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

人类肝癌可分为两大类，其特征分别是β-连环蛋白的激活和基因组的不稳定性。我们研究了连环蛋白激活和基因组不稳定性在小鼠肝癌发生过程中的作用。通过PCR和测序筛选，对来自c-myc、TGF-β、E2F-1、c-myc/TGF-β和c-myc/E2F-1转基因小鼠的大量癌前病变和肿瘤性肝脏病变进行β-连环蛋白突变和缺失分析。通过免疫组织化学（IHC）研究β-连环蛋白的活化。RAPD方法用于评估相同病变中的总体基因组不稳定性。通过微卫星分析确定受基因组改变影响的染色体位点。甲胎蛋白（AFP）的表达通过免疫组化（IHC）测定作为预后标志物。来自转基因小鼠系的肝肿瘤可以分为两类。第一类，最好的例子c-myc/E2F-1肝癌，其特征在于高频率的-连环蛋白激活的存在下，一个相对稳定的基因组和低AFP水平。第二类，以c-myc/TGF-肝癌为代表，显示低的β-连环蛋白激活率，但广泛的基因组不稳定性，在染色体1，2，4，6，7，9，12，14，X上反复出现杂合性丢失。基因组的不稳定性是明显的，从早期发育不良阶段，并伴随着AFP的表达升高。这些数据表明，β-连环蛋白激活和基因组不稳定性定义了两个主要的遗传事件，在发展过程中的小鼠肝肿瘤，类似于那些描述的人类肝癌。这些转基因小鼠为阐明人HCC的分子基础提供了合适的遗传系统。

Human liver cancer can be divided into two broad categories that are characterized by activation of -catenin and genomic instability, respectively. We investigated the role of b-catenin activation and genomic instability in the sequential steps of mouse hepatocarcinogenesis. A large collection of preneoplastic and neoplastic liver lesions from c-myc, TGF- , E2F-1, c-myc/TGF- and c-myc/E2F-1 transgenic mice was analyzed for -catenin mutations and deletions by PCR and sequencing screening. Activation of -catenin was investigated by immunohistochemistry (IHC). The RAPD method was used to assess the overall genomic instability in the same lesions. Chromosomal loci affected by genomic alterations were determined by microsatellite analysis. Expression of alpha-fetoprotein (AFP) was determined by IHC as a prognostic marker. Liver tumors from the transgenic mouse lines could be divided in two categories. The first category, best exemplified by c-myc/E2F-1 HCCs, was characterized by high frequency of -catenin activation in the presence of a relatively stable genome and low AFP levels. The second category, represented by c-myc/TGF- HCCs, displayed low rate of -catenin activation but extensive genomic instability with recurrent loss of heterozygosity at chromosomes 1, 2, 4, 6, 7, 9, 12, 14, X. The genomic instability was evident from early dysplastic stage and occurred concomitantly with elevated expression of AFP. The data indicate that -catenin activation and genomic instability define two major genetic events during development of mouse liver tumors, similar to those described for human HCCs. These transgenic mice provide suitable genetic systems for elucidating the molecular basis of human HCC.