Mechanisms of RET/PTC Rearrangement in Thyroid Cancer

描述（由申请人提供）：由于诊断和治疗放射量的迅速扩大，切尔诺贝利和福岛等核电事故，高海拔旅行和其他暴露，人类越来越多地暴露于电离辐射。暴露在辐射下会增加患各种癌症的风险，包括甲状腺癌。然而，辐射致癌的分子机制仍然知之甚少。在本研究的前几个周期中，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变中的核心作用，并建立了γ辐射诱导人甲状腺细胞RET/PTC的剂量依赖性体外模型。此外，我们还获得了70例切尔诺贝利后甲状腺肿瘤，并对这些患者进行了基因分型，这些患者接受了仔细重建的131I甲状腺剂量，并鉴定出20例与高131I剂量相关的肿瘤，所有已知突变均为阴性。我们最近对这一队列的分析显示，在缺碘地区，RET/PTC与离开之间存在很强的联系，我们将在本建议中对此进行探讨，以研究切尔诺贝利事故后发现的缺碘与癌症风险之间关联的原因。此外，我们对一个与高131I剂量相关的突变阴性肿瘤的第一次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仅次于RET/PTC的第二常见的染色体重排类型。这些有价值的工具将在当前的提案中使用，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，我们将验证甲状腺细胞中辐射引起RET/PTC重排的发生率受暴露时的细胞周期阶段和重组区域基因转录状态的影响。我们还将确定ATM和其他同源重组修复基因的下调是否会增强体外甲状腺细胞辐射对RET/PTC的诱导，以及这些基因是否与人类个体对辐射致癌的易感性有关。最后，我们将继续使用新的测序技术来识别与甲状腺高剂量辐射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理解，并提供新的信息，可用于确定那些最易受辐射致癌影响的个体，并制定措施，更好地保护人类免受电离辐射在各种环境中的致癌作用，如医疗治疗辐射，职业辐射暴露，还有核电事故和核恐怖主义。

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 γ-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.