New insights into the regulation and cellular functions of the ARP2/3 complex
01 Jan 2013-Nature Reviews Molecular Cell Biology (Nature Publishing Group)-Vol. 14, Iss: 1, pp 7-12
TL;DR: The mechanisms underlying NPF-dependent regulation and the cellular functions of ARP2/3 are being unravelled using new chemical and genetic approaches, of particular interest is the role of the ARP/3 complex in vesicular trafficking and directional cell motility.
Abstract: The actin-related protein 2/3 (ARP2/3) complex nucleates branched actin filament networks, but requires nucleation promoting factors (NPFs) to stimulate this activity. NPFs include proteins such as Wiskott-Aldrich syndrome protein (WASP), neural WASP (NWASP), WASP family verprolin-homologous protein (WAVE; also known as SCAR) and the recently identified WASP and SCAR homologue (WASH) complex. The mechanisms underlying NPF-dependent regulation and the cellular functions of ARP2/3 are being unravelled using new chemical and genetic approaches. Of particular interest is the role of the ARP2/3 complex in vesicular trafficking and directional cell motility.
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University of Minnesota1, University of Colorado Boulder2, VU University Amsterdam3, Harvard University4, University of Southern California5, University of Tartu6, University of Queensland7, Erasmus University Rotterdam8, Hospital for Special Surgery9, University of Copenhagen10, Statens Serum Institut11, Broad Institute12, University of Essex13, University of Edinburgh14, University of Cambridge15, University Hospital of Lausanne16, Geisinger Health System17, Wenzhou Medical College18, Stanford University19, University of North Carolina at Chapel Hill20, University of Wisconsin-Madison21, Hofstra University22, The Feinstein Institute for Medical Research23, University of Dundee24, University of Toronto25, Princeton University26, National Bureau of Economic Research27, Queen's University28, New York University Shanghai29, Karolinska Institutet30, Uppsala University31, University of Lausanne32, New York University33, Stockholm School of Economics34
TL;DR: A joint (multi-phenotype) analysis of educational attainment and three related cognitive phenotypes generates polygenic scores that explain 11–13% of the variance ineducational attainment and 7–10% ofthe variance in cognitive performance, which substantially increases the utility ofpolygenic scores as tools in research.
Abstract: Here we conducted a large-scale genetic association analysis of educational attainment in a sample of approximately 1.1 million individuals and identify 1,271 independent genome-wide-significant SNPs. For the SNPs taken together, we found evidence of heterogeneous effects across environments. The SNPs implicate genes involved in brain-development processes and neuron-to-neuron communication. In a separate analysis of the X chromosome, we identify 10 independent genome-wide-significant SNPs and estimate a SNP heritability of around 0.3% in both men and women, consistent with partial dosage compensation. A joint (multi-phenotype) analysis of educational attainment and three related cognitive phenotypes generates polygenic scores that explain 11-13% of the variance in educational attainment and 7-10% of the variance in cognitive performance. This prediction accuracy substantially increases the utility of polygenic scores as tools in research.
1,658 citations
TL;DR: The feedback loop between biochemical and mechanical properties of actin organization at the molecular level in vitro is described and this knowledge is integrated into the current understanding of cellular actin organizations and its physiological roles.
Abstract: Tight coupling between biochemical and mechanical properties of the actin cytoskeleton drives a large range of cellular processes including polarity establishment, morphogenesis, and motility. This is possible because actin filaments are semi-flexible polymers that, in conjunction with the molecular motor myosin, can act as biological active springs or "dashpots" (in laymen's terms, shock absorbers or fluidizers) able to exert or resist against force in a cellular environment. To modulate their mechanical properties, actin filaments can organize into a variety of architectures generating a diversity of cellular organizations including branched or crosslinked networks in the lamellipodium, parallel bundles in filopodia, and antiparallel structures in contractile fibers. In this review we describe the feedback loop between biochemical and mechanical properties of actin organization at the molecular level in vitro, then we integrate this knowledge into our current understanding of cellular actin organization and its physiological roles.
1,128 citations
Cites background from "New insights into the regulation an..."
...WH2 domains are short domains ( 50 amino acids) that bind to monomeric actin and have a range of attributed roles including actin filament nucleation (130, 266)....
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...When the Arp2/3 complex is knocked down more thoroughly than had previously been achieved or even knocked out entirely, cells are still motile, moving via fingerlike protrusions resembling filopodia, although various defects in translocation are observed (266, 303, 342)....
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TL;DR: This review provides an overview of the properties of actin and shows how dozens of proteins control both the assembly and disassembly of actIn filaments, including nucleotide exchange on actin monomers, polymerization, phosphate dissociation, cap the ends of polymers, cross-link filaments to each other and other cellular components, and sever filaments.
Abstract: Organisms from all domains of life depend on filaments of the protein actin to provide structure and to support internal movements. Many eukaryotic cells use forces produced by actin polymerization for their motility, and myosin motor proteins use ATP hydrolysis to produce force on actin filaments. Actin polymerizes spontaneously, followed by hydrolysis of a bound adenosine triphosphate (ATP). Dissociation of the γ-phosphate prepares the polymer for disassembly. This review provides an overview of the properties of actin and shows how dozens of proteins control both the assembly and disassembly of actin filaments. These players catalyze nucleotide exchange on actin monomers, initiate polymerization, promote phosphate dissociation, cap the ends of polymers, cross-link filaments to each other and other cellular components, and sever filaments.
552 citations
Cites background from "New insights into the regulation an..."
...…at the leading edge of motile cells (WASp, N-WASP [neural-WASp], Scar [suppressor of cAMP activator]/WAVE [WASP family verprolin homologous protein]), at sites of endocytosis (WASp), and for internal membrane traffic (Wiskott–Aldrich syndrome protein and Scar homolog [WASH]) (Rotty et al. 2013)....
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...2010), each in a particular cellular context, including at the leading edge of motile cells (WASp, N-WASP [neural-WASp], Scar [suppressor of cAMP activator]/WAVE [WASP family verprolin homologous protein]), at sites of endocytosis (WASp), and for internal membrane traffic (Wiskott–Aldrich syndrome protein and Scar homolog [WASH]) (Rotty et al. 2013)....
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TL;DR: Systematic profiling of proximity interactions combined with functional analysis provides a rich resource for better understanding human centrosome and cilia biology and may be applied to other complex biological structures or pathways.
445 citations
Cites background from "New insights into the regulation an..."
..., 2010), the appendage component C3orf14 identified above (see Figure 3D), a number of MT-associated proteins (ANK2, MTUS1, GTSE1, TRIM36, MAP1S), and subunits of the WASH and Arp2/3 complexes (KIAA1033, WASH1, and CCDC53, ARPC3) (Edwards et al., 2014; Rotty et al., 2013)....
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...…WDR62 (Nicholas et al., 2010), the appendage component C3orf14 identified above (see Figure 3D), a number of MT-associated proteins (ANK2, MTUS1, GTSE1, TRIM36, MAP1S), and subunits of the WASH and Arp2/3 complexes (KIAA1033, WASH1, and CCDC53, ARPC3) (Edwards et al., 2014; Rotty et al., 2013)....
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...Fifty-five of these hits are in CCDB (Tables S1 and S5), and the remaining 67 hits included USP54, a recently identified PLK4 interacting partner (Firat-Karalar et al., 2014), the microcephaly gene WDR62 (Nicholas et al., 2010), the appendage component C3orf14 identified above (see Figure 3D), a number of MT-associated proteins (ANK2, MTUS1, GTSE1, TRIM36, MAP1S), and subunits of the WASH and Arp2/3 complexes (KIAA1033, WASH1, and CCDC53, ARPC3) (Edwards et al., 2014; Rotty et al., 2013)....
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TL;DR: Improved understanding of how the cytoskeleton and its interacting partners influence tumour cell migration and metastasis has led to the development of novel therapeutics against aggressive and metastatic disease.
Abstract: Metastasis is responsible for the greatest number of cancer deaths. Metastatic disease, or the movement of cancer cells from one site to another, is a complex process requiring dramatic remodelling of the cell cytoskeleton. The various components of the cytoskeleton, actin (microfilaments), microtubules (MTs) and intermediate filaments, are highly integrated and their functions are well orchestrated in normal cells. In contrast, mutations and abnormal expression of cytoskeletal and cytoskeletal-associated proteins play an important role in the ability of cancer cells to resist chemotherapy and metastasize. Studies on the role of actin and its interacting partners have highlighted key signalling pathways, such as the Rho GTPases, and downstream effector proteins that, through the cytoskeleton, mediate tumour cell migration, invasion and metastasis. An emerging role for MTs in tumour cell metastasis is being unravelled and there is increasing interest in the crosstalk between key MT interacting proteins and the actin cytoskeleton, which may provide novel treatment avenues for metastatic disease. Improved understanding of how the cytoskeleton and its interacting partners influence tumour cell migration and metastasis has led to the development of novel therapeutics against aggressive and metastatic disease.
Linked Articles
This article is part of a themed section on Cytoskeleton, Extracellular Matrix, Cell Migration, Wound Healing and Related Topics. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-24
412 citations
Cites background from "New insights into the regulation an..."
...The Arp2/3 complex is involved in both directional cell motility and vesicular transport of cells (Rotty et al., 2013)....
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...The Arp2/3 complex facilitated by nucleation promoting factors, through initiation of dendritic nucleation (filament formation on the sides of preexisting actin filaments), generates a branched actin network (Rotty et al., 2013)....
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References
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TL;DR: It is shown that Arp2/3 complex purified from Acanthamoeba caps the pointed ends of actin filaments with high affinity and increases the critical concentration for polymerization at the pointed end from 0.6 to 1.0 microM.
Abstract: The Arp2/3 complex is a stable assembly of seven protein subunits including two actin-related proteins (Arp2 and Arp3) and five novel proteins. Previous work showed that this complex binds to the sides of actin filaments and is concentrated at the leading edges of motile cells. Here, we show that Arp2/3 complex purified from Acanthamoeba caps the pointed ends of actin filaments with high affinity. Arp2/3 complex inhibits both monomer addition and dissociation at the pointed ends of actin filaments with apparent nanomolar affinity and increases the critical concentration for polymerization at the pointed end from 0.6 to 1.0 μM. The high affinity of Arp2/3 complex for pointed ends and its abundance in amoebae suggest that in vivo all actin filament pointed ends are capped by Arp2/3 complex. Arp2/3 complex also nucleates formation of actin filaments that elongate only from their barbed ends. From kinetic analysis, the nucleation mechanism appears to involve stabilization of polymerization intermediates (probably actin dimers). In electron micrographs of quick-frozen, deep-etched samples, we see Arp2/3 bound to sides and pointed ends of actin filaments and examples of Arp2/3 complex attaching pointed ends of filaments to sides of other filaments. In these cases, the angle of attachment is a remarkably constant 70 ± 7°. From these in vitro biochemical properties, we propose a model for how Arp2/3 complex controls the assembly of a branching network of actin filaments at the leading edge of motile cells.
1,432 citations
TL;DR: This review summarizes what is known about the biochemical and biophysical mechanisms that initiate the assembly of actin filaments in cells and focuses on Arp2/3 complex and formins.
Abstract: This review summarizes what is known about the biochemical and biophysical mechanisms that initiate the assembly of actin filaments in cells. Assembly and disassembly of these filaments contribute to many types of cellular movements. Numerous proteins regulate actin assembly, but Arp2/3 complex and formins are the focus of this review because more is known about them than other proteins that stimulate the formation of new filaments. Arp2/3 complex is active at the leading edge of motile cells, where it produces branches on the sides of existing filaments. Growth of these filaments produces force to protrude the membrane. Crystal structures, reconstructions from electron micrographs, and biophysical experiments have started to map out the steps through which proteins called nucleation-promoting factors stimulate the formation of branches. Formins nucleate and support the elongation of unbranched actin filaments for cytokinesis and various types of actin filament bundles. Formins associate processively with the fast-growing ends of filaments and protect them from capping.
997 citations
TL;DR: A decade of study has begun to shed light on the molecular mechanisms by which this powerful machine controls the polymerization, organization and recycling of actin-filament networks, both in vitro and in the living cell.
Abstract: The cellular functions of the actin cytoskeleton require precise regulation of both the initiation of actin polymerization and the organization of the resulting filaments. The actin-related protein-2/3 (ARP2/3) complex is a central player in this regulation. A decade of study has begun to shed light on the molecular mechanisms by which this powerful machine controls the polymerization, organization and recycling of actin-filament networks, both in vitro and in the living cell.
975 citations
TL;DR: The Spire, cordon-bleu and leiomodin nucleators have revealed new ways of overcoming the kinetic barriers to actin polymerization.
Abstract: For more than a decade the Arp2/3 complex, a handful of nucleation-promoting factors, and formins were the only molecules known to directly nucleate actin filament formation de novo However, the past several years have brought a surge in the discovery of mammalian proteins with roles in actin nucleation and dynamics Newly recognized nucleation-promoting factors, such as WASH, WHAMM, and JMY stimulate Arp2/3 complex activity at distinct cellular locations Formin nucleators with additional biochemical and cellular activities have also been uncovered Finally, the Spire, Cordon-bleu, and Leiomodin nucleators have revealed new ways of overcoming the kinetic barriers to actin polymerization
860 citations
TL;DR: It is proposed that Rac1 and Nck cause dissociation of the WAVE1 complex, which releases activeWAVE1–HSPC300 and leads to actin nucleation.
Abstract: Rac signalling to actin -- a pathway that is thought to be mediated by the protein Scar/WAVE (WASP (Wiskott-Aldrich syndrome protein)-family verprolin homologous protein -- has a principal role in cell motility. In an analogous pathway, direct interaction of Cdc42 with the related protein N-WASP stimulates actin polymerization. For the Rac-WAVE pathway, no such direct interaction has been identified. Here we report a mechanism by which Rac and the adapter protein Nck activate actin nucleation through WAVE1. WAVE1 exists in a heterotetrameric complex that includes orthologues of human PIR121 (p53-inducible messenger RNA with a relative molecular mass (M(r)) of 140,000), Nap125 (NCK-associated protein with an M(r) of 125,000) and HSPC300. Whereas recombinant WAVE1 is constitutively active, the WAVE1 complex is inactive. We therefore propose that Rac1 and Nck cause dissociation of the WAVE1 complex, which releases active WAVE1-HSPC300 and leads to actin nucleation.
844 citations