Reduced levels of reactive oxygen species correlate with inhibition of apoptosis, rise in thioredoxin expression and increased bovine leukemia virus proviral loads

BACKGROUND: Bovine Leukemia virus (BLV) is a deltaretrovirus that induces lymphoproliferation and leukemia in ruminants. In ex vivo cultures of B lymphocytes isolated from BLV-infected sheep show that spontaneous apoptosis is reduced. Here, we investigated the involvement of reactive oxygen species (ROS) in this process. RESULTS: We demonstrate that (i) the levels of ROS and a major product of oxidative stress (8-OHdG) are reduced, while the thioredoxin antioxidant protein is highly expressed in BLV-infected B lymphocytes, (ii) induction of ROS by valproate (VPA) is pro-apoptotic, (iii) inversely, the scavenging of ROS with N-acetylcysteine inhibits apoptosis, and finally (iv) the levels of ROS inversely correlate with the proviral loads. CONCLUSION: Together, these observations underline the importance of ROS in the mechanisms of inhibition of apoptosis linked to BLV infection

Mechanisms of leukemogenesis induced by bovine leukemia virus: prospects for novel anti-retroviral therapies in human

In 1871, the observation of yellowish nodules in the enlarged spleen of a cow was considered to be the first reported case of bovine leukemia. The etiological agent of this lymphoproliferative disease, bovine leukemia virus (BLV), belongs to the deltaretrovirus genus which also includes the related human T-lymphotropic virus type 1 (HTLV-1). This review summarizes current knowledge of this viral system, which is important as a model for leukemogenesis. Recently, the BLV model has also cast light onto novel prospects for therapies of HTLV induced diseases, for which no satisfactory treatment exists so far

Etude du rôle des gènes accessoires nef, vpr et vpx du virus de l'immunodéficience simienne (SIV) dans le modèle du virus de l'arthrite et de l'encéphalite caprine (CAEV)

Les Virus de l'Immunodéficience Humaine (HIV) et Simienne (SIV), agents étiologiques du SIDA sont des lentivirus appartenant à la famille des rétrovirus. Il existe chez la chèvre un lentivirus : Virus de l'Arthrite et de l'Encéphalite Caprine (CAEV) apparenté au HIV et SIV qui ne cause pas d'immunodéficience. Cette propriété est en corrélation avec son tropisme restreint aux monocytes/macrophages et sa structure génomique simple caractérisée par l'absence des gènes accessoires nef, vpr, vpx et vpu présents uniquement dans le génome du HIV et SIV. L'objectif de nos travaux a été de développer un modèle d'étude des fonctions des gènes nef, vpr et vpx. Notre stratégie a comporté d'abord la construction de génomes recombinants à base du CAEV portant le gène nef ou vpr/vpx du SIV. Les virus recombinants CAEVnef et CAEVvpxvpr restent réplicatifs et acquièrent des propriétés cytopathogènes exacerbées. Les protéines Vpx/Vpr du SIV induisent l'arrêt des cellules caprines en phase G2 du cycle cellulaire. Par ailleurs, elles induisent l'apoptose des lymphocytes de chèvre en dépit de l'absence de leur infection. Quant à la protéine Nef, elle induit la diminution de l'expression des molécules CD4 et CMH-I à la surface des lymphocytes. Nef induit également l'activation des PBMC de chèvre associée à une augmentation de leur prolifération. Enfin, Nef exerce un rôle apoptotique double, puisqu'elle protége les lymphocytes de l'apoptose, puis elle induit leur mort apoptotique et ce, en fonction du stade de l'infection. Toutes ces actions sont observées en l'absence de l'infection des lymphocytes par CAEVnef. Notre hypothèse de travail implique donc une voie de signalisation extracellulaire activée par Nef ou Vpr/Vpx pour induire les effets observés. Ainsi, nous avons développé un modèle unique permettant d'étudier d'une manière aisée les fonctions non encore explorées des gènes accessoires impliquées dans l'altération fonctionnelle des cellules non infectées.LYON1-BU Santé (693882101) / SudocPARIS-BIUP (751062107) / SudocSudocFranceF

Maedi-visna virus and caprine arthritis encephalitis virus genomes encode a Vpr-like but no Tat protein

A small open reading frame (ORF) in maedi-visna virus (MVV) and caprine arthritis encephalitis virus (CAEV) was initially named “tat” by analogy with a similarly placed ORF in the primate lentiviruses. The encoded “Tat” protein was ascribed the function of up regulation of the viral transcription from the long terminal repeat (LTR) promoter, but we have recently reported that MVV and CAEV Tat proteins lack trans-activation function activity under physiological conditions (S. Villet, C. Faure, B. Bouzar, G. Verdien, Y. Chebloune, and C. Legras, Virology 307:317-327, 2003). In the present work, we show that MVV Tat localizes to the nucleus of transfected cells, probably through the action of a nuclear localization signal in its C-terminal portion. We also show that, unlike the human immunodeficiency virus (HIV) Tat protein, MVV Tat was not secreted into the medium by transfected human or caprine cells in the absence of cell lysis but that, like the primate accessory protein Vpr, MVV and CAEV Tat proteins were incorporated into viral particles. In addition, analysis of the primary protein structures showed that small-ruminant lentivirus (SRLV) Tat proteins are more similar to the HIV type 1 (HIV-1) Vpr protein than to HIV-1 Tat. We also demonstrate a functional similarity between the SRLV Tat proteins and the HIV-1 Vpr product in the induction of a specific G(2) arrest of the cell cycle in MVV Tat-transfected cells, which increases the G(2)/G(1) ratio 2.8-fold. Together, these data strongly suggest that the tat ORF in the SRLV genomes does not code for a regulatory transactivator of the LTR but, rather, for a Vpr-like accessory protein

Rôle des protéines Vpr et Vpx des lentivirus (SIV et HIV) dans les mort des lymphocytes T non infectés

National audienc

A Single Envelope N-linked Glycosylation Site Defines Hyperpathogenicity of Bovine Leukemia Virus

Pathogens have co-evolved with their host to allow efficient replication and transmission without inducing excessive pathogenicity that would indirectly impair their persistence. This is exemplified by the bovine leukemia virus (BLV) model that induces lymphoproliferative disorders in ruminants only after extended latency periods of several years. In principle, the equilibrium reached between the virus and its host could be disrupted by emergence of more pathogenic strains. Intriguingly, this type of hyperpathogenic BLV strain could never been isolated in vivo nor designed in vitro. Using reverse genetics of an infectious molecular provirus, we have now identified a N-linked envelope glycosylation site that limits viral replication and pathogenicity. Onset of this particular mutation may thus represent a potential threat associated with emergence of hyperpathogenic BLV strains and possibly of new variants of the related primate T-lymphotropic viruses

Hyper-replicative bovine leukemia virus by mutation of an envelope N-linked glycosylation site

Reverse genetics can be used in the bovine leukemia virus (BLV) system to characterize mechanisms of viral persistence and pathogenesis. The question addressed here pertains to the role of glycans bound to the BLV envelope glycoprotein (SU). A commonly accepted hypothesis is that addition of carbohydrates to the SU protein potentially creates a structure called « glycan shield » that confers resistance to the virus against the host immune response. On the other hand, glycosylation can also modulate attachment of the virus to the cell membrane. To unravel the role of SU glycosylation, three complementary strategies were developed: pharmacological inhibition of different glycosylation pathways, interference with glycan attachment and site-directed mutagenesis of N-glycosylation sites in an infectious BLV provirus. The different approaches show that glycosylation is required for cell fusion, as expected. Simultaneous mutation of all 8 potential N-glycosylation sites destroys infectivity. Surprisingly, mutation of the asparagine residue at position 230 creates a virus having an increased capacity to form syncytia in vitro. Compared to wild-type BLV, mutant N230 also replicates at accelerated rates in vivo. Collectively, this data thus illustrates an example of a N-glycosylation site that restricts viral replication, contrasting with the hypothesis supported by glycan shield model

Bovine but not porcine are productively experimentally infected with caprine arthritis encephalitis virus (CAEV)

National audienc

Mutation of a Single Envelope N-linked Glycosylation Site Enhances the Pathogenicity of Bovine Leukemia Virus

Viruses have co-evolved with their host to ensure efficient replication and transmission without inducing excessive pathogenicity that would indirectly impair their persistence. This is exemplified by the bovine leukemia virus (BLV) system in which lymphoproliferative disorders develop in ruminants after latency periods of several years. In principle, the equilibrium reached between the virus and its host could be disrupted by emergence of more pathogenic strains. Intriguingly but fortunately, such a hyperpathogenic BLV strain was never observed in the field nor designed in vitro. In this study, we aimed at understanding the role of envelope N-linked glycosylation with the hypothesis that this posttranslational modification could either favor BLV infection by allowing viral entry or allow immune escape by using glycans as a shield. Using reverse genetics of an infectious molecular provirus, we have identified a N-linked envelope glycosylation site (N230) that limits viral replication and pathogenicity. Indeed, mutation N230E unexpectedly leads to enhanced fusogenicity and protein stability. Occurrence of this mutation may thus represent a potential threat associated with emergence of hyperpathogenic BLV strains and possibly of new variants of the related primate T-lymphotropic viruses