RhoE Regulates Actin Cytoskeleton Organization and Cell Migration

ABSTRACT The actin cytoskeleton is regulated by Rho family proteins: in fibroblasts, Rho mediates the formation of actin stress fibers, whereas Rac regulates lamellipodium formation and Cdc42 controls filopodium formation. We have cloned the mouse RhoE gene, whose product is a member of the Rho family that shares (except in one amino acid) the conserved effector domain of RhoA, RhoB, and RhoC. RhoE is able to bind GTP but does not detectably bind GDP and has low intrinsic GTPase activity compared with Rac. The role of RhoE in regulating actin organization was investigated by microinjection in Bac1.2F5 macrophages and MDCK cells. In macrophages, RhoE induced actin reorganization, leading to the formation of extensions resembling filopodia and pseudopodia. In MDCK cells, RhoE induced the complete disappearance of stress fibers, together with cell spreading. However, RhoE did not detectably affect the actin bundles that run parallel to the outer membranes of cells at the periphery of colonies, which are known to be dependent on RhoA. In addition, RhoE induced an increase in the speed of migration of hepatocyte growth factor/scatter factor-stimulated MDCK cells, in contrast to the previously reported inhibition produced by activated RhoA. The subcellular localization of RhoE at the lateral membranes of MDCK cells suggests a role in cell-cell adhesion, as has been shown for RhoA. These results suggest that RhoE may act to inhibit signalling downstream of RhoA, altering some RhoA-regulated responses, such as stress fiber formation, but not affecting others, such as peripheral actin bundle formation.

Download Full-text

The actin cytoskeleton is required to elaborate and maintain spatial patterning during trichome cell morphogenesis in Arabidopsis thaliana

Development ◽

10.1242/dev.126.24.5559 ◽

1999 ◽

Vol 126 (24) ◽

pp. 5559-5568 ◽

Cited By ~ 1

Author(s):

J. Mathur ◽

P. Spielhofer ◽

B. Kost ◽

N. Chua

Keyword(s):

Arabidopsis Thaliana ◽

Actin Cytoskeleton ◽

Spatial Patterning ◽

Actin Microfilaments ◽

Cell Morphogenesis ◽

Actin Organization ◽

Cytoskeleton Organization ◽

Branch Formation ◽

Actin Cytoskeleton Organization ◽

Trichome Cell

Arabidopsis thaliana trichomes provide an attractive model system to dissect molecular processes involved in the generation of shape and form in single cell morphogenesis in plants. We have used transgenic Arabidopsis plants carrying a GFP-talin chimeric gene to analyze the role of the actin cytoskeleton in trichome cell morphogenesis. We found that during trichome cell development the actin microfilaments assumed an increasing degree of complexity from fine filaments to thick, longitudinally stretched cables. Disruption of the F-actin cytoskeleton by actin antagonists produced distorted but branched trichomes which phenocopied trichomes of mutants belonging to the ‘distorted’ class. Subsequent analysis of the actin cytoskeleton in trichomes of the distorted mutants, alien, crooked, distorted1, gnarled, klunker and wurm uncovered actin organization defects in each case. Treatments of wild-type seedlings with microtubule-interacting drugs elicited a radically different trichome phenotype characterized by isotropic growth and a severe inhibition of branch formation; these trichomes did not show defects in actin cytoskeleton organization. A normal actin cytoskeleton was also observed in trichomes of the zwichel mutant which have reduced branching. ZWICHEL, which was previously shown to encode a kinesin-like protein is thought to be involved in microtubule-linked processes. Based on our results we propose that microtubules establish the spatial patterning of trichome branches whilst actin microfilaments elaborate and maintain the overall trichome pattern during development.

Download Full-text

Socius Is a Novel Rnd GTPase-Interacting Protein Involved in Disassembly of Actin Stress Fibers

Molecular and Cellular Biology ◽

10.1128/mcb.22.9.2952-2964.2002 ◽

2002 ◽

Vol 22 (9) ◽

pp. 2952-2964 ◽

Cited By ~ 58

Author(s):

Hironori Katoh ◽

Amane Harada ◽

Kazutoshi Mori ◽

Manabu Negishi

Keyword(s):

Actin Cytoskeleton ◽

Cell Body ◽

Inhibitory Effect ◽

Small Gtpases ◽

Fiber Formation ◽

Stress Fibers ◽

Cell Periphery ◽

Cellular Processes ◽

Rho Family ◽

Actin Stress Fibers

ABSTRACT Rho family small GTPases are key regulators of the actin cytoskeleton in various cell types. The Rnd proteins, Rnd1, Rnd2, and Rnd3/RhoE, have been recently identified as new members of the Rho family of GTPases, and expression of Rnd1 or Rnd3 in fibroblasts causes the disassembly of actin stress fibers and the retraction of the cell body to produce extensively branching cellular processes. Here we have performed a yeast two-hybrid screening by using Rnd1 as bait and identified a novel protein that specifically binds to Rnd GTPases. We named this protein Socius. Socius directly binds to Rnd GTPases through its COOH-terminal region. When transfected into COS-7 cells, Socius is translocated to the cell periphery in response to Rnd1 and Rnd3 and colocalized with the GTPases. While expression of wild-type Socius in Swiss 3T3 fibroblasts has little effect on the actin cytoskeleton, the expression of a membrane-targeted form of Socius, containing a COOH-terminal farnesylation motif (Socius-CAAX), induces a dramatic loss of stress fibers. The inhibitory effect of Socius-CAAX on stress fiber formation is enhanced by truncation of its NH2 terminus. On the other hand, the expression of Socius-CAAX or its NH2 terminus-truncated form suppresses the Rnd-induced retraction of the cell body and the production of extensively branching cellular processes, although the disassembly of stress fibers is observed. We propose that Socius participates in the Rnd GTPase-induced signal transduction pathways, leading to reorganization of the actin cytoskeleton.

Download Full-text

Overexpression of a Novel Rho Family GTPase, RacC, Induces Unusual Actin-based Structures and Positively Affects Phagocytosis inDictyostelium discoideum

Molecular Biology of the Cell ◽

10.1091/mbc.9.10.2891 ◽

1998 ◽

Vol 9 (10) ◽

pp. 2891-2904 ◽

Cited By ~ 50

Author(s):

David J. Seastone ◽

Eunkyung Lee ◽

John Bush ◽

David Knecht ◽

James Cardelli

Keyword(s):

Actin Cytoskeleton ◽

Kinase Inhibitors ◽

Morphological Changes ◽

Fluid Phase ◽

Binding Motif ◽

Cytoskeleton Organization ◽

Cellular Processes ◽

Actin Cytoskeleton Organization ◽

A Cell ◽

Rho Family

Rho family proteins have been implicated in regulating various cellular processes, including actin cytoskeleton organization, endocytosis, cell cycle, and gene expression. In this study, we analyzed the function of a novel Dictyostelium discoideum Rho family protein (RacC). A cell line was generated that conditionally overexpressed wild-type RacC three- to fourfold relative to endogenous RacC. Light and scanning electron microscopy indicated that the morphology of the RacC-overexpressing cells [RacC WT(+) cells] was significantly altered compared with control cells. In contrast to the cortical F-actin distribution normally observed, RacC WT(+) cells displayed unusual dorsal and peripheral F-actin–rich surface blebs (petalopodia, for flower-like). Furthermore, phagocytosis in the RacC WT(+) cells was induced threefold relative to control Ax2 cells, whereas fluid-phase pinocytosis was reduced threefold, primarily as the result of an inhibition of macropinocytosis. Efflux of fluid-phase markers was also reduced in the RacC WT(+) cells, suggesting that RacC may regulate postinternalization steps along the endolysosomal pathway. Treatment of cells with Wortmannin and LY294002 (phosphatidylinositol 3-kinase inhibitors) prevented the RacC-induced morphological changes but did not affect phagocytosis, suggesting that petalopodia are probably not required for RacC-induced phagocytosis. In contrast, inactivating diacylglycerol-binding motif–containing proteins by treating cells with the drug calphostin C completely inhibited phagocytosis in control and RacC WT(+) cells. These results suggest that RacC plays a role in actin cytoskeleton organization and phagocytosis inDictyostelium.

Download Full-text

The Phosphatidylinositol 4,5-Biphosphate and TORC2 Binding Proteins Slm1 and Slm2 Function in Sphingolipid Regulation

Molecular and Cellular Biology ◽

10.1128/mcb.02403-05 ◽

2006 ◽

Vol 26 (15) ◽

pp. 5861-5875 ◽

Cited By ~ 101

Author(s):

Mitsuaki Tabuchi ◽

Anjon Audhya ◽

Ainslie B. Parsons ◽

Charles Boone ◽

Scott D. Emr

Keyword(s):

Actin Cytoskeleton ◽

Essential Role ◽

Synthetic Lethality ◽

Sphingolipid Metabolism ◽

Actin Organization ◽

Cytoskeleton Organization ◽

Calcium Calmodulin Dependent ◽

Actin Cytoskeleton Organization ◽

Phosphatidylinositol 4

ABSTRACT The Stt4 phosphatidylinositol 4-kinase has been shown to generate a pool of phosphatidylinositol 4-phosphate (PI4P) at the plasma membrane, critical for actin cytoskeleton organization and cell viability. To further understand the essential role of Stt4-mediated PI4P production, we performed a genetic screen using the stt4 ts mutation to identify candidate regulators and effectors of PI4P. From this analysis, we identified several genes that have been previously implicated in lipid metabolism. In particular, we observed synthetic lethality when both sphingolipid and PI4P synthesis were modestly diminished. Consistent with these data, we show that the previously characterized phosphoinositide effectors, Slm1 and Slm2, which regulate actin organization, are also necessary for normal sphingolipid metabolism, at least in part through regulation of the calcium/calmodulin-dependent phosphatase calcineurin, which binds directly to both proteins. Additionally, we identify Isc1, an inositol phosphosphingolipid phospholipase C, as an additional target of Slm1 and Slm2 negative regulation. Together, our data suggest that Slm1 and Slm2 define a molecular link between phosphoinositide and sphingolipid signaling and thereby regulate actin cytoskeleton organization.

Download Full-text

Phospholipase Dδ regulates pollen tube growth by modulating actin cytoskeleton organization in Arabidopsis

Plant Signaling & Behavior ◽

10.1080/15592324.2021.1915610 ◽

2021 ◽

pp. 1915610

Author(s):

Qianru Jia ◽

Shujuan Zhang ◽

Yaoxi Lin ◽

Jixiu Zhang ◽

Li Li ◽

...

Keyword(s):

Pollen Tube ◽

Actin Cytoskeleton ◽

Pollen Tube Growth ◽

Tube Growth ◽

Cytoskeleton Organization ◽

Actin Cytoskeleton Organization

Download Full-text

FAP52 – a new partner for filamin in actin cytoskeleton organization

Trends in Cell Biology ◽

10.1016/s0962-8924(02)02288-2 ◽

2002 ◽

Vol 12 (5) ◽

pp. 213 ◽

Cited By ~ 1

Author(s):

B Behrendt

Keyword(s):

Actin Cytoskeleton ◽

Cytoskeleton Organization ◽

Actin Cytoskeleton Organization

Download Full-text

Pan1p, End3p, and Sla1p, Three Yeast Proteins Required for Normal Cortical Actin Cytoskeleton Organization, Associate with Each Other and Play Essential Roles in Cell Wall Morphogenesis

Molecular and Cellular Biology ◽

10.1128/mcb.20.1.12-25.2000 ◽

2000 ◽

Vol 20 (1) ◽

pp. 12-25 ◽

Cited By ~ 112

Author(s):

Hsin-Yao Tang ◽

Jing Xu ◽

Mingjie Cai

Keyword(s):

Cell Wall ◽

Actin Cytoskeleton ◽

Normal Cell ◽

Cell Cortex ◽

Repeat Region ◽

Cortical Actin ◽

Cytoskeleton Organization ◽

Eh Domain ◽

Actin Cytoskeleton Organization ◽

Cell Wall Morphogenesis

ABSTRACT The EH domain proteins Pan1p and End3p of budding yeast have been known to form a complex in vivo and play important roles in organization of the actin cytoskeleton and endocytosis. In this report, we describe new findings concerning the function of the Pan1p-End3p complex. First, we found that the Pan1p-End3p complex associates with Sla1p, another protein known to be required for the assembly of cortical actin structures. Sla1p interacts with the first long repeat region of Pan1p and the N-terminal EH domain of End3p, thus leaving the Pan1p-End3p interaction, which requires the second long repeat of Pan1p and the C-terminal repeat region of End3p, undisturbed. Second, Pan1p, End3p, and Sla1p are also required for normal cell wall morphogenesis. Each of the Pan1-4, sla1Δ, andend3Δ mutants displays the abnormal cell wall morphology previously reported for the act1-1 mutant. These cell wall defects are also exhibited by wild-type cells overproducing the C-terminal region of Sla1p that is responsible for interactions with Pan1p and End3p. These results indicate that the functions of Pan1p, End3p, and Sla1p in cell wall morphogenesis may depend on the formation of a heterotrimeric complex. Interestingly, the cell wall abnormalities exhibited by these cells are independent of the actin cytoskeleton organization on the cell cortex, as they manifest despite the presence of apparently normal cortical actin cytoskeleton. Examination of several act1 mutants also supports this conclusion. These observations suggest that the Pan1p-End3p-Sla1p complex is required not only for normal actin cytoskeleton organization but also for normal cell wall morphogenesis in yeast.

Download Full-text