Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0019163 (hepatitis B)
 38,309 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To study the functional mechanism of the hepatitis B virus (HBV) X (hbx) gene product, we have expressed the hbx protein in E. coli and purified it by HPLC. The purified hbx protein was shown to be active in transactivating transcription directed by the LTR sequence of HIV-1. The hbx protein was found to have an intrinsic serine/threonine protein kinase activity. The hbx protein was detected in hepatitis B virions, and tryptic phosphopeptide maps of the hbx protein phosphorylated in the virion and of the in vitro phosphorylated bacterially expressed hbx protein were similar. Inactivation of the hbx protein by heat, protein-denaturing agents, or an ATP affinity analog, p-fluorosulfonylbenzoyl 5'-adenosine, resulted in loss of both protein kinase activity and trans-activation activity. These results suggest that the HBV-encoded trans-activator hbx is a novel protein kinase.
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PMID:The hepatitis B virus-encoded transcriptional trans-activator hbx appears to be a novel protein serine/threonine kinase. 222 72

The duck hepatitis B virus (DHBV)-associated activities of reverse transcriptase and DNA polymerase and their inhibition in vitro were studied. Replicative complexes (RCs) were isolated from DHBV-infected liver by gel chromatography followed by sucrose gradient centrifugation. The RCs were detected by dot blot hybridization, using radiolabeled cloned DHBV DNA as a probe, and by the incorporation of 32P-TTP in the presence of dATP, dCTP, dGTP, and Mg2+ (endogenous DNA polymerase activity). The endogenous DNA polymerase activity associated with RCs was further studied using exogenous templates: reverse transcriptase and DNA polymerase activities were demonstrated using as substrates 32P-TTP and poly(rA) p(dT)12 or poly(dA) p(dT)12-18, respectively. Both activities were biochemically characterized. Their inhibition by various antiviral agents was studied in vitro: actinomycin D, ara-ATP, aphidicolin, suramin, chloroquin, and phosphonoformate. Among these, suramin, chloroquin, phosphonoformate, and ara-ATP were shown to be potent inhibitors of viral reverse transcriptase and DNA polymerase. Studies are now in progress to establish their antiviral activity in vivo.
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PMID:Duck hepatitis B virus: DNA polymerase and reverse transcriptase activities of replicative complexes isolated from liver and their inhibition in vitro. 245 18

The present studies examined the immunoregulatory factors that modulate T-lymphocyte cytotoxic activity against tumor cells. At 30 days postvaccination with hepatitis B virus surface antigen(s) (HBsAg), peripheral blood lymphocytes (PBL) from HBsAb-seropositive healthy donors showed 8-10-fold increase in their cytotoxic activity against human hepatocellular carcinoma PLC/PRF/5 cells. However, there was no effect against human embryonic liver or lung fibroblasts (WI-35) cells. After cloning, these cytotoxic lymphocytes responded to HBsAg, phytohemagglutinin (PHA), and neuraminidase (VCN) with significant increases in cytotoxicity. These cloned, activated PBL also had no effect on human embryonic liver or lung fibroblasts. Exogenous 5'-triphosphate (ATP) inhibited the lymphocyte cytotoxic activities. The inhibition was ATP concentration-dependent. Also, colchicine, a tubuline depolymerizing agent, inhibited effector cell cytotoxic lymphocyte activity. Colchicine binds to the target cells without causing cell lysis. Preincubation of the cytotoxic lymphocytes with "cold-insoluble globulin" (CIg) protected the cells from ATP and colchicine inhibition.
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PMID:Plasma "cold-insoluble globulin" protects cytotoxic lymphocytes from ATP inhibition: 2. Immunization against viral cell surface antigen stimulates cytotoxic cells to lyse tumor cells. 301 58

Protein kinase activity has been found in hepatitis B virions (Dane particles) purified from the plasma of hepatitis B surface antigen carriers [Albin, C., and Robinson, W.S. (1980) J. Virol. 34, 297-302]. Dane particles were purified from the pooled, HBeAg-positive plasma. When this preparation was incubated with [gamma 32P]ATP in the presence of 10mM MnCl2 and 0.5% NP-40 for 15 seconds at 30 degrees C, several phosphorylated polypeptides of 20,000, 42,000, 48,000, 50,000 and 56,000 daltons were detected in sodium dodecyl sulfate-polyacrylamide gels. When the Dane particles were incubated with [gamma 32P]ATP, 10 mM MnCl2, and 0.5% NP-40 in the presence of human hepatoma cell (J-5) particulate fraction at 30 degrees C, 15 seconds, the 42,000, 48,000 and 50,000 daltons phosphorylated polypeptides were not found. When human peripheral blood lymphocytes particulate fraction was incubated with Dane particles under the same conditions, no change of Dane particle phosphorylated polypeptides was detected. Previous publications [Albin, C., and Robinson, W.S. (1980) J. Virol. 34, 297-302; Gerlich, W.H. et al. (1982) J. Virol. 42, 761-766] showed that when hepatitis B core particles purified from hepatoma tissues contained protein kinase activity, only phosphorylated polypeptide was 20,000 daltons. Our data suggested that when Dane particles were put in an environment of hepatoma cells (or tissues), the protein kinase could only phosphorylate selected polypeptides in these particles.
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PMID:Change of hepatitis B virions (Dane particles) phosphorylation pattern by human hepatoma cell particulate fraction. 610 Sep 36

9-beta-D-Arabinofuranosyladenine (ara-A), 1-beta-D-arabinofuranosylcytosine (ara-C), and their 5'-triphosphates (ara-ATP and ara-CTP) were tested for ability to inhibit the hepatitis B virus (HBV)-associated deoxyribonucleic acid (DNA) polymerase. Ara-C did not inhibit the HBV DNA polymerase at the concentrations tested, ara-A did so by 50% at a concentration of 30 mM, with the inhibition noncompetitive with respect to deoxyadenosine 5-triphosphate (dATP). Ara-ATP and ara-CTP inhibited the DNA polymerase test competitively with respect to dATP and dCTP, respectively. Both compounds were also active after initiation of the DNA polymerase reaction. The inhibition caused by ara-ATP and ara-CTP was shown to be reversible, with no evidence that ara-ATP or ara-CTP was incorporated into the HBV DNA.
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PMID:Inhibition of hepatitis B virus deoxyribonucleic acid polymerase by the 5'-triphosphates of 9-beta-D-arabinofuranosyladenine and 1-beta-D-arabinofuranosylcytosine. 616 46

The nature of the protein kinase (PK) which phosphorylates the core protein of hepatitis B virus in vitro was studied. The PK copurified with the core particles during rate zonal centrifugation and gel chromatography. It showed the same size heterogeneity as the core particles, which consisted of a main fraction of 28-nm particles and a subfraction of 22- to 26-nm particles. DNA-containing heavy core particles with a density of 1.33 to 1.35 g/ml and less endogenous PK than did the light cores. The phosphorylation reaction had a rapid initial phase (several minutes) and a slow but long-lasting second phase (many hours). The PK had a high affinity for ATP (KM = 0.5 mumol/liter). Only few of the several hundred P21.9 subunits in one core particle were phosphorylated in vitro. The only amino acid which was phosphorylated in vitro was serine. The resistance of the introduced phospho group against alkaline phosphatase showed that the PK acceptor, and probably the enzyme itself, was located inside the core particle.
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PMID:Specificity and localization of the hepatitis B virus-associated protein kinase. 680 56

Several viral transcriptional activators have been shown to interact with the basal transcription factor TATA-binding protein (TBP). These associations have been implicated in facilitating the assembly of the transcriptional preinitiation complex. We report here that the hepatitis B virus protein X (pX) specifically binds to TBP in vitro. While truncations of the highly conserved carboxyl terminus of TBP abolished this binding, amino-terminal deletions had no effect. Deletion analysis suggests that a domain consisting of 71 aa in the highly conserved carboxyl-terminal region of TBP is necessary for its interaction with pX. The minimal region in pX sufficient for its interaction with TBP includes aa 110-143. Furthermore, TBP from phylogenetically distinct species including Arabidopsis thaliana, Saccharomyces cerevisiae, Drosophila melanogaster, and Solanum tuberosum (potato) bound to pX. The pX-TBP interaction was inhibited in the presence of nonhydrolyzable analogs of ATP, suggesting a requirement for ATP. These results provide an explanation for the promiscuous behavior of pX in the transactivation of a large repertoire of cellular promoters. This study further implicates a fundamental role for pX in modulating transcriptional regulatory pathways by interacting with the basal transcription factor TBP.
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PMID:Hepatitis B virus transactivator protein X interacts with the TATA-binding protein. 786 23

The hepatitis B virus 17 kDa x gene product expressed in bacteria transactivates a human U6 promoter three- to eightfold in an ATP-independent manner in HeLa cell NTP-depleted extracts containing preassembled transcription preinitiation complexes. However, if added prior to assembly, HBx squelches the promoter. Both the HBx dependent "squelching" of U6 transcription observed in transient transfection analysis, and the transactivation observed in vitro is dependent on the presence of an upstream octamer element. HBx is incorporated via protein-protein interactions into DNA complexes containing the activation domains of Oct-1, and into a stable U6 preinitiation complex. This is consistent with a role as a coactivator interacting with the basal transcription machinery. We propose that the HBx dependent transactivation and repression of U6 transcription occurs by changes in the transcription factor limiting initiation, and propose that HBx may have a dual role in the regulation of transcription in vivo.
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PMID:The 17 kDa HBx protein encoded by hepatitis B virus interacts with the activation domains of Oct-1, and functions as a coactivator in the activation and repression of a human U6 promoter. 817 91

The two enantiomers of 2',3'-dideoxy-3'-thiacytidine (BCH-189) and their 5-fluoro analogs (FTC) were found to be good substrates for human 2'-deoxycytidine kinase with Km values in the 5.7 to 42.1 microM range. The affinity of the (-)-enantiomers was greater than that of the (+)-compounds. These results may explain the greater in vitro antiviral potency against human immunodeficiency virus and hepatitis B virus of the (-)-enantiomers when compared to their (+)-counterparts. The (+)- and (-)-enantiomers of FTC and BCH-189 are the first nucleoside analogs for which we have observed lower apparent kinetic constants for this enzyme in the presence of ATP compared to UTP.
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PMID:Affinity of the antiviral enantiomers of oxathiolane cytosine nucleosides for human 2'-deoxycytidine kinase. 838 48

The hepatitis B virus X-protein (HBx) has been expressed in Escherichia coli both as an unfused protein and with an N-terminal hexaHis-containing fusion sequence. Both forms of HBx, after purification, displayed a potent AMP kinase activity, in which HBx phosphorylates AMP to ADP, using ATP as the exclusive phosphate donor. We also found that HBx has previously unreported GTPase and GTP-ADP nucleoside diphosphate kinase activities.
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PMID:The hepatitis B virus X protein is a potent AMP kinase. 862 19


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