Effect of single-nucleotide polymorphism in TERT promoter on follicular thyroid tumor development

Regulatory Single Nucleotide Polymorphism Increases TERT Promoter Activity in Thyroid Carcinoma Cells

BACKGROUND/AIM

The telomerase reverse transcriptase (TERT) promoter has a regulatory single nucleotide polymorphism (rSNP), rs2853669, and occasionally shows point mutations C228T and C250T. Although C228T and C250T have been well examined to increase TERT promoter activity and are known as risk factors for thyroid carcinoma, the significance of rs2853669 has not been well investigated. This study aimed to clarify the influence of rs2853669 on TERT promoter activity in thyroid carcinoma cells.

MATERIALS

Seven of 8 examined thyroid cell lines had rs2853669, 5 had C228T, and 1 had C250T.

RESULTS

Three papillary thyroid carcinoma cell lines, harboring both rs2853669 and C228T, showed higher TERT mRNA expression on real-time PCR than the other cell lines. Anaplastic thyroid carcinoma cell lines, in contrast, showed variable TERT mRNA expression depending on the combination of rs2853669, C228T, and C250T. Luciferase assays, performed to compare the influences of rs2853669, C228T, and C250T on TERT promoter activity in thyroid carcinoma, showed that rs2853669, as well as C228T, increased the promoter activity, and the combination of rs2853669 and C228T increased the promoter activity even more strongly than C228T alone.

CONCLUSION

We conclude that the presence of rs2853669 within the TERT promoter could be as significant as the C228T mutation in thyroid carcinoma.

Spatial Distribution Patterns of Clinically Relevant TERT Promoter Mutations in Follicular Thyroid Tumors of Uncertain Malignant Potential: Advantages of the Digital Droplet PCR Technique

In thyroid carcinomas, telomerase reverse transcriptase (TERT) promoter mutations C228T and C250T predict an unfavorable clinical outcome. The analysis is particularly valuable when assessing histologically equivocal follicular thyroid tumors of uncertain malignant potential (FT-UMPs). Given recent findings of TERT promoter mutational heterogeneity in thyroid cancer, we determined the frequency of this phenomenon in FT-UMPs and minimally invasive follicular thyroid carcinomas. DNA was extracted from several tissue blocks from 16 FT-UMPs as well as 10 minimally invasive follicular thyroid carcinomas, and interrogated using Sanger sequencing as well as digital droplet PCR (ddPCR). Mutational heterogeneity was observed by Sanger sequencing in four of seven (57%) FT-UMPs. In two FT-UMPs with C228T mutations, analyses of additional blocks gave wild-type results using Sanger sequencing in one or several blocks interrogated, whereas ddPCR found low-frequency C228T mutations in one of these fractions. In two additional FT-UMPs with the C228T and C250T mutation, respectively, sequencing of additional blocks revealed the opposite mutation. Moreover, in the C250T mutated area in one of these tumors, the ddPCR displayed a co-occurring C228T mutation that failed detection through Sanger sequencing. To conclude, most TERT promoter mutated FT-UMPs display mutational heterogeneity when analyzed by Sanger sequencing, thereby emphasizing the importance of the tissue sampling process. The ddPCR technique might overcome this phenomenon because of increased sensitivity and should be considered for clinical screening purposes.