MEGF6 Promotes the Epithelial-to-Mesenchymal Transition via the TGF beta/SMAD Signaling Pathway in Colorectal Cancer Metastasis

Background/Aims: Colorectal cancer (CRC) is a malignancy that has high morbidity and mortality and is initiated from accumulative genetic events. Although much effort has been made to elucidate the genetic mechanism underlying this disease, it still remains unknown. Here, we discovered a novel role for multiple epidermal growth factor-like domains protein 6 (MEGF6) in CRC, namely, that it induces the epithelial-to-mesenchymal transition (EMT) to promote CRC metastasis via the transforming growth factor beta (TGF beta)/SMAD signaling pathway. Methods: RNA sequencing data from the Gene Expression Omnibus database were analyzed using R software. Based on The Cancer Genome Atlas Colon Adenocarcinoma (TCGA-COAD) cohort, the clinical significance of MEGF6 was investigated. HCT8R, HCT116, and LoVo CRC cells were transfected with small interfering RNA against MEGF6, and their proliferation and sensitivity to fluorouracil were evaluated with the MTT cell proliferation and colony formation assays. Proteins associated with cell growth were detected by western blot analysis. The apoptosis of cells was evaluated by Annexin V/propidium iodide staining, and transwell assays were performed to assess the involvement of MEGF6 in cell migration. Markers of EMT and TGF beta/SMAD signaling were evaluated by quantitative PCR and western blotting, and the correlation between MEGF6 and these markers was assessed in the TCGA colon and renal adenocarcinoma cohort. Results: The results showed that MEGF6 was upregulated in HCT8R cells. In addition, MEGF6 was significantly overexpressed in tumor tissue and predicted a poor survival in the TCGA-COAD cohort. Moreover, MEGF6 accelerated CRC cell growth and inhibited apoptosis, and promoted CRC metastasis by inducing the EMT. Finally, we found that TGF beta/SMAD signaling triggered the expression of Slug, which regulates the MEGF6-mediated EMT. Conclusions: MEGF6 may serve as an oncogene to promote cell proliferation and inhibit apoptosis. MEGF6 can also accelerate cell migration via TGF beta/SMAD signaling-mediated EMT. (C) 2018 The Author(s) Published by S. Karger AG, Basel