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 793 records · Page 44Linked to original sources
PubMed1997

Calponin inhibits actin-activated MgATPase of myosin subfragment 1 (S1) without displacing S1 from its binding site on actin.

Calponin is a smooth-muscle thin-filament protein implicated in the regulation of contraction. Its binding to actin is a prerequisite for inhibition of actin-activated myosin MgATPase. Investigating the molecular mechanism of this inhibition, it was found that titration of acto-myosin subfragment 1 with calponin in the presence of either ADP or ATP does not displace weakly or strongly bound myosin subfragment 1 (S1) from actin. S1.ADP, however, is able to release about two-thirds of the calponin from saturated (equimolar) complexes of actin-calponin. The remaining calponin is sufficient for almost full inhibition of acto-S1 MgATPase activity. Bunding of actin filaments by calponin takes place at a higher ratio calponin/actin (above 1:3) and, therefore, is not responsible for inhibition of the ATPase. Bundle formation is inhibited by S1.ADP. These results suggest the existence of two calponin-binding sites on actin; one, that is insensitive to S1, which is responsible for inhibition of the ATPase, the other, from which calponin is readily displaced by S1.

Actins↗
PubMed1990

Time-dependent effect of melatonin on actin mRNA levels and incorporation of 35S-methionine into actin and proteins by the rat hypothalamus.

The synthesis of the cytoskeletal protein actin exhibits, in the rat hypothalamus, a diurnal variation with maxima during morning hours. The objective of the present study was to assess whether melatonin injection could affect the in vitro incorporation of 35S-methionine into actin, as well as the levels of actin mRNA, in the hypothalamus of adult male rats treated either acutely or chronically with the hormone at 10:00 or 18:00. Injection of 100 micrograms/kg of melatonin for ten days at either time induced a significant depression in the incorporation of 35S-methionine into a 43 kDa protein with the electrophoretic mobility of actin. The specific activity of total soluble proteins after labeled methionine incubations decreased only after evening melatonin administration (100 micrograms/kg, ten days). Hypothalamic actin mRNA levels, quantitated by dot-blot analysis, decreased only after the injection of 100 micrograms/kg melatonin for ten days at 10:00. Neither a 10-micrograms/kg dose of melatonin, nor a single injection of 100 micrograms/kg melatonin, caused any significant change in the parameters examined. Melatonin (100 micrograms/kg for ten days) did not modify hypothalamic somatostatin or H-Ras mRNA concentration. These results suggest the existence of an inhibitory effect of melatonin on hypothalamic actin synthesis.

Actins↗
PubMed1996

Characterization of F-actin bundling activity of Tetrahymena elongation factor 1 alpha investigated with rabbit skeletal muscle actin.

Elongation factor 1 alpha (EF-1 alpha) is an essential factor for protein synthesis in eukaryotes. Here, we demonstrated that Tetrahymena EF-1 alpha induced bundles of rabbit skeletal muscle F-actin as well as Tetrahymena F-actin in vitro, although Tetrahymena and skeletal muscle actins are different in some parts of their primary structures and in the binding abilities to some actin-binding proteins. Co-sedimentation experiments showed that the binding ratio of Tetrahymena EF-1 alpha to skeletal muscle F-actin in the bundles was 1 : 1. Electron microscopic observation showed that alkaline pH or high ionic strength reduced the bundling activity of Tetrahymena EF-1 alpha to some extent, although the EF-1 alpha seemed to be able to induce bundling of the F-actin within the range of physiological condition.

Actins↗
PubMed1992

Protein phosphatase inhibitors okadaic acid and calyculin A alter cell shape and F-actin distribution and inhibit stimulus-dependent increases in cytoskeletal actin of human neutrophils.

The phosphatase inhibitors okadaic acid and calyculin A were found to elicit or to modify several neutrophil responses, suggesting that dephosphorylation plays a regulatory role. The concentrations of okadaic acid (> or = 1 mumol/L) that were effective on neutrophil functions (shape changes and marginal stimulation of pinocytosis) were shown to stimulate the incorporation of 32PO4 into many neutrophil proteins several-fold. Calyculin A was effective at 50-fold lower concentrations. In the presence of the inhibitors, the cells exhibited a nonpolar shape and the polarization response induced by chemotactic peptide was inhibited. Both phosphatase inhibitors also induced the association of F-actin with the cell membrane. A steady-state phosphatase activity is thus involved in maintaining shape and F-actin localization of resting cells. Inhibitors alone had no significant effect on the amount of cytoskeleton-associated actin. The increase in cytoskeletal actin observed at 30 minutes of stimulation with phorbol ester or 5 to 30 minutes of stimulation with chemotactic peptide, however, was abolished by okadaic acid or calyculin A, suggesting an important role of a phosphatase. In contrast, the early increase in cytoskeleton-associated actin observed at 1 minute of stimulation with peptide was not affected. This finding indicates that the increased association of actin with the cytoskeleton in the early and the later stages of neutrophil activation may be mediated by different signalling pathways.

Actins↗
PubMed2006

Actin cytoskeleton and beta-actin expression in correlation with higher invasiveness of selected hepatoma Morris 5123 cells.

Our studies were focused on the isolation and characterization of highly motile fraction of cells from hepatoma Morris 5123 population. Cells that underwent several migration cycles through Matrigel - coated filters were successfully cultured. The invasion index was determined by means of Matrigel invasion assay. Statically significant increase in the value of invasion factor for selected cells variant in comparison to the parental population was observed. The considerable changes in the cell shape were followed by the reorganization of the actin cytoskeleton structure including a dense subcortical congestion in the distribution of beta -actin isoform. The visualization of this protein in tumor cells was performed by immunostaining and scanning fluorescent confocal microscopy. The results were confirmed by densitometry analysis of Western blots. In addition, the increased state of actin polymerization in the cytoplasmic fraction of selected cells was determined as measured by filamentous to monomeric (F:G) actin ratio. Concluding, the selected fraction of hepatoma Morris 5123 cells with higher invasion capacity was characterized by rounded shape, remarkable increase of beta -actin level, its submembrane concentration as well as with the increased state of actin polymerization with respect to parental cells population.

Actins↗
PubMed1988

Localization of the domain of actin-binding protein that binds to membrane glycoprotein Ib and actin in human platelets.

The Mr approximately 540,000 dimeric actin gelation protein, actin-binding protein (ABP), has previously been shown in human platelets to link actin to membrane glycoprotein Ib (GPIb) (Fox, J. E. B. (1985) J. Biol. Chem. 260, 11970-11977; Okita, J. R., Pidard, D., Newman, P. J., Montgomery, R. R., and Kunicki, T. J. (1985) J. Cell Biol. 100, 317-321). We have examined further the interaction between ABP and GPIb. Platelet extracts were depleted of ABP by precipitation with anti-ABP monoclonal antibodies (mAbs); in resulting precipitates, ABP monomer is complexed with GPIb in a 5:1 molar ratio. The ABP.GPIb complex is resistant to chaotropic solvents but dissociated by the ionic detergent, sodium dodecyl sulfate. Treatment of intact platelets with the ionophore A23187 activates a Ca2+-dependent protease which cleaves the Mr approximately 270,000 ABP subunit into three fragments of Mr 190,000, 100,000, and 90,000; the latter fragment is derived from the Mr 100,000 fragment. Anti-ABP mAbs coprecipitated GPIb with the Mr 100,000 and 90,000 fragments, but not with the Mr 190,000 fragment which contains the ABP self-association site. In the reciprocal experiment, anti-GPIb antibodies co-precipitated only the Mr 100,000 and 90,000 ABP fragments. Actin also co-precipitated with the Mr 100,000 and 90,000, but not with the Mr 190,000 ABP fragment. The anti-ABP mAb that precipitated the Mr 100,000-90,000 GPIb-binding ABP fragment recognizes a trypsin cleavage fragment of ABP that binds actin filaments in vitro. These findings establish that both the GPIb-binding site and actin-binding sites are in the same region of the ABP monomer. Because of the extended bipolar conformation of the ABP molecule, the data suggest that the GPIb.actin-binding region is located remote from the self-association, or dimerization, site of the ABP subunit.

Actins↗
PubMed1987

Further characterization of a conserved actin-binding 27-kDa fragment of actinogelin and alpha-actinins and mapping of their binding sites on the actin molecule by chemical cross-linking.

A conserved actin-binding domain (Mr = 27,000) of rat hepatic actinogelin, rat skeletal muscle, and chicken gizzard alpha-actinins (Mimura, N., and Asano, A. (1986) J. Biol. Chem. 261, 10680-10687) was separated into two components having different isoelectric points (peptides A and B) by chromatofocusing. Thermolysin digestion of peptide A generated peptide B with concomitant loss of peptide A. Amino acid compositions and tryptic maps of peptides A and B also demonstrated that peptide A is a precursor of peptide B upon thermolysin digestion. All of peptides A and B retained the activity to bind with F-actin competitively to each other. By the gel-filtration method, it was also shown that the native actin-binding 27-kDa fragments are monomeric and globular. The non-actin-binding 50- or 53.5-kDa fragment of actinogelin/alpha-actinins was, however, found to be asymmetric and dimeric in the native state. Chemical cross-linking of the 27-kDa fragment with F-actin with a water-soluble carbodiimide produced at least four different complexes (I-IV). Chemical cleaving analysis of the cross-linked products (complexes I and II) indicated that the 27-kDa fragment possesses two possible binding sites on actin at the NH2-terminal residues 1-12 (for complex I) and at residues spanning 86-119 or 123 (for complex II).

Actinin↗
PubMed1981

[Phalloidin counteracts the destruction of F-actin by osmic acid. II. Protection by phalloidin of F-actin crosslinked with aldehydes (author's transl)].

We have studied by viscometry and spectrophotometry the effects of glutaraldehyde, acetaldehyde, acrolein and formaldehyde on F-actin in vitro. Pretreatment with acrolein and, to a lesser extent, with glutaraldehyde, results in increased destruction of F-actin during the subsequent degradation with osmic acid. Formaldehyde alone disintegrates actin filaments. Acetaldehyde gives the best results and does not seem to damage F-actin. Phalloidin protects F-actin against destruction by osmic acid and this protection is also observed in the F-actin which has been pretreated with the four aldehydes mentioned.

Acetaldehyde↗
PubMed1995

Protein phosphatase 2A, a potential regulator of actin dynamics and actin-based organelle motility in the green alga Acetabularia.

The giant, unicellular alga Acetabularia is a well known experimental model for the study of actin-dependent intracellular organelle motility. In the cyst stage, however, which is equivalent to the gametophytic stage, organelles are immobile, even though an actin cytoskeleton is present. The reason for the lack of organelle motility at this stage has not been known. To test the hypothesis that organelle motility could be under the control of posttranslational modification by protein phosphorylation, we have treated cysts with submicromolar concentrations of okadaic acid or calyculin A, both potent inhibitors of serine/threonine protein phosphatases (ser/thr-PPases). The effects were dramatic: Instead of linear actin bundles typical for control cysts, circular arrays of actin bundles formed in the cortical cyst cytoplasm. Concomitant with the formation of these action rings, the cytoplasmic layers beneath the rings began to slowly rotate in a continuous and uniform counter-clockwise fashion. This effect suggests that protein phosphorylation acts on the actin cytoskeleton at two levels: (1) It changes the assembly properties of the actin filament system to the extent that novel cytoskeletal configurations are formed and (2) it raises the activity of putative motor proteins involved in the rotational movements to levels sufficiently high to support motility at a stage when organelle motility does not normally occur. Northern blot analysis of cyst stage-mRNA using probes specific to protein phosphatase type 1 (PP1) and type 2A (PP2A) reveals that PP2A is strongly expressed at this developmental stage whereas PP1 is not detectable, suggesting that PP2A is the likely target to the protein phosphatase inhibitors.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetabularia↗
PubMed1994

[The effect of different antitubercular agents on phagosome fusion with lysosomes, on the F-actin content in mouse peritoneal macrophages and on G-actin polymerization in vitro].

Effects of various antituberculosis remedies (ATR)--isoniazid (INA), saluzid (SA), streptosaluzid (SS), ethambutol (EB), sodium para-aminosalicylate (SPAS) on phagosome-lysosome (PL) fusion, on F-actin content in mouse macrophages and on G-actin polymerization in vitro were studied. The ATR of choice have been shown to stimulate the PL fusion. INA (0.2 mM), SA (0.02 mM), SS (0.05 mM), EB (0.08 mM) and SPAS (0.5 mM) increased the F-actin content and changed its localization within macrophages. ATR changed the character of G-actin polymerization in vitro. Possible mechanisms of interrelation between cytoskeleton (actin part) changes and PL fusion are discussed. The results obtained suggest to use the ATR-induced changes in PL fusion and F-actin content in the cells for estimating therapeutic effects of respective antituberculosis remedies.

Actins↗
PubMed1994

Gelsolin displaces phalloidin from actin filaments. A new fluorescence method shows that both Ca2+ and Mg2+ affect the rate at which gelsolin severs F-actin.

We describe an assay for measuring both the extent and kinetics of the severing of F-actin, based on the enhanced fluorescence emission of tetramethylrhodamine-phalloidin bound to F-actin. The enhanced fluorescence is lost after exposure to active gelsolin by displacement of the phalloidin from actin during severing. This assay requires small amounts of actin and gelsolin, can be used to measure reaction times ranging from 1 to 10(3) s, and does not require covalent modification of either protein. The rate of fluorescence loss is linearly related to the concentrations of both actin and gelsolin. However, the apparent rate constant of the reaction is highly dependent on the divalent cation concentration, varying between 10(4) and 10(6) M-1 s-1 when the [Ca2+] varies between 20 and 200 microM. Addition of Mg2+ increases the apparent rate constant at equivalent Ca2+ concentration. These results suggest that in vitro the rate-limiting step in the severing process is the activation of gelsolin by the binding of Ca2+ and Mg2+ to several low affinity (Kd approximately 100 microM) sites on gelsolin. While activation of gelsolin by Ca2+ is a slow process, the binding and severing of actin occurs at a rate approaching the diffusion limit.

Actins↗
PubMed1996

Recombinant scinderin, an F-actin severing protein, increases calcium-induced release of serotonin from permeabilized platelets, an effect blocked by two scinderin-derived actin-binding peptides and phosphatidylinositol 4,5-bisphosphate.

In response to vessel injury or exposure to different substances, platelets undergo activation which consists of shape changes, formation of cellular pseudopodia, aggregation, and secretion. These dramatic changes are accompanied by cycles of actin depolymerization and polymerization. Previous work has shown the presence in platelets of gelsolin and scinderin, two Ca(2+)-dependent F-actin severing proteins. Recent published evidence suggests that scinderin is a component of the exocytotic machinery in chromaffin cells. The present work describes the preparation of recombinant scinderin and peptides Sc-ABP1 and Sc-ABP2 with sequences corresponding to two actin-binding sites of scinderin. Recombinant scinderin and peptides Sc-ABP1 and Sc-ABP2 were tested for their effects on Ca(2+)-induced serotonin release from digitonin permeabilized platelets. The results indicated that recombinant scinderin potentiates Ca(2+)-evoked serotonin release, an effect blocked in the presence of Sc-ABP1, Sc-ABP2, exogenous gamma-actin, or the addition of phosphatidylinositol 4,5-bisphosphate (PIP2). In the presence of a mismatched peptide (MMP) the potentiating effect of recombinant scinderin was not affected. Moreover, Sc-ABP1, Sc-ABP2, and gamma-actin inhibited Ca(2+)-induced release of serotonin in the absence of recombinant scinderin, suggesting an inhibition of platelet endogenous scinderin. MMP was ineffective under these conditions. The results suggest that F-actin disassembly, perhaps at a specific site, is required for platelet secretion and that scinderin might be an important component of the exocytotic machinery in platelets.

Actins↗
PubMed1996

A novel type of protein kinase phosphorylates actin in the actin-fragmin complex.

Actin-fragmin kinase (AFK) from Physarum polycephalum specifically phosphorylates actin in the EGTA-resistant 1:1 actin-fragmin complex. The cDNA deduced amino acid sequence reveals two major domains of approximately 35 kDa each that are separated by a hinge-like proline/serine-rich segment of 50 residues. Whereas the N-terminal domain does not show any significant similarity to protein sequences from databases, there are six complete kelch repeats in the protein that comprise almost the entire C-terminal half of the molecule. To prove the intrinsic phosphorylation activity of AFK, full-length or partial cDNA fragments were expressed both in a reticulocyte lysate and in Escherichia coli. In both expression systems, we obtained specific actin phosphorylation and located the catalytic domain in the N-terminal half. Interestingly, this region did not contain any of the known protein kinase consensus sequences. The only known sequence motif present that could have been involved in nucleotide binding was a nearly perfect phosphate binding loop (P-loop). However, introduction of two different point mutations into this putative P-loop sequence did not alter the catalytic activity of the kinase, which indicates an as yet unknown mechanism for phosphate transfer. Our data suggest that AFK belongs to a new class of protein kinases and that this actin phosphorylation might be the first example of a widely distributed novel type of regulation of the actin cytoskeleton in non-muscle cells.

Actins↗
PubMed1999

Putting a new twist on actin: ADF/cofilins modulate actin dynamics.

The actin-depolymerizing factor (ADF)/cofilins are a family of essential actin regulatory proteins, ubiquitous among eukaryotes, that enhance the turnover of actin by regulating the rate constants of polymerization and depolymerization at filament ends, changing the twist of the filament and severing actin filaments. Genetic and cell-biological studies have shown that an ADF/cofilin is required to drive the high turnover of the actin cytoskeleton observed in vivo. The activity of ADF/cofilin is regulated by a variety of mechanisms, including specific phosphorylation and dephosphorylation. This review addresses aspects of ADF/cofilin structure, dynamics, regulation and function.

3T3 Cells↗
PubMed1996

The Saccharomyces cerevisiae actin-related protein Arp2 is involved in the actin cytoskeleton.

Arp2p is an essential yeast actin-related protein. Disruption of the corresponding ARP2 gene leads to a terminal phenotype characterized by the presence of a single large bud. Thus, Arp2p may be important for a late stage of the cell cycle (Schwob, E., and R.P. Martin, 1992. Nature (Lond.). 355:179-182). We have localized Arp2p by indirect immunofluorescence. Specific peptide antibodies revealed punctate staining under the plasma membrane, which partially colocalizes with actin. Temperature-sensitive arp2 mutations were created by PCR mutagenesis and selected by an ade2/SUP11 sectoring screen. One temperature-sensitive mutant that was characterized, arp2-H330L, was osmosensitive and had an altered actin cytoskeleton at a nonpermissive temperature, suggesting a role of Arp2p in the actin cytoskeleton. Random budding patterns were observed in both haploid and diploid arp2-H330L mutant cells. Endocytosis, as judged by Lucifer yellow uptake, was severely reduced in the mutant, at all temperatures. In addition, genetic interaction was observed between temperature-sensitive alleles arp2-H330L and cdc10-1. CDC10 is a gene encoding a neck filament-associated protein that is necessary for polarized growth and cytokinesis. Overall, the immunolocalization, mutant phenotypes, and genetic interaction suggest that the Arp2 protein is an essential component of the actin cytoskeleton that is involved in membrane growth and polarity, as well as in endocytosis.

Actin Cytoskeleton↗