ATRX loss induces telomere DNA dysfunction and genomic instability in human astrocytes
10%-15% of human cancers utilize the recombination-based alternative lengthening of telomeres (ALT) pathway to potentiate their replicative immortality. ALT cancers is associated with genome instability marked by extensive micronucleation and chromosome rearrangements. Mutation/loss of gene encoding histone H3.3 chaperon protein ATRX is the most common genetic event of human ALT cancers including malignant gliomas, yet its role in genome stability remains incompletely understood. Here we show that ATRX depletion in human astrocytes triggers progressively aggravated telomere DNA replication dysfunction that consequentially induces genome instability. The fragmentation and sequencing-based SMASH analysis of immortalized ATRX-depleted human astrocytes reveals complex copy number alterations and chromosomal rearrangements. We further reveal that the ALT astrocytes undergo chronic telomere replication stresses with pervasive signs of ongoing genome instability even after their immortalization. Considering the significance of genomic instability in tumor initiation and evolution, we propose that the ongoing telomere dysfunction and genomic instability of ALT cells may potentiate their tumorigenic capacity.