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At least 217 records · Page 12Linked to original sources
PubMed2003

Independent expression of Rep and RepA and their roles in regulating bean yellow dwarf virus replication.

Bean yellow dwarf virus (BeYDV) is a mastrevirus specific for dicotyledenous hosts. It contains four ORFs encoding a movement protein, a coat protein, and two Rep gene products, Rep and RepA, which are encoded by two overlapping ORFs. In this study, the roles of Rep and RepA in regulating replication of the BeYDV-based replicon were investigated by uncoupling them and placing Rep and RepA each under constitutive promoter control. Constitutive expression of both Rep and RepA supported replication and enhanced gene expression. When a reporter plasmid containing the Rep gene in the context of its native promoter was supplemented with additional Rep protein, replication was enhanced but the increase in gene expression was found to be more modest. Furthermore, expression of constitutively expressed RepA alone was found to reduce replication of this reporter construct as well as delay BeYDV replication in general. The effect of a RepA mutant with an altered retinoblastoma-related-protein binding motif on the efficiency of BeYDV replication was also examined. This mutant was found to severely diminish replication efficiency. Finally, the relationship of BeYDV coat protein to virus replication and reporter gene expression was investigated. Addition of coat protein increased accumulation of single-stranded DNA and had a detrimental effect on reporter gene expression.

Capsid Proteins↗
PubMed1976

Dengue virus replication enhancement in peripheral blood leukocytes from immune human beings.

Dengue 2 virus replication in peripheral blood leukocyte cultures from 10 of 13 Asian or Polynesian subjects with actively acquired dengue immunity and two of three infants with passively acquired dengue antibody. Only 2 of 11 cultures from nonimmune infants or children supported viral replication. This study establishes a parallel in the biological behavior of human and simian PBL with respect to the immunological dependence of dengue virus replication in vitro. Elucidation of the mechanism (or mechamisms) regulating growth of dengue virus in leukocytes from immune hosts may contribute to an understanding of the role that virus-leukocyte interactions play in the pathogenesis of human dengue illness.

Adolescent↗
PubMed2006

Site-directed mutagenesis of the VP2 gene of Chicken anemia virus affects virus replication, cytopathology and host-cell MHC class I expression.

Chicken anemia virus (CAV) is an immunosuppressive pathogen of chickens. To further examine the role of viral protein 2 (VP2), which possesses dual-specificity protein phosphatase (DSP) activity, in viral cytopathogenicity and its influence on viral growth and virulence, an infectious genomic clone of CAV was subjected to site-directed mutagenesis. Substitution mutations C87R, R101G, K102D and H103Y were introduced into the DSP catalytic motif and R129G, Q131P, R/K/K150/151/152G/A/A, D/E161/162G/G, L163P, D169G and E186G into a region predicted to have a high degree of secondary structure. All mutant constructs were infectious, but their growth curves differed. The growth curve for mutant virus R/K/K150/151/152G/A/A was similar to that for wild-type virus, a second cluster of mutant viruses had an extended latent period and a third cluster of mutant viruses had extended latent and eclipse periods. All mutants had a reduced cytopathogenic effect in infected cells and VP3 was restricted to the cytoplasm. Mutation of the second basic residue (K102D) in the atypical DSP signature motif resulted in a marked reduction in virus replication efficiency, whereas mutation of the first basic residue (R101G) attenuated cytopathogenicity, but did not reduce replication efficiency. Expression of major histocompatibility complex (MHC) class I was markedly downregulated in cells infected with wild-type CAV, but not in those infected with mutants. This study further demonstrates the significance of VP2 in CAV replication and shows that specific mutations introduced into the gene encoding this protein can reduce virus replication, cytopathogenicity and downregulation of MHC I in infected cells.

Animals↗
PubMed1998

On the role of the second coding exon of the HIV-1 Tat protein in virus replication and MHC class I downregulation.

Tat is an essential protein of human immunodeficiency virus type 1 (HIV-1) and activates transcription from the viral long terminal repeat (LTR) promoter. The tat gene is composed of two coding exons of which the first, corresponding to the N-terminal 72 amino acid residues, has been reported to be sufficient for its transcription function. We introduced a stop codon at the end of the first Tat-coding exon in an expression vector that produces a truncated 71-amino acid Tat protein. This Q72stop mutant displays reduced transcriptional activity of approximately 54% in transient LTR-CAT transfection assays. To test the contribution of the second Tat-coding exon to virus replication, the Q72stop mutation was also introduced in the infectious pLAI molecular clone. The effect on virus replication was analyzed in primary cells and in a transformed T cell line. The fitness of the mutant virus was calculated to be approximately 75% compared with the wild-type control. Thus, a small contribution of the C-terminal Tat domain to viral fitness was measured. It has been proposed that the second Tat-coding exon is involved in transcriptional downregulation of the MHC class I gene of the infected host cell. Cell surface expression of the MHC protein was analyzed in T cells infected with the wild-type LAI virus and the replication-competent Q72stop mutant. MHC expression was transiently reduced on infection with either virus, indicating that the second Tat-coding exon is not involved in this downregulation.

Animals↗
PubMed2006

Involvement of multiple epitope-specific cytotoxic T-lymphocyte responses in vaccine-based control of simian immunodeficiency virus replication in rhesus macaques.

Cytotoxic T-lymphocyte (CTL) responses are crucial for the control of immunodeficiency virus replication. Possible involvement of a dominant single epitope-specific CTL in control of viral replication has recently been indicated in preclinical AIDS vaccine trials, but it has remained unclear if multiple epitope-specific CTLs can be involved in the vaccine-based control. Here, by following up five rhesus macaques that showed vaccine-based control of primary replication of a simian immunodeficiency virus, SIVmac239, we present evidence indicating involvement of multiple epitope-specific CTL responses in this control. Three macaques maintained control for more than 2 years without additional mutations in the provirus. However, in the other two that shared a major histocompatibility complex haplotype, viral mutations were accumulated in a similar order, leading to viral evasion from three epitope-specific CTL responses with viral fitness costs. Accumulation of these multiple escape mutations resulted in the reappearance of plasma viremia around week 60 after challenge. Our results implicate multiple epitope-specific CTL responses in control of immunodeficiency virus replication and furthermore suggest that sequential accumulation of multiple CTL escape mutations, if allowed, can result in viral evasion from this control.

Amino Acid Substitution↗
PubMed1996

The cytoplasmic tail of influenza A virus neuraminidase (NA) affects NA incorporation into virions, virion morphology, and virulence in mice but is not essential for virus replication.

In this study, we investigated the role of the conserved neuraminidase (NA) cytoplasmic tail residues in influenza virus replication. Mutants of influenza A virus (A/WSN/33 [H1N1]) with deletions of the NA cytoplasmic tail region were generated by reverse genetics. The resulting viruses, designated NOTAIL, contain only the initiating methionine of the conserved six amino-terminal residues. The mutant viruses grew much less readily and produced smaller plaques than did the wild-type virus. Despite similar levels of NA cell surface expression by the NOTAIL mutants and wild-type virus, incorporation of mutant NA molecules into virions was decreased by 86%. This reduction resulted in less NA activity per virion, leading to the formation of large aggregates of progeny mutant virions on the surface of infected cells. A NOTAIL virus containing an additional mutation (Ser-12 to Pro) in the transmembrane domain incorporated three times more NA molecules into virions than did the NOTAIL parent but approximately half of the amount incorporated by the wild-type virus. However, aggregation of the progeny virions still occurred at the cell surface. All NOTAIL viruses were attenuated in mice. We conclude that the cytoplasmic tail of NA is not absolutely essential for virus replication but exerts important effects on the incorporation of NA into virions and thus on the aggregation and virulence of progeny virus. In addition, the relative abundance of long filamentous particles formed by the NOTAIL mutants, compared with the largely spherical wild-type particles, indicates a role for the NA cytoplasmic tail in virion morphogenesis.

Amino Acid Sequence↗
PubMed1998

Inhibition of Mayaro virus replication by cerulenin in Aedes albopictus cells.

The antibiotic cerulenin, an inhibitor of lipid synthesis, was shown to suppress Mayaro virus replication in Aedes albopictus cells at non-cytotoxic doses. Cerulenin blocked the incorporation of [3H]glycerol into lipids when present at any time post infection (p.i.). Cerulenin added at the beginning of infection inhibited the synthesis of virus proteins. However, when this antibiotic was added at later stages of infection, it had only a mild effect on the virus protein synthesis. The possibility that cerulenin acts by blocking an initial step in the Mayaro virus replication after virus entry and before late viral translation is discussed.

Animals↗
PubMed1995

Effects of anti-E2 monoclonal antibody on sindbis virus replication in AT3 cells expressing bcl-2.

Antibodies directed to Sindbis virus (SV) envelope protein E2 are able to control virus replication in vivo and in persistently infected cultures of neurons in vitro. We investigated the mechanisms by which anti-E2 monoclonal antibody (MAb) alters virus replication by using AT3 rat prostatic carcinoma cells expressing the inhibitor of apoptosis bcl-2. Treatment of SV-infected AT3-bcl-2 cells with anti-E2 MAb G5 for 2 h decreased the rate of virus release for 6 to 8 h after removal of the antibody. Electron microscopic analysis of MAb-treated cells revealed that failure of virus release was linked to a defect in the budding process. The decrease in extracellular virus particles occurred despite continued formation of nucleocapsids and synthesis of envelope glycoproteins. MAb treatment delayed the inhibition of K+ influx and shutoff of host cell protein synthesis by SV infection in a dose-dependent manner. Synthesis of host cell factors and of nonstructural polyprotein precursors required for the formation of initial replication complexes was also prolonged, causing a slower shutdown of overall viral RNA synthesis. We conclude that one mechanism by which anti-E2 MAb treatment down-regulates SV replication is by reestablishing certain critical host cell functions in infected cells.

Animals↗
PubMed1998

CNI-H0294, a nuclear importation inhibitor of the human immunodeficiency virus type 1 genome, abrogates virus replication in infected activated peripheral blood mononuclear cells.

Active nuclear importation of the human immunodeficiency virus (HIV) type 1 (HIV-1) preintegration complex (PIC) is required for the productive infection of nondividing cells, but it is believed to be dispensable for the infection of proliferating cells, such as activated T lymphocytes. To investigate this question, we exploited the properties of the small arylene bis (methyl ketone) compound CNI-H0294. We have previously shown that this compound associated with the HIV-1 matrix protein nuclear localization sequence and blocked binding of the HIV-1 PIC to yeast karyopherin alpha. CNI-H0294 abrogated nuclear importation of the HIV-1 genome in macrophages and effectively inhibited infection of nondividing cells. In this study we demonstrate that CNI-H0294 inhibits binding of the HIV-1 PIC to human karyopherin alpha and reduces nuclear importation of the viral genome in primary peripheral blood mononuclear cells (PBMCs). We also demonstrate that CNI-H0294 inhibits acute infection of PBMC cultures in vitro with a primary isolate of HIV-1 and reduces virus replication and virus load in cultures of endogenously infected PBMCs from seropositive individuals. Thus, as for infection of nondividing, terminally differentiated macrophages, HIV-1 uses active nuclear importation of the virus genome to infect activated CD4+ T cells. These results support nuclear importation as a novel target and CNI-H0294 and its derivatives as novel compounds for therapeutic intervention in HIV infection and AIDS.

Anti-HIV Agents↗
PubMed1998

Effect of immune activation on the dynamics of human immunodeficiency virus replication and on the distribution of viral quasispecies.

Virus replication in a human immunodeficiency virus (HIV)-infected individual, as determined by the steady-state level of plasma viremia, reflects a complex balance of viral and host factors. We have previously demonstrated that immunization of HIV-infected individuals with the common recall antigen, tetanus toxoid, disrupts this steady state, resulting in transient bursts of plasma viremia after immunization. The present study defines the viral genetic basis for the transient bursts in viremia after immune activation. Tetanus immunization was associated with dramatic and generally reversible shifts in the composition of plasma viral quasispecies. The viral bursts in most cases reflected a nonspecific increase in viral replication secondary to an expanded pool of susceptible CD4(+) T cells. An exception to this was in a patient who harbored viruses of differing tropisms (syncytium inducing and non-syncytium inducing [NSI]). In this situation, immunization appeared to select for the replication of NSI viruses. In one of three patients, the data suggested that immune activation resulted in the appearance in plasma of virus induced from latently infected cells. These findings illustrate certain mechanisms whereby antigenic stimulation may influence the dynamics of HIV replication, including the relative expression of different viral variants.

Amino Acid Sequence↗
PubMedDate not supplied

[Study of hepatitis E virus replication in FRhK-4 cell culture].

The cytolytic form of hepatitis E virus reproduction in FRhk-4 cells is described. The cytopathic effect was observed by days 6-7 of the 25th passage in this cell culture. Reverse transcription with polymerase chain reaction were used to study virus reproduction daily for 10 days postinfection. The virus replication starts on day 4 after inoculation. The development of the cytopathic effect depended on the serum concentration in culture medium, whereas the virus replication did not depend on this factor. The replicative form (-RNA) of viral RNA appeared on day 4 postinoculation, as did the new genomic one (+RNA).

Animals↗
PubMed1983

Wild mouse retrovirus-induced neurogenic paralysis in laboratory mice. I. Virus replication and expression in central nervous system.

Ecotropic wild mouse retrovirus (1504 M)-induced neurogenic paralytic disease has been studied in inbred strains of mice. The major criterion for the successful transmission of the disease in the laboratory strains of mice is inoculation of high titer ecotropic virus in FV-1n strains of mice at newborn stage (less than or equal to 1 day old), Hybridization studies using 1504 M viral cDNA as probe indicate that in nonparalyzed mice, the inoculated virus replicates primarily in spleen tissue, whereas virus replication is evident in both spleen and central nervous system (CNS) tissue of paralyzed mice. Our studies on virus gene expression indicate that both viral gag gene product p30 and env gene product gp70 are expressed in brain, spinal cord and spleen tissues of paralyzed mice. Together, these results indicate that inoculation of neurotropic wild mouse virus into FV-1n strains of newborn laboratory mice is necessary for the establishment of infection in CNS tissue leading to virus replication and expression and resulting in the paralytic disease.

Animals↗
PubMed1988

Human immunodeficiency virus infection of monoblastoid cells: cellular differentiation determines the pattern of virus replication.

Stringent control of human immunodeficiency virus (HIV) replication was observed in the human monoblastoid cell line U937. A low-multiplicity infection of these cells by the LAV1 strain of HIV was productive for 2.5 days; then virus replication became restricted and no further evidence of virion production was observed. The dramatic decrease in HIV production was due in part of reduced accumulation of cytoplasmic viral RNA and occurred in the absence of evident cytopathic effects. In contrast, infected cells induced to differentiate by phorbol ester, vitamin D3, or lymphokine supernatant did not release markers of HIV despite the accumulation of significant levels of cytoplasmic viral RNA. HIV infection altered the pattern of c-myc RNA accumulation in U937 cells. Expression of this gene changes normally in response to the state of cellular differentiation; in infected cells the level of c-myc expression was correlated to the levels of viral RNA accumulation and not to cellular differentiation. These results suggest that restricted replication of HIV in monocytes might be an important mechanism of virus persistence and demonstrate a relationship between HIV replication and monocyte differentiation.

Cell Differentiation↗
PubMed2004

Capacity of Epstein-Barr virus to infect monocytes and inhibit their development into dendritic cells is affected by the cell type supporting virus replication.

Epstein-Barr virus (EBV) is a ubiquitous human herpesvirus that is involved in the pathogenesis of a wide spectrum of malignant and non-malignant diseases. Strong evidence implicates T lymphocytes in the control of EBV replication and tumorigenesis, but cellular components of the innate immune system are poorly characterized in terms of their function in the development of EBV-specific immunity or interaction with the virus. This study demonstrates that EBV virions produced in epithelial cells surpass their B cell-derived counterparts in the capacity to enter monocytes and inhibit their development into dendritic cells (DCs). Different ratios of the gp42 and gH glycoproteins in the envelope of virions that were derived from major histocompatibility complex class II-positive or -negative cells accounted primarily for the differences in EBV tropism. EBV is shown to enter both monocytes and DCs, although the cells are susceptible to virus-induced apoptosis only if infected at early stages of DC differentiation. The purified gH/gL heterodimer binds efficiently to monocytes and DCs, but not to B cells, suggesting that high expression levels of a putative binding partner for gH contribute to virus entry. This entry takes place despite very low or undetectable expression of CD21, the canonical EBV receptor. These results indicate that the site of virus replication, either in B cells or epithelial cells, alters EBV tropism for monocytes and DCs. This results in a change in the virus's immunomodulating capacity and may have important implications for the regulation of virus-host interactions during primary and chronic EBV infection.

Apoptosis↗
PubMed2006

Expanded tissue targets for foamy virus replication with simian immunodeficiency virus-induced immunosuppression.

Foamy viruses (FV) are the oldest known genus of retroviruses and have persisted in nonhuman primates for over 60 million years. FV are efficiently transmitted, leading to a lifelong nonpathogenic infection. Transmission is thought to occur through saliva, but the detailed mechanism is unknown. Interestingly, this persistent infection contrasts with the rapid cytopathicity caused by FV in vitro, suggesting a host defense against FV. To better understand the tissue specificity of FV replication and host immunologic defense against FV cytopathicity, we quantified FV in tissues of healthy rhesus macaques (RM) and those severely immunosuppressed by simian immunodeficiency virus (SIV). Contrary to earlier findings, we find that all immunocompetent animals consistently have high levels of viral RNA in oral tissues but not in other tissues examined, including the small intestine. Strikingly, abundant viral transcripts were detected in the small intestine of all of the SIV-infected RM, which has been shown to be a major site of SIV (and human immunodeficiency virus)-induced CD4+ T-cell depletion. In contrast, there was a trend to lower viral RNA levels in oropharyngeal tissues of SIV-infected animals. The expansion of FV replication to the small intestine but not to other CD4+ T-cell-depleted tissues suggests that factors other than T-cell depletion, such as dysregulation of the jejunal microenvironment after SIV infection, likely account for the expanded tissue tropism of FV replication.

Animals↗
PubMed1971

Inhibition by rifampin of African swine fever virus replication in tissue culture.

Vaccinia virus and African swine fever virus are deoxyribonucleic acid viruses of cytoplasmic origin. The fact that rifampin inhibits the replication of the former virus led to an investigation of its effect on African swine fever virus. The virus used was cytopathogenic to a PK-15 cell line, hemadsorbing in pig leukocyte cultures and lethal to pigs. Rifampin clearly inhibited the multiplication and cytopathogenicity of the virus in PK-15 cells. There was a 1- to 5-log reduction in virus titer depending upon the rifampin concentration, the multiplicity of infection, and the time after infection. Inhibition was greatest at a concentration of 200 mug of rifampin/ml. The drug was not viricidal per se, and the inhibition of virus replication was not due to the cell-granulating effect of rifampin since cultures which were transiently pretreated for long as 90 hr with 200 mug of drug/ml supported viral replication to the same degree as untreated cultures.

African Swine Fever↗
PubMed2002

Detection of dengue virus replication in peripheral blood mononuclear cells from dengue virus type 2-infected patients by a reverse transcription-real-time PCR assay.

While dengue virus is thought to replicate in mononuclear phagocytic cells in vivo, attempts to detect it in peripheral blood mononuclear cells (PBMC) by virus isolation or antigen detection have had variable and generally low rates. In this study, we developed a reverse transcription (RT)-real-time PCR assay to quantify positive- and negative-sense RNA of dengue virus type 2 within the cells. The assay includes an RT step using either sense or antisense primer followed by a real-time PCR step using the designed primers and probe, which target a capsid region highly conserved in dengue virus type 2 strains. It can be used to monitor the dynamic change of intracellular dengue virus RNA species during the course of infection. When this assay is employed in quantification of dengue virus RNA species in PBMC from 10 patients infected with dengue virus type 2, both positive- and negative-sense dengue RNA can be detected, indicating that dengue virus is actively replicating in PBMC in vivo. Moreover, the amounts of negative-sense dengue virus RNA in PBMC correlate very well with the viral load of dengue virus in plasma, suggesting that quantification of negative-sense dengue virus RNA in PBMC may provide another indicator of dengue virus replication in vivo. Use of this convenient, sensitive, and accurate method of quantification in clinical samples from patients with different disease severity would further our understanding of the pathogenesis of dengue.

Animals↗