Butyrate-induced cytoarchitectural reorganization of Mallory body-containing rat hepatic tumor cells.

Diethylnitrosamine (CAS: 55-18-5)-transformed 72/22 rat hepatic tumor cells undergo marked cytoarchitectural changes during exposure to sodium butyrate in vitro. Butyrate treatment of this cell line resulted in an increased cell size, volume, and protein content and in structural reorganization within both the intermediate filament and microfilament networks resulting in the generation of a more normal appearing hepatocytic phenotype. Induced changes in the microfilament system involved the accumulation of F-actin at the cellular margins in the form of a peripheral band and in the development of an extensive, predominantly centralized network of thickened cytoplasmic filament bundles. Such butyrate-induced changes in hepatic tumor cellular morphology and microfilament organization were reflected in a 26-51% increase in the amount of cytoskeletal-associated actin in 72/22 cells, as determined by flow cytofluorimetry of permeabilized intact cells or by scanning densitometry of the electrophoretically separated, detergent-resistant cytoskeletal protein fraction, respectively. It is unlikely that this increase in cellular microfilament content was due to a direct effect of butyrate on actin polymerization per se since butyrate (in final concentrations equal to that used in culture) did not alter either actin monomer-polymer transitions or the nucleation reaction in a defined in vitro polymerization assay. The available data suggest that butyrate may regulate the synthesis or modulate the actin-binding capacity of microfilament-associating proteins in cultured cells. Butyrate-induced "normalization" of 72/22 cytoarchitecture was previously shown to be reflected in a reduction or loss in the expression of specific growth traits characteristic of the transformed phenotype. The experimental reversal of defined cytoarchitectural abnormalities and transformed growth characteristics of 72/22 cells by butyrate provided an in vitro model to elucidate both particular cytoskeletal events associated with epithelial cell transformation and the mechanism of action of apparent differentiation-inducing agents, such as sodium butyrate, on responsive tumor cells.