Transfection of mouse erythroleukemia cells with myc sequences changes the rate of induced commitment to differentiate.

We have examined the role of the c-myc protooncogene in chemically induced differentiation of mouse erythroleukemia (MEL) cells by transfecting the cells with recombinant plasmids in which c-myc coding sequences were cloned downstream from the mouse metallothionein I promoter in sense and antisense orientations. We previously showed that treatment of MEL cells with inducers of differentiation leads to a rapid (less than 2 hr) decrease in the level of c-myc mRNA. c-myc mRNA is then transiently restored to pretreatment levels approximately 12-18 hr later. These events occur prior to the detection of cells that are irreversibly committed to erythroid differentiation. MEL cell transfectants containing the plasmid with myc in the sense orientation express a chimeric MT-myc mRNA, which also decreases shortly after addition of inducer. However, these clones reexpress myc RNA more rapidly than the parental line and they also differentiate more rapidly. On the other hand, transfectants containing the plasmid with myc in the antisense orientation exhibited a delay in the reexpression of c-myc mRNA and were found to differentiate more slowly than parental cells. Thus, we find a correlation between the time at which myc RNA is reexpressed following inducer treatment and the rate of entry of cells into the terminal differentiation program.