Pre-S1 antigens and antibodies early in the course of acute hepatitis B virus infection

The presence of the two "large" surface proteins of hepatitis B virus (HBV), P39 and GP42 of pre-S1-hepatitis B surface antigen, was assayed in the serum of an experimentally infected chimpanzee by using antibodies to a pre-S1-specific fusion protein synthesized in Escherichia coli. The immune response to pre-S1-hepatitis B surface antigen was monitored by using the pre-S1 fusion protein as an antigen. pre-S1 proteins were detected in the serum early in the course of infection and prevailed as long as hepatitis B surface antigen did, together with hepatitis B e antigen and viral DNA. Thus, the pre-S1 antigen can be considered a novel diagnostic marker for acute HBV infection. Antibodies to pre-S1, both immunoglobulin M and G classes, were also detected early in infection, shortly after the appearance of the pre-S1 antigen, suggesting its strong immunogenicity in vivo. The anti-pre-S1 antibodies therefore also represent an early serological marker for acute HBV infection and, owing to their early appearance and persistence, may play a role in the neutralization of the virus.     

Analysis of a tyrosine-specific protein kinase activity associated with the retroviral erbB oncogene product

The transforming protein erbB of avian erythroblastosis virus (AEV) has considerable sequence homology with the epidermal growth factor (EGF) and appears to represent a truncated form of this receptor. The sequence of the erbB gene is furthermore related to that of other viral transforming genes such as src, fps, yes or abl. The transforming proteins of these src-related oncogenes as well as receptors for EGF, platelet-derived growth factor (PDGF), and insulin are associated with tyrosine-specific protein kinases. It has been difficult to demonstrate this activity for the erbB protein. To analyze the erbB gene product, we prepared polyclonal antibodies against a bacterially expressed erbB DNA restriction fragment (BamHI/BamHI). The antiserum is shown to immunoprecipitate the erbB protein from AEV-transformed chicken fibroblasts and also recognizes the EGF receptor protein. Both proteins become phosphorylated in vitro on tyrosine residues upon the addition of [gamma-32P]ATP. The protein kinase activity is low compared to other oncogene-specific kinases. This is not due to kinase blocking by the serum, because erbB carboxyterminal synthetic peptide antibodies give rise to low levels of protein kinase activity as well indicating that this may be a characteristic property of erbB in vitro.     

On the mechanisms of ATP-induced and succinate-induced redistribution of cations in isolated rat liver cells

1. The ability of external ATP to induce calcium uptake in isolated rat liver cells was further characterized. Stimulation of calcium uptake was specific for ATP, other nucleotides or ATP metabolites had no comparable effect. ATP was dephosphorylated while stimulating calcium uptake, but there was no stoichiometry between ATP hydrolysis and calcium uptake nor did dephosphorylation depend on calcium concentration. ATP acted from outside and was dephosphorylated by an ecto-ATPase of the cells. 2. In addition to its direct action, ATP enhanced succinate-dependent calcium uptake in a cooperative fashion. This is best explained by different sites of action. ATP increases cell membrane permeability while succinate stimulates uptake into mitochondria. 3. ATP was able to lower Na+ and K+ gradients and the pH gradient between cells and incubation medium. Increasing calcium concentration counteracted this effect though calcium uptake was then stimulated. 4. Succinate alone did not affect monovalent cation gradients but raised the pH gradient. It partially counteracted the ATP effects on these gradients. 5. Since catecholamine-like actions of ATP may be mediated by an increase in cytoplasmic calcium concentration, the action of extracellular ATP can be taken as a model to study the role of calcium as a transmitter of hormone actions. From interdependence between ATP-stimulated and succinate-stimulated calcium uptake, conclusions can be drawn on the resulting cytoplasmic calcium concentration and its effect on plasma membrane permeability.     

Antigenic determinants and functional domains in core antigen and e antigen from hepatitis B virus.

The precore/core gene of hepatitis B virus directs the synthesis of two polypeptides, the 21-kilodalton subunit (p21c) forming the viral nucleocapsid (serologically defined as core antigen [HBcAg]) and a secreted processed protein (p17e, serologically defined as HBe antigen [HBeAg]). Although most of their primary amino acid sequences are identical, HBcAg and HBeAg display different antigenic properties that are widely used in hepatitis B virus diagnosis. To locate and to characterize the corresponding determinants, segments of the core gene were expressed in Escherichia coli and probed with a panel of polyclonal or monoclonal antibodies in radioimmunoassays or enzyme-linked immunosorbent assays, Western blots, and competition assays. Three distinct major determinants were characterized. The single conformational determinant responsible for HBc antigenicity in the assembled core (HBc) and a linear HBe-related determinant (HBe1) were both mapped to an overlapping hydrophilic sequence around amino acid 80; a second HBe determinant (HBe2) was assigned to a location in the vicinity of amino acid 138 but found to require for its antigenicity the intramolecular participation of the extended sequence between amino acids 10 and 140. It is postulated that HBcAg and HBeAg share common basic three-dimensional structure exposing the common linear determinant HBe1 but that they differ in the presentation of two conformational determinants that are either introduced (HBc) or masked (HBe2) in the assembled core. The simultaneous presentation of HBe1 and HBc, two distinctly different antigenic determinants with overlapping amino acid sequences, is interpreted to indicate the presence of slightly differently folded, stable conformational states of p21c in the hepatitis B virus nucleocapsid.     

Ultrastructure and enzyme digestion of nucleoli and associated structures in hypothalamic nerve cells viewed in resinless sections

Estrogen has been shown to affect ventromedial hypothalamic (VMH) nerve cell nucleoli in ovariectomized rats, by causing an increase in the number of electron-dense aggregates associated with nucleoli. In order to characterize these nucleolus-associated structures and other nuclear components, we examined the ultrastructure of ventromedial hypothalamic nucleoli and nuclei revealed by enzyme digestions (pepsin, RNase and DNase) in resinless thin sections. Digestion by pepsin did not cause obvious alterations in the morphology of the nucleolus or its related structures. Pepsin treatment followed by RNase, however, reduced the density of the nucleolus, while that of the nucleolus-associated structure and other related structures remained unchanged. Conversely pepsin treatment followed by DNase, reduced the density of nucleolus-associated and other chromatin structures, but had no effect on the density of the nucleolus. Pepsin treatment followed by RNase and then DNase treatment, reduced the density of the nucleolus and nucleolus-associated structures. A residual nucleolus and nucleolus-associated structure remained after this treatment. Stereo viewing of resinless sections shows that the nucleolus, its associated structures, and other related structures, are associated with fine filaments that may comprise the nuclear matrix. The nucleolus-associated structure containing DNA may direct RNA synthesis at an increased rate in estrogen-treated hypothalamic cells.     

Alteration by estrogen of the nucleoli in nerve cells of the rat hypothalamus

Summary Estrogen is accumulated from the blood by nerve cells in the ventromedial nucleus of the hypothalamus and can facilitate female reproductive behavior by acting on this region of the brain. This cell group was examined in ovariectomized female rats, given estrogen or control treatment, by use of light and electron microscopy. A significantly greater portion of the nerve cells in the estrogen-treated animals had protuberances on their nucleolar surfaces, apparent under the light microscope. The fine structure of such protuberances included dense, aggregated material, which is shown to contain DNA by the sodium tungstate staining technique. Because increased numbers of such protuberances were found in nuclei of cells of the experimental group where previous studies demonstrated a significant increase in ultrastructural signs of biosynthetic activity, they may be associated with increased RNA synthesis. Thus, they could indicate, ultrastructurally, increased synthetic rates for RNA in nerve cells through which estrogen promotes reproductive behavior.     

Hormones are no causal links in phytochrome-mediated adventitious root formation in mustard seedlings (Sinapis alba L.)

The question of whether or not hormones are causal links in the realization of phytochrome control during photomorphogenesis was investigated using the phytochrome-dependent formation of adventitious roots in hypocotyl cuttings excised from mustard seedlings as a test system. Histological examination of regenerating rest seedlings revealed that phytochrome (operationally, continuous far-red light) mediates the de novo formation of root primordia in the pericycle region of the hypocotyl near the cutting surface withing 12–24 h after excision.Auxin (IAA), gibberellin (GA₃), Cytokinin (kinetin), abscisic acid (ABA), and ethylene had no promotive effect on primordium formation in dark-grown or far-red irradiated rest seedlings. Depending on concentration, the application of these hormones was either ineffective or inhibitory in the rooting response. It is concluded that phytochrome does not operate through changes of hormone (auxin, gibberellin, cytokinin, ABA, ethylene) levels.While externally applied ethylene had no specific effect on primordium formation, the number of primordia produced in darkness could be increased to the far-red light level by removing the endogenously formed ethylene. Since the stimulatory effect of light could not be related to a lower ethylene level, it is concluded that ethylene interferes with primordium formation by modulating the susceptibility of this process to phytochrome control. This ethylene effect takes place in a concentration range below the range that can be manipulated by external application of the hormone.Abbreviations ABA abscisic acid - GA₃ gibberellic acid - IAA indole-3-acetic acid - P_r P_fr red and far-red absorbing forms of phytochrome