Uncoupling of growth inhibition and differentiation in dexamethasonetreated human rhabdomyosarcoma cells

The effects of dexamethasone, a synthetic glucocorticoid, and of N, N-dimethylformamide on in vitro growth and differentiation and on proto-oncogene expression of human rhabdomyosarcoma cells were studied. RD/18 clone cells (derived from the embryonal rhabdomyosarcoma cell line RD) treated with 100 nM dexamethasone showed an almost complete block of differentiation: about 5% myosin-positive cells were observed after 2 weeks of culture in dexamethasone-supplemented differentiation medium, compared to 20% of untreated cultures. Dexamethasone also induced a 20-30% growth inhibition and a more flattened morphology. The treatment with N, N-dimethylformamide induced a significantly increased proportion of myosin-positive cells (reaching about 30%) and a 40% growth inhibition. Induction of differentiation inversely correlated with the levels of c-myc proto-oncogene expression: after a 2 week culture dexamethasone-treated cells showed the highest c-myc expression and N, N-dimethylformamide-tre...