C. elegans as a Model for Telomere Maintenance in Cancer

描述（由申请人提供）：端粒是线性染色体末端的特殊结构，保护它们免受酶的攻击并保持染色体的稳定性。在人类细胞的生长过程中，端粒随着每次分裂而缩短，直到达到临界长度。这样的短端粒变得功能失调，失去了保护功能，细胞识别出它们，并以永久性的停止或死亡作为回应。因此，与复制相关的端粒缩短代表了一种强大的肿瘤抑制机制，事实证明，几乎所有的人类肿瘤都能找到一种方法来保持端粒的恒定长度。肿瘤细胞激活两种潜在途径中的一种来抵消端粒缩短。90%的癌症上调端粒酶复合物，能够通过逆转录延长端粒。10%的肿瘤激活一种基于重组的机制，称为ALT。虽然较少的肿瘤最初依赖于ALT，但它可以被认为是主要的机制，因为ALT可以在端粒酶被抑制时启动，使得靶向端粒酶作为癌症治疗没有效果。虽然酵母、小鼠和人类细胞等模型都强调了端粒对细胞和生物体生存的重要性，但迄今为止，它们未能提供端粒酶和ALT两者调节的详细信息。此外，还没有研究ALT在衰老和癌症中的作用的多细胞系统。在这里，我建议利用我们的发现，秀丽隐杆线虫的端粒代表原始端粒，依赖和调节ALT和端粒酶。我假设线虫的端粒蛋白是这些途径的调节因子，我们可以利用它们来了解ALT在生物体生存和肿瘤发生中的作用。AIM 1旨在分离调节端粒酶和ALT的复合物，表征复合物中的单个蛋白质，并详细分析其端粒功能。AIM 2旨在详细研究线虫和哺乳动物端粒C和G悬垂的产生和维持，基于C悬垂是ALT细胞的决定性特征的假设。在AIM 3中，我们将研究ALT如何在多细胞系统中取代端粒酶作为端粒维持机制。我们创造了这样一个有机体；我们将对其进行表征，并将其用作ALT通路调节因子的筛选工具。综上所述，本研究建议将秀丽隐杆线虫作为癌症端粒维持的模型系统，并在线虫和癌细胞的研究结果之间进行翻译。

DESCRIPTION (provided by applicant): Telomeres are specialized structures at the ends of linear chromosomes that protect them from enzymatic attack and preserve chromosome stability. During the growth of human cells the telomeres shorten with every division until they reach a critical length. Such short telomeres become dysfunctional, lose their protective features, and the cells recognize them and respond with permanent arrest or death. Consequently, replication associated telomere-shortening represents a powerful tumor suppressive mechanism, evidenced by the fact that almost all human tumors find a way to maintain their telomeres at a constant length. Tumor cells activate one of two potential pathways to counteract telomere shortening. 90% of cancers up-regulate the telomerase complex, capable of elongating telomeres by reverse transcription. 10% of tumors activate a recombination-based mechanism termed ALT. While fewer tumors initially rely on ALT, it can be considered the dominant mechanism, since ALT can be initiated upon inhibition of telomerase, rendering targeting of telomerase as cancer therapy without effect. While models such as yeast, mice and human cells have emphasized the importance of telomeres for cellular and organismal survival, they have so far failed to provide detailed information about regulation of both, telomerase and ALT. Furthermore, no multicellular system for studying the role of ALT in aging and cancer is available. Here I propose to take advantage of our finding that C. elegans telomeres represent primitive telomeres that rely on and regulate ALT as well as telomerase. I hypothesize that nematode telomeric proteins are regulators of these pathways, and that we can take advantage of them to understand the roles of ALT in organismal survival and tumorigenesis. AIM 1 is designed to isolate the complexes that regulate telomerase and ALT, to characterize the individual proteins in the complex, and to analyze their telomeric functions in detail. AIM 2 is designed to investigate the generation and maintenance of telomeric C and G overhangs in nematodes and mammals in detail, based on the hypothesis that C overhangs are defining features of ALT cells. In AIM 3 we will study how ALT can replace telomerase as telomere maintenance mechanism in a multicellular system. We have generated such an organism; we will characterize it and use it as a screening tool for regulators of the ALT pathway. In summary, this proposal suggests to establish C. elegans as a model system for telomere maintenance in cancer, and to translate between findings in nematodes and cancer cells. PUBLIC HEALTH RELEVANCE: Cancer is an extremely variable disease, and the multiple different tumor types share few common aspects that can be targeted for therapy. Given that all cancers need to find a way to maintain telomere length in order to obtain immortality, telomeres, the natural ends of linear chromosomes, represent one of these universal targets. This proposal consists of three specific aims designed to understand telomere length maintenance mechanisms in the more primitive regulative system of the nematode C elegans, which can be decoded more efficiently, with the final goal of the development of inhibitors of these pathways as cancer therapy tools.