DOUBLE STRAND BREAKS AND CARCINOGENESIS

肿瘤细胞的特征之一是基因重排，包括 缺失、易位、倒置和有丝分裂重组。在许多 这些损害导致致癌突变或 肿瘤抑制基因杂合性缺失。发起人 这些类型的重组的损害是DNA链断裂(590)。因此， 链断裂的产生很可能是 一些肿瘤类型的演变，尽管还不清楚演变到什么程度 这可能是肿瘤发生的速率限制。P53功能丧失是 肿瘤中另一种非常常见的基因改变。在正常细胞中，P53是 对DNA损伤，特别是双链断裂的反应而诱导，导致细胞 损伤细胞的周期停滞和/或凋亡。P53的丢失将会 允许细胞积累额外的遗传损伤，例如 DSB引起的重排的例子。严重联合免疫缺陷 (SCID)小鼠在DSB修复方面存在严重缺陷，并对 自发性和辐射诱导的淋巴肿大。我们建议这些 小鼠代表了一种非常有用的模型来研究DSB在其中的作用 几种不同组织的肿瘤发生。它们也将对以下方面有用 从DSB到P53诱导细胞凋亡的分子途径剖析 特定于组织的上下文。目标一号将确定SCID/SCID和SCID/+ 小鼠易受多种组织特异性致癌方案的影响 包括皮肤、肝脏和肺。这将解决 DSB在不同肿瘤类型演变中的重要性。会的 也揭示了这种缺陷的杂合子携带者是否有更高的风险。 如果是这样的话，这可能对人类杂合子携带者产生影响 类似的缺陷。目标二将检查SCID/SCID的易感性 小鼠对特定的DSB诱导的化疗药物，包括依托泊苷， 环丙沙星和博莱霉素。这将决定DSB诱导是否可以成为 致癌的限速步骤。目标三将决定是否 P53诱导后，SCID小鼠细胞凋亡通路异常。目标三意志 还确定辐射诱导的P53表达和细胞凋亡是否不同 肿瘤类型(皮肤、肝脏和肺)和如果p53 基因分型可预测体内肿瘤细胞的凋亡反应。目标四 将检测在SCID小鼠诱导的肿瘤中P53的突变失活 以确定是否存在针对P53功能的异常强烈的选择。 目标5中的等位基因分析将被用来确定频率 大规模的基因重排，如缺失，在 来自SCID小鼠的肿瘤，以及确定替代的遗传途径 这可能是对P53失活的补充。

One of the hallmarks of tumor cells is genetic rearrangements, including deletions, translocations, inversions, and mitotic recombination. In many cases these lesions result in the activation of oncogenic mutations or loss of heterozygosity (LOH) of tumor suppressor genes. The initiating lesion for these types of recombination is DNA strand breaks (590). Thus the generation of strand breaks could well be a necessary step for the evolution of some tumor types, although it is not clear to what extent this might be rate limiting for tumorigenesis. Loss of p53 function is another very common genetic alteration in tumors. In normal cells p53 is induced in response to DNA damage, specifically dsbs, resulting in cell cycle arrest and/or apoptosis of the damage cell. Loss of p53 would render the cells permissive to accumulate additional genetic lesions, for example dsb-induced rearrangements. Severe combined immunodeficient (SCID) mice are severely defective in repair of dsbs and are sensitive to spontaneous and radiation-induced lymphomagenesis. We suggest that these mice represent a very useful model to examine the role of dsbs in tumorigenesis of several different tissues. They will also be useful to dissect the molecular pathway from dsbs to p53 induction to apoptosis in a tissue specific context. Aim one will determine if scid/scid and scid/+ mice are susceptible to several tissue specific carcinogenesis protocols including skin, liver, and lung. This will address the question of the importance of dsbs in the evolution of different tumor types. It will also reveal if heterozygous carriers of this defect are at increased risk. If so this could have implications for human heterozygous carriers of similar defects. Aim two will examine the susceptibility of scid/scid mice to specific dsb-inducing chemotherapeutic agents including etoposide, campothecin and bleomycin. This will determine if dsb induction can be a rate limiting step for carcinogenesis. Aim three will determine if the p53 induction, apoptosis pathway is abnormal in SCID mice. Aim three will also determine if radiation-induced p53 expression and apoptosis differ substantially between tumor types (skin, liver and lung) and if p53 genotype predicts the apoptotic response of tumor cells in vivo. Aim four will examine mutational inactivation of p53 in tumors induced in SCID mice to determine if there is unusually strong selection against p53 function. Allelotype analysis in aim five will be used to determine if the frequency of large scale genetic rearrangements, such as deletions, is increased in tumors from SCID mice, as well as to identify alternative genetic pathways which might complement p53 inactivation.