Uracil DNA Glycosylase 2 negatively regulates HIV-1 LTR transcription

Numerous cellular factors belonging to the DNA repair machineries, including RAD18, RAD52, XPB and XPD, have been described to counteract human immunodeficiency virus type 1 (HIV-1) replication. Recently, Uracil DNA glycosylase 2 (UNG2), a major determinant of the uracil base excision repair pathway, was shown to undergo rapid proteasome-dependent degradation following HIV-1 infection. However, the specific role of intracellular UNG2 depletion during the course of HIV-1 infection is not clearly understood. Our study shows for the first time that overexpression of UNG2 inhibits HIV-1 replication. We demonstrate that this viral inhibition is correlated with a marked decrease in transcription efficiency as shown by monitoring HIV-1 LTR promoter activity and quantification of HIV-1 RNA levels. Interestingly, UNG2 inhibits LTR activity when stimulated by Tat transactivator or TNFα, while barely affected using Phorbol ester activation. Mutational analysis of UNG2 indicates that antiviral activity may require the integrity of the UNG2 catalytic domain. Altogether, our data indicate that UNG2 is likely to represent a new host defense factor specifically counteracted by HIV-1 Vpr. The molecular mechanisms involved in the UNG2 antiviral activity still remain elusive but may rely on the sequestration of specific cellular factor(s) critical for viral transcription

Cardioprotective Effects of Glycyrrhizic Acid Against Isoproterenol-Induced Myocardial Ischemia in Rats

The aim of the present study was to look into the possible protective effects of glycyrrhizic acid (GA) against isoproterenol-induced acute myocardial infarction in Sprague-Dawley rats. The effect of three doses of glycyrrhizic acid in response to isoproterenol (ISO)-induced changes in 8-isoprostane, lipid hydroperoxides, super oxide dismutase and total glutathione were evaluated. Male Sprague-Dawley rats were divided into control, ISO-control, glycyrrhizic acid alone (in three doses-5, 10 and 20 mg/kg BW) and ISO with glycyrrhizic acid (in three doses) groups. ISO was administered at 85 mg/kg BW at two consecutive days and glycyrrhizic acid was administered intraperitoneally for 14 days. There was a significant increase in 8-isoprostane (IP) and lipid hydroperoxide (LPO) level in ISO-control group. A significant decrease in total superoxide dismutase (SOD) and total glutathione (GSH) was seen with ISO-induced acute myocardial infarction. Treatment with GA significantly increased SOD and GSH levels and decreased myocardial LPO and IP levels. Histopathologically, severe myocardial necrosis and nuclear pyknosis and hypertrophy were seen in ISO-control group, which was significantly reduced with GA treatment. Gycyrrhizic acid treatment proved to be effective against isoproterenol-induced acute myocardial infarction in rats and GA acts as a powerful antioxidant and reduces the myocardial lipid hydroperoxide and 8-isoprostane level

Characterization of the Interaction of Full-Length HIV-1 Vif Protein with its Key Regulator CBFβ and CRL5 E3 Ubiquitin Ligase Components

Human immunodeficiency virus-1 (HIV-1) viral infectivity factor (Vif) is essential for viral replication because of its ability to eliminate the host's antiviral response to HIV-1 that is mediated by the APOBEC3 family of cellular cytidine deaminases. Vif targets these proteins, including APOBEC3G, for polyubiquitination and subsequent proteasome-mediated degradation via the formation of a Cullin5-ElonginB/C-based E3 ubiquitin ligase. Determining how the cellular components of this E3 ligase complex interact with Vif is critical to the intelligent design of new antiviral drugs. However, structural studies of Vif, both alone and in complex with cellular partners, have been hampered by an inability to express soluble full-length Vif protein. Here we demonstrate that a newly identified host regulator of Vif, core-binding factor-beta (CBFβ), interacts directly with Vif, including various isoforms and a truncated form of this regulator. In addition, carboxyl-terminal truncations of Vif lacking the BC-box and cullin box motifs were sufficient for CBFβ interaction. Furthermore, association of Vif with CBFβ, alone or in combination with Elongin B/C (EloB/C), greatly increased the solubility of full-length Vif. Finally, a stable complex containing Vif-CBFβ-EloB/C was purified in large quantity and shown to bind purified Cullin5 (Cul5). This efficient strategy for purifying Vif-Cul5-CBFβ-EloB/C complexes will facilitate future structural and biochemical studies of Vif function and may provide the basis for useful screening approaches for identifying novel anti-HIV drug candidates

Evolutionarily conserved and non-conserved retrovirus restriction activities of artiodactyl APOBEC3F proteins

The APOBEC3 proteins are unique to mammals. Many inhibit retrovirus infection through a cDNA cytosine deamination mechanism. HIV-1 neutralizes this host defense through Vif, which triggers APOBEC3 ubiquitination and degradation. Here, we report an APOBEC3F-like, double deaminase domain protein from three artiodactyls: cattle, pigs and sheep. Like their human counterparts, APOBEC3F and APOBEC3G, the artiodactyl APOBEC3F proteins are DNA cytosine deaminases that locate predominantly to the cytosol and can inhibit the replication of HIV-1 and MLV. Retrovirus restriction is attributable to deaminase-dependent and -independent mechanisms, as deaminase-defective mutants retain significant anti-retroviral activity. However, unlike human APOBEC3F and APOBEC3G, the artiodactyl APOBEC3F proteins have an active N-terminal DNA cytosine deaminase domain, which elicits a broader dinucleotide deamination preference, and they are resistant to HIV-1 Vif. These data indicate that DNA cytosine deamination; sub-cellular localization and retrovirus restriction activities are conserved in mammals, whereas active site location, local mutational preferences and Vif susceptibility are not. Together, these studies indicate that some properties of the mammal-specific, APOBEC3-dependent retroelement restriction system are necessary and conserved, but others are simultaneously modular and highly adaptable

Encapsidation of APOBEC3G into HIV-1 virions involves lipid raft association and does not correlate with APOBEC3G oligomerization

<p>Abstract</p> <p>Background</p> <p>The cellular cytidine deaminase APOBEC3G (A3G), when incorporated into the human immunodeficiency virus type 1 (HIV-1), renders viral particles non-infectious. We previously observed that mutation of a single cysteine residue of A3G (C100S) inhibited A3G packaging. In addition, several recent studies showed that mutation of tryptophan 127 (W127) and tyrosine 124 (Y124) inhibited A3G encapsidation suggesting that the N-terminal CDA constitutes a viral packaging signal in A3G. It was also reported that W127 and Y124 affect A3G oligomerization.</p> <p>Results</p> <p>Here we studied the mechanistic basis of the packaging defect of A3G W127A and Y124A mutants. Interestingly, cell fractionation studies revealed a strong correlation between encapsidation, lipid raft association, and genomic RNA binding of A3G. Surprisingly, the presence of a C-terminal epitope tag affected lipid raft association and encapsidation of the A3G W127A mutant but had no effect on wt A3G encapsidation, lipid raft association, and interaction with viral genomic RNA. Mutation of Y124 abolished A3G encapsidation irrespective of the presence or absence of an epitope tag. Contrasting a recent report, our co-immunoprecipitation studies failed to reveal a correlation between A3G oligomerization and A3G encapsidation. In fact, our W127A and Y124A mutants both retained the ability to oligomerize.</p> <p>Conclusion</p> <p>Our results confirm that W127 and Y124 residues in A3G are important for encapsidation into HIV-1 virions and our data establish a novel correlation between genomic RNA binding, lipid raft association, and viral packaging of A3G. In contrast, we were unable to confirm a role of W127 and Y124 in A3G oligomerization and we thus failed to confirm a correlation between A3G oligomerization and virus encapsidation.</p

Model Structure of Human APOBEC3G

BACKGROUND: APOBEC3G (apolipoprotein B mRNA-editing enzyme, catalytic polypeptide-like 3G) has antiretroviral activity associated with the hypermutation of viral DNA through cytosine deamination. APOBEC3G has two cytosine deaminase (CDA) domains; the catalytically inactive amino-terminal domain of APOBEC3G (N-CDA) carries the Vif interaction domain. There is no 3-D structure of APOBEC3G solved by X-ray or nuclear magnetic resonance. METHODOLOGY/PRINCIPAL FINDINGS: We predicted the structure of human APOBEC3G based on the crystal structure of APOBEC2. To assess the model structure, we evaluated 48 mutants of APOBEC3G N-CDA that identify novel variants altering ΔVif HIV-1 infectivity and packaging of APOBEC3G. Results indicated that the key residue D128 is exposed at the surface of the model, with a negative local electrostatic potential. Mutation D128K changes the sign of that local potential. In addition, two novel functionally relevant residues that result in defective APOBEC3G encapsidation, R122 and W127, cluster at the surface. CONCLUSIONS/SIGNIFICANCE: The structure model identifies a cluster of residues important for packaging of APOBEC3G into virions, and may serve to guide functional analysis of APOBEC3G

Mouse Apolipoprotein B Editing Complex 3 (APOBEC3) Is Expressed in Germ Cells and Interacts with Dead-End (DND1)

encoded protein, DND1, is able to bind to the 3′-untranslated region (UTR) of messenger RNAs (mRNAs) to displace micro-RNA (miRNA) interaction with mRNA. Thus, one function of DND1 is to prevent miRNA mediated repression of mRNA. We report that DND1 interacts specifically with APOBEC3. APOBEC3 is a multi-functional protein. It inhibits retroviral replication. In addition, recent studies show that APOBEC3 interacts with cellular RNA-binding proteins and to mRNA to inhibit miRNA-mediated repression of mRNA.Here we show that DND1 specifically interacts with another cellular protein, APOBEC3. We present our data which shows that DND1 co-immunoprecipitates APOBEC3 from mammalian cells and also endogenous APOBEC3 from mouse gonads. Whether the two proteins interact directly remains to be elucidated. We show that both DND1 and APOBEC3 are expressed in germ cells and in the early gonads of mouse embryo. Expression of fluorescently-tagged DND1 and APOBEC3 indicate they localize to the cytoplasm and when DND1 and APOBEC3 are expressed together in cells, they sequester near peri-nuclear sites.The 3′-UTR of mRNAs generally encode multiple miRNA binding sites as well as binding sites for a variety of RNA binding proteins. In light of our findings of DND1-APOBEC3 interaction and taking into consideration reports that DND1 and APOBEC3 bind to mRNA to inhibit miRNA mediated repression, our studies implicate a possible role of DND1-APOBEC3 interaction in modulating miRNA-mediated mRNA repression. The interaction of DND1 and APOBEC3 could be one mechanism for maintaining viability of germ cells and for preventing germ cell tumor development

Characterization of the Molecular Determinants of Primary HIV-1 Vpr Proteins: Impact of the Q65R and R77Q Substitutions on Vpr Functions

Although HIV-1 Vpr displays several functions in vitro, limited information exists concerning their relevance during infection. Here, we characterized Vpr variants isolated from a rapid and a long-term non-progressor (LTNP). Interestingly, vpr alleles isolated from longitudinal samples of the LTNP revealed a dominant sequence that subsequently led to diversity similar to that observed in the progressor patient. Most of primary Vpr proteins accumulated at the nuclear envelope and interacted with host-cell partners of Vpr. They displayed cytostatic and proapoptotic activities, although a LTNP allele, harboring the Q65R substitution, failed to bind the DCAF1 subunit of the Cul4a/DDB1 E3 ligase and was inactive. This Q65R substitution correlated with impairment of Vpr docking at the nuclear envelope, raising the possibility of a functional link between this property and the Vpr cytostatic activity. In contradiction with published results, the R77Q substitution, found in LTNP alleles, did not influence Vpr proapoptotic activity

RNA-Dependent Oligomerization of APOBEC3G Is Required for Restriction of HIV-1

The human cytidine deaminase APOBEC3G (A3G) is a potent inhibitor of retroviruses and transposable elements and is able to deaminate cytidines to uridines in single-stranded DNA replication intermediates. A3G contains two canonical cytidine deaminase domains (CDAs), of which only the C-terminal one is known to mediate cytidine deamination. By exploiting the crystal structure of the related tetrameric APOBEC2 (A2) protein, we identified residues within A3G that have the potential to mediate oligomerization of the protein. Using yeast two-hybrid assays, co-immunoprecipitation, and chemical crosslinking, we show that tyrosine-124 and tryptophan-127 within the enzymatically inactive N-terminal CDA domain mediate A3G oligomerization, and this coincides with packaging into HIV-1 virions. In addition to the importance of specific residues in A3G, oligomerization is also shown to be RNA-dependent. Homology modelling of A3G onto the A2 template structure indicates an accumulation of positive charge in a pocket formed by a putative dimer interface. Substitution of arginine residues at positions 24, 30, and 136 within this pocket resulted in reduced virus inhibition, virion packaging, and oligomerization. Consistent with RNA serving a central role in all these activities, the oligomerization-deficient A3G proteins associated less efficiently with several cellular RNA molecules. Accordingly, we propose that occupation of the positively charged pocket by RNA promotes A3G oligomerization, packaging into virions and antiviral function

Genomics meets HIV-1

Genomics is now a core element in the effort to develop a vaccine against HIV-1. Thanks to unprecedented progress in high-throughput genotyping and sequencing, in knowledge about genetic variation in humans, and in evolutionary genomics, it is finally possible to systematically search the genome for common genetic variants that influence the human response to HIV-1. The identification of such variants would help to determine which aspects of the response to the virus are the most promising targets for intervention. However, a key obstacle to progress remains the scarcity of appropriate human cohorts available for genomic research