New somatic TERT promoter variants enhance the Telomerase activity in Glioblastoma

Abstract

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 ( TERT p), i.e. c.1-124 C > T, c.1-146 C > T, confers a proliferative advantage to neoplastic cells. In gliomas, TERT p mutations ( TERT p mut ) mainly occur in oligodendroglioma and glioblastoma. We screened, for TERT p 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 TERT p variants, which consisted of a tandem duplications of 22 nucleotides, i.e. a TERT p c.1-100_1-79dup and TERT p 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 TERT p c.1-100_1-79dup and TERT p c.1-110_1-89, respectively. TERT p duplications ( TERT p 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 TERT p dup 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 TERT p mut . On the other hand, they were distinguished by enhanced affinity for the Krüppel proteins. The luciferase assay confirmed that TERT p 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 TERT p 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.