375. The Function of F12-Vif Mutant in the Context of APOBEC3G/Vif Model

Abstract

Viral infectivity factor (Vif) is required for high HIV-1 infectivity in non-permissive cells, which include the natural targets of HIV-1, whereas it is dispensable in several cell lines called permissive. This requirement depends on the ability of Vif to counteract the action of the cellular inhibitor APOBEC3G, whose expression is restricted to non-permissive cells. APOBEC3G is a cytidine deaminase which is incorporated, in the absence of Vif, into viral particles and induces massive G-to-A hyper mutation in the nascent plus strand cDNA during reverse transcription in new target cells. Vif overcomes the action of APOBEC3G by inducing, without the need of any other viral components, its proteasome-dependent degradation. We have constructed, in the context of a potential new approach of anti-HIV-1 gene therapy, a second generation, VSV-G pseudo-typed lentiviral vector carrying the F12-vif gene, which is transcriptionally regulated by the HIV 5 LTR. F12-Vif derives from the natural variant F12-HIV provirus, which confers homologous interference to HIV-1 super-infection. We have transduced several T cell lines and primary T lymphocytes with F12-vif and WT-vif vectors and then challenged them with either CCR5 or CXCR4 HIV-1 strains. Here, we show that the level of p24 Ag released in the culture medium of infected cells is 5 logs lower in cells expressing F12-Vif, compared to the mock transduced and the control WT-Vif expressing cells. To understand whether F12-Vif inhibits HIV-1 replication in a dominant negative fashion, we have infected with Δvif HIV-1 non-permissive cells, transduced with the Vif vectors. Of note, similarly to WT-Vif, F12-Vif rescues viral replication, suggesting that in the absence of WT-Vif, F12-Vif vicariates its function. Finally, to investigate whether F12-Vif interferes with APOBEC3G function, we have monitored the expression of endogenous APOBEC3G in transduced non-permissive cells infected with either wild type or Δvif HIV-1 strains. Results of this analysis will be presented.