A role for RNA in sister chromatid cohesion at human telomeres

项目摘要 端粒是由TTAGGG重复序列和六亚基shelterin复合物组成的特殊结构， 它们的保护、复制和凝聚力的独特机制。在S期复制后， 染色单体保持在一起（凝聚），直到有丝分裂时它们被分配到子细胞。解决 姐妹端粒之间的结合需要聚（ADP-核糖）聚合酶，端锚聚合酶1。端锚聚合酶定位 通过结合到TTAGGG-重复结合shelterin亚基TRF 1，在后期S/G2中解决凝聚力。 在端锚聚合酶1耗尽的细胞中，姐妹端粒在有丝分裂中保持凝聚（称为持久端粒凝聚）， 尽管姐妹染色单体臂和着丝粒的分辨率正常。该提案建立在我们最近的发现之上 持续的端粒凝聚力在关键的短时间内起到保护作用（在没有端粒酶的情况下）。 端粒我们发现，在缩短的端粒中TRF 1的减少（以及随之而来的端锚聚合酶缺乏） 在衰老细胞（或端粒阴性癌细胞）中，阻止了凝聚力的消退，这（出乎意料地） 起到保护作用，防止过早衰老或生长停滞。我们将阐明其机制， 我们发现它们是基于RNA的。我们鉴定的RNA结合蛋白是一组重要的端锚聚合酶 蛋白质组学筛选中的相互作用物促使对RNA在凝聚中的功能进行研究。我确已 揭示了含有端粒重复序列的长非编码RNA（TERRA）在持久端粒中的作用， 凝聚力我们发现TERRA和TERRA R环（RNA/DNA杂合体）的积累是伴随着 用持久的端粒凝聚力来保护严重缩短的端粒。我们将阐明蛋白质， 降低TERRA水平以解决端粒内聚所需的途径，决定了它们在确保 保护衰老细胞中的短端粒，并探索一种潜在的相变机制， 端锚聚合酶来解决端粒凝聚。我们的研究提供了一个统一的和新的机制，依赖于RNA， R环和持久的端粒内聚，以缓冲缩短的端粒并促进基因组的完整性。

Project Summary Telomeres, specialized structures comprised of TTAGGG repeats and the six-subunit shelterin complex, require distinct mechanisms for their protection, replication, and cohesion. Following replication in S phase, sister chromatids are held together (cohered) until mitosis when they are distributed to daughter cells. Resolution of cohesion between sister telomeres requires the poly(ADP-ribose) polymerase, tankyrase 1. Tankyrase localizes to telomeres by binding to the TTAGGG-repeat binding shelterin subunit TRF1, in late S/G2 to resolve cohesion. In tankyrase 1 depleted cells sister telomeres remain cohered in mitosis (termed persistent telomere cohesion), despite normal resolution of sister chromatid arms and centromeres. This proposal builds on our recent discovery that persistent telomere cohesion serves a protective function (in the absence of telomerase) at critically short telomeres. We found that reduction of TRF1 (and the consequent tankyrase deficiency) at shortened telomeres in aged cells (or telomeres negative cancer cells) prevents resolution of cohesion and that this (unexpectedly) serves a protective role to prevent premature senescence or growth arrest. We will elucidate the mechanisms, which we show are RNA-based. Our identification of RNA-binding proteins as a significant group of tankyrase interactors in a proteomic screen prompted an investigation into a function for RNA in cohesion. Indeed, we have uncovered a role for the long non-coding telomere repeat-containing RNA (TERRA) in persistent telomere cohesion. We show that accumulation of TERRA and TERRA R-loops (RNA/DNA hybrids) occurs concomitant with persistent telomere cohesion to protect critically shortened telomeres. We will elucidate the proteins and pathways required to reduce TERRA levels for resolution of telomere cohesion, determine their role in ensuring protection of short telomeres in presenescent cells, and explore a potential phase transition mechanism used by tankyrase to resolve telomere cohesion. Our study provides a unifying and novel mechanism that relies on RNA, R-loops, and persistent telomere cohesion to buffer shortened telomeres and promote genome integrity.