Exosomal miR-451a Functions as a Tumor Suppressor in Hepatocellular Carcinoma by Targeting LPIN1

Emerging evidence suggests that exosomal microRNAs (miRNAs) mediate hepatoma progression through the post-translational regulation of their targets. However, characteristically-expressed miRNAs and their functions in the tumor and tumor-associated angiogenesis remain poorly understood. miRNA sequencing (HiSeq 2500 SE50) was performed to identify miRNA species that are involved in the hepatocellular carcinoma (HCC) pathogenesis. We identified miR-451a downregulation according to its expression and TCGA analysis. miR-451a was found to be mainly involved in cell viability, apoptosis, cell cycle and migration both in HCC and endothelial cell lines. LPIN1 was predicted to be a target of this miRNA based on TargetScan, GSEA analysis, and the Uniprot database. We performed real time PCR and dual luciferase assays to confirm these results. We identified that miR-451a is significantly downregulated in serum-derived exosomes from HCC patients, as compared to expression in those from normal individuals. We further confirmed that overexpression of miR-451a functions in HCC and endothelia cells in vitro and in vivo. Exosomal miR-451a, as a tumor suppressor, was found to induce apoptosis both in HCC cell lines and human umbilical vein endothelial cells (HUVECs). In addition, miR-451a suppressed HUVEC migration, tube formation, and vascular permeability. Importantly, we demonstrated that LPIN1 is a critical target of miR-451a, and promotes apoptosis in both HCC and endothelial cells. Our study provides the novel finding that exosomal miR-451a targets LPIN1 to inhibit hepatocellular tumorigenesis by regulating tumor cell apoptosis and angiogenesis. These results have clinical implications regarding the deregulation of miRNAs in HCC.