Recent Insights into HIV Accessory Proteins

Gene therapy progress and prospects: viral trafficking during infection

The intracellular steps involved in viral infection, namely cytoplasmic trafficking and nuclear import, are critical events in the viral life cycle that have lagged behind other areas of viral research. This review examines recent advances in our understanding of these steps for viruses commonly employed as viral gene delivery vectors. Steps governing the cytoplasmic trafficking and nuclear import of Herpes Simplex virus, Human Immunodeficiency virus and Adenovirus are reviewed in this article.

HIV accessory proteins and surviving the host cell

Human immunodeficiency virus generates the accessory proteins Nef, viral infectivity factor (Vif), viral protein R, and viral protein U or viral protein X during viral replication in host cells. Although the significance of these accessory proteins is often lost in vitro, they are essential for viral pathogenesis in vivo. Therefore, these proteins have much potential as antiviral targets. Recent data reveal Vif perturbs an ill-defined antiviral pathway in host cells allowing HIV replication. These data highlight a common feature among HIV accessory proteins in manipulating the host to aid viral pathogenesis. Therefore, these new insights into Vif and other HIV accessory proteins are reviewed, emphasizing host cell interactions and new targets for therapeutic intervention.

Human immunodeficiency virus (HIV)-1 proteins and cytoskeleton: partners in viral life and host cell death

Cytoskeletal components play a major role in the human immunodeficiency virus-1 (HIV-1) infection. A wide variety of molecules belonging to the microfilament system, including actin filaments and actin binding proteins, as well as microtubules have a key role in regulating both cell life and death. Cell shape maintenance, cell polarity and cell movements as well as cytoplasmic trafficking of molecules determining cell fate, including apoptosis, are in fact instructed by the cytoskeleton components. HIV infection and viral particle production seem to be controlled by cytoskeleton as well. Furthermore, HIV-associated apoptosis failure can also be regulated by the actin network function. In fact, HIV protein gp120 is able to induce cytoskeleton-driven polarization, thus sensitizing T cells to CD95/Fas-mediated apoptosis. The microfilament system seems thus to be a sort of cytoplasmic supervisor of the viral particle, the host cell and the bystander cell's very fate.

HIV-host interactions: vital to the virus and key to its inhibition

Much progress has been made in recent years in the investigation of the interplay between HIV-1 and its host cells. Most of these interactions are complex and have not yet been fully unraveled. Nevertheless, current knowledge on the molecular interactions between HIV and host-cell factors has substantially broadened our understanding of the viral life cycle and opened new investigative areas for drug intervention.

HIV-host interactions: vital to the virus and key to its inhibition

Much progress has been made in recent years in the investigation of the interplay between HIV-1 and its host cells. Most of these interactions are complex and have not yet been fully unraveled. Nevertheless, current knowledge on the molecular interactions between HIV and host-cell factors has substantially broadened our understanding of the viral life cycle and opened new investigative areas for drug intervention.

Characterization of a DNA vaccine expressing a human immunodeficiency virus-like particle

An ideal human immunodeficiency virus type-1 (HIV-1) vaccine will most likely need to elicit cross-reactive neutralizing antibodies and a strong cell-mediated immune response against multiple HIV-1 antigens to confer protection against challenge. In this study, DNA vaccines were constructed to express virally regulated human immunodeficiency virus-like particles (VLP) to elicit broad-spectrum immune responses to multiple HIV-1 antigens. VLPs were efficiently produced using sequences encoding gag and pol gene products from an X4 isolate and sequences encoding for tat, rev, vpu, and env from R5 or R5X4 isolates. The integrase, vpr, vif, and nef genes were deleted. In addition, the long terminal repeats (LTRs) were removed and transcription of the VLP insert was driven by the addition of the cytomegalovirus immediate-early (CMV-IE) promoter. A second generation of VLP vaccine plasmids was constructed with mutations engineered into the VLP DNA to produce particles deficient in activities associated with viral reverse transcriptase and protease. Primate cell lines, transiently transfected with DNA, efficiently secreted VLP into the supernatant that banded within a sucrose gradient at densities similar to infectious virions. In addition, these particles incorporated Env on the particle surface that bound soluble human CD4. These VLPs provide a safe and efficient strategy for presenting multiple HIV-1 antigens, expressed from a single insert, to the immune system in a structure that mimics the infectious virion.

Disruption of the actin cytoskeleton can complement the ability of Nef to enhance human immunodeficiency virus type 1 infectivity

The human immunodeficiency virus (HIV) protein Nef has been shown to increase the infectivity of HIV at an early point during infection. Since Nef is known to interact with proteins involved in actin cytoskeleton rearrangements, we tested the possibility that Nef may enhance HIV infectivity via a mechanism that involves the actin cytoskeleton. We find that disruption of the actin cytoskeleton complements the Nef infectivity defect. The ability of disruption of the actin cytoskeleton to complement the Nef defect was specific to envelopes that fuse at the cell surface, including a variety of HIV envelopes and the murine leukemia virus amphotropic envelope. In contrast, the infectivity of HIV virions pseudotyped to enter cells via endocytosis, which is known to complement the HIV Nef infectivity defect and can naturally penetrate the cortical actin barrier, was not altered by actin cytoskeleton disruption. The results presented here suggest that Nef functions to allow the HIV genome to penetrate the cortical actin network, a known barrier for intracellular parasitic organisms.