Epco-15. Chromosome Breaks at Interstitial Telomeric Sequences Enable Pre-Cancerous Astrocytes to Survive Genome Instability Caused by Telomere Dysfunction

Genome instability, a hallmark of diffuse glioma, can arise from unprotected chromosome ends due to telomere dysfunction (TD). We successfully modeled TD in normal human astrocyte (NHA) cells by dysregulating cell cycle checkpoints using retroviruses containing HPV-18 E6/E7 and expanding the resulting cells over long periods of time. TD was confirmed by the detection of progressive telomere shortening and anaphase bridges with increasing population doublings (PDLs). We hypothesized that NHA-E6E7 cells undergoing TD would progressively accumulate structural variation (SV) and aneuploidy, which was confirmed using copy number and SV analysis from long and short-read sequencing data of increasing PDLs. Notably, we detected telomeric SV junctions and found that telomere-associated SVs were more prevalent in NHA-E6E7 cells. Analysis of telomeric long reads demonstrated that reads with internal telomeric sequences were significantly enriched at later PDLs, reflecting recombination events involving telomeres. Intriguingly, we identified an SV breakpoint on chromosome 3 at an interstitial telomeric sequence (ITS). Telomeric chromatin interaction profiling using Telomere-C showed a long-range chromatin interaction involving this ITS and the telomere in both normal and cancer cells, suggesting that this site could be a site of telomeric recombination. While genome instability fuels oncogenic alterations, large-scale rearrangements can be detrimental. We propose that the exposed ITS might serve as a neo-telomere, protecting chromosome segments from further DNA damage and conferring pre-cancerous cells with survival advantages. Our findings confirmed that TD contributes to genome instability in glioma and suggest that cancer cell progression could be influenced by underlying telomere-related mechanisms.