Publications by authors named "Dorothy A Schafer"

23 Publications

  • Page 1 of 1

Cortactin Phosphorylation by Casein Kinase 2 Regulates Actin-Related Protein 2/3 Complex Activity, Invadopodia Function, and Tumor Cell Invasion.

Mol Cancer Res 2019 04 4;17(4):987-1001. Epub 2019 Jan 4.

Program in Cancer Cell Biology, Department of Biochemistry, West Virginia University, Morgantown, West Virginia.

Malregulation of the actin cytoskeleton enhances tumor cell motility and invasion. The actin-binding protein cortactin facilitates branched actin network formation through activation of the actin-related protein (Arp) 2/3 complex. Increased cortactin expression due to gene amplification is observed in head and neck squamous cell carcinoma (HNSCC) and other cancers, corresponding with elevated tumor progression and poor patient outcome. Arp2/3 complex activation is responsible for driving increased migration and extracellular matrix (ECM) degradation by governing invadopodia formation and activity. Although cortactin-mediated activation of Arp2/3 complex and invadopodia regulation has been well established, signaling pathways responsible for governing cortactin binding to Arp2/3 are unknown and potentially present a new avenue for anti-invasive therapeutic targeting. Here we identify casein kinase (CK) 2α phosphorylation of cortactin as a negative regulator of Arp2/3 binding. CK2α directly phosphorylates cortactin at a conserved threonine (T24) adjacent to the canonical Arp2/3 binding motif. Phosphorylation of cortactin T24 by CK2α impairs the ability of cortactin to bind Arp2/3 and activate actin nucleation. Decreased invadopodia activity is observed in HNSCC cells with expression of CK2α phosphorylation-null cortactin mutants, shRNA-mediated CK2α knockdown, and with the CK2α inhibitor Silmitasertib. Silmitasertib inhibits HNSCC collective invasion in tumor spheroids and orthotopic tongue tumors in mice. Collectively these data suggest that CK2α-mediated cortactin phosphorylation at T24 is critical in regulating cortactin binding to Arp2/3 complex and pro-invasive activity, identifying a potential targetable mechanism for impairing HNSCC invasion. IMPLICATIONS: This study identifies a new signaling pathway that contributes to enhancing cancer cell invasion. http://mcr.aacrjournals.org/content/molcanres/17/4/987/F1.large.jpg.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1158/1541-7786.MCR-18-0391DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6445698PMC
April 2019

CPI motif interaction is necessary for capping protein function in cells.

Nat Commun 2015 Sep 28;6:8415. Epub 2015 Sep 28.

Department of Cell Biology and Physiology, Washington University School of Medicine, St Louis, Missouri 63110-1093, USA.

Capping protein (CP) has critical roles in actin assembly in vivo and in vitro. CP binds with high affinity to the barbed end of actin filaments, blocking the addition and loss of actin subunits. Heretofore, models for actin assembly in cells generally assumed that CP is constitutively active, diffusing freely to find and cap barbed ends. However, CP can be regulated by binding of the 'capping protein interaction' (CPI) motif, found in a diverse and otherwise unrelated set of proteins that decreases, but does not abolish, the actin-capping activity of CP and promotes uncapping in biochemical experiments. Here, we report that CP localization and the ability of CP to function in cells requires interaction with a CPI-motif-containing protein. Our discovery shows that cells target and/or modulate the capping activity of CP via CPI motif interactions in order for CP to localize and function in cells.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/ncomms9415DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4598739PMC
September 2015

The Drosophila planar polarity gene multiple wing hairs directly regulates the actin cytoskeleton.

Development 2015 Jul 7;142(14):2478-86. Epub 2015 Jul 7.

Departments of Biology and Cell Biology, University of Virginia, Charlottesville, VA 22904, USA

The evolutionarily conserved frizzled/starry night (fz/stan) pathway regulates planar cell polarity (PCP) in vertebrates and invertebrates. This pathway has been extensively studied in the Drosophila wing, where it is manifested by an array of distally pointing cuticular hairs. Using in vivo imaging we found that, early in hair growth, cells have multiple actin bundles and hairs that subsequently fuse into a single growing hair. The downstream PCP gene multiple wing hairs (mwh) plays a key role in this process and acts to antagonize the actin cytoskeleton. In mwh mutants hair initiation is not limited to a small region at the distal edge of pupal wing cells as in wild type, resulting in multiple hairs with aberrant polarity. Extra actin bundles/hairs are formed and do not completely fuse, in contrast to wild type. As development proceeded additional hairs continued to form, further increasing hair number. We identified a fragment of Mwh with in vivo rescue activity and that bound and bundled F-actin filaments and inhibited actin polymerization in in vitro actin assays. The loss of these activities can explain the mwh mutant phenotype. Our data suggest a model whereby, prior to hair initiation, proximally localized Mwh inhibits actin polymerization resulting in polarized activation of the cytoskeleton and hair formation on the distal side of wing cells. During hair growth Mwh is found in growing hairs, where we suggest it functions to promote the fusion of actin bundles and inhibit the formation of additional actin bundles that could lead to extra hairs.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1242/dev.122119DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4510862PMC
July 2015

Capping protein regulators fine-tune actin assembly dynamics.

Nat Rev Mol Cell Biol 2014 Oct 10;15(10):677-89. Epub 2014 Sep 10.

Department of Cell Biology and Physiology, Washington University, St. Louis, Missouri 63110, USA.

Capping protein (CP) binds the fast growing barbed end of the actin filament and regulates actin assembly by blocking the addition and loss of actin subunits. Recent studies provide new insights into how CP and barbed-end capping are regulated. Filament elongation factors, such as formins and ENA/VASP (enabled/vasodilator-stimulated phosphoprotein), indirectly regulate CP by competing with CP for binding to the barbed end, whereas other molecules, including V-1 and phospholipids, directly bind to CP and sterically block its interaction with the filament. In addition, a diverse and unrelated group of proteins interact with CP through a conserved 'capping protein interaction' (CPI) motif. These proteins, including CARMIL (capping protein, ARP2/3 and myosin I linker), CD2AP (CD2-associated protein) and the WASH (WASP and SCAR homologue) complex subunit FAM21, recruit CP to specific subcellular locations and modulate its actin-capping activity via allosteric effects.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/nrm3869DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4271544PMC
October 2014

Dynamin2 organizes lamellipodial actin networks to orchestrate lamellar actomyosin.

PLoS One 2014 7;9(4):e94330. Epub 2014 Apr 7.

Department of Biology, University of Virginia, Charlottesville, Virginia, United States of America; Department of Cell Biology, University of Virginia, Charlottesville, Virginia, United States of America.

Actin networks in migrating cells exist as several interdependent structures: sheet-like networks of branched actin filaments in lamellipodia; arrays of bundled actin filaments co-assembled with myosin II in lamellae; and actin filaments that engage focal adhesions. How these dynamic networks are integrated and coordinated to maintain a coherent actin cytoskeleton in migrating cells is not known. We show that the large GTPase dynamin2 is enriched in the distal lamellipod where it regulates lamellipodial actin networks as they form and flow in U2-OS cells. Within lamellipodia, dynamin2 regulated the spatiotemporal distributions of α-actinin and cortactin, two actin-binding proteins that specify actin network architecture. Dynamin2's action on lamellipodial F-actin influenced the formation and retrograde flow of lamellar actomyosin via direct and indirect interactions with actin filaments and a finely tuned GTP hydrolysis activity. Expression in dynamin2-depleted cells of a mutant dynamin2 protein that restores endocytic activity, but not activities that remodel actin filaments, demonstrated that actin filament remodeling by dynamin2 did not depend of its functions in endocytosis. Thus, dynamin2 acts within lamellipodia to organize actin filaments and regulate assembly and flow of lamellar actomyosin. We hypothesize that through its actions on lamellipodial F-actin, dynamin2 generates F-actin structures that give rise to lamellar actomyosin and for efficient coupling of F-actin at focal adhesions. In this way, dynamin2 orchestrates the global actin cytoskeleton.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0094330PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3978067PMC
December 2014

IQGAP1 interactome analysis by in vitro reconstitution and live cell 3-color FRET microscopy.

Cytoskeleton (Hoboken) 2013 Dec 16;70(12):819-36. Epub 2013 Oct 16.

Department of Biology, University of Virginia, Charlottesville, Virginia; Keck Center for Cellular Imaging; University of Virginia, Charlottesville, Virginia.

IQGAP1 stimulates branched actin filament nucleation by activating N-WASP, which then activates the Arp2/3 complex. N-WASP can be activated by other factors, including GTP-bound Cdc42 or Rac1, which also bind IQGAP1. Here we report the use of purified proteins for in vitro binding and actin polymerization assays, and Förster (or fluorescence) resonance energy transfer (FRET) microscopy of cultured cells to illuminate functional interactions among IQGAP1, N-WASP, actin, and either Cdc42 or Rac1. In pyrene-actin assembly assays containing N-WASP and Arp2/3 complex, IQGAP1 plus either small G protein cooperatively stimulated actin filament nucleation by reducing the lag time before 50% maximum actin polymerization was reached. Similarly, Cdc42 and Rac1 modulated the binding of IQGAP1 to N-WASP in a dose-dependent manner, with Cdc42 enhancing the interaction and Rac1 reducing the interaction. These in vitro reconstitution results suggested that IQGAP1 interacts by similar, yet distinct mechanisms with Cdc42 versus Rac1 to regulate actin filament assembly through N-WASP in vivo. The physiological relevance of these multi-protein interactions was substantiated by 3-color FRET microscopy of live MDCK cells expressing various combinations of fluorescent N-WASP, IQGAP1, Cdc42, Rac1, and actin. This study also establishes 3-color FRET microscopy as a powerful tool for studying dynamic intermolecular interactions in live cells.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/cm.21146DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3917506PMC
December 2013

Dynamin: expanding its scope to the cytoskeleton.

Int Rev Cell Mol Biol 2013 ;302:187-219

Department of Biology, University of Virginia, Charlottesville, VA, USA.

The large GTPase dynamin is well known for its actions on budded cellular membranes to generate vesicles, most often, clathrin-coated endocytic vesicles. The scope of cellular processes in which dynamin-mediated vesicle formation occurs, has expanded to include secretory vesicle formation at the Golgi, from other endosomes and nonclathrin structures, such as caveolae, as well as membrane remodeling during exocytosis and vesicle fusion. An intriguing new facet of dynamin's sphere of influence is the cytoskeleton. Cytoskeletal filament networks maintain cell shape, provide cell movement, execute cell division and orchestrate vesicle trafficking. Recent evidence supports the hypothesis that dynamin influences actin filaments and microtubules via mechanisms that are independent of its membrane-remodeling activities. This chapter discusses this emerging evidence and considers possible mechanisms of action.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/B978-0-12-407699-0.00003-0DOI Listing
July 2013

Psidin, a conserved protein that regulates protrusion dynamics and cell migration.

Genes Dev 2011 Apr 15;25(7):730-41. Epub 2011 Mar 15.

Department of Biological Chemistry, Center for Cell Dynamics, Johns Hopkins School of Medicine, Baltimore, Maryland 21205, USA.

Dynamic assembly and disassembly of actin filaments is a major driving force for cell movements. Border cells in the Drosophila ovary provide a simple and genetically tractable model to study the mechanisms regulating cell migration. To identify new genes that regulate cell movement in vivo, we screened lethal mutations on chromosome 3R for defects in border cell migration and identified two alleles of the gene psidin (psid). In vitro, purified Psid protein bound F-actin and inhibited the interaction of tropomyosin with F-actin. In vivo, psid mutations exhibited genetic interactions with the genes encoding tropomyosin and cofilin. Border cells overexpressing Psid together with GFP-actin exhibited altered protrusion/retraction dynamics. Psid knockdown in cultured S2 cells reduced, and Psid overexpression enhanced, lamellipodial dynamics. Knockdown of the human homolog of Psid reduced the speed and directionality of migration in wounded MCF10A breast epithelial monolayers, whereas overexpression of the protein increased migration speed and altered protrusion dynamics in EGF-stimulated cells. These results indicate that Psid is an actin regulatory protein that plays a conserved role in protrusion dynamics and cell migration.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1101/gad.2028611DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3070935PMC
April 2011

Multiplexing MIM.

Dev Cell 2010 Aug;19(2):189-90

Department of Biology, University of Virginia, Charlottesville, 22904, USA.

Signaling circuits often coordinate cellular membranes and actin filaments at distinct sites to direct cell behavior. In this issue of Developmental Cell, Bershteyn et al. outline how the molecular scaffold protein, MIM, which bends membranes and binds actin filaments, is at the middle of one such circuit to regulate ciliogenesis.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.devcel.2010.07.021DOI Listing
August 2010

Constricting membranes at the nano and micro scale.

Proc Natl Acad Sci U S A 2009 Dec 1;106(49):20559-60. Epub 2009 Dec 1.

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

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1073/pnas.0911630106DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2791622PMC
December 2009

Dynamin2 GTPase and cortactin remodel actin filaments.

J Biol Chem 2009 Sep 15;284(36):23995-4005. Epub 2009 Jul 15.

Department of Biology, University of Virginia, Charlottesville, Virginia 22903, USA.

The large GTPase dynamin, best known for its activities that remodel membranes during endocytosis, also regulates F-actin-rich structures, including podosomes, phagocytic cups, actin comet tails, subcortical ruffles, and stress fibers. The mechanisms by which dynamin regulates actin filaments are not known, but an emerging view is that dynamin influences F-actin via its interactions with proteins that interact directly or indirectly with actin filaments. We show here that dynamin2 GTPase activity remodels actin filaments in vitro via a mechanism that depends on the binding partner and F-actin-binding protein, cortactin. Tightly associated actin filaments cross-linked by dynamin2 and cortactin became loosely associated after GTP addition when viewed by transmission electron microscopy. Actin filaments were dynamically unraveled and fragmented after GTP addition when viewed in real time using total internal reflection fluorescence microscopy. Cortactin stimulated the intrinsic GTPase activity of dynamin2 and maintained a stable link between actin filaments and dynamin2, even in the presence of GTP. Filaments remodeled by dynamin2 GTPase in vitro exhibit enhanced sensitivity to severing by the actin depolymerizing factor, cofilin, suggesting that GTPase-dependent remodeling influences the interactions of actin regulatory proteins and F-actin. The global organization of the actomyosin cytoskeleton was perturbed in U2-OS cells depleted of dynamin2, implicating dynamin2 in remodeling actin filaments that comprise supramolecular F-actin arrays in vivo. We conclude that dynamin2 GTPase remodels actin filaments and plays a role in orchestrating the global actomyosin cytoskeleton.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1074/jbc.M109.024398DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2781994PMC
September 2009

Coronin 1B antagonizes cortactin and remodels Arp2/3-containing actin branches in lamellipodia.

Cell 2008 Sep;134(5):828-42

Department of Cell and Developmental Biology, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7295, USA.

The dendritic actin network generated by the Arp2/3 complex in lamellipodia underlies formation of protrusions, directional sensing, and migration. While the generation of this network is well studied, the mechanisms regulating network disassembly are poorly understood. We report that Coronin 1B disassembles Arp2/3-containing actin filament branches by inducing Arp2/3 dissociation. This activity is antagonized by Cortactin, a filament branch stabilizer. Consistent with this biochemical competition, depletion of both proteins partially rescues defects in lamellipodial dynamics observed upon depletion of either protein alone. Coronin 1B targets actin branches in a manner that is mutually exclusive with the Arp2/3 complex and alters the branch angle. We conclude that Coronin 1B replaces the Arp2/3 complex at actin filament branches as the dendritic network matures and drives the turnover of branched actin networks.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.cell.2008.06.054DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2570342PMC
September 2008

Ena/VASP proteins capture actin filament barbed ends.

J Biol Chem 2008 Apr 18;283(15):9814-9. Epub 2008 Feb 18.

Departments of Biology and Cell Biology, University of Virginia, Charlottesville, VA 22903, USA.

Ena/VASP (vasodialator-stimulated protein) proteins regulate many actin-dependent events, including formation of protrusive structures, fibroblast migration, neurite extension, cell-cell adhesion, and Listeria pathogenesis. In vitro, Ena/VASP activities on actin are complex and varied. They promote actin assembly, protect filaments from cappers, bundle filaments, and inhibit filament branching. To determine the mechanisms by which Ena/VASP proteins regulate actin dynamics at barbed ends, we monitored individual actin filaments growing in the presence of VASP and profilin using total internal reflection fluorescence microscopy. Filament growth was unchanged by VASP, but filaments grew faster in profilin-actin and VASP than with profilin-actin alone. Actin filaments were captured directly by VASP-coated surfaces via interactions with growing barbed ends. End-attached filaments transiently paused but resumed growth after becoming bound to the surface via a filament side attachment. Thus, Ena/VASP proteins promote actin assembly by interacting directly with actin filament barbed ends, recruiting profilin-actin, and blocking capping.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1074/jbc.M710475200DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2442276PMC
April 2008

Cordon-bleu: a new taste in actin nucleation.

Cell 2007 Oct;131(2):236-8

Department of Neuroscience, University of Virginia, Charlottesville, VA 22093, USA.

Polymerization of actin filaments powers many dynamic cellular events and is directed by a small group of actin nucleators. In this issue, Ahuja et al. (2007) identify and characterize a new actin nucleator called cordon-bleu (Cobl) that may drive morphogenesis of the central nervous system during development.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.cell.2007.10.003DOI Listing
October 2007

Coronin 1B coordinates Arp2/3 complex and cofilin activities at the leading edge.

Cell 2007 Mar;128(5):915-29

Lineberger Comprehensive Cancer Center and Department of Cell and Developmental Biology, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.

Actin filament formation and turnover within the treadmilling actin filament array at the leading edge of migrating cells are interdependent and coupled, but the mechanisms coordinating these two activities are not understood. We report that Coronin 1B interacts simultaneously with Arp2/3 complex and Slingshot (SSH1L) phosphatase, two regulators of actin filament formation and turnover, respectively. Coronin 1B inhibits filament nucleation by Arp2/3 complex and this inhibition is attenuated by phosphorylation of Coronin 1B at Serine 2, a site targeted by SSH1L. Coronin 1B also directs SSH1L to lamellipodia where SSH1L likely regulates Cofilin activity via dephosphorylation. Accordingly, depleting Coronin 1B increases phospho-Cofilin levels, and alters lamellipodial dynamics and actin filament architecture at the leading edge. We conclude that Coronin 1B's coordination of filament formation by Arp2/3 complex and filament turnover by Cofilin is required for effective lamellipodial protrusion and cell migration.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.cell.2007.01.031DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2630706PMC
March 2007

IQGAP1 regulates cell motility by linking growth factor signaling to actin assembly.

J Cell Sci 2007 Feb 30;120(Pt 4):658-69. Epub 2007 Jan 30.

Department of Biology, University of Virginia, Charlottesville, VA 22904, USA.

IQGAP1 has been implicated as a regulator of cell motility because its overexpression or underexpression stimulates or inhibits cell migration, respectively, but the underlying mechanisms are not well understood. Here, we present evidence that IQGAP1 stimulates branched actin filament assembly, which provides the force for lamellipodial protrusion, and that this function of IQGAP1 is regulated by binding of type 2 fibroblast growth factor (FGF2) to a cognate receptor, FGFR1. Stimulation of serum-starved MDBK cells with FGF2 promoted IQGAP1-dependent lamellipodial protrusion and cell migration, and intracellular associations of IQGAP1 with FGFR1--and two other factors--the Arp2/3 complex and its activator N-WASP, that coordinately promote nucleation of branched actin filament networks. FGF2 also induced recruitment of IQGAP1, FGFR1, N-WASP and Arp2/3 complex to lamellipodia. N-WASP was also required for FGF2-stimulated migration of MDBK cells. In vitro, IQGAP1 bound directly to the cytoplasmic tail of FGFR1 and to N-WASP, and stimulated branched actin filament nucleation in the presence of N-WASP and the Arp2/3 complex. Based on these observations, we conclude that IQGAP1 links FGF2 signaling to Arp2/3 complex-dependent actin assembly by serving as a binding partner for FGFR1 and as an activator of N-WASP.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1242/jcs.03376DOI Listing
February 2007

Ena/VASP proteins enhance actin polymerization in the presence of barbed end capping proteins.

J Biol Chem 2005 Aug 6;280(31):28653-62. Epub 2005 Jun 6.

Department of Biology, University of Virginia, Charlottesville, Virginia 22903, USA.

Ena/VASP proteins influence the organization of actin filament networks within lamellipodia and filopodia of migrating cells and in actin comet tails. The molecular mechanisms by which Ena/VASP proteins control actin dynamics are unknown. We investigated how Ena/VASP proteins regulate actin polymerization at actin filament barbed ends in vitro in the presence and absence of barbed end capping proteins. Recombinant His-tagged VASP increased the rate of actin polymerization in the presence of the barbed end cappers, heterodimeric capping protein (CP), CapG, and gelsolin-actin complex. Profilin enhanced the ability of VASP to protect barbed ends from capping by CP, and this required interactions of profilin with G-actin and VASP. The VASP EVH2 domain was sufficient to protect barbed ends from capping, and the F-actin and G-actin binding motifs within EVH2 were required. Phosphorylation by protein kinase A at sites within the VASP EVH2 domain regulated anti-capping and F-actin bundling by VASP. We propose that Ena/VASP proteins associate at or near actin filament barbed ends, promote actin assembly, and restrict the access of barbed end capping proteins.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1074/jbc.M503957200DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1747414PMC
August 2005

Cell biology: barbed ends rule.

Nature 2004 Aug;430(7001):734-5

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/430734aDOI Listing
August 2004

Regulating actin dynamics at membranes: a focus on dynamin.

Traffic 2004 Jul;5(7):463-9

Department of Biology, University of Virginia, Charlottesville, VA 22904, USA.

Dynamin, the large guanosine triphosphatase, is generally considered to have a key role in deforming membranes to create tubules or vesicles. Dynamin, particularly dynamin2 isoforms, also are localized with actin filaments, often at locations where cellular membranes undergo remodeling. Perturbing dynamin function interferes with endocytic traffic and actin function. Thus, dynamin may regulate actin filaments coordinately with its activities that remodel membranes. This review will highlight recent observations that provide clues to mechanisms whereby dynamin might coordinate membrane remodeling and actin filament dynamics during endocytic traffic, cell morphogenesis and cell migration.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/j.1600-0854.2004.00199.xDOI Listing
July 2004

Actin puts on the squeeze.

Nat Cell Biol 2003 Aug;5(8):693-4

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/ncb0803-693DOI Listing
August 2003

Dynamin2 and cortactin regulate actin assembly and filament organization.

Curr Biol 2002 Oct;12(21):1852-7

Department of Biology, University of Virginia, Charlottesville, VA 22904, USA.

The GTPase dynamin is required for endocytic vesicle formation. Dynamin has also been implicated in regulating the actin cytoskeleton, but the mechanism by which it does so is unclear. Through interactions via its proline-rich domain (PRD), dynamin binds several proteins, including cortactin, profilin, syndapin, and murine Abp1, that regulate the actin cytoskeleton. We investigated the interaction of dynamin2 and cortactin in regulating actin assembly in vivo and in vitro. When expressed in cultured cells, a dynamin2 mutant with decreased affinity for GTP decreased actin dynamics within the cortical actin network. Expressed mutants of cortactin that have decreased binding of Arp2/3 complex or dynamin2 also decreased actin dynamics. Dynamin2 influenced actin nucleation by purified Arp2/3 complex and cortactin in vitro in a biphasic manner. Low concentrations of dynamin2 enhanced actin nucleation by Arp2/3 complex and cortactin, and high concentrations were inhibitory. Dynamin2 promoted the association of actin filaments nucleated by Arp2/3 complex and cortactin with phosphatidylinositol 4,5-bisphosphate (PIP2)-containing lipid vesicles. GTP hydrolysis altered the organization of the filaments and the lipid vesicles. We conclude that dynamin2, through an interaction with cortactin, regulates actin assembly and actin filament organization at membranes.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/s0960-9822(02)01228-9DOI Listing
October 2002

Antagonism between Ena/VASP proteins and actin filament capping regulates fibroblast motility.

Cell 2002 May;109(4):509-21

Massachusetts Institute of Technology, Department of Biology, Cambridge 02139, USA.

Cell motility requires lamellipodial protrusion, a process driven by actin polymerization. Ena/VASP proteins accumulate in protruding lamellipodia and promote the rapid actin-driven motility of the pathogen Listeria. In contrast, Ena/VASP negatively regulate cell translocation. To resolve this paradox, we analyzed the function of Ena/VASP during lamellipodial protrusion. Ena/VASP-deficient lamellipodia protruded slower but more persistently, consistent with their increased cell translocation rates. Actin networks in Ena/VASP-deficient lamellipodia contained shorter, more highly branched filaments compared to controls. Lamellipodia with excess Ena/VASP contained longer, less branched filaments. In vitro, Ena/VASP promoted actin filament elongation by interacting with barbed ends, shielding them from capping protein. We conclude that Ena/VASP regulates cell motility by controlling the geometry of actin filament networks within lamellipodia.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/s0092-8674(02)00731-6DOI Listing
May 2002

Coupling actin dynamics and membrane dynamics during endocytosis.

Curr Opin Cell Biol 2002 Feb;14(1):76-81

Department of Cell Biology and Physiology, Washington University School of Medicine, St Louis, Missouri 63119, USA.

A convergence of cellular, genetic and biochemical studies supports the hypothesis that the actin cytoskeleton is coupled to endocytic processes, but the roles played by actin filaments during endocytosis are not yet clear. Recent studies have identified several proteins that may functionally link the endocytic machinery with actin filament dynamics. Three of these proteins, Abp1p, Pan1p and cortactin, are activators of actin assembly nucleated by the Arp2/3 complex, a key regulator of actin assembly in vivo. Two others, intersectin and syndapin, bind N-WASp, a potent activator of actin assembly via the Arp2/3 complex. All of these proteins also bind components of the endocytic machinery, and thus, could coordinately regulate actin assembly and trafficking events. Hip1R, an F-actin-binding protein that associates with clathrin-coated vesicles, may physically link endocytic vesicles to actin filaments. The GTPase dynamin is implicated in modulating actin filaments at specialized actin-rich structures of the cell cortex, suggesting that dynamin may regulate the organization of cortical actin filaments as well as regulate actin dynamics during endocytosis. Finally, myosin VI may generate actin-dependent forces for membrane invagination or vesicle movement during the early stages of endocytosis.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/s0955-0674(01)00297-6DOI Listing
February 2002
-->