In contrast, miR-122 was found to inhibit hepatitis B virus replication. Furthermore, in chronic HBV infection patients, miR-122 was negatively correlated with intra-hepatic viral load and hepatic necro-inflammation. Until now, there are two different explanations for the mechanism of HBV-related miR-122 downregulation. One hypothesis is that the highly redundant HBV transcripts are involved in HBV-mediated miR-122 suppression by binding and sequestering endogenous miR-122, and in this process, the transcription level of miR-122 is not affected directly ; while the other is that hepatitis B virus X protein binds PPARc and results the inhibition of the miR-122 transcription level which is in conflict with the former. Hence, more experimental evidence is needed to explore the mechanism of HBV-related inhibition of miR-122. Germline development 2 is a cytoplasmic poly RNA polymerase that adds successive AMP Vemurafenib 918504-65-1 monomers to the 39-end of specific RNAs, thereby forming a poly tail, and controls mRNA translation. Gld2 enzymes acquire substrate specificity by interacting with RNA-binding proteins and are recruited to only a subset of mRNAs. Previous studies have mostly focused on the effect of Gld2 on mRNA. Recently, Joel D. et al. demonstrated that Gld2 could increase specific miRNA stabilisation via monoadenylation in human fibroblasts, and specifically, miR-122 could be stabilized by Gld2. A previous study performed in Japan also demonstrated significantly lower levels of miR-122 in the livers of Gld2-null mice. These two studies indicated that Gld2 could regulate microRNA expression at the post-transcription level. Here, we studied the effect of HBV on the expression of miR122 in vitro. Interestingly, we found that HBV reduced miR-122 levels by down-regulating the Gld2 gene, which might represent a new mechanism for regulating the expression of miRNAs by HBV. In addition, we confirmed that the HBx protein plays a critical role in down-regulating Gld2 protein and subsequently results in a reduction in miR-122 levels. In the present study, we explored the mechanism of downregulation of miR-122 induced by HBV in vitro. First, we confirmed that the miR-122 levels in HepG2.2.15 were significantly lower compared to HepG2 cells, which was consistent with the results previously reported by Wu et al. In addition, Meng et al. found that transfection with the HBV replication plasmid pHBV1.3 significantly decreased miR-122 levels in Huh-7 cells. Furthermore, HBV transgenic mice had lower miR-122 levels in the liver compared to BALB/c mice. Using pHBV1.3, we confirmed the negative effect of HBV on miR-122 in three different cell lines. More importantly, we screened the four HBV proteins and identified the exact protein that reduced miR-122 levels in hepatic cells; HBx was the most effective protein. In this study, we tried to design a siRNA expression vector to silence HBx in HepG2.2.15 cells.