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At least 433 records · Page 24Linked to original sources
PubMed2001

A new family of Cdc42 effector proteins, CEPs, function in fibroblast and epithelial cell shape changes.

Cdc42, a Rho GTPase, regulates the organization of the actin cytoskeleton by its interaction with several distinct families of downstream effector proteins. Here, we report the identification of four new Cdc42-binding proteins that, along with MSE55, constitute a new family of effector proteins. These molecules, designated CEPs, contain three regions of homology, including a Cdc42 binding domain and two unique domains called CI and CII. Experimentally, we have verified that CEP2 and CEP5 bind Cdc42. Expression of CEP2, CEP3, CEP4, and CEP5 in NIH-3T3 fibroblasts induced pseudopodia formation. Fibroblasts coexpressing dominant negative Cdc42 with CEP2 or expressing a Cdc42/Rac interactive binding domain mutant of CEP2 did not induce pseudopodia formation. In primary keratinocytes, CEP2- and CEP5-expressing cells showed reduced F-actin localization at the adherens junctions with an increase in thin stress fibers that extended the length of the cell body. Keratinocytes expressing CEPs also showed an altered vinculin distribution and a loss of E-cadherin from adherens junctions. Similar effects were observed in keratinocytes expressing constitutively active Cdc42, but were not seen with a Cdc42/Rac interactive binding domain mutant of CEP2. These results suggest that CEPs act downstream of Cdc42 to induce actin filament assembly leading to cell shape changes.

3T3 Cells↗
PubMed2002

Dmoesin controls actin-based cell shape and polarity during Drosophila melanogaster oogenesis.

Ezrin, Radixin and Moesin (ERM) proteins are thought to constitute a bridge between the actin cytoskeleton and the plasma membrane (PM). Here we report a genetic analysis of Dmoesin, the sole member of the ERM family in Drosophila. We show that Dmoesin is required during oogenesis for anchoring microfilaments to the oocyte cortex. Alteration of the actin cytoskeleton resulting from Dmoesin mutations impairs the localization of maternal determinants, thus disrupting antero-posterior polarity. This study also demonstrates the requirement of Dmoesin for the specific organization of cortical microfilaments in nurse cells and, consequently, mutations in Dmoesin produce severe defects in cell shape.

Actin Cytoskeleton↗
PubMed2001

The small muscle-specific protein Csl modifies cell shape and promotes myocyte fusion in an insulin-like growth factor 1-dependent manner.

We have isolated a murine cDNA encoding a 9-kD protein, Chisel (Csl), in a screen for transcriptional targets of the cardiac homeodomain factor Nkx2-5. Csl transcripts were detected in atria and ventricles of the heart and in all skeletal muscles and smooth muscles of the stomach and pulmonary veins. Csl protein was distributed throughout the cytoplasm in fetal muscles, although costameric and M-line localization to the muscle cytoskeleton became obvious after further maturation. Targeted disruption of Csl showed no overt muscle phenotype. However, ectopic expression in C2C12 myoblasts induced formation of lamellipodia in which Csl protein became tethered to membrane ruffles. Migration of these cells was retarded in a monolayer wound repair assay. Csl-expressing myoblasts differentiated and fused normally, although in the presence of insulin-like growth factor (IGF)-1 they showed dramatically enhanced fusion, leading to formation of large dysmorphogenic "myosacs." The activities of transcription factors nuclear factor of activated T cells (NFAT) and myocyte enhancer-binding factor (MEF)2, were also enhanced in an IGF-1 signaling-dependent manner. The dynamic cytoskeletal localization of Csl and its dominant effects on cell shape and behavior and transcription factor activity suggest that Csl plays a role in the regulatory network through which muscle cells coordinate their structural and functional states during growth, adaptation, and repair.

Aging↗
PubMed2001

The Drosophila cell shape regulator c-Jun N-terminal kinase also functions as a stress-activated protein kinase.

Mammalian c-Jun N-terminal kinases (JNKs) are members of a group of stress-activated intracellular signalling molecules within the MAP kinase family. Molecular genetic analysis of a highly evolutionarily conserved Drosophila JNK homologue, DJNK, has demonstrated that this molecule plays an essential developmental role in cell shape regulation. However, it remains to be determined whether DJNK also responds to the broad range of cellular stresses and other stimuli that affect its mammalian counterpart. Here we demonstrate that c-Jun, a substrate for mammalian JNKs, is a specific substrate for DJNK and that an antiserum that cross-reacts with activated mammalian JNK at the conserved threonyl-prolyl-tyrosyl (TPY) motif within the activation loop also specifically recognises the activated form of DJNK. Using these two assays, we show that DJNK activity is stimulated in cultured cells by several treatments that activate mammalian JNKs, including addition of arsenite, vanadate and ceramide derivatives. It is therefore concluded that in addition to its essential developmental functions, DJNK plays an important role in stress responses that mirrors its mammalian counterpart.

Animals↗
PubMed2000

Synergistic role of cAMP and IP(3) in corticotropin-releasing hormone-induced cell shape changes in invertebrate immunocytes.

Immunocytes from the mollusc Mytilus galloprovincialis express corticotropin-releasing hormone (CRH) receptor subtype (CRH-R1 and CRH-R2)-like mRNAs. Using computer-assisted microscopic image analysis, we have found that exogenous CRH provokes changes in the cellular shape of immunocytes, and that this response is extracellular Ca(2+)-dependent. The various inhibitors of transduction signaling pathways, i.e. suramin sodium, 2', 5'-dideoxyadenosine, neomycin sulfate, calphostin C, H-89, and wortmannin, completely or partially inhibit these changes. The present findings demonstrate that PKA, PKC, and PKB/Akt are involved in CRH-induced cell shape changes in immunocytes, and that the cellular effect of CRH needs the synergistic action of the two second messengers, cAMP and IP(3).

Animals↗
PubMed1987

Mutant isolation and molecular cloning of mre genes, which determine cell shape, sensitivity to mecillinam, and amount of penicillin-binding proteins in Escherichia coli.

A chromosomal region of Escherichia coli contiguous to the fabE gene at 71 min on the chromosomal map contains multiple genes that are responsible for determination of the rod shape and sensitivity to the amidinopenicillin mecillinam. The so-called mre region was cloned and analyzed by complementation of two closely related but distinct E. coli mutants characterized, respectively, by the mutations mre-129 and mre-678, that showed a rounded to irregular cell shape and altered sensitivities to mecillinam; the mre-129 mutant was supersensitive to mecillinam at 30 degrees C, but the mre-678 mutant was resistant. The mre-678 mutation also caused simultaneous overproduction of penicillin-binding proteins 1Bs and 3. A chromosomal region of the wild-type DNA containing the total mre region and the fabE gene was first cloned on a lambda phage; a 7-kilobase (kb) fragment containing the whole mre region, but not the fabE gene, was then recloned on a mini F plasmid, pLG339; and finally, a 2.8-kb fragment complementing only mre-129 was also cloned on this low-copy-number plasmid. The whole 7-kb fragment was required for complementing the mre-678 mutant phenotypes. Fragments containing fabE but not the mre-129 region could be cloned on a high-copy-number plasmid. Southern blot hybridization indicated that the mre-678 mutant had a large deletion of 5.25 kb in its DNA, covering at least part of the mre-129 gene.

Amdinocillin↗
PubMed1996

Human red blood cell shape and volume are changed by physiological levels of hydrostatic pressure.

Application of hydrostatic pressure of several atmospheres (atm), such as that applied in diving or hyperbaric treatment, has been previously shown to induce the release of membrane components into the extracellular medium. As the shape of red blood cells (RBC) is sensitive to membrane composition, this might imply a subsequent change in RBC shape and volume. The present study demonstrates that application of hydrostatic pressure of up to 15 atm changes the shape of RBC from the normal discoids to stomatocytes (cup-shaped) and accordingly increases their volume. Changes in RBC shape and volume are known to impair physiological and cellular function. Thus, these changes might be pertinent to hemodynamic and physiological disorders observed in humans subjected to elevated pressure.

Cell Size↗
PubMed1988

Nuclear transport in 3T3 fibroblasts: effects of growth factors, transformation, and cell shape.

Nucleocytoplasmic transport of fluorescent-labeled macromolecules was investigated in transformed and nontransformed 3T3 fibroblasts. Insulin and epidermal growth factor enhanced transport three-fold after 1-2-h incubation with nontransformed adhering fibroblasts; no enhancement of transport was observed for spherical unattached fibroblasts. The concentration of growth factor for maximal enhancement was 3-10 nM. Nuclear transport for Kirsten murine sarcoma virus-transformed BALB/c 3T3 fibroblasts, however, was maximally enhanced before addition of growth factors; addition of insulin or epidermal growth factor causes no additional transport enhancement. Transformation also minimizes cell shape effects on macromolecular nuclear transport. These results provide evidence that protein growth factors and oncogenic transformation may use a similar mechanism for activation of nuclear transport.

Animals↗
PubMed1998

HLA DR and AB surface antigens correlate with cell shape (surface area).

In order to help explain some of the various phenomena associated with both benign and malignant cells, this study was undertaken to determine if changes in the shape of the cell could alter the recognition of the cell. Non-transformed Human cells, HEL 299, were evaluated for their shape and surface antigens. A direct statistical correlation was found between the two surface antigens HLA AB and DR and the cell shape (surface area). The possible significance of this phenomena in non transformed human cells to neoplastic proliferation is suggested.

Animals↗
PubMed1980

Some remarks on red cell shape and on surface and volume relationships.

Red cell (RBC) form is of interest for its own sake and for its role in characterizing physiologically altered and pathological cell types. RBC shape is also identified as one of the three principal factors enabling (and limiting) flow-induced cellular deformability processes. It has become common practice to discuss and analyze RBC form in terms of the ratio of the cell's surface area to its volume, and indeed to use the two concepts interchangeably. The inadequacy of the S/V ratio to serve this purpose is pointed out, a long with the qualitative and quantitative errors that it leads to, with cells of either very small size (as in iron-deficiency anemia) or large size (as in Addison's associated anemia). The substitution of a normalied, dimensionless, relative surface-to-volume function that can accurately quantitate this facet of form is necessary. The relationship between this function and other measures of form and "sphericity" are specified, and some applications of these functions to studies on cell form and deformability are indicated.

Blood Volume↗
PubMed2005

A cell cycle arrest is necessary for bottle cell formation in the early Xenopus gastrula: integrating cell shape change, local mitotic control and mesodermal patterning.

During development cell proliferation and morphogenetic movements are tightly intermingled. Both processes depend on the same cytoskeletal elements. Therefore, precise regulation of local mitotic activity seems to be basic for proper embryogenesis. Here, I report on bottle cells as an early non-mitotic cell population in the Xenopus gastrula. Endogenous and activin/BVg1-induced ectopic bottle cells do not proliferate. Overexpression of the mitosis-promoting phosphatase cdc25C increases the proliferation rate and interferes with bottle cell formation whereas the phosphatase-dead mutant cdc25C(C457A) does not. Cdc25C also affects other gastrulation processes such as epiboly, vegetal rotation or tissue separation as inferred from histological inspection of early gastrulae. Double stainings of gsc/Xbra transcripts and mitotic nuclei in ectopic and endogenous lips demonstrated that non-mitotic cells occur in the bottle cell region and, to a lesser extent, in the gsc domain which both are indicative of high TGF-beta signalling. In contrast, the Xbra-region and the remainder of the animal cap appear to be permissive for higher rates of cell proliferation. These data suggest inhibition of cell proliferation by high levels of activin-type signals and a close link of mesodermal and mitotic patterning. Finally, coexpression of eFGF together with activin/BVg1 interferes with TGF-beta-induced bottle cell formation. This inhibitory effect correlates with increased cell proliferation as compared to embryos injected with activin/BVg1 alone. Taken together, these data suggest that TGF-beta and FGF signals play antagonistic roles in bottle cell formation and the spatial control of the cell cycle in early Xenopus gastrulae.

Activins↗
PubMed1976

Red blood cell shapes as explained on the basis of curvature elasticity.

Assuming that the shape of red blood cells is controlled by the curvature elasticity of the surrounding membrane, we fit theoretical shapes to the contours Evans and co-workers determined by interference microscopy. Very good agreement is obtained for disc shapes. The fit is not so good for less common shapes, which may result from Evans' parametric representation and from the interference of shear elasticity.

Elasticity↗
PubMed1998

Amphiphile induced echinocyte-spheroechinocyte transformation of red blood cell shape.

A possible physical explanation of the echinocyte -spheroechinocyte red blood cell (RBC) shape transformation induced by the intercalation of amphiphilic molecules into the outer layer of the RBC plasma membrane bilayer is given. The stable RBC shape is determined by the minimization of the membrane elastic energy, consisting of the bilayer bending energy, the bilayer relative stretching energy and the skeleton shear elastic energy. It is shown that for a given relative cell volume the calculated number of echinocyte spicula increases while their size decreases as the number of the intercalated amphiphilic molecules in the outer layer of the cell membrane bilayer is increased, which is in agreement with experimental observations. Further, it is show that the equilibrium difference between the outer and the inner membrane leaflet areas of the stable RBC shapes increases if the amount of the intercalated amphiphiles is increased, thereby verifying theoretically the original bilayer couple hypothesis of Sheetz and Singer (1974) and Evans (1974).

Biophysical Phenomena↗
PubMed1987

Correlation among endothelial cell shape, F-actin arrangement, and prostacyclin synthesis.

Though many factors have been identified which modulate prostacyclin (PGI2) synthesis, there is little information on cellular mechanisms whereby endothelial cells (EC) regulate their basal eicosanoid metabolism. Using substrates of various adhesive capacities, bovine and porcine aortic EC shape and cytoskeletal F-actin arrangement could be modulated. Staining with rhodamine-phalloidin (R-P) permitted analysis of F-actin arrangement, while differences in cell shape were determined by measurement of cell perimeter surface area (CPSA). Spectrophotoflurometric measurements were used to quantitate the R-P binding capacity of the cultures. Cultures of reduced CPSA (225.2 +/- 13.5 mu2) generated the highest levels of basal PGl2 (6.14 +/- 0.51 pg/ug cell protein); had a diffuse arrangement of F-actin and an increased binding capacity for R-P (463.55 +/- 50.58 nmoles/ug cell protein). Cultures of enlarged CPSA (1399.3 +/- 148.3 mu2), with many actin cables and a significantly reduced (p less than 0.001) R-P binding capacity (74.941 +/- 11.79 nmoles/ug of cell protein) produced significantly smaller (p less than 0.001) basal quantities of PGl2 (1.33 +/- 0.14 pg/ug cell protein). Similarly, arachidonic acid stimulation of cultures of reduced CPSA resulted in an increased synthesis of PGl2 when compared to stimulated cultures of enlarged cells. These findings suggest a role for cell shape and the cytoskeleton in the mechanism controlling PGl2 production and indicate that alteration of the arrangement of F-actin may be of importance in regulation of EC eicosanoid metabolism.

Actins↗
PubMed2001

Contributions of PBP 5 and DD-carboxypeptidase penicillin binding proteins to maintenance of cell shape in Escherichia coli.

Escherichia coli has 12 recognized penicillin binding proteins (PBPs), four of which (PBPs 4, 5, and 6 and DacD) have DD-carboxypeptidase activity. Although the enzymology of the DD-carboxypeptidases has been studied extensively, the in vivo functions of these proteins are poorly understood. To explain why E. coli maintains four independent loci encoding enzymes of considerable sequence identity and comparable in vitro activity, it has been proposed that the DD-carboxypeptidases may substitute for one another in vivo. We tested the validity of this equivalent substitution hypothesis by investigating the effects of these proteins on the aberrant morphology of DeltadacA mutants, which produce no PBP 5. Although cloned PBP 5 complemented the morphological phenotype of a DeltadacA mutant lacking a total of seven PBPs, controlled expression of PBP 4, PBP 6, or DacD did not. Also, a truncated PBP 5 protein lacking its amphipathic C-terminal membrane binding sequence did not reverse the morphological defects and was lethal at low levels of expression, implying that membrane anchoring is essential for the proper functioning of PBP 5. By examining a set of mutants from which multiple PBP genes were deleted, we found that significant morphological aberrations required the absence of at least three different PBPs. The greatest defects were observed in cells lacking, at minimum, PBPs 5 and 6 and one of the endopeptidases (either PBP 4 or PBP 7). The results further differentiate the roles of the low-molecular-weight PBPs, suggest a functional significance for the amphipathic membrane anchor of PBP 5 and, when combined with the recently determined crystal structure of PBP 5, suggest possible mechanisms by which these PBPs may contribute to maintenance of a uniform cell shape in E. coli.

Bacterial Proteins↗
PubMed1983

Influence of cell shape and surface charge on attachment of Mycoplasma pneumoniae to glass surfaces.

Attachment of Mycoplasma pneumoniae to glass is reduced in the presence of protein, and fatty acid-free bovine serum albumin is more effective than Cohn fraction V. Cultures in the early log phase (pH 7.45 to 7.25) and cultures in the stationary or decline phase (pH 6.9 to 6.4) were more sensitive to this inhibiting effect of protein-containing buffer. Treatment of the glass surface with bovine serum albumin, concanavalin A, or polylysine reduced attachment of the mycoplasma cells. The inhibiting effects of both proteins in buffer or on the glass surface could be overcome by the addition of glucose. Modification of the mycoplasma surface charge by blocking of carboxyl groups or neutralization of ionic lipids by tetracaine altered the attachment level, whereas fibronectin and its corresponding antiserum were without effect. The results suggest that the mycoplasma interaction with glass is a complex multifactorial process. In protein-free buffer both hydrophobic and electrostatic forces are involved; in protein-containing fluid, other factors seem to be involved. The energy required for this type of attachment could be necessary for maintenance of cell shape or synthesis of polypeptides.

Adhesiveness↗
PubMed2003

G Protein betagamma subunits stimulate p114RhoGEF, a guanine nucleotide exchange factor for RhoA and Rac1: regulation of cell shape and reactive oxygen species production.

Rho GTPases integrate the intracellular signaling in a wide range of cellular processes. Activation of these G proteins is tightly controlled by a number of guanine nucleotide exchange factors (GEFs). In this study, we addressed the functional role of the recently identified p114RhoGEF in in vivo experiments. Activation of endogenous G protein-coupled receptors with lysophosphatidic acid resulted in activation of a transcription factor, serum response element (SRE), that was enhanced by p114RhoGEF. This stimulation was inhibited by the functional scavenger of Gbetagamma subunits, transducin. We have determined that Gbetagamma subunits but not Galpha subunits of heterotrimeric G proteins stimulated p114RhoGEF-dependent SRE activity. Using coimmunoprecipitation assay, we have determined that Gbetagamma subunits interacted with full-length and DH/PH domain of p114RhoGEF. Similarly, Gbetagamma subunits stimulated SRE activity induced by full-length and DH/PH domain of p114RhoGEF. Using in vivo pull-down assays and dominant-negative mutants of Rho GTPases, we have determined that p114RhoGEF activated RhoA and Rac1 but not Cdc42 proteins. Functional significance of RhoA activation was established by the ability of p114RhoGEF to induce actin stress fibers and cell rounding. Functional significance of Rac1 activation was established by the ability of p114RhoGEF to induce production of reactive oxygen species (ROS) followed by activation of NADPH oxidase enzyme complex. In summary, our data showed that the novel guanine nucleotide exchange factor p114RhoGEF regulates the activity of RhoA and Rac1, and that Gbetagamma subunits of heterotrimeric G proteins are activators of p114RhoGEF under physiological conditions. The findings help to explain the integrated effects of LPA and other G-protein receptor-coupled agonists on actin stress fiber formation, cell shape change, and ROS production.

Actins↗