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功能障碍。最终，基因剂量失衡和基因组不稳定是由肿瘤前细胞的克隆衍生和不受控制的程序性细胞死亡和增殖引起的，这与啮齿动物和人类肿瘤的发生有关。我们观察到，C57BL/6-Trp53和B6C3F1-Trp53单倍体不足的小鼠更容易受到遗传毒性致癌物或电离辐射诱导的造血干细胞（HSC）肿瘤的杂合性丧失（LOH）和基因组不稳定性的影响（发病时间和患病率）。129B6F1或C3B6F1 N12 Trp53单倍不足小鼠在暴露于多种人类致癌物（包括电离辐射、苯、环磷酰胺、melphalan等）后，发生HSC肿瘤的速度非常快（快2-3倍），患病率（60-100%）高于B6129N5 Trp53野生型小鼠，且在B6129-Trp53+/- N5 < N12同型小鼠中患病率（具有高外显率）。这些致癌物诱导的HSC肿瘤在11号染色体上涉及Trp53位点的杂合性缺失的发生率增加。此外，LOH的致癌物特异性诱导模式与非连接异常或非法重组一致。迄今为止进行的研究缺乏完全的杂合性（每个遗传位点上都有不同的等位基因），这使得无法准确定位与肿瘤抑制基因功能丧失相关的LOH位点。为了增加确定LOH位点（染色体和基因组范围）所需的所有遗传位点的杂合性，我们使用对HSC肿瘤具有不同易感性的小鼠品系（129 × B6， C3H × B6和B6 × D2）进行了一系列交叉。这些菌株对致癌物诱导的HSC肿瘤诱导表现出不同的易感性（外显率）。利用F1杂交体，我们正在研究双链染色体断裂和修复途径功能障碍后肿瘤抑制基因位点的丢失，以及与潜在丢失机制（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（CGH阵列）相关联，我们可以确定特异性和决定性的遗传事件（数量性状位点）。该方法还将在易感和耐药小鼠品系中鉴定改变HSC肿瘤诱导和发展的基因，以推断人类单倍型和基因型。

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.