Telomere length heterogeneity in ALT cells is maintained by PML-dependent localization of the BTR complex to telomeres
Telomere length heterogeneity in ALT cells is maintained by PML-dependent localization of the BTR complex to telomeres
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DOI：
10.1101/gad.333963.119
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发表时间：
2020-05-01
影响因子：
10.5
通讯作者：
Denchi, Eros Lazzerini
中科院分区：
文献类型：
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作者：
Loe, Taylor K.;Li, Julia Su Zhou;Denchi, Eros Lazzerini
端粒由蛋白质复合物结合的TTAGGG重复序列组成，蛋白质复合物用于保护线性染色体的天然末端。大多数细胞通过使用端粒酶来维持端粒重复长度，尽管也有一些癌细胞使用端粒延伸的非端粒酶依赖机制，称为端粒替代延长（ALT）。使用ALT的细胞的特征部分在于存在称为ALT相关PML小体（APB）的特化PML核小体。APB定位于端粒末端，并与端粒和DNA损伤因子一起聚集，这导致了这些机构作为ALT发生的平台的建议。然而，APB的必要性及其在ALT途径中的功能仍不清楚。在这里，我们使用CRISPR/Cas9从ALT阳性细胞中删除PML和APB组分，以清晰地定义APB在ALT中的功能。我们发现PML是ALT机制所必需的，并且这种必要性源于APB在将BLM-TOP 3A-RMI（BTR）复合物定位于ALT端粒末端中的作用。引人注目的是，BTR复合物以不依赖PML的方式募集到端粒绕过了ALT途径中对PML的需要，这表明BTR定位到端粒足以维持ALT活性。
Telomeres consist of TTAGGG repeats bound by protein complexes that serve to protect the natural end of linear chromosomes. Most cells maintain telomere repeat lengths by using the enzyme telomerase, although there are some cancer cells that use a telomerase-independent mechanism of telomere extension, termed alternative lengthening of telomeres (ALT). Cells that use ALT are characterized, in part, by the presence of specialized PML nuclear bodies called ALT-associated PML bodies (APBs). APBs localize to and cluster telomeric ends together with telomeric and DNA damage factors, which led to the proposal that these bodies act as a platform on which ALT can occur. However, the necessity of APBs and their function in the ALT pathway has remained unclear. Here, we used CRISPR/Cas9 to delete PML and APB components from ALT-positive cells to cleanly define the function of APBs in ALT. We found that PML is required for the ALT mechanism, and that this necessity stems from APBs' role in localizing the BLM-TOP3A-RMI (BTR) complex to ALT telomere ends. Strikingly, recruitment of the BTR complex to telomeres in a PML-independent manner bypasses the need for PML in the ALT pathway, suggesting that BTR localization to telomeres is sufficient to sustain ALT activity.