The Role of Fragile Sites in RET/PTC Rearrangement

 描述（申请人提供）：染色体重排是肿瘤细胞中常见的基因组异常，可改变相关基因的正常功能，从而促进癌症发展。尽管它们普遍存在，但关于形成易位的机制仍有许多未知之处。几种常见的染色体重排，RET/PTC，AKAP 9/BRAF，STRN/ALK，ETV 6/NTRK 3和几种NTRK 1基因融合，有助于甲状腺乳头状癌（PTC），一种主要类型的甲状腺癌的发展。在美国一般人群中，甲状腺癌是增长最快的癌症类型。与普通人群相比，美国空军现役人员的发病率增加了4至7倍，尽管总体癌症在军事人员中的发生率较低。我们首次证明了染色体脆性位点的DNA断裂直接参与了人甲状腺细胞中致癌性RET/PTC 1重排的产生。脆性位点对一系列化学物质敏感，并且已经在缺失和染色体重排区域中被鉴定。所有参与PTC重排的伴侣基因都位于已知的脆性位点。一般人群每天都会遇到和/或军事人员会遇到的几种环境暴露，如苯（炸药、喷气式飞机和汽车尾气以及凝固汽油弹）和二乙基亚硝胺（香烟烟雾和杀虫剂），也会引起脆弱部位的断裂。其中许多，包括苯，与甲状腺癌的风险呈正相关。我们假设这些药物单独或联合使用会增加甲状腺癌的发病率。在这项提案中，我们将研究环境暴露是否会产生RET脆性，通过检查各种已知诱导脆性位点的环境和治疗药物，导致人类甲状腺细胞中的RET/PTC重排，并将这项研究扩展到其他PTC特异性重排。接下来，我们将通过确定DNA复制过程中二级结构的形成是否有助于RET基因在RET/PTC重排形成中的不稳定性，来确定脆弱位点介导的RET/PTC重排对这些环境暴露的反应机制。然后，为了将DNA脆性应用于DNA诊断试验的临床应用，我们将测试具有重排的PTC患者的正常细胞中RET和其他参与重排的基因的断裂是否高于正常个体，作为评估个体对PTC的易感性的手段。这一建议将对我们理解环境因素在RET/PTC和其他甲状腺癌重排中的直接作用产生重大影响。这些机制的研究将提供新的知识，以更好地了解脆性位点断裂及其在散发性癌症发生中的作用。此外，使用参与重排的基因的优先断裂特性的数据来创建DNA测试可以潜在地扩展到由脆性位点介导的重排引起的其他癌症。

 DESCRIPTION (provided by applicant): Chromosomal rearrangements are a common genomic abnormality found in tumor cells, which can alter the normal function of the genes involved, thus contributing to cancer development. Despite their prevalence, much remains unknown about the mechanisms that form translocations. Several commonly occurring chromosomal rearrangements, RET/PTC, AKAP9/BRAF, STRN/ALK, ETV6/NTRK3 and several NTRK1 gene fusions, contribute to the development of papillary thyroid carcinomas (PTC), a major type of thyroid cancer. In the US general population, thyroid cancer is the fastest increasing type of cancer. Its incidence has increased 4 to 7-fold in US Air Force active-duty personnel compared to the general population, even though overall cancers are less frequent in military personnel. We have demonstrated for the first time that DNA breaks at chromosomal fragile sites participate directly in the generation of oncogenic RET/PTC1 rearrangements in human thyroid cells. Fragile sites are sensitive to a range of chemicals, and have been identified in the regions of deletions and chromosomal rearrangements. All partner genes participating in PTC rearrangements are located in known fragile sites. Several environmental exposures, which are daily encountered by the general population and/or intensified in military personnel, such as benzene (in explosives, jet and automobile exhausts, and napalm) and diethylnitrosamine (in cigarette smoke and pesticides), also induce fragile site breakage. Many of them, including benzene, show a positive association with the risk of thyroid cancer. We hypothesize that these agents alone or in combination contribute to the increased incidence of thyroid cancer. In this proposal, we will investigate whether environmental exposures generate RET fragility, leading to RET/PTC rearrangements in human thyroid cells by examining a variety of environmental and therapeutic agents known to induce fragile sites, and will expand this study to other PTC-specific rearrangements as well. Next, we will identify the mechanism of fragile site-mediated RET/PTC rearrangements in response to these environmental exposures, by determining whether the formation of secondary structures during DNA replication contribute to RET gene instability in the formation of RET/PTC rearrangements. Then, to work towards clinical application of DNA fragility to a DNA diagnostic test, we will test whether breakage of RET and other rearrangement-participating genes in normal cells of PTC patients with rearrangements is higher than that in normal individuals, as a means to evaluate individual susceptibility to PTC. This proposal will have significant impact on our understanding of the direct role of environmental factors in the RET/PTC and other rearrangements of thyroid cancers. These mechanistic studies will provide new knowledge to better understand fragile site breakage and its role in sporadic cancer initiation. Further, using data on preferential breakage properties of rearrangement-participating genes to create a DNA test can potentially be extended to other cancers caused by fragile site-mediated rearrangements.