[Cytochalasin B (phomin): degradation reactions and cyclization of B-cytochalasinic acid to 21,22-dihydro-isocytochalasin A (author's transl)].
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Cyclization↗
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Reversible inhibition of the motility of human spermatozoa by cytochalasin B.
Cytochalasin B inhibits the motility and metabolism of washed human spermatozoa at low concentrations (20 to 200 mum). Spermatozoal motility (primarily the frequency of flagellar contraction) declines slowly after addition of the antibiotic but is not abolished even after treatment for several hours. The addition of caffeine or dibutyrylcyclic adenosine 3' :5'-monophosphate to washed sperm suspensions increases the percentage of motile cells, the frequency of flagellar contraction, and the rate of glycolysis. These effects are blocked by cytochalasin B. However, cytochalasin B-treated spermatozoa regain their responsiveness to these agents when the antibiotic is washed out of supporting media. These effects are discussed in terms of an interaction of cytochalasin B with the sperm plasma membrane.
Bucladesine↗
Prostaglandin production by methylcholanthrene-transformed mouse BALB/3T3: inhibition by cytochalasin B.
Cytochalasin B inhibits the production of prostaglandins by serum-, thrombin-, and bradykinin-stimulated MC5-5 cells. The serum-stimulated release of arachidonic acid from cellular phospholipids also is inhibited. Cytochalasin B does not affect the cells' prostaglandin synthetase activity when exogenous arachidonic acid is present. Deacylation of phospholipids may be the step affected by cytochalasin B possibly as a result of disruption of microfilament organization. Colchicine and vinblastine, two drugs that can disrupt microtubule organization, do not inhibit prostaglandin production by cells.
Animals↗
The binding sites of cytochalasin D. II. Their relationship to hexose transport and to cytochalasin B.
Cytochalasin B (CB) was able to compete with tritiated cytochalasin D (3H-CD) for binding sites in HEp-2 cells. The pattern of inhibition suggested that CB associates with a low affinity class of CD binding sites. Glucose and maltose did not inhibit binding of 3H-CD to isolated HEp-2 plasma membrane. Inhibition of hexose transport by CD was negligible, but CD did not block the potent inhibition of this transport by CB. These results indicate that CD does not bind to the high affinity CB receptor reportedly associated with the hexose transport system, and that this receptor cannot mediate the morphological effects of CD. Both CD and CB induced contraction-zeoisis in HEp-2 cells; CB was less potent than CD, and their effects appeared to be additive. It was concluded that the high affinity binding sites for CD and CB are different, but that these congeners share a low affinity site. Both high and low affinity sites for CD appear to mediate its morphological effects; only the low affinity class appears to be involved for CB. Possible identification of the common low affinity binding site as actomyosin (detailed in Tannenbaum et al., '77) is further discussed.
Binding Sites↗
Inhibition of antigen-induced B lymphocyte activation in vitro by cytochalasin B.
Cytochalasin B (CB), a fungal metabolite which disrupts microfilaments. and will inhibit capping and other events requiring membrane movement, suppressed the production of antibody-forming cells (AFC) in both mouse whole spleen cultures immunized with sheep erythrocytes (SRBC) and in mouse B lymphocyte cultures immunized with the thymic independent antigen DNP-Ficoll (DF). CB at a concentration of 1 mug/ml inhibited the AFC response by more than 90% in spleen cell cultures immunized with SRBC. This inhibition was completely reversible by removal of CB up to 24 hr after the start of culture. Spleen cells cultured in the presence of CB for the first 48 to 72 hr had a decreased AFC response similar to that of cultures in which SRBC had been withheld for thocyte the same period of time. Incubating whole spleen cell or B lymphocyte cultures immunized with DF for as short as 6 hr decreased the AFC response more than 60%. Antibody secretion, cell viability, and antigenicity of the SRBC and DF were not affected by CB. The results of these experiments favor the concept that movement of surface receptors is necessary in activating lymphocytes to differentiate into AFC. The differential response to CB observed in SRBC and DF stimulated cultures makes the technique employed a useful tool to study membrane events occuring between antigen interaction with surface receptor and the initiation of differentiative events.
Animals↗
Differential response of cultured mammalian cells to cytochalasin B in multinucleation.
Cytochalasin B (CB) was applied to 13 kinds of non-tumorigenic or tumorigenic cells in vitro to investigate whether the drug would be applicable as an indicator to identify the transformation of cells. Normal cell strains suffered from more deteriorative changes in morphology than cell lines, showing arborization of their cytoplasm at 5 mug/ml. CB at 2.5 mug/ml consistently prevented cytoplasmic cleavage without interfering with nuclear division. Multinucleation of the cells exposed to CB was not related to their generation time. The correlation between multinucleation and tumorigenicity of the cells was found with some exceptions. It appears, however, that multinucleation induced by CB would not be a reliable parameter for identifying malignant transformation of cells in vitro.
Animals↗
Response of adrenal tumor cells to adrenocorticotropin: site of inhibition by cytochalasin B.
The ability of cytochalasin B to inhibit the steroidogenic response of mouse adrenal tumor cells (Y-1) to adrenocorticotropin (ACTH) was examined with two aims: to consider the specificity of the inhibitor and to determine at what point(s) in the steroidogenic pathway it acts. Cytochalasin B did not inhibit protein synthesis or transport of [3H]-cholesterol into the cells nor did it alter total cell concentration of ATP. Together with previous evidence, this suggests that the effects of cytochalasin observed are relatively specific in these cells. Cytochalasin inhibits the increase in conversion of [3H]cholesterol to 20alpha-[3H]dihydroprogesterone (20alpha-hydroxypregn-4-en-3-one: a major product of the steroid pathway in Y-1 cells) produced by ACTH but does not inhibit conversion of cholesterol to pregnenolone by mitochondrial and purified enzyme preparations from Y-1 cells and bovine adrenal, respectively. Cytochalasin does not inhibit the conversion of pregnenolone to 20alpha-dihydroprogesterone but was shown to inhibit increased transport of [3H]cholesterol to mitochondria resulting from the action of ACTH. These findings indicate that cytochalasin acts after cholesterol has entered the cells and before it is subjected to side-chain cleavage in mitochondria. In view of the known action of cytochalasin on microfilaments, it is proposed that these organelles are necessary for the transport of cholesterol to the mitochondrial cleavage enzyme and that at least one effect of ACTH (and cyclic AMP) is exerted upon this transport process. The specificity of the effects of cytochalasin is considered in relation to this conclusion.
20-alpha-Dihydroprogesterone↗
Human T-lymphocyte rosette formation: inhibition by cytochalasin B.
The effects of cytochalasin B, colchicine and vinblastine on the rosette formation of human T lymphocytes with neuraminidase-treated human erythrocytes (nHRBC) and with sheep red blood cells (SRBC) have been studied. Pretreatment of the lymphocytes with cytochalasin B which affects microfilament action reversibly inhibits both nHRBC and SRBC rosette formation. Colchicine and vinblastine known to interact with microtubules causes no major reduction in rosette-forming cells. The results suggest that normally functioning microfilaments are necessary for nHRBC and SRBC rosetting, whereas microtubules are not essential for the blinding of the erythrocytes to the lymphocytes.
Colchicine↗
Effect of cytochalasin B on formation and properties of muscle F-actin.
Cytochalasin B stimulated polymerization and decreased the concentration of G-actin remaining in equilibrium with F-actin filaments. Polymerization in the presence of cytochalasin B gave rise to a smaller increase of viscosity but to the same increase in light scattering, compared to polymerization in the absence of cytochalasin B. Cytochalasin B reduced the viscosity of F-actin and caused the appearance of ATP hydrolysis by F-actin. The cytochalasin B-induced ATPase activity was inhibited by concentrations of KCl higher than 50 mM. The cytochalasin B-induced ATPase activity was enhanced by ethyleneglycol bis(alpha-aminoethyl ether)-N,N'-tetraacetic acid and reduced by MgCl2 at concentrations higher than 0.75 mM. The findings suggest that the stability of actin filaments is reduced by cytochalasin B.
Actins↗
The oral apparatus of Tetrahymena pyriformis, strain WH-6. II. Cytochalasin B inhibition of oral apparatus morphogenesis.
The effects of cytochalasin B on oral apparatus morphogenesis and cell division were studied in synchronized Tetrahymena pyriformis, strain WH-6 syngen 1. Cytochalasin B brought about the rapid arrest of oral apparatus primordium development when added prior to the completion of oral apparatus membranelle differentiation. Cells arrested in development did not divide. When cytochalasin B was added after this transition point, oral apparatus morphogenesis and cell division were completed. The effects of cytochalasin B could be reversed by washing it from the medium. Even though cytochalasin B (at 400 mug/ml) reduced protein synthesis by 30%, the data are consistent with the interpretation that cytochalasin B prevents an assembly process during the membranelle differentiation phase of oral apparatus development.
Animals↗
The effect of cytochalasin B on hyphal morphogenesis in Polyporus biennis.
Cytochalasin B inhibited the radial growth rate of Polyporus biennis, and caused an increase in hyphal density through a reduction in the distance between successive branches. Cytochalasin B also produced irregular hyphal profiles and, in a small percentage of hyphae, forked apices. The position of clamp connexions was little affected by cytochalasin B, but the developmental process was specifically inhibited during initiation and during the last two stages, when contact and dissolution of the clamp were occurring. There were no major disruptions of the ultrastructure of the dolipore/parenthesome septum caused by cytochalasin B treatment.
Basidiomycota↗
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.
Animals↗
The oral apparatus of Tetrahymena pyriformis, strain WH-6. III. The binding of 3H-cytochalasin B by the isolated oral apparatus.
The binding of tritium-labelled cytochalasin B by the isolated oral apparatus of Tetrahymena pyriformis, strain WH-6, syngen 1, was investigated. Equilibrium binding studies revealed approximately 1.4 x 10(5) cytochalasin B binding sites per oral apparatus. A Scatchard plot indicates a single class of binding affinities with an association constant of 10(5) liters/mole. Rapid release of oral apparatus-bound cytochalasin B occurred when oral apparatuses were washed and resuspended in 1 mM TRIS without cytochalasin B. Because cytochalasin B binding to oral apparatus microtubular protein was not detected, microtubules are probably not the cytochalasin B binding site. The probable nature of the cytochalasin B binding site within the oral apparatus is discussed.
Animals↗
Regulation of lymphocyte responses in vitro. VI. -Potentiation of the response to phytohemagglutinin by cytochalasin B.
Low concentrations of cytochalasin B (CB) potentiated the DNA-synthetic response of rat lymph node cells (LNC) to PHA. Maximal potentiation was observed at suboptimal concentrations of the mitogen, less at optimal and usually none at supraoptimal concentrations. Other metabolic responses (RNA and protein synthesis) as well as the actual number of morphologically transformed lymphocytes were also enhanced. The presence of serum in the culture was an absolute requirement for CB potentiation. A maximal effect was usually obtained when CB was present from the start of the culture. However, addition of CB as late as 46 h after PHA produced a lower but consistent potentiation. The responses to PHA of thymus cells and spleen cells were respectively more and less increased by the drug than that of LNC. These results suggest that CB acts by opposing a serum-dependent cell interaction.
Animals↗
Effects of cytochalasin B on endocytosis and exocytosis.
The complex effects of cytochalasin B on endocytosis and exocytosis are reviewed. Cytochalasin B inhibits phagocytosis by both mononulcear phagocytes and polymorphonuclear leukocytes but it does not affect the micropinocytic activity of mononulear phagocytes and other cell types. Cytochalasin B causes increased selective release of acid hydrolase from phagocytic cells but its effect on other secretory cells is more variable, stimulating secretion by some cell types, inhibiting secretion in others and having no effect at all in some instances. The possible mechanisms of action of cytochalsin B are discussed with particular emphasis being placed on its effect on the activity of various protein components of cellular contractile systems. We suggest that many of the biolgoical effects of cytochalasin B may be accounted for by such effects.
Animals↗
Inhibition of macrophage-lymphocyte interaction by cytochalasin B during antigen recognition by T lymphocytes.
The effects of cytochalasin B on functional and physical macrophage-lymphocyte interaction have been examined. Cytochalasin B, an inhibitor of a variety of membrane activities blocks antigen-dependent bindings of immune lymphocytes to macrophages and antigen-triggered lymphocytes proliferation if added at the initiation of culture. Cytochalasin B becomes progressively less inhibitory if addition is delayed by increasing intervals from the onset of culture. Under these conditions neither antigen handling by macrophages nor the proliferative response of lymphocytes to PHA is inhibited by cytochalasin B. These data are interpreted to suggest that cytochalasin B inhibits antigen-specific macrophage-lymphocyte interaction either by inhibition of an initial antigen-independent phase of macrophage-lymphocyte interaction or by interfering with a lymphocyte membrane event necessary for the interaction of the antigen-specific lymphocyte receptor with the macrophage-bound antigenic signal.
Animals↗
Fine structure and RNA synthesis of Tetrahymena during cytochalasin B inhibition of phagocytosis.
Cytochalasin B inhibits the formation of normal-sized food vacuoles in Tetrahymena but the cells do not starve. Treated cells differ from starved cells in that they retain a high rate of incorporation of tritiated uridine. Large numbers of smaller vacuoles, about 1 micrometer in diameter, are formed, presumably by pinocytic activity of the cytopharyngeal membrane. This effect may perhaps be due to interference with the mechanism by which food vacuoles are sealed off at the cytostome, in which microfilaments may participate. Inhibited organisms may form tubes continuous with the cytopharynx instead of separate food vacuoles. It is not clear, however, why the formation of the small vacuoles is resistant to the drug.
Animals↗
Effect of cytochalasin B and D on groups of insulin receptors and on insulin action in rat adipocytes. Possible evidence for a structural relationship of the insulin receptor to the glucose transport system.
The possible physiological importance of the groups of insulin receptors on rat adipocytes and the relationship of these groups to insulin action were investigated. The effect of cytochalasin B and D on biological actions of insulin was measured and compared with the effect of these agents on the ultrastructural distribution of groups of insulin receptors. Cytochalasin B had no effect on epinephrine-stimulated lipolysis, insulin inhibition of epinephrine-stimulated lipolysis, or insulin stimulation of protein synthesis. Cytochalasin B, over a concentration range of 50 nM to 5 muM, progressively inhibited the basal glucose transport system, as measured by glucose oxidation, 2-deoxyglucose transport, and 3-O-methylglucose transport. Insulin was capable of fully stimulating remaining basal transport at submaximal concentrations of cytochalasin B. Insulin pretreatment of adipocytes partially protected the glucose transport system from inhibition by cytochalasin B. Cytochalasin B markedly altered the distribution pattern of insulin receptors, which caused an increase in the number of single receptor molecules by decreasing the number of larger groups. A significant correlation (r = 0.964; P < 0.001) was found between the percent increase in single receptors and the percent decrease in glucose transport. Ferritin-insulin pretreatment of adipocytes prevented disruption of the groups of insulin receptors by cytochalasin B. Cytochalasin D had no effect on the biological actions of insulin or on the groups of insulin receptors. These data suggest that the ability of insulin to affect adipocyte metabolism is independent of the hormone occupying adjacent, grouped receptor sites. The marked contrast in effects of cytochalasin B and D on groups of insulin receptors and glucose transport suggests that the microfilament system is not involved in insulin action or in holding the groups of insulin receptors together, as both agents are known disrupters of microfilaments and inhibitors of actin gelation. The correlation between the effects of cytochalasin B on insulin receptor distribution and glucose transport leads to the speculation that the glycoprotein molecules containing the insulin receptor are functionally linked with the glucose transport system.
Adipose Tissue↗