HIV-1 auxiliary regulatory protein Vpr promotes ubiquitination and turnover of Vpr mutants containing the L64P mutation

HIV-1 Vpr Functions in Primary CD4+ T Cells

HIV-1 encodes four accesory proteins in addition to its structural and regulatory genes. Uniquely amongst them, Vpr is abundantly present within virions, meaning it is poised to exert various biological effects on the host cell upon delivery. In this way, Vpr contributes towards the establishment of a successful infection, as evidenced by the extent to which HIV-1 depends on this factor to achieve full pathogenicity in vivo. Although HIV infects various cell types in the host organism, CD4+ T cells are preferentially targeted since they are highly permissive towards productive infection, concomitantly bringing about the hallmark immune dysfunction that accompanies HIV-1 spread. The last several decades have seen unprecedented progress in unraveling the activities Vpr possesses in the host cell at the molecular scale, increasingly underscoring the importance of this viral component. Nevertheless, it remains controversial whether some of these advances bear in vivo relevance, since commonly employed cellular models significantly differ from primary T lymphocytes. One prominent example is the "established" ability of Vpr to induce G2 cell cycle arrest, with enigmatic physiological relevance in infected primary T lymphocytes. The objective of this review is to present these discoveries in their biological context to illustrate the mechanisms whereby Vpr supports HIV-1 infection in CD4+ T cells, whilst identifying findings that require validation in physiologically relevant models.

Drug-induced reactivation of apoptosis abrogates HIV-1 infection

HIV-1 blocks apoptosis, programmed cell death, an innate defense of cells against viral invasion. However, apoptosis can be selectively reactivated in HIV-infected cells by chemical agents that interfere with HIV-1 gene expression. We studied two globally used medicines, the topical antifungal ciclopirox and the iron chelator deferiprone, for their effect on apoptosis in HIV-infected H9 cells and in peripheral blood mononuclear cells infected with clinical HIV-1 isolates. Both medicines activated apoptosis preferentially in HIV-infected cells, suggesting that the drugs mediate escape from the viral suppression of defensive apoptosis. In infected H9 cells, ciclopirox and deferiprone enhanced mitochondrial membrane depolarization, initiating the intrinsic pathway of apoptosis to execution, as evidenced by caspase-3 activation, poly(ADP-ribose) polymerase proteolysis, DNA degradation, and apoptotic cell morphology. In isolate-infected peripheral blood mononuclear cells, ciclopirox collapsed HIV-1 production to the limit of viral protein and RNA detection. Despite prolonged monotherapy, ciclopirox did not elicit breakthrough. No viral re-emergence was observed even 12 weeks after drug cessation, suggesting elimination of the proviral reservoir. Tests in mice predictive for cytotoxicity to human epithelia did not detect tissue damage or activation of apoptosis at a ciclopirox concentration that exceeded by orders of magnitude the concentration causing death of infected cells. We infer that ciclopirox and deferiprone act via therapeutic reclamation of apoptotic proficiency (TRAP) in HIV-infected cells and trigger their preferential elimination. Perturbations in viral protein expression suggest that the antiretroviral activity of both drugs stems from their ability to inhibit hydroxylation of cellular proteins essential for apoptosis and for viral infection, exemplified by eIF5A. Our findings identify ciclopirox and deferiprone as prototypes of selectively cytocidal antivirals that eliminate viral infection by destroying infected cells. A drug-based drug discovery program, based on these compounds, is warranted to determine the potential of such agents in clinical trials of HIV-infected patients.

Viral ubiquitin ligase WSSV222 is required for efficient white spot syndrome virus replication in shrimp

The E3 ligase WSSV222 of white spot syndrome virus (WSSV) is involved in anti-apoptosis regulation by ubiquitin-mediated degradation of tumour suppressor-like protein (TSL), a shrimp tumour suppressor. In the present study, WSSV222 gene expression was silenced by using specific small interfering RNA (siRNA) in Sf9 and BHK cells. Based on the results of the in vitro silencing, WSSV-challenged shrimp were treated with anti-WSSV222 siRNA to knock down WSSV222 protein expression. The survival rate of shrimp and the efficiency of WSSV replication were assessed to evaluate the efficacy of anti-WSSV222 siRNA in regulating WSSV infection in shrimp. The anti-WSSV222 siRNA reduced the cumulative mortality in shrimp challenged with 10(3) copies of WSSV and delayed the mean time to death in shrimp challenged with the higher dose of 10(6) copies. The results of real-time quantitative PCR showed that virus replication was delayed and reduced in WSSV-challenged shrimp treated with anti-WSSV222 siRNA in comparison with challenged shrimp treated with random-control siRNA. Co-immunoprecipitation assays revealed that WSSV222 silencing inhibited the degradation of TSL in WSSV-challenged shrimp, indicating the requirement for WSSV222 for efficient replication of WSSV in shrimp.

The HIV-1 Vif protein mediates degradation of Vpr and reduces Vpr-induced cell cycle arrest

Prior work has implicated viral protein R (Vpr) in the arrest of human immunodeficiency virus type 1 (HIV-1)-infected cells in the G2 phase of the cell cycle, associated with increased viral replication and host cell apoptosis. We and others have recently shown that virion infectivity factor (Vif ) also plays a role in the G2 arrest of HIV-1-infected cells. Here, we demonstrate that, paradoxically, at early time points postinfection, Vif expression blocks Vpr-mediated G2 arrest, while deletion of Vif from the HIV-1 genome leads to a marked increase in G2 arrest of infected CD4 T-cells. Consistent with this increased G2 arrest, T-cells infected with Vif-deleted HIV-1 express higher levels of Vpr protein than cells infected with wild-type virus. Further, expression of exogenous Vif inhibits the expression of Vpr, associated with a decrease in G2 arrest of both infected and transfected cells. Treatment with the proteasome inhibitor MG132 increases Vpr protein expression and G2 arrest in wild-type, but not Vif-deleted, NL4-3-infected cells, and in cells cotransfected with Vif and Vpr. In addition, Vpr coimmunoprecipitates with Vif in cotransfected cells in the presence of MG132. This suggests that inhibition of Vpr by Vif is mediated at least in part by proteasomal degradation, similar to Vif-induced degradation of APOBEC3G. Together, these data show that Vif mediates the degradation of Vpr and modulates Vpr-induced G2 arrest in HIV-1-infected T-cells.