Exosomal miR-663b exposed to TGF-β1 promotes cervical cancer metastasis and epithelial-mesenchymal transition by targeting MGAT3

Transforming growth factor (TGF)-β1 is a key cytokine affecting the pathogenesis and progression of cervical cancer. Tumor-derived exosomes contain microRNAs (miRNAs/miRs) that interact with cancer and stromal cells, thereby contributing to tissue remodeling in the tumor microenvironment (TME). The present study was designed to clarify how TGF-β1 affects tumor biological functions through exosomes released by cervical cancer cells. Deep RNA sequencing found that TGF-β1 stimulated cervical cancer cells to secrete more miR-663b-containing exosomes, which could be transferred into new target cells to promote metastasis. Further studies have shown that miR-663b directly targets the 3′-untranslated regions (3′-UTR) of mannoside acetylglucosaminyltransferase 3 (MGAT3) and is involved in the epithelial-mesenchymal transition (EMT) process. Remarkably, the overexpression of MGAT3 suppressed cervical cancer cell metastasis promoted by exosomal miR-663b, causing increased expression of epithelial differentiation marker E-cadherin and decreased expression of mesenchymal markers N-cadherin and β-catenin. Throughout our study, online bioinformation tools and dual luciferase reporter assay were applied to identify MGAT3 as a novel direct target of miR-663b. Exosome PKH67-labeling experiment verified that exosomal miR-663b could be endocytosed by cervical cancer cells and subsequently influence its migration and invasion functions which were measured by wound healing and Transwell assays. The expression of miR-663b and MGAT3 and the regulation of the EMT pathway caused by MGAT3 were detected by quantitative real-time transcription-polymerase chain reaction (qPCR) and western blot analysis. These results, thus, provide evidence that cancer cell-derived exosomal miR-663b is endocytosed by cervical cancer cells adjacent or distant after TGF-β1 exposure and inhibits the expression of MGAT3, thereby accelerating the EMT process and ultimately promoting local and distant metastasis.