Khandagale Prashant, Sun Yilun, Saha Sourav, Saha Liton Kumar, Pommier Yves
bioRxiv. 2024 Nov 18:2024.11.18.624152. doi: 10.1101/2024.11.18.624152.
Alternative Lengthening of Telomeres (ALT) is a homologous recombination-dependent telomere elongation mechanism utilized by at least 10-15% of all cancers. Here we identified that the DNA topoisomerase, TOP3A is enriched at the telomeres of ALT cells but not at the telomeres of telomerase-positive (Tel) cancer cells. We demonstrate that TOP3A stabilizes the shelterin protein TERF2 in ALT cancer cell lines but not in Tel cells and that long non-coding telomere transcribed RNA (TERRA) enrichment at telomeres depends upon TOP3A. TOP3A also promotes the generation of single-stranded telomeric C-strand (ssTeloC) DNA, which is a recently discovered marker for ALT. Additionally, we found that inducing TOP3A-DNA-protein crosslinks in ALT cells suppresses TERRA enrichment as well as destabilizes TERF2. Taken together these observations uncover the unexplored functions of TOP3A at ALT telomeres and suggest the potential of developing an ALT-specific cancer therapeutic strategy targeting TOP3A.
端粒替代延长（ALT）是一种依赖同源重组的端粒延长机制，所有癌症中至少有10%-15%的癌细胞会利用该机制。在此，我们发现DNA拓扑异构酶TOP3A在ALT细胞的端粒处富集，但在端粒酶阳性（Tel）癌细胞的端粒处未富集。我们证明，TOP3A在ALT癌细胞系中可稳定保护素蛋白TERF2，但在Tel细胞中则不然，并且端粒处的长链非编码端粒转录RNA（TERRA）富集依赖于TOP3A。TOP3A还促进单链端粒C链（ssTeloC）DNA的生成，这是最近发现的ALT标志物。此外，我们发现，在ALT细胞中诱导TOP3A-DNA-蛋白质交联会抑制TERRA富集，并使TERF2不稳定。综合这些观察结果，揭示了TOP3A在ALT端粒处尚未被探索的功能，并提示了开发针对TOP3A的ALT特异性癌症治疗策略的潜力。
