Programming of cells for death under experimental conditions: relevance to the tumor problem.

An attempt was made in this study to determine more precisely the nature of the factors that are involved in the programming of cells for a form of terminal cellular differentiation that results in death. These studies demonstrated that both the cytokinesins, which are potent inhibitors of plant and animal adenosine 3':5'-cyclic monophosphate phosphodiesterases, and 8-bromoadenosine 3':5'-cyclic monophosphate, which is a stable, biologically active form of adenosine 3':5'-cyclic monophosphate, are highly effective in encouraging differentiation of parenchyma cells into tracheary elements with accompanying death. Since adenosine 3':5'-cyclic monophosphate and theophylline when used together were also effective, the results reported here suggest that adenosine 3':5'-cyclic monophosphate is somehow importantly involved in the conversion of parenchyma cells into tracheary elements in this system. The possible significance to the tumor problem generally of the programming of cells for terminal differentiation, with or without resulting death, is discussed.