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Gag, vif, and nef genes contribute to the homologous viral interference induced by a nonproducer human immunodeficiency virus type 1 (HIV-1) variant: identification of novel HIV-1-inhibiting viral protein mutants.

ABSTRACT: We previously demonstrated that expression of the nonproducer F12-human immunodeficiency virus type 1 (HIV-1) variant induces a block in the replication of superinfecting HIV that does not depend on the down-regulation of CD4 HIV receptors. In order to individuate the gene(s) involved in F12-HIV-induced interference, vectors expressing each of the nine F12-HIV proteins were transfected in HIV-susceptible HeLa CD4 cells. Pools of cell clones stably producing each viral protein were infected with HIV-1, and virus release was measured in terms of reverse transcriptase activity in supernatants. We hereby demonstrate that HeLa CD4 cells expressing the F12-HIV gag, vif, or nef gene were resistant, to different degrees, to infection with T-cell-line-adapted HIV-1 strains. Conversely, expression of either the tat, rev, or vpu F12-HIV gene increased the rate of HIV release, and no apparent effects on HIV replication were observed in cells expressing either the F12-HIV vpr, pol, or env gene. No variation of CD4 exposure was detected in any of the uninfected HeLa CD4 pools. These data indicate that F12-HIV homologous viral interference is the consequence of the synergistic anti-HIV effects of Gag, Vif, and Nef proteins. Retrovirus vectors expressing F12-HIV vif or nef allowed us to further establish that the expression of each mutated protein (i) inhibits the replication of clinical HIV-1 isolates as well, (ii) impairs the infectivity of the virus released by cells chronically infected with HIV-1, and (iii) limitedly to F12-HIV Vif protein, induces HIV resistance in both vif-permissive and vif-nonpermissive cells. The levels of action of F12-HIV vif and nef anti-HIV effects were also determined. We observed that HIV virions emerging from the first viral cycle on F12-HIV vif-expressing cells, although released in unaltered amounts, had a strongly reduced ability to initiate the retrotranscription process when they reinfected parental HeLa CD4 cells. Differently, we observed that expression of F12-HIV Nef protein affects the HIV life cycle at the level of viral assembling and/or release. For the first time, an inhibitory effect on the HIV life cycle in both acutely and chronically infected cells induced by mutated Vif and Nef HIV-1 proteins is described. These genes could thus be proposed as new useful reagents for anti-HIV gene therapy.

SUBMITTER: D'Aloja P

PROVIDER: S-EPMC109661 | biostudies-literature | 1998 May

REPOSITORIES: biostudies-literature

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gag, vif, and nef genes contribute to the homologous viral interference induced by a nonproducer human immunodeficiency virus type 1 (HIV-1) variant: identification of novel HIV-1-inhibiting viral protein mutants.

D'Aloja P P Olivetta E E Bona R R Nappi F F Pedacchia D D Pugliese K K Ferrari G G Verani P P Federico M M

Journal of virology 19980501 5

We previously demonstrated that expression of the nonproducer F12-human immunodeficiency virus type 1 (HIV-1) variant induces a block in the replication of superinfecting HIV that does not depend on the down-regulation of CD4 HIV receptors. In order to individuate the gene(s) involved in F12-HIV-induced interference, vectors expressing each of the nine F12-HIV proteins were transfected in HIV-susceptible HeLa CD4 cells. Pools of cell clones stably producing each viral protein were infected with ...[more]

PMID: 9557721

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Project description:Broadly targeted cellular immune responses are thought to be important for controlling replication of human and simian immunodeficiency viruses (HIV and SIV). However, eliciting such responses by vaccination is complicated by immunodominance, the preferential targeting of only a few of the many possible epitopes of a given antigen. This phenomenon may be due to the coexpression of dominant and subdominant epitopes by the same antigen-presenting cell and may be overcome by distributing these sequences among several different vaccine constructs. Accordingly, we tested whether vaccinating rhesus macaques with "minigenes" encoding fragments of Gag, Vif, and Nef resulted in broadened cellular responses capable of controlling SIV replication. We delivered these minigenes through combinations of recombinant Mycobacterium bovis BCG (rBCG), electroporated recombinant DNA (rDNA) along with an interleukin-12 (IL-12)-expressing plasmid (EP rDNA plus pIL-12), yellow fever vaccine virus 17D (rYF17D), and recombinant adenovirus serotype 5 (rAd5). Although priming with EP rDNA plus pIL-12 increased the breadth of vaccine-induced T-cell responses, this effect was likely due to the improved antigen delivery afforded by electroporation rather than modulation of immunodominance. Indeed, Mamu-A*01(+) vaccinees mounted CD8(+) T cells directed against only one subdominant epitope, regardless of the vaccination regimen. After challenge with SIVmac239, vaccine efficacy was limited to a modest reduction in set point in some of the groups and did not correlate with standard T-cell measurements. These findings suggest that broad T-cell responses elicited by conventional vectors may not be sufficient to substantially contain AIDS virus replication.Immunodominance poses a major obstacle to the generation of broadly targeted, HIV-specific cellular responses by vaccination. Here we attempted to circumvent this phenomenon and thereby broaden the repertoire of SIV-specific cellular responses by vaccinating rhesus macaques with minigenes encoding fragments of Gag, Vif, and Nef. In contrast to previous mouse studies, this strategy appeared to minimally affect monkey CD8(+) T-cell immundominance hierarchies, as seen by the detection of only one subdominant epitope in Mamu-A*01(+) vaccinees. This finding underscores the difficulty of inducing subdominant CD8(+) T cells by vaccination and demonstrates that strategies other than gene fragmentation may be required to significantly alter immunodominance in primates. Although some of the regimens tested here were extremely immunogenic, vaccine efficacy was limited to a modest reduction in set point viremia after challenge with SIVmac239. No correlates of protection were identified. These results reinforce the notion that vaccine immunogenicity does not predict control of AIDS virus replication.

Project description:The virion infectivity factor (Vif) open reading frame is conserved among most lentiviruses. Vif molecules contribute to viral replication by inactivating host antiviral factors, the APOBEC3 cytidine deaminases. However, various species of lentiviral Vif proteins have evolved different strategies for overcoming host APOBEC3. Whether different species of lentiviral Vif proteins still preserve certain common features has not been reported. Here, we show for the first time that diverse lentiviral Vif molecules maintain the ability to interact with the human immunodeficiency virus type 1 (HIV-1) Gag precursor (Pr55Gag) polyprotein. Surprisingly, bovine immunodeficiency virus (BIV) Vif, but not HIV-1 Vif, interfered with HIV-1 production and viral infectivity even in the absence of APOBEC3. Further analysis revealed that BIV Vif demonstrated an enhanced interaction with Pr55Gag compared to that of HIV-1 Vif, and BIV Vif defective for the Pr55Gag interaction lost its ability to inhibit HIV-1. The C-terminal region of capsid (CA) and the p2 region of Pr55Gag, which are important for virus assembly and maturation, were involved in the interaction. Transduction of CD4+ T cells with BIV Vif blocked HIV-1 replication. Thus, the conserved Vif-Pr55Gag interaction provides a potential target for the future development of antiviral strategies.IMPORTANCE The conserved Vif accessory proteins of primate lentiviruses HIV-1, simian immunodeficiency virus (SIV), and BIV all form ubiquitin ligase complexes to target host antiviral APOBEC3 proteins for degradation, with different cellular requirements and using different molecular mechanisms. Here, we demonstrate that BIV Vif can interfere with HIV-1 Gag maturation and suppress HIV-1 replication through interaction with the precursor of the Gag (Pr55Gag) of HIV-1 in virus-producing cells. Moreover, the HIV-1 and SIV Vif proteins are conserved in terms of their interactions with HIV-1 Pr55Gag although HIV-1 Vif proteins bind Pr55Gag less efficiently than those of BIV Vif. Our research not only sheds new light on this feature of these conserved lentiviral Vif proteins but also provides a formerly unrecognized target for the development of antiviral strategies. Since increasing the Vif-Pr55Gag interaction could potentially suppress virus proliferation, this approach could offer a new strategy for the development of HIV inhibitors.

Project description:Several members of the APOBEC3 DNA cytosine deaminase family can potently inhibit Vif-deficient human immunodeficiency virus type 1 (HIV-1) by catalyzing cytosine deamination in viral cDNA and impeding reverse transcription. HIV-1 counteracts restriction with the virally encoded Vif protein, which targets relevant APOBEC3 proteins for proteasomal degradation. HIV-1 Vif is optimized for degrading the restrictive human APOBEC3 repertoire, and, in general, lentiviral Vif proteins specifically target the restricting APOBEC3 enzymes of each host species. However, simian immunodeficiency virus SIVmac239 Vif elicits a curiously wide range of APOBEC3 degradation capabilities that include degradation of several human APOBEC3s and even human APOBEC3B, a non-HIV-1-restricting APOBEC3 enzyme. To better understand the molecular determinants of the interaction between SIVmac239 Vif and human APOBEC3B, we analyzed an extensive series of mutants. We found that SIVmac239 Vif interacts with the N-terminal domain of human APOBEC3B and, interestingly, that this occurs within a structural region homologous to the HIV-1 Vif interaction surface of human APOBEC3G. An alanine scan of SIVmac239 Vif revealed several residues required for human APOBEC3B degradation activity. These residues overlap HIV-1 Vif surface residues that interact with human APOBEC3G and are distinct from those that engage APOBEC3F or APOBEC3H. Overall, these studies indicate that the molecular determinants of the functional interaction between human APOBEC3B and SIVmac239 Vif resemble those between human APOBEC3G and HIV-1 Vif. These studies contribute to the growing knowledge of the APOBEC-Vif interaction and may help guide future efforts to disrupt this interaction as an antiviral therapy or exploit the interaction as a novel strategy to inhibit APOBEC3B-dependent tumor evolution.IMPORTANCE Primate APOBEC3 proteins provide innate immunity against retroviruses such as HIV and SIV. HIV-1, the primary cause of AIDS, utilizes its Vif protein to specifically counteract restrictive human APOBEC3 enzymes. SIVmac239 Vif exhibits a much wider range of anti-APOBEC3 activities that includes several rhesus macaque enzymes and extends to multiple proteins in the human APOBEC3 repertoire, including APOBEC3B. Understanding the molecular determinants of the interaction between SIVmac239 Vif and human APOBEC3B adds to existing knowledge on the APOBEC3-Vif interaction and has potential to shed light on what processes may have shaped Vif functionality over evolutionary time. An intimate understanding of this interaction may also lead to a novel cancer therapy because, for instance, creating a derivative of SIVmac239 Vif that specifically targets human APOBEC3B could be used to suppress tumor genomic DNA mutagenesis by this enzyme, slow ongoing tumor evolution, and help prevent poor clinical outcomes.

Dataset Information

Gag, vif, and nef genes contribute to the homologous viral interference induced by a nonproducer human immunodeficiency virus type 1 (HIV-1) variant: identification of novel HIV-1-inhibiting viral protein mutants.

Publications

gag, vif, and nef genes contribute to the homologous viral interference induced by a nonproducer human immunodeficiency virus type 1 (HIV-1) variant: identification of novel HIV-1-inhibiting viral protein mutants.

Similar Datasets

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