Alternative lengthening of telomeres is the major telomere maintenance mechanism in astrocytoma with isocitrate dehydrogenase 1 mutation

Monica Sofia Ventura Ferreira,Tim Henrik Brümmendorf,Anne-Sophie Bouillon,Fabian Beier,Bjarne Winther Kristensen,Mia Dahl Sørensen,Christoph Patrick Beier,Dagmar Beier,Stefan Pusch

doi:10.1007/s11060-020-03394-y

Abstract

PurposeIsocitrate dehydrogenase 1 (IDH1) mutations are associated with improved survival in gliomas. Depending on the IDH1 status, TERT promoter mutations affect prognosis. IDH1 mutations are associated with alpha-thalassemia/mental retardation syndrome X-linked (ATRX) mutations and alternative lengthening of telomeres (ALT), suggesting an interaction between IDH1 and telomeres. However, little is known how IDH1 mutations affect telomere maintenance.MethodsWe analyzed cell-specific telomere length (CS-TL) on a single cell level in 46 astrocytoma samples (WHO II-IV) by modified immune-quantitative fluorescence in situ hybridization, using endothelial cells as internal reference. In the same samples, we determined IDH1/TERT promoter mutation status and ATRX expression. The interaction of IDH1R132H mutation and CS-TL was studied in vitro using an IDH1R132H doxycycline-inducible glioma cell line system.ResultsVirtually all ALTpositive astrocytomas had normal TERT promoter and lacked ATRX expression. Further, all ALTpositive samples had IDH1R132H mutations, resulting in a significantly longer CS-TL of IDH1R132H gliomas, when compared to their wildtype counterparts. Conversely, TERT promotor mutations were associated with IDHwildtype, ATRX expression, lack of ALT and short CS-TL. ALT, TERT promoter mutations, and CS-TL remained without prognostic significance, when correcting for IDH1 status. In vitro, overexpression of IDHR132H in the glioma cell line LN319 resulted in downregulation of ATRX and rapid TERT-independent telomere lengthening consistent with ALT.ConclusionALT is the major telomere maintenance mechanism in IDHR132H mutated astrocytomas, while TERT promoter mutations were associated with IDHwildtype glioma. IDH1R132H downregulates ATRX expression in vitro resulting in ALT, which may contribute to the strong association of IDH1R132H mutations, ATRX loss, and ALT.

Highlights

Gliomas are the most common primary brain tumors in adults and represent a histologically defined entity with a high molecular heterogeneity determining prognosis and responseSdr
The cell-specific telomere length (CS-Telomere length (TL)) was significantly longer in IDH1R132H-mutated tumors as compared to IDH1WT tumors (Fig. 1c) irrespective of tumor grade (Fig. 1d), while there were no significant differences among the different tumor types (p = 0.19, Supplementary Figure S1C). IDH1R132H mutation was significantly associated with improved patient survival (HR 0.28; 95% CI 0.14–0.50; p < 0.001, Supplementary Figure S1C) with similar tendency (HR 0.47; 95% CI 0.21–1.08; p = 0.076) when adjusting for age and WHO grade
Exact understanding of telomere biology in glioma is of high translational importance, given the completely diverse prognostic impact of TERTp mutations according to the Isocitrate dehydrogenase 1 (IDH1) mutation status

Summary

Introduction

Gliomas are the most common primary brain tumors in adults and represent a histologically defined entity with a high molecular heterogeneity determining prognosis and responseSdr. Journal of Neuro-Oncology (2020) 147:1–14 to therapy [1, 2]. Along this line, determination of isocitrate dehydrogenase (IDH) 1 mutation status became mandatory in the updated 2016 WHO classification [3]. The most common IDH1 mutations in glioma (> 95%) result in an amino acid substitution at arginine 132 (R132), which resides in the enzyme’s active site [4]. While IDH1 has a major role in the citric acid cycle, R132H mutation (IDHR132H) results in a gain of function; IDH1R132H catalyzes conversion of alpha-ketoglutarate into the oncometabolite D-2-hydroxyglutarate (D2HG) [9]. D2HG inhibits dioxygenases that depend on alpha-ketoglutarate, like Ten-eleven translocation methylcytosine dioxygenase 1 (TET1) and histone-lysine demethylases [10]; this results in increased CpG island methylation [11] and a stable reshaping of the epigenome (CpG island methylation phenotype, CIMP) changing transcriptional programs and altering the differentiation state [12]

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