Histone deacetylation of NIS promoter underlies BRAF V600E-promoted NIS silencing in thyroid cancer

Abstract

The BRAF V600E mutation causes impaired expression of sodium iodide symporter (NIS) and radioiodine refractoriness of thyroid cancer, but the underlying mechanism remains undefined. In this study, we hypothesized that histone deacetylation at the NIS (SLC5A5) promoter was the mechanism. Using the chromatin immunoprecipitation approach, we examined histone acetylation status on the lysine residues H3K9/14, H3K18, total H4, and H4K16 at the NIS promoter under the influence of BRAF V600E. We found that expression of stably or transiently transfected BRAF V600E inhibited NIS expression while the deacetylase inhibitor SAHA stimulated NIS expression in PCCL3 rat thyroid cells. Although BRAF V600E enhanced global histone acetylation, it caused histone deacetylation at the NIS promoter while SAHA caused acetylation in the cells. In human thyroid cancer BCPAP cells harboring homozygous BRAF V600E mutation, BRAF V600E inhibitor, PLX4032, and MEK inhibitor, AZD6244, increased histone acetylation of the NIS promoter, suggesting that BRAF V600E normally maintained histone in a deacetylated state at the NIS promoter. The regions most commonly affected with deacetylation by BRAF V600E were the transcriptionally active areas upstream of the translation start that contained important transcription factor binding sites, including nucleotides −297/−107 in the rat NIS promoter and −692/−370 in the human NIS promoter. Our findings not only reveal an epigenetic mechanism for BRAF V600E-promoted NIS silencing involving histone deacetylation at critical regulatory regions of the NIS promoter but also provide further support for our previously proposed combination therapy targeting major signaling pathways and histone deacetylase to restore thyroid gene expression for radioiodine treatment of thyroid cancer.

Are we really at the dawn of understanding sporadic pediatric thyroid carcinoma?

“…Finally, it has been suggested that overactivation of the MAPK pathway, mainly through BRAF V600E mutation, leads to tumor dedifferentiation and, hence, reduced expression of proteins involved in iodine uptake and metabolism in PTC of adults (Romei et al 2008, The Cancer Genome Atlas Research Network 2014, Zhang et al 2014. However, it is becoming clear that the BRAF V600E-mutated group consists of distinct subgroups with variable degrees of thyroid differentiation (The Cancer Genome Atlas Research Network 2014), which suggests that additional genetic events may be associated with dedifferentiation status of the thyroid.…”

Anaplastic thyroid cancer

“…A specific BRAF mutation, BRAFV600E, is known to cause constitutive activation of the MAPK pathway. The consequences are increased tumor growth and aggressiveness and reduced Sodium-Iodide symporter gene expression [24], which correlates with radioiodine resistance. This mutation, therefore, represents a potential target [25], and reintroduction of the NIS gene has been proposed as a part of gene therapy.…”

Novel analogs targeting histone deacetylase suppress aggressive thyroid cancer cell growth and induce re-differentiation

“…46 A recent study demonstrated that BRAF V600E leads to deacetylation by HDACs of multiple critical promoter regions on the NIS gene, which deregulates the binding of key transcriptional factors and consequently suppresses NIS expression. 47 In this current study, the AB treatments could have inhibited HDACs, which would lead to the maintenance of the acetylation status of the NIS promoter region in 8505C, prompting its induction despite the low levels of PAX8 and TTF1.…”