Regulation of secretion of the hepatitis B virus major surface antigen by the preS-1 protein

P24, P30, and P39, the three major surface antigens of the envelope of hepatitis B virus, are co-carboxy-terminal proteins with different amino-terminal extensions. We prompted expression of these proteins in Chinese hamster ovary (CHO) cells by placing the appropriate coding sequence(s) under the control of the simian virus 40 early promoter. P24 and P30 formed 22-nm particles which were efficiently secreted. In contrast, P39 accumulated in a perinuclear structure, presumably the Golgi complex, and was not secreted. Coexpressing P39 and P24 resulted in the localization of both in the perinuclear region and restricted the secretion of P24. We found that P39 must be expressed at a relatively low level to allow efficient secretion of P24 in typical spherical particles. We hypothesize that P39, by inhibiting the formation of spherical particles, helps to induce formation of filamentous particles and mature Hepatitis B virus.

Characterisation of the polymerised and monomeric human serum albumin binding sites on hepatitis B surface antigen

Receptors for polymerised human albumin are present on the pre-S sequence of the envelope protein of HBV and on the hepatocyte membrane and are thought to be involved in uptake of the virus by hepatocytes. Using a solid phase radioimmunoassay we demonstrate binding of HBsAg to polymerised human serum albumin (pHSA) in both HBe antigen-positive and -negative patients, and this binding is linearly related to the HBsAg titre in both groups. There are probably several modes of interaction between HBsAg and pHSA. Here we show that pHSA binds to the 22,000-dalton polypeptide of HBsAg, which does not contain the pre-S sequence. This pHSA-HBsAg interaction is inhibited by physiological concentrations of human serum albumin, suggesting that the albumin known to be present in the envelop of HBsAg plays a role in this binding. The inhibition of pHSA/HBsAg interaction by native albumin suggests that this interaction is probably not an important mechanism of virus uptake during infection of hepatocytes.

Inhibition of secretion of hepatitis B surface antigen by a related presurface polypeptide

The presurface (preS) proteins of hepatitis B virus are structural components of the viral envelope that may play important roles in virion assembly and infectivity. They are specified by a large open reading frame that includes the coding region for the major surface (S) protein in its 3' half. Translation of the preS proteins initiates upstream from the S region, giving rise to proteins that are composed of the S domain and an additional 163 (preS1) or 55 (preS2) amino acids. Little is known about the biosynthesis and assembly of these proteins. The expression of the S and preS1 proteins was examined by transfecting cultured mammalian cells with viral DNA and injecting synthetic messenger RNA's into Xenopus oocytes. In contrast to the proteins encoded by the S region, the preS1 proteins are not detectably secreted into the culture medium. Furthermore, when the S and preS1 proteins are synthesized together, secretion of the S proteins is specifically and strongly inhibited. The results suggest a unique molecular interaction during secretion of the S and preS proteins that may be important for virus assembly.

Expression of hepatitis B virus large envelope polypeptide inhibits hepatitis B surface antigen secretion in transgenic mice

The outer membrane of the hepatitis B virus consists of host lipid and the hepatitis B virus major (p25, gp28), middle (gp33, gp36), and large (p39, gp42) envelope polypeptides. These polypeptides are encoded by a large open reading frame that contains three in-phase translation start codons and a shared termination signal. The influence of the large envelope polypeptide on the secretion of hepatitis B surface antigen (HBsAg) subviral particles in transgenic mice was examined. The major polypeptide is the dominant structural component of the HBsAg particles, which are readily secreted into the blood. A relative increase in production of the large envelope polypeptide compared with that of the major envelope polypeptide led to profound reduction of the HBsAg concentration in serum as a result of accumulation of both envelope polypeptides in a relatively insoluble compartment within the cell. We conclude that inhibition of HBsAg secretion is related to a hitherto unknown property of the pre-S-containing domain of the large envelope polypeptide.

Direct introduction of genes into rats and expression of the genes

A method of introducing actively expressed genes into intact mammals is described. DNA precipitated with calcium phosphate has been injected intraperitoneally into newborn rats. The injected genes have been taken up and expressed by the animal tissues. To examine the generality of the method we have injected newborn rats with the chloramphenicol acetyltransferase prokaryotic gene fused with various viral and cellular gene promoters and the gene for hepatitis B surface antigen, and we observed appearance of chloramphenicol acetyltransferase activity and hepatitis B surface antigen in liver and spleen. In addition, administration of genes coding for hormones (insulin or growth hormone) resulted in their expression.

[Relation between serum markers of hepatitis B virus and alpha fetoprotein in hepatocellular carcinoma in France]

Prevalences of serum markers of hepatitis B virus and alphafetoprotein levels were investigated in 96 patients with hepatocellular carcinoma. Serum HBs Ag was present in 17 patients (17.5 p. 100), anti-HBc antibody alone in 10 patients (10.5 p. 100), and anti-HBs antibody with or without associated anti-HBc antibody in 32 patients (33.5 p. 100). Serum alphafetoprotein levels were increased (greater than 20 ng/ml) in 71 patients (74 p. 100). Serum alphafetoprotein levels were significantly higher in patients with than in patients without serum HBs Ag. Serum alphafetoprotein levels above 1,000 ng/ml were more frequently found in patients with serum HBs Ag or anti-HBc antibody than in other patients. These results suggest the presence of a link between HBs Ag and alphafetoprotein in hepatocellular carcinoma.

Identification and chemical synthesis of a host cell receptor binding site on hepatitis B virus

Hepatitis B virus (HBV) has not yet been propagated in vitro, and knowledge concerning its reaction with receptors on target cells remained scant. We have located within the HBV envelope proteins a sequence mediating the attachment of HBV to human hepatoma HepG2 cells. A synthetic peptide analog (PLGFFPDHQLDPAFGANSNNPDWDFNP) is recognized by both cell receptors and anti-HBV antibodies and elicits antibodies reacting with native HBV. The synthetic peptide is a promising immunogen expected to elicit protective antibodies based on the concept of the attachment blockade pathway of virus neutralization. The approach described here, based on anti-peptide antisera and the binding of peptide analogs to cell receptors is generally applicable for the delineation of cell receptor binding sites on viruses with known gene sequences.

HBsAg clearance in chronic active hepatitis B. A possible cause of cryptogenic cirrhosis

Three patients with chronic hepatitis B infection, two with chronic active hepatitis and cirrhosis, and the third with quiescent cirrhosis, cleared HBsAg from their serum and eventually developed anti-HBs. All three were asymptomatic and had nearly normal serum aminotransferases following loss of HBsAg. Liver biopsy revealed cirrhosis in each patient. With the development of anti-HBs, these patients became serologically indistinguishable from patients with a cryptogenic cirrhosis who had prior unrelated exposure to hepatitis B. Remote chronic hepatitis B infection may be a more common cause of cryptogenic cirrhosis than is commonly appreciated.

Intracellular assembly and packaging of hepatitis B surface antigen particles occur in the endoplasmic reticulum

Hepatitis B surface antigen (HBsAg) particles are secreted by Chinese hamster ovary cells that are stably transfected with the S gene of hepatitis B virus. The assembly of HBsAg into cylindrical and spherical particles occurred intracellularly within the endoplasmic reticulum. HBsAg particles accumulated within large dilated areas of the endoplasmic reticulum and remained within these structures for most of the time prior to secretion from the cells. Once the particles were formed, the HBsAg polypeptides did not appear to become associated with subsequent intracellular organelle membranes or the plasma membrane. HBsAg within the dilated structures did not bind wheat germ agglutinin, indicating that its oligosaccharide chains had not yet been processed to the complex form (containing terminal sialic acid-N-acetylglucosamine residues). The oligosaccharide chains of HBsAg are processed to the complex form and can be detected on the HBsAg after secretion, but this event was not detected within cells. In addition, HBsAg was not observed on the cell surface by indirect immunofluorescence or immunoprecipitation, although immunoelectron microscopy revealed some staining at or near the cell surface. These results suggested that HBsAg was either secreted from cells without being incorporated into the plasma membrane, or that the levels of HBsAg in the plasma membrane were below the limits of detection.

Large hepatitis B surface antigen polypeptides of Dane particles with the receptor for polymerized human serum albumin

Large hepatitis B surface antigen polypeptides with apparent molecular sizes of 39,000 and 43,000 daltons (P39 and P43) were liberated from a purified preparation of Dane particles of subtype adr. They were tested for reactivity with monoclonal antibodies raised against three synthetic oligopeptides representing fundamental sequences of the pre-S region in deoxyribonucleic acid of hepatitis B virus (subtype adr), as well as with monoclonal antibody against the major surface antigen polypeptide (P22) coded for by the S gene. Both P39 and its glycosylated form P43 bound to all four monoclonal antibodies, thereby indicating that they were coded for by the sequence of 1200 nucleotides, from the second ATG codon in the pre-S region to the stop codon of the S gene. Both P39 and P43 bound to polymerized human and chimpanzee albumins, but not to polymerized albumin from species without susceptibility to hepatitis B virus. Due to their presence in Dane particles and the expression of a polyalbumin receptor, the immune responses against P39 and P43 may have significance in infection with hepatitis B virus and its immunoprophylaxis.

Effects of suramin on in vitro HBsAg production by PLC/PRF/5 cells and hepatitis B virus DNA polymerase activity

The effects of suramin, an antiparasitic agent, upon in vitro hepatitis B surface antigen production by the human hepatoma cell line PLC/PRF/5 and hepatitis B virus associated DNA polymerase activity in the serum of a chronically infected patient were examined. Treatment with suramin resulted in decreases in hepatitis B surface antigen production and hepatitis B-virus associated DNA polymerase activity. The decrease in hepatitis B surface antigen production was paralleled by a general decrease in hepatoma cell viability and cellular protein synthesis. Although the inhibitory effects of suramin for hepatitis B virus appear to be nonspecific as demonstrated in these two in vitro systems, the recently announced trial of suramin for the treatment of the acquired immunodeficiency syndrome should afford an unusual opportunity to evaluate the effectiveness of suramin in the treatment of chronic hepatitis B virus infection.

Interaction between various polymerized human albumins and hepatitis B surface antigen

A variety of albumin polymers were prepared and tested for binding with hepatitis B surface antigen (HBsAg): synthetic polymers cross-linked by either glutaraldehyde or carbodiimide; heat-aggregated polymers made by heating albumin solutions at 60 degrees C for 10 h with or without albumin stabilizer; and polymers isolated from fresh or long-stored commercial therapeutic albumin solutions. A sensitive solid-phase, competitive-inhibition radioimmunoassay, which can detect as little as 10 ng of glutaraldehyde-cross-linked human albumin polymer (PHALB-G), was developed and used to measure binding. The binding of PHALB-G with HBsAg was 150- to 1,000-fold greater than that of any other albumin polymer. Glutaraldehyde-cross-linked bovine albumin polymer showed no binding. Albumin monomer and dimer fractions produced by glutaraldehyde treatment exhibited some binding, albeit much weaker than PHALB-G. As measured by a direct-binding assay with solid-phase PHALB-G, the attachment of HBsAg particles from sera positive for antibody to the e antigen was less efficient than that from sera positive for e antigen, even when all sera were tested at equal HBsAg concentrations. In protein blot experiments with radiolabeled albumin preparations, PHALB-G bound almost exclusively to HBsAg polypeptide P31 and showed no binding with the major polypeptides P23 and P26. None of the other radiolabeled albumin polymers was reactive. These results indicate that the interaction between PHALB-G and HBsAg is not due to polymerization of albumin per se, but rather is unique and site specific.

Binding activity of HBsAg particles from chronic HBsAg carriers to polystyrene beads coated with polymerized human serum albumin: diagnostic relevance of the assay

The binding activity of HBsAg particles to polystyrene beads coated with polymerized human serum albumin (pHSA) was studied by radioimmunoassay in 48 patients with chronic HBsAg carrier state. The pHSA assay was positive in all 16 HBeAg-positive patients and in 22 HBeAg-negative HBsAg carriers with chronic hepatitis. Asymptomatic, "healthy" HBsAg carriers did not react in the pHSA assay. Mean binding activity was significantly higher in the HBeAg-positive group (P/N ratio 39.3) than in HBeAg-negative carriers with chronic hepatitis in various stages (P/N ratio 19.2). Fractionation of five representative HBeAg-positive sera by density gradient ultracentrifugation in cesium chloride yielded three peaks of HBsAg particles at 1.28, 1.22 and. 1.18 g/ml. The first HBsAg peak contained Dane particles and exhibited strong reactivity in pHSA assay. The second and third peaks, both consisting of 22 nm particles, reacted differently in pHSA assay. While about half of the HBsAg particles in the second peak were bound, reaction in the third HBsAg peak was predominantly negative. Intrahepatic HBsAg was detectable with the immunofluorescence technique in 19 of 22 HBsAg carriers. HBcAg was found in seven of 10 HBeAg-positive cases and in three of 16 HBeAg-negative patients with chronic hepatitis. The diagnostic value of pHSA assay might be seen in differentiation between HBeAg-negative chronic HBsAg carriers with liver disease or "healthy" carrier state.

Chronic liver disease: the detection and characterization of circulating immune complexes

Circulating immune complexes containing IgG, IgM and hepatitis B surface antigen (HBsAg) in sera from groups of patients with various liver diseases were detected by both the C1q and conglutinin solid phase assays. Elevated levels of antigen non-specific immune complexes were observed in sera from all groups and complexes containing IgG were present to a greater extent than were IgM-containing complexes. Higher levels of complexes were generally obtained using the conglutinin assay than the C1q assay and the two assays were shown to preferentially bind complexes of different size ranges and antigen-antibody ratios. Only sera from HBsAg-positive patients had complexes containing HBsAg, and although serum HBsAg titres and levels of HBsAg-containing complexes were correlated, the correlation coefficient was low. The mean levels of immune complexes and the frequency of positive sera varied between different disease categories, but there was little correlation between levels of the three types of complexes detected by the two tests. Assay of immune complexes in sequential serum samples from an individual patient revealed considerable variation in the levels of the three complex types, demonstrating that the measurement of complexes in single serum samples is of limited value in assessing the potential significance of circulating immune complexes in hepatitis B.

Detection of HBsAg in a clone derived from the PLC/PRF/5 human hepatoma cell line

A total of 28 clones were established from the PLC/PRF/5 hepatoma cell line by a plating procedure. All clones were found to secrete HBsAg into the supernatant culture fluids. Of these, one clone (No. 23) free of detectable mycoplasma contamination and showing smooth epithelial morphology was selected for further study. Maximum accumulation of HBsAg occurred 9 days after sub-culture and intracellular antigen was detected by indirect immunofluorescence both in the cytoplasm and at the plasma membrane. Granules and perinuclear staining reactions were also observed in clone 23 cells and these findings are compared to the previously published properties of the parental PLC/PRF/5 cell line.

Nonimmunologic binding of horseradish peroxidase to hepatitis B surface antigen. A possible source of error in immunohistochemistry

In the process of establishing the specificity of direct immunoperoxidase staining of liver tissue for hepatitis B surface antigen (HBsAg), an affinity of free horseradish peroxidase (HRP) for HBsAg in hepatocytes (ground-glass cells) was found. Of 95 patients, the horseradish peroxidase reaction was only positive in the livers of the 35 who were chronically HBsAg seropositive and not in the livers from 60 control patients with alcoholic cirrhosis who were HBsAg seronegative. Comparison studies using the orcein technic and immunoperoxidase methods confirmed the observation that both free horseradish peroxidase (not conjugated to an antibody) and HRP conjugated to an antibody unrelated to HBsAg had an affinity to the cytoplasm of hepatocytes containing HBsAg. The precise nature of this affinity is not known, but it is probably due to a reaction between an activated carbohydrate moiety of horseradish peroxidase and the free amino group of HBsAG.