Hepatitis B virus DNA in Dane particles: evidence for the presence of replicative intermediates

Hepatitis B virus particles in serum contain minus strand DNA and degraded pregenomic RNA of variable and inverse lengths

This study utilized digital PCR to quantify HBV RNA and HBV DNA within three regions of the HBV genome. Analysis of 75 serum samples from patients with chronic infection showed that HBV RNA levels were higher in core than in S and X regions (median 7.20 vs. 6.80 and 6.58 log copies/mL; p < .0001), whereas HBV DNA levels showed an inverse gradient (7.71 vs. 7.73 and 7.77 log copies/mL, p < .001). On average 80% of the nucleic acid was DNA by quantification in core. The core DNA/RNA ratio was associated with viral load and genotype. In individual patients, the relations between RNA levels in core, S and X were stable over time (n = 29; p = .006). The results suggest that pregenomic RNA is completely reverse transcribed to minus DNA in ≈75% of the virus particles, whereas the remaining 25% contain both RNA and DNA of lengths that reflect variable progress of the polymerase.

The Hepatitis B Virus Envelope Proteins: Molecular Gymnastics Throughout the Viral Life Cycle

New hepatitis B virions released from infected hepatocytes are the result of an intricate maturation process that starts with the formation of the nucleocapsid providing a confined space where the viral DNA genome is synthesized via reverse transcription. Virion assembly is finalized by the enclosure of the icosahedral nucleocapsid within a heterogeneous envelope. The latter contains integral membrane proteins of three sizes, collectively known as hepatitis B surface antigen, and adopts multiple conformations in the course of the viral life cycle. The nucleocapsid conformation depends on the reverse transcription status of the genome, which in turn controls nucleocapsid interaction with the envelope proteins for virus exit. In addition, after secretion the virions undergo a distinct maturation step during which a topological switch of the large envelope protein confers infectivity. Here we review molecular determinants for envelopment and models that postulate molecular signals encoded in the capsid scaffold conducive or adverse to the recruitment of envelope proteins.

Molecular bases for the development of hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC)

Hepatocellular carcinoma (HCC) is the most common histological form of primary liver cancer; the tumor cells having retained features of hepatocytic differentiation. It is important to emphasize the heterogeneity of the histological background on which the tumor develops. Most HCCs complicate the evolution of an active or inactive cirrhosis. However, some tumors occur on livers with minimal histological changes; the prevalence of such cases varies from one geographical region to the other; being much higher in the southern half of Africa (around 40% of HCCs) than in Asia, America and Europe, where at least 90% of HCCs are associated in the cirrhosis. This heterogeneity is probably a reflection of different environmental and genetic factors. A large number of epidemiological and molecular studies have indeed clearly demonstrated the prime importance of environmental factors to the development of primary liver cancers in humans. Chronic hepatitis B (HBV) and C (HCV) infections are major risk factors. This review will mainly analyse the impact of chronic HBV infection but it is important to emphasize the potential synergistic effects between HBV and HCV, as well as between viral infections and other environmental factors, such as alcohol, chemical carcinogens (see review by Dr Wogan) and other, still poorly defined, hormonal factors which may account for the higher incidence of the tumor in man. Finally the review by Dr Buendia highlights the emerging issue of liver-cancer genetics.

The GDPAL region of the pre-S1 envelope protein is important for morphogenesis of woodchuck hepatitis virus

The pre-S envelope protein of duck hepatitis B virus (DHBV) contains a region, Asp-Asp-Pro-Leu-Leu (DDPLL), that is specifically required for virus assembly and secretion (Lenhoff and Summers, J Virol 1994;68:4565-4571). We found that amino acids 201 to 205 of the pre-S envelope protein of woodchuck hepatitis virus (WHV) form a conserved amino acid cluster, Gly-Asp-Pro-Ala-Leu (GDPAL), which resembles the DDPLL sequence of DHBV. To determine whether the GDPAL region was functionally equivalent to the DDPLL region, we deleted this region from the pre-S protein of WHV or mutated individual amino acids within the region. The mutant DNA was transfected into human hepatoma cell line Huh7, and the medium was assayed for virion production by immunoprecipitation and Southern blot analysis. We found that an in-frame deletion of this small region inhibited virion formation, suggesting that the GDPAL region of the pre-S envelope protein was required for virus assembly and/or secretion of WHV. Individual replacement of alanine 204, leucine 205, or serine 206 with other amino acid residues did not affect virus production. However, substitution of either aspartic acid 202 with valine or proline 203 with leucine dramatically inhibited WHV production. Furthermore, the GDPAL mutants were individually tested for their abilities to complement a pre-S1 defective genome. The results showed that the GDPAL region functioned as part of the pre-S1 protein but was not required to function as part of the pre-S2 protein.

Hepatitis B virus nucleocapsid envelopment does not occur without genomic DNA synthesis

Assembly of the enveloped hepatitis B virus (HBV) is initiated by packaging of the RNA pregenome and the viral reverse transcriptase-DNA polymerase into a nucleocapsid. The pregenome is then reverse transcribed into single-stranded minus-polarity DNA, which is subsequently replicated to double-stranded DNA. All replicative intermediates are observable in capsids within infected liver, but only relatively mature nucleocapsids containing partially double stranded DNA are found in secreted virions. This observation suggests that maturation of the genome within the capsid is required for envelopment and secretion. We show that the differential distribution of replicative intermediates between intracellular nucleocapsids and secreted virions is also observable in human hepatoma cells transfected with wild-type HBV genomes. However, nucleocapsids were not enveloped or secreted when they were produced by an HBV genome carrying a missense mutation in the DNA polymerase that eliminates all DNA synthesis. An HBV missense mutant defective in the RNase H activity of the polymerase which allowed minus-strand DNA synthesis but not formation of double-stranded DNA was able to form virion-like particles. These experiments demonstrate that immature nucleocapsids containing pregenomic RNA are incompetent for envelopment and that minus-strand DNA synthesis in the interior lumen of the capsid is coupled to the appearance of a signal on the exterior of the nucleocapsid that is essential for its envelopment.

Hepatitis B and C viruses and primary liver cancer

The data presented indicate that viral agents (namely, HBV and HCV) are major environmental aetiological factors for human primary liver cancer. It is important to elucidate the molecular mechanisms further because HCC is one of the few examples of virus-related human cancers. In addition, the available evidence points to the possibility of at least partial prevention of the tumour by large-scale vaccination.

Rapid purification of hepatitis B virus DNA from serum

We describe two rapid, simple, and reliable procedures for routine purification of hepatitis B virus (HBV) DNA from serum. HBV DNA could be purified from 24 serum samples in 1.5 to 2 h and was recovered in the initial reaction vessel. Both procedures have in common that HBV DNA is complexed with silica particles in the chaotropic agent guanidinium thiocyanate (GuSCN) but differ in lysis conditions and in the conditions used to elute HBV DNA from the silica particles after purification of the silica-DNA complexes. In one procedure (protocol H), serum HBV lysis was mediated by sodium dodecyl sulfate-proteinase treatment and HBV DNA was subsequently complexed with silica particles in the presence of GuSCN. After washing and drying of the silica-DNA complexes, HBV DNA was eluted from the silica particles in a low-salt buffer. In the other procedure (protocol Y*), serum HBV was directly lysed in GuSCN and HBV DNA was simultaneously complexed with silica particles. After washing and drying of the complexes, HBV DNA was eluted by proteinase treatment in low-salt buffer. Omission of proteinase treatment prevented efficient elution, presumably because of copurification of the protein which is covalently bound to the HBV DNA genome. We show, by Southern blot analysis, that HBV DNA could be reproducibly purified from human serum with the same yields by either procedure (30 to 50% relative to a classic procedure) and apparently independent of serum composition. HBV DNA purified by either method was a good substrate in the polymerase chain reaction compared with DNA purified by the classic procedure.(ABSTRACT TRUNCATED AT 250 WORDS)

Detection of supercoiled hepatitis B virus DNA and related forms by means of molecular hybridization to an oligonucleotide probe

A novel assay for supercoiled and other fully double-stranded forms of hepatitis B virus (HBV) DNA in blood is presented that utilizes molecular hybridisation to a radiophosphorous-labeled oligonucleotide probe. The probe [5'-d(ACGTGCAGAGGTGAAGCGA)] is complementary to the S(+)-strand sequence furthest downstream, at the end of the gap. We examined blood specimens from 137 healthy HBsAg-positive individuals, applying the probe to dots representing 2-3.5 ml serum or plasma. We found that supercoiled HBV is present in many HBV DNA-positive blood specimens albeit in small quantities. Of the 104 specimens that were positive for HBV DNA of any form, 53 annealed to the probe. Serial specimens from the same subject taken over a period of months showed that the proportion of supercoil to other HBV DNA forms was variable. The presence of supercoil HBV DNA was not closely correlated with the level of serum HBV DNA polymerase. The supercoil is an HBV DNA form that can persist in the liver in the presence or absence of other replicative intermediates. This assay may enable further characterization of the status of HBV infection.

Isolation and characterization of cytoplasmic and nuclear particles of hepatitis B virus

The properties of hepatitis B virus (HBV) core particles from liver tissue of two patients with acute HBV infection were investigated. Cores were isolated from cytoplasm and nuclear fractions by centrifugation and two thirds of the cores were located in the cytoplasm. In all properties examined cores isolated from the cytoplasm or nucleus were the same. The cores had a density of 1.38 g/ml and had the same DNA and protein content when analyzed by Southern blotting and by Western blotting with C-specific antisera. Cores from both subcellular fractions had endogenous polymerase activity. We conclude that core particles with identical properties are found in both the cytoplasm and nucleus of cells during acute infection.

Nucleic acid hybridization in viral hepatitis research

Nucleic acid hybridization is extremely important in viral hepatitis research and the newly emerging techniques are now becoming an indispensable resource also in the diagnostic laboratory. This paper provides information on methods currently used for detection of viral nucleic acids with special emphasis on the importance of hepatitis B virus DNA in the serum. Herein, we describe the procedures for preparation and labeling of DNA probes and the principles that regulate dot, slot and Southern blot hybridization. Advantages and shortcomings of filter hybridization are discussed together with the alternative approaches to it. Finally, a collection of laboratory protocols is presented in Appendix #1.

Replication strategy of human hepatitis B virus

To study the replication strategy of the human hepatitis B virus, the 5' end of the RNA pregenome and the initiation sites of DNA plus and minus strands have been mapped. The RNA pregenome was found to be terminally redundant by 120 nucleotides; it is initiated within the pre-C region and may also function as mRNA for synthesis of the major core protein and the hepatitis B virus reverse transcriptase. The hepatitis B virus DNA minus strand is initiated within the direct repeat sequence DR1, it contains a terminal redundancy of up to eight nucleotides, and its synthesis does not require any template switch. The DNA plus strand is primed by a short oligoribonucleotide probably derived from the 5' end of the RNA pregenome, and its synthesis is initiated close to the direct repeat sequence DR2. For its elongation to pass the discontinuity in the DNA minus strand an intramolecular template switch occurs using the terminal redundancy of this template. Thus, the route of reverse transcription and DNA replication of hepatitis B viruses is fundamentally different from that of retroviruses.

Detection of HBV infectivity by spot hybridization in HBeAg-negative chronic carriers: HBV DNA in sera from asymptomatic and symptomatic subjects

DNA of hepatitis B virus (HBV DNA) in sera from HBeAg-positive carriers is now the most important and reliable marker of infectivity, but its significance in the progression of chronic hepatitis in anti-HBe carrier status is still under discussion. In this study, viral DNA was tested by a simplified spot hybridization method in sera of 206 HBeAg-negative Italian subjects. In a group of 153 HBsAg carriers, we found that 15.6% of anti-HBe-positive and 10.5% of anti-HBe-negative samples contained viral DNA. No HBV DNA was revealed in 38 HBsAg-negative nor in 15 anti-HBs-positive subjects with different serological markers of HBV. Viral DNA in sera of HBeAg-negative patients with severe chronic liver disease was correlated with increased alaninetransferase activity and IgM anti-HBc. Thus the presence of HBV DNA in these sera not only predicts which subjects are potentially infectious but also indicates chronic progression of hepatitis. Finally, viral DNA extracted from Dane particles of nine anti-HBe-positive sera was characterized by the Southern blot technique. The hybridization pattern shows bands indicating the presence of replicative intermediates.

Hepatitis B virus DNA in mononuclear blood cells. A frequent event in hepatitis B surface antigen-positive and -negative patients with acute and chronic liver disease

We have investigated 38 hepatitis B surface antigen (HBsAg)-positive and 34-negative patients with acute and chronic liver disease for the presence of hepatitis B virus (HBV) DNA in peripheral mononuclear blood cells. Among the HBsAg-positive subjects HBV DNA was detected in the mononuclear cells of asymptomatic HBV carriers (2/6), patients with acute hepatitis (8/8), chronic active hepatitis (18/21), and with hepatocellular carcinoma (2/3); the viral DNA sequences were also identified in the mononuclear cells of patients with HBsAg-negative acute hepatitis (2/3), chronic active hepatitis (5/15) and hepatocellular carcinoma (5/16), some of these showing no evidence of HBV by conventional serological markers. By contrast HBV DNA was not detected after resolution of the acute viral infection. For 7 patients different mononuclear cell-enriched subpopulations were assayed and the viral DNA was observed in T lymphocytes (both OKT4+ and OKT8+ enriched subsets) and/or in B enriched lymphocytes; the restriction DNA patterns showed in some patients a genetic organisation of the viral DNA similar to those observed in the liver (including free monomeric and oligomeric HBV DNA and results consistent with integrated viral sequences); however, no HBV DNA replicative forms were detected. These results show that the hepatitis B virus infection of mononuclear blood cells (including lymphoid cells) is a frequent event at all stages of the viral infection which might be related to immunological abnormalities observed in HBV carriers; in addition the mononuclear blood cells analysis may provide an insight to the liver cells status.