C. elegans as a Model for Telomere Maintenance in Cancer

描述(申请人提供)：端粒是位于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，端粒随着每一次分裂而变短，直到它们达到临界长度。这样的短端粒会功能失调，失去它们的保护功能，细胞识别它们，并以永久停滞或死亡做出反应。因此，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。肿瘤细胞激活两条可能的途径中的一条来抵消端粒缩短。90%的癌症会上调端粒酶复合体的表达，端粒酶复合体能够通过逆转录延长端粒。10%的肿瘤激活了一种基于重组的机制，称为ALT。虽然最初依赖ALT的肿瘤较少，但它可以被认为是主导机制，因为ALT可以在端粒酶被抑制时启动，从而使靶向端粒酶作为癌症治疗没有效果。尽管酵母、小鼠和人类细胞等模型强调了端粒对细胞和生物生存的重要性，但它们迄今未能提供关于端粒酶和丙氨酸氨基转移酶两者调节的详细信息。此外，还没有多细胞系统来研究ALT在衰老和癌症中的作用。在这里，我建议利用我们的发现，线虫端粒代表依赖和调节ALT和端粒酶的原始端粒。我推测线虫端粒蛋白是这些途径的调节者，我们可以利用它们来了解ALT在有机体生存和肿瘤发生中的作用。目的1旨在分离调节端粒酶和丙氨酸氨基转移酶的复合体，鉴定复合体中的单个蛋白质，并详细分析它们的端粒功能。目的2旨在详细研究线虫和哺乳动物中端粒C和G悬垂的产生和维持，基于C悬垂是ALT细胞的定义特征的假设。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。我们已经创造了这样一种有机体；我们将对其进行表征，并将其用作ALT途径调节器的筛选工具。总之，这项建议建议建立线虫作为癌症端粒维持的模式系统，并在线虫和癌细胞中的发现之间进行转换。 公共卫生相关性：癌症是一种极其多变的疾病，多种不同的肿瘤类型几乎没有共同的方面可以作为治疗的靶点。鉴于所有癌症都需要找到一种保持端粒长度的方法才能获得永生，端粒，即线性染色体的自然末端，是这些普遍存在的目标之一。这项提案由三个具体目标组成，旨在了解线虫线虫更原始的调节系统中的端粒长度维持机制，该机制可以更有效地解码，最终目标是开发这些途径的抑制剂作为癌症治疗工具。

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.