Decline in c-myc mRNA expression but not the induction of c-fos mRNA expression is associated with differentiation of SH-SY5Y human neuroblastoma cells

The induction of differentiation in SH-SY5Y human neuroblastoma cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) is accompanied by a rapid and a transient expression of c-fos mRNA and a down-regulation of c-myc mRNA. The TPA-induced expression of c-fos mRNA was inhibited by H-7, a specific inhibitor of protein kinase C (PK-C). Dioctanoylglycerol (DiC8) failed to induce differentiation of SH-SY5Y cells or to down-regulate c-myc mRNA but it did induce the expression of c-fos mRNA. Treatment of IMR-32 human neuroblastoma cells with TPA did not cause differentiation although c-fos mRNA was induced. Since PK-C in SH-SY5Y cells was activated by both TPA and DiC8 it is suggested that the activation of PK-C alone is not sufficient to induce differentiation in SH-SY5Y cells. The down-regulation of c-myc mRNA rather than the induction of c-fos mRNA seems to be associated with differentiation process in SH-SY5Y cells.