Yeh Shiou-Hwei, Wu Dai-Chen, Tsai Ching-Yi, Kuo Ti-Jung, Yu Wei-Che, Chang Yuan-Shau, Chen Chi-Ling, Chang Ching-Fang, Chen Ding-Shinn, Chen Pei-Jer
Department of Microbiology, National Taiwan University College of Medicine, Taipei, Taiwan.
Clin Cancer Res. 2006 Feb 15;12(4):1097-108. doi: 10.1158/1078-0432.CCR-05-1383.
Allelic loss at chromosome 4q21-23 occurs frequently in human hepatocellular carcinoma, and the putative tumor suppressor gene (TSG) has not yet been identified. We studied the Fas-associated phosphatase-1 (FAP-1) gene as a potential candidate TSG in this region.
The expression level of FAP-1 RNA in hepatocellular carcinomas was evaluated by RNase protection and quantitative PCR. Sodium bisulfite modification and subsequent single-strand conformational polymorphism and sequence analyses were used to assay the methylation of CpGs at FAP-1 promoter. Direct sequencing of the FAP-1 coding region was conducted for detecting the genetic mutations. Two common single nucleotide polymorphisms of FAP-1 were selected for evaluating their association with the hepatocellular carcinoma trait in sporadic and familial hepatocellular carcinomas. Moreover, the functional effect of FAP-1 on cellular proliferation has been evaluated by small interfering RNA approach.
Around 50% of hepatocellular carcinomas showed significantly decreased expression of FAP-1 compared with the corresponding nontumorous liver tissues. In most cases, the RNA level was well correlated with the methylation status of promoter CpGs, suggesting that the promoter methylation may contribute to the down-regulation. Several genetic mutations of FAP-1 have been identified in hepatocellular carcinomas. The G/G genotype of FAP-1 cSNP6304 was significantly associated with the increased risk of multiplex familial hepatocellular carcinomas (odds ratio, 2.44; 95% confidence interval, 1.19-5.01). Finally, knockdown expression of FAP-1 was shown to enhance the cellular proliferation in PLC5 cells.
FAP-1 could be inactivated during hepatocarcinogenesis, mainly attributed by allelic loss and promoter methylation. The genetic mutations and polymorphisms may also confront with the higher hepatocellular carcinoma risk. These results first suggested FAP-1 as a putative TSG in hepatocarcinogenesis.
4q21 - 23染色体上的等位基因缺失在人类肝细胞癌中频繁发生，且尚未鉴定出假定的肿瘤抑制基因（TSG）。我们研究了Fas相关磷酸酶-1（FAP-1）基因作为该区域潜在的候选肿瘤抑制基因。
通过核糖核酸酶保护法和定量PCR评估肝细胞癌中FAP-1 RNA的表达水平。采用亚硫酸氢钠修饰及随后的单链构象多态性和序列分析来检测FAP-1启动子处CpG的甲基化情况。对FAP-1编码区进行直接测序以检测基因突变。选择FAP-1的两个常见单核苷酸多态性来评估它们与散发性和家族性肝细胞癌中肝细胞癌特征的关联。此外，通过小干扰RNA方法评估FAP-1对细胞增殖的功能作用。
与相应的非肿瘤肝组织相比，约50%的肝细胞癌显示FAP-1表达显著降低。在大多数情况下，RNA水平与启动子CpG的甲基化状态密切相关，表明启动子甲基化可能导致表达下调。在肝细胞癌中已鉴定出FAP-1的几种基因突变。FAP-1 cSNP6304的G/G基因型与多发性家族性肝细胞癌风险增加显著相关（优势比，2.44；95%置信区间，1.19 - 5.01）。最后，FAP-1的敲低表达显示可增强PLC5细胞中的细胞增殖。
FAP-1在肝癌发生过程中可能失活，主要归因于等位基因缺失和启动子甲基化。基因突变和多态性也可能面临更高的肝细胞癌风险。这些结果首次表明FAP-1是肝癌发生中假定的肿瘤抑制基因。
