PP2A1 Binding, Cell Transducing and Apoptotic Properties of Vpr77–92: A New Functional Domain of HIV-1 Vpr Proteins

Angélique N Godet,Amélie Croset,Julien Guergnon,Jean-Hervé Colle,Pierre Barthélemy Falanga,Xavier Cayla,Alphonse Garcia

doi:10.1371/journal.pone.0013760

Abstract

BackgroundThe 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 Vpr71-82 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 FindingsExperiments combining pull-down, cell penetration and apoptosis analyses in distinct human cells indicate that the PP2A1 binding sequence from Vpr77–92 is a new cell penetrating apoptotic sequence. We also found that the I84P mutation or the IIQ/VTR83–85 and T89A substitutions in the Vpr77–92 sequence prevent PP2A1 binding, cell penetration and apoptosis. In addition the double R77A and R80A mutation known to inactivate the mitochondriotoxic Vpr71–82 domain, has no effect on the biological properties of the Vpr77–92 domain.ConclusionTogether our data provide evidence for the first time that the Vpr77–92 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 Vpr77–92 domain in full length Vpr protein and also in entire HIV provirus.

Highlights

HIV infection leads to the depletion of CD4+ T cells in patients
Together our data provide evidence for the first time that the Vpr77–92 sequence delineates a biological active domain of viral protein R (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
Other reports have clearly documented a major apoptotic mechanism which is based on the physical interaction of Vpr with the Adenine Nucleotide Translocator (ANT), a component of the permeability transition pore of mitochondria localized in the inner mitochondrial membrane [5,6]

Summary

Introduction

HIV infection leads to the depletion of CD4+ T cells in patients. The CD4+ T cells depletion of non-infected CD4+ T cells has been correlated to an increased propensity to apoptosis, which relays on induced host and viral factors [1]. Other reports have clearly documented a major apoptotic mechanism which is based on the physical interaction of Vpr with the Adenine Nucleotide Translocator (ANT), a component of the permeability transition pore of mitochondria localized in the inner mitochondrial membrane [5,6]. This mitochondriotoxic domain contains Vpr sequence that is partially located at the end of the third a-helix of Vpr (Vpr). 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

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Conclusion