Terminal differentiation and growth inhibition of a rat rhabdomyosarcoma cell line (BA-HAN-1C) in vitro after exposure to retinoic acid.

BA-HAN-1C is a clonal rat rhabdomyosarcoma cell line composed of proliferating mononuclear cells, which partly fuse to terminally differentiated postmitotic myotube-like giant cells. The exposure to retinoic acid in vitro resulted in time- and dose-dependent changes of both cell differentiation and cell growth. The mononuclear cells revealed bundles of newly formed thick and thin myofilaments, never observed in untreated cultures, and exhibited signs of contact inhibition. In addition, there was a statistically significant increase (P less than 0.001) in the number of terminally differentiated postmitotic myotube-like giant cells and in the creatine kinase activity (P less than 0.05) which was used as a biochemical differentiation marker. At the same time cell growth was significantly inhibited (P less than 0.001) in vitro and a decrease in plating efficiency, as well as in saturation density, was observed. These data demonstrate that retinoic acid can suppress cell growth and simultaneously initiate differentiation in a malignant mesenchymal tumor cell line. However, despite the clonal nature of BA-HAN-1C, the complete status of terminal differentiation was not achieved by all tumor cells. The reason why not all tumor cells responded to retinoic acid is unknown at the present time and will have to be the subject of further studies.