Zhao Rongwei, Wivagg Allison, Lackner Rachel M, Salsman Jayme, Dellaire Graham, Matunis Michael J, Chenoweth David M, Zhao Xiaolan, Zhang Huaiying
Department of Biology, Carnegie Mellon University, Pittsburgh, PA 15213, USA.
Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19014, USA.
bioRxiv. 2025 Jan 20:2025.01.16.633463. doi: 10.1101/2025.01.16.633463.
Many cancers use an alternative lengthening of telomeres (ALT) pathway for telomere maintenance. ALT telomeric DNA synthesis occurs in ALT telomere-associated PML bodies (APBs). However, the mechanisms by which APBs form are not well understood. Here, we monitored the formation of APBs with time-lapse imaging employing CRISPR knock-in to track the promyelocytic leukemia (PML) protein at endogenous levels. We found APBs form via two pathways: telomeres recruit PML proteins to nucleate PML bodies de novo, or telomeres fuse with preformed PML bodies. Both nucleation and fusion of APBs require interactions between SUMO and SUMO interaction motifs (SIMs). Moreover, APB nucleation is associated with higher levels of SUMOs and SUMO-mediated recruitment of DNA helicase BLM, resulting in more robust telomeric DNA synthesis. Finally, further boosting SUMO levels at telomeres enhances APB nucleation, BLM enrichment, and telomeric DNA synthesis. Thus, high SUMO levels at telomeres promote APB formation via nucleation, resulting in stronger ALT activity.
许多癌症利用端粒延长替代途径（ALT）来维持端粒。ALT端粒DNA合成发生在与ALT相关的端粒早幼粒细胞白血病小体（APB）中。然而，APB形成的机制尚不清楚。在这里，我们利用CRISPR敲入技术在体内水平追踪早幼粒细胞白血病（PML）蛋白，通过延时成像监测APB的形成。我们发现APB通过两种途径形成：端粒招募PML蛋白从头形成PML小体，或端粒与预先形成的PML小体融合。APB的成核和融合都需要小泛素相关修饰物（SUMO）与SUMO相互作用基序（SIM）之间的相互作用。此外，APB成核与更高水平的SUMO以及SUMO介导的DNA解旋酶BLM的招募有关，从而导致更强的端粒DNA合成。最后，进一步提高端粒处的SUMO水平可增强APB成核、BLM富集和端粒DNA合成。因此，端粒处的高SUMO水平通过成核促进APB形成，从而导致更强的ALT活性。
