Abstract
Murine embryonal carcinoma cells from line PCC4.aza1R differentiate readily in response to retinoic acid. By treating PCC4.aza1R cells with the mutagen N-methyl-N′-nitro-N-nitrosoguanidine, we derived two embryonal carcinoma lines in which the cells failed to differentiate during exposure to retinoic acid. Although these dif(RA)-cells maintained the tumorigenic potential of the parental cells, they differentiated poorly in tumor form. Similarly, the tendency of dif(RA)-cells to differentiate when aggregated in vitro was diminished relative to that of PCC4.aza1R cells. The rate of retinoic acid uptake in cells from the two mutant lines did not appear to be reduced compared with the rate in cells from the parental line; however, specific cytoplasmic retinoic acid-binding protein activity was virtually absent in both mutants. These results strengthen the view that differentiation of embryonal carcinoma cells in response to retinoic acid requires formation of retinoic acid--cytoplasmic retinoic acid-binding protein complexes.