ABSTRACT
Rap2B, a member of the Ras family of small GTP-binding proteins, was found to be highly expressed in various human tumors and plays an important role in the development of tumors. However, the function of Rap2B in hepatocellular carcinoma (HCC) remains unclear. Therefore, in this study, we investigated the biological functions of Rap2B in HCC and the potential underlying mechanisms. Our results indicated that Rap2B was highly expressed in HCC tissues and cell lines. Rap2B silencing obviously inhibited the proliferation, migration, and invasion of HCC cells, as well as attenuated xenografted tumor growth in vivo. Furthermore, Rap2B silencing greatly reduced the expression levels of phosphorylated focal adhesion kinase (p-FAK), matrix metalloproteinase-2 (MMP-2), and MMP-9 in HCC cells. In conclusion, our data suggest that Rap2B silencing inhibits the proliferation and invasion in HCC cells. Thus, Rap2B may have potential as a treatment for HCC.
Subject(s)
Carcinoma, Hepatocellular/genetics , Gene Silencing , Liver Neoplasms/genetics , rap GTP-Binding Proteins/genetics , Animals , Carcinoma, Hepatocellular/metabolism , Carcinoma, Hepatocellular/pathology , Cell Line, Tumor , Cell Movement , Cell Proliferation , Disease Models, Animal , Focal Adhesion Kinase 1/metabolism , Gene Expression Regulation , Gene Knockdown Techniques , Humans , Liver Neoplasms/metabolism , Liver Neoplasms/pathology , Mice , RNA, Messenger/genetics , RNA, Small Interfering/genetics , Signal Transduction , Xenograft Model Antitumor AssaysABSTRACT
MEN1, which encodes the nuclear protein menin, acts as a tumor suppressor in lung cancer and is often inactivated in human primary lung adenocarcinoma. Here, we show that the inactivation of MEN1 is associated with increased DNA methylation at the MEN1 promoter by K-Ras. On one hand, the activated K-Ras up-regulates the expression of DNA methyltransferases and enhances the binding of DNA methyltransferase 1 to the MEN1 promoter, leading to increased DNA methylation at the MEN1 gene in lung cancer cells; on the other hand, menin reduces the level of active Ras-GTP at least partly by preventing GRB2 and SOS1 from binding to Ras, without affecting the expression of GRB2 and SOS1. In human lung adenocarcinoma samples, we further demonstrate that reduced menin expression is associated with the enhanced expression of Ras (p < 0.05). Finally, excision of the Men1 gene markedly accelerates the K-Ras(G12D)-induced tumor formation in the Men1(f/f);K-Ras(G12D/+);Cre ER mouse model. Together, these findings uncover a previously unknown link between activated K-Ras and menin, an important interplay governing tumor activation and suppression in the development of lung cancer.