Phosphorylation of endogenous proteins by adenosine 3':5'-monophosphate-dependent protein kinase in mouse neuroblastoma cells

Morphological and biochemical differentiation of the human medulloblastoma cell line TE671

Cells of the human medulloblastoma clonal line TE671 exhibit polymorphism when grown in vitro in serum-supplemented medium. Under these conditions, cell numbers double every 18 h during log phase growth. These tumorigenic precursors of cerebellar interneurons are not contact-inhibited and approach densities of one million cells per cm2. TE671 cells in proliferative growth express a class of nicotinic acetylcholine receptors that are fully sensitive to functional blockade by the neurotoxin alpha-bungarotoxin (Bgt). TE671 cells grown in medium containing dibutyryl cyclic adenosine monophosphate (dbcAMP) rapidly undergo a distinctive morphological transformation characterized by neurite extension and formation of cell-cell contacts. The rate of cell division and cell saturation densities are diminished coordinately with these treatments. Sodium fluoride and forskolin induce similar changes in cell division and morphology as does dbcAMP, and these effects are potentiated by aluminum and the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine, respectively. The high-affinity binding of Bgt to TE671 cells also is reduced on exposure to dbcAMP in a time and dose-dependent manner. The results suggest that activation of adenylate cyclase and the concomitant elevation of intracellular cAMP levels may be involved in the morphological transformation of TE671 cells to a mature, neuronal phenotype and in changes in the level of expression of a subtype of human neuronal nicotinic receptors. These studies establish a unique, neural tube-derived model system for investigation of the mechanisms involved in these processes.

12-O-tetradecanoyl-phorbol-13-acetate-induced differentiation of human neuroblastoma cells is not accompanied by an increase in the intracellular concentration of cyclic AMP

Cultured human SH-SY5Y neuroblastoma cells could be induced to differentiate morphologically and biochemically followed by growth inhibition, by treatment with 12-O-tetradecanoyl-phorbol-13-acetate (TPA). The cells showed a limited differentiation when treated with substances known to increase the intracellular concentration of cyclic AMP. When these substances were combined with TPA, morphological differentiation and growth inhibition of the cells were potentiated. In contrast, these substances inhibited the TPA-induced increase in noradrenaline concentration and the relative activity of neuron-specific enolase. Both the intracellular concentration of cyclic AMP and the cytosolic level of cyclic AMP-binding components were similar in control and TPA-treated cells. It is suggested that cyclic AMP has a limited and non-regulatory role in the initiation of differentiation of SH-SY5Y cells. The effect of cyclic AMP is probably coupled mainly to the polymerization of microtubules, thus enhancing the morphological differentiation of the cells.