Antagonism of PP2A is an independent and conserved function of HIV-1 Vif and causes cell cycle arrest.

Sara Marelli,Adi Naamati,Nicholas J Matheson,Janet E Deane,James C Williamson,Anna V Protasio,Edward Jd Greenwood,Paul J Lehner

doi:10.7554/elife.53036

Abstract

The seminal description of the cellular restriction factor APOBEC3G and its antagonism by HIV-1 Vif has underpinned two decades of research on the host-virus interaction. We recently reported that HIV-1 Vif is also able to degrade the PPP2R5 family of regulatory subunits of key cellular phosphatase PP2A (PPP2R5A-E; Greenwood et al., 2016; Naamati et al., 2019). We now identify amino acid polymorphisms at positions 31 and 128 of HIV-1 Vif which selectively regulate the degradation of PPP2R5 family proteins. These residues covary across HIV-1 viruses in vivo, favouring depletion of PPP2R5A-E. Through analysis of point mutants and naturally occurring Vif variants, we further show that degradation of PPP2R5 family subunits is both necessary and sufficient for Vif-dependent G2/M cell cycle arrest. Antagonism of PP2A by HIV-1 Vif is therefore independent of APOBEC3 family proteins, and regulates cell cycle progression in HIV-infected cells.

Highlights

To determine whether antagonism of PPP2R5 and APOBEC3 family proteins are independent functions of Vif 789 (Vif), we first used the published structure of the Vif-CUL5 complex (Guo et al, 2014) to construct a library of 34 HIV-1 NL4-3 Vif variants with point mutations in solvent-exposed residues, focussing predominantly on regions distant from known APOBEC3 family protein interaction interfaces (Figure 1B and Figure 1–figure supplement 1A, residues highlighted in yellow)
Amongst the five PPP2R5 family subunits, we previously showed that depletion of PPP2R5B is most conserved across Vif variants from HIV-1/2 and the non-human primate lentiviruses (Greenwood et al, 2016)
We transfected our library into HEK 293T cells (293Ts) stably expressing HA-tagged PPP2R5B or APOBEC3G, and used flow cytometry to quantify PPP2R5B and APOBEC3G depletion by each Vif variant (Figure 1–figure supplement 1B82 C and Figure 1–figure supplement 2A-C)

Summary

Introduction

The canonical function of HIV-1 Vif is to recruit the cellular restriction factor APOBEC3G for CUL5 E3 ligase and ubiquitin-proteasome-dependent degradation in infected cells, preventing APOBEC3G encapsidation and enhancing virion infectivity (Conticello et al, 2003; Kobayashi et al, 2005; Marin et al, 2003; Mehle et al, 2004; Sheehy et al, 2002; Sheehy et al, 2003; Stopak et al, 2003; Yu et al, 2003) This interaction is very likely to be important in vivo, because the ability of Vif to antagonise APOBEC3G and its homologues is broadly conserved across lentiviral phylogeny, and has driven co-evolution of the mammalian APOBEC3 family (Compton et al, 2013; Nakano et al, 2017). Why only certain HIV-1 Vif variants mediate this effect (Evans et al, 2018; Zhao et al, 2015), and how widely conserved it is across the lentiviral lineage, have remained unclear

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Conclusion