Changes in the Expression of Pre-Replicative Complex Genes in hTERT and ALT Pediatric Brain Tumors.

Manuel Bernabé,Emanuela Kerschbamer,María Luisa Cayuela,Francesca Pagani,Francesco Berardinelli,Pietro Luigi Poliani,Aurora Irene Idilli,Maria Caterina Mione,Emilio Cusanelli,Silvano Piazza

doi:10.3390/cancers12041028

Abstract

Background: The up-regulation of a telomere maintenance mechanism (TMM) is a common feature of cancer cells and a hallmark of cancer. Routine methods for detecting TMMs in tumor samples are still missing, whereas telomerase targeting treatments are becoming available. In paediatric cancers, alternative lengthening of telomeres (ALT) is found in a subset of sarcomas and malignant brain tumors. ALT is a non-canonical mechanism of telomere maintenance developed by cancer cells with no-functional telomerase. Methods: To identify drivers and/or markers of ALT, we performed a differential gene expression analysis between two zebrafish models of juvenile brain tumors, that differ only for the telomere maintenance mechanism adopted by tumor cells: one is ALT while the other is telomerase-dependent. Results: Comparative analysis of gene expression identified five genes of the pre-replicative complex, ORC4, ORC6, MCM2, CDC45 and RPA3 as upregulated in ALT. We searched for a correlation between telomerase levels and expression of the pre-replicative complex genes in a cohort of paediatric brain cancers and identified a counter-correlation between telomerase expression and the genes of the pre-replicative complex. Moreover, the analysis of ALT markers in a group of 20 patients confirmed the association between ALT and increased RPA and decreased H3K9me3 localization at telomeres. Conclusions: Our study suggests that telomere maintenance mechanisms may act as a driver of telomeric DNA replication and chromatin status in brain cancers and identifies markers of ALT that could be exploited for precise prognostic and therapeutic purposes.

Highlights

alternative lengthening of telomeres (ALT), an alternative mechanism to maintain telomere length based on homologous recombination, is found mostly in tumors with a mesenchymal origin and in a subset of malignant pediatric brain tumors [1], including High Grade Glioma (HGG, 51%), Diffuse Intrinsic PontineGlioma (DIPG) (18%), Choroid Plexus Carcinoma (CPC) (22.6%), and Primitive NeuroectodermalTumors (PNET) (11.6%) [2,3]
We previously established two isogenic models of juvenile brain tumors in zebrafish, that differs for the telomere maintenance mechanism (TMM) adopted by cancer cells [20]
Principal component analysis (PCA) identified two well separate clusters corresponding to ALT and telomerase+ brain tumors (Figure 1b)

Summary

Introduction

ALT, an alternative mechanism to maintain telomere length based on homologous recombination, is found mostly in tumors with a mesenchymal origin (sarcomas) and in a subset of malignant pediatric brain tumors [1], including High Grade Glioma (HGG, 51%), Diffuse Intrinsic PontineGlioma (DIPG) (18%), Choroid Plexus Carcinoma (CPC) (22.6%), and Primitive NeuroectodermalTumors (PNET) (11.6%) [2,3]. H3 [7,8] and inactivating mutations in the Death-domain associated protein/Alpha thalassemia-mental retardation (DAXX/ATRX) genes, leading to DNA hypomethylation [9,10,11] These findings suggest that telomeric chromatin plays an important role in ALT. Methods: To identify drivers and/or markers of ALT, we performed a differential gene expression analysis between two zebrafish models of juvenile brain tumors, that differ only for the telomere maintenance mechanism adopted by tumor cells: one is ALT while the other is telomerase-dependent. Conclusions: Our study suggests that telomere maintenance mechanisms may act as a driver of telomeric DNA replication and chromatin status in brain cancers and identifies markers of ALT that could be exploited for precise prognostic and therapeutic purposes

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Results

Discussion

Conclusion