Acta Neuropathologica Communications (Aug 2019)

TERT expression is susceptible to BRAF and ETS-factor inhibition in BRAF V600E /TERT promoter double-mutated glioma

  • Lisa Gabler,
  • Daniela Lötsch,
  • Dominik Kirchhofer,
  • Sushilla van Schoonhoven,
  • Hannah M. Schmidt,
  • Lisa Mayr,
  • Christine Pirker,
  • Katharina Neumayer,
  • Carina Dinhof,
  • Lucia Kastler,
  • Amedeo A. Azizi,
  • Christian Dorfer,
  • Thomas Czech,
  • Christine Haberler,
  • Andreas Peyrl,
  • Rajiv Kumar,
  • Irene Slavc,
  • Sabine Spiegl-Kreinecker,
  • Johannes Gojo,
  • Walter Berger

DOI
https://doi.org/10.1186/s40478-019-0775-6
Journal volume & issue
Vol. 7, no. 1
pp. 1 – 16

Abstract

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Abstract The BRAF gene and the TERT promoter are among the most frequently altered genomic loci in low-grade (LGG) and high-grade-glioma (HGG), respectively. The coexistence of BRAF and TERT promoter aberrations characterizes a subset of aggressive glioma. Therefore, we investigated interactions between those alterations in malignant glioma. We analyzed co-occurrence of BRAF V600E and TERT promoter mutations in our clinical data (n = 8) in addition to published datasets (n = 103) and established a BRAF V600E -positive glioma cell panel (n = 9) for in vitro analyses. We investigated altered gene expression, signaling events and TERT promoter activity upon BRAF- and E-twenty-six (ETS)-factor inhibition by qRT-PCR, chromatin immunoprecipitation (ChIP), Western blots and luciferase reporter assays. TERT promoter mutations were significantly enriched in BRAF V600E -mutated HGG as compared to BRAF V600E -mutated LGG. In vitro, BRAF V600E /TERT promoter double-mutant glioma cells showed exceptional sensitivity towards BRAF-targeting agents. Remarkably, BRAF-inhibition attenuated TERT expression and TERT promoter activity exclusively in double-mutant models, while TERT expression was undetectable in BRAF V600E -only cells. Various ETS-factors were broadly expressed, however, only ETS1 expression and phosphorylation were consistently downregulated following BRAF-inhibition. Knock-down experiments and ChIP corroborated the notion of a functional role for ETS1 and, accordingly, all double-mutant tumor cells were highly sensitive towards the ETS-factor inhibitor YK-4-279. In conclusion, our data suggest that concomitant BRAF V600E and TERT promoter mutations synergistically support cancer cell proliferation and immortalization. ETS1 links these two driver alterations functionally and may represent a promising therapeutic target in this aggressive glioma subgroup.

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