Role of b-Catenin Wingless/Wnt Pathway in Liver Carcinog

人类肝细胞癌（HCC）的两种发展机制已经被提出。一种涉及通过激活b-连环蛋白破坏无翼/Wnt信号通路，而另一种以基因组不稳定为特征。我们以前已经产生了一些肝癌转基因小鼠模型。在这里，我们研究这两种分子途径与小鼠肝癌发生的相关性。采用PCR和测序筛选的方法，对大量来自c-myc、TGF-a、E2F-1、c-myc/TGF-a和c-myc/E2F-1转基因小鼠的肿瘤肝脏病变进行b-连环蛋白突变和缺失分析。此外，作为b-连环蛋白激活的一种测量方法，该蛋白的亚细胞定位通过免疫组织化学进行评估。RAPD方法用于评估肿瘤前和肿瘤病变的总体基因组不稳定性，并通过微卫星分析确定受基因组改变影响的染色体位点。来自转基因小鼠系的肝脏肿瘤可分为两类。第一类，最好的例子是c-myc/E2F-1转基因系，其特点是在相对稳定的基因组存在下，b-连环蛋白的激活频率很高。b-连环蛋白的核积累仅限于瘤前病变和肿瘤病变，具有良好分化的嗜酸性表型。第二类，以c-myc/TGF-a转基因系为代表，从早期发育不良阶段开始就表现出广泛的基因组不稳定性，b-catenin激活率低。在该肝癌模型中检测到1、2、4、5、6、7、8、9、12、14、15和X染色体的杂合性反复丢失。这些数据表明，在人类HCC中描述的类似分子途径在人类HCC中得到了概括。

Two mechanisms of liver cancer development have been proposed for human hepatocellular carcinoma (HCC). One involves the disruption of the Wingless/Wnt signaling pathway by activation of b-catenin, while the other is characterized by genomic instability. We have previously generated a number of transgenic mouse models of liver cancer. Here we investigate the relevance of these two molecular pathways to murine hepatocarcinogenesis. A large number of neoplastic liver lesions from c-myc, TGF-a, E2F-1, c-myc/TGF-a and c-myc/E2F-1 transgenic mice were analyzed for b-catenin mutations and deletions by PCR and sequencing screening. Also, as a measure of b-catenin activation, the subcellular localization of the protein was evaluated by immunohistochemistry. The RAPD method was used to assess the overall genomic instability in preneoplastic and neoplastic lesions and chromosomal loci affected by genomic alterations were determined by microsatellite analysis. Liver tumors from the transgenic mouse lines could be divided in two categories. The first category, best exemplified by the c-myc/E2F-1 transgenic line, was characterized by high frequency of b-catenin activation in the presence of a relatively stable genome. The nuclear accumulation of b-catenin was limited to preneoplastic and neoplastic lesions with a well-differentiated eosinophilic phenotype. The second category, represented by c-myc/TGF-a transgenic line, displayed extensive genomic instability starting from the early dysplastic stage and a low rate of b-catenin activation. Recurrent loss of heterozygosity at chromosomes 1, 2, 4, 5, 6, 7, 8, 9, 12, 14, 15 and X was detected in this model of liver cancer. The data indicate that similar molecular pathways described for human HCC are recapitulated in human HCC.