Radiation-induced Thyroid Cancer

描述(申请人提供)：1986年，苏联切尔诺贝利核电站发生事故，导致高水平的放射性同位素泄漏。十年后，切尔诺贝利附近儿童乳头状甲状腺癌(ChPTC)的发病率上升了两个数量级，很可能是由于暴露在电离辐射中的增加。辐射导致这些额外的甲状腺癌的途径和机制仍然是个谜。10多年前，我们和我们在德国的合作者开始存档核电站附近接受甲状腺切除术的患者的甲状腺肿瘤组织，其中包括214份来自儿童的标本。由于涉及10号染色体的ret/ptc1或ret/ptc3染色体重排，该标本中的一些肿瘤异常表达ret酪氨酸激酶转录本。然而，许多其他chPTC肿瘤的表型与ret异常表达无关。相反，大多数细胞表现出正常的G显带核型。此外，即使在ret阳性的chPTC肿瘤中，并不是所有的细胞都表达ret或含有重排的10号染色体。我们假设这些其他类型的肿瘤可能由于染色体重排而不适当地表达不同的癌基因或失去了肿瘤抑制基因的功能，了解导致chPTC的基因改变可能有助于肿瘤的早期发现和分期，并为治疗干预提供指导。为了验证这一假设，我们建议定位29例辐射诱导的chPTC的染色体断裂点位置，并识别表达模式异常的基因。使用我们最近开发的一种名为BAC-FISH的灵敏的全基因组筛查技术，我们将定位10个辐射诱导的肿瘤(9例chPTC和1例成人)的断裂点，我们对这些肿瘤有细胞系以及G显带和光谱核型分析结果。断点大致确定后，我们将准备跨越断点的BAC重叠群和重新排列的高分辨率物理图。基于Matrigel的细胞侵袭分析将为进一步的细胞遗传学研究提供侵袭细胞的亚群，以研究侵袭细胞结构异常的存在或不存在以及候选基因的表达。下一步，我们将确定另外20例chPTC中是否存在这些易位，我们已经对这些病例的中期分裂相进行了归档。对照组将包括没有事先接受过辐射暴露而患上甲状腺癌的儿童，以及在儿童或成人时接受过放射治疗的成年患者的肿瘤。其他对照样本将由来自没有已知电离辐射暴露史的患者的甲状腺癌细胞株组成。来自对照组的间期细胞准备将用针对候选基因座的DNA探针进行研究，以检测重排。对于六种最常见的重排，我们将使用公开可用的数据库和生物信息学工具来识别在染色体断裂点或附近映射的基因。最后，我们将使用多靶点原位杂交分析来检测候选基因的潜在致癌转录本(MRNAs)的水平和细胞内的定位，以及断点区的表达序列。与公共卫生相关：我们对隐蔽易位的创新筛查试验比现有的肿瘤核型分析程序至少敏感一个数量级，因此可能为更好的风险评估、诊断或个性化疾病管理提供丰富的信息。具体地说，拟议的研究将有助于加强我们对复杂生物系统的了解，例如放射性核素的甲状腺特异性致癌作用。我们期望这项研究能够在早期发现疾病和更好地管理疾病方面改善对PTC的控制，从而加强公共卫生服务。

DESCRIPTION (provided by applicant): In 1986, an accident at the nuclear power plant in Chernobyl, USSR, led to the release of high levels of radioisotopes. Ten years later, the incidence of childhood papillary thyroid cancer (chPTC) near Chernobyl had risen by 2 orders of magnitude, most likely as a consequence of increased exposure to ionizing radiation. The routes and mechanisms by which radiation generated these additional thyroid cancers remain mysterious. More than 10 years ago, we and our collaborators in Germany began to archive thyroid tumor tissues from patients who underwent thyroidectomy near the site of the power plant, among them 214 specimens from children. Several tumors from this collection aberrantly expressed ret tyrosine kinase transcripts due to a ret/PTC1 or ret/PTC3 chromosomal rearrangements involving chromosome 10. However, many other chPTC tumors have phenotypes not attributable to aberrant ret expression. Instead, most cells showed a normal G-banded karyotype. Moreover, even within a ret-positive chPTC tumor, not all cells express ret or contain a rearranged chromosome 10. We hypothesize that these other classes of tumors may inappropriately express a different oncogene or have lost function of a tumor suppressor as a result of chromosomal rearrangements and that knowledge of the kind of genetic alterations leading to chPTC may facilitate the early detection and staging of tumors as well as provide guidance for therapeutic intervention. To test this hypothesis, we propose to map the sites of chromosomal breakpoints in 29 cases of radiation-induced chPTC and identify genes with abnormal pattern of expression. Using a sensitive, genome-wide screening technique termed 'BAC-FISH', which we developed recently, we will localize the breakpoints in 10 radiation-induced tumors (9 chPTC cases and 1 adult case) for which we have cell lines as well as G-banding and Spectral Karyotyping results. With the breakpoints grossly determined, we will prepare breakpoint-spanning BAC contigs and high- resolution physical maps of the rearrangements. Matrigel-based cell invasion assays will provide us with subsets of invasive cells for further cytogenetic studies investigating the presence or absence of structural abnormalities in invasive cells as well as the expression of candidate genes. Next, we will determine the presence or absence of these translocations in 20 additional cases of chPTC for which we already archived metaphase spreads. Control groups will be comprised of children who developed thyroid cancer without prior radiation exposure as well as tumors in adult patients who underwent radiotherapy as children or adults. Additional controls samples will be comprised of thyroid cancer cell lines from patients without a known history of exposure to ionizing radiation. Interphase cell preparations from the control groups will be studied with DNA probes specific for candidate loci to detect rearrangements. For the six most common rearrangements, we will identify genes that map at or near the chromosomal breakpoints using publicly available databases and bioinformatics tools. Finally, we will examine the levels and intracellular localization of potentially oncogenic transcripts (mRNAs) from candidate genes and expressed sequences in the breakpoint regions using multi-target in situ hybridization analyses. PUBLIC HEALTH RELEVANCE: Our innovative screening assay for cryptic translocations is at least one order of magnitude more sensitive than existing tumor karyotyping procedures and might thus provide a wealth of information for a better risk assessment, diagnosis or individualized disease management. Specifically, the proposed studies will help to enhance our understanding of complex biological systems such as the thyroid- specific carcinogenicity of radionuclides. We expect this research to lead to improved control of PTC with regard to early disease detection and better disease management and, thus, to enhance public health services.