Correlation between effects of 24 different cytochalasins on cellular structures and cellular events and those on actin in vitro

Abstract

To compare the effects of cytochalasins on the cellular level with those on the molecular level, 24 cytochalasins, 20 natural compounds and 4 derivatives were used. The following effects were tested [in C3H mouse fibroblast cells] for each of 24 cytochalasins: 4 high dose (2-20 .mu.M) effects on the cellular level: rounding up of fibroblastic cells, contraction of actin cables, formation of hairy filaments containing actin, and inhibition of lymphocyte capping; a low dose (0.2-2 .mu.M) effect: inhibition of membrane ruffling; and 2 in vitro effects: an inhibition of actin filament elongation (the high affinity effect [low dose effect] in vitro) and an effect on viscosity of actin filaments (the low affinity effect [high dose effect] in vitro). There apparently are almost the same hierarchic orders of relative effectiveness of different cytochalasins between low and high dose effects and between cellular and molecular effects. From the data obtained with the 24 cytochalasins, of correlation coefficients 0.87 and 0.79 were calculated between an effect in vivo, inhibition of capping and an effect in vitro, inhibition of actin filament elongation, as well as between inhibition of capping and another effect in vitro, effect on viscosity of actin filaments, respectively. The correlation coefficient between the high affinity effect and the low affinity effect determined in vitro was 0.90. The strong positive correlation among low and high dose effects in vivo and those in vitro suggests that most of the effects caused by a cytochalasin, irrespective of doses or affected phenomena, might be attributed to the interaction between the drug and the common target protein, actin. In the course of the immunofluorescence microscope study on cytochalasin-treated cells using actin antibody, aspochalasin D, a 10-isopropylcytochalasin, strongly induced the formation of rodlets containing actin in the cytoplasm of the treated fibroblasts. Other cytochalasins, including cytochalasin B, cytochalasin C, cytochalasin D and cytochalasin H, induced the formation of nuclear rodlets. Among them, cytochalasin was the most potent in the ability to induce the rodlets. Both cytoplasmic and nuclear rodlets found in the cytochalasin-treated cells were similar in ultrastructures to those induced by 5-10% (vol/vol) dimethyl sulfoxide in the same type of cells.