Demethylation of TMS1 gene sensitizes thyroid cancer cells to TRAIL-induced apoptosis.

CONTEXT

TMS1 is a tumor suppressor gene that encodes for caspase recruitment domain containing regulatory protein and has been shown to be hypermethylated in various cancers. However, its methylation status has not been investigated in thyroid cancer. Therefore, we studied the methylation of TMS1 and its functional consequence in thyroid cancer.

DESIGN

The methylation status of the promoter region of the TMS1 gene was determined using methylation-specific PCR in 40 papillary thyroid cancer samples, 10 normal thyroid tissue, and seven thyroid cancer cell lines. RT-PCR and Western blot analysis were used to assess the expression levels. 5-aza-2'-deoxycytidine was used to demethylate the thyroid cancer cell lines. Cell viability and apoptosis was determined by dimethylthiazoldiphenyltetra-zoliumbromide and flow cytometry.

RESULTS

Twenty-three percent of the papillary thyroid carcinoma samples were found to be methylated for the TMS1 gene. Two of seven thyroid cell lines were either completely or partially methylated for the TMS1 gene. The treatment of methylated thyroid cancer cell lines with 5-aza-2'-deoxycytidine resulted in the demethylation of the TMS1 gene leading to the restoration of its expression. After demethylation, treatment of cells with TNF-related apoptosis-inducing ligand (TRAIL) led to the induction of apoptosis via activation of caspases-8, caspase-3, and poly(ADP-ribose) polymerase. Interestingly, gene silencing of TMS1 using TMS1-specific small interfering RNA prevented TRAIL-mediated apoptosis.

CONCLUSION

Our results demonstrated that the TMSI gene is methylated in thyroid cancer cells and repression of methylation by 5-aza-2'-deoxycytidine restored expression of the TMS1 gene and sensitized cells to TRAIL-induced apoptosis. These findings suggest that the TMS1 gene can be targeted by combination of demethylating agents with TRAIL to induce efficient apoptosis in thyroid cancer cells.