Contributions of IDH1 mutation to alternative lengthening of telomeres in lower-grade glioma

这项建议的长期目标是改进低级别星形细胞瘤的治疗。 (LGA)通过定义突变型IDH1蛋白的表达如何促进 另类端粒延长(ALT)。免疫球蛋白A占所有恶性胶质瘤的20%， 随着时间的推移，几乎所有的进展都会发展成致命的高级别胶质瘤。大多数LGA表达一种突变形式的 产生肿块代谢物2-羟基戊二酸的异柠檬酸脱氢酶(IDH1mut)改变 基因表达，并推动肿瘤的发生。IDH1mut如何驱动的一个未被探索的方面 胶质瘤的发生是其与端粒调控的潜在联系。端粒是DNA的重复序列 在没有TERT的情况下，染色体的末端最终会随着每个细胞周期的缩短而缩短 导致端粒保护性屏蔽帽的解离、染色体融合和细胞 死亡。在大多数胶质瘤细胞中，端粒功能障碍可以通过TERT的重新激活得到解决。几乎所有的 然而，LGA使用另一种基于同源重组(HR)的机制来 延长端粒，并在没有TERT的情况下存活。我们最近展示了它的表达 ATRX缺乏背景中的IDH1突变足以驱动P53/PRB的ALT表型- 缺乏人类星形胶质细胞。这些ALT细胞，以及IDH1mut LGA，一直 下调的RAP1和XRCC1，以及XRCC1和/或RAP1的重新表达抑制了 ALT表型。Rap1是谢尔特林复合体的一部分，它的缺失可以引起端粒 不封顶。而XRCC1又是选择性非同源末端的关键成分 连接(ANHEJ)途径，产生致命的染色体端到端融合 端粒脱帽。基于这些观察，我们假设IDH1mut驱动的- RAP1和XRCC1的调节导致端粒功能障碍和aNHEJ抑制 途径，使IDH1mut/ATRX缺陷细胞使用HR和ALT来解析端粒 功能障碍和逃逸细胞死亡。这一假设将通过确定1)来检验 RAP1的下调导致端粒功能障碍，如果这有助于IDH1突变驱动 ALT，2)如果XRCC1的下调改变了未封顶的端粒的途径 修复，如果这有助于IDH1mut驱动的ALT，以及3)如果IDH1mut驱动DNA变化 修复提供了附带的治疗脆弱性。

The long term objective of this proposal is to improve the therapy of lower-grade astrocytoma (LGA) by glioma by defining how expression of the mutant IDH1 protein contributes to alternative lengthening of telomeres (ALT). LGA account for 20% of all malignant glioma, and nearly all progress over time to fatal high-grade glioma. Most LGA express a mutant form of isocitrate dehydrogenase (IDH1mut) that generates the oncometabolite 2-hydroxyglutarate, alters gene expression, and drives tumorigenesis. An unexplored aspect of how IDH1mut drives gliomagenesis is its potential link to telomere regulation. Telomeres are DNA repeats at the ends of chromosomes that, in the absence of TERT, shorten with each cell cycle, eventually leading to dissociation of a telomere-protective sheltrin cap, chromosomal fusion, and cell death. Telomeric dysfunction is resolved in most glioma cells by TERT reactivation. Virtually all LGA, however, use an alternative, homologous recombination (HR)-based mechanism to elongate telomeres and survive in the absence of TERT. We recently showed that expression of IDH1mut in an ATRX-deficient background was sufficient to drive the ALT phenotype in p53/pRb- deficient human astrocytes. These ALT cells, as well as IDH1mut LGA, consistently downregulated RAP1 and XRCC1, and re-expression of XRCC1 and/or RAP1 suppressed the ALT phenotype. RAP1 is part of the sheltrin complex, and its loss can cause telomere uncapping. XRCC1 in turn is a critical component of the alternative non-homologous end joining (aNHEJ) pathway that generates lethal chromosome end-to-end fusions following telomere uncapping. Based on these observations we hypothesize that IDH1mut-driven down- regulation of RAP1 and XRCC1 leads to telomere dysfunction and inhibition of the aNHEJ pathway, enabling IDH1mut /ATRX-deficient cells to use HR and ALT to resolve telomeric dysfunction and escape cell death. This hypothesis will be tested by determining 1) if downregulation of RAP1 causes telomeric dysfunction, and if this contributes to IDH1mut- driven ALT, 2) if downregulation of XRCC1 changes the pathway by which uncapped telomeres are repaired, and if this contributes to IDH1mut- driven ALT, and 3) if IDH1mut-driven changes in DNA repair provide collateral therapeutic vulnerability.