Hepatocyte nuclear factor 3beta inhibits hepatitis B virus replication in vivo

Multiomics Analysis of Endocytosis upon HBV Infection and Identification of SCAMP1 as a Novel Host Restriction Factor against HBV Replication

Hepatitis B virus (HBV) infection remains a major global health problem and the primary cause of cirrhosis and hepatocellular carcinoma (HCC). HBV intrusion into host cells is prompted by virus–receptor interactions in clathrin-mediated endocytosis. Here, we report a comprehensive view of the cellular endocytosis-associated transcriptome, proteome and ubiquitylome upon HBV infection. In this study, we quantified 273 genes in the transcriptome and 190 endocytosis-associated proteins in the proteome by performing multi-omics analysis. We further identified 221 Lys sites in 77 endocytosis-associated ubiquitinated proteins. A weak negative correlation was observed among endocytosis-associated transcriptome, proteome and ubiquitylome. We found 33 common differentially expressed genes (DEGs), differentially expressed proteins (DEPs), and Kub-sites. Notably, we reported the HBV-induced ubiquitination change of secretory carrier membrane protein (SCAMP1) for the first time, differentially expressed across all three omics data sets. Overexpression of SCAMP1 efficiently inhibited HBV RNAs/pgRNA and secreted viral proteins, whereas knockdown of SCAMP1 significantly increased viral production. Mechanistically, the EnhI/XP, SP1, and SP2 promoters were inhibited by SCAMP1, which accounts for HBV X and S mRNA inhibition. Overall, our study unveils the previously unknown role of SCAMP1 in viral replication and HBV pathogenesis and provides cumulative and novel information for a better understanding of endocytosis in response to HBV infection.

Hepatocyte Growth Factor-Dependent Antiviral Activity of Activated cdc42-Associated Kinase 1 Against Hepatitis B Virus

Activated cdc42-associated kinase 1 (ACK1) is a well-known non-receptor tyrosine kinase that regulates cell proliferation and growth through activation of cellular signaling pathways, including mitogen-activated protein kinase (MAPK). However, the anti-HBV activity of ACK1 has not been elucidated. This study aimed to investigate the role of ACK1 in the HBV life cycle and the mechanism underlying the anti-HBV activity of ACK1. To examine the antiviral activity of ACK1, we established HepG2-ACK1 cells stably overexpressing ACK1. The HBV life cycle, including HBeAg/HBsAg secretion, HBV DNA/transcription, and enhancer activity, was analyzed in HepG2 and HepG2-ACK1 cells with HBV replication-competent HBV 1.2mer (HBV 1.2). Finally, the anti-HBV activity of ACK1 was examined in an HBV infection system. ACK1 suppressed HBV gene expression and transcription in HepG2 and HepG2-ACK1 cells. Furthermore, ACK1 inhibited HBV replication by decreasing viral enhancer activity. ACK1 exhibited its anti-HBV activity via activation of Erk1/2, which consequently downregulated the expression of HNF4α binding to HBV enhancers. Furthermore, hepatocyte growth factor (HGF) induced ACK1 expression at an early stage. Finally, ACK1 mediated the antiviral effect of HGF in the HBV infection system. These results indicated that ACK1 induced by HGF inhibited HBV replication at the transcriptional level by activating the MAPK-HNF signaling pathway. Our findings suggest that ACK1 is a potentially novel upstream molecule of MAPK-mediated anti-HBV activity.

Relative DNA Methylation and Demethylation Efficiencies during Postnatal Liver Development Regulate Hepatitis B Virus Biosynthesis

Hepatitis B virus (HBV) transcription and replication increase progressively throughout postnatal liver development with maximal viral biosynthesis occurring at around 4 weeks of age in the HBV transgenic mouse model of chronic infection. Increasing viral biosynthesis is associated with a corresponding progressive loss of DNA methylation. The loss of DNA methylation is associated with increasing levels of 5-hydroxymethylcytosine (5hmC) residues which correlate with increased liver-enriched pioneer transcription factor Forkhead box protein A (FoxA) RNA levels, a rapid decline in postnatal liver DNA methyltransferase (Dnmt) transcripts, and a very modest reduction in ten-eleven translocation (Tet) methylcytosine dioxygenase expression. These observations are consistent with the suggestion that the balance between active HBV DNA methylation and demethylation is regulated by FoxA recruitment of Tet in the presence of declining Dnmt activity. These changes lead to demethylation of the viral genome during hepatocyte maturation with associated increases in viral biosynthesis. Consequently, manipulation of the relative activities of these two counterbalancing processes might permit the specific silencing of HBV gene expression with the loss of viral biosynthesis and the resolution of chronic HBV infections.IMPORTANCE HBV biosynthesis begins at birth and increases during early postnatal liver development in the HBV transgenic mouse model of chronic infection. The levels of viral RNA and DNA synthesis correlate with pioneer transcription factor FoxA transcript plus Tet methylcytosine dioxygenase-generated 5hmC abundance but inversely with Dnmt transcript levels and HBV DNA methylation. Together, these findings suggest that HBV DNA methylation during neonatal liver development is actively modulated by the relative contributions of FoxA-recruited Tet-mediated DNA demethylation and Dnmt-mediated DNA methylation activities. This mode of gene regulation, mediated by the loss of DNA methylation at hepatocyte-specific viral and cellular promoters, likely contributes to hepatocyte maturation during liver development in addition to the postnatal activation of HBV transcription and replication.

The Regulation of HBV Transcription and Replication

Hepatitis B virus (HBV) is a major human pathogen lacking a reliable curative therapy. Current therapeutics target the viral reverse transcriptase/DNA polymerase to inhibit viral replication but generally fail to resolve chronic HBV infections. Due to the limited coding potential of the HBV genome, alternative approaches for the treatment of chronic infections are desperately needed. An alternative approach to the development of antiviral therapeutics is to target cellular gene products that are critical to the viral life cycle. As transcription of the viral genome is an essential step in the viral life cycle, the selective inhibition of viral RNA synthesis is a possible approach for the development of additional therapeutic modalities that might be used in combination with currently available therapies. To address this possibility, a molecular understanding of the relationship between viral transcription and replication is required. The first step is to identify the transcription factors that are the most critical in controlling the levels of HBV RNA synthesis and to determine their in vivo role in viral biosynthesis. Mapping studies in cell culture utilizing reporter gene constructs permitted the identification of both ubiquitous and liver-enriched transcription factors capable of modulating transcription from the four HBV promoters. However, it was challenging to determine their relative importance for viral biosynthesis in the available human hepatoma replication systems. This technical limitation was addressed, in part, by the development of non-hepatoma HBV replication systems where viral biosynthesis was dependent on complementation with exogenously expressed transcription factors. These systems revealed the importance of specific nuclear receptors and hepatocyte nuclear factor 3 (HNF3)/forkhead box A (FoxA) transcription factors for HBV biosynthesis. Furthermore, using the HBV transgenic mouse model of chronic viral infection, the importance of various nuclear receptors and FoxA isoforms could be established in vivo. The availability of this combination of systems now permits a rational approach toward the development of selective host transcription factor inhibitors. This might permit the development of a new class of therapeutics to aid in the treatment and resolution of chronic HBV infections, which currently affects approximately 1 in 30 individuals worldwide and kills up to a million people annually.

Intracellular interleukin-32γ mediates antiviral activity of cytokines against hepatitis B virus

Cytokines are involved in early host defense against pathogen infections. In particular, tumor necrosis factor (TNF) and interferon-gamma (IFN-γ) have critical functions in non-cytopathic elimination of hepatitis B virus (HBV) in hepatocytes. However, the molecular mechanisms and mediator molecules are largely unknown. Here we show that interleukin-32 (IL-32) is induced by TNF and IFN-γ in hepatocytes, and inhibits the replication of HBV by acting intracellularly to suppress HBV transcription and replication. The gamma isoform of IL-32 (IL-32γ) inhibits viral enhancer activities by downregulating liver-enriched transcription factors. Our data are validated in both an in vivo HBV mouse model and primary human hepatocytes. This study thus suggests that IL-32γ functions as intracellular effector in hepatocytes for suppressing HBV replication to implicate a possible mechanism of non-cytopathic viral clearance.

Cytokines such as TNF and IFN-γ are important for immunity against hepatitis B virus (HBV). Here the authors show that interleukin-32 gamma (IL-32γ) acts downstream of TNF and IFN-γ as an intracellular effector, and that IL-32γ negatively regulates host factors contributing to HBV transcription to promote HBV clearance.

Multiple Functions of Cellular FLIP Are Essential for Replication of Hepatitis B Virus

Hepatitis B virus (HBV) infection is a leading cause of liver diseases; however, the host factors which facilitate the replication and persistence of HBV are largely unidentified. Cellular FLICE inhibitory protein (c-FLIP) is a typical antiapoptotic protein. In many cases of liver diseases, the expression level of c-FLIP is altered, which affects the fate of hepatocytes. We previously found that c-FLIP and its cleaved form interact with HBV X protein (HBx), which is essential for HBV replication, and regulate diverse cellular signals. In this study, we investigated the role of endogenous c-FLIP in HBV replication and its underlying mechanisms. The knockdown of endogenous c-FLIP revealed that this protein regulates HBV replication through two different mechanisms. (i) c-FLIP interacts with HBx and protects it from ubiquitin-dependent degradation. The N-terminal DED1 domain of c-FLIP is required for HBx stabilization. (ii) c-FLIP regulates the expression or stability of hepatocyte nuclear factors (HNFs), which have critical roles in HBV transcription and maintenance of hepatocytes. c-FLIP regulates the stability of HNFs through physical interactions. We verified our findings in three HBV infection systems: HepG2-NTCP cells, differentiated HepaRG cells, and primary human hepatocytes. In conclusion, our results identify c-FLIP as an essential factor in HBV replication. c-FLIP regulates viral replication through its multiple effects on viral and host proteins that have critical roles in HBV replication.IMPORTANCE Although the chronic hepatitis B virus (HBV) infection still poses a major health concern, the host factors which are required for the replication of HBV are largely uncharacterized. Our studies identify cellular FLICE inhibitory protein (c-FLIP) as an essential factor in HBV replication. We found the dual roles of c-FLIP in regulation of HBV replication: c-FLIP interacts with HBx and enhances its stability and regulates the expression or stability of hepatocyte nuclear factors which are essential for transcription of HBV genome. Our findings may provide a new target for intervention in persistent HBV infection.

PGC1α Transcriptional Adaptor Function Governs Hepatitis B Virus Replication by Controlling HBcAg/p21 Protein-Mediated Capsid Formation

In the human hepatoma cell line Huh7, the coexpression of the coactivators peroxisome proliferator-activated receptor γ coactivator 1α (PGC1α), cyclic AMP-responsive element binding protein binding protein (CBP), steroid receptor coactivator 1 (SRC1), and protein arginine methyltransferase 1 (PRMT1) only modestly increase hepatitis B virus (HBV) biosynthesis. However, by utilizing the human embryonic kidney cell line HEK293T, it was possible to demonstrate that PGC1α alone can support viral biosynthesis independently of the expression of additional coactivators or transcription factors. In contrast, additional coactivators failed to support robust HBV replication in the absence of PGC1α. These observations indicate that PGC1α represents a novel adaptor molecule capable of recruiting the necessary transcriptional machinery to the HBV nucleocapsid promoter to modestly enhance viral pregenomic 3.5-kb RNA synthesis. Although this change in transcription is associated with a similar modest change in hepatitis B virus core antigen polypeptide (HBcAg/p21) synthesis, it mediates a dramatic increase in viral capsid production and robust viral replication. Therefore, it is apparent that the synthesis of cytoplasmic HBcAg/p21 above a critical threshold level is required for the efficient assembly of HBV replication-competent viral capsids.IMPORTANCE Hepatitis B virus (HBV) is a major human pathogen, and novel targets for the development of additional therapeutic agents are urgently needed. Here we demonstrate that the coactivator peroxisome proliferator-activated receptor γ coactivator 1α (PGC1α) serves as a unique adaptor molecule for the recruitment of additional coactivator proteins, which can finely regulate HBV transcription. The consequence of this precise regulation of viral RNA levels by PGC1α is a subtle increase in cytoplasmic HBcAg/p21 polypeptide translation, which shifts the equilibrium from dimer formation dramatically in favor of viral capsid assembly. These findings suggest that both PGC1α and capsid assembly may represent attractive targets for the development of antiviral agents against chronic HBV infection.

Hepatic deficiency of the pioneer transcription factor FoxA restricts hepatitis B virus biosynthesis by the developmental regulation of viral DNA methylation

The FoxA family of pioneer transcription factors regulates hepatitis B virus (HBV) transcription, and hence viral replication. Hepatocyte-specific FoxA-deficiency in the HBV transgenic mouse model of chronic infection prevents the transcription of the viral DNA genome as a result of the failure of the developmentally controlled conversion of 5-methylcytosine residues to cytosine during postnatal hepatic maturation. These observations suggest that pioneer transcription factors such as FoxA, which mark genes for expression at subsequent developmental steps in the cellular differentiation program, mediate their effects by reversing the DNA methylation status of their target genes to permit their ensuing expression when the appropriate tissue-specific transcription factor combinations arise during development. Furthermore, as the FoxA-deficient HBV transgenic mice are viable, the specific developmental timing, abundance and isoform type of pioneer factor expression must permit all essential liver gene expression to occur at a level sufficient to support adequate liver function. This implies that pioneer transcription factors can recognize and mark their target genes in distinct developmental manners dependent upon, at least in part, the concentration and affinity of FoxA for its binding sites within enhancer and promoter regulatory sequence elements. This selective marking of cellular genes for expression by the FoxA pioneer factor compared to HBV may offer the opportunity for the specific silencing of HBV gene expression and hence the resolution of chronic HBV infections which are responsible for approximately one million deaths worldwide annually due to liver cirrhosis and hepatocellular carcinoma.

This study demonstrates the connection between FoxA expression and gene silencing by DNA methylation in vivo during liver maturation. Insufficient FoxA expression results in selective developmentally regulated hepatitis B virus (HBV) silencing by DNA methylation. To our knowledge, this is the first in vivo demonstration that pioneer factors such as FoxA function by mediating the developmental demethylation of their target genes, leading to their tissue specific gene expression. Furthermore, our results strongly imply that the marking of cellular target genes for subsequent transcription later in development is dependent upon the level and timing of FoxA expression plus its affinity for its target sequences within enhancer and promoter regions. Consequently, these findings suggest that the appropriate control of FoxA activity during development could lead to the transcriptional inactivation of nuclear HBV covalently closed circular DNA by methylation and hence resolution of chronic HBV infection. This represents a clinical goal that current therapies are unable to attain, and hence suggests a potential route to a cure for this chronic infection which kills approximately 1 million individuals annually.

Cleaved c-FLIP mediates the antiviral effect of TNF-α against hepatitis B virus by dysregulating hepatocyte nuclear factors

BACKGROUND & AIMS

Cytokines are key molecules implicated in the defense against virus infection. Tumor necrosis factor-alpha (TNF-α) is well known to block the replication of hepatitis B virus (HBV). However, the molecular mechanism and the downstream effector molecules remain largely unknown.

METHODS

In this study, we investigated the antiviral effect and mechanism of p22-FLIP (FLICE-inhibitory protein) by ectopic expression in vitro and in vivo. In addition, to provide the biological relevance of our study, we examined that the p22-FLIP is involved in TNF-α-mediated suppression of HBV in primary human hepatocytes.

RESULTS

We found that p22-FLIP, a newly discovered c-FLIP cleavage product, inhibited HBV replication at the transcriptional level in both hepatoma cells and primary human hepatocytes, and that c-FLIP conversion to p22-FLIP was stimulated by the TNF-α/NF-κB pathway. p22-FLIP inhibited HBV replication through the upregulation of HNF3β but downregulation of HNF4α, thus inhibiting both HBV enhancer elements. Finally, p22-FLIP potently inhibited HBV DNA replication in a mouse model of HBV replication.

CONCLUSIONS

Taken together, these findings suggest that the anti-apoptotic p22-FLIP serves a novel function of inhibiting HBV transcription, and mediates the antiviral effect of TNF-α against HBV replication.

Inhibition of hepatitis B virus gene expression and replication by hepatocyte nuclear factor 6

Hepatitis B virus (HBV), a small enveloped DNA virus, chronically infects more than 350 million people worldwide and causes liver diseases from hepatitis to cirrhosis and liver cancer. Here, we report that hepatocyte nuclear factor 6 (HNF6), a liver-enriched transcription factor, can inhibit HBV gene expression and DNA replication. Overexpression of HNF6 inhibited, while knockdown of HNF6 expression enhanced, HBV gene expression and replication in hepatoma cells. Mechanistically, the SP2 promoter was inhibited by HNF6, which partly accounts for the inhibition on S mRNA. Detailed analysis showed that a cis element on the HBV genome (nucleotides [nt] 3009 to 3019) was responsible for the inhibition of the SP2 promoter by HNF6. Moreover, further analysis showed that HNF6 reduced viral pregenomic RNA (pgRNA) posttranscriptionally via accelerating the degradation of HBV pgRNA independent of La protein. Furthermore, by using truncated mutation experiments, we demonstrated that the N-terminal region of HNF6 was responsible for its inhibitory effects. Importantly, introduction of an HNF6 expression construct with the HBV genome into the mouse liver using hydrodynamic injection resulted in a significant reduction in viral gene expression and DNA replication. Overall, our data demonstrated that HNF6 is a novel host factor that can restrict HBV replication via both transcriptional and posttranscriptional mechanisms.

IMPORTANCE

HBV is a major human pathogen whose replication is regulated by host factors. Liver-enriched transcription factors are critical for many liver functions, including metabolism, development, and cell proliferation, and some of them have been shown to regulate HBV gene expression or replication in different manners. In this study, we showed that HNF6 could inhibit the gene expression and DNA replication of HBV via both transcriptional and posttranscriptional mechanisms. As HNF6 is differentially expressed in men and women, the current results may suggest a role of HNF6 in the gender dimorphism of HBV infection.

Molecular mechanisms of hepatic apoptosis regulated by nuclear factors

Apoptosis is a prominent characteristic in the pathogenesis of liver disease. The mechanism of hepatic apoptosis is not well understood. Hepatic apoptosis alters relative levels of nuclear factors such as Foxa2, NF-κB, C/EBPβ, and p53. Regulation of nuclear factors modulates the degree of hepatic apoptosis and the progression of liver disease. Nuclear factors have distinctive mechanisms to mediate hepatic apoptosis. The modification of nuclear factors is a novel therapeutic strategy for liver disease as demonstrated by pre-clinical models and clinical trials.

Hepatocystin contributes to interferon-mediated antiviral response to hepatitis B virus by regulating hepatocyte nuclear factor 4α

Hepatocystin/80K-H is known as a causative gene for autosomal dominant polycystic liver disease. However, the role of hepatocystin in hepatitis B virus-related liver disease remains unknown. Here, we investigated the role of hepatocystin on the cytokine-mediated antiviral response against hepatitis B virus infection. We investigated the antiviral effect and mechanism of hepatocystin by ectopic expression and RNAi knockdown in cell culture and mouse livers. Hepatocystin suppressed the replication of hepatitis B virus both in vitro and in vivo. This inhibitory effect was HBx-independent and mediated by the transcriptional regulation of viral genome via the activation of exogenous signal-regulated kinase 1/2 and the reduced expression of hepatocyte nuclear factor 4α, a transcription factor essential for hepatitis B virus replication. The amino-terminal region of hepatocystin was essential for regulation of this antiviral signaling pathway. We also found that hepatocystin acts as a critical component in interferon-mediated mitogen-activated protein kinase signaling pathway, and the interferon-induced antiviral activity against hepatitis B virus is associated with the expression levels of hepatocystin. We demonstrated that hepatocystin plays a critical role in modulating the susceptibility of hepatitis B virus to interferon, suggesting that the modulation of hepatocystin expression is important for cytokine-mediated viral clearance during hepatitis B virus infection.

Identification and characterization of multiple TRIM proteins that inhibit hepatitis B virus transcription

Tripartite motif (TRIM) proteins constitute a family of over 100 members that share conserved tripartite motifs and exhibit diverse biological functions. Several TRIM proteins have been shown to restrict viral infections and regulate host cellular innate immune responses. In order to identify TRIM proteins that modulate the infection of hepatitis B virus (HBV), we tested 38 human TRIMs for their effects on HBV gene expression, capsid assembly and DNA synthesis in human hepatoma cells (HepG2). The study revealed that ectopic expression of 8 TRIM proteins in HepG2 cells potently reduced the amounts of secreted HBV surface and e antigens as well as intracellular capsid and capsid DNA. Mechanistic analyses further demonstrated that the 8 TRIMs not only reduced the expression of HBV mRNAs, but also inhibited HBV enhancer I and enhancer II activities. Studies focused on TRIM41 revealed that a HBV DNA segment spanning nucleotide 1638 to nucleotide 1763 was essential for TRIM41-mediated inhibition of HBV enhancer II activity and the inhibitory effect depended on the E3 ubiquitin ligase activity of TRIM41 as well as the integrity of TRIM41 C-terminal domain. Moreover, knockdown of endogenous TRIM41 in a HepG2-derived stable cell line significantly increased the level of HBV preC/C RNA, leading to an increase in viral core protein, capsid and capsid DNA. Our studies have thus identified eight TRIM proteins that are able to inhibit HBV transcription and provided strong evidences suggesting the endogenous role of TRIM41 in regulating HBV transcription in human hepatoma cells.

Impact of Nucleotide Mutations at the HNF3- and HNF4-Binding Sites in Enhancer 1 on Viral Replication in Patients with Chronic Hepatitis B Virus Infection

Background/Aims

The hepatitis B virus (HBV) genome contains binding sites for hepatocyte nuclear factors (HNF) 3 and 4 in the core domain of enhancer 1 (Enh1), and mutations in this domain have a strong impact on virus replication. We aimed to identify frequent base-mutation sites in the core domain of Enh1 and to examine the impact of these mutations on viral replication.

Methods

We studied virological characteristics and genetic sequences in 387 patients with chronic hepatitis B. We evaluated functional differences associated with specific mutations within the core domain of Enh1.

Results

Mutations in the core domain were found with significant frequency in C1126 (122/387 [31.5%], the binding site for HNF3) and in C1134 (106/387 [27.4%], the binding site for HNF4). A single mutation at nt 1126 (C1126) was identified in 17/123 (13.8%), and 105/123 (85.4%) had double mutations (C1126/1134). The level of HBV DNA (log10 copies/mL) was lower in single mutants (C1126, 5.81±1.25) than in wild (6.80±1.65) and double mutants (C1126/1134, 6.81±1.54). Similarly, the relative luciferase activity of C1126 and C1126/C1134 was 0.18 and 1.12 times that of the wild-type virus, respectively.

Conclusions

Mutations in the HNF3 binding site inhibit viral replication, whereas mutations at the HNF4 binding site restore viral replication.

Study of the expression levels of Hepatocyte nuclear factor 4 alpha and 3 beta in patients with different outcome of HBV infection

Hepatocyte nuclear factors 4 alpha (HNF4α) and 3 beta (HNF3β) are members of a group of liver-enriched transcription factors (LETFs) that play important roles in regulating the replication of hepatitis B virus (HBV) and liver inflammation. However, the relationship of the level of HNF4α and HNF3β with the severity of HBV-infected liver diseases is unclear. In this study, liver tissue samples from different types of HBV patients were collected, and HNF4α and HNF3β expression were detected by immunohistochemistry. The expression of HNF4α was significant higher in patients with severe hepatitis B(SHB) than those with chronic hepatitis B(CHB) and liver cirrhosis(LC) (both P < 0.05), but similar between patients with CHB and LC (P > 0.05). And the expression of HNF3β was similar among patients with CHB, LC and SHB (P > 0.05 for all pairwise comparison). This suggests that the expression level of HNF4α was different in patients with different outcome of HBV infection, high expression level of HNF4α may correlate with occurrence of SHB

Limited effects of bile acids and small heterodimer partner on hepatitis B virus biosynthesis in vivo

Multiple nuclear receptors, including hepatocyte nuclear factor 4α (HNF4α), retinoid X receptor α (RXRα) plus peroxisome proliferator-activated receptor α (PPARα), RXRα plus farnesoid X receptor α (FXRα), liver receptor homolog 1 (LRH1), and estrogen-related receptors (ERRs), have been shown to support efficient viral biosynthesis in nonhepatoma cells in the absence of additional liver-enriched transcription factors. Although HNF4α has been shown to be critical for the developmental expression of hepatitis B virus (HBV) biosynthesis in the liver, the relative importance of the various nuclear receptors capable of supporting viral transcription and replication in the adult in vivo has not been clearly established. To investigate the role of the nuclear receptor FXR and the corepressor small heterodimer partner (SHP) in viral biosynthesis in vivo, SHP-expressing and SHP-null HBV transgenic mice were fed a bile acid-supplemented diet. The increased FXR activity and SHP expression levels resulting from bile acid treatment did not greatly modulate HBV RNA and DNA synthesis. Therefore, FXR and SHP appear to play a limited role in modulating HBV biosynthesis, suggesting that alternative nuclear receptors are more critical determinants of viral transcription in the HBV transgenic mouse model of chronic viral infection. These observations suggest that hepatic bile acid levels or therapeutic agents targeting FXR may not greatly modulate viremia during natural infection.

Hepatocyte metabolic signalling pathways and regulation of hepatitis B virus expression

Hepatitis B virus (HBV) is a small DNA virus responsible for significant morbidity and mortality worldwide. The liver, which is the main target organ for HBV infection, provides the virus with the machinery necessary for persistent infection and propagation, a process that might ultimately lead to severe liver pathologies such as chronic hepatitis, cirrhosis and liver cancer. HBV gene expression is regulated mainly at the transcriptional level by recruitment of a whole set of cellular transcription factors (TFs) and co-activators to support transcription. Over the years, many of these TFs were identified and interestingly enough most are associated with the body's nutritional state. These include the hepatocyte nuclear factors, forkhead Box O1, Farnesoid X receptor, cyclic-AMP response element-binding (CREB), CCAAT/enhancer-binding protein (C/EBP) and glucocorticoid receptor TFs and the transcription coactivator PPARγ coactivator-1α. Consequently, HBV gene expression is linked to hepatic metabolic processes such as glucose and fat production and utilization as well as bile acids' production and secretion. Furthermore, recent evidence indicates that HBV actively interferes with some of these hepatic metabolic processes by manipulating key TFs, such as CREB and C/EBP, to meet its requirements. The discovery of the mechanisms by which HBV is controlled by the hepatic metabolic milieu may broaden our understanding of the unique regulation of HBV expression and may also explain the mechanisms by which HBV induces liver pathologies. The emerging principle of the intimate link between HBV and liver metabolism can be further exploited for host-targeted therapeutic strategies.

The correlation of hepatocyte nuclear factor 4 alpha and 3 beta with hepatitis B virus replication in the liver of chronic hepatitis B patients

Hepatocyte nuclear factors 4 alpha (HNF4alpha) and 3 beta (HNF3beta) are members of a group of liver-enriched transcription factors (LETFs) that play important roles in regulating the replication of hepatitis B virus (HBV). Using cell culture and animal models, we showed that HNF4alpha supports HBV replication in nonhepatic cells and HNF3beta inhibits HBV replication. However, the expression of HNF4alpha and HNF3beta in the liver tissue of chronic HBV-infected patients and the relationship between the levels of HNF4alpha and HNF3beta and HBV replication are unclear. In this study, liver biopsy specimens from 86 chronic HBV-infected patients were collected. The expression levels of HNF4alpha, HNF3beta, hepatitis B surface antigen (HBsAg) and hepatitis B core antigen (HBcAg) were detected by an immunohistochemical technique and the level of HBV DNA was checked by in situ hybridization with serial sections from liver biopsy tissue samples. We show here that samples with higher levels of HNF4alpha expression also have higher levels of HBsAg, HBcAg and HBV DNA. In contrast, in samples with higher levels of HNF3beta expression, levels of HBsAg, HBcAg and HBV DNA were lower. There was a positive correlation between HNF4alpha expression and HBV replication, and a negative correlation between HNF3beta expression and HBV replication, in the liver of chronic HBV-infected patients. This suggests that HNF4alpha and HNF3beta likely participate in HBV replication in patients with HBV infection, or that HBV replication may somehow influence the expression of HNF4alpha and HNF3beta in the liver.

Limited effects of fasting on hepatitis B virus (HBV) biosynthesis in HBV transgenic mice

Nuclear receptors have a unique role in governing hepatitis B virus (HBV) transcription and replication. Hepatocyte nuclear factor 4alpha (HNF4alpha) and retinoid X receptor alpha (RXRalpha) plus peroxisome proliferator-activated receptor alpha (PPARalpha) have been shown to support viral biosynthesis in nonhepatoma cells in the absence of additional liver-enriched transcription factors. However, the in vivo importance of these nuclear receptors in HBV biosynthesis has been investigated only to a limited extent. Fasting has been shown to activate gluconeogenesis, in part, by activating PPARgamma coactivator 1 alpha, which in turn leads to activation of HNF4alpha- and RXRalpha/PPARalpha-mediated transcription. As HBV pregenomic RNA synthesis is primarily believed to be regulated by HNF4alpha under normal physiological conditions, it was of interest to determine the effect of fasting on the levels of HBV RNA and DNA synthesis. Fasting was shown to rather modestly increase the levels of viral proteins, transcripts, and replication intermediates in the HBV transgenic mouse model of chronic viral infection, suggesting that caloric restriction may modulate viremia to some extent during natural infection.

Differential inhibition of nuclear hormone receptor-dependent hepatitis B virus replication by the small heterodimer partner

The nuclear hormone receptors hepatocyte nuclear factor 4 (HNF4) and retinoid X receptor alpha (RXRalpha) plus peroxisome proliferator-activated receptor alpha (PPARalpha) heterodimer support hepatitis B virus (HBV) pregenomic RNA synthesis and viral replication in nonhepatoma cells. Small heterodimer partner (SHP), an orphan nuclear hormone receptor lacking a DNA binding domain, inhibits nuclear hormone receptor-mediated viral transcription and replication. The inhibition of HBV replication by SHP is dependent on the presence of nuclear hormone receptors. HBV replication that is dependent on HNF4 is considerably more sensitive to SHP-mediated inhibition than RXRalpha/PPARalpha-directed viral biosynthesis. SHP inhibition of HBV biosynthesis in HepG2 cells suggests that multiple nuclear hormone receptors mediate viral replication in this human hepatoma cell line. These observations suggest that the physiological regulation of HBV biosynthesis by SHP in the liver will depend on both the level of SHP expression and the relative contribution of HNF4 and RXRalpha/PPARalpha, plus potentially additional nuclear hormone receptors, to HBV RNA synthesis and replication.

Regulation of hepatitis B virus transcription and replication by liver-enriched transcriptional factors

Hepatotropism is a prominent feature of hepatitis B virus (HBV). Cell lines of nonhepatic origin do not independently support HBV replication. In this review, we show that the nuclear hormone receptors, hepatocyte nuclear factor 4 and retinoid X receptor plus peroxisome proliferator-activated receptor, support HBV replication in nonhepatic cells by controlling pregenomic RNA synthesis, indicating that these liver-enriched transcription factors control a unique molecular switch restricting viral tropism. In contrast, hepatocyte nuclear factor 3 antagonizes nuclear hormone receptor-mediated viral replication, demonstrating distinct regulatory roles for these liver-enriched transcription factors.

Expression of hepatocyte nuclear factor 4α and 3β in human tissues

AIM: To investigate the expression patterns of hepatocyte nuclear factor 4α (HNF-4α) and HNF-3b in normal human tissues, so as to provide the bases for further exploration of their relationships with hepatitis B virus (HBV) replication in hepatitis B patients.

METHODS: Immunohistochemistry was used to detect the expression of HNF-4α and HNF-3b in human tissues of liver, brain, lung, kidney, heart, spleen, intestine, pancreas, stomach and thyroid from 14 corpses. The differences of their expression in different tissues were analyzed.

RESULTS: The expression patterns of HNF-4α and HNF-3b was different among the 10 kinds of human tissues (HNF-4α: F = 22.479, P < 0.01; HNF-3b: F = 13.021, P < 0.01). Both HNF-4α and HNF-3b expression were not detected in brain, lung, stomach, appendix, thymus, adrenal gland and tonsil. Besides the tissues mentioned above, the expression of HNF-4α was significantly higher in liver, kidney, heart, spleen and intestines than that in the other tissues; the expression of HNF-3b was markedly higher in liver, kidney, heart and pancreas than that in the other tissues. The difference between high-level expression and low-level expression group has statistical significance (P < 0.05); however, the difference among those tissues with high-level expression had no statistical significance (P > 0.05).

CONCLUSION: The expression of HNF-4a and HNF-3b are different among human tissues, and they are highly expressed in some tissues such as liver. This result indicates that HNF-4a and HNF-3b might participate in the tissue-specific replication of HBV.

Effects of liver growth factors on hepadnavirus replication in chronically infected duck hepatocytes

BACKGROUND/AIMS

Duck hepatitis B virus (DHBV) replication is up-regulated by cell cycle during the early infection of primary duck but the effect of cell cycle on DHBV replication in chronically infected hepatocyte is not known.

METHODS

Hepatocytes obtained from DHBV congenitally infected embryos were used. Cell proliferation was controlled by addition of liver growth factors and the impact on viral replication analyzed.

RESULTS

EGF induced cell proliferation is associated with a slight increase in CCC DNA synthesis and a decrease in viral transcription. Conversely, TGFbeta blocked cell cycle progression, diminished CCC DNA synthesis but increased viral transcription.

CONCLUSIONS

Cell proliferation decreases DHBV transcription but this effect seems to be compensated by an opposite effect on the synthesis of CCC DNA resulting in a global moderate effect on viral replication. Our results also indicate that after division of chronically infected hepatocytes both daughter cells are infected, confirming that liver regeneration is not sufficient to induce CCC DNA eradication as suggested by the lack of effect of some long term anti-HBV therapies.