S-Space College of Medicine/School of Medicine (의과대학/대학원) Dept. of Medicine (의학과) Theses (Ph.D. / Sc.D._의학과)
TERT promoter mutation and its synergistic interaction with BRAF and RAS mutations in thyroid cancer
갑상선암에서 TERT promoter 변이의 의의와 BRAF, RAS 변이와의 시너지 상호작용
- 의과대학 의학과
- Issue Date
- 서울대학교 대학원
- 학위논문 (박사)-- 서울대학교 대학원 : 의과대학 의학과, 2018. 2. 박영주.
- Recent reports suggest that mutations in the promoter of the gene encoding telomerase reverse transcriptase (TERT) affect thyroid cancer outcomes. I aimed to investigate the clinical significance of TERT promoter mutation in thyroid cancer and its synergistic interaction with BRAF and RAS mutations. Furthermore, molecular mechanisms of the oncogene interaction by genomic analysis using next-generation sequencing database were explored. TERT promoter mutations were detected in 4.5% of all differentiated thyroid cancers and associated with poor prognosis. These mutations were more frequent in tumors also harboring either BRAF (4.8%) or RAS mutations (11.3%). The prevalence of TERT promoter mutations was higher in high-risk patients: 9.1% and 12.9% in the ATA high-risk and advanced TNM stage groups, respectively. Among high-risk patients, the presence of TERT promoter mutations additively increased the risk of both recurrence and disease-specific mortality. The coexistence of BRAF and TERT promoter mutations had a synergistic effect on the clinicopathological characteristics and long-term prognosis of papillary thyroid cancer (PTC) and I firstly confirmed this by meta-analysis. From the analyses of RNA sequencing data and in vitro experiments, I could confirm that TERT mRNA expression was increased by adding the BRAF mutation to the TERT promoter mutation (fold change, 17.00
q-value = 1.36×10-13). Furthermore, this increase was due to, at least in part, the upregulated expression of E-twenty-six (ETS), especially ETV1, ETV4, and ETV5 by BRAF mutation. The coexisting mutations showed changes in the almost same intracellular signaling pathways as BRAF mutation alone, however, amplified the changes of the expression level of genes associated with altered pathways. Moreover, the inflammation and adhesion-related pathways were activated by adding TERT expression in BRAF-mutated PTCs. Notably, I firstly reported that the coexistence of RAS and TERT promoter mutations was associated with a higher rate of recurrence, suggesting that they had additive effects on the prognosis, similarly to BRAF and TERT promoter mutations. As for the mechanism, I could confirm that this genetic duet significantly increased TERT expression (fold change, 5.58
q-value = 0.004) compared with the expression in tumors harboring RAS or TERT promoter mutation alone. Moreover, adding the TERT promoter mutation or expression to the RAS mutation, there were significant changes in transcriptional profile, which activated the aggressive intracellular pathways including MAPK pathways. In conclusion, genetic screening for TERT promoter mutations in high-risk patients with thyroid cancer might bolster the prediction of mortality and recurrence. In addition, molecular testing of TERT promoter mutation with BRAF or RAS mutation together may be useful in assisting with risk stratification in clinical settings. Furthermore, I can suggest that the mechanism of synergistic oncogene interaction between TERT and BRAF or RAS be explained by increased TERT expression, which may result from the BRAF or RAS-induced upregulation of several ETS transcription factors. Pathways related to aggressive behaviors of tumors are activated by the genetic duet
BRAF and TERT or RAS and TERT.