Peroxisome proliferator-activated receptors in HBV-related infection

Hepatitis B and circadian rhythm of the liver

The circadian rhythm in humans is determined by the central clock located in the hypothalamus’s suprachiasmatic nucleus, and it synchronizes the peripheral clocks in other tissues. Circadian clock genes and clock-controlled genes exist in almost all cell types. They have an essential role in many physiological processes, including lipid metabolism in the liver, regulation of the immune system, and the severity of infections. In addition, circadian rhythm genes can stimulate the immune response of host cells to virus infection. Hepatitis B virus (HBV) infection is the leading cause of liver disease and liver cancer globally. HBV infection depends on the host cell, and hepatocyte circadian rhythm genes are associated with HBV replication, survival, and spread. The core circadian rhythm proteins, REV-ERB and brain and muscle ARNTL-like protein 1, have a crucial role in HBV replication in hepatocytes. In addition to influencing the virus’s life cycle, the circadian rhythm also affects the pharmacokinetics and efficacy of antiviral vaccines. Therefore, it is vital to apply antiviral therapy at the appropriate time of day to reduce toxicity and improve the effectiveness of antiviral treatment. For these reasons, understanding the role of the circadian rhythm in the regulation of HBV infection and host responses to the virus provides us with a new perspective of the interplay of the circadian rhythm and anti-HBV therapy. Therefore, this review emphasizes the importance of the circadian rhythm in HBV infection and the optimization of antiviral treatment based on the circadian rhythm-dependent immune response.

Signaling Induced by Chronic Viral Hepatitis: Dependence and Consequences

Chronic viral hepatitis is a main cause of liver disease and hepatocellular carcinoma. There are striking similarities in the pathological impact of hepatitis B, C, and D, although these diseases are caused by very different viruses. Paired with the conventional study of protein-host interactions, the rapid technological development of -omics and bioinformatics has allowed highlighting the important role of signaling networks in viral pathogenesis. In this review, we provide an integrated look on the three major viruses associated with chronic viral hepatitis in patients, summarizing similarities and differences in virus-induced cellular signaling relevant to the viral life cycles and liver disease progression.

Inhibitory effect of a novel thiazolidinedione derivative on hepatitis B virus entry

The development of novel antivirals to treat hepatitis B virus (HBV) infection is still needed because currently available drugs do not completely eradicate chronic HBV in some patients. Recently, troglitazone and ciglitazone, classified among the compounds including the thiazolidinedione (TZD) moiety, were found to inhibit HBV infection, but these compounds are not clinically available. In this study, we synthesized 11 TZD derivatives, compounds 1-11, and examined the effect of each compound on HBV infection in HepG2 cells expressing NTCP (HepG2/NTCP cells). Among the derivatives, (Z)-5-((4'-(naphthalen-1-yl)-[1,1'-biphenyl]-4-yl)methylene)thiazolidine-2,4-dione (compound 6) showed the highest antiviral activity, with an IC₅₀ value of 0.3 μM and a selectivity index (SI) of 85, but compound 6 did not affect HCV infection. Treatment with compound 6 inhibited HBV infection in primary human hepatocytes (PHHs) but did not inhibit viral replication in HepG2.2.15 cells or HBV DNA-transfected Huh7 cells. Moreover, treatment with compound 6 significantly impaired hepatitis delta virus (HDV) infection and inhibited a step in HBV particle internalization but did not inhibit attachment of the preS1 lipopeptide or viral particles to the cell surface. These findings suggest that compound 6 interferes with HBV infection via inhibition of the internalization process.

Host Transcription Factors in Hepatitis B Virus RNA Synthesis

The hepatitis B virus (HBV) chronically infects over 250 million people worldwide and is one of the leading causes of liver cancer and hepatocellular carcinoma. HBV persistence is due in part to the highly stable HBV minichromosome or HBV covalently closed circular DNA (cccDNA) that resides in the nucleus. As HBV replication requires the help of host transcription factors to replicate, focusing on host protein–HBV genome interactions may reveal insights into new drug targets against cccDNA. The structural details on such complexes, however, remain poorly defined. In this review, the current literature regarding host transcription factors’ interactions with HBV cccDNA is discussed.

Silencing Retinoid X Receptor Alpha Expression Enhances Early-Stage Hepatitis B Virus Infection In Cell Cultures

Multiple steps of the life cycle of hepatitis B virus (HBV) are known to be coupled to hepatic metabolism. However, the details of involvement of the hepatic metabolic milieu in HBV infection remain incompletely understood. Hepatic lipid metabolism is controlled by a complicated transcription factor network centered on retinoid X receptor alpha (RXRα). Here, we report that RXRα negatively regulates HBV infection at an early stage in cell cultures. The RXR-specific agonist bexarotene inhibits HBV in HepG2 cells expressing the sodium taurocholate cotransporting polypeptide (NTCP) (HepG2-NTCP), HepaRG cells, and primary Tupaia hepatocytes (PTHs); reducing RXRα expression significantly enhanced HBV infection in the cells. Transcriptome sequencing (RNA-seq) analysis of HepG2-NTCP cells with a disrupted RXRα gene revealed that reduced gene expression in arachidonic acid (AA)/eicosanoid biosynthesis pathways, including the AA synthases phospholipase A2 group IIA (PLA2G2A), is associated with increased HBV infection. Moreover, exogenous treatment of AA inhibits HBV infection in HepG2-NTCP cells. These data demonstrate that RXRα is an important cellular factor in modulating HBV infection and implicate the participation of AA/eicosanoid biosynthesis pathways in the regulation of HBV infection.IMPORTANCE Understanding how HBV infection is connected with hepatic lipid metabolism may provide new insights into virus infection and its pathogenesis. By a series of genetic studies in combination with transcriptome analysis and pharmacological assays, we here investigated the role of cellular retinoid X receptor alpha (RXRα), a crucial transcription factor for controlling hepatic lipid metabolism, in de novo HBV infection in cell cultures. We found that silencing of RXRα resulted in elevated HBV covalently closed circular DNA (cccDNA) formation and viral antigen production, while activation of RXRα reduced HBV infection efficiency. Our results also showed that silencing phospholipase A2 group IIA (PLA2G2A), a key enzyme of arachidonic acid (AA) synthases, enhanced HBV infection efficiency in HepG2-NTCP cells and that exogenous AA treatment reduced de novo HBV infection in the cells. These findings unveil RXRα as an important cellular factor in modulating HBV infection and may point to a new strategy for host-targeted therapies against HBV.

LncRNA expression profiles in HBV-transformed human hepatocellular carcinoma cells treated with a novel inhibitor of human La protein

We previously identified a novel inhibitor of La protein, H11, which inhibited hepatitis B virus (HBV) replication by inhibiting the interaction between La protein and HBV RNA. However, the other cellular factors involved in this process remain unclear. To investigate the mechanism of H11-mediated inhibition of HBV infection, a lncRNA microarray analysis was performed using H11-treated and untreated stable HBV-expressing human hepatoblastoma HepG2.2.15 cells. The profiles of differentially expressed lncRNAs and mRNAs were generated and analysed using Gene Ontology (GO) and pathway analyses. The microarray data showed that 61 lncRNAs were upregulated, 74 lncRNAs were downregulated, 43 mRNAs were upregulated, and 44 mRNAs were downregulated in H11 treatment group when compared with the control group, and these results were consistent with qRT-PCR expression data. Bioinformatic analysis indicated that the differentially expressed lncRNAs were involved in RNA-mediated post-transcriptional gene silencing, regulation of viral genome replication and Jak-STAT signalling and apoptosis pathways. GO analysis showed that differentially expressed mRNAs were enriched in negative regulation of the Wnt signalling pathway and negative regulation of growth. Pathways analysis indicated that the differentially expressed mRNAs were involved in regulation of nuclear β-catenin signalling and target gene transcription, as direct p53 effectors, and in the peroxisome proliferator-activated receptors signalling and peroxisome pathways. Microarray data and qRT-PCR results indicated that H11 mediates inhibition of HBV replication by regulating the Wnt, β-catenin and PPAR signalling pathways.

Identification of acetyltransferase genes (HAT1 and KAT8) regulating HBV replication by RNAi screening

Background

The initiation of hepatitis B virus (HBV) replication involves the formation of covalently closed circular DNA (cccDNA) and its transcription into pregenomic RNA (pgRNA) in hepatocyte nuclei. The regulatory mechanism of HBV replication by acetyltransferase is thus far not well understood, but human acetyltransferase has been reported as being involved in the regulation of HBV replication.

Results

Depletion of KAT8 or HAT1 via RNA interference (RNAi) markedly down-regulated HBV-DNA and pgRNA levels in HepG2.2.15 cells, with KAT8 knockdown reducing both HBsAg and HBeAg more than HAT1 knockdown. Consistent with these observations, HBV replication regulators hepatocyte nuclear factor-4-α (HNF4α) and peroxisome proliferator-activated receptor gamma coactivator- (PPARGC-) 1-α were decreased following knockdown of HAT1 or KAT8.

Conclusions

These data suggest that KAT8 or HAT1 regulate HBV replication and may be potential drug targets of anti-HBV therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s13578-015-0059-1) contains supplementary material, which is available to authorized users.

PPARα and PPARγ protect against HIV-1-induced MMP-9 overexpression via caveolae-associated ERK and Akt signaling

Activation of matrix metalloproteinase-9 (MMP-9) is involved in HIV-1-induced disruption of the blood-brain barrier (BBB). In the present study, we hypothesize that peroxisome proliferator-activated receptor (PPAR)-α or PPARγ can protect against HIV-1-induced MMP-9 overexpression in brain endothelial cells (hCMEC cell line) by attenuating cellular oxidative stress and down-regulation of caveolae-associated redox signaling. Exposure to HIV-1-infected monocytes induced phosphorylation of ERK1/2 and Akt in hCMEC by 2.5- and 3.6-fold, respectively; however, these effects were attenuated by overexpression of PPARα or PPARγ and by silencing of caveolin-1 (cav-1). Coculture of hCMEC with HIV-1-infected monocytes significantly induced MMP-9 promoter and enzyme activity by 3- to 3.5-fold. Promoter mutation studies indicated that SP-1 (g1940t_g1941t) is an essential transcription factor involved in induction of MMP-9 promoter by HIV-1. In addition, HIV-1-stimulated activity of MMP-9 promoter was inhibited by mutation of AP-1 site 2 (c1918t_a1919g) and both (but not individual) NF-κB binding sites (g1389c and g1664c). PPAR overexpression, ERK1/2 or Akt inhibition, and silencing of cav-1 all effectively protected against HIV-1-induced MMP-9 promoter activity, indicating a close relationship among HIV-1-induced cerebrovascular toxicity, redox-regulated mechanisms, and functional caveolae. Such a link was further confirmed in MMP-9-deficient mice exposed to PPARα or PPARγ agonist and injected with the HIV-1-specific protein Tat into cerebral vasculature. Overall, our results indicate that ERK1/2, Akt, and cav-1 are involved in the regulatory mechanisms of PPAR-mediated protection against HIV-1-induced MMP-9 expression in brain endothelial cells.

Modulation of hepatitis B virus replication and hepatocyte differentiation by MicroRNA-1

MicroRNAs (miRNAs) are highly conserved small noncoding RNAs participating in regulation of various cellular processes. Viruses have been shown to utilize cellular miRNAs to increase their replication in host cells. Until now, the role of miRNAs in hepatitis B virus (HBV) replication has remained largely unknown. In this study, a number of miRNA mimics were transfected into hepatoma cell lines with HBV replication. It was noted that microRNA-1 (miR-1) transfection resulted in a marked increase of HBV replication, accompanied with up-regulated HBV transcription, antigen expression, and progeny secretion. However, bioinformatics and luciferase reporter analysis suggested that miR-1 may not target the HBV genome directly but regulate the expression of host genes to enhance HBV replication. Further studies showed that miR-1 was able to enhance the HBV core promoter transcription activity by augmenting farnesoid X receptor α expression. In addition, miR-1 arrested the cell cycle at the G(1) phase and inhibited cell proliferation by targeting histone deacetylase 4 and E2F transcription factor 5. Analysis of the cellular gene expression profile indicated that miR-1 transfected hepatoma cells developed a differentiated phenotype of hepatocytes.

CONCLUSION

MiR-1 regulates the expression of several host genes to enhance HBV replication and reverse cancer cell phenotype, which is apparently beneficial for HBV replication. Our findings provide a novel perspective on the role of miRNAs in host-virus interactions in HBV infection.

Inhibition of cellular proteasome activities mediates HBX-independent hepatitis B virus replication in vivo

The X protein (HBX) of the hepatitis B virus (HBV) is essential for HBV productive infection in vivo. Our previous study (Z. Hu, Z. Zhang, E. Doo, O. Coux, A. L. Goldberg, and T. J. Liang, J. Virol. 73:7231-7240, 1999) shows that interaction of HBX with the proteasome complex may underlie the pleiotropic functions of HBX. Previously, we demonstrated that HBX affects hepadnaviral replication through a proteasome-dependent pathway in cell culture models. In the present study, we studied the effect of the proteasome inhibitor MLN-273 in two HBV mouse models. We demonstrated that administration of MLN-273 to transgenic mice containing the replication-competent HBV genome with the defective HBX gene substantially enhanced HBV replication, while the compound had a minor effect on wild-type HBV transgenic mice. Similar results were obtained by using C57BL/6 mice infected with recombinant adenoviruses expressing the replicating HBV genome. Our data suggest that HBV replication is subjected to regulation by cellular proteasome and HBX functions through the inhibition of proteasome activities to enhance HBV replication in vivo.

Mycobacterium tuberculosis activates human macrophage peroxisome proliferator-activated receptor gamma linking mannose receptor recognition to regulation of immune responses

Mycobacterium tuberculosis enhances its survival in macrophages by suppressing immune responses in part through its complex cell wall structures. Peroxisome proliferator-activated receptor gamma (PPARgamma), a nuclear receptor superfamily member, is a transcriptional factor that regulates inflammation and has high expression in alternatively activated alveolar macrophages and macrophage-derived foam cells, both cell types relevant to tuberculosis pathogenesis. In this study, we show that virulent M. tuberculosis and its cell wall mannose-capped lipoarabinomannan induce PPARgamma expression through a macrophage mannose receptor-dependent pathway. When activated, PPARgamma promotes IL-8 and cyclooxygenase 2 expression, a process modulated by a PPARgamma agonist or antagonist. Upstream, MAPK-p38 mediates cytosolic phospholipase A(2) activation, which is required for PPARgamma ligand production. The induced IL-8 response mediated by mannose-capped lipoarabinomannan and the mannose receptor is independent of TLR2 and NF-kappaB activation. In contrast, the attenuated Mycobacterium bovis bacillus Calmette-Guérin induces less PPARgamma and preferentially uses the NF-kappaB-mediated pathway to induce IL-8 production. Finally, PPARgamma knockdown in human macrophages enhances TNF production and controls the intracellular growth of M. tuberculosis. These data identify a new molecular pathway that links engagement of the mannose receptor, an important pattern recognition receptor for M. tuberculosis, with PPARgamma activation, which regulates the macrophage inflammatory response, thereby playing a role in tuberculosis pathogenesis.