Histone deacetylation of NIS promoter underlies BRAF V600E-promoted NIS silencing in thyroid cancer.
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.
Division of Endocrinology, Diabetes, and Metabolism, Laboratory for Cellular and Molecular Thyroid Research, Johns Hopkins University School of Medicine, 1830 East Monument Street, Suite 333, Baltimore, Maryland 21287, USA Department of Endocrinology and Metabolism, Changzheng Hospital, the Second Military Medical University, Shanghai, China.
Zongjing
Z
Zhang
Dingxie
D
Liu
Avaniyapuram Kannan
AK
Murugan
Zhimin
Z
Liu
Mingzhao
M
Xing
D000107:Acetylation; D000818:Animals; D002460:Cell Line; D045744:Cell Line, Tumor; D020868:Gene Silencing; D006657:Histones / Q000378:metabolism*; D006801:Humans; D009154:Mutation; D011401:Promoter Regions, Genetic; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D027981:Symporters / Q000235:genetics*; D013964:Thyroid Neoplasms / Q000235:genetics* / Q000378:metabolism; D000099209:Sodium-Iodide Symporters
D006657:Histones; D048493:Proto-Oncogene Proteins B-raf; D027981:Symporters; D000099209:Sodium-Iodide Symporters
BRAF V600E mutation; NIS gene; histone acetylation; histone deacetylation; radioiodine; thyroid cancer