Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “ACTIN”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 937 records · Page 52Linked to original sources
PubMedDate not supplied

Study of Cryptococcus neoformans actin gene regulation with a beta-galactosidase-actin fusion.

An expression plasmid carrying a heterologous gene fusion between the Cryptococcus neoformans actin promoter and the Escherichia coli reporter gene, LACZ, was constructed to study actin regulation in C. neoformans. Two randomly stable transformants, designated 20.6 and 20.9, were selected for further examination. Both ectopic and homologous recombination with vector insertion in tandem repeats occurred in these transformants. Transformant 20.9 carried more copies of ACTp::LACZ in its genome than 20.6 and this was reflected in expressing higher levels of beta-galactosidase activity. In vitro, these transformants showed higher levels of beta-galactosidase activity expressed when the transformants were propagated at higher temperatures (37 degrees C vs 30 degrees C). However, beta-galactosidase expression in the transformants was variable during logarithmic and stationary growth phases and this differential expression was temperature dependent. This report shows that the constitutive actin gene in C. neoformans is regulated by temperature and growth and this fact should be taken into consideration when actin expression is used as a standard to compare the expression of other regulated genes. Also, a more sensitive reporter construct will be needed for in vivo gene analysis of regulation.

Actins↗
PubMed1997

Jasplakinolide, a novel actin targeting peptide, inhibits cell growth and induces actin filament polymerization in the green alga Micrasterias.

Jasplakinolide, a naturally occurring cyclodepsipeptide from the marine sponge Jaspis sp., known to induce actin polymerization and stabilization in vitro, markedly influences the morphogenetic process in the green alga Micrasterias when used in concentrations higher than 3 microM. Development of Micrasterias is inhibited or strongly retarded, malformations occur, and large vacuoles are formed. At the ultrastructural level, dense abnormal accumulations of filamentous structures have been found indicating actin filament polymerizing activities of the drug in situ. Moreover, displacement of organelles and aggregations of endoplasmic reticulum (ER) cisternae have been observed. Microtubule (MT) arrangement and MT-dependent processes remain undisturbed. Cells allowed to recover from jasplakinolide treatment continue their growth but show severe changes in the cell pattern and displacement of organelles, suggesting that even after removal of the drug, some basic features for the morphogenetic process remain altered. Jasplakinolide might be a useful tool for investigations on actin-dependent processes in the future.

Actin Cytoskeleton↗
PubMed2001

Thermolabile and calcium-dependent serum factor interferes with polymerized actin, and impairs anti-actin antibody detection.

The detection of anti-actin (AAA) by immunofluorescence is hindered by the presence of a serum factor. To better understand how it interferes with AAA detection, we tested sera from 20 patients with autoimmune hepatitis, and from 21 healthy adults, diluted 1:10 and prepared as follows: (A) diluted with PBS; (B) inactivated at 56 degrees C, and diluted with PBS; (C) diluted with 34 mM EDTA/PBS; (D) heated and diluted with EDTA/PBS. To reveal AAA, a fluorescein-labelled anti-human IgG was used in the process of indirect immunofluorescence. In a parallel assay, the substrate, acetone-fixed human fibroblasts, was preincubated with sera prepared as if it were to identify AAA, but instead, a rhodamine-phalloidin was used to identify F-actin, by direct immunofluorescence. All sera from patients were reactive to AAA when heat-inactivated and/or calcium-chelated, and 60% of them when diluted with unmodified sera (P=0.004). F-actin continued to be present after preincubation with heat-inactivated or calcium-chelated sera from patients and healthy controls, and in 41.5% of reactions with unmodified serum (P=0.0000001). The heat inactivation and the calcium chelation were both efficient procedures for maintaining the microfilament structure intact after serum incubation and, therefore, for identifying AAA.

Actin Depolymerizing Factors↗
PubMed2004

Phosphorylation of actin-binding protein (ABP-280; filamin) by tyrosine kinase p56lck modulates actin filament cross-linking.

Actin-binding protein (ABP-280; filamin) is a phosphoprotein present in the periphery of the cytoplasm where it can cross-link actin filaments, associate with lipid membranes, and bind to membrane surface receptors. Given its function and localization in the cell, we decided to investigate the possibility of whether it serves as substrate for p56lck, a lymphocyte-specific member of the src family of protein tyrosine kinases associated with cell surface glycoproteins. The interaction of p56lck with membrane glycoproteins is important for cell development and functional activation. Here, we show that purified p56lck interacts and catalyzes in vitro kinase reactions. Tyrosine phosphorylation by p56lck is restricted to a single peptide of labeled ABP-280 shown by protease digest. The addition of phorbol ester to cells results in the inhibition of phosphorylation of ABP-280 by p56lck. These results show a decrease in phosphorylation suggesting conformationally induced regulation. Dynamic light scattering confirmed increased actin filament cross-linking due to phosphorylation of ABP-280 by p56lck.

Actin Cytoskeleton↗
PubMed2006

Short-term retention of actin filament binding proteins on lamellipodial actin bundles.

Actin filaments are organised into sub-compartments of meshwork and bundles in lamellipodia. Localisation of fascin, the LIM and SH3 domain protein 1 (lasp-1), and lasp-2 to the bundles suggest their involvement in that organisation; however, their contributions remain unclear. We have compared the turnover of these proteins with actin at the bundle. After photobleaching, EGFP-actin recovered inwards from the bundle tip, consistent with the retrograde flow by treadmilling. In contrast, the recovery of EGFP-fascin, -lasp-1 and -lasp-2 occurred from the anterograde direction. These results suggest that these molecules would participate in the stabilisation of bundles but not in initiation.

Actin Cytoskeleton↗
PubMed2004

Fluorescence depolarization of actin filaments in reconstructed myofibers: the effect of S1 or pPDM-S1 on movements of distinct areas of actin.

Fluorescence polarization measurements were used to study changes in the orientation and order of different sites on actin monomers within muscle thin filaments during weak or strong binding states with myosin subfragment-1. Ghost muscle fibers were supplemented with actin monomers specifically labeled with different fluorescent probes at Cys-10, Gln-41, Lys-61, Lys-373, Cys-374, and the nucleotide binding site. We also used fluorescent phalloidin as a probe near the filament axis. Changes in the orientation of the fluorophores depend not only on the state of acto-myosin binding but also on the location of the fluorescent probes. We observed changes in polarization (i.e., orientation) for those fluorophores attached at the sites directly involved in myosin binding (and located at high radii from the filament axis) that were contrary to the fluorophores located at the sites close to the axis of thin filament. These altered probe orientations suggest that myosin binding alters the conformation of F-actin. Strong binding by myosin heads produces changes in probe orientation that are opposite to those observed during weak binding.

Actin Cytoskeleton↗
PubMed1988

Tropomyosin inhibits the rate of actin polymerization by stabilizing actin filaments.

Tropomyosin inhibition of the rate of spontaneous polymerization of actin is associated with binding of tropomyosin to actin filaments. Rate constants determined by using a direct electron microscopic assay of elongation showed that alpha alpha- and alpha beta-tropomyosin have a small or no effect on the rate of elongation at either end of the filaments. The most likely explanation for the inhibition of the rate of polymerization of actin in bulk samples is that tropomyosin reduces the number of filament ends by mechanical stabilization of the filaments.

Actin Cytoskeleton↗
PubMed1986

Intracellular localization of the 55-kD actin-bundling protein in cultured cells: spatial relationships with actin, alpha-actinin, tropomyosin, and fimbrin.

The 55-kD protein is a new actin-bundling protein purified from HeLa cells (Yamashiro-Matsumura, S., and F. Matsumura, 1985, J. Biol. Chem., 260:5087-5097). We have prepared monoclonal antibodies against the 55-kD protein and examined its intracellular localization, as well as its spatial relationships with other components of microfilaments in cultured cells by double-label immunofluorescence. The localization of the 55-kD protein is similar to that of actin. The antibody to the 55-kD protein stained strongly both microspikes and stress fibers. The 55-kD protein was found from the basal portions to the extremities of microspikes while alpha-actinin was localized only in the basal portions. In stress fibers, the 55-kD protein was found rather continuously in comparison to the periodic localizations of alpha-actinin and tropomyosin. Although fimbrin is located in microspikes and ruffling membranes, fimbrin is hardly found in stress fibers unlike the 55-kD protein. These observations coupled with the actin-bundling activity of the 55-kD protein imply that the 55-kD protein is involved in the formation of microfilament bundles in both microspikes and stress fibers.

Actin Cytoskeleton↗
PubMed1999

Two activities of cofilin, severing and accelerating directional depolymerization of actin filaments, are affected differentially by mutations around the actin-binding helix.

The biochemical activities of cofilin are controversial. We demonstrated that porcine cofilin severs actin filaments and accelerates monomer release at the pointed ends. At pH 7.1, 0.8 microM cofilin cut filaments (2.2 microM actin) about every 290 subunits and increased the depolymerization rate 6.4-fold. A kink in the major alpha-helix of cofilin is thought to constitute a contact site for actin. Side chain hydroxyl groups of Ser119, Ser120 and Tyr82 in cofilin form hydrogen bonds with main chain carbonyl moieties from the helix, causing the kink. We eliminated side chain hydroxyls by Ser-->Ala and/or Tyr-->Phe mutagenesis. Severing and depolymerization-enhancing activities were reduced dramatically in an Ala120 mutant, whereas the latter was decreased in a Phe82 mutant with a relatively small effect on severing, suggesting different structural bases for the two activities of cofilin. The Ala120-equivalent mutation in yeast cofilin affected cell growth, whereas that of the Phe82-equivalent had no effect in yeast. These results indicate the physiological significance of the severing activity of cofilin that is brought about by the kink in the helix.

Actin Depolymerizing Factors↗
PubMed1990

Dynamics of F-actin and F-actin/filamin networks as studied by photon correlation spectroscopy.

Photon correlation spectroscopy was used to study both F-actin and F-actin/filamin networks in solution. The measured autocorrelation functions were analyzed with the inverse Laplace transform CONTIN. The resulting frequency distributions consist of maximal five relatively narrow peaks. This rather unexpected finding disagrees with the frequency spectra calculated for an entangled rigid rod model. For this model, we expect spectra consisting of a single broad peak. Factors like flexibility, deviation from an experimental length distribution, interference with chemical reactions, and translation-rotation coupling that would influence the profile of the frequency distribution could be excluded by comparison of the data with model calculations or qualitative estimates. We conclude that our data for F-actin are consistent with the dynamics of an infinite network stable on the time scale of the observed modes. Further support for this interpretation is provided by a comparison with frequency spectra of actin/filamin networks. These appear to be very similar in shape. The main peak of these spectra that corresponds to the slow motions shifts to lower frequencies with increasing cross-link density. It appears that higher frequency modes of the gel are more efficiently damped with progressive cross-link density, resulting in a predominance of the slow motions in the spectra. This behavior has been already found in other systems and seems to be a general feature of cross-linked systems.

Actins↗
PubMed1980

Dissolution of cytoplasmic actin bundles and the induction of nuclear actin bundles by dimethyl sulfoxide.

Within 30 minutes of exposure to medium containing 10% dimethyl sulfoxide, PtK2 cells begin to round up and lose their cytoplasmic actin bundles. At the same time, bundles of actin filaments appear in the nuclei of the cells. One to 2 hours after the dimethyl sulfoxide is removed from the medium, the cells revert to their flattened shape, losing the nuclear actin bundles and regaining the cytoplasmic bundles.

Actins↗
PubMed1998

How to analyze electron micrographs of rafts of actin filaments crosslinked by actin-binding proteins.

Actin bundles are common cytoskeletal structures but ones which are usually polymorphic, varying from bundle to bundle. Two-dimensional arrays of actin filaments crosslinked by actin-bundling proteins are more tractable structures to analyze than are the three-dimensional bundles found in cells. The first step in analyzing these two-dimensional "rafts" is to determine the spatial relationships between neighboring filaments. It is difficult to discern such relationships by inspection of the electron micrographs of rafts, but easy by examination of the Fourier transforms. We provide theory and examples of the analysis of transforms of rafts, and show that different bundling proteins give rise to different kinds of rafts.

Actins↗
PubMed2006

Actin cytoskeleton remodelling in the anterior pituitary folliculostellate cell line TtT/GF: participation of the actin-binding protein cortactin.

We have previously shown that the folliculostellate (FS) cells of the anterior pituitary change their shape from stellate (type I) to polygonal (type II) coincidently with variations in the secretory activity of the pituitary. To elucidate the mechanisms involved in this switch in phenotypes, here we studied the impact of serum factors on the morphology of the FS cell line TtT/GF. TtT/GF cells cultured in serum-containing medium displayed elongated shapes and membrane ruffles similarly to type I cells. Serum deprivation caused the loss of plasma membrane activity and the acquisition by the cells of a sedentary phenotype and of a polygonal shape typical of type II FS cells. Addition of serum to the starved cells induced the reappearance of membrane raffles and lamellipodia. The switch in phenotypes and the maintenance of a motile phenotype depended on tyrosine kinase but not on Erk activity. Because the transition between phenotypes involved the tyrosine kinase-dependent reorganization of cortical actin filaments, we studied the participation of the actin-binding protein, cortactin, a tyrosine kinase substrate. Cortactin and its tyrosine-phosphorylated form, pY421-cortactin, localized to membrane ruffles and lamellipodia in serum-cultured TtT/GF cells, while they were evenly distributed over the whole cell cortex in serum-starved cells. Serum treatment of starved cells induced a transient increase in pY421-cortactin levels and the clustering of pY421-cortactin in membrane regions where protrusions were developing. Both serum responses were blocked by a tyrosine kinase inhibitor. Together, the results indicate that the transition from a polygonal to an elongated shape entails the acquisition of a dynamic cortical actin cytoskeleton that involves the tyrosine kinase-dependent phosphorylation of cortactin and the translocation of cortical pY421-cortactin to sites of ruffle formation at the plasma membrane.

Actins↗
PubMed1990

Actin critical concentration optimizes at intermediate [cytochalasin B]/[actin] ratios.

Effect of cytochalasin B on actin critical concentration has been assayed using the fluorescence enhancement of pyrene-labeled actin. A peak effect of cytochalasin B on the critical concentration is observed in the presence of either 100 mM K+, or 100 mM K+ plus 2 mM Mg2+. This may result from two competing activities of cytochalasin B, one associated with its capping activity to the barbed end of actin filaments, and the other associated with its lateral binding site(s) along the filaments resulting in a severing activity of cytochalasin B.

Actins↗
PubMed1986

Kinetics of actin depolymerization: influence of ions, temperature, age of F-actin, cytochalasin B and phalloidin.

Actin, labelled with the fluorescent dye N-(3-pyrenyl)maleimide, was diluted below its critical concentration and depolymerization was followed by measuring the declining fluorescence intensity. The time courses of depolymerization were fitted to a sum of three exponentials. In most cases there was a fast initial phase followed by one or three slower ones. Increasing MgCl2 concentration slowed down depolymerization velocity, as did substitution of Tris-maleate buffer by phosphate buffer. Older F-actin preparations depolymerized more slowly than younger ones. Phalloidin strongly decreased depolymerization velocity even after sonication. In the presence of cytochalasin B depolymerization was more uniformly exponential than in the absence of cytochalasin B; overall depolymerization velocity was decreased by cytochalasin B. The results are discussed on the assumption that depolymerization kinetics reflect the length distribution of actin filaments during depolymerization.

Actins↗
PubMed1993

The cortical actin cytoskeleton in a Dipteran embryo: analysis of the spatial reorganization of F-actin aggregates during the early nuclear division cycles.

Rhodamine phalloidin-staining was used to study the organization of the cortical actin cytoskeleton of the early Ceratitis capitata embryo. The dynamics of the actin aggregates and their changes in distribution during the formation of the syncytial blastoderm, were followed in detail. It was found that these aggregates formed a shell-like cluster around the interphase nuclei, and concentrated toward the poles of the mitotic apparatus when the nuclei divided. Laser scanning confocal microscopy revealed that aggregates not clustered at the poles of the mitotic apparatus were closely associated with fine fibers of a dense cytoplasmic network of actin filaments.

Actins↗
PubMed1993

Expression of a Bombyx cytoplasmic actin gene in cultured Drosophila cells: influence of 20-hydroxyecdysone and interference with expression of endogenous cytoplasmic actin genes.

The expression of the Bombyx cytoplasmic actin A3 gene and its response to 20-hydroxyecdysone are studied after transfection in hormone responsive Drosophila cells and are compared to the expression of homologous resident genes. The host cells accumulate correct transcripts of the Bombyx gene in a gene dosage dependent way. The relative amount of endogenous cytoplasmic actin mRNAs is decreased in transfected cells, whether the transgene is integrated into the genome or not. When 20-hydroxyecdysone is added to the culture medium, the accumulation of the foreign mRNA is decreased whereas those of endogenous cytoplasmic actin transcripts are increased. These results are discussed in terms of competition for transcription and regulatory factors.

Actins↗