HIV-1 Vif's Capacity To Manipulate the Cell Cycle Is Species Specific

Abstract

Cells derived from mice and other rodents exhibit profound blocks to HIV-1 virion production, reflecting species-specific incompatibilities between viral Tat and Rev proteins and essential host factors cyclin T1 (CCNT1) and exportin-1 (XPO1, also known as CRM1), respectively. To determine if mouse cell blocks other than CCNT1 and XPO1 affect HIV's postintegration stages, we studied HIV-1 gene expression in mouse NIH 3T3 cells modified to constitutively express HIV-1-compatible versions of CCNT1 and XPO1 (3T3.CX cells). 3T3.CX cells supported both Rev-independent and Rev-dependent viral gene expression and produced relatively robust levels of virus particles, confirming that CCNT1 and XPO1 represent the predominant blocks to these stages. Unexpectedly, however, 3T3.CX cells were remarkably resistant to virus-induced cytopathic effects observed in human cell lines, which we mapped to the viral protein Vif and its apparent species-specific capacity to induce G/M cell cycle arrest. Vif was able to mediate rapid degradation of human APOBEC3G and the PPP2R5D regulatory B56 subunit of the PP2A phosphatase holoenzyme in mouse cells, thus demonstrating that Vif's modulation of the cell cycle can be functionally uncoupled from some of its other defined roles in CUL5-dependent protein degradation. Vif was also unable to induce G/M cell cycle arrest in other nonhuman cell types, including cells derived from nonhuman primates, leading us to propose that one or more human-specific cofactors underpin Vif's ability to modulate the cell cycle. Cells derived from mice and other rodents exhibit profound blocks to HIV-1 replication, thus hindering the development of a low-cost small-animal model for studying HIV/AIDS. Here, we engineered otherwise-nonpermissive mouse cells to express HIV-1-compatible versions of two species-specific host dependency factors, cyclin T1 (CCNT1) and exportin-1 (XPO1) (3T3.CX cells). We show that 3T3.CX cells rescue HIV-1 particle production but, unexpectedly, are completely resistant to virus-induced cytopathic effects. We mapped these effects to the viral accessory protein Vif, which induces a prolonged G/M cell cycle arrest followed by apoptosis in human cells. Combined, our results indicate that one or more additional human-specific cofactors govern HIV-1's capacity to modulate the cell cycle, with potential relevance to viral pathogenesis in people and existing animal models.

HIV-1 RNA genomes initiate host protein packaging in the cytosol independently of Gag capsid proteins

“…We also observed cell rounding at the latest time points (Fig. 1d and Video 1, see 48 h time point) consistent with real-time visualization of Vif-induced cell cycle arrest 31 . Taken together, these movies validated our use of YFP-A3G as a proxy sensor for detecting HIV-1 infection and tracking multivariate single-cell responses to Vif.…”

“…Because HIV-1 Gag was recently reported to inhibit SG formation 33,34 , we also tested the effects of treating HeLa.YFP-A3G or HeLa.YFP-TIA1 biosensor cells with Ars at 31 hpi when NL4-3 Gag expression in HeLa cells is relatively high ( e.g. , see 31 ). Contrary to our expectations, both YFP-A3G and YFP-TIA1 accumulated in SGs in Ars-treated cells infected with either Vif+ or Vifxx viruses (Fig.…”

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

“…As a functional readout, we tested the ability of the same panel of Vif variants to cause cell 250 cycle arrest. Consistent with previous reports (Evans et al, 2018;Zhao et al, 2015) and 251 correlating with their impaired activity against PPP2R5 family subunits, HXB2 and NL4-3 I31V 252…”

“…The other cell biological phenotype associated with Vif in multiple studies is the induction of 36 variants mediate this effect (Evans et al, 2018;Zhao et al, 2015), and how widely conserved 43 it is across the lentiviral lineage, have remained unclear. 44…”

“…First, expression of HIV-1 Vif in mouse or COS cells results in depletion of PPP2R5D, but 348 does not cause cell cycle arrest (Evans et al, 2018). As with Vif point mutants and naturally 349 occurring variants in human cells, it seems likely that another PPP2R5 subunit escapes 350 depletion in these species-mismatched cells.…”