Regulation of 14-3-3σ expression in human thyroid carcinoma is epigenetically regulated by aberrant cytosine methylation

Increased 14-3-3sigma expression has been observed by immunohistochemistry in papillary and anaplastic tumors, but not follicular thyroid cancers. 14-3-3sigma mRNA expression and methylation status was examined in tumor cell lines and primary thyroid tissues using real-time RT-PCR, bisulfite sequencing and methylation-specific PCR. Most of the 27 CpG's in the gene's CpG island were methylated in normal thyroid, TPC-1, NPA, FTC-238 and 2-7, which did not express 14-3-3sigma. In contrast, they were unmethylated in KAK-1 and anaplastic lines KAT4 and DRO-90. 14-3-3sigma expression was not increased in thyroid carcinomas, the majority of which had a methylated CpG island. In addition, 5-aza-dC treatment increased 14-3-3sigma expression in the FTC-238 and NPA cell lines, which had low baseline expression. We conclude 14-3-3sigma expression in thyroid carcinomas is regulated by CpG island hypermethylation.