Enhancement of human neuroblastoma cell apoptosis by combined treatment with valproic acid and interferonβ

DEDONI, SIMONA;OLIANAS, MARIA CONCETTA;ONALI, PIER LUIGI

2015-01-01

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Abstract

Type I interferons (IFNs), including IFNα and IFNβ, possess antitumoral activity and have been proposed to be potentially useful in the treatment of neuroblastoma. We have previously shown that IFNβ causes cell death of human SHSY5Y neuroblastoma cells by inducing apoptosis through the intrinsic mitochondrial pathway (Dedoni et al. J. Neurochem. 115,14211433, 2010). As valproic acid, an histone deacetylase inhibitor (HDACi) has been reported to enhance the antitumoral effects of type I IFNs, in the present study we have examined the effects of this drug on IFNβinduced apoptosis of neuroblastoma cells. We found that prolonged exposure (24 h) of SHSY5Y cells to therapeutic concentrations of valproic acid (0.61 mM) had no effect on cell viability. However, when combined with IFNβ, valproic acid markedly enhanced cell apoptosis induced by the cytokine, as demonstrated by the increase in annexin V staining, caspase activation and poly( ADP ribose) polymerase (PARP) cleavage. Acetylation of histone 2B at Lys5 was markedly enhanced by valproic acid, but this response was not affected by cotreatment with IFNβ. Conversely, valproic acid enhanced the IFNβstimulated Tyrphosphorylation of STAT1, which is crucial for cytokineinduced apoptosis. Sodium butyrate (1 mM), another HDACi, elicited similar potentiating effects on IFNβinduced apoptosis and STAT1 phosphorylation, whereas valpromide (1 mM), which did not enhance histone acetylation, had no effects. MYCNamplified human LAN1 neuroblastoma cells displayed no sensitivity to the proapoptotic activity of IFNβ, but underwent apoptosis when treated with either valproic acid or sodium butyrate. Cotreatment of LAN1 cells with IFNβ and HDACi, but not valpromide, resulted in a significant increase in cell apoptosis. These data show a synergistic interaction of IFNβ and valproic acid in promoting neuroblastoma cells apoptosis, which appears to be related to enhancementof histone acetylation.