Cytochalasins block actin filament elongation by binding to high affinity sites associated with F-actin

We have found that addition of a small amount of filamentous muscle actin (F-actin) to a solution of globular actin (G-actin) in a low ionic strength medium resulted in rapid polymerization of the G-actin. This reaction was inhibited by substoichiometric levels of cytochalasins (relative potency: cytochalasin D greater than cytochalasin E approximately equal to cytochalasin B greater than dihydrocytochalasin B). Binding experiments show that F-actin, but not G-actin, contains high affinity binding sites for [3H]cytochalasin B; the number of sites detected was on the order of about one per actin filament (one site/500 actin monomers). This number remained unchanged when the actin (prepared by polymerization-depolymerization cycles) was further purified by ion exchange and gel filtration chromatography. Competitive displacement experiments showed that the relative affinity of several cytochalasins for these sites corresponds to their relative effectiveness in inhibiting actin polymerization induced by F-actin. These results suggest that actin filaments can accelerate the rate of polymerization of G-actin in low ionic strength medium by providing sites onto which actin monomers can be added, and that cytochalasins inhibit actin filament elongation by binding to high affinity sites located at the polymerization end of the filaments.

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.

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.

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.

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.

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.

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.

The mechanism of action of diphenylhydantoin or invertebrate neurons. I. Effects on basic membrane properties

The effect of diphenylhydantoin (DPH) has been studied on certain membrane properties of the crayfish stretch receptor neuron (SRN) and of neurons in the abdominal and buccal ganglia of Aplysia. DPH decreases the amplitude of post-tetanic hyperpolarization of the SRN, which is thought to be an expression of the electrogenic pump, and does not antagonize the effect of ouabain on this activity. DPH decreases the membrane resistance of all the different types of neurons studied, with little or no change in the resting membrane potential. It decreases the overshoot of the action potential in some of the neurons studied and prolongs the falling phase and the undershoot in other neurons. DPH also decreases repetitive firing. These effects have also been observed at different external concentrations of potassium. It is concluded that DPH, in the different preparations studied, does not have any effect on or decreases the electrogenic pump, but produces changes in other membrane properties which are consistent with its anticonvulsant action.

The mechanism of action of diphenylhydantoin on invertebrate neurons. II. Effects on synaptic mechanisms

The effect of diphenylhydantoin (DPH) on certain synapses of neurons in the abdominal ganglion of Aplysia and on the gamma-aminobutyric acid (GABA) mediated inhibitory synapse of the crayfish stretch receptor neuron (SRN) has been studied. DPH decreases the amplitude of the excitatory postsynaptic potential, but is ineffective on the "short" ACh mediated, Cl- dependent, inhibitory postsynaptic potential (IPSP) in Aplysia. However, it facilitates the "long" ACh mediated, K+ dependent, IPSP, in this same group of neurons. DHP has a profound effect on the GABA mediated, Cl- dependent, inhibitory synapse of the SRN. The time course of the IPSP is prolonged up to 10 times control values, due to an increased and prolonged postsynaptic conductance. Similar results have been obtained in the SRN with iontophoretic application of GABA. This selective effect of DPH on synaptic mechanisms, especially in view of the role of GABA and ACh as putative transmitters in the mammalian nervous system, may play an important role for the anticonvulsant action of DPH.

Development and use of analytical systems based on mass spectrometry

Contemporary analytical systems based on mass spectrometry include as components a gas chromatograph, a mass spectrometer, and a computer. The form of operation is usually in electron impact ionization mode for identification and structural studies, and in chemical ionization mode for quantitative analyses. Important stages in the development of these systems included the design of "molecule separators" for the concentration of solutes in the gas phase, the use of mass spectrometers as specific ion detectors, the introduction of chemical ionization techniques, and the development of computer-based operation, data acquisition, and data analysis capabilities. A current line of investigation is concerned with the design and use of systems based on atmospheric pressure ionization. Samples are ionized in a small reaction chamber external to the low-pressure region of a quadrupole mass analyzer. The primary source of electrons is a 63Ni foil or a corona discharge. The ionization process leading to positive ions involves a sequence of ion molecule reactions, usually electrons leads to carrier gas ions leads to reagent ions leads to sample component ions. Negative ions may be formed by direct electron attachment, or by ion molecule reactions that include new types of elimination reactions. The source will accept a variety of gases and solvents. The sample may be introduced in the gas phase without solvents, by probe injection, or in the effluent stream from a gas chromatograph. Samples may be introduced in the liquid phase in solvents by injection after the fashion of gas chromatography or in the effluent stream from a high-performance liquid chromatograph. The novel aspects of atmospheric pressure ionization mass spectrometry lie in its versatility and high sensitivity of detection. Few clinical chemistry laboratories now use these systems. Significant future uses are likely to be in analytical work involving therapeutic drug monitoring and studies of drug metabolism, and in analyses for environmental biohazards including pesticides, herbicides, polyhalobiphenyls, dibenzodioxins, and other toxic compounds.

Development and use of analytical systems based on mass spectrometry

Contemporary analytical systems based on mass spectrometry include as components a gas chromatograph, a mass spectrometer, and a computer. The form of operation is usually in electron impact ionization mode for identification and structural studies, and in chemical ionization mode for quantitative analyses. Important stages in the development of these systems included the design of "molecule separators" for the concentration of solutes in the gas phase, the use of mass spectrometers as specific ion detectors, the introduction of chemical ionization techniques, and the development of computer-based operation, data acquisition, and data analysis capabilities. A current line of investigation is concerned with the design and use of systems based on atmospheric pressure ionization. Samples are ionized in a small reaction chamber external to the low-pressure region of a quadrupole mass analyzer. The primary source of electrons is a 63Ni foil or a corona discharge. The ionization process leading to positive ions involves a sequence of ion molecule reactions, usually electrons leads to carrier gas ions leads to reagent ions leads to sample component ions. Negative ions may be formed by direct electron attachment, or by ion molecule reactions that include new types of elimination reactions. The source will accept a variety of gases and solvents. The sample may be introduced in the gas phase without solvents, by probe injection, or in the effluent stream from a gas chromatograph. Samples may be introduced in the liquid phase in solvents by injection after the fashion of gas chromatography or in the effluent stream from a high-performance liquid chromatograph. The novel aspects of atmospheric pressure ionization mass spectrometry lie in its versatility and high sensitivity of detection. Few clinical chemistry laboratories now use these systems. Significant future uses are likely to be in analytical work involving therapeutic drug monitoring and studies of drug metabolism, and in analyses for environmental biohazards including pesticides, herbicides, polyhalobiphenyls, dibenzodioxins, and other toxic compounds.

High-affinity cytochalasin B binding to normal and transformed BALB/3T3 cells

To study the molecular basis of changes in sugar uptake rate in cultured mouse fibroblasts with different physiological states, we have measured the high affinity binding of [3H] cytochalsin B, a potent sugar transport inhibitor, to actively growing and contact inhibited Balb/3T3 cells as well as to 3T12 and SV3T3 cells. Binding was the same whether the cells were detached from dishes with EDTA or trypsin. The amount of drug bound to intact cells measured with a centrifugation assay was essentially the same as that bound to cell sonicates measured with equilibrium dialysis. Cytochalasin B binding to intact cells was extremely rapid and reversible over a wide range of drug concentrations, and was not affected by 0.1 M D--glucose in the assay medium. Actively growing and contact inhibited 3T3 cells had a similar number of high affinity cytochalasin B binding sites per cell, while 3T12 and SV3T3 cells had one third to one fourth the number of sites per cell. However, the number of sites per mug cellular protein appeared to be similar for cells in all of the physiological states examined.

Histones bind more tightly to bromodeoxyuridine-substituted DNA than to normal DNA

Using a membrane filter assay, we have obtained results from both kinetic and competition experiments indicating that histones bind more strongly to bromodeoxyuridine-substituted DNA than to normal DNA. At 37 degrees C in our standard buffer of 0.2 M ionic strength, the rate of dissociation of histones H1, H2, and h4 from BrdU-substituted DNA is respectively 7, 4, and 2 times slower than it is from normal DNA. Competition experiments show an even greater difference between BrdU-substituted and normal DNA with respect to histone binding. The tighter binding of histones to BrdU-substituted DNA is of interest because of the known effects of BrdU on eukaryotic chromosome condensation and staining, virus induction, and the inhibition of differentiation.

High resolution scanning electron microscopy at the subcellular level

Recently developed scanning electron microscopes provide sufficient resolution to allow useful observation of subcellular biological objects. Preparation methods for such objects need not be limited to the traditional coating and mounting procedures. Many methods developed for transmission electron microscopy are immediately adaptable to scanning electron microscopy. We show that a number of techniques are available to the microscopist which yield adequate contrast and high resolution. As examples we show skeletal muscle myofibrils dispersed to reveal thick filaments, uncoated on a thin carbon film; a tropomyosin tactoid, negatively stained with uranyl acetate; oncornavirus, conventionally coated; and T4 bacteriophage on an aluminium substrate.

The general affinity of lac repressor for E. coli DNA: implications for gene regulation in procaryotes and eucaryotes

By equilibrium competition experiments, the dissociation constant (K(RD)) of lac repressor for E. coli DNA carrying a deletion of the lac operon was measured at a variety of salt concentrations. These data are used in the consideration of several aspects of protein-DNA interaction: Quantitative estimates of specificity are made. Specificity changes only slightly with salt concentration. We calculate that in vivo, 98 percent or more of repressor is bound to DNA predominately at sites other than the lac operator. Inducers shift repressor from operator to nonoperator DNA, but do not free it from DNA. The general affinity of repressor for E. coli DNA is sufficient to support a model where repressor slides along DNA for significant distances. The effective dissociation constant of repressor for operator (K(eff)) is very sensitive to the total DNA concentration. We propose that "junk" DNA in eucaryotes functions to maintain total DNA at an optimum concentration. We consider the lac operon in the nucleus of a lymphocyte, point out that severe difficulties would be encountered, and suggest possible solutions.

Bacteriological assessment of Spoon River water quality

Data from a study of five stations on the Spoon River, Ill., during June 1971 through May 1973 were analyzed for compliance with Illinois Pollution Control Board's water quality standards of a geometric mean limitation of 200 fecal coliforms per 100 ml. This bacterial limit was achieved about 20% of the time during June 1971 through May 1972, and was never achieved during June 1972 through May 1973. Ratios of fecal coliform to total coliform are presented. By using fecal coliform-to-fecal streptococcus ratios to sort out fecal pollution origins, it was evident that a concern must be expressed not only for municipal wastewater effluents to the receiving stream, but also for nonpoint sources of pollution in assessing the bacterial quality of a stream.

Lac repressor binding to synthetic DNAs of defined nucleotide sequence

Binding of lac repressor to 20 synthetic DNAs of high molecular weight with defined repeating sequences was investigated by competition experiments. Although none of these DNAs binds repressor as tightly as does lac operator, most do bind to a measurable extent. Their affinity for repressor varies greatly and is a function of both nucleotide composition and sequence. Poly(dC-dC).poly(dG-dC) competes for repressor 200-times less well than either poly(dA-dT).poly(dA-dT) or poly(dT-dT-dG).poly(dC-dA-dA). The other DNAs show a broad spectrum of affinities for repressor between these extremes. These results show that the lac repressor has affinity for, and can distinguish between, sequences distantly related to its operator.

Cytochalasin B, its interaction with actin and actomyosin from muscle (cell movement-microfilaments-rabbit striated muscle)

Cytochalasin B, an alkaloid that inhibits a wide variety of cellular movements, interacts with actomyosin, the contractile protein complex of striated muscle. This interaction causes a decrease in viscosity of the actomyosin complex and an inhibition of acto-heavy meromyosin ATPase activity of at least 60%. Cytochalasin B does not affect the viscosity of myosin nor the ATPase activity of heavy meromyosin, suggesting that the drug might interact directly with the actin moiety of the actomyosin complex. Indeed, as judged by viscometry, there is a strong interaction of cytochalasin B with actin, at nearly stoichiometric concentrations. Myosin appears to compete with cytochalasin for binding to actin.