Downregulation of MicroRNA-145 Caused by Hepatitis B Virus X Protein Promotes Expression of CUL5 and Contributes to Pathogenesis of Hepatitis B Virus-Associated Hepatocellular Carcinoma.

BACKGROUND

Hepatitis B viral infection-induced hepatocellular carcinoma (HCC) is a major threat to human health in China. Hepatitis B virus X protein (HBX), an HBV protein, has been reported to be involved in regulating the cellular activities of the host cells and is responsible for HCC oncogenesis.

METHODS AND RESULTS

In this study, we performed real-time PCR in tumor tissue samples collected from 53 HCC patients (25 HBV-positive cases and 28 HBV-negative cases) to screen the candidate miRNAs that have previously been reported to be aberrantly expressed in HBV-associated HCC and found that miR-145 was significantly downregulated. The following computational analysis identified CUL5 and RAB5C as virtual targets of miR-145, whereas only CUL5 was verified as a validated target gene of miR-145 in liver cells via luciferase reporter assay. In line with this result, we found that both the mRNA and protein expression levels of CUL5 were significantly higher in HBV-positive than in HBV-negative HCC. An in vitro experiment demonstrated a significant decrease in the expression of miRNA-145, a substantial increase in the mRNA and protein expression of CUL5, and an enhanced proliferation of HBX over-expressing HepG2 cells compared with the control. In HepG2.2.15, we found significant decreases in both the expression of CUL5 and the cell growth rate of H cells transfected with 60 nM miR-145 mimics compared with the scramble controls.

CONCLUSION

HBV infection promotes cell growth, at least partially, through the HBX-induced downregulation of miRNA-145 expression, which is responsible for the oncogenesis of HBV-associated HCC.