Regulation of the HBV Entry Receptor NTCP and its Potential in Hepatitis B Treatment

The loss of hepatitis B virus receptor NTCP/SLC10A1 in human liver cancer cells is due to epigenetic silencing

Human Na+-taurocholate cotransporting polypeptide (hNTCP) is predominantly expressed in hepatocytes, maintaining bile salt homeostasis and serving as a receptor for hepatitis B virus (HBV). hNTCP expression is downregulated during hepatocellular carcinoma (HCC) development. In this study, we investigated the molecular mechanisms underlying hNTCP dysregulation using HCC tissues and cell lines, and primary human hepatocytes (PHHs). Firstly, we observed a significant reduction of hNTCP in HCC tumors compared to adjacent and normal tissues. Additionally, hNTCP mRNA levels were markedly lower in HepG2 cells compared to PHHs, which was corroborated at the protein level by immunoblotting. Sanger sequencing confirmed identical sequences for hNTCP promoter, exons, and mRNA coding sequences between PHH and HepG2 cells, indicating no mutations or splicing alterations. We then assessed the epigenetic status of hNTCP. The hNTCP promoter, with low CG content, showed no significant methylation differences between PHH and HepG2 cells. Chromatin immunoprecipitation coupled with qPCR (ChIP-qPCR) revealed a loss of activating histone posttranslational modification (PTM) H3K27ac near the hNTCP transcription start site (TSS) in HepG2 cells. This loss was also confirmed in HCC tumor cells compared to adjacent and background cells. Treating HepG2 cells with histone deacetylase inhibitors enhanced H3K27ac accumulation and glucocorticoid receptor (GR) binding at the hNTCP TSS, significantly increasing hNTCP mRNA and protein levels, and rendering the cells susceptible to HBV infection. In summary, histone PTM-related epigenetic mechanisms play a critical role in hNTCP dysregulation in liver cancer cells, providing insights into hepatocarcinogenesis and its impact on chronic HBV infection.

IMPORTANCE

HBV is a hepatotropic virus that infects human hepatocytes expressing the viral receptor hNTCP. Without effective antiviral therapy, chronic HBV infection poses a high risk of liver cancer. However, most liver cancer cell lines, including HepG2 and Huh7, do not support HBV infection due to the absence of hNTCP expression, and the mechanism underlying this defect remains unclear. This study demonstrates a significant reduction of hNTCP in hepatocellular carcinoma samples and HepG2 cells compared to normal liver tissues and primary human hepatocytes. Despite identical hNTCP genetic sequences, epigenetic analyses revealed a loss of the activating histone modification H3K27ac near the hNTCP transcription start site in cancer cells. Treatment with histone deacetylase inhibitors restored H3K27ac levels, reactivated hNTCP expression, and rendered HepG2 cells susceptible to HBV infection. These findings highlight the role of epigenetic modulation in hNTCP dysregulation, offering insights into hepatocarcinogenesis and its implications for chronic HBV infection.

Transporter Proteins as Therapeutic Drug Targets-With a Focus on SGLT2 Inhibitors

Membrane transporters interact not only with endogenous substrates but are also engaged in the transport of xenobiotics, including drugs. While the coordinated function of uptake (solute carrier family-SLC and SLCO) and efflux (ATP-binding cassette family-ABC, multidrug and toxic compound extrusion family-MATE) transporter system allows vectorial drug transport, efflux carriers alone achieve barrier functions. The modulation of transport functions was proved to be effective in the treatment strategies of various pathological states. Sodium-glucose cotransporter-2 (SGLT2) inhibitors are the drugs most widely applied in clinical practice, especially in the treatment of diabetes mellitus and heart failure. Sodium taurocholate co-transporting polypeptide (NTCP) serves as virus particles (HBV/HDV) carrier, and inhibition of its function is applied in the treatment of hepatitis B and hepatitis D by myrcludex B. Inherited cholestatic diseases, such as Alagille syndrome (ALGS) and progressive familial intrahepatic cholestasis (PFIC) can be treated by odevixibat and maralixibat, which inhibit activity of apical sodium-dependent bile salt transporter (ASBT). Probenecid can be considered to increase uric acid excretion in the urine mainly via the inhibition of urate transporter 1 (URAT1), and due to pharmacokinetic interactions involving organic anion transporters 1 and 3 (OAT1 and OAT3), it modifies renal excretion of penicillins or ciprofloxacin as well as nephrotoxicity of cidofovir. This review discusses clinically approved drugs that affect membrane/drug transporter function.

Progress of Infection and Replication Systems of Hepatitis B Virus

Despite the long-standing availability of effective prophylaxis, chronic hepatitis B virus (HBV) infection remains a formidable public health threat. Antiviral treatments can limit viral propagation, but prolonged therapy is necessary to control HBV replication. Robust in vitro models of HBV infection are indispensable prerequisites for elucidating viral pathogenesis, delineating virus-host interplay and developing novel therapeutic, preventative countermeasures. Buoyed by advances in molecular techniques and tissue culture systems, investigators have engineered numerous in vitro models of the HBV life cycle. However, all current platforms harbor limitations in the recapitulation of natural infection. In this article, we comprehensively review the HBV life cycle, provide an overview of existing in vitro HBV infection and replication systems, and succinctly present the benefits and caveats in each model with the primary objective of constructing refined experimental models that closely mimic native viral infection and offering robust support for the ambitious "elimination of hepatitis by 2030" initiative.

Conversion of Host Cell Receptor into Virus Destructor by Immunodisc to Neutralize Diverse SARS-CoV-2 Variants

The decreasing efficacy of antiviral drugs due to viral mutations highlights the challenge of developing a single agent targeting multiple strains. Using host cell viral receptors as competitive inhibitors is promising, but their low potency and membrane-bound nature have limited this strategy. In this study, the authors show that angiotensin-converting enzyme 2 (ACE2) in a planar membrane patch can effectively neutralize all tested severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants that emerged during the COVID-19 pandemic. The ACE2-incorporated membrane patch implemented using nanodiscs replicated the spike-mediated membrane fusion process outside the host cell, resulting in virus lysis, extracellular RNA release, and potent antiviral activity. While neutralizing antibodies became ineffective as the SARS-CoV-2 evolved to better penetrate host cells the ACE2-incorporated nanodiscs became more potent, highlighting the advantages of using receptor-incorporated nanodiscs for antiviral purposes. ACE2-incorporated immunodisc, an Fc fusion nanodisc developed in this study, completely protected humanized mice infected with SARS-CoV-2 after prolonged retention in the airways. This study demonstrates that the incorporation of viral receptors into immunodisc transforms the entry gate into a potent virucide for all current and future variants, a concept that can be extended to different viruses.

Characterization of mutations in hepatitis B virus DNA isolated from Japanese HBsAg-positive blood donors in 2021 and 2022

Missense mutations in certain small envelope proteins diminish the efficacy of antibodies. Consequently, tracking the incidence and types of vaccine-escape mutations (VEMs) was crucial both before and after the introduction of universal hepatitis B vaccination in Japan in 2016. In this study, we isolated hepatitis B virus (HBV) DNA from 58 of 169 hepatitis B surface antigen (HBsAg)-positive blood samples from Japanese blood donors and determined the nucleotide sequence encoding the small envelope protein. DNA from six (10%) of the samples had VEMs, but no missense mutations, such as G145R, were detected. Complete HBV genome sequences were obtained from 29 of the 58 samples; the viral genotype was A1 in one (3%), A2 in three (10%), B1 in nine (31%), B2 in five (17%), B4 in one (3%), and C2 in 10 (34%) samples. Tenofovir-resistance mutations were detected in two (7%) samples. In addition, several core promoter mutations, such as 1762A>T and 1764G>A, and a precore nonsense mutation, 1986G>A, which are risk factors for HBV-related chronic liver disease, were detected. These findings provide a baseline for future research and highlight the importance of ongoing monitoring of VEMs and drug resistance mutations in HBV DNA from HBsAg-positive blood donors without HBV antibodies.

Association between NTCP hepatic expression and inflammation/fibrosis as well as gender-specific differences in chronic HBV-infected patients

To investigate the relationship between the expression of hepatitis B virus (HBV) functional receptor sodium taurocholate cotransporting polypeptide (NTCP) with disease progression and gender-specific differences in chronic HBV-infected patients. Liver samples were collected from chronic HBV-infected patients who underwent percutaneous liver biopsy or liver surgery. HBV DNA levels and the mRNA and protein expression levels of NTCP in liver tissues were determined. The relationship between NTCP expression and HBV DNA levels, inflammatory activity, fibrosis, and gender-specific differences were analyzed. A total of 94 chronic HBV-infected patients were included. Compared with patients with a METAVIR score of A0-1 or F0-1, patients with score of A2 or F2/F3 had a relatively higher level of NTCP expression. NTCP levels were positively correlated with HBV DNA levels. The inflammatory activity scores and fibrosis scores of women <50 years were significantly lower than those of women ≥50 years and age-matched males. In patients with score A0-2 or F0-3, women <50 years have lower NTCP expression level compared to women ≥50 years and age-matched males. NTCP can promote the disease progression by affecting the viral load of HBV. The NTCP expression difference may be why male and postmenopausal women are more prone to disease progression than reproductive women.

Hepatitis B Virus Modulated Transcriptional Regulatory Map of Hepatic Cellular MicroRNAs

Hepatitis B virus (HBV) is an enveloped, hepatotropic, noncytopathic virus with a partially double-stranded DNA genome. It infects hepatocytes and is associated with progression to liver fibrosis and cirrhosis, culminating in hepatocellular carcinoma (HCC), accounting for 55% of total HCC cases. MicroRNAs (miRNAs) regulated by HBV play an important role in these pathologies. Mapping the miRNAs responsive to HBV and HBV-specific proteins, including HBV X protein (HBx) that harbor the majority of HBV-human protein interactions, could aid accelerate the diagnostics and therapeutics innovation against the infection and associated diseases. With this in mind, we used a unique annotation strategy whereby we first amassed 362 mature HBV responsive-human Differentially Expressed miRNAs (HBV-hDEmiRs). The core experimentally-validated messenger RNA targets of the HBV-hDEmiRs were mostly associated with viral infections and hepatic inflammation processes. Moreover, our annotation strategy enabled the characterization of HBx-dependent/independent HBV-hDEmiRs as a tool for evaluation of the impact of HBx as a therapeutic target. Bioinformatics analysis of the HBV-human protein-protein interactome revealed new insights into the transcriptional regulatory network of the HBV-hDEmiRs. We performed a comparative analysis of data on miRNAs gathered from HBV infected cell line studies and from tissue studies of fibrosis, cirrhosis, and HCC. Accordingly, we propose hsa-miR-15a-5p that is downregulated by multiple HBV proteins, including HBx, as a potential biomarker of HBV infection, and its progression to HCC. In all, this study underscores (1) the complexity of miRNA regulation in response to HBV infection and its progression into other liver pathologies and (2) provides a regulatory map of HBV-hDEmiRs and the underlying mechanisms modulating their expression through a cross talk between HBV viral proteins and human transcription factors.

Hepatitis B Virus Epsilon (ε) RNA Element: Dynamic Regulator of Viral Replication and Attractive Therapeutic Target

Hepatitis B virus (HBV) chronically infects millions of people worldwide, which underscores the importance of discovering and designing novel anti-HBV therapeutics to complement current treatment strategies. An underexploited but attractive therapeutic target is ε, a cis-acting regulatory stem-loop RNA situated within the HBV pregenomic RNA (pgRNA). The binding of ε to the viral polymerase protein (P) is pivotal, as it triggers the packaging of pgRNA and P, as well as the reverse transcription of the viral genome. Consequently, small molecules capable of disrupting this interaction hold the potential to inhibit the early stages of HBV replication. The rational design of such ligands necessitates high-resolution structural information for the ε-P complex or its individual components. While these data are currently unavailable for P, our recent structural elucidation of ε through solution nuclear magnetic resonance spectroscopy marks a significant advancement in this area. In this review, we provide a brief overview of HBV replication and some of the therapeutic strategies to combat chronic HBV infection. These descriptions are intended to contextualize our recent experimental efforts to characterize ε and identify ε-targeting ligands, with the ultimate goal of developing novel anti-HBV therapeutics.

Forthcoming Developments in Models to Study the Hepatitis B Virus Replication Cycle, Pathogenesis, and Pharmacological Advancements

Hepatitis, liver cirrhosis, and hepatocellular carcinoma are all manifestations of chronic hepatitis B. Its pathogenesis and molecular mechanism remain mysterious. As medical science progresses, different models are being used to study the disease from the physiological and molecular levels. Animal models have played an unprecedented role in achieving in-depth knowledge of the disease while posing no risk of harming humans throughout the study. The scarcity of acceptable animal models has slowed progress in hepatitis B virus (HBV) research and preclinical testing of antiviral medicines since HBV has a narrow species tropism and exclusively infects humans and higher primates. The development of human chimeric mice was supported by a better understanding of the obstacles to interspecies transmission, which has substantially opened the way for HBV research in vivo and the evaluation of possible chronic hepatitis B therapeutics. Animal models are cumbersome to handle, not accessible, and expensive. Hence, it is herculean to investigate the HBV replication cycle in animal models. Therefore, it becomes essential to build a splendid in vitro cell culture system to demonstrate the mechanisms attained by the HBV for its multiplication and sustenance. We also addressed the advantages and caveats associated with different models in examining HBV.

HBV Infection and Host Interactions: The Role in Viral Persistence and Oncogenesis

Hepatitis B virus (HBV) is a major cause of chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma. Despite the advent of vaccines and potent antiviral agents able to suppress viral replication, recovery from chronic HBV infection is still an extremely difficult goal to achieve. Complex interactions between virus and host are responsible for HBV persistence and the risk of oncogenesis. Through multiple pathways, HBV is able to silence both innate and adaptive immunological responses and become out of control. Furthermore, the integration of the viral genome into that of the host and the production of covalently closed circular DNA (cccDNA) represent reservoirs of viral persistence and account for the difficult eradication of the infection. An adequate knowledge of the virus-host interaction mechanisms responsible for viral persistence and the risk of hepatocarcinogenesis is necessary for the development of functional cures for chronic HBV infection. The purpose of this review is, therefore, to analyze how interactions between HBV and host concur in the mechanisms of infection, persistence, and oncogenesis and what are the implications and the therapeutic perspectives that follow.