Apoptosis of human embryonal carcinoma cells with in vitro differentiation

An in vitro model of apoptosis and differentiation in human embryonal carcinoma (EC) cells was developed to study the mode of cell death and mechanisms of cell death in early development. Death of these cells was induced by treatment with retinoic acid (RA) under the same conditions as those for induction of differentiation. The manner of this cell death was apoptosis, not necrosis, with the morphological criterion for apoptosis. Serum deprivation likewise caused apoptosis in both undifferentiated and differentiated EC cells. In differentiated EC cells, DNA fragmentation was observed in a smear pattern lacking the ladder pattern typically associated with apoptosis. However, in differentiated EC cells, DNA fragmentation occurred in various sizes. The expression of a carbohydrate antigen, Le(Y), a reported marker of apoptotic cancer cells, was increased by the treatment with RA. However, two-color analysis by flow cytometry with nick end labelling method revealed that Le(Y) expression was closely correlated with cellular differentiation but not apoptosis after RA treatment in the human EC cell system. Collection of Le(Y) positive cells by the magnetic bead method demonstrated that this expression was not due to apoptosis but rather to differentiation. On the other hand, Le(Y) expression associated with apoptosis was induced by serum deprivation in both undifferentiated and differentiated EC cells. These results show that a subpopulation of undifferentiated EC cells takes the apoptotic pathway by induction of differentiation. The results also suggest that the population of cells taking an apoptotic pathway differs from a population of cells taking a differentiation pathway. This in vitro system for apoptosis in human EC cells will be useful for studies concerning apoptosis or programmed cell death in human developmental biology.