为了应对 DNA 复制过程中端粒磨损的挑战，癌细胞主要使用端粒酶，或者在 10-15% 的情况下使用端粒替代延长 (ALT)。然而，ALT 的复杂细节仍然难以捉摸。在这项研究中，我们发现 ALT 细胞中核纤层相关多肽 2 α (LAP2α) 的敲低会导致端粒功能障碍，引发 ALT 相关标志显着增加，包括高频率的 PML 体 (APB)、富含 C染色体外环（C 环）和端粒姐妹染色单体交换（T-SCE）。此外，LAP2α 在端粒双链断裂后端粒酶阳性细胞的断裂诱导端粒复制中发挥着关键作用。从机制上讲，我们的研究表明 LAP2α 可能影响端粒异染色质状态的调节，从而影响端粒的可及性。与我们的研究结果一致，LAP2α 表达在 ALT 阳性骨肉瘤中显着降低。使用甲氨蝶呤 (MTX) 可以恢复因 LAP2α 耗竭而改变的异染色质状态。 ALT 阳性患者来源的异种移植 (PDX) 小鼠模型中肿瘤增殖的显着抑制证明了这一点。这些结果表明 LAP2α 在调节 ALT 活性中的重要作用，并为了解核纤层相关蛋白和端粒之间在维持端粒长度方面的相互作用提供了见解。重要的是，我们的研究结果可能有助于确定骨肉瘤治疗药物 MTX 更合适的目标人群。© 2024。作者。

In response to the challenge of telomere attrition during DNA replication, cancer cells predominantly employ telomerase or, in 10-15% of cases, the alternative lengthening of telomeres (ALT). The intricate details of ALT, however, remain elusive. In this study, we unveil that the knockdown of lamina-associated polypeptide 2 alpha (LAP2α) in ALT cells results in telomere dysfunction, triggering a notable increase in ALT-associated hallmarks, including high frequencies of PML bodies (APBs), C-rich extrachromosomal circles (C-circles), and telomere sister chromatid exchange (T-SCE). Furthermore, LAP2α emerges as a crucial player in break-induced telomere replication for telomerase-positive cells following telomeric double-strand breaks. Mechanistically, our investigation suggests that LAP2α may influence the regulation of the heterochromatic state of telomeres, thereby affecting telomeric accessibility. In line with our findings, LAP2α expression is markedly reduced in ALT-positive osteosarcoma. And the use of methotrexate (MTX) can restore the heterochromatin state altered by LAP2α depletion. This is evidenced by a significant inhibition of tumor proliferation in ALT-positive patient-derived xenograft (PDX) mouse models. These results indicate the important role of LAP2α in regulating ALT activity and offer insights into the interplay between lamina-associated proteins and telomeres in maintaining telomere length. Importantly, our findings may help identify a more appropriate target population for the osteosarcoma therapeutic drug, MTX.© 2024. The Author(s).