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6个亚单位组成的复合体组成的特殊结构，需要 它们的保护、复制和凝聚力的独特机制。继S阶段复制后，姐妹 染色单体聚集在一起，直到有丝分裂，当它们分布到子细胞时。解决方案 姐妹端粒之间的凝聚需要聚(ADP-核糖)聚合酶，tankyrase 1。tankyrase定位于 通过与端粒结合的TTAGGG-Repeat结合屏蔽在亚单位TRF1中，在晚期S/G2细胞中分解凝聚力。 在tankyrase 1耗尽的细胞中，姐妹端粒在有丝分裂中保持粘连(称为持续端粒凝聚)， 尽管姐妹染色单体臂和着丝粒的分辨率正常。这项建议是以我们最近的发现为基础的。 这种持续的端粒凝聚力(在没有端粒酶的情况下)在极短的时间内起到了保护作用 端粒。我们发现在缩短的端粒上TRF1的减少(以及随之而来的tankyrase缺乏症) 在衰老的细胞(或端粒阴性的癌细胞)中，阻止凝聚力的分解，这(出乎意料地) 起到保护作用，防止过早衰老或生长停滞。我们将阐明其中的机制， 我们展示的是基于RNA的。我们鉴定的RNA结合蛋白是一组重要的Tankyrase 蛋白质组筛选中的相互作用促使人们对RNA在凝聚力中的功能进行了研究。事实上，我们有 发现长的非编码端粒重复序列RNA(Terra)在持久端粒中的作用 凝聚力。我们表明，Terra和Terra R环(RNA/DNA杂交体)的积累是同时发生的 具有持久的端粒凝聚力，以保护严重缩短的端粒。我们将阐明这些蛋白质和 降低端粒凝聚力的Terra水平所需的途径，决定了它们在确保 保护早衰细胞中的短端粒，并探索一种潜在的相变机制 Tankyrase可以分解端粒凝聚力。我们的研究提供了一种依赖于RNA的统一而新颖的机制， R-环和持久的端粒凝聚力可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.