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1.  Prostaglandins regulate nuclear localization of Fascin and its function in nucleolar architecture 
Molecular Biology of the Cell  2015;26(10):1901-1917.
Fascin, a conserved actin-bundling protein, is not only cytoplasmic but also localizes to the nucleus and nuclear periphery in both Drosophila and mammalian cell contexts. In Drosophila, prostaglandin signaling regulates this localization. In addition, Fascin plays a critical role in nucleolar architecture in both Drosophila and mammalian cells.
Fascin, a highly conserved actin-bundling protein, localizes and functions at new cellular sites in both Drosophila and multiple mammalian cell types. During Drosophila follicle development, in addition to being cytoplasmic, Fascin is in the nuclei of the germline-derived nurse cells during stages 10B–12 (S10B–12) and at the nuclear periphery during stage 13 (S13). This localization is specific to Fascin, as other actin-binding proteins, Villin and Profilin, do not exhibit the same subcellular distribution. In addition, localization of fascin1 to the nucleus and nuclear periphery is observed in multiple mammalian cell types. Thus the regulation and function of Fascin at these new cellular locations is likely to be highly conserved. In Drosophila, loss of prostaglandin signaling causes a global reduction in nuclear Fascin and a failure to relocalize to the nuclear periphery. Alterations in nuclear Fascin levels result in defects in nucleolar morphology in both Drosophila follicles and cultured mammalian cells, suggesting that nuclear Fascin plays an important role in nucleolar architecture. Given the numerous roles of Fascin in development and disease, including cancer, our novel finding that Fascin has functions within the nucleus sheds new light on the potential roles of Fascin in these contexts.
PMCID: PMC4436834  PMID: 25808493
2.  Epithelial inflammation resulting from an inherited loss-of-function mutation in EGFR 
Epidermal growth factor receptor (EGFR) signaling is fundamentally important for tissue homeostasis through EGFR/ligand interactions that stimulate numerous signal transduction pathways. Aberrant EGFR signaling has been reported in inflammatory and malignant diseases but thus far no primary inherited defects in EGFR have been recorded. Using whole-exome sequencing, we identified a homozygous loss-of-function missense mutation in EGFR (c.1283G>A; p.Gly428Asp) in a male infant with life-long inflammation affecting the skin, bowel and lungs. During the first year of life, his skin showed erosions, dry scale, and alopecia. Subsequently, there were numerous papules and pustules – similar to the rash seen in patients receiving EGFR inhibitor drugs. Skin biopsy demonstrated an altered cellular distribution of EGFR in the epidermis with reduced cell membrane labeling, and in vitro analysis of the mutant receptor revealed abrogated EGFR phosphorylation and EGF-stimulated downstream signaling. Microarray analysis on the patient’s skin highlighted disturbed differentiation/premature terminal differentiation of keratinocytes and upregulation of several inflammatory/innate immune response networks. The boy died aged 2.5 years from extensive skin and chest infections as well as electrolyte imbalance. This case highlights the major mechanism of epithelial dysfunction following EGFR signaling ablation and illustrates the broader impact of EGFR inhibition on other tissues.
PMCID: PMC4090136  PMID: 24691054
3.  Alternative Mechanisms for Talin to Mediate Integrin Function 
Current Biology  2015;25(7):847-857.
Cell-matrix adhesion is essential for building animals, promoting tissue cohesion, and enabling cells to migrate and resist mechanical force. Talin is an intracellular protein that is critical for linking integrin extracellular-matrix receptors to the actin cytoskeleton. A key question raised by structure-function studies is whether talin, which is critical for all integrin-mediated adhesion, acts in the same way in every context. We show that distinct combinations of talin domains are required for each of three different integrin functions during Drosophila development. The partial function of some mutant talins requires vinculin, indicating that recruitment of vinculin allows talin to duplicate its own activities. The different requirements are best explained by alternative mechanisms of talin function, with talin using one or both of its integrin-binding sites. We confirmed these alternatives by showing that the proximity between the second integrin-binding site and integrins differs, suggesting that talin adopts different orientations relative to integrins. Finally, we show that vinculin and actomyosin activity help change talin’s orientation. These findings demonstrate that the mechanism of talin function differs in each developmental context examined. The different arrangements of the talin molecule relative to integrins suggest that talin is able to sense different force vectors, either parallel or perpendicular to the membrane. This provides a paradigm for proteins whose apparent uniform function is in fact achieved by a variety of distinct mechanisms involving different molecular architectures.
Graphical Abstract
•Integrin function requires distinct sets of talin domains in three different tissues•Vinculin helps talin retain function when domains are removed•Talin IBS2 is separated from integrins in muscle but not wing adhesion sites•Vinculin and actomyosin contribute to separating IBS2 from integrins
Klapholz et al. show that talin domains have variable importance in different developmental events in Drosophila, suggesting distinct mechanisms of action, with altered configurations of talin, vinculin, and integrins. These were validated by advanced imaging in vivo. Such diverse configurations may allow talin to sense a variety of forces.
PMCID: PMC4386027  PMID: 25754646
4.  Golgi Anti-apoptotic Proteins Are Highly Conserved Ion Channels That Affect Apoptosis and Cell Migration* 
The Journal of Biological Chemistry  2015;290(18):11785-11801.
Background: GAAPs regulate intracellular Ca2+ fluxes, cell migration, and apoptosis.
Results: GAAP forms a cation-selective channel, and residues involved in its ion-conducting properties were identified.
Conclusion: Mutations within the pore demonstrate that GAAP effects on apoptosis and migration are separable.
Significance: Characterization of the pore region of GAAP provides insight into the mechanism of action of this novel and highly conserved ion channel.
Golgi anti-apoptotic proteins (GAAPs) are multitransmembrane proteins that are expressed in the Golgi apparatus and are able to homo-oligomerize. They are highly conserved throughout eukaryotes and are present in some prokaryotes and orthopoxviruses. Within eukaryotes, GAAPs regulate the Ca2+ content of intracellular stores, inhibit apoptosis, and promote cell adhesion and migration. Data presented here demonstrate that purified viral GAAPs (vGAAPs) and human Bax inhibitor 1 form ion channels and that vGAAP from camelpox virus is selective for cations. Mutagenesis of vGAAP, including some residues conserved in the recently solved structure of a related bacterial protein, BsYetJ, altered the conductance (E207Q and D219N) and ion selectivity (E207Q) of the channel. Mutation of residue Glu-207 or -178 reduced the effects of GAAP on cell migration and adhesion without affecting protection from apoptosis. In contrast, mutation of Asp-219 abrogated the anti-apoptotic activity of GAAP but not its effects on cell migration and adhesion. These results demonstrate that GAAPs are ion channels and define residues that contribute to the ion-conducting pore and affect apoptosis, cell adhesion, and migration independently.
PMCID: PMC4416878  PMID: 25713081
Electrophysiology; Ion Channel; Lipid Bilayer; Membrane Protein; Viral Protein
5.  In vivo collective cell migration requires an LPAR2-dependent increase in tissue fluidity 
The Journal of Cell Biology  2014;206(1):113-127.
Neural crest epithelial–mesenchymal transition (EMT) and collective cell migration rely on a solid-to-liquid-like transition triggered by internalization of N-cadherin downstream of lysophosphatidic acid receptor 2.
Collective cell migration (CCM) and epithelial–mesenchymal transition (EMT) are common to cancer and morphogenesis, and are often considered to be mutually exclusive in spite of the fact that many cancer and embryonic cells that have gone through EMT still cooperate to migrate collectively. Here we use neural crest (NC) cells to address the question of how cells that have down-regulated cell–cell adhesions can migrate collectively. NC cell dissociation relies on a qualitative and quantitative change of the cadherin repertoire. We found that the level of cell–cell adhesion is precisely regulated by internalization of N-cadherin downstream of lysophosphatidic acid (LPA) receptor 2. Rather than promoting the generation of single, fully mesenchymal cells, this reduction of membrane N-cadherin only triggers a partial mesenchymal phenotype. This intermediate phenotype is characterized by an increase in tissue fluidity akin to a solid-like–to–fluid-like transition. This change of plasticity allows cells to migrate under physical constraints without abolishing cell cooperation required for collectiveness.
PMCID: PMC4085712  PMID: 25002680
6.  An antagonistic interaction between PlexinB2 and Rnd3 controls RhoA activity and cortical neuron migration 
Nature communications  2014;5:3405.
A transcriptional programme initiated by the proneural factors Neurog2 and Ascl1 controls successive steps of neurogenesis in the embryonic cerebral cortex. Previous work has shown that proneural factors also confer a migratory behaviour to cortical neurons by inducing the expression of the small GTP-binding proteins Rnd2 and Rnd3. However, the directionality of radial migration suggests that migrating neurons also respond to extracellular signal-regulated pathways. Here we show that the Plexin B2 receptor interacts physically and functionally with Rnd3 and stimulates RhoA activity in migrating cortical neurons. Plexin B2 competes with p190RhoGAP for binding to Rnd3, thus blocking the Rnd3-mediated inhibition of RhoA and also recruits RhoGEFs to directly stimulate RhoA activity. Thus, an interaction between a cell-extrinsic Plexin signaling pathway and the cell-intrinsic Ascl1-Rnd3 pathway determines the level of RhoA activity appropriate for cortical neuron migration.
PMCID: PMC3939360  PMID: 24572910
7.  hGAAP promotes cell adhesion and migration via the stimulation of store-operated Ca2+ entry and calpain 2 
The Journal of Cell Biology  2013;202(4):699-713.
hGAAP promotes cell adhesion and migration by increasing localized Ca2+-dependent activation of calpain, leading to increased focal adhesion dynamics.
Golgi antiapoptotic proteins (GAAPs) are highly conserved Golgi membrane proteins that inhibit apoptosis and promote Ca2+ release from intracellular stores. Given the role of Ca2+ in controlling cell adhesion and motility, we hypothesized that human GAAP (hGAAP) might influence these events. In this paper, we present evidence that hGAAP increased cell adhesion, spreading, and migration in a manner that depended on the C-terminal domain of hGAAP. We show that hGAAP increased store-operated Ca2+ entry and thereby the activity of calpain at newly forming protrusions. These hGAAP-dependent effects regulated focal adhesion dynamics and cell migration. Indeed, inhibition or knockdown of calpain 2 abrogated the effects of hGAAP on cell spreading and migration. Our data reveal that hGAAP is a novel regulator of focal adhesion dynamics, cell adhesion, and migration by controlling localized Ca2+-dependent activation of calpain.
PMCID: PMC3747308  PMID: 23940116
8.  ADAM8 expression in invasive breast cancer promotes tumor dissemination and metastasis 
EMBO Molecular Medicine  2013;6(2):278-294.
The transmembrane metalloprotease-disintegrin ADAM8 mediates cell adhesion and shedding of ligands, receptors and extracellular matrix components. Here, we report that ADAM8 is abundantly expressed in breast tumors and derived metastases compared to normal tissue, especially in triple-negative breast cancers (TNBCs). Furthermore, high ADAM8 levels predicted poor patient outcome. Consistently, ADAM8 promoted an aggressive phenotype of TNBC cells in culture. In a mouse orthotopic model, tumors derived from TNBC cells with ADAM8 knockdown failed to grow beyond a palpable size and displayed poor vascularization. Circulating tumor cells and brain metastases were also significantly reduced. Mechanistically, ADAM8 stimulated both angiogenesis through release of VEGF-A and transendothelial cell migration via β1-integrin activation. In vivo, treatment with an anti-ADAM8 antibody from the time of cell inoculation reduced primary tumor burden and metastases. Furthermore, antibody treatment of established tumors profoundly decreased metastases in a resection model. As a non-essential protein under physiological conditions, ADAM8 represents a promising novel target for treatment of TNBCs, which currently lack targeted therapies and frequently progress with fatal dissemination.
Subject Category Cancer
PMCID: PMC3927960  PMID: 24375628
ADAM8; cancer progression; metastasis; therapeutic target; triple-negative; breast cancer
9.  Fascin Regulates the Migration of Subventricular Zone-Derived Neuroblasts in the Postnatal Brain 
The Journal of Neuroscience  2013;33(30):12171-12185.
After birth, stem cells in the subventricular zone (SVZ) generate neuroblasts that migrate along the rostral migratory stream (RMS) to become interneurons in the olfactory bulb (OB). This migration is a fundamental event controlling the proper integration of new neurons in a pre-existing synaptic network. Many regulators of neuroblast migration have been identified; however, still very little is known about the intracellular molecular mechanisms controlling this process. Here, we show that the actin-bundling protein fascin is highly upregulated in mouse SVZ-derived migratory neuroblasts. Fascin-1ko mice display an abnormal RMS and a smaller OB. Bromodeoxyuridine labeling experiments show that lack of fascin significantly impairs neuroblast migration, but does not appear to affect cell proliferation. Moreover, fascin depletion substantially alters the polarized morphology of rat neuroblasts. Protein kinase C (PKC)-dependent phosphorylation of fascin on Ser39 regulates its actin-bundling activity. In vivo postnatal electroporation of phosphomimetic (S39D) or nonphosphorylatable (S39A) fascin variants followed by time-lapse imaging of brain slices demonstrates that the phospho-dependent modulation of fascin activity ensures efficient neuroblast migration. Finally, fluorescence lifetime imaging microscopy studies in rat neuroblasts reveal that the interaction between fascin and PKC can be modulated by cannabinoid signaling, which controls neuroblast migration in vivo. We conclude that fascin, whose upregulation appears to mark the transition to the migratory neuroblast stage, is a crucial regulator of neuroblast motility. We propose that a tightly regulated phospho/dephospho-fascin cycle modulated by extracellular signals is required for the polarized morphology and migration in neuroblasts, thus contributing to efficient neurogenesis.
PMCID: PMC3721833  PMID: 23884926
10.  FAK-heterozygous mice display enhanced tumour angiogenesis 
Nature communications  2013;4:2020.
Genetic ablation of endothelial Focal Adhesion Kinase (FAK) can inhibit pathological angiogenesis, suggesting that loss of endothelial FAK is sufficient to reduce neovascularisation. Here we show that reduced stromal-FAK expression in FAK-heterozygous mice unexpectedly enhances both B16F0 and CMT19T tumour growth and angiogenesis. We further demonstrate that cell proliferation and microvessel sprouting, but not migration, are increased in serum-stimulated FAK-heterozygous endothelial cells. FAK-heterozygous endothelial cells display an imbalance in FAK phosphorylation at pY397 and pY861 without changes in Pyk2 or Erk1/2 activity. By contrast, serum-stimulated phosphorylation of Akt is enhanced in FAK-heterozygous endothelial cells and these cells are more sensitive to Akt inhibition. Additionally, low doses of a pharmacological FAK inhibitor, although too low to affect FAK autophosphorylation in vitro, can enhance angiogenesis ex vivo and tumor growth in vivo. Our results highlight a potential novel role for FAK as a non-linear, dose-dependent regulator of angiogenesis where heterozygous levels of FAK enhance angiogenesis.
PMCID: PMC3712492  PMID: 23799510
11.  CAR regulates epithelial cell junction stability through control of E-cadherin trafficking 
Scientific Reports  2013;3:2889.
CAR (Coxsackie and Adenovirus Receptor) is the primary docking receptor for typeB coxsackie viruses and subgroup C adenoviruses. CAR is a member of the JAM family of adhesion receptors and is located to both tight and adherens junctions between epithelial cells where it can assemble adhesive contacts through homodimerisation in trans. However, the role of CAR in controlling epithelial junction dynamics remains poorly understood. Here we demonstrate that levels of CAR in human epithelial cells play a key role in determining epithelial cell adhesion through control of E-cadherin stability at cell-cell junctions. Mechanistically, we show that CAR is phosphorylated within the C-terminus by PKCδ and that this in turn controls Src-dependent endocytosis of E-cadherin at cell junctions. This data demonstrates a novel role for CAR in regulating epithelial homeostasis.
PMCID: PMC3791454  PMID: 24096322
13.  Integrin-Specific Control of Focal Adhesion Kinase and RhoA Regulates Membrane Protrusion and Invasion 
PLoS ONE  2013;8(9):e74659.
Cell invasion through extracellular matrix (ECM) is a hallmark of the metastatic cascade. Cancer cells require adhesion to surrounding tissues for efficient migration to occur, which is mediated through the integrin family of receptors. Alterations in expression levels of β1 and β3 integrins have previously been reported in a number of human cancers. However, whether there are specific roles for these ubiquitous receptors in mediating cell invasion remains unclear. Here we demonstrate that loss of β1 but not β3 integrins leads to increased spread cell area and focal adhesion number in cells on 2D immobilized fibronectin. Increased adhesion numbers in β1 knockdown cells correlated with decreased cell migration on 2D surfaces. Conversely, cells depleted of β1 integrins showed increased migration speed on 3D cell-derived matrix as well as in 3D organotypic cultures and inverted invasion assays. This increased invasive potential was also seen in cells lacking β3 integrin but only in 3D cultures containing fibroblasts. Mechanistically, in situ analysis using FRET biosensors revealed that enhanced invasion in cells lacking β1 integrins was directly coupled with reduced activation of focal adhesion kinase (FAK) and the small GTPase RhoA resulting in formation of enhanced dynamic protrusions and increased invasion. These reductions in FAK-RhoA signal activationwere not detected in β3 knockdown cells under the same conditions. This data demonstrates a specific role for β1 integrins in the modulation of a FAK-RhoA-actomyosin signaling axis to regulate cell invasion through complex ECM environments.
PMCID: PMC3767638  PMID: 24040310
14.  Phosphorylation of the Actin Binding Protein Drebrin at S647 Is Regulated by Neuronal Activity and PTEN 
PLoS ONE  2013;8(8):e71957.
Defects in actin dynamics affect activity-dependent modulation of synaptic transmission and neuronal plasticity, and can cause cognitive impairment. A salient candidate actin-binding protein linking synaptic dysfunction to cognitive deficits is Drebrin (DBN). However, the specific mode of how DBN is regulated at the central synapse is largely unknown. In this study we identify and characterize the interaction of the PTEN tumor suppressor with DBN. Our results demonstrate that PTEN binds DBN and that this interaction results in the dephosphorylation of a site present in the DBN C-terminus - serine 647. PTEN and pS647-DBN segregate into distinct and complimentary compartments in neurons, supporting the idea that PTEN negatively regulates DBN phosphorylation at this site. We further demonstrate that neuronal activity increases phosphorylation of DBN at S647 in hippocampal neurons in vitro and in ex vivo hippocampus slices exhibiting seizure activity, potentially by inducing rapid dissociation of the PTEN:DBN complex. Our results identify a novel mechanism by which PTEN is required to maintain DBN phosphorylation at dynamic range and signifies an unusual regulation of an actin-binding protein linked to cognitive decline and degenerative conditions at the CNS synapse.
PMCID: PMC3733845  PMID: 23940795
15.  Stromal Claudin14-Heterozygosity, but Not Deletion, Increases Tumour Blood Leakage without Affecting Tumour Growth 
PLoS ONE  2013;8(5):e62516.
The maintenance of endothelial cell-cell junctions is vital for the control of blood vessel leakage and is known to be important in the growth and maturation of new blood vessels during angiogenesis. Here we have investigated the role of a tight junction molecule, Claudin14, in tumour blood vessel leakage, angiogenesis and tumour growth. Using syngeneic tumour models our results showed that genetic ablation of Claudin14 was not sufficient to affect tumour blood vessel morphology or function. However, and surprisingly, Claudin14-heterozygous mice displayed several blood vessel-related phenotypes including: disruption of ZO-1-positive cell-cell junctions in tumour blood vessels; abnormal distribution of basement membrane laminin around tumour blood vessels; increased intratumoural leakage and decreased intratumoural hypoxia. Additionally, although total numbers of tumour blood vessels were increased in Claudin14-heterozygous mice, and in VEGF-stimulated angiogenesis ex vivo, the number of lumenated vessels was not changed between genotypes and this correlated with no difference in syngeneic tumour growth between wild-type, Claudin14-heterozygous and Claudin14-null mice. Lastly, Claudin14-heterozygosity, but not complete deficiency, also enhanced endothelial cell proliferation significantly. These data establish a new role for Claudin14 in the regulation of tumour blood vessel integrity and angiogenesis that is evident only after the partial loss of this molecule in Claudin14-heterozyous mice but not in Claudin14-null mice.
PMCID: PMC3652830  PMID: 23675413
16.  Fascin promotes filopodia formation independent of its role in actin bundling 
The Journal of Cell Biology  2012;197(4):477-486.
Mutation of a critical residue of fascin eliminates the protein’s actin-bundling activity but maintains its positive role in filopodia formation
Fascin is an evolutionarily conserved actin-binding protein that plays a key role in forming filopodia. It is widely thought that this function involves fascin directly bundling actin filaments, which is controlled by an N-terminal regulatory serine residue. In this paper, by studying cellular processes in Drosophila melanogaster that require fascin activity, we identify a regulatory residue within the C-terminal region of the protein (S289). Unexpectedly, although mutation (S289A) of this residue disrupted the actin-bundling capacity of fascin, fascin S289A fully rescued filopodia formation in fascin mutant flies. Live imaging of migrating macrophages in vivo revealed that this mutation restricted the localization of fascin to the distal ends of filopodia. The corresponding mutation of human fascin (S274) similarly affected its interaction with actin and altered filopodia dynamics within carcinoma cells. These data reveal an evolutionarily conserved role for this regulatory region and unveil a function for fascin, uncoupled from actin bundling, at the distal end of filopodia.
PMCID: PMC3352952  PMID: 22564415
17.  A novel Rho-dependent pathway that drives interaction of fascin-1 with p-Lin-11/Isl-1/Mec-3 kinase (LIMK) 1/2 to promote fascin-1/actin binding and filopodia stability 
BMC Biology  2012;10:72.
Fascin-1 is an actin crosslinking protein that is important for the assembly of cell protrusions in neurons, skeletal and smooth muscle, fibroblasts, and dendritic cells. Although absent from most normal adult epithelia, fascin-1 is upregulated in many human carcinomas, and is associated with poor prognosis because of its promotion of carcinoma cell migration, invasion, and metastasis. Rac and Cdc42 small guanine triphosphatases have been identified as upstream regulators of the association of fascin-1 with actin, but the possible role of Rho has remained obscure. Additionally, experiments have been hampered by the inability to measure the fascin-1/actin interaction directly in intact cells. We investigated the hypothesis that fascin-1 is a functional target of Rho in normal and carcinoma cells, using experimental approaches that included a novel fluorescence resonance energy transfer (FRET)/fluorescence lifetime imaging (FLIM) method to measure the interaction of fascin-1 with actin.
Rho activity modulates the interaction of fascin-1 with actin, as detected by a novel FRET method, in skeletal myoblasts and human colon carcinoma cells. Mechanistically, Rho regulation depends on Rho kinase activity, is independent of the status of myosin II activity, and is not mediated by promotion of the fascin/PKC complex. The p-Lin-11/Isl-1/Mec-3 kinases (LIMK), LIMK1 and LIMK2, act downstream of Rho kinases as novel binding partners of fascin-1, and this complex regulates the stability of filopodia.
We have identified a novel activity of Rho in promoting a complex between fascin-1 and LIMK1/2 that modulates the interaction of fascin-1 with actin. These data provide new mechanistic insight into the intracellular coordination of contractile and protrusive actin-based structures. During the course of the study, we developed a novel FRET method for analysis of the fascin-1/actin interaction, with potential general applicability for analyzing the activities of actin-binding proteins in intact cells.
PMCID: PMC3488970  PMID: 22883572
18.  Dissecting cell adhesion architecture using advanced imaging techniques 
Cell Adhesion & Migration  2011;5(4):351-359.
Cell adhesion to extracellular matrix proteins or to other cells is essential for the control of embryonic development, tissue integrity, immune function and wound healing. Adhesions are tightly spatially regulated structures containing over one hundred different proteins that coordinate both dynamics and signaling events at these sites. Extensive biochemical and morphological analysis of adhesion types over the past three decades has greatly improved understanding of individual protein contributions to adhesion signaling and, in some cases, dynamics. However, it is becoming increasingly clear that these diverse macromolecular complexes contain a variety of protein sub-networks, as well as distinct sub-domains that likely play important roles in regulating adhesion behavior. Until recently, resolving these structures, which are often less than a micron in size, was hampered by the limitations of conventional light microscopy. However, recent advances in optical techniques and imaging methods have revealed exciting insight into the intricate control of adhesion structure and assembly. Here we provide an overview of the recent data arising from such studies of cell:matrix and cell:cell contact and an overview of the imaging strategies that have been applied to study the intricacies and hierarchy of proteins within adhesions.
PMCID: PMC3210303  PMID: 21785274
adhesion; migration; microscopy; dynamics; cytoskeleton; photobleaching; super-resolution imaging; fluorescence
19.  Quantitation of integrin receptor agonism by fluorescence lifetime imaging 
Journal of cell science  2008;121(Pt 3):265-271.
Both spatiotemporal analyses of adhesion signalling and the development of pharmacological inhibitors of integrin adhesion receptors currently suffer from the lack of an assay to measure integrin-effector binding and the response of these interactions to agonists. Here, we have expressed integrin-GFP and effector-mRFP pairs in living cells and quantified their association using FLIM to measure FRET. Talin-β1 and paxillin-α4 association was both ligand- and receptor activation state-dependent, and sensitive to inhibition with small molecule RGD and LDV mimetics, respectively. An adaptation of the assay revealed the agonistic activity of these small molecules and provides a new, quantitative assay for the screening of activity of small molecule integrin inhibitors.
PMCID: PMC3328206  PMID: 18216331
20.  Differential Regulation of Adhesion Complex Turnover by ROCK1 and ROCK2 
PLoS ONE  2012;7(2):e31423.
ROCK1 and ROCK2 are serine/threonine kinases that function downstream of the small GTP-binding protein RhoA. Rho signalling via ROCK regulates a number of cellular functions including organisation of the actin cytoskeleton, cell adhesion and cell migration.
Methodology/Principal Findings
In this study we use RNAi to specifically knockdown ROCK1 and ROCK2 and analyse their role in assembly of adhesion complexes in human epidermal keratinocytes. We observe that loss of ROCK1 inhibits signalling via focal adhesion kinase resulting in a failure of immature adhesion complexes to form mature stable focal adhesions. In contrast, loss of ROCK2 expression results in a significant reduction in adhesion complex turnover leading to formation of large, stable focal adhesions. Interestingly, loss of either ROCK1 or ROCK2 expression significantly impairs cell migration indicating both ROCK isoforms are required for normal keratinocyte migration.
ROCK1 and ROCK2 have distinct and separate roles in adhesion complex assembly and turnover in human epidermal keratinocytes.
PMCID: PMC3278444  PMID: 22348083
21.  SHARPIN is an endogenous inhibitor of beta1-integrin activation 
Nature Cell Biology  2011;13(11):1315-1324.
Regulated activation of integrins is critical for cell adhesion, motility and tissue homeostasis. Talin and Kindlins activate β1-integrins, but the counteracting inhibiting mechanisms are poorly defined. Here we identified SHARPIN as an important inactivator of β1-integrins in an RNAi-screen. SHARPIN inhibited β1-integrin functions in human cancer cells and primary leukocytes. Fibroblasts, leukocytes and keratinocytes from SHARPIN-deficient mice exhibited increased β1-integrin activity which was fully rescued by re-expression of SHARPIN. SHARPIN directly bound to a conserved cytoplasmic region of integrin α-subunits and inhibited recruitment of Talin and Kindlin to the integrin. Therefore, SHARPIN inhibits the critical switching of β1-integrins from inactive to active conformations.
PMCID: PMC3257806  PMID: 21947080
22.  Complement Fragment C3a Controls Mutual Cell Attraction during Collective Cell Migration 
Developmental Cell  2011;21(6):1026-1037.
Collective cell migration is a mode of movement crucial for morphogenesis and cancer metastasis. However, little is known about how migratory cells coordinate collectively. Here we show that mutual cell-cell attraction (named here coattraction) is required to maintain cohesive clusters of migrating mesenchymal cells. Coattraction can counterbalance the natural tendency of cells to disperse via mechanisms such as contact inhibition and epithelial-to-mesenchymal transition. Neural crest cells are coattracted via the complement fragment C3a and its receptor C3aR, revealing an unexpected role of complement proteins in early vertebrate development. Loss of coattraction disrupts collective and coordinated movements of these cells. We propose that coattraction and contact inhibition act in concert to allow cell collectives to self-organize and respond efficiently to external signals, such as chemoattractants and repellents.
Graphical Abstract
► Neural crest (NC) cells mutually attract each other (coattraction) ► NC coattraction is mediated by the complement fragment C3a and its receptor C3aR ► Coattraction is required for the swarm-like behavior of migratory NC cells ► Coattraction and contact inhibition suffice to generate collective migration
PMCID: PMC3272547  PMID: 22118769
23.  CAR Modulates E-Cadherin Dynamics in the Presence of Adenovirus Type 5 
PLoS ONE  2011;6(8):e23056.
Adenovirus (Ad) serotype 5 (Ad5) fiber competitively binds to the coxsackievirus and Ad receptor (CAR) to attach Ad5 to target cells and also disrupts cell junctions and facilitates virus escape at a late stage in Ad5 infection. Here we demonstrate that paracellular permeability in MCF7 and CAR overexpressing MCF7 (FLCARMCF7) cells is increased within minutes following the addition of Ad5 to cells. This is brought about, at least in part, by altering the molecular dynamics of E-cadherin, a key component of the cell-cell adhesion complex. We also demonstrate that the increase in E-cadherin mobility is constitutively altered by the presence of CAR at FLCARMCF7 cell junctions. As increased paracellular permeability was observed early after the addition of Ad5 to cells, we postulate that this may represent a mechanism by which Ad5 could disrupt cell junctions to facilitate further access to its cell receptors.
PMCID: PMC3151283  PMID: 21850251
24.  Proneural Transcription Factors Regulate Different Steps of Cortical Neuron Migration through Rnd-Mediated Inhibition of RhoA Signaling 
Neuron  2011;69-540(6-7):1069-1084.
Little is known of the intracellular machinery that controls the motility of newborn neurons. We have previously shown that the proneural protein Neurog2 promotes the migration of nascent cortical neurons by inducing the expression of the atypical Rho GTPase Rnd2. Here, we show that another proneural factor, Ascl1, promotes neuronal migration in the cortex through direct regulation of a second Rnd family member, Rnd3. Both Rnd2 and Rnd3 promote neuronal migration by inhibiting RhoA signaling, but they control distinct steps of the migratory process, multipolar to bipolar transition in the intermediate zone and locomotion in the cortical plate, respectively. Interestingly, these divergent functions directly result from the distinct subcellular distributions of the two Rnd proteins. Because Rnd proteins also regulate progenitor divisions and neurite outgrowth, we propose that proneural factors, through spatiotemporal regulation of Rnd proteins, integrate the process of neuronal migration with other events in the neurogenic program.
► The small GTPase Rnd3 is a direct target of the proneural transcription factor Ascl1 ► Rnd3 promotes cortical neuron migration by inhibiting RhoA signaling ► Rnd3 and the related protein Rnd2 have distinct roles in neuronal migration ► Rnd3 and Rnd2 have distinct subcellular distributions in cortical neurons
PMCID: PMC3383999  PMID: 21435554
25.  Podoplanin Associates with CD44 to Promote Directional Cell Migration 
Molecular Biology of the Cell  2010;21(24):4387-4399.
Podoplanin, a cancer-associated glycoprotein, interacts with CD44. Both glycoproteins are coordinately upregulated during tumor progression. Podoplanin–CD44 interaction in the cell membrane occurs mainly in migrating cells, and it seems to be required for podoplanin-mediated cell migration and directionality.
Podoplanin is a transmembrane glycoprotein up-regulated in different human tumors, especially those derived from squamous stratified epithelia (SCCs). Its expression in tumor cells is linked to increased cell migration and invasiveness; however, the mechanisms underlying this process remain poorly understood. Here we report that CD44, the major hyaluronan (HA) receptor, is a novel partner for podoplanin. Expression of the CD44 standard isoform (CD44s) is coordinately up-regulated together with that of podoplanin during progression to highly aggressive SCCs in a mouse skin model of carcinogenesis, and during epithelial-mesenchymal transition (EMT). In carcinoma cells, CD44 and podoplanin colocalize at cell surface protrusions. Moreover, CD44 recruitment promoted by HA-coated beads or cross-linking with a specific CD44 antibody induced corecruitment of podoplanin. Podoplanin–CD44s interaction was demonstrated both by coimmunoprecipitation experiments and, in vivo, by fluorescence resonance energy transfer/fluorescence lifetime imaging microscopy (FRET/FLIM), the later confirming its association on the plasma membrane of cells with a migratory phenotype. Importantly, we also show that podoplanin promotes directional persistence of motility in epithelial cells, a feature that requires CD44, and that both molecules cooperate to promote directional migration in SCC cells. Our results support a role for CD44-podoplanin interaction in driving tumor cell migration during malignancy.
PMCID: PMC3002391  PMID: 20962267

Results 1-25 (38)