Reverse transcriptase activity of hepatitis B virus polymerase in eukaryotic cell extracts in vitro

ALTEX ◽  
2008 ◽  
pp. 197-211 ◽  
Author(s):  
Daniel Favre
Keyword(s):  
Hepatitis B Virus ◽  
Hepatitis B ◽  
Reverse Transcriptase ◽  
Eukaryotic Cell ◽  
Reverse Transcriptase Activity ◽  
Transcriptase Activity ◽  
Cell Extracts ◽  
B Virus

scholarly journals In Vitro Reconstitution of a Functional Duck Hepatitis B Virus Reverse Transcriptase: Posttranslational Activation by Hsp90

2000 ◽  
Vol 74 (24) ◽  
pp. 11447-11455 ◽  
Author(s):  
Jianming Hu ◽  
Dana Anselmo
Keyword(s):  
Hepatitis B Virus ◽  
Hepatitis B ◽  
Reverse Transcriptase ◽  
Host Factors ◽  
Duck Hepatitis B Virus ◽  
Duck Hepatitis ◽  
B Virus ◽  
Protein Priming ◽  
Hsp90 Function

ABSTRACT Reverse transcription in hepatitis B viruses is initiated through a unique protein priming mechanism whereby the viral reverse transcriptase (RT) first assembles into a ribonucleoprotein (RNP) complex with its RNA template and then initiates DNA synthesis de novo using the RT itself as a protein primer. RNP formation and protein priming require the assistance of host cell factors, including the molecular chaperone heat shock protein 90 (Hsp90). To better understand the mechanism of RT activation by Hsp90, we have now mapped the minimal RT sequences of the duck hepatitis B virus that are required for chaperone binding, RNP formation, and protein priming. Furthermore, we have reconstituted in vitro both RNP formation and protein priming using purified RT proteins and host factors. Our results show that (i) Hsp90 recognizes two independent domains of the RT, both of which are necessary for RNP formation and protein priming; (ii) Hsp90 function is required not only to establish, but also to maintain, the RT in a state competent for RNA binding; and (iii) Hsp90 is not required during RT synthesis and can activate the RT posttranslationally. Based on these findings, we propose a model for Hsp90 function whereby the chaperone acts as an active interdomain bridge to bring the two RT domains into a poised but labile conformation competent for RNP formation. It is anticipated that the reconstitution system established here will facilitate the isolation of additional host factors required for RT functions and further elucidation of the mechanisms of RT activation.

scholarly journals Entecavir for Treatment of Hepatitis B Virus Displays No In Vitro Mitochondrial Toxicity or DNA Polymerase Gamma Inhibition

2007 ◽  
Vol 52 (2) ◽  
pp. 598-605 ◽  
Author(s):  
Charles E. Mazzucco ◽  
Robert K. Hamatake ◽  
Richard J. Colonno ◽  
Daniel J. Tenney
Keyword(s):  
Mitochondrial Dna ◽  
Hepatitis B Virus ◽  
Hepatitis B ◽  
Reverse Transcriptase ◽  
Dna Polymerase ◽  
Mitochondrial Proteins ◽  
Mitochondrial Toxicity ◽  
Chronic Hepatitis B Virus ◽  
B Virus

ABSTRACT Therapy with nucleoside reverse transcriptase inhibitors (NRTIs) can be associated with mitochondrial toxicity. In vitro studies have been used to predict the predisposition for and characterize the mechanisms causing mitochondrial toxicity. Entecavir (ETV) is an approved deoxyguanosine nucleoside for the treatment of chronic hepatitis B virus (HBV) infection that exhibits potent activity against viral reverse transcriptase. We assessed the potential for mitochondrial toxicity of ETV in long-term cultures of HepG2 hepatoma cells by measuring mitochondrial function (through lactate secretion), levels of mitochondrial DNA (mtDNA), and levels of mitochondrial proteins COX II and COX IV. Furthermore, we tested the activity of ETV-triphosphate (ETV-TP) against mitochondrial DNA polymerase γ (Pol γ) in vitro. ETV concentrations as high as 100 times the maximal clinical exposure (C max) did not affect cell proliferation, levels of lactate, mitochondrial DNA, or mitochondrial proteins throughout the 15-day culture. The lack of mitochondrial toxicity was consistent with the finding that ETV-TP was not recognized by mitochondrial DNA Pol γ and failed to be incorporated into DNA or inhibit the polymerase assay at the highest levels tested, 300 μM. Combinations of ETV with each of the other HBV NRTI antivirals, adefovir, tenofovir, and lamivudine at 10 times their respective C max levels also failed to result in cellular or mitochondrial toxicity. In summary, cell culture and enzymatic studies yielded no evidence that would predict mitochondrial toxicity of ETV at exposure levels in excess of those expected to be achieved clinically.

scholarly journals Inhibition of Hepatitis B Virus Polymerase by Entecavir

2007 ◽  
Vol 81 (8) ◽  
pp. 3992-4001 ◽  
Author(s):  
David R. Langley ◽  
Ann W. Walsh ◽  
Carl J. Baldick ◽  
Betsy J. Eggers ◽  
Ronald E. Rose ◽  
...  
Keyword(s):  
Hepatitis B Virus ◽  
Hepatitis B ◽  
Reverse Transcriptase ◽  
Kinetic Studies ◽  
Hbv Dna ◽  
Cross Resistance ◽  
Significant Activity ◽  
B Virus ◽  
Dna Chain

ABSTRACT Entecavir (ETV; Baraclude) is a novel deoxyguanosine analog with activity against hepatitis B virus (HBV). ETV differs from the other nucleoside/tide reverse transcriptase inhibitors approved for HBV therapy, lamivudine (LVD) and adefovir (ADV), in several ways: ETV is >100-fold more potent against HBV in culture and, at concentrations below 1 μM, displays no significant activity against human immunodeficiency virus (HIV). Additionally, while LVD and ADV are obligate DNA chain terminators, ETV halts HBV DNA elongation after incorporating a few additional bases. Three-dimensional homology models of the catalytic center of the HBV reverse transcriptase (RT)-DNA-deoxynucleoside triphosphate (dNTP) complex, based on the HIV RT-DNA structure, were used with in vitro enzyme kinetic studies to examine the mechanism of action of ETV against HBV RT. A novel hydrophobic pocket in the rear of the RT dNTP binding site that accommodates the exocyclic alkene moiety of ETV was predicted, establishing a basis for the superior potency observed experimentally. HBV DNA chain termination by ETV was accomplished through disfavored energy requirements as well as steric constraints during subsequent nucleotide addition. Validation of the model was accomplished through modeling of LVD resistance substitutions, which caused an eightfold decrease in ETV susceptibility and were predicted to reduce, but not eliminate, the ETV-binding pocket, in agreement with experimental observations. ADV resistance changes did not affect the ETV docking model, also agreeing with experimental results. Overall, these studies explain the potency, mechanism, and cross-resistance profile of ETV against HBV and account for the successful treatment of naive and LVD- or ADV-experienced chronic HBV patients.

scholarly journals Hepatitis B Virus Reverse Transcriptase and ε RNA Sequences Required for Specific Interaction In Vitro

2006 ◽  
Vol 80 (5) ◽  
pp. 2141-2150 ◽  
Author(s):  
Jianming Hu ◽  
Morgan Boyer
Keyword(s):  
Hepatitis B Virus ◽  
Hepatitis B ◽  
Reverse Transcriptase ◽  
Specific Interaction ◽  
Heat Shock Protein 90 ◽  
Protein Domain ◽  
Rna Sequences ◽  
B Virus

ABSTRACT Initiation of reverse transcription and nucleocapsid assembly in hepatitis B virus (HBV) depends on the specific recognition of an RNA signal (the packaging signal, ε) on the pregenomic RNA by the viral reverse transcriptase (RT). Using an in vitro reconstitution system whereby the cellular heat shock protein 90 chaperone system activates recombinant HBV RT for specific ε binding, we have defined the protein and RNA sequences required for specific HBV RT-ε interaction in vitro. Our results indicated that approximately 150 amino acid residues from the terminal protein domain and 230 from the RT domain were necessary and sufficient for ε binding. With respect to the ε RNA sequence, its internal bulge and, in particular, the first nucleotide (C) of the bulge were specifically required for RT binding. Sequences from the upper portion of the lower stem and the lower portion of the upper stem also contributed to RT binding, as did the base pairing of the upper portion and the single unpaired U residue of the upper stem. Surprisingly, the apical loop of ε, known to be required for RNA packaging, was entirely dispensable for RT binding. A comparison of the requirements for in vitro RT-ε interaction with those for in vivo pregenomic RNA (pgRNA) packaging clearly indicated that RT-ε interaction was necessary but not sufficient for pgRNA packaging. In addition, our results suggest that recognition of some ε sequences by the RT may be required specifically for viral DNA synthesis.

scholarly journals Two-Year Assessment of Entecavir Resistance in Lamivudine-Refractory Hepatitis B Virus Patients Reveals Different Clinical Outcomes Depending on the Resistance Substitutions Present

2006 ◽  
Vol 51 (3) ◽  
pp. 902-911 ◽  
Author(s):  
Daniel J. Tenney ◽  
Ronald E. Rose ◽  
Carl J. Baldick ◽  
Steven M. Levine ◽  
Kevin A. Pokornowski ◽  
...  
Keyword(s):  
Hepatitis B Virus ◽  
Hepatitis B ◽  
Reverse Transcriptase ◽  
Clinical Outcomes ◽  
Chronic Infection ◽  
Hbv Dna ◽  
Wild Type ◽  
Pcr Assay ◽  
B Virus

ABSTRACT Entecavir (ETV) is a deoxyguanosine analog approved for use for the treatment of chronic infection with wild-type and lamivudine-resistant (LVDr) hepatitis B virus (HBV). In LVD-refractory patients, 1.0 mg ETV suppressed HBV DNA levels to below the level of detection by PCR (<300 copies/ml) in 21% and 34% of patients by Weeks 48 and 96, respectively. Prior studies showed that virologic rebound due to ETV resistance (ETVr) required preexisting LVDr HBV reverse transcriptase substitutions M204V and L180M plus additional changes at T184, S202, or M250. To monitor for resistance, available isolates from 192 ETV-treated patients were sequenced, with phenotyping performed for all isolates with all emerging substitutions, in addition to isolates from all patients experiencing virologic rebounds. The T184, S202, or M250 substitution was found in LVDr HBV at baseline in 6% of patients and emerged in isolates from another 11/187 (6%) and 12/151 (8%) ETV-treated patients by Weeks 48 and 96, respectively. However, use of a more sensitive PCR assay detected many of the emerging changes at baseline, suggesting that they originated during LVD therapy. Only a subset of the changes in ETVr isolates altered their susceptibilities, and virtually all isolates were significantly replication impaired in vitro. Consequently, only 2/187 (1%) patients experienced ETVr rebounds in year 1, with an additional 14/151 (9%) patients experiencing ETVr rebounds in year 2. Isolates from all 16 patients with rebounds were LVDr and harbored the T184 and/or S202 change. Seventeen other novel substitutions emerged during ETV therapy, but none reduced the susceptibility to ETV or resulted in a rebound. In summary, ETV was effective in LVD-refractory patients, with resistant sequences arising from a subset of patients harboring preexisting LVDr/ETVr variants and with approximately half of the patients experiencing a virologic rebound.

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