Characterization of the interaction between the HIV-1 Gag structural polyprotein and the cellular ribosomal protein L7 and its implication in viral nucleic acid remodeling

Background: In HIV-1 infected cells, the integrated viral DNA is transcribed by the host cell machinery to generate the full length HIV-1 RNA (FL RNA) that serves as mRNA encoding for the Gag and GagPol precursors. Virion formation is orchestrated by Gag, and the current view is that a specific interaction between newly made Gag molecules and FL RNA initiates the process. This in turn would cause FL RNA dimerization by the NC domain of Gag (GagNC). However the RNA chaperoning activity of unprocessed Gag is low as compared to the mature NC protein. This prompted us to search for GagNC co-factors. Results: Here we report that RPL7, a major ribosomal protein involved in translation regulation, is a partner of Gag via its interaction with the NC domain. This interaction is mediated by the NC zinc fingers and the N- and C-termini of RPL7, respectively, but seems independent of RNA binding, Gag oligomerization and its interaction with the plasma membrane. Interestingly, RPL7 is shown for the first time to exhibit a potent DNA/RNA chaperone activity higher than that of Gag. In addition, Gag and RPL7 can function in concert to drive rapid nucleic acid hybridization. Conclusions: Our results show that GagNC interacts with the ribosomal protein RPL7 endowed with nucleic acid chaperone activity, favoring the notion that RPL7 could be a Gag helper chaperoning factor possibly contributing to the start of Gag assembly.Instituto de Estudios Inmunológicos y Fisiopatológico

Glucose-Dependent Regulation of NR2F2 Promoter and Influence of SNP-rs3743462 on Whole Body Insulin Sensitivity

Background: The Nuclear Receptor 2F2 (NR2F2/COUP-TFII) heterozygous knockout mice display low basal insulinemia and enhanced insulin sensitivity. We previously established that insulin represses NR2F2 gene expression in pancreatic β-cells. The cis-regulatory region of the NR2F2 promoter is unknown and its influence on metabolism in humans is poorly understood. The present study aimed to identify the regulatory regions that control NR2F2 gene transcription and to evaluate the effect of NR2F2 promoter variation on glucose homeostasis in humans. Methodology/Principal Findings: Regulation of the NR2F2 promoter was assessed using gene reporter assays, ChIP and gel shift experiments. The effects of variation at SNP rs3743462 in NR2F2 on quantitative metabolic traits were studied in two European prospective cohorts. We identified a minimal promoter region that down-regulates NR2F2 expression by attenuating HNF4α activation in response to high glucose concentrations. Subjects of the French DESIR population, who carried the rs3743462 T-to-C polymorphism, located in the distal glucose-responsive promoter, displayed lower basal insulin levels and lower HOMA-IR index. The C-allele at rs3743462 was associated with increased NR2F2 binding and decreased NR2F2 gene expression. Conclusions/Significance: The rs3743462 polymorphism affects glucose-responsive NR2F2 promoter regulation and thereby may influence whole-body insulin sensitivity, suggesting a role of NR2F2 in the control of glucose homeostasis in humans. © 2012 Boutant et al

HIV-1 Vpr mediates the depletion of the cellular repressor CTIP2 to counteract viral gene silencing

Mammals have evolved many antiviral factors impacting different steps of the viral life cycle. Associated with chromatin-modifying enzymes, the cellular cofactor CTIP2 contributes to HIV-1 gene silencing in latently infected reservoirs that constitute the major block toward an HIV cure. We report, for the first time, that the virus has developed a strategy to overcome this major transcriptional block. Productive HIV-1 infection results in a Vpr-mediated depletion of CTIP2 in microglial cells and CD4+ T cells, two of the major viral reservoirs. Associated to the Cul4A-DDB1-DCAF1 ubiquitin ligase complex, Vpr promotes CTIP2 degradation via the proteasome pathway in the nuclei of target cells and notably at the latent HIV-1 promoter. Importantly, Vpr targets CTIP2 associated with heterochromatin-promoting enzymes dedicated to HIV-1 gene silencing. Thereby, Vpr reactivates HIV-1 expression in a microglial model of HIV-1 latency. Altogether our results suggest that HIV-1 Vpr mediates the depletion of the cellular repressor CTIP2 to counteract viral gene silencing.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

A Family of Plasmodesmal Proteins with Receptor-Like Properties for Plant Viral Movement Proteins

Plasmodesmata (PD) are essential but poorly understood structures in plant cell walls that provide symplastic continuity and intercellular communication pathways between adjacent cells and thus play fundamental roles in development and pathogenesis. Viruses encode movement proteins (MPs) that modify these tightly regulated pores to facilitate their spread from cell to cell. The most striking of these modifications is observed for groups of viruses whose MPs form tubules that assemble in PDs and through which virions are transported to neighbouring cells. The nature of the molecular interactions between viral MPs and PD components and their role in viral movement has remained essentially unknown. Here, we show that the family of PD-located proteins (PDLPs) promotes the movement of viruses that use tubule-guided movement by interacting redundantly with tubule-forming MPs within PDs. Genetic disruption of this interaction leads to reduced tubule formation, delayed infection and attenuated symptoms. Our results implicate PDLPs as PD proteins with receptor-like properties involved the assembly of viral MPs into tubules to promote viral movement

Characterisation of interactions between the movement protein (MP) of Tobacco mosaic virus and cellulars factors and analysis of the targeting of the MP to plasmodesmata

Le virus de la mosaïque du tabac possède un génome d'ARN codant pour quatre protéines dont la MP. Lors de la virose, la MP:GFP s'accumule au niveau des plasmodesmes (pd), du réticulum endoplasmique et des microtubules (MT). L'essentiel des résultats décrits dans ce mémoire concernent la caractérisation de l'association de la MP avec les MT notamment le mécanisme d'association de la MP, l'influence sur la dynamique des MT, l'incidence sur la division cellulaire, l'oligomérisation de la MP, la caractérisation d'interactions in vivo et in vitro de la MP avec des facteurs cellulaires comme la protéine End Binding 1, les protéines du complexe de nucléation ou encore la MAP65.5. Nous nous sommes également intéressés à l'implication de la voie de sécrétion dans le mécanisme d'adressage de la MP aux pd. Il apparaît que l'adressage de la MP aux pd est indépendant du système de sécrétion qui serait plutôt impliqué dans la formation des corps d'inclusion servant à la réplication virale.The RNA genome of Tobacco mosaic virus encodes four proteins of which one is the movement protein (MP). MP accumulates with plasmodesmata (pd), with the endoplasmic reticulum (ER) and microtubules (MT). In this manuscript we therefore focused on the following aspects: 1.Characterisation of the association of MP with MTs. We demonstrate that MP is recruited to MTs by a lateral anchoring mechanism in a multimeric state. We show that MT-associated MP protects MTs in vivo against destabilizing agents but, binding of MP to mitotic MTs does not affect mitosis. Our analysis of the in vitro and in vivo interactions between MP and the MT-EndBinding protein1 show that MP alters EB1 localisation and dynamics. We also demonstrate that MP interacts with proteins from the MTs nucleation complex. 2.Analysis of MP transport to pd. We investigated whether Pd-targeting of MP involves the secretory pathway and demonstrate, that the targeting of MP to pd is independent of a functional secretory pathway

Characterisation of interactions between the movement protein (MP) of Tobacco mosaic virus and cellulars factors and analysis of the targeting of the MP to plasmodesmata

Le virus de la mosaïque du tabac possède un génome d'ARN codant pour quatre protéines dont la MP. Lors de la virose, la MP:GFP s'accumule au niveau des plasmodesmes (pd), du réticulum endoplasmique et des microtubules (MT). L'essentiel des résultats décriThe RNA genome of Tobacco mosaic virus encodes four proteins of which one is the movement protein (MP). MP accumulates with plasmodesmata (pd), with the endoplasmic reticulum (ER) and microtubules (MT). In this manuscript we therefore focused on the foll

Interaction of the Tobacco mosaic virus movement protein with microtubules during the cell cycle in tobacco BY-2 cells

Cell-to-cell movement of Tobacco mosaic virus (TMV) involves the interaction of virus-encoded 30-kDa movement protein (MP) with microtubules. In cells behind the infection front that accumulate high levels of MP, this activity is reflected by the formation of stabilized MP/microtubule complexes. The ability of MP to bind along and stabilize microtubules is conserved upon expression in mammalian cells. In mammalian cells, the protein also leads to inhibition of mitosis and cell division through a microtubule-independent process correlated with the loss of centrosomal !-tubulin and of centrosomal microtubulenucleation activity. Since MP has the capacity to interact with plant factors involved in microtubule nucleation and dynamics, we used inducible expression in BY-2 cells to test whether MP expression inhibits mitosis and cell division also in plants. We demonstrate that MP:GFP associates with all plant microtubule arrays and, unlike in mammalian cells, does not interfere with mitosis. Thus, MP function and the interaction of MP with factors of the cytoskeleton do not entail an inhibition of mitosis in plants. We also report that the protein targets primary plasmodesmata in BY-2 cells immediately upon or during cytokinesis and that the accumulation of MP in plasmodesmata occurs in the presence of inhibitors of the cytoskeleton and the secretory pathway