scholarly journals Involvement of the Cytoskeleton in Controlling Leading-Edge Function during Chemotaxis

2010 ◽  
Vol 21 (11) ◽  
pp. 1810-1824 ◽  
Author(s):  
Susan Lee ◽  
Zhouxin Shen ◽  
Douglas N. Robinson ◽  
Steven Briggs ◽  
Richard A. Firtel
Keyword(s):  
Signaling Pathways ◽  
Actin Polymerization ◽  
Myosin Ii ◽  
Leading Edge ◽  
Ras Proteins ◽  
Ras Activation ◽  
Directional Movement ◽  
Edge Function

In response to directional stimulation by a chemoattractant, cells rapidly activate a series of signaling pathways at the site closest to the chemoattractant source that leads to F-actin polymerization, pseudopod formation, and directional movement up the gradient. Ras proteins are major regulators of chemotaxis in Dictyostelium; they are activated at the leading edge, are required for chemoattractant-mediated activation of PI3K and TORC2, and are one of the most rapid responders, with activity peaking at ∼3 s after stimulation. We demonstrate that in myosin II (MyoII) null cells, Ras activation is highly extended and is not restricted to the site closest to the chemoattractant source. This causes elevated, extended, and spatially misregulated activation of PI3K and TORC2 and their effectors Akt/PKB and PKBR1, as well as elevated F-actin polymerization. We further demonstrate that disruption of specific IQGAP/cortexillin complexes, which also regulate cortical mechanics, causes extended activation of PI3K and Akt/PKB but not Ras activation. Our findings suggest that MyoII and IQGAP/cortexillin play key roles in spatially and temporally regulating leading-edge activity and, through this, the ability of cells to restrict the site of pseudopod formation.

scholarly journals Localized Ras signaling at the leading edge regulates PI3K, cell polarity, and directional cell movement

2004 ◽  
Vol 167 (3) ◽  
pp. 505-518 ◽  
Author(s):  
Atsuo T. Sasaki ◽  
Cheryl Chun ◽  
Kosuke Takeda ◽  
Richard A. Firtel
Keyword(s):  
Actin Polymerization ◽  
Cell Movement ◽  
Leading Edge ◽  
Ras Signaling ◽  
Phosphatidylinositol 3 Kinase ◽  
Ras Activation ◽  
Directional Movement ◽  
Ras Effectors ◽  
Chemotaxis Receptors ◽  
Intermediate Event

During chemotaxis, receptors and heterotrimeric G-protein subunits are distributed and activated almost uniformly along the cell membrane, whereas PI(3,4,5)P3, the product of phosphatidylinositol 3-kinase (PI3K), accumulates locally at the leading edge. The key intermediate event that creates this strong PI(3,4,5)P3 asymmetry remains unclear. Here, we show that Ras is rapidly and transiently activated in response to chemoattractant stimulation and regulates PI3K activity. Ras activation occurs at the leading edge of chemotaxing cells, and this local activation is independent of the F-actin cytoskeleton, whereas PI3K localization is dependent on F-actin polymerization. Inhibition of Ras results in severe defects in directional movement, indicating that Ras is an upstream component of the cell's compass. These results support a mechanism by which localized Ras activation mediates leading edge formation through activation of basal PI3K present on the plasma membrane and other Ras effectors required for chemotaxis. A feedback loop, mediated through localized F-actin polymerization, recruits cytosolic PI3K to the leading edge to amplify the signal.

scholarly journals Contribution of Filopodia to Cell Migration: A Mechanical Link between Protrusion and Contraction

2010 ◽  
Vol 2010 ◽  
pp. 1-13 ◽  
Author(s):  
Fei Xue ◽  
Deanna M. Janzen ◽  
David A. Knecht
Keyword(s):  
Cell Migration ◽  
Actin Polymerization ◽  
Myosin Ii ◽  
Temporal Distribution ◽  
Leading Edge ◽  
Distal Portion ◽  
Actin Binding ◽  
Actin Networks ◽  
Motile Cells ◽  
A Cell

Numerous F-actin containing structures are involved in regulating protrusion of membrane at the leading edge of motile cells. We have investigated the structure and dynamics of filopodia as they relate to events at the leading edge and the function of the trailing actin networks. We have found that although filopodia contain parallel bundles of actin, they contain a surprisingly nonuniform spatial and temporal distribution of actin binding proteins. Along the length of the actin filaments in a single filopodium, the most distal portion contains primarily T-plastin, while the proximal portion is primarily bound byα-actinin and coronin. Some filopodia are stationary, but lateral filopodia move with respect to the leading edge. They appear to form a mechanical link between the actin polymerization network at the front of the cell and the myosin motor activity in the cell body. The direction of lateral filopodial movement is associated with the direction of cell migration. When lateral filopodia initiate from and move toward only one side of a cell, the cell will turn opposite to the direction of filopodial flow. Therefore, this filopodia-myosin II system allows actin polymerization driven protrusion forces and myosin II mediated contractile force to be mechanically coordinated.

scholarly journals Analysis of the Actin–Myosin II System in Fish Epidermal Keratocytes: Mechanism of Cell Body Translocation

1997 ◽  
Vol 139 (2) ◽  
pp. 397-415 ◽  
Author(s):  
Tatyana M. Svitkina ◽  
Alexander B. Verkhovsky ◽  
Kyle M. McQuade ◽  
Gary G. Borisy
Keyword(s):  
Cell Body ◽  
Actin Filaments ◽  
Actin Polymerization ◽  
Myosin Ii ◽  
Leading Edge ◽  
Time Lapse ◽  
Supramolecular Organization ◽  
Retrograde Flow ◽  
Body Boundary ◽  
Filament Bundles

While the protrusive event of cell locomotion is thought to be driven by actin polymerization, the mechanism of forward translocation of the cell body is unclear. To elucidate the mechanism of cell body translocation, we analyzed the supramolecular organization of the actin–myosin II system and the dynamics of myosin II in fish epidermal keratocytes. In lamellipodia, long actin filaments formed dense networks with numerous free ends in a brushlike manner near the leading edge. Shorter actin filaments often formed T junctions with longer filaments in the brushlike area, suggesting that new filaments could be nucleated at sides of preexisting filaments or linked to them immediately after nucleation. The polarity of actin filaments was almost uniform, with barbed ends forward throughout most of the lamellipodia but mixed in arc-shaped filament bundles at the lamellipodial/cell body boundary. Myosin II formed discrete clusters of bipolar minifilaments in lamellipodia that increased in size and density towards the cell body boundary and colocalized with actin in boundary bundles. Time-lapse observation demonstrated that myosin clusters appeared in the lamellipodia and remained stationary with respect to the substratum in locomoting cells, but they exhibited retrograde flow in cells tethered in epithelioid colonies. Consequently, both in locomoting and stationary cells, myosin clusters approached the cell body boundary, where they became compressed and aligned, resulting in the formation of boundary bundles. In locomoting cells, the compression was associated with forward displacement of myosin features. These data are not consistent with either sarcomeric or polarized transport mechanisms of cell body translocation. We propose that the forward translocation of the cell body and retrograde flow in the lamellipodia are both driven by contraction of an actin–myosin network in the lamellipodial/cell body transition zone.

Myosin II-dependent cylindrical protrusions induced by quinine inDictyostelium: antagonizing effects of actin polymerization at the leading edge

2001 ◽  
Vol 114 (11) ◽  
pp. 2155-2165
Author(s):  
Kunito Yoshida ◽  
Kei Inouye
Keyword(s):  
Cell Membrane ◽  
Actin Polymerization ◽  
Myosin Ii ◽  
Cell Movement ◽  
Leading Edge ◽  
Contractile Vacuole ◽  
Cell Periphery ◽  
Slowing Down ◽  
On Line ◽  
Cylindrical Protrusion

We found that amoeboid cells of Dictyostelium are induced by a millimolar concentration of quinine to form a rapidly elongating, cylindrical protrusion, which often led to sustained locomotion of the cells. Formation of the protrusion was initiated by fusion of a contractile vacuole with the cell membrane. During protrusion extension, a patch of the contractile vacuole membrane stayed undiffused on the leading edge of the protrusion for over 30 seconds. Protrusion formation was not inhibited by high osmolarity of the external medium (at least up to 400 mosM). By contrast, mutant cells lacking myosin II (mhc− cells) failed to extend protrusions upon exposure to quinine. When GFP-myosin-expressing cells were exposed to quinine, GFP-myosin was accumulated in the cell periphery forming a layer under the cell membrane, but a newly formed protrusion was initially devoid of a GFP-myosin layer, which gradually formed and extended from the base of the protrusion. F-actin was absent in the leading front of the protrusion during the period of its rapid elongation, and the formation of a layer of F-actin in the front was closely correlated with its slowing-down or retraction. Periodical or continuous detachment of the F-actin layer from the apical membrane of the protrusion, accompanied by a transient increase in the elongation speed at the site of detachment, was observed in some of the protrusions. The detached F-actin layers, which formed a spiral layer of F-actin in the case of continuous detachment, moved in the opposite direction of protrusion elongation. In the presence of both cytochalasin A and quinine, the protrusions formed were not cylindrical but spherical, which swallowed up the entire cellular contents. The estimated bulk flux into the expanding spherical protrusions of such cells was four-times higher than the flux into the elongating cylindrical protrusions of the cells treated with quinine alone. These results indicate that the force responsible for the quinine-induced protrusion is mainly due to contraction of the cell body, which requires normal myosin II functions, while actin polymerization is important in restricting the direction of its expansion. We will discuss the possible significance of tail contraction in cell movement in the multicellular phase of Dictyostelium development, where cell locomotion similar to that induced by quinine is often observed without quinine treatment, and in protrusion elongation in general.Movies available on-line

scholarly journals Bleb-driven chemotaxis of Dictyostelium cells

2014 ◽  
Vol 204 (6) ◽  
pp. 1027-1044 ◽  
Author(s):  
Evgeny Zatulovskiy ◽  
Richard Tyson ◽  
Till Bretschneider ◽  
Robert R. Kay
Keyword(s):  
Cyclic Amp ◽  
Actin Polymerization ◽  
Myosin Ii ◽  
Leading Edge ◽  
Pi3 Kinase ◽  
Mechanical Resistance ◽  
Ph Domain ◽  
Cortical Function ◽  
Pi3 Kinase Pathway ◽  
Kinase Pathway

Blebs and F-actin–driven pseudopods are alternative ways of extending the leading edge of migrating cells. We show that Dictyostelium cells switch from using predominantly pseudopods to blebs when migrating under agarose overlays of increasing stiffness. Blebs expand faster than pseudopods leaving behind F-actin scars, but are less persistent. Blebbing cells are strongly chemotactic to cyclic-AMP, producing nearly all of their blebs up-gradient. When cells re-orientate to a needle releasing cyclic-AMP, they stereotypically produce first microspikes, then blebs and pseudopods only later. Genetically, blebbing requires myosin-II and increases when actin polymerization or cortical function is impaired. Cyclic-AMP induces transient blebbing independently of much of the known chemotactic signal transduction machinery, but involving PI3-kinase and downstream PH domain proteins, CRAC and PhdA. Impairment of this PI3-kinase pathway results in slow movement under agarose and cells that produce few blebs, though actin polymerization appears unaffected. We propose that mechanical resistance induces bleb-driven movement in Dictyostelium, which is chemotactic and controlled through PI3-kinase.

scholarly journals Cell Mechanics at the Rear Act To Steer the Direction of Cell Migration

2018 ◽  
Author(s):  
Greg M. Allen ◽  
Kun Chun Lee ◽  
Erin L. Barnhart ◽  
Mark A. Tsuchida ◽  
Cyrus A. Wilson ◽  
...  
Keyword(s):  
Computational Model ◽  
Network Flow ◽  
Actin Polymerization ◽  
Myosin Ii ◽  
Leading Edge ◽  
Minor Role ◽  
List Type ◽  
Motile Cells ◽  
Cell Shapes ◽  
A Minor

SummaryMotile cells navigate complex environments by changing their direction of travel, generating left-right asymmetries in their mechanical subsystems to physically turn. Currently little is known about how external directional cues are propagated along the length scale of the whole cell and integrated with its force-generating apparatus to steer migration mechanically. We examine the mechanics of spontaneous cell turning in fish epidermal keratocytes and find that the mechanical asymmetries responsible for turning behavior predominate at the rear of the cell, where there is asymmetric centripetal actin flow. Using experimental perturbations we identify two linked feedback loops connecting myosin II contractility, adhesion strength and actin network flow in turning cells that are sufficient to recreate observed cell shapes and trajectories in a computational model. Surprisingly, asymmetries in actin polymerization at the cell leading edge play only a minor role in the mechanics of cell turning – that is, cells steer from the rear.HighlightsFish keratocytes can migrate with persistent angular velocity, straight or in circles.Asymmetry in protrusion at the leading edge is not sufficient to generate persistent turning.Asymmetries in myosin II contraction, actin flow and adhesion at the cell rear cause turns.Our new computational model of migration predicts observed cell trajectories.

Current Study of RhoA and Associated Signaling Pathways in Gastric Cancer

2020 ◽  
Vol 15 (7) ◽  
pp. 607-613 ◽  
Author(s):  
Haiping Liu ◽  
Yiqian Liu ◽  
Xiaochuan Zhang ◽  
Xiaodong Wang
Keyword(s):  
Gastric Cancer ◽  
Survival Rate ◽  
Signaling Pathways ◽  
Tumor Cells ◽  
Actin Polymerization ◽  
Cell Transformation ◽  
Cell Movement ◽  
Invasion And Metastasis ◽  
Common Cancer

Gastric cancer (GC) is the fourth-most common cancer in the world, with an estimated 1.034 million new cases in 2015, and the third-highest cause of cancer deaths, estimated at 785,558, in 2014. Early diagnosis and treatment greatly affect the survival rate in patients with GC: the 5‐year survival rate of early GC reaches 90%‐95%, while the mortality rate significantly increases if GC develops to the late stage. Recently, studies for the role of RhoA in the diseases have become a hot topic, especially in the development of tumors. A study found that RhoA can regulate actin polymerization, cell adhesion, motor-myosin, cell transformation, and the ability to participate in the activities of cell movement, proliferation, migration, which are closely related to the invasion and metastasis of tumor cells. However, the specific role of RhoA in tumor cells remains to be studied. Therefore, our current study aimed to briefly review the role of RhoA in GC, especially for its associated signaling pathways involved in the GC progression.

scholarly journals Ras-mediated activation of the TORC2–PKB pathway is critical for chemotaxis

2010 ◽  
Vol 190 (2) ◽  
pp. 233-245 ◽  
Author(s):  
Huaqing Cai ◽  
Satarupa Das ◽  
Yoichiro Kamimura ◽  
Yu Long ◽  
Carole A. Parent ◽  
...  
Keyword(s):  
Cell Migration ◽  
Actin Polymerization ◽  
Time Course ◽  
Specific Inhibitor ◽  
Ras Proteins ◽  
Extracellular Signaling ◽  
Upstream Regulator ◽  
Pkb Phosphorylation ◽  
G Protein Coupled

In chemotactic cells, G protein–coupled receptors activate Ras proteins, but it is unclear how Ras-associated pathways link extracellular signaling to cell migration. We show that, in Dictyostelium discoideum, activated forms of RasC prolong the time course of TORC2 (target of rapamycin [Tor] complex 2)-mediated activation of a myristoylated protein kinase B (PKB; PKBR1) and the phosphorylation of PKB substrates, independently of phosphatidylinositol-(3,4,5)-trisphosphate. Paralleling these changes, the kinetics of chemoattractant-induced adenylyl cyclase activation and actin polymerization are extended, pseudopodial activity is increased and mislocalized, and chemotaxis is impaired. The effects of activated RasC are suppressed by deletion of the TORC2 subunit PiaA. In vitro RasCQ62L-dependent PKB phosphorylation can be rapidly initiated by the addition of a PiaA-associated immunocomplex to membranes of TORC2-deficient cells and blocked by TOR-specific inhibitor PP242. Furthermore, TORC2 binds specifically to the activated form of RasC. These results demonstrate that RasC is an upstream regulator of TORC2 and that the TORC2–PKB signaling mediates effects of activated Ras proteins on the cytoskeleton and cell migration.

scholarly journals The Crossroads between RAS and RHO Signaling Pathways in Cellular Transformation, Motility and Contraction

Genes ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 819
Author(s):  
Olga Soriano ◽  
Marta Alcón-Pérez ◽  
Miguel Vicente-Manzanares ◽  
Esther Castellano
Keyword(s):  
Signaling Pathways ◽  
Actin Polymerization ◽  
Mapk Pathway ◽  
Human Cancer ◽  
Cellular Transformation ◽  
Dependent Manner ◽  
Rho Proteins ◽  
Filament Assembly ◽  
Multiple Signaling ◽  
Mechanical Feedback

Ras and Rho proteins are GTP-regulated molecular switches that control multiple signaling pathways in eukaryotic cells. Ras was among the first identified oncogenes, and it appears mutated in many forms of human cancer. It mainly promotes proliferation and survival through the MAPK pathway and the PI3K/AKT pathways, respectively. However, the myriad proteins close to the plasma membrane that activate or inhibit Ras make it a major regulator of many apparently unrelated pathways. On the other hand, Rho is weakly oncogenic by itself, but it critically regulates microfilament dynamics; that is, actin polymerization, disassembly and contraction. Polymerization is driven mainly by the Arp2/3 complex and formins, whereas contraction depends on myosin mini-filament assembly and activity. These two pathways intersect at numerous points: from Ras-dependent triggering of Rho activators, some of which act through PI3K, to mechanical feedback driven by actomyosin action. Here, we describe the main points of connection between the Ras and Rho pathways as they coordinately drive oncogenic transformation. We emphasize the biochemical crosstalk that drives actomyosin contraction driven by Ras in a Rho-dependent manner. We also describe possible routes of mechanical feedback through which myosin II activation may control Ras/Rho activation.

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