We report the first atomic resolution structure of an animal virus, human rhinovirus 14. It is strikingly similar to known icosahedral plant RNA viruses. Four neutralizing immunogenic regions have been identified. These, and corresponding antigenic sequences of polio and foot-and-mouth disease viruses, reside on external protrusions. A large cleft on each icosahedral face is probably the host cell receptor binding site.

The mechanisms underlying the profound suppression of cell-mediated immunity (CMI) accompanying measles are unclear. Interleukin-12 (IL-12), derived principally from monocytes and macrophages, is critical for the generation of CMI. Measles virus (MV) infection of primary human monocytes specifically down-regulated IL-12 production. Cross-linking of CD46, a complement regulatory protein that is the cellular receptor for MV, with antibody or with the complement activation product C3b similarly inhibited monocyte IL-12 production, providing a plausible mechanism for MV-induced immunosuppression. CD46 provides a regulatory link between the complement system and cellular immune responses.

The issue of whether viruses are subject to restriction by endogenous microRNAs (miRNAs) and/or by virus-induced small interfering RNAs (siRNAs) in infected human somatic cells has been controversial. Here, we address this question in two ways. First, using deep sequencing, we demonstrate that infection of human cells by the RNA virus dengue virus (DENV) or West Nile virus (WNV) does not result in the production of any virus-derived siRNAs or viral miRNAs. Second, to more globally assess the potential of small regulatory RNAs to inhibit virus replication, we used gene editing to derive human cell lines that lack a functional Dicer enzyme and that therefore are unable to produce miRNAs or siRNAs. Infection of these cells with a wide range of viruses, including DENV, WNV, yellow fever virus, Sindbis virus, Venezuelan equine encephalitis virus, measles virus, influenza A virus, reovirus, vesicular stomatitis virus, human immunodeficiency virus type 1, or herpes simplex virus 1 (HSV-1), failed to reveal any enhancement in the replication of any of these viruses, although HSV-1, which encodes at least eight Dicer-dependent viral miRNAs, did replicate somewhat more slowly in the absence of Dicer. We conclude that most, and perhaps all, human viruses have evolved to be resistant to inhibition by endogenous human miRNAs during productive replication and that dependence on a cellular miRNA, as seen with hepatitis C virus, is rare. How viruses have evolved to avoid inhibition by endogenous cellular miRNAs, which are generally highly conserved during metazoan evolution, remains to be determined. IMPORTANCEEukaryotic cells express a wide range of small regulatory RNAs, including miRNAs, that have the potential to inhibit the expression of mRNAs that show sequence complementarity. Indeed, previous work has suggested that endogenous miRNAs have the potential to inhibit viral gene expression and replication. Here, we demonstrate that the replication of a wide range of pathogenic viruses is not enhanced in human cells engineered to be unable to produce miRNAs, indicating that viruses have evolved to be resistant to inhibition by miRNAs. This result is important, as it implies that manipulation of miRNA levels is not likely to prove useful in inhibiting virus replication. It also focuses attention on the question of how viruses have evolved to resist inhibition by miRNAs and whether virus mutants that have lost this resistance might prove useful, for example, in the development of attenuated virus vaccines.T wo forms of small-RNA-mediated RNA interference (RNAi) in somatic eukaryotic cells have been described. One form of RNAi, mediated by small interfering RNAs (siRNAs), was initially discovered in nematodes (1) and involves the sequential exonucleolytic processing of long, perfect, double-stranded RNAs (dsRNAs) by the RNase III enzyme Dicer to yield ϳ22-bp siRNA duplexes, one strand of which is then incorporated into the RNA-induced silencing complex (RISC) (2, 3). The siRNA guides RISC to RNA molecules that generally ...

During viral infection, cells initiate antiviral responses to contain replication and inhibit virus spread. One protective mechanism involves activation of transcription factors interferon regulatory factor-3 (IRF-3) and NF-B, resulting in secretion of the antiviral cytokine, interferon-␤. Another is induction of apoptosis, killing the host cell before virus disseminates. Mammalian reovirus induces both interferon-␤ and apoptosis, raising the possibility that both pathways are initiated by a common cellular sensor. We show here that reovirus activates IRF-3 with kinetics that parallel the activation of NF-B, a known mediator of reovirus-induced apoptosis. Activation of IRF-3 requires functional retinoic acid inducible gene-I and interferon-␤ promoter stimulator-1, but these intracellular sensors are dispensable for activation of NF-B. Interferon-␤ promoter stimulator-1 and IRF-3 are required for efficient apoptosis following reovirus infection, suggesting a common mechanism of antiviral cytokine induction and activation of the cell death response.A primary function of the innate immune system is to detect nascent viral infections and direct subsequent cellular responses. The innate immune system responds to infection by producing a range of soluble cytokines, such as interferon-␤ (IFN-␤), 5 that create an antiviral state in surrounding tissue. In response to these immune pressures, viruses have evolved multiple strategies for subverting innate immunity, which frequently center on manipulating cell death pathways. The interface between the innate immune response, viral infection, and the cellular apoptotic machinery is therefore a critical nexus of disease pathogenesis.Cells possess a variety of sensors to detect invading pathogens. Toll-like receptors (TLRs) and other pattern recognition receptors, including the nucleotide-binding oligomerization domain proteins and RNA helicases such as retinoic acid-inducible gene-I (RIG-I) and melanoma differentiation-associated protein-5 (Mda-5), recognize viral pathogen-associated molecular patterns (1). TLRs are expressed on the cell surface and recognize extracellular pathogen-associated molecular patterns, whereas RIG-I and Mda-5 detect intracellular viral RNA products (2-4). RIG-I recognizes viral RNAs from the Flaviviridae, Orthomyxoviridae, Paramyxoviridae, and Rhabdoviridae families, whereas Mda-5 is involved in the response to Picornaviridae (4). The ligand for RIG-I has been identified as a 5Ј triphosphate moiety on single-or double-stranded RNA (5, 6); the molecular ligand for Mda-5 is unknown. Following ligand engagement, these intracellular sensors signal through caspase activation and recruitment domains to activate the adaptor, interferon-␤ promoter stimulator-1 (IPS-1/MAVS/ VISA/Cardif) (7-10). IPS-1 activates inhibitor of B kinase (IKK)-␣, IKK-␤, IKK-⑀, and Tank-binding kinase 1 to phosphorylate transcription factors, including activating transcription factor-2/c-Jun, NF-B, and interferon regulatory factor-3 (IRF-3), which direct transcription of antiviral g...

Reovirus induces apoptosis in cultured cells and in vivo.In cell culture models, apoptosis is contingent upon a mechanism involving reovirus-induced activation of transcription factor NF-κB complexes containing p50 and p65/RelA subunits. To explore the in vivo role of NF-κB in this process, we tested the capacity of reovirus to induce apoptosis in mice lacking a functional nfkb1/p50 gene. The genetic defect had no apparent effect on reovirus replication in the intestine or dissemination to secondary sites of infection. In comparison to what was observed in wild-type controls, apoptosis was significantly diminished in the CNS of p50-null mice following reovirus infection. In sharp contrast, the loss of p50 was associated with massive reovirusinduced apoptosis and uncontrolled reovirus replication in the heart. Levels of IFN-β mRNA were markedly increased in the hearts of wild-type animals but not p50-null animals infected with reovirus. Treatment of p50-null mice with IFN-β substantially diminished reovirus replication and apoptosis, which suggests that IFN-β induction by NF-κB protects against reovirus-induced myocarditis. These findings reveal an organspecific role for NF-κB in the regulation of reovirus-induced apoptosis, which modulates encephalitis and myocarditis associated with reovirus infection.