Effect of retinoic acid on growth and morphological differentiation of mouse NB2a neuroblastoma cells in culture.

We have characterized the effects of retinoic acid (RA) on the growth, morphology and biosynthesis of cytoskeletal proteins in NB2a mouse neuroblastoma cells. In addition, the morphological and biochemical changes were compared to those induced by dibutyryl cyclic AMP (db cAMP). Growth inhibition by RA was concentration-dependent and was first detected 24 h after addition of RA. The proliferation of RA-treated NB2a was more dependent on serum than was the proliferation of untreated cultures and RA decreased the saturation density of NB2a cells grown in serum. Morphological changes induced by RA include the formation of an elaborate network of branching neurites in NB2a cells. In contrast, neurites induced by db cAMP or serum deprivation were bipolar and unbranching. Ultrastructural observations of neurites induced by RA revealed dendritic characteristics such as polysomes, spines and absence of intermediate filaments, while neurites induced by db cAMP had axonal characteristics such as filament bundles, absence of ribosomes, and the formation of membrane densities when neurite endings contacted another cell body. These morphological differences were also reflected in a number of changes in the biosynthesis of cytoskeletal proteins. These results suggest that NB2a cells treated with RA and db cAMP are a model system for the study of distinct stages of differentiation.