While 5% to 10% of cancers are known to activate an alternative lengthening of telomeres (ALT) process, the resulting genomic and epigenomic alterations remain unclear. In this study, Bhargava and colleagues used telomere sequencing (Telo-seq) and directed methylation with long-read sequencing (DiMeLo-seq) to decipher the mechanism by which ALT supports telomere integrity to enable cancer cell survival. Fluorescence in situ hybridization (FISH) experiments revealed overlaps between centromeres and telomeres within promyelocytic leukemia (PML) bodies in ALT+, but not ALT–, cells. In ALT– cells, activation of ALT through ATRX disruption produced similar levels of centromere–telomere overlaps. In ALT+ cells, synchronization of the cell cycle maximized EdU incorporation at the centromere–telomere–PML contacts in G2, suggesting that the process involves break-induced replication and illegitimate recombination. Centromeric DNA sequences, including α-satellite repeats, were inserted at the telomere–subtelomere boundary exclusively in ALT+ cells, while no corresponding telomeric DNA sequences were observed in centromeres. Additionally, samples from patients with ALT+ neuroblastoma contained significantly higher levels of α-satellite sequences. Centromeric levels of CENP-A, the centromere-associated histone 3 variant, were similar in ALT+ and ALT– cells driven to replicative crisis. However, DNA hypomethylation, α-satellite insertion, and newly synthesized CENP-A were only detected on the telomeres of chromosomes 1p, 11p, and 14q in ALT+ cells. Treatment with decitabine, a DNA methyltransferase inhibitor, enhanced ALT activation and CENP-A assembly at telomeres. Depletion of HJURP, the enzyme responsible for CENP-A deposition, decreased the formation of telomere-centromere contacts and promoted mitotic DNA synthesis (MiDAS) at telomeres, resulting in increased telomere fragility and loss. Altogether, this study deepens the mechanistic understanding of ALT and identifies novel targets to explore for the treatment of ALT neoplasms.Bhargava R, Mahlke MA, Schmidt TT, Bartenhagen C, Smith BA, Ramsey KL, et al. Centromeric footprints preserve telomere integrity in ALT cancers. Nature 2026 Jun 3 Epub ahead of print.Note: Research Watch is written by Cancer Discovery editorial staff. Readers are encouraged to consult the original articles for full details. For more Research Watch, visit Cancer Discovery online at https://aacrjournals.org/cdnews.
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