Regulation of Hepatitis B Virus replication by AKT and NF-kappaB signaling pathways in primary hepatocytes

Chronic infection with the hepatitis B virus (HBV) is a major risk factor for developing severe liver diseases such as hepatocellular carcinoma (HCC). Despite the availability of a vaccine, HBV-associated liver diseases remain a major worldwide health problem. HBx is a multifunctional protein encoded by the HBV genome; HBx stimulates HBV replication and is thought to play an important role in the development of HBV-associated HCC. HBx can activate the phosphatidylinositol 3 kinase (PI3K)/AKT signaling pathway in some cell lines; however, whether HBx regulates the PI3K/AKT signaling in normal hepatocytes has not been evaluated. In studies described here, we assessed HBx activation of PI3K/AKT signaling in an ex vivo model of cultured primary rat and human hepatocytes and determined how this HBx activity affected HBV replication. We report that HBx activates AKT in primary rat and human hepatocytes and that activation of AKT decreases HBV replication in these cells. HBx activation of AKT in primary hepatocytes decreased HBV mRNA and core protein levels, suggesting that AKT regulates HBV replication by affecting transcription of HBV mRNAs. In agreement with this, we show that the transcription factor hepatocyte nuclear factor (HNP) 4alpha is a target of HBx-regulated AKT, and we directly link HNF4alpha to HBx-regulated AKT modulation of HBV transcription and replication. Although 14Bx activates AKT to diminish HBV replication, we also show that an important effect of HBx activation of AKT is inhibition of apoptosis.;HBx also activates the transcription factor NF-kappaB to inhibit apoptosis in cultured primary rat hepatocytes. The molecular mechanisms that underlie HBx activation of NF-kappaB in normal hepatocytes are undefined. We now report that HBx increases the levels of reactive oxygen species (ROS) in primary rat hepatocytes and that this elevation of ROS is responsible for HBx activation of NF-kappaB. Activation of NF-kappaB by HBx decreases HBV replication in primary rat hepatocytes.;Consequently, our studies suggest that HBx activates cellular signaling pathways that simultaneously regulate HBV replication and cell survival. We propose that HBx functions as a rheostat that controls the level of HBV replication and the cellular environment to ensure non-cytopathic HBV replication.