13 research outputs found
Study of GBF1-Arf signaling pathway during viral replication
Depuis une dĂ©cennie, GBF1 a Ă©mergĂ© comme Ă©tant un facteur cellulaire essentiel Ă la rĂ©plication de plusieurs virus Ă ARN de polaritĂ© positive (ARN(+)), issus de diffĂ©rentes familles. GBF1 est un facteur dâĂ©change nuclĂ©otidique de petites protĂ©ines G de la famille Arf, connu pour son action rĂ©gulatrice des Ă©tapes prĂ©coces de la voie de sĂ©crĂ©tion. En Ă©tudiant le virus de lâhĂ©patite C (VHC) comme virus modĂšle, nous avons montrĂ© que le rĂŽle de GBF1 dans la rĂ©plication virale est distinct de sa fonction rĂ©gulatrice de la voie de sĂ©crĂ©tion. En effet,GBF1 participe Ă la rĂ©plication du VHC par lâintermĂ©diaire de la paire Arf4 et Arf5, alors que câest la paire Arf1et Arf4 qui est impliquĂ©e dans la voie sĂ©crĂ©tion. Pour dĂ©terminer si ce mĂ©canisme dâaction est conservĂ© parmi les virus Ă ARN(+), nous avons dâabord montrĂ© que GBF1 est impliquĂ©e dans lâinfection par le virus de la fiĂšvre jaune (YFV), le virus sindbis (SINV), le coronavirus 229E humain (HCoV-229E) et le coxsackievirus B4(CVB4). Puis, nos rĂ©sultats indiquent que les infections YFV, SINV et HCoV-229E dĂ©pendent, tout comme le VHC, des protĂ©ines Arf4 et Arf5. Toutefois, le YFV et le SINV utiliseraient Ă©galement une autre paire dâArf,Arf1 et Arf4, lors de leur cycle viral. Par ailleurs, lâinfection par le coxsackievirus B4 (CVB4) est dĂ©pendante de GBF1 mais ne semble pas dĂ©pendre des protĂ©ines Arf. Bien que GBF1 soit un facteur crucial pour la rĂ©plication des virus ARN(+), son mĂ©canisme dâaction ne semble donc pas ĂȘtre conservĂ©.La paire Arf4-Arf5 semble impliquĂ©e dans la rĂ©plication de plusieurs virus Ă ARN(+). Cependant, ces deux Arf ont Ă©tĂ© trĂšs peu Ă©tudiĂ©es, contrairement Ă la protĂ©ine Arf1. Nous faisons lâhypothĂšse que la paire Arf4-Arf5 agit en rĂ©gulant une sĂ©rie dâeffecteurs spĂ©cifiques qui sont importants pour la rĂ©plication virale. Nos rĂ©sultats montrent que la dĂ©plĂ©tion simultanĂ©e de Arf4 et de Arf5 perturbe la morphologie de lâappareil de Golgi, qui devient condensĂ©, et des gouttelettes lipidiques (GL), qui sâaccumulent et grossissent en pĂ©riphĂ©rie cellulaire.Toutefois, une analyse lipidomique de cellules dĂ©plĂ©tĂ©es de Arf4 et Arf5 montre une composition lipidique inchangĂ©e, ce qui suggĂšre un effet sur la morphologie des GL et non pas sur le mĂ©tabolisme des lipides. Une analyse transcriptomique nous a permis de mettre en Ă©vidence une sĂ©rie de protĂ©ines, dont lâexpression est modulĂ©e, suite Ă la dĂ©plĂ©tion de Arf4 et Arf5. Nous avons Ă©valuĂ© lâimplication potentielle de certaines dâentre elles dans lâinfection du VHC, mais aucune ne sâest rĂ©vĂ©lĂ©e importante pour ce virus. En conclusion, nos rĂ©sultats ont permis de mettre en Ă©vidence de nouvelles fonctions de GBF1, mĂ©diĂ©es par la paire de protĂ©ines Arf4 et Arf5. Arf4 et Arf5 sont impliquĂ©es dans la rĂ©gulation de la morphologie de lâappareil de Golgi et des GL ainsi que dans la rĂ©plication de plusieurs virus Ă ARN(+). Il reste Ă Ă©valuer si ces fonctions sont indĂ©pendantes les unes des autres ou liĂ©es entre elles et quels effecteurs spĂ©cifiques elles font intervenir.GBF1 has recently emerged as a cellular factor essential for the replication of single-stranded positive-sense RNA ((+)RNA) viruses from different families. GBF1 is a guanine-nucleotide exchange factor of small G proteins of the Arf family, known to regulate the early secretory pathway. By studying the hepatitis C virus (HCV) as a model, we have shown that the role of GBF1 in viral replication is distinct from its regulatoryfunction of the sercretory pathway. Indeed, GBF1 function in HCV replication is mediated by Arf4 and Arf5,whereas another pair, Arf1 and Arf4, mediates the regulation of the secretion. To determine if this mechanism ofaction is conserved among (+)RNA viruses, we showed that GBF1 is involved in yellow fever virus (YFV),sindbis virus (SINV), human coronavirus 229E (HCoV-229E) and coxsackievirus B4 (CVB4) infection. Our results indicate that YFV, SINV and HCoV-229E infections are Arf4 and Arf5 dependent, as we previouslyshowed for HCV. However, YFV and SINV would also use another Arf pair, Arf1 and Arf4, during their lifecycle. In addition, CVB4 infection depends on GBF1, but doesnât seem to depend on any Arf. Although GBF1 is required for (+)RNA viruses replication, its mechanism of action appears not to be conserved.The Arf4-Arf5 pair appears to be involved in the replication of several (+)RNA viruses. However, these twoproteins have been poorly studied so far, contrary to Arf1. Our hypothesis is that the Arf4-Arf5 pair regulatesspecific effectors involved in viral replication. Our results indicate that Arf4 and Arf5 simultaneous depletionalters the morphology of the Golgi apparatus, which becomes condense, and of lipid droplets (LD), whichaccumulate and grow bigger at the cell periphery. However, a lipidomic analysis of Arf4 and Arf5 depleted cellsdisplayed an unaltered lipid composition, which suggests a morphologic impact on LD, rather than a disruptionof the lipid metabolism. A transcriptomic analysis identified proteins up- or down-regulated after Arf4 and Arf5 depletion. We assessed the function of some of these proteins in HCV replication, but none of them proved implicated.In conclusion, our results hightlighed new GBF1 functions, mediated by the pair Arf4-Arf5. Arf4 and Arf5 are involved in regulating the morphology of Golgi complex and of LDs, as well as the replication of (+) RNA viruses. It remains to assess if these functions are independent or related to each other, and which specific effectors they use
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Investigation of the role of GBF1 in the replication of positive-sense single-stranded RNA viruses
International audienceGBF1 has emerged as a host factor required for the replication of positive-sense single-stranded RNA viruses of different families, but its mechanism of action is still unknown. GBF1 is a guanine nucleotide exchange factor for Arf family members. Recently, we identified Arf4 and Arf5 (class II Arfs) as host factors required for the replication of hepatitis C virus (HCV), a GBF1-dependent virus. To assess whether a GBF1/class II Arf pathway is conserved among positive-sense single-stranded RNA viruses, we investigated yellow fever virus (YFV), Sindbis virus (SINV), coxsackievirus B4 (CVB4) and human coronavirus 229E (HCoV-229E). We found that GBF1 is involved in the replication of these viruses. However, using siRNA or CRISPR-Cas9 technologies, it was seen that the depletion of Arf1, Arf3, Arf4 or Arf5 had no impact on viral replication. In contrast, the depletion of Arf pairs suggested that class II Arfs could be involved in HCoV-229E, YFV and SINV infection, as for HCV, but not in CVB4 infection. In addition, another Arf pair, Arf1 and Arf4, appears to be essential for YFV and SINV infection, but not for infection by other viruses. Finally, CVB4 infection was not inhibited by any combination of Arf depletion. We conclude that the mechanism of action of GBF1 in viral replication appears not to be conserved, and that a subset of positive-sense single-stranded RNA viruses from different families might require class II Arfs for their replication
Identification of class II ADP-ribosylation factors as cellular factors required for hepatitis C virus replication
International audienceGBF1 is a host factor required for hepatitis C virus (HCV) replication. GBF1 functions as a guanine nucleotide exchange factor for Gâproteins of the Arf family, which regulate membrane dynamics in the early secretory pathway and the metabolism of cytoplasmic lipid droplets. Here we established that the Arfâguanine nucleotide exchange factor activity of GBF1 is critical for its function in HCV replication, indicating that it promotes viral replication by activating one or more Arf family members. Arf involvement was confirmed with the use of two dominant negative Arf1 mutants. However, siRNAâmediated depletion of Arf1, Arf3 (class I Arfs), Arf4 or Arf5 (class II Arfs), which potentially interact with GBF1, did not significantly inhibit HCV infection. In contrast, the simultaneous depletion of both Arf4 and Arf5, but not of any other Arf pair, imposed a significant inhibition of HCV infection. Interestingly, the simultaneous depletion of both Arf4 and Arf5 had no impact on the activity of the secretory pathway and induced a compaction of the Golgi and an accumulation of lipid droplets. A similar phenotype of lipid droplet accumulation was also observed when GBF1 was inhibited by brefeldin A. In contrast, the simultaneous depletion of both Arf1 and Arf4 resulted in secretion inhibition and Golgi scattering, two actions reminiscent of GBF1 inhibition. We conclude that GBF1 could regulate different metabolic pathways through the activation of different pairs of Arf proteins