bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intracellular Localization and Protein Interactions of the Gene 1 Protein p28 during Mouse Hepatitis Virus Replication
Authors: Brockway Sarah M. , Lu Xiao Tao , Peters Timothy R. , Dermody Terence S. , Denison Mark R. 
Published: October 2004

ABSTRACT
Coronaviruses encode the largest replicase polyprotein of any known positive-strand RNA virus. Replicase protein precursors and mature products are thought to mediate the formation and function of viral replication complexes on the surfaces of intracellular double-membrane vesicles. However, the functions of only a few of these proteins are known. For the coronavirus mouse hepatitis virus (MHV), the first proteolytic processing event of the replicase polyprotein liberates an amino-terminal 28-kDa product (p28). While previous biochemical studies have suggested that p28 is associated with viral replication complexes, the intracellular localization and interactions of p28 with other proteins during the course of MHV replication have not been defined. We used immunofluorescence confocal microscopy to show that p28 localizes to viral replication complexes in the cytoplasm during early times postinfection. However, at late times postinfection, p28 localizes to sites of M accumulation distinct from the replication complex. Furthermore, by yeast two-hybrid and coimmunoprecipitation analyses, we demonstrate that p28 specifically binds to p10 and p15, two coronavirus replicase proteins of unknown function. Deletion mutagenesis experiments determined that the carboxy terminus of p28 is not required for its interactions with p10 and p15. These results suggest that p28 may play a part at the replication complex by interacting with p10 and p15. Moreover, our findings highlight a potential role for p28 at virion assembly sites.
Infection of Vero Cells by BK Virus Is Dependent on Caveolae
Authors: Eash Sylvia , Querbes William , Atwood Walter J. 
Published: October 2004

ABSTRACT
Polyomavirus-associated nephropathy occurs in ∼5% of renal transplant recipients and results in loss of graft function in 50 to 70% of these patients. The disease is caused by reactivation of the common human polyomavirus BK (BKV) in the transplanted kidney. The early events in productive BKV infection are unknown. In this report, we focus on elucidating the mechanisms of BKV internalization in its target cell. Our data reveal that BKV entry into permissive Vero cells is slow, is independent of clathrin-coated-pit assembly, is dependent on an intact caveolin-1 scaffolding domain, is sensitive to tyrosine kinase inhibition, and requires cholesterol. BKV colocalizes with the caveola-mediated endocytic marker cholera toxin subunit B but not with the clathrin-dependent endocytic marker transferrin. In addition, BKV infectious entry is sensitive to elevation in intracellular pH. These findings indicate that BKV entry into Vero cells occurs by caveola-mediated endocytosis involving a pH-dependent step.
trans
-Packaged West Nile Virus-Like Particles: Infectious Properties In Vitro and in Infected Mosquito Vectors
Authors: Scholle Frank , Girard Yvette A. , Zhao Qizu , Higgs Stephen , Mason Peter W. 
Published: October 2004

ABSTRACT

A
trans
-packaging system for West Nile virus (WNV) subgenomic replicon RNAs (repRNAs), deleted for the structural coding region, was developed. WNV repRNAs were efficiently encapsidated by the WNV C/prM/E structural proteins expressed in
trans
from replication-competent, noncytopathic Sindbis virus-derived RNAs. Infectious virus-like particles (VLPs) were produced in titers of up to 10
9
infectious units/ml. WNV VLPs established a single round of infection in a variety of different cell lines without production of progeny virions. The infectious properties of WNV and VLPs were indistinguishable when efficiencies of infection of a number of different cell lines and inhibition of infection by neutralizing antibodies were determined. To investigate the usefulness of VLPs to address biological questions in vivo,
Culex pipiens quinquefasciatus
mosquitoes were orally and parenterally infected with VLPs, and dissected tissues were analyzed for WNV antigen expression. Antigen-positive cells in midguts of orally infected mosquitoes were detected as early as 2 days postinfection and as late as 8 days. Intrathoracic inoculation of VLPs into mosquitoes demonstrated a dose-dependent pattern of infection of secondary tissues and identified fat body, salivary glands, tracheal cells, and midgut muscle as susceptible WNV VLP infection targets. These results demonstrate that VLPs can serve as a valuable tool for the investigation of tissue tropism during the early stages of infection, where virus spread and the need for biosafety level 3 containment complicate the use of wild-type virus.
Measles Virus Phosphoprotein Gene Products: Conformational Flexibility of the P/V Protein Amino-Terminal Domain and C Protein Infectivity Factor Function
Authors: Devaux Patricia , Cattaneo Roberto 
Published: October 2004

ABSTRACT
The measles virus (MV) P gene codes for three proteins: P, an essential polymerase cofactor, and V and C, which have multiple functions but are not strictly required for viral propagation in cultured cells. V shares the amino-terminal domain with P but has a zinc-binding carboxyl-terminal domain, whereas C is translated from an overlapping reading frame. During replication, the P protein binds incoming monomeric nucleocapsid (N) proteins with its amino-terminal domain and positions them for assembly into the nascent ribonucleocapsid. The P protein amino-terminal domain is natively unfolded; to probe its conformational flexibility, we fused it to the green fluorescent protein (GFP), thereby also silencing C protein expression. A recombinant virus (MV-GFP/P) expressing hybrid GFP/P and GFP/V proteins in place of standard P and V proteins and not expressing the C protein was rescued and produced normal ratios of mono-, bi-, and tricistronic RNAs, but its replication was slower than that of the parental virus. Thus, the P protein retained nearly intact polymerase cofactor function, even with a large domain added to its amino terminus. Having noted that titers of cell-associated and especially released MV-GFP/P were reduced and knowing that the C protein of the related Sendai virus has particle assembly and infectivity factor functions, we produced an MV-GFP/P derivative expressing C. Intracellular titers of this virus were almost completely restored, and those of released virus were partially restored. Thus, the MV C protein is an infectivity factor.
Reduction of Retrovirus-Induced Immunosuppression by In Vivo Modulation of T Cells during Acute Infection
Authors: He Hong , Messer Ronald J. , Sakaguchi Shimon , Yang Guojun , Robertson Shelly J. , Hasenkrug Kim J. 
Published: October 2004

ABSTRACTChronic infection with Friend retrovirus is associated with suppressed antitumor immune responses. In the present study we investigated whether modulation of T-cell responses during acute infection would restore antitumor immunity in persistently infected mice. T-cell modulation was done by treatments with DTA-1 anti- glucocorticoid-induced tumor necrosis factor receptor monoclonal antibodies. The DTA-1 monoclonal antibody is nondepleting and delivers costimulatory signals that both enhance the activation of effector T cells and inhibit suppression by regulatory T cells. DTA-1 therapy produced faster Th1 immune responses, significant reductions in both acute virus loads and pathology and, most importantly, long-term improvement of CD8+T-cell-mediated antitumor responses.
Human Cytomegalovirus DNA Replication Requires Transcriptional Activation via an IE2- and UL84-Responsive Bidirectional Promoter Element within
ori
Lyt
Authors: Xu Yiyang , Cei Sylvia A. , Rodriguez Huete Alicia , Colletti Kelly S. , Pari Gregory S. 
Published: October 2004

ABSTRACT

Amplification of the human cytomegalovirus (HCMV) lytic origin (
ori
Lyt) in human fibroblasts is dependent upon six core replication proteins and UL84, IE2, and UL36-38. Using a telomerase-immortalized human fibroblast cell line (T-HFs),
ori
Lyt-dependent DNA replication no longer required the gene products of UL36-38. To determine the role of IE2 in DNA replication in human fibroblasts, we examined potential IE2-binding sites within HCMV
ori
Lyt. We now show that a strong bidirectional promoter (
ori
Lyt
PM
) (nucleotides 91754 to 92030) is located in the previously identified core region of the origin and is required for efficient amplification of
ori
Lyt. It was determined that a 14-bp novel DNA motif (
ori
Lyt promoter activation element), which was initially identified as a binding element for the immediate-early protein IE2, was essential for
ori
Lyt
PM
activity. In Vero cells the
ori
Lyt
PM
was constitutively active and strongly repressed by IE2, but it was reactivated by UL84. In contrast, transfection of the
ori
Lyt
PM
into human fibroblasts resulted in a very low basal level of promoter activity that was dramatically up-regulated upon infection with HCMV. Cotransfection assays demonstrated that the transfection of UL84 along with IE2 transactivated the
ori
Lyt
PM
in human fibroblasts. Further activation was observed upon cotransfection of the set of plasmids expressing the entire replication complex. Efficient
ori
Lyt amplification in the absence of IE2 in human fibroblasts was observed by replacing the
ori
Lyt
PM
with the simian virus 40 early promoter. Under these conditions, however, UL84 was still required for amplification of
ori
Lyt. These results suggest that the mechanism of initiation of HCMV lytic replication in part involves transcriptional activation.
Evolutionary Transition toward Defective RNAs That Are Infectious by Complementation
Authors: García-Arriaza Juan , Manrubia Susanna C. , Toja Miguel , Domingo Esteban , Escarmís Cristina 
Published: October 2004

ABSTRACT
Passage of foot-and-mouth disease virus (FMDV) in cell culture resulted in the generation of defective RNAs that were infectious by complementation. Deletions (of nucleotides 417, 999, and 1017) mapped in the L proteinase and capsid protein-coding regions. Cell killing followed two-hit kinetics, defective genomes were encapsidated into separate viral particles, and individual viral plaques contained defective genomes with no detectable standard FMDV RNA. Infection in the absence of standard FMDV RNA was achieved by cotransfection of susceptible cells with transcripts produced in vitro from plasmids encoding the defective genomes. These results document the first step of an evolutionary transition toward genome segmentation of an unsegmented RNA virus and provide an experimental system to compare rates of RNA progeny production and resistance to enhanced mutagenesis of a segmented genome versus its unsegmented counterpart.
Evidence for both Lytic Replication and Tightly Regulated Human Herpesvirus 8 Latency in Circulating Mononuclear Cells, with Virus Loads Frequently below Common Thresholds of Detection
Authors: Martró Elisa , Cannon Michael J. , Dollard Sheila C. , Spira Thomas J. , Laney A. Scott , Ou Chin-Yih , Pellett Philip E. 
Published: October 2004

ABSTRACT

To address whether human herpesvirus 8 (HHV-8) DNA in peripheral blood mononuclear cells (PBMCs) might be the product of latent or lytic infection and to shed light on sporadic detection of HHV-8 DNA in individuals seropositive for the virus, we studied the frequency of infected cells, total virus load, and virus load per infected cell in PBMCs from men coinfected with HHV-8 and human immunodeficiency virus (HIV), some of whom had Kaposi's sarcoma. The low frequencies of infected cells detected (fewer than one per million cells in some individuals) suggest that the prevalence of the virus in circulating leukocytes was underestimated in previous studies that employed more conventional sampling methods (single, small-volume specimens). Mean virus loads ranged from 3 to 330 copies per infected PBMC; these numbers can represent much higher loads in individual lytically infected cells (>10
3
genomes/cell) in mixtures that consist predominantly of latently (relatively few genomes) infected cells. The presence in some subjects of high HHV-8 mean genome copy numbers per infected cell, together with viral DNA being found in plasma only from subjects with positive PBMCs, supports earlier suggestions that the virus can actively replicate in PBMCs. In some individuals, mean virus loads were less than 10 genomes per infected cell, suggesting a tightly controlled purely latent state. HHV-8 genome copy numbers are substantially higher in latently infected cells derived from primary effusion lymphomas; thus, it appears that HHV-8 is able to adopt more than one latency program, perhaps analogous to the several types of Epstein-Barr virus latency.
Lv1 Inhibition of Human Immunodeficiency Virus Type 1 Is Counteracted by Factors That Stimulate Synthesis or Nuclear Translocation of Viral cDNA
Authors: Berthoux Lionel , Sebastian Sarah , Sokolskaja Elena , Luban Jeremy 
Published: October 2004

ABSTRACT

Human immunodeficiency virus type 1 (HIV-1) cDNA synthesis is inhibited in cells from some nonhuman primates by an activity called Lv1. Sensitivity to restriction by Lv1 maps to a region of the HIV-1 CA required for interaction with the cellular protein cyclophilin A. A similar antiviral activity in mammalian cells, Ref1, inhibits reverse transcription of murine leukemia virus (MLV), but only with viral strains bearing N-tropic CA. Disruption of the HIV-1 CA-cyclophilin A interaction inhibits Lv1 restriction in some cells and, paradoxically, seems to render HIV-1 sensitive to Ref1. Lv1 and Ref1 activities are overcome by high-titer infection and are saturable with nonreplicating, virus-like particles encoded by susceptible viruses. Two compounds that disrupt mitochondrial membrane potential, As
2
O
3
and m-Cl-CCP, reduce Ref1 activity. Here we show that these drugs, as well as a third compound with similar effects on mitochondria, PK11195, attenuate Lv1 activity in rhesus macaque and African green monkey cells. Effects of PK11195 and virus-like particles on HIV-1 infectivity in these cells were largely redundant, each associated with increased HIV-1 cDNA. Comparison of acutely infected macaque and human cells suggested that, in addition to effects on cDNA synthesis, Lv1 inhibits the accumulation of nuclear forms of HIV-1 cDNA. Disruption of the HIV-1 CA-cyclophilin A interaction caused a minimal increase in total viral cDNA but increased the proportion of viral cDNA in the nucleus. Consistent with a model in which Lv1 inhibits both synthesis and nuclear translocation of HIV-1 cDNA, complete suppression of macaque or African green monkey Lv1 was achieved by the additive effect of factors that stimulate both processes.
Between-Host Evolution of Cytotoxic T-Lymphocyte Epitopes in Human Immunodeficiency Virus Type 1: an Approach Based on Phylogenetically Independent Comparisons
Authors: Piontkivska Helen , Hughes Austin L. 
Published: October 2004

ABSTRACTIn human immunodeficiency virus type 1 (HIV-1), mutations that escape from cytotoxic T-lymphocyte (CTL) recognition have been documented, and sequence analyses have provided indirect support for the hypothesis that natural selection has favored CTL escape mutants within an infected host. In spite of such evidence for within-host selection by CTL, it has been more difficult to determine how natural selection by host CTL has influenced long-term evolution of HIV-1. We used statistical analysis of published HIV-1 genomic sequences to examine the role of natural selection in between-host evolution of CTL epitopes. Based on a phylogenetic analysis, we identified 21 pairs of closely related genomes isolated from different hosts and examined the pattern of nucleotide substitution in genomic regions encoding well-characterized CTL epitopes. The results revealed that certain CTL epitopes have been subject to repeated positive selection across the population, while others are generally conserved. Furthermore, evidence of positive selection was associated with divergence from the canonical epitope sequence and with an enhanced frequency of convergent amino acid sequence changes in CTL epitopes. The results support the hypothesis that CTL-driven selection has been a major factor in the long-term evolution of HIV-1.
Coevolution of RANTES Sensitivity and Mode of CCR5 Receptor Use by Human Immunodeficiency Virus Type 1 of the R5 Phenotype
Authors: Karlsson Ingrid , Antonsson Liselotte , Shi Yu , Öberg Monica , Karlsson Anders , Albert Jan , Olde Björn , Owman Christer , Jansson Marianne , Fenyö Eva Maria 
Published: October 2004

ABSTRACT

The evolution of human immunodeficiency virus type 1 (HIV-1) coreceptor use has been described as the acquisition of CXCR4 use linked to accelerated disease progression. However, CXCR4-using virus can be isolated only from approximately one-half of individuals with progressive HIV-1 disease. The other half continue to yield only CCR5-using viruses (R5 phenotype) throughout the course of disease. In the present work, the use of receptor chimeras between CCR5 and CXCR4 allowed us to study the evolution of HIV-1 with the R5 phenotype, which was not revealed by studies of wild-type coreceptor use. All together, 246 isolates (173 with the R5 phenotype) from 31 individuals were tested for their ability to infect cells through receptor chimeras. R5
narrow
virus was able to use only wild-type CCR5, whereas R5
broad(1)
to R5
broad(3)
viruses were able to use one to three chimeric receptors, respectively. Broad use of chimeric receptors was interpreted as an increased flexibility in the mode of receptor use. R5
broad
isolates showed higher infectivity in cells expressing wild-type CCR5 than R5
narrow
isolates. Also, the increased flexibility of R5
broad
isolates was concomitant with a lower sensitivity to inhibition by the CC chemokine RANTES. Our results indicate a close relationship between HIV-1 phenotypic changes and the pathogenic process, since the mode and efficiency of CCR5 use as well as the decrease in the RANTES sensitivities of isolated viruses are significantly correlated with CD4
+
-T-cell decline in a patient. One possible explanation is that ligand competition at the CCR5 receptor or changed CCR5 availability may shape the outcome of HIV-1 infection.
Stable Ubiquitination of Human T-Cell Leukemia Virus Type 1 Tax Is Required for Proteasome Binding
Authors: Chiari Estelle , Lamsoul Isabelle , Lodewick Julie , Chopin Cécile , Bex Françoise , Pique Claudine 
Published: October 2004

ABSTRACTHuman T-cell leukemia virus type 1 (HTLV-1) is the retrovirus responsible for adult T-cell leukemia and HTLV-1-associated myelopathy. Adult T-cell leukemia development is mainly due to the ability of the viral oncoprotein Tax to promote T-cell proliferation, whereas the appearance of HTLV-1-associated myelopathy involves the antigenic properties of Tax. Understanding the events regulating the intracellular level of Tax is therefore an important issue. How Tax is degraded has not been determined, but it is known that Tax binds to proteasomes, the major sites for degradation of intracellular proteins, generally tagged through polyubiquitin conjugation. In this study, we investigated the relationship between Tax, ubiquitin, and proteasomes. We report that mono- and polyubiquitinated Tax proteins can be recovered from both transfected 293T cells and T lymphocytes. We also show that lysine residues located in the carboxy-terminal domain of Tax are the principal targets of this process. Remarkably, we further demonstrate that mutation of lysine residues in the C-terminal part of Tax, which massively reduces Tax ubiquitination, impairs proteasome binding, and conversely, that a Tax mutant that binds poorly to this particle (M22) is faintly ubiquitinated, suggesting that Tax ubiquitination is required for association with cellular proteasomes. Finally, we document that comparable amounts of ubiquitinated species were found whether proteasome activities were inhibited or not, providing evidence that they are not directly addressed to proteasomes for degradation. These findings indicate that although it is ubiquitinated and binds to proteasomes, Tax is not massively degraded via the ubiquitin-proteasome pathway and therefore reveal that Tax conjugation to ubiquitin mediates a nonproteolytic function.
Calcium-Dependent Calpain Proteases Are Implicated in Processing of the Hepatitis C Virus NS5A Protein
Authors: Kalamvoki M. , Mavromara P. 
Published: October 2004

ABSTRACTThe nonstructural 5A (NS5A) protein of the hepatitis C virus (HCV) is a multifunctional phosphoprotein that is implicated in viral replication and HCV-mediated pathogenesis. We report here that the NS5A protein from the HCV genotype 1a is processed into shorter distinct forms when expressed in mammalian cells (Vero, HepG2, HuH-7, and WRL68) infected with an NS5A-expressing HSV-1-based amplicon vector or when transiently transfected with NS5A-expressing plasmids in the absence of exogenous apoptotic stimuli. Inhibitor studies combined with cell-free cleavage assays suggest that calcium-dependent calpain proteases, in addition to caspase-like proteases, are involved in NS5A processing. Interestingly, His-tagging experiments indicated that all the detectable NS5A-cleaved products are N-terminal forms of the protein. Additionally, immunofluorescence studies showed that, despite proteolytic cleavage, the NS5A protein exhibits a cytoplasm-perinuclear localization similar to that of the full-length protein. Thus, our results are consistent with recent data that demonstrated that NS5A is capable of perturbing intracellular calcium homeostasis and suggest that NS5A is both an inducer and a substrate of the calcium-dependent calpain protease(s). This may imply that cleavage of NS5A by calpain(s) could play a role in the modulation of NS5A function.
Essential Function of the Pseudorabies Virus UL36 Gene Product Is Independent of Its Interaction with the UL37 Protein
Authors: Fuchs Walter , Klupp Barbara G. , Granzow Harald , Mettenleiter Thomas C. 
Published: October 2004

ABSTRACT

The large tegument protein encoded by the UL36 gene of pseudorabies virus (PrV) physically interacts with the product of the adjacent UL37 gene (B. G. Klupp, W. Fuchs, H. Granzow, R. Nixdorf, and T. C. Mettenleiter,
J. Virol.
76:
3065-3071, 2002). To analyze UL36 function, two PrV recombinants were generated by mutagenesis of an infectious PrV full-length clone in
Escherichia coli
: PrV-ΔUL36F exhibited a deletion of virtually the complete UL36 coding region, whereas PrV-UL36BSF contained two in-frame deletions of 238 codons spanning the predicted UL37 binding domain. Coimmunoprecipitation experiments confirmed that the mutated gene product of PrV-UL36BSF did not interact with the UL37 protein. Like the previously described PrV-ΔUL37 (B. G. Klupp, H. Granzow, and T. C. Mettenleiter,
J. Virol.
75:
8927-8936, 2001) but in contrast to PrV-ΔUL36F, PrV-UL36BSF was able to replicate in rabbit kidney (RK13) cells, although maximum virus titers were reduced ca. 50-fold and plaque diameters were reduced by ca. 45% compared to wild-type PrV. PrV-ΔUL36F was able to productively replicate after repair of the deleted gene or in a
trans
-complementing cell line. Electron microscopy of infected RK13 cells revealed that PrV-UL36BSF and phenotypically complemented PrV-ΔUL36F were capable of nucleocapsid formation and egress from the nucleus by primary envelopment and deenvelopment at the nuclear membrane. However, reenvelopment of nucleocapsids in the cytoplasm was blocked. Only virus-like particles without capsids were released efficiently from cells. Interestingly, cytoplasmic nucleocapsids of PrV-UL36BSF but not of PrV-ΔUL36F were found in large ordered structures similar to those which had previously been observed with PrV-ΔUL37. In summary, our results demonstrate that the interaction between the UL36 and UL37 proteins is important but not strictly essential for the formation of secondary enveloped, infectious PrV particles. Furthermore, UL36 possesses an essential function during virus replication which is independent of its ability to bind the UL37 protein.