Dibutyryl cyclic AMP induces differentiation of human neuroblastoma SH-SY5Y cells into a noradrenergic phenotype.

Dibutyryl cyclic AMP (dbcAMP) and retinoic acid (RA) have been demonstrated to be the inducers of morphological differentiation in SH-SY5Y cells, a human catecholaminergic neuroblastoma cell line. However, it remains unclear whether morphologically differentiated SH-SY5Y cells by these compounds acquire catecholaminergic properties. We focused on the alteration of tyrosine hydroxylase (TH) expression and intracellular content of noradrenaline (NA) as the indicators of functional differentiation. Three days treatment with dbcAMP (1mM) and RA (10microM) induced morphological changes and an increase of TH-positive cells using immunocytochemical analysis in SH-SY5Y cells. The percentage of TH-expressing cells in dbcAMP (1mM) treatment was larger than that in RA (10microM) treatment. In addition, dbcAMP increased intracellular NA content, whereas RA did not. The dbcAMP-induced increase in TH-expressing cells is partially inhibited by KT5720, a protein kinase A (PKA) inhibitor. We also investigated the effect of butyrate on SH-SY5Y cells, because dbcAMP is enzymatically degraded by intracellular esterase, thereby resulting in the formation of butyrate. Butyrate induced the increase of NA content at lower concentrations than dbcAMP, although the increase in TH-expressing cells by butyrate was smaller than that by dbcAMP. The dbcAMP (1mM)- and butyrate (0.3mM)-induced increase in NA content was completely suppressed by alpha-methyl-p-tyrosine (1mM), an inhibitor of TH. These results suggest that dbcAMP induces differentiation into the noradrenergic phenotype through both PKA activation and butyrate.