Abstract

Histone deacetylase inhibitors (HDACi) have shown both anti-proliferative and redifferentiating effects in thyroid cancer cells. Also, they induce the expression of the sodium–iodide symporter gene (NIS (SLC5A5)), a crucial step for radioiodine treatment of thyroid malignancies. Here we investigated the effects of suberoylanilide hydroxamic acid (SAHA) and valproic acid (VPA) on BCPAP and FRO thyroid cancer cells, extending our analysis on the epigenetic mechanisms underlying the NIS gene expression stimulation. In both cell lines we found a cooperative effect of the two compounds on either cell viability and NIS gene expression, resulting in acquired/increased ability to uptake the radioiodine. Such effect was specific since it was not observed for expression of other genes or when SAHA was used in combination with trichostatin A. By using chromatin immunoprecipitation, we investigated epigenetic mechanisms underlying SAHA and VPA effects. Cooperation among the two HDACi occurred on H3 histone trimethylation at lysine 4 (H3K4me3) and not on histone acetylation. However, effects on H3K4me3 were detected only at the level of NIS Proximal Basal Promoter (NIS-PBP) in FRO cells and only at the level of NIS Upstream Enhancer (NIS-NUE) in BCPAP cells. Our data indicate that epigenetic changes are involved in the synergistic effects of VPA and SAHA on NIS gene expression and that the cellular context modifies effects of HDACi in terms of H3K4me3 target sequence. Investigation of cooperation among different HDACi may provide clues for better defining their mechanism of action in view of their use in thyroid cancer treatment.