Retinoic Acid-Inducible Gene I Mediates Early Antiviral Response and Toll-Like Receptor 3 Expression in Respiratory Syncytial Virus-Infected Airway Epithelial Cells

Departments of Medicine, University of Texas Medical Branch, Galveston, Texas 77555-1060, USA.
Journal of Virology (Impact Factor: 4.44). 03/2007; 81(3):1401-11. DOI: 10.1128/JVI.01740-06
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Respiratory syncytial virus (RSV) is one of the most common viral pathogens causing severe lower respiratory tract infections in infants and young children. Infected host cells detect and respond to RNA viruses using different mechanisms in a cell-type-specific manner, including retinoic acid-inducible gene I (RIG-I)-dependent and Toll-like receptor (TLR)-dependent pathways. Because the relative contributions of these two pathways in the recognition of RSV infection are unknown, we examined their roles in this study. We found that RIG-I helicase binds RSV transcripts within 12 h of infection. Short interfering RNA (siRNA)-mediated RIG-I "knockdown" significantly inhibited early nuclear factor-kappaB (NF-kappaB) and interferon response factor 3 (IRF3) activation 9 h postinfection (p.i.). Consistent with this finding, RSV-induced beta interferon (IFN-beta), interferon-inducible protein 10 (IP-10), chemokine ligand 5 (CCL-5), and IFN-stimulated gene 15 (ISG15) expression levels were decreased in RIG-I-silenced cells during the early phase of infection but not at later times (18 h p.i.). In contrast, siRNA-mediated TLR3 knockdown did not affect RSV-induced NF-kappaB binding but did inhibit IFN-beta, IP-10, CCL-5, and ISG15 expression at late times of infection. Further studies revealed that TLR3 knockdown significantly reduced NF-kappaB/RelA transcription by its ability to block the activating phosphorylation of NF-kappaB/RelA at serine residue 276. We further found that TLR3 induction following RSV infection was regulated by RIG-I-dependent IFN-beta secreted from infected airway epithelial cells and was mediated by both IFN response-stimulated element (ISRE) and signal transducer and activator of transcription (STAT) sites in its proximal promoter. Together these findings indicate distinct temporal roles of RIG-I and TLR3 in mediating RSV-induced innate immune responses, which are coupled to distinct pathways controlling NF-kappaB activation.

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    • "phase, RSV replication evokes retinoic acid inducible gene-I (RIG-I) to mediate the early antiviral response, and Toll-like receptor 3 (TLR3) to mediate chemokine expression in airway epithelial cells (Le Goffic et al., 2007; Liu et al., 2007; Oshansky et al., 2009). To avoid clearance, the virus adopts certain strategies to subvert the host's antiviral response, including upregulation of suppressor of cytokine signaling (SOCS) proteins, which negatively regulate interferon (IFN)-dependent signaling pathways (Vlotides et al., 2004; Pothlichet et al., 2008; Hashimoto et al., 2009). "
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    ABSTRACT: HEp-2 cells persistently infected with respiratory syncytial virus (RSV) are a heterogeneous mixture of viral antigen-positive and -negative variants; however, the mechanism through which viral replication becomes latent remains unclear. In this study, we investigated the potential mechanism by which RSV escapes from innate immune surveillance. Persistent-infected RSV HEp- 2 cells were isolated and cell clones were passaged. The RSV-persistent cells produced viruses at a lower titer, resisted wild-type RSV re-infection, and secreted high levels of interferon-β (IFN-β), macrophage inflammatory protein-1α (Mip-1α), interleukin-8 (IL-8), and Rantes. Toll-like receptor 3 (TLR3), retinoic acid inducible gene-I (RIG-I), and suppressor of cytokine signaling 1 (SOCS1) levels were upregulated in these cells. The silencing of TLR3 mRNA decreased the expression of SOCS1 protein and the secretion of cytokines. RSV-persistent cells are in an inflammatory state; upregulation of SOCS1 is related to the TLR3 signaling pathway, which could be associated with the mechanism of viral persistence.
    Virologica Sinica 06/2015; 30(3):190-199.
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    • "TLRs convert pathogen recognition to active cellular responses through a complex network of intracellular molecules leading to the activation of transcription factors collaborating with each other to produce a large number of cytokines and co-stimulatory molecules, and the combination of signals produced in response to infection is dependent on the TLRs activated. Both RSV and hMPV have been shown to activate TLR4 in primary immune cells [74]–[77]; however, RSV has also been shown to mediate host immune responses through TLR3 dependent-signaling pathways [75], [78]–[80]. Moreover, BDCA-1+ and BDCA-3+ mDCs have been shown to express discreet TLR profiles [24], [81], [82] and differences in the way RSV interacts with each mDC subset may also underlie the subset-specific effect of RSV on mDC function. "
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    ABSTRACT: Respiratory syncytial virus (RSV) and human Metapneumovirus (hMPV), viruses belonging to the family Paramyxoviridae, are the most important causes of lower respiratory tract infection in young children. Infections with RSV and hMPV are clinically indistinguishable, and both RSV and hMPV infection have been associated with aberrant adaptive immune responses. Myeloid Dendritic cells (mDCs) play a pivotal role in shaping adaptive immune responses during infection; however, few studies have examined how interactions of RSV and hMPV with individual mDC subsets (BDCA-1+ and BDCA-3+ mDCs) affect the outcome of anti-viral responses. To determine whether RSV and hMPV induce virus-specific responses from each subset, we examined co-stimulatory molecules and cytokines expressed by BDCA-1+ and BDCA-3+ mDCs isolated from peripheral blood after infection with hMPV and RSV, and examined their ability to stimulate T cell proliferation and differentiation. Our data show that RSV and hMPV induce virus-specific and subset-specific patterns of co-stimulatory molecule and cytokine expression. RSV, but not hMPV, impaired the capacity of infected mDCs to stimulate T cell proliferation. Whereas hMPV-infected BDCA-1+ and BDCA-3+ mDCs induced expansion of Th17 cells, in response to RSV, BDCA-1+ mDCs induced expansion of Th1 cells and BDCA-3+ mDCs induced expansion of Th2 cells and Tregs. These results demonstrate a virus-specific and subset-specific effect of RSV and hMPV infection on mDC function, suggesting that these viruses may induce different adaptive immune responses.
    PLoS ONE 06/2014; 9(6):e99227. DOI:10.1371/journal.pone.0099227 · 3.23 Impact Factor
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    • "Wark et al. show that the impairment of virus-induced IFN-β expression is associated with enhanced viral replication in cell cultures [47]. Liu et al. has also suggested that IFN-β secreted from respiratory syncytial virus-infected epithelial cells induces TLR expression in a paracrine fashion in A549 cells [48]. This underscores the importance of RIG-I/MDA-5 on epithelial cells mediating an early antiviral response to viral infections in the nasal mucosa. "
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    ABSTRACT: Background The human nasal epithelium is an important physical barrier, and a part of the innate immune defense that protect against pathogens. The epithelial cells recognize microbial components by pattern-recognition receptors (PRRs), and thereby trigger an immune response. Even though TLR3, TLR7, TLR9, RIG-I and MDA-5 are all known to respond to viral stimulation, their potential role in chronic airway inflammation triggered by local cytokine release remains to be established. Methods mRNA and corresponding protein expression of TLR3, TLR7, TLR9, RIG-I and MDA-5 were analyzed in nasal biopsies and various upper airway epithelial cell lines using real-time reverse transcription PCR, immunohistochemistry and flow cytometry. Ligand induced, cytokine release, was evaluated with ELISA. Results Nasal biopsies were found to express TLR3, TLR7, TLR9, RIG-I and MDA-5, with the most abundant expression in the surface epithelium. These receptors were verified in primary human nasal epithelial cell (HNEC) as well as in the airway epithelial cell lines Detroit-562 and FaDu. Poly(I:C) (TLR3) and R-837 (TLR7) stimulation increased secretion of IL-6 and GM-CSF from the nasal mucosa and the epithelial cell lines. CpG (TLR9) stimulation caused release of IL-8 in the nasal mucosa and in FaDu. Poly(I:C)/LyoVec (RIG-I/MDA-5) stimulation activated the secretion of IFN-β in the nasal mucosa. A corresponding release was also detected from HNEC and Detroit-562. Conclusion The nasal epithelium has the ability to recognize viral intrusion through TLR and RLR receptors, and the subsequent response might have a role in exacerbation of inflammatory diseases like allergic rhinitis and chronic rhinosinusitis.
    PLoS ONE 06/2014; 9(6):e98239. DOI:10.1371/journal.pone.0098239 · 3.23 Impact Factor
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