Department of Biological Sciences & Institute of Molecular Biology and Genetics (IMBG), Seoul National University, 1 Gwanak-Ro, Gwanak-Gu, Seoul 08826, Korea.
Interdisciplinary Program in Bioengineering, Seoul National University, Seoul 08826, Korea.
Nucleic Acids Res. 2024 Jun 10;52(10):5756-5773. doi: 10.1093/nar/gkae251.
Dynamic interaction between BRCA2 and telomeric G-quadruplexes (G4) is crucial for maintaining telomere replication homeostasis. Cells lacking BRCA2 display telomeric damage with a subset of these cells bypassing senescence to initiate break-induced replication (BIR) for telomere synthesis. Here we show that the abnormal stabilization of telomeric G4 following BRCA2 depletion leads to telomeric repeat-containing RNA (TERRA)-R-loop accumulation, triggering liquid-liquid phase separation (LLPS) and the assembly of Alternative Lengthening of Telomeres (ALT)-associated promyelocytic leukemia (PML) bodies (APBs). Disruption of R-loops abolishes LLPS and impairs telomere synthesis. Artificial engineering of telomeric LLPS restores telomere synthesis, underscoring the critical role of LLPS in ALT. TERRA-R-loops also recruit Polycomb Repressive Complex 2 (PRC2), leading to tri-methylation of Lys27 on histone H3 (H3K27me3) at telomeres. Half of paraffin-embedded tissue sections from human breast cancers exhibit APBs and telomere length heterogeneity, suggesting that BRCA2 mutations can predispose individuals to ALT-type tumorigenesis. Overall, BRCA2 abrogation disrupts the dynamicity of telomeric G4, producing TERRA-R-loops, finally leading to the assembly of telomeric liquid condensates crucial for ALT. We propose that modulating the dynamicity of telomeric G4 and targeting TERRA-R-loops in telomeric LLPS maintenance may represent effective therapeutic strategies for treating ALT-like cancers with APBs, including those with BRCA2 disruptions.
BRCA2 与端粒 G-四链体（G4）之间的动态相互作用对于维持端粒复制稳态至关重要。缺乏 BRCA2 的细胞显示出端粒损伤，其中一部分细胞绕过衰老，启动引发复制（BIR）以合成端粒。在这里，我们表明 BRCA2 耗竭后端粒 G4 的异常稳定导致端粒重复包含 RNA（TERRA）-R 环积累，触发液-液相分离（LLPS）和形成替代端粒延长（ALT）相关早幼粒细胞白血病（PML）体（APBs）。R 环的破坏消除了 LLPS 并损害了端粒合成。端粒 LLPS 的人工工程恢复了端粒合成，强调了 LLPS 在 ALT 中的关键作用。TERRA-R 环还招募 Polycomb 抑制复合物 2（PRC2），导致组蛋白 H3 赖氨酸 27 三甲基化（H3K27me3）在端粒上。人类乳腺癌石蜡包埋组织切片的一半表现出 APBs 和端粒长度异质性，表明 BRCA2 突变可以使个体易患 ALT 型肿瘤发生。总体而言，BRCA2 缺失破坏了端粒 G4 的动态性，产生 TERRA-R 环，最终导致端粒液体凝聚的组装对于 ALT 至关重要。我们提出，调节端粒 G4 的动态性和靶向端粒 LLPS 维护中的 TERRA-R 环可能代表治疗具有 APB 的 ALT 样癌症的有效治疗策略，包括那些具有 BRCA2 中断的癌症。
