Date Published: March 20, 2017
Publisher: Public Library of Science
Author(s): Junyu Lin, Chenjian Gu, Zhongliang Shen, Yanfeng Liu, Wei Wang, Shuai Tao, Xiaoxian Cui, Jing Liu, Youhua Xie, Wang-Shick Ryu.
The role of hepatocyte nuclear factor 1α (HNF1α) in the regulation of gene expression and replication of hepatitis B virus (HBV) is not fully understood. Previous reports have documented the induction of the expression of viral large surface protein (LHBs) by HNF1α through activating viral Sp1 promoter. Large amount of LHBs can block the secretion of hepatitis B surface antigen (HBsAg). Here we found that HNF1α overexpression inhibited HBV gene expression and replication in Huh7 cells, resulting in marked decreases in HBsAg, hepatitis B e antigen (HBeAg) and virion productions. In contrast, knockdown of endogenous HNF1α expression enhanced viral gene expression and replication. This HNF1α-mediated inhibition did not depend on LHBs. Instead, HNF1α promoted the expression of NF-κB p65 and slowed p65 protein degradation, leading to nuclear accumulation of p65 and activation of the NF-κB signaling, which in turn inhibited HBV gene expression and replication. The inhibitor of the NF-κB signaling, IκBα-SR, could abrogate this HNF1α-mediated inhibition. While the dimerization domain of HNF1α was dispensable for the induction of LHBs expression, all the domains of HNF1α was required for the inhibition of HBV gene expression. Our findings identify a novel role of HNF1α in the regulation of HBV gene expression and replication.
The infection of hepatitis B virus (HBV), which affects 240 million people worldwide, can cause acute and chronic liver diseases . HBV is an enveloped virus with a genome of 3.2kb partially double-stranded relaxed circular DNA (rcDNA) within its nucleocapsid. After infection of the hepatocyte, rcDNA is converted in the nucleus to covalently closed circular DNA (cccDNA) that serves as the template for viral transcription. Four promoters (Sp1, Sp2, Cp, and Xp) in concert with two enhancers (EnI, EnII) control HBV transcription. The 3.5kb preC mRNA and pregenomic (pg) RNA encode hepatitis e antigen (HBeAg) and the core and polymerase proteins, respectively. The 2.4kb preS1 mRNA encodes the large surface protein (LHBs) and the 2.1kb preS2/S mRNA the middle and small surface proteins (MHBs & SHBs). The 0.7kb mRNA encodes HBx. HBV polymerase associates with pgRNA, resulting in their encapsidation by core proteins. In the nucleocapsid, pgRNA is reverse transcribed to rcDNA by viral polymerase. New nucleocapsids are enveloped by viral surface proteins and secreted, or traffick rcDNA back to the nucleus to supplement the cccDNA pool [2, 3].
HNF1α as a key member of the liver enriched transcription factor family collaborates with other family factors to participate in a wide range of hepatocellular biochemical processes including lipid metabolism, gluconeogenesis and deoxygenation of xenobiotics. The role of HNF1α in the regulation of HBV replication is not fully understood. HNF1α is required to induce the expression of LHBs in vitro by binding to and activate viral Sp1 promoter . However, there is no obvious increase in the preS1 mRNA level in HNF1α-null HBV transgenic mice compared to normal HBV transgenic mice . Both positive and negative regulations of HBV replication have been documented for HNF1α [12–17]. In this study, we found that HNF1α overexpression downregulates HBV gene expression and replication in Huh7 cells while HNF1α-knockdown facilitates HBV transcription and replication. HNF1α can promote the expression of p65 protein via up-regulating p65 mRNA transcription and p65 protein stability, resulting in the activation of the NF-κB signaling that in turn inhibits HBV gene expression and replication. Our findings may help explain the puzzling observation in HNF1α-null HBV transgenic mice wherein the HBV replication intermediates in hepatocytes were increased and cccDNA more readily detected .