TERT Promoter Mutations Increase Tumor Aggressiveness by Altering TERT mRNA Splicing in Papillary Thyroid Carcinoma

Abstract

Abstract Context Telomerase reverse transcriptase promoter (TERT-p) mutations, which upregulate TERT expression, are strongly associated with tumor aggressiveness and worse prognosis in papillary thyroid carcinomas (PTCs). TERT expression is also observed in a proportion of PTCs without TERT-p mutations, but such tumors show less aggressiveness and better prognosis than TERT-p mutation–positive tumors. Objective TERT has multiple splicing variants whose relationships with the TERT-p status and clinicopathological characteristics remain poorly understood. We examined the relationship between the TERT-p mutational status, the TERT splicing pattern, and clinicopathological features. Methods We investigated the expression of 2 major variants, α deletion (dA) and β deletion (dB), in a series of 207 PTCs operated on between November 2001 and March 2020 in Nagasaki University Hospital and Kuma Hospital. Results The TERT-p mutations were found in 33 cases, and among 174 mutation-negative cases, 24 showed TERT expression. All cases were classified into 3 groups: the TERT-p mutation–negative/expression–negative group (mut−/exp−), the TERT-p mutation–negative/expression–positive group (mut−/exp+), and the TERT-p mutation–positive group (mut+/exp+). The +A+B/dB ratio in mut+/exp+ was significantly higher than that in mut−/exp+ PTCs. Analysis with clinicopathological data revealed that +A+B expression was associated with higher PTC aggressiveness, whereas dB expression counteracted this effect. Functional in vitro study demonstrated that dB strongly inhibited cell growth, migration, and clonogenicity, suggesting its tumor-suppressive role. Conclusion These results provide evidence that the TERT-p mutations alter the expression of different TERT splice variants, which, in turn, associates with different tumor aggressiveness.