Methylation of the thyroid-stimulating hormone receptor gene in epithelial thyroid tumors: a marker of malignancy and a cause of gene silencing.

Thyroid-stimulating hormone receptor (TSHR) expression is frequently silenced in epithelial thyroid cancers associated with decreased or absent TSH-promoted iodine uptake. To study the underlying molecular mechanism of decreased TSHR expression, we examined the methylation status of the TSHR gene promoter by sequencing bisulfite-treated DNA from thyroid tumors. After identification of methylated sites by sequencing bisulfite-treated DNA, we used methylation-specific polymerase chain reaction and found frequent CpG methylation in papillary thyroid cancer (23 of 39 patients; 59%) and follicular thyroid cancers (7 of 15 patients; 47%).

Hypermethylation of the Pendred syndrome gene SLC26A4 is an early event in thyroid tumorigenesis.

Expression of the recently cloned Pendred syndrome gene SLC26A4 or PDS has been found to be decreased or even absent in various thyroid tumors. To explore the underlying mechanism, we conducted DNA sequencing and methylation-specific PCR studies in 64 primary thyroid tumors and 6 thyroid cell lines. We found aberrant hypermethylation of the SLC26A4 gene in 44% of histologically benign adenomas, 46% of follicular thyroid cancers, 71% of papillary thyroid cancers, 71% of anaplastic thyroid cancers, and 100% of cell lines.