Zinc chelation inhibits HIV Vif activity and liberates antiviral function of the cytidine deaminase APOBEC3G.

APOBEC3 proteins are cellular antiviral proteins that are targeted for proteasomal degradation by primate lentiviral Vif proteins. Vif acts as a substrate receptor for the Cullin5 (Cul5) E3 ubiquitin ligase, specifically interacting with Cul5 through a novel H-(x5)-C-(x17-18)-C-(x3-5)-H zinc binding motif. Using the membrane-permeable zinc chelator, N,N,N',N'-tetrakis-(2-pyridylmethyl) ethylenediamine (TPEN), we demonstrated a requirement for zinc for Vif function in vivo. Treatment with TPEN at an IC50 of 1.79 microM inhibits Cul5 recruitment and APOBEC3G (A3G) degradation. Zinc chelation prevented Vif function in infectivity assays, allowing the virus to become sensitive to the antiviral activity of A3G. Zinc chelation had no effect on cellular Cul5-SOCS3 E3 ligase assembly, suggesting that zinc-dependent E3 ligase assembly may be unique to HIV-1 Vif, representing a new target for novel drug design.

Cellular interactions of virion infectivity factor (Vif) as potential therapeutic targets: APOBEC3G and more?

Vif is an HIV accessory protein whose primary function is to negate the action of APOBEC3G, a naturally occurring cellular inhibitor of HIV replication. Vif acts by binding to APOBEC3G, inducing its protein degradation within infected cells and reducing its levels in progeny virions. Interventions that interfere with the Vif-APOBEC3G interaction, raise intracellular or virion associated levels of APOBEC3G, or reduce intracellular levels of Vif, all could hold promise as potential therapeutic approaches aimed at enhancing the cells innate antiviral activity. Levels of APOBEC3G might be increased or Vif levels decreased, by strategies targeting protein synthesis, protein degradation or cellular localisation and function, and properties of APOBEC3G and Vif relevant to these strategies are discussed. Recent data have suggested that Vif may have other mechanisms of action apart from the above activities against APOBEC3G, including effects against other anti-viral mechanisms independent of APOBEC3G cytidine deaminase activity. In addition to interaction with APOBEC3G, Vif may have other accessory functions, which are discussed in relation to potential therapies that may affect multiple stages of the HIV life cycle. Future development of strategies that combine enhancement of APBOEC3G functional with inhibition of multiple Vif functions may become useful tools for HIV therapy.

Reversal of HIV drug resistance and novel strategies to curb HIV infection: the viral infectivity factor Vif as a target and tool of therapy.

Due to the high genetic variability of human immunodeficiency virus (HIV), treatment of AIDS (acquired immunodeficiency syndrome) patients with inhibitors of reverse trancriptase (RT) and drugs blocking the viral protease regularly results in the accumulation of drug resistant HIV variants and treatment failure. The sensitivity of clinically derived resistant HIV-1 strains to nucleotide RT inhibitors could be restored, however, in several laboratories by pharmacological depletion of the appropriate endogenous deoxynucleotide triphosphate (dNTP), and such a manipulation (induction of dCTP pool imbalance during reverse transcription in the presence of a non-nucleoside RT inhibitor) altered the mutation spectrum of the HIV-1 genome, resulting in a lower level of HIV resistance to certain drugs. The cytoplasmic single-stranded DNA cytidine deaminases APOBEC3G and APOBEC3F block HIV replication by introducing premature stop codons into the viral genome. We suggest that the resulting crippled, defective HIV (dHIV) variants could interfere with replication of "wild type" viruses and curbe disese progression in long term non-progressor individuals. Vif, an accessory protein encoded by HIV, counteracts APOBEC3G/F action. We speculate that small molecule inhibitors of Vif could permit lethal or sublethal mutagenesis of HIV genomes. We suggest that an artificial dHIV construct carrying a mutated vif gene (coding for a Vif protein unable to block APOBEC3G/F) could have a therapeutic effect as well in HIV infected individuals and AIDS patients.

[Assembly and maturation of HIV-1--targets for new anti-HIV compounds].

Much progress has been recently made in research of the final stages of the HIV-1 life cycle, i.e. of its assembly, gemmation and maturation. The virus was shown, in particular, to use widely cell mechanisms in its replication and assembly. The TSG 101 cellular endosomal sorting protein interacting with the p6 viral protein is necessary for gemmation. Cyclophilin and HP68 (cell proteins) needed for marphogenesis of the virus were identified. The recently obtained data on the interaction of Vif (a viral protein) and Apobec (a cell protein) showed that HIV-1 has an action mechanism overcoming the cell barriers. The "early" virus phenomenon, which is deprived of any mature structure or the ability to infect and does not contain mature Gag and Env proteins, illustrates that the proteolytic pressing of the Gag p55 precursor is not enough for the maturation of the virus and additional viral or cellular factors are needed for the virus to become infectious. Although the current antiviral therapy has been successful enough, it is far from being effective in all cases; one of the reasons is resistance to chemodrugs developing rapidly in patients. Fast mutations and exceptional plasticity of the viral genome (which helps the virus to develop rapidly resistance to drugs) belong to the major problems. The circulation of persistent virus variants has been quickly increasing. There is an urgent need in developing new antiviral drugs acting on new viral targets; progress in experimental virology would speed it up. Thus, new drugs can be created, which block the activity of Vif, that would make Apobec block the virus replication. Compounds can be developed, which block the interaction of cyclophilin and TSG101 with viral proteins. The recently described importance of cholesterol in the sexual transfer of viruses is expected to bring simple and inexpensive compounds destroying cholesterol in the mucous tunic of genitals into clinical use. The identification of additional factors needed for the maturation of the virus and for its becoming infectious can be a basis for the development of drugs blocking their packaging into virions. Future research is expected to define new targets for the chemotherapy of AIDS and to promote the designing of new chemodrugs.

Blocking HIV-1 Vif restores a natural mechanism of intracellular antiviral defense.

AIDS has become the greatest pandemic in the human history counting approximately 40 millions people worldwide. To purge HIV-1 infection, new therapeutic approaches need to be searched in alternative and/or in addition to the current pharmacological ones. Recently, several independent laboratories have unveiled a non-immune intracellular anti-HIV-1 defense strategy based on the cytidine deaminase APOBEC3G, which restricts HIV-1 production by directly mutating the proviral DNA in infected cells. To counteract this defense pathway, HIV-1 has developed an evasion strategy by acquiring the accessory protein Vif, which blocks the action of APOBEC3G by inducing its proteasome-mediated degradation.

Abrogation of Vif function by peptide derived from the N-terminal region of the human immunodeficiency virus type 1 (HIV-1) protease.

The human immunodeficiency virus type 1 (HIV-1) auxiliary gene vif is essential for virus propagation in peripheral blood lymphocytes, macrophages, and in some T-cell lines. Previously, it was demonstrated that Vif inhibits the autoprocessing of truncated HIV-1 Gag-Pol polyproteins expressed in bacterial cells, and that purified recombinant Vif and Vif-derived peptides inhibit and bind HIV-1 protease (PR). Here we show that Vif interacts with the N-terminal region of HIV-1 PR, and demonstrate that peptide derived from the N-terminal region of PR abrogates Vif function in non-permissive cells. Specifically, we show that (i) Vif protein binds HIV-1 PR, but not covalently linked tethered PR-PR; (ii) the four amino acids residing at the N terminus of HIV-1 PR are essential for Vif/PR interaction; (iii) synthetic peptide derived from the N terminus of HIV-1 PR inhibits Vif/PR binding; and (iv) this peptide inhibits the propagation of HIV-1 in restrictive cells. Based on these data, we suggest that Vif interacts with the dimerization sites of the viral protease, and that peptide residing at the N terminus of PR abrogates Vif function(s).

The Vif protein of human immunodeficiency virus type 1 (HIV-1): enigmas and solutions.

HIV-1 and other complex retroviruses express six auxiliary genes in addition to the canonical retroviral genes, gag, pol and env. Vif (virion infectivity factor) protein is absolutely essential for productive HIV-1 infection of peripheral blood lymphocytes and macrophages, the two major HIV-1 target cells in vivo. However, Vif is not required for production of infectious particles in several human cell lines. In spite of the prominent phenotype of Vif mutations, the mechanism of its action remains unknown. During the last decade several models were suggested to explain the mechanism of Vif activity. One view holds that Vif is active in virions after budding or after entry into target cells during the early stages of HIV-1 replications. The second view places the action of Vif at the late stage of HIV-1 replication in virus producing cells, which affects the production of infectious virus. According to this view, Vif either compensates the cell factor required for production of infectious virus, or alternatively, it neutralizes a cell factor, which prevents the production of infectious particles in these cells. This review is addressed to summarize the models envisioned to explain Vif activities. The findings described here, that Vif interacts with viral and cellular components, elaborates the importance of Vif as a novel target for developing anti HIV-1 drugs.