The Immunosuppressive Properties of the HIV Vpr Protein Are Linked to a Single Highly Conserved Residue, R90

Abstract

BackgroundA hallmark of AIDS progression is a switch of cytokines from Th1 to Th2 in the plasma of patients. IL-12, a critical Th1 cytokine secreted by antigen presenting cells (APCs) is suppressed by Vpr, implicating it as an important virulence factor. We hypothesize that Vpr protein packaged in the virion may be required for disabling APCs of the first infected mucosal tissues. Consistent with this idea are reports that defects in the C-terminus of Vpr are associated with long-term non-progression.Principal FindingsVpr RNA amplified from various sources was electroporated into monocyte-derived DC and IL-12 levels in supernatants were analyzed. The analysis of previously reported C-terminal Vpr mutations demonstrate that they do not alleviate the block of IL-12 secretion. However, a novel single conservative amino acid substitution, R90K, reverses the IL-12 suppression. Analysis of 1226 Vpr protein sequences demonstrated arginine (R) present at position 90 in 98.8%, with other substitutions at low frequency. Furthermore, none of sequences report lysine (K) in position 90. Vpr clones harboring the reported substitutions in position 90 were studied for their ability to suppress IL-12. Our data demonstrates that none of tested substitutions other than K relieve IL-12 suppression. This suggests a natural selection for sequences which suppress IL-12 secretion by DC and against mutations which relieve such suppression. Further analyses demonstrated that the R90K, as well as deletion of the C-terminus, directs the Vpr protein for rapid degradation.ConclusionThis study supports Vpr as an HIV virulence factor during HIV infection and for the first time provides a link between evolutionary conservation of Vpr and its ability to suppress IL-12 secretion by DC. DC activated in the presence of Vpr would be defective in the production of IL-12, thus contributing to the prevailing Th2 cytokine profile associated with progressive HIV disease. These findings should be considered in the design of future immunotherapies that incorporate Vpr as an antigen.

Immunogenicity of AGS-004 Dendritic Cell Therapy in Patients Treated During Acute HIV Infection

“…9 A reduced quantity of Nef RNA is used to preserve DC functionality by minimizing HLA downregulation. 21 Vpr RNA is truncated due to its ability to inhibit production of IL-12 22 and reduce activation of antigen-specific memory and recall CD8…”

Dendritic Cell Immunotherapy for HIV-1 Infection Using Autologous HIV-1 RNA

“…6 However, the patient to patient protein sequence variability makes the detection of protein expression levels unreliable using commercially available anti-HIV antibodies to Gag, Vpr, Rev and Nef proteins. Therefore, detection of protein expression for each subject was not conducted in this cohort.…”

Defining the roles for Vpr in HIV-1-associated neuropathogenesis

“…However, reductions in β-chemokines MIP-1α, MIP-1β, and RANTES/CCL5 as a result of Vpr expression suggest Vpr-associated mechanisms that increase HIV-1 replication while making a lesser contribution to the pro-inflammatory environment in the CNS (Muthumani et al , 2000). Reduced secretion of IL-12 from monocyte-derived dendritic cells (Tcherepanova et al , 2009) suggests a similar effect in HIV-1-infected macrophages and microglial cells in the brain. Vpr in brain-resident macrophages and microglia may also impact innate immune responses in these cells, as indicated by Vpr-induced STAT1 phosphorylation, expression of interferon-stimulated genes (ISGs), and differential expression of genes involved in innate immune responses (Zahoor et al , 2014).…”