Steroid receptor coactivator 3 inhibits hepatitis B virus gene expression through activating Akt signaling to prevent HNF4α nuclear translocation.

Chronic hepatitis B virus (HBV) infection is one of the most serious global public health problems. The role of steroid receptor coactivator 3 (SRC-3) in HBV biosynthesis is unknown. The aim of this study is to investigate the function of SRC-3 in regulating HBV biosynthesis both in vitro and in vivo and to identify the underlying mechanism. In this study, we found that knockdown of SRC-3 could increase the levels of HBV mRNA and HBV proteins HBsAg and HBeAg in human liver cancer cell line HepG2 transfected with pHBV1.3 plasmids. In contrast, enforced expression of SRC-3 in SRC-3-knockdown HepG2 cells reduced the levels of HBV mRNA and HBV proteins HBsAg and HBeAg. Knockdown of SRC-3 dampened the Akt signaling, which has been shown to play a negative role in HBV transcription. Ectopic expression of constitutively activated Akt impaired the enhancement of HBV transcription by SRC-3 knockdown, indicating that SRC-3 inhibits HBV transcription by enhancing Akt signaling. Both SRC-3 and constitutively activated Akt could inhibit hepatocyte nuclear factor 4α (HNF4α)-mediated upregulation of HBV core promoter activity by preventing HNF4α nuclear translocation. Consistent with the in vitro results, in an in vivo chronic HBV replication mouse model developed by hydrodynamic injection of pHBV1.3 plasmids into mouse tail vein, enforced expression of SRC-3 in mouse liver reduced the levels of HBV mRNA in the liver and HBV antigens in serum, whereas knockout of SRC-3 in mouse increased the levels of HBV mRNA in the liver and HBV antigens in the serum. Our study suggests that SRC-3 inhibits HBV gene expression by activating Akt signaling to prevent HNF4α nuclear translocation.