Yau Tai-On, Chan Chung-Yiu, Chan Kok-Lung, Lee Man-Fong, Wong Chun-Ming, Fan Sheung-Tat, Ng Irene Oi-Lin
Department of Pathology, Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong.
Oncogene. 2005 Feb 24;24(9):1607-14. doi: 10.1038/sj.onc.1208340.
Oncogenic activation of the WNT/beta-catenin signaling pathway is common in hepatocellular carcinoma (HCC). Dishevelled (Dvl), a key activator of the pathway, inhibits the adenomatous polyposis coli complex, and this leads to the accumulation of beta-catenin and promotes tumorigenesis. Recently, a novel inhibitor of Dishevelled, namely Dapper (Dpr), was isolated in Xenopus. To explore whether HDPR1, the human homologue of Dpr, has an anti-oncogenic role in hepatocarcinogenesis, we studied the expression of this gene in HCCs. We found that there were two alternatively spliced transcripts of HDPR1, designated as alpha and beta forms, in human liver. Downregulation of the gene expression was observed in 31 (43%) of the 72 human HCC samples using the primer pair that amplified both transcripts. Furthermore, the HDPR1alpha was downregulated in 42 (58%) of 72 human HCCs and the downregulation significantly correlated with accumulation of beta-catenin. Also, downregulation of HDPR1 by RNA interference in HLE cells led to cytoplasmic accumulation of beta-catenin. Furthermore, a CpG island located at the promoter region and exon 1 of the HDPR1 gene was methylated in 22 (51%) of human HCCs. We showed that downregulation of HDPR1, in hepatoma cell lines, was associated with methylation of this CpG island using bisulfite sequencing and 5-aza-2'-deoxycytidine demethylation experiment. In addition to methylation-mediated downregulation of HDPR1, allelic loss (13-28% of informative cases) was detected using microsatellite markers flanking the HDPR1 locus. To conclude, downregulation of HDPR1 is common in HCCs, frequently involves hypermethylation of the promoter region, and allelic loss of the HDPR1 locus may also play a role.
WNT/β-连环蛋白信号通路的致癌激活在肝细胞癌（HCC）中很常见。该通路的关键激活因子Dishevelled（Dvl）可抑制腺瘤性息肉病大肠杆菌复合物，这会导致β-连环蛋白的积累并促进肿瘤发生。最近，在非洲爪蟾中分离出一种新型的Dishevelled抑制剂，即Dapper（Dpr）。为了探究Dpr的人类同源物HDPR1在肝癌发生过程中是否具有抗癌作用，我们研究了该基因在肝癌中的表达。我们发现在人类肝脏中存在HDPR1的两种选择性剪接转录本，分别命名为α和β形式。使用能扩增这两种转录本的引物对，在72例人类肝癌样本中有31例（43%）观察到基因表达下调。此外，在72例人类肝癌中有42例（58%）的HDPR1α下调，且这种下调与β-连环蛋白的积累显著相关。同样，在HLE细胞中通过RNA干扰下调HDPR1会导致β-连环蛋白在细胞质中积累。此外，HDPR1基因启动子区域和外显子1处的一个CpG岛在22例（51%）人类肝癌中发生了甲基化。我们通过亚硫酸氢盐测序和5-氮杂-2'-脱氧胞苷去甲基化实验表明，在肝癌细胞系中HDPR1的下调与该CpG岛的甲基化有关。除了甲基化介导的HDPR1下调外，使用HDPR1基因座侧翼的微卫星标记检测到等位基因缺失（在信息性病例中占13 - 28%）。总之，HDPR1的下调在肝癌中很常见，常涉及启动子区域的高甲基化，且HDPR1基因座的等位基因缺失可能也起作用。
