Abstract
In the presence of suboptimal inducing amounts of dimethylsulfoxide or hexamethylenebisacetamide, a major proportion of uncommitted murine erythroleukemia (MEL) cells was found to be precommitted or primed for commitment, which was demonstrated by their rapid commitment to terminal differentiation when recultured for short periods of time (three to six hours) with fresh inducer. These same cells did not commit if left in the original inducer-containing media or if replated in fresh media without inducer. The two inducers could be interchanged in the priming and postpriming period without affecting the commitment event. However, hemin, an agent that induces hemoglobin synthesis without commitment, showed no ability to enhance commitment of a primed cell population. The rapid commitment of primed cells was inhibited by 12-O-tetradecanoylphorbol-13-acetate and cordycepin but not by cycloheximide. The latter finding indicated that this rapid inducer- dependent commitment event required new RNA synthesis but not new protein synthesis. The precommitment state was lost within six hours of the growth of cells in the absence of inducer but could be sustained longer if cells were incubated in cycloheximide. These studies characterize a precommitment state not previously described and one that appears during chemically induced differentiation in the absence of metabolic inhibitors. The stabilization of these precommitted cells by cycloheximide suggests that the reversibility of precommitment involves new protein synthesis. These findings show that MEL cells proceed to terminal differentiation by accumulating unstable products that must be maintained by the inducer until the final commitment event.
