scholarly journals Production and Function of the Cytoplasmic Deproteinized Relaxed Circular DNA of Hepadnaviruses

2009 ◽  
Vol 84 (1) ◽  
pp. 387-396 ◽  
Author(s):  
Haitao Guo ◽  
Richeng Mao ◽  
Timothy M. Block ◽  
Ju-Tao Guo
Keyword(s):  
Dna Polymerase ◽  
Structural Changes ◽  
Core Protein ◽  
Dnase I ◽  
Dominant Negative ◽  
Stable Cell Line ◽  
Circular Dna ◽  
Nuclear Localization Signals ◽  
Infected Cells

ABSTRACT Removal of genome-bound viral DNA polymerase ought to be an essential step in the formation of hepadnavirus covalently closed circular DNA (cccDNA). We previously demonstrated that deproteinized (DP) relaxed circular DNA (rcDNA) of hepatitis B virus (HBV) existed in both the cytoplasm and nuclei of infected cells and the vast majority of cytoplasmic DP rcDNA was associated with DNase I-permeable nucleocapsids. In our efforts to investigate the role of the cytoplasmic DP rcDNA in cccDNA formation, we demonstrated that rcDNA deproteinization could occur in an endogenous DNA polymerase reaction with either virion-derived or intracellular nucleocapsids. As observed in the cytoplasm of virally infected cells, in vitro deproteinization requires the maturation of plus-strand DNA and results in changes in nucleocapsid structure that render the DP rcDNA susceptible to DNase I digestion. Remarkably, we found that the cytoplasmic DP rcDNA-containing nucleocapsids could be selectively immunoprecipitated with an antibody against the carboxyl-terminal peptide of HBV core protein and are associated with cellular nuclear transport receptors karyopherin-α and -β. Moreover, transfection of small interfering RNA targeting karyopherin-β1 mRNA or expression of a dominant-negative karyopherin-β1 in a stable cell line supporting HBV replication resulted in the accumulation of DP rcDNA in cytoplasm and reduction of nuclear DP rcDNA and cccDNA. Our results thus favor a hypothesis that completion of plus-strand DNA synthesis triggers the genomic DNA deproteinization and structural changes of nucleocapsids, which leads to the exposure of nuclear localization signals in the C terminus of core protein and mediates the nuclear transportation of DP rcDNA via interaction with karyopherin-α and -β.

scholarly journals Modulation of Nuclear Localization of the Influenza Virus Nucleoprotein through Interaction with Actin Filaments

1999 ◽  
Vol 73 (3) ◽  
pp. 2222-2231 ◽  
Author(s):  
Paul Digard ◽  
Debra Elton ◽  
Konrad Bishop ◽  
Elizabeth Medcalf ◽  
Alan Weeds ◽  
...  
Keyword(s):  
Influenza Virus ◽  
Nuclear Localization ◽  
Virus Genome ◽  
Actin Binding ◽  
Filamentous Actin ◽  
Nuclear Localization Signals ◽  
Infected Cells ◽  
Cytoplasmic Accumulation ◽  
High Level

ABSTRACT The influenza virus genome is transcribed in the nuclei of infected cells but assembled into progeny virions in the cytoplasm. This is reflected in the cellular distribution of the virus nucleoprotein (NP), a protein which encapsidates genomic RNA to form ribonucleoprotein structures. At early times postinfection NP is found in the nucleus, but at later times it is found predominantly in the cytoplasm. NP contains several sequences proposed to act as nuclear localization signals (NLSs), and it is not clear how these are overridden to allow cytoplasmic accumulation of the protein. We find that NP binds tightly to filamentous actin in vitro and have identified a cluster of residues in NP essential for the interaction. Complexes containing RNA, NP, and actin could be formed, suggesting that viral ribonucleoproteins also bind actin. In cells, exogenously expressed NP when expressed at a high level partitioned to the cytoplasm, where it associated with F-actin stress fibers. In contrast, mutants unable to bind F-actin efficiently were imported into the nucleus even under conditions of high-level expression. Similarly, nuclear import of NLS-deficient NP molecules was restored by concomitant disruption of F-actin binding. We propose that the interaction of NP with F-actin causes the cytoplasmic retention of influenza virus ribonucleoproteins.

scholarly journals Replication Complex of Human Parechovirus 1

2003 ◽  
Vol 77 (15) ◽  
pp. 8512-8523 ◽  
Author(s):  
Camilla Krogerus ◽  
Denise Egger ◽  
Olga Samuilova ◽  
Timo Hyypiä ◽  
Kurt Bienz
Keyword(s):  
Viral Protein ◽  
Structural Changes ◽  
Rna Replication ◽  
Viral Rna ◽  
Human Parechovirus ◽  
Electron Microscopic ◽  
Vitro Assay ◽  
Replication Complex ◽  
Infected Cells

ABSTRACT The parechoviruses differ in many biological properties from other picornaviruses, and their replication strategy is largely unknown. In order to identify the viral RNA replication complex in human parechovirus type 1 (HPEV-1)-infected cells, we located viral protein and RNA in correlation to virus-induced membrane alterations. Structural changes in the infected cells included a disintegrated Golgi apparatus and disorganized, dilated endoplasmic reticulum (ER) which had lost its ribosomes. Viral plus-strand RNA, located by electron microscopic (EM) in situ hybridization, and the viral protein 2C, located by EM immunocytochemistry were found on clusters of small vesicles. Nascent viral RNA, visualized by 5-bromo-UTP incorporation, localized to compartments which were immunocytochemically found to contain the viral protein 2C and the trans-Golgi marker 1,4-galactosyltransferase. Protein 2C was immunodetected additionally on altered ER membranes which displayed a complex network-like structure devoid of cytoskeletal elements and with no apparent involvement in viral RNA replication. This protein also exhibited membrane binding properties in an in vitro assay. Our data suggest that the HPEV-1 replication complex is built up from vesicles carrying a Golgi marker and forming a structure different from that of replication complexes induced by other picornaviruses.

scholarly journals Lobucavir is phosphorylated in human cytomegalovirus-infected and -uninfected cells and inhibits the viral DNA polymerase.

1997 ◽  
Vol 41 (12) ◽  
pp. 2680-2685 ◽  
Author(s):  
D J Tenney ◽  
G Yamanaka ◽  
S M Voss ◽  
C W Cianci ◽  
A V Tuomari ◽  
...  
Keyword(s):  
Protein Kinase ◽  
Dna Synthesis ◽  
Dna Polymerase ◽  
Human Cytomegalovirus ◽  
Potent Inhibitor ◽  
Viral Dna ◽  
Infected Cells ◽  
Simplex Virus ◽  
Hsv Thymidine Kinase

Lobucavir (LBV) is a deoxyguanine nucleoside analog with broad-spectrum antiviral activity. LBV was previously shown to inhibit herpes simplex virus (HSV) DNA polymerase after phosphorylation by the HSV thymidine kinase. Here we determined the mechanism of action of LBV against human cytomegalovirus (HCMV). LBV inhibited HCMV DNA synthesis to a degree comparable to that of ganciclovir (GCV), a drug known to target the viral DNA polymerase. The expression of late proteins and RNA, dependent on viral DNA synthesis, was also inhibited by LBV. Immediate-early and early HCMV gene expression was unaffected, suggesting that LBV acts temporally coincident with HCMV DNA synthesis and not through cytotoxicity. In vitro, the triphosphate of LBV was a potent inhibitor of HCMV DNA polymerase with a Ki of 5 nM. LBV was phosphorylated to its triphosphate form intracellularly in both infected and uninfected cells, with phosphorylated metabolite levels two- to threefold higher in infected cells. GCV-resistant HCMV isolates, with deficient GCV phosphorylation due to mutations in the UL97 protein kinase, remained sensitive to LBV. Overall, these results suggest that LBV-triphosphate halts HCMV DNA replication by inhibiting the viral DNA polymerase and that LBV phosphorylation can occur in the absence of viral factors including the UL97 protein kinase. Furthermore, LBV may be effective in the treatment of GCV-resistant HCMV.

FINE STRUCTURAL CHANGES IN ISOLATED MITOCHONDRIA OF HEALTHY AND VIRUS-INFECTED VICIA FABA L.

1966 ◽  
Vol 44 (8) ◽  
pp. 1017-1024 ◽  
Author(s):  
M. Weintraub ◽  
H. W. J. Ragetli ◽  
V. T. John
Keyword(s):  
Structural Changes ◽  
Broad Bean ◽  
Plant Mitochondria ◽  
Yellow Mosaic Virus ◽  
Normal Appearance ◽  
Isolated Mitochondria ◽  
Vicia Faba L ◽  
Infected Cells

Mitochondria within leaf cells of healthy broad bean had the normal appearance of plant mitochondria, while within cells infected with bean yellow mosaic virus they had matrices that were electron-opaque and cristae that were swollen and angular. However, upon isolation, mitochondria from healthy broad bean cells became indistinguishable from either mitochondria in situ in virus-infected cells, or from mitochondria in vitro isolated from virus-infected cells. Cristae of the isolated mitochondria were greatly inflated, while the matrices were reduced to a thin network in which spherical substructural components, 130–140 A in diameter, were visible. These changes in isolated healthy mitochondria could not be prevented by the use of tannin inhibitors. No significant differences were found in the succinoxidase activities of the isolated healthy and infected mitochondria.

scholarly journals Involvement of Template-Activating Factor I/SET in Transcription of Adenovirus Early Genes as a Positive-Acting Factor

2006 ◽  
Vol 80 (2) ◽  
pp. 794-801 ◽  
Author(s):  
Hirohito Haruki ◽  
Mitsuru Okuwaki ◽  
Makoto Miyagishi ◽  
Kazunari Taira ◽  
Kyosuke Nagata
Keyword(s):  
Core Protein ◽  
Negative Regulator ◽  
Factor I ◽  
Early Genes ◽  
Infected Cells ◽  
Bona Fide ◽  
Acidic Proteins ◽  
Interfering Rna ◽  
Early Phases

ABSTRACT The adenovirus genome complexed with viral core protein VII (adenovirus DNA-protein VII complex) at least is the bona fide template for transcription of adenovirus early genes. It is believed that the highly basic protein VII, like cellular histones, is a negative regulator for genome functions. Analyses with in vitro replication and transcription systems using the adenovirus DNA-protein VII complex have revealed that remodeling of the complex is crucial for efficient DNA replication and transcription. We identified host acidic proteins, template-activating factor I (TAF-I), TAF-II, and TAF-III as stimulatory factors for replication from the adenovirus DNA-protein VII complex. Recently, it was reported that the adenovirus DNA interacts with TAF-I and pp32, another host acidic protein (Y. Xue, J. S. Johnson, D. A. Ornelles, J. Lieberman, and D. A. Engel, J. Virol. 79:2474-2483, 2005). We found that TAF-I interacts and colocalizes with protein VII in adenovirus-infected cells during the early phases of infection, but pp32 does not. Although pp32 had the potential ability to interact with protein VII, pp32 did not remodel the adenovirus DNA-protein VII complex in vitro. Small interfering RNA-mediated knockdown of TAF-I expression leads to the delay of the transcription timing of early genes. These results provide evidence that TAF-I plays an important role in the early stages of the adenovirus infection cycle.

scholarly journals Human Cytomegalovirus UL97 Phosphorylates the Viral Nuclear Egress Complex

2014 ◽  
Vol 89 (1) ◽  
pp. 523-534 ◽  
Author(s):  
Mayuri Sharma ◽  
Brian J. Bender ◽  
Jeremy P. Kamil ◽  
Ming F. Lye ◽  
Jean M. Pesola ◽  
...  
Keyword(s):  
Human Cytomegalovirus ◽  
Continuous Distribution ◽  
Virus Production ◽  
Nuclear Lamina ◽  
Dominant Negative ◽  
Lamin A ◽  
Nuclear Egress ◽  
Dividing Cells ◽  
Infected Cells

ABSTRACTHerpesvirus nucleocapsids exit the host cell nucleus in an unusual process known as nuclear egress. The human cytomegalovirus (HCMV) UL97 protein kinase is required for efficient nuclear egress, which can be explained by its phosphorylation of the nuclear lamina component lamin A/C, which disrupts the nuclear lamina. We found that a dominant negative lamin A/C mutant complemented the replication defect of a virus lacking UL97 in dividing cells, validating this explanation. However, as complementation was incomplete, we investigated whether the HCMV nuclear egress complex (NEC) subunits UL50 and UL53, which are required for nuclear egress and recruit UL97 to the nuclear rim, are UL97 substrates. Using mass spectrometry, we detected UL97-dependent phosphorylation of UL50 residue S216 (UL50-S216) and UL53-S19 in infected cells. Moreover, UL53-S19 was specifically phosphorylated by UL97in vitro. Notably, treatment of infected cells with the UL97 inhibitor maribavir or infection with aUL97mutant led to a punctate rather than a continuous distribution of the NEC at the nuclear rim. Alanine substitutions in both UL50-S216 and UL53-S19 resulted in a punctate distribution of the NEC in infected cells and also decreased virus production and nuclear egress in the absence of maribavir. These results indicate that UL97 phosphorylates the NEC and suggest that this phosphorylation modulates nuclear egress. Thus, the UL97-NEC interaction appears to recruit UL97 to the nuclear rim both for disruption of the nuclear lamina and phosphorylation of the NEC.IMPORTANCEHuman cytomegalovirus (HCMV) causes birth defects and it can cause life-threatening diseases in immunocompromised patients. HCMV assembles in the nucleus and then translocates to the cytoplasm in an unusual process termed nuclear egress, an attractive target for antiviral therapy. A viral enzyme, UL97, is important for nuclear egress. It has been proposed that this is due to its role in disruption of the nuclear lamina, which would otherwise impede nuclear egress. In validating this proposal, we showed that independent disruption of the lamina can overcome a loss of UL97, but only partly, suggesting additional roles for UL97 during nuclear egress. We then found that UL97 phosphorylates the viral nuclear egress complex (NEC), which is essential for nuclear egress, and we obtained evidence that this phosphorylation modulates this process. Our results highlight a new role for UL97, the mutual dependence of the viral NEC and UL97 during nuclear egress, and differences among herpesviruses.

scholarly journals Clustered Charge-to-Alanine Mutagenesis of the Vaccinia Virus A20 Gene: Temperature-Sensitive Mutants Have a DNA-Minus Phenotype and Are Defective in the Production of Processive DNA Polymerase Activity

2001 ◽  
Vol 75 (24) ◽  
pp. 12308-12318 ◽  
Author(s):  
Almira Punjabi ◽  
Kathleen Boyle ◽  
Joseph DeMasi ◽  
Olivera Grubisha ◽  
Beth Unger ◽  
...  
Keyword(s):  
Vaccinia Virus ◽  
Dna Polymerase ◽  
Polymerase Activity ◽  
Temperature Sensitive ◽  
Permissive Temperature ◽  
Nonpermissive Temperature ◽  
Infected Cells ◽  
And Function ◽  
A20 Gene

ABSTRACT Although the vaccinia virus DNA polymerase is inherently distributive, a highly processive form of the enzyme exists within the cytoplasm of infected cells (W. F. McDonald, N. Klemperer, and P. Traktman, Virology 234:168–175, 1997). In the accompanying report we outline the purification of the 49-kDa A20 protein as a stoichiometric component of the processive polymerase complex (N. Klemperer, W. McDonald, K. Boyle, B. Unger, and P. Traktman, J. Virol. 75:12298–12307, 2001). To complement this biochemical analysis, we undertook a genetic approach to the analysis of the structure and function of the A20 protein. Here we report the application of clustered charge-to-alanine mutagenesis of the A20 gene. Eight mutant viruses containing altered A20 alleles were isolated using this approach; two of these, tsA20-6 andtsA20-ER5, have tight temperature-sensitive phenotypes. At the nonpermissive temperature, neither virus forms macroscopic plaques and the yield of infectious virus is <1% of that obtained at the permissive temperature. Both viruses show a profound defect in the accumulation of viral DNA at the nonpermissive temperature, although both the A20 protein and DNA polymerase accumulate to wild-type levels. Cytoplasmic extracts prepared from cells infected with thetsA20 viruses show a defect in processive polymerase activity; they are unable to direct the formation of RFII product using a singly primed M13 template. In sum, these data indicate that the A20 protein plays an essential role in the viral life cycle and that viruses with A20 lesions exhibit a DNA− phenotype that is correlated with a loss in processive polymerase activity as assayed in vitro. The vaccinia virus A20 protein can, therefore, be considered a new member of the family of proteins (E9, B1, D4, and D5) with essential roles in vaccinia virus DNA replication.

scholarly journals Designing CXCL8-based decoy proteins with strong anti-inflammatory activity in vivo

2013 ◽  
Vol 33 (5) ◽  
Author(s):  
Angelika Falsone ◽  
Veronica Wabitsch ◽  
Elena Geretti ◽  
Heide Potzinger ◽  
Tanja Gerlza ◽  
...  
Keyword(s):  
Structural Changes ◽  
Therapeutic Potential ◽  
Heparan Sulphate ◽  
Dominant Negative ◽  
Inflammatory Activity ◽  
Boyden Chamber ◽  
Cxc Chemokine ◽  
Anti Inflammatory

IL (interleukin)-8 [CXCL8 (CXC chemokine ligand 8)] exerts its role in inflammation by triggering neutrophils via its specific GPCRs (G-protein-coupled receptors), CXCR1 (CXC chemokine receptor 1) and CXCR2, for which additional binding to endothelial HS-GAGs (heparan sulphate-glycosaminoglycans) is required. We present here a novel approach for blocking the CXCL8-related inflammatory cascade by generating dominant-negative CXCL8 mutants with improved GAG-binding affinity and knocked-out CXCR1/CXCR2 activity. These non-signalling CXCL8 decoy proteins are able to displace WT (wild-type) CXCL8 and to prevent CXCR1/CXCR2 signalling thereby interfering with the inflammatory response. We have designed 14 CXCL8 mutants that we subdivided into three classes according to number and site of mutations. The decoys were characterized by IFTs (isothermal fluorescence titrations) and SPR (surface plasmon resonance) to determine GAG affinity. Protein stability and structural changes were evaluated by far-UV CD spectroscopy and knocked-out GPCR response was shown by Boyden chamber and Ca2+ release assays. From these experiments, CXCL8(Δ6F17KF21KE70KN71K) emerged with the most promising in vitro characteristics. This mutant was therefore further investigated in a murine model of mBSA (methylated BSA)-induced arthritis in mice where it showed strong anti-inflammatory activity. Based on these results, we propose that dominant-negative CXCL8 decoy proteins are a promising class of novel biopharmaceuticals with high therapeutic potential in inflammatory diseases.

scholarly journals Sumoylation of the Carboxy-Terminal of Human Cytomegalovirus DNA Polymerase Processivity Factor UL44 Attenuates Viral DNA Replication

2021 ◽  
Vol 12 ◽  
Author(s):  
Jun Chen ◽  
Guanlie Li ◽  
Haiqing He ◽  
Xin Li ◽  
Wenjing Niu ◽  
...  
Keyword(s):  
Dna Polymerase ◽  
Human Cytomegalovirus ◽  
Sumoylation Site ◽  
Viral Dna ◽  
Viral Dna Replication ◽  
Infected Cells ◽  
Processivity Factor ◽  
Carboxy Terminal

Controlled regulation of genomic DNA synthesis is a universally conserved process for all herpesviruses, including human cytomegalovirus (HCMV), and plays a key role in viral pathogenesis, such as persistent infections. HCMV DNA polymerase processivity factor UL44 plays an essential role in viral DNA replication. To better understand the biology of UL44, we performed a yeast two-hybrid screen for host proteins that could interact with UL44. The most frequently isolated result was the SUMO-conjugating enzyme UBC9, a protein involved in the sumoylation pathway. The UBC9-UL44 interaction was confirmed by in vitro His-tag pull-down and in vivo co-immunoprecipitation assays. Using deletion mutants of UL44, we mapped two small regions of UL44, aa 11–16, and 260–269, which might be critical for the interaction with UBC9. We then demonstrated that UL44 was a target for sumoylation by in vitro and in vivo sumoylation assays, as well as in HCMV-infected cells. We further confirmed that 410lysine located within a ψKxE consensus motif on UL44 carboxy-terminal was the major sumoylation site of UL44. Interestingly, although 410lysine had no effects on subcellular localization or protein stability of UL44, the removal of 410lysine sumoylation site enhanced both viral DNA synthesis in transfection-replication assays and viral progeny production in infected cells for HCMV, suggesting sumoylation can attenuate HCMV replication through targeting UL44. Our results suggest that sumoylation plays a key role in regulating UL44 functions and viral replication, and reveal the crucial role of the carboxy-terminal of UL44, for which little function has been known before.

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