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Query: UMLS:C0021051 (immunodeficiency)
 71,517 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The envelope of class I viruses can be a target for potent viral inhibitors, such as the human immunodeficiency virus type 1 (HIV-1) inhibitor enfuvirtide, which are derived from the C-terminal heptad repeat (HR2) of the transmembrane (TM) subunit. Resistance to an HR2-based peptide inhibitor of a model retrovirus, subgroup A of the Avian Sarcoma and Leukosis Virus genus (ASLV-A), was studied by examining mutants derived by viral passage in the presence of inhibitor. Variants with reduced sensitivity to inhibitor were readily selected in vitro. Sensitivity determinants were identified for 13 different isolates, all of which mapped to the TM subunit. These determinants were identified in two regions: (i) the N-terminal heptad repeat (HR1) and (ii) the N-terminal segment of TM, between the subunit cleavage site and the fusion peptide. The latter class of mutants identified a region outside of the predicted HR2-binding site that can significantly alter sensitivity to inhibitor. A subset of the HR1 mutants displayed the unanticipated ability to infect nonavian cells. This expanded tropism was associated with increased efficiency of envelope triggering by soluble receptor at low temperatures, as measured by protease sensitivity of the surface subunit (SU) of envelope. In addition, expanded tropism was linked for the most readily triggered mutants with increased sensitivity to neutralization by SU-specific antiserum. These observations depict a class of HR2 peptide-selected mutations with a reduced activation threshold, thereby allowing the utilization of alternative receptors for viral entry.
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PMID:Expanded tropism and altered activation of a retroviral glycoprotein resistant to an entry inhibitor peptide. 1635 60

We mapped 226 unique integration sites in human hepatoma cells following gene transfer with a feline immunodeficiency virus (FIV)-based lentivirus vector. FIV integrated across the entire length of the transcriptional units. Microarray data indicated that FIV integration favored actively transcribed genes. Approximately 21% of FIV integrations within transcriptional units occurred in genes regulated by the LEDGF/p75 transcriptional coactivator. DNA in regions of FIV insertion sites exhibited a "bendable" structure and a pattern of duplex destabilization favoring strand separation. FIV integration preferences are more similar to those of primate lentiviruses and distinct from those of Moloney murine leukemia virus, avian sarcoma leukosis virus, and foamy virus.
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PMID:Integration site choice of a feline immunodeficiency virus vector. 1691 28

Retroviral integration into the host genome is not entirely random, and integration site preferences vary among different retroviruses. Human immunodeficiency virus (HIV) prefers to integrate within active genes, whereas murine leukemia virus (MLV) prefers to integrate near transcription start sites and CpG islands. On the other hand, integration of avian sarcoma-leukosis virus (ASLV) shows little preference either for genes, transcription start sites, or CpG islands. While host cellular factors play important roles in target site selection, the viral integrase is probably the major viral determinant. It is reasonable to hypothesize that retroviruses with similar integrases have similar preferences for target site selection. Although integration profiles are well defined for members of the lentivirus, spumaretrovirus, alpharetrovirus, and gammaretrovirus genera, no members of the deltaretroviruses, for example, human T-cell leukemia virus type 1 (HTLV-1), have been evaluated. We have mapped 541 HTLV-1 integration sites in human HeLa cells and show that HTLV-1, like ASLV, does not specifically target transcription units and transcription start sites. Comparing the integration sites of HTLV-1 with those of ASLV, HIV, simian immunodeficiency virus, MLV, and foamy virus, we show that global and local integration site preferences correlate with the sequence/structure of virus-encoded integrases, supporting the idea that integrase is the major determinant of retroviral integration site selection. Our results suggest that the global integration profiles of other retroviruses could be predicted from phylogenetic comparisons of the integrase proteins. Our results show that retroviruses that engender different insertional mutagenesis risks can have similar integration profiles.
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PMID:Human T-cell leukemia virus type 1 integration target sites in the human genome: comparison with those of other retroviruses. 1740 38

Genome-wide integration site analyses showed that Moloney murine leukemia virus (MoMLV)- and lentivirus-derived vectors integrate preferentially into the coding regions of genes, posing a risk of insertional mutagenesis. Avian sarcoma and leukosis viruses (ASLVs) were previously reported to have a weak preference for gene-coding regions in a cell line study as compared with human immunodeficiency virus and MoMLV; however, thus far these vectors have not been studied for their potential efficacy in transduction of hematopoietic progenitor and stem cells. In this study we investigated for the first time the ability of ASLV-derived RCAS (replication-competent ALV LTR [avian leukosis virus long terminal repeat] with a splice acceptor) vectors to transduce rhesus macaque hematopoietic progenitors and long-term repopulating cells, in an autologous transplantation model. RCAS vectors can efficiently and stably transduce rhesus macaque CD34+ hematopoietic progenitor cells with an efficiency of transduction of up to 34% ex vivo. In two animals transplanted with RCAS vector-transduced autologous CD34+ cells, highly polyclonal hematopoietic reconstitution with sustained gene-marking levels in myeloid and lymphoid lineages was observed up to 18 months post-transplantation. These findings are encouraging and suggest that this vector system should be explored and further optimized for gene therapy applications targeting hematopoietic stem and progenitor cells.
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PMID:Transduction of rhesus macaque hematopoietic stem and progenitor cells with avian sarcoma and leukosis virus vectors. 1765 93

Cells expressing the low pH-triggered class II viral fusion protein E1 of Semliki Forest virus (SFV) were fused to target cells. Fusion was monitored by electrical capacitance and aqueous dye measurements. Electrical voltage-clamp measurements showed that SFV E1-induced cell-cell fusion occurred quickly after acidification for a trans-negative potential across the target membrane (i.e., negative potential inside the target cell) but that a trans-positive potential eliminated all fusion. Use of an ionophore to control potentials for a large population of cells confirmed the dependence of fusion on voltage polarity. In contrast, fusion induced by the class I fusion proteins of human immunodeficiency virus, avian sarcoma leukosis virus, and influenza virus was independent of the voltage polarity across the target cell. Initial pore size and pore growth were also independent of voltage polarity for the class I proteins. An intermediate of SFV E1-induced fusion was created by transient acidification at low temperature. Membranes were hemifused at this intermediate state, and raising the temperature at neutral pH allowed full fusion to occur. Capacitance measurements showed that maintaining a trans-positive potential definitely blocked fusion at steps following the creation of the hemifusion intermediate and may have inhibited fusion at prior steps. It is proposed that the trans-negative voltage across the endosomal membrane facilitates fusion after low-pH-induced conformational changes of SFV E1 have occurred.
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PMID:Fusion induced by a class II viral fusion protein, semliki forest virus E1, is dependent on the voltage of the target cell. 1768 70

Integrase (IN) catalyzes insertion of the retroviral genome into the host via two sequential reactions. The processing activity cleaves the 3'-dinucleotides from the two ends of the viral DNA which are then inserted into the host DNA. Tetramers are required for the joining step. While dimers have been shown to catalyze processing, they do so inefficiently, and the oligomeric requirement for processing is unknown. We have replaced loop202-208 at the putative dimer-dimer interface of the avian sarcoma virus IN with its analogue, loop188-194, from human immunodeficiency virus IN. The mutation abolished disintegration activity and a 2 x 10(-2) s-1 fast phase during single-turnover processing. A 3 x 10(-4) s-1 slow processing phase was unaffected. Preincubation with a DNA substrate known to promote tetramerization increased products formed during the fast phase by 2.5-fold only for wild-type IN, correlating the fast and slow phases with processing by tetramers and dimers, respectively. We propose a novel tetramer model for coupling processing and integration based on efficient processing by the tetramer. We provide for the first time direct evidence of the functional relevance of a structural element, loop202-208, which appears to be required for mediating the interaction between dimer halves of the active tetramer.
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PMID:Loop202-208 in avian sarcoma virus integrase mediates tetramer assembly and processing activity. 1784 8

Based on integration site preferences, retroviruses can be placed into three groups. Viruses that comprise the first group, murine leukemia virus and foamy virus, integrate preferentially near transcription start sites. The second group, notably human immunodeficiency virus and simian immunodeficiency virus, preferentially targets transcription units. Avian sarcoma-leukosis virus (ASLV) and human T-cell leukemia virus (HTLV), forming the third group, show little preference for any genomic feature. We have previously shown that some human cells sustain mouse mammary tumor virus (MMTV) infection; therefore, we infected a susceptible human breast cell line, Hs578T, and, without introducing a species-specific bias, compared the MMTV integration profile to those of other retroviruses. Additionally, we infected a mouse cell line, NMuMG, and thus we could compare MMTV integration site selection in human and mouse cells. In total, we examined 468 unique MMTV integration sites. Irrespective of whether human or mouse cells were infected, no integration bias favoring transcription start sites was detected, a profile that is reminiscent of that of ASLV and HTLV. However, in contrast to ASLV and HTLV, not even a modest tendency in favor of integration within genes was observed. Similarly, repetitive sequences and genes that are frequently tagged by MMTV in mammary tumors were not preferentially targeted in cell culture either in mouse or in human cells; hence, we conclude that MMTV displays the most random dispersion of integration sites among retroviruses determined so far.
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PMID:Mouse mammary tumor virus integration site selection in human and mouse genomes. 1803 9

Insertional mutagenesis continues to be a major concern in hematopoietic stem-cell gene therapy. Nonconventional gene transfer vectors with more favorable integration features in comparison with conventional retrovirus and lentivirus vectors are being developed and optimized. In this study, we report for the first time a systematic analysis of 198 avian sarcoma leukosis virus (ASLV) insertion sites identified in rhesus long-term repopulating cells, and a comparison of ASLV insertion patterns to Moloney murine leukemia virus (MLV) (n = 396) and simian immunodeficiency virus (SIV) (n = 289) using the newly released rhesus genome databank. Despite a weak preference toward gene-coding regions, ASLV integration is nonclustered, does not favor gene-rich regions, transcription start sites, or CpG islands. There was no propensity for ASLV insertions within or near proto-oncogenes, and most importantly, no insertions close to or within the Mds1-Evi1 locus, which is in contrast to the significant over-representation of this insertion site for MLV vectors in the same transplantation model. Furthermore, ASLV long terminal repeats (LTRs) do not have detectable promoter and enhancer activity in a quantitative luciferase assay to measure neighboring gene activation. The combination of these features is unique for ASLV and suggests that optimized vectors based on this virus could be useful and safe for gene transfer to hematopoietic stem cells and progenitor cells.
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PMID:Reduced genotoxicity of avian sarcoma leukosis virus vectors in rhesus long-term repopulating cells compared to standard murine retrovirus vectors. 1857 11

A tetramer model for human immunodeficiency virus type 1 (HIV-1) integrase (IN) with DNA representing long terminal repeat (LTR) termini was previously assembled to predict the IN residues that interact with the LTR termini; these predictions were experimentally verified for nine amino acid residues [Chen, A., Weber, I. T., Harrison, R. W. & Leis, J. (2006). Identification of amino acids in HIV-1 and avian sarcoma virus integrase subsites required for specific recognition of the long terminal repeat ends. J. Biol. Chem., 281, 4173-4182]. In a similar strategy, the unique amino acids found in avian sarcoma virus IN, rather than HIV-1 or Mason-Pfizer monkey virus IN, were substituted into the structurally related positions of HIV-1 IN. Substitutions of six additional residues (Q44, L68, E69, D229, S230, and D253) showed changes in the 3' processing specificity of the enzyme, verifying their predicted interaction with the LTR DNA. The newly identified residues extend interactions along a 16-bp length of the LTR termini and are consistent with known LTR DNA/HIV-1 IN cross-links. The tetramer model for HIV-1 IN with LTR termini was modified to include two IN binding domains for lens-epithelium-derived growth factor/p75. The target DNA was predicted to bind in a surface trench perpendicular to the plane of the LTR DNA binding sites of HIV-1 IN and extending alongside lens-epithelium-derived growth factor. This hypothesis is supported by the in vitro activity phenotype of HIV-1 IN mutant, with a K219S substitution showing loss in strand transfer activity while maintaining 3' processing on an HIV-1 substrate. Mutations at seven other residues reported in the literature have the same phenotype, and all eight residues align along the length of the putative target DNA binding trench.
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PMID:Defining the DNA substrate binding sites on HIV-1 integrase. 1901 51

Establishment of the stable provirus is an essential step in retroviral replication, orchestrated by integrase (IN), a virus-derived enzyme. Until now, available structural information was limited to the INs of human immunodeficiency virus type 1 (HIV-1), avian sarcoma virus (ASV) and their close orthologs from the Lentivirus and Alpharetrovirus genera. Here, we characterized the in vitro activity of the prototype foamy virus (PFV) IN from the Spumavirus genus and determined the three-dimensional structure of its catalytic core domain (CCD). Recombinant PFV IN displayed robust and almost exclusively concerted integration activity in vitro utilizing donor DNA substrates as short as 16 bp, underscoring its significance as a model for detailed structural studies. Comparison of the HIV-1, ASV and PFV CCD structures highlighted both conserved as well as unique structural features such as organization of the active site and the putative host factor binding face. Despite possessing very limited sequence identity to its HIV counterpart, PFV IN was sensitive to HIV IN strand transfer inhibitors, suggesting that this class of inhibitors target the most conserved features of retroviral IN-DNA complexes.
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PMID:Functional and structural characterization of the integrase from the prototype foamy virus. 1903 93


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