TY - JOUR T1 - Dissecting telomere maintenance mechanisms in pediatric glioblastoma JF - bioRxiv DO - 10.1101/129106 SP - 129106 AU - Katharina I. Deeg AU - Inn Chung AU - Alexandra M. Poos AU - Delia M. Braun AU - Andrey Korshunov AU - Marcus Oswald AU - Nick Kepper AU - Sebastian Bender AU - David Castel AU - Peter Lichter AU - Jacques Grill AU - Stefan M. Pfister AU - Rainer König AU - David T. W. Jones AU - Karsten Rippe Y1 - 2017/01/01 UR - http://biorxiv.org/content/early/2017/04/20/129106.abstract N2 - Pediatric glioblastoma (pedGBM) represent a highly malignant primary brain tumor with recurrent mutations in the chromatin remodeler ATRX and the histone variant H3.3 that is typically associated with a fatal outcome. ATRX acts as suppressor of the alternative lengthening of telomeres (ALT) pathway, which is frequently activated in pedGBM. However, telomere features of pedGBMs have not been studied in detail, and ALT-positive model cell lines are lacking. Here, we systematically characterized a panel of pedGBM models that carry a representative set of recurrent genomic mutations for a variety of telomere features. These included the presence of ALT-associated promyelocytic leukemia nuclear bodies and C-circles, a specific type of extrachromosomal telomeric repeats, the telomere repeat content, and phosphorylation of histone H3.3 at serine 31. From an integrated analysis of seven pedGBM cell lines and 57 primary tumor samples we identified cell lines and tumors that represent the different telomere maintenance mechanisms and conclude the following: (i) A positive signal in the C-circle assay is a reliable ALT marker. (ii) ALT features occur heterogeneously and one pedGBM subgroup uses a ‘non-canonical’ ALT mechanism in the presence of wild-type ATRX. (iii) The spreading of H3.3S31 phosphorylation during mitosis is associated with loss of ATRX but not with ALT per se. (iv) In contrast to a previous study in glioma stem cells, we did not find a hypersensitivity of ALT cells towards the ATR inhibitor VE-821. (v) ALT-positive pedGBMs can be reliably identified from a classification scheme developed here that evaluates various combinations of cytogenetic and/or genomic data. Thus, our findings elucidate further details of the ALT pathway in pedGBMs, provide valuable models for evaluating ALT targeted therapies in a preclinical setting, and introduce an ALT classification scheme for primary tumor samples. ER -