Molecular Mechanisms Regulating the Alternative Lengthening of Telomeres Pathway

项目总结/摘要 端粒覆盖线性染色体的末端，为人类基因组提供分子屏障。 在每次细胞分裂之后，进行性端粒缩短侵蚀了这一屏障，并威胁到细胞的稳定性。 基因组极短或功能失调的端粒诱导复制性衰老和/或细胞死亡， 最终导致细胞老化。然而，癌细胞克服了与癌症相关的复制性衰老。 通过利用端粒延长的机制来缩短端粒。酶的再活化 端粒酶，或端粒替代性延长（ALT）途径的激活，解释了细胞凋亡的原因。 在大多数人类癌症中的永生化。端粒延长机制在大多数情况下是活跃的 然而，在所有的癌细胞中，它们是不存在的或无效的，在正常的体细胞中使它们成为理想的候选者。 用于靶向癌症治疗。目前，临床试验正在进行中，以测试端粒酶抑制剂的疗效 然而，在癌症的治疗中，没有依赖于ALT途径的癌症治疗， 端粒维持这些努力受到限制，部分原因是对分子生物学的不完全理解。 调节ALT途径的机制。最近，我们证明共济失调毛细血管扩张症和Rad 3- DNA损伤反应相关激酶（ATR）是ALT途径的关键调节因子。ATR抑制 激酶活性不仅减少端粒重组，而且导致显著的和选择性的致死性， ALT阳性癌细胞。虽然这些研究是第一次证明ATR的功能要求， ALT通路的维持，ATR究竟如何调节ALT活性以及ATR是否可以靶向 在ALT癌症的背景下治疗，仍然不清楚。因此，这个提案的目的是为了 分离ATR在ALT通路中的功能，验证ATR抑制在ALT中的治疗效果。 积极的癌症，并继续确定调节ALT活性的分子机制。

PROJECT SUMMARY/ABSTRACT Telomeres cap the ends of linear chromosomes and provide a molecular barrier for the human genome. Following each cell division, progressive telomere shortening erodes that barrier and threatens the stability of the genome. Critically short, or dysfunctional telomeres induce replicative senescence and/or cell death and ultimately, lead to cellular aging. Cancer cells, however, overcome the replicative senescence associated with critically short telomeres by exploiting mechanisms of telomere elongation. Reactivation of the enzyme telomerase, or activation of the Alternative Lengthening of Telomeres (ALT) pathway, account for cellular immortalization in the majority of human cancers. Telomere lengthening mechanisms are active in the majority of all cancer cells, however, they are absent or ineffective, in normal somatic cells making them ideal candidates for targeted cancer therapies. Currently, clinical trials are underway to test the efficacy of telomerase inhibitors in the treatment of cancer, however, there are no treatments for cancers that rely on the ALT pathway for telomere maintenance. These efforts have been limited, in part, by an incomplete understanding of the molecular mechanisms regulating the ALT pathway. Recently, we demonstrated that the ataxia telangiectasia and Rad3- related (ATR) DNA damage response kinase was a critical regulator of the ALT pathway. Inhibition of ATR kinase activity not only decreased telomeric recombination, but also led to significant and selective lethality in ALT positive cancer cells. While these studies were the first to demonstrate a functional requirement for ATR in maintenance of the ALT pathway, exactly how ATR regulates ALT activity and whether ATR can be targeted therapeutically in the context of ALT cancers, remains unclear. Therefore, the goal of this proposal is to tease apart the function of ATR within the ALT pathway, validate the therapeutic efficacy of ATR inhibition in ALT positive cancers, and continue to define the molecular mechanisms regulating ALT activity.