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

Effects of retinoic acid on expression of the transformed phenotype in C6 glioma cells

Retinoic acid (RA) inhibited the growth and induced morphological changes in C6 rat glioma cells. The effects of RA on growth rate became apparent after 48 hr and were concentration-dependent and reversible. There was a 60% inhibition of growth using 10(-5) RA, which increased at low serum concentration to over 90% inhibition and was minimized at high concentration of serum. RA did not change the saturation density of the cells. The morphology of C6 cells, was altered from its normal pattern of randomly oriented spindle shaped cells, to cells which aligned to form palisades of fibroblast-like cells. Biochemical analysis of the cells showed no significant change in the activities of several lysosomal hydrolyses or the level of total protein in RA-treated cells compared to control cells. There was, however, a significant decrease in the activity of ornithine decarboxylase early during the treatment with RA, and an increase in the levels of fibronectin secreted into the media by the RA-treated cell. These results suggest that RA can suppress the expression of the transformed phenotype of glioma cells.

Induction of lysosomal glycosidases by dibutyryl cAMP in neuroblastoma cells

We have studied the regulation of lysosomal glycosidases during morphological differentiation of NB2a neuroblastoma cells. Cells treated with dibutyryl cAMP induced axon-like neuritis and showed a 2-4 fold increase in the activity of 6 lysosomal glycosidases, reaching their highest level after 5 days of treatment. Cells treated with retinoic acid, which induced dendrite-like neurites, did not show significant changes in the glycosidases activity although cell proliferation was also inhibited. There was no change in the pattern of the enzyme secretion during the dibutyryl cAMP treatment and morphological analysis using electron microscopy and cytochemical staining with acid phosphatase indicated the presence of lysosomes in the induced neurites.

Expression and distribution of microtubule-associated protein 2 (MAP2) in neuroblastoma and primary neuronal cells

We examined the expression and distribution of microtubule-associated protein 2 (MAP2) during the differentiation in culture of both mouse NB2a neuroblastoma and primary embryonic rat neurons. The differentiation of NB2a cells was induced with retinoic acid (RA) which stimulated the extension of a highly branched neuritic network and dibutyryl cAMP which stimulated the outgrowth of long bipolar or monopolar processes. We found that although monoclonal antibodies to MAP2 stained the cell bodies of control and differentiated cells, only the RA-induced neurites were positive for this antigen. These data support our ultrastructural studies indicating that the RA-induced neurites were dendrite-like and that the dibutyryl cAMP-induced processes were axon-like. Studies on the biosynthesis of MAP2 indicated that RA induced a 2-3-fold increase in MAP2 synthesis in 24 h; however, this effect was transient, with the synthesis of MAP2 in RA-treated cells returning to control level by 72 h. Although biosynthetic studies suggested the synthesis of species at 250-300 kdalton, the major molecular weight form in the neuroblastoma cells was 230 kdalton. Immunocytochemical analysis of primary neurons showed staining of neuronal cell bodies and of short processes, but virtually no staining of the long axon-like processes. The staining of neuronal cell bodies and processes was evident at all stages of cell differentiation. This finding was corroborated by immunoblots which showed significant amounts of MAP2 throughout cell development. The molecular weight of the immunoreactive material was ca. 300 kdalton in both primary neurons and rat brain. Immunoblots also revealed that embryonic neurons expressed only MAP2B as they differentiated in culture for 14 days. Biosynthesis studies suggested that early in culture there was a modest increase in MAP2 synthesis, but no detectable change was observed thereafter. We concluded therefore that both neuroblastoma cells and primary neurons can differentiate neuritic processes, which show dendritic properties in terms of morphology and preferential distribution of MAP2.