Comprehensive molecular analysis of immortalization hallmarks in thyroid cancer reveals new prognostic markers

Abstract

Background Comprehensive molecular studies on tumours are needed to delineate immortalization process steps and identify sensitive prognostic biomarkers in thyroid cancer. Methods and Results In this study, we extensively characterize telomere‐related alterations in a series of 106 thyroid tumours with heterogeneous clinical outcomes. Using a custom‐designed RNA‐seq panel, we identified five telomerase holoenzyme‐complex genes upregulated in clinically aggressive tumours compared to tumours from long‐term disease‐free patients, being TERT and TERC denoted as independent prognostic markers by multivariate regression model analysis. Characterization of alterations related to TERT re‐expression revealed that promoter mutations, methylation and/or copy gains exclusively co‐occurred in clinically aggressive tumours. Quantitative‐FISH (fluorescence in situ hybridization) analysis of telomere lengths showed a significant shortening in these carcinomas, which matched with a high proliferative rate measured by Ki‐67 immunohistochemistry. RNA‐seq data analysis indicated that short‐telomere tumours exhibit an increased transcriptional activity in the 5‐Mb‐subtelomeric regions, site of several telomerase‐complex genes. Gene upregulation enrichment was significant for specific chromosome‐ends such as the 5p, where TERT is located. Co‐FISH analysis of 5p‐end and TERT loci showed a more relaxed chromatin configuration in short telomere‐length tumours compared to normal telomere‐length tumours. Conclusions Overall, our findings support that telomere shortening leads to a 5p subtelomeric region reorganization, facilitating the transcription and accumulation of alterations at TERT‐locus.

Telomerase reactivation induces progression of mouse BrafV600E-driven thyroid cancers without telomere lengthening

“…All three mouse cell lines showed a two to three-fold increase in Tert promoter activity for the mutant promoter ("mTert -123T") compared to wildtype ("mTert -123C") constructs (Fig 1B). This is consistent with the effect seen in luciferase assays for human TERT -124C>T/-146C>T constructs (31), as well as with TERT expression in patients' tumors carrying TPMs (32,33). We then followed a small cohort of Braf Overall, Tert reactivation accelerated Braf-driven PTC progression towards more advanced forms, as observed in patients' tumors carrying this genetic combination.…”

Thyroid carcinoma‐featured telomerase activation and telomere maintenance: Biology and translational/clinical significance

“…In addition to TERT, Montero‐Conde et al. also observed TERC as an independent factor for progression‐free survival prediction of TCs 9 . This finding may be especially important for TC tumours without detectable TERT expression.…”

“…showed robustly enhanced TERC expression in aggressive TCs. Moreover, TERC RNA levels were independently associated with progression‐free survival in TC patients, indicating a driver‐effect on the TC pathogenesis 9 …”

“… 13,16–21 Montero‐Conde et al. showed a robustly higher frequency of TERT promoter mutations in aggressive TC tumours (45.7%) compared with those in disease‐free TCs (3.4%) 9 . Third, TERT promoter and BRAF or RAS mutations co‐occur at a high frequency in DTCs 18,21 …”

“…13,[16][17][18][19][20][21] Montero-Conde et al showed a robustly higher frequency of TERT promoter mutations in aggressive TC tumours (45.7%) compared with those in disease-free TCs (3.4%). 9 Third, TERT promoter and BRAF or RAS mutations co-occur at a high frequency in DTCs. 18,21 TERT promoter mutations (both C228T and C250T) create de novo ETS binding motifs that are bound by the ETS transcription factors, thereby activating TERT transcription (Figure 2B).…”