New somatic TERT promoter variants enhance the Telomerase activity in Glioblastoma

Abstract

The catalytic activity of human Telomerase Reverse Transcriptase (TERT) compensates for the loss of telomere length, eroded during each cell cycle, to ensure a correct division of stem and germinal cells. In human tumors, ectopic TERT reactivation, most frequently due to hotspot mutations in the promoter region (TERTp), i.e. c.1-124 C > T, c.1-146 C > T, confers a proliferative advantage to neoplastic cells. In gliomas, TERTp mutations (TERTp mut) mainly occur in oligodendroglioma and glioblastoma. We screened, for TERTp hotspot mutations, 301 adult patients with gliomas and identified heterozygous mutations in 239 cases: 94% of oligodendroglioma, 85% of glioblastoma, and 37.5% of diffuse/anaplastic astrocytoma. Besides the recurrent c.1-124 C > T and c.1-146 C > T, two cases of glioblastoma harbored novel somatic TERTp variants, which consisted of a tandem duplications of 22 nucleotides, i.e. a TERTp c.1-100_1-79dup and TERTp c.1-110_1-89, both located downstream c.1-124 C > T and c.1-146 C > T. In silico analysis predicted the formation of 119 and 108 new transcription factor's recognition sites for TERTp c.1-100_1-79dup and TERTp c.1-110_1-89, respectively. TERTp duplications (TERTp dup) mainly affected the binding capacity of two transcription factors' families, i.e. the members of the E-twenty-six and the Specificity Protein/Krüppel-Like Factor groups. In fact, these new TERTpdup significantly enhanced the E-twenty-six transcription factors' binding capacity, which is also typically increased by the two c.1-124 C > T/c.1-146 C > T hotspot TERTp mut. On the other hand, they were distinguished by enhanced affinity for the Krüppel proteins. The luciferase assay confirmed that TERTp dup behaved as gain-of-function mutations causing a 2,3-2,5 fold increase of TERT transcription. The present study provides new insights into TERTp mutational spectrum occurring in central nervous system tumors, with the identification of new recurrent somatic gain-of-function mutations, occurring in 0.8% of glioblastoma IDH-wildtype.

Human MettL3-MettL14 RNA adenine methyltransferase complex is active on double-stranded DNA containing lesions

“…Interestingly, two highly recurrent, cancer specific C-to-T mutations in the TC dinucleotides in the promoter of TERT (telomerase reverse transcriptase) ( 56–61 ), created an identical 11-bp sequence [5′-CCCCT( C → T )CCGGG-3′] that contains an ETS binding site (TTCCG). Similar creation of a new ETS binding site within this promoter is also associated with thyroid carcinoma ( 62 ), glioblastoma ( 63 ), meningioma ( 64 ), and hepatocellular carcinoma ( 65 ). While these other cancers are unlikely to result directly from UV exposure, we note that it is possible to generate CPDs without the direct contribution of UV radiation ( 66–68 ).…”

TERT Promoter Alterations in Glioblastoma: A Systematic Review

“…Recently, two other TERTp gain-of-function alterations were described: TERTp c.1-100_1-79dup and TERTp c.1-110_1-89. These newly-described alterations occur in less than 1% of glioblastoma IDH -wild type ( IDH -wt) and were not integrated into our systematic review [ 23 ].…”

Conserved features of TERT promoter duplications reveal an activation mechanism that mimics hotspot mutations in cancer

“…In support, two of the 22 bp TERT p duplications previously reported and included in Table 1 increase activity of the TERT p in a promoter-reporter assay. Based on sequence motif analysis of the duplication, over one hundred potential TF were predicted that could play a role in TERT activation 22 , 23 . From the conserved features in our relatively large number of cases and in our prior studies, we hypothesized that any 22 bp TERT p duplication that specifically includes the native ETS motif could increase promoter activity and the increase would be dependent on insertion point and GABP.…”