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

人类肝癌可分为两大类，分别以-连环蛋白激活和基因组不稳定为特征。我们研究了b-连环蛋白的激活和基因组不稳定性在小鼠肝癌发生的一系列步骤中的作用。通过聚合酶链式反应和测序筛选，对c-myc、转化生长因子-1、E2F-1、c-myc/转化生长因子-1和c-myc/E2F-1转基因小鼠肝脏癌前病变和肿瘤性病变进行了-catenin突变和缺失分析。免疫组织化学(IHC)法检测-连环蛋白的激活情况。用随机扩增多态性DNA方法对同一病变的基因组整体不稳定性进行了评估。通过微卫星分析确定受基因组改变影响的染色体位点。免疫组化检测甲胎蛋白(AFP)的表达作为预后指标。转基因小鼠的肝脏肿瘤可以分为两类。第一类以c-myc/E2F-1肝癌为最好的例证，其特征是在相对稳定的基因组和低AFP水平的情况下，-catenin激活的频率很高。第二类以c-myc/TGF-Hcs为代表，表现为低的连环蛋白活化率，但广泛的基因组不稳定，在第1、2、4、6、7、9、12、14、X染色体上反复出现杂合性丢失。这些数据表明，-连环蛋白激活和基因组不稳定定义了小鼠肝肿瘤发展过程中的两个主要遗传事件，类似于对人类肝癌的描述。这些转基因小鼠为阐明人类肝细胞癌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.