TERT expression is susceptible to BRAF and ETS-factor inhibition in BRAF V600E /TERT promoter double-mutated glioma | Acta Neuropathologica Communications | Full Text

TERT expression is susceptible to BRAF and ETS-factor inhibition in BRAF V600E /TERT promoter double-mutated glioma | Acta Neuropathologica Communications | Full Text



Acta Neuropathologica Communications

TERT expression is susceptible to BRAF and ETS-factor inhibition in BRAFV600E/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 

Acta Neuropathologica Communicationsvolume 7, Article number: 128 (2019) | Download Citation

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 BRAFV600E and TERTpromoter mutations in our clinical data (n = 8) in addition to published datasets (n = 103) and established a BRAFV600E-positive glioma cell panel (n = 9) for in vitro analyses. We investigated altered gene expression, signaling events and TERTpromoter 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 BRAFV600E-mutated HGG as compared to BRAFV600E-mutated LGG. In vitro, BRAFV600E/TERT promoter double-mutant glioma cells showed exceptional sensitivity towards BRAF-targeting agents. Remarkably, BRAF-inhibition attenuated TERT expression and TERTpromoter activity exclusively in double-mutant models, while TERT expression was undetectable in BRAFV600E-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 BRAFV600E 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.