Cyclic-AMP-induced differentiation in neuroblastoma is independent of cell division rate.

Abstract

CLONED, cultured mouse neuroblastoma cells, when grown in conditions which restrict cell division, extend neurites1–6 and increase the activity of neurotransmitter-related enzymes7–9. Treatments that can induce this differentiation include lowered serum concentrations3, prostaglandins4, phosphodiesterase inhibitors5 and analogues of cyclic-3′,5′-AMP (cyclic-AMP)6,10–11. These treatments have been proposed to act by elevating intracellular cyclic-AMP levels, but because they also inhibit cell division it has been difficult to determine whether their effects are due directly to cyclic-AMP or indirectly to inhibition of cell division12. As neurite growth and enzyme elevation occur during the interphase portion of the cell cycle (and are retarded during cell division), cyclic-AMP may simply allow differentiation by stopping the cell cycle in interphase3. The butyryl analogues of cyclic-AMP, in particular, markedly restrict cell division (ref. 10; see also Fig. 1a). Because butyrate, which can dissociate from the dibutyryl analogue of cyclic-AMP, can itself markedly inhibit cell division we reasoned that other analogues may exist which are not inhibitors of cell division but which effectively mimic the action of cyclic-AMP. We report here that 8-bromo-cyclic-3′,5′-AMP (8Br-cyclic-AMP) effects biochemical and morphological changes in the neuroblastoma clone NBD-2 (ref. 9) without concomitant inhibition of cell division.