Inhibition of DNA synthesis in adrenocortical cells by cytochalasin B

ACTH inhibits DNA synthesis in normal rat and mouse tumor Y-1 adrenocortical cells within the same concentration range that it stimulates steroidogenesis. These processes can be independently regulated as demonstrated by the divergent actions of cytochalasin B on these cells. In the normal cells, cytochalasin B does not increase steroidogenesis in serum-free or serum-containing media, and it decreases the stimulation produced by ACTH. In the absence of serum, the Y-1 cells respond in a similar way. However, in serum-containing media, cytochalasin B increases steroidogenesis in these cells and does not inhibit the response to ACTH. In both cell types, cytochalasin B inhibits [3H]thymidine incorporation into DNA by a mechanism different than that of ACTH. In the Y-1 cells, this inhibition is caused by a decreased uptake of [3H]thymidine into the cell, which probably reflects a decreased transport across the cell membrane. In the normal cells, cytochalasin B, like ACTH, does not affect [3H]thymidine transport, but it decreases DNA synthesis much more rapidly than does ACTH. This inhibition may be the result of the disruption of microfilaments by cytochalasinB, because our evidence indicates that it is not caused by a decrease in glucose uptake by the cells.     

Analysis of hexose transport in untransformed and sarcoma virus-transformed mouse 3T3 cells by photoaffinity binding of cytochalasin B

The effect of simian virus 40 transformation on the hexose transport system in mouse embryo fibroblast Swiss 3T3 cells was examined. The concentration of hexose transporters was estimated by measuring D-glucose-inhibitable cytochalasin B binding. The binding of cytochalasin B to the plasma membranes of simian virus 40-transformed mouse 3T3 cells (SV3T3 cells) was significantly greater than that of 3T3 cells. On the other hand, cytochalasin B binding to the microsomal membranes of SV3T3 cells was decreased, and the total amount of binding to plasma and microsomal membranes was not significantly changed in both cell lines. The electrophoretic analysis demonstrated that both hexose-transporter components of Mr 46 000 and Mr 58 000 affinity labeled were responsible for an increase in the hexose transport by viral transformation. These results suggested that the higher hexose-transport activity of transformed cells is caused by a redistribution of transporter from intracellular membranes to plasma membranes.     

Variants of asynchronous DNA synthesis and mitoses in multinucleate cells induced by cytochalasin B

Cases of asynchronous progression with separate nuclei of S-period and initial mitotic stages in multinucleate cells were discovered in Chinese hamster cell cultures during a prolonged action of cytochalasin B (7 days) and after its stopping (7 days of cell cultivation without drug). The interphase asynchrony under experimental conditions vary in value corresponding to the level of interphase asynchrony in spontaneous multinucleate cells in control cultures. So, the interphase asynchrony in cytochalasin B-induced multinucleate cells is suggested not to be connected with the drug action. Fusion of heterophase cells and a high level of proliferation activity of multinucleate cells seem to be the main reason of interphase asynchrony both in control cultures and in experimental conditions. Unlike the interphase asynchrony, the appearance of the mitotic asynchrony in multinucleate cells is shown to be connected with the action of cytochalasin B. The high level of the mitotic asynchrony remains after the stopping of drug action. A conclusion is made that mitotic asynchrony of nuclei, along with multipolar mitosis and cytokinesis inhibition, is one more display of the cytotoxic action of cytochalasin B on mitosis.     

The stimulation of DNA synthesis by cytochalasin B in proliferative epidermal and dermal cells

Cytochalasin B influences a variety of cellular events that are associated with the contractile microfilament system and the formation of binucleate cells. Along with the formation of binucleate cells, cytochalasin B also causes an acceleration of cells from G1 to S in the cell cycle. By pulsing the cytochalasin B for 30 minutes and allowing for a previously established lag time (17.5 hours) a stimulation of thymidine incorporation into DNA of proliferative epidermal and dermal cells was found in both control and stripped epidermis. Autoradiographic analysis confirmed that the stimulation was due to an increased number of basal cells accelerated from G1 to S phase. A minimal number of binucleate basal cells, 1 in 300, was observed, which suggests that the stimulated synthesis is independent of binucleate cell formation. The amount of stimulation is maximum with cytochalasin B concentration pulse between 5gamma and 30gamma/ml. The results suggest a possible link in coupling cell membrane and surface events with subsequent increased cell nuclei synthetic activity.     

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.     

Regulation of DNA synthesis in cytochalasin B (CB)-induced binucleate HeLa cells

The effects of timing and duration of cytochalasin B (CB) treatment on the kinetics of the initiation of DNA synthesis in mono- and binucleate HeLa cells, synchronized in the G1 phase of the cell cycle by the reversal of a mitotic block (N₂O at 80 PSI), were studied. In the control, bi-, tri- and tetranucleate cells entered S phase slightly earlier than the mononucleate cells at a rate proportional to the number of their nuclei. The difference between any two adjacent sub-populations was less than 0.5 h. However, the binucleate cells produced by a 90 min CB treatment immediately after the reversal of the mitotic block exhibited a considerably shorter G1 period as compared to mononucleate cells (a difference of 1.5 h). This exaggerated difference in the duration of G1 period between mono- and binucleate cells disappeared when the CB treatment was delayed by 75 or 90 min indicating that it was an experimental artifact. From this study, we conclude that there is naturally some degree of nuclear cooperation in the multinucleate systems, particularly with regard to the initiation of DNA synthesis, which is not influenced by CB treatment.     

Dissociation of uridine and (86Rb+) uptake from stimulation of DNA synthesis in Swiss 3T3 cells

The importance of the stimulation of uridine and (⁸⁶Rb⁺) uptake to the stimulation of DNA synthesis was investigated using three defined growth factors, EGF,FGF and PGF_2α′ and three hormones, hydrocortisone, insulin and PGE_1′, which do not stimulate proliferation of Swiss 3T3 cells but modify the response to these growth factors. Uridine uptake is stimulated by insulin, but not by PGF_2α′ indicating that its activation is neither sufficient nor necessary for stimulation of cell proliferation. (⁸⁶Rb⁺) uptake was stimulated by each growth factor tested, but also by insulin and PGE₁. Modifying effects of insulin, hydrocortisone or PGE₁ in combination with growth factors on the level of DNA synthesis were not reflected in changes in stimulation of these uptake systems. We conclude that these events are regulated separately and are not tightly coupled to the initiation of DNA synthesis.     

Initiation of DNA synthesis in quiescent Swiss 3T3 and 3T6 cells by lanthanum

La³⁺ stimulated quiescent Swiss 3T3 and 3T6 ceils to enter the DNA-synthesizing S phase of the cell cycle. La³⁺ and insulin interacted synergistically to increase DNA synthesis. A brief exposure of the cells to soluble LaCl₃ optimally stimulated entry into S. La³⁺ was similar to Al³⁺ in its mitogenic properties (J. Cell. Physiol.118 , 298, 1984), but La³⁺ was 10 times more potent than Al³⁺.     

Dihydrocytochalasin B disorganizes actin cytoarchitecture and inhibits initiation of DNA synthesis in 3T3 cells

Dihydrocytochalasin B (H2CB) disrupts the actin structure of Swiss/3T3 mouse fibroblasts and inhibits the ability of serum growth factors to stimulate DNA synthesis in quiescent cultures. Low doses of H2CB (2-10 X 10(-7) M) added to serum-arrested cells reversibly block initiation of DNA synthesis by serum; by epidermal growth factor and insulin; or by epidermal growth factor, fibroblast growth factor and insulin. H2CB is effective only when added to cells within 8-10 hr after stimulation. Low doses of H2CB cause cell rounding and a loss of actin microfilament bundles, but they do not interfere with glucose or thymidine transport. These results suggest that stimulation of 3T3 cells involves at least one obligatory actin-mediated step. Transformed cells appear to obviate this step, for H2CB does not inhibit the entry into S phase of SV40-transformed or Moloney murine sarcoma virus-transformed 3T3 cells synchronized by mitotic shake-off.     

Dissociation of tumour-promoter-induced effects on prostaglandin release, polyamine synthesis and cell proliferation of 3T3 cells.

The phorbol ester 12-O-tetradecanoylphorbol 13-acetate induces tumour promotion, inflammation, cell proliferation and prostaglandin release. Recent reports suggest that the prostaglandins released by 12-O-tetradecanoylphorbol 13-acetate (TPA) initiate a cascade of events leading to polyamine synthesis and cell proliferation. In experiments designed to test this contention, it was found that addition of TPA (1 microM to 1 nM) to confluent mouse 3T3 fibroblasts successively caused the release of prostaglandins E2 and I2, induction of the enzyme ornithine decarboxylase (EC 4.1.1.17), stimulation of [3H]thymidine incorporation into DNA, and cell proliferation. Pretreatment of the cells with the anti-inflammatory steroid dexamethasone (1 microM) or the non-steroidal anti-inflammatory drug indomethacin (1 microM) inhibited TPA-induced prostaglandin release. However, dexamethasone enhanced the other effects of TPA, whereas indomethacin was ineffective. Addition of prostaglandin E2 to the cultures did not induce ornithine decarboxylase activity and cell proliferation. Pretreatment of the cells with 1,3-diaminopropane (1 mM) or alpha-methylornithine (5 mM), inhibitors of polyamine synthesis, decreased TPA-induced ornithine decarboxylase activity without affecting DNA synthesis. TPA stimulated [3H]thymidine incorporation into DNA, even when the ornithine decarboxylase activity was completely blocked. These data suggest that the proliferative effect of TPA on 3T3 cells is independent of prostaglandin release and polyamine synthesis.     

Effect of cytochalasin D on DNA synthesis in cultured cells

The effect of cytochalasin D (CD), an agent specifically destroying actin cytoskeleton, on DNA replication of cultured mouse embryonic fibroblasts (MEF) and BALB/3T3 strain cells was studied. Incubation of normal cells with CD resulted in progressive inhibition of DNA synthesis: in the first 16-20 h the percentage of cells pulse-labelled with 3H-thymidine was similar to that in control cultures, on day 8 the percentage of labelled cells was 7-8 times lower than in the control. The transfer of cells into fresh medium upon 8-day incubation in the presence of CD resulted in the recovery of DNA synthesis. Similar curves of DNA synthesis inhibition in the presence of CD and of DNA synthesis recovery in fresh medium were observed both in mononuclear and binuclear cells. Thus, CD-induced reorganization of actin cytoskeleton can have an abrupt but reversible disturbing effect on normal cell cycle.     

Evaluation of proximity inhibition of DNA synthesis in 3T3 cells.

A microphotometric technique that displays rapid length changes of Spirostomum has been used to follow the variation with temperature of three kinetic parameters of myonemal contraction: contraction rate, relaxation rate and stimulus duration at threshold. In each case the exponential form of the relationship indicated that the gross rate constant might be equated with the limiting rate constant, k, of a driving chemical reaction, and from standard expressions of chemical kinetics the change in activation free energy appropriate to this reaction has been computed. The thermal dependence of contraction is described by an activation enthalpy (ΔLH?) of 21.7 kcal mol^?1, and the activation entropy (ΔLS?) of 26.8 e.u. is consistent with a model of contraction requiring neutralization of fixed myonemal charges by divalent cations. The analysis of thermal dependence of relaxation gives a negative activation entropy, a result predicted for a rate-limiting reaction involving dissociation of a neutral molecule. On the other hand, values of ΔLS? and ΔLH? for relaxation fall close to an isokinetic correlation drawn in the literature from analysis of the thermal dependence of ciliary beat frequency in different organisms, and for which breakdown of an ATP-ATPase complex could be the common rate-limiting reaction. ΔLS? for stimulus duration suggests that the rate-limiting step in excitation-contraction coupling is a reaction between ions of like charge, or ion pair formation from a neutral molecule.     

Stimulation by amphotericin B of uridine transport, RNA synthesis and DNA synthesis in density-inhibited fibroblasts

Nine new colchicine-resistant, three vinblastine-resistant, two colchicine-sensitive and one colchicine-dependent mutant of Chlamydomonas reinhardii have been isolated. Some of the mutants have abnormal cell morphology in the absence of the drug. Some of the mutants have altered levels of resistance to puromycin and to caffeine, which may indicate that their phenotypes involve a non-specific permeability change. However, uptake of labelled colchicine is indistin-guishable from wild type in all of these mutants except two. The discrepancy between these two results is discussed. All the resistant mutants except one behave as if they have a single gene defect in crosses to wild type, although zygote germination is consistently very poor. Strains carrying certain pairs of resistance mutations are much more resistant than those carrying single mutations indicating that gene effects are additive. Recombination frequencies between some genes have been measured. The colchicine-sensitive mutations are thought not to be cell wall deficient mutations because of their appearance in the electron microscope, growth on low agar concentrations and their colony morphology. The colchicine-dependent strain had a very low viability even in the presence of optimal concentrations of colchicine.     

Dissociation of histone and DNA synthesis in x-irradiated HeLa cells

Although histone synthesis and DNA synthesis are normally very well coordinated in HeLa cells, their histone synthesis proved relatively resistant to inhibition by ionizing radiation. During the first 24 h after 1 000 R the rate of cellular DNA synthesis progressively fell to small fractions of control values while histone synthesis continued with much less relative reduction. Acrylamide gel electropherograms of the acid soluble nuclear histones synthesized by irradiated HeLa cells were qualitatively normal.     

Synergistic stimulation of DNA synthesis by bradykinin and vasopressin in swiss 3T3 cells

Vasopressin and bradykinin bind to receptors coupled to GTP-binding proteins and rapidly induce polyphosphoinositide breakdown leading to Ca²⁺ mobilization and activation of protein kinase C. Both peptides are known to induce mitogenesis in the presence of growth factors that act through receptors with intrinsic tyrosine kinase activity. Surprisingly, addition of a combination of vaso-pressin and bradykinin to Swiss 3T3 cells synergistically stimulates DNA synthesis in the absence of any other growth factors. This effect is induced at nanomolar concentrations of the peptides and could be inhibited by addition of specific receptor antagonists or broad spectrum neuropeptide antagonists. Bradykinin, which stimulates transient activation of protein kinase C, induces DNA synthesis in synergy with substances that cause long-term activation of protein kinase C, like vasopression or phorbol 12, 13-dibutyrate. Down-regulation of protein kinase C inhibited the induction of mitogenesis by the combination of vasopressin and bradykinin, thus demonstrating the importance of long-term activation of this enzyme for DNA synthesis. Analysis of tyrosine phosphorylated proteins of M_r = 110,000–130,000 and M_r = 70,000–80,000 revealed a biphasic response after stimulation with bradykinin, whereas the response induced by vasopressin declined after the initial maximum. The combination of bradykinin with vasopressin caused an enhanced and prolonged increase in tyrosine phosphorylation of these proteins as compared with the individual peptides. Inhibition of tyrosine phosphorylation by tyrphostin was paralleled by inhibition of DNA synthesis. Together, these results demonstrate synergistic stimulation of DNA synthesis by bradykinin and vasopressin via prolonged stimulation of multiple signaling pathways and imply that the interactive effects of Ca²⁺ -mobilizing peptides on mitogenesis may be more general than previously thought. © 1994 Wiley-Liss, Inc.     

Effect of dihydrocytochalasin B on the induction of DNA synthesis by epidermal growth factor, insulin and serum in Swiss 3T3 cells

The addition of a microfilament-disorganizing agent--dihydrocytochalasin B B (5-10 micrograms/ml)--to to quiescent confluent or sparse (in 0.5% serum) Swiss 3T3 cells, 1-2 hours prior to stimulation, inhibited the initiation of DNA synthesis induced by an epidermal growth factor (7.5-10 ng/ml) and insulin (0.5-1.0 micrograms/ml), but exerted a low effect on serum stimulation. DNA synthesis was measured 21-23 hours after the growth factor administration by 14C-thymidine incorporation in acid-insoluble material and the ratio of this fraction to exogenous thymidine uptake. Moreover, the polar solvent dimethylsulfoxide, present in culture medium at low concentration (0.1-0.5%), also caused a decrease in the basal level of 14C-thymidine incorporation in resting cells, and a less decrease in the induced incorporation.     

Endocytosis in Chang liver cells. Quantitation by sucrose- 3 H uptake and inhibition by cytochalasin B

The addition of 0.08 M sucrose to a culture medium containing Chang-strain human liver cells causes intense cytoplasmic vacuolation. Electron microscopy of these cells grown inferritin, time-lapse cinematography, and radioautography reveal that the vacuoles arise by endocytosis and that the sucrose is taken into the cell and localized in the vacuoles. Tracer studies demonstrate that sucrose-³H provides a marker for quantitation of endocytosis and that it neither induces nor stimulates endocytosis. Electron micrographs of vacuolated liver cells show microfilaments in close proximity to the inside of the plasma membrane, in the pseudopodia, and to the cytoplasmic side of the membrane surrounding endocytosis vacuoles. Cytochalasin B (CB), a mold metabolite that inhibits various types of cell motility, has a dose-dependent inhibitory effect on the uptake of sucrose-³H by these cells. This inhibition is accompanied by a cessation of the movement of ruffles and pseudopodia on the surface of the cells and the formation of blebs which arise from the cell''s surface. These morphological changes are quickly reversible upon removal of CB. Alterations in the appearance and location of microfilaments are also observed in CB-treated cells.