Moloney leukemia virus 10 (MOV10) protein is a superfamily-1 RNA helicase, and it is also a component of the RNA-induced silencing complex. Recent studies have shown that MOV10 plays an active role in the RNA interference pathway. Here, we report that MOV10 inhibits retrovirus replication. When it was overexpressed in viral producer cells, MOV10 was able to reduce the infectivity of human immunodeficiency virus type 1 (HIV-1), simian immunodeficiency virus, and murine leukemia virus. Conversely, when MOV10 expression was reduced by small interfering RNAs, HIV-1 infectivity was increased. Consistently, silencing of MOV10 expression in a human T cell line enhanced HIV-1 replication. Furthermore, we found that MOV10 interacts with HIV-1 nucleocapsid protein in an RNAdependent manner and is packaged into virions. It blocks HIV-1 replication at a postentry step. In addition, we also found that HIV-1 could suppress MOV10 protein expression to counteract this cellular resistance. All of these results indicate that MOV10 has a broad antiretroviral activity that can target a wide range of retroviruses, and it could be actively involved in host defense against retroviral infection.Helicases share seven conserved motifs (I, Ia, II, III, IV, V, and VI), and are classified into three superfamilies (SF-1 to SF-3) and two smaller families (F4 and F5) (1, 2). Most helicases belong to SF-2 and are known as DExH/D (DEAD, DEAH, DExH) box proteins that are named for a sequence fingerprint in the motif II.The MOV10 gene was discovered from the MOV-10 mouse strain. The MOV mouse strains were derived from preimplantation embryos infected with Moloney murine leukemia virus (MLV).2 A total of nine strains that carry a single copy of the provirus at different chromosomal positions were created and designated MOV-5 to MOV-13.

A highly pathogenic pig disease emerged in China in 2006, which was characterized by prolonged high fever, red discoloration of the body, and blue ears associated with high mortality. Porcine reproductive and respiratory syndrome virus (PRRSV) was isolated as the single most prominent virus in the samples collected from affected pigs. The full-length genomic sequence of the virus revealed two distinct deletions in the non-structural protein 2 (NSP2) in comparison to all previously reported North American genotype PRRSV. Through extensive surveys in 14 different provinces, 56 additional PRRSV isolates were obtained from affected farms. All of the isolates were found to contain identical deletions in NSP2. To confirm the etiology, eight 60-day-old PRRSV-free pigs were divided into two groups and the test group was intranasally infected at a titer of 2 x 10(5.0) tissue culture infectious dose 50 per pig. The inoculated pigs all died at 7, 8, 12, 16, or 21 days post-inoculation with their clinical and pathological findings similar to those in the field. The viruses recovered from dead pigs were identical to the inoculated virus in NSP2 and GP5 genes. Our study shows that the recently emerged PRRSV in China is characterized by two discontiguous deletions in NSP2 and is the cause for the current epizootics in China.

The primate lentiviral accessory protein Nef downregulates CD4 and major histocompatibility complex class I (MHC-I) from the cell surface via independent endosomal trafficking pathways to promote viral pathogenesis. In addition, Nef antagonizes a novel restriction factor, SERINC5 (Ser5), to increase viral infectivity. To explore the molecular mechanism of Ser5 antagonism by Nef, we determined how Nef affects Ser5 expression and intracellular trafficking in comparison to CD4 and MHC-I. We confirm that Nef excludes Ser5 from human immunodeficiency virus type 1 (HIV-1) virions by downregulating its cell surface expression via similar functional motifs required for CD4 downregulation. We find that Nef decreases both Ser5 and CD4 expression at steady-state levels, which are rescued by NHCl or bafilomycin A1 treatment. Nef binding to Ser5 was detected in living cells using a bimolecular fluorescence complementation assay, where Nef membrane association is required for interaction. In addition, Nef triggers rapid Ser5 internalization via receptor-mediated endocytosis and relocalizes Ser5 to Rab5 early, Rab7 late, and Rab11 recycling endosomes. Manipulation of AP-2, Rab5, Rab7, and Rab11 expression levels affects the Nef-dependent Ser5 and CD4 downregulation. Moreover, although Nef does not promote Ser5 polyubiquitination, Ser5 downregulation relies on the ubiquitination pathway, and both K48- and K63-specific ubiquitin linkages are required for the downregulation. Finally, Nef promotes Ser5 colocalization with LAMP1, which is enhanced by bafilomycin A1 treatment, suggesting that Ser5 is targeted to lysosomes for destruction. We conclude that Nef uses a similar mechanism to downregulate Ser5 and CD4, which sorts Ser5 into a point-of-no-return degradative pathway to counteract its restriction. Human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) express an accessory protein called Nef to promote viral pathogenesis. Nef drives immune escape through downregulation of CD4 and MHC-I from the host cell surface. Recently, Nef was reported to counteract a novel host restriction factor, Ser5, to increase viral infectivity. Nef downregulates cell surface Ser5, thus preventing its incorporation into virus particles, resulting in disruption of its antiviral activity. Here, we report mechanistic studies of Nef-mediated Ser5 downregulation in comparison to CD4 and MHC-I. We demonstrate that Nef binds directly to Ser5 in living cells and that Nef-Ser5 interaction requires Nef association with the plasma membrane. Subsequently, Nef internalizes Ser5 from the plasma membrane via receptor-mediated endocytosis, and targets ubiquitinated Ser5 to endosomes and lysosomes for destruction. Collectively, these results provide new insights into our ongoing understanding of the Nef-Ser5 arms race in HIV-1 infection.

The function of lentiviral Vif proteins is to neutralize the host antiviral cytidine deaminases APOBEC3G (A3G) and APOBEC3F (A3F

Among the five serine incorporator (SERINC) family members, SERINC5 (Ser5) was reported to strongly inhibit HIV-1 replication, which is counteracted by Nef. Ser5 produces 5 alternatively spliced isoforms: Ser5-001 has 10 putative transmembrane domains, whereas Ser5-004, -005, -008a, and -008b do not have the last one. Here, we confirmed the strong Ser5 anti-HIV-1 activity and investigated its isoforms' expression and antiviral activities. It was found that Ser5-001 transcripts were detected at least 10-fold more than the other isoforms by real-time quantitative PCR. When Ser5-001 and its two isoforms Ser5-005 and Ser5-008a were expressed from the same mammalian expression vector, only Ser5-001 was stably expressed, whereas the others were poorly expressed due to rapid degradation. In addition, unlike the other isoforms, which are located mainly in the cytoplasm, Ser5-001 is localized primarily to the plasma membrane. To map the critical determinant, Ser5 mutants bearing C-terminal deletions were created. It was found that the 10th transmembrane domain is required for Ser5 stable expression and plasma membrane localization. As expected, only Ser5-001 strongly inhibits HIV-1 infectivity, whereas the other Ser5 isoforms and mutants that do not have the 10th transmembrane domain show very poor activity. It was also observed that the Nef counteractive activity could be easily saturated by Ser5 overexpression. Thus, we conclude that Ser5-001 is the predominant antiviral isoform that restricts HIV-1, and the 10th transmembrane domain plays a critical role in this process by regulating its protein stability and plasma membrane targeting. IMPORTANCE Human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) express a small protein, Nef, to enhance viral pathogenesis in vivo.Nef has an important in vitro function, which is to make virus particles more infectious, but the mechanism has been unclear. Recently, Nef was reported to counteract a novel anti-HIV host protein, SERINC5 (Ser5). Ser5 has five alternatively spliced isoforms, Ser5-001, -004, -005, -008a, and -008b, and only Ser5-001 has an extra C-terminal transmembrane domain. We now show that the Ser5-001 transcripts are produced at least 10-fold more than the others, and only Ser5-001 produces stable proteins that are targeted to the plasma membrane. Importantly, only Ser5-001 shows strong anti-HIV-1 activity. We further demonstrate that the extra transmembrane domain is required for Ser5 stable expression and plasma membrane localization. These results suggest that plasma membrane localization is required for Ser5 antiviral activity, and Ser5-001 is the predominant isoform that contributes to the activity.KEYWORDS HIV-1, Nef, SERINC3, SERINC5, infectivity, restriction factor

Background: MOV10 inhibits HIV-1 replication after being packaged. Results: A Gag binding plus all but one of seven helicase domains are required for MOV10 packaging. Nearly all residues are required for anti-HIV-1 activity. Conclusion: Gag binding is not sufficient for MOV10 packaging, and multiple discontinuous domains regulate MOV10 activity. Significance: These findings uncover a new packaging mechanism and provide new insights into MOV10 antiviral activity.

BackgroundSheeppox virus (SPPV) and goatpox virus (GTPV), members of the Capripoxvirus genus of the Poxviridae family are causative agents of sheep pox and goat pox respectively, which are important contagious diseases and endemic in central and northern Africa, the Middle and Far East, and the Indian sub-continent. Both sheep pox and goat pox can cause wool and hide damage, and reduce the production of mutton and milk, which may result in significant economic losses and threaten the stockbreeding. In this study, three SPPVs and two GTPVs were collected from China in 2009 and 2011. We described the sequence features and phylogenetic analysis of the P32 gene, GPCR gene and RPO30 gene of the SPPVs and GTPVs to reveal their genetic relatedness.ResultsSequence and phylogenetic analysis showed that there was a close relationship among SPPV/GanS/2/2011/China, SPPV/GanS/1/2011/China and SPPV/NingX/2009/China. They were clustered on the same SPPV clade. GTPV/HuB/2009/China and GS-V1 belonged to the GTPV lineage. GS-V1 was closely related to other GTPV vaccine strains. GTPV/HuB/2009/China and GS-V1 were clustered with GTPVs from China and some southern Asian countries.ConclusionThis study may expand the datum for spread trend research of Chinese SPPVs and GTPVs, meanwhile provide theoretical references to improve the preventive and control strategy.

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