generation-amplification-titration-recombinant-respiratory-syncytial

Generation, Amplification, and Titration of Recombinant Respiratory Syncytial Viruses

The use of recombinant viruses has become crucial in basic or applied virology. Reverse genetics has been proven to be an extremely powerful technology, ...

Université de Versailles St. Quentin

In this study, we have compared several features of cell death triggered by classical inducers of apoptotic pathways (etoposide and tumour necrosis factor (TNF)-α) versus exogenous reactive oxygen species (ROS; hydrogen peroxide (H₂O₂), tert-butyl hydroperoxide (t-BHP)) or a ROS generator (paraquat). Our aim was to characterize relationships that exist between ROS, mitochondrial perturbations, Bcl-2 and caspases, depending on source and identity of ROS. First, we have found that these five inducers trigger oxidative stress, mitochondrial membrane permeabilization (MMP), cytochrome c (cyt c) release from mitochondria and cell death. In each case, cell death could be inhibited by several antioxidants, showing that it is primarily ROS dependent. Second, we have highlighted that during etoposide or TNF-α treatments, intracellular ROS level, MMP and cell death are all regulated by caspases and Bcl-2, with caspases acting early in the process. Third, we have demonstrated that H₂O₂-induced cell death shares many of these characteristics with etoposide and TNF-α, whereas t-BHP induces both caspase-dependent and caspase-independent cell death. Surprisingly, paraquat-induced cell death, which harbours some characteristics of apoptosis such as cyt c release and caspase-3 activation, is not modulated by Bcl-2 and caspase inhibitors, suggesting that paraquat also triggers non-apoptotic cell death signals. On the one hand, these results show that endogenous or exogenous ROS can trigger multiple cell death pathways with Bcl-2 and caspases acting differentially. On the other hand, they suggest that H₂O₂ could be an important mediator of etoposide and TNF-α-dependent cell death since these inducers trigger similar phenotypes.

Differential effects of Bcl-2 and caspases on mitochondrial permeabilization during endogenous or exogenous reactive oxygen species-induced cell death: a comparative study of H₂O₂, paraquat, t-BHP, etoposide and TNF-α-induced cell death.

Infection of cells by respiratory syncytial virus induces the formation of cytoplasmic inclusion bodies (IBs) where all the components of the viral RNA polymerase complex are concentrated. However, the exact organization and function of these IBs remain unclear. In this study, we use conventional and super-resolution imaging to dissect the internal structure of IBs. We observe that newly synthetized viral mRNA and the viral transcription anti-terminator M2-1 concentrate in IB sub-compartments, which we term "IB-associated granules" (IBAGs). In contrast, viral genomic RNA, the nucleoprotein, the L polymerase and its cofactor P are excluded from IBAGs. Live imaging reveals that IBAGs are highly dynamic structures. Our data show that IBs are the main site of viral RNA synthesis. They further suggest that shortly after synthesis in IBs, viral mRNAs and M2-1 transiently concentrate in IBAGs before reaching the cytosol and suggest a novel post-transcriptional function for M2-1.Respiratory syncytial virus (RSV) induces formation of inclusion bodies (IBs) sheltering viral RNA synthesis. Here, Rincheval et al. identify highly dynamic IB-associated granules (IBAGs) that accumulate newly synthetized viral mRNA and the viral M2-1 protein but exclude viral genomic RNA and RNA polymerase complexes.

Functional organization of cytoplasmic inclusion bodies in cells infected by respiratory syncytial virus.

Respiratory syncytial virus (RSV) RNA synthesis occurs in cytoplasmic inclusion bodies (IBs) in which all the components of the viral RNA polymerase are concentrated. In this work, we show that RSV P protein recruits the essential RSV transcription factor M2-1 to IBs independently of the phosphorylation state of M2-1. We also show that M2-1 dephosphorylation is achieved by a complex formed between P and the cellular phosphatase PP1. We identified the PP1 binding site of P, which is an RVxF-like motif located nearby and upstream of the M2-1 binding region. NMR confirmed both P-M2-1 and P-PP1 interaction regions in P. When the P-PP1 interaction was disrupted, M2-1 remained phosphorylated and viral transcription was impaired, showing that M2-1 dephosphorylation is required, in a cyclic manner, for efficient viral transcription. IBs contain substructures called inclusion bodies associated granules (IBAGs), where M2-1 and neo-synthesized viral mRNAs concentrate. Disruption of the P-PP1 interaction was correlated with M2-1 exclusion from IBAGs, indicating that only dephosphorylated M2-1 is competent for viral mRNA binding and hence for a previously proposed post-transcriptional function.

Article	Year
Differential effects of Bcl-2 and caspases on mitochondrial permeabilization during endogenous or exogenous reactive oxygen species-induced cell death: a comparative study of H₂O₂, paraquat,... Cell biology and toxicology\| PubMed ID: 22491967	2012
Functional organization of cytoplasmic inclusion bodies in cells infected by respiratory syncytial virus. Nature communications\| PubMed ID: 28916773	2017
RSV hijacks cellular protein phosphatase 1 to regulate M2-1 phosphorylation and viral transcription. PLoS pathogens\| PubMed ID: 29489893	2018

Vincent Rincheval

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