lamellipodial protrusion and spreading on fibronectin. The recruitment of the Arp2/3 complex to vinculin may be one mechanism through which actin polymerization and membrane protrusion are coupled to integrin-mediated adhesion.

    Funded by: NHLBI NIH HHS: HL45100, P01 HL045100; NIGMS NIH HHS: F32 GM020610, GM20610, GM29860, R01 GM029860

    The Journal of cell biology 2002;159;5;881-91

  • Motility determinants in WASP family proteins.

    Yarar D, D'Alessio JA, Jeng RL and Welch MD

    Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, California 94720, USA.

    In response to upstream signals, proteins in the Wiskott-Aldrich Syndrome protein (WASP) family regulate actin nucleation via the Arp2/3 complex. Despite intensive study of the function of WASP family proteins in nucleation, it is not yet understood how their distinct structural organization contributes to actin-based motility. Herein, we analyzed the activities of WASP and Scar1 truncation derivatives by using a bead-based motility assay. The minimal region of WASP sufficient to direct movement was the C-terminal WCA fragment, whereas the corresponding region of Scar1 was insufficient. In addition, the proline-rich regions of WASP and Scar1 and the Ena/VASP homology 1 (EVH1) domain of WASP independently enhanced motility rates. The contributions of these regions to motility could not be accounted for by their direct effects on actin nucleation with the Arp2/3 complex, suggesting that they stimulate motility by recruiting additional factors. We have identified profilin as one such factor. WASP- and Scar1-coated bead motility rates were significantly reduced by depletion of profilin and VASP and could be more efficiently rescued by a combination of VASP and wild-type profilin than by VASP and a mutant profilin that cannot bind proline-rich sequences. Moreover, motility of WASP WCA beads was not affected by the depletion or addback of VASP and profilin. Our results suggest that recruitment of factors, including profilin, by the proline-rich regions of WASP and Scar1 and the EVH1 domain of WASP stimulates cellular actin-based motility.

    Funded by: NIGMS NIH HHS: GM-59609, R01 GM059609, R01 GM059609-04

    Molecular biology of the cell 2002;13;11;4045-59

  • Normal Arp2/3 complex activation in platelets lacking WASp.

    Falet H, Hoffmeister KM, Neujahr R and Hartwig JH

    Department of Medicine, Division of Hematology, Brigham and Women's Hospital, Harvard Medical School, 221 Longwood Avenue, LMRC 301, Boston, MA 02115, USA. hfalet@rics.bwh.harvard.edu

    Arp2/3 complex is believed to induce de novo nucleation of actin filaments at the edge of motile cells downstream of WASp family proteins. In this study, the signaling pathways leading to Arp2/3 complex activation, actin assembly, and shape change were investigated in platelets isolated from patients with Wiskott-Aldrich Syndrome (WAS), that is, who lack WASp, and in WASp-deficient mouse platelets. WASp-deficient human and mouse platelets elaborate filopodia, spread lamellae, and assemble actin, identical to control WASp-expressing platelets. Human platelets contain 2 microM Arp2/3 complex, or 8600 molecules/cell. Arp2/3 complex redistributes to the edge of the lamellae and to the Triton X-100-insoluble actin cytoskeleton of activated WASp-deficient platelets. Furthermore, the C-terminal CA domain of N-WASp, which sequesters Arp2/3 complex, inhibits by half the actin nucleation capacity of octylglucoside-permeabilized and activated WAS platelets, similar to its effect in WASp-expressing cells. Along with WASp, platelets express WAVE-2 as a physiologic activator of Arp2/3 complex and a small amount of N-WASp. Taken together, our findings show that platelets activate Arp2/3 complex, assemble actin, and change shape in the absence of WASp, indicating a more specialized role for WASp in these cells.

    Funded by: NHLBI NIH HHS: HL 56252, HL 56949

    Blood 2002;100;6;2113-22

  • Interaction of cortactin and N-WASp with Arp2/3 complex.

    Weaver AM, Heuser JE, Karginov AV, Lee WL, Parsons JT and Cooper JA

    Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110, USA.

    Background: Dynamic actin assembly is required for diverse cellular processes and often involves activation of Arp2/3 complex. Cortactin and N-WASp activate Arp2/3 complex, alone or in concert. Both cortactin and N-WASp contain an acidic (A) domain that is required for Arp2/3 complex binding.

    Results: We investigated how cortactin and the constitutively active VCA domain of N-WASp interact with Arp2/3 complex. Structural studies showed that cortactin is a thin, elongated monomer. Chemical crosslinking studies demonstrated selective interaction of the Arp2/3 binding NTA domain of cortactin (cortactin NTA) with the Arp3 subunit and VCA with Arp3, Arp2, and ARPC1/p40. Cortactin NTA and VCA crosslinking to the Arp3 subunit were mutually exclusive; however, cortactin NTA did not inhibit VCA crosslinking to Arp2 or ARPC1/p40, nor did it inhibit activation of Arp2/3 complex by VCA. We conducted an experiment in which a saturating concentration of cortactin NTA modestly lowered the binding affinity of VCA for Arp2/3; the results of this experiment provided further evidence for ternary complex formation. Consistent with a common binding site on Arp3, a saturating concentration of VCA abolished binding of cortactin to Arp2/3 complex.

    Conclusions: Under certain circumstances, cortactin and N-WASp can bind simultaneously to Arp2/3 complex, accounting for their synergy in activation of actin assembly. The interaction of cortactin NTA with Arp2/3 complex does not inhibit Arp2/3 activation by N-WASp, despite competition for a common binding site located on the Arp3 subunit. These results suggest a model in which cortactin may bridge Arp2/3 complex to actin filaments via Arp3 and N-WASp activates Arp2/3 complex by binding Arp2 and/or ARPC1/p40.

    Funded by: NIGMS NIH HHS: R01 GM038542, R01 GM038542-14

    Current biology : CB 2002;12;15;1270-8

  • Arp2/3 complex is required for actin polymerization during platelet shape change.

    Li Z, Kim ES and Bearer EL

    Department of Pathology and Laboratory Medicine, Brown University, Providence, RI 02912, USA.

    Platelets undergo a series of actin-dependent morphologic changes when activated by thrombin receptor activating peptide (TRAP) or when spreading on glass. Polymerization of actin results in the sequential formation of filopodia, lamellipodia, and stress fibers, but the molecular mechanisms regulating this polymerization are unknown. The Arp2/3 complex nucleates actin polymerization in vitro and could perform this function inside cells as well. To test whether Arp2/3 regulated platelet actin polymerization, we used recombinant Arp2 protein (rArp2) to generate Arp2-specific antibodies (alpha Arp2). Intact and Fab fragments of alpha Arp2 inhibited TRAP-stimulated actin-polymerizing activity in platelet extracts as measured by the pyrene assay. Inhibition was reversed by the addition of rArp2 protein. To test the effect of Arp2/3 inhibition on the formation of specific actin structures, we designed a new method to permeabilize resting platelets while preserving their ability to adhere and to form filopodia and lamellipodia on exposure to glass. Inhibition of Arp2/3 froze platelets at the rounded, early stage of activation, before the formation of filopodia and lamellipodia. By morphometric analysis, the proportion of platelets in the rounded stage rose from 2.85% in untreated to 63% after treatment with alpha Arp2. This effect was also seen with Fab fragments and was reversed by the addition of rArp2 protein. By immunofluorescence of platelets at various stages of spreading, the Arp2/3 complex was found in filopodia and lamellipodia. These results suggest that activation of the Arp2/3 complex at the cortex by TRAP stimulation initiates an explosive polymerization of actin filaments that is required for all subsequent actin-dependent events.

    Funded by: NIGMS NIH HHS: R01 GM047368, R01 GM047368-05, R01 GM47368

    Blood 2002;99;12;4466-74

  • Actin dynamics in platelets.

    Bearer EL, Prakash JM and Li Z

    Department of Pathology and Laboratory Medicine, Brown University, Providence, Rhode Island 02912, USA.

    The human blood platelet circulates in the blood as a non-adherent disk. Upon receiving signals of blood vessel damage, the platelet reorganizes its actin cytoskeleton which transforms it into a spiky dynamic adherent glue. This transformation involves a temporal sequence of four morphologically distinct steps which is reproducible in vitro. The actin dynamics underlying these shape changes depend on a large number of actin-binding proteins. Maintenance of the discoid shape requires actin-binding proteins that inhibit these reorganizations, whereas transformation involves other proteins, some to disassemble old filaments and others to polymerize new ones. F-Actin-affinity chromatography identified a large set of actin-binding proteins including VASP, Arp2 and 2E4/kaptin. Recent discoveries show that VASP inhibits filament disassembly and Arp2/3 is required to polymerize new filaments. Morphological analysis of the distribution of these actin-binding proteins in spread platelets together with biochemical measurements of their interactions with actin lead to a model of interactions with actin that mediate shape change.

    Funded by: NIGMS NIH HHS: R01 GM047368, R01 GM047368-05

    International review of cytology 2002;217;137-82

  • Actin-related protein (Arp2) inserts into artificial lipid membranes.

    Goldmann WH and Isenberg G

    Renal Unit, Dept. of Medicine, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA 02129, USA. wgoldmann@partners.org

    Arp2 is localized in the cytoplasm of eukaryotic cells where it controls actin dynamics. Computer analyses have suggested one possible lipid binding site, residues 185-202 of the primary amino acid sequence on Arp2, that could allow for membrane attachment/insertion. We expressed this region as a fusion protein with schistosomal glutathione S-transferase (GST) and investigated the interaction of this fragment with mixtures of dioleoylphosphatidylserine (DOPS) and dioleoylphosphatidylglycerol (DOPG) phospholipids in reconstituted lipid bilayers using differential scanning calorimetry (DSC). Calorimetric measurements showed that as the fusion protein increased, the main chain transition enthalpy decreased and the chain-melting temperature shifted, which is indicative of partial protein insertion into the hydrophobic region of the lipid membrane. This was confirmed using the Langmuir Blodgett technique (film balance) on lipid monolayers. The dissociation constant (K(d)) determined by the temperature jump method was approximately 1.1 microM.

    Cell biology international 2002;26;12;1073-8

  • Crystal structure of Arp2/3 complex.

    Robinson RC, Turbedsky K, Kaiser DA, Marchand JB, Higgs HN, Choe S and Pollard TD

    Structural Biology Laboratory, Salk Institute for Biological Studies, 10010 North Torrey Pines Road, La Jolla, CA 92037, USA.

    We determined a crystal structure of bovine Arp2/3 complex, an assembly of seven proteins that initiates actin polymerization in eukaryotic cells, at 2.0 angstrom resolution. Actin-related protein 2 (Arp2) and Arp3 are folded like actin, with distinctive surface features. Subunits ARPC2 p34 and ARPC4 p20 in the core of the complex associate through long carboxyl-terminal alpha helices and have similarly folded amino-terminal alpha/beta domains. ARPC1 p40 is a seven-blade beta propeller with an insertion that may associate with the side of an actin filament. ARPC3 p21 and ARPC5 p16 are globular alpha-helical subunits. We predict that WASp/Scar proteins activate Arp2/3 complex by bringing Arp2 into proximity with Arp3 for nucleation of a branch on the side of a preexisting actin filament.

    Funded by: NIGMS NIH HHS: GM-26132, GM-26338, GM-56653

    Science (New York, N.Y.) 2001;294;5547;1679-84

  • Filamin A, the Arp2/3 complex, and the morphology and function of cortical actin filaments in human melanoma cells.

    Flanagan LA, Chou J, Falet H, Neujahr R, Hartwig JH and Stossel TP

    Hematology Division, Brigham and Women's Hospital, Department of Medicine, Harvard Medical School, Boston, MA 02115, USA.

    The Arp2/3 complex and filamin A (FLNa) branch actin filaments. To define the role of these actin-binding proteins in cellular actin architecture, we compared the morphology of FLNa-deficient human melanoma (M2) cells and three stable derivatives of these cells expressing normal FLNa concentrations. All the cell lines contain similar amounts of the Arp2/3 complex. Serum addition causes serum-starved M2 cells to extend flat protrusions transiently; thereafter, the protrusions turn into spherical blebs and the cells do not crawl. The short-lived lamellae of M2 cells contain a dense mat of long actin filaments in contrast to a more three-dimensional orthogonal network of shorter actin filaments in lamellae of identically treated FLNa-expressing cells capable of translational locomotion. FLNa-specific antibodies localize throughout the leading lamellae of these cells at junctions between orthogonally intersecting actin filaments. Arp2/3 complex-specific antibodies stain diffusely and label a few, although not the same, actin filament overlap sites as FLNa antibody. We conclude that FLNa is essential in cells that express it for stabilizing orthogonal actin networks suitable for locomotion. Contrary to some proposals, Arp2/3 complex-mediated branching of actin alone is insufficient for establishing an orthogonal actin organization or maintaining mechanical stability at the leading edge.

    Funded by: NHLBI NIH HHS: HL19429, HL56252, R01 HL019429, R01 HL056252

    The Journal of cell biology 2001;155;4;511-7

  • Reconstitution of human Arp2/3 complex reveals critical roles of individual subunits in complex structure and activity.

    Gournier H, Goley ED, Niederstrasser H, Trinh T and Welch MD

    Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA.

    The Arp2/3 complex is a seven-protein assembly that is critical for actin nucleation and branching in cells. Here we report the reconstitution of active human Arp2/3 complex after expression of all seven subunits in insect cells. Expression of partial complexes revealed that a heterodimer of the p34 and p20 subunits constitutes a critical structural core of the complex, whereas the remaining subunits are peripherally located. Arp3 is crucial for nucleation, consistent with it being a structural component of the nucleation site. p41, p21, and p16 contribute differently to nucleation and stimulation by ActA and WASP, whereas p34/p20 bind actin filaments and likely function in actin branching. This study reveals that the nucleating and organizing functions of Arp2/3 complex subunits are separable, indicating that these activities may be differentially regulated in cells.

    Funded by: NIGMS NIH HHS: GM59609, R01 GM059609, R01 GM059609-03

    Molecular cell 2001;8;5;1041-52

  • Interactions among subunits of human Arp2/3 complex: p20-Arc as the hub.

    Zhao X, Yang Z, Qian M and Zhu X

    Shanghai Research Center of Life Sciences and Open Laboratory of Molecular Cell Biology, Institute of Biochemistry and Cell Biology, Shanghai Institute for Biological Sciences, Chinese Academy of Sciences, 320 Yue Yang Road, Shanghai, 200031, China.

    The Arp2/3 complex is critical for nucleation and crosslinking of actin filaments. To gain insight into its subunit topology and assembly pathway, we systematically examined interactions among subunits of human Arp2/3 complex by yeast two-hybrid assays. It was shown that p20-Arc was able to interact with p21-Arc, p34-Arc, and p16-Arc, respectively. In contrast, p41-Arc only interacted with p20-Arc/p16-Arc heterodimer. In addition, we found that structural integrity was important for association between p20-Arc and p21-Arc, while the N-terminal half of p34-Arc was dispensable for its binding to p20-Arc. Our data suggest a key role of p20-Arc and a multistep pathway for the complex formation.

    Biochemical and biophysical research communications 2001;280;2;513-7

  • Interaction of WASP/Scar proteins with actin and vertebrate Arp2/3 complex.

    Marchand JB, Kaiser DA, Pollard TD and Higgs HN

    Structural Biology Laboratory, Salk Institute for Biological Studies, 10010 North Torrey Pines Road, La Jolla, California 92037, USA.

    The Wiskott-Aldrich-syndrome protein (WASP) regulates polymerization of actin by the Arp2/3 complex. Here we show, using fluorescence anisotropy assays, that the carboxy-terminal WA domain of WASP binds to a single actin monomer with a Kd of 0.6 microM in an equilibrium with rapid exchange rates. Both WH-2 and CA sequences contribute to actin binding. A favourable DeltaH of -10 kcal mol(-1) drives binding. The WA domain binds to the Arp2/3 complex with a Kd of 0.9 microM; both the C and A sequences contribute to binding to the Arp2/3 complex. Wiskott-Aldrich-syndrome mutations in the WA domain that alter nucleation by the Arp2/3 complex over a tenfold range without affecting affinity for actin or the Arp2/3 complex indicate that there may be an activation step in the nucleation pathway. Actin filaments stimulate nucleation by producing a fivefold increase in the affinity of WASP-WA for the Arp2/3 complex.

    Funded by: NIGMS NIH HHS: GM-26338

    Nature cell biology 2001;3;1;76-82

  • Integration of multiple signals through cooperative regulation of the N-WASP-Arp2/3 complex.

    Prehoda KE, Scott JA, Mullins RD and Lim WA

    Department of Cellular and Molecular Pharmacology, University of California, San Francisco, CA 94143-0450, USA.

    The protein N-WASP [a homolog to the Wiskott-Aldrich syndrome protein (WASP)] regulates actin polymerization by stimulating the actin-nucleating activity of the actin-related protein 2/3 (Arp2/3) complex. N-WASP is tightly regulated by multiple signals: Only costimulation by Cdc42 and phosphatidylinositol (4,5)-bisphosphate (PIP2) yields potent polymerization. We found that regulation requires N-WASP's constitutively active output domain (VCA) and two regulatory domains: a Cdc42-binding domain and a previously undescribed PIP(2)-binding domain. In the absence of stimuli, the regulatory modules together hold the VCA-Arp2/3 complex in an inactive "closed" conformation. In this state, both the Cdc42- and PIP2-binding sites are masked. Binding of either input destabilizes the closed state and enhances binding of the other input. This cooperative activation mechanism shows how combinations of simple binding domains can be used to integrate and amplify coincident signals.

    Science (New York, N.Y.) 2000;290;5492;801-6

  • Cortactin localization to sites of actin assembly in lamellipodia requires interactions with F-actin and the Arp2/3 complex.

    Weed SA, Karginov AV, Schafer DA, Weaver AM, Kinley AW, Cooper JA and Parsons JT

    Department of Microbiology and Cancer Center, University of Virginia Health Sciences Center, Charlottesville, Virginia 22908, USA.

    Cortactin is an actin-binding protein that is enriched within the lamellipodia of motile cells and in neuronal growth cones. Here, we report that cortactin is localized with the actin-related protein (Arp) 2/3 complex at sites of actin polymerization within the lamellipodia. Two distinct sequence motifs of cortactin contribute to its interaction with the cortical actin network: the fourth of six tandem repeats and the amino-terminal acidic region (NTA). Cortactin variants lacking either the fourth tandem repeat or the NTA failed to localize at the cell periphery. Tandem repeat four was necessary for cortactin to stably bind F-actin in vitro. The NTA region interacts directly with the Arp2/3 complex based on affinity chromatography, immunoprecipitation assays, and binding assays using purified components. Cortactin variants containing the NTA region were inefficient at promoting Arp2/3 actin nucleation activity. These data provide strong evidence that cortactin is specifically localized to sites of dynamic cortical actin assembly via simultaneous interaction with F-actin and the Arp2/3 complex. Cortactin interacts via its Src homology 3 (SH3) domain with ZO-1 and the SHANK family of postsynaptic density 95/dlg/ZO-1 homology (PDZ) domain-containing proteins, suggesting that cortactin contributes to the spatial organization of sites of actin polymerization coupled to selected cell surface transmembrane receptor complexes.

    Funded by: NCI NIH HHS: CA29243, CA40042, F32 CA075695, P01 CA040042, R01 CA029243, R37 CA029243; NIGMS NIH HHS: GM38542, R01 GM038542, R01 GM038542-11S1

    The Journal of cell biology 2000;151;1;29-40

  • GRB2 links signaling to actin assembly by enhancing interaction of neural Wiskott-Aldrich syndrome protein (N-WASp) with actin-related protein (ARP2/3) complex.

    Carlier MF, Nioche P, Broutin-L'Hermite I, Boujemaa R, Le Clainche C, Egile C, Garbay C, Ducruix A, Sansonetti P and Pantaloni D

    Dynamique du Cytosquelette, Cristallographie et RMN Biologiques, Laboratoire d'Enzymologie et Biochimie Structurale, CNRS 91198 Gif-sur-Yvette, Paris, France. Pasteur, carlier@lebs.cnrs-gif.fr

    Proteins of the Wiskott-Aldrich Syndrome protein (WASp) family connect signaling pathways to the actin polymerization-driven cell motility. The ubiquitous homolog of WASp, N-WASp, is a multidomain protein that interacts with the Arp2/3 complex and G-actin via its C-terminal WA domain to stimulate actin polymerization. The activity of N-WASp is enhanced by the binding of effectors like Cdc42-guanosine 5'-3-O-(thio)triphosphate, phosphatidylinositol bisphosphate, or the Shigella IcsA protein. Here we show that the SH3-SH2-SH3 adaptor Grb2 is another activator of N-WASp that stimulates actin polymerization by increasing the amount of N-WASp. Arp2/3 complex. The concentration dependence of N-WASp activity, sedimentation velocity and cross-linking experiments together suggest that N-WASp is subject to self-association, and Grb2 enhances N-WASp activity by binding preferentially to its active monomeric form. Use of peptide inhibitors, mutated Grb2, and isolated SH3 domains demonstrate that the effect of Grb2 is mediated by the interaction of its C-terminal SH3 domain with the proline-rich region of N-WASp. Cdc42 and Grb2 bind simultaneously to N-WASp and enhance actin polymerization synergistically. Grb2 shortens the delay preceding the onset of Escherichia coli (IcsA) actin-based reconstituted movement. These results suggest that Grb2 may activate Arp2/3 complex-mediated actin polymerization downstream from the receptor tyrosine kinase signaling pathway.

    The Journal of biological chemistry 2000;275;29;21946-52

  • BMP-2 antagonists emerge from alterations in the low-affinity binding epitope for receptor BMPR-II.

    Kirsch T, Nickel J and Sebald W

    Lehrstuhl für Physiologische Chemie II, Theodor-Boveri-Institut für Biowissenschaften (Biozentrum) der Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.

    Bone morphogenetic protein-2 (BMP-2) induces bone formation and regeneration in adult vertebrates and regulates important developmental processes in all animals. BMP-2 is a homodimeric cysteine knot protein that, as a member of the transforming growth factor-beta (TGF-beta) superfamily, signals by oligomerizing type I and type II receptor serine-kinases in the cell membrane. The binding epitopes of BMP-2 for BMPR-IA (type I) and BMPR-II or ActR-II (type II) were characterized using BMP-2 mutant proteins for analysis of interactions with receptor ectodomains. A large epitope 1 for high-affinity BMPR-IA binding was detected spanning the interface of the BMP-2 dimer. A smaller epitope 2 for the low-affinity binding of BMPR-II was found to be assembled by determinants of a single monomer. Symmetry-related pairs of the two juxtaposed epitopes occur near the BMP-2 poles. Mutations in both epitopes yielded variants with reduced biological activity in C2C12 cells; however, only epitope 2 variants behaved as antagonists partially or completely inhibiting BMP-2 activity. These findings provide a framework for the molecular description of receptor recognition and activation in the BMP/TGF-beta superfamily.

    The EMBO journal 2000;19;13;3314-24

  • Influence of the C terminus of Wiskott-Aldrich syndrome protein (WASp) and the Arp2/3 complex on actin polymerization.

    Higgs HN, Blanchoin L and Pollard TD

    Structural Biology Laboratory, The Salk Institute for Biological Studies, La Jolla, California 92037, USA.

    The 70 C-terminal amino acids of Wiskott-Aldrich syndrome protein (WASp WA) activate the actin nucleation activity of the Arp2/3 complex. WASp WA binds both the Arp2/3 complex and actin monomers, but the mechanism by which it activates the Arp2/3 complex is not known. We characterized the effect of WASp WA on actin polymerization in the absence and presence of the human Arp2/3 complex. WASp WA binds actin monomers with an apparent K(d) of 0.4 microM, inhibiting spontaneous nucleation and subunit addition to pointed ends, but not addition to barbed ends. A peptide containing only the WASp homology 2 motif behaves similarly but with a 10-fold lower affinity. In contrast to previously published results, neither WASp WA nor a similar region of the protein Scar1 significantly depolymerizes actin filaments under a variety of conditions. WASp WA and the Arp2/3 complex nucleate actin filaments, and the rate of this nucleation is a function of the concentrations of both WASp WA and the Arp2/3 complex. With excess WASp WA and <10 nM Arp2/3 complex, there is a 1:1 correspondence between the Arp2/3 complex and the concentration of filaments produced, but the filament concentration plateaus at an Arp2/3 complex concentration far below the cellular concentration determined to be 9.7 microM in human neutrophils. Preformed filaments increase the rate of nucleation by WASp WA and the Arp2/3 complex but not the number of filaments that are generated. We propose that filament side binding by the Arp2/3 complex enhances its activation by WASp WA.

    Funded by: NIGMS NIH HHS: GM-26338

    Biochemistry 1999;38;46;15212-22

  • Reconstitution of actin-based motility of Listeria and Shigella using pure proteins.

    Loisel TP, Boujemaa R, Pantaloni D and Carlier MF

    Dynamique du Cytosquelette, LEBS, CNRS, Gif-sur-Yvette, France.

    Actin polymerization is essential for cell locomotion and is thought to generate the force responsible for cellular protrusions. The Arp2/3 complex is required to stimulate actin assembly at the leading edge in response to signalling. The bacteria Listeria and Shigella bypass the signalling pathway and harness the Arp2/3 complex to induce actin assembly and to propel themselves in living cells. However, the Arp2/3 complex alone is insufficient to promote movement. Here we have used pure components of the actin cytoskeleton to reconstitute sustained movement in Listeria and Shigella in vitro. Actin-based propulsion is driven by the free energy released by ATP hydrolysis linked to actin polymerization, and does not require myosin. In addition to actin and activated Arp2/3 complex, actin depolymerizing factor (ADF, or cofilin) and capping protein are also required for motility as they maintain a high steady-state level of G-actin, which controls the rate of unidirectional growth of actin filaments at the surface of the bacterium. The movement is more effective when profilin, alpha-actinin and VASP (for Listeria) are also included. These results have implications for our understanding of the mechanism of actin-based motility in cells.

    Nature 1999;401;6753;613-6

  • The Arp2/3 complex is essential for the actin-based motility of Listeria monocytogenes.

    May RC, Hall ME, Higgs HN, Pollard TD, Chakraborty T, Wehland J, Machesky LM and Sechi AS

    Department of Biochemistry, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK.

    Actin polymerisation is thought to drive the movement of eukaryotic cells and some intracellular pathogens such as Listeria monocytogenes. The Listeria surface protein ActA synergises with recruited host proteins to induce actin polymerisation, propelling the bacterium through the host cytoplasm [1]. The Arp2/3 complex is one recruited host factor [2] [3]; it is also believed to regulate actin dynamics in lamellipodia [4] [5]. The Arp2/3 complex promotes actin filament nucleation in vitro, which is further enhanced by ActA [6] [7]. The Arp2/3 complex also interacts with members of the Wiskott-Aldrich syndrome protein (WASP) [8] family - Scar1 [9] [10] and WASP itself [11]. We interfered with the targeting of the Arp2/3 complex to Listeria by using carboxy-terminal fragments of Scar1 that bind the Arp2/3 complex [11]. These fragments completely blocked actin tail formation and motility of Listeria, both in mouse brain extract and in Ptk2 cells overexpressing Scar1 constructs. In both systems, Listeria could initiate actin cloud formation, but tail formation was blocked. Full motility in vitro was restored by adding purified Arp2/3 complex. We conclude that the Arp2/3 complex is a host-cell factor essential for the actin-based motility of L. monocytogenes, suggesting that it plays a pivotal role in regulating the actin cytoskeleton.

    Funded by: NIGMS NIH HHS: GM-26338

    Current biology : CB 1999;9;14;759-62

  • Identification of two human WAVE/SCAR homologues as general actin regulatory molecules which associate with the Arp2/3 complex.

    Suetsugu S, Miki H and Takenawa T

    Department of Biochemistry, Institute of Medical Science, Tokyo, Japan.

    WAVE/SCAR protein was identified as a protein which has similarity to WASP and N-WASP, especially in its C terminal. Recently, WAVE/SCAR protein has been shown to cooperate with the Arp2/3 complex, a nucleation core for actin polymerization in vitro. However, in spite of its general function, WAVE/SCAR expression is mainly restricted to the brain, suggesting the existence of related molecule(s). We here identified two human WAVE/SCAR homologues, which cover other organs. We named the original WAVE1 and newly identified ones WAVE2 and WAVE3. WAVE2 had a very wide distribution with strong expression in peripheral blood leukocytes and mapped on chromosome Xp11.21, next to the WASP locus. WAVE3 and WAVE1 had similar distributions. WAVE3 was strongly expressed in brain and mapped on chromosome 13q12. WAVE1 was mapped on chromosome 6q21-22. Ectopically expressed WAVE2 and WAVE3 induced actin filament clusters in a similar manner with WAVE1. These actin cluster formations were suppressed by deletion of their C-terminal VPH (verproline homology)/WH2 (WASP homology 2) domain. Further, WAVE2 and WAVE3 associate with the Arp2/3 complex as does WAVE1. Our identification of WAVE homologues suggests that WAVE family proteins have general function for regulating the actin cytoskeleton in many tissues.

    Biochemical and biophysical research communications 1999;260;1;296-302

  • Scar1 and the related Wiskott-Aldrich syndrome protein, WASP, regulate the actin cytoskeleton through the Arp2/3 complex.

    Machesky LM and Insall RH

    MRC-LMCB, Department of Molecular Medicine, University College London, Gower Street, London WC1E 6BT, UK. machesky@pugh.bip.bham

    Background: The actin-related proteins Arp2 and Arp3 are part of a seven-protein complex which is localized in the lamellipodia of a variety of cell types, and in actin-rich spots of unknown function. The Arp2/3 complex enhances actin nucleation and causes branching and crosslinking of actin filaments in vitro; in vivo it is thought to drive the formation of lamellipodia and to be a control center for actin-based motility. The Wiskott-Aldrich syndrome protein, WASP, is an adaptor protein implicated in the transmission of signals from tyrosine kinase receptors and small GTPases to the actin cytoskeleton. Scar1 is a member of a new family of proteins related to WASP, and it may also have a role in regulating the actin cytoskeleton. Scar1 is the human homologue of Dictyostelium Scar1, which is thought to connect G-protein-coupled receptors to the actin cytoskeleton. The mammalian Scar family contains at least four members. We have examined the relationships between WASP, Scar1, and the Arp2/3 complex.

    Results: We have identified WASP and its relative Scar1 as proteins that interact with the Arp2/3 complex. We have used deletion analysis to show that both WASP and Scar1 interact with the p21 subunit of the Arp2/3 complex through their carboxyl termini. Overexpression of carboxy-terminal fragments of Scar1 or WASP in cells caused a disruption in the localization of the Arp2/3 complex and, concomitantly, induced a complete loss of lamellipodia and actin spots. The induction of lamellipodia by platelet-derived growth factor was also suppressed by overexpression of the fragment of Scar1 that binds to the Arp2/3 complex.

    Conclusions: We have identified a conserved sequence domain in proteins of the WASP family that binds to the Arp2/3 complex. Overexpression of this domain in cells disrupts the localization of the Arp2/3 complex and inhibits lamellipodia formation. Our data suggest that WASP-related proteins may regulate the actin cytoskeleton through the Arp2/3 complex.

    Current biology : CB 1998;8;25;1347-56

  • Mammalian actin-related protein 2/3 complex localizes to regions of lamellipodial protrusion and is composed of evolutionarily conserved proteins.

    Machesky LM, Reeves E, Wientjes F, Mattheyse FJ, Grogan A, Totty NF, Burlingame AL, Hsuan JJ and Segal AW

    Department of Medicine, University College London, U.K.

    Human neutrophils contain a complex of proteins similar to the actin-related protein 2/3 (Arp2/3) complex of Acanthamoeba. We have obtained peptide sequence information for each member of the putative seven-protein complex previously described for Acanthamoeba and human platelets. From the peptide sequences we have identified cDNA species encoding three novel proteins in this complex. We find that in addition to Arp2 and Arp3, this complex contains a relative of the human (Suppressor of Profilin) SOP2Hs protein and four previously unknown proteins. These proteins localize in the cytoplasm of fibroblasts that lack lamellipodia, but are enriched in lamellipodia on stimulation with serum or platelet-derived growth factor. We propose a conserved and dynamic role for this complex in the organization of the actin cytoskeleton.

    Funded by: Wellcome Trust

    The Biochemical journal 1997;328 ( Pt 1);105-12

  • The human Arp2/3 complex is composed of evolutionarily conserved subunits and is localized to cellular regions of dynamic actin filament assembly.

    Welch MD, DePace AH, Verma S, Iwamatsu A and Mitchison TJ

    Department of Cellular and Molecular Pharmacology, University of California, San Francisco, California 94143-0450, USA. welch@cgl.ucsf.edu

    The Arp2/3 protein complex has been implicated in the control of actin polymerization in cells. The human complex consists of seven subunits which include the actin related proteins Arp2 and Arp3, and five others referred to as p41-Arc, p34-Arc, p21-Arc, p20-Arc, and p16-Arc (p omplex). We have determined the predicted amino acid sequence of all seven subunits. Each has homologues in diverse eukaryotes, implying that the structure and function of the complex has been conserved through evolution. Human Arp2 and Arp3 are very similar to family members from other species. p41-Arc is a new member of the Sop2 family of WD (tryptophan and aspartate) repeat-containing proteins and may be posttranslationally modified, suggesting that it may be involved in regulating the activity and/or localization of the complex. p34-Arc, p21-Arc, p20-Arc, and p16-Arc define novel protein families. We sought to evaluate the function of the Arp2/3 complex in cells by determining its intracellular distribution. Arp3, p34-Arc, and p21-Arc were localized to the lamellipodia of stationary and locomoting fibroblasts, as well to Listeria monocytogenes assembled actin tails. They were not detected in cellular bundles of actin filaments. Taken together with the ability of the Arp2/3 complex to induce actin polymerization, these observations suggest that the complex promotes actin assembly in lamellipodia and may participate in lamellipodial protrusion.

    Funded by: NIGMS NIH HHS: GM48027, R01 GM048027

    The Journal of cell biology 1997;138;2;375-84

  • The complex containing actin-related proteins Arp2 and Arp3 is required for the motility and integrity of yeast actin patches.

    Winter D, Podtelejnikov AV, Mann M and Li R

    Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, USA.

    Background: Structural modeling and biochemical experiments in vitro have implicated a multi-protein complex containing two actin-related proteins, Arp2 and Arp3, as a potential actin-filament nucleation factor. This 'Arp2/3 complex' has been identified in Acanthamoeba and human cells and has been shown to localize to regions involved in actin-based motility, such as the leading edge of moving cells and the 'tail' of actin that forms behind the intracellular pathogen Listeria. The function of this complex in vivo has not been characterized, however, and the sequences of the non-actin-related subunits remain to be determined.

    Results: An Arp3 homologue from the budding yeast Saccharomyces cerevisiae was found to localize to cortical actin patches, highly motile structures that concentrate at sites of polarized growth during the yeast cell cycle. A conditional arp3 mutant allele inhibited cortical actin motility at the restrictive temperature and eventually disrupted actin patches. Most Arp3 protein is found in a multi-protein complex; we purified this complex and determined the sequences of each of the protein subunits using a high-accuracy mass peptide-mapping technique. The proteins found in the complex are similar to those in the Acanthamoeba and human Arp2/3 complexes except that the yeast complex lacks a 40 kDa subunit, which is therefore not required for the structural integrity of the complex.

    Conclusions: The Arp2/3 protein complex is conserved from yeast to man, and in yeast the complex is required in vivo for the motility and integrity of cortical actin patches. We hypothesize that these patches may move by a Listeria-like mechanism driven by actin polymerization.

    Current biology : CB 1997;7;7;519-29

  • Actin polymerization is induced by Arp2/3 protein complex at the surface of Listeria monocytogenes.

    Welch MD, Iwamatsu A and Mitchison TJ

    Department of Cellular and Molecular Pharmacology, University of California at San Francisco, 94143, USA. welch@cgl.ucsf.edu

    The pathogenic bacterium Listeria monocytogenes is capable of directed movement within the cytoplasm of infected host cells. Propulsion is thought to be driven by actin polymerization at the bacterial cell surface, and moving bacteria leave in their wake a tail of actin filaments. Determining the mechanism by which L. monocytogenes polymerizes actin may aid the understanding of how actin polymerization is controlled in the cell. Actin assembly by L. monocytogenes requires the bacterial surface protein ActA and protein components present in host cell cytoplasm. We have purified an eight-polypeptide complex that possesses the properties of the host-cell actin polymerization factor. The pure complex is sufficient to initiate ActA-dependent actin polymerization at the surface of L. monocytogenes, and is required to mediate actin tail formation and motility. Two subunits of this protein complex are actin-related proteins (ARPs) belonging to the Arp2 and Arp3 subfamilies. The Arp3 subunit localizes to the surface of stationary bacteria and the tails of motile bacteria in tissue culture cells infected with L. monocytogenes; this is consistent with a role for the complex in promoting actin assembly in vivo. The activity and subunit composition of the Arp2/3 complex suggests that it forms a template that nucleates actin polymerization.

    Nature 1997;385;6613;265-9

Gene lists (6)

Gene List Source Species Name Description Gene count
L00000009 G2C Homo sapiens Human PSD Human orthologues of mouse PSD adapted from Collins et al (2006) 1080
L00000016 G2C Homo sapiens Human PSP Human orthologues of mouse PSP adapted from Collins et al (2006) 1121
L00000059 G2C Homo sapiens BAYES-COLLINS-HUMAN-PSD-CONSENSUS Human cortex PSD consensus 748
L00000061 G2C Homo sapiens BAYES-COLLINS-MOUSE-PSD-CONSENSUS Mouse cortex PSD consensus (ortho) 984
L00000069 G2C Homo sapiens BAYES-COLLINS-HUMAN-PSD-FULL Human cortex biopsy PSD full list 1461
L00000071 G2C Homo sapiens BAYES-COLLINS-MOUSE-PSD-FULL Mouse cortex PSD full list (ortho) 1556
© G2C 2014. The Genes to Cognition Programme received funding from The Wellcome Trust and the EU FP7 Framework Programmes:
EUROSPIN (FP7-HEALTH-241498), SynSys (FP7-HEALTH-242167) and GENCODYS (FP7-HEALTH-241995).

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