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S Lin

Publications and source records attributed to S Lin.

At least 613 records · Page 34Linked to original sources
PubMed1980

A platelet inhibitor protein with cytochalasin-like activity against actin polymerization in vitro.

We have obtained an inhibitor fraction containing cytochalasin-like activity from human platelets. Using a procedure involving DEAE-cellulose, hydroxyapatite and gel filtration column chromatography, we obtained a fraction from human platelets which apparently can compete with 3H--cytochalasin B for binding to spectrin-actin complexes from human erythrocytes. The inhibitor activity is nondialyzable, sensitive to heat and to trypsin and has a Stoke's radius of 40 A. This fraction stops nuclei-induced actin polymerization in 0.4 mM MgCl2 and reduces the viscosity of F actin to that of G actin, which suggests depolymerization of the filaments. These results suggest that the inhibitor fraction contains a protein which interacts with actin filaments and nuclei in a manner similar to that of cytochalasin B. It is possible that such a protein is involved in the control of cell motility by affecting assembly and disassembly of actin-containing microfilaments in vivo.

Actins↗
PubMed1980

Cytochalasins inhibit nuclei-induced actin polymerization by blocking filament elongation.

Polylysine was found to induce polymerization of muscle actin in a low ionic strength buffer containing 0.4 mM MgCl2. The rate of induced polymerization was dependent on the amount and on the molecular size of the polylysine added. A similar effect was obtained by adding actin nuclei (containing about 2-4 actin subunits) cross-linked by p-N,N'-phenylenebismaleimide to G-actin under the same conditions, suggesting that the effect of polylysine is due to promotion of the formation of actin nuclei. Polymerization induced by polylysine and by cross-linked actin nuclei was inhibited by low concentrations (10(-8)-10(-6)M) of cytochalasins. Binding experiments showed that actin filaments, but not actin monomers, contained high-affinity binding sites for [3H]cytochalasin B (one site per 600 actin monomers). The relative affinity of several cytochalasins for these sites (determined by competitive displacement of [3H]dihydrocytochalasin B) was: cytochalasin D greater than cytochalasin E approximately equal to dihydrocytochalasin B. The results of this study suggest that cytochalasins inhibit nuclei-induced actin polymerization by binding to highly specific sites at the point of monomer addition, i.e., the elongation site, in actin nuclei and filaments.

Actins↗
PubMed1980

The relationship between high-affinity binding of cytochalasin B to 3T3 cells and inhibition of sugar transport and cell motility.

Transport and motility inhibitors have been used to classify different types of high-affinity cytochalasin B (CB) binding sites in 3T3 cells. The potency of phloretin and phlorizin as inhibitors of sugar uptake paralleled their effectiveness in displacing high-affinity bound CB from the cells, indicating that the two compounds compete with CB for binding to sites associated with sugar transport proteins. On the other hand, cytochalasins D and E, which did not inhibit sugar uptake, inhibited binding of CB to a portion of the high-affinity sites, most probably those associated with actin-containing cytoskeletal-contractile structures. A small amount of high-affinity CB binding remained in the presence of both phloretin and cytochalasin E, indicating that the cells have a third class of sites which is not related to either sugar transport or cell motility, When isolated membranes were examined, it was found that a fraction of each class of high-affinity CB binding sites were associated with the fraction. In contrast, only sites sensitive to cytochalasin D were recovered in a soluble extract of the cells.

Animals↗
PubMed1979

Specific interaction of cytochalasins with muscle and platelet actin filaments in vitro.

The cytochalasins (CE, CD, CB and H2CB) inhibit numerous cellular processes which require the interaction of actin with other structural and contractile proteins. In this report we describe the effects of the cytochalasins on the viscosity and morphology of muscle and platelet actin. The cytochalasins decreased the viscosity of F-actin solutions. The effect of H2CB, CB and CD ON F-actin viscosity was maximal at concentrations of 20-50 micro M and did not increase with time. In contrast, CE caused a progressive decrease in the viscosity of F-actin solutions which was dependent upon the concentration of CE and the duration of incubation of the CE-actin mixture. After two hours of incubation of drug-actin mixtures, the relative effectiveness of the cytochalasins in reducing the viscosity of F-actin was CE greater than CD greater than CB=H2CB. The effects of CD and CE were paralleled by morphologic changes in negatively stained actin filaments. The effects of the cytochalasins on the viscosity and morphology of muscle and platelet actin were the same whether the drugs were added before or after the polymerization of the protein. These studies show that the interaction of the cytochalasins with actin is highly specific. Because the relative potencies of these drugs for affecting motile processes and the relative affinities of the drugs for binding sites within a variety of cells are CE greater than CD greater than CB=H2CB, the effects of cytochalasins on actin described here may contribute to some of the biological effects of the drugs on motile processes.

Actins↗
PubMed1979

7-Acetylcytochalasin B: differential effects on sugar transport and cell motility.

Cytochalasin B (CB) is a potent inhibitor of sugar transport and cell motility in animal cells. We have synthesized and characterized the CB derivative 7-acetylcytochalasin B (CBAc) and have found that it has differential effects on transport and motile processes in fibroblasts. The derivative inhibited sugar transport in human red cells, 3T3 cells, and chicken embryo fibroblasts at micromolar concentrations, although it was less potent than its parent compound. Unlike CB, which causes fibroblasts to round up and arborize at less than 10 microM, CBAc had no effect on fibroblast morphology and membrane ruffling at concentrations as high as 90 microM. Competitive binding experiments using [3H] CB showed that the affinity of CBAc for sites related to sugar transport in the red cell membrane is about one-fourth of that of CB. In contrast, similar experiments using [3H] dihydrocytochalasin B (a derivative which inhibits cell motility but not sugar transport) showed that the affinity of CBAc for sites associated with red cell spectrin and actin is only about 1/20 of that of dihydrocytochalasin B. This study demonstrates that acetylation of the C-7 hydroxyl group of CB reduces its effect on cell morphology and motility much more than its ability to inhibit sugar transport. This observation, together with our earlier work with dihydrocytochalasin B, establishes that the pharmacologic effects of CB on fibroblasts result from the binding of the drug to two distinct classes of receptors and that these receptors interact with different parts of the cytochalasin molecule.

Animals↗
PubMed1979

Actin polymerization induced by a motility-related high-affinity cytochalasin binding complex from human erythrocyte membrane.

A high molecular weight complex (sedimentation coefficient approximately 27 S) containing high-affinity binding site(s) for [(3)H]dihydrocytochalasin B has been isolated from a low ionic strength extract of human erythrocyte membranes by sucrose density gradient centrifugation. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis showed that actin, spectrin, and other minor components, including two polypeptides with the electrophoretic mobility of band 4.1, were present in the complex-containing fraction. Addition of this complex to a solution of muscle monomeric actin (G-actin) in a low ionic strength medium resulted in a rapid increase in viscosity to a level comparable to that of a solution of filamentous actin (F-actin). Electron microscopy showed that the viscosity increase reflected actin filament formation. The rate of induced actin polymerization was dependent on the amount of complex added to the G-actin; in less than 1 hr, less than 1 mug of protein from the complex-containing fraction induced the conversion of 0.4 mg of G-actin to the "F" from. Binding studies indicated that, upon polymerization of the actin, the cytochalasin binding complex became associated with the actin filaments. Low concentrations of cytochalasins D and E and dihydrocytochalasin B inhibited actin polymerization induced by the complex; the relative potencies of the drugs in inhibiting this process corresponded to their relative affinities for the complex, as well as their relative potencies in affecting cell motility. These results suggest that the cytochalasin binding complex functions as a regulatory site for cell motility by controlling formation and membrane attachment of actin-containing microfilaments in the cell.

Actins↗
PubMed1979

Inhibition of carboxypeptidase A catalyzed peptide hydrolysis by 3-phenylpropanoate at activating and nonactivating substrate concentrations.

The carboxypeptidase A catalyzed hydrolyses of five structurally related dipeptide substrates in the presence of the inhibitor 3-phenylpropanoate have been studied. At nonactivating substrate concentrations, 3-phenylpropanoate is a mixed inhibitor of carbobenzoxyglycyl-L-phenylalanine hydrolysis and a noncompetitive inhibitor of the hydrolyses of benzoylglycyl-L-phenylalanine, cinnamoylglycyl-L-phenylalanine, hydrocinnamoylglycyl-L-phenylalanine, and acetylglycyl-L-phenylalanine. When carbobenzoxyglycyl-L-phenylalanine and benzoylglycyl-L-phenylalanine exhibit substrate activation, inhibition by 3-phenylpropanoate is mixed but appears to be mostly competitive. Proposed here is a site for the binding of 3-phenylpropanoate along with a kinetic mechanism consistent with these data.

Carboxypeptidases↗
PubMed1978

Specificity of the effects of cytochalasin B on transport and motile processes.

The effects of cytochalasin B (CB) and dihydrocytochalasin B (H2CB) on a variety of transport and motile processes have been compared. CB inhibited transport of D-glucose and L-glucose but not transport of thymidine in human erythrocytes. In contrast, H2CB, which differs from CB by the absence of a single double bond, had little or no effect on any of these processes. Both cytochalasins, however, affected the morphology of cultured fibroblasts and inhibited motile processes such as membrane ruffling, axon growth cone activity, blood clot retraction, cytoplasmic streaming, photodinesis, and cytokinesis. Determination of the partition coefficient of the two cytochalasins in several organic solvent/phosphate-buffered saline systems showed that H2CB has a higher affinity for the hydrophobic phase than CB. These results indicate that the inhibitory effects of CB on sugar transport and on cell motility and morphology are separable and independent events, mediated by the binding of the drug to specific cellular receptors.

Axons↗
PubMed1978

Dihydrocytochalasin B. Biological effects and binding to 3T3 cells.

Dihydrocytochalasin B (H2CB) does not inhibit sugar uptake in BALB/c 3T3 cells. Excess H2CB does not affect inhibition of sugar uptake by cytochalasin B (CB), indicating that it does not compete with CB for binding to high-affinity sites. As in the case of CB, H2CB inhibits cytokinesis and changes the morphology of the cells. These results demonstrate that the effects of CB on sugar transport and on cell motility and morphology involve separate and independent sites. Comparison of the effects of H2CB, CB, and cytochalasin D (CD) indicates that treatment of cells with any one of the compounds results in the same series of morphological changes; the cells undergo zeiosis and elongation at 2-4 microM CB and become arborized and rounded up at 10-50 microM CB. H2CB is slightly less potent than CB, whereas CD is five to eight times more potent than CB in causing a given state of morphological change. These results indicate that the cytochalasin-induced changes in cell morphology are mediated by a specific site(s) which can distinguish the subtle differences in the structures of the three compounds. Competitive binding studies indicate that excess H2CB displaces essentially all of the high-affinity bound [3H]CB, but, at less than 5 x 10(-5) M H2CB is not so efficient as unlabeled CB in the displacement reaction. In contrast, excess CD displaces up to 40% of the bound [3H]CB. These results suggest that three different classes of high-affinity CB binding sites exist in 3T3 cells: sites related to sugar transport, sites related to cell motility and morphology, and sites with undetermined function.

3T3 Cells↗