MicroRNA-581 promotes hepatitis B virus surface antigen expression by targeting Dicer and EDEM1

Hepatitis B virus surface antigen (HBsAg) is an important risk factor for hepatocellular carcinoma (HCC) and is downregulated during hepatocarcinogenesis. MicroRNAs (miRNAs) are frequently deregulated in HCC tissues. However, whether the deregulation of certain miRNAs in HCC has an impact on HBsAg expression remains unclear. We found here that microRNA-581 (miR-581), which is deregulated during hepatocarcinogenesis, promoted HBsAg expression. Additionally, miR-581 targeted Dicer and endoplasmic reticulum degradation-enhancing alpha-mannosidase-like protein 1 (EDEM1) and repressed their expression. Although Dicer cannot process HBV transcripts, Dicer knockdown led to increased HBsAg secretion, most likely due to a reduction in the levels of Dicer-processed 7SL RNA fragments. Moreover, Dicer-processed 7SL RNA fragments partially inhibited the ability of miR-581 to stimulate HBsAg expression. Furthermore, we found that forced EDEM1 expression inhibited miR-581-mediated induction of HBsAg. Finally, transfection of miR-581 into HepG2.2.15 cells promoted cell proliferation and led to upregulation of genes involved in development, cell proliferation and protein secretion. Altogether, we conclude that miR-581 promotes HBsAg expression by targeting Dicer and EDEM1. Our findings suggest that downregulation of miR-581 during hepatocarcinogenesis may lead to a reduction in HBsAg expression and impede HCC development.