Ah Ram Lee

Hepatitis B virus (HBV) is a sex-specific pathogen that is more severe in males than in females. Sex disparities in HBV infection have been attributed to hormonal differences between males and females. However, whether HBV infection affects the metabolic signatures of steroid hormones and how these influences viral replication remains unclear. In this study, we investigated whether HBV infection alters steroid metabolism and its effects on HBV replication. Serum samples from male and female mice obtained after the hydrodynamic injection of replication-competent HBV plasmids were subjected to quantitative steroid profiling. Serum steroid levels in mice were analyzed using an in vitro metabolism assay with the mouse liver S9 fraction. The alteration of steroids by HBV infection was observed only in male mice, particularly with significant changes in androgens, whereas no significant hormonal changes were observed in female mice. Among the altered steroids, dehydroepiandrosterone (DHEA) levels increased the most in male mice after HBV infection. An in vitro metabolism assay revealed that androgen levels were significantly reduced in HBV-infected male mice. Furthermore, the genes involved in DHEA biosynthesis were significantly upregulated in HBV-infected male mice. Interestingly, reduced dihydrotestosterone in male mice significantly inhibits viral replication by suppressing HBV promoter activity, suggesting a viral strategy to overcome the antiviral effects of steroid hormones in males. Our data demonstrated that HBV infection can cause sex-specific changes in steroid metabolism.

The liver is unique in its ability to regenerate in response to damage. The complex process of liver regeneration consists of multiple interactive pathways. About 2 billion people worldwide have been infected with hepatitis B virus (HBV), and HBV causes 686,000 deaths each year due to its complications. Long-term infection with HBV, which causes chronic inflammation, leads to serious liver-related diseases, including cirrhosis and hepatocellular carcinoma. HBV infection has been reported to interfere with the critical mechanisms required for liver regeneration. In this review, the studies on liver tissue characteristics and liver regeneration mechanisms are summarized. Moreover, the inhibitory mechanisms of HBV infection in liver regeneration are investigated. Finally, the association between interrupted liver regeneration and hepatocarcinogenesis, which are both triggered by HBV infection, is outlined. Understanding the fundamental and complex liver regeneration process is expected to provide significant therapeutic advantages for HBV-associated hepatocellular carcinoma.

Currently, interferon alpha and nucleos(t)ide analogues (NAs) are clinically available to treat hepatitis B virus (HBV) infection. Several NAs, including lamivudine (LMV), adefovir (ADV), entecavir (ETV) and tenofovir (TDF or TAF) have been approved and administered to chronic hepatitis B (CHB) patients. NAs inhibit HBV DNA synthesis by targeting the reverse transcriptase (RT) domain of HBV polymerase. Several mutations in the RT domain which lead to drug resistance against NAs have been reported, even for TDF and TAF which are highly potent with very low resistance rate. Besifovir (BFV) is a new antiviral dGMP analogue able to be used as a new NA drug for the control of CHB infection. Drug resistance to BFV is not well known due to its shorter duration of clinical use. Recently, we reported that rtL180M (M) and rtM204V (V) mutations, already resistant to LMV, are associated with BFV resistance. However, the susceptibility to BFV of previously known HBV mutants resistant to various drugs has not been studied. To investigate this, we performed in vitro drug susceptibility assays using natural and artificial mutants that are associated with resistance to LMV, ADV, ETV or TDF. As a result, LMV-resistant mutants were not susceptible to BFV and ETV-resistant clones showed partial resistance against BFV as well. However, ADV-resistant mutants were highly sensitive to BFV. In case of tenofovir-resistant mutations, the HBV mutants harboring primary mutations to tenofovir resistance were susceptible to BFV. Therefore, our study revealed that BSV may serve as an alternative drug for patients with ADV-, ETV-, TDF- or TAF-resistance.

The ubiquitin system denotes a potent post-translational modification machinery that is capable of activation or deactivation of target proteins through reversible linkage of a single ubiquitin or ubiquitin chains. Ubiquitination regulates major cellular functions such as protein degradation, trafficking and signaling pathways, innate immune response, antiviral defense, and virus replication. The RNA sensor RIG-I ubiquitination is specifically induced by influenza A virus (IAV) to activate type I IFN production. Influenza virus modulates the activity of major antiviral proteins in the host cell to complete its full life cycle. Its structural and non-structural proteins, matrix proteins and the polymerase complex can regulate host immunity and antiviral response. The polymerase PB1-F2 of mutated 1918 IAV, adapts a novel IFN antagonist function by sending the DDX3 into proteasomal degradation. Ultimately the fate of virus is determined by the outcome of interplay between viral components and host antiviral proteins and ubiquitination has a central role in the encounter of virus and its host cell.

During viral evolution and adaptation, many viruses have utilized host cellular factors and machinery as their partners. HBx, as a multifunctional viral protein encoded by the hepatitis B virus (HBV), promotes HBV replication and greatly contributes to the development of HBV-associated hepatocellular carcinoma (HCC). HBx interacts with several host factors in order to regulate HBV replication and evolve carcinogenesis. The cellular FADD-like IL-1β-converting enzyme (FLICE)-like inhibitory protein (c-FLIP) is a major factor that functions in a variety of cellular pathways and specifically in apoptosis. It has been shown that the interaction between HBx and c-FLIP determines HBV fate. In this review, we provide a comprehensive and detailed overview of the interplay between c-FLIP and HBV in various environmental circumstances. We describe strategies adapted by HBV to establish its chronic infection. We also summarize the conventional roles of c-FLIP and highlight the functional outcome of the interaction between c-FLIP and HBV or other viruses in viral replication and the innate immune system.

Hepatitis B virus (HBV) is known to cause severe liver diseases such as acute or chronic hepatitis, liver cirrhosis and hepatocellular carcinoma. Chronic hepatitis B (CHB) infection is a major health problem with nearly 300 million individuals infected worldwide. Currently, nucleos(t)ide analogs (NAs) and interferon alpha are clinically approved treatments for HBV infection. NAs are potent antiviral agents that bind to HBV polymerase and block viral reverse transcription and replication. Besifovir dipivoxil maleate (BSV) is a newly developed NA against HBV in the form of acyclic nucleotide phosphonate that is available for oral administration similar to adefovir and tenofovir. Until now, resistance to BSV treatment has not been reported. In this study, we found a CHB patient who showed viral breakthrough after long-term treatment with BSV. The isolated HBV DNA from patient’s serum were cloned into the replication-competent HBV 1.2 mer and the sequence of reverse transcriptase (RT) domain of HBV polymerase were analyzed. We also examined the drug susceptibility of generated clones in vitro. Several mutations were identified in HBV RT domain. A particular mutant harboring ten RT mutations showed resistance to BSV treatment in vitro. The ten mutations include rtV23I (I), rtH55R (R), rtY124H (H), rtD134E (E), rtN139K (K), rtL180M (M), rtM204V (V), rtQ267L (L), rtL269I (I) and rtL336M (M). To further identify the responsible mutations for BSV resistance, we performed in vitro drug susceptibility assay on several artificial clones. As a result, our study revealed that rtL180M (M) and rtM204V (V) mutations, already known as lamivudine-resistant mutations, confer resistance to BSV in the CHB patient.

Tenofovir disoproxil fumarate (TDF) has been regarded as the most potent drug for treating patients with chronic hepatitis B (CHB). However recently, viral mutations associated with tenofovir have been reported. Here, we found a CHB patient with suboptimal response after more than 4 years of TDF treatment. Clonal analysis of hepatitis B virus (HBV) isolated from sequential sera of this patient identified the seven previously reported TDF-resistant mutations (CYELMVI). Interestingly, a threonine to alanine mutation at the 301 amino acid position of the reverse-transcriptase (RT) domain, (rtT301A), was commonly accompanied with CYELMVI at a high rate (72.7%). Since the rtT301A mutation has not been reported yet, we investigated the role of this naturally occurring mutation on the viral replication and susceptibility to tenofovir in various liver cells (hepatoma cells as well as primary human hepatocytes). A cell-based phenotypic assay revealed that the rtT301A mutation dramatically impaired the replication ability with meaningful reduction in sensitivity to tenofovir in hepatoma cell lines. However, attenuated viral replication by the rtT301A mutation was significantly restored in primary human hepatocytes (PHHs). Our findings suggest that the replication capability and drug sensitivity of HBV is different between hepatoma cell lines and PHHs. Therefore, our study emphasizes that validation studies should be performed not only in the liver cancer cell lines but also in the PHHs to understand the exact viral fitness under antiviral pressure in patients.

Hepatitis B virus (HBV) infection is a major factor in the development of various liver diseases such as hepatocellular carcinoma (HCC). Among HBV encoded proteins, HBV X protein (HBx) is known to play a key role in the development of HCC. Hepatocyte nuclear factor 4α (HNF4α) is a nuclear transcription factor which is critical for hepatocyte differentiation. However, the expression level as well as its regulatory mechanism in HBV infection have yet to be clarified. Here, we observed the suppression of HNF4α in cells which stably express HBV whole genome or HBx protein alone, while transient transfection of HBV replicon or HBx plasmid had no effect on the HNF4α level. Importantly, in the stable HBV- or HBx-expressing hepatocytes, the downregulated level of HNF4α was restored by inhibiting the ERK signaling pathway. Our data show that HNF4α was suppressed during long-term HBV infection in cultured HepG2-NTCP cells as well as in a mouse model following hydrodynamic injection of pAAV-HBV or in mice intravenously infected with rAAV-HBV. Importantly, HNF4α downregulation increased cell proliferation, which contributed to the formation and development of tumor in xenograft nude mice. The data presented here provide proof of the effect of HBV infection in manipulating the HNF4α regulatory pathway in HCC development.