PP2A1 binding, cell transducing and apoptotic properties of Vpr(77-92): a new functional domain of HIV-1 Vpr proteins

Background

The hallmark of HIV-1 pathogenesis is the progressive CD4⁺ T cell depletion and high propensity of CD4⁺ T cells to apoptosis. HIV-1 viral protein R (Vpr) is a major pro-apoptotic gene product. A first Vpr-mediated apoptotic mechanism that requires a physical interaction of HIV-1 Vpr_71-82 mitochondriotoxic domain containing the conserved sequence _71-HFRIGCRHSRIG_-82 with the Adenine Nucleotide Translocator (ANT) has been characterized. The family of Ser/Thr protein phosphatase PP2A interacts with several viral proteins to regulate cell growth and apoptotic pathways. Previous studies based on yeast two hybrid assays and mutational experiments indicated that PP2A₁ is involved in the induction of G2 arrest by HIV-1 Vpr.

Principal Findings

Experiments combining pull-down, cell penetration and apoptosis analyses in distinct human cells indicate that the PP2A₁ binding sequence from Vpr_77–92 is a new cell penetrating apoptotic sequence. We also found that the I84P mutation or the IIQ/VTR_83–85 and T89A substitutions in the Vpr_77–92 sequence prevent PP2A₁ binding, cell penetration and apoptosis. In addition the double R77A and R80A mutation known to inactivate the mitochondriotoxic Vpr_71–82 domain, has no effect on the biological properties of the Vpr_77–92 domain.

Conclusion

Together our data provide evidence for the first time that the Vpr_77–92 sequence delineates a biological active domain of Vpr with PP2A₁ binding and pro-apopototic capacities and, it is conceivable that this cell penetrating sequence may account for the Vpr internalization in uninfected cells. Finally, our data also implicate the existence of two partially overlapping pro-apoptotic domains in the Vpr C-terminal part, a redundancy that represents a new approach to address the question of biological relevance of HIV-1 Vpr. In this context, future studies will be required to determine the functional relevance of the Vpr_77–92 domain in full length Vpr protein and also in entire HIV provirus.