14-3-3ε Overexpression Contributes to Epithelial-Mesenchymal Transition of Hepatocellular Carcinoma

Background14-3-3ε is implicated in regulating tumor progression, including hepatocellular carcinoma (HCC). Our earlier study indicated that elevated 14-3-3ε expression is significantly associated with higher risk of metastasis and lower survival rates of HCC patients. However, the molecular mechanisms of how 14-3-3ε regulates HCC tumor metastasis are still unclear. Methodology and Principal FindingsIn this study, we show that increased 14-3-3ε expression induces HCC cell migration and promotes epithelial-mesenchymal transition (EMT), which is determined by the reduction of E-cadherin expression and induction of N-cadherin and vimentin expression. Knockdown with specific siRNA abolished 14-3-3ε-induced cell migration and EMT. Furthermore, 14-3-3ε selectively induced Zeb-1 and Snail expression, and 14-3-3ε-induced cell migration was abrogated by Zeb-1 or Snail siRNA. In addition, the effect of 14-3-3ε-reduced E-cadherin was specifically restored by Zeb-1 siRNA. Positive 14-3-3ε expression was significantly correlated with negative E-cadherin expression, as determined by immunohistochemistry analysis in HCC tumors. Analysis of 14-3-3ε/E-cadherin expression associated with clinicopathological characteristics revealed that the combination of positive 14-3-3ε and negative E-cadherin expression is significantly correlated with higher incidence of HCC metastasis and poor 5-year overall survival. In contrast, patients with positive 14-3-3ε and positive E-cadherin expression had better prognostic outcomes than did those with negative E-cadherin expression. SignificanceOur findings show for the first time that E-cadherin is one of the downstream targets of 14-3-3ε in modulating HCC tumor progression. Thus, 14-3-3ε may act as an important regulator in modulating tumor metastasis by promoting EMT as well as cell migration, and it may serve as a novel prognostic biomarker or therapeutic target for HCC.背景 14-3-3ε参与调控包括肝细胞癌（hepatocellular carcinoma, HCC）在内的肿瘤进展。本团队前期研究显示，14-3-3ε表达升高与肝癌患者转移风险升高、生存率降低显著相关。然而，14-3-3ε调控肝癌肿瘤转移的分子机制仍不明确。 研究方法与主要发现 本研究证实，14-3-3ε表达上调可诱导肝癌细胞迁移并促进上皮间质转化（epithelial-mesenchymal transition, EMT），该效应通过下调E-钙粘蛋白（E-cadherin）的表达，同时上调N-钙粘蛋白（N-cadherin）与波形蛋白（vimentin）的表达得以验证。采用特异性小干扰RNA（small interfering RNA, siRNA）敲低14-3-3ε，可阻断其诱导的细胞迁移与EMT进程。进一步研究发现，14-3-3ε可选择性诱导Zeb-1与Snail的表达，且通过Zeb-1或Snail的siRNA可抵消14-3-3ε介导的细胞迁移。此外，Zeb-1的siRNA可特异性恢复14-3-3ε所致的E-钙粘蛋白表达下调。对肝癌肿瘤组织的免疫组化分析显示，14-3-3ε阳性表达与E-钙粘蛋白阴性表达显著相关。针对14-3-3ε/E-钙粘蛋白表达与临床病理特征的关联分析表明，14-3-3ε阳性且E-钙粘蛋白阴性的患者，其肝癌转移发生率更高、5年总生存率更差。与之相反，14-3-3ε阳性且E-钙粘蛋白阳性的患者，预后优于E-钙粘蛋白阴性的患者。 研究意义 本研究首次证实，E-钙粘蛋白是14-3-3ε调控肝癌肿瘤进展的下游靶点之一。综上，14-3-3ε可通过促进上皮间质转化与细胞迁移，成为调控肿瘤转移的关键调控因子，有望成为肝癌新型预后生物标志物或治疗靶点。