Mechanisms of RET/PTC Rearrangement in Thyroid Cancer

描述（由申请人提供）：由于诊断和治疗辐射量的迅速增加、切尔诺贝利和福岛等核电事故、高海拔旅行和其他暴露，人类暴露于电离辐射的情况日益增加。众所周知，暴露于辐射会增加包括甲状腺癌在内的各种癌症的风险。然而，对辐射致癌的分子机制仍然知之甚少。 在该建议的前几个周期中，我们已经确定了染色体重排（如RET/PTC）在辐射诱导的甲状腺癌发生中的核心作用，并建立了人甲状腺细胞中RET/PTC剂量依赖性诱导的体外模型。辐射此外，我们还从接受131 I仔细重建甲状腺剂量的患者中获得了70例切尔诺贝利后甲状腺肿瘤并进行了基因分型，并确定了20例与高131 I剂量相关的肿瘤，这些肿瘤对所有已知突变均呈阴性。我们最近对这一队列的分析显示，RET/PTC与碘缺乏地区的离开之间存在密切联系，我们将在本提案中探讨碘缺乏与切尔诺贝利事故后发现的癌症风险之间关联的原因。此外，我们对与高131 I剂量相关的突变阴性肿瘤之一进行的第一次RNA-Seq运行导致发现了一种新的染色体重排，我们发现这是切尔诺贝利后癌症中第二种最常见的染色体重排类型，仅次于RET/PTC。这些宝贵的工具将用于本提案，该提案将继续剖析甲状腺中染色体重排和辐射致癌的机制。具体而言，我们将测试的假设，即在甲状腺细胞中的RET/PTC重排的辐射的产生率的影响，在曝光时的细胞周期阶段和基因的转录状态的区域进行重组。我们还将确定是否下调ATM和其他同源重组修复基因增强RET/PTC诱导甲状腺细胞在体外辐射，如果这些基因参与在个人对辐射致癌的易感性。 最后，我们将继续使用新的测序技术来确定与甲状腺高辐射剂量相关的甲状腺癌中发生的新型染色体重排，并将测试新发现的遗传事件是否可以通过体外辐射在人类甲状腺细胞中诱导。这些研究将扩大我们对辐射诱发甲状腺癌的遗传机制的了解，并提供新的信息，可用于确定最易受辐射致癌作用影响的个人，并制定措施，更好地保护人类在各种情况下免受电离辐射的致癌影响，如医疗辐射、职业辐射照射、核事故和核恐怖主义。

DESCRIPTION (provided by applicant): Humans are increasingly exposed to ionizing radiation as a result of rapidly expanding volume of diagnostic and therapeutic radiation, nuclear power accidents such as Chernobyl and Fukushima, high altitude travel, and other exposures. Exposure to radiation is known to increase the risk of various cancers including thyroid cancer. However, the molecular mechanisms of radiation-induced carcinogenesis remain poorly understood. During the previous cycles of this proposal, we have established the central role of chromosomal rearrangements, such as RET/PTC, in radiation-induced thyroid carcinogenesis, and created in vitro models of dose-dependent induction of RET/PTC in human thyroid cells by ?-radiation. Moreover, we have also obtained and genotyped 70 post-Chernobyl thyroid tumors from patients with carefully reconstructed thyroid dose received from 131I and identified 20 tumors associated with high 131I dose that were negative for all known mutations. Our recent analysis of this cohort revealed a strong link between RET/PTC and leaving in the regions of iodine deficiency, which we will explore in this proposal to study the reasons for the association between iodine deficiency and cancer risk found after Chernobyl. Moreover, our first RNA-Seq run of one of the mutation-negative tumors associated with high 131I dose led to the discovery of a novel chromosomal rearrangement, which we find to be the second most common type of chromosomal rearrangements in post- Chernobyl cancers after RET/PTC. These valuable tools will be used in the current proposal, which will continue to dissect the mechanisms of chromosomal rearrangements and radiation carcinogenesis in the thyroid. Specifically, we will test the hypothesis that the rate of generation of RET/PTC rearrangements by radiation in thyroid cells is influenced by cell cycle stage at the time of exposure and transcriptional status of genes in the regions undergoing recombination. We will also determine whether downregulation of ATM and other homologous recombination repair genes enhances RET/PTC induction by radiation in thyroid cells in vitro, and if these genes are involved in the individual susceptibility to radiation carcinogenesis in humans. Finally, we will continue using new sequencing technologies to identify novel types of chromosomal rearrangements occurring in thyroid cancer associated with high radiation dose to the thyroid, and will test if the newly identified genetic events can be induced in human thyroid cells by in vitro radiation. These studies will expand our understanding of the genetic mechanisms of radiation-induced thyroid cancer and provide novel information that can be used to identify those individuals who are most susceptible to radiation carcinogenesis and to develop measures for better protection of human populations against the carcinogenic effects of ionizing radiation in a variety of settings such as medical therapeutic radiation, occupational radiation exposure, and nuclear power accidents and nuclear terrorism.