Tetherin, also known as BST-2/CD317/HM1.24, is an antiviral cellular protein that inhibits the release of HIV-1 particles from infected cells. HIV-1 viral protein U (Vpu) is a specific antagonist of human tetherin that might contribute to the high virulence of HIV-1. In this study, we show that three amino acid residues (I34, L37, and L41) in the transmembrane (TM) domain of human tetherin are critical for the interaction with Vpu by using a live cell-based assay. We also found that the conservation of an additional amino acid at position 45 and two residues downstream of position 22, which are absent from monkey tetherins, are required for the antagonism by Vpu. Moreover, computer-assisted structural modeling and mutagenesis studies suggest that an alignment of these four amino acid residues (I34, L37, L41, and T45) on the same helical face in the TM domain is crucial for the Vpu-mediated antagonism of human tetherin. These results contribute to the molecular understanding of human tetherin-specific antagonism by HIV-1 Vpu.

Rotavirus A (RVA) genotype G1P[8], a hallmark of the Wa-like strain, typically contains only genotype 1 genes. However, an unusual RVA G1P[8] with genotype 2 genes was recently detected in Japan. We determined the complete genomic constellation of this RVA. Our findings suggest that mixed RVAs may be more competitive than once thought.

Enteric viruses are an important cause of viral food-borne disease. Shellfish, especially oysters, are well recognized as a source of food-borne diseases, and oyster-associated gastroenteritis outbreaks have on occasion become international occurrences. In this study, 286 fecal specimens from 88 oyster-associated gastroenteritis outbreaks were examined for the presence of 10 human enteric viruses using antigenic or genetic detection methods in order to determine the prevalence of these infections. All virus-positive patients were over 18 years old. The most common enteric virus in outbreaks (96.6%) and fecal specimens (68.9%) was norovirus (NoV), indicating a high prevalence of NoV infection associated with the consumption of raw or under-cooked oysters. Five other enteric viruses, aichiviruses, astroviruses, sapoviruses, enteroviruses (EVs), and rotavirus A, were detected in 30.7% of outbreaks. EV strains were characterized into three rare genotypes, coxsackievirus (CV) A1, A19, and EV76. No reports of CVA19 or EV76 have been made since 1981 in the Infectious Agents Surveillance Report by the National Infectious Diseases Surveillance Center, Japan. Their detection suggested that rare types of EVs are circulating in human populations inconspicuously and one of their transmission modes could be the consumption of contaminated oysters. Rapid identification of pathogens is important for the development of means for control and prevention. The results of the present study will be useful to establish an efficient approach for the identification of viral pathogens in oyster-associated gastroenteritis in adults.

In this study, we first demonstrate that endogenous hBST-2 is predominantly expressed on the plasma membrane of a human T cell line, MT-4 cells, and that Vpu-deficient HIV-1 was less efficiently released than wild-type HIV-1 from MT-4 cells. In addition, surface hBST-2 was rapidly down-regulated in wild-type but not Vpu-deficient HIV-1-infected cells. This is a direct insight showing that provirus-encoded Vpu has the potential to down-regulate endogenous hBST-2 from the surface of HIV-1-infected T cells. Corresponding to previous reports, the aforementioned findings suggested that hBST-2 has the potential to suppress the release of Vpu-deficient HIV-1. However, the molecular mechanism(s) for tethering HIV-1 particles by hBST-2 remains unclear, and we speculated about the requirement for cellular co-factor(s) to trigger or assist its tethering ability. To explore this possibility, we utilize several cell lines derived from various species including human, AGM, dog, cat, rabbit, pig, mink, potoroo, and quail. We found that ectopic hBST-2 was efficiently expressed on the surface of all analyzed cells, and its expression suppressed the release of viral particles in a dose-dependent manner. These findings suggest that hBST-2 can tether HIV-1 particles without the need of additional co-factor(s) that may be expressed exclusively in primates, and thus, hBST-2 can also exert its function in many cells derived from a broad range of species. Interestingly, the suppressive effect of hBST-2 on HIV-1 release in Vero cells was much less pronounced than in the other examined cells despite the augmented surface expression of ectopic hBST-2 on Vero cells. Taken together, our findings suggest the existence of certain cell types in which hBST-2 cannot efficiently exert its inhibitory effect on virus release. The cell type-specific effect of hBST-2 may be critical to elucidate the mechanism of BST-2-dependent suppression of virus release.

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RIG-I-like receptor (RLR) plays a pivotal role in the detection of invading pathogens to initiate type I interferon (IFN) gene transcription. Since aberrant IFN production is harmful, RLR signaling is strictly regulated. However, the regulatory mechanisms are not fully understood. By expression cloning, we identified Pumilio proteins, PUM1 and PUM2, as candidate positive regulators of RIG-I signaling. Overexpression of Pumilio proteins and their knockdown augmented and diminished IFN-β promoter activity induced by Newcastle disease virus (NDV), respectively. Both proteins showed a specific association with LGP2, but not with RIG-I or MDA5. Furthermore, all of these components were recruited to NDV-induced antiviral stress granules. Interestingly, biochemical analyses revealed that Pumilio increased double-stranded (ds) RNA binding affinity of LGP2; however, Pumilio was absent in the dsRNA-LGP2 complex, suggesting that Pumilio facilitates viral RNA recognition by LGP2 through its chaperon-like function. Collectively, our results demonstrate an unknown function of Pumilio in viral recognition by LGP2.

Pyroligneous acids (PA) from hardwood, softwood, and bamboo significantly disinfected encephalomyocarditis virus (EMCV). Twenty-five kinds of phenolic derivatives in the PAs were identified and quantified. The total amounts of phenolic compounds in bamboo PA is higher than those in the PAs from softwood and hardwood. Phenol, 2-methoxyphenol, 2-methoxy-4-methylphenol, and 2-methoxy-4-ethylphenol are the most abundant compounds in the PAs examined. The activities of all the phenolic compounds against the encephalomyocarditis virus were assessed. The number of phenolic hydroxyl groups significantly affects the antiviral activity, and catechol and its derivatives exhibit higher viral inhibition effects than other phenolic derivatives. In addition, substituents affect the antiviral activity of the compounds. Phenolic compounds with a methyl group show higher activities than with a methoxyl group (e.g., 2-methylphenol > 2-methoxyphenol). Moreover, the relative position of functional groups also plays a key role in the viral inhibition activity (e.g., 2,6-dimethoxyphenol > 3,4-dimethoxyphenol). Thus, PAs contain phenol derivatives with considerable structural diversity and viral inhibition activities, providing a new strategy for virus-inactivation treatment through the optimization of PA-derived phenol structures.

APOBEC1 (A1) is a cytidine deaminase involved in the regulation of lipids in the small intestine. Herpes simplex virus 1 (HSV-1) is a ubiquitous pathogen that is capable of infecting neurons in the brain, causing encephalitis. Here, we show that A1 is induced during encephalitis in neurons of rats infected with HSV-1. In cells stably expressing A1, HSV-1 infection resulted in significantly reduced virus replication compared to that in control cells. Infectivity could be restored to levels comparable to those observed for control cells if A1 expression was silenced by specific A1 short hairpin RNAs (shRNA). Moreover, cytidine deaminase activity appeared to be essential for this inhibition and led to an impaired accumulation of viral mRNA transcripts and DNA copy numbers. The sequencing of viral gene UL54 DNA, extracted from infected A1-expressing cells, revealed G-to-A and C-to-T transitions, indicating that A1 associates with HSV-1 DNA. Taken together, our results demonstrate a model in which A1 induction during encephalitis in neurons may aid in thwarting HSV-1 infection.The human apolipoprotein B-editing catalytic polypeptide (ABOBEC) family is a group of zinc-dependent DNA and RNA cytidine deaminases and consists of AID, APOBEC1 (A1), APOBEC2 (A2), seven APOBEC3s (APOBEC3A [A3A] to A3H), and APOBEC4 (A4). A1, the first APOBEC to be discovered, is known to introduce a premature stop codon into host apolipoprotein B mRNA in the gastrointestinal tract, an event critical for lipid metabolism (17,40,61). The editing by A1 is highly precise and specifically converts C to U at position 6666 of the apolipoprotein B mRNA substrate (46). Along with APOBEC1 complementation factor (ACF), these two proteins constitute the minimal required components necessary for the editing of apolipoprotein B mRNA in vitro (37).Cytidine deaminases first came into the limelight as antiviral factors after A3G was identified as a cellular restriction factor capable of inhibiting HIV-1 dissemination in the absence of HIV-1 virus infectivity factor (Vif) (56). This molecule was later shown to inhibit retrovirus infection by inducing a massive hypermutation of the murine leukemia virus (MLV) genome (23). Further detailed studies revealed that APOBEC molecules are packaged into HIV-1 virions in virus producer cells via a specific interaction with Gag and viral RNA and then exert their deaminase activity in subsequent target cells on a single-stranded DNA (ssDNA) intermediate synthesized by reverse transcriptase (3, 28, 55). Editing can lead to nonsynonymous mutations, such as premature stop codons, in critical proteins (e.g., reverse transcriptase) necessary for virus replication and infectivity, severely impairing the next round of infection (54,64). Extensive studies to assess the antiviral nature of these APOBEC enzymes have been performed across a broad range of retroviruses and hepatitis B virus (HBV) (7,35,36,42,43,50,56,58).Herpes simplex virus (HSV) is an enveloped, double-stranded DNA (dsDNA) virus and a member of the genus Alphaherpe...