Radiation-induced Thyroid Cancer

描述（由申请人提供）：1986年，苏联切尔诺贝利核电站发生事故，导致高水平放射性同位素释放。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2个数量级，很可能是电离辐射暴露增加的结果。辐射产生这些额外甲状腺癌的途径和机制仍然是个谜。十多年前，我们和我们在德国的合作者开始对在核电站附近接受甲状腺切除术的患者的甲状腺肿瘤组织进行存档，其中有214份来自儿童的样本。来自这个集合的一些肿瘤由于ret/PTC1或ret/PTC3染色体重排涉及10号染色体而异常表达ret酪氨酸激酶转录本。然而，许多其他chPTC肿瘤具有不归因于异常ret表达的表型。相反，大多数细胞显示正常的g带核型。此外，即使在ret阳性的chPTC肿瘤中，并非所有细胞都表达ret或包含重排的10号染色体。我们假设这些其他类型的肿瘤可能不恰当地表达不同的癌基因或由于染色体重排而失去肿瘤抑制因子的功能，并且对导致chPTC的遗传改变的了解可能有助于肿瘤的早期检测和分期，并为治疗干预提供指导。为了验证这一假设，我们建议在29例辐射诱导的chPTC中绘制染色体断点位点，并确定异常表达模式的基因。使用我们最近开发的一种称为“BAC-FISH”的敏感全基因组筛选技术，我们将定位10个辐射诱导肿瘤（9个chPTC病例和1个成人病例）的断点，我们有细胞系以及g带和光谱核型结果。随着断点的粗略确定，我们将准备跨越断点的BAC结构和重排的高分辨率物理图。基于矩阵的细胞侵袭试验将为我们提供侵袭细胞的亚群，用于进一步的细胞遗传学研究，研究侵袭细胞中结构异常的存在与否以及候选基因的表达。接下来，我们将在另外20例chPTC病例中确定这些易位的存在或不存在，我们已经存档了中期扩散。对照组将由未接受过放射治疗的患甲状腺癌的儿童以及在儿童或成人时期接受过放射治疗的成年患者的肿瘤组成。另外的对照样本将由没有已知电离辐射暴露史的患者的甲状腺癌细胞系组成。对照组间期细胞的制备将用候选基因座特异性的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识别位于染色体断点或其附近的基因。最后，我们将使用多靶点原位杂交分析检查候选基因和断点区域表达序列的潜在致癌转录物（mrna）的水平和细胞内定位。公共卫生相关性：我们对隐性易位的创新筛选试验比现有的肿瘤核型方法至少敏感一个数量级，因此可能为更好的风险评估、诊断或个体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提高我们对复杂生物系统的理解，如放射性核素的甲状腺特异性致癌性。我们期望这项研究能够在早期疾病检测和更好的疾病管理方面改善对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.