Increased N-myc mRNA expression associated with dibutyryl cyclic AMP induced neuroblastoma differentiation.

The N-myc cellular oncogene is frequently amplified and expressed at a high level in neuroectodermal tumor cells such as neuroblastoma and retinoblastoma. We examined N-myc expression in NCB-20 hybrid (N18TG2 neuroblastoma x embryonic Chinese Hamster brain) cells. After five days of culture, cells treated with 1 mM db cAMP show extensive neurite outgrowth and secrete acetylcholinesterase into the media at a level three times higher than untreated control. In situ hybridizations, dot blots, and Northern analyses reveal four- to eight-fold higher levels of N-myc mRNA in the treated, differentiated cells than in the untreated, undifferentiated controls. Our results show that the highly differentiated state is not incompatible with a high level of N-myc mRNA.