恶性肿瘤必须激活端粒维护机制才能实现复制的不朽性。人类端粒保护1（POT1）基因的突变常常在具有异常长端粒的癌症中检测到，这表明POT1功能的丧失会破坏端粒长度稳态调控，促进端粒的延长。然而，我们对导致端粒延长的机制的理解尚不完整。小鼠基因组编码两种POT1蛋白，即POT1a和POT1b，具有hPOT1功能分离的特点。我们对Pot1b-/-肉瘤进行了连续移植，以更好地了解POT1b在调节端粒长度维护中的作用。早期的Pot1b-/-肉瘤虽然最初具有缩短的端粒，但是晚期的Pot1b-/-细胞显示明显过度延长的端粒，被复制蛋白A（RPA）复合物识别为损伤的DNA。位于端粒的RPA-ATR依赖性DNA损伤响应促进端粒酶的招募，以促进端粒的超长度延伸。POT1b，而不是POT1a，能够解折在超长度端粒中存在的G四链体，以抑制DNA损伤响应。我们的发现表明RPA-ATR DDR的抑制在POT1b和人类POT1之间是保守的，这表明类似的机制可能解释了携带人类POT1突变的人类癌症观察到的表型。© 作者（们） 2023. 由牛津大学出版社代表核酸研究出版。

Malignant cancers must activate telomere maintenance mechanisms to achieve replicative immortality. Mutations in the human Protection of Telomeres 1 (POT1) gene are frequently detected in cancers with abnormally long telomeres, suggesting that the loss of POT1 function disrupts the regulation of telomere length homeostasis to promote telomere elongation. However, our understanding of the mechanisms leading to elongated telomeres remains incomplete. The mouse genome encodes two POT1 proteins, POT1a and POT1b possessing separation of hPOT1 functions. We performed serial transplantation of Pot1b-/- sarcomas to better understand the role of POT1b in regulating telomere length maintenance. While early-generation Pot1b-/- sarcomas initially possessed shortened telomeres, late-generation Pot1b-/- cells display markedly hyper-elongated telomeres that were recognized as damaged DNA by the Replication Protein A (RPA) complex. The RPA-ATR-dependent DNA damage response at telomeres promotes telomerase recruitment to facilitate telomere hyper-elongation. POT1b, but not POT1a, was able to unfold G-quadruplex present in hyper-elongated telomeres to repress the DNA damage response. Our findings demonstrate that the repression of the RPA-ATR DDR is conserved between POT1b and human POT1, suggesting that similar mechanisms may underly the phenotypes observed in human cancers harboring human POT1 mutations.© The Author(s) 2023. Published by Oxford University Press on behalf of Nucleic Acids Research.