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

b-Catenin Wingless/Wnt 通路在肝癌中的作用

• 批准号: 6559112
• 负责人: SNORRI S THORGEIRSSON
• 金额: --
• 依托单位: DIVISION OF BASIC SCIENCES - NCI
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/6559112
• 关键词: animal genetic material tag; biological signal transduction; cell growth regulation; cellular oncology; cytoskeletal proteins; disease /disorder model; gene expression; genetic polymorphism; genetic screening; genetic susceptibility; genetically modified animals; laboratory mouse; liver cells; liver neoplasms; loss of heterozygosity; neoplasm /cancer genetics; neoplastic growth; nucleic acid sequence; polymerase chain reaction; protein localization; protein structure function; protooncogene; transforming growth factors

We have investigated the involvement of the b-catenin gene in hepatocarcinogenesis, we used several transgenic mouse models of hepatic tumors induced by over-expression of c-myc in the liver either alone or in combination with TGF-a or TGF-b1. Activation of b-catenin, as judged by the presence of mutations and/or nuclear translocation of the protein, was most frequent in liver tumors from c-myc (4/17, 23.5%) and c-myc/TGF-b1 (6/18, 33.3%) transgenic mice. However, it was very rare in faster growing and histologically more aggressive hepatocellular carcinomas developed in c-myc/TGF-a mice (1/20, 5%). Administration of diethylnitrosamine, phenobarbital or 2-amino-3,8-diethylimidazo[4,5-f]quinoxaline (MeIQx) to the c-myc mouse did not significantly affect the occurrence of b-catenin mutations. Notably, nuclear accumulation of b-catenin was observed only in adenomas and highly-differentiated carcinomas with eosinophilic phenotype. Furthermore, preneoplastic lesions with eosinophilic phenotype frequently displayed focal nuclear positivity, co-localized with areas of high proliferation. In contrast, basophilic and clear-cell foci, as well as pseudo-glandular and poorly-differentiated hepatocellular carcinomas, exhibited a normal or reduced membranous immunoreactivity for b-catenin. These studies suggest that nuclear translocation of b-catenin and activation of Wingless/Wnt signaling may represent an early event in liver carcinogenesis, providing a growth advantage in a subset of hepatic tumors with a more differentiated phenotype. This is of considerable interest since mutations in b-catenin are associated with a decreased loss of heterozygosity in human HCC). We have therefore hypothesized that development of liver cancer may advance via two broad pathways. The first pathway would involve b-catenin activation, while the second one would generate genomic instability and produce a mutator phenotype. We are currently investigating correlation between b-catenin activation and genomic instability by analyzing the genomic profiles of mouse liver tumors by the random amplified polymorphic DNA (RAPD) analysis using 22 arbitrary primers. The results so far have revealed that genomic instability was absent in c-myc and was very low in c-myc/TGF-b1 (5.8 ? 1.3%) tumors which displayed b-catenin activation. In contrast, 10 out of 10 HCCs developed in c-myc/TGF-a mice exhibited a high rate of genomic instability (25 ? 3.0%). The latter was comparable with the rate of genomic instability found in c-myc/ lacZ HCCs after treatment with the potent hepatocarcinogen 2-amino-3,8-dimethyl-imidazo[4,5-f]quinoxaline (32.3 ? 2.4%). The frequency of genomic instability was inversely correlated with the degree of HCC differentiation. Furthermore, loss of heterozygosity of b-catenin and TGF-a RII genes was detected only in c-myc/TGF-a (60%) and c-myc/lacZ (80%) poorly-differentiated HCCs, presumably representing a marker of tumor progression in both transgenic models. Taken together, the present data are consistent with the existence of two pathways of hepatocarcinogenesis in the transgenic mouse models. The first pathway would imply the cooperation between c-myc and b-catenin oncogenes in the presence of a stable genome, while the second pathway is operative in a context of genomic instability.

我们已经研究了β-连环蛋白基因在肝癌发生中的参与，我们使用了几种由c-myc在肝脏中单独或与TGF-α或TGF-β 1组合过表达诱导的肝肿瘤转基因小鼠模型。通过蛋白质的突变和/或核易位的存在来判断，b-连环蛋白的激活在c-myc（4/17，23.5%）和c-myc/TGF-β 1（6/18，33.3%）转基因小鼠的肝肿瘤中最常见。然而，在c-myc/TGF-α小鼠中发展的生长更快且组织学上更具侵袭性的肝细胞癌中非常罕见（1/20，5%）。给予二乙基亚硝胺、苯巴比妥或2-氨基-3，8-二乙基咪唑[4，5-f]喹喔啉（MeIQx）对c-myc小鼠的b-连环蛋白突变的发生没有显著影响。值得注意的是，仅在腺瘤和具有嗜酸性表型的高分化癌中观察到b-连环蛋白的核积聚。此外，具有嗜酸性表型的癌前病变经常显示局灶性核阳性，与高增殖区域共定位。相比之下，嗜碱性和透明细胞灶，以及假腺性和低分化肝细胞癌，表现出正常或降低的膜免疫反应性的b-连环蛋白。这些研究表明，B-连环蛋白的核转位和Wingless/Wnt信号的激活可能代表了肝癌发生的早期事件，在具有更分化表型的肝肿瘤亚组中提供了生长优势。这是相当令人感兴趣的，因为b-连环蛋白中的突变与人HCC中杂合性丢失的减少有关。因此，我们假设肝癌的发展可能通过两条广泛的途径进行。第一个途径将涉及b-连环蛋白激活，而第二个途径将产生基因组不稳定性并产生突变表型。目前，我们正在调查的相关性b-连环蛋白激活和基因组不稳定性，通过分析小鼠肝肿瘤的基因组图谱的随机扩增多态性DNA（RAPD）分析，使用22个任意引物。目前的研究结果表明，c-myc基因组不稳定，c-myc/TGF-β 1（5.8？1.3%）显示出b-连环蛋白活化的肿瘤。相比之下，c-myc/TGF-α小鼠中10/10的HCC表现出高的基因组不稳定率（25？3.0%）。后者与c-myc/ lacZ肝癌细胞用强致癌物2-氨基-3，8-二甲基咪唑并[4，5-f]喹喔啉治疗后发现的基因组不稳定率（32.3？2.4%）。基因组不稳定性的频率与HCC分化程度呈负相关。此外，仅在c-myc/TGF-α（60%）和c-myc/lacZ（80%）低分化HCC中检测到β-连环蛋白和TGF-α RII基因的杂合性缺失，这可能代表两种转基因模型中肿瘤进展的标志物。总之，目前的数据与转基因小鼠模型中存在两种肝癌发生途径一致。第一条途径意味着在稳定基因组存在下c-myc和b-连环蛋白癌基因之间的合作，而第二条途径在基因组不稳定的背景下起作用。