Loci Affecting Colon Cancer Susceptibility

描述(申请人提供)：结肠癌是最常见的人类恶性肿瘤之一，在美国每年有15万新病例和6万人死亡。一些与结肠癌发生发展有关的分子变化是已知的，在大约20%的病例中，已经确定了结肠癌易感性的遗传基础，要么是APC基因的突变，要么是编码参与DNA合成/修复的蛋白质的基因突变。大约80%的病例对零星谣言的易感性的遗传基础是未知的，而且可能是复杂的。我们一直在用小鼠模型研究致癌物诱导的结肠癌的易感性，首先使用致癌物1，2-二甲基肼二盐酸盐(DMH)，然后使用其代谢物偶氮甲烷(AOM)，它更稳定，需要更少的注射。ICR/Ha菌株对DMH诱导的结肠肿瘤高度敏感，而C57BL/6ha菌株对DMH诱导的结肠肿瘤高度敏感。将(ICRxC57BL/6)F1回交到C57BL/6ha，对122个后代进行DMH处理。在这些后代中的一些人中发现了结肠癌，并对所有染色体上的遗传位点进行了分类。利用每只动物的肿瘤数量进行的QTL分析表明，在KRAS5、12、13和14上的四个染色体区域包含有等位基因差异的基因，这些基因影响致癌物诱导的结肠肿瘤的数量。已构建了一组同源菌株，将敏感等位基因分别放置在抗性品系背景上的四个染色体区域中的每一个区域。这些菌株的N5F2代的动物都用DMH处理，在所有四个同源系的大多数动物中都发现了结肠癌。已为所有染色体产生了亚基因系，并检测了对AOM敏感的两组(CLAS 12和14)。我们现在提出四个具体目标。在第一个目标中，我们计划通过减少同源区域的长度来进一步完善每个基因的定位。在第二个目标中，我们计划改进我们的使用AOM的方案，以确定最佳的注射方案，以便所有ICR/Ha小鼠都能发展成肿瘤。随后，将对来自亚基因株系的动物进行测试，以确定包含决定敏感性的基因的最小亚基因间隔。在第三个目标中，我们将解决在肿瘤本身中发生什么基因变化的问题，以及是否存在特异性，从而使任何一种同源菌株产生的肿瘤显示出一致的变化概况。

DESCRIPTION (provided by applicant): Colon cancer is one of the most frequent human malignancies, with 150,000 new cases and 60,000 deaths per year in the United States. Some of the molecular changes involved in the development of colon tumors are known, and in about 20% of the cases the genetic basis for colon tumor susceptibility has been identified, either as a mutation in the Apc locus or as a mutation in a locus encoding a protein involved in DNA synthesis/repair. The genetic basis for susceptibility to sporadic rumors, about 80% of cases, is unknown and is probably complex. We have been working with a mouse model for susceptibility to carcinogen-induced colon cancer, first using the carcinogen 1,2-dimethylhydrazine dihydrochloride (DMH) and later its metabolite azoxymethane, (AOM), which is more stable and requires fewer injections. Strain ICR/Ha is highly sensitive to DMH-induced colon tumors, while strain C57BL/6Ha is resistant. The (ICRxC57BL/6) F1 hybrid was backcrossed to C57BL/6Ha, and 122 progeny were treated with DMH. Colon tumors were detected in some of these progeny, which were typed for genetic loci on all chromosomes. QTL analysis using the number of tumors per animal suggested that four chromosomal regions, on Chrs 5, 12, 13 and 14, contained genes with allelic differences that affected the number of carcinogen-induced colon tumors. A set of congenic strains have been constructed that separately place the sensitive alleles at each of the four chromosomal regions on the background of the resistant strain. Animals from generation N5F2 of each of these strains were treated with DMH and colon tumors were found in most animals from all four congenic lines. Subcongenic lines have been generated for all chromosomes and two sets (Chrs 12 and 14) have been tested and are sensitive to AOM. We now propose four Specific Aims. In the first aim we plan to further refine the mapping of each gene by decreasing the length of the congenic region. In the second aim we plan to refine our protocol for use of AOM to determine the best injection schedule so that all ICR/Ha mice develop tumors. Following this, animals from the subcongenic strains will be tested to identify the smallest subcongenic interval containing the gene determining sensitivity. In the third aim we will address the question of what genetic changes occur in the tumors themselves, and whether there is specificity such that tumors arising from any one of the congenic strains show a consistent profile of changes.