Morphological and biochemical differentiation in HeLa cells: Effects of cycloheximide on butyrate-induced process formation and ganglioside metabolism

Abstract

When butyrate-treated HeLa cells are trypsinized and replated in the absence of butyrate, their neurite-like processes re-extend transiently. Process formation after replating is prevented when the cells are exposed to cycloheximide during butyrate treatment, whereas it is not prevented by prior exposure to the calcium ionophore A23187 plus butyrate. These results indicate that butyrate induces protein(s) required for process extension which can accumulate in the absence of processing and promote processing in the absence of inducer. Transient process re-extension is followed by spontaneous retraction of processes and reversion to normal morphology. Reversion is not prevented or delayed by puromycin. Surprisingly, however, cycloheximide completely prevents reversion even at low concentrations (< 0.5 μg/ml). Levels of the ganglioside sialolactosylceramide (G M3), synthesis of which is induced by butyrate, return to basal levels after removal of the inducer. Cycloheximide at 0.5 μg/ml prevents the decline of G M3 levels after removal of butyrate although the biosynthetic enzyme sialyltransferase decays at the same rate in the presence or absence of the drug and the activity of the sialidase is not affected. The results further support the hypothesis that the ganglioside G M3 is necessary for the morphological differentiation induced in HeLa cells by butyrate.