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The HIV-1 Vpu protein is required for efficient viral release from human cells. For HIV-2, the envelope (Env) protein replaces the role of Vpu. Both Vpu and HIV-2 Env enhance virus release by counteracting an innate host-cell block within human cells that is absent in African green monkey (AGM) cells. Here we identify calcium-modulating cyclophilin ligand (CAML) as a Vpu-interacting host factor that restricts HIV-1 release. Expression of human CAML (encoded by CAMLG) in AGM cells conferred a strong restriction of virus release that was reversed by Vpu and HIV-2 Env, suggesting that CAML is the mechanistic link between these two viral regulators. Depletion of CAML in human cells eliminated the need for Vpu in enhancing HIV-1 and murine leukemia virus release. These results point to CAML as a Vpu-sensitive host restriction factor that inhibits HIV release from human cells. The ability of CAML to inhibit virus release should illuminate new therapeutic strategies against HIV.

We previously reported the detection of bat coronaviruses (bat CoVs 1A, 1B, HKU7, HKU8 and bat-severe acute respiratory syndrome coronavirus) in Miniopterus spp. that cohabit a cave in Hong Kong. Here, we report the full genomic sequences of bat CoVs 1A, 1B and HKU8. Bat CoVs 1A and 1B, which are commonly found in the Miniopterus, are phylogenetically closely related. Using species-specific RT-PCR assays, bat CoVs 1A and 1B were confirmed to have distinct host specificities to Miniopterus magnater and Miniopterus pusillus, respectively. Interestingly, co-infections of bat CoVs 1B and HKU8 in M. pusillus are detected in seven of 38 virus-positive specimens collected from 2004 to 2006. These findings highlight that co-infections of some coronaviruses might be common events in nature. The biological basis for the host restriction of bat coronaviruses, however, is yet to be determined.

ObjectiveThe eradication of HIV necessitates elimination of the HIV latent reservoir. Identifying host determinants governing latency and reservoir size in the setting of antiretroviral therapy (ART) is an important step in developing strategies to cure HIV infection. We sought to determine the impact of cell-intrinsic immunity on the HIV latent reservoir.DesignWe investigated the relevance of a comprehensive panel of established anti-HIV-1 host restriction factors to multiple established virologic and immunologic measures of viral persistence in HIV-1-infected, ART-suppressed individuals.MethodsWe measured the mRNA expression of 42 anti-HIV-1 host restriction factors, levels of cell-associated HIV-1 RNA, levels of total pol and 2-long terminal repeat (2-LTR) circle HIV-1 DNA and immunophenotypes of CD4 T cells in 72 HIV-1-infected individuals on suppressive ART (23 individuals initiated ART less than 1 year post-infection, and 49 individuals initiated ART greater than 1 year post-infection). Correlations were analysed using nonparametric tests.ResultsThe enhanced expression of a few select host restriction factors, p21, schlafen 11 and PAF1, was strongly associated with reduced CD4 T-cell associated HIV RNA during ART (P

HIV-1 infection is restricted at a post-entry stage in some simian cell lines by species-specific variants of TRIM5 alpha. Restriction targets the viral capsid protein (CA) and results in attenuated reverse transcription. TRIM5 alpha restriction can be inhibited by the addition of noninfectious virus-like particles (VLPs), thus rendering cells permissive for infection by an HIV-1 reporter virus. Through the use of HIV-1 VLPs containing Gag cleavage site substitutions and point mutations in CA which alter the stability of the viral capsid, we demonstrate that saturation of TRIM5 alpha restriction depends on the stability of the capsid in the incoming VLPs. Differences in the requirement for cleavage of the specific sites in Gag were observed between distinct African green monkey cell lines. The results strongly suggest that the mechanism of HIV-1 restriction by TRIM5 alpha involves engagement of the viral capsid by the restriction factor prior to completion of uncoating.

Host restriction of vaccinia virus has been previously described in CHO and RK13 cells in which a cowpox virus CP77 gene rescues vaccinia virus growth at the viral protein translation level. Here we investigate the restrictive stage of vaccinia virus in HeLa cells using a vaccinia mutant virus (VV-hr) that contains a deletion of 18-kb genome sequences resulting in no growth in HeLa cells. Insertion of CP77 gene into VV-hr generated a recombinant virus (VV-36hr) that multiplied well in HeLa cells. Both viruses could enter cells, initiate viral DNA replication and intermediate gene transcription. However, translation of viral intermediate gene was only detected in cells infected with VV-36hr, indicating that CP77 relieves host restriction at the intermediate gene translation stage in HeLa cells. Caspase-2 and -3 activation was observed in HeLa cells infected with VV-hr coupled with dramatic morphological alterations and cleavage of the translation initiation factor eIF4G. Caspase activation was reduced in HeLa cells infected with VV-36hr, indicating that CP77 acts upstream of caspase activation. Enhanced phosphorylation of PKR and eIF2alpha was also observed in cells infected with VV-hr and was suppressed by CP77. Suppression of eIF4G cleavage with the caspase inhibitor ZVAD did not rescue virus translation, whereas expression of a mutant eIF2alpha protein with an alanine substitution of serine at amino acid position 51 (eIF2alphaS51A) partially restored viral translation and moderately increased virus growth in HeLa cells.

Background The HIV-1 accessory proteins, Viral Infectivity Factor (Vif) and the pleiotropic Viral Protein R (Vpr) are important for efficient virus replication. While in non-permissive cells an appropriate amount of Vif is critical to counteract APOBEC3G-mediated host restriction, the Vpr-induced G2 arrest sets the stage for highest transcriptional activity of the HIV-1 long terminal repeat. Both vif and vpr mRNAs harbor their translational start codons within the intron bordering the non-coding leader exons 2 and 3, respectively. Intron retention relies on functional cross-exon interactions between splice sites A1 and D2 (for vif mRNA) and A2 and D3 (for vpr mRNA). More precisely, prior to the catalytic step of splicing, which would lead to inclusion of the non-coding leader exons, binding of U1 snRNP to the 5' splice site (5'ss) facilitates recognition of the 3'ss by U2 snRNP and also supports formation of vif and vpr mRNA. Results We identified a G run localized deep in the vpr AUG containing intron 3 (GI3-2), which was critical for balanced splicing of both vif and vpr non-coding leader exons. Inactivation of GI3-2 resulted in excessive exon 3 splicing as well as exon-definition mediated vpr mRNA formation. However, in an apparently mutually exclusive manner this was incompatible with recognition of upstream exon 2 and vif mRNA processing. As a consequence, inactivation of GI3-2 led to accumulation of Vpr protein with a concomitant reduction in Vif protein. We further demonstrate that preventing hnRNP binding to intron 3 by GI3-2 mutation diminished levels of vif mRNA. In APOBEC3G-expressing but not in APOBEC3G-deficient T cell lines, mutation of GI3-2 led to a considerable replication defect. Moreover, in HIV-1 isolates carrying an inactivating mutation in GI3-2, we identified an adjacent G-rich sequence (GI3-1), which was able to substitute for the inactivated GI3-2. Conclusions The functionally conserved intronic G run in HIV-1 intron 3 plays a major role in the apparently mutually exclusive exon selection of vif and vpr leader exons and hence in vif and vpr mRNA formation. The competition between these exons determines the ability to evade APOBEC3G-mediated antiviral effects due to optimal vif expression. Electronic supplementary material The online version of this article (doi:10.1186/s12977-014-0072-1) contains supplementary material, which is available to authorized users.

In this paper, the distribution, host restriction, and taxonomic position of Valsa mali are discussed.

Humans encode seven APOBEC3 (A3A-A3H) cytidine deaminase proteins that differ in their expression profiles, preferred nucleotide recognition sequence and capacity for restriction of RNA and DNA viruses. We identified APOBEC3 hotspots in numerous herpesvirus genomes. To determine the impact of host APOBEC3 on herpesvirus biology in vivo, we examined whether murine APOBEC3 (mA3) restricts murine gammaherpesvirus 68 (MHV68). Viral replication was impaired by several human APOBEC3 proteins, but not mA3, upon transfection of the viral genome. The restriction was abrogated upon mutation of the A3A and A3B active sites. Interestingly, virus restriction by A3A, A3B, A3C, and A3DE was lost if the infectious DNA was delivered by the virion. MHV68 pathogenesis, including lung replication and splenic latency, was not altered in mice lacking mA3. We infer that mA3 does not restrict wild type MHV68 and restriction by human A3s may be limited in the herpesvirus replication process.

The HIV-1 viral infectivity factor (Vif) neutralizes cell-encoded antiviral APOBEC3 proteins by recruiting a cellular ElonginB (EloB)/ElonginC (EloC)/Cullin5-containing ubiquitin ligase complex, resulting in APOBEC3 ubiquitination and proteolysis. The suppressors-of-cytokine-signalling-like domain (SOCS-box) of HIV-1 Vif is essential for E3 ligase engagement, and contains a BC box as well as an unusual proline-rich motif. Here, we report the NMR solution structure of the Vif SOCS–ElonginBC (EloBC) complex. In contrast to SOCS-boxes described in other proteins, the HIV-1 Vif SOCS-box contains only one α-helical domain followed by a β-sheet fold. The SOCS-box of Vif binds primarily to EloC by hydrophobic interactions. The functionally essential proline-rich motif mediates a direct but weak interaction with residues 101–104 of EloB, inducing a conformational change from an unstructured state to a structured state. The structure of the complex and biophysical studies provide detailed insight into the function of Vif's proline-rich motif and reveal novel dynamic information on the Vif–EloBC interaction.

The research on virion infectivity factor (Vif) protein had started in late 1980s right after HIV-1 was cloned, and the function of Vif had been a mystery for a long time. However, the research on Vif has finally lead to the identification of APOBEC3G, which opens up a new era in the research field of host restriction factors in HIV-1 infection followed by TRIM5α, Tetherin/BST-2, and SAMHD1. This suggests that continuation of basic research on fundamental questions is quite important. We still have many questions on Vif and APOBEC3 and should continue to work on these proteins in the future in order to better regulate HIV-1. We will discuss not only the history but also recent advances in Vif research.

Modified vaccinia virus Ankara (MVA), a host range restricted and highly attenuated vaccinia virus strain, is unable to multiply in human and most other mammalian cell lines. Since viral gene expression is unimpaired in non-permissive cells recombinant MVA viruses are efficient as well as exceptionally safe expression vectors. We constructed a recombinant MVA that expresses the bacteriophage T7 RNA polymerase and tested its usefulness for transient expression of recombinant genes under the control of a T7 promoter. Using the chloramphenicol acetyltransferase (CAT) gene as a reporter gene, infection with MVA-T7pol allowed efficient synthesis of recombinant enzyme in mammalian cells. Despite the severe host restriction of MVA, enzyme activities induced by infection with MVA-T7pol were similar to those determined after infection with a replication-competent vaccinia-T7pol recombinant virus. Thus, MVA-T7pol may be used as a novel vaccinia vector to achieve T7 RNA polymerase-specific recombinant gene expression in the absence of productive vaccinia virus replication.

Before a pathogen even enters a cell, intrinsic immune defenses are active. This first-line defense is mediated by a variety of constitutively expressed cell proteins collectively termed "restriction factors" (RFs), and they form a vital element of the immune response to virus infections. Over time, however, viruses have evolved in a variety ways so that they are able to overcome these RF defenses via mechanisms that are specific for each virus. This review provides a summary of the universal characteristics of RFs, and goes on to focus on the strategies employed by some of the most important RFs in their attempt to control human cytomegalovirus (HCMV) infection. This is followed by a discussion of the counter-restriction mechanisms evolved by viruses to circumvent the host cell's intrinsic immune defenses. RFs include nuclear proteins IFN-γ inducible protein 16 (IFI16) (a Pyrin/HIN domain protein), Sp100, promyelocytic leukemia, and hDaxx; the latter three being the keys elements of nuclear domain 10 (ND10). IFI16 inhibits the synthesis of virus DNA by down-regulating UL54 transcription - a gene encoding a CMV DNA polymerase; in response, the virus antagonizes IFI16 via a process involving viral proteins UL97 and pp65 (pUL83), which results in the mislocalizing of IFI16 into the cytoplasm. In contrast, viral regulatory proteins, including pp71 and IE1, seek to modify or disrupt the ND10 proteins and thus block or reverse their inhibitory effects upon virus replication. All in all, detailed knowledge of these HCMV counter-restriction mechanisms will be fundamental for the future development of new strategies for combating HCMV infection and for identifying novel therapeutic agents.

Extensive investigations have identified two cellular proteins in humans that potently inhibit HIV type 1 (HIV-1) replication and are widely accepted as “restriction factors.” APOBEC3G was identified as a restriction factor that diminishes HIV-1 replication by inducing G-to-A hypermutation in the viral genome, while BST2 has been identified as another restriction factor that impairs the release of nascent virions by tethering them on the surface of infected cells. To counter these restriction factors, HIV-1 has equipped itself with its own weapons: viral infectivity factor (Vif) degrades APOBEC3G, while viral protein U (Vpu) antagonizes BST2. These findings have allowed us to further our understanding of virus–host interaction, namely, the interplay between viral factors versus host restriction factors. In the first case, the interplay between APOBEC3G and Vif is clear: vif-deficient HIV-1 is incapable of replicating in APOBEC3G-expressing cells. This insight directly indicates that APOBEC3G is a bona fide restriction factor and has intrinsic immunity against HIV-1, and that Vif is a prerequisite for HIV-1 infection. In other words, the relationship between Vif and APOBEC3G has already “matured,” and Vif has highly evolved to overcome APOBEC3G. On the other hand, although BST2 drastically impairs the release of vpu-deficient HIV-1 virions, it is puzzling that vpu-deficient HIV-1 is still able to replicate in BST2-expressing cells. These insights imply that BST2-mediated anti-HIV-1 activity is vulnerable, and that Vpu is dispensable for HIV-1 infection. If so, why has Vpu acquired the counteracting potential against BST2? Was it necessary or important for HIV-1? Or is the relationship between Vpu and BST2 still “immature”? In this review, we particularly focus on the interplay between Vpu and BST2. We discuss the possibility that Vpu has evolved as a potent antagonist against BST2, and finally, propose a hypothesis that Vpu has evolved as a promoter of human-to-human HIV-1 transmission. Since the first report of acquired immunodeficiency syndrome patients in 1981, HIV-1 has spread explosively worldwide and is currently a pandemic. This review proposes a concept suggesting that the current HIV-1 pandemic may be partly attributed by Vpu.

The HIV-1 capsid protein consists of two independently folded domains connected by a flexible peptide linker (residues 146–150), the function of which remains to be defined. To investigate the role of this region in virus replication, we made alanine or leucine substitutions in each linker residue and two flanking residues. Three classes of mutants were identified: (i) S146A and T148A behave like wild type (WT); (ii) Y145A, I150A, and L151A are noninfectious, assemble unstable cores with aberrant morphology, and synthesize almost no viral DNA; and (iii) P147L and S149A display a poorly infectious, attenuated phenotype. Infectivity of P147L and S149A is rescued specifically by pseudotyping with vesicular stomatitis virus envelope glycoprotein. Moreover, despite having unstable cores, these mutants assemble WT-like structures and synthesize viral DNA, although less efficiently than WT. Collectively, these findings demonstrate that the linker region is essential for proper assembly and stability of cores and efficient replication.

Species of the subgenus Trypanosoma (Megatrypanum) have been reported in cattle and other domestic and wild ruminants worldwide. A previous study in Brazil found at least four genotypes infecting cattle (Bos taurus), but only one in water buffalo (Bubalus bubalis). However, the small number of isolates examined from buffalo, all inhabiting nearby areas, has precluded evaluation of their diversity, host associations and geographical structure. To address these questions, we evaluated the genetic diversity and phylogeographical patterns of 25 isolates from water buffalo and 28 from cattle from four separate locations in Brazil and Venezuela. Multigene phylogenetic analyses of ssrRNA, internal transcribed spacer of rDNA (ITSrDNA), 5SrRNA, glycosomal glyceraldehyde 3-phosphate dehydrogenase (gGAPDH), mitochondrial cytochrome b (Cyt b), spliced leader (SL) and cathepsin L-like (CATL) sequences positioned all isolates from sympatric and allopatric buffalo populations into the highly homogeneous genotype TthIA, while the cattle isolates were assigned to three different genotypes, all distinct from TthIA. Polymorphisms in all of these sequences separated the trypanosomes infecting water buffalo, cattle, sheep, antelope and deer, and suggested that they correspond to separate species. Congruent phylogenies inferred with all genes indicated a predominant clonal structure of the genotypes. The multilocus analysis revealed one monophyletic assemblage formed exclusively by trypanosomes of ruminants, which corresponds to the subgenus T. (Megatrypanum). The high degree of host specificity, evidenced by genotypes exclusive to each ruminant species and lack of genotype shared by different host species, suggested that the evolutionary history of trypanosomes of this subgenus was strongly constrained by their ruminant hosts. However, incongruence between ruminant and trypanosome phylogenies did not support host– parasite co-evolution, indicating that host switches have occurred across ruminants followed by divergences, giving rise to new trypanosome genotypes adapted exclusively to one host species.

Intrinsic antiviral resistance mediated by constitutively expressed cellular proteins is one arm of defence against virus infection. Promyelocytic leukaemia nuclear bodies (PML-NBs, also known as ND10) contribute to host restriction of herpes simplex virus type 1 (HSV-1) replication via mechanisms that are counteracted by viral regulatory protein ICP0. ND10 assembly is dependent on PML, which comprises several different isoforms, and depletion of all PML isoforms decreases cellular resistance to ICP0-null mutant HSV-1. We report that individual expression of PML isoforms I and II partially reverses the increase in ICP0-null mutant HSV-1 plaque formation that occurs in PML-depleted cells. This activity of PML isoform I is dependent on SUMO modification, its SUMO interaction motif (SIM), and each element of its TRIM domain. Detailed analysis revealed that the punctate foci formed by individual PML isoforms differ subtly from normal ND10 in terms of composition and/or Sp100 modification. Surprisingly, deletion of the SIM motif from PML isoform I resulted in increased colocalisation with other major ND10 components in cells lacking endogenous PML. Our observations suggest that complete functionality of PML is dependent on isoform-specific C-terminal sequences acting in concert.

Viruses, including retroviruses like human immunodeficiency virus (HIV) and mouse mammary tumor virus (MMTV), are transmitted from mother to infants through milk. Lymphoid cells and antibodies are thought to provide mammary gland and milk-borne immunity. In contrast, little is known about the role of mammary epithelial cells (MECs). The APOBEC3 family of retroviral restriction factors is highly expressed in macrophages, lymphoid and dendritic cells. We now show that APOBEC3 proteins are also expressed in mouse and human MECs. Lymphoid cell expressed APOBEC3 restricts in vivo spread of MMTV to lymphoid and mammary tissue. In contrast, mammary gland expressed APOBEC3 is packaged into MMTV virions and decreases the infectivity of milk-borne viruses. Moreover, APOBEC3G and other APOBEC3 genes are expressed in human mammary cells and have the potential to restrict viruses produced in this cell type. These data point to a role for APOBEC3 proteins in limiting infectivity of milk-transmitted viruses.

Competitive relationships among Bradyrhizobium japonicum USDA serogroup 123, 122 and 138 were screened versus the standard commercial soybean variety Williams and two introductions P1 377578 "671" in a field trial. Displacement of strain 123 by an effective strain should improved N2 fixation. Root nodules were collected and strain occupancy percentage was determined using strain specific fluorescent antibodies technique. As anticipated the strain USDA 123 dominated 92% of nodules due to the high affinity between the host and the symbiont. This dominance was consistent and not changed materially either by inoculation practice or by introducing new strainan. The interrelationship between the genotype Williams and serogroup 122 & 138 was found very weak although the cell density of the strain in the rhizosphere area was equal. On the other hand, the nodule occupancy of genotypes 671 and 166 with rhizobia serogroup 123 was almost diminished to zero. . The data further exhibited that the genotypes P1 671 and P1 166 have high affinity to colonize with strains 122 and 138 whereas Williams was highly promiscuous to strain 123., {"references":["Amerger, N and Lobreau, J.P. (1982). Quantitive study of nodulation\ncompetitiveness in Rhizobium strains. Appl. Environ. Microbiol. 44: 583\n- 588.","Ham, G.E. (1980). Ineractions of Glycine max. and Rhizobium\njaponicum. In.R.J. Summerfield and A.H. Bunting (ed.) Advances in\nLegume Science. Royal Botinical Gardens. Kew, UK.: 289 - 296.","Cregan, B.E. and van Berkum, P. (1984). Genetics of nitrogen\nmetabolism and physiological / biochemical selection for increased grain\ncrop productivity. Theor. Appl. Genet. 67: 97 - 111.","Lohrke, S,M.; Orf, J.H.; Martinez-Romero, E. and Sadowsky, M.J.\n(1995). Host control restriction of nodulation by Bradyrhizobium\njaponicum strains in serogroup 110. Appl. Environ. Microbiol., 61 (6):\n2378 - 2383.","Ham, G.E.; Frederick, L.R. and Anderson, I.C. (1971). Serogroups of\nRhizobium japonicum in soybean nodules. Agron. J. 63: 69 - 72.","Kvien, C.S.; Ham, J.E. and Lambert, J.W. (1981). Recovery of\nintroduced Rhizobium japonicum strains by soybean genotypes. Agron J.\n73: 900 - 905.","Moawad, H.A.; Ellis, W.R. and Schmidt, E.L. (1984). Rhizosphere\nresponse as a factor of competition among three serogroups of\nindigenious Rhizobium japonicum for nodulation of field grown\nsoybeans. Appl. Environ. Microbiol. 47: 607 - 612.","Ham, G.E. (1976). Competition among strains of rhizobia. In. I.D. Hill\n(ed.). World Soybean Research. Institute Printers and Puplishers,\nDanville,IL.","Cregan, P.B. and Keyser, H.H. (1986). Host restrication of nodulation\nby Bradyrhizobium japonicum strain USDA 123 in soybean. Crop\nScience, 26: 911 - 916.\n[10] Weiser, G.C.; Skipper, H.D. and Wollum, A.G. 11 (1990). Exclusion of\ninefficient Bradyrhizobium japonicum serogroups by soybean\ngenotypes. Plant and Soil, 121 (1): 99 - 105.\n[11] Ferrey, M.L.; Graham, P.H. and Russelle, M.P. (1994). Nodulation\nefficiency of Bradyrhizobium japonicum strains with genotypes of\nsoybean varying in the ability to restrict nodulation. Canadian Journal of\nMicrobiolgy, 40 (6): 456 - 460.\n[12] Schmidt, E.L.; Bankole, R.O. and Bohlool, B.B. (1968). Fluorscentantibody\napproach to study rhizobia in soil. J. Bacteriol. 95: 1987 -\n1992.\n[13] Vincent, J.M. (1970). A Manual for The Practical Study of The Rootnodule\nBacteria. Int. Biological Programme Handbook no. 15. Blackwell\nScientific Puplication, Oxford, UK.\n[14] Reyes, V.G. and Schmidt,E.L. (1981). Population of Rhizobium\njaponicum associated with the surfaces of soil grown roots. Plant and\nSoil, 61: 71 - 80.\n[15] Pazdernik, D.L.; Vance, C.P.; Sadowsky, M.J.; Graham, P.H. and Orf,\nJ.H. (1997). A host- controlled, serogroup- specific, ineffectivenodulation\nsystem in the Bradyrhizobium-soybean (Glycine max)\nsymbiosis. Molecular-Plant-Microbe-Interaction, 10 (8): 994 -1001.\n[16] Caldwell, B.E. and Vest, G. (1970). Effect of Rhizobium japonicum\nstrains on soybean yields. Crop. Sci. 10: 19 - 21.\n[17] Cregan P.B.; Keyser, H.H. and Sadowsky, M.J. (1989). Host plant\neffects on nodulation and competitiveness of the Bradyrhizobium\njaponicum serotype strains consisting serocluster 123. Appl. Environ.\nMicrobiol., 55 (10): 2532 - 2536."]}

Background Host restriction factors (HRFs) TRIM5alpha and APOBECs effect post-entry inhibition of HIV-1 replication in vitro but in vivo significance remains unclear. By acting as a first line of defense, HRFs could potentially act synergistically with adaptive/vaccine-induced immunity. HRFs are polymorphic in world populations, but little is known about their variation in East Africa, despite its high rate of HIV-1 infection. This study describes trim5 and apobec polymorphisms in East African populations.

Host Restriction of HIV-1 by APOBEC3 and Viral Evasion Through Vif.- Interactions of Viral protein U (Vpu) with Cellular Factors.- TRIM5alpha.- Human Immunodeficiency Virus Type-1 Gag and Host Vesicular Trafficking Pathways.- The Roles of Tetraspanins in HIV-1 Replication.- Imaging of HIV/Host Protein Interactions.- Virological and Cellular Roles of the Transcriptional Coactivator LEDGF/p75.- Implications of Nef: Host Cell Interactions in Viral Persistence and Progression to AIDS.- Vpr and Its Interactions with Cellular Proteins.

APOBEC-mediated cytidine cleamination of HIV-1 genomes during reverse transcription has been shown to be a potent mechanism of host restriction for HIV-1 infection ex vivo and in vitro. However, this defense system can be overcome by the viral protein Vif. Unlike other mechanisms of host restriction, the APOCEC-Vif interaction leaves an imprint on integrated proviruses in the form of G-A hypermutation. in the current work we systematically studied levels, contexts, and patterns of HIV-1 hypermutation in vivo. the analysis of 24 full-genome HIV-1 sequences retrieved from primary PBMCs, representing infections with several HIV-1 clades, and the inclusion of 7 cognate pairs of hypermutated/non-hypermutated sequences derived from the same patient sample, provided a comprehensive view of the characteristics of APOBEC-mediated restriction in vivo. Levels of hypermutation varied nearly 5-fold among the studied proviruses. GpG motifs were most frequently affected (22/24 proviruses). Levels of hypermutation varied across the genome. the reported twin peak pattern of hypermutation was observed in 18/24 hypermutants, but the remainder exhibited singular non-conforming patterns. These data suggest considerable complexity in the interplay of host restriction and viral defense during HIV-1 infection. (c) 2008 Elsevier Inc. All rights reserved. Henry M Jackson Fdn Advancement Mil Med, US Mil HIV Res Program, Rockville, MD 20850 USA Universidade Federal de São Paulo, Paulista Sch Med, Div Infect Dis, BR-04039 São Paulo, Brazil Walter Reed Army Inst Res, Div Retrovirol, Rockville, MD 20850 USA Universidade Federal de São Paulo, Paulista Sch Med, Div Infect Dis, BR-04039 São Paulo, Brazil Web of Science

Background Vpr is exclusively expressed in primate lentiviruses and contributes to viral replication and disease progression in vivo. HIV-1 Vpr has two major activities in vitro: arrest of cell cycle in the G2 phase (G2 arrest), and enhancement of viral replication in macrophages. Previously, we reported a potent HIV-1 restriction in the human CD4+ CEM.NKR (NKR) T cells, where wild-type (WT) HIV-1 replication was inhibited by almost 1,000-fold. From the parental NKR cells, we isolated eight clones by limiting dilution. These clones showed three levels of resistance to the WT HIV-1 infection: non-permissive (NP), semi-permissive (SP), and permissive (P). Here, we compared the replication of WT, Vif-defective, Vpr-defective, and Vpu-defective viruses in these cells. Results Although both WT and Vpu-defective viruses could replicate in the permissive and semi-permissive clones, the replication of Vif-defective and Vpr-defective viruses was completely restricted. The expression of APOBEC3G (A3G) cytidine deaminase in NKR cells explains why Vif, but not Vpr, was required for HIV-1 replication. When the Vpr-defective virus life cycle was compared with the WT virus life cycle in the semi-permissive cells, it was found that the Vpr-defective virus could enter the cell and produce virions containing properly processed Gag and Env proteins, but these virions showed much less efficiency for reverse transcription during the next-round of infection. In addition, although viral replication was restricted in the non-permissive cells, treatment with arsenic trioxide (As2O3) could completely restore WT, but not Vpr-defective virus replication. Moreover, disruption of Vpr binding to its cofactor DCAF1 and/or induction of G2 arrest activity did not disrupt the Vpr activity in enhancing HIV-1 replication in NKR cells. Conclusions These results demonstrate that HIV-1 replication in NKR cells is Vpr-dependent. Vpr promotes HIV-1 replication from the 2nd cycle likely by overcoming a block at early stage of viral replication; and this activity does not require DCAF1 and G2 arrest. Further studies of this mechanism should provide new understanding of Vpr function in the HIV-1 life cycle.

Controlled animal experiments with the ovine maedi-visna virus, the prototype lentivirus, have been carried out for almost 40 years. This non-oncogenic virus leads to a life-long, persistent infection with slow development of lesions in the lungs and in the central nervous system. The virus is present in many cells in a DNA provirus state and its replication and expression is highly restricted in vivo. The basic biological features of maedi-visna virus are quite similar to those of HIV and this ovine lentiviral disease may be useful as a model for infection with human lentiviruses.

On the assumption that there may be significant differences in the length of ascospores of Claviceps purpurea from different hosts, and that such differences are primarily under genetic control, a comparative study was made of 85 samples of ascospores obtained from ergots that had been collected from 28 species of British grasses belonging to 24 genera and 10 tribes. Because it is shown that different samples of ascospores from the same hosts could reasonably represent parts of the same population, it is possible to separate populations of ascospores obtained from different hosts into groups by using Duncan's multiple range test. On the basis of the mean length of their ascospores, the population means for 17 different grasses, covering 16 different genera, may be divided at a probability level of 005% into three groups. One group (with ascospores averaging > 100 μm long) includes the strains of C. purpurea infecting Triticum aestivum, Glyceria fluitans and Brachypodium sylvaticum , a second group (with ascospores averaging 79–91 μm long) contains the strains infecting all the other grasses included in the test except Deschampsia caespitosa , which is the only member of a third group (with ascospores averaging C. purpurea infecting the four abovementioned grasses are host-restricted. This conclusion is discussed in relation to the results of cross-inoculation experiments, and alkaloid analyses of ergot sclerotia, carried out by other workers.

Acinetobacter calcoaceticus strain EBF65/65 harbours a cryptic plasmid, pAV2, which has been shown by electrophoretic separation on agarose gels to have a molecular mass of approximately 13.5 megadaltons (Md). Transfer of the previously described sex factor pAV1 (Hinchliffe & Vivian, 1980a, b) from the hospital strain JC17 into strains possessing pAV2 occurs only at a low frequency, whereas transfer to similar strains lacking pAV2 occurs at a much higher frequency. In EBF65/65, pAV1 may be present in strains possessing or lacking pAV2; pAV1 strains lacking pAV2 correspond to strains previously described as pAV1a (Hinchliffe & Vivian, 1980b) whereas pAV1 strains which also possess pAV2 correspond to pAV1b strains. The genetic evidence presented here is consistent with the hypothesis that pAV2 specifies a host restriction and modification system that is active against pAV1. Physical evidence from agarose gel electrophoresis indicates that pAV1 corresponds to a band of approximately 85 Md in strain JC17. The corresponding band in strains of EBF65/65 is difficult to distinguish because of the presence of a further cryptic plasmid band of approximately 88 Md, designated pAV3. A small cryptic plasmid of approximately 6 Md, designated pAV4, is reported for EBF65/65.

A review of the pleioxenous genera of fleas, those genera whose species are confined to hosts of a single family, indicates that such a restriction results from one of several situations. Genera of 10 or more taxa (species and subspecies) were considered, so as to exclude very small genera that might be relicts. Polyxenous genera, whose species occur regularly on two or more families (and frequently on two or more orders) of hosts are far more numerous than pleioxenous genera. Bat fleas (Ischnopsyllidae) are unique in that all genera are pleioxenous. This seems to reflect the fact that most bat fleas occur on cave-dwelling bats, and that the cave provides for larval development of bat fleas. Five pleioxenous genera occur on rodents in deserts or semiarid regions. The extreme climatic changes that have been concomitant with desertification from the Mid-Cenozoic, and especially in the Pleistocene, are paralleled by the proliferation of the mammalian hosts themselves in deserts. Three pleioxenous genera are ...

Rescue of wild-type markers from transfecting phage DNA in cómpetent Haemophilus influenzae cells by superinfection with temperature-sensitive phage (marker rescue) is approximately linearly dependent upon the concentration of transfecting DNA. The amount of marker rescue with a constant amount of transfecting DNA increases with increasing multiplicities of superinfecting phage up to about 4, and then decreases at higher multiplicities. Host restriction of transfecting DNA does not affect marker rescue. The frequency of wild-type recombinants from marker rescue is much greater than that from multiple infection with whole phages, and is comparable to that obtained with two mutant-transfecting DNAs. The amount of marker rescue decreases exponentially with time between entrance of the transfecting DNA and superinfection, and the rate of decrease is independent of map position of the rescued marker. Marker rescue is drastically reduced in the recombination-defective strains, rec1 and rec2.

Notwithstanding the far-reaching importance of the host affinities of plant-feeding insects and the large volume of available data on host relations of particular insect pests, little attention has been devoted to the general aspects of host restriction. This condition is the more remarkable because virtually all problems in applied agricultural entomology are vitally affected by the degree of restriction of feeding habits exhibited by economic species.

The gammaretrovirus, xenotropic murine leukemia virus-related virus (XMRV), replicates to high titers in some human cell lines and is able to infect non-human primates. To determine whether APOBEC3 (A3) proteins restrict XMRV infections in a non-human primate model, we sequenced proviral DNA from peripheral blood mononuclear cells of XMRV-infected rhesus macaques. Hypermutation characteristic of A3DE, A3F and A3G activities was observed in the XMRV proviral sequences in vivo. Furthermore, expression of rhesus A3DE, A3F, or A3G in human cells inhibited XMRV infection and caused hypermutation of XMRV DNA. These studies show that some rhesus A3 isoforms are highly effective against XMRV in the blood of a non-human primate model of infection and in cultured human cells.

Mammalian cells are equipped with so-called "restriction factors" that suppress virus replication and help to prevent virus transmission from one species to another. This Essay discusses the host restriction factor tetherin, which blocks the release of enveloped viruses like HIV-1, and the factors evolved by primate lentiviruses, such as Vpu and Nef, that antagonize tetherin's action.

The host restriction factor SAMHD1 hinders lentiviral infection of myeloid cells, a function counteracted by the viral protein Vpx. Two papers in this issue of Cell Host & Microbe document the genetic conflict between SAMHD1 and the Vpr/Vpx proteins, which has subjected SAMHD1 to intense periods of diversifying selection through primate evolution.