Complementation of human immunodeficiency virus type 1 vif mutants in some CD4+ T-cell lines

The inhibition of hepatitis B virus by APOBEC cytidine deaminases

APOBEC3 (A3) cytidine deaminases are a family of enzymes that have been shown to inhibit the replication of HIV-1 and other retroviruses as part of the innate immune responses to virus infection. They can also hyperedit HBV DNA and inhibit HBV replication. Although A3 proteins are present at low levels in normal liver, A3 gene expression is highly stimulated by both interferon-α and interferon-γ. A3 deaminases are incorporated into nascent HBV capsids where they cleave amino groups from cytidine bases converting them to uracil in newly synthesized DNA following reverse transcription of pregenomic RNA. This modified HBV DNA is susceptible to degradation, or alternatively, numerous G-to-A nucleotide mutations are incorporated into positive-strand viral DNA disrupting coding sequences. A3 proteins in which the cytidine deaminase activity has been lost can also inhibit HBV replication, suggesting that there may be more than one way in which inhibition can occur. There is also evidence that A3 proteins might play a role in the development of hepatocellular carcinoma during chronic HBV infection.

Differences in APOBEC3G expression in CD4+ T helper lymphocyte subtypes modulate HIV-1 infectivity

The cytidine deaminases APOBEC3G and APOBEC3F exert anti–HIV-1 activity that is countered by the HIV-1 vif protein. Based on potential transcription factor binding sites in their putative promoters, we hypothesized that expression of APOBEC3G and APOBEC3F would vary with T helper lymphocyte differentiation. Naive CD4+ T lymphocytes were differentiated to T helper type 1 (Th1) and 2 (Th2) effector cells by expression of transcription factors Tbet and GATA3, respectively, as well as by cytokine polarization. APOBEC3G and APOBEC3F RNA levels, and APOBEC3G protein levels, were higher in Th1 than in Th2 cells. T cell receptor stimulation further increased APOBEC3G and APOBEC3F expression in Tbet- and control-transduced, but not in GATA3-transduced, cells. Neutralizing anti–interferon-γ antibodies reduced both basal and T cell receptor-stimulated APOBEC3G and APOBEC3F expression in Tbet- and control-transduced cells. HIV-1 produced from Th1 cells had more virion APOBEC3G, and decreased infectivity, compared to virions produced from Th2 cells. These differences between Th1- and Th2-produced virions were greater for viruses lacking functional vif, but also seen with vif-positive viruses. Over-expression of APOBEC3G in Th2 cells decreased the infectivity of virions produced from Th2 cells, and reduction of APOBEC3G in Th1 cells increased infectivity of virions produced from Th1 cells, consistent with a causal role for APOBEC3G in the infectivity difference. These results indicate that APOBEC3G and APOBEC3F levels vary physiologically during CD4+ T lymphocyte differentiation, that interferon-γ contributes to this modulation, and that this physiological regulation can cause changes in infectivity of progeny virions, even in the presence of HIV-1 vif.

Some host cell proteins can hinder, or restrict, the life cycle of HIV-1. APOBEC3G and APOBEC3F are cellular enzymes that decrease HIV-1's ability to replicate in a subsequent target cell if they are present in the virus particle. As a countermeasure, HIV-1 virion infectivity factor (vif) induces degradation of APOBEC3G and APOBEC3F, thereby preventing them from getting into the budding virus. Although vif-defective viruses cannot evade the antiviral effect of APOBEC3G, such viruses are very rarely present in HIV-1-infected humans. It is not yet known whether physiological variation in APOBEC3G and APOBEC3F expression in CD4+ T lymphocytes is substantial enough to reduce vif-positive HIV-1 infectivity. In this study, we found that T helper type 1 (Th1) cells, a subtype of CD4+ lymphocytes, expressed greater amounts of APOBEC3G and APOBEC3F than T helper type 2 (Th2) cells. This difference led to a difference in infectivity of HIV-1 produced from the two cell types, whether vif was expressed or not. These results demonstrate that physiological regulation of APOBEC3G does restrict vif-positive HIV-1, as well as vif-negative HIV-1. In addition, this study reveals biological factors regulating expression of these proteins that may be exploitable for new therapeutic or preventive strategies against HIV-1.

Regulated production and anti-HIV type 1 activities of cytidine deaminases APOBEC3B, 3F, and 3G

APOBEC3G and 3F (A3G and A3F) cytidine deaminases incorporate into retroviral cores where they lethally hypermutate nascent DNA reverse transcripts. As substantiated here, the viral infectivity factor (Vif) encoded by human immunodeficiency virus type-1 (HIV-1) binds A3G and A3F and induces their degradation, thereby precluding their incorporation into viral progeny. Previous evidence suggested that A3G is expressed in H9 and other nonpermissive cells that contain this antiviral defense but not in several permissive cells, and that overexpression of A3G or A3F makes permissive cells nonpermissive. Using a broader panel of cell lines, we confirmed a correlation between A3G and cellular abilities to inactivate HIV-1(Deltavif). However, there was a quantitative discrepancy because several cells with weak antiviral activities had similar amounts of wild-type A3G mRNA and protein compared to H9 cells. Antiviral activity of H9 cells was also attenuated in some conditions. These quantitative discrepancies could not be explained by the presence of A3F or other A3G paralogs in some of the cell lines. Thus, A3A, A3B, and A3C had weak but significant anti-HIV-1 activities and did not dominantly interfere with A3G or A3F antiviral functions. Control of A3G synthesis by the protein kinase C/mitogen-activated protein kinase kinase/extracellular signal-regulated kinase pathway was also similar in permissive and nonpermissive cells. A3G in highly permissive cells is degraded by Vif, suggesting that it is not in a sequestered site, and is specifically incorporated in low amounts into HIV-1(Deltavif). Although A3G and/or A3F inactivate HIV-1(Deltavif) and are neutralized by Vif, the antiviral properties of cell lines are also influenced by other cellular and viral factors.

Nuclear localization of HIV type 1 Vif isolated from a long-term asymptomatic individual and potential role in virus attenuation

Recent reports have determined that HIV-1 Vif counteracts an innate antiviral cellular factor, Apobec3G. However, the function of Vif during HIV-1 pathogenesis remains poorly understood. To gain a better understanding of Vif function, the viral isolate from an HIV-1-infected long-term nonprogressor (LTNP) that displayed a Vif-mutant replication phenotype was studied. This LTNP has been infected since before 1983 and has no HIV-related disease in the absence of antiretroviral therapy. From separate samples, obtained on more than one study visit, virus grew in cocultures of LTNP cells with Vif-complementing T cell lines, but not the parental T cell lines. An unusual amino acid motif (KKRK) was found in the Vif sequence at positions 90 to 93. Since this motif commonly functions as a nuclear localization sequence, experiments were performed to determine the ability of this KKRK motif to mediate nuclear localization of Vif. Wild-type Vif displayed a predominantly cytoplasmic distribution. In contrast, the KKRK Vif showed a predominantly nuclear localization. The effect of the KKRK mutation on virus production and infectivity was also studied. The KKRK motif that mislocalizes Vif to the nucleus also reduces viral replication and infectivity in nonpermissive cells. Our data highlight the importance of Vif in HIV-1 pathogenesis and also provide a unique tool to investigate the interaction of Vif and Apobec3G.

An update on bioactive plant lignans

Lignans are a class of secondary plant metabolites produced by oxidative dimerization of two phenylpropanoid units. Although their molecular backbone consists only of two phenylpropane (C6-C3) units, lignans show an enormous structural diversity. There is a growing interest in lignans and their synthetic derivatives due to applications in cancer chemotherapy and various other pharmacological effects. This review deals with lignans possessing anticancer, antioxidant, antimicrobial, anti-inflammatory and immunosuppressive activities, and comprises the data reported in more than 100 peer-reviewed articles, so as to highlight the recently reported bioactive lignans that could be a first step towards the development of potential new therapeutic agents.

In vitro antiinflammatory effects of neolignan woorenosides from the rhizomes of Coptis japonica

Five dihydrobenzofuran neolignans, woorenosides I (1), II (2), III (3), IV (4), and V (5), isolated from Coptis japonica (Ranunculaceae), suppressed tumor necrosis factor (TNF)-alpha and nitric oxide (NuOmicron) production, as well as lymphocyte proliferation triggered by inflammatory signals such as various mitogens, in a dose-dependent manner. The results indicate that the woorenosides strongly inhibit the mitogenic response by activated macrophage and lymphocytes and suggest that these compounds may participate in regulating inflammatory processes.

Feline immunodeficiency virus Vif localizes to the nucleus

Monoclonal antibodies prepared against recombinant Vif derived from the 34TF10 strain of feline immunodeficiency virus (FIV) were used to assess the expression and localization of Vif in virus-infected cells. Analyses by Western blotting and by immunoprecipitation from cells infected with FIV-34TF10 revealed the presence of a single 29-kDa species specific for virus-infected cells. Confirmation of antibody specificity was also performed by specific immunoprecipitation of in vitro-transcribed and -translated recombinant Vif. Localization experiments were also performed on virus-infected cells, using different fixation procedures. Results for methanol fixation protocols similar to those reported for localization of human immunodeficiency virus (HIV) Vif showed a predominant cytoplasmic localization for FIV Vif, very similar to localization of HIV type 1 Vif and virtually identical to the localization observed for the Gag antigens of the virus. However, with milder fixation procedures that used 2% formaldehyde at 4 degrees C, FIV Vif was strongly evident in the nucleus. The localization was distinct from the nuclear localization noted with Rev and did not involve the nucleolus. Attempts to show colocalization or coprecipitation of Vif with Gag antigens were unsuccessful. In addition, Vif was not detected in purified FIV virions. The results are consistent with the notion that the primary role of Vif in virus infection initiates in the nucleus.

Development of genetic vaccines for pathogenic genes: construction of attenuated vif DNA immunization cassettes

OBJECTIVE

To develop a putative immunization cassette using HIV-1 vif accessory gene derived from HIV-1 clinical specimens as a component of a DNA vaccine for HIV-1.

METHODS

vif genes were cloned from HIV-1-infected patients and the sequence variation present within the patients was analyzed. Prototypic genetic variants were selected and the ability of these clones to induce humoral and cellular immune responses was studied in animals. The selected protective genetic variants were biologically characterized through transcomplementation assays using primary cells infected with a vif-defective HIV-1 proviral clone.

RESULTS

Analysis of vif variants from different patients revealed that vif is highly conserved with the open reading frame remaining intact in vivo. It was shown that attenuated vif clones from HIV-1-infected subjects can effectively induce both humoral and cellular responses against Vif protein in mice. Evaluation of the cellular responses in vitro using human cellular targets infected with a clinical HIV-1 isolate showed that vif clones could induce cellular responses capable of destroying the virus.

CONCLUSIONS

The vif variants developed in this study exhibited non-productive phenotypes, yet were capable of inducing specific immune responses against HIV-1. These constructs could be used as part of a DNA vaccine strategy for HIV-1. This vaccine adaptation strategy could be used for the development of immunogens for any pathogen resulting in cross-reactive immunity and attenuated gene pathogenesis.