Genetic Susceptibility to Loss of Tumor Suppressor Gene

肿瘤抑制基因功能的丧失和/或原癌基因的激活通过遗传或表观遗传改变导致控制细胞周期、进展和增殖的相关信号通路的功能障碍。最终，由于不受控制的程序性细胞死亡和增殖的前肿瘤细胞的克隆衍生而导致的基因剂量失衡和基因组不稳定与啮齿动物和人类的肿瘤的发展有关。我们观察到C57BL/6-Trp53和B6C3F1-Trp53单倍体缺陷小鼠对遗传毒性致癌物或电离辐射诱导的杂合性丢失(LOH)和造血干细胞(HSC)肿瘤的基因组不稳定性更敏感(致癌时间和患病率)。129B6F1或C3B6F1 N12 Trp53单倍体缺陷小鼠在暴露于各种人类致癌物(包括电离辐射、苯、环磷酰胺、马法兰等)后会发生HSC肿瘤。与B6129N5TrP53野生型小鼠和B6129-TrP53+/-N5&lt；N12同型小鼠相比，B6129-TrP53+/-N5&lt；N12小鼠的患病率非常快(~2-3倍)，患病率(60%-100%)更高(外显率高)。这些致癌物诱导的HSC肿瘤中11号染色体TrP53位点杂合性缺失的发生率增加。此外，致癌物特异性的LOH诱导模式与非错配或非法重组相一致。到目前为止进行的研究缺乏完全的杂合性(每个遗传位点上不同的等位基因)，这阻碍了与肿瘤抑制基因功能丧失相关的LOH位点的准确定位。为了增加确定LOH(染色体和基因组范围)位置所需的所有遗传基因座的杂合性，我们使用对HSC肿瘤具有不同易感性的小鼠品系(129×B6、C3Hx B6和B6×D2)进行了一系列杂交。这些菌株对致癌物诱导的HSC肿瘤诱导表现出不同的敏感性(外显性)。利用F1杂交种，我们正在研究肿瘤抑制基因座的丢失，以及与双链染色体断裂和修复途径功能障碍后潜在的丢失机制(非分离、同源序列定向修复或非同源序列定向修复)相关的丢失模式。通过定位LOH位点(SSLP和单倍型标记)，并与基因表达谱(cDNA和蛋白质微阵列)和基因剂量失衡(阵列CGH)相关联，我们可以确定特定的和决定性的遗传事件(数量性状基因座)。这种方法还将识别在敏感和耐药小鼠品系中修改HSC肿瘤诱导和发展的基因，以推断出人类单倍型和基因类型。

The loss of tumor suppressor gene function and/or activation of proto-oncogenes through genetic or epigenetic alterations lead to the dysfunction of associated signaling pathways that control the cell cycle, progression, and proliferation. Ultimately, the gene dosage imbalance and genomic instability resulting from the clonal derivation of pre-neoplastic cells with uncontrolled programmed cell death and proliferation is associated with the development of neoplasms in both rodents and humans. We have observed that C57BL/6-Trp53 and B6C3F1-Trp53 haploinsufficient mice are more susceptible (time to tumor and prevalence) to genotoxic carcinogen or ionizing radiation induced loss of heterozygosity (LOH) and genomic instability in hematopoietic stem cell (HSC) neoplasms. 129B6F1 or C3B6F1 N12 Trp53 haploinsufficient mice develop HSC neoplasms after exposure to a variety of human carcinogens (including ionizing radiation, benzene, cyclophosphamide, melphalan, etc.) very rapidly (~2-3x faster) and with greater prevalence (60-100%) than B6129N5 Trp53 wild type mice and prevalence (with a high degree of penetrance) in B6129-Trp53+/- N5 < N12 isotype. These carcinogen induced HSC neoplasms have an increased prevalence for loss of heterozygosity involving the Trp53 locus on chromosome 11. In addition, the carcinogen specific induced pattern of LOH is consistent with either non-dysjunction or illegitimate recombination. Studies performed to date have lacked complete heterozygosity (different alleles at each genetic locus), which has prevented accurate mapping of sites of LOH associated with loss of tumor suppressor gene functions. To increase heterozygosity at all genetic loci required to determine the sites of LOH (chromosome and genome wide) we have made a series of intercrosses using mouse strains with varying susceptibility to HSC neoplasms (129 x B6, C3H x B6, and B6 x D2). Each of these strains shows varying susceptibility (penetrance) to carcinogen induced HSC neoplasm induction. Using F1 hybrids we are investigating the loss of tumor suppressor gene loci, the pattern of loss associated with potential mechanisms of loss (non-disjunction, homologous sequence directed repair, or non-homologous sequence directed repair) following double stranded chromosome breaks and repair pathway dysfunction. By mapping sites of LOH (SSLP and haplotype markers) and correlating with gene expression profiles (cDNA and protein microarrays), and gene dosage imbalance (array CGH) we can determine the specific and determinant genetic events (quantitative trait loci). This approach will also identify genes that modify the induction and development of HSC neoplasms in susceptible and resistant mouse strains for extrapolation to human haplotypes and genotypes.