IONIZING RADIATION MUTAGENESIS IN ATAXIA TELANGIECTASIA

共济失调毛细血管扩张(AT)是一种遗传性(隐性)神经系统疾病 以各种病理情况为特征的疾病，包括 对电离辐射(IR)的敏感度提高以及癌症倾向。 即使AT基因的无症状携带者(AT杂合子)也表现出较高的 癌症发病率。最近，AT互补组A、C和D已经 被定位在染色体11q23上，虽然这些座位上的基因(S)， 它们的产品，因此，它们的功能仍未确定。因为 AT患者的细胞比正常细胞更敏感 并表现出更高的染色体异常发生率 在暴露于IR之后，AT的主要缺陷与 对红外线造成的DNA损伤的错误修复。然而，尽管有几个 研究发现，辐射后AT细胞的DNA修复存在缺陷。近期 对酵母和其他细胞的研究表明，G2停滞可能起到 在细胞对IR损伤的反应中起关键作用；抵抗细胞 显示出比敏感单元格更长的延迟。G2中的细胞周期延迟， 在有丝分裂之前可能会增加(DNA)损伤评估的时间和 修理。这项提议将调查这样一个假设，即，而不是 一个错误的DNA损伤修复过程(ES)，AT细胞缺乏对DNA- 损伤修复，在照射正常但不能在G2-停滞期间诱导 在照射后的AT细胞中。此外，蛋白激酶C的参与 (PKC)依赖的通路，都与细胞对IR的反应有关，在 这些过程和AT细胞中一个通路的缺陷将是 调查过了。拟议的研究涉及到使用具有良好特征的 能够在人类细胞中复制的穿梭质粒。Ir.-损坏 将质粒导入并经辐照或 评估未照射的AT和正常细胞的DNA损伤修复能力和 富达。将回收和分析该质粒的后代 重新激活(存活)、突变频率，以及通过基因测序， 突变类型以确定细胞对DNA的反应是否存在差异 AT细胞与正常细胞之间存在损伤。通过将诱变作用与 经辐照和未辐照的细胞处理的损伤质粒， 辐射对DNA加工的影响可以与那些 DNA损伤修复过程中产生的特定突变。Ir.-损坏 修理。建立PKC激活、DNA修复和G2的连锁 阻止，我们将研究修复IR受损的质粒，细胞存活 以及PKC活性被阻断或被阻断的细胞的G2期阻滞程度 由特定的化学物质刺激。最后，AT和AT之间的区别 正常细胞在PKC的激活和近端台阶的刺激下 在通路中的PKC及其远端，将进行IR检查。这个 IR诱导AT细胞DNA损伤修复的研究进展 细胞周期和PKC信号转导在修复过程中的作用 旨在促进对AT分子基础的理解 叛逃。这样的认识将有助于发展有效的 这一复杂综合征患者的筛查方法和治疗。

Ataxia telangiectasia (AT) is an inherited (recessive) neurologic disorder characterized by diverse pathological conditions including heightened sensitivity to ionizing radiation (I.R.) and cancer proneness. Even asymptomatic carriers of the AT gene (AT heterozygote) show a higher incidence of cancer. Recently, AT complementation groups A, C and D have been localized to chromosome 11q23, although the gene(s) at these loci, their products and, thus, their functions remain unidentified. Because cells from AT patients are more sensitive than are normal cells to killing by and show a greater incidence of chromosomal aberrations followings exposure to I.R., the primary defect in AT has been associated with faulty repair of I.R.-caused DNA damage. However, despite several studies, a defect in DNA repair in AT cells, after irradiation. Recent studies with yeast and other cells suggest that G2 arrest may play a crucial role in the response of cells to I.R. damage; resistant cells show longer delays than do sensitive cells. Cell-cycle delay in G2, prior to mitosis may increase the time for (DNA) damage assessment and repair. This proposal will investigate the hypothesis that, rather than a faulty DNA-damage repair process(es), AT cells lack control of DNA- damage repair, inducible during G2-arrest in irradiated normal but not in irradiated AT cells. Furthermore, involvement of a protein kinase C (PKC)-dependent pathway, both implicated in cell responses to I.R., in these processes and a defect of a pathway in AT cells will be investigated. The proposed study involves the use of well-characterized shuttle plasmid capable of replicating in human cells. I.R. -damaged plasmid will be transfected into and processed by irradiated or unirradiated AT and normal cells to assess DNA damage-repair capacity and fidelity. Progenies of the plasmid will be recovered and analyzed for reactivation (survival), mutation frequencies and, by gene sequencing, mutation types to determine whether differences in cell response to DNA- damage exist between AT and normal cells. By comparing mutagenesis of damage plasmid processed by irradiated and unirradiated cells, the effects of radiation on DNA, processing can be distinguished from those of specific mutations arising from DNA damage repair. I.R.-damage repair. To establish linkage of PKC activation, DNA repair, and G2 arrest, we will study the repair of I.R. damaged plasmid, cell survival and the degree of G2-arrest in cells with PKC activity blocked or stimulated by specific chemicals. Finally, differences between AT and normal cells in PKC activation and in the stimulation of steps, proximal to and distal to PKC in the pathway, by I.R. will be examined. The proposed studies of I.R. induced DNA-damage repair by AT cells and the roles of cell cycle and signal transduction via PKC in the repair process are designed to promote understanding of the molecular basis of the AT defect. Such an understanding will aid the development of effective screening methods and treatment for patients with this complex syndrome.