Abstract
Hepatocellular carcinoma (HCC) is the second leading cause of cancer-related death. High recurrence rates after curative resection and the lack of specific biomarkers for intrahepatic metastases are major clinical problems. Recently, exosomal microRNAs (miRNAs) have been reported to have a role in the formation of the pre-metastatic niche and as promising biomarkers in patients with malignancy. Here we aimed to clarify the molecular mechanisms of intrahepatic metastasis and to identify a novel biomarker miRNA in patients with HCC. A highly intrahepatic metastatic cell line (HuH-7M) was established by in vivo selection. HuH-7M showed increased proliferative ability and suppression of apoptosis and anoikis. HuH-7M and the parental cell (HuH-7P) showed the similar expression of epithelial-mesenchymal transition markers and cancer stem cell markers. In vivo, mice treated with exosomes derived from HuH-7M showed increased tumorigenesis of liver metastases. Exosomes from HuH-7M downregulated endothelial cell expression of vascular endothelial-cadherin (VE-cadherin) and zonula occludens-1 (ZO-1) in non-cancerous regions of liver and increased the permeability of FITC-dextran through the monolayer of endothelial cells. The miRNAs (miR-638, miR-663a, miR-3648, and miR-4258) could attenuate endothelial junction integrity by inhibiting VE-cadherin and ZO-1 expression. In patients with HCC, higher serum exosomal miR-638 expression was associated with tumor recurrence. In conclusion, the miRNAs secreted from a highly metastatic cancer cell can promote vascular permeability via downregulation of endothelial expression of VE-cadherin and ZO-1. Serum exosomal miR-638 expression holds potential for serving as a significant and independent prognostic marker in HCC.