A new strategy for constructing in vitro replication-competent 1.3 copies of hepatitis B virus genome

Fluorescent protein tagged hepatitis B virus capsid protein with long glycine-serine linker that supports nucleocapsid formation

Fusion core proteins of Hepatitis B virus can be used to study core protein functions or capsid trafficking. A problem in constructing fusion core proteins is functional impairment of the individual domains in these fusion proteins, might due to structural interference. We reported a method to construct fusion proteins of Hepatitis B virus core protein (HBc) in which the functions of fused domains were partially kept. This method follows two principles: (1) fuse heterogeneous proteins at the N terminus of HBc; (2) use long Glycine-serine linkers between the two domains. Using EGFP and RFP as examples, we showed that long flexible G₄S linkers can effectively separate the two domains in function. Among these fusion proteins constructed, GFP-G₄S186-HBc and RFP-G4S47-HBc showed the best efficiency in rescuing the replication of an HBV replicon deficient in the core protein expression, though both of the two fusion proteins failed to support the formation of the relaxed circular DNA. These fluorescent protein-tagged HBcs might help study related to HBc or capsids tracking in cells.

Pre-S2 Start Codon Mutation of Hepatitis B Virus Subgenotype B3 Effects on NF-κB Expression and Activation in Huh7 Cell Lines

A cross-sectional study on hepatitis B patients in Indonesia showed association of pre-S2 start codon mutation (M120 V) with cirrhosis and hepatocellular carcinoma (HCC), which was dissimilar from studies from other populations where pre-S2 deletion mutation was more prevalent. Different mutation patterns were attributed to different hepatitis B virus (HBV) subgenotypes in each population study. HBV surface proteins are reported to induce the activation of NF-κB, a transcriptional factor known to play an important role in the development of liver disease. This study aimed to see the effects of HBs variants in HBV subgenotype B3 on the expression and activation of NF-κB as one of the mechanisms in inducing advanced liver disease. HBV subgenotypes B3, each carrying wild-type (wt) HBs, M120 V, and pre-S2 deletion mutation were isolated from three HCC patients. HBs genes were amplified and cloned into pcDNA3.1 and were transfected using Lipofectamine into a Huh7 cell line. NF-κB activation was measured through IκB-α expression, which is regulated by NF-κB. RNA expressions for HBs, IκB-α, and NF-κB subunit (p50) were evaluated using real-time PCR. M120 V mutant had a significantly higher mRNA level compared with wt and pre-S2 deletion mutant; however, there were no significant differences in HBs protein expressions. The transcription level of p50 was higher in M120 V mutation compared with HBs wild-type and pre-S2 deletion mutant. NF-κB activation was higher in HBs wild-type compared with the two mutant variants. Pre-S2 mutations had no effect on the increment of NF-κB activation. However, M120 V mutation may utilize a different pathway in liver disease progression that involves high expression of NF-κB subunit, p50.

A novel method for nucleos(t)ide analogues susceptibility assay of hepatitis B virus by viral polymerase transcomplementation

Nucleos(t)ide analogues (NUCs) susceptibility assay is important for the study of hepatitis B virus (HBV) drug resistance. The purpose of susceptibility assay is to test the sensitivity of a specific HBV variant to NUCs in vitro, by which assesses if and to what extent the mutant virus is resistant to a specific NUC. Among the existing susceptibility assay methods, stable cell line expressing the specific variant is one of the commonly used assessment systems based on its high repeatability. However, establishment of stable cell lines expressing individual variant is laborious and time-consuming. In the present study, we developed a novel strategy for rapidly establishing HBV replicating stable cell lines. We first established an acceptor cell line stably transfected with a polymerase-null HBV 1.1mer genome DNA, then lentiviruses expressing different mutant HBV polymerases were transduced into the acceptor cell line respectively. Stable cell lines replicating HBV DNA with the trans-complemented HBV polymerases were established by antibiotics selection. Lamivudine and entecavir susceptibility data from these polymerase-complementing cell lines were validated by comparing with other assays. Taken together, this transcomplementation strategy for establishment of stable cell lines replicating HBV DNA with clinically isolated HBV polymerase provides a new tool for NUC susceptibility assay of HBV.

Construction of replication competent plasmids of hepatitis B virus subgenotypes A1, A2 and D3 with authentic endogenous promoters

Hepatitis B virus (HBV) is hyperendemic to southern Africa, with genotype A of HBV being the predominant genotype, and subgenotype A1 prevailing. Infection with this subgenotype is associated with rapid disease progression, and high frequency of hepatocellular carcinoma development. The objectives of our study was to construct recombinant 1.28 mer replication competent HBV DNA plasmids of subgenotypes A1, A2 and D3 containing authentic endogenous HBV promoters and to follow their replication in vitro after transfection of Huh7 cells. We found that subgenotype D3 replicated at a lower level, as measured by HBsAg and HBV DNA levels, when compared to cells transfected with genotype A. There was no difference in the intracellular and extracellular HBsAg between cells transfected with subgenotypes A1 or A2. Cells transfected with subgenotype A1 had higher levels of intracellular replicative intermediates and HBcAg, and lower extracellular expression of HBeAg from days 1 to 3, when compared to cells transfected with subgenotype A2. In conclusion, the generation of these replication competent clones is an important step in the functional characterization of subgenotypes of HBV circulating in Africa and their comparison to strains circulating in other geographical regions of the world.

Effects of hepatitis B virus mutations on its replication and liver disease severity

Hepatitis B virus (HBV), nowadays, is one of the major human pathogens worldwide. Approximately, 400 million people worldwide have chronic HBV infection. Only 5% of persons infected during adulthood develop chronic infection. The reverse is true for those infected at birth or in early childhood, i.e. more than 90% of these persons progress to chronic infection. Currently, eight different genotypes o f HBV have been identified, differing in nucleotide sequence by greater than 8%. In addition, numerous subgenotypes have a l s o been recognized based on the nucleotide sequence variability of 4- 8%. It has invariably been found that these genotypes and mutations play a pivotal role in the liver disease aggravation and virus replication. The precore mutations (G1896A) and the double mutation (T1762/A1764) in the basal core promoter are important mutations that alter expression of the hepatitis B e antigen (HBeAg). The HBeAg is important for establishing viral persistence. The precore G1896A mutation abrogates the expression of HBeAg. Numerous other mutations alter the disease severity and progression. It is predictive that the infected patient has high risk of hepatocellular carcinoma if the genotype C is incriminated or if HBV possesses basal core promoter double mutation. Association of the remaining genotypes have been noted but with less degree than genotype C. Phenotypic assays of the different HBV protein markers with different molecular techniques illustrate the replication efficiency of the virus in cell lines. This review will discuss various mutations into their association with liver disease severity and progression as well as virus replication.

Phenotypic assay of a hepatitis B virus strain carrying an rtS246T variant using a new strategy

Phenotypic assays of hepatitis B virus (HBV) play an important role in research related to the problem of drug resistance that emerges during long-term nucleot(s)ide therapy in patients with chronic hepatitis B. Most of the phenotypic assay systems that are available currently rely on the transfection of recombinant replication-competent HBV DNA into hepatoma cell lines. Cloning clinical HBV isolates using conventional digestion-and-ligation techniques to generate replication-competent recombinants can be very difficult because of the sequence heterogeneity and unique structure of the HBV genome. In this study, a new strategy for constructing an HBV 1.1× recombinant was developed. The core of this strategy is the "fragment substitution reaction" (FSR). FSR allows PCR fragments to be cloned without digestion or ligation, providing a new tool for cloning fragments or genomes amplified from serum HBV DNA, and therefore making the assay of HBV phenotypes more convenient. Using this strategy, a phenotypic assay was performed on an HBV strain carrying an rtS246T variant isolated from a patient with chronic hepatitis B that was only responsive partially to entecavir therapy. The results indicated that this strain is sensitive to entecavir in vitro.

APOBEC3G directly binds Hepatitis B virus core protein in cell and cell free systems

APOBEC3G (A3G) is an intrinsic antiretroviral factor which can inhibit Hepatitis B virus (HBV) replication. This antiviral activity mainly depends on A3G incorporation into viral particles. However, the mechanisms of A3G packaging into HBV particles have not been well characterized. In this paper, we demonstrated that A3G interacted with the HBV core protein (HBc) directly in co-transfected HepG2 cells using the fluorescence resonance energy transfer (FRET) approach. In addition, we further found that this interaction did not require other factors in vitro using surface plasmon resonance (SPR) technology on BIAcore 3000. While cellular RNA or viral RNA was added to A3G protein solution before flow through the BIAcore chip, the interaction was not affected. In conclusion, these results suggest the possibility that A3G is incorporated into HBV viral particles via direct binding with HBc protein.