Exosome‐associated microRNA‐375 induces cell proliferation by regulating IGFBP4 upon hepatitis C virus infection

Hepatitis C virus (HCV) infection is one of the most common causes of liver cancer. HCV infection causes chronic disease followed by cirrhosis, which often leads to hepatocellular carcinoma (HCC). In this study, we investigated the roles of exosome-associated miRNAs in HCV-induced disease pathology. Small RNA sequencing was performed to identify miRNAs that are differentially regulated in exosomes isolated from patient sera at two different stages of HCV infection: cirrhosis and hepatocellular carcinoma. Among the differentially expressed miRNAs, miR-375 was found to be significantly upregulated in exosomes isolated from patients with cirrhosis and HCC. A similar upregulation was observed in intracellular and extracellular/exosomal levels of miR-375 in HCV-JFH1 infected Huh7.5 cells. The depletion of miR-375 in infected cells inhibited HCV-induced cell migration and proliferation, suggesting a supportive role for miR-375 in HCV pathogenesis. miR-375, secreted through exosomes derived from HCV-infected cells, could also be transferred to naïve Huh7.5 cells, resulting in an increase in cell proliferation and migration in the recipient cells. Furthermore, we identified Insulin growth factor binding protein 4 (IGFBP4), a gene involved in cell growth and malignancy, as a novel target of miR-375. Our results demonstrate the critical involvement of exosome-associated miR-375 in HCV-induced disease progression.