Epigenetic silencing of sFRP1 activates the canonical Wnt pathway and contributes to increased cell growth and proliferation in hepatocellular carcinoma
Epigenetic silencing of sFRP1 activates the canonical Wnt pathway and contributes to increased cell growth and proliferation in hepatocellular carcinoma
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DOI：
10.1007/s13277-012-0331-5
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发表时间：
2012-04-01
期刊：
影响因子：
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通讯作者：
Herceg, Zdenko
中科院分区：
文献类型：
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作者：
Kaur, Pushpinder;Mani, Samson;Herceg, Zdenko
Wnt 通路是胚胎发育和干细胞的关键调节因子，其异常激活与人类恶性肿瘤相关，尤其是肝细胞癌 (HCC)。编码分泌性卷曲相关蛋白 (sFRP)（Wnt 信号传导拮抗剂）的基因的表观遗传失调与 HCC 细胞中 Wnt 信号传导的异常过度激活有关。然而，确切的潜在机制仍然难以捉摸。我们研究了 HCC 发展不同阶段的肝脏样本和肝癌细胞系中 Wnt 拮抗剂的甲基化谱，并研究了 sFRP 的异常表观遗传沉默对经典 Wnt 通路和细胞活力的功能影响。我们发现编码该亚基的 sFRP1 基因是 HCC 肿瘤中异常 DNA 高甲基化和沉默的常见靶标，而其他细胞外 Wnt 拮抗剂 WIF1 和 Dkk3 在肿瘤细胞中没有表现出甲基化，这与癌细胞中的异常甲基化事件在基因之间非随机分布以及 HCC 中特定基因高度甲基化具有强烈偏好的观点一致。此外，通过比较HCC肿瘤与正常、肝硬化和慢性肝炎肝组织中的sFRP1甲基化状态，我们确定sFRP1基因作为HCC的潜在早期标志物。通过异位表达恢复癌细胞中的 sFRP1 表达，抑制 Wnt 活性，同时导致 β-catenin 不稳定以及 Wnt 通路已知下游靶标 c-Myc 和细胞周期蛋白 D1 的下调。重要的是，恢复癌细胞中的 sFRP1 水平会抑制细胞生长并诱导细胞凋亡。这项研究支持了 sFRP1 沉默在肝细胞癌中的关键作用，并强调了 Wnt 拮抗剂在防止 β-catenin 致癌稳定和经典 Wnt 通路慢性激活方面的重要性，表明 sFRP1 可能是早期癌症检测和治疗干预的一个有吸引力的靶点。
The Wnt pathway is a key regulator of embryonic development and stem cells, and its aberrant activation is associated with human malignancies, most notably hepatocellular carcinoma (HCC). Epigenetic deregulation of the genes encoding the secreted frizzled-related proteins (sFRPs), the Wnt signalling antagonists, has been linked with aberrant hyperactivation of the Wnt signalling in HCC cells; however, the precise underlying mechanism remains elusive. We investigated the methylation profiles of Wnt antagonists in liver samples of different stages of HCC development and liver cancer cell lines and studied the functional impact of aberrant epigenetic silencing of sFRPs on the canonical Wnt pathway and cell viability. We found that the sFRP1 gene encoding the subunit is a frequent target of aberrant DNA hypermethylation and silencing in HCC tumours, whereas other extracellular Wnt antagonists, WIF1 and Dkk3, exhibited no methylation in tumour cells, consistent with the notion that aberrant methylation events in cancer cells are non-randomly distributed among the genes and that there is a strong preference for hypermethylation of specific genes in HCC. In addition, by comparing sFRP1 methylation status in HCC tumours with normal, cirrhotic and chronic hepatitis liver tissues, we identified sFRP1 gene as a potential early marker of HCC. The restoration of sFRP1 expression in cancer cells by ectopic expression inhibited Wnt activity accompanied with destabilization of beta-catenin and downregulation of c-Myc and cyclin D1, the known downstream targets of Wnt pathway. Importantly, restoring sFRP1 levels in cancer cells inhibited cell growth and induced apoptotic cell death. This study supports the critical role for sFRP1 silencing in hepatocellular carcinoma and reinforces the importance of the Wnt antagonists in preventing oncogenic stabilization of beta-catenin and chronic activation of the canonical Wnt pathway, suggesting that sFRP1 may be an attractive target for early cancer detection and therapeutic intervention.