Mutant IDH1 Expression Drives TERT Promoter Reactivation as Part of the Cellular Transformation Process

Abstract

Mutations in the isocitrate dehydrogenase gene IDH1 are common in lower-grade glioma where they result in the production of 2-hydroxyglutarate (2HG), disrupted patterns of histone methylation and gliomagenesis. IDH1 mutations also co-segregate with mutations in the ATRX gene and the TERT promoter, suggesting that IDH mutation may drive the creation or selection of telomere-stabilizing events as part of immortalization/transformation process. To determine if and how this may occur, we investigated the phenotype of pRb/p53-deficient human astrocytes engineered with IDH1 wild-type (WT) or R132H mutant (IDH1mut) genes as they progressed through their lifespan. IDH1mut expression promoted 2HG production and altered histone methylation within 20 population doublings (PD), but had no effect on telomerase expression or telomere length. Accordingly, cells expressing either IDH1 WT or IDH1mut entered a telomere-induced crisis at PD 70. In contrast, only IDH1mut cells emerged from crisis, grew indefinitely in culture and formed colonies in soft agar and tumors in vivo. Clonal populations of post-crisis IDH1mut cells displayed shared genetic alterations, but no mutations in ATRX or the TERT promoter were detected. Instead, these cells reactivated telomerase and stabilized their telomeres in association with increased histone lysine methylation (H3K4me3) and c-Myc/Max binding at the TERT promoter. Overall, these results show that while IDH1mut does not create or select for ATRX or TERT promoter mutations, it can indirectly reactivate TERT, and in doing so contribute to astrocytic immortalization and transformation.

Isocitrate dehydrogenase mutations suppress STAT1 and CD8+ T cell accumulation in gliomas

“…As 2HG is known to cause CpG site hypermethylation (47), we hypothesize that STAT1 expression might be regulated by the methylation of its promoter. However, our analysis of STAT1 methylation site β values from TCGA 450k methylation data (Supplemental Figure 12) and Illumina 850k array on NHA cells revealed no significant differences in STAT1 promoter methylation between IDH-WT and IDH-MUT samples (48). Further studies are warranted to understand the mechanism by which mutant IDH and 2HG suppress STAT1 protein levels.…”

Cancer-specific loss ofTERTactivation sensitizes glioblastoma to DNA damage

“…Mechanistically, the early effects seen in response to full knockout of GABPB1L are inconsistent with the expected timeframe associated with canonical telomere shortening 50,51 .…”

“…The normal human astrocyte cell line NHA-PC5 was previously described 51 , and is puromycin resistant. For our experiments, we established a puromycin-sensitive monoclonal derivative, termed NHA-S2, through CRISPR editing of the previously inserted puromycin resistance cassette.…”

Metabolic reprogramming in the pathogenesis of glioma: Update

“…The altered metabolic landscape in IDH ‐mutant gliomas also affects phospholipid, energy, and oxidative stress pathways . Further, IDH mutations can indirectly reactivate telomerase reverse transcriptase (TERT), which regulates a part of metabolic pathways in GBM …”

“…15 The altered metabolic landscape in IDH-mutant gliomas also affects phospholipid, energy, and oxidative stress pathways. 16 Further, IDH mutations can indirectly reactivate telomerase reverse transcriptase (TERT), 17,18 which regulates a part of metabolic pathways in GBM. 19,20 Hypoxia promotes metabolic reprogramming in IDH wildtype gliomas Primary GBM (GBM, IDH wild-type) and IDH-wild-type…”