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PubMed2000

Covalent modification of the transactivator protein IE2-p86 of human cytomegalovirus by conjugation to the ubiquitin-homologous proteins SUMO-1 and hSMT3b.

The 86-kDa IE2 protein (IE2-p86) of human cytomegalovirus (HCMV) is a potent transactivator of viral as well as cellular promoters. Several lines of evidence indicate that this broad transactivation spectrum is mediated by protein-protein interactions. To identify novel cellular binding partners, we performed a yeast two-hybrid screen using a N-terminal deletion mutant of IE2-p86 comprising amino acids 135 to 579 as a bait. Here, we report the isolation of two ubiquitin-homologous proteins, SUMO-1 and hSMT3b, as well as their conjugating activity hUBC9 (human ubiquitin-conjugating enzyme 9) as specific interaction partners of HCMV IE2. The polypeptides SUMO-1 and hSMT3b have previously been shown to be covalently coupled to a subset of nuclear proteins such as the nuclear domain 10 (ND10) proteins PML and Sp100 in a manner analogous to ubiquitinylation, which we call SUMOylation. By Western blot analysis, we were able to show that the IE2-p86 protein can be partially converted to a 105-kDa isoform in a dose-dependent manner after cotransfection of an epitope-tagged SUMO-1. Immunoprecipitation experiments of the conjugated isoforms using denaturing conditions further confirmed the covalent coupling of SUMO-1 or hSMT3b to IE2-p86 both after transient transfection and after lytic infection of human primary fibroblasts. Moreover, we defined two modification sites within IE2, located in an immediate vicinity at amino acid positions 175 and 180, which appear to be used alternatively for coupling. By using a SUMOylation-defective mutant, we showed that the targeting of IE2-p86 to ND10 occurs independent of this modification. However, a strong reduction of IE2-mediated transactivation of two viral early promoters and a heterologous promoter was observed in cotransfection analysis with the SUMOylation-defective mutant. This suggests a functional relevance of covalent modification by ubiquitin-homologous proteins for IE2-mediated transactivation, possibly by providing an additional interaction motif for cellular cofactors.

Binding Sites↗
PubMed1999

A temporal analysis of acyclovir inhibition of induced herpes simplex virus type 1 In vivo reactivation in the mouse trigeminal ganglia.

It is generally assumed that reactivation of latent herpes simplex virus occurs through initiation of lytic viral gene transcription from the latent viral genome. Thus, antiviral compounds such as acyclovir, whose activation is dependent upon viral thymidine kinase, should be effective in preventing the initial production of infectious virus associated with reactivation. To test this concept, the ability of acyclovir to prevent the production of infectious virus was determined in the murine hyperthermic stress (HS) model of in vivo reactivation. Acyclovir treatment after HS blocked the production of infectious virus within the ganglia. Efficacy was dependent upon the timing of the first post-HS dose and the length of exposure to acyclovir. A single dose administered 6-9 h after HS resulted in >90% reduction in reactivation. Acyclovir administered 12 h after HS resulted in 75% reduction, but there was no effect if treatment was delayed for 18 h after HS.

Acyclovir↗
PubMed1989

Interaction of staphylococcal delta-toxin and synthetic analogues with erythrocytes and phospholipid vesicles. Biological and physical properties of the amphipathic peptides.

Staphylococcal delta-toxin, a 26-residue amphiphilic peptide is lytic for cells and phospholipid vesicles and is assumed to insert as an amphipathic helix and oligomerize in membranes. For the first time, the relationship between these properties and toxin structure is investigated by means of eight synthetic peptides, one identical in sequence to the natural toxin, five 26-residue analogues and two shorter peptides corresponding to residues 1-11 and 11-26. These peptides were designed by the Edmundson wheel axial projection in order to maintain: (a) the hydrophilic/hydrophobic balance while rationalizing the sequence, (b) the alpha-helical configuration and (c) the common epitopic structure. The fluorescence of the single Trp residue was used to monitor the behaviour of the natural toxin and analogues. All 26-residue analogues were hemolytically active although to a lesser extent than natural toxin. The peptide of residues 11-26 bound lipids weakly and was hemolytic at high concentration. The peptide of residues 1-11 did not bind lipids and was hemolytically inactive. All peptides except the latter cross-reacted in immunoprecipitation tests with the natural toxin. The study of a 26-residue analogue by circular dichroism revealed an alpha-helical configuration in both the free and lipid-bound state. Changes in the fluorescence of the peptides in the presence of lipid micelles and bilayers varied according to the position of the reporter group. When bound to lipids, Trp5, Trp16 and the Fmoc-1 positions of the analogues became buried while Trp15 of the natural toxin and its synthetic replicate remained more exposed. All changes are rationalized by the proposal of an amphipathic helix whose hydrophobic face is embedded within the apolar core of bilayers while the hydrophilic and charged face remains more exposed to solvent.

Animals↗
PubMed1998

Productive infection of Epstein-Barr virus (EBV) in EBV-genome-positive epithelial cell lines (GT38 and GT39) derived from gastric tissues.

We characterized the expression of Epstein-Barr virus (EBV) on two epithelial cell lines, GT38 and GT39, derived from human gastric tissues. The EBV nuclear antigen (EBNA) was detected in all cells of both cell lines. The EBV immediate-early BZLF 1 protein (ZEBRA), the early antigen diffuse component (EA-D), and one of the EBV envelope proteins (gp350/220) were expressed spontaneously in small proportions in the cells. EBNA 1, EBNA2, latent membrane protein 1, ZEBRA, and EA-D molecules were then observed by Western blotting in the cells. The lytic cycle was enhanced with treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA) or n-butyrate. The virus particles were observed in the TPA treated GT38 cells by electron microscopy. Infectious EBV was detected with the transformation of cord blood lymphocytes and also with the induction of early antigen to Raji cells by the supernatants of both cells lines. A major single and minor multiple fused terminal fragments and a ladder of smaller fragments of the EBV genome were detected with a Xhol probe in both cell lines. These epithelial cells lines and viruses will be useful in studying their association with EBV in gastric epithelial cells.

Animals↗
PubMed1973

Production of bacteriophage by temperature-sensitive sporulation mutants of Bacillus cereus T.

Five temperature-sensitive sporulation mutants of Bacillus cereus T have been isolated. These mutants are blocked at stage 0 of sporulation at the restrictive temperature (37 C) but are able to sporulate at nearly normal frequencies at the permissive temperature (26 C). A bacteriophage that forms a stable lysogen in the parent strain is induced at increased frequencies in the mutants. This induction is accompanied, in some of the mutants, by a reduction in immunity to the phage. Revertants, selected for their ability to sporulate normally at both temperatures, lose their ability to produce high titers of the phage. In addition to this lytic phage, an apparently defective phage has been found in lysates of the mutants. Strains cured of the plaque-forming phage still carry the defective phage. Comparisons of physical and biological properties of the plaque-forming phage with those of the two Bacillus cereus phages most similar to it have shown that this phage is not identical to either of them. The maximal titer of phage produced in cultures of the parent strain is about 10(3) plaque-forming units (PFU) per ml at both temperatures. The maximal titers of phage produced by the mutant are 4 x 10(9) PFU/ml at 37 C and 7 x 10(8) PFU/ml at 26 C. Both mutant and parent strains release over 90% of the phage they produce after the onset of stationary phase.

Animals↗
PubMed1986

The mitogenic activity of staphylococcal enterotoxin B (SEB): a monovalent T cell mitogen that stimulates cytolytic T lymphocytes but cannot mediate their lytic interaction.

Staphylococcal enterotoxin B (SEB), a monovalent T cell mitogen and inducer of T suppressor cells, was found to be a potent polyclonal activator of cytolytic T lymphocytes (CTL) effective against concanavalin A (Con A)-treated target cells. In addition to polyclonal stimulation of CTL, SEB could reactivate "memory" CTL, alloimmunized 60 to 90 days earlier, into "secondary" CTL detectable as early as 24 hr after onset of stimulation and specific for the original priming target cells. Optimal cytolytic activity was induced at 0.5 to 10 micrograms/ml SEB; optimal priming time was 3 days, correlating well with the proliferative activity and morphologic transformation of small lymphocytes into large T lymphoblasts. Long-term cultures of splenocytes, stimulated by SEB, continued to express high cytolytic activity. It is noteworthy that although SEB and Con A are comparable CTL inducers, SEB, unlike Con A, is an ineffective mediator of nonspecific, CTL/target cell interactions. To the best of our knowledge this is the first example of a CTL inducer unable to mediate CTL-target interaction and lysis. The latter observations suggests that different receptors are involved in CTL activation and in CTL-target interaction resulting in lysis.

Animals↗
PubMed1986

Persistent infection with a nontransforming RNA virus leads to impaired growth factor receptors and response.

The potential role of viral persistence with nontransforming viruses on cellular growth and cellular function has received little attention. We found that when infected with type 3 reovirus (five plaque-forming units (PFU/cell), balb/C 3T3 cells (a mouse embryo fibroblast cell line) undergo a limited lytic phase. The surviving cells, about 90% of the original cells, appear morphologically normal by light microscopy and exhibit normal growth patterns in serum-supplemented medium but are persistently infected by electron microscopy. These persistently infected cells shed infectious virus in the culture medium (1.6-60 X 10(6) PFU per 10(6) cells per 24 h). In comparison to control uninfected 3T3 cells, the persistently infected cells exhibit a 70-90% decrease in receptor number for epidermal growth factor (EGF). This occurs without production of any EGF-like material and is associated with a parallel decrease in EGF-stimulated DNA synthesis. By contrast, insulin receptors are increased in number three-fold and insulin and serum stimulated DNA synthesis are comparable to control uninfected cells. These results suggest that persistent infection with a nontransforming virus may lead to major alteration in control of cell growth by specific growth factors.

Animals↗
PubMed2004

Granule-dependent mechanisms of lysis are defective in CD8 T cells of HIV-infected, antiretroviral therapy-treated individuals.

BACKGROUND: HIV-specific cytotoxic T-cell (CTL) responses are defective in HIV-infected patients undergoing antiretroviral therapy (ART). This defect has been attributed to the decreased antigenic burden secondary to ART-associated suppression of HIV-replication, and is responsible for the rebounds of viraemia that occur when patients interrupt therapy. CTL are stimulated by type 1 cytokines and can kill targets via granule-dependent (perforin and granzymes) and -independent (tumour necrosis factor-alpha, CD95) mechanisms. METHODS: Granule-dependent and granule-independent mechanisms of CTL killing, as well as type 1 cytokine production by CD4 T cells, were analysed in 57 chronically HIV-infected ART-treated or ART-untreated individuals. RESULTS: The results can be summarized as follows: the frequency of gp160 (env)-specific interferon-gamma-secreting CD8 T lymphocytes correlates positively with HIV viraemia in ART-treated and -untreated patients; Env-specific perforin- and granzymes-expressing CD8 T lymphocytes, and Env-stimulated perforin and granzymes mRNA, are reduced in ART-treated patients independently of HIV viral load and of type 1 cytokine production; tumour necrosis factor-alpha production is increased in ART-treated individuals; and Env-specific immature CD8+28+27+ cells are only marginally augmented in ART-treated patients, Similar results are observed in cytomegalovirus-specific CD8 T cells and peripheral blood mononuclear cells. CONCLUSIONS: A defect of CTL function that selectively affects the granule-dependent mechanisms of lysis is observed in ART-treated individuals. Because interferon-gamma production is higher in these patients, this could be a defect primarily involving CTL. These data suggest an independence of CD8 T-cell numbers and their lytic ability in HIV-infected, ART-receiving patients. Immunomodulants are needed to successfully treat HIV infection.

Adult↗
PubMed2006

Evidence that the herpes simplex virus type 1 ICP0 protein does not initiate reactivation from latency in vivo.

The stress-induced host cell factors initiating the expression of the herpes simplex virus lytic cycle from the latent viral genome are not known. Previous studies have focused on the effect of specific viral proteins on reactivation, i.e., the production of detectable infectious virus. However, identification of the viral protein(s) through which host cell factors transduce entry into the lytic cycle and analysis of the promoter(s) of this (these) first protein(s) will provide clues to the identity of the stress-induced host cell factors important for reactivation. In this report, we present the first strategy developed for this type of analysis and use this strategy to test the established hypothesis that the herpes simplex virus ICP0 protein initiates reactivation from the latent state. To this end, ICP0 null and promoter mutants were analyzed for the abilities (i) to exit latency and produce lytic-phase viral proteins (initiate reactivation) and (ii) to produce infectious viral progeny (reactivate) in explant and in vivo. Infection conditions were manipulated so that approximately equal numbers of latent infections were established by the parental strains, the mutants, and their genomically restored counterparts, eliminating disparate latent pool sizes as a complicating factor. Following hyperthermic stress (HS), which induces reactivation in vivo, equivalent numbers of neurons exited latency (as evidenced by the expression of lytic-phase viral proteins) in ganglia latently infected with either the ICP0 null mutant dl1403 or the parental strain. In contrast, infectious virus was detected in the ganglia of mice latently infected with the parental strain but not with ICP0 null mutant dl1403 or FXE. These data demonstrate that the role of ICP0 in the process of reactivation is not as a component of the switch from latency to lytic-phase gene expression; rather, ICP0 is required after entry into the lytic cycle has occurred. Similar analyses were carried out with the DeltaTfi mutant, which contains a 350-bp deletion in the ICP0 promoter, and the genomically restored isolate, DeltaTfiR. The numbers of latently infected neurons exiting latency were not different for DeltaTfi and DeltaTfiR. However, DeltaTfi did not reactivate in vivo, whereas DeltaTfiR reactivated in approximately 38% of the mice. In addition, ICP0 was detected in DeltaTfiR-infected neurons exiting latency but was not detected in those neurons exiting latency infected with DeltaTfi. We conclude that while ICP0 is important and perhaps essential for infectious virus production during reactivation in vivo, this protein is not required and appears to play no major role in the initiation of reactivation in vivo.

Animals↗
PubMed1972

Isolation of a polyvalent bacteriophage for Escherichia coli, Klebsiella pneumoniae, and Aerobacter aerogenes.

A lytic bacteriophage isolated from sewage was found to attack strains of Aerobacter aerogenes, Escherichia coli, and Klebsiella pneumoniae, but not members of the genera Salmonella, Proteus, and Serratia. The phage, designated phimp, contained deoxyribonucleic acid with a 50% guanine plus cytosine ratio and a molecular weight of 23.1 x 10(6) daltons. Single-step growth experiments of phimp plated at 37 C on A. aerogenes A2 gave a mean latent period of 20 min, an average burst size of 103 plaque-forming units/infected cell, and an average adsorption rate constant of 3 x 10(-10) ml/min. Electron microscopy of phimp revealed a phage with a flexible tail (165 nm long and 6 nm wide). The phage head had a hexagonal outline (62 nm in diameter).

Bacteriophages↗
PubMed2003

Activation of adenovirus early promoters and lytic phase in differentiated strata of organotypic cultures of human keratinocytes.

Human oncolytic adenoviruses have been used in clinical trials targeting cancers of epithelial origin. To gain a better understanding of the infectious cycle of adenovirus in normal human squamous tissues, we examined the viral infection process in organotypic cultures of primary human keratinocytes. We show that for the infection to occur, wounding of the epithelium is required. In addition, infection appears to initiate at the basal or parabasal cells that express the high-affinity coxsackievirus-adenovirus receptor, CAR, whereas the productive phase takes place in differentiated cells. This is due, at least in part, to the differentiation-dependent activation of the E1A and E2A early promoters and E4 promoters. We also show that adenovirus infection triggers a response mediated by the abnormal accumulation of cyclin E and p21cip1 proteins similar to the one previously observed in human papillomavirus-infected tissues. However, the virus seems to be able to overcome it, at least partially.

Adenoviridae↗
PubMed2003

Human cytomegalovirus proteins PP65 and IEP72 are targeted to distinct compartments in nuclei and nuclear matrices of infected human embryo fibroblasts.

The cellular distribution of the human cytomegalovirus (HCMV)-specific UL83 phosphoprotein (pp65) and UL123 immediate-early protein (IEp72) in lytically infected human embryo fibroblasts was studied by means of indirect immunofluorescence and confocal microscopy. Both proteins were found to have a nuclear localization, but they were concentrated in different compartments within the nuclei. The pp65 was located predominantly in the nucleoli; this was already evident with the parental viral protein, which was targeted to the above nuclear compartment very soon after infection. The nucleolar localization of pp65 was also observed at later stages of the HCMV infectious cycle. After chromatin extraction (in the so-called in situ nuclear matrices), a significant portion of the pp65 remained associated with nucleoli within the first hour after infection, then gradually redistributed in a perinucleolar area, as well as throughout the nucleus, with a granular pattern. A quite different distribution was observed for IEp72 at very early stages after infection of human embryo fibroblasts with HCMV; indeed, this viral protein was found in bright foci, clearly observable in both non-extracted nuclei and in nuclear matrices. At later stages of infection, IEp72 became almost homogeneously distributed within the whole nucleus, while the foci increased in size and were more evenly spread; in several infected cells some of them lay within nucleoli. This peculiar nuclear distribution of IEp72 was preserved in nuclear matrices as well. The entire set of data is discussed in terms of the necessity of integration for HCMV-specific products into the pre-existing nuclear architecture, with the possibility of subsequent adaptation of nuclear compartments to fit the needs of the HCMV replicative cycle.

Cell Fractionation↗
PubMed1986

Infection of the HTLV-II-bearing T-cell line C3 with HTLV-III/LAV is highly permissive and lytic.

The recent discovery that HTLV-I infected T-cells have an enhanced susceptibility to HTLV-III/LAV infection with concurrent cell lysis (S. Harada, Y. Koyanagi, and N. Yamamoto (1985) Science, 229, 563-566) led us to investigate a possible role for HTLV-II infected T cells in this respect. HTLV-II-bearing C3 cells were exposed to HTLV-III/LAV and the subsequent infection monitored by indirect immunofluorescence (IIF) of cells, reverse transcriptase (RT) activity in culture fluids, and hemacytometer cell counts. HTLV-III/LAV antigen expression was detected within 2 days whereas RT activity was detected within 3 days postinfection. The presence of immunofluorescent positive cells and RT activity was accompanied by cell lysis. Double infection of C3 cells was confirmed by IIF using a goat polyclonal antibody directed against the core p24 protein for detecting HTLV-II, and high titer serum from a pre-AIDS patient for detecting HTLV-III/LAV. We conclude that HTLV-I and HTLV-II infected T-cells share an enhanced susceptibility to HTLV-III/LAV infection with the promotion of cell lysis.

Antigens, Viral↗
PubMed1995

The dominant phosphoprotein pp65 (UL83) of human cytomegalovirus is dispensable for growth in cell culture.

The phosphoprotein pp65 (ppUL83) of human cytomegalovirus (HCMV) is abundantly synthesized during lytic infection in cultured fibroblasts. As a major constituent of extracellular particles, it gains entry to infected cells immediately after adsorption and subsequently translocates to the cell nucleus. This efficient transport is mediated by unique nuclear localization signals. To study the function of pp65, a viral deletion mutant was constructed by replacing the pp65 gene with the bacterial neomycin phosphotransferase gene, driven by the simian virus 40 early promoter. The resulting virus, RVAd65, could be grown and selected on human fibroblasts without complementation. The deletion of the pp65 gene in RVAd65 was verified by using Southern blot and PCR analyses. The lack of expression from the gene was investigated by immunoblotting with pp65-specific monoclonal antibodies. Single-cycle growth analyses showed that RVAd65 grew to levels of infectivity comparable to those of the wild-type virus. Therefore, pp65 is nonessential for the growth of HCMV in human fibroblasts. Electron microscopy revealed no differences in the processes of virion morphogenesis, although the maturation appeared to be delayed. However, the kinetics of expression of the immediate-early genes UL122 and UL123, the early gene UL44, and the late gene UL32 were the same in RVAd65-infected cells as in wild-type virus-infected cells in immunoblot analyses. In vitro phosphorylation assays showed that some of the virion proteins were labelled to a markedly reduced extent by virion-associated kinases in RVAd65 compared with wild-type virus. We therefore conclude that although deletion of the pp65 gene does not abolish replication of HCMV, a recombinant virus lacking pp65 displays phenotypic alterations compared with wild-type virus during growth in cultured fibroblasts.

Base Sequence↗
PubMed1993

Stable expression of the transfected HIV-1 env gene in a human B cell line: characterization of gp120-expressing clones and immunobiological studies.

The env gene of human immunodeficiency virus type 1 (HIV-1) encodes gp 120/41 which plays an important role in the viral infection process and pathogenesis. The surface glycoprotein gp120 is a candidate molecule for the development of a subunit vaccine against HIV-1-induced acquired immunodeficiency syndrome (AIDS). However, thorough studies on the immunobiology of this molecule are hampered by the lack of a suitable model. With this background in mind, and in order to learn more on anti-gp120 cellular immunity, we attempted to develop gp120-expressing human cell clones. Thus by transfecting a human lymphoid cell line of B lineage (Raji), which is known to be resistant to the natural killer cell activity, with an expression vector encoding the envelope and vpu, we established three clones that stably express gp120/41 and vpu. The surface glycoprotein gp 120 is also expressed on the cell surface of these clones. The transfected cells from syncytia with CD4+ human cell lines as well as with peripheral blood mononuclear cells (PBMC) leading to the death of the fused cells. This observation represents additional evidence for the eventual depletion of CD4+ viral targets that fuse with adjacent HIV-infected, gp 120-expressing cells. The latent Epstein-Barr virus genome present in the transfected cells, was not induced to express the lytic cycle antigens. The densities of the surface expression of a number of molecules examined remained unchanged in the transfected cells except for the surface IgM, which increased significantly (P < 0.05) in two clones. One of the clones exhibited a significantly (P < 0.05) reduced proliferation rate as compared to the other clones. The transfected cells of all the three clones showed a significantly (P < 0.01) increased susceptibility to lysis by the PBMC from normal, healthy individuals in a 16-hr 51Cr-release assay. This is the first report of the MHC- and antibody-independent lysis of human cells transfected with the HIV-1 surface glycoprotein. The transfected cells also served as targets in a gp120-specific antibody-dependent cellular cytotoxicity assay. We anticipate that the present model will prove very useful for studying the gp120-specific immune responses in HIV-infected individuals.

Acquired Immunodeficiency Syndrome↗
PubMed2001

Human neuron-committed teratocarcinoma NT2 cell line has abnormal ND10 structures and is poorly infected by herpes simplex virus type 1.

Herpes simplex virus type 1 (HSV-1) immediate-early regulatory protein ICP0 stimulates the initiation of lytic infection and reactivation from quiescence in human fibroblast cells. These functions correlate with its ability to localize to and disrupt centromeres and specific subnuclear structures known as ND10, PML nuclear bodies, or promyelocytic oncogenic domains. Since the natural site of herpesvirus latency is in neurons, we investigated the status of ND10 and centromeres in uninfected and infected human cells with neuronal characteristics. We found that NT2 cells, a neuronally committed human teratocarcinoma cell line, have abnormal ND10 characterized by low expression of the major ND10 component PML and no detectable expression of another major ND10 antigen, Sp100. In addition, PML is less extensively modified by the ubiquitin-like protein SUMO-1 in NT2 cells compared to fibroblasts. After treatment with retinoic acid, NT2 cells differentiate into neuron-like hNT cells which express very high levels of both PML and Sp100. Infection of both NT2 and hNT cells by HSV-1 was poor compared to human fibroblasts, and after low-multiplicity infection yields of virus were reduced by 2 to 3 orders of magnitude. ICP0-deficient mutants were also disabled in the neuron-related cell lines, and cells quiescently infected with an ICP0-null virus could be established. These results correlated with less-efficient disruption of ND10 and centromeres induced by ICP0 in NT2 and hNT cells. Furthermore, the ability of ICP0 to activate gene expression in transfection assays in NT2 cells was poor compared to Vero cells. These results suggest that a contributory factor in the reduced HSV-1 replication in the neuron-related cells is inefficient ICP0 function; it is possible that this is pertinent to the establishment of latent infection in neurons in vivo.

Cell Differentiation↗
PubMed2004

Cell culture propagation and biochemical analysis of the Ljungan virus prototype strain.

Ljungan virus (LV) is proposed as a potentially important rodent harbored viral human pathogen. Little is known about the biophysical nature of the virus and despite being molecularly characterized, progress in epidemiological and basic biological studies of LV has been hampered by the lack of a robust and reliable cell culture propagation system. Here we report the first description of an efficient lytic multi-cycle cell culture propagation of the LV prototype strain (87-012). Biophysical analysis of gradient purified LV virions generated by this system identified mature infectious virions to possess a sedimentation coefficient of 160S and in agreement with previous molecular prediction, polyprotein analysis suggests that the native virion is composed of only three major structural proteins. The nucleotide composition of the complete genome of the LV cell culture adapted virus was determined and compared to that of the parental prototype LV. Numerous mutations were observed scattered throughout the viral genome and particularly in VP1. The development of this cell culture system for LV should open new avenues in the study of LV biology, structure, pathogenesis, and prevalence of natural infection in the wider community.

Animals↗
PubMed2002

Perspectives in studies of human tumor viruses.

Tumor viruses can be found in both the RNA and DNA virus kingdoms. All RNA tumor viruses belong to the retrovirus family. Directly transforming Class I RNA tumor viruses carry cellular oncogenes, picked up by accidental recombination, and usually selected for secondary modifications and high tumorigenicity by the investigator. They are not known to play any role for tumor causation in nature. Class II or chronic RNA tumor viruses do not carry cell-derived oncogenes but they often act by proviral DNA insertion into the immediate neighborhood of a cellular oncogene. Feline, murine, and avian leukemia viruses belong to this category. The human adult T-cell leukemia virus, (HTLV-1) and bovine leukemia virus (BLV) act by expanding the preneoplastic cell population and thereby provides the soil for secondary, cellular changes. The DNA tumor viruses belong to three very different categories, the papovaviruses, adenoviruses and herpesviruses. Inactivation of the Rb and the p53 pathway by the viral transforming proteins is a convergent feature of the papova- and the adenoviruses. Since all DNA tumor viruses kill their host cell following their entry into the lytic phase, transformation and tumorigenicity are entirely dependent on a non-lytic interaction. Cells transformed by DNA tumor viruses depend on the continued expression of the virally encoded oncogene. They provide thereby a convenient target for the immune surveillance of the host. Depending on the epidemiological history of the virus in relation to its natural host species, the immune surveillance of the host and the strategy of viral latency and survival can evolve into a truly symbiotic relationship, as best illustrated by the Epstein-Barr virus (EBV). Tumor development occurs only as an accident at the level of the host (immunosuppression) or the cell (specific translocations or other genetic changes). The list of human viruses presently known to cause or to contribute to tumor development comprise four DNA viruses, namely Epstein-Barr virus, certain human papilloma viruses subtypes, hepatitis B virus, and Kaposi sarcoma herpesvirus (HHV-8); and two RNA viruses, adult T-cell leukemia virus (HTLV-1) and hepatitis virus C.

Animals↗