Circular RNA SETD2 (circSETD2) elevates DDX3 expression to inhibit autophagy in hepatitis B virus infection via targeting miR-181a-5p

Hepatitis B virus (HBV) is one of the major causes for chronic liver disease leading to cirrhosis and hepatocellular carcinoma (HCC). It utilizes the host cell machinery, such as host factors and non-coding RNAs, to modulate its survival and proliferation. CircRNAs, a special class of non-coding RNAs, play a crucial role in regulating HBV infection. A recent study reported that circular RNA SET domain containing 2 (circSETD2) was down-regulated in HCC, however, there is no study available on its role in modulating HBV-infection. The hepatic cell lines were cultured in DMEM with 10% FBS and antibiotics. HepG2 cells were transfected with empty vector, HBV or HBx expression plasmids. HepG2.2.15 cells were transfected with non-specific RNA, circSETD2, miR-181a-5p mimic or miR-181a-5p inhibitor. The expression of circSETD2 and miR-181a-5p were determined by qPCR, and Western blots were performed for analyzing autophagic marker proteins. Autophagy flux assays were performed in circSETD2, miR-181a-5p mimic or miR-181a-5p inhibitor-transfected cells. Significance of the data were analyzed using unpaired student t-test. The expression of circSETD2 was significantly lower (76%) in HepG2.215 cells, compared to non-HBV infected cells. Overexpression of HBV and HBx in HepG2 cells significantly reduced the expression of circSETD2. CircSETD2 overexpression decreased the HBsAg levels and the expression of miR-181a-5p. Overexpression of miR-181a-5p decreased Dead-Box RNA Helicase 3 (DDX3) expression and induced autophagy proteins. Inhibition of miR-181a-5p enhanced the expression of DDX3, which led to decreased autophagy. Overexpression of circSETD2 increased the expression of DDX3 and decreased autophagy proteins. The data showed that HBx suppressed circSETD2 to induce miR-181a-5p expression, which in turn resulted in the decreased DDX3, leading to the increased autophagy in HBV-infected hepatic cells.