Induction of cyclic AMP phosphodiesterase by disaggregation of the multicellular complexes of Dictyostelium discoideum.

When the multicellular complexes (slugs) of Dictyostelium discoideum were disaggregated, the activity of phosphodiesterase for adenosine 3':5'-monophosphate increased. The increase occurred first with the enzyme in the particulate fraction of the cell. Cytoplasmic and extracellular phosphodiesterase, as well as the macromolecular inhibitor for this enzyme, also increased at later times. The increase in these activities was blocked by inhibitors of protein and RNA synthesis. This indicates that the increase is not due to the activation of the enzyme, but due to its synthesis de novo, and that the synthesis is induced at the transcriptional level by the loss of cell contact. In the case of cellular phosphodiesterase, inhibitors of protein synthesis (cycloheximide and emetine) not only blocked the increase, but also caused a decrease in activity. The mechanism of such decrease was further investigated.