National Institute of Cancer Research, National Health Research Institutes, Miaoli, Taiwan.
PLoS One. 2012;7(8):e43593. doi: 10.1371/journal.pone.0043593. Epub 2012 Aug 24.
Krüppel-like factor 4 (KLF4) is a zinc-finger transcription factor that plays an important role in differentiation and pathogenesis. KLF4 has been suggested to act as an oncogene or tumor suppressor in different tumor types. However, the role of KLF4 in hepatocellular carcinoma (HCC) remains unclear. Here, we demonstrate that forced expression of Klf4 in murine HCC cell lines reduced anchorage-independent growth in soft agar as well as cell migration and invasion activities in vitro. Ectopic Klf4 expression impaired subcutaneous tumor growth and lung colonization in vivo. By contrast, Klf4 knockdown enhanced HCC cell migration. Interestingly, ectopic expression of Klf4 changed the morphology of murine HCC cells to a more epithelial phenotype. Associated with this, we found that expression of Slug, a critical epithelial mesenchymal transition (EMT)-related transcription factor, was significantly down-regulated in Klf4-expressing cells. Chromatin immunoprecipitation (ChIP) and luciferase reporter assays showed that Klf4 is able to bind and repress the activity of the Slug promoter. Furthermore, ectopic Slug expression partially reverts the Klf4-mediated phenotypes. Consistent with a role as a tumor suppressor in HCC, analysis of the public microarray databases from Oncomine revealed reduced KLF4 expression in human HCC tissues in comparison with normal liver tissues in 3 out of 4 data sets. By quantitative reverse transcription-polymerase chain reaction (qRT-PCR), we found reduced KLF4 mRNA in 50% of HCC tissues. Importantly, an inverse correlation between the expression of KLF4 and SLUG was found in HCC tissues. Our data suggest that KLF4 acts as a tumor suppressor in HCC cells, in part by suppressing SLUG transcription.
Krüppel 样因子 4（KLF4）是一种锌指转录因子，在分化和发病机制中发挥重要作用。KLF4 被认为在不同的肿瘤类型中充当癌基因或肿瘤抑制因子。然而，KLF4 在肝细胞癌（HCC）中的作用尚不清楚。在这里，我们证明在鼠 HCC 细胞系中强制表达 Klf4 可降低软琼脂中的锚定非依赖性生长以及体外细胞迁移和侵袭活性。异位 Klf4 表达可损害体内皮下肿瘤生长和肺定植。相比之下，Klf4 敲低增强了 HCC 细胞的迁移。有趣的是，异位表达 Klf4 使鼠 HCC 细胞的形态向更上皮表型转变。与此相关，我们发现 Slug 的表达，一种关键的上皮间质转化（EMT）相关转录因子，在 Klf4 表达细胞中显著下调。染色质免疫沉淀（ChIP）和荧光素酶报告基因检测表明，Klf4 能够结合并抑制 Slug 启动子的活性。此外，异位 Slug 表达部分逆转了 Klf4 介导的表型。与 HCC 中的肿瘤抑制因子作用一致，对 Oncomine 公共微阵列数据库的分析显示，在 4 个数据集的 3 个中，与正常肝组织相比，人 HCC 组织中的 KLF4 表达减少。通过定量逆转录聚合酶链反应（qRT-PCR），我们发现 50%的 HCC 组织中 Klf4 mRNA 减少。重要的是，在 HCC 组织中发现 KLF4 表达与 SLUG 呈负相关。我们的数据表明，KLF4 在 HCC 细胞中作为肿瘤抑制因子发挥作用，部分通过抑制 SLUG 转录。
